MULTIPLE EQUILIBRIUM STUDIES ON SOME ZINC(II) MIXED-LIGAND COMPLEX-SYSTEMS

Multiple equilibrium studies involved in some Zn(II) ternary systems v iz. Zn(II)-L-cysteine (cys)/D-pencillamine (pen)/L-cysteic acid (cya) (A)-DL-2,3-diaminopropionic acid (dapa), DL-2,4-diaminobutyric acid (d aba) and DL-ornithine torn) (B) by the computer analysis of the pH tit ration data have shown the presence of ZnABH(2), ZnABH or ZnAB type te rnary species. The trends in the results demonstrate the possibility o f attachment of an extra proton in the ZnABH species to be with ligand (B). In the ZnABH, species, one proton resides with ligand (A) and th e other with ligand (B). The mode of coordination of cys, pen, dapa, d aba and orn ligands in the ZnAB type species is similar to their coord ination in the corresponding binary species. However, in the ZnAB and ZnABH species in the Zn(II)-cya(A)-dapa, daba and orn (B) systems, cya (A) ligand binds the metal in a glycine-like mode though it is monode ntate in its ZnA and ZnA, binary species.