Structure and Dynamics of Water Within Single Wall Carbon Nanotubes and Self-Assembled Cyclic Peptide Nanotubes

Structure and flow behavior of water in nanoscale confinement are critical for nanotechnology applications. In addition to influence of decreasing in dimensions imposed by the confinement, the nature of interaction may have substantial effect on structure and dynamics of water. In this work, we have utilized two distinct nanotube structures to assess the affect of these two factors. To emphasize the influence of atomic detail interactions play in this problem we have chosen two physically well defined systems: close packed single wall carbon nanotubes with varying diameter, length and chirality, and the self assembled cyclic peptide nanotubes formed by cyclic-[-(D-Ala-Gln-D-Ala-Glu)(2)-] subunits. We have employed molecular dynamics simulation method to study the behavior of water in these two model nano-scale membranes. To assess the similarities and differences, we have evaluated the dipole-dipole correlations, diffusion coefficient, density profiles along the nanotube, radial and axial distribution functions for water in nanotubes. The hydrophilic peptide nanotubes showed a higher value of diffusion coefficient when compared with the hydrophobic CNTs channels of equivalent diameter.