Structures of the Peptide–Water Complexes Studied by the Hybrid Quantum Mechanical—Molecular Mechanical (QM/MM) Technique

Applications of a new approach to the hybrid quantum mechanical and molecular mechanical (QM/MM) theory based on the effective fragment potential technique to calculations of the structures of the peptide—water complexes are described. Our approach assumes that the MM subsystem is viewed as a flexible composition of effective fragments, while fragment–fragment interactions are replaced by MM force fields. In this work, the QM subsystem is composed of water molecules and the MM part refers to peptides. Different isomers of the hydrogen-bonded complex of the dipeptide N-acetyl-L-alanine N′-methylamide (AAMA) with four water molecules are considered, and the results of QM/MM calculations are compared to experimental data and to the results of the density functional theory (DFT) treatment. The properties of water chains inside polypeptide tubes, modeling proton wires inside ionic channels, are described.