研究领域

Inorganic Chemistry

Magnetic Field Effects on Chemical Reactions There is only one established mechanism by which a magnetic field can affect a chemical reaction known as the Radical Pair Mechanism: radicals, typically formed by photolysis, are generated under conservation of total spin angular momentum in either a singlet state or the triplet. The efficiency of the consequent interconversion between singlet and triplet pairs can be affected by oscillating and/or static magnetic fields. If singlet and triplet pairs recombine to different products or do so at different rates, magnetic field effects on the yield and/or kinetics of radical concentration can be determined. (i) Molecular Compasses We have been able to demonstrate recently that magnetic fields as weak as that of the Earth can affect the outcome of chemical reactions. Moreover, we could show that the radical pair system involved could act as a molecular compass, i.e., the kinetics of the radical pair reaction depended strongly on the relative orientation of the molecular biradical studied with respect to that of the applied magnetic field. In our laboratory, we are now aiming to create and investigate other radical pair systems acting as molecular compasses particularly those that are functioning in magnetic fields as weak as that of the Earth. [1] (ii) Bird Migration There are few biological systems that are known to harbor radical pair systems of the right characteristics to display magnetic field sensitivity. Our particular focus lies in the investigation of the magnetic field response of flavin/tryptophane radical pairs in proteins of the photolyase/crytpochrome family with the latter being speculated to be the protein involved in avian magnetosensitivity. [2] (iii) Low and Zero Field ESR development Detection of weak static and oscillating magnetic field effects such as those discussed above is only possible with sophisticated apparatus: obviously zero and weak field optical detection spectrometers are not commercially available. Hence, all technique development is carried out in our group. [3] Electron Spin Resonance (ESR) CRT is the director of the Centre for Advanced Electron Spin Resonance (CAESR) housing state-of-the-art spectrometers (commissioned in 2007) working at both continuous and pulsed modes and well as at X- and W-band. Our group exploits ESR to investigate long-range structure in chemical and biological systems with a particular focus on a technique called Double Electron Electron Resonance (DEER). Previous (and present) part II and DPhil projects have spanned the whole spectrum from purely theoretical data analysis and model development to protein synthesis and experimental DEER (in collaboration with Labs in chemistry and biology). [4]

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Magnetically sensitive light-induced reactions in cryptochrome are consistent with its proposed role as a magnetoreceptor Kiminori Maeda, Alexander J. Robinson, Kevin B. Henbest, Hannah J. Hogben, Till Biskup, Margaret Ahmad, Erik Schleicher, Stefan Weber, Christiane R. Timmel and Peter J. Hore, Proc. Natl. Acad. Sci. USA, 109(13), 4774-4779 (2012). DOI: 10.1073/pnas.1118959109 Characterisation of the paramagnetic [2Fe-2S](+) centre in palustrisredoxin-B (PuxB) from Rhodopseudomonas palustris CGA009: g-matrix determination and spin coupling analysis Joseph A.B. Abdalla, Alice M. Bowen, Stephen G. Bell, Luet L. Wong, Christiane R. Timmel and Jeffrey Harmer, Phys. Chem. Chem. Phys., 14(18), 6526-6537 (2012). DOI: 10.1039/c2cp24112a Following Radical Pair Reactions in Solution: A Step Change in Sensitivity Using Cavity Ring-Down Detection Kiminori Maeda, Simon R.T. Neil, Kevin B. Henbest, Stefan Weber, Erik Schleicher, Peter J. Hore, Stuart R. Mackenzie and Christiane R. Timmel, J. Am. Chem. Soc, 133(44), 17807-17815 (2011). DOI: 10.1021/ja206783t The Short-Lived Signaling State of the Photoactive Yellow Protein Photoreceptor Revealed by Combined Structural Probes Pradeep L. Ramachandran, Janet E. Lovett, Patrick J. Carl, Marco Cammarata, Jae Hyuk Lee, Yang Ouk Jung, Hyotcherl Ihee, Christiane R. Timmel and Jasper J. van Thor, J. Am. Chem. Soc., 133(24), 9395-9404 (2011). DOI: 10.1021/ja200617t Shigella flexneri Spa15 Crystal Structure Verified in Solution by Double Electron Electron Resonance James E.D. Lillington, Janet E. Lovett, Steven Johnson, Pietro Roversi, Christiane R. Timmel and Susan M. Lea, J. Mol. Biol., 405(2), 427-435 (2011). DOI: 10.1016/j.jmb.2010.10.053 Spin selective recombination kinetics of a model chemical magnetoreceptor Kiminori Maeda, Christopher J. Wedge, Jonathan G. Storey, Kevin B. Henbest, Paul A. Liddell, Gerdenis Kodis, Devens Gust, P. J. Hore and Christiane R. Timmel, Chem. Commun., 47(23), 6563-6565 (2011). DOI: 10.1039/c1cc11625h Shigella flexneri Spa15 Crystal Structure Verified in Solution by Double Electron Electron Resonance James E.D. Lillington, Janet E. Lovett, Steven Johnson, Pietro Roversi, Christiane R. Timmel and Susan M. Lea, J Mol. Bio., 405(2), 427-435 (2011). DOI: 10.1016/j.jmb.2010.10.053 Cavity enhanced detection methods for probing the dynamics of spin correlated radical pairs in solution Simon R.T. Neil, Kiminori Maeda, Kevin B. Henbest, Martin Goez, Robert Hemmens, Christiane R. Timmel and Stuart R. Mackenzie, Mol. Phys., 108(7-9), 993-1003 (2010). DOI: 10.1080/00268971003614368 Protein Surface Interactions Probed by Magnetic Field Effects on Chemical Reactions Kiminori Maeda, Alexander J. Robinson, Kevin B. Henbest, Emma J. Dell and Christiane R. Timmel, J. Am. Chem. Soc., 132(5), 1466-1467 (2010). DOI: 10.1021/ja908988u Read the feature in C&E News Possible involvement of superoxide and dioxygen with cryptochrome in avian magnetoreception: Origin of Zeeman resonances observed by in vivo EPR spectroscopy Hannah J. Hogben, Olga Efimova, Nicola Wagner-Rundell, Christiane R. Timmel and P. J. Hore, Chem. Phys. Lett., 480(1-3), 118-122 (2009). DOI: 10.1016/j.cplett.2009.08.051 Probing Flexibility in Porphyrin-Based Molecular Wires using Double Electron Electron Resonance Janet E. Lovett, Markus Hoffmann, Arjen Cnossen, Alexander T. J. Shutter, Hannah J. Hogben, John E. Warren, Sofia I. Pascu, Christopher W. M. Kay, Christiane R. Timmel and Harry L. Anderson, J. Am. Chem. Soc., 131(38), 13852-13859 (2009). DOI: 10.1021/ja905796z Effect of magnetic fields on cryptochrome-dependent responses in Arabidopsis thaliana Sue-Re Harris, Kevin B. Henbest, Kiminori Maeda, John R. Pannell, Christiane R. Timmel, P. J. Hore and Haruko Okamoto, J. R. Soc. Interface, 6(41), 1193-1205 (2009). DOI: 10.1098/rsif.2008.0519 Structural Information from Orientationally Selective DEER Spectroscopy J. E. Lovett, A. M. Bowen, C. R. Timmel, M. W. Jones, J. R. Dilworth, D. Caprotti, S. G. Bell, L. L. Wong and J. Harmer, Phys. Chem. Chem. Phys., 11(31), 6840-6848 (2009). DOI: 10.1039/b907010a Radiofrequency Polarization Effects in Low-Field Electron Paramagnetic Resonance C. J. Wedge, Christopher T. Rodgers, Stuart A. Norman, Neville Baker, Kiminori Maeda, Kevin B. Henbest, P. Styles, P. J. Hore and C. R. Timmel, Phys. Chem. Chem. Phys., 11(31), 6573-6579 (2009). DOI: 10.1039/b907915g Radiofrequency Polarization Effects in Zero-Field Electron Paramagnetic Resonance Christopher T. Rodgers, C. J. Wedge, Stuart A. Norman, Philipp Kukura, Karen Nelson, Neville Baker, Kiminori Maeda, Kevin B. Henbest, P. J. Hore and C. R. Timmel, Phys. Chem. Chem. Phys., 11(31), 6569-6572 (2009). DOI: 10.1039/b906102a Magnetic Compass of Birds Is Based on a Molecule with Optimal Directional Sensitivity Thorsten Ritz, Roswitha Wiltschko, P. J. Hore, Christopher T. Rodgers, Katrin Stapput, Peter Thalau, Christiane R. Timmel and Wolfgang Wiltschko, Biophys. J., 96(8), 3451-3457 (2009). DOI: 10.1016/j.bpj.2008.11.072 Quenching Mechanisms and Diffusional Pathways in Micellar Systems Unravelled by Time-Resolved Magnetic-Field Effects Martin Goez, Kevin B. Henbest, Emma G. Windham, Kiminori Maeda and C. R. Timmel, Chem. Eur. J., 15(24), 6058-6064 (2009). DOI: 10.1002/chem.200802502 M. Britton and C. R. Timmel in Magnetic Resonance Microscopy: Spatially Resolved NMR Techniques and Applications, edited by S. L. Codd and J. D. Seymour Wiley-VCH Weinheim 2009 ISBN: 978-3-527-32008-0 SQUID Magnetometry as a Tool for Following a Clock Reaction in Solution R. Evans, K. B Henbest, M. A. Hayward, M. M. Britton, K. Maeda and C. R. Timmel, Dalton Trans., (14), 2467 (2009). DOI: 10.1039/b819977a Magnetic Field Effect on the Photoactivation Reaction of Escherichia coli DNA photolyase K. B. Henbest, K. Maeda, P. J. Hore, M. Joshi, A. Bacher, R. Bittl, S. Weber, C. R. Timmel and E. Schleicher, PNAS, 105(38), 14395-14399 (2008). DOI: 10.1073/pnas.0803620105 Chemical Compass Model of Avian Magnetoreception K. Maeda, K. B Henbest, F. Cintolesi, I. Kuprov, C. T. Rodgers, P. A. Liddell, D. Gust, C. R. Timmel and P. J. Hore, Nature, 453(7193), 387 (2008). DOI: 10.1038/nature06834 DOI: 10.1038/news.2008.788 (Nature News)