Synthesis, DNA interactions and antibacterial PDT of Cu(II) complexes of phenanthroline based photosensitizers via singlet oxygen generation

• Synthesis of biologically active Cu(II) mixed ligand metal complexes and their characterization.
• All the complexes exhibited efficient DNA groove-binding propensity.
• The complexes were able to cleave pUC19 DNA effectively via singlet oxygen generation.
• Screening of newly synthesized complexes as an antibacterial photosensitizer.

Cu(II) complexes [Cu(mqt)(B)H2O]ClO4(1–3) of 2-thiol 4-methylquinoline and phenanthroline bases (B), viz 1,10-phenanthroline (phen in 1), Dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and Dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3) have been prepared and characterized by elemental analysis, IR, UV–Vis, magnetic moment values, EPR spectra and conductivity measurements. The spectral data reveal that all the complexes exhibit square-pyramidal geometry. The DNA-binding behaviors of the three complexes were investigated by absorption spectra, viscosity measurements and thermal denaturation studies. The DNA binding constants for complexes (1), (2) and (3) were determined to 2.2 × 103, 1.3 × 104 and 8.6 × 104 M−1 respectively. The experimental results suggest that these complexes interact with DNA through groove-binding mode. The photo induced cleavage studies shows that the complexes possess photonuclease property against pUC19 DNA under UV–Visible irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. Antimicrobial photodynamic therapy was studied using photodynamic antimicrobial chemotherapy (PACT) assay against Escherichiacoli and all complexes exhibited significant reduction in bacterial growth on photoirradiation.

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