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 (SnMe3)-Me-IV, (SnMe2)-Me-IV and Snn(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 Sn-119 Mossbauer studies on condensed DNA phases. The effects of tin-phosphate oxygen bonding on the DNA melting profile in DNA-(SnMe)-Me-IV 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 (SnMen)-Me-IV species, even in experimental conditions near the onset of DNA condensation. Gel electrophoresis indicates that DNA is not degraded by (SnMen)-Me-IV; 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 (SnMen)-Me-IV 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 (SnMen)-Me-IV compounds, even approaching DNA precipitation, suggests that the condensation process involves isolated DNA chains, Copyright (C) 2000 John Wiley & Sons, Ltd.