Molecular dynamics simulations of carbon nanotube porins in lipid bilayers

Artificial channels made of carbon nanotube (CNT) porins are promising candidates for applications in filtration and molecular delivery devices. Their symmetric shape and high mechanical, chemical, and thermal stability ensure well-defined transport properties, and at the same time make them ideal model systems for more complicated membrane protein pores. As the technology to produce and tune CNTs advances, simulations can aid in the design of customized membrane porins. Here we concentrate on CNTs embedded in lipid membranes. To derive design guidelines, we systematically studied the interaction of CNT porins with their surrounding lipids. For our simulations, we developed an AMBER- and Lipid14-compatible parameterization scheme for CNTs with different chirality and with functional groups attached to their rim, and a flexible coarse-grained description for open-ended CNTs fitting to the MARTINI lipid model. We found that the interaction with lipid acyl chains is independent of the CNT chirality and the chemical details of functional groups at the CNT rims. The latter, however, are important for the interactions with lipid head groups, and for water permeability. The orientation and permeability of the pore are mainly determined by how well its hydrophobicity pattern matches the membrane. By identifying the factors that determine the structure both of isolated CNTs in lipid membranes and of CNT clusters, we set the foundation for a targeted design of CNT-membrane systems.