Conformational behavior of macromolecules in solution. Homopolypeptides ofalpha-aminoisobutyric acid as test cases

Solvent effects on the conformational preferences of homopolypeptides const ituted by alpha -aminoisobutyric acid (polyAib) have been investigated coup ling the polarizable continuum model (PCM) either to a quantum mechanical ( PBE0/6-31G(d)) or to a molecular-mechanical (Amber) representation of the s olute. The results allow a deeper insight into the influence of the solvent on the 3(10)/alpha -helix equilibrium in polyAib and show that PCM/Amber i s a useful tool to study the conformational preferences of large peptides i n condensed phase. As a matter of fact, all the PCM/Amber results are close to their PCM/PBE0 counterparts, except for some underestimation of the abs olute solvation energies in polar solvents.