Investigation of carbohydrate conformation in solution and in powders by double-quantum NMR

Double-quantum heteronuclear local field NMR was appl icd to two C-13(2)-la beled;ci carbohydrate: samples [1,2-C-13(2)]-glucose and methyl-alpha-D-[1, 3-C-13(2)]-glucose. The geometry of the H-C-13-C-13-H moeity was estimated using the evolution of double-quantum coherences under correlated heteronuc lear dipolar interactions. For [1.2-C-13(2)]-glucose, double-quantum techni ques were used, both in solution and solid phases; The measured H-C1-C2-N t orsion angles in crystalline glucose were: 170 degrees +/- 5 degrees for th e beta-anomer and 40 degrees +/- 15 degrees for the a-anomer, in good agree ment with reported crystal structures. In the solution phase we give a full analysis of an experiment in which the cross-correlation effects are isola ted by the use of a heteronuclear multiple-quantum filter. We consider the influence of anisotropic rotational diffusion, chemical shift anisotropy, a nd proton-proton spin diffusion on the torsion angle estimate, We show that it is possible to determine the torsion angle and the rotational correlati on time independently. The measured H-C1-C2-H torsion angles in solution di ffer slightly from the solid-state results: 159 degrees +/- 10 degrees for the P-anomer and 57 degrees rt iio for the alpha-anamer. For methyl-alpha-D -[1,3-C-13(2)]-glucose, the solid phase double-quantum heteronuclear local field experiment was applied for the first time to a HCCH moiety in which t he carbons are not directly bonded. These techniques may be applied to othe r structural problems such as the determination of glycosidic linkage confo rmations and the conformation of sugar rings in nucleotides.