RESEARCH ARTICLE
Synthesis, Characterization of Mixed Cu(II) Pyridyl Tetrazoles and 1,10-Phenanthroline Complexes - DFT and Biological Activity

Mixed ligand copper complexes with 1,10-phenanthroline show good chemical nuclease activity and anticancer activity. Recently, tetrazole derivatives are also promising candidates for anticancer activity. Hence, it is significant to study the DNA binding and anticancer activity of two active N-donor ligands and their copper complexes.

The main objective of this study was to investigate the regioisomeric mixed ligand copper complexes response with calf thymus DNA binding and anti-toxic activity against MCF-7 cell line.

The DNA binding interactions of complexes 1-4 with calf thymus DNA (CT-DNA) were monitored by UV/VIS spectroscopy. The absorption spectra of the Cu complexes are compared with and without CT-DNA at 400-450 nm. The cell proliferation was measured by using the standard 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium- 5-carboxanilide (XTT) assay with four different concentrations of the compounds (5, 10, 50, and 100 mm) and cisplatin (as a positive control) was tested in triplicate for 48 h. The results obtained by the XTTassay are expressed as the average standard deviation of two experiments. The IC₅₀ values of the complexes exhibited differential and dose-dependent inhibitory activities on the growth of MCF-7 cancer cells.

Based on the elemental analysis, molar conductance, magnetic moments, mass, electronic, ESR and IR spectral data, the copper is coordinated by N-atoms of 1,10- phenanthroline and pyridyl tetrazole with octahedral structure. DFT calculations of HOMO and LUMO studies showed that electron density is localized on pyridyl tetrazole ring and phenanthroline ring. The calculated DNA binding constant (K_b) values of 1-4 complexes are in the range 4.2 - 7.6 x10⁴M^-1 (Table 4) with similar binding affinity to reported copper tetrazole derivative complexes. The 1-4 complexes with CT DNA interaction are through planar phenanthroline and pyridyl tetrazole ring likely via π-stacking interactions. The IC₅₀ values of complexes show excellent activity with 24(± 0.5); 18(± 0.5); 20(±0.5); (±0.5) and 38 (±0.8) for 1, 2, 3, 4 and cis platin complexes, respectively. After 72 h of the treatment of 1 on MCF-7 cell, IC₅₀ values hinder the cell growth upto 24(± 0.5) µg/ml at 5 µM concentration range (Fig. 5). It is apparent from IC₅₀ values that the order inhibition is 1 > 3 >2 > 4.

Experimental results are highly encouraging to explore the mixed ligand regio isomeric copper complexes which have shown the parallel result with Cisplatin. By proper structural modification of pyridyl tetrazole ligand, substituent better anticancer agents can be prepared.