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 NH···OC hydrogen‐bonding energies in glycine and alanine peptides. In this article, the method is further applied to evaluate the intramolecular 10‐membered ring NH···OC hydrogen‐bonding energies in peptides. The optimal structures of the intramolecular 10‐membered ring NH···OC 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 NH···OC 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 NH···OC 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. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009