Rectification, the tendency of bidirectional ionic conductors to favor ion flow in a specific direction, is an intrinsic property of many ion channels and synthetic nanopores. Despite its frequent occurrence in ion channels and its phenomenological explanation using Eyring’s rate theory, a quantitative relationship between the rectified current and the underlying ion-specific and voltage-dependent free energy profile has been lacking. In this study, we designed nanopores in which potassium and chloride current rectification can be manipulated by altering the electrostatic pore polarity. Using molecular dynamics-based free energy simulations, we quantified voltage-dependent changes of free energy barriers in six ion-nanopore systems. Our results illustrate how the energy barriers for inward and outward fluxes become unequal in the presence of an electromotive driving force, leading to varying degrees of rectification for cation and anion currents. By establishing a direct link between potential of mean force and current rectification rate, we demonstrate that rectification caused by energy barrier asymmetry depends on the nature of the permeating ion, can be tuned by pore polarity, does not require ion binding sites, conformational flexibility, or specific pore geometry, and, as such, may be widespread among ion channels.

中文翻译：

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通过不对称纳米孔剖析电流整流


整流是双向离子导体倾向于在特定方向上促进离子流动的趋势，是许多离子通道和合成纳米孔的固有特性。尽管它经常出现在离子通道中，并且使用艾宁速率理论进行现象学解释，但整流电流与潜在的离子特异性和电压依赖性自由能分布之间一直缺乏定量关系。在这项研究中，我们设计了纳米孔，其中可以通过改变静电孔极性来操纵钾和氯电流整流。使用基于分子动力学的自由能模拟，我们量化了六个离子纳米孔系统中自由能垒的电压依赖性变化。我们的结果表明，在电动势存在的情况下，向内和向外磁通量的能量势垒如何变得不相等，从而导致阳离子和阴离子电流出现不同程度的整流。通过建立平均力电位和电流整流率之间的直接联系，我们证明了由能量势垒不对称引起的整流取决于渗透离子的性质，可以通过孔极性进行调整，不需要离子结合位点、构象柔韧性或特定的孔几何形状，因此，可能在离子通道中广泛存在。