Hydration and aggregation in aqueous xylitol solutions in the wide temperature range

Abstract

An extensive dielectric relaxation study of aqueous xylitol solutions for solute concentration c< 3.4 M at 5, 25, 45, and 65 °C is presented. The spectra of solutions recorded in the wide frequency range of 0.05 ⩽ν/GHz ⩽ 89 can be interpreted in terms of a 5D model. Detailed analysis of the cooperative dynamics and hydration indicates that xylitol hydration is weak and all dynamically retarded H2O molecules bind to the inner OH groups of xylitol. Activation parameters for the bulk-water relaxation time, τ3(T), and slow-water relaxation time, τ2(T), were determined as well as the equilibrium constant of the self-association of xylitol molecules. Approximately four OH groups per xylitol molecule are involved in aggregate formation in aqueous xylitol solutions. The xylitol aggregation is very week and strongly perturbed by rising temperature. It is driven by the lack of separating bulk water and apparently rather larger fluctuating entities are formed.