Kinetic processes in supercooled monosaccharides upon melting: Application of dielectric spectroscopy in the mutarotation studies of D-ribose.

Dielectric spectroscopy has been recently used to monitor mutarotation in undercooled D-fructose. This method can be viewed as a universal method to study mutarotation phenomenon in the whole family of monosaccharides. In this paper, we studied kinetics of mutaration of anhydrous D-ribose at ambient pressure as well as pressure effect on the rate constant of this process. Ribose mutarotation behavior is compared to the one obtained for D-fructose. In addition, we attempted to determine the "direction" of mutarotation in undercooled monosaccharides after quenching the melted sample. To this end, analysis of dipole moments of different tautomers of D-fructose and D-ribose have been performed. Conformational analysis of studied carbohydrates was done with use of density functional theory. Geometry optimizations as well as calculations of dipole moments were done on the 6-311++G(d,p)/B3LYP level. Finally, it turned out that data obtained from the mutarotation experiment might be helpful in understanding the origin of gamma-process occurring in the whole family of carbohydrates.