S. Magazù

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...

Puzzle of Protein Dynamical Transition

Despite recent extensive efforts, the nature of the dynamics of biological macromolecules still remains unclear. In particular, contradicting models have been proposed for explaining the temperature behavior of the mean square displacement, MSD, and of the system relaxation time, τ. To solve this puzzle, different neutron scattering experiments with different instrumental energy resolutions were performed on dry and hydrated lysozyme. The obtained results show that the so called dynamical transition: (i) is a finite instrumental energy resolution effect, and more specifically, it appears when the characteristic system relaxation time intersects the resolution time, (ii) it does not imply any transition in the dynamical properties of the systems, (iii) it is not due to the fragile-to-strong dynamical crossover (FSC) in the temperature behavior of the system relaxation time, differently to what S. H. Chen et al. proposed [Proc. Natl. Acad. Sci. U.S.A.2006, 103, 9012]. Furthermore, the obtained results confirm the change in the τ-temperature dependence at T = 220 K of S. H. Chen et al., and show that it is not due to finite instrumental energy resolution effects and it is not connected to numerical errors in the data analysis protocol, differently to what W. Doster et al. proposed [Phys. Rev. Lett.2010, 104, 098101].

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.

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.

Study of the dynamical properties of water in disaccharide solutions

This work presents quasi-elastic neutron scattering (QENS) and neutron spin echo (NSE) findings on homologous disaccharide (i.e. trehalose, maltose and sucrose)/water solutions as a function of temperature. The dynamical properties of these systems are investigated by QENS, which, on the picosecond scale, allows for the characterisation of the diffusion of both solutes and solvent. On the other hand, NSE investigates the dynamics on the nanosecond scale, allowing for the relaxation times of the disaccharide/water systems to be evaluated. The experimental data highlight a strong slowing down of water in the presence of disaccharides. The whole set of findings indicates, therefore, a noticeable disaccharide–water interaction, which is more intense in the case of trehalose. This feature can justify its higher bioprotective effectiveness.

Mean square displacements from elastic incoherent neutron scattering evaluated by spectrometers working with different energy resolution on dry and hydrated (H2O and D2O) lysozyme.

The main aim of the present paper is the evaluation of the effects of the instrumental energy resolution on the mean square displacement (MSD) obtained by elastic incoherent neutron scattering (EINS). In particular, this study is performed in the time domain, through the time-Fourier transform of the elastically scattered neutron intensity, and is mainly focused on the connection between the system MSD and the measured MSD. It is shown how in the case of EINS, the instrumental energy resolution gives rise to the time integration of the time-dependent system MSD function weighted in time by the resolution function. The formulated approach is applied to the data collected on dry and hydrated (H(2)O and D(2)O with h = 0.4) lysozyme samples by two spectrometers working with a different instrumental resolution (the IN10 and IN13 spectrometers of the Institute Laue-Langevin). As a result, the procedure furnishes an excellent agreement for the system MSD evaluated in the low temperature range up to T = 40 K.

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...

NMR, static and dynamic light and neutron scattering investigations on polymeric aqueous solutions

Abstract The topic dealt with in the present work is concerned with an overview of some experimental studies, performed by light scattering, QENS and NMR, on the structural and dynamical properties of aqueous solutions of PEO. The experimental findings show that PEO in water tends to assume, with respect to the melt case, a more ordered conformation closer to the crystalline one, and that the H 2 O/D 2 O substitution gives rise to different conformational arrangements. The reported evidence demonstrates that aggregation is not an inherent property of the PEO/water system. Finally, QENS shows that PEO affects the dynamics of water molecules in its neighbourhood.

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.

Amphiphiles Self-Assembly: Basic Concepts and Future Perspectives of Supramolecular Approaches

Amphiphiles are synthetic or natural molecules with the ability to self-assemble into a wide variety of structures including micelles, vesicles, nanotubes, nanofibers, and lamellae. Self-assembly processes of amphiphiles have been widely used to mimic biological systems, such as assembly of lipids and proteins, while their integrated actions allow the performance of highly specific cellular functions which has paved a way for bottom-up bionanotechnology. While amphiphiles self-assembly has attracted considerable attention for decades due to their extensive applications in material science, drug and gene delivery, recent developments in nanoscience stimulated the combination of the simple approaches of amphiphile assembly with the advanced concept of supramolecular self-assembly for the development of more complex, hierarchical nanostructures. Introduction of stimulus responsive supramolecular amphiphile assembly-disassembly processes provides particularly novel approaches for impacting bionanotechnology applications. Leading examples of these novel self-assembly processes can be found, in fact, in biosystems where assemblies of different amphiphilic macrocomponents and their integrated actions allow the performance of highly specific biological functions. In this perspective, we summarize in this tutorial review the basic concept and recent research on self-assembly of traditional amphiphilic molecules (such as surfactants, amphiphile-like polymers, or lipids) and more recent concepts of supramolecular amphiphiles assembly which have become increasingly important in emerging nanotechnology.