Carbon nanotube screening effects on the water-ion channels

Abstract

A self-consistent tight-binding method is used to investigate the screening effects of semiconducting and metallic single-wall carbon nanotubes ͑SWCNTs͒ when the water molecules and various charged ions pass through the nanotubes. The trajectories of ions and water molecules are obtained from molecular dynamics simulations. It is shown that metallic SWCNTs have much stronger screening abilities than semiconducting SWCNTs. Our results indicate that it is possible to distinctly identify different ions and also to differentiate between armchair and zig-zag nanotubes. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2963975͔ Carbon nanotubes ͑CNTs͒ have many exquisite properties that can be exploited to develop next generation devices with high sensitivity, fast response, low cost, and large volume production. 1,2 Recently, CNT membranes have been demonstrated as ultraefficient gas and liquid transporters. 3 The flow of a liquid on single-walled CNT ͑SWCNT͒ bundles has been shown to induce a voltage in the sample along the direction of the flow. 4 CNTs have been used for various sensing applications-for example, as chemical sensors for selective detection of nitrogen oxide ͑NO 2 ͒ and ammonia ͑NH 3 ͒. 5 Molecular dynamics ͑MD͒ simulations reveal that water and ions enter the hydrophobic interior of SWCNTs with a radius as small as a few nanometers by forming well-organized structures. 6 Despite many successful predictions by MD simulations, the nanotube models used in existing MD simulations provide an incomplete description of nanotube electrostatics as they ignore the nanotube polarizability. 7 SWCNTs can be semiconducting or metallic depending upon the tube diameter and the chirality. 8 Among the general chiral ͑n , m͒ CNTs with infinite lengths, all armchair nanotubes and those with n − m =3j ͑j being a nonzero integer͒ are metallic. All others are semiconductors with band gap inversely related to the diameter of the nanotube. Prior studies have investigated screening effects of CNTs under uniform parallel and transverse electric fields. [7][8][9][10][11] Semiconducting CNTs demonstrated significantly weaker screening compared to metallic CNTs. Relatively less efforts have been invested to study the polarizability and screening effects of CNTs under general electric fields generated by water dipoles and charged ions inside SWCNTs. In this paper, we investigate screening abilities of metallic and semiconducting SWCNTs when they are filled with water and various ions. The structure of water and ions inside the SWCNTs is obtained by performing MD simulations. The results from MD simulations are then used in tight-binding ͑TB͒ simulations to investigate the screening effects of metallic and semiconducting SWCNTs.A schematic of the system is shown in Fig. 1. Positively and negatively charged monovalent and divalent ions such as Ca 2+ , K + , Cl − , SO 4 2− , and NH 4 + together with water molecules, are transported from reservoir A to reservoir B through the CNT. We considered 5.3 nm long hydrogenterminated ͑10,...

Molecular dynamics simulation of nanoscale liquid flows

“…Xu and Aluru (2008) investigated the screening effects of semiconducting and metallic single-walled CNTs (SWCNTs) when the water molecules and various charged ions pass through the nanotubes. It is shown that metallic SWCNTs have much stronger screening abilities than semiconducting SWCNTs.…”

Tetrandrine protects mouse retinal ganglion cells from ischemic injury

“…Furthermore, Tet treatment resulted in a significant increase in RGC survival in vivo, with transient elevation of IOP, 1 day after I/R. The protective effects of Tet could involve multiple pharmacologic actions such as blocking the calcium influx, 3 , 4 inhibiting lipid peroxidation, 5 reducing the generation of ROS, 6 suppressing the production of cytokines and inflammatory mediators, and reducing neuronal apoptosis. 9 , 47 …”

“…Tetrandrine (Tet) is a bisbenzylisoquinoline alkaloid extracted from the root of the Chinese herb creeper Stephania tetrandra . 1 , 2 It is a calcium channel blocker 3 , 4 that inhibits lipid peroxidation 5 and the generation of reactive oxygen species (ROS) 6 and suppresses the production of cytokines and inflammatory mediators in the brain after ischemia reperfusion injury, 6 , 7 anoxia, 8 or Alzheimer’s disease. 9 Tet ameliorates amyloid-β(1–42)-induced spatial learning and memory impairment, and the beneficial effect of tetrandrine treatment may be linked to the inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activity and downregulation of interleukin-1β and tumor necrosis factor-α.…”

Detection of defective DNA in carbon nanotubes by combined molecular dynamics/tight-binding technique

“…[11][12][13] The possibility to detect and identify different charged ions translocating through CNTs has recently been reported. 14 Since DNA bases with backbones are negatively charged, the confinement of DNA inside CNT makes the detection of electrostatic signals generated by DNA bases possible. Furthermore, abnormal and normal DNA segments have different charge distribution, so it is also possible to differentiate them by measuring the electrical signals.…”

“…The screening ef-fects are computed by self-consistent tight-binding ͑TB͒ simulations. 15 Since semiconducting CNTs have much weaker screening ability than metallic CNTs, 14 we use semiconducting CNTs to obtain stronger electrical signals when DNA bases are present inside the CNT. The TIP3P model is used for the geometry and atomic charges of water molecules.…”