Transmembrane Distribution of Membrane Constituents in Organic Nanotubes Driven by Electric Charge and Intrinsic Anisotropy of Molecules

The transmembrane distribution of membrane constituents in the two leaflets of a cylindrical bilayer, which is in contact on both sides with an electrolyte solution, was studied by mathematical modeling. The model considers electrostatic interactions between the charged membrane molecules and the monovalent ions of the electrolyte solution, the bending elasticity of the membrane, as well as the anisotropy of the molecular intrinsic shape in the membrane. We showed that the strongly anisotropic uncharged membrane constituents are distributed asymmetrically between the two leaflets of the membrane. The asymmetric transmembrane distribution of charged weakly anisotropic membrane constituents is caused by the difference between the ionic strengths in the outer solutions and those in the inner solutions. For strongly anisotropic charged constituents in the membrane, we found that the asymmetric transmembrane distribution is driven by an interplay between the shape and the charge of the membrane constituents, as well as the difference between the ionic strengths in the outer solutions and those in the inner solutions. We also showed that the composition of the bilayer and the intrinsic curvatures of membrane components influence the stability of the tube.