title: Transport behavior of a single Ca(2+), K(+), and Na(+) in a water-filled transmembrane cyclic peptide nanotube.
abstract: Molecular dynamics simulations have been performed to investigate the transport properties of a single Ca(2+), K(+), and Na(+) in a water-filled transmembrane cyclic peptide nanotube (CPNT). Two transmembrane CPNTs, i.e., 8×(WL)n=4,5/POPE (with uniform lengths but various radii), were applied to clarify the dependence of ionic transport properties on the channel radius. A huge energy barrier keeps Ca(2+) out of the octa-CPNT, while Na(+) and K(+) can be trapped in two CPNTs. The dominant electrostatic interaction of a cation with water molecules leads to a high distribution of channel water around the cation and D-defects in the first and last gaps, and significantly reduces the axial diffusion of channel water. Water-bridged interactions were mostly found between the artificially introduced Ca(2+) and the framework of the octa-CPNT, and direct coordinations with the tube wall mostly occur for K(+) in the octa-CPNT. A cation may drift rapidly or behave lazily in a CPNT. K(+) behaves most actively and can visit the whole deca-CPNT quickly. The first solvation shells of Ca(2+) and Na(+) are basically saturated in two CPNTs, while the hydration of K(+) is incomplete in the octa-CPNT. The solvation structure of Ca(2+) in the octa-CPNT is most stable, while that of K(+) in the deca-CPNT is most labile. Increasing the channel radius induces numerous interchange attempts between the first-shell water molecules of a cation and the ones in the outer region, especially for the K(+) system.
authors.affiliation: College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China.
authors.forename: Xiliang
authors.initials: X
authors.lastname: Yan
authors.affiliation: College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China.
authors.forename: Jianfen
authors.initials: J
authors.lastname: Fan
authors.affiliation: College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yu
authors.affiliation: College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China.
authors.forename: Jian
authors.initials: J
authors.lastname: Xu
authors.affiliation: College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China.
authors.forename: Mingming
authors.initials: M
authors.lastname: Zhang
mesh_terms: D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D004058:Diffusion; D017136:Ion Transport; D008567:Membranes, Artificial; D008670:Metals / Q000737:chemistry* / Q000378:metabolism; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D045333:Nanotubes, Peptide / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry / Q000378:metabolism; D012964:Sodium / Q000737:chemistry / Q000378:metabolism; D012997:Solvents / Q000737:chemistry / Q000378:metabolism; D055672:Static Electricity; D014867:Water / Q000737:chemistry*
chemical_list: D008567:Membranes, Artificial; D008670:Metals; D045333:Nanotubes, Peptide; D012997:Solvents; D014867:Water; D012964:Sodium; D011188:Potassium; D002118:Calcium