Ab initio CHF‐GIAO ¹³C nuclear shielding calculations on carbohydrates

Abstract

SUMMARYThe effect of basis set quality and glycosidic conformation on the calculated chemical shieldings of the C-1 and C-4 glycosidic carbon atoms of some naturally and commercially important model β-(1 → 4), α-(1 → 4) and α-(1 → 3) linkage systems have been investigated using ab initio molecular orbital coupled Hartree-Fock gauge included atomic orbital (CHF-GIAO) methods. The STO-3G, 3-21G, 4-31G and 6-31G * * basis sets have been tested in our calculations.

Conformational features of crystal‐surface cellulose from higher plants

“…Ab initio modelling suggests that in general, chemical shift displacements due directly to hydrogen bonding are of the order of 1–2 p.p.m., not approximately 5 p.p.m. as observed here (Wilson et al ., 1996). Further, C‐4 in cellulose carries no hydroxyl to act as a hydrogen bond donor, nor is O‐4 an acceptor for a hydrogen bond in the structures generally suggested for cellulose I.…”

“…(1983) first established empirical correlations for (1,4′)‐glucans, it has been widely assumed that peak positions in solid state 13 C NMR spectra of polysaccharides depend on conformation. For α (1,4′)‐glucans the correlation with chain conformation is supported by both ab initio modelling (Wilson et al ., 1996) and orbital symmetry considerations based on the anomeric effect (Jarvis, 1994). However, the orbital geometry around the β (1,4′) glycosidic linkage is completely different and, even though the empirical correlation of the C‐4 chemical shift with rotation around the C‐1 − O‐4′ bond is just as strong as for the α ‐linkage, it has not so far been explained by either theoretical approach.…”

“…However, the orbital geometry around the β (1,4′) glycosidic linkage is completely different and, even though the empirical correlation of the C‐4 chemical shift with rotation around the C‐1 − O‐4′ bond is just as strong as for the α ‐linkage, it has not so far been explained by either theoretical approach. The 13 C NMR behaviour of C‐4 in cellulose Iα and Iβ is particularly divergent from theoretical predictions (Koch et al ., 2000, Wilson et al ., 1996).…”

Spectroscopic study of interactions between model direct dyes and cotton

“…The 13 C NMR behavior of C 4 in cellulose is particularly divergent from theoretical predictions, Koch et al,42 Wilson et al43 Differences in the chemical environment of C 4 must be due to noncovalent effect, either intramolecular (conformation) or intermolecular (chain packing , which in cellulose means intermolecular hydrogen bonding), Viëtor et al44 Intermolecular hydrogen bonding could affect the C 4 chemical shift indirectly by locking the rotation of O 2 , O 3 , or C 6 and altering their stereoelectronic interactions with C 4 , Viëtor et al44…”