Sedimentation, diffusion, and osmotic pressure of sodium DNA in salt‐free solution

Abstract

SynopsisThe osmotic, sedimentation, arid diffusion coefficients of sonicated sodium DNA in aqueous solutions which were rendered rigorously free of salts have been obtained iii order to study the polyelectrolyte effect on these parameters. Both native and heatdenatured DNA's were studied. All three parameters were forind to be independent of concentration between 2 and 10 mmole/l. The osmotic coefficient gives the fraction of counterions not immobilized by the polyelectrolyte potential, under conditions of equilibrium. The value (ca. 0.18) obtained for this fraction agrees very well with that, predicted by a theory of rodlike polyelectrolytes. A simplified model that permits the computation of fractions of mobile ions from sedimentation and diff iision coefficients, when applied to the experimental data, showed t,hat tinder these conditions of flow between 0.5 to 0.9 of counterions are not, immobilized. The experimental dat,a also showed that for native DNA the translation frictional coefficient seems to have different values in sedimentation and diffusion, which agrees with a finding reported for another saltfree polyelectrolyte. For denatured DNA, however, the valiies were found to be equal; no satisfactory explanation coiild be found for this difference of behavior.

Effective charge saturation in colloidal suspensions

“…15, the corresponding results for the osmotic coefficient are confronted against the experimental data of Refs. [50,51] for various ionic strengths, showing again a good quantitative agreement. As in Ref.…”

“…For completeness, we compare in what follows our estimate for the osmotic pressure to the experimental results on B-DNA solutions reported in [50,51]. In this work, the authors measured the osmotic coefficient φ = Π osm /Π c , defined as the ratio between the osmotic pressure Π osm to the pressure Π c of releasable counter-ions having bare density c c (Π c = k B T c c ) against the concentration of B-DNA, a rigid cylindrical polyelectrolyte.…”

“…The dots are the experimental points obtained from Refs. [50,51], while the solid lines correspond to the predictions for φ using our prescription in cylindrical geometry. The dashed line is the prediction of Oosawa-Manning condensation theory.…”

The osmotic coefficient of rod-like polyelectrolytes: Computer simulation, analytical theory, and experiment

“…10,17 Possible reasons for this shortcoming may be related to the two state model or the random phase approximation employed in Ref.. 36 …”

“…A great number of experimental studies of φ for strongly charged polyelectrolytes is now available in literature, demonstrating that φ is of the order of 0.2 to 0.3 for univalent counterions in the dilute regime. [1][2][3][10][11][12][13][14][15][16][17] Furthermore, a comparison of experimental data obtained for different counterions show that specific interactions between counterions and the macroion can lead to an additional reduction of the measured osmotic pressure. 1,3 In case of monovalent counterions, these specific effects are small as compared to the effect of counterion condensation that presents the dominant feature of strongly charged polyelectrolytes.…”