Interfacial solvation can explain attraction between like-charged objects in aqueous solution

Abstract

Over the past few decades the experimental literature has consistently reported observations of attraction between like-charged colloidal particles and macromolecules in solution. Examples include nucleic acids and colloidal particles in bulk solution and under confinement, and biological liquid-liquid phase separation. This observation is at odds with the intuitive expectation of an interparticle repulsion that decays monotonically with distance. Although attraction between like-charged particles can be theoretically rationalised in the strong-coupling regime, e.g., in the presence of multivalent counterions, recurring accounts of long-range attraction in aqueous solution containing monovalent ions at low ionic strength have posed an open conundrum. Here we show that the behaviour of molecular water at an interface -traditionally disregarded in the continuum electrostatics picture -provides a mechanism to explain attraction between like-charged objects in a broad spectrum of experiments. This basic principle will have important ramifications in the ongoing quest to better understand intermolecular interactions in solution.

Diffusion and Viscosity of Unentangled Polyelectrolytes

“…A possible explanation for the observed high-concentration dynamics could be a slowdown in the solvent diffusion with increasing polymer concentrations. This phenomenon has been observed for many polymer–solvent systems and might be particularly strong for polyelectrolytes due to the ordering of water around the ionic groups. − In this scenario, the scaling laws outlined in Section 2.1 need to be applied with β­( c ) > η s . Mackie et al’s obstruction model expects the solvent diffusion coefficient ( D s ) to depend on the polymer volume fraction (ϕ) as Equation has been shown to correctly describe the dependence of D s on polymer concentration for many polymer–solvent pairs, including polyelectrolytes .…”

Systematic optimization of a fragment-based force field against experimental pure-liquid properties considering large compound families: application to oxygen and nitrogen compounds

“…The latter restriction could for example be alleviated by using a more general EE scheme 8 (see Conclusion section therein) involving damped charge transfers throughout the entire molecule, applied with a smooth atom-based truncation of the non-bonded interactions in the simulations. 152 Efforts are currently in progress along these different lines.…”

Local structure of DNA toroids reveals curvature-dependent intermolecular forces

“…The electrostatic forces between helices may turn from repulsive to attractive thanks to the presence of high-valence cations such as spermine (4+) and spermidine (3+) or small proteins such as protamines and H1 histones [17][18][19][20]. Several theoretical accounts of these effects have been proposed, suggesting that the hydration forces [21][22][23], ion chemisorption [24], structuring of the ion clouds [25,26] or bridging [27][28][29] may all play a role in the effective DNA-DNA attraction, although no consensus exists as to their relative contributions.…”