Interaction modes between asymmetrically and oppositely charged rods

Abstract

The interaction of oppositely and asymmetrically charged rods in salt-a simple model of (bio)macromolecular assembly-is observed via simulation to exhibit two free energy minima, separated by a repulsive barrier. In contrast to similar minima in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the governing mechanism includes electrostatic attraction at large separation, osmotic repulsion at close range, and depletion attraction near contact. A model accounting for ion condensation and excluded volume is shown to be superior to a mean-field treatment in predicting the effect of charge asymmetry on the free-energy profile.

Repulsion between oppositely charged rod-shaped macromolecules: Role of overcharging and ionic confinement

“…Theoretically, the repulsion between asymmetrically charged objects can be predicted by the non-linear Poisson-Boltzmann equation in planar 13,20 , spherical 13,14 and cylindrical geometries 36 . However, the prediction has been shown to be quantitatively inaccurate in the case of asymmetric cylinders studied here due to, e.g., the assumption of point like ions in the Poisson-Boltzmann equation 21 .…”

“…Studies on the interactions of oppositely charged objects [13][14][15][16][17][18][19][20][21] tend to be more rare than their like-charge counterparts [22][23][24][25][26][27][28][29][30] , possibly because of the intuitive preconception that oppositely charged objects always attract one another, and thus do not present interesting phase behavior. Indeed, many mean field theoretical approaches, like Debye-Hückel 31 or Derjaquin, Landau, Verwey, and Overbeek (DLVO) 32,33 theory, along with the common superposition approximation, predict an electrostatic attraction between oppositely charged objects, and screening by added electrolyte 34,35 .…”

“…Related simulations have been previously conducted on ions around a single charged rod [46][47][48] , and on two rigid cylinders carrying the same charge (motivated largely by the counterintuitive DNA-DNA condensation 24,25,28 and bundle formation 26,29,30 ). To our knowledge, prior studies on oppositely charged rod-like objects consist only of the PB study by Harries 36 and our recent work on asymmetrically charged rods at moderate concentrations of 1 : 1 micro ion electrolyte 21 . Here we extend our previous study to cover a wider range of parameters: we investigate asymmetrically charged rods in a z : z micro ion solution along with symmetrically charged rods in a z : 1 micro ion solution, and decipher the effects of finite rod and ion size.…”

Ability of the Poisson–Boltzmann equation to capture molecular dynamics predicted ion distribution around polyelectrolytes

“…All these effects in PE-ion systems, however, can be captured by particle level descriptions, such as Monte Carlo, or molecular dynamics (MD). Both, primitive numerical models in which the PEs are described as a rigid rod or a line charge with varying charge density 37,42,[48][49][50] and detailed all-atom simulations 20,46,51,52 have outlined the significance of chemistry specific effects via charge correlations. Specifically, the effect of ion species on the condensation of ions has been demonstrated in Refs.…”

Interaction of polymer-coated silicon nanocrystals with lipid bilayers and surfactant interfaces

“…In general, mesoscale colloidal interactions in complex fluids are a topic of considerable current interest [49][50][51][52][53][54][55][56][57][58]. Here, we present a photoluminescence-based study of the interaction between PEGylated SiNCs and two model interfaces of generic importance to soft matter and biological physics; water-in-oil emulsions to simulate the hydrophobic/hydrophilic interface and GUVs for the barest physical representation of a cell.…”