Computer based stability constants and absorption maximum values for the copper(II) ternary complexes containing L-cysteic acid and some selected ligands

Abstract

The present paper deals with the determination of stability constants for sixteen ternary systems viz. Cu(II)- L-cysteic acid (cya) (A)-L.-pbenylalanine (pha), dopamine (dopm), dopa, imidazole(Him), benzimidazole(Bimz), histamine(Hist), L- histidine(His), DL-2- aminobutyric acid(2aba), DL-3- aminobutyric acid(3aba), 4- aminobutyric acid (4aba), DL-4-amino-3-hydroxybutyric acidi( ahba), 1,2-diaminopropane( tp), 1,3- diaminopropane(tp), DL-2,3-diaminopropionic acid (dapa), DL-2,4- diaminobutyric acid (daba), and DL-ornithine (orn) (B). These systems have given rise to the formation of ternary complexes of the types CuAB, CuAB₂, CuABH or CuABH₂. Though dopa ligand binds Cu(II) in a mixed mode in its CuB complex, in the CuAB species, it binds in a pyrocatechol-like mode. In all other systems, the binding modes of the ligands A and B in the CuAB species are similar to their binding in their respective binary systems. In the CuABH₂ species in the Cu(II)-cya-dopm and dopa systems, the two protons reside with the ɸ-phenolato oxygen atoms of the respective secondary ligands. The possible protonation sites in the other CuABH and CuABH₂ ternary complexes in this study are discussed.