In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

Organic Photoredox Catalysis

Heme-Containing Oxygenases

How Easily Oxidizable Is DNA? One-Electron Reduction Potentials of Adenosine and Guanosine Radicals in Aqueous Solution

The oxidative environment and protein damage

Many, if not most, redox reactions are coupled to proton transfers. This includes most common sources of chemical potential energy, from the bioenergetic processes that power cells to the fossil fuel combustion that powers cars. These proton-coupled electron transfer or PCET processes may involve multiple electrons and multiple protons, as in the 4 e–, 4 H+ reduction of dioxygen (O2) to water (eq 1), or can involve one electron and one proton such as the formation of tyrosyl radicals from tyrosine residues (TyrOH) in enzymatic catalytic cycles (eq 2). In addition, many multi-electron, multi-proton processes proceed in one-electron and one-proton steps. Organic reactions that proceed in one-electron steps involve radical intermediates, which play critical roles in a wide range of chemical, biological, and industrial processes. This broad and diverse class of PCET reactions are central to a great many chemical and biochemical processes, from biological catalysis and energy transduction, to bulk industrial chemical processes, to new approaches to solar energy conversion. PCET is therefore of broad and increasing interest, as illustrated by this issue and a number of other recent reviews.

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Thermochemistry of Proton-Coupled Electron Transfer Reagents and its Implications

With the technique of pulse radiolysis we have measured the redox midpoint potentials of the tryptophan side chain neutral indolyl radical (105 +/- 001 V vs NHE, pH 70 and 25 degrees C) and the tyrosine side chain neutral phenoxy radical (094 +/- 001 vs NHE, pH 70 and 25 degrees C) These potentials were obtained by using a variety of inorganic reference compounds in both kinetic and equilibrium protocols We compare these results with others already in the literature, and we also present data useful in establishing a pulse radiolysis redox reference scale over the range 042-128 V

Pulse radiolytic measurement of redox potentials: the tyrosine and tryptophan radicals.

Reported here are the redox potentials of the tyrosine phenoxy (tyrO{sup {sm bullet}}) and tryptophan indolyl (trp{sup {sm bullet}}) radicals in peptides containing tyrosine or tryptophan residues. These were determined with pulse radiolysis, and the electrochemical techniques of cyclic voltammetry and differential pulse polarography. The pulse radiolytic and electrochemical methods yield comparable results. There are small differences (relative to the free amino acid) in redox potentials among the different tryptophan and tyrosine containing peptides; in the case of tryptophan these changes may correlate with the position of amino acid in the peptide. The authors also present the redox potentials of some tyrosine and tryptophan derivatives and the acid/base properties of the tryptophan radical cation, when both free and peptide bound.

Electrochemical properties of tyrosine phenoxy and tryptophan indolyl radicals in peptides and amino acid analogues

On etudie les constantes de vitesses du transfert d'electron intramoleculaire entre la tyrosine et le tryptophane dans les peptides tyrosinyl(prolinyl) n -tryptophane

Michael R. DeFelippis

Papers

Pulse radiolytic measurement of redox potentials: the tyrosine and tryptophan radicals.

Electrochemical properties of tyrosine phenoxy and tryptophan indolyl radicals in peptides and amino acid analogues

Long-range electron transfer between tyrosine and tryptophan in peptides

Evidence for through-bond long-range electron transfer in peptides

Long range electron transfer between tyrosine and tryptophan in hen egg-white lysozyme.