Proton exchange in aqueous solutions of glucose. Hydration of carbohydrates

Abstract

Under limited conditions of pH and temperature, high resolution ¹H n.m.r. spectra of sugars in H₂O reveal well resolved —OH proton signals downfield from the water peak. Exchangeable proton spectra are presented for glucose, mannose and galactose. Widths range from 30–70 Hz. Exchange has been studied in detail for the anomeric protons of glucose. Residence times are of the order of 10 ms in the accessible temperature range, exchange being slower for the α-anomer. Activation energies range from 30–50 kJ mol^–1, depending on concentration and type of anomer.