MD Simulations on the Transport Behaviors of Mixed Na+ and Li+ in a Transmembrane Cyclic Peptide Nanotube under an Electric Field

Due to its inherently stronger hydration, Li+ faces a higher dehydration energy than Na+ at the entrance of the 8X(WL)(4)/POPE-CPNT. Present MD simulations show that it can enter the channel from a NaCl/LiCl solution only under an electric field stronger than 0.3 V nm(-1), while Na+ is easier to move into the channel, which is well elucidated by two cations' PMF profiles. The cation-O-w, radial distribution functions, the electrostatic interactions with water, and the orientations of neighboring water all refer to a more compact solvation structure and stronger hydration of Li+. Regardless of whether there is an external electric field, Na+ mainly appears in an alpha-plane zone, while Li+ does so in a midplane region. The increase in the electric field strength significantly accelerates the cations' axial diffusions, shortening the residence times of two cations in the channel. Furthermore, it makes channel water tend to take positive dipole states.