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Spin Probes and Spin Labels

Nuclear Magnetic Resonance and Electron Spin Resonance Spectroscopy

  1. Tatyana I. Smirnova,
  2. Maxim A. Voinov,
  3. Alex I. Smirnov

Published Online: 15 DEC 2009

DOI: 10.1002/9780470027318.a9049

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Smirnova, T. I., Voinov, M. A. and Smirnov, A. I. 2009. Spin Probes and Spin Labels. Encyclopedia of Analytical Chemistry. .

Author Information

  1. North Carolina State University, Raleigh, NC, USA

Publication History

  1. Published Online: 15 DEC 2009


Electron paramagnetic resonance (EPR) spectroscopy is a versatile and exceptionally sensitive technique for detecting and studying molecular systems possessing unpaired electronic spins. It finds substantial use in characterizing paramagnetic metal ions and organic free radicals. The scope of EPR applications in analytical chemistry can be expanded significantly by means of spin labels and spin probes — exogenous EPR-active species that are introduced solely for the purpose of gaining information on the system under study. These labels and probes are persistent free radicals or paramagnetic metal ions designed to be partitioned or attached to specific molecular sites. To be suitable for analytical applications, spin labels and probes should readily report on properties of interest, exhibit distinguishable from background EPR signals, and leave the system only minimally perturbed by their presence. In this article, we describe a series of spin labels and probes as well as the associated EPR methods that are tailored to specific analytical applications of EPR spectroscopy — from assessing local oxygen and proton concentration to profiling electrostatic properties of biopolymers and lipid bilayers. The primary focus is bioanalytical applications of spin label/probe methods, with an emphasis on the synergy between the rational design of spin-bearing molecules using the tools of organic chemistry and desired analytical capabilities.


  • spin probe;
  • spin label;
  • electron paramagnetic resonance spectroscopy;
  • nitroxide;
  • free radical;
  • spin probe;
  • pH measurements;
  • oximetry;
  • electrostatic potential