Temperature-dependent DNA condensation triggered by rearrangement of adsorbed cations

A model is suggested explaining observed temperature-favored aggregation of DNA in the presence of Mn2+ salts. The interaction between DNA helices is described in terms of screened Coulomb forces and the entropy gain upon DNA aggregation is ascribed to Mn2+ repartitioning between binding sites in minor and major grooves. The model rationalizes both the observed force vs separation and entropy vs separation curves provided that the energy and entropy associated with transition of one Mn2+ ion from minor to major groove are DeltaE(ads)=3-5 k(B)T and DeltaS(ads)=2-5 k(B) correspondingly. Although these values appear to be reasonable, no experimental information that would allow their validation is presently available and other interpretations of the observed force curves cannot be excluded.