title: Magnetic isotope effects in biology: a marker for radical pair reactions and electromagnetic field effects?
abstract: OBJECTIVE
  To explore the possible usefulness of magnetic isotope effects, especially to detect processes affected by magnetic fields.
  
  
  METHODS
  The theoretical model of Brocklehurst and McLauchlan is used to estimate the effects of isotopic substitution (e.g. 13C for 12C) on the yields of chemical reactions involving radical pairs.
  
  
  RESULTS
  It is demonstrated that in some circumstances isotope effects on the yields from initially singlet pairs (bond breaking to give radicals) could be very large and easily detected. The effects on radical pairs formed by random encounters are necessarily much smaller but may be detectable. Illustrative calculations are presented for carbon, hydrogen and oxygen isotopes; deuterium substitution also produces very large mass effects but its study could be useful to support work on carbon.
  
  
  CONCLUSIONS
  Effects may be small but worth looking for: distinguishing them from mass effects will be aided by measuring distributions within product molecules. In laboratory experiments (especially tomography) a combination of isotopic substitution and applied fields is a potentially powerful technique.
authors.affiliation: Chemistry Department, University of Sheffield, UK.
authors.forename: B
authors.initials: B
authors.lastname: Brocklehurst
mesh_terms: D004574:Electromagnetic Fields; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D011868:Radioisotopes
chemical_list: D005609:Free Radicals; D011868:Radioisotopes