Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125, China.
J Am Chem Soc. 2010 Feb 17;132(6):1873-7. doi: 10.1021/ja905753p.
The selective rate of specific ion transport across nanoporous material is critical to biological and nanofluidic systems. Molecular sieves for ions can be achieved by steric and electrical effects. However, the radii of Na(+) and K(+) are quite similar; they both carry a positive charge, making them difficult to separate. Biological ionic channels contain precisely arranged arrays of amino acids that can efficiently recognize and guide the passage of K(+) or Na(+) across the cell membrane. However, the design of inorganic channels with novel recognition mechanisms that control the ionic selectivity remains a challenge. We present here a design for a controllable ion-selective nanopore (molecular sieve) based on a single-walled carbon nanotube with specially arranged carbonyl oxygen atoms modified inside the nanopore, which was inspired by the structure of potassium channels in membrane spanning proteins (e.g., KcsA). Our molecular dynamics simulations show that the remarkable selectivity is attributed to the hydration structure of Na(+) or K(+) confined in the nanochannels, which can be precisely tuned by different patterns of the carbonyl oxygen atoms. The results also suggest that a confined environment plays a dominant role in the selectivity process. These studies provide a better understanding of the mechanism of ionic selectivity in the KcsA channel and possible technical applications in nanotechnology and biotechnology, including serving as a laboratory-in-nanotube for special chemical interactions and as a high-efficiency nanodevice for purification or desalination of sea and brackish water.
纳米多孔材料中特定离子选择性传输的速率对于生物和纳流系统至关重要。可以通过空间和静电效应来实现离子分子筛。然而，Na(+)和 K(+)的半径非常相似；它们都带有正电荷，这使得它们难以分离。生物离子通道包含精确排列的氨基酸阵列，能够有效地识别和引导 K(+)或 Na(+)穿过细胞膜。然而，设计具有新颖识别机制的无机通道来控制离子选择性仍然是一个挑战。我们在这里提出了一种基于单壁碳纳米管的可控离子选择性纳米孔（分子筛）的设计，该纳米孔内的纳米孔内修饰有特殊排列的羰基氧原子，灵感来自于跨膜蛋白（例如 KcsA）中钾通道的结构。我们的分子动力学模拟表明，这种显著的选择性归因于 Na(+)或 K(+)在纳米通道中受限的水合结构，通过羰基氧原子的不同图案可以对其进行精确调节。结果还表明，受限环境在选择性过程中起着主导作用。这些研究为理解 KcsA 通道中离子选择性的机制提供了更好的认识，并为纳米技术和生物技术中的可能技术应用提供了参考，包括作为特殊化学相互作用的纳米管内实验室以及作为海水和咸水净化或脱盐的高效纳米器件。
