Modeling the Interactions of Amphiphilic Nanotubes and Lipid Bilayers

Using both Dissipative Particle Dynamics (DPD) simulations and

free energy calculations, we investigate the interactions

between amphiphilic nanotubes and a lipid bilayer. Each

nanotube encompasses a triblock (TB) architecture, with a

hydrophobic stalk and two hydrophilic ends. Individual lipids

are composed of a hydrophilic head group and two hydrophobic

tails. The DPD method is a coarse-grained (CG) molecular

dynamics (MD) approach that can capture effectively the

hydrodynamics of complex fluids while retaining essential

information about the structural properties of the system’s

components. An advantageous feature of DPD is that it utilizes

soft repulsive interactions between the beads, which are CG

representation of clusters of molecules. Consequently, one can

use a significantly larger time step between successive

iterations than those required by MD simulations. This, in turn,

allows the approach to be used for modeling physical phenomena

occurring at greater time and spatial scales than that captured

by MD. Via this simulation approach, we begin with a stable

lipid bilayer membrane immersed in a hydrophilic solvent, and

introduce the TB nanotubes into the surrounding solution. The

energetically unfavorable interaction between the solvent and

the hydrophobic segment of the TB tube could potentially drive

these nanotubes to penetrate the membrane, with the hydrophobic

stalk being buried within the hydrophobic domains of the

bilayer. This process, however, depends upon the hydrophobic

fraction of TB tube, and the degree of hydrophobic mismatch

between the tube and the bilayer. We isolate the conditions that

promote the insertion of the tubes into membrane. The

simulations are supported by free energy calculations for the TB

tube-lipid-solvent system. Ultimately, these embedded nanotubes

could be used to regulate the passage of molecules through

synthetic membranes.