Hydrophilic interactions between charged amino acids and the effect of ions on the strength of interaction

The interaction between oppositely charged amino acids was studied by charge-transfer reversed-phase thin-layer chromatography. The dependence of the lipophilicity of Arg, Lys and Orn on the concentration of Glu, Asp, Gln and Asn in the eluent was considered to be related to the strength of interaction. The interaction of dibasic amino acids with Glu and Asp was stronger than with Gln and Asn. Mono- (Li+, Na+, K+, Rb+ and Cs+) and divalent (Mg2+ and Ca2+) cations decreased the strength of interaction suggesting the electrostatic character of the interaction. Their inhibitory effect mainly depended on their concentration and to a lesser extent on the ion charge and hydrated ion radii. Stepwise regression analysis proved that the strength of interaction depends on the polarity parameters of amino acids and is independent of their chemical structure.