Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai, China.
J Phys Chem B. 2011 Apr 28;115(16):4768-73. doi: 10.1021/jp2025297. Epub 2011 Apr 5.
On the basis of molecular dynamics simulations, we investigate water permeation across a single-walled carbon nanotube (SWCNT) under the influence of four symmetrical half-rings, each having six LiF dipolar molecules. The flux remains almost fixed as the separation, R, between the rings and SWCNT is larger than 1.562 nm, but decreases significantly as 0.944 nm < R < 1.562 nm, and reaches zero as R < 0.944 nm. This nanochannel shows an excellent on-off gate that is both effectively resistant to dipole noises and sensitive to available signals. The finite element method reveals that the electrostatic field generated by LiF molecules plays a unique role in achieving the gating of the water SWCNT. Each water molecule tends to stay at the most stable state by moving to the location with the highest field strength in order to maintain its lowest electric energy. These findings may have biological implications because membrane water nanochannels made up of proteins accompanied with co-ions and counterions (due to ionization) share a similar single-file water chain inside the SWCNT with dipoles. The Appendix shows a possible link between the model system and a membrane water nanochannel with co-ions and counterions. Furthermore, our observations may have significance for the design of SWCNT-based nanoscale devices with dipolar molecules.
基于分子动力学模拟，我们研究了在四个对称半环的影响下，每个半环有六个 LiF 偶极分子穿过单壁碳纳米管 (SWCNT) 的水渗透。当环和 SWCNT 之间的间距 R 大于 1.562nm 时，通量几乎保持不变，但当 0.944nm<R<1.562nm 时，通量显著下降，当 R<0.944nm 时，通量降为零。这个纳米通道显示出极好的开关特性，既能有效抵抗偶极噪声，又能对可用信号敏感。有限元方法揭示了 LiF 分子产生的静电场在实现水 SWCNT 的门控方面起着独特的作用。为了保持最低的电能，每个水分子都倾向于移动到电场强度最高的位置，以保持其最稳定的状态。这些发现可能具有生物学意义，因为由蛋白质组成的膜水纳米通道伴随着共离子和反离子（由于电离）在 SWCNT 内共享类似的单链水链和偶极子。附录显示了模型系统与带有共离子和反离子的膜水纳米通道之间的可能联系。此外，我们的观察结果可能对基于 SWCNT 的纳米级设备与偶极子的设计具有重要意义。
