Synthesis, spectroscopic characterization, X-ray structure and preliminary evaluation of DNA binding parameters of organotin "IV" dithiocarboxylates

Abstract

In the present study, a series of tri- chlorodi- and diorganotin(IV) dithiocarboxylates have been synthesized by the metathesis reaction oftri- and diorganotin(IV) chlorides with aryl substituted piperaziniumlpiperidinium salts of various dithiocarboxylates in dry methanol. The ligands used were 4-( 4-nitrophenyl)piperazine-l-carbodithioate (L), 4-(2-methoxyphenyl)piperazine- l -carbodithioate (L a), 4-( 4-methoxyphenyl) piperazine-l-carbodithioate (L b), 4-Benzhydrylpiperazine-l-carbodithioate (L C) and 4-Benzylpiperidinine- l -carbodithioate (L d). The coordination mode of ligands, structural confirmation and geometry assignment of the complexes in solid and in solution states were made, using different analytical techniques such as elemental analysis, Raman, FT-IR, multinuclear eH, 13C and 119Sn) NMR, mass spectrometry and X-ray single crystal analysis. Based on results, the ligand appeared to coordinate the Sn atom through CSS moiety. The triorganotin(IV) derivatives mostly demonstrate trigonal bipyramidal geometry both in solid and solution state with few exceptions with tetrahedral geometry in solution. For all chlorodiorganotin(IV) complexes, the ligands retain their solid state bidentate mode of chelation even in solution. Octahedral geometry was exhibited by all diorganotin(IV) dithiocarboxylates in solid state, however, the coordination around Sn alter from six to five in solution, in most cases. The interaction of R3SnL (where R = n-C4H9, C6HII and C6Hs), R2SnClL (R = n-C4H9 and C2Hs) and Ph2SnL2 with DNA were investigated by cyclic voltammetry (CV) and UV -Vis spectroscopy. The diffusion coefficient of the free and DNA bound complexes were determined by Randles-Sevcik equation. The positive peak potential shift in CV and hypochromic effect in spectroscopy evidenced intercalative mode of interaction of these complexes with DNA except for (n- C~9)2SnClL where electrostatic interaction was observed. The CV results revealed the following increasing order of binding strength: (C6Hll)3SnL (2.4 x 103 ) < (C6HS)3SnL (3.6 x 103 ) < (n-C4H9)2SnClL (5.4 x 103 ) < (n-C4H9)3SnL (6.9 x 103 ) < (C6Hs)2SnL (8.4 x 103 ) < (C2Hs)2SnClL (1.24 x 104) M-1 . The UV-Vis spectroscopic data also indicated the same order of binding strength. The negative values of ~G designate the spontaneity of complex-DNA binding. iii Some of the synthesized complexes were also screened for their antibacterial and antifungal activities against various medically important bacteria and fungi. The triorganotin(IV) derivatives have strong bactericidal and fungicidal action than chlorodi- and diorganotin(IV) complexes. Most of the compounds were found to have biological activity comparable to the reference drugs and some were found even more active. These observations suggest that these compounds may be used as bactericides and fungicides in future.