二维情况下两组分带电囊泡形变耦合相分离的理论模拟研究

Theoretical simulations of deformation coupling with phase separation of two-component charged vesicles in a two-dimensional plane

结合离散空间变分方法和耗散动力学研究了二维两组分带电囊泡的形变耦合相分离,系统地考察了囊泡带电量组分含量、带电组分的电荷密度、两组分间的相容性和温度等因素对形变耦合相分离动力学的影响.模拟结果表明电荷引入可增加不同组分间的表观相溶性.当温度较高时,静电相互作用可直接抑制囊泡相分离,避免了同种组分的团聚;当温度较低时,静电相互作用则可明显增加分相相区数目,使其呈微观相分离,从而避免了同种组分大范围的团聚.

The real bio-membranes are of multi-component, and they usually carry a certain quantity of charges. Therefore, it is of great biological significance to study charged multicomponent vesicles. However, the charged multi-component vesicles have been not yet systematically studied due mainly to the following two reasons： first, there are too many factors that will influence the behaviors of charged multi-component vesicles; second, theoretically it is difficult to deal with the phase separation of the multiple components from the Coulomb interaction of charged components at the same time. This work shows that the combination of the discrete-spatial variational method and dissipative dynamics can be used to address the above issues. For simplicity, we will consider only the deformation coupled with the phase separation of two-component charged vesicles in a two-dimensional plane rather than in three-dimensional space, which can present us more systematic research results. Besides, we have not considered the screening effects of counter ions or salts in this work, or equivalently we consider only the case where the screening length is relatively big. The charged vesicle is composed of two components A and B, where component A is negatively charged while component B is neutral. In particular, the charges on the vesicle can freely move in the membrane, which may be described by a time-dependent Ginzburg Landau equation. Initially, the two components are uniformly distributed on the vesicle.In this work, we specially focus on the influence of the electrostatic interaction on the compatibility of different components. It is found that introduction of charges will promote the apparent miscibility between different components. This could explain that the electrostatic interactions may contribute to the increase of the compatibility of different biomolecules in biological system. When temperature is relatively high, the electrostatic interaction will completely inhibit the phase separation which actually prevents the same component from being clustered. When temperature is relatively low, the electrostatic interaction will increase the number of phase domains, which actually turns the original macro phase separation into the micro one, thus reducing the cluster size. In this work, we also systematically study the influences of other factors, such as temperature, charge density of charged components, and the averaged concentration of charged component, on the final configuration of charged multicomponent vesicle. In particular, a phase diagram of the temperature and the averaged concentration of the charged component is obtained, and it is found that the number of phase domains will increase with the increase of charge density of component A. These conclusions are also qualitatively applicable to three-dimensional two-component charged vesicles.