The B-DNA to Z-DNA transition in alkali and tetraalkylammonium salts correlated with cation effects on solvent structure.

The B-to-Z transition in DNA with alternating purine and pyrimidine sequences is driven by high concentrations of monovalent cations. In addition to screening of phosphate repulsion, an important factor may be the influence of ions on DNA hydration. The relative efficiencies of tetraalkylammonium and alkali metal salts in promoting the formation of Z-DNA, monitored by CD, in poly[d(G-C)] and poly[d(G-m5C)] was correlated with the degree to which the cations tie up water molecules in ordered arrangements and therefore decrease the availability of the solvent to hydrate DNA.