Zoltán Varga and Attila Kovács

Hydrogen bonding in peptide secondary structures.

International Journal of Quantum Chemistry, 105 (2005) 302-312

Hydrogen bonding interactions in various peptide secondary structures (b-sheet, 2₇-ribbon, 3₁₀-helix, a-helix, p-helix, b-turn II and g-turn) have been investigated in small oligopeptides by quantum chemical calculations at the B3LYP/6-31G** level. Beside the primary O^…H–N interactions the optimized structures revealed the importance of N^…H–N hydrogen bonding in several structures. The effect of substitution on the energy and structural properties was investigated comparing the properties of glycine, alanine, valine and serine. The aliphatic substituents weaken generally the hydrogen bonds, the strongest effects being observed in crowded valine conformers. Additional hydrogen bonding interactions introduced by the OH group of serine can both strengthen (by polarizing the amide moiety through N^…H interaction) and weaken (constraining the C=O oxygen by O^…H–O interaction) the backbone hydrogen bonds. The effect of water as a polarizable medium on the energy properties was assessed by the COSMO model.