1
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Doktorov AB, Lukzen NN. Magnetic Field Effect in Bimolecular Rate Constant of Radical Recombination. Int J Mol Sci 2023; 24:ijms24087555. [PMID: 37108719 PMCID: PMC10139179 DOI: 10.3390/ijms24087555] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 04/17/2023] [Accepted: 04/18/2023] [Indexed: 04/29/2023] Open
Abstract
The influence of magnetic fields on chemical reactions, including biological ones, has been and still is a topical subject in the field of scientific research. Experimentally discovered and theoretically substantiated magnetic and spin effects in chemical radical reactions form the basis of research in the field of spin chemistry. In the present work, the effect of a magnetic field on the rate constant of the bimolecular spin-selective recombination of radicals in the bulk of a solution is considered theoretically for the first time, taking into account the hyperfine interaction of radical spins with their magnetic nuclei. In addition, the paramagnetic relaxation of unpaired spins of the radicals and the non-equality of their g-factors that also influence the recombination process are taken into account. It is found that the reaction rate constant can vary in magnetic field from a few to half a dozen percent, depending on the relative diffusion coefficient of radicals, which is determined by the solution viscosity. It is shown that the consideration of hyperfine interactions gives rise to the presence of resonances in the dependence of the rate constant on the magnetic field. The magnitudes of the magnetic fields of these resonances are determined by the hyperfine coupling constants and difference in the g-factors of the recombining radicals. Analytical expressions for the reaction rate constant of the bulk recombination for magnetic fields larger than hfi (hyperfine interaction) constants are obtained. In general, it is shown for the first time that accounting for hyperfine interactions of radical spins with magnetic nuclei significantly affects the dependence of the reaction rate constant of the bulk radical recombination on the magnetic field.
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Affiliation(s)
- Alexander B Doktorov
- International Tomography Center SB RAS, 630090 Novosibirsk, Russia
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 630090 Novosibirsk, Russia
| | - Nikita N Lukzen
- International Tomography Center SB RAS, 630090 Novosibirsk, Russia
- Physics Faculty, Novosibirsk State University, 630090 Novosibirsk, Russia
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2
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Pažėra G, Benjamin P, Mouritsen H, Hore PJ. Isotope Substitution Effects on the Magnetic Compass Properties of Cryptochrome-Based Radical Pairs: A Computational Study. J Phys Chem B 2023; 127:838-845. [PMID: 36669149 PMCID: PMC9900586 DOI: 10.1021/acs.jpcb.2c05335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The biophysical mechanism of the magnetic compass sense of migratory songbirds is thought to rely on the photochemical reactions of flavin-containing radical pairs in cryptochrome proteins located in the birds' eyes. A consequence of this hypothesis is that the effect of the Earth's magnetic field on the quantum yields of reaction products should be sensitive to isotopic substitutions that modify the hyperfine interactions in the radicals. In this report, we use spin dynamics simulations to explore the effects of 1H → 2H, 12C → 13C, and 14N → 15N isotopic substitutions on the functioning of cryptochrome 4a as a magnetic direction sensor. Two main conclusions emerge. (1) Uniform deuteration of the flavin chromophore appears to be the best way to boost the anisotropy of the magnetic field effect and to change its symmetry. (2) 13C substitution of three of the 12 flavin carbons, in particular C4, C4a, and C8α, seems to be the best recipe for attenuating the anisotropy. These predictions should give insight into the factors that control the magnetic sensitivity once spectroscopic techniques are available for measuring magnetic field effects on oriented protein samples.
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Affiliation(s)
| | - Philip Benjamin
- Department
of Chemistry, University of Oxford, Oxford OX1 3QZ, U.K.
| | - Henrik Mouritsen
- Institut
für Biologie und Umweltwissenschaften, Carl-von-Ossietzky Universität Oldenburg, Oldenburg 26111, Germany,Research
Centre for Neurosensory Science, University
of Oldenburg, Oldenburg 26111, Germany
| | - P. J. Hore
- Department
of Chemistry, University of Oxford, Oxford OX1 3QZ, U.K.,
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3
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Jiang X, Chen Y, Zhang X, You F, Yao J, Yang H, Xia BY. Magnetic Field-Assisted Construction and Enhancement of Electrocatalysts. CHEMSUSCHEM 2022; 15:e202201551. [PMID: 36193685 DOI: 10.1002/cssc.202201551] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Revised: 09/30/2022] [Indexed: 06/16/2023]
Abstract
Driven by the energy crisis and environmental pollution, developing sustainable clean energy is an effective strategy to realize carbon neutrality. Electrocatalytic reactions are crucial to sustainable energy conversion and storage technologies, and advanced electrocatalysts are required to improve the sluggish electrocatalytic reactions. The magnetic field, as a thermodynamic parameter independent of temperature and pressure, is vital in the construction of electrocatalysts and enhancement of electrocatalysis. In this Review, the recent progress of magnetic field-assisted construction of electrocatalysts and enhancement of electrocatalysis is comprehensively summarized. Originating from the structure-activity-performance relationship of electrocatalysts, the fundamentals of the magnetic field-induced construction of electrocatalysts, including the magnetocaloric effect, nucleation and growth, and phase regulation, have been illustrated. In addition, the magnetic effect on the electrocatalytic reaction, namely, the magnetothermal, magnetohydrodynamic and micro magnetohydrodynamic, Maxwell stress, Kelvin force, and spin selection effects, are discussed. Finally, the perspective and challenges for magnetic field-assisted construction of electrocatalysts and enhancement of electrocatalysis are proposed.
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Affiliation(s)
- Xueliang Jiang
- Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, School of Materials Science and Engineering, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Wuhan Institute of Technology, No. 206 Guanggu 1st Road, Wuhan, 430205, P. R. China
| | - Yana Chen
- Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, School of Materials Science and Engineering, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Wuhan Institute of Technology, No. 206 Guanggu 1st Road, Wuhan, 430205, P. R. China
| | - Xianzheng Zhang
- Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, School of Materials Science and Engineering, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Wuhan Institute of Technology, No. 206 Guanggu 1st Road, Wuhan, 430205, P. R. China
| | - Feng You
- Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, School of Materials Science and Engineering, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Wuhan Institute of Technology, No. 206 Guanggu 1st Road, Wuhan, 430205, P. R. China
| | - Junlong Yao
- Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, School of Materials Science and Engineering, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Wuhan Institute of Technology, No. 206 Guanggu 1st Road, Wuhan, 430205, P. R. China
| | - Huan Yang
- Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, School of Materials Science and Engineering, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Wuhan Institute of Technology, No. 206 Guanggu 1st Road, Wuhan, 430205, P. R. China
| | - Bao Yu Xia
- Key Laboratory of Material Chemistry for Energy Conversion and Storage, Hubei Key Laboratory of Material Chemistry and Service Failure, Hubei Engineering Research Center for Biomaterials and Medical Protective Materials, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, 430074, P. R. China
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4
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Magnetic sensitivity of cryptochrome 4 from a migratory songbird. Nature 2021; 594:535-540. [PMID: 34163056 DOI: 10.1038/s41586-021-03618-9] [Citation(s) in RCA: 124] [Impact Index Per Article: 41.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Accepted: 05/06/2021] [Indexed: 02/06/2023]
Abstract
Night-migratory songbirds are remarkably proficient navigators1. Flying alone and often over great distances, they use various directional cues including, crucially, a light-dependent magnetic compass2,3. The mechanism of this compass has been suggested to rely on the quantum spin dynamics of photoinduced radical pairs in cryptochrome flavoproteins located in the retinas of the birds4-7. Here we show that the photochemistry of cryptochrome 4 (CRY4) from the night-migratory European robin (Erithacus rubecula) is magnetically sensitive in vitro, and more so than CRY4 from two non-migratory bird species, chicken (Gallus gallus) and pigeon (Columba livia). Site-specific mutations of ErCRY4 reveal the roles of four successive flavin-tryptophan radical pairs in generating magnetic field effects and in stabilizing potential signalling states in a way that could enable sensing and signalling functions to be independently optimized in night-migratory birds.
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5
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Déjean V, Konowalczyk M, Gravell J, Golesworthy MJ, Gunn C, Pompe N, Foster Vander Elst O, Tan KJ, Oxborrow M, Aarts DGAL, Mackenzie SR, Timmel CR. Detection of magnetic field effects by confocal microscopy. Chem Sci 2020; 11:7772-7781. [PMID: 34094150 PMCID: PMC8163210 DOI: 10.1039/d0sc01986k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Certain pairs of paramagnetic species generated under conservation of total spin angular momentum are known to undergo magnetosensitive processes. Two prominent examples of systems exhibiting these so-called magnetic field effects (MFEs) are photogenerated radical pairs created from either singlet or triplet molecular precursors, and pairs of triplet states generated by singlet fission. Here, we showcase confocal microscopy as a powerful technique for the investigation of such phenomena. We first characterise the instrument by studying the field-sensitive chemistry of two systems in solution: radical pairs formed in a cryptochrome protein and the flavin mononucleotide/hen egg-white lysozyme model system. We then extend these studies to single crystals. Firstly, we report temporally and spatially resolved MFEs in flavin-doped lysozyme single crystals. Anisotropic magnetic field effects are then reported in tetracene single crystals. Finally, we discuss the future applications of confocal microscopy for the study of magnetosensitive processes with a particular focus on the cryptochrome-based chemical compass believed to lie at the heart of animal magnetoreception. Confocal microscopy is showcased as a powerful technique for the measurement of spatiotemporally-resolved magnetic field effects in both solutions and single crystals.![]()
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Affiliation(s)
- Victoire Déjean
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory Oxford OX1 3QR UK
| | - Marcin Konowalczyk
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory Oxford OX1 3QR UK .,Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory Oxford OX1 3QZ UK
| | - Jamie Gravell
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory Oxford OX1 3QR UK
| | - Matthew J Golesworthy
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory Oxford OX1 3QR UK
| | - Catlin Gunn
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory Oxford OX1 3QR UK
| | - Nils Pompe
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory Oxford OX1 3QR UK
| | | | - Ke-Jie Tan
- Department of Materials, Imperial College London London SW7 2AZ UK
| | - Mark Oxborrow
- Department of Materials, Imperial College London London SW7 2AZ UK
| | - Dirk G A L Aarts
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory Oxford OX1 3QZ UK
| | - Stuart R Mackenzie
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory Oxford OX1 3QZ UK
| | - Christiane R Timmel
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory Oxford OX1 3QR UK .,Centre for Advanced Electron Spin Resonance (CAESR), Department of Chemistry, University of Oxford Oxford OX1 3QR UK
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6
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Pan H, Jiang X, Wang X, Wang Q, Wang M, Shen Y. Effective Magnetic Field Regulation of the Radical Pair Spin States in Electrocatalytic CO 2 Reduction. J Phys Chem Lett 2020; 11:48-53. [PMID: 31821005 DOI: 10.1021/acs.jpclett.9b03146] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Regulation of the radical pair spin states allows effective optimization of the electrocatalytic CO2 reduction reaction. This study for the first time reports an experimental observation of significantly boosting the catalytic activity of tin nanoparticle catalysts by an external magnetic field for electrocatalytic CO2 reduction to formate/formic acid. We reveal that enhancing the amount of singlet radical pairs via magnetic field-facilitated triplet → singlet spin evolution can significantly increase the catalytic activity toward an efficient overall electrochemical CO2 reduction reaction. When a common Sn nanoparticle electrode was used as an example, in a constant applied magnetic field (about 0.9 T), the yield of formic acid can be nearly doubled compared to that of zero magnetic field. This finding suggests the merits of radical pair spin states in the electron-transfer process and paves the way toward high formate production in electrocatalytic reduction of CO2.
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Affiliation(s)
- Haiping Pan
- Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China
- School of Physics and Optoelectronic Engineering , Foshan University , Foshan , Guangdong 528000 , China
| | - XingXing Jiang
- Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China
| | - Xikui Wang
- Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China
| | - Qinglong Wang
- Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China
| | - Mingkui Wang
- Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China
| | - Yan Shen
- Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China
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7
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Miura T. Studies on coherent and incoherent spin dynamics that control the magnetic field effect on photogenerated radical pairs. Mol Phys 2019. [DOI: 10.1080/00268976.2019.1643510] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Tomoaki Miura
- Department of Science, Niigata University, Niigata, Japan
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8
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Nielsen C, Hui R, Lui WY, Solov’yov IA. Towards predicting intracellular radiofrequency radiation effects. PLoS One 2019; 14:e0213286. [PMID: 30870450 PMCID: PMC6417702 DOI: 10.1371/journal.pone.0213286] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Accepted: 02/12/2019] [Indexed: 11/19/2022] Open
Abstract
Recent experiments have reported an effect of weak radiofrequency magnetic fields in the MHz-range on the concentrations of reactive oxygen species (ROS) in living cells. Since the energy that could possibly be deposited by the radiation is orders of magnitude smaller than the energy of molecular thermal motion, it was suggested that the effect was caused by the interaction of RF magnetic fields with transient radical pairs within the cells, affecting the ROS formation rates through the radical pair mechanism. It is, however, at present not entirely clear how to predict RF magnetic field effects at certain field frequency and intensity in nanoscale biomolecular systems. We suggest a possible recipe for interpreting the radiofrequency effects in cells by presenting a general workflow for calculation of the reactive perturbations inside a cell as a function of RF magnetic field strength and frequency. To justify the workflow, we discuss the effects of radiofrequency magnetic fields on generic spin systems to particularly illustrate how the reactive radicals could be affected by specific parameters of the experiment. We finally argue that the suggested workflow can be used to predict effects of radiofrequency magnetic fields on radical pairs in biological cells, which is specially important for wireless recharging technologies where one has to know of any harmful effects that exposure to such radiation might cause.
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Affiliation(s)
- Claus Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense M, Denmark
| | - Ron Hui
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China
| | - Wing-Yee Lui
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China
| | - Ilia A. Solov’yov
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense M, Denmark
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9
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Wu Z, Chen C, Liu J, Lu Y, Xu J, Liu X, Cui G, Trabelsi T, Francisco JS, Mardyukov A, Eckhardt AK, Schreiner PR, Zeng X. Caged Nitric Oxide-Thiyl Radical Pairs. J Am Chem Soc 2019; 141:3361-3365. [PMID: 30758958 DOI: 10.1021/jacs.8b12746] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
S-Nitrosothiols (RSNO) are exogenous and endogenous sources of nitric oxide in biological systems due to facile homolytic cleavage of the S-N bonds. By following the photolytic decomposition of prototypical RSNO (R = Me and Et) in Ne, Ar, and N2 matrixes (<10 K), elusive caged radical pairs consisting of nitric oxide (NO•) and thiyl radicals (RS•), bridged by O···S and H···N connections, were identified with IR and UV/vis spectroscopy. Upon red-light irradiation, both caged radical pairs (RS•···•ON) vanish and reform RSNO. According to the calculation at the CASPT2(10,8)/cc-pVDZ level (298.15 K), the dissociation energy of MeS•···•ON amounts to 4.7 kcal mol-1.
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Affiliation(s)
- Zhuang Wu
- College of Chemistry, Chemical Engineering and Materials Science , Soochow University , Suzhou 215123 , China
| | - Changyun Chen
- College of Chemistry, Chemical Engineering and Materials Science , Soochow University , Suzhou 215123 , China
| | - Jie Liu
- College of Chemistry, Chemical Engineering and Materials Science , Soochow University , Suzhou 215123 , China
| | - Yan Lu
- College of Chemistry, Chemical Engineering and Materials Science , Soochow University , Suzhou 215123 , China
| | - Jian Xu
- College of Chemistry, Chemical Engineering and Materials Science , Soochow University , Suzhou 215123 , China
| | - Xiangyang Liu
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry , Beijing Normal University , Beijing 100875 , China
| | - Ganglong Cui
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry , Beijing Normal University , Beijing 100875 , China
| | - Tarek Trabelsi
- Department of Earth and Environmental Science and Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - Joseph S Francisco
- Department of Earth and Environmental Science and Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - Artur Mardyukov
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - André K Eckhardt
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Peter R Schreiner
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Xiaoqing Zeng
- College of Chemistry, Chemical Engineering and Materials Science , Soochow University , Suzhou 215123 , China
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10
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Bajuszova Z, Naif H, Ali Z, McGinnis J, Islam M. Cavity enhanced liquid-phase stopped-flow kinetics. Analyst 2018; 143:493-502. [PMID: 29271423 DOI: 10.1039/c7an01823a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The first application of liquid-phase broadband cavity enhanced spectroscopy (BBCEAS) to the measurement of stopped-flow kinetics is reported. The stopped-flow technique is widely used for the study of the kinetics of fast liquid-phase reactions down to millisecond timescales. UV-visible absorption spectroscopy is commonly used as the detection method. Increased sensitivity can potentially allow reactions which are too fast to be measured, to be studied by slowing down the reaction rate through the use of lower concentration of reactants. A simple low cost BBCEAS experimental setup was coupled to a commercial stopped-flow instrument. Comparative standard absorption measurements were also made using a UV-visible double-beam spectrometer as the detector. Measurements were made on the reaction of potassium ferricyanide with sodium ascorbate under pseudo-first order conditions at pH 8 and pH 9.2 A cavity enhancement factor (CEF) of 78 at 434 nm was obtained whilst the minimum detectable change in the absorption coefficient αmin(t), was 1.35 × 10-5 cm-1 Hz-1/2. The kinetic data at pH 9.2 was too fast to be measured using conventional spectroscopy, whilst the BBCEAS measurements allowed 30 fold lower concentration of reactants to be used which slowed down the reaction rate enough to allow the rate constant to be determined. The BBCEAS results showed a 58 fold improvement in sensitivity over the conventional measurements and also compared favourably with the relatively few previous liquid-phase cavity enhanced kinetic studies which have been performed using significantly more complex and expensive experimental setups.
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Affiliation(s)
- Zuzana Bajuszova
- School of Science and Engineering, Teesside University, Borough Road, Middlesbrough, TS1 3BA, UK.
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11
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Zollitsch TM, Jarocha LE, Bialas C, Henbest KB, Kodali G, Dutton PL, Moser CC, Timmel CR, Hore PJ, Mackenzie SR. Magnetically Sensitive Radical Photochemistry of Non-natural Flavoproteins. J Am Chem Soc 2018; 140:8705-8713. [PMID: 29940116 DOI: 10.1021/jacs.8b03104] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It is a remarkable fact that ∼50 μT magnetic fields can alter the rates and yields of certain free-radical reactions and that such effects might be the basis of the light-dependent ability of migratory birds to sense the direction of the Earth's magnetic field. The most likely sensory molecule at the heart of this chemical compass is cryptochrome, a flavin-containing protein that undergoes intramolecular, blue-light-induced electron transfer to produce magnetically sensitive radical pairs. To learn more about the factors that control the magnetic sensitivity of cryptochromes, we have used a set of de novo designed protein maquettes that self-assemble as four-α-helical proteins incorporating a single tryptophan residue as an electron donor placed approximately 0.6, 1.1, or 1.7 nm away from a covalently attached riboflavin as chromophore and electron acceptor. Using a specifically developed form of cavity ring-down spectroscopy, we have characterized the photochemistry of these designed flavoprotein maquettes to determine the identities and kinetics of the transient radicals responsible for the magnetic field effects. Given the gross structural and dynamic differences from the natural proteins, it is remarkable that the maquettes show magnetic field effects that are so similar to those observed for cryptochromes.
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Affiliation(s)
- Tilo M Zollitsch
- Department of Chemistry , University of Oxford, Physical and Theoretical Chemistry Laboratory , Oxford OX1 3QZ , United Kingdom
| | - Lauren E Jarocha
- Department of Chemistry , University of Oxford, Physical and Theoretical Chemistry Laboratory , Oxford OX1 3QZ , United Kingdom
| | - Chris Bialas
- Johnson Research Foundation, Department of Biochemistry and Biophysics , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - Kevin B Henbest
- Department of Chemistry , University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory , Oxford OX1 3QR , United Kingdom
| | - Goutham Kodali
- Johnson Research Foundation, Department of Biochemistry and Biophysics , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - P Leslie Dutton
- Johnson Research Foundation, Department of Biochemistry and Biophysics , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - Christopher C Moser
- Johnson Research Foundation, Department of Biochemistry and Biophysics , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - Christiane R Timmel
- Department of Chemistry , University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory , Oxford OX1 3QR , United Kingdom
| | - P J Hore
- Department of Chemistry , University of Oxford, Physical and Theoretical Chemistry Laboratory , Oxford OX1 3QZ , United Kingdom
| | - Stuart R Mackenzie
- Department of Chemistry , University of Oxford, Physical and Theoretical Chemistry Laboratory , Oxford OX1 3QZ , United Kingdom
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12
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Sheppard DMW, Li J, Henbest KB, Neil SRT, Maeda K, Storey J, Schleicher E, Biskup T, Rodriguez R, Weber S, Hore PJ, Timmel CR, Mackenzie SR. Millitesla magnetic field effects on the photocycle of an animal cryptochrome. Sci Rep 2017; 7:42228. [PMID: 28176875 PMCID: PMC5296725 DOI: 10.1038/srep42228] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Accepted: 01/06/2017] [Indexed: 11/09/2022] Open
Abstract
Drosophila have been used as model organisms to explore both the biophysical mechanisms of animal magnetoreception and the possibility that weak, low-frequency anthropogenic electromagnetic fields may have biological consequences. In both cases, the presumed receptor is cryptochrome, a protein thought to be responsible for magnetic compass sensing in migratory birds and a variety of magnetic behavioural responses in insects. Here, we demonstrate that photo-induced electron transfer reactions in Drosophila melanogaster cryptochrome are indeed influenced by magnetic fields of a few millitesla. The form of the protein containing flavin and tryptophan radicals shows kinetics that differ markedly from those of closely related members of the cryptochrome-photolyase family. These differences and the magnetic sensitivity of Drosophila cryptochrome are interpreted in terms of the radical pair mechanism and a photocycle involving the recently discovered fourth tryptophan electron donor.
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Affiliation(s)
- Dean M. W. Sheppard
- Department of Chemistry, University of Oxford, Physical & Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - Jing Li
- Department of Chemistry, University of Oxford, Physical & Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - Kevin B. Henbest
- Department of Chemistry, University of Oxford, Physical & Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford OX1 3QR, United Kingdom
| | - Simon R. T. Neil
- Department of Chemistry, University of Oxford, Physical & Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - Kiminori Maeda
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford OX1 3QR, United Kingdom
- Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570, Japan
| | - Jonathan Storey
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford OX1 3QR, United Kingdom
| | - Erik Schleicher
- Institute of Physical Chemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - Till Biskup
- Institute of Physical Chemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - Ryan Rodriguez
- Institute of Physical Chemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - Stefan Weber
- Institute of Physical Chemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - P. J. Hore
- Department of Chemistry, University of Oxford, Physical & Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - Christiane R. Timmel
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford OX1 3QR, United Kingdom
| | - Stuart R. Mackenzie
- Department of Chemistry, University of Oxford, Physical & Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
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13
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Bialas C, Jarocha LE, Henbest KB, Zollitsch TM, Kodali G, Timmel CR, Mackenzie SR, Dutton PL, Moser CC, Hore PJ. Engineering an Artificial Flavoprotein Magnetosensor. J Am Chem Soc 2016; 138:16584-16587. [PMID: 27958724 DOI: 10.1021/jacs.6b09682] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Migratory birds use the Earth's magnetic field as a source of navigational information. This light-dependent magnetic compass is thought to be mediated by cryptochrome proteins in the retina. Upon light activation, electron transfer between the flavin adenine dinucleotide cofactor and tryptophan residues leads to the formation of a spin-correlated radical pair, whose subsequent fate is sensitive to external magnetic fields. To learn more about the functional requirements of this complex chemical compass, we have created a family of simplified, adaptable proteins-maquettes-that contain a single tryptophan residue at different distances from a covalently bound flavin. Despite the complete absence of structural resemblance to the native cryptochrome fold or sequence, the maquettes exhibit a strong magnetic field effect that rivals those observed in the natural proteins in vitro. These novel maquette designs offer unprecedented flexibility to explore the basic requirements for magnetic sensing in a protein environment.
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Affiliation(s)
- Chris Bialas
- Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - Lauren E Jarocha
- Department of Chemistry, University of Oxford , Physical and Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - Kevin B Henbest
- Department of Chemistry, University of Oxford , Inorganic Chemistry Laboratory, Oxford OX1 3QR, United Kingdom
| | - Tilo M Zollitsch
- Department of Chemistry, University of Oxford , Physical and Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - Goutham Kodali
- Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - Christiane R Timmel
- Department of Chemistry, University of Oxford , Inorganic Chemistry Laboratory, Oxford OX1 3QR, United Kingdom
| | - Stuart R Mackenzie
- Department of Chemistry, University of Oxford , Physical and Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - P Leslie Dutton
- Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - Christopher C Moser
- Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - P J Hore
- Department of Chemistry, University of Oxford , Physical and Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
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14
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Albuquerque W, Nascimento T, Brandão-Costa R, Fernandes T, Porto A. Static magnetic field effects on proteases with fibrinolytic activity produced byMucor subtilissimus. Bioelectromagnetics 2016; 38:109-120. [DOI: 10.1002/bem.22016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2015] [Accepted: 10/15/2016] [Indexed: 11/09/2022]
Affiliation(s)
- Wendell Albuquerque
- Department of Animal Morphology and Physiology; Federal Rural University of Pernambuco; Recife Pernambuco Brazil
| | - Thiago Nascimento
- Laboratory of Immunopathology Keizo Asami (LIKA), Federal University of Pernambuco; Recife Pernambuco Brazil
| | - Romero Brandão-Costa
- Department of Animal Morphology and Physiology; Federal Rural University of Pernambuco; Recife Pernambuco Brazil
| | - Thiago Fernandes
- Department of Biophysics and Radiobiology; Federal University of Pernambuco; Recife Pernambuco Brazil
| | - Ana Porto
- Department of Animal Morphology and Physiology; Federal Rural University of Pernambuco; Recife Pernambuco Brazil
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15
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Evans EW, Li J, Storey JG, Maeda K, Henbest KB, Dodson CA, Hore PJ, Mackenzie SR, Timmel CR. Sensitive fluorescence-based detection of magnetic field effects in photoreactions of flavins. Phys Chem Chem Phys 2016; 17:18456-63. [PMID: 26108474 DOI: 10.1039/c5cp00723b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Magnetic field effect studies have been conducted on a variety of flavin-based radical pair systems chosen to model the magnetosensitivity of the photoinduced radical pairs found in cryptochrome flavoproteins. Cryptochromes are blue-light photoreceptor proteins which are thought to mediate avian magnetoreception, an hypothesis supported by recent in vitro observations of magnetic field-dependent reaction kinetics for a light-induced radical pair in a cryptochrome from the plant Arabidopsis thaliana. Many cryptochromes are difficult to express in large quantities or high concentrations and are easily photodegraded. Magnetic field effects are typically measured by spectroscopic detection of the transient radical (pair) concentrations. Due to its low sensitivity, single-pass transient absorption spectroscopy can be of limited use in such experiments and much recent work has involved development of other methodologies offering improved sensitivity. Here we explore the use of flavin fluorescence as the magnetosensitive probe and demonstrate the exceptional sensitivity of this technique which allows the detection of magnetic field effects in flavin samples at sub-nanomolar concentrations and in cryptochromes.
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Affiliation(s)
- Emrys W Evans
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Oxford, OX1 3QR, UK.
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16
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Müller P, Brettel K, Grama L, Nyitrai M, Lukacs A. Photochemistry of Wild-Type and N378D Mutant E. coli DNA Photolyase with Oxidized FAD Cofactor Studied by Transient Absorption Spectroscopy. Chemphyschem 2016; 17:1329-40. [PMID: 26852903 DOI: 10.1002/cphc.201501077] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Indexed: 01/02/2023]
Abstract
DNA photolyases (PLs) and evolutionarily related cryptochrome (CRY) blue-light receptors form a widespread superfamily of flavoproteins involved in DNA photorepair and signaling functions. They share a flavin adenine dinucleotide (FAD) cofactor and an electron-transfer (ET) chain composed typically of three tryptophan residues that connect the flavin to the protein surface. Four redox states of FAD are relevant for the various functions of PLs and CRYs: fully reduced FADH(-) (required for DNA photorepair), fully oxidized FADox (blue-light-absorbing dark state of CRYs), and the two semireduced radical states FAD(.-) and FADH(.) formed in ET reactions. The PL of Escherichia coli (EcPL) has been studied for a long time and is often used as a reference system; however, EcPL containing FADox has so far not been investigated on all relevant timescales. Herein, a detailed transient absorption study of EcPL on timescales from nanoseconds to seconds after excitation of FADox is presented. Wild-type EcPL and its N378D mutant, in which the asparagine facing the N5 of the FAD isoalloxazine is replaced by aspartic acid, known to protonate FAD(.-) (formed by ET from the tryptophan chain) in plant CRYs in about 1.5 μs, are characterized. Surprisingly, the mutant protein does not show this protonation. Instead, FAD(.-) is converted in 3.3 μs into a state with spectral features that are different from both FADH(.) and FAD(.-) . Such a conversion does not occur in wild-type EcPL. The chemical nature and formation mechanism of the atypical FAD radical in N378D mutant EcPL are discussed.
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Affiliation(s)
- Pavel Müller
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France.
| | - Klaus Brettel
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France.
| | - Laszlo Grama
- Department of Biophysics, Medical School, University of Pecs, 12 str. Szigeti, 7624, Pecs, Hungary
| | - Miklos Nyitrai
- Department of Biophysics, Medical School, University of Pecs, 12 str. Szigeti, 7624, Pecs, Hungary
| | - Andras Lukacs
- Department of Biophysics, Medical School, University of Pecs, 12 str. Szigeti, 7624, Pecs, Hungary.
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17
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Kattnig DR, Evans EW, Déjean V, Dodson CA, Wallace MI, Mackenzie SR, Timmel CR, Hore PJ. Chemical amplification of magnetic field effects relevant to avian magnetoreception. Nat Chem 2016; 8:384-91. [PMID: 27001735 DOI: 10.1038/nchem.2447] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Accepted: 12/18/2015] [Indexed: 12/15/2022]
Abstract
Magnetic fields as weak as the Earth's can change the yields of radical pair reactions even though the energies involved are orders of magnitude smaller than the thermal energy, kBT, at room temperature. Proposed as the source of the light-dependent magnetic compass in migratory birds, the radical pair mechanism is thought to operate in cryptochrome flavoproteins in the retina. Here we demonstrate that the primary magnetic field effect on flavin photoreactions can be amplified chemically by slow radical termination reactions under conditions of continuous photoexcitation. The nature and origin of the amplification are revealed by studies of the intermolecular flavin-tryptophan and flavin-ascorbic acid photocycles and the closely related intramolecular flavin-tryptophan radical pair in cryptochrome. Amplification factors of up to 5.6 were observed for magnetic fields weaker than 1 mT. Substantial chemical amplification could have a significant impact on the viability of a cryptochrome-based magnetic compass sensor.
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Affiliation(s)
- Daniel R Kattnig
- Department of Chemistry, University of Oxford, Physical &Theoretical Chemistry Laboratory, Oxford OX1 3QZ, UK
| | - Emrys W Evans
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK
| | - Victoire Déjean
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK
| | - Charlotte A Dodson
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, UK
| | - Mark I Wallace
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, UK
| | - Stuart R Mackenzie
- Department of Chemistry, University of Oxford, Physical &Theoretical Chemistry Laboratory, Oxford OX1 3QZ, UK
| | - Christiane R Timmel
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK
| | - P J Hore
- Department of Chemistry, University of Oxford, Physical &Theoretical Chemistry Laboratory, Oxford OX1 3QZ, UK
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18
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Dodson CA, Wedge CJ, Murakami M, Maeda K, Wallace MI, Hore PJ. Fluorescence-detected magnetic field effects on radical pair reactions from femtolitre volumes. Chem Commun (Camb) 2015; 51:8023-6. [PMID: 25865161 DOI: 10.1039/c5cc01099c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
We show that the effects of applied magnetic fields on radical pair reactions can be sensitively measured from sample volumes as low as ∼100 femtolitres using total internal reflection fluorescence microscopy. Development of a fluorescence-based microscope method is likely to be a key step in further miniaturisation that will allow detection of magnetic field effects on single molecules.
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Affiliation(s)
- C A Dodson
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, UK
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19
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Neil SRT, Li J, Sheppard DMW, Storey J, Maeda K, Henbest KB, Hore PJ, Timmel CR, Mackenzie SR. Broadband Cavity-Enhanced Detection of Magnetic Field Effects in Chemical Models of a Cryptochrome Magnetoreceptor. J Phys Chem B 2014; 118:4177-84. [DOI: 10.1021/jp500732u] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Simon R. T. Neil
- Department of Chemistry, Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
| | - Jing Li
- Department of Chemistry, Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
| | - Dean M. W. Sheppard
- Department of Chemistry, Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
| | - Jonathan Storey
- Department of Chemistry, Inorganic
Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, United Kingdom
| | - Kiminori Maeda
- Department of Chemistry, Inorganic
Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, United Kingdom
| | - Kevin B. Henbest
- Department of Chemistry, Inorganic
Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, United Kingdom
| | - P. J. Hore
- Department of Chemistry, Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
| | - Christiane R. Timmel
- Department of Chemistry, Inorganic
Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, United Kingdom
| | - Stuart R. Mackenzie
- Department of Chemistry, Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
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20
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Evans EW, Dodson CA, Maeda K, Biskup T, Wedge CJ, Timmel CR. Magnetic field effects in flavoproteins and related systems. Interface Focus 2013; 3:20130037. [PMID: 24511388 PMCID: PMC3915827 DOI: 10.1098/rsfs.2013.0037] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Within the framework of the radical pair mechanism, magnetic fields may alter the rate and yields of chemical reactions involving spin-correlated radical pairs as intermediates. Such effects have been studied in detail in a variety of chemical systems both experimentally and theoretically. In recent years, there has been growing interest in whether such magnetic field effects (MFEs) also occur in biological systems, a question driven most notably by the increasing body of evidence for the involvement of such effects in the magnetic compass sense of animals. The blue-light photoreceptor cryptochrome is placed at the centre of this debate and photoexcitation of its bound flavin cofactor has indeed been shown to result in the formation of radical pairs. Here, we review studies of MFEs on free flavins in model systems as well as in blue-light photoreceptor proteins and discuss the properties that are crucial in determining the magnetosensitivity of these systems.
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Affiliation(s)
- Emrys W. Evans
- Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
| | - Charlotte A. Dodson
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | - Kiminori Maeda
- Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
| | - Till Biskup
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg, Germany
| | - C. J. Wedge
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK
| | - Christiane R. Timmel
- Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
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21
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Richert S, Rosspeintner A, Landgraf S, Grampp G, Vauthey E, Kattnig DR. Time-resolved magnetic field effects distinguish loose ion pairs from exciplexes. J Am Chem Soc 2013; 135:15144-52. [PMID: 24041160 PMCID: PMC3797520 DOI: 10.1021/ja407052t] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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We describe the experimental investigation
of time-resolved magnetic
field effects in exciplex-forming organic donor–acceptor systems.
In these systems, the photoexcited acceptor state is predominantly
deactivated by bimolecular electron transfer reactions (yielding radical
ion pairs) or by direct exciplex formation. The delayed fluorescence
emitted by the exciplex is magnetosensitive if the reaction pathway
involves loose radical ion pair states. This magnetic field effect
results from the coherent interconversion between the electronic singlet
and triplet radical ion pair states as described by the radical pair
mechanism. By monitoring the changes in the exciplex luminescence
intensity when applying external magnetic fields, details of the reaction
mechanism can be elucidated. In this work we present results obtained
with the fluorophore-quencher pair 9,10-dimethylanthracene/N,N-dimethylaniline (DMA) in solvents of
systematically varied permittivity. A simple theoretical model is
introduced that allows discriminating the initial state of quenching,
viz., the loose ion pair and the exciplex, based on the time-resolved
magnetic field effect. The approach is validated by applying it to
the isotopologous fluorophore-quencher pairs pyrene/DMA and pyrene-d10/DMA. We detect that both the exciplex and
the radical ion pair are formed during the initial quenching stage.
Upon increasing the solvent polarity, the relative importance of the
distant electron transfer quenching increases. However, even in comparably
polar media, the exciplex pathway remains remarkably significant.
We discuss our results in relation to recent findings on the involvement
of exciplexes in photoinduced electron transfer reactions.
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Affiliation(s)
- Sabine Richert
- Department of Physical Chemistry, University of Geneva , 30 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
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22
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Mouritsen H, Hore PJ. The magnetic retina: light-dependent and trigeminal magnetoreception in migratory birds. Curr Opin Neurobiol 2012; 22:343-52. [DOI: 10.1016/j.conb.2012.01.005] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Revised: 01/03/2012] [Accepted: 01/17/2012] [Indexed: 10/28/2022]
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