Synthesis, structural characterization, and DNA binding/cleavage studies of diorganotin(IV) carboxylates and their complexes with 1,10-phenanthro- line: X-ray structures of [Me8Sn4(p-FC6H4CO2)4O2], [Bu2Sn (p-NO2C6H4CO2)2.phen], and DFT studies

The present study is focused on the mode of DNA-interactions with diorganotin(IV) carboxylates and their 1,10phenanthroline (phen) complexes, and revealed that the planarity and extended pi system of phen may increase the probability of DNA intercalation. Diorganotin(IV) derivatives of p-fluoro-/p-hydroxy-/p-nitro benzoic acid, viz. Bu2Sn(p-XC6H4CO2)2: X = F (1), OH (2), NO2 (3), Oct2Sn(p-NO2C6H4CO2)2 (4), and Me8Sn4(pFC6H4CO2)4O2 (5), and their complexes with phen viz. Bu2Sn(p-XC6H4CO2)2.phen: X = F (6), OH (7), NO2 (8), Oct2Sn(p-NO2C6H4CO2)2.phen (9), and Me2Sn(p-FC6H4CO2)2.phen (10) have been synthesized and characterized by using various techniques including single crystal X-ray diffraction studies, nuclear magnetic resonance (1H, 13C, and 119Sn NMR), electrospray ionization mass spectrometry (ESI-MS), infrared (FT-IR), and elemental analysis. Based on crystal data, complexes (5) and (8) have a P-1 space group with a triclinic crystal system. In the octahedral geometry of complex (5), Sn atom has a tetranuclear Sn4O2 core, whereas complex (8) has a pentagonal bipyramidal geometry around Sn atom. The LanL2Z basis set has been employed for optimized gasphase geometries, and the calculated angle C-Sn-C bond angles agree with those obtained from NMR/X-ray studies. UV-visible, fluorescence and circular dichroism (CD) titrations showed interaction with Calf Thymus DNA (CTDNA), and Kb and KSV values in the order of 103-105 M-1 indicate intercalation within the base pairs or in minor groove. Further, gel electrophoreses studies indicate that all of the complexes have efficiently cleaved plasmid pBR322 DNA into three bands; supercoiled, nicked/circular along with linear structure. The intriguing biophysical results suggest that these complexes may have anticancer potential.