Organotin (2-amino-4-fluorobenzoates): Synthesis, characterization, DFT studies, DNA interaction and cleavage studies

Synthesis of organotin(IV) complexes of 2-amino-4-fluorobenzoic acid (AFA), namely C16H16F2N2O4Sn (1), C22H28F2N2O4Sn (2), C10H14FNO2Sn (3), and C25H20FNO2Sn (4), have been accomplished, and all complexes 1–4 have been characterized using various spectroscopic and analytical techniques, viz. FT–IR and NMR spectroscopy (1H, 13C and 119Sn), ESI–mass spectrometry and elemental analysis. DFT calculations revealed that complexes 1 and 2 exhibited bicapped tetrahedral geometry, while 3 and 4 exhibited distorted tetrahedral environments around tin. Intrinsic binding constants (Kb ≈ 105 M−1) for AFA and complexes 1–4 have been determined by performing UV–vis spectral titration with Calf thymus-DNA (CT-DNA). Further, AFA and complexes 1–4 are luminescent with Kb values of the order of 104 M−1. A significant shift is observed in the circular dichroism (CD) spectra of CT-DNA in the presence of AFA and organotin(IV) complexes 1–4. Based on the UV–vis, fluorescence, and CD studies, it is concluded that AFA and it’s all complexes 1–4 may interact with CT-DNA by minor/major groove binding or electrostatic interaction. Interestingly, triorgano-tin(IV) complexes 3 and 4 more efficiently cleave the supercoiled form (SC, I) into linear form (L, III) along with the nicked form (NC, II) as compared to complexes 1 and 2, and AFA.