One of the major challenges in membrane science is to design polymer thin films that self-assemble in solution into continuous, rectilinear pores that are less than a nanometer in dimension and can exhibit a variety of chemical features in the pore lumen in a way that mimics transmembrane proteins in our cells. We aimed to address this issue by synthesizing and characterizing novel polymer-conjugated cyclic peptide nanotubes that are capable of self-assembly in solution or with block copolymers. Towards this goal, we characterized first the mechanical behavior of cyclic peptide nanotubes, which revealed that they are among the most rigid and self-assembling peptide materials known, which makes them favorable for membrane applications. Using simulations as guidance, we designed nanotubes with non-polar and polar groups presented in the lumen, which enabled highly tunable transport properties in homogenous tubes. For example, we found that non-polar functional groups allowed water transport in single file at reasonably high flux while dramatically improving monovalent cation rejection, which is useful for desalination membranes but remained challenging with existing peptide nanotubes. Transport simulations revealed how lumen size, chemistry and conformational dynamics of the nanotubes during ion passage influence flux and rejection properties. We also found that polymer conjugation can be utilized to control the growth of nanotubes, where increasing the number of polymer arms attached can change binding energies. Binary mixtures of cyclic peptides with varying conjugation degree revealed a strategy for stochastically ordering functional groups into striped patterns along the length of the nanotube during self-assembly. These findings pave the way for using simulations to design and synthesize supramolecular nanotubes that have versatile interiors and exterior to make membranes that have superior flux and rejection. These result have changed our fundamental understanding of factors governing transport in polymeric and peptide-based membranes, which is important for improving separation membrane performance in desalination, gas separation, and ion-exchange applications. We anticipate that advancing separation performance through membranes inspired from this work will impact many societal issues ranging from water purification to battery technology. 

This research project provided support for two graduate students, and led to the completion of a Master's Thesis and Doctoral Thesis as well as numerous publications in leading journals in the field. the project involved training of several undergraduate students through REUs and research opportunities, introducing them to scientific research as a first step toward building their careers in STEM fields.  Methods developed and new knowledge gained on transport and self-assembly mechanisms were incorporated into graduate courses. A "Computational Nanodynamics" tool for learning molecular simulations was deposited in the NSF sponsored NanoHUB.org. This tool alllows anyone with access to an internet browser to run state-of-the-art molecular simulations related to self-assembly and other physical phenomena directly related to this research. 

Last Modified: 01/30/2017
Modified by: Sinan Keten