H-Bonding Cooperativity and Energetics of α-Helix Formation of Five 17-Amino Acid Peptides

摘要: Five peptides, each containing 17 amino acids, have been completely geometrically optimized in their α-helical and β-strand forms using a mixed DFT/AM1 procedure. B3LYP/D95** was used for the entire helical structures, while AM1 initially to optimize side chains, followed by reoptimization at DFT level. The energetic structural results show (1) that helices are favored over strands 29.5 37.4 kcal/mol; (2) alkyl groups on acid chains favor helix formation even absence of solvent; (3) C−H···O hydrogen bonds contribute relative stability contain acids (val, leu ile) with β-hydrogens chains; (4) these entails approximately 6.6 kcal/mol strain within backbone per bond; (5) H-bond cooperativity is essential α-helix become more stable than corresponding β-strand. This last observation strongly suggests pairwise potentials ...