Engineering and design concepts for quasioptical high‐field electron paramagnetic resonance

Gullá, Andrea F.; Budil, David E.

doi:10.1002/cmr.b.20014

Cited by 11 publications

(3 citation statements)

References 63 publications

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“…In a uniform waveguide this can be readily achieved by using separate transmitting and receiving antennas on opposite sides of the sample. Alternatively, a gradient encoding blip could be applied between excitation and reception to compensate for variable phase delay, effectively refocusing the spin radiation for reception by the transmitter antenna Entering the far-field realm, travelling-wave NMR prompts analogies with electron spin resonance 22 and nonlinear optics 23 . Adopting principles and devices from these fields may enable studying phenomena analogous to, e.g., photon echoes 24 , four-wave mixing 25 , and self-induced transparency 26 .…”

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confidence: 99%

Travelling-wave nuclear magnetic resonance

Brunner

Zanche

Fröhlich

et al. 2009

Nature

172

164

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Nuclear magnetic resonance (NMR) is one of the most versatile experimental methods in chemistry, physics and biology, providing insight into the structure and dynamics of matter at the molecular scale. Its imaging variant-magnetic resonance imaging (MRI)-is widely used to examine the anatomy, physiology and metabolism of the human body. NMR signal detection is traditionally based on Faraday induction in one or multiple radio-frequency resonators that are brought into close proximity with the sample. Alternative principles involving structured-material flux guides, superconducting quantum interference devices, atomic magnetometers, Hall probes or magnetoresistive elements have been explored. However, a common feature of all NMR implementations until now is that they rely on close coupling between the detector and the object under investigation. Here we show that NMR can also be excited and detected by long-range interaction, relying on travelling radio-frequency waves sent and received by an antenna. One benefit of this approach is more uniform coverage of samples that are larger than the wavelength of the NMR signal-an important current issue in MRI of humans at very high magnetic fields. By allowing a significant distance between the probe and the sample, travelling-wave interaction also introduces new possibilities in the design of NMR experiments and systems. E-mail: paska@ifh.ee.ethz.ch, Telephone: +41 44 6320430, 5 Institute for Biomedical Engineering, University and ETH Zürich, Gloriastrasse 35, 8092 Zürich, Telephone: +41 44 632 66 96, Fax: +41 44 632 11 93 In this work we introduce a novel concept of signal excitation and detection to NMR and MRI. We propose to abandon the long-standing principle of near-field inductive coupling between nuclear magnetization and the detector, commonly an RF resonator, by far-range travelling-wave interaction with an antenna probe. Along with the feasibility of this approach we demonstrate that it addresses a key obstacle to high-field MRI in large samples, particularly in humans. We believe that the transition to travelling-wave excitation and detection is significant both from a fundamental, physical point of view and with respect to the numerous applications that NMR and MRI have in the sciences and medicine. Uniform spatial coverage in NMR and MRI is traditionally achieved by tailoring the reactive near field of resonant Faraday probes 7-10 . This approach is valid when the RF wavelength at the Larmor frequency is substantially larger than the target volume, which 3 does not hold for recent wide-bore high-field systems. At the currently highest field strength that is used for human studies, 9.4 tesla 16,17 , the resonance frequency of hydrogen nuclei reaches 400 MHz, corresponding to a wavelength in tissue on the order of 10 cm. At such short wavelengths head or body resonators form standing-wave field patterns, which degrade MRI results by causing regional signal losses and perturbing the contrast between different types of tissue. Travelling-Wave ...

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mentioning

confidence: 99%

Travelling-wave nuclear magnetic resonance

Brunner

Zanche

Fröhlich

et al. 2009

Nature

172

164

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“…Calculations using the Jones matrix formalism [51,52] constitute a another way of analyzing the microwaves and describing their polarization. The polarization of the electric field of the radiation can be described by a Jones vector containing two complex amplitudes E 0x and E 0y ,…”

Section: Investigation Based On Jones Matrix Calculusmentioning

confidence: 99%

Control and Manipulation of Microwave Polarization, and Power of a frequency-agile 198 GHz Gyrotron for Magnetic Resonance

Millen

Pagonakis

Björgvinsdóttir

et al. 2022

Preprint

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The measurement and manipulation of the microwave polarization emitted from a frequency-agile 198 GHz gyrotron for dynamic nuclear polarization (DNP) is demonstrated. In general, gyrotrons emit linearly polarized radiation, yet in this case elliptical polarization is observed from the 198 GHz gyrotron window. Indeed, half of the microwave power is circularly polarized while the other half is linearly polarized with a polarization of 60° with respect to the horizontal plane. For optimal use of microwave power for DNP experiments, the elliptical polarization from the gyrotron is converted into circular polarization with a Martin-Puplett interferometer (MPI). The dependence of the DNP enhancement on the microwave polarization was investigated by modifying the microwave polarization with the MPI. In addition the MPI can generate a linearly polarized beam, which holds promise for future development of induction-mode electron spin detected experiments.

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“…For more details about the remarkable features of high-field/high-frequency EPR spectroscopy in (bio)molecular systems such as transient paramagnetic reaction intermediates or spin-labeled proteins, we refer to recent books and overview articles, for example [17,23,42,70,90,129,131,300,474,496,497,[512][513][514][515][516][517][518][519][520][521]. .…”

Section: An Illustrative Example: High-field Epr On Nitroxide Spin-lamentioning

confidence: 99%

Biomolecular EPR Meets NMR at High Magnetic Fields

et al. 2018

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In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.

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Engineering and design concepts for quasioptical high‐field electron paramagnetic resonance

Cited by 11 publications

References 63 publications

Travelling-wave nuclear magnetic resonance

Travelling-wave nuclear magnetic resonance

Control and Manipulation of Microwave Polarization, and Power of a frequency-agile 198 GHz Gyrotron for Magnetic Resonance

Biomolecular EPR Meets NMR at High Magnetic Fields

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