for Journals by Title or ISSN for Articles by Keywords help

Publisher: Springer-Verlag (Total: 2354 journals)

 Applied Magnetic Resonance   [SJR: 0.358]   [H-I: 34]   [4 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1613-7507 - ISSN (Online) 0937-9347    Published by Springer-Verlag  [2354 journals]
• Six Decades of Progress in Magnetic Resonance: The Contributions of James
S. Hyde
• Authors: Gareth R. Eaton; Wayne L. Hubbell; Wojciech Froncisz
Pages: 1093 - 1102
Abstract: The development of electron paramagnetic resonance (EPR) and magnetic resonance imaging (MRI) over six decades is sketched with an emphasis on the contributions of James S. Hyde. For twenty years starting three years after the first commercial EPR spectrometer was shipped by Varian, he led commercial EPR developments, and then for more than forty years, he led development of instrumentation and biomedical applications of EPR at the Medical College of Wisconsin. It was there that he also made major contributions to MRI, and especially functional MRI.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0954-1
Issue No: Vol. 48, No. 11-12 (2017)

• EPR Uniform Field Signal Enhancement by Dielectric Tubes in Cavities
• Authors: James S. Hyde; Richard R. Mett
Pages: 1185 - 1204
Abstract: The dielectric tube resonator (DTR) for electron paramagnetic resonance spectroscopy is introduced. It is defined as a metallic cylindrical TE011 microwave cavity that contains a dielectric tube centered on the axis of the cylinder. Contour plots of dimensions of the metallic cylinder to achieve resonance at 9.5 GHz are shown for quartz, sapphire, and rutile tubes as a function of wall thickness and average radius. These contour plots were developed using analytical equations and confirmed by finite-element modeling. They can be used in two ways: design of the metallic cylinder for use at 9.5 GHz that incorporates a readily available tube such as a sapphire tube intended for NMR and design of a custom procured tube for optimized performance for specific sample-size constraints. The charts extend to the limiting condition where the dielectric fills the tube. However, the structure at this limit is not a dielectric resonator due to the metal wall and does not radiate. In addition, the uniform field (UF) DTR is introduced. Development of the UF resonator starting with a DTR is shown. The diameter of the tube remains constant along the cavity axis, and the diameter of the cylindrical metallic enclosure increases at the ends of the cavity to satisfy the uniform field condition. This structure has advantages over the previously developed UF TE011 resonators: higher resonator efficiency parameter Λ, convenient overall size when using sapphire tubes, and higher quality data for small samples. The DTR and UF DTR structures fill the gap between free space and dielectric resonator limits in a continuous manner.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0935-4
Issue No: Vol. 48, No. 11-12 (2017)

• Modes and Fields of Two Stacked Dielectric Resonators in a Cavity of an
Electron Paramagnetic Resonance Probe
• Authors: Saba M. Mattar; Sameh Y. Elnaggar
Pages: 1205 - 1217
Abstract: An electron paramagnetic resonance (EPR) probe consisting of two dielectric resonators (DRs) and a cavity (CV) is ideal for EPR experiments where both signal enhancement and tuning capabilities are required. The coupling of two DRs, resonating in their $${\text{TE}}_{01\delta }$$ mode and a CV resonating in its $${\text{TE}}_{011}$$ mode, is studied using energy-coupled mode theory (ECMT). The frequencies and eigenvectors of the three coupled modes are analytically derived. As predicted numerically, ECMT confirms that the $${\text{TE}}^{ + + - }$$ and $${\text{TE}}^{ + - - }$$ modes are indeed found to be degenerate at a specific distance between the two DRs $$d_{12}$$ . Additionally, the condition at which degeneracy occurs is specified. For a considerable range, the calculated frequency of the $${\text{TE}}^{ + + + }$$ mode changes linearly with respect to $$d_{12}$$ . The $${\text{TE}}^{ + + + }$$ mode showed a 500 MHz frequency change over a distance of 2 cm, when the resonance frequency is around 9.7 GHz. This enables the experimentalist to linearly tune the probe over this large frequency range. Finally the asymmetric configuration, where one of the resonators (DR2) is kept at the cavity center and the other one is allowed to move along the cavity axis, is studied. It is estimated that the frequency changes by 600 MHz over a distance of 1.5 cm. A formula for the magnitude of the magnetic field along the cavity axis, where the EPR samples are usually placed, is developed. This is crucial in determining the magnetic field in the vicinity of the sample and the probe’s filling factor.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0931-8
Issue No: Vol. 48, No. 11-12 (2017)

• An X-Band Crossed-Loop EPR Resonator
• Authors: George A. Rinard; Richard W. Quine; Joseph McPeak; Laura Buchanan; Sandra S. Eaton; Gareth R. Eaton
Pages: 1219 - 1226
Abstract: A copper X-band (9.22 GHz) cross-loop resonator has been constructed for use with 4 mm sample tubes. The Q for the two resonators is 380 and 350, respectively. The resonator efficiency is about 1 G per square root of watt. Operation has been demonstrated with measurement of T 1 by saturation recovery for samples of coal and an immobilized nitroxide.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0945-2
Issue No: Vol. 48, No. 11-12 (2017)

• Optimization Methods for the Design of Sensitive Surface ESR Resonators
• Authors: Yakir Ishay; Aharon Blank
Pages: 1249 - 1262
Abstract: Electron spin resonance (ESR) is a powerful spectroscopic technique that has many applications in a wide variety of scientific fields, including chemistry, biology, materials science, and physics. One significant drawback of conventional ESR, however, is its relatively low sensitivity compared to other spectroscopic techniques. Arguably, the most dominant element affecting ESR sensitivity is the microwave resonator used to pick up the ESR signal of the spins. Traditionally, ESR mostly employs a limited set of resonator configurations (e.g., rectangular cavity, dielectric, or loop-gap resonator) that are suboptimal with respect to a wide range of samples. In principle, a smart resonator design can be used to optimize spin sensitivity for a given sample’s properties. In this work, we make use of an efficient Genetic Algorithm (GA) approach to numerically solve, analyze, and optimize a unique class of surface microresonators. The GA is based on a method of moments code, customized directly to render the complexity of a particular resonator’s geometries in our search. The main purposes of the algorithm are to routinely generate more sensitive microresonators, optimized for a predefined sample’s dimensions, and to study the functional relations between the devices’ resonance frequency, quality, and filling factors and their topology, in order to reach a rational optimal design. Preliminary results associated with new, unique, and sensitive surface microresonators are shown and analyzed. Such resonators are cheap and easy to produce on a mass scale with an arbitrary surface geometry.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0941-6
Issue No: Vol. 48, No. 11-12 (2017)

• Q-Band Loop-Gap Resonator for EPR Applications with Broadband-Shaped
Pulses
• Authors: Vasyl Denysenkov; Philipp van Os; Thomas F. Prisner
Pages: 1263 - 1272
Abstract: Recently, Q-band-pulsed electron paramagnetic resonance spectroscopy has strongly advanced its performance by the introduction of high-power microwave amplifiers and the use of shaped pulses. For such applications, the resonator Q value has to be low enough to achieve sufficient bandwidth for short microwave pulses and to reduce the ring-down time after the pulses. However, a low Q value reduces the detection sensitivity as well as the conversion efficiency of the microwave input power to the magnetic field strength at the sample position. Therefore, the resonator Q value has to be optimized for a given microwave input power and specific application. We designed a three-loop/two-gap resonator using CST Microwave Studio for such applications, and tested its performance in comparison with a standard Bruker D2 Q-band microwave resonator by accomplishing broadband SIFTER experiments on a nitroxide model compound.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0930-9
Issue No: Vol. 48, No. 11-12 (2017)

• High-Pressure EPR Spectroscopy Studies of the E. coli Lipopolysaccharide
Transport Proteins LptA and LptC
• Authors: Kathryn M. Schultz; Candice S. Klug
Pages: 1341 - 1353
Abstract: The use of pressure is an advantageous approach to the study of protein structure and dynamics, because it can shift the equilibrium populations of protein conformations toward higher energy states that are not of sufficient population to be observable at atmospheric pressure. Recently, the Hubbell group at the University of California, Los Angeles, reintroduced the application of high pressure to the study of proteins by electron paramagnetic resonance (EPR) spectroscopy. This methodology is possible using X-band EPR spectroscopy due to advances in pressure intensifiers, sample cells, and resonators. In addition to the commercial availability of the pressure generation and sample cells by Pressure Biosciences Inc., a five-loop–four-gap resonator required for the initial high-pressure EPR spectroscopy experiments by the Hubbell group, and those reported here, was designed by James S. Hyde and built and modified at the National Biomedical EPR Center. With these technological advances, we determined the effect of pressure on the essential periplasmic lipopolysaccharide (LPS) transport protein from Escherichia coli, LptA, and one of its binding partners, LptC. LptA unfolds from the N-terminus to the C-terminus, binding of LPS does not appreciably stabilize the protein under pressure, and monomeric LptA unfolds somewhat more readily than oligomeric LptA upon pressurization to 2 kbar. LptC exhibits a fold and relative lack of stability upon LPS binding similar to LptA, yet adopts an altered, likely monomeric, folded conformation under pressure with only its C-terminus unraveling. The pressure-induced changes likely correlate with functional changes associated with binding and transport of LPS.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0948-z
Issue No: Vol. 48, No. 11-12 (2017)

• Saturation Recovery EPR Spin-Labeling Method for Quantification of Lipids
in Biological Membrane Domains
• Authors: Laxman Mainali; Theodore G. Camenisch; James S. Hyde; Witold K. Subczynski
Pages: 1355 - 1373
Abstract: The presence of integral membrane proteins induces the formation of distinct domains in the lipid bilayer portion of biological membranes. Qualitative application of both continuous wave (CW) and saturation recovery (SR) electron paramagnetic resonance (EPR) spin-labeling methods allowed discrimination of the bulk, boundary, and trapped lipid domains. A recently developed method, which is based on the CW EPR spectra of phospholipid (PL) and cholesterol (Chol) analog spin labels, allows evaluation of the relative amount of PLs (% of total PLs) in the boundary plus trapped lipid domain and the relative amount of Chol (% of total Chol) in the trapped lipid domain (Raguz et al. Exp Eye Res 140:179–186, 24). Here, a new method is presented that, based on SR EPR spin-labeling, allows quantitative evaluation of the relative amounts of PLs and Chol in the trapped lipid domain of intact membranes. This new method complements the existing one, allowing acquisition of more detailed information about the distribution of lipids between domains in intact membranes. The methodological transition of the SR EPR spin-labeling approach from qualitative to quantitative is demonstrated. The abilities of this method are illustrated for intact cortical and nuclear fiber cell plasma membranes from porcine eye lenses. Statistical analysis (Student’s t test) of the data allowed determination of the separations of mean values above which differences can be treated as statistically significant (P ≤ 0.05) and can be attributed to sources other than preparation/technique.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0921-x
Issue No: Vol. 48, No. 11-12 (2017)

• ELDOR-detected NMR at Q-Band
• Authors: Thilo Hetzke; Alice M. Bowen; Thomas F. Prisner
Pages: 1375 - 1397
Abstract: In recent years, electron–electron double resonance detected nuclear magnetic resonance (EDNMR) has gained considerable attention as a pulsed electron paramagnetic resonance technique to probe hyperfine interactions. Most experiments published so far were performed at W-band frequencies or higher, as at lower frequencies detection of weakly coupled low-γ nuclei is hampered by the presence of a central blind spot, which occurs at zero frequency. In this article we show that EDNMR measurements and a meaningful data analysis is indeed possible at intermediate microwave frequencies (Q-band, 34 GHz), once experimental parameters have been optimized. With highly selective detection pulses and Gaussian shaped electron–electron double resonance (ELDOR) pulses it is possible to detect low-γ nuclei coupled to paramagnetic Mn2+. Weakly coupled 14N resonances, which are separated from the zero frequency by only 2.8 MHz, were readily detected. In systems where different spin active nuclei are coupled to the electron spin, particular care has to be taken when using higher powered ELDOR pulses, as combination frequencies from the two nuclei (∆m S = ±1, ∆m I,1 = ±1, ∆m I,2 = ±1) can lead to severe line broadening and complicated EDNMR spectra. We also compare the EDNMR spectra of 13C-labeled Mn–DOTA to 13C-Mims electron–nuclear double resonance to get a better insight into the similarities and differences in the results of the two techniques for 13C hyperfine coupling.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0927-4
Issue No: Vol. 48, No. 11-12 (2017)

• ODMR Spectroscopy of NV − Centers in Diamond Under High MW Power
• Authors: I. V. Zhukov; S. V. Anishchik; Yu. N. Molin
Pages: 1461 - 1469
Abstract: We have studied negatively charged nitrogen vacancy centers (NV $$^-$$ centers) in diamond using the technique of optically detected magnetic resonance (ODMR). Due to the use of the MW power amplifier we have easily observed in the ODMR spectrum all the lines known to date, including the lines of the excited state of the NV $$^-$$ centers. The g values and the hyperfine interaction constants of the ground and the excited triplet states of the NV $$^-$$ center are given. Hamiltonian parameters of the ground and the excited triplet states of the NV $$^-$$ center at ambient temperature have been confirmed and refined. In addition, an evidence of a slight g value asymmetry of the excited state of the NV $$^-$$ center has been obtained.
PubDate: 2017-12-01
DOI: 10.1007/s00723-017-0933-6
Issue No: Vol. 48, No. 11-12 (2017)

• Pulse EPR Study of Gas Adsorption in Cu 2+ -Doped Metal–Organic
Framework [Zn 2 (1,4-bdc) 2 (dabco)]
• Authors: A. S. Poryvaev; A. M. Sheveleva; P. A. Demakov; S. S. Arzumanov; A. G. Stepanov; D. N. Dybtsev; M. V. Fedin
Abstract: Gas separation and storage are the hot topics for addressing current challenges in energy and environmental science, including the air pollution problems and alternative fuels, and metal–organic frameworks (MOFs) have a great potential in these fields. Herewith, we present the electron paramagnetic resonance (EPR) study of the adsorption of several gases (hydrogen D2, methane 13CH4 and CD4, and carbon dioxide 13CO2) in Cu2+-doped MOF [Zn2(1,4-bdc)2(dabco)]. The obtained compound of composition [Zn1.993Cu0.007(1,4-bdc)2(dabco)] is suitable for studying adsorption geometries at Cu2+ ions and in their closest environments using pulse EPR. In attempt to characterize D2, 13CH4, CD4, and 13CO2 adsorption sites, we applied echo-detected EPR along with hyperfine sublevel correlation spectroscopy and pulse electron-nuclear double resonance spectroscopy. Altogether, these methods demonstrated the preferred location of gas molecules in the framework being at least 6 Å away from the copper ions. In addition, EPR spectroscopy allowed determination of the proton environment of copper and confirmed its incorporation into the MOF lattice, which is hard to establish using other techniques.
PubDate: 2017-11-16
DOI: 10.1007/s00723-017-0962-1

• Electron Spin Polarization of Photo-Excited Copper Coproporphyrin I: From
Monomers to Dimers
• Authors: A. A. Sukhanov; Yu. E. Kandrashkin; V. K. Voronkova; V. S. Tyurin
Abstract: The results of the electron paramagnetic resonance (EPR) and transient EPR (TREPR) of copper complexes of coproporphyrin I in different solvents before and after the laser pulse photo-excitation have been presented. Continuous-wave EPR spectra of the CuCPP-1 complex in o-terphenyl indicate the presence of only monomer fragments, while in the solution of the chloroform and isopropanol mixture, the complexes dimerize and the amount of dimers is five times larger than that of monomer complexes. Parameters describing EPR spectra of monomer and dimer CuCPP-1 complexes have been determined. It was established that the fine structure tensor of the dimer complex is rotated with respect to the g-tensor, which coincides with the tensor of monomer complexes. TREPR spectra of CuCPP-1 complexes in o-terphenyl and in the chloroform and isopropanol mixture after the laser photo-excitation are mainly due to spin-polarized ground states of monomer and dimer complexes, respectively. The TREPR spectra of the monomer CuCPP-1 show the emissive spin-polarized signal of the ground state. For dimer fragments, the net polarization is observed in the form of absorption and there is a small contribution from the multiplet polarization, which decays fast in time. The time dependence of TREPR of CuCPP-1 complexes in the chloroform and isopropanol mixture is described with allowance for these contributions from the ground state of the dimer and the contribution from the ground state of the monomer, which is manifested at larger times. Differences in the spin polarization of ground states and their possible origin are discussed.
PubDate: 2017-11-13
DOI: 10.1007/s00723-017-0961-2

• Autobiography of James S. Hyde
• Authors: James S. Hyde
Abstract: The papers, book chapters, reviews, and patents by James S. Hyde in the bibliography of this document have been separated into EPR and MRI sections and within each section by topics. Within each topic, publications are listed chronologically. A brief summary is provided for each patent listed. A few publications and patents that do not fit this schema have been omitted. This list of publications is preceded by a scientific autobiography that focuses on selected topics that are judged to have been of most scientific importance. References to many of the publications and patents in the bibliography are made in the autobiography.
PubDate: 2017-10-27
DOI: 10.1007/s00723-017-0950-5

• Jim Hyde and the ENDOR Connection: A Personal Account
• Authors: Klaus Möbius; Wolfgang Lubitz; Anton Savitsky
Abstract: In this minireview, we report on our year-long EPR work, such as electron–nuclear double resonance (ENDOR), pulse electron double resonance (PELDOR) and ELDOR-detected NMR (EDNMR) at X-band and W-band microwave frequencies and magnetic fields. This report is dedicated to James S. Hyde and honors his pioneering contributions to the measurement of spin interactions in large (bio)molecules. From these interactions, detailed information is revealed on structure and dynamics of macromolecules embedded in liquid-solution or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultra-fast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy and its multi-frequency extensions to new horizons concerning sensitivity of detection, selectivity of molecular interactions and time resolution. Among the most important advances is the upgrading of EPR to high magnetic fields, very much in analogy to what happened in NMR. The ongoing progress in EPR spectroscopy is exemplified by reviewing various multi-frequency electron–nuclear double-resonance experiments on organic radicals, light-generated donor–acceptor radical pairs in photosynthesis, and site-specifically nitroxide spin-labeled bacteriorhodopsin, the light-driven proton pump, as well as EDNMR and ENDOR on nitroxides. Signal and resolution enhancements are particularly spectacular for ENDOR, EDNMR and PELDOR on frozen-solution samples at high Zeeman fields. They provide orientation selection for disordered samples approaching single-crystal resolution at canonical g-tensor orientations—even for molecules with small g-anisotropies. Dramatic improvements of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Thus, unique structural and dynamic information is revealed that can hardly be obtained by other analytical techniques. Micromolar concentrations of sample molecules have become sufficient to characterize stable and transient reaction intermediates of complex molecular systems—offering exciting applications for physicists, chemists, biochemists and molecular biologists.
PubDate: 2017-10-23
DOI: 10.1007/s00723-017-0959-9

• The Current State of Measuring Bimolecular Spin Exchange Rates by the EPR
Spectral Manifestations of the Exchange and Dipole–Dipole Interactions
in Dilute Solutions of Nitroxide Free Radicals with Proton Hyperfine
Structure
• Authors: Barney L. Bales; M. M. Bakirov; R. T. Galeev; I. A. Kirilyuk; A. I. Kokorin; K. M. Salikhov
Abstract: Experimental studies of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (Tempol) in 60 wt% aqueous glycerol were carried out for temperatures from 273 to 340 K. Selective isotope substitution allowed comparisons between the experimental spectral manifestations of spin exchange and dipole–dipole interactions for protonated, deuterated, 15N, and 14N Tempol. Theoretical spectra were computed from a rigorous theory specifically formulated to include proton hyperfine interactions over a wide range of spin exchange and dipole–dipole interactions to compare with the experimental data. For spin exchange and dipole–dipole interactions small compared with the proton hyperfine coupling constant, spectra were calculated with perturbation theory to gain insight into the behavior of individual proton lines. The theoretical and experimental spectra were analyzed by least-squares fitting to Voigt shapes or by a new two-point method. For most accessible experimental designs, the comparisons are rather good; however, for an experiment constrained to low concentrations and high viscosities, the methods are less accurate.
PubDate: 2017-10-09
DOI: 10.1007/s00723-017-0958-x

• Analysis of Saturation Recovery Amplitudes to Characterize Conformational
Exchange in Spin-Labeled Proteins
• Authors: Michael D. Bridges; Zhongyu Yang; Christian Altenbach; Wayne L. Hubbell
Abstract: Analysis of saturation recovery data from spin-labeled proteins is extended to include the amplitudes in addition to the recovery rates for two-site exchange. It is shown that the recovery amplitudes depend strongly on the exchange rate between states as well as their populations and this dependence provides a simple criterion to identify exchange rates in the 10–1000 kHz range. Analysis of experimental SR relaxation curves via the uniform penalty (UPEN) method allows for reliable identification of single, double, or other multiple-component traces, and global fitting of a set of relaxation curves using both relaxation rates and amplitudes determined from the UPEN fits allows for the estimation of exchange rate in the above domain. The theory is tested on simple model systems, and applied to the determination of conformational exchange rates in spin-labeled mutants of T4 Lysozyme and intestinal fatty acid binding protein. Finally, an example of T 1-weighted spectral editing is provided for systems in the slow exchange limit.
PubDate: 2017-10-05
DOI: 10.1007/s00723-017-0936-3

• Uniform Field Re-entrant Cylindrical TE $$_{01\text {U}}$$ 01 U Cavity for
Pulse Electron Paramagnetic Resonance Spectroscopy at Q-band
• Authors: Jason W. Sidabras; Edward J. Reijerse; Wolfgang Lubitz
Abstract: Uniform field (UF) resonators create a region-of-interest, where the sample volume receives a homogeneous microwave magnetic field ( $$B_1$$ ) excitation. However, as the region-of-interest is increased, resonator efficiency is reduced. In this work, a new class of uniform field resonators is introduced: the uniform field re-entrant cylindrical TE $$_{\text {01U}}$$ cavity. Here, a UF cylindrical TE $$_{\text {01U}}$$ cavity is designed with re-entrant fins to increase the overall resonator efficiency to match the resonator efficiency maximum of a typical cylindrical TE $$_{011}$$ cavity. The new UF re-entrant cylindrical TE $$_{\text {01U}}$$ cavity is designed for Q-band (34 GHz) and is calculated to have the same electron paramagnetic resonance (EPR) signal intensity as a TE $$_{011}$$ cavity, a 60% increase in average resonator efficiency $$\Lambda _\mathrm{ave}$$ over the sample, and has a $$B_1$$ profile that is 79.8% uniform over the entire sample volume (98% uniform over the region-of-interest). A new H-type T-junction waveguide coupler with inductive obstacles is introduced that increases the dynamic range of a movable short coupler while reducing the frequency shift by 43% during over-coupling. The resonator assembly is fabricated and tested both on the bench and with EPR experiments. This resonator provides a template to improve EPR spectroscopy for pulse experiments at high frequencies.
PubDate: 2017-09-30
DOI: 10.1007/s00723-017-0955-0

• High-Bandwidth Q-Band EPR Resonators
• Authors: Rene Tschaggelar; Frauke D. Breitgoff; Oliver Oberhänsli; Mian Qi; Adelheid Godt; Gunnar Jeschke
Abstract: The emerging technology of ultra-wide-band spectrometers in electron paramagnetic resonance—enabled by recent technological advances—provides the means for new experimental schemes, a broader range of samples, and huge gains in measurement time. Broadband detection does, however, require that the resonator provides sufficient bandwidth and, despite resonator compensation schemes, excitation bandwidth is ultimately limited by resonator bandwidth. Here, we present the design of three resonators for Q-band frequencies (33–36 GHz) with a larger bandwidth than what was reported so far. The new resonators are of a loop-gap type with 4–6 loops and were designed for 1.6 mm sample tubes to achieve higher field homogeneity than in existing resonators for 3 mm samples, a feature that is beneficial for precise spin control. The loop-gap design provides good separation of the B 1 and E field, enabling robust modes with powder samples as well as with frozen water samples as the resonant behavior is largely independent of the dielectric properties of the samples. Experiments confirm the trends in bandwidth and field strength and the increased B 1 field homogeneity predicted by the simulations. Variation of the position of the coupling rod allows the adjustment of the quality factor Q and thus the bandwidth over a broad range. The increased bandwidth of the loop-gap resonators was exploited in double electron–electron resonance measurements of a Cu(II)-PyMTA ruler to yield significantly higher modulation depth and thus higher sensitivity.
PubDate: 2017-09-23
DOI: 10.1007/s00723-017-0956-z

• Resonators for In Vivo Imaging: Practical Experience
• Authors: George A. Rinard; Richard W. Quine; Laura A. Buchanan; Sandra S. Eaton; Gareth R. Eaton; Boris Epel; Subramanian V. Sundramoorthy; Howard J. Halpern
Abstract: Resonators for preclinical electron paramagnetic resonance imaging have been designed primarily for rodents and rabbits and have internal diameters between 16 and 51 mm. Lumped-circuit resonators include loop-gap, Alderman–Grant, and saddle coil topologies and surface coils. Bimodal resonators are useful for isolating the detected signal from incident power and reducing dead time in pulse experiments. Resonators for continuous wave, rapid scan, and pulse experiments are described. Experience at the University of Chicago and University of Denver in design of resonators for in vivo imaging is summarized.
PubDate: 2017-09-22
DOI: 10.1007/s00723-017-0947-0

• Unseen Coherences Can Be Felt
• Authors: Alexander G. Maryasov; Michael K. Bowman
Abstract: Forbidden transitions are not observed in the continuous-wave electron paramagnetic resonance (EPR) spectrum nor in the free induction decay because, unlike allowed transitions, their coherences have no observable magnetic moment and are spectroscopically silent. Yet, the paramagnetic relaxation described by Redfield theory can cause coherence transfer between any types of transitions. Coherence transfer between allowed transitions is now known to cause noticeable changes in EPR spectra, but coherence transfer involving forbidden transitions has long been considered to be negligible because those coherences are silent and unseen. However, our simulations of a simple model system indicate that coherence transfer with silent transitions can introduce new features into EPR spectra. The EPR-silent coherence of a forbidden transition can be transferred to an allowed transition by paramagnetic relaxation. A silent coherence can have consequences felt in the EPR spectrum.
PubDate: 2017-09-21
DOI: 10.1007/s00723-017-0949-y

JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327

Home (Search)
Subjects A-Z
Publishers A-Z
Customise
APIs