Trispyrazolylborate Complexes: An Advanced Synthesis Experiment Using Paramagnetic NMR, Variable-Temperature NMR, and EPR Spectroscopies

ERIC Educational Resources Information Center

Abell, Timothy N.; McCarrick, Robert M.; Bretz, Stacey Lowery; Tierney, David L.

2017-01-01

A structured inquiry experiment for inorganic synthesis has been developed to introduce undergraduate students to advanced spectroscopic techniques including paramagnetic nuclear magnetic resonance and electron paramagnetic resonance. Students synthesize multiple complexes with unknown first row transition metals and identify the unknown metals by…

Complexation of β-cyclodextrin with dual molecular probes bearing fluorescent and paramagnetic moieties linked by short polyether chains.

PubMed

Mocanu, S; Matei, I; Ionescu, S; Tecuceanu, V; Marinescu, G; Ionita, P; Culita, D; Leonties, A; Ionita, Gabriela

2017-10-18

Electron paramagnetic resonance (EPR) and fluorescence spectroscopies provide molecular-level insights on the interaction of paramagnetic and fluorescent species with the microenvironment. A series of dual molecular probes bearing fluorescent and paramagnetic moieties linked by flexible short polyether chains have been synthesized. These new molecular probes open the possibility to investigate various multi-component systems such as host-guest systems, polymeric micelles, gels and protein solutions by using EPR and fluorescence spectroscopies concertedly. The EPR and fluorescence spectra of these compounds show that the dependence of the rotational correlation time and fluorescence quantum yield on the chain length of the linker is not linear, due to the flexibility of the polyether linker. The quenching effect of the nitroxide moiety on the fluorescence intensity of the pyrene group varies with the linker length and flexibility. The interaction of these dual molecular probes with β-cyclodextrin, in solution and in polymeric gels, was evaluated and demonstrated by analysis of EPR and fluorescence spectra.

Measurement of electron paramagnetic resonance using terahertz time-domain spectroscopy.

PubMed

Kozuki, Kohei; Nagashima, Takeshi; Hangyo, Masanori

2011-12-05

We present a frequency-domain electron spin resonance (ESR) measurement system using terahertz time-domain spectroscopy. A crossed polarizer technique is utilized to increase the sensitivity in detecting weak ESR signals of paramagnets caused by magnetic dipole transitions between magnetic sublevels. We demonstrate the measurements of ESR signal of paramagnetic copper(II) sulfate pentahydrate with uniaxial anisotropy of the g-factor under magnetic fields up to 10 T. The lineshape of the obtained ESR signals agrees well with the theoretical predictions for a powder sample with the uniaxial anisotropy.

Ferromagnetism observed in silicon-carbide-derived carbon

NASA Astrophysics Data System (ADS)

Peng, Bo; Zhang, Yuming; Wang, Yutian; Guo, Hui; Yuan, Lei; Jia, Renxu

2018-02-01

Carbide-derived carbon (CDC) is prepared by etching high purity 4H-SiC single crystals in a mixed atmosphere of 5% Cl2 and 95% Ar for 120 min and 240 min. The secondary ion mass spectroscopy (SIMS) bulk analysis technique excludes the possibility of ferromagnetic transition metal (TM) contamination arising during the experimental process. The paramagnetic and ferromagnetic components are separated from the measured magnetization-magnetic field curves of the samples. Through the use of the Brillouin function, paramagnetic centers carrying a magnetic moment of ˜1.3 μB are fitted. A resolvable hysteresis loop in the low magnetic field area is preserved at room temperature. The temperature dependence of the relative intensity of the Lorentzian-like electron spin resonance (ESR) line observed by electron spin spectroscopy reveals the existence of exchange interaction between the localized paramagnetic centers. First-principles calculations show the dominant configuration of defects in the graphitic CDC films. By calculating the energy difference between the antiferromagnetic and ferromagnetic phases, we deduce that the ferromagnetic coupling is sensitive to the concentration of defects.

Electron Paramagnetic Resonance of a Single NV Nanodiamond Attached to an Individual Biomolecule

NASA Astrophysics Data System (ADS)

Teeling-Smith, Richelle M.; Jung, Young Woo; Scozzaro, Nicolas; Cardellino, Jeremy; Rampersaud, Isaac; North, Justin A.; Šimon, Marek; Bhallamudi, Vidya P.; Rampersaud, Arfaan; Johnston-Halperin, Ezekiel; Poirier, Michael G.; Hammel, P. Chris

2016-05-01

A key limitation of electron paramagnetic resonance (EPR), an established and powerful tool for studying atomic-scale biomolecular structure and dynamics is its poor sensitivity, samples containing in excess of 10^12 labeled biomolecules are required in typical experiments. In contrast, single molecule measurements provide improved insights into heterogeneous behaviors that can be masked by ensemble measurements and are often essential for illuminating the molecular mechanisms behind the function of a biomolecule. We report EPR measurements of a single labeled biomolecule that merge these two powerful techniques. We selectively label an individual double-stranded DNA molecule with a single nanodiamond containing nitrogen-vacancy (NV) centers, and optically detect the paramagnetic resonance of NV spins in the nanodiamond probe. Analysis of the spectrum reveals that the nanodiamond probe has complete rotational freedom and that the characteristic time scale for reorientation of the nanodiamond probe is slow compared to the transverse spin relaxation time. This demonstration of EPR spectroscopy of a single nanodiamond labeled DNA provides the foundation for the development of single molecule magnetic resonance studies of complex biomolecular systems.

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…

Effect of the lattice dynamics on the electronic structure of paramagnetic NiO within the disordered local moment picture

NASA Astrophysics Data System (ADS)

Mozafari, Elham; Alling, Björn; Belov, Maxim P.; Abrikosov, Igor A.

2018-01-01

Using the disordered local moments approach in combination with the ab initio molecular dynamics method, we simulate the behavior of a paramagnetic phase of NiO at finite temperatures to investigate the effect of magnetic disorder, thermal expansion, and lattice vibrations on its electronic structure. In addition, we study its lattice dynamics. We verify the reliability of our theoretical scheme via comparison of our results with available experiment and earlier theoretical studies carried out within static approximations. We present the phonon dispersion relations for the paramagnetic rock-salt (B1) phase of NiO and demonstrate that it is dynamically stable. We observe that including the magnetic disorder to simulate the paramagnetic phase has a small yet visible effect on the band gap. The amplitude of the local magnetic moment of Ni ions from our calculations for both antiferromagnetic and paramagnetic phases agree well with other theoretical and experimental values. We demonstrate that the increase of temperature up to 1000 K does not affect the electronic structure strongly. Taking into account the lattice vibrations and thermal expansion at higher temperatures have a major impact on the electronic structure, reducing the band gap from ˜3.5 eV at 600 K to ˜2.5 eV at 2000 K. We conclude that static lattice approximations can be safely employed in simulations of the paramagnetic state of NiO up to relatively high temperatures (˜1000 K), but as we get closer to the melting temperature vibrational effects become quite large and therefore should be included in the calculations.

Computer simulation of magnetic resonance spectra employing homotopy.

PubMed

Gates, K E; Griffin, M; Hanson, G R; Burrage, K

1998-11-01

Multidimensional homotopy provides an efficient method for accurately tracing energy levels and hence transitions in the presence of energy level anticrossings and looping transitions. Herein we describe the application and implementation of homotopy to the analysis of continuous wave electron paramagnetic resonance spectra. The method can also be applied to electron nuclear double resonance, electron spin echo envelope modulation, solid-state nuclear magnetic resonance, and nuclear quadrupole resonance spectra. Copyright 1998 Academic Press.

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).

The Demonstration of the Feasibility of the Tuning and Stimulation of Nuclear Radiation.

DTIC Science & Technology

1988-10-31

line, or the center of a resonance pattern, is called the isomer shift. It is due to the electrostatic interaction of the nucleus with the electron ...magnetic moment due to the presence of unpaired electrons , the material is either paramagnetic or ferromagnetic. In paramagnetic materials these moments...capture and fission.4,5,8 A very fertile interdisciplinary area of nuclear quantum electronics 7 appeared to be developing, encouraged by the

Magnetic and thermoelectric properties of electron doped Ca0.85Pr0.15MnO3

NASA Astrophysics Data System (ADS)

Hossain Khan, Momin; Pal, Sudipta; Bose, Esa

2015-10-01

We have investigated temperature-dependent magnetization (M), magnetic susceptibility (χ) and thermoelectric (S) properties of the electron-doped Ca0.85Pr0.15MnO3. With decrease of temperature, paramagnetic (PM) to antiferromagnetic (AFM) phase transition occurs with a well-defined Néel temperature (TN=122 K). Magnetic susceptibility measurements reveal that the paramagnetic state involves modified Curie-Weiss paramagnetism. Field cooled and zero field cooled magnetization measurements indicate a signature of magnetic frustration. Ferromagnetic (FM) double-exchange interactions associated with doped eg electrons are favored over competing AFM interactions below Tirr=112 K. Magnetization data also shows a second-order phase transition. The sign reversal in S(T) has been interpreted in terms of the change in the electronic structure relating to the orbital degrees of freedom of the doped eg electron. Low temperature (5-140 K) thermoelectric power, S (T) signifies the importance of electron-magnon scattering process.

USSR Report, Cybernetics, Computers and Automation Technology.

DTIC Science & Technology

1987-03-02

Studies in the Area of EPR of Non- Ordered Solids, Spectral Recording, Processing and Analysis System (A.N. Bals, L.M. Kuzmina ; AVTOMETRIYA, No 2, Feb...L.M. Kuzmina , Riga] [Abstract] An automated system has been developed for electron paramagnetic resonance studies, oriented toward achievement of

Structural, magnetic, and magnetocaloric properties of bilayer manganite La1.38Sr1.62Mn2O7

NASA Astrophysics Data System (ADS)

Yang, Yu-E.; Xie, Yunfei; Xu, Lisha; Hu, Dazhi; Ma, Chunlan; Ling, Langsheng; Tong, Wei; Pi, Li; Zhang, Yuheng; Fan, Jiyu

2018-04-01

In this study, we investigated the structural, magnetic phase transition, and magnetocaloric properties of bilayer perovskite manganite La1.38Sr1.62Mn2O7 based on X-ray diffraction, electron paramagnetic resonance, and temperature-/magnetic field-dependent magnetization measurements. The structural characterization results showed the prepared sample had a tetragonal structure with the space group I4/mmm. The Curie temperature was determined as 114 K in the magnetization studies and a second-order paramagnetic-ferromagnetic transition was confirmed by the Arrott plot, which showed that the slopes were positive for all the curves. According to the variation in the electron paramagnetic resonance spectrum, we detected obvious electronic phase separation across a broad temperature range from 220 to 80 K in this magnetic material, thereby indicating that the paramagnetic and ferromagnetic phases coexist above as well as below the Curie temperature. Based on a plot of the isothermal magnetization versus the magnetic applied field, we deduced the maximum magnetic entropy change, which only reached 1.89 J/kg.K under an applied magnetic field of 7.0 T. These theoretical investigations indicated that in addition to the magnetoelastic couplings and electron interaction, electronic phase separation and anisotropic exchange interactions also affect the magnetic entropy changes in this bilayer manganite.

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suleman, N.K.

1994-12-01

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,more » 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.« less

Paramagnet induced signal quenching in MAS-DNP experiments in frozen homogeneous solutions

NASA Astrophysics Data System (ADS)

Corzilius, Björn; Andreas, Loren B.; Smith, Albert A.; Ni, Qing Zhe; Griffin, Robert G.

2014-03-01

The effects of nuclear signal quenching induced by the presence of a paramagnetic polarizing agent are documented for conditions used in magic angle spinning (MAS)-dynamic nuclear polarization (DNP) experiments on homogeneous solutions. In particular, we present a detailed analysis of three time constants: (1) the longitudinal build-up time constant TB for 1H; (2) the rotating frame relaxation time constant T1ρ for 1H and 13C and (3) T2 of 13C, the transverse relaxation time constant in the laboratory frame. These relaxation times were measured during microwave irradiation at a magnetic field of 5 T (140 GHz) as a function of the concentration of four polarizing agents: TOTAPOL, 4-amino-TEMPO, trityl (OX063), and Gd-DOTA and are compared to those obtained for a sample lacking paramagnetic doping. We also report the EPR relaxation time constants T1S and T2S, the DNP enhancements, ε, and the parameter E, defined below, which measures the sensitivity enhancement for the four polarizing agents as a function of the electron concentration. We observe substantial intensity losses (paramagnetic quenching) with all of the polarizing agents due to broadening mechanisms and cross relaxation during MAS. In particular, the monoradical trityl and biradical TOTAPOL induce ∼40% and 50% loss of signal intensity. In contrast there is little suppression of signal intensity in static samples containing these paramagnetic species. Despite the losses due to quenching, we find that all of the polarizing agents provide substantial gains in signal intensity with DNP, and in particular that the net enhancement is optimal for biradicals that operate with the cross effect. We discuss the possibility that much of this polarization loss can be regained with the development of instrumentation and methods to perform electron decoupling.

Computing distance distributions from dipolar evolution data with overtones: RIDME spectroscopy with Gd(iii)-based spin labels.

PubMed

Keller, Katharina; Mertens, Valerie; Qi, Mian; Nalepa, Anna I; Godt, Adelheid; Savitsky, Anton; Jeschke, Gunnar; Yulikov, Maxim

2017-07-21

Extraction of distance distributions between high-spin paramagnetic centers from relaxation induced dipolar modulation enhancement (RIDME) data is affected by the presence of overtones of dipolar frequencies. As previously proposed, we account for these overtones by using a modified kernel function in Tikhonov regularization analysis. This paper analyzes the performance of such an approach on a series of model compounds with the Gd(iii)-PyMTA complex serving as paramagnetic high-spin label. We describe the calibration of the overtone coefficients for the RIDME kernel, demonstrate the accuracy of distance distributions obtained with this approach, and show that for our series of Gd-rulers RIDME technique provides more accurate distance distributions than Gd(iii)-Gd(iii) double electron-electron resonance (DEER). The analysis of RIDME data including harmonic overtones can be performed using the MATLAB-based program OvertoneAnalysis, which is available as open-source software from the web page of ETH Zurich. This approach opens a perspective for the routine use of the RIDME technique with high-spin labels in structural biology and structural studies of other soft matter.

EPR Studies of Spin-Spin Exchange Processes: A Physical Chemistry Experiment.

ERIC Educational Resources Information Center

Eastman, Michael P.

1982-01-01

Theoretical background, experimental procedures, and analysis of experimental results are provided for an undergraduate physical chemistry experiment on electron paramagnetic resonance (EPR) linewidths. Source of line broadening observed in a spin-spin exchange process between radicals formed in aqueous solutions of potassium peroxylamine…

In Vivo Imaging of Tissue Physiological Function using EPR Spectroscopy | NCI Technology Transfer Center | TTC

Cancer.gov

Electron paramagnetic resonance (EPR) is a technique for studying chemical species that have one or more unpaired electrons.  The current invention describes Echo-based Single Point Imaging (ESPI), a novel EPR image formation strategy that allows in vivo imaging of physiological function.  The National Cancer Institute's Radiation Biology Branch is seeking statements of capability or interest from parties interested in in-licensing an in vivo imaging using Electron paramagnetic resonance (EPR) to measure active oxygen species.

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.

Effect of ferroelastic domain pattern changes on the EPR spectra in TDM

NASA Astrophysics Data System (ADS)

Zapart, W.; Zapart, M. B.

2011-09-01

This article presents polarized light microscopy studies of the ferroelastic domain structure and the analysis of electron paramagnetic resonance spectra of Cr3+ admixture ions in trigonal double molybdates. The correlation has been found between abnormal EPR lineshape and domain structure in ferroelastic phases of these crystals.

Electron paramagnetic resonance study of radiation-induced paramagnetic centers in succinic anhydride single crystal

NASA Astrophysics Data System (ADS)

Caliskan, Betul; Caliskan, Ali Cengiz; Er, Emine

2017-09-01

Succinic anhydride single crystals were exposed to 60Co-gamma irradiation at room temperature. The irradiated single crystals were investigated at 125 K by Electron Paramagnetic Resonance (EPR) Spectroscopy. The investigation of EPR spectra of irradiated single crystals of succinic anhydride showed the presence of two succinic anhydride anion radicals. The anion radicals observed in gamma-irradiated succinic anhydride single crystal were created by the scission of the carbon-oxygen double bond. The structure of EPR spectra demonstrated that the hyperfine splittings arise from the same radical species. The reduction of succinic anhydride was identified which is formed by the addition of an electron to oxygen of the Csbnd O bond. The g values, the hyperfine structure constants and direction cosines of the radiation damage centers observed in succinic anhydride single crystal were obtained.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rocker, J.; Cornu, D.; Kieseritzky, E.

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 themore » 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 species with a density of approximately 5 × 10{sup 11} spins/cm{sup 2}, which is comparable to the limit obtained for the presently available UHV-EPR spectrometer operating at 10 GHz (X-band). Investigation of electron trapped centers in MgO(001) films shows that the increased resolution offered by the experiments at W-band allows to identify new paramagnetic species, that cannot be differentiated with the currently available methodology.« less

Electron paramagnetic resonance of gamma-irradiated single crystals of 3-nitroacetanilide

NASA Astrophysics Data System (ADS)

Aşik, Biray

2008-06-01

The electron paramagnetic resonance of single crystals of 3-nitroacetanilide has been observed and analyzed for different orientations of the crystal in the magnetic field, after being damaged at 300 K by γ-irradiation. The crystals have been investigated between 123 and 300 K. The spectra were found to be temperature independent. The irradiation of 3-nitroacetanilide by γ-rays produces radicals at the nitrogen atoms in the molecule. The principal values of the hyperfine coupling tensor of the unpaired electron and the principal values of the g-tensor were determined.

Measurement of Rate Constants for Homodimer Subunit Exchange Using Double Electron-Electron Resonance and Paramagnetic Relaxation Enhancements

PubMed Central

Yang, Yunhuang; Ramelot, Theresa A.; Ni, Shuisong; McCarrick, Robert M.; Kennedy, Michael A.

2013-01-01

Here, we report novel methods to measure rate constants for homodimer subunit exchange using double electron-electron resonance (DEER) electron paramagnetic resonance spectroscopy measurements and nuclear magnetic resonance spectroscopy based paramagnetic relaxation enhancement (PRE) measurements. The techniques were demonstrated using the homodimeric protein Dsy0195 from the strictly anaerobic bacterium Desulfitobacterium hafniense Y51. At specific times following mixing site-specific MTSL-labeled Dsy0195 with uniformly 15N-labeled Dsy0195, the extent of exchange was determined either by monitoring the decrease of MTSL-labeled homodimer from the decay of the DEER modulation depth or by quantifying the increase of MTSL-labeled/15N-labeled heterodimer using PREs. Repeated measurements at several time points following mixing enabled determination of the homodimer subunit dissociation rate constant, k−1;, which was 0.037 ± 0.005 min−1 derived from DEER experiments with a corresponding half-life time of 18.7 minutes. These numbers agreed with independent measurements obtained from PRE experiments. These methods can be broadly applied to protein-protein and protein-DNA complex studies. PMID:23180051

Gas-Surface Interactions in Cryogenic Whole Air Sampling.

DTIC Science & Technology

1981-05-01

analysis using electron paramagnetic resonance (EPR) for the cryofrost in the solid phase, and gas chromatography for samples desorbed to the gas...e.g. cryogenic-fraction (used on occasion), and/or controlled vaporization, followed by analysis using NO xchemiluminescence, gas chromatography , and...CS202 closed cycle cryogenic refrigerator, which employs helium as the working fluid . This refrigerator is comprised of two basic sections - an

Chemical disorder influence on magnetic state of optimally-doped La0.7Ca0.3MnO3

NASA Astrophysics Data System (ADS)

Rozenberg, E.; Auslender, M.; Shames, A. I.; Jung, G.; Felner, I.; Tsindlekht, M. I.; Mogilyansky, D.; Sominski, E.; Gedanken, A.; Mukovskii, Ya. M.; Gorodetsky, G.

2011-10-01

X-band electron magnetic resonance and dc/ac magnetic measurements have been employed to study the effects of chemical disorder on magnetic ordering in bulk and nanometer-sized single crystals and bulk ceramics of optimally-doped La0.7Ca0.3MnO3 manganite. The magnetic ground state of bulk samples appeared to be ferromagnetic with the lower Curie temperature and higher magnetic homogeneity in the vicinity of the ferromagnetic-paramagnetic phase transition in the crystal, as compared with those characteristics in the ceramics. The influence of technological driven "macroscopic" fluctuations of Ca-dopant level in crystal and "mesoscopic" disorder within grain boundary regions in ceramics was proposed to be responsible for these effects. Surface spin disorder together with pronounced inter-particle interactions within agglomerated nano-sample results in well defined core/shell spin configuration in La0.7Ca0.3MnO3 nano-crystals. The analysis of the electron paramagnetic resonance data enlightened the reasons for the observed difference in the magnetic order. Lattice effects dominate the first-order nature of magnetic phase transition in bulk samples. However, mesoscale chemical disorder seems to be responsible for the appearance of small ferromagnetic polarons in the paramagnetic state of bulk ceramics. The experimental results and their analysis indicate that a chemical/magnetic disorder has a strong impact on the magnetic state even in the case of mostly stable optimally hole-doped manganites.

Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy

PubMed Central

Hogg, Neil

2010-01-01

Electron paramagnetic resonance (EPR) spectroscopy has been used in a number of ways to study nitric oxide chemistry and biology. As an intrinsically stable and relatively unreactive diatomic free radical, the challenges for detecting this species by EPR are somewhat different than those for transient radical species. This review gives a basic introduction to EPR spectroscopy and discusses its uses to assess and quantify nitric oxide formation in biological systems. PMID:20304044

Optical manifestation of the Stoner ferromagnetic transition in two-dimensional electron systems

NASA Astrophysics Data System (ADS)

Van'kov, A. B.; Kaysin, B. D.; Kukushkin, I. V.

2017-12-01

We perform a magneto-optical study of a two-dimensional electron systems in the regime of the Stoner ferromagnetic instability for even quantum Hall filling factors on MgxZn1 -xO /ZnO heterostructures. Under conditions of Landau-level crossing, caused by enhanced spin susceptibility in combination with the tilting of the magnetic field, the transition between two rivaling phases, paramagnetic and ferromagnetic, is traced in terms of optical spectra reconstruction. Synchronous sharp transformations are observed both in the photoluminescence structure and parameters of collective excitations upon transition from paramagnetic to ferromagnetic ordering. Based on these measurements, a phase diagram is constructed in terms of the two-dimensional electron density and tilt angle of the magnetic field. Apart from stable paramagnetic and ferromagnetic phases, an instability region is found at intermediate parameters with the Stoner transition occurring at ν ≈2 . The spin configuration in all cases is unambiguously determined by means of inelastic light scattering by spin-sensitive collective excitations. One indicator of the spin ordering is the intra-Landau-level spin exciton, which acquires a large spectral weight in the ferromagnetic phases. The other is an abrupt energy shift of the intersubband charge density excitation due to reconstruction of the many-particle energy contribution. From our analysis of photoluminescence and light scattering data, we estimate the ratio of surface areas occupied by the domains of the two phases in the vicinity of a transition point. In addition, the thermal smearing of a phase transition is characterized.

Effect of body temperature on the pharmacokinetics of a triarylmethyl-type paramagnetic contrast agent used in EPR oximetry.

PubMed

Matsumoto, Ken-Ichiro; Hyodo, Fuminori; Mitchell, James B; Krishna, Murali C

2018-02-01

Pharmacokinetics of the tri[8-carboxy-2,2,6,6-tetrakis(2-hydroxymethyl)benzo[1,2-d:4,5-d']bis(1,3)dithio-4-yl]methyl radical (Oxo63) after a single bolus and/or continuous intravenous infusion was investigated in tumor-bearing C3H mice with or without body temperature control while under anesthesia. The in vivo time course of Oxo63 in blood was measured using X-band electron paramagnetic resonance spectroscopy. Distribution of Oxo63 in normal muscle and tumor tissues was obtained using a surface coil resonator and a 700-MHz electron paramagnetic resonance spectrometer. The whole-body distribution of Oxo63 was obtained by 300-MHz continuous-wave electron paramagnetic resonance imaging. The high-resolution 300-MHz time-domain electron paramagnetic resonance imaging was also carried out to probe the distribution of Oxo63. Urination of mice was retarded at low body temperature, causing the concentration of Oxo63 in blood to attain high levels. However, the concentration of Oxo63 in tumor tissue was lower with no control of body temperature than active body temperature control. The nonsystemized blood flow in the tumor tissues may pool Oxo63 at lower body temperature. Pharmacokinetics of the contrast agent were found to be significantly affected by body temperature of the experimental animal, and can influence the probe distribution and the image patterns. Magn Reson Med 79:1212-1218, 2018. © Published 2017. This article is a U.S. Government work and is in the public domain in the USA. © Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Alfven seismic vibrations of crustal solid-state plasma in quaking paramagnetic neutron star

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bastrukov, S.; Xu, R.-X.; Molodtsova, I.

2010-11-15

Magneto-solid-mechanical model of two-component, core-crust, paramagnetic neutron star responding to quake-induced perturbation by differentially rotational, torsional, oscillations of crustal electron-nuclear solid-state plasma about axis of magnetic field frozen in the immobile paramagnetic core is developed. Particular attention is given to the node-free torsional crust-against-core vibrations under combined action of Lorentz magnetic and Hooke's elastic forces; the damping is attributed to Newtonian force of shear viscose stresses in crustal solid-state plasma. The spectral formulas for the frequency and lifetime of this toroidal mode are derived in analytic form and discussed in the context of quasiperiodic oscillations of the x-ray outburst fluxmore » from quaking magnetars. The application of obtained theoretical spectra to modal analysis of available data on frequencies of oscillating outburst emission suggests that detected variability is the manifestation of crustal Alfven's seismic vibrations restored by Lorentz force of magnetic field stresses.« less

Metal Ion Interactions with Immunoglobulin G (IgG). 1. Preliminary Studies with Electron Paramagnetic Resonance (EPR) Spectroscopy and Ultrafiltration

DTIC Science & Technology

1978-12-12

EPR and ultrafiltration studies are recommceided to conduct luture metal ion- IgG binding research. Using Scatchard plots, bind.ng levels can be...of the binding sites can be best pursued by EPR and ultrafiltration using the fragments of IgG . This report noted some difference in the binding...immunoelectrophoresis, ultrafiltration, UV spectroscopy, atomic absorption spectroscopy, and electron paramagnetic resonance (EPR). IgG used ,- ,is non

Laser Spectroscopy Investigations of Materials for Solid State Laser Systems.

DTIC Science & Technology

1988-02-01

34 ing tools such as electron paramagnetic resonance and ". oc Be11 uniaxial stress. 19 However, the lattice structure of chryso- .,Pt AI3 PAIR 4 beryl... paramagnetic of these new emission bands is not known at the present time. resonance spectrum. 15The other features of the optical spectra cannot be...solution is peak absorption c-iefficient, and E, is the saturation field. The detuning parameter which accounts for the width of the resonant electronic

Electron-beam generated porous dextran gels: experimental and quantum chemical studies.

PubMed

Naumov, Sergej; Knolle, Wolfgang; Becher, Jana; Schnabelrauch, Matthias; Reichelt, Senta

2014-06-01

The aim of this work was to investigate the reaction mechanism of electron-beam generated macroporous dextran cryogels by quantum chemical calculation and electron paramagnetic resonance measurements. Electron-beam radiation was used to initiate the cross-linking reaction of methacrylated dextran in semifrozen aqueous solutions. The pore morphology of the resulting cryogels was visualized by scanning electron microscopy. Quantum chemical calculations and electron paramagnetic resonance studies provided information on the most probable reaction pathway and the chain growth radicals. The most probable reaction pathway was a ring opening reaction and the addition of a C-atom to the double-bond of the methacrylated dextran molecule. First detailed quantum chemical calculation on the reaction mechanism of electron-beam initiated cross-linking reaction of methacrylated dextran are presented.

A Paramagnetic Molecular Voltmeter

PubMed Central

Surek, Jack T.; Thomas, David D.

2008-01-01

We have developed a general electron paramagnetic resonance (EPR) method to measure electrostatic potential at spin labels on proteins to millivolt accuracy. Electrostatic potential is fundamental to energy-transducing proteins like myosin, because molecular energy storage and retrieval is primarily electrostatic. Quantitative analysis of protein electrostatics demands a site-specific spectroscopic method sensitive to millivolt changes. Previous electrostatic potential studies on macromolecules fell short in sensitivity, accuracy and/or specificity. Our approach uses fast-relaxing charged and neutral paramagnetic relaxation agents (PRAs) to increase nitroxide spin label relaxation rate solely through collisional spin exchange. These PRAs were calibrated in experiments on small nitroxides of known structure and charge to account for differences in their relaxation efficiency. Nitroxide longitudinal (R1) and transverse (R2) relaxation rates were separated by applying lineshape analysis to progressive saturation spectra. The ratio of measured R1 increases for each pair of charged and neutral PRAs measures the shift in local PRA concentration due to electrostatic potential. Voltage at the spin label is then calculated using the Boltzmann equation. Measured voltages for two small charged nitroxides agree with Debye-Hückel calculations. Voltage for spin-labeled myosin fragment S1 also agrees with calculation based on the pK shift of the reacted cysteine. PMID:17964835

OPTESIM, a Versatile Toolbox for Numerical Simulation of Electron Spin Echo Envelope Modulation (ESEEM) that Features Hybrid Optimization and Statistical Assessment of Parameters

PubMed Central

Sun, Li; Hernandez-Guzman, Jessica; Warncke, Kurt

2009-01-01

Electron spin echo envelope modulation (ESEEM) is a technique of pulsed-electron paramagnetic resonance (EPR) spectroscopy. The analyis of ESEEM data to extract information about the nuclear and electronic structure of a disordered (powder) paramagnetic system requires accurate and efficient numerical simulations. A single coupled nucleus of known nuclear g value (gN) and spin I=1 can have up to eight adjustable parameters in the nuclear part of the spin Hamiltonian. We have developed OPTESIM, an ESEEM simulation toolbox, for automated numerical simulation of powder two- and three-pulse one-dimensional ESEEM for arbitrary number (N) and type (I, gN) of coupled nuclei, and arbitrary mutual orientations of the hyperfine tensor principal axis systems for N>1. OPTESIM is based in the Matlab environment, and includes the following features: (1) a fast algorithm for translation of the spin Hamiltonian into simulated ESEEM, (2) different optimization methods that can be hybridized to achieve an efficient coarse-to-fine grained search of the parameter space and convergence to a global minimum, (3) statistical analysis of the simulation parameters, which allows the identification of simultaneous confidence regions at specific confidence levels. OPTESIM also includes a geometry-preserving spherical averaging algorithm as default for N>1, and global optimization over multiple experimental conditions, such as the dephasing time ( ) for three-pulse ESEEM, and external magnetic field values. Application examples for simulation of 14N coupling (N=1, N=2) in biological and chemical model paramagnets are included. Automated, optimized simulations by using OPTESIM lead to a convergence on dramatically shorter time scales, relative to manual simulations. PMID:19553148

The role of spinning electrons in paramagnetic phenomena

NASA Technical Reports Server (NTRS)

Bose, D. M.

1986-01-01

An attempt is made to explain paramagnetic phenomena without assuming the orientation of a molecule or ion in a magnetic field. Only the spin angular momentum is assumed to be responsible. A derivative of the Gurie-Langevin law and the magnetic moments of ions are given as a function of the number of electrons in an inner, incomplete shell. An explanation of Gerlach's experiments with iron and nickel vapors is attempted. An explanation of magnetomechanical experiments with ferromagne elements is given.

Electron Spin Polarization Transfer to ortho-H2 by Interaction of para-H2 with Paramagnetic Species: A Key to a Novel para → ortho Conversion Mechanism.

PubMed

Terenzi, Camilla; Bouguet-Bonnet, Sabine; Canet, Daniel

2015-05-07

We report that at ambient temperature and with 100% enriched para-hydrogen (p-H2) dissolved in organic solvents, paramagnetic spin catalysis of para → ortho hydrogen conversion is accompanied at the onset by a negative ortho-hydrogen (o-H2) proton NMR signal. This novel finding indicates an electron spin polarization transfer, and we show here that this can only occur if the H2 molecule is dissociated upon its transient adsorption by the paramagnetic catalyst. Following desorption, o-H2 is created until the thermodynamic equilibrium is reached. A simple theory confirms that in the presence of a static magnetic field, the hyperfine coupling between unpaired electrons and nuclear spins is responsible for the observed polarization transfer. Owing to the negative electron gyromagnetic ratio, this explains the experimental results and ascertains an as yet unexplored mechanism for para → ortho conversion. Finally, we show that the recovery of o-H2 magnetization toward equilibrium can be simply modeled, leading to the para → ortho conversion rate.

Paramagnetic Defects in Electron-Irradiated Yttria-Stabilized Zirconia: Effect of Yttria Content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Costantini, Jean-Marc; Beuneu, Francois; Morrison-Smith, Sarah

2011-01-01

We have studied the effect of the yttria content on the paramagnetic centres in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol% or 18 mol% Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0 and 2.5 MeV. The paramagnetic centre production was studied by X-band EPR spectroscopy. The same paramagnetic centres were identified for both chemical compositions, namely two electron centres, i.e. i) F+-type centres (involving singly ionized oxygen vacancies), and ii) so-called T centres (Zr3+ in a trigonal symmetry site), and hole-centres. A strong effect is observed on the production of hole-centres which are stronglymore » enhanced when doubling the yttria content. However, no striking effect is found on the electron centres (except the enhancement of an extra line associated to the F+-type centres). It is concluded that hole-centres are produced by inelastic interactions, whereas F+-type centres are produced by elastic collisions with no effect of the yttria content on the defect production rate. In the latter case, the threshold displacement energy (Ed) of oxygen is estimated from the electron-energy dependence of the F+-type centre production rate, with no significant effect of the yttria content on Ed. An Ed value larger than 120 eV is found. Accordingly, classical molecular dynamics (MD) simulations with a Buckingham-type potential show that Ed values for Y and O are likely to be in excess of 200 eV. Due to the difficulty in displacing O or Y atoms, the radiation-induced defects may alternatively be a result of Zr atom displacements for Ed = 80 1 eV with subsequent defect re-arrangement.« less

"Dark" Singlet Oxygen and Electron Paramagnetic Resonance Spin Trapping as Convenient Tools to Assess Photolytic Drug Degradation.

PubMed

Persich, Peter; Hostyn, Steven; Joie, Céline; Winderickx, Guy; Pikkemaat, Jeroen; Romijn, Edwin P; Maes, Bert U W

2017-05-01

Forced degradation studies are an important tool for a systematic assessment of decomposition pathways and identification of reactive sites in active pharmaceutical ingredients (APIs). Two methodologies have been combined in order to provide a deeper understanding of singlet oxygen-related degradation pathways of APIs under light irradiation. First, we report that a "dark" singlet oxygen test enables the investigation of drug reactivity toward singlet oxygen independently of photolytic irradiation processes. Second, the photosensitizing properties of the API producing the singlet oxygen was proven and quantified by spin trapping and electron paramagnetic resonance analysis. A combination of these techniques is an interesting addition to the forced degradation portfolio as it can be used for (1) revealing unexpected degradation pathways of APIs due to singlet oxygen, (2) clarifying photolytic drug-drug interactions in fixed-dose combinations, and (3) synthesizing larger quantities of hardly accessible oxidative drug degradants. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

High-Frequency Electron Paramagnetic Resonance Spectroscopy of Nitroxide-Functionalized Nanodiamonds in Aqueous Solution.

PubMed

Akiel, R D; Stepanov, V; Takahashi, S

2017-06-01

Nanodiamond (ND) is an attractive class of nanomaterial for fluorescent labeling, magnetic sensing of biological molecules, and targeted drug delivery. Many of those applications require tethering of target biological molecules on the ND surface. Even though many approaches have been developed to attach macromolecules to the ND surface, it remains challenging to characterize dynamics of tethered molecule. Here, we show high-frequency electron paramagnetic resonance (HF EPR) spectroscopy of nitroxide-functionalized NDs. Nitroxide radical is a commonly used spin label to investigate dynamics of biological molecules. In the investigation, we developed a sample holder to overcome water absorption of HF microwave. Then, we demonstrated HF EPR spectroscopy of nitroxide-functionalized NDs in aqueous solution and showed clear spectral distinction of ND and nitroxide EPR signals. Moreover, through EPR spectral analysis, we investigate dynamics of nitroxide radicals on the ND surface. The demonstration sheds light on the use of HF EPR spectroscopy to investigate biological molecule-functionalized nanoparticles.

57Fe Mössbauer spectroscopy and electron paramagnetic resonance studies of human liver ferritin, Ferrum Lek and Maltofer®

NASA Astrophysics Data System (ADS)

Alenkina, I. V.; Oshtrakh, M. I.; Klencsár, Z.; Kuzmann, E.; Chukin, A. V.; Semionkin, V. A.

2014-09-01

A human liver ferritin, commercial Ferrum Lek and Maltofer® samples were studied using Mössbauer spectroscopy and electron paramagnetic resonance. Two Mössbauer spectrometers have been used: (i) a high velocity resolution (4096 channels) at 90 and 295 K, (ii) and a low velocity resolution (250 channels) at 20 and 40 K. It is shown that the three studied materials have different superparamagnetic features at various temperatures. This may be caused by different magnetic anisotropy energy barriers, sizes (volume), structures and compositions of the iron cores. The electron paramagnetic resonance spectra of the ferritin, Ferrum Lek and Maltofer® were decomposed into multiple spectral components demonstrating the presence of minor ferro- or ferrimagnetic phases along with revealing marked differences among the studied substances. Mössbauer spectroscopy provides evidences on several components in the measured spectra which could be related to different regions, layers, nanocrystallites, etc. in the iron cores that coincides with heterogeneous and multiphase models for the ferritin iron cores.

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 were generated for the irradiated specimens showed that the electrons penetrated the material to a depth of approximately 0.125 inch. These data show a very high degree of correlation to the energy deposition profile as predicted by the Tiger Code, a Monte Carlo code that provides guidelines for the transport of electrons in matter. Subsequent efforts will focus on delineating the transport properties of energetic protons in Ultem(R).

Theory for electron transfer from a mixed-valence dimer with paramagnetic sites to a mononuclear acceptor

NASA Astrophysics Data System (ADS)

Bominaar, E. L.; Achim, C.; Borshch, S. A.

1999-06-01

Polynuclear transition-metal complexes, such as Fe-S clusters, are the prosthetic groups in a large number of metalloproteins and serve as temporary electron storage units in a number of important redox-based biological processes. Polynuclearity distinguishes clusters from mononuclear centers and confers upon them unique properties, such as spin ordering and the presence of thermally accessible excited spin states in clusters with paramagnetic sites, and fractional valencies in clusters of the mixed-valence type. In an earlier study we presented an effective-mode (EM) analysis of electron transfer from a binuclear mixed-valence donor with paramagnetic sites to a mononuclear acceptor which revealed that the cluster-specific attributes have an important impact on the kinetics of long-range electron transfer. In the present study, the validity of these results is tested in the framework of more detailed theories which we have termed the multimode semiclassical (SC) model and the quantum-mechanical (QM) model. It is found that the qualitative trends in the rate constant are the same in all treatments and that the semiclassical models provide a good approximation of the more rigorous quantum-mechanical description of electron transfer under physiologically relevant conditions. In particular, the present results corroborate the importance of electron transfer via excited spin states in reactions with a low driving force and justify the use of semiclassical theory in cases in which the QM model is computationally too demanding. We consider cases in which either one or two donor sites of a dimer are electronically coupled to the acceptor. In the case of multiconnectivity, the rate constant for electron transfer from a valence-delocalized (class-III) donor is nonadditive with respect to transfer from individual metal sites of the donor and undergoes an order-of-magnitude change by reversing the sign of the intradimer metal-metal resonance parameter (β). In the case of single connectivity, the rate constant for electron transfer from a valence-localized (class-II) donor can readily be tuned over several orders of magnitude by introducing differences in the electronic potentials at the two metal sites of the donor. These results indicate that theories of cluster-based electron transfer, in order to be realistic, need to consider both intrinsic electronic structure and extrinsic interactions of the cluster with the protein environment.

A 1-2 GHz pulsed and continuous wave electron paramagnetic resonance spectrometer

NASA Astrophysics Data System (ADS)

Quine, Richard W.; Rinard, George A.; Ghim, Barnard T.; Eaton, Sandra S.; Eaton, Gareth R.

1996-07-01

A microwave bridge has been constructed that performs three types of electron paramagnetic resonance experiments: continuous wave, pulsed saturation recovery, and pulsed electron spin echo. Switching between experiment types can be accomplished via front-panel switches without moving the sample. Design features and performance of the bridge and of a resonator used in testing the bridge are described. The bridge is constructed of coaxial components connected with semirigid cable. Particular attention has been paid to low-noise design of the preamplifier and stability of automatic frequency control circuits. The bridge incorporates a Smith chart display and phase adjustment meter for ease of tuning.

Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy.

PubMed

Segawa, Takuya F; Doll, Andrin; Pribitzer, Stephan; Jeschke, Gunnar

2015-07-28

The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclear modulation spectrum.

THE INTERACTION OF PARAMAGNETIC RELAXATION REAGENTS WITH INTRA- AND INTERMOLECULAR HYDROGEN BONDED PHENOLS

EPA Science Inventory

Intermolecular electron-nuclear 13-C relaxation times (T(1)sup e's) from solutions containing the paramagnetic relaxation reagent (PARR), Cr(acac)3, used in conjunction with 13-C T(1)'s in diamagnetic solutions (intramolecular 13-C - (1)H dipolar T(1)'s) provide a significant inc...

EPR investigation of electronic excitations in rare gas solids (Review Article)

NASA Astrophysics Data System (ADS)

Zhitnikov, R. A.; Dmitriev, Yu. A.

1998-10-01

The methods are described for producing unstable paramagnetic excited states in rare gas cryocrystals Ne, Ar, Kr, and Xe through the trapping, in the cryocrystals growing from the gas phase, the products of the gas discharge taking place in the same or other rare gas. The paper presents a technique and results of an observation and investigation of excited states in rare gas cryocrystals with electron paramagnetic resonance (EPR). The discovered unstable paramagnetic centers are interpreted as being local metastable excited np5(n+1)s atomic-type states in rare gas cryocrystals which are subject to the action of the anisotropic electric field resulted from the crystal surroundings distorted by the center. An account is given of the mechanisms for formation of observed paramagnetic excited states in cryocrystals which arise owing to the excitation energy of the metastable 3P2 atoms of Ne, Ar, Kr, Xe and He 23S1 and 21S0 atoms that form in the discharge in an appropriate gas and trap in the growing cryocrystal.

The EPR of the triplet state of aryl cations in crystals of diazonium salts

NASA Astrophysics Data System (ADS)

Kondratenko, P. A.; Shrubovich, E. V.; Shulga, S. Z.

The spectra of the electron paramagnetic resonance (EPR) of aryl cations possessing a principle triplet ground-state and orientated in a monocrystal of diazonium salts is studied. It is shown that two nonequivalent paramagnetic centers, which differ in orientation are formed within the crystal. A theoretic description of experimental results is possible only when allowing for the effect of low symmetry. This symmetry is invoked by the interactivity of the paramagnetic center of symmetry C(sub 2v) with the crystal field of symmetry C(sub i).

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.

Benign Synthesis of Black Microspheres of Anatase TiO2 with Paramagnetic Oxygen Vacancies through NH3 Treatment.

PubMed

Maqbool, Qysar; Srivastava, Aasheesh

2017-10-09

Coloured TiO 2 is coveted for its ability to extract energy from the visible region of electromagnetic spectrum. Here a facile synthesis of black anatase titania microspheres (B-TiO 2 ) through a two-step process is reported. In the first step, amorphous white TiO 2 microspheres (W-TiO 2 ) are obtained by hydrolysing titanium tetraisopropoxide by ammonia vapours in ethanol. In the second step, the W-TiO 2 is thermally annealed at 500 °C to obtain B-TiO 2 . The diffuse reflectance analysis showed that B-TiO 2 absorbs across visible spectrum with absorption extending well into NIR region. Raman scattering together with EPR analysis showed compelling evidence of the existence of oxygen deficiency within the crystal in B-TiO 2 that induces black colouration in the sample. The defects present in the black anatase sample were confirmed to be single-electron-trapped (or paramagnetic) oxygen vacancies (V o ⋅) by XPS and EPR studies. The magnetic susceptibility studies showed existence of antiferromagnetic interactions between these unpaired electron spins. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

NASA Astrophysics Data System (ADS)

Gafurov, M.; Biktagirov, T.; Yavkin, B.; Mamin, G.; Filippov, Y.; Klimashina, E.; Putlayev, V.; Orlinskii, S.

2014-04-01

Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20-50 nm and 1 μm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (byproducts) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO{3/2-} paramagnetic centers detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from 1H and 31P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO{3/2-} radicals preferably occupy PO{4/3-} site in the HAp structure.

New strategy to identify radicals in a time evolving EPR data set by multivariate curve resolution-alternating least squares.

PubMed

Fadel, Maya Abou; de Juan, Anna; Vezin, Hervé; Duponchel, Ludovic

2016-12-01

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique that is able to characterize radicals formed in kinetic reactions. However, spectral characterization of individual chemical species is often limited or even unmanageable due to the severe kinetic and spectral overlap among species in kinetic processes. Therefore, we applied, for the first time, multivariate curve resolution-alternating least squares (MCR-ALS) method to EPR time evolving data sets to model and characterize the different constituents in a kinetic reaction. Here we demonstrate the advantage of multivariate analysis in the investigation of radicals formed along the kinetic process of hydroxycoumarin in alkaline medium. Multiset analysis of several EPR-monitored kinetic experiments performed in different conditions revealed the individual paramagnetic centres as well as their kinetic profiles. The results obtained by MCR-ALS method demonstrate its prominent potential in analysis of EPR time evolved spectra. Copyright © 2016 Elsevier B.V. All rights reserved.

A portable version of the program of nettar and villafranca for the simulation of electron paramagnetic resonance spectra of powders

NASA Astrophysics Data System (ADS)

Soulié, Edgar; Gaugenot, Jacques

1995-04-01

Nettar and Villafranca wrote in the FORTRAN programming language a computer program which simulates the electron paramagnetic resonance (EPR) spectra of powders (Journal of Magnetic Resonance, vol. 64 (1985) pp. 61-65). The spin Hamiltonian which their program can handle includes the Zeeman electronic interaction, the fine interaction up to the sixth order in the electron spin, a general hyperfine interaction, an isotropic nuclear Zeeman term; anisotropic ligand hyperfine terms are treated to first order in perturbation. The above Hamiltonian, without the ligand hyperfine terms, is treated exactly, i.e. the resonance equation for a transition between states labeled i and j is solved numerically: h.ν=Ei(H)-Ej(H).

Negative electric susceptibility and magnetism from translational invariance and rotational invariance

NASA Astrophysics Data System (ADS)

Koo, Je Huan

2015-02-01

In this work we investigate magnetic effects in terms of the translational and rotational invariances of magnetisation. Whilst Landau-type diamagnetism originates from translational invariance, a new diamagnetism could result from rotational invariance. Translational invariance results in only conventional Landau-type diamagnetism, whereas rotational invariance can induce a paramagnetic susceptibility for localised electrons and also a new kind of diamagnetism that is specific to conducting electrons. In solids, the moving electron shows a paramagnetic susceptibility but the surrounding screening of electrons may produce a new diamagnetic response by Lenz's law, resulting in a total susceptibility that tends to zero. For electricity, similar behaviours are obtained. We also derive the DC-type negative electric susceptibility via two methods in analogy with Landau diamagnetism.

EPR study of free radical in gamma-irradiated bis(cyclopentadienyl)zirconium dichloride single crystal

NASA Astrophysics Data System (ADS)

Caliskan, Betul; Caliskan, Ali Cengiz

2017-06-01

Bis(cyclopentadienyl)zirconium dichloride (BCZD; zirconocene dichloride) single crystals were exposed to 60Co-γ irradiation at room temperature. The irradiated single crystals were investigated between 125 and 470 K by electron paramagnetic resonance spectroscopy. The spectra of the crystals were found to be temperature independent. The paramagnetic center was attributed to the cyclopentadienyl radical. The g values of the radiation damage center observed in BCZD single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained.

Evolution of Triplet Paramagnetic Centers in Diamonds Obtained by Sintering of Detonation Nanodiamonds at High Pressure and Temperature

NASA Astrophysics Data System (ADS)

Osipov, V. Yu.; Shames, A. I.; Efimov, N. N.; Shakhov, F. M.; Kidalov, S. V.; Minin, V. V.; Vul', A. Ya.

2018-04-01

The electron paramagnetic resonance (EPR) spectra of triplet centers in detonation nanodiamonds (DNDs) and diamond single crystals of submicrometer size, synthesized from those DNDs at high pressures and temperatures, are studied. In the EPR spectra of DNDs, signals from negatively charged nitrogen- vacancy centers (NV)/sup(-) with a g factor of g 1 = 4.24 and multivacancies with g 2 = 4.00 are observed. The signals from (NV)/sup(-) centers disappear in the spectra of diamond single crystals, and a quintet signal with g = 4.00 is detected at the position of the signal from multivacancies. Analysis of the shape and position of the quintet' lines showed that this ESR signal is due to the pairs of nitrogen substitution centers in diamond, separated from each other by distances not exceeding 0.7 nm, between which a strong exchange interaction takes place. A comparison of the experimental data and the simulation results allows determining the spin-Hamiltonian parameters of the exchange-coupled pairs of paramagnetic impurity nitrogen atoms.

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 ?, ?-diphenyl ?-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.

Magnetic-field-induced effects in the electronic structure of itinerant d- and f-metal systems

NASA Astrophysics Data System (ADS)

Grechnev, G. E.

2009-08-01

A paramagnetic response of transition metals and itinerant d- and f-metal compounds in an external magnetic field is studied by employing ab initio full-potential LMTO method in the framework of the local spin density approximation. Within this method the anisotropy of the magnetic susceptibility in hexagonal close-packed transition metals is evaluated for the first time. This anisotropy is owing to the orbital Van Vleck-like paramagnetic susceptibility, which is revealed to be substantial in transition-metal systems due to hybridization effects in the electronic structure. It is demonstrated that compounds TiCo, Ni3Al, YCo2, CeCo2, YNi5, LaNi5, and CeNi5 are strong paramagnets close to the quantum critical point. For these systems the Stoner approximation underestimates the spin susceptibility, whereas the calculated field-induced spin moments provide a good description of the large paramagnetic susceptibilities and magnetovolume effects. It is revealed that an itinerant description of hybridized f electrons produces magnetic properties of the compounds CeCo2, CeNi5, UAl3, UGa3, USi3, and UGe3 in close agreement with experiment. In the uranium compounds UX3 the strong spin-orbit coupling together with hybridization effects give rise to peculiar magnetic states in which the field-induced spin moments are antiparallel to the external field, and the magnetic response is dominated by the orbital contribution.

Mechanism for the occurrence of paramagnetic planes within magnetically ordered cerium systems

NASA Astrophysics Data System (ADS)

Kioussis, Nicholas; Cooper, Bernard R.; Banerjea, Amitava

1988-11-01

Hybridization of moderately delocalized f electrons with band electrons gives rise to a highly anisotropic two-ion interaction. Previously it has been shown that such an interaction explains the experimentally observed unusual magnetic behavior of CeBi, yielding a phase transition from a higher-temperature type-I (↑↓) to a lower-temperature type-IA (↑↑↓↓) antiferromagnetic structure. If the hybridization-mediated interaction is the key to understanding the magnetic behavior of such moderately delocalized f-electron systems, we should expect to be able to understand on this basis the even more unusual magnetic behavior of CeSb. In CeSb, there is a sequence of magnetic structures in which the higher-temperature structures involve a periodic stacking of paramagnetic \\{001\\} planes alternating with magnetically ordered \\{001\\} planes of [001]-moment alignment. In this paper we show that such a coexistence of paramagnetic and magnetically ordered Ce3+ sites can be understood on the basis of the hybridization-mediated interionic interaction when there are cubic crystal-field (CF) interactions of comparable strength. The tendency to form paramagnetic planes is found to increase with increasing CF strength (Γ7 ground state); and the stability of the up-down paramagnetic plane arrangement at high temperatures is shown to arise from the reconciliation of the magnetic ordering with the CF interactions. We also find that for a certain range of parameters a different novel situation occurs, with a fully nonmagnetic (singlet) ground state for the Ce3+ ion. This singlet state is not Kondo-like, and occurs in such a way that the system would be expected to fluctuate between two differently polarized states, one of which is the singlet state.

Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Segawa, Takuya F.; Doll, Andrin; Pribitzer, Stephan

2015-07-28

The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclearmore » modulation spectrum.« less

Study of the oxidized and non- oxidized bitumen modified with additive «Adgezolin» by using electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Mukhamatdinov, I.; Gafurov, M.; Kemalov, A.; Rodionov, A.; Mamin, G.; Fakhretdinov, P.

2018-05-01

Cationic surfactant (adhesion additive) «Adgezolin» has been developed. It is shown that introduction of «Adgezolin» into the oxidized bitumen increases the relative amount of asphaltenes and monocyclearomatic hydrocarbons. By means of electron paramagnetic resonance (EPR) it is demonstrated that the introduction of additive «Adgezolin» increases the number of paramagnetic «free» carbon radicals (FR) in the oxidized bitumen and decreases that in the unoxidized species. In both types of bitumen shift from the Lorentzian to Gaussian EPR lineshape of FR is obtained that could be connected with as an increase of the samples homogeneity. It is supposed that while in the oxygenated bitumens introduction of additives leads to the disaggregation of asphaltene-resins compounds, in the unoxidized samples the balance is shifted towards formation of di-radicals.

Time-dependent broken-symmetry density functional theory simulation of the optical response of entangled paramagnetic defects: Color centers in lithium fluoride

NASA Astrophysics Data System (ADS)

Janesko, Benjamin G.

2018-02-01

Parameter-free atomistic simulations of entangled solid-state paramagnetic defects may aid in the rational design of devices for quantum information science. This work applies time-dependent density functional theory (TDDFT) embedded-cluster simulations to a prototype entangled-defect system, namely two adjacent singlet-coupled F color centers in lithium fluoride. TDDFT calculations accurately reproduce the experimental visible absorption of both isolated and coupled F centers. The most accurate results are obtained by combining spin symmetry breaking to simulate strong correlation, a large fraction of exact (Hartree-Fock-like) exchange to minimize the defect electrons' self-interaction error, and a standard semilocal approximation for dynamical correlations between the defect electrons and the surrounding ionic lattice. These results motivate application of two-reference correlated ab initio approximations to the M-center, and application of TDDFT in parameter-free simulations of more complex entangled paramagnetic defect architectures.

ESR lineshape and {sup 1}H spin-lattice relaxation dispersion in propylene glycol solutions of nitroxide radicals – Joint analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruk, D., E-mail: danuta.kruk@matman.uwm.edu.pl; Hoffmann, S. K.; Goslar, J.

2013-12-28

Electron Spin Resonance (ESR) spectroscopy and Nuclear Magnetic Relaxation Dispersion (NMRD) experiments are reported for propylene glycol solutions of the nitroxide radical: 4-oxo-TEMPO-d{sub 16} containing {sup 15}N and {sup 14}N isotopes. The NMRD experiments refer to {sup 1}H spin-lattice relaxation measurements in a broad frequency range (10 kHz–20 MHz). A joint analysis of the ESR and NMRD data is performed. The ESR lineshapes give access to the nitrogen hyperfine tensor components and the rotational correlation time of the paramagnetic molecule. The NMRD data are interpreted in terms of the theory of paramagnetic relaxation enhancement in solutions of nitroxide radicals, recentlymore » presented by Kruk et al. [J. Chem. Phys. 138, 124506 (2013)]. The theory includes the effect of the electron spin relaxation on the {sup 1}H relaxation of the solvent. The {sup 1}H relaxation is caused by dipole-dipole interactions between the electron spin of the radical and the proton spins of the solvent molecules. These interactions are modulated by three dynamic processes: relative translational dynamics of the involved molecules, molecular rotation, and electron spin relaxation. The sensitivity to rotation originates from the non-central positions of the interacting spin in the molecules. The electronic relaxation is assumed to stem from the electron spin–nitrogen spin hyperfine coupling, modulated by rotation of the radical molecule. For the interpretation of the NMRD data, we use the nitrogen hyperfine coupling tensor obtained from ESR and fit the other relevant parameters. The consistency of the unified analysis of ESR and NMRD, evaluated by the agreement between the rotational correlation times obtained from ESR and NMRD, respectively, and the agreement of the translation diffusion coefficients with literature values obtained for pure propylene glycol, is demonstrated to be satisfactory.« less

Small substrate transport and mechanism of a molybdate ATP binding cassette transporter in a lipid environment.

PubMed

Rice, Austin J; Harrison, Alistair; Alvarez, Frances J D; Davidson, Amy L; Pinkett, Heather W

2014-05-23

Embedded in the plasma membrane of all bacteria, ATP binding cassette (ABC) importers facilitate the uptake of several vital nutrients and cofactors. The ABC transporter, MolBC-A, imports molybdate by passing substrate from the binding protein MolA to a membrane-spanning translocation pathway of MolB. To understand the mechanism of transport in the biological membrane as a whole, the effects of the lipid bilayer on transport needed to be addressed. Continuous wave-electron paramagnetic resonance and in vivo molybdate uptake studies were used to test the impact of the lipid environment on the mechanism and function of MolBC-A. Working with the bacterium Haemophilus influenzae, we found that MolBC-A functions as a low affinity molybdate transporter in its native environment. In periods of high extracellular molybdate concentration, H. influenzae makes use of parallel molybdate transport systems (MolBC-A and ModBC-A) to take up a greater amount of molybdate than a strain with ModBC-A alone. In addition, the movement of the translocation pathway in response to nucleotide binding and hydrolysis in a lipid environment is conserved when compared with in-detergent analysis. However, electron paramagnetic resonance spectroscopy indicates that a lipid environment restricts the flexibility of the MolBC translocation pathway. By combining continuous wave-electron paramagnetic resonance spectroscopy and substrate uptake studies, we reveal details of molybdate transport and the logistics of uptake systems that employ multiple transporters for the same substrate, offering insight into the mechanisms of nutrient uptake in bacteria. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

Electron Paramagnetic Resonance (EPR) Spectroscopy in Studies of the Protective Effects of 24-Epibrasinoide and Selenium against Zearalenone-Stimulation of the Oxidative Stress in Germinating Grains of Wheat.

PubMed

Filek, Maria; Łabanowska, Maria; Kurdziel, Magdalena; Sieprawska, Apolonia

2017-05-27

These studies concentrate on the possibility of using selenium ions and/or 24-epibrassinolide at non-toxic levels as protectors of wheat plants against zearalenone, which is a common and widespread mycotoxin. Analysis using the UHPLC-MS technique allowed for identification of grains having the stress-tolerant and stress-sensitive wheat genotype. When germinating in the presence of 30 µM of zearalenone, this mycotoxin can accumulate in both grains and hypocotyls germinating from these grains. Selenium ions (10 µM) and 24-epibrassinolide (0.1 µM) introduced together with zearalenone decreased the uptake of zearalenone from about 295 to 200 ng/g and from about 350 to 300 ng/g in the grains of tolerant and sensitive genotypes, respectively. As a consequence, this also resulted in a reduction in the uptake of zearalenone from about 100 to 80 ng/g and from about 155 to 128 ng/g in the hypocotyls from the germinated grains of tolerant and sensitive wheat, respectively. In the mechanism of protection against the zearalenone-induced oxidative stress, the antioxidative enzymes-mainly superoxide dismutase (SOD) and catalase (CAT)-were engaged, especially in the sensitive genotype. Electron paramagnetic resonance (EPR) studies allowed for a description of the chemical character of the long-lived organic radicals formed in biomolecular structures which are able to stabilize electrons released from reactive oxygen species as well as the changes in the status of transition paramagnetic metal ions. The presence of zearalenone drastically decreased the amount of paramagnetic metal ions-mainly Mn(II) and Fe(III)-bonded in the organic matrix. This effect was particularly found in the sensitive genotype, in which these species were found at a smaller level. The protective effect of selenium ions and 24-epibrassinolide originated from their ability to inhibit the destruction of biomolecules by reactive oxygen species. An increased ability to defend biomolecules against zearalenone action was observed for 24-epibrassinolide.

Paramagnetic defects in electron-irradiated yttria-stabilized zirconia: Effect of yttria content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Costantini, Jean-Marc; Beuneu, Francois; Morrison-Smith, Sarah E.

2011-12-20

We have studied the effect of the yttria content on the paramagnetic centres in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol% or 18 mol% Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0 and 2.5 MeV. The paramagnetic centre production was studied by X-band EPR spectroscopy. The same paramagnetic centres were identified for both chemical compositions, namely two electron centres, i.e. i) F+-type centres (involving singly ionized oxygen vacancies), and ii) so-called T centres (Zr3+ in a trigonal symmetry site), and hole-centres. A strong effect is observed on the production of hole-centres which are stronglymore » enhanced when doubling the yttria content. However, no striking effect is found on the electron centres (except the enhancement of an extra line associated to the F+-type centres). It is concluded that hole-centres are produced by inelastic interactions, whereas F+-type centres are produced by elastic collisions with no effect of the yttria content on the defect production rate. In the latter case, the threshold displacement energy (Ed) of oxygen is estimated from the electron-energy dependence of the F+-type centre production rate, with no significant effect of the yttria content on Ed. An Ed value larger than 120 eV is found. Accordingly, classical molecular dynamics (MD) simulations with a Buckingham-type potential show that Ed values for Y and O are likely to be in excess of 200 eV. It is concluded that F+-type centres might be actually oxygen divacancies (F2+-type centres). Due to the difficulty in displacing O or Y atoms, the radiation-induced defects may alternatively be a result of Zr atom displacements for Ed = 80 ± 1 eV with subsequent defect re-arrangement.« less

Electron paramagnetic resonance g-tensors from state interaction spin-orbit coupling density matrix renormalization group

NASA Astrophysics Data System (ADS)

Sayfutyarova, Elvira R.; Chan, Garnet Kin-Lic

2018-05-01

We present a state interaction spin-orbit coupling method to calculate electron paramagnetic resonance g-tensors from density matrix renormalization group wavefunctions. We apply the technique to compute g-tensors for the TiF3 and CuCl42 - complexes, a [2Fe-2S] model of the active center of ferredoxins, and a Mn4CaO5 model of the S2 state of the oxygen evolving complex. These calculations raise the prospects of determining g-tensors in multireference calculations with a large number of open shells.

The tight binding model study of the role of band filling on the charge gap in graphene-on-substrate in paramagnetic state

NASA Astrophysics Data System (ADS)

Panda, Rudrashish; Sahu, Sivabrata; Rout, G. C.

2017-05-01

We communicate here a tight binding theoretical model study of the band filling effect on the charge gap in graphene-on-substrate. The Hamiltonian consists of nearest neighbor electron hopping and substrate induced gap. Besides this the Coulomb interaction is considered here within mean-field approximation in the paramagnetic limit. The electron occupancies at two sublattices are calculated by Green's function technique and are solved self consistently. Finally the charge gap i.e. Δ ¯=U [ < na > -< nb > ] is calculated and computed numerically. The results are reported.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shadangi, Asit Ku., E-mail: asitshad@iopb.res.in; Rout, G. C., E-mail: gcr@iopb.res.in

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 onmore » 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.« less

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.

Experimental proof of the existence of water clusters in fullerene-like PrF3 nanoparticles

NASA Astrophysics Data System (ADS)

Alakshin, E. M.; Blokhin, D. S.; Sabitova, A. M.; Klochkov, A. V.; Klochkov, V. V.; Kono, K.; Korableva, S. L.; Tagirov, M. S.

2012-10-01

Synthesized fullerene-like nanoparticles of the Van Vleck paramagnet PrF3 have been studied by nuclear magnetic resonance cryoporometry. Water clusters have been discovered in the internal cavities of the nanoparticles. The analysis of the experimental data indicates that the cluster radius is 1-2.3 nm. The obtained data agree well with the high-resolution transmission electron microscopy data.

Role of crystal field in mixed alkali metal effect: electron paramagnetic resonance study of mixed alkali metal oxyfluoro vanadate glasses.

PubMed

Honnavar, Gajanan V; Ramesh, K P; Bhat, S V

2014-01-23

The mixed alkali metal effect is a long-standing problem in glasses. Electron paramagnetic resonance (EPR) is used by several researchers to study the mixed alkali metal effect, but a detailed analysis of the nearest neighbor environment of the glass former using spin-Hamiltonian parameters was elusive. In this study we have prepared a series of vanadate glasses having general formula (mol %) 40 V2O5-30BaF2-(30 - x)LiF-xRbF with x = 5, 10, 15, 20, 25, and 30. Spin-Hamiltonian parameters of V(4+) ions were extracted by simulating and fitting to the experimental spectra using EasySpin. From the analysis of these parameters it is observed that the replacement of lithium ions by rubidium ions follows a "preferential substitution model". Using this proposed model, we were able to account for the observed variation in the ratio of the g parameter, which goes through a maximum. This reflects an asymmetric to symmetric changeover of the alkali metal ion environment around the vanadium site. Further, this model also accounts for the variation in oxidation state of vanadium ion, which was confirmed from the variation in signal intensity of EPR spectra.

Electron paramagnetic resonance oximetry as a quantitative method to measure cellular respiration: a consideration of oxygen diffusion interference.

PubMed

Presley, Tennille; Kuppusamy, Periannan; Zweier, Jay L; Ilangovan, Govindasamy

2006-12-15

Electron paramagnetic resonance (EPR) oximetry is being widely used to measure the oxygen consumption of cells, mitochondria, and submitochondrial particles. However, further improvement of this technique, in terms of data analysis, is required to use it as a quantitative tool. Here, we present a new approach for quantitative analysis of cellular respiration using EPR oximetry. The course of oxygen consumption by cells in suspension has been observed to have three distinct zones: pO(2)-independent respiration at higher pO(2) ranges, pO(2)-dependent respiration at low pO(2) ranges, and a static equilibrium with no change in pO(2) at very low pO(2) values. The approach here enables one to comprehensively analyze all of the three zones together-where the progression of O(2) diffusion zones around each cell, their overlap within time, and their potential impact on the measured pO(2) data are considered. The obtained results agree with previously established methods such as high-resolution respirometry measurements. Additionally, it is also demonstrated how the diffusion limitations can depend on cell density and consumption rate. In conclusion, the new approach establishes a more accurate and meaningful model to evaluate the EPR oximetry data on cellular respiration to quantify related parameters using EPR oximetry.

Electron paramagnetic resonance of a 10B-containing heterocyclic radical

NASA Astrophysics Data System (ADS)

Eaton, Sandra S.; Ngendahimana, Thacien; Eaton, Gareth R.; Jupp, Andrew R.; Stephan, Douglas W.

2018-05-01

Electron paramagnetic resonance measurements for a 10B-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), were made at X-band in 9:1 toluene:dichloromethane from 10 to 293 K and in toluene from 180 to 293 K. In well-deoxygenated 0.1 mM toluene solution at room temperature hyperfine couplings to 10B, four pairs of protons and five pairs of fluorines contribute to a continuous wave spectrum with many resolved lines. Hyperfine couplings were adjusted to provide the best fit for spectra of the radical enriched in 10B and the analogous radical synthesized with 10,11B in natural abundance, resulting in small refinements of the hyperfine coupling constants previously reported for the natural abundance sample. Electron spin relaxation rates at temperatures between 15 and 293 K were similar for samples containing 10B and natural isotope abundance. Analysis of electron spin echo envelope modulation and hyperfine correlation spectroscopy data at 80 K found Axx = -7.5 ± 0.3, Ayy = -8.5 ± 0.3, and Azz = -10.8 ± 0.3 MHz for 11B, which indicates small spin density on the boron. The spin echo and hyperfine spectroscopy data for the 10B -containing radical are consistent with the factor of 2.99 smaller hyperfine values for 10B than for 11B.

High resolution in-operando microimaging of solar cells with pulsed electrically-detected magnetic resonance

NASA Astrophysics Data System (ADS)

Katz, Itai; Fehr, Matthias; Schnegg, Alexander; Lips, Klaus; Blank, Aharon

2015-02-01

The in-operando detection and high resolution spatial imaging of paramagnetic defects, impurities, and states becomes increasingly important for understanding loss mechanisms in solid-state electronic devices. Electron spin resonance (ESR), commonly employed for observing these species, cannot meet this challenge since it suffers from limited sensitivity and spatial resolution. An alternative and much more sensitive method, called electrically-detected magnetic resonance (EDMR), detects the species through their magnetic fingerprint, which can be traced in the device's electrical current. However, until now it could not obtain high resolution images in operating electronic devices. In this work, the first spatially-resolved electrically-detected magnetic resonance images (EDMRI) of paramagnetic states in an operating real-world electronic device are provided. The presented method is based on a novel microwave pulse sequence allowing for the coherent electrical detection of spin echoes in combination with powerful pulsed magnetic-field gradients. The applicability of the method is demonstrated on a device-grade 1-μm-thick amorphous silicon (a-Si:H) solar cell and an identical device that was degraded locally by an electron beam. The degraded areas with increased concentrations of paramagnetic defects lead to a local increase in recombination that is mapped by EDMRI with ∼20-μm-scale pixel resolution. The novel approach presented here can be widely used in the nondestructive in-operando three-dimensional characterization of solid-state electronic devices with a resolution potential of less than 100 nm.

CoAs: The line of 3 d demarcation

NASA Astrophysics Data System (ADS)

Campbell, Daniel J.; Wang, Limin; Eckberg, Chris; Graf, Dave; Hodovanets, Halyna; Paglione, Johnpierre

2018-05-01

Transition metal-pnictide compounds have received attention for their tendency to combine magnetism and unconventional superconductivity. Binary CoAs lies on the border of paramagnetism and the more complex behavior seen in isostructural CrAs, MnP, FeAs, and FeP. Here we report the properties of CoAs single crystals grown with two distinct techniques along with density functional theory calculations of its electronic structure and magnetic ground state. While all indications are that CoAs is paramagnetic, both experiment and theory suggest proximity to a ferromagnetic instability. Quantum oscillations are seen in torque measurements up to 31.5 T and support the calculated paramagnetic Fermiology.

Effects of intermediate-energy electrons on mechanical and molecular properties of a polyetherimide

NASA Technical Reports Server (NTRS)

Long, S. A. T.; Long, E. R., Jr.

1984-01-01

An experiment, using 100-keV electrons and 10 to the 9th -rad doses, was conducted on Ultem polyetherimide film. Mechanical, electron paramagnetic resonance, and infrared spectroscopic data suggested that the radiation produced crosslinking and embrittlement of the material.

Conventional electron paramagnetic resonance of Mn2+ in synthetic hydroxyapatite at different concentrations of the doped manganese

NASA Astrophysics Data System (ADS)

Murzakhanov, F.; Mamin, G.; Voloshin, A.; Klimashina, E.; Putlyaev, V.; Doronin, V.; Bakhteev, S.; Yusupov, R.; Gafurov, M.; Orlinskii, S.

2018-05-01

Powders of synthetic hydroxyapatite doped with Mn2+ ions in concentrations from 0.05 till 5 wt. % were investigated by conventional electron paramagnetic resonance (EPR). The parameters of the spin-Hamiltonian are derived. Partially resolved hyperfine structure in the magnetic fields corresponding to g ≈ 4.3 and g ≈ 9.4 is observed. The narrowing of the central peak with concentration is reported. A possibility to use the linewidth and intensity of the central peak for concentration measurements are discussed. The results could be used for the identification and qualification of Mn2+ in oil, mining and ore formations.

General magnetic transition dipole moments for electron paramagnetic resonance.

PubMed

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

2015-01-09

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.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorai, Prashun; Toberer, Eric S.; Stevanović, Vladan

Here, at room temperature and above, most magnetic materials adopt a spin-disordered (paramagnetic) state whose electronic properties can differ significantly from their low-temperature, spin-ordered counterparts. Yet computational searches for new functional materials usually assume some type of magnetic order. In the present work, we demonstrate a methodology to incorporate spin disorder in computational searches and predict the electronic properties of the paramagnetic phase. We implement this method in a high-throughput framework to assess the potential for thermoelectric performance of 1350 transition-metal sulfides and find that all magnetic systems we identify as promising in the spin-ordered ground state cease to bemore » promising in the paramagnetic phase due to disorder-induced deterioration of the charge carrier transport properties. We also identify promising non-magnetic candidates that do not suffer from these spin disorder effects. In addition to identifying promising materials, our results offer insights into the apparent scarcity of magnetic systems among known thermoelectrics and highlight the importance of including spin disorder in computational searches.« less

Anisotropic rotational diffusion studied by passage saturation transfer electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Robinson, Bruce H.; Dalton, Larry R.

1980-01-01

The stochastic Liouville equation for the spin density matrix is modified to consider the effects of Brownian anisotropic rotational diffusion upon electron paramagnetic resonance (EPR) and saturation transfer electron paramagnetic resonance (ST-EPR) spectra. Spectral shapes and the ST-EPR parameters L″/L, C'/C, and H″/H defined by Thomas, Dalton, and Hyde at X-band microwave frequencies [J. Chem. Phys. 65, 3006 (1976)] are examined and discussed in terms of the rotational times τ∥ and τ⊥ and in terms of other defined correlation times for systems characterized by magnetic tensors of axial symmetry and for systems characterized by nonaxially symmetric magnetic tensors. For nearly axially symmetric magnetic tensors, such as nitroxide spin labels studied employing 1-3 GHz microwaves, ST-EPR spectra for systems undergoing anisotropic rotational diffusion are virtually indistinguishable from spectra for systems characterized by isotropic diffusion. For nonaxially symmetric magnetic tensors, such as nitroxide spin labels studied employing 8-35 GHz microwaves, the high field region of the ST-EPR spectra, and hence the H″/H parameter, will be virtually indistinguishable from spectra, and parameter values, obtained for isotropic diffusion. On the other hand, the central spectral region at x-band microwave frequencies, and hence the C'/C parameter, is sensitive to the anisotropic diffusion model provided that a unique and static relationship exists between the magnetic and diffusion tensors. Random labeling or motion of the spin label relative to the biomolecule whose hydrodynamic properties are to be investigated will destroy spectral sensitivity to anisotropic motion. The sensitivity to anisotropic motion is enhanced in proceeding to 35 GHz with the increased sensitivity evident in the low field half of the EPR and ST-EPR spectra. The L″/L parameter is thus a meaningful indicator of anisotropic motion when compared with H″/H parameter analysis. However, consideration of spectral shapes suggests that the C'/C parameter definition is not meaningfully extended from 9.5 to 35 GHz. Alternative definitions of the L″/L and C'/C parameters are proposed for those microwave frequencies for which the electron Zeeman anisotropy is comparable to or greater than the electron-nitrogen nuclear hyperfine anisotropy.

Investigating the Distribution of Stable Paramagnetic Species in an Apple Seed Using X-Band EPR and EPR Imaging.

PubMed

Nakagawa, Kouichi; Epel, Boris

2017-03-01

This study investigated the location and distribution of paramagnetic species in apple seeds using electron paramagnetic resonance (EPR) and X-band (9 GHz) EPR imaging (EPRI). EPR primarily detected two paramagnetic species per measured seed. These two different radical species were assigned as stable radicals and Mn 2+ species based on the g values and hyperfine components. The signal from the stable radical was noted at g ≈ 2.00 and was strong and relatively stable. The subsequent noninvasive EPRI of the radical present in each seed revealed that the stable radicals were located primarily in the seed coat, with very few radicals observed in the cotyledon of the seed. These results indicate that the stable radical species were only found within the seed coat, and few radical species were found in other seed parts.

Strongly driven electron spins using a Ku band stripline electron paramagnetic resonance resonator

NASA Astrophysics Data System (ADS)

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

2013-07-01

This article details our work to obtain strong excitation for electron paramagnetic resonance (EPR) experiments by improving the resonator's efficiency. The advantages and application of strong excitation are discussed. Two 17 GHz transmission-type, stripline resonators were designed, simulated and fabricated. Scattering parameter measurements were carried out and quality factor were measured to be around 160 and 85. Simulation results of the microwave's magnetic field distribution are also presented. To determine the excitation field at the sample, nutation experiments were carried out and power dependence were measured using two organic samples at room temperature. The highest recorded Rabi frequency was rated at 210 MHz with an input power of about 1 W, which corresponds to a π/2 pulse of about 1.2 ns.

High-Yield Spin Labeling of Long RNAs for Electron Paramagnetic Resonance Spectroscopy.

PubMed

Kerzhner, Mark; Matsuoka, Hideto; Wuebben, Christine; Famulok, Michael; Schiemann, Olav

2018-05-10

Site-directed spin labeling is a powerful tool for investigating the conformation and dynamics of biomacromolecules such as RNA. Here we introduce a spin labeling strategy based on click chemistry in solution that, in combination with enzymatic ligation, allows highly efficient labeling of complex and long RNAs with short reaction times and suppressed RNA degradation. With this approach, a 34-nucleotide aptamer domain of the preQ1 riboswitch and an 81-nucleotide TPP riboswitch aptamer could be labeled with two labels in several positions. We then show that conformations of the preQ1 aptamer and its dynamics can be monitored in the absence and presence of Mg 2+ and a preQ1 ligand by continuous wave electron paramagnetic resonance spectroscopy at room temperature and pulsed electron-electron double resonance spectroscopy (PELDOR or DEER) in the frozen state.

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.

An EPR study on tea: Identification of paramagnetic species, effect of heat and sweeteners

NASA Astrophysics Data System (ADS)

Bıyık, Recep; Tapramaz, Recep

2009-10-01

Tea ( Camellia Sinensis) is the most widely consumed beverage in the world, and is known to be having therapeutic, antioxidant and nutritional effects. Electron paramagnetic resonance (EPR) spectral studies made on the tea cultivated along the shore of Black Sea, Turkey, show Mn 2+ and Fe 3+ centers in green tea leaves and in black tea extract. Dry black tea flakes and dry extract show additional sharp line attributed to semiquinone radical. The origins of the paramagnetic species in black tea are defined and discussed. Effect of humidity and heat are investigated. It is observed that dry extract of black tea melts at 100 °C and the semiquinone radical lives up to 140 °C while Mn 2+ sextet disappears just above 100 °C in tea extract. Natural and synthetics sweeteners have different effects on the paramagnetic centers. White sugar (sucrose) quenches the Mn 2+ and semiquinone lines in black tea EPR spectrum, and glucose, fructose, lactose and maltose quench Fe 3+ line while synthetic sweeteners acesulfam potassium, aspartame and sodium saccharine do not have any effect on paramagnetic species in tea.

An EPR study on tea: identification of paramagnetic species, effect of heat and sweeteners.

PubMed

Biyik, Recep; Tapramaz, Recep

2009-10-15

Tea (Camellia Sinensis) is the most widely consumed beverage in the world, and is known to be having therapeutic, antioxidant and nutritional effects. Electron paramagnetic resonance (EPR) spectral studies made on the tea cultivated along the shore of Black Sea, Turkey, show Mn(2+) and Fe(3+) centers in green tea leaves and in black tea extract. Dry black tea flakes and dry extract show additional sharp line attributed to semiquinone radical. The origins of the paramagnetic species in black tea are defined and discussed. Effect of humidity and heat are investigated. It is observed that dry extract of black tea melts at 100 degrees C and the semiquinone radical lives up to 140 degrees C while Mn(2+) sextet disappears just above 100 degrees C in tea extract. Natural and synthetics sweeteners have different effects on the paramagnetic centers. White sugar (sucrose) quenches the Mn(2+) and semiquinone lines in black tea EPR spectrum, and glucose, fructose, lactose and maltose quench Fe(3+) line while synthetic sweeteners acesulfam potassium, aspartame and sodium saccharine do not have any effect on paramagnetic species in tea.

Magnetic properties and electronic structure of manganese-based blue pigments: a high-frequency and -field EPR study.

PubMed

Krzystek, J; Telser, Joshua; Li, Jun; Subramanian, M A

2015-09-21

A variety of new oxide-based materials based on hexagonal phase of YInO3 have been recently described. In some of these materials, the In(III) ions are substituted by Mn(III), which finds itself in a trigonal-bipyramidal (TBP) coordination environment. While YInO3 is colorless and YMnO3 is black, mixed systems YIn1-xMnxO3 (0.02 < x < 0.25) display intense blue color and have been proposed as novel blue pigments. Since the Mn(III) ion is paramagnetic, its presence imparts distinct magnetic properties to the whole class of materials. These properties were investigated by electron paramagnetic resonance (EPR) in its high-frequency and -field version (HFEPR), a technique ideally suited for transition metal ions such as Mn(III) that, in contrast to, for example, Mn(II), are difficult to study by EPR at (conventional) low frequency and field. YIn1-xMnxO3 with 0.02 < x < 0.2 exhibited high-quality HFEPR spectra up to room temperature that could be interpreted as arising from isolated S = 2 paramagnets. A simple ligand-field model, based on the structure and optical spectra, explains the spin Hamiltonian parameters provided by HFEPR, which were D = +3.0 cm(-1), E = 0; g⊥ = 1.99, g∥ = 2.0. This study demonstrates the general applicability of a combined spectroscopic and classical theoretical approach to understanding the electronic structure of novel materials containing paramagnetic dopants. Moreover, HFEPR complements optical and other experimental methods as being a sensitive probe of dopant level.

Excess-Si related defect centers in buried SiO2 thin films

NASA Astrophysics Data System (ADS)

Warren, W. L.; Fleetwood, D. M.; Shaneyfelt, M. R.; Schwank, J. R.; Winokur, P. S.; Devine, R. A. B.

1993-06-01

Using electron paramagnetic resonance (EPR) and capacitance-voltage measurements we have investigated the role of excess-silicon related defect centers as charge traps in separation by the implantation of oxygen materials. Three types of EPR-active centers were investigated: oxygen vacancy Eγ' centers (O3≡Si• +Si≡O3), delocalized Eδ' centers, and D centers (Si3≡Si•). It was found that all of these paramagnetic centers are created by selective hole injection, and are reasonably ascribed as positively charged when paramagnetic. These results provide the first experimental evidence for (1) the charge state of the Eδ' center, and (2) that the D center is an electrically active point defect in these materials.

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate—Part I: Cu(II)—a case of orthorhombic symmetry

NASA Astrophysics Data System (ADS)

Sambasiva Rao, P.; Rajendiran, T. M.; Venkatesan, R.; Madhu, N.; Chandrasekhar, A. V.; Reddy, B. J.; Reddy, Y. P.; Ravikumar, R. V. S. S. N.

2001-12-01

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II) doped zinc potassium phosphate hexahydrate (ZPPH) were carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice substitutionally in place of Zn(II) and the spin Hamiltonian parameters calculated from these spectra are gxx=2.188, gyy=2.032, gzz=2.373, Axx=50 G, Ayy=65.0 G and Azz=80 G. The g and A tensors were coincident and these values matched fairly well with the values obtained from powder spectrum. The bonding parameters have also been calculated.

Development of double-pulse lasers ablation system and electron paramagnetic resonance spectroscopy for direct spectral analysis of manganese doped PVA polymer

NASA Astrophysics Data System (ADS)

Khalil, A. A. I.; Morsy, M. A.; El-Deen, H. Z.

2017-11-01

Series of manganese-co-precipitated poly (vinyl alcohol) (PVA) polymer were quantitatively and qualitatively analyzed using laser ablation system (LAS) based on double-pulse laser induced breakdown spectroscopy (DP-LIBS) and electron paramagnetic resonance (EPR) spectroscopy. The collinear nanosecond laser beams of 266 and 1064 nm were optimized to focus on the surface of the PVA polymer target. Both laser beams were employed to estimate the natural properties of the excited Mn-PVA plasma, such as electron number density (Ne), electron temperature (Te), and Mn concentration. Individual transition lines of manganese (Mn), carbon (C), lithium (Li), hydrogen (H) and oxygen (O) atoms are identified based on the NIST spectral database. The results show better responses with DP-LIBS than the single-pulse laser induced breakdown spectroscopy (SP-LIBS). On the other hand, the EPR investigation shows characteristic broad peak of Mn-nano-particles (Mn-NPs) in the range of quantum dots of superparamagnetic materials. The line width (peak-to-peak, ΔHpp) and g-value of the observed Mn-EPR peak are ∼20 mT and 2.0046, respectively. The intensities of Mn-emission line at a wavelength 403.07 nm and the Mn-EPR absorption peak were used to accurate quantify the Mn-content in the polymer matrix. The results produce linear trends within the studied concentration range with regression coefficient (R2) value of ∼0.99, and limit of detection (LOD) of 0.026 mol.% and 0.016 mol.%, respectively. The LOD values are at a fold change of about -0.2 of the studied lowest mol.%. The proposed protocols of trace element detection are of significant advantage and can be applied to the other metal analysis.

Changes in mitochondrial functioning with electromagnetic radiation of ultra high frequency as revealed by electron paramagnetic resonance methods.

PubMed

Burlaka, Anatoly; Selyuk, Marina; Gafurov, Marat; Lukin, Sergei; Potaskalova, Viktoria; Sidorik, Evgeny

2014-05-01

To study the effects of electromagnetic radiation (EMR) of ultra high frequency (UHF) in the doses equivalent to the maximal permitted energy load for the staffs of the radar stations on the biochemical processes that occur in the cell organelles. Liver, cardiac and aorta tissues from the male rats exposed to non-thermal UHF EMR in pulsed and continuous modes were studied during 28 days after the irradiation by the electron paramagnetic resonance (EPR) methods including a spin trapping of superoxide radicals. The qualitative and quantitative disturbances in electron transport chain (ETC) of mitochondria are registered. A formation of the iron-nitrosyl complexes of nitric oxide (NO) radicals with the iron-sulphide (FeS) proteins, the decreased activity of FeS-protein N2 of NADH-ubiquinone oxidoreductase complex and flavo-ubisemiquinone growth combined with the increased rates of superoxide production are obtained. (i) Abnormalities in the mitochondrial ETC of liver and aorta cells are more pronounced for animals radiated in a pulsed mode; (ii) the alterations in the functioning of the mitochondrial ETC cause increase of superoxide radicals generation rate in all samples, formation of cellular hypoxia, and intensification of the oxide-initiated metabolic changes; and (iii) electron paramagnetic resonance methods could be used to track the qualitative and quantitative changes in the mitochondrial ETC caused by the UHF EMR.

Paramagnetic resonance studies of bistrispyrazolylborate cobalt(II) and related derivatives

NASA Astrophysics Data System (ADS)

Myers, William K.

Herein, a systematic frozen solution electron-nuclear double resonance (ENDOR) study of high-spin Co(II) complexes is reported to demonstrate the efficacy of methyl substitutions as a means of separating dipolar and contact coupling, and further, to increase the utility of high-spin Co(II) as a spectroscopic probe for the ubiquitous, but spectroscopically-silent Zn(II) metalloenzymes. High-spin (hs) Co(II) has been subject of paramagnetic resonance studies for over 50 years and has been used as a spectroscopic probe for Zn metalloenzymes for over 35 years. However, as will be seen, the inherent complexity of the electronic properties of the cobaltous ion remains to be exploited to offer a wealth of information on Zn(II) enzymatic environments. Specifically, ENDOR measurements on bistrispyrazolylborate cobalt(II) confirm the utility of the novel method of methyl substitution to differentiate dipolar and Fermi contact couplings. An extensive set of electron paramagnetic resonance (EPR) simulations were performed. Software was developed to implement an ENDOR control interface. Finally, proton relaxation measurements were made in the range of 12-42 MHz, which were accounted for with the large g-value anisotropy of the Co(II) compounds. Taken as a whole, these studies point to the rich complexity of the electronic structure of high-spin cobalt(II) and, when sufficiently well-characterized, the great utility it has as a surrogate of biological Zn(II).

Stable and rigid DTPA-like paramagnetic tags suitable for in vitro and in situ protein NMR analysis.

PubMed

Chen, Jia-Liang; Zhao, Yu; Gong, Yan-Jun; Pan, Bin-Bin; Wang, Xiao; Su, Xun-Cheng

2018-02-01

Organic synthesis of a ligand with high binding affinities for paramagnetic lanthanide ions is an effective way of generating paramagnetic effects on proteins. These paramagnetic effects manifested in high-resolution NMR spectroscopy are valuable dynamic and structural restraints of proteins and protein-ligand complexes. A paramagnetic tag generally contains a metal chelating moiety and a reactive group for protein modification. Herein we report two new DTPA-like tags, 4PS-PyDTTA and 4PS-6M-PyDTTA that can be site-specifically attached to a protein with a stable thioether bond. Both protein-tag adducts form stable lanthanide complexes, of which the binding affinities and paramagnetic tensors are tunable with respect to the 6-methyl group in pyridine. Paramagnetic relaxation enhancement (PRE) effects of Gd(III) complex on protein-tag adducts were evaluated in comparison with pseudocontact shift (PCS), and the results indicated that both 4PS-PyDTTA and 4PS-6M-PyDTTA tags are rigid and present high-quality PREs that are crucially important in elucidation of the dynamics and interactions of proteins and protein-ligand complexes. We also show that these two tags are suitable for in-situ protein NMR analysis.

Electron paramagnetic resonance image reconstruction with total variation and curvelets regularization

NASA Astrophysics Data System (ADS)

Durand, Sylvain; Frapart, Yves-Michel; Kerebel, Maud

2017-11-01

Spatial electron paramagnetic resonance imaging (EPRI) is a recent method to localize and characterize free radicals in vivo or in vitro, leading to applications in material and biomedical sciences. To improve the quality of the reconstruction obtained by EPRI, a variational method is proposed to inverse the image formation model. It is based on a least-square data-fidelity term and the total variation and Besov seminorm for the regularization term. To fully comprehend the Besov seminorm, an implementation using the curvelet transform and the L 1 norm enforcing the sparsity is proposed. It allows our model to reconstruct both image where acquisition information are missing and image with details in textured areas, thus opening possibilities to reduce acquisition times. To implement the minimization problem using the algorithm developed by Chambolle and Pock, a thorough analysis of the direct model is undertaken and the latter is inverted while avoiding the use of filtered backprojection (FBP) and of non-uniform Fourier transform. Numerical experiments are carried out on simulated data, where the proposed model outperforms both visually and quantitatively the classical model using deconvolution and FBP. Improved reconstructions on real data, acquired on an irradiated distal phalanx, were successfully obtained.

Possible observation of Griffith phase over large temperature range in plasma sintered La0.67Ca0.33MnO3

NASA Astrophysics Data System (ADS)

Mishra, D. K.; Roul, B. K.; Singh, S. K.; Srinivasu, V. V.

2018-02-01

We report on the possible observation of Griffith phase in a wide range of temperature (>272-378 K) in the 2.5 min plasma sintered La0.67Ca0.33MnO3 (LCMO) as deduced from careful electron spin resonance studies. This is 106 K higher than the paramagnetic to ferromagnetic transition (Curie transition ∼272 K) temperature. The indication of Griffith phase in such a wide range is not reported earlier by any group. We purposefully prepared LCMO samples by plasma sintering technique so as to create a disordered structure by rapid quenching which we believe, is the prime reason for the observation of Griffith Phase above the Curie transition temperature. The inverse susceptibility curve represents the existence of ferromagnetic cluster in paramagnetic region. The large resonance peak width (40-60 mT) within the temperature range 330-378 K confirms the sample magnetically inhomogeneity which is also established from our electron probe microstructure analysis (EPMA). EPMA establishes the presence of higher percentage of Mn3+ cluster in comparison to Mn4+. This is the reason for which Griffith state is enhanced largely to a higher range of temperature.

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

2012-08-08

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.

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.

A Paramagnetic Copper(III) Complex Containing an Octahedral CuIII S6 Coordination Polyhedron.

PubMed

Krebs, Carsten; Glaser, Thorsten; Bill, Eckhard; Weyhermüller, Thomas; Meyer-Klaucke, Wolfram; Wieghardt, Karl

1999-02-01

Only the second octahedral, paramagnetic copper(III) complex (S=1) has now been synthesized and characterized. Six thiolato bridging ligands in the heterotrinuclear species [LCo III Cu III Co III L](ClO 4 ) 3 ⋅2 Me 2 CO (L=1,4,7-tris(4-tert-butyl-2-sulfidobenzyl)-1,4,7-triazacyclononane) stabilize this rare electron configuration. A section of the structure of the reduced form (Cu II , S=½) is shown. XAS, EXAFS, and EPR spectroscopy prove unambiguously that the one-electron oxidation to the copper(III) is metal- rather than ligand-centered. © 1999 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.

Electron Paramagnetic Resonance Oximetry as a Quantitative Method to Measure Cellular Respiration: A Consideration of Oxygen Diffusion Interference

PubMed Central

Presley, Tennille; Kuppusamy, Periannan; Zweier, Jay L.; Ilangovan, Govindasamy

2006-01-01

Electron paramagnetic resonance (EPR) oximetry is being widely used to measure the oxygen consumption of cells, mitochondria, and submitochondrial particles. However, further improvement of this technique, in terms of data analysis, is required to use it as a quantitative tool. Here, we present a new approach for quantitative analysis of cellular respiration using EPR oximetry. The course of oxygen consumption by cells in suspension has been observed to have three distinct zones: pO2-independent respiration at higher pO2 ranges, pO2-dependent respiration at low pO2 ranges, and a static equilibrium with no change in pO2 at very low pO2 values. The approach here enables one to comprehensively analyze all of the three zones together—where the progression of O2 diffusion zones around each cell, their overlap within time, and their potential impact on the measured pO2 data are considered. The obtained results agree with previously established methods such as high-resolution respirometry measurements. Additionally, it is also demonstrated how the diffusion limitations can depend on cell density and consumption rate. In conclusion, the new approach establishes a more accurate and meaningful model to evaluate the EPR oximetry data on cellular respiration to quantify related parameters using EPR oximetry. PMID:17012319

Growth and characterization of manganese doped gallium nitride nanowires.

PubMed

Kumar, V Suresh; Kesavamoorthy, R; Kumar, J

2008-08-01

Manganese doped GaN nanowires have been grown by chemical vapour transport method on sapphire (0001) substrates in the temperature range of 800-1050 degrees C. The surface features of nanowires have been investigated using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDAX), Raman scattering studies and Electron Paramagnetic Resonance (EPR). SEM images showed that the morphology of the one dimensional materials included straight nanorods and nanowires around 70-80 nm. Raman spectrum showed the GaMnN vibrational modes at 380, 432 and 445 cm(-1). EPR measurements were performed on Mn doped GaN nanowires in order to evaluate the magnetic behaviour.

Characterization of the Solution Structure of Human Serum Albumin Loaded with a Metal Porphyrin and Fatty Acids

PubMed Central

Junk, Matthias J.N.; Spiess, Hans W.; Hinderberger, Dariush

2011-01-01

The structure of human serum albumin loaded with a metal porphyrin and fatty acids in solution is characterized by orientation-selective double electron-electron resonance (DEER) spectroscopy. Human serum albumin, spin-labeled fatty acids, and Cu(II) protoporphyrin IX—a hemin analog—form a fully self-assembled system that allows obtaining distances and mutual orientations between the paramagnetic guest molecules. We report a simplified analysis for the orientation-selective DEER data which can be applied when the orientation selection of one spin in the spin pair dominates the orientation selection of the other spin. The dipolar spectra reveal a dominant distance of 3.85 nm and a dominant orientation of the spin-spin vectors between Cu(II) protoporphyrin IX and 16-doxyl stearic acid, the electron paramagnetic resonance reporter group of the latter being located near the entry points to the fatty acid binding sites. This observation is in contrast to crystallographic data that suggest an asymmetric distribution of the entry points in the protein and hence the occurrence of various distances. In conjunction with the findings of a recent DEER study, the obtained data are indicative of a symmetric distribution of the binding site entries on the protein's surface. The overall anisotropic shape of the protein is reflected by one spin-spin vector orientation dominating the DEER data. PMID:21539799

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate--part I: Cu(II)--a case of orthorhombic symmetry.

PubMed

Sambasiva Rao, P; Rajendiran, T M; Venkatesan, R; Madhu, N; Chandrasekhar, A V; Reddy, B J; Reddy, Y P; Ravikumar, R V

2001-12-01

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II) doped zinc potassium phosphate hexahydrate (ZPPH) were carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice substitutionally in place of Zn(II) and the spin Hamiltonian parameters calculated from these spectra are g(xx) = 2.188, g(yy) = 2.032, g(zz) = 2.373, Axx = 50 G, Ayy = 65.0 G and Azz = 80 G. The g and A tensors were coincident and these values matched fairly well with the values obtained from powder spectrum. The bonding parameters have also been calculated.

2D FTIR correlation spectroscopy and EPR analysis of Urtica dioica leaves from areas of different environmental pollution

NASA Astrophysics Data System (ADS)

Moskal, Paulina; Wesełucha-Birczyńska, Aleksandra; Łabanowska, Maria; Kurdziel, Magdalena; Filek, Maria

2018-01-01

Leaves of Urtica dioica collected from two areas of different environmental pollution were analysed by fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR) spectroscopy. Analysis of FTIR spectra allows to describe main component of plant like proteins, lipids and carbohydrates. Although the FTIR spectra of plants from these two geographical locations of different environmental pollution appear to be relatively similar, 2D correlation shows completely different patterns. Synchronous and asynchronous correlation maps showed sequences of changes occurring during development of plant, manly in Amide I and Amide II, lignin, lipids and cellulose. In addition, 2D analysis revealed another sequence of changes as the function of plant growth depending on the degree of the environmental pollution. Two various kinds of paramagnetic species, transition metal ions (Mn(II), Fe(III)) and stable organic radicals (chlorophyll, semiquinone, tyrosyl and carbon centered) were found in leaves of nettle collected at different stages of development and growing in clean and polluted environment. In plants growing in polluted area the injuries of protein molecules bonding metal ions and the disturbances of photosynthesis and redox equilibrium in cells, as well as instability of polysaccharide structure of cell walls were observed.

Thermoelectricity in transition metal compounds: The role of spin disorder

DOE PAGES

Gorai, Prashun; Toberer, Eric S.; Stevanović, Vladan

2016-11-01

Here, at room temperature and above, most magnetic materials adopt a spin-disordered (paramagnetic) state whose electronic properties can differ significantly from their low-temperature, spin-ordered counterparts. Yet computational searches for new functional materials usually assume some type of magnetic order. In the present work, we demonstrate a methodology to incorporate spin disorder in computational searches and predict the electronic properties of the paramagnetic phase. We implement this method in a high-throughput framework to assess the potential for thermoelectric performance of 1350 transition-metal sulfides and find that all magnetic systems we identify as promising in the spin-ordered ground state cease to bemore » promising in the paramagnetic phase due to disorder-induced deterioration of the charge carrier transport properties. We also identify promising non-magnetic candidates that do not suffer from these spin disorder effects. In addition to identifying promising materials, our results offer insights into the apparent scarcity of magnetic systems among known thermoelectrics and highlight the importance of including spin disorder in computational searches.« less

300 MHz continuous wave electron paramagnetic resonance spectrometer for small animal in vivo imaging

NASA Astrophysics Data System (ADS)

Koscielniak, J.; Devasahayam, N.; Moni, M. S.; Kuppusamy, P.; Yamada, K.; Mitchell, J. B.; Krishna, M. C.; Subramanian, S.

2000-11-01

Design and construction of an electron paramagnetic resonance (EPR) spectrometer, operating in the continuous wave mode in the radio frequency (rf) region, and capable of performing spectroscopy and in vivo imaging of paramagnetic spin probes is described. A resonant frequency of 300 MHz was chosen to provide the required sensitivity at nontoxic levels of commonly used spin probes and penetration of the rf in small animals. Three major components, the magnet, the radio frequency signal detection bridge, and the data acquisition module are described in this article. Integration of a rapid scan capability to reduce imaging time is also described. Two- and three-dimensional EPR images of the spin probe distribution in phantom objects as well as from in vivo experiments are reported. From the EPR images, morphology of some internal organs could be recognized. EPR images of the spin probe distribution in mice suggest differences in perfusion of the spin probe between normal and tumor regions. Addition of a spectral dimension to spatial images should enable differentiation of oxygen status in normal and pathological conditions.

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. Copyright © 2012 Elsevier GmbH. All rights reserved.

X-band Electron Paramagnetic Resonance Investigation of Stable Organic Radicals Present under Cold Stratification in 'Fuji' Apple Seeds.

PubMed

Nakagawa, Kouichi; Matsumoto, Kazuhiro; Chaiserm, Nattakan; Priprem, Aroonsri

2017-01-01

We investigated stable organic radicals formed in response to cold stratification in 'Fuji' apple seeds using X-band (9 GHz) electron paramagnetic resonance (EPR) technique. This technique primarily detected two paramagnetic species in each seed. These two different radical species were assigned as a stable organic radical and Mn 2+ species based on the g values and hyperfine components. Signal from the stable radicals was noted at a g value of about 2.00 and was strong and relatively stable. Significant radical intensity changes were observed in apple seeds on refrigeration along with water supplementation. The strongest radical intensity and a very weak Mn 2+ signal were also observed for the seeds kept in moisture-containing sand in a refrigerator. Noninvasive EPR of the radicals present in each seed revealed that the stable radicals were located primarily in the seed coat. These results indicate that the significant radical intensity changes in apple seeds under refrigeration for at least 90 days followed by water supplementation for one week, can be related to cold stratification of the seeds.

Observation of superconductivity in BaNb2S5

NASA Astrophysics Data System (ADS)

Smith, M. G.; Neumeier, J. J.

2018-06-01

Bulk superconductivity is reported in BaNb2S5 at the transition temperature Tc = 0.85(1) K. The electrical resistivity ρ versus T is metallic with ρ(2 K) = 42.4 μΩ cm. The magnetic susceptibility is paramagnetic, with temperature-independent contributions due to diamagnetism, Pauli paramagnetism, and Van Vleck paramagnetism; a Curie-Weiss contribution appears to be impurity related. Hall effect measurements show that the majority charge carriers are electrons with charge-carrier concentration n(3 K) = 2.40(2) × 1021 cm-3. Specific heat measurements reveal an electronic specific heat coefficient γ = 11.2(1) mJ/mol K2, a Debye temperature ΘD = 126.4(8) K, and an energy gap associated with the superconducting state of Eg = 0.184(4) meV. Measurements of ρ(T) in magnetic field provide the upper critical magnetic field of about 3055(74) Oe as T → 0 K, which was used to estimate the coherence length ξ = 6.21(15) nm. The results allow classification of BaNb2S5 as a Type II, BCS superconductor in the dirty limit.

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.

High-precision measurement of the electron spin g factor of trapped atomic nitrogen in the endohedral fullerene N@C60

NASA Astrophysics Data System (ADS)

Wittmann, J. J.; Can, T. V.; Eckardt, M.; Harneit, W.; Griffin, R. G.; Corzilius, B.

2018-05-01

The electronic g factor carries highly useful information about the electronic structure of a paramagnetic species, such as spin-orbit coupling and dia- or paramagnetic (de-)shielding due to local fields of surrounding electron pairs. However, in many cases, a near "spin-only" case is observed, in particular for light elements, necessitating accurate and precise measurement of the g factors. Such measurement is typically impeded by a "chicken and egg situation": internal or external reference standards are used for relative comparison of electron paramagnetic resonance (EPR) Larmor frequencies. However, the g factor of the standard itself usually is subject to a significant uncertainty which directly limits the precision and/or accuracy of the sought after sample g factor. Here, we apply an EPR reference-free approach for determining the g factor of atomic nitrogen trapped within the endohedral fullerene C60:N@C60 in its polycrystalline state by measuring the 1H NMR resonance frequency of dispersing toluene at room temperature. We found a value of g = 2.00204 (4) with a finally reached relative precision of ∼20 ppm. This accurate measurement allows us to directly compare the electronic properties of N@C60 to those found in atomic nitrogen in the gas phase or trapped in other solid matrices at liquid helium temperature. We conclude that spin-orbit coupling in N@C60 at room temperature is very similar in magnitude and of same sign as found in other inert solid matrices and that interactions between the quartet spin system and the C60 molecular orbitals are thus negligible.

CW EPR and 9 GHz EPR imaging investigation of stable paramagnetic species and their antioxidant activities in dry shiitake mushroom (Lentinus edodes).

PubMed

Nakagawa, Kouichi; Hara, Hideyuki

2016-01-01

We investigated the antioxidant activities and locations of stable paramagnetic species in dry (or drying) shiitake mushroom (Lentinus edodes) using continuous wave (CW) electron paramagnetic resonance (EPR) and 9 GHz EPR imaging. CW 9 GHz EPR detected paramagnetic species (peak-to-peak linewidth (ΔHpp) = 0.57 mT) in the mushroom. Two-dimensional imaging of the sharp line using a 9 GHz EPR imager showed that the species were located in the cap and shortened stem portions of the mushroom. No other location of the species was found in the mushroom. However, radical locations and concentrations varied along the cap of the mushroom. The 9 GHz EPR imaging determined the exact location of stable paramagnetic species in the shiitake mushroom. Distilled water extracts of the pigmented cap surface and the inner cap of the mushroom showed similar antioxidant activities that reduced an aqueous solution of 0.1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl. The present results suggest that the antioxidant activities of the edible mushroom extracts are much weaker than those of ascorbic acid. Thus, CW EPR and EPR imaging revealed the location and distribution of stable paramagnetic species and the antioxidant activities in the shiitake mushroom for the first time.

Superlattice Structures, Electronic Properties, and Spin Dynamics of the Partially Cu-Extracted Phase for the Composite Crystal System CuxV4O11

NASA Astrophysics Data System (ADS)

Onoda, Masashige; Tamura, Asato

2017-02-01

The crystal structures, electronic properties, and spin dynamics of CuxV4O11 with 1.2 ≤ x < 2, classified as the partially Cu-extracted phase for the composite crystal system, are explored through measurements of x-ray four-circle diffraction, electrochemistry, electrical resistivity, thermoelectric power, magnetization, and electron paramagnetic resonance. This system has superlattice structures mainly ascribed to the partial ordering of Cu ions. Cu1.78V4O11 is triclinic with space group Pbar{1} and the double supercell of the V4O11 substructure of the composite crystal. The significantly Cu-extracted crystal Cu1.40V4O11 has a quadruple supercell with space group P1. The electron transport for V ions is nonmetallic owing to the polaronic nature and/or phonon softening and to the random potential of Cu ions. The Curie-Weiss-type paramagnetism basically originates from the Cu2+ chain coordinated octahedrally, and the EPR relaxation at low temperatures is understood through the exchange mechanism for the dipole-dipole and anisotropic exchange interactions. The near absence of paramagnetic behaviors of V4+ ions might be due to the spin-singlet ladder model or alternating-exchange chain model depending on the superlattice structure and valence distribution. The electrochemical performance of Li rechargeable batteries using this superlattice system is about 300 A h kg-1 at voltages above 2 V.

Optical detection of electron paramagnetic resonance in room-temperature electron-irradiated ZnO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlasenko, L.S.; Watkins, G.D.

The dominant defect observed in the photoluminescence (PL) of room-temperature electron-irradiated ZnO by optical detection of electron paramagnetic resonance (ODEPR) is determined to be the positively charged oxygen vacancy (V{sub O}{sup +}). Its spectrum, labeled L3, was previously observed in a 4.2 K in situ irradiation study [Yu. V. Gorelkinskii and G. D. Watkins, Phys. Rev. B 69, 115212 (2004)], but it was thought there not to be stable at room temperature and was not identified. Here it is found to be stable to 400 deg. C, where it disappears. It is observed as a competing process (negative signal) tomore » the dominant PL band produced by the irradiation at {approx}700 nm, but is positive in a weaker band at {approx}600 nm. Models are presented for its electrical level position in the gap to explain the results. Two other ODEPR signals are also detected, one of which is tentatively identified as also associated with the oxygen vacancy.« less

Ultrafast Magnetization of a Dense Molecular Gas with an Optical Centrifuge.

PubMed

Milner, A A; Korobenko, A; Milner, V

2017-06-16

Strong laser-induced magnetization of oxygen gas at room temperature and atmospheric pressure is achieved experimentally on the subnanosecond time scale. The method is based on controlling the electronic spin of paramagnetic molecules by means of manipulating their rotation with an optical centrifuge. Spin-rotational coupling results in a high degree of spin polarization on the order of one Bohr magneton per centrifuged molecule. Owing to the nonresonant interaction with the laser pulses, the demonstrated technique is applicable to a broad class of paramagnetic rotors. Executed in a high-density gas, it may offer an efficient way of generating macroscopic magnetic fields remotely (as shown in this work) and producing a large amount of spin-polarized electrons.

Ultrafast Magnetization of a Dense Molecular Gas with an Optical Centrifuge

NASA Astrophysics Data System (ADS)

Milner, A. A.; Korobenko, A.; Milner, V.

2017-06-01

Strong laser-induced magnetization of oxygen gas at room temperature and atmospheric pressure is achieved experimentally on the subnanosecond time scale. The method is based on controlling the electronic spin of paramagnetic molecules by means of manipulating their rotation with an optical centrifuge. Spin-rotational coupling results in a high degree of spin polarization on the order of one Bohr magneton per centrifuged molecule. Owing to the nonresonant interaction with the laser pulses, the demonstrated technique is applicable to a broad class of paramagnetic rotors. Executed in a high-density gas, it may offer an efficient way of generating macroscopic magnetic fields remotely (as shown in this work) and producing a large amount of spin-polarized electrons.

Transport and magnetic properties of disordered Li xV yO 2 ( x=0.8 and y=0.8)

NASA Astrophysics Data System (ADS)

Du, Fei; Li, Ang; Liu, Daliang; Zhan, Shiying; Hu, Fang; Wang, Chunzhong; Chen, Yan; Feng, Shouhua; Chen, Gang

2009-07-01

The magnetic and electron transport properties of rhombohedral Li xV yO 2 ( x=0.8 and y=0.8) are studied. The dc susceptibility of Li xV yO 2 can be well fitted to the modified Curie-Weiss law, which verified the paramagnetic ground state. The magnetic hysteresis and ac susceptibility also confirm this paramagnetism. The Li xV yO 2 exhibits semiconducting behavior, which is explained by thermal activated process at high temperature and variable-range hopping mechanism at low temperature. Anderson localization plays an important role in both the electron transport behavior and the magnetic behavior due to the site disorder between the Li + ion and V 4+ ion.

Electronic phase separation in insulating (Ga, Mn) As with low compensation: super-paramagnetism and hopping conduction

NASA Astrophysics Data System (ADS)

Yuan, Ye; Wang, Mao; Xu, Chi; Hübner, René; Böttger, Roman; Jakiela, Rafal; Helm, Manfred; Sawicki, Maciej; Zhou, Shengqiang

2018-03-01

In the present work, low compensated insulating (Ga,Mn)As with 0.7% Mn is obtained by ion implantation combined with pulsed laser melting. The sample shows variable-range hopping transport behavior with a Coulomb gap in the vicinity of the Fermi energy, and the activation energy is reduced by an external magnetic field. A blocking super-paramagnetism is observed rather than ferromagnetism. Below the blocking temperature, the sample exhibits a colossal negative magnetoresistance. Our studies confirm that the disorder-induced electronic phase separation occurs in (Ga,Mn)As samples with a Mn concentration in the insulator-metal transition regime, and it can account for the observed superparamagnetism and the colossal magnetoresistance.

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

Growth Kinetics of the S Sub H Center on Magnesium Oxide Using Electron Paramagnetic Resonance

NASA Technical Reports Server (NTRS)

Jayne, J. P.

1971-01-01

Electron paramagnetic resonance spectroscopy was used to study the growth of S sub H centers on magnesium oxide powder which had hydrogen adsorbed on its surface. The centers were produced by ultraviolet radiation. The effects of both radiation intensity and hydrogen pressure were also studied. At constant hydrogen pressure and radiation dose, the initial S sub H center growth rate was found to be zero order. Beyond the initial region the growth rate deviated from zero order and finally approached saturation. The results are interpreted in terms of a model which assumes that the S sub H center is a hydrogen atom associated with a surface vacancy. Saturation appears to result from a limited supply of surface vacancies.

Search for exotic short-range interactions using paramagnetic insulators

DOE PAGES

Chu, Pinghan; Weisman, E.; Liu, C. -Y.; ...

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

Carbon-related platinum defects in silicon: An electron paramagnetic resonance study of high spin states

NASA Astrophysics Data System (ADS)

Scheerer, O.; Höhne, M.; Juda, U.; Riemann, H.

1997-10-01

In this article, we report about complexes in silicon investigated by electron paramagnetic resonance (EPR). In silicon doped with C and Pt we detected two different complexes: cr-1Pt (cr: carbon-related, 1Pt: one Pt atom) and cr-3Pt. The complexes have similar EPR properties. They show a trigonal symmetry with effective g-values geff,⊥=2g⊥≈4 and geff,‖=g‖≈2 (g⊥, g‖ true g-values). The g-values can be explained by a spin Hamiltonian with large fine-structure energy (electron spin S=3/2) and smaller Zeeman interaction. The participation of platinum in the complexes is proved by the hyperfine interaction. From experiments with varying carbon concentration we conclude that the complexes contain carbon. Atomistic models based on the Watkins vacancy-model for substitutional Pt were developed.

Electrical detection of electron-spin-echo envelope modulations in thin-film silicon solar cells

NASA Astrophysics Data System (ADS)

Fehr, M.; Behrends, J.; Haas, S.; Rech, B.; Lips, K.; Schnegg, A.

2011-11-01

Electrically detected electron-spin-echo envelope modulations (ED-ESEEM) were employed to detect hyperfine interactions between nuclear spins and paramagnetic sites, determining spin-dependent transport processes in multilayer thin-film microcrystalline silicon solar cells. Electrical detection in combination with a modified Hahn-echo sequence was used to measure echo modulations induced by 29Si, 31P, and 1H nuclei weakly coupled to electron spins of paramagnetic sites in the amorphous and microcrystalline solar cell layers. In the case of CE centers in the μc-Si:H i-layer, the absence of 1H ESEEM modulations indicates that the adjacencies of CE centers are depleted from hydrogen atoms. On the basis of this result, we discuss several models for the microscopic origin of the CE center and conclusively assign those centers to coherent twin boundaries inside of crystalline grains in μc-Si:H.

Paramagnetic NMR Investigation of Dendrimer-Based Host-Guest Interactions

PubMed Central

Wang, Fei; Shao, Naimin; Cheng, Yiyun

2013-01-01

In this study, the host-guest behavior of poly(amidoamine) (PAMAM) dendrimers bearing amine, hydroxyl, or carboxylate surface functionalities were investigated by paramagnetic NMR studies. 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO) derivatives were used as paramagnetic guest molecules. The results showed that TEMPO-COOH significantly broaden the 1H NMR peaks of amine- and hydroxyl-terminated PAMAM dendrimers. In comparison, no paramagnetic relaxation enhancement (PRE) was observed between TEMPO-NH2, TEMPO-OH and the three types of PAMAM dendrimers. The PRE phenomenon observed is correlated with the encapsulation of TEMPO-COOH within dendrimer pockets. Protonation of the tertiary amine groups within PAMAM dendrimers plays an important role during this process. Interestingly, the absence of TEMPO-COOH encapsulation within carboxylate-terminated PAMAM dendrimer is observed due to the repulsion of TEMPO-COO- anion and anionic dendrimer surface. The combination of paramagnetic probes and 1H NMR linewidth analysis can be used as a powerful tool in the analysis of dendrimer-based host-guest systems. PMID:23762249

Structural and electronic studies of metal carbide clusterfullerene Sc2C2@Cs-C72

NASA Astrophysics Data System (ADS)

Feng, Yongqiang; Wang, Taishan; Wu, Jingyi; Feng, Lai; Xiang, Junfeng; Ma, Yihan; Zhang, Zhuxia; Jiang, Li; Shu, Chunying; Wang, Chunru

2013-07-01

We present a metal carbide clusterfullerene Sc2C2@Cs(10528)-C72, whose structure has been baffling for many years. A motional endohedral Sc2C2 cluster, special molecule geometry and electronic structure were found in Sc2C2@Cs(10528)-C72. The paramagnetic Sc2C2@Cs-C72 anion radical was successfully prepared by a chemical reduction method and hyperfine couplings in the ESR spectrum were observed.We present a metal carbide clusterfullerene Sc2C2@Cs(10528)-C72, whose structure has been baffling for many years. A motional endohedral Sc2C2 cluster, special molecule geometry and electronic structure were found in Sc2C2@Cs(10528)-C72. The paramagnetic Sc2C2@Cs-C72 anion radical was successfully prepared by a chemical reduction method and hyperfine couplings in the ESR spectrum were observed. Electronic supplementary information (ESI) available: Experimental details, HPLC chromatogram, and DFT calculations. CCDC 917712. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nr01739g

Lethal effect of uv and $gamma$ irradiation on some species of Dematiaceae (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhdanova, N.N.; Gavryushina, A.I.; Bondar, A.I.

1972-01-01

A comparative study was conducted of relation of four species of Dematiaceae and a mutant with lowered content of melanine to gamma and uv rays. Under uv irradiation, survival iate of all studied species was characterized by a complex exponential curve with a large, sharply pronounced resistant area. An assumption is advanced that a sharp fall of survival rate during the first minutes of uv irradiation is conditioned by specificity of the protective effect of melanine pigment tint needs time for transition into the active state. Species resistant to gamma irradiation had sygmoid curves of survival rate and sensitive speciesmore » had the exponential ones. Increased resistance to gamma rays was accompanied by an increase in concentration of paramagnetic-particles that were determined by the method of electronic paramagnetic resonance. Analysis of the data obtained makes it possible to suppose that the protective effect of fungal melanine is various under gamma and uv irradiation. (auth)« less

Magnetization hysteresis electron paramagnetic resonance. A new null phase insensitive saturation transfer EPR technique with high sensitivity to slow motion.

PubMed Central

Vistnes, A I

1983-01-01

In electron paramagnetic resonance (EPR) nonlinear phenomena with respect to magnetic-field modulation are often studied by out-of-phase spectra recordings. The existence of a nonzero out-of-phase signal implies that the EPR signal is phase shifted relative to the modulation signal. This phase shift is called a magnetization hysteresis. The hysteresis angle varies during a sweep through the resonance conditions for a free radical. By recording this variation, a magnetization hysteresis (MH) spectrum results. In practice, a MH spectrum is computer calculated from two EPR spectra detected with a 90 degree difference in phase setting. There is no need for a careful null-phase calibration like that in traditional analysis of nonlinearities. The MH spectra calculated from second harmonic EPR spectra of spin labels were highly dependent on the rotational correlation time. The technique can therefore be used to study slow molecular motion. In the present work MH spectra and Hemminga and deJager's magnitude saturation transfer EPR spectra (Hemminga, M. A., and P. A. deJager, 1981, J. Magn. Reson., 43:324-327) have been analyzed to define parameters that can describe variations in the rotational correlation time. A novel modification of the sample holder and temperature regulation equipment is described. PMID:6309263

Charge order suppression, emergence of ferromagnetism and absence of exchange bias effect in Bi0.25Ca0.75MnO3 nanoparticles: Electron paramagnetic resonance and magnetization studies

NASA Astrophysics Data System (ADS)

Singh, Geetanjali; Bhat, S. V.

2012-06-01

We report the results of magnetization and electron paramagnetic resonance (EPR) studies on nanoparticles (average diameter ˜ 30 nm) of Bi0.25Ca0.75MnO3 (BCMO) and compare them with the results on bulk BCMO. The nanoparticles were prepared using the nonaqueous sol-gel technique and characterized by XRD and TEM analysis. Magnetization measurements were carried out with a commercial physical property measurement system (PPMS). While the bulk BCMO exhibits a charge ordering transition at ˜230 K and an antiferromagnetic (AFM) transition at ˜130 K, in the nanoparticles, the CO phase is seen to have disappeared and a transition to a ferromagnetic (FM) state is observed at Tc ˜ 120 K. However, interestingly, the exchange bias effect observed in other nanomanganite ferromagnets is absent in BCMO nanoparticles. EPR measurements were carried out in the X-band between 8 and 300 K. Lineshape fitting to a Lorentzian with two terms (accounting for both the clockwise and anticlockwise rotations of the microwave field) was employed to obtain the relevant EPR parameters as functions of temperature. The results confirm the occurrence of ferromagnetism in the nanoparticles of BCMO.

Development of a Hybrid EPR/NMR Coimaging System

PubMed Central

Samouilov, Alexandre; Caia, George L.; Kesselring, Eric; Petryakov, Sergey; Wasowicz, Tomasz; Zweier, Jay L.

2010-01-01

Electron paramagnetic resonance imaging (EPRI) is a powerful technique that enables spatial mapping of free radicals or other paramagnetic compounds; however, it does not in itself provide anatomic visualization of the body. Proton magnetic resonance imaging (MRI) is well suited to provide anatomical visualization. A hybrid EPR/NMR coimaging instrument was constructed that utilizes the complementary capabilities of both techniques, superimposing EPR and proton-MR images to provide the distribution of paramagnetic species in the body. A common magnet and field gradient system is utilized along with a dual EPR and proton-NMR resonator assembly, enabling coimaging without the need to move the sample. EPRI is performed at ~1.2 GHz/~40 mT and proton MRI is performed at 16.18 MHz/~380 mT; hence the method is suitable for whole-body coimaging of living mice. The gradient system used is calibrated and controlled in such a manner that the spatial geometry of the two acquired images is matched, enabling their superposition without additional postprocessing or marker registration. The performance of the system was tested in a series of phantoms and in vivo applications by mapping the location of a paramagnetic probe in the gastrointestinal (GI) tract of mice. This hybrid EPR/NMR coimaging instrument enables imaging of paramagnetic molecules along with their anatomic localization in the body. PMID:17659621

Detection of Redox Imbalance in Normal Lymphocytes with Induced Mitochondrial Dysfunction - EPR Study.

PubMed

Georgieva, Ekaterina; Zhelev, Zhivko; Aoki, Ichio; Bakalova, Rumiana; Higashi, Tatsuya

2016-10-01

The present study describes a new approach for direct imaging of redox status in live cells using paramagnetic spin-probes, which allows evaluation of the level of oxidative stress due to overproduction of superoxide. The method is based on redox cycling of cell/mitochondria-penetrating nitroxide radicals (e.g. mito-TEMPO) and their electron-paramagnetic resonance (EPR) contrast, which makes them useful molecular sensors for analysis of redox status and oxidative stress in cells and tissues. Oxidative stress was induced in normal human lymphocytes by treatment with 2-methoxyestradiol and rotenone (ME/Rot) at different concentrations. This combination provokes mitochondrial dysfunction, which is accompanied by overproduction of superoxide. The EPR measurements were performed in dynamics on X-Band spectrometer after addition of mito-TEMPO to cell suspensions. The intensity of the EPR signal in untreated cells decreased significantly, which indicates a conversion of paramagnetic mito-TEMPO to its non-contrast diamagnetic form (hydroxylamine - mito-TEMPOH) due to reduction. In ME/Rot-treated cells, the signal decreased more slowly and to a lower level with increasing the concentration of ME/Rot. These data indicate an induction of oxidative stress in the cells in a concentration-dependent manner. A very good positive correlation between the intensity of EPR signal of mito-TEMPO and the intracellular level of superoxide was found, analyzed by conventional dihydroethidium test (R=0.9143, p<0.001). In conclusion, our study demonstrated that cell-penetrating paramagnetic spin-probes, such as mito-TEMPO, are valuable tools for EPR imaging of the superoxide level in live cells, as well as for EPR imaging of mitochondrial dysfunction and metabolic activity, accompanied by superoxide imbalance. Copyright© 2016 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.

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

NASA Astrophysics Data System (ADS)

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.

Tuning Magnetic Order in Transition Metal Oxide Thin Films

NASA Astrophysics Data System (ADS)

Grutter, Alexander John

In recent decades, one of the most active and promising areas of condensed matter research has been that of complex oxides. With the advent of new growth techniques such as pulsed laser deposition and molecular beam epitaxy, a wealth of new magnetic and electronic ground states have emerged in complex oxide heterostructures. The wide variety of ground states in complex oxides is well known and generally attributed to the unprecedented variety of valence, structure, and bonding available in these systems. The tunability of this already diverse playground of states and interactions is greatly multiplied in thin films and heterostructures by the addition of parameters such as substrate induced strain and interfacial electronic reconstruction. Thus, recent studies have shown emergent properties such as the stabilization of ferromagnetism in a paramagnetic system, conductivity at the interface of two insulators, and even exchange bias at the interface between a paramagnet and a ferromagnet. Despite these steps forward, there remains remarkable disagreement on the mechanisms by which these emergent phenomena are stabilized. The contributions of strain, stoichiometry, defects, intermixing, and electronic reconstruction are often very difficult to isolate in thin films and superlattices. This thesis will present model systems for isolating the effects of strain and interfacial electronic interactions on the magnetic state of complex oxides from alternative contributions. We will focus first on SrRuO3, an ideal system in which to isolate substrate induced strain effects. We explore the effects of structural distortions in the simplest case of growth on (100) oriented substrates. We find that parameters including saturated magnetic moment and Curie temperature are all highly tunable through substrate induced lattice distortions. We also report the stabilization of a nonmagnetic spin-zero configuration of Ru4+ in tetragonally distorted films under tensile strain. Through growth on (110) and (111) oriented substrates we explore the effects of different distortion symmetries on SrRuO3 and demonstrate the first reported strain induced transition to a high-spin state of Ru 4+. Finally, we examine the effects of strain on SrRuO3 thin films and demonstrate a completely reversible universal out-of-plane magnetic easy axis on films grown on different substrate orientations. Having demonstrated the ability to tune nearly every magnetic parameter of SrRuO 3 through strain, we turn to magnetic properties at interfaces. We study the emergent interfacial ferromagnetism in superlattices of the paramagnetic metal CaRuO3 and the antiferromagnetic insulator CaMnO3 and demonstrate that the interfacial ferromagnetic layer in this system is confined to a single unit cell of CaMnO3 at the interface. We discuss the remarkable oscillatory dependence of the saturated magnetic moment on the thickness of the CaMnO3 layers and explore mechanisms by which this oscillation may be stabilized. We find long range coherence of the antiferromagnetism of the CaMnO3 layers across intervening layers of paramagnetic CaRuO3. Finally, we utilize the system of LaNiO3/CaMnO3 to separate the effects of intermixing and interfacial electronic reconstruction and conclusively demonstrate intrinsic interfacial ferromagnetism at the interface between a paramagnetic metal and an antiferromagnetic insulator. We find that the emergent ferromagnetism is stabilized through interfacial double exchange and that the leakage of conduction electrons from the paramagnetic metal to the antiferromagnetic insulator is critical to establishing the ferromagnetic ground state.

Effect of UV irradiation on Echinaceae purpureae interactions with free radicals examined by an X-band (9.3 GHz) EPR spectroscopy.

PubMed

Ramos, Paweł; Pilawa, Barbara

The effect of UVA (315-400 nm) irradiation on Echinaceae purpureae interactions with free radicals was examined by the use of electron paramagnetic resonance (EPR) spectroscopy. The changes of antioxidant properties of E. purpureae with time of UV irradiation from 10 to 110 min (10 min steps) were determined. DPPH as the paramagnetic reference was used in this study. Changes of EPR signals of the reference after interactions with nonirradiated and UV-irradiated E. purpureae were detected. Interactions of the tested E. purpureae samples caused decrease of the EPR signal of DPPH as the result of its antioxidant properties. The decrease of the amplitude of EPR line of DPPH was lower for interactions with UV-irradiated E. purpureae . EPR examination confirmed antioxidant properties of E. purpureae . The weaker antioxidant properties of E. purpureae after UV irradiation were pointed out. E. purpureae should be storage in the dark. The tests bring to light usefulness of electron paramagnetic resonance with microwave frequency of 9.3 GHz (an X-band) in examination of storage conditions of pharmacological herbs.

Electron Spin Resonance (ESR) studies of returned comet nucleus samples

NASA Technical Reports Server (NTRS)

Tsay, Fun-Dow; Kim, Soon Sam; Liang, Ranty H.

1989-01-01

The most important objective of the Comet Nucleus Sample Returm Mission is to return samples which could reflect formation conditions and evolutionary processes in the early solar nebula. It is expected that the returned samples will consist of fine-grained silicate materials mixed with ices composed of simple molecules such as H2O, NH3, CH4 as well as organics and/or more complex compounds. Because of the exposure to ionizing radiation from cosmic-ray, gamma-ray, and solar wind protons at low temperature, free radicals are expected to be formed and trapped in the solid ice matrices. The kind of trapped radical species together with their concentration and thermal stability can be used as a dosimeter as well as a geothermometer to determine thermal and radiation histories as well as outgassing and other possible alternation effects since the nucleus material was formed. Since free radicals that are known to contain unpaired electrons are all paramagnetic in nature, they can be readily detected and characterized in their native form by the Electron Spin Resonance (ESR) method. In fact, ESR has been shown to be a non-destructive, highly sensitive tool for the detection and characterization of paramagnetic, ferromagnetic, and radiation damage centers in terrestrial and extraterrestrial geological samples. The potential use of ESR as an effective method in the study of returned comet nucleus samples, in particular, in the analysis of fine-grained solid state icy samples is discussed.

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. Copyright © 2016 Elsevier B.V. All rights reserved.

Electrical, thermal and magnetic studies on 7.5 MeV electron beam irradiated PrCoO3 polycrystalline samples

NASA Astrophysics Data System (ADS)

Christopher, Benedict; Rao, Ashok; Deka, Utpal; Prasad K, Shyam; Okram, G. S.; Sanjeev, Ganesh; Chandra Petwal, Vikash; Verma, Vijay Pal; Dwivedi, Jishnu

2018-07-01

The study of electronic and magnetic properties of electron beam (EB) irradiated PrCoO3 manganites is presented in this communication. The diffraction data confirms that pristine as well as electron beam irradiated samples are single phased and they crystalize at orthorhombic distorted structure with Pbnm space group. The electrical resistivity of all the samples reveals semiconducting behavior. Small polaron hopping model is appropriately employed to investigate the semiconducting nature of the pristine and EB irradiated samples. The Seebeck coefficient (S) data of the pristine sample exhibits colossally high positive value (about 300 mV/K) and substantial decrease in S value is noticed in the irradiated samples. The high temperature analysis of thermopower data validates the small polaron hopping model. The magnetic measurements display possible existence of super-paramagnetic characteristics in the samples.

Locations of radical species in black pepper seeds investigated by CW EPR and 9 GHz EPR imaging

NASA Astrophysics Data System (ADS)

Nakagawa, Kouichi; Epel, Boris

2014-10-01

In this study, noninvasive 9 GHz electron paramagnetic resonance (EPR)-imaging and continuous wave (CW) EPR were used to investigate the locations of paramagnetic species in black pepper seeds without further irradiation. First, lithium phthalocyanine (LiPC) phantom was used to examine 9 GHz EPR imaging capabilities. The 9 GHz EPR-imager easily resolved the LiPC samples at a distance of ∼2 mm. Then, commercially available black pepper seeds were measured. We observed signatures from three different radical species, which were assigned to stable organic radicals, Fe3+, and Mn2+ complexes. In addition, no EPR spectral change in the seed was observed after it was submerged in distilled H2O for 1 h. The EPR and spectral-spatial EPR imaging results suggested that the three paramagnetic species were mostly located at the seed surface. Fewer radicals were found inside the seed. We demonstrated that the CW EPR and 9 GHz EPR imaging were useful for the determination of the spatial distribution of paramagnetic species in various seeds.

Locations of radical species in black pepper seeds investigated by CW EPR and 9GHz EPR imaging.

PubMed

Nakagawa, Kouichi; Epel, Boris

2014-10-15

In this study, noninvasive 9GHz electron paramagnetic resonance (EPR)-imaging and continuous wave (CW) EPR were used to investigate the locations of paramagnetic species in black pepper seeds without further irradiation. First, lithium phthalocyanine (LiPC) phantom was used to examine 9GHz EPR imaging capabilities. The 9GHz EPR-imager easily resolved the LiPC samples at a distance of ∼2mm. Then, commercially available black pepper seeds were measured. We observed signatures from three different radical species, which were assigned to stable organic radicals, Fe(3+), and Mn(2+) complexes. In addition, no EPR spectral change in the seed was observed after it was submerged in distilled H2O for 1h. The EPR and spectral-spatial EPR imaging results suggested that the three paramagnetic species were mostly located at the seed surface. Fewer radicals were found inside the seed. We demonstrated that the CW EPR and 9GHz EPR imaging were useful for the determination of the spatial distribution of paramagnetic species in various seeds. Copyright © 2014 Elsevier B.V. All rights reserved.

High-frequency EPR of surface impurities on nanodiamond

NASA Astrophysics Data System (ADS)

Peng, Zaili; Stepanov, Viktor; Takahashi, Susumu

Diamond is a fascinating material, hosting nitrogen-vacancy (NV) defect centers with unique magnetic and optical properties. There have been many reports that suggest the existence of paramagnetic impurities near surface of various kinds of diamonds. Electron paramagnetic resonance (EPR) investigation of mechanically crushed nanodiamonds (NDs) as well as detonation NDs revealed g 2 like signals that are attributed to structural defects and dangling bonds near the diamond surface. In this presentation, we investigate paramagnetic impurities in various sizes of NDs using high-frequency (HF) continuous wave (cw) and pulsed EPR spectroscopy. Strong size dependence on the linewidth of HF cw EPR spectra reveals the existence of paramagnetic impurities in the vicinity of the diamond surface. We also study the size dependence of the spin-lattice and spin-spin relaxation times (T1 and T2) of single substitutional nitrogen defects in NDs Significant deviations from the temperature dependence of the phonon-assisted T1 process were observed in the ND samples, and were attributed to the contribution from the surface impurities. This work was supported by the Searle Scholars Program and the National Science Foundation (DMR-1508661 and CHE-1611134).

Properties of nonaqueous electrolytes

NASA Technical Reports Server (NTRS)

Foster, J. N.; Hanson, D. C.; Hon, J. F.; Keller, R.; Muirhead, J. S.

1970-01-01

Physical property measurements and structural studies conducted in aprotic solvents using various solutes are applicable to the further development of lithum batteries. Structural studies utilize nuclear magnetic resonance and electron paramagnetic resonance techniques.

Imaging single spin probes embedded in a conductive diamagnetic layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Messina, P.; Fradin, F.

2009-01-01

The detection of spin noise by means of scanning tunneling microscopy (STM) has recently been substantially improved by the work presented by Komeda and Manassen (Komeda, T.; Manassen, Y. Appl. Phys. Lett. 2008, 92, 212506). The application of this technique to molecular paramagnets requires the positioning and anchoring of paramagnetic molecules at surfaces. It also requires the possibility of tunneling high current densities into the STM-molecule-substrate tunneling junction. In this letter, we exploit the self-assembly of 1,10-phenantroline on the Au(111) surface to form a diamagnetic matrix that hosts individual molecules and dimers of diphenyl-2-picryl-hydrazyl (DPPH). STM measurements are used tomore » characterize the molecular layer. Electron spin resonance (ESR) measurements elucidate the role of thermal annealing in the preservation of the paramagnetic nature of the DPPH molecules.« less

Spontaneous magnetic order in complex materials: Role of longitudinal spin-orbit interactions

NASA Astrophysics Data System (ADS)

Chakraborty, Subrata; Vijay, Amrendra

2017-06-01

We show that the longitudinal spin-orbit interactions (SOI) critically determine the fate of spontaneous magnetic order (SMO) in complex materials. To study the magnetic response of interacting electrons constituting the material, we implement an extension of the Hubbard model that faithfully accounts for the SOI. Next, we use the double-time Green functions of quantum statistical mechanics to obtain the spontaneous magnetization, Msp , and thence ascertain the possibility of SMO. For materials with quenched SOI, in an arbitrary dimension, Msp vanishes at finite temperatures, implying the presence of the disordered (paramagnetic) phase. This is consistent with and goes beyond the Bogolyubov's inequality based analysis in one and two dimensions. In the presence of longitudinal SOI, Msp , for materials in an arbitrary dimension, remains non-zero at finite temperatures, which indicates the existence of the ordered (ferromagnetic) phase. As a plausible experimental evidence of the present SOI-based phenomenology, we discuss, inter alia, a recent experimental study on Y4Mn1-xGa12-yGey, an intermetallic compound, which exhibits a magnetic phase transition (paramagnetic to ferromagnetic) upon tuning the fraction of Ge atoms and thence the vacancies of the magnetic centers in this system. The availability of Ge atoms to form a direct chemical bond with octahedral Mn in this material appears to quench the SOI and, as a consequence, favours the formation of the disordered (paramagnetic) phase.

Spectral analysis of paramagnetic centers induced in human tooth enamel by x-rays and gamma radiation

NASA Astrophysics Data System (ADS)

Kirillov, V. A.; Kuchuro, I. I.

2010-03-01

Based on study of spectral and relaxation characteristics, we have established that paramagnetic centers induced in tooth enamel by x-rays and gamma radiation are identical in nature. We show that for the same exposure dose, the intensity of the electron paramagnetic resonance (EPR) signal induced by x-radiation with effective energy 34 keV is about an order of magnitude higher than the amplitude of the signal induced by gamma radiation. We have identified a three-fold attenuation of the EPR signal along the path of the x-radiation from the buccal to the lingual side of a tooth, which is evidence that the individual had undergone diagnostic x-ray examination of the dentition or skull. We have shown that the x-ray exposure doses reconstructed from the EPR spectra are an order of magnitude higher than the applied doses, while the dose loads due to gamma radiation are equal to the applied doses. The data obtained indicate that for adequate reconstruction of individual absorbed doses from EPR spectra of tooth enamel in the population subjected to the combined effect of x-radiation and accidental external gamma radiation as a result of the disaster at the Chernobyl nuclear power plant, we need to take into account the contribution to the dose load from diagnostic x-rays in examination of the teeth, jaw, or skull.

The NMR contribution to protein-protein networking in Fe-S protein maturation.

PubMed

Banci, Lucia; Camponeschi, Francesca; Ciofi-Baffoni, Simone; Piccioli, Mario

2018-03-22

Iron-sulfur proteins were among the first class of metalloproteins that were actively studied using NMR spectroscopy tailored to paramagnetic systems. The hyperfine shifts, their temperature dependencies and the relaxation rates of nuclei of cluster-bound residues are an efficient fingerprint of the nature and the oxidation state of the Fe-S cluster. NMR significantly contributed to the analysis of the magnetic coupling patterns and to the understanding of the electronic structure occurring in [2Fe-2S], [3Fe-4S] and [4Fe-4S] clusters bound to proteins. After the first NMR structure of a paramagnetic protein was obtained for the reduced E. halophila HiPIP I, many NMR structures were determined for several Fe-S proteins in different oxidation states. It was found that differences in chemical shifts, in patterns of unobserved residues, in internal mobility and in thermodynamic stability are suitable data to map subtle changes between the two different oxidation states of the protein. Recently, the interaction networks responsible for maturing human mitochondrial and cytosolic Fe-S proteins have been largely characterized by combining solution NMR standard experiments with those tailored to paramagnetic systems. We show here the contribution of solution NMR in providing a detailed molecular view of "Fe-S interactomics". This contribution was particularly effective when protein-protein interactions are weak and transient, and thus difficult to be characterized at high resolution with other methodologies.

2D FTIR correlation spectroscopy and EPR analysis of Urtica dioica leaves from areas of different environmental pollution.

PubMed

Moskal, Paulina; Wesełucha-Birczyńska, Aleksandra; Łabanowska, Maria; Kurdziel, Magdalena; Filek, Maria

2018-01-15

Leaves of Urtica dioica collected from two areas of different environmental pollution were analysed by fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR) spectroscopy. Analysis of FTIR spectra allows to describe main component of plant like proteins, lipids and carbohydrates. Although the FTIR spectra of plants from these two geographical locations of different environmental pollution appear to be relatively similar, 2D correlation shows completely different patterns. Synchronous and asynchronous correlation maps showed sequences of changes occurring during development of plant, manly in Amide I and Amide II, lignin, lipids and cellulose. In addition, 2D analysis revealed another sequence of changes as the function of plant growth depending on the degree of the environmental pollution. Two various kinds of paramagnetic species, transition metal ions (Mn(II), Fe(III)) and stable organic radicals (chlorophyll, semiquinone, tyrosyl and carbon centered) were found in leaves of nettle collected at different stages of development and growing in clean and polluted environment. In plants growing in polluted area the injuries of protein molecules bonding metal ions and the disturbances of photosynthesis and redox equilibrium in cells, as well as instability of polysaccharide structure of cell walls were observed. Copyright © 2017 Elsevier B.V. All rights reserved.

Ordered phases in the Holstein-Hubbard model: Interplay of strong Coulomb interaction and electron-phonon coupling

NASA Astrophysics Data System (ADS)

Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo

2013-09-01

We study the Holstein-Hubbard model at half filling to explore ordered phases including superconductivity (SC), antiferromagnetism (AF), and charge order (CO) in situations where the electron-electron and electron-phonon interactions are strong (comparable to the electronic bandwidth). The model is solved in the dynamical mean-field approximation with a continuous-time quantum Monte Carlo impurity solver. We determine the superconducting transition temperature Tc and the SC order parameter and show that the phonon-induced retardation or the strong Coulomb interaction leads to a significant reduction and shift of the Tc dome against the effective electron-electron interaction Ueff given by the Hubbard U reduced by the phonon-mediated attraction in the static limit. This behavior is analyzed by comparison to an effective static model in the polaron representation with a renormalized bandwidth. In addition, we discuss the superconducting gap Δ and 2Δ/Tc to reveal the effect of the retardation and the Coulomb interaction. We also determine the finite-temperature phase diagram including AF and CO. In the moderate-coupling regime, there is a hysteretic region of AF and CO around Ueff=0, while the two phases are separated by a paramagnetic metal in the weak-coupling regime and a paramagnetic insulator in the strong-coupling regime.

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

Features of the electronic structure of FeTe compounds

NASA Astrophysics Data System (ADS)

Grechnev, G. E.; Lyogenkaya, A. A.; Panfilov, A. S.; Logosha, A. V.; Kotlyar, O. V.; Gnezdilov, V. P.; Makarova, I. P.; Chareev, D. A.; Mitrofanova, E. S.

2015-12-01

A theoretical and experimental study of the electronic structure and nature of the chemical bonds in FeTe compounds in antiferromagnetic (AFM) and paramagnetic phases was carried out. It is established that the nature of the chemical bonds is mainly metallic, and the presence of covalent bonds Fe-Te and Te-Te helps to stabilize the structural distortions of the tetragonal phase of FeTe in the low-temperature region. It is found that the bicollinear AFM structure corresponds to the ground state of the FeTe compound and the calculated value of the magnetic moment MFe = -2.4μB is in good agreement with the data from neutron diffraction measurements. At the same time, the Fermi surface (FS) of the low-temperature AFM phase is radically different from the FS of the paramagnetic FeTe. Reconstructing the FS can lead to a sign change of the Hall coefficient observed in FeTe. The calculation results serve as evidence of the fact that the electronic structures and magnetic properties of FeTe are well-described by the model of itinerant d-electrons and the density functional theory (DFT-GGA).

Nanopatterning of magnetic domains: Fe coverage of self-assembled alumina nanostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Qibin; Wang, Bo -Yao; Lin, Wen -Chin

2015-08-19

Nanosized ultrathin magnetic films were prepared by controlling the deposition of Fe onto an oxidized NiAl(001) surface with an alumina nanostructure on it. Because the ultrathin ferromagnetic Fe films on the bare NiAl(001) surface are separated by paramagnetic Fe nanoparticles on the alumina stripes, as determined by scanning electron microscopy with spin analysis, they form rectangular domains with sizes ranging from tens of nanometer to larger than a micrometer. Furthermore, magnetic domain patterning can thus be achieved by controlling the Fe coverage and nanostructured template.

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.

One- and two-dimensional pulse electron paramagnetic resonance spectroscopy: concepts and applications.

PubMed

Van Doorslaer, S; Schweiger, A

2000-06-01

During the last two decades, the possibilities of pulse electron paramagnetic resonance (EPR) and pulse electron nuclear double resonance (ENDOR) spectroscopy have increased tremendously. While at the beginning of the 1980s pulse-EPR and ENDOR applications were still a rarity, the techniques are now very frequently applied in chemistry, physics, materials science, biology and mineralogy. This is mainly due to the considerable efforts invested in the last few years on instrument development and pulse-sequence design. Pulse-EPR spectrometers are now commercially available, which enables many research groups to use these techniques. In this work, an overview of state-of-the-art pulse EPR and ENDOR spectroscopy is given. The rapid expansion of the field, however, does not allow us to give an exhaustive record of all the pulse methods introduced so far. After a brief and very qualitative description of the basic principles of pulse EPR, we discuss some of the experiments in more detail and illustrate the potential of the methods with a number of selected applications.

Electrochemistry and electron paramagnetic resonance spectroscopy of cytochrome c and its heme-disrupted analogs.

PubMed

Novak, David; Mojovic, Milos; Pavicevic, Aleksandra; Zatloukalova, Martina; Hernychova, Lenka; Bartosik, Martin; Vacek, Jan

2018-02-01

Cytochrome c (cyt c) is one of the most studied conjugated proteins due to its electron-transfer properties and ability to regulate the processes involved in homeostasis or apoptosis. Here we report an electrochemical strategy for investigating the electroactivity of cyt c and its analogs with a disrupted heme moiety, i.e. apocytochrome c (acyt c) and porphyrin cytochrome c (pcyt c). The electrochemical data are supplemented with low-temperature and spin-probe electron paramagnetic resonance (EPR) spectroscopy. The main contribution of this report is a complex evaluation of cyt c reduction and oxidation at the level of surface-localized amino acid residues and the heme moiety in a single electrochemical scan. The electrochemical pattern of cyt c is substantially different to both analogs acyt c and pcyt c, which could be applicable in further studies on the redox properties and structural stability of cytochromes and other hemeproteins. Copyright © 2017 Elsevier B.V. All rights reserved.

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.

A compensating point defect in carbon-doped GaN substrates studied with electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Willoughby, W. R.; Zvanut, M. E.; Paudel, Subash; Iwinska, M.; Sochacki, T.; Bockowski, M.

2018-04-01

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate a type of point defect present in 1019 cm-3 carbon-doped GaN substrates grown by hydride vapor phase epitaxy. A broad, isotropic resonance at g ˜ 1.987 was observed at 3.5 K, and the EPR intensity increased with illumination at energies greater than 2.75 eV and decreased with photon energies greater than 0.95 eV. The latter is consistent with a deep level of 0.95 eV above the valence band maximum and implies that the associated defect likely participates in donor compensation. The ionization energy for this defect is close to the predicted value for the (-/0) transition level of CN and transition levels associated with Ga vacancies such as VGa and VGa-ON-2H.

Studying metal impurities (Mn2+, Cu2+, Fe3+) in calcium phosphates by electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Iskhakova, K.; Murzakhanov, F.; Mamin, G.; Putlyaev, V.; Klimashina, E.; Fadeeva, I.; Fomin, A.; Barinov, S.; Maltsev, A.; Bakhteev, S.; Yusupov, R.; Gafurov, M.; Orlinskii, S.

2018-05-01

Calcium phosphates (CaP) are exploited in many fields of science, including geology, chemistry, biology and medicine due to their abundance in the nature and presence in the living organism. Various analytical and biochemical methods are used for controlling their chemical content, structure, morphology, etc. Unfortunately, magnetic resonance techniques are usually not even considered as necessary tools for CaP inspection. Some aspects of application of the commercially realized electron paramagnetic resonance (EPR) approaches for characterization of CaP powders and ceramics (including the nanosized materails) such as hydroxyapatite and tricalcium phosphates of biogenic and synthetic origins containing intrinsic impurities or intentional dopants are demonstrated. The key features and advantages of the EPR techniques for CaP based materials characterization that could compliment the data obtained with the recognized analytical methods are pointed out.

Magnetic behavior of the nanophase of YbNi2 alloys

NASA Astrophysics Data System (ADS)

Ivanshin, V. A.; Gataullin, E. M.; Sukhanov, A. A.; Ivanshin, N. A.; Rojas, D. P.; Fernández Barquín, L.

2017-04-01

Variations in magnetic properties of the heavy-fermion YbNi2 alloy when milled in a high energy ball milling system have been investigated. The ferromagnetic transition ( T C = 10.4 K) in the initial sample almost vanishes after milling, which leads to the appearance of a magnetic transition at T* = 3.2 K in nanocrystallites. Before milling, processes of spin-lattice relaxation of the Orbach-Aminov type with the participation of the first excited Stark sublevel of the Yb3+ ion located at 75 K are dominating in the electron spin dynamics in the paramagnetic phase of the alloy. A comparative study of the temperature dependence of the magnetic properties and spectra of electron paramagnetic resonance in poly- and nanocrystalline samples indicates the existence of a magnetic inhomogeneity of the compound arising upon milling.

Effect of ultraviolet irradiation on free radical scavenging activity of immunosuppressants used in lung transplantation and comparative electron paramagnetic resonance study of kinetics of their interactions with model free radicals.

PubMed

Stanjek-Cichoracka, A; Żegleń, S; Ramos, P; Pilawa, B; Wojarski, J

2018-06-01

The immunosuppressive drugs used in solid organ transplantation or autoimmunological processes were studied by electron paramagnetic resonance (EPR) spectroscopy to estimate their free radical scavenging activity. The interactions of immunosuppressants with free radicals were examined by an X-band (9.3 GHz) EPR spectroscopy and a model of DPPH free radicals. The EPR spectra of DPPH and DPPH interacting with individual drugs were compared. Kinetic studies were performed, and the effect of ultraviolet (UV) irradiation on the free radical scavenging activity of the tested drugs was determined. The free radical scavenging activity of non-irradiated drugs decreased in the order: rapamycin > mycophenolate mofetil > ciclosporin > tacrolimus. UV irradiation increased the free radical scavenging activity of all the tested immunosuppressive drugs, and the effect was highest for tacrolimus. For the non-irradiated samples, the speed of free radical interactions decreased in the order: ciclosporin > tacrolimus > mycophenolate mofetil > rapamycin. UV irradiation only slightly affected the speed of interactions of the immunosuppressive drugs with the model DPPH free radicals. Electron paramagnetic resonance spectroscopy is useful for obtaining information on interactions of immunosuppressive drugs with free radicals. We hypothesized that the long-term immunosuppressive effects of these drugs after transplantation or during autoimmune disorders may be mediated by anti-inflammatory action in addition to the known receptor/cell cycle inhibition. © 2018 John Wiley & Sons Ltd.

Combined multifrequency EPR and DFT study of dangling bonds in a-Si:H

NASA Astrophysics Data System (ADS)

Fehr, M.; Schnegg, A.; Rech, B.; Lips, K.; Astakhov, O.; Finger, F.; Pfanner, G.; Freysoldt, C.; Neugebauer, J.; Bittl, R.; Teutloff, C.

2011-12-01

Multifrequency pulsed electron paramagnetic resonance (EPR) spectroscopy using S-, X-, Q-, and W-band frequencies (3.6, 9.7, 34, and 94 GHz, respectively) was employed to study paramagnetic coordination defects in undoped hydrogenated amorphous silicon (a-Si:H). The improved spectral resolution at high magnetic field reveals a rhombic splitting of the g tensor with the following principal values: gx=2.0079, gy=2.0061, and gz=2.0034, and shows pronounced g strain, i.e., the principal values are widely distributed. The multifrequency approach furthermore yields precise 29Si hyperfine data. Density functional theory (DFT) calculations on 26 computer-generated a-Si:H dangling-bond models yielded g values close to the experimental data but deviating hyperfine interaction values. We show that paramagnetic coordination defects in a-Si:H are more delocalized than computer-generated dangling-bond defects and discuss models to explain this discrepancy.

Biocompatible Collagen Paramagnetic Scaffold for Controlled Drug Release.

PubMed

Bettini, Simona; Bonfrate, Valentina; Syrgiannis, Zois; Sannino, Alessandro; Salvatore, Luca; Madaghiele, Marta; Valli, Ludovico; Giancane, Gabriele

2015-09-14

A porous collagen-based hydrogel scaffold was prepared in the presence of iron oxide nanoparticles (NPs) and was characterized by means of infrared spectroscopy and scanning electron microscopy. The hybrid scaffold was then loaded with fluorescein sodium salt as a model compound. The release of the hydrosoluble species was triggered and accurately controlled by the application of an external magnetic field, as monitored by fluorescence spectroscopy. The biocompatibility of the proposed matrix was also tested by the MTT assay performed on 3T3 cells. Cell viability was only slightly reduced when the cells were incubated in the presence of the collagen-NP hydrogel, compared to controls. The economicity of the chemical protocol used to obtain the paramagnetic scaffolds as well as their biocompatibility and the safety of the external trigger needed to induce the drug release suggest the proposed collagen paramagnetic matrices for a number of applications including tissue engeneering and drug delivery.

Unravelling electronic and structural requisites of triplet-triplet energy transfer by advanced electron paramagnetic resonance and density functional theory

NASA Astrophysics Data System (ADS)

Di Valentin, M.; Salvadori, E.; Barone, V.; Carbonera, D.

2013-10-01

Advanced electron paramagnetic resonance (EPR) techniques, in combination with Density Functional theory (DFT), have been applied to the comparative study of carotenoid triplet states in two major photosynthetic antenna complexes, the Peridinin-chlorophyll a-protein of dinoflagellates and the light-harvesting complex II of higher plants. Carotenoid triplet states are populated by triplet-triplet energy transfer (TTET) from chlorophyll molecules to photoprotect the system from singlet oxygen formation under light-stress conditions. The TTET process is strongly dependent on the relative arrangement and on the electronic properties of the triplet states involved. The proposed spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognisable spin polarisation effects in the time-resolved and field-swept echo-detected EPR spectra. The electron spin polarisation produced at the carotenoid acceptor site depends on the initial polarisation of the chlorophyll donor and on the relative geometrical arrangement of the donor-acceptor zero-field splitting axes. We have demonstrated that a proper analysis of the spectra in the framework of spin angular momentum conservation allows to derive the pathways of TTET and to gain insight into the structural requirements of this mechanism for those antenna complexes, whose X-ray structure is available. We have further proved that this method, developed for natural antenna complexes of known X-ray structure, can be extended to systems lacking structural information in order to derive the relative arrangement of the partners in the energy transfer process. The structural requirements for efficient TTET, obtained from time-resolved and pulse EPR, have been complemented by a detailed description of the electronic structure of the carotenoid triplet state, provided by pulse Electron-Nuclear DOuble Resonance (ENDOR) experiments. Triplet-state hyperfine couplings of the α- and β-protons of the carotenoid conjugated chain have been assigned with the aid of quantum chemical calculation. DFT predictions of the electronic structure of the carotenoid triplet state, in terms of spin density distribution, frontier orbital description and orbital excitation represent suitable building blocks toward a deeper understanding of electronic requirements for efficient TTET.

Electron paramagnetic resonance of Nb-doped BaTiO3 ceramics with positive temperature coefficient of resistivity

NASA Astrophysics Data System (ADS)

Jida, Shin'suke; Miki, Toshikatsu

1996-11-01

Paramagnetic centers in Nb-doped BaTiO3 ceramics are measured at 77-500 K by electron paramagnetic resonance (EPR) for investigating the role of the centers on the well-known positive temperature coefficient of resistivity (PTCR) effect (PTCR at the Curie temperature). EPR detects four signals; an anisotropically broad singlet signal at g=2.005, a sextet signal due to Mn2+, a Cr3+ signal, and a Ti3+ signal. The former two signals arise in the rhombohedral and cubic phases, but disappear in the tetragonal and orthorhombic phases. The Cr3+ signal appears in all of the phases, while the Ti3+ signal is detected only at low temperatures. The singlet signal also arises in undoped, barium-deficient BaTiO3 ceramics, therefore the signal is attributable to barium-vacancy-associated centers rather than Nb4+ ions or Fe3+ ions proposed by several authors. In this article, we propose that the singlet signal is due to vacancy-pairs of VBa-F+ type, i.e., the vacancy pair of VBa-VO capturing one electron. The electrical resistivity data show a polaronic character of low-temperature conduction and a high resistivity jump around the Curie temperature. The low-temperature polaronic conduction is explained in terms of electron-hopping between Ti4+ and Ti3+ ions. The resistivity jump at the Curie temperature occurs along with the EPR intensity increase of the singlet signal, the Mn2+ signal and the Cr3+ signal. We conclude that the PTCR of Nb-doped BaTiO3 ceramics is strongly associated with the trap activation of the VBa-VO vacancy-pairs and manganese centers at the tetragonal-to-cubic transition.

Center for Cement Composite Materials

DTIC Science & Technology

1990-01-31

metal-oxygen structures G. Kordas MSE-Ceramics Electron paramagnetic resonance W. M. Kriven MSE-Ceramics Electron microscopy Microstructural...SPONSORING iSb. OFFICE SYMBOL 9. PROWIREMENT INSTRUMENT IDENTIFICATION NUMBER ORGANIZATION (If applicable) C S(2is _ _ _- r_,__’ Contract F49620-87-C...novel in-situ technique involving nuclear magnetic resonance . Fiber- matrix interactions in MDF laminates were also studied. Characterization of DSP

The world as viewed by and with unpaired electrons.

PubMed

Eaton, Sandra S; Eaton, Gareth R

2012-10-01

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. Copyright © 2012 Elsevier Inc. All rights reserved.

Electronic correlation in magnetic contributions to structural energies

NASA Astrophysics Data System (ADS)

Haydock, Roger

For interacting electrons the density of transitions [see http://arxiv.org/abs/1405.2288] replaces the density of states in calculations of structural energies. Extending previous work on paramagnetic metals, this approach is applied to correlation effects on the structural stability of magnetic transition metals. Supported by the H. V. Snyder Gift to the University of Oregon.

Probing the Dipolar Coupling in a Heterospin Endohedral Fullerene-Phthalocyanine Dyad.

PubMed

Zhou, Shen; Yamamoto, Masanori; Briggs, G Andrew D; Imahori, Hiroshi; Porfyrakis, Kyriakos

2016-02-03

Paramagnetic endohedral fullerenes and phthalocyanine (Pc) complexes are promising building blocks for molecular quantum information processing, for which tunable dipolar coupling is required. We have linked these two spin qubit candidates together and characterized the resulting electron paramagnetic resonance properties, including the spin dipolar coupling between the fullerene spin and the copper spin. Having interpreted the distance-dependent coupling strength quantitatively and further discussed the antiferromagnetic aggregation effect of the CuPc moieties, we demonstrate two ways of tuning the dipolar coupling in such dyad systems: changing the spacer group and adjusting the solution concentration.

Combined optical/MCD/ODMR investigations of photochromism in doubly-doped Bi12GeO20

NASA Astrophysics Data System (ADS)

Briat, B.; Borowiec, M. T.; Rjeily, H. B.; Ramaz, F.; Hamri, A.; Szymczak, H.

Electron paramagnetic resonance is detected optically via the change of magnetic circular dichroism under microwaves at 35 GHz. The technique is applied to Bi12GeO20 samples co-doped with vanadium and a second transition metal (Cr, Mn, Co, Cu). The optical and magnetic properties of several paramagnetic defects (V-Ge(4+) and Cr-Ge(4+)) are directly correlated. The basic photochromic processes occuring in samples doped with V, Mn, and Mn+V are explained. The V-Ge(4+/5+) level is positioned roughly 2.2 eV above the valence band.

Single-aliquot EPR dosimetry of wallboard (drywall).

PubMed

Mistry, R; Thompson, J W; Boreham, D R; Rink, W J

2011-11-01

Electron paramagnetic resonance spectra and dose-response curves are presented for a variety of wallboard samples obtained from different manufacturing facilities, as well as for source gypsum and anhydrite. The intensity of the CO(3)(-) paramagnetic centre (G2) is enhanced with gamma radiation. Isothermal decay curves are used to propose annealing methods for the removal of the radiosensitive CO(3)(-) radical without affecting the unirradiated baseline. Post-irradiation annealing of wallboard prevents recuperation of the radiosensitive CO(3)(-) radical with additional irradiation. A single-aliquot additive dose procedure is developed that successfully measures test doses as low as 0.76 Gy.

Emulsion Polymerization of Butyl Acrylate: Spin Trapping and EPR Study

NASA Technical Reports Server (NTRS)

Kim, S.; Westmoreland, D.

1994-01-01

The propagating radical in the emulsion polymerization reaction of butyl acrylate was detected by Electron Paramagnetic Resonance spectroscopy using two spin trapping agents, 2-methyl-2nitrosopropane and alpha -N-tert-butylnitrone.

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.

The fine tuning of carotenoid-chlorophyll interactions in light-harvesting complexes: an important requisite to guarantee efficient photoprotection via triplet-triplet energy transfer in the complex balance of the energy transfer processes

NASA Astrophysics Data System (ADS)

Di Valentin, Marilena; Carbonera, Donatella

2017-08-01

Triplet-triplet energy transfer (TTET) from the chlorophyll to the carotenoid triplet state is the process exploited by photosynthetic systems to protect themselves from singlet oxygen formation under light-stress conditions. A deep comprehension of the molecular strategies adopted to guarantee TTET efficiency, while at the same time maintaining minimal energy loss and efficient light-harvesting capability, is still lacking. The paramagnetic nature of the triplet state makes electron paramagnetic resonance (EPR) the method of choice when investigating TTET. In this review, we focus on our extended comparative study of two photosynthetic antenna complexes, the Peridinin-chlorophyll a-protein of dinoflagellates and the light-harvesting complex II of higher plants, in order to point out important aspects of the molecular design adopted in the photoprotection strategy. We have demonstrated that a proper analysis of the EPR data allows one to identify the pigments involved in TTET and, consequently, gain an insight into the structure of the photoprotective sites. The structural information has been complemented by a detailed description of the electronic structure provided by hyperfine spectroscopy. All these elements represent the fundamental building blocks toward a deeper understanding of the requirements for efficient photoprotection, which is fundamental to guarantee the prolonged energy conversion action of photosynthesis.

Axially uniform resonant cavity modes for potential use in electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Mett, Richard R.; Froncisz, Wojciech; Hyde, James S.

2001-11-01

This article is concerned with cylindrical transverse electric TE011 and rectangular TE102 microwave cavity resonators commonly used in electron paramagnetic resonance (EPR) spectroscopy. In the cylindrical mode geometry considered here, the sample is along the z axis of the cylinder, dielectric disks of 1/4 wavelength thickness are placed at each end wall, and the diameter of the cylinder is set at the cutoff condition for propagation of microwave energy in a cylindrical waveguide at the desired microwave frequency. The microwave magnetic field is exactly uniform along the sample in the region between the dielectric disks and the resonant frequency is independent of the length of the cylinder without limit. The rectangular TE102 geometry is analogous, but here the microwave magnetic field is exactly uniform in a plane. A uniform microwave field along a line sample is highly advantageous in EPR spectroscopy compared with the usual sinusoidal variation, and these geometries are called "uniform field" modes. Extensive theoretical analysis as well as finite element calculation of field patterns are presented. The perturbation of field patterns caused by sample insertion as functions of the overall length of the resonator and diameter of the sample is analyzed. The article is intended to provide a basis for design of practical structures in the range of 10 to 100 GHz.

Electron paramagnetic resonance field-modulation eddy-current analysis of silver-plated graphite resonators

NASA Astrophysics Data System (ADS)

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

2005-09-01

Magnetic field modulation is often introduced into a cylindrical TE011 electron paramagnetic resonance (EPR) cavity through silver plating over a nonconductive substrate. The plating thickness must be many times the skin depth of the rf and smaller than the skin depth of the modulation. We derive a parameter that quantifies the modulation field penetration and find that it also depends on resonator dimensions. Design criteria based on this parameter are presented graphically. This parameter is then used to predict the behavior of eddy currents in substrates of moderate conductivity, such as graphite. The conductivity of the graphite permits improved plating uniformity and permits use of electric discharge machining (EDM) techniques to make the resonator. EDM offers precision tolerances of 0.005 mm and is suitable for small, complicated shapes that are difficult to machine by other methods. Analytic predictions of the modulation penetration are compared with the results of finite-element simulations. Simulated magnetic field modulation uniformity and penetration are shown for several elemental coils and structures including the plated graphite TE011 cavity. Fabrication and experimental testing of the structure are discussed. Spatial inhomogeneity of the modulation phase is also investigated by computer simulation. We find that the modulation phase is uniform to within 1% over the TE011 cavity. Structures of lower symmetry have increased phase nonuniformity.

Rapid determination of environmentally persistent free radicals (EPFRs) in atmospheric particles with a quartz sheet-based approach using electron paramagnetic resonance (EPR) spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Qingcai; Wang, Mamin; Wang, Yuqin; Zhang, Lixin; Xue, Jian; Sun, Haoyao; Mu, Zhen

2018-07-01

Environmentally persistent free radicals (EPFRs) are present within atmospheric fine particles, and they are assumed to be a potential factor responsible for human pneumonia and lung cancer. This study presents a new method for the rapid quantification of EPFRs in atmospheric particles with a quartz sheet-based approach using electron paramagnetic resonance (EPR) spectroscopy. The three-dimensional distributions of the relative response factors in a cavity resonator were simulated and utilized for an accurate quantitative determination of EPFRs in samples. Comparisons between the proposed method and conventional quantitative methods were also performed to illustrate the advantages of the proposed method. The results suggest that the reproducibility and accuracy of the proposed method are superior to those of the quartz tube-based method. Although the solvent extraction method is capable of extracting specific EPFR species, the developed method can be used to determine the total EPFR content; moreover, the analysis process of the proposed approach is substantially quicker than that of the solvent extraction method. The proposed method has been applied in this study to determine the EPFRs in ambient PM2.5 samples collected over Xi'an, the results of which will be useful for extensive research on the sources, concentrations, and physical-chemical characteristics of EPFRs in the atmosphere.

Analysis of gamma-irradiated melon, pumpkin, and sunflower seeds by electron paramagnetic resonance spectroscopy and gas chromatography-mass spectrometry.

PubMed

Sin, Della W M; Wong, Yiu Chung; Yao, Wai Yin

2006-09-20

Seeds of melon (Citrullus lanatus var. sp.), pumpkin (Cucurbita moschata), and sunflower (Heliantus annus) were gamma-irradiated at 1, 3, 5, and 10 kGy and analyzed by electron paramagnetic resonance (EPR) and gas chromatography-mass spectrometry (GC-MS) according to EN1787:2000 and EN1785:2003, respectively. Distinguishable triplet signals due to the presence of induced cellulose radicals were found at 2.0010-2.0047 g in the EPR spectra. The gamma-irradiated radiolytic markers of 2-dodecylcyclobutanone (2-DCB) and 2-tetradecylcyclobutanone (2-TCB) were identified in all irradiated seed samples. Both the free radicals and the alkylcyclobutanones were found to increase with irradiation dose. In general, linear relationships between the amount of radicals and irradiation dosage could be established. Studies at an ambient temperature (20-25 degrees C) in a humidity-controlled environment showed a complete disappearance of the cellulosic peaks for irradiated samples upon 60 days of storage. Such instability behavior was considered to render the usefulness of using EPR alone in the determination of irradiated seed samples. On the other hand, 2-DCB and 2-TCB were also found to decompose rapidly (>85% loss after 120 days of storage), but the radiolytic markers remained quantifiable after 120 days of postirradiation storage. These results suggest that GC-MS is a versatile and complimentary technique for the confirmation of irradiation treatment to seeds.

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).

Fermi surface properties of paramagnetic NpCd11 with a large unit cell

NASA Astrophysics Data System (ADS)

Homma, Yoshiya; Aoki, Dai; Haga, Yoshinori; Settai, Rikio; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; Takeuchi, Tetsuya; Yamagami, Hiroshi; Ōnuki, Yoshichika

2010-03-01

We succeeded in growing a high-quality single crystal of NpCd11 with the cubic BaHg11-type structure by the Cd-self flux method. The lattice parameter of a = 9.2968(2) Å and crystallographic positions of the atoms were determined by x-ray single-crystal structure analysis. From the results of the magnetic susceptibility and specific heat experiments, this compound is found to be a 5f-localized paramagnet with the singlet ground state in the crystalline electric field (CEF) scheme. Fermi surface properties were measured using the de Haas-van Alphen (dHvA) technique. Long-period oscillations were observed in the dHvA frequency range of 9.1 x 105 to 1.9 x 107 Oe, indicating small cross-sectional areas of Fermi surfaces, which is consistent with a small Brillouin zone based on a large unit cell. From the results of dHvA and magnetoresistance experiments, the Fermi surface of NpCd11 is found to consist of many kinds of closed Fermi surfaces and a multiply-connected-like Fermi surface, although the result of energy band calculations based on the 5f-localized Np3+(5f4) configuration reveals the existence of only closed Fermi surfaces. The corresponding cyclotron effective mass is small, ranging from 0.1 to 0.7 m0, which is consistent with a small electronic specific heat coefficient γ ≅ 10mJ/K2·mol, revealing no hybridization between the 5f electrons and conduction electrons.

Synthesis, characterization, and growth mechanism of motifs of ultrathin cobalt-substituted NaFeSi 2O 6 nanowires

DOE PAGES

Lewis, Crystal S.; Moronta, Dominic; Terban, Maxwell W.; ...

2017-12-12

In this report, we have synthesized and structurally characterized nanowire bundles of cobalt-substituted pyroxenes, similar to the crystal structure of aegirine (i.e. Co-substituted XYSi 2O 6 with X and Y referring to metallic elements such as but not limited to Co, Na, and Fe), using a readily scalable hydrothermal technique. We then propose a growth mechanism for these bundles, based on detailed time and temperature dependent studies as well as complementary control experiments, particularly reactions in the absence of either 3-aminopropyltriethoxysilane (APTES) or sodium hydroxide (NaOH), via a transmission electron microscopy visualization study. Moreover, these nanowire bundles were probed formore » their magnetic properties and chemical composition using superconducting quantum interference device (SQUID) measurements, X-ray diffraction, and pair distribution function analysis, respectively. Specifically, SQUID measurement observations highlighted that these bundles evince (i) unique and interesting super-paramagnetic properties at 5 K that are consistent with that of our previously published ~2 nm ultra-small nanoparticles as well as (ii) paramagnetic behavior at 300 K.« less

Nonexponential London Penetration Depth of FeAs-Based Superconducting RFeAsO[subscript 0.9]F[subscript 0.1] (R=La, Nd) Single Crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, C.; Tillman, M.E.; Kim, H.

2009-07-31

The superconducting penetration depth {lambda}(T) has been measured in RFeAsO{sub 0.9}F{sub 0.1} (R=La, Nd) single crystals (R-1111). In Nd-1111, we find an upturn in {lambda}(T) upon cooling and attribute it to the paramagnetism of the Nd ions, similar to the case of the electron-doped cuprate Nd-Ce-Cu-O. After the correction for paramagnetism, the London penetration depth variation is found to follow a power-law behavior, {Delta}{lambda}L(T) {proportional_to} T{sup 2} at low temperatures. The same T{sup 2} variation of {lambda}(T) was found in nonmagnetic La-1111 crystals. Analysis of the superfluid density and of penetration depth anisotropy over the full temperature range is consistentmore » with two-gap superconductivity. Based on this and on our previous work, we conclude that both the RFeAsO (1111) and BaFe{sub 2}As{sub 2} (122) families of pnictide superconductors exhibit unconventional two-gap superconductivity.« less

Analysis of spin-Hamiltonian and molecular orbital coefficients of Cu2+ doped C8H11KO8 single crystal through EPR technique

NASA Astrophysics Data System (ADS)

Juliet sheela, K.; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.

2018-04-01

Electron paramagnetic resonance (EPR) studies have been investigated at X-band microwave frequency on Cu2+ ion incorporated into the single crystal of potassium succinate-succinic acid (KSSA) at room temperature. The angular variation of the EPR spectra has shown two magnetically in-equivalent Cu2+ sites in the KSSA single crystal system. The spin Hamiltonian parameters g and A are determined which reveals that the site I and site II occupied in rhombic and axial local field symmetry around the impurity ion. Among the two paramagnetic impurity ions, sites one occupies at substituitional position in the place of monovalent cation (K+) in the crystal whereas the other enters in its lattice interstitially by the correlation of EPR and crystal structure data. From the calculated principle values gxx, gyy, gzz and Axx, Ayy, Azz of both the sites, the admixture coefficients and molecular orbital coefficients were evaluated which gives the information of ground state wave function and types of bonding of impurity ions with the ligands.

Synthesis, characterization, and growth mechanism of motifs of ultrathin cobalt-substituted NaFeSi 2O 6 nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewis, Crystal S.; Moronta, Dominic; Terban, Maxwell W.

In this report, we have synthesized and structurally characterized nanowire bundles of cobalt-substituted pyroxenes, similar to the crystal structure of aegirine (i.e. Co-substituted XYSi 2O 6 with X and Y referring to metallic elements such as but not limited to Co, Na, and Fe), using a readily scalable hydrothermal technique. We then propose a growth mechanism for these bundles, based on detailed time and temperature dependent studies as well as complementary control experiments, particularly reactions in the absence of either 3-aminopropyltriethoxysilane (APTES) or sodium hydroxide (NaOH), via a transmission electron microscopy visualization study. Moreover, these nanowire bundles were probed formore » their magnetic properties and chemical composition using superconducting quantum interference device (SQUID) measurements, X-ray diffraction, and pair distribution function analysis, respectively. Specifically, SQUID measurement observations highlighted that these bundles evince (i) unique and interesting super-paramagnetic properties at 5 K that are consistent with that of our previously published ~2 nm ultra-small nanoparticles as well as (ii) paramagnetic behavior at 300 K.« less

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

... that is a unique combination of: (1) multi-gradient Single Point Imaging involving global phase...-encoding gradients. The combination approach of single point imaging with the spin-echo signal detection...

An electron paramagnetic resonance study on irradiated triphenylphosphinselenid single crystal

NASA Astrophysics Data System (ADS)

Aras, Erdal; Karatas, Ozgul; Meric, Yasemin; Abbass, Hind Kh; Birey, Mehmet; Kilic, Ahmet

2014-09-01

The single crystals of triphenylphosphinselenid [C18H15PSe] were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to 60Co gamma (γ) rays with a dose speed of 0.980 kGy/h at the room temperature for 72 h. The free radical over the sample was observed using electron paramagnetic resonance (EPR)-X band spectrometer. The EPR spectra were recorded between 120 and 400 K. Furthermore, the sample irradiated was rotated in steps of 10° and analyzed for different orientations of the crystal in the magnetic field. Only one radical structure was determined on the molecule. The hyperfine constants of the sample were found to be anisotropic. The average values of these constants and value of g were calculated as following: g=2.007656, aSe=37.47 G, aP=27.44 G, aHa=17.28 G, and aHb=18.16 G.

Systematic approach to cutoff frequency selection in continuous-wave electron paramagnetic resonance imaging

NASA Astrophysics Data System (ADS)

Hirata, Hiroshi; Itoh, Toshiharu; Hosokawa, Kouichi; Deng, Yuanmu; Susaki, Hitoshi

2005-08-01

This article describes a systematic method for determining the cutoff frequency of the low-pass window function that is used for deconvolution in two-dimensional continuous-wave electron paramagnetic resonance (EPR) imaging. An evaluation function for the criterion used to select the cutoff frequency is proposed, and is the product of the effective width of the point spread function for a localized point signal and the noise amplitude of a resultant EPR image. The present method was applied to EPR imaging for a phantom, and the result of cutoff frequency selection was compared with that based on a previously reported method for the same projection data set. The evaluation function has a global minimum point that gives the appropriate cutoff frequency. Images with reasonably good resolution and noise suppression can be obtained from projections with an automatically selected cutoff frequency based on the present method.

Resonance magnetoplasticity in ultralow magnetic fields

NASA Astrophysics Data System (ADS)

Alshits, V. I.; Darinskaya, E. V.; Koldaeva, M. V.; Petrzhik, E. A.

2016-09-01

Resonance relaxation displacements of dislocations in NaCl crystals placed in crossed static and alternating ultralow magnetic fields in the electron paramagnetic resonance scheme are discussed. The Earth's magnetic field B Earth ≈ 50μT and other fields in the range of 26-261 μT are used as the static field. New strongly anisotropic properties of the effect have been revealed. Frequency spectra including numerous peaks of paths at low pump frequencies beginning with 10 kHz, as well as the quartet of equidistant peaks at high frequencies ( 1.4 MHz at B= B Earth), have been measured. The effect is also observed in the pulsed pump field with a resonance duration of 0.5 μs. Resonance changes have been detected in the microhardness of ZnO, triglycine sulfate, and potassium hydrogen phthalate crystals after their exposure in the Earth's magnetic field in the same electron paramagnetic resonance scheme.

EPR investigations of silicon carbide nanoparticles functionalized by acid doped polyaniline

NASA Astrophysics Data System (ADS)

Karray, Fekri; Kassiba, Abdelhadi

2012-06-01

Nanocomposites (SiC-PANI) based on silicon carbide nanoparticles (SiC) encapsulated in conducting polyaniline (PANI) are synthesized by direct polymerization of PANI on the nanoparticle surfaces. The conductivity of PANI and the nanocomposites was modulated by several doping levels of camphor sulfonic acid (CSA). Electron paramagnetic resonance (EPR) investigations were carried out on representative SiC-PANI samples over the temperature range [100-300 K]. The features of the EPR spectra were analyzed taking into account the paramagnetic species such as polarons with spin S=1/2 involved in two main environments realized in the composites as well as their thermal activation. A critical temperature range 200-225 K was revealed through crossover changes in the thermal behavior of the EPR spectral parameters. Insights on the electronic transport properties and their thermal evolutions were inferred from polarons species probed by EPR and the electrical conductivity in doped nanocomposites.

Phase diagram and re-entrant fermionic entanglement in a hybrid Ising-Hubbard ladder

NASA Astrophysics Data System (ADS)

Sousa, H. S.; Pereira, M. S. S.; de Oliveira, I. N.; Strečka, J.; Lyra, M. L.

2018-05-01

The degree of fermionic entanglement is examined in an exactly solvable Ising-Hubbard ladder, which involves interacting electrons on the ladder's rungs described by Hubbard dimers at half-filling on each rung, accounting for intrarung hopping and Coulomb terms. The coupling between neighboring Hubbard dimers is assumed to have an Ising-like nature. The ground-state phase diagram consists of four distinct regions corresponding to the saturated paramagnetic, the classical antiferromagnetic, the quantum antiferromagnetic, and the mixed classical-quantum phase. We have exactly computed the fermionic concurrence, which measures the degree of quantum entanglement between the pair of electrons on the ladder rungs. The effects of the hopping amplitude, the Coulomb term, temperature, and magnetic fields on the fermionic entanglement are explored in detail. It is shown that the fermionic concurrence displays a re-entrant behavior when quantum entanglement is being generated at moderate temperatures above the classical saturated paramagnetic ground state.

Elemental, morphological, structural, optical, and magnetic properties of erbium doped ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Poornaprakash, B.; Chalapathi, U.; Purusottam Reddy, B.; Prabhakar Vattikuti, S. V.; Siva Pratap Reddy, M.; Park, Si-Hyun

2018-03-01

The sensible tuning of the structural, optical, and magnetic properties of ZnO nanoparticles (NPs) with suitable doping can enhance their applicability in diverse fields. In this study, we synthesized ZnO NPs with Er (0-4 at%) doping and their elemental, structural, optical, and magnetic properties were studied. Both field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) studies of the suspensions consist of hexagonal shaped NPs. All the prepared NPs exhibited hexagonal phase as demonstrated by powder x-ray diffraction studies. A blue shift was observed in the Er doped ZnO NPs compared to pure ZnO, indicating the increased optical bandgap. Vibrating sample magnetometer studies exhibited the pure ZnO NPs was typical diamagnetic feature whereas all the Er doped ZnO NPs were paramagnetic feature at 300 K. This is the first paramagnetic report on Er doped ZnO NPs.

Electron paramagnetic resonance of globin proteins - a successful match between spectroscopic development and protein research

NASA Astrophysics Data System (ADS)

Van Doorslaer, Sabine; Cuypers, Bert

2018-02-01

At the start of the twenty-first century, the research into the haem-containing globins got a considerable impetus with the discovery of three new mammalian globins: neuroglobin, cytoglobin and androglobin. Globins are by now found in all kingdoms of life and, in many cases, their functions are still under debate. This revival in globin research increased the demand for adequate physico-chemical research tools to determine the structure-function relationships of these proteins. From early days onwards, electron paramagnetic resonance (EPR) has been used in globin research. In recent decades, the field of EPR has been revolutionised with the introduction of many new pulsed and high-field EPR techniques. In this review, we highlight how EPR has become an essential tool in globin research, and how globins equally provide ideal model systems to push technical developments in EPR.

Electron paramagnetic resonance spectral study of [Mn(acs){sub 2}(2–pic){sub 2}(H{sub 2}O){sub 2}] single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocakoç, Mehpeyker, E-mail: mkocakoc@cu.edu.tr; Tapramaz, Recep, E-mail: recept@omu.edu.tr

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{sup +2} ion complex with mixed ligand, [Mn(acs){sub 2}(2-pic){sub 2}(H{sub 2}O){sub 2}], was studied with electron paramagnetic resonance (EPR) spectroscopy. EPR parameters were determined. Zero field splitting parameters indicated that themore » complex was highly symmetric. Variable temperature studies showed no detectable chance in spectra.« less

Imaging thiol redox status in murine tumors in vivo with rapid-scan electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Epel, Boris; Sundramoorthy, Subramanian V.; Krzykawska-Serda, Martyna; Maggio, Matthew C.; Tseytlin, Mark; Eaton, Gareth R.; Eaton, Sandra S.; Rosen, Gerald M.; Kao, Joseph P. Y.; Halpern, Howard J.

2017-03-01

Thiol redox status is an important physiologic parameter that affects the success or failure of cancer treatment. Rapid scan electron paramagnetic resonance (RS EPR) is a novel technique that has shown higher signal-to-noise ratio than conventional continuous-wave EPR in in vitro studies. Here we used RS EPR to acquire rapid three-dimensional images of the thiol redox status of tumors in living mice. This work presents, for the first time, in vivo RS EPR images of the kinetics of the reaction of 2H,15N-substituted disulfide-linked dinitroxide (PxSSPx) spin probe with intracellular glutathione. The cleavage rate is proportional to the intracellular glutathione concentration. Feasibility was demonstrated in a FSa fibrosarcoma tumor model in C3H mice. Similar to other in vivo and cell model studies, decreasing intracellular glutathione concentration by treating mice with L-buthionine sulfoximine (BSO) markedly altered the kinetic images.

Probing the electronic structure and photoactivation process of nitrogen-doped TiO2 using DRS, PL, and EPR.

PubMed

Zhang, Zizhong; Long, Jinlin; Xie, Xiuqiang; Lin, Huan; Zhou, Yangen; Yuan, Rusheng; Dai, Wenxin; Ding, Zhengxin; Wang, Xuxu; Fu, Xianzhi

2012-04-23

The electronic structure and photoactivation process in N-doped TiO(2) is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat- and photoinduced N-doped TiO(2) catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti(3+) states are formed to enhance the optical absorption in the visible-light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N-doped TiO(2), the DRS absorption and PL emission in the visible spectral region of 450-700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N(s)·, oxygen vacancies with one electron (V(o)·), and Ti(3+) ions are produced with light irradiation and the intensity of N(s)· species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO(2) corresponding to the main absorption band at 410 nm of N-doped TiO(2), but oxygen vacancies and Ti(3+) states as defects contribute to the visible-light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N-doped TiO(2) is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen-vacancy-related defects leads to quenching of paramagnetic N(s)· species but they stabilize the active nitrogen species N(s)(-). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

TRIAGE of Irradiated Personnel

DTIC Science & Technology

1996-09-25

Vivo Electron Paramagnetic Resonance, Electron Spin Resonance (EPR, ESR) for In Vivo Dosimetry Under Field Conditions Dr. Harold M. Swartz Dartmouth...Force Medical Center Andrews Air Force Base, MD • Status and Limitations of Physical Dosimetry in the Field Environment David A. Schauer, LCDR, MSC...USN Naval Dosimetry Center Navy Environmental Health Center Detachment Bethesda, MD • NATO Policy and Guidance on Antiemetic Usage Robert Kehlet

Electronic structure and magnetic ordering in manganese hydride

NASA Astrophysics Data System (ADS)

Magnitskaya, M. V.; Kulikov, N. I.

1991-03-01

The self-consistent electron energy bands of antiferromagnetic (AFM) and non-magnetic manganese hydride are calculated using the linear muffintin orbital method (LMTO). The calculated values of equilibrium volume and of magnetic moment on the manganese site are in good agreement with experiment. The Fermi surface of paramagnetic MnH contains two nesting parts, and their superposition gives rise to AFM gap.

The impact of adsorption on the localization of spins in graphene oxide and reduced graphene oxide, observed with electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Kempiński, Mateusz; Florczak, Patryk; Jurga, Stefan; Śliwińska-Bartkowiak, Małgorzata; Kempiński, Wojciech

2017-08-01

We report the observations of electronic properties of graphene oxide and reduced graphene oxide, performed with electron paramagnetic resonance technique in a broad temperature range. Both materials were examined in pure form and saturated with air, helium, and heavy water molecules. We show that spin localization strongly depends on the type and amount of molecules adsorbed at the graphene layer edges (and possible in-plane defects). Physical and chemical states of edges play crucial role in electrical transport within graphene-based materials, with hopping as the leading mechanism of charge carrier transport. Presented results are a good basis to understand the electronic properties of other carbon structures made of graphene-like building blocks. Most active carbons show some degree of functionalization and are known of having good adsorptive properties; thus, controlling both phenomena is important for many applications. Sample treatment with temperature, vacuum, and various adsorbents allowed for the observation of a possible metal-insulator transition and sorption pumping effects. The influence of adsorption on the localization phenomena in graphene would be very important if to consider the graphene-based material as possible candidates for the future spintronics that works in ambient conditions.

Considerations regarding the implementation of EPR dosimetry for the population in the vicinity of Semipalatinsk nuclear test site based on experience from other radiation accidents.

PubMed

Skvortsov, Valeriy; Ivannikov, Alexander; Tikunov, Dimitri; Stepanenko, Valeriy; Borysheva, Natalie; Orlenko, Sergey; Nalapko, Mikhail; Hoshi, Masaharu

2006-02-01

General aspects of applying the method of retrospective dose estimation by electron paramagnetic resonance spectroscopy of human tooth enamel (EPR dosimetry) to the population residing in the vicinity of the Semipalatinsk nuclear test site are analyzed and summarized. The analysis is based on the results obtained during 20 years of investigations conducted in the Medical Radiological Research Center regarding the development and practical application of this method for wide-scale dosimetrical investigation of populations exposed to radiation after the Chernobyl accident and other radiation accidents.

An improved approach to identify irradiated spices using electronic nose, FTIR, and EPR spectroscopy.

PubMed

Sanyal, Bhaskar; Ahn, Jae-Jun; Maeng, Jeong-Hwan; Kyung, Hyun-Kyu; Lim, Ha-Kyeong; Sharma, Arun; Kwon, Joong-Ho

2014-09-01

Changes in cumin and chili powder from India resulting from electron-beam irradiation were investigated using 3 analytical methods: electronic nose (E-nose), Fourier transform infrared (FTIR) spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. The spices had been exposed to 6 to 14 kGy doses recommended for microbial decontamination. E-nose measured a clear difference in flavor patterns of the irradiated spices in comparison with the nonirradiated samples. Principal component analysis further showed a dose-dependent variation. FTIR spectra of the samples showed strong absorption bands at 3425, 3007 to 2854, and 1746 cm(-1). However, both nonirradiated and irradiated spice samples had comparable patterns without any noteworthy changes in functional groups. EPR spectroscopy of the irradiated samples showed a radiation-specific triplet signal at g = 2.006 with a hyper-fine coupling constant of 3 mT confirming the results obtained with the E-nose technique. Thus, E-nose was found to be a potential tool to identify irradiated spices. © 2014 Institute of Food Technologists®

Pulsed-High Field/High-Frequency EPR Spectroscopy

NASA Astrophysics Data System (ADS)

Fuhs, Michael; Moebius, Klaus

Pulsed high-field/high-frequency electron paramagnetic resonance (EPR) spectroscopy is used to disentangle many kinds of different effects often obscured in continuous wave (cw) EPR spectra at lower magnetic fields/microwave frequencies. While the high magnetic field increases the resolution of G tensors and of nuclear Larmor frequencies, the high frequencies allow for higher time resolution for molecular dynamics as well as for transient paramagnetic intermediates studied with time-resolved EPR. Pulsed EPR methods are used for example for relaxation-time studies, and pulsed Electron Nuclear DOuble Resonance (ENDOR) is used to resolve unresolved hyperfine structure hidden in inhomogeneous linewidths. In the present article we introduce the basic concepts and selected applications to structure and mobility studies on electron transfer systems, reaction centers of photosynthesis as well as biomimetic models. The article concludes with an introduction to stochastic EPR which makes use of an other concept for investigating resonance systems in order to increase the excitation bandwidth of pulsed EPR. The limited excitation bandwidth of pulses at high frequency is one of the main limitations which, so far, made Fourier transform methods hardly feasible.

New developments in high field electron paramagnetic resonance with applications in structural biology

NASA Astrophysics Data System (ADS)

Bennati, Marina; Prisner, Thomas F.

2005-02-01

Recent developments in microwave technologies have led to a renaissance of electron paramagnetic resonance (EPR) due to the implementation of new spectrometers operating at frequencies >=90 GHz. EPR at high fields and high frequencies (HF-EPR) has been established up to THz (very high frequency (VHF) EPR) in continuous wave (cw) operation and up to about 300 GHz in pulsed operation. To date, its most prominent application field is structural biology. This review article first gives an overview of the theoretical basics and the technical aspects of HF-EPR methodologies, such as cw and pulsed HF-EPR, as well as electron nuclear double resonance at high fields (HF-ENDOR). In the second part, the article illustrates different application areas of HF-EPR in studies of protein structure and function. In particular, HF-EPR has delivered essential contributions to disentangling complex spectra of radical cofactors or reaction intermediates in photosynthetic reaction centres, radical enzymes (such as ribonucleotide reductase) and in metalloproteins. Furthermore, HF-EPR combined with site-directed spin labelling in membranes and soluble proteins provides new methods of investigating complex molecular dynamics and intermolecular distances.

The effect of PVP on morphology, optical properties and electron paramagnetic resonance of Zn0.5Co0.5Fe2-xPrxO4 nanoparticles

NASA Astrophysics Data System (ADS)

Bitar, Z.; El-Said Bakeer, D.; Awad, R.

2017-07-01

Zinc Cobalt nano ferrite doped with Praseodymium, Zn0.5Co0.5Fe2-xPrxO4 (0 ≤ x ≤ 0.2), were prepared by co-precipitation method from an aqueous solution containing metal chlorides and two concentrations of poly(vinylpyrrolidone) (PVP) 0 and 30g/L as capping agent. The samples were characterized using X-ray powder diffraction (XRD), Transmission Electron Microscope (TEM), UV-visible optical spectroscopy, Fourier transform infrared (FTIR) and Electron Paramagnetic Resonance (EPR). XRD results display the formation of cubic spinel structure with space group Fd3m and the lattice parameter (a) is slightly decreased for PVP capping samples. The particle size that determined by TEM, decreases for PVP capping samples. The optical band energy Eg increases for PVP capping samples, confirming the variation of energy gap with the particle size. The FTIR results indicate that the metal oxide bands were shifted for the PVP capping samples. EPR data shows that the PVP addition increases the magnetic resonance field and hence decreases the g-factor.

The ground state of metallic nano-structures in heavily irradiated NaCl-KBF4

NASA Astrophysics Data System (ADS)

Cherkasov, F. G.; L'Vov, S. G.; Tikhonov, D. A.; den Hartog, H. W.; Vainshtein, D. I.

ESR, NMR and static magnetic susceptibility measurements of heavily irradiated NaCl-K and NaCl-KBF4 are reported. Up to 10% of the NaCl-molecules are transformed into metallic Na nanoparticles and Cl-2 precipitates. In addition, there are paramagnetic F- and F-aggregates, which are coupled by exchange interactions to the conduction electrons in the nanoparticles. Above 160 K the NMR and ESR signals of NaCl-K and NaCl-KBF4 show Pauli paramagnetism and the properties of the Na nanoparticles are similar to bulk sodium. A single ESR line is observed revealing exchange interaction between conduction electrons in the nano-particles and F-aggregates. The observed decrease of the ESR susceptibility with decreasing temperature is due to a metal-insulator transition. The conduction electrons are localized below 40 K and the above mentioned F-aggregate centers contribute significantly to the overall ESR signal. For NaCl-KBF4 we observed that with decreasing temperature the ESR line shifts towards lower fields due to antiferromagnetic ordering and internal magnetic fields.

Ethylene Glycol Quenching of Nitrogenase Catalysis: An Electron Paramagnetic Resonance Spectroscopic Study of Nitrogenase Turnover States and CO Bonding.

PubMed

Hales, Brian J

2015-07-14

Most hydrophilic organic solvents inhibit enzymatic activity. Nitrogenase is shown to be approximately 3 times more sensitive to organic inhibition than most other soluble enzymes. Ethylene glycol (EG) is demonstrated to rapidly inhibit nitrogenase activity without uncoupling ATP hydrolysis. Our data suggest the mechanism of inhibition is EG's blocking of binding of MgATP to the nitrogenase Fe protein. EG quenching allows, for the first time, the observation of the relaxation of the intermediate reaction states at room temperature. Electron paramagnetic resonance (EPR) spectroscopy is used to monitor the room-temperature decay of the nitrogenase turnover states following EG quenching of catalytic activity. The return of the intermediate states to the resting state occurs in multiple phases over 2 h. During the initial stage, nitrogenase still possesses the ability to generate CO-induced EPR signals even though catalytic activity has ceased. During the last phase of relaxation, the one-electron reduced state of the MoFe protein (E1) relaxes to the resting state (E0) in a slow first-order reaction.

Multi-photon Rabi oscillations in high spin paramagnetic impurity

NASA Astrophysics Data System (ADS)

Bertaina, S.; Groll, N.; Chen, L.; Chiorescu, I.

2011-10-01

We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn2+ (S = 5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large than the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S = l/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.

X-ray photoelectron spectroscopy and paramagnetic resonance evidence for shock-induced intramolecular bond breaking in some energetic solids

NASA Astrophysics Data System (ADS)

Owens, F. J.; Sharma, J.

1980-03-01

Solid samples of 1,3,5, trinitro 1,3,5, triazacyclohexane (RDX), trinitrotoluene (TNT), and ammonium nitrate were subjected to shock pulses of strength and duration less than the threshold to cause detonation. The recovered shocked samples were studied by x-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The results of these measurements indicate that the shock pulse either broke or altered the internal bonds of the molecules of the solid. The results of the shock decomposition are compared with measurements of the uv and slow thermal decomposition of these materials using the same experimental techniques.

The electron-spin--nuclear-spin interaction studied by polarized neutron scattering.

PubMed

Stuhrmann, Heinrich B

2007-11-01

Dynamic nuclear spin polarization (DNP) is mediated by the dipolar interaction of paramagnetic centres with nuclear spins. This process is most likely to occur near paramagnetic centres at an angle close to 45 degrees with respect to the direction of the external magnetic field. The resulting distribution of polarized nuclear spins leads to an anisotropy of the polarized neutron scattering pattern, even with randomly oriented radical molecules. The corresponding cross section of polarized coherent neutron scattering in terms of a multipole expansion is derived for radical molecules in solution. An application using data of time-resolved polarized neutron scattering from an organic chromium(V) molecule is tested.

Magnetization of InAs parabolic quantum dot: An exact diagonalization approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aswathy, K. M., E-mail: aswathykm20@gmail.com; Sanjeev Kumar, D.

2016-04-13

The magnetization of two electron InAs quantum dot has been studied as a function of magnetic field. The electron-electron interaction has been taken into account by using exact diagonalization method numerically. The magnetization at zero external magnetic field is zero and increases in the negative direction. There is also a paramagnetic peak where the energy levels cross from singlet state to triplet state. Finally, the magnetization falls again to even negative values and saturates.

Effects of the Electronic Spin-Orbit Interaction on the Anomalous Asymmetric Scattering of the Spin-Polarized He+ Beam with Paramagnetic Target Materials II. Partial Wave Representation

NASA Astrophysics Data System (ADS)

Sakai, Osamu; Suzuki, Taku T.

2018-05-01

The scattering of an electron-spin-polarized 4He+ beam on paramagnetic materials has an anomalously large asymmetric scattering component (ASC) around 10%, which is 104 times that expected from the spin-orbit coupling for the potential of the target nucleus. The scattering angle (θ) dependence of the ASC has been measured. It changes sign near 90° for some materials (for example, Au and Pt), while it does not change sign for other materials (for example, Pb and Bi). It has been noted that the spin-orbit interaction of electrons on the target in the electron-transfer intermediate state causes the ASC of He nucleus motion, and it has also been predicted that the sign change in the θ dependence occurs when the d electron transfer is dominant. This seems to correspond to the cases of Au and Pt, but not to the cases of Pb and Bi. The previous approach is refined on the basis of the partial wave representation, which can give a more correct estimation of the ASC. It is shown that the sign change appears in the weak-resonance domain in the case of d electron excitation, whereas the sign change disappears in the strong-resonance domain. Our calculated results qualitatively agree with the material dependence of the ASC observed experimentally.

Iron- and 4-hydroxy-2-alkylquinoline-containing periplasmic inclusion bodies of Pseudomonas aeruginosa: A chemical analysis

USGS Publications Warehouse

Royt, P.W.; Honeychuck, R.V.; Pant, R.R.; Rogers, M.L.; Asher, L.V.; Lloyd, J.R.; Carlos, W.E.; Belkin, H.E.; Patwardhan, S.

2007-01-01

Dark aggregated particles were seen on pellets of iron-rich, mid-logarithmic phase Pseudomonas aeruginosa. Transmission electron microscopy of these cells showed inclusion bodies in periplasmic vacuoles. Aggregated particles isolated from the spent medium of these cells contained iron as indicated by atomic absorption spectroscopy and by electron paramagnetic resonance spectroscopy that revealed Fe3+. Scanning electron microscopy/energy dispersive X-ray analysis of whole cells revealed the presence of iron-containing particles beneath the surface of the cell, indicating that the isolated aggregates were the intracellular inclusion bodies. Collectively, mass spectroscopy and nuclear magnetic resonance spectroscopy of the isolated inclusion bodies revealed the presence of 3,4-dihydroxy-2-heptylquinoline which is the Pseudomonas quinolone signaling compound (PQS) and an iron chelator; 4-hydroxy-2-heptylquinoline (pseudan VII), which is an iron chelator, antibacterial compound and precursor of PQS; 4-hydroxy-2-nonylquinoline (pseudan IX) which is an iron chelator and antibacterial compound; 4-hydroxy-2-methylquinoline (pseudan I), and 4-hydroxy-2-nonylquinoline N-oxide. ?? 2006 Elsevier Inc. All rights reserved.

Quench of paramagnetic orbital selective Mott phase and appearance of antiferromagnetic orbital selective slater phase in multiorbital correlated systems

NASA Astrophysics Data System (ADS)

Quan, Ya-Min; Liu, Da-Yong; Lin, Hai-Qing; Zou, Liang-Jian

2018-06-01

We present the modulation of magnetic order on the orbital selective Mott phases (OSMP) and the metal-insulator transitions (MIT) of multi-orbital Hubbard models by employing the rotationally invariant slave-boson methods. We show that at half filling, the well-known paramagnetic (PM) OSMP is completely covered by an antiferromagnetic (AFM) Slater insulator, and the PM Mott phase by an AFM Mott insulator when electron correlation strength varies from intermediate to strong both in two- and three-orbitals Hubbard systems. Away from half-filling, we find that a partial-polarized AFM orbital-selective Slater phase appears in the intermediate correlation regime, and an almost full-polarized AFM OSMP fully covers the paramagnetic OSMP. In addition, the ferromagnetic phase in the three-orbital case is more robust than that in the two-orbital case. These results demonstrate that the modulation of magnetic correlation to the quasiparticle spectra leads to much rich and more interesting MIT scenario in multiorbital correlated systems.

How can EPR spectroscopy help to unravel molecular mechanisms of flavin-dependent photoreceptors?

PubMed

Nohr, Daniel; Rodriguez, Ryan; Weber, Stefan; Schleicher, Erik

2015-01-01

Electron paramagnetic resonance (EPR) spectroscopy is a well-established spectroscopic method for the examination of paramagnetic molecules. Proteins can contain paramagnetic moieties in form of stable cofactors, transiently formed intermediates, or spin labels artificially introduced to cysteine sites. The focus of this review is to evaluate potential scopes of application of EPR to the emerging field of optogenetics. The main objective for EPR spectroscopy in this context is to unravel the complex mechanisms of light-active proteins, from their primary photoreaction to downstream signal transduction. An overview of recent results from the family of flavin-containing, blue-light dependent photoreceptors is given. In detail, mechanistic similarities and differences are condensed from the three classes of flavoproteins, the cryptochromes, LOV (Light-oxygen-voltage), and BLUF (blue-light using FAD) domains. Additionally, a concept that includes spin-labeled proteins and examination using modern pulsed EPR is introduced, which allows for a precise mapping of light-induced conformational changes.

Investigating Pigment Radicals in Black Rice Using HPLC and Multi-EPR.

PubMed

Nakagawa, Kouichi; Maeda, Hayato

2017-01-01

We investigated the location and distribution of paramagnetic species in black and white rice using electron paramagnetic resonance (EPR), X-band (9 GHz) EPR imaging (EPRI), and HPLC. EPR primarily detected two paramagnetic species in black rice, which were identified as a stable radical and Mn 2+ species, based on the g values and hyperfine components of the EPR signals. The signal from the stable radical appeared at g ≈ 2.00 and was relatively strong and stable. Subsequent noninvasive two-dimensional (2D) EPRI revealed that this stable radical was primarily located in the pigmented region of black rice, while very few radicals were observed in the rice interior. Pigments extracted from black rice were analyzed using HPLC; the major compound was found to be cyanidin-3-glucoside. EPR and HPLC results indicate that the stable radical was only found within the pigmented region of the rice, and that it could either be cyanidin-3-glucoside, or one of its oxidative decomposition products.

How can EPR spectroscopy help to unravel molecular mechanisms of flavin-dependent photoreceptors?

PubMed Central

Nohr, Daniel; Rodriguez, Ryan; Weber, Stefan; Schleicher, Erik

2015-01-01

Electron paramagnetic resonance (EPR) spectroscopy is a well-established spectroscopic method for the examination of paramagnetic molecules. Proteins can contain paramagnetic moieties in form of stable cofactors, transiently formed intermediates, or spin labels artificially introduced to cysteine sites. The focus of this review is to evaluate potential scopes of application of EPR to the emerging field of optogenetics. The main objective for EPR spectroscopy in this context is to unravel the complex mechanisms of light-active proteins, from their primary photoreaction to downstream signal transduction. An overview of recent results from the family of flavin-containing, blue-light dependent photoreceptors is given. In detail, mechanistic similarities and differences are condensed from the three classes of flavoproteins, the cryptochromes, LOV (Light-oxygen-voltage), and BLUF (blue-light using FAD) domains. Additionally, a concept that includes spin-labeled proteins and examination using modern pulsed EPR is introduced, which allows for a precise mapping of light-induced conformational changes. PMID:26389123

Is an Apple Magnetic: Magnetic Response of Everyday Materials Supporting Views About the Nature of Science

NASA Astrophysics Data System (ADS)

Laumann, Daniel

2017-03-01

Magnetism and its various applications are essential for our daily life and for many technological developments. The term magnetism is almost always used as a synonym for ferromagnetism. However, the magnetic properties of the elements of the periodic table indicate that the vast majority of elements are not ferromagnetic, but rather, diamagnetic or paramagnetic. Typically, only ferromagnetism is discussed in classrooms, which can create a distorted picture. This article supplies the further development of an experiment demonstrating the dia- and paramagnetic properties with an electronic balance and a neodymium magnet. It focuses on an investigation of ordinary materials that occur in pupils' everyday environment. The experiment is applicable both for a quantitative measurement of the magnetic (volume) susceptibility χV and can serve as a phenomenological approach to dia- and paramagnetism. Moreover, it encourages a discussion about typical beliefs regarding the nature of science, comparing the behavior of common objects in weak and in strong magnetic fields.

Origin of negative resistivity slope in U-based ferromagnets

NASA Astrophysics Data System (ADS)

Havela, L.; Paukov, M.; Buturlim, V.; Tkach, I.; Mašková, S.; Dopita, M.

2018-05-01

Ultra-nanocrystalline UH3-based ferromagnets with TC ≈ 200 K exhibit a flat temperature dependence of electrical resistivity with a negative slope both in the ferromagnetic and paramagnetic range. The ordered state with randomness on atomic scale, equivalent to a non-collinear ferromagnetism, can be affected by magnetic field, supressing the static magnetic disorder, which reduces the resistivity and removes the negative slope. It is deduced that the dynamic magnetic disorder in the paramagnetic state can be conceived as continuation of the static disorder in the ordered state. The experiments, performed for (UH3)0.78Mo0.12Ti0.10, demonstrate that the negative resistivity slope, observed for numerous U-based intermetallics in the paramagnetic state, can be due to the strong disorder effect on resistivity. The resulting weak localization, as a quantum interference effect which increases resistivity, is gradually suppressed by enhanced temperature, contributing by electron-phonon scattering, inelastic in nature and removing the quantum coherence.

Isolation of EPR spectra and estimation of spin-states in two-component mixtures of paramagnets.

PubMed

Chabbra, Sonia; Smith, David M; Bode, Bela E

2018-04-26

The presence of multiple paramagnetic species can lead to overlapping electron paramagnetic resonance (EPR) signals. This complication can be a critical obstacle for the use of EPR to unravel mechanisms and aid the understanding of earth abundant metal catalysis. Furthermore, redox or spin-crossover processes can result in the simultaneous presence of metal centres in different oxidation or spin states. In this contribution, pulse EPR experiments on model systems containing discrete mixtures of Cr(i) and Cr(iii) or Cu(ii) and Mn(ii) complexes demonstrate the feasibility of the separation of the EPR spectra of these species by inversion recovery filters and the identification of the relevant spin states by transient nutation experiments. We demonstrate the isolation of component spectra and identification of spin states in a mixture of catalyst precursors. The usefulness of the approach is emphasised by monitoring the fate of the chromium species upon activation of an industrially used precatalyst system.

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.

Paramagnetic defects in KH{sub 2}PO{sub 4} crystals with high concentration of embedded TiO{sub 2} nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grachev, Valentin G., E-mail: grachev@physics.montana.edu; Tse, Romand; Malovichko, Galina I.

2016-01-21

Qualitative transformations of spectra of Electron Paramagnetic Resonance, EPR, were found in KH{sub 2}PO{sub 4} crystals grown from liquor with 10{sup −5}–10{sup −1 }wt. % of anatase TiO{sub 2} nanoparticles in comparison with nominally pure KH{sub 2}PO{sub 4}. The nanoparticles have larger segregation coefficient for prismatic parts of the crystals than for pyramidal ones. Significant decrease in resonance absorption, complete disappearance of EPR lines of Fe{sup 3+} and Cr{sup 3+} centers, and appearance of four weak lines of equal intensities together with broad asymmetric lines with g-factors about 2.07–2.5 was observed in pyramidal parts grown with concentration of TiO{sub 2} nanoparticlesmore » larger than the threshold value 10{sup −2 }wt. %. The four lines were attributed to non-controlled impurity As substituted for P. In the presence of TiO{sub 2} nanoparticles, non-paramagnetic AsO{sub 4}{sup 3−} clusters trap electrons becoming AsO{sub 4}{sup 4−}. Disappearance of Fe{sup 3+} and Cr{sup 3+} centers was explained by their recharge to “EPR-silent” states and/or pairing at the surface of TiO{sub 2} nanoparticles.« less

Upcycling : converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres.

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 reactormore » 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.« less

Genomic, proteomic, and biochemical analysis of the organohalide respiratory pathway in Desulfitobacterium dehalogenans.

PubMed

Kruse, Thomas; van de Pas, Bram A; Atteia, Ariane; Krab, Klaas; Hagen, Wilfred R; Goodwin, Lynne; Chain, Patrick; Boeren, Sjef; Maphosa, Farai; Schraa, Gosse; de Vos, Willem M; van der Oost, John; Smidt, Hauke; Stams, Alfons J M

2015-03-01

Desulfitobacterium dehalogenans is able to grow by organohalide respiration using 3-chloro-4-hydroxyphenyl acetate (Cl-OHPA) as an electron acceptor. We used a combination of genome sequencing, biochemical analysis of redox active components, and shotgun proteomics to study elements of the organohalide respiratory electron transport chain. The genome of Desulfitobacterium dehalogenans JW/IU-DC1(T) consists of a single circular chromosome of 4,321,753 bp with a GC content of 44.97%. The genome contains 4,252 genes, including six rRNA operons and six predicted reductive dehalogenases. One of the reductive dehalogenases, CprA, is encoded by a well-characterized cprTKZEBACD gene cluster. Redox active components were identified in concentrated suspensions of cells grown on formate and Cl-OHPA or formate and fumarate, using electron paramagnetic resonance (EPR), visible spectroscopy, and high-performance liquid chromatography (HPLC) analysis of membrane extracts. In cell suspensions, these components were reduced upon addition of formate and oxidized after addition of Cl-OHPA, indicating involvement in organohalide respiration. Genome analysis revealed genes that likely encode the identified components of the electron transport chain from formate to fumarate or Cl-OHPA. Data presented here suggest that the first part of the electron transport chain from formate to fumarate or Cl-OHPA is shared. Electrons are channeled from an outward-facing formate dehydrogenase via menaquinones to a fumarate reductase located at the cytoplasmic face of the membrane. When Cl-OHPA is the terminal electron acceptor, electrons are transferred from menaquinones to outward-facing CprA, via an as-yet-unidentified membrane complex, and potentially an extracellular flavoprotein acting as an electron shuttle between the quinol dehydrogenase membrane complex and CprA. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Genomic, Proteomic, and Biochemical Analysis of the Organohalide Respiratory Pathway in Desulfitobacterium dehalogenans

PubMed Central

van de Pas, Bram A.; Atteia, Ariane; Krab, Klaas; Hagen, Wilfred R.; Goodwin, Lynne; Chain, Patrick; Boeren, Sjef; Maphosa, Farai; Schraa, Gosse; de Vos, Willem M.; van der Oost, John; Smidt, Hauke

2014-01-01

Desulfitobacterium dehalogenans is able to grow by organohalide respiration using 3-chloro-4-hydroxyphenyl acetate (Cl-OHPA) as an electron acceptor. We used a combination of genome sequencing, biochemical analysis of redox active components, and shotgun proteomics to study elements of the organohalide respiratory electron transport chain. The genome of Desulfitobacterium dehalogenans JW/IU-DC1T consists of a single circular chromosome of 4,321,753 bp with a GC content of 44.97%. The genome contains 4,252 genes, including six rRNA operons and six predicted reductive dehalogenases. One of the reductive dehalogenases, CprA, is encoded by a well-characterized cprTKZEBACD gene cluster. Redox active components were identified in concentrated suspensions of cells grown on formate and Cl-OHPA or formate and fumarate, using electron paramagnetic resonance (EPR), visible spectroscopy, and high-performance liquid chromatography (HPLC) analysis of membrane extracts. In cell suspensions, these components were reduced upon addition of formate and oxidized after addition of Cl-OHPA, indicating involvement in organohalide respiration. Genome analysis revealed genes that likely encode the identified components of the electron transport chain from formate to fumarate or Cl-OHPA. Data presented here suggest that the first part of the electron transport chain from formate to fumarate or Cl-OHPA is shared. Electrons are channeled from an outward-facing formate dehydrogenase via menaquinones to a fumarate reductase located at the cytoplasmic face of the membrane. When Cl-OHPA is the terminal electron acceptor, electrons are transferred from menaquinones to outward-facing CprA, via an as-yet-unidentified membrane complex, and potentially an extracellular flavoprotein acting as an electron shuttle between the quinol dehydrogenase membrane complex and CprA. PMID:25512312

Change of Auger-electron emission from Ni-Pd alloys under magnetic phase transition

NASA Astrophysics Data System (ADS)

Elovikov, S. S.; Zykova, E. Y.; Gvozdover, R. S.; Colligon, J. S.; Yurasova, V. E.

2006-04-01

The change of Auger-electron emission from polycrystals of disordered ferromagnetic NiPd 3 and Ni 3 Pd alloys, under ferro- to paramagnetic transition, has been studied experimentally. It has been shown that the intensity of the Auger-lines, which are formed because of transition of valent zone 3d 3/2 and 3d 5/2 electrons, has local maxima near the Curie point T C for the alloys. Thus, the sensitivity of Auger-electron emission to a magnetic state of the alloy has been established.

Influence of the electron intrinsic magnetic moment on the transverse dielectric permittivity of degenerate electron gas

NASA Astrophysics Data System (ADS)

Maslov, S. A.; Bobrov, V. B.; Kirillin, A. V.; Trigger, S. A.

2018-01-01

Using the linear response theory, the transverse dielectric permittivity of a homogeneous and isotropic system of charged particles is considered. In the ideal gas approximation for the polarization function, an explicit analytical expression for the transverse permittivity of a degenerate electron plasma, which takes into account electron spin, is found. This result describes both the Landau diamagnetism and Pauli paramagnetism in electron plasma. The influence of the electron intrinsic magnetic moment on the spatial and frequency dispersion of the transverse dielectric permittivity of degenerate electron plasma is numerically studied, that is crucial for determining the optical characteristics of plasma.

Electric Field Generation and Control of Bipartite Quantum Entanglement between Electronic Spins in Mixed Valence Polyoxovanadate [GeV14O40]8.

PubMed

Palii, Andrew; Aldoshin, Sergey; Tsukerblat, Boris; Borràs-Almenar, Juan José; Clemente-Juan, Juan Modesto; Cardona-Serra, Salvador; Coronado, Eugenio

2017-08-21

As part of the search for systems in which control of quantum entanglement can be achieved, here we consider the paramagnetic mixed valence polyoxometalate K 2 Na 6 [GeV 14 O 40 ]·10H 2 O in which two electrons are delocalized over the 14 vanadium ions. Applying a homogeneous electric field can induce an antiferromagnetic coupling between the two delocalized electronic spins that behave independently in the absence of the field. On the basis of the proposed theoretical model, we show that the external field can be used to generate controllable quantum entanglement between the two electronic spins traveling over a vanadium network of mixed valence polyoxoanion [GeV 14 O 40 ] 8- . Within a simplified two-level picture of the energy pattern of the electronic pair based on the previous ab initio analysis, we evaluate the temperature and field dependencies of concurrence and thus indicate that the entanglement can be controlled via the temperature, magnitude, and orientation of the electric field with respect to molecular axes of [GeV 14 O 40 ] 8- .

Low-temperature binding of NO adsorbed on MIL-100(Al)-A case study for the application of high resolution pulsed EPR methods and DFT calculations.

PubMed

Mendt, Matthias; Barth, Benjamin; Hartmann, Martin; Pöppl, Andreas

2017-12-14

The low-temperature binding of nitric oxide (NO) in the metal-organic framework MIL-100(Al) has been investigated by pulsed electron nuclear double resonance and hyperfine sublevel correlation spectroscopy. Three NO adsorption species have been identified. Among them, one species has been verified experimentally to bind directly to an 27 Al atom and all its relevant 14 N and 27 Al hyperfine interaction parameters have been determined spectroscopically. Those parameters fit well to the calculated ones of a theoretical cluster model, which was derived by density functional theory (DFT) in the present work and describes the low temperature binding of NO to the regular coordinatively unsaturated Al 3+ site of the MIL-100(Al) structure. As a result, the Lewis acidity of that site has been characterized using the NO molecule as an electron paramagnetic resonance active probe. The DFT derived wave function analysis revealed a bent end-on coordination of the NO molecule adsorbed at that site which is almost purely ionic and has a weak binding energy. The calculated flat potential energy surface of this species indicates the ability of the NO molecule to freely rotate at intermediate temperatures while it is still binding to the Al 3+ site. For the other two NO adsorption species, no structural models could be derived, but one of them is indicated to be adsorbed at the organic part of the metal-organic framework. Hyperfine interactions with protons, weakly coupled to the observed NO adsorption species, have also been measured by pulsed electron paramagnetic resonance and found to be consistent with their attribution to protons of the MIL-100(Al) benzenetricarboxylate ligand molecules.

Structure and Function of Iron-Loaded Synthetic Melanin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yiwen; Xie, Yijun; Wang, Zhao

We describe a synthetic method for increasing and controlling the iron loading of synthetic melanin nanoparticles and use the resulting materials to perform a systematic quantitative investigation on their structure- property relationship. A comprehensive analysis by magnetometry, electron paramagnetic resonance, and nuclear magnetic relaxation dispersion reveals the complexities of their magnetic behavior and how these intraparticle magnetic interactions manifest in useful material properties such as their performance as MRI contrast agents. This analysis allows predictions of the optimal iron loading through a quantitative modeling of antiferromagnetic coupling that arises from proximal iron ions. This study provides a detailed understanding ofmore » this complex class of synthetic biomaterials and gives insight into interactions and structures prevalent in naturally occurring melanins.« less

Effects of electron irradiation on LDPE/MWCNT composites

NASA Astrophysics Data System (ADS)

Yang, Jianqun; Li, Xingji; Liu, Chaoming; Rui, Erming; Wang, Liqin

2015-12-01

In this study, mutiwalled carbon nanotubes (MWCNTs) were incorporated into low density polyethylene (LDPE) in different concentrations (2%, 4% and 8%) using a melt blending process. Structural, thermal stability and tensile property of the unirradiated/irradiated LDPE/MWCNT composites by 110 keV electrons were investigated by means of scanning electron microscopy (SEM), small angle X-ray scattering (SAXS), Raman spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, thermogravimetric analysis (TGA) and uniaxial tensile techniques. Experimental results show that the addition of MWCNTs obviously increases the ultimate tensile strength of LDPE and decreases the elongation at break, which is attributed to the homogeneous distribution of the MWCNTs in LDPE and intense interaction between MWCNTs and LDPE matrix. Also, the electron irradiation further increases the ultimate tensile strength of LDPE/MWCNT composites, which can be ascribed to the more intense interaction between MWCNTs and LDPE matrix, and the formation of crosslinking sites in LDPE matrix induced by the electron irradiation. The addition of MWCNTs significantly enhances thermal stability of the LDPE due to the hindering effect and the scavenging free radicals, while the electron irradiation decreases thermal stability of the LDPE/MWCNT composites since the structure of the MWCNTs and LDPE matrix damages.

Interpretation of the Electron Paramagnetic Resonance Spectra of Copper(II)-Tyrosine Complex

NASA Astrophysics Data System (ADS)

Xu, Xiao-Hui; Kuang, Min-Quan

2017-12-01

The electron paramagnetic resonance (EPR) spectra of [Cu(l-tyrosine)2]n (CuA) were interpreted based on the fourth-order perturbation treatments where the contributions due to the local distortion, ligand orbit and spin-orbit coupling were included. The calculated band transitions d_{x^2} - y^2 to dxy (≈16412 cm-1) and d_{z^2} (≈14845 cm-1) agree well with the band analysis results (d_{x^2} - y^2 \\to d_{xy} ≈16410 and d_{x^2} - y^2 \\to d_{z^2} ≈14850 cm-1). The unresolved separations d_{x^2} - y^2 \\to d_{xz} and d_{x^2} - y^2 \\to d_{yz} in the absorption spectra were evaluated as 26283 and 26262 cm-1, respectively. For CuA, copper chromophores in 1,3-diaminorpropane isophtalate copper(II) complex (CuB) and N-methyl-1,2-diaminoetaane-bis copper(II) polymer (CuC), the transition d_{x^2} - y^2 \\to d_{xy} (=E1≈10Dq) suffered an increase with a decrease in R̅L which was evaluated as the mean value of the copper-ligand bond lengths. The correlations between the tetragonal elongation ratio ρ (=(Rz-R̅L)/R̅L) (or the ratio G=(gz-ge)/((gx+gy)/2-ge)) and the g isotropy gav (=(gx+gy+gz)/3) (or the covalency factor N) for CuA, CuB and CuC were acquired and all the results were discussed.

Magnetic Ordering in Gold Nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agrachev, Mikhail; Antonello, Sabrina; Dainese, Tiziano

Here, several research groups have observed magnetism in monolayer-protected gold-cluster samples, but the results were often contradictory and thus a clear understanding of this phenomenon is still missing. We used Au 25(SCH 2CH 2Ph) 18 0, which is a paramagnetic cluster that can be prepared with atomic precision and whose structure is known precisely. Previous magnetometry studies only detected paramagnetism. We used samples representing a range of crystallographic orders and studied their magnetic behaviors by electron paramagnetic resonance (EPR). As a film, Au 25(SCH 2CH 2Ph) 18 0 displays paramagnetic behavior but, at low temperature, ferromagnetic interactions are detectable. Onemore » or few single crystals undergo physical reorientation with the applied field and display ferromagnetism, as detected through hysteresis experiments. A large collection of microcrystals is magnetic even at room temperature and shows distinct paramagnetic, superparamagnetic, and ferromagnetic behaviors. Simulation of the EPR spectra shows that both spin-orbit coupling and crystal distortion are important to determine the observed magnetic behaviors. DFT calculations carried out on single cluster and periodic models predict values of spin6orbit coupling and crystal6splitting effects in agreement with the EPR derived quantities. Magnetism in gold nanoclusters is thus demonstrated to be the outcome of a very delicate balance of factors. To obtain reproducible results, the samples must be (i) controlled for composition and thus be monodispersed with atomic precision, (ii) of known charge state, and (iii) well defined also in terms of crystallinity and experimental conditions. This study highlights the efficacy of EPR spectroscopy to provide a molecular understanding of these phenomena« less

Magnetic Ordering in Gold Nanoclusters

DOE PAGES

Agrachev, Mikhail; Antonello, Sabrina; Dainese, Tiziano; ...

2017-06-12

Here, several research groups have observed magnetism in monolayer-protected gold-cluster samples, but the results were often contradictory and thus a clear understanding of this phenomenon is still missing. We used Au 25(SCH 2CH 2Ph) 18 0, which is a paramagnetic cluster that can be prepared with atomic precision and whose structure is known precisely. Previous magnetometry studies only detected paramagnetism. We used samples representing a range of crystallographic orders and studied their magnetic behaviors by electron paramagnetic resonance (EPR). As a film, Au 25(SCH 2CH 2Ph) 18 0 displays paramagnetic behavior but, at low temperature, ferromagnetic interactions are detectable. Onemore » or few single crystals undergo physical reorientation with the applied field and display ferromagnetism, as detected through hysteresis experiments. A large collection of microcrystals is magnetic even at room temperature and shows distinct paramagnetic, superparamagnetic, and ferromagnetic behaviors. Simulation of the EPR spectra shows that both spin-orbit coupling and crystal distortion are important to determine the observed magnetic behaviors. DFT calculations carried out on single cluster and periodic models predict values of spin6orbit coupling and crystal6splitting effects in agreement with the EPR derived quantities. Magnetism in gold nanoclusters is thus demonstrated to be the outcome of a very delicate balance of factors. To obtain reproducible results, the samples must be (i) controlled for composition and thus be monodispersed with atomic precision, (ii) of known charge state, and (iii) well defined also in terms of crystallinity and experimental conditions. This study highlights the efficacy of EPR spectroscopy to provide a molecular understanding of these phenomena« less

Magnetic characterization of mixed phases in FeVO4sbnd Co3V2O8 system

NASA Astrophysics Data System (ADS)

Guskos, N.; Zolnierkiewicz, G.; Pilarska, M.; Typek, J.; Berczynski, P.; Blonska-Tabero, A.; Aidinis, K.

2018-04-01

Dynamic and static magnetic properties of four nFeVO4/(1-n)Co3V2O8 composites obtained in reactions between nFeVO4 and (1-n)Co3V2O8 (n = 0.82, 0.80, 0.78 and 0.76) have been investigated by dc magnetometry and electron paramagnetic resonance (EPR). All samples were diphase containing both the howardevansite-type and the lyonsite-type phases in different proportions. Dc magnetic susceptibility study showed the Curie-Weiss paramagnetic behavior with strong antiferromagnetic (AFM) interaction in the high-temperature range and the phase transition to the AFM state at low temperatures. The calculated effective magnetic moment could be justified by the presence of high spin Fe3+ and Co2+ ions. The appearance of hysteresis loop in isothermal magnetisation at low temperature indicates the existence of the ferromagnetic component in all four samples, but only 0.5% of all magnetic ions are involved in this phase. EPR spectra recorded in high-temperature range (T > 90 K) consisted of a single broad line centred at ∼3.2 kG. The fitting of observed spectra with two Gaussian lineshape functions allowed to study the temperature dependence of EPR parameters (resonance field, linewidth, integrated intensity). This analysis suggests that EPR signal arises from two spin subsystems: paramagnetic Fe3+ ions subjected to AFM interaction and AFM spin pairs/clusters of iron/cobalt visible only at high temperatures. At low temperatures two transitions to AFM states, due to the mixture of two structural phases, are registered in magnetic susceptibility measurements.

Time-resolved luminescence measurements of the magnetic field effect on paramagnetic photosensitizers in photodynamic reactions

NASA Astrophysics Data System (ADS)

Mermut, O.; Bouchard, J.-P.; Cormier, J.-F.; Desroches, P.; Diamond, K. R.; Fortin, M.; Gallant, P.; Leclair, S.; Marois, J.-S.; Noiseux, I.; Morin, J.-F.; Patterson, M. S.; Vernon, M.

2008-02-01

The development of multimodal molecular probes and photosensitizing agents for use in photodynamic therapy (PDT) is vital for optimizing and monitoring cytotoxic responses. We propose a combinatorial approach utilizing photosensitizing molecules that are both paramagnetic and luminescent with multimodal functionality to perturb, control, and monitor molecular-scale reaction pathways in PDT. To this end, a time-domain single photon counting lifetime apparatus with a 400 nm excitation source has been developed and integrated with a variable low field magnet (0- 350mT). The luminescence lifetime decay function was measured in the presence of a sweeping magnetic field for a custom designed photosensitizing molecule in which photoinduced electron transfer was studied The photosensitizer studied was a donor-acceptor complex synthesized using a porphyrin linked to a fullerene molecule. The magneto-optic properties were investigated for the free-base photosensitizer complex as well as those containing either diamagnetic (paired electron) or paramagnetic (unpaired electron) metal centers, Zn(II) and Cu(II). The magnetic field was employed to affect and modify the spin states of radical pairs of the photosensitizing agents via magnetically induced hyperfine and Zeeman effects. Since the Type 1 reaction pathway of an excited triplet state photosensitizer involves the production of radical species, lifetime measurements were conducted at low dissolved oxygen concentration (0.01ppm) to elucidate the dependence of the magnetic perturbation on the photosensitization mechanistic pathway. To optimize the magnetic response, a solvent study was performed examining the dependence of the emission properties on the magnetic field in solutions of varying dielectric constants. Lastly, the cytotoxicity in murine tumor cell suspensions was investigated for the novel porphyrin-fullerene complex by inducing photodynamic treatments and determining the associated cell survival.

Paramagnetic Europium Salen Complex and Sickle-Cell Anemia

NASA Astrophysics Data System (ADS)

Wynter, Clive I.; Ryan, D. H.; May, Leopold; Oliver, F. W.; Brown, Eugene; Hoffman, Eugene J.; Bernstein, David

2005-04-01

A new europium salen complex, Eu(salen)2NH4, was synthesized, and its composition was confirmed by chemical analysis and infrared spectroscopy. Further characterization was carried out by 151 Eu Mössbauer spectroscopy and magnetic susceptibility measurements. Mössbauer spectroscopic measurements were made at varying temperatures between 9 K and room temperature and a value of Debye temperature of 133 ±5 K was computed. Both Mössbauer and magnetic susceptibility measurements confirmed the paramagnetic behavior of this complex and the trivalent state of the europium ion. In view of the fact that the "odd" paramagnetic molecule NO has been shown to reverse sickling of red blood cells in sickle cell anemia, the interaction between the paramagnetic europium salen complex and sickle cells was examined after incubation with this europium complex and shown to have similar effects.

Local moment formation and magnetic coupling of Mn dopants in Bi2Se3: A low-temperature ferromagnetic resonance study

NASA Astrophysics Data System (ADS)

Savchenko, D.; Tarasenko, R.; Vališka, M.; Kopeček, J.; Fekete, L.; Carva, K.; Holý, V.; Springholz, G.; Sechovský, V.; Honolka, J.

2018-05-01

We compare the magnetic and electronic configuration of single Mn atoms in molecular beam epitaxy (MBE) grown Bi2Se3 thin films, focusing on electron paramagnetic (ferromagnetic) resonance (EPR and FMR, respectively) and superconducting quantum interference device (SQUID) techniques. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) reveal the expected increase of disorder with increasing concentration of magnetic guest atoms, however, Kikuchi patterns show that disorder consists majorly of μm-scale 60° twin domains in the hexagonal Bi2Se3 structure, which are promoted by the presence of single unclustered Mn impurities. Ferromagnetism below TC (5.4±0.3) K can be well described by critical scaling laws M (T) (1 - T /TC) β with a critical exponent β = (0.34 ± 0.2) , suggesting 3D Heisenberg class magnetism instead of e.g. 2D-type coupling between Mn-spins in van der Waals gap sites. From EPR hyperfine structure data we determine a Mn2+ (d5, S = 5/2) electronic configuration with a g-factor of 2.002 for -1/2 → +1/2 transitions. In addition, from the strong dependence of the low temperature FMR fields and linewidth on the field strength and orientation with respect to the Bi2Se3 (0001) plane, we derive magnetic anisotropy energies of up to K1 = -3720 erg/cm3 in MBE-grown Mn-doped Bi2Se3, reflecting the first order magneto-crystalline anisotropy of an in-plane magnetic easy plane in a hexagonal (0001) crystal symmetry. We observe an increase of K1 with increasing Mn concentration, which we interpret to be correlated to a Mn-induced in-plane lattice contraction. Across the ferromagnetic-paramagnetic transition the FMR intensity is suppressed and resonance fields converge the paramagnetic limit of Mn2+ (d5, S = 5/2).

Ab initio theory of point defects in oxide materials: structure, properties, chemical reactivity

NASA Astrophysics Data System (ADS)

Pacchioni, Gianfranco

2000-05-01

Point defects play a fundamental role in determining the physical and chemical properties of inorganic materials. This holds not only for the bulk properties but also for the surface of oxides where several kinds of point defects exist and exhibit a rich and complex chemistry. A particularly important defect in oxides is the oxygen vacancy. Depending on the electronic structure of the material the nature of oxygen vacancies changes dramatically. In this article we provide a rationalization of the very different electronic structure of neutral and charged oxygen vacancies in SiO 2 and MgO, two oxide materials with completely different electronic structure (from very ionic, MgO, to largely covalent, SiO 2). We used methods of ab initio quantum chemistry, from density functional theory (DFT) to configuration interaction (CI), to determine the ground and excited state properties of these defects. The theoretical results are combined with recent spectroscopic measurements. A series of observable properties has been determined in this way: defect formation energies, hyperfine interactions in electron paramagnetic resonance (EPR) spectra of paramagnetic centers, optical spectra, surface chemical reactivity. The interplay between experimental and theoretical information allows one to unambiguously identify the structure of oxygen vacancies in these binary oxides and on their surfaces.

Segmented surface coil resonator for in vivo EPR applications at 1.1GHz.

PubMed

Petryakov, Sergey; Samouilov, Alexandre; Chzhan-Roytenberg, Michael; Kesselring, Eric; Sun, Ziqi; Zweier, Jay L

2009-05-01

A four-loop segmented surface coil resonator (SSCR) with electronic frequency and coupling adjustments was constructed with 18mm aperture and loading capability suitable for in vivo Electron Paramagnetic Resonance (EPR) spectroscopy and imaging applications at L-band. Increased sample volume and loading capability were achieved by employing a multi-loop three-dimensional surface coil structure. Symmetrical design of the resonator with coupling to each loop resulted in high homogeneity of RF magnetic field. Parallel loops were coupled to the feeder cable via balancing circuitry containing varactor diodes for electronic coupling and tuning over a wide range of loading conditions. Manually adjusted high Q trimmer capacitors were used for initial tuning with subsequent tuning electronically controlled using varactor diodes. This design provides transparency and homogeneity of magnetic field modulation in the sample volume, while matching components are shielded to minimize interference with modulation and ambient RF fields. It can accommodate lossy samples up to 90% of its aperture with high homogeneity of RF and modulation magnetic fields and can function as a surface loop or a slice volume resonator. Along with an outer coaxial NMR surface coil, the SSCR enabled EPR/NMR co-imaging of paramagnetic probes in living rats to a depth of 20mm.

Suppression of Raman electron spin relaxation of radicals in crystals. Comparison of Cu2+ and free radical relaxation in triglycine sulfate and Tutton salt single crystals.

PubMed

Hoffmann, S K; Goslar, J; Lijewski, S

2011-08-31

Electron spin-lattice relaxation was measured by the electron spin echo method in a broad temperature range above 4.2 K for Cu(2+) ions and free radicals produced by ionizing radiation in triglycine sulfate (TGS) and Tutton salt (NH4)(2)Zn(SO4)2 ⋅ 6H2O crystals. Localization of the paramagnetic centres in the crystal unit cells was determined from continuous wave electron paramagnetic resonance spectra. Various spin relaxation processes and mechanisms are outlined. Cu(2+) ions relax fast via two-phonon Raman processes in both crystals involving the whole phonon spectrum of the host lattice. This relaxation is slightly slower for TGS where Cu(2+) ions are in the interstitial position. The ordinary Raman processes do not contribute to the radical relaxation which relaxes via the local phonon mode. The local mode lies within the acoustic phonon band for radicals in TGS but within the optical phonon range in (NH4)(2)Zn(SO4)2 ⋅ 6H2O. In the latter the cross-relaxation was considered. A lack of phonons around the radical molecules suggested a local crystal amorphisation produced by x- or γ-rays.

Segmented surface coil resonator for in vivo EPR applications at 1.1 GHz

PubMed Central

Petryakov, Sergey; Samouilov, Alexandre; Chzhan-Roytenberg, Michael; Kesselring, Eric; Sun, Ziqi; Zweier, Jay L.

2010-01-01

A four-loop segmented surface coil resonator (SSCR) with electronic frequency and coupling adjustments was constructed with 18 mm aperture and loading capability suitable for in vivo Electron Paramagnetic Resonance (EPR) spectroscopy and imaging applications at L-band. Increased sample volume and loading capability were achieved by employing a multi-loop three-dimensional surface coil structure. Symmetrical design of the resonator with coupling to each loop resulted in high homogeneity of RF magnetic field. Parallel loops were coupled to the feeder cable via balancing circuitry containing varactor diodes for electronic coupling and tuning over a wide range of loading conditions. Manually adjusted high Q trimmer capacitors were used for initial tuning with subsequent tuning electronically controlled using varactor diodes. This design provides transparency and homogeneity of magnetic field modulation in the sample volume, while matching components are shielded to minimize interference with modulation and ambient RF fields. It can accommodate lossy samples up to 90% of its aperture with high homogeneity of RF and modulation magnetic fields and can function as a surface loop or a slice volume resonator. Along with an outer coaxial NMR surface coil, the SSCR enabled EPR/NMR co-imaging of paramagnetic probes in living rats to a depth of 20 mm. PMID:19268615

Spectroscopic fingerprints for charge localization in the organic semiconductor (DOEO)4[HgBr4]·TCE

NASA Astrophysics Data System (ADS)

Koplak, Oksana V.; Chernenkaya, Alisa; Medjanik, Katerina; Brambilla, Alberto; Gloskovskii, Andrei; Calloni, Alberto; Elmers, Hans-Joachim; Schönhense, Gerd; Ciccacci, Franco; Morgunov, Roman B.

2015-05-01

Changes of the electronic structure accompanied by charge localization and a transition to an antiferromagnetic ground state were observed in the organic semiconductor (DOEO)4[HgBr4]·TCE. Localization starts in the temperature region of about 150 K and the antiferromagnetic state occurs below 60 K. The magnetic moment of the crystal contains contributions of inclusions (droplets), and individual paramagnetic centers formed by localized holes and free charge carriers at 2 K. Two types of inclusions of 100-400 nm and 2-5 nm sizes were revealed by transmission electron microscopy. Studying the temperature- and angular dependence of electron spin resonance (ESR) spectra revealed fingerprints of antiferromagnetic contributions as well as paramagnetic resonance spectra of individual localized charge carriers. The results point on coexistence of antiferromagnetic long and short range order as evident from a second ESR line. Photoelectron spectroscopy in the VUV, soft and hard X-ray range shows temperature-dependent effects upon crossing the critical temperatures around 60 K and 150 K. The substantially different probing depths of soft and hard X-ray photoelectron spectroscopy yield information on the surface termination. The combined investigation using complementary methods at the same sample reveals the close relation of changes in the transport properties and in the energy distribution of electronic states.

Electronic state of PuCoGa5 and NpCoGa5 as probed by polarized neutrons.

PubMed

Hiess, A; Stunault, A; Colineau, E; Rebizant, J; Wastin, F; Caciuffo, R; Lander, G H

2008-02-22

By using single crystals and polarized neutrons, we have measured the orbital and spin components of the microscopic magnetization in the paramagnetic state of NpCoGa(5) and PuCoGa(5). The microscopic magnetization of NpCoGa(5) agrees with that observed in bulk susceptibility measurements and the magnetic moment has spin and orbital contributions as expected for intermediate coupling. In contrast, for PuCoGa(5), which is a superconductor with a high transition temperature, the microscopic magnetization in the paramagnetic state is small, temperature-independent, and significantly below the value found with bulk techniques at low temperatures. The orbital moment dominates the magnetization.

Structural and dynamic characterization of ultrafine fibers based on the poly-3-hydroxybutyrate-dipyridamole system

NASA Astrophysics Data System (ADS)

Olkhov, A. A.; Karpova, S. G.; Staroverova, O. V.; Krutikova, A. A.; Orlov, N. A.; Kucherenko, E. L.; Iordanskii, A. L.

2016-11-01

The fibrous materials (the mats) based on poly-3-hydroxybutyrate (PHB) containing the drug, dipiridomole (DPD) were produced by electrospinning (ES). Thermophysical and dynamical properties of the single filaments and the mats were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and probe electron paramagnetic resonance spectroscopy (EPR). The effect of annealing temperature on the structure and crystallinity of the fibers was examined. It was shown that the loading of DPD influences on both the melting enthalpy and the morphology of the fibers. Besides the analysis of EPR spectra revealed that there are two populations of spin-probes distributed in the rigid and nonrigid amorphous regions of the PHB fibers respectively. For all fibrous materials with different content of DPD (0-5%) the correlation between thermophysical (DSC) and dynamic data (EPR) was observed.

EPR investigation of the trivalent chromium complexes in SrTiO3

NASA Astrophysics Data System (ADS)

Azamat, D. V.; Dejneka, A.; Lančok, J.; Jastrabik, L.; Trepakov, V. A.; Bryknar, Z.; Neverova, E. V.; Badalyan, A. G.

2014-02-01

The trivalent chromium centers were investigated by means of electron paramagnetic resonance (EPR) in SrTiO3 single crystals grown using the Verneuil technique. It was shown that the charge compensation of the Cr3+-VO dominant centers in octahedral environment is due to the remote oxygen vacancy located on the axial axis of the center. In order to provide insight into spin-phonon relaxation processes the studies of axial distortion of Cr3+-VO centers have been performed as function of temperature. The analysis of the trigonal Cr3+ centers found in SrTiO3 indicates the presence of the nearest-neighbor strontium vacancy. The next-nearest-neighbor exchange-coupled pairs of Cr3+ in SrTiO3 has been analyzed from the angular variation of the total electron spin of S=2 resonance lines.

Enhanced antibacterial activity of zinc oxide nanoparticles synthesized using Petroselinum crispum extracts

NASA Astrophysics Data System (ADS)

Stan, Manuela; Popa, Adriana; Toloman, Dana; Silipas, Teofil-Danut; Vodnar, Dan Cristian; Katona, Gabriel

2015-12-01

The present contribution reports the synthesis of zinc oxide nanoparticles (ZnO NPs) using aqueous leaf and root extracts of Petroselinum crispum (parsley) and characterization of as-prepared samples. ZnO NPs are subjected to X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) studies. The XRD studies reveal a hexagonal wurtzite structure without supplementary diffraction lines for all ZnO samples. TEM analysis shows that the particle size is influenced by the type of plant extract. The EPR spectra indicate the presence of Mn2+ ions in ZnO sample synthesized using P. crispum leaf extract, while zinc vacancy complexes and oxygen vacancies are evidenced in all analyzed samples. ZnO NPs synthesized using P. crispum extracts exhibit increased (2-16 times) antibacterial activity as compared to chemically synthesized ZnO NPs.

PubMed Central

Serteyn, D; Pincemail, J; Mottart, E; Caudron, I; Deby, C; Deby-Dupont, G; Philippart, C; Lamy, M

1994-01-01

This preliminary study demonstrated the existence of a free radical generation during an experimental postischemic muscular reperfusion in a halothane anesthetized horse. The authors used alpha-phényl-N-tert-butylnitrone as a spin trap agent and the electronic paramagnetic resonance method to observe in vivo a free radical generation. PMID:7889465

Effect of magnetic coupling on non-radiative relaxation time of Fe3+ sites on LaAl1-xFexO3 pigments

NASA Astrophysics Data System (ADS)

Novatski, A.; Somer, A.; Maranha, F. G.; de Souza, E. C. F.; Andrade, A. V. C.; Antunes, S. R. M.; Borges, C. P. F.; Dias, D. T.; Medina, A. N.; Astrath, N. G. C.

2018-02-01

Inorganic pigments of the system LaAl1-xFexO3 were prepared by the Pechini and the Solid State Reaction (SSR) methods. Magnetic interactions and non-radiative relaxation time were analyzed by means of phase-resolved photoacoustic spectroscopy and electron paramagnetic resonance (EPR) techniques. EPR results show a change in the magnetic behavior from paramagnetic (x = 0.2 and 0.4) to antiferromagnetic (x = 1.0), which is believed to be a result of the SSR preparation method. Trends in the optical absorption bands of the Fe3+ are attributed to their electronic transitions, and the increase in the band's intensity at 480 and 550 nm was assigned to the increase in the magnetic coupling between Fe-Fe. The phase-resolved method is capable of distinguishing between the two preparation methods, and it is possible to infer that SSR modifies the magnetic coupling of Fe-Fe with x.

Electron spin resonance (ESR) dose measurement in bone of Hiroshima A-bomb victim.

PubMed

Kinoshita, Angela; Baffa, Oswaldo; Mascarenhas, Sérgio

2018-01-01

Explosion of the bombs in Hiroshima and Nagasaki corresponds to the only historical moment when atomic bombs were used against civilians. This event triggered countless investigations into the effects and dosimetry of ionizing radiation. However, none of the investigations has used the victims' bones as dosimeter. Here, we assess samples of bones obtained from fatal victims of the explosion by Electron Spin Resonance (ESR). In 1973, one of the authors of the present study (SM) traveled to Japan and conducted a preliminary experiment on the victims' bone samples. The idea was to use the paramagnetism induced in bone after irradiation to measure the radiation dose. Technological advances involved in the construction of spectrometers, better knowledge of the paramagnetic center, and improvement in signal processing techniques have allowed us to resume the investigation. We obtained a reconstructed dose of 9.46 ± 3.4 Gy from the jawbone, which was compatible with the dose distribution in different locations as measured in non-biological materials such as wall bricks and roof tiles.

Temperature-dependent electron paramagnetic resonance detect oxygen vacancy defects and Cr valence of tetragonal Ba(Ti1-xCrx)O3 ceramics

NASA Astrophysics Data System (ADS)

Han, Dan-Dan; Lu, Da-Yong; Meng, Fan-Ling; Yu, Xin-Yu

2018-03-01

Temperature-dependent electron paramagnetic resonance (EPR) study was employed to detect oxygen vacancy defects in the tetragonal Ba(Ti1-xCrx)O3 (x = 5%) ceramic for the first time. In the rhombohedral phase below -150 °C, an EPR signal at g = 1.955 appeared in the insulating Ba(Ti1-xCrx)O3 (x = 5%) ceramic with an electrical resistivity of 108 Ω cm and was assigned to ionized oxygen vacancy defects. Ba(Ti1-xCrx)O3 ceramics exhibited a tetragonal structure except Ba(Ti1-xCrx)O3 (x = 10%) with a tetragonal-hexagonal mixed phase and a first-order phase transition dielectric behavior (ε‧m > 11,000). Mixed valence Cr ions could coexist in ceramics, form CrTi‧-VOrad rad or CrTirad-TiTi‧ defect complexes and make no contribution to a dielectric peak shift towards low temperature.

Some recent multi-frequency electron paramagnetic resonance results on systems relevant for dosimetry and dating.

PubMed

Callens, F; Vanhaelewyn, G; Matthys, P

2002-04-01

Electron Paramagnetic Resonance (EPR) applications like e.g. EPR dosimetry and dating, are usually performed at X-band frequencies because of practical reasons (cost, sample size, etc.). However, it is increasingly recognized that the radiation-induced EPR signals are strongly composite, what might affect dose/age estimates. A few recent examples from both the dosimetry and dating field, illustrating the problems, will be presented. The involved spectra are mainly due to carbonate-derived radicals (CO2-, CO3(3-), etc.). Measurements at higher microwave frequencies are often recommended to improve the insight into the spectra and/or the practical signal quantification. Recent results at Q- and W-band frequencies will show that a multi-frequency approach indeed opens many interesting perspectives in this field but also that each frequency may have specific (dis)advantages depending on the EPR probe and application involved. The discussion will concern carbonate-containing apatite single crystals, shells, modern and fossil tooth enamel.

Positive Effect of Propolis on Free Radicals in Burn Wounds

PubMed Central

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

2013-01-01

Concentration and properties of free radicals in the burn wounds treated with propolis were examined by the use of electron paramagnetic resonance spectroscopy. Magnetic spin-spin interactions and complex free radicals structures in wound beds were studied. The results were compared to those obtained for silver sulphadiazine used as a standard pharmaceutical agent. The changes of free radicals in the matrix of injury with time of exposition on these substances were tested. The aim of this study was to check the hypothesis about the best influence of propolis on the burn wounds healing. It was confirmed that a relatively lower concentration of free radicals exists in the burn wounds treated with propolis. The homogeneously broadened spectra and a complex free radical system characterize the tested tissue samples. The fastening of spin-lattice relaxation processes in the matrix of injury after treatment with propolis and silver sulphadiazine was observed. Practical usefulness of electron paramagnetic resonance spectroscopy in alternative medicine was proved. PMID:23762125

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.

Theoretical Studies of the Electron Paramagnetic Resonance Parameters and Local Structure for VO2+ in Oxyfluoroborate Glasses

NASA Astrophysics Data System (ADS)

Zhang, Huaming; Yu, Xiaopeng; Xiao, Wenbo

2017-12-01

The electron paramagnetic resonance parameters (g factors g ‖, g ⊥ and hyperfine structure constants A ‖, A ⊥) of a tetragonal V4+ center in oxyfluoroborate glasses (20Li2O-10Li2F2-70B2O3) are theoretically investigated by using the perturbation formulas for a 3d1 ion in tetragonally compressed octahedra. The calculated results are in good agreement with the experimental data. Local structure parameters of [VO6]8- clusters are obtained from the calculation (i.e., R‖ ≈ 1.74 Å and R⊥ ≈ 1.985 Å for the metal-ligand distances parallel and perpendicular to the C4 axis, respectively). It is shown that the local structure around the V4+ ion possesses a compressed tetragonal distortion along C 4 axis. The signs of the hyperfine structure constants A‖ and A ⊥ for V4+ centers in oxyfluoroborate glasses were also suggested in the discussion.

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

PubMed

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. Copyright © 2015 Elsevier Inc. All rights reserved.

Evaluation of sub-microsecond recovery resonators for In Vivo Electron Paramagnetic Resonance Imaging

PubMed Central

F, Hyodo; S, Subramanian; N, Devasahayam; R, Murugesan; K, Matsumoto; JB, Mitchell; MC, Krishna

2008-01-01

Time-domain (TD) electron paramagnetic resonance (EPR) imaging at 300 MHz for in vivo applications requires resonators with recovery times less than 1 microsecond after pulsed excitation to reliably capture the rapidly decaying free induction decay (FID). In this study, we tested the suitability of the Litz foil coil resonator (LCR), commonly used in MRI, for in vivo EPR/EPRI applications in the TD mode and compared with parallel coil resonator (PCR). In TD mode, the sensitivity of LCR was lower than that of the PCR. However, in continuous wave (CW) mode, the LCR showed better sensitivity. The RF homogeneity was similar in both the resonators. The axis of the RF magnetic field is transverse to the cylindrical axis of the LCR, making the resonator and the magnet co-axial. Therefore, the loading of animals, and placing of the anesthesia nose cone and temperature monitors was more convenient in the LCR compared to the PCR whose axis is perpendicular to the magnet axis. PMID:18042414

Hydrodynamic interpretation on the rotational diffusion of peroxylamine disulfonate solute dissolved in room temperature ionic liquids as studied by electron paramagnetic resonance spectroscopy.

PubMed

Miyake, Yusuke; Akai, Nobuyuki; Kawai, Akio; Shibuya, Kazuhiko

2011-06-23

Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.

Synthesis, X-ray structure, magnetic resonance, and DFT analysis of a soluble copper(II) phthalocyanine lacking C-H bonds.

PubMed

Moons, Hans; Łapok, Łukasz; Loas, Andrei; Van Doorslaer, Sabine; Gorun, Sergiu M

2010-10-04

The synthesis, crystal structure, and electronic properties of perfluoro-isopropyl-substituted perfluorophthalocyanine bearing a copper atom in the central cavity (F(64)PcCu) are reported. While most halogenated phthalocyanines do not exhibit long-term order sufficient to form large single crystals, this is not the case for F(64)PcCu. Its crystal structure was determined by X-ray analysis and linked to the electronic properties determined by electron paramagnetic resonance (EPR). The findings are corroborated by density functional theory (DFT) computations, which agree well with the experiment. X-band continuous-wave EPR spectra of undiluted F(64)PcCu powder, indicate the existence of isolated metal centers. The electron-withdrawing effect of the perfluoroalkyl (R(f)) groups significantly enhances the complexes solubility in organic solvents like alcohols, including via their axial coordination. This coordination is confirmed by X-band (1)H HYSCORE experiments and is also seen in the solid state via the X-ray structure. Detailed X-band CW-EPR, X-band Davies and Mims ENDOR, and W-band electron spin-echo-detected EPR studies of F(64)PcCu in ethanol allow the determination of the principal g values and the hyperfine couplings of the metal, nitrogen, and fluorine nuclei. Comparison of the g and metal hyperfine values of F(64)PcCu and other PcCu complexes in different matrices reveals a dominant effect of the matrix on these EPR parameters, while variations in the ring substituents have only a secondary effect. The relatively strong axial coordination occurs despite the diminished covalency of the C-N bonds and potentially weakening Jahn-Teller effects. Surprisingly, natural abundance (13)C HYSCORE signals could be observed for a frozen ethanol solution of F(64)PcCu. The (13)C nuclei contributing to the HYSCORE spectra could be identified as the pyrrole carbons by means of DFT. Finally, (19)F ENDOR and easily observable paramagnetic NMR were found to relate well to the DFT computations, revealing negligible isotropic hyperfine (Fermi contact) contributions. The single-site isolation in solution and solid state and the relatively strong coordination of axial ligands, both attributed to the introduction of R(f) groups, are features important for materials and catalyst design.

Hydride Conformers of the Nitrogenase FeMo-cofactor Two-Electron Reduced State E2(2H), Assigned Using Cryogenic Intra Electron Paramagnetic Resonance Cavity Photolysis.

PubMed

Lukoyanov, Dmitriy A; Khadka, Nimesh; Yang, Zhi-Yong; Dean, Dennis R; Seefeldt, Lance C; Hoffman, Brian M

2018-03-24

Early studies in which nitrogenase was freeze-trapped during enzymatic turnover revealed the presence of high-spin ( S = 3 / 2 ) electron paramagnetic resonance (EPR) signals from the active-site FeMo-cofactor (FeMo-co) in electron-reduced intermediates of the MoFe protein. Historically denoted as 1b and 1c, each of the signals is describable as a fictitious spin system, S' = 1 / 2 , with anisotropic g' tensor, 1b with g' = [4.21, 3.76, ?] and 1c with g' = [4.69, ∼3.20, ?]. A clear discrepancy between the magnetic properties of 1b and 1c and the kinetic analysis of their appearance during pre-steady-state turnover left their identities in doubt, however. We subsequently associated 1b with the state having accumulated 2[e - /H + ], denoted as E 2 (2H), and suggested that the reducing equivalents are stored on the catalytic FeMo-co cluster as an iron hydride, likely an [Fe-H-Fe] hydride bridge. Intra-EPR cavity photolysis (450 nm; temperature-independent from 4 to 12 K) of the E 2 (2H)/1b state now corroborates the identification of this state as storing two reducing equivalents as a hydride. Photolysis converts E 2 (2H)/1b to a state with the same EPR spectrum, and thus the same cofactor structure as pre-steady-state turnover 1c, but with a different active-site environment. Upon annealing of the photogenerated state at temperature T = 145 K, it relaxes back to E 2 (2H)/1b. This implies that the 1c signal comes from an E 2 (2H) hydride isomer of E 2 (2H)/1b that stores its two reducing equivalents either as a hydride bridge between a different pair of iron atoms or an Fe-H terminal hydride.

Electron paramagnetic resonance and density-functional theory studies of Cu(II)-bis(oxamato) complexes.

PubMed

Bräuer, Björn; Weigend, Florian; Fittipaldi, Maria; Gatteschi, Dante; Reijerse, Edward J; Guerri, Annalisa; Ciattini, Samuele; Salvan, Georgeta; Rüffer, Tobias

2008-08-04

In this work we present the investigation of the influence of electronic and structural variations induced by varying the N,N'-bridge on the magnetic properties of Cu(II)- bis(oxamato) complexes. For this study the complexes [Cu(opba)] (2-) ( 1, opba = o-phenylene- bis(oxamato)), [Cu(nabo)] (2-) ( 2, nabo = 2,3-naphthalene- bis(oxamato)), [Cu(acbo)] (2-) ( 3, acbo = 2,3-anthrachinone- bis(oxamato)), [Cu(pba)] (2-) ( 4, pba = propylene- bis(oxamato)), [Cu(obbo)] (2-) ( 5, obbo = o-benzyl- bis(oxamato)), and [Cu(npbo)] (2-) ( 6, npbo = 1,8-naphthalene- bis(oxamato)), and the respective structurally isomorphic Ni(II) complexes ( 8- 13) have been prepared as ( (n)Bu 4N) (+) salts. The new complex ( (n)Bu 4N) 2[Cu(R-bnbo)].2H 2O ( 7, R-bnbo = (R)-1,1'-binaphthalene-2,2'- bis(oxamato)) was synthesized and is the first chiral complex in the series of Cu(II)-bis(oxamato) complexes. The molecular structure of 7 has been determined by single crystal X-ray analysis. The Cu(II) ions of the complexes 1- 7 are eta (4)(kappa (2) N, kappa (2) O) coordinated with a more or less distorted square planar geometry for 1- 6 and a distorted tetrahedral geometry for 7. Using pulsed Electron Nuclear Double Resonance on complex 6, detailed information about the relative orientation of the hyperfine ( A) and nuclear quadrupole tensors ( Q) of the coordinating nitrogens with respect to the g tensor were obtained. Electron Paramagnetic Resonance studies in the X, Q, and W-band at variable temperatures were carried out to extract g and A values of N ligands and Cu ion for 1- 7. The hyperfine values were interpreted in terms of spin population on the corresponding atoms. The obtained trends of the spin population for the monomeric building blocks were shown to correlate to the trends obtained in the dependence of the exchange interaction of the corresponding trinuclear complexes on their geometry.

Presence of Peierls pairing and absence of insulator-to-metal transition in VO2 (A): a structure-property relationship study.

PubMed

Popuri, S R; Artemenko, A; Decourt, R; Villesuzanne, A; Pollet, M

2017-03-01

Layered vanadium oxides have been extensively explored due to their interesting metal-insulator transitions and energy conversion/storage applications. In the present study, we have successfully synthesized VO 2 (A) polymorph powder samples by a single-step hydrothermal synthesis process and consolidated them using spark plasma sintering. The structural and electronic properties of VO 2 (A) are measured over a large temperature range from liquid helium, across the structural transition (400-440 K) and up to 500 K. The structural analysis around this transition reveals an antiferrodistorsive to partially ferrodistorsive ordering upon cooling. It is followed by a progressive antiferromagnetic spin pairing which fully settles at about 150 K. The transport measurements show that, in contrast to the rutile archetype VO 2 (R/M1), the structural transition comes with a transition from semiconductor to band-type insulator. Under these circumstances, we propose a scenario with a high temperature antiferrodistorsive paramagnetic semiconducting phase, followed by an intermediate regime with a partially ferrodistorsive paramagnetic semiconducting phase, and finally a low temperature partially ferrodistorsive antiferromagnetic band insulator phase with a possible V-V Peierls-type pairing.

Paramagnetic Manganese in the Atherosclerotic Plaque of Carotid Arteries

PubMed Central

Chelyshev, Yury; Ignatyev, Igor; Zanochkin, Alexey; Mamin, Georgy; Sorokin, Boris; Sorokina, Alexandra; Lyapkalo, Natalya; Gizatullina, Nazima; Orlinskii, Sergei

2016-01-01

The search for adequate markers of atherosclerotic plaque (AP) instability in the context of assessment of the ischemic stroke risk in patients with atherosclerosis of the carotid arteries as well as for solid physical and chemical factors that are connected with the AP stability is extremely important. We investigate the inner lining of the carotid artery specimens from the male patients with atherosclerosis (27 patients, 42–64 years old) obtained during carotid endarterectomy by using different analytical tools including ultrasound angiography, X-ray analysis, immunological, histochemical analyses, and high-field (3.4 T) pulse electron paramagnetic resonance (EPR) at 94 GHz. No correlation between the stable and unstable APs in the sense of the calcification is revealed. In all of the investigated samples, the EPR spectra of manganese, namely, Mn2+ ions, are registered. Spectral and relaxation characteristics of Mn2+ ions are close to those obtained for the synthetic (nano) hydroxyapatite species but differ from each other for stable and unstable APs. This demonstrates that AP stability could be specified by the molecular organization of their hydroxyapatite components. The origin of the obtained differences and the possibility of using EPR of Mn2+ as an AP stability marker are discussed. PMID:28078287

Synthesis and characterization of amorphous mesoporous silica using TEMPO-functionalized amphiphilic templates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vries, Wilke de; Doerenkamp, Carsten; Zeng, Zhaoyang

Inorganic–organic hybrid materials based on amorphous mesoporous silica containing organized nitroxide radicals within its mesopores have been prepared using the micellar self-assembly of TEOS solutions containing the nitroxide functionalized amphiphile (4-(N,N-dimethyl-N-hexadecylammonium)-2,2,6, 6-tetramethyl-piperidin-N-oxyl-iodide) (CAT-16). This template has been used both in its pure form and in various mixtures with cetyl trimethylammonium bromide (CTAB). The samples have been characterized by chemical analysis, N{sub 2} sorption studies, magnetic susceptibility measurements, and various spectroscopic methods. While electron paramagnetic resonance (EPR) spectra indicate that the strength of the intermolecular spin–spin interactions can be controlled via the CAT-16/CTAB ratio, nuclear magnetic resonance (NMR) data suggest thatmore » these interactions are too weak to facilitate cooperative magnetism. - Graphical abstract: The amphiphilic radical CAT-16 is used as a template for the synthesis of amorphous mesoporous silica. The resulting paramagnetic hybrid materials are characterized by BET, FTIR, NMR, EPR and magnetic susceptibility studies. - Highlights: • Amphiphilic CAT-16 as a template for mesoporous silica. • Comprehensive structural characterization by BET, FTIR; EPR and NMR. • Strength of radical-radical interactions tuable within CAT-16/CTAB mixtures.« less

Room temperature ferromagnetism of nanocrystalline Nd1.90Ni0.10O3-δ

NASA Astrophysics Data System (ADS)

Sarkar, B. J.; Mandal, J.; Dalal, M.; Bandyopadhyay, A.; Chakrabarti, P. K.

2018-05-01

Nanocrystalline sample of Ni2+ doped neodymium oxide (Nd1.90Ni0.10O3-δ, NNO) is synthesized by co-precipitation method. Analysis of X-ray diffraction (XRD) pattern by Rietveld refinement method confirms the desired phase of NNO and complete substitution of Ni2+ ions in the Nd2O3 lattice. Analyses of transmission electron microscopy (TEM) and Raman spectroscopy of NNO recorded at room temperature (RT) also substantiate this fact. Besides, no traces of impurities are found in the analyses of XRD, TEM and Raman data. Room temperature hysteresis loop of NNO suggests the presence of weak ferromagnetism (FM) in low field region ( 600 mT), but in high field region paramagnetism of the host is more prominent. Magnetization vs. temperature ( M- T) curve in the entire temperature range (300-5 K) is analyzed successfully by a combined equation generated from three-dimensional (3D) spin wave model and Curie-Weiss law, which suggests the presence of mixed paramagnetic phase together with ferromagnetic phase in the doped sample. The onset of magnetic ordering is analyzed by oxygen vacancy mediated F-center exchange (FCE) coupling mechanism.

Electron spin resonance as a high sensitivity technique for environmental magnetism: determination of contamination in carbonate sediments

NASA Astrophysics Data System (ADS)

Crook, Nigel P.; Hoon, Stephen R.; Taylor, Kevin G.; Perry, Chris T.

2002-05-01

This study investigates the application of high sensitivity electron spin resonance (ESR) to environmental magnetism in conjunction with the more conventional techniques of magnetic susceptibility, vibrating sample magnetometry (VSM) and chemical compositional analysis. Using these techniques we have studied carbonate sediment samples from Discovery Bay, Jamaica, which has been impacted to varying degrees by a bauxite loading facility. The carbonate sediment samples contain magnetic minerals ranging from moderate to low concentrations. The ESR spectra for all sites essentially contain three components. First, a six-line spectra centred around g = 2 resulting from Mn2+ ions within a carbonate matrix; second a g = 4.3 signal from isolated Fe3+ ions incorporated as impurities within minerals such as gibbsite, kaolinite or quartz; third a ferrimagnetic resonance with a maxima at 230 mT resulting from the ferrimagnetic minerals present within the bauxite contamination. Depending upon the location of the sites within the embayment these signals vary in their relative amplitude in a systematic manner related to the degree of bauxite input. Analysis of the ESR spectral components reveals linear relationships between the amplitude of the Mn2+ and ferrimagnetic signals and total Mn and Fe concentrations. To assist in determining the origin of the ESR signals coral and bauxite reference samples were employed. Coral representative of the matrix of the sediment was taken remote from the bauxite loading facility whilst pure bauxite was collected from nearby mining facilities. We find ESR to be a very sensitive technique particularly appropriate to magnetic analysis of ferri- and para-magnetic components within environmental samples otherwise dominated by diamagnetic (carbonate) minerals. When employing typical sample masses of 200 mg the practical detection limit of ESR to ferri- and para-magnetic minerals within a diamagnetic carbonate matrix is of the order of 1 ppm and 1 ppb respectively, approximately 102 and 105 times the sensitivity achievable employing the VSM in our laboratory.

The leap-frog effect of ring currents in benzene.

PubMed

Ligabue, Andrea; Soncini, Alessandro; Lazzeretti, Paolo

2002-03-06

Symmetry arguments show that the ring-current model proposed by Pauling, Lonsdale, and London to explain the enhanced diamagnetism of benzene is flawed by an intrinsic drawback. The minimal basis set of six atomic 2p orbitals taken into account to develop such a model is inherently insufficient to predict a paramagnetic contribution to the perpendicular component of magnetic susceptibility in planar ring systems such as benzene. Analogous considerations can be made for the hypothetical H(6) cyclic molecule. A model allowing for extended basis sets is necessary to rationalize the magnetism of aromatics. According to high-quality coupled Hartree-Fock calculations, the trajectories of the current density vector field induced by a magnetic field perpendicular to the skeletal plane of benzene in the pi electrons are noticeably different from those typical of a Larmor diamagnetic circulation, in that (i) significant deformation of the orbits from circular to hexagonal symmetry occurs, which is responsible for a paramagnetic contribution of pi electrons to the out-of-plane component of susceptibility, and (ii) a sizable component of the pi current density vector parallel to the inducing field is predicted. This causes a waving motion of pi electrons; streamlines are characterized by a "leap-frog effect".

The O-(Al2) centre in topaz and its relation to the blue colour

NASA Astrophysics Data System (ADS)

da Silva, D. N.; Guedes, K. J.; Pinheiro, M. V. B.; Schweizer, S.; Spaeth, J.-M.; Krambrock, K.

2005-01-01

Colour-enhanced blue topaz is one of the most traded gemstones. Naturally very rare, mostly topaz is irradiated by neutrons, electrons, gamma radiation and combinations of them. The colour centre is still not identified. It was speculated that it is related to a Si dangling bond defect occupied by two electrons with spin S = 0. We investigated natural blue as well as colourless topaz from different regions in Brazil by electron paramagnetic resonance (EPR), optical absorption and Raman spectroscopy. The results are compared with neutron and gamma-irradiated blue topaz. By EPR two paramagnetic defects are identified in all samples: (i) the peroxy radical (O2-) measured at room temperature and (ii) an (O-) hole centre interacting with two equivalent Al neighbours measured at low temperature. Blue samples show an absorption band centred at 620 nm which is responsible for the blue colour. From our investigation we find that the O-(Al2) hole centre has nearly the same thermal stability as the optical absorption band. However, we cannot say whether it is responsible for the absorption band and the blue colour. We suggest that at least it plays a dominant role in the stabilization of the blue colour.

Synthesis and characterization of ZnS@Fe3O4 fluorescent-magnetic bifunctional nanospheres

NASA Astrophysics Data System (ADS)

Koc, Kenan; Karakus, Baris; Rajar, Kausar; Alveroglu, Esra

2017-10-01

Herein, we synthesized and characterized fluorescent and super paramagnetic ZnS@Fe3O4 nanospheres. First, (3-mercaptopropyl) trimethoxysilane (MPS) capped ZnS quantum dots (QDs) and SiO2 coated Fe3O4 nanoparticles were synthesized separately by using solution growth and co-precipitation techniques. After synthesis and characterization of these two nanoparticles, they were conglutinated together in a nano sized sphere. The QDs were attached to the surface of the Fe3O4 nanoparticles by Sisbnd Osbnd Si bonds and so Sisbnd Osbnd Si bonds created a SiO2 network around the nanoparticles during the formation of the ZnS@Fe3O4 nanospheres. The synthesized MPS capped ZnS fluorescent QDs, SiO2 coated magnetite super paramagnetic nanoparticles and ZnS@Fe3O4 fluorescent-magnetic bifunctional nanospheres were characterized by using UV-Vis Absorption Spectroscopy, Fluorescence Spectroscopy, X-ray analysis, Vibrating Sample Magnetometer analysis, Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy, Scanning Electron Microscope and Energy-dispersive X-ray spectroscopy. ZnS@Fe3O4 bifunctional nanospheres were shown to retain the magnetic properties of magnetite, while exhibiting the luminescent optical properties of ZnS nanoparticles. The combination of fluorescent and magnetic behaviors of nano composites make them useful for potential applications in the field of bio-medical and environmental.

Pulse EPR distance measurements to study multimers and multimerisation

NASA Astrophysics Data System (ADS)

Ackermann, Katrin; Bode, Bela E.

2018-06-01

Pulse dipolar electron paramagnetic resonance (PD-EPR) has become a powerful tool for structural biology determining distances on the nanometre scale. Recent advances in hardware, methodology, and data analysis have widened the scope to complex biological systems. PD-EPR can be applied to systems containing lowly populated conformers or displaying large intrinsic flexibility, making them all but intractable for cryo-electron microscopy and crystallography. Membrane protein applications are of particular interest due to the intrinsic difficulties for obtaining high-resolution structures of all relevant conformations. Many drug targets involved in critical cell functions are multimeric channels or transporters. Here, common approaches for introducing spin labels for PD-EPR cause the presence of more than two electron spins per multimeric complex. This requires careful experimental design to overcome detrimental multi-spin effects and to secure sufficient distance resolution in presence of multiple distances. In addition to obtaining mere distances, PD-EPR can also provide information on multimerisation degrees allowing to study binding equilibria and to determine dissociation constants.

Spectral methods for study of the G-protein-coupled receptor rhodopsin: I. Vibrational and electronic spectroscopy

NASA Astrophysics Data System (ADS)

Struts, A. V.; Barmasov, A. V.; Brown, M. F.

2015-05-01

Here we review the application of modern spectral methods for the study of G-protein-coupled receptors (GPCRs) using rhodopsin as a prototype. Because X-ray analysis gives us immobile snapshots of protein conformations, it is imperative to apply spectroscopic methods for elucidating their function: vibrational (Raman, FTIR), electronic (UV-visible absorption, fluorescence) spectroscopies, and magnetic resonance (electron paramagnetic resonance, EPR), and nuclear magnetic resonance (NMR). In the first of the two companion articles, we discuss the application of optical spectroscopy for studying rhodopsin in a membrane environment. Information is obtained regarding the time-ordered sequence of events in rhodopsin activation. Isomerization of the chromophore and deprotonation of the retinal Schiff base leads to a structural change of the protein involving the motion of helices H5 and H6 in a pH-dependent process. Information is obtained that is unavailable from X-ray crystallography, which can be combined with spectroscopic studies to achieve a more complete understanding of GPCR function.

Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4

PubMed Central

Sutter, D.; Fatuzzo, C. G.; Moser, S.; Kim, M.; Fittipaldi, R.; Vecchione, A.; Granata, V.; Sassa, Y.; Cossalter, F.; Gatti, G.; Grioni, M.; Rønnow, H. M.; Plumb, N. C.; Matt, C. E.; Shi, M.; Hoesch, M.; Kim, T. K.; Chang, T-R; Jeng, H-T; Jozwiak, C.; Bostwick, A.; Rotenberg, E.; Georges, A.; Neupert, T.; Chang, J.

2017-01-01

A paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling is realized in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide—using angle-resolved photoemission electron spectroscopy—the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund's coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund's coupling that together generate the Mott insulating state of Ca2RuO4. PMID:28474681

Low field electron paramagnetic resonance imaging with SQUID detection

NASA Technical Reports Server (NTRS)

Hahn, Inseob (Inventor); Day, Peter K. (Inventor); Penanen, Konstantin I. (Inventor); Eom, Byeong H. (Inventor); Cohen, Mark S. (Inventor)

2012-01-01

In one embodiment, a flux transformer with a gradiometer pickup coil is magnetically coupled to a SQUID, and a SQUID array amplifier comprising a plurality of SQUIDs, connected in series, is magnetically coupled to the output of the SQUID. Other embodiments are described and claimed.

Free Radicals in Precision Cut Bovine Testicle Slices: Effects of 1,3,5 Trinitrobenzene Measured by Electron Paramagnetic Resonance.

DTIC Science & Technology

1996-04-01

toluene or dinitrotoluene and toluene diamine have oligoasthenoteratozoospermia ( Radike , 1985). Oligoasthenoteratozoospermiais a condition of...transfer interations between Superoxide ion and organic compounds. J. Phys Chem 77: 1722-1724. Radike , M. Reproductive Toxicology Chpterl6 In

Silicon displacement threshold energy determined by electron paramagnetic resonance and positron annihilation spectroscopy in cubic and hexagonal polytypes of silicon carbide

NASA Astrophysics Data System (ADS)

Kerbiriou, X.; Barthe, M.-F.; Esnouf, S.; Desgardin, P.; Blondiaux, G.; Petite, G.

2007-05-01

Both for electronic and nuclear applications, it is of major interest to understand the properties of point defects into silicon carbide (SiC). Low energy electron irradiations are supposed to create primary defects into materials. SiC single crystals have been irradiated with electrons at two beam energies in order to investigate the silicon displacement threshold energy into SiC. This paper presents the characterization of the electron irradiation-induced point defects into both polytypes hexagonal (6H) and cubic (3C) SiC single crystals by using both positron annihilation spectroscopy (PAS) and electron paramagnetic resonance (EPR). The nature and the concentration of the generated point defects depend on the energy of the electron beam and the polytype. After an electron irradiation at an energy of 800 keV vSi mono-vacancies and vSi-vC di-vacancies are detected in both 3C and 6H-SiC polytypes. On the contrary, the nature of point defects detected after an electron irradiation at 190 keV strongly depends on the polytype. Into 6H-SiC crystals, silicon Frenkel pairs vSi-Si are detected whereas only carbon vacancy related defects are detected into 3C-SiC crystals. The difference observed in the distribution of defects detected into the two polytypes can be explained by the different values of the silicon displacement threshold energies for 3C and 6H-SiC. By comparing the calculated theoretical numbers of displaced atoms with the defects numbers measured using EPR, the silicon displacement threshold energy has been estimated to be slightly lower than 20 eV in the 6H polytype and close to 25 eV in the 3C polytype.

Concentration of point defects in 4H-SiC characterized by a magnetic measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, B.; Jia, R. X., E-mail: rxjia@mail.xidian.edu.cn; Wang, Y. T.

A magnetic method is presented to characterize the concentration of point defects in silicon carbide. In this method, the concentration of common charged point defects, which is related to the density of paramagnetic centers, is determined by fitting the paramagnetic component of the specimen to the Brillouin function. Several parameters in the Brillouin function can be measured such as: the g-factor can be obtained from electron spin resonance spectroscopy, and the magnetic moment of paramagnetic centers can be obtained from positron lifetime spectroscopy combined with a first-principles calculation. To evaluate the characterization method, silicon carbide specimens with different concentrations ofmore » point defects are prepared with aluminum ion implantation. The fitting results of the densities of paramagnetic centers for the implanted doses of 1 × 10{sup 14} cm{sup −2}, 1 × 10{sup 15} cm{sup −2} and 1 × 10{sup 16} cm{sup −2} are 6.52 × 10{sup 14}/g, 1.14 × 10{sup 15}/g and 9.45 × 10{sup 14}/g, respectively. The same trends are also observed for the S-parameters in the Doppler broadening spectra. It is shown that this method is an accurate and convenient way to obtain the concentration of point defects in 4H-SiC.« less

Dual nature of 3 d electrons in YbT 2 Zn 20 (T = Co; Fe) evidenced by electron spin resonance

DOE PAGES

Ivanshin, V. A.; Litvinova, T. O.; Gimranova, K.; ...

2015-03-18

The electron spin resonance experiments were carried out in the single crystals YbFe 2Zn 20. The observed spin dynamics is compared with that in YbCo 2Zn 20 and Yb 2Co 12P 7 as well as with the data of inelastic neutron scattering and electronic band structure calculations. Our results provide direct evidence that 3d electrons are itinerant in YbFe 2Zn 20 and localized in YbCo 2Zn 20. Possible connection between spin paramagnetism of dense heavy fermion systems, quantum criticality effects, and ESR spectra is discussed.

Pertinent parameters in photo-generation of electrons: Comparative study of anatase-based nano-TiO2 suspensions.

PubMed

Martel, D; Guerra, A; Turek, P; Weiss, J; Vileno, B

2016-04-01

In the field of solar fuel cells, the development of efficient photo-converting semiconductors remains a major challenge. A rational analysis of experimental photocatalytic results obtained with material in colloïdal suspensions is needed to access fundamental knowledge required to improve the design and properties of new materials. In this study, a simple system electron donor/nano-TiO2 is considered and examined via spin scavenging electron paramagnetic resonance as well as a panel of analytical techniques (composition, optical spectroscopy and dynamic light scattering) for selected type of nano-TiO2. Independent variables (pH, electron donor concentration and TiO2 amount) have been varied and interdependent variables (aggregate size, aggregate surface vs. volume and acid/base groups distribution) are discussed. This work shows that reliable understanding involves thoughtful combination of interdependent parameters, whereas the specific surface area seems not a pertinent parameter. The conclusion emphasizes the difficulty to identify the key features of the mechanisms governing photocatalytic properties in nano-TiO2. Copyright © 2016 Elsevier Inc. All rights reserved.

Thermodynamic and electron paramagnetic resonance characterization of flavin in succinate dehydrogenase.

PubMed

Ohnishi, T; King, T E; Salerno, J C; Blum, H; Bowyer, J R; Maida, T

1981-06-10

Thermodynamic parameters of succinate dehydrogenase flavin were determined potentiometrically from the analysis of free radical signal levels as a function of the oxidation-reduction potential. Midpoint redox potentials of consecutive 1-electron transfer steps are -127 and -31 mV at pH 7.0. This corresponds to a stability constant of intermediate stability, 2.5 x 10(-2), which suggests flavin itself may be a converter from n = 2 to n = 1 electron transfer steps. The pK values of the free radical (FlH . in equilibrium Fl . -) and the fully reduced form (FlH2 in equilibrium FlH-) were estimated as 8.0 +/- 0.2 and 7.7 +/- 0.2, respectively. Succinate dehydrogenase flavosemiquinone elicits an EPR spectrum at g = 2.00 with a peak to peak width of 1.2 mT even in the protonated form, suggesting the delocalization in the unpaired electron density. A close proximity of succinate dehydrogenase flavin and iron-sulfur cluster S-1 was demonstrated based on the enhancement of flavin spin relaxation by Center S-1.

EPR imaging and HPLC characterization of the pigment-based organic free radical in black soybean seeds.

PubMed

Nakagawa, Kouichi; Maeda, Hayato

2017-02-01

We investigated the location and distribution of paramagnetic species in dry black, brown, and yellow (normal) soybean seeds using electron paramagnetic resonance (EPR), X-band (9 GHz) EPR imaging (EPRI), and HPLC. EPR primarily detected two paramagnetic species in black soybean. These two different radical species were assigned as stable organic radical and Mn 2+  species based on the g values and hyperfine structures. The signal from the stable radical was noted at g ≈ 2.00 and was relatively strong and stable. Subsequent noninvasive two-dimensional (2D) EPRI of the radical present in black soybean revealed that the stable radical was primarily located in the pigmented region of the soybean coat, with very few radicals observed in the soybean cotyledon (interior). Pigments extracted from black soybean were analyzed using HPLC. The major compound was found to be cyanidin-3-glucoside. Multi-EPR and HPLC results indicate that the stable radical was only found within the pigmented region of the soybean coat, and it could be cyanidin-3-glucoside or an oxidative decomposition product.

Specific features of the EPR spectra of KTaO3: Mn nanopowders

NASA Astrophysics Data System (ADS)

Golovina, I. S.; Shanina, B. D.; Geifman, I. N.; Andriiko, A. A.; Chernenko, L. V.

2012-03-01

The electron paramagnetic resonance spectra of KTaO3: Mn nanocrystalline powders in the temperature range from 77 to 620 K have been measured and studied for the first time. The change observed in the spectra has been investigated as a function of the doping level. The doping regions in which Mn2+ ions are individual paramagnetic impurities have been established, as well as the regions where the dipole-dipole and exchange interactions of these ions begin to occur. The spin-Hamiltonian constants for the spectrum of non-interacting individual Mn2+ ions have been determined as follows: g = 2.0022, D = 0.0170 cm-1, and A = 85 × 10-4 cm-1. A significant decrease in the axial constant D in the KTaO3: Mn nanopowder, as compared to the single crystal, has been explained by the remoteness of the charge compensator from the paramagnetic ion and by the influence of the surface of the nanoparticle. It has been assumed that the Mn2+ ions are located near the surface and do not penetrate deep into the crystallites.

Anisotropy reversal of the upper critical field at low temperatures and spin-locked superconductivity in K 2 Cr 3 As 3

DOE PAGES

Balakirev, F. F.; Kong, T.; Jaime, M.; ...

2015-06-23

We report measurements of the anisotropic upper critical field H c2(T) for K 2Cr 3As 3 single crystals up to 60 T and T>0.6K. Our results show that the upper critical field parallel to the Cr chains, H ∥ c2(T), exhibits a paramagnetically limited behavior, whereas the shape of the H ⊥ c2(T) curve (perpendicular to the Cr chains) has no evidence of paramagnetic effects. As a result, the curves H ⊥ c2(T) and H ∥ c2(T) cross at T≈4K, so that the anisotropy parameter γ H(T)=H ⊥ c2/H ∥ c2(T) increases from γ H(T c)≈0.35 near T c tomore » γ H(0)≈1.7 at 0.6 K. The paramagnetically limited behavior of H ∥ c2(T) is inconsistent with triplet superconductivity but suggests a form of singlet superconductivity with the electron spins locked onto the direction of Cr chains.« less

A dual-beam actinic light source for photosynthesis research

NASA Technical Reports Server (NTRS)

Margozzi, A. P.; Henderson, M. E.

1972-01-01

Simulation of photosynthetic process in plants is accomplished by using two separate and identical optical channels that provide independently adjustable wavelengths (filters), shutter sequencing, and control intensity of illumination. In addition to experiments using electron paramagnetic resonance spectroscopy, system may be applicable to other types of research in photosynthetic field.

An EPR and EMF study of Belousov-Zhabotinsky oscillators: Veratric acid and veratraidehyde in a water-acetonitrile medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lalitha, P.V.; Ramaswamy, R.; Ramakrishnan, G.

1992-09-17

Electron paramagnetic resonance and potentiometric techniques using a platinium indicator electrode/ion selective electrode, are used to study Belousov-Zhabotinsky oscillatory reactions involving veratric acid and veratraldehyde as substrates in a mixed medium. These two techniques have yield a good correlation.

Consensus structures of the Mo(v) sites of sulfite-oxidizing enzymes derived from variable frequency pulsed EPR spectroscopy, isotopic labelling and DFT calculations.

PubMed

Enemark, John H

2017-10-10

Sulfite-oxidizing enzymes from eukaryotes and prokaryotes have five-coordinate distorted square-pyramidal coordination about the molybdenum atom. The paramagnetic Mo(v) state is easily generated, and over the years four distinct CW EPR spectra have been identified, depending upon enzyme source and the reaction conditions, namely high and low pH (hpH and lpH), phosphate inhibited (P i ) and sulfite (or blocked). Extensive studies of these paramagnetic forms of sulfite-oxidizing enzymes using variable frequency pulsed electron spin echo (ESE) spectroscopy, isotopic labeling and density functional theory (DFT) calculations have led to the consensus structures that are described here. Errors in some of the previously proposed structures are corrected.

High pressure synthesis, crystal growth and magnetic properties of TiOF

NASA Astrophysics Data System (ADS)

Cumby, J.; Burchell, M. B.; Attfield, J. P.

2018-06-01

Polycrystalline samples of TiOF have been prepared at 1300 °C and 8 GPa, with small single crystals grown at the same conditions. The crystal structure remains tetragonal rutile-type down to at least 90 K (space group P42/mnm, a = 4.6533 (2) Å and c = 3.0143 (2) Å at 90 K) and the Ti(O,F)6 octahedra are slightly compressed, consistent with Jahn-Teller distortion of 3d1 Ti3+. Diffuse scattering reveals disordered structural correlations that may arise from local cis-order of oxide anions driven by covalency. TiOF is paramagnetic down to 5 K and observation of a small paramagnetic moment and a substantial Pauli term indicates that the d-electrons are partially delocalised.

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 sample will be used to assess the linearity of the magnetic field gradient and to ensure authentic image reconstruction. A second major task was to secure the computer capability to enable image reconstruction from projection data generated by the magnetic field gradients. To this end, commercially available and public domain software packages which perform inverse Fourier Transform and convoluted (filtered) back projection functions are being integrated into the existing EPR data processing system.

Electron spin relaxation enhancement measurements of interspin distances in human, porcine, and Rhodobacter electron transfer flavoprotein ubiquinone oxidoreductase (ETF QO)

NASA Astrophysics Data System (ADS)

Fielding, Alistair J.; Usselman, Robert J.; Watmough, Nicholas; Simkovic, Martin; Frerman, Frank E.; Eaton, Gareth R.; Eaton, Sandra S.

2008-02-01

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is a membrane-bound electron transfer protein that links primary flavoprotein dehydrogenases with the main respiratory chain. Human, porcine, and Rhodobacter sphaeroides ETF-QO each contain a single [4Fe-4S] 2+,1+ cluster and one equivalent of FAD, which are diamagnetic in the isolated enzyme and become paramagnetic on reduction with the enzymatic electron donor or with dithionite. The anionic flavin semiquinone can be reduced further to diamagnetic hydroquinone. The redox potentials for the three redox couples are so similar that it is not possible to poise the proteins in a state where both the [4Fe-4S] + cluster and the flavoquinone are fully in the paramagnetic form. Inversion recovery was used to measure the electron spin-lattice relaxation rates for the [4Fe-4S] + between 8 and 18 K and for semiquinone between 25 and 65 K. At higher temperatures the spin-lattice relaxation rates for the [4Fe-4S] + were calculated from the temperature-dependent contributions to the continuous wave linewidths. Although mixtures of the redox states are present, it was possible to analyze the enhancement of the electron spin relaxation of the FAD semiquinone signal due to dipolar interaction with the more rapidly relaxing [4Fe-4S] + and obtain point-dipole interspin distances of 18.6 ± 1 Å for the three proteins. The point-dipole distances are within experimental uncertainty of the value calculated based on the crystal structure of porcine ETF-QO when spin delocalization is taken into account. The results demonstrate that electron spin relaxation enhancement can be used to measure distances in redox poised proteins even when several redox states are present.

Electron Spin Relaxation Enhancement Measurements of Interspin Distances in Human, Porcine, and Rhodobacter Electron Transfer Flavoprotein-ubiquinone Oxidoreductase (ETF-QO)

PubMed Central

Fielding, Alistair J.; Usselman, Robert J.; Watmough, Nicholas; Simkovic, Martin; Frerman, Frank E.; Eaton, Gareth R.; Eaton, Sandra S.

2008-01-01

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is a membrane-bound electron transfer protein that links primary flavoprotein dehydrogenases with the main respiratory chain. Human, porcine, and Rhodobacter sphaeroides ETF-QO each contain a single [4Fe-4S]2+,1+ cluster and one equivalent of FAD, which are diamagnetic in the isolated enzyme and become paramagnetic on reduction with the enzymatic electron donor or with dithionite. The anionic flavin semiquinone can be reduced further to diamagnetic hydroquinone. The redox potentials for the three redox couples are so similar that it is not possible to poise the proteins in a state where both the [4Fe-4S]+ cluster and the flavoquinone are fully in the paramagnetic form. Inversion recovery was used to measure the electron spin-lattice relaxation rates for the [4Fe-4S]+ between 8 and 18 K and for semiquinone between 25 and 65 K. At higher temperatures the spin-lattice relaxation rates for the [4Fe-4S]+ were calculated from the temperature-dependent contributions to the continuous wave linewidths. Although mixtures of the redox states are present, it was possible to analyze the enhancement of the electron spin relaxation of the FAD semiquinone signal due to dipolar interaction with the more rapidly relaxing [4Fe-4S]+ and obtain point dipole interspin distances of 18.6 ± 1 Å for the three proteins. The point-dipole distances are within experimental uncertainty of the value calculated based on the crystal structure of porcine ETF-QO when spin delocalization is taken into account. The results demonstrate that electron spin relaxation enhancement can be used to measure distances in redox poised proteins even when several redox states are present. PMID:18037314

Electron spin relaxation enhancement measurements of interspin distances in human, porcine, and Rhodobacter electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO).

PubMed

Fielding, Alistair J; Usselman, Robert J; Watmough, Nicholas; Simkovic, Martin; Frerman, Frank E; Eaton, Gareth R; Eaton, Sandra S

2008-02-01

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is a membrane-bound electron transfer protein that links primary flavoprotein dehydrogenases with the main respiratory chain. Human, porcine, and Rhodobacter sphaeroides ETF-QO each contain a single [4Fe-4S](2+,1+) cluster and one equivalent of FAD, which are diamagnetic in the isolated enzyme and become paramagnetic on reduction with the enzymatic electron donor or with dithionite. The anionic flavin semiquinone can be reduced further to diamagnetic hydroquinone. The redox potentials for the three redox couples are so similar that it is not possible to poise the proteins in a state where both the [4Fe-4S](+) cluster and the flavoquinone are fully in the paramagnetic form. Inversion recovery was used to measure the electron spin-lattice relaxation rates for the [4Fe-4S](+) between 8 and 18K and for semiquinone between 25 and 65K. At higher temperatures the spin-lattice relaxation rates for the [4Fe-4S](+) were calculated from the temperature-dependent contributions to the continuous wave linewidths. Although mixtures of the redox states are present, it was possible to analyze the enhancement of the electron spin relaxation of the FAD semiquinone signal due to dipolar interaction with the more rapidly relaxing [4Fe-4S](+) and obtain point-dipole interspin distances of 18.6+/-1A for the three proteins. The point-dipole distances are within experimental uncertainty of the value calculated based on the crystal structure of porcine ETF-QO when spin delocalization is taken into account. The results demonstrate that electron spin relaxation enhancement can be used to measure distances in redox poised proteins even when several redox states are present.

Synthesis, X-ray crystallography, spectroscopic characterization and spectroscopic/electrochemical evidence of formation of phenoxy free radical in active center analogs of galactose oxidase - [Cu(Salgly)H₂O] and [Cu(Salphenylalanine)H₂O].

PubMed

Das, Biva; Medhi, Okhil K

2013-03-01

The formation of phenolate free radical is the factor of high turnover for catalytic activity of galactose oxidase (GO) compared to that by inorganic complexes. A new active center analog of GO, [Cu(II)(Salphenylalanine)H(2)O] have been synthesized and its single crystal X-ray analysis was done. In aqueous surfactant micellar solution chemical oxidation as well as electrochemical oxidation of structural models of galactose oxidase - [Cu(II)Salgly·H(2)O] and [Cu(II)(Salphenylalanine)·H(2)O], have been found to generate free radical originating at the phenolate group. Formation of the free radical have been proved by electron paramagnetic resonance spectroscopy, electronic spectroscopy and electrochemistry. Copyright © 2012 Elsevier B.V. All rights reserved.

Enhanced antibacterial activity of zinc oxide nanoparticles synthesized using Petroselinum crispum extracts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stan, Manuela, E-mail: manuela.stan@itim-cj.ro; Popa, Adriana; Toloman, Dana

The present contribution reports the synthesis of zinc oxide nanoparticles (ZnO NPs) using aqueous leaf and root extracts of Petroselinum crispum (parsley) and characterization of as-prepared samples. ZnO NPs are subjected to X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) studies. The XRD studies reveal a hexagonal wurtzite structure without supplementary diffraction lines for all ZnO samples. TEM analysis shows that the particle size is influenced by the type of plant extract. The EPR spectra indicate the presence of Mn{sup 2+} ions in ZnO sample synthesized using P. crispum leaf extract, while zinc vacancy complexes andmore » oxygen vacancies are evidenced in all analyzed samples. ZnO NPs synthesized using P. crispum extracts exhibit increased (2-16 times) antibacterial activity as compared to chemically synthesized ZnO NPs.« less

Spin-dependent analysis of two-dimensional electron liquids

NASA Astrophysics Data System (ADS)

Bulutay, C.; Tanatar, B.

2002-05-01

Two-dimensional electron liquid (2D EL) at full Fermi degeneracy is revisited, giving special attention to the spin-polarization effects. First, we extend the recently proposed classical-map hypernetted-chain (CHNC) technique to the 2D EL, while preserving the simplicity of the original proposal. An efficient implementation of CHNC is given utilizing Lado's quadrature expressions for the isotropic Fourier transforms. Our results indicate that the paramagnetic phase stays to be the ground state until the Wigner crystallization density, even though the energy separation with the ferromagnetic and other partially polarized states become minute. We analyze compressibility and spin stiffness variations with respect to density and spin polarization, the latter being overlooked until now. Spin-dependent static structure factor and pair-distribution functions are computed; agreement with the available quantum Monte Carlo data persists even in the strong-coupling regime of the 2D EL.

Defect characterization and magnetic properties in un-doped ZnO thin film annealed in a strong magnetic field

NASA Astrophysics Data System (ADS)

Ning, Shuai; Zhan, Peng; Wang, Wei-Peng; Li, Zheng-Cao; Zhang, Zheng-Jun

2014-12-01

Highly c-axis oriented un-doped zinc oxide (ZnO) thin films, each with a thickness of ~ 100 nm, are deposited on Si (001) substrates by pulsed electron beam deposition at a temperature of ~ 320 °C, followed by annealing at 650 °C in argon in a strong magnetic field. X-ray photoelectron spectroscopy (XPS), positron annihilation analysis (PAS), and electron paramagnetic resonance (EPR) characterizations suggest that the major defects generated in these ZnO films are oxygen vacancies. Photoluminescence (PL) and magnetic property measurements indicate that the room-temperature ferromagnetism in the un-doped ZnO film originates from the singly ionized oxygen vacancies whose number depends on the strength of the magnetic field applied in the thermal annealing process. The effects of the magnetic field on the defect generation in the ZnO films are also discussed.

Controlling Thermodynamic Properties of Ferromagnetic Group-IV Graphene-Like Nanosheets by Dilute Charged Impurity

NASA Astrophysics Data System (ADS)

Yarmohammadi, Mohsen; Mirabbaszadeh, Kavoos

2017-05-01

Using the Kane-Mele Hamiltonian, Dirac theory and self-consistent Born approximation, we investigate the effect of dilute charged impurity on the electronic heat capacity and magnetic susceptibility of two-dimensional ferromagnetic honeycomb structure of group-IV elements including silicene, germanene and stanene within the Green’s function approach. We also find these quantities in the presence of applied external electric field. Our results show that the silicene (stanene) has the maximum (minimum) heat capacity and magnetic susceptibility at uniform electric fields. From the behavior of theses quantities, the band gap has been changed with impurity concentration, impurity scattering strength and electric field. The analysis on the impurity-dependent magnetic susceptibility curves shows a phase transition from ferromagnetic to paramagnetic and antiferromagnetic phases. Interestingly, electronic heat capacity increases (decreases) with impurity concentration in silicene (germanene and stanene) structure.

The bipolar assembly domain of the mitotic motor kinesin-5

PubMed Central

Acar, Seyda; Carlson, David B.; Budamagunta, Madhu S.; Yarov-Yarovoy, Vladimir; Correia, John J.; Niñonuevo, Milady R.; Jia, Weitao; Tao, Li; Leary, Julie A.; Voss, John C.; Evans, James E.; Scholey, Jonathan M.

2013-01-01

An outstanding unresolved question is how does the mitotic spindle utilize microtubules and mitotic motors to coordinate accurate chromosome segregation during mitosis? This process depends upon the mitotic motor, kinesin-5, whose unique bipolar architecture, with pairs of motor domains lying at opposite ends of a central rod, allows it to crosslink microtubules within the mitotic spindle and to coordinate their relative sliding during spindle assembly, maintenance and elongation. The structural basis of kinesin-5’s bipolarity is, however, unknown, as protein asymmetry has so far precluded its crystallization. Here we use electron microscopy of single molecules of kinesin-5 and its subfragments, combined with hydrodynamic analysis plus mass spectrometry, circular dichroism and site-directed spin label electron paramagnetic resonance spectroscopy, to show how a staggered antiparallel coiled-coil ‘BASS’ (bipolar assembly) domain directs the assembly of four kinesin-5 polypeptides into bipolar minifilaments. PMID:23299893

Zero-field splitting in the isoelectronic aqueous Gd(III) and Eu(II) complexes from a first principles analysis

NASA Astrophysics Data System (ADS)

Khan, S.; Peters, V.; Kowalewski, J.; Odelius, M.

2018-03-01

The zero-field splitting (ZFS) of the ground state octet in aqueous Eu(II) and Gd(III) solutions was investigated through multi- configurational quantum chemical calculations and ab initio molecular dynamics (AIMD) simulations. Investigation of the ZFS of the lanthanide ions is essential to understand the electron spin dynamics and nuclear spin relaxation around paramagnetic ions and consequently the mechanisms underlying applications like magnetic resonance imaging. We found by comparing clusters at identical geometries but different metallic centres that there is not a simple relationship for their ZFS, in spite of the complexes being isoelectronic - each containing 7 unpaired f electrons. Through sampling it was established that inclusion of the first hydration shell has a dominant (over 90 %) influence on the ZFS. Extended sampling of aqueous Gd(III) showed that the 2 nd order spin Hamiltonian formalism is valid and that the rhombic ZFS component is decisive.

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

2015-07-06

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.

Characterisation of the rare cadmium chromate pigment in a 19th century tube colour by Raman, FTIR, X-ray and EPR

NASA Astrophysics Data System (ADS)

Christiansen, Marie Bitsch; Sørensen, Mikkel Agerbæk; Sanyova, Jana; Bendix, Jesper; Simonsen, Kim Pilkjær

2017-03-01

In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube colours found in Krøyer's painting cabinet were examined. In most cases, the results of the pigment analyses were as expected based on our knowledge of artists' colours used in the late 1800s and early 1900s. However, in one of the tube colours labelled "Jaune de Cadmium Citron" (cadmium lemon yellow) an extremely rare cadmium chromate pigment was found. The pigment was analysed and characterised by Raman microscopy (MRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), powder X-ray diffraction (PXRD), single-crystal X-ray crystallography, and electron paramagnetic resonance (EPR) spectroscopy. Cadmium chromate was synthesised by precipitation from an aqueous solution of cadmium nitrate and potassium chromate, and the resulting yellow crystals proved identical to the pigment found in the tube colour "Jaune de Cadmium Citron". The structure determined by single-crystal X-ray diffraction identified the pigment as 2CdCrO4·KOH·H2O or more accurately as KCd2(CrO4)2(H3O2) illustrating the μ-H3O2- species. The yellow colour of the paint sample taken from the tube had a greenish hue, which became even more prominent upon storage and drying. EPR analysis of the sample showed the presence of paramagnetic degradation products containing Cr(III) and Cr(V).

Characterisation of the rare cadmium chromate pigment in a 19th century tube colour by Raman, FTIR, X-ray and EPR.

PubMed

Christiansen, Marie Bitsch; Sørensen, Mikkel Agerbæk; Sanyova, Jana; Bendix, Jesper; Simonsen, Kim Pilkjær

2017-03-15

In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube colours found in Krøyer's painting cabinet were examined. In most cases, the results of the pigment analyses were as expected based on our knowledge of artists' colours used in the late 1800s and early 1900s. However, in one of the tube colours labelled "Jaune de Cadmium Citron" (cadmium lemon yellow) an extremely rare cadmium chromate pigment was found. The pigment was analysed and characterised by Raman microscopy (MRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), powder X-ray diffraction (PXRD), single-crystal X-ray crystallography, and electron paramagnetic resonance (EPR) spectroscopy. Cadmium chromate was synthesised by precipitation from an aqueous solution of cadmium nitrate and potassium chromate, and the resulting yellow crystals proved identical to the pigment found in the tube colour "Jaune de Cadmium Citron". The structure determined by single-crystal X-ray diffraction identified the pigment as 2CdCrO 4 ·KOH·H 2 O or more accurately as KCd 2 (CrO 4 ) 2 (H 3 O 2 ) illustrating the μ-H 3 O 2 - species. The yellow colour of the paint sample taken from the tube had a greenish hue, which became even more prominent upon storage and drying. EPR analysis of the sample showed the presence of paramagnetic degradation products containing Cr(III) and Cr(V). Copyright © 2016 Elsevier B.V. All rights reserved.

In vivo high-resolution magic angle spinning magnetic and electron paramagnetic resonance spectroscopic analysis of mitochondria-targeted peptide in Drosophila melanogaster with trauma-induced thoracic injury.

PubMed

Constantinou, Caterina; Apidianakis, Yiorgos; Psychogios, Nikolaos; Righi, Valeria; Mindrinos, Michael N; Khan, Nadeem; Swartz, Harold M; Szeto, Hazel H; Tompkins, Ronald G; Rahme, Laurence G; Tzika, A Aria

2016-02-01

Trauma is the most common cause of mortality among individuals aged between 1 and 44 years and the third leading cause of mortality overall in the US. In this study, we examined the effects of trauma on the expression of genes in Drosophila melanogaster, a useful model for investigating genetics and physiology. After trauma was induced by a non-lethal needle puncture of the thorax, we observed the differential expression of genes encoding for mitochondrial uncoupling proteins, as well as those encoding for apoptosis-related and insulin signaling-related proteins, thus indicating muscle functional dysregulation. These results prompted us to examine the link between insulin signaling and mitochondrial dysfunction using in vivo nuclear magnetic resonance (NMR) with complementary electron paramagnetic resonance (EPR) spectroscopy. Trauma significantly increased insulin resistance biomarkers, and the NMR spectral profile of the aged flies with trauma-induced thoracic injury resembled that of insulin-resistant chico mutant flies. In addition, the mitochondrial redox status, as measured by EPR, was significantly altered following trauma, indicating mitochondrial uncoupling. A mitochondria-targeted compound, Szeto-Schiller (SS)-31 that promotes adenosine triphosphate (ATP) synthesis normalized the NMR spectral profile, as well as the mitochondrial redox status of the flies with trauma-induced thoracic injury, as assessed by EPR. Based on these findings, we propose a molecular mechanism responsible for trauma-related mortality and also propose that trauma sequelae in aging are linked to insulin signaling and mitochondrial dysfunction. Our findings further suggest that SS-31 attenuates trauma-associated pathological changes.

Probing Fe-V Bonding in a C3-Symmetric Heterobimetallic Complex.

PubMed

Greer, Samuel M; McKay, Johannes; Gramigna, Kathryn M; Thomas, Christine M; Stoian, Sebastian A; Hill, Stephen

2018-04-30

Direct metal-metal bonding of two distinct first-row transition metals remains relatively unexplored compared to their second- and third-row heterobimetallic counterparts. Herein, a recently reported Fe-V triply bonded species, [V( i PrNPPh 2 ) 3 FeI] (1; Kuppuswamy, S.; Powers, T. M.; Krogman, J. P.; Bezpalko, M. W.; Foxman, B. M.; Thomas, C. M. Vanadium-iron complexes featuring metal-metal multiple bonds. Chem. Sci. 2013, 4, 3557-3565), is investigated using high-frequency electron paramagnetic resonance, field- and temperature-dependent 57 Fe nuclear gamma resonance (Mössbauer) spectroscopy, and high-field electron-electron double resonance detected nuclear magnetic resonance. From the use of this suite of physical methods, we have assessed the electronic structure of 1. These studies allow us to establish the effective g̃ tensors as well as the Fe/V electro-nuclear hyperfine interaction tensors of the spin S = 1 / 2 ground state. We have rationalized these tensors in the context of ligand field theory supported by quantum chemical calculations. This theoretical analysis suggests that the S = 1 / 2 ground state originates from a single unpaired electron predominately localized on the Fe site.

Basic magnetic properties of bituminous coal

USGS Publications Warehouse

Alexander, C.C.; Thorpe, A.N.; Senftle, F.E.

1979-01-01

Magnetic susceptibility and other static magnetic parameters have been measured on a number of bituminous coals from various locations in the United States. The paramagnetic Curie constant correlates negatively with carbon concentration on a moisture-free basis. The major contribution to the total paramagnetism comes from the mineral matter rather than from free radicals or broken bonds. Analysis of the data indicates that the specific paramagnetism is generally lower in the mineral matter found in high-ash compared to low-ash coal. A substantial number of the coal specimens tested also had a ferromagnetic susceptibility which appeared to be associated with magnetite. Magnetite and ??-iron spherules, possibly of meteoritic or volcanic origin, were found in several specimens. ?? 1979.

Production and aging of paramagnetic point defects in P-doped floating zone silicon irradiated with high fluence 27 MeV electrons

NASA Astrophysics Data System (ADS)

Joita, A. C.; Nistor, S. V.

2018-04-01

Enhancing the long term stable performance of silicon detectors used for monitoring the position and flux of the particle beams in high energy physics experiments requires a better knowledge of the nature, stability, and transformation properties of the radiation defects created over the operation time. We report the results of an electron spin resonance investigation in the nature, transformation, and long term stability of the irradiation paramagnetic point defects (IPPDs) produced by high fluence (2 × 1016 cm-2), high energy (27 MeV) electrons in n-type, P-doped standard floating zone silicon. We found out that both freshly irradiated and aged (i.e., stored after irradiation for 3.5 years at 250 K) samples mainly contain negatively charged tetravacancy and pentavacancy defects in the first case and tetravacancy defects in the second one. The fact that such small cluster vacancy defects have not been observed by irradiation with low energy (below 5 MeV) electrons, but were abundantly produced by irradiation with neutrons, strongly suggests the presence of the same mechanism of direct formation of small vacancy clusters by irradiation with neutrons and high energy, high fluence electrons, in agreement with theoretical predictions. Differences in the nature and annealing properties of the IPPDs observed between the 27 MeV electrons freshly irradiated, and irradiated and aged samples were attributed to the presence of a high concentration of divacancies in the freshly irradiated samples, defects which transform during storage at 250 K through diffusion and recombination processes.

Rabi oscillation and electron-spin-echo envelope modulation of the photoexcited triplet spin system in silicon

NASA Astrophysics Data System (ADS)

Akhtar, Waseem; Sekiguchi, Takeharu; Itahashi, Tatsumasa; Filidou, Vasileia; Morton, John J. L.; Vlasenko, Leonid; Itoh, Kohei M.

2012-09-01

We report on a pulsed electron paramagnetic resonance (EPR) study of the photoexcited triplet state (S=1) of oxygen-vacancy centers in silicon. Rabi oscillations between the triplet sublevels are observed using coherent manipulation with a resonant microwave pulse. The Hahn echo and stimulated echo decay profiles are superimposed with strong modulations known as electron-spin-echo envelope modulation (ESEEM). The ESEEM spectra reveal a weak but anisotropic hyperfine coupling between the triplet electron spin and a 29Si nuclear spin (I=1/2) residing at a nearby lattice site, that cannot be resolved in conventional field-swept EPR spectra.

Using Hyperfine Electron Paramagnetic Resonance Spectroscopy to Define the Proton-Coupled Electron Transfer Reaction at Fe-S Cluster N2 in Respiratory Complex I.

PubMed

Le Breton, Nolwenn; Wright, John J; Jones, Andrew J Y; Salvadori, Enrico; Bridges, Hannah R; Hirst, Judy; Roessler, Maxie M

2017-11-15

Energy-transducing respiratory complex I (NADH:ubiquinone oxidoreductase) is one of the largest and most complicated enzymes in mammalian cells. Here, we used hyperfine electron paramagnetic resonance (EPR) spectroscopic methods, combined with site-directed mutagenesis, to determine the mechanism of a single proton-coupled electron transfer reaction at one of eight iron-sulfur clusters in complex I, [4Fe-4S] cluster N2. N2 is the terminal cluster of the enzyme's intramolecular electron-transfer chain and the electron donor to ubiquinone. Because of its position and pH-dependent reduction potential, N2 has long been considered a candidate for the elusive "energy-coupling" site in complex I at which energy generated by the redox reaction is used to initiate proton translocation. Here, we used hyperfine sublevel correlation (HYSCORE) spectroscopy, including relaxation-filtered hyperfine and single-matched resonance transfer (SMART) HYSCORE, to detect two weakly coupled exchangeable protons near N2. We assign the larger coupling with A( 1 H) = [-3.0, -3.0, 8.7] MHz to the exchangeable proton of a conserved histidine and conclude that the histidine is hydrogen-bonded to N2, tuning its reduction potential. The histidine protonation state responds to the cluster oxidation state, but the two are not coupled sufficiently strongly to catalyze a stoichiometric and efficient energy transduction reaction. We thus exclude cluster N2, despite its proton-coupled electron transfer chemistry, as the energy-coupling site in complex I. Our work demonstrates the capability of pulse EPR methods for providing detailed information on the properties of individual protons in even the most challenging of energy-converting enzymes.

Especially for High School Teachers

NASA Astrophysics Data System (ADS)

Howell, J. Emory

1998-01-01

Secondary School Feature Articles * Heat Capacity, Body Temperature, and Hypothermia, by Doris Kimbrough, p 48. * The Electromotive Series and Other Non-Absolute Scales, by Gavin Peckham, p 49. * Demonstrations on Paramagnetism with an Electronic Balance, by Adolf Cortel, p 61. * Toward More Performance Evaluation in Chemistry, by Sharon Rasp, p 64. A Wealth of Useful Information

Computation of Chemical Shifts for Paramagnetic Molecules: A Laboratory Experiment for the Undergraduate Curriculum

ERIC Educational Resources Information Center

Pritchard, Benjamin P.; Simpson, Scott; Zurek, Eva; Autschbach, Jochen

2014-01-01

A computational experiment investigating the [superscript 1]H and [superscript 13]C nuclear magnetic resonance (NMR) chemical shifts of molecules with unpaired electrons has been developed and implemented. This experiment is appropriate for an upper-level undergraduate laboratory course in computational, physical, or inorganic chemistry. The…

Niobium hyperfine structure in crystal calcium tungstate

NASA Technical Reports Server (NTRS)

Tseng, D. L.; Kikuchi, C.

1972-01-01

A study of the niobium hyperfine structure in single crystal calcium tungstate was made by the combination of the technique of electron paramagnetic resonance and electron nuclear double resonance (EPR/ENDOR). The microwave frequency was about 9.4 GHz and the radio frequency from 20MHz to 70 MHz. The rare earth ions Nd(3+), U(3+), or Tm(3+) were added as the charge compensator for Nb(5+). To create niobium paramagnetic centers, the sample was irradiated at 77 deg K with a 10 thousand curie Co-60 gamma source for 1 to 2 hours at a dose rate of 200 K rads per hour and then transferred quickly into the cavity. In a general direction of magnetic field, the spectra showed 4 sets of 10 main lines corresponding to 4 nonequivalent sites of niobium with I = 9/2. These 4 sets of lines coalesced into 2 sets of 10 in the ab-plane and into a single set of 10 along the c-axis. This symmetry suggested that the tungsten ions are substituted by the niobium ions in the crystal.

Microstrip resonators for electron paramagnetic resonance experiments

NASA Astrophysics Data System (ADS)

Torrezan, A. C.; Mayer Alegre, T. P.; Medeiros-Ribeiro, G.

2009-07-01

In this article we evaluate the performance of an electron paramagnetic resonance (EPR) setup using a microstrip resonator (MR). The design and characterization of the resonator are described and parameters of importance to EPR and spin manipulation are examined, including cavity quality factor, filling factor, and microwave magnetic field in the sample region. Simulated microwave electric and magnetic field distributions in the resonator are also presented and compared with qualitative measurements of the field distribution obtained by a perturbation technique. Based on EPR experiments carried out with a standard marker at room temperature and a MR resonating at 8.17 GHz, the minimum detectable number of spins was found to be 5×1010 spins/GHz1/2 despite the low MR unloaded quality factor Q0=60. The functionality of the EPR setup was further evaluated at low temperature, where the spin resonance of Cr dopants present in a GaAs wafer was detected at 2.3 K. The design and characterization of a more versatile MR targeting an improved EPR sensitivity and featuring an integrated biasing circuit for the study of samples that require an electrical contact are also discussed.

Assessing topology and surface orientation of an antimicrobial peptide magainin 2 using mechanically aligned bilayers and electron paramagnetic resonance spectroscopy.

PubMed

Mayo, Daniel J; Sahu, Indra D; Lorigan, Gary A

2018-07-01

Aligned CW-EPR membrane protein samples provide additional topology interactions that are absent from conventional randomly dispersed samples. These samples are aptly suited to studying antimicrobial peptides because of their dynamic peripheral topology. In this study, four consecutive substitutions of the model antimicrobial peptide magainin 2 were synthesized and labeled with the rigid TOAC spin label. The results revealed the helical tilts to be 66° ± 5°, 76° ± 5°, 70° ± 5°, and 72° ± 5° for the TOAC substitutions H7, S8, A9, and K10 respectively. These results are consistent with previously published literature. Using the EPR (electron paramagnetic resonance) mechanical alignment technique, these substitutions were used to critically assess the topology and surface orientation of the peptide with respect to the membrane. This methodology offers a rapid and simple approach to investigate the structural topology of antimicrobial peptides. Copyright © 2018 Elsevier B.V. All rights reserved.

Electron spin resonance (ESR) dose measurement in bone of Hiroshima A-bomb victim

PubMed Central

2018-01-01

Explosion of the bombs in Hiroshima and Nagasaki corresponds to the only historical moment when atomic bombs were used against civilians. This event triggered countless investigations into the effects and dosimetry of ionizing radiation. However, none of the investigations has used the victims’ bones as dosimeter. Here, we assess samples of bones obtained from fatal victims of the explosion by Electron Spin Resonance (ESR). In 1973, one of the authors of the present study (SM) traveled to Japan and conducted a preliminary experiment on the victims’ bone samples. The idea was to use the paramagnetism induced in bone after irradiation to measure the radiation dose. Technological advances involved in the construction of spectrometers, better knowledge of the paramagnetic center, and improvement in signal processing techniques have allowed us to resume the investigation. We obtained a reconstructed dose of 9.46 ± 3.4 Gy from the jawbone, which was compatible with the dose distribution in different locations as measured in non-biological materials such as wall bricks and roof tiles. PMID:29408890

Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide

NASA Astrophysics Data System (ADS)

Ivády, Viktor; Szász, Krisztián; Falk, Abram L.; Klimov, Paul V.; Christle, David J.; Janzén, Erik; Abrikosov, Igor A.; Awschalom, David D.; Gali, Adam

2015-09-01

Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.

Redox-controlled dinitrosyl formation at the diiron-oxo center of NorA.

PubMed

Cramm, Rainer; Strube, Katja

2008-01-01

In the denitrifying bacterium Ralstonia eutropha H16, the NorA protein is coproduced with the respiratory nitric oxide (NO) reductase. NorA contains a diiron-oxo center, which can form stable adducts with dioxygen and NO. In contrast to other diiron proteins, the formation of NorA-NO requires both fully reduced protein and additional electrons. A minor fraction of in vitro NorA-NO represents a paramagnetic dinitrosyl iron complex (DNIC), while the major fraction is attributed to a DNIC of the structure {Fe(NO)(2)}, which shows no electron paramagnetic resonance. The NorA-DNIC may be formed either upon direct reaction of the protein with NO or upon incubation with nitrite due to an intrinsic nitrite reduction activity of NorA that liberates NO. NorA can be purified rapidly as a six histidine-tagged derivative from overproducing cells of Escherichia coli. This chapter describes procedures for the preparation of different redox forms of NorA for the formation of NorA adducts with NO, dioxygen, and azide, as well as for the quantification of NorA-bound NO.

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.

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.

Investigation of 3C-SiC/SiO2 interfacial point defects from ab initio g-tensor calculations and electron paramagnetic resonance measurements

NASA Astrophysics Data System (ADS)

Nugraha, T. A.; Rohrmueller, M.; Gerstmann, U.; Greulich-Weber, S.; Stellhorn, A.; Cantin, J. L.; von Bardeleben, J.; Schmidt, W. G.; Wippermann, S.

SiC is widely used in high-power, high-frequency electronic devices. Recently, it has also been employed as a building block in nanocomposites used as light absorbers in solar energy conversion devices. Analogous to Si, SiC features SiO2 as native oxide that can be used for passivation and insulating layers. However, a significant number of defect states are reported to form at SiC/SiO2 interfaces, limiting mobility and increasing recombination of free charge carriers. We investigated the growth of oxide on different 3C-SiC surfaces from first principles. Carbon antisite Csi defects are found to be strongly stabilized in particular at the interface, because carbon changes its hybridization from sp3 in the SiC-bulk to sp2 at the interface, creating a dangling bond inside a porous region of the SiO2 passivating layer. Combining ab initio g-tensor calculations and electron paramagnetic resonance (EPR) measurements, we show that Csi defects explain the measured EPR signatures, while the hyperfine structure allows to obtain local structural information of the oxide layer. Financial support from BMBF NanoMatFutur Grant 13N12972 and DFG priority program SPP-1601 is gratefully acknowledged.

Synthesis, structural and electron paramagnetic resonance studies on Pb0.9Bi0.1Fe0.7W0.3O3 ceramic

NASA Astrophysics Data System (ADS)

Shivaraja, I.; Matteppanvar, Shidaling; Dadami, Sunanda T.; Rayaprol, Sudhindra; Angadi, Basavaraj

2018-04-01

A single phase Pb0.9Bi0.1Fe0.7W0.3O3 (0.9Pb(Fe2/3W1/3)O3 - 0.1BiFeO3 or PBFW) polycrystalline ceramic was synthesized by the two step solid state reaction method, with low-temperature sintering at 800°C for 30 mins and slow cooling to room temperature (RT). Detailed studies of RT X-ray diffraction (XRD) and Raman spectroscopy measurements confirm the formation of high symmetry cubic structure with Pm-3m space group. The Rietveld refinement was carried out on RT XRD data and the obtained structural parameters are a = b = c = 3.97563(6) Å and unit cell volume = 62.837 (2) Å3. Scanning Electron Microscopy (SEM) images show the uniform distribution of grains with some agglomerated nature. RT Raman spectroscopy reveals the main broad peak at 770 cm-1, related to the A1g mode, which confirms the formation of cubic (ABO3 perovskite) structure. The single symmetric electron paramagnetic resonance (EPR) line shape with g = 2.13985 observed in PBFW was identified to be due to Fe3+ ions.

W-band PELDOR with 1 kW microwave power: molecular geometry, flexibility and exchange coupling.

PubMed

Reginsson, Gunnar W; Hunter, Robert I; Cruickshank, Paul A S; Bolton, David R; Sigurdsson, Snorri Th; Smith, Graham M; Schiemann, Olav

2012-03-01

A technique that is increasingly being used to determine the structure and conformational flexibility of biomacromolecules is Pulsed Electron-Electron Double Resonance (PELDOR or DEER), an Electron Paramagnetic Resonance (EPR) based technique. At X-band frequencies (9.5 GHz), PELDOR is capable of precisely measuring distances in the range of 1.5-8 nm between paramagnetic centres but the orientation selectivity is weak. In contrast, working at higher frequencies increases the orientation selection but usually at the expense of decreased microwave power and PELDOR modulation depth. Here it is shown that a home-built high-power pulsed W-band EPR spectrometer (HiPER) with a large instantaneous bandwidth enables one to achieve PELDOR data with a high degree of orientation selectivity and large modulation depths. We demonstrate a measurement methodology that gives a set of PELDOR time traces that yield highly constrained data sets. Simulating the resulting time traces provides a deeper insight into the conformational flexibility and exchange coupling of three bisnitroxide model systems. These measurements provide strong evidence that W-band PELDOR may prove to be an accurate and quantitative tool in assessing the relative orientations of nitroxide spin labels and to correlate those orientations to the underlying biological structure and dynamics. Copyright © 2012 Elsevier Inc. All rights reserved.

Perturbation of nuclear spin polarizations in solid state NMR of nitroxide-doped samples by magic-angle spinning without microwaves.

PubMed

Thurber, Kent R; Tycko, Robert

2014-05-14

We report solid state (13)C and (1)H nuclear magnetic resonance (NMR) experiments with magic-angle spinning (MAS) on frozen solutions containing nitroxide-based paramagnetic dopants that indicate significant perturbations of nuclear spin polarizations without microwave irradiation. At temperatures near 25 K, (1)H and cross-polarized (13)C NMR signals from (15)N,(13)C-labeled L-alanine in trinitroxide-doped glycerol/water are reduced by factors as large as six compared to signals from samples without nitroxide doping. Without MAS or at temperatures near 100 K, differences between signals with and without nitroxide doping are much smaller. We attribute most of the reduction of NMR signals under MAS near 25 K to nuclear spin depolarization through the cross-effect dynamic nuclear polarization mechanism, in which three-spin flips drive nuclear polarizations toward equilibrium with spin polarization differences between electron pairs. When T1e is sufficiently long relative to the MAS rotation period, the distribution of electron spin polarization across the nitroxide electron paramagnetic resonance lineshape can be very different from the corresponding distribution in a static sample at thermal equilibrium, leading to the observed effects. We describe three-spin and 3000-spin calculations that qualitatively reproduce the experimental observations.

Defect induced electronic states and magnetism in ball-milled graphite.

PubMed

Milev, Adriyan; Dissanayake, D M A S; Kannangara, G S K; Kumarasinghe, A R

2013-10-14

The electronic structure and magnetism of nanocrystalline graphite prepared by ball milling of graphite in an inert atmosphere have been investigated using valence band spectroscopy (VB), core level near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and magnetic measurements as a function of the milling time. The NEXAFS spectroscopy of graphite milled for 30 hours shows simultaneous evolution of new states at ~284.0 eV and at ~290.5 eV superimposed upon the characteristic transitions at 285.4 eV and 291.6 eV, respectively. The modulation of the density of states is explained by evolution of discontinuities within the sheets and along the fracture lines in the milled graphite. The magnetic measurements in the temperature interval 2-300-2 K at constant magnetic field strength show a correlation between magnetic properties and evolution of the new electronic states. With the reduction of the crystallite sizes of the graphite fragments, the milled material progressively changes its magnetic properties from diamagnetic to paramagnetic with contributions from both Pauli and Curie paramagnetism due to the evolution of new states at ~284 and ~290.5 eV, respectively. These results indicate that the magnetic behaviour of ball-milled graphite can be manipulated by changing the milling conditions.

Characterization of Point Defects in Lithium Aluminate (LiAlO2) Single Crystals

DTIC Science & Technology

2015-09-17

high-quality neutron detectors since 235U and 239Pu, the two isotopes used to fuel nuclear weapons , both emit neu- trons through spontaneous fission of...dissertation has iden- tified and characterized the major point defects created and induced through x ray and neutron radiation using electron paramagnetic... neutron irradiation is an F+ center; an oxygen vacancy with one trapped electron. This defect has two states, a stable state that survives up to 500 ◦C and

Plasmon-mediated circularly polarized luminescence of GaAs in a scanning tunneling microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mühlenberend, Svenja; Gruyters, Markus; Berndt, Richard, E-mail: berndt@physik.uni-kiel.de

2015-12-14

The electroluminescence from p-type GaAs(110) in a scanning tunneling microscope has been investigated at 6 K. Unexpectedly, high degrees of circular polarization have often been observed with ferromagnetic Ni tips and also with paramagnetic W and Ag tips. The data are interpreted in terms of two distinct excitation mechanisms. Electron injection generates intense luminescence with low polarization. Plasmon-mediated generation of electron-hole pairs leads to less intense emission, which, however, is highly polarized for many tips.

Mechanically detected terahertz electron spin resonance using SOI-based thin piezoresistive microcantilevers

NASA Astrophysics Data System (ADS)

Ohmichi, Eiji; Miki, Toshihiro; Horie, Hidekazu; Okamoto, Tsubasa; Takahashi, Hideyuki; Higashi, Yoshinori; Itoh, Shoichi; Ohta, Hitoshi

2018-02-01

We developed piezoresistive microcantilevers for mechanically detected electron spin resonance (ESR) in the millimeter-wave region. In this article, fabrication process and device characterization of our self-sensing microcantilevers are presented. High-frequency ESR measurements of a microcrystal of paramagnetic sample is also demonstrated at multiple frequencies up to 160 GHz at liquid helium temperature. Our fabrication is based on relatively simplified processes with silicon-on-insulator (SOI) wafers and spin-on diffusion doping, thus enabling cost-effective and time-saving cantilever fabrication.

Demetalation of Fe, Mn, and Cu chelates and complexes: application to the NMR analysis of micronutrient fertilizers.

PubMed

López-Rayo, Sandra; Lucena, Juan J; Laghi, Luca; Cremonini, Mauro A

2011-12-28

The application of nuclear magnetic resonance (NMR) for the quality control of fertilizers based on Fe(3+), Mn(2+), and Cu(2+) chelates and complexes is precluded by the strong paramagnetism of metals. Recently, a method based on the use of ferrocyanide has been described to remove iron from commercial iron chelates based on the o,o-EDDHA [ethylenediamine-N,N'bis(2-hydroxyphenylacetic)acid] chelating agent for their analysis and quantification by NMR. The present work extended that procedure to other paramagnetic ions, manganese and copper, and other chelating, EDTA (ethylenediaminetetraacetic acid), IDHA [N-(1,2-dicarboxyethyl)-d,l-aspartic acid], and complexing agents, gluconate and heptagluconate. Results showed that the removal of the paramagnetic ions was complete, allowing us to obtain (1)H NMR spectra characterized by narrow peaks. The quantification of the ligands by NMR and high-performance liquid chromatography showed that their complete recovery was granted. The NMR analysis enabled detection and quantification of unknown impurities without the need of pure compounds as internal standards.

Change in the Magnetocapacity in the Paramagnetic Region in a Cation-Substituted Manganese Selenide

NASA Astrophysics Data System (ADS)

Aplesnin, S. S.; Sitnikov, M. N.; Zhivul'ko, A. M.

2018-04-01

The capacity and the dielectric loss tangent of a Gd x Mn1- x Se ( x ≤ 0.2) solid solution have been measured in the frequency range 1-300 kHz without a magnetic field and in a magnetic field of 8 kOe in the temperature range 100-450 K, and the magnetic moment of the solid solution has been measured in a field of 8.6 kOe. The magnetocapacity effect and the change in the magnetocapacity sign have been observed in room temperature in the paramagnetic region. A correlation of the changes in the dielectric permittivity and the magnetic susceptibility with temperature has been revealed. The magnetocapacity is described using the model with orbital electron ordering and the Maxwell-Wagner model.

Paramagnetic resonance of Mn4+ and Mn2+ centers in lanthanum gallate single crystals

NASA Astrophysics Data System (ADS)

Vazhenin, V. A.; Potapov, A. P.; Guseva, V. B.; Artyomov, M. Yu.

2010-03-01

An increase in the manganese concentration in lanthanum gallate in the range 0.5-5.0% has been found to result in a complete replacement of individual Mn4+ ions by Mn2+ ions. The relative concentrations and binding energies of individual Mn4+, Mn3+, and Mn2+ ions have been determined. The spin Hamiltonians of the Mn2+ and Mn4+ centers in the rhombohedral and orthorhombic phases, respectively, have been constructed and the orientation of the principal axes of the fine-structure tensor of Mn4+ at room temperature has been found. The possibility of using electron paramagnetic resonance for determining the rotation angles of oxygen octahedra of lanthanum gallate with respect to the perovskite structure has been discussed.

Optical and Piezoelectric Study of KNN Solid Solutions Co-Doped with La-Mn and Eu-Fe.

PubMed

Peña-Jiménez, Jesús-Alejandro; González, Federico; López-Juárez, Rigoberto; Hernández-Alcántara, José-Manuel; Camarillo, Enrique; Murrieta-Sánchez, Héctor; Pardo, Lorena; Villafuerte-Castrejón, María-Elena

2016-09-28

The solid-state method was used to synthesize single phase potassium-sodium niobate (KNN) co-doped with the La 3+ -Mn 4+ and Eu 3+ -Fe 3+ ion pairs. Structural determination of all studied solid solutions was accomplished by XRD and Rietveld refinement method. Electron paramagnetic resonance (EPR) studies were performed to determine the oxidation state of paramagnetic centers. Optical spectroscopy measurements, excitation, emission and decay lifetime were carried out for each solid solution. The present study reveals that doping KNN with La 3+ -Mn 4+ and Eu 3+ -Fe 3+ at concentrations of 0.5 mol % and 1 mol %, respectively, improves the ferroelectric and piezoelectric behavior and induce the generation of optical properties in the material for potential applications.

Optical and Piezoelectric Study of KNN Solid Solutions Co-Doped with La-Mn and Eu-Fe

PubMed Central

Peña-Jiménez, Jesús-Alejandro; González, Federico; López-Juárez, Rigoberto; Hernández-Alcántara, José-Manuel; Camarillo, Enrique; Murrieta-Sánchez, Héctor; Pardo, Lorena; Villafuerte-Castrejón, María-Elena

2016-01-01

The solid-state method was used to synthesize single phase potassium-sodium niobate (KNN) co-doped with the La3+–Mn4+ and Eu3+–Fe3+ ion pairs. Structural determination of all studied solid solutions was accomplished by XRD and Rietveld refinement method. Electron paramagnetic resonance (EPR) studies were performed to determine the oxidation state of paramagnetic centers. Optical spectroscopy measurements, excitation, emission and decay lifetime were carried out for each solid solution. The present study reveals that doping KNN with La3+–Mn4+ and Eu3+–Fe3+ at concentrations of 0.5 mol % and 1 mol %, respectively, improves the ferroelectric and piezoelectric behavior and induce the generation of optical properties in the material for potential applications. PMID:28773925

Theoretical and experimental studies of the molecular orbital bonding coefficients for Cu{sup 2+} ion in cesium hydrogen oxalate single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalfaoğlu, Emel, E-mail: emelkalfaoglu@mynet.com; Karabulut, Bünyamin

2016-03-25

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu{sup 2+} ions in cesium hydrogen oxalate single crystals have been investigated at room temperature. The spin-Hamiltonian parameters (g and A), have been determined. Crystalline field around the Cu{sup 2+} ion is almost axially symmetric. The results show a single paramagnetic site which confirms the triclinic crystal symmetry. Molecular orbital bonding coefficients are studied from the EPR and optical data. Theoretical octahedral field parameter and the tetragonal field parameters have been evaluated from the superposition model. Using these parameters, various bonding parameters are analyzed and the nature of bonding in themore » complex is discussed. The theoretical results are supported by experimental results.« less

SimLabel: a graphical user interface to simulate continuous wave EPR spectra from site-directed spin labeling experiments.

PubMed

Etienne, E; Le Breton, N; Martinho, M; Mileo, E; Belle, V

2017-08-01

Site-directed spin labeling (SDSL) combined with continuous wave electron paramagnetic resonance (cw EPR) spectroscopy is a powerful technique to reveal, at the residue level, structural transitions in proteins. SDSL-EPR is based on the selective grafting of a paramagnetic label on the protein under study, followed by cw EPR analysis. To extract valuable quantitative information from SDSL-EPR spectra and thus give reliable interpretation on biological system dynamics, numerical simulations of the spectra are required. Such spectral simulations can be carried out by coding in MATLAB using functions from the EasySpin toolbox. For non-expert users of MATLAB, this could be a complex task or even impede the use of such simulation tool. We developed a graphical user interface called SimLabel dedicated to run cw EPR spectra simulations particularly coming from SDSL-EPR experiments. Simlabel provides an intuitive way to visualize, simulate, and fit such cw EPR spectra. An example of SDSL-EPR spectra simulation concerning the study of an intrinsically disordered region undergoing a local induced folding is described and discussed. We believe that this new tool will help the users to rapidly obtain reliable simulated spectra and hence facilitate the interpretation of their results. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

Synthesis, structural and paramagnetic properties of SnO{sub 2} doped NiO nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Islam, I., E-mail: ishtihadahislam@gmail.com; Dwivedi, Sonam; Dar, Hilal A.

2016-05-06

In this work, Sn doped NiO nanoparticles were synthesized by co-precipitation route to explore the impact of doping on lattice structure, dielectric constant and magnetization. X-ray diffraction analysis confirmed cubic (Fd-3m) structure of Sn doped NiO. Average crystallite size decreases from 78.2 nm (Ni{sub 0.95}Sn{sub 0.05}O) to 64.23 nm (Ni{sub 0.8}Sn{sub 0.2}O). Scanning electron microscopy images confirm that nanocrystals have agglomerated spherical morphology. The Raman spectrum exhibits a strong, broad peak at 410 cm{sup -1} and is attributed to the Ni-O stretching mode and doped samples show a blue shift. The dielectric constants at about 1 Hz are measured to be about 1.795,more » 1.030, 0.442, and 0.302 × 10{sup 3} Ni{sub 1-x}Sn{sub x}O (x = 0.05, 0.1, 0.15, 0.2), respectively. The dielectric constant in nanoparticles of doped Ni{sub 1-x}Sn{sub x}O is three orders of magnitude higher as compared to pure NiO ceramics. The nature of magnetization - applied field (M-H) infers paramagnetic behaviour for Sn doped NiO nanoparticles.« less

Room Temperature Antiferromagnetic Ordering of Nanocrystalline Tb1.90Ni0.10O3

NASA Astrophysics Data System (ADS)

Mandal, J.; Dalal, M.; Sarkar, B. J.; Chakrabarti, P. K.

2017-02-01

Nanocrystalline Ni-doped terbium oxide (Tb1.90Ni0.10O3) has been synthesized by the co-precipitation method followed by annealing at 700°C for 6 h in vacuum. The crystallographic phase and the substitution of Ni2+ ions in the lattice of Tb2O3 are confirmed by Rietveld analysis of the x-ray diffraction pattern using the software MAUD. High-resolution transmission electron microscopy is also carried out to study the morphology of the sample. Magnetic measurements are carried out at different temperatures from 5 K to 300 K using a superconducting quantum interference device (SQUID) magnetometer. The dependence of the magnetization of Tb1.90Ni0.10O3 as a function of temperature ( M- T) and magnetic field ( M- H) suggests the presence of both paramagnetic and antiferromagnetic phase at room temperature, but antiferromagnetic phase dominates below ˜120 K. The lack of saturation in the M- H curve and good fitting of the M- T curve by the Johnston formula also indicate the presence of both paramagnetic and antiferromagnetic phase at room temperature. Interestingly, an antiferromagnetic to ferromagnetic phase transition is observed below ˜40 K. The result also shows a high value of magnetization at 5 K.

Hydrogen evolution from aqueous-phase photocatalytic reforming of ethylene glycol over Pt/TiO2 catalysts: Role of Pt and product distribution

NASA Astrophysics Data System (ADS)

Li, Fuying; Gu, Quan; Niu, Yu; Wang, Renzhang; Tong, Yuecong; Zhu, Shuying; Zhang, Hualei; Zhang, Zizhong; Wang, Xuxu

2017-01-01

Pt nanoparticles were loaded on anatase TiO2 by the photodeposition method to investigate their photocatalytic activity for H2 evolution in an aqueous solution containing a certain amount of ethylene glycol (EG) as the sacrificial agent. The surface properties and chemical states of the Pt/TiO2 sample were characterized by X-ray powder diffraction analysis, Brunauer-Emmett-Teller surface area analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and electrochemical resistance. The aqueous-phase photocatalytic EG reforming using Pt/TiO2 and anatase TiO2 generated not only H2 and CO2, but also CO, CH4, C2H6, and C2H4. Moreover, the amount of formate and acetate complexes in the solution increased gradually. The EG adsorption and gas-phase intermediates during photocatalytic reaction processes were investigated by the in situ FTIR spectrum. Finally, the photocatalytic EG reforming reaction mechanism was elucidated. This helped to better understand the role of a sacrificial agent in a photocatalytic hydrogen production.

Pulsed EPR measurements on reaction rate constants for addition of photo-generated radicals to double bonds of diethyl fumarate and diethyl maleate

NASA Astrophysics Data System (ADS)

Takahashi, Hirona; Hagiwara, Kenta; Kawai, Akio

2016-11-01

Addition reaction of photo-generated radicals to double bonds of diethyl fumarate (deF) and diethyl maleate (deM), which are geometrical isomers, was studied by means of time-resolved- (TR-) and pulsed-electron paramagnetic resonance (EPR). Analysis of TR-EPR spectra indicates that adduct radicals from deF and deM should have the same structure. The double bonds of these monomers are converted to single ones by addition reaction, which allows hindered internal rotation to give the same structure of adduct radical. The rate constants for addition reaction of photo-generated radicals were determined by Stern-Volmer analysis of the decay time of electron spin-echo intensity of these radicals measured by the pulsed EPR method. Rate constants for deF were found to be larger than those for deM. This relation is in good consistent with efficiency of polymerisation of deF and deM. Experimentally determined rate constants were evaluated by introducing the addition reaction model on the basis of two important factors enthalpy and polar effects.

Methods of chemical and phase composition analysis of gallstones

NASA Astrophysics Data System (ADS)

Suvorova, E. I.; Pantushev, V. V.; Voloshin, A. E.

2017-11-01

This review presents the instrumental methods used for chemical and phase composition investigation of gallstones. A great body of data has been collected in the literature on the presence of elements and their concentrations, obtained by fluorescence microscopy, X-ray fluorescence spectroscopy, neutron activation analysis, proton (particle) induced X-ray emission, atomic absorption spectroscopy, high-resolution gamma-ray spectrometry, electron paramagnetic resonance. Structural methods—powder X-ray diffraction, infrared spectroscopy, Raman spectroscopy—provide information about organic and inorganic phases in gallstones. Stone morphology was studied at the macrolevel with optical microscopy. Results obtained by analytical scanning and transmission electron microscopy with X-ray energy dispersive spectrometry are discussed. The chemical composition and structure of gallstones determine the strategy of removing stone from the body and treatment of patients: surgery or dissolution in the body. Therefore one chapter of the review describes the potential of dissolution methods. Early diagnosis and appropriate treatment of the disease depend on the development of clinical methods for in vivo investigation, which gave grounds to present the main characteristics and potential of ultrasonography (ultrasound scanning), magnetic resonance imaging, and X-ray computed tomography.

Electronic Interactions of n-Doped Perylene Diimide Groups Appended to Polynorbornene Chains: Implications for Electron Transport in Organic Electronics.

PubMed

Nguyen, Minh T; Biberdorf, Joshua D; Holliday, Bradley J; Jones, Richard A

2017-11-01

A polymer consisting of a polynorbornene backbone with perylene diimide (PDI) pendant groups on each monomeric unit is synthesized via ring opening metathesis polymerization. The PDI pendant groups along the polymer backbone, studied by UV-vis absorption, fluorescence emission, and electron paramagnetic resonance spectroscopy in addition to electrochemical methods, show evidence of molecular aggregation and corresponding electronic coupling with neighboring groups, which forms pathways for efficient electron transport from one group to another in a specific reduced form. When n-doped, the title polymer shows redox conductivity of 5.4 × 10 -3 S cm -1 , comparable with crystalline PDI materials, and is therefore a promising material for use in organic electronics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mesostructure, electron paramagnetic resonance, and magnetic properties of polymer carbon black composites

NASA Astrophysics Data System (ADS)

Brosseau, C.; Molinié, P.; Boulic, F.; Carmona, F.

2001-06-01

Electron paramagnetic resonance (EPR) has now become firmly established as one of the methods of choice for analyzing the carbon network over a range of different volume fraction of the carbon black in the composite, i.e., below and above the respective conduction threshold concentration. In the present article, two types of carbon blacks, having very different primary structures, surface areas, and percolation thresholds, were used; Raven 7000 (of high surface area and high percolation threshold volume fraction) and Y50A (of low surface area and low percolation threshold volume fraction). A semiquantitative image analysis of the microstructure from transmission electron microscopy reveals information about the spatial distribution of the carbon aggregates and agglomerates inside the composite. We observe that the apparent surface of agglomerates increases significantly with increasing carbon black content for the two types of blacks investigated. Adsorbed oxygen on the carbon black cristallites and dynamic coalescence under mixing conditions can be responsible for the broadening of the dispersed phase surface distribution. The interagglomerate distance in two samples of concentrations f

Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by Fe impurities [Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by modest Fe substitution

DOE PAGES

Zhu, M.; Wang, Y.; Li, P. G.; ...

2017-05-19

We report the magnetic and electronic properties of the bilayer ruthenate Sr 3Ru 2O 7 upon Fe substitution for Ru. We find that Sr 3(Ru 1-xFe x) 2O 7 shows spin-glass-like phase below 4 K for x = 0.01 and commensurate E-type antiferromagnetically ordered insulating ground state characterized by the propagation vector q c = (0.25 0.25 0) for x ≥ 0.03, in contrast to the paramagnetic metallic state in the parent compound with strong spin fluctuations occurring at wave vectors q = (0.09 0 0) and (0.25 0 0). The observed antiferromagnetic ordering is quasitwo-dimensional with very short correlationmore » length along the c axis, a feature similar to the Mndoped Sr 3Ru 2O 7. Lastly, our results suggest that this ordered ground state is associated with the intrinsic magnetic instability in the pristine compound, which can be readily tipped by the local magnetic coupling between the 3d orbitals of the magnetic dopants and Ru 4d orbitals.« less

Electron interactions, spin-orbit coupling, intersite correlations in pyrochlore iridates: a comparison of single-site and cluster calculations

NASA Astrophysics Data System (ADS)

Wang, Runzhi; Go, Ara; Millis, Andrew

Pyrochlore iridates (R2 Ir2O7) are studied using density functional theory plus single-site and cluster dynamical mean-field theory (DFT+DMFT). The calculations include spin-orbit coupling. Significant differences between the single-site and cluster calculations are found. The single-site approximation fails to account for the properties of the paramagnetic insulator phase, in particular predicting a larger gap than found in experiments, while cluster calculations yield gaps consistent with transport data. A ground-state phase diagram is computed. Paramagnetic metal, metallic all-in/all-out (AIAO) and insulating AIAO phases are found. Tilted Weyl cones are observed in the AIAO metallic phase for a relatively wide range of interaction strength. Our paramagnetic calculations predict almost identical behaviors for the Y and Eu compound, conflicting with the strong material dependence reported in experiments. Inclusion of magnetic order restores the material difference. The physical origin of the difference is discussed. The results indicate that intersite effects, most likely of antiferromagnetic origin, play an important role in studying the physics of pyrochlore iridates. This work is supported by DOE-ER046169.

Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

DOE PAGES

Niklas, Jens; Poluektov, Oleg

2017-03-03

Understanding charge separation and charge transport at a molecular level is crucial for improving the efficiency of organic photovoltaic (OPV) cells. Under illumination of Bulk Heterojunction (BHJ) blends of polymers and fullerenes, various paramagnetic species are formed including polymer and fullerene radicals, radical pairs, and photoexcited triplet states. Light-induced Electron Paramagnetic Resonance (EPR) spectroscopy is ideally suited to study these states in BHJ due to its selectivity in probing the paramagnetic intermediates. Some advanced EPR techniques like light-induced ENDOR spectroscopy and pulsed techniques allow the determination of hyperfine coupling tensors, while high-frequency EPR allows the EPR signals of the individualmore » species to be resolved and their g-tensors to be determined. In these magnetic resonance parameters reveal details about the delocalization of the positive polaron on the various polymer donors which is important for the efficient charge separation in BHJ systems. Time-resolved EPR can contribute to the study of the dynamics of charge separation, charge transfer and recombination in BHJ by probing the unique spectral signatures of charge transfer and triplet states. Furthermore, the potential of the EPR also allows characterization of the intermediates and products of BHJ degradation.« less

Magnetic properties of Cu80Co20 and Cu80Co15Fe5 melt-spun ribbons

NASA Astrophysics Data System (ADS)

Rubinstein, Mark; Harris, V. G.; Das, B. N.; Koon, N. C.

1994-11-01

The magnetic properties of granular, annealed, melt-spun ribbons of the ``giant'' magnetoresistors, Cu80Co20 and Cu80Co15Fe5, have been studied by a variety of techniques. These include x-ray dfiffraction, electron microscopy, ferromagnetic resonance, SQUID magnetometry, Mössbauer-effect spectroscopy, and magnetoresistance. We utilize each of these measurements to reveal different aspects of the particle size distribution as a function of annealing temperatures. These melt-spun alloys require large magnetic fields for magnetic saturation, impairing their utility as magnetic sensors. However, the properties of melt-spun ribbons provide an understanding of why all granular magnetic materials are difficult to saturate. The magnetoresistance ratio of these alloys is maximized by a 500 °C anneal with Δρ/ρ~=14% at 4.2 K. The paramagnetic fraction determined by SQUID magnetometry at 4.2 K is 33% for this annealing temperature. The paramagnetic fraction determined by Mössbauer spectroscopy is 14% for samples annealed by 500 °C, and vanishes when the sample is annealed at 900 °C. The discrepancy between the two measurements of the paramagnetic fraction is due to the vastly different averaging times of the two techniques.

Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by Fe impurities [Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by modest Fe substitution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, M.; Wang, Y.; Li, P. G.

We report the magnetic and electronic properties of the bilayer ruthenate Sr 3Ru 2O 7 upon Fe substitution for Ru. We find that Sr 3(Ru 1-xFe x) 2O 7 shows spin-glass-like phase below 4 K for x = 0.01 and commensurate E-type antiferromagnetically ordered insulating ground state characterized by the propagation vector q c = (0.25 0.25 0) for x ≥ 0.03, in contrast to the paramagnetic metallic state in the parent compound with strong spin fluctuations occurring at wave vectors q = (0.09 0 0) and (0.25 0 0). The observed antiferromagnetic ordering is quasitwo-dimensional with very short correlationmore » length along the c axis, a feature similar to the Mndoped Sr 3Ru 2O 7. Lastly, our results suggest that this ordered ground state is associated with the intrinsic magnetic instability in the pristine compound, which can be readily tipped by the local magnetic coupling between the 3d orbitals of the magnetic dopants and Ru 4d orbitals.« less

EPR and optical absorption studies of paramagnetic molecular ion (VO2+) in Lithium Sodium Acid Phthalate single crystal

NASA Astrophysics Data System (ADS)

Subbulakshmi, N.; Kumar, M. Saravana; Sheela, K. Juliet; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.

2017-12-01

Electron Paramagnetic Resonance (EPR) spectroscopic studies of VO2+ ions as paramagnetic impurity in Lithium Sodium Acid Phthalate (LiNaP) single crystal have been done at room temperature on X-Band microwave frequency. The lattice parameter values are obtained for the chosen system from Single crystal X-ray diffraction study. Among the number of hyperfine lines in the EPR spectra only two sets are reported from EPR data. The principal values of g and A tensors are evaluated for the two different VO2+ sites I and II. They possess the crystalline field around the VO2+ as orthorhombic. Site II VO2+ ion is identified as substitutional in place of Na1 location and the other site I is identified as interstitial location. For both sites in LiNaP, VO2+ are identified in octahedral coordination with tetragonal distortion as seen from the spin Hamiltonian parameter values. The ground state of vanadyl ion in the LiNaP single crystal is dxy. Using optical absorption data the octahedral and tetragonal parameters are calculated. By correlating EPR and optical data, the molecular orbital bonding parameters have been discussed for both sites.

Matrix Isolation Spectroscopy and Photochemistry of Triplet 1,3-DIMETHYLPROPYNYLIDENE (MeC3Me)

NASA Astrophysics Data System (ADS)

Knezz, Stephanie N.; Waltz, Terese A.; Haenni, Benjamin C.; Burrmann, Nicola J.; McMahon, Robert J.

2015-06-01

Acetylenic carbenes and conjugated carbon chain molecules of the HCnH family are relevant to the study of combustion and chemistry in the interstellar medium (ISM). Propynylidene (HC3H) has been thoroughly studied and its structure and photochemistry determined. Here, we produce triplet diradical 1,3-dimethylpropynylidene (MeC3Me) photochemically from a precursor diazo compound in a cryogenic matrix (N2 or Ar) at 10 K, and spectroscopic analysis is carried out. The infrared, electronic absorption, and electron paramagnetic resonance spectra were examined in light of the parent (HC3H) system to ascertain the effect of alkyl substituents on delocalized carbon chains of this type. Computational analysis, EPR, and infrared analysis indicate a triplet ground state with a quasilinear structure. Infrared experiments reveal photochemical reaction to penten-3-yne upon UV irradiation. Further experimental and computational results pertaining to the structure and photochemistry will be presented. Seburg, R. A.; Patterson, E. V.; McMahon, R. J., Structure of Triplet Propynylidene (HCCCH) as Probed by IR, UV/vis, and EPR Spectroscopy of Isotopomers. Journal of the American Chemical Society 2009, 131 (26), 9442-9455.

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

In Vivo Application of Proton-Electron Double-Resonance Imaging

PubMed Central

Kishimoto, Shun; Krishna, Murali C.; Khramtsov, Valery V.; Utsumi, Hideo

2018-01-01

Abstract Significance: Proton-electron double-resonance imaging (PEDRI) employs electron paramagnetic resonance irradiation with low-field magnetic resonance imaging so that the electron spin polarization is transferred to nearby protons, resulting in higher signals. PEDRI provides information about free radical distribution and, indirectly, about the local microenvironment such as partial pressure of oxygen (pO2), tissue permeability, redox status, and acid-base balance. Recent Advances: Local acid-base balance can be imaged by exploiting the different resonance frequency of radical probes between R and RH+ forms. Redox status can also be imaged by using the loss of radical-related signal after reduction. These methods require optimized radical probes and pulse sequences. Critical Issues: High-power radio frequency irradiation is needed for optimum signal enhancement, which may be harmful to living tissue by unwanted heat deposition. Free radical probes differ depending on the purpose of PEDRI. Some probes are less effective for enhancing signal than others, which can reduce image quality. It is so far not possible to image endogenous radicals by PEDRI because low concentrations and broad line widths of the radicals lead to negligible signal enhancement. Future Directions: PEDRI has similarities with electron paramagnetic resonance imaging (EPRI) because both techniques observe the EPR signal, directly in the case of EPRI and indirectly with PEDRI. PEDRI provides information that is vital to research on homeostasis, development of diseases, or treatment responses in vivo. It is expected that the development of new EPR techniques will give insights into novel PEDRI applications and vice versa. Antioxid. Redox Signal. 28, 1345–1364. PMID:28990406

Increasing sensitivity of pulse EPR experiments using echo train detection schemes.

PubMed

Mentink-Vigier, F; Collauto, A; Feintuch, A; Kaminker, I; Tarle, V; Goldfarb, D

2013-11-01

Modern pulse EPR experiments are routinely used to study the structural features of paramagnetic centers. They are usually performed at low temperatures, where relaxation times are long and polarization is high, to achieve a sufficient Signal/Noise Ratio (SNR). However, when working with samples whose amount and/or concentration are limited, sensitivity becomes an issue and therefore measurements may require a significant accumulation time, up to 12h or more. As the detection scheme of practically all pulse EPR sequences is based on the integration of a spin echo--either primary, stimulated or refocused--a considerable increase in SNR can be obtained by replacing the single echo detection scheme by a train of echoes. All these echoes, generated by Carr-Purcell type sequences, are integrated and summed together to improve the SNR. This scheme is commonly used in NMR and here we demonstrate its applicability to a number of frequently used pulse EPR experiments: Echo-Detected EPR, Davies and Mims ENDOR (Electron-Nuclear Double Resonance), DEER (Electron-Electron Double Resonance|) and EDNMR (Electron-Electron Double Resonance (ELDOR)-Detected NMR), which were combined with a Carr-Purcell-Meiboom-Gill (CPMG) type detection scheme at W-band. By collecting the transient signal and integrating a number of refocused echoes, this detection scheme yielded a 1.6-5 folds SNR improvement, depending on the paramagnetic center and the pulse sequence applied. This improvement is achieved while keeping the experimental time constant and it does not introduce signal distortion. Copyright © 2013 Elsevier Inc. All rights reserved.

Electron paramagnetic resonance, scanning electron microscopy with energy dispersion X-ray spectrometry, X-ray powder diffraction, and NMR characterization of iron-rich fired clays.

PubMed

Presciutti, Federica; Capitani, Donatella; Sgamellotti, Antonio; Brunetti, Brunetto Giovanni; Costantino, Ferdinando; Viel, Stéphane; Segre, Annalaura

2005-12-01

The aim of this study is to clarify the structure of an iron-rich clay and the structural changes involved in the firing process as a preliminary step to get information on ancient ceramic technology. To this purpose, illite-rich clay samples fired at different temperatures were characterized using a multitechnique approach, i.e., by electron paramagnetic resonance, scanning electron microscopy with electron dispersion X-ray spectrometry, X-ray powder diffraction, magic angle spinning and multiple quantum magic angle spinning NMR. During firing, four main reaction processes occur: dehydration, dehydroxylation, structural breakdown, and recrystallization. When the results are combined from all characterization methods, the following conclusions could be obtained. Interlayer H2O is located close to aluminum in octahedral sites and is driven off at temperatures lower than 600 degrees C. Between 600 and 700 degrees C dehydroxylation occurs whereas, between 800 and 900 degrees C, the aluminum in octahedral sites disappears, due to the breakdown of the illite structure, and all iron present is oxidized to Fe3+. In samples fired at 1000 and 1100 degrees C iron clustering was observed as well as large single crystals of iron with the occurrence of ferro- or ferrimagnetic effects. Below 900 degrees C the aluminum in octahedral sites presents a continuous distribution of chemical shift, suggesting the presence of slightly distorted sites. Finally, over the whole temperature range, the presence of at least two tetrahedral aluminum sites was revealed, characterized by different values of the quadrupolar coupling constant.

Enhanced photocatalytic H2-production activity of C-dots modified g-C3N4/TiO2 nanosheets composites.

PubMed

Li, Yang; Feng, Xionghan; Lu, Zhexue; Yin, Hui; Liu, Fan; Xiang, Quanjun

2018-03-01

As a new carbon-based material, carbon dots (C-dots) have got widely preference because of its excellent electronic transfer capability. In this work, a novel ternary layered C-dots/g-C 3 N 4 /TiO 2 nanosheets (CGT) composite photocatalysts were prepared by impregnation precipitation methods. The optimal ternary CGT composite samples revealed high photocatalytic hydrogen evolution rate in triethanolamine aqueous solutions, which exceeded the rate of the optimal g-C 3 N 4 /TiO 2 composite sample by a factor of 5 times. The improved photocatalytic activity is owed to the positive effects of C-dots and layered heterojunction structure of TiO 2 nanosheets and g-C 3 N 4 sheets. C-dots in the CGT composites can serve as electron reservoirs to capture the photo-induced electrons. The well-defined layered heterojunction structure of CGT provides the intimate contact and the strong interaction of anatase TiO 2 nanosheets and g-C 3 N 4 sheets via face-to-face orientation, which restrains the recombination of photogenerated charge carriers, and thus enhances the photocatalytic H 2 -production activity. Electron paramagnetic resonance and transient photocurrent response proved the strong interaction and improved interfacial charge transfer of TiO 2 nanosheets and g-C 3 N 4 sheets, respectively. The mechanism of improving the photocatalytic H 2 -evolution activity was further confirmed by time-resolved fluorescence, electron paramagnetic resonance, transient photocurrent response and electrochemical impedance spectroscopy. Copyright © 2017 Elsevier Inc. All rights reserved.

Electron spin resonance microscopic imaging of oxygen concentration in cancer spheroids

NASA Astrophysics Data System (ADS)

Hashem, Mada; Weiler-Sagie, Michal; Kuppusamy, Periannan; Neufeld, Gera; Neeman, Michal; Blank, Aharon

2015-07-01

Oxygen (O2) plays a central role in most living organisms. The concentration of O2 is important in physiology and pathology. Despite the importance of accurate knowledge of the O2 levels, there is very limited capability to measure with high spatial resolution its distribution in millimeter-scale live biological samples. Many of the current oximetric methods, such as oxygen microelectrodes and fluorescence lifetime imaging, are compromised by O2 consumption, sample destruction, invasiveness, and difficulty to calibrate. Here, we present a new method, based on the use of the pulsed electron spin resonance (ESR) microimaging technique to obtain a 3D mapping of oxygen concentration in millimeter-scale biological samples. ESR imaging requires the incorporation of a suitable stable and inert paramagnetic spin probe into the desirable object. In this work, we use microcrystals of a paramagnetic spin probe in a new crystallographic packing form (denoted tg-LiNc-BuO). These paramagnetic species interact with paramagnetic oxygen molecules, causing a spectral line broadening that is linearly proportional to the oxygen concentration. Typical ESR results include 4D spatial-spectral images that give an indication about the oxygen concentration in different regions of the sample. This new oximetry microimaging method addresses all the problems mentioned above. It is noninvasive, sensitive to physiological oxygen levels, and easy to calibrate. Furthermore, in principle, it can be used for repetitive measurements without causing cell damage. The tissue model used in this research is spheroids of Human Colorectal carcinoma cell line (HCT-116) with a typical diameter of ∼600 μm. Most studies of the microenvironmental O2 conditions inside such viable spheroids carried out in the past used microelectrodes, which require an invasive puncturing of the spheroid and are also not applicable to 3D O2 imaging. High resolution 3D oxygen maps could make it possible to evaluate the relationship between morphological and physiological alterations in the spheroids, which would help understand the oxygen metabolism in solid tumors and its correlation with the susceptibility of tumors to various oncologic treatments.

Electron spin resonance microscopic imaging of oxygen concentration in cancer spheroids.

PubMed

Hashem, Mada; Weiler-Sagie, Michal; Kuppusamy, Periannan; Neufeld, Gera; Neeman, Michal; Blank, Aharon

2015-07-01

Oxygen (O2) plays a central role in most living organisms. The concentration of O2 is important in physiology and pathology. Despite the importance of accurate knowledge of the O2 levels, there is very limited capability to measure with high spatial resolution its distribution in millimeter-scale live biological samples. Many of the current oximetric methods, such as oxygen microelectrodes and fluorescence lifetime imaging, are compromised by O2 consumption, sample destruction, invasiveness, and difficulty to calibrate. Here, we present a new method, based on the use of the pulsed electron spin resonance (ESR) microimaging technique to obtain a 3D mapping of oxygen concentration in millimeter-scale biological samples. ESR imaging requires the incorporation of a suitable stable and inert paramagnetic spin probe into the desirable object. In this work, we use microcrystals of a paramagnetic spin probe in a new crystallographic packing form (denoted tg-LiNc-BuO). These paramagnetic species interact with paramagnetic oxygen molecules, causing a spectral line broadening that is linearly proportional to the oxygen concentration. Typical ESR results include 4D spatial-spectral images that give an indication about the oxygen concentration in different regions of the sample. This new oximetry microimaging method addresses all the problems mentioned above. It is noninvasive, sensitive to physiological oxygen levels, and easy to calibrate. Furthermore, in principle, it can be used for repetitive measurements without causing cell damage. The tissue model used in this research is spheroids of Human Colorectal carcinoma cell line (HCT-116) with a typical diameter of ∼600μm. Most studies of the microenvironmental O2 conditions inside such viable spheroids carried out in the past used microelectrodes, which require an invasive puncturing of the spheroid and are also not applicable to 3D O2 imaging. High resolution 3D oxygen maps could make it possible to evaluate the relationship between morphological and physiological alterations in the spheroids, which would help understand the oxygen metabolism in solid tumors and its correlation with the susceptibility of tumors to various oncologic treatments. Copyright © 2015 Elsevier Inc. All rights reserved.

Doping of wide-bandgap titanium-dioxide nanotubes: optical, electronic and magnetic properties

NASA Astrophysics Data System (ADS)

Alivov, Yahya; Singh, Vivek; Ding, Yuchen; Cerkovnik, Logan Jerome; Nagpal, Prashant

2014-08-01

Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO2) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications.Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO2) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications. Electronic supplementary information (ESI) available: See DOI: 10.1039/c4nr02417f

Models And Experiments Of Laminar Diffusion Flames In Non-Uniform Magnetic Fields

NASA Technical Reports Server (NTRS)

Baker, J.; Varagani, R.; Saito, K.

2003-01-01

Non-uniform magnetic fields affect laminar diffusion flames as a result of the paramagnetic and diamagnetic properties of the products and reactants. Paramagnetism is the weak attraction to a magnetic field a material exhibits as a result of permanent magnetic dipole moments in the atoms of the material. Diamagnetism is the weak repulsion to a magnetic field exhibited by a material due to the lack of permanent magnetic dipole moments in the atoms of a material. The forces associated with paramagnetic and diamagnetism are several orders of magnitude less than the forces associated with the more familiar ferromagnetism. A typical example of a paramagnetic gas is oxygen while hydrocarbon fuels and products of combustion are almost always diamagnetic. The fact that magnets can affect flame behavior has been recognized for more than one hundred years. Early speculation was that such behavior was due to the magnetic interaction with the ionized gases associated with a flame. Using a scaling analysis, it was later shown that for laminar diffusion flames the magnetic field/ionized gas interaction was insignificant to the paramagnetic and diamagnetic influences. In this effort, the focus has been on examining laminar diffusion slot flames in the presence of non-uniform upward decreasing magnetic fields produced using permanent magnets. The principal reason for choosing slot flames was mathematical models of such flames show an explicit dependence on gravitational body forces, in the buoyancy-controlled regime, and an applied magnetic field would also impose a body force. In addition, the behavior of such flames was more easily visualized while maintaining the symmetry of the two-dimensional problem whereas it would have been impossible to obtain a symmetric magnetic field around a circular flame and still visually record the flame height and shape along the burner axis. The motivation for choosing permanent magnets to produce the magnetic fields was the assumption that space-related technologies based on the knowledge gained during this investigation would more likely involve permanent magnets as opposed to electromagnets. While no analysis has been done here to quantify the impact that an electric field, associated with an electromagnetic, would have relative to the paramagnetic and diamagnetic interactions, by using permanent magnets this potential effect was completely eliminated and thus paramagnetic and diamagnetic effects were isolated.

New insight into the promoting role of process on the CeO₂-WO₃/TiO₂ catalyst for NO reduction with NH₃ at low-temperature.

PubMed

Zhang, Shule; Zhong, Qin; Shen, Yuge; Zhu, Li; Ding, Jie

2015-06-15

This study aimed at investigating the reason of high catalytic activity for CeO2-WO3/TiO2 catalyst from the aspects of WO3 interaction with other species and the NO oxidation process. Analysis by X-ray diffractometry, photoluminescence spectra, diffuse reflectance UV-visible, X-ray photoelectron spectroscopy, density functional theory calculations, electron paramagnetic resonance spectroscopy, temperature-programmed-desorption of NO and in situ diffuse reflectance infrared transform spectroscopy showed that WO3 could interact with CeO2 to improve the electron gaining capability of CeO2 species. In addition, WO3 species acted as electron donating groups to transfer the electrons to CeO2 species. The two aspects enhanced the formation of reduced CeO2 species to improve the formation of superoxide ions. Furthermore, the Ce species were the active sites for the NO adsorption and the superoxide ions over the catalyst needed oxidizing the adsorbed NO to improve the NO oxidation. This process was responsible for the high catalytic activity of CeO2-WO3/TiO2 catalyst. Copyright © 2015 Elsevier Inc. All rights reserved.

Radiation-induced defects in manganese-doped lithium tetraborate phosphor.

PubMed

Annalakshmi, O; Jose, M T; Madhusoodanan, U; Sridevi, J; Venkatraman, B; Amarendra, G; Mandal, A B

2015-01-01

Lithium tetraborate doped with manganese synthesised by solid-state sintering technique exhibits a dosimetric peak at 280°C. The high-temperature glow curve results in no fading for three months. The sensitivity of Li2B4O7:Mn is determined to be 0.9 times that of TLD-100. The infrared spectrum of this phosphor indicates the presence of bond vibrations corresponding to BO4 tetrahedral and BO3 triangles. The mechanism for thermoluminescence in this phosphor was proposed based on the thermoluminescence (TL) emission spectra, kinetic analysis of TL glow curves and electron paramagnetic resonance (EPR) measurements on non-irradiated and gamma-irradiated phosphors. It was identified that oxygen vacancies and Boron oxygen hole centre (BOHC) are the electron and hole trap centres for TL in this phosphor. When the phosphor is heated, the electrons are released from the electron trap and recombine with the trapped holes. The excitation energy during the recombination is transferred to the nearby Mn(2+) ions, which emit light at 580 nm. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Nuclear spin relaxation in ligands outside of the first coordination sphere in a gadolinium (III) complex: Effects of intermolecular forces

NASA Astrophysics Data System (ADS)

Kruk, Danuta; Kowalewski, Jozef

2002-07-01

This article describes paramagnetic relaxation enhancement (PRE) in systems with high electron spin, S, where there is molecular interaction between a paramagnetic ion and a ligand outside of the first coordination sphere. The new feature of our treatment is an improved handling of the electron-spin relaxation, making use of the Redfield theory. Following a common approach, a well-defined second coordination sphere is assumed, and the PRE contribution from these more distant and shorter-lived ligands is treated in a way similar to that used for the first coordination sphere. This model is called "ordered second sphere," OSS. In addition, we develop here a formalism similar to that of Hwang and Freed [J. Chem. Phys. 63, 4017 (1975)], but accounting for the electron-spin relaxation effects. We denote this formalism "diffuse second sphere," DSS. The description of the dynamics of the intermolecular dipole-dipole interaction is based on the Smoluchowski equation, with a potential of mean force related to the radial distribution function. We have used a finite-difference method to calculate numerically a correlation function for translational motion, taking into account the intermolecular forces leading to an arbitrary radial distribution of the ligand protons. The OSS and DSS models, including the Redfield description of the electron-spin relaxation, were used to interpret the PRE in an aqueous solution of a slowly rotating gadolinium (III) complex (S=7/2) bound to a protein.

Study on dioxygen reduction by mutational modifications of the hydrogen bond network leading from bulk water to the trinuclear copper center in bilirubin oxidase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morishita, Hirotoshi; Kurita, Daisuke; Kataoka, Kunishige

2014-07-18

Highlights: • Proton transport pathway in bilirubin oxidase was mutated. • Two intermediates in the dioxygen reduction steps were trapped and characterized. • A specific glutamate for dioxygen reduction by multicopper oxidases was identified. - Abstract: The hydrogen bond network leading from bulk water to the trinuclear copper center in bilirubin oxidase is constructed with Glu463 and water molecules to transport protons for the four-electron reduction of dioxygen. Substitutions of Glu463 with Gln or Ala were attributed to virtually complete loss or significant reduction in enzymatic activities due to an inhibition of the proton transfer steps to dioxygen. The singlemore » turnover reaction of the Glu463Gln mutant afforded the highly magnetically interacted intermediate II (native intermediate) with a broad g = 1.96 electron paramagnetic resonance signal detectable at cryogenic temperatures. Reactions of the double mutants, Cys457Ser/Glu463Gln and Cys457Ser/Glu463Ala afforded the intermediate I (peroxide intermediate) because the type I copper center to donate the fourth electron to dioxygen was vacant in addition to the interference of proton transport due to the mutation at Glu463. The intermediate I gave no electron paramagnetic resonance signal, but the type II copper signal became detectable with the decay of the intermediate I. Structural and functional similarities between multicopper oxidases are discussed based on the present mutation at Glu463 in bilirubin oxidase.« less

Mechanistic insights into energy conservation by flavin-based electron bifurcation.

PubMed

Lubner, Carolyn E; Jennings, David P; Mulder, David W; Schut, Gerrit J; Zadvornyy, Oleg A; Hoben, John P; Tokmina-Lukaszewska, Monika; Berry, Luke; Nguyen, Diep M; Lipscomb, Gina L; Bothner, Brian; Jones, Anne K; Miller, Anne-Frances; King, Paul W; Adams, Michael W W; Peters, John W

2017-06-01

The recently realized biochemical phenomenon of energy conservation through electron bifurcation provides biology with an elegant means to maximize utilization of metabolic energy. The mechanism of coordinated coupling of exergonic and endergonic oxidation-reduction reactions by a single enzyme complex has been elucidated through optical and paramagnetic spectroscopic studies revealing unprecedented features. Pairs of electrons are bifurcated over more than 1 volt of electrochemical potential by generating a low-potential, highly energetic, unstable flavin semiquinone and directing electron flow to an iron-sulfur cluster with a highly negative potential to overcome the barrier of the endergonic half reaction. The unprecedented range of thermodynamic driving force that is generated by flavin-based electron bifurcation accounts for unique chemical reactions that are catalyzed by these enzymes.

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

2015-03-04

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.

Emergent Interfacial Ferromagnetism in CaMnO3-based Superlattices

NASA Astrophysics Data System (ADS)

Grutter, Alexander

2014-03-01

Interfaces of complex oxide materials provide a rich playground not only for the exploration of properties not found in the bulk constituents but also for the development of functional interfaces to be incorporated in spintronic applications. Emergent interfacial magnetic phenomena have been of great interest but surprisingly there have been few examples of emergent interfacial ferromagnetism. In this talk, I will describe our recent work on the stabilization of ferromagnetism in CaMnO3-based superlattices. We have demonstrated ferromagnetism at the interface between the antiferromagnetic insulator CaMnO3 and a paramagnetic metallic layer, including CaRuO3 and LaNiO3. Theoretically the ferromagnetism has been attributed to an interfacial double exchange interaction among the interfacial Mn ions that is mediated by itinerant electrons from the paramagnetic metallic layer. Through polarized neutron reflectivity and observation of exchange bias, we have demonstrated that the ferromagnetism comes from Mn ions in a single unit cell at the interfaces just as theory has predicted. We have also demonstrated that the metallicity of the paramagnetic layer is critical in stabilizing ferromagnetism at the interface and that the interfacial ferromagnetism can be suppressed by suppressing the metallicity of the paramagnetic layer. Despite the agreement with theory, there remain open questions as to the magnetic interactions among the interfacial ferromagnetic layers. For example, the saturated magnetic moment modulates as a function of the thickness of both the CaMnO3 and paramagnetic metal layers. The origins of this oscillation are not well understood and may stem from either structural effects or long-range oscillatory magnetic coupling interactions reminiscent of RKKY interactions. Evidence of the doubling of the unit cell and long range antiferromagnetic correlations support these speculations. This work was supported by the U.S. Department of Energy, Office of Science, Division of Materials Sciences and Engineering, under Contract # DE-AC05-76RL01830 and DE-SC0008505.

ESEEM of industrial silica-bearing powders: reactivity of defects during wet processing in the ceramics production

NASA Astrophysics Data System (ADS)

Romanelli, Maurizio; Di Benedetto, Francesco; Fornaciai, Gabriele; Innocenti, Massimo; Montegrossi, Giordano; Pardi, Luca A.; Zoleo, Alfonso; Capacci, Fabio

2015-05-01

A study is undertaken to ascertain whether changes in the speciation of inorganic radicals are occurring during the ceramic industrial production that involves abundant silica powders as raw material. Industrial dusts were sampled in two ceramic firms, immediately after the wet mixing stage, performed with the aid of a relevant pressure. The dusts were then characterised by means of X-ray diffraction, analysis of the trace elements through chemical methods, granulometry, continuous-wave electron paramagnetic resonance (EPR) and pulsed electron spin echo envelope modulation (ESEEM) spectroscopies. The results of the characterisation point to a relevant change in the speciation of the two samples; namely, a prevailing contribution due to an inorganic radical different from that pertaining to pure quartz is pointed out. The combined interpretation of EPR and ESEEM data suggests the attribution of the main paramagnetic contribution to the A-centre in kaolinite, a constituent that is added to pure quartz at the initial stage of the ceramic production. In one of the two samples, a second weak EPR signal is attributed to the quartz's hAl species. By taking into account the relative quantities of quartz and kaolinite mixed in the two samples, and the relative abundances of the two radical species, we propose that the partial or complete suppression of the hAl species in favour of the A-centre of kaolinite has occurred. Although this change is apparently fostered by the mixture between quartz and another radical-bearing raw material, kaolinite, the suppression of the hAl centre of quartz is ascribed to the role played by the pressure and the wet environment during the industrial mixing procedure. This suppression provides a net change of radical speciation associated with quartz, when this phase is in contact with workers' respiratory system.

Electron Paramagnetic Resonance Studies of Spin-Labeled Hemoglobins and Their Implications to the Nature of Cooperative Oxygen Binding to Hemoglobin*

PubMed Central

Ho, Chien; Baldassare, Joseph J.; Charache, Samuel

1970-01-01

The spin label technique has been used to study human hemoglobins A, F, Zürich, and Chesapeake as a function of carbon monoxide saturation. The experimental results suggest that the changes in the electron paramagnetic resonance spectra of hemoglobin labeled with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)iodoacetamide depend on the state of ligation of more than one heme group. For those hemoglobins with full or large cooperative ligand binding (such as A, F, and Zürich), there is a lack of isosbestic points in the spectra as a function of CO saturation. However, for those hemoglobins with little or no cooperative ligand binding (such as Chesapeake and methemoglobins), there is a sharp set of isosbestic points. These findings confirm and extend the early work of McConnell and co-workers. The absence of a set of isosbestic points in those hemoglobins with full cooperative ligand binding is consistent with the sequential model of Koshland, Némethy, and Filmer for cooperative oxygen binding to hemoglobin. The present results, with hemoglobin variants having known amino acid substitutions, also focus on the importance of the interactions among the amino acid residues located at α1-β2 or α2-β1 subunit contacts for the functioning of hemoglobin as an oxygen carrier. In addition, the resonance spectra of the spin label are very sensitive to small structural variations around the heme groups in the β- or γ-chains where the labels are attached. The results of the spin label experiment are discussed in relation to recent findings on the mechanism of oxygenation of hemoglobin from the nuclear magnetic resonance studies of this laboratory and the x-ray crystallographic analysis of Perutz and co-workers. PMID:4316679

In Vivo Formation of Electron Paramagnetic Resonance-Detectable Nitric Oxide and of Nitrotyrosine Is Not Impaired during Murine Leishmaniasis

PubMed Central

Giorgio, Selma; Linares, Edlaine; Ischiropoulos, Harry; Von Zuben, Fernando José; Yamada, Aureo; Augusto, Ohara

1998-01-01

Recent studies have provided evidence for a dual role of nitric oxide (NO) during murine leishmaniasis. To explore this problem, we monitored the formation of NO and its derived oxidants during the course of Leishmania amazonensis infection in tissues of susceptible (BALB/c) and relatively resistant (C57BL/6) mice. NO production was detected directly by low-temperature electron paramagnetic resonance spectra of animal tissues. Both mouse strains presented detectable levels of hemoglobin nitrosyl (HbNO) complexes and of heme nitrosyl and iron-dithiol-dinitrosyl complexes in the blood and footpad lesions, respectively. Estimation of the nitrosyl complex levels demonstrated that most of the NO is synthesized in the footpad lesions. In agreement, immunohistochemical analysis of the lesions demonstrated the presence of nitrotyrosine in proteins of macrophage vacuoles and parasites. Since macrophages lack myeloperoxidase, peroxynitrite is likely to be the nitrating NO metabolite produced during the infection. The levels of HbNO complexes in the blood reflected changes occurring during the infection such as those in parasite burden and lesion size. The maximum levels of HbNO complexes detected in the blood of susceptible mice were higher than those of C57BL/6 mice but occurred at late stages of infection and were accompanied by the presence of bacteria in the cutaneous lesions. The results indicate that the local production of NO is an important mechanism for the elimination of parasites if it occurs before the parasite burden becomes too high. From then on, elevated production of NO and derived oxidants aggravates the inflammatory process with the occurrence of a hypoxic environment that may favor secondary infections. PMID:9453645

Thermodynamic properties of paramagnetic α - and β -Mn from first principles: The effect of transverse spin fluctuations

NASA Astrophysics Data System (ADS)

Ehteshami, Hossein; Korzhavyi, Pavel A.

2017-12-01

First-principles-based thermodynamic modeling of cubic α and β phases of Mn represent a challenge due to their structural complexity and the necessity of simultaneous treatment of several types of disorder (electronic, magnetic, and vibrational) that have very different characteristic time scales. Here we employ mean-field theoretical models to describe the different types of disorder and then we connect each layer of theory to the others using the adiabatic principle of separating faster and slower degrees of freedom. The slowest (vibrational) degrees of freedom are treated using the Moruzzi, Janak, and Schwarz formalism [Phys. Rev. B 37, 790 (1988), 10.1103/PhysRevB.37.790] of the Debye-Grüneisen model parametrized based on the first-principles calculated equation of state which includes the free-energy contributions due to the fast (electronic and magnetic) degrees of freedom via the Fermi-Dirac distribution function and a mean-field theory of transverse spin fluctuations. The magnetic contribution due to transverse spin fluctuations has been computed self-consistently within the disordered local moment picture of the paramagnetic state. The obtained results for thermodynamic properties such as lattice parameter, linear thermal expansion coefficient, and heat capacity of both phases show a good agreement with available experimental data. We also tested the assumption about the nature (localized versus delocalized) of magnetic moment on site IV in α -Mn and site I in β -Mn on the thermodynamic properties of these two phases. Similar to the findings of experimental studies, we conclude that magnetic moment on site IV in α -Mn is not of a localized character. However, a similar analysis suggests that the magnetic moment of site I in β -Mn should be treated as localized.

Solution NMR characterization of magnetic/electronic properties of azide and cyanide-inhibited substrate complexes of human heme oxygenase: implications for steric ligand tilt.

PubMed

Peng, Dungeng; Ogura, Hiroshi; Ma, Li-Hua; Evans, John P; de Montellano, Paul R Ortiz; La Mar, Gerd N

2013-04-01

Solution 2D (1)H NMR was carried out on the azide-ligated substrate complex of human heme oxygenase, hHO, to provide information on the active site molecular structure, chromophore electronic/magnetic properties, and the distal H-bond network linked to the exogenous ligand by catalytically relevant oriented water molecules. While 2D NMR exhibited very similar patterns of two-dimensional nuclear Overhauser spectroscopy cross peaks of residues with substrate and among residues as the previously characterized cyanide complex, significant, broadly distributed chemical shift differences were observed for both labile and non-labile protons. The anisotropy and orientation of the paramagnetic susceptibility tensor, χ, were determined for both the azide and cyanide complexes. The most significant difference observed is the tilt of the major magnetic axes from the heme normal, which is only half as large for the azide than cyanide ligand, with each ligand tilted toward the catalytically cleaved α-meso position. The difference in chemical shifts is quantitatively correlated with differences in dipolar shifts in the respective complexes for all but the distal helix. The necessity of considering dipolar shifts, and hence determination of the orientation/anisotropy of χ, in comparing chemical shifts involving paramagnetic complexes, is emphasized. The analysis shows that the H-bond network cannot detect significant differences in H-bond acceptor properties of cyanide versus azide ligands. Lastly, significant retardation of distal helix labile proton exchange upon replacing cyanide with azide indicates that the dynamic stability of the distal helix is increased upon decreasing the steric interaction of the ligand with the distal helix. Copyright © 2013. Published by Elsevier Inc.

Enzymatic cellulose oxidation is linked to lignin by long-range electron transfer

PubMed Central

Westereng, Bjørge; Cannella, David; Wittrup Agger, Jane; Jørgensen, Henning; Larsen Andersen, Mogens; Eijsink, Vincent G.H.; Felby, Claus

2015-01-01

Enzymatic oxidation of cell wall polysaccharides by lytic polysaccharide monooxygenases (LPMOs) plays a pivotal role in the degradation of plant biomass. While experiments have shown that LPMOs are copper dependent enzymes requiring an electron donor, the mechanism and origin of the electron supply in biological systems are only partly understood. We show here that insoluble high molecular weight lignin functions as a reservoir of electrons facilitating LPMO activity. The electrons are donated to the enzyme by long-range electron transfer involving soluble low molecular weight lignins present in plant cell walls. Electron transfer was confirmed by electron paramagnetic resonance spectroscopy showing that LPMO activity on cellulose changes the level of unpaired electrons in the lignin. The discovery of a long-range electron transfer mechanism links the biodegradation of cellulose and lignin and sheds new light on how oxidative enzymes present in plant degraders may act in concert. PMID:26686263

Characterization of vanadium ion uptake in sulfonated diels alder poly(phenylene) membranes

DOE PAGES

Lawton, Jamie; Jones, Amanda; Tang, Zhijiang; ...

2015-11-28

Sulfonated diels alder poly(phenylene) (SDAPP), alternative aromatic hydrocarbon membranes for vanadium redox flow batteries (VRFBs) are characterized using electron paramagnetic resonance (EPR). Membranes soaked in sulfuric acid and vanadyl sulfate are analyzed to determine the membrane environment in which the vanadyl ion (VO 2+) diffuses in the membranes. These results are compared to Nafion 117 membranes. In contrast to Nafion, the VO 2+ in SDAPP membranes exists in two different environments. The results of analysis of rotational diffusion determined from fits the EPR spectral lineshapes in comparison with previously reported permeation studies and measurements of partitioning functions reported here suggestmore » that the diffusion pathways in SDAPP are very different than in Nafion.« less

Low temperature phase of the trigonal RbIn(MoO4)2 crystal

NASA Astrophysics Data System (ADS)

Zapart, W.; Zapart, M. B.; Schranz, W.; Reinecker, M.

2013-02-01

The present article is devoted to a new low-temperature phase transition found at about T pt = 84 K in the layered RbIn(MoO4)2 crystal. This phase transition is well proved by dynamical mechanical analysis through anomalies in the temperature behaviour of both real and imaginary parts of the Young's modulus. From the polarizing microscope observations it was found that below T pt the ferroelastic phase disappears. This transition has also been seen through strong changes in the shape of the electron paramagnetic resonance lines. EPR studies, performed in the liquid nitrogen temperature, yield evidence of strong rebuilding of the crystal unit cell in comparison with that of the high temperature paraelastic phase.

Influence of deep defects on device performance of thin-film polycrystalline silicon solar cells

NASA Astrophysics Data System (ADS)

Fehr, M.; Simon, P.; Sontheimer, T.; Leendertz, C.; Gorka, B.; Schnegg, A.; Rech, B.; Lips, K.

2012-09-01

Employing quantitative electron-paramagnetic resonance analysis and numerical simulations, we investigate the performance of thin-film polycrystalline silicon solar cells as a function of defect density. We find that the open-circuit voltage is correlated to the density of defects, which we assign to coordination defects at grain boundaries and in dislocation cores. Numerical device simulations confirm the observed correlation and indicate that the device performance is limited by deep defects in the absorber bulk. Analyzing the defect density as a function of grain size indicates a high concentration of intra-grain defects. For large grains (>2 μm), we find that intra-grain defects dominate over grain boundary defects and limit the solar cell performance.

EPR investigation of gamma-irradiated L-citrulline, α-methyl-DL-serine, 3-fluoro-DL-valine and N-acetyl-L-cysteine

NASA Astrophysics Data System (ADS)

Osmanoğlu, Y. Emre; Sütçü, Kerem; Başkan, M. Halim

2017-02-01

The spectroscopic parameters of the paramagnetic species produced in gamma-irradiated L-citrulline, α-methyl-DL-serine, 3-fluoro-DL-valine and N-acetyl-L-cysteine were investigated at room temperature at a dose of 20 kGy by using EPR technique. The paramagnetic species were attributed to NH2CONH(CH2)3ĊNH2COOH, HOCH2ĊCH3COOH and HOĊHCCH3NH2COOH, CH3CH3ĊCHNH2COOH and SHCH2ĊNHCOCH3COOH radicals, respectively. EPR data of the unpaired electron with the environmental protons and 14N nucleus were used to characterize the contributing radicals produced in gamma irradiated compounds. In this paper, the stability of these compounds at room temperature after irradiation was also studied.

EPR oximetry in three spatial dimensions using sparse spin distribution

NASA Astrophysics Data System (ADS)

Som, Subhojit; Potter, Lee C.; Ahmad, Rizwan; Vikram, Deepti S.; Kuppusamy, Periannan

2008-08-01

A method is presented to use continuous wave electron paramagnetic resonance imaging for rapid measurement of oxygen partial pressure in three spatial dimensions. A particulate paramagnetic probe is employed to create a sparse distribution of spins in a volume of interest. Information encoding location and spectral linewidth is collected by varying the spatial orientation and strength of an applied magnetic gradient field. Data processing exploits the spatial sparseness of spins to detect voxels with nonzero spin and to estimate the spectral linewidth for those voxels. The parsimonious representation of spin locations and linewidths permits an order of magnitude reduction in data acquisition time, compared to four-dimensional tomographic reconstruction using traditional spectral-spatial imaging. The proposed oximetry method is experimentally demonstrated for a lithium octa- n-butoxy naphthalocyanine (LiNc-BuO) probe using an L-band EPR spectrometer.

Filling-enforced nonsymmorphic Kondo semimetals in two dimensions

NASA Astrophysics Data System (ADS)

Pixley, J. H.; Lee, SungBin; Brandom, B.; Parameswaran, S. A.

2017-08-01

We study the competition between Kondo screening and frustrated magnetism on the nonsymmorphic Shastry-Sutherland Kondo lattice at a filling of two conduction electrons per unit cell. This model is known to host a set of gapless partially Kondo screened phases intermediate between the Kondo-destroyed paramagnet and the heavy Fermi liquid. Based on crystal symmetries, we argue that (i) both the paramagnet and the heavy Fermi liquid are semimetals protected by a glide symmetry; and (ii) partial Kondo screening breaks the symmetry, removing this protection and allowing the partially Kondo screened phase to be deformed into a Kondo insulator via a Lifshitz transition. We confirm these results using large-N mean-field theory and then use nonperturbative arguments to derive a generalized Luttinger sum rule constraining the phase structure of two-dimensional nonsymmorphic Kondo lattices beyond the mean-field limit.

Weak arrest-like and field-driven first order magnetic phase transitions of itinerant Fe3Ga4 revealed by magnetization and magnetoresistance isotherms

NASA Astrophysics Data System (ADS)

Samatham, S. Shanmukharao; Suresh, K. G.

2017-01-01

The detailed magnetic study of complex 3d-electron based Fe3Ga4 is reported. It undergoes paramagnetic to antiferromagnetic (TN) and antiferromagnetic to ferromagnetic (TC) transitions respectively around 380 and 70 K. The thermal hysteresis of field-cooled cooling (FCC) and field-cooled warming (FCW) hints at first order phase transition below Curie temperature. A weak phase coexistence of ferro and antiferromagnetic phases is suggested by exploring the arrest-like first-order phenomenon. In the intermediate temperature range, field-driven metamagnetic transition from antiferro to ferromagnetic phase is confirmed. Further bringing the system very near to TN, field-induced transitions disappear and above TN predominant paramagnetic contribution is evident. The magnetic H-T phase diagram distinguishing different magnetic phases of Fe3Ga4 is obtained.

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.

Magnetic properties of graphene quantum dots

NASA Astrophysics Data System (ADS)

Espinosa-Ortega, T.; Luk'yanchuk, I. A.; Rubo, Y. G.

2013-05-01

Using the tight-binding approximation we calculated the diamagnetic susceptibility of graphene quantum dots (GQDs) of different geometrical shapes and characteristic sizes of 2-10 nm, when the magnetic properties are governed by the electron edge states. Two types of edge states can be discerned: the zero-energy states (ZESs), located exactly at the zero-energy Dirac point, and the dispersed edge states (DESs), with the energy close but not exactly equal to zero. DESs are responsible for a temperature-independent diamagnetic response, while ZESs provide a temperature-dependent spin paramagnetism. Hexagonal, circular, and randomly shaped GQDs contain mainly DESs, and, as a result, they are diamagnetic. The edge states of the triangular GQDs are of ZES type. These dots reveal the crossover between spin paramagnetism, dominating for small dots and at low temperatures, and orbital diamagnetism, dominating for large dots and at high temperatures.

Anti-HER2 immunoliposomes for selective delivery of electron paramagnetic resonance imaging probes to HER2-overexpressing breast tumor cells

PubMed Central

Burks, Scott R.; Macedo, Luciana F.; Barth, Eugene D.; Tkaczuk, Katherine H.; Martin, Stuart S.; Rosen, Gerald M.; Halpern, Howard J.; Brodie, Angela M.

2014-01-01

Electron paramagnetic resonance (EPR) imaging is an emerging modality that can detect and localize paramagnetic molecular probes (so-called spin probes) in vivo. We previously demonstrated that nitroxide spin probes can be encapsulated in liposomes at concentrations exceeding 100 mM, at which nitroxides exhibit a concentration-dependent quenching of their EPR signal that is analogous to the self-quenching of fluorescent molecules. Therefore, intact liposomes encapsulating high concentrations of nitroxides exhibit greatly attenuated EPR spectral signals, and endocytosis of such liposomes represents a cell-activated contrast-generating mechanism. After endocytosis, the encapsulated nitroxide is liberated and becomes greatly diluted in the intracellular milieu. This dequenches the nitroxides to generate a robust intracellular EPR signal. It is therefore possible to deliver a high concentration of nitroxides to cells while minimizing background signal from unendocytosed liposomes. We report here that intracellular EPR signal can be selectively generated in a specific cell type by exploiting its expression of Human Epidermal Growth Factor Receptor 2 (HER2). When targeted by anti-HER2 immunoliposomes encapsulating quenched nitroxides, Hc7 cells, which are novel HER2-overexpressing cells derived from the MCF7 breast tumor cell line, endocytose the liposomes copiously, in contrast to the parent MCF7 cells or control CV1 cells, which do not express HER2. HER2-dependent liposomal delivery enables Hc7 cells to accumulate 750 μM nitroxide intracellularly. Through the use of phantom models, we verify that this concentration of nitroxides is more than sufficient for EPR imaging, thus laying the foundation for using EPR imaging to visualize HER2-overexpressing Hc7 tumors in animals. PMID:20066490

Investigating electron spin resonance spectroscopy of a spin-½ compound in a home-built spectrometer

NASA Astrophysics Data System (ADS)

Sarkar, Jit; Roy, Subhadip; Singh, Jitendra Kumar; Singh, Sourabh; Chakraborty, Tanmoy; Mitra, Chiranjib

2018-05-01

In this work we report electron spin resonance (ESR) measurements performed on NH4CuPO4.H2O, a Heisenberg spin ½ dimer compound. We carried out the experiments both at room temperature and at 78 K, which are well above the antiferromagnetic ordering temperature of the system where the paramagnetic spins have a dominant role in determining its magnetic behavior. We performed the measurements in a home built custom designed continuous wave electron spin resonance (CW-ESR) spectrometer. By analyzing the experimental data, we were able to quantify the Landé g-factor and the ESR line-width of the sample.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovacs, Andras; Ney, A.; Duchamp, Martial

2013-12-23

We have studied planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al2O3) and the Co:ZnO/Al2O3 interface structure at atomic resolution using aberration-corrected transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Comparing Co:ZnO samples deposited by pulsed laser deposition and reactive magnetron sputtering, both exhibit extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers at the interface.. In addition, we have measured the local strain which reveals the lattice distortion around the stacking faults.

EPR/ENDOR and Theoretical Study of the Jahn-Teller-Active [HIPTN3N]MoVL Complexes (L = N-, NH).

PubMed

Sharma, Ajay; Roemelt, Michael; Reithofer, Michael; Schrock, Richard R; Hoffman, Brian M; Neese, Frank

2017-06-19

The molybdenum trisamidoamine (TAA) complex [Mo] {[3,5-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 3 NCH 2 CH 2 N]Mo} carries out catalytic reduction of N 2 to ammonia (NH 3 ) by protons and electrons at room temperature. A key intermediate in the proposed [Mo] nitrogen reduction cycle is nitridomolybdenum(VI), [Mo(VI)]N. The addition of [e - /H + ] to [Mo(VI)]N to generate [Mo(V)]NH might, in principle, follow one of three possible pathways: direct proton-coupled electron transfer; H + first and then e - ; e - and then H + . In this study, the paramagnetic Mo(V) intermediate {[Mo]N} - and the [Mo]NH transfer product were generated by irradiating the diamagnetic [Mo]N and {[Mo]NH} + Mo(VI) complexes, respectively, with γ-rays at 77 K, and their electronic and geometric structures were characterized by electron paramagnetic resonance and electron nuclear double resonance spectroscopies, combined with quantum-chemical computations. In combination with previous X-ray studies, this creates the rare situation in which each one of the four possible states of [e - /H + ] delivery has been characterized. Because of the degeneracy of the electronic ground states of both {[Mo(V)]N} - and [Mo(V)]NH, only multireference-based methods such as the complete active-space self-consistent field (CASSCF) and related methods provide a qualitatively correct description of the electronic ground state and vibronic coupling. The molecular g values of {[Mo]N} - and [Mo]NH exhibit large deviations from the free-electron value g e . Their actual values reflect the relative strengths of vibronic and spin-orbit coupling. In the course of the computational treatment, the utility and limitations of a formal two-state model that describes this competition between couplings are illustrated, and the implications of our results for the chemical reactivity of these states are discussed.

REVIEW ARTICLE: Unconventional isotope effects in the high-temperature cuprate superconductors

NASA Astrophysics Data System (ADS)

Zhao, Guo-meng; Keller, H.; Conder, K.

2001-07-01

We review various isotope effects in the high-Tc cuprate superconductors to assess the role of the electron-phonon interaction in the basic physics of these materials. Of particular interest are the unconventional isotope effects on the supercarrier mass, on the charge-stripe formation temperature, on the pseudogap formation temperature, on the electron paramagnetic resonance (EPR) linewidth, on the spin-glass freezing temperature and on the antiferromagnetic ordering temperature. The observed unconventional isotope effects strongly suggest that lattice vibrations play an important role in the microscopic pairing mechanism of high-temperature superconductivity.

Multidisciplinary Approach to the Science and Technology of Sub-Micron Electronics.

DTIC Science & Technology

1987-03-10

19densities as high as 3x1O1 2 electrons cm- 2 could be obtained with GaAs doping densities on the order of 3x1O18 cm-3 . Many-body effects are shown to be...heterinterfaces include studies of the effects of paramagnetic impurities and structural disorder at the interface of mismatched Mo-Ni superlattices in Dr...inverted mecelles. The ’caoing’ effect of the inverted micelles ensures a narrow distribution of particle size, and a uniform composition. This

Iron(III)-oxo centers on TiO{sub 2} for visible light photocatalysis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Libera, J. A.; Elam, J. W.; Sather, N. F.

Isolated iron(III)-oxo clusters were synthesized onto TiO{sub 2} using atomic layer deposition. The Fe{sub x}O{sub y}/TiO{sub 2} nanocomposites have unique properties that enable not only absorption of visible light, but efficient photocatalysis as demonstrated by methylene blue degradation. The localization of photogenerated electrons in core TiO{sub 2} nanocrystallites upon visible light excitation demonstrates coupling of conduction bands of mixed oxides. The redox properties of photogenerated charges in nanocomposites were studied using in situ electron paramagnetic resonance spectroscopy.

The human Krebs cycle 2-oxoglutarate dehydrogenase complex creates an additional source of superoxide/hydrogen peroxide from 2-oxoadipate as alternative substrate.

PubMed

Nemeria, Natalia S; Gerfen, Gary; Guevara, Elena; Nareddy, Pradeep Reddy; Szostak, Michal; Jordan, Frank

2017-07-01

Recently, we reported that the human 2-oxoglutarate dehydrogenase (hE1o) component of the 2-oxoglutarate dehydrogenase complex (OGDHc) could produce the reactive oxygen species superoxide and hydrogen peroxide (detected by chemical means) from its substrate 2-oxoglutarate (OG), most likely concurrently with one-electron oxidation by dioxygen of the thiamin diphosphate (ThDP)-derived enamine intermediate to a C2α-centered radical (detected by Electron Paramagnetic Resonance) [Nemeria et al., 2014 [17]; Ambrus et al. 2015 [18

Strongly correlated electron behavior in single crystalline U2Os3Al9

NASA Astrophysics Data System (ADS)

Kumar, Neeraj; Das, Pranab Kumar; Kulkarni, Ruta; Thamizhavel, A.; Dhar, S. K.

2012-12-01

We report the magnetic properties of a single crystal of a new compound U2Os3Al9 which crystallizes in the well known Y2Co3Ga9 type orthorhombic structure with space group Cmcm. The susceptibility of U2Os3Al9 shows a peak at 7 K typical of antiferromagnetic ordering. The susceptibility in the paramagnetic state is anisotropic, the easy axis of magnetization lying in the ab-plane of the orthorhombic crystal lattice. The magnetization at 2 K, measured up to a maximum field of 160 kOe, shows a metamagnetic transition near 118 kOe when the field is aligned along [010] in addition to a small metamagnetic transition near 25 kOe. The bulk antiferromagnetic ordering of the uranium ions at TN = 7 K is confirmed by a peak in the heat capacity with ΔC nearly 7 J/U.mol K. An extrapolation of the heat capacity data from the paramagnetic regime to T = 0 gives an enhanced electronic specific heat coefficient of 120 mJ/U.mol K2. The electrical resistivity of U2Os3Al9 shows a negative temperature coefficient between 300 and TN which is a signature of spin fluctuations in a narrow band or a Kondo type of interaction. The data thus suggest the presence of strong electron correlations in this compound.

Electron Paramagnetic Resonance Spectroscopic Study on Nonequilibrium Reaction Pathways in the Photolysis of Solid Nitromethane (CH3NO2) and D3-Nitromethane (CD3NO2).

PubMed

Tsegaw, Yetsedaw Andargie; Sander, Wolfram; Kaiser, Ralf I

2016-03-10

Thin films of nitromethane (CH3NO2) along with its isotopically labeled counterpart D3-nitromethane (CD3NO2) were photolyzed at discrete wavelength between 266 nm (4.7 eV) and 121 nm (10.2 eV) to explore the underlying mechanisms involved in the decomposition of model compounds of energetic materials in the condensed phase at 5 K. The chemical modifications of the ices were traced in situ via electron paramagnetic resonance, thus focusing on the detection of (hitherto elusive) reaction intermediates and products with unpaired electrons. These studies revealed the formation of two carbon-centered radicals [methyl (CH3), nitromethyl (CH2NO2)], one oxygen-centered radical [methoxy (CH3O)], two nitrogen-centered radicals [nitrogen monoxide (NO), nitrogen dioxide (NO2)], as well as atomic hydrogen (H). The decomposition products of these channels and the carbon-centered nitromethyl (CH2NO2) radical in particular represent crucial reaction intermediates leading via sequential molecular mass growth processes in the exposed nitromethane samples to complex organic molecules as predicted previously by dynamics calculations. The detection of the nitromethyl (CH2NO2) radical along with atomic hydrogen (H) demonstrated the existence of a high-energy decomposition pathway, which is closed under collisionless conditions in the gas phase.

DFT with larger supercells explains the band gap formation in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

NASA Astrophysics Data System (ADS)

Zunger, Alex; Trimarchi, Giancarlo

The existence of large band gaps both in the antiferromagnetic (AFM) and the paramagnetic (PM) phases of the classic Mott insulators MnO, FeO, CoO, and NiO has traditionally been discussed in terms of theoretical methods requiring both (i) simple (often primitive) unit cells and (ii) correlated-electron methodologies. We show that if condition (i) is avoided (by using supercells, such as PM special quasi-random structures, in which chemically identical atoms can have different local environments), then even without condition (ii) one can describe the gaps and moments within a single-determinant DFT band structure approach. In this approach gapping is caused by basic structure, magnetism, and bonding effects underlying DFT, not via dynamic correlation (absent from DFT). As long as correlation is simplistically considered as ``anything that DFT does not get right'', gap formation in the AFM and PM phases is not due to correlation. This result defines the minimal theoretical methods needed to explain gapping and points to the possibility that some transition-metal oxides generally considered to have localized electrons detrimental to transport, could, in fact, rejoin the family of electronic semiconductors, to the benefit of a carrier transport technologies. A. Z. supported by DOE-OS-BES-MSE, Grant DE-FG02-13ER46959.

Electron paramagnetic resonance study of neutral Mg acceptors in β-Ga2O3 crystals

NASA Astrophysics Data System (ADS)

Kananen, B. E.; Halliburton, L. E.; Scherrer, E. M.; Stevens, K. T.; Foundos, G. K.; Chang, K. B.; Giles, N. C.

2017-08-01

Electron paramagnetic resonance (EPR) is used to directly observe and characterize neutral Mg acceptors ( M gGa0 ) in a β-Ga2O3 crystal. These acceptors, best considered as small polarons, are produced when the Mg-doped crystal is irradiated at or near 77 K with x rays. During the irradiation, neutral acceptors are formed when holes are trapped at singly ionized Mg acceptors ( M gGa- ). Unintentionally present Fe3+ (3d5) and Cr3+ (3d3) transition-metal ions serve as the corresponding electron traps. The hole is localized in a nonbonding p orbital on a threefold-coordinated oxygen ion adjacent to an Mg ion at a sixfold-coordinated Ga site. These M gGa0 acceptors (S = 1/2) have a slightly anisotropic g matrix (principal values are 2.0038, 2.0153, and 2.0371). There is also partially resolved 69Ga and 71Ga hyperfine structure resulting from unequal interactions with the two Ga ions adjacent to the hole. With the magnetic field along the a direction, hyperfine parameters are 2.61 and 1.18 mT for the 69Ga nuclei at the two inequivalent neighboring Ga sites. The M gGa0 acceptors thermally convert back to their nonparamagnetic M gGa- charge state when the temperature of the crystal is raised above approximately 250 K.

Thermophysical properties of paramagnetic Fe from first principles

NASA Astrophysics Data System (ADS)

Ehteshami, Hossein; Korzhavyi, Pavel A.

2017-12-01

A computationally efficient, yet general, free-energy modeling scheme is developed based on first-principles calculations. Finite-temperature disorder associated with the fast (electronic and magnetic) degrees of freedom is directly included in the electronic structure calculations, whereas the vibrational free energy is evaluated by a proposed model that uses elastic constants to calculate average sound velocity of the quasiharmonic Debye model. The proposed scheme is tested by calculating the lattice parameter, heat capacity, and single-crystal elastic constants of α -, γ -, and δ -iron as functions of temperature in the range 1000-1800 K. The calculations accurately reproduce the well-established experimental data on thermal expansion and heat capacity of γ - and δ -iron. Electronic and magnetic excitations are shown to account for about 20% of the heat capacity for the two phases. Nonphonon contributions to thermal expansion are 12% and 10% for α - and δ -Fe and about 30% for γ -Fe. The elastic properties predicted by the model are in good agreement with those obtained in previous theoretical treatments of paramagnetic phases of iron, as well as with the bulk moduli derived from isothermal compressibility measurements [N. Tsujino et al., Earth Planet. Sci. Lett. 375, 244 (2013), 10.1016/j.epsl.2013.05.040]. Less agreement is found between theoretically calculated and experimentally derived single-crystal elastic constants of γ - and δ -iron.

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.

Rapid and precise determination of zero-field splittings by terahertz time-domain electron paramagnetic resonance spectroscopy† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00830a Click here for additional data file.

PubMed Central

Lu, Jian; Ozel, I. Ozge; Belvin, Carina A.; Li, Xian; Skorupskii, Grigorii; Sun, Lei; Ofori-Okai, Benjamin K.; Dincă, Mircea; Gedik, Nuh

2017-01-01

Zero-field splitting (ZFS) parameters are fundamentally tied to the geometries of metal ion complexes. Despite their critical importance for understanding the magnetism and spectroscopy of metal complexes, they are not routinely available through general laboratory-based techniques, and are often inferred from magnetism data. Here we demonstrate a simple tabletop experimental approach that enables direct and reliable determination of ZFS parameters in the terahertz (THz) regime. We report time-domain measurements of electron paramagnetic resonance (EPR) signals associated with THz-frequency ZFSs in molecular complexes containing high-spin transition-metal ions. We measure the temporal profiles of the free-induction decays of spin resonances in the complexes at zero and nonzero external magnetic fields, and we derive the EPR spectra via numerical Fourier transformation of the time-domain signals. In most cases, absolute values of the ZFS parameters are extracted from the measured zero-field EPR frequencies, and the signs can be determined by zero-field measurements at two different temperatures. Field-dependent EPR measurements further allow refined determination of the ZFS parameters and access to the g-factor. The results show good agreement with those obtained by other methods. The simplicity of the method portends wide applicability in chemistry, biology and material science. PMID:29163882

Activation of Hydrogen Peroxide in Horseradish Peroxidase Occurs within ∼200 μs Observed by a New Freeze-Quench Device

PubMed Central

Tanaka, Motomasa; Matsuura, Koji; Yoshioka, Shiro; Takahashi, Satoshi; Ishimori, Koichiro; Hori, Hiroshi; Morishima, Isao

2003-01-01

To observe the formation process of compound I in horseradish peroxidase (HRP), we developed a new freeze-quench device with ∼200 μs of the mixing-to-freezing time interval and observed the reaction between HRP and hydrogen peroxide (H2O2). The developed device consists of a submillisecond solution mixer and rotating copper or silver plates cooled at 77 K; it freezes the small droplets of mixed solution on the surface of the rotating plates. The ultraviolet-visible spectra of the sample quenched at ∼1 ms after the mixing of HRP and H2O2 suggest the formation of compound I. The electron paramagnetic resonance spectra of the same reaction quenched at ∼200 μs show a convex peak at g = 2.00, which is identified as compound I due to its microwave power and temperature dependencies. The absence of ferric signals in the electron paramagnetic resonance spectra of the quenched sample indicates that compound I is formed within ∼200 μs after mixing HRP and H2O2. We conclude that the activation of H2O2 in HRP at ambient temperature completes within ∼200 μs. The developed device can be generally applied to investigate the electronic structures of short-lived intermediates of metalloenzymes. PMID:12609902

Characterization of oxygen defects in diamond by means of density functional theory calculations

NASA Astrophysics Data System (ADS)

Thiering, Gergő; Gali, Adam

2016-09-01

Point defects in diamond are of high interest as candidates for realizing solid state quantum bits, bioimaging agents, or ultrasensitive electric or magnetic field sensors. Various artificial diamond synthesis methods should introduce oxygen contamination in diamond, however, the incorporation of oxygen into diamond crystal and the nature of oxygen-related point defects are largely unknown. Oxygen may be potentially interesting as a source of quantum bits or it may interact with other point defects which are well established solid state qubits. Here we employ plane-wave supercell calculations within density functional theory, in order to characterize the electronic and magneto-optical properties of various oxygen-related defects. Besides the trivial single interstitial and substitutional oxygen defects we also consider their complexes with vacancies and hydrogen atoms. We find that oxygen defects are mostly electrically active and introduce highly correlated orbitals that pose a challenge for density functional theory modeling. Nevertheless, we are able to identify the fingerprints of substitutional oxygen defect, the oxygen-vacancy and oxygen-vacancy-hydrogen complexes in the electron paramagnetic resonance spectrum. We demonstrate that first principles calculations can predict the motional averaging of the electron paramagnetic resonance spectrum of defects that are subject to Jahn-Teller distortion. We show that the high-spin neutral oxygen-vacancy defect exhibits very fast nonradiative decay from its optical excited state that might hinder applying it as a qubit.

Surface water retardation around single-chain polymeric nanoparticles: critical for catalytic function?

PubMed

Stals, Patrick J M; Cheng, Chi-Yuan; van Beek, Lotte; Wauters, Annelies C; Palmans, Anja R A; Han, Songi; Meijer, E W

2016-03-01

A library of water-soluble dynamic single-chain polymeric nanoparticles (SCPN) was prepared using a controlled radical polymerisation technique followed by the introduction of functional groups, including probes at targeted positions. The combined tools of electron paramagnetic resonance (EPR) and Overhauser dynamic nuclear polarization (ODNP) reveal that these SCPNs have structural and surface hydration properties resembling that of enzymes.

Oxygen-related 1-platinum defects in silicon: An electron paramagnetic resonance study

NASA Astrophysics Data System (ADS)

Juda, U.; Scheerer, O.; Höhne, M.; Riemann, H.; Schilling, H.-J.; Donecker, J.; Gerhardt, A.

1996-09-01

A monoclinic 1-platinum defect recently detected was investigated more thoroughly by electron paramagnetic resonance (EPR). The defect is one of the dominating defects in platinum doped silicon. With a perfect reproducibility it is observed in samples prepared from n-type silicon as well as from p-type silicon, in float zone (FZ) silicon as well as in Czochralski (Cz) silicon. Its concentration varies with the conditions of preparation and nearly reaches that of isolated substitutional platinum in Cz silicon annealed for 2 h at 540 °C after quenching from the temperature of platinum diffusion. Because of its concentration which in Cz-Si exceeds that in FZ-Si the defect is assumed to be oxygen-related though a hyperfine structure with 17O could not be resolved. The defect causes a level close to the valence band. This is concluded from variations of the Fermi level and from a discussion of the spin Hamiltonian parameters. In photo-EPR experiments the defect is coupled to recently detected acceptorlike self-interstitial related defects (SIRDs); their level position turns out to be near-midgap. These defects belong to the lifetime limiting defects in Pt-doped Si.

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. © 2012 Institute of Food Technologists®

High field nuclear magnetic resonance in transition metal substituted BaFe{sub 2}As{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garitezi, T. M., E-mail: thalesmg@ifi.unicamp.br; Lesseux, G. G.; Rosa, P. F. S.

2014-05-07

We report high field {sup 75}As nuclear magnetic resonance (NMR) measurements on Co and Cu substituted BaFe{sub 2}As{sub 2} single crystals displaying same structural/magnetic transition T{sub 0}≃128  K. From our anisotropy studies in the paramagnetic state, we strikingly found virtually identical quadrupolar splitting and consequently the quadrupole frequency ν{sub Q}≃2.57(1)  MHz for both compounds, despite the claim that each Cu delivers 2 extra 3d electrons in BaFe{sub 2}As{sub 2} compared to Co substitution. These results allow us to conclude that a subtle change in the crystallographic structure, particularly in the Fe–As tetrahedra, must be the most probable tuning parameter to determine T{submore » 0} in this class of superconductors rather than electronic doping. Furthermore, our NMR data around T{sub 0} suggest coexistence of tetragonal/paramagnetic and orthorhombic/antiferromagnetic phases between the structural and the spin density wave magnetic phase transitions, similarly to what was reported for K-doped BaFe{sub 2}As{sub 2} [Urbano et al., Phys. Rev. Lett. 105, 107001 (2010)].« less

ELECTRON PARAMAGNETIC RESONANCE AND BAKING STUDIES ON GAMMA-IRRADIATED FLOUR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, C.C.

1962-03-01

The irradiation of flour (from Western Canadian hard red spring wheat) at its usual moisture level of 12 to 14% with up to 10/sup 6/ rads of Co/sup 60/ gamma rays gave no observable electron paramagnetic resonance (EPR) spectrum. However, after reduction of the moisture contert to 8 or 4%, irradiation resulted in EPR absorption indicating presence of radioinduced free radicals, which were destroyed rapidly in the presence of water vapor. With the irradiated flour kept in a sealed tube, the EPR spectrum faded with time. The fading was quite rapid for the first few days and then proceeded moremore » slowly. Irradiation resulted in a moderate increase in baked bread loaf volume at fairly low radiation dosages, followed by a gradual decrease in loaf volume at higher dosages (0.25 Mrad). Also, loaf volume tended to decrease as the elapsed time between irradiation and baking increased. This finding, when considered with the fading of the EPR spectrum, indicated that the EPR-detectable free radicals in the irradiated flour did not cause a strengthenlng of the gluten to produce an increase in loaf volume, as the radicals disappeared on becoming stable compounds. (H.H.D.)« less

New method to measure the carbamoylating activity of nitrosoureas by electron paramagnetic resonance spectroscopy.

PubMed

Gadzheva, V; Ichimori, K; Raikov, Z; Nakazawa, H

1997-08-01

A new method for measuring the carbamoylating activity of nitrosoureas and isocyanates using electron paramagnetic resonance (EPR) spectroscopy is described. The extent and time course of carbamoylation reaction of chloroethyl isocyanate and a series of 9 nitrosoureas toward amino group of 4-amino-2,2,6,6-tetramethyl-piperidine-1-oxyl were examined with both the EPR method and the HPLC method which has been proposed by Brubaker et al. [Biochem. Pharmacol. 35:2359 (1986)]. Spin-labeled nitrosoureas we synthesized are included in this study since they have less toxicity or more efficiency than commercially available drug in some cases. The concentration of carbamoylated product was easily determined with the EPR spectra. There is a very high correlation (r = 0.982, t = 2.58, N = 10, p < 0.001) between the EPR and HPLC methods. Spin-labeled nitrosoureas showed lower carbamoylating activity than non-labeled analogues. The carbamoylating activity for these nitrosourea depended on the reactivity of isocyanate intermediate and almost independent of their half life. This rapid and simple EPR method is suitable for the detailed investigation of the rate and extent of carbamoylation reaction.

Appearance of Membrane-bound Iron-Sulfur Centers and the Photosystem I Reaction Center during Greening of Barley Leaves 1

PubMed Central

Baltimore, Barbara G.; Malkin, Richard

1977-01-01

Dark-grown barley (Hordeum vulgare) etioplasts were examined for their content of membrane-bound iron-sulfur centers by electron paramagnetic resonance spectroscopy at 15K. They were found to contain the high potential iron-sulfur center characterized (in the reduced state) by an electron paramagnetic resonance g value of 1.89 (the “Rieske” center) but did not contain any low potential iron-sulfur centers. Per mole of cytochrome f, dark-grown etioplasts and fully developed chloroplasts had the same content of the Rieske center. During greening of etioplasts under continuous light, low potential bound iron-sulfur centers appear. In addition, the photosystem I reaction center, as measured by the photooxidation of P700 at 15K, also became functional; during greening the appearance of a photoreducible low potential iron-sulfur center paralleled the appearance of P700 photoactivity. These findings indicate the close association of the low potential iron-sulfur centers with the photosystem I reaction center; they also support the concept that the development of stable charge separation in the photosystem I reaction center requires, in addition to P700, a low potential iron-sulfur center. PMID:16660048

The influence of genistein on free radicals in normal dermal fibroblasts and keloid fibroblasts examined by EPR spectroscopy.

PubMed

Jurzak, Magdalena; Ramos, Paweł; Pilawa, Barbara

2017-01-01

Normal and keloid fibroblasts were examined using X-band (9.3 GHz) electron paramagnetic resonance spectroscopy. The effect of genistein on the concentration of free radicals in both normal dermal and keloid fibroblasts after ultraviolet irradiation was investigated. The highest concentration of free radicals was seen in keloid fibroblasts, with normal fibroblasts containing a lower concentration. The concentration of free radicals in both normal and keloid fibroblasts was altered in a concentration-dependent manner by the presence of genistein. The change in intra-cellular free radical concentration after the ultraviolet irradiation of both normal and keloid fibroblasts is also discussed. The antioxidant properties of genistein, using its 1,1-Diphenyl-2-picrylhydrazyl (DPPH) free radical-scavenging activity as a model, were tested, and the effect of ultraviolet irradiation on its interaction with free radicals was examined. The electron paramagnetic resonance spectra of DPPH showed quenching by genistein. The interaction of genistein with DPPH free radicals in the absence of ultraviolet irradiation was shown to be slow, but this interaction was much faster under ultraviolet irradiation. Ultraviolet irradiation enhanced the free radical-scavenging activity of genistein.

Free radicals generated during oxidation of green tea polyphenols: electron paramagnetic resonance spectroscopy combined with density functional theory calculations.

PubMed

Severino, Joyce Ferreira; Goodman, Bernard A; Kay, Christopher W M; Stolze, Klaus; Tunega, Daniel; Reichenauer, Thomas G; Pirker, Katharina F

2009-04-15

Electron paramagnetic resonance spectroscopy and density functional theory calculations have been used to investigate the redox properties of the green tea polyphenols (GTPs) (-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin gallate (ECG). Aqueous extracts of green tea and these individual phenols were autoxidized at alkaline pH and oxidized by superoxide anion (O(2)(-)) radicals in dimethyl sulfoxide. Several new aspects of the free radical chemistry of GTPs were revealed. EGCG can be oxidized on both the B and the D ring. The B ring was the main oxidation site during autoxidation, but the D ring was the preferred site for O(2)(-) oxidation. Oxidation of the D ring was followed by structural degradation, leading to generation of a radical identical to that of oxidized gallic acid. Alkaline autoxidation of green tea extracts produced four radicals that were related to products of the oxidation of EGCG, EGC, ECG, and gallic acid, whereas the spectra from O(2)(-) oxidation could be explained solely by radicals generated from EGCG. Assignments of hyperfine coupling constants were made by DFT calculations, allowing the identities of the radicals observed to be confirmed.

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.

Spectroscopic and Kinetic Properties of the Molybdenum-containing, NAD+-dependent Formate Dehydrogenase from Ralstonia eutropha*

PubMed Central

Niks, Dimitri; Duvvuru, Jayant; Escalona, Miguel; Hille, Russ

2016-01-01

We have examined the rapid reaction kinetics and spectroscopic properties of the molybdenum-containing, NAD+-dependent FdsABG formate dehydrogenase from Ralstonia eutropha. We confirm previous steady-state studies of the enzyme and extend its characterization to a rapid kinetic study of the reductive half-reaction (the reaction of formate with oxidized enzyme). We have also characterized the electron paramagnetic resonance signal of the molybdenum center in its MoV state and demonstrated the direct transfer of the substrate Cα hydrogen to the molybdenum center in the course of the reaction. Varying temperature, microwave power, and level of enzyme reduction, we are able to clearly identify the electron paramagnetic resonance signals for four of the iron/sulfur clusters of the enzyme and find suggestive evidence for two others; we observe a magnetic interaction between the molybdenum center and one of the iron/sulfur centers, permitting assignment of this signal to a specific iron/sulfur cluster in the enzyme. In light of recent advances in our understanding of the structure of the molybdenum center, we propose a reaction mechanism involving direct hydride transfer from formate to a molybdenum-sulfur group of the molybdenum center. PMID:26553877

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.

Developing multifunctional nanoparticles in a 1-D coordination polymer of Cd(II)

NASA Astrophysics Data System (ADS)

Agarwal, Rashmi A.; Gupta, Neeraj K.

2017-11-01

A simple synthesis for the integration of different nanoparticles (NPs) including Ag, Au, Pd, Cr and mixed (Cu/Fe), has been demonstrated within the nanopores of a non-activated one dimensional porous coordination polymer (PCP) of Cd(II) due to its high flexible structure. There are two different mechanisms (acid formation (HCl/HNO3) and redox activity of the framework) elucidated by electron paramagnetic resonance (EPR). Presence of -NO2 groups of the ligand act as anchoring sites for metal ions of metal precursors leading to NPs growth within the PCP explained by FTIR. High resolution transmission electron microscopy (HRTEM) images provided insight of the chemical and physical characteristics of the NPs within the framework. Ag/AgO NPs exhibit excellent antibacterial properties at extremely low concentrations. The polymer shows potential for sequestration and reduction of hexavalent Cr (highly toxic) to elemental, trivalent and tetravalent Cr (non toxic). This framework is also an excellent template for fabrication and dry storage of nanoparticles synthesized by mixed metal precursors. Ferromagnetic properties have been shown by Ag and Au NPs integrated frameworks while Cu/Fe@Cd-PCP behaves as a paramagnet material at room temperature.

Optical and electron paramagnetic resonance studies of the excited triplet states of UV-B absorbers: 2-ethylhexyl salicylate and homomenthyl salicylate.

PubMed

Sugiyama, Kazuto; Tsuchiya, Takumi; Kikuchi, Azusa; Yagi, Mikio

2015-09-26

The energy levels and lifetimes of the lowest excited triplet (T1) states of UV-B absorbers, 2-ethylhexyl salicylate (EHS) and homomenthyl salicylate (HMS), and their deprotonated anions (EHS(-) and HMS(-)) were determined through measurements of phosphorescence and electron paramagnetic resonance (EPR) spectra in rigid solutions at 77 K. The observed T1 energies of EHS and HMS are higher than those of butylmethoxydibenzoylmethane, the most widely used UV-A absorber, and octyl methoxycinnamate, the most widely used UV-B absorber. The T1 states of EHS, HMS, EHS(-) and HMS(-) were assigned to almost pure (3)ππ* state from the observed T1 lifetimes and zero-field splitting parameters. EHS and HMS with an intramolecular hydrogen bond show a photoinduced phosphorescence enhancement in ethanol at 77 K. The EPR signals of the T1 states of EHS and HMS also increase in intensity with UV-irradiation time (photoinduced EPR enhancement). The T1 lifetimes of EHS and HMS at room temperature were determined through triplet-triplet absorption measurements in ethanol. The quantum yields of singlet oxygen production by EHS and HMS were determined by using time-resolved near-IR phosphorescence.

Microstrip resonators for electron paramagnetic resonance experiments.

PubMed

Torrezan, A C; Mayer Alegre, T P; Medeiros-Ribeiro, G

2009-07-01

In this article we evaluate the performance of an electron paramagnetic resonance (EPR) setup using a microstrip resonator (MR). The design and characterization of the resonator are described and parameters of importance to EPR and spin manipulation are examined, including cavity quality factor, filling factor, and microwave magnetic field in the sample region. Simulated microwave electric and magnetic field distributions in the resonator are also presented and compared with qualitative measurements of the field distribution obtained by a perturbation technique. Based on EPR experiments carried out with a standard marker at room temperature and a MR resonating at 8.17 GHz, the minimum detectable number of spins was found to be 5 x 10(10) spins/GHz(1/2) despite the low MR unloaded quality factor Q0=60. The functionality of the EPR setup was further evaluated at low temperature, where the spin resonance of Cr dopants present in a GaAs wafer was detected at 2.3 K. The design and characterization of a more versatile MR targeting an improved EPR sensitivity and featuring an integrated biasing circuit for the study of samples that require an electrical contact are also discussed.

Quantitative estimation of magnetic nanoparticle distributions in one dimension using low-frequency continuous wave electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

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

2013-06-01

In recent years, magnetic nanoparticles (MNPs) have gained increased attention due to their superparamagnetic properties. These properties allow the development of innovative biomedical applications such as targeted drug delivery and tumour heating. However, these modalities lack effective operation arising from the inaccurate quantification of the spatial MNP distribution. This paper proposes an approach for assessing the one-dimensional (1D) MNP distribution using electron paramagnetic resonance (EPR). EPR is able to accurately determine the MNP concentration in a single volume but not the MNP distribution throughout this volume. A new approach that exploits the solution of inverse problems for the correct interpretation of the measured EPR signals, is investigated. We achieve reconstruction of the 1D distribution of MNPs using EPR. Furthermore, the impact of temperature control on the reconstructed distributions is analysed by comparing two EPR setups where the latter setup is temperature controlled. Reconstruction quality for the temperature-controlled setup increases with an average of 5% and with a maximum increase of 13% for distributions with relatively lower iron concentrations and higher resolutions. However, these measurements are only a validation of our new method and form no hard limits.

Nuclear magnetic biosignatures in the carbonaceous matter of ancient cherts: comparison with carbonaceous meteorites.

PubMed

Gourier, Didier; Delpoux, Olivier; Binet, Laurent; Vezin, Hervé

2013-10-01

The search for organic biosignatures is motivated by the hope of understanding the conditions of emergence of life on Earth and the perspective of finding traces of extinct life in martian sediments. Paramagnetic radicals, which exist naturally in amorphous carbonaceous matter fossilized in Precambrian cherts, were used as local structural probes and studied by electron paramagnetic resonance (EPR) spectroscopy. The nuclear magnetic resonance transitions of elements inside and around these radicals were detected by monitoring the nuclear modulations of electron spin echo in pulsed EPR. We found that the carbonaceous matter of fossilized microorganisms with age up to 3.5 billion years gives specific nuclear magnetic signatures of hydrogen (¹H), carbon (¹³C), and phosphorus (³¹P) nuclei. We observed that these potential biosignatures of extinct life are found neither in the carbonaceous matter of carbonaceous meteorites (4.56 billion years), the most ancient objects of the Solar System, nor in any carbonaceous matter resulting from carbonization of organic and bioorganic precursors. These results indicate that these nuclear signatures are sensitive to thermal episodes and can be used for Archean cherts with metamorphism not higher than the greenschist facies.

Spectroscopic analysis of radiation-generated changes in tensile properties of a polyetherimide film

NASA Technical Reports Server (NTRS)

Long, E. R., Jr.; Long, S. A. T.

1985-01-01

The effects of electron radiation on Ultem, a polyetherimide were studied for doses from 2 x 10 to the 9th power to 6 x 10 to the 9th power rad. Specimens were studied for tensile property testing and for electron paramagnetic resonance and infrared spectroscopic measurements of molecular structure. A Faraday cup design and a method for remote temperature measurement were developed. The spectroscopic data show that radiation caused dehydrogenation of methyl groups, rupture of main-chain ether linkage, and opening of imide rings, all to form radicals and indicate that the so-formed atomic hydrogen attached to phenyl radicals, but not to phenoxyl radicals, which would have formed hydroxyls. The observed decays of the radiation-generated phenoxyl, gem-dimethyl, and carbonyl radicals were interpreted as a combining of the radicals to form crosslinking. This crosslinking is the probable cause of the major reduction in the elongation of the tensile specimens after irradiation. Subsequent classical solubility tests indicate that the irradiation caused massive crosslinking.

Systematic theoretical investigation of the zero-field splitting in Gd(III) complexes: Wave function and density functional approaches

NASA Astrophysics Data System (ADS)

Khan, Shehryar; Kubica-Misztal, Aleksandra; Kruk, Danuta; Kowalewski, Jozef; Odelius, Michael

2015-01-01

The zero-field splitting (ZFS) of the electronic ground state in paramagnetic ions is a sensitive probe of the variations in the electronic and molecular structure with an impact on fields ranging from fundamental physical chemistry to medical applications. A detailed analysis of the ZFS in a series of symmetric Gd(III) complexes is presented in order to establish the applicability and accuracy of computational methods using multiconfigurational complete-active-space self-consistent field wave functions and of density functional theory calculations. The various computational schemes are then applied to larger complexes Gd(III)DOTA(H2O)-, Gd(III)DTPA(H2O)2-, and Gd(III)(H2O)83+ in order to analyze how the theoretical results compare to experimentally derived parameters. In contrast to approximations based on density functional theory, the multiconfigurational methods produce results for the ZFS of Gd(III) complexes on the correct order of magnitude.

Chiroplasmonic magnetic gold nanocomposites produced by one-step aqueous method using κ-carrageenan.

PubMed

Lesnichaya, Marina V; Sukhov, Boris G; Aleksandrova, Galina P; Gasilova, Ekaterina R; Vakul'skaya, Tamara I; Khutsishvili, Spartak S; Sapozhnikov, Anatoliy N; Klimenkov, Igor V; Trofimov, Boris A

2017-11-01

Novel water-soluble chiroplasmonic nanobiocomposites with directly varied gold content were synthesized by a one-step redox method in water using a biocompatible polysaccharide κ-carrageenan (industrial product from algae) as both reducing and stabilizing matrix. The influence of the reactants ratio, temperature, and pH on the reaction was studied and the optimal reaction parameters were found. The structure and the properties of composite nanomaterials were examined in solid state and aqueous solutions by using complementary physical-chemical methods X-ray diffraction analysis, transmission electron microscopy, spectroscopy of electron paramagnetic resonance, atomic absorption and optical spectroscopy, polarimetry including optical rotatory dispersion with registration of interphase-crossbred Cotton effect of a chiral polysaccharide matrix on plasmonic chromophore of gold nanoparticles, dynamic and static light scattering. The new perspective multi-purpose nanocomposites demonstrate a complex of chiroplasmonic and magnetic properties, imparted by both nanoparticles and radicals enriched chiral polysaccharide matrix. Copyright © 2017 Elsevier Ltd. All rights reserved.

Development of Iron Doped Silicon Nanoparticles as Bimodal Imaging Agents

PubMed Central

Singh, Mani P.; Atkins, Tonya M.; Muthuswamy, Elayaraja; Kamali, Saeed; Tu, Chuqiao; Louie, Angelique Y.; Kauzlarich, Susan M.

2012-01-01

We demonstrate the synthesis of water-soluble allylamine terminated Fe doped Si (SixFe) nanoparticles as bimodal agents for optical and magnetic imaging. The preparation involves the synthesis of a single source iron containing precursor, Na4Si4 with x% Fe (x = 1, 5, 10), and its subsequent reaction with NH4Br to produce hydrogen terminated SixFe nanoparticles. The hydrogen-capped nanoparticles are further terminated with allylamine via thermal hydrosilylation. Transmission electron microscopy (TEM) indicates that the average particle diameter is ~3.0±1.0 nm. The Si5Fe nanoparticles show strong photoluminescence quantum yield in water (~ 10 %) with significant T2 contrast (r2/r1value of 4.31). Electron paramagnetic resonance (EPR) and Mössbauer spectroscopies indicate that iron in the nanoparticles is in the +3 oxidation state. Analysis of cytotoxicity using the resazurin assay on HepG2 liver cells indicates that the particles have minimal toxicity. PMID:22616623

Development of iron-doped silicon nanoparticles as bimodal imaging agents.

PubMed

Singh, Mani P; Atkins, Tonya M; Muthuswamy, Elayaraja; Kamali, Saeed; Tu, Chuqiao; Louie, Angelique Y; Kauzlarich, Susan M

2012-06-26

We demonstrate the synthesis of water-soluble allylamine-terminated Fe-doped Si (Si(xFe)) nanoparticles as bimodal agents for optical and magnetic imaging. The preparation involves the synthesis of a single-source iron-containing precursor, Na(4)Si(4) with x% Fe (x = 1, 5, 10), and its subsequent reaction with NH(4)Br to produce hydrogen-terminated Si(xFe) nanoparticles. The hydrogen-capped nanoparticles are further terminated with allylamine via thermal hydrosilylation. Transmission electron microscopy indicates that the average particle diameter is ∼3.0 ± 1.0 nm. The Si(5Fe) nanoparticles show strong photoluminescence quantum yield in water (∼10%) with significant T(2) contrast (r(2)/r(1) value of 4.31). Electron paramagnetic resonance and Mössbauer spectroscopies indicate that iron in the nanoparticles is in the +3 oxidation state. Analysis of cytotoxicity using the resazurin assay on HepG2 liver cells indicates that the particles have minimal toxicity.

Studies of Diamonds Using Electron Paramagnetic Resonance and Other Techniques

NASA Astrophysics Data System (ADS)

Zhang, Shigang

Studies of impurities/defects in diamonds grown with the high-temperature high-pressure technique (HTHP) and B- and P-doped diamond films using fast ion implantation and chemical evaporation have been carried out. The main technique employed in the study is electron paramagnetic resonance (EPR). Raman, laser and X-ray fluorescence are also used to characterize the samples. While other commonly used techniques such as infrared (IR) spectroscopy detect no nitrogen in an isotopically enriched ^ {12}C diamond, the clear EPR spectrum consistently measures a nitrogen concentration of about 0.05ppm by calibration against a few standards. The ^{12}C diamond is evaluated to be ideal for optical window application and studies of diamond properties. Neither the EPR lineshape nor the second moment supports a random nitrogen distribution in the ^{12}C diamond. Instead, the average nitrogen distance is found to be larger than the of the random nitrogen distribution. The g-tensor for substitutional nitrogen is found to be axially symmetric along the (111) direction with g_| - g_| = 0.00002(5). In the study of a HTHP IIb blue semiconducting diamond, neutral N is measured with a concentration of 0.02ppm. The result is not well understood since neutral nitrogen is expected to lose its extra electron to boron due to electron-hole recombination. Further studies are suggested to better understand this result. EPR studies of two sets of P-doped diamond films grown using fast ion implantation and chemical incorporation reveal that defect levels caused by diamond doping are still too high for semiconductor applications. As expected, P doping causes a defect level two orders of magnitude higher than B doping, which can be explained by the relatively larger size of P than B. The theoretical analysis based on EPR hyperfine interaction suggest that P forms a shallow donor in diamond and that the electron density at the P site is |psi(0)|^2 = 0.27 times 10^{24} cm^ {-3}. This is consistent with the temperature dependent EPR experimental results. The EPR spectra for all diamond samples I have studied are compared, revealing that the HTHP diamonds show no defect related spectrum, which are commonly observed in natural IIa and IIb diamonds. This result indicates that HTHP diamond has superior quality compared to other diamonds.

On the Oxidation State of Manganese Ions in Li-Ion Battery Electrolyte Solutions.

PubMed

Banerjee, Anjan; Shilina, Yuliya; Ziv, Baruch; Ziegelbauer, Joseph M; Luski, Shalom; Aurbach, Doron; Halalay, Ion C

2017-02-08

We demonstrate herein that Mn 3+ and not Mn 2+ , as commonly accepted, is the dominant dissolved manganese cation in LiPF 6 -based electrolyte solutions of Li-ion batteries with lithium manganate spinel positive and graphite negative electrodes chemistry. The Mn 3+ fractions in solution, derived from a combined analysis of electron paramagnetic resonance and inductively coupled plasma spectroscopy data, are ∼80% for either fully discharged (3.0 V hold) or fully charged (4.2 V hold) cells, and ∼60% for galvanostatically cycled cells. These findings agree with the average oxidation state of dissolved Mn ions determined from X-ray absorption near-edge spectroscopy data, as verified through a speciation diagram analysis. We also show that the fractions of Mn 3+ in the aprotic nonaqueous electrolyte solution are constant over the duration of our experiments and that disproportionation of Mn 3+ occurs at a very slow rate.

Alcoholic extraction enables EPR analysis to characterize radiation-induced cellulosic signals in spices.

PubMed

Ahn, Jae-Jun; Sanyal, Bhaskar; Akram, Kashif; Kwon, Joong-Ho

2014-11-19

Different spices such as turmeric, oregano, and cinnamon were γ-irradiated at 1 and 10 kGy. The electron paramagnetic resonance (EPR) spectra of the nonirradiated samples were characterized by a single central signal (g = 2.006), the intensity of which was significantly enhanced upon irradiation. The EPR spectra of the irradiated spice samples were characterized by an additional triplet signal at g = 2.006 with a hyperfine coupling constant of 3 mT, associated with the cellulose radical. EPR analysis on various sample pretreatments in the irradiated spice samples demonstrated that the spectral features of the cellulose radical varied on the basis of the pretreatment protocol. Alcoholic extraction pretreatment produced considerable improvements of the EPR signals of the irradiated spice samples relative to the conventional oven and freeze-drying techniques. The alcoholic extraction process is therefore proposed as the most suitable sample pretreatment for unambiguous detection of irradiated spices by EPR spectroscopy.

Separation of Diamagnetic and Paramagnetic Fabrics Reveals Strain Directions in Carbonate Rocks

NASA Astrophysics Data System (ADS)

Issachar, R.; Levi, T.; Marco, S.; Weinberger, R.

2018-03-01

We present a new procedure for separating magnetic fabrics in coccolith-bearing chalk samples, demonstrated in the case studies of three sites located within the Dead Sea Fault (DSF) plate boundary. The separation is achieved by combining measurements of room temperature and low-temperature anisotropy of magnetic susceptibility (RT-AMS and LT-AMS, respectively) with anisotropy of anhysteretic remanence magnetization (AARM). The LT-AMS, measured at 77 K, enhances the fabric of paramagnetic clay minerals. The AARM represents the fabric of ferromagnetic Fe oxides. By subtracting the paramagnetic and ferromagnetic fabrics from the RT-AMS, the diamagnetic fabric is separated. In the studied samples, we found that the ferromagnetic contribution to the bulk magnetic fabric is negligible and could be excluded from the subtraction procedure. Our analysis indicates that in chalks with a negligible ferromagnetic contribution, diamagnetic fabric predominates the rock bulk magnetic fabric, if the mean susceptibility is <-6 × 10-6 SI, whereas with a mean susceptibility >11 × 10-6 SI, paramagnetic fabric predominates. In the studied rocks, the paramagnetic clay minerals preserve the original depositional fabric, whereas the diamagnetic minerals show a tectonic fabric. We propose a mechanism by which coccolith rotation under tectonic strain contributes to the development of the diamagnetic fabric parallel to the shortening direction. We infer that the diamagnetic fabrics of the studied rocks indicate strain regime of approximately N-S horizontal shortening near strands of the DSF system. This suggests a deflection of the regional principal strain axes near the DSF. The diamagnetic fabric is more sensitive to tectonic strain than paramagnetic fabric in chalks and provides a valuable strain indicator near major faults.

Mechanistic insights into energy conservation by flavin-based electron bifurcation

DOE PAGES

Lubner, Carolyn E.; Jennings, David P.; Mulder, David W.; ...

2017-04-10

The recently realized biochemical phenomenon of energy conservation through electron bifurcation provides biology with an elegant means to maximize utilization of metabolic energy. The mechanism of coordinated coupling of exergonic and endergonic oxidation-reduction reactions by a single enzyme complex has been elucidated through optical and paramagnetic spectroscopic studies revealing unprecedented features. Pairs of electrons are bifurcated over more than 1 volt of electrochemical potential by generating a low-potential, highly energetic, unstable flavin semiquinone and directing electron flow to an iron-sulfur cluster with a highly negative potential to overcome the barrier of the endergonic half reaction. As a result, the unprecedentedmore » range of thermodynamic driving force that is generated by flavin-based electron bifurcation accounts for unique chemical reactions that are catalyzed by these enzymes.« less

Mechanistic insights into energy conservation by flavin-based electron bifurcation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lubner, Carolyn E.; Jennings, David P.; Mulder, David W.

The recently realized biochemical phenomenon of energy conservation through electron bifurcation provides biology with an elegant means to maximize utilization of metabolic energy. The mechanism of coordinated coupling of exergonic and endergonic oxidation-reduction reactions by a single enzyme complex has been elucidated through optical and paramagnetic spectroscopic studies revealing unprecedented features. Pairs of electrons are bifurcated over more than 1 volt of electrochemical potential by generating a low-potential, highly energetic, unstable flavin semiquinone and directing electron flow to an iron-sulfur cluster with a highly negative potential to overcome the barrier of the endergonic half reaction. As a result, the unprecedentedmore » range of thermodynamic driving force that is generated by flavin-based electron bifurcation accounts for unique chemical reactions that are catalyzed by these enzymes.« less

Effect of chromium doping on the correlated electronic structure of V2O3

NASA Astrophysics Data System (ADS)

Grieger, Daniel; Lechermann, Frank

2014-09-01

The archetypical strongly correlated Mott-phenomena compound V2O3 is known to show a paramagnetic metal-insulator transition driven by doping with chromium atoms and/or (negative) pressure. Via charge self-consistent density-functional theory+dynamical mean-field theory calculations we demonstrate that these two routes cannot be understood as equivalent. An explicit description of Cr-doped V2O3 by means of supercell calculations and the virtual crystal approximation is performed. Introducing chromium's additional electron to the system is shown to modify the overall many-body electronic structure substantially. Chromium doping increases electronic correlations which in addition induce charge transfers between Cr and the remaining V ions. Thereby the transition-metal orbital polarization is increased by the electron doping, in close agreement with experimental findings.

Optical, Structural and Paramagnetic Properties of Eu-Doped Ternary Sulfides ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y)

PubMed Central

Jarý, Vítězslav; Havlák, Lubomír; Bárta, Jan; Buryi, Maksym; Mihóková, Eva; Rejman, Martin; Laguta, Valentin; Nikl, Martin

2015-01-01

Eu-doped ternary sulfides of general formula ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y) are presented as a novel interesting material family which may find usage as X-ray phosphors or solid state white light emitting diode (LED) lighting. Samples were synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, time-resolved photoluminescence spectroscopy, electron paramagnetic resonance, and X-ray excited fluorescence. Corresponding characteristics, including absorption, radioluminescence, photoluminescence excitation and emission spectra, and decay kinetics curves, were measured and evaluated in a broad temperature range (8–800 K). Calculations including quantum local crystal field potential and spin-Hamiltonian for a paramagnetic particle in D3d local symmetry and phenomenological model dealing with excited state dynamics were performed to explain the experimentally observed features. Based on the results, an energy diagram of lanthanide energy levels in KLuS2 is proposed. Color model xy-coordinates are used to compare effects of dopants on the resulting spectrum. The application potential of the mentioned compounds in the field of white LED solid state lighting or X-ray phosphors is thoroughly discussed. PMID:28793612

Partitioning of nitroxides in dispersed systems investigated by ultrafiltration, EPR and NMR spectroscopy.

PubMed

Krudopp, Heimke; Sönnichsen, Frank D; Steffen-Heins, Anja

2015-08-15

The partitioning behavior of paramagnetic nitroxides in dispersed systems can be determined by deconvolution of electron paramagnetic resonance (EPR) spectra giving equivalent results with the validated methods of ultrafiltration techniques (UF) and pulsed-field gradient nuclear magnetic resonance spectroscopy (PFG-NMR). The partitioning behavior of nitroxides with increasing lipophilicity was investigated in anionic, cationic and nonionic micellar systems and 10 wt% o/w emulsions. Apart from EPR spectra deconvolution, the PFG-NMR was used in micellar solutions as a non-destructive approach, while UF based on separation of very small volume of the aqueous phase. As a function of their substituent and lipophilicity, the proportions of nitroxides that were solubilized in the micellar or emulsion interface increased with increasing nitroxide lipophilicity for all emulsifier used. Comparing the different approaches, EPR deconvolution and UF revealed comparable nitroxide proportions that were solubilized in the interfaces. Those proportions were higher than found with PFG-NMR. For PFG-NMR self-diffusion experiments the reduced nitroxides were used revealing a high dynamic of hydroxylamines and emulsifiers. Deconvolution of EPR spectra turned out to be the preferred method for measuring the partitioning behavior of paramagnetic molecules as it enables distinguishing between several populations at their individual solubilization sites. Copyright © 2015 Elsevier Inc. All rights reserved.

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 DNIC with cysteine, most probably, an appropriate Roussin's black salt thioesters and cannot be prepared by simple substitution of capital EM, Cyrillic-DNIC cysteine for glutathione. Treatment of capital EM, Cyrillic-DNIC with sodium dithionite attenuates the EPR signal at g(aver.)=2.03 and stimulates the appearance of an EPR signal at g(aver.)=2.0 with a hypothetical electronic configuration {Fe(NO)(2)}(9). These changes can be reversed by storage of DNIC solutions in atmospheric air. The EPR signal at g(aver.)=2.0 generated upon treatment of B-DNICs with dithionite also disappears after incubation of B-DNIC solutions in air. In all probability, the center responsible for this EPR signal represents capital EM, Cyrillic-DNIC formed in a small amount during dithionite-induced decomposition of B-DNIC. Copyright 2010 Elsevier Inc. All rights reserved.

Interactions of short-acting, intermediate-acting and pre-mixed human insulins with free radicals--Comparative EPR examination.

PubMed

Olczyk, Paweł; Komosinska-Vassev, Katarzyna; Ramos, Paweł; Mencner, Łukasz; Olczyk, Krystyna; Pilawa, Barbara

2015-07-25

Electron paramagnetic resonance (EPR) spectroscopy was used to examine insulins interactions with free radicals. Human recombinant DNA insulins of three groups were studied: short-acting insulin (Insuman Rapid); intermediate-acting insulins (Humulin N, Insuman Basal), and pre-mixed insulins (Humulin M3, Gensulin M50, Gensulin M40, Gensulin M30). The aim of an X-band (9.3GHz) study was comparative analysis of antioxidative properties of the three groups of human insulins. DPPH was used as a stable free radical model. Amplitudes of EPR lines of DPPH as the paramagnetic free radical reference, and DPPH interacting with the individual tested insulins were compared. For all the examined insulins kinetics of their interactions with free radicals up to 60 min were obtained. The strongest interactions with free radicals were observed for the short-acting insulin - Insuman Rapid. The lowest interactions with free radicals were characteristic for intermediate-acting insulin - Insuman Basal. The pre-mixed insulins i.e. Humulin M3 and Gensulin M50 revealed the fastest interactions with free radicals. The short acting, intermediate acting and premixed insulins have been found to be effective agents in reducing free radical formation in vitro and should be further considered as potential useful tools in attenuation of oxidative stress in diabetic patients. Copyright © 2015 Elsevier B.V. All rights reserved.

Solid-state EPR strategies for the structural characterization of paramagnetic NO adducts of frustrated Lewis pairs (FLPs)

NASA Astrophysics Data System (ADS)

de Oliveira, Marcos; Wiegand, Thomas; Elmer, Lisa-Maria; Sajid, Muhammad; Kehr, Gerald; Erker, Gerhard; Magon, Claudio José; Eckert, Hellmut

2015-03-01

Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and 11B, 14N, and 31P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that different from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to 14N and 31P, the ESEEM and HYSCORE spectra contain important information about the 11B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.

Solid-state EPR strategies for the structural characterization of paramagnetic NO adducts of frustrated Lewis pairs (FLPs)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oliveira, Marcos de; Magon, Claudio José; Wiegand, Thomas

2015-03-28

Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and {sup 11}B, {sup 14}N, and {sup 31}P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that differentmore » from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to {sup 14}N and {sup 31}P, the ESEEM and HYSCORE spectra contain important information about the {sup 11}B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.« less

Spectroscopic study of active phase-support interactions on a RhO{sub x}/CeO{sub 2} catalyst: Evidence for electronic interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez-Arias, A.; Soria, J.; Conesa, J.C.

The effects of thermal treatments under vacuum, used as a way to generate reduced centers on Rh{sub 2}O{sub 3} and RhO{sub x}/CeO{sub 2}, have been studied by ESR and FTIR, using respectively oxygen and carbon monoxide as probe molecules. The results obtained for the outgassed samples reveal the presence of ceria-rhodia interactions favoring the stabilization of paramagnetic Rh{sup 2+} cations in rhodium oxide clusters on the ceria surface. Subsequent O{sub 2} adsorption leads to the formation of different oxygen-related paramagnetic species located on ceria, on rhodium oxide clusters and at the boundary between both oxides; their contribution to the spectramore » depends on outgassing conditions and O{sub 2} adsorption temperature. The unexpected absence of O{sub 2}{sup -}-Ce{sup 4+} species after O{sub 2} contact at 77 K with RhO{sub x}/CeO{sub 2} outgassed above 573 K evidences the existence of electronic interactions between the RhO{sub x}, and CeO{sub 2} phases, being explained on the basis of electron transfer to the mixed valence RhO{sub x}, phase from the surface-reduced ceria, leading to electron depletion of the latter. This effect is inhibited by CO adsorption, showing the dependence between the electron-accepting properties of the rhodia clusters and the presence of vacant coordination sites at the surface Rh ions. An effect of similar kind may be responsible for shifts observed in the IR bands of rhodium dicarbonyls formed in the RhO{sub x}/CeO{sub 2} system. The latter results suggest the possibility that thermal enhancement of surface reactions in complex systems could depend on electron transfer between adjacent phases and that adsorption on one phase may influence the surface reactivity of another phase by affecting to the electron transfer between them. 34 refs., 8 figs., 2 tabs.« less

Oxidation of hydroxylamine by cytochrome P-460 of the obligate methylotroph Methylococcus capsulatus Bath.

PubMed Central

Zahn, J A; Duncan, C; DiSpirito, A A

1994-01-01

An enzyme capable of the oxidation of hydroxylamine to nitrite was isolated from the obligate methylotroph Methylococcus capsulatus Bath. The absorption spectra in cell extracts, electron paramagnetic resonance spectra, molecular weight, covalent attachment of heme group to polypeptide, and enzymatic activities suggest that the enzyme is similar to cytochrome P-460, a novel iron-containing protein previously observed only in Nitrosomonas europaea. The native and subunit molecular masses of the M. capsulatus Bath protein were 38,900 and 16,390 Da, respectively; the isoelectric point was 6.98. The enzyme has approximately one iron and one copper atom per subunit. The electron paramagnetic resonance spectrum of the protein showed evidence for a high-spin ferric heme. In contrast to the enzyme from N. europaea, a 13-nm blue shift in the soret band of the ferrocytochrome (463 nm in cell extracts to 450 nm in the final sample) occurred during purification. The amino acid composition and N-terminal amino acid sequence of the enzyme from M. capsulatus Bath was similar but not identical to those of cytochrome P-460 of N. europaea. In cell extracts, the identity of the biological electron acceptor is as yet unestablished. Cytochrome c-555 is able to accept electrons from cytochrome P-460, although the purified enzyme required phenazine methosulfate for maximum hydroxylamine oxidation activity (specific activity, 366 mol of O2 per s per mol of enzyme). Hydroxylamine oxidation rates were stimulated approximately 2-fold by 1 mM cyanide and 1.5-fold by 0.1 mM 8-hydroxyquinoline. Images PMID:7928947

Experimental investigation on the microscopic structure of intrinsic paramagnetic point defects in amorphous silicon dioxide

NASA Astrophysics Data System (ADS)

Buscarino, G.

2007-11-01

In the present Ph.D. Thesis we report an experimental investigation on the effects of gamma- and beta-ray irradiation and of subsequent thermal treatment on many types of a-SiO2 materials, differing in the production methods, OH- and Al-content, and oxygen deficiencies. Our main objective is to gain further insight on the microscopic structures of the E'_gamma, E'_delta, E'_alpha and triplet paramagnetic centers, which are among the most important and studied class of radiation induced intrinsic point defects in a-SiO2. To pursue this objective, we use prevalently the EPR spectroscopy. In particular, our work is focused on the properties of the unpaired electrons wave functions involved in the defects, and this aspect is mainly investigated through the study of the EPR signals originating from the interaction of the unpaired electrons with 29Si magnetic nuclei (with nuclear spin I=1/2 and natural abundance 4.7 %). In addition, in some cases of interest, OA measurements are also performed with the aim to further characterize the electronic properties of the defects. Furthermore, due to its relevance for electronics application, the charge state of the defects is investigated by looking at the processes responsible for the generation of the defects of interest. Once these information were gained, the possible sites that can serve as precursors for defects formation are deduced, with the definitive purpose to obtain in the future more radiation resistant a-SiO2 materials in which the deleterious effects connected with the point defects are significantly reduced.

Giant Paramagnetism of Copper Nanoparticles in Nanocomposites Cu@C

NASA Astrophysics Data System (ADS)

Sharoyan, Eduard; Mirzakhanyan, Armen; Gyulasaryan, Harutyun; Manukyan, Aram; Estiphanos, Medhanie; Goff, Michael; Bernal, Oscar; Kocharian, Armen

The copper nanoparticles in nanocomposites Cu@C, encapsulated in graphitized carbon shell was obtained by the solid-phase pyrolysis method of polycrystalline phthalocyanine (CuPc, Pc =C32N8H16) . The average sizes of the nanoparticles are in the range of 2-6 nm. Magnetic measurements were carried out by vibrational magnetometer in the temperature range 10-300 K. At low temperatures (<70K) we observed a giant paramagnetism, apparently due to the (ballistic) conduction electron (large orbital magnetism). The values of the specific susceptibility at T = 10K with magnetic specific susceptibility of 510-5 emu/gOe order. This work was supported by the RA MES State Committee of Science, in the frames of the research project SCS-13-1C090. The work at California State University was supported by the National Science Foundation-Partnerships for Research and Education in Materials under Grant DMR-1523588.

Fast Gated EPR Imaging of the Beating Heart: Spatiotemporally-Resolved 3D Imaging of Free Radical Distribution during the Cardiac Cycle

PubMed Central

Chen, Zhiyu; Reyes, Levy A.; Johnson, David H.; Velayutham, Murugesan; Yang, Changjun; Samouilov, Alexandre; Zweier, Jay L.

2012-01-01

In vivo or ex vivo electron paramagnetic resonance imaging (EPRI) is a powerful technique for determining the spatial distribution of free radicals and other paramagnetic species in living organs and tissues. However, applications of EPRI have been limited by long projection acquisition times and the consequent fact that rapid gated EPRI was not possible. Hence in vivo EPRI typically provided only time-averaged information. In order to achieve direct gated EPRI, a fast EPR acquisition scheme was developed to decrease EPR projection acquisition time down to 10 – 20 ms, along with corresponding software and instrumentation to achieve fast gated EPRI of the isolated beating heart with submillimeter spatial resolution in as little as 2 to 3 minutes. Reconstructed images display temporal and spatial variations of the free radical distribution, anatomical structure, and contractile function within the rat heart during the cardiac cycle. PMID:22473660

Physical and Instrumental Considerations in the Use of Lithium Phthalocyanine for Measurements of the Concentration of the Oxygen

NASA Astrophysics Data System (ADS)

Smirnov, A. I.; Norby, S. W.; Walczak, T.; Liu, K. J.; Swartz, H. M.

The use of crystals of lithium phthalocyanine (LiPc) to measure the concentration of oxygen in vivo and in vitro by electron paramagnetic resonance leads to experimental constraints due to the very narrow EPR lines that may occur (as narrow as 11-13 mG in the absence of O 2), distortions induced by the automatic frequency control system, anisotropy in the spectra (orientation-dependent linewidth is 11-17 mG in the absence of O 2), microwave power saturation, and the effect of physiological motion. These constraints can be overcome if recognized. This article highlights the experimental and theoretical basis of these properties of the EPR signal of LiPc and suggests some technical solutions. It is most important to recognize that paramagnetic species such as LiPc present problems that are not commonly encountered in EPR spectroscopy.

[The role of oxidative metabolism disturbance in the development of NO-related endothelial dysfunction during chronic hearth failure].

PubMed

Goishvili, N; Kakauridze, N; Sanikidze, T

2005-05-01

The aim of the work was to establish the oxidative metabolism changes and NO data in Chronic Hearth Failure (HF). 52 patients were included in the investigation, among them 37 patients with CHD and chronic HF (II-IV functional class by NIHA) and 17 without it (control group). For revealing of organism redox-status (ceruloplasmine, Fe3+-transfferine, Mn2+, methemoglobine) the blood paramagnetic centers was studied by electron paramagnetic resonance method. For revealing of blood free NO, the diethyldithiocarbamat (SIGMA) was used. In chronic HF the oxidative process intensification and organism compensate reaction reduction with low Fe3+-transferine levels, increased Mn2++, methaemoglobin and inactivation of erythrocytes membranes adrenergic receptors were revealed. In chronic HF the accumulation of reactive oxygen levels provoke NO transformation in peroxynitrote with following decreases of blood free NO and develop the endothelial dysfunction.

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.

Large dielectric permittivity and possible correlation between magnetic and dielectric properties in bulk BaFeO{sub 3−δ}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagdeo, Archna; Gautam, Kamini; Singh, M. N.

2014-07-28

We report structural, magnetic, and dielectric properties of oxygen deficient hexagonal BaFeO{sub 3−δ}. A large dielectric permittivity comparable to that of other semiconducting oxides is observed in BaFeO{sub 3−δ}. Magnetization measurements indicate magnetic inhomogeneity and the system shows a paramagnetic to antiferromagnetic transition at ∼160 K. Remarkably, the temperature, at which paramagnetic to antiferromagnetic transition occurs, around this temperature, a huge drop in the dissipation factor takes place and resistivity shoots up; this indicates the possible correlation among magnetic and dielectric properties. First principle simulations reveal that some of these behaviors may be explained in terms of many body electron correlationmore » effect in the presence of oxygen vacancy present in BaFeO{sub 3−δ} indicating its importance in both fundamental science as well as in applications.« less

Magnetic phase composition of strontium titanate implanted with iron ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dulov, E.N., E-mail: evgeny.dulov@ksu.ru; Ivoilov, N.G.; Strebkov, O.A.

2011-12-15

Highlights: Black-Right-Pointing-Pointer The origin of RT-ferromagnetism in iron implanted strontium titanate. Black-Right-Pointing-Pointer Metallic iron nanoclusters form during implantation and define magnetic behaviour. Black-Right-Pointing-Pointer Paramagnetic at room temperature iron-substituted strontium titanate identified. -- Abstract: Thin magnetic films were synthesized by means of implantation of iron ions into single-crystalline (1 0 0) substrates of strontium titanate. Depth-selective conversion electron Moessbauer spectroscopy (DCEMS) indicates that origin of the samples magnetism is {alpha}-Fe nanoparticles. Iron-substituted strontium titanate was also identified but with paramagnetic behaviour at room temperature. Surface magneto-optical Kerr effect (SMOKE) confirms that the films reveal superparamagnetism (the low-fluence sample) or ferromagnetism (themore » high-fluence sample), and demonstrate absence of magnetic in-plane anisotropy. These findings highlight iron implanted strontium titanate as a promising candidate for composite multiferroic material and also for gas sensing applications.« less

^17O NMR Study of Sr_2CuO_2Cl_2, a Single-Layer Parent Compound of a High Tc Superconductor

NASA Astrophysics Data System (ADS)

Thurber, Kent; Hunt, Allen; Imai, Takashi; Chou, Fang-Cheng; Lee, Young

1997-03-01

We report NMR measurements of the ^17O nuclear spin-lattice relaxation rate 1/T_1, and the ^17O Knight shift of Sr_2CuO_2Cl2 (TN = 257 K) in the paramagnetic state from the Néel temperature up to 700 K. This establishes, for the first time, the temperature and frequency dependence of ^17O NMR in the paramagnetic state of a clean, single-layer, undoped parent compound of a high Tc superconductor. The ^17O NMR results test the nature of elementary spin excitations around q = 0 and give insight into the spin wave damping, Γ. The observation, ^17 1/T1 ~ a T^3 [ 1 + O(T/J) ], agrees semi-quantitatively with theoretical predictions based on spin waves in the spin S=1/2 2D Heisenberg model. electronically.

W-band EPR of vanadyl complexes aggregates on the surface of Al2O3

NASA Astrophysics Data System (ADS)

Mamin, G.; Gafurov, M.; Galukhin, A.; Gracheva, I.; Murzakhanov, F.; Rodionov, A.; Orlinskii, S.

2018-05-01

Structural characterization of metalloporphyrins, asphaltenes and their aggregates in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. We present W-band (95 GHz) electron paramagnetic resonance (EPR) study in the magnetic field of about 3.4 T and temperature of 100 K for Karmalinskoe oil, asphaltens and asphaltenes deposited on the surface of Al2O3. Features of the obtained spectra are described. Shift to the higher frequencies allows to separate spectrally the contributions from paramagnetic complexes of different origin and define the EPR parameters more accurately comparing to the conventional X-band (9 GHz). Changes of the EPR parameters are tracked. We suggest that the proposed approach can be used for the investigation of structure of vanadyl complexes aggregates in crude oil and their fractions.

Polarized Neutron Diffraction to Probe Local Magnetic Anisotropy of a Low-Spin Fe(III) Complex.

PubMed

Ridier, Karl; Mondal, Abhishake; Boilleau, Corentin; Cador, Olivier; Gillon, Béatrice; Chaboussant, Grégory; Le Guennic, Boris; Costuas, Karine; Lescouëzec, Rodrigue

2016-03-14

We have determined by polarized neutron diffraction (PND) the low-temperature molecular magnetic susceptibility tensor of the anisotropic low-spin complex PPh4 [Fe(III) (Tp)(CN)3]⋅H2O. We found the existence of a pronounced molecular easy magnetization axis, almost parallel to the C3 pseudo-axis of the molecule, which also corresponds to a trigonal elongation direction of the octahedral coordination sphere of the Fe(III) ion. The PND results are coherent with electron paramagnetic resonance (EPR) spectroscopy, magnetometry, and ab initio investigations. Through this particular example, we demonstrate the capabilities of PND to provide a unique, direct, and straightforward picture of the magnetic anisotropy and susceptibility tensors, offering a clear-cut way to establish magneto-structural correlations in paramagnetic molecular complexes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural, optical, electron paramagnetic, thermal and dielectric characterization of chalcopyrite.

PubMed

Prameena, B; Anbalagan, G; Gunasekaran, S; Ramkumaar, G R; Gowtham, B

2014-03-25

Chalcopyrite (CuFeS2) a variety of pyrite minerals was investigated through spectroscopic techniques and thermal analysis. The morphology and elemental analysis of the chalcopyrite have been done by high resolution SEM with EDAX. The lattice parameters were from the powder diffraction data (a=5.3003±0.0089 Å, c=10.3679±0.0289 Å; the volume of the unit cell=291.266 Å(3) with space group I42d (122)). The thermal decomposition behavior of chalcopyrite was studied by means of thermogravimetric analysis at three different heating rates 10, 15 and 20 °C/min. The values of effective activation energy (Ea), pre-exponential factor (ln A) for thermal decomposition have been measured at three different heating rates by employing Kissinger, Kim-Park and Flynn-Wall methods. Dielectric studies at different temperatures have also been carried out and it was found that both dielectric constant and dielectric loss decreases with the increase of frequency. Copyright © 2013 Elsevier B.V. All rights reserved.

Electron paramagnetic resonance studies of slowly tumbling vanadyl spin probes in nematic liquid crystals

NASA Technical Reports Server (NTRS)

Bruno, G. V.; Harrington, J. K.; Eastman, M. P.

1978-01-01

An analysis of EPR line shapes by the method of Polnaszek, Bruno, and Freed is made for slowly tumbling vanadyl spin probes in viscous nematic liquid crystals. The use of typical vanadyl complexes as spin probes for nematic liquid crystals is shown to simplify the theoretical analysis and the subsequent interpretation. Rotational correlation times tau and orientational ordering parameters S sub Z where slow tumbling effects are expected to be observed in vanadyl EPR spectra are indicated in a plot. Analysis of the inertial effects on the probe reorientation, which are induced by slowly fluctuating torque components of the local solvent structure, yield quantitative values for tau and S sub Z. The weakly ordered probe VOAA is in the slow tumbling region and displays these inertial effects throughout the nematic range of BEPC and Phase V. VOAA exhibits different reorientation behavior near the isotropic-nematic transition temperature than that displayed far below this transition temperature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mbarki, Mohammed; Touzani, Rachid St.; Rehorn, Christian W.G.

The new ternary transition metal-rich borides Ta{sub 2}OsB{sub 2} and TaRuB have been successfully synthesized by arc-melting the elements in a water-cooled crucible under an argon atmosphere. The crystal structures of both compounds were solved by single-crystal X-ray diffraction and their metal compositions were confirmed by EDX analysis. It was found that Ta{sub 2}OsB{sub 2} and TaRuB crystallize in the tetragonal Nb{sub 2}OsB{sub 2} (space group P4/mnc, no. 128) and the orthorhombic NbRuB (space group Pmma, no. 51) structure types with lattice parameters a=5.878(2) Å, c=6.857(2) Å and a=10.806(2) Å, b=3.196(1) Å, c=6.312(2) Å, respectively. Furthermore, crystallographic, electronic and bondingmore » characteristics have been studied by density functional theory (DFT). Electronic structure relaxation has confirmed the crystallographic parameters while COHP bonding analysis indicates that B{sub 2}-dummbells are the strongest bonds in both compounds. Moreover, the formation of osmium dumbbells in Ta{sub 2}OsB{sub 2} through a Peierls distortion along the c-axis, is found to be the origin of superstructure formation. Magnetic susceptibility measurements reveal that the two phases are Pauli paramagnets, thus confirming the theoretical DOS prediction of metallic character. Also hints of superconductivity are found in the two phases, however lack of single phase samples has prevented confirmation. Furthermore, the thermodynamic stability of the two modifications of AMB (A=Nb, Ta; M =Ru, Os) are studied using DFT, as new possible phases containing either B{sub 4}- or B{sub 2}-units are predicted, the former being the most thermodynamically stable modification. - Graphical abstract: The two new ternary tantalum borides, Ta{sub 2}OsB{sub 2} and TaRuB, have been discovered. Their crystal structures contain boron dumbbells, which are the strongest bonds. Peirls distortion is found responsible for Os{sub 2}-dumbbells formation in Ta{sub 2}OsB{sub 2}. Ta{sub 2}OsB{sub 2} and TaRuB are Pauli paramagnet and potential superconductors. - Highlights: • Two new ternary tantalum borides, Ta{sub 2}OsB{sub 2} and TaRuB, discovered. • Boron dumbbells are the strongest bonds in Ta{sub 2}OsB{sub 2} and TaRuB. • Peierls distortion responsible for Os{sub 2}-dumbbells formation in Ta{sub 2}OsB{sub 2.} • Ta{sub 2}OsB{sub 2} and TaRuB are Pauli paramagnet. • Ta{sub 2}OsB{sub 2} and TaRuB contain pseudogaps and are potential superconductors.« less

Curie-type paramagnetic NMR relaxation in the aqueous solution of Ni(II).

PubMed

Mareš, Jiří; Hanni, Matti; Lantto, Perttu; Lounila, Juhani; Vaara, Juha

2014-04-21

Ni(2+)(aq) has been used for many decades as a model system for paramagnetic nuclear magnetic resonance (pNMR) relaxation studies. More recently, its magnetic properties and also nuclear magnetic relaxation rates have been studied computationally. We have calculated electron paramagnetic resonance and NMR parameters using quantum-mechanical (QM) computation of molecular dynamics snapshots, obtained using a polarizable empirical force field. Statistical averages of hyperfine coupling, g- and zero-field splitting tensors, as well as the pNMR shielding terms, are compared to the available experimental and computational data. In accordance with our previous work, the isotropic hyperfine coupling as well as nuclear shielding values agree well with experimental measurements for the (17)O nuclei of water molecules in the first solvation shell of the nickel ion, whereas larger deviations are found for (1)H centers. We report, for the first time, the Curie-type contribution to the pNMR relaxation rate using QM calculations together with Redfield relaxation theory. The Curie relaxation mechanism is analogous to chemical shift anisotropy relaxation, well-known in diamagnetic NMR. Due to the predominance of other types of paramagnetic relaxation mechanisms for this system, it is possible to extract the Curie term only computationally. The Curie mechanism alone would result in around 16 and 20 s(-1) of relaxation rates (R1 and R2 respectively) for the (1)H nuclei of water molecules bonded to the Ni(2+) center, in a magnetic field of 11.7 T. The corresponding (17)O relaxation rates are around 33 and 38 s(-1). We also report the Curie contribution to the relaxation rate for molecules beyond the first solvation shell in a 1 M solution of Ni(2+) in water.

Electrical, structural and thermal studies of carbon nanotubes from natural legume seeds: kala chana

NASA Astrophysics Data System (ADS)

Ranu, Rachana; Chauhan, Yatishwar; Singh, Pramod K.; Bhattacharya, B.; Tomar, S. K.

2016-12-01

Carbon nanotubes (CNTs) are the carbon materials measured at nanoscale level and they are defined in two types according to the number of concentric layers, i.e. single-layer tube is single-walled nanotubes, while multi-layer tube structure is called multi-walled nanotubes. The green method synthesis for the preparation of CNTs begins with the smashing of legume seeds kala chana, and then they form complex with cobalt salt. Desiccation of the complex compound forms cobalt salt and seed protein. The complex is then decomposed at 625 °C in muffle furnace for 20 min. Purification of the decomposed sample is done through acid wash treatment and dried in vacuum oven. The confirmations of CNTs are done by nuclear magnetic resonance and Fourier transform infrared, which analyzes the denatured protein, reacted to the metal salt. X-Ray diffraction determines the MWNTs with transmission electron microscope (TEM) reports the network structure of CNTs. thermal gravimetric analysis (TGA)-differential thermal analysis (DTA)-thermogravimetric analysis (DTG) tests the amount of sample under thermal treatment. Vibrating sample magnetometer determines the paramagnetic nature of CNTs. CNTs thus prepared can be used in mechanical fields, in solar cells, in electronics fields, etc. because of their multidisciplinary properties. The synthesized CNTs are eco-friendly in nature, prepared by the legume seed natural precursor.

Effects of iodinated contrast agent, xylocaine and gadolinium concentration on the signal emitted in magnetic resonance arthrography: a samples study*

PubMed Central

da Silva, Yvana Lopes Pinheiro; Costa, Rita Zanlorensi Visneck; Pinho, Kátia Elisa Prus; Ferreira, Ricardo Rabello; Schuindt, Sueliton Miyamoto

2015-01-01

Objective To investigate the effects of dilution of paramagnetic contrast agent with iodinated contrast and xylocaine on the signal intensity during magnetic resonance arthrography, and to improve the paramagnetic contrast agent concentration utilized in this imaging modality. Materials and Methods Samples specially prepared for the study with three different concentrations of paramagnetic contrast agent diluted in saline, iodinated contrast agent and xylocaine were imaged with fast spin echo T1-weighted sequences with fat saturation. The samples were placed into flasks and graphical analysis of the signal intensity was performed as a function of the paramagnetic contrast concentration. Results As compared with samples of equal concentrations diluted only with saline, the authors have observed an average signal intensity decrease of 20.67% for iodinated contrast agent, and of 28.34% for xylocaine. However, the increased gadolinium concentration in the samples caused decrease in signal intensity with all the dilutions. Conclusion Minimizing the use of iodinated contrast media and xylocaine and/or the use of a gadolinium concentration of 2.5 mmol/L diluted in saline will improve the sensitivity of magnetic resonance arthrography. PMID:25987746

Mars Oxidant and Radical Detector

NASA Technical Reports Server (NTRS)

Yen, A. S.; Kim, S. S.

2003-01-01

The Mars Oxidant and Radical Detector is an instrument designed to characterize the reactive nature of the martian surface environment. Using Electron Paramagnetic Resonance (EPR) techniques, this instrument can detect, identify, and quantify radical species in soil samples, including those inferred to be present by the Viking experiments. This instrument is currently funded by the Mars Instrument Development Program and is compatible with the Mars Science Laboratory mission.

Neutron-induced defects in optical fibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rizzolo, S., E-mail: serena.rizzolo@univ-st-etienne.fr; Dipartimento di Fisica e Chimica, Università di Palermo, Palermo; and Areva Centre Technique, Le Creusot

2014-10-21

We present a study on 0.8 MeV neutron-induced defects up to fluences of 10{sup 17} n/cm{sup 2} in fluorine doped optical fibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E', H(I), POR and NBOH Centers.

Electron paramagnetic resonance investigation on modulatory effect of 17beta-estradiol on membrane fluidity of erythrocytes in postmenopausal women.

PubMed

Tsuda, K; Kinoshita, Y; Kimura, K; Nishio, I; Masuyama, Y

2001-08-01

Many studies have shown that estrogen may exert cardioprotective effects and reduce the risk of hypertension and coronary events. On the other hand, it has been proposed that cell membrane abnormalities play a role in the pathophysiology of hypertension, although it is not clear whether estrogen would influence membrane function in essential hypertension. The present study was performed to investigate the effects of 17beta-estradiol (E(2)) on membrane fluidity of erythrocytes in normotensive and hypertensive postmenopausal women. We determined the membrane fluidity of erythrocytes by means of an electron paramagnetic resonance and spin-labeling method. In an in vitro study, E(2) significantly decreased the order parameter for 5-nitroxide stearate and the peak height ratio for 16-nitroxide stearate obtained from electron paramagnetic resonance spectra of erythrocyte membranes in normotensive postmenopausal women. The finding indicates that E(2) might increase the membrane fluidity of erythrocytes. The effect of E(2) was significantly potentiated by the NO donor, S-nitroso-N-acetylpenicillamine, and a cGMP analogue, 8-bromo-cGMP. In contrast, the change in the membrane fluidity evoked by E(2) was attenuated in the presence of the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester, and asymmetric dimethyl-L-arginine. In hypertensive postmenopausal women, the membrane fluidity of erythrocytes was significantly lower than that in normotensive postmenopausal women. The effect of E(2) on membrane fluidity was significantly more pronounced in the erythrocytes of hypertensive postmenopausal women than in the erythrocytes of normotensive postmenopausal women. The results of the present study showed that E(2) significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the greater action of E(2) in hypertension might be consistent with the hypothesis that E(2) could have a beneficial effect in regulating rheological behavior of erythrocytes and could have a crucial role in the improvement of the microcirculation in hypertension.

Correlational and thermodynamic properties of finite-temperature electron liquids in the hypernetted-chain approximation.

PubMed

Tanaka, Shigenori

2016-12-07

Correlational and thermodynamic properties of homogeneous electron liquids at finite temperatures are theoretically analyzed in terms of dielectric response formalism with the hypernetted-chain (HNC) approximation and its modified version. The static structure factor and the local-field correction to describe the strong Coulomb-coupling effects beyond the random-phase approximation are self-consistently calculated through solution to integral equations in the paramagnetic (spin unpolarized) and ferromagnetic (spin polarized) states. In the ground state with the normalized temperature θ=0, the present HNC scheme well reproduces the exchange-correlation energies obtained by quantum Monte Carlo (QMC) simulations over the whole fluid phase (the coupling constant r s ≤100), i.e., within 1% and 2% deviations from putative best QMC values in the paramagnetic and ferromagnetic states, respectively. As compared with earlier studies based on the Singwi-Tosi-Land-Sjölander and modified convolution approximations, some improvements on the correlation energies and the correlation functions including the compressibility sum rule are found in the intermediate to strong coupling regimes. When applied to the electron fluids at intermediate Fermi degeneracies (θ≈1), the static structure factors calculated in the HNC scheme show good agreements with the results obtained by the path integral Monte Carlo (PIMC) simulation, while a small negative region in the radial distribution function is observed near the origin, which may be associated with a slight overestimation for the exchange-correlation hole in the HNC approximation. The interaction energies are calculated for various combinations of density and temperature parameters ranging from strong to weak degeneracy and from weak to strong coupling, and the HNC values are then parametrized as functions of r s and θ. The HNC exchange-correlation free energies obtained through the coupling-constant integration show reasonable agreements with earlier results including the PIMC-based fitting over the whole fluid region at finite degeneracies in the paramagnetic state. In contrast, a systematic difference between the HNC and PIMC results is observed in the ferromagnetic state, which suggests a necessity of further studies on the exchange-correlation free energies from both aspects of analytical theory and simulation.

Crystal Structure and Magnetic Properties of New Cubic Quaternary Compounds RT2Sn2Zn18 (R = La, Ce, Pr, and Nd, and T = Co and Fe)

NASA Astrophysics Data System (ADS)

Isikawa, Yosikazu; Mizushima, Toshio; Ejiri, Jun-ichi; Kitayama, Shiori; Kumagai, Keigou; Kuwai, Tomohiko; Bordet, Pierre; Lejay, Pascal

2015-07-01

The new cubic quaternary intermetallic compounds RT2Sn2Zn18 (R = La, Ce, Pr, and Nd, and T = Co and Fe) were synthesized by the mixture-metal flux method using Zn and Sn. The crystal structure was investigated by powder X-ray diffraction and with a four-circle X-ray diffractometer using single crystals. The space group of the compounds is Fdbar{3}m (No. 227). The rare-earth atom is at the cubic site which is the center of a cage composed of Zn and Sn atoms. The crystal structure is the same as the CeCr2Al20-type crystal structure except the atoms at the 16c site, i.e., the Zn atoms at the 16c site are completely replaced by Sn atoms, indicating that the compounds are crystallographically new ordered quaternary compounds. The lattice parameter a and the physical properties of the magnetic susceptibility χ, the magnetization M, and the specific heat C of these cubic caged compounds were investigated. LaCo2Sn2Zn18 and LaFe2Sn2Zn18 are enhanced Pauli paramagnets that originate from the Co and Fe itinerant 3d electrons. CeCo2Sn2Zn18 and CeFe2Sn2Zn18 are also enhanced Pauli paramagnets that originate from both the 3d electrons and Ce 4f electrons. PrCo2Sn2Zn18 and PrFe2Sn2Zn18 are nonmagnetic materials with huge values of C divided by temperature, which indicates that the ground state of Pr ions is a non-Kramers' doublet. NdCo2Sn2Zn18 and NdFe2Sn2Zn18 are magnetic materials with the Néel temperatures of 1.0 and 3.8 K, respectively. All eight compounds have large magnetic moments of Co/Fe in the paramagnetic temperature region, and thus their magnetic moments are inferred to be magnetically frustrating owing to the pyrochlore lattice in the low-temperature region.

Color centers of a borosilicate glass induced by 10 MeV proton, 1.85 MeV electron and 60Co-γ ray

NASA Astrophysics Data System (ADS)

Du, Jishi; Wu, Jiehua; Zhao, Lili; Song, Lixin

2013-05-01

Optical absorption spectra, electron paramagnetic resonance (EPR) spectra, Raman spectra of a borosilicate glass after irradiation by 10 MeV proton, 1.85 MeV electron and 60Co-γ ray were studied. The process of irradiation inducing color centers in the glass was discussed. The band gap of the glass before and after 60Co-γ ray irradiation was studied using Mott and Davis's theory, and it was found that calculated change of the band gap introduced a paradox, because Mott and Davis's theory on the band gap cannot be adopted in the study on the irradiated glass.

Highly reactive free radicals in electronic cigarette aerosols.

PubMed

Goel, Reema; Durand, Erwann; Trushin, Neil; Prokopczyk, Bogdan; Foulds, Jonathan; Elias, Ryan J; Richie, John P

2015-09-21

Electronic cigarette (EC) usage has increased exponentially, but limited data are available on its potential harmful effects. We tested for the presence of reactive, short-lived free radicals in EC aerosols by electron paramagnetic resonance spectroscopy (EPR) using the spin-trap phenyl-N-tert-butylnitrone (PBN). Radicals were detected in aerosols from all ECs and eliquids tested (2.5 × 10(13) to 10.3 × 10(13) radicals per puff at 3.3 V) and from eliquid solvents propylene glycol and glycerol and from "dry puffing". These results demonstrate, for the first time, the production of highly oxidizing free radicals from ECs which may present a potential toxicological risk to EC users.

Diffusional mechanisms augment the fluorine magnetic resonance relaxation in paramagnetic perfluorocarbon nanoparticles that provides a “relaxation switch” for detecting cellular endosomal activation

PubMed Central

Hu, Lingzhi; Zhang, Lei; Chen, Junjie; Lanza, Gregory M.; Wickline, Samuel A.

2011-01-01

Purpose To develop a physical model for the 19F relaxation enhancement in paramagnetic perfluorocarbon nanoparticles (PFC NP) and demonstrate its application in monitoring cellular endosomal functionality through a “19F relaxation switch” phenomenon. Materials and Methods An explicit expression for 19F longitudinal relaxation enhancement was derived analytically. Monte-Carlo simulation was performed to confirm the gadolinium induced magnetic field inhomogenity inside the PFC NP. Field dependent T1 measurements for three types of paramagnetic PFC NPs were carried out to validate the theoretical prediction. Based on the physical model, 19F and 1H relaxation properties of macrophage internalized paramagnetic PFC NPs were measured to evaluate the intracellular process of NPs by macrophages in vitro. Results The theoretical description was confirmed experimentally by field-dependent T1 measurements. The shortening of 19F T1 was found to be attributed to the Brownian motion of PFC molecules inside the NP in conjunction with their ability to permeate into the lipid surfactant coating. A dramatic change of 19F T1 was observed upon endocytosis, revealing the transition from intact bound PFC NP to processed constituents. Conclusion The proposed first-principle analysis of 19F spins in paramagnetic PFC NP relates their structural parameters to the special MR relaxation features. The demonstrated “19F relaxation switch” phenomenon is potentially useful for monitoring cellular endosomal functionality. PMID:21761488

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

NASA Astrophysics Data System (ADS)

Zhang, Huiming; Xie, Yang; Ji, Tongyu

2007-06-01

The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T1 ρ can significantly increase the sensitivity of detecting paramagnetic labeling at high magnetic fields by MRI. However, the in vivo detectable dimension for labeled cell clusters/tissues in T1 ρ-weighted images is limited by the water diffusion-exchange between mesoscopic scale compartments. An experimental investigation of the effect of water diffusion-exchange between compartments on the paramagnetic relaxation enhancement of paramagnetic agent compartment is presented for in vitro/ in vivo models. In these models, the size of paramagnetic agent compartment is comparable to the mean diffusion displacement of water molecules during the long RF pulses that are used to generate the off-resonance rotating frame. The three main objectives of this study were: (1) to qualitatively correlate the effect of water diffusion-exchange with the RF parameters of the long pulse and the rates of water diffusion, (2) to explore the effect of water diffusion-exchange on the paramagnetic relaxation enhancement in vitro, and (3) to demonstrate the paramagnetic relaxation enhancement in vivo. The in vitro models include the water permeable dialysis tubes or water permeable hollow fibers embedded in cross-linked proteins gels. The MWCO of the dialysis tubes was chosen from 0.1 to 15 kDa to control the water diffusion rate. Thin hollow fibers were chosen to provide sub-millimeter scale compartments for the paramagnetic agents. The in vivo model utilized the rat cerebral vasculatures as a paramagnetic agent compartment, and intravascular agents (Gd-DTPA) 30-BSA were administrated into the compartment via bolus injections. Both in vitro and in vivo results demonstrate that the paramagnetic relaxation enhancement is predominant in the T1 ρ-weighted image in the presence of water diffusion-exchange. The T1 ρ contrast has substantially higher sensitivity than the conventional T1 contrast in detecting paramagnetic agents, especially at low paramagnetic agent volumetric fractions, low paramagnetic agent concentrations, and low RF amplitudes. Short pulse duration, short pulse recycle delay and efficient paramagnetic relaxation can reduce the influence of water diffusion-exchange on the paramagnetic enhancement. This study paves the way for the design of off-resonance rotating experiments to detect labeled cell clusters/tissue compartments in vivo at a sub-millimeter scale.

Preparation of manganese doped cadmium sulfide nanoparticles in zincblende phase and their magnetic properties.

PubMed

Nakaya, Masafumi; Tanaka, Itaru; Muramatsu, Atsushi

2012-12-01

In this study, the random dope of Mn into CdS nanoparticles in zincblende phase has been carried out under the mild reaction condition. The resulting nanoparticles were characterized by energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), X-ray diffractometer (XRD), UV-Vis spectrometer, PL spectrometer, and SQUID. EDX showed that the compositions of Mn doped CdS nanoparticles were readily controlled. TEM showed the particle sizes were not significantly affected by the compositions, retaining to be ca. 3 nm with a narrow size distribution. UV-Vis and PL spectra of the resulting nanoparticles showed the intra-Mn level may be affected by the quantum size effect. SQUID measurement showed that the resulting nanoparticles showed diamagnetism, paramagnetism and superparamagnetism dependent on Mn content.

Recycling of the High Valence States of Heme Proteins by Cysteine Residues of Thimet-Oligopeptidase

PubMed Central

Ferreira, Juliana C.; Icimoto, Marcelo Y.; Marcondes, Marcelo F.; Oliveira, Vitor; Nascimento, Otaciro R.; Nantes, Iseli L.

2013-01-01

The peptidolytic enzyme THIMET-oligopeptidase (TOP) is able to act as a reducing agent in the peroxidase cycle of myoglobin (Mb) and horseradish peroxidase (HRP). The TOP-promoted recycling of the high valence states of the peroxidases to the respective resting form was accompanied by a significant decrease in the thiol content of the peptidolytic enzyme. EPR (electron paramagnetic resonance) analysis using DBNBS spin trapping revealed that TOP also prevented the formation of tryptophanyl radical in Mb challenged by H2O2. The oxidation of TOP thiol groups by peroxidases did not promote the inactivating oligomerization observed in the oxidation promoted by the enzyme aging. These findings are discussed towards a possible occurrence of these reactions in cells. PMID:24223886

Uranium 5f shell in UPd2Al3 and URu2Si2 studied by x-ray magnetic circular dichroism

NASA Astrophysics Data System (ADS)

Yaouanc, A.; Dalmas de Réotier, P.; van der Laan, G.; Hiess, A.; Goulon, J.; Neumann, C.; Lejay, P.; Sato, N.

1998-10-01

We report x-ray magnetic circular dichroism (XMCD) measurements performed at the uranium M4,5 edges in the paramagnetic phase of the heavy fermion superconductors UPd2Al3 and URu2Si2. The analysis of the spectra with the first sum rule yields the orbital moment of the 5f shell for both compounds. The shape of the dichroic spectrum at the M5 edge for the two compounds is qualitatively different: a single lobe is observed for URu2Si2 and two lobes are detected for UPd2Al3. This two lobe structure reflects the strong effect of the interaction of the uranium 5f electrons with their environment in the latter compound.

A Study of Ziegler–Natta Propylene Polymerization Catalysts by Spectroscopic Methods

PubMed Central

Tkachenko, Olga P.; Kucherov, Alexey V.; Kustov, Leonid M.; Virkkunen, Ville; Leinonen, Timo; Denifl, Peter

2017-01-01

Ziegler–Natta polymerization catalysts were characterized by a complex of surface- and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti4+, Ti3+, Ti2+, and Ti1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom. PMID:28772850

Dielectric relaxation in epitaxial films of paraelectric-magnetic SrTiO3-SrMnO3 solid solution

NASA Astrophysics Data System (ADS)

Savinov, M.; Bovtun, V.; Tereshina-Chitrova, E.; Stupakov, A.; Dejneka, A.; Tyunina, M.

2018-01-01

Magneto-dielectric properties of (A2+)MnO3-type perovskites are attractive for applications and stimulate extensive studies of these materials. Here, the complex dielectric and magnetic responses are investigated as in epitaxial films of SrTi0.6Mn0.4O3, solid solution of paraelectric SrTiO3 and magnetic SrMnO3. The impedance and resonance measurements at frequencies of 10-2-1010 Hz and temperatures of 10-500 K reveal broad dielectric anomalies centered at 100-200 K, while the films are paramagnetic at all temperatures. Analysis shows polaronic electrical conductivity behind the observed behavior. Electron-phonon correlations, rather than spin-phonon correlations, are suggested to produce the apparent magneto-dielectric responses in many multiferroic manganites.

40 CFR 91.304 - Test equipment overview.

Code of Federal Regulations, 2014 CFR

2014-07-01

... infrared detector (NDIR) absorption type for carbon monoxide and carbon dioxide analysis; paramagnetic detector (PMD), zirconia (ZRDO), or electrochemical type (ECS) for oxygen analysis; a flame ionization detector (FID) or heated flame ionization detector (HFID) type for hydrocarbon analysis; and a...

Dependence of Van-Vleck paramagnetism on the size of nanocrystals in superstoichiometric TiO{sub y}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valeeva, A. A., E-mail: valeeva@ihim.uran.ru; Nazarova, S. Z.; Rempel, A. A.

2016-04-15

In situ measurements of the magnetic susceptibility of titanium monoxide nanocrystals with superstoichiometric composition TiO{sub y} (y > 1) in the 300–1200 K temperature range showed that this value depends not only on the structural state of a sample, but also on the size of crystals. Analysis of data obtained for both ordered and disordered TiO{sub y} showed that the Van-Vleck paramagnetism is inversely proportional to the nanocrystal size because of breakage of the symmetry of local environment of the near-surface atoms of titanium and oxygen. The Van-Vleck paramagnetism contribution due to atomic-vacancy disorder in superstoichiometric titanium monoxide nanocrystals, asmore » well as in the stoichiometric composition, is proportional to a deviation of the degree of long-range order from its maximum value.« less

Low-temperature thermal decomposition of heavy petroleum distillates: interconnection between the electrical properties and concentration of paramagnetic centres

NASA Astrophysics Data System (ADS)

Dolomatov, M.; Gafurov, M.; Rodionov, A.; Mamin, G.; González, L. Miquel; Vakhin, A.; Petrov, A.; Bakhtizin, R.; Khairudinov, I.; Orlinskii, S.

2018-05-01

Changes of paramagnetic centers (PC) concentration in petroleum dispersed systems (PDS) are studied in the process of low-temperature thermolysis. Complex investigation of physicochemical, rheological and electrophysical properties of high-boiling oil fractions is performed. Based on the analysis of the experimental results it can be concluded that the PDS under investigation can be regarded as amorphous broadband organic semiconductors for which PC plays a role of dopant. It shows the perspectives of the asphaltenes usage as a basis for the photovoltaic devices.

Spectroscopic Characterization of YedY: The Role of Sulfur Coordination in a Mo(V) Sulfite Oxidase Family Enzyme Form

PubMed Central

Yang, Jing; Rothery, Richard; Sempombe, Joseph

2011-01-01

Electronic paramagnetic resonance, electronic absorption, and magnetic circular dichroism spectroscopies have been performed on YedY, a SUOX fold protein with a Mo domain that is remarkably similar to that found in chicken sulfite oxidase, A. thaliana plant sulfite oxidase, and the bacterial sulfite dehydrogenase from S. novella. Low-energy dithiolene→Mo and cysteine thiolate→Mo charge transfer bands have been assigned for the first time in a Mo(V) form of a SUOX fold protein, and the spectroscopic data have been used to interpret the results of bonding calculations. The analysis shows that second coordination sphere effects modulate dithiolene and cysteine sulfur covalency contributions to the Mo bonding scheme. Namely, a more acute Ooxo-Mo-SCys-C dihedral angle results in increased cysteine thiolate S→Mo charge transfer and a high g1 in the EPR spectrum. The spectrosocopic results, coupled with the available structural data, indicate that these second coordination sphere effects may play key roles in modulating the active site redox potential, facilitating hole superexchange pathways for electron transfer regeneration, and affecting the type of reactions catalyzed by sulfite oxidase family enzymes. PMID:19860477

Electronic and magnetic properties of epitaxial SrRh O 3 films

DOE PAGES

Nichols, John A.; Yuk, Simuck F.; Sohn, Changhee; ...

2017-06-16

The strong interplay of fundamental order parameters in complex oxides is known to give rise to exotic physical phenomena. The 4$d$ transition-metal oxide SrRh O 3 has generated much interest, but advances have been hindered by difficulties in preparing single-crystalline phases. Here we epitaxially stabilize high-quality single-crystalline SrRh O 3 films and investigate their structural, electronic, and magnetic properties. Lastly, we determine that their properties significantly differ from the paramagnetic metallic ground state that governs bulk samples and are strongly related to rotations of Rh O 6 octahedra.

The 13C nuclear magnetic resonance in graphite intercalation compounds

NASA Technical Reports Server (NTRS)

Tsang, T.; Resing, H. A.

1985-01-01

The (13)C NMR chemical shifts of graphite intercalation compounds were calculated. For acceptor types, the shifts come mainly from the paramagnetic (Ramsey) intra-atomic terms. They are related to the gross features of the two-dimensional band structures. The calculated anisotropy is about -140 ppm and is independent of the finer details such as charge transfer. For donor types, the carbon 2p pi orbitals are spin-polarized because of mixing with metal conduction electrons, thus there is an additional dipolar contribution which may be correlated with the electronic specific heat. The general agreement with experimental data is satisfactory.

C-13 nuclear magnetic resonance in graphite intercalation compounds

NASA Technical Reports Server (NTRS)

Tsang, T.; Resing, H. A.

1985-01-01

The C-13 NMR chemical shifts of graphite intercalation compounds have been calculated. For acceptor types, the shifts come mainly from the paramagnetic (Ramsey) intra-atomic terms. They are related to the gross features of the two-dimensional band structures. The calculated anisotropy is about - 140 ppm and is independent of the finer details such as charge transfer. For donor types, the carbon 2p pi orbitals are spin-polarized because of mixing with metal-conduction electrons, thus there is an additional dipolar contribution which may be correlated with the electronic specific heat. The general agreement with experimental data is satisfactory.

Hydrogen control of ferromagnetism in a dilute magnetic semiconductor.

PubMed

Goennenwein, Sebastian T B; Wassner, Thomas A; Huebl, Hans; Brandt, Martin S; Philipp, Jan B; Opel, Matthias; Gross, Rudolf; Koeder, Achim; Schoch, Wladimir; Waag, Andreas

2004-06-04

We show that upon exposure to a remote dc hydrogen plasma, the magnetic and electronic properties of the dilute magnetic semiconductor Ga1-xMnxAs change qualitatively. While the as-grown Ga1-xMnxAs thin films are ferromagnetic at temperatures T less, similar 70 K, the samples are found to be paramagnetic after the hydrogenation, with a Brillouin-type magnetization curve even at T=2 K. Comparing magnetization and electronic transport measurements, we conclude that the density of free holes p is significantly reduced by the plasma process, while the density of Mn magnetic moments does not change.

Amplification of Dynamic Nuclear Polarization at 200 GHz by Arbitrary Pulse Shaping of the Electron Spin Saturation Profile.

PubMed

Kaminker, Ilia; Han, Songi

2018-06-07

Dynamic nuclear polarization (DNP) takes center stage in nuclear magnetic resonance (NMR) as a tool to amplify its signal by orders of magnitude through the transfer of polarization from electron to nuclear spins. In contrast to modern NMR and electron paramagnetic resonance (EPR) that extensively rely on pulses for spin manipulation in the time domain, the current mainstream DNP technology exclusively relies on monochromatic continuous wave (CW) irradiation. This study introduces arbitrary phase shaped pulses that constitute a train of coherent chirp pulses in the time domain at 200 GHz (7 T) to dramatically enhance the saturation bandwidth and DNP performance compared to CW DNP, yielding up to 500-fold in NMR signal enhancements. The observed improvement is attributed to the recruitment of additional electron spins contributing to DNP via the cross-effect mechanism, as experimentally confirmed by two-frequency pump-probe electron-electron double resonance (ELDOR).

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yap, Yung Szen, E-mail: yungszen@utm.my; Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor; Tabuchi, Yutaka

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, wemore » 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.« less

Investigations of the local distortions and EPR parameters for Cu2+ in xNa2 O-(30-x)K2 O-70B2 O3 (5 ≤ x ≤ 25 mol%) glasses.

PubMed

Zhang, Zhen-Ya; Wu, Shao-Yi; Zhang, Fu; Zhang, Cheng-Xi; Qin, Rui-Jie; Gao, Han

2018-03-01

The local distortions and electron paramagnetic resonance parameters for Cu 2+ in the mixed alkali borate glasses xNa 2 O-(30-x)K 2 O-70B 2 O 3 (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na 2 O compositions x. Owing to the Jahn-Teller effect, the octahedral [CuO 6 ] 10- clusters show significant tetragonal elongation ratios p ~19% along the C 4 axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi-linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi-linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi-linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal-fields and the electronic cloud distribution around Cu 2+ with the variation of the composition of Na 2 O. Copyright © 2017 John Wiley & Sons, Ltd.

Progress towards an electron electric dipole moment search in Europium-Barium Titanates

NASA Astrophysics Data System (ADS)

Eckel, Stephen; Sushkov, Alexander; Lamoreaux, Steven

2012-06-01

We report on recent progress on a search for the electron's electric dipole moment (eEDM) using solid- state Eu0.5Ba0.5TiO3. This material has many desirable properties including ferroelectricity below 200 K and paramagnetism above 1.8 K. When the sample has a non-zero electric polarization, the seven unpaired 4f electrons of the Eu^2+ ions in the lattice feel a large effective electric field of order 10 MV/cm in the direction of the polarization. This causes the electron spins to align with the electric polarization and generate a magnetization, which is measured using DC SQUID magnetometers. We will detail measurements of systematic effects along with recent results toward a measurement of the eEDM.

Origin of the decoherence of the extended electron spin state in Ti-doped β-Ga2O3.

PubMed

Mentink-Vigier, F; Binet, L; Gourier, D; Vezin, H

2013-08-07

The mechanism of decoherence of the electron spin of Ti(3+) in β-Ga2O3 was investigated by pulsed electron paramagnetic resonance. At 4.2 K, both instantaneous and spectral diffusion contribute to the decoherence. For electron spin concentrations ≈10(25) m(-3) in the studied samples, calculations indicate that electron-electron couplings and electron couplings with (69)Ga and (71)Ga nuclei yield similar contributions to the spectral diffusion, but that electron-nuclei interactions could become the dominant cause of spectral diffusion for only slightly lower spin concentrations. Above 20 K, an additional contribution to the decoherence as well as to the spin-lattice relaxation arises from a two-optical-phonon Raman process, which becomes the leading decoherence mechanism for T > 39 K. Rabi oscillations with a damping time of about 79 ns at 4.2 K could also be observed. The damping of the Rabi oscillations, independent of the oscillation frequency, is suspected to arise from electron-nuclei interactions.

Manganese Binding Properties of Human Calprotectin under Conditions of High and Low Calcium: X-ray Crystallographic and Advanced Electron Paramagnetic Resonance Spectroscopic Analysis

DOE PAGES

Gagnon, Derek M.; Brophy, Megan Brunjes; Bowman, Sarah E. J.; ...

2015-01-18

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. Here in this paper, 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 heterodimermore » 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 15N (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 His 6 site of human calprotectin.« less

Manganese Binding Properties of Human Calprotectin under Conditions of High and Low Calcium: X-ray Crystallographic and Advanced Electron Paramagnetic Resonance Spectroscopic Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gagnon, Derek M.; Brophy, Megan Brunjes; Bowman, Sarah E. J.

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. Here in this paper, 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 heterodimermore » 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 15N (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 His 6 site of human calprotectin.« less

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 prehistoric shock damage. This is demonstrated by our study of shocked Kaibab limestone from the 49,000-year-old Meteor (Barringer) Crater Arizona.

EPR hyperfine structure of the Mo-related defect in CdWO4

NASA Astrophysics Data System (ADS)

Elsts, E.; Rogulis, U.

2005-01-01

The hyperfine structure (hf) of the electron paramagnetic resonance (EPR) spectrum of Mo-related impurity defects in CdWO4 crystals observed previously (U. Rogulis, Radiat. Meas. 29, 287 (1998) [1]) is reconsidered taking into account interactions with two different groups of neighbouring Cd nuclei. The best fit calculated EPR spectrum to the experimental is obtained considering 2 groups of 3 and 2 equivalent Cd nuclei, respectively.

Small-Angle Neutron Scattering on Crosslink Distribution of Epoxy Networks.

DTIC Science & Technology

1985-10-01

distinct second phase or heterogeneity has been detected. Small- angle X-ray scattering (SAXS), 1 nuclear magnetic resonance (NMR) ,2 electron ... paramagnetic resonance (EPR),3 and glass transition 4temperature (Tg) measurements reveal a second phase which is attri- . buted to a heterogeneous...FUNDING/SPONSORING lab. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER * ORGANIZATION I (If applticable)j F3361 5-84-C-5020 * Bc ADDRESS

Estriol improves membrane fluidity of erythrocytes by the nitric oxide-dependent mechanism: an electron paramagnetic resonance study.

PubMed

Tsuda, K; Shimamoto, Y; Kimura, K; Nishio, I; Masuyama, Y

2001-05-01

The present in vitro study was performed to investigate the effects of estriol (E3) on membrane fluidity of erythrocytes by means of an electron paramagnetic resonance (EPR) and spin-labeling method. E3 was shown to significantly decrease the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes. This finding indicated that E3 might increase the membrane fluidity of erythrocytes. The effect of E3 was significantly potentiated by the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine 3',5'-monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change in the membrane fluidity induced by E3 was antagonized by the NO synthase inhibitor, L-NG-nitroarginine-methyl-ester (L-NAME), and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that E3 significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the data might be consistent with the hypothesis that E3 could have a beneficial effect on the rheological behavior of erythrocytes and may play a crucial role in the regulation of microcirculation.

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

2008-10-08

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.

A Versatile High Speed 250 MHz Pulse Imager for Biomedical Applications

PubMed Central

Epel, Boris; Sundramoorthy, Subramanian V.; Mailer, Colin; Halpern, Howard J.

2009-01-01

A versatile 250 MHz pulse electron paramagnetic resonance (EPR) instrument for imaging of small animals is presented. Flexible design of the imager hardware and software makes it possible to use virtually any pulse EPR imaging modality. A fast pulse generation and data acquisition system based on general purpose PCI boards performs measurements with minimal additional delays. Careful design of receiver protection circuitry allowed us to achieve very high sensitivity of the instrument. In this article we demonstrate the ability of the instrument to obtain three dimensional images using the electron spin echo (ESE) and single point imaging (SPI) methods. In a phantom that contains a 1 mM solution of narrow line (16 μT, peak-to-peak) paramagnetic spin probe we achieved an acquisition time of 32 seconds per image with a fast 3D ESE imaging protocol. Using an 18 minute 3D phase relaxation (T2e) ESE imaging protocol in a homogeneous sample a spatial resolution of 1.4 mm and a standard deviation of T2e of 8.5% were achieved. When applied to in vivo imaging this precision of T2e determination would be equivalent to 2 torr resolution of oxygen partial pressure in animal tissues. PMID:19924261

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.

In vitro electron paramagnetic resonance characterization of free radicals: relevance to exercise-induced lipid peroxidation and implications of ascorbate prophylaxis.

PubMed

Davison, Gareth W; Ashton, Tony; Davies, Bruce; Bailey, Damian M

2008-04-01

This study tested the hypothesis that exercise-induced oxidative stress is caused by free radical-mediated damage to polyunsaturated fatty acids (PUFA) which can be prevented following ascorbate prophylaxis. Hyperfine coupling constants (HCC) of alpha-phenyl-tert-butylnitrone (PBN)-adducts were measured via room temperature electron paramagnetic resonance (EPR) spectroscopy in the venous blood of 12 subjects at rest and following maximal exercise during a randomized double-blind placebo-controlled trial and compared to those observed following room-air incubation (2 h at 37 degrees C) of L-alpha-phosphatidycholine, linoleic acid, alpha-linolenic acid and arachidonic acid. All adducts exhibited similar HCC [a(N) 13.6 Gauss (G) and a beta(H) 1.8 G] with the exception of L-alpha-phosphatidycholine [a(N1)=13.4 G, a beta(H1)=1.6 G (37%) and a(N2)=14.9 G, a beta(H2)=0.3 G (63%)] consistent with the trapping of lipid-derived alkoxyl and oleate radicals, respectively. Ascorbate pre-treatment ablated radical formation in both systems. These findings identify circulating PUFA as a potential source of secondary radicals that are capable of initiating oxidative stress in the exercising human.

Electronic paramagnetic resonance (EPR) for the study of ascorbyl radical and lipid radicals in marine organisms.

PubMed

González, Paula Mariela; Aguiar, María Belén; Malanga, Gabriela; Puntarulo, Susana

2013-08-01

Electron paramagnetic resonance (EPR) spectroscopy detects the presence of radicals of biological interest, such as ascorbyl radical (A(•)) and lipid radicals. A(•) is easily detectable by EPR even in aqueous solution at room-temperature. Under oxidative conditions leading to changes in total ascorbate (AH(-)) content, the A(•)/AH(-) ratio could be used to estimate early oxidative stress in the hydrophilic milieu. This methodology was applied to a wide range of aquatic systems including algae, sea urchin, limpets, bivalves and fish, under physiological and oxidative stress conditions as well. The A(•)/AH(-) ratio reflected the state of one part of the oxidative defense system and provided an early and simple diagnosis of environmental stressing conditions. Oxidative damage to lipids was assessed by the EPR-sensitive adduct formation that correlates well with cell membrane damage with no interference from other biological compounds. Probe instability, tissue metabolism, and lack of spin specificity are drawback factors for employing EPR for in vivo determination of free radicals. However, the dependability of this technique, mostly by combining it with other biochemical strategies, enhances the value of these procedures as contributors to the knowledge of oxidative condition in aquatic organisms. Copyright © 2013 Elsevier Inc. All rights reserved.