The stability constants of the ternary complexes of type MAB and of the corresponding binary complexes MA, MA2, MB and MB2 have been determine by potentiometric pH titration technique at 25 ?0.1癈 and at 0.10 ionic strength (NaNO3), where M = Zn2+; A = bipyridyl (bipy), phenanthroline (phen); B = glycinate (gly), alaninate (ala), valinate (val), leucinate (leu), phenylalaninate (phe) and tryptophanate (trp). The results combining with those of 1H NMR research confirmed the presence of the intramol. hydrophobic interaction between ligands in the ternary complexes, except those with gly or ala. The interaction increases in the amino acid ligand order: val < leu << phe < trp, which corresponds with the order of hydrophobic properties of the noncoordinating hydrophobic moieties in these amino acid ligands. The equilibrium constants of transition between open species (absence of ligand-ligand interaction) and close species (hydrophobic interaction having occurred) have also been calculated The results show that the close species of the ternary complexes with phe or trp as one of ligands have become the major components presented in solution The solvent influence on the hydrophobic interaction between ligands has also been studied preliminary.

Key words: AMINO ACID, TRYPTOPHAN, ZINC COMPLEX, LEUCINE, PROTON MAGNETIC RESONANCE SPECTROMETRY, PHENYLALANINE, EQUILIBRIUM CONSTANT, TERNARY COMPLEX, ALANINE, VALINE