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The effects of chiral discrimination of ibuprofen (IBP) on the complexation process with methyl-β-cyclodextrin (Me-β-CD) were investigated in the solid phase by FTIR-ATR spectroscopy and numerical simulation. The inclusion mechanism was deduced from the temperature-dependent analysis of the vibrational spectra, in the C=O stretching region, of complexes formed by Me-β-CD with the two enantiomeric and the racemic forms of IBP. The mechanism turned out to be enthalpy-driven, with IBP enantiomers giving rise to more stable inclusion complexes with respect to the racemate. [ABSTRACT FROM AUTHOR]

The O-H stretching vibration of propylene glycol (PG) has been investigated by Raman spectroscopy in the -15 to +60°C temperature range, in the bulk state and confined to the ∼26 Å pores of a controlled porous glass. By modifying the nature of the substrate (from hydrophilic to hydrophobic), we separated the surface-like and the finite-size contributions to the high-frequency vibrational dynamics of this glass-forming system. The spectra have been fitted by four Gaussian peaks associated with PG molecules exhibiting different H-binding states (i.e. non H-bonded, chain-end and doubly bonded). The T-dependencies of the peak wavenumbers and relative areas of the resolved components furnished a quantitative description of the role played by polymer-surface interactions and topological effects on the connectivity distribution of confined PG molecules. [ABSTRACT FROM AUTHOR]

In this paper, an incoherent quasi-elastic neutron scattering (IQENS) study of the single-particle dynamics of water in fully hydrated Na-A and Mg50-A zeolites at T ?=?293?K and T ?=?333?K is presented. In order to probe different time scales, measurements were made at two resolutions, ~8?µeV and ~28?µeV. The high-resolution data allowed us to investigate the slower dynamics, which is mainly translational. The low-resolution spectra were used to probe the faster dynamics and distinguish between diffusional and rotational motion. We found that the partial exchange of Na + with Mg 2+ induces: (a) an increase of the available volume for diffusion; (b) a decrease of the fraction of water molecules taking part in the observed jump diffusion process; and (c) a shortening of the residence time. [ABSTRACT FROM AUTHOR]

The spectral substructure of the O-H stretching mode of water confined in Mg50-A zeolites is demonstrated, in full hydration conditions and in the temperature range 20-80°C, using Fourier transform Infrared (FT-IR) spectroscopy. Band shapes have been fitted to individual components, according to the actual theories for associated liquids, and three major constituent peaks were derived, at 3230 cm -1 (ω 1 ), 3460 cm -1 (ω 2 ), and 3600 cm -1 (ω 3 ). They have been related, respectively, to an ice-like molecular environment and other hydrogen-bonding configurations. A detailed quantitative analysis of their centre frequencies and relative intensities, traced over the full temperature range investigated, has led to the conclusion that these subbands show direct evidence, under confinement, of bifurcated hydrogen bonds (BHB) among three water molecules as a main feature of the structure of liquid water. The most interesting result comes from the observation, at all temperatures, of the tetrahedral connectivity typical of bulk water. In this sense, we attributed to the zeolitic surface a 'structure-maker' role on physisorbed water. This role becomes particularly relevant at the lowest temperature, where the ice-like contribution appears to be the favoured one even under confinement. Furthermore, preliminary results are presented of an incoherent quasi-elastic neutron scattering (IQENS) investigation of the diffusional dynamics of water in the same system, at T =20°C, analysed in the framework of the Confined Diffusion Model (CDM). [ABSTRACT FROM AUTHOR]

In the present work, we report a spectroscopic analysis of water confined in a powdered zeolite, Na A type, which is able to entrap 27 H2O molecules, by Fourier transform infrared absorption, performed in the OH stretching region, 3000-3800 cm-1. The investigation was carried out as a function of temperature and at different hydration levels. The spectroscopic results were interpreted in the framework of actual theories for associated liquids and on the basis of previously measurements performed in water confined in a different environment, a controlled silica glass (GelSil), by Raman scattering, always in the OH stretching region. The comparison between these two distinct cases of confinement condition unambiguously showed the role of structure maker played by the zeolite for confined water as opposed to the structure breaker character observed in the case of the GelSil matrix. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a spectroscopic analysis of the structural and dynamic properties of water solutions of uncharged star-polymers at different molecular masses, characterized by a porphyrin core and four poly(ethylene glycol) methoxy arms. The investigation has been performed by small angle neutron scattering (SANS) and Fourier transform infrared (FTIR) absorption technique. The aim of the present work is to investigate the aggregation processes in the above-mentioned systems by altering their natural pH and ionic strength upon the addition of an acid (hydrochloric acid, HCl) or a salt (potassium chloride, KCl). SANS data permitted us to check the size of the star-polymer in solution as a function of the 'perturbation substance' concentration. On the other hand, as far as the dynamical properties are concerned, the FTIR analysis performed at low frequency in the region from 200 to 700 cm[SUP-1], claimed a greater tendency to self-aggregate by porphyrin, having the lowest molecular mass. [ABSTRACT FROM AUTHOR]

We studied, versus temperature, the vibrational properties of ethylene glycol (EG) (H—(O—CH[sub 2]—CH[sub 2])—OH) and ethylene glycol monomethyl ether (EGmE) (CH[sub 3]—(O—CH[sub 2]—CH[sub 2])—OH), in solution with poly(ethylene oxide) (PEO) (H—(O—CH[sub 2]—CH[sub 2])[sub n]—OH) at different concentrations, by Fourier transform infrared spectroscopy. These homologous systems differ for the number of OH end groups, in particular two for EG, and one for EGmE. Connecting the O—H stretching band shape to the different hydrogen bond imposed local environments, we clarified the role of this bond in the solute-solvent interactions, obtaining information on the quality of these solvents. [ABSTRACT FROM AUTHOR]

In this paper we report the results of a study of low-frequency vibrational dynamics and electron-vibration coupling in water in the bulk and confined state, at different hydration percentages. The simultaneous use of both Raman spectroscopy and time-of-flight inelastic neutron scattering allowed us to determine the respective vibrational densities of states (VDOSs), g[sup R][sub eff](ω) and g[sup N](ω). Both the VDOSs show clear evidence of surface-induced vibrational modes, due to the local order distortion with respect to the bulk state. [ABSTRACT FROM AUTHOR]

A study has been made of vibrational properties in ethylene glycol (EG; H(OCH[sub 2]CH[sub 2])OH) and EG monomethyl ether (EGmE; CH[sub 3](OCH[sub 2]CH[sub 2])OH) in solution together with poly(ethylene oxide) (PEO; H(OCH[sub 2]CH[sub 2])[sub n]OH) at different concentrations, performed by Fourier transform infrared absorbance (FT-IR) spectroscopy. The results ae compared with previous viscometry and photon correlation spectroscopy (PCS) studies, using EG dimethyl ether (EGdE; CH[sub 3](OCH[sub 2]CH[sub 2])OCH[sub 3]) as solvent as well. These homologous systems differ from each other in the number of OH end groups, in particular two for EG, one for EgmE and zero for EGdE. Combining analysis of the vibrational and transport properties of EG, EGmE and EGdE in solution with PEO over a wide range of concentration made it possible to check the quality (good theta or poor) of these three different solvents and the role played by the hydrogen bond in the various solute-solvent interaction mechanisms, resulting in the well known de Gennes scaling law. [ABSTRACT FROM AUTHOR]

Infrared (IR) absorption measurements are employed to investigate the vibrational spectra of propylene glycol (PG) and its oligomers the poly(propylene glycols) (PPGs) with different molecular weights (425 and 725 Da) in the OH stretching region. The goals are to identify the intramolecular, hydrogen bond imposed, sub-band and to connect the various sub-bands to different intermolecular aggregates originated by the existence of the hydrogen bond potential. The observed experimental data, compared with those of previous IR measurements on other similar polymers, ethylene glycol (EG) and poly(ethylene glycols) (PEGs), confirm the role played by the hydrogen bond in the structure of these liquids, discussed on the basis of current theories for associated systems. [ABSTRACT FROM AUTHOR]

The reorientational dynamics of polymers passing from the monomers (ethylene glycol and propylene glycol) to corresponding oligomers (poly(propylene glycols)) or to homologous systems (ethylene glycol monomethyl ether and ethylene glycol dimethyl ether), in the bulk state and confined in a sol-gel porous glass with 25 A pores, has been investigated by means of Rayleigh wing scattering, at low frequencies. The goal was to study the influence of the chain length and of the physical and chemical traps, connected to the surface interactions and geometric restrictions respectively, on the mobility of the studied H-bonded liquids. This was possible because of the capability of preventing the interactions with the surfaces of the confining matrix that contain the active silanol groups (Si - OH). [ABSTRACT FROM AUTHOR]

We performed viscosity measurements, at T = 50 C, on poly(ethylene oxide) (H-(O-CH2-CH[sub 2])n-OH) at different molecular weight, dissolved in ethylene glycol (H-(O-CH[sub 2]-CH[sub 2])-OH) and in one of its homologous systems, namely ethylene glycol dimethyl ether (CH[sub 3]-(O-CH[sub 2]-CH[sub 2])-OCH[sub 3]). The goal is to investigate the effects of the monomer end groups on solute-solvent interactions and, on this basis, to check the quality of these two solvents by using the Mark-Houwink-Sakurada scaling law. [ABSTRACT FROM AUTHOR]

Ultrasonic velocity and density measurements were performed in polymeric aqueous solutions of ethylene glycol (EG) and poly(ethylene glycol) (PEG) as functions of concentration and temperature in the stable liquid region. The non-ideal behaviour of the compressibility allows us to evaluate the hydration number of the polymer as a function of temperature. The experimental data show the presence of an arrangement in which two water molecules are bonded for each oxygen of the oxirane monomeric group. [ABSTRACT FROM AUTHOR]