Ali Naji
(Institute for Research in Fundamental Sciences, Iran)

 
Coulomb interactions contribute significantly to the effective forces that act between molecular constituents of life such as proteins, biopolymers and membranes. Macromolecular and other contact surfaces in the soft and biomatter contexts are often heterogeneously (or even randomly) charged and their interactions are mediated through aqueous Coulomb fluids that often contain highly charged species entailing statistical correlations and electrostatic surface couplings. Yet, electrostatic theories dealing with these systems mostly rely on textbook models where surface charge distributions are treated as uniform (or regularly patterned) and the surrounding Coulomb fluid is treated as a mean-field medium described by traditional Poisson-Boltzmann-type approximations. Non-mean-field effects become relevant especially when the Coulomb fluid involves multivalent ions. In this talk, I will discuss how the theoretical advances made in describing electrostatics of non-mean-field phenomena in the said contexts (e.g., formation of large bundles of like-charged biopolymers such as F-actin and microtubules and condensation of DNA in bulk and in viruses) have led to a major paradigm shift in the electrostatic theory of charged fluids where likes can attract, opposites can repel and net-neutral (albeit randomly charged) objects can do both. When strong electrostatic couplings transpire in the presence of quenched surface charge disorder, an otherwise standard electrical double layer can become antifragile and lose entropy upon increasing the disorder strength even as it becomes thermodynamically more stable.

 

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