Proton-assisted electron transfer

The case for highly selective long range "proton assisted" electron transfe r in biomolecules (PA-ET), involving the hopping of protons and hydrogen at oms along H-bond chains connecting two redox sites, is discussed and analyz ed on systems closely resembling typical biochemical sequences. These syste ms consist of an electron acceptor, an H-bond/covalent-bridge chain and an electron donor, and monohydroparabenzoquinone as the electron acceptor and a xanthine-like molecule as the electron donor and acceptor species held to gether by one or more peptide bridges. It is shown that, in biochemical str uctures, despite the involvement of the imidol (oximine) form of the peptid e link, (a) PA-ET is energetically efficient and (b) the rate constants for proton-transfer, which is arguably the rate-controlling step, are reasonab ly high, the transfer times being on the order of hundreds of picoseconds.