Stability of ternary amino acid complexes and its computer simulation under physiological conditions

The binary and ternary formation constants of mixed amino acid complexes with Zn(II), Cu(II), Ni(II) and Cd(II) have been potentiometrically determined under physiological conditions. The symbiosis of HSAB does play a role in the formation of ternary amino acid complexes. Comparing with Zn(II), as a softer Lewis acid Ni(II) shows its preference to softer Lewis bases cysteinate and histidinate. These soft Lewis bases more likely gather together in the mixed amino acid complexes. It is expected that the ternary amino acid complexes are overwhelming in the distribution of complex species especially at biological conditions. In the case of zinc, differring from previous study the alaninate-containing mixed complexes become the predominant species formed in the region of pH 7.4.