The conformational properties of sucrose in aqueous solution: intramolecular hydrogen-bonding

A detailed analysis is presented of the nuclear (¹H and ¹³C) magnetic resonance (n.m.r.) properties of sucrose, using both D₂O and dimethyl sulfoxide-d₆ as solvents, based on measurements of coupling constants, chemical shifts, T₁ relaxation times, and nuclear Overhauser enhancements. Molecular modelling (HSEA calculations) suggests a strong conformational preference about the glycosidic linkages that is near to that for sucrose in the crystalline state, and this conformational rigidity is fully supported by the n.m.r. data, in terms of lack of influence of changes in concentration and temperature on the relevant n.m.r. parameters. The restricted rotation for the 1-hydroxymethyl group of the fructose residue is related to the persistence of the intramolecular hydrogen-bond between O-1^f and O-2^g. The presence of this bond was established for solutions in (CD₃)₂SO by the observation of isotopic chemicashifts on partial deuteration of the hydroxyl groups. The orientation of the 6-hydroxyl methyl group of the fructose residue is not that present in the crystalline state but, in (CD₃)₂SO, it may be intramolecularly hydrogen-bonded, as was demonstrated by titration of the hydroxyl groups with CD₃OD. Observations are made regarding hydrophobic topographies common to sucrose, saccharin, and 1-chloro-1-deoxysucrose, which may have a bearing on sweetness.