Oligosaccharide trans-glycoside 3JCOCC Karplus curves are not equivalent: effect of internal electronegative
Hongqiu Zhao1, Ian Carmichael, Anthony S Serianni
1Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, USA.
Abstract:
Density functional theory (DFT) calculations show that internal electronegative substituents perturb 3JCOCC Karplus curves by phase shifting them with respect to analogous pathways devoid of this substitution. Thus, the J-coupling maximum, which normally is observed near 180 degrees , is shifted by approximately 15 degrees . These findings suggest that the two types of inter-residue C-O-C-C coupling pathways observed in many oligosaccharides cannot be treated using a generalized 3JCOCC Karplus equation. Quantitative interpretations of trans-glycoside J-couplings to evaluate linkage conformations will need to take this effect into account.
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