Synthesis, spectroscopic characterisation, thermal analysis, DNA interaction and antibacterial activity of copper(I) complexes with N, N′- disubstituted thiourea

•Four novel binary and ternary copper(I) complexes of thiourea having general formulation [Cu(MTU)2Cl] (2, 5), [Cu(MTU) (B)Cl] (3, 6) where, MTU is 1-Benzyl-3-(4-methyl-pyridin-2-yl)-thiourea and 1-Benzyl-3-(6-methyl-pyridin-2-yl)-thiourea, B is a N,N-donor heterocyclic planar phenanthroline base, were synthesized, characterized by various spectroscopic methods.•The spectral data are in consistent with the proposed structures of Cu(I) complexes.•Complex 6 shows maximum DNA Cleavage activity. Hydroxyl radical was investigated to be the DNA cleavage active species.•All complexes show a profound antibacterial activity against both Gram-negative and Gram-positive bacteria.

copper(I) complexes [Cu(4MTU)2Cl] (2), [Cu(4MTU) (B)Cl] (3), [Cu(6MTU)2Cl] (5) and [Cu(6MTU) (B)Cl] (6) where 4MTU = 1-Benzyl-3-(4-methyl-pyridin-2-yl)-thiourea (1) and 6MTU = 1-Benzyl-3-(6-methyl-pyridin-2-yl)-thiourea (4), B is a N,N-donor heterocyclic base, viz. 1,10-phenanthroline (phen 3, 6), were synthesized, characterized by various physico-chemical and spectroscopic techniques. The elemental analysis suggests that the stoichiometry to be 1:2 (metal:ligand) for 2, 5 1:1:1 (metal:ligand:B) for 3, 6. X-ray powder diffraction illustrates that the complexes have crystalline nature. IR data coupled with electronic spectra and molar conductance values suggest that the complex 2, 5 show the presence of a trigonal planar geometry and the complex 3, 6 show the presence of a tetrahedral geometry about the Cu(I) centre. The binding affinity towards calf thymus (CT) DNA was determined using UV-Vis, fluorescence spectroscopic titrations and viscosity studies. These studies showed that the tested phen complexes 3, 6 bind moderately (in the order of 105 M−1) to CT DNA. The complex 2, 5 does not show any apparent binding to the DNA and hence poor cleavage efficiency. Complex 3, 6 shows efficient oxidative cleavage of plasmid DNA in the presence of H2O2 involving hydroxyl radical species as evidenced from the control data showing inhibition of DNA cleavage in the presence of DMSO and KI. The in vitro antibacterial assay indicates that these complexes are good antimicrobial agents against various pathogens. Anti-bacterial activity is higher when thiourea coordinates to metal ion than the thiourea alone.