In vitro binding studies of organotin(IV) complexes of 1,2-bis(1H-benzimidazol-2-yl)ethane-1,2-diol with CT-DNA and nucleotides (5′-GMP and 5′-TMP): Effect of the ancillary ligand on the binding propensity

The chiral benzimidazole ligand, 1,2-Bis(1H-benzimidazol-2-yl)ethane-1,2-diol, L, exhibiting coordination mode with an oxygen atom of alcohol group directed towards the metal ion and another –OH group with different molecular axis directed away from the metal center was utilized as a building block for organotin complexes [C18H19N4O2SnCl], [C28H23N4O2SnCl] and [C52H42N4O2Sn2] (1–3). Complexes 1 and 3 exhibit a pentacoordinate geometry while the complex 2 reveals hexacoordinated environment around the Sn(IV) metal ions as evidenced by 119Sn NMR studies. The DNA binding ability of benzimidazole ligand and their organotin(IV) complexes 1–3 were examined by employing different biophysical methods. The absorption titration of the complexes with CT-DNA reveal significant hyperchromic effect together with strong bathochromic shift of 4–5 nm which infer substantial binding of the complexes with CT-DNA. The intrinsic binding constant Kb values of the complexes 1–3 were found to be 2.16 ± 0.04 × 104, 3.47 ± 0.04 × 104 and 4.60 ± 0.04 × 103 M−1, respectively, suggesting pronounced binding of complex 2 with DNA double helix. The mechanism of binding of the complexes was further ascertained by the interaction studies of these complexes with nucleotides (5′-GMP and 5′-TMP) using absorption spectroscopy suggesting a clear preference for 5′-GMP binding which was further authenticated by NMR (1H and 31P NMR) studies.