Evidence for a transient interresidue hydrogen bond in sucrose in aqueous solution obtained by rotating-frame exchange NMR spectroscopy under supercooled conditions.

We have used the hydroxyl protons of sucrose dissolved in supercooled water as NMR probes for the detection of intramolecular hydrogen bonds. Neither the measured OH temperature shift coefficients, 3JHCOH scalar couplings, isotope-induced 13C chemical shifts (delta delta COH/COD), nor OH exchange rates allowed us to single out any hydroxyl group in sucrose with characteristics indicative of involvement in strong hydrogen bonding. However, two-dimensional rotating-frame exchange (ROESY) spectroscopy revealed a direct exchange between the glucosyl OH2 and fructosyl OH1 protons. We conclude that an O2g::H::O1f interresidue hydrogen bond transiently exists in sucrose in aqueous solution. ROESY of sugars in supercooled water is proposed as a novel method to detect this type of weak hydrogen bonding.