title: A new scheme for determining the intramolecular seven-membered ring N-H...O=C hydrogen-bonding energies of glycine and alanine peptides.
abstract: In this paper a new scheme was proposed to calculate the intramolecular hydrogen-bonding energies in peptides and was applied to calculate the intramolecular seven-membered ring N-H...O=C hydrogen-bonding energies of the glycine and alanine peptides. The density-functional theory B3LYP6-31G(d) and B3LYP6-311G(d,p) methods and the second-order Moller-Plesset perturbation theory MP26-31G(d) method were used to calculate the optimal geometries and frequencies of glycine and alanine peptides and related structures. MP26-311++G(d,p), MP26-311++G(3df,2p), and MP2/aug-cc-pVTZ methods were then used to evaluate the single-point energies. It was found that the B3LYP6-31G(d), MP26-31G(d), and B3LYP6-311G(d,p) methods yield almost similar structural parameters for the conformers of the glycine and alanine dipeptides. MP2/aug-cc-pVTZ predicts that the intramolecular seven-membered ring N-H...O=C hydrogen-bonding strength has a value of 5.54 kcal/mol in glycine dipeptide and 5.73 and 5.19 kcal/mol in alanine dipeptides, while the steric repulsive interactions of the seven-membered ring conformers are 4.13 kcal/mol in glycine dipeptide and 6.62 and 3.71 kcal/mol in alanine dipeptides. It was also found that MP26-311++G(3df,2p) gives as accurate intramolecular N-H...O=C hydrogen-bonding energies and steric repulsive interactions as the much more costly MP2/aug-cc-pVTZ does.
authors.affiliation: Department of Chemistry, Liaoning Normal University, Dalian 116029, People's Republic of China. chwangcs@yahoo.com
authors.forename: Chang-Sheng
authors.initials: CS
authors.lastname: Wang
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Kun
authors.initials: K
authors.lastname: Gao
authors.forename: Zhong-Zhi
authors.initials: ZZ
authors.lastname: Yang
mesh_terms: D000409:Alanine / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods; D005998:Glycine / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D012984:Software; D055672:Static Electricity
chemical_list: D010455:Peptides; D006859:Hydrogen; D000409:Alanine; D005998:Glycine