Effect of spatial inhomogeneity in dielectric permittivity oar DNA double layer formation

In solutions of tetramethylammonium (TMA(+)) DNA (double stranded) without added low-molecular-weight salt, the counterion radial density is calculate d using the cylindrical Poisson-Boltzmann equation with a distance-dependen t quasimacroscopic dielectric permittivity. Comparisons with small-angle ne utron scattering data indicate that any inhomogeneity in dielectric permitt ivity is confined to one or two solvent layers from the DNA surface. At fea st for TMA(+), which may be too large to penetrate the grooves of DNA to an y significant extent, dielectric inhomogeneity modeled in this way has no d etectable effect on the radial distribution.