Excited State Proton Transfer Across Short Peptide

Electron and proton transfer (PT) are two fundamental biological processes. The mechanism of PT has been studied for the last 200 years since the early studies of Grotthuss on the proton transport mechanism through water. Proteins have an important role in PT involved in biological processes. For example, the crucial role of PT in the respiratory system for the formation of the cellular energetic coin, where protons are being mediated within transmembrane proteins. Still, there are many unknowns involved in protein mediated PT, such as the contribution of different amino acids (AA) to the PT mechanism across the protein. In our study, we wish to explore the latter question by investigating the spectroscopic properties of photo-induced PT through a donor-bridge-acceptor system. In our designed system, the bridge is a short peptide (consisting of 8-10 AA), while the donor and acceptor molecules are excited state proton donor and acceptor, respectively. This way, we initiate the PT process by light, and in addition to exploring the role of the AA in mediating the protons, we would like also to investigate the role of the secondary structure and the role of water in PT. Here we report the synthesis of our probe system, where the photo-induced PT takes place through a poly-histidine bridge connected (through amide linkage) with 1-naphthol (proton donor) and acridine (proton acceptor) at the C- terminal the N- terminal, respectively.

Figure1: A scheme of donor- bridge-acceptor system.