New cobalt(II) and nickel(II) complexes of benzyl carbazate Schiff bases: Syntheses, crystal structures, in vitro DNA and HSA binding studies

•Syntheses of Co(II) and Ni(II) Schiff base complexes of benzyl carbazate with ketones.•Metal complexes have similar structural motif with same coordination environment.•Interaction of the complexes with CT-DNA/HSA was investigated using spectroscopic studies.•Complexes interact with CT-DNA via a partial intercalation mechanism.•Complexes quench the intrinsic fluorescence of HSA by a static quenching process.

In the present study, new Schiff base complexes with the composition [M(NCS)2(L1)2]·nH2O, where M = Co (n = 0) (1) and Ni (n = 2) (2); [M(NCS)2(L2)2], M = Co (3) and Ni (4) as well as [M(NCS)2(L3)2], M = Co (5) and Ni (6); (L1 = benzyl 2-(propan-2-ylidene)hydrazinecarboxylate, L2 = benzyl 2-(butan-2-ylidene)hydrazinecarboxylate and L3 = benzyl 2-(pentan-3-ylidene)hydrazinecarboxylate) have been synthesized by a template method. The complexes were characterised by analytical methods, spectroscopic studies, thermal and X-ray diffraction techniques. The structures of all the complexes explore that the metal(II) cation has a trans-planar coordination environment, the monomeric units containing a six-coordinated metal center in octahedral geometry with N-bound isothiocyanate anions coordinated as terminal ligands. Furthermore, the binding of the two Schiff base ligands to the metal centers involves the azomethine nitrogen and the carbonyl oxygen in mutually trans configuration. The binding interactions of all the complexes with Calf thymus-deoxyribonucleic acid (CT-DNA) and human serum albumin (HSA) have been investigated using absorption and emission spectral techniques. The CT-DNA binding properties of these complexes reveal that they bind to CT-DNA through a partial intercalation mode and the binding constant values were calculated using the absorption and emission spectral data. The binding constant values (~ 10 × 106 mol dm− 3) indicate strong binding of metal complexes with CT-DNA. HSA binding interaction studies showed that the cobalt and nickel complexes can quench the intrinsic fluorescence of HSA through static quenching process. Also, molecular docking studies were supported out to apprehend the binding interactions of these complexes with DNA and HSA which offer new understandings into the experimental model observations.

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