New mixed-ligand Ni(II) and Zn(II) macrocyclic complexes with bridged (endo,endo)-bicyclo [2.2.1]hept-5-ene-2,3-dicarboxylate: Synthesis, characterization, antimicrobial and cytotoxic activity

Abstract

New carboxylate complexes of the tetraazamacrocyclic ligand N,N',N'',N'''-tetrakis(2-pyridilmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) with Ni(II) and Zn(II) as central ions were prepared. In mixed-ligand complexes (endo,endo)-bicyclo?2.2.1?hept-5-ene-2,3-dicarboxylate dianion (C9H8O4 2-) is also coordinated to metal ions. The complexes were characterized by elemental analysis (C, H, N), FTIR and UV?Vis spectroscopy, molar conductivity determination and magnetic susceptibility measurement at room temperature. The analytical data of the complexes show the formation of binuclear [Ni2(C9H8O4)tpmc](ClO4)2?4H2O and tetranuclear [Zn4(C9H8O4)(tpmc)2](ClO4)6? ?CH3CN?KClO4?4H2O complexes. In tetranuclear Zn(II) complex bicyclic dicarboxylate ligand is most likely to be bridge coordinated, and in binuclear Ni(II) complex it is coordinated in a combined bridged manner with chelate rings formation. In both complexes macrocyclic ligand was exo coordinated, out of cyclam ring and adopts a boat conformation. The Zn(II) complex is one of the rare tetranuclear Zn(II)-tpmc complexes with carboxylate ion bridging two Zn2tpmc units. The complexes were tested for antibacterial activity against Gram-positive bacteria Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (ATCC 6633), Gram-negative bacterium Escherichia coli (ATCC 25922), and yeast Candida albicans (ATCC 10231), and were screened for antiproliferative activity against human cervix adenocarcinoma (HeLa) and human myelogenous leukemia (K562) cell lines.