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

A study on D20 solutions of trehalose, maltose, and sucrose have been performed by using quasi-elastic light-scattering (QELS) and H-1 and H-2 pulse-gradient-spin-echo NMR (PGSE-NMR). The self-diffusion coefficient of disaccharide (D) and the apparent diffusion coefficient D-app have been obtained as a function of disaccharide weight fraction c and temperature (20-60 degreesC). 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 D-app in the dilute region (c less than or equal to 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 (D-s) at 20 degreesC has also been measured for the DO 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 D, as a function of c. The hydration numbers rank trehalose > maltose > sucrose has been observed in agreement with data reported in the literature.