Hydration and proton conductivity in the Gly-Pro crystal

Abstract

Recently, the use of biomaterials in electronic devices has been demanded from the viewpoint of the biocompatibility of devices. In this study, to clarify the relationship between the hydration in peptides and proton conduction, we have investigated the proton conductivity of Glycyl-l-proline (Gly-Pro). We found that proton conductivity in Gly-Pro is realized by hydration. It is deduced from the crystal data and conductivity data that proton conductivity in the hydrated Gly-Pro crystal is caused by the breaking and rearrangement of hydrogen bonds along the c-axis between hydration shells, which are formed by the hydrogen bond between the amino acid and water molecules. We also found that the steep increases in proton conductivity at the hydration numbers n ∼ 0.15 and n ∼ 0.35 result from the formation of the percolation network and faster rearrangement of hydrogen bonds inter-/intra-hydrated shells, respectively.