Pharmacologically significant tetraaza macrocyclic metal complexes derived from isatin and 3,4-diaminobenzophenone: Synthesis, spectral studies and comparative in vitro biological assessment

Abstract

The 12-membered Schiff base macrocyclic complexes, [Dichloro [5,6;11,12-dibenzophenone-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene-2,3,8,9-diindole] metal(II) [M = Co(II), 1; Ni(II), 2; Cu(II), 3 and Zn(II), 4] were synthesized via template condensation of isatin and 3,4-diaminobenzophenone. These four complexes were characterized employing the analytical, spectral viz., FTIR, NMR, Mass, UV-Vis, EPR, TGA/DTA and SEM. The formation of metal complexes has been confirmed on account of the characteristic band positions in FTIR spectra and resonance signals in NMR spectra while the absorption bands in UV-Vis spectra and magnetic moment analysis signify the geometry of the complexes. However, the EPR study inferred distorted octahedral geometry in Cu(II) complex. The binding profile of the metal complexes (1–4) with CT-DNA was monitored by fluorescence and circular dichroism (CD) spectroscopy coupled with molecular docking studies. The binding constants were found to be highest for complex 3. Further, the hypothesis of preferential binding in the minor groove of double-stranded DNA is supported by CD and docking results. The antioxidative properties showed substantial radical scavenging potency of the complex 3. The comparative in vitro antibacterial study of the metal complexes against different pathogenic microbes (S. aureus, E. coli and C. albicans) revealed enhanced activity for complex 3 which is further certified by its efficacy to resist biofilm formation as investigated by XTT reduction assay. SYNOPSIS 12-membered Schiff base macrocyclic complexes (1–4) were synthesized via template condensation of isatin and 3,4-diaminobenzophenone and the binding mode of complexes with CT-DNA was divulged through the fluorescence and circular dichroism studies. Molecular docking studies are reported for complexes 3 and 4. In addition, the pharmacological efficacy of the newly synthesized complexes was explored by examining their antioxidant, antimicrobial, antibiofilm activities.