Valentina Venuti

Evidence of the existence of the low-density liquid phase in supercooled, confined water

By confining water in a nanoporous structure so narrow that the liquid could not freeze, it is possible to study properties of this previously undescribed system well below its homogeneous nucleation temperature TH = 231 K. Using this trick, we were able to study, by means of a Fourier transform infrared spectroscopy, vibrational spectra (HOH bending and OH-stretching modes) of deeply supercooled water in the temperature range 183 < T < 273 K. We observed, upon decreasing temperature, the building up of a new population of hydrogen-bonded oscillators centered around 3,120 cm−1, the contribution of which progressively dominates the spectra as one enters into the deeply supercooled regime. We determined that the fractional weight of this spectral component reaches 50% just at the temperature, TL ≈ 225 K, where the confined water shows a fragile-to-strong dynamic cross-over phenomenon [Ito, K., Moynihan, C. T., Angell, C. A. (1999) Nature 398:492–494]. Furthermore, the fact that the corresponding OH stretching spectral peak position of the low-density-amorphous solid water occurs exactly at 3,120 cm−1 [Sivakumar, T. C., Rice, S. A., Sceats, M. G. (1978) J. Chem. Phys. 69:3468–3476.] strongly suggests that these oscillators originate from existence of the low-density-liquid phase derived from the occurrence of the first-order liquid–liquid (LL) phase transition and the associated LL critical point in supercooled water proposed earlier by a computer molecular dynamics simulation [Poole, P. H., Sciortino, F., Essmann, U., Stanley, H. E. (1992) Nature 360:324–328].

Role of the solvent in the dynamical transitions of proteins: The case of the lysozyme-water system

We study the dynamics of hydration water in the protein lysozyme in the temperature range 180 K<T<360 K using Fourier-transform-infrared and nuclear magnetic resonance (NMR) spectroscopies. By analyzing the thermal evolution of spectra of the OH-stretching vibration modes and the NMR self-diffusion (DS) and spin-lattice relaxation time (T1), we demonstrate the existence of two dynamical transitions in the protein hydration water. Below the first transition, at about 220 K, the hydration water displays an unambiguous fragile-to-strong dynamic crossover, resulting in the loss of the protein conformational flexibility. Above the second transition, at about 346 K, where the protein unfolds, the dynamics of the hydration water appears to be dominated by the non-hydrogen-bonded fraction of water molecules.

Physico-chemical characterization of an amphiphilic cyclodextrin/genistein complex.

Specific recognition of cell-targeting systems as host-carriers modified with receptor targeting groups, is a major ambition in the application of supramolecular science to medicine and life science. Genistein (Gen), an isoflavone belonging to the class of phytoestrogens, is of great interest because it has been considered as potential remedy for many kinds of disease. In this work, genistein in aqueous medium and in the presence of an host nanocarrier as amphiphilic cyclodextrin (CyD) modified in the upper rim with oligoethylene hydroxyl groups [(2-oligo(ethyleneoxide)-6-hexylthio)-beta-CyD, SC6OH] at 1:1 molar ratio, has been firstly investigated by UV-vis measurements coupled with circular dichroism data, in order to characterize the drug/macrocycle binding affinity through the formation of the complex. Furthermore, FTIR-ATR technique has been used to detect the complex formation in solid phase and to characterize the functional groups responsible of the solid Gen/SC6OH complex stability. The infrared absorbance spectra of the complex, collected in a wide range of wavenumber and around the physiological temperature, have been analysed and compared with the spectra of the pure compounds and their physical mixture. By monitoring the most significant changes in the shape and position of the absorbance bands of the Gen functional groups, we showed that the formation and/or modification of polar bonds play the main role in the interaction of the drug with the amphiphilic CyD. From the results, Gen is shown to be entangled in SC6OH nanoaggregates, establishing hydrogen bonding with the hydrophilic PEG chains.

Structure and dynamics of water confined in a nanoporous sol-gel silica glass: a neutron scattering study

During recent years, the understanding of the modification of the structure and dynamics of water confined in different environments has been the focus of much interest in scientific research. This topic is in fact of great relevance in a lot of technological areas and, in living systems, essential water-related phenomena occur in restricted geometries in cells, and active sites of proteins and membranes, or at their surface. In this paper we report on the most recent up to date account of structural and dynamical properties of confined water in comparison with the bulk state. In particular, as far as structure is concerned, we present new neutron diffraction results on heavy water confined in a fully hydrated sol-gel silica glass (GelSil) as a function of the temperature. At low T, the nucleation of cubic ice superimposed to liquid water, already observed for water within Vycor glasses, is discussed. As far as the dynamics is concerned, we report results of a detailed spectroscopic analysis of diffusive relaxation and vibrational properties of water confined in nanopores of Gelsil glass, at different temperatures and hydration percentages, performed by our research group during recent years by means of incoherent quasi-elastic (IQENS) and inelastic (IINS) neutron scattering. IQENS spectra are analysed in the framework of the relaxing cage model (RCM). IINS spectra show the evolution of the one-phonon-amplitude weighted proton vibrational density of states (VDOS), Z(ω), when water loses its peculiar bulk properties and originates new structural environments due to its surface interactions.

Temperature Effect on the Vibrational Dynamics of Cyclodextrin Inclusion Complexes: Investigation by FTIR-ATR Spectroscopy and Numerical Simulation

The vibrational dynamics of solid inclusion complexes of the nonsteroidal anti-inflammatory drug Ibuprofen (IBP) with beta-cyclodextrin (beta-CD) and methyl-beta-cyclodextrin (Me-beta-CD) has been investigated by using attenuated total reflection-Fourier transform infrared FTIR-ATR spectroscopy, in order to monitor the changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, in the wavenumber range 600-4000 cm(-1). Quantum chemical calculations were performed on monomeric and dimeric structures of IBP, derived from symmetric hydrogen bonding of the two carboxylic groups, in order to unambiguously assign some characteristic IR bands in the IBP spectrum. The evolution in temperature from 250 to 340 K of the C horizontal lineO stretching vibration, described by a best-fit procedure, allowed us to extract the thermodynamic parameter DeltaH associated to the binding of IBP with betaCDs in the solid phase. By comparing these results, Me-beta-CD has been shown to be the most effective carrier for IBP.

Effect of Cross-Linking Properties on the Vibrational Dynamics of Cyclodextrins-Based Polymers: An Experimental–Numerical Study

The vibrational dynamics of cyclodextrin nanosponges (CDNS), a new class of nanostructured soft materials synthesized via cross-linking reaction of natural cyclic oligosaccharide β-cyclodextrin (β-CD) with suitable organic reagents, is investigated by means of the combined use of Raman and infrared spectroscopy, supported by numerical simulations. The vibrational spectra of the polymers show significant changes in the frequency ranges 3000-3700 and 1500-1800 cm(-1) correlated to the relative amount of cross-linker with respect to monomeric CD. By using band deconvolution and best-fit procedure of the experimental data and quantum chemical computations, a correlation between such changes and the degree of cross-linking of the polymeric network is proposed. This experimental-numerical approach, here applied to a model class of nanoporous polymeric systems, appears to be of general application for the study of polymeric matrixes of interest for biolife applications.

DYNAMIC EVIDENCE OF CHEMICAL AND PHYSICAL TRAPS IN H-BONDED CONFINED LIQUIDS

Rayleigh wing, infrared (IR) absorption, and Raman-scattering measurements are employed to investigate the reorientational and vibrational dynamics of ethylene glycol and its homologous systems, namely ethylene glycol monomethyl ether and ethylene glycol dimethyl ether, in the bulk state and confined into 25 A pores of a sol-gel porous glass. As far as the Rayleigh wing data are concerned, the quantitative analysis of the different contributions in the spectra shows the clear influence of the physical and chemical confinement on the mobility of the studied liquids. In addition the IR and Raman measurements, performed in the O–H stretching region, allowed to identify the intramolecular, H-bond imposed, sub-band, as well as to connect the various sub-bands to different intermolecular environments originated by the existence of the H-bond potential. The observed dynamics is discussed on the basis of current theories for associated liquids.

UV–vis and FTIR-ATR characterization of 9-fluorenon-2-carboxyester/(2-hydroxypropyl)-β-cyclodextrin inclusion complex

In this work, the usefulness of (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CyD) as a tool to form an inclusion complex with 9-fluorenonic derivative (AG11) has been investigated, in pure water, by UV absorption. Phase-solubility diagrams allowed the determination of the association constant between AG11 and HP-beta-CyD. At the same time, solid binary systems between AG11 and HP-beta-CyD have been prepared in 1:1 stoichiometry by co-precipitation method. In order to confirm the complexation, FTIR spectroscopy in ATR geometry measurements have been performed and the results have been compared with the free compounds and the corresponding physical mixture in the same molar ratio. The nature of the interactions between AG11 and HP-beta-CyD has been elucidated also by applying mathematical procedures such as deconvolution and curve fitting. Improvement of the aqueous solubility is expected to improve the bioavailability of the drug in oral administration.

Combined non-destructive XRF and SR-XAS study of archaeological artefacts

AbstractWe report on a non-destructive study of Sicilian ceramic fragments of cultural heritage interest, classified as “proto-majolica” pottery and dating back to the twelfth to thirteen centuries AD. The analytical approach used is based on the employment of two totally non-invasive spectroscopic techniques: X-ray fluorescence (XRF), using a portable energy-dispersive XRF analyser, and X-ray absorption spectroscopy, using synchrotron radiation as a probe (SR-XAS). XRF measurements allowed us to collect elemental and spatially resolved information on major and minor constituents of the decorated coating of archaeological pottery fragments, so providing preliminary results on the main components characterizing the surface. In particular, we assigned to Fe and Mn the role of key elements of the colouring agent. With the aim of obtaining more detailed information, we performed SR-XAS measurements at the Fe and Mn K-edges at the Italian BM08 beamline at the European Synchrotron Radiation Facility (Grenoble, France). The experimental data were analysed by applying principal component analysis and least-squares fitting to the near-edge part of the spectra (X-ray absorption near-edge structure) to determine the samples’ speciation. From the overall results, umber, a class of brownish pigments characterized by a mixture of hydrated iron and manganese oxides, has been ascribed as a pigmenting agent. FigureFe K-edge XANES spectra of selected proto-majolica samples and reference compounds (FeO, Fe3O4, Fe2O3, Fe+SiO2). D pigmented, L not pigmented.

Spectroscopic investigation of Greek ceramic artefacts

Abstract The aim of the present work is the characterization of ceramics artefacts coming from Locri Epizephiri, in order to understand the area of production and the baking temperatures. The macroscopic investigation, performed from an archaeological and chronological point of view, permitted the classification of the studied samples into two different groups: the former was constituted of amphorae fragments used for transport, characterized by a mixture of medium-fine grain, and the latter was constituted of tiles fragments with a mixture of coarse grain. All the samples date back to a period between the V and the IV century bc and present similar mineralogical–compositional characteristics. The ceramic samples were analyzed by X-ray diffraction (XRD), X-ray fluorescence and Fourier transform infrared (FT-IR) spectroscopy. XRD spectroscopy allowed us to identify the present crystalline substances. In particular, both in the amphorae and in the tiles, the main mineral is quartz. Furthermore, larger quantities of calcite, hematite and illite are present in the amphorae rather than in the tiles, while a larger amount of K-feldspar is present in the tiles rather than in the amphorae, finally gehlenite is definitively absent in the tiles. The FT-IR investigation was performed both at low and high frequencies. From all the obtained results it was possible to conclude that the provenance area of the ceramics was the Calabro–Peloritano one. The compositional variations could be attributed to the presence of the different workshops in the same zone and to the existence of several quarries of clay materials.