The Influence of Chemistry and Microstructure on the Proton Conductivity of Natural and Synthetic Biopolymers

Most biological systems are predominantly made of water. Given that water is not a good electronic conductor, electrical currents in biology often involve fluxes of ions such as H+, K+, Na+, Cl-. H+, as the lightest ion,involves a transport mechanism that has more aspects in common with the transport of electrons and holes in conjugated systems than the transport of the heavier ions. This mechanism- known as the Grotthus mechanism- involves the exchange of hydrogen bonds with covalent bonds in water molecules and the hydrophilic residues of the hydrated biomaterials. Thus, hydrated proton conductors often comprise a network of hydrogen bonds referred to proton wires.<br/><br/>In this presentation, I will discuss fundamental aspects of proton conductivity in hydrated natural and synthetic polymers and how materials chemistry and microstructure affect this conductivity. To this end, I will present three biomaterials: 1) The biopolymer found in the Ampullae of Lorenzini of sharks and rays, 2) Sulfated polysaccharides, and 3) A synthetic hydrogel with a tunable microstructure and porosity. I will compare data from impedance measurements, DC measurements with proton-conducting PdHx contacts, and solution-based measurements. I will draw trends in this data as a function of biomaterial chemistry and microstructure. With these trends, I will provide insights on how proton conductivity can be used to predict the conductivity of other ions and discuss simple design rules for maximizing proton conductivity while maintaining the stability of the materials.