AN NMR, DSC AND X-RAY-INVESTIGATION OF THE DISACCHARIDES SUCROSE, MALTOSE AND LACTOSE

Polycrystalline samples of anhydrous sucrose and the monohydrates of α -lactose and β -maltose have been studied by using nuclear magnetic resonance, differential scanning calorimetry and X-ray diffraction methods. The results show that, apart from twofold reorientations of water molecules, these lattices are fairly rigid below room temperature. The NMR results in the case of sucrose and lactose reveal that above room temperature molecular motions reduce the dipolar interactions to almost zero, even below the melting points. In each of these compounds an endothermic DSC peak occurs at approximately 421K. Proton T1 and T1p values change noticeably in the vicinity of this temperature. Interpretation of the results leads to the conclusion that these DSC peaks are not associated with the loss of water, but are most likely due to the breaking of hydrogen bonds. A similar DSC peak was not observed in the case of β-maltose, while the NMR results show that molecular motions start to reduce the dipolar interactions much closer to the melting point than in the other two compounds. © 1990 Taylor & Francis Ltd.