Phase separation between phospholipids and grafted polymer chains onto a fluctuating membrane

Abstract

We re-examine here the theoretical study of the phase separation between phospholipids and grafted long polymer chains onto a fluid membrane. The polymer chains are assumed to be anchored to the membrane by one extremity (anchor). The anchors are big amphiphile lipid molecules. The anchors and phospholipids forming the bilayer phase separate under the variation of a suitable parameter (temperature, pressure, membrane environment, ...). To investigate the demixtion transition, we elaborate a new approach that takes into account the membrane undulations. We show that these undulations have the tendency to induce additional attractive forces between anchors, and consequently, the separation transition is accentuated and occurs at high temperature. Quantitatively, we show that the membrane undulations contribute with an extra positive segregation parameter chi m > 0 , which scales as chi m approximately kappa(-2) , where kappa is the bending rigidity constant. Therefore, the attraction phenomenon between species of the same kind is significant only for those membranes of small bending rigidity constant. Finally, the study is extended to the case where the lengths of the anchored polymer chains are randomly distributed. To achieve calculations, we choose a length distribution of fractal form. The essential conclusion is that the polydispersity increases the size of domains alternatively rich in phospholipids and anchors.

Beyond the lipid-bilayer: interaction of polymers and nanoparticles with membranes

“…[30][31][32][33] Hydrophilic polymers, especially those bearing poly(ethylene oxides) (PEOs) or poly(oxazolines) (POZOs), can insert into membranes, resulting in ''mushroom''-or ''brush''-type decorations. 34 Charged polymers (polyelectrolytes) such as polycarboxylates or polyamines can adsorb onto oppositely charged lipid bilayers 35 producing lateral phase separation via electrostatically induced flip/flops. [36][37][38][39][40] Finally, membrane distortions can result if the interacting forces are larger than the bending modulus, visible in increased curvature of the membranes.…”

Organization of Lipid Molecules within Biomembranes

“…This extra contribution is the spatial integral of the induced attractive pair-potential between anchors, U(r). It was found [39,40] that the latter decreases with the distance as…”

“…[34], by considering, for simplicity, that the substrate is a planar surface. The problem was re-examined in a very recent work [39]. The main difference is that, in the new work, the infl uence of the membrane undulations on the LST is taken into account.…”

“…with the amplitude B H that is directly proportional to the inverse of the squared bending rigidity constant κ, that is B H ∝ κ −2 . Return to the additional interaction parameter χ m , and notice that it scales as [39]…”

“…In the previous work [39], the temperaturecomposition phase diagram has been drawn, and the effects of the polydispersity of grafted polymer chains on the LST have been studied. As shown in this work, the polydispersity increases the segregation parameter.…”