G. Maisano

Raman scattering and structure of normal and supercooled water

Raman spectra in the O–H stretching band in normal and supercooled water have been investigated. Spectra are taken as a function of temperature in the range +95 to −24°C. Absolute Raman cross sections corrected for instrumental and physical factors are obtained. It is shown that the isotropic O–H stretching bands in the range +20 to +95 °C are due to the contribution of ’’open’’ (or tetrahedrically bonded) and ’’closed’’ water that are temperature independent. The percentage of open water α(T) is connected and interpreted in the frame of the Stanley site percolation model. As a consequence, the isobestic point is obtained. In the supercooled region, a third spectral contribution arises, which is centered near the main peak of the isotropic O–H band of ice. Such a contribution is tentatively explained as the presence in supercooled water of true ice, as a heterophase fluctuation.

Anomalous cryoprotective effectiveness of trehalose: Raman scattering evidences

Results of Raman scattering measurements performed on aqueous solutions of the homologous disaccharides (trehalose, maltose, and sucrose) are reported. To get some insight into the effects of disaccharides on the hydrogen bond network of water, and to clarify the reasons that make trehalose the most effective in protecting organisms from dehydration and freezing, we investigate the intramolecular OH stretching mode. To carry out this study, two different approaches are employed: namely, a decomposition of the isotropic spectra into an “open” and a “closed” contribution, and a spectral stripping procedure to extract the “collective” contribution from the polarized spectra. Both procedures agree in suggesting that disaccharides promote, with a different strength, a destructuring effect on the tetrahedral H-bond network of pure water. This result makes plausible the hypothesis that disaccharides obstruct the crystallization process reducing the amount of freezable water, namely destroying the network of wate...

Mean-Square Displacement Relationship in Bioprotectant Systems by Elastic Neutron Scattering

Neutron intensity elastic scans on trehalose, maltose, and sucrose/H(2)O mixtures as a function of concentration, temperature, and exchanged wave vector are presented. The experimental findings show a crossover in molecular fluctuations between harmonic and anharmonic dynamical regimes. A new operative definition for the degree of fragility of glass-forming systems is furnished by using explicitly the connection between viscosity and mean-square displacement. The procedure is tested for the investigated mixtures and for a set of glass-forming systems. In this frame, the stronger character of trehalose/H(2)O mixture indicates a better attitude in respect to maltose and sucrose/H(2)O mixtures to encapsulate biostructures in a more rigid matrix.

Raman spectroscopy and local order in aqueous solutions of strong II–I electrolytes

We report polarized Raman spectra for aqueous solutions of NiCl2, CdCl2, ZnCl2, CuCl2, Cu(NO3)2, and SrCl2. Our analysis of the Raman data provides an interpretation for the diffuse low frequency Raman scattering in transition metal halide–water solutions in terms of a vibrational density of states. Such a density corresponds to collective vibrational modes in a solute‐connected middle range lattice. The results are also discussed on the basis of recent measurements of viscosity, thermodynamic quantities, and EXAFS.

The puzzle of poly(ethylene oxide) aggregation in water: Experimental findings

Aqueous solutions of poly(ethylene oxide) were investigated using the ultrasonic technique, photon correlation spectroscopy (PCS) and nuclear magnetic resonance (NMR), in a wide range of molecular weight (from ethylene glycol to poly(ethylene oxide) 4 000 000 Da). Ultrasonic data reveal that the mixing process is not ideal and show that the polymer–water interaction strength increases with the polymerization degree. PCS and NMR, on the other hand, furnish a free particle diffusion coefficient which satisfies a unique scaling law from 8000 to 4 000 000 Da and demonstrates the good solvent nature of water. These experimental findings indicate that polymer–polymer aggregation processes are not an inherent property of these systems.

Rayleigh wing and Fourier transform infrared studies of intermolecular and intramolecular hydrogen bonds in liquid ethylene glycol

Depolarized low frequency light scattering and infrared data for ethylene glycol are presented. The measurements, performed in the temperature range 7–160 °C, help clarify the processes that characterize the dynamic response of the system. Rayleigh-wing data analysis suggests, through the width and intensity temperature evolution, the existence of a thermally activated process that can be rationalized in terms of a simple two-state model. The extracted activation (ΔH) and binding (ΔG) energies, have been attributed to the ‘transition’ from a gauche configuration, stabilized by an intramolecular H bond, to a simple gauche configuration. In addition, the study of the O-H stretching region, performed on ethylene glycol and on poly(ethylene glycol) by means of the Fourier transform infrared technique allows one to identify the intramolecular, H-bond imposed, sub-band, as well as to assign the various sub-bands originated by the existence of the H-bond potential. The observed dynamics are also discussed within...

Sound velocity and hydration phenomena in aqueous polymeric solutions

Sound velocity and density measurements were performed in polymeric aqueous solutions of poly(ethylene glycol) (PEG 600) and poly(ethylene glycol methyl ether) (PEGME 550) as a function of concentration and temperature. The experimental data unambiguously show that the presence of the polymer changes the water structure near the solute, building up a more compact arrangement in which up to two water molecules for each monomeric unity are allowed. Moreover we tested, at low concentration, a model to study the change induced in the polymer hydration by the addition of salt. No direct evidence of interaction between the hydration water of the polymer and salt is brought to light by the obtained results.

Vibrational dynamics of glassy and molten ZnCl2

Polarized Raman spectra of ZnCl2 were obtained in the liquid phase near the melting point (T = 598 K), and in the glassy phase (T = 293 K). Measurements were performed down to a very low frequency shift (2 cm−1) from the exciting line. Our analysis of the Raman data provides an interpretation of the collision‐like contribution in terms of a structural relaxation time in the picosecond range, while the phonon‐like contribution gives an effective Raman density of states. These results are also discussed in terms of existing structureal models.

Experimental simulation of macromolecules in trehalose aqueous solutions: A photon correlation spectroscopy study

The protective effect of trehalose on biological membranes against freezing or dehydration has been the subject of many studies aimed to understand the reasons why some lower organisms, under stress conditions, synthesize trehalose. In this work we report the results of a study on Poly(Ethylene Oxide)/trehalose/water mixtures performed by Photon Correlation Spectroscopy. The chemical structure of the polymer, simpler than that of proteins and its helical conformation in water, constitute a useful starting point for understanding the more complex protein/trehalose/water interactions. In order to distinguish the different dynamics, trehalose and PEO have been studied separately in water, at different concentration and temperature values; then the ternary PEO/trehalose/water system has been investigated at different sugar amounts. The obtained findings support the “water-replacement” hypothesis, indicating that a direct polymer–trehalose interaction occurs. Furthermore, trehalose is shown to affect the swell...

Structural properties of macromolecular solutions

We report measurements of viscosity and light scattering in an aqueous solution of BSA. Like the lysozyme solutions, previously investigated, the BSA solutions show thixotropic properties. Optical measurements of both elastic and inelastic light scattering indicate the existence of a structure in which the BSA molecule tends to clusterize, each cluster being correlated to the others. A k‐dependent diffusion coefficient D(k) is found. The static structure factor deduced from the values of DL(k) agrees well with the indications given by the elastically scattered intensity J(k). Also, the statical properties of scattered light appear to be consistent with the proposed model. A qualitative explanation, in terms of a dominant component in the fluctuations of concentration, is briefly sketched.