PROTON CONDUCTION IN SELF-ASSEMBLED AMYLOID β PEPTIDE FIBRILS: THE EFFECT OF PEPTIDE SIDE CHAINS

The chemical diversity, ease of synthesis, and self-assembly propensity of peptides make them attractive materials for bioelectronics applications. Taking example from nature, conduction in such bio mimetic materials could be facilitated either by electrons, protons or both. In particular, the presence of hydrogen donating and accepting groups, such as carboxylic acid and amino groups, at the peptide side chains may facilitate affective proton conduction. Aiming at revealing the effect of such side chains on the unexplored proton conduction of self-assembling peptide nanostructures, we present here a systematic study that examines the dependence of protonic conductance on peptide side chains in amyloid β- based peptide fibers.

The peptides used in this work are mutations of the core sequence of the amyloid β protein, AAKLVFF and AAELVFF, with amine and carboxylic acid side chain residue at the third amino acid in the sequence, respectively. The self-assembly of the peptides into fibrous nanostructures with a varying diameter is verified using atomic force microscopy and scanning electron microscopy. Current-voltage measurements reveal an exponential dependence of the conductance on the relative humidity, as expected for proton conduction. Moreover, the conductance was found to be higher for AAELVFF peptide assemblies than for AAKLVFF assembly at each of the measured relative humidity conditions. This behavior is related to the higher mobility of protons (H⁺) vs. proton holes (OH^-). Our findings demonstrate that protonic conduction may be tuned by a proper peptide sequence design. The ability to generate both proton and proton holes may lay the ground to proton based switches and transistor devices.