 Dr C. R. Timmel
Inorganic Chemistry Laboratory
Telephone: 44 (0) 1865 272 682
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
(CASER) 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]
Recent Publications
[1] Chemical Compass Model of Avian Magnetoreception Nature,
453, 387 (2008)
[2] Magnetic Field Effects on Photolyase PNAS, 105, 14395
(2008).
[3] Radiofrequency Polarization Effects in Zero-Field Electron
Paramagnetic Resonance Phys. Chem. Chem. Phys., 11(31),
6569-6572 (2009).
[4] Structural Information from Orientationally Selective DEER
Spectroscopy Phys. Chem. Chem. Phys., 11(31), 6840-6848
(2009).
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