Charge-signal multiplication mediated by urea wires inside Y-shaped carbon nanotubes

Abstract

In previous studies, we reported molecular dynamics (MD) simulations showing that single-file water wires confined inside Y-shaped single-walled carbon nanotubes (Y-SWNTs) held strong and robust capability to convert and multiply charge signals [Y. S. Tu, P. Xiu, R. Z. Wan, J. Hu, R. H. Zhou, and H. P. Fang, Proc. Natl. Acad. Sci. U.S.A. 106, 18120 (2009); Y. Tu, H. Lu, Y. Zhang, T. Huynh, and R. Zhou, J. Chem. Phys. 138, 015104 (2013)]. It is fascinating to see whether the signal multiplication can be realized by other kinds of polar molecules with larger dipole moments (which make the experimental realization easier). In this article, we use MD simulations to study the urea-mediated signal conversion and multiplication with Y-SWNTs. We observe that when a Y-SWNT with an external charge of magnitude 1.0 e (the model of a signal at the single-electron level) is solvated in 1 M urea solutions, urea can induce drying of the Y-SWNT and fill its interiors in single-file, forming Y-shaped urea wires. The external charge can effectively control the dipole orientation of the urea wire inside the main channel (i.e., the signal can be readily converted), and this signal can further be multiplied into 2 (or more) output signals by modulating dipole orientations of urea wires in bifurcated branch channels of the Y-SWNT. This remarkable signal transduction capability arises from the strong dipole-induced ordering of urea wires under extreme confinement. We also discuss the advantage of urea as compared with water in the signal multiplication, as well as the robustness and biological implications of our findings. This study provides the possibility for multiplying signals by using urea molecules (or other polar organic molecules) with Y-shaped nanochannels and might also help understand the mechanism behind signal conduction in both physical and biological systems.

From dimers to collective dipoles: Structure and dynamics of methanol/ethanol partition by narrow carbon nanotubes

“…We envision two types of applications: nano-filtering appliances for polar molecules and signal-amplification devices that can take advantage of the strong dipolar alignment; indeed, such constructs have been previously explored by other authors. [69][70][71] Even though all evidence indicate that electrostatic interactions rising from nanotube polarization are rather weak, 65 the persistent dipoles formed by the collective arrangement of single-file alcohols, e.g., (7,7) methanolloaded tube might lead to an instantaneous axial polarization of the tube, e↵ect that is not accounted in our current model. We are currently implementing a polarizable carbon nanotube model that in conjunction with (an already developed) polarizable methanol force-field 68 will serve to assess polarization e↵ects of confined alcohols within SWCNTs.…”

Selective Transport through the Ultrashort Carbon Nanotubes Embedded in Lipid Bilayers

“…Interestingly, we observe that these two ranges are supplementary, which implies the flipping of DMSO wires (the orientations of DMSO dipoles turn upward to downward). This remarkable phenomenon is of great importance and is related to the signal transduction , in biological applications that need further exploration.…”

Manipulating the Flipping of Water Dipoles in Carbon Nanotubes*

“…Using the same method, Lv et al replaced the water molecules in the Y-shaped CNTs with other polar molecules (urea), and achieved the similar results. [14] These previous studies demonstrate that water and small polar molecules confined in the CNTs can form a concerted single-file chain, and they then collectively flip. Furthermore, the flipping of these dipoles can be manipulated by external charges.…”