Ab initio MP2 and density functional theory computational study of AcAlaNH2 peptide hydration: a bottom-up approach.

AcAlaNH2 ⋅ n H2O (n=1-13) complexes have been proposed as models to account for water solvent effects on the molecular properties of N-acetyl-L-alanine amide. Ab initio computations are planned to evaluate peptide-water interactions and to provide a means for approximating relative effects of the short-range many-body interactions arising in real solution without introducing any external parameters intended to quantify empirical or semiempirical potential-energy functions. The present bottom-up approach reveals the formation of compact ring clusters of water molecules strongly bonded to peptidic polar groups throughout hydrogen bonds. The explicit coordination of water molecules around the peptide renders the fully extended (FE) and polyproline II (PPII) conformers more stable with respect to the 310 helix or γ turn. The alternance of donor and acceptor groups on both sides of the FE and PPII conformers allows for synergy and extensive H-bonding.