Quantum theory of a potential biological magnetic field sensor: radical pair mechanism in flavin adenine dinucleotide biradicals

TL;DR

This paper develops a comprehensive quantum model for the radical pair mechanism in FAD molecules, explaining how they could serve as biological magnetic field sensors, aligning with experimental data.

Contribution

It introduces a detailed quantum theoretical model for FAD's radical pair mechanism, surpassing previous semi-classical models by predicting full magnetic field dependence.

Findings

Quantum model matches experimental observations.

Predicts magnetic field effects across a wide range.

Provides insights into biological magnetic sensing.

Abstract

Recent studies in vitro and in vivo suggest that flavin adenine dinucleotide (FAD) on its own might be able to act as a biological magnetic field sensor. Motivated by these observations, in this study, we develop a detailed quantum theoretical model for the radical pair mechanism (RPM) for the flavin adenine biradical within the FAD molecule. We perform molecular dynamics simulations to determine the distance between the radicals on FAD, which we then feed into a quantum master equation treatment of the RPM. In contrast to previous semi-classical models which are limited to the low-field and high-field cases, our quantum model can predict the full magnetic field dependence of the transient absorption signal. Our model's predictions are consistent with experiments.