Influence of defects on the electrophoretic, thermodynamic and dielectric properties of a 21 base pair DNA in solution.

The thermodynamic and dielectric properties of a 21 base pair DNA have been evaluated and compared with those of samples with some defects. In particular, fragments in which the absence of a phosphate group (nick) or of two nucleotides (gap) causes chain interruptions were studied. Measurements of ultraviolet absorption as a function of temperature at different oligomer concentrations and at various ionic strengths were performed. Dielectric spectroscopy at radiofrequencies (1 MHz-1 GHz) was applied on aqueous solutions of the duplexes at 5 degrees C, where the solutes are thermally stable. Dielectric dispersions with 30-40 MHz characteristic frequencies were defined. The results of melting experiments indicate a thermal destabilization of the oligomers containing the defects. Electrophoretic data and the dielectric results show that the conformations of the nicked and control samples are very similar, while the oligomer with a gap is more compact with a different charge distribution at the ends.