Synthesis, calf-thymus DNA interaction with trimethyl-/triphenyl-tin(IV) derivatives of ɑ-lipoic acid and their mixed ligand complexes with N-donor (1,10-phenanthroline/2,2′-bipyridyl/benzimidazole)

Abstract

The mixed ligand complexes of trimethyl-/triphenyl-tin(IV) derivatives of ɑ-lipoic acid (HLA), viz. R3Sn(LA) {R = Me (1), and Ph (2)}with 1,10-phenanthroline (phen), viz. [Me3Sn(LA).phen] (3), 2,2′-bipyridyl, viz. [Ph3Sn(LA).by] (4) and benzimidazole (bz), viz. [R3Sn(LA).bz] {R = Me (5), and Ph (6)} were synthesised and satisfactorily characterized by analytical and spectroscopic techniques, especially FT-IR, NMR (1H, 13C, and 119Sn NMR) spectroscopy and ESI-MS spectrometry. The ∠C-Sn-C bond angle calculated by optimization of their gas-phase geometry revealed that complexes (1) and (2) have distorted tetrahedral geometry and complexes (3) and (4) exhibited distorted octahedral geometry while complexes (5) and (6) exhibited trigonal bipyramidal environment around the tin, which agreed with the data obtained from NMR. Spectroscopic titrations (UV–visible absorption, fluorescence titration, and circular dichroism) were performed to ascertain the binding mode of the complex with calf thymus DNA (CT-DNA). The obtained values of Kb in the order of 105 M−1 suggested partial intercalative interactions of complexes with DNA grooves/base pairs. The complexes efficiently cleaved plasmid DNA (pBR322) into supercoiled (Form I), nicked/circular (From II), and linear structure (Form III). The fascinating biophysical data suggests the potential of these complexes as anticancer agents.