Palladium-mediated C–O bond activation of benzopyrone in 4-oxo-4H-chromone-3-carbaldehyde-4(N)-substituted thiosemicarbazone: synthesis, structure, nucleic acid/albumin interaction, DNA cleavage, antioxidant and cytotoxic studies

Abstract

Palladium ion-mediated C–O activation at the C2 carbon of the benzopyrone moiety of 3-formylchromone-4(N)-substituted thiosemicarbazone (HL^1–4) has been observed in square-planar palladium(II) complexes. All the complexes were characterised by IR, electronic, ¹H-NMR, ¹³C-NMR and ESI mass spectroscopy. Further, the structure of complex 3 was confirmed by single-crystal X-ray diffraction studies, which revealed the monobasic bidentate coordination of the ligand to the palladium(II) ion using thiolic sulphur and pyrazole nitrogen N(1) atoms. The binding ability of the complexes (1–4) with calf thymus (CT-DNA) and Bovine Serum Albumin (BSA) was studied by UV-Vis and fluorescence spectroscopy. Moreover, the complexes cleaved supercoiled DNA pBR322 without the addition of any external agents. The complexes were tested for their antioxidant activity and were found to exhibit significant activity. The cytotoxic nature of the complexes was investigated against MCF-7, A549, NCI-H460, L132 cell lines and demonstrated significant growth inhibition against cancer cells. Cytological observations using an inverted phase-contrast microscope and AO/EB dual staining assay exhibited the typical apoptotic morphology of cancer cells upon treatment with complexes 2 and 3. It can thus be suggested that complexes 2 and 3 are modulated by apoptosis.