Molecular dynamics of carbohydrate aqueous solutions. Dielectric relaxation as a function of glucose and fructose concentration

At some solute concentrations c between 1 and 5.4 mom, the complex (electri c) permittivity of aqueous solutions of D-glucose and D-fructose has been d etermined as a function of frequency v between 300 kHz and 40 GHz. The perm ittivity spectrum of the 5.4 mol/L D-fructose solution has been measured at six temperatures between 10 and 35 degreesC, and the other spectra have be en taken at 25 degreesC. All dielectric spectra revealed one dispersion/die lectric loss region, which indicated a rather homogeneous relaxation of the solute and solvent dipole moments. Analytically, the measured spectra were represented by the Cole-Cole relaxation spectral function, which correspon ds with a continuous, symmetrically bell shaped relaxation time distributio n. The parameters of the spectral function are discussed to show that the m onosaccharides exhibit unusual hydration properties. Particularly, when tre ated in terms of a wait-and-switch model of dipole reorientation, the princ ipal dielectric relaxation time is indicative of the extraordinary hydratio n behavior of the saccharides. It is suggested that this behavior reflects the compatibility of the ring molecule's -OH group topology with the water structure.