EAGER: Understanding Molecular Control and Phase Behavior of Random Heteropolymer Materials for Selective Transport

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

NON-TECHNICAL SUMMARY: In nature, membrane proteins are the gatekeepers that mediate molecular transport to maintain cellular processes. If polymers can be generated with separation performance similar to that of membrane proteins, they could offer very significant impacts on the environment, energy, separation technologies, and life sciences. For example, membranes are in high use for water purification and desalination, carbon dioxide capture and separation, chemical purification, and lithium battery applications. Over decades there have been significant efforts in improving polymer chemistry and self-assembly to better mimic the known structures of membrane proteins, which have led to limited advances in membrane performance. The bottleneck is to identify critical design parameters in these highly complex and diverse biological systems. By fundamentally understanding the spatial arrangement of a polymer chain inserted in a cellular lipid analogue and correlating it with molecular transport, this project aims to provide insights to the long-standing question: "what level of molecular control over polymeric materials is needed to replicate protein transport properties?" If successful, the project may result in new design rules for bio-inspired polymers, change the pathways for membrane development, and lead to technologically relevant membranes. The proposed studies are highly interdisciplinary and afford an excellent platform for training students at all levels. They will also provide software tools for polymer analysis as well as multiple outreach opportunities. TECHNICAL SUMMARY: For membrane proteins the common belief is that well-defined protein structure is requisite to simultaneously achieving high flux and selectivity. For decades, various porous materials have been designed following this rule and explored for selective transport with limited success. Based on preliminary results using random heteropolymers, the central hypothesis for the proposed study is that once the heteropolymer composition is fixed, the statistical monomer distribution, rather than the atomically precise polymer structure, is the key parameter governing the resulting transport properties. This project aims to test this hypothesis by: (1) developing software tools to perform in-depth analysis of random heteropolymer sequence; (2) characterizing heteropolymer chain conformation upon lipid insertion to correlate the heteropolymer phase behavior with rapid, selective proton transport; (3) exploring heteropolymer-based block copolymers for analysis of heteropolymer chain conformation and transport properties for future membrane design. Preliminary results point to the potential that unstructured polymer chains can perform at similar level as well-folded proteins for proton transport. The planned exploratory studies will identify the critical design parameters behind such behavior, which may impact the current approach to designing membranes. The results may also change the traditional view on structure-function relationships in naturally occurring biopolymers and affect future development of bio-inspired polymers. Based on recent advances in living polymerization, the results would be well posed to generate technologically important membranes. Furthermore, the planned studies will: (1) provide graduate and undergraduate research opportunities, as well as outreach opportunities through a joint effort with the California Academy for educating the public and middle school students on polymers; (2) develop new software tools for heteropolymer analysis and make them publicly available; and (3) provide the materials communities with a mechanism to overcome a barrier in starting heteropolymer-related projects. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.