title: Estimation on the intramolecular 10-membered ring N-H...O=C hydrogen-bonding energies in glycine and alanine peptides.
abstract: Computation of accurate intramolecular hydrogen-bonding energies for peptides is of great importance in understanding the conformational stabilities of peptides and developing a more accurate force field for proteins. We have proposed a method to determine the intramolecular seven-membered ring N-H...O=C hydrogen-bonding energies in glycine and alanine peptides. In this article, the method is further applied to evaluate the intramolecular 10-membered ring N-H...O=C hydrogen-bonding energies in peptides. The optimal structures of the intramolecular 10-membered ring N-H...O=C hydrogen bonds in glycine and alanine tripetide molecules are obtained at the MP2 level with 6-31G(d), 6-31G(d,p), and 6-31+G(d,p) basis sets. The intramolecular 10-membered ring N-H...O=C hydrogen-bonding energies are then evaluated based on our method at the MP2/6-311++G(3df,2p) level with basis set superposition error correction. The intramolecular 10-membered ring N-H...O=C hydrogen-bonding energies are calculated to be in the range of -6.84 to -7.66, -4.44 to -4.98, and -6.95 to -7.88 kcal/mol. The method is also applied to estimate the individual intermolecular hydrogen-bonding energies in the dimers of amino-acetaldehyde, 2-amino-acetamide, formamide, and oxalamide, each dimer having two identical intermolecular hydrogen bonds. According to our method, the individual intermolecular hydrogen-bonding energies in the four dimers are calculated to be -1.77, -1.67, -6.35, and -4.82 kcal/mol at the MP2/6-311++G(d,p) level, which are in good agreement with the values of -1.84, -1.72, -6.23, and -4.93 kcal/mol predicted by the supermolecular method.
authors.affiliation: Department of Chemistry, Liaoning Normal University, Dalian 116029, People's Republic of China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Chang-Sheng
authors.initials: CS
authors.lastname: Wang
mesh_terms: D000409:Alanine / Q000737:chemistry*; D003198:Computer Simulation; D005998:Glycine / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D010455:Peptides; D000409:Alanine; D005998:Glycine