title: Theoretical 13C chemical shift, 14N, and 2H quadrupole coupling- constant studies of hydrogen bonding in L-alanylglycine dipeptide.
abstract: (13)C chemical shieldings and (14)N and (2)H electric field gradient (EFG) tensors of L-alanylglycine (L-alagly) dipeptide were calculated at RHF/6-31 + + G** and B3LYP/6-31 + + G** levels of theory respectively. For these calculations a crystal structure of this dipeptide obtained from X-ray crystallography was used. Atomic coordinates of different clusters containing several L-alagly molecules were used as input files for calculations. These clusters consist of central and surrounding L-alagly molecules, the latter forming short, strong, hydrogen bonds with the central molecule. Since the calculations did not converge for these clusters, the surrounding L-alagly molecules were replaced by glycine molecules. In order to improve the accuracy of calculated chemical shifts and nuclear quadrupole coupling constants (NQCCs), different geometry-optimization strategies were applied for hydrogen nuclei. Agreement between calculated and experimental data confirms that our optimized coordinates for hydrogen nuclei are more accurate than those obtained by X-ray diffraction.
authors.affiliation: Department of Chemistry, Sharif University of Technology, Tehran, Iran. tafazzoli@sharif.edu
authors.forename: M
authors.initials: M
authors.lastname: Tafazzoli
authors.forename: S K
authors.initials: SK
authors.lastname: Amini
mesh_terms: D002247:Carbon Isotopes; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D003903:Deuterium / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards*; D008956:Models, Chemical; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry; D011789:Quantum Theory; D012015:Reference Standards
chemical_list: D002247:Carbon Isotopes; D004151:Dipeptides; C028872:alanylglycine; D003903:Deuterium; D009584:Nitrogen