Generalized Poisson‐Boltzmann calculation of the distribution of electrolyte ions around the B‐ and Z‐conformers of DNA

A solution to the three‐dimensional Poisson‐Boltzmann equation, generalized to include the finite size of the ions, is presented for the environment of DNA in the B‐ and Z‐conformations. The results clearly indicate that despite the lower linear charge density of the left‐handed Z‐conformer, there is a higher concentration of Na+ at the immediate surface of the Z‐from than at the surface of the B‐form. The average concentration of counterions within a 12‐Å radius of the DNA is, nonetheless, higher for the B‐ than for the Z‐form. Calculations of the electrostatic interactions of these conformers with an environment of 0.01M monovalent salt show that the salt exerts a greater stabilizing effect on the left‐handed conformer than on the right‐handed form.