Abstract
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 Sn-119 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 K-b values of the complexes 1-3 were found to be 2.16 +/- 0.04 x 10(4), 3.47 +/- 0.04 x 10(4) and 4.60 +/- 0.04 x 10(3) 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 (H-1 and P-31 NMR) studies. (C) 2011 Elsevier B.V. All rights reserved.