Duan Xiaozheng, Ding Mingming, Zhang Ran, Li Liangyi, Shi Tongfei, An Lijia, Huang Qingrong, Xu Wen-Sheng
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, P. R. China.
‡Department of Food Science, Rutgers University, 65 Dudley Road, New Brunswick, New Jersey 08901, United States.
J Phys Chem B. 2015 May 14;119(19):6041-9. doi: 10.1021/acs.jpcb.5b00515. Epub 2015 May 1.
We apply Monte Carlo simulation to explore the adsorption of a positively charged polyelectrolyte on a lipid monolayer membrane, composed of electronically neutral, monovalent anionic and mulvitalent anionic phospholipids. We systematically assess the influence of various factors, including the intrinsic rigidity of the polyelectrolyte chain, the bead charge density of the polyelectrolyte, and the ionic strength of the saline solution, on the interfacial structural properties of the polyelectrolyte/monolayer complex. The enhancement of the polyelectrolyte chain intrinsic rigidity reduces the polyelectrolyte conformational entropy loss and the energy gains in electrostatic interaction, but elevates the segregated anionic lipid demixing entropy loss. This energy-entropy competition results in a nonmonotonic dependence of the polyelectrolyte/monolayer association strength on the degree of chain rigidity. The semiflexible polyelectrolyte, i.e., the one with an intermediate degree of chain rigidity, is shown to associate onto the ternary membane below a higher critical ionic concentration. In this ionic concentration regime, the semiflexible polyelectrolyte binds onto the monolayer more firmly than the pancake-like flexible one and exhibits a stretched conformation. When the chain is very rigid, the polyelectrolyte with bead charge density Zb = +1 exhibits a larger tail and tends to dissociate from the membrane, whereas the one with Zb = +2 can still bind onto the membrane in a bridge-like conformation. Our results imply that chain intrinsic rigidity serves as an efficient molecular factor for tailoring the adsorption/desorption transition and interfacial structure of the polyelectrolyte/monolayer complex.
我们应用蒙特卡罗模拟来探究带正电的聚电解质在由电中性、单价阴离子和多价阴离子磷脂组成的脂质单层膜上的吸附情况。我们系统地评估了各种因素的影响，包括聚电解质链的固有刚性、聚电解质的珠子电荷密度以及盐溶液的离子强度，对聚电解质/单层复合物的界面结构性质的影响。聚电解质链固有刚性的增强减少了聚电解质构象熵的损失以及静电相互作用中的能量增益，但增加了分离的阴离子脂质混合熵的损失。这种能量 - 熵的竞争导致聚电解质/单层结合强度对链刚性程度呈现非单调依赖性。半柔性聚电解质，即具有中等链刚性程度的聚电解质，在高于临界离子浓度时会吸附到三元膜上。在这个离子浓度范围内，半柔性聚电解质比煎饼状柔性聚电解质更牢固地结合到单层上，并呈现伸展构象。当链非常刚性时，珠子电荷密度Zb = +1的聚电解质会出现较大的尾部并倾向于从膜上解离，而Zb = +2的聚电解质仍能以桥状构象结合到膜上。我们的结果表明，链固有刚性是调节聚电解质/单层复合物吸附/解吸转变和界面结构的有效分子因素。
