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An NMR investigation of putative interresidue H-bonding in methyl alpha-cellobioside in solution
Wenhui Zhang1, Hongqiu Zhao, Ian Carmichael
1Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, United States.
Abstract:
Methyl alpha-cellobioside (methyl beta-D-glucopyranosyl-(1-->4)-alpha-D-glucopyranoside) was labeled with (13)C at C4' for use in NMR studies in DMSO-d(6) solvent to attempt the detection of a trans-H-bond J-coupling ((3h)J(CCOH)) between C4' and OH3. Analysis of the OH3 signal at 600 MHz revealed only the presence of two homonuclear J-couplings: (3)J(H3,OH3) and a smaller, longer range J(HH). No evidence for (3h)J(C4',OH3) was found. The longer range J(HH) was traced to (4)J(H4,OH3) based on 2D (1)H-(1)H COSY data and inspection of the H2 and H4 signal lineshapes. A limited set of DFT calculations was performed on a methyl cellobioside mimic to evaluate the structural dependencies of (4)J(H2,O3H) and (4)J(H4,O3H) on the H3-C3-O3-H torsion angle. Computed couplings range from about -0.7 to about +1.1 Hz, with maximal values observed when the C-H and O-H bonds are roughly diaxial.
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