Journal
CANADIAN JOURNAL OF CHEMISTRY
Volume 84, Issue 4, Pages 569-579Publisher
CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS
DOI: 10.1139/V06-036
Keywords
carbohydrate; rotamer; molecular dynamics simulation; MD; NMR
Categories
Funding
- NCRR NIH HHS [P41 RR005351] Funding Source: Medline
- NIGMS NIH HHS [R01 GM055230, R29 GM055230] Funding Source: Medline
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The rotational preferences of the hydroxymethyl group in pyranosides is known to depend on the local environment, whether in solid, solution, or gas phase. By combining molecular dynamics (MD) simulations with NMR spectroscopy the rotational preferences for the omega angle in methyl 2,3-di-O-methyl-alpha-D-glucopyranoside (3) and methyl 2,3-di-O-methyl-alpha-D-galactopyranoside (6) in a variety of solvents, with polarities ranging from 80 to 2.3 D have been determined. The effects of solvent polarity on intramolecular hydrogen bonding have been identified and quantified. In water, the internal hydrogen bonding networks are disrupted by competition with hydrogen bonds to the solvent. When the internal hydrogen bonds are differentially disrupted, the rotamer populations associated with the omega angle may be altered. In the case of 3 in water, the preferential disruption of the interaction between HO6 and O4 destabilizes the tg rotamer, leading to the observed preference for gauche rotamers. Without the hydrogen bond enhancement offered by a low polarity environment, both 3 and 6 display rotamer populations that are consistent with expectations based on the minimization of repulsive intramolecular oxygen-oxygen interactions. In a low polarity environment, HO6 prefers to interact with O4, however, in water these interactions are markedly weakened, indicating that HO6 acts as a hydrogen bond donor to water.
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