Peptide models XXXI. Conformational properties of hydrophobic residues shaping the core of proteins. An ab initio study of N-formyl-L-valinamide and N-formyl-L-phenylalaninamide

Employing introductory (3-21G RHF) and medium-size (6-311++G∗∗ B3LYP) ab initio calculations, complete conformational libraries, containing as many as 27 conformers, have been determined for diamide model systems incorporating the amino acids valine (Val) and phenylalanine (Phe). Conformational and energetic properties of these libraries were analyzed. For example, significant correlation was found between relative energies from 6-311++G∗∗ B3LYP and single-point B3LYP/6-311++G∗∗//RHF/3-21G calculations. Comparison of populations of molecular conformations of hydrophobic aromatic and nonaromatic residues, based on their ab initio relative energies, with their natural abundance indicates that, at least for the hydrophobic core of proteins, the conformations of Val (Ile, Leu) and Phe (Tyr, Trp) are controlled by the local energetic preferences of the respective amino acids. c © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 732–751, 2001