Synthesis, characterization, catalytic, and biological studies of macrobicyclic binuclear nickel(II) complexes of 1,8-difunctionalized cyclam derivatives

Abstract

New Schiff base binuclear nickel(II) complexes of N-substituted cyclam derivatives have been prepared by template condensation of 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. The ligand possesses two coordination sites, an N₄O₂ amine compartment and N₃O₂/N₄O₂ imine compartment. The structural features of the complexes have been confirmed by elemental analysis, IR, UV–Vis, and mass spectra. From the data, octahedral geometry around the two nickels has been suggested. The electrochemical behavior of the complexes show two irreversible one-electron reduction process in the cathodic region and show two irreversible one-electron oxidation process at the anode. Hydrolysis of 4-nitrophenylphosphate using the complexes as catalysts have been carried out. Antimicrobial screening data show good results. The binding of the complexes to calf thymus DNA (CT DNA) has been investigated with absorption and emission spectroscopy. Ni₂L¹ displays significant cleavage of circular plasmid pBR322 DNA to linear form. Spectral, electrochemical, and catalytic studies support distortion of the nickel geometry that arises as the macrocyclic ring size increases.

Keywords:

• Cyclam
• Binuclear Ni(II) complexes
• Cyclic voltammetry
• Antimicrobial activity
• DNA binding and cleavage studies

Acknowledgment

Financial support from University Grants Commission, New Delhi, is gratefully acknowledged.

Notes

Present address: Department of Chemistry, Karpaga Vinayaka College of Engineering and Technology, GST Road, Chinna Kolambakkam, Palayanoor, Kancheepuram 603 308, India.