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McPeak JE, Höfer P, Kacprzak S, Carl P, Weber R, Eaton SS, Eaton GR. Rapid-Scan Electron Paramagnetic Resonance of Highly Resolved Hyperfine Lines in Organic Radicals. Chemphyschem 2020; 21:2564-2570. [PMID: 32935420 DOI: 10.1002/cphc.202000701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 09/09/2020] [Indexed: 11/12/2022]
Abstract
X-band (ca. 9 GHz) fluid solution rapid-scan electron paramagnetic resonance spectra are reported for radicals with multiline spectra and resolution of hyperfine lines as narrow as 30 mG. Highly-resolved spectra of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy, diphenylnitroxide, galvinoxyl, and perylene cation radical with excellent signal-to-noise are shown, demonstrating the capabilities of the rapid-scan technique to characterize very small, well-resolved hyperfine couplings. To acquire high resolution spectra the signal bandwidth must be less than the resonator bandwidth. Signal bandwidth is inversely proportional to linewidth and proportional to scan rate. Resonator bandwidth is inversely proportional to resonator Q. Proper selection of scan rate and resonator Q is needed to achieve resolution of closely-spaced narrow EPR lines.
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Affiliation(s)
- Joseph E McPeak
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210, USA
| | - Peter Höfer
- Bruker Biospin GMBH, Silberstreifen 4, Rheinstetten, Germany
| | - Sylwia Kacprzak
- Bruker Biospin GMBH, Silberstreifen 4, Rheinstetten, Germany
| | - Patrick Carl
- Bruker Biospin GMBH, Silberstreifen 4, Rheinstetten, Germany
| | - Ralph Weber
- Bruker BioSpin Corporation, Billerica, MA 01821, USA
| | - Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210, USA
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210, USA
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Eaton SS, Shi Y, Woodcock L, Buchanan LA, McPeak J, Quine RW, Rinard GA, Epel B, Halpern HJ, Eaton GR. Rapid-scan EPR imaging. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 280:140-148. [PMID: 28579099 PMCID: PMC5523658 DOI: 10.1016/j.jmr.2017.02.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 02/17/2017] [Accepted: 02/18/2017] [Indexed: 05/12/2023]
Abstract
In rapid-scan EPR the magnetic field or frequency is repeatedly scanned through the spectrum at rates that are much faster than in conventional continuous wave EPR. The signal is directly-detected with a mixer at the source frequency. Rapid-scan EPR is particularly advantageous when the scan rate through resonance is fast relative to electron spin relaxation rates. In such scans, there may be oscillations on the trailing edge of the spectrum. These oscillations can be removed by mathematical deconvolution to recover the slow-scan absorption spectrum. In cases of inhomogeneous broadening, the oscillations may interfere destructively to the extent that they are not visible. The deconvolution can be used even when it is not required, so spectra can be obtained in which some portions of the spectrum are in the rapid-scan regime and some are not. The technology developed for rapid-scan EPR can be applied generally so long as spectra are obtained in the linear response region. The detection of the full spectrum in each scan, the ability to use higher microwave power without saturation, and the noise filtering inherent in coherent averaging results in substantial improvement in signal-to-noise relative to conventional continuous wave spectroscopy, which is particularly advantageous for low-frequency EPR imaging. This overview describes the principles of rapid-scan EPR and the hardware used to generate the spectra. Examples are provided of its application to imaging of nitroxide radicals, diradicals, and spin-trapped radicals at a Larmor frequency of ca. 250MHz.
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Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States
| | - Yilin Shi
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States
| | - Lukas Woodcock
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States
| | - Laura A Buchanan
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States
| | - Joseph McPeak
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States
| | - Richard W Quine
- School of Engineering and Computer Science and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States
| | - George A Rinard
- School of Engineering and Computer Science and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States
| | - Boris Epel
- Department of Radiation and Cellular Oncology and Center for EPR Imaging In Vivo Physiology, University of Chicago, Chicago, IL 60637, United States
| | - Howard J Halpern
- Department of Radiation and Cellular Oncology and Center for EPR Imaging In Vivo Physiology, University of Chicago, Chicago, IL 60637, United States
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80210, United States.
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