Data from: "Ion transport in carbon nanotube porins with a pH-switchable entrance gate"

Molecular transport in nanofluidic channels whose sizes approach molecular dimensions often differs drastically from conventional bulk transport. Strong confinement forces molecules in those channels into close proximity with channel walls, amplifying the roles of surface transport, surface defects, and molecular gates. Here we use defect-induced chemical etching (DICE) to introduce a defined chemical functionality at the nanotube rim that acts as a pH-triggered molecular gate by forming a movable lid that blocks the pore entrance. We use single channel ion and proton transport measurement to show that these sub-1-nm diameter fluorescent ultra-short carbon nanotube porins (FUNPs) are able to modulate ion transport by switching between the ``open'' and ``closed'' conformations of this molecular gate. Specifically, at neutral pH the channel lid is open, allowing virtually unimpeded ion transport through the gate, where as at the acidic pH values the lid forms a ``closed'' conformation that blocks transport through the nanotube. We also report first-principles MD simulations that confirm this gating mechanism and reveal further molecular details of the ion and proton transport processes in these functional nanopores.当纳米流体通道（nanofluidic channels）的尺寸接近分子尺度时，其中的分子输运过程往往与传统体相输运存在显著差异。极强的限域效应会使通道内的分子紧贴通道壁表面，从而放大了表面输运、表面缺陷与分子门控（molecular gates）的作用。本研究采用缺陷诱导化学刻蚀（defect-induced chemical etching, DICE）技术，在纳米管边缘引入特定化学官能团；该官能团可形成可移动的盖状结构以封堵孔道入口，进而作为pH触发型分子门控。本研究通过单通道离子与质子输运测量证实，这类直径小于1纳米的荧光超短碳纳米管孔蛋白（fluorescent ultra-short carbon nanotube porins, FUNPs）可通过该分子门控的“开放”与“闭合”构象切换调控离子输运。具体而言，在中性pH条件下，通道盖呈开放状态，离子可几乎无阻碍地通过该门控结构；而在酸性pH条件下，通道盖会形成闭合构象，阻断离子通过纳米管的输运。本研究还通过第一性原理分子动力学（MD）模拟验证了该门控机制，并进一步揭示了这类功能化纳米孔内离子与质子输运过程的分子层面细节。