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FRANCESCO MUNIZ MIRANDA

Ricercatore t.d. art. 24 c. 3 lett. B
Dipartimento di Scienze Chimiche e Geologiche - Sede Dipartimento di Scienze Chimiche e Geologiche

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Pubblicazioni

2024 - Iron nuclearity in mineral fibres: Unravelling the catalytic activity for predictive modelling of toxicity [Articolo su rivista]
Gualtieri, Alessandro F.; Cocchi, Marina; Muniz-Miranda, Francesco; Pedone, Alfonso; Castellini, Elena; Strani, Lorenzo
abstract

: Chronic inflammation induced in vivo by mineral fibres, such as asbestos, is sustained by the cyclic formation of cytotoxic/genotoxic oxidant species that are catalysed by iron. High catalytic activity is observed when iron atoms are isolated in the crystal lattice (nuclearity=1), whereas the catalytic activity is expected to be reduced or null when iron forms clusters of higher nuclearity. This study presents a novel approach for systematically measuring iron nuclearity across a large range of iron-containing standards and mineral fibres of social and economic importance, and for quantitatively assessing the relation between nuclearity and toxicity. The multivariate curve resolution (MCR) empirical approach and density functional theory (DFT) calculations were applied to the analysis of UV-Vis spectra to obtain information on the nature of iron and nuclearity. This approach led to the determination of the nuclearity of selected mineral fibres which was subsequently used to calculate a toxicity-related index. High nuclearity-related toxicity was estimated for chrysotile samples, fibrous glaucophane, asbestos tremolite, and fibrous wollastonite. Intermediate values of toxicity, corresponding to a mean nuclearity of 2, were assigned to actinolite asbestos, amosite, and crocidolite. Finally, a low nuclearity-related toxicity parameter, corresponding to an iron-cluster with a lower catalytic power to produce oxidants, was assigned to asbestos anthophyllite.

2024 - Quantum-Chemistry Study of the Hydrolysis Reaction Profile in Borate Networks: A Benchmark [Articolo su rivista]
Muniz-Miranda, Francesco; Occhi, Leonardo; Fontanive, Francesco; Menziani, Maria Cristina; Pedone, Alfonso
abstract

This investigation involved an ab initio and Density Functional Theory (DFT) analysis of the hydrolysis mechanism and energetics in a borate network. The focus was on understanding how water molecules interact with and disrupt the borate network, an area where the experimental data are scarce and unreliable. The modeled system consisted of two boron atoms, bridging oxygen atoms, and varying numbers of water molecules. This setup allows for an exploration of hydrolysis under different environmental conditions, including the presence of OH− or H+ ions to simulate basic or acidic environments, respectively. Our investigation utilized both ab initio calculations at the MP2 and CCSD(T) levels and DFT with a range of exchange–correlation functionals. The findings indicate that the borate network is significantly more susceptible to hydrolysis in a basic environment, with respect to an acidic or to a neutral pH setting. The inclusion of explicit water molecules in the calculations can significantly affect the results, depending on the nature of the transition state. In fact, some transition states exhibited closed-ring configurations involving water and the boron–oxygen–boron network; in these cases, there were indeed more water molecules corresponding to lower energy barriers for the reaction, suggesting a crucial role of water in stabilizing the transition states. This study provides valuable insights into the hydrolysis process of borate networks, offering a detailed comparison between different computational approaches. The results demonstrate that the functionals B3LYP, PBE0, and wB97Xd closely approximated the reference MP2 and CCSD(T) calculated reaction pathways, both qualitatively in terms of the mechanism, and quantitatively in terms of the differences in the reaction barriers within the 0.1–0.2 eV interval for the most plausible reaction pathways. In addition, CAM-B3LYP also yielded acceptable results in all cases except for the most complicated pathway. These findings are useful for guiding further computational studies, including those employing machine learning approaches, and experimental investigations requiring accurate reference data for hydrolysis reactions in borate networks.

2024 - Trapping an unprecedented octacoordinated iron(ii) complex with neutral bis-tetrazolylpyridyl ligands and solvent molecules [Articolo su rivista]
Rigamonti, Luca; Marchi, Lorenzo; Fiorini, Valentina; Stagni, Stefano; Zacchini, Stefano; Pinkowicz, Dawid; Dziedzic-Kocurek, Katarzyna; Forni, Alessandra; Muniz Miranda, Francesco; Mazzoni, Rita
abstract

: Iron(II) can show a very rich coordination chemistry with concomitant modulation of its properties as promising functional materials. Metalation of the neutral tridentate nitrogen-donor mer-coordinating ligand 2,6-bis(2-(methyl)-2H-tetrazol-5-yl)pyridine (Me2btp) with Fe(ClO4)2·6H2O through accurate solvent polarity control enables the selective crystallization of [FeHS/LS(Me2btp)2](ClO4)2·MeCN·2.75H2O (2HS/LS·MeCN·2.75H2O) as red rods, where half of the iron(II) centres resides in the low spin (LS, S = 0) state and the other half is in the high spin (HS, S = 2) state. The red rods spontaneously convert into yellow crystals once removed from the mother liquor and exposed to air due to solvent rearrangement within the crystal packing; these new crystals can be assigned to [FeHS(Me2btp)2](ClO4)2·solvent (2HS·solvent) where all the iron(II) centres are now blocked in the HS state, as confirmed by magnetic measurements. The polarity of the crystallization solvent, together with the maintenance of the crystals within the mother liquor, are pivotal for the reactivity and interconversion of different species. Indeed, upon long standing in solution, 2HS/LS·MeCN·2.75H2O converts to another form of red crystals belonging to [FeLS(Me2btp)2][FeHS(Me2btp)(MeCN)2(H2O)](ClO4)4·MeCN (2LS·3HS·MeCN), as confirmed by single crystal X-ray diffraction data. In this co-crystal, the iron(II) in 2 resides in the LS state at all temperatures while the iron(II) in 3 is blocked in the HS state. Well-formed yellow crystals could be also isolated among the red crystals of 2HS/LS·MeCN·2.75H2O, and they could be identified as the unprecedented octacoordinated species [Fe(Me2btp)2(MeCN)(H2O)](ClO4)2·H2O (1·H2O) by single-crystal X-ray diffraction. These yellow crystals are stable in the air, but slowly convert into 2LS·3HS·MeCN if kept in the mother liquor for about one week. 1·H2O can be considered the trapped intermediate in the solid state during the conversion of [FeHS(Me2btp)2]2+ into [FeHS(Me2btp)(MeCN)2(H2O)]2+ in solution, where the two tridentate ligands in the starting species can unfold to accommodate coordinated MeCN and H2O molecules, as confirmed by theoretical calculations, and eventually one of the two Me2btp is completely replaced by the solvent.

2023 - Can DFT Calculations Provide Useful Information for SERS Applications? [Articolo su rivista]
Muniz-Miranda, Maurizio; Muniz-Miranda, Francesco; Menziani, Maria Cristina; Pedone, Alfonso
abstract

: Density functional theory (DFT) calculations allow us to reproduce the SERS (surface-enhanced Raman scattering) spectra of molecules adsorbed on nanostructured metal surfaces and extract the most information this spectroscopy is potentially able to provide. The latter point mainly concerns the anchoring mechanism and the bond strength between molecule and metal as well as the structural and electronic modifications of the adsorbed molecule. These findings are of fundamental importance for the application of this spectroscopic technique. This review presents and discusses some SERS-DFT studies carried out in Italy as a collaboration between the universities of Modena and Reggio-Emilia and of Florence, giving an overview of the information that we can extract with a combination of experimental SERS spectra and DFT modeling. In addition, a selection of the most recent studies and advancements on the DFT approach to SERS spectroscopy is reported with commentary.

2022 - DFT and TD-DFT Study of the Chemical Effect in the SERS Spectra of Piperidine Adsorbed on Silver Colloidal Nanoparticles [Articolo su rivista]
Muniz-Miranda, Francesco; Pedone, Alfonso; Menziani, Maria Cristina; Muniz-Miranda, Maurizio
abstract

2022 - Ephemeral ice-like local environments in classical rigid models of liquid water [Articolo su rivista]
Capelli, Riccardo; MUNIZ MIRANDA, Francesco; Pavan, Giovanni M.
abstract

2022 - Structure Analysis and Properties Calculations [Capitolo/Saggio]
Presti, D.; Muniz-Miranda, F.; Tavanti, F.; Pedone, A.
abstract

2021 - Computational Approaches to the Electronic Properties of Noble Metal Nanoclusters Protected by Organic Ligands [Articolo su rivista]
MUNIZ MIRANDA, Francesco
abstract

2021 - Elucidation of the pre-nucleation phase directing metal-organic framework formation [Articolo su rivista]
Filez, M.; Caratelli, C.; Rivera-Torrente, M.; Muniz Miranda, F.; Hoek, M.; Altelaar, M.; Heck, A. J. R.; Van Speybroeck, V.; Weckhuysen, B. M.
abstract

Metal-organic framework (MOF) crystallization is governed by molecular assembly processes in the pre-nucleation stage. Yet, unravelling these pre-nucleation pathways and rationalizing their impact on crystal formation poses a great challenge since probing molecular-scale assemblies and macroscopic particles simultaneously is very complex. Herein, we present a multimodal, integrated approach to monitor MOF nucleation across multiple length scales by combining in situ optical spectroscopy, mass spectrometry, and molecular simulations. This approach allows tracing initial metal-organic complexes in solution and their assembly into oligomeric nuclei and simultaneously probing particle formation. During Co-ZIF-67 nucleation, a metal-organic pool forms with a variety of complexes caused by ligand exchange and symmetry reduction reactions. We discriminate complexes capable of initiating nucleation from growth species required for oligomerization into frameworks. Co4-nuclei are observed, which grow into particles following autocatalytic kinetics. The geometric and compositional variability of metal-organic pool species clarifies long-debated amorphous zeolitic imidazolate framework (ZIF)-particle nucleation and non-classic pathways of MOF crystallization.

2021 - Mechanochromic LLDPE Films Doped with NIR Reflective Paliogen Black [Articolo su rivista]
Micheletti, C.; Minei, P.; Carlotti, M.; Mattoli, V.; Muniz Miranda, F.; Perfetto, A.; Ciofini, I.; Adamo, C.; Ruggeri, Giacomo; Pucci, Andrea
abstract

The perylene bisimide derivative Paliogen Black (P-black) is proposed as a new chromogenic probe that shows visible (vis) and near-infrared (NIR) responses after mechanical solicitations of host linear low-density polyethylene (LLDPE) films. P-black is reported to display strong absorption in the vis spectrum and unusual reflective and cooling features in the NIR region. Uniaxial deformation of the 2.5, 5, and 10 wt% P-black/LLDPE films yields a dichroic absorption under polarized light with color variations attributed by the computational analysis to the distinct anisotropic behavior of the transition dipole moments of P-black chromophores. When LLDPE films are deformed, P-black aggregates reduce their size from ≈30–40 µm to ≈5–10 µm that, in turn, causes reflectivity losses of about 30–40% at the maximum elongation. This gives rise to warming of 5–6 °C of the locally oriented film placed in contact with a black substrate under the illumination with an IR lamp for 5 s. These features combined with the high sensitivity of the vis-NIR response toward mechanical solicitations render P-black as a new solution to detect uniaxial deformations of plastic films through both optical and thermal outputs.

2020 - Charting the Metal-Dependent High-Pressure Stability of Bimetallic UiO-66 Materials [Articolo su rivista]
Rogge, S. M. J.; Yot, P. G.; Jacobsen, J.; Muniz Miranda, F.; Vandenbrande, S.; Gosch, J.; Ortiz, V.; Collings, I. E.; Devautour-Vinot, S.; Maurin, G.; Stock, N.; Van Speybroeck, V.
abstract

In theory, bimetallic UiO-66(Zr:Ce) and UiO-66(Zr:Hf) metal-organic frameworks (MOFs) are extremely versatile and attractive nanoporous materials as they combine the high catalytic activity of UiO-66(Ce) or UiO-66(Hf) with the outstanding stability of UiO-66(Zr). Using in situ high-pressure powder X-ray diffraction, however, we observe that this expected mechanical stability is not achieved when incorporating cerium or hafnium in UiO-66(Zr). This observation is akin to the earlier observed reduced thermal stability of UiO-66(Zr:Ce) compounds. To elucidate the atomic origin of this phenomenon, we chart the loss-of-crystallinity pressures of 22 monometallic and bimetallic UiO-66 materials and systematically isolate their intrinsic mechanical stability from their defect-induced weakening. This complementary experimental/computational approach reveals that the intrinsic mechanical stability of these bimetallic MOFs decreases nonlinearly upon cerium incorporation but remains unaffected by the zirconium: hafnium ratio. Additionally, all experimental samples suffer from defect-induced weakening, a synthesis-controlled effect that is observed to be independent of their intrinsic stability.

2020 - Elucidating the promotional effect of a covalent triazine framework in aerobic oxidation [Articolo su rivista]
Abednatanzi, S.; Gohari Derakhshandeh, P.; Tack, P.; Muniz Miranda, F.; Liu, Y. -Y.; Everaert, J.; Meledina, M.; Vanden Bussche, F.; Vincze, L.; Stevens, C. V.; Van Speybroeck, V.; Vrielinck, H.; Callens, F.; Leus, K.; Van Der Voort, P.
abstract

Synergistic catalysis holds great promise to enhance the catalytic performance of heterogeneous catalysts suffering from sluggish reaction kinetics. Much effort has been dedicated to the development of bimetallic systems in which the two promoter elements display synergistic benefits compared to monometallic counterparts. However, the use of bimetallic catalysts inescapably raises the cost of preparation and environmental issues. This study discovers a synergistic effect when using a bipyridine covalent triazine framework (bipy-CTF) as support for an IrIII complex in the aerobic oxidation reaction. The detailed mechanistic study provides insights into the function of the bipy-CTF in this synergistic catalysis. The EPR and in-situ XANES analyses confirm the applicability of bipy-CTF to activate oxygen and alcohol, resulting in an enhancement of the performance of the IrIII complex to exceed the activity of the homogeneous counterpart. This is an unprecedented report on promoting the activity of a heterogeneous catalyst through its solid support.

2020 - General Density-Based Index to Analyze Charge Transfer Phenomena: From Models to Butterfly Molecules [Articolo su rivista]
Huet, L.; Perfetto, A.; Muniz Miranda, F.; Campetella, M.; Adamo, C.; Ciofini, I.
abstract

We present a new formula and implementation for a descriptor enabling quantification of the electron-hole distance associated with a charge transfer of an optical transition, on the basis of the knowledge of the densities of the electronic ground and excited states. This index is able to define a charge-transfer length even for systems that would be otherwise difficult to treat, like symmetric molecules, while maintaining a very low computational cost and the possibility to be coupled to any method providing ground and excited state electron densities. After a benchmark of its performance on a series of push-pull molecules, the index has been applied to a set of large symmetric luminophores, the so-called "butterfly molecules", showing promising applications in optoelectronics, to highlight its potential use in the design of new compounds.

2020 - Palladium oxide nanoparticles: Preparation, characterization and catalytic activity evaluation [Articolo su rivista]
Muniz Miranda, M.; Zoppi, A.; Muniz Miranda, F.; Calisi, N.
abstract

Stable palladium oxide nanoparticles were prepared in aqueous suspension with a very simple procedure, by dissolving palladium nitrate in water at a concentration around 10-4 M. UV-visible absorption spectroscopy was adopted to follow the formation of these nanoparticles, which were characterized by TEM microscopy, along with XRD, XPS and Raman measurements. DFT calculations allowed to interpret the Raman data and to clarify the species present at the surface of the nanoparticles. The catalytic activity of the latter was evaluated by monitoring the reduction of p-nitrophenol to p-aminophenol. This investigation paves the way to the use of these colloidal nanoparticles in processes of heterogeneous catalysis, in particular those concerning the catalytic degradation of aromatic derivatives that represent a serious danger for the environment as pollutants, as in the case of p-nitrophenol.

2020 - Spectroscopic and microscopic analyses of Fe3O4/au nanoparticles obtained by laser ablation in water [Articolo su rivista]
Muniz-miranda, M.; Muniz Miranda, F.; Giorgetti, E.
abstract

Magneto-plasmonic nanoparticles constituted of gold and iron oxide were obtained in an aqueous environment by laser ablation of iron and gold targets in two successive steps. Gold nanoparticles are embedded in a mucilaginous matrix of iron oxide, which was identified as magnetite by both microscopic and spectroscopic analyses. The plasmonic properties of the obtained colloids, as well as their adsorption capability, were tested by surface-enhanced Raman scattering (SERS) spectroscopy using 2,2′-bipyridine as a probe molecule. DFT calculations allowed for obtaining information on the adsorption of the ligand molecules that strongly interact with positively charged surface active sites of the gold nanoparticles, thus providing efficient SERS enhancement. The presence of iron oxide gives the bimetallic colloid new possibilities of adsorption in addition to those inherent to gold nanoparticles, especially regarding organic pollutants and heavy metals, allowing to remove them from the aqueous environment by applying a magnetic field. Moreover, these nanoparticles, thanks to their low toxicity, are potentially useful not only in the field of sensors, but also for biomedical applications.

2019 - A DFT approach to the surface-enhanced raman scattering of 4-cyanopyridine adsorbed on silver nanoparticles [Articolo su rivista]
Lopez-Tocon, I.; Valdivia, S.; Soto, J.; Otero, J. C.; Muniz-Miranda, F.; Menziani, Maria Cristina; Muniz-Miranda, M.
abstract

A Surface-Enhanced Raman Scattering (SERS) spectrum of 4-cyanopyridine (4CNPy) was recorded on silver plasmonic nanoparticles and analyzed by using Density Functional Theory (DFT) calculations. Two simple molecular models of the metal–4CNPy surface complex with a single silver cation or with a neutral dimer (Ag+ –4CNPy, Ag2 –4CNPy), linked through the two possible interacting sites of 4CNPy (aromatic nitrogen, N, and nitrile group, CN), were considered. The calculated vibrational wavenumbers and intensities of the adsorbate and the isolated species are compared with the experimental Raman and SERS results. The analysis of the DFT predictions and the experimental data indicates that 4CNPy adsorbs preferentially on neutral/charged active sites of the silver nanoparticles through the nitrogen atom of the aromatic ring with a perpendicular orientation.

2019 - Adsorption of Trans-Zeatin on Laser-Ablated Gold Nanoparticles for Transport into Plant Cells and Growth Stimulation [Articolo su rivista]
Zoppi, A.; Caporali, S.; Muniz-Miranda, F.; Pedone, A.; Muniz-Miranda, M.
abstract

Gold nanoparticles can serve as nanovectors for trans-zeatin, a natural cytokinin used in plant culture to stimulate growth and bud formation. Here, we have used Raman scattering, X-ray photoelectron spectroscopy, UV-vis absorption, transmission electron microscopy, and density functional theory calculations to explain the role of citrate anions in both the formation and the reactivity of the gold colloidal nanoparticles obtained by laser ablation and to go deeper inside into the interaction between metal and zeatin. In particular, the SERS (surface-enhanced Raman scattering) spectroscopy has been employed to study the adsorption of zeatin on different gold colloidal substrates. It is established that the molecule links to gold as tautomer N7(H), predominant in the aqueous suspension, in close similarity with adenine adsorbed on gold. Moreover, the laser ablation of a gold target in citrate solution results in small, stable, and reactive Au nanoparticles, able to transport zeatin inside plant cells, where it can act as a growth hormone.

2019 - Aggregation effects on pigment coatings: Pigment red 179 as a case study [Articolo su rivista]
Muniz Miranda, Francesco; Minei, P.; Contiero, L.; Labat, F.; Ciofini, I.; Adamo, C.; Bellina, F.; Pucci, Andrea
abstract

Here, we have studied, with a combined experimental and computational approach, the effect of the crystal environment and aggregation on the electronic properties of Pigment Red 179, which affect both its color and optical energy gap. Spectra acquired in the near-infrared and visible range of energies suggest that this molecule is indeed a "cool" dye, which can be employed as a red pigment that provides effective color coverage to different substrates without contributing to their heating during light irradiation. Spectra acquired on different polymer mixtures at different pigment concentrations (i.e., 2.5-10 wt %) suggest that absorption features depend on chromophoric arrangements promoted by the strong intermolecular I -πinteractions. Calculations, performed at the time-dependent density functional theory level, allowed to both attribute the nature of the electronic transitions causing the observed spectra involved and understand the effect of the environment. Indeed, the visible spectra of the pigment is dominated by two localized transitions, with negligible charge transfer for both a dye monomer and dimer either in vacuum or acetonitrile solution. Instead, models including the crystal environment of the pigment show the presence of a high-wavelength S1 â S0 charge transfer transition between two adjacent molecules, in quantitative agreement with the experimental absorption energy of the crystal pigment.

2019 - Electronic properties of heterogenized Ru(ii) polypyridyl photoredox complexes on covalent triazine frameworks [Articolo su rivista]
De Vos, A.; Lejaeghere, K.; Muniz Miranda, F.; Stevens, C. V.; Van Der Voort, P.; Van Speybroeck, V.
abstract

Ru(ii) polypyridyl complexes have been successful for a wide range of photoredox applications thanks to their efficient light-induced metal-to-ligand charge transfer. Using the computational framework of density-functional theory, we report how these complexes can be anchored onto covalent triazine frameworks while maintaining their favorable electronic properties. We moreover show that variation of the nitrogen content of the framework linkers or complex ligands endows the heterogenized catalyst with a unique versatility, spanning a wide range of absorption characteristics and redox potentials. By judiciously choosing the catalyst building blocks, it is even possible to selectively guide the charge transfer toward either the scaffold or the accessible pore sites. Rational design of sustainable and efficient photocatalysts thus comes within reach.

2019 - Immobilization of Ir(I) complex on covalent triazine frameworks for C–H borylation reactions: A combined experimental and computational study [Articolo su rivista]
Tahir, N.; Muniz Miranda, F.; Everaert, J.; Tack, P.; Heugebaert, T.; Leus, K.; Vincze, L.; Stevens, C. V.; Van Speybroeck, V.; Van Der Voort, P.
abstract

Metal-modified covalent triazine frameworks (CTFs) have attracted considerable attention in heterogeneous catalysis due to their strong nitrogen-metal interactions exhibiting superior activity, stability and hence recyclability. Herein, we report on a post-metalation of a bipyridine-based CTFs with an Ir(I) complex for C–H borylation of aromatic compounds. Physical characterization of the Ir(I)-based bipyCTF catalyst in combination with density functional theory (DFT) calculations exhibit a high stabilization energy of the Ir-bipy moiety in the frameworks in the presence of B2Pin2. By using B2Pin2 as a boron source, Ir(I)@bipyCTF efficiently catalyzed the C–H borylation of various aromatic compounds with excellent activity and good recyclability. In addition, XAS analysis of the Ir(I)@bipyCTF gave clear evidence for the coordination environment of the Ir.

2019 - Optical properties of isolated and covalent organic framework-embedded ruthenium complexes [Articolo su rivista]
Muniz Miranda, F.; De Bruecker, L.; De Vos, A.; Vanden Bussche, F.; Stevens, C. V.; Van Der Voort, P.; Lejaeghere, K.; Van Speybroeck, V.
abstract

Heterogenization of RuL3 complexes on a support with proper anchor points provides a route toward design of green catalysts. In this paper, Ru(II) polypyridyl complexes are investigated with the aim to unravel the influence on the photocatalytic properties of varying nitrogen content in the ligands and of embedding the complex in a triazine-based covalent organic framework. To provide fundamental insight into the electronic mechanisms underlying this behavior, a computational study is performed. Both the ground and excited state properties of isolated and anchored ruthenium complexes are theoretically investigated by means of density functional theory and time-dependent density functional theory. Varying the ligands among 2,2′-bipyridine, 2,2′-bipyrimidine, and 2,2′-bipyrazine allows us to tune to a certain extent the optical gaps and the metal to ligand charge transfer excitations. Heterogenization of the complex within a CTF support has a significant effect on the nature and energy of the electronic transitions. The allowed transitions are significantly red-shifted toward the near IR region and involve transitions from states localized on the CTF toward ligands attached to the ruthenium. The study shows how variations in ligands and anchoring on proper supports allows us to increase the range of wavelengths that may be exploited for photocatalysis.

2019 - SERS, XPS and DFT study of xanthine adsorbed on citrate-stabilized gold nanoparticles [Articolo su rivista]
Caporali, S.; Muniz-Miranda, F.; Pedone, A.; Muniz-Miranda, M.
abstract

We have studied the adsorption of xanthine, a nucleobase present in human tissue and fluids that is involved in important metabolic processes, on citrate-reduced gold colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS), absorption, and X-ray photoelectron spectroscopy (XPS) measurements, along with density functional theory (DFT) calculations. The citrate anions stabilize the colloidal suspensions by strongly binding the gold nanoparticles. However, these anions do not impair the adsorption of xanthine on positively-charged active sites present on the metal surface. We have obtained the Fourier transform (FT)-SERS spectra of adsorbed xanthine by laser excitation in the near infrared spectral region, where interference due to fluorescence emission does not usually occur. In fact, the addition of chloride ions to the Au/xanthine colloid induces the aggregation of the gold nanoparticles, whose plasmonic band is shifted to the near infrared region where there is the exciting laser line of the FT–Raman instrument. Hence, this analytical approach is potentially suitable for spectroscopic determination of xanthine directly in body fluids, avoiding fluorescence phenomena induced by visible laser irradiation.

2018 - Raman and Computational Study on the Adsorption of Xanthine on Silver Nanocolloids [Articolo su rivista]
Muniz-Miranda, Francesco; Pedone, Alfonso; Muniz-Miranda, Maurizio
abstract

Xanthine is a nucleobase, deriving from adenine and guanine by deamination and oxidation processes, which may deposit in the human body causing diseases, similar to uric acid. Here, we have investigated the adsorption of xanthine on silver colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS) with an exciting radiation in the near-infrared spectral region, where interference due to fluorescence does not occur, along with density functional theory calculations of molecule/metal model systems. By adopting a combined experimental and computational approach, we have identified the "marker" SERS bands of xanthine and the tautomer that preferentially binds the silver particles, as well as the molecular group involved in the interaction with metal. This investigation allows using the FT-SERS spectroscopy for biosensory and diagnostic purposes in body fluids, detecting abnormal levels of xanthine, and preventing metabolic diseases.

2018 - SERS active Ag-SiO2 nanoparticles obtained by laser ablation of silver in colloidal silica [Articolo su rivista]
Gellini, Cristina; Muniz-Miranda, Francesco; Pedone, Alfonso; Muniz-Miranda, Maurizio
abstract

Highly stable Ag-SiO2 nanoparticle composites were first obtained by laser ablation of a silver target in an aqueous colloidal dispersion of silica and examined by UV-vis absorption spectroscopy, transmission electron microscopy and Raman spectroscopy. The surface enhanced Raman scattering (SERS) activity of these nanocomposites was tested using 2,2'-bipyridine as a molecular reporter and excitation in the visible and near-IR spectral regions. The computational DFT approach provided evidence of ligand adsorption on positively charged adatoms of the silver nanostructured surface, in a very similar way to the metal/molecule interaction occurring in the corresponding Ag(I) coordination compound.

2018 - SERS and DFT investigation on push-pull molecules: 4-Dimethylamino- 4’-nitrostilbene adsorbed on silver colloidal nanoparticles [Articolo su rivista]
Muniz-Miranda, Maurizio; Muniz-Miranda, Francesco; Pedone, Alfonso
abstract

The adsorption of 4-dimethylamino-4’-nitrostilbene, a typical push-pull chromophore, on Ag colloidal nanoparticles has been studied for the first time by SERS spectroscopy with different exciting lines and interpreted by the help of density functional theory calculations. This study allowed ascertaining the adsorption of DANS on silver via nitro-group and collecting information on the structural changes of the molecule induced by the interaction with the metal surface, leading to augmented nonlinear optical properties. In addition, under blue-green light irradiation the adsorbed molecules undergo a photoreduction of the nitro-group by a plasmon-induced catalyzing effect of the nanostructured silver surface.

2018 - SERS, XPS and DFT investigation on palladium surfaces coated with 2,2′-bipyridine monolayers [Articolo su rivista]
Muniz-Miranda, Maurizio; Muniz-Miranda, Francesco; Caporali, Stefano; Calisi, Nicola; Pedone, Alfonso
abstract

Palladium surfaces, pretreated with a solution of 2,2′-bipyridine (bpy) as ligand molecule, were SERS-activated by means of laser-ablated Ag colloidal nanoparticles. XPS and Raman measurements, along with DFT simulations, evidenced the species formed on the metal surface as bpy-Pd(OH) 2 , which appears quite similar, from both structural and spectroscopic points of view, to the bpy-PdCl 2 coordination compound, whose catalytic activity is well known. Based on these observations, the use of Pd substrates coated with bpy is proposed for reactions of heterogeneous catalysis, instead of using bpy-PdCl 2 as homogeneous catalyst. Moreover, palladium nanoparticles could be prepared by laser ablation in aqueous solution of bpy, exhibiting both colloidal stability and catalytic activity.

2018 - Spectroscopic and Computational Studies on Ligand-Capped Metal Nanoparticles and Clusters [Capitolo/Saggio]
Muniz-Miranda, M.; Muniz-Miranda, F.; Pedone, A.
abstract

Metal nanoparticles represent a bridge between single atoms and bulk materials, presenting peculiar chemical and optical properties. Under irradiation with an appropriate electromagnetic wave, the conduction electrons do not oscillate freely, because they are trapped in the nanometric size of the metal particles, which exhibit collective excitations called “localized plasmons.” These latter are needed to promote enhancements for both the Raman signal and the fluorescence emission of molecules adhering to the metal surface, when the exciting radiation wavelengths match those of the plasmon bands. Hence, Raman enhancements up to 107 factors are generally observed for molecules adsorbed on silver or gold nanoparticles in the SERS (surface-enhanced Raman scattering) measurements. When, instead, metal particles have sizes below about 2 nm, they do not have metallic properties owing to the existence of discrete electronic energy levels and the loss of overlapping electronic bands. These metal clusters exhibit a typical quantum size behavior, with optical and electronic properties different from those relative to plasmons. In this work, the spectroscopic properties of silver and gold nanoparticles and clusters, capped with organic ligands, are investigated by Raman scattering, absorption, and fluorescence measurements and interpreted by different computational approaches.

2018 - Spectroscopic and DFT investigation on the photo-chemical properties of a push-pull chromophore: 4-Dimethylamino-4′-nitrostilbene [Articolo su rivista]
Muniz-Miranda, Francesco; Pedone, Alfonso; Muniz-Miranda, Maurizio
abstract

4-Dimethylamino-4′-nitrostilbene (DANS), a π-conjugated push-pull molecule, has been investigated by means of a combined spectroscopic and computational approach. When the Raman excitation is close to the visible electronic transition of DANS, vibrational bands not belonging to DANS appear in the spectra, increasing with the laser power. These bands are observed at room temperature in the solid phase, but not at low temperature or in solution, and we interpret them as due to a thermally-activated photoreaction occurring under laser irradiation in the visible spectral region. Density-functional calculations correctly reproducing the electronic and vibrational spectra of DANS, describe the charge-transfer process, indicate that an azo-derivative is the product of the photoreaction of DANS and provide a reasonable interpretation of this process.

2018 - The Effect of Alkaline Cations on the Intercalation of Carbon Dioxide in Sepiolite Minerals: A Molecular Dynamics Investigation [Articolo su rivista]
Tavanti, F.; Muniz-Miranda, F.; Pedone, A.
abstract

The ability of the sepiolite mineral to intercalate CO2 molecules inside its channels in the presence of different alkaline cations (K+, Na+, and Li+) has been studied by classical molecular dynamics simulations. Starting from an alkaline-free sepiolite crystalline model, we built three models with stoichiometry Mg320Si440Al40O1200(OH)160X+40·480H2O. On these models, we gradually replaced the water molecules present in the channels with carbon dioxide and determined the energy of this exchange reaction as well as the structural organization and dynamics of carbon dioxide in the channels. The adsorption energy shows that the Li-containing sepiolite mineral retains more carbon dioxide with respect to those with sodium and potassium cations in the channels. Moreover, the ordered patterns of CO2 molecules observed in the alkaline-free sepiolite mineral are in part destabilized by the presence of cations decreasing the adsorption capacity of this clay mineral.

2017 - Magneto-Plasmonic Colloidal Nanoparticles Obtained by Laser Ablation of Nickel and Silver Targets in Water [Articolo su rivista]
Gellini, Cristina; Deepak, Francis Leonard; Muniz Miranda, Maurizio; Caporali, Stefano; Muniz Miranda, Francesco; Pedone, Alfonso; Innocenti, Claudia; Sangregorio, Claudio
abstract

Stable magneto-plasmonic nanoparticles in colloidal suspensions are fabricated by two-step nanosecond pulsed laser ablation of nickel and silver targets in pure water and characterized by UV-visible absorption, Raman, X-ray photoelectron spectroscopic, and magnetic measurements, along with high-resolution electron microscopy analysis. These systems are constituted by a low-crystallinity matrix of ferromagnetic nickel hydroxide, where nickel oxide nanocrystals are embedded,, with silver nanoparticles intimately linked to them. The surface enhanced Raman scattering activity is assessed by adsorption of adenine as probe ligand. Spectroscopic investigation and density functional theory calculations revealed that adenine is linked to nickel oxide, while nanosilver essentially plays the role of ensuring the Raman enhancement for the adsorbed organic ligand. Both magnetic and plasmonic properties allow using these nanostructured bimetallic platforms as catalysts in chemical reactions or nanosensors in biomedicine as well as in environmental research.

2016 - Assessment of the basis set effect on the structural and electronic properties of organic-protected gold nanoclusters [Articolo su rivista]
MUNIZ MIRANDA, Francesco; Menziani, Maria Cristina; Pedone, Alfonso
abstract

We have investigated the structural and optical properties of five monolayer-protected gold nanoclusters with a combination of exchange–correlation functionals, namely B-PBE for the geometry relaxation and CAM-B3LYP for the time-dependent calculations. We have tested the accuracy of five different basis sets in reproducing the experimental structures of these nanoclusters, and we have found that even a rather small basis set (single zeta) can outperform a significantly larger one (double zeta) if some selected atoms are treated with polarization functions. Namely, the sulfur and phosphorous atoms of the capping thiols and phosphines usually are hypervalent when bonded to the gold inner core; therefore, polarization functions allow them significantly more structural flexibility. With the two best performing basis sets, we carried out optical calculations and found that the resulting UV–Vis profiles are largely similar, in particular the energy and orbital contributions of the optical gaps are very close. The results support the use of the small basis set proposed here to investigate larger nanoclusters with general hybrid and range-corrected hybrid functionals.

2016 - Electronic and optical properties of the Au22[1,8-bis(diphenylphosphino) octane]6 nanoclusters disclosed by DFT and TD-DFT calculations [Articolo su rivista]
MUNIZ MIRANDA, Francesco; Presti, Davide; Menziani, Maria Cristina; Pedone, Alfonso
abstract

Time-dependent density functional theory calculations have been used to investigate the electronic and optical properties of a nanocluster composed of two directly bonded Au11 subunits, held together by six bidentate diphosphine ligands: 1,8-bis(diphenylphosphino) octane. Three exchange–correlation functionals have been adopted, a general hybrid (PBE0) and two range-separated hybrids (ωB97X and CAM-B3LYP). The results obtained show that the aforementioned properties are significantly different from those of a previously studied Au11-based nanocluster formed by just one single subunit. In particular, charge transfer excitations from the inner metal core to the outer ligands affect most of the UV–visible spectrum and occur for both alkyl and aromatic ligands. This is particularly evident when thiazole molecules are bonded to the gold core: In this case Au → ligand transitions affect also the first HOMO → LUMO excitation. Moreover, the gold core of this Au22 nanocluster has eight under-coordinated Au surface atoms not engaged in bonds with the ligands. No other known organic-protected gold nanocluster has a similar feature. These gold atoms can be considered as potential in situ active sites for catalysis, their catalytic efficiency and selectivity being modulated by charge distribution.

2016 - Raman and DFT study of methimazole chemisorbed on gold colloidal nanoparticles [Articolo su rivista]
Muniz Miranda, Maurizio; Muniz Miranda, Francesco; Pedone, Alfonso
abstract

The adsorption of methimazole on gold colloidal nanoparticles was investigated using a combination of surface-enhanced Raman scattering and density functional theory calculations, which allowed identifying the thiolate anion as the molecular species chemically interacting with the active sites of the gold surface, modeled as zero-charge metal adatoms, only through the sulfur atom. This result can be important for the use of these ligand/metal nanohybrids in the process of drug delivery. Moreover, functionalized gold nanoparticles are able to promote the Raman enhancement in the red-light region as well as in the near-infrared, where generally no fluorescence emission occurs. This paves the way for the use of these nanosystems in a biological environment, even in vivo experiments.

2016 - Supercritical CO2 Confined in Palygorskite and Sepiolite Minerals: A Classical Molecular Dynamics Investigation [Articolo su rivista]
MUNIZ MIRANDA, Francesco; Lodesani, Federica; Tavanti, Francesco; Presti, Davide; Malferrari, Daniele; Pedone, Alfonso
abstract

We have investigated the ability of two modular phyllosilicates (palygorskite and sepiolite) to store CO2 molecules inside their structural channels by means of classical molecular dynamics. Several models containing an increasing supercritical-CO2/H2O ratio into the phyllosilicate channels have been built and the structural and dynamic properties of carbon dioxide and water molecules investigated in detail. We found that both clay minerals can achieve this goal, with sepiolite being able to store more carbon dioxide molecules (and more stably) than palygorskite, due to the larger channels of the former. Interestingly, with the increase of CO2 molecules inside the minerals, the diffusivity of both water and carbon dioxide drastically decreases and carbon dioxide molecules tend to arrange themselves in an ordered pattern. (Figure Presented).

2016 - The antioxidant properties of Ce-containing bioactive glass nanoparticles explained by Molecular Dynamics simulations [Articolo su rivista]
Pedone, Alfonso; MUNIZ MIRANDA, Francesco; Menziani, Maria Cristina; Tilocca, Antonio
abstract

Molecular dynamics simulations of two glass nanoparticles with composition 25Na2O·25CaO 50SiO2 mol% (Ce-K NP) and 46.1SiO2·24.4Na2O·26.9CaO· 2.6P2O5 mol.% (Ce-BG NP) doped with 3.6 mol% of CeO2 have been carried out in order to explain the enhanced antioxidant properties of the former glass with respect to the latter. The present models show that the different catalase mimetic activity of the two NPs is related to the Ce3+/Ce4+ ratio exposed at their surface. In fact, this ratio is about 3.5 and 13 in the bulk and at the surface of the Ce-BG NP, and 1.0 and 2.1 in the bulk and at the surface of the Ce-K NPs, respectively. Since both oxidation states are necessary for the catalysis of the dismutation reaction of hydrogen peroxides, NPs with a very high Ce3+/Ce4+ ratio possess poorer antioxidant properties. Moreover, our simulations reveal that the already low silicate connectivity found in the bulk glasses examined here is further reduced on the nanoparticle surface, whereas the Na+/Ca2+ ratio rapidly increases. Sodium, calcium and cerium sites in proximity of the surface are found to be under-coordinated, prone to quickly react with water present in physiological environments, thus accelerating the glass biodegradation

2015 - Benchmarking TD-DFT against vibrationally resolved absorption spectra at room temperature: 7-aminocoumarins as test cases [Articolo su rivista]
MUNIZ MIRANDA, Francesco; Pedone, Alfonso; Battistelli, Giulia; Montalti, Marco; Bloino, Julien; Barone, Vincenzo
abstract

Time-dependent density functional theory (TD-DFT) is usually benchmarked by evaluating how the vertical excitation energies computed by using different exchange-correlation (XC) functionals compare with the maximum of the absorption spectra. However, the latter does not necessarily coincide with the vertical energies because it is affected by the vibronic band structure that has to be properly taken into account. In this work, we have evaluated the performance of several functionals belonging to different families in reproducing the vibronic structure (band shape) of four 7-aminocoumarin molecules of technological interest, whose spectra have been recorded in methylcyclohexane and acetonitrile solvents. In order to compare the computed vibronic spectra with the experimental ones in the most consistent way, the effect of temperature, often neglected, was also taken into account. We have found that no single functional provides simultaneously accurate band positions and shapes, but the combination of ωB97X vibronic couplings with PBE0 vertical energies can lead to very satisfactory results. In addition to the assessment of XC functionals, several adiabatic and vertical models proposed in the literature to compute vibrationally resolved electronic spectra have been tested and validated with respect to experiments. On these grounds, the adiabatic Hessian model has been used to perform a complete analysis of the ωB97X/PBE0 vibronic transitions contributing to the final band shapes of the investigated aminocoumarin molecules.

2015 - DFT and TD-DFT assessment of the structural and optoelectronic properties of an organic-Ag14 nanocluster [Articolo su rivista]
Muniz-Miranda, F.; Menziani, M. C.; Pedone, A.
abstract

An extensive benchmark of exchange-correlation functionals on the structure of the X-ray resolved phosphine and thiolate-protected Ag14-based nanocluster, named XMC1, is reported. Calculations were performed both on simplified model systems, with the complexity of the ligands greatly reduced, and on the complete XMC1 particle. Most of the density functionals that yielded good relaxed structures on analogous calculations on gold nanoclusters (viz. those employing the generalized gradient approximation) significantly deform the structure of XMC1. On the contrary, some of the exchange-correlation functionals including part of the exact Hartree-Fock exchange (hybrid functionals) reproduce the experimental geometry with minimal errors. In particular, the widely adopted B3LYP yields fairly accurate structures for XMC1, whereas it is outperformed by many other functionals (both hybrids and generalized gradient corrected) in similar calculations on analogous gold-based systems. Time-dependent density functional calculations have been employed to recover the experimental UV-vis spectrum. The present investigation shows that to correctly reproduce the optical feature of XMC1 the ligands cannot be omitted, because they interact with the metal core at energies much closer to the optical gap than in the case of gold-based nanoclusters of similar sizes. Due to this fact, a functional that accurately describes charge-transfer electronic transitions (such as the long-range corrected CAM-B3LYP) has to be adopted.

2015 - Influence of Silver Doping on the Photoluminescence of Protected AgnAu25–n Nanoclusters: A Time-Dependent Density Functional Theory Investigation [Articolo su rivista]
Muniz Miranda, Francesco; Menziani, Maria Cristina; Pedone, Alfonso
abstract

The effect of silver doping on the electronic properties and photoluminescence of a class of structurally similar AgnAu25–n2+ nanoclusters (0 ≤ n ≤ 13) has been investigated here by means of time-dependent density functional calculations. As very recently reported in the literature, a mixture of these clusters showed an unexpected 200-fold fluorescence quantum yield boost with respect to Au252+, but no mechanism has been proposed to date to explain this phenomenon. The results presented here suggest that the origin of this boost lies in the nature of the first excited state (S1), which is affected differently by the increasing presence of Ag atoms into the network of Au atoms. In fact, doping the cluster with silver atoms has the effect of shifting the lowest-energy “dark” excited states to higher energy, leaving a very “bright” highest occupied molecular orbital → lowest unoccupied molecular orbital (HOMO → LUMO) transition as the lowest-energy excitation. We propose that when fluorescence occurs from “bright” S1 states, it receives a boost in the quantum yield because of the high oscillator strength of these HOMO → LUMO transitions.

2015 - SERS effect from Pd surfaces coated with thin films of Ag colloidal nanoparticles [Articolo su rivista]
Muniz Miranda, Maurizio; Pergolese, B.; MUNIZ MIRANDA, Francesco; Caporali, S.
abstract

Surface-enhanced Raman scattering (SERS) effect provides huge intensification of the Raman signal of molecules adhering to nanostructured surfaces of high reflectivity metals as silver, gold and copper. Here, we present a method to provide SERS activation of palladium substrates by depositing thin layers of colloidal silver onto Pd surfaces pretreated with 1,10-phenanthroline. Density functional theory calculations have been carried out in order to simulate the structural and spectroscopic properties of the surface complex formed with the active sites of the Pd substrate and to get information about the type and strength of interaction between ligand molecules and palladium.

2014 - Arylsulfonyl Groups: The Best Cyclization Auxiliaries for the Preparation of ATRC γ-Lactams can be Acidolytically Removed [Articolo su rivista]
Clark, A. J.; Cornia, Andrea; Felluga, F.; Gennaro, A.; Ghelfi, Franco; Isse, A. A.; Menziani, Maria Cristina; Muniz Miranda, F.; Roncaglia, Fabrizio; Spinelli, D.
abstract

The N-arylsulfonyl group, which is the best and most useful cyclization auxiliary for the transition-metal-catalyzed atom transfer radical cyclization (ATRC) of N-allyl-α-polychloroamides, can be effectively removed from the target γ-lactams by using H2SO4–HOAc, without impairing the halogen functions. The reaction involves H+ attack on the aromatic moiety, and is strongly responsive to the electronic properties of the substituent bound to the aromatic ring: electron-donating groups, such as methyl or methoxy are, in fact, required for efficient “deprotection”. The N-p-nitrophenylsulfonyl cyclization auxiliary, in contrast to all the other sulfonyl groups tested, proved to be unsuitable for the ATRC, owing to a side reductive transposition that halts the redox cycle.

2014 - Assessment of Exchange-Correlation Functionals in Reproducing the Structure and Optical Gap of Organic-Protected Gold Nanoclusters [Articolo su rivista]
Francesco Muniz, Miranda; Menziani, Maria Cristina; Pedone, Alfonso
abstract

Extensive benchmarks of exchange-correlation functionals on real X-ray resolved nanoclusters have been carried out and reported here for the first time. The systems investigated and used for the tests are two undecagold and one Au24+-based nanoclusters stabilized by thiol and phosphine ligands. Time-dependent density-functional theory has been used to compare calculations with experimental data on optical gaps. It has been observed that GGA functionals employing PBE-like correlation (viz., PBE itself, B-PBE, B-P86, and B-PW91) coupled with an improved version of the LANL2DZ pseudopotential and basis set provide accurate results for both the structure and optical gap of gold nanoclusters, at a reasonable computational cost. Good geometries have been also obtained using some global hybrid (e.g., PBE0, B3-P86, mPW1-PW91) and range-separated hybrid (e.g., HSE06) functionals making use of PBE-like correlation, even though they yield optical gaps overestimating the experimental findings up to 0.5 eV. Popular exchange-correlation combinations such as B-LYP and B3-LYP deform cluster geometry during structural optimization, probably due to the LYP correlation. Effects of the stabilizing organic ligands on the properties of metal cores have been probed simulating the nanoclusters at the density-functional level of theory retaining the organic coating. This paper provides a useful contribution to the simulations of structural and optoelectronic properties of larger metal–organic particles suitable for a wide range of nanotechnological applications.

2014 - Modelling of spectroscopic and structural properties using molecular dynamics [Monografia/Trattato scientifico]
Muniz Miranda, Francesco
abstract

2014 - On the opto-electronic properties of phosphine and thiolate-protected undecagold nanoclusters [Articolo su rivista]
Francesco Muniz, Miranda; Menziani, Maria Cristina; Pedone, Alfonso
abstract

We present here a detailed time-dependent density-functional theory investigation aimed at systematically dissecting the electronic spectra of two thiolate and phosphine protected undecagold nanoclusters. Calculations performed on the experimental structures of Au11(PPh3)7Cl3 and Au11(PPh3)7(SPyr)3 show that ligands have negligible contributions in the visible region. Metal → ligand charge transfer transitions appear at energies well above the visible threshold, while transitions with some small ligand → metal and ligand → ligand character occur sporadically at even higher energies. Thus, the conjugation effect between the π-electrons of the ligand and electrons of gold, recently hypothesized to interpret the spectra of phosphine and thiolate-protected nanoclusters, is not confirmed by the results of this study.

2014 - SERS and DFT study of copper surfaces coated with corrosion inhibitor [Articolo su rivista]
Muniz Miranda, Maurizio; Muniz Miranda, Francesco; Caporali, Stefano
abstract

Azole derivatives are common inhibitors of copper corrosion due to the chemical adsorption occurring on the metal surface that gives rise to a protective film. In particular, 1,2,4-triazole performs comparable to benzotriazole, which is much more widely used, but is by no means an environmentally friendly agent. In this study, we have analyzed the adsorption of 1,2,4-triazole on copper by taking advantage of the surface-enhanced Raman scattering (SERS) effect, which highlights the vibrational features of organic ligand monolayers adhering to rough surfaces of some metals such as gold, silver and copper. To ensure the necessary SERS activation, a roughening procedure was implemented on the copper substrates, resulting in nanoscale surface structures, as evidenced by microscopic investigation. To obtain sufficient information on the molecule-metal interaction and the formation of an anticorrosive thin film, the SERS spectra were interpreted with the aid of theoretical calculations based on the density functional theory (DFT) approach.

2012 - Bifurcated hydrogen bond in lithium nitrate trihydrate probed by ab initio molecular dynamics [Articolo su rivista]
Muniz Miranda, Francesco; Pagliai, Marco; Cardini, G.; Righini, R.
abstract

The hydrogen-bond dynamics of lithium nitrate trihydrate has been studied by a combined approach based on ab initio molecular dynamics simulations and wavelet analysis. The simultaneous bifurcated interaction between one hydrogen atom of water molecules and two oxygen atoms of nitrate ions is the pivotal feature of the crystal structure: this bifurcated interaction has deep effects on the O-H stretching region of the vibrational spectrum. The structural, dynamic, spectroscopic, and electronic properties of the bifurcated hydrogen bond have been investigated computationally, elucidating at the molecular level the differences with weak and strong hydrogen bonds present in the crystal. These studies corroborate the very recent IR experiments performed on the lithium nitrate trihydrate crystal, offering new perspectives to interpreting the vibrational spectra. In fact, this approach allows obtaining two-dimensional plots, which summarize the essential features of both the hydrogen-bond network and IR spectra, resulting in a peculiar "signature" of the bifurcated interaction. © 2012 American Chemical Society.

2012 - Hydrogen bond effects in the vibrational spectra of 1,3-propanediol in acetonitrile: Ab initio and experimental study [Articolo su rivista]
Muniz Miranda, F.; Pagliai, Marco; Cardini, G.; Righini, R.
abstract

Hydrogen bond interactions strongly affect vibrational properties and frequencies, the most common consequence being a redshift of the stretching vibration involved; there are, however, few exceptions to this general trend. In previous works, we have proved the effectiveness of ab initio simulations combined with wavelet analysis to investigate these effects and put them into relation to structural environment. In this work, we investigate the hydrogen bond effects on the structural and vibrational properties of 1,3-propanediol in acetonitrile by a combined experimental and computational approach. We explain the appearance of two spectral components in the O-H stretching band on the basis of intra- and intermolecular hydrogen bond interactions. We also elucidate the blueshift of the CN stretching band as due to a hydrogen bond interaction between the glycol and acetonitrile that modify the electron density distribution inside the CN group. This effect is well reproduced by ab initio molecular dynamics simulations and density functional calculations reported in this work. © 2012 American Institute of Physics.

2011 - Competitive solvation and chemisorption in silver colloidal suspensions [Capitolo/Saggio]
Pagliai, Marco; MUNIZ MIRANDA, Francesco; Schettino, Vincenzo; Muniz Miranda, Maurizio
abstract

Raman spectra and ab initio computational analysis involving Car-Parrinello molecular dynamics simulations and Density Functional Theory approach have been employed to obtain information on the behaviour of oxazole and thiazole in aqueous suspensions of silver nanoparticles, where solvation and chemisorption processes competitively occur. The solvation of both oxazole and thiazole is dependent on stable hydrogen bonds with water, mainly involving the nitrogen atoms of the heterocycles. The adsorption on silver colloidal nanoparticles is, instead, ensured by replacing water molecules of the aqueous environment with surface active sites that can be modelled as Ag3+ clusters. These surface complexes can reproduce accurately the observed surface-enhanced Raman spectra, particularly concerning the most significant frequency-shifts with respect to the normal Raman spectra in aqueous solutions and the relative intensity changes. © Springer-Verlag Berlin Heidelberg 2012.

2011 - Raman and computational study of solvation and chemisorption of thiazole in silver hydrosol [Articolo su rivista]
Muniz Miranda, Maurizio; Pagliai, Marco; Muniz Miranda, Francesco; Schettino, Vincenzo
abstract

A SERS investigation combined with ab initio computational analysis involving Car-Parrinello molecular dynamics simulations and Density Functional Theory approach allows fundamental information to be obtained on the behaviour of thiazole in silver aqueous suspension where solvation and chemisorption processes competitively occur. © 2011 Royal Society of Chemistry.

2011 - Spectroscopic properties with a combined approach of ab initio molecular dynamics and wavelet analysis [Articolo su rivista]
Pagliai, Marco; Muniz Miranda, Francesco; Cardini, G.; Righini, R.; Schettino, V.
abstract

In order to extract spectroscopic information from trajectories obtained by classical or ab initio molecular dynamics simulations, usually Fourier transforms are employed. In recent years wavelet transforms have been shown to be a valid alternative tool to analyze time-series, due to their capability of localizing a signal both in time and frequency. In this article wavelet transforms are applied for the analysis of Car-Parrinello molecular dynamics simulations to the purpose of time-correlating structural and spectroscopic properties of methyl acetate dissolved in water and methanol. The results demonstrate the possibility of obtaining information that may be of valuable help in the interpretation of time-resolved spectroscopic data. © 2010 Elsevier B.V. All rights reserved.

2011 - Structural properties of a membrane associated anchor dipeptide [Articolo su rivista]
Volkov, V. V.; Chelli, R.; Muniz Miranda, F.; Righini, R.
abstract

The association of peptides to phospholipid membranes through the insertion of an anchoring hydrocarbon tail is common to some viruses and to several anticancer drugs. We investigate the association of an anchor dipeptide, N- myristoylated methyl glycine (MrG), to phospholipid membrane fragments made of 1-palmitoyl-2-linoleyl phosphatidylcholine (PLPC). Here we report on the experimental findings of two-dimensional infrared spectroscopy of an MrG backbone in the 6 μm wavelength region. The experimental outcomes are supported by ab initio calculations and by a molecular dynamics simulation accomplished with the replica exchange method. We find that the guest molecule has a preferential unfolded conformation, with dihedral anglesφ = -90 ( 20° andψ =-180 ± 20°, while the average orientational distribution of the amide I transition dipole moments with respect to the neighbor PLPC carbonyls is peaked at angles in the range 21-33°. The depth of penetration ofMrG inside the membrane corresponds rather well to the one estimated in our previous paper [j.Phys. Chem. B, 2009, 113, 16246], where we found that the backbone moieties ofMrG are localized slightly above the carbonyl groups of PLPC. According to the simulation results, the anchor tail is completely inserted in the hydrophobic region of the bilayer, with a largely prevalent extended conformation and a preferential alignment along the average direction of the PLPC hydrocarbon tails. © 2011 American Chemical Society.

2011 - Wavelet transform for spectroscopic analysis: Application to diols in water [Articolo su rivista]
MUNIZ MIRANDA, Francesco; Pagliai, Marco; Cardini, Gianni; Schettino, Vincenzo
abstract

Wavelet transform has been used to correlate spectroscopic and structural properties from trajectories obtained by ab initio molecular dynamics simulations. This method has been applied to hydrogen bond dynamics of glycols in heavy water solutions, showing how the stretching frequency of the intramolecular O-H bond changes with the intermolecular hydrogen-bond distance. The resulting wavelet spectrograms have been interpreted according to H-bond strength and stability. © 2011 American Chemical Society.

2010 - Hydrogen bond dynamics of methyl acetate in methanol [Articolo su rivista]
Pagliai, Marco; MUNIZ MIRANDA, Francesco; Cardini, Gianni; Righini, Roberto; Schettino, Vincenzo
abstract

The H-bond interactions of methyl acetate in methanol have been studied by means of ab initio molecular dynamics simulations within the Car-Parrinello approach. It has been observed that the C=O stretching band of methyl acetate splits into a doublet as a consequence of the interaction with the solvent. The H-bond effects on the spectroscopic properties of methyl acetate in methanol have been interpreted by wavelet transform analysis in conjunction with a structural and dynamic characterization of the solvation cage. Localizing a vibrational mode in time and frequency during the simulations has allowed association of the different interactions with the solvent to the vibrational properties. This represents an important development in the capability of molecular dynamics simulations to explain experimental data obtained by time-resolved spectroscopic methods. © 2010 American Chemical Society.