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 in itio calculations, complete conformational libraries, containing as many as 27 conformers, have been determined for diamide model systems incorporatin g the amino acids valine (Val) and phenylalanine (Phe). Conformational and energetic properties of these libraries were analyzed. For example, signifi cant correlation was found between relative energies from 6-311++G** B3LYP and single-point B3LYP/6-311++G**//RHF/3-21G calculations. Comparison of po pulations of molecular conformations of hydrophobic aromatic and nonaromati c residues, based on their ab initio relative energies, with their natural abundance indicates that, at least for the hydrophobic core of proteins, th e conformations of Val (Ile, Leu) and Phe (Tyr, Trp) are controlled by the local energetic preferences of the respective amino acids. (C) 2001 John Wi ley & Sons, Inc.