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A computational evaluation of the steric and electronic contributions to the stability of the structures of α− and β−D‐glucopyanose Part 4: energy versus geometry for α− and β−D‐glucopyanose in aqueous solution (593.5)
Author(s) -
Balilli Rahih,
Abdulsalam Maryam,
Baello Rofe,
Brutofsky Christian,
Kasner Marc
Publication year - 2014
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.28.1_supplement.593.5
Subject(s) - dihedral angle , energy minimization , hydroxymethyl , solvation , chemistry , thermochemistry , steric effects , polarizable continuum model , gas phase , conformational isomerism , aqueous solution , molecule , geometry , computational chemistry , crystallography , mathematics , stereochemistry , hydrogen bond , organic chemistry
Previous work has established the stable structures and energetics of α− and β−D‐glucopyranose in the gas phase but some examination of the behavior of glucose in aqueous solution is necessary to provide a more realistic picture. By starting with the gas phase optimized geometries of α− and β−D‐glucose, thermochemistry calculations were done and gas phase conformational free energies (ΔG°) were calculated. The geometry optimizations were done using 6‐31G+(d,p), 6‐31G++(d,p), 6‐311G+(d,p) and 6‐311++(d,p) basis sets with HF, DFT (B3LYP) and MP2 methods. The B3LYP/6‐311G++(d,p) gas phase optimized geometries were reoptimized with several solvent models: IEF‐PCM (Integral Equation Formalism of the Polarized Continuum Model) , CPCM (the Conductor‐like Polarized Continuum Model, and SMD (the Solvation Model based on electron Density). CPCM gave results most consistent with experimental values and was used for examining the relationships between energy and geometry. Two‐dimensional scans of energy versus the H‐O‐C1‐O dihedral, the H‐O‐C6‐C5 dihedral and the O‐C6‐C5‐O dihedrals show results consistent with the gas phase results: Only the orientation of hydroxymethyl substituent at C5 ring makes any significant contribution to the energy. The stable rotamers seen in the gas phase (gg, gt, and tg relating the orientation of the hydroxymethyl group at C5) are also seen the solvated molecules but with different relative energies. Three‐dimensional scans of energy versus the two dihedrals in in the hydroxymethyl group (HOCC and OCCO) were done for both α− and β−D‐glucopyranose to develop a potential energy surface to confirm the geometries of the low energy structures and establish consistency with the gas phase results. These scans were also relaxed scans in which the geometry was optimized at each 5° step using the B3LYP method with the 6‐311G++(d,p) basis set and the CPCM solvation model with water as the solvent.