Effects of Polarizable Solvent Models upon the Relative Stability of an α-Helical and a β-Hairpin Structure of an Alanine Decapeptide.

The free enthalpy of changing a nonpolarizable solvent into a polarizable solvent is calculated for an alanine decapeptide solvated in water, methanol, chloroform, or carbon tetrachloride. Introducing polarizability into a water solvent does not change the relative stability between the α-helix and the β-hairpin, while for methanol and chloroform the α-helix is stabilized by about 1 kJ mol(-1) per residue and for carbon tetrachloride by about 2 kJ mol(-1) per residue. These results suggest that the less polar the solvent is, the more the α-helical structure is stabilized with respect to the β-hairpin structure by the use of a polarizable solvent model instead of a nonpolarizable one. This highlights that inclusion of polarizability in models for less polar and nonpolar solvents or protein environments is as important as, if not more important than, including polarizability in models for liquid water.