Unified Description of Electrophoresis and Diffusion for DNA and Other Polyions

Abstract

The electrophoretic mobilities and diffusion coefficients of single- and double-stranded DNA molecules up to 50,000 bases or base pairs in size have been analyzed, using mobilities and diffusion coefficients either measured by capillary electrophoresis or taken from the literature. The Einstein equation suggests that the electrophoretic mobilities (mu) and diffusion coefficients (D) should be related by the expression mu/D = Q/k(B)T, where Q is the charge of the polyion (Q = ze(o), where z is the number of charged residues and e(o) is the fundamental electronic charge), k(B) is Boltzmann's constant, and T is the absolute temperature. If this equation were true, the ratio mu/zD should be a constant equal to e(o)/k(B)T (39.6 V(-1)) at 20 degrees C. However, the ratio mu/zD decreases with an increase in molecular weight for both single- and double-stranded DNAs. The mobilities and diffusion coefficients are better described by the modified Einstein equation mu/N(m)D = e(o)/k(B)T, where N is the number of repeat units (bases or base pairs) in the DNA and m is a constant equal to the power law dependence of the diffusion coefficients on molecular weight. The average value of the ratio mu/N(m)D is 40 +/- 4 V(-1) for 36 single- and double-stranded DNA molecules of different sizes, close to the theoretically expected value. The generality of the modified Einstein equation is demonstrated by analyzing literature values for sodium polystyrenesulfonate (PSS). The average value of the ratio mu/N(m)D is 35 +/- 6 V(-1) for 14 PSS samples containing up to 855 monomers.

Do zwitterions contribute to the ionic strength of a solution?

“…2A. As shown by the open circles, the mobility of ds26 decreased progressively with increasing [TEA + Cl − ], in agreement with the results observed for DNA in other buffer/salt solutions [ 19,20 ]. However the mobility of ds26 was independent of the concentration of added tricine +/− , as shown by the solid circles in Fig.…”

Theory of capture rate in polymer translocation

“…For dilute solutions, the diffusion coefficient of the polyelectrolyte in sufficiently salty solutions obeys the StokesEinstein law, 28,29 …”

“…34,35 Since the volume occupied by the macromolecule is larger than the local volume within which the electroneutrality is maintained on an average, the hydrodynamic correlations among the polymer segments and the net movement of the polymer are coupled to those of the counterion cloud. Experimental data 29 on direct measurements of D and for different values of N have clearly demonstrated the inapplicability of the Einstein relation, Eq. ͑15͒, for the coupled polyelectrolytecounterion system.…”

On the importance of hydrodynamic interactions in polyelectrolyte electrophoresis

“…In an earlier publication this year [12], we compared the simulation results to experimental data for short PSS obtained by two different experimental methods, namely, capillary electrophoresis [8,20] and pulsed field gradient or electrophoretic NMR [21,22,23,24] 1 . In Figure 1 [ 11,25,26,27]. Here, the simulated data is normalized by D 0 = 0.052, the monomer diffusion as obtained by a power law fit, and the experimental data by the monomer diffusion coefficient of D 0 = 5.7 · 10 −10 m 2 /s.…”