NMR INVESTIGATION OF OLIGOSACCHARIDE CONFORMATION USING DIPOLAR COUPLINGS IN AN AQUEOUS DILUTE LIQUID-CRYSTALLINE MEDIUM

The tetrasaccharide lacto-N-neotetraose beta-D-Galp-(1 --> 4)-beta-D-G lcpNAc-(1 --> 3)-beta-D-Galp-(1 --> 4)-D-Glcp was dissolved in a dilut e mixture of dimyristoyl- and dihexanoylphosphatidylcholine in deuteri um oxide and (1)J(C,H) spin-spin coupling constants were measured in a n isotropic solution at 25 degrees C. On raising the temperature to 38 degrees C, an ordering of the system occurs which permits determinati on of dipolar couplings. An energy minimized molecular mechanics model was generated showing that the molecule is anisotropic and can be tre ated as a cylinder. A fit of the expression for the carbon-proton dipo lar couplings in a uniaxial molecule in a uniaxial liquid crystal reve aled good agreement with experimental data, emphasizing the future pot ential of the method in studies of carbohydrate conformation. (C) 1998 John Wiley & Sons, Ltd.