The Solubility of Amino Acids and Two Glycine Peptides in Aqueous Ethanol and Dioxane Solutions

The solubilities of amino acids, diglycine, and triglycine have been measured in water and aqueous ethanol as well as dioxane solutions. Free energies of transfer of amino acid side chains and backbone peptide units from water to ethanol and dioxane solutions have been calculated from these data. The results show the similarity between the effects of ethanol and dioxane on the stability of those side chains and peptide units. In particular, the free energies of transfer of hydrophobic side chains to 100% ethanol and dioxane are essentially identical, and have been used to establish a hydrophobicity scale for hydrophobic side chains.