An Integrated Quasi-Elastic Light-Scattering, Pulse-Gradient-Spin−Echo Study on the Transport Properties of α,α-Trehalose, Sucrose, and Maltose Deuterium Oxide Solutions

Abstract

A study on D2O solutions of trehalose, maltose, and sucrose have been performed by using quasi-elastic light-scattering (QELS) and 1H and 2H pulse-gradient-spin−echo NMR (PGSE-NMR). The self-diffusion coefficient of disaccharide (D) and the apparent diffusion coefficient Dapp have been obtained as a function of disaccharide weight fraction c and temperature (20−60 °C). Hydrodynamic radii at infinite dilution have been evaluated. In case of trehalose and sucrose a model of monodisperse hard spheres has been used to interpret the concentration dependence of D and Dapp in the dilute region (c ≤ 0.1), thus obtaining the values of the hydrodynamic radii together with the diffusing particles volume fractions as a function of c and T. The invariance of the hydrodynamic radii and the agreement with the model suggest that T and c neither induce self-aggregation of the sugars nor affect sensitively their structure and hydration. The self-diffusion coefficient of D2O (Ds) at 20 °C has also been measured for the D2O solutions of the three sugars. By following an interpretation commonly used to rationalize the self-diffusion coefficient of small molecules in colloidal systems, obstruction and hydration of disaccharide have been invoked to explain the decrease of Ds as a function of c. The hydration numbers rank trehalose > maltose > sucrose has been observed in agreement with data reported in the literature.