Energies of polypeptides: theoretical conformational study of polyglycine using quantum mechanical partitioning.

A method is developed for evaluating the total energy of polypeptides based on a combination of quantum mechanical and empirical potentials. Adjacent and nonadjacent peptide units are allowed to interact through these respective means. Our hybrid procedure is applied to a study of polyglycine and compared to the results obtained by the method of Scheraga and coworkers. We find the alpha helical conformation of a single strand of polyglycine to be most stable in vacuo. Other less-stable configurations include the 3(10) helix, the 2(7) ribbon structure, and the fully extended conformation.