A C-13 T1 STUDY OF CONFORMATIONAL AND MOLECULAR MOBILITY OF MONOSYLLACTOSES AND DIFUCOSYLLACTOSES

Overall and internal motions of lactose Galbeta(1 --> 4)Glcalpha and its three fucosylated derivatives Fucalpha(1 --> 2)Galbeta(1 --> 4)Glcalpha, Galbeta(1 --> 4) [Fucalpha(1 --> 3)] Glcalpha and Fucalpha(1 --> 2)Galbeta(1 --> 4) [Fucalpha(1 --> 3)] Glcalpha were investigated in Me2SO-d6 using the spin-lattice relaxation times of C-13 nuclei, T1(C-13), measured at 8.5 and 11.7T. The relaxation data of the ring carbons in lactose and the lactosyl core of its derivatives were well described by the axially symmetric motion of the molecule. However, the interpretation of the T1(C-13) of ring carbons in fucose residues required the assumption of a conformational mobility about the appropriate glycosidic bonds. For this purpose, a bistable, jump model of internal motion with a varying angle between the rotation axis and the symmetry axis of the overall tumbling was developed. The internal rotation of hydroxymethyl groups in Glc and Gal residues was also analysed quantitatively; the rotation in Glc was found to be slower than that in Gal. The internal rotation of methyl groups in fucoses undergoing a complex motion was interpreted semi-quantitatively.