Electron Paramagnetic Resonance (EPR) or Electron Spin Resonance (ESR) spectroscopy is similar to Nuclear Magnetic Resonance (NMR) spectroscopy except electron spins are excited, instead of the spins of atomic nuclei. Therefore, EPR requires the presence of unpaired electrons.

There are many applications of EPR spectroscopy. In Biology and Biophysics, EPR can for example be used to study organic radicals in proteins (E.g. tyrocyl, tryptophanyl, glycyl, semiquinones, flavines) or metal centers in protein complexes (E.g. Cu, Ni, Co, Mn, Mo, Fe, Cr, Heme, FeS clusters, Mn/Cr ATP complexes). Site-directed spin labeling with nitroxide based spin labels can be used to extend EPR studies to proteins, nucleic acids, lipids, and nucleotides without an indigenous paramagnetic center. Researchers can gain information about structure, conformational changes, membrane insertion and much more.

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Exciting Possibilities in Biology, Biochemistry and Biophysics:

  • Investigation of proteins, peptides, RNA, DNA, lipids, membrane bound complexes,...
  • Samples under near physiological conditions, often requiring as little as 4 ul of a 25 to 100 μM sample
  • No size or solubility restrictions
  • Secondary structure elements and tertiary /quaternary interaction sites
  • Protein and DNA/RNA folding
  • Conformational changes
  • Protein membrane insertion (depth, geometry, changes during ligand binding, etc.)
  • Binding curves and stoichiometry's by directly measuring the amount of bound (EPR active) ligand
  • Spin trapping of small radicals (hydroxyls, superoxides, carbon based radicals, etc.) for example in  wound healing, immune defense or in aging related processes
  • And a lot more...