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Spectroscopy Tools and Techniques
Published in Jay L. Nadeau, Introduction to Experimental Biophysics, 2017
Most biomolecules are EPR silent, and radicals produced during biological reactions tend to be short-lived. The greatest use of EPR spectroscopy in biological applications thus makes use of spin probes (or spin labels) and spin traps.
Electron paramagnetic resonance of globin proteins – a successful match between spectroscopic development and protein research
Published in Molecular Physics, 2018
Sabine Van Doorslaer, Bert Cuypers
When CW EPR is applied at room temperature to biomolecules in solution, the spectra reflect the motional behaviour of the biomolecules. As the tumbling motion of the molecule slows down, the spectra change dramatically. The detailed information on this tumbling can be obtained from spectral simulations based on the slow-motional theory, an approach based on the stochastic Liouville equation [26]. The spectra of course only reflect the dynamics of the paramagnetic site. This site can be an intrinsic paramagnetic centre of the biomolecule (if detectable at room temperature) or one can connect a paramagnetic tag to the biomolecule (so-called site-directed spin-labelling technique [27]). In protein research, these spin labels are mostly nitroxide labels, titryl radicals or Gd(III) complexes, and are covalently linked to the protein at the specific sites. Use of a spin label has the advantage that the motional behaviour of different areas of the biomolecule can be selectively probed, by attaching the tags at specific points in the biomolecule. Room-temperature CW EPR is also often used to detect reactive radical intermediates, such as reactive oxygen species (ROS), in biosystems using the spin-trapping technique [28]. Specific diamagnetic trapping molecules are then added to the solution that react very rapidly with the short-living radicals to form a stable radical that can be detected by CW EPR. The observation of the EPR signature of this secondary radical is then a fingerprint for the presence of the specific radical intermediate.
Applications of electron spin resonance spectroscopy in photoinduced nanomaterial charge separation and reactive oxygen species generation
Published in Journal of Environmental Science and Health, Part C, 2021
Xiumei Jiang, Mary D. Boudreau, Peter P. Fu, Jun-Jie Yin
Spin labels, on the other hand, contain unpaired electrons and can be used to label target molecules that do not contain unpaired electrons, such as proteins, lipids, and other membrane components, thereby making them ESR detectable. The most common spin labels are nitroxide compounds, such as derivatives of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-1-yloxy (CTPO), and 15N-perdeuterated 4-oxo-2,2,6,6-tetramethyl piperidine-d16-1-oxyl (15N-PDT). TEMPO derivatives are widely utilized in ESR detection of biomolecules,30 while CTPO and 15N-PDT have advantages in ESR detection of oxygen.31