Nuclear shielding calculations on the primary structure of the gellan polysaccharide

Use of 13C chemical shift surfaces in the study of carbohydrate conformation. Application to cyclomaltooligosaccharides (cyclodextrins) in the solid state and in solution

“…10;11 In fact, preliminary results from our laboratory indicate that the experimental CP/MAS shifts for the C-4 0 carbons in a-, Table 5. Glycosidic bond hU; Wi dihedral angles, calculated anomeric 13 C shifts in the solid state and in solution, and observed anomeric 13 b, and c-CD can be predicted using the corresponding chemical shift surface and hU; Wi angles from the X-ray structures. Although the approach requires the computation of new surfaces for glycosidic linkages not yet considered in our earlier studies, the increasing availability of powerful and inexpensive computer hardware will make this task trivial in the near future.…”

“…Our results show that the methodology is capable of predicting the anomeric carbon chemical shifts of cyclomaltooligosaccharides and their complexes reliably, both in the solid state as well as in solution. Results from calculations of solid-state 13 C shifts indicate that the approach is particularly sensitive to variations in the glycosidic linkage conformation. In principle, the method could be used to guide the building of 3D molecular models of CDs from high-quality CP/MAS NMR data when X-ray data is not available.…”

“…Even in these cases, some of the glycosidic bond conformers observed in certain CD polymorphs may be absent in solution. For example, 13 C CP/MAS measurements on frozen aqueous solutions of a-CD indicate that the conformation found in crystalline samples of a-CD hexahydrate is not significantly populated in solution. 37 In addition, the calculations neglect the effects that crystal packing forces and solvation have on the conformation of the cyclomaltooligosaccharides.…”

“…In particular, the anomeric carbon chemical shift is known to depend systematically with the glycosidic bond hU; Wi dihedral angles, 10;11 and several experimental and theoretical studies have explained this relationship qualitatively. [12][13][14][15] Recently, 16 we revisited these original investigations and carried out an exhaustive ab initio study of the anomeric carbon chemical shift dependence versus U and W for D D -Glcp-D D -Glcp disaccharides models with (1 fi 1), (1 fi 2), (1 fi 3), and (1 fi 4) linkages in both a-and b-configurations. Our work lead to the development of chemical shift surfaces for carbohydrates, 16 empirical functions relating anomeric carbon chemical shift with glycosidic bond conformation.…”

“…Our work lead to the development of chemical shift surfaces for carbohydrates, 16 empirical functions relating anomeric carbon chemical shift with glycosidic bond conformation. These equations, of the form 13 C d anom ¼ f ðU; WÞ, can be used to quantitatively incorporate isotropic 13 C shift measurements into the analysis of oligosaccharide 3D structure and dynamics.…”