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Glauco PONTERINI

Professore Ordinario presso: Dipartimento di Scienze della Vita sede ex Chimica V.Campi 103


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Pubblicazioni

2020 - A Peptidic Thymidylate-Synthase Inhibitor Loaded on Pegylated Liposomes Enhances the Antitumour Effect of Chemotherapy Drugs in Human Ovarian Cancer Cells [Articolo su rivista]
Marverti, Gaetano; Gozzi, Gaia; Maretti, Eleonora; Lauriola, Angela; Severi, Leda; Sacchetti, Francesca; Losi, Lorena; Pacifico, Salvatore; Ferrari, Stefania; Ponterini, Glauco; Leo, Eliana Grazia; Costi, Maria Paola; D'Arca, Domenico
abstract

There is currently no effective long-term treatment for ovarian cancer (OC) resistant to poly-chemotherapy regimens based on platinum drugs. Preclinical and clinical studies have demonstrated a strong association between development of Pt-drug resistance and increased thymidylate synthase (hTS) expression, and the consequent cross-resistance to the hTS inhibitors 5-fluorouracil (5-FU) and raltitrexed (RTX). In the present work, we propose a new tool to combat drug resistance. We propose to treat OC cell lines, both Pt-sensitive and -resistant, with dual combinations of one of the four chemotherapeutic agents that are widely used in the clinic, and the new peptide, hTS inhibitor, [D-Gln4]LR. This binds hTS allosterically and, unlike classical inhibitors that bind at the catalytic pocket, causes cell growth inhibition without inducing hTS overexpression. The dual drug combinations showed schedule-dependent synergistic antiproliferative and apoptotic effects. We observed that the simultaneous treatment or 24h pre-treatment of OC cells with the peptide followed by either agent produced synergistic effects even in resistant cells. Similar synergistic or antagonistic effects were obtained by delivering the peptide into OC cells either by means of a commercial delivery system (SAINT-PhD) or by pH sensitive PEGylated liposomes. Relative to non-PEGylated liposomes, the latter had been previously characterized and found to allow macrophage escape, thus increasing their chance to reach the tumour tissue. The transition from the SAINT-PhD delivery system to the engineered liposomes represents an advancement towards a more drug-like delivery system and a further step towards the use of peptides for in vivo studies. Overall, the results suggest that the association of standard drugs, such as cDDP and/or 5-FU and/or RTX, with the novel peptidic TS inhibitor encapsulated into PEGylated pH-sensitive liposomes can represent a promising strategy for fighting resistance to cDDP and anti-hTS drugs.


2020 - Approcci non convenzionali agli enzimi del ciclo dei folati: intercambio attivo - inattivo della timidilato sintasi, suo equilibrio e fotoattivazione di un "device" molecolare "methotrexate - like" [Tesi di dottorato]
VITIELLO, SIMONE
abstract

Human thymidylate synthase (hTS) is a homodimeric enzyme and a renewed anti-cancer target. X-ray crystallography studies demonstrated the existence of two different conformers; catalytic activity is exclusive to di-active dimers. Di-inactive dimers tend to disassociate into monomers which are regarded to inhibit transcription binding its own mRNA via a negative feedback process. And through unknown structural changes, both conformers are at equilibrium in solution. Notwithstanding, molecular effectors can induce the switch to a specific conformer: sulfates and phosphates ions to the inactive conformer, 2’- deoxyuridine – 5’ – monophosphate (dUMP) to the active one. Current pharmacological treatments base their activity on miming substrates’ structure, binding to the catalytic site. The main drawback of this approach is protein overexpression, leading to unwanted pharmacoresistance. Such an issue sparks the need for new approaches. A successful one based on peptidic inhibitors binding at a protein – protein interface, as the “LR” peptide. The main aim of the thesis was to present the importance of different inhibitory approaches to solve pharmacoresistance and the enrichment in knowledge derived by structural studies of the target. The first step was to express – E. coli BL21(DE3) cells + pQE80L plasmid – and purify – affinity chromatography – the hTS wildtype (hTSwt) and its mutants (K47A, F59A, W182A). Functionality of all purified proteins followed through and has been assessed via spectrophotometry – based kinetic assay. The choice of the purification buffer depended on the experiment: phosphate – free for structure delving; phosphate – based for enzymatic assays. Structure – based data comes from Isothermal Titration Calorimetry and Spectrofluorometry techniques. The former was employed to explore any thermodynamic change due to binding or structural rearrangement; the latter to follow Trp – Tyr emission properties changes. Spectroscopy based enzymatic assays have been carried out to test peptidic inhibitors derived from the proline mutation of LR. Enzyme conjugation with fluorescein and tetramethylrhodamine maleimide was performed, attempting to obtain 1:2:1 (F-TS-T) molar ratio. Such a product was used in FRET - Förster Resonance Energy Transfer – based experiments to quantitatively define the equilibrium between the monomeric and the dimeric assemblies in the presence of candidate dissociative inhibitors. WT and mutants were successfully purified in their respective buffers. Km and Kcat values are comparable between the two buffers. Fluorescence data indicate comparable Trp – Tyr behaviors in hTSwt with increased concentrations of both phosphate and sulfate ions; moreover, spectrum shape may underline more data than at a glance. Proline mutated LR peptides shown 24-56% inhibition; [Pro2]LR the most active. Conjugation was successfully achieved, with a molar ratio close to 1:2:1. Fluorescence anisotropy data of the enzyme – inhibitor interaction is still under evaluation, yet indicating a decrease in the observable, thus under further analysis. During my six months period abroad, two bladder carcinoma lines (5637, RT112) have been employed in testing a methotrexate – like photosensitive molecule. Such an assessment was carried out through MTS assay and treated / control cell survival ratio. Preliminary data from show comparable activity between the photosensitive molecule and methotrexate, albeit with an increased sensibility from the former rather than the latter. The data presented in the thesis poses as a spark to ignite further discussion and experiments. Thermodynamic techniques may find fertile ground in such sense, quantifying the energy footprint in molecules’ binding and structural changes.


2019 - Cyclic Peptides Acting as Allosteric Inhibitors of Human Thymidylate Synthase and Cancer Cell Growth [Articolo su rivista]
Pacifico, Salvatore; Santucci, Matteo; Luciani, Rosaria; Saxena, Puneet; Linciano, Pasquale; Ponterini, Glauco; Lauriola, Angela; D'Arca, Domenico; Marverti, Gaetano; Guerrini, Remo; Costi, Maria Paola
abstract

Thymidylate synthase (TS) is a prominent drug target for different cancer types. However, the prolonged use of its classical inhibitors, substrate analogs that bind at the active site, leads to TS overexpression and drug resistance in the clinic. In the effort to identify anti-TS drugs with new modes of action and able to overcome platinum drug resistance in ovarian cancer, octapeptides with a new allosteric inhibition mechanism were identified as cancer cell growth inhibitors that do not cause TS overexpression. To improve the biological properties, 10 cyclic peptides (cPs) were designed from the lead peptides and synthesized. The cPs were screened for the ability to inhibit recombinant human thymidylate synthase (hTS), and peptide 7 was found to act as an allosteric inhibitor more potent than its parent open-chain peptide [Pro3]LR. In cytotoxicity studies on three human ovarian cancer cell lines, IGROV-1, A2780, and A2780/CP, peptide 5 and two other cPs, including 7, showed IC50 values comparable with those of the reference drug 5-fluorouracil, of the open-chain peptide [d-Gln4]LR, and of another seven prolyl derivatives of the lead peptide LR. These promising results indicate cP 7 as a possible lead compound to be chemically modified with the aim of improving both allosteric TS inhibitory activity and anticancer effectiveness.


2019 - Discovery of a benzothiophene-flavonol halting miltefosine and antimonial drug resistance in Leishmania parasites through the application of medicinal chemistry, screening and genomics [Articolo su rivista]
Borsari, Chiara; Dolores Jimenez-Anton, María; Eick, Julia; Bifeld, Eugenia; Jose Torrado, Juan; Isabel Olías-Molero, Ana; Jesús Corral, María; Santarem, Nuno; Baptista, Catarina; SEVERI, LEDA; Gul, Sheraz; Wolf, Markus; Kuzikov, Maria; Ellinger, Bernhard; Reinshagen, Jeanette; Witt, Gesa; LINCIANO, PASQUALE; TAIT, Annalisa; COSTANTINO, Luca; LUCIANI, Rosaria; Tejera Nevado, Paloma; Zander-Dinse, Dorothea; Franco, Caio H.; Ferrari, Stefania; Moraes, Carolina B.; Cordeiro-da-Silva, Anabela; PONTERINI, Glauco; Clos, Joachim; María Alunda, Jose; COSTI, Maria Paola
abstract

Leishmaniasis, a major health problem worldwide, has a limited arsenal of drugs for its control. The appearance of resistance to first- and second-line anti-leishmanial drugs confirms the need to develop new and less toxic drugs that overcome spontaneous resistance. In the present study, we report the design and synthesis of a novel library of 38 flavonol-like compounds and their evaluation in a panel of assays encompassing parasite killing, pharmacokinetics, genomics and ADME-Toxicity resulting in the progression of a compound in the drug discovery value chain. Compound 19, 2-(benzo[b]thiophen-3-yl)- 3-hydroxy-6-methoxy-4H-chromen-4-one, exhibited a broad-spectrum activity against Leishmania spp. (EC50 1.9 mM for Leishmania infantum, 3.4 mM for L. donovani, 6.7 mM for L. major), Trypanosoma cruzi (EC50 7.5 mM) and T. brucei (EC50 0.8 mM). Focusing on anti-Leishmania activity, compound 19 challenge in vitro did not select for resistance markers in L. donovani, while a Cos-Seq screening for dominant resistance genes identified a gene locus on chromosome 36 that became ineffective at concentrations beyond EC50. Thus, compound 19 is a promising scaffold to tackle drug resistance in Leishmania infection. In vivo pharmacokinetic studies indicated that compound 19 has a long half-life (intravenous (IV): 63.2 h; per os (PO): 46.9 h) with an acceptable ADME-Toxicity profile. When tested in Leishmania infected hamsters, no toxicity and limited efficacy were observed. Low solubility and degradation were investigated spectroscopically as possible causes for the sub-optimal pharmacokinetic properties. Compound 19 resulted a specific compound based on the screening against a protein set, following the intrinsic fluorescence changes.


2019 - Excited-state intramolecular proton transfer in a bioactive flavonoid provides fluorescence observables for recognizing its engagement with target proteins [Articolo su rivista]
Vanossi, D.; Caselli, M.; Pavesi, G.; Borsari, C.; Linciano, P.; Costi, M. P.; Ponterini, G.
abstract

A benzothiophene-substituted chromenone with promising activity against Leishmania and Trypanosoma species exhibits peculiar fluorescence properties useful for identifying its complexes with target proteins in the microorganism proteomes. The emission spectra, anisotropy and time profiles of this flavonoid strongly change when moving from the free to the protein-bound forms. The same two types of emission are observed in organic solvents and their mixtures with water, with the relative band intensities depending on the solvent ability to establish hydrogen bonds with the solute. The regular emission prevails in protic solvents, while in aprotic solvents the anomalously red-shifted emission occurs from a zwitterionic tautomeric form, produced in the excited state by proton transfer within the intramolecularly H-bonded form. This interpretation finds support from an experimental and theoretical investigation of the conformational preferences of this compound in the ground and lowest excited state, with a focus on the relative twisting about the chromenone-benzothiophene interconnecting bond. An analysis of the absorption and emission spectra and of the photophysical properties of the two emitting tautomers highlights the relevance of the local microenvironment, particularly of the intra- and intermolecular hydrogen bonds in which this bioactive compound is involved, in determining both its steady-state and time-resolved fluorescence behaviour.


2019 - IL GIOCO MOLECOLARE TRA DRUG DISCOVERY E CHEMICAL BIOLOGY [Articolo su rivista]
Costi, Maria Paola; Guerrini, Remo; Ponterini, Glauco
abstract

La chemical biology è una disciplina vicina alla chimica farmaceutica strettamente connessa al processo di drug discovery mediante uno scambio di ruolo di inibitori/ligandi e probe molecolari. In tre esempi di applicazione della chemical biology-drug discovery vengono illustrati i linker per la bioconiugazione, le sonde fluorescenti in studi di interazione farmacorecettore cellulare (target engagement) e l’indagine proteomica dei meccanismi biologici d’azione di inibitori specifici.


2019 - SAR Studies and Biological Characterization of a Chromen-4-one Derivative as an Anti-Trypanosoma brucei Agent [Articolo su rivista]
Borsari, Chiara; Santarem, Nuno; Macedo, Sara; Jiménez-Antón, María Dolores; Torrado, Juan J.; Olías-Molero, Ana Isabel; Corral, María J.; Tait, Annalisa; Ferrari, Stefania; Costantino, Luca; Luciani, Rosaria; Ponterini, Glauco; Gul, Sheraz; Kuzikov, Maria; Ellinger, Bernhard; Behrens, Birte; Reinshagen, Jeanette; Alunda, José María; Cordeiro-da-Silva, Anabela; Costi, Maria Paola
abstract

Chemical modulation of the flavonol 2-(benzo[d][1,3]dioxol-5-yl)-chromen-4-one (1), a promising anti-Trypanosomatid agent previously identified, was evaluated through a phenotypic screening approach. Herein, we have performed structure–activity relationship studies around hit compound 1. The pivaloyl derivative (13) showed significant anti-T. brucei activity (EC50 = 1.1 μM) together with a selectivity index higher than 92. The early in vitro ADME-tox properties (cytotoxicity, mitochondrial toxicity, cytochrome P450 and hERG inhibition) were determined for compound 1 and its derivatives, and these led to the identification of some liabilities. The 1,3-benzodioxole moiety in the presented compounds confers better in vivo pharmacokinetic properties than those of classical flavonols. Further studies using different delivery systems could lead to an increase of compound blood levels.


2019 - The 1,10-phenanthroline ligand enhances the antiproliferative activity of DNA-intercalating thiourea-Pd(II) and -Pt(II) complexes against cisplatin-sensitive and –resistant human ovarian cancer cell lines. [Articolo su rivista]
Marverti, G.; Gozzi, G.; Lauriola, A.; Ponterini, G.; Belluti, S.; Imbriano, C.; Costi, M. P.; D’Arca, D.
abstract

Ovarian cancer is the most lethal gynecological malignancy, often because of the frequent insurgence of chemoresistance to the drugs currently used. Thus, new therapeutical agents are needed. We tested the toxicity of 16 new DNA-intercalating agents to cisplatin (cDDP)-sensitive human ovarian carcinoma cell lines and their resistant counterparts. The compounds were the complexes of Pt(II) or Pd(II) with bipyridyl (bipy) and phenanthrolyl (phen) and with four dierent thiourea ancillary ligands. Within each of the four series of complexes characterized by the same thiourea ligand, the Pd(phen) drugs invariably showed the highest anti-proliferative ecacy. This paralleled both a higher intracellular drug accumulation and a more ecient DNA intercalation than all the other metal-bidentate ligand combinations. The consequent inhibition of topoisomerase II activity led to the greatest inhibition of DNA metabolism, evidenced by the inhibition of the expression of the folate cycle enzymes and a marked perturbation of cell-cycle distribution in both cell lines. These findings indicate that the particular interaction of Pd(II) with phenanthroline confers the best pharmacokinetic and pharmacodynamic properties that make this class of DNA intercalators remarkable inhibitors, even of the resistant cell growth.


2018 - Conformational Propensity and Biological Studies of Proline Mutated LR Peptides Inhibiting Human Thymidylate Synthase and Ovarian Cancer Cell Growth [Articolo su rivista]
Saxena, Puneet; Severi, Leda; Santucci, Matteo; Taddia, Laura; Ferrari, Stefania; Luciani, Rosaria; Marverti, Gaetano; Marraccini, Chiara; Tondi, Donatella; Mor, Marco; Laura, Scalvini; Vitiello, Simone; Losi, Lorena; Fonda, Sergio; Pacifico, Salvatore; Guerrini, Remo; D'Arca, Domenico; Ponterini, Glauco; Costi, Maria Paola
abstract

LR and [D-Gln4]LR peptides bind the mono- mer−monomer interface of human thymidylate synthase and inhibit cancer cell growth. Here, proline-mutated LR peptides were synthesized. Molecular dynamics calculations and circular dichroism spectra have provided a consistent picture of the conformational propensities of the [Pron]-peptides. [Pro3]LR and [Pro4]LR show improved cell growth inhibition and similar intracellular protein modulation compared with LR. These represent a step forward to the identification of more rigid and metabolically stable peptides.


2018 - Fluorometric detection of protein-ligand engagement: The case of phosphodiesterase5 [Articolo su rivista]
Di Rocco, Giulia; Martinelli, Ilaria; Pacifico, Salvatore; Guerrini, Remo; Cichero, Elena; Fossa, Paola; Franchini, Silvia; Cardarelli, Silvia; Giorgi, Mauro; Sola, Marco; Ponterini, Glauco
abstract

Phosphodiesterases (PDEs) regulate the intracellular levels of cAMP and cGMP. The great clinical success of the PDE5 inhibitors, Sildenafil (Viagra), Vardenafil (Levitra) and Tadalafil (Cialis) has led to an increasing interest for this class of enzymes. Recent studies have shown a correlation between tumor growth and PDE5 overexpression, making PDE5-selective inhibitors promising candidates for cancer treatment. The search for such inhibitors rests today on radioactive assays. In this work, we exploit the conserved catalytic domain of the enzyme and propose a faster and safer method for detecting the binding of ligands and evaluate their affinities. The new approach takes advantage of Förster Resonance Energy Transfer (FRET) between, as the donor, a fluorescein-like diarsenical probe able to covalently bind a tetracysteine motif fused to the recombinant PDE5 catalytic domain and, as the acceptor, a rhodamine probe covalently bound to the pseudosubstrate cGMPS. The FRET efficiency decreases when a competitive ligand binds the PDE5 catalytic site and displaces the cGMPS-rhodamine conjugate. We have structurally investigated the PDE5/cGMPS-rhodamine complex by molecular modelling and have used the FRET signal to quantitatively characterize its binding equilibrium. Competitive displacement experiments were carried out with tadalafil and cGMPS. An adaptation of the competitive-displacement equilibrium model yielded the affinities for PDE5 of the incoming ligands, nano- and micromolar, respectively.


2018 - Human Thymidylate Synthase Inhibitors Halting Ovarian Cancer Growth [Articolo su rivista]
Ferrari, Stefania; Severi, Leda; Cecilia, Pozzi; Quotadamo, Antonio; Ponterini, Glauco; Losi, Lorena; Marverti, Gaetano; Costi, Maria Paola
abstract

Human thymidylate synthase (hTS) has an important role in DNA biosynthesis, thus it is essential for cell survival. TS is involved in the folate pathways, specifically in the de novo pyrimidine biosynthesis. Structure and functions are intimately correlated, account for cellular activity and, in a broader view, with in vivo mechanisms. hTS is a target for anticancer agents, some of which are clinical drugs. The understanding of the detailed mechanism of TS inhibition by currently used drugs and of the interaction with the mechanism of action of other anticancer agents can suggest new perspective of TS inhibition able to improve the anticancer effect and to overcome drug resistance. TS-targeting drugs in therapy today are inhibitors that bind at the active site and that mostly resemble the substrates. Nonsubstrate analogs offer an opportunity for allosteric binding and novel mode of inhibition in the cancer cells. This chapter illustrates the relationship among the large number of hTS actions at molecular and clinical levels, its role as a target for ovarian cancer therapy, in particular in cases of overexpression of hTS and other folate proteins such as those induced by platinum drug treatments, and address the potential combination of TS inhibitors with other suitable anticancer agents.


2018 - New TRAP1 and Hsp90 chaperone inhibitors with cationic components: Preliminary studies on mitochondrial targeting [Articolo su rivista]
Rondanin, R.; Lettini, G.; Oliva, P.; Baruchello, R.; Costantini, C.; Trapella, C.; Simoni, D.; Bernardi, T.; Sisinni, L.; Pietrafesa, M.; Ponterini, G.; Costi, M. P.; Vignudelli, T.; Luciani, R.; Matassa, D. S.; Esposito, F.; Landriscina, Matteo
abstract

TRAP1 (Hsp75) is the mitochondrial paralog of the Hsp90 molecular chaperone family. Due to structural similarity among Hsp90 chaperones, a potential strategy to induce apoptosis through mitochondrial TRAP1 ATPase inhibition has been envisaged and a series of compounds has been developed by binding the simple pharmacophoric core of known Hsp90 inhibitors with various appendages bearing a permanent cationic head, or a basic group highly ionizable at physiologic pH. Cationic appendages were selected as vehicles to deliver drugs to mitochondria. Indeed, masses of new derivatives were evidenced to accumulate in the mitochondrial fraction from colon carcinoma cells and a compound in the series, with a guanidine appendage, demonstrated good activity in inhibiting recombinant TRAP1 ATPase and cell growth and in inducing apoptotic cell death in colon carcinoma cells.


2018 - pH-Promoted Release of a Novel Anti-Tumour Peptide by “Stealth” Liposomes: Effect of Nanocarriers on the Drug Activity in Cis-Platinum Resistant Cancer Cells [Articolo su rivista]
Sacchetti, Francesca; Marverti, Gaetano; D’Arca, Domenico; Severi, Leda; Maretti, Eleonora; Iannuccelli, Valentina; Pacifico, Salvatore; Ponterini, Glauco; Costi, Maria Paola; Leo, Eliana
abstract

Purpose: To evaluate the potential effects of PEGylated pH-sensitive liposomes on the intracellular activity of a new peptide recently characterized as a novel inhibitor of the human thymidylate synthase (hTS) over-expressed in many drug-resistant human cancer cell lines. Methods: Peptide-loaded pH-sensitive PEGylated (PpHL) and non-PEGylated liposomes (nPpHL) were carefully characterized and delivered to cis-platinum resistant ovarian cancer C13* cells; the influence of the PpHL on the drug intracellular activity was investigated by the Western Blot analysis of proteins involved in the pathway affected by hTS inhibition. Results: Although PpHL and nPpHL showed different sizes, surface hydrophilicities and serum stabilities, both carriers entrapped the drug efficiently and stably demonstrating a pH dependent release; moreover, the different behavior against J774 macrophage cells confirmed the ability of PEGylation in protecting liposomes from the reticuloendothelial system. Comparable effects were instead observed against C13* cells and biochemical data by immunoblot analysis indicated that PEGylated pH-sensitive liposomes do not modify the proteomic profile of the cells, fully preserving the activity of the biomolecule. Conclusion: PpHL can be considered as efficient delivery systems for the new promising anti-cancer peptide.


2016 - Excitation-Energy Transfer Paths from Tryptophans to Coordinated Copper Ions in Engineered Azurins: a Source of Observables for Monitoring Protein Structural Changes [Articolo su rivista]
DI ROCCO, Giulia; Bernini, Fabrizio; Borsari, Marco; Martinelli, Ilaria; Bortolotti, Carlo Augusto; Battistuzzi, Gianantonio; Ranieri, Antonio; Caselli, Monica; Sola, Marco; Ponterini, Glauco
abstract

The intrinsic fluorescence of recombinant proteins offers a powerful tool to detect and characterize structural changes induced by chemical or biological stimuli. We show that metal-ion binding to a hexahistidine tail can significantly broaden the range of such structurally sensitive fluorescence observables. Bipositive metal-ions as Cu2+, Ni2+ and Zn2+ bind 6xHis-tag azurin and its 6xHis-tagged R129W and W48A-R129W mutants with good efficiency and, thereby, quench their intrinsic fluorescence. Due to a much more favourable spectral overlap, the 6xHis-tag/Cu2+ complex(es) are the most efficient quenchers of both W48 and W129 emissions. Based on simple Förster-type dependence of energy-transfer efficiency on donor/acceptor distance, we can trace several excitation-energy transfer paths across the protein structure. Unexpected lifetime components in the azurin 6xHis-tag/Cu2+ complex emission decays reveal underneath complexity in the conformational landscape of these systems. The new tryptophan emission quenching paths provide additional signals for detecting and identifying protein structural changes.


2016 - Intracellular quantitative detection of human thymidylate synthase engagement with an unconventional inhibitor using tetracysteine-diarsenical-probe technology [Articolo su rivista]
Ponterini, Glauco; Martello, Andrea; Pavesi, Giorgia; Lauriola, Angela; Luciani, Rosaria; Santucci, Matteo; Pela', Michela; Gozzi, Gaia; Pacifico, Salvatore; Guerrini, Remo; Marverti, Gaetano; Costi, Maria Paola; D'Arca, Domenico
abstract

Demonstrating a candidate drug' s interaction with its target protein in live cells is of pivotal relevance to the successful outcome of the drug discovery process. Although thymidylate synthase (hTS) is an important anticancer target protein, the efficacy of the few anti-hTS drugs currently used in clinical practice is limited by the development of resistance. Hence, there is an intense search for new, unconventional anti-hTS drugs; there are approximately 1600 ongoing clinical trials involving hTS-targeting drugs, both alone and in combination protocols. We recently discovered new, unconventional peptidic inhibitors of hTS that are active against cancer cells and do not result in the overexpression of hTS, which is a known molecular source of resistance. Here, we propose an adaptation of the recently proposed tetracysteine-arsenic-binding-motif technology to detect and quantitatively characterize the engagement of hTS with one such peptidic inhibitor in cell lysates. This new model can be developed into a test for high-throughput screening studies of intracellular target-protein/small-molecule binding.


2016 - Optical and photophysical properties of anisole and cyanobenzene-substituted perylene diimides [Articolo su rivista]
Pagoaga, Bernard; Mongin, Olivier; Caselli, Monica; Vanossi, Davide; Momicchioli, Fabio; Blanchard Desce, Mireille; Lemercier, Gilles; Hoffmann, Norbert; Ponterini, Glauco
abstract

One- and two-photon absorption cross-sections and spectra and the photophysical properties of eight perylenetetracarboxy-3,4:9,10-diimide (PDI) derivatives are reported and analyzed. The investigated compounds are characterized by direct binding of the phenyl rings of the substituents to the bay positions of the perylene core. They have been designed to test the effects of differences in the electronic nature – electron donating (anisole) or accepting (cyanobenzene) – and binding topology (cis or trans, meta or para disubstitution or tetrasubstitution) of the bay substituents on the above optical and photophysical observables. (TD)DFT and Hu¨ckel MO calculations have provided theoretical information on the ground-state geometries, the MOs and the electronic spectra of several model compounds. For tetrasubstituted and cis disubstituted derivatives, strong steric interactions in the bay area determined the preferred conformations, with perylene cores distorted near the substituted bay(s) and a 42–441 twisting of the substituent rings relative to the core, quite irrespective of the electronic nature of the substituents. On the other hand, in trans-disubstituted PDI steric hindrance in the bay areas was much weaker and similar in the cyanobenzene and the anisole derivatives. So, the large differences found in the conformational preferences were completely attributable to electronic effects. With electron-accepting cyanobenzene, the substituent rings were found normal to the central planar perylene core, thus enabling the assignment of the moderate spectroscopic effects to inductive interactions. The DFT analysis of the PDI trans-disubstituted with electron-donating anisoles gave quite strongly distorted perylene-core geometries and less twisted (591) substituent rings. The corresponding increased substituent/core conjugative interactions resulted in new CT allowed electronic transitions and an extremely pronounced solvent-polarity dependence of the emission spectra and intensities. All anisole substituted PDI feature a very fast radiationless decay path in polar solvents, likely related to a relaxation to a charge-separated configuration in the lowest excited-state.


2016 - Virtual Screening and X-ray Crystallography Identify Non-Substrate Analog Inhibitors of Flavin-Dependent Thymidylate Synthase [Articolo su rivista]
Luciani, Rosaria; Saxena, Puneet; Surade, Sachin; Santucci, Matteo; Venturelli, Alberto; Borsari, Chiara; Marverti, Gaetano; Ponterini, Glauco; Ferrari, Stefania; Blundell, Tom L; Costi, Maria Paola
abstract

Thymidylate synthase-X (ThyX) represents an attractive target for tuberculosis drug discovery. Herein, we selected 16 compounds through a virtual screening approach. We solved the first X-ray crystal structure of Thermatoga maritima ThyX in complex with a non-substrate analog inhibitor. Given the active site similarities between Mtb-ThyX and Tm-ThyX, our crystal structure paves the way for a structure-based design of novel antimycobacterial compounds. The 1H-imidazo[4,5-d]pyridazine was identified as scaffold for the development of Mtb-ThyX inhibitors.


2015 - ANTICANCER DRUGS [Brevetto]
Costantino, Luca; Costi, Maria Paola; Ponterini, Glauco; Marverti, Gaetano; Franchini, Silvia; Tondi, Donatella; D'Arca, Domenico; Ferrari, Stefania; Luciani, Rosaria; Venturelli, Alberto; Sammak, Susan; Lauriola, Angela; Gozzi, Gaia
abstract

Composti destabilizzanti l’omodimero timidilato sintasi


2015 - Hotspots in an obligate homodimeric anticancer target. structural and functional effects of interfacial mutations in human thymidylate synthase [Articolo su rivista]
Salo Ahen, Outi M. H.; Tochowicz, Anna; Pozzi, Cecilia; Cardinale, Daniela; Ferrari, Stefania; Boum, Yap; Mangani, Stefano; Stroud, Robert M.; Saxena, Puneet; Myllykallio, Hannu; Costi, Maria Paola; Ponterini, Glauco; Wade, Rebecca C.
abstract

Human thymidylate synthase (hTS), a target for antiproliferative drugs, is an obligate homodimer. Single-point mutations to alanine at the monomer-monomer interface may enable the identification of specific residues that delineate sites for drugs aimed at perturbing the protein-protein interactions critical for activity. We computationally identified putative hotspot residues at the interface and designed mutants to perturb the intersubunit interaction. Dimer dissociation constants measured by a FRET-based assay range from 60 nM for wild-type hTS up to about 1 mM for single-point mutants and agree with computational predictions of the effects of these mutations. Mutations that are remote from the active site retain full or partial activity, although the substrate KM values were generally higher and the dimer was less stable. The lower dimer stability of the mutants can facilitate access to the dimer interface by small molecules and thereby aid the design of inhibitors that bind at the dimer interface.


2015 - Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance [Articolo su rivista]
Taddia, Laura; D'Arca, Domenico; Ferrari, Stefania; Marraccini, Chiara; Severi, Leda; Ponterini, Glauco; Assaraf, Yahuda G.; Marverti, Gaetano; Costi, Maria Paola
abstract

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemo-resistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug esistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.


2014 - A 5-(difluorenyl)-1,10-phenanthroline-based Ru(II) complex as a coating agent for potential multifunctional gold nanoparticles [Articolo su rivista]
J., Moreau; F., Lux; M., Four; J., Olesiak Banska; K., Matczyszyn; P., Perriat; C., Frochot; P., Arnoux; O., Tillement; M., Samoc; Ponterini, Glauco; S., Roux; G., Lemercier
abstract

The synthesis and photophysical properties of small gold nanoparticles (NPs, AuNP-[Ru-PFF]) surface functionalized by 5-substituted-1,10-phenanthroline-ligand based Ru(II) complexes are described. Luminescence of the grafted and confined Ru(II) complexes is totally quenched on the gold surface. Nonlinear optical properties were determined via Z-scan measurements in the range 600–1300 nm for both the free Ru(II) complex and the related NPs. In the short wavelength range (around 600 nm) the behaviour switches from that of two-photon absorption (2PA) for the complex to saturable absorption for the NPs. 2PA applications such as optical power limiting or two-photon dioxygen sensitization can be anticipated for these nanoplatforms.


2014 - EVALUATION OF LR STABILITY BY LC CHIP Q-TOF AND QUANTITATIVE DETERMINATION OF LR PEPTIDE CELL PENETRATION BY LC-MS/MS [Articolo su rivista]
Cazzato, ADDOLORATA STEFANIA; Cannazza, Giuseppe; Ponterini, Glauco; Marraccini, Chiara; Pirondi, Silvia; Genovese, Filippo; Costi, Maria Paola
abstract

In the present work the degradation profile of an anticancer peptide in different biological matrixes like DMEM (Dulbecco’s Modified Eagle Medium) and cell lysates by LC Chip Q-TOF was shown. Subsequently, an LC-MS/MS method for the quantitative analysis of LR in cell lysates was developed and fully validated.


2014 - Internalization and stability of a thymidylate synthase peptide inhibitor in ovarian cancer cells [Articolo su rivista]
Cannazza, Giuseppe; Cazzato, ADDOLORATA STEFANIA; Marraccini, Chiara; Pavesi, Giorgia; Pirondi, Silvia; R., Guerrini; M., Pelà; Frassineti, Chiara; Ferrari, Stefania; Marverti, Gaetano; Ponterini, Glauco; Costi, Maria Paola
abstract

Information on the cellular internalization and stability of the ovarian cancer cell growth inhibitor peptide, LSCQLYQR (LR), is vital for lead optimization. Ad-hoc-synthesized LR/fluorescent-probe conjugates were used to monitor the internalization of the peptide. Mass spectrometry was used to identify adducts resulting from the thiol reactivity of the cysteine residue in LR. A mechanistic model is proposed to explain the observed change in intracellular peptide amount over time. Structural modifications can be foreseen to improve the peptide stability.


2014 - Linear and nonlinear optical properties of V-shaped D–p–A–p–D chromophores: effects of the incorporation of aromatic rings in the polyenic p-bridges of open-chain ketocyanines [Articolo su rivista]
Momicchioli, Fabio; Ponterini, Glauco; Vanossi, Davide
abstract

Following previous studies on a and b polarizabilities of ketocyanines, a subgroup of D–p–A–p–D quadrupolar chromophores with moderately V-shaped structure, the present work analyses the effects of modifying the p-bridges connecting the D (NMe2) and A (CO) groups. This aim is pursued through a detailed comparison between the previously studied ketocyanines (KC2, KC3) and a Michler’s ketone analogue (KM1) bearing styrenic (in the place of polyenic) p-bridges. First, we report a spectroscopic study, including absorption and fluorescence anisotropy spectra, aimed to probe the electronic peculiarities of KM1 as well as to derive consistent three-state model (TSM) parameters for the three compounds. The paper goes on with an extensive theoretical study, carried out in the framework of the density functional theory (DFT), encompassing the structure, the electronic spectrum, a and b polarizabilities and two-photon absorption (TPA) cross-sections (sTP). Calculations performed according to the sum-over-states (SOS) approach are discussed with reference to the performances of few-state descriptions, it is shown that such descriptions (including TSM), which have been proved to be quite reliable in the case of KC2 and KC3, lose their effectiveness with KM1 because of the electronic characteristics related to the styrenic p-bridges. As to the TPA cross-sections, the results of TSM and SOS approaches concerning the TSM g - c and g - e transitions are supplemented by those obtained using the quadratic response theory. A common qualitative conclusion, traceable to the degree of bending of the V-shaped structure, is that in the case of KM1 the allowed (g - e) and the ‘‘forbidden’’ (g - c) transitions both should be observable in the TPA spectrum, as confirmed by experiment.


2014 - Mass Spectrometric/Bioinformatic Identification of a Protein Subset That Characterizes the Cellular Activity of Anticancer Peptides [Articolo su rivista]
Genovese, Filippo; A., Gualandi; L., Taddia; Marverti, Gaetano; S., Pirondi; C., Marraccini; P., Perco; M., Pelà; R., Guerrini; M. R., Amoroso; F., Esposito; A., Martello; Ponterini, Glauco; D'Arca, Domenico; Costi, Maria Paola
abstract

The preclinical study of the mechanism of action of anticancer small molecules is challenging due to the complexity of cancer biology and the fragmentary nature of available data. With the aim of identifying a protein subset characterizing the cellular activity of anticancer peptides, we used differential mass spectrometry to identify proteomic changes induced by two peptides, LR and [D-Gln4]LR, that inhibit cell growth and compared them with the changes induced by a known drug, pemetrexed, targeting the same enzyme, thymidylate synthase. The quantification of the proteome of an ovarian cancer cell model treated with LR yielded a differentially expressed protein data set with respect to untreated cells. This core set was expanded by bioinformatic data interpretation, the biologically relevant proteins were selected, and their differential expression was validated on three cis-platinum sensitive and resistant ovarian cancer cell lines. Via clustering of the protein network features, a broader view of the peptides’ cellular activity was obtained. Differences from the mechanism of action of pemetrexed were inferred from different modulation of the selected proteins. The protein subset identification represents a method of general applicability to characterize the cellular activity of preclinical compounds and a tool for monitoring the cellular activity of novel drug candidates.


2014 - Optimization of Peptides That Target Human Thymidylate Synthase to Inhibit Ovarian Cancer Cell Growth [Articolo su rivista]
M., Pelà; Saxena, Puneet; Luciani, Rosaria; Santucci, Matteo; Ferrari, Stefania; Marverti, Gaetano; Marraccini, Chiara; Martello, Andrea; Pirondi, Silvia; Genovese, Filippo; S., Salvadori; D'Arca, Domenico; Ponterini, Glauco; Costi, Maria Paola; R., Guerrini
abstract

Thymidylate synthase (TS) is a target for pemetrexed and the prodrug 5-fluorouracil (5-FU) that inhibit the protein by binding at its active site. Prolonged administration of these drugs causes TS overexpression, leading to drug resistance. The peptide lead, LR (LSCQLYQR), allosterically stabilizes the inactive form of the protein and inhibits ovarian cancer (OC) cell growth with stable TS and decreased dihydrofolate reductase (DHFR) expression. To improve TS inhibition and the anticancer effect, we have developed 35 peptides by modifying the lead. The D-glutamine-modified peptide displayed the best inhibition of cisplatin-sensitive and -resistant OC cell growth, was more active than LR and 5-FU, and showed a TS/DHFR expression pattern similar to LR. Circular dichroism spectroscopy and molecular dynamics studies provided a molecular-level rationale for the differences in structural preferences and the enzyme inhibitory activities. By combining target inhibition studies and the modulation pattern of associated proteins, this work avenues a concept to develop more specific inhibitors of OC cell growth and drug leads.


2014 - Peptides binding to the dimer interface of thymidylate synthase for the treatment of cancer [Brevetto]
Costi, Maria Paola; Ferrari, Stefania; Venturelli, Alberto; Ponterini, Glauco; Cardinale, Daniela; Marverti, Gaetano
abstract

The present invention relates to peptides binding to the thymidylate synthase protein, in particular to human thymidylate synthase (hTS) protein, for the treatment of cancer.The present invention relates to peptides that can bind at a binding site located at the interface of thymdylate synthase protein. These peptides range from 3 to 10, preferably 4-8 amino acids and have a sequence that binds to each subunit of the thymidylate synthase dimer at the level of dimer interface, stabilizing the dimeric inactive form of the thymdylate synthase enzyme. In addition, the present invention relates to pharmaceutical compositions comprising these compounds as active agents, and uses thereof for the treatment of cancer and to reverse or/and be active in cancer drug resistance.


2014 - Peptides binding to the dimer interface of thymidylate synthase for the treatment of cancer-US8916679 “B2 - Granted patent as second publication”. [Brevetto]
Costi, Maria Paola; Marverti, Gaetano; Cardinale, Daniela; Venturelli, Alberto; Ferrari, Stefania; Ponterini, Glauco
abstract

Peptides binding to the dimer interface of thymidylate synthase for the treatment of cancer AB (EP2507255) Provided are peptides that bind to the thymidylate synthase protein, in particular to human thymidylate synthase (hTS) protein, for the treatment of cancer. Further provided are peptides that can bind at a binding site located at the interface of thymidylate synthase protein. These peptides range from 3 to 10, preferably 4-8 amino acids and have a sequence that binds to each subunit of the thymidylate synthase dimer at the level of dimer interface, stabilizing the dimeric inactive form of the thymidylate synthase enzyme. In addition, provided are pharmaceutical compositions including these compounds as active agents, and uses thereof for the treatment of cancer and to reverse or/and be active in cancer drug resistance. (From US8916679 B2)


2013 - A comparative study of two amphiphilic merocyanines: from monomers to aggregates in Langmuir and Langmuir–Blodgett mixed films [Articolo su rivista]
LODI, ANDREA; MOMICCHIOLI, Fabio; CASELLI, Monica; G., Giancane; PONTERINI, Glauco
abstract

The Langmuir–Blodgett (LB) films with J aggregates of the amphiphilic MC2 merocyanine have been deeply investigated for more than two decades, mainly because of their interest for applications in photonic devices. To extend the excitation/emission wavelength range, we have studied an homologous dye, MC1, based on a shorter merocyanine chromophore, aiming at checking the ability of this compound to arrange into J aggregates within stable LB films. In this comparative MC1/MC2 investigation, we have addressed the structural and spectroscopic properties of the monomers in solution, the thermodynamic and morphological properties of the Langmuir monolayers at the air–water interface and the spectroscopic and photophysical properties, and the structural features thence obtainable, of the aggregates in the LB films. 1H NMR experiments have shown that, in chloroform solutions, both dyes adopt planar conformations with the hydrophilic and hydrophobic groups pointing to opposite directions. Strongly attractive interactions are exhibited by both dyes towards arachidic acid in monolayers at the air– subphase interface, with a maximum stability for the 1 : 2 MC(1/2) : AA mixture. Relatively homogeneous LB multilayers have been obtained from 1 : 4 and 1 : 2 MC : AA mixtures with good transfer ratios. Absorption and emission of the LB films of MC1 are dominated by J aggregates, while those of MC2 show some H aggregate contributions too. The J aggregates of both compounds exhibit a tendency to align with the transition dipoles along the film dipping direction, only slightly tilted relative to the substrate surface; however, this tendency is more pronounced for the MC1 J aggregates. Overall, MC1 yields slightly more stable monolayers and more solid multilayers compared to MC2.


2013 - A proteomic approach to investigate the mechanism of action of anticancer peptides [Relazione in Atti di Convegno]
Genovese, Filippo; Gualandi, Alessandra; Taddia, Laura; Caselli, Monica; Ponterini, Glauco; Ferrari, Stefania; Marverti, Gaetano; R., Guerrini; M., Pela'; Pavesi, Giorgia; C., Trapella; Costi, Maria Paola
abstract

Many efforts to improve survival of patients affected by Ovarian Cancer (OC) have focused on more effective systemic therapies and on the search for new therapeutic targets. One of the molecular targets for OC is human Thymidylate Synthase (hTS), a homodimeric enzyme essential for DNA biosynthesis. The main goal of our research is to identify compounds able to inhibit hTS by interfering with its dimerization, without causing its over-expression and the onset of cellular drug resistance against the traditional hTStargeted compounds. We have recently discovered some peptides which specifically target the hTS dimer interface and inhibit the enzyme by stabilizing its di-inactive form [1]. These molecules have been recently investigated for their SAR profile. LR, our lead compound, inhibits the intracellular enzyme in both cisplatin (cDDP)-sensitive and -resistant ovarian cancer cells without causing protein overexpression, thus showing a potential for overcoming the limits of OC chemotherapy. This work aims at setting up a proteomic approach able to provide information on the changes in the protein expression profile induced in OC cells by treatment with LR with respect to a well-known folate antimetabolite, Pemetrexed (PTX) and identify key proteins that are involved in its mechanism of action.


2013 - Fluorescence Observables and Enzyme Kinetics in the Investigation of PPI Modulation by Small Molecules: Detection, Mechanistic Insight, and Functional Consequences [Capitolo/Saggio]
Ponterini, Glauco
abstract

The potential of fluorescence-based methods and kinetic analysis in the screening and molecular-scale mechanistic investigation of PPI modulation by small molecules is discussed through several representative examples collected and commented. These experimental approaches take advantage of a variety of observables. Changes in the protein aggregation pattern have been monitored through fluorescence properties such as spectra, intensities (related to quantum yields), time-decays, and anisotropies of intrinsic protein fluorophores, of extrinsic fluorescent tags and, even, of the same small molecules added to modulate PPIs, as well as through bimolecular excited-state processes such as static and collisional quenching, including electron and excitation-energy transfer, or exciton interaction, whose efficiencies are crucially structure dependent. Besides allowing for quali/quantitative information on the small-molecule induced PPI modulation, these approaches can take advantage from the sensitivity of fluorescence observables on fine structural details to shed light on the molecular-scale mechanisms of action and their functional consequences. Direct investigation of the latter by kinetic inhibition analysis represents a useful change in perspective whenever PPI are relevant for enzyme activity. Dissociative inhibition, that is, the ability of some small molecules to inhibit enzymes by disrupting their active oligomeric assembly is shortly reviewed.


2013 - Fragment Based Discovery of Thymidylate Synthase Dimeric Interface Inhibitors Through Mass Spectrometry. Invited lecture to the Fragment Based Lead Discovery track. [Relazione in Atti di Convegno]
Costi, Maria Paola; Ponterini, Glauco; Ferrari, Stefania; Costantino, Luca; Franchini, Silvia; Venturelli, Alberto; Genovese, Filippo
abstract

Fragment-based drug design has been applied to Thymidylate synthase.The strategy applied is Mass Spectrometry related. identification of small molecule library that can bind to the protein represents the starting point for further drug design of a novel class of TS inhibitors with high potential as anticancer agents.


2013 - NUOVE MOLECOLE, PER USO COME AGENTI ANTITUMORALI [Brevetto]
Costi, Maria Paola; Costantino, Luca; Sammak, Susan; Ponterini, Glauco; Ferrari, Stefania; Luciani, Rosaria; Farina, Davide Salvatore Francesco; Franchini, Silvia; Santucci, Matteo; Gabriele, Cruciani; Emanuele, Carosati
abstract

Oggetto del presente brevetto è una classe di prodotti chimici sintetizzati presso i laboratori del Dipartimento Scienze della Vita. Questi prodotti si sono dimostrati in grado di destabilizzare l’omodimero della timidilato sintasi umana, e sono i primi composti noti dotati di tale attività; quindi, come viene dettagliato nel testo del brevetto, rappresentano degli ottimi leads per lo sviluppo di farmaci antitumorali in possesso di un meccanismo di azione completamente nuovo.


2013 - Translational repression of thymidylate synthase by targeting its mRNA [Articolo su rivista]
D., Garg; A. V., Beribisky; Ponterini, Glauco; Ligabue, Alessio; Marverti, Gaetano; Martello, Andrea; Costi, Maria Paola; M., Sattler; R. C., Wade
abstract

Resistance to drugs targeting human thymidylate synthase (TS) poses a major challenge in the field of anti-cancer therapeutics. Overexpression of the TS protein has been implicated as one of the factors leading to the development of resistance. Therefore, repressing translation by targeting the TS mRNA could help to overcome this problem. In this study, we report that the compound Hoechst 33258 (HT) can reduce cellular TS protein levels without altering TS mRNA levels, suggesting that it modulates TS expression at the translation level. We have combined nuclear magnetic resonance, UV-visible and fluorescence spectroscopy methods with docking and molecular dynamics simulations to study the interaction of HT with a region in the TS mRNA. The interaction predominantly involves intercalation of HT at a CC mismatch in the region near the translational initiation site. Our results support the use of HT-like compounds to guide the design of therapeutic agents targeting TS mRNA.


2012 - Aggregation behaviour of a water-soluble ammonium-functionalizedpolythiophene: Luminescence enhancement induced by bile-acid anions [Articolo su rivista]
R., Cagnoli; Caselli, Monica; Libertini, Emanuela; Mucci, Adele; Parenti, Francesca; Ponterini, Glauco; Schenetti, Luisa
abstract

The water-soluble poly{trimethyl-[7-(3-thienylsulfanyl)heptyl]ammonium iodide-co-thiophene} (PTNDMe3) forms aggregates whose size span a large range of values, depending on solvent, concentrationand film formation conditions. Larger aggregates were detected by atomic force microscopy and dynamic light scattering, smaller ones by DOSY NMR, UVevisible and fluorescence. All techniques indicate a reduced aggregation of PTNDMe3 in DMSO relative to water and a marked de-aggregation of PTNDMe3 in water following addition of bile-acid anions such as deoxycholate and ursodeoxycholate.The latter effect shows itself through a very large enhancement of the polymer photoluminescence likely caused by disruption of aggregated non-emissive exciton traps. A tailored combination of electrostaticand hydrophobic interactions between the polymer and the bile-acid anions seems to be necessary to achieve this effect. These observations suggest that this polythiophene might provide a basis for the development of fluorescent sensors suitable for the detection of medium-sized amphiphilic biomolecules.


2012 - Chemical asymmetry and alpha and beta polarizabilities of D-A-D' chromophores: a three-state-model and TDDFT-SOS analysis of apenta-heptamethine ketocyanine [Articolo su rivista]
PONTERINI, Glauco; VANOSSI, Davide; MOMICCHIOLI, Fabio
abstract

The essential-state model, here amounting to a three-state model, has been employed to account for the effects of chemical asymmetry on the electronic alpha and beta polarizabilities of a pentaheptamethine ketocyanine (KC2,3), a prototypic D-A-D' chromophore. A suitable model, based on the idea of a ‘chromophoric site’, has been set up in terms of the three-state model features previously derived for the parent symmetric pentamethine and heptamethine ketocyanines, KC2 and KC3. This approach has been found to reproduce very well the experimental transition energies and dipoles. From the resulting properties of the ground and two relevant lowest excitedstates, average alpha and beta vec have been evaluated according to the SOS approach. The performances of themodel have been tested by comparison with the results of TDDFT SOS (hyper) polarizability calculations considering up to twenty excited states. A detailed analysis of the results for the threeketocyanines has shown a rapid convergence of the SOS expansion that supports the reliability of descriptions based on a few low lying excited states (here corresponding to p - p* excitations). However, while only two excited states were necessary for the symmetric compounds, for KC2,3 avalue of beta vec comparable with the converged value, as well as with that predicted by the experimentally-based three-state model, has been obtained including at least three excited states.Both the TDDFT SOS and the three-state model descriptions have emphasized the important role played by the three-level term contributions in the determination of beta vec. Moreover, bothdescriptions agree in predicting that KC2,3 features average alpha and beta vec values in between those of KC2 and KC3


2012 - Dottorato regionale Spinner-Nuove molecole per il controllo e la differenziazione delle cellule staminali-NovaMolStam- Università di Bologna, Ferrara, Modena e Reggio Emilia, Parma-Anno 2012-2015- [Altro]
Costi, Maria Paola; Costantino, Luca; Ponterini, Glauco; Cannazza, Giuseppe
abstract

L’uso di cellule staminali rappresenta un approccio promettente nel trattamento di malattie degenerative e di altre patologie che richiedono la rigenerazione tissutale. Tuttavia, nell’applicazione di questa strategia si incontrano numerosi problemi, quali il controllo della differenziazione, le reazioni immunitarie che si scatenano nell’applicazione, la specificità della differenziazione e della produzione stessa delle cellule. Per affrontare questi problemi è necessario conoscere la biologia cellulare, e i cammini (“pathway”) metabolici più importanti che governano i processi di differenziazione. Alcuni prodotti naturali e piccole molecole di origine sintetica si sono rivelati utili nel controllo e nella differenziazione delle cellule staminali. Tra questi, ad es., l’acido retinoico, il forskolin, il desametasone, l’azacitidina, che tuttavia mancano di specificità d’azione ed in generale hanno caratteristiche non ottimali. Sulla base delle conoscenze esistenti e dei composti attualmente in uso, appare quindi necessario e possibile ricercare nuove molecole dotate di profili biologici specifici. Il presente progetto ha l’obiettivo di identificare nuovi composti dotati di specificità d’azione verso cammini metabolici importanti per il controllo e la differenziazione delle cellule staminali. Tali composti saranno molecole di origine naturale e/o sintetica e potranno essere utilizzati per ottimizzare la produzione delle staminali da usare per scopi clinici. Non sono da intendere come farmaci, ma come sostanze che supportano e promuovono il miglioramento della tecnologia di produzione delle cellule per uso clinico. Per raggiungere questo obiettivo, il progetto si articolerà in fasi successive che prevedono: a) l’identificazione dei cammini metabolici più adatti per controllare le cellule staminali e la selezione dei bersagli molecolari più adeguati all’interno dei pathway; b) la progettazione di molecole potenzialmente attive su questi bersagli mediante strategie quali il “virtual screening”, l’analogia strutturale rispetto a composti attivi esistenti e lo screening biologico diretto; c) la sintesi dei composti o il loro isolamento da fonti naturali; d) la valutazione biologica su panel di enzimi e proteine e su cellule; e) l’ottimizzazione dei prodotti migliori selezionati dalle fasi b-d mediante criteri di “drug-likeness” e successivi cicli di sintesi e valutazione biologica. Per raggiungere i suddetti obiettivi verranno applicate strategie proprie della ricerca farmaceutica. Il punto a) prevede l’utilizzo di strumenti bioinformatici per la ricerca e l’analisi di database, lo studio di proprietà strutturali e funzionali delle proteine coinvolte per la prioritizzazione dei bersagli più adeguati. Il punto b) prevede l’utilizzo di protocolli per l’identificazione di composti nuovi da banche dati di composti noti (“virtual screening”), la progettazione di composti basati sulla conoscenza delle strutture 3D dei bersagli selezionati, lo screening sperimentale di librerie molecolari disponibili nei laboratori di ricerca dei partecipanti al progetto e/o la loro valutazione diretta sulle linee cellulari staminali presso i laboratori di collaboratori interessati al progetto (Centro di Medicina Rigenerativa di Modena). Il punto c) prevede l’utilizzo di tecniche di sintesi chimica per ottenere i composti progettati, l’estrazione di prodotti naturali da piante studiate nei laboratori coinvolti nel progetto, la caratterizzazione, separazione e sintesi dei prodotti naturali identificati come interessanti. Il punto d) prevede la valutazione biologica dei nuovi composti sintetizzati verso le biomolecole bersaglio scelte. Successivamente i composti migliori saranno valutati sulle linee cellulari staminali presso i laboratori del Centro di Medicina Rigenerativa di Modena, similmente al punto b), ma con metodiche più raffinate per val


2012 - Proteomic Approach to the Detection of the Mechanism of Action of Anticancer Peptides [Abstract in Rivista]
Genovese, Filippo; Gualandi, Alessandra; Taddia, Laura; Caselli, Monica; Ponterini, Glauco; Marverti, Gaetano; Pirondi, Silvia; R., Guerrini; M., Pela'; Pavesi, Giorgia; C., Trapella; Costi, Maria Paola
abstract

A label-free quantitative proteomic approach has been undertaken to study the effects of the peptide on the proteins involved in the modulated metabolic pathways, in particular those involved in the folate metabolism. Structure-activity relationships (SAR) have been performed to improve the lead peptide pharmacodynamics. All the compounds have been assayed and a protein profile set was studied to mark and validate their behavior as inhibitor of OC cell growth.


2012 - Unusual Targeting of the human Thymidylate synthase interface: a tethering approach with mass-spectrometric detection. [Relazione in Atti di Convegno]
Costi, Maria Paola; Franchini, Silvia; Ferrari, Stefania; R., Wade; S., Henrich; O., Salo; Genovese, Filippo; S., Mangani; Pozzi, Cristina; M., Santucci; Costantino, Luca; Sammak, Susan; G., Cruciani; E., Carosati; Ponterini, Glauco
abstract

Ovarian cancer is the fifth most common cause of death from cancer in women. The standard first-line treatment is a combination of paclitaxel and carboplatin (DDP) or carboplatin alone. In the case of progressive disease or drug resistance treatment with platinum, either alone or in combination, investigational compounds should be used (1). In the human ovarian carcinoma cell DDP-resistance was associated with cross-resistance to the thymidylate synthase (TS) inhibitor 5-fluorouracil (prodrug of 5FdUMP, fluorodeoxyuridine monophosphate) and methotrexate (2). We aim at restoring the sensibility to Platinum-based drugs through direct inhibition of Thymidylate synthase (TS) changing the mechanism of action from active site binders (classical TS inhibitors) to inhibitors of the regulatory function of monomeric TS through small molecule cellular perturbation. To this aim we applied a multidisciplinary approach to identify new molecules that could bind to specific pocket at the protein interface. We applied the tethering approach (3) that leads to the selection of disulfide compounds to anchor at the cystein on the monomeric interface (gray coloured balls on the left in the picture). Mass Spectrometry (MS) identification of the covalent TS-thiol complexes, and medicinal chemistry development of the identified hits (coloured structure on the right in the picture). We included cystein mutants design, site directed mutagenesis, disulfide library selection, tethering of thiol ligands at the protein interface through Mass spectrometry, X-ray crystallography, structure-based drug design and synthetic chemistry. The validation of the TS-interface inhibitor binders was accomplished trough FRET (Fluorescence resonance energy transfer) and enzyme kinetic assay. The strategies adopted and the midpoint/final results of the discovery processes will be presented. 1. Ozols RF et al. Lancet 2002;. 2. D.Cardinale et al, CMC, 2010, D.Cardinale et al, PNAS, 2011 ; 3. Stroud R et al PNAS 2000 and www.light-eu.org. The project is supported by FP6 european grant (LIGHTS, www.light-eu.org), LSH 038752 and AIRC-DROC-2012(http://www.droc-airc.unimore.it/site/home.html).


2012 - Zing meeting on Medicinal Chemistry 2012-Lanzarote-invitated lecture [Relazione in Atti di Convegno]
Costi, Maria Paola; Ferrari, Stefania; Ponterini, Glauco; Cardinale, Daniela; Guaitoli, Giambattista; Tondi, Donatella
abstract

Allosteric modulators of Thymidylate synthase, an anticancer drug target Costi MP, Wade Rc, Ferrari Sa, Ponterini Gd, Cardinale Da, Guaitoli Ga, Tondi Da, Marverti Ge, Myllikallio H.f Mangani S.g Thymdylate synthase (TS) plays a key role in the biosynthetic supply of thymidylate, an essential precursor for DNA replication and repair. Indeed, in human cells, downregulation of this pathway halts cellular replication and leads to apoptosis of cancer cells so, hTS active-site inhibitors are largely used in cancer chemotherapy. On the other hand, resistance frequently sets in during treatment with these drugs. While the molecular bases of this phenomenon are complex, there are evidences that it is correlated with protein overexpression presumably connected with the loss of RNA-binding capacity when the protein is bound to its inhibitors. It is therefore desirable to identify inhibitors that act through new mechanisms, such that RNA regulation is not altered1. The design of peptides that mimic portions of the monomer-monomer interface of multimeric proteins has been shown to be a useful approach for the discovery of inhibitors that bind at such interfaces2. In this contribution, we wish to show how these peptides interact with hTS in vitro: the main thermodynamic and structural aspects of this interaction, as well as its consequences on the enzyme catalytic efficiency, have been determined through a multidisciplinary approach of computational design, synthesis, X-ray crystallography and other biophysical techniques. These findings suggest a new mechanism of action and provide useful information for testing against ovarian cancer cells. We have tested the most potent peptides against ovarian cancer cells sensitive and resistant to cis-platin. The peptides were able to inhibit cancer cell growth and, differently from the classical inhibitors, do not show protein over expression. References. 1. E. Chu, et al. Identification of an RNA binding site for human thymidylate synthase. Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 517-521. 2. D. Cardinale, and M.P.Costi et al. Homodimeric enzymes as drug targets. Curr Med Chem. 2010,17, 826-46. The project is supported by FP6 european grant (LIGHTS, Small ligands to interfere with Thymidylate synthase dimer formation as new tools for development of anticancer agents against ovarian carcinoma. www.light-eu.org), LSH 038752. 


2011 - Electronic spectra and (hyper)polarizabilities of non-centrosymmetric D–A–D chromophores. An experimentally based three-state model and a theoretical TDDFT study of ketocyanines [Articolo su rivista]
Ponterini, Glauco; Vanossi, Davide; Krasnaya, Z. h. A.; A. S., Tatikolovc; Momicchioli, Fabio
abstract

The electronic structure, spectra and linear and second-order polarizabilities of two symmetricketocyanines, which are prototypic examples of D–A–D chromophores, have been investigatedwith two different toolsets: (i) the so-called ‘essential-state model’, here comprising three states,the ground and two lowest excited 1pp* states, has been adapted for these non-centrosymmetric,yet symmetric compounds to determine their permanent electric dipole moments, polarizabilitiesand first hyperpolarizabilities making use of experimental transition energies and moments; (ii)extensive TDDFT calculations have provided ground-state conformational results consistent withNMR-derived structural information, energies and dipole moments of up to 20 lowest-lyingelectronic states as well as, within the sum-over-states (SOS) scheme, the most relevantcomponents of the polarizabilities and first hyperpolarizabilities. The two levels of descriptionform consistent pictures of the ketocyanine excited states that provide the most relevantcontributions to hyperpolarizabilities: extension of the SOS set beyond the three states of thebasic model left unchanged (within B10%) the calculated vector component of the second-orderpolarizability tensor along the direction of the ground-state dipole moment (by). Both approachesindicate that these D–A–D compounds, in spite of their quasi-linear structure, reminiscent of thatof centrosymmetric quadrupolar chromophores, feature significant second-order molecularpolarizabilities. These rapidly increase with the length of the polyenic bridges in thechromophores. About half of the total value of by is predicted to come from the three-level-termpart, by,3, most of which derives from the contribution involving the three electronic states of theessential-state model.


2011 - Erratum: Protein-protein interface-binding peptides inhibit the cancer therapy target human thymidylate synthase (Proceedings of the National Academy of Sciences of the United States of America (2011) 108, 34 (E542-E549) DOI: 10.1073/pnas.1104829108) [Articolo su rivista]
Cardinale, D.; Guaitoli, G.; Tondi, D.; Luciani, R.; Henrich, S.; Salo-Ahen, O. M. H.; Ferrari, S.; Marverti, G.; Guerrieri, D.; Ligabue, A.; Frassineti, C.; Pozzi, C.; Mangani, S.; Fessas, D.; Guerrini, R.; Ponterini, G.; Wade, R. C.; Costi, M. P.
abstract


2011 - Protein–protein interface-binding peptides inhibit the cancer therapy target human thymidylate synthase [Articolo su rivista]
Cardinale, Daniela; Guaitoli, Giambattista; Tondi, Donatella; Luciani, Rosaria; S., Henrich; O. M. H., Salo Ahen; Ferrari, Stefania; Marverti, Gaetano; Guerrieri, Davide; Ligabue, Alessio; Frassineti, Chiara; C., Pozzi; S., Mangani; D., Fessas; R., Guerrini; Ponterini, Glauco; R. C., Wade; Costi, Maria Paola
abstract

Human thymidylate synthase is a homodimeric enzyme that playsa key role in DNA synthesis and is a target for several clinicallyimportant anticancer drugs that bind to its active site. We have designed peptides to specifically target its dimer interface. Here we show through X-ray diffraction, spectroscopic, kinetic, and calorimetric evidence that the peptides do indeed bind at the interface of the dimeric protein and stabilize its di-inactive form. The “LR” peptide binds at a previously unknown binding site and shows a previously undescribed mechanism for the allosteric inhibition of a homodimeric enzyme. It inhibits the intracellular enzyme in ovarian cancer cells and reduces cellular growth at low micromolar concentrations in both cisplatin-sensitive and -resistant cells without causing protein overexpression. This peptide demonstrates the potential of allosteric inhibition of hTS for overcoming platinum drug resistance in ovarian cancer.


2011 - XANES, UV-VIS and luminescence spectroscopic studyof chromophores in ancient HIMT glass [Articolo su rivista]
DE FERRI, Lavinia; Arletti, Rossella; Ponterini, Glauco; Quartieri, Simona
abstract

This work is aimed to the study of a series of Late Roman glass fragments belonging to the peculiar group called HIMT (High Iron Magnesium Titanium glass), characterized by different color nuances, and previously chemically characterized by our group. XANES, UV-VIS and luminescence spectroscopies are exploited for determining the distribution of the oxidation states ofthe two chromophores Fe and Mn. In all the ancient glass samples, Fe results to be mostly in its oxidate state 3+. The prevalent Mn oxidation state is 2+, however the presence of minor amounts of Mn3+ has been proved. The different spectroscopic techniques, used in a combined approach, areable to interpret the apparent anomalous colour of some of the ancient glass samples.


2010 - Design and characterization of a mutation outside the active site of human thymidylate synthase that affects ligand binding. [Articolo su rivista]
Cardinale, Daniela; O. M. H., Salo Ahen; Guaitoli, Giambattista; Ferrari, Stefania; Venturelli, Alberto; Franchini, Silvia; Battini, Renata; Ponterini, Glauco; R. C., Wade; Costi, Maria Paola
abstract

Due to its central role in DNA synthesis, human thymidylate synthase (hTS) is a well-established target for chemotherapeutic agents, such as fluoropyrimidines. The use of hTS inhibitors in cancer therapy is limited by their toxicity and the development of cellular drug resistance. Here, with the aim of shedding light on the structural role of the A-helix in fluoropyrimidine resistance, and we have created a fluoropyrimidine-resistant mutant by making a single point mutation, Glu30Trp. We postulated that residue 30, which is located in the A-helix, close to but outside the enzyme active site, could have a long-range effect on inhibitor binding. The mutant shows 100 times lower specific activity with respect to the wild-type hTS and is resistant to the classical inhibitor, FdUMP, as shown by a 6-fold higher inhibition constant. Circular dichroism experiments show that the mutant is folded. The results of molecular modeling and simulation suggest that the Glu30Trp mutation gives rise to resistance by altering the hydrogen-bond network between residue 30 and the active site.


2010 - Dimer-monomer equilibrium of human thymidylate synthase monitored by fluorescenceresonance energy transfer. [Articolo su rivista]
Genovese, Filippo; Ferrari, Stefania; Guaitoli, Giambattista; Caselli, Monica; Costi, Maria Paola; Ponterini, Glauco
abstract

An ad hoc bioconjugation/fluorescence resonance energy transfer (FRET) assay has been designed to spectroscopically monitor the quaternary state of human thymidylate synthase dimeric protein. The approach enables the chemoselective engineering of allosteric residues while preserving the native protein functions through reversible masking of residues within the catalytic site, and is therefore suitable for activity/oligomerization dual assay screenings. It is applied to tag the two subunits of human thymidylate synthase at cysteines 43 and 43' with an excitation energy donor/acceptor pair. The dimer-monomer equilibrium of the enzyme is then characterized through steady-state fluorescence determination of the inter-subunit resonance energy transfer efficiency.


2010 - Homodimeric Enzymes as Drug Targets [Articolo su rivista]
Cardinale, Daniela; O. M. H., Salo Ahen; Ferrari, Stefania; Ponterini, Glauco; G., Cruciani; E., Carosati; A. M., Tochowicz; S., Mangani; R. C., Wade; Costi, Maria Paola
abstract

Many enzymes and proteins are regulated by their quaternary structure and/or by their association in homoand/or hetero-oligomer complexes. Thus, these protein-protein interactions can be good targets for blocking or modulatingprotein function therapeutically. The large number of oligomeric structures in the Protein Data Bank (http://www.rcsb.org/) reflects growing interest in proteins that function as multimeric complexes. In this review, we consider the particularcase of homodimeric enzymes as drug targets. There is intense interest in drugs that inhibit dimerization of a functionallyobligate homodimeric enzyme. Because amino acid conservation within enzyme interfaces is often low compared to conservationin active sites, it may be easier to achieve drugs that target protein interfaces selectively and specifically. Twomain types of dimerization inhibitors have been developed: peptides or peptidomimetics based on sequences involved inprotein-protein interactions, and small molecules that act at hot spots in protein-protein interfaces. Examples include inhibitorsof HIV protease and HIV integrase. Studying the mechanisms of action and locating the binding sites of such inhibitorsrequires different techniques for different proteins. For some enzymes, ligand binding is only detectable in vivo orafter unfolding of the complexes. Here, we review the structural features of dimeric enzymes and give examples of inhibitionthrough interference in dimer stability. Several techniques for studying these complex phenomena will be presented.


2010 - Probing solute–solvent hydrogen bonding with fluorescent water-soluble curcuminoids [Articolo su rivista]
Caselli, Monica; Ferrari, Erika; Imbriano, Carol; Pignedoli, Francesca; Saladini, Monica; Ponterini, Glauco
abstract

Glycosylated water-soluble curcuminoids (C1–C3, first scheme of this article) differing in the 3,3-ringsubstituents (–OH, –OCH3 and H) equilibrate between the di-keto and the keto–enol forms. The formerare well observable in the absorption spectra in water, but their emissions are always negligible. Theketo–enol forms of C1–C3 exhibit a broad range of fluorescence quantum yields in different solvents,organic and water: formation of solute–solvent hydrogen bonds through the 3,3-ring substituents maychange the radiationless S1-state decay constant by up to a factor 200. Such a fluorescence quenchingmechanism is extremely efficient in water and, for C1, in accepting organic media. On the contrary, noeffects traceable to intermolecular hydrogen bonds involving the central -dicarbonyl moiety have beenobserved. So, fluorescence of these curcuminoids may probe the hydrogen bonding ability, particularly asacceptor, of their microenvironments, including hydrophilic/hydrophobic domains in complex biologicalsystems. Interaction of C1 and C2 with bovine serum albumin results in emission enhancements inverseto the quantum yields of the curcuminoids in water. The observations support the idea that, although thecurcuminoid microenvironment within its complex with the protein is less polar and hydrogen bondingthan water itself, residual water/ligand hydrogen bonds are active in enhancing radiationless transitions.Finally, fluorescence confocal images of HCT116 cells treated with C1–C3 suggest the apparently smallstructural differences to affect, besides their fluorescence behaviour, their interactions and fate withinliving cells.


2010 - Tethering low affinity ligands to the dimeric interface of human thymidylate synthase. [Relazione in Atti di Convegno]
Costi, Maria Paola; Genovese, Filippo; Franchini, Silvia; Venturelli, Alberto; Lazzari, Sandra; Farina, Davide Salvatore Francesco; Pirondi, Silvia; R. C., Wade; S., Mangani; C., Pozzi; S., Henrich; Ferrari, Stefania; Ponterini, Glauco; Guaitoli, Giambattista; G., Cruciani
abstract

...


2009 - A novel class of tetrairon(III) single-molecule magnets with graphene-binding groups [Articolo su rivista]
Danieli, Chiara; Cornia, Andrea; C., Cecchelli; R., Sessoli; A. L., Barra; Ponterini, Glauco; Zanfrognini, Barbara
abstract

Tripods of general formula R’–O–CH2C(CH2OH)3 are excellent site-specific ligands for the preparation offunctionalized Fe4 single-molecule magnets. Herein, we describe the synthesis and characterization oftwo novel complexes designed to bind graphene surfaces, in which the R group consists of an alkyl spacer–(CH2)n– (n = 6 and 10) and a terminal pyrenyl moiety. The site-specific ligand substitution on [Fe4(OMe)6(dpm)6] (Hdpm = dipivaloylmethane) with the new tripods has been studied with 2H NMR on isotopically-enriched samples, revealing that, once formed, these clusters are stable in solution over longtimescales. It was not possible to isolate the new compounds as crystalline solids, nevertheless they werechemically characterized by elemental analysis and 1H NMR. The presence of the pyrenyl ending groupsprompted us to investigate the effect of metal complexation on fluorescence, and a full pyrene-to-ironcluster excitation energy transfer was observed. The analysis of the magnetic behaviour revealed anS = 5 ground spin state with a negative zero-field splitting parameter D = 0.42 cm1.


2008 - "Aminoalkylsulfanyl substituted polithiophene: an aggregation study" [Abstract in Atti di Convegno]
Parenti, Francesca; Cagnoli, Rita; Caselli, Monica; Libertini, Emanuela; Mucci, Adele; Pinetti, Diego; Ponterini, Glauco; L., Preti; Schenetti, Luisa
abstract

The aggregation properties of poly{trimethyl-[7-(3-thienylsulfanyl)heptyl]ammonium iodide-co-thiophene} (PTN+Me3) (Fig.1) were investigated through NMR, AFM, light scattering and fluorescence spectroscopy.


2008 - Aminoalkylsulfanyl Substituted Polythiophene: an Aggregation Study [Relazione in Atti di Convegno]
Parenti, Francesca; Pinetti, Diego; Ponterini, Glauco; Preti, Lisa; Schenetti, Luisa; Cagnoli, Rita; Caselli, Monica; Libertini, Emanuela; Mucci, Adele
abstract

The aggregation behaviour of poly{trimethyl-[7-(3-thienylsulfanyl)heptyl]ammonium iodide-co-thiophene} (PTN+Me3) was investigated through NMR, atomic force microscopy (AFM), dynamic light scattering (DLS), UV-Vis and fluorescence spectroscopy. The interaction with sodium ursodesoxycholate (NaUDC) causes a marked enhancement of fluorescence emission.


2008 - FRET-based assay for sensing a cancer key protein functional state and inhibition by oligopeptides: Sitespecific Protein Chemical Modifications [Abstract in Rivista]
Genovese, Filippo; M., Vargiu; M. A., Ariza Mateos; Guaitoli, Giambattista; Ferrari, Stefania; Ponterini, Glauco; Costi, Maria Paola
abstract

FRET-based assay for sensing a cancer key protein functional state and inhibition by oligopeptides: Sitespecific Protein Chemical Modifications


2008 - First- and Second-Order Polarizabilities of Simple Merocyanines. An Experimental and Theoretical Reassessment of the Two-Level Model [Articolo su rivista]
MOMICCHIOLI, Fabio; PONTERINI, Glauco; VANOSSI, Davide
abstract

Taking four merocyanines [(CH3)2N-(CHdCH)n-C(CH3)O; n ) 1-4] (Mc1-4) as test D-A systems, weperformed a close experimental and theoretical examination of the two level model with reference to itsability to provide correct predictions of both absolute values and dependence on the conjugation path lengthof first- and second-order molecular polarizabilities. By 1H NMR spectroscopy merocyanines Mc1-4 werefound to be ∼1:1 mixtures of two planar conformers with cis and trans arrangements of the sC(CH3)Oelectron-acceptor group and all trans structure of the polyene like fragment. The degree of bond lengthalternancy (BLA) in the -(CHdCH)n- fragment, was quantified by extensive full geometry optimizations atboth semiempirical and ab initio level. DFT (6-31G**/B3LYP) optimized geometries were considered to bemost reliable and were used for calculations of the excited-state properties. The applicability of the two levelmodel, reducing the general sum-over-states (SOS) expansion to only one term involving the ground state (g)and the lowest-lying 1(ππ*) CT state (e), was checked by analysis of fluorescence and near UV absorptionspectra. Measurements of the basic two-level model quantities (Ege, μge and Δμeg), by which the dominantcomponents of r and tensors are expressed (RXX, XXX, X ≡ long molecular axis), were designed to giveapproximate free-molecule values. It is proposed, in particular, an adjustment of the solvatochromic methodfor the determination of Δμeg, based on accurate measurements of absorption spectral shifts in n-hexane/diethyl ether mixtures with small diethyl ether volume fractions. Such an approach led to Mc1-4 XXX’smatching well in both value and n-dependence with EFISH data reported in the literature for similarmerocyanines. For the fluorescent Mc4, the results were qualitatively well reproduced by an approach, whichcombines absorption and fluorescence solvent shifts. All the measured quantities were calculated for bothtrans and cis Mc1-4 by three semiempirical INDO-based approaches aiming at evaluating the performancesof different integral parametrizations and CI extensions: ZINDO/S, CS INDO SCI, CS INDO SDCI. In allcases, RXX and XXX were found to rise proportionally to about n1.3 and n2, respectively, in qualitatively goodagreement with the experimental values. As to the absolute values, however, experimental RXX’s and XXX’swere best reproduced by CS INDO SDCI combining Ohno-Klopman parametrization and CI including bothsingle and double excitations. The validity of the two-level model was checked by comparison with convergedSOS calculations for the longest chain merocyanine (Mc4) and finite field calculations of linear polarizabilitiesfor all of the four dyes (Mc1-4).


2008 - Metodo per la funzionalizzazione sito specifica di molecole proteiche [Brevetto]
Genovese, Filippo; Ferrari, Stefania; Costi, Maria Paola; Ponterini, Glauco
abstract

Viene qui fornito un metodo in soluzione per le modifiche chimiche sito-specifiche di proteine, sfruttando l’affinità di cavità strutturate di proteine (come le cavità catalitiche degli enzimi) verso miscele di inibitori (ir)reversibili/(co)substrati o ligandi per mascherare i residui coinvolti nella formazione del complesso, permettendo la funzionalizzazione chemoselettiva di residui opportunamente selezionati al di fuori della tasca. Pertanto, grazie al mascheramento di residui di cavità strutturate, è possibile studiare ed esplorare siti allosterici a bassa affinità sia chimicamente, come porzioni funzionalizzabili, che funzionalmente. Alcune delle applicazioni in campo diagnostico, analitico e terapeutico dell’enzima ingegnerizzato risultante vengono qui discusse. Questa piattaforma di coniugazione potrebbe portare alla progettazione di un kit di coniugazione per eseguire modifiche chimiche sito-specifiche di proteine per applicazioni di ricerca, diagnostiche e terapeutiche.


2008 - Strategies to Reduce Inter-chain Aggregation and Fluorescence Quenching in Alternated Multilayers of a Polythiophene [Articolo su rivista]
Lodi, Andrea; Caselli, Monica; Zanfrognini, Barbara; Cagnoli, Rita; Mucci, Adele; Parenti, Francesca; Schenetti, Luisa; Ponterini, Glauco
abstract

Electrostatically self-assembled multilayers of a fluorescent carboxyalkylsulfanyl polythiophene and poly(diallyldimethylammonium) were prepared using the layer-by-layer deposition approach and were structurally characterized by linear dichroism and atomic-force microscopy. Steady-state measurements revealed that fluorescence was quenched relative to the solution behaviour. The emission quantum yield was found to increase upon decreasing the polymer concentration in the dipping solution as well as by codepositing polythiophene with another polyanion, poly(sodium-4-styrenesulfonate). Fluorescence quenching was therefore attributed to the formation of non-emitting inter-chain aggregate exciton traps.Intercalation of polythiophene layers with non-emitting polymers having larger energy gaps did not result in enhanced fluorescence, thus suggesting negligible polythiophene aggregation and exciton migration across different layers. At best, we could obtain quantum yields around 0.1–0.15, about half the solution value but almost two orders of magnitude larger than found with cast or spin-cast films.


2007 - Electronic spectra and fluorescence properties of multichromophoric sulfonylureas [Articolo su rivista]
Baraldi, Ivan; Caselli, Monica; Ponterini, Glauco; Vanossi, Davide
abstract

The multichromophoric character of two sulfonylurea herbicides, SMT and BNS, has been investigated in its manifestations in the electronic absorption spectra and in some fluorescence properties through a combined experimental and theoretical approach. After a theoretical analysis of the most stable structures of these flexible systems, the UV absorption spectra of the two multichromophoric compounds have been analysed both experimentally and theoretically, and most transitions have been assigned to individual chromophores, also by comparison with four suitable reference compounds (5-8). Finally, some experimental information concerning the fluorescence spectra and quantum yields have been analysed with reference to the contributions from single fluorophores and the role of low-lying n -> pi* states. (c) 2006 Elsevier B.V. All rights reserved.


2007 - Solvent-dependent host-guest complexation of two homologous merocyanines by a water-soluble calyx[8]arene. Spectroscopic analysis and structural calculations [Articolo su rivista]
A., Lodi; Caselli, Monica; A., Casnati; Momicchioli, Fabio; F., Sansone; Vanossi, Davide; Ponterini, Glauco
abstract

The sulfonated calixarene I8C12 acts as a host for homologous merocyanines Mc1 and Mc2 in organic solvents, exhibiting neither selectivity towards the guest dyes nor solvent dependence of the complexation equilibria. In water, on the contrary, only the lower homologue, Mc1, is solubilized in the presence of the calixarene. A combination of UV–visible and fluorescence spectroscopic and photophysical analysis and MD structural simulation of the calixarene-dye complexes was employed to account for the observations, and suggests that a radical change in the complexation mode occurs upon moving from an organic to an aqueous environment.


2006 - A poly(alkylsulfanyl)thiophene functionalized with carboxylic groups [Articolo su rivista]
Cagnoli, Rita; Mucci, Adele; Parenti, Francesca; Schenetti, Luisa; Borsari, Marco; Lodi, Andrea; Ponterini, Glauco
abstract

Different routes, based on the Stille coupling, to the obtainment of a polythiophene bearing a carboxyhexylsulfanyl chain every two thiophene rings (PTCOOH) are here reported and discussed. Two PTCOOHs with different chain lengths were obtained: the shorter by hydrolysis of a polymeric ester precursor and the longer by direct Stille coupling from suitable monomers. They possess similar electrochemical properties but behave differently when aggregation and fluorescence are concerned. The PTCOOH obtained by hydrolysis is found to be fluorescent in a good solvent such as THF, and its fluorescence quantum yield decreases as the extent of aggregation increases. The polymer obtained by direct Stille coupling is less fluorescent, consistently with its proneness to aggregate. The PTCOOH obtained by hydrolysis is therefore more promising in view of the build-up of solid-state devices with exploitable fluorescence properties.


2006 - Aggregation modes of anionic oxacarbocyanines with polycations in solution and in ESAMs [Articolo su rivista]
Lodi, A; Ponterini, Glauco
abstract

Interaction of oxacarbocyanines D-G with three polycations in aqueous solutions results in the formation of two types of likely small, distorted aggregates rather than the classical J aggregates. On the contrary, the latter are extensively and almost exclusively obtained in electrostatically self-assembled multilayers (ESAMs) prepared by alternate polycation/dye adsorption on quartz substrates. The J-aggregate growth on supported polycations is qualitatively shared by the four cyanines, a fact that reveals the crucial role of the double anionic substitutions on the dyes. On the other hand, films with D and E, which are known to have a stronger tendency to give dimers in water, exhibit higher J-band intensities and stability upon drying relative to those with F and G. Based on these observations, we suggest that energetic factors associated with cofacial dye/dye van der Waals interactions, ultimately related with the degree of planarity of the conjugated chromophores, may still play a major role in controlling aggregation equilibria in these complex systems.


2006 - Excitation energy transfer in ion pairs of polymethine cyanine dyes: Efficiency and dynamics [Articolo su rivista]
PONTERINI, Glauco; M., Fiorini; VANOSSI, Davide; A. S., Tatikolov; MOMICCHIOLI, Fabio
abstract

The present work deals with singlet excitation energy transfer (EET) occurring in contact ion pairs (CIPs) of several anionic oxonol analogues (acting as EE donors) and cationic cyanines (acting as acceptors) characterized by off resonance individual transitions. Combining conductometric and spectroscopic measurements with decreasing solvent polarity, we were able to observe a progressive ion pairing leading first to solvent-separated ion pairs (SSIPs) and then to CIPs. Analysis of the absorption spectra of three selected salts (A2, C1, A2, C2, and A1, C4) in chloroform-toluene mixtures showed that the transformation of SSIP into CIP involves the appearance of a certain exciton coupling, the extent of which decreases regularly with increasing gap between the local excitation energies. Fluorescence excitation spectra showed that EET occurs in CIP, and EET efficiencies were evaluated with a procedure expressly devised for weakly emitting donors. These were between 0.2 and 0.65 for the examined ion pairs involving anions A1 and A2. The spectroscopic study was complemented by a theoretical investigation aimed at establishing the dynamic regime of the observed EET. From classical MD simulations and local full geometry optimizations, A2, C1 and A2, C2 were found to form rather stable sandwich-type CIP structures with interchromophore distances (R) of about 0.45-0.50 nm. The donor-acceptor electronic coupling was calculated in terms of Coulombic interactions between atomic transition charges. For CIP, the electronic coupling was decidedly beyond the limit of the weak coupling required for an incoherent Forster-type mechanism. Thus, we tried to arrange the EET dynamics within the theory developed by Kimura, Kakitani, and Yamato (J. Phys. Chem. B 2000, 104, 9276) for the intermediate coupling case, which provides analytical expressions of time- dependent occupation probability, EET rate, and coherency in terms of two basic quantities: the electronic coupling and a correlation time related to the Franck-Condon factor. The latter was shown to be primarily modulated by Forster's spectral overlap integral (related in turn to the excitation energy gap). Calculations were carried out for the three sample systems using three values of the electronic coupling roughly corresponding to CIP, 1.0, and 2.0 nm interchromophore distances. At the CIP distance, EET in both A2, C1 and A2, C2 was predicted to occur with a partial exciton mechanism, very short transfer times (about 10 fs), and high degree of coherence. In A1, C4 (having the largest energy gap), EET was found to occur with a hot-transfer mechanism. More or less hot-transfer dynamics appeared to be retained by all three systems at R=1.0 nm. Fully incoherent EET appeared to become operative only at distances larger than 2.0 nm.


2006 - J-aggregation of an anionic oxacarbocyanine in electrostatically self-assembled multilayers [Articolo su rivista]
A., Lodi; Ponterini, Glauco
abstract

Unlike in water Solution, interaction of the anionic oxacarbocyanine E (structure in Fig. 1) with three polycations electrostatically adsorbed oil a quartz substrate results in an extensive J aggregation of the dye. J-aggregates grow oil the film Surface beyond charge saturation, making possible the fort-nation of alternately adsorbed polycation/E multilayers. UV-visible absorption and fluorescence spectra have revealed that, although less ordered than in solution, J aggregates are dominant in dry films. They are characterized by some heterogeneity and exhibit a reorganization dynamics in the presence of water. Polarized absorption has shown that the J-band transition-dipole moments lie preferentially parallel to the film plane, thus suggesting a plausible arrangement for a bidimensional brickwork aggregate. An exploration of the effects of various preparation variables (solution concentrations and ionic strengths, dipping times, film drying speed, polycation nature and molecular weight) has afforded some insight into the processes involved in polycation/J-aggregate multilayer formation.


2006 - Large third-order nonlinear optical response of porphyrin J-aggregates oriented in self-assembled thin films [Articolo su rivista]
Collini, E; Ferrante, C; Bozio, R; Lodi, A; Ponterini, Glauco
abstract

The preparation and characterization of a self-assembled material showing a high nonlinear response and good photostability to ultrashort laser pulses is presented. The material is built by alternate deposition of tetrakis(4-sulfonatophenyl) porphyrin diacid (H4TPPS2-) and poly(diallyldimethylammonium chloride) (PDDA) forming electrostatically self-assembled multilayers (ESAMs). UV-visible absorption and emission experiments show that in this matrix H4TPPS2- is present mainly in its J-aggregated form. Furthermore, linear dichroism experiments on a 3 bilayer film show a preferential alignment of the porphyrin aggregate with the J-band transition dipole moment parallel to the film surface. The two photon absorption (TPA) properties of these films are investigated with the Z-scan technique at 806 nm, employing 130 fs pulses. The samples exhibit strong nonlinearities with a very large two-photon absorption coefficient beta(TPA) of 50 cm GW(-1). The origin of this large response is investigated. It has been already demonstrated that aggregation enhances the molecular TPA cross section of H4TPPS2- from 30 to 1000 GM in water solution thanks to cooperative effects. In a 20 bilayer film a further increase by a factor of 1.7 is observed and explained in terms of preferential alignment of J-aggregates in the multilayers.


2004 - Consequences of H-dimerization on the photophysics and photochemistry of oxacarbocyanines [Articolo su rivista]
Caselli, Monica; L., Latterini; Ponterini, Glauco
abstract

The photophysical/photochemical behaviour of the monomers and the H dimers of four oxacarbocyanines (dyes D-G in the scheme) was investigated in water. In contrast with the usually observed effect of H dimerization, the dimers of dyes D-G were found to fluoresce with efficiencies comparable to or larger than those of the corresponding monomers. Analysis of the decay paths of the lowest excited singlet state showed, however, that dimerization causes a decrease of the radiative rate constants and an enhancement of intersystem crossing to the triplet manifold, as expected from application of exciton theory to a model H dimer. Twisting about one of the polymethine bonds contributes to the decay from the spectroscopic minimum of monomers, though yielding a rather small amount of a distorted cis isomer. The process is inhibited in dimers, likely due to a pronounced increase of activation energy connected with a loss of van der Waals attractive energy at the twisted geometry.


2004 - Electronic structure and photochemistry of squaraine dyes: basic theoretical analysis and direct detection of the photoisomer of a symmetrical squarylium cyanine [Articolo su rivista]
MOMICCHIOLI, Fabio; A. S., Tatikolov; VANOSSI, Davide; PONTERINI, Glauco
abstract

The photoisomerization kinetics of a squaraine dye has been the object both of experimental investigation and of interpretation in the framework of a qualitative theoretical model formulated by the aid of simple HMO calculations and orbital symmetry considerations. Such a model has first confirmed that the electronic structure and the spectroscopic properties of symmetrical squaraines are related to those of the parent cyanines, with ketocyanines as intermediate systems. Extension of the approach to structures twisted by 90degrees about a polymethine bond has then provided insight into the electronic aspects and the mechanism of the photoisomerization of the squaraine under study. The reaction, previously indirectly investigated by. uorescence analysis, has been directly monitored by laser. ash photolysis. These experiments indicate that, while photoisomerization is likely the main radiationless decay route from the spectroscopic minimum of the lowest excited singlet state (S-1), the cis photoisomer is produced with only a 1% yield, likely because of an unfavourable cis/trans branching ratio from the perpendicular minimum of the S-1-state potential energy surface. In contrast with what found for symmetrical cyanines, an increase in the solvent polarity was found to accelerate both the direct, excited-state reaction and, to a much larger extent, the ground-state back-isomerization. Such observations are consistent with predictions of the theoretical model and provide a clue for the identification of the isomerization coordinate.


2003 - Photoisomerization of simple merocyanines: a theoretical and experimental comparison with polyenes and symmetric cyanines [Articolo su rivista]
Baraldi, Ivan; Momicchioli, Fabio; Ponterini, Glauco; A. S., Tatikolov; Vanossi, Davide
abstract

The structure and electronic spectra of merocyanines are intermediate between those of acyclic polyenes and cationic symmetric cyanines of comparable sizes, shifting from one to the other as a result of a solvent polarity change. In this paper we address, both theoretically and experimentally, the question of how the photochemical behaviour of simple merocyanines compares with that of polyenes and symmetric cyanines. After a brief theoretical re-appraisal of the absorption maxima dependence on the chain length in the three classes of chromogens, we analyse the calculated potential-energy curves for two photoisomerization coordinates of a polyene, a symmetric cyanine and a merocyanine of comparable sizes. The results concerning both the energy curves and the nature of the relevant electronic states, particularly the TICT (twisted intramolecular charge transfer) character of the S-1 state at the perpendicular geometry, reveal the existence of a near relationship between merocyanines and symmetric ionic polymethines, traceable back to their being odd-alternant systems. The presence of a low-lying (1)(npi*) state at the trans geometry and the associated solvent-modulated vibronic coupling with the (1)(pi(H)pi(L)*) state dominate the experimentally accessible photochemical behaviour of two simple merocyanines and make it peculiar with respect to those of both polyenes and symmetric ionic cyanines.


2003 - Solvent influence on absorption and fluorescence spectra of merocyanine dyes: a theoretical and experimental study [Articolo su rivista]
Baraldi, Ivan; G., Brancolini; Momicchioli, Fabio; Ponterini, Glauco; Vanossi, Davide
abstract

The solvaton-CS INDO model, previously successfully used to describe the solvatochromic properties of merocyanines, has been extended to the study of the solvent influence on the fluorescence spectra (fluorosolvatochromism) of these dyes. A ketocyanine (M1) and a stilbazolium betaine (M2) were chosen as representatives of positively and negatively solvatochromic behaviours, respectively. The gap of experimental knowledge concerning the emission properties of M2 was filled by a spectrofluorometric analysis in a set of solvents covering a large range of the E-T(30) scale. Solvato- and fluorosolvatochromism were described by calculating the S-0 (eq.) --> S-1 (Franck-Condon) and S-1 (eq.) --> S-0 (Franck-Condon) transition energies as a function of a polarity factor related to the static dielectric constant of the solvent, and ranging from 0 to 1. The absorbing S-0 (eq.) and emitting S-1 (eq.) units (solute molecule + solvent cage) were approximated using the S-0 and S-1 geometries of the unsolvated molecule and the respective charge distributions fitted to the current value of k(epsilon). The calculation results fully confirm that S-0 and S-1 states of merocyanines can be viewed as a mixture of a neutral and a zwitterionic structure whose composition is controlled by the solvent polarity. The plots of the calculated spectral data (absorption and emission maxima and corresponding Stokes shifts) vs k(epsilon) are in fairly good agreement with those of the experimental data over almost the entire range of the normalized E-T(N) values, thus showing that specific solvent interactions are at least partly simulated within the solvaton-CS INDO scheme. The methodological prerequisites for a correct prediction of solvatochromic shifts are recalled with reference to previous conflicting theoretical interpretations.


2002 - Dimerization of green sensitizing cyanines in solution. A spectroscopic and theoretical study of the bonding nature [Articolo su rivista]
Baraldi, Ivan; Caselli, Monica; Momicchioli, Fabio; Ponterini, Glauco; Vanossi, Davide
abstract

The bonding nature in cyanine-dye aggregates has been investigated by studying dimerization in solution of 3, 3'-disulfopropyl-4,5,4',5'-dibenzo-9-ethyloxacarbocyanine (D) and three other oxacarbocyanine analogues (E, F, G) used as photographic sensitizers in the green spectral region. Quantitative information on the monomer-dimer equilibrium of dye D in different solvents and of its analogues (E, F, G) in water was obtained by measurement of the absorption spectrum as a function of dye concentration and of temperature. Dimerization was found to be generally driven by enthalpic factors traceable to strong attractive van der Waals interactions between the two large and highly polarizable dye molecules. Entropic contributions to DeltaG(0) usually favour dissociation but are smaller than the enthalpic ones. The visible absorption spectrum of the dimer consists in a classic two-branched exciton band with a marked splitting (1600 cm(-1) in water). The experimental observations were the subject of a theoretical study including classical molecular dynamics (MD) and Monte Carlo (MC) calculations of the dimer structure and comparative analysis of monomer and dimer spectra by the CS INDO CI method. Computer simulations led to three similar H-type structures, the most stable of which is characterized by a distance of 4.7 Angstrom between the planes of the chromophores and an endoendo configuration of the sulfopropyl substituents. The calculated dimer spectrum was clearly interpreted in terms of exciton model but a quantitative agreement with the two-maximum exciton band could be obtained only by assuming substantial deviation of the long molecular axes from parallelism. On the basis of normal coordinate calculations it is suggested that such configurations may occur with a high probability in virtue of twisting vibrational motions of extremely low frequency. (C) 2002 Elsevier Science B.V. All rights reserved.


2001 - Exciton-like and charge-transfer states in cyanine-oxonol ion pairs. An experimental and theoretical study [Articolo su rivista]
Baraldi, Ivan; Momicchioli, Fabio; Ponterini, Glauco; A. S., Tatikolov; Vanossi, Davide
abstract

Absorption and fluorescence emission properties of cyanine-oxonol mixed dyes, i.e., salts formed by a cationic cyanine with an anionic oxonol as counterion, were investigated both theoretically and experimentally in order to probe the effects of ion pairing occurring in low-polarity solvents. We analyzed, in particular, three model systems (S1, S2, and S3) built combining thiacarbo- and thiadicarbocyanine (C1, C2) with two vinylogous oxonol chromophores (A1/A1F, A2). in systems S1 (C1-A1) and S2 (C2-A2), where the visible absorption bands of the individual ions are almost superimposed, the formation of ion pairs gives rise to marked spectral alterations traceable to interchromophore resonance interactions. On the contrary, in system 53 (C2-A1F), whose components absorb widely apart, the spectrum of the contact ion pair and that of the dissociated form differ only for the relative band intensities. In both cases, however, contact ion pairing results in complete quenching of the emission of the chromophoric units. Such behaviors, emphasized by absorption and fluorescence emission and excitation spectra of both the mixed dyes and their components in solvents of different polarities, were the subject of a theoretical study based in particular on the calculation of structures and electronic spectra of the contact ion pairs. Molecular dynamics (MD) simulations and local full geometry optimizations led to two types of structures characterized by almost parallel and orthogonal arrangements of the long molecular axes. CS INDO SCI calculations using both arrangements emphasized the role of the exciton coupling between the local HOMO-LUMO excitations of the two chromophoric units. The most striking spectral characteristics in low-polarity solvent turned out to be explainable in terms of parallel type arrangements, even if an appreciable contribution of the orthogonal type structure was to be invoked for a complete interpretation of the S1 spectral properties. In all contact ion pairs, independently of the structure, the lowest excited singlet is a forbidden anion --> cation charge transfer (CT) state explaining why no fluorescence emission was observed in such systems.


2001 - Intermolecular electron transfer in merocyanine aggregates studied by optical and transient EPR methods [Articolo su rivista]
L., Franco; L., Pasimeni; Ponterini, Glauco; M., Ruzzi; Segre, Ulderico
abstract

Excited states of two merocyanine chromophores have been studied by means of optical and magnetic resonance techniques. The dye molecules were dissolved in solvents of different polarity and cast in thin films on quartz surfaces. The optical absorption and emission spectra of both molecules indicate a little charge-transfer character in the S-0-S-1 transition. The cast films contain monomers and H type aggregates. EPR spectra have been obtained by time resolved techniques at low temperature after illumination of the sample. EPR spectra of isolated molecules in frozen solutions are typical of triplet excited states generated by spin-orbit promoted intersystem crossing. Two signals are observed in EPR spectra of the cast films, with a narrow line in emission superimposed on a very weak molecular triplet lineshape. The polarization and lineshape analysis suggest that a radical ion pair with a lifetime of the order of microseconds is formed by intermolecular charge migration following the photoinduced electron-transfer reaction between the donor and acceptor moieties of the chromophore.


2001 - Irradiation-wavelength dependent photochemistry of the bichromophoric sulfonylurea chlorsulfuron [Articolo su rivista]
Caselli, Monica; Ponterini, Glauco; M., Vignali
abstract

The photochemistry of the bichromophoric sulfonylurea chlorsulfuron has been investigated at different irradiation wavelengths and environmental conditions. The identified products indicate that different reaction paths are followed, depending whether the benzene or the triazine component chromophores are excited. In the first case, the chlorine atom is substituted by hydrogen or hydroxyl in water; in the second one three competitive photodegradation paths may be followed, the most efficient one being the cleavage of the S-N bond in the sulfonylurea bridge. Photodegradation quantum yield measurements, combined with laser flash photolysis experiments have shown that, while both singlet and tripler states contribute to all photolytic paths in deaerated solution, quenching by oxygen makes the triplet contribution negligible in samples equilibrated with air. (C) 2001 Elsevier Science B.V. All rights reserved.


2001 - Structural and thermodynamic combined studies for inhibitors binding to Thymidylate Synthase [Abstract in Atti di Convegno]
Venturelli, Alberto; Tondi, Donatella; Skinner, M. A.; Brown, K. A.; Ponterini, Glauco; Costi, Maria Paola
abstract

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2000 - A recent development of the CSINDO model. Treatment of solvent effects on structures and optical properties of organic dyes [Articolo su rivista]
Baraldi, Ivan; Momicchioli, Fabio; Ponterini, Glauco; Vanossi, Davide
abstract

Treatment of solvent effects on structures and optical properties of organic dyes


2000 - Aggregation of cation-anionic and related polymethine dyes [Articolo su rivista]
A. S., Tatikolov; Ponterini, Glauco; Z. A., Krasnaya
abstract

Absorption, fluorescence, and fluorescence excitation spectra were studied for a number of cation-anionic and related anionic polymethine dyes in weakly polarand nonpolarsolvents, as well as in binary mixtures of solvents of different polarity. For some dyes, aggregation is observed in toluene or acetonitrile-toluene mixtures with low amounts of acetonitrile, which is revealed as appearance of new absorption bands and/or broadening of the initial bands of a monomeric dye. Solvent mixtures butyronitrilehexane with low butyronitrile content were found to greatly stimulate the formation of dye aggregates for most of the dyes studied. The absorption spectra of the aggregates are often blue-shifted with respect to the corresponding absorption spectra of parent monomeric dyes and/or represent broad continuums located both in the blue and red regions. For one of the cation-anionic dyes studied, which consists of 3,3′-diethylthiamonomethinecyanine cation and trimethinebenzoxanine anion, fluorescent aggregates were observed; their broad fluorescence band is located in the long-wavelength region. For this dye, gradual transition from nonfluorescent aggregates to fluorescent ones and then to monomeric ion pairs and dissociated ions was observed in butyronitrile-hexane mixtures with growing butyronitrile content.


2000 - Structures and reactivities of 1-oxo-cycloalkan-2-ylidenacetic acids. A 1H-NMR, modeling and photochemical study [Articolo su rivista]
S., Ghelli; L., Toma; D., Barlocco; Costi, Maria Paola; Ponterini, Glauco
abstract

Four 1-oxo-cycloalkan-2-ylideneacetic acids, differing in the size of the aliphatic ring and in the nature of the condensedunsaturated cycle, exhibit different reactivities towards hydrazine, leading in only one case to the desired tryciclic pyridazinone. The observed differences in behaviour cannot be ascribed to different configurations at the exocyclic double bond of the four acids: 1H NMR experiments, combined with UV photolysis, have shown that all compounds have been prepared in the E form and are stable in the absence of light and catalysts. The photochemically obtained Z isomers show an increasing tendency to form tricyclic lactones with increasing size ofthe aliphatic ring. A theoretical structural analysis of the E and Z isomers, the tricyclic lactones and some of the hypothetical intermediates of the reaction with hydrazine suggests the size of the aliphatic ring and the associated flexibility to be crucial in modulating the ability of these compounds to form tricyclic products.


1998 - Influence of ion pair formation on the photochemistry of asymmetric cationic indobenzimidazolo cyanines [Articolo su rivista]
Tatikolov, As; Ponterini, Glauco
abstract

The influence of counterions in ion pairs of asymmetric cationic indobenzimidazolo cyanines formed in low polarity solvents on the main photochemical processes of the cyanine cations (fluorescence emission, photoisomerization and thermal ground state back isomerization, S-1 --> T and T --> S-0 intersystem crossings) was experimentally studied. The previously found structural similarity of the ion pairs of symmetric benzimidazolo cyanines and those of asymmetric indobenzimidazolo cyanines is reflected in the similarity of the effects of ion pairing on the dynamics of isomerization of these dyes in the ground and lowest excited singlet states. Indirect evidence based on fluorescence steady-state and time-resolved measurements indicates a weak catalytic counterion effect on the S-1-state isomerization dynamics of the investigated benzimidazolo and indobenzimidazolo cyanines. The I- counterion in ion pairs strongly affects the S-1 state of the asymmetric cyanines by inducing S-1 --> T and T-1 --> S-0 intersystem crossings (heavy atom effect). (C) 1998 Elsevier Science S.A. All rights reserved.


1998 - Ion pairs of indobenzimidazolo cyanines: a structural study based on conductivity, absorption, fluorescence and H-1-NMR [Articolo su rivista]
Tatikolov, As; Ishchenko, Aa; Ghelli, S; Ponterini, Glauco
abstract

Asymmetric benzimidazolo carbo, di- and tricarbocyanines form ion pairs of the solvent-separated and contact types with different counterions in tetrahydrofuran, toluene and toluene-nitrile mixtures. The dissociation constants of the ion pairs in tetrahydrofuran, evaluated from conductivity data, do not depend on the length of the polymethine chain and show only a small decrease with decreasing counterion size. The absorption and fluorescence excitation spectra of the contact ion pairs exhibit a pronounced hypsochromic shift with respect to the solvated ions and the solvent-separated ion pairs. H-1-NMR experiments have provided information about the electronic structures of the ions of both the asymmetric dyes and the corresponding symmetric carbocyanines. They have also revealed different preferred anion locations in the contact ion pairs of the symmetric indocarbocyanine on one hand, and of the benzimidazolo carbocyanine and the asymmetric dyes on the other. This structural difference is suggested to be a cause of the observed opposite effects of ion pairing on the isomerization kinetics of the two groups of dyes. (C) 1998 Elsevier Science B.V. All rights reserved.


1998 - Solvent effects within the CS INDO method. Geometrical distortion and solvatochromism of merocyanine dyes [Articolo su rivista]
Baraldi, Ivan; Momicchioli, Fabio; Ponterini, Glauco; Vanossi, Davide
abstract

This work represents the first step of a theoretical study aiming at explicitly including solvation in the CS INDO CI calculations of ground and excited state properties of organic dyes. The reported theoretical treatment falls within the electrostatic continuum theories and introduces solute-solvent interaction in the SCF calculation according to Klopman's solvaton model. The procedure was tested on two merocyanines characterized by opposite solvatochromic behaviours. It was found that solvaton systems most suitable for pi-conjugated donor-acceptor dyes, like merocyanines, can be built from the net pi-electron charges. The results show that the combined solvaton/CS INDO scheme is able to describe rather well the modifications of both geometries and absorption spectra of merocyanines as a function of the medium polarity. The advantages of the proposed approach with respect to other semi-empirical procedures are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.


1997 - Ion pairing of bisdimethylamino pentamethinecyanine perchlorate and its consequences on the cis-trans photoisomerization dynamics [Articolo su rivista]
Ponterini, Glauco
abstract

Ion pairing of the title compound is shown to occur in several solvents and solvent mixtures by electrical conductivity measurements, Both solvent separated and contact ion pairs have been found, depending on the solvent nature, Whereas for ion pairs of the former kind the absorption and fluorescence properties are homogeneous with those of the solvated cation and the isomerization dynamics is only slightly modified, significant changes in these properties result from contact ion pair formation, Based on structural and dynamic information obtained from proton-NMR spectra, an interpretation of these observations is attempted, that invokes three different counterion effects, two electrostatic and one steric in nature, to be operative with different consequences and efficiencies.


1997 - The stable and photochemical isomers of some merocyanines: A H-1 NMR and theoretical CS INDO study of the structures and electronic spectra [Articolo su rivista]
Baraldi, Ivan; S., Ghelli; Z. A., Krasnaya; Momicchioli, Fabio; A. S., Tatikolov; Vanossi, Davide; Ponterini, Glauco
abstract

The conformations and electron distributions of four merocyanines were investigated by H-1 NMR spectroscopy in low-polarity solvents and CS INDO calculations on the isolated molecules. The two approaches gave consistent results. Some information about the torsional dynamics of these dyes in the ground state was obtained from a rough H-1 NMR line shape analysis, and H-1 NMR experiments performed on photolysed samples made it possible to identify the conformations of the longest-lived photoisomers of three compounds and to provide an estimate of their lifetimes. The effects of an increase in the solvent polarity on the structures and absorption spectra of the four dyes were investigated by, respectively, measuring their H-1 NMR spectra in three more solvents with increasing dielectric constants, and CS INDO CI calculations of the electronic spectra, including solvent shift effects, evaluated within the classical solvaton model. All the results related to the medium polarity effects could be interpreted according to the generally accepted description of the merocyanine chromophore as the resonance hybrid of a neutral and a charge-separated form.


1996 - Investigation of photochemical paths by a combined theoretical and experimental approach. [Capitolo/Saggio]
Momicchioli, Fabio; Baraldi, Ivan; Carnevali, A.; Ponterini, Glauco
abstract

Investigation of photochemical paths in condensed phases by a combined theoretical and experimental approach


1996 - Photoisomerization of 3,3'-diethyloxacarbocyanine (DOC) and 3,3'-diethylthiacarbocyanine (DTC): CS INDO CI potential energy curves for the free and solvated molecules [Articolo su rivista]
Baraldi, Ivan; Carnevali, A; Momicchioli, Fabio; Ponterini, Glauco; Berthier, G.
abstract

The photochemical trans-cis isomerizations of the two title carbocyanines (DOG and DTC) have been investigated theoretically with a dual objective: 1) to verify the applicability to more complex cyanines of a previously proposed theoretical model derived fr om calculations on a prototype compound (pentamethinecyanine) formally neglecting the solvent; 2) to try to establish the structure of the photoisomers. The potential energy curves of the ground (S-o) and lowest excited singlet (S-1) states were calculated by the CS INDO CI method along the paths leading to the two distinct mono-cis isomers, and the electrostatic solute-solvent interaction energy was evaluated for the two states according to the simple virtual charge (solvaton) model. It was found that solvation energy must be explicitly taken into account for the calculated potential energy curves to be consistent with the early model and the general photochemical behaviour of carbocyanines. From a thorough comparison between the calculated potential curves and the available experimental data the photoisomers appeared to be identifiable as the C(8)-C(9) cis for DOC and C(2)-C(8) cis for DTC.


1995 - Electronic spectrum of porphyrins. CS INDO CI study [Articolo su rivista]
Baraldi, Ivan; A., Carnevali; Ponterini, Glauco; Vanossi, Davide
abstract

The electronic spectra of porphin, chlorin and their magnesium derivatives have been studied quantum-mechanicallywith the CS INDO CI method. Both the SOPS, and T,-T, one-photon absorption spectra have been analyzed togetherwith the correlation effects. The main result regards the T-T spectrum of porphin. To obtain a correct description of thecomplete spectrum it is necessary to take account of the correlation effects. Gouterman’s model of four orbitals is toosimple to describe the region of the Soret band.


1995 - IDENTIFICATION OF THE PHOTOISOMERS OF 2 CARBOCYANINES BY H-1-NMR SPECTROSCOPY [Articolo su rivista]
Ghelli, S; Ponterini, Glauco
abstract

The H-1 NMR spectra of the labile photoisomers of 3,3'-diethyloxa- and 3,3'-diethylthiacarbocyanines have been recorded for the first time. Analysis of these spectra leads to the identification of the photoisomer of the first dye as a mono-cis form obtained by twisting about the central polymethine bond, and to the suggestion that the photoisomerization of the second dye takes place around the external polymethine bond. These assignments are shown to be generally consistent with the results of earlier experimental and theoretical studies of the ground- and excited-state behaviour of these compounds.


1995 - PHOTOISOMERIZATION OF ASYMMETRIC INDOBENZIMIDAZOLO CYANINE DYES [Articolo su rivista]
Tatikolov, As; Derevyanko, Na; Ishchenko, Aa; Baraldi, Ivan; Caselli, Monica; Momicchioli, Fabio; Ponterini, Glauco
abstract

The isomerization kinetics of three indobenzimidazolo polymethine cyanines have been investigated and compared with the corresponding properties of the parent symmetric dyes. A significant alternation of the pi bond orders in the polymethine chain was found in the ground states (S-0) of the asymmetric dyes. A similarly alternant behaviour was exhibited by the calculated S-0 potential energy barriers for twisting around the polymethine chain bonds of the asymmetric carbocyanine, whereas uniform barriers were found for the symmetric parent compounds. The experimentally observed sequence of back-isomerization activation energies was interpreted on the basis of these theoretical results. It was suggested by some spectral and kinetic fluorescence properties, and it was confirmed by the calculated polymethine-chain pi bond orders of the lowest singlet excited slates (S-1) that the electronic asymmetry induced by the different terminal heterocycles was strongly reduced upon excitation of these dyes to their S-1 states. In spite of this, the trans-cis photoisomerization of asymmetric cyanines occurred invariably around those bonds having the highest pi bond orders in the ground state. A tentative theoretical explanation of this systematic behaviour is reported.


1995 - Theoretical and photophysical study of photoisomerism of cyanine dyes : bisphenylaminopentamethine cyanine (BPPC) [Articolo su rivista]
Baraldi, Ivan; Carnevali, A.; Caselli, Monica; Momicchioli, Fabio; Ponterini, Glauco; Berthier, G.
abstract

The trans-cis photoisomerism of BPPC was investigated as part of a comprehensive, both theoretical and experimental, study on the photophysical and photochemical properties of cyanines having pentamethine cyanine as a common chromophore. In this work the determination of the trans → cis photoisomerization and thermal back isomerizatkm kinetics in alcohols was combined with CS INDO CI calculations of S0 and S1 potential energy curves for the paths leading to mono-cis isomers, where the dielectric solvent effects were taken into account by the simple virtual charge model. In agreement with the indications of a previous steady-state spectroscopy study, it was concluded that irradiation of BPPC into the visible absorption region gives rise to formation of the C(3)–C(4) cis planar isomer, already observed with the parent chromophore (BMPC), and an additional isomer, N(1)-C(2) cis, peculiar to BPPC. The role of the solute-solvent interactions is discussed with reference to the purely intramolecular model previously proposed for the cyanine photoisomerization.


1994 - A condensed thiadiazolo-pyrimidine as a new efficient fluorophore. Theoretical and experimental investigation of the electronic spectra and photophysics [Articolo su rivista]
Baraldi, Ivan; Carnevali, A.; Caselli, Monica; Costi, Maria Paola; Pecorari, P.; Ponterini, Glauco; Rinaldi, M.
abstract

A recently synthesized condensed thiadiazolo-pyrimidine (MTP) has been found to exhibit a very intense fluorescence emission in aprotic solvents. The origins of such an unusual property for a compound containing many different heteroatoms (four nitrogens, two sulphurs and one oxygen) have been investigated by a combined theoretical and experimental approach. The nature and peculiarity of the MTP chromophore have been analysed using both computed electron densities and crystallographic data from the literature. The singlet and triplet spectra have been measured and calculated, and a good agreement has been found between the two sets of results. On this basis, we have attempted to interpret the rather peculiar photophysical behaviour of MTP.


1994 - GENERATION OF SINGLET OXYGEN BY 2,2'/5',2''-TERTHIOPHENE AND SOME OF ITS DERIVATIVES [Articolo su rivista]
Ciofalo, M; Ponterini, Glauco
abstract

The kinetics of oxygen quenching of the lowest triplet states of 2,2':5',2#-terthiophene and several of its substituted derivatives in 95% ethanol were analysed as part of an investigation of the chemical and physicochemical basis of the phototoxicity of these compounds. Overall bimolecular rate constants and singlet oxygen (O-2((1) Delta(g))) formation quantum yields were measured by laser flash photolysis and time-resolved phosphorescence detection. With the exception of one compound, both parameters proved to be almost independent of the chemical nature, position and number of substituents, thus failing to indicate an explanation for the very large differences in phototoxicity observed between the various derivatives during in vivo experiments. On the basis of the measured kinetic parameters, a schematic description of the mechanism of interaction with oxygen of these compounds in their lowest triplet states is proposed.


1993 - Concerning medium polarity effects on the photophysics andphotochemistry of TICT-forming dyes [Articolo su rivista]
Momicchioli, Fabio; Baraldi, Ivan; A., Carnevali; Caselli, Monica; Ponterini, Glauco
abstract

Mechanism and dynamics of the excited state relaxation in compounds able to form TICT states were investigated from a theoretical point of view with special reference to the dielectric solvent effects. The study included 4-dimethylamino-4’-cyanostilbene (DCS) and Michler’s Hydrol Blue (MHB), which are thought to involve emitting and non-emitting TICT states, respectively. It was found that in DCS the formation ofTICT states, by twisting either the dimethylamino or the dimethylanilino groups, may in principle be induced by the solvent polarity but requires extreme conditions. InMHB, both calculations and new fluorescence quantum-yield measurements in a variety of solvents indicated that the TICT-state formation is essentially controlled by the solvent viscosity.


1993 - Electronic spectra and trans-cis photoisomerism of carbocyanines. A theoretical (CS INDO CI) and experimental study [Articolo su rivista]
Baraldi, Ivan; A., Carnevali; Momicchioli, Fabio; Ponterini, Glauco
abstract

Two carbocyanine dyes, DOC(3,3’-diethyloxacarbocyanine) and DTC (3,3’-diethylthiacarbocyanine), were studied in detail by a combined experimental and theoretical treatment previously adjusted on simple streptocyanines. The BPPC (bisphenylaminopentamethine cyanine) dye was also studied to better correlate the properties of DOC and DTC with those of their parent streptocyanine BMPC (bisdimethylaminopentamethinecyanine). In the experimental part of the work, carried out on methanol solutions of BPPC+, Cl-, DOC+, I- and DTC+, I-, we determined the separate spectra of the stable forms and the photoisomers produced by irradiation into the visible absorption region. The theoretical part, based on CS INDO S+ D + T- CI calculations, was especially devised to provide as thorough an interpretation as possible of the electronic spectra (both S,-.S, and S,-T,,) of BPPC, DOC and DTC in terms of molecular subunits and to try to identify each observed species as a specific geometrical isomer (all-rrans or mono&). In all cases theproperties of the stable forms were consistent with the molecules assuming the all-trans structure. The lowest singlet excited state (S,), responsible for the colour band, retained nearly pure cyanine character (‘E in Platt’s notation), while the states falling in the second (medium UV) absorption region had prevailing aromatic (‘H) or charge transfer (‘G) character. This provided an explanation for the absence of a definite “cis peak” effect inthese compounds. BPPC was found to give rise to the same photoisomer as BMPC (3-4 ci.r) and an additionalphotoisomer clearly identified as the l-2 cis form. On the other hand, in DOC and DTC, where the spectral changes caused by the irradiation were far weaker, the single observed photoisomer could be better assigned as 2-8 cis, i.e. corresponding to the 2-3 cir form of BMPC.


1993 - Modelling of the cis-trans partitioning in the photoisomerizations of cyanines and stilbene derivatives [Articolo su rivista]
Caselli, Monica; Momicchioli, Fabio; Ponterini, Glauco
abstract

In the course of photoisomerization, polymethine cyanines as well as stilbene and its derivates decay from the S1 potential energy minimum, corresponding to the perpendicular geometry, to yield either cis or trans ground-state molecules. The fraction of cis isomers obtained, alpha, spans a larger range of values for symmetric cyanines than for stilbene derivatives. It is argued that such different behaviour for the two classes of compounds should be traceable to the electronically different nature of their S1 perp species. Making use of radiationless transition theory results, it is shown that the relative location of the S1 minimum and S0 maximum along the internal rotation coordinate is crucial to the evaluation of alpha: even small differences between these critical twisting angles, which are more reasonably expected for polymethine cyanines than for stilbene-like compounds, may cause strong deviations from equipartitioning (alpha = 0. 5 ).


1993 - SINGLET TRIPLET INTERSYSTEM CROSSING IN 2,2' 5',2''-TERTHIOPHENE AND SOME OF ITS DERIVATIVES [Articolo su rivista]
Rossi, R; Ciofalo, M; Carpita, A; Ponterini, Glauco
abstract

During the course of a study devoted to the investigation of the existence of a relationship between the phototoxic and photophysical properties of 2,2':5',2''-terthiophene (1a) and related compounds, the singlet-to-triplet intersystem crossing quantum yields of compound la and six of its monosubstituted derivatives (1b-1g) were determined in 95% ethanol solution. The variations in the phototoxicity of these compounds against some insect and mite species are large in comparison with changes in the quantum yields of triplet state formation. The latter were very similar in the compounds studied (range, 0.88-0.99), with the exception of 5-formyl-2,2':5',2''-terthiophene. (1c) (PHI(T)=0.50). Moreover, a complete characterization of the S1 decays of compounds la-1g was obtained by combining these data with the corresponding fluorescence quantum yields and lifetimes. Finally, the consequences of the nature and position of the substituents on the measured triplet-triplet absorption and rate constants of the two S1 decay paths, i.e. fluorescence emission and intersystem crossing, are qualitatively discussed.


1992 - PHOTOISOMERIZATION DYNAMICS OF 3,3'-DIETHYL OXACARBOCYANINE - INTRAMOLECULAR AND SOLVENT VISCOSITY EFFECTS [Articolo su rivista]
Ponterini, Glauco; Caselli, Monica
abstract

The dynamics of photoisomerization and of ground-state back isomerization of 3,3'-diethyl oxacarbocyanine (DOC) in linear alcohols are analyzed. Intramolecular activation energies are obtained and compared with those of the corresponding dicarbocyanine (DODCI) in an attempt at establishing the consequence of the polymethine chain lengthening on the isomerization dynamics. The activation energy for the photoisomerization of DOC is slightly lower than that of DODCI, whereas the reverse is found for the ground-state back isomerization. The coupling of the internal twisting coordinate with solvent drag is analyzed within the framework of the hydrodynamic Kramers model. Although this approach does not provide a fully satisfactory description of the experimental points, it has been taken as a reference model: the parameters obtained from the data fitting have been assigned a semi-quantitative significance and a number of possible reasons of breakdown of the hydrodynamic Kramers description have been considered and qualitatively discussed.


1992 - Theoretical and experimental study of the electronic spectrumand photophysics of Michler’s hydrol blue [Articolo su rivista]
Baraldi, Ivan; A., Carnevali; Momicchioli, Fabio; Ponterini, Glauco
abstract

The propertles of the lowest electronic states of Michler’s hydrol blue, the prototypic dlarylmethane dye, were investigated byphotophysical measurements and CS-INDO CI calculations. MHB solutions showed very weak fluorescence emissions (&x 2.0-3.0~ 10m4) at room temperature and, from the sensitized T,-T. absorption spectrum of MHB in acetic acid, the T, formatlonquantum yield (&) was estimated to be below 3.5 x 1 O-‘. Starting from these observations, which point to a cyanme-like natureof MHB, a detailed theoretical study was carried out taking BMNC (bisdlmethylammononamethine cyanine) as the suitablereference chromophore. Calculations included the ground state conformation, the electronic So-S,, and T,-T, absorption spectraand the potential energy curves for twisting about one central C-C bond in the SO. T, and S, states. On the whole, the reportedresults support the existence of a close relationship between MHB and BMNC and indicate that the fast deactivation of the lowestexcited singlet state occurs via internal conversion from twisted configurations characterized by charge localization


1991 - TRANS CIS PHOTOISOMERIZATION MECHANISM OF CARBOCYANINES - EXPERIMENTAL CHECK OF THEORETICAL-MODELS [Articolo su rivista]
Ponterini, Glauco; Momicchioli, Fabio
abstract

Two different theoretical models for the cyanine photoisomerization, emphasizing, respectively, the role of the solvent effects (model a) and that of the intramolecular forces (model b), have been experimentally tested by investigating the photophysical and photochemical behaviour of two carbocyanines (DOC and DTC). The decay kinetics of the excited-state (Sl) stable isomer and of the ground-state (S0) unstable photoisomer have been measured in solvents of very different polarities, but similar and low viscosities (methanol, methylene chloride and chlorobenzene were extensively investigated, but some test measurements were also carried out in p-dioxane and in 1:1 toluene-chlorobenzene). The activation energy for the non radiative decay of the spectroscopic S(l) minimum, corresponding to a twisting around one of the polymethine bonds, is independent of solvent polarity, whereas a small but significant dependence is displayed by the activation energy and preexponential factor of the S(O) back isomerization. These results can be easily accounted for within model b, while they sharply contrast with the predictions of model a. We have also measured the quantum yields of photoisomer formation for DOC and DTC at various temperatures and have shown that, in both cases, radiationless decay occurs from the perp S(l) minimum to ground state, with a branching ratio favouring reformation of the stable (trans) isomer. The parallel temperature dependence of the fluorescence decay and photoisomer formation has provided further support to model b. Finally, the temperature dependence of the quantum yield for the cis --> trans photoisomerization of DOC has been analyzed. A very low activation energy has been found suggesting that this process is probably intrinsically barrierless.


1990 - Electronic spectra and truns-cis isomerism of streptopolymethinecyanines. A CS INDO CI study [Articolo su rivista]
Momicchioli, Fabio; Baraldi, Ivan; Ponterini, Glauco; G., Berthier
abstract

The understanding of the role played by cyanine dyes in various fields of application calls for a thorough knowledge of the excited state properties of their parent chromophores, i.e. cationic streptopolymethyne cyanines. For this aim we performed a detailed CS INDO CI investigation on the electronic spectra oftri-, penta- and heptamethine cyanines, both unsubstituted (TC, PC, HC) and terminally substituted by methyl groups (BMTC, BMPC, BMHC). The study comprised 5,-S, and S,-T, transitions of the truns and all mono-& isomers. CI expansions involved solely n orbitals of the polymethine chains and pseudo-n orbitals ofthe substituents and included all singly-excited and the most important doubly- and triply-excited configurations.The spectroscopic effects of methyl substitution are fairly well described and are shown to be especially important in the upper excited states. The identification of the photochemically formed stereoisomers is attempted in terms of mono-cir isomers. For BMPC, in particular, we report the absorption spectrum of thephototropic form and show that the photoisomer is identifiable as the 3-4 cb form.


1989 - Formation and decay kinetics of the TICT state of 4,4'-diaminodiphenylsulfone [Articolo su rivista]
Ponterini, Glauco; J. C., Mialocq
abstract

Formation and decay kinetics of the TICT state of 4,4'-diaminodiphenylsulfone


1989 - Photophysics and Photochemistry of Diphenyl Sulfone. 2. Investigation of the S1 Decay Pathways [Articolo su rivista]
Bruni, Maria Cristina; Ponterini, Glauco; M., Scoponi
abstract

An extensive analysis of the SI deactivation pathways of diphenyl sulfone (DPS) in alcohols and some other solvents is presented.The combined results of steady-state photolysis, time-resolved fluorescence, and steady-state fluorescence measurements atvariable temperature and of SI -- TI intersystem crossing quantum yield determinations enable a complete characterizationof the SI photophysics and photochemistry of DPS to be obtained. The main S1 decay channel appears to be an activatedSI -- T, intersystem crossing (Ea= 2 kcal/mol), other than SI -- TI. Although the fluorescence emission and SI -- TI quantum yields show some solvent dependence, they play minor roles in the solvents studied. The state eventually reachedin the SI -- T, activated intersystem crossing is proposed to be a dissociative 3ss* state localized on a C-S bond, on thebasis of experimental evidence and of some preliminary theoretical data. A simple rationalization of the observations is provided by a model potential energy diagram obtained as an extension of the one previously proposed to account for the results concerning the TI decay of the same molecule. Two hypotheses on the mechanism of the abovementioned SI -- T, activated intersystem crossing are put forward and briefly discussed


1989 - Rotamerism in 2,2’-binaphthyl. A study based on fluorescence analysis and CS-INDO/CI calculations [Articolo su rivista]
Baraldi, Ivan; M. C., Bruni; Caselli, Monica; Ponterini, Glauco
abstract

The torsional isomerism of 2-2’-binaphthyl in the ground state and lowest excited singlet states has been investigated theoretically and experimentally. The combined results of a fluorescence steady-state and time-resolved analysis and of CS-INDO/CI calculations showed that this molecule exists in the ground state in two rotameric forms in which the naphthyls are rotated around the interconnecting quasi-single bond by different angles. The absorption spectrum of 2-2’-binaphthyl was assigned and resolved into the individual spectra of the two rotamers. The fluorescence spectra, lifetimes and quantum yields of the two isomers at room temperature were also derived. The effects of solvent viscosity increase and of temperature decrease on the measured fluorescence lifetimes were found to be small. Lastly, a discussion of the rotational behaviour of this molecule as opposed to that of other biaryls is offered on the basis of the calculated torsional energy curves.


1988 - CS-INDO/CI calculation of the singlet and triplet spectra of naphthalene and phenanthrene [Articolo su rivista]
Baraldi, Ivan; Ponterini, Glauco
abstract

CS-INDO/CI calculation of the singlet and triplet spectra of naphthalene and phenanthrene


1988 - Photophysics and photochemistry of diphenylsulfone. 1. The triplet mechanism of photodissociation [Articolo su rivista]
Ponterini, Glauco; Momicchioli, Fabio
abstract

A laser flash photolysis study of diphenylsulfone was carried out.


1988 - Picosecond laser fluorescence studies of intramolecular charge transfer processes [Capitolo/Saggio]
Ponterini, Glauco; M., Meyer; J. C., Mialocq
abstract

The dual fluorescence of p,p'.diaminodiphenylsulphone has been studied in methanol solution using picosecond laser fluorescence spectroscopy.


1987 - Potential-energy curves of the torsional mode of 1,1′-binaphthyl in the ground and lowest excited singlet states. A CS–INDO/CI study [Articolo su rivista]
Baraldi, Ivan; Ponterini, Glauco; Momicchioli, Fabio
abstract

The application of a recently developed theoretical method, CS–INDO/CI, to the study of the sections of the potential-energy surfaces of the ground and four lowest excited singlet states of 1,1′-binaphthyl corresponding to the coordinate of twisting around the inter-ring 1,1′-bond has proved to be successful in explaining the measured spectroscopic and photophysical properties of this molecule. All the changes observed in its spectroscopy and photophysics on going from low-temperature rigid solutions to room-temperature fluid solutions (strong bathochromic shift of the fluorescence maximum, change in the Snâ†�S1 absorption spectrum, shortening of the fluorescence lifetime by an order of magnitude) are qualitatively accounted for in terms of the calculated potential-energy curves. In particular, the S1 state experiences a drastic change in its electronic nature (from Lb to La) when the interplanar angle is allowed to relax from the near-orthogonal ground-state conformation to the trans twisted S1 equilibrium conformation (ϕ≈ 130 °). A comparison with the results of previous theoretical approaches stresses the reliability of the CS–INDO/CI method and the wealth of information on potential-energy surfaces which can be achieved through its application.


1986 - Real-Time Acquisition and Preprocessing of Kinetic and Spectroscopic Data in Laser Flash Photolysis [Articolo su rivista]
A., Longoni; Ponterini, Glauco
abstract

An automatic flash photolysis system for the measurement of absorption decays and transient difference spectra is described. The apparatus performs a digital measurement of the light transmitted by the sample and a few on-line preprocessing operations on the measured data, such as the digital averaging of the signal and the computation of the change in absorbance. A boxcar averager, used as a gated integrator, constitutes the sampling head of the apparatus. A microprocessor-based acquisition and control unit performs a digital conversion of the value sampled by the boxcar, provides an on-line preprocessing of the data, and supervises every operation required by the measurement process. This unit is interfaced to a personal computer which allows a friendly interaction with the operator as well as the on-line display of the data. The electronic instrumentation features a time resolution of a few nanoseconds, with a boxcar averager as input head, and of a few hundreds of picoseconds, with a sampling oscilloscope as input head


1985 - Theoretical conformational analysis of p-, m-, and o-terphenyl [Articolo su rivista]
Baraldi, Ivan; Ponterini, Glauco
abstract

A ground state conformational analysis has been carried out on p-, m-, and o-terphenyl using a recently developed semiempirical calculation method (CS-INDO). The potential energy surface has been calculated as a function of the torsion angles of the two terminal phenyls relative to the central one. Two nearly isoenergetic rotamers are found to exist for both p- and m-terphenyl, at geometries corresponding to D2, and C2h symmetries for p-terphenyl, C2, and Cs symmetries for m-terphenyl. The torsion angles are ca. 35° in all cases. The barriers separating the two minima of each potential surface are low enough to allow a rapid interconversion of the rotamers at room temperature in the gas phase (they are in “dynamic” equilibrium). o-Terphenyl presents only one equilibrium geometry. These findings are compared with the results of previous experimental and theoretical studies, which are extensively reviewed.


1984 - Conformations and barriers to internal rotation in trans-diarylethylenes: Theoretical investigation using a new INDO-type method (C-INDO) [Articolo su rivista]
Baraldi, Ivan; Momicchioli, Fabio; Ponterini, Glauco
abstract

C-INDO, a new INDO-based technique specially devised for conformational studies of conjugated systems, is used to investigate conformational equilibria in ground state trans-diarylethylenes, as revealed by a number of emission spectroscopic observations (both steady-state and time resolved). Conformations, ΔE and barriers to internal rotation are provided for all the possible rotamers of 1-StN (1-styrilnaphthalene), 2-StN, 2,2′-DNE (2,2′-dinaphthylethylene) and 1,2′-DNE. Energetic parameters are used to predict the relative abundances of the distinct rotameric species at equilibrium as well as to estimate the rate at which equilibria are established (at different T). The results prove to be a consistent basis on which experimentally observed behaviour can be rationalized.


1983 - Comparison of radiationless decay processes in osmium and platinum porphyrins [Articolo su rivista]
Ponterini, Glauco; N., Serpone; M. A., Bergkamp; T. L., Netzel
abstract

Two Osmium porphyrin complexes were investigated by picosecond laser spectroscopy


1983 - Covalent hydration and pseudobase formation in transition metal polypyridyl complexes: Reality or myth? [Articolo su rivista]
N., Serpone; Ponterini, Glauco; M. A., Jamieson; F., Bolletta; M., Maestri
abstract

Covalent hydration and pseudobase formation in transition metal polypyridyl complexes: Reality or myth?


1981 - Sudden polarization effect in methyl-substituted twisted polyenes [Articolo su rivista]
Baraldi, Ivan; Bruni, Maria Cristina; Momicchioli, Fabio; Ponterini, Glauco
abstract

Sudden polarization effect in methyl-substituted twisted polyenes


1980 - Polarization of cis-trans photoisomerization funnels, size and suddenness [Articolo su rivista]
Baraldi, Ivan; Bruni, Maria Cristina; Momicchioli, Fabio; Ponterini, Glauco
abstract

Size and suddenness of the polarization effect in the lowest lying excited states (S1, S2) of twisted polyenes were theoretically investigated at the INDO level of approximation.The simple 3 × 3 CI scheme of Salem and Rowland was first reconsidered and the effects of more extended CI's (selected with references to the basic three-configuration wavefunctions) were then analysed by using MO's optimized for both the closed shell (ψ21) and the open shell (ψ1ψ −1) configurations (ψ1 and ψ−1 being the two almost degenerate frontier orbitals). Our results indicate that: (i) introduction of not very large, but properly selected, CI is generally advisable in order that “artifacts” inherent in the adopted monoconfigurational SCF techniques (and/or symmetry constraints) be avoided, (ii) in strongly dissymmetric systems (e.g. terminally-twisted polyenes) S1 and S2 states are characterized by broad well-shaped dipole moment peaks, whose maxima range from ≈3 D (in dienes) to an upper limit of ≈6 D (in larger polyenes), (iii) in slightly dissymmetric systems (e.g. “centrally” twisted polyenes) (at least) two sharp dipole moment maxima (not excessively high in value) are likely to be present in S1 and S2 states on either side of the perpendicular configuration, at the points where avoided crossings of the two closely lying S1 andS2 potential surfaces occur.