Mixed ligand complexes of nickel(II) with imidazoles and some dipeptides

The computer based analysis of the pH titration data in the Ni(II)-imidazole (him)/histamine (hist)/L-histidine(his) (A)glycyl-l-phenylalanine(glyphe), glycyl-l-tyrosine(glytyr) and L-tyrosylglycine (tyrgly) (B) systems shows the presence of NiAB, NiABH(-1), NiA(2)B or NiAB(2) mixed ligand species. The results demonstrate that him, hist and his(A) are respectively mono-, bi- and tri-dentate and the dipeptide(B) ligands are bidentate in NiAB, NiA(2)B and NiAB(2) complexes. The amide deprotonated dipeptide (BH-1) appears to bind in a tridentate mode in the NiABH(-1) species in the him(A) systems, while the trends in results clearly demonstrate the bidentate binding of (BH-1) in the hist/his(A) mixed ligand systems.