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Nakai T. Perturbation Approach for NMR Signals with Infinite-Order Corrections and Its Application to Solid-State MAS INADEQUATE Spectra Exhibiting Auto-Correlation Peaks due to Chemically-Equivalent Spin Pairs: Analogy to Renormalization Theory. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2021. [DOI: 10.1246/bcsj.20200360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Toshihito Nakai
- JEOL RESONANCE Inc., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
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2
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Dutoit CE, Binet L, Fujii H, Lattuati-Derieux A, Gourier D. Nondestructive Analysis of Mummification Balms in Ancient Egypt Based on EPR of Vanadyl and Organic Radical Markers of Bitumen. Anal Chem 2020; 92:15445-15453. [PMID: 33197168 DOI: 10.1021/acs.analchem.0c03116] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The black matter employed in the funeral context by ancient Egyptians is a complex mixture of plant-based compounds with variable amounts of bitumen. Asphaltene, the most resistant component of bitumen, contains vanadyl porphyrins and carbonaceous radicals, which can be used as paramagnetic probes to investigate embalming materials without sample preparation. Electron paramagnetic resonance (EPR) at the X-band, combining in-phase and out-of-phase detection schemes, provides new information in a nondestructive way about the presence, the origin, and the evolution of bitumen in these complex materials. It is found that the relative EPR intensity of radicals and vanadyl porphyrins is sensitive to the origin of the bitumen. The presence of nonporphyrinic vanadyl complexes in historical samples is likely due to the complexation of VO2+ ions by carboxylic functions at the interface between bitumen and other biological components of the embalming matter. The absence of such oxygenated vanadyl complex in natural bitumen and in one case of historical human mummy acquired by a museum in the 19th century reveals a possible, nondocumented, ancient restoration of this mummy by pure bitumen. The linear correlation between in-phase and out-of-phase EPR intensities of radicals and vanadyl porphyrins in balms and in natural bitumen reveals a nanostructuration of radicals and vanadyl porphyrin complexes, which was not affected by the preparation of the balm. This points to the remarkable chemical stability of paramagnetic probes in historical bitumen in ancient Egypt.
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Affiliation(s)
- Charles E Dutoit
- Chimie-ParisTech, PSL University, CNRS, Institut de Recherche de Chimie-Paris (IRCP), F-75005 Paris, France
| | - Laurent Binet
- Chimie-ParisTech, PSL University, CNRS, Institut de Recherche de Chimie-Paris (IRCP), F-75005 Paris, France
| | - Hitomi Fujii
- Centre de Recherche et de Restauration des Musées de France (C2RMF), Palais du Louvre, F-75001 Paris, France
| | - Agnes Lattuati-Derieux
- Centre de Recherche et de Restauration des Musées de France (C2RMF), Palais du Louvre, F-75001 Paris, France
| | - Didier Gourier
- Chimie-ParisTech, PSL University, CNRS, Institut de Recherche de Chimie-Paris (IRCP), F-75005 Paris, France
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3
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Rakvin B, Carić D, Kveder M. Modulation sidebands spectra within inhomogeneous CW-EPR line detected by double modulation EPR spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 307:106587. [PMID: 31499471 DOI: 10.1016/j.jmr.2019.106587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 08/26/2019] [Accepted: 08/28/2019] [Indexed: 06/10/2023]
Abstract
Conventional modulation spectrum, MS, in continuous wave electron paramagnetic resonance, CW-EPR, is produced by applying longitudinal radiofrequency (RF) fields with the frequencies, ωrf, which exceeds the linewidth, 2πδ, of a single spectral line given in frequency units. The second longitudinal RF field with frequency, ωrf2, is employed to produce double modulation spectrum, DMS. In this work DMS are presented as a specific type of MS which can be produced from an ordinary homogenous line. The numerical simulations of DMS in the limit of low power saturation relied on the recently introduced multi-photon transitions formalism which includes one microwave photon in combination with an arbitrary number of radiofrequency photons. It is shown that DMS of an inhomogeneous line exhibits similar basic structure as MS and exhibits sideband peaks at multiples of basic radiofrequencies. Linewidths of these peaks are significantly narrower (cca. two - three orders of magnitude) than the inhomogeneous linewidth and can be correlated with the underlying homogeneous linewidth components on the basis of characteristic spin-lattice, T1, and spin-spin, T2, relaxation times. The capability to extract T1 and T2 from DMS was tested on the well-known E' defect in irradiated vitreous SiO2. The obtained results revealed the impact of "rapid passage" effect on DMS in improving the detection sensitivity of DMS in the study of paramagnetic centers with long relaxation times. Therefore, double modulation method can be considered as a complementary method for studying inhomegeneous broadening in the EPR spectra.
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Affiliation(s)
- B Rakvin
- Ruđer Bošković Institute, Division of Physical Chemistry, Bijenička 54, Zagreb, Croatia.
| | - D Carić
- Ruđer Bošković Institute, Division of Physical Chemistry, Bijenička 54, Zagreb, Croatia
| | - M Kveder
- Ruđer Bošković Institute, Division of Physical Chemistry, Bijenička 54, Zagreb, Croatia
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4
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Rakvin B, Carić D, Kveder M. Enhanced accuracy of the microwave field strength measurement in a CW-EPR by pulsed modulation technique. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 287:123-127. [PMID: 29413325 DOI: 10.1016/j.jmr.2018.01.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 01/09/2018] [Accepted: 01/10/2018] [Indexed: 06/08/2023]
Abstract
The microwave magnetic field strength, B1, in the cavity of a conventional continuous wave electron paramagnetic resonance, CW-EPR, spectrometer was measured by employing modulation sidebands, MS, in the EPR spectrum. MS spectrum in CW-EPR is produced by applying the modulation frequency, ωrf, which exceeds the linewidth, δB, given in frequency units. An amplitude-modulated CW-EPR, AM-CW-EPR, was selected as detection method. Theoretical description of AM-CW-EPR spectrum was modified by adding Bloch-Siegert-like shift obtained by taking into account the cumulative effect of the non-resonant interactions between the driving fields and the spin system. This approach enables to enhance the precision of B1 measurement. In order to increase the sensitivity of the method when saturation effects, due to higher intensity of B1, decrease the resolution of AM-CW-EPR spectrum, detection at the second harmonic of CW-EPR has been employed.
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Affiliation(s)
- B Rakvin
- Ruđer Bošković Institute, Division of Physical Chemistry, Bijenička 54, Zagreb, Croatia.
| | - D Carić
- Ruđer Bošković Institute, Division of Physical Chemistry, Bijenička 54, Zagreb, Croatia
| | - M Kveder
- Ruđer Bošković Institute, Division of Physical Chemistry, Bijenička 54, Zagreb, Croatia
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5
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Detection of Reactive Oxygen and Nitrogen Species by Electron Paramagnetic Resonance (EPR) Technique. Molecules 2017; 22:molecules22010181. [PMID: 28117726 PMCID: PMC6155876 DOI: 10.3390/molecules22010181] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 01/05/2017] [Accepted: 01/17/2017] [Indexed: 01/15/2023] Open
Abstract
During the last decade there has been growing interest in physical-chemical oxidation processes and the behavior of free radicals in living systems. Radicals are known as intermediate species in a variety of biochemical reactions. Numerous techniques, assays and biomarkers have been used to measure reactive oxygen and nitrogen species (ROS and RNS), and to examine oxidative stress. However, many of these assays are not entirely satisfactory or are used inappropriately. The purpose of this chapter is to review current EPR (Electron Paramagnetic Resonance) spectroscopy methods for measuring ROS, RNS, and their secondary products, and to discuss the strengths and limitations of specific methodological approaches.
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6
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Saiko AP, Fedaruk R, Markevich SA. Multi-photon transitions and Rabi resonance in continuous wave EPR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 259:47-55. [PMID: 26295168 DOI: 10.1016/j.jmr.2015.07.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 07/20/2015] [Accepted: 07/21/2015] [Indexed: 06/04/2023]
Abstract
The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines.
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Affiliation(s)
- Alexander P Saiko
- Scientific-Practical Materials Research Centre NAS of Belarus, Minsk, Belarus.
| | - Ryhor Fedaruk
- Institute of Physics, University of Szczecin, 70-451 Szczecin, Poland.
| | - Siarhei A Markevich
- Scientific-Practical Materials Research Centre NAS of Belarus, Minsk, Belarus
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7
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Beuneu F. Unusual behaviour of a very narrow electron spin resonance signal. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 227:46-50. [PMID: 23262332 DOI: 10.1016/j.jmr.2012.11.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Revised: 11/07/2012] [Accepted: 11/09/2012] [Indexed: 06/01/2023]
Abstract
Unusually narrow electron spin resonance lines can give birth to spectacular and interesting phenomena. We use here very pure lithium metal colloids created in electron-irradiated LiF, giving rise to a very narrow Li metal line. In these samples, three interesting phenomena are discussed and interpreted: signal saturation in particularly good conditions; oscillations appearing on strongly overmodulated lines; signal bistability, when the signal shape seems to depend on the sample magnetic history.
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Affiliation(s)
- François Beuneu
- Laboratoire des Solides Irradiés, CNRS-CEA, École Polytechnique, Palaiseau, France.
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8
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Mitchell DG, Quine RW, Tseitlin M, Weber RT, Meyer V, Avery A, Eaton SS, Eaton GR. Electron Spin Relaxation and Heterogeneity of the 1:1 α,γ-Bisdiphenylene-β-phenylallyl (BDPA)/Benzene Complex. J Phys Chem B 2011; 115:7986-90. [DOI: 10.1021/jp201978w] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Deborah G. Mitchell
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, United States
| | - Richard W. Quine
- School of Engineering and Computer Science, University of Denver, Denver, Colorado 80208, United States
| | - Mark Tseitlin
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, United States
| | - Ralph T. Weber
- Bruker BioSpin, Billerica, Massachusetts 01821, United States
| | - Virginia Meyer
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, United States
| | - Azure Avery
- Department of Physics and Astronomy, University of Denver, Denver, Colorado 80208, United States
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, United States
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, United States
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9
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Free radical processes in green tea polyphenols (GTP) investigated by electron paramagnetic resonance (EPR) spectroscopy. ACTA ACUST UNITED AC 2008; 14:349-401. [DOI: 10.1016/s1387-2656(08)00013-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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10
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Riveiro ME, Moglioni A, Vazquez R, Gomez N, Facorro G, Piehl L, de Celis ER, Shayo C, Davio C. Structural insights into hydroxycoumarin-induced apoptosis in U-937 cells. Bioorg Med Chem 2007; 16:2665-75. [PMID: 18060791 DOI: 10.1016/j.bmc.2007.11.038] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Revised: 11/10/2007] [Accepted: 11/13/2007] [Indexed: 10/22/2022]
Abstract
In the present study, we sought to establish the effect of diverse structural-related hydroxycoumarins on the proliferation, cytotoxicity, and induction of apoptosis in promonocytic leukemic cells (U-937). The dihydroxylated coumarins, 7,8-dihydroxy-coumarin and esculetin, induced DNA fragmentation as well as characteristic morphological changes of programmed cell death in U-937 cells. With the aim to perform a structure-activity relationship study, the correlation between the physicochemical properties of the molecules and their pro-apoptotic activity was carried out. Results showed that the presence of two adjacent phenolic hydroxyl groups was the most important factor in terms of the SAR. The exposure of leukemic cells to 7,8-dihydroxy-coumarin evoked a phenoxyl radical generation that was detected by electron spin resonance spectroscopy. The present study suggests that reactive oxygen species generation plays a critical role in dihydroxycoumarin-induced apoptosis in U-937 cells. These findings further suggest that these compounds may have a potential therapeutic role in the treatment of hematological malignancies.
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Affiliation(s)
- Maria E Riveiro
- Laboratorio de Radioisótopos, Facultad de Farmacia y Bioquímica, Argentina
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11
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Granwehr J, Leggett J, Köckenberger W. A low-cost implementation of EPR detection in a dissolution DNP setup. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 187:266-76. [PMID: 17560151 DOI: 10.1016/j.jmr.2007.05.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Revised: 05/04/2007] [Accepted: 05/17/2007] [Indexed: 05/15/2023]
Abstract
The implementation of electron paramagnetic resonance (EPR) detection in a low-temperature dissolution dynamic nuclear polarization (DNP) setup is presented. Using a coil oriented parallel to the static magnetic field, the change of the longitudinal magnetization of free radicals is measured upon resonant irradiation of an amplitude or frequency modulated microwave (mw) field. The absorption EPR spectrum is measured if the amplitude of the mw field is modulated, whilst the first derivative of the spectrum is obtained with frequency modulation. Using a burst of pulses, it is also possible to perform pump-probe experiments such as saturation-recovery or electron-electron double resonance experiments. Furthermore, the magnetization could be monitored in a time-resolved manner during amplitude modulation, thus making it possible to record its transient as it is approaching an equilibrium value. Experimental examples are shown with frozen solutions of trityl radical and TEMPO, two commonly used radicals for dissolution DNP experiments.
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Affiliation(s)
- Josef Granwehr
- Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
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12
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Piehl L, Capani F, Facorro G, López EM, de Celis ER, Pustovrh C, Hager A, Coirini H, López-Costa JJ. Nitric oxide increases in the rat retina after continuous illumination. Brain Res 2007; 1156:112-9. [PMID: 17499222 DOI: 10.1016/j.brainres.2007.04.030] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Revised: 04/09/2007] [Accepted: 04/12/2007] [Indexed: 11/20/2022]
Abstract
Continuous illumination (CI) of the retina induces an oxidative stress followed by the degeneration of photoreceptors. This phenomenon may be partially related to the excessive production of nitric oxide (NO). In order to confirm this hypothesis, the aims of this work are to determine NO levels during the illumination of the retina by electron paramagnetic resonance (EPR), and if an increase of NO is found, to characterize the NOS isoform responsible of the increment by using Western blot. Sprague-Dawley rats were continuously illuminated with white light (12,000 lux) for 2, 24, 48 h, 5 and 7 days while control rats were maintained at light/dark cycles of 12/12 h. Using EPR, an increase of NO signal was observed in the light exposed retinas peaking at 24 h of CI. Western blot analysis showed the expression of iNOS in the illuminated retinas with a peak after 24 h of CI, but did not show significant differences of nNOS among illuminated and control retinas. In summary, there is an increase of NO during CI. Further studies will reveal whether this mechanism is responsible for light induced photoreceptor degeneration.
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Affiliation(s)
- L Piehl
- Cátedra de Física, Facultad de Farmacia y Bioquímica, UBA. Lanais RLBM, Argentina
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13
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Hyde JS, Froncisz W, Sidabras JW, Camenisch TG, Anderson JR, Strangeway RA. Microwave frequency modulation in CW EPR at W-band using a loop-gap resonator. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 185:259-63. [PMID: 17267251 DOI: 10.1016/j.jmr.2007.01.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Revised: 12/19/2006] [Accepted: 01/03/2007] [Indexed: 05/13/2023]
Abstract
Loop-gap resonator (LGR) technology has been extended to W-band (94GHz). One output of a multiarm Q-band (35GHz) EPR bridge was translated to W-band for sample irradiation by mixing with 59 GHz; similarly, the EPR signal was translated back to Q-band for detection. A cavity resonant in the cylindrical TE011 mode suitable for use with 100 kHz field modulation has also been developed. Results using microwave frequency modulation (FM) at 50 kHz as an alternative to magnetic field modulation are described. FM was accomplished by modulating a varactor coupled to the 59 GHz oscillator. A spin-label study of sensitivity was performed under conditions of overmodulation and gamma2H1(2)T1T2<1. EPR spectra were obtained, both absorption and dispersion, by lock-in detection at the fundamental modulation frequency (50 kHz), and also at the second and third harmonics (100 and 150 kHz). Source noise was deleterious in first harmonic spectra, but was very low in second and third harmonic spectra. First harmonic microwave FM was transferred to microwave modulation at second and third harmonics by the spins, thus satisfying the "transfer of modulation" principle. The loaded Q-value of the LGR with sample was 90 (i.e., a bandwidth between 3 dB points of about 1 GHz), the resonator efficiency parameter was calculated to be 9.3 G at one W incident power, and the frequency deviation was 11.3 MHz p-p, which is equivalent to a field modulation amplitude of 4 G. W-band EPR using an LGR is a favorable configuration for microwave FM experiments.
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Affiliation(s)
- James S Hyde
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226-0509, USA.
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14
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Fedin M, Gromov I, Schweiger A. Sensitivity optimization in amplitude-modulated CW-EPR experiment. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 182:293-7. [PMID: 16875856 DOI: 10.1016/j.jmr.2006.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2006] [Revised: 07/10/2006] [Accepted: 07/12/2006] [Indexed: 05/11/2023]
Abstract
A sensitivity of recently developed method of amplitude-modulated continuous wave EPR (AM-CW-EPR) is studied depending on the parameters of the modulation field. The case of the significant saturation and high modulation frequency is addressed. It is found, that the rapid resonance passage effect is essential for AM-CW-EPR. However, its manifestation is different comparing to the conventional CW-EPR experiment. Both experimental data and numerical simulations support the enhancement of the AM-CW-EPR sensitivity under the rapid passage conditions for the modulating magnetic field, which is important for practical use of the method.
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Affiliation(s)
- Matvey Fedin
- International Tomography Center SB RAS, Novosibirsk 630090, Russia.
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15
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Stoll S, Schweiger A. EasySpin, a comprehensive software package for spectral simulation and analysis in EPR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 178:42-55. [PMID: 16188474 DOI: 10.1016/j.jmr.2005.08.013] [Citation(s) in RCA: 3771] [Impact Index Per Article: 209.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2005] [Revised: 08/29/2005] [Accepted: 08/29/2005] [Indexed: 05/04/2023]
Abstract
EasySpin, a computational package for spectral simulation and analysis in EPR, is described. It is based on Matlab, a commercial technical computation software. EasySpin provides extensive EPR-related functionality, ranging from elementary spin physics to data analysis. In addition, it provides routines for the simulation of liquid- and solid-state EPR and ENDOR spectra. These simulation functions are built on a series of novel algorithms that enhance scope, speed and accuracy of spectral simulations. Spin systems with an arbitrary number of electron and nuclear spins are supported. The structure of the toolbox as well as the theoretical background underlying its simulation functionality are presented, and some illustrative examples are given.
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Affiliation(s)
- Stefan Stoll
- Physical Chemistry Laboratory, ETH Hönggerberg, CH-8093 Zürich, Switzerland.
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16
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Fedin M, Gromov I, Schweiger A. Absorption line CW EPR using an amplitude modulated longitudinal field. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2004; 171:80-89. [PMID: 15504685 DOI: 10.1016/j.jmr.2004.07.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2004] [Revised: 07/27/2004] [Indexed: 05/24/2023]
Abstract
In standard continuous wave electron paramagnetic resonance (CW-EPR) experiments, the first derivative of absorption lines is detected. This type of a line shape is caused by the magnetic field modulation and is usually an undesired feature, since the sensitivity of CW-EPR drastically decreases with increasing linewidth. A new approach is introduced, which allows for the measurement of absorption line EPR spectra in systems with broad inhomogeneous lines. The method makes use of multiple-photon transitions that are induced in spin systems when a transverse microwave and a longitudinal radio frequency field are simultaneously applied. The absorption lines are obtained by using amplitude modulation of the radio frequency field and slight saturation of the spectral lines. The basics of the new approach are discussed and experimental examples are given.
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Affiliation(s)
- Matvey Fedin
- Physical Chemistry Laboratory, Department of Chemistry and Applied Biosciences, ETH-Hönggerberg, 8093 Zürich, Switzerland.
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17
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Nielsen RD, Hustedt EJ, Beth AH, Robinson BH. Formulation of Zeeman modulation as a signal filter. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2004; 170:345-371. [PMID: 15388099 DOI: 10.1016/j.jmr.2004.07.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2004] [Revised: 07/09/2004] [Indexed: 05/24/2023]
Abstract
The Bloch equation containing a Zeeman modulation field is solved analytically by treating the Zeeman modulation frequency as a perturbation. The absorption and dispersion signals at both 0 degrees and 90 degrees modulation phase are obtained. The solutions are valid to first order in the modulation frequency, but are otherwise valid for any value of modulation amplitude or microwave amplitude. A first order treatment of modulation frequency is shown to be a valid approximation over a wide range of typical experimental EPR conditions. The solutions derived from the Bloch equation suggest that the effect of over-modulation on first and second harmonic EPR spectra can be formulated as a mathematical filter that smoothes and broadens the under-modulated signal. The only adjustable filter parameter is a width that is equivalent to the applied peak-to-peak modulation amplitude. The true spin-spin and spin-lattice relaxation rates are completely determined from the under-modulated spectrum. The filters derived from the analytic solutions of the Bloch equation in the linear limit of modulation frequency are tested against numerical solutions of the Bloch equation that are valid for any modulation frequency to show their applicability. The filters are further tested using experimental EPR spectra. Experimental under-modulated spectra are mathematically filtered and compared with the experimental over-modulated spectra. The application of modulation filters to STEPR spectra is explored and limitations are discussed.
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Affiliation(s)
- Robert D Nielsen
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA
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18
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Hirata H, Kuyama T, Ono M, Shimoyama Y. Nonequivalent spectra of unpaired electrons in field and frequency modulation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2004; 168:252-258. [PMID: 15140435 DOI: 10.1016/j.jmr.2004.03.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2003] [Revised: 03/12/2004] [Indexed: 05/24/2023]
Abstract
We report a difference in the spectral lineshapes of continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy between field and frequency modulation. This finding addresses the long-standing question of the effect of modulation in EPR absorption. We compared the first-derivative EPR spectra at 1.1 GHz for lithium phthalocyanine crystals, which have a single narrow linewidth in the EPR absorption spectrum, using field and frequency modulation. The experimental findings suggest that unpaired electrons have different behaviors under perturbation due to field and frequency modulation.
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Affiliation(s)
- Hiroshi Hirata
- Department of Electrical Engineering, Yamagata University, Yonezawa, Yamagata 992-8510, Japan.
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19
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Fedin M, Kalin M, Gromov I, Schweiger A. Applications of π-photon-induced transparency in two-frequency pulse electron paramagnetic resonance experiments. J Chem Phys 2004; 120:1361-8. [PMID: 15268261 DOI: 10.1063/1.1633259] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
An approach to pulse electron paramagnetic resonance (EPR) experiments which are based on two different resonance fields is introduced. Instead of using two microwave (mw) sources or a magnetic field jump, bichromatic pulses consisting of a transverse microwave field with frequency omega(mw) and a longitudinal radio frequency field with frequency omega(rf) are employed. Such bichromatic pulses excite a number of multiple photon transitions at frequencies omega(mw)+komega(rf) (k in Z). The pi-photon-induced transparency phenomenon is used to select the required transitions. This approach is used in the stimulated soft electron spin echo envelope modulation and the four-pulse double electron-electron resonance experiments. The results obtained using the bichromatic pulse approach are in agreement with those obtained with the standard pulse EPR techniques. It is shown that applying bichromatic pulses is straightforward and advantageous in several respects.
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Affiliation(s)
- Matvey Fedin
- Physical Chemistry Laboratory, ETH, CH-8093 Zurich, Switzerland
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Hirata H, Kuyama T, Ono M, Shimoyama Y. Detection of electron paramagnetic resonance absorption using frequency modulation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2003; 164:233-241. [PMID: 14511592 DOI: 10.1016/s1090-7807(03)00236-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A frequency modulation (FM) method was developed to measure electron paramagnetic resonance (EPR) absorption. The first-derivative spectrum of 1,1-diphenyl-2-picrylhydrazyl (DPPH) powder was measured with this FM method. Frequency modulation of up to 1.6 MHz (peak-to-peak) was achieved at a microwave carrier frequency of 1.1 GHz. This corresponds to a magnetic field modulation of 57microT (peak-to-peak) at 40.3 mT. By using a tunable microwave resonator and automatic control systems, we achieved a practical continuous-wave (CW) EPR spectrometer that incorporates the FM method. In the present experiments, the EPR signal intensity was proportional to the magnitude of frequency modulation. The background signal at the modulation frequency (1 kHz) for EPR detection was also proportional to the magnitude of frequency modulation. An automatic matching control (AMC) system reduced the amplitude of noise in microwave detection and improved the baseline stability. Distortion of the spectral lineshape was seen when the spectrometer settings were not appropriate, e.g., with a lack of the open-loop gain in automatic tuning control (ATC). FM is an alternative to field modulation when the side-effect of field modulation is detrimental for EPR detection. The present spectroscopic technique based on the FM scheme is useful for measuring the first derivative with respect to the microwave frequency in investigations of electron-spin-related phenomena.
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Affiliation(s)
- Hiroshi Hirata
- Department of Electrical Engineering, Yamagata University, 4-3-16 Johnan, Yonezawa, Yamagata 992-8510, Japan.
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