Phase phenomena in supported lipid films under varying electric potential
Phase phenomena in supported lipid films under varying electric potential
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DOI：
10.1039/c0sm00724b
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发表时间：
2011-01-01
期刊：
影响因子：
3.4
通讯作者：
Auer, Stefan
中科院分区：
文献类型：
--
作者：
Brukhno, Andrey V.;Akinshina, Anna;Auer, Stefan
我们支持的脂质膜上的循环伏安法实验模型的电容上施加的电压的一个非平凡的依赖性被观察到。以前，基于Flory-Huggins类型的平均场处理，在强屏蔽静电相互作用的假设下，已经假设电容-vs.-电压分布对应于吸附膜内的结构或相变序列。为了检验这一假设，在这项研究中，我们使用平均场计算和蒙特卡罗模拟，由于不同的电势和盐的存在下的静电效应明确占。我们的主要重点是对膜的结构和解吸-再吸附现象。这些被发现是由脂烃尾部和电极反离子（阳离子）之间的逐步充电（疏水）表面的强烈竞争所驱动的。随着表面电荷密度的升高，在界面内清楚地观察到以下现象：（i）通过抗衡离子使单层从表面逐渐位移，导致完全的单层脱附并通过表面形成双电层，（ii）在其脱附时单层转化为双层，（iii）在两性离子（或强极性）脂质头部基团的情况下，解吸之后是通过与双电层的相互作用双层再吸附到电极上，并将过量的抗衡离子释放到本体溶液中。然后，我们认为，伏安峰与形成交替电荷层的逐步过程：双电层-膜解吸，三层或多层-膜readsoption。
We model cyclic voltammetry experiments on supported lipid films where a non-trivial dependence of the capacitance on the applied voltage is observed. Previously, based on a mean-field treatment of the Flory-Huggins type, under the assumption of strongly screened electrostatic interactions, it has been hypothesized that peaks in the capacitance-vs.-voltage profiles correspond to a sequence of structural or phase transitions within the adsorbed film. To examine this hypothesis, in this study we use both mean-field calculations and Monte Carlo simulations where the electrostatic effects due to the varying electric potential and the presence of salt are accounted for explicitly. Our main focus is on the structure of the film and the desorption-readsorption phenomena. These are found to be driven by a strong competition for the progressively charged-up (hydrophobic) surface between lipid hydrocarbon tails and the electrode counterions (cations). As the surface charge density is raised, the following phenomena within the interface are clearly observed: (i) a gradual displacement of the monolayer from the surface by the counterions, leading to complete monolayer desorption and formation of an electric double layer by the surface, (ii) a transformation of the monolayer into a bilayer upon its desorption, (iii) in the case of zwitterionic (or strongly polar) lipid head groups, the desorption is followed by the bilayer readsorption to the electrode via interaction with the electric double layer and release of the excess counterions into the bulk solution. We argue then that the voltammetry peaks are associated with a stepwise process of formation of layers of alternating charge: electric double layer - upon film desorption, triple or multi-layer - upon film readsoption.