Solvation properties of non-polar amino acids in water and methanol: a molecular dynamics study

Solvation properties of the amino acids alanine, valine, leucine and phenyl alanine in water and in methanol at infinite dilution have been studied by using molecular dynamics simulations. The free energy transfer of the solut es from water to methanol has been calculated by means of a slow-growth tec hnique and the results compared with diverse hydrophobicity scales availabl e in the literature. Chothia's linear relation between the accessible surfa ce area and the hydrophobicity is shown. The line obtained has a slope equi valent to 49 cal mol(-1) Angstrom (-2). The radial distribution of solvent molecules around the amino acids residues is considered, and a comparison i s made of the number of hydrogen bonds formed between water molecules in th e presence and in the absence, respectively, of the amino acids. The calcul ations show clearly that the solvation structure near the non-polar amino a cids is richer for methanol than for water.