Conformational Behavior of Macromolecules in Solution. Homopolypeptides of α-Aminoisobutyric Acid as Test Cases

Solvent effects on the conformational preferences of homopolypeptides constituted by α-aminoisobutyric acid (polyAib) have been investigated coupling the polarizable continuum model (PCM) either to a quantum mechanical (PBE0/6-31G(d)) or to a molecular−mechanical (Amber) representation of the solute. The results allow a deeper insight into the influence of the solvent on the 3<INF>10</INF>/α-helix equilibrium in polyAib and show that PCM/Amber is a useful tool to study the conformational preferences of large peptides in 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 absolute solvation energies in polar solvents.