Vibrational Studies on Disaccharide/H₂O Systems by Inelastic Neutron Scattering, Raman, and IR Spectroscopy

Abstract

Inelastic neutron scattering (INS), Raman scattering, and infrared spectroscopy experiments on pure water and on aqueous solutions of homologous disaccharides, such as trehalose and sucrose, are presented. Neutron spectra were collected by using the spectrometer MARI at the ISIS pulsed neutron source of the Rutheford Appleton Laboratory (Chilton, U.K.). The principal aim of this work is to analyze the structural modifications induced on water by trehalose and sucrose to look for different structural arrangements that can account for their different effectiveness as bioprotectors. Special emphasis was addressed to the intramolecular stretching and bending spectral contributions and to the intermolecular librational mode. A comparison of the INS spectra from pure water with those of homologous disaccharide/water mixtures showed the same peculiar behavior as found in Raman scattering, infrared spectroscopy, and computational results derived from density functional theory (DFT).

Bio-protective effects of homologous disaccharides on biological macromolecules

“…In particular, such dynamic suppression correlates with weaker temperature dependence of viscosity and with lower fragility, which explains the higher bio-protectant effectiveness of trehalose compare with sucrose (Magazù et al 2010c). Furthermore, this finding is in agreement with other experimental findings obtained by inelastic neutron scattering which reveal a higher downshift of the OH the intramolecular stretching contribution for the trehalosewater system, which indicates a stronger hydrogen bonded network in the trehalose-water system than in the sucrosewater system (Branca et al 2003).…”

Broadband dielectric spectroscopy of glucose aqueous solution: Analysis of the hydration state and the hydrogen bond network

“…Such a destructured HB network of water is thought to hinder dehydration and freezing in plants or microorganisms. 10 Branca et al 8,9 intensively investigated this topic using, mainly, Raman scattering and focused on the anharmonic intramolecular OH stretching vibration around 100 THz, whose absorption peak can be disentangled into two OH stretching components; one is an orderly bonded water in the tetrahedral coordination and the other is disorderly bonded water. They concluded that the presence of saccharides tends to decrease the fraction of the former and increase the fraction of the latter.…”

“…2 Moreover, saccharides' role as a bioprotectant agent in promoting anti-freezing and dehydration properties has attracted wide attention. 3 Recent studies suggest, both computationally 4-7 and experimentally, [8][9][10] that these peculiar properties of the saccharides arise from changes in the structural and dynamical properties of the water surrounding the saccharide molecules when in an aqueous phase. The abundant polar hydroxyl groups, with their strong dipole interaction capability, in the saccharides are thought to alter the local tetrahedral coordination of the hydrogen bond (HB) network of water in the vicinity of the saccharide a) Author to whom correspondence should be addressed.…”

“…In particular, a recent hypothesis links the bioprotective properties of saccharides to their strong modification of the tetrahedral structure of water. 6,8,9 Therefore, detailed experimental observations of the HB network of water in the vicinity of saccharide solutions are essential for understanding the underlying mechanisms for some of the saccharides' chemical and physical properties. The HBs of the water surrounding polar groups are believed to have a distorted three-dimensional coordination, as well as having their reorientation dynamically retarded.…”

“…Although the results from a number of experimental methods, including the Raman spectroscopy, [8][9][10] depolarized light scattering, [14][15][16][17][18] nuclear magnetic resonance (NMR), 19 neutron diffraction, 20 infrared (IR) spectroscopy, 9 polarizationresolved femtosecond spectroscopy, 21 and dielectric spectroscopy, [22][23][24] have been compared to those from MD simulations to characterize the hydration state and the destructuring effect of saccharides in aqueous solution, each has its limitations.…”