Nitroxyl Biradicals

  • Yuri D. TsvetkovEmail author
  • Michael K. Bowman
  • Yuri A. Grishin


Nitroxyl radicals, also known as nitroxide, imidoxyl and aminoxyl radicals, are ubiquitous in PELDOR and DEER studies because of their stability, solubility, and ability to be chemically modified. They provided the molecular testbed for the measurement of distance and distance distributions; the measurement of weak exchange interactions; and the determination of the mutual orientation of radical fragments. As soon as reliable synthetic methods were developed for stable nitroxyl radicals [1], these free radicals, also known as nitroxide, imidoxyl and aminoxyl radicals, became widely used in chemical and physical studies employing CW EPR spectroscopy. This work is described in detail in monographs [2, 3, 4, 5, 6, 7], numerous reviews, and collected volumes, e.g., [8, 9]. The development of pulsed EPR, including ESE, spectroscopy and subsequent applications to physical, chemical, and biological problems also made extensive use of nitroxyl radicals [10, 11]. Nitroxyl radicals and the paramagnetic >N-O· moiety are ubiquitous in PELDOR studies over the last 30 years because of their chemical and biological stability; their solubility in polar and non-polar media; their ability to be chemically modified; and the strong localization of the unpaired electron to the N-O· bond. Nitroxyl biradicals provided the first demonstration of PELDOR modulation from dipole interactions [12]. They provided the molecular testbed for the development of methods to measure the distance between spins and the distance distribution; to measure exchange interactions; and to determine the mutual orientation of radical fragments and other structural features. Today nitroxyl radicals continue to play a major role as spin labels in many PELDOR applications and their EPR properties influence the evolution of PELDOR methods. This Chapter considers some of the nitroxyl radicals that are prominent in PELDOR.


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© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Yuri D. Tsvetkov
    • 1
    Email author
  • Michael K. Bowman
    • 2
  • Yuri A. Grishin
    • 3
  1. 1.The Voevodsky Institute of Chemical Kinetics and CombustionNovosibirskRussia
  2. 2.Department of Chemistry and BiochemistryUniversity of AlabamaTuscaloosaUSA
  3. 3.The Voevodsky Institute of Chemical Kinetics and CombustionNovosibirskRussia

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