Interaction between macroions mediated by divalent rod-like ions

Abstract

Abstract. -Attractive interactions between identical like-charged macroions in aqueous multivalent salt solution arise due to ion-ion correlations. The mean-field level Poisson-Boltzmann (PB) theory does not predict such behavior for point-like structureless ions. Various multivalent ions, such as certain DNA condensing agents or short stiff polyelectrolytes, do have an internal, often rod-like, structure. Applying PB theory to the generic case of divalent rod-like salt ions, we find attraction between like-charged macroions above a critical distance between the two individual charges of the rod-like ions. We calculate this distance analytically within linearized PB theory. Numerical results for the non-linear PB theory indicate strong enhancement of the tendency to mediate attractive interactions.Introduction. -Poisson-Boltzmann (PB) theory is a widely used mean-field level method to calculate interactions between macroions in aqueous (salty) solutions. For monovalent salt, its predictions are generally found to agree well with experimental results and computer simulations. However, the presence of multivalent ions can affect the nature of the interactions between macroions in a way that qualitatively differs from the PB prediction. A remarkable example is the possibility of attraction between two identical, like-charged, macroions that the mean-field approach is unable to predict. This attraction currently receives much interest [1] because it is observed for a number of biologically relevant processes such as condensation of DNA [2], network formation in actin solutions [3], virus aggregation [4] and interactions between lipid membranes that occur during adhesion and fusion. Various theoretical approaches ascribe this attraction to the presence of ion-ion correlations [5,6]. An intuitive understanding of these correlations can be based on the formation of a periodic counterion arrangement in the vicinity of each macroion, similar to a Wigner crystal. The two inter-locked counteriondecorated macroions then experience short-ranged attraction.

The role of multipoles in counterion-mediated interactions between charged surfaces: strong and weak coupling

“…2, as was shown before [6,7,8]. Again this attractive contribution is obtained here on the mean-field level where the intercounterionic correlations, essential in the strong coupling limit, play no role.…”

“…The inclusion of structured counterions of a dipolar [5,6] and quadrupolar [7,8] type into the theory of electrostatic colloidal interactions has brought fourth some of the salient features of the counterion structure effects, which on face value appear to be quite distinct from the standard Poisson-Boltzmann framework. In view of these advances in the study of interactions between charged colloids it thus seems appropriate to explore the ramifications of the emerging paradigm if applied to these more complicated structured colloidal molecules.…”

Blood and Synovial Microparticles as Revealed by Atomic Force and Scanning Electron Microscope

“…However, biophysical methods that have recently been given attention point to nonspecific interactions and their origins [51][52][53]. We believe that approaches with different points of view will help to improve understanding of microvesiculation and related phenomena.…”

A field theoretic approach to the electric interfacial layer — Mixture of trivalent rod-like and monovalent point-like ions between charged walls

“…In real solutions, ions usually have an internal structure, with individually separated charges and with possibly additional rotational degrees of freedom. Charge correlations as a result of bonding between charges within an ion (e.g., the intraionic correlations induced by the fixed distance between charges in a rod-like ion) can be sufficient to change repulsive into attractive interaction between like-charged surfaces 18,19,22 . In these weak coupling studies, the rod-like ions carry a single elementary charge on each end.…”