Interactions of DNA with divalent metal ions. III. Extent of metal binding: Experiment and theory

Abstract

Abstract DNA with Mn 2+ as the only counterion has been prepared, and the extent of the Mn 2+ binding was determined under a variety of conditions through measurements of the proton relaxation enhancement of water. The total extent of Mn 2+ binding per DNA phosphate is found to be 0.43 ± 0.04, independent of the metal ion concentration in the experimental range of 2.8 × 10 −5 to 2.1 × 10 −3 M . The predictions of Manning's condensation theory and those obtained from solution of the generalized Poisson‐Boltzmann equation regarding the extent of divalent ion binding to polyelectrolytes, in the presence and absence of monovalent counterions, are compared with one another and with the experimental results. Good agreement between the two theoretical approaches is found, with less than 14% variance in the predicted extent of binding over a large range of mono‐ and divalent ion concentrations. While the predictions of both theoretical approaches generally agree with the experimental results, some discrepancies are noted and their possible origins discussed.