Ultrasonic and dielectric study of nonequilibrium monosaccharide solutions in water Original Research Article

Based on broadband acoustical (10 kHz≤ν≤2 GHz) and dielectric (1 MHz≤ν≤40 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 β-arabinopyranoside and the increase of the α-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 °C) 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 °C) is smaller than that from rotary polarization (m=0.054 min−1, 20 °C) and dielectric permittivity (m=(0.058±0.007) min−1, 20 °C), likely because the latter methods probe parallel pathways in the tautomer equilibrium whereas the former one reflects only one pathway.