EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK.
Phys Chem Chem Phys. 2013 Nov 7;15(41):18223-34. doi: 10.1039/c3cp52987h.
We have developed novel NMR methods for the measurement of heteronuclear residual dipolar couplings (RDCs) in molecules with severely overlapping NMR resonances. These and other methods enabled us to obtain 31 RDCs for α-D-cellobiose and 24 RDCs for β-D-cellobiose. The interpretation of the data in the approximation of a rigid disaccharide structure, using RDCs and interglycosidic (3)J coupling constants, yielded conformation that is very close to that determined using X-ray crystallography. However, depending on which ring was used to calculate the order parameters, the dihedral angle ψH varied up to 30° or 40°, while the φH angle was always the same. This indicates residual flexibility of the glycosidic linkage between the two monosaccharide rings and was observed for both α- and β-D-cellobiose. The RDC analysis using rigid fragments rather than a complete molecule has thus shown that the glycosidic bond of cellobiose is not completely rigid and exhibits low-level flexibility. The sources of this flexibility are discussed and evidence presented to support a hypothesis that it is associated with the ψ more than the φ angle.
我们开发了新的 NMR 方法，用于测量具有严重重叠 NMR 共振的分子中的异核残余偶极耦合 (RDC)。这些方法和其他方法使我们能够获得α-D-纤维二糖的 31 个 RDC 和β-D-纤维二糖的 24 个 RDC。在刚性二糖结构的近似值下，使用 RDC 和糖苷内（3）J 耦合常数对数据进行解释，得到的构象与使用 X 射线晶体学确定的构象非常接近。然而，根据用于计算序参数的环的不同，二面角 ψH 变化可达 30°或 40°，而 φH 角始终相同。这表明两个单糖环之间的糖苷键具有残留的灵活性，在α-D-和β-D-纤维二糖中都观察到了这种情况。使用刚性片段而不是完整分子的 RDC 分析表明，纤维二糖的糖苷键不是完全刚性的，而是具有低水平的灵活性。讨论了这种灵活性的来源，并提出了证据支持这样一种假设，即它与 ψ 角而不是 φ 角有关。
