Proton magnetic resonance study of the hydration of glucose

Abstract

THE solvation of sugars by water has not been extensively studied in spite of its biochemical importance. Relaxation rates for ¹⁷O in monosaccharides have been used to study solvation^1,2, the revised² estimate of the solvation number being 5±1 water molecules for D-glucose and 2.5±1 for D-ribose at 5 °C, in agreement with 6±1 and 2.5±1 (respectively) derived from dielectric relaxation amplitudes. Again, compressibility data for aqueous sugars have been used³ to derive solvation numbers for monosaccharides, with results ranging from 2.5 to 4.0 at 25 °C. One limiting factor in nuclear magnetic resonance (NMR) studies of aqueous sugars is that the rate of proton exchange is fast and no separate resonances from the hydroxyl protons appear. We now report that at low temperatures the exchange rate becomes sufficiently slow in the pH range 4 to 8 to enable us to detect resolved resonances from the individual hydroxyl protons. The results are interpreted in terms of strong hydrogen bonding between water and glucose, the effective solvation number being at least 10.