Studies on magnetic effects in flavin based photocatalytic reactions

• Applicant: Dr. Roger Jan Kutta
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2013 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 246536940

Studies of animal magnetoreception, such as that by migratory birds, have demonstrated that even the low magnetic field strength of the earth (about 50µT) can be perceived and used efficiently for orientation. A light-induced radical pair reaction in a photoreceptor protein containing a flavin chromophore has been proposed as a chemical compass model of animal magnetoreception. It is well established (by both theory and experiment) that the application of external magnetic fields can significantly influence the reactivity, and hence the product yields, of radical pair reactions by singlet-triplet spin-state interconversion. In this project, the goal is to use such magnetic field effects (MFEs) to help fully optimize a photocatalytic reaction using flavin chromophores. The insights gained can then be used to inform the design of various new photocatalytic reactions that exploit MFEs on radical pair reactions to maximize their product yields. One prominent photocatalyst, which nature also uses as a cofactor within proteins, is flavin. Flavins have been reported to photocatalyze the oxidation of benzyl alcohols, benzyl amines, methylbenzenes, styrenes and phenylacetic acids using dissolved oxygen to complete the cycle.Additionally, it is used to selectively remove benzyl protecting groups. Such photocatalytic reactions can achieve important transformations either inaccessible to thermal reactions or under more mild conditions. I have previously investigated the conversion of the benzylic alcohol to its corresponding aldehyde and identified a MFE that enhances the product yield. The bottleneck in this photocatalytic cycle is the formation of a radical ion pair after electron transfer from benzylic alcohol to either the excited singlet or triplet state of the flavin. Only the triplet state is productive. The application of an external magnetic field in the mT range increases the triplet population of the longer lived radical pairs and results in an increase of the overall product yield. This proof-of-principle project will fully investigate and optimize the MFE in this system, and hence explore the potential for the use of MFEs in photocatalytic reactions. On the one hand we will investigate the environmental effects on the MFE, such as magnetic field strength, temperature, and viscosity. On the other hand we will begin to explore the modification of the structure of the flavin photocatalysts, aided by theoretical studies, to tailor the electronic properties of the radical pairs for optimal photo- and magneto-catalytic conditions.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Dr. Alex Richard Jones