Electron paramagnetic resonance spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is widely used to study proteins that contain naturally occurring paramagnetic centers and/or artificially introduced spin labels. In this chapter we present a mainly qualitative overview of the application of EPR spectroscopy to the study biological systems. The chapter begins with a short description of the physical principles underlying the method and the basic experimental techniques. An overview of characteristic lineshapes observed under various experimental conditions is then presented to show how quantities such as hyperfine couplings, g-anisotropy and zero-field splitting manifest themselves in EPR data. A number of specific examples are used to illustrate how these quantities can be used to obtain information about the geometry, bonding, electronic structure, etc. of biological systems.