COMPUTER-BASED STABILITY-CONSTANTS AND ABSORPTION MAXIMUM VALUES FOR THE COPPER(II) TERNARY COMPLEXES CONTAINING L-CYSTEIC ACID AND SOME SELECTED LIGANDS

The present paper deals with the determination of stability constants for sixteen ternary systems viz. Cu(II)-L-cysteic acid (cya) (A)-L-phe nylalanine (pha), dopamine (dopm), dopa, imidazole(Him), benzimidazole (Bimz), histamine(Hist), L-histidine(His), DL-2- aminobutyric acid(2ab a), DL-3-aminobutyric acid(3aba), 4- aminobutyric acid (4aba), DL-4-am ino-3-hydroxybutyric acid(ahba), 1,2-diaminopropane(dp), 1,3-diaminopr opane(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, CuAB(2), CuA BH or CuABH(2). Though dopa ligand binds Cu(II) in a mixed mode in its CuB complex, in the CuAB species, it binds in a pyrocatechol-like mod e. In all other systems, the binding modes of the ligands A and B in t he CuAB species are similar to their binding in their respective binar y systems. in the CuABH(2) species in the Cu(II)-cya-dopm and dopa sys tems, the two protons reside with the phi-phenolato oxygen atoms of th e respective secondary ligands. The possible protonation sites in the other CuABH and CuABH(2) ternary complexes in this study are discussed .