Conformational properties of and a reorientation triggered by sugar-water vibrational resonance in the hydroxymethyl group in hydrated beta-glucopyranose.
In this paper, we discuss the conformational properties of the hydroxymethyl group of beta-glucopyranose in aqueous solution and its reorientation mechanism. First, using the values for the hydroxymethyl torsion (O5-C5-C6-O6) angle obtained by our ab initio simulations, we reestimate the experimental ratio of the hydroxymethyl rotamer populations. The reestimated ratio is found to be in agreement with those previously reported in several computational studies, which probably partly explains the discrepancies between theoretical and experimental studies that have been discussed in the literature. Second, our time-frequency analysis on a reorientation in the hydroxymethyl group in an ab initio molecular dynamics trajectory suggests that, before the reorientation, the O6-H6 stretching mode is vibrationally coupled with a proton-accepting first-hydration-shell water molecule, whereas the C6-O6 stretching mode is vibrationally coupled with a proton-donating one. The amount of the total vibrational energy induced by these vibrational couplings is estimated to be comparable to typical values for the potential barriers between hydroxymethyl rotamers. To elucidate the vibrational couplings, we investigate the hydrogen-bonding properties around the hydroxymethyl group during the pretransition period. The implications, validity, and limitation of a possible reorientation mechanism based on these findings are also discussed.
Integrative Bioscience and Biomedical Engineering, Graduate School of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan. teppei_suzuki@moegi.waseda.jp
Teppei
T
Suzuki
Hirotaka
H
Kawashima
Takayuki
T
Sota
D002236:Carbohydrate Conformation; D002241:Carbohydrates / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry*; D006860:Hydrogen Bonding; D006900:Hydroxylation; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008697:Methane / Q000737:chemistry; D011522:Protons; D013237:Stereoisomerism; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D002241:Carbohydrates; D006027:Glycosides; D011522:Protons; D014867:Water; D008697:Methane