Quantum Dynamics of Radical Pairs Reactions in Membranes: Elucidating Magnetic Field Effects in Lipid Autoxidation

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Radicals are ubiquitous short-lived reaction intermediates that contain a single unpaired electron and are usually created in pairs in a well-defined electronic spin state, either singlet ("anti-parallel spins") or triplet ("parallel spins"). For chemical reactions involving such pairs of radicals, quantum effects can induce a remarkable sensitivity to the intensity and/or orientation of external static magnetic fields as weak as the Earth's magnetic field. The underlying mechanism, the so-called Radical Pair Mechanism, has attracted widespread interest from the scientific community and general audiences owing to its putative relevance to animal magnetoreception and possibly adverse effects of weak electromagnetic fields on human health. Indeed, a multitude of studies have suggested an association between weak magnetic field exposure and increased levels of oxidative stress, genotoxic effects and apoptosis/necrosis. While detailed interaction models are still lacking - a factor that severely impedes the assessment of partly controversial literature on this subject and the advancement of guidelines for magnetic field exposure - the oxidative degradation of phospholipids appears as an overarching motif in many exposure studies. Indeed, reactive oxygen species and the free radicals they induce are known to attack polyunsaturated fatty acids in phospholipid membranes, thereby initiating lipid peroxidation reactions, which alter membrane characteristics and induce cell damage. Through termination and degenerate chain branching steps of this free-radical chain reaction, magnetosensitivity is feasibly imparted. Unfortunately, mechanistic details and a sound theoretical understanding of these effects are still lacking: the Radical Pair Mechanism has not yet been developed for systems confined to two dimensions, such as lipid bilayers, and the properties of the involved radicals have not been characterized with respect to magnetosensitive pathways and spin relaxation.Here, I propose a theoretical and computational investigation of intricacies of the radical pair mechanism at two-dimensional interfaces and the exploration of related amplification mechanisms beyond the standard Radical Pair Mechanism that I have recently suggested in the field of magnetoreception, but which are utterly unexplored in this context. In particular, I will focus on:a) the effect of confining the diffusion of coupled radical pairs to two dimensions,b) the potential for molecular motion to result in noise-enhanced magnetic field effects (MFEs), andc) the so-called chemical Zeno effect, by which MFEs are amplified by scavenging reactions with spin-carrying reaction partners.I envisage to find support for the hypothesis that unexpectedly large MFEs could ensue in these confined systems, intrinsically and as a consequence of the abovementioned secondary amplification effects. In addition to providing a better, more complete understanding of MFEs, our work will also reveal how subtle quantum effects can be sustained and amplified in noisy environments. These insights are essential to the emerging field of Quantum Biology and could pave the way to enhanced quantum devices and sensors with improved resilience to environmental noise. Furthermore, if such amplification schemes are found to apply to biologically relevant reactions, it could prompt a reassessment of the health risks of weak magnetic field exposure and future research into the use of MFEs as therapeutics to boost the immune response via the radical pair mechanism.Abbreviations: MFE = Magnetic Field Effect; RPM = Radical Pair Mechanism.