Ion Polymer Interactions in DNA Solutions and Gels

摘要

Systematic investigations using small angle neutron scattering (SANS) were made to reveal the effect of calcium ions on the structure of DNA gels and solutions in near-physiological salt solutions. To describe the neutron scattering response two characteristic distances are required. The shorter length scale, R (≈10 A ?), was found to be governed by the geometry of the DNA chain and is close to the cross-sectional radius of the double helix. The longer length scale L corresponds to the mesh size of the network of overlapping polymer chains. L decreases with increasing DNA concentration as L ∝c_(DNA)~(-0.73). With increasing CaCl2 concentration both L and the scattering intensity increase. The increase in the scattering intensity re?ects the reduction of the osmotic modulus as the calcium ion concentration increases. The values of the osmotic modulus derived from osmotic swelling pressure measurements are in reasonable agreement with those obtained from SANS.