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Electron Spin Echo Envelope Modulation (ESEEM) Spectroscopy

  1. John McCracken

Published Online: 15 MAR 2008

DOI: 10.1002/0470862106.ia337

Encyclopedia of Inorganic Chemistry

Encyclopedia of Inorganic Chemistry

How to Cite

McCracken, J. 2008. Electron Spin Echo Envelope Modulation (ESEEM) Spectroscopy. Encyclopedia of Inorganic Chemistry. .

Author Information

  1. Michigan State University, East Lansing, MI, USA

Publication History

  1. Published Online: 15 MAR 2008

Abstract

In the 46 years since its discovery in Ce(III)-doped CaWO4 single crystals, electron spin echo envelope modulation (ESEEM) spectroscopy has developed into an important method for the characterization of paramagnetic centers. The capability of ESEEM to resolve ligand hyperfine couplings to paramagnetic transition metal ions in powder or frozen solution samples, and its sensitivity to the orientation and number of coupled nuclei, make it a valuable tool for structural biology and materials chemistry. This article presents a brief history of the method from its discovery to the development of commercial instrumentation that has provided an opportunity for scientists to address difficult questions regarding coordination chemistry in paramagnetic systems. The technical background section presents the three most basic ESEEM experiments: the one-dimensional primary echo (two-pulse) and stimulated echo (three-pulse) experiments and the two-dimensional, four-pulse hyperfine sublevel correlation (HYSCORE) experiment. The mathematical expressions developed for these experiments and the simple S = 1/2, I = 1/2 coupled spin system, will be used together with sample ESEEM data from Cu(II) centers in a model complex and an enzyme to illustrate the strengths and weaknesses of these pulse schemes. The article will conclude with a case study of the nonheme Fe(II) site in taurine/α-ketoglutarate dioxygenase (TauD) that will feature some of the strengths of one-dimensional and two-dimensional ESEEM spectroscopy and show that the method has matured into a powerful technique for elucidating the coordination chemistry of this important class of enzymes as well as many other systems.

Keywords:

  • electron paramagnetic resonance spectroscopy (EPR);
  • electron-nuclear double resonance (ENDOR);
  • electron spin echo envelope modulation (ESEEM);
  • hyperfine coupling;
  • hyperfine sublevel correlation (HYSCORE);
  • nuclear quadrupole interaction (nqi);
  • nonheme Fe hydroxylases