How Single and Bifurcated Hydrogen Bonds Influence Proton-Migration Rate Constants,Redox,and Electronic Properties of Phenoxyl Radicals

摘要

Tyrosine/tyrosyl radical redox systems are involved in many biological processes.Among tyrosyl-radical enzymes,inter-est has been mainly focused on photosystem II,prostaglan-din H synthase,galactose oxidase and ribonucleotide reductase.The phenolic(or phenolate)oxygen may be either bonded to a metal center(as in galactose oxydase)or hydrogen bonded to an appropriately orientated acidic residue of the protein.Despite the crucial role of hydrogen bonding on free radical properties,only two pioneering works have appeared recently in the literature concerning simple biomimetic models of hydrogen bonded phenoxyl radicals.The single intramolecular hydrogen-bonded phenoxyl radicals were evidenced through the reversibility of the phenol/phenoxyl redox couple,but unfortunately no rate constants for the proton transfer were reported.