Dielectric spectra of mono- and disaccharide aqueous solutions

Complex (dielectric) permittivity spectra of aqueous solutions of the monosaccharides D-Xylose, D-Galactose, D-Glucose, D-Fructose, Methyl-beta-D-xylose, and Methyl-beta-D-glucose, as well as the disaccharides D-Lactose, D-Maltose, and D-Sucrose have been measured. In order to avoid any systematic errors, various experimental setups, each matched to a particular measuring range, have been used to cover the frequency domain from 300 kHz to 40 GHz. In some characteristic details our spectra for maltose solutions deviate from those recently reported by Weingartner [J. Chem. Phys. 115, 1463 (2001)]. The monosaccharide spectra at c=1 mol/l and the disaccharide spectra at cless than or equal to0.5 mol/l reveal a rather homogeneous relaxation of the carbohydrate and water dipole moments, which can be well represented by a Cole-Cole relaxation time distribution. At higher solute concentration the dielectric spectra are favorably represented by two relaxation terms, though interpolation of the experimental data by the Cole-Cole spectral function is possible within the limits of errors. There are indications that these terms might be due to local fluctuations in the carbohydrate concentration, in conformity with previous ultrasonic spectra of monosaccharide solutions. (C) 2002 American Institute of Physics.