(751d) Diffusion through Biomimetic m-Phenylene Ethynylene Channels: A Computational Study

Functionalized meta-phenylene ethynylene polymers (mPPEs) have recently found use in a variety of antimicrobial and related biological applications. This biological activity results from the helical architecture of the mPPEs, which affords the transport of small molecules through the core of the helical channel in much the same way as integral membrane proteins (ion channels). Of particular interest is whether these same helical polymers, which are easily functionalized with different pendent groups, can be used for other membrane separation applications. The key advantages of the mPPE helical structure are: (i) the environment (size, channel polarity, and specific chemical interactions) inside the cylindrical cavity can be precisely tailored using appropriate interior functional groups; (ii) the functional groups and solvophilic pendants on the exterior of the mPPE helix enable the polymer to be compatible with a variety of polymer or liquid supports; and (iii) the overall channel length can be varied, enabling greater control over transport rates through the channels. In this study, we conducted a series of molecular dynamic (MD) simulations to explore the concept of using helical mPPEs as water and small molecule channels for molecular selective membrane applications. During the diffusion simulations, the 6 nm long helical mPPEs were localized in the organic layer of an octane-water system, which mimics hydrophobic polymer films as well as the phospholipid bilayer of cells. Five interior functional groups were selected creating five different channel environments; five water models, including spc, spce, tip3p, tip4p, tip5p, were also used in our simulations, forming a total of 25 systems. The diffusion kinetics for each system was investigated via 100 ns MD semi-isotropic NPT simulations. These simulation results allow us to better understand the mechanism and rates of water diffusion through mPPE channels, and they also help identify possible mPPE structures that are ideally suited for membrane separation applications.