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 (electric) permittivity of aqueous solutions of D-glucose and D-fructose has been determined as a function of frequency v between 300 kHz and 40 GHz. The permittivity 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 been taken at 25 degreesC. All dielectric spectra revealed one dispersion/dielectric 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 corresponds with a continuous, symmetrically bell shaped relaxation time distribution. The parameters of the spectral function are discussed to show that the monosaccharides exhibit unusual hydration properties. Particularly, when treated in terms of a wait-and-switch model of dipole reorientation, the principal dielectric relaxation time is indicative of the extraordinary hydration 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.