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Luo J, Benjamin P, Gerhards L, Hogben HJ, Hore PJ. Orientation of birds in radiofrequency fields in the absence of the Earth's magnetic field: a possible test for the radical pair mechanism of magnetoreception. J R Soc Interface 2024; 21:20240133. [PMID: 39110232 PMCID: PMC11305414 DOI: 10.1098/rsif.2024.0133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 05/29/2024] [Accepted: 05/30/2024] [Indexed: 08/10/2024] Open
Abstract
The magnetic compass sense of migratory songbirds is thought to derive from magnetically sensitive photochemical reactions in cryptochromes located in photoreceptor cells in the birds' retinas. More specifically, transient radical pairs formed by light-activation of these proteins have been proposed to account for the birds' ability to orient themselves using the Earth's magnetic field and for the observation that radiofrequency magnetic fields, superimposed on the Earth's magnetic field, can disrupt this ability. Here, by means of spin dynamics simulations, we show that it may be possible for the birds to orient in a monochromatic radiofrequency field in the absence of the Earth's magnetic field. If such a behavioural test were successful, it would provide powerful additional evidence for a radical pair mechanism of avian magnetoreception.
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Affiliation(s)
- Jiate Luo
- Department of Chemistry, University of Oxford, Oxford, UK
| | | | - Luca Gerhards
- Department of Chemistry, University of Oxford, Oxford, UK
| | | | - P. J. Hore
- Department of Chemistry, University of Oxford, Oxford, UK
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Grüning G, Gerhards L, Wong SY, Kattnig DR, Solov'yov IA. The Effect of Spin Relaxation on Magnetic Compass Sensitivity in ErCry4a. Chemphyschem 2024:e202400129. [PMID: 38668824 DOI: 10.1002/cphc.202400129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 04/16/2024] [Indexed: 09/04/2024]
Abstract
This study explores the impact of thermal motion on the magnetic compass mechanism in migratory birds, focusing on the radical pair mechanism within cryptochrome photoreceptors. The coherence of radical pairs, crucial for magnetic field inference, is curbed by spin relaxation induced by intra-protein motion. Molecular dynamics simulations, density-functional-theory-based calculations, and spin dynamics calculations were employed, utilizing Bloch-Redfield-Wangsness (BRW) relaxation theory, to investigate compass sensitivity. Previous research hypothesized that European robin's cryptochrome 4a (ErCry4a) optimized intra-protein motion to minimize spin relaxation, enhancing magnetic sensing compared to the plant Arabidopsis thaliana's cryptochrome 1 (AtCry1). Different correlation times of the nuclear hyperfine coupling constants in AtCry1 and ErCry4a were indeed found, leading to distinct radical pair recombination yields in the two species, with ErCry4a showing optimized sensitivity. However, this optimization is likely negligible in realistic spin systems with numerous nuclear spins. Beyond insights in magnetic sensing, the study presents a detailed method employing molecular dynamics simulations to assess for spin relaxation effects on chemical reactions with realistically modelled protein motion, relevant for studying radical pair reactions at finite temperature.
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Affiliation(s)
- Gesa Grüning
- Institute of Physics, Carl von Ossietzky Universität Oldenburg, Ammerländer Heerstr. 114-118, 26129, Oldenburg, Germany
| | - Luca Gerhards
- Institute of Physics, Carl von Ossietzky Universität Oldenburg, Ammerländer Heerstr. 114-118, 26129, Oldenburg, Germany
| | - Siu Y Wong
- Institute of Physics, Carl von Ossietzky Universität Oldenburg, Ammerländer Heerstr. 114-118, 26129, Oldenburg, Germany
| | - Daniel R Kattnig
- Department of Physics and Living Systems Institute, University of Exeter, Stocker Road, Exeter, EX4 4QD, United Kingdom
| | - Ilia A Solov'yov
- Institute of Physics, Carl von Ossietzky Universität Oldenburg, Ammerländer Heerstr. 114-118, 26129, Oldenburg, Germany
- Research Center for Neurosensory Science, Carl von Ossietzky University Oldenburg, 26111, Oldenburg, Germany
- Center for Nanoscale Dynamics (CENAD), Carl von Ossietzky University Oldenburg, Ammerländer Heerstr. 114-118, 26129, Oldenburg, Germany
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Luo J. Sensitivity enhancement of radical-pair magnetoreceptors as a result of spin decoherence. J Chem Phys 2024; 160:074306. [PMID: 38380753 DOI: 10.1063/5.0182172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Accepted: 01/15/2024] [Indexed: 02/22/2024] Open
Abstract
Electron spin relaxation is, on many occasions, considered an elephant in the room that challenges the idea of a radical-pair compass, a leading hypothesis for the navigation of migratory avian species. It has been widely recognized that an effective radical-pair magnetoreceptor requires a relaxation time that is long enough for an external magnetic field as weak as the geomagnetic field to significantly modify the coherent spin dynamics. However, previous studies proposed that certain spin relaxation, far quicker than the radical recombination reactions, could enhance, rather than degrade, the directional sensitivity of a radical-pair magnetoreceptor. Here, I investigate relaxation effects on the singlet-triplet interconversion of a model radical pair and find that the enhancement effect originates from population relaxation over a period of several microseconds as a result of efficient spin decoherence. Insights into the truncated spin systems shed light on the physics behind them. I further investigate the possibilities of such enhancement in cryptochrome-based magnetoreception, in which electron hopping takes place between tryptophan residues.
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Affiliation(s)
- Jiate Luo
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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Fay TP, Limmer DT. Spin selective charge recombination in chiral donor-bridge-acceptor triads. J Chem Phys 2023; 158:2890465. [PMID: 37184005 DOI: 10.1063/5.0150269] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 05/02/2023] [Indexed: 05/16/2023] Open
Abstract
In this paper, we outline a physically motivated framework for describing spin-selective recombination processes in chiral systems, from which we derive spin-selective reaction operators for recombination reactions of donor-bridge-acceptor molecules, where the electron transfer is mediated by chirality and spin-orbit coupling. In general, the recombination process is selective only for spin-coherence between singlet and triplet states, and it is not, in general, selective for spin polarization. We find that spin polarization selectivity only arises in hopping-mediated electron transfer. We describe how this effective spin-polarization selectivity is a consequence of spin-polarization generated transiently in the intermediate state. The recombination process also augments the coherent spin dynamics of the charge separated state, which is found to have a significant effect on the recombination dynamics and to destroy any long-lived spin polarization. Although we only consider a simple donor-bridge-acceptor system, the framework we present here can be straightforwardly extended to describe spin-selective recombination processes in more complex systems.
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Affiliation(s)
- Thomas P Fay
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - David T Limmer
- Department of Chemistry, University of California, Berkeley, California 94720, USA
- Kavli Energy Nanoscience Institute at Berkeley, Berkeley, California 94720, USA
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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Wong SY, Benjamin P, Hore PJ. Magnetic field effects on radical pair reactions: estimation of B1/2 for flavin-tryptophan radical pairs in cryptochromes. Phys Chem Chem Phys 2023; 25:975-982. [PMID: 36519379 PMCID: PMC9811481 DOI: 10.1039/d2cp03793a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Magnetic field effects on the yields of radical pair reactions are often characterised by the "half-field" parameter, B1/2, which encodes useful information on spin relaxation, radical recombination kinetics and electron-electron couplings as well as electron-nuclear hyperfine interactions. Here we use a variety of spin dynamics simulation methods to estimate the hyperfine-only values of B1/2 for the flavin-tryptophan radical pair, [FAD˙- TrpH˙+], thought to be the detector in the magnetic compass sense of migratory songbirds. The main findings are: (a) in the absence of fast recombination and spin relaxation, [FAD˙- TrpH˙+] radical pairs in solution and in the putative magnetoreceptor protein, cryptochrome, have B1/2 ≈ 1.89 mT and 2.46 mT, respectively. (b) The widely used expression for B1/2 due to Weller et al. (Chem. Phys. Lett, 1983, 96, 24-27) is only applicable to small, short-lived (∼5 ns), rapidly tumbling radical pairs in solution, and is quantitatively unreliable in the context of magnetoreception. (c) In the absence of molecular tumbling, the low-field effect for [FAD˙- TrpH˙+] is predicted to be abolished by the anisotropic components of the hyperfine interactions. Armed with the 2.46 mT "base value" for cryptochrome, measurements of B1/2 can be used to understand the impact of spin relaxation on its performance as a magnetic compass sensor.
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Affiliation(s)
- Siu Ying Wong
- Institut für Physik, Carl-von-Ossietzky Universität OldenburgOldenburg 26111Germany
| | - Philip Benjamin
- Department of Chemistry, University of OxfordOxfordOX1 3QZUK
| | - P. J. Hore
- Department of Chemistry, University of OxfordOxfordOX1 3QZUK
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Smith LD, Chowdhury FT, Peasgood I, Dawkins N, Kattnig DR. Driven Radical Motion Enhances Cryptochrome Magnetoreception: Toward Live Quantum Sensing. J Phys Chem Lett 2022; 13:10500-10506. [PMID: 36332112 PMCID: PMC9677492 DOI: 10.1021/acs.jpclett.2c02840] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 10/25/2022] [Indexed: 06/16/2023]
Abstract
The mechanism underlying magnetoreception has long eluded explanation. A popular hypothesis attributes this sense to the quantum coherent spin dynamics and spin-selective recombination reactions of radical pairs in the protein cryptochrome. However, concerns about the validity of the hypothesis have been raised because unavoidable inter-radical interactions, such as the strong electron-electron dipolar coupling, appear to suppress its sensitivity. We demonstrate that sensitivity can be restored by driving the spin system through a modulation of the inter-radical distance. It is shown that this dynamical process markedly enhances geomagnetic field sensitivity in strongly coupled radical pairs via Landau-Zener-Stückelberg-Majorana transitions between singlet and triplet states. These findings suggest that a "live" harmonically driven magnetoreceptor can be more sensitive than its "dead" static counterpart.
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Hughes JA, Hardman SJO, Lukinović V, Woodward JR, Jones AR. Investigating radical pair reaction dynamics of B 12 coenzymes 1: Transient absorption spectroscopy and magnetic field effects. Methods Enzymol 2022; 669:261-281. [PMID: 35644174 DOI: 10.1016/bs.mie.2021.12.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
B12 coenzymes are vital to healthy biological function across nature. They undergo radical chemistry in a variety of contexts, where spin-correlated radical pairs can be generated both thermally and photochemically. Owing to the unusual magnetic properties of B12 radical pairs, however, most of the reaction and spin dynamics occur on a timescale (picoseconds-nanoseconds) that cannot be resolved by most measurement techniques. Here, we describe a method that combines femtosecond transient absorption spectroscopy with magnetic field exposure, which enables the direct scrutiny of such rapid processes. This approach should provide a means by which to investigate the apparently profound effect protein environments have on the generation and reactivity of B12 radical pairs.
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Affiliation(s)
- Joanna A Hughes
- Laboratory of Ultrafast Spectroscopy, ISIC, and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Samantha J O Hardman
- Manchester Institute of Biotechnology, The University of Manchester, Manchester, United Kingdom
| | | | | | - Alex R Jones
- Biometrology, Department of Chemical and Biological Sciences, National Physical Laboratory, Middlesex, United Kingdom.
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