Stability and structure of copper(II), nickel(II) and zinc(II) heterobinuclear complexes containing some biologically important ligands

Abstract

The stability constants of heterobinuclear complexes formed in aqueous solution for the biologically important ligands, viz., (i) dopa, (ii) dopamine (dopm) and (iii) <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-histidine(his) with Cu(II)-Ni(II), Cu(II)-Zn(ll) and Ni(II)-Zn(II) and (iv) <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-cysteine (cys) and (v) <img src='http://www.niscair.res.in/jinfo/smaller.gif' border=0>-penicillamine(pen) with Ni(II)-Zn(lI) have been evaluated by computer based analysis of the <i>p</i>H titration data. The binary systems Ni(II)/Zn(II)-dopa and dopm have also been studied. The heterobinuc1ear species of the types MAM' or MA₂M' have been detected with dopa, dopm, cys and pen ligands, while in the his ligand systems MA₂HM', MA₂M', MA₂H_-1M' and MA₂H_{- 2}M' mixed metal species have been found to be present. A qualitative attempt has been made on the comparison of the log b values, to study the Irving-Williams order of stabilities. The higher stabilities of mixed metal complexes over the mixed ligand system is also discussed.