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Sample records for advanced electron paramagnetic

  1. Advanced Paramagnetic Resonance Spectroscopies of Iron-Sulfur Proteins: Electron Nuclear Double Resonance (ENDOR) and Electron Spin Echo Envelope Modulation (ESEEM)

    PubMed Central

    Cutsail, George E.; Telser, Joshua; Hoffman, Brian M.

    2015-01-01

    The advanced electron paramagnetic resonance (EPR) techniques, electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopies, provide unique insights into the structure, coordination chemistry, and biochemical mechanism of Nature’s widely distributed iron-sulfur cluster (FeS) proteins. This review describes the ENDOR and ESEEM techniques and then provides a series of case studies on their application to a wide variety of FeS proteins including ferredoxins, nitrogenase, and radical SAM enzymes. PMID:25686535

  2. Advanced paramagnetic resonance spectroscopies of iron-sulfur proteins: Electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM).

    PubMed

    Cutsail, George E; Telser, Joshua; Hoffman, Brian M

    2015-06-01

    The advanced electron paramagnetic resonance (EPR) techniques, electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopies, provide unique insights into the structure, coordination chemistry, and biochemical mechanism of nature's widely distributed iron-sulfur cluster (FeS) proteins. This review describes the ENDOR and ESEEM techniques and then provides a series of case studies on their application to a wide variety of FeS proteins including ferredoxins, nitrogenase, and radical SAM enzymes. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.

  3. Electron Paramagnetic Resonance Retrospective Dosimetry

    SciTech Connect

    Romanyukha, Alex; Trompier, Francois

    2011-05-05

    Necessity for, principles of, and general concepts of the electron paramagnetic resonance (EPR) retrospective dosimetry are presented. Also presented and given in details are examples of EPR retrospective dosimetry applications in tooth enamel, bone, and fingernails with focus on general approaches for solving technical and methodological problems. Advantages, drawbacks, and possible future developments are discussed and an extensive bibliography on EPR retrospective dosimetry is provided.

  4. Demonstrations on Paramagnetism with an Electronic Balance.

    ERIC Educational Resources Information Center

    Cortel, Adolf

    1998-01-01

    A paramagnetic substance is attracted by a magnetic field with a force proportional to its magnetic susceptibility which is related to the number of unpaired electrons in the atoms. Data are used to establish oxidation states and bonding properties. Describes a simple setup to demonstrate the paramagnetism of common inorganic compounds. (DKM)

  5. Multifrequency pulsed electron paramagnetic resonance on metalloproteins.

    PubMed

    Lyubenova, Sevdalina; Maly, Thorsten; Zwicker, Klaus; Brandt, Ulrich; Ludwig, Bernd; Prisner, Thomas

    2010-02-16

    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

  6. Electron Paramagnetic Resonance Study of Pr

    SciTech Connect

    Tezuka, Keitaro; Hinatsu, Yukio

    2001-01-01

    Electron paramagnetic resonance (EPR) spectra of tetravalent praseodymium ions doped in the cubic perovskite compound BaHfO{sub 3} have been measured at 4.2 K. A very large hyperfine interaction with the {sup 141}Pr nucleus was observed in the spectrum of Pr{sup 4+}/ BaHfO{sub 3}. The results were analyzed based on the weak field approximation, and the g value (|g|=0.619) and a hyperfine coupling constant (A=0.0589 cm{sup {minus}1}) were obtained. The measured g value is much smaller than |-10/7|, which indicates that the crystal field effect on the behavior of a 4f electron is large. These g and A values were compared with the EPR results for other f{sup 1} ions in an octahedral crystal field.

  7. Electron paramagnetic resonance at dislocations in germanium

    SciTech Connect

    Pakulis, E.J.

    1982-06-01

    The first observation of the paramagnetic resonance of electrons at dislocations in germanium single crystals is reported. Under subband gap optical excitation, two sets of lines are detected: four lines about the <111> axes with g/sub perpendicular to/ = 0.34 and g/sub parallel/ = 1.94, and 24 lines with g/sub perpendicular to/ = 0.73 and g/sub parallel/ = 1.89 about <111> axes with the six-fold 1.2/sup 0/ distortion. This represents the first measurement of the disortion angle of a dislocation dangling bond. The possibility that the distortion results from a Peierls transition along the dislocation line is discussed.

  8. Electron paramagnetic resonance of several lunar rock samples

    NASA Technical Reports Server (NTRS)

    Marov, P. N.; Dubrov, Y. N.; Yermakov, A. N.

    1974-01-01

    The results are presented of investigating lunar rock samples returned by the Luna 16 automatic station, using electron paramagnetic resonance (EPR). The EPR technique makes it possible to detect paramagnetic centers and investigate their nature, with high sensitivity. Regolith (finely dispersed material) and five particles from it, 0.3 mm in size, consisting mostly of olivine, were investigated with EPR.

  9. Study of metalloproteins using continuous wave electron paramagnetic resonance (EPR).

    PubMed

    Gambarelli, Serge; Maurel, Vincent

    2014-01-01

    Electron paramagnetic resonance (EPR) is an invaluable tool when studying systems with paramagnetic centers. It is a sensitive spectroscopic method, which can be used with dilute samples in aqueous buffer solutions. Here, we describe the basic procedure for recording an X-band EPR spectrum of a metalloprotein sample at low temperature. We also discuss basic optimization techniques to provide spectra with a high signal to noise ratio and minimum distortion.

  10. Manganese binding properties of human calprotectin under conditions of high and low calcium: X-ray crystallographic and advanced electron paramagnetic resonance spectroscopic analysis.

    PubMed

    Gagnon, Derek M; Brophy, Megan Brunjes; Bowman, Sarah E J; Stich, Troy A; Drennan, Catherine L; Britt, R David; Nolan, Elizabeth M

    2015-03-01

    The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is the only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at a biologically unprecedented hexahistidine site that forms at the S100A8/S100A9 interface, and the molecular basis for this phenomenon requires elucidation. Herein, we investigate the remarkable Mn(II) coordination chemistry of human CP using X-ray crystallography as well as continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies. An X-ray crystallographic structure of Mn(II)-CP containing one Mn(II), two Ca(II), and two Na(I) ions per CP heterodimer is reported. The CW EPR spectrum of Ca(II)- and Mn(II)-bound CP prepared with a 10:0.9:1 Ca(II):Mn(II):CP ratio is characterized by an unusually low zero-field splitting of 485 MHz (E/D = 0.30) for the S = 5/2 Mn(II) ion, consistent with the high symmetry of the His6 binding site observed crystallographically. Results from electron spin-echo envelope modulation and electron-nuclear double resonance experiments reveal that the six Mn(II)-coordinating histidine residues of Ca(II)- and Mn(II)-bound CP are spectroscopically equivalent. The observed (15)N (I = 1/2) hyperfine couplings (A) arise from two distinct classes of nitrogen atoms: the coordinating ε-nitrogen of the imidazole ring of each histidine ligand (A = [3.45, 3.71, 5.91] MHz) and the distal δ-nitrogen (A = [0.11, 0.18, 0.42] MHz). In the absence of Ca(II), the binding affinity of CP for Mn(II) drops by two to three orders of magnitude and coincides with Mn(II) binding at the His6 site as well as other sites. This study demonstrates the role of Ca(II) in enabling high-affinity and specific binding of Mn(II) to the His6 site of human calprotectin. PMID:25597447

  11. In-situ electron paramagnetic resonance studies of paramagnetic point defects in superconducting microwave resonators

    NASA Astrophysics Data System (ADS)

    Zhang, Shengke; Kopas, Cameron; Wagner, Brian; Queen, Daniel; Newman, N.

    2016-09-01

    The physical nature and concentration of paramagnetic point defects in the dielectrics of superconducting planar microwave resonators have been determined using in-situ electron paramagnetic resonance spectroscopy. To perform this work, the quality factor of parallel plate and stripline resonators was measured as a function of the magnitude of a magnetic-field applied parallel to the electrode surfaces. YBa2Cu3O7-δ thin film electrodes proved to be a preferred choice over Nb and MgB2 because they are readily available and have a small surface resistance (Rs) up to high temperatures (˜77 K) and magnetic fields (i.e., <1 T). Stripline resonators with a widely used high performance microwave dielectric, Co2+-doped Ba(Zn1/3Nb2/3)O3, are shown to have losses dominated by d-electron spin-excitations in exchange-coupled Co2+ point-defect clusters, even in the absence of an applied magnetic field. A significant enhanced microwave loss in stripline and parallel plate resonators is found to correlate with the presence of paramagnetic Mn2+ dopants in Ba(Zn1/3Ta2/3)O3 ceramics and dangling bond states in amorphous Si thin films, although the identification of the dominant loss mechanism(s) in these dielectrics requires further investigation.

  12. Introduction to Spin Label Electron Paramagnetic Resonance Spectroscopy of Proteins

    ERIC Educational Resources Information Center

    Melanson, Michelle; Sood, Abha; Torok, Fanni; Torok, Marianna

    2013-01-01

    An undergraduate laboratory exercise is described to demonstrate the biochemical applications of electron paramagnetic resonance (EPR) spectroscopy. The beta93 cysteine residue of hemoglobin is labeled by the covalent binding of 3-maleimido-proxyl (5-MSL) and 2,2,5,5-tetramethyl-1-oxyl-3-methyl methanethiosulfonate (MTSL), respectively. The excess…

  13. Free-electron laser-based pulsed electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Takahashi, Susumu; Sherwin, Mark S.; Ramian, Gerald; Brunel, Louis-Claude; van Tol, Johan

    2008-03-01

    High-power pulsed electron paramagnetic resonance (EPR) is extremely useful to study the ultrafast dynamics of spins. At present, most high-power pulsed EPR spectrometers operate near the X-band frequency of 9.5 GHz with kW-level power. A trend in the evolution of next generation pulsed EPR is for higher magnetic field and frequency, both for finer spectral and time resolution and because motional averaging becomes negligible. Since the linewidth of resonances studied by pulsed EPR tends to be extremely narrow, the source radiation also has to be stable and have narrow bandwidth. High-power pulsed EPR, using few-ns pulses to rapidly manipulate spins for spin-echo and related experiments, has been demonstrated at 95 GHz using kW- power Klystron-based sources. A bottleneck for higher frequency pulsed EPR spectroscopy is a lack of sources with high power and narrow bandwidth. The University of California Santa Barbara (UCSB) free-electron lasers (FEL) are potential sources for high-power pulsed EPR because they generate kW of power tunable from 120 GHz to 4.7 THz. We present the current status of the UCSB FEL-based 240 GHz pulsed EPR spectrometer.

  14. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite

    NASA Astrophysics Data System (ADS)

    Reddy, S. Lakshmi; Fayazuddin, Md.; Frost, Ray L.; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals.

  15. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite.

    PubMed

    Reddy, S Lakshmi; Fayazuddin, Md; Frost, Ray L; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals. PMID:17324611

  16. ELECTRON PARAMAGNETIC RESONANCE DOSIMETRY FOR A LARGE-SCALE RADIATION INCIDENT

    PubMed Central

    Swartz, Harold M.; Flood, Ann Barry; Williams, Benjamin B.; Dong, Ruhong; Swarts, Steven G.; He, Xiaoming; Grinberg, Oleg; Sidabras, Jason; Demidenko, Eugene; Gui, Jiang; Gladstone, David J.; Jarvis, Lesley A.; Kmiec, Maciej M.; Kobayashi, Kyo; Lesniewski, Piotr N.; Marsh, Stephen D.P.; Matthews, Thomas P.; Nicolalde, Roberto J.; Pennington, Patrick M.; Raynolds, Timothy; Salikhov, Ildar; Wilcox, Dean E.; Zaki, Bassem I.

    2013-01-01

    With possibilities for radiation terrorism and intensified concerns about nuclear accidents since the recent Fukushima Daiichi event, the potential exposure of large numbers of individuals to radiation that could lead to acute clinical effects has become a major concern. For the medical community to cope with such an event and avoid overwhelming the medical care system, it is essential to identify not only individuals who have received clinically significant exposures and need medical intervention but also those who do not need treatment. The ability of electron paramagnetic resonance to measure radiation-induced paramagnetic species, which persist in certain tissues (e.g., teeth, fingernails, toenails, bone, and hair), has led this technique to become a prominent method for screening significantly exposed individuals. Although the technical requirements needed to develop this method for effective application in a radiation event are daunting, remarkable progress has been made. In collaboration with General Electric, and through funding committed by the Biomedical Advanced Research and Development Authority, electron paramagnetic resonance tooth dosimetry of the upper incisors is being developed to become a Food and Drug Administration-approved and manufacturable device designed to carry out triage for a threshold dose of 2 Gy. Significant progress has also been made in the development of electron paramagnetic resonance nail dosimetry based on measurements of nails in situ under point-of-care conditions, and in the near future this may become a second field-ready technique. Based on recent progress in measurements of nail clippings, we anticipate that this technique may be implementable at remotely located laboratories to provide additional information when the measurements of dose on site need to be supplemented. We conclude that electron paramagnetic resonance dosimetry is likely to be a useful part of triage for a large-scale radiation incident. PMID:22850230

  17. General magnetic transition dipole moments for electron paramagnetic resonance.

    PubMed

    Nehrkorn, Joscha; Schnegg, Alexander; Holldack, Karsten; Stoll, Stefan

    2015-01-01

    We present general expressions for the magnetic transition rates in electron paramagnetic resonance (EPR) experiments of anisotropic spin systems in the solid state. The expressions apply to general spin centers and arbitrary excitation geometry (Voigt, Faraday, and intermediate). They work for linear and circular polarized as well as unpolarized excitation, and for crystals and powders. The expressions are based on the concept of the (complex) magnetic transition dipole moment vector. Using the new theory, we determine the parities of ground and excited spin states of high-spin (S=5/2) Fe(III) in hemin from the polarization dependence of experimental EPR line intensities.

  18. Electron Paramagnetic Resonance -- Nuclear Magnetic Resonance Three Axis Vector Magnetometer

    NASA Astrophysics Data System (ADS)

    Bulatowicz, Michael; Clark, Philip; Griffith, Robert; Larsen, Michael; Mirijanian, James

    2012-06-01

    The Northrop Grumman Corporation is leveraging the technology developed for the Nuclear Magnetic Resonance Gyroscope (NMRG) to build a combined Electron Paramagnetic Resonance -- Nuclear Magnetic Resonance (EPR-NMR) magnetometer. The EPR-NMR approach provides a high bandwidth and high sensitivity simultaneous measurement of all three vector components of the magnetic field averaged over the small volume of the sensor's one vapor cell. This poster will describe the history, operational principles, and design basics of the EPR-NMR magnetometer including an overview of the NSD designs developed and demonstrated to date. General performance results will also be presented.

  19. Electron paramagnetic resonance of nitroxide-doped magnetic fluids

    NASA Astrophysics Data System (ADS)

    Morais, P. C.; Alonso, A.; Silva, O.; Buske, N.

    2002-11-01

    Electron paramagnetic resonance was used to investigate surface-coated magnetite-based magnetic fluids doped with TEMPOL. Two magnetic fluid samples, having magnetite nanoparticles with average diameter of 94 Å and coated with different coating layers (lauric acid plus ethoxylated polyalcohol in one case and oleoylsarcosine in the other case), were doped with TEMPOL (6 mM and pH 7.4) and investigated as a function of the nanoparticle concentration. The resonance field and the resonance linewidth both scale linearly with the nanoparticle concentration.

  20. Electron paramagnetic resonance study of paramagnetic centers in carbon-fumed silica adsorbent

    SciTech Connect

    Savchenko, D. V.; Shanina, B. D.; Kalabukhova, E. N.; Sitnikov, A. A.; Lysenko, V. S.; Tertykh, V. A.

    2014-04-07

    Fumed silica A-300 was carbonized by means of pyrolysis of CH{sub 2}Cl{sub 2}. The obtained initial SiO{sub 2}:C nanopowders of black color, with an average diameter of 14–16 nm and carbon (C) concentration 7 wt. %, subjected to the oxidation and passivation treatment were studied by electron paramagnetic resonance (EPR) in the temperature range 4–400 K. Two EPR signals of Lorentzian lineshape with nearly equal g-factors and different linewidth were observed in the initial, oxidized, and passivated SiO{sub 2}:C nanopowders. The two-component EPR spectrum was explained by the presence of C in two electronic states. The intensive narrow EPR signal, which has a temperature-dependent intensity, linewidth, and resonance field position, was attributed to the carbon-related defect with non-localized electron hopping between neighboring C-dangling bonds. The striking effect is that the temperature dependence of the EPR linewidth demonstrates the motional narrowing of the EPR signal at very low temperatures from 4 K to 20 K, which is not typically for nonmetallic materials and was explained by the quantum character of C layer conductivity in the SiO{sub 2}:C. The observed peaks in the temperature dependence of the conduction electron EPR signal integral intensity in the high-temperature range 200–440 K was explained by the presence of the C nanodots at the surface of SiO{sub 2} nanoparticles and the ejection of electrons from the confinement energy levels of C quantum dot when the temperature becomes comparable to the confinement energy.

  1. Electron paramagnetic resonance of individual atoms on a surface.

    PubMed

    Baumann, Susanne; Paul, William; Choi, Taeyoung; Lutz, Christopher P; Ardavan, Arzhang; Heinrich, Andreas J

    2015-10-23

    We combined the high-energy resolution of conventional spin resonance (here ~10 nano-electron volts) with scanning tunneling microscopy to measure electron paramagnetic resonance of individual iron (Fe) atoms placed on a magnesium oxide film. We drove the spin resonance with an oscillating electric field (20 to 30 gigahertz) between tip and sample. The readout of the Fe atom's quantum state was performed by spin-polarized detection of the atomic-scale tunneling magnetoresistance. We determine an energy relaxation time of T1 ≈ 100 microseconds and a phase-coherence time of T2 ≈ 210 nanoseconds. The spin resonance signals of different Fe atoms differ by much more than their resonance linewidth; in a traditional ensemble measurement, this difference would appear as inhomogeneous broadening.

  2. Electron paramagnetic resonance in Cu-doped ZnO

    NASA Astrophysics Data System (ADS)

    Buchheit, R.; Acosta-Humánez, F.; Almanza, O.

    2016-04-01

    In this work, ZnO and Cu-doped ZnO nanoparticles (Zn1-xCuxO, x = 3%), with a calcination temperature of 500∘C were synthesized using the sol-gel method. The particles were analyzed using atomic absorption spectroscopy (AAS), X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) at X-band, measurement in a temperature range from 90 K to room temperature. AAS confirmed a good correspondence between the experimental doping concentration and the theoretical value. XRD reveals the presence of ZnO phase in hexagonal wurtzite structure and a nanoparticle size for the samples synthesized. EPR spectroscopy shows the presence of point defects in both samples with g-values of g = 1.959 for shallow donors and g = 2.004 for ionized vacancies. It is important when these materials are required have been used as catalysts, as suggested that it is not necessary prepare them at higher temperature. A simulation of the Cu EPR signal using an anisotropic spin Hamiltonian was performed and showed good coincidence with the experimental spectra. It was shown that Cu2+ ions enter interstitial octahedral sites of orthorhombic symmetry in the wurtzite crystal structure. Temperature dependence of the EPR linewidth and signal intensity shows a paramagnetic behavior of the sample in the measurement range. A Néel temperature TN = 78 ± 19 K was determined.

  3. Magnetic nanoparticle imaging using multiple electron paramagnetic resonance activation sequences

    SciTech Connect

    Coene, A. Dupré, L.; Crevecoeur, G.

    2015-05-07

    Magnetic nanoparticles play an important role in several biomedical applications such as hyperthermia, drug targeting, and disease detection. To realize an effective working of these applications, the spatial distribution of the particles needs to be accurately known, in a non-invasive way. Electron Paramagnetic Resonance (EPR) is a promising and sensitive measurement technique for recovering these distributions. In the conventional approach, EPR is applied with a homogeneous magnetic field. In this paper, we employ different heterogeneous magnetic fields that allow to stabilize the solution of the associated inverse problem and to obtain localized spatial information. A comparison is made between the two approaches and our novel adaptation shows an average increase in reconstruction quality by 5% and is 12 times more robust towards noise. Furthermore, our approach allows to speed up the EPR measurements while still obtaining reconstructions with an improved accuracy and noise robustness compared to homogeneous EPR.

  4. Novel multisample dielectric resonators for electron paramagnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Golovina, Iryna S.; Kolesnik, Sergiy P.; Geifman, Ilia N.; Belous, Anatoliy G.

    2010-04-01

    We have developed and tested two types of novel dielectric resonators for simultaneous recording of electron paramagnetic resonance (EPR) spectra from two to four samples. The resonator of the first type contains two holes, and the other resonator contains four holes for introduction of the samples. Also, the resonator structure includes a pair of gradient coils. Dielectric resonators made of materials with high dielectric constant with low losses can be inserted into the standard EPR cavity or waveguide in the maximum microwave magnetic field. Gradient coils are located outside the cavity (or waveguide) so that their axes are parallel to the static magnetic field. Computer simulations were made to obtain microwave characteristics of the resonators such as resonant frequency, sizes, and distribution of the fields. Spacing of the point samples and optimum value of the magnetic-field gradient have been chosen correctly. The designed resonators can be applied in express analysis using EPR technique, for instance.

  5. Electron Paramagnetic Resonance in II-Vi Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Yang, Gui-Lin

    This dissertation is devoted to investigation of the electron paramagnetic resonance (EPR) of Mn ^{++} ions in II-VI semiconductor heterostructures, in order to determine how EPR is affected by this layered environment and what new information can be extracted by this technique. We first introduce the concept of the effective spin, and we review the theoretical background of the spin Hamiltonian, for describing the ground state of a paramagnetic ion in a solid. The physical origin of the constituent terms in the spin Hamiltonion are discussed, and their characteristics described, for use at later stages in the thesis. We then analyze the effect on EPR of the potential exchange interaction between the localized d-electrons of the Mn^{++} ions and the band electrons. We predict that such exchange interaction can lead to significant changes in the g-factors of Mn ^{++} ions due to the spin polarization of band electrons, resulting in line shifts of EPR spectra. Although such shifts would be too small to be observed for Mn^{++} ions introduced into bulk semiconductors, we show that the shifts can be significantly larger for Mn^ {++} ions in quantum wells, superlattices, and similar heterostructures, due to the electron confinement effect. This effect of the potential exchange interaction on the EPR spectra of Mn^{++} ions leads us to propose to use the Mn ^{++} ions as built-in localized probes for mapping the wave functions of electronic states in II-VI semiconductor quantum wells and superlattices. We then consider the influence of internal strain on the EPR transitions of Mn^{++} in II-VI semiconductor heterostructures. Our analysis of the changes of the Mn^{++} fine structure indicates that EPR can be used to detect even minute amounts of strain (e.g., strain resulting from as little as 0.01% lattice mismatch can readily be measured). Accordingly, we demonstrate EPR to be an ultrasensitive and probably unique tool for small strain measurements in II

  6. 76 FR 67200 - Prospective Grant of Exclusive License: Electron Paramagnetic Resonance Devices and Systems for...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-31

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF HEALTH AND HUMAN SERVICES National Institutes of Health Prospective Grant of Exclusive License: Electron... of use limited to electron paramagnetic resonance devices and systems for oximetry. DATES:...

  7. Single Acquisition Quantitative Single Point Electron Paramagnetic Resonance Imaging

    PubMed Central

    Jang, Hyungseok; Subramanian, Sankaran; Devasahayam, Nallathamby; Saito, Keita; Matsumoto, Shingo; Krishna, Murali C; McMillan, Alan B

    2013-01-01

    Purpose Electron paramagnetic resonance imaging (EPRI) has emerged as a promising non-invasive technology to dynamically image tissue oxygenation. Due to its extremely short spin-spin relaxation times, EPRI benefits from a single-point imaging (SPI) scheme where the entire FID signal is captured using pure phase encoding. However, direct T2*/pO2 quantification is inhibited due to constant magnitude gradients which result in time-decreasing FOV. Therefore, conventional acquisition techniques require repeated imaging experiments with differing gradient amplitudes (typically 3), which results in long acquisition time. Methods In this study, gridding was evaluated as a method to reconstruct images with equal FOV to enable direct T2*/pO2 quantification within a single imaging experiment. Additionally, an enhanced reconstruction technique that shares high spatial k-space regions throughout different phase encoding time delays was investigated (k-space extrapolation). Results The combined application of gridding and k-space extrapolation enables pixelwise quantification of T2* from a single acquisition with improved image quality across a wide range of phase encoding delay times. The calculated T2*/pO2 does not vary across this time range. Conclusion By utilizing gridding and k-space extrapolation, accurate T2*/pO2 quantification can be achieved within a single dataset to allow enhanced temporal resolution (by a factor of 3). PMID:23913515

  8. Reconstruction of images from radiofrequency electron paramagnetic resonance spectra.

    PubMed

    Smith, C M; Stevens, A D

    1994-12-01

    This paper discusses methods for obtaining image reconstructions from electron paramagnetic resonance (EPR) spectra which constitute object projections. An automatic baselining technique is described which treats each spectrum consistently; rotating the non-horizontal baselines which are caused by stray magnetic effects onto the horizontal axis. The convolved backprojection method is described for both two- and three-dimensional reconstruction and the effect of cut-off frequency on the reconstruction is illustrated. A slower, indirect, iterative method, which does a non-linear fit to the projection data, is shown to give a far smoother reconstructed image when the method of maximum entropy is used to determine the value of the final residual sum of squares. Although this requires more computing time than the convolved backprojection method, it is more flexible and overcomes the problem of numerical instability encountered in deconvolution. Images from phantom samples in vitro are discussed. The spectral data for these have been accumulated quickly and have a low signal-to-noise ratio. The results show that as few as 16 spectra can still be processed to give an image. Artifacts in the image due to a small number of projections using the convolved backprojection reconstruction method can be removed by applying a threshold, i.e. only plotting contours higher than a given value. These artifacts are not present in an image which has been reconstructed by the maximum entropy technique. At present these techniques are being applied directly to in vivo studies.

  9. Maximally spaced projection sequencing in electron paramagnetic resonance imaging

    PubMed Central

    Redler, Gage; Epel, Boris; Halpern, Howard J.

    2015-01-01

    Electron paramagnetic resonance imaging (EPRI) provides 3D images of absolute oxygen concentration (pO2) in vivo with excellent spatial and pO2 resolution. When investigating such physiologic parameters in living animals, the situation is inherently dynamic. Improvements in temporal resolution and experimental versatility are necessary to properly study such a system. Uniformly distributed projections result in efficient use of data for image reconstruction. This has dictated current methods such as equal-solid-angle (ESA) spacing of projections. However, acquisition sequencing must still be optimized to achieve uniformity throughout imaging. An object-independent method for uniform acquisition of projections, using the ESA uniform distribution for the final set of projections, is presented. Each successive projection maximizes the distance in the gradient space between itself and prior projections. This maximally spaced projection sequencing (MSPS) method improves image quality for intermediate images reconstructed from incomplete projection sets, enabling useful real-time reconstruction. This method also provides improved experimental versatility, reduced artifacts, and the ability to adjust temporal resolution post factum to best fit the data and its application. The MSPS method in EPRI provides the improvements necessary to more appropriately study a dynamic system. PMID:26185490

  10. Identification of irradiated cashew nut by electron paramagnetic resonance spectroscopy.

    PubMed

    Sanyal, Bhaskar; Sajilata, M G; Chatterjee, Suchandra; Singhal, Rekha S; Variyar, Prasad S; Kamat, M Y; Sharma, Arun

    2008-10-01

    Cashew nut samples were irradiated at gamma-radiation doses of 0.25, 0.5, 0.75, and 1 kGy, the permissible dose range for insect disinfestation of food commodities. A weak and short-lived triplet (g = 2.004 and hfcc = 30 G) along with an anisotropic signal (g perpendicular = 2.0069 and g parallel = 2.000) were produced immediately after irradiation. These signals were assigned to that of cellulose and CO 2 (-) radicals. However, the irradiated samples showed a dose-dependent increase of the central line (g = 2.0045 +/- 0.0002). The nature of the free radicals formed during conventional processing such as thermal treatment was investigated and showed an increase in intensity of the central line (g = 2.0045) similar to that of irradiation. Characteristics of the free radicals were studied by their relaxation and thermal behaviors. The present work explores the possibility to identify irradiated cashew nuts from nonirradiated ones by the thermal behaviors of the radicals beyond the period, when the characteristic electron paramagnetic resonance spectral lines of the cellulose free radicals have essentially disappeared. In addition, this study for the first time reports that relaxation behavior of the radicals could be a useful tool to distinguish between roasted and irradiated cashew nuts.

  11. Effects of water on fingernail electron paramagnetic resonance dosimetry

    PubMed Central

    Zhang, Tengda; Zhao, Zhixin; Zhang, Haiying; Zhai, Hezheng; Ruan, Shuzhou; Jiao, Ling; Zhang, Wenyi

    2016-01-01

    Electron paramagnetic resonance (EPR) is a promising biodosimetric method, and fingernails are sensitive biomaterials to ionizing radiation. Therefore, kinetic energy released per unit mass (kerma) can be estimated by measuring the level of free radicals within fingernails, using EPR. However, to date this dosimetry has been deficient and insufficiently accurate. In the sampling processes and measurements, water plays a significant role. This paper discusses many effects of water on fingernail EPR dosimetry, including disturbance to EPR measurements and two different effects on the production of free radicals. Water that is unable to contact free radicals can promote the production of free radicals due to indirect ionizing effects. Therefore, varying water content within fingernails can lead to varying growth rates in the free radical concentration after irradiation—these two variables have a linear relationship, with a slope of 1.8143. Thus, EPR dosimetry needs to be adjusted according to the water content of the fingernails of an individual. When the free radicals are exposed to water, the eliminating effect will appear. Therefore, soaking fingernail pieces in water before irradiation, as many researchers have previously done, can cause estimation errors. In addition, nails need to be dehydrated before making accurately quantitative EPR measurements. PMID:27342838

  12. A new electron paramagnetic resonance method to identify irradiated soybean.

    PubMed

    Sanyal, Bhaskar; Sharma, Arun

    2009-10-01

    Low-dose gamma irradiation causes minimal changes in food matrix making identification of radiation-processed foods a challenging task. In the present study, soybean samples were irradiated with commercially permitted gamma radiation dose in the 0.25 to 1.0 kGy range for insect disinfestations of food. Immediately after irradiation electron paramagnetic resonance (EPR) spectrum of the skin part of soybean showed a triplet signal (g = 2.0046, hyperfine coupling constant hfcc = 3.0 mT) superimposed on naturally present singlet. These signals were characterized as cellulose and phenoxyl radicals using EPR spectrum simulation technique. Kernel part of the samples exhibited a short-lived, radiation-induced singlet of carbon-centered radical superimposed on naturally present sextet signal of Mn2+. A detailed study on relaxation and thermal behavior of induced radicals in skin part was carried out using EPR spectroscopy. These findings revealed that progressive saturation and thermal characteristics of the induced radicals may be the most suitable parameters to distinguish soybean subjected to radiation dose as low as 0.25 kGy from thermally treated and nonirradiated samples, even after a prolonged period of storage.

  13. The continuous wave electron paramagnetic resonance experiment revisited

    NASA Astrophysics Data System (ADS)

    Kälin, Moritz; Gromov, Igor; Schweiger, Arthur

    2003-02-01

    When the modulation frequency used in continuous wave electron paramagnetic resonance (cw EPR) spectroscopy exceeds the linewidth, modulation sidebands appear in the spectrum. It is shown theoretically and experimentally that these sidebands are actually multiple photon transitions, σ ++ k×π, where one microwave (mw) σ + photon is absorbed from the mw radiation field and an arbitrary number k of radio frequency (rf) π photons are absorbed from or emitted to the modulation rf field. Furthermore, it is demonstrated that both the derivative shape of the lines in standard cw EPR spectra and the distortions due to overmodulation are caused by the unresolved sideband pattern of these lines. The single-photon transition does not even give a contribution to the first-harmonic cw EPR signal. Multiple photon transitions are described semiclassically in a toggling frame and their existence is proven using second quantization. With the toggling frame approach and perturbation theory an effective Hamiltonian for an arbitrary sideband transition is derived. Based on the effective Hamiltonians an expression for the steady-state density operator in the singly rotating frame is derived, completely describing all sidebands in all modulation frequency harmonics of the cw EPR signal. The relative intensities of the sidebands are found to depend in a very sensitive way on the actual rf amplitude and the saturation of single sidebands is shown to depend strongly on the effective field amplitude of the multiple photon transitions. By comparison with the analogous solutions for frequency-modulation EPR it is shown that the field-modulation and the frequency-modulation technique are not equivalent. The experimental data fully verify the theoretical predictions with respect to intensities and lineshapes.

  14. Dating carbonaceous matter in archean cherts by electron paramagnetic resonance.

    PubMed

    Bourbin, M; Gourier, D; Derenne, S; Binet, L; Le Du, Y; Westall, F; Kremer, B; Gautret, P

    2013-02-01

    Ancient geological materials are likely to be contaminated through geological times. Thus, establishing the syngeneity of the organic matter embedded in a mineral matrix is a crucial step in the study of very ancient rocks. This is particularly the case for Archean siliceous sedimentary rocks (cherts), which record the earliest traces of life. We used electron paramagnetic resonance (EPR) for assessing the syngeneity of organic matter in cherts that have a metamorphic grade no higher than greenschist. A correlation between the age of Precambrian samples and the shape of their EPR signal was established and statistically tested. As thermal treatments impact organic matter maturity, the effect of temperature on this syngeneity proxy was studied; cyanobacteria were submitted to cumulative short thermal treatment at high temperatures followed by an analysis of their EPR parameters. The resulting carbonaceous matter showed an evolution similar to that of a thermally treated young chert. Furthermore, the possible effect of metamorphism, which is a longer thermal event at lower temperatures, was ruled out for cherts older than 2 Gyr, based on the study of Silurian cherts of the same age and same precursors but various metamorphic grades. We determined that even the most metamorphosed sample did not exhibit the lineshape of an Archean sample. In the hope of detecting organic contamination in Archean cherts, a "contamination-like" mixture was prepared and studied by EPR. It resulted that the lineshape analysis alone does not allow contamination detection and that it must be performed along with cumulative thermal treatments. Such treatments were applied to three Archean chert samples, making dating of their carbonaceous matter possible. We concluded that EPR is a powerful tool to study primitive organic matter and could be used in further exobiology studies on low-metamorphic grade samples (from Mars for example).

  15. Dating Carbonaceous Matter in Archean Cherts by Electron Paramagnetic Resonance

    PubMed Central

    Bourbin, M.; Derenne, S.; Binet, L.; Le Du, Y.; Westall, F.; Kremer, B.; Gautret, P.

    2013-01-01

    Abstract Ancient geological materials are likely to be contaminated through geological times. Thus, establishing the syngeneity of the organic matter embedded in a mineral matrix is a crucial step in the study of very ancient rocks. This is particularly the case for Archean siliceous sedimentary rocks (cherts), which record the earliest traces of life. We used electron paramagnetic resonance (EPR) for assessing the syngeneity of organic matter in cherts that have a metamorphic grade no higher than greenschist. A correlation between the age of Precambrian samples and the shape of their EPR signal was established and statistically tested. As thermal treatments impact organic matter maturity, the effect of temperature on this syngeneity proxy was studied; cyanobacteria were submitted to cumulative short thermal treatment at high temperatures followed by an analysis of their EPR parameters. The resulting carbonaceous matter showed an evolution similar to that of a thermally treated young chert. Furthermore, the possible effect of metamorphism, which is a longer thermal event at lower temperatures, was ruled out for cherts older than 2 Gyr, based on the study of Silurian cherts of the same age and same precursors but various metamorphic grades. We determined that even the most metamorphosed sample did not exhibit the lineshape of an Archean sample. In the hope of detecting organic contamination in Archean cherts, a “contamination-like” mixture was prepared and studied by EPR. It resulted that the lineshape analysis alone does not allow contamination detection and that it must be performed along with cumulative thermal treatments. Such treatments were applied to three Archean chert samples, making dating of their carbonaceous matter possible. We concluded that EPR is a powerful tool to study primitive organic matter and could be used in further exobiology studies on low-metamorphic grade samples (from Mars for example). Key Words: Kerogen—Sedimentary rocks

  16. Electron paramagnetic resonance dosimetry: Methodology and material characterization

    NASA Astrophysics Data System (ADS)

    Hayes, Robert Bruce

    Electron Paramagnetic Resonance (EPR) methodologies for radiation dose reconstruction are investigated using various dosimeter materials. Specifically, methodologies were developed and used that were intended to improve the accuracy and precision of EPR dosimetric techniques, including combining specimen rotation during measurement, use of an internal manganese standard, instrument stabilization techniques and strict measurement protocols. Characterization and quantification of these improvements were preformed on three specific EPR dosimeter materials. The dosimeter materials investigated using these optimized EPR techniques were Walrus teeth, human tooth enamel and alanine dosimeters. Walrus teeth showed the least desirable properties for EPR dosimetry yielding large native signals and low sensitivity (EPR signal per unit dose). The methods for tooth enamel and alanine resulted in large improvements in precision and accuracy. The minimum detectable dose (MDD) found for alanine was approximately 30 mGy (three standard deviations from the measured zero dose value). This is a sensitivity improvement of 5 to 10 over other specialized techniques published in the literature that offer MDD's in the range of 150 mGy to 300 mGy. The accuracy of the method on tooth enamel was comparable to that typically reported in the literature although the measurement precision was increased by about 7. This improvement in measurement precision enables various applications including dose vs. depth profile analysis and a more nondestructive testing evaluation (where the whole sample need not be additively irradiated in order to calibrate its radiation response). A nondestructive evaluation of numerous samples showed that the method could reconstruct the same doses to within 10 mGy of those evaluated destructively. Doses used for this assessment were in the range of 100 to 250 mGy. The method had sufficient stability to measure tooth enamel samples exhibiting extreme anisotropy with a

  17. Dating carbonaceous matter in archean cherts by electron paramagnetic resonance.

    PubMed

    Bourbin, M; Gourier, D; Derenne, S; Binet, L; Le Du, Y; Westall, F; Kremer, B; Gautret, P

    2013-02-01

    Ancient geological materials are likely to be contaminated through geological times. Thus, establishing the syngeneity of the organic matter embedded in a mineral matrix is a crucial step in the study of very ancient rocks. This is particularly the case for Archean siliceous sedimentary rocks (cherts), which record the earliest traces of life. We used electron paramagnetic resonance (EPR) for assessing the syngeneity of organic matter in cherts that have a metamorphic grade no higher than greenschist. A correlation between the age of Precambrian samples and the shape of their EPR signal was established and statistically tested. As thermal treatments impact organic matter maturity, the effect of temperature on this syngeneity proxy was studied; cyanobacteria were submitted to cumulative short thermal treatment at high temperatures followed by an analysis of their EPR parameters. The resulting carbonaceous matter showed an evolution similar to that of a thermally treated young chert. Furthermore, the possible effect of metamorphism, which is a longer thermal event at lower temperatures, was ruled out for cherts older than 2 Gyr, based on the study of Silurian cherts of the same age and same precursors but various metamorphic grades. We determined that even the most metamorphosed sample did not exhibit the lineshape of an Archean sample. In the hope of detecting organic contamination in Archean cherts, a "contamination-like" mixture was prepared and studied by EPR. It resulted that the lineshape analysis alone does not allow contamination detection and that it must be performed along with cumulative thermal treatments. Such treatments were applied to three Archean chert samples, making dating of their carbonaceous matter possible. We concluded that EPR is a powerful tool to study primitive organic matter and could be used in further exobiology studies on low-metamorphic grade samples (from Mars for example). PMID:23397956

  18. Using Electron Paramagnetic Resonance Spectroscopy To Facilitate Problem Solving in Pharmaceutical Research and Development.

    PubMed

    Mangion, Ian; Liu, Yizhou; Reibarkh, Mikhail; Williamson, R Thomas; Welch, Christopher J

    2016-08-19

    As new chemical methodologies driven by single-electron chemistry emerge, process and analytical chemists must develop approaches to rapidly solve problems in this nontraditional arena. Electron paramagnetic resonance spectroscopy has been long known as a preferred technique for the study of paramagnetic species. However, it is only recently finding application in contemporary pharmaceutical development, both to study reactions and to track the presence of undesired impurities. Several case studies are presented here to illustrate its utility in modern pharmaceutical development efforts.

  19. Electron paramagnetic resonance study of two smectic A liquid crystals.

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Gelerinter, E.; Fishel, D. L.

    1972-01-01

    Study of the molecular ordering in two smectic A liquid crystals using vanadyl acetylacetonate as a paramagnetic probe. The average hyperfine splitting of the spectrum in the smectic A mesophase is measured as a function of the orientation relative to the dc magnetic field of the spectrometer after alignment of the molecules of the liquid crystal.

  20. Towards Human Oxygen Images with Electron Paramagnetic Resonance Imaging.

    PubMed

    Epel, Boris; Redler, Gage; Tormyshev, Victor; Halpern, Howard J

    2016-01-01

    Electron paramagnetic resonance imaging (EPRI) has been used to noninvasively provide 3D images of absolute oxygen concentration (pO2) in small animals. These oxygen images are well resolved both spatially (~1 mm) and in pO2 (1-3 mmHg). EPRI preclinical images of pO2 have demonstrated extremely promising results for various applications investigating oxygen related physiologic and biologic processes as well as the dependence of various disease states on pO2, such as the role of hypoxia in cancer. Recent developments have been made that help to progress EPRI towards the eventual goal of human application. For example, a bimodal crossed-wire surface coil has been developed. Very preliminary tests demonstrated a 20 dB isolation between transmit and receive for this coil, with an anticipated additional 20 dB achievable. This could potentially be used to image local pO2 in human subjects with superficial tumors with EPRI. Local excitation and detection will reduce the specific absorption rate limitations on images and eliminate any possible power deposition concerns. Additionally, a large 9 mT EPRI magnet has been constructed which can fit and provide static main and gradient fields for imaging local anatomy in an entire human. One potential obstacle that must be overcome in order to use EPRI to image humans is the approved use of the requisite EPRI spin probe imaging agent (trityl). While nontoxic, EPRI trityl spin probes have been injected intravenously when imaging small animals, and require relatively high total body injection doses that would not be suitable for human imaging applications. Work has been done demonstrating the alternative use of intratumoral (IT) injections, which can reduce the amount of trityl required for imaging by a factor of 2000- relative to a whole body intravenous injection. The development of a large magnet that can accommodate human subjects, the design of a surface coil for imaging of superficial pO2, and the reduction of required spin

  1. Towards Human Oxygen Images with Electron Paramagnetic Resonance Imaging

    PubMed Central

    Epel, Boris; Redler, Gage; Tormyshev, Victor; Halpern, Howard J.

    2016-01-01

    Electron paramagnetic resonance imaging (EPRI) has been used to noninvasively provide 3D images of absolute oxygen concentration (pO2) in small animals. These oxygen images are well resolved both spatially (∼1mm) and in pO2 (1-3 torr). EPRI preclinical images of pO2 have demonstrated extremely promising results for various applications investigating oxygen related physiologic and biologic processes as well as the dependence of various disease states on pO2, such as the role of hypoxia in cancer. Recent developments have been made that help to progress EPRI towards the eventual goal of human application. For example, a bimodal crossed-wire surface coil has been developed. Very preliminary tests demonstrated a 20 dB isolation between transmit and receive for this coil, with an anticipated additional 20dB achievable. This could potentially be used to image local pO2 in human subjects with superficial tumors with EPRI. Local excitation and detection will reduce the specific absorption rate limitations on images and eliminate any possible power deposition concerns. Additionally, a large 9 mT EPRI magnet has been constructed which can fit and provide static main and gradient fields for imaging local anatomy in an entire human. One potential obstacle that must be overcome in order to use EPRI to image humans is the approved use of the requisite EPRI spin probe imaging agent (trityl). While nontoxic, EPRI trityl spin probes have been injected intravenously when imaging small animals, which results in relatively high total body injection doses that would not be suitable for human imaging applications. Work has been done demonstrating the alternative use of intratumoral (IT) injections, which can reduce the amount of trityl required for imaging by a factor of 2000- relative to a whole body intravenous injection. The development of a large magnet that can accommodate human subjects, the design of a surface coil for imaging of superficial pO2, and the reduction of required

  2. Electron paramagnetic resonance in human fingernails: the sponge model implication.

    PubMed

    Reyes, R A; Romanyukha, A; Trompier, F; Mitchell, C A; Clairand, I; De, T; Benevides, L A; Swartz, H M

    2008-11-01

    The most significant problem of electron paramagnetic resonance (EPR) fingernail dosimetry is the presence of two signals of non-radiation origin that overlap the radiation-induced signal (RIS), making it almost impossible to perform dose measurements below 5 Gy. Historically, these two non-radiation components were named mechanically induced signal (MIS) and background signal (BKS). In order to investigate them in detail, three different methods of MIS and BKS mutual isolation have been developed and implemented. After applying these methods, it is shown here that fingernail tissue, after cut, can be modeled as a deformed sponge, where the MIS and BKS are associated with the stress from elastic and plastic deformations, respectively. A sponge has a unique mechanism of mechanical stress absorption, which is necessary for fingernails in order to perform its everyday function of protecting the fingertips from hits and trauma. Like a sponge, fingernails are also known to be an effective water absorber. When a sponge is saturated with water, it tends to restore to its original shape, and when it loses water, it becomes deformed again. The same happens to fingernail tissue. It is proposed that the MIS and BKS signals of mechanical origin be named MIS1 and MIS2 for MISs 1 and 2, respectively. Our suggested interpretation of the mechanical deformation in fingernails gives also a way to distinguish between the MIS and RIS. The results obtained show that the MIS in irradiated fingernails can be almost completely eliminated without a significant change to the RIS by soaking the sample for 10 min in water. The proposed method to measure porosity (the fraction of void space in spongy material) of the fingernails gave values of 0.46-0.48 for three of the studied samples. Existing results of fingernail dosimetry have been obtained on mechanically stressed samples and are not related to the "real" in vivo dosimetric properties of fingernails. A preliminary study of these

  3. Site directed spin labelling and pulsed dipolar electron paramagnetic resonance (double electron electron resonance) of force activation in muscle

    NASA Astrophysics Data System (ADS)

    Fajer, Piotr G.

    2005-05-01

    The recent development of site specific spin labelling and advances in pulsed electron paramagnetic resonance (EPR) have established spin labelling as a viable structural biology technique. Specific protein sites or whole domains can be selectively targeted for spin labelling by cysteine mutagenesis. The secondary structure of the proteins is determined from the trends in EPR signals of labels attached to consecutive residues. Solvent accessibility or label mobility display periodicities along the labelled polypeptide chain that are characteristic of β-strands (periodicity of 2 residues) or α-helices (3.6 residues). Low-resolution 3D structure of proteins is determined from the distance restraints. Two spin labels placed within 60-70 Å of each other create a local dipolar field experienced by the other spin labels. The strength of this field is related to the interspin distance, {\\propto } r^{-3 } . The dipolar field can be measured by the broadening of the EPR lines for the short distances (8-20 Å) or for the longer distances (17-70 Å) by the pulsed EPR methods, double electron-electron resonance (DEER) and double quantum coherence (DQC). A brief review of the methodology and its applications to the multisubunit muscle protein troponin is presented below.

  4. Stationary and high-frequency pulsed electron paramagnetic resonance of a calcified atherosclerotic plaque

    NASA Astrophysics Data System (ADS)

    Abdul'Yanov, V. A.; Galiullina, L. F.; Galyavich, A. S.; Izotov, V. G.; Mamin, G. V.; Orlinskii, S. B.; Rodionov, A. A.; Salakhov, M. Kh.; Silkin, N. I.; Sitdikova, L. M.; Khairullin, R. N.; Chelyshev, Yu. A.

    2008-09-01

    New possibilities of applying high-frequency electron paramagnetic resonance in medicine are demonstrated on an example of the investigation of a calcified atherosclerotic plaque. After the irradiation of the atherosclerotic plaque by x rays, a new type of paramagnetic centers—organomineral radicals—is detected. The spectral and relaxation characteristics of these radicals depend on the calcification degree of the atherosclerotic plaque and can be used for diagnostics.

  5. Cut and paste RNA for nuclear magnetic resonance, paramagnetic resonance enhancement, and electron paramagnetic resonance structural studies.

    PubMed

    Duss, Olivier; Diarra Dit Konté, Nana; Allain, Frédéric H-T

    2015-01-01

    RNA is a crucial regulator involved in most molecular processes of life. Understanding its function at the molecular level requires high-resolution structural information. However, the dynamic nature of RNA complicates structure determination because crystallization is often not possible or can result in crystal-packing artifacts resulting in nonnative structures. To study RNA and its complexes in solution, we described an approach in which large multi-domain RNA or protein-RNA complex structures can be determined at high resolution from isolated domains determined by nuclear magnetic resonance (NMR) spectroscopy, and then constructing the entire macromolecular structure using electron paramagnetic resonance (EPR) long-range distance constraints. Every step in this structure determination approach requires different types of isotope or spin-labeled RNAs. Here, we present a simple modular RNA cut and paste approach including protocols to generate (1) small isotopically labeled RNAs (<10 nucleotides) for NMR structural studies, which cannot be obtained by standard protocols, (2) large segmentally isotope and/or spin-labeled RNAs for diamagnetic NMR and paramagnetic relaxation enhancement NMR, and (3) large spin-labeled RNAs for pulse EPR spectroscopy.

  6. Enhanced dynamic electron paramagnetic resonance imaging of in vivo physiology

    NASA Astrophysics Data System (ADS)

    Redler, Gage

    It is well established that low oxygen concentration (hypoxia) in tumors strongly affects their malignant state and resistance to therapy. The importance of tumor oxygenation status has led to increased interest in the development of robust oxygen imaging modalities. One such method is electron paramagnetic resonance imaging (EPRI). EPRI has provided a non-invasive, quantitative imaging modality with sensitivity deep in tissues, capable of investigating static oxygen concentration (pO2) in vivo and has helped to corroborate the correlation between chronic states of hypoxia and tumor malignancy. However, when studying the complicated physiology of a living animal, the situation tends to be inherently dynamic. It has been found that in certain tumor regions there may exist steady states of hypoxia, or chronic hypoxia, whereas in other regions there may exist transient states of hypoxia, or acute hypoxia. It has been postulated that the negative prognostic implications associated with hypoxic tumors may be amplified for acutely hypoxic tumors. However, controversial data and a current lack in methods with the capability to noninvasively image tumor pO2 in vivo with sufficient spatial, temporal, and pO 2 resolution preclude definitive conclusions on the relationships between the different forms of hypoxia and the differences in their clinical implications. A particularly promising oxygen imaging modality that can help to study both chronic and acute hypoxia and elucidate important physiological and clinical differences is rapid Dynamic EPRI. The focus of this work is the development of methods enabling Dynamic EPRI of in vivo physiology as well as its potential applications. This work describes methods which enhance various aspects of EPRI in order to establish a more robust Dynamic EPRI capable of noninvasively studying and quantifying acute hypoxia in vivo. These enhancements are achieved through improvements that span from methods for the acquisition of individual

  7. Pulsed electron paramagnetic resonance experiments identify the paramagnetic intermediates in the pyruvate ferredoxin oxidoreductase catalytic cycle.

    PubMed

    Astashkin, Andrei V; Seravalli, Javier; Mansoorabadi, Steven O; Reed, George H; Ragsdale, Stephen W

    2006-03-29

    Pyruvate ferredoxin oxidoreductase (PFOR) is central to the anaerobic metabolism of many bacteria and amitochondriate eukaryotes. PFOR contains thiamine pyrophosphate (TPP) and three [4Fe-4S] clusters, which link pyruvate oxidation to reduction of ferredoxin. In the PFOR reaction, TPP reacts with pyruvate to form lactyl-TPP, which undergoes decarboxylation to form a hydroxyethyl-TPP (HE-TPP) intermediate. One electron is then transferred from HE-TPP to one of the three [4Fe-4S] clusters to form an HE-TPP radical and a [4Fe-4S]1+ intermediate. Pulsed EPR methods have been used to measure the distance between the HE-TPP radical and the [4Fe-4S]1+ cluster to which it is coupled. Computational analysis including the PFOR crystal structure and the spin distribution in the HE-TPP radical and in the reduced [4Fe-4S] cluster demonstrates that the distance between the HE-TPP radical and the medial cluster B matches the experimentally determined dipolar interaction, while one of the other two clusters is too close and the other is too far away. These results clearly demonstrate that it is the medial cluster (cluster B) that is reduced. Thus, rapid electron transfer occurs through the electron-transfer chain, which leaves an oxidized proximal cluster poised to accept an electron from the HE-TPP radical in the subsequent reaction step. PMID:16551078

  8. The Effect of Electronic Paramagnetism on Nuclear Magnetic Resonance Frequencies in Metals

    DOE R&D Accomplishments Database

    Townes, C. H.; Herring, C.; Knight, W. D.

    1950-09-22

    Observations on the shifts of nuclear resonances in metals ( Li{sup 7}, Na{sup 23}, Cu {sup 63}, Be{sup 9}, Pb{sup 207}, Al{sup 27}, and Ca{sup 69} ) due to free electron paramagnetism; comparison with theoretical values.

  9. [Electron paramagnetic resonance study of blood of anemic patients with urological cancer].

    PubMed

    Ibragimova, M I; Chushnikov, V N; Moiseev, V N; Petukhov, V Iu; Zheglov, E P; Cherepnev, G V

    2013-01-01

    Changes in Fe(3+)-transferrin (Fe(3+)-Tf) and Cu(2+)-ceruloplasmin (Cu(2+)-Cp) concentrations in venous blood sampled from anemic patients with urinary bladder and kidney cancer in I-IV stages were investigated using electron paramagnetic resonance spectroscopy. It was established that at malignancy-associated anemia the paramagnetic Fe3+ ion concentration in transferrin is below a norm, while in anemic non-oncology patients the Tf iron saturation is normal. Moreover, in patients with malignancy-associated anemia the Cu(2+)-Cp average value is nearly twice as large as that for healthy volunteers (confidence probability P). It was shown that simultaneous EPR measuring of paramagnetic centers (such as Fe(3+)-Tf and Cu(2+)-Cp) in blood of anemic patients can be used as a biomarker for urological cancer diagnosis even at early stages of the growth of a malignant tumor.

  10. Three-dimensional electron paramagnetic resonance imaging technique for mapping porosity in ceramics

    SciTech Connect

    Kordas, G.; Kang, Y.H. )

    1991-04-01

    This paper reports on a three-dimensional (3D) electron paramagnetic resonance imaging (EPRI) method which was developed to probe the structure and size of pores in ceramic materials. The imaging device that was added to the EPR instrument consisted of a computer-controlled current source and magnetic field gradient. This add-on facility was tested using a well-defined diphenlpicrylhydrazzyl phantom sample. Pumice was then used to demonstrate the potential of the technique. This stone was immersed in a 0.5 mm {sup 15}N-substituted per-deutereted tempone water solution to fill the pores with spin labels. Images were reconstructed using a filtered back-projection technique. A two-dimensional (2D) imaging plane was constructed by collecting 33 projection planes over 180 {degrees}. A 3D image was derived from 22 planes each constructed by 22 projections. At present, the facility allows a resolution of 69 and 46 {mu}m for 2D and 3D imaging, respectively. Advancements of the imaging apparatus, software, and line width of the spin labels will be needed to enhance the resolution of this technique.

  11. Electron Paramagnetic Resonance of Single Magnetic Moment on a Surface

    PubMed Central

    Berggren, P.; Fransson, J.

    2016-01-01

    We address electron spin resonance of single magnetic moments in a tunnel junction using time-dependent electric fields and spin-polarized current. We show that the tunneling current directly depends on the local magnetic moment and that the frequency of the external electric field mixes with the characteristic Larmor frequency of the local spin. The importance of the spin-polarized current induced anisotropy fields acting on the local spin moment is, moreover, demonstrated. Our proposed model thus explains the absence of an electron spin resonance for a half integer spin, in contrast with the strong signal observed for an integer spin. PMID:27156935

  12. Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser.

    PubMed

    Takahashi, S; Brunel, L-C; Edwards, D T; van Tol, J; Ramian, G; Han, S; Sherwin, M S

    2012-09-20

    Electron paramagnetic resonance (EPR) spectroscopy interrogates unpaired electron spins in solids and liquids to reveal local structure and dynamics; for example, EPR has elucidated parts of the structure of protein complexes that other techniques in structural biology have not been able to reveal. EPR can also probe the interplay of light and electricity in organic solar cells and light-emitting diodes, and the origin of decoherence in condensed matter, which is of fundamental importance to the development of quantum information processors. Like nuclear magnetic resonance, EPR spectroscopy becomes more powerful at high magnetic fields and frequencies, and with excitation by coherent pulses rather than continuous waves. However, the difficulty of generating sequences of powerful pulses at frequencies above 100 gigahertz has, until now, confined high-power pulsed EPR to magnetic fields of 3.5 teslas and below. Here we demonstrate that one-kilowatt pulses from a free-electron laser can power a pulsed EPR spectrometer at 240 gigahertz (8.5 teslas), providing transformative enhancements over the alternative, a state-of-the-art ∼30-milliwatt solid-state source. Our spectrometer can rotate spin-1/2 electrons through π/2 in only 6 nanoseconds (compared to 300 nanoseconds with the solid-state source). Fourier-transform EPR on nitrogen impurities in diamond demonstrates excitation and detection of EPR lines separated by about 200 megahertz. We measured decoherence times as short as 63 nanoseconds, in a frozen solution of nitroxide free-radicals at temperatures as high as 190 kelvin. Both free-electron lasers and the quasi-optical technology developed for the spectrometer are scalable to frequencies well in excess of one terahertz, opening the way to high-power pulsed EPR spectroscopy up to the highest static magnetic fields currently available. PMID:22996555

  13. Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser.

    PubMed

    Takahashi, S; Brunel, L-C; Edwards, D T; van Tol, J; Ramian, G; Han, S; Sherwin, M S

    2012-09-20

    Electron paramagnetic resonance (EPR) spectroscopy interrogates unpaired electron spins in solids and liquids to reveal local structure and dynamics; for example, EPR has elucidated parts of the structure of protein complexes that other techniques in structural biology have not been able to reveal. EPR can also probe the interplay of light and electricity in organic solar cells and light-emitting diodes, and the origin of decoherence in condensed matter, which is of fundamental importance to the development of quantum information processors. Like nuclear magnetic resonance, EPR spectroscopy becomes more powerful at high magnetic fields and frequencies, and with excitation by coherent pulses rather than continuous waves. However, the difficulty of generating sequences of powerful pulses at frequencies above 100 gigahertz has, until now, confined high-power pulsed EPR to magnetic fields of 3.5 teslas and below. Here we demonstrate that one-kilowatt pulses from a free-electron laser can power a pulsed EPR spectrometer at 240 gigahertz (8.5 teslas), providing transformative enhancements over the alternative, a state-of-the-art ∼30-milliwatt solid-state source. Our spectrometer can rotate spin-1/2 electrons through π/2 in only 6 nanoseconds (compared to 300 nanoseconds with the solid-state source). Fourier-transform EPR on nitrogen impurities in diamond demonstrates excitation and detection of EPR lines separated by about 200 megahertz. We measured decoherence times as short as 63 nanoseconds, in a frozen solution of nitroxide free-radicals at temperatures as high as 190 kelvin. Both free-electron lasers and the quasi-optical technology developed for the spectrometer are scalable to frequencies well in excess of one terahertz, opening the way to high-power pulsed EPR spectroscopy up to the highest static magnetic fields currently available.

  14. Electron paramagnetic resonance of natural and gamma-irradiated alunite and kaolin mineral powders

    NASA Astrophysics Data System (ADS)

    Koksal, F.; Koseoglu, R.; Saka, I.; Basaran, E.; Sener, F.

    2004-06-01

    Natural alunite and kaolin minerals obtained from West Anatolia were investigated by electron paramagnetic resonance (EPR) in natural and gamma-irradiated states at room temperature and at 113 K. The paramagnetic centres at ambient temperature in natural alunite were attributed to the (C) over dot H 2OH, (C) over dot O-3(-), (S) over dot O-2(-), (C) over dot O-2(-) and [AlO4 ](0) radicals. In natural kaolin, the paramagnetic centres were attributed to the (C) over dot O-3(-), (S) over dot O-2(-) (C) over dot O-2(-) and [AlO4](0) radicals. The gamma-irradiation does not produce any detectable effects on these radicals. At 113 K, the lines for (C) over dot H2OH could not be observed well, probably due to the anisotropic behaviour of the hyperfine interaction of the methylene protons, but the lines for [AlO4](0) centres were found to be perfectly observable at above 20 mW microwave power in both alunite and kaolin powders before and after gamma-irradiation. The EPR parameters of the observed paramagnetic centres were reported.

  15. Optical and paramagnetic properties of synthetic diamond crystals irradiated with electrons and annealed

    SciTech Connect

    Poklonski, N. A. Gusakov, G. A.; Bayev, V. G. Lapchuk, N. M.

    2009-05-15

    The optical and paramagnetic properties of single crystals of synthetic diamond grown by the temperature-gradient method in high-pressure apparatuses with the systems of catalytic solvents (Co, Fe) and (Ni, Fe) are studied at room temperature. The optical absorption spectra (in the wavelength range {lambda} = 400-800 nm) and the spectra of electron spin resonance are registered for the initial diamond crystals, the crystals irradiated with 6 MeV electrons (the fluence 1.5 x 10{sup 18} cm{sup -2}), and the irradiated diamonds subjected to isochronous thermal annealing in vacuum (for 60 min). It is shown that, with such treatment, the diamond crystals synthesized with different metal catalysts (Co or Ni) exhibit similar optical properties, but different paramagnetic properties. The data obtained by infrared spectroscopy and electron spin resonance spectroscopy are coincident for radiation defects and different for nitrogen centers (the P1 centers and exchange-coupled pairs of nitrogen atoms). The spectra of the electron spin resonance of the samples annealed at temperatures below 1273 K (in the case of the Co-containing catalyst) and 1073 K (in the case of Ni-containing catalyst) exhibited broad lines produced by residual impurities of the catalyst metal and were accompanied by a distortion of the spectrum of paramagnetic nitrogen in the form of a tilt of the ESR spectra with respect to the zero line.

  16. Electron paramagnetic resonance and FT-IR spectroscopic studies of glycine anhydride and betaine hydrochloride

    NASA Astrophysics Data System (ADS)

    Halim Başkan, M.; Kartal, Zeki; Aydın, Murat

    2015-12-01

    Gamma irradiated powders of glycine anhydride and betaine hydrochloride have been investigated at room temperature by electron paramagnetic resonance (EPR). In these compounds, the observed paramagnetic species were attributed to the R1 and R2 radicals, respectively. It was determined that the free electron interacted with environmental protons and 14N nucleus in both radicals. The EPR spectra of gamma irradiated powder samples remained unchanged at room temperature for two weeks after irradiation. Also, the Fourier Transform Infrared (FT-IR), FT-Raman and thermal analyses of both compounds were investigated. The functional groups in the molecular structures of glycine anhydride and betaine hydrochloride were identified by vibrational spectroscopies (FT-IR and FT-Raman).

  17. Biodosimetry: chromosome aberration in lymphocytes and electron paramagnetic resonance in tooth enamel from atomic bomb survivors.

    PubMed

    Nakamura, N; Miyazawa, C; Akiyama, M; Sawada, S; Awa, A A

    1996-01-01

    One hundred enamel samples isolated from extracted teeth donated by atomic bomb survivors were subjected to free radical measurement by means of electron paramagnetic resonance (ESR). Results comparing ESR with the chromosome aberration frequency in lymphocytes of the tooth donors, and with the physically estimated DS86 dose suggested that ESR data correlated more closely with chromosome data than with the estimated DS86 doses, probably because DS86 may depend on erroneous memory in some cases.

  18. Cavity- and waveguide-resonators in electron paramagnetic resonance, nuclear magnetic resonance, and magnetic resonance imaging.

    PubMed

    Webb, Andrew

    2014-11-01

    Cavity resonators are widely used in electron paramagnetic resonance, very high field magnetic resonance microimaging and also in high field human imaging. The basic principles and designs of different forms of cavity resonators including rectangular, cylindrical, re-entrant, cavity magnetrons, toroidal cavities and dielectric resonators are reviewed. Applications in EPR and MRI are summarized, and finally the topic of traveling wave MRI using the magnet bore as a waveguide is discussed.

  19. Anomaly of the rotational nonergodicity parameter of glass formers probed by high field electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Bercu, V.; Martinelli, M.; Massa, C. A.; Pardi, L. A.; Rössler, E. A.; Leporini, D.

    2008-08-01

    Exploiting the high angular resolution of high field electron paramagnetic resonance measured at 95, 190, and 285 GHz we determine the rotational nonergodicity parameter of different probe molecules in the glass former o-terphenyl and polybutadiene in a model-independent way. Our results clearly show a characteristic change in the temperature of the nonergodicity parameter proving a rather sharp dynamic crossover in both systems, in contrast to previous results from other techniques.

  20. Electron Paramagnetic Resonance Resolves Effects of Oxidative Stress on Muscle Proteins

    PubMed Central

    Moen, Rebecca J.; Klein, Jennifer C.; Thomas, David D.

    2014-01-01

    We have used site-directed spin labeling and electron paramagnetic resonance (EPR) to explore the effects of oxidation on muscle function, with particular focus on the actin-myosin interaction. EPR measurements show that aging or oxidative modification cause a decrease in the fraction of myosins in the strong-binding state, which can be traced to the actin-binding cleft of the myosin catalytic domain. PMID:24188980

  1. Magnetic field dependence of spin-forbidden electronic excitations reflects the Haldane or paramagnetic ground state

    NASA Astrophysics Data System (ADS)

    Long, V. C.; Montague, J. R.; Kozen, A. C.; Wei, X.; Landry, B. R.; Pearson, K. R.; Turnbull, M. M.; Landee, C. P.

    2007-03-01

    We compare the zero-field and magnetic field-dependent optical spectra of the Haldane chain compound NENB (Ni[en]2NO2BF4; en = C2N2H8) and the paramagnetic compound, Ni(en) 3(ClO4)2,H2O. Due to similar electronic coordination of Ni^2+, the two materials show similar zero-field d-d electronic transitions, including a spin-forbidden (SF) transition at 1.58 eV, overlapping a broad spin-allowed band at 1.45 eV. The relatively greater intensity of the SF band in the Haldane compound suggests activation by a spin exchange mechanism, whereas a spin-orbit coupling origin is likely in the paramagnet. A second narrower SF spin flip transition appears in NENB at 1.66 eV. In both compounds, the SF excitations are sensitive to applied field H. In NENB, the SF intensity is suppressed by H, consistent with behavior of spin exchange-activated bands. In Ni(en)3(ClO4)-2,H2O, the SF field sensitivity appears to combine an energy shift and intensity decrease. Details of the H dependence reflect the magnetic ground state of the material: the field sensitivity commences only above HC 10 T, in the Haldane compound, whereas the field-induced modifications begin immediately at H = 0 T in the paramagnet.

  2. Electron paramagnetic resonance imaging for real-time monitoring of Li-ion batteries

    PubMed Central

    Sathiya, M.; Leriche, J.-B.; Salager, E.; Gourier, D.; Tarascon, J.-M.; Vezin, H.

    2015-01-01

    Batteries for electrical storage are central to any future alternative energy paradigm. The ability to probe the redox mechanisms occurring at electrodes during their operation is essential to improve battery performances. Here we present the first report on Electron Paramagnetic Resonance operando spectroscopy and in situ imaging of a Li-ion battery using Li2Ru0.75Sn0.25O3, a high-capacity (>270 mAh g−1) Li-rich layered oxide, as positive electrode. By monitoring operando the electron paramagnetic resonance signals of Ru5+ and paramagnetic oxygen species, we unambiguously prove the formation of reversible (O2)n− species that contribute to their high capacity. In addition, we visualize by imaging with micrometric resolution the plating/stripping of Li at the negative electrode and highlight the zones of nucleation and growth of Ru5+/oxygen species at the positive electrode. This efficient way to locate ‘electron’-related phenomena opens a new area in the field of battery characterization that should enable future breakthroughs in battery research. PMID:25662295

  3. Lithium phthalocyanine: a probe for electron paramagnetic resonance oximetry in viable biological systems.

    PubMed Central

    Liu, K J; Gast, P; Moussavi, M; Norby, S W; Vahidi, N; Walczak, T; Wu, M; Swartz, H M

    1993-01-01

    Lithium phthalocyanine (LiPc) is a prototype of another generation of synthetic, metallic-organic, paramagnetic crystallites that appear very useful for in vitro and in vivo electron paramagnetic resonance oximetry. The peak-to-peak line width of the electron paramagnetic resonance spectrum of LiPc is a linear function of the partial pressure of oxygen (pO2); this linear relation is independent of the medium surrounding the LiPc. It has an extremely exchange-narrowed spectrum (peak-to-peak line width = 14 mG in the absence of O2). Physicochemically LiPc is very stable; its response to pO2 does not change with conditions and environments (e.g., pH, temperature, redox conditions) likely to occur in viable biological systems. These characteristics provide the sensitivity, accuracy, and range to measure physiologically and pathologically pertinent O2 tensions (0.1-50 mmHg; 1 mmHg = 133 Pa). The application of LiPc in biological systems is demonstrated in measurements of pO2 in vivo in the heart, brain, and kidney of rats. PMID:8390665

  4. Electron paramagnetic resonance: a powerful tool to support magnetic resonance imaging research.

    PubMed

    Danhier, Pierre; Gallez, Bernard

    2015-01-01

    The purpose of this paper is to describe some of the areas where electron paramagnetic resonance (EPR) has provided unique information to MRI developments. The field of application mainly encompasses the EPR characterization of MRI paramagnetic contrast agents (gadolinium and manganese chelates, nitroxides) and superparamagnetic agents (iron oxide particles). The combined use of MRI and EPR has also been used to qualify or disqualify sources of contrast in MRI. Illustrative examples are presented with attempts to qualify oxygen sensitive contrast (i.e. T1 - and T2 *-based methods), redox status or melanin content in tissues. Other areas are likely to benefit from the combined EPR/MRI approach, namely cell tracking studies. Finally, the combination of EPR and MRI studies on the same models provides invaluable data regarding tissue oxygenation, hemodynamics and energetics. Our description will be illustrative rather than exhaustive to give to the readers a flavour of 'what EPR can do for MRI'.

  5. Temperature dependence of Q-band electron paramagnetic resonance spectra of nitrosyl heme proteins.

    PubMed Central

    Flores, M; Wajnberg, E; Bemski, G

    1997-01-01

    The Q-band (35 GHz) electron paramagnetic resonance (EPR) spectra of nitrosyl hemoglobin (HbNO) and nitrosyl myoglobin (MbNO) were studied as a function of temperature between 19 K and 200 K. The spectra of both heme proteins show two classes of variations as a function of temperature. The first one has previously been associated with the existence of two paramagnetic species, one with rhombic and the other with axial symmetry. The second one manifests itself in changes in the g-factors and linewidths of each species. These changes are correlated with the conformational substates model and associate the variations of g-values with changes in the angle of the N(his)-Fe-N(NO) bond in the rhombic species and with changes in the distance between Fe and N of the proximal (F8) histidine in the axial species. PMID:9414233

  6. Characterization of iron, manganese, and copper synthetic hydroxyapatites by electron paramagnetic resonance spectroscopy

    NASA Technical Reports Server (NTRS)

    Sutter, B.; Wasowicz, T.; Howard, T.; Hossner, L. R.; Ming, D. W.

    2002-01-01

    The incorporation of micronutrients (e.g., Fe, Mn, Cu) into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in NASA's Advanced Life Support (ALS) program for long-duration space missions. Separate Fe3+ (Fe-SHA), Mn2+ (Mn-SHA), and Cu2+ (Cu-SHA) containing SHA materials were synthesized by a precipitation method. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the location of Fe3+, Mn2+, and Cu2+ ions in the SHA structure and to identify other Fe(3+)-, Mn(2+)-, and Cu(2+)-containing phases that formed during precipitation. The EPR parameters for Fe3+ (g=4.20 and 8.93) and for Mn2+ (g=2.01, A=9.4 mT, D=39.0 mT and E=10.5 mT) indicated that Fe3+ and Mn2+ possessed rhombic ion crystal fields within the SHA structure. The Cu2+ EPR parameters (g(z)=2.488, A(z)=5.2 mT) indicated that Cu2+ was coordinated to more than six oxygens. The rhombic environments of Fe3+ and Mn2+ along with the unique Cu2+ environment suggested that these metals substituted for the 7 or 9 coordinate Ca2+ in SHA. The EPR analyses also detected poorly crystalline metal oxyhydroxides or metal-phosphates associated with SHA. The Fe-, Mn-, and Cu-SHA materials are potential slow release sources of Fe, Mn, and Cu for ALS and terrestrial cropping systems.

  7. Paramagnetic defects induced by electron irradiation in barium hollandite ceramics for caesium storage.

    PubMed

    Aubin-Chevaldonnet, V; Gourier, D; Caurant, D; Esnouf, S; Charpentier, T; Costantini, J M

    2006-04-26

    We have studied by electron paramagnetic resonance the mechanism of defect production by electron irradiation in barium hollandite, a material used for immobilization of radioactive caesium. The irradiation conditions were the closest possible to those occurring in Cs storage waste forms. Three paramagnetic defects were observed, independently of the irradiation conditions. A hole centre (H centre) is attributed to a superoxide ion O(2)(-) originating from hole trapping by interstitial oxygen produced by electron irradiation. An electron centre (E(1) centre) is attributed to a Ti(3+) ion adjacent to the resulting oxygen vacancy. Another electron centre (E(2) centre) is attributed to a Ti(3+) ion in a cation site adjacent to an extra Ba(2+) ion in a neighbouring tunnel, originating from barium displacement by elastic collisions. Comparison of the effects of external irradiations by electrons with the β-decay of Cs in storage waste forms is discussed. It is concluded that the latter would be dominated by E(1) and H centres rather than E(2) centres. PMID:21690754

  8. Electron paramagnetic resonance as an effective method for a characterization of functionalized iron oxide

    NASA Astrophysics Data System (ADS)

    Dobosz, Bernadeta; Krzyminiewski, Ryszard; Schroeder, Grzegorz; Kurczewska, Joanna

    2014-05-01

    Iron(II, III) oxide magnetic nanoparticles (NPs) have been coated with (3-Chloropropyl) trimethoxysilane and subsequently functionalized with 4-Amino-2,2,6,6-tetramethylpiperidine-N-oxyl and Amoxicillin. Finally, the functionalized iron oxide NPs have been coated with natural polymer, chitosan, in order to prevent NPs agglomeration in aqueous environment. The product was characterized by Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). It was studied by the electron paramagnetic resonance method and the parameters describing the magnetic properties of the investigated nanoparticles, such as g-factor and line width, were calculated.

  9. High field electron paramagnetic resonance spectroscopy under ultrahigh vacuum conditions—A multipurpose machine to study paramagnetic species on well defined single crystal surfaces

    NASA Astrophysics Data System (ADS)

    Rocker, J.; Cornu, D.; Kieseritzky, E.; Seiler, A.; Bondarchuk, O.; Hänsel-Ziegler, W.; Risse, T.; Freund, H.-J.

    2014-08-01

    A new ultrahigh vacuum (UHV) electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz to investigate paramagnetic centers on single crystal surfaces is described. It is particularly designed to study paramagnetic centers on well-defined model catalysts using epitaxial thin oxide films grown on metal single crystals. The EPR setup is based on a commercial Bruker E600 spectrometer, which is adapted to ultrahigh vacuum conditions using a home made Fabry Perot resonator. The key idea of the resonator is to use the planar metal single crystal required to grow the single crystalline oxide films as one of the mirrors of the resonator. EPR spectroscopy is solely sensitive to paramagnetic species, which are typically minority species in such a system. Hence, additional experimental characterization tools are required to allow for a comprehensive investigation of the surface. The apparatus includes a preparation chamber hosting equipment, which is required to prepare supported model catalysts. In addition, surface characterization tools such as low energy electron diffraction (LEED)/Auger spectroscopy, temperature programmed desorption (TPD), and infrared reflection absorption spectroscopy (IRAS) are available to characterize the surfaces. A second chamber used to perform EPR spectroscopy at 94 GHz has a room temperature scanning tunneling microscope attached to it, which allows for real space structural characterization. The heart of the UHV adaptation of the EPR experiment is the sealing of the Fabry-Perot resonator against atmosphere. To this end it is possible to use a thin sapphire window glued to the backside of the coupling orifice of the Fabry Perot resonator. With the help of a variety of stabilization measures reducing vibrations as well as thermal drift it is possible to accumulate data for a time span, which is for low temperature measurements only limited by the amount of liquid helium. Test measurements show that the system can detect paramagnetic

  10. High field electron paramagnetic resonance spectroscopy under ultrahigh vacuum conditions—A multipurpose machine to study paramagnetic species on well defined single crystal surfaces

    SciTech Connect

    Rocker, J.; Cornu, D.; Kieseritzky, E.; Hänsel-Ziegler, W.; Freund, H.-J.; Seiler, A.; Bondarchuk, O.

    2014-08-01

    A new ultrahigh vacuum (UHV) electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz to investigate paramagnetic centers on single crystal surfaces is described. It is particularly designed to study paramagnetic centers on well-defined model catalysts using epitaxial thin oxide films grown on metal single crystals. The EPR setup is based on a commercial Bruker E600 spectrometer, which is adapted to ultrahigh vacuum conditions using a home made Fabry Perot resonator. The key idea of the resonator is to use the planar metal single crystal required to grow the single crystalline oxide films as one of the mirrors of the resonator. EPR spectroscopy is solely sensitive to paramagnetic species, which are typically minority species in such a system. Hence, additional experimental characterization tools are required to allow for a comprehensive investigation of the surface. The apparatus includes a preparation chamber hosting equipment, which is required to prepare supported model catalysts. In addition, surface characterization tools such as low energy electron diffraction (LEED)/Auger spectroscopy, temperature programmed desorption (TPD), and infrared reflection absorption spectroscopy (IRAS) are available to characterize the surfaces. A second chamber used to perform EPR spectroscopy at 94 GHz has a room temperature scanning tunneling microscope attached to it, which allows for real space structural characterization. The heart of the UHV adaptation of the EPR experiment is the sealing of the Fabry-Perot resonator against atmosphere. To this end it is possible to use a thin sapphire window glued to the backside of the coupling orifice of the Fabry Perot resonator. With the help of a variety of stabilization measures reducing vibrations as well as thermal drift it is possible to accumulate data for a time span, which is for low temperature measurements only limited by the amount of liquid helium. Test measurements show that the system can detect paramagnetic

  11. Study of ultrasonic attenuation in f-electron systems in the paramagnetic limit of Coulomb interaction

    SciTech Connect

    Shadangi, Asit Ku.; Rout, G. C.

    2015-05-15

    We report here a microscopic model study of ultrasonic attenuation in f-electron systems based on Periodic Anderson Model in which Coulomb interaction is considered within a mean-field approximation for a weak interaction. The Phonon is coupled to the conduction band and f-electrons. The phonon Green's function is calculated by Zubarev's technique of the Green's function method. The temperature dependent ultrasonic attenuation co-efficient is calculated from the imaginary part of the phonon self-energy in the dynamic and long wave length limit. The f-electron occupation number is calculated self-consistently in paramagnetic limit of Coulomb interaction. The effect of the Coulomb interaction on ultrasonic attenuation is studied by varying the phonon coupling parameters to the conduction and f-electrons, hybridization strength, the position of f-level and the Coulomb interaction Strength. Results are discussed on the basis of experimental results.

  12. Electron paramagnetic resonance and low-field microwave absorption in the manganese-gallium oxide

    NASA Astrophysics Data System (ADS)

    Montiel, H.; Alvarez, G.; Conde-Gallardo, A.; Zamorano, R.

    2015-07-01

    Microwave absorption measurements in MnGa2O4 powders are carried out at X-band (8.8-9.8 GHz) in 92-296 K temperature range. For all temperatures, the electron paramagnetic resonance (EPR) spectra show a single broad line due to Mn2+ ions. Temperature dependence of the EPR parameters: the peak-to-peak linewidth (ΔHpp), the integrated intensity (IEPR) and the g-factor, suggests the presence of magnetic fluctuations that precede to antiferromagnetic ordering at low temperature. Additionally, the low-field microwave absorption (LFMA) is used to give further information on this material, giving also evidence of these magnetic fluctuations.

  13. Degradation of edible oil during food processing by ultrasound: electron paramagnetic resonance, physicochemical, and sensory appreciation.

    PubMed

    Pingret, Daniella; Durand, Grégory; Fabiano-Tixier, Anne-Sylvie; Rockenbauer, Antal; Ginies, Christian; Chemat, Farid

    2012-08-01

    During ultrasound processing of lipid-containing food, some off-flavors can be detected, which can incite depreciation by consumers. The impacts of ultrasound treatment on sunflower oil using two different ultrasound horns (titanium and pyrex) were evaluated. An electron paramagnetic resonance study was performed to identify and quantify the formed radicals, along with the assessment of classical physicochemical parameters such as peroxide value, acid value, anisidine value, conjugated dienes, polar compounds, water content, polymer quantification, fatty acid composition, and volatiles profile. The study shows an increase of formed radicals in sonicated oils, as well as the modification of physicochemical parameters evidencing an oxidation of treated oils. PMID:22804736

  14. Use of alanine-silicone pellets for electron paramagnetic resonance gamma dosimetry

    SciTech Connect

    Flores, J.; Galindo, S. )

    1991-03-01

    Silicone is proposed as an alternative binding substance in the production of D-L alanine pellets used in electron paramagnetic resonance (EPR) dosimetry of gamma rays. The dosimeters are manufactured at room temperature, making the production simple. Examination by EPR silicone-alanine pellets irradiated with 60Co gamma rays in the dose range 10 to 10(6) Gy shows that the proposed silicone binder does not affect typical alanine dose-response curves. Thermal stability of the pellets below 40 degrees C is good, but their pre-dose EPR signal amplitude is slightly higher than for nonirradiated alanine.

  15. Al-doped MgB2 materials studied using electron paramagnetic resonance and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Bateni, Ali; Erdem, Emre; Repp, Sergej; Weber, Stefan; Somer, Mehmet

    2016-05-01

    Undoped and aluminum (Al) doped magnesium diboride (MgB2) samples were synthesized using a high-temperature solid-state synthesis method. The microscopic defect structures of Al-doped MgB2 samples were systematically investigated using X-ray powder diffraction, Raman spectroscopy, and electron paramagnetic resonance. It was found that Mg-vacancies are responsible for defect-induced peculiarities in MgB2. Above a certain level of Al doping, enhanced conductive properties of MgB2 disappear due to filling of vacancies or trapping of Al in Mg-related vacancy sites.

  16. Single-ion anisotropy in the gadolinium pyrochlores studied by electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Glazkov, V. N.; Zhitomirsky, M. E.; Smirnov, A. I.; Krug von Nidda, H.-A.; Loidl, A.; Marin, C.; Sanchez, J.-P.

    2005-07-01

    The electron paramagnetic resonance is used to measure the single-ion anisotropy of Gd3+ ions in the pyrochlore structure of (Y1-xGdx)2Ti2O7 . A rather strong easy-plane-type anisotropy is found. The anisotropy constant D is comparable to the exchange integral J in the prototype Gd2Ti2O7 , D≃0.75J , and exceeds the dipolar energy scale. Physical implications of an easy-plane anisotropy for a pyrochlore antiferromagnet are considered. We calculate the magnetization curves at T=0 and discuss phase transitions in a magnetic field.

  17. Nondestructive measurement of large objects with electron paramagnetic resonance: Pottery, sculpture, and jewel ornament

    NASA Astrophysics Data System (ADS)

    Ikeya, Motoji; Yamamoto, Masahiro; Ishii, Hiroshi

    1994-12-01

    A cylindicral cavity of TE111 mode with an aperture of 3 mm in diameter has been used to measure the electron paramagnetic resonance (EPR) spectrum of a large object placed over the aperture. EPR spectra of a precious fossil of a dinosaur tooth piece and a fossil bone of the Machikane Alligator were measured nondestructively in addition to a jadeite sculpture, a pearl and turquoise necklace, a large turmaline, a star ruby, and ceramic pottery. Thus, EPR can be a nondestructive tool to detect forgery and to test the authenticity in art as well as to allocate ancient objects in archaeological provenance study.

  18. Bulk Quantum Computation with Pulsed Electron Paramagnetic Resonance: Simulations of Single-Qubit Error Correction Schemes

    NASA Astrophysics Data System (ADS)

    Ishmuratov, I. K.; Baibekov, E. I.

    2015-12-01

    We investigate the possibility to restore transient nutations of electron spin centers embedded in the solid using specific composite pulse sequences developed previously for the application in nuclear magnetic resonance spectroscopy. We treat two types of systematic errors simultaneously: (i) rotation angle errors related to the spatial distribution of microwave field amplitude in the sample volume, and (ii) off-resonance errors related to the spectral distribution of Larmor precession frequencies of the electron spin centers. Our direct simulations of the transient signal in erbium- and chromium-doped CaWO4 crystal samples with and without error corrections show that the application of the selected composite pulse sequences can substantially increase the lifetime of Rabi oscillations. Finally, we discuss the applicability limitations of the studied pulse sequences for the use in solid-state electron paramagnetic resonance spectroscopy.

  19. Study of the effects of hydroxyapatite nanocrystal codoping by pulsed electron paramagnetic resonance methods

    NASA Astrophysics Data System (ADS)

    Gafurov, M. R.; Biktagirov, T. B.; Mamin, G. V.; Shurtakova, D. V.; Klimashina, E. S.; Putlyaev, V. I.; Orlinskii, S. B.

    2016-03-01

    The effect of codoping of hydroxyapatite (HAP) nanocrystals with average sizes of 35 ± 15 nm during "wet" synthesis by CO 3 2- carbonate anions and Mn2+ cations on relaxation characteristics (for the times of electron spin-spin relaxation) of the NO 3 2- nitrate radical anion has been studied. By the example of HAP, it has been demonstrated that the electron paramagnetic resonance (EPR) is an efficient method for studying anion-cation (co)doping of nanoscale particles. It has been shown experimentally and by quantummechanical calculations that simultaneous introduction of several ions can be energetically more favorable than their separate inclusion. Possible codoping models have been proposed, and their energy parameters have been calculated.

  20. Electrochemical electron paramagnetic resonance utilizing loop gap resonators and micro-electrochemical cells.

    PubMed

    Tamski, Mika A; Macpherson, Julie V; Unwin, Patrick R; Newton, Mark E

    2015-09-28

    A miniaturised electrochemical cell design for Electron Paramagnetic Resonance (EPR) studies is reported. The cell incorporates a Loop Gap Resonator (LGR) for EPR investigation of electrochemically generated radicals in aqueous (and other large dielectric loss) samples and achieves accurate potential control for electrochemistry by using micro-wires as working electrodes. The electrochemical behaviour of the cell is analysed with COMSOL finite element models and the EPR sensitivity compared to a commercial TE011 cavity resonator using 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) as a reference. The electrochemical EPR performance is demonstrated using the reduction of methyl viologen as a redox probe in both water and acetonitrile. The data reported herein suggest that sub-micromolar concentrations of radical species can be detected in aqueous samples with accurate potential control, and that subtle solution processes coupled to electron transfer, such as comproportionation reactions, can be studied quantitatively using EPR. PMID:26291423

  1. Electrochemical electron paramagnetic resonance utilizing loop gap resonators and micro-electrochemical cells.

    PubMed

    Tamski, Mika A; Macpherson, Julie V; Unwin, Patrick R; Newton, Mark E

    2015-09-28

    A miniaturised electrochemical cell design for Electron Paramagnetic Resonance (EPR) studies is reported. The cell incorporates a Loop Gap Resonator (LGR) for EPR investigation of electrochemically generated radicals in aqueous (and other large dielectric loss) samples and achieves accurate potential control for electrochemistry by using micro-wires as working electrodes. The electrochemical behaviour of the cell is analysed with COMSOL finite element models and the EPR sensitivity compared to a commercial TE011 cavity resonator using 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) as a reference. The electrochemical EPR performance is demonstrated using the reduction of methyl viologen as a redox probe in both water and acetonitrile. The data reported herein suggest that sub-micromolar concentrations of radical species can be detected in aqueous samples with accurate potential control, and that subtle solution processes coupled to electron transfer, such as comproportionation reactions, can be studied quantitatively using EPR.

  2. Application of electron paramagnetic resonance (EPR) spectroscopy and imaging in drug delivery research - chances and challenges.

    PubMed

    Kempe, Sabine; Metz, Hendrik; Mäder, Karsten

    2010-01-01

    Electron Paramagnetic Resonance (EPR) spectroscopy is a powerful technique to study chemical species with unpaired electrons. Since its discovery in 1944, it has been widely used in a number of research fields such as physics, chemistry, biology and material and food science. This review is focused on its application in drug delivery research. EPR permits the direct measurement of microviscosity and micropolarity inside drug delivery systems (DDS), the detection of microacidity, phase transitions and the characterization of colloidal drug carriers. Additional information about the spatial distribution can be obtained by EPR imaging. The chances and also the challenges of in vitro and in vivo EPR spectroscopy and imaging in the field of drug delivery are discussed.

  3. Electron paramagnetic resonance study of 3,4,5-trimethoxytetraphenyl porphyrinoxovanadium (IV) complex.

    PubMed

    Sharma, Swati; Kumar, Anil; Chand, Prem; Sharma, B K; Sarkar, Sabyasachi

    2006-03-01

    3,4,5-Trimetoxytetraphenylporphyrinoxovanadium (IV) complex (3,4,5-TMVOTPP) was synthesized by a new one pot synthetic method. The complex was studied in the form of single crystal, powder (polycrystalline state), solution and frozen solution (glassy state) by electron paramagnetic resonance (EPR) between room temperature (RT) and liquid nitrogen temperature (LNT). Interestingly a well-resolved octet in the EPR spectrum at RT is observed in the pure paramagnetic state of the crystal. This observation is attributed to a greatly reduced dipolar interaction between paramagnetic vanadyl ions due to the large size of the molecule and the resultant stacking in the crystalline state. The line width of the EPR signals in single crystal at RT is approximately 3.3 mT which is more than the usual line width in diluted paramagnets ( approximately 1.5 mT) and is attributed to some kind of broadening effect akin to slow motion broadening. The line width in solvents is more than the crystal value but decreases appreciably at low temperatures. The decrease in line width at low temperature is attributed to the increase in spin-lattice-relaxation time and quenching of RT broadening motion. Only one octet is observed in the crystal EPR spectra which suggests only one formula unit per unit cell or a parallel/antiparallel ordering of V=O vectors in case the formula units per unit cell are more than one. This result needs verification by a detailed X-ray investigation. The crystalline field symmetry around the V(4+) metal ion is revealed to be axial by the observed angular dependence of the EPR spectrum and the powder EPR spectrum. No super hyperfine splitting of the hyperfine lines of the vanadyl ion is observed in solid state or diluted glass up to liquid nitrogen temperature. This suggests an expected weak in-plane pi-bonding with ligands. The spin Hamiltonian parameters for vanadyl ion in crystal, powder, diluted solutions and frozen glasses are evaluated and discussed.

  4. Calculation of electron paramagnetic resonance spectra from Brownian dynamics trajectories: application to nitroxide side chains in proteins.

    PubMed Central

    Steinhoff, H J; Hubbell, W L

    1996-01-01

    We present a method to simulate electron paramagnetic resonance spectra of spin-labeled proteins that explicitly includes the protein structure in the vicinity of the attached spin label. The method is applied to a spin-labeled polyleucine alpha-helix trimer. From short (6 ns) stochastic dynamics simulations of this trimer, an effective potential energy function is calculated. Interaction with secondary and tertiary structures determine the reorientational motion of the spin label side chains. After reduction to a single particle problem, long stochastic dynamic trajectories (700 ns) of the spin label side-chain reorientation are calculated from which the Lamor frequency trajectory and subsequently the electron paramagnetic resonance spectrum is determined. The simulated spectra agree well with experimental electron paramagnetic resonance spectra of bacteriorhodopsin mutants with spin labels in similar secondary and tertiary environments as in the polyleucine. Images FIGURE 1 PMID:8889196

  5. Magnetometry and electron paramagnetic resonance studies of phosphine- and thiol-capped gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Guerrero, E.; Muñoz-Márquez, M. A.; Fernández, A.; Crespo, P.; Hernando, A.; Lucena, R.; Conesa, J. C.

    2010-03-01

    In the last years, the number of studies performed by wholly independent research groups that confirm the permanent magnetism, first observed in our research lab, for thiol-capped Au nanoparticles (NPs) has rapidly increased. Throughout the years, the initial magnetometry studies have been completed with element-specific magnetization measurements based on, for example, the x-ray magnetic circular dichroism technique that have allowed the identification of gold as the magnetic moment carrier. In the research work here presented, we have focused our efforts in the evaluation of the magnetic behavior and iron impurities content in the synthesized samples by means of superconducting quantum interference device magnetometry and electron paramagnetic resonance spectrometry, respectively. As a result, hysteresis cycles typical of a ferromagnetic material have been measured from nominally iron-free gold NPs protected with thiol, phosphine, and chlorine ligands. It is also observed that for samples containing both, capped gold NPs and highly diluted iron concentrations, the magnetic behavior of the NPs is not affected by the presence of paramagnetic iron impurities. The hysteresis cycles reported for phosphine-chlorine-capped gold NPs confirm that the magnetic behavior is not exclusively for the metal-thiol system.

  6. Electron paramagnetic resonance (EPR) spectroscopy characterization of wheat grains from plants of different water stress tolerance.

    PubMed

    Łabanowska, Maria; Filek, Maria; Kurdziel, Magdalena; Bednarska, Elżbieta; Dłubacz, Aleksandra; Hartikainen, Helina

    2012-09-01

    Grains of five genotypes of wheat (four Polish and one Finnish), differing in their tolerance to drought stress were chosen for this investigation. Electron paramagnetic resonance spectroscopy allowed observation of transition metal ions (Mn, Fe, Cu) and different types of stable radicals, including semiquinone centers, present in seed coats, as well as several types of carbohydrate radicals found mainly in the inner parts of grains. The content of paramagnetic metal centers was higher in sensitive genotypes (Radunia, Raweta) than in tolerant ones (Parabola, Nawra), whereas the Finnish genotype (Manu) exhibited intermediate amounts. Similarly, the concentrations of both types of radicals, carbohydrates and semiquinone were significantly higher in the grains originating from more sensitive wheat genotypes. The nature of carbohydrate radicals and their concentrations were confronted with the kinds and amounts of sugars found by the biochemical analyses and microscopy observations. It is suggested that some long lived radicals (semiquinone and starch radicals) occurring in grains could be indicators of stress resistance of wheat plants.

  7. Identification of the deep level defects in AlN single crystals by electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Soltamov, V. A.; Ilyin, I. V.; Soltamova, A. A.; Mokhov, E. N.; Baranov, P. G.

    2010-06-01

    Electron paramagnetic resonance (EPR) at 9.4 and 35 GHz were studied on two types of AlN single crystals, grown by a sublimation sandwich method. These investigations revealed the presence of transition metals impurities in the first sample: Fe2+ (S =2) and some paramagnetic centers with S =3/2, we suggest Cr3+ or Ni3+ as the possible candidates. The EPR spectra of Fe2+ were observed up to the room temperature. After sample illumination at 5 K with light (wavelength shorter 700 nm) strong EPR signal with a g factor of shallow donors (SDs) and slightly anisotropic linewidth appears. This light-induced EPR signal, once excited at low temperature, still persists after switching off the light and is about constant up to 30 K then it drops quickly. SDs show a negative correlation energy U and oxygen in the N position (ON) is the most probable model. EPR spectra of deep-donor center which was assumed to be the nitrogen vacancy VN have been observed in the second sample. The x-ray irradiation leads to considerable enhancement of deep donor's (VN) signals intensity. The annealing resulted in recombination thermoluminescence and the deep donor (VN) energy level was estimated to be about 0.5 eV. The models of shallow (ON) and deep (VN) donor centers were supported by comprehensive hyperfine structure analysis.

  8. Assessment of tumor oxygenation by electron paramagnetic resonance: principles and applications.

    PubMed

    Gallez, Bernard; Baudelet, Christine; Jordan, Bénédicte F

    2004-08-01

    This review paper attempts to provide an overview of the principles and techniques that are often termed electron paramagnetic resonance (EPR) oximetry. The paper discusses the potential of such methods and illustrates they have been successfully applied to measure oxygen tension, an essential parameter of the tumor microenvironment. To help the reader understand the motivation for carrying out these measurements, the importance of tumor hypoxia is first discussed: the basic issues of why a tumor is hypoxic, why these hypoxic microenvironments promote processes driving malignant progression and why hypoxia dramatically influences the response of tumors to cytotoxic treatments will be explained. The different methods that have been used to estimate the oxygenation in tumors will be reviewed. To introduce the basics of EPR oximetry, the specificity of in vivo EPR will be discussed by comparing this technique with NMR and MRI. The different types of paramagnetic oxygen sensors will be presented, as well as the methods for recording the information (EPR spectroscopy, EPR imaging, dynamic nuclear polarization). Several applications of EPR for characterizing tumor oxygenation will be illustrated, with a special emphasis on pharmacological interventions that modulate the tumor microenvironment. Finally, the challenges for transposing the method into the clinic will also be discussed. PMID:15366026

  9. Time-resolved electron paramagnetic resonance of radical pair intermediates in cryptochromes

    NASA Astrophysics Data System (ADS)

    Biskup, Till

    2013-12-01

    Electron transfer plays a key role in many biological systems, including core complexes of photosynthesis and respiration. As this involves unpaired electron spins, electron paramagnetic resonance (EPR) is the method of choice to investigate such processes. Systems that show photo-induced charge separation and electron transfer are of particular interest, as here the processes can easily be synchronised to the experiment and therefore followed directly over its time course. One particular class of proteins, the cryptochromes, showing charge separation and in turn spin-correlated radical pairs upon excitation with blue light, have been investigated by time-resolved EPR spectroscopy in great detail and the results obtained so far are summarised in this contribution. Highlights include the first observation of spin-correlated radical pairs in these proteins, a fact with great impact on the proposed role as key part of a magnetic compass of migratory birds, as well as the assignment of the radical-pair partners and the unravelling of alternative and unexpected electron transfer pathways in these proteins, giving new insights into aspects of biological electron transfer itself.

  10. Electron Paramagnetic Resonance and DTA Investigation of Cr3+ in Tris(guanidinium) Hexafluoroaluminate Single Crystals

    NASA Astrophysics Data System (ADS)

    Lakshmi Kasturi, T.; Krishnan, V. G.

    1998-05-01

    Electron Paramagnetic Resonance (EPR) studies of Cr 3+ in single crystals of tris(guanidinium) hexafluoroaluminate, [C(NH2)3]3 AlF6 , have been carried out in the X-band region. A temperature dependent study of the zero-field splitting parameter D in the range 77-398 K shows the presence of a phase transition, which is supported by Differential Thermal Analysis. In addition, 19F superhyperfine struc-ture has been observed in the 9.3% naturally abundant 53Cr isotope hyperfine structure. D shows a large decrease with increasing temperature. The phase transition brings about a chemical inequivalence in the two chemically equivalent but magnetically inequivalent room temperature (CrF6)3- species. Compar-ison is made with the alums AlCl3 • 6H20, as well as other guanidinium aluminum salts.

  11. Nanostructured lipid carriers as nitroxide depot system measured by electron paramagnetic resonance spectroscopy.

    PubMed

    Haag, S F; Chen, M; Peters, D; Keck, C M; Taskoparan, B; Fahr, A; Teutloff, C; Bittl, R; Lademann, J; Schäfer-Korting, M; Meinke, M C

    2011-12-15

    Various nanometer scaled transport systems are used in pharmaceutics and cosmetics to increase penetration or storage of actives. Nanostructured lipid carriers (NLCs) are efficient drug delivery systems for dermatological applications. Electron paramagnetic resonance (EPR) spectroscopy was used for the determination of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) distribution within the carrier and to investigate the dynamics of skin penetration. Results of ex vivo penetration of porcine skin and in vivo data - forearm of human volunteers - are compared and discussed to previously obtained results with invasomes under comparable conditions. W-band measurements show 35% of TEMPO associated with the lipid compartments of the NLC. Application of TEMPO loaded NLC to skin ex vivo increases the observation time by 12min showing a stabilisation of the nitroxide radical. Moreover, stabilisation is also seen with data generated in vivo. Thus, same as invasomes NLCs are a suitable slow release depot system. PMID:22001533

  12. Effect of surfactants on human stratum corneum: electron paramagnetic resonance study.

    PubMed

    Mizushima, J; Kawasaki, Y; Tabohashi, T; Kitano, T; Sakamoto, K; Kawashima, M; Cooke, R; Maibach, H I

    2000-03-20

    Electron paramagnetic resonance (EPR) spectra of nitroxide spin probes are useful for studying biological membranes and chemical-membrane interactions. Recently, we established a stripping method to remove stratum corneum (SC) for this purpose. To assess this stripping method with EPR and correlate with standard methods, we quantified the irritant effects of three types of surfactants by measurements of visual score and transepidermal water loss (TEWL), SC hydration and chromametry and studied EPR spectra measurements of surfactant-treated cadaver SC (C-SC) and stripped off SC (S-SC) on patch tested sites. 5-Doxyl stearic acid was the spin label. The order parameter S obtained from the spectra of S-SC correlated with those of C-SC and TEWL values. The results suggest that this method is capable of evaluating the fluidity of SC and correlates with the above bioengineering parameters.

  13. Radical scavenging of white tea and its flavonoid constituents by electron paramagnetic resonance (EPR) spectroscopy.

    PubMed

    Azman, Nurul A M; Peiró, Sara; Fajarí, Lluís; Julià, Luis; Almajano, Maria Pilar

    2014-06-25

    White tea (WT) presents high levels of catechins, which are known to reduce oxidative stress. WT is the least processed tea, unfermented and prepared only from very young tea leaves. The subject of this paper is the use of the spin trap method and electron paramagnetic resonance (EPR) spectroscopy as the analytical tool to measure, for the first time, the radical scavenging activity of WT and its major catechin components, epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG), against the methoxy radical, using ferulic acid as antioxidant pattern. The antioxidant activity has been measured by the decrease of the intensity of the spectral bands of the adduct DMPO-OCH3 in the EPR with the amount of antioxidant in the reactive mixture. Tea leaves and buds were extracted with waterless methanol. It has been proved that tea compounds with more antiradical activity against methoxy radical are those with the gallate group, EGCG and ECG. PMID:24885813

  14. Optically detected electron paramagnetic resonance by microwave modulated magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Börger, Birgit; Bingham, Stephen J.; Gutschank, Jörg; Schweika, Marc Oliver; Suter, Dieter; Thomson, Andrew J.

    1999-11-01

    Electron paramagnetic resonance (EPR) can be detected optically, with a laser beam propagating perpendicular to the static magnetic field. As in conventional EPR, excitation uses a resonant microwave field. The detection process can be interpreted as coherent Raman scattering or as a modulation of the laser beam by the circular dichroism of the sample oscillating at the microwave frequency. The latter model suggests that the signal should show the same dependence on the optical wavelength as the MCD signal. We check this for two different samples [cytochrome c-551, a metalloprotein, and ruby (Cr3+:Al2O3)]. In both cases, the observed wavelength dependence is almost identical to that of the MCD signal. A quantitative estimate of the amplitude of the optically detected EPR signal from the MCD also shows good agreement with the experimental results.

  15. Electron paramagnetic resonance spectroscopy of fast neutron-generated defects in GaAs

    NASA Astrophysics Data System (ADS)

    Goltzene, A.; Meyer, B.; Schwab, C.; Greenbaum, S. G.; Wagner, R. J.; Kennedy, T. A.

    1984-12-01

    A series of fast neutron-irradiated GaAs samples (neutron fluence range of 2×1015-2.5×1017 cm-2) has been investigated by electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra at 9 GHz exhibit a broad (˜1 kG) Lorentzian singlet at g≊2.09 superimposed on the AsGa quadruplet. The singlet intensity scales linearly with neutron fluence as does that of the quadruplet. The presence of this new defect has not been reported in as-grown GaAs known to have large concentrations of AsGa defects. EPR measurements at 35, 159, and 337 GHz indicate that the singlet linewidth increases with the microwave frequency.

  16. Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy: Spin-Trapping with Iron-Dithiocarbamates.

    PubMed

    Maia, Luisa B; Moura, José J G

    2016-01-01

    Electron paramagnetic resonance (EPR) spectroscopy is the ideal methodology to identify radicals (detection and characterization of molecular structure) and to study their kinetics, in both simple and complex biological systems. The very low concentration and short life-time of NO and of many other radicals do not favor its direct detection and spin-traps are needed to produce a new and persistent radical that can be subsequently detected by EPR spectroscopy.In this chapter, we present the basic concepts of EPR spectroscopy and of some spin-trapping methodologies to study NO. The "strengths and weaknesses" of iron-dithiocarbamates utilization, the NO traps of choice for the authors, are thoroughly discussed and a detailed description of the method to quantify the NO formation by molybdoenzymes is provided. PMID:27094413

  17. Comparison of pulse sequences for R1-based electron paramagnetic resonance oxygen imaging

    NASA Astrophysics Data System (ADS)

    Epel, Boris; Halpern, Howard J.

    2015-05-01

    Electron paramagnetic resonance (EPR) spin-lattice relaxation (SLR) oxygen imaging has proven to be an indispensable tool for assessing oxygen partial pressure in live animals. EPR oxygen images show remarkable oxygen accuracy when combined with high precision and spatial resolution. Developing more effective means for obtaining SLR rates is of great practical, biological and medical importance. In this work we compared different pulse EPR imaging protocols and pulse sequences to establish advantages and areas of applicability for each method. Tests were performed using phantoms containing spin probes with oxygen concentrations relevant to in vivo oxymetry. We have found that for small animal size objects the inversion recovery sequence combined with the filtered backprojection reconstruction method delivers the best accuracy and precision. For large animals, in which large radio frequency energy deposition might be critical, free induction decay and three pulse stimulated echo sequences might find better practical usage.

  18. Electron paramagnetic resonance studies of the tungsten-containing formate dehydrogenase from Clostridium thermoaceticum.

    PubMed

    Deaton, J C; Solomon, E I; Watt, G D; Wetherbee, P J; Durfor, C N

    1987-12-16

    The redox centers in the tungsten-containing formate dehydrogenase from Clostridium thermoaceticum were examined by potentiometric titration and electron paramagnetic resonance spectroscopy. At low temperature two overlapping iron-sulfur signals which correlated with enzymatic activity were observed with formal potentials near -400 mV vs. SHE. Based on their temperature dependences, one signal is assigned to a reduced Fe2S2 cluster and one to a reduced Fe4S4 cluster. Quantitation of signal intensity suggests two Fe2S2 and two Fe4S4 clusters per formate dehydrogenase molecule. Another signal (g = 2.101, 1.980, 1.950) present in low concentrations at more negative potentials was observable up to 200 degrees K and is not attributed to any iron-sulfur cluster. The possible origin of this signal is analyzed using ligand field theory, and the redox behavior is considered with respect to possible ligation at the active site. PMID:2827642

  19. Effects of genistein and daidzein on erythrocyte membrane fluidity: an electron paramagnetic resonance study.

    PubMed

    Ajdzanović, Vladimir; Spasojević, Ivan; Filipović, Branko; Sosić-Jurjević, Branka; Sekulić, Milka; Milosević, Verica

    2010-04-01

    The maintenance of erythrocyte membrane fluidity at the physiological level is an important factor affecting the ability of erythrocytes to pass through blood vessels of small luminal diameter. Genistein and daidzein, which are used as alternative therapeutics in cardiovascular conditions, can be incorporated into the cell membrane and change its fluidity. The aim of this study was to examine the effects of genistein and daidzein on erythrocyte membrane fluidity at graded depths. We used electron paramagnetic resonance (EPR) spectroscopy and fatty acid spin probes (5-DS and 12-DS) where EPR spectra were dependent on fluidity. The results showed that genistein significantly (p < 0.05) decreased erythrocyte membrane fluidity near the hydrophilic surface, while daidzein significantly (p < 0.05) increased the same parameter in deeper regions of the membrane. These data suggest that the deep fluidizing effects of daidzein on erythrocyte membranes make it a better therapeutic choice than genistein in some cardiovascular conditions.

  20. The negative effect of soy extract on erythrocyte membrane fluidity: an electron paramagnetic resonance study.

    PubMed

    Ajdžanović, Vladimir; Spasojević, Ivan; Sošić-Jurjević, Branka; Filipović, Branko; Trifunović, Svetlana; Sekulić, Milka; Milošević, Verica

    2011-02-01

    A decrease of erythrocyte membrane fluidity can contribute to the pathophysiology of hypertension. Soy products, which are used as alternative therapeutics in some cardiovascular conditions, contain various isoflavones (genistein, daidzein, and their glucosides, genistin and daidzin), which can incorporate cellular membrane and change its fluidity. The aim of this study was to examine the effects of soy extract (which generally corresponds to the soy products of isoflavone composition) on erythrocyte membrane fluidity at graded depths. We used electron paramagnetic resonance spectroscopy and fatty acid spin probes (5-DS and 12-DS), the spectra of which are dependent on membrane fluidity. After being treated with soy extract, erythrocytes showed a significant (P = 0.016) decrease of membrane fluidity near the hydrophilic surface, while there were no significant changes of fluidity in deeper hydrophobic membrane regions. These results suggest that soy products containing high levels of genistein and isoflavone glucosides may not be suitable for use in hypertension because they decrease erythrocyte membrane fluidity.

  1. A novel probe head for high-field, high-frequency electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Annino, G.; Cassettari, M.; Longo, I.; Martinelli, M.; Van Bentum, P. J. M.; Van der Horst, E.

    1999-03-01

    A probe head especially useful for electron paramagnetic resonance (EPR) spectrometers working at high field—high frequency is presented. The probe head is based on the whispering gallery mode dielectric resonators that proved very effective in the ultrahigh frequency range. The excitation network uses a properly shaped dielectric waveguide sharing its external field pattern with the field of the resonators. Very simple resonators made with polyethylene in both single and doubly stacked disk configurations are used. The experimental characterization by a submillimeter network analyzer shows for the resonances studied in a wide range of frequencies up to ≈400 GHz high loaded merit factor QL values and good coupling factors. Resonators also maintain their general characteristics when large quantities of low loss samples for EPR measurements are properly inserted. Preliminary EPR spectra of diphenylpicrylhyldrazyl at 7 and 10 T obtained with the novel apparatus are finally presented.

  2. Study of free radicals in gamma irradiated cellulose of cultural heritage materials using Electron Paramagnetic Resonance

    NASA Astrophysics Data System (ADS)

    Kodama, Yasko; Rodrigues, Orlando, Jr.; Garcia, Rafael Henrique Lazzari; Santos, Paulo de Souza; Vasquez, Pablo A. S.

    2016-07-01

    Main subject of this article was to study room temperature stable radicals in Co-60 gamma irradiated contemporary paper using Electron Paramagnetic Resonance spectrometer (EPR). XRD was used to study the effect of ionizing radiation on the morphology of book paper. SEM images presented regions with cellulose fibers and regions with particles agglomeration on the cellulose fibers. Those agglomerations were rich in calcium, observed by EDS. XRD analysis confirmed presence of calcium carbonate diffraction peaks. The main objective of this study was to propose a method using conventional kinetics chemical reactions for the observed radical formed by ionizing radiation. Therefore, further analyses were made to study the half-life and the kinetics of the free radical created. This method can be suitably applied to study radicals on cultural heritage objects.

  3. Electron paramagnetic resonance spectroscopy in radiation research: Current status and perspectives

    PubMed Central

    Rana, Sudha; Chawla, Raman; Kumar, Raj; Singh, Shefali; Zheleva, Antoaneta; Dimitrova, Yanka; Gadjeva, Veselina; Arora, Rajesh; Sultana, Sarwat; Sharma, Rakesh Kumar

    2010-01-01

    Exposure to radiation leads to a number of health-related malfunctions. Ionizing radiation is more harmful than non-ionizing radiation, as it causes both direct and indirect effects. Irradiation with ionizing radiation results in free radical-induced oxidative stress. Free radical-mediated oxidative stress has been implicated in a plethora of diseased states, including cancer, arthritis, aging, Parkinson's disease, and so on. Electron Paramagnetic Resonance (EPR) spectroscopy has various applications to measure free radicals, in radiation research. Free radicals disintegrate immediately in aqueous environment. Free radicals can be detected indirectly by the EPR spin trapping technique in which these forms stabilize the radical adduct and produce characteristic EPR spectra for specific radicals. Ionizing radiation-induced free radicals in calcified tissues, for example, teeth, bone, and fingernail, can be detected directly by EPR spectroscopy, due to their extended stability. Various applications of EPR in radiation research studies are discussed in this review. PMID:21814437

  4. New experimental limit on the electric dipole moment of the electron in a paramagnetic insulator

    NASA Astrophysics Data System (ADS)

    Kim, Y. J.; Liu, C.-Y.; Lamoreaux, S. K.; Visser, G.; Kunkler, B.; Matlashov, A. N.; Long, J. C.; Reddy, T. G.

    2015-05-01

    We report results of an experimental search for the intrinsic electric dipole moment of the electron (eEDM) using a solid-state technique. The experiment employs a paramagnetic, insulating gadolinium gallium garnet (GGG) that has a large magnetic response at low temperatures. The presence of the eEDM would lead to a small but nonzero magnetization as the GGG sample is subjected to a strong electric field. We search for the resulting Stark-induced magnetization with a sensitive magnetometer. Recent progress on the suppression of several sources of background allows the experiment to run free of spurious signals at the level of the statistical uncertainties. We report our first limit on the eEDM of (-5.57 ±7.98 ±0.12 )×10-25 e cm with 5 days of data averaging.

  5. Imaging of Nitroxides at 250 MHz using Rapid-Scan Electron Paramagnetic Resonance

    PubMed Central

    Biller, Joshua R.; Tseitlin, Mark; Quine, Richard W.; Rinard, George A.; Weismiller, Hilary A.; Elajaili, Hanan; Rosen, Gerald M.; Kao, Joseph P. Y.; Eaton, Sandra S.; Eaton, Gareth R.

    2014-01-01

    Projections for 2D spectral-spatial images were obtained by continuous wave and rapid-scan electron paramagnetic resonance using a bimodal cross-loop resonator at 251 MHz. The phantom consisted of three 4 mm tubes containing different 15N,2H-substituted nitroxides. Rapid-scan and continuous wave images were obtained with 5 min total acquisition times. For comparison, images also were obtained with 29 s acquisition time for rapid scan and 15 min for continuous wave. Relative to continuous wave projections obtained for the same data acquisition time, rapid-scan projections had significantly less low-frequency noise and substantially higher signal-to-noise at higher gradients. Because of the improved image quality for the same data acquisition time, linewidths could be determined more accurately from the rapid-scan images than from the continuous wave images. PMID:24650729

  6. Denaturation studies of active-site labeled papain using electron paramagnetic resonance and fluorescence spectroscopy.

    PubMed Central

    Ping, Z A; Butterfiel, D A

    1991-01-01

    A spin-labeled p-chloromercuribenzoate (SL-PMB) and a fluorescence probe, 6-acryloyl-2-dimethylaminonaphthalene (Acrylodan), both of which bind to the single SH group located in the active site of papain, were used to investigate the interaction of papain (EC 3.4.22.2) with two protein denaturants. It was found that the active site of papain was highly stable in urea solution, but underwent a large conformational change in guanidine hydrochloride solution. Electron paramagnetic resonance and fluorescence results were in agreement and both paralleled enzymatic activity of papain with respect to both the variation in pH and denaturation. These results strongly suggest that SL-PMB and Acrylodan labels can be used to characterize the physical state of the active site of the enzyme. PMID:1657229

  7. Searching for biosignatures using electron paramagnetic resonance (EPR) analysis of manganese oxides.

    PubMed

    Kim, Soon Sam; Bargar, John R; Nealson, Kenneth H; Flood, Beverly E; Kirschvink, Joseph L; Raub, Timothy D; Tebo, Bradley M; Villalobos, Mario

    2011-10-01

    Manganese oxide (Mn oxide) minerals from bacterial sources produce electron paramagnetic resonance (EPR) spectral signatures that are mostly distinct from those of synthetic simulants and abiogenic mineral Mn oxides. Biogenic Mn oxides exhibit only narrow EPR spectral linewidths (∼500 G), whereas abiogenic Mn oxides produce spectral linewidths that are 2-6 times broader and range from 1200 to 3000 G. This distinction is consistent with X-ray structural observations that biogenic Mn oxides have abundant layer site vacancies and edge terminations and are mostly of single ionic species [i.e., Mn(IV)], all of which favor narrow EPR linewidths. In contrast, abiogenic Mn oxides have fewer lattice vacancies, larger particle sizes, and mixed ionic species [Mn(III) and Mn(IV)], which lead to the broader linewidths. These properties could be utilized in the search for extraterrestrial physicochemical biosignatures, for example, on Mars missions that include a miniature version of an EPR spectrometer.

  8. A new pulse width reduction technique for pulsed electron paramagnetic resonance spectroscopy.

    PubMed

    Ohba, Yasunori; Nakazawa, Shigeaki; Kazama, Shunji; Mizuta, Yukio

    2008-03-01

    We present a new technique for a microwave pulse modulator that generates a short microwave pulse of approximately 1ns for use in an electron paramagnetic resonance (EPR) spectrometer. A quadruple-frequency multiplier that generates a signal of 16-20GHz from an input of 4-5GHz was employed to reduce the rise and fall times of the pulse prepared by a PIN diode switch. We examined the transient response characteristics of a commercial frequency multiplier and found that the device can function as a multiplier for pulsed signal even though it was designed for continuous wave operation. We applied the technique to a Ku band pulsed EPR spectrometer and successfully observed a spin echo signal with a broad excitation bandwidth of approximately 1.6mT using 80 degrees pulses of 1.5ns. PMID:18248828

  9. Age of an Indonesian Fossil Tooth Determined by Electron Paramagnetic Resonance

    SciTech Connect

    Bogard, JS

    2004-04-07

    The first fossil hominid tooth recovered during 1999 excavations from the Cisanca River region in West Java, Indonesia, was associated with a series of bovid teeth from a single individual that was recovered 190 cm beneath the hominid tooth. The age of the fossil bovid teeth was determined using electron paramagnetic resonance (EPR) analysis as part of an effort to bracket the age of the hominid tooth. The EPR-derived age of the bovid teeth is (5.16 {+-} 2.01) x 10{sup 5} years. However, the age estimate reported here is likely an underestimate of the actual age of deposition since evidence of heating was detected in the EPR spectra of the bovid teeth, and the heating may have caused a decrease in the intensity of EPR components on which the age calculation is based.

  10. Characterization of radiation-induced damage in high performance polymers by electron paramagnetic resonance imaging spectroscopy

    NASA Technical Reports Server (NTRS)

    Suleman, Naushadalli K.

    1992-01-01

    The potential for long-term human activity beyond the Earth's protective magnetosphere is limited in part by the lack of detailed information on the effectiveness and performance of existing structural materials to shield the crew and spacecraft from highly penetrating space radiations. The two radiations of greatest concern are high energy protons emitted during solar flares and galactic cosmic rays which are energetic ions ranging from protons to highly oxidized iron. Although the interactions of such high-energy radiations with matter are not completely understood at this time, the effects of the incident radiation are clearly expected to include the formation of paramagnetic spin centers via ionization and bond-scission reactions in the molecular matrices of structural materials. Since this type of radiation damage is readily characterized by Electron Paramagnetic Resonance (EPR) spectroscopy, the NASA Langley Research Center EPR system was repaired and brought on-line during the 1991 ASEE term. A major goal of the 1992 ASEE term was to adapt the existing core of the LaRC EPR system to meet the requirements for EPR Imaging--a powerful new technique which provides detailed information on the internal structure of materials by mapping the spatial distribution of unpaired spin density in bulk media. Major impetus for this adaptation arises from the fact that information derived from EPRI complements other methods such as scanning electron microscopy which primarily characterize surface phenomena. The modification of the EPR system has been initiated by the construction of specially designed, counterwound Helmholtz coils which will be mounted on the main EPR electromagnet. The specifications of the coils have been set to achieve a static linear magnetic field gradient of 10 gauss/mm/amp along the principal (Z) axis of the Zeeman field. Construction is also in progress of a paramagnetic standard in which the spin distribution is known in all three dimensions. This

  11. The effect of implanting boron on the optical absorption and electron paramagnetic resonance spectra of silica

    NASA Astrophysics Data System (ADS)

    Magruder, R. H.; Stesmans, A.; Weeks, R. A.; Weller, R. A.

    2008-09-01

    Silica samples (type III, Corning 7940) were implanted with B using multiple energies to produce a layer ˜600 nm thick in which the concentration of B ranged from 0.034 to 2.04 at. %. Optical absorption spectra were measured from 1.8 to 6.5 eV. Electron paramagnetic resonance (EPR) measurements were generally made at ˜20.3 and 33 GHz for sample temperatures ranging from 77 to 100 K. Based on the EPR spectra three types of defects, namely, Eγ', the E'-type 73 G split doublet (E73'), and the peroxyradical (POR) were identified. No oxygen-associated hole centers (OHCs) nor specific B-associated paramagnetic defects were detected, not even at the largest B concentration of 2.04 at. %. Unlike previous assignments, there was no correlation between the 4.83 eV optical absorption band and the observed PORs. From these results, we infer that in addition to POR, there is at least one additional Si-related state absorbing in the 4.8-4.9 eV range that is likely diamagnetic. The 5.85 eV optical absorption band is found to be due to the Eγ' and E73' centers, with, in average, quite similar oscillator strengths inferred as before. Both the optical absorption and the electron spin resonance data can be satisfactorily explained without the need for specific B-associated defect site (s). As no OHCs are detected by ESR, these do not seem to make a detectable contribution to the optical spectra.

  12. A Spectrometer for Dynamic Nuclear Polarization and Electron Paramagnetic Resonance at High Frequencies

    NASA Astrophysics Data System (ADS)

    Becerra, L. R.; Gerfen, G. J.; Bellew, B. F.; Bryant, J. A.; Hall, D. A.; Inati, S. J.; Weber, R. T.; Un, S.; Prisner, T. F.; McDermott, A. E.; Fishbein, K. W.; Kreischer, K. E.; Temkin, R. J.; Singel, D. J.; Griffin, R. G.

    A high-frequency dynamic nuclear polarization (DNP)/electron paramagnetic resonance spectrometer operating at 211 MHz for 1H and 140 GHz for g= 2 paramagnetic centers (5 T static field) is described. The salient feature of the instrument is a cyclotron-resonance maser (gyrotron) which generates high-frequency, high-power microwave radiation. This gyrotron, which under conventional operation produces millisecond pulses at kilowatt powers, has been adapted to operate at ˜100 W for 1 to 20 s pulses and in the continuous wave mode at the 10 W power level. Experiments combining DNP with magic-angle spinning (MAS) nuclear magnetic resonance were performed on samples consisting of 2% by weight of the free radical BDPA doped into polystyrene. Room-temperature DNP enhancement factors of 10 for 1H and 40 for 13C were obtained in the NMR-MAS spectra. Static DNP NMR has also been performed on samples containing nitroxides dissolved in water:glycerol solvent mixtures. Enhancements of approximately 200 have been obtained for low-temperature (14 K) 1H NMR. A pulsed/CW EPR spectrometer operating at 140 GHz has been developed in conjunction with the DNP spectrometer. Microwave sources include Gunn-diode oscillators which provide low-power (20 mW) radiation, and the gyrotron, which has been used to deliver higher power levels in pulsed experiments. Results using this spectrometer are presented for continuous-wave and echo-detected EPR, electron spin-echo-envelope modulation (ESEEM), and Fourier-transform EPR.

  13. Zero-field signal in the electron paramagnetic resonance spectrum of Mn{sup +2} in silicate glasses

    SciTech Connect

    Rakhimov, Rakhim R.; Jones, David E.

    2000-07-22

    A 9.4-9.8 GHz electron paramagnetic resonance (EPR) study of Mn{sup +2}-doped Na{sub 2}O-CaO-MgO-SiO{sub 2} glasses has revealed a nonresonant microwave magneto-absorption near zero magnetic field in addition to normal paramagnetic absorption due to Mn{sup +2} ions, electron spin S=5/2. The low-field response has an opposite phase relative to paramagnetic signal and is independent of the mutual orientation of the magnetic field of the microwave H{sub 1} and static magnetic field H. In contrast, the paramagnetic signal is different for perpendicular H{sub 1}(perpendicular sign)H and parallel H{sub 1}(parallel sign)H polarization of the microwave field, which is attributed to enhancement of forbidden magnetic dipolar transitions and suppression of the allowed transitions for parallel polarization. The low-field response is described in terms of microwave dielectric losses that derive from the magneto-induced charge migration in the first coordination sphere of Mn{sup +2}. As opposed to the spin-polarized tunneling that was described in ferromagnets between different valence forms of Mn, the observed effect is due to spin-dependent tunneling that occurs in the vicinity of Mn{sup +2} in a diluted paramagnetic system. (c) 2000 American Institute of Physics.

  14. Analyzing Xanthine Dehydrogenase Iron-Sulfur Clusters Using Electron Paramagnetic Resonance Spectroscopy

    SciTech Connect

    Hodson, R.

    2004-02-05

    Xanthine dehydrogenase is a metalloenzyme that is present in a variety of eukaryotic and prokaryotic organisms. The oxidation of the xanthine occurs at the molybdenum site, and the catalytic cycle is completed by electron transfer to the iron-sulfur (Fe/S) clusters and finally the flavin, where they are accepted by nicotinamide adenine dinucleotide (NAD). Since the site giving rise to the Fe/S I electron paramagnetic resonance (EPR) signal is thought to be the initial recipient of the electrons from the Mo, we wish to understand which EPR signal is associated with which Fe/S cluster in the structure in order to develop an understanding of the electron flow within the molecule. Samples of xanthine dehydrogenase wild-type and mutant forms were analyzed with EPR spectroscopy techniques at low and high temperatures. The results showed an altered Fe/S I signal along with an unaltered Fe/S II signal. The converted Cysteine, in the mutant, did affect the Fe/S cluster immediately adjacent to it. Therefore, the Fe/S I signal arises from the Fe/S cluster closest to the Mo and immediately adjacent to the mutated amino acid, and the Fe/S II signal must arise from the more distant Fe/S cluster.

  15. Assessment of melanoma extent and melanoma metastases invasion using electron paramagnetic resonance and bioluminescence imaging.

    PubMed

    Godechal, Quentin; Defresne, Florence; Danhier, Pierre; Leveque, Philippe; Porporato, Paolo Ettore; Sonveaux, Pierre; Baurain, Jean-François; Feron, Olivier; Gallez, Bernard

    2011-01-01

    The clinical outcome of melanoma depends on the local and distant spread of the disease at the time of diagnosis, as the estimated 5-year survival rate is about 100% for superficial melanoma diagnosed early, but less than 10% for melanoma that has disseminated to major organs such as lungs. There is a crucial need for new effective methods for the detection and the characterization of melanomas. In the pre-clinical setting, this will help to understand the factors that contribute to the malignancy while the transfer into the clinic will contribute to an early effective treatment of patients. Melanoma lesions can be detected by electron paramagnetic resonance (EPR) using paramagnetic properties of melanin pigments. As part of the development of EPR imaging to characterize melanomas, we evaluated in the present study the usefulness of EPR to report on the extension of lung metastases by comparing the method with bioluminescence imaging using B16 melanoma cells expressing luciferase. B16 melanoma cells were injected subcutaneously or intravenously in C57/BL6 mice. The primary tumors or the lung colonization by melanoma cells was measured after several delay periods to obtain several degrees of invasiveness. The animals were measured in-vivo with bioluminescence after i.v. injection of luciferin. The primary tumors or lungs were then excised. After freeze-drying, the content of melanin in lungs was measured and imaged by EPR at 9 GHz. We observed a direct relationship between the EPR intensity and the bioluminescence intensity. Another tumor model (KHT sarcoma), non-pigmented but expressing luciferase, was used to confirm that the EPR signal was directly linked to the melanin pigment present in the tumors. PMID:21861288

  16. Temperature dependence on the electron paramagnetic resonance spectra of natural jasper from Taroko Gorge (Taiwan)

    NASA Astrophysics Data System (ADS)

    Hemantha Kumar, G. N.; Parthasarathy, G.; Chakradhar, R. P. S.; Rao, J. Lakshmana; Ratnakaram, Y. C.

    2010-04-01

    Structural properties of natural jasper from Taroko Gorge (Taiwan) have been investigated by means of powder X-ray diffraction, electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopic techniques. The EPR spectrum at room temperature exhibits a sharp resonance signal at g = 2.007 and two more resonance signals centered at g ≈ 4.3 and 14.0. The resonance signal at g = 2.007 has been attributed to the E' center and is related to a natural radiation-induced paramagnetic defect. Two more resonance signals centered at g ≈ 4.3 and 14.0 are characteristic of Fe3+ ions. The EPR spectra recorded at room temperature of jasper samples, heat-treated at temperatures ranging from 473 to 1,473 K exhibit marked temperature dependence. The resonance signal corresponding to E' center disappears at elevated temperatures. A broad, intense resonance signal centered at g ≈ 2.0 appears at elevated temperatures. This resonance signal is a characteristic of Fe3+ ions, which are present as hematite in the jasper sample. The intensity of the resonance signal becomes dominant at elevated temperatures at ≥873 K, masking g ≈ 4.3 and g ≈ 14.0 resonance signals. The EPR spectra of jasper heat-treated at 673 K have been recorded at temperatures between 123 and 296 K. The population of spin levels ( N) has been calculated for the broad g ≈ 2.0 resonance signal. It is found that N decreases with decreasing temperature. The linewidth (ΔH) of g ≈ 2.0 resonance signal of the heat-treated jasper is found to increase with decreasing temperature. This has been attributed to spin-spin interaction of the Fe3+ ions present in the form of hematite in the studied jasper sample.

  17. Absolute Oxygen R1e Imaging In Vivo with Pulse Electron Paramagnetic Resonance

    PubMed Central

    Epel, Boris; Bowman, Michael K.; Mailer, Colin; Halpern, Howard J.

    2015-01-01

    Purpose Tissue oxygen (O2) levels are among the most important and most quantifiable stimuli to which cells and tissues respond through inducible signaling pathways. Tumor O2 levels are major determinants of the response to cancer therapy. Developing more accurate measurements and images of tissue O2 partial pressure (pO2), assumes enormous practical, biological, and medical importance. Methods We present a fundamentally new technique to image pO2 in tumors and tissues with pulse electron paramagnetic resonance (EPR) imaging enabled by an injected, nontoxic, triaryl methyl (trityl) spin probe whose unpaired electron’s slow relaxation rates report the tissue pO2. Heretofore, virtually all in vivo EPR O2 imaging measures pO2 with the transverse electron spin relaxation rate, R2e, which is susceptible to the self-relaxation confounding O2 sensitivity. Results We found that the trityl electron longitudinal relaxation rate, R1e, is an order of magnitude less sensitive to confounding self-relaxation. R1e imaging has greater accuracy and brings EPR O2 images to an absolute pO2 image, within uncertainties. Conclusion R1e imaging more accurately determines oxygenation of cancer and normal tissue in animal models than has been available. It will enable enhanced, rapid, noninvasive O2 images for understanding oxygen biology and the relationship of oxygenation patterns to therapy outcome in living animal systems. PMID:24006331

  18. Ageing and thermal recovery of paramagnetic centers induced by electron irradiation in yttria-stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Costantini, J. M.; Beuneu, F.

    We have used electron spin resonance spectroscopy to study the defects induced in yttria-stabilized zirconia (YSZ) single crystals by 2.5-MeV electron irradiations. Two paramagnetic centers are produced: the first one with an axial <111> symmetry is similar to the trigonal Zr3+ electron center (T center) found after X-ray irradiation or thermo-chemical reduction, whereas the second one is a new oxygen hole center with an axial <100> symmetry different from the orthorhombic O- center induced by X-ray irradiation. At a fluence around 10(18) e/cm(2) , both centers are bleached out near 600 K, like the corresponding X-ray induced defects. At a fluence around 10(19) e/cm(2) , defects are much more stable, since complete thermal bleaching occurs near 1000 K. Accordingly, ageing of as-irradiated samples shows that high-dose defects at more stable than the low-dose ones.

  19. Characterization of the Iron-Sulfur Clusters in Xanthine Dehydrogenase Using Electron Paramagnetic Resonance Spectroscopy and Magnetic Coupling Interactions

    SciTech Connect

    Scott, J. Robert

    2004-02-04

    Xanthine dehydrogenase is a metalloenzyme that is present in numerous eukaryotic and prokaryotic organisms. It contains molybdenum, two different iron-sulfur clusters, and flavin. While the structures of both iron-sulfur clusters were known, it was unclear as to which structure was in which location. Electron paramagnetic resonance spectroscopy probes the paramagnetic qualities of molecules or ions. With this technology we wished to understand which EPR spectrum was associated with which iron-sulfur cluster by looking at magnetic coupling between the paramagnetic Mo(V) oxidation state and the reduced iron-sulfur clusters. We then assigned the clusters to their corresponding locations. The spin-spin interactions observed between Mo(V) and Fe-S I in xanthine dehydrogenase at low temperature show that Fe-S I is the closer site in contrast to Fe-S II.

  20. Electron paramagnetic resonance study of radiation damage in photosynthetic reaction center crystals.

    SciTech Connect

    Utschig, L. M.; Chemerisov, S. D.; Tiede, D. M.; Poluektov, O. G.; Chemical Sciences and Engineering Division

    2008-01-01

    Electron paramagnetic resonance (EPR) was used to simultaneously study radiation-induced cofactor reduction and damaging radical formation in single crystals of the bacterial reaction center (RC). Crystals of Fe-removed/Zn-replaced RC protein from Rhodobacter (R.) sphaeroides R26 were irradiated with varied radiation doses at cryogenic temperature and analyzed for radiation-induced free radical formation and alteration of light-induced photosynthetic electron transfer activity using high-field (HF) D-band (130 GHz) and X-band (9.5 GHz) EPR spectroscopies. These analyses show that the formation of radiation-induced free radicals saturated at doses 1 order of magnitude smaller than the amount of radiation at which protein crystals lose their diffraction quality, while light-induced RC activity was found to be lost at radiation doses at least 1 order of magnitude lower than the dose at which radiation-induced radicals exhibited saturation. HF D-band EPR spectra provide direct evidence for radiation-induced reduction of the quinones and possibly other cofactors. These results demonstrate that substantial radiation damage is likely to have occurred during X-ray diffraction data collection used for photosynthetic RC structure determination. Thus, both radiation-induced loss of photochemical activity in RC crystals and reduction of the quinones are important factors that must be considered when correlating spectroscopic and crystallographic measurements of quinone site structures.

  1. Copper Environment in Artificial Metalloproteins Probed by Electron Paramagnetic Resonance Spectroscopy.

    PubMed

    Flores, Marco; Olson, Tien L; Wang, Dong; Edwardraja, Selvakumar; Shinde, Sandip; Williams, JoAnn C; Ghirlanda, Giovanna; Allen, James P

    2015-10-29

    The design of binding sites for divalent metals in artificial proteins is a productive platform for examining the characteristics of metal-ligand interactions. In this report, we investigate the spectroscopic properties of small peptides and four-helix bundles that bind Cu(II). Three small peptides, consisting of 15 amino acid residues, were designed to have two arms, each containing a metal-binding site comprised of different combinations of imidazole and carboxylate side chains. Two four-helix bundles each had a binding site for a central dinuclear metal cofactor, with one design incorporating additional potential metal ligands at two identical sites. The small peptides displayed pH-dependent, metal-induced changes in the circular dichroism spectra, consistent with large changes in the secondary structure upon metal binding, while the spectra of the four-helix bundles showed a predominant α-helix content but only small structural changes upon metal binding. Electron paramagnetic resonance spectra were measured at X-band revealing classic Cu(II) axial patterns with hyperfine coupling peaks for the small peptides and four-helix bundles exhibiting a range of values that were related to the specific chemical natures of the ligands. The variety of electronic structures allow us to define the distinctive environment of each metal-binding site in these artificial systems, including the designed additional binding sites in one of the four-helix bundles.

  2. Membrane-Sugar Interactions Probed by Pulsed Electron Paramagnetic Resonance of Spin Labels.

    PubMed

    Konov, Konstantin B; Leonov, Dmitry V; Isaev, Nikolay P; Fedotov, Kirill Yu; Voronkova, Violeta K; Dzuba, Sergei A

    2015-08-13

    Sugars can stabilize biological systems under extreme desiccation and freezing conditions. Hypothetical molecular mechanisms suggest that the stabilization effect may be determined either by specific interactions of sugars with biological molecules or by the influence of sugars on the solvating shell of the biomolecule. To explore membrane-sugar interactions, we applied electron spin echo envelope modulation (ESEEM) spectroscopy, a pulsed version of electron paramagnetic resonance (EPR), to phospholipid bilayers with spin-labeled lipids added and solvated by aqueous deuterated sucrose and trehalose solutions. The phospholipids were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The spin-labeled lipids were 1,2-dipalmitoyl-sn-glycero-3-phospho(TEMPO)choline (T-PCSL), with spin-label TEMPO at the lipid polar headgroup. The deuterium ESEEM amplitude was calibrated using known concentrations of glassy deuterated sugar solvents. The data obtained indicated that the sugar concentration near the membrane surface obeyed a simple Langmuir model of monolayer adsorption, which assumes direct sugar-molecule bonding to the bilayer surface. PMID:26214261

  3. Electron paramagnetic resonance of the SO{4/3-} radical in barite and celestite

    NASA Astrophysics Data System (ADS)

    Ryabov, I. D.

    1995-09-01

    The electron paramagnetic resonance (EPR) study of gammaor x-ray-irradiated natural barite and celestite has revealed the presence of a radiation center with principal values of the g tensor and the A tensor [MHz] of hyperfine interaction (from the 33S isotope): gxx=1.9963, gyy=2.0073, gzz=2.0025, Axx=434, Ayy=447, Azz=528 in BaSO4, gxx=1.9990, gyy=2.0075, gzz=2.0027, Axx=426, Ayy=439, Azz=520 in SrSO4. The center has been identified as SO{3-/4}radical. The electron centers SO{4/3-}in barite have been found to be produced along with the hole centers SO{4/3-}, and maximum concentration of both centers is reached at a gamma-ray-radiation dose of about 5·105 Gy. UV or thermal treatment causes both centers to disappear. The SO{4/3-}radicals proved to be more thermally stable than the SO{4/3-}radicals: within about 0.5 h the latter disappear at 125° C, whereas the former do so at 180° C.

  4. Electron Paramagnetic Resonance Study of a Photosynthetic Microbial Mat and Comparison with Archean Cherts

    NASA Astrophysics Data System (ADS)

    Bourbin, M.; Derenne, S.; Gourier, D.; Rouzaud, J.-N.; Gautret, P.; Westall, F.

    2012-12-01

    Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts.

  5. Electron paramagnetic resonance study of a photosynthetic microbial mat and comparison with Archean cherts.

    PubMed

    Bourbin, M; Derenne, S; Gourier, D; Rouzaud, J-N; Gautret, P; Westall, F

    2012-12-01

    Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts.

  6. Electron paramagnetic resonance study of a photosynthetic microbial mat and comparison with Archean cherts.

    PubMed

    Bourbin, M; Derenne, S; Gourier, D; Rouzaud, J-N; Gautret, P; Westall, F

    2012-12-01

    Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts. PMID:23254854

  7. Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

    SciTech Connect

    Kovács, A.; Duchamp, M.; Boothroyd, C. B.; Dunin-Borkowski, R. E.; Ney, A.; Ney, V.; Galindo, P. L.; Kaspar, T. C.; Chambers, S. A.

    2013-12-28

    We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al{sub 2}O{sub 3}), as well as the Co:ZnO/Al{sub 2}O{sub 3} interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3–4 Co:ZnO layers next to the Al{sub 2}O{sub 3} substrate. The stacking fault density is in the range of 10{sup 17} cm{sup −3}. We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties.

  8. Electron paramagnetic resonance spectroscopy of Fe3+ ions in amethyst: thermodynamic potentials and magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Sivaramaiah, Gobburu; Lin, Jinru; Pan, Yuanming

    2011-02-01

    Single-crystal and powder electron paramagnetic resonance (EPR) spectroscopic studies of natural amethyst quartz, before and after isochronal annealing between 573 and 1,173 K, have been made from 90 to 294 K. Single-crystal EPR spectra confirm the presence of two substitutional Fe3+ centers. Powder EPR spectra are characterized by two broad resonance signals at g = ~10.8 and 4.0 and a sharp signal at g = 2.002. The sharp signal is readily attributed to the well-established oxygen vacancy electron center E 1'. However, the two broad signals do not correspond to any known Fe3+ centers in the quartz lattice, but are most likely attributable to Fe3+ clusters on surfaces. The absolute numbers of spins of the Fe3+ species at g = ~10.8 have been calculated from powder EPR spectra measured at temperatures from 90 to 294 K. These results have been used to extract thermodynamic potentials, including Gibbs energy of activation Δ G, activation energy E a, entropy of activation Δ S and enthalpy of activation Δ H for the Fe3+ species in amethyst. In addition, magnetic susceptibilities ( χ) have been calculated from EPR data at different temperatures. A linear relationship between magnetic susceptibility and temperature is consistent with the Curie-Weiss law. Knowledge about the stability and properties of Fe3+ species on the surfaces of quartz is important to better understanding of the reactivity, bioavailability and heath effects of iron in silica particles.

  9. Advanced Power Electronics Components

    NASA Technical Reports Server (NTRS)

    Schwarze, Gene E.

    2004-01-01

    This paper will give a description and status of the Advanced Power Electronics Materials and Components Technology program being conducted by the NASA Glenn Research Center for future aerospace power applications. The focus of this research program is on the following: 1) New and/or significantly improved dielectric materials for the development of power capacitors with increased volumetric efficiency, energy density, and operating temperature. Materials being investigated include nanocrystalline and composite ceramic dielectrics and diamond-like carbon films; 2) New and/or significantly improved high frequency, high temperature, low loss soft magnetic materials for the development of transformers/inductors with increased power/energy density, electrical efficiency, and operating temperature. Materials being investigated include nanocrystalline and nanocomposite soft magnetic materials; 3) Packaged high temperature, high power density, high voltage, and low loss SiC diodes and switches. Development of high quality 4H- and 6H- SiC atomically smooth substrates to significantly improve device performance is a major emphasis of the SiC materials program; 4) Demonstration of high temperature (> 200 C) circuits using the components developed above.

  10. Use of Electron Paramagnetic Resonance Spectroscopy to Evaluate the Redox State In Vivo

    PubMed Central

    SWARTZ, HAROLD M.; KHAN, NADEEM; KHRAMTSOV, VALERY V.

    2009-01-01

    The aim of this article is to provide an overview of how electron paramagnetic resonance (EPR) can be used to measure redox-related parameters in vivo. The values of this approach include that the measurements are made under fully physiological conditions, and some of the measurements cannot be made by other means. Three complementary approaches are used with in vivo EPR: the rate of reduction or reactions of nitroxides, spin trapping of free radicals, and measurements of thiols. All three approaches already have produced unique and useful information. The measurement of the rate of decrease of nitroxides technically is the simplest, but difficult to interpret because the measured parameter, reduction in the intensity of the nitroxide signal, can occur by several different mechanisms. In vivo spin trapping can provide direct evidence for the occurrence of specific free radicals in vivo and reflect relative changes, but accurate absolute quantification remains challenging. The measurement of thiols in vivo also appears likely to be useful, but its development as an in vivo technique is at an early stage. It seems likely that the use of in vivo EPR to measure redox processes will become an increasingly utilized and valuable tool. PMID:17678441

  11. Stabilization of reactive nitroxides using invasomes to allow prolonged electron paramagnetic resonance measurements.

    PubMed

    Haag, S F; Taskoparan, B; Bittl, R; Teutloff, C; Wenzel, R; Fahr, A; Chen, M; Lademann, J; Schäfer-Korting, M; Meinke, M C

    2011-01-01

    The detection of the antioxidative capacity of the skin is of great practical relevance since free radicals are involved in many skin damaging processes, including aging and inflammation. The nitroxide TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl) in combination with electron paramagnetic resonance spectroscopy was found suitable for measuring the antioxidative capacity since its reaction with reducing agents is considerably fast. Yet, in order to achieve longer measurement times, e.g. in inflammatory skin diseases, the stabilizing effect of an invasome (ultraflexible vesicle/liposome) suspension with TEMPO was investigated ex vivo on porcine skin and in vivo on human skin. Invasomes increased the measurement time ex vivo 2-fold and the reduction was significantly slowed down in vivo, which is due to membrane-associated and therefore protected TEMPO. Furthermore, TEMPO accumulation in the membrane phase as well as the decreasing polarity of the ultimate surroundings of TEMPO during skin penetration explains the stabilizing effect. Thus, an invasome suspension with TEMPO exhibits stabilizing effects ex vivo and in vivo. PMID:21822032

  12. Multi-frequency electron paramagnetic resonance study of irradiated human finger phalanxes

    NASA Astrophysics Data System (ADS)

    Zdravkova, M.; Vanhaelewyn, G.; Callens, F.; Gallez, B.; Debuyst, R.

    2005-10-01

    Electron paramagnetic resonance (EPR) is often used in dosimetry using biological samples such as teeth and bones. It is generally assumed that the radicals, formed after irradiation, are similar in both tissues as the mineral part of bone and tooth is carbonated hydroxyapatite. However, there is a lack of experimental evidence to support this assumption. The aim of the present study was to contribute to that field by studying powder and block samples of human finger phalanxes that were irradiated and analyzed by multi-frequency EPR. The results obtained from bones are different from the ones obtained in enamel by several respects: the ordering of the apatite crystallites is much smaller in bone, complicating the assignment of the observed CO 2- radicals to a specific location, and one type of CO 33- radical was only found in enamel. Moreover, a major difference was found in the non-CO 2- and non-CO 33- signals. The elucidation of the nature of these native signals (in bone and tooth enamel) still represents a big challenge.

  13. Oxymetry Deep in Tissues With Low-Frequency Electron Paramagnetic Resonance

    NASA Astrophysics Data System (ADS)

    Halpern, Howard J.; Yu, Cheng; Peric, Miroslav; Barth, Eugene; Grdina, David J.; Teicher, Beverly A.

    1994-12-01

    We have measured the oxygen concentration in the body water of murine FSa and NFSa fibrosarcomas using a new method for quantitative oxygen concentration determination deep in the tissues of a living animal. The measurement uses unusually low-frequency electron paramagnetic spectroscopy sensitive to substrate 7 cm deep in tissue, partially deuterated spin probes (spin labels of molecular mass 195, approximating that of glucose) whose distribution compartment can be targeted with facile adduct substitution, and novel analytic techniques. We show that the water-compartment oxygen concentration of the tumors decreases as the tumor size increases and also shows a trend to decrease as radiobiologic hypoxia increases. An oxymetric spectral image of the tumor is presented. The technique will improve with larger human tissue samples. It provides the potential to quantitatively assess tissue hypoxia in ischemic or preischemic states in stroke and myocardial infarction. It will allow direct assessment of tumor hypoxia to determine the usefulness of radiation and chemotherapy adjuvants directed to hypoxic cell compartments.

  14. Structural investigation and electron paramagnetic resonance of vanadyl doped alkali niobium borate glasses.

    PubMed

    Agarwal, A; Sheoran, A; Sanghi, S; Bhatnagar, V; Gupta, S K; Arora, M

    2010-03-01

    Glasses with compositions xNb(2)O(5).(30-x)M(2)O.69B(2)O(3) (where M=Li, Na, K; x=0, 4, 8 mol%) doped with 1 mol% V(2)O(5) have been prepared using normal melt quench technique. The IR transmission spectra of the glasses have been studied over the range 400-4000 cm(-1). The changes caused by the addition of Nb(2)O(5) on the structure of these glasses have been reported. The electron paramagnetic resonance spectra of VO(2+) ions in these glasses have been recorded in X-band (9.14 GHz) at room temperature (300 K). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) due to V(4+) ions which exist as VO(2+) ions in octahedral coordination with a tetragonal compression in the present glasses. The tetragonality of V(4+)O(6) complex decreases with increasing concentration of Nb(2)O(5). The 3d(xy) orbit contracts with increase in Nb(2)O(5):M(2)O ratio. Values of the theoretical optical basicity, Lambda(th), have also been reported.

  15. Electron paramagnetic resonance oxygen mapping (EPROM): direct visualization of oxygen concentration in tissue.

    PubMed

    Velan, S S; Spencer, R G; Zweier, J L; Kuppusamy, P

    2000-06-01

    Tissue oxygen content is a central parameter in physiology but is difficult to measure. We report a novel procedure for spatial mapping of oxygen by electron paramagnetic resonance (EPR) utilizing a spectral-spatial imaging data set, in which an EPR spectrum is obtained from each image volume element. From this data set, spatial maps corresponding to local spin density and maximum EPR spectral line amplitude are generated. A map of local EPR spectral linewidth is then computed. Because linewidth directly correlates with oxygen concentration, the linewidth image provides a map of oxygenation. This method avoids a difficulty inherent in other oxygen content mapping techniques using EPR, that is, the unwanted influence of local spin probe density on the image. We provide simulation results and data from phantom studies demonstrating the validity of this method. We then apply the method to map oxygen content in rat tail tissue and vasculature. This method provides a new, widely applicable, approach to direct visualization of oxygen concentration in living tissue. Magn Reson Med 43:804-809, 2000.

  16. Electron paramagnetic resonance measurements of absorbed dose in teeth from citizens of Ozyorsk.

    PubMed

    Wieser, A; Vasilenko, E; Aladova, E; Fattibene, P; Semiochkina, N; Smetanin, M

    2014-05-01

    In 1945, within the frame of the Uranium Project for the production of nuclear weapons, the Mayak nuclear facilities were constructed at the Lake Irtyash in the Southern Urals, Russia. The nuclear workers of the Mayak Production Association (MPA), who lived in the city of Ozyorsk, are the focus of epidemiological studies for the assessment of health risks due to protracted exposure to ionising radiation. Electron paramagnetic resonance measurements of absorbed dose in tooth enamel have already been used in the past, in an effort to validate occupational external doses that were evaluated in the Mayak Worker Dosimetry System. In the present study, 229 teeth of Ozyorsk citizens not employed at MPA were investigated for the assessment of external background exposure in Ozyorsk. The annually absorbed dose in tooth enamel from natural background radiation was estimated to be (0.7 ± 0.3) mGy. For citizens living in Ozyorsk during the time of routine noble gas releases of the MPA, which peaked in 1953, the average excess absorbed dose in enamel above natural background was (36 ± 29) mGy, which is consistent with the gamma dose obtained by model calculations. In addition, there were indications of possible accidental gaseous MPA releases that affected the population of Ozyorsk, during the early and late MPA operation periods, before 1951 and after 1960. PMID:24604722

  17. Simulation of Nitroxide Electron Paramagnetic Resonance Spectra from Brownian Trajectories and Molecular Dynamics Simulations

    PubMed Central

    DeSensi, Susan C.; Rangel, David P.; Beth, Albert H.; Lybrand, Terry P.; Hustedt, Eric J.

    2008-01-01

    A simulated continuous wave electron paramagnetic resonance spectrum of a nitroxide spin label can be obtained from the Fourier transform of a free induction decay. It has been previously shown that the free induction decay can be calculated by solving the time-dependent stochastic Liouville equation for a set of Brownian trajectories defining the rotational dynamics of the label. In this work, a quaternion-based Monte Carlo algorithm has been developed to generate Brownian trajectories describing the global rotational diffusion of a spin-labeled protein. Also, molecular dynamics simulations of two spin-labeled mutants of T4 lysozyme, T4L F153R1, and T4L K65R1 have been used to generate trajectories describing the internal dynamics of the protein and the local dynamics of the spin-label side chain. Trajectories from the molecular dynamics simulations combined with trajectories describing the global rotational diffusion of the protein are used to account for all of the dynamics of a spin-labeled protein. Spectra calculated from these combined trajectories correspond well to the experimental spectra for the buried site T4L F153R1 and the helix surface site T4L K65R1. This work provides a framework to further explore the modeling of the dynamics of the spin-label side chain in the wide variety of labeling environments encountered in site-directed spin labeling studies. PMID:18234808

  18. Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

    NASA Technical Reports Server (NTRS)

    Ahn, Myong K.; Eaton, Sandra S.; Eaton, Gareth R.; Meador, Mary Ann B.

    1997-01-01

    Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron Paramagnetic Resonance Imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of about 0.18 mm along a 2 mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2 mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 one-hour cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

  19. Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

    NASA Technical Reports Server (NTRS)

    Ahn, Myong K.; Eaton, Sandra S.; Eaton, Gareth R.; Meador, Mary Ann B.

    1997-01-01

    Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron paramagnetic resonance imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of approximately 0.18 mm along a 2-mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2-mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 1-h cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

  20. Isotope effect on electron paramagnetic resonance of boron acceptors in silicon

    NASA Astrophysics Data System (ADS)

    Stegner, A. R.; Tezuka, H.; Andlauer, T.; Stutzmann, M.; Thewalt, M. L. W.; Brandt, M. S.; Itoh, K. M.

    2010-09-01

    The fourfold degeneracy of the boron acceptor ground state in silicon, which is easily lifted by any symmetry-breaking perturbation, allows for a strong inhomogeneous broadening of the boron-related electron paramagnetic resonance (EPR) lines, e.g., by a random distribution of local strains. However, since EPR of boron acceptors in externally unstrained silicon was reported initially, neither the line shape nor the magnitude of the residual broadening observed in samples with high-crystalline purity were compatible with the low concentrations of carbon and oxygen point defects, being the predominant source of random local strain. Adapting a theoretical model which has been applied to understand the acceptor ground-state splitting in the absence of a magnetic field as an effect due to the presence of different silicon isotopes, we show that local fluctuations of the valence-band edge due to different isotopic configurations in the vicinity of the boron acceptors can quantitatively account for all inhomogeneous broadening effects in high-purity Si with a natural isotope composition. Our calculations show that such an isotopic perturbation also leads to a shift in the g value of different boron-related resonances, which we could verify in our experiments. Further, our results provide an independent test and verification of the valence-band offsets between the different Si isotopes determined in previous works.

  1. Disulfide-Linked Dinitroxides for Monitoring Cellular Thiol Redox Status through Electron Paramagnetic Resonance Spectroscopy.

    PubMed

    Legenzov, Eric A; Sims, Stephen J; Dirda, Nathaniel D A; Rosen, Gerald M; Kao, Joseph P Y

    2015-12-01

    Intracellular thiol-disulfide redox balance is crucial to cell health, and may be a key determinant of a cancer's response to chemotherapy and radiation therapy. The ability to assess intracellular thiol-disulfide balance may thus be useful not only in predicting responsiveness of cancers to therapy, but in assessing predisposition to disease. Assays of thiols in biology have relied on colorimetry or fluorimetry, both of which require UV-visible photons, which do not penetrate the body. Low-frequency electron paramagnetic resonance imaging (EPRI) is an emerging magnetic imaging technique that uses radio waves, which penetrate the body well. Therefore, in combination with tailored imaging agents, EPRI affords the opportunity to image physiology within the body. In this study, we have prepared water-soluble and membrane-permeant disulfide-linked dinitroxides, at natural isotopic abundance, and with D,(15)N-substitution. Thiols such as glutathione cleave the disulfides, with simple bimolecular kinetics, to yield the monomeric nitroxide species, with distinctive changes in the EPR spectrum. Using the D,(15)N-substituted disulfide-dinitroxide and EPR spectroscopy, we have obtained quantitative estimates of accessible intracellular thiol in cultured human lymphocytes. Our estimates are in good agreement with published measurements. This suggests that in vivo EPRI of thiol-disulfide balance is feasible. Finally, we discuss the constraints on the design of probe molecules that would be useful for in vivo EPRI of thiol redox status. PMID:26523485

  2. Identification of free radical intermediates in oxidized wine using electron paramagnetic resonance spin trapping.

    PubMed

    Elias, Ryan J; Andersen, Mogens L; Skibsted, Leif H; Waterhouse, Andrew L

    2009-05-27

    Free radicals are thought to be key intermediates in the oxidation of wine, but their nature has not been established. Electron paramagnetic resonance spectroscopy was used to detect and identify several free radical species in wine under oxidative conditions with the aid of spin traps. The 1-hydroxylethyl radical was the sole radical species observed when α-(4-pyridyl-1-oxide)-N-tert-butylnitrone was used as a spin trap in a heated (55 °C), low-sulfite (15 mg L(-1)) red wine. This radical appears to arise from ethanol oxidation via the hydroxyl radical, and this latter species was confirmed by using a high concentration (1.5 M) of the 5,5-dimethylpyrroline-N-oxide spin trap, thus providing the first direct evidence of the Fenton reaction in wine. Hydroxyl radical formation in wine was corroborated by converting hydroxyl radicals to methyl radicals by its reaction with dimethyl sulfoxide. The novel spin trap 5-tert-butoxycarbonyl 5-methyl-1-pyrroline N-oxide was also used in this study to identify sulfite radicals in wine for the first time. This spin trap has also been shown to trap hydroperoxyl radicals, the generation of which is predicted in wine; however, no evidence of this species was observed. PMID:19358607

  3. Robustness assessment of 1-d electron paramagnetic resonance for improved magnetic nanoparticle reconstructions.

    PubMed

    Coene, Annelies; Crevecoeur, Guillaume; Dupre, Luc

    2015-06-01

    Electron paramagnetic resonance (EPR) is a sensitive measurement technique which can be used to recover the 1-D spatial distribution of magnetic nanoparticles (MNP) noninvasively. This can be achieved by solving an inverse problem that requires a numerical model for interpreting the EPR measurement data. This paper assesses the robustness of this technique by including different types of errors such as setup errors, measurement errors, and sample positioning errors in the numerical model. The impact of each error is estimated for different spatial MNP distributions. Additionally, our error models are validated by comparing the simulated impact of errors to the impact on lab EPR measurements. Furthermore, we improve the solution of the inverse problem by introducing a combination of truncated singular value decomposition and nonnegative least squares. This combination enables to recover both smooth and discontinuous MNP distributions. From this analysis, conclusions are drawn to improve MNP reconstructions with EPR and to state requirements for using EPR as a 2-D and 3-D imaging technique for MNP. PMID:25667347

  4. Stabilization of reactive nitroxides using invasomes to allow prolonged electron paramagnetic resonance measurements.

    PubMed

    Haag, S F; Taskoparan, B; Bittl, R; Teutloff, C; Wenzel, R; Fahr, A; Chen, M; Lademann, J; Schäfer-Korting, M; Meinke, M C

    2011-01-01

    The detection of the antioxidative capacity of the skin is of great practical relevance since free radicals are involved in many skin damaging processes, including aging and inflammation. The nitroxide TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl) in combination with electron paramagnetic resonance spectroscopy was found suitable for measuring the antioxidative capacity since its reaction with reducing agents is considerably fast. Yet, in order to achieve longer measurement times, e.g. in inflammatory skin diseases, the stabilizing effect of an invasome (ultraflexible vesicle/liposome) suspension with TEMPO was investigated ex vivo on porcine skin and in vivo on human skin. Invasomes increased the measurement time ex vivo 2-fold and the reduction was significantly slowed down in vivo, which is due to membrane-associated and therefore protected TEMPO. Furthermore, TEMPO accumulation in the membrane phase as well as the decreasing polarity of the ultimate surroundings of TEMPO during skin penetration explains the stabilizing effect. Thus, an invasome suspension with TEMPO exhibits stabilizing effects ex vivo and in vivo.

  5. Training Effects on ROS Production Determined by Electron Paramagnetic Resonance in Master Swimmers

    PubMed Central

    Mrakic-Sposta, Simona; Gussoni, Maristella; Porcelli, Simone; Pugliese, Lorenzo; Pavei, Gaspare; Bellistri, Giuseppe; Montorsi, Michela; Tacchini, Philippe; Vezzoli, Alessandra

    2015-01-01

    Acute exercise induces an increase in Reactive Oxygen Species (ROS) production dependent on exercise intensity with highest ROS amount generated by strenuous exercise. However, chronic repetition of exercise, that is, exercise training, may reduce exercise-induced oxidative stress. Aim of this study was to evaluate the effects of 6-weeks high-intensity discontinuous training (HIDT), characterized by repeated variations of intensity and changes of redox potential, on ROS production and antioxidant capacity in sixteen master swimmers. Time course changes of ROS generation were assessed by Electron Paramagnetic Resonance in capillary blood by a microinvasive approach. An incremental arm-ergometer exercise (IE) until exhaustion was carried out at both before (PRE) and after (POST) training (Trg) period. A significant (P < 0.01) increase of ROS production from REST to the END of IE in PRE Trg (2.82 ± 0.66 versus 3.28 ± 0.66 µmol·min−1) was observed. HIDT increased peak oxygen consumption (36.1 ± 4.3 versus 40.6 ± 5.7 mL·kg−1·min−1 PRE and POST Trg, resp.) and the antioxidant capacity (+13%) while it significantly decreased the ROS production both at REST (−20%) and after IE (−25%). The observed link between ROS production, adaptive antioxidant defense mechanisms, and peak oxygen consumption provides new insight into the correlation between ROS response pathways and muscle metabolic function. PMID:25874024

  6. Electron paramagnetic resonance spectroscopy studies of Eu-Y and coexchanged EuFe-Y zeolites

    SciTech Connect

    Ulla, M.A.; Millman, W.S. ); Aparicio, L.A.; Balse, V.R.; Dumesic, J.A. )

    1990-05-01

    Electron paramagnetic resonance (EPR) was used to probe the oxidation state of europium and the location of divalent europium cations in Eu-Y and EuFe-Y zeolite samples. Europium was present as trivalent cations following treatment in O{sub 2} at 770 K. Treatments in H{sub 2} or CO at 770 K led to formation of divalent cations, and perhaps also caused some reduction to lower oxidation states. Three EPR signals were observed for Eu{sup 2+}, giving rise to effective g values of 3, 4.9, and 6. The first and last signals are interpreted as being due to Eu{sup 2+} cations at sites I and II, respectively, while the latter signal is due to Eu{sup 2+} cations at sites I{prime} and II{prime}. The majority of the Eu{sup 2+} cations are at site I, and the amount of Eu at this site can be increased by reducing the sample in H{sub 2}, compared with reduction in CO. The presence of europium in site I forces the Fe{sup 2+} cations to occupy sites of lower coordination in the sodalite unit (sites I{prime} and II{prime}) and in the supercages (sites II and III{prime}).

  7. Novel antioxidant capacity assay for lipophilic compounds using electron paramagnetic resonance spectroscopy

    PubMed Central

    Takahashi, Yushi; Ichimori, Kohji; Okano, Masahito; Goto, Hirofumi

    2015-01-01

    A novel antioxidant capacity assay for lipophilic compounds was developed using electron paramagnetic resonance (EPR) spectroscopy. The assay is based on antioxidant’s scavenging ability against the tert-butoxyl radical generated photolytically from di-tert-butyl peroxide in ethyl acetate, and named the tert-butoxyl-based antioxidant capacity (BAC) assay. The radical was trapped by spin trap, 5,5-dimethyl-1-pyrroline-N-oxide, and EPR signal intensity of the spin adduct was used as a quantitative marker of radical levels. Signal intensity decreased in a dose-dependent manner in the presence of an antioxidant that competitively reacts with the radical, which was utilized to evaluate BAC values. The BAC method enabled the accurate estimation of antioxidant capacity for lipophilic materials that may counteract lipid peroxidation in biological membranes. The BAC values for quercetin and caffeic acid are 0.639 ± 0.020 and 0.118 ± 0.012 trolox equivalents, respectively, which are much smaller than values obtained by other aqueous methods such as H-ORAC and ORAC-EPR. Thus, antioxidants present in a non-aqueous environment should be evaluated using a non-aqueous system. In combination with in situ ascorbate reduction, the BAC method was capable of accurately determining the antioxidant capacity of water-insoluble materials that may be reduced in living cells. PMID:25759515

  8. A study of Roman glass by reflectance and electron paramagnetic resonance spectroscopies

    NASA Astrophysics Data System (ADS)

    Mirti, P.; Ferrari, R. P.; Laurenti, E.; Casoli, A.

    1993-08-01

    Reflectance and electron paramagnetic resonance (EPR) spectroscopies were used to study 25 fragments of Roman glass. Colour coordinates were used for an unbiased classification of the glasses in colour groups, which accounted for the presence of blue, blue-green, green, yellow-green, yellow and purple samples. Reflectance spectra were recorded in the 250-2500 nm wavelength range and showed absorption bands characteristic of Fe II, Fe III and Mn III ions; furthermore, Co II and Cu II bands were observed in the spectra of the blue glasses. A decrease of the absorbance ratio of Fe II to Fe III ions was observed moving from blue-green to green and yellow-green glasses; however, yellow fragments still proved to be reduced glasses. EPR spectra displayed the characteristic patterns of Fe III and Mn II ions, with g-values in the 2-5 interval and spectral features depending on the relative content of the two elements. The characteristic pattern of the V IV ion ( g ≈ 2) and signals due to the formation of iron-sulphur complexes ( g ≈ 6) appeared in the spectrum of a dark yellow glass, recorded at 77 K.

  9. Fe(3+) ions in alkali lead tetraborate glasses--an electron paramagnetic resonance and optical study.

    PubMed

    Chakradhar, R P Sreekanth; Sivaramaiah, G; Rao, J Lakshmana; Gopal, N O

    2005-11-01

    Glass systems of composition 90R(2)B(4)O(7)+9PbO+1Fe(2)O(3) (R=Li, Na and K) and 90Li(2)B(4)O(7)+(10-x)PbO+xFe(2)O(3) (x=0.5, 1, 3, 4, 5, 7 and 9 mol %) have been investigated by means of electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra exhibit three resonance signals at g approximately 6.0, 4.2 and 2.0. The resonances at g approximately 6.0 and 4.2 are attributed to Fe(3+) ions in rhombic and axial symmetry sites, respectively. The g approximately 2.0 resonance signal is due to two or more Fe(3+) ions coupled together with dipolar interaction. The EPR spectra of 1 mol % of Fe(2)O(3) doped in lithium lead tetraborate glass samples have been studied at different temperatures (123-433 K). The intensity of g approximately 4.2 resonance signal decreases and the intensity of g approximately 2.0 resonance signal increases with the increase of temperature. The line widths are found to be independent of temperature. The EPR spectra exhibit a marked concentration dependence on iron content. A decrease in intensity for the resonance signal at g approximately 4.2 with increase in iron content for more than 4 mol % has been observed in lithium lead tetraborate glass samples and this has been attributed to the formation of Fe(3+) ion clusters in the glass samples. The paramagnetic susceptibility (chi) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/chi versus T graph. The optical absorption spectrum of Fe(3+) ions in lithium lead tetraborate glasses exhibits three bands characteristic of Fe(3+) ions in an octahedral symmetry. The crystal field parameter D(q) and the Racah interelectronic repulsion parameters B and C have also been evaluated. The value of interelectronic repulsion parameter B (825 cm(-1)) obtained in the present work suggests that the bonding is moderately covalent.

  10. Advanced electron microscopy for advanced materials.

    PubMed

    Van Tendeloo, Gustaaf; Bals, Sara; Van Aert, Sandra; Verbeeck, Jo; Van Dyck, Dirk

    2012-11-01

    The idea of this Review is to introduce newly developed possibilities of advanced electron microscopy to the materials science community. Over the last decade, electron microscopy has evolved into a full analytical tool, able to provide atomic scale information on the position, nature, and even the valency atoms. This information is classically obtained in two dimensions (2D), but can now also be obtained in 3D. We show examples of applications in the field of nanoparticles and interfaces.

  11. Pulse radiolysis of alkanes: A time-resolved electron paramagnetic resonance study

    SciTech Connect

    Shkrob, I.A.; Trifunac, A.D.

    1994-02-14

    Time-resolved spin-echo-detected electron paramagnetic resonance (EPR) was applied to examine short-lived alkyl radicals formed in pulse radiolysis of liquid alkanes. It was found that the ratio of yields of penultimate and interior radicals in n-alkanes at the instant of their generation is temperature-independent and is ca. 1.25 times greater than the statistical quantity. This higher-than-statistical production of penultimate radicals indicates that the fast ion molecule reactions involving radical cations are a significant route of radical generation. The analysis of spin-echo kinetics in n-alkanes suggests that the alkyl radicals are emissively polarized in spur reactions. this initial polarization rapidly increases with shortening of the aliphatic chain. Another finding is that a long-chain structure of these radicals results in much higher rate of Heisenberg spin exchange relative to the recombination rate. The relative yields of hydrogen abstraction and fragmentation for various branched alkanes are estimated. It is concluded that the fragmentation occurs prior to the formation of radicals in an excited precursor species. Effects of phenolic and alkene additives in radiolysis of n-alkanes are examined. It is demonstrated that phenoxy radicals are produced in dissociative capture of electrons and alkane holes. Another route is a reaction of phenols with free hydrogen atoms. A rapid transfer of singlet correlation from the geminate radical ion pairs is responsible for unusual polarization patterns in the phenoxy and cyclohexadienyl radicals. The significance of these results in the context of cross-linking in polyethylene and higher paraffins is discussed. 56 refs.

  12. Triplet State Delocalization in a Conjugated Porphyrin Dimer Probed by Transient Electron Paramagnetic Resonance Techniques

    PubMed Central

    2015-01-01

    The delocalization of the photoexcited triplet state in a linear butadiyne-linked porphyrin dimer is investigated by time-resolved and pulse electron paramagnetic resonance (EPR) with laser excitation. The transient EPR spectra of the photoexcited triplet states of the porphyrin monomer and dimer are characterized by significantly different spin polarizations and an increase of the zero-field splitting parameter D from monomer to dimer. The proton and nitrogen hyperfine couplings, determined using electron nuclear double resonance (ENDOR) and X- and Q-band HYSCORE, are reduced to about half in the porphyrin dimer. These data unequivocally prove the delocalization of the triplet state over both porphyrin units, in contrast to the conclusions from previous studies on the triplet states of closely related porphyrin dimers. The results presented here demonstrate that the most accurate estimate of the extent of triplet state delocalization can be obtained from the hyperfine couplings, while interpretation of the zero-field splitting parameter D can lead to underestimation of the delocalization length, unless combined with quantum chemical calculations. Furthermore, orientation-selective ENDOR and HYSCORE results, in combination with the results of density functional theory (DFT) calculations, allowed determination of the orientations of the zero-field splitting tensors with respect to the molecular frame in both porphyrin monomer and dimer. The results provide evidence for a reorientation of the zero-field splitting tensor and a change in the sign of the zero-field splitting D value. The direction of maximum dipolar coupling shifts from the out-of-plane direction in the porphyrin monomer to the vector connecting the two porphyrin units in the dimer. This reorientation, leading to an alignment of the principal optical transition moment and the axis of maximum dipolar coupling, is also confirmed by magnetophotoselection experiments. PMID:25914154

  13. Electron Paramagnetic Resonance and Photoluminescence Studies of LaMgAl11O19:Mn2+ Green Phosphors

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Chakradhar, R. P. S.; Rao, J. L.; Dhoble, S. J.; Kim, S. H.

    2014-09-01

    Manganese-doped LaMgAl11O19 powder has been prepared by an easy combustion method. Powder x-ray diffraction and scanning electron microscopy have been used to characterize the as-prepared phosphor. The electron paramagnetic resonance (EPR) spectrum of LaMgAl11O19:Mn2+ phosphor exhibits six-line hyperfine structure centered at g ≈ 1.973. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) for the resonance signal at g ≈ 1.973 have been calculated as a function of temperature. The photoluminescence spectrum exhibits green emission at 516 nm, which is attributed to 4T1 → 6A1 transition of Mn2+ ions. From EPR and luminescence studies, it is observed that Mn2+ ions occupy Mg2+ sites and Mn2+ ions are located at tetrahedral sites in the prepared phosphors.

  14. Lipid chain dynamics in stratum corneum studied by spin label electron paramagnetic resonance.

    PubMed

    Alonso, A; Meirelles, N C; Tabak, M

    2000-02-01

    The lipid chain motions in stratum corneum (SC) membranes have been studied through electron paramagnetic resonance (EPR) spectroscopy of stearic acid spin-labeled at the 5th, 12th and 16th carbon atom positions of the acyl chain. Lipids have been extracted from SC with a series of chloroform/methanol mixtures, in order to compare the molecular dynamics and the thermotropic behavior in intact SC, lipid-depleted SC (containing covalently bound lipids of the corneocyte envelope) and dispersion of extracted SC lipids. The segmental motion of 5- and 12-doxylstearic acid (5- and 12-DSA) and the rotational correlation time of 16-doxylstearic acid (16-DSA) showed that the envelope lipids are more rigid and the extracted lipids are more fluid than the lipids of the intact SC over the range of temperature measured. The lower fluidity observed for the corneocyte envelope, that may be caused mainly due to lipid-protein interactions, suggests a major contribution of this lipid domain to the barrier function of SC. Changes in the activation energy for reorientational diffusion of the 16-DSA spin label showed apparent phase transitions around 54 degrees C, for the three SC samples. Some lipid reorganization may occur in SC above 54 degrees C, in agreement with results reported from studies with several other techniques. This reorganization is sensitive to the presence of the extractable intercellular lipids, being different in the lipid-depleted sample as compared to native SC and lipid dispersion. The results contribute to the understanding of alkyl chain packing and mobility in the SC membranes, which are involved in the mechanisms that control the permeability of different compounds through skin, suggesting an important involvement of the envelope in the skin barrier.

  15. Radiation Dosimetry Study in Dental Enamel of Human Tooth Using Electron Paramagnetic Resonance

    NASA Astrophysics Data System (ADS)

    De, Tania; Romanyukha, Alex; Pass, Barry; Misra, Prabhakar

    2009-07-01

    Electron paramagnetic resonance (EPR) dosimetry of tooth enamel is used for individual dose reconstruction following radiation accidents. The purpose of this study is to develop a rapid, minimally invasive technique of obtaining a sample of dental enamel small enough to not disturb the structure and functionality of a tooth and to improve the sensitivity of the spectral signals using X-band (9.4 GHz) and Q-band (34 GHz) EPR technique. In this study EPR measurements in X-band were performed on 100 mg isotropic powdered enamel samples and Q-band was performed on 4 mg, 1×1×3 mm enamel biopsy samples. All samples were obtained from discarded teeth collected during normal dental treatment. To study the variation of the Radiation-Induced Signal (RIS) at different orientations in the applied magnetic field, samples were placed in the resonance cavity for Q-band EPR. X-band EPR measurements were performed on 100 mg isotropic powdered enamel samples. In X-band spectra, the RIS is distinct from the "native" radiation-independent signal only for doses >0.5 Gy. Q-band, however, resolves the RIS and "native" signals and improves sensitivity by a factor of 20, enabling measurements in 2-4 mg tooth enamel samples, as compared to 100 mg for X-band. The estimated lower limit of Q-band dose measurement is 0.5 Gy. Q-band EPR enamel dosimetry results in greater sensitivity and smaller sample size through enhanced spectral resolution. Thus, this can be a valuable technique for population triage in the event of detonation of a radiation dispersal device ("dirty" bomb) or other radiation event with massive casualties. Further, the small 4 mg samples can be obtained by a minimally-invasive biopsy technique.

  16. A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

    NASA Astrophysics Data System (ADS)

    Sidabras, Jason W.; Varanasi, Shiv K.; Mett, Richard R.; Swarts, Steven G.; Swartz, Harold M.; Hyde, James S.

    2014-10-01

    A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

  17. Study of nanostructural organization of ionic liquids by electron paramagnetic resonance spectroscopy.

    PubMed

    Merunka, Dalibor; Peric, Mirna; Peric, Miroslav

    2015-02-19

    The X-band electron paramagnetic resonance spectroscopy (EPR) of a stable, spherical nitroxide spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDTO) has been used to study the nanostructural organization of a series of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids (ILs) with alkyl chain lengths from two to eight carbons. By employing nonlinear least-squares fitting of the EPR spectra, we have obtained values of the rotational correlation time and hyperfine coupling splitting of pDTO to high precision. The rotational correlation time of pDTO in ILs and squalane, a viscous alkane, can be fit very well to a power law functionality with a singular temperature, which often describes a number of physical quantities measured in supercooled liquids. The viscosity of the ILs and squalane, taken from the literature, can also be fit to the same power law expression, which means that the rotational correlation times and the ionic liquid viscosities have similar functional dependence on temperature. The apparent activation energy of both the rotational correlation time of pDTO and the viscous flow of ILs and squalane increases with decreasing temperature; in other words, they exhibit strong non-Arrhenius behavior. The rotational correlation time of pDTO as a function of η/T, where η is the shear viscosity and T is the temperature, is well described by the Stokes-Einstein-Debye (SED) law, while the hydrodynamic probe radii are solvent dependent and are smaller than the geometric radius of the probe. The temperature dependence of hyperfine coupling splitting is the same in all four ionic liquids. The value of the hyperfine coupling splitting starts decreasing with increasing alkyl chain length in the ionic liquids in which the number of carbons in the alkyl chain is greater than four. This decrease together with the decrease in the hydrodynamic radius of the probe indicates a possible existence of nonpolar nanodomains.

  18. Multiharmonic electron paramagnetic resonance for extended samples with both narrow and broad lines

    NASA Astrophysics Data System (ADS)

    Yu, Zhelin; Tseytlin, Mark; Eaton, Sandra S.; Eaton, Gareth R.

    2015-05-01

    Multiharmonic electron paramagnetic resonance spectroscopy was demonstrated for two samples with both narrow and broad lines: (i) α,γ-Bisdiphenylene-β-phenylallyl (BDPA) with ΔBpp of 0.85 G plus ultramarine blue with ΔBpp of 17 G, and (ii) a nitroxide radical immobilized in sucrose octaacetate. Modulation amplitudes up to 17 G at 41 kHz were generated with a rapid scan coil driver and Litz wire coils that provide uniform magnetic field sweeps over samples with heights of 5 mm. Data were acquired with a 2-D experiment in the Xepr software through the transient signal path of a Bruker E500T and digitized in quadrature with a Bruker SpecJet II. Signals at the modulation frequency and its harmonics were calculated by digital phase-sensitive detection. The number of harmonics with signal intensity greater than noise increases as the ratio of the modulation amplitude to the narrowest peak increases. Spectra reconstructed by the multiharmonic method from data obtained with modulation amplitudes up to five times the peak-to-peak linewidths of the narrowest features have linewidths that are broadened by up to only about 10% relative to linewidths in spectra obtained at low modulation amplitudes. The signal-to-noise improves with increasing modulation amplitude up to the point where the modulation amplitude is slightly larger than the linewidth of the narrowest features. If this high a modulation amplitude had been used in conventional methodology the linewidth of the narrowest features would have been severely broadened. The multiharmonic reconstruction methodology means that the selection of the modulation amplitude that can be used without spectral distortion is no longer tightly tied to the linewidth of the narrowest line.

  19. Thermoluminescence, electron paramagnetic resonance and optical absorption in natural and synthetic rhodonite crystals

    NASA Astrophysics Data System (ADS)

    Paião, J. R. B.; Watanabe, S.

    2008-10-01

    Thermoluminescence, electron paramagnetic resonance and optical absorption properties of rhodonite, a natural silicate mineral, have been investigated and compared to those of synthetic crystal, pure and doped. The TL peaks grow linearly for radiation dose up to 4 kGy, and then saturate. In all the synthetic samples, 140 and 340°C TL peaks are observed; the difference occurs in their relative intensities, but only 340°C peak grows strongly for high doses. Al2O3 and Al2O3 + CaO-doped synthetic samples presented several decades intenser TL compared to that of synthetic samples doped with other impurities. A heating rate of 4°C/s has been used in all the TL readings. The EPR spectrum of natural rhodonite mineral has only one huge signal around g = 2.0 with width extending from 1,000 to 6,000 G. This is due to Mn dipolar interaction, a fact proved by numerical calculation based on Van Vleck dipolar broadening expression. The optical absorption spectrum is rich in absorption bands in near-UV, visible and near-IR intervals. Several bands in the region from 540 to 340 nm are interpreted as being due to Mn3+ in distorted octahedral environment. A broad and intense band around 1,040 nm is due to Fe2+. It decays under heating up to 900°C. At this temperature it is reduced by 80% of its original intensity. The pink, natural rhodonite, heated in air starts becoming black at approximately 600°C.

  20. A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

    SciTech Connect

    Sidabras, Jason W.; Varanasi, Shiv K.; Hyde, James S.; Mett, Richard R.; Swarts, Steven G.; Swartz, Harold M.

    2014-10-15

    A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg{sup 2+} doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

  1. A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

    PubMed Central

    Sidabras, Jason W.; Varanasi, Shiv K.; Mett, Richard R.; Swarts, Steven G.; Swartz, Harold M.; Hyde, James S.

    2014-01-01

    A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown. PMID:25362434

  2. Electron paramagnetic resonance studies on conformation states and metal ion exchange properties of vanadium bromoperoxidase

    SciTech Connect

    de Boer, E.; Boon, K.; Wever, R.

    1988-03-08

    An electron paramagnetic resonance (EPR) study was carried out to examine structural aspects of vanadium-containing bromoperoxidase from the brown seaweed Ascophyllum nodosum. At high pH, the reduced form of bromoperoxidase showed an apparently axially symmetric EPR signal with 16 hyperfine lines. When the pH was lowered, a new EPR spectrum was formed. When EPR spectra of the reduced enzyme were recorded in the pH range from 4.2 to 8.4, it appeared that these changes were linked to a functional group with an apparent pK/sub a/ of about 5.4. In D/sub 2/O this value for the pK/sub a/ was 5.3. It is suggested that these effects arise from protonation of histidine or aspartate/glutamate residues near the metal ion. The values for the isotropic hyperfine coupling constant of the reduced enzyme at both high and low pH are also consistent with a ligand field containing nitrogen and/or oxygen donor atoms. When reduced bromoperoxidase was dissolved in D/sub 2/O or H/sub 2//sup 17/O instead of H/sub 2//sup 16/O, vanadium (IV) hyperfine line widths were markedly affected, demonstrating that water is a ligand of the metal ion. Together with previous work these findings suggest that vanadium (IV) is not involved in catalytic turnover and confirm the model in which the vanadium (V) ion of the native enzyme only serves to bind both hydrogen peroxide and bromide. After excess vanadate was added to a homogeneous preparation of purified bromoperoxidase, the extent of vanadium bound to the protein increased from 0.5 to 1.1, with a concomitant enhancement of enzymic activity. Finally, it is demonstrated that both vanadate (VO/sub 4//sup 3 -/) and molybdate (MoO/sub 4//sup 2 -/) compete for the same site on apobromoperoxidase.

  3. Tooth Retrospective Dosimetry Using Electron Paramagnetic Resonance: Influence of Irradiated Dental Composites.

    PubMed

    Desmet, Céline M; Djurkin, Andrej; Dos Santos-Goncalvez, Ana Maria; Dong, Ruhong; Kmiec, Maciej M; Kobayashi, Kyo; Rychert, Kevin; Beun, Sébastien; Leprince, Julian G; Leloup, Gaëtane; Levêque, Philippe; Gallez, Bernard

    2015-01-01

    In the aftermath of a major radiological accident, the medical management of overexposed individuals will rely on the determination of the dose of ionizing radiations absorbed by the victims. Because people in the general population do not possess conventional dosimeters, after the fact dose reconstruction methods are needed. Free radicals are induced by radiations in the tooth enamel of victims, in direct proportion to dose, and can be quantified using Electron Paramagnetic Resonance (EPR) spectrometry, a technique that was demonstrated to be very appropriate for mass triage. The presence of dimethacrylate based restorations on teeth can interfere with the dosimetric signal from the enamel, as free radicals could also be induced in the various composites used. The aim of the present study was to screen irradiated composites for a possible radiation-induced EPR signal, to characterize it, and evaluate a possible interference with the dosimetric signal of the enamel. We investigated the most common commercial composites, and experimental compositions, for a possible class effect. The effect of the dose was studied between 10 Gy and 100 Gy using high sensitivity X-band spectrometer. The influence of this radiation-induced signal from the composite on the dosimetric signal of the enamel was also investigated using a clinical L-Band EPR spectrometer, specifically developed in the EPR center at Dartmouth College. In X-band, a radiation-induced signal was observed for high doses (25-100 Gy); it was rapidly decaying, and not detected after only 24 h post irradiation. At 10 Gy, the signal was in most cases not measurable in the commercial composites tested, with the exception of 3 composites showing a significant intensity. In L-band study, only one irradiated commercial composite influenced significantly the dosimetric signal of the tooth, with an overestimation about 30%. In conclusion, the presence of the radiation-induced signal from dental composites should not

  4. Comparative electron paramagnetic resonance study of radical intermediates in turnip peroxidase isozymes.

    PubMed

    Ivancich, A; Mazza, G; Desbois, A

    2001-06-12

    The occurrence of isozymes in plant peroxidases is poorly understood. Turnip roots contain seven season-dependent isoperoxidases with distinct physicochemical properties. In the work presented here, multifrequency electron paramagnetic resonance spectroscopy has been used to characterize the Compound I intermediate obtained by the reaction of turnip isoperoxidases 1, 3, and 7 with hydrogen peroxide. The broad (2500 G) Compound I EPR spectrum of all three peroxidases was consistent with the formation of an exchange-coupled oxoferryl-porphyrinyl radical species. A dramatic pH dependence of the exchange interaction of the [Fe(IV)=O por(*+)] intermediate was observed for all three isoperoxidases and for a pH range of 4.5-7.7. This result provides substantial experimental evidence for previous proposals concerning the protein effect on the ferro- or antiferromagnetic character of the exchange coupling of Compound I based on model complexes. Turnip isoperoxidase 7 exhibited an unexpected pH effect related to the nature of the Compound I radical. At basic pH, a narrow radical species ( approximately 50 G) was formed together with the porphyrinyl radical. The g anisotropy of the narrow radical Delta(g) = 0.0046, obtained from the high-field (190 and 285 GHz) EPR spectrum, was that expected for tyrosyl radicals. The broad g(x) edge of the Tyr* spectrum centered at a low g(x) value (2.00660) strongly argues for a hydrogen-bonded tyrosyl radical in a heterogeneous microenvironment. The relationship between tyrosyl radical formation and the higher redox potential of turnip isozyme 7, as compared to that of isozyme 1, is discussed. PMID:11389600

  5. Application of Electron Paramagnetic Resonance (EPR) Oximetry to Monitor Oxygen in Wounds in Diabetic Models

    PubMed Central

    Desmet, Céline M.; Lafosse, Aurore; Vériter, Sophie; Porporato, Paolo E.; Sonveaux, Pierre; Dufrane, Denis; Levêque, Philippe; Gallez, Bernard

    2015-01-01

    A lack of oxygen is classically described as a major cause of impaired wound healing in diabetic patients. Even if the role of oxygen in the wound healing process is well recognized, measurement of oxygen levels in a wound remains challenging. The purpose of the present study was to assess the value of electron paramagnetic resonance (EPR) oximetry to monitor pO2 in wounds during the healing process in diabetic mouse models. Kinetics of wound closure were carried out in streptozotocin (STZ)-treated and db/db mice. The pO2 was followed repeatedly during the healing process by 1 GHz EPR spectroscopy with lithium phthalocyanine (LiPc) crystals used as oxygen sensor in two different wound models: a full-thickness excisional skin wound and a pedicled skin flap. Wound closure kinetics were dramatically slower in 12-week-old db/db compared to control (db/+) mice, whereas kinetics were not statistically different in STZ-treated compared to control mice. At the center of excisional wounds, measurements were highly influenced by atmospheric oxygen early in the healing process. In pedicled flaps, hypoxia was observed early after wounding. While reoxygenation occurred over time in db/+ mice, hypoxia was prolonged in the diabetic db/db model. This observation was consistent with impaired healing and microangiopathies observed using intravital microscopy. In conclusion, EPR oximetry using LiPc crystals as the oxygen sensor is an appropriate technique to follow wound oxygenation in acute and chronic wounds, in normal and diabetic animals. Nevertheless, the technique is limited for measurements in pedicled skin flaps and cannot be applied to excisional wounds in which diffusion of atmospheric oxygen significantly affects the measurements. PMID:26659378

  6. A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces.

    PubMed

    Sidabras, Jason W; Varanasi, Shiv K; Mett, Richard R; Swarts, Steven G; Swartz, Harold M; Hyde, James S

    2014-10-01

    A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg(2+) doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

  7. Application of Electron Paramagnetic Resonance (EPR) Oximetry to Monitor Oxygen in Wounds in Diabetic Models.

    PubMed

    Desmet, Céline M; Lafosse, Aurore; Vériter, Sophie; Porporato, Paolo E; Sonveaux, Pierre; Dufrane, Denis; Levêque, Philippe; Gallez, Bernard

    2015-01-01

    A lack of oxygen is classically described as a major cause of impaired wound healing in diabetic patients. Even if the role of oxygen in the wound healing process is well recognized, measurement of oxygen levels in a wound remains challenging. The purpose of the present study was to assess the value of electron paramagnetic resonance (EPR) oximetry to monitor pO2 in wounds during the healing process in diabetic mouse models. Kinetics of wound closure were carried out in streptozotocin (STZ)-treated and db/db mice. The pO2 was followed repeatedly during the healing process by 1 GHz EPR spectroscopy with lithium phthalocyanine (LiPc) crystals used as oxygen sensor in two different wound models: a full-thickness excisional skin wound and a pedicled skin flap. Wound closure kinetics were dramatically slower in 12-week-old db/db compared to control (db/+) mice, whereas kinetics were not statistically different in STZ-treated compared to control mice. At the center of excisional wounds, measurements were highly influenced by atmospheric oxygen early in the healing process. In pedicled flaps, hypoxia was observed early after wounding. While reoxygenation occurred over time in db/+ mice, hypoxia was prolonged in the diabetic db/db model. This observation was consistent with impaired healing and microangiopathies observed using intravital microscopy. In conclusion, EPR oximetry using LiPc crystals as the oxygen sensor is an appropriate technique to follow wound oxygenation in acute and chronic wounds, in normal and diabetic animals. Nevertheless, the technique is limited for measurements in pedicled skin flaps and cannot be applied to excisional wounds in which diffusion of atmospheric oxygen significantly affects the measurements. PMID:26659378

  8. Electron paramagnetic resonance method for the quantitative assay of ketoconazole in pharmaceutical preparations.

    PubMed

    Morsy, Mohamed A; Sultan, Salah M; Dafalla, Hatim

    2009-08-15

    In this study, electron paramagnetic resonance (EPR) is used, for the first time, as an analytical tool for the quantitative assay of ketoconazole (KTZ) in drug formulations. The drug was successfully characterized by the prominent signals by two radical species produced as a result of its oxidation with 400 microg/mL cerium(IV) in 0.10 mol dm(-3) sulfuric acid. The EPR signal of the reaction mixture was measured in eight capillary tubes housed in a 4 mm EPR sample tube. The radical stability was investigated by obtaining multi-EPR scans of each KTZ sample solution at time intervals of 2.5 min of the reaction mixing time. The plot of the disappearance of the radical species show that the disappearance is apparently of zero order. The zero-time intercept of the EPR signal amplitude, which should be proportional to the initial radical concentration, is linear in the sample concentration in the range between 100 and 400 microg/mL, with a correlation coefficient, r, of 0.999. The detection limit was determined to be 11.7 +/- 2.5 microg/mL. The method newly adopted was fully validated following the United States Pharmacopeia (USP) monograph protocol in both the generic and the proprietary forms. The method is very accurate, such that we were able to measure the concentration at confidence levels of 99.9%. The method was also found to be suitable for the assay of KTZ in its tablet and cream pharmaceutical preparations, as no interferences were encountered from excipients of the proprietary drugs. High specificity, simplicity, and rapidity are the merits of the present method compared to the previously reported methods.

  9. Tooth Retrospective Dosimetry Using Electron Paramagnetic Resonance: Influence of Irradiated Dental Composites

    PubMed Central

    Desmet, Céline M.; Djurkin, Andrej; Dos Santos-Goncalvez, Ana Maria; Dong, Ruhong; Kmiec, Maciej M.; Kobayashi, Kyo; Rychert, Kevin; Beun, Sébastien; Leprince, Julian G.; Leloup, Gaëtane; Levêque, Philippe; Gallez, Bernard

    2015-01-01

    In the aftermath of a major radiological accident, the medical management of overexposed individuals will rely on the determination of the dose of ionizing radiations absorbed by the victims. Because people in the general population do not possess conventional dosimeters, after the fact dose reconstruction methods are needed. Free radicals are induced by radiations in the tooth enamel of victims, in direct proportion to dose, and can be quantified using Electron Paramagnetic Resonance (EPR) spectrometry, a technique that was demonstrated to be very appropriate for mass triage. The presence of dimethacrylate based restorations on teeth can interfere with the dosimetric signal from the enamel, as free radicals could also be induced in the various composites used. The aim of the present study was to screen irradiated composites for a possible radiation-induced EPR signal, to characterize it, and evaluate a possible interference with the dosimetric signal of the enamel. We investigated the most common commercial composites, and experimental compositions, for a possible class effect. The effect of the dose was studied between 10 Gy and 100 Gy using high sensitivity X-band spectrometer. The influence of this radiation-induced signal from the composite on the dosimetric signal of the enamel was also investigated using a clinical L-Band EPR spectrometer, specifically developed in the EPR center at Dartmouth College. In X-band, a radiation-induced signal was observed for high doses (25-100 Gy); it was rapidly decaying, and not detected after only 24h post irradiation. At 10 Gy, the signal was in most cases not measurable in the commercial composites tested, with the exception of 3 composites showing a significant intensity. In L-band study, only one irradiated commercial composite influenced significantly the dosimetric signal of the tooth, with an overestimation about 30%. In conclusion, the presence of the radiation-induced signal from dental composites should not

  10. Methodology for increased precision in saturation transfer electron paramagnetic resonance studies of rotational dynamics.

    PubMed Central

    Squier, T C; Thomas, D D

    1986-01-01

    Microsecond rotational motions of nitroxide spin labels are measured primarily with saturation transfer electron paramagnetic resonance (ST-EPR). In the present study we have used model system experiments to quantitatively evaluate different ST-EPR spectral parameters, both in-phase and out-of-phase, with an emphasis on techniques for suppressing the interference from weakly immobilized probes. Analyses of both systematic and random errors show that maximum sensitivity to small changes in correlation time and minimum ambiguity of interpretation are best achieved by combining measurements of both spectral line-shape, i.e., the ratio of line-heights, and spectral intensity, i.e., the absolute amplitude of either a position within a spectrum or a spectral integral. Errors in the measurement of correlation times for the two types of parameters tend to be complementary. Integrated intensity parameters are particularly useful in measuring microsecond probe motions in the presence of weakly immobilized components. We confirm that integrated intensity parameters are sometimes effective in rejecting signals from weakly immobilized probes, but the effectiveness of this rejection is more limited than previously supposed and depends on the type of parameter being measured. We describe procedures for evaluating and minimizing errors due to weakly immobilized probes, emphasizing the advantages of a new kind of intensity parameter obtained from integrated in-phase spectra. We provide detailed descriptions of experimental procedures, along with calibration plots of the most useful spectral parameters vs. rotational correlation time, which should make it possible for workers in other laboratories, using different instruments and sample geometries, to reproduce spectra quantitatively and to make accurate correlation time measurements. PMID:3013330

  11. Dielectric microwave resonators in TE011 cavities for electron paramagnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Mett, Richard R.; Sidabras, Jason W.; Golovina, Iryna S.; Hyde, James S.

    2008-09-01

    The coupled system of the microwave cylindrical TE011 cavity and the TE01δ dielectric modes has been analyzed in order to determine the maximum achievable resonator efficiency parameter of a dielectric inserted into a cavity, and whether this value can exceed that of a dedicated TE01δ mode dielectric resonator. The frequency, Q value, and resonator efficiency parameter Λ for each mode of the coupled system were calculated as the size of the dielectric was varied. Other output parameters include the relative field magnitudes and phases. Two modes are found: one with fields in the dielectric parallel to the fields in the cavity center and the other with antiparallel fields. Results closely match those from a computer program that solves Maxwell's equations by finite element methods. Depending on the relative natural resonance frequencies of the cavity and dielectric, one mode has a higher Q value and correspondingly lower Λ than the other. The mode with the higher Q value is preferentially excited by a coupling iris or loop in or near the cavity wall. However, depending on the frequency separation between modes, either can be excited in this way. A relatively narrow optimum is found for the size of the insert that produces maximum signal for both modes simultaneously. It occurs when the self-resonance frequencies of the two resonators are nearly equal. The maximum signal is almost the same as that of the dedicated TE01δ mode dielectric resonator alone, Λ ≅40 G/W1/2 at X-band for a KTaO3 crystal. The cavity is analogous to the second stage of a two-stage coupler. In general, there is no electron paramagnetic resonance (EPR) signal benefit by use of a second stage. However, there is a benefit of convenience. A properly designed sample-mounted resonator inserted into a cavity can give EPR signals as large as what one would expect from the dielectric resonator alone.

  12. In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging.

    PubMed

    Spitzbarth, Martin; Lemke, Tobias; Drescher, Malte

    2016-01-01

    A method is demonstrated to monitor macroscopic translational diffusion using electron paramagnetic resonance (EPR) imaging. A host-guest system with nitroxide spin probe 3-(2-Iodoacetamido)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (IPSL) as a guest inside the periodic mesoporous organosilica (PMO) aerogel UKON1-GEL as a host and ethanol as a solvent is used as an example to describe the protocol. Data is shown from a previous publication, where the protocol has been applied to both IPSL and Tris(8-carboxy-2,2,6,6-perdeutero-tetramethyl-benzo[1,2-d:4,5-d']bis(1,3)dithiole) methyl (Trityl) as guest molecules and UKON1-GEL and SILICA-GEL as host systems. A method is shown to prepare aerogel samples that cannot be synthesized directly in the sample tube for measurement due to a size change during synthesis. The aerogel is attached to sample tubes using heat shrink tubing and a pressure cooker to reach the necessary temperature without evaporating the solvent in the process. The method does not assume a clearly defined initial distribution of guest molecules at the start of the measurement. Instead, it requires a reservoir on top of the aerogel and experimentally determines the influx rate during data analysis. The diffusion is monitored continually over a period of 20 hr by recording the 1d spin density profile within the sample. The spectrometer settings for the imaging experiment are described quantitatively. Data analysis software is provided to take the resonator sensitivity profile into account and to numerically solve the diffusion equation. The software determines the macroscopic translational diffusion coefficient by least square minimization of the difference between the experiment and the numerical solution of the diffusion equation. PMID:27685166

  13. Crystallization and electron paramagnetic resonance characterization of the complex of photosystem I with its natural electron acceptor ferredoxin.

    PubMed Central

    Fromme, Petra; Bottin, Hervé; Krauss, Norbert; Sétif, Pierre

    2002-01-01

    The formation of a transient complex between photosystem I and ferredoxin is involved in the process of ferredoxin photoreduction in oxygenic photosynthetic organisms. Reduced ferredoxin is an essential redox intermediate involved in many assimilatory processes and is necessary for the reduction of NADP(+) to NADPH. Single crystals from a complex of photosystem I with ferredoxin were grown using PEG 400 and CaCl(2) as precipitation agents. The crystals diffract x-rays to a resolution of 7-8 A. The space group was determined to be orthorhombic with the unit cell dimensions a = 194 A, b = 208 A, and c = 354 A. The crystals contain photosystem I and ferredoxin in a 1:1 ratio. Electron paramagnetic resonance (EPR) measurements on these crystals are reported, where EPR signals of the three [4Fe-4S] clusters F(A), F(B), F(X), and the [2Fe-2S] cluster of ferredoxin were detected. From the EPR spectra observed at three particular orientations of the crystal in the magnetic field, the full orientation pattern of the F g-tensor was simulated. This simulation is consistent with the presence of 12 magnetically inequivalent F clusters per unit cell with the C(3) axis of the PSI trimers oriented at (23 degrees, 72 degrees, 77 degrees ) to the unit cell axes. PMID:12324399

  14. A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument.

    PubMed

    Siaw, Ting Ann; Leavesley, Alisa; Lund, Alicia; Kaminker, Ilia; Han, Songi

    2016-03-01

    Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3T) and cryogenic temperatures (∼ 2-90K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the "DNP power curve", i.e. the microwave (MW) power dependence of DNP enhancement, the "DNP spectrum", i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW

  15. A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument.

    PubMed

    Siaw, Ting Ann; Leavesley, Alisa; Lund, Alicia; Kaminker, Ilia; Han, Songi

    2016-03-01

    Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3T) and cryogenic temperatures (∼ 2-90K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the "DNP power curve", i.e. the microwave (MW) power dependence of DNP enhancement, the "DNP spectrum", i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW

  16. A versatile and modular quasi optics-based 200 GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument

    NASA Astrophysics Data System (ADS)

    Siaw, Ting Ann; Leavesley, Alisa; Lund, Alicia; Kaminker, Ilia; Han, Songi

    2016-03-01

    Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3 T) and cryogenic temperatures (∼2-90 K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the "DNP power curve", i.e. the microwave (MW) power dependence of DNP enhancement, the "DNP spectrum", i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW

  17. Biophysical Characterisation of Globins and Multi-Heme Cytochromes Using Electron Paramagnetic Resonance and Optical Spectroscopy

    NASA Astrophysics Data System (ADS)

    Desmet, Filip

    Heme proteins of different families were investigated in this work, using a combination of pulsed and continuous-wave electron paramagnetic resonance (EPR) spectroscopy, optical absorption spectroscopy, resonance Raman spectroscopy and laser flash photolysis. The first class of proteins that were investigated, were the globins. The globin-domain of the globin-coupled sensor of the bacterium Geobacter sulfurreducens was studied in detail using different pulsed EPR techniques (HYSCORE and Mims ENDOR). The results of this pulsed EPR study are compared with the results of the optical investigation and the crystal structure of the protein. The second globin, which was studied, is the Protoglobin of Methanosarcina acetivorans, various mutants of this protein were studied using laser flash photolysis and Raman spectroscopy to unravel the link between this protein's unusual structure and its ligand-binding kinetics. In addition to this, the CN -bound form of this protein was investigated using EPR and the influence of the strong deformation of the heme on the unusual low gz values is discussed. Finally, the neuroglobins of three species of fishes, Danio rerio, Dissostichus mawsoni and Chaenocephalus aceratus are studied. The influence of the presence or absence of two cysteine residues in the C-D and D-region of the protein on the EPR spectrum, and the possible formation of a disulfide bond is studied. The second group of proteins that were studied in this thesis belong to the family of the cytochromes. First the Mouse tumor suppressor cytochrome b561 was studied, the results of a Raman and EPR investigation are compared to the Human orthologue of the protein. Secondly, the tonoplast cytochrome b561 of Arabidopsis was investigated in its natural form and in two double-mutant forms, in which the heme at the extravesicular side was removed. The results of this investigation are then compared with two models in literature that predict the localisation of the hemes in this

  18. Scaling craters in carbonates: Electron paramagnetic resonance analysis of shock damage

    NASA Technical Reports Server (NTRS)

    Polanskey, Carol A.; Ahrens, Thomas J.

    1994-01-01

    Carbonate samples from the 8.9-Mt nuclear (near-surface explosion) crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance (EPR). Samples from below the OAK apparent crater floor were obtained from six boreholes, as well as ejecta recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to the spectra of Solenhofen and Kaibab limestone, which had been skocked to known pressures. Analysis of the OAK Crater borehole samples has identified a thin zone of allocthonous highly shocked (10-13 GPa) carbonate material underneath the apparent crater floor. This approx. 5- to 15-m-thick zone occurs at a maximum depth of approx. 125 m below current seafloor at the borehole, sited at the initial position of the OAK explosive, and decreases in depth towards the apparent crater edge. Because this zone of allocthonous shocked rock delineates deformed rock below, and a breccia of mobilized sand and collapse debris above, it appears to outline the transient crater. The transient crater volume inferred in this way is found to by 3.2 +/- 0.2 times 10(exp 6)cu m, which is in good agreement with a volume of 5.3 times 10(exp 6)cu m inferred from gravity scaling of laboratory experiments. A layer of highly shocked material is also found near the surface outside the crater. The latter material could represent a fallout ejecta layer. The ejecta boulders recovered from the present crater floor experienced a range of shock pressures from approx. 0 to 15 GPa with the more heavily shocked samples all occurring between radii of 360 and approx. 600 m. Moreover, the fossil content, lithology and Sr isotopic composition all demonstrate that the initial position of the bulk of the heavily shocked rock ejecta sampled was originally near surface rock at initial depths in the 32 to 45-m depth (below sea level) range. The EPR technique is also sensitive to

  19. Electron paramagnetic resonance in irradiated fingernails: variability of dose dependence and possibilities of initial dose assessment.

    PubMed

    Reyes, R A; Romanyukha, Alexander; Olsen, C; Trompier, F; Benevides, L A

    2009-08-01

    The results of electron paramagnetic resonance (EPR) measurements in irradiated fingernails are presented. In total, 83 samples of different fingernails were studied. Five different groups of samples were selected based on the collection time of fingernail samples, their level of mechanical stress, and the number and size of clippings: (1) recently (<24 h) cut, irradiated and measured with EPR without any treatment of samples, and with rigorous control of size and number of clippings (stressed-fresh, controlled); (2) recently (<24 h) cut, irradiated and measured with EPR after application of a special treatment (10 min of water soaking, 5 min of drying time) to reduce the mechanical stress caused by cutting the samples, and with rigorous control of size and number of clippings (unstressed-fresh, controlled); (3) previously (>24 h) cut, stored at room temperature, additionally cut into small pieces immediately prior to study, irradiated and measured with EPR without any treatment of samples, and with rigorous control of size and number of clippings (stressed-old, controlled); (4) previously (>24 h) cut, stored at room temperature, additionally cut into small pieces immediately prior to the study, irradiated and measured with EPR after application of a special treatment to reduce mechanical stress caused by cut, and with rigorous control of size and number of clippings (unstressed-old, controlled); and (5) recently (<24 h) cut, irradiated and measured with EPR after application of a special treatment to reduce the mechanical stress caused by cut, and without rigorous control of size and number of clippings (unstressed-fresh, uncontrolled). Except for the fifth selected group, variability of the dose dependence inside all groups was found to be not statistically significant, although the variability among the different groups was significant. Comparison of the mean dose dependences obtained for each group allowed selection of key factors responsible for radiation

  20. Skylab electronic technological advancements

    NASA Technical Reports Server (NTRS)

    Hornback, G. L.

    1974-01-01

    The present work describes three electronic devices designed for use in the Skylab airlock module: the teleprinter system, the quartz crystal microbalance contamination monitor (QCM), and the speaker. Design considerations, operation, characteristics, and system development are described for these systems, with accompanying diagrams, graphs, and photographs. The teleprinter is a thermal dot printer used to produce hard copy messages by electrically heating print elements in contact with heat-sensitive paper. The QCM was designed to estimate contamination buildup on optical surfaces of the earth resources experiment package. A vibrating quartz crystal is used as a microbalance relating deposited mass to shifts in the crystal's resonant frequency. Audio devices provide communication between crew members and between crew and STDN, and also provide audible alarms, via the caution and warning system, of out-of-limit-conditions.

  1. Electron Paramagnetic Resonance of MANGANESE(2+), COPPER(2+) and GADOLINIUM(3+) Ions Doping Some - and - Magnetic Single Crystals.

    NASA Astrophysics Data System (ADS)

    Kahrizi, Mojtaba

    X-band EPR measurements on several Mn('2+)-doped single crystals have been made at room and low temperatures. The spin-Hamiltonian parameters are evaluated from the data using a rigorous least-squares-fitting program suitable for electron-nuclear spin coupled systems. The signs of the parameters are determined from the observed relative intensities of EPR lines at liquid helium temperature. The temperature variation of zero-field splitting parameter b(,2)('0), as well as that of the linewidths have been studied. Using the shift of g-values in the paramagnetic Ni('2+) lattices, from those in the corresponding isostructural diagmagnetic lattices, the exchange constant between Mn('2+) -Ni('2+) ions in nickel salts has been estimated. For the case of hosts containing paramagnetic Co('2+) ions the spin-lattice relaxation time was estimated at room and liquid nitrogen temperatures. X-band EPR measurements on Cu('2+) in copper pentakisantipyrine perchlorate were performed at room and low temperatures. The principal values of g and A tensors and their direction cosines were evaluated using a rigorous least-squares fitting technique. Finally, X-band EPR studies of Gd('3+)-doped single crystals of LiYF(,4) and LiYbF(,4) have been made at room and low temperatures. In the case of paramagnetic host LiYbF(,4) the EPR lines broadened very fast as the temperature was lowered from room temperature, and below 270 K no EPR lines were observed. The parameters were evaluated using a least squares fitting method. The temperature variation of the parameters was studied. Using the g-shift in LiYbF(,4) from its value in LiYF(,4) the exchange constant between Gd('3+) and its paramagnetic neighbor ions Yb('3+), was estimated.

  2. Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

    NASA Astrophysics Data System (ADS)

    Pham, Chuyen V.; Krueger, Michael; Eck, Michael; Weber, Stefan; Erdem, Emre

    2014-03-01

    Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

  3. Exploring Structure, Dynamics, and Topology of Nitroxide Spin-Labeled Proteins Using Continuous-Wave Electron Paramagnetic Resonance Spectroscopy.

    PubMed

    Altenbach, Christian; López, Carlos J; Hideg, Kálmán; Hubbell, Wayne L

    2015-01-01

    Structural and dynamical characterization of proteins is of central importance in understanding the mechanisms underlying their biological functions. Site-directed spin labeling (SDSL) combined with continuous-wave electron paramagnetic resonance (CW EPR) spectroscopy has shown the capability of providing this information with site-specific resolution under physiological conditions for proteins of any degree of complexity, including those associated with membranes. This chapter introduces methods commonly employed for SDSL and describes selected CW EPR-based methods that can be applied to (1) map secondary and tertiary protein structure, (2) determine membrane protein topology, (3) measure protein backbone flexibility, and (4) reveal the existence of conformational exchange at equilibrium. PMID:26477248

  4. Electron Paramagnetic Resonance and Electron-Nuclear Double Resonance Studies of the Reactions of Cryogenerated Hydroperoxoferric–Hemoprotein Intermediates

    PubMed Central

    2015-01-01

    The fleeting ferric peroxo and hydroperoxo intermediates of dioxygen activation by hemoproteins can be readily trapped and characterized during cryoradiolytic reduction of ferrous hemoprotein–O2 complexes at 77 K. Previous cryoannealing studies suggested that the relaxation of cryogenerated hydroperoxoferric intermediates of myoglobin (Mb), hemoglobin, and horseradish peroxidase (HRP), either trapped directly at 77 K or generated by cryoannealing of a trapped peroxo-ferric state, proceeds through dissociation of bound H2O2 and formation of the ferric heme without formation of the ferryl porphyrin π-cation radical intermediate, compound I (Cpd I). Herein we have reinvestigated the mechanism of decays of the cryogenerated hydroperoxyferric intermediates of α- and β-chains of human hemoglobin, HRP, and chloroperoxidase (CPO). The latter two proteins are well-known to form spectroscopically detectable quasistable Cpds I. Peroxoferric intermediates are trapped during 77 K cryoreduction of oxy Mb, α-chains, and β-chains of human hemoglobin and CPO. They convert into hydroperoxoferric intermediates during annealing at temperatures above 160 K. The hydroperoxoferric intermediate of HRP is trapped directly at 77 K. All studied hydroperoxoferric intermediates decay with measurable rates at temperatures above 170 K with appreciable solvent kinetic isotope effects. The hydroperoxoferric intermediate of β-chains converts to the S = 3/2 Cpd I, which in turn decays to an electron paramagnetic resonance (EPR)-silent product at temperature above 220 K. For all the other hemoproteins studied, cryoannealing of the hydroperoxo intermediate directly yields an EPR-silent majority product. In each case, a second follow-up 77 K γ-irradiation of the annealed samples yields low-spin EPR signals characteristic of cryoreduced ferrylheme (compound II, Cpd II). This indicates that in general the hydroperoxoferric intermediates relax to Cpd I during cryoanealing at low temperatures, but

  5. Cathodoluminescence, laser ablasion inductively coupled plasma mass spectrometry, electron probe microanalysis and electron paramagnetic resonance analyses of natural sphalerite

    USGS Publications Warehouse

    Karakus, M.; Hagni, R.D.; Koenig, A.; Ciftc, E.

    2008-01-01

    Natural sphalerite associated with copper, silver, lead-zinc, tin and tungsten deposits from various world-famous mineral deposits have been studied by cathodoluminescence (CL), laser ablasion inductively coupled plasma mass spectrometry (LA-ICP-MS), electron probe microanalysis (EPMA) and electron paramagnetic resonance (EPR) to determine the relationship between trace element type and content and the CL properties of sphalerite. In general, sphalerite produces a spectrum of CL colour under electron bombardment that includes deep blue, turquoise, lime green, yellow-orange, orange-red and dull dark red depending on the type and concentration of trace quantities of activator ions. Sphalerite from most deposits shows a bright yellow-orange CL colour with ??max centred at 585 nm due to Mn2+ ion, and the intensity of CL is strongly dependent primarily on Fe2+ concentration. The blue emission band with ??max centred at 470-490 nm correlates with Ga and Ag at the Tsumeb, Horn Silver, Balmat and Kankoy mines. Colloform sphalerite from older well-known European lead-zinc deposits and late Cretaceous Kuroko-type VMS deposits of Turkey shows intense yellowish CL colour and their CL spectra are characterised by extremely broad emission bands ranging from 450 to 750 nm. These samples are characterised by low Mn (<10 ppm) and Ag (<1 ppm), and they are enriched in Tl (1-30 ppm) and Pb (80-1500 ppm). Strong green CL is produced by sphalerite from the Balmat-Edwards district. Amber, lime-green and red-orange sphalerite produced weak orange-red CL at room temperatures, with several emission bands centred at 490, 580, 630, 680, 745, with ??max at 630 nm being the strongest. These emission bands are well correlated with trace quantities of Sn, In, Cu and Mn activators. Sphalerite from the famous Ogdensburg and Franklin mines exhibited brilliant deep blue and orange CL colours and the blue CL may be related to Se. Cathodoluminescence behaviour of sphalerite serves to characterise ore

  6. Photoactivation of the flavin cofactor in Xenopus laevis (6–4) photolyase: Observation of a transient tyrosyl radical by time-resolved electron paramagnetic resonance

    PubMed Central

    Weber, Stefan; Kay, Christopher W. M.; Mögling, Heike; Möbius, Klaus; Hitomi, Kenichi; Todo, Takeshi

    2002-01-01

    The light-induced electron transfer reaction of flavin cofactor photoactivation in Xenopus laevis (6–4) photolyase has been studied by continuous-wave and time-resolved electron paramagnetic resonance spectroscopy. When the photoactivation is initiated from the fully oxidized form of the flavin, a neutral flavin radical is observed as a long-lived paramagnetic intermediate of two consecutive single-electron reductions under participation of redox-active amino acid residues. By time-resolved electron paramagnetic resonance, a spin-polarized transient radical-pair signal was detected that shows remarkable differences to the signals observed in the related cyclobutane pyrimidine dimer photolyase enzyme. In (6–4) photolyase, a neutral tyrosine radical has been identified as the final electron donor, on the basis of the characteristic line width, hyperfine splitting pattern, and resonance magnetic field position of the tyrosine resonances of the transient radical pair. PMID:11805294

  7. Cryogen-free superconducting magnet system for multifrequency electron paramagnetic resonance up to 12.1 T

    NASA Astrophysics Data System (ADS)

    Smirnov, Alex I.; Smirnova, Tatyana I.; MacArthur, Ryan L.; Good, Jeremy A.; Hall, Renny

    2006-03-01

    Multifrequency and high field/high frequency (HF) electron paramagnetic resonance (EPR) is a powerful spectroscopy for studying paramagnetic spin systems ranging from organic-free radicals to catalytic paramagnetic metal ion centers in metalloproteins. Typically, HF EPR experiments are carried out at resonant frequencies ν =95-300GHz and this requires magnetic fields of 3.4-10.7T for electronic spins with g ≈2.0. Such fields could be easily achieved with superconducting magnets, but, unlike NMR, these magnets cannot operate in a persistent mode in order to satisfy a wide range of resonant fields required by the experiment. Operating and maintaining conventional passively cooled superconducting magnets in EPR laboratories require frequent transfer of cryogens by trained personnel. Here we describe and characterize a versatile cryogen-free magnet system for HF EPR at magnetic fields up to 12.1T that is suitable for ramping the magnetic field over the entire range, precision scans around the target field, and/or holding the field at the target value. We also demonstrate that in a nonpersistent mode of operation the magnetic field can be stabilized to better than 0.3ppm/h over 15h period by employing a transducer-controlled power supply. Such stability is sufficient for many HF EPR experiments. An important feature of the system is that it is virtually maintenance-free because it is based on a cryogen-free technology and therefore does not require any liquid cryogens (liquid helium or nitrogen) for operation. We believe that actively cooled superconducting magnets are ideally suited for a wide range of HF EPR experiments including studies of spin-labeled nucleic acids and proteins, single-molecule magnets, and metalloproteins.

  8. Reactive oxygen species' role in endothelial dysfunction by electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Wassall, Cynthia D.

    The endothelium is a single layer of cells lining the arteries and is involved in many physiological reactions which are responsible for vascular tone. Free radicals are important participants in these chemical reactions in the endothelium. Here we quantify free radicals, ex vivo, in biological tissue with continuous wave electron paramagnetic resonance (EPR). In all of the experiments in this thesis, we use a novel EPR spin trapping technique that has been developed for tissue segments. EPR spin trapping is often considered the 'gold standard' in reactive oxygen species (ROS) detection because of its sensitivity and non-invasive nature. In all experiments, tissue was placed in physiological saline solution with 190-mM PBN (N-tert -butyl-α-phenylnitrone), 10% by volume dimethyl-sulphoxide (DMSO) for cryopreservation, and incubated in the dark for between 30 minutes up to 2 hours at 37°C while gently being stirred. Tissue and supernatant were then loaded into a syringe and frozen at -80°C until EPR analysis. In our experiments, the EPR spectra were normalized with respect to tissue volume. Conducting experiments at liquid nitrogen temperature leads to some experimental advantages. The freezing of the spin adducts renders them stable over a longer period, which allows ample time to analyze tissue samples for ROS. The dielectric constant of ice is greatly reduced over its liquid counterpart; this property of water enables larger sample volumes to be inserted into the EPR cavity without overloading it and leads to enhanced signal detection. Due to Maxwell-Boltzmann statistics, the population difference goes up as the temperature goes down, so this phenomenon enhances the signal intensity as well. With the 'gold standard' assertion in mind, we investigated whether slicing tissue to assay ROS that is commonly used in fluorescence experiments will show more free radical generation than tissue of a similar volume that remains unsliced. Sliced tissue exhibited a 76

  9. Reactive oxygen species' role in endothelial dysfunction by electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Wassall, Cynthia D.

    The endothelium is a single layer of cells lining the arteries and is involved in many physiological reactions which are responsible for vascular tone. Free radicals are important participants in these chemical reactions in the endothelium. Here we quantify free radicals, ex vivo, in biological tissue with continuous wave electron paramagnetic resonance (EPR). In all of the experiments in this thesis, we use a novel EPR spin trapping technique that has been developed for tissue segments. EPR spin trapping is often considered the 'gold standard' in reactive oxygen species (ROS) detection because of its sensitivity and non-invasive nature. In all experiments, tissue was placed in physiological saline solution with 190-mM PBN (N-tert -butyl-α-phenylnitrone), 10% by volume dimethyl-sulphoxide (DMSO) for cryopreservation, and incubated in the dark for between 30 minutes up to 2 hours at 37°C while gently being stirred. Tissue and supernatant were then loaded into a syringe and frozen at -80°C until EPR analysis. In our experiments, the EPR spectra were normalized with respect to tissue volume. Conducting experiments at liquid nitrogen temperature leads to some experimental advantages. The freezing of the spin adducts renders them stable over a longer period, which allows ample time to analyze tissue samples for ROS. The dielectric constant of ice is greatly reduced over its liquid counterpart; this property of water enables larger sample volumes to be inserted into the EPR cavity without overloading it and leads to enhanced signal detection. Due to Maxwell-Boltzmann statistics, the population difference goes up as the temperature goes down, so this phenomenon enhances the signal intensity as well. With the 'gold standard' assertion in mind, we investigated whether slicing tissue to assay ROS that is commonly used in fluorescence experiments will show more free radical generation than tissue of a similar volume that remains unsliced. Sliced tissue exhibited a 76

  10. SU-C-BRD-05: Non-Invasive in Vivo Biodosimetry in Radiotherapy Patients Using Electron Paramagnetic Resonance (EPR) Spectroscopy

    SciTech Connect

    Bahar, N; Roberts, K; Stabile, F; Mongillo, N; Decker, RD; Wilson, LD; Husain, Z; Contessa, J; Carlson, DJ; Williams, BB; Flood, AB; Swartz, HM

    2015-06-15

    Purpose: Medical intervention following a major, unplanned radiation event can elevate the human whole body exposure LD50 from 3 to 7 Gy. On a large scale, intervention cannot be achieved effectively without accurate and efficient triage. Current methods of retrospective biodosimetry are restricted in capability and applicability; published human data is limited. We aim to further develop, validate, and optimize an automated field-deployable in vivo electron paramagnetic resonance (EPR) instrument that can fill this need. Methods: Ionizing radiation creates highly-stable, carbonate-based free radicals within tooth enamel. Using a process similar to nuclear magnetic resonance, EPR directly measures the presence of radiation-induced free radicals. We performed baseline EPR measurements on one of the upper central incisors of total body irradiation (TBI) and head and neck (H&N) radiotherapy patients before their first treatment. Additional measurements were performed between subsequent fractions to examine the EPR response with increasing radiation dose. Independent dosimetry measurements were performed with optically-stimulated luminescent dosimeters (OSLDs) and diodes to more accurately establish the relationship between EPR signal and delivered radiation dose. Results: 36 EPR measurements were performed over the course of four months on two TBI and four H & N radiotherapy patients. We observe a linear increase in EPR signal with increasing dose across the entirety of the tested range. A linear least squares-weighted fit of delivered dose versus measured signal amplitude yields an adjusted R-square of 0.966. The standard error of inverse prediction (SEIP) is 1.77 Gy. For doses up to 7 Gy, the range most relevant to triage, we calculate an SEIP of 1.29 Gy. Conclusion: EPR spectroscopy provides a promising method of retrospective, non-invasive, in vivo biodosimetry. Our preliminary data show an excellent correlation between predicted signal amplitude and delivered

  11. Electron-paramagnetic-resonance study of the Sn DX center in direct-gap Ga0.69Al0.31As

    NASA Astrophysics Data System (ADS)

    von Bardeleben, H. J.; Bourgoin, J. C.; Basmaji, P.; Gibart, P.

    1989-09-01

    An electron-paramagnetic-resonance study of the Sn-related DX center in direct-gap Ga0.69Al0.31As shows that the DX center can be transformed by photoexcitation into an excited paramagnetic state, which is metastable at 4 K. This excited state has the characteristics of a strain-split T2 state; its asymmetric line can be decomposed into two Gaussians with the parameters g1=1.92,ΔB1=500 G and g2=1.95,ΔB2=200 G. The photoexcitation spectrum of this paramagnetic state, which is of the Lucovsky type with a threshold at 0.8 eV, is interpreted as an internal A1-T2 transition. No paramagnetic spectrum associated with the ground state of DX has been observed.

  12. Applications of electron paramagnetic resonance spectroscopy to study interactions of iron proteins in cells with nitric oxide

    NASA Astrophysics Data System (ADS)

    Cammack, R.; Shergill, J. K.; Ananda Inalsingh, V.; Hughes, Martin N.

    1998-12-01

    Nitric oxide and species derived from it have a wide range of biological functions. Some applications of electron paramagnetic resonance (EPR) spectroscopy are reviewed, for observing nitrosyl species in biological systems. Nitrite has long been used as a food preservative owing to its bacteriostatic effect on spoilage bacteria. Nitrosyl complexes such as sodium nitroprusside, which are added experimentally as NO-generators, themselves produce paramagnetic nitrosyl species, which may be seen by EPR. We have used this to observe the effects of nitroprusside on clostridial cells. After growth in the presence of sublethal concentrations of nitroprusside, the cells show they have been converted into other, presumably less toxic, nitrosyl complexes such as (RS) 2Fe(NO) 2. Nitric oxide is cytotoxic, partly due to its effects on mitochondria. This is exploited in the destruction of cancer cells by the immune system. The targets include iron-sulfur proteins. It appears that species derived from nitric oxide such as peroxynitrite may be responsible. Addition of peroxynitrite to mitochondria led to depletion of the EPR-detectable iron-sulfur clusters. Paramagnetic complexes are formed in vivo from hemoglobin, in conditions such as experimental endotoxic shock. This has been used to follow the course of production of NO by macrophages. We have examined the effects of suppression of NO synthase using biopterin antagonists. Another method is to use an injected NO-trapping agent, Fe-diethyldithiocarbamate (Fe-DETC) to detect accumulated NO by EPR. In this way we have observed the effects of depletion of serum arginine by arginase. In brains from victims of Parkinson's disease, a nitrosyl species, identified as nitrosyl hemoglobin, has been observed in substantia nigra. This is an indication for the involvement of nitric oxide or a derived species in the damage to this organ.

  13. Electron paramagnetic resonance spectroscopy of Cr3+ in hexagonal Cs2NaGaF6 crystals

    NASA Astrophysics Data System (ADS)

    Vrielinck, H.; Khaidukov, N. M.; Callens, F.; Matthys, P.

    Powder samples of hydrothermally grown Cr3+ -doped Cs-2 NaGaF6 crystals have been investigated with electron paramagnetic resonance spectroscopy at X - (9.5 GHz) and Q -band (34 GHz). Analysis of the spectra clearly demonstrates that there are two distinct Cr3+ centres in the Cs2NaGaF6 crystal, having nearly identical g factors, but differing largely from the viewpoint of their zero field splitting. By using the Cr-53 hyperfine spectra observed with electron nuclear double resonance spectroscopy, it is deduced that these centres have opposite signs for the zero field splitting. The spectroscopic properties of the Cr3+ centres in the isostructural Cs2NaGaF6 and Cs2NaAlF6 crystals are compared and discussed.

  14. [Electron paramagnetic resonance determination of ceruloplasmin concentration in the blood of patients for the diagnosis of urological cancer diseases].

    PubMed

    Ibragimova, M I; Chushnikov, A I; Moiseev, V N; Petukhov, V Iu; Zheglov, E P; Pogorel'tsev, V I; Khardina, N B

    2010-04-01

    The electron paramagnetic resonance technique was used to study the venous blood levels of ceruloplasmin (CP) in 93 cancer patients with Stages I-IV malignancies of the urinary bladder and kidneys. Two groups were selected as a control; one of them comprised 44 donors who were considered to be apparently healthy and the other included 32 outpatients, some of whom had noncancer diseases. It has been established that in urological cancer, the level of the paramagnetic phase of Cu2+ -CP may vary in the wide range: from the lower to exceeding upper normal range in noncancer disease. The content of Cu2+ -CP does not virtually depend on the site and differentiation of a tumor. A correlation between the blood concentration of Cu2+ -CP and erythrocyte sedimentation rate (ESR) in urological cancer patients has been considered. Determination of CP levels at the ESR exceeding the normal values may be expedient for the early diagnosis of cancer and also an addition to the biological individual screening of patients in the preoperative period to choose the correct and effective treatment tactics.

  15. Magnetic resonance force microscopy of paramagnetic electron spins at millikelvin temperatures.

    PubMed

    Vinante, A; Wijts, G; Usenko, O; Schinkelshoek, L; Oosterkamp, T H

    2011-12-06

    Magnetic resonance force microscopy (MRFM) is a powerful technique to detect a small number of spins that relies on force detection by an ultrasoft magnetically tipped cantilever and selective magnetic resonance manipulation of the spins. MRFM would greatly benefit from ultralow temperature operation, because of lower thermomechanical noise and increased thermal spin polarization. Here we demonstrate MRFM operation at temperatures as low as 30 mK, thanks to a recently developed superconducting quantum interference device (SQUID)-based cantilever detection technique, which avoids cantilever overheating. In our experiment, we detect dangling bond paramagnetic centres on a silicon surface down to millikelvin temperatures. Fluctuations of such defects are supposedly linked to 1/f magnetic noise and decoherence in SQUIDs, as well as in several superconducting and single spin qubits. We find evidence that spin diffusion has a key role in the low-temperature spin dynamics.

  16. Site selective substitution Pt for Ti in KTiOPO{sub 4}:Ga crystals revealed by electron paramagnetic resonance

    SciTech Connect

    Grachev, V.; Meyer, M.; Jorgensen, J.; Malovichko, G.; Hunt, A. W.

    2014-07-28

    Electron Paramagnetic Resonance at low temperatures has been used to characterize potassium titanyl phosphate (KTiOPO{sub 4}) single crystals grown by different techniques. Irradiation with 20 MeV electrons performed at room temperature and liquid nitrogen temperature caused an appearance of electrons and holes. Platinum impurities act as electron traps in KTiOPO{sub 4} creating Pt{sup 3+} centers. Two different Pt{sup 3+} centers were observed, Pt(A) and Pt(D). The Pt(A) centers are dominant in undoped samples, whereas Pt(D)—in Ga-doped KTP crystals. Superhyperfine structure registered for Pt(D) centers was attributed to interactions of platinum electrons with {sup 39}K and two {sup 31}P nuclei in their surroundings. In both Pt(A) and Pt(D) centers, Pt{sup 3+} ions substitute for Ti{sup 4+} ions, but with a preference to one of two electrically distinct crystallographic positions. The site selective substitution can be controlled by the Ga-doping.

  17. Site selective substitution Pt for Ti in KTiOPO4:Ga crystals revealed by electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Grachev, V.; Meyer, M.; Jorgensen, J.; Hunt, A. W.; Malovichko, G.

    2014-07-01

    Electron Paramagnetic Resonance at low temperatures has been used to characterize potassium titanyl phosphate (KTiOPO4) single crystals grown by different techniques. Irradiation with 20 MeV electrons performed at room temperature and liquid nitrogen temperature caused an appearance of electrons and holes. Platinum impurities act as electron traps in KTiOPO4 creating Pt3+ centers. Two different Pt3+ centers were observed, Pt(A) and Pt(D). The Pt(A) centers are dominant in undoped samples, whereas Pt(D)—in Ga-doped KTP crystals. Superhyperfine structure registered for Pt(D) centers was attributed to interactions of platinum electrons with 39K and two 31P nuclei in their surroundings. In both Pt(A) and Pt(D) centers, Pt3+ ions substitute for Ti4+ ions, but with a preference to one of two electrically distinct crystallographic positions. The site selective substitution can be controlled by the Ga-doping.

  18. Effect of electron scavengers on the formation of paramagnetic species upon radiolysis of polystyrene and its low-molecular-weight analogs

    SciTech Connect

    Zezin, A.A.; Fel`dman, V.I.; Sukhov, F.F.

    1995-05-01

    The effect of electron scavengers on the composition and the yields of paramagnetic species upon the radiolysis of polystyrene was examined. Various mechanisms of the reactions of radical cations (holes) in low-molecular-weight aromatic hydrocarbons and polystyrene are discussed. The dimeric radical cations were found to be trapped in polystyrene and benzene irradiated in the presence of electron scavengers at 77 K. The yield of paramagnetic species was shown to increase markedly in the presence of small amounts (<1%) of chloroform of benzyl chloride. The results obtained show that the ionic processes make a large contribution to the formation of paramagnetic species. It is concluded that the radiation resistance of polystyrene is due not only to its chemical structure, but to the association of phenyl rings in the solid polymer.

  19. X-Band Rapid-Scan Electron Paramagnetic Resonance of Radiation-Induced Defects in Tooth Enamel.

    PubMed

    Yu, Zhelin; Romanyukha, Alexander; Eaton, Sandra S; Eaton, Gareth R

    2015-08-01

    X-band rapid-scan electron paramagnetic resonance (EPR) spectra from tooth enamel samples irradiated with doses of 0.5, 1 and 10 Gy had substantially improved signal-to-noise relative to conventional continuous wave EPR. The radiation-induced signal in a 60 mg of a tooth enamel sample irradiated with a 0.5 Gy dose was readily characterized in spectra recorded with 34 min data acquisition times. The coefficient of variance of the calculated dose for a 1 Gy irradiated sample, based on simulation of the first-derivative spectra for three replicates as the sum of native and radiation-induced signals, was 3.9% for continuous wave and 0.4% for rapid scan.

  20. Electron paramagnetic resonance spectral study of [Mn(acs)2(2-pic)2(H2O)2] single crystals

    NASA Astrophysics Data System (ADS)

    Kocakoç, Mehpeyker; Tapramaz, Recep

    2016-03-01

    Acesulfame potassium salt is a synthetic and non-caloric sweetener. It is also important chemically for its capability of being ligand in coordination compounds, because it can bind over Nitrogen and Oxygen atoms of carbonyl and sulfonyl groups and ring oxygen. Some acesulfame containing transition metal ion complexes with mixed ligands exhibit solvato and thermo chromic properties and these properties make them physically important. In this work single crystals of Mn+2 ion complex with mixed ligand, [Mn(acs)2(2-pic)2(H2O)2], was studied with electron paramagnetic resonance (EPR) spectroscopy. EPR parameters were determined. Zero field splitting parameters indicated that the complex was highly symmetric. Variable temperature studies showed no detectable chance in spectra.

  1. Theoretical and electron paramagnetic resonance studies of hyperfine interaction in nitrogen doped 4H and 6H SiC

    SciTech Connect

    Szász, K.; Gali, A.

    2014-02-21

    Motivated by recent experimental findings on the hyperfine signal of nitrogen donor (N{sub C}) in 4 H and 6 H SiC, we calculate the hyperfine tensors within the framework of density functional theory. We find that there is negligible hyperfine coupling with {sup 29}Si isotopes when N{sub C} resides at h site both in 4 H and 6 H SiC. We observe measurable hyperfine coupling to a single {sup 29}Si at k site in 4 H SiC and k{sub 1} site in 6 H SiC. Our calculations unravel that such {sup 29}Si hyperfine coupling does not occur at k{sub 2} site in 6 H SiC. Our findings are well corroborated by our new electron paramagnetic resonance studies in nitrogen doped 6 H SiC.

  2. In vivo pO2 imaging of tumors: Oxymetry with very low frequency Electron Paramagnetic Resonance

    PubMed Central

    Epel, Boris; Halpern, Howard J.

    2016-01-01

    For over a century it has been known that tumor hypoxia, regions of a tumor with low levels of oxygenation, are important contributors to tumor resistance to radiation therapy and failure of radiation treatment of cancer. Recently, using novel pulse electron paramagnetic resonance (EPR) oxygen imaging, near absolute images of the partial pressure of oxygen (pO2) in tumors of living animals have been obtained. We discuss here the means by which EPR signals can be obtained in living tissues and tumors. We review development of EPR methods to image the pO2 in tumors and the potential for the pO2 image acquisition in human subjects. PMID:26477263

  3. X-Band Rapid-Scan Electron Paramagnetic Resonance of Radiation-Induced Defects in Tooth Enamel

    PubMed Central

    Yu, Zhelin; Romanyukha, Alexander; Eaton, Sandra S.; Eaton, Gareth R.

    2015-01-01

    X-band rapid-scan electron paramagnetic resonance (EPR) spectra from tooth enamel samples irradiated with doses of 0.5, 1 and 10 Gy had substantially improved signal-to-noise relative to conventional continuous wave EPR. The radiation-induced signal in 60 mg of a tooth enamel sample irradiated with a 0.5 Gy dose was readily characterized in spectra recorded with 34 min data acquisition times. The coefficient of variance of the calculated dose for a 1 Gy irradiated sample, based on simulation of the first-derivative spectra for three replicates as the sum of native and radiation-induced signals, was 3.9% for continuous wave and 0.4% for rapid scan. PMID:26207683

  4. Superoxide Anion Radical Production in the Tardigrade Paramacrobiotus richtersi, the First Electron Paramagnetic Resonance Spin-Trapping Study.

    PubMed

    Savic, Aleksandar G; Guidetti, Roberto; Turi, Ana; Pavicevic, Aleksandra; Giovannini, Ilaria; Rebecchi, Lorena; Mojovic, Milos

    2015-01-01

    Anhydrobiosis is an adaptive strategy that allows withstanding almost complete body water loss. It has been developed independently by many organisms belonging to different evolutionary lines, including tardigrades. The loss of water during anhydrobiotic processes leads to oxidative stress. To date, the metabolism of free radicals in tardigrades remained unclear. We present a method for in vivo monitoring of free radical production in tardigrades, based on electron paramagnetic resonance and spin-trap DEPMPO, which provides simultaneous identification of various spin adducts (i.e., different types of free radicals). The spin trap can be easily absorbed in animals, and tardigrades stay alive during the measurements and during 24-h monitoring after the treatment. The results show that hydrated specimens of the tardigrade Paramacrobiotus richtersi produce the pure superoxide anion radical ((•)O2(-)). This is an unexpected result, as all previously examined animals and plants produce both superoxide anion radical and hydroxyl radical ((•)OH) or exclusively hydroxyl radical.

  5. Electron paramagnetic resonance and Raman spectroscopy studies on carbon-doped MgB{sub 2} superconductor nanomaterials

    SciTech Connect

    Bateni, Ali; Somer, Mehmet E-mail: msomer@ku.edu.tr; Erdem, Emre E-mail: msomer@ku.edu.tr; Repp, Sergej; Weber, Stefan; Acar, Selcuk; Kokal, Ilkin; Häßler, Wolfgang

    2015-04-21

    Undoped and carbon-doped magnesium diboride (MgB{sub 2}) samples were synthesized using two sets of mixtures prepared from the precursors, amorphous nanoboron, and as-received amorphous carbon-doped nanoboron. The microscopic defect structures of carbon-doped MgB{sub 2} samples were systematically investigated using X-ray powder diffraction, Raman and electron paramagnetic resonance spectroscopy. Mg vacancies and C-related dangling-bond active centers could be distinguished, and sp{sup 3}-hybridized carbon radicals were detected. A strong reduction in the critical temperature T{sub c} was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra.

  6. Electron paramagnetic resonance studies of Cu 2+ ion in Tetraaqua-di(nicotinamide)Ni(II)-saccharinates single crystals

    NASA Astrophysics Data System (ADS)

    Yerli, Y.; Kazan, S.; Yalçın, O.; Aktaş, B.

    2006-06-01

    X-band (˜9.8 GHz) electron paramagnetic resonance (EPR) measurement at ambient temperature in three mutually perpendicular planes have been carried out on a single crystal of Cu 2+ doped mixed ligand complex of Ni(II) with saccharin and nicotinamide [Ni(Nic) 2(H 2O) 4](sac) 2. The angular dependent spectra showed that the Cu 2+ ion enters Ni 2+ sites in the lattice and distorted local environment of Ni 2+ site. The principal g and A values, covalency parameter ( α' 2), mixing coefficients ( α and β) and Fermi contact term ( K) have been evaluated from the EPR analysis. The ground-state wave function of the Cu 2+ ion has been constructed using the α' 2, α and β values. The nature of the distortion present in the lattice is obtained from the values of the mixing coefficients.

  7. Comparative identification of irradiated herbs by the methods of electron paramagnetic resonance and thermoluminescence

    NASA Astrophysics Data System (ADS)

    Yordanov, N. D.; Gancheva, V.; Radicheva, M.; Hristova, B.; Guelev, M.; Penchev, O.

    1998-12-01

    Non irradiated and γ-irradiated dry herbs savoury ( Savoury), wild thyme ( Thymus serpollorium) and marjoram ( Origanum) with absorbed dose of 8 kGy have been investigated by the methods of elecrtron paramagnetic resonance (EPR) and thermoluminescence (TL). Non-irradiated herbs exhibit only one weak siglet EPR signal whereas in irradiated samples its intensity increase and in addition two satelite lines are recorded. This triplet EPR spectrum is attributed to cellulose free radical generated by irradiation. It has been found that upon keeping the samples under the normal stock conditions the life-time of the cellulose free radical in the examined samples is ˜60-80 days. Thus the conclusion has been made that the presence of the EPR signal of cellulose free radical is unambiguous indication that the sample under study has been irradiated but its absence can not be considered as the opposite evidence. In the case when EPR signal was absent the method of TL has been used to give the final decision about the previous radiation treatment of the sample.

  8. Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

    SciTech Connect

    Pham, Chuyen V.; Krueger, Michael E-mail: emre.erdem@physchem.uni-freiburg.de; Eck, Michael; Weber, Stefan; Erdem, Emre E-mail: emre.erdem@physchem.uni-freiburg.de

    2014-03-31

    Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

  9. Electron paramagnetic resonance spectroscopic investigation of the inhibition of the phosphoroclastic system of Clostridium sporogenes by nitrite.

    PubMed

    Payne, M J; Woods, L F; Gibbs, P; Cammack, R

    1990-10-01

    The proposal that nitrite exerts its inhibitory effect on anaerobic bacteria by direct interaction with the iron-sulphur proteins of the phosphoroclastic system was investigated. The effects of nitrate, nitrite with or without ascorbate, and nitric oxide on the growth of Clostridium sporogenes in liquid cultures at pH 7.4, on the rates of hydrogen production, and on the activities of the enzymes pyruvate-ferredoxin oxidoreductase and hydrogenase, and of ferredoxin were investigated. In agreement with previous studies, nitrate was the least effective inhibitor of cell growth, and nitric oxide the most effective. Nitrite reductase activity was very low in C. sporogenes, indicating that the presence of external reducing agents would be necessary for the reduction of nitrite to nitric oxide. Inhibition by nitrite was enhanced by ascorbate; 0.5 mM-nitrite with 10 mM-ascorbate stopped growth completely. In partially-purified preparations 4.1 mM-NaNO2 and equimolar ascorbate caused complete inactivation of hydrogenase activity but only partial (up to 78%) inactivation of pyruvate-ferredoxin oxidoreductase. This agreed with the loss of hydrogen production observed with nitrite in vivo. Inhibition occurred within 5 min, and was irreversible in each case. Electron paramagnetic resonance (EPR) spectroscopy showed that paramagnetic [Fe(NO)2(SR)2] species were formed during growth in the presence of nitrite, and were associated with cells. However, the intensity of these EPR signals did not correlate with the inhibition of cell growth. The [4Fe-4S] clusters in ferredoxin were shown by EPR spectroscopy to be resistant to treatment with 3.6 mM-NaNO2 and 3.6 mM-ascorbate. It is concluded that the effects of nitrite on pre-formed iron-sulphur proteins are not convincing as a basis for the lethal effects on bacterial cells.

  10. Electron spin resonance spectroscopy of small ensemble paramagnetic spins using a single nitrogen-vacancy center in diamond

    NASA Astrophysics Data System (ADS)

    Abeywardana, Chathuranga; Stepanov, Viktor; Cho, Franklin H.; Takahashi, Susumu

    2016-09-01

    A nitrogen-vacancy (NV) center in diamond is a promising sensor for nanoscale magnetic sensing. Here, we report on electron spin resonance (ESR) spectroscopy using a single NV center in diamond. First, using a 230 GHz ESR spectrometer, we performed ensemble ESR of a type-Ib sample crystal and identified a substitutional single nitrogen impurity as a major paramagnetic center in the sample crystal. Then, we carried out free-induction decay and spin echo measurements of the single NV center to study static and dynamic properties of nanoscale bath spins surrounding the NV center. We also measured ESR spectrum of the bath spins using double electron-electron resonance spectroscopy with the single NV center. The spectrum analysis of the NV-based ESR measurement identified that the detected spins are the nitrogen impurity spins. The experiment was also performed with several other single NV centers in the diamond sample and demonstrated that the properties of the bath spins are unique to the NV centers indicating the probe of spins in the microscopic volume using NV-based ESR. Finally, we discussed the number of spins detected by the NV-based ESR spectroscopy. By comparing the experimental result with simulation, we estimated the number of the detected spins to be ≤50 spins.

  11. A QUANTUM MECHANICAL STUDY OF STRUCTURAL AND ELECTRONIC DILUTION EFFECTS IN PARAMAGNETIC CHEMICAL EXCHANGE SATURATION TRANSFER AGENTS

    PubMed Central

    Miller, Whelton A.; Moore, Preston B.

    2014-01-01

    We present a computational study of the effect of chemical modifications of the meta and para substituents in the coordinating pendant arm of a modified 1,4,7,10-tetraazacyclododecane-N, N’, N″, N‴-tetraamide (DOTAM) ligand on the Chemical Exchange Saturation Transfer (CEST) signal. Magnetic Resonance Imaging (MRI) is currently one of the most widely used techniques available. MRI has led to a new class of pharmaceuticals termed “imagining” or “contrast” agents. These agents usually work by incorporating lanthanide metals such as Gadolinium (Gd) and Europium (Eu). This allows the contrast agents to take advantage of the paramagnetic properties of the metals, which in turn enhances the signal detectable by MRI. The effect of simple electron-withdrawing (e.g., nitro) and electron-donating (e.g., methyl) substituents chemically attached to a modified chelate arm (pendant arm) is quantified by charge transfer interactions in the coordinated water-chelate system computed from quantum mechanics. This study attempts to reveal the origin of the substituent effect on the CEST signal and the electronic structure of the complex. We find that the extent of Charge Transfer (CT) depends on orbital orientations and overlaps. However, CT interactions occur simultaneously from all arms, which causes a dilution effect with respect to the pendant arm. PMID:25485283

  12. A QUANTUM MECHANICAL STUDY OF STRUCTURAL AND ELECTRONIC DILUTION EFFECTS IN PARAMAGNETIC CHEMICAL EXCHANGE SATURATION TRANSFER AGENTS.

    PubMed

    Miller, Whelton A; Moore, Preston B

    2014-01-01

    We present a computational study of the effect of chemical modifications of the meta and para substituents in the coordinating pendant arm of a modified 1,4,7,10-tetraazacyclododecane-N, N', N″, N‴-tetraamide (DOTAM) ligand on the Chemical Exchange Saturation Transfer (CEST) signal. Magnetic Resonance Imaging (MRI) is currently one of the most widely used techniques available. MRI has led to a new class of pharmaceuticals termed "imagining" or "contrast" agents. These agents usually work by incorporating lanthanide metals such as Gadolinium (Gd) and Europium (Eu). This allows the contrast agents to take advantage of the paramagnetic properties of the metals, which in turn enhances the signal detectable by MRI. The effect of simple electron-withdrawing (e.g., nitro) and electron-donating (e.g., methyl) substituents chemically attached to a modified chelate arm (pendant arm) is quantified by charge transfer interactions in the coordinated water-chelate system computed from quantum mechanics. This study attempts to reveal the origin of the substituent effect on the CEST signal and the electronic structure of the complex. We find that the extent of Charge Transfer (CT) depends on orbital orientations and overlaps. However, CT interactions occur simultaneously from all arms, which causes a dilution effect with respect to the pendant arm. PMID:25485283

  13. New roles of flavoproteins in molecular cell biology: blue-light active flavoproteins studied by electron paramagnetic resonance.

    PubMed

    Schleicher, Erik; Bittl, Robert; Weber, Stefan

    2009-08-01

    Exploring enzymatic mechanisms at a molecular level is one of the major challenges in modern biophysics. Based on enzyme structure data, as obtained by X-ray crystallography or NMR spectroscopy, one can suggest how substrates and products bind for catalysis. However, from the 3D structure alone it is very rarely possible to identify how intermediates are formed and how they are interconverted. Molecular spectroscopy can provide such information and thus supplement our knowledge on the specific enzymatic reaction under consideration. In the case of enzymatic processes in which paramagnetic molecules play a role, EPR and related methods such as electron-nuclear double resonance (ENDOR) are powerful techniques to unravel important details, e.g. the electronic structure or the protonation state of the intermediate(s) carrying (the) unpaired electron spin(s). Here, we review recent EPR/ENDOR studies of blue-light active flavoproteins with emphasis on photolyases that catalyze the enzymatic repair of UV damaged DNA, and on cryptochrome blue-light photoreceptors that act in several species as central components of the circadian clock. PMID:19624734

  14. Optical absorption and electron paramagnetic resonance of the E{sub {alpha}}{sup '} center in amorphous silicon dioxide

    SciTech Connect

    Buscarino, G.; Boscaino, R.; Agnello, S.; Gelardi, F. M.

    2008-04-15

    We report a combined study by optical absorption (OA) and electron paramagnetic resonance (EPR) spectroscopy on the E{sub {alpha}}{sup '} point defect in amorphous silicon dioxide (a-SiO{sub 2}). This defect has been studied in {beta}-ray irradiated and thermally treated oxygen-deficient a-SiO{sub 2} materials. Our results have pointed out that the E{sub {alpha}}{sup '} center is responsible for an OA Gaussian band peaked at {approx}5.8 eV and having a full width at half maximum of {approx}0.6 eV. The estimated oscillator strength of the related electronic transition is {approx}0.14. Furthermore, we have found that this OA band is quite similar to that of the E{sub {gamma}}{sup '} center induced in the same materials, indicating that the related electronic transitions involve states highly localized on a structure common to both defects: the O{identical_to}Si{sup {center_dot}} moiety.

  15. New roles of flavoproteins in molecular cell biology: blue-light active flavoproteins studied by electron paramagnetic resonance.

    PubMed

    Schleicher, Erik; Bittl, Robert; Weber, Stefan

    2009-08-01

    Exploring enzymatic mechanisms at a molecular level is one of the major challenges in modern biophysics. Based on enzyme structure data, as obtained by X-ray crystallography or NMR spectroscopy, one can suggest how substrates and products bind for catalysis. However, from the 3D structure alone it is very rarely possible to identify how intermediates are formed and how they are interconverted. Molecular spectroscopy can provide such information and thus supplement our knowledge on the specific enzymatic reaction under consideration. In the case of enzymatic processes in which paramagnetic molecules play a role, EPR and related methods such as electron-nuclear double resonance (ENDOR) are powerful techniques to unravel important details, e.g. the electronic structure or the protonation state of the intermediate(s) carrying (the) unpaired electron spin(s). Here, we review recent EPR/ENDOR studies of blue-light active flavoproteins with emphasis on photolyases that catalyze the enzymatic repair of UV damaged DNA, and on cryptochrome blue-light photoreceptors that act in several species as central components of the circadian clock.

  16. Electron Paramagnetic Resonance: Elementary Theory and Practical Applications, Second Edition (John A. Weil and James R. Bolton)

    NASA Astrophysics Data System (ADS)

    Williams, Ffrancon

    2009-01-01

    The detection of electron magnetic resonance by Zavoiskii in the mid 1940s (1) ushered in a golden age of physical and chemical applications. Perhaps no single book did more to stimulate this development of EPR spectroscopy than the classic text by Wertz and Bolton (2) , which appeared in 1972. A revised version, with John A. Weil added as a co-author, was published by Wiley in 1994. This 2007 text is formally described as the second edition of the 1994 version. Wertz died shortly after the publication of the 1994 edition leaving Weil and Bolton as authors. In noting that the senior author (JAW) takes most of the responsibility for the content of this 2007 version, the Preface refers to it at one point as the "third edition", which of course is precisely how older readers will regard it. The main thrust of the book is decidedly on the physical aspects of EPR, so that it nicely complements the more chemical emphasis provided in the recent comprehensive text by Gerson and Hüber (3) . As the authors remark, the 2007 edition does not differ dramatically from the 1994 version. The titles of the 13 chapters remain the same except for chapter 11, which now refers to the "Noncontinuous" instead of the "Time-Dependent" Excitation of Spins. Recent developments are generally accommodated by a few extra pages in each chapter. Thus, chapter 1 on Basic Principles of Paramagnetic Resonance has been expanded from 31 to 36 pages to introduce the topics of parallel-field EPR, time-resolved EPR, "computerology", and EPR imaging. Chapter 2 on Magnetic Interactions is essentially unchanged while chapter 3 on Isotropic Hyperfine Effects has been expanded to include new sections on Deviations from the Simple Multinomial Scheme (3.7) and Some Interesting π-Type Free Radicals (3.9). Section 3.9 provides a useful corrective to the notion that the EPR method can detect and characterize almost any type of radical species. This welcome touch of realism is nicely illustrated by mentioning

  17. Design and implementation of an FPGA-based timing pulse programmer for pulsed-electron paramagnetic resonance applications.

    PubMed

    Sun, Li; Savory, Joshua J; Warncke, Kurt

    2013-08-01

    The design, construction and implementation of a field-programmable gate array (FPGA) -based pulse programmer for pulsed-electron paramagnetic resonance (EPR) experiments is described. The FPGA pulse programmer offers advantages in design flexibility and cost over previous pulse programmers, that are based on commercial digital delay generators, logic pattern generators, and application-specific integrated circuit (ASIC) designs. The FPGA pulse progammer features a novel transition-based algorithm and command protocol, that is optimized for the timing structure required for most pulsed magnetic resonance experiments. The algorithm was implemented by using a Spartan-6 FPGA (Xilinx), which provides an easily accessible and cost effective solution for FPGA interfacing. An auxiliary board was designed for the FPGA-instrument interface, which buffers the FPGA outputs for increased power consumption and capacitive load requirements. Device specifications include: Nanosecond pulse formation (transition edge rise/fall times, ≤3 ns), low jitter (≤150 ps), large number of channels (16 implemented; 48 available), and long pulse duration (no limit). The hardware and software for the device were designed for facile reconfiguration to match user experimental requirements and constraints. Operation of the device is demonstrated and benchmarked by applications to 1-D electron spin echo envelope modulation (ESEEM) and 2-D hyperfine sublevel correlation (HYSCORE) experiments. The FPGA approach is transferrable to applications in nuclear magnetic resonance (NMR; magnetic resonance imaging, MRI), and to pulse perturbation and detection bandwidths in spectroscopies up through the optical range.

  18. Quantitative determination of copper in a glass matrix using double pulse laser induced breakdown and electron paramagnetic resonance spectroscopic techniques.

    PubMed

    Khalil, Ahmed A I; Morsy, Mohamed A

    2016-07-01

    A series of lithium-lead-borate glasses of a variable copper oxide loading were quantitatively analyzed in this work using two distinct spectroscopic techniques, namely double pulse laser induced breakdown spectroscopy (DP-LIBS) and electron paramagnetic resonance (EPR). DP-LIBS results measured upon a combined nanosecond lasers irradiation running at 266nm and 1064nm pulses of a collinear configuration directed to the surface of borate glass samples with a known composition. This arrangement was employed to predict the electron's temperature (Te) and density (Ne) of the excited plasma from the recorded spectra. The intensity of elements' responses using this scheme is higher than that of single-pulse laser induced breakdown spectroscopy (SP-LIBS) setup under the same experimental conditions. On the other hand, the EPR data shows typical Cu (II) EPR-signals in the borate glass system that is networked at a distorted tetragonal Borate-arrangement. The signal intensity of the Cu (II) peak at g⊥=2.0596 has been used to quantify the Cu-content accurately in the glass matrix. Both techniques produced linear calibration curves of Cu-metals in glasses with excellent linear regression coefficient (R(2)) values. This study establishes a good correlation between DP-LIBS analysis of glass and the results obtained using EPR spectroscopy. The proposed protocols prove the great advantage of DP-LIBS system for the detection of a trace copper on the surface of glasses. PMID:27154655

  19. A Ku band pulsed electron paramagnetic resonance spectrometer using an arbitrary waveform generator for quantum control experiments at millikelvin temperatures

    SciTech Connect

    Yap, Yung Szen; Tabuchi, Yutaka; Negoro, Makoto; Kagawa, Akinori; Kitagawa, Masahiro

    2015-06-15

    We present a 17 GHz (Ku band) arbitrary waveform pulsed electron paramagnetic resonance spectrometer for experiments down to millikelvin temperatures. The spectrometer is located at room temperature, while the resonator is placed either in a room temperature magnet or inside a cryogen-free dilution refrigerator; the operating temperature range of the dilution unit is from ca. 10 mK to 8 K. This combination provides the opportunity to perform quantum control experiments on electron spins in the pure-state regime. At 0.6 T, spin echo experiments were carried out using γ-irradiated quartz glass from 1 K to 12.3 mK. With decreasing temperatures, we observed an increase in spin echo signal intensities due to increasing spin polarizations, in accordance with theoretical predictions. Through experimental data fitting, thermal spin polarization at 100 mK was estimated to be at least 99%, which was almost pure state. Next, to demonstrate the ability to create arbitrary waveform pulses, we generate a shaped pulse by superposing three Gaussian pulses of different frequencies. The resulting pulse was able to selectively and coherently excite three different spin packets simultaneously—a useful ability for analyzing multi-spin system and for controlling a multi-qubit quantum computer. By applying this pulse to the inhomogeneously broadened sample, we obtain three well-resolved excitations at 8 K, 1 K, and 14 mK.

  20. Design and implementation of an FPGA-based timing pulse programmer for pulsed-electron paramagnetic resonance applications

    PubMed Central

    Sun, Li; Savory, Joshua J.; Warncke, Kurt

    2014-01-01

    The design, construction and implementation of a field-programmable gate array (FPGA) -based pulse programmer for pulsed-electron paramagnetic resonance (EPR) experiments is described. The FPGA pulse programmer offers advantages in design flexibility and cost over previous pulse programmers, that are based on commercial digital delay generators, logic pattern generators, and application-specific integrated circuit (ASIC) designs. The FPGA pulse progammer features a novel transition-based algorithm and command protocol, that is optimized for the timing structure required for most pulsed magnetic resonance experiments. The algorithm was implemented by using a Spartan-6 FPGA (Xilinx), which provides an easily accessible and cost effective solution for FPGA interfacing. An auxiliary board was designed for the FPGA-instrument interface, which buffers the FPGA outputs for increased power consumption and capacitive load requirements. Device specifications include: Nanosecond pulse formation (transition edge rise/fall times, ≤3 ns), low jitter (≤150 ps), large number of channels (16 implemented; 48 available), and long pulse duration (no limit). The hardware and software for the device were designed for facile reconfiguration to match user experimental requirements and constraints. Operation of the device is demonstrated and benchmarked by applications to 1-D electron spin echo envelope modulation (ESEEM) and 2-D hyperfine sublevel correlation (HYSCORE) experiments. The FPGA approach is transferrable to applications in nuclear magnetic resonance (NMR; magnetic resonance imaging, MRI), and to pulse perturbation and detection bandwidths in spectroscopies up through the optical range. PMID:25076864

  1. Experimental and Theoretical Electron Paramagnetic Resonance (EPR) Study on the Temperature-Dependent Structural Changes of Methylsulfanylmethane

    PubMed Central

    Tapramaz, Recep; Türkkan, Ercan; Dereli, Ömer

    2011-01-01

    Methylsulfonylmethane (or dimethyl sulfone), a naturally produced and vitally important organosulfur compound in living organisms, was irradiated with gamma rays, and the produced radicals were investigated using electron paramagnetic resonance spectroscopy at different temperatures. The structure and behavior of the radical changed when the temperatures varied. The hyperfine splitting of the CH3 group was small, and the 33S splitting was relatively high between 80 and −50 °C. When the temperature was between −50 and −160 °C, the 33S splitting became small and the CH3 splitting was higher. However, the group kept rotating; therefore, only the isotropic splitting values were measured, and the g-values were anisotropic. When the temperature decreased below −180 °C, the CH3 group stopped rotating, and the hydrogen splitting values became nonequivalent due to an inhomogeneous electron distribution. The observed structures can be explained by referring to both the experimental and theoretically calculated values reported. PMID:21954334

  2. A Ku band pulsed electron paramagnetic resonance spectrometer using an arbitrary waveform generator for quantum control experiments at millikelvin temperatures.

    PubMed

    Yap, Yung Szen; Tabuchi, Yutaka; Negoro, Makoto; Kagawa, Akinori; Kitagawa, Masahiro

    2015-06-01

    We present a 17 GHz (Ku band) arbitrary waveform pulsed electron paramagnetic resonance spectrometer for experiments down to millikelvin temperatures. The spectrometer is located at room temperature, while the resonator is placed either in a room temperature magnet or inside a cryogen-free dilution refrigerator; the operating temperature range of the dilution unit is from ca. 10 mK to 8 K. This combination provides the opportunity to perform quantum control experiments on electron spins in the pure-state regime. At 0.6 T, spin echo experiments were carried out using γ-irradiated quartz glass from 1 K to 12.3 mK. With decreasing temperatures, we observed an increase in spin echo signal intensities due to increasing spin polarizations, in accordance with theoretical predictions. Through experimental data fitting, thermal spin polarization at 100 mK was estimated to be at least 99%, which was almost pure state. Next, to demonstrate the ability to create arbitrary waveform pulses, we generate a shaped pulse by superposing three Gaussian pulses of different frequencies. The resulting pulse was able to selectively and coherently excite three different spin packets simultaneously-a useful ability for analyzing multi-spin system and for controlling a multi-qubit quantum computer. By applying this pulse to the inhomogeneously broadened sample, we obtain three well-resolved excitations at 8 K, 1 K, and 14 mK.

  3. One and Two Dimensional Pulsed Electron Paramagnetic Resonance Studies of in vivo Vanadyl Coordination in Rat Kidney

    PubMed Central

    Liboiron, Barry D.; Thompson, Katherine H.; Vera, Erika; Yuen, Violet G.; McNeill, John H.

    2003-01-01

    The biological fate of a chelated vanadium source is investigated by/n vivo spectroscopic methods to elucidate the chemical form in which the metal ion is accumulated. A pulsed electron paramagnetic resonance study of vanadyl ions in kidney tissue, taken from rats previously treated with bis(ethylmaltolato)oxovanadium(IV) (BEOV) in drinking water, is presented. A combined approach using stimulated echo (3-pulse) electron spin echo envelope modulation (ESEEM) and the two dimensional 4-pulse hyperfine sublevel correlation (HYSCORE) spectroscopies has shown that at least some of the VO2+ ions are involved in the coordination with nitrogen-containing ligands. From the experimental spectra, a 4N hyperfine coupling constant of 4.9 MHz and a quadrupole coupling constant of 0.6 + 0.04 MHz were determined, consistent with amine coordination of the vanadyl ions. Study of VO-histidine model complexes allowed for a determination of the percentage of nitrogen-coordinated VO2+ ions in the tissue sample that is found nitrogen-coordinated. By taking into account the bidentate nature of histidine coordination to VO2+ ions, a more accurate determination of this value is reported. The biological fate of chelated versus free (i.e. salts) vanadyl ion sources has been deduced by comparison to earlier reports. In contrast to its superior pharmacological efficacy over VOSO4, BEOV shares a remarkably similar biological fate after uptake into kidney tissue. PMID:18365044

  4. Hyperfine interactions of Ho3+ ions in KY3F10: Electron paramagnetic resonance and optical spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Pytalev, D. S.; Chukalina, E. P.; Popova, M. N.; Shakurov, G. S.; Malkin, B. Z.; Korableva, S. L.

    2012-09-01

    We use high-frequency electron paramagnetic resonance (EPR) and high-resolution optical Fourier spectroscopies to characterize hyperfine interactions of the impurity Ho3+ ions in KY3F10 crystals. Well-resolved hyperfine structure is observed in the EPR spectra for several transitions within the ground 5I8 multiplet of the Ho3+ ion and in the optical spectra for many lines in the infrared and visible ranges. The observed hyperfine patterns and field dependences of the resonance frequencies in the EPR spectra are well reproduced by calculations based on the crystal field (CF) theory. This favors reliability of calculated energies and wave functions of the electron-nuclear states within the ground and excited levels of Ho3+ in KY3F10. Finally, the dc magnetic susceptibility of the concentrated KHo3F10 crystal taken from literature is successfully modeled in the temperature range 0.01-20 K, using CF parameters of the impurity Ho3+ ions in KY3F10.

  5. Electronic structure of the Mn-cofactor of modified bacterial reaction centers measured by electron paramagnetic resonance and electron spin echo envelope modulation spectroscopies.

    PubMed

    Tufts, A A; Flores, M; Olson, T L; Williams, J C; Allen, J P

    2014-05-01

    The electronic structure of a Mn(II) ion bound to highly oxidizing reaction centers of Rhodobacter sphaeroides was studied in a mutant modified to possess a metal binding site at a location comparable to the Mn4Ca cluster of photosystem II. The Mn-binding site of the previously described mutant, M2, contains three carboxylates and one His at the binding site (Thielges et al., Biochemistry 44:389-7394, 2005). The redox-active Mn-cofactor was characterized using electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies. In the light without bound metal, the Mn-binding mutants showed an EPR spectrum characteristic of the oxidized bacteriochlorophyll dimer and reduced quinone whose intensity was significantly reduced due to the diminished quantum yield of charge separation in the mutant compared to wild type. In the presence of the metal and in the dark, the EPR spectrum measured at the X-band frequency of 9.4 GHz showed a distinctive spin 5/2 Mn(II) signal consisting of 16 lines associated with both allowed and forbidden transitions. Upon illumination, the amplitude of the spectrum is decreased by over 80 % due to oxidation of the metal upon electron transfer to the oxidized bacteriochlorophyll dimer. The EPR spectrum of the Mn-cofactor was also measured at the Q-band frequency of 34 GHz and was better resolved as the signal was composed of the six allowed electronic transitions with only minor contributions from other transitions. A fit of the Q-band EPR spectrum shows that the Mn-cofactor is a high spin Mn(II) species (S = 5/2) that is six-coordinated with an isotropic g-value of 2.0006, a weak zero-field splitting and E/D ratio of approximately 1/3. The ESEEM experiments showed the presence of one (14)N coordinating the Mn-cofactor. The nitrogen atom is assigned to a His by comparing our ESEEM results to those previously reported for Mn(II) ions bound to other proteins and on the basis of the X-ray structure of the M2

  6. Advances in nonlethal electronic weaponry

    NASA Astrophysics Data System (ADS)

    McNulty, James F.

    1998-12-01

    Non-lethal electronic weapons in the form of tasers (a stand-off incapacitation device with a range of about 15 feet) and stun guns (which are not a gun, but a close contact stun device) have been used by law enforcement for over 18 years. The taser has dominated this market, since it does not require the close physical contact (with the resultant injuries) that the stun gun requires. Tasers are effective against even determined assailants where OC or pepper sprays consistently fail. The taser also does not have the close range lethality of low impact munitions. These electronic non-lethal weapons have saved the lives of thousands of suspects and have prevented the injury of thousands of law enforcement officers. Recent advances in laser sight technology have permitted the development of a patented dual laser sight that not only increased accuracy, but have made these weapons even more intimidating, increasing surrender rates. Now increased ranges are feasible and r & d on non-lethal military weapons to replace the anti-personnel landmine has resulted in new, unmanned, non-lethal taser weapons for law enforcement corrections and border patrol perimeter control use.

  7. Polynuclear water-soluble dinitrosyl iron complexes with cysteine or glutathione ligands: electron paramagnetic resonance and optical studies.

    PubMed

    Vanin, Anatoly F; Poltorakov, Alexander P; Mikoyan, Vasak D; Kubrina, Lyudmila N; Burbaev, Dosymzhan S

    2010-09-15

    Electron paramagnetic resonance and optical spectrophotometric studies have demonstrated that low-molecular dinitrosyl iron complexes (DNICs) with cysteine or glutathione exist in aqueous solutions in the form of paramagnetic mononuclear (capital EM, Cyrillic-DNICs) and diamagnetic binuclear complexes (B-DNICs). The latter represent Roussin's red salt esters and can be prepared by treatment of aqueous solutions of Fe(2+) and thiols (small er, Cyrilliccapital EN, Cyrillic 7.4) with gaseous nitric oxide (NO) at the thiol:Fe(2+) ratio 1:1. capital EM, Cyrillic-DNICs are synthesized under identical conditions at the thiol:Fe(2+) ratios above 20 and produce an EPR signal with an electronic configuration {Fe(NO)(2)}(7) at g(aver.)=2.03. At neutral pH, aqueous solutions contain both M-DNICs and B-DNICs (the content of the latter makes up to 50% of the total DNIC pool). The concentration of B-DNICs decreases with a rise in pH; at small er, Cyrilliccapital EN, Cyrillic 9-10, the solutions contain predominantly M-DNICs. The addition of thiol excess to aqueous solutions of B-DNICs synthesized at the thiol:Fe(2+) ratio 1:2 results in their conversion into capital EM, Cyrillic-DNICs, the total amount of iron incorporated into M-DNICs not exceeding 50% of the total iron pool in B-DNICs. Air bubbling of cys-capital EM, Cyrillic-DNIC solutions results in cysteine oxidation-controlled conversion of capital EM, Cyrillic-DNICs first into cys-B-DNICs and then into the EPR-silent compound capital HA, Cyrillic able to generate a strong absorption band at 278 nm. In the presence of glutathione or cysteine excess, compound capital HA, Cyrillic is converted into B-DNIC/M-DNIC and is completely decomposed under effect of the Fe(2+) chelator small o, Cyrillic-phenanthroline or N-methyl-d-glucamine dithiocarbamate (MGD). Moreover, MGD initiates the synthesis of paramagnetic mononitrosyl iron complexes with MGD. It is hypothesized that compound capital HA, Cyrillic represents a polynuclear

  8. Electron Paramagnetic Resonance: a tool for in situ detection, imaging and dating of biosignatures in primitive organic matter

    NASA Astrophysics Data System (ADS)

    Gourier, D.; Binet, L.; Vezin, H.

    2012-04-01

    Electron Paramagnetic Resonance (EPR) spectroscopy and imaging are based on the interaction of a microwave electromagnetic field (typically in the GHz range) with electron spins in presence of an external magnetic field. Contrary to UV-visible and Infrared light, microwave radiation can penetrate in most non conducting materials, so that EPR is sensitive to the bulk (and not to the surface) of samples. All the paramagnetic defects, impurities, point defects in the mineral matrix, radicals in carbonaceous matter of an ancient rock can be detected by this technique. As the most ancient traces of life, as old as 3.5 Gy, are recorded as carbonaceous microstructures in siliceous sedimentary structures (cherts), the radical defects of these microstructures can be probed in situ without sample preparation. By using continuous-wave EPR, the fossilized carbonaceous matter can be mapped at the sub-millimeter scale (EPR imaging)[1], and can be dated with respect to the host rock (evolution of the EPR lineshape)[2]. Thus this method could be used for contamination detection (endolithic bacteria, infiltration etc…). By using pulsed-EPR spectroscopy (instead of continuous wave), nuclear magnetic transitions of elements in and around radicals can be detected with a high resolution and sensitivity. We show that specific nuclear transitions for hydrogen (1H and 2D) and 13C (and other nuclei such as 29Si and 31P) can be identified in extraterrestrial carbonaceous matter (meteorites) and in Precambrian and younger cherts. These pulsed techniques provide molecular scale biosignatures for primitive life detection and internal probes to study the history of organic matter in the early solar system [3,4]. Paramagnetic biosignatures are not limited to the organic component of cherts. Specific EPR biosignatures of metal ions can be detected in biominerals such as MnO2 [5] or in molecular V4+ complexes [6]. EPR is thus a potential technique for the search of primitive life on Earth and

  9. Kissing G Domains of MnmE Monitored by X-Ray Crystallography and Pulse Electron Paramagnetic Resonance Spectroscopy

    PubMed Central

    Meyer, Simon; Böhme, Sabine; Krüger, André; Steinhoff, Heinz-Jürgen; Klare, Johann P.; Wittinghofer, Alfred

    2009-01-01

    MnmE, which is involved in the modification of the wobble position of certain tRNAs, belongs to the expanding class of G proteins activated by nucleotide-dependent dimerization (GADs). Previous models suggested the protein to be a multidomain protein whose G domains contact each other in a nucleotide dependent manner. Here we employ a combined approach of X-ray crystallography and pulse electron paramagnetic resonance (EPR) spectroscopy to show that large domain movements are coupled to the G protein cycle of MnmE. The X-ray structures show MnmE to be a constitutive homodimer where the highly mobile G domains face each other in various orientations but are not in close contact as suggested by the GDP-AlFx structure of the isolated domains. Distance measurements by pulse double electron-electron resonance (DEER) spectroscopy show that the G domains adopt an open conformation in the nucleotide free/GDP-bound and an open/closed two-state equilibrium in the GTP-bound state, with maximal distance variations of 18 Å. With GDP and AlFx, which mimic the transition state of the phosphoryl transfer reaction, only the closed conformation is observed. Dimerization of the active sites with GDP-AlFx requires the presence of specific monovalent cations, thus reflecting the requirements for the GTPase reaction of MnmE. Our results directly demonstrate the nature of the conformational changes MnmE was previously suggested to undergo during its GTPase cycle. They show the nucleotide-dependent dynamic movements of the G domains around two swivel positions relative to the rest of the protein, and they are of crucial importance for understanding the mechanistic principles of this GAD. PMID:19806182

  10. Investigation of Antioxidant Activity of Pomegranate Juices by Means of Electron Paramagnetic Resonance and UV-Vis Spectroscopy.

    PubMed

    Kozik, Violetta; Jarzembek, Krystyna; Jędrzejowska, Agnieszka; Bąk, Andrzej; Polak, Justyna; Bartoszek, Mariola; Pytlakowska, Katarzyna

    2015-01-01

    Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r)=0.90 and determination coefficient (r2)=0.81 (P<0.05).

  11. Electron paramagnetic resonance evidence of hydroxyl radical generation and oxidative damage induced by tetrabromobisphenol A in Carassius auratus.

    PubMed

    Shi, Huahong; Wang, Xiaorong; Luo, Yi; Su, Yan

    2005-09-30

    Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants (BFRs). To confirm its putative oxidative stress-inducing activity, freshwater fish Carassius auratus were injected intraperitoneally with TBBPA. One experiment lasted 3h to 28 days after a single injection of 100mg/kg TBBPA, and the other lasted 24h after a single injection of 0-300 mg/kg TBBPA. Reactive oxygen species (ROS) were trapped by phenyl-tert-butyl nitrone (PBN) and detected by electron paramagnetic resonance (EPR). Protein carbonyl (PCO) and lipid peroxidation product (LPO) content were also determined. A six-line EPR spectrum was detected in the sample prepared in air, and a multiple one was obtained in nitrogen. The observed spectrum in nitrogen fits the simulation one with PBN/OCH(3) and PBN/CH(3) quite well. As compared to the control group, TBBPA significantly induced ROS production marked by the intensity of the prominent spectra in liver and bile. TBBPA (100mg/kg) also significantly increased PCO content in liver starting 24h and LPO content 3 days after injection. Either PCO or LPO content showed significant relation with ROS production. Based on the hyperfine constants and shape of the spectrum, ROS induced by TBBPA was determined as OH. The results clearly indicated that TBBPA could induce OH generation and result in oxidative damage in liver of C. auratus.

  12. Evaluation of synergistic antioxidant potential of complex mixtures using oxygen radical absorbance capacity (ORAC) and electron paramagnetic resonance (EPR).

    PubMed

    Parker, Tory L; Miller, Samantha A; Myers, Lauren E; Miguez, Fernando E; Engeseth, Nicki J

    2010-01-13

    Previous research has demonstrated that certain combinations of compounds result in a decrease in toxic or pro-oxidative effects, previously noted when compounds were administered singly. Thus, there is a need to study many complex interactions further. Two in vitro techniques [electron paramagnetic resonance (EPR) and oxygen radical absorbance capacity (ORAC) assays] were used in this study to assess pro- and antioxidant capacity and synergistic potential of various compounds. Rutin, p-coumaric acid, abscisic acid, ascorbic acid, and a sugar solution were evaluated individually at various concentrations and in all 26 possible combinations at concentrations found in certain foods (honey or papaya), both before and after simulated digestion. EPR results indicated sugar-containing combinations provided significantly higher antioxidant capacity; those combinations containing sugars and ascorbic acid demonstrated synergistic potential. The ORAC assay suggested additive effects, with some combinations having synergistic potential, although fewer combinations were significantly synergistic after digestion. Finally, ascorbic acid, caffeic acid, quercetin, and urate were evaluated at serum-achievable levels. EPR analysis did not demonstrate additive or synergistic potential, although ORAC analysis did, principally in combinations containing ascorbic acid.

  13. Electron paramagnetic resonance studies of the soluble CuA protein from the cytochrome ba3 of Thermus thermophilus.

    PubMed Central

    Karpefors, M; Slutter, C E; Fee, J A; Aasa, R; Källebring, B; Larsson, S; Vänngård, T

    1996-01-01

    The electron paramagnetic resonance (EPR) spectrum of the binuclear CuA center in the water-soluble subunit II fragment from cytochrome ba3 of Thermus thermophilus was recorded at 3.93, 9.45, and 34.03 GHz, and the EPR parameters were determined by computer simulations. The frequency and M1 dependence of the linewidth was discussed in terms of g strain superimposed on a correlation between the A and g values. The g values were found to be gx = 1.996, gy = 2.011, gz = 2.187, and the two Cu ions contribute nearly equally to the hyperfine structure, with magnitude of Ax magnitude of approximately 15 G, magnitude of Ay magnitude = 29 G, and magnitude of Az magnitude of = 28.5 G (65Cu). Theoretical CNDO/S calculations, based on the x-ray structure of the Paracoccus denitrificans enzyme, yield a singly occupied antibonding orbital in which each Cu is pi*-bonded to one S and sigma*-bonded to the other. In contrast to the equal spin distribution suggested by the EPR simulations, the calculated contributions from the Cu ions differ by a factor of 2. However, only small changes in the ligand geometry are needed to reproduce the experimental results. PMID:8913619

  14. Electron paramagnetic resonance studies of the soluble CuA protein from the cytochrome ba3 of Thermus thermophilus.

    PubMed

    Karpefors, M; Slutter, C E; Fee, J A; Aasa, R; Källebring, B; Larsson, S; Vänngård, T

    1996-11-01

    The electron paramagnetic resonance (EPR) spectrum of the binuclear CuA center in the water-soluble subunit II fragment from cytochrome ba3 of Thermus thermophilus was recorded at 3.93, 9.45, and 34.03 GHz, and the EPR parameters were determined by computer simulations. The frequency and M1 dependence of the linewidth was discussed in terms of g strain superimposed on a correlation between the A and g values. The g values were found to be gx = 1.996, gy = 2.011, gz = 2.187, and the two Cu ions contribute nearly equally to the hyperfine structure, with magnitude of Ax magnitude of approximately 15 G, magnitude of Ay magnitude = 29 G, and magnitude of Az magnitude of = 28.5 G (65Cu). Theoretical CNDO/S calculations, based on the x-ray structure of the Paracoccus denitrificans enzyme, yield a singly occupied antibonding orbital in which each Cu is pi*-bonded to one S and sigma*-bonded to the other. In contrast to the equal spin distribution suggested by the EPR simulations, the calculated contributions from the Cu ions differ by a factor of 2. However, only small changes in the ligand geometry are needed to reproduce the experimental results.

  15. Identifying the Constituents of and Transformations in Diatomaceous Earth and Polysiloxane Foams Through the Use of Electron Paramagnetic Resonance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Blair, Michael; Muenchausen, Ross; Bennett, Bryan; Smith, James; Stephens, Thomas; Cooke, Wayne

    2007-03-01

    The chemical aging of polymeric materials is largely governed by the characteristics of the storage environment. For polysiloxane foams, the diatomaceous earth (DE) filler is a small component of the foam, but it plays a large role in the handling of water in the system. The DE filler can act as either a ``source'' or a ``sink'' for water via both chemical hydroxylation/ dehydroxylation and physical adsorption/ desorption processes, depending on the processing history and storage conditions. We have used electron paramagnetic resonance (EPR) spectroscopy to examine composite foam material as well as the DE filler alone. Intense, broad (400 Gauss) resonances were recorded at room temperature as a function of the microwave power at X-band frequency. The observed spectra have been assigned to the iron oxide compounds goethite, lepidocrocite, hematite, and magnetite based upon the measured EPR spectra of these minerals. As the presence or absence of free H2O and the temperature of processing and storage also affects the interconversion of these various iron oxides, we indicate how this process can be followed by monitoring changes in the EPR spectra.

  16. Evaluation of synergistic antioxidant potential of complex mixtures using oxygen radical absorbance capacity (ORAC) and electron paramagnetic resonance (EPR).

    PubMed

    Parker, Tory L; Miller, Samantha A; Myers, Lauren E; Miguez, Fernando E; Engeseth, Nicki J

    2010-01-13

    Previous research has demonstrated that certain combinations of compounds result in a decrease in toxic or pro-oxidative effects, previously noted when compounds were administered singly. Thus, there is a need to study many complex interactions further. Two in vitro techniques [electron paramagnetic resonance (EPR) and oxygen radical absorbance capacity (ORAC) assays] were used in this study to assess pro- and antioxidant capacity and synergistic potential of various compounds. Rutin, p-coumaric acid, abscisic acid, ascorbic acid, and a sugar solution were evaluated individually at various concentrations and in all 26 possible combinations at concentrations found in certain foods (honey or papaya), both before and after simulated digestion. EPR results indicated sugar-containing combinations provided significantly higher antioxidant capacity; those combinations containing sugars and ascorbic acid demonstrated synergistic potential. The ORAC assay suggested additive effects, with some combinations having synergistic potential, although fewer combinations were significantly synergistic after digestion. Finally, ascorbic acid, caffeic acid, quercetin, and urate were evaluated at serum-achievable levels. EPR analysis did not demonstrate additive or synergistic potential, although ORAC analysis did, principally in combinations containing ascorbic acid. PMID:19957934

  17. Early folding events during light harvesting complex II assembly in vitro monitored by pulsed electron paramagnetic resonance.

    PubMed

    Fehr, Niklas; García-Rubio, Inés; Jeschke, Gunnar; Paulsen, Harald

    2016-06-01

    Efficient energy transfer in the major light harvesting complex II (LHCII) of green plants is facilitated by the precise alignment of pigments due to the protein matrix they are bound to. Much is known about the import of the LHCII apoprotein into the chloroplast via the TOC/TIC system and its targeting to the thylakoid membrane but information is sparse about when and where the pigments are bound and how this is coordinated with protein folding. In vitro, the LHCII apoprotein spontaneously folds and binds its pigments if the detergent-solubilized protein is combined with a mixture of chlorophylls a and b and carotenoids. In the present work, we employed this approach to study apoprotein folding and pigment binding in a time-resolved manner by using pulsed electron paramagnetic resonance (EPR). Intra-molecular distances were measured before folding, after 255 ms and 40 s folding time in the absence of cryoprotectant, and in the fully folded and assembled LHCII. In accordance with earlier results, the most of the folding of the three membrane-spanning alpha helices precedes their apposition into the final tertiary structure. However, their formation follows different kinetics, partially extending into the final phase of LHCII formation during which much of the condensation of the pigment-protein structure occurs, presumably governed by the binding of chlorophyll b. A rough timetable is proposed to sort partial events into the LHCII formation process. PMID:27063475

  18. Combustion Synthesized Europium Doped LaAI₁₁O₁₈ Phosphors--An Electron Paramagnetic Resonance and Optical Study.

    PubMed

    Singh, Vijay; Sivaramaiah, G; Rao, J L; Kumaran, R Senthil; Dhoble, S J

    2016-01-01

    By adopting a facile solution combustion synthesis, crystallized europium doped blue phosphors were successfully prepared. These phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared absorption (FT-IR), energy dispersive analysis of X-ray, Electron Paramagnetic Resonance (EPR) and Photoluminescence (PL) experimental methods. The photoluminescence spectrum indicates Eu²⁺ and Eu³⁺ ions in these phosphors. The band at around 442 nm is attributed to the spin-allowed 4f⁶5d¹ (2D) --> 4f⁷(⁸S₇/2) transition of Eu²⁺ ions. The sharp bands at 591 (⁵D₀ --> ⁷F₁) and 616 (⁵D₀ --> ⁷F₂) nm are attributed to the spin-forbidden transitions of Eu³⁺ ions. The EPR spectra of as-prepared and post-treated LaAl₁₁O₁₈:Eu phosphors exhibit signals characteristic of La²⁺ and Eu²⁺ ions. The number of spins, Gibbs energy, magnetic susceptibility, Curie constant and effective magnetic moment values were calculated and compared at 296 and 110 K. PMID:27398524

  19. Electron paramagnetic resonance of [(CH3)3NH]CuCl3.2H2O

    NASA Astrophysics Data System (ADS)

    Ritter, Mark B.; Drumheller, John E.; Kite, Terence M.; Snively, Leslie O.; Emerson, Kenneth

    1983-11-01

    The electron paramagnetic resonance of [(CH3)3NH]CuCl3.2H2O has been studied in the temperature range of 4 K to room temperature. This compound is known to behave magnetically as a spin- 1/2 , one-dimensional Heisenberg ferromagnetic with ordering below 1K. In the high-temperature regime the EPR data show a rich angular dependence of the linewidths as the magnetic field is rotated away from the chain. The data were analyzed in manner similar to that used by McGregor and Soos, who used the Blume-Hubbard result for spin dynamics and extracted exchange anisotropies in one dimension. For adequate fit, we reduced the symmetry of symmetric anisotropic exchange to orthorhombic and included the antisymmetric exchange. Isotropic symmetric, dipolar, anisotropic symmetric, and antisymmetric exchange therefore were included with the room temperature results of J0=0.8 K, Dd=0.058 K, De=0.032 K, and d=0.043 K, respectively, and further show about a 12% XY character to the exchange. These results are reasonably consistent with the previous results on this compound. Splitting of the EPR lines indicate that there are two inequivalent chains along the needle axis. Data to 4 K indicate no significant changes in the angle dependence but an anomalous monotonic broadening of the linewidths is observed as temperature is lowered.

  20. Superoxide Anion Radical Production in the Tardigrade Paramacrobiotus richtersi, the First Electron Paramagnetic Resonance Spin-Trapping Study.

    PubMed

    Savic, Aleksandar G; Guidetti, Roberto; Turi, Ana; Pavicevic, Aleksandra; Giovannini, Ilaria; Rebecchi, Lorena; Mojovic, Milos

    2015-01-01

    Anhydrobiosis is an adaptive strategy that allows withstanding almost complete body water loss. It has been developed independently by many organisms belonging to different evolutionary lines, including tardigrades. The loss of water during anhydrobiotic processes leads to oxidative stress. To date, the metabolism of free radicals in tardigrades remained unclear. We present a method for in vivo monitoring of free radical production in tardigrades, based on electron paramagnetic resonance and spin-trap DEPMPO, which provides simultaneous identification of various spin adducts (i.e., different types of free radicals). The spin trap can be easily absorbed in animals, and tardigrades stay alive during the measurements and during 24-h monitoring after the treatment. The results show that hydrated specimens of the tardigrade Paramacrobiotus richtersi produce the pure superoxide anion radical ((•)O2(-)). This is an unexpected result, as all previously examined animals and plants produce both superoxide anion radical and hydroxyl radical ((•)OH) or exclusively hydroxyl radical. PMID:26052642

  1. Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N : The relationship between structural, electronic, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Bonanni, Alberta; Kiecana, Michał; Simbrunner, Clemens; Li, Tian; Sawicki, Maciej; Wegscheider, Matthias; Quast, Martin; Przybylińska, Hanka; Navarro-Quezada, Andrea; Jakieła, Rafał; Wolos, Agnieszka; Jantsch, Wolfgang; Dietl, Tomasz

    2007-03-01

    We report on the metalorganic chemical vapor deposition of GaN:Fe and (Ga,Fe)N layers on c -sapphire substrates and their thorough characterization via high-resolution x-ray diffraction, transmission electron microscopy (TEM), spatially resolved energy dispersive x-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect, electron-paramagnetic resonance (EPR), and magnetometry employing a superconducting quantum interference device (SQUID). A combination of TEM and EDS reveals the presence of coherent nanocrystals presumably FexN with the composition and lattice parameter imposed by the host. From both TEM and SIMS studies, it is stated that the density of nanocrystals and, thus the Fe concentration increases towards the surface. According to Hall effect measurements, electrons from residual donors are trapped by midgap Fe acceptor states in the limit of low iron content x≲0.4% , indicating that the concentration of Fe2+ ions increases at the expense of Fe ions in the 3+ charge state. This effect is witnessed by PL measurements as changes in the intensity of the Fe3+ -related intraionic transition, which can be controlled by codoping with Si donors and Mg acceptors. In this regime, EPR of Fe3+ ions and Curie-like magnetic susceptibility are observed. As a result of the spin-orbit interaction, Fe2+ does not produce any EPR response. However, the presence of Fe ions in the 2+ charge state may account for a temperature-independent Van Vleck-type paramagnetic signal that we observe by SQUID magnetometry. Surprisingly, at higher Fe concentrations, the electron density is found to increase substantially with the Fe content. The coexistence of electrons in the conduction band and Fe in the 3+ charge state is linked to the gradient in the Fe concentration. In layers with iron content x≳0.4% the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. A set of

  2. Probing the donor side of photosystem II in spinach chloroplasts and algae using electron paramagnetic resonance

    SciTech Connect

    Boska, M.D.

    1985-11-01

    this work concerns electron transfer reactions in photosystem II (PS II). Investigations carried out in this work examine the redox reaction rates in PS II using EPR. In Tris-washed PS II preparations from spinach, it is observed that the oxidation kinetics of S II/sub f/, the EPR signal formed by Z/sup +/ after deactivation of oxygen evolution, mirror the reduction kinetics of P680/sup +/ seen by EPR in samples poised at a variety of pH's. These data agree with previous data on the optically measured reduction kinetics of P680/sup +/. The oxidation kinetics of S II/sub vf/, the EPR transient seen from Z/sup +/ in samples active in O/sub 2/ evolving samples, were instrument limited (t/sub 1/2/ less than 4 ..mu..s) and thus could not be directly measured. These results taken together support a model where Z donates electrons directly to P680/sup +/. The examination of the oxidation and reduction kinetics of S II in monovalent and divalent salt-washed PS II preparations from spinach correlated most of the change of Z oxidation and re-reduction kinetics seen upon Tris-treatment with the loss of a 33 kDa polypeptide associated with the donor side of PS II. These data coupled with observations of stead-state light-induced amplitude changes in S II give evidence for the existance of an electron carrier between the water-splitting enzyme and Z. Observation of S II amplitude and kinetics in highly resolved PS II protein complexes from Synechoccus sp., consisting of either a 5 polypeptide PS II core complex (E-1) or a 4 polypeptide PS II core complex (CP2b), localize Z and P680 within the 4 polypeptide complex. 187 refs., 17 figs., 7 tabs.

  3. Strategy for the study of paramagnetic proteins with slow electronic relaxation rates by nmr spectroscopy: application to oxidized human [2Fe-2S] ferredoxin.

    PubMed

    Machonkin, Timothy E; Westler, William M; Markley, John L

    2004-05-01

    NMR studies of paramagnetic proteins are hampered by the rapid relaxation of nuclei near the paramagnetic center, which prevents the application of conventional methods to investigations of the most interesting regions of such molecules. This problem is particularly acute in systems with slow electronic relaxation rates. We present a strategy that can be used with a protein with slow electronic relaxation to identify and assign resonances from nuclei near the paramagnetic center. Oxidized human [2Fe-2S] ferredoxin (adrenodoxin) was used to test the approach. The strategy involves six steps: (1) NMR signals from (1)H, (13)C, and (15)N nuclei unaffected or minimally affected by paramagnetic effects are assigned by standard multinuclear two- and three-dimensional (2D and 3D) spectroscopic methods with protein samples labeled uniformly with (13)C and (15)N. (2) The very broad, hyperfine-shifted signals from carbons in the residues that ligate the metal center are classified by amino acid and atom type by selective (13)C labeling and one-dimensional (1D) (13)C NMR spectroscopy. (3) Spin systems involving carbons near the paramagnetic center that are broadened but not hyperfine-shifted are elucidated by (13)C[(13)C] constant time correlation spectroscopy (CT-COSY). (4) Signals from amide nitrogens affected by the paramagnetic center are assigned to amino acid type by selective (15)N labeling and 1D (15)N NMR spectroscopy. (5) Sequence-specific assignments of these carbon and nitrogen signals are determined by 1D (13)C[(15)N] difference decoupling experiments. (6) Signals from (1)H nuclei in these spin systems are assigned by paramagnetic-optimized 2D and 3D (1)H[(13)C] experiments. For oxidized human ferredoxin, this strategy led to assignments (to amino acid and atom type) for 88% of the carbons in the [2Fe-2S] cluster-binding loops (residues 43-58 and 89-94). These included complete carbon spin-system assignments for eight of the 22 residues and partial assignments for

  4. Biologic dosimetry for nuclear environments by electron paramagnetic resonance (EPR) methods. Conference paper

    SciTech Connect

    McCreery, M.J.; Swenberg, C.E.; Basso, M.J.; Conklin, J.J.; Hsieh, J.

    1982-06-18

    A number of stable and unstable free radicals are produced by exposure of calcified tissues to ionizing radiation. Identification of the exact molecular nature of these radicals and their kinetic annealing properties awaits further investigation. However, the high stability and the dose-response characteristics of the signal at g = 2.0023 make it very promising for use in biologic dosimetry. A 10-25 mg sample of enamel is enough to determine absorbed dose from 10-10 to the 7th power rads of gamma, X-ray, and accelerated electron exposures. This sample, which is no more than a chip from the ridge of a human tooth, does not expose the living portion of the tooth and so is relatively noninvasive. Investigations to establish a standard method for this procedure and to evaluate neutron dose is in progress. Although the procedures outlined here are relatively noninvasive, this technique affords other approaches that are even less invasive. Unlike optical methods, the sample for EPR analysis does not have to be transparent. It is not even necessary to suspend the sample as a fine powder. As long as the bone or tooth sample is within the dimensional limits of the tuned EPR cavity, it can be analyzed intact. This fact makes in vivo analysis feasible. We are currently making attempts to enlarge the EPR cavity with modification of the corresponding electronic components so that a finger can be analyzed. If this approach is successful, the expedient evaluation of large numbers of casualties might be possible by a method that is noninvasive and nondestructive.

  5. Structural characterization of titania by X-ray diffraction, photoacoustic, Raman spectroscopy and electron paramagnetic resonance spectroscopy.

    PubMed

    Kadam, R M; Rajeswari, B; Sengupta, Arijit; Achary, S N; Kshirsagar, R J; Natarajan, V

    2015-02-25

    A titania mineral (obtained from East coast, Orissa, India) was investigated by X-ray diffraction (XRD), photoacoustic spectroscopy (PAS), Raman and Electron Paramagnetic Resonance (EPR) studies. XRD studies indicated the presence of rutile (91%) and anatase (9%) phases in the mineral. Raman investigation supported this information. Both rutile and anatase phases have tetragonal structure (rutile: space group P4(2)/mnm, a=4.5946(1) Å, c=2.9597(1) Å, V=62.48(1) (Å)(3), Z=2; anatase: space group I4(1)/amd, 3.7848(2) Å, 9.5098(11) Å, V=136.22(2) (Å)(3), Z=4). The deconvoluted PAS spectrum showed nine peaks around 335, 370, 415,485, 555, 605, 659, 690,730 and 785 nm and according to the ligand field theory, these peaks were attributed to the presence of V(4+), Cr(3+), Mn(4+) and Fe(3+) species. EPR studies revealed the presence of transition metal ions V(4+)(d(1)), Cr(3+)(d(3)), Mn(4+)(d(3)) and Fe(3+)(d(5)) at Ti(4+) sites. The EPR spectra are characterized by very large crystal filed splitting (D term) and orthorhombic distortion term (E term) for multiple electron system (s>1) suggesting that the transition metal ions substitute the Ti(4+) in the lattice which is situated in distorted octahedral coordination of oxygen. The possible reasons for observation of unusually large D and E term in the EPR spectra of transition metal ions (S=3/2 and 5/2) are discussed. PMID:25233027

  6. Structural characterization of titania by X-ray diffraction, photoacoustic, Raman spectroscopy and electron paramagnetic resonance spectroscopy.

    PubMed

    Kadam, R M; Rajeswari, B; Sengupta, Arijit; Achary, S N; Kshirsagar, R J; Natarajan, V

    2015-02-25

    A titania mineral (obtained from East coast, Orissa, India) was investigated by X-ray diffraction (XRD), photoacoustic spectroscopy (PAS), Raman and Electron Paramagnetic Resonance (EPR) studies. XRD studies indicated the presence of rutile (91%) and anatase (9%) phases in the mineral. Raman investigation supported this information. Both rutile and anatase phases have tetragonal structure (rutile: space group P4(2)/mnm, a=4.5946(1) Å, c=2.9597(1) Å, V=62.48(1) (Å)(3), Z=2; anatase: space group I4(1)/amd, 3.7848(2) Å, 9.5098(11) Å, V=136.22(2) (Å)(3), Z=4). The deconvoluted PAS spectrum showed nine peaks around 335, 370, 415,485, 555, 605, 659, 690,730 and 785 nm and according to the ligand field theory, these peaks were attributed to the presence of V(4+), Cr(3+), Mn(4+) and Fe(3+) species. EPR studies revealed the presence of transition metal ions V(4+)(d(1)), Cr(3+)(d(3)), Mn(4+)(d(3)) and Fe(3+)(d(5)) at Ti(4+) sites. The EPR spectra are characterized by very large crystal filed splitting (D term) and orthorhombic distortion term (E term) for multiple electron system (s>1) suggesting that the transition metal ions substitute the Ti(4+) in the lattice which is situated in distorted octahedral coordination of oxygen. The possible reasons for observation of unusually large D and E term in the EPR spectra of transition metal ions (S=3/2 and 5/2) are discussed.

  7. Binding of manganese(II) to a tertiary stabilized hammerhead ribozyme as studied by electron paramagnetic resonance spectroscopy

    PubMed Central

    KISSELEVA, NATALIA; KHVOROVA, ANASTASIA; WESTHOF, ERIC; SCHIEMANN, OLAV

    2005-01-01

    Electron paramagnetic resonance (EPR) spectroscopy is used to study the binding of MnII ions to a tertiary stabilized hammer-head ribozyme (tsHHRz) and to compare it with the binding to the minimal hammerhead ribozyme (mHHRz). Continuous wave EPR measurements show that the tsHHRz possesses a single high-affinity MnII binding site with a KD of ≤10 nM at an NaCl concentration of 0.1 M. This dissociation constant is at least two orders of magnitude smaller than the KD determined previously for the single high-affinity MnII site in the mHHRz. In addition, whereas the high-affinity MnII is displaced from the mHHRz upon binding of the aminoglycoside antibiotic neomycin B, it is not from the tsHHRz. Despite these pronounced differences in binding, a comparison between the electron spin echo envelope modulation and hyperfine sublevel correlation spectra of the minimal and tertiary stabilized HHRz demonstrates that the structure of both binding sites is very similar. This suggests that the MnII is located in both ribozymes between the bases A9 and G10.1 of the sheared G · A tandem base pair, as shown previously and in detail for the mHHRz. Thus, the much stronger MnII binding in the tsHHRz is attributed to the interaction between the two external loops, which locks in the RNA fold, trapping the MnII in the tightly bound conformation, whereas the absence of long-range loop–loop interactions in the mHHRz leads to more dynamical and open conformations, decreasing MnII binding. PMID:15611296

  8. Electron paramagnetic resonance and theoretical studies of Nb in 4H- and 6H-SiC

    NASA Astrophysics Data System (ADS)

    Tien Son, Nguyen; Thang Trinh, Xuan; Gällström, Andreas; Leone, Stefano; Kordina, Olof; Janzén, Erik; Szász, Krisztián; Ivády, Viktor; Gali, Adam

    2012-10-01

    High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H- and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H- and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S = 1/2 and the nuclear spin of 93Nb. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of ˜37.4% was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (VC). Calculations of the 93Nb and 29Si hf constants of the neutral Nb on Si site, NbSi0, and the Nb-vacancy defect, NbSiVC0, support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H- and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others.

  9. Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance investigations of Tb{sup 3+} doped SrBPO{sub 5}

    SciTech Connect

    Kumar, Mithlesh; Seshagiri, T.K.; Kadam, R.M.; Godbole, S.V.

    2011-09-15

    Graphical abstract: EPR spectra of BOHC's in 2 kGy {gamma}-irradiated SrBPO{sub 5}:Tb sample using Receiver Gain RG = 4 x 10{sup 4}, Modulation Amplitude MA = 0.25 G, Microwave power setting 6.3 mW: (A) un-annealed sample recorded at 300 K, (B) un-annealed sample recorded at 100 K and (C) sample annealed at 550 K for 10 min and recorded at 100 K. Highlights: {yields} PL studies on Tb doped SrBPO{sub 5} phosphor have shown emission due to Tb{sup 3+} associated with {sup 5}D{sub 3} {yields} {sup 7}F{sub J} and {sup 5}D{sub 4} {yields} {sup 7}F{sub J} (J = 3, 4, 5 and 6) transitions. {yields} The EPR studies on {gamma}-irradiated samples revealed formation of three types of boron oxygen hole trapped centres viz., BOHC{sub 1}, BOHC{sub 2} and BOHC{sub 3} and an electron trapped centre. {yields} The TSL peak at 475 K was associated with the thermal destruction of BOHC{sub 2}. -- Abstract: Trap level spectroscopic studies were carried out on {gamma}-irradiated Tb (1 mole%) doped SrBPO{sub 5} were carried out using photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) techniques. The incorporation of Tb in the 3+ oxidation state was ascertained from PL studies. Life time for Tb{sup 3+} emission corresponding to the intense transition {sup 5}D{sub 4} {yields} {sup 7}F{sub 5} at 543 nm was determined. The spectral characteristics of the TSL glows have shown that Tb{sup 3+} ions act as the emission center for the glow peak at 475 K. The trap parameters of the glow peak were determined. EPR investigations at room temperature/77 K revealed the stabilization of three boron oxygen hole trapped centers (BOHC's) and oxygen centered radicals such as O{sup -} and O{sub 2}{sup -} and trapped electrons in room temperature {gamma}-irradiated samples. TSL glow peak at 475 K was found to be associated with recombination of electron released from trapped electron center and the BOHC{sub 2} center.

  10. Theoretical investigations of the electron paramagnetic resonance for Cr 3+ ions at tetragonal sites in K 2ZnF 4 crystal

    NASA Astrophysics Data System (ADS)

    Zeng, Ti-xian; Chen, Jia-jun; Chen, Tai-hong; Dai, Xiao-jing; Liao, Guo

    2010-06-01

    In tetragonal ligand-field, based on the Zhao’s semi-SCF d-orbit wave functions model, the Macfarlane’s perturbation loop method and point-charge crystal field model, the third-order perturbation formulas of electron paramagnetic resonance parameters (zero-field splitting D and g-factors) for 3d 3/7 configuration ions have been constructed. In these formulas, the contributions from configuration interaction, covalency effect, Racah-Trees corrections and local structure distortion (Δ R) have been considered. By using these formulas, the electron paramagnetic resonance parameters of Cr 3+ ion at tetragonal site in K 2ZnF 4 crystal have been calculated. The theoretically calculated values are consistent with the experimentally observed.

  11. Electron paramagnetic resonance study of free radicals in γ-irradiated L-glutamine and L-glutamine-t-butyl ester hydrochloride

    NASA Astrophysics Data System (ADS)

    Yeşim Dicle, Işık; Osmanğolu, Şemsettin; İpek, Nazenin

    2015-01-01

    Electron paramagnetic resonance (EPR) spectra of γ-irradiated single crystals of l-glutamine (LG) and l-glutamine-t-butyl ester hydrochloride (LGBESHCI) powders were studied and analyzed for different orientations of the crystals in the magnetic field, after γ-irradiation. The spectra were observed to be independent of temperature down to 130 K. The hyperfine interaction tensors for one α proton and two β protons of radical have been determined at 295 K. An analysis of the EPR of γ-irradiated single crystals of LG and LGBESHCI powders shows that the paramagnetic species produced by the radiation damage is CH2ĊH. The g values of the radical and the hyperfine structure constants of the free electron with nearby protons and 14N nucleus were determined. The results were found to be in good agreement with the existing literature data.

  12. Electron paramagnetic resonance characteristics of some non-heme low-spin iron(III) complexes

    NASA Astrophysics Data System (ADS)

    Duelund, Lars; Toftlund, Hans

    2000-02-01

    We have recorded the powder EPR-spectra of some near octahedral iron(III) complexes with tridentate ligands donors and analysed their spectra with simple ligand field analysis and for some cases with the angular overlap model (AOM). We have determined the electron praramagnetic resonance (EPR) characteristic of bis 1,4,7-triazacyclonane iron(III)chloride at 4 K and found that it was similar to the characteristics of the so-called 'highly anisotropic low spin' complexes. We have recorded the powder spectra of bis (2,6-bis(benzimidazoly-2-yl)pyridine) iron(III) perchlorate and made an AOM-analyses of the structural similar complex bis-(2,6 (N-carbamoyl)-pyridine) iron(III). With a combination of ligand field analyses and AOM, we could determine the π-donor properties of these ligands. The same approach have been used to determine the π-donor properties of the hydroperoxo ligand. Finally we have recorded the powder EPR-spectrum of [Fe(CN) 6] 3- doped in K 3[Co(CN) 6] and [Co(NH 3) 6][Co(CN) 6] at 4 and 100 K and in water at 4 K. The spectra are interpreted as the effect of a dynamic Jahn-Teller distortion.

  13. Electron paramagnetic resonance and photoluminescence investigation on ultraviolet-emitting gadolinium-ion-doped CaAl₁₂O₁₉ phosphors.

    PubMed

    Singh, Vijay; Borkotoky, S; Murali, A; Rao, J L; Rao, T K Gundu; Dhoble, S J

    2015-03-15

    The gadolinium doped CaAl12O19 phosphor has been prepared by a low temperature solution combustion method in a short time and characterized using powder X-ray diffraction, energy dispersive analysis of X-ray mapping, electron paramagnetic resonance (EPR) and photoluminescence spectroscopic techniques. EPR and optical analysis of the sample confirm the presence of Gd(3+) in the CaAl12O19 matrix. PMID:25546490

  14. Application of electron paramagnetic resonance spectroscopy to comparative examination of different groups of free radicals in thermal injuries treated with propolis and silver sulphadiazine.

    PubMed

    Olczyk, Pawel; Ramos, Pawel; Bernas, Marcin; Komosinska-Vassev, Katarzyna; Stojko, Jerzy; Pilawa, Barbara

    2013-01-01

    Different groups of free radicals expressed in burn wounds treated with propolis and silver sulphadiazine were examined. The thermal effect forms major types of free radicals in a wound because of the breaking of chemical bonds. Free radicals, located in the heated skin, were tested after 21 days of treating by these two substances. The aim of this work was to find the method for determination of types and concentrations of different groups of free radicals in wound after high temperature impact during burning. The effects of the therapy by propolis and silver sulphadiazine on free radicals were studied. Since the chemical methods of free radicals studies are destructive, the usefulness of the electron paramagnetic resonance spectroscopy was tested in this work. The electron paramagnetic resonance spectra measured with the microwave power of 2.2 mW were numerically fitted by theoretical curves of Gaussian and Lorentzian shapes. The experimental electron paramagnetic resonance spectra of tissue samples are best fitted by the sum of one Gauss and two Lorentz lines. An innovatory numerical procedure of spectroscopic skin analysis was presented. It is very useful in the alternative medicine studies.

  15. Application of Electron Paramagnetic Resonance Spectroscopy to Comparative Examination of Different Groups of Free Radicals in Thermal Injuries Treated with Propolis and Silver Sulphadiazine

    PubMed Central

    Olczyk, Pawel; Ramos, Pawel; Bernas, Marcin; Komosinska-Vassev, Katarzyna; Stojko, Jerzy; Pilawa, Barbara

    2013-01-01

    Different groups of free radicals expressed in burn wounds treated with propolis and silver sulphadiazine were examined. The thermal effect forms major types of free radicals in a wound because of the breaking of chemical bonds. Free radicals, located in the heated skin, were tested after 21 days of treating by these two substances. The aim of this work was to find the method for determination of types and concentrations of different groups of free radicals in wound after high temperature impact during burning. The effects of the therapy by propolis and silver sulphadiazine on free radicals were studied. Since the chemical methods of free radicals studies are destructive, the usefulness of the electron paramagnetic resonance spectroscopy was tested in this work. The electron paramagnetic resonance spectra measured with the microwave power of 2.2 mW were numerically fitted by theoretical curves of Gaussian and Lorentzian shapes. The experimental electron paramagnetic resonance spectra of tissue samples are best fitted by the sum of one Gauss and two Lorentz lines. An innovatory numerical procedure of spectroscopic skin analysis was presented. It is very useful in the alternative medicine studies. PMID:23762162

  16. Models for Copper Dynamic Behavior in Doped Cadmium dl-Histidine Crystals: Electron Paramagnetic Resonance and Crystallographic Analysis.

    PubMed

    Colaneri, Michael J; Teat, Simon J; Vitali, Jacqueline

    2015-11-12

    Electron paramagnetic resonance and crystallographic studies of copper-doped cadmium dl-histidine, abbreviated as CdDLHis, were undertaken to gain further understanding on the relationship between site structure and dynamic behavior in biological model complexes. X-ray diffraction measurements determined the crystal structure of CdDLHis at 100 and 298 K. CdDLHis crystallizes in the monoclinic space group P21/c with two cadmium complexes per asymmetric unit. In each complex, the Cd is hexacoordinated to two histidine molecules. Both histidines are l in one complex and d in the other. Additionally, each complex contains multiple waters of varying disorder. Single crystal EPR spectroscopic splitting (g) and copper hyperfine (A(Cu)) tensors at room temperature (principal values: g = 2.249, 2.089, 2.050; A(Cu) = -453, -30.5, -0.08 MHz) were determined from rotational experiments. Alignments of the tensor directions with the host structure were used to position the copper unpaired dx(2)-y(2) orbital in an approximate plane made by four proposed ligand atoms: the N-imidazole and N-amino of one histidine, and the N-amino and O-carboxyl of the other. Each complex has two such planes related by noncrystallographic symmetry, which make an angle of 65° and have a 1.56 Å distance between their midpoints. These findings are consistent with three interpretations that can adequately explain previous temperature-dependent EPR powder spectra of this system: (1) a local structural distortion (static strain) at the copper site has a temperature dependence significant enough to affect the EPR pattern, (2) the copper can hop between the two sites in each complex at high temperature, and (3) there exists a dynamic Jahn-Teller effect involving the copper ligands. PMID:26501364

  17. Electron paramagnetic resonance (EPR) oxygen image hypoxic fraction plus radiation dose strongly correlates with tumor cure in FSa fibrosarcomas

    PubMed Central

    Elas, Martyna; Bell, Rebecca; Hleihel, Danielle; Barth, Eugene D.; McFaul, Colin; Haney, Chad R.; Bielanska, Joanna; Pustelny, Katarzyna; Ahn, Kang-Hyun; Pelizzari, Charles A.; Kocherginsky, Masha; Halpern, Howard J.

    2008-01-01

    Purpose Tumor hypoxia has long been known to produce resistance to radiation. In this study, electron paramagnetic resonance (EPR) oxygen imaging was investigated for its power to predict the success of tumor control depending on tumor oxygenation level and radiation therapy dose. Methods and Materials Thirty-four EPR oxygen images were obtained from the legs of C3H mice bearing 0.5 ml FSa fibrosarcomas under both normal (air breathing) and clamped tumor conditions. Under the same conditions as those during which the images were obtained, tumors were irradiated to a variety doses near the FSa TCD50. Tumor tissue was distinguished from normal tissue using co-registration of the EPR oxygen images with spin-echo MRI images of the tumor and/or stereotactic localization. Tumor voxel statistics in the EPR oxygen image included mean and median pO2, and the fraction of tumor voxels below the specified pO2 values of 3, 6 and 10 torr. Bivariate logistic regression analysis using radiation dose and each of the EPR oxygen image statistics determined which best separated treatment failure from success. Results and Conclusions TCD50 measurements were similar to those found in the literature for this syngeneic tumor. Bivariate analysis of 34 tumors demonstrated that tumor cure correlated with dose (p=0.004) and with <10 torr hypoxic fraction (p=0.023). Together, radiation dose and EPR image hypoxic fraction separate the population of FSa fibrosarcomas which are cured from those which fail, thus predicting curability. PMID:18474313

  18. 2-Chlorophenol induced hydroxyl radical production in mitochondria in Carassius auratus and oxidative stress--an electron paramagnetic resonance study.

    PubMed

    Luo, Yi; Sui, Yun-xia; Wang, Xiao-rong; Tian, Yuan

    2008-04-01

    In our previous study, electron paramagnetic resonance (EPR) evidence of reactive oxygen species (ROS) production in Carassius auratus following 2-chlorophenol (2-CP) administration was provided. To further investigate the potential pathway of ROS production, liver mitochondria of C. auratus was isolated and incubated with 2-CP for 30 min. An EPR analysis indicated ROS was produced, and intensities of ROS increased with increasing concentrations of 2-CP. The ROS was then assigned OH by comparing with Fenton reaction. Either catalase or superoxide dismutase, extinguished OH completely in the mitochondria mixture. These facts suggested that O2(.-) and H2O2 contributed to the formation of OH in mitochondria in C. auratus stressed by 2-CP. Combining previous references and our own data, it is reasonable to suggest that 2-CP is first oxidized by H2O2 present in vivo to form phenoxyl radical under the catalytic action of cellular peroxidase (1); phenoxyl radical oxidizes mitochondria NADH to NAD in the presence of NADH (2); NAD reacts with oxygen in vivo to produce O2(.-) (3); O2(.-) is spontaneously dismutated by SOD to form H2O2 and O2, which creates a renewable supply of H2O2 as the initiators of the chain reactions until NADH is consumed (4); simultaneously with reaction (4), O2(.-) reacts with H2O2 to form OH radical via the Haber-Weiss reaction (5). A strong negative correlation (r=-0.9278, p<0.01) between glutathione (GSH) pool and OH production was observed after fish were i.p. injected with 2-CP (250 mg kg(-1)), indicating the depletion of GSH caused by OH.

  19. An Electron Paramagnetic Resonance Spectroscopic Study of Copper Hopping in Doped Bis(L-histidinato)cadmium Dihydrate

    PubMed Central

    Colaneri, Michael J.; Vitali, Jacqueline; Kirschbaum, Kristin

    2013-01-01

    Electron Paramagnetic Resonance (EPR) spectroscopy was used to study Cu(II) dynamic behavior in a doped biological model crystal; bis(L-histidinato)cadmium dihydrate, in order to gain better insight into copper site stability in metalloproteins. Temperature dependent changes in the low temperature X-band EPR spectra became visible around 100 K and continued up to room temperature. The measured 298 K g-tensor (principal values: 2.17, 2.16, 2.07) and copper hyperfine coupling tensor (principal values: −260, − 190, −37 MHz) were similar to the average of the 77 K tensor values pertaining to two neighboring histidine binding sites. The observed temperature dependence was interpreted using Anderson’s theory of motional narrowing, where the magnetic parameters for the different states are averaged as the copper rapidly hops between sites. The EPR pattern was also found to undergo a sharp sigmoidal-shaped, temperature dependent conversion between two species with a critical temperature Tc ≈ 160 K. The species below Tc hops between the two low temperature site patterns, and the one above Tc represents an average of the molecular spin Hamiltonian coupling tensors of the two 77 K sites. In addition, the low and high temperature species hop between one another, contributing to the dynamic averaging. Spectral simulations using this 4-state model determined a hop rate between the two low temperature sites νh4 = 4.5 × 108 s−1 and between the low and high temperature states νh2 = 1.7 × 108 s−1 at 160 K. An Arrhenius relationship of hop rate and temperature gave energy barriers of ΔE4 = 389 cm−1 and ΔE2 = 656 cm−1 between the two low temperature sites, and between the low and high temperature states, respectively. PMID:23530765

  20. Measuring "free" iron levels in Caenorhabditis elegans using low-temperature Fe(III) electron paramagnetic resonance spectroscopy.

    PubMed

    Pate, Kira T; Rangel, Natalie A; Fraser, Brian; Clement, Matthew H S; Srinivasan, Chandra

    2006-11-15

    Oxidative stress, caused by free radicals within the body, has been associated with the process of aging and many human diseases. Because free radicals, in particular superoxide, are difficult to measure, an alternative indirect method for measuring oxidative stress levels has been used successfully in Escherichia coli and yeast. This method is based on a proposed connection between elevated superoxide levels and release of iron from solvent-exposed [4Fe-4S] enzyme clusters that eventually leads to an increase in hydroxyl radical production. In past studies using bacteria and yeast, a positive correlation was found between superoxide production or oxidative stress due to superoxide within the organism and electron paramagnetic resonance (EPR) detectable "free" iron levels. In the current study, we have developed a reliable and efficient method for measuring "free" iron levels in Caenorhabditis elegans using low-temperature Fe(III) EPR at g=4.3. This method uses synchronized worm cultures grown on plates that are homogenized and treated with desferrioxamine, an Fe(III) chelator, prior to packing the EPR tube. Homogenization was found not to alter "free" iron levels, whereas desferrioxamine treatment significantly raised these levels, indicating the presence of both Fe(II) and Fe(III) in the "free" iron pool. The correlation between free radical levels and the observed "free" iron levels was examined by using heat stress and paraquat treatment. The intensity of the Fe(III) EPR signal, and thus the concentration of the "free" iron pool, varied with the treatments that altered radical levels without changing the total iron levels. This study provides the groundwork needed to uncover the correlation among oxidative stress, "free" iron levels, and longevity in C. elegans.

  1. Electron paramagnetic resonance study of the C e3 + pair centers in YAl O3 :Ce scintillator crystals

    NASA Astrophysics Data System (ADS)

    Buryi, M.; Laguta, V. V.; Mihóková, E.; Novák, P.; Nikl, M.

    2015-12-01

    Single crystals of YAl O3 doped with Ce have been studied by electron paramagnetic resonance (EPR) at the 9.4 and 34 GHz microwave bands. Besides the single-ion C e3 + spectrum, measurements have revealed many satellite lines which belong to the C e3 +-C e3 + pair centers. Their spectra have been fitted by a general effective spin Hamiltonian describing two interacting particles with the spin S =1 /2 . Corresponding g factors and spin-spin coupling constants have been determined. The spin-spin coupling constants are in the range from 0.1 up to 0.65 c m-1 for the nearest and next-nearest neighbors depending on the distance between Ce ions and their position. The exchange interaction between next-nearest neighbors (NNNs) is comparable to or even bigger than that between nearest neighbors (NNs), being in the range 0.4 -0.6 c m-1 . For a single C e3 + ion, crystal field parameters, energy sublevels of the 2F5 /2 and 2F7 /2 multiplets and principal g tensor components were obtained from the density functional theory calculation. They are in satisfactory agreement with those determined experimentally. The principal g tensor components of C e3 + pair centers are also calculated. Nevertheless, it was impossible to assign each of the satellite lines to actual positions of the six NN and 12 NNN Ce pairs in the lattice due to lack of valid information on the sign of the exchange interactions. The influence of C e3 + pairs on the luminescence efficiency is discussed as well.

  2. Electron paramagnetic resonance radiation dose assessment in fingernails of the victim exposed to high dose as result of an accident.

    PubMed

    Romanyukha, Alexander; Trompier, François; Reyes, Ricardo A; Christensen, Doran M; Iddins, Carol J; Sugarman, Stephen L

    2014-11-01

    In this paper, we report results of radiation dose measurements in fingernails of a worker who sustained a radiation injury to his right thumb while using 130 kVp X-ray for nondestructive testing. Clinically estimated absorbed dose was about 20-25 Gy. Electron paramagnetic resonance (EPR) dose assessment was independently carried out by two laboratories, the Naval Dosimetry Center (NDC) and French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The laboratories used different equipments and protocols to estimate doses in the same fingernail samples. NDC used an X-band transportable EPR spectrometer, e-scan produced by Bruker BioSpin, and a universal dose calibration curve. In contrast, IRSN used a more sensitive Q-band stationary spectrometer (EMXplus) with a new approach for the dose assessment (dose saturation method), derived by additional dose irradiation to known doses. The protocol used by NDC is significantly faster than that used by IRSN, nondestructive, and could be done in field conditions, but it is probably less accurate and requires more sample for the measurements. The IRSN protocol, on the other hand, potentially is more accurate and requires very small amount of sample but requires more time and labor. In both EPR laboratories, the intense radiation-induced signal was measured in the accidentally irradiated fingernails and the resulting dose assessments were different. The dose on the fingernails from the right thumb was estimated as 14 ± 3 Gy at NDC and as 19 ± 6 Gy at IRSN. Both EPR dose assessments are given in terms of tissue kerma. This paper discusses the experience gained by using EPR for dose assessment in fingernails with a stationary spectrometer versus a portable one, the reasons for the observed discrepancies in dose, and potential advantages and disadvantages of each approach for EPR measurements in fingernails.

  3. The local environment of Cr3+ impurities in normal and x-rays irradiated carbon doped ruby: An electron paramagnetic resonance (EPR) study

    NASA Astrophysics Data System (ADS)

    Kazan, S.; Açıkgöz, M.; Yalçın, O.

    2015-01-01

    Local environment of substitutional paramagnetic point defect (impurity) in normal and x-ray irradiated commercially available α-Al2O3:C samples (commercial product of Landauer, Inc.) has been studied by using the electron paramagnetic resonance (EPR) technique at room temperature. In both samples the EPR spectra showed strongly angular dependent behavior. The zero-field splitting (ZFS) parameters (ZFSPs) have been determined for substitutional Cr3+ centers. The observed additional EPR signals for x-ray irradiated sample were attributed to another center with different spin Hamiltonian (SH) parameters. In addition to the experimental findings, the ZFSPs and the local structure of the Cr3+ ions were theoretically determined using superposition model (SPM) calculations.

  4. Electron paramagnetic resonance crystallography of 17O-enriched oxycobaltomyoglobin: Stereoelectronic structure of the cobalt dioxygen system

    PubMed Central

    Dickinson, L. Charles; Chien, James C. W.

    1980-01-01

    An electron paramagnetic resonance crystallographic study was made on oxycobaltomyoglobin with the dioxygen ligand enriched to 19.1% in 17O. There are two spectroscopically distinct cobalt dioxygen species. The less abundant species, II (40%), has nonequivalent oxygen atoms with superhyperfine tensors OAα = (5, -67.5, 22.4)G and OAβ = (5.4, -83.3, 30.3)G. Together with the previously reported 59Co hyperfine tensor [Chien, J. C. W. & Dickinson, L. C. (1972) Proc. Natl. Acad. Sci. USA 69, 2783-2787], the orbital spin densities are found to be Oα(pη) = 0.48, Oα(pζ) = -0.11, Oβ(pη) = 0.74, Oβ(pζ) = -0.16, Co(dxz) = -0.01, Co(dyz) = 0.06 for a total electron density of 1.01. The O—O axis is directed toward His-E7, suggesting a possible hydrogen bonding interaction which may contribute to the nonequivalency of the oxygen atoms; its projection approximately bisects N1—Fe—N2. The z axis of the CoA tensor is tilted at an angle of 28° from the heme normal, resulting in a Co—O—O angle of 120°. The more abundant species, I (60%), has equivalent oxygen atoms with OAγ = (12, -72.5, 20)G and orbital spin densities of Oγ(pη) = 0.54, Oγ(pζ) = -0.05, Co(dxz) = -0.02, Co(dyz) = 0.09 for a total spin density of 1.10. Although the direction cosines for this molecule cannot be precisely determined, the projection of its O—O axis approximately bisects N2—Fe—N3 and is parallel to the imidazole ring of His-F8. Increase of temperature changes g, CoA, and OA values, with the largest effect seen with OA. This temperature dependence indicates averaging of the two bond structures which are stabilized at 77 K. PMID:6246485

  5. Characterization of endothelial nitric-oxide synthase and its reaction with ligand by electron paramagnetic resonance spectroscopy.

    PubMed

    Tsai, A L; Berka, V; Chen, P F; Palmer, G

    1996-12-20

    Electron paramagnetic resonance was used to characterize the heme structure of resting endothelial nitric-oxide synthase (eNOS), eNOS devoid of its myristoylation site (G2A mutant), and their heme complexes formed with 16 different ligands. Resting eNOS and the G2A mutant have a mixture of low spin and high spin P450-heme with widely different relaxation behavior and a stable flavin semiquinone radical identified by EPR as a neutral radical. This flavin radical showed efficient electron spin relaxation as a consequence of dipolar interaction with the heme center; P1/2 is independent of Ca2+-calmodulin and tetrahydrobiopterin. Seven of the 16 ligands led to the formation of low spin heme complexes. In order of increasing rhombicity they are pyrimidine, pyridine, thiazole, L-lysine, cyanide, imidazole, and 4-methylimidazole. These seven low spin eNOS complexes fell in a region between the P and O zones on the "truth diagram" originally derived by Blumberg and Peisach (Blumberg, W. E., and Peisach, J. (1971) in Probes and Structure and Function of Macromolecules and Membranes (Chance, B., Yonetani, T., and Mildvan, A. S., eds) Vol. 2, pp. 215-229, Academic Press, New York) and had significant overlap with complexes of chloroperoxidase. A re-definition of the P and O zones is proposed. As eNOS and chloroperoxidase lie closer than do eNOS and P450cam on the truth diagram, it implies that the distal heme environment in eNOS resembles chloroperoxidase more than P450cam. In contrast, 4-ethylpyridine, 4-methylpyrimidine, acetylguanidine, ethylguanidine, 2-aminothiazole, 2amino-4,5-dimethylthiazole, L-histidine, and 7-nitroindazole resulted in high spin heme complexes of eNOS, similar to that observed with L-arginine. This contrasting EPR behavior caused by families of ligands such as imidazole/L-histidine or thiazole/2-aminothiazole confirms the conclusion derived from parallel optical and kinetic studies. The ligands resulting in the low spin complexes bind directly to the

  6. Role of the coordinating histidine in altering the mixed valency of Cu(A): an electron nuclear double resonance-electron paramagnetic resonance investigation.

    PubMed Central

    Lukoyanov, Dmitriy; Berry, Steven M; Lu, Yi; Antholine, William E; Scholes, Charles P

    2002-01-01

    The binuclear Cu(A) site engineered into Pseudomonas aeruginosa azurin has provided a Cu(A)-azurin with a well-defined crystal structure and a CuSSCu core having two equatorial histidine ligands, His120 and His46. The mutations His120Asn and His120Gly were made at the equatorial His120 ligand to understand the histidine-related modulation to Cu(A), notably to the valence delocalization over the CuSSCu core. For these His120 mutants Q-band electron nuclear double resonance (ENDOR) and multifrequency electron paramagnetic resonance (EPR) (X, C, and S-band), all carried out under comparable cryogenic conditions, have provided markedly different electronic measures of the mutation-induced change. Q-band ENDOR of cysteine C(beta) protons, of weakly dipolar-coupled protons, and of the remaining His46 nitrogen ligand provided hyperfine couplings that were like those of other binuclear mixed-valence Cu(A) systems and were essentially unperturbed by the mutation at His120. The ENDOR findings imply that the Cu(A) core electronic structure remains unchanged by the His120 mutation. On the other hand, multifrequency EPR indicated that the H120N and H120G mutations had changed the EPR hyperfine signature from a 7-line to a 4-line pattern, consistent with trapped-valence, Type 1 mononuclear copper. The multifrequency EPR data imply that the electron spin had become localized on one copper by the His120 mutation. To reconcile the EPR and ENDOR findings for the His120 mutants requires that either: if valence localization to one copper has occurred, the spin density on the cysteine sulfurs and the remaining histidine (His46) must remain as it was for a delocalized binuclear Cu(A) center, or if valence delocalization persists, the hyperfine coupling for one copper must markedly diminish while the overall spin distribution on the CuSSCu core is preserved. PMID:11964261

  7. Effects of MnO doping on the electronic properties of zinc oxide: 406 GHz electron paramagnetic resonance spectroscopy and Newman superposition model analysis

    SciTech Connect

    Yüksel Price, Berat E-mail: muhammed.acikgoz@eng.bahcesehir.edu.tr Hardal, Gökhan; Açıkgöz, Muhammed E-mail: muhammed.acikgoz@eng.bahcesehir.edu.tr; Repp, Sergej; Erdem, Emre E-mail: muhammed.acikgoz@eng.bahcesehir.edu.tr

    2015-11-07

    MnO-doped ZnO ceramics have been synthesized through the conventional ceramic processing route. Mn{sup 2+} ions have been incorporated into the ZnO lattice within the limits of solid solubility. By using X-band-frequency and high-field electron paramagnetic resonance (EPR), we have resolved some of the main electronic transitions for the S = 5/2, I = 5/2 high-spin system and have determined accurately the EPR spin-Hamiltonian parameters. By combining data from crystallographic X-ray diffraction and EPR with the semi-empirical Newman superposition model, we have found the local configurational position of Mn{sup 2+} and have confirmed the symmetry of the lattice. The results presented in this contribution indicate that Mn ions substitute at Zn sites in ZnO. The effect of Mn{sup 2+} ions on the intrinsic defects becomes remarkable, thus the vacancy related intrinsic defect signals cannot be visible in the EPR spectrum. MnO doping affects the band gap energy of ZnO system which was confirmed via UV-Vis spectroscopy.

  8. Effects of MnO doping on the electronic properties of zinc oxide: 406 GHz electron paramagnetic resonance spectroscopy and Newman superposition model analysis

    NASA Astrophysics Data System (ADS)

    Yüksel Price, Berat; Hardal, Gökhan; Açıkgöz, Muhammed; Repp, Sergej; Erdem, Emre

    2015-11-01

    MnO-doped ZnO ceramics have been synthesized through the conventional ceramic processing route. Mn2+ ions have been incorporated into the ZnO lattice within the limits of solid solubility. By using X-band-frequency and high-field electron paramagnetic resonance (EPR), we have resolved some of the main electronic transitions for the S = 5/2, I = 5/2 high-spin system and have determined accurately the EPR spin-Hamiltonian parameters. By combining data from crystallographic X-ray diffraction and EPR with the semi-empirical Newman superposition model, we have found the local configurational position of Mn2+ and have confirmed the symmetry of the lattice. The results presented in this contribution indicate that Mn ions substitute at Zn sites in ZnO. The effect of Mn2+ ions on the intrinsic defects becomes remarkable, thus the vacancy related intrinsic defect signals cannot be visible in the EPR spectrum. MnO doping affects the band gap energy of ZnO system which was confirmed via UV-Vis spectroscopy.

  9. Electronic structure of Q-A in reaction centers from Rhodobacter sphaeroides. I. Electron paramagnetic resonance in single crystals.

    PubMed Central

    Isaacson, R A; Lendzian, F; Abresch, E C; Lubitz, W; Feher, G

    1995-01-01

    The magnitude and orientation of the electronic g-tensor of the primary electron acceptor quinone radical anion, Q-A, has been determined in single crystals of zinc-substituted reaction centers of Rhodobacter sphaeroides R-26 at 275 K and at 80 K. To obtain high spectral resolution, EPR experiments were performed at 35 GHz and the native ubiquinone-10 (UQ10) in the reaction center was replaced by fully deuterated UQ10. The principal values and the direction cosines of the g-tensor axes with respect to the crystal axes a, b, c were determined. Freezing of the single crystals resulted in only minor changes in magnitude and orientation of the g-tensor. The orientation of Q-A as determined by the g-tensor axes deviates only by a few degrees (< or = 8 degrees) from the orientation of the neutral QA obtained from an average of four different x-ray structures of Rb. sphaeroides reaction centers. This deviation lies within the accuracy of the x-ray structure determinations. The g-tensor values measured in single crystals agree well with those in frozen solutions. Variations in g-values between Q-A, Q-B, and UQ10 radical ion in frozen solutions were observed and attributed to different environments. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 9 PMID:8527644

  10. Intramolecular electron transfer versus substrate oxidation in lactoperoxidase: investigation of radical intermediates by stopped-flow absorption spectrophotometry and (9-285 GHz) electron paramagnetic resonance spectroscopy.

    PubMed

    Fielding, Alistair J; Singh, Rahul; Boscolo, Barbara; Loewen, Peter C; Ghibaudi, Elena M; Ivancich, Anabella

    2008-09-16

    We have combined the information obtained from rapid-scan electronic absorption spectrophotometry and multifrequency (9-295 GHz) electron paramagnetic resonance (EPR) spectroscopy to unequivocally determine the electronic nature of the intermediates in milk lactoperoxidase as a function of pH and to monitor their reactivity with organic substrates selected by their different accessibilities to the heme site. The aim was to address the question of the putative catalytic role of the protein-based radicals. This experimental approach allowed us to discriminate between the protein-based radical intermediates and [Fe(IV)=O] species, as well as to directly detect the oxidation products by EPR. The advantageous resolution of the g anisotropy of the Tyr (*) EPR spectrum at high fields showed that the tyrosine of the [Fe(IV)=O Tyr (*)] intermediate has an electropositive and pH-dependent microenvironment [g(x) value of 2.0077(0) at pH >or= 8.0 and 2.0066(2) at 4.0 electron transfer (favored at pH 8) not involving the tyrosyl radical, the formation of which competed with the substrate oxidation at pH 5. In contrast, the very efficient reaction with ABTS at pH 5 is consistent with [Fe(IV)=O Tyr (*)] being the oxidizing species. Accordingly, the identification of the ABTS binding site by X-ray crystallography may be a valuable tool in rational drug design.

  11. Host spin-lattice relaxation narrowing and the electron paramagnetic resonance of Mn(II) in single crystals of hexakis(pyridine N-oxide)cobalt(II) complexes

    NASA Astrophysics Data System (ADS)

    Murugesan, R.; Thamaraichelvan, A.; Milton Franklin, A.; Ramakrishnan, V.

    The electron paramagnetic resonance spectra of Mn(C5H5NO)6. X2 (X ≡ ClO-4, BF-4 and NO-3) doped in single crystals of isomorphous paramagnetic Co(C5H5NO)6. X2 are studied at various temperatures. Zero-field splitting in all three crystals is axially symmetric and the magnitude of D is unusually large for an octahedral coordination polyhedron with all ligands identical. The sharp resonance of Mn(II) in the paramagnetic host observed at high temperatures is interpreted in terms of random modulation of the dipolar interaction between the guest Mn(II) and host Co(II) ions by the rapid spin-lattice relaxation of Co(II). The spin-lattice relaxation times of Co(II) ions at 300 K, estimated from the temperature dependent linewidth of the Mn(II) resonance, are 24 × 10-12, 28 × 10-12 and 23 × 10-12 s in perchlorate, fluoborate and nitrate crystals respectively. The temperature dependence of the relaxation is of the form 1/(at + bt5) and below 270 K the direct process dominates.

  12. [Theoretical Investigation of the Electron Paramagnetic Resonance Parameters and Local Structures for Zinc Phosphate Glass Doped with VO2+].

    PubMed

    Li, Chao-ying; Yuang, Xian-Kai; Tu, Qiu; Wang, Wei-yang; Zheng, Xue-mei

    2015-07-01

    As an important model system, 3d(1) ions (VO2+, V4+ et al) have been extensively investigated by means of electron paramagnetic resonance (EPR), and many experimental results of EPR parameters were also measured. The optical absorption and EPR parameters (g factors g||, g⊥ and hyperfine structure constants A||, A⊥) of a tetragonal V4+ center in zinc phosphate glass are theoretically investigated, using the perturbation formulas for a 3d(1) ion in tetragonally compressed octahedra. Since the spin-orbit coupling parameter r (150 cm(-1)) of ligand O2- is close to that ξp(0) (≈248 cm(-1)) of the central 3d(1) ion in zinc phosphate glass doped VO2+, the effect of the spin-orbit coupling parameter ξp(0) on the EPR spectra and optical absorption spectra should be taken into account. In this work, the relationship between the EPR parameters as well as the optical absorption spectra and the local structure of the impurity center are established based on the superposition model. By fitting the calculated EPR parameters and optical absorption spectra for V4+ center in zinc phosphate glass to the experimental data, the local structure parameters of [VO6](8-) cluster are obtained. According to the investigation, the magnitudes of the metal-ligand distances parallel and perpendicular to the C4-axis of [VO6](8-) cluster are, respectively, R|| ≈ 0.175 nm and R⊥ ≈ 0.197 nm, the local structure around the V4+ ions possesses a compressed tetragonal distortion along C4 axis. Theoretical results of EPR parameters and optical absorption spectra are in good agreement with experimental data, the validity of the calculated results has also been discussed. Thus, perturbation method is effective to the studies the EPR parameters and optical spectra of transition-metal 3d ions in crystals. In addition, based on the studies of the hyperfine structure constants (All and A1), one can found that the large value of kappa indicates a large contribution to the hyperfine constant by the

  13. Detection of nitric oxide and superoxide radical anion by electron paramagnetic resonance spectroscopy from cells using spin traps.

    PubMed

    Gopalakrishnan, Bhavani; Nash, Kevin M; Velayutham, Murugesan; Villamena, Frederick A

    2012-01-01

    spin adduct which can be detected by electron paramagnetic resonance (EPR) spectroscopy. The various radical adducts exhibit distinctive spectrum which can be used to identify the radicals being generated and can provide a wealth of information about the nature and kinetics of radical production. The cyclic nitrones, 5,5-dimethyl-pyrroline-N-oxide, DMPO, the phosphoryl-substituted DEPMPO, and the ester-substituted, EMPO and BMPO, have been widely employed as spin traps--the latter spin traps exhibiting longer half-lives for O2•- adduct. Iron (II)-N-methyl-D-glucamine dithiocarbamate, Fe(MGD)2 is commonly used to trap NO due to high rate of adduct formation and the high stability of the spin adduct. PMID:22929836

  14. Electron paramagnetic resonance spectroscopic measurement of Mn2+ binding affinities to the hammerhead ribozyme and correlation with cleavage activity.

    PubMed

    Horton, T E; Clardy, D R; DeRose, V J

    1998-12-22

    Efficient phosphodiester bond cleavage activity by the hammerhead ribozyme requires divalent cations. Toward understanding this metal ion requirement, the Mn2+-binding properties of hammerhead model ribozymes have been investigated under dilute solution conditions, using electron paramagnetic resonance spectroscopy (EPR) to detect free Mn2+ in the presence of added ribozyme. Numbers and affinities of bound Mn2+ were obtained at pH 7.8 (5 mM triethanolamine) in the presence of 0, 0.1, and 1.0 M NaCl for an RNA-DNA model consisting of a 13-nucleotide DNA "substrate" hybridized to a 34-nucleotide RNA "enzyme" [Pley, H. W., Flaherty, K. M., and McKay, D. B. (1994) Nature 372, 68-74]. In 0.1 M NaCl, two classes of Mn2+ sites are found with n1 = 3.7 +/- 0.4, Kd(1) = 4 +/- 1 microM (type 1) and n2 = 5.2 +/- 0.4, Kd(2) = 460 +/- 130 microM (type 2). The high-affinity type 1 sites are confirmed for an active RNA-RNA hybrid (34-nucleotide RNA enzyme:13-nucleotide RNA substrate) by EPR measurements at low Mn2+ concentrations. Decreasing NaCl concentration results in an increased number of bound Mn2+ per hammerhead. By contrast, a binding titration in 1 M NaCl indicates that a single Mn2+ site with apparent Kd approximately 10 microM is populated in low concentrations of Mn2+, and apparent cooperative effects at higher Mn2+ concentrations result in population of a similar total number of Mn2+ sites (n1 = 8-10) as found in 0.1 M NaCl. Mn2+-dependent activity profiles are similar for the active RNA-RNA hybrid in 0.1 and 1 M NaCl. Correlation with binding affinities determined by EPR indicates that hammerhead activity in 0.1 M NaCl is only observed after all four of the high-affinity Mn2+ sites are occupied, rises with population of the type 2 sites, and is independent of Mn2+ concentrations corresponding to > 8-9 Mn2+ bound per hammerhead. Equivalent measurements in 1 M NaCl demonstrate a rise in activity with the cooperative transition observed in the Mn2+ binding curve. These

  15. Cerebral Oxygenation in Awake Rats during Acclimation and Deacclimation to Hypoxia: An In Vivo Electron Paramagnetic Resonance Study

    PubMed Central

    Khan, Mohammad N.; Hou, Huagang G.; Merlis, Jennifer; Abajian, Michelle A.; Demidenko, Eugene; Grinberg, Oleg Y.; Swartz, Harold M.

    2011-01-01

    Abstract Dunn, J. F., N. Khan, H. G. Hou, J. Merlis, M. A. Abajian, E. Demidenko, O.Y. Grinberg, and H. M. Swartz. Cerebral oxygenation in awake rats during acclimation and deacclimation to hypoxia: an in vivo EPR study. High Alt. Med. Biol. 12:71–77, 2011.— Exposure to high altitude or hypobaric hypoxia results in a series of metabolic, physiologic, and genetic changes that serve to acclimate the brain to hypoxia. Tissue Po2 (Pto2) is a sensitive index of the balance between oxygen delivery and utilization and can be considered to represent the summation of such factors as cerebral blood flow, capillary density, hematocrit, arterial Po2, and metabolic rate. As such, it can be used as a marker of the extent of acclimation. We developed a method using electron paramagnetic resonance (EPR) to measure Pto2 in unanesthetized subjects with a chronically implanted sensor. EPR was used to measure rat cortical tissue Pto2 in awake rats during acute hypoxia and over a time course of acclimation and deacclimation to hypobaric hypoxia. This was done to simulate the effects on brain Pto2 of traveling to altitude for a limited period. Acute reduction of inspired O2 to 10% caused a decline from 26.7 ± 2.2 to 13.0 ± 1.5 mmHg (mean ± SD). Addition of 10% CO2 to animals breathing 10% O2 returned Pto2 to values measured while breathing 21% O2, indicating that hypercapnia can reverse the effects of acute hypoxia. Pto2 in animals acclimated to 10% O2 was similar to that measured preacclimation when breathing 21% O2. Using a novel, individualized statistical model, it was shown that the T1/2 of the Pto2 response during exposure to chronic hypoxia was approximately 2 days. This indicates a capacity for rapid adaptation to hypoxia. When subjects were returned to normoxia, there was a transient hyperoxygenation, followed by a return to lower values with a T1/2 of deacclimation of 1.5 to 3 days. These data indicate that exposure to hypoxia results in significant

  16. Electron paramagnetic resonance of the excited triplet state of metal-free and metal-substituted cytochrome c.

    PubMed Central

    Angiolillo, P J; Vanderkooi, J M

    1995-01-01

    The photoactivated metastable triplate states of the porphyrin (free-base, i.e., metal-free) zinc and tin derivatives of horse cytochrome c were investigated using electron paramagnetic resonance. Zero-field splitting parameters, line shape, and Jahn-Teller distortion in the temperature range 3.8-150 K are discussed in terms of porphyrin-protein interactions. The zero-field splitting parameters D for the free-base, Zn and Sn derivatives are 465 x 10(-4), 342 x 10(-4) and 353 x 10(-4) cm-1, respectively, and are temperature invariant over the temperature ranges studied. AN E value at 4 K of 73 x 10(-4) cm-1 was obtained for Zn cytochrome c, larger than any previously found for Zn porphyrins derivatives of hemeproteins, showing that the heme site of cytochrome c imposes an asymmetric field. Though the E value for Zn cytochrome c is large, the geometry of the site appears quite constrained, as indicated by a spectral line shape showing a single species. Intersystem crossing occurred predominantly to the T2 > zero-field spin sublevel. EPR line shape changes with respect to temperature of Zn cyt c are interpreted in terms of vibronic coupling, and a maximum Jahn-Teller crystal-field splitting of approximately 180 cm-1 is obtained. Sn cytochrome c in comparison with the Zn protein exhibits a photoactivated triplet line shape that is less well resolved in the X-Y region. The magnitude of E value is approximately 60 x 10(-4) cm-1 at 4 K; its value rapidly tends toward zero with increasing temperature, from which a value for the Jahn-Teller crystal-field splitting of > or = 40 cm-1 is estimated. In contrast to those for the metal cytochromes, the magnitude of E value for the free-base derivative was essentially zero at all temperatures studied. This finding is discussed as a consequence of an excited-state tautomerization process that occurs even at 4 K. PMID:7647253

  17. Advanced Electronics. Curriculum Development. Bulletin 1778.

    ERIC Educational Resources Information Center

    Eppler, Thomas

    This document is a curriculum guide for a 180-hour course in advanced electronics for 11th and 12th grades that has four instructional units. The instructional units are orientation, discrete components, integrated circuits, and electronic systems. The document includes a course flow chart; a two-page section that describes the course, lists…

  18. Programmed electronic advance for engines

    SciTech Connect

    Dogadko, P.

    1987-03-03

    An ignition advance control is described for an internal combustion engine including a crankshaft, a throttle control, and at least one cylinder, the ignition advance control comprising a spark ignition circuit associated with the cylinder and including trigger means operative to cause an ignition spark, means for generating a control pulse associated with the cylinder, latch means for enabling the trigger means in response to generation of the control pulse, means for generating a constant plurality of sequentially occurring electrical reference pulses during each revolution of the crankshaft, means for counting the reference pulses developed during each revolution of the crankshaft, means for firing the enabled trigger means in response to the counting means counting a predetermined number of the reference pulses to cause the ignition spark at a predetermined ignition point in each revolution of the crankshaft, means for sensing the position of the throttle control, and means responsive to the throttle sensing means for varying the predetermined number of reference pulses solely in accordance with the position of the throttle control to vary the predetermined ignition point as appropriate for the position of the throttle control.

  19. Improved apparatus for trapped radical and other studies down to 1.5 K. [microwave cavity cryogenic equipment for electron paramagnetic resonance experiments

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Sugawara, K.

    1978-01-01

    A Dewar system and associated equipment for electron paramagnetic resonance (EPR) studies of trapped free radicals and other optical or irradiation experiments are described. The apparatus is capable of reaching a temperature of 1.5 K and transporting on the order of 20 W per K temperature gradient; its principal advantages are for use at pumped cryogen temperatures and for experiments with large heat inputs. Two versions of the apparatus are discussed, one of which is designed for EPR in a rectangular cavity operating in a TE(102) mode and another in which EPR is performed in a cylindrical microwave cavity.

  20. Investigation of electron relaxation in the metal proteins containing the single paramagnetic centers of integer spin by nuclear forward scattering of synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Popov, E. A.; Yanvarev, Eugene A.; Bashkirov, Sh. S.; Kouznetsov, V. I.

    2001-11-01

    Nuclear forward scattering (NFS) of synchrotron radiation (SR) is being modeled in metal proteins containing the single paramagnetic centers of integer spin (Fe2+). It is known the spin fluctuations in the electron environment of Moessbauer ion Fe2+ will be manifested itself in NFS if a sample undergoes the influence of applied magnetic field of a few Tesla. Under the condition we are analyzing how the resonant response (RR) of a sample to SR pulse will be changed due to the both spin-lattice and spin-spin interactions.

  1. Location of Trapped Electron Centers in the Bulk of Epitaxial MgO(001) Films Grown on Mo(001) Using in situ W-band Electron Paramagnetic Resonance Spectroscopy.

    PubMed

    Cornu, Damien; Rocker, Jan; Gonchar, Anastasia; Risse, Thomas; Freund, Hans-Joachim

    2016-07-01

    We present the first in situ W-band (94-GHz) electron paramagnetic resonance (EPR) study of a trapped electron center in thin MgO(001) films. The improved resolution of the high-field EPR experiments proves that the signal originate from a well-defined species present in the bulk of the films, whose projection of the principal g-tensor components onto the (001) plane are oriented along the [110] direction of the MgO lattice. Based on a comparison between the structural properties of the films, knowledge of the ability of bulk defects to trap electrons, and the properties of the EPR signal, it is possible to propose that the paramagnetic species are located at the origin of a screw dislocation in the bulk of the film.

  2. Electron Paramagnetic Resonance: Elementary Theory and Practical Applications, Second Edition (John A. Weil and James R. Bolton)

    NASA Astrophysics Data System (ADS)

    Williams, Ffrancon

    2009-01-01

    The detection of electron magnetic resonance by Zavoiskii in the mid 1940s (1) ushered in a golden age of physical and chemical applications. Perhaps no single book did more to stimulate this development of EPR spectroscopy than the classic text by Wertz and Bolton (2) , which appeared in 1972. A revised version, with John A. Weil added as a co-author, was published by Wiley in 1994. This 2007 text is formally described as the second edition of the 1994 version. Wertz died shortly after the publication of the 1994 edition leaving Weil and Bolton as authors. In noting that the senior author (JAW) takes most of the responsibility for the content of this 2007 version, the Preface refers to it at one point as the "third edition", which of course is precisely how older readers will regard it. The main thrust of the book is decidedly on the physical aspects of EPR, so that it nicely complements the more chemical emphasis provided in the recent comprehensive text by Gerson and Hüber (3) . As the authors remark, the 2007 edition does not differ dramatically from the 1994 version. The titles of the 13 chapters remain the same except for chapter 11, which now refers to the "Noncontinuous" instead of the "Time-Dependent" Excitation of Spins. Recent developments are generally accommodated by a few extra pages in each chapter. Thus, chapter 1 on Basic Principles of Paramagnetic Resonance has been expanded from 31 to 36 pages to introduce the topics of parallel-field EPR, time-resolved EPR, "computerology", and EPR imaging. Chapter 2 on Magnetic Interactions is essentially unchanged while chapter 3 on Isotropic Hyperfine Effects has been expanded to include new sections on Deviations from the Simple Multinomial Scheme (3.7) and Some Interesting π-Type Free Radicals (3.9). Section 3.9 provides a useful corrective to the notion that the EPR method can detect and characterize almost any type of radical species. This welcome touch of realism is nicely illustrated by mentioning

  3. Ion beam processing of advanced electronic materials

    SciTech Connect

    Cheung, N.W.; Marwick, A.D.; Roberto, J.B.; International Business Machines Corp., Yorktown Heights, NY . Thomas J. Watson Research Center; Oak Ridge National Lab., TN )

    1989-01-01

    This report contains research programs discussed at the materials research society symposia on ion beam processing of advanced electronic materials. Major topics include: shallow implantation and solid-phase epitaxy; damage effects; focused ion beams; MeV implantation; high-dose implantation; implantation in III-V materials and multilayers; and implantation in electronic materials. Individual projects are processed separately for the data bases. (CBS)

  4. Electron paramagnetic resonance studies of a viscous nematic liquid crystal: Evidence counter to a second-order phase change

    NASA Technical Reports Server (NTRS)

    Shutt, W. E.; Gelerinter, E.; Fryburg, G. C.; Sheley, C. F.

    1972-01-01

    The ordering in a viscous, nematic, liquid crystal was studied using vanadyl acetyl acetonate and several nitroxides as paramagnetic probes. The ordering curve for VAAC at both K-band and X-band shows a slope discontinuity at a reduced temperature of 0.85. This discontinuity is caused by the tumbling time of the VAAC becoming comparable with the hyperfine splitting. The slope discontinuity is not present in the ordering curves of the nitroxides. The results are taken as evidence counter to the presence of a second-order phase transition.

  5. Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

    NASA Astrophysics Data System (ADS)

    Shames, A. I.; Osipov, V. Yu.; von Bardeleben, H.-J.; Boudou, J.-P.; Treussart, F.; Vul', A. Ya.

    2014-02-01

    Multiple frequency electron paramagnetic resonance (EPR) study of small (4-25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved gHF1 = 4.26 and gHF2 = 4.00 signals. This feature is attributed to "forbidden" ΔMS = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D1 = 0.0950 ± 0.002 cm-1 and D2 = 0.030 ± 0.005 cm-1. Nanodiamonds of ˜50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-field TR1 EPR signals with gHF1 = 4.26, observed in nano- and micron-diamond powders, to triplet negatively charged nitrogen-vacancy centers. These signals are proposed as reliable and convenient fingerprints in both qualitative and quantitative study of fluorescent nano- and micron-diamonds.

  6. The Origin of the Multiline and g = 4.1 Electron Paramagnetic Resonance Signals from the Oxygen-Evolving System of Photosystem II

    PubMed Central

    Hansson, Örjan; Aasa, Roland; Vänngȧrd, Tore

    1987-01-01

    Continuous illumination at 200 K of photosystem (PS) II-enriched membranes generates two electron paramagnetic resonance (EPR) signals that both are connected with the S2 state: a multiline signal at g 2 and a single line at g = 4.1. From measurements at three different X-band frequencies and at 34 GHz, the g tensor of the multiline species was found to be isotropic with g = 1.982. It has an excited spin multiplet at ∼30 cm-1, inferred from the temperature-dependence of the linewidth. The intensity ratio of the g = 4.1 signal to the multiline signal was found to be almost constant from 5 to 23 K. Based on these findings and on spin quantitation of the two signals in samples with and without 4% ethanol, it is concluded that they arise from the ground doublets of paramagnetic species in different PS II centers. It is suggested that the two signals originate from separate PS II electron donors that are in a redox equilibrium with each other in the S2 state and that the g = 4.1 signal arises from monomeric Mn(IV). PMID:19431697

  7. The influence of oxygen-17 enriched oxygen-donor ligands on the electronic spin relaxation behaviour of paramagnetic metal ions

    NASA Astrophysics Data System (ADS)

    Wells, Gregg B.; Yim, Moon B.; Makinen, Marvin W.

    Continuous wave microwave power saturation of high-spin paramagnetic metalloprotein complexes of Co2+ and Fe3+ showed that the value of the saturation parameter P1/2 is influenced by the coordination of oxygen-17 enriched water to the metal ion. No change was observed for H218O or 2H2O. Pulse saturation and recovery of paramagnetic high-spin Fe3+ heme proteins identified a fast relaxation component sensitive to isotopic oxygen-17 composition that was assigned to the process of spectral diffusion. It is shown that the change in relaxation time for spectral diffusion can alter the (apparent) spin-lattice relaxation to account for the observed changes in continuous wave microwave power saturation experiments. These changes are shown to correlate with alterations in the extent of covalency between the metal ion and oxygen-donor ligand. The experimental results provide a basis for use of continuous wave microwave saturation to identify the presence of oxygen-donor ligands within the inner coordination shell of high-spin Co2+ or Fe3+ in metalloprotein and small molecule complexes and to qualitatively assess the extent of covalency between the metal ion and the oxygen-donor ligand.

  8. Effects of thermal annealing on the radiation produced electron paramagnetic resonance spectra of bovine and equine tooth enamel: Fossil and modern

    NASA Astrophysics Data System (ADS)

    Weeks, Robert A.; Bogard, James S.; Elam, J. Michael; Weinand, Daniel C.; Kramer, Andrew

    2003-06-01

    The concentration of stable radiation-induced paramagnetic states in fossil teeth can be used as a measure of sample age. Temperature excursions >100 °C, however, can cause the paramagnetic state clock to differ from the actual postmortem time. We have heated irradiated enamel from both fossilized bovid and modern equine (MEQ) teeth for 30 min in 50 °C increments from 100 to 300 °C, measuring the electron paramagnetic resonance (EPR) spectrum after each anneal, to investigate such effects. Samples were irradiated again after the last anneal, with doses of 300-1200 Gy from 60Co photons, and measured. Two unirradiated MEQ samples were also annealed for 30 min at 300 °C, one in an evacuated EPR tube and the other in a tube open to the atmosphere, and subsequently irradiated. The data showed that hyperfine components attributed to the alanine radical were not detected in the irradiated MEQ sample until after the anneals. The spectrum of the MEQ sample heated in air and then irradiated was similar to that of the heat treated fossil sample. We conclude that the hyperfine components are due to sample heating to temperatures/times >100 °C/30 min and that similarities between fossil and MEQ spectra after the 300 °C/30 min MEQ anneal are also due to sample heating. We conclude that the presence of the hyperfine components in spectra of fossil tooth enamel indicate that such thermal events occurred either at the time of death, or during the postmortem history.

  9. Advanced Electronics Systems 1, Industrial Electronics 3: 9327.03.

    ERIC Educational Resources Information Center

    Dade County Public Schools, Miami, FL.

    The 135 clock-hour course for the 12th year consists of outlines for blocks of instruction on transistor applications to basic circuits, principles of single sideband communications, maintenance practices, preparation for FCC licenses, application of circuits to advanced electronic systems, nonsinusoidal wave shapes, multivibrators, and blocking…

  10. Overview of advanced law enforcement electronic technology

    NASA Astrophysics Data System (ADS)

    Harden, W. R.

    1995-05-01

    Law enforcement and security management are using advanced electronic equipment to increase the effectiveness and efficiency of the budget restricted police officer force. Currently there is also significant national attention concerning the possible utilization of 'military' electronic hardware to implement the much sought after 'force multiplier' which can help to alleviate each jurisdictions economic restrictions. However, as we are now finding, the transfer of 'military' hardware for utilization by law enforcement personnel is not as economically viable as hoped. This paper will address some of the recent advances in electronic technology that are being derived from the military technology base. Additionally, comments are given concerning the economic impact as the technology is transferred to the law enforcement community.

  11. Advanced Electron Microscopy in Materials Physics

    SciTech Connect

    Zhu, Y.; Jarausch, K.

    2009-06-01

    Aberration correction has opened a new frontier in electron microscopy by overcoming the limitations of conventional round lenses, providing sub-angstrom-sized probes and extending information limits. The imaging and analytical performance of these corrector-equipped microscopes affords an unprecedented opportunity to study structure-property relationships of matter at the atomic scale. This new generation of microscopes is able to retrieve high-quality structural information comparable to neutron and synchrotron x-ray experiments, but with local atomic resolution. These advances in instrumentation are accelerating the research and development of various functional materials ranging from those for energy generation, conversion, transportation and storage to those for catalysis and nano-device applications. The dramatic improvements in electron-beam illumination and detection also present a host of new challenges for the interpretation and optimization of experiments. During 7-9 November 2007, a workshop, entitled 'Aberration Corrected Electron Microscopy in Material Physics', was convened at the Center for Functional Nanomaterials, Brookhaven National Laboratories (BNL) to address these opportunities and challenges. The workshop was co-sponsored by Hitachi High Technologies, a leader in electron microscopy instrumentation, and BNL's Institute of Advanced Electron Microscopy, a leader in materials physics research using electron microscopy. The workshop featured presentations by internationally prominent scientists working at the frontiers of electron microscopy, both on developing instrumentation and applying it in materials physics. The meeting, structured to stimulate scientific exchanges and explore new capabilities, brought together {approx}100 people from over 10 countries. This special issue complies many of the advances in instrument performance and materials physics reported by the invited speakers and attendees at the workshop.

  12. Electron paramagnetic resonance and magnetization in Co doped La{sub 2/3}Ca{sub 1/3}MnO{sub 3}

    SciTech Connect

    Rivadulla, F.; Sande, P.; Causa, M. T.; Hueso, L. E.; Lopez-Quintela, M. A.; Rivas, J.

    2001-06-01

    Spin dynamics of the Mn-site substituted colossal magnetoresistance system were studied by means of electron paramagnetic resonance (EPR) and dc magnetic susceptibility in La{sub 2/3}Ca{sub 1/3}Mn{sub 1{minus}x}Co{sub x}O{sub 3} (0{le}x{le}0.1,{Delta}x=0.025). A dramatic increase in the high temperature limiting value for the EPR linewidth ({Delta}H{sub pp}({infinity})) was observed with doping. Structural analysis revealed that only negligible changes are produced in bond distances and angles at these low doping levels. On the other hand, dipolar contribution to {Delta}H{sub pp}({infinity}) was estimated in a few Gauss. To explain the effect of doping on {Delta}H{sub pp}({infinity}), we propose here a scenario including fast Mn-spin lattice relaxation through paramagnetic Co ions. {copyright} 2001 American Institute of Physics.

  13. A high-frequency electron paramagnetic resonance spectrometer for multi-dimensional, multi-frequency, and multi-phase pulsed measurements.

    PubMed

    Cho, F H; Stepanov, V; Takahashi, S

    2014-07-01

    We describe instrumentation for a high-frequency electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) spectroscopy. The instrumentation is operated in the frequency range of 107-120 GHz and 215-240 GHz and in the magnetic field range of 0-12.1 T. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a cryogenic-free superconducting magnet, and a (4)He cryostat enables multi-frequency continuous-wave EPR spectroscopy as well as pulsed EPR measurements with a few hundred nanosecond pulses. Here we discuss the details of the design and the pulsed EPR sensitivity of the instrumentation. We also present performance of the instrumentation in unique experiments including PELDOR spectroscopy to probe correlations in an insulating electronic spin system and application of dynamical decoupling techniques to extend spin coherence of electron spins in an insulating solid-state system. PMID:25085176

  14. A high-frequency electron paramagnetic resonance spectrometer for multi-dimensional, multi-frequency, and multi-phase pulsed measurements

    SciTech Connect

    Cho, F. H.; Stepanov, V.; Takahashi, S.

    2014-07-15

    We describe instrumentation for a high-frequency electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) spectroscopy. The instrumentation is operated in the frequency range of 107−120 GHz and 215−240 GHz and in the magnetic field range of 0−12.1 T. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a cryogenic-free superconducting magnet, and a {sup 4}He cryostat enables multi-frequency continuous-wave EPR spectroscopy as well as pulsed EPR measurements with a few hundred nanosecond pulses. Here we discuss the details of the design and the pulsed EPR sensitivity of the instrumentation. We also present performance of the instrumentation in unique experiments including PELDOR spectroscopy to probe correlations in an insulating electronic spin system and application of dynamical decoupling techniques to extend spin coherence of electron spins in an insulating solid-state system.

  15. Parallel image-acquisition in continuous-wave electron paramagnetic resonance imaging with a surface coil array: Proof-of-concept experiments.

    PubMed

    Enomoto, Ayano; Hirata, Hiroshi

    2014-02-01

    This article describes a feasibility study of parallel image-acquisition using a two-channel surface coil array in continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Parallel EPR imaging was performed by multiplexing of EPR detection in the frequency domain. The parallel acquisition system consists of two surface coil resonators and radiofrequency (RF) bridges for EPR detection. To demonstrate the feasibility of this method of parallel image-acquisition with a surface coil array, three-dimensional EPR imaging was carried out using a tube phantom. Technical issues in the multiplexing method of EPR detection were also clarified. We found that degradation in the signal-to-noise ratio due to the interference of RF carriers is a key problem to be solved.

  16. Single-crystal electron paramagnetic resonance study of cytochrome c3 from Desulfovibrio desulfuricans Norway Strain. Assignment of the heme midpoint redox potentials.

    PubMed

    Guigliarelli, B; Bertrand, P; More, C; Haser, R; Gayda, J P

    1990-11-01

    A single crystal of cytochrome c3 from Desulfovibrio desulfuricans Norway is studied by electron paramagnetic resonance at low temperature. The orientation of the principal axis corresponding to the largest g value is determined for the 12 heme groups in the crystal unit cell. The comparison of these directions to the normals to the heme planes, determined from the crystallographic data at 2.5 A resolution, gives strong evidence for the following assignment of the midpoint redox potentials to the heme groups H1 to H4, defined in the three-dimensional structure: -150 mV is assigned to H3, -300 mV to H4, -330 mV to H1 and -355 mV to H2. This assignment is in agreement with a partial correspondence previously established from an independent study performed on cytochrome c3 in solution. PMID:2172551

  17. Electron Paramagnetic Resonance Characterization of Three Iron-Sulfur Clusters Present in the Nitrogenase Cofactor Maturase NifB from Methanocaldococcus infernus.

    PubMed

    Wilcoxen, Jarett; Arragain, Simon; Scandurra, Alessandro A; Jimenez-Vicente, Emilio; Echavarri-Erasun, Carlos; Pollmann, Stephan; Britt, R David; Rubio, Luis M

    2016-06-22

    NifB utilizes two equivalents of S-adenosyl methionine (SAM) to insert a carbide atom and fuse two substrate [Fe-S] clusters forming the NifB cofactor (NifB-co), which is then passed to NifEN for further modification to form the iron-molybdenum cofactor (FeMo-co) of nitrogenase. Here, we demonstrate that NifB from the methanogen Methanocaldococcus infernus is a radical SAM enzyme able to reductively cleave SAM to 5'-deoxyadenosine radical and is competent in FeMo-co maturation. Using electron paramagnetic resonance spectroscopy we have characterized three [4Fe-4S] clusters, one SAM binding cluster, and two auxiliary clusters probably acting as substrates for NifB-co formation. Nitrogen coordination to one or more of the auxiliary clusters in NifB was observed, and its mechanistic implications for NifB-co dissociation from the maturase are discussed. PMID:27268267

  18. From a paramagnetic, mononuclear supersulfidonickel(II) complex to a diamagnetic dimer with a four-sulfur two-electron bond.

    PubMed

    Yao, Shenglai; Milsmann, Carsten; Bill, Eckhard; Wieghardt, Karl; Driess, Matthias

    2008-10-15

    The first isolable "side-on" supersulfidonickel(II) complex 1(1) with the elusive S2-. ligand has been synthesized by facile oxidation of the corresponding nickel(I) precursor [LNi] with elemental sulfur. Remarkably, paramagnetic 1(1) associates voluntarily to give the diamagnetic dimer 1(2) with a four-sulfur two-electron bond as proven by X-ray diffraction analysis, spectroscopic measurements (1H NMR, EPR, SQUID), and DFT calculations. Gentle sulfur transfer of 1(1) to Ph3P or its reaction with [LNi] affords solely the genuine disulfide complex 3 having a Ni2(mu-mu2:mu2-S2) core. PMID:18803388

  19. Evaluation of the effect of dietary lycopene, the main carotenoid in tomato (Lycopersicon esculentum), on the in vivo renal reducing ability by a radiofrequency electron paramagnetic resonance method.

    PubMed

    Yoshida, Kazutaka; Yokoyama, Hidekatsu; Oteki, Takaaki; Matsumoto, Gaku; Aizawa, Koichi; Inakuma, Takahiro

    2011-04-13

    Although it has been reported that dietary lycopene, the main carotenoid in tomato, improved drug-induced nephropathy, there are no reports on the effect of orally administered lycopene on the in vivo renal reducing (i.e., antioxidant) ability. The radiofrequency electron paramagnetic resonance (EPR) method is a unique technique by which the in vivo reducing ability of an experimental animal can be studied. In this study, the in vivo changes in the renal reducing ability of rats orally administered lycopene were investigated using a 700 MHz EPR spectrometer equipped with a surface-coil-type resonator. Rats were fed either a control diet or a diet containing lycopene. After 2 weeks, in vivo EPR measurements were conducted. The renal reducing ability of lycopene-treated rats was significantly greater than that of the control. This is the first verification of in vivo antioxidant enhancement via dietary lycopene administration. PMID:21381743

  20. Application of electron paramagnetic resonance imaging to the characterization of the Ultem(R) exposed to 1 MeV electrons. Correlation of radical density data to tiger code calculations

    NASA Technical Reports Server (NTRS)

    Suleman, Naushadalli K.

    1994-01-01

    A major long-term goal of the Materials Division at the NASA Langley Research Center is the characterization of new high-performance materials that have potential applications in the aircraft industry, and in space. The materials used for space applications are often subjected to a harsh and potentially damaging radiation environment. The present study constitutes the application of a novel technique to obtain reliable data for ascertaining the molecular basis for the resilience and durability of materials that have been exposed to simulated space radiations. The radiations of greatest concern are energetic electrons and protons, as well as galactic cosmic rays. Presently, the effects of such radiation on matter are not understood in their entirety. It is clear however, that electron radiation causes ionization and homolytic bond rupture, resulting in the formation of paramagnetic spin centers in the polymer matrices of the structural materials. Since the detection and structure elucidation of paramagnetic species are most readily accomplished using Electron Paramagnetic Resonance (EPR) Spectroscopy, the NASA LaRC EPR system was brought back on-line during the 1991 ASEE term. The subsequent 1992 ASEE term was devoted to the adaptation of the EPR core system to meet the requirements for EPR Imaging (EPRI), which provides detailed information on the spatial distribution of paramagnetic species in bulk media. The present (1994) ASEE term was devoted to the calibration of this EPR Imaging system, as well as to the application of this technology to study the effects of electron irradiation on Ultem(exp R), a high performance polymer which is a candidate for applications in aerospace. The Ultem was exposed to a dose of 2.4 x 10(exp 9) Rads (1-MeV energy/electron) at the LaRC electron accelerator facility. Subsequently, the exposed specimens were stored in liquid nitrogen, until immediately prior to analyses by EPRI. The intensity and dimensions of the EPR Images that

  1. Electronic spark advance-type ignition system

    SciTech Connect

    Koike, H.

    1986-12-09

    An electronic spark advance-type ignition system is described for an internal combustion engine comprising: an ignition coil; a magnetic pickup for generating a pair of pulse signals with a time interval therebetween substantially corresponding to a maximum advance angle in terms of crankshaft rotation degrees for each rotation of a crankshaft of the engine; signal generating means responsive to the pair of pulse signals for the pickup for generating a pair of comparison signals of different levels within each of the crankshaft rotation degrees of the maximum advance angle and the other crankshaft rotation degrees; and control means for comparing the signal levels of each of the pairs of comparison signals to generate an energization starting position signal and an ignition timing determining ignition position signal for the ignition coil, the signal generating means including means for controlling the waveform of one of the pair of comparison signals so that the ignition position signal is advanced in angle with respect to the energization starting position signal. The energization starting position signal is generated under all conditions prior to the timing of generation of the earlier one of the next pair of pulse signals generated from the pickup. The ignition position signal is generated within the maximum advance angle at a point in time following generation of the earlier one of the next pair of pulse signals by at least a predetermined amount.

  2. Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

    SciTech Connect

    Shames, A. I.; Osipov, V. Yu.; Vul’, A. Ya.; Bardeleben, H.-J. von

    2014-02-10

    Multiple frequency electron paramagnetic resonance (EPR) study of small (4–25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved g{sub HF1} = 4.26 and g{sub HF2} = 4.00 signals. This feature is attributed to “forbidden” ΔM{sub S} = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D{sub 1} = 0.0950 ± 0.002 cm{sup −1} and D{sub 2} = 0.030 ± 0.005 cm{sup −1}. Nanodiamonds of ∼50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-field TR1 EPR signals with g{sub HF1} = 4.26, observed in nano- and micron-diamond powders, to triplet negatively charged nitrogen-vacancy centers. These signals are proposed as reliable and convenient fingerprints in both qualitative and quantitative study of fluorescent nano- and micron-diamonds.

  3. Advanced thermal management technologies for defense electronics

    NASA Astrophysics Data System (ADS)

    Bloschock, Kristen P.; Bar-Cohen, Avram

    2012-05-01

    Thermal management technology plays a key role in the continuing miniaturization, performance improvements, and higher reliability of electronic systems. For the past decade, and particularly, the past 4 years, the Defense Advanced Research Projects Agency (DARPA) has aggressively pursued the application of micro- and nano-technology to reduce or remove thermal constraints on the performance of defense electronic systems. The DARPA Thermal Management Technologies (TMT) portfolio is comprised of five technical thrust areas: Thermal Ground Plane (TGP), Microtechnologies for Air-Cooled Exchangers (MACE), NanoThermal Interfaces (NTI), Active Cooling Modules (ACM), and Near Junction Thermal Transport (NJTT). An overview of the TMT program will be presented with emphasis on the goals and status of these efforts relative to the current State-of-the-Art. The presentation will close with future challenges and opportunities in the thermal management of defense electronics.

  4. Advances in positron and electron scattering*

    NASA Astrophysics Data System (ADS)

    Limão-Vieira, Paulo; García, Gustavo; Krishnakumar, E.; Petrović, Zoran; Sullivan, James; Tanuma, Hajime

    2016-10-01

    The topical issue on Advances in Positron and Electron Scattering" combines contributions from POSMOL 2015 together with others devoted to celebrate the unprecedented scientific careers of our loyal colleagues and trusted friends Steve Buckman (Australian National University, Australia) and Michael Allan (University of Fribourg, Switzerland) on the occasion of their retirements. POSMOL 2015, the XVIII International Workshop on Low-Energy Positron and Positronium Physics and the XIX International Symposium on Electron-Molecule Collisions and Swarms, was held at Universidade NOVA de Lisboa, Lisboa, Portugal, from 17-20 July 2015. The international workshop and symposium allowed to achieve a very privileged forum of sharing and developing our scientific expertise on current aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and related topics, as well as electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent developments in the study of swarms are also fully addressed.

  5. Electronic structure description of a [Co(III)3Co(IV)O4] cluster: a model for the paramagnetic intermediate in cobalt-catalyzed water oxidation.

    PubMed

    McAlpin, J Gregory; Stich, Troy A; Ohlin, C André; Surendranath, Yogesh; Nocera, Daniel G; Casey, William H; Britt, R David

    2011-10-01

    Multifrequency electron paramagnetic resonace (EPR) spectroscopy and electronic structure calculations were performed on [Co(4)O(4)(C(5)H(5)N)(4)(CH(3)CO(2))(4)](+) (1(+)), a cobalt tetramer with total electron spin S = 1/2 and formal cobalt oxidation states III, III, III, and IV. The cuboidal arrangement of its cobalt and oxygen atoms is similar to that of proposed structures for the molecular cobaltate clusters of the cobalt-phosphate (Co-Pi) water-oxidizing catalyst. The Davies electron-nuclear double resonance (ENDOR) spectrum is well-modeled using a single class of hyperfine-coupled (59)Co nuclei with a modestly strong interaction (principal elements of the hyperfine tensor are equal to [-20(±2), 77(±1), -5(±15)] MHz). Mims (1)H ENDOR spectra of 1(+) with selectively deuterated pyridine ligands confirm that the amount of unpaired spin on the cobalt-bonding partner is significantly reduced from unity. Multifrequency (14)N ESEEM spectra (acquired at 9.5 and 34.0 GHz) indicate that four nearly equivalent nitrogen nuclei are coupled to the electron spin. Cumulatively, our EPR spectroscopic findings indicate that the unpaired spin is delocalized almost equally across the eight core atoms, a finding corroborated by results from DFT calculations. Each octahedrally coordinated cobalt ion is forced into a low-spin electron configuration by the anionic oxo and carboxylato ligands, and a fractional electron hole is localized on each metal center in a Co 3d(xz,yz)-based molecular orbital for this essentially [Co(+3.125)(4)O(4)] system. Comparing the EPR spectrum of 1(+) with that of the catalyst film allows us to draw conclusions about the electronic structure of this water-oxidation catalyst.

  6. Disappearance of electron-hole asymmetry in nanoparticles of Nd{sub 1−x}Ca{sub x}MnO{sub 3}(x=0.6,0.4): magnetization and electron paramagnetic resonance evidence

    SciTech Connect

    Bhagyashree, K. S. Bhat, S. V.

    2015-05-07

    We study and compare magnetic and electron paramagnetic resonance behaviors of bulk and nanoparticles of Nd{sub 1−x}Ca{sub x}MnO{sub 3} in hole doped (x=0.4;NCMOH) and electron doped (x=0.6;NCMOE) samples. NCMOH in bulk form shows a complex temperature dependence of magnetization M(T), with a charge ordering transition at ∼250 K, an antiferromagnetic (AFM) transition at ∼150 K, and a transition to a canted AFM phase/mixed phase at ∼80 K. Bulk NCMOE behaves quite differently with just a charge ordering transition at ∼280 K, thus providing a striking example of the so called electron-hole asymmetry. While our magnetization data on bulk samples are consistent with the earlier reports, the new results on the nanoparticles bring out drastic effects of size reduction. They show that M(T) behaviors of the two nanosamples are essentially similar in addition to the absence of the charge order in them thus providing strong evidence for vanishing of the electron-hole asymmetry in nanomanganites. This conclusion is further corroborated by electron paramagnetic resonance studies which show that the large difference in the “g” values and their temperature dependences found for the two bulk samples disappears as they approach a common behavior in the corresponding nanosamples.

  7. Paramagnetic ultrasmall gadolinium oxide nanoparticles as advanced T1 MRI contrast agent: account for large longitudinal relaxivity, optimal particle diameter, and in vivo T1 MR images.

    PubMed

    Park, Ja Young; Baek, Myung Ju; Choi, Eun Sook; Woo, Seungtae; Kim, Joo Hyun; Kim, Tae Jeong; Jung, Jae Chang; Chae, Kwon Seok; Chang, Yongmin; Lee, Gang Ho

    2009-11-24

    Paramagnetic ultrasmall gadolinium oxide (Gd(2)O(3)) nanoparticles with particle diameters (d) of approximately 1 nm were synthesized by using three kinds of Gd(III) ion precursors and by refluxing each of them in tripropylene glycol under an O(2) flow. A large longitudinal relaxivity (r(1)) of water proton of 9.9 s(-1) mM(-1) was estimated. As a result, high contrast in vivo T(1) MR images of the brain tumor of a rat were observed. This large r(1) is discussed in terms of the huge surface to volume ratio (S/V) of the ultrasmall gadolinium oxide nanoparticles coupled with the cooperative induction of surface Gd(III) ions for the longitudinal relaxation of a water proton. It is found from the d dependence of r(1) that the optimal range of d for the maximal r(1), which may be used as an advanced T(1) MRI contrast agent, is 1-2.5 nm.

  8. Advanced electronics for the CTF MEG system.

    PubMed

    McCubbin, J; Vrba, J; Spear, P; McKenzie, D; Willis, R; Loewen, R; Robinson, S E; Fife, A A

    2004-11-30

    Development of the CTF MEG system has been advanced with the introduction of a computer processing cluster between the data acquisition electronics and the host computer. The advent of fast processors, memory, and network interfaces has made this innovation feasible for large data streams at high sampling rates. We have implemented tasks including anti-alias filter, sample rate decimation, higher gradient balancing, crosstalk correction, and optional filters with a cluster consisting of 4 dual Intel Xeon processors operating on up to 275 channel MEG systems at 12 kHz sample rate. The architecture is expandable with additional processors to implement advanced processing tasks which may include e.g., continuous head localization/motion correction, optional display filters, coherence calculations, or real time synthetic channels (via beamformer). We also describe an electronics configuration upgrade to provide operator console access to the peripheral interface features such as analog signal and trigger I/O. This allows remote location of the acoustically noisy electronics cabinet and fitting of the cabinet with doors for improved EMI shielding. Finally, we present the latest performance results available for the CTF 275 channel MEG system including an unshielded SEF (median nerve electrical stimulation) measurement enhanced by application of an adaptive beamformer technique (SAM) which allows recognition of the nominal 20-ms response in the unaveraged signal.

  9. Advanced electronics for the CTF MEG system.

    PubMed

    McCubbin, J; Vrba, J; Spear, P; McKenzie, D; Willis, R; Loewen, R; Robinson, S E; Fife, A A

    2004-01-01

    Development of the CTF MEG system has been advanced with the introduction of a computer processing cluster between the data acquisition electronics and the host computer. The advent of fast processors, memory, and network interfaces has made this innovation feasible for large data streams at high sampling rates. We have implemented tasks including anti-alias filter, sample rate decimation, higher gradient balancing, crosstalk correction, and optional filters with a cluster consisting of 4 dual Intel Xeon processors operating on up to 275 channel MEG systems at 12 kHz sample rate. The architecture is expandable with additional processors to implement advanced processing tasks which may include e.g., continuous head localization/motion correction, optional display filters, coherence calculations, or real time synthetic channels (via beamformer). We also describe an electronics configuration upgrade to provide operator console access to the peripheral interface features such as analog signal and trigger I/O. This allows remote location of the acoustically noisy electronics cabinet and fitting of the cabinet with doors for improved EMI shielding. Finally, we present the latest performance results available for the CTF 275 channel MEG system including an unshielded SEF (median nerve electrical stimulation) measurement enhanced by application of an adaptive beamformer technique (SAM) which allows recognition of the nominal 20-ms response in the unaveraged signal. PMID:16012695

  10. Phosphonated Trityl Probes for Concurrent in Vivo Tissue Oxygen and pH Monitoring Using Electron Paramagnetic Resonance-Based Techniques

    PubMed Central

    Dhimitruka, Ilirian; Bobko, Andrey A.; Eubank, Timothy D.; Komarov, Denis A.; Khramtsov, Valery V.

    2014-01-01

    Previously we proposed the concept of dual function pH and oxygen paramagnetic probes based on the incorporation of ionizable groups into the structure of persistent triarylmethyl radicals, TAMs (J. Am. Chem. Soc. 2007, 129, 7240–7241). In this paper, we synthesized an asymmetric monophosphonated TAM probe with the simplest doublet hfs pattern ideally suited for dual function electron paramagnetic resonance (EPR)-based applications. An extraordinary low line width of the synthesized deuterated derivative, p1TAM-D (ΔHpp ≤ 50 mG, Lorentz line width, ≤20 mG) results in high sensitivity to pO2 due to oxygen-induced line broadening (ΔLW/ΔpO2 ≈ 0.5 mG/mmHg or ≈400 mG/mM); accuracy of pO2 measurement, ≈1 mmHg). The presence of a phosphono group in the p1TAM-D structure provides pH sensitivity to its EPR spectra in the physiological range of pH from 5.9 to 8.2 with the ratio of signal intensities of protonated and deprotonated states being a reliable pH marker (accuracy of pH measurements, ± 0.05). The independent character of pH and [O2] effects on the EPR spectra of p1TAM-D provides dual functionality to this probe. The L-band EPR studies performed in breast tumor-bearing mice show a significant difference in extracellular pH and pO2 between tumor and normal mammary gland tissues, as well as the effect of animal breathing with 100% O2 on tissue oxygenation. The developed dual function phosphonated p1TAM-D probe provides a unique tool for in vivo concurrent tissue oxygen and pH monitoring. PMID:23517077

  11. Phosphonated trityl probes for concurrent in vivo tissue oxygen and pH monitoring using electron paramagnetic resonance-based techniques.

    PubMed

    Dhimitruka, Ilirian; Bobko, Andrey A; Eubank, Timothy D; Komarov, Denis A; Khramtsov, Valery V

    2013-04-17

    Previously we proposed the concept of dual function pH and oxygen paramagnetic probes based on the incorporation of ionizable groups into the structure of persistent triarylmethyl radicals, TAMs (J. Am. Chem. Soc.2007, 129, 7240-7241). In this paper, we synthesized an asymmetric monophosphonated TAM probe with the simplest doublet hfs pattern ideally suited for dual function electron paramagnetic resonance (EPR)-based applications. An extraordinary low line width of the synthesized deuterated derivative, p1TAM-D (ΔHpp ≤ 50 mG, Lorentz line width, ≤20 mG) results in high sensitivity to pO2 due to oxygen-induced line broadening (ΔLW/ΔpO2 ≈ 0.5 mG/mmHg or ≈400 mG/mM); accuracy of pO2 measurement, ≈1 mmHg). The presence of a phosphono group in the p1TAM-D structure provides pH sensitivity to its EPR spectra in the physiological range of pH from 5.9 to 8.2 with the ratio of signal intensities of protonated and deprotonated states being a reliable pH marker (accuracy of pH measurements, ± 0.05). The independent character of pH and [O2] effects on the EPR spectra of p1TAM-D provides dual functionality to this probe. The L-band EPR studies performed in breast tumor-bearing mice show a significant difference in extracellular pH and pO2 between tumor and normal mammary gland tissues, as well as the effect of animal breathing with 100% O2 on tissue oxygenation. The developed dual function phosphonated p1TAM-D probe provides a unique tool for in vivo concurrent tissue oxygen and pH monitoring.

  12. Electron spin resonance of Ni-doped CuGeO3 in the paramagnetic, spin-Peierls, and antiferromagnetic states: Comparison with nonmagnetic impurities

    NASA Astrophysics Data System (ADS)

    Grenier, B.; Monod, P.; Hagiwara, M.; Matsuda, M.; Katsumata, K.; Clément, S.; Renard, J.-P.; Barra, A. L.; Dhalenne, G.; Revcolevschi, A.

    2002-03-01

    We have performed electron-spin-resonance measurements on single crystals of the doped spin-Peierls compounds CuGe1-ySiyO3 and Cu1-xMxGeO3 with M=Zn, Mg, Ni (x,y<=0.1). The first part of our experiments was performed in the paramagnetic and spin-Peierls phases at 9.5, 95, and 190 GHz. All nonmagnetic impurities (Si, Zn and Mg) were found to hardly affect the position and linewidth of the single line resonance, in spite of the moment formation due to the broken chains. In contrast to Si, Zn, and Mg dopings, the presence of Ni (S=1) at low concentration induces a spectacular shift toward high fields of the ESR line (up to 40% for x=0.002), together with a large broadening. This shift is strictly proportional to the ratio of Ni to Cu susceptibilities: Hence it is strongly enhanced below the spin-Peierls transition. We interpret this shift and the broadening as due to the exchange field induced by the Ni ions onto strongly exchange coupled Cu spins. Second, the antiferromagnetic resonance was investigated in Ni-doped samples. The frequency vs magnetic-field relation of the resonance is well explained by the classical theory with orthorhombic anisotropy, with g values remarkably reduced, in accordance with the study of the spin-Peierls and paramagnetic phases. The easy, second-easy, and hard axes are found to be a, c, and b axes, respectively. These results, which are dominated by the single ion anisotropy of Ni2+, are discussed in comparison with those in the Zn- and Si-doped CuGeO3.

  13. Light-induced electron paramagnetic resonance evidence of charge transfer in electrospun fibers containing conjugated polymer/fullerene and conjugated polymer/fullerene/carbon nanotube blends

    SciTech Connect

    Shames, Alexander I.; Bounioux, Celine; Katz, Eugene A.; Yerushalmi-Rozen, Rachel; Zussman, Eyal

    2012-03-12

    Electrospun sub-micron fibers containing conjugated polymer (poly(3-hexylthiophene), P3HT) with a fullerene derivative, phenyl-C61-butyric acid methylester (PCBM) or a mixture of PCBM and single-walled carbon nanotubes (SWCNTs) were studied by light-induced electron paramagnetic resonance spectroscopy. The results provide experimental evidence of electron transfer between PCBM and P3HT components in both fiber systems and suggest that the presence of a dispersing block-copolymer, which acts via physical adsorption onto the PCBM and SWCNT moieties, does not prevent electron transfer at the P3HT-PCBM interface. These findings suggest a research perspective towards utilization of fibers of functional nanocomposites in fiber-based organic optoelectronic and photovoltaic devices. The latter can be developed in the textile-type large area photovoltaics or individual fiber-based solar cells that will broaden energy applications from macro-power tools to micro-nanoscale power conversion devices and smart textiles.

  14. Light-induced electron paramagnetic resonance evidence of charge transfer in electrospun fibers containing conjugated polymer/fullerene and conjugated polymer/fullerene/carbon nanotube blends

    NASA Astrophysics Data System (ADS)

    Shames, Alexander I.; Bounioux, Céline; Katz, Eugene A.; Yerushalmi-Rozen, Rachel; Zussman, Eyal

    2012-03-01

    Electrospun sub-micron fibers containing conjugated polymer (poly(3-hexylthiophene), P3HT) with a fullerene derivative, phenyl-C61-butyric acid methylester (PCBM) or a mixture of PCBM and single-walled carbon nanotubes (SWCNTs) were studied by light-induced electron paramagnetic resonance spectroscopy. The results provide experimental evidence of electron transfer between PCBM and P3HT components in both fiber systems and suggest that the presence of a dispersing block-copolymer, which acts via physical adsorption onto the PCBM and SWCNT moieties, does not prevent electron transfer at the P3HT-PCBM interface. These findings suggest a research perspective towards utilization of fibers of functional nanocomposites in fiber-based organic optoelectronic and photovoltaic devices. The latter can be developed in the textile-type large area photovoltaics or individual fiber-based solar cells that will broaden energy applications from macro-power tools to micro-nanoscale power conversion devices and smart textiles.

  15. Advanced diesel electronic fuel injection and turbocharging

    NASA Astrophysics Data System (ADS)

    Beck, N. J.; Barkhimer, R. L.; Steinmeyer, D. C.; Kelly, J. E.

    1993-12-01

    The program investigated advanced diesel air charging and fuel injection systems to improve specific power, fuel economy, noise, exhaust emissions, and cold startability. The techniques explored included variable fuel injection rate shaping, variable injection timing, full-authority electronic engine control, turbo-compound cooling, regenerative air circulation as a cold start aid, and variable geometry turbocharging. A Servojet electronic fuel injection system was designed and manufactured for the Cummins VTA-903 engine. A special Servojet twin turbocharger exhaust system was also installed. A series of high speed combustion flame photos was taken using the single cylinder optical engine at Michigan Technological University. Various fuel injection rate shapes and nozzle configurations were evaluated. Single-cylinder bench tests were performed to evaluate regenerative inlet air heating techniques as an aid to cold starting. An exhaust-driven axial cooling air fan was manufactured and tested on the VTA-903 engine.

  16. Study of a DNA Duplex by Nuclear Magnetic Resonance and Molecular Dynamics Simulations. Validation of Pulsed Dipolar Electron Paramagnetic Resonance Distance Measurements Using Triarylmethyl-Based Spin Labels.

    PubMed

    Lomzov, Alexander A; Sviridov, Eugeniy A; Shernuykov, Andrey V; Shevelev, Georgiy Yu; Pyshnyi, Dmitrii V; Bagryanskaya, Elena G

    2016-06-16

    Pulse dipole-dipole electron paramagnetic resonance (EPR) spectroscopy (double electron-electron resonance [DEER] or pulse electron-electron double resonance [PELDOR] and double quantum coherence [DQC]) allows for measurement of distances in biomolecules and can be used at low temperatures in a frozen solution. Recently, the possibility of distance measurement in a nucleic acid at a physiological temperature using pulse EPR was demonstrated. In these experiments, triarylmethyl (TAM) radicals with long memory time of the electron spin served as a spin label. In addition, the duplex was immobilized on modified silica gel particles (Nucleosil DMA); this approach enables measurement of interspin distances close to 4.5 nm. Nevertheless, the possible influence of TAM on the structure of a biopolymer under study and validity of the data obtained by DQC are debated. In this paper, a combination of molecular dynamics (MD) and nuclear magnetic resonance (NMR) methods was used for verification of interspin distances measured by the X-band DQC method. NMR is widely used for structural analysis of biomolecules under natural conditions (room temperature and an aqueous solution). The ultraviolet (UV) melting method and thermal series (1)H NMR in the range 5-95 °C revealed the presence of only the DNA duplex in solution at oligonucleotide concentrations 1 μM to 1.1 mM at temperatures below 40 °C. The duplex structures and conformation flexibility of native and TAM-labeled DNA complexes obtained by MD simulation were the same as the structure obtained by NMR refinement. Thus, we showed that distance measurements at physiological temperatures by the X-band DQC method allow researchers to obtain valid structural information on an unperturbed DNA duplex using terminal TAM spin labels.

  17. Advanced Power Electronics and Electric Motors Annual Report -- 2013

    SciTech Connect

    Narumanchi, S.; Bennion, K.; DeVoto, D.; Moreno, G.; Rugh, J.; Waye, S.

    2015-01-01

    This report describes the research into advanced liquid cooling, integrated power module cooling, high temperature air cooled power electronics, two-phase cooling for power electronics, and electric motor thermal management by NREL's Power Electronics group in FY13.

  18. Sn vacancies in photorefractive Sn2P2S6 crystals: An electron paramagnetic resonance study of an optically active hole trap

    NASA Astrophysics Data System (ADS)

    Golden, E. M.; Basun, S. A.; Evans, D. R.; Grabar, A. A.; Stoika, I. M.; Giles, N. C.; Halliburton, L. E.

    2016-10-01

    Electron paramagnetic resonance (EPR) is used to identify the singly ionized charge state of the Sn vacancy ( VSn - ) in single crystals of Sn2P2S6 (often referred to as SPS). These vacancies, acting as a hole trap, are expected to be important participants in the photorefractive effect observed in undoped SPS crystals. In as-grown crystals, the Sn vacancies are doubly ionized ( VSn 2 - ) with no unpaired spins. They are then converted to a stable EPR-active state when an electron is removed (i.e., a hole is trapped) during an illumination below 100 K with 633 nm laser light. The resulting EPR spectrum has g-matrix principal values of 2.0079, 2.0231, and 1.9717. There are resolved hyperfine interactions with two P neighbors and one Sn neighbor. The isotropic portions of these hyperfine matrices are 167 and 79 MHz for the two 31P neighbors and 8504 MHz for the one Sn neighbor (this latter value is the average for 117Sn and 119Sn). These VSn - vacancies are shallow acceptors with the hole occupying a diffuse wave function that overlaps the neighboring Sn2+ ion and (P2S6)4- anionic unit. Using a general-order kinetics approach, an analysis of isothermal decay curves of the VSn - EPR spectrum in the 107-115 K region gives an activation energy of 283 meV.

  19. Strong reduction of V4+ amount in vanadium oxide/hexadecylamine nanotubes by doping with Co2+ and Ni2+ ions: Electron paramagnetic resonance and magnetic studies

    NASA Astrophysics Data System (ADS)

    Saleta, M. E.; Troiani, H. E.; Ribeiro Guevara, S.; Ruano, G.; Sánchez, R. D.; Malta, M.; Torresi, R. M.

    2011-05-01

    In this work we present a complete characterization and magnetic study of vanadium oxide/hexadecylamine nanotubes (VOx/Hexa NT's) doped with Co2+ and Ni2+ ions. The morphology of the NT's has been characterized by transmission electron microscopy, while the metallic elements have been quantified by the instrumental neutron activation analysis technique. The static and dynamic magnetic properties were studied by collecting data of magnetization as a function of magnetic field and temperature and by electron paramagnetic resonance. At difference of the majority reports in the literature, we do not observe magnetic dimers in vanadium oxide nanotubes. Also, we observed that the incorporation of metallic ions (Co2+, S = 3/2 and Ni2+, S = 1) decreases notably the amount of V4+ ions in the system, from 14-16% (nondoped case) to 2%-4%, with respect to the total vanadium atoms (fact corroborated by XPS experiments) anyway preserving the tubular nanostructure. The method to decrease the amount of V4+ in the nanotubes improves considerably their potential technological applications as Li-ion batteries cathodes.

  20. Electron Paramagnetic Resonance and Fluorescence In Situ Hybridization-Based Investigations of Individual Doses for Persons Living at Metlino in the Upper Reaches of the Techa River

    SciTech Connect

    Degteva, M. O.; Anspaugh, L. R.; Akleyev, A V.; Jacob, Peter; Ivanov, Denis V.; Wieser, Albrecht; Vorobiova, M I.; Shishkina, Elena A.; Shved, Valentina A.; Vozilova, Alexandra; Bayankin, Sergey N.; Napier, Bruce A.

    2005-02-01

    Waterborne releases to the Techa River from the Mayak Production Association in Russia during 1949-1956 resulted in significant doses to persons living downstream; the most contaminated village was Metlino, about 7 km from the site of release. Internal and external doses have been estimated for these residents using the Techa River Dosimetry System-2000 (TRDS-2000); the primary purpose is to support epidemiological studies of the members of the Extended Techa River Cohort. Efforts to validate the calculations of external and internal dose are considered essential. One validation study of the TRDS-2000 system has been performed by the comparison of calculated doses to quartz from bricks in old buildings at Metlino with those measured by luminescence dosimetry. Two additional methods of validation considered here are electron paramagnetic resonance (EPR) measurements of teeth and fluorescence in situ hybridization (FISH) measurements of chromosome translocations in circulating lymphocytes. For electron paramagnetic resonance, 36 measurements on 26 teeth from 16 donors from Metlino were made at the GSF-National Research Center for Environment and Health (16 measurements) and the Institute of Metal Physics (20 measurements); the correlation among measurements made at the two laboratories has been found to be 0.99. Background measurements were also made on 218 teeth (63 molars, 128 premolars, and 27 incisors). Fluorescence in situ hybridization measurements were made for 31 residents of Metlino. These measurements were handicapped by the analysis of a limited number of cells; for several individuals no stable translocations were observed. Fluorescence in situ hybridization measurements were also made for 39 individuals believed to be unexposed. The EPR- and FISH-based estimates agreed well for permanent residents of Metlino: 0.67 +/- 0.21 Gy and 0.48 +/- 0.18 Gy (mean +/- standard error of the mean), respectively. Results of the two experimental methods also agreed well

  1. Inter-spin distance determination using L-band (1-2 GHz) non-adiabatic rapid sweep electron paramagnetic resonance (NARS EPR)

    PubMed Central

    Kittell, Aaron W.; Hustedt, Eric J.; Hyde, James S.

    2014-01-01

    Site-directed spin-labeling electron paramagnetic resonance (SDSL EPR) provides insight into the local structure and motion of a spin probe strategically attached to a molecule. When a second spin is introduced to the system, macromolecular information can be obtained through measurement of inter-spin distances either by continuous wave (CW) or pulsed electron double resonance (ELDOR) techniques. If both methodologies are considered, inter-spin distances of 8 to 80 Å can be experimentally determined. However, there exists a region at the upper limit of the conventional X-band (9.5 GHz) CW technique and the lower limit of the four-pulse double electron-electron resonance (DEER) experiment where neither method is particularly reliable. The work presented here utilizes L-band (1.9 GHz) in combination with non-adiabatic rapid sweep (NARS) EPR to address this opportunity by increasing the upper limit of the CW technique. Because L-band linewidths are three to seven times narrower than those at X-band, dipolar broadenings that are small relative to the X-band inhomogeneous linewidth become observable, but the signal loss due to the frequency dependence of the Boltzmann factor, has made L-band especially challenging. NARS has been shown to increase sensitivity by a factor of five, and overcomes much of this loss, making L-band distance determination more feasible [1]. Two different systems are presented and distances of 18–30 Å have been experimentally determined at physiologically relevant temperatures. Measurements are in excellent agreement with a helical model and values determined by DEER. PMID:22750251

  2. {sup 13}C, {sup 1}H, {sup 6}Li magic-angle spinning nuclear magnetic resonance, electron paramagnetic resonance, and Fourier transform infrared study of intercalation electrodes based in ultrasoft carbons obtained below 3100 K

    SciTech Connect

    Alcantara, R.; Madrigal, F.J.F.; Lavela, P.; Tirado, J.L.; Mateos, J.M.J.; Stoyanova, R.; Zhecheva, E.

    1999-01-01

    The past decade has seen an important development of materials for high-performance energy storage systems. Particularly, the field of electrode materials for advanced lithium batteries has attracted the interest of numerous researchers. Petroleum coke samples of different origins and heat treated at different temperatures below 3100 K have been studied by spectroscopic and electrochemical procedures. According to {sup 13}C and {sup 1}H magic-angle spinning (MAS) nuclear magnetic resonance (NMR), infrared (IR), and electron paramagnetic resonance (EPR) data, aromatic compounds and surface OH groups are present in green coke samples. The preparation of CMB (combustible) sample from 1673 K leads to a low-temperature graphitization process, as shown by the occurrence of multiphase products containing both turbostatic and graphitized solid. This process is accompanied by the loss of aromatic compounds and surface hydroxyls. The optimization of the lithium intercalation electrodes based in the green coke materials was carried out by thermal treatment at 1023 K under dynamic vacuum conditions. Such pretreatment of the electrode material leads to marked enhancement of reversible capacities without the higher temperatures usually required for other soft carbon materials. Finally, the results of {sup 6}Li MAS NMR and EPR have been correlated with the experimental determination of lithium diffusion coefficients and surface properties. On the basis of these results, spin resonance spectroscopies are found to be a powerful tool to discern between the different petroleum coke samples to select the active electrode material with best performance.

  3. Low-temperature interquinone electron transfer in photosynthetic reaction centers from Rhodobacter sphaeroides and Blastochloris viridis: characterization of Q(B)- states by high-frequency electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR).

    PubMed

    Utschig, Lisa M; Thurnauer, Marion C; Tiede, David M; Poluektov, Oleg G

    2005-11-01

    High-frequency electron paramagnetic resonance (HF EPR) techniques have been employed to look for localized light-induced conformational changes in the protein environments around the reduced secondary quinone acceptor (Q(B)(-)) in Rhodobacter sphaeroides and Blastochloris viridis RCs. The Q(A)(-) and Q(B)(-) radical species in Fe-removed/Zn-replaced protonated RCs substituted with deuterated quinones are distinguishable with pulsed D-band (130 GHz) EPR and provide native probes of both the low-temperature Q(A)(-)Q(B) --> Q(A)Q(B)(-) electron-transfer event and the structure of trapped conformational substates. We report here the first spectroscopic evidence that cryogenically trapped, light-induced changes enable low-temperature Q(A)(-)Q(B) --> Q(A)Q(B)(-) electron transfer in the B. viridis RC and the first observation of an inactive, trapped P(+)Q(B)(-) state in both R. sphaeroides and B. viridis RCs that does not recombine at 20 K. The high resolution and orientational selectivity of HF electron-nuclear double resonance (ENDOR) allows us to directly probe protein environments around Q(B)(-) for distinct P(+)Q(B)(-) kinetic RC states by spectrally selecting specific nuclei in isotopically labeled samples. No structural differences in the protein structure near Q(B)(-) or reorientation (within 5 degrees ) of Q(B)(-) was observed with HF ENDOR spectra of two states of P(+)Q(B)(-): "active" and "inactive" states with regards to low-temperature electron transfer. These results reveal a remarkably enforced local protein environment for Q(B) in its reduced semiquinone state and suggest that the conformational change that controls reactivity resides beyond the Q(B) local environment.

  4. Advanced Electronic Systems. Curriculum Guide for Technology Education.

    ERIC Educational Resources Information Center

    Patrick, Dale R.

    This curriculum for a 1-semester or 1-year course in electronics is designed to take students from basic through advanced electronic systems. It covers several electronic areas, such as digital electronics, communication electronics, industrial process control, instrumentation, programmable controllers, and robotics. The guide contains…

  5. Artifact suppression in electron paramagnetic resonance imaging of 14N- and 15N-labeled nitroxyl radicals with asymmetric absorption spectra

    NASA Astrophysics Data System (ADS)

    Takahashi, Wataru; Miyake, Yusuke; Hirata, Hiroshi

    2014-10-01

    This article describes an improved method for suppressing image artifacts in the visualization of 14N- and 15N-labeled nitroxyl radicals in a single image scan using electron paramagnetic resonance (EPR). The purpose of this work was to solve the problem of asymmetric EPR absorption spectra in spectral processing. A hybrid function of Gaussian and Lorentzian lineshapes was used to perform spectral line-fitting to successfully separate the two kinds of nitroxyl radicals. This approach can process the asymmetric EPR absorption spectra of the nitroxyl radicals being measured, and can suppress image artifacts due to spectral asymmetry. With this improved visualization method and a 750-MHz continuous-wave EPR imager, a temporal change in the distributions of a two-phase paraffin oil and water/glycerin solution system was visualized using lipophilic and hydrophilic nitroxyl radicals, i.e., 2-(14-carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy (16-DOXYL stearic acid) and 4-hydroxyl-2,2,6,6-tetramethylpiperidine-d17-1-15N-1-oxyl (TEMPOL-d17-15N). The results of the two-phase separation experiment verified that reasonable artifact suppression could be achieved by the present method that deals with asymmetric absorption spectra in the EPR imaging of 14N- and 15N-labeled nitroxyl radicals.

  6. Potentially diagnostic electron paramagnetic resonance spectra elucidate the underlying mechanism of mitochondrial dysfunction in the deoxyguanosine kinase deficient rat model of a genetic mitochondrial DNA depletion syndrome.

    PubMed

    Bennett, Brian; Helbling, Daniel; Meng, Hui; Jarzembowski, Jason; Geurts, Aron M; Friederich, Marisa W; Van Hove, Johan L K; Lawlor, Michael W; Dimmock, David P

    2016-03-01

    A novel rat model for a well-characterized human mitochondrial disease, mitochondrial DNA depletion syndrome with associated deoxyguanosine kinase (DGUOK) deficiency, is described. The rat model recapitulates the pathologic and biochemical signatures of the human disease. The application of electron paramagnetic (spin) resonance (EPR) spectroscopy to the identification and characterization of respiratory chain abnormalities in the mitochondria from freshly frozen tissue of the mitochondrial disease model rat is introduced. EPR is shown to be a sensitive technique for detecting mitochondrial functional abnormalities in situ and, here, is particularly useful in characterizing the redox state changes and oxidative stress that can result from depressed expression and/or diminished specific activity of the distinct respiratory chain complexes. As EPR requires no sample preparation or non-physiological reagents, it provides information on the status of the mitochondrion as it was in the functioning state. On its own, this information is of use in identifying respiratory chain dysfunction; in conjunction with other techniques, the information from EPR shows how the respiratory chain is affected at the molecular level by the dysfunction. It is proposed that EPR has a role in mechanistic pathophysiological studies of mitochondrial disease and could be used to study the impact of new treatment modalities or as an additional diagnostic tool. PMID:26773591

  7. Evaluation of oxidative stress in the brain of a transgenic mouse model of Alzheimer disease by in vivo electron paramagnetic resonance imaging.

    PubMed

    Matsumura, Akihiro; Emoto, Miho C; Suzuki, Syuuichirou; Iwahara, Naotoshi; Hisahara, Shin; Kawamata, Jun; Suzuki, Hiromi; Yamauchi, Ayano; Sato-Akaba, Hideo; Fujii, Hirotada G; Shimohama, Shun

    2015-08-01

    Alzheimer disease (AD) is a neurodegenerative disease clinically characterized by progressive cognitive dysfunction. Deposition of amyloid-β (Aβ) peptides is the most important pathophysiological hallmark of AD. Oxidative stress induced by reactive oxygen species is prominent in AD, and several reports suggest the relationship between a change in redox status and AD pathology containing progressive Aβ deposition, the activation of glial cells, and mitochondrial dysfunction. Therefore, we performed immunohistochemical analysis using a transgenic mouse model of AD (APdE9) and evaluated the activity of superoxide dismutase in brain tissue homogenates of APdE9 mice in vitro. Together with those analyses, in vivo changes in redox status with age in both wild-type (WT) and APdE9 mouse brains were measured noninvasively by three-dimensional electron paramagnetic resonance (EPR) imaging using nitroxide (3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-yloxy) as a redox-sensitive probe. Both methods found similar changes in redox status with age, and in particular a significant change in redox status in the hippocampus was observed noninvasively by EPR imaging between APdE9 mice and age-matched WT mice from 9 to 18 months of age. EPR imaging clearly visualized the accelerated change in redox status of APdE9 mouse brain compared with WT. The evaluation of the redox status in the brain of AD model rodents by EPR imaging should be useful for diagnostic study of AD.

  8. Binding of transition metals to monosilicic acid in aqueous and xylem (Cucumis sativus L.) solutions: a low-T electron paramagnetic resonance study.

    PubMed

    Stevic, Nenad; Korac, Jelena; Pavlovic, Jelena; Nikolic, Miroslav

    2016-10-01

    The supplementation of monosilicic acid [Si(OH)4] to the root growing medium is known to protect plants from toxic levels of iron (Fe), copper (Cu) and manganese (Mn), but also to mitigate deficiency of Fe and Mn. However, the physicochemical bases of these alleviating mechanisms are not fully understood. Here we applied low-T electron paramagnetic resonance (EPR) spectroscopy to examine the formation of complexes of Si(OH)4 with Mn(2+), Fe(3+), and Cu(2+) in water and in xylem sap of cucumber (Cucumis sativus L.) grown without or with supply of Si(OH)4. EPR, which is also useful in establishing the redox state of these metals, was combined with measurements of total concentrations of metals in xylem sap by inductive coupled plasma. Our results show that Si(OH)4 forms coordination bonds with all three metals. The strongest interactions of Si(OH)4 appear to be with Cu(2+) (1/1 stoichiometry) which might lead to Cu precipitation. In line with this in vitro findings, Si(OH)4 supply to cucumber resulted in dramatically lower concentration of this metal in the xylem sap. Further, it was demonstrated that Si(OH)4 supplementation causes pro-reductive changes that contribute to the maintenance of Fe and, in particular, Mn in the xylem sap in bioavailable 2+ form. Our results shed more light on the intertwined reactions between Si(OH)4 and transition metals in plant fluids (e.g. xylem sap).

  9. Temperature-Dependent Electron Paramagnetic Resonance Studies of Docosahexaenoic Acid and Gamma Linolenic Acid Effects on Phospholipid Membranes With and Without Cholesterol

    NASA Astrophysics Data System (ADS)

    Yonar, D.; Horasanb, N.; Sünnetçioğlu, M. Maral

    2016-07-01

    Free docosahexaenoic acid (DHAn-3) and gamma linolenic acid (GLAn-6) effects on dimyristoyl phosphatidylcholine (DMPC) membranes were studied as a function of temperature by electron paramagnetic resonance (EPR) spectroscopy. 5- and 16-doxyl stearic acid (5-, 16-DS) spin labels were utilized to obtain information from the interfacial and alkyl chain region, respectively. In the studied temperature range, the presence of DHAn-3 or GLAn-6 caused decreases in maximum hyperfi ne splitting values and correlation times of DMPC membranes. Both in the interfacial region and depths of membrane, changes were more pronounced for DHAn-3 in pure DMPC. In the presence of cholesterol (CH), DHAn-3 and GLAn-6 effects were similar and more pronounced in the depths of the membrane. The changes in the structure and dynamics of samples were obtained from simulations of spectra, which indicated some changes in the number of spectral components by incorporation of DHAn-3 and GLAn-6. In the interfacial region and below the main phase transition temperature of DMPC, there was an increase in heterogeneity. For temperatures above the phase transition, a more homogeneous environment for spin label was obtained in the presence of fatty acids.

  10. Electron paramagnetic resonance study of hydrogen peroxide/ascorbic acid ratio as initiator redox pair in the inulin-gallic acid molecular grafting reaction.

    PubMed

    Arizmendi-Cotero, Daniel; Gómez-Espinosa, Rosa María; Dublán García, Octavio; Gómez-Vidales, Virginia; Dominguez-Lopez, Aurelio

    2016-01-20

    Gallic acid (GA) was grafted onto inulin using the free radicals method, generated by the hydrogen peroxide/ascorbic acid (H2O2/AA) redox pair. Molar ratios of H2O2/AA at 9, 20, 39 and 49 were evaluated by Electron Paramagnetic Resonance in order to find the effect of the oxidation of the inulin and the efficiency in the inulin-gallic acid grafting (IGA). The highest concentration of the inulin macro-radical was obtained with H2O2/AA molar ratios of 20 and 49 with the removal of a hydrogen atom from a methyl group of the inulin fructose monomers. The highest grafting ratio (30.4 mg GA eq/g IGA) was obtained at 9 M of H2O2/AA. UV-Vis, FT-IR-ATR and XDR results confirmed a successful IGA grafting. The efficiency of the grafting reaction depends on the concentration of the macro-radical, it depends on the molar ratio of H2O2/AA, being affected by simultaneous reactions between components of the mixture (H2O2, AA, inulin, GA and eventually atmospheric oxygen) as well.

  11. Electron Paramagnetic Resonance Measurements of Free Radicals in the Intact Beating Heart: A Technique for Detection and Characterization of Free Radicals in Whole Biological Tissues

    NASA Astrophysics Data System (ADS)

    Zweier, Jay L.; Kuppusamy, Periannan

    1988-08-01

    Free radicals have been hypothesized to be important mediators of disease in a variety of organs and tissues. Electron paramagnetic resonance (EPR) spectroscopy can be applied to directly measure free radicals; however, it has not been possible to measure important biological radicals in situ because conventional spectrometer designs are not suitable for the performance of measurements on whole organs or tissues. We report the development of an EPR spectrometer designed for optimum performance in measuring free radicals in intact biological organs or tissues. This spectrometer consists of a 1- to 2-GHz microwave bridge with the source locked to the resonant frequency of a recessed gap loop-gap resonator. With this spectrometer, radical concentrations as low as 0.4 μ M can be measured. Isolated beating hearts were studied in which simultaneous real time measurements of free radicals and cardiac contractile function were performed. This in vivo EPR technique was applied to study the kinetics of free radical uptake and metabolism in normally perfused and globally ischemic hearts. In addition, we show that this technique can be used to noninvasively measure tissue oxygen consumption. Thus, it is demonstrated that EPR spectroscopy can be applied to directly measure in vivo free radical metabolism and tissue oxygen consumption. This technique offers great promise in the study of in vivo free radical generation and the effects of this radical generation on whole biological tissues.

  12. Physical, Optical and Electron paramagnetic resonance studies of PbBr2-PbO-B2O3 glasses containing Cu2+ ions

    NASA Astrophysics Data System (ADS)

    Sekhar, K. Chandra; Hameed, Abdul; Chary, M. Narasimha; Shareefuddin, Md

    2016-09-01

    The glasses with the composition PbBr2-PbO-B2O3 glasses containing Cu2+ ions were prepared by melt quenching technique. X-ray diffractograms revealed the amorphous nature of the glasses. Density and molar volume were determined. Density is found to decrease while the molar volume increases with increase of PbBr2 content. The optical absorption spectra exhibited a broad band corresponding to the d- d transition of Cu2+ ion. From optical absorption spectra Eopt and Urbach energies were determined. Electron Paramagnetic Resonance (EPR) studies were carried out by introducing Cu2+ as the spin probe. Glasses containing transition metal(TM) ions such as Cu2+ give the information about the structure and the site symmetry around the TM ions. EPR spectra of all the glass samples were recorded at X-band frequencies. From the EPR spectra spin-Hamiltonian parameters were evaluated. It was observed that g∥ >g±>ge (2.0023) and A∥>A±. From this values it is concluded that the ground state of Cu2+ is dx2-y2 (2B1g) and the site symmetry around Cu2+ ion is tetragonally distorted octahedral. From the EPR and Optical data bonding coefficients were evaluated. The in plane o-bonding(α2) is moderately ionic while out of plane 7t-bonding(β2) and in plane 7t-bonding(β1 2) are ionic nature

  13. Optical and time-resolved electron paramagnetic resonance studies of the excited states of a UV-B absorber (4-methylbenzylidene)camphor.

    PubMed

    Kikuchi, Azusa; Shibata, Kenji; Kumasaka, Ryo; Yagi, Mikio

    2013-02-21

    The excited states of UV-B absorber (4-methylbenzylidene)camphor (MBC) have been studied through measurements of UV absorption, phosphorescence, triplet-triplet (T-T) absorption, and steady-state and time-resolved electron paramagnetic resonance spectra in ethanol. The energy level and lifetime of the lowest excited triplet (T(1)) state of MBC were determined. The energy level of the T(1) state of MBC is much lower than that of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The weak phosphorescence and strong time-resolved EPR signals, and T-T absorption band of MBC were observed. These facts suggest that the significant proportion of the lowest excited singlet (S(1)) molecules undergoes intersystem crossing to the T(1) state and the deactivation process from the T(1) state is predominantly radiationless. The quantum yields of singlet oxygen production by MBC determined by time-resolved near-IR luminescence measurements are 0.05 ± 0.01 and 0.06 ± 0.01 in ethanol and in acetonitrile, respectively. The photostability of MBC arises from the (3)ππ* character in the T(1) state. The zero-field splitting parameters in the T(1) state are D = 0.0901 cm(-1) and E = -0.0498 cm(-1). The sublevel preferentially populated by intersystem crossing is T(y) (y close to in-plane short axis and to the C═O direction). PMID:23320917

  14. Effects of diffusion and surface interactions on the line shape of electron paramagnetic resonances in the presence of a magnetic field gradient

    SciTech Connect

    Schaden, M.; Zhao, K. F.; Wu, Z.

    2007-12-15

    In an evanescent wave magnetometer the Zeeman polarization is probed at micrometer to submicrometer distances from the cell surface. The electron paramagnetic resonance lines of an evanescent wave magnetometer in the presence of a magnetic field gradient exhibit edge enhancement seen previously in nuclear magnetic resonance lines. We present a theoretical model that describes quantitatively the shape of the magnetic resonance lines of an evanescent wave magnetometer under a wide range of experimental conditions. It accounts for diffusion broadening in the presence of a magnetic field gradient as well as interactions of spin polarized Rb atoms with the coated Pyrex glass surfaces. Depending on the field gradient, cell thickness, and buffer gas pressure, the resonance line may have the form of a single asymmetric peak or two peaks localized near the front and back surfaces in frequency space. The double-peaked response depends on average characteristics of the surface interactions. Its shape is sensitive to the dwell time, relaxation probability, and average phase shift of adsorbed spin polarized Rb atoms.

  15. Dose-dependent vitamin C uptake and radical scavenging activity in human skin measured with in vivo electron paramagnetic resonance spectroscopy.

    PubMed

    Lauer, Anna-Christina; Groth, Norbert; Haag, Stefan F; Darvin, Maxim E; Lademann, Jürgen; Meinke, Martina C

    2013-01-01

    Vitamin C is a potent radical scavenger and a physiological part of the antioxidant system in human skin. The aim of this study was to measure changes in the radical-scavenging activity of human skin in vivo due to supplementation with different doses of vitamin C and at different time points. Therefore, 33 volunteers were supplemented with vitamin C or placebo for 4 weeks. The skin radical-scavenging activity was measured with electron paramagnetic resonance spectroscopy. After 4 weeks, the intake of 100 mg vitamin C/day resulted in a significant increase in the radical-scavenging activity by 22%. Intake of 180 mg/day even resulted in a significant increase of 37%. No changes were found in the placebo group. A part of the study population was additionally measured after 2 weeks: in this group radical scavenging had already reached maximal activity after 2 weeks. In conclusion, orally administered vitamin C increases the radical-scavenging activity of the skin. The effect occurs fast and is enhanced with higher doses of vitamin C.

  16. Using nitroxide spin labels. How to obtain T1e from continuous wave electron paramagnetic resonance spectra at all rotational rates.

    PubMed Central

    Haas, D A; Mailer, C; Robinson, B H

    1993-01-01

    Historically, the continuous wave electron paramagnetic resonance (CW-EPR) progressive saturation method has been used to obtain information on the spin-lattice relaxation time (T1e) and those processes, such as motion and spin exchange, that occur on a competitive timescale. For example, qualitative information on local dynamics and solvent accessibility of proteins and nucleic acids has been obtained by this method. However, making quantitative estimates of T1e from CW-EPR spectra have been frustrated by a lack of understanding of the role of T1e (and T2e) in the slow-motion regime. Theoretical simulation of the CW-EPR lineshapes in the slow-motion region under increasing power levels has been used in this work to test whether the saturation technique can produce quantitative estimates of the spin-lattice relaxation rates. A method is presented by which the correct T1e may be extracted from an analysis of the power-saturation rollover curve, regardless of the amount of inhomogeneous broadening or the rates of molecular reorientation. The range of motional correlation times from 10 to 200 ns should be optimal for extracting quantitative estimates of T1e values in spin-labeled biomolecules. The progressive-saturation rollover curve method should find wide application in those areas of biophysics where information on molecular interactions and solvent exposure as well as molecular reorientation rates are desired. PMID:8386009

  17. Detection of undistorted continuous wave (CW) electron paramagnetic resonance (EPR) spectra with non-adiabatic rapid sweep (NARS) of the magnetic field

    PubMed Central

    Kittell, Aaron W.; Camenisch, Theodore G.; Ratke, Joseph J.; Sidabras, Jason W.; Hyde, James S.

    2011-01-01

    A continuous wave (CW) electron paramagnetic resonance (EPR) spectrum is typically displayed as the first harmonic response to the application of 100 kHz magnetic field modulation, which is used to enhance sensitivity by reducing the level of 1/f noise. However, magnetic field modulation of any amplitude causes spectral broadening and sacrifices EPR spectral intensity by at least a factor of two. In the work presented here, a CW rapid-scan spectroscopic technique that avoids these compromises and also provides a means of avoiding 1/f noise is developed. This technique, termed non-adiabatic rapid sweep (NARS) EPR, consists of repetitively sweeping the polarizing magnetic field in a linear manner over a spectral fragment with a small coil at a repetition rate that is sufficiently high that receiver noise, microwave phase noise, and environmental microphonics, each of which has 1/f characteristics, are overcome. Nevertheless, the rate of sweep is sufficiently slow that adiabatic responses are avoided and the spin system is always close to thermal equilibrium. The repetitively acquired spectra from the spectral fragment are averaged. Under these conditions, undistorted pure absorption spectra are obtained without broadening or loss of signal intensity. A digital filter such as a moving average is applied to remove high frequency noise, which is approximately equivalent in bandwidth to use of an integrating time constant in conventional field modulation with lock-in detection. Nitroxide spectra at L- and X-band are presented. PMID:21741868

  18. Nd3+ ions at the low-symmetry sites of β-Ba B2 O4 single crystals studied by electron paramagnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Bravo, D.; Solé, R.; Aguiló, M.; Díaz, F.; López, F. J.

    2004-11-01

    An electron paramagnetic resonance (EPR) study of Nd3+ ions in single crystals of the low-temperature phase of barium metaborate ( β-BaB2O4 or BBO) is presented. The EPR spectrum shows the existence of various slightly different Nd3+ centers. The g matrices of the three more abundant centers have been determined through the analysis of the angular dependencies of the spectrum in two planes of the crystal. The principal g -axis systems do not allow a straightforward assignment of the centers to a specific lattice cation site because of the low site symmetry ( C1 in all cases). To overcome this problem we have developed a method to calculate principal g -axis systems by constructing and diagonalizing the crystal-field energy matrix for the ground I9/24 level of Nd3+ , including the Zeeman interaction. The superposition model of the crystal field has been employed to estimate the crystal-field Bnm parameters for this ion in BBO, as they are unknown. From this study it is concluded that neodymium is incorporated in the low-symmetry Ba2+ site. Possible reasons for the appearance of different Nd3+ centers are discussed.

  19. New opportunities of the application of natural herb and spice extracts in plant oils: application of electron paramagnetic resonance in examining the oxidative stability.

    PubMed

    Kozłowska, Mariola; Szterk, Arkadiusz; Zawada, Katarzyna; Ząbkowski, Tomasz

    2012-09-01

    The aim of this study was to establish the applicability of natural water-ethanol extracts of herbs and spices in increasing the oxidative stability of plant oils and in the production of novel food. Different concentrations (0, 100, 300, 500, and 700 ppm) of spice extracts and butylated hydroxyanisole (BHA) (100 ppm) were added to the studied oils. The antioxidant activity of spice extracts was determined with electron paramagnetic resonance (EPR) spectroscopy using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay. The study showed that the extracts significantly increased the oxidative stability of the examined oils when compared to one of the strongest synthetic antioxidants--BHA. The applied simple production technology and addition of herb and spice extracts to plant oils enabled enhancement of their oxidative stability. The extracts are an alternative to the oils aromatized with an addition of fresh herbs, spices, and vegetables because it did not generate additional flavors thus enabling the maintenance of the characteristic ones. Moreover, it will increase the intake of natural substances in human diet, which are known to possess anticarcinogenic properties.

  20. Advanced electron microscopy characterization of multimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Khanal, Subarna Raj

    Research in noble metal nanoparticles has led to exciting progress in a versatile array of applications. For the purpose of better tailoring of nanoparticles activities and understanding the correlation between their structures and properties, control over the composition, shape, size and architecture of bimetallic and multimetallic nanomaterials plays an important role on revealing their new or enhanced functions for potentials application. Advance electron microscopy techniques were used to provide atomic scale insights into the structure-properties of different materials: PtPd, Au-Au3Cu, Cu-Pt, AgPd/Pt and AuCu/Pt nanoparticles. The objective of this work is to understand the physical and chemical properties of nanomaterials and describe synthesis, characterization, surface properties and growth mechanism of various bimetallic and multimetallic nanoparticles. The findings have provided us with novel and significant insights into the physical and chemical properties of noble metal nanoparticles. Different synthesis routes allowed us to synthesize bimetallic: Pt-Pd, Au-Au3Cu, Cu-Pt and trimetallic: AgPd/Pt, AuCu/Pt, core-shell and alloyed nanoparticles with monodispersed sizes, controlled shapes and tunable surface properties. For example, we have synthesized the polyhedral PtPd core-shell nanoparticles with octahedral, decahedral, and triangular plates. Decahedral PtPd core-shell structures are novel morphologies for this system. For the first time we fabricated that the Au core and Au3Cu alloyed shell nanoparticles passivated with CuS2 surface layers and characterized by Cs-corrected scanning transmission electron microscopy. The analysis of the high-resolution micrographs reveals that these nanoparticles have decahedral structure with shell periodicity, and that each of the particles is composed by Au core and Au3Cu ordered superlattice alloyed shell surrounded by CuS 2 surface layer. Additionally, we have described both experimental and theoretical methods of

  1. Analysis of saturation transfer electron paramagnetic resonance spectra of a spin-labeled integral membrane protein, band 3, in terms of the uniaxial rotational diffusion model.

    PubMed Central

    Hustedt, E J; Beth, A H

    1995-01-01

    Algorithms have been developed for the calculation of saturation transfer electron paramagnetic resonance (ST-EPR) spectra of a nitroxide spin-label assuming uniaxial rotational diffusion, a model that is frequently used to describe the global rotational dynamics of large integral membrane proteins. One algorithm explicitly includes terms describing Zeeman overmodulation effects, whereas the second more rapid algorithm treats these effects approximately using modified electron spin-lattice and spin-spin relaxation times. Simulations are presented to demonstrate the sensitivity of X-band ST-EPR spectra to the rate of uniaxial rotational diffusion and the orientation of the nitroxide probe with respect to the diffusion axis. Results obtained by using the algorithms presented, which are based on the transition-rate formalism, are in close agreement with those obtained by using an eigenfunction expansion approach. The effects of various approximations used in the simulation algorithms are considered in detail. Optimizing the transition-rate formalism to model uniaxial rotational diffusion results in over an order of magnitude reduction in computation time while allowing treatment of nonaxial A- and g-tensors. The algorithms presented here are used to perform nonlinear least-squares analyses of ST-EPR spectra of the anion exchange protein of the human erythrocyte membrane, band 3, which has been affinity spin-labeled with a recently developed dihydrostilbene disulfonate derivative, [15N,2H13]-SL-H2DADS-MAL. These results suggest that all copies of band 3 present in intact erythrocytes undergo rotational diffusion about the membrane normal axis at a rate consistent with a band 3 dimer. PMID:8534811

  2. Backbone Dynamics of Alamethicin Bound to Lipid Membranes: Spin-Echo Electron Paramagnetic Resonance of TOAC-Spin Labels

    PubMed Central

    Bartucci, Rosa; Guzzi, Rita; De Zotti, Marta; Toniolo, Claudio; Sportelli, Luigi; Marsh, Derek

    2008-01-01

    Alamethicin F50/5 is a hydrophobic peptide that is devoid of charged residues and that induces voltage-dependent ion channels in lipid membranes. The peptide backbone is likely to be involved in the ion conduction pathway. Electron spin-echo spectroscopy of alamethicin F50/5 analogs in which a selected Aib residue (at position n = 1, 8, or 16) is replaced by the TOAC amino-acid spin label was used to study torsional dynamics of the peptide backbone in association with phosphatidylcholine bilayer membranes. Rapid librational motions of limited angular amplitude were observed at each of the three TOAC sites by recording echo-detected spectra as a function of echo delay time, 2τ. Simulation of the time-resolved spectra, combined with conventional EPR measurements of the librational amplitude, shows that torsional fluctuations of the peptide backbone take place on the subnanosecond to nanosecond timescale, with little temperature dependence. Associated fluctuations in polar fields from the peptide could facilitate ion permeation. PMID:18096632

  3. Advances in digital video for electronic media.

    PubMed

    McAfooes, J A

    1997-01-01

    From media's early days of film strips and records, to today's multimedia CD-ROMs, nurses have embraced educational tools. Today, the capabilities of these tools have placed a tremendous demand for providing information any time, any where. This has led to increasing digitization of sights and sounds. Once digitized, this information can travel over information highways made up of telephone lines, fiberoptic cables, microwaves and satellites, or it can be stored on magnetic and optical media. Technological advances have made it possible for computer users to create, store and retrieve high quality digital still and moving video and audio for inclusion in electronic media. Methods for digitizing include capturing and converting the information with cameras, scanners and capture boards. Digital video compression/decompression (codec) standards vary in quality. Potential uses of digital video abound including video on demand, videoconferencing, distance learning, telemedicine, on-line education and computer-based training. Examples illustrating the differences in digital video formats will be shown during the presentation. PMID:10175444

  4. Advances in digital video for electronic media.

    PubMed

    McAfooes, J A

    1997-01-01

    From media's early days of film strips and records, to today's multimedia CD-ROMs, nurses have embraced educational tools. Today, the capabilities of these tools have placed a tremendous demand for providing information any time, any where. This has led to increasing digitization of sights and sounds. Once digitized, this information can travel over information highways made up of telephone lines, fiberoptic cables, microwaves and satellites, or it can be stored on magnetic and optical media. Technological advances have made it possible for computer users to create, store and retrieve high quality digital still and moving video and audio for inclusion in electronic media. Methods for digitizing include capturing and converting the information with cameras, scanners and capture boards. Digital video compression/decompression (codec) standards vary in quality. Potential uses of digital video abound including video on demand, videoconferencing, distance learning, telemedicine, on-line education and computer-based training. Examples illustrating the differences in digital video formats will be shown during the presentation.

  5. Membrane Docking of the Synaptotagmin 7 C2A Domain: Electron Paramagnetic Resonance Measurements Show Contributions from Two Membrane Binding Loops

    PubMed Central

    Osterberg, J. Ryan; Chon, Nara Lee; Boo, Arthur; Maynard, Favinn A.; Lin, Hai; Knight, Jefferson D.

    2015-01-01

    The synaptotagmin (Syt) family of proteins plays an important role in vesicle docking and fusion during Ca2+-induced exocytosis in a wide variety of cell types. Its role as a Ca2+ sensor derives primarily from its two C2 domains, C2A and C2B, which insert into anionic lipid membranes upon binding Ca2+. Syt isoforms 1 and 7 differ significantly in their Ca2+ sensitivity; the C2A domain from Syt7 binds Ca2+ and membranes much more tightly than the C2A domain from Syt1, due at least in part to greater contributions from the hydrophobic effect. While the structure and membrane activity of Syt1 have been extensively studied, the structural origins of differences between Syt7 and Syt1 are unknown. The present study used site-directed spin labeling and electron paramagnetic resonance spectroscopy to determine depth parameters for the Syt7 C2A domain, for comparison to analogous previous measurements with Syt1 C2A. In a novel approach, the membrane docking geometry of both Syt1 and Syt7 C2A was modeled by mapping depth parameters onto multiple molecular dynamics simulated structures of the Ca2+-bound protein. The models reveal membrane penetration of Ca2+ binding loops (CBLs) 1 and 3, and membrane binding is more sensitive to mutations in CBL3. On average, Syt7 C2A inserts more deeply in the membrane than Syt1 C2A, although depths vary among the different structural models. This observation provides a partial structural explanation for the hydrophobically driven membrane docking of Syt7 C2A. PMID:26322740

  6. Brain redox imaging in the pentylenetetrazole (PTZ)-induced kindling model of epilepsy by using in vivo electron paramagnetic resonance and a nitroxide imaging probe.

    PubMed

    Emoto, Miho C; Yamato, Mayumi; Sato-Akaba, Hideo; Yamada, Ken-ichi; Fujii, Hirotada G

    2015-11-01

    Much evidence supports the idea that oxidative stress is involved in the pathogenesis of epilepsy, and therapeutic interventions with antioxidants are expected as adjunct antiepileptic therapy. The aims of this study were to non-invasively obtain spatially resolved redox data from control and pentylenetetrazole (PTZ)-induced kindled mouse brains by electron paramagnetic resonance (EPR) imaging and to visualize the brain regions that are sensitive to oxidative damage. After infusion of the redox-sensitive imaging probe 3-methoxycarbonyl-2,2,5,5-tetramethyl-piperidine-1-oxyl (MCP), a series of EPR images of PTZ-induced mouse heads were measured. Based on the pharmacokinetics of the reduction reaction of MCP in the mouse heads, the pixel-based rate constant of its reduction reaction was calculated as an index of redox status in vivo and mapped as a redox map. The obtained redox map showed heterogeneity in the redox status in PTZ-induced mouse brains compared with control. The co-registered image of the redox map and magnetic resonance imaging (MRI) for both control and PTZ-induced mice showed a clear change in the redox status around the hippocampus after PTZ. To examine the role of antioxidants on the brain redox status, the levels of antioxidants were measured in brain tissues of control and PTZ-induced mice. Significantly lower concentrations of glutathione in the hippocampus of PTZ-kindled mice were detected compared with control. From the results of both EPR imaging and the biochemical assay, the hippocampus was found to be susceptible to oxidative damage in the PTZ-induced animal model of epilepsy.

  7. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy

    PubMed Central

    Mett, R. R.; Sidabras, J. W.; Anderson, J. R.; Hyde, J. S.

    2011-01-01

    The two-way insertion loss of a 1 m length of waveguide was reduced by nearly 5 dB over a 4% bandwidth at W-band (94 GHz) for an electron paramagnetic resonance (EPR) spectrometer relative to WR10 waveguide. The waveguide has an oversize section of commercially available rectangular WR28 and a novel pair of tapers that vary in cross section with axial position according to a hyperbolic-cosine (HC) function. The tapers connect conventional rectangular WR10 waveguide to the WR28. For minimum loss, the main mode electric field is parallel to the long side of the WR28. Using mode coupling theory, the position of maximum flare (inflection point) in the taper was optimized with respect to the coupling to higher order modes and the reflection of the main mode. The optimum inflection point position is about one-tenth of the taper length from the small end of the taper. Reflection and coupling were reduced by about 20 dB relative to a pyramidal (linear) taper of the same length. Comb-like dips in the transmission coefficient produced by resonances of the higher order modes in the oversize section were about 0.03 dB. Specially designed high-precision, adjustable WR28 flanges with alignment to about 5 μm were required to keep higher order mode amplitudes arising from the flanges comparable to those from the HC tapers. Minimum return loss was about 30 dB. This paper provides a foundation for further optimization, if needed. Methods are not specific to EPR or the microwave frequency band. PMID:21806211

  8. Electron paramagnetic resonance study of ferrous cytochrome P-450/sub scc/-nitric oxide complexes: effects of cholesterol and its analogs

    SciTech Connect

    Tsubaki, M.; Hiwatashi, A.; Ichikawa, Y.; Hori, H.

    1987-07-14

    Electron paramagnetic resonance (EPR) spectra of nitric oxide (NO) complexes of ferrous cytochrome P-450/sub scc/ were measured at 77 K for the first time without using the rapid-mixing and freeze-quenching technique. Without substrate the EPR spectra were very similar to those of cytochrome P-450/sub cam/ (from Pseudomonas putida) and cytochrome P-450/sub LM/ (from rat liver microsomes) with rhombic symmetry; g/sub x/ = 2.071, g/sub z/ = 2.001, g/sub y/ = 1.962, and A/sub z/ = 2.2 mT for /sup 14/NO complexes. Upon addition of substrates, the EPR spectra exhibited many variations having rhombic symmetry in the major component and an additional minor component with less rhombic symmetry. Furthermore, addition of 20(S)-hydroxycholesterol caused a striking change in the EPR spectrum. The component with rhombic symmetry disappeared completely, and the component with less rhombic symmetry dominated (g/sub x/ = 2.027, g/sub z/ = 2.007, g/sub y/ = 1.984, and A/sub z/ = 1.76 mT for /sup 14/NO complexes). These observations suggest the existence of the following physiologically important natures: (1) the conformational flexibility of the active site of the enzyme due to the steric interaction between the substrate and the heme-bound ligand molecule and (2) the importance of the hydroxylation of the cholesterol side chain at the 20S position to proceed the side-chain cleavage reaction in cytochrome P-450/sub scc/.

  9. A comparative electron paramagnetic resonance study of the nucleotide-binding domains' catalytic cycle in the assembled maltose ATP-binding cassette importer.

    PubMed

    Grote, Mathias; Bordignon, Enrica; Polyhach, Yevhen; Jeschke, Gunnar; Steinhoff, Heinz-Jürgen; Schneider, Erwin

    2008-09-15

    We present a quantitative analysis of conformational changes of the nucleotide-binding subunits, MalK(2), of the maltose ATP-binding cassette importer MalFGK(2) during the transport cycle. Distance changes occurring between selected residues were monitored in the full transporter by site-directed spin-labeling electron paramagnetic resonance spectroscopy and site-directed chemical cross-linking. We considered S83C and A85C from the conserved Q-loop and V117C located on the outer surface of MalK. Additionally, two native cysteines (C350, C360) were included in the study. On ATP binding, small rearrangements between the native sites, and no distance changes between positions 117 were detected. In contrast, positions 85 come closer together in the ATP-bound state and in the vanadate-trapped intermediate and move back toward the apo-state after ATP hydrolysis. The distance between positions 83 is shown to slightly decrease on ATP binding, and to further decrease after ATP hydrolysis. Results from cross-linking experiments are in agreement with these findings. The data are compared with in silico spin-labeled x-ray structures from both isolated MalK(2) and the MalFGK(2)-E complex. Our results are consistent with a slightly modified "tweezers-like" model of closure and reopening of MalK(2) during the catalytic cycle, and show an unforeseen potential interaction between MalK and the transmembrane subunit MalG.

  10. Copper doping of ZnO crystals by transmutation of {sup 64}Zn to {sup 65}Cu: An electron paramagnetic resonance and gamma spectroscopy study

    SciTech Connect

    Recker, M. C.; McClory, J. W. Holston, M. S.; Golden, E. M.; Giles, N. C.; Halliburton, L. E.

    2014-06-28

    Transmutation of {sup 64}Zn to {sup 65}Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the {sup 65}Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of {sup 64}Zn nuclei to {sup 65}Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu{sup 2+} ions (where {sup 63}Cu and {sup 65}Cu hyperfine lines are easily resolved). A spectrum from isolated Cu{sup 2+} (3d{sup 9}) ions acquired after the neutron irradiation showed only hyperfine lines from {sup 65}Cu nuclei. The absence of {sup 63}Cu lines in this Cu{sup 2+} spectrum left no doubt that the observed {sup 65}Cu signals were due to transmuted {sup 65}Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu{sup +}-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu{sup +}-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900 °C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

  11. Binding of transition metals to monosilicic acid in aqueous and xylem (Cucumis sativus L.) solutions: a low-T electron paramagnetic resonance study.

    PubMed

    Stevic, Nenad; Korac, Jelena; Pavlovic, Jelena; Nikolic, Miroslav

    2016-10-01

    The supplementation of monosilicic acid [Si(OH)4] to the root growing medium is known to protect plants from toxic levels of iron (Fe), copper (Cu) and manganese (Mn), but also to mitigate deficiency of Fe and Mn. However, the physicochemical bases of these alleviating mechanisms are not fully understood. Here we applied low-T electron paramagnetic resonance (EPR) spectroscopy to examine the formation of complexes of Si(OH)4 with Mn(2+), Fe(3+), and Cu(2+) in water and in xylem sap of cucumber (Cucumis sativus L.) grown without or with supply of Si(OH)4. EPR, which is also useful in establishing the redox state of these metals, was combined with measurements of total concentrations of metals in xylem sap by inductive coupled plasma. Our results show that Si(OH)4 forms coordination bonds with all three metals. The strongest interactions of Si(OH)4 appear to be with Cu(2+) (1/1 stoichiometry) which might lead to Cu precipitation. In line with this in vitro findings, Si(OH)4 supply to cucumber resulted in dramatically lower concentration of this metal in the xylem sap. Further, it was demonstrated that Si(OH)4 supplementation causes pro-reductive changes that contribute to the maintenance of Fe and, in particular, Mn in the xylem sap in bioavailable 2+ form. Our results shed more light on the intertwined reactions between Si(OH)4 and transition metals in plant fluids (e.g. xylem sap). PMID:27502949

  12. Structure of the P700(+ )A1(-) radical pair intermediate in photosystem I by high time resolution multifrequency electron paramagnetic resonance: analysis of quantum beat oscillations.

    PubMed

    Link, G; Berthold, T; Bechtold, M; Weidner, J U; Ohmes, E; Tang, J; Poluektov, O; Utschig, L; Schlesselman, S L; Thurnauer, M C; Kothe, G

    2001-05-01

    The geometry of the secondary radical pair P700(+)A1(-), in photosystem I (PSI) from the deuterated and 15N-substituted cyanobacterium Synechococcus lividus, has been determined by high time resolution electron paramagnetic resonance (EPR), performed at three different microwave frequencies. Structural information is extracted from light-induced quantum beats observed in the transverse magnetization of P700(+)A1(-) at early times after laser excitation. A computer analysis of the two-dimensional Q-band experiment provides the orientation of the various magnetic tensors of with respect to a magnetic reference frame. The orientation of the cofactors of the primary donor in the g-tensor system of is then evaluated by analyzing time-dependent X-band EPR spectra, extracted from a two-dimensional data set. Finally, the cofactor arrangement of P700(+)A1(-) in the photosynthetic membrane is deduced from angular-dependent W-band spectra, observed for a magnetically aligned sample. Thus, the orientation of the g-tensor of P700(+) with respect to a chlorophyll based reference system could be determined. The angle between the g1(z) axis and the chlorophyll plane normal is found to be 29 +/- 7 degrees, while the g1(y) axis lies in the chlorophyll plane. In addition, a complete structural model for the reduced quinone acceptor, A1(-), is evaluated. In this model, the quinone plane of is found to be inclined by 68 +/- 7 degrees relative to the membrane plane, while the P700(+)-A1(-) axis makes an angle of 35 +/- 6 degrees with the membrane normal. All of these values refer to the charge separated state, observed at low temperatures, where forward electron transfer to the iron-sulfur centers is partially blocked. Preliminary room temperature studies of P700(+)A1(-), employing X-band quantum beat oscillations, indicate a different orientation of A1(-) in its binding pocket. A comparison with crystallographic data provides information on the electron-transfer pathway in PSI. It

  13. Determination of g-tensors of low-symmetry Nd{sup 3+} centers in LiNbO{sub 3} by rectification of angular dependence of electron paramagnetic resonance spectra

    SciTech Connect

    Grachev, V. Malovichko, G.; Munro, M.; Kokanyan, E.

    2015-07-28

    Two procedures for facilitation of line tracing and deciphering of complicated spectra of electron paramagnetic resonance (EPR) were developed: a correction of microwave frequencies for every orientation of external magnetic field on the base of known values of g-tensor components for a reference paramagnetic center and followed rectification of measured angular dependences using plots of effective deviation of g{sup 2}-factors of observed lines from effective g{sup 2}-factors of the reference center versus angles or squared cosines of angles describing magnetic field orientations. Their application to EPR spectra of nearly stoichiometric lithium niobate crystals doped with neodymium allowed identifying two axial and six different low-symmetry Nd{sup 3+} centers, to determine all components of their g-tensors, and to propose common divacancy models for a whole family of Nd{sup 3+} centers.

  14. Effect of gamma radiation and accelerated electron beam on stable paramagnetic centers induction in bone mineral: influence of dose, irradiation temperature and bone defatting.

    PubMed

    Jastrzebska, Anna; Kaminski, Artur; Grazka, Ewelina; Marowska, Joanna; Sadlo, Jaroslaw; Gut, Grzegorz; Uhrynowska-Tyszkiewicz, Izabela

    2014-09-01

    Ionizing radiation has been found to induce stable defects in the crystalline lattice of bone mineral hydroxyapatite, defined as CO(2) (-) radical ions possessing spins. The purpose of our study was to evaluate CO(2) (-) radical ions induced in non-defatted or defatted human compact bone by gamma radiation (G) and accelerated electron beam (EB), applied with two doses at different temperatures. Moreover, the potential effect of free radical ion formation on mechanical parameters of compact bone, tested under compression in the previous studies, was evaluated. Bone rings from femoral shafts of six male donors (age 51 ± 3 years) were collected and assigned to sixteen experimental groups according to different processing methods (non-defatted or defatted), G and EB irradiation dose (25 or 35 kGy), and irradiation temperature [ambient temperature (AT) or dry ice (DI)]. Untreated group served as control. Following grinding under LN2 and lyophilization, CO(2) (-) radical ions in bone powder were measured by electron paramagnetic resonance spectrometry. We have found that irradiation of bone with G and EB induces formation of enormous amounts of CO(2) (-) radical ions, absent from native tissue. Free radical ion formation was dose-dependent when irradiation was performed at AT, and significantly lower in EB as compared to G-irradiated groups. In contrast, no marked effect of dose was observed when deep-frozen (DI) bone samples were irradiated with G or EB, and free radical ion numbers seemed to be slightly higher in EB-irradiated groups. Irradiation at AT induced much higher quantities of CO(2) (-) radical ions then on DI. That effect was more pronounced in G-irradiated bone specimens, probably due to longer exposure time. Similarly, bone defatting protective effect on free radical ion formation was found only in groups irradiated for several hours with gamma radiation at ambient temperature. Ambient irradiation temperature together with exposure time seem to be key

  15. Surface chemical deposition of advanced electronic materials

    NASA Astrophysics Data System (ADS)

    Bjelkevig, Cameron

    The focus of this work was to examine the direct plating of Cu on Ru diffusion barriers for use in interconnect technology and the substrate mediated growth of graphene on boron nitride for use in advanced electronic applications. The electrodeposition of Cu on Ru(0001) and polycrystalline substrates (with and without pretreatment in an iodine containing solution) has been studied by cyclic voltammetry (CV), current--time transient measurements (CTT), in situ electrochemical atomic force microscopy (EC-AFM), and X-ray photoelectron spectroscopy (XPS). The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. XPS measurements confirmed the presence and stability of adsorbed I on the Ru surface following pre-treatment in a KI/H2SO4 solution and following polarization to at least -200 mV vs. Ag/AgCl. CV data of samples pre-reduced in I-containing electrolyte exhibited a narrow Cu deposition peak in the overpotential region and a UPD peak. The kinetics of the electrodeposited Cu films was investigated by CTT measurements and applied to theoretical models of nucleation. The data indicated that a protective I adlayer may be deposited on an airexposed Ru electrode as the oxide surface is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electroplating process. A novel method for epitaxial graphene growth directly on a dielectric substrate of systematically variable thickness was studied. Mono/multilayers of BN(111) were grown on Ru(0001) by atomic layer deposition (ALD), exhibiting a flat (non-nanomesh) R30(✓3x✓3) structure. BN(111) was used as a template for growth of graphene by chemical vapor deposition (CVD) of C2H4 at 1000 K. Characterization by LEED, Auger, STM/STS and Raman indicate the graphene is in registry with the BN substrate, and exhibits a HOPG-like 0 eV bandgap density

  16. Advanced Concepts for Electron-Ion Collider

    SciTech Connect

    Yaroslav Derbenev

    2002-08-01

    A superconducting energy recovery linac (ERL) of 5 to 10 GeV was proposed earlier as an alternative to electron storage rings to deliver polarized electron beam for electron-ion collider (EIC). To enhance the utilization efficiency of electron beam from a polarized source, it is proposed to complement the ERL by circulator ring (CR) wherein the injected electrons undergo up to 100 revolutions colliding with the ion beam. In this way, electron injector and linac operate in pulsed current (beam energy recovery) regime of a relatively low average current, while the polarization is still easily delivered and preserved. To make it also easier delivering and manipulating the proton and light ion polarization, twisted (figure 8) synchrotrons are proposed for heavy particle booster and collider ring. Same type of beam orbit can be used then for electron circulator. Electron cooling (EC) of the ion beam is considered an inevitable component of high luminosity EIC (1033/s. cm2 or above). It is recognized that EC also gives a possibility to obtain very short ion bunches, that allows much stronger final focusing. At the same time, short bunches make feasible the crab crossing (and traveling focus for ion beam) at collision points, hence, allow maximizing the collision rate. As a result, one can anticipate the luminosity increase by one or two orders of magnitude.

  17. Drafting. Advanced Print Reading--Electronics.

    ERIC Educational Resources Information Center

    Oregon State Dept. of Education, Salem.

    This document is a workbook for drafting students learning the basics of reading and interpreting electronic drawings and diagrams. The workbook contains eight units covering the following material: basic symbols; circuit symbols; electron tube symbols; winding symbols; semiconductor symbols; miscellaneous symbols; schematic diagrams; and…

  18. The active site of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans. I. Light sensitivity and magnetic hyperfine interactions as observed by electron paramagnetic resonance.

    PubMed

    Albracht, Simon P J; Roseboom, Winfried; Hatchikian, E Claude

    2006-01-01

    The hydrogen-activating cluster (H cluster) in [FeFe]-hydrogenases consists of two moieties. The [2Fe]H subcluster is a (L)(CO)(CN)Fe(mu-RS2)(mu-CO)Fe(CysS)(CO)(CN) centre. The Cys-bound Fe is called Fe1, the other iron Fe2. The Cys-thiol forms a bridge to a [4Fe-4S] cluster, the [4Fe-4S]H subcluster. We report that electron paramagnetic resonance (EPR) spectra of the 57Fe-enriched enzyme from Desulfovibrio desulfuricans in the H(ox)-CO state are consistent with a magnetic hyperfine interaction of the unpaired spin with all six Fe atoms of the H cluster. In contrast to the inactive aerobic enzyme, the active enzyme is easily destroyed by light. The [2Fe]H subcluster in some enzyme molecules loses CO by photolysis, whereupon other molecules firmly bind the released CO to form the H(ox)-CO state giving rise to the so-called axial 2.06 EPR signal. Though not destroyed by light, the H(ox)-CO state is affected by it. As demonstrated in the accompanying paper [49] two of the intrinsic COs, both bound to Fe2, can be exchanged by extrinsic 13CO during illumination at 2 degrees C. We found that only one of the three 13COs, the one at the extrinsic position, gives an EPR-detectable isotropic superhyperfine interaction of 0.6 mT. At 30 K both the inhibiting extrinsic CO bound to Fe2 and one more CO can be photolysed. EPR spectra of the photolysed products are consistent with a 3d7 system of Fe with the formal oxidation state +1. The damaged enzyme shows a light-sensitive g = 5 signal which is ascribed to an S = 3/2 form of the [2Fe](H) subcluster. The light sensitivity of the enzyme explains the occurrence of the g = 5 signal and the axial 2.06 signal in published EPR spectra of nearly all preparations studied thus far.

  19. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization.

    PubMed

    Sidabras, Jason W; Strangeway, Robert A; Mett, Richard R; Anderson, James R; Mainali, Laxman; Hyde, James S

    2016-03-01

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  20. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization.

    PubMed

    Sidabras, Jason W; Strangeway, Robert A; Mett, Richard R; Anderson, James R; Mainali, Laxman; Hyde, James S

    2016-03-01

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  1. Probing Structural Dynamics and Topology of the KCNE1 Membrane Protein in Lipid Bilayers via Site-Directed Spin Labeling and Electron Paramagnetic Resonance Spectroscopy.

    PubMed

    Sahu, Indra D; Craig, Andrew F; Dunagan, Megan M; Troxel, Kaylee R; Zhang, Rongfu; Meiberg, Andrew G; Harmon, Corrinne N; McCarrick, Robert M; Kroncke, Brett M; Sanders, Charles R; Lorigan, Gary A

    2015-10-20

    KCNE1 is a single transmembrane protein that modulates the function of voltage-gated potassium channels, including KCNQ1. Hereditary mutations in the genes encoding either protein can result in diseases such as congenital deafness, long QT syndrome, ventricular tachyarrhythmia, syncope, and sudden cardiac death. Despite the biological significance of KCNE1, the structure and dynamic properties of its physiologically relevant native membrane-bound state are not fully understood. In this study, the structural dynamics and topology of KCNE1 in bilayered lipid vesicles was investigated using site-directed spin labeling (SDSL) and electron paramagnetic resonance (EPR) spectroscopy. A 53-residue nitroxide EPR scan of the KCNE1 protein sequence including all 27 residues of the transmembrane domain (45-71) and 26 residues of the N- and C-termini of KCNE1 in lipid bilayered vesicles was analyzed in terms of nitroxide side-chain motion. Continuous wave-EPR spectral line shape analysis indicated the nitroxide spin label side-chains located in the KCNE1 TMD are less mobile when compared to the extracellular region of KCNE1. The EPR data also revealed that the C-terminus of KCNE1 is more mobile when compared to the N-terminus. EPR power saturation experiments were performed on 41 sites including 18 residues previously proposed to reside in the transmembrane domain (TMD) and 23 residues of the N- and C-termini to determine the topology of KCNE1 with respect to the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG) lipid bilayers. The results indicated that the transmembrane domain is indeed buried within the membrane, spanning the width of the lipid bilayer. Power saturation data also revealed that the extracellular region of KCNE1 is solvent-exposed with some of the portions partially or weakly interacting with the membrane surface. These results are consistent with the previously published solution NMR

  2. A comparative study by electron paramagnetic resonance of free radical species in the mainstream and sidestream smoke of cigarettes with conventional acetate filters and 'bio-filters'.

    PubMed

    Valavanidis, A; Haralambous, E

    2001-01-01

    Tobacco smoking is the most important extrinsic cause, after the diet, for increasing morbidity and mortality in humans. Unless current tobacco smoking patterns in industrialised and non-industrialised countries change, cigarettes will kill prematurely 10 million people a year by 2025. Greece is at the top of the list of European countries in cigarette consumption. In 1997, a Greek tobacco company introduced a new 'bio-filter' (BF) claiming that it reduces substantially the risks of smoking. In a recent publication [Deliconstantinos G, Villiotou V, Stavrides J. Scavenging effects of hemoglobin and related heme containing compounds on nitric oxide, reactive oxidants and carcinogenic volatile nitrosocompounds of cigarette smoke. A new method for protection against the dangerous cigarette constituents. Anticancer Res 1994; 14: 2717-2726] it was claimed that the new 'bio-filter' (activated carbon impregnated with dry hemoglobin) reduces certain toxic substances and oxidants (like NO, CO, NOx, H2O2, aldehydes, trace elements and nitroso-compounds) in the gas-phase of the mainstream smoke. We have investigated by electron paramagnetic resonance (EPR) the mainstream and sidestream smoke of the BF cigarette, in comparison with three other cigarettes with similar tar and nicotine contents, that have conventional acetate filters. We found that BF cigarette smoke has similar tar radical species with the same intensity EPR signals to those of the other cigarettes. The ability of the aqueous cigarette tar extracts to produce hydroxyl radicals (HO*), which were spin trapped by DMPO, was very similar to, or even higher than, the other 3 brands. The gas-phase of the mainstream smoke of the BF cigarette showed a 30-35% reduction in the production of oxygen-centered radicals (spin trapped with PBN). In the case of the sidestream smoke, BF cigarettes produced substantially higher concentrations of gas-phase radicals, compared to the other brands. These results suggest that BF is

  3. A comparative study by electron paramagnetic resonance of free radical species in the mainstream and sidestream smoke of cigarettes with conventional acetate filters and 'bio-filters'.

    PubMed

    Valavanidis, A; Haralambous, E

    2001-01-01

    Tobacco smoking is the most important extrinsic cause, after the diet, for increasing morbidity and mortality in humans. Unless current tobacco smoking patterns in industrialised and non-industrialised countries change, cigarettes will kill prematurely 10 million people a year by 2025. Greece is at the top of the list of European countries in cigarette consumption. In 1997, a Greek tobacco company introduced a new 'bio-filter' (BF) claiming that it reduces substantially the risks of smoking. In a recent publication [Deliconstantinos G, Villiotou V, Stavrides J. Scavenging effects of hemoglobin and related heme containing compounds on nitric oxide, reactive oxidants and carcinogenic volatile nitrosocompounds of cigarette smoke. A new method for protection against the dangerous cigarette constituents. Anticancer Res 1994; 14: 2717-2726] it was claimed that the new 'bio-filter' (activated carbon impregnated with dry hemoglobin) reduces certain toxic substances and oxidants (like NO, CO, NOx, H2O2, aldehydes, trace elements and nitroso-compounds) in the gas-phase of the mainstream smoke. We have investigated by electron paramagnetic resonance (EPR) the mainstream and sidestream smoke of the BF cigarette, in comparison with three other cigarettes with similar tar and nicotine contents, that have conventional acetate filters. We found that BF cigarette smoke has similar tar radical species with the same intensity EPR signals to those of the other cigarettes. The ability of the aqueous cigarette tar extracts to produce hydroxyl radicals (HO*), which were spin trapped by DMPO, was very similar to, or even higher than, the other 3 brands. The gas-phase of the mainstream smoke of the BF cigarette showed a 30-35% reduction in the production of oxygen-centered radicals (spin trapped with PBN). In the case of the sidestream smoke, BF cigarettes produced substantially higher concentrations of gas-phase radicals, compared to the other brands. These results suggest that BF is

  4. In vivo visualization and ex vivo quantification of murine breast cancer cells in the mouse brain using MRI cell tracking and electron paramagnetic resonance.

    PubMed

    Danhier, Pierre; Magat, Julie; Levêque, Philippe; De Preter, Géraldine; Porporato, Paolo E; Bouzin, Caroline; Jordan, Bénédicte F; Demeur, Gladys; Haufroid, Vincent; Feron, Olivier; Sonveaux, Pierre; Gallez, Bernard

    2015-03-01

    Cell tracking could be useful to elucidate fundamental processes of cancer biology such as metastasis. The aim of this study was to visualize, using MRI, and to quantify, using electron paramagnetic resonance (EPR), the entrapment of murine breast cancer cells labeled with superparamagnetic iron oxide particles (SPIOs) in the mouse brain after intracardiac injection. For this purpose, luciferase-expressing murine 4 T1-luc breast cancer cells were labeled with fluorescent Molday ION Rhodamine B SPIOs. Following intracardiac injection, SPIO-labeled 4 T1-luc cells were imaged using multiple gradient-echo sequences. Ex vivo iron oxide quantification in the mouse brain was performed using EPR (9 GHz). The long-term fate of 4 T1-luc cells after injection was characterized using bioluminescence imaging (BLI), brain MRI and immunofluorescence. We observed hypointense spots due to SPIO-labeled cells in the mouse brain 4 h after injection on T2 *-weighted images. Histology studies showed that SPIO-labeled cancer cells were localized within blood vessels shortly after delivery. Ex vivo quantification of SPIOs showed that less than 1% of the injected cells were taken up by the mouse brain after injection. MRI experiments did not reveal the development of macrometastases in the mouse brain several days after injection, but immunofluorescence studies demonstrated that these cells found in the brain established micrometastases. Concerning the metastatic patterns of 4 T1-luc cells, an EPR biodistribution study demonstrated that SPIO-labeled 4 T1-luc cells were also entrapped in the lungs of mice after intracardiac injection. BLI performed 6 days after injection of 4 T1-luc cells showed that this cell line formed macrometastases in the lungs and in the bones. Conclusively, EPR and MRI were found to be complementary for cell tracking applications. MRI cell tracking at 11.7 T allowed sensitive detection of isolated SPIO-labeled cells in the mouse brain, whereas EPR

  5. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization

    NASA Astrophysics Data System (ADS)

    Sidabras, Jason W.; Strangeway, Robert A.; Mett, Richard R.; Anderson, James R.; Mainali, Laxman; Hyde, James S.

    2016-03-01

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  6. In vivo visualization and ex vivo quantification of murine breast cancer cells in the mouse brain using MRI cell tracking and electron paramagnetic resonance.

    PubMed

    Danhier, Pierre; Magat, Julie; Levêque, Philippe; De Preter, Géraldine; Porporato, Paolo E; Bouzin, Caroline; Jordan, Bénédicte F; Demeur, Gladys; Haufroid, Vincent; Feron, Olivier; Sonveaux, Pierre; Gallez, Bernard

    2015-03-01

    Cell tracking could be useful to elucidate fundamental processes of cancer biology such as metastasis. The aim of this study was to visualize, using MRI, and to quantify, using electron paramagnetic resonance (EPR), the entrapment of murine breast cancer cells labeled with superparamagnetic iron oxide particles (SPIOs) in the mouse brain after intracardiac injection. For this purpose, luciferase-expressing murine 4 T1-luc breast cancer cells were labeled with fluorescent Molday ION Rhodamine B SPIOs. Following intracardiac injection, SPIO-labeled 4 T1-luc cells were imaged using multiple gradient-echo sequences. Ex vivo iron oxide quantification in the mouse brain was performed using EPR (9 GHz). The long-term fate of 4 T1-luc cells after injection was characterized using bioluminescence imaging (BLI), brain MRI and immunofluorescence. We observed hypointense spots due to SPIO-labeled cells in the mouse brain 4 h after injection on T2 *-weighted images. Histology studies showed that SPIO-labeled cancer cells were localized within blood vessels shortly after delivery. Ex vivo quantification of SPIOs showed that less than 1% of the injected cells were taken up by the mouse brain after injection. MRI experiments did not reveal the development of macrometastases in the mouse brain several days after injection, but immunofluorescence studies demonstrated that these cells found in the brain established micrometastases. Concerning the metastatic patterns of 4 T1-luc cells, an EPR biodistribution study demonstrated that SPIO-labeled 4 T1-luc cells were also entrapped in the lungs of mice after intracardiac injection. BLI performed 6 days after injection of 4 T1-luc cells showed that this cell line formed macrometastases in the lungs and in the bones. Conclusively, EPR and MRI were found to be complementary for cell tracking applications. MRI cell tracking at 11.7 T allowed sensitive detection of isolated SPIO-labeled cells in the mouse brain, whereas EPR

  7. Electron Paramagnetic Resonance and Fluorescence In Situ Hybridization-Based Investigations of Individual Doses for Persons Living at Metlino in the Upper Reaches of the Techa River

    SciTech Connect

    Degteva, M. O.; Anspaugh, L. R.; Akleyev, A. V.; Jacob, Peter; Ivanov, Denis V.; Wieser, Albrecht; Vorobiova, M. I.; Shishkina, Elena A.; Shved, Valentina A.; Vozilova, Alexandra; Bayankin, Sergey N.; Napier, Bruce A.

    2005-02-01

    Waterborne releases from the Mayak Production Association in Russia during 1949–1956 resulted in significant doses to persons living downstream; the most contaminated village was Metlino about 7 km downstream. Internal and external doses have been estimated for these residents using the Techa River Dosimetry System–2000; the primary purpose is to support epidemiological studies of the members of the Extended Techa River Cohort (ETRC). Efforts to validate the calculations of external and internal dose are considered essential. Two methods used for the validation of external dose are electron paramagnetic resonance (EPR) measurements of teeth and fluorescence in situ hybridization (FISH) measurements of chromosome translocations in circulating lymphocytes. For EPR, 36 measurements on 26 teeth from 16 donors from Metlino were made at the GSF (16 measurements) and the IMP (20 measurements); the correlation between measurements made at the two laboratories has been found to be 0.99. Background measurements were also made on 218 teeth (63 molars, 128 premolars, and 27 incisors). FISH measurements were made for 31 residents of Metlino at the GSF. These measurements were handicapped by the analysis of a limited number of cells; for several individuals no stable translocations were observed. FISH measurements were also made for 39 individuals believed to be unexposed. The majority of EPR-measurement results fell within the range of 70 to 2700 mGy (including background). The results of FISH-based measurements fell within the range of nondetectable to 2 Gy (background subtracted). The results of individual measurements using EPR and FISH methods were generally consistent with each other and with results of other assays, including thermoluminescent measurements of quartz extracted from bricks taken from old buildings. Results were also consistent with those estimated with the TRDS-2000. Thus, the limited sets of data currently available tend to validate the present

  8. Unitized paramagnetic salt thermometer

    SciTech Connect

    Abraham, B.M.

    1982-06-01

    The details of construction and assembly of a cerous magnesium nitrate (CMN) paramagnetic thermometer are presented. The thermometer is a small unit consisting of a primary, two secondaries, the salt pill, and thermal links. The thermometer calibration changes very little on successive coolings and is reliable to 35 mK. A typical calibration curve is also presented.

  9. Paramagnetic and Diamagnetic Materials

    ERIC Educational Resources Information Center

    Thompson, Frank

    2011-01-01

    Paramagnetic and diamagnetic materials are now generally known as the "Cinderella" materials of the magnetic world. However, susceptibility measurements made on these materials in the past have revealed many details about the molecular bonding and the atomic structure of the so-called "transition" elements. Indeed, the magnetic moment of neodymium…

  10. Demonstrating Paramagnetism Using Liquid Nitrogen.

    ERIC Educational Resources Information Center

    Simmonds, Ray; And Others

    1994-01-01

    Describes how liquid nitrogen is attracted to the poles of neodymium magnets. Nitrogen is not paramagnetic, so the attraction suggests that the liquid nitrogen contains a small amount of oxygen, which causes the paramagnetism. (MVL)

  11. Collective modes in cold paramagnetic gases

    SciTech Connect

    Andreeva, T L; Rubin, P L

    2014-02-28

    We have obtained a condition for the emergence of spin waves in paramagnetic gases Re >> ImÂ, which is fulfilled only at temperatures of the order of 1 μK. (laser applications and other topics in quantum electronics)

  12. Protein structure determination with paramagnetic solid-state NMR spectroscopy.

    PubMed

    Sengupta, Ishita; Nadaud, Philippe S; Jaroniec, Christopher P

    2013-09-17

    Many structures of the proteins and protein assemblies that play central roles in fundamental biological processes and disease pathogenesis are not readily accessible via the conventional techniques of single-crystal X-ray diffraction and solution-state nuclear magnetic resonance (NMR). On the other hand, many of these challenging biological systems are suitable targets for atomic-level structural and dynamic analysis by magic-angle spinning (MAS) solid-state NMR spectroscopy, a technique that has far less stringent limitations on the molecular size and crystalline state. Over the past decade, major advances in instrumentation and methodology have prompted rapid growth in the field of biological solid-state NMR. However, despite this progress, one challenge for the elucidation of three-dimensional (3D) protein structures via conventional MAS NMR methods is the relative lack of long-distance data. Specifically, extracting unambiguous interatomic distance restraints larger than ∼5 Å from through-space magnetic dipole-dipole couplings among the protein (1)H, (13)C, and (15)N nuclei has proven to be a considerable challenge for researchers. It is possible to circumvent this problem by extending the structural studies to include several analogs of the protein of interest, intentionally modified to contain covalently attached paramagnetic tags at selected sites. In these paramagnetic proteins, the hyperfine couplings between the nuclei and unpaired electrons can manifest themselves in NMR spectra in the form of relaxation enhancements of the nuclear spins that depend on the electron-nucleus distance. These effects can be significant for nuclei located up to ∼20 Å away from the paramagnetic center. In this Account, we discuss MAS NMR structural studies of nitroxide and EDTA-Cu(2+) labeled variants of a model 56 amino acid globular protein, B1 immunoglobulin-binding domain of protein G (GB1), in the microcrystalline solid phase. We used a set of six EDTA-Cu(2

  13. Electron processing of fibre-reinforced advanced composites

    NASA Astrophysics Data System (ADS)

    Singh, Ajit; Saunders, Chris B.; Barnard, John W.; Lopata, Vince J.; Kremers, Walter; McDougall, Tom E.; Chung, Minda; Tateishi, Miyoko

    1996-08-01

    Advanced composites, such as carbon-fibre-reinforced epoxies, are used in the aircraft, aerospace, sporting goods, and transportation industries. Though thermal curing is the dominant industrial process for advanced composites, electron curing of similar composites containing acrylated epoxy matrices has been demonstrated by our work. The main attraction of electron processing technology over thermal technology is the advantages it offers which include ambient temperature curing, reduced curing times, reduced volatile emissions, better material handling, and reduced costs. Electron curing technology allows for the curing of many types of products, such as complex shaped, those containing different types of fibres, and up to 15 cm thick. Our work has been done principally with the AECL's 10 MeV, 1 kW electron accelerator; we have also done some comparative work with an AECL Gammacell 220. In this paper we briefly review our work on the various aspects of electron curing of advanced composites and their properties.

  14. Advances in DC photocathode electron guns

    SciTech Connect

    Bruce M. Dunham; P. Heartmann; Reza Kazimi; Hongxiu Liu; B. M. Poelker; J. S. Price; P. M. Rutt; W. J. Schneider; Charles K. Sinclair

    1998-07-01

    At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides a source of polarized electrons for the main accelerator. The gun is required to produce high average current with long operational lifetimes and high system throughout. Recent work has shown that careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source operation. These conditions include vacuum and the related effect of ion backbombardment, and precise control of all of the electrons emitted from the cathode. In this paper, the authors will review recent results and discuss implications for future photocathode guns.

  15. Advances in superconducting quantum electronic microcircuit fabrication

    NASA Technical Reports Server (NTRS)

    Kirschman, R. K.; Notarys, H. A.; Mercereau, J. E.

    1975-01-01

    Standard microelectronic fabrication techniques have been utilized to produce batch quantities of superconducting quantum electronic devices and circuits. The overall goal is a fabrication technology yielding circuits that are rugged and stable and capable of being fabricated controllably and reproducibly in sizeable quantities. Our progress toward this goal is presented, with primary emphasis on the most recent work, which includes the use of electron-beam lithography and techniques of hybrid microelectronics. Several prototype microcircuits have been successfully fabricated. These microcircuits are formed in a thin-film parent material consisting of layers of superconducting and normal metals, and use proximity-effect structures as the active circuit elements.

  16. Recent Advancements in Functionalized Paper-Based Electronics.

    PubMed

    Lin, Yang; Gritsenko, Dmitry; Liu, Qian; Lu, Xiaonan; Xu, Jie

    2016-08-17

    Building electronic devices on ubiquitous paper substrates has recently drawn extensive attention due to its light weight, low cost, environmental friendliness, and ease of fabrication. Recently, a myriad of advancements have been made to improve the performance of paper electronics for various applications, such as basic electronic components, energy storage devices, generators, antennas, and electronic circuits. This review aims to summarize this progress and discuss different perspectives of paper electronics as well as the remaining challenges yet to be overcome in this field. Other aspects included in this review are the fundamental characteristics of paper, modification of paper with functional materials, and various methods for device fabrication. PMID:27463253

  17. Recent Advancements in Functionalized Paper-Based Electronics.

    PubMed

    Lin, Yang; Gritsenko, Dmitry; Liu, Qian; Lu, Xiaonan; Xu, Jie

    2016-08-17

    Building electronic devices on ubiquitous paper substrates has recently drawn extensive attention due to its light weight, low cost, environmental friendliness, and ease of fabrication. Recently, a myriad of advancements have been made to improve the performance of paper electronics for various applications, such as basic electronic components, energy storage devices, generators, antennas, and electronic circuits. This review aims to summarize this progress and discuss different perspectives of paper electronics as well as the remaining challenges yet to be overcome in this field. Other aspects included in this review are the fundamental characteristics of paper, modification of paper with functional materials, and various methods for device fabrication.

  18. Advanced fabrication technologies for nano-electronics

    SciTech Connect

    Simmons, J.A.; Weckwerth, M.V.; Baca, W.E.

    1996-03-01

    Three novel fabrication technologies are presented which greatly increase the tools available for the realization of nano-electronic devices. First, a sub-micron area post structure descending from a metallic airbridge allows gating of regions as small as 0.1 {mu}m in diameter. This has enabled the study of such quantum phenomena as coupling of parallel quantum point contacts, and electron focusing around a tunable quantum antidot. We also describe two new techniques for backgating multiquantum well structures with submicron lateral resolution. These techniques enable separate ohmic contacts to individual quantum wells spaced as closely as 100 {Angstrom}, and thus allow the fabrication of novel quantum tunneling devices. The first technique uses regrowth over a patterned ion-implanted substrate. The second involves a novel epoxy-bond-and-stop-etch (EBASE) processing scheme, whereby the original substrate is etched away and the backside then patterned using conventional methods.

  19. Acoustic paramagnetic logging tool

    DOEpatents

    Vail, III, William B.

    1988-01-01

    New methods and apparatus are disclosed which allow measurement of the presence of oil and water in geological formations using a new physical effect called the Acoustic Paramagnetic Logging Effect (APLE). The presence of petroleum in formation causes a slight increase in the earth's magnetic field in the vicinity of the reservoir. This is the phenomena of paramagnetism. Application of an acoustic source to a geological formation at the Larmor frequency of the nucleons present causes the paramagnetism of the formation to disappear. This results in a decrease in the earth3 s magnetic field in the vicinity of the oil bearing formation. Repetitively frequency sweeping the acoustic source through the Larmor frequency of the nucleons present (approx. 2 kHz) causes an amplitude modulation of the earth's magnetic field which is a consequence of the APLE. The amplitude modulation of the earth's magnetic field is measured with an induction coil gradiometer and provides a direct measure of the amount of oil and water in the excitation zone of the formation . The phase of the signal is used to infer the longitudinal relaxation times of the fluids present, which results in the ability in general to separate oil and water and to measure the viscosity of the oil present. Such measurements may be preformed in open boreholes and in cased well bores.

  20. Advanced power electronics and electric machinery program

    SciTech Connect

    None, None

    2007-12-01

    The U.S. Department of Energy (DOE) and the U.S. Council for Automotive Research (composed of automakers Ford, General Motors, and Chrysler) announced in January 2002 a new cooperative research effort. Known as "FreedomCAR" (derived from "Freedom" and "Cooperative Automotive Research"), it represents DOE's commitment to developing public/private partnerships to fund high-risk, high-payoff research into advanced automotive technologies. Efficient fuel cell technology, which uses hydrogen to power automobiles without air pollution, is a very promising pathway to achieving the ultimate vision. The new partnership replaces and builds upon the Partnership for a New Generation of Vehicles initiative that ran from 1993 through 2001.

  1. A cyanide-bridged heterometallic coordination polymer constructed from square-planar [Ni(CN)4](2-): synthesis, crystal structure, thermal decomposition, electron paramagnetic resonance (EPR) spectrum and magnetic properties.

    PubMed

    Qin, Ying Lian; Yang, Bin Wu; Wang, Gao Feng; Sun, Hong

    2016-07-01

    Square-planar complexes are commonly formed by transition metal ions having a d(8) electron configuration. Planar cyanometallate anions have been used extensively as design elements in supramolecular coordination systems. In particular, square-planar tetracyanometallate(II) ions, i.e. [M(CN)4](2-) (M(II) = Ni, Pd or Pt), are used as good building blocks for bimetallic Hofmann-type assemblies and their analogues. Square-planar tetracyanonickellate(II) complexes have been extensively developed with N-donor groups as additional co-ligands, but studies of these systems using O-donor ligands are scarce. A new cyanide-bridged Cu(II)-Ni(II) heterometallic compound, poly[[diaquatetra-μ2-cyanido-κ(8)C:N-nickel(II)copper(II)] monohydrate], {[Cu(II)Ni(II)(CN)4(H2O)2]·H2O}n, has been synthesized and characterized by X-ray single-crystal diffraction analyses, vibrational spectroscopy (FT-IR), thermal analysis, electron paramagnetic resonance (EPR) and magnetic moment measurements. The structural analysis revealed that it has a two-dimensional grid-like structure built up of cationic [Cu(H2O)2](2+) and anionic [Ni(CN)4](2-) units connected through bridging cyanide ligands. The overall three-dimensional supramolecular network is expanded by a combination of interlayer O-H...N and intralayer O-H...O hydrogen-bond interactions. The first decomposition reactions take place at 335 K under a static air atmosphere, which illustrates the existence of guest water molecules in the interlayer spaces. The electron paramagnetic resonance (EPR) spectrum confirms that the Cu(II) cation has an axial coordination symmetry and that the unpaired electrons occupy the d(x(2)-y(2)) orbital. In addition, magnetic investigations showed that antiferromagnetic interactions exist in the Cu(II) atoms through the diamagnetic [Ni(CN)4](2-) ion.

  2. Spin-lattice relaxation of ligand nuclei in slowly reorienting paramagnetic complexes in the electronic doublet spin state ( S = {1}/{2}). A theoretical approach for strongly coupled two-spin systems

    NASA Astrophysics Data System (ADS)

    Benetis, Nikolas P.

    In this paper a general theory for treating the spin-lattice relaxation of a ligand nucleus (denoted by I) is derived for a metal complex in a doublet electron spin state ( S = {1}/{2}). The dipole-dipole SI interaction is treated for the case where the electron spin is also strongly coupled to the metal nucleus K. The SK interaction considered here is the hyperfine coupling, both scalar (SC) and dipolar (DD). The present theory is valid for slowly reorienting complexes in solution and can, furthermore, incorporate relaxation effects of the electron spin S, and the metal nucleus K due to processes which are faster than, and independent of, reorientation, i.e., for processes that fulfil the strong narrowing conditions. The effects of chemical exchange of the ligands and of anisotropic reorientation of the complex are also studied. Together with our previous studies of paramagnetic complexes with electron spin S ≧ 1, that have been recently reviewed by J. Kowalewski, L. Nordenskiöld, N. Benetis, and P. O. Westlund, ( Prog. NMR Spectrosc.17, 141 (1985)), the present work completes the elementary relaxation features of ligand nuclei of metal complexes in the slow motional regime. The present theory is shown to be more general than the theory of Bertini and co-workers ( J. Magn. Reson.59 , 213 (1984)), which can be obtained as a limit of the present approach by decoupling the reorientation from the motions of the S-K two spin system. The treatment of a strongly coupled two-spin system is emphasized since it provides a necessary step to the treatment of the relaxation of paramagnetic doublets.

  3. Electron paramagnetic resonance study of alinement induced by magnetic fields in two smectic-A liquid crystals not exhibiting nematic phases

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Gelerinter, E.

    1972-01-01

    Using vanadyl acetylacetonate (VAAC) as a paramagnetic probe, the molecular ordering in two smectic-A liquid crystals that do not display nematic phases were studied. Reproducible alinement was attained by slow cooling throughout the isotropic smectic-A transition in dc magnetic fields of 1.1 and 2.15 teslas. The degree of order attained is small for a smectic-A liquid crystal. Measurements were made of the variation of the average hyperfine splitting of the alined samples as a function of orientation relative to the dc magnetic field of the spectrometer. This functional dependence is in agreement with the theoretical prediction except where the viscosity of the liquid crystal becomes large enough to slow the tumbling of the VAAC, as indicated by asymmetry in the end lines of the spectrum.

  4. FY2009 Annual Progress Report for Advanced Power Electronics

    SciTech Connect

    Rogers, Susan A.

    2010-01-01

    The Advanced Power Electronics and Electric Machines (APEEM) subprogram within the Vehicle Technologies Program provides support and guidance for many cutting-edge automotive technologies now under development. Research is focused on understanding and improving the way the various new components of tomorrow's automobiles will function as a unified system to improve fuel efficiency.

  5. BORON NITRIDE CAPACITORS FOR ADVANCED POWER ELECTRONIC DEVICES

    SciTech Connect

    N. Badi; D. Starikov; C. Boney; A. Bensaoula; D. Johnstone

    2010-11-01

    This project fabricates long-life boron nitride/boron oxynitride thin film -based capacitors for advanced SiC power electronics with a broad operating temperature range using a physical vapor deposition (PVD) technique. The use of vapor deposition provides for precise control and quality material formation.

  6. Epidermal electronics with advanced capabilities in near-field communication.

    PubMed

    Kim, Jeonghyun; Banks, Anthony; Cheng, Huanyu; Xie, Zhaoqian; Xu, Sheng; Jang, Kyung-In; Lee, Jung Woo; Liu, Zhuangjian; Gutruf, Philipp; Huang, Xian; Wei, Pinghung; Liu, Fei; Li, Kan; Dalal, Mitul; Ghaffari, Roozbeh; Feng, Xue; Huang, Yonggang; Gupta, Sanjay; Paik, Ungyu; Rogers, John A

    2015-02-25

    Epidermal electronics with advanced capabilities in near field communications (NFC) are presented. The systems include stretchable coils and thinned NFC chips on thin, low modulus stretchable adhesives, to allow seamless, conformal contact with the skin and simultaneous capabilities for wireless interfaces to any standard, NFC-enabled smartphone, even under extreme deformation and after/during normal daily activities.

  7. Low dimensional quantum paramagnets

    NASA Astrophysics Data System (ADS)

    Hong, Tao

    A quantum paramagnet is a material with interacting spins that possesses a paramagnetic ground state and an energy gap to all excitations. This dissertation focuses on studying the magnetic excitation spectrum and the quantum critical phenomena of such low dimensional quantum paramagnet systems. Inelastic neutron scattering (INS) measurements of Cu(Quinoxaline)Br 2 was performed on a partially deuterated powder sample. Magnetic neutron scattering was identified above an energy gap of 1.9 meV. Consideration of the sharp spectral max imum and wave vector dependence of the scattering and polymeric structure further identifies the material as a two-legged spin-1/2 ladder. The continuous uniform transformation theory provides an excellent account of the data with leg exchange J‖ =2.0 meV and the rung exchange J⊥ =3.3 meV. INS study of (2,3 - dimethylpyridinium)2CuBr4 (DIMPY) in both powder and single crystalline form are presented to understand the origin of the spin gap and what is the right spin Hamiltonian. Magnetic excitations are found above a 0.3 meV energy gap. The excitation only disperses along the a-direction with a bandwidth that exceeds 1.7 meV. The conclusion to be a S=1/2 two-legged spin ladder is supported by the material structure and INS measurement. External magnetic field drives the system into a critical region and induced low energy excitation continuum above critical field was studied. Piperazinium Hexachlorodicuprate (PHCC) is a two-dimensional antiferromagnet. We studied the behavior in the vicinity of the quantum critical point (QCP) where the spin gap is closed by an applied magnetic field by INS. The energy and damping of the low energy excitations were measured in the vicinity of the QCP where both quantities become strongly temperature dependent, which can be successfully described by a selfconsistent Hartree-Fock theory of strongly interacting bosons developed by Sachdev and Dunkel. A preliminary study of hydrostatic pressure effects

  8. Advanced Accelerating Structures and Their Interaction with Electron Beams

    SciTech Connect

    Gai Wei

    2009-01-22

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  9. Advanced accelerating structures and their interaction with electron beams.

    SciTech Connect

    Gai, W.; High Energy Physics

    2008-01-01

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  10. Future Opportunities for Advancing Glucose Test Device Electronics

    PubMed Central

    Young, Brian R; Young, Teresa L; Joyce, Margaret K; Kennedy, Spencer I; Atashbar, Massood Z

    2011-01-01

    Advancements in the field of printed electronics can be applied to the field of diabetes testing. A brief history and some new developments in printed electronics components applicable to personal test devices, including circuitry, batteries, transmission devices, displays, and sensors, are presented. Low-cost, thin, and lightweight materials containing printed circuits with energy storage or harvest capability and reactive/display centers, made using new printing/imaging technologies, are ideal for incorporation into personal-use medical devices such as glucose test meters. Semicontinuous rotogravure printing, which utilizes flexible substrates and polymeric, metallic, and/or nano “ink” composite materials to effect rapidly produced, lower-cost printed electronics, is showing promise. Continuing research advancing substrate, “ink,” and continuous processing development presents the opportunity for research collaboration with medical device designers. PMID:22027300

  11. Future opportunities for advancing glucose test device electronics.

    PubMed

    Young, Brian R; Young, Teresa L; Joyce, Margaret K; Kennedy, Spencer I; Atashbar, Massood Z

    2011-09-01

    Advancements in the field of printed electronics can be applied to the field of diabetes testing. A brief history and some new developments in printed electronics components applicable to personal test devices, including circuitry, batteries, transmission devices, displays, and sensors, are presented. Low-cost, thin, and lightweight materials containing printed circuits with energy storage or harvest capability and reactive/display centers, made using new printing/imaging technologies, are ideal for incorporation into personal-use medical devices such as glucose test meters. Semicontinuous rotogravure printing, which utilizes flexible substrates and polymeric, metallic, and/or nano "ink" composite materials to effect rapidly produced, lower-cost printed electronics, is showing promise. Continuing research advancing substrate, "ink," and continuous processing development presents the opportunity for research collaboration with medical device designers.

  12. Recent progress of the Los Alamos advanced free electron laser

    SciTech Connect

    Nguyen, D.C.; Austin, R.H.; Chan, K.C.D.; Feldman, D.W.; Goldstein, J.C.; Gierman, S.M.; Kinross-Wright, J.M.; Kong, S.H.; Plato, J.G.; Russell, S.J.

    1994-05-01

    Many industrial and research applications can benefit from the availability of a compact, user-friendly, broadly tunable and high average power free electron laser (FEL). Over the past four years, the Los Alamos Advanced FEL has been built with these design goals. The key to a compact FEL is the integration of advanced beam technologies such as a high-brightness photoinjector, a high-gradient compact linac, and permanent magnet beamline components. These technologies enable the authors to shrink the FEL size yet maintain its high average power capability. The Advanced FEL has been in operation in the near ir (4-6 {mu}m) since early 1993. Recent results of the Advanced FEL lasing at saturation and upgrades to improve its average power are presented.

  13. Theoretical studies of the local structures and electron paramagnetic resonance parameters for Cu2+ center in Zn(C3H3O4)2(H2O)2 single crystal

    NASA Astrophysics Data System (ADS)

    Zhang, Hua-Ming; Xiao, Wen-Bo; Wan, Xiong

    2014-07-01

    The electron paramagnetic resonance (EPR) parameters (g factors gxx, gyy, gzz and hyperfine structure constants Axx, Ayy, Azz) are interpreted by taking account of the admixture of d-orbitals in the ground state wave function of the Cu2+ ion in a Zn(C3H3O4)2(H2O)2 (DABMZ) single crystal. Based on the calculation, local structural parameters of the impurity Cu2+ center were obtained (i.e. Ra≈1.92 Å, Rb≈1.96 Å, Rc≈1.99 Å). The theoretical EPR parameters based on the above Cu2+-O2- bond lengths in the DABMZ crystal show good agreement with the observed values and some improvements have been made as compared with those in the previous studies.

  14. Materials Advances for Next-Generation Ingestible Electronic Medical Devices.

    PubMed

    Bettinger, Christopher J

    2015-10-01

    Electronic medical implants have collectively transformed the diagnosis and treatment of many diseases, but have many inherent limitations. Electronic implants require invasive surgeries, operate in challenging microenvironments, and are susceptible to bacterial infection and persistent inflammation. Novel materials and nonconventional device fabrication strategies may revolutionize the way electronic devices are integrated with the body. Ingestible electronic devices offer many advantages compared with implantable counterparts that may improve the diagnosis and treatment of pathologies ranging from gastrointestinal infections to diabetes. This review summarizes current technologies and highlights recent materials advances. Specific focus is dedicated to next-generation materials for packaging, circuit design, and on-board power supplies that are benign, nontoxic, and even biodegradable. Future challenges and opportunities are also highlighted.

  15. Applications and Advances in Electronic-Nose Technologies

    PubMed Central

    Wilson, Alphus D.; Baietto, Manuela

    2009-01-01

    Electronic-nose devices have received considerable attention in the field of sensor technology during the past twenty years, largely due to the discovery of numerous applications derived from research in diverse fields of applied sciences. Recent applications of electronic nose technologies have come through advances in sensor design, material improvements, software innovations and progress in microcircuitry design and systems integration. The invention of many new e-nose sensor types and arrays, based on different detection principles and mechanisms, is closely correlated with the expansion of new applications. Electronic noses have provided a plethora of benefits to a variety of commercial industries, including the agricultural, biomedical, cosmetics, environmental, food, manufacturing, military, pharmaceutical, regulatory, and various scientific research fields. Advances have improved product attributes, uniformity, and consistency as a result of increases in quality control capabilities afforded by electronic-nose monitoring of all phases of industrial manufacturing processes. This paper is a review of the major electronic-nose technologies, developed since this specialized field was born and became prominent in the mid 1980s, and a summarization of some of the more important and useful applications that have been of greatest benefit to man. PMID:22346690

  16. Testing aspects of advanced coherent electron cooling technique

    SciTech Connect

    Litvinenko, V.; Jing, Y.; Pinayev, I.; Wang, G.; Samulyak, R.; Ratner, D.

    2015-05-03

    An advanced version of the Coherent-electron Cooling (CeC) based on the micro-bunching instability was proposed. This approach promises significant increase in the bandwidth of the CeC system and, therefore, significant shortening of cooling time in high-energy hadron colliders. In this paper we present our plans of simulating and testing the key aspects of this proposed technique using the set-up of the coherent-electron-cooling proof-of-principle experiment at BNL.

  17. Architectural development of an advanced EVA Electronic System

    NASA Technical Reports Server (NTRS)

    Lavelle, Joseph

    1992-01-01

    An advanced electronic system for future EVA missions (including zero gravity, the lunar surface, and the surface of Mars) is under research and development within the Advanced Life Support Division at NASA Ames Research Center. As a first step in the development, an optimum system architecture has been derived from an analysis of the projected requirements for these missions. The open, modular architecture centers around a distributed multiprocessing concept where the major subsystems independently process their own I/O functions and communicate over a common bus. Supervision and coordination of the subsystems is handled by an embedded real-time operating system kernel employing multitasking software techniques. A discussion of how the architecture most efficiently meets the electronic system functional requirements, maximizes flexibility for future development and mission applications, and enhances the reliability and serviceability of the system in these remote, hostile environments is included.

  18. Advanced Power Electronics for LED Drivers: Advanced Technologies for integrated Power Electronics

    SciTech Connect

    2010-09-01

    ADEPT Project: MIT is teaming with Georgia Institute of Technology, Dartmouth College, and the University of Pennsylvania (UPenn) to create more efficient power circuits for energy-efficient light-emitting diodes (LEDs) through advances in 3 related areas. First, the team is using semiconductors made of high-performing gallium nitride grown on a low-cost silicon base (GaN-on-Si). These GaN-on-Si semiconductors conduct electricity more efficiently than traditional silicon semiconductors. Second, the team is developing new magnetic materials and structures to reduce the size and increase the efficiency of an important LED power component, the inductor. This advancement is important because magnetics are the largest and most expensive part of a circuit. Finally, the team is creating an entirely new circuit design to optimize the performance of the new semiconductors and magnetic devices it is using.

  19. X-ray Crystallographic, Multifrequency Electron Paramagnetic Resonance, and Density Functional Theory Characterization of the Ni(P(Cy)2N(tBu)2)2(n+) Hydrogen Oxidation Catalyst in the Ni(I) Oxidation State.

    PubMed

    Niklas, Jens; Westwood, Mark; Mardis, Kristy L; Brown, Tiara L; Pitts-McCoy, Anthony M; Hopkins, Michael D; Poluektov, Oleg G

    2015-07-01

    The Ni(I) hydrogen oxidation catalyst [Ni(P(Cy)2N(tBu)2)2](+) (1(+); P(Cy)2N(tBu)2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane) has been studied using a combination of electron paramagnetic resonance (EPR) techniques (X-, Q-, and D-band, electron-nuclear double resonance, hyperfine sublevel correlation spectroscopy), X-ray crystallography, and density functional theory (DFT) calculations. Crystallographic and DFT studies indicate that the molecular structure of 1(+) is highly symmetrical. EPR spectroscopy has allowed determination of the electronic g tensor and the spin density distribution on the ligands, and revealed that the Ni(I) center does not interact strongly with the potentially coordinating solvents acetonitrile and butyronitrile. The EPR spectra and magnetic parameters of 1(+) are found to be distinctly different from those for the related compound [Ni(P(Ph)2N(Ph)2)2](+) (4(+)). One significant contributor to these differences is that the molecular structure of 4(+) is unsymmetrical, unlike that of 1(+). DFT calculations on derivatives in which the R and R' groups are systematically varied have allowed elucidation of structure/substituent relationships and their corresponding influence on the magnetic resonance parameters.

  20. Electron paramagnetic resonance applications: promising developments at the E K Zavoisky Kazan Physical-Technical Institute of the Russian Academy of Sciences

    NASA Astrophysics Data System (ADS)

    Salikhov, K. M.

    2016-06-01

    This paper briefly reviews the advances made in recent years at the E K Zavoisky Kazan Physical-Technical Institute of the Russian Academy of Sciences in EPR spectroscopy and its applications to overcoming the topical problems

  1. Advances in Electronic-Nose Technologies Developed for Biomedical Applications

    PubMed Central

    Wilson, Alphus D.; Baietto, Manuela

    2011-01-01

    The research and development of new electronic-nose applications in the biomedical field has accelerated at a phenomenal rate over the past 25 years. Many innovative e-nose technologies have provided solutions and applications to a wide variety of complex biomedical and healthcare problems. The purposes of this review are to present a comprehensive analysis of past and recent biomedical research findings and developments of electronic-nose sensor technologies, and to identify current and future potential e-nose applications that will continue to advance the effectiveness and efficiency of biomedical treatments and healthcare services for many years. An abundance of electronic-nose applications has been developed for a variety of healthcare sectors including diagnostics, immunology, pathology, patient recovery, pharmacology, physical therapy, physiology, preventative medicine, remote healthcare, and wound and graft healing. Specific biomedical e-nose applications range from uses in biochemical testing, blood-compatibility evaluations, disease diagnoses, and drug delivery to monitoring of metabolic levels, organ dysfunctions, and patient conditions through telemedicine. This paper summarizes the major electronic-nose technologies developed for healthcare and biomedical applications since the late 1980s when electronic aroma detection technologies were first recognized to be potentially useful in providing effective solutions to problems in the healthcare industry. PMID:22346620

  2. 76 FR 12144 - Advanced Optics Electronics, Inc.; Order of Suspension of Trading

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-04

    ... COMMISSION Advanced Optics Electronics, Inc.; Order of Suspension of Trading March 2, 2011. It appears to the... securities of Advanced Optics Electronics, Inc. because it has not filed any periodic reports since the... of investors require a suspension of trading in Advanced Optics Electronics, Inc. Therefore, it...

  3. Strong reduction of V{sup 4+} amount in vanadium oxide/hexadecylamine nanotubes by doping with Co{sup 2+} and Ni{sup 2+} ions: Electron paramagnetic resonance and magnetic studies

    SciTech Connect

    Saleta, M. E.; Troiani, H. E.; Ribeiro Guevara, S.; Ruano, G.; Sanchez, R. D.; Malta, M.; Torresi, R. M.

    2011-05-01

    In this work we present a complete characterization and magnetic study of vanadium oxide/hexadecylamine nanotubes (VO{sub x}/Hexa NT's) doped with Co{sup 2+} and Ni{sup 2+} ions. The morphology of the NT's has been characterized by transmission electron microscopy, while the metallic elements have been quantified by the instrumental neutron activation analysis technique. The static and dynamic magnetic properties were studied by collecting data of magnetization as a function of magnetic field and temperature and by electron paramagnetic resonance. At difference of the majority reports in the literature, we do not observe magnetic dimers in vanadium oxide nanotubes. Also, we observed that the incorporation of metallic ions (Co{sup 2+}, S = 3/2 and Ni{sup 2+}, S = 1) decreases notably the amount of V{sup 4+} ions in the system, from 14-16% (nondoped case) to 2%-4%, with respect to the total vanadium atoms (fact corroborated by XPS experiments) anyway preserving the tubular nanostructure. The method to decrease the amount of V{sup 4+} in the nanotubes improves considerably their potential technological applications as Li-ion batteries cathodes.

  4. Upcycling : converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres.

    SciTech Connect

    Pol, V.

    2010-06-15

    The recent tremendous increase in the volume of waste plastics (WP) will have a harmful environmental impact on the health of living beings. Hundreds of years are required to degrade WP in atmospheric conditions. Hence, in coming years, in addition to traditional recycling services, innovative 'upcycling' processes are necessary. This article presents an environmentally benign, solvent-free autogenic process that converts various WP [low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene terephthalate (PET), polystyrene (PS), or their mixtures] into carbon microspheres (CMSs), an industrially significant, value-added product. The thermal dissociation of these individual or mixed WP in a closed reactor under autogenic pressure (1000 psi) produced dry, pure powder of CMSs. In this paper, the optimization of process parameters such as the effect of mixing of WP with other materials, and the role of reaction temperature and time are reported. Employing advanced analytical techniques, the atomic structure, composition, and morphology of as-obtained CMSs were analyzed. The room-temperature paramagnetism in CMSs prepared from waste LDPE, HDPE, and PS was further studied by electron paramagnetic resonance (EPR). The conducting and paramagnetic nature of CMSs holds promise for their potential applications in toners, printers, paints, batteries, lubricants, and tires.

  5. Upcycling: converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres.

    PubMed

    Pol, Vilas Ganpat

    2010-06-15

    The recent tremendous increase in the volume of waste plastics (WP) will have a harmful environmental impact on the health of living beings. Hundreds of years are required to degrade WP in atmospheric conditions. Hence, in coming years, in addition to traditional recycling services, innovative "upcycling" processes are necessary. This article presents an environmentally benign, solvent-free autogenic process that converts various WP [low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene terephthalate (PET), polystyrene (PS), or their mixtures] into carbon microspheres (CMSs), an industrially significant, value-added product. The thermal dissociation of these individual or mixed WP in a closed reactor under autogenic pressure ( approximately 1000 psi) produced dry, pure powder of CMSs. In this paper, the optimization of process parameters such as the effect of mixing of WP with other materials, and the role of reaction temperature and time are reported. Employing advanced analytical techniques, the atomic structure, composition, and morphology of as-obtained CMSs were analyzed. The room-temperature paramagnetism in CMSs prepared from waste LDPE, HDPE, and PS was further studied by electron paramagnetic resonance (EPR). The conducting and paramagnetic nature of CMSs holds promise for their potential applications in toners, printers, paints, batteries, lubricants, and tires.

  6. Radiation-Hardened Electronics for Advanced Communications Systems

    NASA Technical Reports Server (NTRS)

    Whitaker, Sterling

    2015-01-01

    Novel approach enables high-speed special-purpose processors Advanced reconfigurable and reprogrammable communication systems will require sub-130-nanometer electronics. Legacy single event upset (SEU) radiation-tolerant circuits are ineffective at speeds greater than 125 megahertz. In Phase I of this project, ICs, LLC, demonstrated new base-level logic circuits that provide SEU immunity for sub-130-nanometer high-speed circuits. In Phase II, the company developed an innovative self-restoring logic (SRL) circuit and a system approach that provides high-speed, SEU-tolerant solutions that are effective for sub-130-nanometer electronics scalable to at least 22-nanometer processes. The SRL system can be used in the design of NASA's next-generation special-purpose processors, especially reconfigurable communication processors.

  7. Paramagnetic state of the isolated gold impurity in silicon

    NASA Astrophysics Data System (ADS)

    Son, N. T.; Gregorkiewicz, T.; Ammerlaan, C. A. J.

    1992-11-01

    The paper reports on the observation of the electron paramagnetic resonance spectrum of the isolated substitutional gold impurity in silicon. The spectrum has orthorhombic I (C2v) symmetry and an effective spin S=1/2. It has been detected in silver-doped samples with gold being introduced as contamination of the isotope used for diffusion. Parameters of the spectrum are given and an electronic model is proposed. With the results of the current study the puzzling question concerning paramagnetism of the isolated gold impurity in silicon appears to be clarified.

  8. A perspective on RF vacuum electronics: Innovations and recent advances

    SciTech Connect

    Parker, R.K.

    1995-12-31

    Vacuum electronics continues as a vital technology for the generation of coherent radiation in a spectral region extending from the UHF to the infrared. The veritable explosion in this field that occurred in the 1950s and the early 1960s established an effective microwave power tube technology that remains as the basic building block for a wide range of RF transmission and power applications. Drawing on ideas and techniques from relativistic and pulsed power electronics, a resurgence in research began in the mid-1970s that resulted in new capabilities at high frequency and extreme levels of peak power. More recently, solid-state and vacuum electronic interests have converged to create a new technology, vacuum micro-electronics, that promises to yield competitive new products at lower frequency and more moderate power. Many of the advances and innovations from current R and D efforts are associated with two primary technological thrusts. First is the continuing development of fast-wave device concepts for use in heating, particle accelerations, and RF power transmission. The second thrust is defined by the creative blending of solid-state and vacuum concepts, techniques and capabilities. The microwave power module, a new transmitter archetype, highlights the benefits of this approach.

  9. Advanced Diagnostics for Developing High-Brightness Electron Beams

    SciTech Connect

    Ben-Zvi, I.; Babzien, M.; Malone, R.; Wang, X.-J.; Yakimenko, V.

    1998-11-24

    The production of high-brightness particle beams calls for the development of advanced beam diagnostics. High brightness beams, meaning beams with a high density in phase space, are important for many applications, such as short-wavelength Free-Electron Lasers and advanced accelerator systems. A diagnostic that provides detailed information on the density distribution of the electron bunch in multi-dimensional phase-space is an essential tool for obtaining small emittance at a high charge. This diagnostic system has been developed at Brookhaven National Laboratory. One component of the system is the measurement of a slice emittance which provides a measurement of transverse beam properties (such as emittance) as a function of the longitudinal position. Changing the laser pulse profile of a photocathode RF gun has been suggested as one way to achieve non-linear emittance compensation and improve the brightness and that can be diagnosed by the slice emittance system. The other element of the diagnostic is the tomographic reconstruction of the transverse phase. In our work we give special attention to the accuracy of the phase space reconstruction and present an analysis using a transport line with nine focusing magnets and techniques to control the optical functions and phases. This high precision phase space tomography together with the ability to modify the radial charge distribution of the electron beam presents an opportunity to improve the emittance and apply non-linear radial emittance corrections. Combining the slice emittance and tomography diagnostics leads to an unprecedented visualization of phase space distributions in 5 dimensional phase-space and an opportunity to perform high-order emittance corrections. This should lead to great improvements in the beam brightness.

  10. ADVANCED DIAGNOSTICS FOR DEVELOPING HIGH-BRIGHTNESS ELECTRON BEAMS.

    SciTech Connect

    BEN-ZVI,I.

    1998-11-24

    The production of high-brightness particle beams calls for the development of advanced beam diagnostics. High brightness beams, meaning beams with a high density in phase space, are important for many applications, such as short-wavelength Free-Electron Lasers and advanced accelerator systems. A diagnostic that provides detailed information on the density distribution of the electron bunch in multi-dimensional phase-space is an essential tool for obtaining small emittance at a high charge. This diagnostic system has been developed at Brookhaven National Laboratory. One component of the system is the measurement of a slice emittance which provides a measurement of transverse beam properties (such as emittance) as a function of the longitudinal position. Changing the laser pulse profile of a photocathode RF gun has been suggested as one way to achieve non-linear emittance compensation and improve the brightness and that can be diagnosed by the slice emittance system. The other element of the diagnostic is the tomographic reconstruction of the transverse phase. In our work we give special attention to the accuracy of the phase space reconstruction and present an analysis using a transport line with nine focusing magnets and techniques to control the optical functions and phases. This high precision phase space tomography together with the ability to modify the radial charge distribution of the electron beam presents an opportunity to improve the emittance and apply non-linear radial emittance corrections. Combining the slice emittance and tomography diagnostics leads to an unprecedented visualization of phase space distributions in 5 dimensional phase-space and an opportunity to perform high-order emittance corrections. This should lead to great improvements in the beam brightness.

  11. Understanding the magnetic behavior of heat treated CaO-P2O5-Na2O-Fe2O3-SiO2 bioactive glass using electron paramagnetic resonance studies

    NASA Astrophysics Data System (ADS)

    Shankhwar, Nisha; Kothiyal, G. P.; Srinivasan, A.

    2014-09-01

    Bioactive glass of composition 41CaO-44SiO2-4P2O5-8Fe2O3-3Na2O has been heat treated in the temperature (TA) range of 750-1150 °C for time periods (tA) ranging from 1 h to 3 h to yield magnetic bioactive glass ceramics (MBCs). X-ray diffraction studies indicate the presence of bone mineral (hydroxyapatite and wollastonite) and magnetic (magnetite and α-hematite) phases in nanocrystalline form in the MBCs. Electron paramagnetic resonance (EPR) study was carried out to understand the variation in saturation magnetization and coercivity of the MBCs with TA and tA. These studies reveal the nature and amount of iron ions present in the MBCs and their interaction in the glassy oxide matrix as a function of annealing parameters. The deterioration in the magnetic properties of the glass heat treated above 1050 °C is attributed to the crystallization of the non-magnetic α-hematite phase. These results are expected to be useful in the application of these MBCs as thermoseeds in hyperthermia treatment of cancer.

  12. Neutron diffraction, Mössbauer effect and electron paramagnetic resonance studies on multiferroic Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3}

    SciTech Connect

    Matteppanavar, Shidaling; Angadi, Basavaraj; Rayaprol, Sudhindra; AV, Anupama; Sahoo, Balaram

    2015-06-24

    Multiferroic Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3} ceramics were synthesized via a modified two-stage Columbite method. Single phase formation was confirmed from the analysis of x-ray and neutron diffraction patterns recorded at room temperature. Structural analysis of the diffraction data reveals cubic phase (space group Pm-3m) for the title compound. Magnetic structure of the title compound at room temperature exhibits G-type antiferromagnetic structure. The Mössbauer spectroscopy and Electron Paramagnetic Resonance (EPR) studies were carried out at 300 K. The isomer shift and quadrupole splitting of the Mössbauer spectra confirms the trivalent state of iron (Fe{sup 3+}). The Mössbauer spectra also suggest that the iron and tungsten are randomly distributed at the octahedral, B site. EPR spectra show a single broad line associated with Fe{sup 3+} ions. Both spectra clearly exhibit weak ferromagnetic behaviour of Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3} ceramic at 300 K. Considering neutron diffraction, Mössbauer and EPR results together, it may be stated here that Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3} exhibits antiferromagnetic behavior along with weak ferromagnetism at room temperature.

  13. Acceptor-oxygen vacancy defect dipoles and fully coordinated defect centers in a ferroelectric perovskite lattice: Electron paramagnetic resonance analysis of Mn2+ in single crystal BaTiO3

    NASA Astrophysics Data System (ADS)

    Maier, R. A.; Pomorski, T. A.; Lenahan, P. M.; Randall, C. A.

    2015-10-01

    Defect dipoles are significant point defects in perovskite oxides as a result of their impact on oxygen vacancy dynamics. Electron paramagnetic resonance (EPR) was used to investigate the local defect structure of single crystal BaTiO3 doped with manganese. These results, along with a re-analysis of literature data, do not support the conclusion that transition metal-oxygen vacancy nearest neighbor defect dipoles ( M nT i ″ - VO • • ) × in ferroelectric BaTiO3 are majority defect centers as previously reported. Local symmetry analysis of the zero-field splitting term of the spin Hamiltonian supports the assignment of fully coordinated defect centers as opposed to defect dipoles for resonance signals at geff ˜ 2. A newly discovered defect center with g⊥ ˜ 6 is observed in the manganese doped system, and it is argued that this defect center belongs to an associated defect complex or defect dipole. This newly reported strong axial defect center, however, is present in small, minor concentrations compared to the well-known Mn2+ center with zero-field splitting of D ˜ 645 MHz. In regard to relative concentration, it is concluded that the dominant point defect related to the Mn2+ ion doped in BaTiO3 corresponds to B-site substitution with six nearest neighbor anions in octahedral coordination.

  14. The Structure of Vimentin Linker 1 and Rod 1B Domains Characterized by Site-directed Spin-labeling Electron Paramagnetic Resonance (SDSL-EPR) and X-ray Crystallography*

    PubMed Central

    Aziz, Atya; Hess, John F.; Budamagunta, Madhu S.; Voss, John C.; Kuzin, Alexandre P.; Huang, Yuanpeng J.; Xiao, Rong; Montelione, Gaetano T.; FitzGerald, Paul G.; Hunt, John F.

    2012-01-01

    Despite the passage of ∼30 years since the complete primary sequence of the intermediate filament (IF) protein vimentin was reported, the structure remains unknown for both an individual protomer and the assembled filament. In this report, we present data describing the structure of vimentin linker 1 (L1) and rod 1B. Electron paramagnetic resonance spectra collected from samples bearing site-directed spin labels demonstrate that L1 is not a flexible segment between coiled-coils (CCs) but instead forms a rigid, tightly packed structure. An x-ray crystal structure of a construct containing L1 and rod 1B shows that it forms a tetramer comprising two equivalent parallel CC dimers that interact with one another in the form of a symmetrical anti-parallel dimer. Remarkably, the parallel CC dimers are themselves asymmetrical, which enables them to tetramerize rather than undergoing higher order oligomerization. This functionally vital asymmetry in the CC structure, encoded in the primary sequence of rod 1B, provides a striking example of evolutionary exploitation of the structural plasticity of proteins. EPR and crystallographic data consistently suggest that a very short region within L1 represents a minor local distortion in what is likely to be a continuous CC from the end of rod 1A through the entirety of rod 1B. The concordance of this structural model with previously published cross-linking and spectral data supports the conclusion that the crystallographic oligomer represents a native biological structure. PMID:22740688

  15. Characterization of the coral allene oxide synthase active site with UV-visible absorption, magnetic circular dichroism, and electron paramagnetic resonance spectroscopy: evidence for tyrosinate ligation to the ferric enzyme heme iron.

    PubMed

    Abraham, B D; Sono, M; Boutaud, O; Shriner, A; Dawson, J H; Brash, A R; Gaffney, B J

    2001-02-20

    Coral allene oxide synthase (AOS), a hemoprotein with weak sequence homology to catalase, is the N-terminal domain of a naturally occurring fusion protein with an 8R-lipoxygenase. AOS converts 8R-hydroperoxyeicosatetraenoic acid to the corresponding allene oxide. The UV--visible absorption and magnetic circular dichroism spectra of ferric AOS and of its cyanide and azide complexes, and the electron paramagnetic resonance spectra of native AOS (high-spin, g = 6.56, 5.22, 2.00) and of its cyanide adduct (low-spin, g = 2.86, 2.24, 1.60) closely resemble the corresponding spectra of bovine liver catalase (BLC). These results provide strong evidence for tyrosinate ligation to the heme iron of AOS as has been established for catalases. On the other hand, the positive circular dichroism bands in the Soret region for all three derivatives of ferric AOS are almost the mirror image of those in catalase. In addition, the cyanide affinity of native AOS (K(d) = 10 mM at pH 7) is about 3 orders of magnitude lower than that of BLC. Thus, while these results conclusively support a common tyrosinate-ligated heme in AOS as in catalase, significant differences exist in the interaction between their respective heme prosthetic groups and protein environments, and in the access of small molecules to the heme iron. PMID:11329294

  16. Structure and Stability of Pentafluoroaniline and 4-Aminononafluorobiphenyl Radical Anions: Optically Detected Electron Paramagnetic Resonance, Time-Resolved Fluorescence, Time-Resolved Magnetic Field Effect, and Quantum Chemical Study.

    PubMed

    Borovkov, Vsevolod I; Beregovaya, Irina V; Shchegoleva, Lyudmila N; Blinkova, Svetlana V; Ovchinnikov, Dmitry A; Gurskaya, Larisa Yu; Shteingarts, Vitaly D; Bagryansky, Victor A; Molin, Yuriy N

    2015-08-01

    Radical anions (RAs) are the key intermediates of the selective hydrodefluorination of polyfluoroarenes. We used the techniques of optically detected electron paramagnetic resonance (OD EPR), time-resolved fluorescence, time-resolved magnetic field effect (TR MFE), and the density functional theory to study the possibility of RAs formation from 4-aminononafluorobiphenyl (1) and pentafluoroaniline (2) and estimate their lifetimes and decay channels. To our knowledge, both RAs have not been detected earlier. We have registered the OD EPR spectrum for relatively stable in nonpolar solutions 1(-•) but failed to register the spectra for 2(-•). However, we have managed to fix the 2(-•) by the TR MFE method and obtained its hyperfine coupling constants. The lifetime of 2(-•) was found to be only a few nanoseconds. The activation energy of its decay was estimated to be 3.6 ± 0.3 kcal/mol. According to the calculation results, the short lifetime of 2(-•) is due to the RA fast fragmentation with the F(-) elimination from ortho-position to the amine group. The calculated energy barrier, 3.2 kcal/mol, is close to the experimental value. The fragmentation of 2(-•) in a nonpolar solvent is possible due to the stabilization of the incipient F(-) anion by the binding with the amine group proton.

  17. Very high frequency electron paramagnetic resonance of 2,2,6,6-tetramethyl-1-piperidinyloxy in 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine liposomes: partitioning and molecular dynamics.

    PubMed Central

    Smirnov, A I; Smirnova, T I; Morse, P D

    1995-01-01

    Partitioning and molecular dynamics of 2,2,6,6,-tetramethylpiperedine-1-oxyl (TEMPO) nitroxide radicals in large unilamellar liposomes (LUV) composed from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine were investigated by using very high frequency electron paramagnetic resonance (EPR) spectroscopy. Experiments carried out at a microwave frequency of 94.3 GHz completely resolved the TEMPO EPR spectrum in the aqueous and hydrocarbon phases. An accurate computer simulation method combined with Levenberg-Marquardt optimization was used to analyze the TEMPO EPR spectra in both phases. Spectral parameters extracted from the simulations gave the actual partitioning of the TEMPO probe between the LUV hydrocarbon and aqueous phases and allowed analysis of picosecond rotational dynamics of the probe in the LUV hydrocarbon phase. In very high frequency EPR experiments, phase transitions in the LUV-TEMPO system were observed as sharp changes in both partitioning and rotational correlation times of the TEMPO probe. The phase transition temperatures (40.5 +/- 0.2 and 32.7 +/- 0.5 degrees C) are in agreement with previously reported differential scanning microcalorimetry data. Spectral line widths were analyzed by using existing theoretical expressions for motionally narrowed nitroxide spectra. It was found that the motion of the small, nearly spherical, TEMPO probe can be well described by anisotropic Brownian diffusion in isotropic media and is not restricted by the much larger hydrocarbon chains existing in ripple structure (P beta') or fluid bilayer structure (L alpha) phases. PMID:7647239

  18. Spin paramagnetic deformation of a neutron star

    NASA Astrophysics Data System (ADS)

    Suvorov, A. G.; Mastrano, A.; Melatos, A.

    2016-02-01

    Quantum mechanical corrections to the hydromagnetic force balance equation, derived from the microscopic Schrödinger-Pauli theory of quantum plasmas, modify the equilibrium structure and hence the mass quadrupole moment of a neutron star. It is shown here that the dominant effect - spin paramagnetism - is most significant in a magnetar, where one typically has μ _B|B|≳ k_B T_e, where μB is the Bohr magneton, B is the magnetic field, and Te is the electron temperature. The spin paramagnetic deformation of a non-barotropic magnetar with a linked poloidal-toroidal magnetic field is calculated to be up to ˜10 times greater than the deformation caused solely by the Lorentz force. It depends on the degree of Pauli blocking by conduction electrons and the propensity to form magnetic domains, processes which are incompletely modelled at magnetar field strengths. The star becomes more oblate, as the toroidal field component strengthens. The result implies that existing classical predictions underestimate the maximum strength of the gravitational wave signal from rapidly spinning magnetars at birth. Turning the argument around, future gravitational-wave upper limits of increasing sensitivity will place ever-stricter constraints on the physics of Pauli blocking and magnetic domain formation under magnetar conditions.

  19. Advanced analytical electron microscopy for alkali-ion batteries

    DOE PAGES

    Qian, Danna; Ma, Cheng; Meng, Ying Shirley; More, Karren; Chi, Miaofang

    2015-01-01

    Lithium-ion batteries are a leading candidate for electric vehicle and smart grid applications. However, further optimizations of the energy/power density, coulombic efficiency and cycle life are still needed, and this requires a thorough understanding of the dynamic evolution of each component and their synergistic behaviors during battery operation. With the capability of resolving the structure and chemistry at an atomic resolution, advanced analytical transmission electron microscopy (AEM) is an ideal technique for this task. The present review paper focuses on recent contributions of this important technique to the fundamental understanding of the electrochemical processes of battery materials. A detailed reviewmore » of both static (ex situ) and real-time (in situ) studies will be given, and issues that still need to be addressed will be discussed.« less

  20. Advanced analytical electron microscopy for alkali-ion batteries

    SciTech Connect

    Qian, Danna; Ma, Cheng; Meng, Ying Shirley; More, Karren; Chi, Miaofang

    2015-01-01

    Lithium-ion batteries are a leading candidate for electric vehicle and smart grid applications. However, further optimizations of the energy/power density, coulombic efficiency and cycle life are still needed, and this requires a thorough understanding of the dynamic evolution of each component and their synergistic behaviors during battery operation. With the capability of resolving the structure and chemistry at an atomic resolution, advanced analytical transmission electron microscopy (AEM) is an ideal technique for this task. The present review paper focuses on recent contributions of this important technique to the fundamental understanding of the electrochemical processes of battery materials. A detailed review of both static (ex situ) and real-time (in situ) studies will be given, and issues that still need to be addressed will be discussed.

  1. A Long-Lived Fe(III)-(Hydroperoxo) Intermediate in the Active H200C Variant of Homoprotocatechuate 2,3-Dioxygenase: Characterization by Mössbauer, Electron Paramagnetic Resonance, and Density Functional Theory Methods.

    PubMed

    Meier, Katlyn K; Rogers, Melanie S; Kovaleva, Elena G; Mbughuni, Michael M; Bominaar, Emile L; Lipscomb, John D; Münck, Eckard

    2015-11-01

    The extradiol-cleaving dioxygenase homoprotocatechuate 2,3-dioxygenase (HPCD) binds substrate homoprotocatechuate (HPCA) and O2 sequentially in adjacent ligand sites of the active site Fe(II). Kinetic and spectroscopic studies of HPCD have elucidated catalytic roles of several active site residues, including the crucial acid-base chemistry of His200. In the present study, reaction of the His200Cys (H200C) variant with native substrate HPCA resulted in a decrease in both kcat and the rate constants for the activation steps following O2 binding by >400 fold. The reaction proceeds to form the correct extradiol product. This slow reaction allowed a long-lived (t1/2 = 1.5 min) intermediate, H200C-HPCAInt1 (Int1), to be trapped. Mössbauer and parallel mode electron paramagnetic resonance (EPR) studies show that Int1 contains an S1 = 5/2 Fe(III) center coupled to an SR = 1/2 radical to give a ground state with total spin S = 2 (J > 40 cm(-1)) in Hexch = JŜ1·ŜR. Density functional theory (DFT) property calculations for structural models suggest that Int1 is a (HPCA semiquinone(•))Fe(III)(OOH) complex, in which OOH is protonated at the distal O and the substrate hydroxyls are deprotonated. By combining Mössbauer and EPR data of Int1 with DFT calculations, the orientations of the principal axes of the (57)Fe electric field gradient and the zero-field splitting tensors (D = 1.6 cm(-1), E/D = 0.05) were determined. This information was used to predict hyperfine splittings from bound (17)OOH. DFT reactivity analysis suggests that Int1 can evolve from a ferromagnetically coupled Fe(III)-superoxo precursor by an inner-sphere proton-coupled-electron-transfer process. Our spectroscopic and DFT results suggest that a ferric hydroperoxo species is capable of extradiol catalysis. PMID:26485328

  2. A study of C-13-enriched chemical vapor deposited diamond film by means of C-13 nuclear magnetic resonance, electron paramagnetic resonance, and dynamic nuclear polarization

    NASA Astrophysics Data System (ADS)

    Lock, Herman; Wind, Robert A.; Maciel, Gary E.; Johnson, Curtis E.

    1993-09-01

    The results are presented of a study, based on EPR and various NMR techniques, of the effect on the nature of CVD diamond films of the addition of O2 to the methane-hydrogen mixture used to produce the film. The addition of oxygen to the feed gas results in a reduction of the number of unpaired electron spins, roughly from 10 exp 18 spins/g up to 10 exp 17 spins/g. There is a small aromatic signal in the dynamic nuclear polarization (DNP)-cross polarization (CP)-magic angle spinning (MAS) C-13 spectrum and a small peak at 28 ppm in the 14 T DP-MAS C-13 spectrum for only the diamond film sample grown without O2 present in the feed gas. The combination of DNP and CP at 1.4 T enables one to obtain a useful DNP-CP-MAS C-13 spectrum, ostensibly probing only the surface and intergrain boundary regions, in a matter of hours.

  3. Enhancement of Paramagnetic Relaxation by Photoexcited Gold Nanorods

    PubMed Central

    Wen, Tao; Wamer, Wayne G.; Subczynski, Witold K.; Hou, Shuai; Wu, Xiaochun; Yin, Jun-Jie

    2016-01-01

    Electron spin resonance (ESR) spectroscopy was used to investigate the switchable, light-dependent effects of gold nanorods (GNRs) on paramagnetic properties of nitroxide spin probes. The photoexcited GNRs enhanced the spin-spin and spin-lattice relaxations of nitroxide spin probes. It was shown that molecular oxygen plays the key role in this process. Our results demonstrate that ESR is a powerful tool for investigating the events following photoexcitation of GNRs. The novel light-controlled effects observed for GNRs on paramagnetic properties and activities of surrounding molecules have a number of significant applications where oxygen sensing and oxygen activity is important. PMID:27071507

  4. Intrinsic electric dipole moments of paramagnetic atoms: rubidium and cesium.

    PubMed

    Nataraj, H S; Sahoo, B K; Das, B P; Mukherjee, D

    2008-07-18

    The electric dipole moment (EDM) of paramagnetic atoms is sensitive to the intrinsic EDM contribution from that of its constituent electrons and a scalar-pseudoscalar (S-PS) electron-nucleus interaction. The electron EDM and the S-PS contributions to the EDMs of these atoms scale as approximately Z;{3}. Thus, the heavy paramagnetic atoms will exhibit large EDM enhancement factors. However, the sizes of the couplings are so small that they are of interest of high precision atomic experiments. In this work we have computed the EDM enhancement factors of the ground states of Rb and Cs due to both the electron EDM and the S-PS EDM using the relativistic coupled-cluster theory. The importance of determining precise ab initio enhancement factors and experimental results of atomic EDMs in deducing a reliable limit on the electron EDM is emphasized.

  5. Axial ligand modulation of the electronic structures of binuclear copper sites: analysis of paramagnetic 1H NMR spectra of Met160Gln Cu(A).

    PubMed

    Fernández, C O; Cricco, J A; Slutter, C E; Richards, J H; Gray, H B; Vila, A J

    2001-11-28

    Cu(A) is an electron-transfer copper center present in heme-copper oxidases and N2O reductases. The center is a binuclear unit, with two cysteine ligands bridging the metal ions and two terminal histidine residues. A Met residue and a peptide carbonyl group are located on opposite sides of the Cu2S2 plane; these weaker ligands are fully conserved in all known Cu(A) sites. The Met160Gln mutant of the soluble subunit II of Thermus thermophilus ba3 oxidase has been studied by NMR spectroscopy. In its oxidized form, the binuclear copper is a fully delocalized mixed-valence pair, as are all natural Cu(A) centers. The faster nuclear relaxation in this mutant suggests that a low-lying excited state has shifted to higher energies compared to that of the wild-type protein. The introduction of the Gln residue alters the coordination mode of His114 but does not affect His157, thereby confirming the proposal that the axial ligand-to-copper distances influence the copper-His interactions (Robinson, H.; Ang, M. C.; Gao, Y. G.; Hay, M. T.; Lu, Y.; Wang, A. H. Biochemistry 1999, 38, 5677). Changes in the hyperfine coupling constants of the Cys beta-CH2 groups are attributed to minor geometrical changes that affect the Cu-S-C(beta)-H(beta) dihedral angles. These changes, in addition, shift the thermally accessible excited states, thus influencing the spectral position of the Cys beta-CH2 resonances. The Cu-Cys bonds are not substantially altered by the Cu-Gln160 interaction, in contrast to the situation found in the evolutionarily related blue copper proteins. It is possible that regulatory subunits in the mitochondrial oxidases fix the relative positions of thermally accessible Cu(A) excited states by tuning axial ligand interactions.

  6. Investigation of relativistic runaway electrons in electron cyclotron resonance heating discharges on Korea Superconducting Tokamak Advanced Research

    SciTech Connect

    Kang, C. S.; Lee, S. G.

    2014-07-15

    The behavior of relativistic runaway electrons during Electron Cyclotron Resonance Heating (ECRH) discharges is investigated in the Korea Superconducting Tokamak Advanced Research device. The effect of the ECRH on the runaway electron population is discussed. Observations on the generation of superthermal electrons during ECRH will be reported, which will be shown to be consistent with existing theory for the development of a superthermal electron avalanche during ECRH [A. Lazaros, Phys. Plasmas 8, 1263 (2001)].

  7. Effects of hydrostatic pressure and temperature on the electron paramagnetic resonance spectrum of off-centre Jahn Teller [CuF4F4]6- complexes in SrF2 crystal

    NASA Astrophysics Data System (ADS)

    Ulanov, V. A.; Krupski, M.; Hoffmann, S. K.; Zaripov, M. M.

    2003-02-01

    Pressure and temperature variations of the spin-Hamiltonian parameters and electron paramagnetic resonance (EPR) linewidths of non-central Jahn-Teller [CuF4F4]6- complexes in SrF2 crystal were studied by continuous-wave EPR. It was found that the static spin-Hamiltonian parameters, found at T = 85 K and at normal pressure (gparallel = 2.491, gbot = 2.083, aparallel = 360, abot = 26, Ax'' = 96, Ay'' = 99, Az'' = 403 and betaexp = 17°), are slightly changed with hydrostatic pressure and, at T = 85 K and P = 550 MPa, become equal to gparallel = 2.489, gbot = 2.083, aparallel = 348, abot = 27, Ax'' = 99, Ay'' = 102, Az'' = 406 and betaexp = 20° (a and A values in megahertz, x''-, y''-and z''-axes are eigenvectors of the super-hyperfine tensor A, betaexp is the experimental value of the angle between the C4 symmetry axis of the complex and the x''-axis). With increasing temperature the well-resolved EPR spectrum of the complex is transformed continuously into a single broad line both at normal pressure and at a hydrostatic pressure of 550 MPa. But in the first case the coalescence point corresponds to 220-230 K while in the second case it is 195-205 K. Treatment using the linear combination of atomic orbitals representation of molecular orbitals (LCAO MO) model was performed to establish some relations between variations of the spin-Hamiltonian parameters and pressure-induced changes in the molecular structure of the complex. To get some additional information about the molecular structure of the complex and variations of its structural parameters with pressure, treatment using the rigid-ion model was performed. Experimental and theoretical results are discussed in the framework of the Jahn-Teller model of the complex.

  8. Arsenic speciation in newberyite (MgHPO(4)·3H(2)O) determined by synchrotron X-ray absorption and electron paramagnetic resonance spectroscopies: implications for the fate of arsenic in green fertilizers.

    PubMed

    Lin, Jinru; Chen, Ning; Pan, Yuanming

    2014-06-17

    Newberyite (MgHPO4·3H2O), a biomineral and common constituent in guano deposits, is an important decomposition product of struvite that is an increasingly popular green fertilizer recovered from wastewaters. Two samples of newberyite containing 1099 and 25 ppm As have been obtained at pH = 6.4, by using Na2HAsO4·7H2O and NaAsO2 as the dopant, respectively (i.e., Synthesis 1 and Synthesis 2). Synchrotron arsenic K-edge X-ray absorption spectroscopic data of newberyite from Synthesis 1 show that As(5+) is dominant and has a local environment typical of the arsenate species. Single-crystal electron paramagnetic resonance (EPR) spectra of gamma-ray-irradiated newberyite from Synthesis 1 contain two arsenic-associated oxyradicals: [AsO3](2-) and [AsO2](2-) derived from As(5+) and As(3+), respectively, at the P site. Quantitative analyses of powder EPR spectra allow determinations of the As(5+) and As(3+) contents in newberyite from Synthesis 1 and Synthesis 2. Elevated concentrations of arsenic also occur in natural newberyite transformed from struvite in guano deposits and record the accumulation of this metalloid in the food chain. Therefore, newberyite, which sequesters As during crystallization and retains this metalloid during the transformation from struvite, can attenuate arsenic contamination from green fertilizers in moderately acidic soils. Also, the capacity for accommodating both As(5+) and As(3+) in the crystal lattice coupled with simple chemistry and easy crystallization at ambient conditions makes newberyite an attractive material for remediation of arsenic contamination in aqueous environments.

  9. Structural effects of insulin-loading into HII mesophases monitored by electron paramagnetic resonance (EPR), small angle X-ray spectroscopy (SAXS), and attenuated total reflection Fourier transform spectroscopy (ATR-FTIR).

    PubMed

    Mishraki, Tehila; Ottaviani, Maria Francesca; Shames, Alexander I; Aserin, Abraham; Garti, Nissim

    2011-06-30

    Insulin entrapment within a monoolein-based reverse hexagonal (H(II)) mesophase was investigated under temperature-dependent conditions at acidic (pH 3) and basic (pH 8) conditions. Studying the structure of the host H(II) system and the interactions of insulin under temperature-dependent conditions has great impact on the enhancement of its thermal stabilization and controlled release for the purposes of transdermal delivery. Small angle X-ray spectroscopy (SAXS) measurements show that pH variation and/or insulin entrapment preserve the hexagonal structure and do not influence the lattice parameter. Attenuated total reflection Fourier transform spectroscopy (ATR-FTIR) spectra indicate that, although insulin interacts with hydroxyl groups of GMO in the interface region, it is not affected by pH variations. Hence different microenvironments within the H(II) mesophase were monitored by a computer-aided electron paramagnetic resonance (EPR) analysis using 5-doxylstearic acid (5-DSA) as a pH-dependent probe. The microviscosity, micropolarity, order of systems, and distribution of the probes in different microenvironments were influenced by three factors: temperature, pH, and insulin solubilization. When the temperature is increased, microviscosity and order parameters decreased at both pH 3 and 8, presenting different decrease trends. It was found that, at pH 3, the protein perturbs the lipid structure while "pushing aside" the un-ionized 5-DSA probe to fit into the narrow water cylinders. At the interface region (pH 8), the probe was distributed in two differently structured environments that significantly modifies by increasing temperature. Insulin loading within the H(II) mesophase decreased the order and microviscosity of both the microenvironments and increased their micropolarity. Finally, the EPR analysis also provides information about the unfolding/denaturation of insulin within the channel at high temperatures.

  10. X-Band Electron Paramagnetic Resonance Comparison of Mononuclear Mn(IV)-oxo and Mn(IV)-hydroxo Complexes and Quantum Chemical Investigation of Mn(IV) Zero-Field Splitting.

    PubMed

    Leto, Domenick F; Massie, Allyssa A; Colmer, Hannah E; Jackson, Timothy A

    2016-04-01

    X-band electron paramagnetic resonance (EPR) spectroscopy was used to probe the ground-state electronic structures of mononuclear Mn(IV) complexes [Mn(IV)(OH)2(Me2EBC)](2+) and [Mn(IV)(O)(OH)(Me2EBC)](+). These compounds are known to effect C-H bond oxidation reactions by a hydrogen-atom transfer mechanism. They provide an ideal system for comparing Mn(IV)-hydroxo versus Mn(IV)-oxo motifs, as they differ by only a proton. Simulations of 5 K EPR data, along with analysis of variable-temperature EPR signal intensities, allowed for the estimation of ground-state zero-field splitting (ZFS) and (55)Mn hyperfine parameters for both complexes. From this analysis, it was concluded that the Mn(IV)-oxo complex [Mn(IV)(O)(OH)(Me2EBC)](+) has an axial ZFS parameter D (D = +1.2(0.4) cm(-1)) and rhombicity (E/D = 0.22(1)) perturbed relative to the Mn(IV)-hydroxo analogue [Mn(IV)(OH)2(Me2EBC)](2+) (|D| = 0.75(0.25) cm(-1); E/D = 0.15(2)), although the complexes have similar (55)Mn values (a = 7.7 and 7.5 mT, respectively). The ZFS parameters for [Mn(IV)(OH)2(Me2EBC)](2+) were compared with values obtained previously through variable-temperature, variable-field magnetic circular dichroism (VTVH MCD) experiments. While the VTVH MCD analysis can provide a reasonable estimate of the magnitude of D, the E/D values were poorly defined. Using the ZFS parameters reported for these complexes and five other mononuclear Mn(IV) complexes, we employed coupled-perturbed density functional theory (CP-DFT) and complete active space self-consistent field (CASSCF) calculations with second-order n-electron valence-state perturbation theory (NEVPT2) correction, to compare the ability of these two quantum chemical methods for reproducing experimental ZFS parameters for Mn(IV) centers. The CP-DFT approach was found to provide reasonably acceptable values for D, whereas the CASSCF/NEVPT2 method fared worse, considerably overestimating the magnitude of D in several cases. Both methods were poor in

  11. X-Band Electron Paramagnetic Resonance Comparison of Mononuclear Mn(IV)-oxo and Mn(IV)-hydroxo Complexes and Quantum Chemical Investigation of Mn(IV) Zero-Field Splitting.

    PubMed

    Leto, Domenick F; Massie, Allyssa A; Colmer, Hannah E; Jackson, Timothy A

    2016-04-01

    X-band electron paramagnetic resonance (EPR) spectroscopy was used to probe the ground-state electronic structures of mononuclear Mn(IV) complexes [Mn(IV)(OH)2(Me2EBC)](2+) and [Mn(IV)(O)(OH)(Me2EBC)](+). These compounds are known to effect C-H bond oxidation reactions by a hydrogen-atom transfer mechanism. They provide an ideal system for comparing Mn(IV)-hydroxo versus Mn(IV)-oxo motifs, as they differ by only a proton. Simulations of 5 K EPR data, along with analysis of variable-temperature EPR signal intensities, allowed for the estimation of ground-state zero-field splitting (ZFS) and (55)Mn hyperfine parameters for both complexes. From this analysis, it was concluded that the Mn(IV)-oxo complex [Mn(IV)(O)(OH)(Me2EBC)](+) has an axial ZFS parameter D (D = +1.2(0.4) cm(-1)) and rhombicity (E/D = 0.22(1)) perturbed relative to the Mn(IV)-hydroxo analogue [Mn(IV)(OH)2(Me2EBC)](2+) (|D| = 0.75(0.25) cm(-1); E/D = 0.15(2)), although the complexes have similar (55)Mn values (a = 7.7 and 7.5 mT, respectively). The ZFS parameters for [Mn(IV)(OH)2(Me2EBC)](2+) were compared with values obtained previously through variable-temperature, variable-field magnetic circular dichroism (VTVH MCD) experiments. While the VTVH MCD analysis can provide a reasonable estimate of the magnitude of D, the E/D values were poorly defined. Using the ZFS parameters reported for these complexes and five other mononuclear Mn(IV) complexes, we employed coupled-perturbed density functional theory (CP-DFT) and complete active space self-consistent field (CASSCF) calculations with second-order n-electron valence-state perturbation theory (NEVPT2) correction, to compare the ability of these two quantum chemical methods for reproducing experimental ZFS parameters for Mn(IV) centers. The CP-DFT approach was found to provide reasonably acceptable values for D, whereas the CASSCF/NEVPT2 method fared worse, considerably overestimating the magnitude of D in several cases. Both methods were poor in

  12. Barnett effect in paramagnetic states

    NASA Astrophysics Data System (ADS)

    Ono, Masao; Chudo, Hiroyuki; Harii, Kazuya; Okayasu, Satoru; Matsuo, Mamoru; Ieda, Jun'ichi; Takahashi, Ryo; Maekawa, Sadamichi; Saitoh, Eiji

    2015-11-01

    We report the observation of the Barnett effect in paramagnetic states by mechanically rotating gadolinium (Gd) metal with a rotational frequency of up to 1.5 kHz above the Curie temperature. An in situ magnetic measurement setup comprising a high-speed rotational system and a fluxgate magnetic sensor was developed for the measurement. Temperature dependence of the observed magnetization follows that of paramagnetic susceptibility, indicating that any emergent magnetic field is proportional to the rotational frequency and is independent of temperature. From the proportionality constant of the emergent field, the gyromagnetic ratio of Gd is calculated to be -29 ±5 GHz /T . This study revisits the primordial issue of magnetism with modern technologies to shed new light on the fundamental spin-rotation coupling.

  13. Paramagnetically induced gapful topological superconductors

    NASA Astrophysics Data System (ADS)

    Daido, Akito; Yanase, Youichi

    2016-08-01

    We propose a generic scenario for realizing gapful topological superconductors (TSCs) from gapless spin-singlet superconductors (SCs). Noncentrosymmetric nodal SCs in two dimensions are shown to be gapful under a Zeeman field, as a result of the cooperation of inversion-symmetry breaking and time-reversal-symmetry breaking. In particular, non-s -wave SCs acquire a large excitation gap. Such paramagnetically induced gapful SCs may be classified into TSCs in the symmetry class D specified by the Chern number. We show nontrivial Chern numbers over a wide parameter range for spin-singlet SCs. A variety of the paramagnetically induced gapful TSCs are demonstrated, including D +p -wave TSC, extended S +p -wave TSC, p +D +f -wave TSC, and s +P -wave TSC. Natural extension toward three-dimensional Weyl SCs is also discussed.

  14. Advanced Power Electronic Interfaces for Distributed Energy Systems Part 1: Systems and Topologies

    SciTech Connect

    Kramer, W.; Chakraborty, S.; Kroposki, B.; Thomas, H.

    2008-03-01

    This report summarizes power electronic interfaces for DE applications and the topologies needed for advanced power electronic interfaces. It focuses on photovoltaic, wind, microturbine, fuel cell, internal combustion engine, battery storage, and flywheel storage systems.

  15. Development and Applications of Advanced Electronic Structure Methods

    NASA Astrophysics Data System (ADS)

    Bell, Franziska

    This dissertation contributes to three different areas in electronic structure theory. The first part of this thesis advances the fundamentals of orbital active spaces. Orbital active spaces are not only essential in multi-reference approaches, but have also become of interest in single-reference methods as they allow otherwise intractably large systems to be studied. However, despite their great importance, the optimal choice and, more importantly, their physical significance are still not fully understood. In order to address this problem, we studied the higher-order singular value decomposition (HOSVD) in the context of electronic structure methods. We were able to gain a physical understanding of the resulting orbitals and proved a connection to unrelaxed natural orbitals in the case of Moller-Plesset perturbation theory to second order (MP2). In the quest to find the optimal choice of the active space, we proposed a HOSVD for energy-weighted integrals, which yielded the fastest convergence in MP2 correlation energy for small- to medium-sized active spaces to date, and is also potentially transferable to coupled-cluster theory. In the second part, we studied monomeric and dimeric glycerol radical cations and their photo-induced dissociation in collaboration with Prof. Leone and his group. Understanding the mechanistic details involved in these processes are essential for further studies on the combustion of glycerol and carbohydrates. To our surprise, we found that in most cases, the experimentally observed appearance energies arise from the separation of product fragments from one another rather than rearrangement to products. The final chapters of this work focus on the development, assessment, and application of the spin-flip method, which is a single-reference approach, but capable of describing multi-reference problems. Systems exhibiting multi-reference character, which arises from the (near-) degeneracy of orbital energies, are amongst the most

  16. Using advanced electron microscopy for the characterization of catalytic materials

    NASA Astrophysics Data System (ADS)

    Pyrz, William D.

    Catalysis will continue to be vitally important to the advancement and sustainability of industrialized societies. Unfortunately, the petroleum-based resources that currently fuel the energy and consumer product needs of an advancing society are becoming increasingly difficult and expensive to extract as supplies diminish and the quality of sources degrade. Therefore, the development of sustainable energy sources and the improvement of the carbon efficiency of existing chemical processes are critical. Further challenges require that these initiatives are accomplished in an environmentally friendly fashion since the effects of carbon-based emissions are proving to be a serious threat to global climate stability. In this dissertation, materials being developed for sustainable energy and process improvement initiatives are studied. Our approach is to use materials characterization, namely advanced electron microscopy, to analyze the targeted systems at the nano- or Angstrom-scale with the goal of developing useful relationships between structure, composition, crystalline order, morphology, and catalytic performance. One area of interest is the complex Mo-V-M-O (M=Te, Sb, Ta, Nb) oxide system currently being developed for the selective oxidation/ammoxidation of propane to acrylic acid or acrylonitrile, respectively. Currently, the production of acrylic acid and acrylonitrile rely on propylene-based processes, yet significant cost savings could be realized if the olefin-based feeds could be replaced by paraffin-based ones. The major challenge preventing this feedstock replacement is the development of a suitable paraffin-activating catalyst. Currently, the best candidate is the Mo-V-Nb-Te-O complex oxide catalyst that is composed of two majority phases that are commonly referred to as M1 and M2. However, there is a limited understanding of the roles of each component with respect to how they contribute to catalyst stability and the reaction mechanism. Aberration

  17. In vivo proton-electron double-resonance imaging of extracellular tumor pH using an advanced nitroxide probe.

    PubMed

    Samouilov, Alexandre; Efimova, Olga V; Bobko, Andrey A; Sun, Ziqi; Petryakov, Sergey; Eubank, Timothy D; Trofimov, Dmitrii G; Kirilyuk, Igor A; Grigor'ev, Igor A; Takahashi, Wataru; Zweier, Jay L; Khramtsov, Valery V

    2014-01-21

    A variable radio frequency proton-electron double-resonance imaging (VRF PEDRI) approach for pH mapping of aqueous samples has been recently developed (Efimova et al. J. Magn. Reson. 2011, 209, 227-232). A pH map is extracted from two PEDRI acquisitions performed at electron paramagnetic resonance (EPR) frequencies of protonated and unprotonated forms of a pH-sensitive probe. To translate VRF PEDRI to an in vivo setting, an advanced pH probe was synthesized. Probe deuteration resulted in a narrow spectral line of 1.2 G compared to a nondeuterated analogue line width of 2.1 G allowing for an increase of Overhauser enhancements and reduction in rf power deposition. Binding of the probe to the cell-impermeable tripeptide, glutathione (GSH), allows for targeting to extracellular tissue space for monitoring extracellular tumor acidosis, a prognostic factor in tumor pathophysiology. The probe demonstrated pH sensitivity in the 5.8-7.8 range, optimum for measurement of acidic extracellular tumor pH (pH(e)). In vivo VRF PEDRI was performed on Met-1 tumor-bearing mice. Compared to normal mammary glands with a neutral mean pH(e) (7.1 ± 0.1), we observed broader pH distribution with acidic mean pH(e) (6.8 ± 0.1) in tumor tissue. In summary, VRF PEDRI in combination with a newly developed pH probe provides an analytical approach for spatially resolved noninvasive pHe monitoring, in vivo.

  18. In vivo proton-electron double-resonance imaging of extracellular tumor pH using an advanced nitroxide probe.

    PubMed

    Samouilov, Alexandre; Efimova, Olga V; Bobko, Andrey A; Sun, Ziqi; Petryakov, Sergey; Eubank, Timothy D; Trofimov, Dmitrii G; Kirilyuk, Igor A; Grigor'ev, Igor A; Takahashi, Wataru; Zweier, Jay L; Khramtsov, Valery V

    2014-01-21

    A variable radio frequency proton-electron double-resonance imaging (VRF PEDRI) approach for pH mapping of aqueous samples has been recently developed (Efimova et al. J. Magn. Reson. 2011, 209, 227-232). A pH map is extracted from two PEDRI acquisitions performed at electron paramagnetic resonance (EPR) frequencies of protonated and unprotonated forms of a pH-sensitive probe. To translate VRF PEDRI to an in vivo setting, an advanced pH probe was synthesized. Probe deuteration resulted in a narrow spectral line of 1.2 G compared to a nondeuterated analogue line width of 2.1 G allowing for an increase of Overhauser enhancements and reduction in rf power deposition. Binding of the probe to the cell-impermeable tripeptide, glutathione (GSH), allows for targeting to extracellular tissue space for monitoring extracellular tumor acidosis, a prognostic factor in tumor pathophysiology. The probe demonstrated pH sensitivity in the 5.8-7.8 range, optimum for measurement of acidic extracellular tumor pH (pH(e)). In vivo VRF PEDRI was performed on Met-1 tumor-bearing mice. Compared to normal mammary glands with a neutral mean pH(e) (7.1 ± 0.1), we observed broader pH distribution with acidic mean pH(e) (6.8 ± 0.1) in tumor tissue. In summary, VRF PEDRI in combination with a newly developed pH probe provides an analytical approach for spatially resolved noninvasive pHe monitoring, in vivo. PMID:24372284

  19. Magnetic resonance studies of isotopically labeled paramagnetic proteins: (2FE-2S) ferredoxins

    SciTech Connect

    Cheng, H.; Xia, B.; Chae, Y.K.; Westler, W.M.; Markley, J.L.

    1994-12-01

    Recent developments in NMR spectroscopy, especially multidimensional, multinuclear NMR techniques, have made NMR the most versatile tool available for studying protein structure and function in solution. Unlike diamagnetic proteins, paramagnetic proteins contain centers with unpaired electrons. These unpaired electrons interact with magnetic nuclei either through chemical bonds by a contact mechanism or through space by a pseudocontact mechanism. Such interactions make the acquisition and analysis of NMR spectra of paramagnetic proteins more challenging than those of diamagnetic proteins. Some NMR signals from paramagnetic proteins are shifted outside the chemical shift region characteristic of diamagnetic proteins; these {open_quotes}hyperfine-shifted{close_quotes} resonances originate from nuclei that interact with unpaired electrons from the paramagnetic center. The large chemical shift dispersion in spectra of paramagnetic proteins makes it difficult to excite the entire spectral window and leads to distortions in the baseline. Interactions with paramagnetic centers shorten T{sub 1} and T{sub 2} relaxation times of nuclei; the consequences are line broadening and lower spectral sensitivity. Scalar (through bond) and dipolar (through space) interactions between pairs of nuclei are what give rise to crosspeak signals in multi-dimensional NMR spectra of small diamagnetic proteins. When such interactions involve a nucleus that is strongly relaxed by interaction with a paramagnetic center, specialized methods may be needed for its detection or it may be completely undetectable by present nD NMR methods.

  20. Paramagnetic Meissner effect in Nb

    NASA Astrophysics Data System (ADS)

    Kostić, P.; Veal, B.; Paulikas, A. P.; Welp, U.; Todt, V. R.; Gu, C.; Geiser, U.; Williams, J. M.; Carlson, K. D.; Klemm, R. A.

    1996-01-01

    The paramagnetic Meissner effect (PME), or Wohlleben effect, in which the field-cooled magnetization of superconducting samples is paramagnetic below Tc, has been reported to occur in some samples of a variety of high-Tc cuprate superconductors. It has been proposed that the effect arose in granular hole-doped cuprates from current loops with π phase shifts of the superconducting order parameter at some grain-boundary junctions. It is argued that such behavior would be expected to occur in a d-wave superconductor, but not in a conventional s-wave superconductor. To test this hypothesis, we have searched for the occurrence of the effect in Nb, and have confirmed a recent report by Minhaj et al. of its occurrence in some Nb samples. For these studies, the effects of stray fields and field gradients in the measurement volume of the superconducting quantum interference device magnetometer have been carefully considered to rule out the possibility that measurement artifacts might be responsible for the apparent paramagnetic behavior in Nb. The M(T) and M(H) curves obtained in Nb samples that show the PME also show remarkably strong resemblance to those curves reported for the cuprate materials exhibiting the PME. Evidence is presented that the effect arises from inhomogeneously trapped flux, and is strongly influenced by sample geometry and surface effects. These results suggest that, for the effect to be observable, Tc on the sample surface must be different from the bulk Tc. The occurrence of the PME in Nb strongly suggests that the observation of this effect is unrelated to d-wave superconductivity.

  1. Electron Precipitation at Mars: Advancing Our Understanding with MAVEN

    NASA Astrophysics Data System (ADS)

    Al Noori, H.; Lillis, R. J.; Fillingim, M. O.

    2015-12-01

    Electrons from the solar wind enter the Martian upper atmosphere from space in a process known as electron precipitation. These electrons are confined to move along magnetic field lines and, when those field lines intersect the atmosphere, the electrons collide with atmospheric neutral particles, resulting in heating, dissociation, ionization and excitation of those neutrals. Electron precipitation is an important source of energy input to the Mars upper atmosphere, and is typically the dominant source on the nightside. Past observations from Mars Global Surveyor have characterized patterns of electron precipitation, but only at ~400 km and ~2 AM local time. The MAVEN mission and in particular the SWEA instrument, provides an opportunity to study the distribution of suprathermal electrons in near-Mars space, over a range of altitudes from 120-6000 km and at a range of local times. We will present preliminary observations of flux patterns of these electrons.

  2. Electron paramagnetic resonance line shifts and line shape changes due to heisenberg spin exchange and dipole-dipole interactions of nitroxide free radicals in liquids 8. Further experimental and theoretical efforts to separate the effects of the two interactions.

    PubMed

    Peric, Mirna; Bales, Barney L; Peric, Miroslav

    2012-03-22

    The work in part 6 of this series (J. Phys. Chem. A 2009, 113, 4930), addressing the task of separating the effects of Heisenberg spin exchange (HSE) and dipole-dipole interactions (DD) on electron paramagnetic resonance (EPR) spectra of nitroxide spin probes in solution, is extended experimentally and theoretically. Comprehensive measurements of perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDT) in squalane, a viscous alkane, paying special attention to lower temperatures and lower concentrations, were carried out in an attempt to focus on DD, the lesser understood of the two interactions. Theoretically, the analysis has been extended to include the recent comprehensive treatment by Salikhov (Appl. Magn. Reson. 2010, 38, 237). In dilute solutions, both interactions (1) introduce a dispersion component, (2) broaden the lines, and (3) shift the lines. DD introduces a dispersion component proportional to the concentration and of opposite sign to that of HSE. Equations relating the EPR spectral parameters to the rate constants due to HSE and DD have been derived. By employing nonlinear least-squares fitting of theoretical spectra to a simple analytical function and the proposed equations, the contributions of the two interactions to items 1-3 may be quantified and compared with the same parameters obtained by fitting experimental spectra. This comparison supports the theory in its broad predictions; however, at low temperatures, the DD contribution to the experimental dispersion amplitude does not increase linearly with concentration. We are unable to deduce whether this discrepancy is due to inadequate analysis of the experimental data or an incomplete theory. A new key aspect of the more comprehensive theory is that there is enough information in the experimental spectra to find items 1-3 due to both interactions; however, in principle, appeal must be made to a model of molecular diffusion to separate the two. The permanent diffusion model is used to

  3. High-frequency electron paramagnetic resonance analysis of the oxidation state and local structure of Ni and Mn ions in Ni,Mn-codoped LiCoO(2).

    PubMed

    Stoyanova, R; Barra, A-L; Yoncheva, M; Zhecheva, E; Shinova, E; Tzvetkova, P; Simova, S

    2010-02-15

    High-frequency electron paramagnetic resonance (HF-EPR) spectroscopy was employed to examine the oxidation state and local structure of Ni and Mn ions in Ni,Mn-codoped LiCoO(2). The assignment of EPR signals was based on Mg,Mn-codoped LiCoO(2) and Ni-doped LiCoO(2) used as Mn(4+) and low-spin Ni(3+) EPR references. Complementary information on the oxidation state of transition-metal ions was obtained by solid-state (6,7)Li NMR spectroscopy. For slightly doped oxides (LiCo(1-x)Ni(x)Mn(x)O(2) with x < 0.05), nickel and manganese substitute for cobalt in the CoO(2) layers and are stabilized as Ni(3+) and Mn(4+) ions. The local structure of Mn(4+) ions was determined by modeling of the axial zero-field-splitting parameter in the framework of the Newman superposition model. It has been found that the local trigonal distortion around Mn(4+) is smaller in comparison with that of the host site. To achieve a local compensation of Mn(4+) charge, several defect models are discussed. With an increase in the total dopant content (LiCo(1-x)Ni(x)Mn(x)O(2) and 0.05

  4. Advanced Power Electronics Interfaces for Distributed Energy Workshop Summary: August 24, 2006, Sacramento, California

    SciTech Connect

    Treanton, B.; Palomo, J.; Kroposki, B.; Thomas, H.

    2006-10-01

    The Advanced Power Electronics Interfaces for Distributed Energy Workshop, sponsored by the California Energy Commission Public Interest Energy Research program and organized by the National Renewable Energy Laboratory, was held Aug. 24, 2006, in Sacramento, Calif. The workshop provided a forum for industry stakeholders to share their knowledge and experience about technologies, manufacturing approaches, markets, and issues in power electronics for a range of distributed energy resources. It focused on the development of advanced power electronic interfaces for distributed energy applications and included discussions of modular power electronics, component manufacturing, and power electronic applications.

  5. Finite pulse effects in CPMG pulse trains on paramagnetic materials.

    PubMed

    Leskes, Michal; Grey, Clare P

    2015-09-14

    The Carr-Purcell-Meiboom-Gill (CPMG) sequence is commonly used in high resolution NMR spectroscopy and in magnetic resonance imaging for the measurement of transverse relaxation in systems that are subject to diffusion in internal or external gradients and is superior to the Hahn echo measurement, which is more sensitive to diffusion effects. Similarly, it can potentially be used to study dynamic processes in electrode materials for lithium ion batteries. Here we compare the (7)Li signal decay curves obtained with the CPMG and Hahn echo sequences under static conditions (i.e., in the absence of magic angle spinning) in paramagnetic materials with varying transition metal ion concentrations. Our results indicate that under CPMG pulse trains the lifetime of the (7)Li signal is substantially extended and is correlated with the strength of the electron-nuclear interaction. Numerical simulations and analytical calculations using Floquet theory suggest that the combination of large interactions and a train of finite pulses, results in a spin locking effect which significantly slows the signal's decay. While these effects complicate the interpretation of CPMG-based investigations of diffusion and chemical exchange in paramagnetic materials, they may provide a useful approach to extend the signal's lifetime in these often fast relaxing systems, enabling the use of correlation experiments. Furthermore, these results highlight the importance of developing a deeper understanding of the effects of the large paramagnetic interactions during multiple pulse experiments in order to extend the experimental arsenal available for static and in situ NMR investigations of paramagnetic materials.

  6. Photodarkening and paramagnetism in ultraviolet exposed lead lanthanum zirconate ceramics

    NASA Astrophysics Data System (ADS)

    Seager, C. H.; Warren, W. L.

    1993-06-01

    Electron paramagnetic resonance (EPR) and photothermal deflection spectroscopy (PDS) have been utilized to characterize samples of lead lanthanum zirconate titanate (PLZT) ceramics before and after ultraviolet (uv) irradiation. We find a variety of EPR resonances in the unirradiated samples, including those attributable to Cu+2, Fe+3, Pb+3, and Ti+3 ions. The dark optical absorption spectra show broad, exponential subgap absorption tails which increase in magnitude with decreasing grain size. In addition, some of the larger grain ceramics show a prominent absorption enhancement which seems to correlate well with the density of Ti+3 centers. During and after uv illumination with light near the PLZT band gap, substantial increases are seen in the density of paramagnetic Ti+3 and Pb+3 ions, and a broad absorption peak appears at ˜2.6 eV. The spatial distribution of the induced absorption correlates well with the location of the absorbed uv, suggesting that photoproduced carrier pairs are trapped at Ti+4 and Pb+2 ions producing the observed paramagnetism. The Ti+3 EPR spectra can be successfully fit using the crystal-field-splitting parameters derived from the PDS data. We also observe that both the paramagnetism and the induced absorption are readily bleached by light absorbed in the spectral region where the photoinduced peak is located. We suggest that this effect is due to photoionization of the localized charges.

  7. 19 CFR 123.91 - Electronic information for rail cargo required in advance of arrival.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 19 Customs Duties 1 2013-04-01 2013-04-01 false Electronic information for rail cargo required in... Cargo Arriving by Rail or Truck § 123.91 Electronic information for rail cargo required in advance of..., Customs and Border Protection (CBP) must electronically receive from the rail carrier certain...

  8. 19 CFR 123.91 - Electronic information for rail cargo required in advance of arrival.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 19 Customs Duties 1 2012-04-01 2012-04-01 false Electronic information for rail cargo required in... Cargo Arriving by Rail or Truck § 123.91 Electronic information for rail cargo required in advance of..., Customs and Border Protection (CBP) must electronically receive from the rail carrier certain...

  9. 19 CFR 123.91 - Electronic information for rail cargo required in advance of arrival.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 1 2011-04-01 2011-04-01 false Electronic information for rail cargo required in... Cargo Arriving by Rail or Truck § 123.91 Electronic information for rail cargo required in advance of..., Customs and Border Protection (CBP) must electronically receive from the rail carrier certain...

  10. The World as Viewed by and with Unpaired Electrons

    PubMed Central

    Eaton, Sandra S.; Eaton, Gareth R.

    2012-01-01

    Recent advances in electron paramagnetic resonance (EPR) include capabilities for applications to areas as diverse as archeology, beer shelf life, biological structure, dosimetry, in vivo imaging, molecular magnets, and quantum computing. Enabling technologies include multifrequency continuous wave, pulsed, and rapid scan EPR. Interpretation is enhanced by increasingly powerful computational models. PMID:22975244

  11. Hyperfine Structure and Exchange Narrowing of Paramagnetic Resonance

    DOE R&D Accomplishments Database

    Townes, C. H.; Turkevich, J.

    1950-01-01

    Discussion of electronic paramagnetic resonance for the free radical á, á-diphenyl â-picryl hydrazyl as observed by its effect on the transmission of microwave through a TE{sub 01} cavity with a small amount of the free radical placed approximately on the axis of the cavity; the half-width of this resonance at half maximum absorption was 1.45 oersteds.

  12. Electronic Mentoring: Issues To Advance Research and Practice.

    ERIC Educational Resources Information Center

    Single, Peg Boyle; Muller, Carol B.

    E-mentoring is the merger of mentoring with electronic communications and has been termed telementoring, cybermentoring, or virtual mentoring. By leveraging the growth in information technology, electronic mentoring provides opportunities for mentoring prohibited by face-to-face mentoring programs. Yet, the ease with which e-mentoring programs can…

  13. Novel Pauli-paramagnetic quantum phase in a Mott insulator.

    PubMed

    Watanabe, D; Yamashita, M; Tonegawa, S; Oshima, Y; Yamamoto, H M; Kato, R; Sheikin, I; Behnia, K; Terashima, T; Uji, S; Shibauchi, T; Matsuda, Y

    2012-01-01

    In Mott insulators, the strong electron-electron Coulomb repulsion localizes electrons. In dimensions greater than one, their spins are usually ordered antiferromagnetically at low temperatures. Geometrical frustrations can destroy this long-range order, leading to exotic quantum spin liquid states. However, their magnetic ground states have been a long-standing mystery. Here we show that a quantum spin liquid state in the organic Mott insulator EtMe(3)Sb[Pd(dmit)(2)](2) (where Et is C(2)H(5)-, Me is CH(3)-, and dmit is 1,3-dithiole-2-thione-4,5-dithiolate) with two-dimensional triangular lattice has Pauli-paramagnetic-like low-energy excitations, which are a hallmark of itinerant fermions. Our torque magnetometry down to low temperatures (30 mK) up to high fields (32 T) reveals distinct residual paramagnetic susceptibility comparable to that in a half-filled two-dimensional metal, demonstrating the magnetically gapless nature of the ground state. Moreover, our results are robust against deuteration, pointing toward the emergence of an extended 'quantum critical phase', in which low-energy spin excitations behave as in paramagnetic metals with Fermi surface, despite the frozen charge degree of freedom.

  14. Advanced applications of reduced density matrices in electronic structure theory

    NASA Astrophysics Data System (ADS)

    Rothman, Adam Eric

    This dissertation describes several applications of reduced density matrices (RDMs) in electronic structure theory. RDM methods are a valuable addition to the library of electronic structure theories because they reduce a many-electron problem to the space of just two electrons without approximation. New theoretical and computational avenues enabled by the two-electron RDM (2-RDM) have already shown substantial progress in calculating atomic and molecular energies and properties with an eye toward predictive chemistry. More than simply accurate calculations, RDM methods entail a paradigm shift in quantum chemistry. While one-electron approaches are conceptually easy to understand, the importance of the 2-RDM quantifies the centrality of a two-body framework. The 2-RDM facilitates a two-electron interpretation of quantum mechanics that will undoubtedly lead to a greater understanding of electron correlation. Two applications presented in the dissertation center around near-exact evaluation of the 2-RDM in chemical systems without the many-electron wave function, but approach the problem from different angles. The first applies variational 2-RDM theory to a model quantum dot; the second attempts non-variational determination of the 2-RDM in open-shell atomic and molecular systems using an extension of the anti-Hermitian contracted Schrodinger equation (ACSE). An example reaction is presented to demonstrate how energies computed with the 2-RDM can facilitate an understanding of chemical reactivity. A third application uses the one-electron RDM (1-RDM) as a tool for understanding molecular conductivity. In this case, the 1-RDM is valuable because it integrates out many extraneous degrees of freedom from metal baths, simplifying the electron transport problem but retaining enough information to predict the dependence of current on applied voltage. The results are competitive with other conductivity theories, including a dominant scattering-based understanding, but

  15. Magnetic flocculation of paramagnetic particles

    SciTech Connect

    Tsouris, C.; Scott, T.C.

    1994-09-01

    An experimental apparatus has been assembled for the flocculation study of paramagnetic particles under the influence of a strong magnetic field. A magnetic field of strength up to 6 T is generated by a cryogenic magnet operating near liquid helium temperatures. Experimental information is obtained from fluctuation and intensity measurements of light passing through a particle suspension located in a uniform magnetic field. Particle flocculation is described by a Brownian flocculation model in which hydrodynamic, van der Waals, double-layer, and magnetic forces are incorporated for the estimation of the particle flocculation rate. A population-balance model is employed in conjunction with the flocculation model to predict the evolution of the particle size and composition or magnetic susceptibility with time. The effects of magnetic-field strength, magnetic susceptibility of the particles, particle size, and zeta potential are investigated. Results show that particle size and magnetic susceptibility each play an important role in the selective flocculation of particles of different properties.

  16. 19 CFR 103.31a - Advance electronic information for air, truck, and rail cargo; Importer Security Filing...

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 1 2010-04-01 2010-04-01 false Advance electronic information for air, truck, and... AVAILABILITY OF INFORMATION Other Information Subject to Restricted Access § 103.31a Advance electronic... following types of advance electronic information are per se exempt from disclosure under §...

  17. High-resolution electron microscopy of advanced materials

    SciTech Connect

    Mitchell, T.E.; Kung, H.H.; Sickafus, K.E.; Gray, G.T. III; Field, R.D.; Smith, J.F.

    1997-11-01

    This final report chronicles a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The High-Resolution Electron Microscopy Facility has doubled in size and tripled in quality since the beginning of the three-year period. The facility now includes a field-emission scanning electron microscope, a 100 kV field-emission scanning transmission electron microscope (FE-STEM), a 300 kV field-emission high-resolution transmission electron microscope (FE-HRTEM), and a 300 kV analytical transmission electron microscope. A new orientation imaging microscope is being installed. X-ray energy dispersive spectrometers for chemical analysis are available on all four microscopes; parallel electron energy loss spectrometers are operational on the FE-STEM and FE-HRTEM. These systems enable evaluation of local atomic bonding, as well as chemical composition in nanometer-scale regions. The FE-HRTEM has a point-to-point resolution of 1.6 {angstrom}, but the resolution can be pushed to its information limit of 1 {angstrom} by computer reconstruction of a focal series of images. HRTEM has been used to image the atomic structure of defects such as dislocations, grain boundaries, and interfaces in a variety of materials from superconductors and ferroelectrics to structural ceramics and intermetallics.

  18. Electron Beam Transport in Advanced Plasma Wave Accelerators

    SciTech Connect

    Williams, Ronald L

    2013-01-31

    The primary goal of this grant was to develop a diagnostic for relativistic plasma wave accelerators based on injecting a low energy electron beam (5-50keV) perpendicular to the plasma wave and observing the distortion of the electron beam's cross section due to the plasma wave's electrostatic fields. The amount of distortion would be proportional to the plasma wave amplitude, and is the basis for the diagnostic. The beat-wave scheme for producing plasma waves, using two CO2 laser beam, was modeled using a leap-frog integration scheme to solve the equations of motion. Single electron trajectories and corresponding phase space diagrams were generated in order to study and understand the details of the interaction dynamics. The electron beam was simulated by combining thousands of single electrons, whose initial positions and momenta were selected by random number generators. The model was extended by including the interactions of the electrons with the CO2 laser fields of the beat wave, superimposed with the plasma wave fields. The results of the model were used to guide the design and construction of a small laboratory experiment that may be used to test the diagnostic idea.

  19. Development of advanced electron holographic techniques and application to industrial materials and devices.

    PubMed

    Yamamoto, Kazuo; Hirayama, Tsukasa; Tanji, Takayoshi

    2013-06-01

    The development of a transmission electron microscope equipped with a field emission gun paved the way for electron holography to be put to practical use in various fields. In this paper, we review three advanced electron holography techniques: on-line real-time electron holography, three-dimensional (3D) tomographic holography and phase-shifting electron holography, which are becoming important techniques for materials science and device engineering. We also describe some applications of electron holography to the analysis of industrial materials and devices: GaAs compound semiconductors, solid oxide fuel cells and all-solid-state lithium ion batteries.

  20. Development and characterization of advanced electron beam resists

    NASA Astrophysics Data System (ADS)

    Agrawal, Ankur

    Over the past twenty years, the amount of research and development work for electron beam resists has seriously lagged that performed for optical resists. This has been due mainly to the relatively low volume use of electron beam lithography for production purposes. However, as electron beam lithography is now becoming the primary solution for achieving future critical dimension requirements in mask making and appears to be a promising NGL technology, interest in electron beam resist development has increased in recent years. The primary issue in electron beam resist design centers around finding a single resist system that combines the required sensitivity and etch resistance that is needed to enable high volume production. In this work, the primary goal was to explore the development of a novel two-component non-chemically amplified electron beam resist material for high keV (>10 keV) patterning for mask-making with: (1) high contrast, (2) high sensitivity, (3) high resolution, and, (4) high etch resistance. Poly (2-methyl-1-pentene co 2-ethoxyethyl-methallyl ether sulfone) was used as a polymeric e-beam sensitive material conjunction with a series of commercial novolac resins to formulate electron beam resists. These two-component resists have been termed sulfone-novolac system (SNS) resists. The approach used in this project is to develop a suite of experimental tools and simulation models that can be used to aid in the rational design, formulation, and characterization of new electron beam resists. The main tasks that have been addressed are: (1) development of the electron beam resist characterization tool set, (2) understanding the fundamental material behavior of a non-chemically amplified polysulfone-novolac (SNS) e-beam resist for next generation mask making, (3) lithographic process development and optimization for the SNS resists, (4) evaluation of the lithographic performance of the SNS resists using the optimized processing conditions, and (5) develop

  1. Electron Paramagnetic Resonance Studies of Single Crystals of Manganese Ion-Doped Ammonium Sulfate, Gadolinium Ion-Doped Ammonium Praseodymium SULFATE.WATER, Vanadium Oxide Ion-Doped M Ammonium SULFATE.WATER

    NASA Astrophysics Data System (ADS)

    Sun, Jiansheng

    Detailed X-band electron paramagnetic resonance (EPR) measurements on single crystals of Mn^ {2+}-doped (NH_4)_2 SO_4, Gd^ {3+}-doped NH_4Pr(SO _4)_2cdot4H _2O, VO^{2+} -doped M(NH_4)_2(SO _4)_2cdot6H_2 O (M = Cd, Co, Mg, Fe, Zn) and Mg(ND_4) _2(SO_4)_2cdot 6D_2O, and Cu^ {2+}-doped MNa_2(SO _4)_2cdot4H _2O (M = Mg, Co) are made at variable temperatures. The spin-Hamiltonian parameters for Mn^{2+ }, Gd^{3+}, VO^{2+} and Cu ^{2+} ions are evaluated using a least-squares-fitting procedure. The positions and local symmetries of the impurity ions in these hosts have been well deduced. The ferroelectric transition in (NH_4) _2SO_4 has been extensively studied via the splittings of Mn^{2+ } EPR lines, leading to the determination of the critical exponent beta. The existence of two inequivalent sublattices in the (NH _4)_2SO_4 crystal is confirmed. Temperature variation of Gd^{3+ } EPR spectra reveal two first-order phase transitions in the NH_4Pr(SO _4)_2cdot4H_2 O crystal. The host-ion spin-lattice relaxation (SLR) times (tau) of Pr^ {3+} have been estimated via the EPR linewidths of Gd^{3+} impurity ions using an appropriate expression. The predominant processes of SLR of Pr^{3+} host -ions have been deduced. The superhyperfine structures of VO^ {2+} EPR spectra in the hydrated Tutton -salt hosts M(NH_4)_2(SO _4)_2cdot6H_2 O have been well explained by comparison with the VO^{2+} EPR spectra in the deuterated host crystal Mg(ND_4)_2 (SO_4)_2cdot6D _2O. Using the VO^ {2+} EPR and optical-absorption spectra, the bonding coefficients of the (VO(H_2 O)_5]^{2+ } complex have been estimated. The systematics of EPR of the VO^{2+} ion in this series of Tutton salts is analyzed. The impurity-host exchange-interaction constant of VO^{2+}-Fe ^{2+} pair is determined in the Fe(NH_4)_2(SO_4) _2cdot6H_2O host, using the g-shift due to the exchange interaction and the shape of the crystal at liquid-helium temperature. The tau values of Fe^ {2+} and Co^{2+} in the Fe(NH_4)_2(SO _4

  2. Characterization of the manganese O2-evolving complex and the iron-quinone acceptor complex in photosystem II from a thermophilic cyanobacterium by electron paramagnetic resonance and X-ray absorption spectroscopy.

    PubMed

    McDermott, A E; Yachandra, V K; Guiles, R D; Cole, J L; Dexheimer, S L; Britt, R D; Sauer, K; Klein, M P

    1988-05-31

    The Mn donor complex in the S1 and S2 states and the iron-quinone acceptor complex (Fe2+-Q) in O2-evolving photosystem II (PS II) preparations from a thermophilic cyanobacterium, Synechococcus sp., have been studied with X-ray absorption spectroscopy and electron paramagnetic resonance (EPR). Illumination of these preparations at 220-240 K results in formation of a multiline EPR signal very similar to that assigned to a Mn S2 species observed in spinach PS II, together with g = 1.8 and 1.9 EPR signals similar to the Fe2+-QA- acceptor signals seen in spinach PS II. Illumination at 110-160 K does not produce the g = 1.8 or 1.9 EPR signals, nor the multiline or g = 4.1 EPR signals associated with the S2 state of PS II in spinach; however, a signal which peaks at g = 1.6 appears. The most probable assignment of this signal is an altered configuration of the Fe2+-QA- complex. In addition, no donor signal was seen upon warming the 140 K illuminated sample to 215 K. Following continuous illumination at temperatures between 140 and 215 K, the average X-ray absorption Mn K-edge inflection energy changes from 6550 eV for a dark-adapted (S1) sample to 6551 eV for the illuminated (S2) sample. The shift in edge inflection energy indicates an oxidation of Mn, and the absolute edge inflection energies indicate an average Mn oxidation state higher than Mn(II). Upon illumination a significant change was observed in the shape of the features associated with 1s to 3d transitions. The S1 spectrum resembles those of Mn(III) complexes, and the S2 spectrum resembles those of Mn(IV) complexes. The extended X-ray absorption fine structure (EXAFS) spectrum of the Mn complex is similar in the S1 and S2 states. Simulations indicate O or N ligands at 1.75 +/- 0.05 A, transition metal neighbor(s) at 2.73 +/- 0.05 A, which are assumed to be Mn, and terminal ligands which are probably N and O at a range of distances around 2.2 A. The Mn-O bond length of 1.75 A and the transition metal at 2.7 A

  3. Preface: Special Topic Section on Advanced Electronic Structure Methods for Solids and Surfaces

    SciTech Connect

    Michaelides, Angelos; Martinez, Todd J.; Alavi, Ali; Kresse, Georg

    2015-09-14

    This Special Topic section on Advanced Electronic Structure Methods for Solids and Surfaces contains a collection of research papers that showcase recent advances in the high accuracy prediction of materials and surface properties. It provides a timely snapshot of a growing field that is of broad importance to chemistry, physics, and materials science.

  4. Ultrashort Electron Beam Pulses and Diagnosis by Advanced Linear Accelerators

    NASA Astrophysics Data System (ADS)

    Uesaka, M.; Iijima, H.; Muroya, Y.; Watanabe, T.; Hosokai, T.

    2003-08-01

    240fs 18 MeV low emittance(6 pai mm.mrad) electron beam was generated and its pulse shape was diagnosed by the S-band laser photocathode RF gun and linac. The maximum charge per bunch was 7 nC. This electron pulse was synchronized with 100fs 0.3TW Ti:Sapphire laser with the timing jitter of 330fs(rms). Recently, the Cu cathode(QE10∧-4) was replaced by Mg cathode(QE10∧-3). This system is utilized for radiation chemistry analysis for supercritical water. We have adopted the four diagnostic methods(femtosecond streak camera, coherent transition radiation interferometer, far-infrared polychromator, fluctuation method) and checked their time-resolution precisely. Further, we are doing the experiment on laser plasma cathode by 12TW 50fs laser and He gas jet. Laser plasma wakefield acceleration and electron injection via wavebreaking are planned. We have developed a new theory of self-injection scheme to generate ˜10fs electron pulse. We have already succeeded in observing 40 MeV low emittance electron beam of 14 nC.

  5. Electron beam melting of advanced materials and structures

    NASA Astrophysics Data System (ADS)

    Mahale, Tushar Ramkrishna

    Layered manufacturing has for long been used for the fabrication of non-functional parts using polymer-based processes. Developments in laser beam and electron beam welding technologies and their adoption to layered manufacturing has made it possible to fabricate high-density functional parts in metal irrespective of the level of complexity. The Electron Beam Melting (EBM) process by Arcam AB is one such layered manufacturing process that utilizes a focused electron beam to process metal powder, layer by layer, in a vacuum environment. Research conducted as part of this body of work looks into the development of both bulk materials in the form of metal alloys and ceramic metal-matrix composites as well as the development of tunable mechanical & thermal metamaterials. Simulation models to approximate electron beam melting were suggested using commercial finite element analysis packages. A framework was developed based on the finite difference method to simulate layered manufacturing using Arcam AB's electron beam melting process. The outputs from the simulation data could be used to better understand the local melting, grain evolution, composition and internal stresses within freeform-fabricated metal parts.

  6. Recent advances in molecular electronics based on carbon nanotubes.

    PubMed

    Bourgoin, Jean-Philippe; Campidelli, Stéphane; Chenevier, Pascale; Derycke, Vincent; Filoramo, Arianna; Goffman, Marcelo F

    2010-01-01

    Carbon nanotubes (CNTs) have exceptional physical properties that make them one of the most promising building blocks for future nanotechnologies. They may in particular play an important role in the development of innovative electronic devices in the fields of flexible electronics, ultra-high sensitivity sensors, high frequency electronics, opto-electronics, energy sources and nano-electromechanical systems (NEMS). Proofs of concept of several high performance devices already exist, usually at the single device level, but there remain many serious scientific issues to be solved before the viability of such routes can be evaluated. In particular, the main concern regards the controlled synthesis and positioning of nanotubes. In our opinion, truly innovative use of these nano-objects will come from: (i) the combination of some of their complementary physical properties, such as combining their electrical and mechanical properties, (ii) the combination of their properties with additional benefits coming from other molecules grafted on the nanotubes, and (iii) the use of chemically- or bio-directed self-assembly processes to allow the efficient combination of several devices into functional arrays or circuits. In this article, we outline the main issues concerning the development of carbon nanotubes based electronics applications and review our recent results in the field.

  7. Advanced Opto-Electronics (LIDAR and Microsensor Development)

    NASA Technical Reports Server (NTRS)

    Vanderbilt, Vern C. (Technical Monitor); Spangler, Lee H.

    2005-01-01

    Our overall intent in this aspect of the project were to establish a collaborative effort between several departments at Montana State University for developing advanced optoelectronic technology for advancing the state-of-the-art in optical remote sensing of the environment. Our particular focus was on development of small systems that can eventually be used in a wide variety of applications that might include ground-, air-, and space deployments, possibly in sensor networks. Specific objectives were to: 1) Build a field-deployable direct-detection lidar system for use in measurements of clouds, aerosols, fish, and vegetation; 2) Develop a breadboard prototype water vapor differential absorption lidar (DIAL) system based on highly stable, tunable diode laser technology developed previously at MSU. We accomplished both primary objectives of this project, in developing a field-deployable direct-detection lidar and a breadboard prototype of a water vapor DIAL system. Paper summarizes each of these accomplishments.

  8. Paramagnetism in X-irradiated chalcogenide glasses and crystals

    NASA Astrophysics Data System (ADS)

    Taylor, P. C.; Strom, U.; Bishop, S. G.

    1982-11-01

    In semiconducting chalcogenide glasses, X-irradiation at 77 K produces paramagnetic responses which are similar to those produced by optical excitation at band gap energies. These Electron Spin Resonance (ESR) signals can be bleached with light of less than band gap energies. There is evidence that X-irradiation at low temperature creates a greater density of metastable centers which can subsequently be populated or depopulated (rendered paramagnetic) optically, by excitation with low intensities (of about 10 mW/sq cm) of band-gap light. In addition to the usual, optically induced responses, X-irradiation in the chalcogenide glasses also produces signals attributable to impurities such as copper and iron. In pure crystalline As2Se, X-irradiation at 77 K produces only centers associated with Cu(2+) impurities.

  9. Advances in electron kinetics and theory of gas discharges

    SciTech Connect

    Kolobov, Vladimir I.

    2013-10-15

    Electrons, like people, are fertile and infertile: high-energy electrons are fertile and able to reproduce.”—Lev TsendinModern physics of gas discharges increasingly uses physical kinetics for analysis of non-equilibrium plasmas. The description of underlying physics at the kinetic level appears to be important for plasma applications in modern technologies. In this paper, we attempt to grasp the legacy of Professor Lev Tsendin, who advocated the use of the kinetic approach for understanding fundamental problems of gas discharges. We outline the fundamentals of electron kinetics in low-temperature plasmas, describe elements of the modern kinetic theory of gas discharges, and show examples of the theoretical approach to gas discharge problems used by Lev Tsendin. Important connections between electron kinetics in gas discharges and semiconductors are also discussed. Using several examples, we illustrate how Tsendin's ideas and methods are currently being developed for the implementation of next generation computational tools for adaptive kinetic-fluid simulations of gas discharges used in modern technologies.

  10. Femtosecond, High-Brightness Electron Beam Generation and Advanced Diagnosis

    SciTech Connect

    Anderson, S G; Brown, W J; Tremaine, A M; Kuba, J; Hartemann, F V; Fittinghoff, D N

    2005-02-02

    This document serves as the final report for LDRD project number 04-LW-031, in which we created subpicosecond length, kilo-amp peak current electron beams with the 100 MeV electron/positron linac, using a novel technique designed to produce ultra-short bunch lengths while maintaining the high brightness produced by the S-band photoinjector. In addition, a diagnostic to measure the temporal distribution of the beam was investigated, as conventional pulse length measurement techniques do not apply to extremely short pulses. The creation and diagnosis of beams with both femtosecond length and high transverse brightness is of major concern to next generation acceleration and radiation production experiments. This work leveraged the previous investment in the PLEIADES facility and it's ability to produce high brightness electron beams. In addition, the ultra-short electron pulses generated by this work have been used in conjunction with the PLEIADES X-ray source to produce sub-picosecond, high-brightness X-ray pulses.

  11. Advanced electron crystallography through model-based imaging

    PubMed Central

    Van Aert, Sandra; De Backer, Annick; Martinez, Gerardo T.; den Dekker, Arnold J.; Van Dyck, Dirk; Bals, Sara; Van Tendeloo, Gustaaf

    2016-01-01

    The increasing need for precise determination of the atomic arrangement of non-periodic structures in materials design and the control of nanostructures explains the growing interest in quantitative transmission electron microscopy. The aim is to extract precise and accurate numbers for unknown structure parameters including atomic positions, chemical concentrations and atomic numbers. For this purpose, statistical parameter estimation theory has been shown to provide reliable results. In this theory, observations are considered purely as data planes, from which structure parameters have to be determined using a parametric model describing the images. As such, the positions of atom columns can be measured with a precision of the order of a few picometres, even though the resolution of the electron microscope is still one or two orders of magnitude larger. Moreover, small differences in average atomic number, which cannot be distinguished visually, can be quantified using high-angle annular dark-field scanning transmission electron microscopy images. In addition, this theory allows one to measure compositional changes at interfaces, to count atoms with single-atom sensitivity, and to reconstruct atomic structures in three dimensions. This feature article brings the reader up to date, summarizing the underlying theory and highlighting some of the recent applications of quantitative model-based transmisson electron microscopy. PMID:26870383

  12. Advanced electron crystallography through model-based imaging.

    PubMed

    Van Aert, Sandra; De Backer, Annick; Martinez, Gerardo T; den Dekker, Arnold J; Van Dyck, Dirk; Bals, Sara; Van Tendeloo, Gustaaf

    2016-01-01

    The increasing need for precise determination of the atomic arrangement of non-periodic structures in materials design and the control of nanostructures explains the growing interest in quantitative transmission electron microscopy. The aim is to extract precise and accurate numbers for unknown structure parameters including atomic positions, chemical concentrations and atomic numbers. For this purpose, statistical parameter estimation theory has been shown to provide reliable results. In this theory, observations are considered purely as data planes, from which structure parameters have to be determined using a parametric model describing the images. As such, the positions of atom columns can be measured with a precision of the order of a few picometres, even though the resolution of the electron microscope is still one or two orders of magnitude larger. Moreover, small differences in average atomic number, which cannot be distinguished visually, can be quantified using high-angle annular dark-field scanning transmission electron microscopy images. In addition, this theory allows one to measure compositional changes at interfaces, to count atoms with single-atom sensitivity, and to reconstruct atomic structures in three dimensions. This feature article brings the reader up to date, summarizing the underlying theory and highlighting some of the recent applications of quantitative model-based transmisson electron microscopy. PMID:26870383

  13. Advanced manufacturing of SIMOX for low power electronics

    NASA Astrophysics Data System (ADS)

    Alles, Michael; Krull, Wade

    1996-04-01

    Silicon-on-insulator (SOI) has emerged as a key technology for low power electronics. The merits of SOI technology have been demonstrated, and are gaining acceptance in the semiconductor industry. In order for the SOI approach to be viable, several factors must converge, including the availability of SOI substrates in sufficient quantity, of acceptable quality, and at a competitive price. This work describes developments in SIMOX manufacturing technology and summarizes progress in each of these areas.

  14. Advanced Strained-Superlattice Photocathodes for Polarized Electron Sources

    SciTech Connect

    Dr. Aaron Moy

    2005-01-31

    Polarized electrons have been essential for high-energy parity-violating experiments and measurements of the nucleon spin structure. The availability of a polarized electron beam was crucial to the success of the Stanford Linear Collider (SLC) in achieving a precise measurement of the electroweak mixing angle, and polarized electron beams will be required for all future linear colliders. Polarized electrons are readily produced by GaAs photocathode sources. When a circularly polarized laser beam tuned to the bandgap minimum is directed to the negative-electron-affinity (NEA) surface of a GaAs crystal, longitudinally polarized electrons are emitted into vacuum. The electron polarization is easily reversed by reversing the laser polarization. The important properties of these photocathodes for accelerator applications are: degree of polarization of the extracted beam; ability to extract sufficient charge to meet accelerator pulse-structure requirements; efficiency and stability of operation; and absence of any asymmetries in the beam properties (charge, position, energy, etc.) upon polarization reversal. The performance of GaAs photocathodes has improved significantly since they were first introduced in 1978 [1]. The theoretical maximum polarization of 50% for natural GaAs was first exceeded in 1991 using the lattice mismatch of a thin InGaAs layer epitaxially grown over a GaAs substrate to generate a strain in the former that broke the natural degeneracy between the heavy- and light-hole valence bands [2]. Polarizations as high as 78% were produced for the SLC from photocathodes based on a thin GaAs epilayer grown on GaAsP [3,4]. After 10 years of experience with many cathode samples at several laboratories [5], the maximum polarization using the GaAs/GaAsP single strained-layer cathode remained limited to 80%, while the quantum efficiency (QE) for a 100-nm epilayer is only 0.3% or less. Two factors were known to limit the polarization of these cathodes: (1) the

  15. Applications of advanced electric/electronic technology to conventional aircraft

    NASA Technical Reports Server (NTRS)

    Heimbold, R. L.

    1980-01-01

    The desirability of seven advanced technologies as applied to three commercial aircraft of 1985 to 1995 was investigated. Digital fly by wire, multiplexing, ring laser gyro, integrated avionics, all electric airplane, electric load management, and fiber optics were considered for 500 passenger, 50 passenger, and 30 passenger aircraft. The major figure of merit used was Net Value of Technology based on procurement and operating cost over the life of the aircraft. An existing computer program, ASSET, was used to resize the aircraft and evalute fuel usage and maintenance costs for each candidate configuration. Conclusions were that, for the 500 passenger aircraft, all candidates had a worthwhile payoff with the all electric airplane having a large payoff.

  16. An Advanced Time Averaging Modelling Technique for Power Electronic Circuits

    NASA Astrophysics Data System (ADS)

    Jankuloski, Goce

    For stable and efficient performance of power converters, a good mathematical model is needed. This thesis presents a new modelling technique for DC/DC and DC/AC Pulse Width Modulated (PWM) converters. The new model is more accurate than the existing modelling techniques such as State Space Averaging (SSA) and Discrete Time Modelling. Unlike the SSA model, the new modelling technique, the Advanced Time Averaging Model (ATAM) includes the averaging dynamics of the converter's output. In addition to offering enhanced model accuracy, application of linearization techniques to the ATAM enables the use of conventional linear control design tools. A controller design application demonstrates that a controller designed based on the ATAM outperforms one designed using the ubiquitous SSA model. Unlike the SSA model, ATAM for DC/AC augments the system's dynamics with the dynamics needed for subcycle fundamental contribution (SFC) calculation. This allows for controller design that is based on an exact model.

  17. Giant paramagnetic Meissner effect in multiband superconductors.

    PubMed

    da Silva, R M; Milošević, M V; Shanenko, A A; Peeters, F M; Aguiar, J Albino

    2015-01-01

    Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux. In the absence of pinning such paramagnetic response is weak, and ceases with increasing sample thickness. Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field. We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces. PMID:26244936

  18. Giant paramagnetic Meissner effect in multiband superconductors

    PubMed Central

    da Silva, R. M.; Milošević, M. V.; Shanenko, A. A.; Peeters, F. M.; Aguiar, J. Albino

    2015-01-01

    Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux. In the absence of pinning such paramagnetic response is weak, and ceases with increasing sample thickness. Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field. We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces. PMID:26244936

  19. ELECTRON HOLOGRAPHY OF ELECTROMAGNETIC FIELDS - RECENT THEORETICAL ADVANCES.

    SciTech Connect

    BELEGGIA,M.; POZZI, G.; TONOMURA, A.

    2007-01-01

    It has been shown in this work that the Fourier space approach can be fruitfully applied to the calculation of the fields and the associated electron optical phase shift of several magnetic and electrostatic structures, like superconducting vortices in conventional and high-T{sub c} superconductors, reverse biased p-n junctions, magnetic domains and nanoparticles. In all these cases, this novel approach has led to unexpected but extremely interesting results, very often expressed in analytical form, which allow the quantitative and reliable interpretation of the experimental data collected by means of electron holography or of more conventional Lorentz microscopy techniques. Moreover, it is worth recalling that whenever long-range electromagnetic fields are involved, a physical model of the object under investigation is necessary in order to take into account correctly the perturbation of the reference wave induced by the tail of the field protruding into the vacuum. For these reasons, we believe that the Fourier space approach for phase computations we have introduced and discussed in this chapter will represent an invaluable tool for the investigation of electromagnetic fields at the meso- and nano-scale.

  20. Nanomaterial datasets to advance tomography in scanning transmission electron microscopy

    PubMed Central

    Levin, Barnaby D.A.; Padgett, Elliot; Chen, Chien-Chun; Scott, M.C.; Xu, Rui; Theis, Wolfgang; Jiang, Yi; Yang, Yongsoo; Ophus, Colin; Zhang, Haitao; Ha, Don-Hyung; Wang, Deli; Yu, Yingchao; Abruña, Hector D.; Robinson, Richard D.; Ercius, Peter; Kourkoutis, Lena F.; Miao, Jianwei; Muller, David A.; Hovden, Robert

    2016-01-01

    Electron tomography in materials science has flourished with the demand to characterize nanoscale materials in three dimensions (3D). Access to experimental data is vital for developing and validating reconstruction methods that improve resolution and reduce radiation dose requirements. This work presents five high-quality scanning transmission electron microscope (STEM) tomography datasets in order to address the critical need for open access data in this field. The datasets represent the current limits of experimental technique, are of high quality, and contain materials with structural complexity. Included are tomographic series of a hyperbranched Co2P nanocrystal, platinum nanoparticles on a carbon nanofibre imaged over the complete 180° tilt range, a platinum nanoparticle and a tungsten needle both imaged at atomic resolution by equal slope tomography, and a through-focal tilt series of PtCu nanoparticles. A volumetric reconstruction from every dataset is provided for comparison and development of post-processing and visualization techniques. Researchers interested in creating novel data processing and reconstruction algorithms will now have access to state of the art experimental test data. PMID:27272459

  1. Thin Dielectric Film Thickness Determination by Advanced Transmission Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Diebold, A. C.; Foran, B.; Kisielowski, C.; Muller, D. A.; Pennycook, S. J.; Principe, E.; Stemmer, S.

    2003-12-01

    High-resolution transmission electron microscopy (HR-TEM) has been used as the ultimate method of thickness measurement for thin films. The appearance of phase contrast interference patterns in HR-TEM images has long been confused as the appearance of a crystal lattice by nonspecialists. Relatively easy to interpret crystal lattice images are now directly observed with the introduction of annular dark-field detectors for scanning TEM (STEM). With the recent development of reliable lattice image processing software that creates crystal structure images from phase contrast data, HR-TEM can also provide crystal lattice images. The resolution of both methods has been steadily improved reaching now into the sub-Ångstrom region. Improvements in electron lens and image analysis software are increasing the spatial resolution of both methods. Optimum resolution for STEM requires that the probe beam be highly localized. In STEM, beam localization is enhanced by selection of the correct aperture. When STEM measurement is done using a highly localized probe beam, HR-TEM and STEM measurement of the thickness of silicon oxynitride films agree within experimental error. In this article, the optimum conditions for HR-TEM and STEM measurement are discussed along with a method for repeatable film thickness determination. The impact of sample thickness is also discussed. The key result in this article is the proposal of a reproducible method for film thickness determination.

  2. Nanomaterial datasets to advance tomography in scanning transmission electron microscopy.

    PubMed

    Levin, Barnaby D A; Padgett, Elliot; Chen, Chien-Chun; Scott, M C; Xu, Rui; Theis, Wolfgang; Jiang, Yi; Yang, Yongsoo; Ophus, Colin; Zhang, Haitao; Ha, Don-Hyung; Wang, Deli; Yu, Yingchao; Abruña, Hector D; Robinson, Richard D; Ercius, Peter; Kourkoutis, Lena F; Miao, Jianwei; Muller, David A; Hovden, Robert

    2016-01-01

    Electron tomography in materials science has flourished with the demand to characterize nanoscale materials in three dimensions (3D). Access to experimental data is vital for developing and validating reconstruction methods that improve resolution and reduce radiation dose requirements. This work presents five high-quality scanning transmission electron microscope (STEM) tomography datasets in order to address the critical need for open access data in this field. The datasets represent the current limits of experimental technique, are of high quality, and contain materials with structural complexity. Included are tomographic series of a hyperbranched Co2P nanocrystal, platinum nanoparticles on a carbon nanofibre imaged over the complete 180° tilt range, a platinum nanoparticle and a tungsten needle both imaged at atomic resolution by equal slope tomography, and a through-focal tilt series of PtCu nanoparticles. A volumetric reconstruction from every dataset is provided for comparison and development of post-processing and visualization techniques. Researchers interested in creating novel data processing and reconstruction algorithms will now have access to state of the art experimental test data. PMID:27272459

  3. Advanced characterization of twins using automated electron backscatter diffraction

    SciTech Connect

    Wright, S. I.; Bingert, J. F.; Mason, T. A.; Larson, R. J.

    2002-01-01

    This paper describes results obtained using an automated, crystallographically-based technique for twin identification. The technique is based on the automated collection of spatially specific orientation measurements by electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM). The key features of the analysis are identification of potential twin boundaries by their misorientation character, identification of the distinct boundary planes among the symmetrically equivalent candidates, and validation of these boundaries through comparison with the boundary and twin plane traces in the sample cross section. Results on the application of this technique to deformation twins in zirconium are analyzed for the effect of twin type and amount and sense of uniaxial deformation. The accumulation of strain tends to increase the misorientation deviation at least to the degree of the trace deviation compared with recrystallization twins in nickel. In addition to the results on characterizing the twin character, results on extending the twin analysis to automated identification of parent and daughter material for structures exhibiting twin deformation are reported as well.

  4. Thin dielectric film thickness determination by advanced transmission electron microscopy

    SciTech Connect

    Diebold, A.C.; Foran, B.; Kisielowski, C.; Muller, D.; Pennycook, S.; Principe, E.; Stemmer, S.

    2003-09-01

    High Resolution Transmission Electron Microscopy (HR-TEM) has been used as the ultimate method of thickness measurement for thin films. The appearance of phase contrast interference patterns in HR-TEM images has long been confused as the appearance of a crystal lattice by non-specialists. Relatively easy to interpret crystal lattice images are now directly observed with the introduction of annular dark field detectors for scanning TEM (STEM). With the recent development of reliable lattice image processing software that creates crystal structure images from phase contrast data, HR-TEM can also provide crystal lattice images. The resolution of both methods was steadily improved reaching now into the sub Angstrom region. Improvements in electron lens and image analysis software are increasing the spatial resolution of both methods. Optimum resolution for STEM requires that the probe beam be highly localized. In STEM, beam localization is enhanced by selection of the correct aperture. When STEM measurement is done using a highly localized probe beam, HR-TEM and STEM measurement of the thickness of silicon oxynitride films agree within experimental error. In this paper, the optimum conditions for HR-TEM and STEM measurement are discussed along with a method for repeatable film thickness determination. The impact of sample thickness is also discussed. The key result in this paper is the proposal of a reproducible method for film thickness determination.

  5. Nanomaterial datasets to advance tomography in scanning transmission electron microscopy.

    PubMed

    Levin, Barnaby D A; Padgett, Elliot; Chen, Chien-Chun; Scott, M C; Xu, Rui; Theis, Wolfgang; Jiang, Yi; Yang, Yongsoo; Ophus, Colin; Zhang, Haitao; Ha, Don-Hyung; Wang, Deli; Yu, Yingchao; Abruña, Hector D; Robinson, Richard D; Ercius, Peter; Kourkoutis, Lena F; Miao, Jianwei; Muller, David A; Hovden, Robert

    2016-06-07

    Electron tomography in materials science has flourished with the demand to characterize nanoscale materials in three dimensions (3D). Access to experimental data is vital for developing and validating reconstruction methods that improve resolution and reduce radiation dose requirements. This work presents five high-quality scanning transmission electron microscope (STEM) tomography datasets in order to address the critical need for open access data in this field. The datasets represent the current limits of experimental technique, are of high quality, and contain materials with structural complexity. Included are tomographic series of a hyperbranched Co2P nanocrystal, platinum nanoparticles on a carbon nanofibre imaged over the complete 180° tilt range, a platinum nanoparticle and a tungsten needle both imaged at atomic resolution by equal slope tomography, and a through-focal tilt series of PtCu nanoparticles. A volumetric reconstruction from every dataset is provided for comparison and development of post-processing and visualization techniques. Researchers interested in creating novel data processing and reconstruction algorithms will now have access to state of the art experimental test data.

  6. Electro-optic switching in iron oxide nanoparticle embedded paramagnetic chiral liquid crystal via magneto-electric coupling

    SciTech Connect

    Goel, Puja; Arora, Manju; Biradar, Ashok M.

    2014-03-28

    The variation in optical texture, electro-optic, and dielectric properties of iron oxide nanoparticles (NPs) embedded ferroelectric liquid crystal (FLC) with respect to change in temperature and electrical bias conditions are demonstrated in the current investigations. Improvement in spontaneous polarization and response time in nanocomposites has been attributed to magneto-electric (ME) coupling resulting from the strong interaction among the ferromagnetic nanoparticle's exchange field (due to unpaired e{sup −}) and the field of liquid crystal molecular director. Electron paramagnetic resonance spectrum of FLC material gives a broad resonance signal with superimposed components indicating the presence of a source of spin. This paramagnetic behavior of host FLC material had been a major factor in strengthening the guest host interaction by giving an additional possibility of (a) spin-spin interaction and (b) interactions between magnetic-dipole and electric-dipole moments (ME effects) in the composite materials. Furthermore, the phenomenon of dielectric and static memory effect in these composites are also observed which yet again confirms the coupling of magnetic NP's field with FLC's director orientation. We therefore believe that such advanced soft materials holding the optical and electrical properties of conventional LCs with the magnetic and electronic properties of ferromagnetic nanoparticles are going to play a key role in the development of futuristic multifunctional optical devices.

  7. Recent Advance in Thermoelectric Devices for Electronics Cooling

    NASA Astrophysics Data System (ADS)

    Wang, Peng

    Thermal management of on-chip hot spot, with a heat flux of around 1000 W/cm2, has become one of the major challenges in the development of next-generation microprocessors. Solid state thermoelectric cooler (TEC) offers great promise for hot spot thermal management because of their compact structure, fast response, high reliability, localized cooling, and high flux removal capability. To date TEC has received great attentions in electronics cooling community as one of the potential hot spot cooling solutions. In this paper, recent development and application of hot spot cooling strategies based on micro thermoelectric technologies will be reviewed and discussed, three hot spot cooling concepts, including thinfilm thermoelectric cooling, mini-contact cooling, and semiconductor selfcooling in silicon substrate and germanium substrate will be discussed. The advantages and disadvantages of these on-chip cooling solutions for high flux hot spots will be evaluated.

  8. Advances and applications of electronic speckle pattern interferometry /ESPI/

    NASA Astrophysics Data System (ADS)

    Lokberg, O. J.

    1980-05-01

    The principle of electronic speckle pattern interferometry (ESPI) is explained by means of comparison with conventional holography. Because ESPI image recording and reconstruction are performed by videotechniques, laboratory experiments may be studied through real-time presentations of readily interpretable vibration patterns on a large TV screen, with a new image being formed every 1/25 sec. These properties, combined with the high sensitivity, noncontact, and nondestructive properties of the method, make ESPI a measuring tool uniquely suited for studies of extremely unstable objects. Among examples of applications covered are: the testing of sonar transducers in both air and water, the analysis of loudspeakers, studies of the behavior of piezoelectric transducers, the classification of turbine blade resonances, and the observation of the human eardrum.

  9. Status and Perspectives of Ion Track Electronics for Advanced Biosensing

    NASA Astrophysics Data System (ADS)

    Fink, D.; Muñoz, H. Gerardo; Alfonta, L.; Mandabi, Y.; Dias, J. F.; de Souza, C. T.; Bacakova, L. E.; Vacík, J.; Hnatowicz, V.; Kiv, A. E.; Fuks, D.; Papaleo, R. M.

    New multifunctional ion irradiation-based three-dimensional electronic structures are developed for biotechnological applications, specifically for sensing of biomaterials, bacteria and mammalian cells. This is accomplished by combined micrometric surface and nanometric bulk microstructuring of insulators (specifically of polymer foils and SiO2/Si hybride structures) by adequate ion beams. Our main goal is the production of a cheap small universal generic working platform with multifunctional properties for biomedical analysis. Surface engineering of this platform enables cell bonding and its bulk engineering enables the extraction of cell secrets, for the sake of intercepting and analyzing the biomolecules used in cell communication. The exact knowledge of the spectrum of these cell-secreted signalling molecules should enable one to identify unambiguously the cell type. This knowledge will help developing strategies for preventive quorum sensing of bacteria, with the aim of fighting bacterial infections in an ecologically secure way.

  10. The Assurance Challenges of Advanced Packaging Technologies for Electronics

    NASA Technical Reports Server (NTRS)

    Sampson, Michael J.

    2010-01-01

    Advances in microelectronic parts performance are driving towards finer feature sizes, three-dimensional geometries and ever-increasing number of transistor equivalents that are resulting in increased die sizes and interconnection (I/O) counts. The resultant packaging necessary to provide assemble-ability, environmental protection, testability and interconnection to the circuit board for the active die creates major challenges, particularly for space applications, Traditionally, NASA has used hermetically packaged microcircuits whenever available but the new demands make hermetic packaging less and less practical at the same time as more and more expensive, Some part types of great interest to NASA designers are currently only available in non-hermetic packaging. It is a far more complex quality and reliability assurance challenge to gain confidence in the long-term survivability and effectiveness of nonhermetic packages than for hermetic ones. Although they may provide more rugged environmental protection than the familiar Plastic Encapsulated Microcircuits (PEMs), the non-hermetic Ceramic Column Grid Array (CCGA) packages that are the focus of this presentation present a unique combination of challenges to assessing their suitability for spaceflight use. The presentation will discuss the bases for these challenges, some examples of the techniques proposed to mitigate them and a proposed approach to a US MIL specification Class for non-hermetic microcircuits suitable for space application, Class Y, to be incorporated into M. IL-PRF-38535. It has recently emerged that some major packaging suppliers are offering hermetic area array packages that may offer alternatives to the nonhermetic CCGA styles but have also got their own inspectability and testability issues which will be briefly discussed in the presentation,

  11. Advanced prior modeling for 3D bright field electron tomography

    NASA Astrophysics Data System (ADS)

    Sreehari, Suhas; Venkatakrishnan, S. V.; Drummy, Lawrence F.; Simmons, Jeffrey P.; Bouman, Charles A.

    2015-03-01

    Many important imaging problems in material science involve reconstruction of images containing repetitive non-local structures. Model-based iterative reconstruction (MBIR) could in principle exploit such redundancies through the selection of a log prior probability term. However, in practice, determining such a log prior term that accounts for the similarity between distant structures in the image is quite challenging. Much progress has been made in the development of denoising algorithms like non-local means and BM3D, and these are known to successfully capture non-local redundancies in images. But the fact that these denoising operations are not explicitly formulated as cost functions makes it unclear as to how to incorporate them in the MBIR framework. In this paper, we formulate a solution to bright field electron tomography by augmenting the existing bright field MBIR method to incorporate any non-local denoising operator as a prior model. We accomplish this using a framework we call plug-and-play priors that decouples the log likelihood and the log prior probability terms in the MBIR cost function. We specifically use 3D non-local means (NLM) as the prior model in the plug-and-play framework, and showcase high quality tomographic reconstructions of a simulated aluminum spheres dataset, and two real datasets of aluminum spheres and ferritin structures. We observe that streak and smear artifacts are visibly suppressed, and that edges are preserved. Also, we report lower RMSE values compared to the conventional MBIR reconstruction using qGGMRF as the prior model.

  12. The Scanning Electron Microscope As An Accelerator For The Undergraduate Advanced Physics Laboratory

    SciTech Connect

    Peterson, Randolph S.; Berggren, Karl K.; Mondol, Mark

    2011-06-01

    Few universities or colleges have an accelerator for use with advanced physics laboratories, but many of these institutions have a scanning electron microscope (SEM) on site, often in the biology department. As an accelerator for the undergraduate, advanced physics laboratory, the SEM is an excellent substitute for an ion accelerator. Although there are no nuclear physics experiments that can be performed with a typical 30 kV SEM, there is an opportunity for experimental work on accelerator physics, atomic physics, electron-solid interactions, and the basics of modern e-beam lithography.

  13. On the feasibility to investigate point defects by advanced electron microscopy

    SciTech Connect

    Kisielowski, C.; Jinschek, J.R.

    2002-10-02

    Transmission Electron Microscopy evolves rapidly as a primary tool to investigate nano structures on a truly atomic level. Its resolution reaches into the sub Angstrom region by now. Together with a better correction of lens aberrations, sensitivities are drastically enhanced. Utilizing advanced electron microscopes, it is feasible to promote experiments that aim to detect single atoms. This enables local investigations of non-stoichiometry. This paper reviews the current state-of-the-art.

  14. Theory of the phonon Hall effect in paramagnetic dielectrics.

    PubMed

    Sheng, L; Sheng, D N; Ting, C S

    2006-04-21

    Based upon Raman spin-lattice interaction, we propose a theoretical model for the phonon Hall effect in paramagnetic dielectrics, which was discovered recently in an experiment [C. Strohm, G. L. J. A. Rikken, and P. Wyder, Phys. Rev. Lett. 95, 155901 (2005).]. The phonon Hall effect is revealed to be a phonon analogue to the anomalous Hall effect in electron systems. The thermal Hall conductivity is calculated by using the Kubo formula. Our theory reproduces the essential experimental features of the phonon Hall effect, including the sign, magnitude, and linear magnetic field dependence of the thermal Hall conductivity.

  15. Anomalous Paramagnetic State in Naturally Layered Manganites

    NASA Astrophysics Data System (ADS)

    Berger, Andreas

    2002-03-01

    The nature of the magnetic state near the ferromagnetic phase transition is studied for the layered manganites SrO(La_1-xSr_xMnO_3)2 in the composition range x = 0.32 - 0.40 by means of magnetic field and temperature dependent measurements of the magnetic susceptibility, magnetization and conductivity. In a temperature range T ~ 1.05-1.45 T_C, the paramagnetic phase exhibits a number of very unusual properties, which reflects the fact that the magnetic free energy is distorted due to the existence of a second competing order parameter. In particular, we observe that the field-dependent susceptibility exhibits an anomalous maximum at an intermediate magnetic field value. The size of this field-induced susceptibility enhancement increases dramatically with x from 100.40. The temperature dependence of the effect shows a maximum at T ~ 1.1 TC independent of x. Quantitative analysis of the experimental data reveals that the ferromagnetic exchange coupling is reduced for temperatures above the ferromagnetic phase transition, an effect that is especially pronounced for the x = 0.40 compound. For this material, we also find a strong correlation between the exchange coupling reduction and the measured conductivity, which indicates that the electronic band structure change at the metal-insulator transition also affects the exchange coupling strength in this very compound in contrast to other, mostly perovskite-type manganites. In addition, we observe the appearance of anomalous magnetic losses for temperatures just above TC and applied field values that coincide with the occurrence of the metal-insulator transition. These data suggest that the metal-insulator transition in these layered manganites is associated with a magnetically inhomogeneous state. This work was supported by the U. S. Department of Energy, Basic Energy Sciences - Materials Sciences under Contract W-31-109-ENG-38.

  16. 75 FR 21367 - Advanced Electronics, Inc.; Boston, MA; Notice of Negative Determination on Remand

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-23

    ... Employment and Training Administration Advanced Electronics, Inc.; Boston, MA; Notice of Negative.... United States Secretary of Labor (Court No. 06-00337). On July 18, 2006, the Department issued a Negative... August 4, 2006 (71 FR 44320). Prior to separation, the subject workers produced printed circuit...

  17. Advanced Undergraduate-Laboratory Experiment on Electron Spin Resonance in Single-Crystal Ruby

    ERIC Educational Resources Information Center

    Collins, Lee A.; And Others

    1974-01-01

    An electron-spin-resonance experiment which has been successfully performed in an advanced undergraduate physics laboratory is described. A discussion of that part of the theory of magnetic resonance necessary for the understanding of the experiment is also provided in this article. (DT)

  18. Advanced semiconductor diagnosis by multidimensional electron-beam-induced current technique.

    PubMed

    Chen, J; Yuan, X; Sekiguchi, T

    2008-01-01

    We present advanced semiconductor diagnosis by using electron-beam-induced current (EBIC) technique. By varying the parameters such as temperature, accelerating voltage (V(acc)), bias voltage, and stressing time, it is possible to extend EBIC application from conventional defect characterization to advanced device diagnosis. As an electron beam can excite a certain volume even beneath the surface passive layer, EBIC can be effectively employed to diagnose complicated devices with hybrid structure. Three topics were selected to demonstrate EBIC applications. First, the recombination activities of grain boundaries and their interaction with Fe impurity in photovoltaic multicrystalline Si (mc-Si) are clarified by temperature-dependent EBIC. Second, the detection of dislocations between strained-Si and SiGe virtual substrate are shown to overcome the limitation of depletion region. Third, the observation of leakage sites in high-k gate dielectric is demonstrated for the characterization of advanced hybrid device structures.

  19. Search for exotic short-range interactions using paramagnetic insulators

    SciTech Connect

    Chu, Pinghan; Weisman, E.; Liu, C. -Y.; Long, J. C.

    2015-05-26

    We describe a proposed experimental search for exotic spin-coupled interactions using a solid-state paramagnetic insulator. The experiment is sensitive to the net magnetization induced by the exotic interaction between the unpaired insulator electrons with a dense, nonmagnetic mass in close proximity. An existing experiment has been used to set limits on the electric dipole moment of the electron by probing the magnetization induced in a cryogenic gadolinium gallium garnet sample on application of a strong electric field. With suitable additions, including a movable source mass, this experiment can be used to explore “monopole-dipole” forces on polarized electrons with unique or unprecedented sensitivity. As a result, the solid-state, nonmagnetic construction, combined with the low-noise conditions and extremely sensitive magnetometry available at cryogenic temperatures could lead to a sensitivity over 10 orders of magnitude greater than exiting limits in the range below 1 mm.

  20. Search for exotic short-range interactions using paramagnetic insulators

    DOE PAGES

    Chu, Pinghan; Weisman, E.; Liu, C. -Y.; Long, J. C.

    2015-05-26

    We describe a proposed experimental search for exotic spin-coupled interactions using a solid-state paramagnetic insulator. The experiment is sensitive to the net magnetization induced by the exotic interaction between the unpaired insulator electrons with a dense, nonmagnetic mass in close proximity. An existing experiment has been used to set limits on the electric dipole moment of the electron by probing the magnetization induced in a cryogenic gadolinium gallium garnet sample on application of a strong electric field. With suitable additions, including a movable source mass, this experiment can be used to explore “monopole-dipole” forces on polarized electrons with unique ormore » unprecedented sensitivity. As a result, the solid-state, nonmagnetic construction, combined with the low-noise conditions and extremely sensitive magnetometry available at cryogenic temperatures could lead to a sensitivity over 10 orders of magnitude greater than exiting limits in the range below 1 mm.« less