Research Guides

Department of Chemistry University of Oxford

Dr C.R. Timmel

Magnetic Field Effects on Chemical Reactions

There is only one established mechanism by which a magnetic field can affect a chemical reaction, namely 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 working in both continuous and pulsed modes, at X-, Q- and W-bands. 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]