Quantum Effects in Radical Pair Dynamics and Biological Magnetoreception

• Ilia A. Solov'yov

Room: Auditorium A Life is governed not only by classical physics but also by quantum mechanics, especially in processes involving electron transitions. While all chemical reactions involve quantum phenomena, some biological systems appear to exploit them in surprising ways. A striking example is the ability of migratory birds to sense Earth’s magnetic field, plausibly via light-induced, spin-correlated radical pairs formed in retinal cryptochromes [1,2]. In this talk, I will discuss how such radical pairs may act as a "chemical compass" [3]. I will outline the fundamental reaction steps in cryptochrome activation and deactivation, emphasizing how the interplay between protein structure, cofactors, and magnetic interactions possibly shapes spin dynamics and magnetic sensitivity of the protein [1,4,5]. Because proteins are dynamic, thermal motions modulate local interactions and drive spin relaxation, which can both degrade coherence and, under some conditions, tune sensitivity. Molecular dynamics simulations based on three-dimensional cryptochrome structures provide a way to examine these fluctuations and their consequences for radical-pair behavior [1,4–6]. Theoretical approaches, including Redfield theory and stochastic Schrödinger dynamics, will also be discussed in the context of describing how environmental noise and molecular motion affect spin coherence in biological systems [7,8], alongside the use of modern computational platforms to implement such models efficiently [9]. I will close by highlighting broader implications for spin dynamics and possible quantum effects in biological chemistry beyond avian magnetoreception. References: [1] J. Xu, et al., Nature, 2021, 594, 535–540. [2] D. Timmer, A. Frederiksen, D. C. Lünemann, A. R. Thomas, J. Xu, R. Bartölke, J. Schmidt, T. Kubař, A. D. Sio, I. A. Solov’yov, et al., J. Am. Chem. Soc., 2023, 145, 11566–11578. [3] S. Y. Wong, A. Frederiksen, M. Hanić, et al., Neuroforum, 2021, 27 141–150. [4] F. Schuhmann, D. R. Kattnig, I. A. Solov’yov, J. Phys. Chem. B, 2021, 125, 9652–9659. [5] F. Schuhmann, et al., J. Phys. Chem. B, 2024, 128, 3844–3855. [6] G. Grüning, S. Y. Wong, L. Gerhards, et al., J. Am. Chem. Soc., 2022, 144, 22902–22914. [7] L. Gerhards, C. Nielsen, D. R. Kattnig, et al., J. Comp. Chem., 2023, 44, 1704–1714. [8] G. Jurgis Pažera, T.P. Fay, I.A. Solov’yov, et al., J. Chem. Theor. Comp. 2024, 20, 8412–8421 (2024). [9] V. Korol, P. Husen, E. Sjulstok, et al., ACS Omega, 2020, 5, 1254–1260.

The challenge of large systems: Exploring efficient computational methods for biochromophores

• Susannah Bourne-Worster

Room: Auditorium A One of the big challenges for computationally exploring quantum effects in biological systems is their sheer size. When accurately calculating quantum states, more atoms means more computational effort and this can very quickly get out of hand! In this talk I will discuss some strategies for evaluating the photoexcited states of biological chromophores at very low cost, highlighting the success (or not!) of these approaches, along with some example applications to photosynthetic systems.

A Non-Canonical Radical Pair Mechanism – How the Drosophila CRYPTOCHROME C-terminus mediates magnetosensitivity.

• Adam Bradlaugh

Room: Auditorium A The light-sensitive flavoprotein CRYPTOCHROME (CRY) is now generally believed to be a magnetosensor through the Radical Pair Mechanism (RPM). In this model a light-initiated electron transfer between CRY’s co-factor Flavin Adenine Dinucleotide (FAD) and a chain of essential tryptophan (Trp) residues provides sensitivity to a magnetic field (MF) via a quantum effect on electron spin, ultimately modulating CRY protein activation and downstream signalling. Whilst there is considerable physical and behavioural data to support this Trp-FAD canonical RPM, particularly as the mechanism for navigational magnetoreception in birds, a growing body of evidence suggests that non-canonical radical pairs may underlie other forms of magnetosensitivity. Using the model organism Drosophila melanogaster, renowned for its highly tractable nervous system and genetic malleability we investigated the molecular basis of CRY based magnetosensitivity. Using a combination of electrophysiological and behavioural assays we initially demonstrated that just the 52 amino acids of the C-terminus of Drosophila CRY (Dm-CT) alone were capable of imparting magnetosensitivity to a fly. Lacking in both the chain of Trp residues as well as the entire FAD binding domain this surprising result cannot be explained by the canonical RPM. By manipulating the intracellular concentration of flavins such as FAD and its metabolic precursor Riboflavin we demonstrate that intramolecular radicals from FAD and the Dm-CT interact to provide magnetosensitivity. To investigate how Dm-CT and FAD interact we applied all-atom molecular dynamic (MD) simulations. These revealed that several key positively charged residues distributed across the Dm-CT mediate the direct binding of FAD via electrostatic forces in several possible configurations. As well as localising intramolecular FAD radicals to Dm-CT the MD simulations suggest that upon binding, the FAD molecule is contorted into a ‘open’ conformation, enhancing the sensitivity of the radicals to a MF. Directed by these simulations we generated genetically modified flies with substitutions of the key positively charged residues for structurally conservative residues with negative and neutral charge. In both our electrophysiological and behavioural assays flies lacking the correct positive charge distribution within the CT failed to support magnetosensitivity. Complementary in vitro binding investigations supported our MD simulations and in vivo observations, demonstrating a physical interaction between Dm-CT and FAD through both size exclusion chromatography and fluorescence microspectroscopy. Notably, these investigations reveal an FAD and light dependent propensity for Dm-CT to form aggregates, reminiscent of photobodies found in plant CRYs. Whether this non-canonical RPM has relevance to navigational magnetoreception or is a unique quirk of Drosophila remains to be determined. With accumulating evidence for non-canonical magnetosensitivity, such as that of Human CRY2 (HsCRY2) which despite a defunct FAD binding domain still exhibits light and MF sensitivity in Drosophila, we present preliminary evidence suggestive of a possible similar C-terminus – FAD interaction mediating magnetosensitivity for HsCRY2 in Drosophila. Finally, we explored the dual role of Dm-CT as not just a facilitator of FAD radical formation, but as a transducer of the magnetic signal. Using our electrophysiological and behavioural assays we demonstrate the requirement for protein-protein binding sites for the magnetic signal and evidence that implicates possible signalling candidates in the transduction of the magnetic sense in flies.

Controlling excited-state pathways in photoswitchable proteins

• Nanna Holmgaard List

Room: Auditorium A Photoactive proteins provide natural systems in which biological function is governed by excited-state dynamics of embedded chromophores. This talk will discuss how protein environments control photochemical pathways that enable photoswitching, and how quantum-chemistry and nonadiabatic dynamics approaches help reveal the mechanisms underlying these processes.

Hyperpolarization and Magnetic Field Effects in Cryptochromes and LOV Domains: A Radical Pair Perspective

• Stefan Weber

Room: Auditorium A The ability of living systems to sense and respond to weak magnetic fields has emerged as a compelling frontier in quantum biology. Blue-light photoreceptor proteins, particularly cryptochromes and LOV domain proteins, provide a unique platform in which light-driven function intersects with spin-dependent quantum dynamics. Upon photoexcitation, these systems generate spin-correlated radical pairs whose evolution is governed by the radical pair mechanism [1–4]. The coherent interconversion between singlet and triplet spin states renders reaction pathways sensitive to weak magnetic interactions, including fields on the order of the Earth’s magnetic field. In this lecture, it will be discussed how electron and nuclear spin dynamics in these radical pairs give rise to pronounced hyperpolarization effects under biologically relevant conditions [1–4]. Such non-equilibrium spin polarization, typically associated with magnetic resonance methodologies, emerges here intrinsically from the reaction dynamics and encodes information about the underlying spin Hamiltonian. Recent advances in detecting and quantifying these effects using state-of-the-art spectroscopic techniques, bridging concepts from electron spin resonance and nuclear magnetic resonance will be highlighted. Particular emphasis will be placed on the interplay between molecular structure, spin-selective recombination, and magnetic field effects in shaping observable hyperpolarization signals [4–8]. These findings provide new insight into how weak magnetic interactions can modulate biochemical outcomes through quantum-coherent spin evolution. By integrating experimental results with theoretical modeling, this work advances a unified picture of spin-dependent processes in photoreceptor proteins. It further positions radical pair systems in cryptochromes and LOV domains as model platforms for exploring the limits of quantum coherence in complex biological environments. [1] T. Biskup, E. Schleicher, A. Okafuji, G. Link, K. Hitomi, E.D. Getzoff, S. Weber, Angew. Chem. Int. Ed., 48 (2009) 404–407 [2] S. Weber, T. Biskup, A. Okafuji, A.R. Marino, T. Berthold, G. Link, K. Hitomi, E.D. Getzoff, E. Schleicher, J.R. Norris, J. Phys. Chem. B, 114 (2010) 14745–14754 [3] D. Nohr, S. Franz, R. Rodriguez, B. Paulus, L.-O. Essen, S. Weber, E. Schleicher, Biophys. J., 111 (2016) 301–311 [4] G. Kothe, M. Lukaschek, G. Link, S. Kacprzak, B. Illarionov, M. Fischer, W. Eisenreich, A. Bacher, S. Weber, J. Phys. Chem. B, 118 (2014) 11622–11632 [5] D. Nohr, B. Paulus, R. Rodrigues, A. Okafuji, R. Bittl, E. Schleicher, S. Weber, Angew. Chem. Int. Ed., 56 (2017) 8550–8554 [6] T. Hochstoeger et al., Science Adv., 6 (2020) eabb9110 [7] J. Xu et al., Nature, 594 (2021) 535–540 [8] J. Gravell et al., J. Am. Chem. Soc., 147 (2025) 24286–24298

As simple as possible, but not simpler: Environmental structure in quantum biology

• Luke Smith

Room: Auditorium A The complexity of biological environments is often assumed to act as a source of detrimental noise, destroying delicate quantum effects and potentially negating the need for quantum descriptions. However, their inherent structure may instead provide a resource that nature harnesses to steer quantum dynamics towards biological function. In this talk, I explore this idea by showing how realistic complexity is essential for scrutinising the predictions of idealised models and can reveal new mechanisms that enable functionality. Focusing on radical pair systems, which are proposed to act as quantum magnetosensors within the protein cryptochrome and hypothesised to underlie magnetoreception, I examine how environmental structure can influence and enhance magnetic field sensitivity and metrological performance. These results emphasise the importance of open quantum systems approaches that temper physical insight with sufficient realism and suggest how environmental structure may be harnessed by nature to steer biochemical processes and leveraged in engineered systems.

Weak radiofrequency field effects in biological systems - A challenge for quantum biology

• Luca Gerhards

Room: Auditorium A The widespread use of radiofrequency (RF) communication has increased the exposure of organisms to electromagnetic fields, fueling debate about the potential biological effects of weak RF radiation. Experimental studies have suggested that low-amplitude RF fields may influence cellular metabolism, sleep patterns, or even cancer-related processes; however, these claims remain controversial, largely because the underlying physical mechanisms are unclear. A central concept in this discussion is the radical pair mechanism (RPM), a quantum-mechanical framework proposed to mediate magnetic and RF field effects in biology. Although the RPM has been invoked to explain magnetoreception and other magnetic-field-dependent chemical processes, it often struggles to account for observations at weak, non-thermal RF field strengths. In this talk, the applicability of the RPM to weak RF effects will be examined across different biological systems, highlighting both its potential and its limitations.

From the ultrafast dynamics of photosynthesis to the quantum design of energy harvesting materials

• Alex Chin

Room: Auditorium A In 2008, the unexpected observation of coherent excitonic dynamics in photosynthetic proteins kick-started a vibrant interdisciplinary effort to explore the possible roles and advantages of non-classical effects in biological processes. Today, claims that Nature actually exploits quantum mechanics in vivo remain highly controversial, but a key outcome of 'Quantum Biology' has been to expose the exquisite nano engineering of light-harvesting proteins to powerful theoretical and computational tools from across condensed matter, quantum information and chemical sciences. From these techniques, a deep, microscopic understanding has arisen of how (open) quantum dynamics can drive sophisticated optoelectronic functionalities in protein structures, inspiring light-harvesting concepts that could be realized in artificial nanotechnologies. In this talk I will present an overview of our work on biological light-harvesting, covering the highly tuned electronic structure of pigment-protein complexes, the critical role of structural vibrations in ultrafast energy transport, and how these could be leveraged for quantum-enhanced energy harvesting in man-made systems. Time permitting, I will also present some of the 'bio-inspired' devices in which these ideas have actually been tested, including organic photovoltaics, DNA origami and, even, superconducting qubit circuits.

Ariel Furst (Title TBC) Room: Auditorium A

Generalizing Förster resonance energy transfer to allow for transient coherent effects

• Aurélia Chenu

Room: Auditorium A The traditional Förster theory applies in the limit where the intermolecular coupling is weak, and the system-bath coupling is strong. We use an approximation for the bath to generalize the traditional Förster master equation for the state population probabilities into a complete master equation for the system's reduced statistical operator. The bath ansatz comes from a zero-th order perturbation in the system-system coupling. It allows us to formulate the weak intramolecular coupling Förster resonance energy transfer theory in a form suitable for calculating ultrafast nonlinear response of molecular systems. The theory predicts a rapid initial coherent evolution of populations arising from a transient initial coherence-dependent term, which induces a slippage of the initial condition that persists during subsequent rate-controlled transfer. Comparison with exact numerical results (HEOM) confirms the clear improvement of the present generalization over earlier formulations of the Förster theory and delineates its range of validity. Reference: Förster resonance energy transfer with transient coherent effects, Maximilian Meyer-Mölleringhof, Pablo Martinez-Azcona, Aurélia Chenu, Tomáš Mančal, https://arxiv.org/abs/2602.17789

Did life evolve to make use of quantum mechanics?

• Jim Al-Khalili

Room: Auditorium A In this talk, I will first briefly trace the history of quantum biology back to its origins almost a century ago and the influence of Niels Bohr (as seems appropriate at this meeting's venue) and highlight some of the key landmarks along its sometimes controversial past, up to it emergence in the 21st century as one of the most exciting areas of interdisciplinary research. I will then focus on recent work at Surrey with a focus on my own interests in the quantum tunnelling of H-bond protons between DNA nucleotide bases and their role in point mutations. The work is a synthesis of computational chemistry via density functional theory and an open quantum systems approach to model molecular processes in the cell. I will end with a challenge to the community to answer the fundamental question, first laid out by Schrödinger in his book What Is Life? of whether life not only knows about quantum mechanics, but has evolved the ability to utilise its tricks in order to have, or prevent it from having, a functional role in biology that is distinct from the role of quantum mechanics in inanimate matter of equivalent complexity.