Multiple equilibria involved in some nickel(II) mixed ligand complex systems containing catecholic and dipeptide ligands

Multiple equilibrium studies on Ni-II-dopamine/dopa(A)-giycyl-L-tryosine an d L-tyrosylglycine(B) systems show the formation of NiABH(2), NiABH or NiAB mixed ligand complexes. The results indicate that dopa is ambidentate, i.e . in NIABH(2) species it binds the metal ion in a glycine-like mode, while it coordinates in a pyrocatecholic mode in NIABH and NiAB complexes. Dopami ne(A) binds in a pyrocatechol mode in its mixed ligand complexes. Both the dipeptide(B) ligands bind via N-amino and O-peptide groups in all the mixed ligand complexes.