Probing a self-assembledfdvirus membrane with a microtubule

Abstract

The self-assembly of highly anisotropic colloidal particles leads to a rich variety of morphologies, whose properties are just beginning to be understood. This article uses computer simulations to probe a particle-scale perturbation of a commonly studied colloidal assembly, a monolayer membrane composed of rodlike fd viruses in the presence of a polymer depletant. Motivated by experiments currently in progress, we simulate the interaction between a microtubule and a monolayer membrane as the microtubule "pokes" and penetrates the membrane face-on. Both the viruses and the microtubule are modeled as hard spherocylinders of the same diameter, while the depletant is modeled using ghost spheres. We find that the force exerted on the microtubule by the membrane is zero either when the microtubule is completely outside the membrane or when it has fully penetrated the membrane. The microtubule is initially repelled by the membrane as it begins to penetrate but experiences an attractive force as it penetrates further. We assess the roles played by translational and rotational fluctuations of the viruses and the osmotic pressure of the polymer depletant. We find that rotational fluctuations play a more important role than the translational ones. The dependence on the osmotic pressure of the depletant of the width and height of the repulsive barrier and the depth of the attractive potential well is consistent with the assumed depletion-induced attractive interaction between the microtubule and viruses. We discuss the relevance of these studies to the experimental investigations.

Chiral twist drives raft formation and organization in membranes composed of rod-like particles

“…As shown in previous work [39,40] based on phenomenological models, the difference in chirality between two coexisting phases, which favors different twist rates of viruses relative to membrane normals, is the primary driver of raft formation in viral membranes. When two achiral phases coexist, the interface separating them has a positive line tension (or surface tension in three dimensions) that favors the smallest possible interfacial length (or area).…”

“…These aforementioned theories are based on phenomenological Landau expansions in the concentration difference between the two chiral components (we show how our model can provide values for Landau coefficients in Supporting Information). Complementarily, Xie and colleages investigate raft-raft repulsion by directly minimizing the free energy of both raft and background [39]. They highlight the role of background chiral twist and use values for Frank constants (5 pN) and twist wavenumbers (∼3 µm −1 ) that are within an order of magnitude of those we use (Table I).…”

Chiral molecules on curved colloidal membranes

“…Since all the elastic moduli have the same dimension we will express them in units of K. Henceforth we use K ≡ 1 and K 24 /K ≡ K 24 . In the literature of colloidal membranes, Frank constant K has been estimated to be in the range 125 − 400k B T 20,21 , and using λ p ∼ 0.5µm, the strength of depletion interaction is C ∼ 500 − 1600 k B T /µm 2 . To compare them we note that the Frank energy density is of order (∇ m) 2 ∼ (local curvature) 2 ∼ 1/µm 2 .…”

Abelian decomposition and glueball-quarkonium mixing in QCD

“…Clearly there have been claims that f 2 (1270) and f 2 (1525) are the qq states as PDG suggests [80][81][82]. On the other hand, there have been assertions that they can be viewed as molecular states [83][84][85][86]. So we need more time to understand the physical contents of the 2 ++ states clearly.…”