Interaction of amino acids with the nonionic surfactant nonylphenyl hexaethoxylate

The interaction of amino acids with the nonionic surfactant nonylphenyl hexaethoxylate was studied by charge-transfer reversed-phase thin-layer chromatography and the relative strength of interaction was calculated. In the majority of cases the surfactant has a negligible effect on the hydrophobicity of amino acids. Only the binding of Cys, Gln, Glu, Gly, Hyp, Phe and Tyr to the surfactant was observed, however, the strength of interaction was fairly low. The hydrophobicity of the amino acid side chains significantly influenced the strength of interaction. The findings support the hypothesis that the binding of nonionic surfactants to proteins involves more than one amino acid residues and that the hydrophobic forces have a considerable impact on the interaction.