The Interaction of Deoxyribonucleic Acid with Methyltin(IV) Moieties in Solution Studied by Small-angle X-ray Scattering, Circular Dichroism and UV Spectroscopy

The nature of calf thymus DNA in aqueous solution, in the presence of the organotin(IV) species Sn IV Me 3 , Sn IV Me 2 and Sn IV Me, possibly partly hydrolysed and/or hydrated, was investigated by small-angle X-ray scattering (SAXS), ultraviolet spectroscopy (UV) at different temperatures and circular dichroism (CD). The results are compared with those of previous 119 Sn Mossbauer studies on condensed DNA phases. The effects of tin-phosphate oxygen bonding on the DNA melting profile in DNA-Sn IV Me systems are in agreement with previous reports on DNA-Main Group metal ion interactions. The structure and conformation of the DNA double helix are not influenced by Sn IV Me n species, even in experimental conditions near the onset of DNA condensation. Gel electrophoresis indicates that DNA is not degraded by Sn IV Me n ; the X-ray radii of gyration of the DNA cross-section and its mass per unit length, determined by SAXS from aqueous solutions, are constant and independent of the nature and concentration of the Sn IV Me n species present in the solutions. The invariance of the interparticle distances in solution at very low ionic strengths, in the presence of increasing amounts of Sn IV Me n compounds, even approaching DNA precipitation, suggests that the condensation process involves isolated DNA chains.