The ability of semipermeable membranes to selectively impede the transport of undesirable solutes is key to many applications. Yet obtaining a systematic understanding of how membrane structure affects selectivity remains elusive due to the insufficient spatiotemporal resolution of existing experimental techniques and the inaccessibility of relevant solute transport timescales to conventional molecular simulations. Here, we utilize jumpy forward-flux sampling to probe the transport of sodium and chloride ions through a graphitic membrane with sub-nanometer pores. We find chlorides to traverse the pore at rates over two orders of magnitude faster than sodiums. We also identify two major impediments to the transport of both ion types. In addition to the partial dehydration of the leading ion, its traversal induces charge anisotropy at its rear, which exerts a net restraining force on the ion. Charge anisotropy is therefore a crucial hidden variable controlling the kinetics of ion transport through nanopores.

半透膜选择性阻止不希望的溶质迁移的能力是许多应用的关键。然而，由于现有实验技术的时空分辨率不足以及相关溶质运移时标对于常规分子模拟的不可及性，因此对膜结构如何影响选择性的系统了解仍然遥遥无期。在这里，我们利用跳跃式前向通量采样来探测钠和氯离子通过具有亚纳米孔的石墨膜的传输。我们发现氯化物以比钠更快的两个数量级的速率穿过孔。我们还确定了两种离子类型传输的两个主要障碍。除了前导离子部分脱水外，其遍历还会在其后部引起电荷各向异性，对离子施加净抑制力。因此，电荷各向异性是控制离子通过纳米孔传输动力学的关键隐性变量。