Ultrasonic and dielectric study of nonequilibrium monosaccharide solutions in water

Based on broadband acoustical (10 kHzless than or equal tonuless than or equal to2 GHz) and dielectric (1 MHzless than or equal tonuless than or equal to40 GHz) spectrometry, time-resolved ultrasonic attenuation coefficient and static permittivity measurements have been performed on nonequilibrium tautomer solutions of D-arabinose and D-fructose in water. Via the chair-chair ring inversion the ultrasonic attenuation measurements display the decrease in the content of beta-arabinopyranoside and the increase of the alpha-fructopyranoside concentration during the establishment of the tautomer equilibrium. For the arabinose solutions, the mutarotation decay constant (m=(0.027 +/- 0.004) min(-1), 20 degreesC) from the ultrasonic measurements almost agrees with that from optical activity observations. For D-fructose the ultrasonic decay constant (m=(0.043 +/- 0.007) min(-1), 20 degreesC) is smaller than that from rotary polarization (m = 0.054 min(-1), 20 degreesC) and dielectric permittivity (m=(0.058 +/- 0.007) min(-1), 20 degreesC), likely because the latter methods probe parallel pathways in the tautomer equilibrium whereas the former one reflects only one pathway. (C) 2004 Elsevier B.V. All rights reserved.