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Haeri HH, Duraisamy R, Harmgarth N, Liebing P, Lorenz V, Hinderberger D, Edelmann FT. Electronic and Geometric Structures of Paramagnetic Diazadiene Complexes of Lithium and Sodium. ChemistryOpen 2018; 7:701-708. [PMID: 30202705 PMCID: PMC6123648 DOI: 10.1002/open.201800114] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Indexed: 11/08/2022] Open
Abstract
The electronic and molecular structures of the lithium and sodium complexes of 1,4-bis(2,6-diisopropylphenyl)-2,3-dimethyl-1,4-diazabutadiene (Me2DADDipp) were fully characterized by using a multi-frequency electron paramagnetic resonance (EPR) spectroscopy approach and crystallography, together with density functional theory (DFT) calculations. EPR measurements, using T1 relaxation-time-filtered pulse EPR spectroscopy, revealed the diagonal elements of the A and g tensors for the metal and ligand sites. It was found that the central metals in the lithium complexes had sizable contributions to the SOMO, whereas this contribution was less strongly observed for the sodium complex. Such strong contributions were attributed to structural specifications (e.g. geometrical data and atomic size) rather than electronic effects.
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Affiliation(s)
- Haleh H. Haeri
- Institute of ChemistryMartin Luther University Halle-WittenbergVon-Danckelmann-Platz 406120HalleGermany
| | - Ramesh Duraisamy
- Institute of ChemistryOtto-von-Guericke UniversityMagdeburg39106Germany
| | - Nicole Harmgarth
- Institute of ChemistryOtto-von-Guericke UniversityMagdeburg39106Germany
| | - Phil Liebing
- Laboratory for Inorganic ChemistryETH ZürichVladimir-Prelog-Weg 28093ZürichSwitzerland
| | - Volker Lorenz
- Institute of ChemistryOtto-von-Guericke UniversityMagdeburg39106Germany
| | - Dariush Hinderberger
- Institute of ChemistryMartin Luther University Halle-WittenbergVon-Danckelmann-Platz 406120HalleGermany
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Edwards DT, Takahashi S, Sherwin MS, Han S. Distance measurements across randomly distributed nitroxide probes from the temperature dependence of the electron spin phase memory time at 240 GHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 223:198-206. [PMID: 22975249 DOI: 10.1016/j.jmr.2012.07.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2012] [Revised: 06/27/2012] [Accepted: 07/05/2012] [Indexed: 06/01/2023]
Abstract
At 8.5 T, the polarization of an ensemble of electron spins is essentially 100% at 2 K, and decreases to 30% at 20 K. The strong temperature dependence of the electron spin polarization between 2 and 20 K leads to the phenomenon of spin bath quenching: temporal fluctuations of the dipolar magnetic fields associated with the energy-conserving spin "flip-flop" process are quenched as the temperature of the spin bath is lowered to the point of nearly complete spin polarization. This work uses pulsed electron paramagnetic resonance (EPR) at 240 GHz to investigate the effects of spin bath quenching on the phase memory times (T(M)) of randomly-distributed ensembles of nitroxide molecules below 20 K at 8.5 T. For a given electron spin concentration, a characteristic, dipolar flip-flop rate (W) is extracted by fitting the temperature dependence of T(M) to a simple model of decoherence driven by the spin flip-flop process. In frozen solutions of 4-Amino-TEMPO, a stable nitroxide radical in a deuterated water-glass, a calibration is used to quantify average spin-spin distances as large as r=6.6 nm from the dipolar flip-flop rate. For longer distances, nuclear spin fluctuations, which are not frozen out, begin to dominate over the electron spin flip-flop processes, placing an effective ceiling on this method for nitroxide molecules. For a bulk solution with a three-dimensional distribution of nitroxide molecules at concentration n, we find W∝n∝1/r(3), which is consistent with magnetic dipolar spin interactions. Alternatively, we observe W∝n(32) for nitroxides tethered to a quasi two-dimensional surface of large (Ø∼200 nm), unilamellar, lipid vesicles, demonstrating that the quantification of spin bath quenching can also be used to discern the geometry of molecular assembly or organization.
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Affiliation(s)
- Devin T Edwards
- Department of Physics, University of California, Santa Barbara, CA 93106, United States
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Lyubenova S, Maly T, Zwicker K, Brandt U, Ludwig B, Prisner T. Multifrequency pulsed electron paramagnetic resonance on metalloproteins. Acc Chem Res 2010; 43:181-9. [PMID: 19842617 DOI: 10.1021/ar900050d] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Metalloproteins often contain metal centers that are paramagnetic in some functional state of the protein; hence electron paramagnetic resonance (EPR) spectroscopy can be a powerful tool for studying protein structure and function. Dipolar spectroscopy allows the determination of the dipole-dipole interactions between metal centers in protein complexes, revealing the structural arrangement of different paramagnetic centers at distances of up to 8 nm. Hyperfine spectroscopy can be used to measure the interaction between an unpaired electron spin and nuclear spins within a distance of 0.8 nm; it therefore permits the characterization of the local structure of the paramagnetic center's ligand sphere with very high precision. In this Account, we review our laboratory's recent applications of both dipolar and hyperfine pulsed EPR methods to metalloproteins. We used pulsed dipolar relaxation methods to investigate the complex of cytochrome c and cytochrome c oxidase, a noncovalent protein-protein complex involved in mitochondrial electron-transfer reactions. Hyperfine sublevel correlation spectroscopy (HYSCORE) was used to study the ligand sphere of iron-sulfur clusters in complex I of the mitochondrial respiratory chain and substrate binding to the molybdenum enzyme polysulfide reductase. These examples demonstrate the potential of the two techniques; however, they also highlight the difficulties of data interpretation when several paramagnetic species with overlapping spectra are present in the protein. In such cases, further approaches and data are very useful to enhance the information content. Relaxation filtered hyperfine spectroscopy (REFINE) can be used to separate the individual components of overlapping paramagnetic species on the basis of differences in their longitudinal relaxation rates; it is applicable to any kind of pulsed hyperfine or dipolar spectroscopy. Here, we show that the spectra of the iron-sulfur clusters in complex I can be separated by this method, allowing us to obtain hyperfine (and dipolar) information from the individual species. Furthermore, performing pulsed EPR experiments at different magnetic fields is another important tool to disentangle the spectral components in such complex systems. Despite the fact that high magnetic fields do not usually lead to better spectral separation for metal centers, they provide additional information about the relative orientation of different paramagnetic centers. Our high-field EPR studies on cytochrome c oxidase reveal essential information regarding the structural arrangement of the binuclear Cu(A) center with respect to both the manganese ion within the enzyme and the cytochrome in the protein-protein complex with cytochrome c.
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Affiliation(s)
- Sevdalina Lyubenova
- Cluster of Excellence Macromolecular Complexes, Goethe-University, Frankfurt am Main, Germany
| | - Thorsten Maly
- Cluster of Excellence Macromolecular Complexes, Goethe-University, Frankfurt am Main, Germany
| | - Klaus Zwicker
- Cluster of Excellence Macromolecular Complexes, Goethe-University, Frankfurt am Main, Germany
| | - Ulrich Brandt
- Cluster of Excellence Macromolecular Complexes, Goethe-University, Frankfurt am Main, Germany
| | - Bernd Ludwig
- Cluster of Excellence Macromolecular Complexes, Goethe-University, Frankfurt am Main, Germany
| | - Thomas Prisner
- Cluster of Excellence Macromolecular Complexes, Goethe-University, Frankfurt am Main, Germany
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Savitsky A, Möbius K. High-field EPR. PHOTOSYNTHESIS RESEARCH 2009; 102:311-333. [PMID: 19468856 DOI: 10.1007/s11120-009-9432-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2008] [Accepted: 04/29/2009] [Indexed: 05/27/2023]
Abstract
Among the numerous spectroscopic techniques utilized in photosynthesis research, high-field/high-frequency EPR and its pulse extensions ESE, ENDOR, ESEEM, and PELDOR play an important role in the endeavor to understand, on the basis of structure and dynamics data, dominant factors that control specificity and efficiency of light-induced electron- and proton-transfer processes in primary photosynthesis. Short-lived transient intermediates of the photocycle can be characterized by high-field EPR techniques, and detailed structural information can be obtained even from disordered sample preparations. The chapter describes how multifrequency high-field EPR methodology, in conjunction with mutation strategies for site-specific isotope or spin labeling and with the support of modern quantum-chemical computation methods for data interpretation, is capable of providing new insights into the photosynthetic transfer processes. The information obtained is complementary to that of protein crystallography, solid-state NMR and laser spectroscopy.
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Affiliation(s)
- Anton Savitsky
- Department of Physics, Free University Berlin, Arnimallee 14, 14195 Berlin, Germany
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Eaton SS, Eaton GR. Frequency Dependence of Pulsed EPR Experiments. CONCEPTS IN MAGNETIC RESONANCE. PART A, BRIDGING EDUCATION AND RESEARCH 2009; 34A:315. [PMID: 20148127 PMCID: PMC2818603 DOI: 10.1002/cmr.a.20148] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The frequency dependence of the signal-to-noise ratio (S/N) that is theoretically possible for pulsed EPR experiments is the same as for continuous wave experiments. To select the optimum resonance frequency or frequencies for pulsed EPR experiments it is important to consider not only S/N, but also orientation selection, depth of spin echo modulation, and intensities of forbidden transitions. Evaluation of factors involved in selecting the optimum frequency for pulsed EPR measurements of distances between spins is discussed.
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Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO, USA 80208
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Goldfarb D, Lipkin Y, Potapov A, Gorodetsky Y, Epel B, Raitsimring AM, Radoul M, Kaminker I. HYSCORE and DEER with an upgraded 95GHz pulse EPR spectrometer. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 194:8-15. [PMID: 18571956 DOI: 10.1016/j.jmr.2008.05.019] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2008] [Revised: 05/18/2008] [Accepted: 05/19/2008] [Indexed: 05/26/2023]
Abstract
The set-up of a new microwave bridge for a 95 GHz pulse EPR spectrometer is described. The virtues of the bridge are its simple and flexible design and its relatively high output power (0.7 W) that generates pi pulses of 25 ns and a microwave field, B(1)=0.71 mT. Such a high B(1) enhances considerably the sensitivity of high field double electron-electron resonance (DEER) measurements for distance determination, as we demonstrate on a nitroxide biradical with an interspin distance of 3.6 nm. Moreover, it allowed us to carry out HYSCORE (hyperfine sublevel-correlation) experiments at 95 GHz, observing nuclear modulation frequencies of 14N and 17O as high as 40 MHz. This opens a new window for the observation of relatively large hyperfine couplings, yet not resolved in the EPR spectrum, that are difficult to observe with HYSCORE carried out at conventional X-band frequencies. The correlations provided by the HYSCORE spectra are most important for signal assignment, and the improved resolution due to the two dimensional character of the experiment provides 14N quadrupolar splittings.
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Affiliation(s)
- Daniella Goldfarb
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
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Schiemann O, Prisner TF. Long-range distance determinations in biomacromolecules by EPR spectroscopy. Q Rev Biophys 2007; 40:1-53. [PMID: 17565764 DOI: 10.1017/s003358350700460x] [Citation(s) in RCA: 428] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Electron paramagnetic resonance (EPR) spectroscopy provides a variety of tools to study structures and structural changes of large biomolecules or complexes thereof. In order to unravel secondary structure elements, domain arrangements or complex formation, continuous wave and pulsed EPR methods capable of measuring the magnetic dipole coupling between two unpaired electrons can be used to obtain long-range distance constraints on the nanometer scale. Such methods yield reliably and precisely distances of up to 80 A, can be applied to biomolecules in aqueous buffer solutions or membranes, and are not size limited. They can be applied either at cryogenic or physiological temperatures and down to amounts of a few nanomoles. Spin centers may be metal ions, metal clusters, cofactor radicals, amino acid radicals, or spin labels. In this review, we discuss the advantages and limitations of the different EPR spectroscopic methods, briefly describe their theoretical background, and summarize important biological applications. The main focus of this article will be on pulsed EPR methods like pulsed electron-electron double resonance (PELDOR) and their applications to spin-labeled biosystems.
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Affiliation(s)
- Olav Schiemann
- Institute of Physical and Theoretical Chemistry, Center for Biomolecular Magnetic Resonance, J. W. Goethe-University Frankfurt, 60438 Frankfurt am Main, Germany.
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Asher JR, Kaupp M. Hyperfine Coupling Tensors of the Benzosemiquinone Radical Anion from Car–Parrinello Molecular Dynamics. Chemphyschem 2007; 8:69-79. [PMID: 17121407 DOI: 10.1002/cphc.200600325] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Based on Car-Parrinello ab initio molecular dynamics simulations of the benzosemiquinone radical anion in both aqueous solution and the gas phase, density functional calculations provide the currently most refined EPR hyperfine coupling (HFC) tensors of semiquinone nuclei and solvent protons. For snapshots taken at regular intervals from the molecular dynamics trajectories, cluster models with different criteria for inclusion of water molecules and an additional continuum solvent model are used to analyse the HFCs. These models provide a detailed picture of the effects of dynamics and of different intermolecular interactions on the spin-density distribution and HFC tensors. Comparison with static calculations allows an assessment of the importance of dynamical effects, and of error compensation in static DFT calculations. Solvent proton HFCs depend characteristically on the position relative to the semiquinone radical anion. A point-dipolar model works well for in-plane hydrogen-bonded protons but deviates from the quantum chemical values for out-of-plane hydrogen bonding.
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Affiliation(s)
- James R Asher
- Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
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Denysenkov VP, Prisner TF, Stubbe J, Bennati M. High-field pulsed electron-electron double resonance spectroscopy to determine the orientation of the tyrosyl radicals in ribonucleotide reductase. Proc Natl Acad Sci U S A 2006; 103:13386-90. [PMID: 16938868 PMCID: PMC1569173 DOI: 10.1073/pnas.0605851103] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Class I ribonucleotide reductases (RNRs) are composed of two subunits, R1 and R2. The R2 subunit contains the essential diferric cluster-tyrosyl radical (Y.) cofactor, and R1 is the site of the conversion of nucleoside diphosphates to 2'-deoxynucleoside diphosphates. It has been proposed that the function of the tyrosyl radical in R2 is to generate a transient thiyl radical (C439.) in R1 over a distance of 35 A, which in turn initiates the reduction process. EPR distance measurements provide a tool with which to study the mechanism of radical initiation in class I RNRs. These types of experiments at low magnetic fields and frequencies (0.3 T, 9 GHz) give insight into interradical distances and populations. We present a pulsed electron-electron double resonance (PELDOR) experiment at high EPR frequency (180-GHz electron Larmor frequency) that detects the dipolar interaction between the Y.s in each protomer of RNR R2 from Escherichia coli. We observe a correlation between the orientation-dependent dipolar interaction and their resolved g-tensors. This information has allowed us to define the relative orientation of two radicals embedded in the active homodimeric protein in solution. This experiment demonstrates that high-field PELDOR spectroscopy is a powerful tool with which to study the assembly of proteins that contain multiple paramagnetic centers.
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Affiliation(s)
- V. P. Denysenkov
- *Institute for Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, J. W. Goethe University, 60438 Frankfurt am Main, Germany; and
| | - T. F. Prisner
- *Institute for Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, J. W. Goethe University, 60438 Frankfurt am Main, Germany; and
| | - J. Stubbe
- Departments of Chemistry and Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
- To whom correspondence may be addressed. E-mail:
or
| | - M. Bennati
- *Institute for Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, J. W. Goethe University, 60438 Frankfurt am Main, Germany; and
- To whom correspondence may be addressed. E-mail:
or
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Hertel MM, Denysenkov VP, Bennati M, Prisner TF. Pulsed 180-GHz EPR/ENDOR/PELDOR spectroscopy. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2005; 43 Spec no.:S248-55. [PMID: 16235223 DOI: 10.1002/mrc.1681] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Within this review, we describe a home-built pulsed electron paramagnetic resonance (EPR) spectrometer operating at 180 GHz as well as the incorporation of two double resonance techniques, electron nuclear double resonance (ENDOR) and pulsed electron double resonance (PELDOR), along with first applications. Hahn-echo decays on a TEMPO/polystyrene sample are presented, demonstrating that the observation of anisotropic librational motions is possible in a very precise manner at high magnetic fields. Bisdiphenylene-phenyl-allyl is used as a model system to illustrate the performance of the setup for 1H-ENDOR using the Mims as well as the Davies sequence. Furthermore, first 1H-Mims and Davies ENDOR spectra on a biological sample, the wild-type Ras*Mn2+*GDP protein, are reported. The capability of the 180-GHz PELDOR setup is demonstrated using the three-pulse ELDOR sequence on the protein ribonucleotide reductase (RNR) subunit R2 from Escherichia coli, which contains two tyrosyl radicals at a 33 angstroms distance. At 180 GHz, orientation selectivity is observed and the modulation frequency is found to be in good agreement with theoretical predictions.
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Affiliation(s)
- M M Hertel
- Institute for Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, J. W. Goethe-University, Frankfurt am Main, Germany
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Asher JR, Doltsinis NL, Kaupp M. Extended Car-Parrinello molecular dynamics and electronic g-tensors study of benzosemiquinone radical anion. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2005; 43 Spec no.:S237-47. [PMID: 16235202 DOI: 10.1002/mrc.1669] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Car-Parrinello molecular dynamics simulations of benzoquinone and benzosemiquinone radical anion in both aqueous solution and the gas phase have been carried out at ambient conditions. Hydrogen bonding is considerably more extensive to the anionic than to the neutral aqueous system. In addition to the conventional hydrogen bonding to the carbonyl oxygen atoms, T-stacked hydrogen bonding to the pi-system is statistically and energetically significant for the semiquinone anion but not for the neutral quinone. EPR g-tensors have been calculated at DFT level for snapshots taken at regular intervals from the gas-phase and solution semiquinone anion trajectories. Different criteria for extraction of semiquinone/water clusters from the solution trajectory give insight into the effects of different interactions on the g-tensor, as does correlation of the g-tensor with statistically significant hydrogen-bond configurations identified along the trajectories. Comparison of gas-phase and solution results indicates opposite directions of direct electronic and indirect structural influences of hydrogen bonding on g-tensors. Short-time oscillations in g(x) along the trajectory are due mainly to C-O bond vibrations.
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Affiliation(s)
- James R Asher
- Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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Maly T, Prisner TF. Relaxation filtered hyperfine spectroscopy (REFINE). JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2004; 170:88-96. [PMID: 15324761 DOI: 10.1016/j.jmr.2004.06.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2004] [Revised: 06/04/2004] [Indexed: 05/24/2023]
Abstract
A simple and general applicable method to separate spectrally overlapping hyperfine spectra of two paramagnetic compounds is presented. Overlapping spectral contributions from different paramagnetic species are a common situation in electron paramagnetic resonance (EPR) spectroscopy, resulting in complicate EPR spectra of metal enzymes, organic radicals or in the field of material sciences. On the other hand, the longitudinal relaxation times T1 of these species contributing to the overall EPR signal can vary by several orders of magnitude, depending on the paramagnetic component under study. These differences can be used to selectively study individual species by using an inversion-recovery preparation sequence as a filter. Here, we demonstrate the possibility to separate hyperfine spectra of two spectrally overlapping paramagnetic species by combining an inversion-recovery based relaxation filter together with ESEEM or ENDOR hyperfine spectroscopy (REFINE). The feasibility of the presented method is demonstrated on model compounds and the necessary requirements are discussed.
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Affiliation(s)
- Th Maly
- Institute of Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-University Frankfurt, D-60439 Frankfurt am Main, Germany
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Freed JH. The Development of High-Field /High Frequency ESR. VERY HIGH FREQUENCY (VHF) ESR/EPR 2004. [DOI: 10.1007/978-1-4757-4379-1_2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Schnegg A, Fuhs M, Rohrer M, Lubitz W, Prisner TF, Möbius K. Molecular Dynamics of QA-• and QB-• in Photosynthetic Bacterial Reaction Centers Studied by Pulsed High-Field EPR at 95 GHz. J Phys Chem B 2002. [DOI: 10.1021/jp0203907] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- A. Schnegg
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany, Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Goethe Universität, Marie Curie Strasse 11, 60439 Frankfurt, Germany, and Max-Planck-Institut für Strahlenchemie, 45470 Mülheim an der Ruhr, Germany
| | - M. Fuhs
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany, Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Goethe Universität, Marie Curie Strasse 11, 60439 Frankfurt, Germany, and Max-Planck-Institut für Strahlenchemie, 45470 Mülheim an der Ruhr, Germany
| | - M. Rohrer
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany, Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Goethe Universität, Marie Curie Strasse 11, 60439 Frankfurt, Germany, and Max-Planck-Institut für Strahlenchemie, 45470 Mülheim an der Ruhr, Germany
| | - W. Lubitz
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany, Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Goethe Universität, Marie Curie Strasse 11, 60439 Frankfurt, Germany, and Max-Planck-Institut für Strahlenchemie, 45470 Mülheim an der Ruhr, Germany
| | - T. F. Prisner
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany, Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Goethe Universität, Marie Curie Strasse 11, 60439 Frankfurt, Germany, and Max-Planck-Institut für Strahlenchemie, 45470 Mülheim an der Ruhr, Germany
| | - K. Möbius
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany, Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Goethe Universität, Marie Curie Strasse 11, 60439 Frankfurt, Germany, and Max-Planck-Institut für Strahlenchemie, 45470 Mülheim an der Ruhr, Germany
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Rinard GA, Quine RW, Eaton SS, Eaton GR. Frequency dependence of EPR signal intensity, 250 MHz to 9.1 GHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2002; 156:113-21. [PMID: 12081448 DOI: 10.1006/jmre.2002.2530] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Experimental EPR signal intensities at 250 MHz, 1.5 GHz, and 9.1 GHz agree within experimental error with predictions from first principles. When both the resonator size and the sample size are scaled with the inverse of RF/microwave frequency, omega, the EPR signal at constant B(1) scales as omega(-1/4). Comparisons were made for three different samples in two pairs of loop gap resonators. Each pair was geometrically scaled by a factor of 6. One pair of resonators was scaled from 250 MHz to 1.5 GHz, and the other pair was scaled from 1.5 GHz to 9 GHz. All terms in the comparison were measured directly, and their uncertainties estimated. The theory predicts that the signal at the lower frequency will be larger than the signal at the higher frequency by the ratio 1.57. For 250 MHz to 1.5 GHz, the experimental ratio was 1.52 and for the 1.5-GHz to 9-GHz comparison the ratio was 1.14.
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Affiliation(s)
- George A Rinard
- Department of Engineering, University of Denver, Denver, Colorado 80208-2436, USA
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Brunel LC, Caneschi A, Dei A, Friselli D, Gatteschi D, Hassan AK, Lenci L, Martinelli M, Massa CA, Pardi LA, Popescu F, Ricci I, Sorace L. How and why the characterization of magnetic materials can give directions in the methodological development in high field–high frequency EPR. RESEARCH ON CHEMICAL INTERMEDIATES 2002. [DOI: 10.1163/156856702320267127] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Eaton SS, Eaton GR. Relaxation Times of Organic Radicals and Transition Metal Ions. DISTANCE MEASUREMENTS IN BIOLOGICAL SYSTEMS BY EPR 2002. [DOI: 10.1007/0-306-47109-4_2] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Abstract
Pulsed electron paramagnetic resonance (EPR) methods such as ESEEM, PELDOR, relaxation time measurements, transient EPR, high-field/high-frequency EPR, and pulsed ENDOR, have been used successfully to investigate the local structure and dynamics of paramagnetic centers in biological samples. These methods allow different contributions to the EPR spectra to be distinguished and can help unravel complicated EPR spectra consisting of overlapping resonance lines, as are often found in disordered protein samples. The basic principles, specific potentials, technical requirements, and limitations of these advanced EPR techniques will be reviewed together with recent applications to metal centers, organic radicals, and spin labels in proteins.
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Affiliation(s)
- T Prisner
- Institute for Physical and Theoretical Chemistry, J. W. Goethe-University Frankfurt, Marie-Curie-Strasse 11, Frankfurt am Main, D-60439 Germany.
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Gromov I, Shane J, Forrer J, Rakhmatoullin R, Rozentzwaig Y, Schweiger A. A Q-band pulse EPR/ENDOR spectrometer and the implementation of advanced one- and two-dimensional pulse EPR methodology. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2001; 149:196-203. [PMID: 11318618 DOI: 10.1006/jmre.2001.2298] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A versatile high-power pulse Q-band EPR spectrometer operating at 34.5--35.5 GHz and in a temperature range of 4--300 K is described. The spectrometer allows one to perform one- and two-dimensional multifrequency pulse EPR and pulse ENDOR experiments, as well as continuous wave experiments. It is equipped with two microwave sources and four microwave channels to generate pulse sequences with different amplitudes, phases, and carrier frequencies. A microwave pulse power of up to 100 W is available. Two channels form radiofrequency pulses with adjustable phases for ENDOR experiments. The spectrometer performance is demonstrated by single crystal pulse ENDOR experiments on a copper complex. A HYSCORE experiment demonstrates that the advantages of high-field EPR and correlation spectroscopy can be combined and exploited at Q-band. Furthermore, we illustrate how this combination can be used in cases where the HYSCORE experiment is no longer effective at 35 GHz because of the shallow modulation depth. Even in cases where the echo modulation is virtually absent in the HYSCORE experiment at Q-band, matched microwave pulses allow one to get HYSCORE spectra with a signal-to-noise ratio as good as at X-band. Finally, it is shown that the high microwave power, the short pulses, and the broad resonator bandwidth make the spectrometer well suited to Fourier transform EPR experiments.
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Affiliation(s)
- I Gromov
- Laboratory of Physical Chemistry, ETH-Zentrum, Swiss Federal Institute of Technology, CH-8092 Zürich, Switzerland
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25
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Abstract
New electron spin resonance (ESR) technologies have been developed, which have led to new and improved applications. (a) The development of two-dimensional Fourier transform (FT) ESR required spectrometers providing intense pi/2 microwave pulses of very short (3-5 ns) duration, wide bandwidths, and very short dead times. It has enabled studies that resolve sophisticated details of molecular dynamics in complex fluids. (b) Methods that produce multiple quantum coherences by pulsed ESR now enable accurate measurements of large distances (>12A). (c) One of the most important advances has been the extension of ESR to high magnetic fields and high frequencies. This has benefited from the utilization of quasi-optical methods, especially above 150 GHz. The greatly improved orientational resolution and the faster "snapshot" of motions that are provided by ESR at high frequencies enhance studies of molecular dynamics. The use of both high and lower frequencies enables one to unravel faster and slower modes from the complex dynamics of fluids and macromolecules. (d) The development of FT-ESR imaging required substantial pulsed field gradients lasting only 50-100 ns. ESR imaging is effective in studying diffusion in fluids. Areas for further development are also described.
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Affiliation(s)
- J H Freed
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
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26
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Borbat PP, Costa-Filho AJ, Earle KA, Moscicki JK, Freed JH. Electron spin resonance in studies of membranes and proteins. Science 2001; 291:266-9. [PMID: 11253218 DOI: 10.1126/science.291.5502.266] [Citation(s) in RCA: 240] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We provide a review of current electron spin resonance (ESR) techniques for studying basic molecular mechanisms in membranes and proteins by using nitroxide spin labels. In particular, nitroxide spin label studies with high-field/high-frequency ESR and two-dimensional Fourier transform ESR enable one to accurately determine distances in biomolecules, unravel the details of the complex dynamics in proteins, characterize the dynamic structure of membrane domains, and discriminate between bulk lipids and boundary lipids that coat transmembrane peptides or proteins; these studies can also provide time resolution to studies of functional dynamics of proteins. We illustrate these capabilities with recent examples.
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Affiliation(s)
- P P Borbat
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA
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27
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Deligiannakis Y, Louloudi M, Hadjiliadis N. Electron spin echo envelope modulation (ESEEM) spectroscopy as a tool to investigate the coordination environment of metal centers. Coord Chem Rev 2000. [DOI: 10.1016/s0010-8545(99)00218-0] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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28
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Annino G, Cassettari M, Fittipaldi M, Longo I, Martinelli M, Massa CA, Pardi LA. High-field, multifrequency EPR spectroscopy using whispering gallery dielectric resonators. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2000; 143:88-94. [PMID: 10698649 DOI: 10.1006/jmre.1999.1977] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
High-field/high frequency EPR spectroscopy measurements are shown. Experiments were carried out at 240- and 316-GHz frequencies. The employed apparatus uses a novel combination of far infrared molecular lasers and of probehead exploiting dielectric resonators working in the whispering gallery modes. This approach constitutes a relatively simple method of multifrequency EPR spectroscopy and opens appealing perspectives in high-sensitivity EPR spectroscopy up to the THz regime.
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Affiliation(s)
- G Annino
- Istituto di Fisica Atomica e Molecolare del CNR, Via del Giardino 7, Pisa, 56127, Italy
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29
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Weis V, Bennati M, Rosay M, Bryant JA, Griffin RG. High-field DNP and ENDOR with a novel multiple-frequency resonance structure. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1999; 140:293-299. [PMID: 10479576 DOI: 10.1006/jmre.1999.1841] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We describe a new triply tuned (e(-), (1)H, and (13)C) resonance structure operating at an electron Larmor frequency of 139.5 GHz for dynamic nuclear polarization (DNP) and electron nuclear double-resonance (ENDOR) experiments. In contrast to conventional double-resonance structures, the body of the microwave cavity simultaneously acts as a NMR coil, allowing for increased efficiency of radiofrequency irradiation while maintaining a high quality factor for microwave irradiation. The resonator design is ideal for low-gamma-nuclei ENDOR, where sensitivity is limited by the fact that electron spin relaxation times are on the order of the RF pulse lengths. The performance is demonstrated with (2)H ENDOR on a standard perdeuterated bis-diphenylene-phenyl-allyl stable radical. In DNP experiments, we show that the use of this resonator, combined with a low microwave power setup (17 mW), leads to significantly higher (1)H signal enhancement (epsilon approximately 400 +/- 50) than previously achieved at 5-T fields. The results emphasize the importance of optimizing the microwave B(1) field by improving either the quality factor of the microwave resonator or the microwave power level.
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Affiliation(s)
- V Weis
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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30
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Rinard GA, Quine RW, Harbridge JR, Song R, Eaton GR, Eaton SS. Frequency dependence of EPR signal-to-noise. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1999; 140:218-227. [PMID: 10479565 DOI: 10.1006/jmre.1999.1798] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Direct measurements of electron spin-echo signal and noise in well-characterized X-band and S-band spectrometers agree with predictions of frequency dependence based on first principles. For the particular spectrometers compared, the echo at 9.52 GHz was 9.5 times larger than the echo at 2.68 GHz, after scaling for differences in spectrometer gain. The calculated ratio was 7.6. This result contrasts with prior predictions that the frequency dependence would be much greater.
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Affiliation(s)
- G A Rinard
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, USA
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31
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Gromov I, Krymov V, Manikandan P, Arieli D, Goldfarb D. A W-band pulsed ENDOR spectrometer: setup and application to transition metal centers. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1999; 139:8-17. [PMID: 10388579 DOI: 10.1006/jmre.1999.1762] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The design and performance of a 95 GHz pulsed W-band EPR/ENDOR spectrometer is described with emphasis on the ENDOR part. Its unique feature is the easy and fast sample exchange at 4.2 K for frozen solution and single crystal samples. In addition, the microwave bridge power output is relatively high (maximum 267 mW), which allows the application of short microwave pulses. This increases the sensitivity in echo experiments because of the broader excitation bandwidth and the possibility of employing short pulse intervals, as long as the dead time does not increase significantly with the power. The spectrometer features two microwave and radiofrequency (0.1-220 MHz, 3 kW pulse power) channels and a 6 T superconducting magnet in a solenoid configuration. The magnet is equipped with cryogenic sweep coils providing a sweep range of +/-0. 4 and +/-0.2 T for a center field of 0-4 and 4-6 T, respectively. The spectrometer performance is demonstrated on Cu(II) centers in single crystals, a zeolite polycrystalline sample, and a protein frozen solution.
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Affiliation(s)
- I Gromov
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot, 76100, Israel.
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32
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Bennati M, Farrar CT, Bryant JA, Inati SJ, Weis V, Gerfen GJ, Riggs-Gelasco P, Stubbe J, Griffin RG. Pulsed electron-nuclear double resonance (ENDOR) at 140 GHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1999; 138:232-243. [PMID: 10341127 DOI: 10.1006/jmre.1999.1727] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We describe a spectrometer for pulsed ENDOR at 140 GHz, which is based on microwave IMPATT diode amplifiers and a probe consisting of a TE011 cavity with a high-quality resonance circuit for variable radiofrequency irradiation. For pulsed EPR we obtain an absolute sensitivity of 3x10(9) spins/Gauss at 20 K. The performance of the spectrometer is demonstrated with pulsed ENDOR spectra of a standard bis-diphenylene-phenyl-allyl (BDPA) doped into polystyrene and of the tyrosyl radical from E. coli ribonucleotide reductase (RNR). The EPR spectrum of the RNR tyrosyl radical displays substantial g-anisotropy at 5 T and is used to demonstrate orientation-selective Davies-ENDOR.
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Affiliation(s)
- M Bennati
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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33
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Bloess A, Mobius K, Prisner TF. High-Frequency/High-field electron spin echo envelope modulation study of nitrogen hyperfine and quadrupole interactions on a disordered powder sample. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1998; 134:30-35. [PMID: 9740727 DOI: 10.1006/jmre.1998.1474] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
High-frequency/high-field (95 GHz/3.4 T) electron spin echo envelope modulation (ESEEM) experiments on single crystals and disordered samples of dianisyl-nitroxide (DANO) radicals are reported. At these high microwave frequencies (W-band), the anisotropic g-matrix of the nitroxide radical is resolved in the EPR spectrum. Additionally ESEEM modulations from other than nitrogen nuclei, such as protons, are highly suppressed at these frequencies, because they are too far from the cancellation condition for effective mixing of the nuclear spin functions. Therefore the nitrogen (14N) hyperfine and quadrupole coupling tensors could be determined without ambiguity from powder measurements. The results obtained were checked by ESEEM measurements on single crystals. Advantages and disadvantages of high-field ESEEM on nitrogen couplings are briefly discussed and compared with electron nuclear double resonance (ENDOR) and X-band ESEEM. Copyright 1998 Academic Press.
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Affiliation(s)
- A Bloess
- Freie Universitat Berlin, Arnimallee 14, Berlin, D-14195, Germany
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34
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35
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Rohrer M, MacMillan F, Prisner TF, Gardiner AT, Möbius K, Lubitz W. Pulsed ENDOR at 95 GHz on the Primary Acceptor Ubisemiquinone in Photosynthetic Bacterial Reaction Centers and Related Model Systems. J Phys Chem B 1998. [DOI: 10.1021/jp9805104] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. Rohrer
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany, and Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
| | - F. MacMillan
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany, and Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
| | - T. F. Prisner
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany, and Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
| | - A. T. Gardiner
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany, and Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
| | - K. Möbius
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany, and Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
| | - W. Lubitz
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany, and Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
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36
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Stehlik D, Möbius K. NEW EPR METHODS FOR INVESTIGATING PHOTOPROCESSES WITH PARAMAGNETIC INTERMEDIATES. Annu Rev Phys Chem 1997; 48:745-84. [PMID: 15012455 DOI: 10.1146/annurev.physchem.48.1.745] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
▪ Abstract Some of the significant advances in time-resolved multifrequency electron paramagnetic resonance (EPR) methods are reviewed, with the explicit focus on studies of light-driven processes and photoreactions in real time. Prominent examples are excited state electron transfer reactions with transient charge-separated radical pairs playing a central role. Paramagnetic intermediates and products are key functional states; thus EPR is the method of choice for their characterization. Photogenerated spin polarization and coherences as process-inherent features add the practical advantage of compensation in the trade-off between sensitivity and time resolution. Additionally, they provide detailed structural and dynamic information on the photoreactive system. Significance and specificity of the results achieved for charge separation in photosynthetic reaction centers and donor-acceptor model complexes indicate highly promising perspectives in photochemical research.
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Affiliation(s)
- D Stehlik
- Department of Physics, Free University Berlin, Arnimallee 14, D-14195 Berlin, Germany.
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