Ab initio modeling of glycosyl torsions and anomeric effects in a model carbohydrate: 2-ethoxy tetrahydropyran.

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TitleAb initio modeling of glycosyl torsions and anomeric effects in a model carbohydrate: 2-ethoxy tetrahydropyran.
Publication TypeJournal Article
Year of Publication2007
AuthorsH Woodcock, L, Moran, D, Pastor, RW, Mackerell, AD, Brooks, BR
JournalBiophys J
Volume93
Issue1
Pagination1-10
Date Published2007 Jul 01
ISSN0006-3495
KeywordsComputer Simulation, Dimerization, Models, Chemical, Models, Molecular, Molecular Conformation, Pyrans, Surface Properties
Abstract

A range of ab initio calculations were carried out on the axial and equatorial anomers of the model carbohydrate 2-ethoxy tetrahydropyran to evaluate the level of theory required to accurately evaluate the glycosyl dihedral angle and the anomeric ratio. Vacuum CCSD(T)/CBS extrapolations at the global minimum yield DeltaE = E(equatorial) - E(axial) = 1.42 kcal/mol. When corrected for solvent (by the IEFPCM model), zero-point vibrations and entropy, DeltaG(298) = 0.49 kcal/mol, in excellent agreement with the experimental value of 0.47 +/- 0.3 kcal/mol. A new additivity scheme, the layered composite method (LCM), yields DeltaE to within 0.1 kcal/mol of the CCSD(T)/CBS result at a fraction of the computer requirements. Anomeric ratios and one-dimensional torsional surfaces generated by LCM and the even more efficient MP2/cc-pVTZ level of theory are in excellent agreement, indicating that the latter is suitable for force-field parameterization of carbohydrates. Hartree-Fock and density functional theory differ from CCSD(T)/CBS for DeltaE by approximately 1 kcal/mol; they show similar deviations in torsional surfaces evaluated from LCM. A comparison of vacuum and solvent-corrected one- and two-dimensional torsional surfaces indicates the equatorial form of 2-ethoxy tetrahydropyran is more sensitive to solvent than the axial.

DOI10.1529/biophysj.106.099986
Alternate JournalBiophys. J.
PubMed ID17554075
PubMed Central IDPMC1914444
Grant ListGM 70855 / GM / NIGMS NIH HHS / United States
/ / Intramural NIH HHS / United States