Mechanism of water permeation through modified carbon nanotubes as a model for peptide nanotube channels

It is of interest to explore transfer of fluid through nanopores because of widespread applications for such systems. Carbon Nanotubes (CNTs) with their exceptional properties are the best candidates as building blocks for nanostructures. Water transfer in lots of biological systems acts as an important role for keeping the tissue working properly. Peptide nanotube is one of the best biological channels which was proposed recently. While the mechanism of water permeation through channels is very complex, however, investigations such as effect of charge distributions and temperature on water permeation could shed light on the determinants of water and proton conduction rates in biological water channels. A neutral and two different charge-distributed CNTs have been used to investigate the effect of charge distribution on water permeation as well as investigation of the mechanism of water permeation through them. The charge distribution on CNTs is in accordance with peptide nanotube channels. We have investigated both the osmotic and diffusion permeations in two possible model systems, We have applied a pressure gradient (about 0.12-0.14 MPa/13.4 angstrom) on the systems for applying a chemical potential difference to explore the osmotic permeation. The diffusion permeation is obtained using no pressure difference. The amount of permeation for one model system was inconsistent with the continuous-time random-walk (CTRW) model. The charge distribution in this model prevents water molecules to flip around which shows that the main part of diffusion and permeation mechanism is flipping the water molecules according to water charge interaction. We have also investigated the effect of temperature on water permeation in the range of 280 K to 370 K. An interesting result is an abrupt increase in number of diffusion permeation around 340 K.