Radical-Pair-Based Magnetoreception Amplified by Radical Scavenging: Resilience to Spin Relaxation

This is the author accepted manuscript. The final version is available from American Chemical Society via the DOI in this record.Birds and several other species are equipped with the remarkable ability to sense the geomagnetic field for the purpose of navigation and orientation. The primary detection mechanism of this compass sense is uncertain but appears to originate from a truly quantum process involving spin-correlated radical pairs. In order to elicit sensitivity to weak magnetic fields, such as the Earth’s magnetic field, the underlying spin dynamics must be protected from fast decoherence. In this work, we elucidate the effects of spin relaxation on a recently suggested reaction scheme involving three radicals, instead of a radical pair, doublet-quartet interconversion under magnetic interactions, and a spin-selective scavenging reaction. We show that, besides giving rise to a vastly enhanced reaction anisotropy, this extended reaction scheme is more resilient to spin relaxation than the conventional radical pair mechanism. Surprisingly, the anisotropic magnetic field effect can be enhanced by fast spin relaxation in one of the radicals of the primary pair. We discuss this finding in the context of magnetoreception. Radical scavenging can protect the spin system against fast spin relaxation in one of the radicals, thereby providing a credible model to the involvement of fast relaxing radical pairs, such as FADH•/O2•–, in radical-pair based magnetoreception. This finding will help explain behavioral observations that seem incompatible with the previously proposed flavin semiquinone/tryptophanyl radical pair.The author is indebted to Prof. Peter Hore (University of Oxford) for continuous support and many stimulating discussions. This work was partly conceived during the author affiliation with the Hore group at the University of Oxford, where it was supported by the European Research Council (under the European Union’s seventh Framework Programme, FP7/2007-2013/ERC Grant Agreement No. 340451) and the Air Force Office of Scientific Research (Air Force Materiel Command, USAF award no. FA9550-14-1-0095). The author thanks Dr. Alex Jones (University of Manchester) for discussion of the scavenging mechanism in the context of magnetic field effects in D. melanogaster. The image of the robin used in the TOC graphic is extracted from a photograph by Artur Rydzewski, which is licensed under a Creative Commons Attribution 4.0 International License