Ionic distributions near polyelectrolytes. A comparison of theoretical approaches

Molecular Simulations of DNA Counterion Distributions

“…2 for the mixture of monovalent and divalent counterions with monovalent coins. [23] It is seen that for the given case (0.022 M MgCl 2 and 0.155 M NaCl mixture), the amount of divalent ions within 5 Å from the DNA surface in the PB approximation is underestimated by about 20%. In other cases (e.g., higher concentrations) deviations may reach 40% or even more.…”

“…[19,20] More systematic studies, with varying salt concentrations and/or ion type, have been carried out later. [21][22][23][24][25][26][27] The primary objective of these earlier computer simulation studies was to evaluate the applicability of analytical theories describing ionic distributions around DNA. In most of these works, the primitive model was used [i.e., the DNA was modeled as a hard body (cylinder) with a uniform distribution of surface charge, and the ions were represented as point charges or charged hard spheres].…”

“…In most of these works, the primitive model was used [i.e., the DNA was modeled as a hard body (cylinder) with a uniform distribution of surface charge, and the ions were represented as point charges or charged hard spheres]. In some of these works, a soft short-range ion-ion or ion-DNA interaction potential, [23] or a specific location of the charges on the polyion surface [22] has been used. The main outcome of the early simulations was that the PB approximation is generally valid if only monovalent ions are present in the solution.…”

Role and Applications of Electrostatic Effects on Nucleic Acid Conformational Transitions and Binding Processes

“…As such, PB mirrored MC-predicted distance-dependent changes in ion distributions. Murthy and coworkers (Murthy et al, 1985) noted that PB underestimates the local Na + concentration around an infinite polyion by about 15% relative to MC and hypernetted chain (HNC) calculations done between 1 -10 mM NaCl. However, PB, HNC, and MC predictions become indistinguishable at long distances from the DNA (~120 Å at 10 mM and ~360 Å at 1 mM NaCl) (Murthy et al, 1985).…”

“…Murthy and coworkers (Murthy et al, 1985) noted that PB underestimates the local Na + concentration around an infinite polyion by about 15% relative to MC and hypernetted chain (HNC) calculations done between 1 -10 mM NaCl. However, PB, HNC, and MC predictions become indistinguishable at long distances from the DNA (~120 Å at 10 mM and ~360 Å at 1 mM NaCl) (Murthy et al, 1985). Paulsen et al (1987) found that Γ values predicted by PB and MC calculations agree with experimental Donnan coefficients measured between 1 -31 mM DNA phosphate and 0.2 -111 mM NaCl.…”