Fuel cells are devices that generate electricity by chemical reactions, in which a key component, proton exchange membrane (PEM) allows only hydrogen ions to pass through the cell. Current proton exchange membrane fuel cell (PEMFC) technology involves expensive perfluorinated PEMs that operate effectively only under hydrated conditions. Some rising new PEM materials take advantage of tethered imidazoles as the primary proton translocating functionality because they have both donor and acceptor moieties to form extended hydrogen bonding networks, i.e. proton wires that act as proton transporters through Grotthuss mechanism. There is a considerable application-driven interest in extending the operating window of PEMs in terms of functioning through non solvent-mediated mechanisms to avoid the problems of dehydration due to electro-osmotic drag, and lowering the cost. With the increasing capacity of nanotechnology – allowing for the continued miniaturization of microsystems while increasing performance and maintaining stability – researches have been pursued towards alternative PEMs based on various nanomaterials to achieve more efficient fuel cell applications, among which, helical peptides are much sought after as potential efficient proton wires. Previous calculations have shown that 5-6 Å backbone repeat distance is required for continuous hydrogen-bond networks of imidazoles or triazoles, rendering helical peptides as promising scaffolds, which exhibit electrical dipoles promoting unidirectional proton motion. In our current work, three major helical conformations of polypeptide chains formed from α-amino acids are investigated as potential candidates of proton conducting materials: 310-, α- and π-helical structures. Multiple polyalanine peptides substituted at regular intervals with residues with proton donor-acceptor moieties (Histidines, Glutamate and Aspartate) are modeled using a hybrid computational approach with a semiempirical method (AM1) for peptide scaffolds and the more accurate density functional theory (B3LYP) for the proton wires. The sequences under study are Ala3(His-Ala2)x (x=2-7), Ala2(His-Ala3)yHisAla2 (y=2-5) and Ala2(His-Ala4)zHisAla3 (z=2-4). The proton wires formed upon hydrogen bonds between the H-donors (ε H-acceptors moiety were computationally evaluated based on the difference in the proton translocation energetics, polymerization energy, proton affinity and desorption energy.

Modeling nonaqueous proton wires built from helical peptide

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.