A cross-polarization—magic-angle sample spinning n.m.r. study of several crystal forms of lactose

Abstract

Five different crystalline forms of lactose were investigated by cross-polarization—magic-angle sample spinning (CP—MAS) 13C-n.m.r. spectroscopy. Both the anhydrous β-lactose and the α-lactose monohydrate structures are known, and the CP—MAS n.m.r. data are in agreement with those structures. The structure of the stable, anhydrous α-lactose has not been reported. The CP—MAS n.m.r. results indicate that the crystal must have two or more lactose molecules per unit cell. The chemical shifts measured for two mixed crystals having α:β ratios of 5:3 and 4:1 are a direct observation of the fact that both materials are real mixed crystals rather than glasses or physical mixtures of crystals of pure α- and β-lactose. The chemical shifts also indicate that the lactose molecules in both mixed crystals are in environments similar to the crystalline environment of the stable, anhydrous α-lactose.