Molecular relaxation properties of the monosaccharides (a) D-glucose, (b) methyl -D-glucopyranoside, (c) methyl R-D-mannopyranoside, (d) D-xylose, (e) D-arabinose, (f) methyl -D-xylopyranoside, (g) methyl -Darabinopyranoside, (h) methyl R-L-(6-deoxy)mannopyranoside, and (i) 1,6-anhydro--D-glucopyranoside, all in aqueous solution, have been studied using broad band ultrasonic spectrometry in the frequency range 0.2-2000 MHz.Ultrasonic excess absorption with relaxation characteristics near 80 MHz was found for glucose and the methyl glucosides of D-glucose and D-mannose, but no relaxation process was detected for the other monosaccharides in the same frequency range. From structural aspects it is deduced that the most likely process causing the observed relaxation is the rotation of the exocyclic -CH 2 OH group, placing rotational isomerization on the nanosecond time scale. Relaxation parameters for D-glucose and methyl -D-glucopyranoside solutions were further investigated as a function of concentration and temperature, in order to confirm the assignment of the relaxation process, and to determine some of its thermodynamic and kinetic parameters.

Ultrasonic resonator cells for liquid attenuation and velocity measurements below 1 MHz with one planar and one concave piezoelectric transducer are described. Such cells with a limited sample volume are needed for broad band ultrasonic relaxation spectrometry and for studies in chemical reaction kinetics, particularly for frequencies below 200 kHz. Measurement and evaluation procedures are described and an example of a broad band spectrum is shown.

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