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.

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.

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.

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

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 (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.

Dynamic nuclear polarization of (1)H, (13)C, and (59)Co in a tris(ethylenediamine)cobalt(III) crystalline lattice doped with Cr(III).

PubMed

Corzilius, Björn; Michaelis, Vladimir K; Penzel, Susanne A; Ravera, Enrico; Smith, Albert A; Luchinat, Claudio; Griffin, Robert G

2014-08-20

The study of inorganic crystalline materials by solid-state NMR spectroscopy is often complicated by the low sensitivity of heavy nuclei. However, these materials often contain or can be prepared with paramagnetic dopants without significantly affecting the structure of the crystalline host. Dynamic nuclear polarization (DNP) is generally capable of enhancing NMR signals by transferring the magnetization of unpaired electrons to the nuclei. Therefore, the NMR sensitivity in these paramagnetically doped crystals might be increased by DNP. In this paper we demonstrate the possibility of efficient DNP transfer in polycrystalline samples of [Co(en)3Cl3]2·NaCl·6H2O (en = ethylenediamine, C2H8N2) doped with Cr(III) in varying concentrations between 0.1 and 3 mol %. We demonstrate that (1)H, (13)C, and (59)Co can be polarized by irradiation of Cr(III) with 140 GHz microwaves at a magnetic field of 5 T. We further explain our findings on the basis of electron paramagnetic resonance spectroscopy of the Cr(III) site and analysis of its temperature-dependent zero-field splitting, as well as the dependence of the DNP enhancement factor on the external magnetic field and microwave power. This first demonstration of DNP transfer from one paramagnetic metal ion to its diamagnetic host metal ion will pave the way for future applications of DNP in paramagnetically doped materials or metalloproteins.

Dynamic Nuclear Polarization of 1H, 13C, and 59Co in a Tris(ethylenediamine)cobalt(III) Crystalline Lattice Doped with Cr(III)

PubMed Central

2015-01-01

The study of inorganic crystalline materials by solid-state NMR spectroscopy is often complicated by the low sensitivity of heavy nuclei. However, these materials often contain or can be prepared with paramagnetic dopants without significantly affecting the structure of the crystalline host. Dynamic nuclear polarization (DNP) is generally capable of enhancing NMR signals by transferring the magnetization of unpaired electrons to the nuclei. Therefore, the NMR sensitivity in these paramagnetically doped crystals might be increased by DNP. In this paper we demonstrate the possibility of efficient DNP transfer in polycrystalline samples of [Co(en)3Cl3]2·NaCl·6H2O (en = ethylenediamine, C2H8N2) doped with Cr(III) in varying concentrations between 0.1 and 3 mol %. We demonstrate that 1H, 13C, and 59Co can be polarized by irradiation of Cr(III) with 140 GHz microwaves at a magnetic field of 5 T. We further explain our findings on the basis of electron paramagnetic resonance spectroscopy of the Cr(III) site and analysis of its temperature-dependent zero-field splitting, as well as the dependence of the DNP enhancement factor on the external magnetic field and microwave power. This first demonstration of DNP transfer from one paramagnetic metal ion to its diamagnetic host metal ion will pave the way for future applications of DNP in paramagnetically doped materials or metalloproteins. PMID:25069794

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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

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.

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

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

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.

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.

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.

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.

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.

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.

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®

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.

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

Structure of Biocompatible Coatings Produced from Hydroxyapatite Nanoparticles by Detonation Spraying

NASA Astrophysics Data System (ADS)

Nosenko, Valentyna; Strutynska, Nataliia; Vorona, Igor; Zatovsky, Igor; Dzhagan, Volodymyr; Lemishko, Sergiy; Epple, Matthias; Prymak, Oleg; Baran, Nikolai; Ishchenko, Stanislav; Slobodyanik, Nikolai; Prylutskyy, Yuriy; Klyui, Nickolai; Temchenko, Volodymyr

2015-12-01

Detonation-produced hydroxyapatite coatings were studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Raman spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. The source material for detonation spraying was a B-type carbonated hydroxyapatite powder. The coatings consisted of tetracalcium phosphate and apatite. The ratio depended slightly on the degree of crystallinity of the initial powder and processing parameters of the coating preparation. The tetracalcium phosphate phase was homogeneous; the apatite phase contained defects localized on the sixfold axis and consisted of hydroxyapatite and oxyapatite. Technological factors contributing to the transformation of hydroxyapatite powder structure during coating formation by detonation spraying are discussed.

Structure of Biocompatible Coatings Produced from Hydroxyapatite Nanoparticles by Detonation Spraying.

PubMed

Nosenko, Valentyna; Strutynska, Nataliia; Vorona, Igor; Zatovsky, Igor; Dzhagan, Volodymyr; Lemishko, Sergiy; Epple, Matthias; Prymak, Oleg; Baran, Nikolai; Ishchenko, Stanislav; Slobodyanik, Nikolai; Prylutskyy, Yuriy; Klyui, Nickolai; Temchenko, Volodymyr

2015-12-01

Detonation-produced hydroxyapatite coatings were studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Raman spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. The source material for detonation spraying was a B-type carbonated hydroxyapatite powder. The coatings consisted of tetracalcium phosphate and apatite. The ratio depended slightly on the degree of crystallinity of the initial powder and processing parameters of the coating preparation. The tetracalcium phosphate phase was homogeneous; the apatite phase contained defects localized on the sixfold axis and consisted of hydroxyapatite and oxyapatite. Technological factors contributing to the transformation of hydroxyapatite powder structure during coating formation by detonation spraying are discussed.

Electron Paramagnetic Resonance Spectroscopy of Vanadium (IV) Complexes and Related Species.

DTIC Science & Technology

1980-07-27

Extensive near infrared (4000-650cm " ) investigations on VOCl 2 complexes have been made by many workers [21,39,43-49]. However the far infrared ...to facilitate the assignment of cation and ligand bacds. 4.2.1.2 Near Infrared Spectroscopy There are three principal reasons for measuriiio the... near infrared spectra of the co!;,plexes: (a) To establish the purity of the complex (b) To establish the bondi ng mode of the 1 i ( nd (c) To establish

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

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

Enhancement of room temperature ferromagnetism in tin oxide nanocrystal using organic solvents

NASA Astrophysics Data System (ADS)

Sakthiraj, K.; Hema, M.; Balachandra Kumar, K.

2017-10-01

The effect of organic solvents (ethanol & ethylene glycol) on the room temperature ferromagnetism in nanocrystalline tin oxide has been studied. The samples were synthesized using sol-gel method with the mixture of water & organic liquid as solvent. It is found that pristine SnO2 nanocrystal contain two different types of paramagnetic centres over their surface:(i) surface chemisorbed oxygen species and (ii) Sn interstitial & oxygen vacancy defect pair. The magnetic moment induced in the as-prepared samples is mainly contributed by the alignment of local spin moments resulting from these defects. These surface defect states are highly activated by the usage of ethylene glycol solvent rather than ethylene in tin oxide nanostructure synthesis. Powder X-ray diffraction, transmission electron microscope imaging, energy dispersive spectrometry, Fourier transformed infrared spectroscopy, UV-vis absorption spectroscopy, photoluminescence spectroscopy, vibrating sample magnetometer measurement and electron spin resonance spectroscopy were employed to characterize the nanostructured tin oxide materials.

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.

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.

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.

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.

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.

Ultraviolet radiation and nanoparticle induced intracellular free radicals generation measured in human keratinocytes by electron paramagnetic resonance spectroscopy.

PubMed

Rancan, F; Nazemi, B; Rautenberg, S; Ryll, M; Hadam, S; Gao, Q; Hackbarth, S; Haag, S F; Graf, C; Rühl, E; Blume-Peytavi, U; Lademann, J; Vogt, A; Meinke, M C

2014-05-01

Several nanoparticle-based formulations used in cosmetics and dermatology are exposed to sunlight once applied to the skin. Therefore, it is important to study possible synergistic effects of nanoparticles and ultraviolet radiation. Electron paramagnetic resonance spectroscopy (EPR) was used to detect intracellular free radicals induced by ultraviolet B (UVB) radiation and amorphous silica nanoparticle and to evaluate the influence of nanoparticle surface chemistry on particle cytotoxicity toward HaCaT cells. Uncoated titanium dioxide nanoparticles served as positive control. In addition, particle intracellular uptake, viability, and induction of interleukin-6 were measured. We found that photo-activated titanium dioxide particles induced a significant amount of intracellular free radicals. On the contrary, no intracellular free radicals were generated by the investigated silica nanoparticles in the dark as well as under UVB radiation. However, under UVB exposure, the non-functionalized silica nanoparticles altered the release of IL-6. At the same concentrations, the amino-functionalized silica nanoparticles had no influence on UVB-induced IL-6 release. EPR spectroscopy is a useful technique to measure nanoparticle-induced intracellular free radicals. Non-toxic concentrations of silica particles enhanced the toxicity of UVB radiation. This synergistic effect was not mediated by particle-generated free radicals and correlated with particle surface charge and intracellular distribution. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

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).

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

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

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

PubMed

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

2015-02-25

A titania mineral (obtained from East coast, Orissa, India) was investigated by X-ray diffraction (XRD), photoacoustic spectroscopy (PAS), Raman and Electron Paramagnetic Resonance (EPR) studies. XRD studies indicated the presence of rutile (91%) and anatase (9%) phases in the mineral. Raman investigation supported this information. Both rutile and anatase phases have tetragonal structure (rutile: space group P4(2)/mnm, a=4.5946(1) Å, c=2.9597(1) Å, V=62.48(1) (Å)(3), Z=2; anatase: space group I4(1)/amd, 3.7848(2) Å, 9.5098(11) Å, V=136.22(2) (Å)(3), Z=4). The deconvoluted PAS spectrum showed nine peaks around 335, 370, 415,485, 555, 605, 659, 690,730 and 785 nm and according to the ligand field theory, these peaks were attributed to the presence of V(4+), Cr(3+), Mn(4+) and Fe(3+) species. EPR studies revealed the presence of transition metal ions V(4+)(d(1)), Cr(3+)(d(3)), Mn(4+)(d(3)) and Fe(3+)(d(5)) at Ti(4+) sites. The EPR spectra are characterized by very large crystal filed splitting (D term) and orthorhombic distortion term (E term) for multiple electron system (s>1) suggesting that the transition metal ions substitute the Ti(4+) in the lattice which is situated in distorted octahedral coordination of oxygen. The possible reasons for observation of unusually large D and E term in the EPR spectra of transition metal ions (S=3/2 and 5/2) are discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

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

PubMed

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

2014-10-01

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

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

PubMed Central

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

2014-01-01

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

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

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

Sidabras, Jason W.; Varanasi, Shiv K.; Hyde, James S.

2014-10-15

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

Ultrafast Photoinduced Symmetry-Breaking Charge Separation and Electron Sharing in Perylenediimide Molecular Triangles.

PubMed

Wu, Yilei; Young, Ryan M; Frasconi, Marco; Schneebeli, Severin T; Spenst, Peter; Gardner, Daniel M; Brown, Kristen E; Würthner, Frank; Stoddart, J Fraser; Wasielewski, Michael R

2015-10-21

We report on a visible-light-absorbing chiral molecular triangle composed of three covalently linked 1,6,7,12-tetra(phenoxy)perylene-3,4:9,10-bis(dicarboximide) (PDI) units. The rigid triangular architecture reduces the electronic coupling between the PDIs, so ultrafast symmetry-breaking charge separation is kinetically favored over intramolecular excimer formation, as revealed by femtosecond transient absorption spectroscopy. Photoexcitation of the PDI triangle dissolved in CH2Cl2 gives PDI(+•)-PDI(-•) in τCS = 12.0 ± 0.2 ps. Fast subsequent intramolecular electron/hole hopping can equilibrate the six possible energetically degenerate ion-pair states, as suggested by electron paramagnetic resonance/electron-nuclear double resonance spectroscopy, which shows that one-electron reduction of the PDI triangle results in complete electron sharing among the three PDIs. Charge recombination of PDI(+•)-PDI(-•) to the ground state occurs in τCR = 1.12 ± 0.01 ns with no evidence of triplet excited state formation.

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.

Peptide-membrane Interactions by Spin-labeling EPR

PubMed Central

Smirnova, Tatyana I.; Smirnov, Alex I.

2016-01-01

Site-directed spin labeling (SDSL) in combination with Electron Paramagnetic Resonance (EPR) spectroscopy is a well-established method that has recently grown in popularity as an experimental technique, with multiple applications in protein and peptide science. The growth is driven by development of labeling strategies, as well as by considerable technical advances in the field, that are paralleled by an increased availability of EPR instrumentation. While the method requires an introduction of a paramagnetic probe at a well-defined position in a peptide sequence, it has been shown to be minimally destructive to the peptide structure and energetics of the peptide-membrane interactions. In this chapter, we describe basic approaches for using SDSL EPR spectroscopy to study interactions between small peptides and biological membranes or membrane mimetic systems. We focus on experimental approaches to quantify peptide-membrane binding, topology of bound peptides, and characterize peptide aggregation. Sample preparation protocols including spin-labeling methods and preparation of membrane mimetic systems are also described. PMID:26477253

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.

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).

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.

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.

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.

Effect of replacing Sn4+ ions by Zn2+ ions on structural, optical and magnetic properties of SnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Selvi, E. Thamarai; Sundar, S. Meenakshi

2017-05-01

This paper highlights on the consequence of replacing tetravalent Sn4+ ions of the SnO2 by divalent Zn2+ ions on their structural, optical, and magnetic properties. Samples of Sn1- x Zn x O2 with x = 0, 0.01, 0.02, 0.03, and 0.04 were synthesized using microwave irradiated solvothermal process. The X-ray powder diffraction patterns reveal the rutile tetragonal phase of all doped SnO2 samples with no secondary phases. The transmission electron microscopy results show the formation of spherical nanoparticles of size 10-30 nm. Morphological changes were observed by scanning electron microscopy. The functional groups were investigated using Fourier transform infrared spectroscopy studies. Optical studies were carried by UV-Vis spectroscopy and fluorescence spectroscopy. Electron paramagnetic resonance was used to calculate the Lande splitting factor ` g'. The magnetic properties using vibrating sample magnetometer exhibit room temperature ferromagnetism for all the samples.

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.

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.

Chromium basalts - Experimental determination of redox states and partitioning among synthetic silicate phases

NASA Technical Reports Server (NTRS)

Schreiber, H. D.; Haskin, L. A.

1976-01-01

Experiments were performed on silicate compositions in the forsterite-anorthite-silica and forsterite-anorthite-diopside systems to determine the relative amounts of Cr(II), Cr(III), and Cr(VI) over a wide range of oxygen partial pressures from 10 to the -10th to 1 atm at 1500 and 1550 C. Redox states were measured by visible absorption spectroscopy and electron paramagnetic resonance spectroscopy and titration. It was found that Cr is present almost exclusively as Cr(III) in terrestrial basaltic liquids and as a mixture of Cr(III) and Cr(II) in lunar basaltic liquids.

Effect of size on structural, optical and magnetic properties of SnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Thamarai Selvi, E.; Meenakshi Sundar, S.

2017-07-01

Tin Oxide (SnO2) nanostructures were synthesized by a microwave oven assisted solvothermal method using with and without cetyl trimethyl ammonium bromide (CTAB) capping agent. XRD confirmed the pure rutile-type tetragonal phase of SnO2 for both uncapped and capped samples. The presence of functional groups was analyzed by Fourier transform infrared spectroscopy. Scanning electron microscopy shows the morphology of the samples. Transmission electron microscopy images exposed the size of the SnO2 nanostructures. Surface defect-related g factor of SnO2 nanoparticles using fluorescence spectroscopy is shown. For both uncapped and capped samples, UV-visible spectrum shows a blue shift in absorption edge due to the quantum confinement effect. Defect-related bands were identified by electron paramagnetic resonance (EPR) spectroscopy. The magnetic properties were studied by using vibrating sample magnetometer (VSM). A high value of magnetic moment 0.023 emu g-1 at room temperature for uncapped SnO2 nanoparticles was observed. Capping with CTAB enhanced the saturation magnetic moment to high value of 0.081 emu g-1 by altering the electronic configuration on the surface.

Membrane Disruption Mechanism of a Prion Peptide (106-126) Investigated by Atomic Force Microscopy, Raman and Electron Paramagnetic Resonance Spectroscopy.

PubMed

Pan, Jianjun; Sahoo, Prasana K; Dalzini, Annalisa; Hayati, Zahra; Aryal, Chinta M; Teng, Peng; Cai, Jianfeng; Rodriguez Gutierrez, Humberto; Song, Likai

2017-05-18

A fragment of the human prion protein spanning residues 106-126 (PrP106-126) recapitulates many essential properties of the disease-causing protein such as amyloidogenicity and cytotoxicity. PrP106-126 has an amphipathic characteristic that resembles many antimicrobial peptides (AMPs). Therefore, the toxic effect of PrP106-126 could arise from a direct association of monomeric peptides with the membrane matrix. Several experimental approaches are employed to scrutinize the impacts of monomeric PrP106-126 on model lipid membranes. Porous defects in planar bilayers are observed by using solution atomic force microscopy. Adding cholesterol does not impede defect formation. A force spectroscopy experiment shows that PrP106-126 reduces Young's modulus of planar lipid bilayers. We use Raman microspectroscopy to study the effect of PrP106-126 on lipid atomic vibrational dynamics. For phosphatidylcholine lipids, PrP106-126 disorders the intrachain conformation, while the interchain interaction is not altered; for phosphatidylethanolamine lipids, PrP106-126 increases the interchain interaction, while the intrachain conformational order remains similar. We explain the observed differences by considering different modes of peptide insertion. Finally, electron paramagnetic resonance spectroscopy shows that PrP106-126 progressively decreases the orientational order of lipid acyl chains in magnetically aligned bicelles. Together, our experimental data support the proposition that monomeric PrP106-126 can disrupt lipid membranes by using similar mechanisms found in AMPs.

Membrane Disruption Mechanism of a Prion Peptide (106-126) Investigated by Atomic Force Microscopy, Raman and Electron Paramagnetic Resonance Spectroscopy

PubMed Central

Pan, Jianjun; Sahoo, Prasana K.; Dalzini, Annalisa; Hayati, Zahra; Aryal, Chinta M.; Teng, Peng; Cai, Jianfeng; Gutierrez, Humberto Rodriguez; Song, Likai

2018-01-01

A fragment of the human prion protein spanning residues 106-126 (PrP106-126) recapitulates many essential properties of the disease-causing protein such as amyloidogenicity and cytotoxicity. PrP106-126 has an amphipathic characteristic that resembles many antimicrobial peptides (AMPs). Therefore, the toxic effect of PrP106-126 could arise from a direct association of monomeric peptides with membrane matrix. Several experimental approaches are employed to scrutinize the impacts of monomeric PrP106-126 on model lipid membranes. Porous defects in planar bilayers are observed by using solution atomic force microscopy. Adding cholesterol does not impede defect formation. Force spectroscopy experiment shows that PrP106-126 reduces Young’s modulus of planar lipid bilayers. We use Raman microspectroscopy to study the effect of PrP106-126 on lipid vibrational dynamics. For phosphatidylcholine lipids, PrP106-126 disorders the intra-chain conformation, while the inter-chain interaction is not altered; for phosphatidylethanolamine lipids, PrP106-126 increases the inter-chain interaction, while the intra-chain conformational order remains similar. We explain the observed differences by considering different modes of peptide insertion. Finally, electron paramagnetic resonance spectroscopy shows that PrP106-126 progressively decreases the orientational order of lipid acyl chains in magnetically aligned bicelles. Together, our experimental data support the proposition that monomeric PrP106-126 can disrupt lipid membranes by using similar mechanisms found in AMPs. PMID:28459565

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.

Rapid and precise determination of zero-field splittings by terahertz time-domain electron paramagnetic resonance spectroscopy.

PubMed

Lu, Jian; Ozel, I Ozge; Belvin, Carina A; Li, Xian; Skorupskii, Grigorii; Sun, Lei; Ofori-Okai, Benjamin K; Dincă, Mircea; Gedik, Nuh; Nelson, Keith A

2017-11-01

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.

Redox Active Transition Metal ions Make Melanin Susceptible to Chemical Degradation Induced by Organic Peroxide.

PubMed

Zadlo, Andrzej; Pilat, Anna; Sarna, Michal; Pawlak, Anna; Sarna, Tadeusz

2017-12-01

With aging, retinal pigment epithelium melanosomes, by fusion with the age pigment lipofuscin, form complex granules called melanolipofuscin. Lipofuscin granules may contain oxidized proteins and lipid hydroperoxides, which in melanolipofuscin could chemically modify melanin polymer, while transition metal ions present in melanin can accelerate such oxidative modifications. The aim of this research was to examine the effect of selected transition metal ions on melanin susceptibility to chemical modification induced by the water-soluble tert-butyl hydroperoxide used as an oxidizing agent. Synthetic melanin obtained by DOPA autooxidation and melanosomes isolated from bovine retinal pigment epithelium were analyzed. To monitor tert-butyl hydroperoxide-induced oxidative changes of DMa and BMs, electron paramagnetic resonance spectroscopy, UV-vis absorption spectroscopy, dynamic light scattering, atomic force microscopy and electron paramagnetic resonance oximetry were employed. These measurements revealed that both copper and iron ions accelerated chemical degradation induced by tert-butyl hydroperoxide, while zinc ions had no effect. Strong prooxidant action was detected only in the case of melanosomes and melanin degraded in the presence of iron. It can be postulated that similar chemical processes, if they occur in situ in melanolipofuscin granules of the human retinal pigment epithelium, would modify antioxidant properties of melanin and its reactivity.

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.

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.

Activation Thermodynamics and H/D Kinetic Isotope Effect of the Hox to HredH+ Transition in [FeFe] Hydrogenase.

PubMed

Ratzloff, Michael W; Wilker, Molly B; Mulder, David W; Lubner, Carolyn E; Hamby, Hayden; Brown, Katherine A; Dukovic, Gordana; King, Paul W

2017-09-20

Molecular complexes between CdSe nanocrystals and Clostridium acetobutylicum [FeFe] hydrogenase I (CaI) enabled light-driven control of electron transfer for spectroscopic detection of redox intermediates during catalytic proton reduction. Here we address the route of electron transfer from CdSe→CaI and activation thermodynamics of the initial step of proton reduction in CaI. The electron paramagnetic spectroscopy of illuminated CdSe:CaI showed how the CaI accessory FeS cluster chain (F-clusters) functions in electron transfer with CdSe. The H ox →H red H + reduction step measured by Fourier-transform infrared spectroscopy showed an enthalpy of activation of 19 kJ mol -1 and a ∼2.5-fold kinetic isotope effect. Overall, these results support electron injection from CdSe into CaI involving F-clusters, and that the H ox →H red H + step of catalytic proton reduction in CaI proceeds by a proton-dependent process.

Rare earth ions doped ZnO: Synthesis, characterization and preliminary photoactivity assessment

NASA Astrophysics Data System (ADS)

Cerrato, Erik; Gionco, Chiara; Berruti, Ilaria; Sordello, Fabrizio; Calza, Paola; Paganini, Maria Cristina

2018-08-01

This work reports the effect of doping zinc oxide with lanthanide ions on structural, EPR and UV visible properties. Bare and doped samples were synthesized using the simple and green hydrothermal process. Different rare earth ions (RE = La, Ce, Pr, Er and Yb) with 1% molar ratio RE/Zn were used. The samples have been studied using X Ray Diffraction, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and UV visible diffuse reflectance spectroscopy. Finally, electron paramagnetic resonance (EPR) spectroscopy, was used to assess the materials photoactivity under UV irradiation, both in solid state, to see the charge carriers' generation and in solution, evaluating the OH• radical formation using the DMPO (5,5-Dimethyl-1-Pyrroline-N-Oxide) spin trapping technique. The results suggest that the synthesized materials could be interesting systems for the photocatalytic abatement of emerging organic persistent pollutants in wastewater treatment plants.

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.

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.

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.

Preparation of a Cobalt(II) Cage: An Undergraduate Laboratory Experiment That Produces a ParaSHIFT Agent for Magnetic Resonance Spectroscopy

ERIC Educational Resources Information Center

Burns, Patrick J.; Tsitovich, Pavel B.; Morrow, Janet R.

2016-01-01

Laboratory experiments that demonstrate the effect of paramagnetic complexes on chemical shifts and relaxation times of protons are a useful way to introduce magnetic resonance spectroscopy (MRS) probes or magnetic resonance imaging (MRI) contrast agents. In this undergraduate inorganic chemistry experiment, a paramagnetic Co(II) cage complex is…

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

Room temperature ferromagnetism in Cu doped ZnO

NASA Astrophysics Data System (ADS)

Ali, Nasir; Singh, Budhi; Khan, Zaheer Ahmed; Ghosh, Subhasis

2018-05-01

We report the room temperature ferromagnetism in 2% Cu doped ZnO films grown by RF magnetron sputtering in different argon and oxygen partial pressure. X-ray photoelectron spectroscopy was used to ascertain the oxidation states of Cu in ZnO. The presence of defects within Cu-doped ZnO films can be revealed by electron paramagnetic resonance. It has been observed that saturated magnetic moment increase as we increase the zinc vacancies during deposition.

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.

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.

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.

Influence of Sn on the magnetic ordering of Ni-Sn alloy synthesized using chemical reduction method

NASA Astrophysics Data System (ADS)

Dhanapal, K.; Narayanan, V.; Stephen, A.

2016-05-01

The Ni-Sn alloy was synthesized using borohydride assisted chemical reduction method. The composition of the synthesized alloy was determined using atomic absorption spectroscopy which revealed that the observed composition of Sn is high when compared to the initial composition. The ultrafine particles are clearly observed from field emission scanning electron microscope for all the sample. The X-ray diffraction measurement confirmed that the as-synthesized samples are of amorphous like nature while the samples annealed at 773 K showed crystalline nature. The Fourier transform infrared spectroscopy confirmed metallic bond stretching in the alloy samples. The crystallization and phase transition temperature was observed from differential scanning calorimetry. The shift in the crystallization temperature of Ni with increasing percentage of Sn was observed. The vibrating sample magnetometer was employed to understand the magnetic behavior of the Ni-Sn alloy. As-synthesized alloy samples showed paramagnetic nature while the annealed ones exhibit the soft ferromagnetic, antiferromagnetic and paramagnetic nature. The saturation magnetization value and magnetic ordering in the Ni-Sn alloys depend on the percentage of Sn present in the alloy.

Synthesis and characterization of gadolinium nanosheets with bound rose bengal: potential use in photodynamic therapy and MRI

NASA Astrophysics Data System (ADS)

Stefanakis, Dimitrios; Seimenis, Ioannis; Ghanotakis, Demetrios

2014-11-01

Gadolinium (Gd) is a trivalent paramagnetic element, making it useful as a contrast agent for magnetic resonance imaging (MRI). Gd2(OH)5NO3· xH2O belongs to a new family of nanosheets. The advantages of these materials are their relatively small size, paramagnetic behavior, stability, lack of toxicity and highly ordered structure. In the present study, Gd2(OH)5NO3 nanosheets were functionalized with amino groups and modified with the photosensitiser rose bengal (RB). This surface modification makes possible the use of the nanosheets in photodynamic therapy. The coated nanosheets were characterized with X-ray diffraction, fourier transform infrared spectroscopy and UV-Vis spectroscopy, as well as transmission electron microscopy. The possibility of using these nanosheets as potential spin-lattice ( T 1) and spin-spin relaxation ( T 2) contrast agents in MRI was evaluated at 1.5 T. Finally, the ability of Gd2(OH)5NO3-RB to catalyze photooxidization reactions was examined using nuclear magnetic resonance (1H NMR) and gas chromatography-mass spectrometry (GC/MS).

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.

Investigation of Model Sunscreen Formulations Comparing the Sun Protection Factor, the Universal Sun Protection Factor and the Radical Formation Ratio.

PubMed

Syring, Felicia; Weigmann, Hans-Jürgen; Schanzer, Sabine; Meinke, Martina C; Knorr, Fanny; Lademann, Jürgen

2016-01-01

In view of globally rising skin cancer rates and harmful effects exerted by sunlight throughout the ultraviolet, visible and infrared ranges, an objective, safe and comprehensive method for determining sunscreen efficacy is required in order to warrant safe sun exposure. In this study, the influence of characteristic active ingredients (chemical filters, physical filters and antioxidants) on different sunscreen indicators, including the universal sun protection factor and the radical formation ratio, was determined and compared to their influence on sun protection factor values. Spectroscopic universal sun protection factor measurements were conducted ex vivo by analyzing tape strips taken from human skin, and radical formation ratio determination was performed via electron paramagnetic resonance spectroscopy using porcine ear skin ex vivo. The sun protection factor determination was conducted according to ISO standards (ISO 24444:2010). It was shown that chemical filters provide a protective effect which was measurable by all methods examined (spectroscopy, electron paramagnetic resonance spectroscopy and erythema formation). Physical filters, when used as single active ingredients, increased protective values in universal sun protection factor and sun protection factor measurements but exhibited no significant effect on universal sun protection factor measurements when used in combination with chemical filters or antioxidants. Antioxidants were shown to increase sun protection factor values. Radical formation ratio values were shown to be influenced merely by chemical filters, leading to the conclusion that the universal sun protection factor is the most suitable efficacy indicator for the ultraviolet range. © 2015 S. Karger AG, Basel.

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.

A comparison of antioxidative capacities of fruit juices, drinks and nectars, as determined by EPR and UV-vis spectroscopies

NASA Astrophysics Data System (ADS)

Bartoszek, Mariola; Polak, Justyna

2016-01-01

The differences in the Trolox Equivalent Antioxidant Capacity (TEAC) values at the same incubation time obtained by two different techniques: electron paramagnetic resonance (EPR) spectroscopy and ultraviolet visible (UV-vis) spectroscopy, which use the same antioxidant-free radical reaction mechanism, were determined for fruit juices, nectars and drinks. For this study, the stable free radical 1,1-Diphenyl-2-picryl-hydrazyl (DPPH•) was used. The antioxidant capacity was presented in Trolox Equivalents, e.g., μM trolox per 100 ml of sample. All of the studied fruit juices, drinks and nectars showed antioxidative properties. Dependencies between TEAC values and the percent fruit content and sample color were observed for the studied beverages. It was found that EPR spectroscopy is the more adequate method for determining TEAC values for these kinds of samples.

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.

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.

Sticking non-stick: Surface and Structure control of Diamond-like Carbon in Plasma Enhanced Chemical Vapour Deposition

NASA Astrophysics Data System (ADS)

Jones, B. J.; Nelson, N.

2016-10-01

This short review article explores the practical use of diamond-like carbon (DLC) produced by plasma enhanced chemical vapour deposition (PECVD). Using as an example issues relating to the DLC coating of a hand-held surgical device, we draw on previous works using atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, tensiometry and electron paramagnetic resonance. Utilising data from these techniques, we examine the surface structure, substrate-film interface and thin film microstructure, such as sp2/sp3 ratio (graphitic/diamond-like bonding ratio) and sp2 clustering. We explore the variations in parameters describing these characteristics, and relate these to the final device properties such as friction, wear resistance, and diffusion barrier integrity. The material and device characteristics are linked to the initial plasma and substrate conditions.

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.

Synthesis and characterization of a new Inonotus obliquus polysaccharide-iron(III) complex.

PubMed

Wang, Jia; Chen, Haixia; Wang, Yanwei; Xing, Lisha

2015-04-01

A new Inonotus obliquus polysaccharide-iron(III) complex (IOPS-iron) was synthesized and characterized. The preparation conditions of IOPS-iron(III) were optimized and the physicochemical properties were characterized by physicochemical methods, scanning electron microscopy (SEM), electron paramagnetic resonance (EPR) spectroscopy, fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, respectively. The highest iron content of IOPS-iron(III) complex (19.40%) was obtained at the conditions: the ratio of IOPS and FeCl3 • 6H2O was 3:5 (w/w), the pH value of alkali solution was 10, the reaction temperature was 30 °C and the reaction time was 6h. The iron(III) was shown to be bound through the binding sites of the polysaccharide IOPS and it could form spatially separated iron centers on the polysaccharide backbone. IOPS-iron(III) complex was found to have good digestive availability and antioxidant activities in the in vitro assays, which suggested the IOPS-iron(III) complex might be used as a new iron supplement candidate. Copyright © 2015 Elsevier B.V. All rights reserved.

Metal-Insulator crossover in SrVO3 thin film

NASA Astrophysics Data System (ADS)

Wang, Gaomin; Wang, Zhen; Saghayezhian, Mohammad; Chen, Chen; Chen, Lina; Guo, Hangwen; Zhu, Yimei; Zhang, Jiandi

Paramagnetic metallic oxide SrVO3 (SVO) represents a prototype system for the study of the mechanism behind thickness-induced metal-to-insulator transition (MIT) or crossover due to its simple structure and itinerancy. Here SrVO3 thin films with different thicknesses were obtained through the layer-by-layer growth by laser Molecular Beam Epitaxy on SrTiO3 (001) surface. Ultraviolet Photoemission Spectroscopy and Scanning Tunneling Spectroscopy measurements confirm a MIT at the thickness of 3 unit cell, while atomically resolved Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy analysis reveal the depletion of Sr, change of V-valence and expansion of the out-of-plane lattice constant in the first three unit cell above the interface, thus different from the rest of the films. The existence of significant amount of oxygen vacancies is proposed, which is also supported by X-ray Photoelectron Spectroscopy, therefore providing a possible explanation of MIT. This work is primarily supported by U.S. DOE under Grant No. DOE DE-SC0002136. G.W. was supported by U.S. NSF under Grant No. DMR 16088865.

Optical, electrochemical and thermal properties of Mn2+ doped CdS nanoparticles

NASA Astrophysics Data System (ADS)

Muruganandam, S.; Anbalagan, G.; Murugadoss, G.

2015-08-01

Mn2+ doped (1-5 and 10 %) CdS nanoparticles have been synthesized by the chemical precipitation method using polyvinylpyrrolidone as a capping agent. The particle size, morphology and optical properties have been studied by X-ray powder diffraction, transmission electron microscopy, UV-Visible and photoluminescence spectroscopy. Powder diffraction data have confirmed that the crystallite size is around 2-5 nm. The band gap of the nanoparticles has been calculated using UV-Visible absorption spectra. An optimum concentration, Mn2+ (3 %) has been selected by optical study. The functional groups of the capping agent have been identified by fourier transform infrared spectroscopy study. The presence of dopant (Mn2+) has been confirmed by electron paramagnetic resonance spectroscopy. Thermal properties of CdS:Mn2+ have been analyzed using thermogravimetric-differential thermal analyser. The electrochemical properties of the undoped and doped samples have been studied by cyclic voltammetry for electrode applications. In addition, magnetic properties of Mn2+ doped CdS have been studied using a vibrating sample magnetometer.

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.

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.

Activation Thermodynamics and H/D Kinetic Isotope Effect of the H ox to H red H + Transition in [FeFe] Hydrogenase

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

Ratzloff, Michael W.; Wilker, Molly B.; Mulder, David W.

Molecular complexes between CdSe nanocrystals and Clostridium acetobutylicum [FeFe] hydrogenase I (CaI) enabled light-driven control of electron transfer for spectroscopic detection of redox intermediates during catalytic proton reduction. Here in this paper we address the route of electron transfer from CdSe→CaI and activation thermodynamics of the initial step of proton reduction in CaI. The electron paramagnetic spectroscopy of illuminated CdSe:CaI showed how the CaI accessory FeS cluster chain (F-clusters) functions in electron transfer with CdSe. The H ox→H redH + reduction step measured by Fourier-transform infrared spectroscopy showed an enthalpy of activation of 19 kJ mol -1 and a ~2.5-foldmore » kinetic isotope effect. Overall these results support electron injection from CdSe into CaI involving F-clusters, and that the H ox→H redH + step of catalytic proton reduction in CaI proceeds by a proton-dependent process.« less

Counter-ion and dopant effects on charge carriers in intrinsically conductive polymer

NASA Astrophysics Data System (ADS)

Ogle, Jonathan; Yehulie, Mandefro; Boehme, Christoph; Whittaker-Brooks, Luisa

Recently, a significant amount of attention has been devoted to the optimization and applications of organic electronics. In particular, intrinsically conductive polymers have seen a strong continued interest for their use in thermoelectric and photovoltaic devices. With conductivities ranging from 10-8 to 103 S cm-1, the conductive polymer poly(3,4-ethylenedioxythiophene) -PEDOT is one of the most studied solution-processable polymer material due to its unique optical and electronic properties. While charge carriers at lower conductivities have been identified as polarons, an understanding of the electronic structure of PEDOT as its conductivity increases is not well understood. We have investigated the effect that counter-ion exchange and doping has on the polaron concentration of PEDOT via electron paramagnetic resonance, ultraviolet photoelectron spectroscopy, and X-ray absorption fine structure spectroscopy studies. Such studies have allowed us to correlate charge carriers concentrations and the real and virtual electronic states in PEDOT as a function of various dopants. As discussed in our talk, we believe our findings could be extended to the understanding of other polymeric materials.

Activation Thermodynamics and H/D Kinetic Isotope Effect of the H ox to H red H + Transition in [FeFe] Hydrogenase

DOE PAGES

Ratzloff, Michael W.; Wilker, Molly B.; Mulder, David W.; ...

2017-08-29

Molecular complexes between CdSe nanocrystals and Clostridium acetobutylicum [FeFe] hydrogenase I (CaI) enabled light-driven control of electron transfer for spectroscopic detection of redox intermediates during catalytic proton reduction. Here in this paper we address the route of electron transfer from CdSe→CaI and activation thermodynamics of the initial step of proton reduction in CaI. The electron paramagnetic spectroscopy of illuminated CdSe:CaI showed how the CaI accessory FeS cluster chain (F-clusters) functions in electron transfer with CdSe. The H ox→H redH + reduction step measured by Fourier-transform infrared spectroscopy showed an enthalpy of activation of 19 kJ mol -1 and a ~2.5-foldmore » kinetic isotope effect. Overall these results support electron injection from CdSe into CaI involving F-clusters, and that the H ox→H redH + step of catalytic proton reduction in CaI proceeds by a proton-dependent process.« less

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.

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

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

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

Biomimetic synthesis of chiral erbium-doped silver/peptide/silica core-shell nanoparticles (ESPN)

NASA Astrophysics Data System (ADS)

Mantion, Alexandre; Graf, Philipp; Florea, Ileana; Haase, Andrea; Thünemann, Andreas F.; Mašić, Admir; Ersen, Ovidiu; Rabu, Pierre; Meier, Wolfgang; Luch, Andreas; Taubert, Andreas

2011-12-01

Peptide-modified silver nanoparticles have been coated with an erbium-doped silica layer using a method inspired by silica biomineralization. Electron microscopy and small-angle X-ray scattering confirm the presence of an Ag/peptide core and silica shell. The erbium is present as small Er2O3 particles in and on the silica shell. Raman, IR, UV-Vis, and circular dichroism spectroscopies show that the peptide is still present after shell formation and the nanoparticles conserve a chiral plasmon resonance. Magnetic measurements find a paramagnetic behavior. In vitro tests using a macrophage cell line model show that the resulting multicomponent nanoparticles have a low toxicity for macrophages, even on partial dissolution of the silica shell.Peptide-modified silver nanoparticles have been coated with an erbium-doped silica layer using a method inspired by silica biomineralization. Electron microscopy and small-angle X-ray scattering confirm the presence of an Ag/peptide core and silica shell. The erbium is present as small Er2O3 particles in and on the silica shell. Raman, IR, UV-Vis, and circular dichroism spectroscopies show that the peptide is still present after shell formation and the nanoparticles conserve a chiral plasmon resonance. Magnetic measurements find a paramagnetic behavior. In vitro tests using a macrophage cell line model show that the resulting multicomponent nanoparticles have a low toxicity for macrophages, even on partial dissolution of the silica shell. Electronic supplementary information (ESI) available: Figures S1 to S12, Tables S1 and S2. See DOI: 10.1039/c1nr10930h

Studying the Structure and Dynamics of Biomolecules by Using Soluble Paramagnetic Probes

PubMed Central

Hocking, Henry G; Zangger, Klaus; Madl, Tobias

2013-01-01

Characterisation of the structure and dynamics of large biomolecules and biomolecular complexes by NMR spectroscopy is hampered by increasing overlap and severe broadening of NMR signals. As a consequence, the number of available NMR spectroscopy data is often sparse and new approaches to provide complementary NMR spectroscopy data are needed. Paramagnetic relaxation enhancements (PREs) obtained from inert and soluble paramagnetic probes (solvent PREs) provide detailed quantitative information about the solvent accessibility of NMR-active nuclei. Solvent PREs can be easily measured without modification of the biomolecule; are sensitive to molecular structure and dynamics; and are therefore becoming increasingly powerful for the study of biomolecules, such as proteins, nucleic acids, ligands and their complexes in solution. In this Minireview, we give an overview of the available solvent PRE probes and discuss their applications for structural and dynamic characterisation of biomolecules and biomolecular complexes. PMID:23836693

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.

Fourier Deconvolution Methods for Resolution Enhancement in Continuous-Wave EPR Spectroscopy.

PubMed

Reed, George H; Poyner, Russell R

2015-01-01

An overview of resolution enhancement of conventional, field-swept, continuous-wave electron paramagnetic resonance spectra using Fourier transform-based deconvolution methods is presented. Basic steps that are involved in resolution enhancement of calculated spectra using an implementation based on complex discrete Fourier transform algorithms are illustrated. Advantages and limitations of the method are discussed. An application to an experimentally obtained spectrum is provided to illustrate the power of the method for resolving overlapped transitions. © 2015 Elsevier Inc. All rights reserved.

A comparison of antioxidative capacities of fruit juices, drinks and nectars, as determined by EPR and UV-vis spectroscopies.

PubMed

Bartoszek, Mariola; Polak, Justyna

2016-01-15

The differences in the Trolox Equivalent Antioxidant Capacity (TEAC) values at the same incubation time obtained by two different techniques: electron paramagnetic resonance (EPR) spectroscopy and ultraviolet visible (UV-vis) spectroscopy, which use the same antioxidant-free radical reaction mechanism, were determined for fruit juices, nectars and drinks. For this study, the stable free radical 1,1-Diphenyl-2-picryl-hydrazyl (DPPH(•)) was used. The antioxidant capacity was presented in Trolox Equivalents, e.g., μM trolox per 100 ml of sample. All of the studied fruit juices, drinks and nectars showed antioxidative properties. Dependencies between TEAC values and the percent fruit content and sample color were observed for the studied beverages. It was found that EPR spectroscopy is the more adequate method for determining TEAC values for these kinds of samples. Copyright © 2015 Elsevier B.V. All rights reserved.

Retrospective Reconstruction of Radiation Doses of Chernobyl Liquidators by Electron Paramagnetic Resonance

DTIC Science & Technology

1997-12-01

Armed Forces Rad I Research Institute Retrospective Reconstruction of Radiation Doses of Chernobyl Liquidators by Electron Paramagnetic Resonance A...of Radiation Doses of Chernobyl Liquidators by Electron Paramagnetic Resonance Authored by Scientific Center of Radiation Medicine Academy of Medical...libraries associated with the U.S. Government’s Depository Library System. Preface On April 26, 1986, Reactor #4 at the Chernobyl Nuclear Power Plant near

Aging effects in bulk and fiber TlBr-TlI

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

Wysocki, J.A.; Wilson, R.G.; Standlee, A.G.

1988-05-01

A study of optical aging in bulk and extruded fibers of thallium bromo-iodide (TlBr-TlI) is presented. A variety of techniques including secondary ion mass spectrometry (SIMS), powder neutron and x-ray diffraction, infrared spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy are used to probe the chemical and structural properties of both pristine and aged material. High concentration levels of a hydrogen bearing impurity have been detected by SIMS and neutron scattering in aged TlBr-TlI, and have been shown to be localized in the surface layers of fibers as well as bulk samples. We present EPR evidence which indicates that the hydrogenmore » bearing impurity is water.« less

Structure and dynamics of spin-labeled insulin entrapped in a silica matrix by the sol-gel method.

PubMed

Vanea, E; Gruian, C; Rickert, C; Steinhoff, H-J; Simon, V

2013-08-12

The structure and conformational dynamics of insulin entrapped into a silica matrix was monitored during the sol to maturated-gel transition by electron paramagnetic resonance (EPR) spectroscopy. Insulin was successfully spin-labeled with iodoacetamide and the bifunctional nitroxide reagent HO-1944. Room temperature continuous wave (cw) EPR spectra of insulin were recorded to assess the mobility of the attached spin labels. Insulin conformation and its distribution within the silica matrix were studied using double electron-electron resonance (DEER) and low-temperature cw-EPR. A porous oxide matrix seems to form around insulin molecules with pore diameters in the order of a few nanometers. Secondary structure of the encapsulated insulin investigated by Fourier transform infrared spectroscopy proved a high structural integrity of insulin even in the dried silica matrix. The results show that silica encapsulation can be used as a powerful tool to effectively isolate and functionally preserve biomolecules during preparation, storage, and release.

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.

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.

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.

Effect of analytical proton beam irradiation on lead-white pigments, characterized by EPR spectroscopy

NASA Astrophysics Data System (ADS)

Gourier, Didier; Binet, Laurent; Gonzalez, Victor; Vezin, Hervé; Touati, Nadia; Calligaro, Thomas

2018-01-01

Analytical techniques using proton beams with energy in the MeV range are commonly used to study archeological artefact and artistic objects. However ion beams can induce alteration of fragile materials, which is notably the case of easel paintings, limiting the use of these techniques. We used continuous wave EPR and pulse EPR spectroscopy to reveal the effect of 3 MeV proton irradiation on lead carbonates, which were extensively employed as white pigments from the antiquity to the 20th century. Two kinds of paramagnetic centers were identified in cerussite (PbCO3): the first one is CO3- radicals formed by hole trapping by CO32- ions, and the second one is NO32- radical resulting from electron trapping by NO3- impurities. Hydrocerussite (2PbCO3·Pb(OH)2) is the most darkened material under proton beam, however it exhibits no NO32- radicals and 20 times less CO3- radicals than cerussite. Consequently these paramagnetic centers are not directly responsible for the darkening of lead-white pigments. We proposed that their higher instability in hydrocerussite might be at the origin of the formation of color centers in this material.

High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal-organic frameworks, STAM-1 and HKUST-1.

PubMed

Dawson, Daniel M; Jamieson, Lauren E; Mohideen, M Infas H; McKinlay, Alistair C; Smellie, Iain A; Cadou, Romain; Keddie, Neil S; Morris, Russell E; Ashbrook, Sharon E

2013-01-21

Solid-state (13)C magic-angle spinning (MAS) NMR spectroscopy is used to investigate the structure of the Cu(II)-based metal-organic frameworks (MOFs), HKUST-1 and STAM-1, and the structural changes occurring within these MOFs upon activation (dehydration). NMR spectroscopy is an attractive technique for the investigation of these materials, owing to its high sensitivity to local structure, without any requirement for longer-range order. However, interactions between nuclei and unpaired electrons in paramagnetic systems (e.g., Cu(II)-based MOFs) pose a considerable challenge, not only for spectral acquisition, but also in the assignment and interpretation of the spectral resonances. Here, we exploit the rapid T(1) relaxation of these materials to obtain (13)C NMR spectra using a spin-echo pulse sequence at natural abundance levels, and employ frequency-stepped acquisition to ensure uniform excitation of resonances over a wide frequency range. We then utilise selective (13)C isotopic labelling of the organic linker molecules to enable an unambiguous assignment of NMR spectra of both MOFs for the first time. We show that the monomethylated linker can be recovered from STAM-1 intact, demonstrating not only the interesting use of this MOF as a protecting group, but also the ability (for both STAM-1 and HKUST-1) to recover isotopically-enriched linkers, thereby reducing significantly the overall cost of the approach.

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.

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

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.

The “Beta-Clasp” model of apolipoprotein A-I - a lipid-free solution structure determined by electron paramagnetic resonance spectroscopy

PubMed Central

Lagerstedt, Jens O.; Budamagunta, Madhu S.; Liu, Grace S.; DeValle, Nicole C.; Voss, John C.; Oda, Michael N.

2012-01-01

Apolipoprotein A-I (apoA-I) is the major protein component of high density lipoproteins (HDL) and plays a central role in cholesterol metabolism. The lipid-free / lipid-poor form of apoA-I is the preferred substrate for the ATP-binding cassette transporter A1 (ABCA1). The interaction of apoA-I with ABCA1 leads to the formation of cholesterol laden high density lipoprotein (HDL) particles, a key step in reverse cholesterol transport and the maintenance of cholesterol homeostasis. Knowledge of the structure of lipid-free apoA-I is essential to understanding its critical interaction with ABCA1 and the molecular mechanisms underlying HDL biogenesis. We therefore examined the structure of lipid-free apoA-I by electron paramagnetic resonance spectroscopy (EPR). Through site directed spin label EPR, we mapped the secondary structure of apoA-I and identified sites of spin coupling as residues 26, 44, 64, 167, 217 and 226. We capitalize on the fact that lipid-free apoA-I self-associates in an anti-parallel manner in solution. We employed these sites of spin coupling to define the central plane in the dimeric apoA-I complex. Applying both the constraints of dipolar coupling with the EPR-derived pattern of solvent accessibility, we assembled the secondary structure into a tertiary context, providing a solution structure for lipid-free apoA-I. PMID:22245143

Redefining Nitric Oxide Production in Legume Nodules through Complementary Insights from Electron Paramagnetic Resonance Spectroscopy and Specific Fluorescent Probes.

PubMed

Calvo-Begueria, Laura; Rubio, Maria C; Martínez, Jesús I; Pérez-Rontomé, Carmen; Delgado, Maria J; Bedmar, Eulogio J; Becana, Manuel

2018-04-26

Nitric oxide (NO) is a signaling molecule with multiple functions in plants. Given its critical importance and reactivity as a gaseous free radical, we have examined NO production in legume nodules using electron paramagnetic resonance (EPR) spectroscopy and the specific fluorescent dye 4,5-diaminofluorescein diacetate. Also, in this context, we critically assess previous and current views of NO production and detection in nodules. EPR of intact nodules revealed that nitrosyl-leghemoglobin (Lb2+NO) was absent from bean or soybean nodules regardless of nitrate supply, but accumulated in soybean nodules treated with nitrate that were defective in nitrite or nitric oxide reductases or that were exposed to ambient temperature. Consequently, bacteroids are a major source of NO, denitrification enzymes are required for NO homeostasis, and Lb2+NO is not responsible for the inhibition of nitrogen fixation by nitrate. Further, we noted that Lb2+NO is artifactually generated in nodule extracts or in intact nodules not analyzed immediately after detachment. The fluorescent probe detected NO formation in bean and soybean nodule infected cells and in soybean nodule parenchyma. The NO signal was slightly decreased by inhibitors of nitrate reductase but not of nitric oxide synthase, which could indicate a minor contribution of plant nitrate reductase and supports the existence of nitrate- and arginine-independent pathways for NO production. Collectively, our data indicate that EPR and fluorometric methods are complementary to draw reliable conclusions about NO production in plants.

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

NASA Technical Reports Server (NTRS)

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

2002-01-01

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

Effect of lipophilization on the distribution and reactivity of ingredients in emulsions.

PubMed

Leong, Wai Fun; Berton-Carabin, Claire C; Elias, Ryan J; Lecomte, Jérôme; Villeneuve, Pierre; Zhao, Yu; Coupland, John N

2015-12-01

The reactivity of small molecules in emulsions is believed to depend on their partitioning between phases, yet this is hard to verify experimentally in situ. In the present work, we use electron paramagnetic resonance (EPR) spectroscopy to simultaneously measure the distribution and reactivity of a homologous series of lipophilized spin probes in an emulsion. 4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) was derivatized with saturated fatty acids to create a series of spin probes with increasing lipophilicity (C4-, C8-, C12-, and C16-TEMPO). The probes were added to a 10 wt.% tetradecane-in water emulsions (d32∼190 nm) stabilized with sodium caseinate (1 wt.% in the aqueous phase, pH 7). The distribution of the probes between phases was measured by electron paramagnetic resonance (EPR) spectroscopy. TEMPOL partitioned into the aqueous phase, C4-TEMPO distributed between the lipid and aqueous phases (69% and 31% respectively) while the more lipophilic probes dissolved exclusively within the lipid droplets. Interestingly, the more lipophilic probes initially precipitated upon their addition to the emulsion, and only slowly redistributed to the droplets over hours or days, the rate of which was dependent on their carbon chain length. The reactivity of the probes with aqueous an aqueous phase reductant (ascorbate) generally depended on the proportion in the aqueous phase (i.e., TEMPOL>C4-TEMPO>C8-TEMPO∼C12-TEMPO∼C16-TEMPO). Copyright © 2015 Elsevier Inc. All rights reserved.

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

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

Ledbetter, Rhesa N.; Garcia Costas, Amaya M.; Lubner, Carolyn E.

The biological reduction of dinitrogen (N 2) to ammonia (NH 3) by nitrogenase is an energetically demanding reaction that requires low-potential electrons and ATP; however, pathways used to deliver the electrons from central metabolism to the reductants of nitrogenase, ferredoxin or flavodoxin, remain unknown for many diazotrophic microbes. The FixABCX protein complex has been proposed to reduce flavodoxin or ferredoxin using NADH as the electron donor in a process known as electron bifurcation. Herein, the FixABCX complex from Azotobacter vinelandii was purified and demonstrated to catalyze an electron bifurcation reaction: oxidation of NADH (E m = -320 mV) coupled tomore » reduction of flavodoxin semiquinone (E m = -460 mV) and reduction of coenzyme Q (E m = 10 mV). Knocking out fix genes rendered ..delta..rnf A. vinelandii cells unable to fix dinitrogen, confirming that the FixABCX system provides another route for delivery of electrons to nitrogenase. Characterization of the purified FixABCX complex revealed the presence of flavin and iron-sulfur cofactors confirmed by native mass spectrometry, electron paramagnetic resonance spectroscopy, and transient absorption spectroscopy. Transient absorption spectroscopy further established the presence of a short-lived flavin semiquinone radical, suggesting that a thermodynamically unstable flavin semiquinone may participate as an intermediate in the transfer of an electron to flavodoxin. A structural model of FixABCX, generated using chemical cross-linking in conjunction with homology modeling, revealed plausible electron transfer pathways to both high- and low-potential acceptors. Altogether, this study informs a mechanism for electron bifurcation, offering insight into a unique method for delivery of low-potential electrons required for energy-intensive biochemical conversions.« less

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.

EPR Characterization of Dinitrosyl Iron Complexes with Thiol-Containing Ligands as an Approach to Their Identification in Biological Objects: An Overview.

PubMed

Vanin, Anatoly F

2018-06-01

The overview demonstrates how the use of only one physico-chemical approach, viz., the electron paramagnetic resonance method, allowed detection and identification of dinitrosyl iron complexes with thiol-containing ligands in various animal and bacterial cells. These complexes are formed in biological objects in the paramagnetic (electron paramagnetic resonance-active) mononuclear and diamagnetic (electron paramagnetic resonance-silent) binuclear forms and control the activity of nitrogen monoxide, one of the most universal regulators of metabolic processes in the organism. The analysis of electronic and spatial structures of dinitrosyl iron complex sheds additional light on the mechanism whereby dinitrosyl iron complex with thiol-containing ligands function in human and animal cells as donors of nitrogen monoxide and its ionized form, viz., nitrosonium ions (NO + ).

Electron paramagnetic resonance of several lunar rock samples

NASA Technical Reports Server (NTRS)

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

1974-01-01

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

Paramagnetism of cobalt-doped ZnO nanoparticles obtained by microwave solvothermal synthesis.

PubMed

Wojnarowicz, Jacek; Kusnieruk, Sylwia; Chudoba, Tadeusz; Gierlotka, Stanislaw; Lojkowski, Witold; Knoff, Wojciech; Lukasiewicz, Malgorzata I; Witkowski, Bartlomiej S; Wolska, Anna; Klepka, Marcin T; Story, Tomasz; Godlewski, Marek

2015-01-01

Zinc oxide nanopowders doped with 1-15 mol % cobalt were produced by the microwave solvothermal synthesis (MSS) technique. The obtained nanoparticles were annealed at 800 °C in nitrogen (99.999%) and in synthetic air. The material nanostructure was investigated by means of the following techniques: X-ray diffraction (XRD), helium pycnometry density, specific surface area (SSA), inductively coupled plasma optical emission spectrometry (ICP-OES), extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and with magnetometry using superconducting quantum interference device (SQUID). Irrespective of the Co content, nanoparticles in their initial state present a similar morphology. They are composed of loosely agglomerated spherical particles with wurtzite-type crystal structure with crystallites of a mean size of 30 nm. Annealing to temperatures of up to 800 °C induced the growth of crystallites up to a maximum of 2 μm in diameter. For samples annealed in high purity nitrogen, the precipitation of metallic α-Co was detected for a Co content of 5 mol % or more. For samples annealed in synthetic air, no change of phase structure was detected, except for precipitation of Co3O4 for a Co content of 15 mol %. The results of the magentometry investigation indicated that all as-synthesized samples displayed paramagnetic properties with a contribution of anti-ferromagnetic coupling of Co-Co pairs. After annealing in synthetic air, the samples remained paramagnetic and samples annealed under nitrogen flow showed a magnetic response under the influences of a magnetic field, likely related to the precipitation of metallic Co in nanoparticles.

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

PubMed Central

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

2005-01-01

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

Investigation of Phenols Activity in Early Stage Oxidation of Edible Oils by Electron Paramagnetic Resonance and 19F NMR Spectroscopies Using Novel Lipid Vanadium Complexes As Radical Initiators.

PubMed

Drouza, Chryssoula; Dieronitou, Anthi; Hadjiadamou, Ioanna; Stylianou, Marios

2017-06-21

A novel dynamic method for the investigation of the phenols activity in early stage oxidation of edible oils based on the formation of α-tocopheryl radicals initiated by oil-soluble vanadium complexes is developed. Two new vanadium complexes in oxidation states V and IV were synthesized by reacting 2,2'-((2-hydroxyoctadecyl)azanediyl)bis(ethan-1-ol) (C18DEA) with [VO(acac) 2 ] and 1-(bis(pyridin-2-ylmethyl)amino)octadecan-2-ol (C18DPA) with VOCl 2 . Addition of a solution of either complex in edible oils resulted in the formation of α-tocopheryl radical, which was monitored by electron paramagnetic resonance (EPR) spectroscopy. The intensity of the α-tocopheryl signal in the EPR spectra was measured versus time. It was found that the profile of the intensity of the α-tocopheryl signal versus time depends on the type of oil, the phenolic content, and the storage time of the oil. The time interval until the occurrence of maximum peak intensity be reached (t m ), the height of the maximum intensity, and the rate of the quenching of the α-tocopheryl radical were used for the investigation of the mechanism of the edible oils oxidation. 19 F NMR of the 19 F labeled phenolic compounds (through trifluoroacetate esters) and radical trap experiments showed that the vanadium complexes in edible oil activate the one electron reduction of dioxygen to superperoxide radical. Superperoxide reacts with the lipids to form alkoperoxyl and alkoxyl lipid radicals, and all these radicals react with the phenols contained in oils.

Acetate in mixotrophic growth medium affects photosystem II in Chlamydomonas reinhardtii and protects against photoinhibition.

PubMed

Roach, Thomas; Sedoud, Arezki; Krieger-Liszkay, Anja

2013-10-01

Chlamydomonas reinhardtii is a photoautotrophic green alga, which can be grown mixotrophically in acetate-supplemented media (Tris-acetate-phosphate). We show that acetate has a direct effect on photosystem II (PSII). As a consequence, Tris-acetate-phosphate-grown mixotrophic C. reinhardtii cultures are less susceptible to photoinhibition than photoautotrophic cultures when subjected to high light. Spin-trapping electron paramagnetic resonance spectroscopy showed that thylakoids from mixotrophic C. reinhardtii produced less (1)O2 than those from photoautotrophic cultures. The same was observed in vivo by measuring DanePy oxalate fluorescence quenching. Photoinhibition can be induced by the production of (1)O2 originating from charge recombination events in photosystem II, which are governed by the midpoint potentials (Em) of the quinone electron acceptors. Thermoluminescence indicated that the Em of the primary quinone acceptor (QA/QA(-)) of mixotrophic cells was stabilised while the Em of the secondary quinone acceptor (QB/QB(-)) was destabilised, therefore favouring direct non-radiative charge recombination events that do not lead to (1)O2 production. Acetate treatment of photosystem II-enriched membrane fragments from spinach led to the same thermoluminescence shifts as observed in C. reinhardtii, showing that acetate exhibits a direct effect on photosystem II independent from the metabolic state of a cell. A change in the environment of the non-heme iron of acetate-treated photosystem II particles was detected by low temperature electron paramagnetic resonance spectroscopy. We hypothesise that acetate replaces the bicarbonate associated to the non-heme iron and changes the environment of QA and QB affecting photosystem II charge recombination events and photoinhibition. Copyright © 2013 Elsevier B.V. All rights reserved.

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.

Improving the catalytic activity of magnetic Fe3O4/ZnO-CdO/reduced graphene oxide for ultrasonic degradation of the organic pollutants and the green oxidation of olefins

NASA Astrophysics Data System (ADS)

Mirzazadeh, Hoda; Lashanizadegan, Maryam

2018-05-01

Magnetic Fe3O4/ZnO-CdO/reduced graphene oxide (MFZC/RGO) has been synthesized by simple hydrothermal method. The structure and morphology were investigated by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), Diffuse reflectance spectroscopy (DRS), Vibrating sample magnetometer (VSM), Raman and Fourier-transform infrared spectroscopy (FTIR). MFZC/RGO was applied as catalyst in degradation of methylene blue (MB), rhodamin B (RhB) and methylorange (MO) under ultrasonic irradiation. Based on the results, excellent degradation efficiencies of MB, RhB and MO (>99%) were achieved within 10, 20 and 20 min, respectively under oxygen flow. Moreover the catalytic property of MFZC/RGO was investigated in oxidation of styrene, α-methyl styrene, cyclohexene and cyclooctene under oxygen flow. In addition, MFZC/RGO can be easily collected and separated by an external magnet. The catalyst displayed negligible loss in activity and selectivity within several successive runs due to super paramagnetism.

Freestanding silicon quantum dots: origin of red and blue luminescence.

PubMed

Gupta, Anoop; Wiggers, Hartmut

2011-02-04

In this paper, we studied the behavior of silicon quantum dots (Si-QDs) after etching and surface oxidation by means of photoluminescence (PL) measurements, Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance spectroscopy (EPR). We observed that etching of red luminescing Si-QDs with HF acid drastically reduces the concentration of defects and significantly enhances their PL intensity together with a small shift in the emission spectrum. Additionally, we observed the emergence of blue luminescence from Si-QDs during the re-oxidation of freshly etched particles. Our results indicate that the red emission is related to the quantum confinement effect, while the blue emission from Si-QDs is related to defect states at the newly formed silicon oxide surface.

On magnetic structure of CuFe 2Ge 2: Constrains from the 57Fe Mössbauer spectroscopy

DOE PAGES

Bud’ko, Sergey L.; Jo, Na Hyun; Downing, Savannah S.; ...

2017-09-20

57Fe Mössbauer spectroscopy measurements were performed on a powdered CuFe 2Ge 2 sample that orders antiferromagnetically at ~175 K. Whereas a paramagnetic doublet was observed above the Néel temperature, a superposition of paramagnetic doublet and magnetic sextet (in approximately 0.5:0.5 ratio) was observed in the magnetically ordered state, suggesting a magnetic structure similar to a double-Q spin density wave with half of the Fe paramagnetic and another half bearing static moment of ~0.5–1μ B. Lastly, these results call for a re-evaluation of the recent neutron scattering data and band structure calculations, as well as for deeper examination of details ofmore » sample preparation techniques.« less

Membrane-organized Chemical Photoredox Systems

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

Britt, R. David

2016-09-01

The key photoredox process in photosynthesis is the accumulation of oxidizing equivalents on a tetranuclear manganese cluster that then liberates electrons and protons from water and forms oxygen gas. Our primary goal in this project is to characterize inorganic systems that can perform this same water-splitting chemistry. One such species is the dinuclear ruthenium complex known as the blue dimer. Starting at the Ru(III,III) oxidation state, the blue dimer is oxidized up to a putative Ru(V,V) level prior to O-O bond formation. We employ electron paramagnetic resonance spectroscopy to characterize each step in this reaction cycle to gain insight intomore » the molecular mechanism of water oxidation.« less

First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron

NASA Astrophysics Data System (ADS)

Kakehashi, Yoshiro; Chandra, Sumal

2016-04-01

We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi-Dirac function for the d electrons with eg symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data.

Spectroscopic and Computational Studies of Spin States of Iron(IV) Nitrido and Imido Complexes

DOE PAGES

Bucinsky, Lukas; Breza, Martin; Lee, Wei-Tsung; ...

2017-04-05

High-oxidation state metal complexes with multiply bonded ligands are of great interest for both their reactivity as well as their fundamental bonding properties. This paper reports a combined spectroscopic and theoretical investigation into the effect of the apical multiply bonded ligand on the spin state preferences of three-fold symmetric iron(IV) complexes with tris(carbene) donor ligands. Specifically, singlet (S = 0) nitrido [{PhB(Im R) 3}FeN], R = tBu (1), Mes (mesityl, 2) and the related triplet (S = 1) imido complexes, [{PhB(Im R) 3}Fe(NR')] +, R = Mes, R' = Ad (1- adamantyl, 3), tBu (4), have been investigated by electronicmore » absorption and Mössbauer effect spectroscopies. For comparison, two other Fe(IV) nitrido complexes, [(TIMEN Ar)FeN] +, (TIMEN Ar = tris[2-(3-aryl-imidazol-2-ylidene)ethyl]amine; Ar = Xyl (xylyl), Mes), have been investigated by 57Fe Mössbauer spectroscopy, including applied-field measurements. The paramagnetic imido complexes 3 and 4 were also studied by magnetic susceptibility measurements (for 3) and paramagnetic resonance spectroscopy: high-frequency and -field electron paramagnetic resonance (HFEPR) (for 3 and 4) and frequency-domain Fouriertransform (FD-FT) THz EPR (for 3), which reveal their zero-field splitting (zfs) parameters. Experimentally correlated theoretical studies comprising ligand-field theory (LFT) and quantum chemical theory (QCT), the latter including both density functional theory (DFT) and ab initio methods reveal the key role played by the Fe3 d z2 (a1) orbital in these systems: the nature of its interaction with the nitrido or imido ligand dictates the spin state preference of the complex. Lastly, the ability to tune the spin state through the energy and nature of a single orbital has general relevance to the factors controlling spin states in complexes with applicability as single molecule devices.« less

On the Importance of Electronic Symmetry for Triplet State Delocalization

DOE PAGES

Richert, Sabine; Bullard, George; Rawson, Jeff; ...

2017-03-29

The influence of electronic symmetry on triplet state delocalization in linear zinc porphyrin oligomers is explored by electron paramagnetic resonance techniques. Using a combination of transient continuous wave and pulse electron nuclear double resonance spectroscopies, it is demonstrated experimentally that complete triplet state delocalization requires the chemical equivalence of all porphyrin units. These results are supported by density functional theory calculations, showing uneven delocalization in a porphyrin dimer in which a terminal ethynyl group renders the two porphyrin units inequivalent. When the conjugation length of the molecule is further increased upon addition of a second terminal ethynyl group that restoresmore » the symmetry of the system, the triplet state is again found to be completely delocalized. Finally, the observations suggest that electronic symmetry is of greater importance for triplet state delocalization than other frequently invoked factors such as conformational rigidity or fundamental length-scale limitations.« less

Evidence of CuI/CuII Redox Process by X-ray Absorption and EPR Spectroscopy: Direct Synthesis of Dihydrofurans from b-Ketocarbonyl Derivatives and Olefins

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

Yi, Hong; Liao, Zhixiong; Zhang, Guanghui

Abstract: The CuI/CuII and CuI/CuIII catalytic cycles have been subject to intense debate in the field of copper-catalyzed oxidative coupling reactions. A mechanistic study on the CuI/CuII redox process, by X-ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopies, has elucidated the reduction mechanism of CuII to CuI by 1,3-diketone and detailed investigation revealed that the halide ion is important for the reduction process. The oxidative nature of the thereby-formed CuI has also been studied by XAS and EPR spectroscopy. This mechanistic information is applicable to the copper-catalyzed oxidative cyclization of b-ketocarbonyl derivatives to dihydrofurans. This protocol provides an idealmore » route to highly substituted dihydrofuran rings from easily available 1,3-dicarbonyls and olefins. Copper« less

The Electron Bifurcating FixABCX Protein Complex from Azotobacter vinelandii: Generation of Low-Potential Reducing Equivalents for Nitrogenase Catalysis.

PubMed

Ledbetter, Rhesa N; Garcia Costas, Amaya M; Lubner, Carolyn E; Mulder, David W; Tokmina-Lukaszewska, Monika; Artz, Jacob H; Patterson, Angela; Magnuson, Timothy S; Jay, Zackary J; Duan, H Diessel; Miller, Jacquelyn; Plunkett, Mary H; Hoben, John P; Barney, Brett M; Carlson, Ross P; Miller, Anne-Frances; Bothner, Brian; King, Paul W; Peters, John W; Seefeldt, Lance C

2017-08-15

The biological reduction of dinitrogen (N 2 ) to ammonia (NH 3 ) by nitrogenase is an energetically demanding reaction that requires low-potential electrons and ATP; however, pathways used to deliver the electrons from central metabolism to the reductants of nitrogenase, ferredoxin or flavodoxin, remain unknown for many diazotrophic microbes. The FixABCX protein complex has been proposed to reduce flavodoxin or ferredoxin using NADH as the electron donor in a process known as electron bifurcation. Herein, the FixABCX complex from Azotobacter vinelandii was purified and demonstrated to catalyze an electron bifurcation reaction: oxidation of NADH (E m = -320 mV) coupled to reduction of flavodoxin semiquinone (E m = -460 mV) and reduction of coenzyme Q (E m = 10 mV). Knocking out fix genes rendered Δrnf A. vinelandii cells unable to fix dinitrogen, confirming that the FixABCX system provides another route for delivery of electrons to nitrogenase. Characterization of the purified FixABCX complex revealed the presence of flavin and iron-sulfur cofactors confirmed by native mass spectrometry, electron paramagnetic resonance spectroscopy, and transient absorption spectroscopy. Transient absorption spectroscopy further established the presence of a short-lived flavin semiquinone radical, suggesting that a thermodynamically unstable flavin semiquinone may participate as an intermediate in the transfer of an electron to flavodoxin. A structural model of FixABCX, generated using chemical cross-linking in conjunction with homology modeling, revealed plausible electron transfer pathways to both high- and low-potential acceptors. Overall, this study informs a mechanism for electron bifurcation, offering insight into a unique method for delivery of low-potential electrons required for energy-intensive biochemical conversions.

The Electron Bifurcating FixABCX Protein Complex from Azotobacter vinelandii: Generation of Low-Potential Reducing Equivalents for Nitrogenase Catalysis

DOE PAGES

Ledbetter, Rhesa N.; Garcia Costas, Amaya M.; Lubner, Carolyn E.; ...

2017-07-13

The biological reduction of dinitrogen (N 2) to ammonia (NH 3) by nitrogenase is an energetically demanding reaction that requires low-potential electrons and ATP; however, pathways used to deliver the electrons from central metabolism to the reductants of nitrogenase, ferredoxin or flavodoxin, remain unknown for many diazotrophic microbes. The FixABCX protein complex has been proposed to reduce flavodoxin or ferredoxin using NADH as the electron donor in a process known as electron bifurcation. Herein, the FixABCX complex from Azotobacter vinelandii was purified and demonstrated to catalyze an electron bifurcation reaction: oxidation of NADH (E m = -320 mV) coupled tomore » reduction of flavodoxin semiquinone (E m = -460 mV) and reduction of coenzyme Q (E m = 10 mV). Knocking out fix genes rendered ..delta..rnf A. vinelandii cells unable to fix dinitrogen, confirming that the FixABCX system provides another route for delivery of electrons to nitrogenase. Characterization of the purified FixABCX complex revealed the presence of flavin and iron-sulfur cofactors confirmed by native mass spectrometry, electron paramagnetic resonance spectroscopy, and transient absorption spectroscopy. Transient absorption spectroscopy further established the presence of a short-lived flavin semiquinone radical, suggesting that a thermodynamically unstable flavin semiquinone may participate as an intermediate in the transfer of an electron to flavodoxin. A structural model of FixABCX, generated using chemical cross-linking in conjunction with homology modeling, revealed plausible electron transfer pathways to both high- and low-potential acceptors. Altogether, this study informs a mechanism for electron bifurcation, offering insight into a unique method for delivery of low-potential electrons required for energy-intensive biochemical conversions.« less

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®

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

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.

Point defects in crystalline zircon (zirconium silicate), ZrSiO4: electron paramagnetic resonance studies

NASA Astrophysics Data System (ADS)

Tennant, W. C.; Claridge, R. F. C.; Walsby, C. J.; Lees, N. S.

This article outlines the present state of knowledge of paramagnetic defects in crystalline zircon as obtained mainly, but not exclusively, from electron paramagnetic resonance (EPR) studies in crystalline zircon (zirconium silicate, ZrSiO4). The emphasis is on single-crystal studies where, in principle, unambiguous analysis is possible. Firstly, the crystallography of zircon is presented. Secondly, the relationships between available crystal-site symmetries and the symmetries of observed paramagnetic species in zircon, and how these observations lead to unambiguous assignments of point-group symmetries for particular paramagnetic species are detailed. Next, spin-Hamiltonian (SH) analysis is discussed with emphasis on the symmetry relationships that necessarily exist amongst the Laue classes of the crystal sites in zircon, the paramagnetic species occupying those sites and the SH itself. The final sections of the article then survey the results of EPR studies on zircon over the period 1960-2002.

Gd(III) complexes for electron-electron dipolar spectroscopy: Effects of deuteration, pH and zero field splitting.

PubMed

Garbuio, Luca; Zimmermann, Kaspar; Häussinger, Daniel; Yulikov, Maxim

2015-10-01

Spectral parameters of Gd(III) complexes are intimately linked to the performance of the Gd(III)-nitroxide or Gd(III)-Gd(III) double electron-electron resonance (DEER or PELDOR) techniques, as well as to that of relaxation induced dipolar modulation enhancement (RIDME) spectroscopy with Gd(III) ions. These techniques are of interest for applications in structural biology, since they can selectively detect site-to-site distances in biomolecules or biomolecular complexes in the nanometer range. Here we report relaxation properties, echo detected EPR spectra, as well as the magnitude of the echo reduction effect in Gd(III)-nitroxide DEER for a series of Gadolinium(III) complexes with chelating agents derived from tetraazacyclododecane. We observed that solvent deuteration does not only lengthen the relaxation times of Gd(III) centers but also weakens the DEER echo reduction effect. Both of these phenomena lead to an improved signal-to-noise ratios or, alternatively, longer accessible distance range in pulse EPR measurements. The presented data enrich the knowledge on paramagnetic Gd(III) chelate complexes in frozen solutions, and can help optimize the experimental conditions for most types of the pulse measurements of the electron-electron dipolar interactions. Copyright © 2015 Elsevier Inc. All rights reserved.

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.

Defects induced in cerium dioxide single crystals by electron irradiation

DOE PAGES

Costantini, Jean-Marc; Miro, Sandrine; Touati, Nadia; ...

2018-01-12

In this work, Micro-Raman spectroscopy, X-band electron paramagnetic resonance (EPR) spectroscopy, and UV-visible optical absorption spectroscopy were used to study the damage production in cerium dioxide (CeO 2) single crystals by electron irradiation for three energies (1.0, 1.4, and 2.5 MeV). The Raman-active T 2g peak was left unchanged after 2.5-MeV electron irradiation at a high fluence. This shows that no structural modifications occurred for the cubic fluorite structure. UV-visible optical absorption spectra exhibited a characteristic sub band-gap tail for 1.4-MeV and 2.5-MeV energies, but not for 1.0 MeV. Narrow EPR lines were recorded near liquid-helium temperature after 2.5-MeV electronmore » irradiation; whereas no such signal was found for the virgin un-irradiated crystal or after 1.0-MeV irradiation for the same fluence. The angular variation of these lines in the {111} plane revealed a weak g-factor anisotropy assigned to Ce 3+ ions (with the 4f 1 configuration) in a high-symmetry local environment. Finally, it is concluded that Ce 3+ ions may be produced by a reduction resulting from the displacement damage process. However, no evidence of F + or F 0 center or hole center formation due to irradiation was found from the present EPR and optical absorption spectra.« less

Defects induced in cerium dioxide single crystals by electron irradiation

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

Costantini, Jean-Marc; Miro, Sandrine; Touati, Nadia

In this work, Micro-Raman spectroscopy, X-band electron paramagnetic resonance (EPR) spectroscopy, and UV-visible optical absorption spectroscopy were used to study the damage production in cerium dioxide (CeO 2) single crystals by electron irradiation for three energies (1.0, 1.4, and 2.5 MeV). The Raman-active T 2g peak was left unchanged after 2.5-MeV electron irradiation at a high fluence. This shows that no structural modifications occurred for the cubic fluorite structure. UV-visible optical absorption spectra exhibited a characteristic sub band-gap tail for 1.4-MeV and 2.5-MeV energies, but not for 1.0 MeV. Narrow EPR lines were recorded near liquid-helium temperature after 2.5-MeV electronmore » irradiation; whereas no such signal was found for the virgin un-irradiated crystal or after 1.0-MeV irradiation for the same fluence. The angular variation of these lines in the {111} plane revealed a weak g-factor anisotropy assigned to Ce 3+ ions (with the 4f 1 configuration) in a high-symmetry local environment. Finally, it is concluded that Ce 3+ ions may be produced by a reduction resulting from the displacement damage process. However, no evidence of F + or F 0 center or hole center formation due to irradiation was found from the present EPR and optical absorption spectra.« less

Hyperfine Interactions in the Electron Paramagnetic Resonance Spectra of Point Defects in Wide-Band-Gap Semiconductors

DTIC Science & Technology

2014-09-18

compensation) during growth due to their preferred trivalent charge states. The electron paramagnetic resonance spectrum of the singly ionized chromium ...neutral nitrogen acceptor in ZnO . . . . . . . . . . . . . . . . . . 45 16 Spectrum of the singly ionized chromium acceptor in TiO2 . . . . . . . . . 49...is a single crystal of magnesium oxide that has been doped with chromium . Chromium Cr3+ substitutes for magnesium Mg2+ and creates a paramagnetic

Electron paramagnetic resonance study of lipid and protein membrane components of erythrocytes oxidized with hydrogen peroxide

PubMed Central

Mendanha, S.A.; Anjos, J.L.V.; Silva, A.H.M.; Alonso, A.

2012-01-01

Electron paramagnetic resonance (EPR) spectroscopy of spin labels was used to monitor membrane dynamic changes in erythrocytes subjected to oxidative stress with hydrogen peroxide (H2O2). The lipid spin label, 5-doxyl stearic acid, responded to dramatic reductions in membrane fluidity, which was correlated with increases in the protein content of the membrane. Membrane rigidity, associated with the binding of hemoglobin (Hb) to the erythrocyte membrane, was also indicated by a spin-labeled maleimide, 5-MSL, covalently bound to the sulfhydryl groups of membrane proteins. At 2% hematocrit, these alterations in membrane occurred at very low concentrations of H2O2 (50 µM) after only 5 min of incubation at 37°C in azide phosphate buffer, pH 7.4. Lipid peroxidation, suggested by oxidative hemolysis and malondialdehyde formation, started at 300 µM H2O2 (for incubation of 3 h), which is a concentration about six times higher than those detected with the probes. Ascorbic acid and α-tocopherol protected the membrane against lipoperoxidation, but did not prevent the binding of proteins to the erythrocyte membrane. Moreover, the antioxidant (+)-catechin, which also failed to prevent the cross-linking of cytoskeletal proteins with Hb, was very effective in protecting erythrocyte ghosts from lipid peroxidation induced by the Fenton reaction. This study also showed that EPR spectroscopy can be useful to assess the molecular dynamics of red blood cell membranes in both the lipid and protein domains and examine oxidation processes in a system that is so vulnerable to oxidation. PMID:22473321

Colour centre recovery in yttria-stabilised zirconia: photo-induced versus thermal processes

NASA Astrophysics Data System (ADS)

Costantini, Jean-Marc; Touati, Nadia; Binet, Laurent; Lelong, Gérald; Guillaumet, Maxime; Beuneu, François

2018-05-01

The photo-annealing of colour centres in yttria-stabilised zirconia (YSZ) was studied by electron paramagnetic resonance spectroscopy upon UV-ray or laser light illumination, and compared to thermal annealing. Stable hole centres (HCs) were produced in as-grown YSZ single crystals by UV-ray irradiation at room temperature (RT). The HCs produced by 200-MeV Au ion irradiation, as well as the F+-type centres (? centres involving oxygen vacancies) were left unchanged upon UV illumination. In contrast, a significant photo-annealing of the latter point defects was achieved in 1.4-MeV electron-irradiated YSZ by 553-nm laser light irradiation at RT. Almost complete photo-bleaching was achieved by laser irradiation inside the absorption band of ? centres centred at a wavelength 550 nm. Thermal annealing of these colour centres was also followed by UV-visible absorption spectroscopy showing full bleaching at 523 K. Colour-centre evolutions by photo-induced and thermally activated processes are discussed on the basis of charge exchange processes between point defects.

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.

Physicochemical characteristics and toxic effects of ozone-oxidized black carbon particles

NASA Astrophysics Data System (ADS)

Li, Qian; Shang, Jing; Zhu, Tong

2013-12-01

Black carbon (BC) or soot particles formed by combustion are ubiquitous in the atmosphere and have a significant effect on climate and human health. Oxidation can change the physicochemical characteristics of BC, thereby increasing its toxicity. The physicochemical properties of BC and ozone-oxidized BC are investigated in this study through transmission electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, ultraviolet-visible spectrophotometry, and electron paramagnetic resonance. The contents of oxygen-containing functional groups, hydrophilicity, water-soluble organic compounds, and free radicals increased after ozone treatment. The redox capacity and cytotoxicity of BC particles were enhanced by ozone oxidation as detected by dithiothreitol (DTT) and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide assays. The redox activities of different BC particles are compared. Particle phase contributed significantly to total redox activity as detected by the DTT assay. Results indicate that BC particles that have undergone aging in the atmosphere may be more toxic and harmful to human health.

Integrated Structural Biology for α-Helical Membrane Protein Structure Determination.

PubMed

Xia, Yan; Fischer, Axel W; Teixeira, Pedro; Weiner, Brian; Meiler, Jens

2018-04-03

While great progress has been made, only 10% of the nearly 1,000 integral, α-helical, multi-span membrane protein families are represented by at least one experimentally determined structure in the PDB. Previously, we developed the algorithm BCL::MP-Fold, which samples the large conformational space of membrane proteins de novo by assembling predicted secondary structure elements guided by knowledge-based potentials. Here, we present a case study of rhodopsin fold determination by integrating sparse and/or low-resolution restraints from multiple experimental techniques including electron microscopy, electron paramagnetic resonance spectroscopy, and nuclear magnetic resonance spectroscopy. Simultaneous incorporation of orthogonal experimental restraints not only significantly improved the sampling accuracy but also allowed identification of the correct fold, which is demonstrated by a protein size-normalized transmembrane root-mean-square deviation as low as 1.2 Å. The protocol developed in this case study can be used for the determination of unknown membrane protein folds when limited experimental restraints are available. Copyright © 2018 Elsevier Ltd. All rights reserved.

Facile synthesis of thermal- and photostable titania with paramagnetic oxygen vacancies for visible-light photocatalysis.

PubMed

Zou, Xiaoxin; Liu, Jikai; Su, Juan; Zuo, Fan; Chen, Jiesheng; Feng, Pingyun

2013-02-18

A novel dopant-free TiO(2) photocatalyst (V(o)(.)-TiO(2)), which is self-modified by a large number of paramagnetic (single-electron-trapped) oxygen vacancies, was prepared by calcining a mixture of a porous amorphous TiO(2) precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO(2) precursor, imidazole, and hydrochloric acid are all necessary for the formation of V(o)(.)-TiO(2). Although the synthesis of V(o)(.)-TiO(2) originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X-ray diffraction, XPS, and EPR spectroscopy reveal that the V(o)(.)-TiO(2) material with a high crystallinity embodies a mass of paramagnetic oxygen vacancies, and is free of other dopant species such as nitrogen and carbon. UV/Vis diffuse-reflectance spectroscopy and photoelectrochemical measurement demonstrate that V(o)(.)-TiO(2) is a stable visible-light-responsive material with photogenerated charge separation efficiency higher than N-TiO(2) and P25 under visible-light irradiation. The V(o)(.)-TiO(2) material exhibits not only satisfactory thermal- and photostability, but also superior photocatalytic activity for H(2) evolution (115 μmol h(-1) g(-1)) from water with methanol as sacrificial reagent under visible light (λ>400 nm) irradiation. Furthermore, the effects of reaction temperature, ratio of starting materials (imidazole:TiO(2) precursor) and calcination time on the photocatalytic activity and the microstructure of V(o)(.)-TiO(2) were elucidated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Application of Electron Paramagnetic Resonance to Study of Gallstones

NASA Astrophysics Data System (ADS)

Kiselev, S. A.; Tsyro, L. V.; Afanasiev, D. A.; Unger, F. G.; Soloviev, M. M.

2014-03-01

We present the results of an electron paramagnetic resonance (EPR) study of mixed cholesterol gallstones. We have established that free radicals are distributed nonuniformly within the interior of the stone. The type and number of paramagnetic centers depend on the pigment content in the selected layer. We show that the parameters of the sextet lines in the EPR spectrum of the pigment are close to the parameters of lines in the spectrum of a brown pigment stone.

Electrical detection of nuclear spins in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Malissa, H.; Kavand, M.; Waters, D. P.; Lupton, J. M.; Vardeny, Z. V.; Saam, B.; Boehme, C.

2014-03-01

We present pulsed combined electrically detected electron paramagnetic and nuclear magnetic resonance experiments on MEH-PPV OLEDs. Spin dynamics in these structures are governed by hyperfine interactions between charge carriers and the surrounding hydrogen nuclei, which are abundant in these materials. Hyperfine coupling has been observed by monitoring the device current during coherent spin excitation. Electron spin echoes (ESEs) are detected by applying one additional readout pulse at the time of echo formation. This allows for the application of high-resolution spectroscopy based on ESE detection, such as electron spin echo envelope modulation (ESEEM) and electron nuclear double resonance (ENDOR) available for electrical detection schemes. We conduct electrically detected ESEEM and ENDOR experiments and show how hyperfine interactions in MEH-PPV with and without deuterated polymer side groups can be observed by device current measurements. We acknowledge support by the Department of Energy, Office of Basic Energy Sciences under Award #DE-SC0000909.

Room temperature ferromagnetism in Fe-doped semiconductor ZrS2 single crystals

NASA Astrophysics Data System (ADS)

Muhammad, Zahir; Lv, Haifeng; Wu, Chuanqiang; Habib, Muhammad; Rehman, Zia ur; Khan, Rashid; Chen, Shuangming; Wu, Xiaojun; Song, Li

2018-04-01

Two dimensional (2D) layered magnetic materials have obtained much attention due to their intriguing properties with a potential application in the field of spintronics. Herein, room-temperature ferromagnetism with 0.2 emu g‑1 magnetic moment is realized in Fe-doped ZrS2 single crystals of millimeter size, in comparison with diamagnetic behaviour in ZrS2. The electron paramagnetic resonance spectroscopy reveals that 5.2wt% Fe-doping ZrS2 crystal exhibit high spin value of g-factor about 3.57 at room temperature also confirmed this evidence, due to the unpaired electrons created by doped Fe atoms. First principle static electronic and magnetic calculations further confirm the increased stability of long range ferromagnetic ordering and enhanced magnetic moment in Fe-doped ZrS2, originating from the Fe spin polarized electron near the Fermi level.

Structure and dynamics in B12 enzyme catalysis revealed by electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Warncke, Kurt

2009-03-01

Challenges to the understanding of how protein structure and dynamics contribute to catalysis in enzymes, and the use of time-resolved electron paramagnetic resonance (EPR) spectroscopic techniques to address the challenges, are examined in the context of the coenzyme B12-dependent enzyme, ethanolamine ammonia-lyase (EAL), from Salmonella typhimurium. EAL conducts the homolytic cleavage of the coenzyme cobalt-carbon bond, intraprotein radical migration (5-6 å), and hydrogen atom transfers, which enable the core radical-mediated rearrangement reaction. Thermodynamic and activation parameters are measured in two experimental systems, which were developed to isolate sub-sequences from the multi-step catalytic cycle, as follows: (1) A dimethylsulfoxide (DMSO)/water cryosolvent system is used to prepare the kinetically-arrested enzyme/coenzyme/substrate ternary complex in fluid solution at 230 K.[1] Temperature-step initiated cobalt-carbon bond cleavage and radical pair separation to form the Co(II)-substrate radical pair are monitored by using time-resolved, full-spectrum EPR spectroscopy (234<=T<=250 K).[1] (2) The Co(II)-substrate radical pair is cryotrapped in frozen aqueous solution at T<150 K, and then promoted to react by a temperature step. The reaction of the substrate radical along the native pathway to form the diamagnetic bound products is monitored by using time-resolved, full-spectrum EPR spectroscopy (187<=T<=217 K).[2] High temporal resolution is achieved, because the reactions are dramatically slowed at the low temperatures, relative to the initiation and spectrum acquistion times. The results are combined with high resolution structures of the reactant centers, obtained by pulsed-EPR spectroscopies,[3] and the protein, obtained by structural proteomics[4] and EPR and electron spin echo envelope modulation (ESEEM) in combination with site directed mutagenesis,[5] to approach a molecular level description of protein contributions to catalysis in EAL. [4pt] [1] Wang, M. & Warncke, K. J. Am. Chem. Soc. 2008, 130, 4846. [0pt] [2] Chen, Z. and Warncke, K. Biophys. J. 2008, 95 (December) [0pt] [3] Canfield, J. M. and Warncke, K. J. Phys. Chem. B 2002, 106, 8831. [0pt] [4] Sun, L. and Warncke, K. Proteins 2006, 64, 308. [0pt] [5] Sun, L., Groover, O., Canfield, J. M., and Warncke, K. Biochemistry 2008, 47, 5523.

Structural and Mössbauer characterization of the ball-milled Fex(Al2O3)100-x system

NASA Astrophysics Data System (ADS)

Paesano, A.; Matsuda, C. K.; Cótica, L. F.; de Medeiros, S. N.; da Cunha, J. B. M.; Hallouche, B.; Silva, S. L.

2004-09-01

Metal-oxide composites were synthesized by high-energy ball milling of metallic iron (α-Fe) and alumina (α-Al2O3) powders, varying the starting relative concentration and the milling time. The samples were characterized by scanning electron microscopy, x-ray diffraction, and Mössbauer spectroscopy. The results revealed the formation of a FeAl2O3+W spinel phase (hercynite) and of iron (super)paramagnetic nanoprecipitates, in addition to residual magnetic iron and alumina. We also observed that the relative amounts of nanoprecipitates and hercynite for isochronally milled samples were correlated with the sample nominal concentration x, with the precursor iron being relatively more converted in those phases for low x values. Particularly for x =10 milled sample, the relative amounts of the (super)paramagnetic and spinel phases were observed to increase linearly with the milling time. An x =20/24h milled sample was annealed in H2 atmosphere and revealed the reduction of hercynite, with iron phase separation.

Quantitative Interpretation of Multifrequency Multimode EPR Spectra of Metal Containing Proteins, Enzymes, and Biomimetic Complexes.

PubMed

Petasis, Doros T; Hendrich, Michael P

2015-01-01

Electron paramagnetic resonance (EPR) spectroscopy has long been a primary method for characterization of paramagnetic centers in materials and biological complexes. Transition metals in biological complexes have valence d-orbitals that largely define the chemistry of the metal centers. EPR spectra are distinctive for metal type, oxidation state, protein environment, substrates, and inhibitors. The study of many metal centers in proteins, enzymes, and biomimetic complexes has led to the development of a systematic methodology for quantitative interpretation of EPR spectra from a wide array of metal containing complexes. The methodology is now contained in the computer program SpinCount. SpinCount allows simulation of EPR spectra from any sample containing multiple species composed of one or two metals in any spin state. The simulations are quantitative, thus allowing determination of all species concentrations in a sample directly from spectra. This chapter will focus on applications to transition metals in biological systems using EPR spectra from multiple microwave frequencies and modes. © 2015 Elsevier Inc. All rights reserved.

Investigating the intermediates in the reaction of ribonucleoside triphosphate reductase from Lactobacillus leichmannii : An application of HF EPR-RFQ technology

NASA Astrophysics Data System (ADS)

Manzerova, Julia; Krymov, Vladimir; Gerfen, Gary J.

2011-12-01

In this investigation high-frequency electron paramagnetic resonance spectroscopy (HFEPR) in conjunction with innovative rapid freeze-quench (RFQ) technology is employed to study the exchange-coupled thiyl radical-cob(II)alamin system in ribonucleotide reductase from a prokaryote Lactobacillus leichmannii. The size of the exchange coupling ( Jex) and the values of the thiyl radical g tensor are refined, while confirming the previously determined (Gerfen et al. (1996) [20]) distance between the paramagnets. Conclusions relevant to ribonucleotide reductase catalysis and the architecture of the active site are presented. A key part of this work has been the development of a unique RFQ apparatus for the preparation of millisecond quench time RFQ samples which can be packed into small (0.5 mm ID) sample tubes used for CW and pulsed HFEPR - lack of this ability has heretofore precluded such studies. The technology is compatible with a broad range of spectroscopic techniques and can be readily adopted by other laboratories.

In vivo triarylmethyl radical stabilization through encapsulation in Pluronic F-127 hydrogel

NASA Astrophysics Data System (ADS)

Abbas, Kahina; Boutier-Pischon, Audrey; Auger, Florian; Françon, Dominique; Almario, Antonio; Frapart, Yves-Michel

2016-09-01

In vivo electron paramagnetic resonance (EPR) imaging and spectroscopy are non-invasive technologies used to specifically detect and quantify paramagnetic species. However, the relative instability of spin probes such as triarylmethyl radicals limits their application to conduct oxygen quantification and mapping. In this study we encapsulated tetrathiatriarylmethyl radical (TAM; known as "Finland" probe) in Pluronic F-127 hydrogel (PF-127) in order to limit its degradation and evaluate its in vitro and in vivo EPR properties as a function of oxygen. Our results show that the EPR signal of encapsulated TAM in PF-127 hydrogel is similar to the one in solution. Although it is less sensitive to oxygen, it is suitable for oximetry. We also demonstrated that the incorporation of TAM in PF-127 hydrogel leads to an improved in vivo EPR stability of the radical under anesthesia. This new formulation enables high quality EPR imaging and oximetry and paves the way for the application of TAM radical-based probes in various biomedical fields.

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.

Preparation of Some Homologous TEMPO Nitroxides and Oxoammonium Salts; Notes on the NMR Spectroscopy of Nitroxide Free Radicals; Observed Radical Nature of Oxoammonium Salt Solutions Containing Trace Amounts of Corresponding Nitroxides in an Equilibrium Relationship.

PubMed

Bobbitt, James M; Eddy, Nicholas A; Cady, Clyde X; Jin, Jing; Gascon, Jose A; Gelpí-Dominguez, Svetlana; Zakrzewski, Jerzy; Morton, Martha D

2017-09-15

Three new homologous TEMPO oxoammonium salts and three homologous nitroxide radicals have been prepared and characterized. The oxidation properties of the salts have been explored. The direct 13 C NMR and EPR spectra of the nitroxide free radicals and the oxoammonium salts, along with TEMPO and its oxoammonium salt, have been successfully measured with little peak broadening of the NMR signals. In the spectra of all ten compounds (nitroxides and corresponding oxoammonium salts), the carbons in the 2,2,6,6-tetramethylpiperidine core do not appear, implying paramagnetic properties. This unpredicted overall paramagnetism in the oxoammonium salt solutions is explained by a redox equilibrium as shown between oxoammonium salts and trace amounts of corresponding nitroxide. This equilibrium is confirmed by electron interchange reactions between nitroxides with an N-acetyl substituent and oxoammonium salts with longer acyl side chains.

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

Paramagnetic or diamagnetic persistent currents? A topological point of view

NASA Astrophysics Data System (ADS)

Waintal, Xavier

2009-03-01

A persistent current flows at low temperatures in small conducting rings when they are threaded by a magnetic flux. I will discuss the sign of this persistent current (diamagnetic or paramagnetic response) in the special case of N electrons in a one dimensional ring [1]. One dimension is very special in the sense that the sign of the persistent current is entirely controlled by the topology of the system. I will establish lower bounds for the free energy in the presence of arbitrary electron-electron interactions and external potentials. Those bounds are the counterparts of upper bounds derived by Leggett using another topological argument. Rings with odd (even) numbers of polarized electrons are always diamagnetic (paramagnetic). The situation is more interesting with unpolarized electrons where Leggett upper bound breaks down: rings with N=4n exhibit either paramagnetic behavior or a superconductor-like current-phase relation. The topological argument provides a rigorous justification for the phenomenological Huckel rule which states that cyclic molecules with 4n + 2 electrons like benzene are aromatic while those with 4n electrons are not. [4pt] [1] Xavier Waintal, Geneviève Fleury, Kyryl Kazymyrenko, Manuel Houzet, Peter Schmitteckert, and Dietmar Weinmann Phys. Rev. Lett.101, 106804 (2008).

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

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

Protonated o-semiquinone radical as a mimetic of the humic acids native radicals: A DFT approach to the molecular structure and EPR properties

NASA Astrophysics Data System (ADS)

Witwicki, Maciej; Jezierska, Julia

2012-06-01

Organic radicals are known to be an indispensable component of the humic acids (HA) structure. In HA two forms of radicals, stable (native) and short-lived (transient), are identified. Importantly, these radical forms can be easily differentiated by electron paramagnetic resonance (EPR) spectroscopy. This article provides a DFT-based insight into the electronic and molecular structure of the native radicals. The molecular models including an increase of the radical aromaticity and the hydrogen bonding between the radical and other functional groups of HA are taken under investigation. In consequence the interesting pieces of information on the structure of the native radical centers in HA are revealed and discussed, especially in terms of differences between the electronic structure of the native and transient forms.

Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases

NASA Astrophysics Data System (ADS)

Dwivedi, G. D.; Joshi, Amish G.; Kumar, Shiv; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L.; Ghosh, A. K.; Chatterjee, Sandip

2016-04-01

X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

Analysis of Roman age wall paintings found in Pordenone, Trieste and Montegrotto.

PubMed

Mazzocchin, G A; Agnoli, F; Salvadori, M

2004-10-20

The aim of the present work is the study of many fragments of wall painting from archaeological excavations in three different Roman age sites dating back to the I Century before Common Era: Pordenone (località Torre); Trieste (Crosada) and Padova (Montegrotto). The techniques used were optical microscopy, scanning electron microscopy (SEM), equipped with a EDS microanalysis detector, X-rays powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman spectroscopy (FT-Raman) and electron paramagnetic resonance (EPR) spectroscopy. The identified pigments were: cinnabar, hematite, celadonite, glauconite, cuprorivaite (Egyptian blue), yellow and red ochre, calcite, limonite, coal black. In general, the mortar preparation did not correspond to the complex procedure suggested by Vitruvius (De Architectura), but generally showed a porous layer, with crushed grains under the pigment layer. In some cases, two superimposed pigment layers were found: yellow superimposed on both red and pink, black on pink, green on black. The slight differences we found in the use of the pigments in the three studied sites might show that the same technology, culture and taste spread all over the Roman Empire in North Eastern Italy (X(a) Regio Venetia et Histria).

Acceptors in ZnO nanocrystals: A reinterpretation

NASA Astrophysics Data System (ADS)

Gehlhoff, W.; Hoffmann, A.

2012-12-01

In a recent article, Teklemichael et al. reported on the identification of an uncompensated acceptor in ZnO nanocrystals using infrared spectroscopy and electron paramagnetic resonance (EPR) in the dark and under illumination. Most of their conclusions, interpretations, and suggestions turned out to be erroneous. The observed EPR signals were interpreted to originate from axial and nonaxial VZn-H defects. We show that the given interpretation of the EPR results is based on misinterpretations of EPR spectra arising from defects in nanocrystals. The explanation of the infrared absorption lines is in conflict with recent results of valence band ordering and valence band splitting.

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.

The [4Fe-4S](2+) cluster in reconstituted biotin synthase binds S-adenosyl-L-methionine.

PubMed

Cosper, Michele Mader; Jameson, Guy N L; Davydov, Roman; Eidsness, Marly K; Hoffman, Brian M; Huynh, Boi Hanh; Johnson, Michael K

2002-11-27

The combination of resonance Raman, electron paramagnetic resonance and Mössbauer spectroscopies has been used to investigate the effect of S-adenosyl-l-methionine (SAM) on the spectroscopic properties of the [4Fe-4S]2+ cluster in biotin synthase. The results indicate that SAM interacts directly at a unique iron site of the [4Fe-4S]2+ cluster in BioB and support the hypothesis of a common inner-sphere mechanism for the reductive cleavage of SAM in the radical SAM family of Fe-S enzymes.

Evidence that the reactivity of the martian soil is due to superoxide ions

NASA Technical Reports Server (NTRS)

Yen, A. S.; Kim, S. S.; Hecht, M. H.; Frant, M. S.; Murray, B.

2000-01-01

The Viking Landers were unable to detect evidence of life on Mars but, instead, found a chemically reactive soil capable of decomposing organic molecules. This reactivity was attributed to the presence of one or more as-yet-unidentified inorganic superoxides or peroxides in the martian soil. Using electron paramagnetic resonance spectroscopy, we show that superoxide radical ions (O2-) form directly on Mars-analog mineral surfaces exposed to ultraviolet radiation under a simulated martian atmosphere. These oxygen radicals can explain the reactive nature of the soil and the apparent absence of organic material at the martian surface.

Spin coherence in a Mn3 single-molecule magnet

NASA Astrophysics Data System (ADS)

Abeywardana, Chathuranga; Mowson, Andrew M.; Christou, George; Takahashi, Susumu

2016-01-01

Spin coherence in single crystals of the spin S = 6 single-molecule magnet (SMM) [Mn3O(O2CEt)3(mpko)3]+ (abbreviated Mn3) has been investigated using 230 GHz electron paramagnetic resonance spectroscopy. Coherence in Mn3 was uncovered by significantly suppressing dipolar contribution to the decoherence with complete spin polarization of Mn3 SMMs. The temperature dependence of spin decoherence time (T2) revealed that the dipolar decoherence is the dominant source of decoherence in Mn3 and T2 can be extended up to 267 ns by quenching the dipolar decoherence.

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

DOE R&D Accomplishments Database

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

1950-09-22

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

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.

Evidence of room temperature ferromagnetism in argon/oxygen annealed TiO2 thin films deposited by electron beam evaporation technique

NASA Astrophysics Data System (ADS)

Mohanty, P.; Kabiraj, D.; Mandal, R. K.; Kulriya, P. K.; Sinha, A. S. K.; Rath, Chandana

2014-04-01

TiO2 thin films deposited by electron beam evaporation technique annealed in either O2 or Ar atmosphere showed ferromagnetism at room temperature. The pristine amorphous film demonstrates anatase phase after annealing under Ar/O2 atmosphere. While the pristine film shows a super-paramagnetic behavior, both O2 and Ar annealed films display hysteresis at 300 K. X-ray photo emission spectroscopy (XPS), Raman spectroscopy, Rutherford's backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were used to refute the possible role of impurities/contaminants in magnetic properties of the films. The saturation magnetization of the O2 annealed film is found to be higher than the Ar annealed one. It is revealed from shifting of O 1s and Ti 2p core level spectra as well as from the enhancement of high binding energy component of O 1s spectra that the higher magnetic moment is associated with higher oxygen vacancies. In addition, O2 annealed film demonstrates better crystallinity, uniform deposition and smoother surface than that of the Ar annealed one from glancing angle X-ray diffraction (GAXRD) and atomic force microscopy (AFM). We conclude that although ferromagnetism is due to oxygen vacancies, the higher magnetization in O2 annealed film could be due to crystallinity, which has been observed earlier in Co doped TiO2 film deposited by pulsed laser deposition (Mohanty et al., 2012 [10]).

NARROW LINE ABSORPTION IN CACO3.

DTIC Science & Technology

CARBONATES), (*CALCIUM COMPOUNDS, (*ABSORPTION SPECTRA, CALCITE), (*CALCITE, RADIATION EFFECTS), ELECTRON PARAMAGNETIC RESONANCE, SINGLE CRYSTALS , NEUTRONS, X RAYS, GAMMA RAYS, IONS, CRYSTAL DEFECTS, PARAMAGNETIC RESONANCE.

Excitations and relaxation dynamics in multiferroic GeV4S8 studied by terahertz and dielectric spectroscopy

NASA Astrophysics Data System (ADS)

Reschke, S.; Wang, Zhe; Mayr, F.; Ruff, E.; Lunkenheimer, P.; Tsurkan, V.; Loidl, A.

2017-10-01

We report on THz time-domain spectroscopy on multiferroic GeV4S8 , which undergoes orbital ordering at a Jahn-Teller transition at 30.5 K and exhibits antiferromagnetic order below 14.6 K. The THz experiments are complemented by dielectric experiments at audio and radio frequencies. We identify a low-lying excitation close to 0.5 THz, which is only weakly temperature dependent and probably corresponds to a molecular excitation within the electronic level scheme of the V4 clusters. In addition, we detect complex temperature-dependent behavior of a low-lying phononic excitation, closely linked to the onset of orbitally driven ferroelectricity. In the high-temperature cubic phase, which is paramagnetic and orbitally disordered, this excitation is of relaxational character becomes an overdamped Lorentzian mode in the orbitally ordered phase below the Jahn-Teller transition, and finally appears as well-defined phonon excitation in the antiferromagnetic state. Abrupt changes in the real and imaginary parts of the complex dielectric permittivity show that orbital ordering appears via a structural phase transition with strong first-order character and that the onset of antiferromagnetic order is accompanied by significant structural changes, which are of first-order character, too. Dielectric spectroscopy documents that at low frequencies, significant dipolar relaxations are present in the orbitally ordered, paramagnetic phase only. In contrast to the closely related GaV4S8 , this relaxation dynamics that most likely mirrors coupled orbital and polar fluctuations does not seem to be related to the dynamic processes detected in the THz regime.

Ru–protein–Co biohybrids designed for solar hydrogen production: understanding electron transfer pathways related to photocatalytic function† †Electronic supplementary information (ESI) available: Time traces of photocatalysis, additional EPR spectra and parameters, UV-visible spectroscopy data, and kinetic fits of TA traces. See DOI: 10.1039/c6sc03121h Click here for additional data file.

PubMed Central

Soltau, Sarah R.; Dahlberg, Peter D.; Niklas, Jens; Poluektov, Oleg G.; Mulfort, Karen L.

2016-01-01

A series of Ru–protein–Co biohybrids have been prepared using the electron transfer proteins ferredoxin (Fd) and flavodoxin (Fld) as scaffolds for photocatalytic hydrogen production. The light-generated charge separation within these hybrids has been monitored by transient optical and electron paramagnetic resonance spectroscopies. Two distinct electron transfer pathways are observed. The Ru–Fd–Co biohybrid produces up to 650 turnovers of H2 utilizing an oxidative quenching mechanism for Ru(ii)* and a sequential electron transfer pathway via the native [2Fe–2S] cluster to generate a Ru(iii)–Fd–Co(i) charge separated state that lasts for ∼6 ms. In contrast, a direct electron transfer pathway occurs for the Ru–ApoFld–Co biohybrid, which lacks an internal electron relay, generating Ru(i)–ApoFld–Co(i) charge separated state that persists for ∼800 μs and produces 85 turnovers of H2 by a reductive quenching mechanism for Ru(ii)*. This work demonstrates the utility of protein architectures for linking donor and catalytic function via direct or sequential electron transfer pathways to enable stabilized charge separation which facilitates photocatalysis for solar fuel production. PMID:28451142

Grafting of styrene into pre-irradiated fluoropolymer films: Influence of base material and irradiation temperature

NASA Astrophysics Data System (ADS)

Lappan, Uwe; Geißler, Uwe; Gohs, Uwe; Uhlmann, Steffi

2010-10-01

In this study, the influence of irradiation temperature on mechanical properties of three fluoropolymers and on grafting of styrene into the polymers by the pre-irradiation method was investigated. Electron paramagnetic resonance spectroscopy and infrared spectroscopy were used to characterize the irradiated polymers regarding trapped radical species and changes in the chemical structure, respectively. For poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) the irradiation temperature was found to be an important factor for tensile strength and elongation at break of the pre-irradiated film. No strong effect of irradiation temperature on the mechanical properties was noticed for poly(tetrafluoroethylene-co-ethylene) (ETFE); however the yield of grafting drops at high irradiation temperatures. Finally, mechanical properties of poly(tetrafluoroethylene) (PTFE) were found to be dramatically altered, even if the film was irradiated at elevated temperature.

Low-dimensional quantum magnetism in Cu (NCS) 2: A molecular framework material

NASA Astrophysics Data System (ADS)

Cliffe, Matthew J.; Lee, Jeongjae; Paddison, Joseph A. M.; Schott, Sam; Mukherjee, Paromita; Gaultois, Michael W.; Manuel, Pascal; Sirringhaus, Henning; Dutton, Siân E.; Grey, Clare P.

2018-04-01

Low-dimensional magnetic materials with spin-1/2 moments can host a range of exotic magnetic phenomena due to the intrinsic importance of quantum fluctuations to their behavior. Here, we report the structure, magnetic structure, and magnetic properties of copper ii thiocyanate, Cu(NCS ) 2, a one-dimensional coordination polymer which displays low-dimensional quantum magnetism. Magnetic susceptibility, electron paramagnetic resonance spectroscopy, 13C magic-angle spinning nuclear magnetic resonance spectroscopy, and density functional theory investigations indicate that Cu(NCS ) 2 behaves as a two-dimensional array of weakly coupled antiferromagnetic spin chains [J2=133 (1 ) K , α =J1/J2=0.08 ] . Powder neutron-diffraction measurements confirm that Cu(NCS ) 2 orders as a commensurate antiferromagnet below TN=12 K , with a strongly reduced ordered moment (0.3 μB ) due to quantum fluctuations.

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.

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.

Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes

PubMed Central

King, David M.; Cleaves, Peter A.; Wooles, Ashley J.; Gardner, Benedict M.; Chilton, Nicholas F.; Tuna, Floriana; Lewis, William; McInnes, Eric J. L.; Liddle, Stephen T.

2016-01-01

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field. PMID:27996007

Copper doping of ZnO crystals by transmutation of 64Zn to 65Cu: An electron paramagnetic resonance and gamma spectroscopy study

NASA Astrophysics Data System (ADS)

Recker, M. C.; McClory, J. W.; Holston, M. S.; Golden, E. M.; Giles, N. C.; Halliburton, L. E.

2014-06-01

Transmutation of 64Zn to 65Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the 65Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of 64Zn nuclei to 65Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu2+ ions (where 63Cu and 65Cu hyperfine lines are easily resolved). A spectrum from isolated Cu2+ (3d9) ions acquired after the neutron irradiation showed only hyperfine lines from 65Cu nuclei. The absence of 63Cu lines in this Cu2+ spectrum left no doubt that the observed 65Cu signals were due to transmuted 65Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu+-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu+-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900 °C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

Conformational Mobility in Cytochrome P450 3A4 Explored by Pressure-Perturbation EPR Spectroscopy

PubMed Central

Davydov, Dmitri R.; Yang, Zhongyu; Davydova, Nadezhda; Halpert, James R.; Hubbell, Wayne L.

2016-01-01

We used high hydrostatic pressure as a tool for exploring the conformational landscape of human cytochrome P450 3A4 (CYP3A4) by electron paramagnetic resonance and fluorescence spectroscopy. Site-directed incorporation of a luminescence resonance energy transfer donor-acceptor pair allowed us to identify a pressure-dependent equilibrium between two states of the enzyme, where an increase in pressure increased the spatial separation between the two distantly located fluorophores. This transition is characterized by volume change (ΔV°) and P1/2 values of −36.8 ± 5.0 mL/mol and 1.45 ± 0.33 kbar, respectively, which corresponds to a Keq° of 0.13 ± 0.06, so that only 15% of the enzyme adopts the pressure-promoted conformation at ambient pressure. This pressure-promoted displacement of the equilibrium is eliminated by the addition of testosterone, an allosteric activator. Using site-directed spin labeling, we demonstrated that the pressure- and testosterone-sensitive transition is also revealed by pressure-induced changes in the electron paramagnetic resonance spectra of a nitroxide side chain placed at position 85 or 409 of the enzyme. Furthermore, we observed a pressure-induced displacement of the emission maxima of a solvatochromic fluorophore (7-diethylamino-3-((((2-maleimidyl)ethyl)amino)carbonyl) coumarin) placed at the same positions, which suggests a relocation to a more polar environment. Taken together, the results reveal an effector-dependent conformational equilibrium between open and closed states of CYP3A4 that involves a pronounced change at the interface between the region of α-helices A/A′ and the meander loop of the enzyme, where residues 85 and 409 are located. Our study demonstrates the high potential of pressure-perturbation strategies for studying protein conformational landscapes. PMID:27074675

Spectroscopic and optical properties of the VO2+ ion doped TeO2-TiO2-ZnO-Nb2O5 glass system

NASA Astrophysics Data System (ADS)

Swapna; Upender, G.; Sreenivasulu, V.; Prasad, M.

2016-04-01

Studies such as optical absorption, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Electron paramagnetic resonance (EPR) spectroscopy and Differential scanning calorimetry (DSC) were carried out on VO2+ ion doped TeO2-TiO2-ZnO-Nb2O5 glass system. Raman and FTIR spectra of the glasses revealed the presence of [TeO3], [TeO4] and [NbO6] structural units in the glass network. The Urbach energy (Δ E), cut-off wavelength (λ c ), optical band gap ( E opt ), optical basicity (Λ) and electron polarizability ( α) of the glasses were determined from optical absorption studies. The density ( ρ), molar volume ( V m ), oxygen molar volume ( V o ) and refractive index ( n) were also measured. Spin-Hamiltonian parameters were calculated from the EPR studies. When Nb2O5 was increased at the expense of ZnO, the density, optical band gap and Urbach energy of the glasses increased, and the electronic polarizability and optical basicity decreased. The EPR spectra clearly showed that vanadium was in the glass as VO2+ and occupied octahedral sites with tetrahedral compression. Spin-Hamiltonian parameters g‖ and g⊥ decreased as Nb2O5 content increased in the glass. The glass transition temperature ( T g ) also increased with increasing Nb2O5 content in the glass.

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

Effects of sterilisation by high-energy radiation on biomedical poly-(epsilon-caprolactone)/hydroxyapatite composites.

PubMed

Di Foggia, Michele; Corda, Ugo; Plescia, Elena; Taddei, Paola; Torreggiani, Armida

2010-06-01

The effects of a high energy sterilization treatment on poly-epsilon-caprolactone/carbonated hydroxyapatite composites have been investigated. Poly-epsilon-caprolactone is a biodegradable polymer used as long-term bioresorbable scaffold for bone tissue engineering and carbonated hydroxyapatite is a bioactive material able to promote bone growth. The composites were gamma-irradiated in air or under nitrogen atmosphere with doses ranging from 10 to 50 kGy (i.e. to a value higher than that recommended for sterilization). The effects of the irradiation treatment were evaluated by vibrational spectroscopy (IR and Raman spectroscopies) coupled to thermal analysis (Differential Scanning Calorimetry and Thermogravimetry) and Electron Paramagnetic Resonance spectroscopy. Irradiation with the doses required for sterilization induced acceptable structural changes and damaging effects: only a very slight fragmentation of the polymeric chains and some defects in the inorganic component were observed. Moreover, the radiation sensitivity of the composites proved almost the same under the two different atmospheres.

Coupled aging effects in nanofiber-reinforced siloxane foams

DOE PAGES

Labouriau, Andrea; Robison, Tom; Geller, Drew Adam; ...

2018-01-11

Here, this study investigates the combined effects of ionizing radiation and thermal treatments on the aging of siloxane foams containing small amounts of carbon nanofibers. Our siloxane foams were exposed to accelerated aging conditions for more than two years, resulting in very low dose rates. In addition, foams were aged under compressive load to evaluate the strength of the porous microstructure. Samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), Mössbauer, mass spectroscopy, electron paramagnetic resonance spectroscopy (EPR), solvent swelling, imaging techniques, uniaxial compressive load testing and tearmore » testing. No significant changes in thermal stability or chemistry of the accelerated aged foam were observed, although gas evolution was detected. Changes in crystallization levels at low temperatures, microstructure, and mechanical properties were observed for foams with and without carbon nanofibers. In particular, foams aged under compressive load showed irreversible deformation of the porous microstructure. This study demonstrates that aging effects were enhanced when thermal and radiolysis were coupled together and that the addition of carbon nanofibers did not improve aging effects.« less

Antioxidant Capacity: Experimental Determination by EPR Spectroscopy and Mathematical Modeling.

PubMed

Polak, Justyna; Bartoszek, Mariola; Chorążewski, Mirosław

2015-07-22

A new method of determining antioxidant capacity based on a mathematical model is presented in this paper. The model was fitted to 1000 data points of electron paramagnetic resonance (EPR) spectroscopy measurements of various food product samples such as tea, wine, juice, and herbs with Trolox equivalent antioxidant capacity (TEAC) values from 20 to 2000 μmol TE/100 mL. The proposed mathematical equation allows for a determination of TEAC of food products based on a single EPR spectroscopy measurement. The model was tested on the basis of 80 EPR spectroscopy measurements of herbs, tea, coffee, and juice samples. The proposed model works for both strong and weak antioxidants (TEAC values from 21 to 2347 μmol TE/100 mL). The determination coefficient between TEAC values obtained experimentally and TEAC values calculated with proposed mathematical equation was found to be R(2) = 0.98. Therefore, the proposed new method of TEAC determination based on a mathematical model is a good alternative to the standard EPR method due to its being fast, accurate, inexpensive, and simple to perform.

Coupled aging effects in nanofiber-reinforced siloxane foams

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

Labouriau, Andrea; Robison, Tom; Geller, Drew Adam

Here, this study investigates the combined effects of ionizing radiation and thermal treatments on the aging of siloxane foams containing small amounts of carbon nanofibers. Our siloxane foams were exposed to accelerated aging conditions for more than two years, resulting in very low dose rates. In addition, foams were aged under compressive load to evaluate the strength of the porous microstructure. Samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), Mössbauer, mass spectroscopy, electron paramagnetic resonance spectroscopy (EPR), solvent swelling, imaging techniques, uniaxial compressive load testing and tearmore » testing. No significant changes in thermal stability or chemistry of the accelerated aged foam were observed, although gas evolution was detected. Changes in crystallization levels at low temperatures, microstructure, and mechanical properties were observed for foams with and without carbon nanofibers. In particular, foams aged under compressive load showed irreversible deformation of the porous microstructure. This study demonstrates that aging effects were enhanced when thermal and radiolysis were coupled together and that the addition of carbon nanofibers did not improve aging effects.« less

Direct measurement of ferromagnetic ordering in biaxially strained LaCoO3 thin films

NASA Astrophysics Data System (ADS)

Klie, R. F.; Yuan, T.; Tanase, M.; Yang, G.; Ramasse, Q.

2010-02-01

LaCoO3 undergoes a transition from a nonmagnetic to a paramagnetic semiconductor at 80 K, associated with a spin-state transition of the Co3+ ions. It was proposed that the temperature of the spin-state transition depends strongly on the LaCoO3 lattice parameter, suggesting that strain can stabilize different spin states at different temperatures. By combining atomic-resolution Z-contrast imaging, electron diffraction, and angular-resolved electron energy-loss spectroscopy (EELS) with in situ cooling experiments, we show that epitaxially strained LaCoO3 (001) thin films grown on LaAlO3 (001) do not undergo a low temperature spin-state transition. Our EELS study explores the origins of the ferromagnetic ordering in strained LaCoO3 films.

Complementary study of molecular dynamics and domain sizes in heterogenous nanocomposites PBT/DA-C{sub 60} and PBT/TCNEO-C{sub 60}

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

Woźniak-Braszak, A., E-mail: abraszak@amu.edu.pl; Baranowski, M.; Jurga, K.

2014-05-28

A comprehensive study of molecular dynamics and structure in new heterogenous nanocomposites based on poly(butylene terephthalate) and nanoparticles C{sub 60} modified by n-decylamine or tetracyanoethylene oxide has been performed. The domain structure of new nanocomposites has been investigated by Fourier transform infrared spectroscopy, wide-angle X-ray scattering, and differential scanning calorimetry techniques. Solid-state {sup 1}H NMR techniques were used to study molecular dynamics and domain sizes in new nanocomposites. Information about the electronic properties of these nanocomposites was obtained by means of electron paramagnetic resonance method. It was shown that the structure and molecular dynamics of new nanocomposites were strongly dependentmore » on the properties and concentration of fullerene derivates.« less

Characterization and Reactivity of a Terminal Nickel(III)-Oxygen Adduct

PubMed Central

Pirovano, Paolo; Farquhar, Erik R.; Swart, Marcel; Fitzpatrick, Anthony J.; Morgan, Grace G.; McDonald, Aidan R.

2015-01-01

High-valent terminal metal-oxygen adducts are hypothesized to be the potent oxidising reactants in late transition metal oxidation catalysis. In particular, examples of high-valent terminal nickel-oxygen adducts are sparse, meaning there is a dearth in the understanding of such oxidants. In this study, a monoanionic NiII-bicarbonate complex was found to react in a 1:1 ratio with the one-electron oxidant tris(4-bromophenyl)ammoniumyl hexachloroantimonate, yielding a thermally unstable intermediate in high yield (~95%). Electronic absorption, electronic paramagnetic resonance and X-ray absorption spectroscopies and density functional theory calculations confirm its description as a low-spin (S = ½), square planar NiIII-oxygen adduct. This rare example of a high-valent terminal nickel-oxygen complex performs oxidations of organic substrates, including 2,6-ditertbutylphenol and triphenylphosphine, which are indicative of hydrogen atom abstraction and oxygen atom transfer reactivity, respectively. PMID:25612563

A view of metals through the terahertz window

NASA Astrophysics Data System (ADS)

Dodge, Steve

2006-05-01

As electrons move through a metal, interaction with their environment tends to slow them down, causing the Drude peak in the optical conductivity to become narrower. The resulting peak width is typically in the terahertz frequency range that sits between microwaves the far infrared, too fast for conventional electronics and too slow for conventional infrared spectroscopy. With femtosecond laser techniques, however, coherent, broadband terahertz radiation can now be generated and detected with exquisite sensitivity, providing a new window onto electronic interactions in metals. I will discuss the application of this technique to a variety of metallic systems, including elemental lead, the nearly magnetic oxide metal CaRuO3, and CrV alloys that span the quantum phase transition from spin-density wave to paramagnetic metal. M. A. Gilmore, S. Kamal, D. M. Broun, and J. S. Dodge, Appl. Phys. Lett. 88, 141910 (2006).

Characterization and Reactivity of a Terminal Nickel(III)-Oxygen Adduct

DOE PAGES

Pirovano, Paolo; Farquhar, Erik R.; Swart, Marcel; ...

2015-01-22

Here, high-valent terminal metal–oxygen adducts are hypothesized to be the potent oxidizing reactants in late transition metal oxidation catalysis. In particular, examples of high-valent terminal nickel–oxygen adducts are scarce, meaning there is a dearth in the understanding of such oxidants. A monoanionic Ni II-bicarbonate complex has been found to react in a 1:1 ratio with the one-electron oxidant tris(4-bromophenyl)ammoniumyl hexachloroantimonate, yielding a thermally unstable intermediate in high yield (ca. 95%). Electronic absorption, electronic paramagnetic resonance, and X-ray absorption spectroscopies and density functional theory calculations confirm its description as a low-spin (S=1/2), square planar Ni III–oxygen adduct. Moreover, this rare examplemore » of a high-valent terminal nickel–oxygen complex performs oxidations of organic substrates, including 2,6-di-tert-butylphenol and triphenylphosphine, which are indicative of hydrogen atom abstraction and oxygen atom transfer reactivity, respectively.« less

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.

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.

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.

ENDOR-Induced EPR of Disordered Systems: Application to X-Irradiated Alanine.

PubMed

Kusakovskij, Jevgenij; Maes, Kwinten; Callens, Freddy; Vrielinck, Henk

2018-02-15

The electron paramagnetic resonance (EPR) spectra of radiation-induced radicals in organic solids are generally composed of multiple components that largely overlap due to their similar weak g anisotropy and a large number of hyperfine (HF) interactions. Such properties make these systems difficult to study using standard cw EPR spectroscopy even in single crystals. Electron-nuclear double-resonance (ENDOR) spectroscopy is a powerful and widely used complementary technique. In particular, ENDOR-induced EPR (EIE) experiments are useful for separating the overlapping contributions. In the present work, these techniques were employed to study the EPR spectrum of stable radicals in X-irradiated alanine, which is widely used in dosimetric applications. The principal values of all major proton HF interactions of the dominant radicals were determined by analyzing the magnetic field dependence of the ENDOR spectrum at 50 K, where the rotation of methyl groups is frozen. Accurate simulations of the EPR spectrum were performed after the major components were separated using an EIE analysis. As a result, new evidence in favor of the model of the second dominant radical was obtained.

Synergistic effect on the visible light activity of Ti3+ doped TiO2 nanorods/boron doped graphene composite

PubMed Central

Xing, Mingyang; Li, Xiao; Zhang, Jinlong

2014-01-01

TiO2/graphene (TiO2-x/GR) composites, which are Ti3+ self-doped TiO2 nanorods decorated on boron doped graphene sheets, were synthesized via a simple one-step hydrothermal method using low-cost NaBH4 as both a reducing agent and a boron dopant on graphene. The resulting TiO2 nanorods were about 200 nm in length with exposed (100) and (010) facets. The samples were characterized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy, X-band electron paramagnetic resonance (EPR), X-ray photoelectron spectra (XPS), transmission electron microscope (TEM), Raman, and Fourier-transform infrared spectroscopy (FTIR). The XRD results suggest that the prepared samples have an anatase crystalline structure. All of the composites tested exhibited improved photocatalytic activities as measured by the degradation of methylene blue and phenol under visible light irradiation. This improvement was attributed to the synergistic effect of Ti3+ self-doping on TiO2 nanorods and boron doping on graphene. PMID:24974890

Electron spin-echo envelope modulation (ESEEM) reveals water and phosphate interactions with the KcsA potassium channel.

PubMed

Cieslak, John A; Focia, Pamela J; Gross, Adrian

2010-02-23

Electron spin-echo envelope modulation (ESEEM) spectroscopy is a well-established technique for the study of naturally occurring paramagnetic metal centers. The technique has been used to study copper complexes, hemes, enzyme mechanisms, micellar water content, and water permeation profiles in membranes, among other applications. In the present study, we combine ESEEM spectroscopy with site-directed spin labeling (SDSL) and X-ray crystallography in order to evaluate the technique's potential as a structural tool to describe the native environment of membrane proteins. Using the KcsA potassium channel as a model system, we demonstrate that deuterium ESEEM can detect water permeation along the lipid-exposed surface of the KcsA outer helix. We further demonstrate that (31)P ESEEM is able to identify channel residues that interact with the phosphate headgroup of the lipid bilayer. In combination with X-ray crystallography, the (31)P data may be used to define the phosphate interaction surface of the protein. The results presented here establish ESEEM as a highly informative technique for SDSL studies of membrane proteins.

Optical, Magnetic and Photocatalytic Activity Studies of Li, Mg and Sr Doped and Undoped Zinc Oxide Nanoparticles.

PubMed

Shanthi, S I; Poovaragan, S; Arularasu, M V; Nithya, S; Sundaram, R; Magdalane, C Maria; Kaviyarasu, K; Maaza, M

2018-08-01

Nanoparticles of Li, Mg and Sr doped and undoped zinc oxide was prepared by simple precipitation method. The structural, optical, and magnetic properties of the samples were investigated by the Powder X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Fourier Transform Infrared (FTIR) spectroscopy, Ultra-violet Visible spectroscopy (UV-vis) spectra, Photoluminescence (PL) and Vibrational Sample Magnetometer (VSM). The Powder X-ray diffraction data confirm the formation of hexagonal wurtzite structure of all doped and undoped ZnO. The SEM photograph reveals that the pores availability and particles size in the range of 10 nm-50 nm. FTIR and UV-Visible spectra results confirm the incorporation of the dopant into the ZnO lattice nanostructure. The UV-Visible spectra indicate that the shift of blue region (lower wavelength) due to bandgap widening. Photoluminescence intensity varies with doping due to the increase of oxygen vacancies in prepared ZnO. The pure ZnO exist paramagnetic while doped (Li, Mg and Sr) ZnO exist ferromagnetic property. The photocatalytic activity of the prepared sample also carried out in detail.

A multi-analytical approach for the characterization of powders from the Pompeii archaeological site.

PubMed

Canevali, Carmen; Gentile, Paolo; Orlandi, Marco; Modugno, Francesca; Lucejko, Jeannette Jacqueline; Colombini, Maria Perla; Brambilla, Laura; Goidanich, Sara; Riedo, Chiara; Chiantore, Oscar; Baraldi, Pietro; Baraldi, Cecilia; Gamberini, Maria Cristina

2011-10-01

Nine black powders found in Pompeii houses in three different types of bronze vessels (cylindrical theca atramentaria, unguentaries, and aryballoi) were characterized in order to assess a correspondence between the composition and the type of vessel and, possibly, to verify if these powders were inks or not. For the compositional characterization, a multi-analytical approach was adopted, which involved the use of scanning electron microscopy-energy dispersive X-ray, Fourier-transformed infrared spectroscopy, Raman, X-ray diffraction, electron paramagnetic resonance spectroscopy, thermogravimetric analysis, gas chromatography coupled with mass spectrometry (GC/MS), and pyrolysis GC/MS. Powders contained in cylindrical theca atramentaria form a homogeneous group, and their organic and inorganic compositions suggest that they were writing inks, while powders contained in unguentaries and aryballoi could have had several different uses, including writing inks and cosmetics. Furthermore, the composition profile of the powders found in cylindrical cases shows that, at 79 AD: , in Pompeii, carbon-based inks were still used for writing, and iron gall inks had not been introduced yet.

Study of modifications in the mechanical properties of sodium aluminoborosilicate glass induced by heavy ions and electrons

NASA Astrophysics Data System (ADS)

Chen, L.; Yuan, W.; Nan, S.; Du, X.; Zhang, D. F.; Lv, P.; Peng, H. B.; Wang, T. S.

2016-03-01

Radiation effects on the mechanical properties of sodium aluminoborosilicate glass induced by 4 MeV Kr, 5 MeV Xe ions and 1.2 MeV electrons have been investigated by nano-indentation measurements. Raman and electron paramagnetic resonance (EPR) spectroscopies were used to characterize the microstructure evolution of electron irradiated samples. The nano-indentation results indicated that the mean hardness was reduced by 12.8%, and the mean reduced Young modulus was increased by 3.5% after heavy ion irradiation. Both the hardness and reduced Young modulus variations reached stabilization when the nuclear deposited energy was around 3 × 1021 keVnucl/cm3. Although decreases of hardness (about 6.6%) and reduced Young modulus (about 3.1%) were also observed when the deposited electronic energy reached approximately 1.5 × 1022 keVelec/cm3 after electron irradiation, the results still emphasized that the nuclear energy deposition is the major factor for the evolution in the hardness and modulus of the sodium aluminoborosilicate glass under ion irradiation, rather than a synergy process of the electronic and nuclear energy depositions.

Electronic structures of U X3 (X =Al , Ga, and In) studied by photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Fujimori, Shin-ichi; Kobata, Masaaki; Takeda, Yukiharu; Okane, Tetsuo; Saitoh, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; Ōnuki, Yoshichika

2017-09-01

The electronic structures of U X3 (X =Al , Ga , and In ) were studied by photoelectron spectroscopy to understand the relationship between their electronic structures and magnetic properties. The band structures and Fermi surfaces of UAl3 and UGa3 were revealed experimentally by angle-resolved photoelectron spectroscopy (ARPES), and they were compared with the result of band-structure calculations. The topologies of the Fermi surfaces and the band structures of UAl3 and UGa3 were explained reasonably well by the calculation, although bands near the Fermi level (EF) were renormalized owing to the finite electron correlation effect. The topologies of the Fermi surfaces of UAl3 and UGa3 are very similar to each other, except for some minor differences. Such minor differences in their Fermi surface or electron correlation effect might take an essential role in their different magnetic properties. No significant changes were observed between the ARPES spectra of UGa3 in the paramagnetic and antiferromagnetic phases, suggesting that UGa3 is an itinerant weak antiferromagnet. The effect of chemical pressure on the electronic structures of U X3 compounds was also studied by utilizing the smaller lattice constants of UAl3 and UGa3 than that of UIn3. The valence band spectrum of UIn3 is accompanied by a satellitelike structure on the high-binding-energy side. The core-level spectrum of UIn3 is also qualitatively different from those of UAl3 and UGa3. These findings suggest that the U 5 f states in UIn3 are more localized than those in UAl3 and UGa3.

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.

Spectroscopic study of the humification process during sewage sludge treatment

NASA Astrophysics Data System (ADS)

Pajączkowska, J.; Sułkowska, A.; Sułkowski, W. W.; Jędrzejczyk, M.

2003-06-01

The aim of this work was to study the free radical transition of organic materials during the sewage treatment process. Investigations of sludge from biologic-mechanical sewage treatment plant in Sosnowiec Zagórze were carried out. The course of the humification processes during sewage treatment was studied by electron paramagnetic resonance (EPR) technique. The concentration of free radicals at each process stage and the value g were determined. Sludge samples and extracted fractions of humic acids were examined. Humic acids were extracted from sludge by means of conventional methods elaborated by Stevenson. For study of humic acids structures, besides EPR, the UV-Vis and IR spectroscopy were used.

Fermi Surface of Metallic V_{2}O_{3} from Angle-Resolved Photoemission: Mid-level Filling of e_{g}^{π} Bands.

PubMed

Lo Vecchio, I; Denlinger, J D; Krupin, O; Kim, B J; Metcalf, P A; Lupi, S; Allen, J W; Lanzara, A

2016-10-14

Using angle resolved photoemission spectroscopy, we report the first band dispersions and distinct features of the bulk Fermi surface (FS) in the paramagnetic metallic phase of the prototypical metal-insulator transition material V_{2}O_{3}. Along the c axis we observe both an electron pocket and a triangular holelike FS topology, showing that both V 3d a_{1g} and e_{g}^{π} states contribute to the FS. These results challenge the existing correlation-enhanced crystal field splitting theoretical explanation for the transition mechanism and pave the way for the solution of this mystery.

Dynamics of heavy carriers in the ferromagnetic superconductor UGe2

NASA Astrophysics Data System (ADS)

Storchak, V. G.; Brewer, J. H.; Eshchenko, D. G.; Mengyan, P. W.; Parfenov, O. E.; Tokmachev, A. M.

2018-04-01

Superconductivity and ferromagnetism in a number of uranium-based materials come from the same f-electrons with a relatively large effective mass, suggesting the presence of a band of heavy quasiparticles, whose nature is still a mystery. Here, UGe2 dynamics in both ferromagnetic and paramagnetic phases is studied employing high-field μ +SR spectroscopy. The spectra exhibit a doublet structure characteristic to formation of subnanometer-sized magnetic polarons. This model is thoroughly explored here and correlated with the unconventional physics of UGe2. The heavy-fermion behaviour is ascribed to magnetic polarons; when coherent they form a narrow band, thus reconciling heavy carriers with superconductivity and itinerant ferromagnetism.

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.

EPR investigation of gamma irradiated single crystal guaifenesin: A combined experimental and computational study

NASA Astrophysics Data System (ADS)

Tasdemir, Halil Ugur; Sayin, Ulku; Türkkan, Ercan; Ozmen, Ayhan

2016-04-01

Gamma irradiated single crystal of Guaifenesin (Glyceryl Guaiacolate), an important expectorant drug, were investigated with Electron Paramagnetic Resonance (EPR) spectroscopy between 123 and 333 K temperature at different orientations in the magnetic field. Considering the chemical structure and the experimental spectra of the gamma irradiated single crystal of guaifenesin sample, we assumed that alkoxy or alkyl-type paramagnetic species may be produced by irradiation. Depending on this assumption, eight possible alkoxy and alkyl-type radicals were modeled and EPR parameters of these modeled radicals were calculated using the B3LYP/6-311++G(d,p)-level of density functional theory (DFT). Theoretically calculated values of alkyl-type modeled radical(R3) are in good agreement with experimentally determined EPR parameters of single crystal. Furthermore, simulation spectra which are obtained by using the theoretical initial values are well matched with the experimental spectra. It was determined that a stable Cα •H2αCβHβCγH2γ (R3) alkyl radical was produced in the host crystal as a result of gamma irradiation.

Blue nano titania made in diffusion flames.

PubMed

Teleki, Alexandra; Pratsinis, Sotiris E

2009-05-21

Blue titanium suboxide nanoparticles (including Magneli phases) were formed directly without any post-processing or addition of dopants by combustion of titanium-tetra-isopropoxide (TTIP) vapor at atmospheric pressure. Particle size, phase composition, rutile and anatase crystal sizes as well as the blue coloration were controlled by rapid quenching of the flame with a critical flow nozzle placed at various heights above the burner. The particles showed a broad absorption in the near-infrared region and retained their blue color upon storage in ambient atmosphere. A high concentration of paramagnetic Ti3+ centres was found in the substoichiometric particles by electron paramagnetic resonance (EPR) spectroscopy. Furthermore particles with controlled band gap energy from 3.2 to 3.6 eV were made by controlling the burner-nozzle-distance from 10 to 1 cm, respectively. The color robustness and extent of suboxidation could be further enhanced by co-oxidation of TTIP with hexamethyldisiloxane in the flame resulting in SiO2-coated titanium suboxide particles. The process is cost-effective and green while the particles produced can replace traditional blue colored, cobalt-containing pigments.

Feasibility of reading LiF thermoluminescent dosimeters by electron spin resonance

NASA Astrophysics Data System (ADS)

Breen, S. L.; Battista, J. J.

1999-08-01

Lithium fluoride is a commonly used solid state dosimeter. During irradiation, electrons and holes become trapped in crystal imperfections; thermoluminescence dosimetry measures their thermally induced recombination. Electron paramagnetic resonance (EPR) spectroscopy can be used to measure the resonant absorption of microwaves by the unpaired electrons trapped in LiF. In an effort to extend the use of LiF dosimeters to smaller sizes and to the harsh environments encountered in internal dosimetry, EPR was evaluated as an alternative technique to read the radiation dose delivered to TLD-100 dosimeters. TLD-100 rods were irradiated with a 60Co source to doses of 10 Gy to 100 Gy. A radiation-induced signal (with a g-value of 2.002) could be detected only at liquid nitrogen temperatures at doses above 20 Gy. The EPR spectrum of irradiated LiF contains three components, one of which correlates positively with dose. However, the low sensitivity of the technique, and difficulty in interpreting the EPR spectrum from polycrystalline dosimeters, preclude its use as a dosimetry technique.

Feasibility of reading LiF thermoluminescent dosimeters by electron spin resonance.

PubMed

Breen, S L; Battista, J J

1999-08-01

Lithium fluoride is a commonly used solid state dosimeter. During irradiation, electrons and holes become trapped in crystal imperfections; thermoluminescence dosimetry measures their thermally induced recombination. Electron paramagnetic resonance (EPR) spectroscopy can be used to measure the resonant absorption of microwaves by the unpaired electrons trapped in LiF. In an effort to extend the use of LiF dosimeters to smaller sizes and to the harsh environments encountered in internal dosimetry, EPR was evaluated as an alternative technique to read the radiation dose delivered to TLD-100 dosimeters. TLD-100 rods were irradiated with a 60Co source to doses of 10 Gy to 100 Gy. A radiation-induced signal (with a g-value of 2.002) could be detected only at liquid nitrogen temperatures at doses above 20 Gy. The EPR spectrum of irradiated LiF contains three components, one of which correlates positively with dose. However, the low sensitivity of the technique, and difficulty in interpreting the EPR spectrum from polycrystalline dosimeters, preclude its use as a dosimetry technique.

Cobamide-mediated enzymatic reductive dehalogenation via long-range electron transfer

PubMed Central

Kunze, Cindy; Bommer, Martin; Hagen, Wilfred R.; Uksa, Marie; Dobbek, Holger; Schubert, Torsten; Diekert, Gabriele

2017-01-01

The capacity of metal-containing porphyrinoids to mediate reductive dehalogenation is implemented in cobamide-containing reductive dehalogenases (RDases), which serve as terminal reductases in organohalide-respiring microbes. RDases allow for the exploitation of halogenated compounds as electron acceptors. Their reaction mechanism is under debate. Here we report on substrate–enzyme interactions in a tetrachloroethene RDase (PceA) that also converts aryl halides. The shape of PceA’s highly apolar active site directs binding of bromophenols at some distance from the cobalt and with the hydroxyl substituent towards the metal. A close cobalt–substrate interaction is not observed by electron paramagnetic resonance spectroscopy. Nonetheless, a halogen substituent para to the hydroxyl group is reductively eliminated and the path of the leaving halide is traced in the structure. Based on these findings, an enzymatic mechanism relying on a long-range electron transfer is concluded, which is without parallel in vitamin B12-dependent biochemistry and represents an effective mode of RDase catalysis. PMID:28671181

Cobamide-mediated enzymatic reductive dehalogenation via long-range electron transfer.

PubMed

Kunze, Cindy; Bommer, Martin; Hagen, Wilfred R; Uksa, Marie; Dobbek, Holger; Schubert, Torsten; Diekert, Gabriele

2017-07-03

The capacity of metal-containing porphyrinoids to mediate reductive dehalogenation is implemented in cobamide-containing reductive dehalogenases (RDases), which serve as terminal reductases in organohalide-respiring microbes. RDases allow for the exploitation of halogenated compounds as electron acceptors. Their reaction mechanism is under debate. Here we report on substrate-enzyme interactions in a tetrachloroethene RDase (PceA) that also converts aryl halides. The shape of PceA's highly apolar active site directs binding of bromophenols at some distance from the cobalt and with the hydroxyl substituent towards the metal. A close cobalt-substrate interaction is not observed by electron paramagnetic resonance spectroscopy. Nonetheless, a halogen substituent para to the hydroxyl group is reductively eliminated and the path of the leaving halide is traced in the structure. Based on these findings, an enzymatic mechanism relying on a long-range electron transfer is concluded, which is without parallel in vitamin B 12 -dependent biochemistry and represents an effective mode of RDase catalysis.

A bioinspired redox relay that mimics radical interactions of the Tyr-His pairs of photosystem II

NASA Astrophysics Data System (ADS)

Megiatto, Jackson D., Jr.; Méndez-Hernández, Dalvin D.; Tejeda-Ferrari, Marely E.; Teillout, Anne-Lucie; Llansola-Portolés, Manuel J.; Kodis, Gerdenis; Poluektov, Oleg G.; Rajh, Tijana; Mujica, Vladimiro; Groy, Thomas L.; Gust, Devens; Moore, Thomas A.; Moore, Ana L.

2014-05-01

In water-oxidizing photosynthetic organisms, light absorption generates a powerfully oxidizing chlorophyll complex (P680•+) in the photosystem II reaction centre. This is reduced via an electron transfer pathway from the manganese-containing water-oxidizing catalyst, which includes an electron transfer relay comprising a tyrosine (Tyr)-histidine (His) pair that features a hydrogen bond between a phenol group and an imidazole group. By rapidly reducing P680•+, the relay is thought to mitigate recombination reactions, thereby ensuring a high quantum yield of water oxidation. Here, we show that an artificial reaction centre that features a benzimidazole-phenol model of the Tyr-His pair mimics both the short-internal hydrogen bond in photosystem II and, using electron paramagnetic resonance spectroscopy, the thermal relaxation that accompanies proton-coupled electron transfer. Although this artificial system is much less complex than the natural one, theory suggests that it captures the essential features that are important in the function of the relay.

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.

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.

Incorporation of Pyrazine and Bipyridine Linkers with High-Spin Fe(II) and Co(II) in a Metal–Organic Framework

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

Kawamura, Airi; Greenwood, Arin R.; Filatov, Alexander S.

2017-02-27

A series of isoreticular metal organic frameworks (MOFs) of the formula M(BDC)(L) (M = Fe(II) or Co(II), BDC = 1,4-benzenedicarboxylate, L = pyrazine (pyz) or 4,4'-bipyridine (bipy)) has been synthesized and characterized by N-2 gas uptake Measurements, single crystal and powder X-ray diffraction, magnetometry, X-ray absorption spectroscopy, and Mossbauer spectroscopy. These studies indicate the formation of a permanently porous solid with high-spin Fe(II) and Co(II) centers that are weakly coupled, consistent with first-principles density functional theory calculations. This family of materials represents unusual examples of paramagnetic metal centers coordinated by linkers capable of mediating magnetic or electronic coupling in amore » porous framework. While only weak interactions are observed, the rigid 3D framework of the MOF dramatically impacts the properties of these materials when compared with close structural analogues.« less

Comparative study of singlet oxygen production by photosensitiser dyes encapsulated in silicone: towards rational design of anti-microbial surfaces.

PubMed

Noimark, Sacha; Salvadori, Enrico; Gómez-Bombarelli, Rafael; MacRobert, Alexander J; Parkin, Ivan P; Kay, Christopher W M

2016-10-12

Surfaces with built-in antimicrobial activity have the potential to reduce hospital-acquired infections. One promising strategy is to create functionalised surfaces which, following illumination with visible light, are able to generate singlet oxygen under aerobic conditions. In contrast to antibiotics, the mechanism of bacterial kill by species derived from reactions with singlet oxygen is completely unselective, therefore offering little room for evolutionary adaptation. Here we consider five commercially available organic photosensitiser dyes encapsulated in silicone polymer that show varied antimicrobial activity. We correlate density functional theory calculations with UV-Vis spectroscopy, electron paramagnetic resonance spectroscopy and singlet oxygen production measurements in order to define and test the elements required for efficacious antimicrobial activity. Our approach forms the basis for the rational in silico design and spectroscopic screening of simple and efficient self-sterilising surfaces made from cheap, low toxicity photosensitiser dyes encapsulated in silicone.

Interaction of DNA with Simple and Mixed Ligand Copper(II) Complexes of 1,10-Phenanthrolines as Studied by DNA-Fiber EPR Spectroscopy

PubMed Central

Chikira, Makoto; Ng, Chew Hee; Palaniandavar, Mallayan

2015-01-01

The interaction of simple and ternary Cu(II) complexes of 1,10-phenanthrolines with DNA has been studied extensively because of their various interesting and important functions such as DNA cleavage activity, cytotoxicity towards cancer cells, and DNA based asymmetric catalysis. Such functions are closely related to the DNA binding modes of the complexes such as intercalation, groove binding, and electrostatic surface binding. A variety of spectroscopic methods have been used to study the DNA binding mode of the Cu(II) complexes. Of all these methods, DNA-fiber electron paramagnetic resonance (EPR) spectroscopy affords unique information on the DNA binding structures of the complexes. In this review we summarize the results of our DNA-fiber EPR studies on the DNA binding structure of the complexes and discuss them together with the data accumulated by using other measurements. PMID:26402668

Evaluation of dose uncertainty in radiation processing using EPR spectroscopy and butylated hydroxytoluene rods as dosimetry system

NASA Astrophysics Data System (ADS)

Alkhorayef, M.; Mansour, A.; Sulieman, A.; Alnaaimi, M.; Alduaij, M.; Babikir, E.; Bradley, D. A.

2017-12-01

Butylatedhydroxytoluene (BHT) rods represent a potential dosimeter in radiation processing, with readout via electron paramagnetic resonance (EPR) spectroscopy. Among the possible sources of uncertainty are those associated with the performance of the dosimetric medium and the conditions under which measurements are made, including sampling and environmental conditions. Present study makes estimate of the uncertainties, investigating physical response in different resonance regions. BHT, a white crystalline solid with a melting point of between 70-73 °C, was investigated using 60Co gamma irradiation over the dose range 0.1-100 kGy. The intensity of the EPR signal increases linearly in the range 0.1-35 kGy, the uncertainty budget for high doses being 3.3% at the 2σ confidence level. The rod form represents an excellent alternative dosimeter for high level dosimetry, of small uncertainty compared to powder form.

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.

Direct detection of free radicals and reactive oxygen species in thylakoids.

PubMed

Hideg, Eva; Kálai, Tamás; Hideg, Kálmán

2011-01-01

In plants, reactive oxygen species (ROS), also known as active oxygen species (AOS), are associated with normal, physiologic processes as well as with responses to adverse conditions. ROS are connected to stress in many ways: as primary elicitors, as products and propagators of oxidative damage, or as signal molecules initiating defense or adaptation. The photosynthetic electron transport is a major site of oxidative stress by visible or ultraviolet light, high or low temperature, pollutants or herbicides. ROS production can be presumed from detecting oxidatively damaged lipids, proteins, or pigments as well as from the alleviating effects of added antioxidants. On the contrary, measuring ROS by special sensor molecules provides more direct information. This chapter focuses on the application of spin trapping electron paramagnetic resonance (EPR) spectroscopy for detecting ROS: singlet oxygen and oxygen free radicals in thylakoid membrane preparations.

Unified model for singlet fission within a non-conjugated covalent pentacene dimer

NASA Astrophysics Data System (ADS)

Basel, Bettina S.; Zirzlmeier, Johannes; Hetzer, Constantin; Phelan, Brian T.; Krzyaniak, Matthew D.; Reddy, S. Rajagopala; Coto, Pedro B.; Horwitz, Noah E.; Young, Ryan M.; White, Fraser J.; Hampel, Frank; Clark, Timothy; Thoss, Michael; Tykwinski, Rik R.; Wasielewski, Michael R.; Guldi, Dirk M.

2017-05-01

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron-hole pairs, leading to a predicted ~50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.

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.

Unified model for singlet fission within a non-conjugated covalent pentacene dimer.

PubMed

Basel, Bettina S; Zirzlmeier, Johannes; Hetzer, Constantin; Phelan, Brian T; Krzyaniak, Matthew D; Reddy, S Rajagopala; Coto, Pedro B; Horwitz, Noah E; Young, Ryan M; White, Fraser J; Hampel, Frank; Clark, Timothy; Thoss, Michael; Tykwinski, Rik R; Wasielewski, Michael R; Guldi, Dirk M

2017-05-18

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron-hole pairs, leading to a predicted ∼50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.

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.

High-Capacitance Hybrid Supercapacitor Based on Multi-Colored Fluorescent Carbon-Dots.

PubMed

Genc, Rukan; Alas, Melis Ozge; Harputlu, Ersan; Repp, Sergej; Kremer, Nora; Castellano, Mike; Colak, Suleyman Gokhan; Ocakoglu, Kasim; Erdem, Emre

2017-09-11

Multi-colored, water soluble fluorescent carbon nanodots (C-Dots) with quantum yield changing from 4.6 to 18.3% were synthesized in multi-gram using dated cola beverage through a simple thermal synthesis method and implemented as conductive and ion donating supercapacitor component. Various properties of C-Dots, including size, crystal structure, morphology and surface properties along with their Raman and electron paramagnetic resonance spectra were analyzed and compared by means of their fluorescence and electronic properties. α-Manganese Oxide-Polypyrrole (PPy) nanorods decorated with C-Dots were further conducted as anode materials in a supercapacitor. Reduced graphene oxide was used as cathode along with the dicationic bis-imidazolium based ionic liquid in order to enhance the charge transfer and wetting capacity of electrode surfaces. For this purpose, we used octyl-bis(3-methylimidazolium)diiodide (C8H16BImI) synthesized by N-alkylation reaction as liquid ionic membrane electrolyte. Paramagnetic resonance and impedance spectroscopy have been undertaken in order to understand the origin of the performance of hybrid capacitor in more depth. In particular, we obtained high capacitance value (C = 17.3 μF/cm 2 ) which is exceptionally related not only the quality of synthesis but also the choice of electrode and electrolyte materials. Moreover, each component used in the construction of the hybrid supercapacitor is also played a key role to achieve high capacitance value.

Cation Binding to Xanthorhodopsin: Electron Paramagnetic Resonance and Magnetic Studies.

PubMed

Smolensky Koganov, Elena; Leitus, Gregory; Rozin, Rinat; Weiner, Lev; Friedman, Noga; Sheves, Mordechai

2017-05-04

Xanthorhodopsin (xR) is a member of the retinal protein family and acts as a proton pump in the cell membranes of the extremely halophilic eubacterium Salinibacter ruber. In addition to the retinal chromophore, xR contains a carotenoid, which acts as a light-harvesting antenna as it transfers 40% of the quanta it absorbs to the retinal. Our previous studies have shown that the CD and absorption spectra of xR are dramatically affected due to the protonation of two different residues. It is still unclear whether xR can bind cations. Electron paramagnetic resonance (EPR) spectroscopy used in the present study revealed that xR can bind divalent cations, such as Mn 2+ and Ca 2+ , to deionized xR (DI-xR). We also demonstrate that xR can bind 1 equiv of Mn 2+ to a high-affinity binding site followed by binding of ∼40 equiv in cooperative manner and ∼100 equiv of Mn 2+ that are weakly bound. SQUID magnetic studies suggest that the high cooperative binding of Mn 2+ cations to xR is due to the formation of Mn 2+ clusters. Our data demonstrate that Ca 2+ cations bind to DI-xR with a lower affinity than Mn 2+ , supporting the assumption that binding of Mn 2+ occurs through cluster formation, because Ca 2+ cations cannot form clusters in contrast to Mn 2+ .

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.

Further investigations on the role of ascorbic acid in stratum corneum lipid models after UV exposure.

PubMed

Trommer, Hagen; Böttcher, Rolf; Huschka, Christoph; Wohlrab, Wolfgang; Neubert, Reinhard H H

2005-08-01

This study is the continuation of our research into vitamin C and its possible effects on human skin after topical administration. The effects of ascorbic acid, iron ions and UV irradiation on stratum corneum lipid models were investigated. The lipid models used were: a simple system (linolenic acid dispersion), a complex system (liposomes consisting of dipalmitoylphosphatidylcholine, cholesterol and linolenic acid) and complex systems with additionally incorporated ceramides (types III and IV). The lipid peroxidation was quantified by the thiobarbituric acid assay. A human adult low-calcium high-temperature (HaCaT) keratinocytes cell culture was used as a second in-vitro model. The amount of intracellular peroxides was determined by measuring the fluorescence intensity using the dihydrorhodamine 123 assay. Electron paramagnetic resonance spectroscopy was used to study the influence of ascorbic acid and iron ions on the signal intensity of 5-doxylstearic acid during UV exposure. Ascorbic acid showed prooxidative properties in the thiobarbituric acid assay whereas cell protection was measured in the HaCaT keratinocytes experiments. Electron paramagnetic resonance investigations revealed different extents of free radical production generated by iron ions, ascorbic acid and UV irradiation. In evaluating the results from this study new aspects of the mechanism of lipid damage caused by these three factors were suggested, transcending the simple redox behaviour of ascorbic acid.

Synthesis, structural and electronic properties of monodispersed self-organized single crystalline nanobricks of isocubanite CuFe{sub 2}S{sub 3}

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

Lyubutin, Igor S., E-mail: lyubutinig@mail.ru; Lin, Chun-Rong, E-mail: crlin@mail.nptu.edu.tw; Starchikov, Sergey S.

2015-01-15

The nanoparticles with a pure cubic phase of isocubanite CuFe{sub 2}S{sub 3} are successfully synthesized for the first time. The particles are self-organized into the single crystalline nanocomposites with a shape of “bricks” which are well ordered in a certain anisotropic orientation. All bricks have nearly the same shape and dimensions and may be considered as monodispersed nanobricks. Magnetic measurements show paramagnetic behavior of the compound down to 4.2 K with the antiferromagnetic correlation between iron ions. An average magnetic moment is about 2.8–3.0 μ{sub B} per formula unit CuFe{sub 2}S{sub 3}. Mössbauer spectroscopy data reveal that the ferric ionsmore » in isocubanite are in the high-spin state (spin S=5/2) whereas the ferrous ions are in the intermediate-spin state (S=1). The Fe{sup 3+} and Fe{sup 2+} ions are distributed randomly over tetrahedral sites and the electron exchange between these ions is absent. This can explain nonmagnetic behavior of isocubanite. In the suggested method, the combined nanocomposites containing the magnetic chalcopyrite CuFeS{sub 2} and the nonmagnetic isocubanite CuFe{sub 2}S{sub 3} can be synthesized in a certain sequence. Such composites could be useful for the applied nanotechnology. - Graphical abstract: Self-organized single crystalline “nanobricks” of isocubanite CuFe{sub 2}S{sub 3} synthesized by a thermal pyrolysis method. - Highlights: • Self-organized single crystalline “nanobricks” of CuFe{sub 2}S{sub 3} were synthesized. • All bricks are nearly monodispersed and well-ordered in a certain anisotropic orientation. • XRD, HRTEM, magnetic measurements and Mössbauer spectroscopy were used for characterization. • Nanobricks are paramagnetic down to 4.2 K with effective magnetic moment about 3.0 μ{sub B} per f.u. • Mössbauer spectroscopy data indicate different spin states of Fe{sup 2+} and Fe{sup 3+} ions.« less

Zero Quantum Coherence in a Series of Covalent Spin-Correlated Radical Pairs.

PubMed

Nelson, Jordan N; Krzyaniak, Matthew D; Horwitz, Noah E; Rugg, Brandon K; Phelan, Brian T; Wasielewski, Michael R

2017-03-23

Photoinitiated subnanosecond electron transfer within covalently linked electron donor-acceptor molecules can result in the formation of a spin-correlated radical pair (SCRP) with a well-defined initial singlet spin configuration. Subsequent coherent mixing between the SCRP singlet and triplet m s = 0 spin states, the so-called zero quantum coherence (ZQC), is of potential interest in quantum information processing applications because the ZQC can be probed using pulse electron paramagnetic resonance (pulse-EPR) techniques. Here, pulse-EPR spectroscopy is utilized to examine the ZQC oscillation frequencies and ZQC dephasing in three structurally well-defined D-A systems. While transitions between the singlet and triplet m s = 0 spin states are formally forbidden (Δm s = 0), they can be addressed using specific microwave pulse turning angles to map information from the ZQC onto observable single quantum coherences. In addition, by using structural variations to tune the singlet-triplet energy gap, the ZQC frequencies determined for this series of molecules indicate a stronger dependence on the electronic g-factor than on electron-nuclear hyperfine interactions.

Giant titanium electron wave function in gallium oxide: A potential electron-nuclear spin system for quantum information processing

NASA Astrophysics Data System (ADS)

Mentink-Vigier, Frédéric; Binet, Laurent; Vignoles, Gerard; Gourier, Didier; Vezin, Hervé

2010-11-01

The hyperfine interactions of the unpaired electron with eight surrounding G69a and G71a nuclei in Ti-doped β-Ga2O3 were analyzed by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopies. They are dominated by strong isotropic hyperfine couplings due to a direct Fermi contact interaction with Ga nuclei in octahedral sites of rutile-type chains oriented along b axis, revealing a large anisotropic spatial extension of the electron wave function. Titanium in β-Ga2O3 is thus best described as a diffuse (Ti4+-e-) pair rather than as a localized Ti3+ . Both electron and G69a nuclear spin Rabi oscillations could be observed by pulsed EPR and pulsed ENDOR, respectively. The electron spin decoherence time is about 1μs (at 4 K) and an upper bound of 520μs (at 8 K) is estimated for the nuclear decoherence time. Thus, β-Ga2O3:Ti appears to be a potential spin-bus system for quantum information processing with a large nuclear spin quantum register.

Investigations on the Crystal-Chemical Behavior of Transition-Metal-Bearing Aluminosilicate Garnet Solid Solutions Using 27Al and 29Si NMR Spectroscopy

NASA Astrophysics Data System (ADS)

Palke, A. C.; Geiger, C. A.; Stebbins, J. F.

2015-12-01

The petrological importance of silicate garnet is derived from the presence of three distinct cation sites of varying size and coordination number. This allows for a wide range of trace, minor, and major element substitutions. However, a full and precise crystal-chemical understanding of the nature of transition metals in garnet is not at hand. Possible mechanisms of various charge-balanced substitutions (e.g. octahedral Ti4+ or tetrahedral Al3+) and the structural state of solid solutions (i.e. short- to long-range ordering) need study. We report on ongoing efforts in these directions using 27Al and 29Si Magic-Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. Early work on synthetic and natural Fe- and Mn-bearing pyrope- and grossular-rich garnets focused on the effect these paramagnetic transition metals have in measuring and interpreting NMR spectra. These results have been expanded with NMR measurements on synthetic pyrope-rich garnets containing other paramagnetic transition metals including Cr3+, V3+, Co2+, and Ni2+ as well as diamagnetic Ti4+. NMR peaks are severely broadened in the presence of even small concentrations of Cr3+, Mn2+, and Fe3+ leading to a loss of spectral resolution. On the other hand, the spectra of garnet containing V3+, Fe2+, Co2+, and Ni2+ have better resolution and show separate paramagnetically shifted NMR peaks. In some cases, crystal-chemical information can be obtained because of the large frequency separations between the NMR peaks that can be assigned to various local atomic configurations around Al and Si. Furthermore, the 27Al NMR spectrum of a synthetic pyrope garnet with about 2% diamagnetic Ti4+ on the octahedral site showed the absence of any tetrahedral Al3+, which rules out the substitution mechanism VITi + IVAl = VIAl + IVSi in the solid solution. Our NMR investigations on garnet are now being made at the exploratory level. We think that NMR spectra of diamagnetic garnet can provide information on a number of crystal-chemical properties. Spectra of garnet containing various paramagnetic transition elements can also, in some cases, give local structural information. With a better understanding of paramagnetic effects in NMR spectroscopy, this type of study can possibly be expanded to other geologically important paramagnetic minerals and phases.

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.

EPR Spectroscopy of Radical Ions of a 2,3-Diamino-1,4-naphthoquinone Derivative.

PubMed

Tarábek, Ján; Wen, Jin; Dron, Paul I; Pospíšil, Lubomír; Michl, Josef

2018-05-18

We report the electron paramagnetic resonance spectra of the radical cation and radical anion of 1,2,2,3-tetramethyl-2,3-dihydro-1 H-naphtho[2,3- d]imidazole-4,9-dione (1) and its doubly 13 C labeled analogue 2, of interest for singlet fission. The hyperfine coupling constants are in excellent agreement with density functional theory calculations and establish the structures beyond doubt. Unlike the radical cation 1 •+ , the radical anion 1 •- and its parent 1 have pyramidalized nitrogen atoms and inequivalent methyl groups 15 and 16, in agreement with the calculations. The distinction is particularly clear with the labeled analogue 2 •- .

Negative impact of surface Ti3+ defects on the photocatalytic hydrogen evolution activity of SrTiO3

NASA Astrophysics Data System (ADS)

Chen, Haidong; Zhang, Feng; Zhang, Weifeng; Du, Yingge; Li, Guoqiang

2018-01-01

Defects play an important and in many cases dominant role in the physical and chemical properties of many oxide materials. In this work, we show that the surface Ti3+ defects in SrTiO3 (STO), characterized by electron paramagnetic resonance and X-ray photoelectron spectroscopy, directly impact the photocatalytic activity of STO. O2 species are found to absorb preferentially on Ti3+ defect sites. Hydrogen evolution under ambient air diminishes with the increase in the concentration of surface Ti3+. This is explained by the over-accumulation of Pt cocatalysts on the site of surface Ti3+ defects after the removal of adsorbed O2.

EPR dosimetry in a mixed neutron and gamma radiation field.

PubMed

Trompier, F; Fattibene, P; Tikunov, D; Bartolotta, A; Carosi, A; Doca, M C

2004-01-01

Suitability of Electron Paramagnetic Resonance (EPR) spectroscopy for criticality dosimetry was evaluated for tooth enamel, mannose and alanine pellets during the 'international intercomparison of criticality dosimetry techniques' at the SILENE reactor held in Valduc in June 2002, France. These three materials were irradiated in neutron and gamma-ray fields of various relative intensities and spectral distributions in order to evaluate their neutron sensitivity. The neutron response was found to be around 10% for tooth enamel, 45% for mannose and between 40 and 90% for alanine pellets according their type. According to the IAEA recommendations on the early estimate of criticality accident absorbed dose, analyzed results show the EPR potentiality and complementarity with regular criticality techniques.

Magneto-Structural Correlations in Pseudotetrahedral Forms of the [Co(SPh)4]2- Complex Probed by Magnetometry, MCD Spectroscopy, Advanced EPR Techniques, and ab Initio Electronic Structure Calculations.

PubMed

Suturina, Elizaveta A; Nehrkorn, Joscha; Zadrozny, Joseph M; Liu, Junjie; Atanasov, Mihail; Weyhermüller, Thomas; Maganas, Dimitrios; Hill, Stephen; Schnegg, Alexander; Bill, Eckhard; Long, Jeffrey R; Neese, Frank

2017-03-06

The magnetic properties of pseudotetrahedral Co(II) complexes spawned intense interest after (PPh 4 ) 2 [Co(SPh) 4 ] was shown to be the first mononuclear transition-metal complex displaying slow relaxation of the magnetization in the absence of a direct current magnetic field. However, there are differing reports on its fundamental magnetic spin Hamiltonian (SH) parameters, which arise from inherent experimental challenges in detecting large zero-field splittings. There are also remarkable changes in the SH parameters of [Co(SPh) 4 ] 2- upon structural variations, depending on the counterion and crystallization conditions. In this work, four complementary experimental techniques are utilized to unambiguously determine the SH parameters for two different salts of [Co(SPh) 4 ] 2- : (PPh 4 ) 2 [Co(SPh) 4 ] (1) and (NEt 4 ) 2 [Co(SPh) 4 ] (2). The characterization methods employed include multifield SQUID magnetometry, high-field/high-frequency electron paramagnetic resonance (HF-EPR), variable-field variable-temperature magnetic circular dichroism (VTVH-MCD), and frequency domain Fourier transform THz-EPR (FD-FT THz-EPR). Notably, the paramagnetic Co(II) complex [Co(SPh) 4 ] 2- shows strong axial magnetic anisotropy in 1, with D = -55(1) cm -1 and E/D = 0.00(3), but rhombic anisotropy is seen for 2, with D = +11(1) cm -1 and E/D = 0.18(3). Multireference ab initio CASSCF/NEVPT2 calculations enable interpretation of the remarkable variation of D and its dependence on the electronic structure and geometry.

Effect of Co doping on the structural, optical and magnetic properties of ZnO nanoparticles.

PubMed

Hays, J; Reddy, K M; Graces, N Y; Engelhard, M H; Shutthanandan, V; Luo, M; Xu, C; Giles, N C; Wang, C; Thevuthasan, S; Punnoose, A

2007-07-04

We report the results of a detailed investigation of sol-gel-synthesized nanoscale Zn(1-x)Co(x)O powders processed at 350 °C with 0≤x≤0.12 to understand how the structural, morphological, optical and magnetic properties of ZnO are modified by Co doping, in addition to searching for the theoretically predicted ferromagnetism. With x increasing to 0.03, both lattice parameters a and c of the hexagonal ZnO decreased, suggesting substitutional doping of Co at the tetrahedral Zn(2+) sites. For x>0.03, these trends reversed and the lattice showed a gradual expansion as x approached 0.12, probably due to additional interstitial incorporation of Co. Raman spectroscopy measurements showed a rapid change in the ZnO peak positions for x>0.03, suggesting significant disorder and changes in the ZnO structure, in support of additional interstitial Co doping possibility. Combined x-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy, photoluminescence spectroscopy and diffuse reflectance spectroscopy showed clear evidence for tetrahedrally coordinated high-spin Co(2+) ions occupying the lattice sites of ZnO host system, which became saturated for x>0.03. Magnetic measurements showed a paramagnetic behaviour in Zn(1-x)Co(x)O with increasing antiferromagnetic interactions as x increased to 0.10. Surprisingly, a weak ferromagnetic behaviour was observed for the sample with x = 0.12 with a characteristic hysteresis loop showing a coercivity H(c)∼350 Oe, 25% remanence M(r), a low saturation magnetization M(s)∼0.04 emu g(-1) and with a Curie temperature T(c)∼540 K. The XPS data collected from Zn(1-x)Co(x)O samples showed a gradual increase in the oxygen concentration, changing the oxygen-deficient undoped ZnO to an excess oxygen state for x = 0.12. This indicates that such high Co concentrations and appropriate oxygen stoichiometry may be needed to achieve adequate ferromagnetic exchange coupling between the incorporated Co(2+) ions.

Electronic structure study of wide band gap magnetic semiconductor (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} nanocrystals in paramagnetic and ferromagnetic phases

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

Dwivedi, G. D.; Chou, H.; Yang, K. S.

2016-04-25

X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} near Fermi-level. XMCD results indicate that Mn{sup 3+} and Mn{sup 4+} spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below T{sub C}. The valence bandmore » UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.« less

Development of an electron paramagnetic resonance methodology for studying the photo-generation of reactive species in semiconductor nano-particle assembled films

NASA Astrophysics Data System (ADS)

Twardoch, Marek; Messai, Youcef; Vileno, Bertrand; Hoarau, Yannick; Mekki, Djamel E.; Felix, Olivier; Turek, Philippe; Weiss, Jean; Decher, Gero; Martel, David

2018-06-01

An experimental approach involving electron paramagnetic resonance is proposed for studying photo-generated reactive species in semiconductor nano-particle-based films deposited on the internal wall of glass capillaries. This methodology is applied here to nano-TiO2 and allows a semi-quantitative analysis of the kinetic evolutions of radical production using a spin scavenger probe.

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

Dramatic changes in the electronic structure upon transition to the collapsed tetragonal phase in CaFe 2As 2

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

Dhaka, R. S.; Jiang, Rui; Ran, S.

2014-01-31

We use angle-resolved photoemission spectroscopy and density functional theory calculations to study the electronic structure of CaFe 2As 2 in the collapsed tetragonal (CT) phase. This unusual phase of iron arsenic high-temperature superconductors was hard to measure as it exists only under pressure. By inducing internal strain, via the postgrowth thermal treatment of single crystals, we were able to stabilize the CT phase at ambient pressure. We find significant differences in the Fermi surface topology and band dispersion data from the more common orthorhombic-antiferromagnetic or tetragonal-paramagnetic phases, consistent with electronic structure calculations. The top of the hole bands sinks belowmore » the Fermi level, which destroys the nesting present in parent phases. The absence of nesting in this phase, along with an apparent loss of Fe magnetic moment, are now clearly experimentally correlated with the lack of superconductivity in this phase.« less

Characterization and reactivity of a terminal nickel(III)-oxygen adduct.

PubMed

Pirovano, Paolo; Farquhar, Erik R; Swart, Marcel; Fitzpatrick, Anthony J; Morgan, Grace G; McDonald, Aidan R

2015-02-23

High-valent terminal metal-oxygen adducts are hypothesized to be the potent oxidizing reactants in late transition metal oxidation catalysis. In particular, examples of high-valent terminal nickel-oxygen adducts are scarce, meaning there is a dearth in the understanding of such oxidants. A monoanionic Ni(II)-bicarbonate complex has been found to react in a 1:1 ratio with the one-electron oxidant tris(4-bromophenyl)ammoniumyl hexachloroantimonate, yielding a thermally unstable intermediate in high yield (ca. 95%). Electronic absorption, electronic paramagnetic resonance, and X-ray absorption spectroscopies and density functional theory calculations confirm its description as a low-spin (S = 1/2), square planar Ni(III)-oxygen adduct. This rare example of a high-valent terminal nickel-oxygen complex performs oxidations of organic substrates, including 2,6-di-tert-butylphenol and triphenylphosphine, which are indicative of hydrogen atom abstraction and oxygen atom transfer reactivity, respectively. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selective Electrocatalytic Reduction of Nitrite to Dinitrogen Based on Decoupled Proton-Electron Transfer.

PubMed

He, Daoping; Li, Yamei; Ooka, Hideshi; Go, Yoo Kyung; Jin, Fangming; Kim, Sun Hee; Nakamura, Ryuhei

2018-02-14

The development of denitrification catalysts which can reduce nitrate and nitrite to dinitrogen is critical for sustaining the nitrogen cycle. However, regulating the selectivity has proven to be a challenge, due to the difficulty of controlling complex multielectron/proton reactions. Here we report that utilizing sequential proton-electron transfer (SPET) pathways is a viable strategy to enhance the selectivity of electrochemical reactions. The selectivity of an oxo-molybdenum sulfide electrocatalyst toward nitrite reduction to dinitrogen exhibited a volcano-type pH dependence with a maximum at pH 5. The pH-dependent formation of the intermediate species (distorted Mo(V) oxo species) identified using operando electron paramagnetic resonance (EPR) and Raman spectroscopy was in accord with a mathematical prediction that the pK a of the reaction intermediates determines the pH-dependence of the SPET-derived product. By utilizing this acute pH dependence, we achieved a Faradaic efficiency of 13.5% for nitrite reduction to dinitrogen, which is the highest value reported to date under neutral conditions.

Hydrothermal green synthesis of magnetic Fe3O4-carbon dots by lemon and grape fruit extracts and as a photoluminescence sensor for detecting of E. coli bacteria.

PubMed

Ahmadian-Fard-Fini, Shahla; Salavati-Niasari, Masoud; Ghanbari, Davood

2018-10-05

The aim of this work is preparing of a photoluminescence nanostructures for rapid detection of bacterial pathogens. Firstly, carbon dots (CDs) were synthesized by grape fruit, lemon, turmeric extracts and hydrothermal method. Then Fe 3 O 4 (magnetite) nanoparticles was achieved using these bio-compatible capping agents. Finally, magnetite-carbon dots were synthesized as a novel magnetic and photoluminescence nanocomposite. X-ray diffraction (XRD) confirms the crystallinity and phase of the products, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigate the morphology, shape and size of the magnetite, carbon dot and nanocomposites. Fourier transform infrared (FT-IR) spectroscopy shows the purity of the nanostructures. Ultraviolet-visible (UV-Vis) absorption and photo-luminescence (PL) spectroscopy show suitable photo-luminescence under ultraviolet irradiation. Vibrating sample magnetometer (VSM) shows super paramagnetic property of the product. Interestingly carbon dots were used as a non-toxic photoluminescence sensor for detecting of Escherichia coli (E. coli) bacteria. Results show quenching of photoluminescence of the CDs nanocomposite by increasing amount of E. coli bacteria. Copyright © 2018 Elsevier B.V. All rights reserved.

Incorporation of Mg in Free-Standing HVPE GaN Substrates

NASA Astrophysics Data System (ADS)

Zvanut, M. E.; Dashdorj, J.; Freitas, J. A.; Glaser, E. R.; Willoughby, W. R.; Leach, J. H.; Udwary, K.

2016-06-01

Mg, the only effective p-type dopant for nitrides, is well studied in thin films due to the important role of the impurity in light-emitting diodes and high-power electronics. However, there are few reports of Mg in thick free-standing GaN substrates. Here, we demonstrate successful incorporation of Mg into GaN grown by hydride vapor-phase epitaxy (HVPE) using metallic Mg as the doping source. The concentration of Mg obtained from four separate growth runs ranged between 1016 cm-3 and 1019 cm-3. Raman spectroscopy and x-ray diffraction revealed that Mg did not induce stress or perturb the crystalline quality of the HVPE GaN substrates. Photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies were performed to investigate the types of point defects in the crystals. The near-band-edge excitonic and shallow donor-shallow acceptor radiative recombination processes involving shallow Mg acceptors were prominent in the PL spectrum of a sample doped to 3 × 1018 cm-3, while the EPR signal was also thought to represent a shallow Mg acceptor. Detection of this signal reflects minimization of nonuniform strain obtained in the thick free-standing HVPE GaN compared with heteroepitaxial thin films.

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.

Radical SAM catalysis via an organometallic intermediate with an Fe-[5'-C]-deoxyadenosyl bond.

PubMed

Horitani, Masaki; Shisler, Krista; Broderick, William E; Hutcheson, Rachel U; Duschene, Kaitlin S; Marts, Amy R; Hoffman, Brian M; Broderick, Joan B

2016-05-13

Radical S-adenosylmethionine (SAM) enzymes use a [4Fe-4S] cluster to cleave SAM to initiate diverse radical reactions. These reactions are thought to involve the 5'-deoxyadenosyl radical intermediate, which has not yet been detected. We used rapid freeze-quenching to trap a catalytically competent intermediate in the reaction catalyzed by the radical SAM enzyme pyruvate formate-lyase activating enzyme. Characterization of the intermediate by electron paramagnetic resonance and (13)C, (57)Fe electron nuclear double-resonance spectroscopies reveals that it contains an organometallic center in which the 5' carbon of a SAM-derived deoxyadenosyl moiety forms a bond with the unique iron site of the [4Fe-4S] cluster. Discovery of this intermediate extends the list of enzymatic bioorganometallic centers to the radical SAM enzymes, the largest enzyme superfamily known, and reveals intriguing parallels to B12 radical enzymes. Copyright © 2016, American Association for the Advancement of Science.

Water-repellent coatings prepared by modification of ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Chakradhar, R. P. S.; Dinesh Kumar, V.

Superhydrophobic coatings with a static water contact angle (WCA) > 150° were prepared by modifying ZnO nanoparticles with stearic acid (ZnO@SA). ZnO nanoparticles of size ˜14 nm were prepared by solution combustion method. X-ray diffraction (XRD) studies reveal that as prepared ZnO has hexagonal wurtzite structure whereas the modified coatings convert to zinc stearate. Field emission scanning electron micrographs (FE-SEM) show the dual morphology of the coatings exhibiting both particles and flakes. The flakes are highly fluffy in nature with voids and nanopores. Fourier transformed infrared (FTIR) spectrum shows the stearate ion co-ordinates with Zn2+ in the bidentate form. The surface properties such as surface free energy (γp) and work of adhesion (W) of the unmodified and modified ZnO coatings have been evaluated. The electron paramagnetic resonance (EPR) spectroscopy reveals that surface defects play a major role in the wetting behavior.

Photoinduced electron transfer pathways in hydrogen-evolving reduced graphene oxide-boosted hybrid nano-bio catalyst.

PubMed

Wang, Peng; Dimitrijevic, Nada M; Chang, Angela Y; Schaller, Richard D; Liu, Yuzi; Rajh, Tijana; Rozhkova, Elena A

2014-08-26

Photocatalytic production of clean hydrogen fuels using water and sunlight has attracted remarkable attention due to the increasing global energy demand. Natural and synthetic dyes can be utilized to sensitize semiconductors for solar energy transformation using visible light. In this study, reduced graphene oxide (rGO) and a membrane protein bacteriorhodopsin (bR) were employed as building modules to harness visible light by a Pt/TiO2 nanocatalyst. Introduction of the rGO boosts the nano-bio catalyst performance that results in hydrogen production rates of approximately 11.24 mmol of H2 (μmol protein)(-1) h(-1). Photoelectrochemical measurements show a 9-fold increase in photocurrent density when TiO2 electrodes were modified with rGO and bR. Electron paramagnetic resonance and transient absorption spectroscopy demonstrate an interfacial charge transfer from the photoexcited rGO to the semiconductor under visible light.

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.

Experimental mixture design as a tool for the synthesis of antimicrobial selective molecularly imprinted monodisperse microbeads.

PubMed

Benito-Peña, Elena; Navarro-Villoslada, Fernando; Carrasco, Sergio; Jockusch, Steffen; Ottaviani, M Francesca; Moreno-Bondi, Maria C

2015-05-27

The effect of the cross-linker on the shape and size of molecular imprinted polymer (MIP) beads prepared by precipitation polymerization has been evaluated using a chemometric approach. Molecularly imprinted microspheres for the selective recognition of fluoroquinolone antimicrobials were prepared in a one-step precipitation polymerization procedure using enrofloxacin (ENR) as the template molecule, methacrylic acid as functional monomer, 2-hydroxyethyl methacrylate as hydrophilic comonomer, and acetonitrile as the porogen. The type and amount of cross-linker, namely ethylene glycol dimethacrylate, divinylbenzene or trimethylolpropane trimethacrylate, to obtain monodispersed MIP spherical beads in the micrometer range was optimized using a simplex lattice design. Particle size and morphology were assessed by scanning electron microscopy, dynamic light scattering, and nitrogen adsorption measurements. Electron paramagnetic resonance spectroscopy in conjunction with a nitroxide as spin probe revealed information about the microviscosity and polarity of the binding sites in imprinted and nonimprinted polymer beads.

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

Studies of molecular properties of polymeric materials: Aerospace environmental effects on three linear polymers

NASA Technical Reports Server (NTRS)

Harries, W. L.; Ries, H. R.; Bradbury, C. A.; Gray, S. L.; Collins, W. D.; Long, S. A. T.; Long, E. R., Jr.

1985-01-01

The development of crystal handling techniques for reflection infrared spectroscopy and methods for the fabrication and testing of tensile specimens are discussed. Data from mechanical, ac and dc electrical, and electron paramagnetic resonance studies conducted to determine the effects of 0.1-MeV and 1.0-MeV electron radiation on Mylar, Kapton, Ultem, and metal-doped Ultem are presented. Total doses ranging from 1 X 10 to the 8 rads to 1 X 10 to the 10 rads and dose rates from 5 X 10 to the 7 rads/hr to 1 X 10 to the 9 rads/hr were employed. The results of a study on the effects of aircraft service-environment fluids on Ultem are also reported. The weights and mechanical properties of Ultem were evaluated before and after exposure to water, JP4, Skydrol, an antifreeze, and a paint stripper.

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.

Lanthanide paramagnetic probes for NMR spectroscopic studies of fast molecular conformational dynamics and temperature control. Effective six-site proton exchange in 18-crown-6 by exchange spectroscopy.

PubMed

Babailov, Sergey P

2012-02-06

(1)H and (13)C NMR measurements are reported for the CDCl(3) and CD(2)Cl(2) solutions of [La(18-crown-6)(NO(3))(3)] (I), [Pr(18-crown-6) (NO(3))(3)] (II), [Ce(18-crown-6)(NO(3))(3)] (III), and [Nd(18-crown-6)(NO(3))(3)] (IV) complexes. Temperature dependencies of the (1)H NMR spectra of paramagnetic II-IV have been analyzed using the dynamic NMR (DNMR) methods for six-site exchange. Two types of conformational dynamic processes were identified (the first one is conditioned by interconversion of complex enantiomeric forms and pseudorotation of a macrocycle molecule upon the C(2) symmetry axis; the second one is conditioned by macrocycle molecule inversion). Application of exchange spectroscopy (2D-EXSY) of DNMR for investigation of this dynamic system (II-IV) simplifies the assignment of the NMR signals and represents the first experimental study of multisite exchange. In the present work, the methodology of paramagnetic 4f (Ce, Pr, and Nd) probe applications for the study of free-energy, enthalpy, and entropy changes in chemical exchange processes, as well as the advantages of this method in a comparison with DNMR studies of diamagnetic substances, is discussed. In particular, as a result of paramagnetic chemical shifts in 4f complexes, the range of measurable rate constants expands considerably compared to the analogous range in diamagnetic compounds. Coordination compounds investigated in the paper represent new types of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solution.

Organozinc Precursor-Derived Crystalline ZnO Nanoparticles: Synthesis, Characterization and Their Spectroscopic Properties.

PubMed

Liang, Yucang; Wicker, Susanne; Wang, Xiao; Erichsen, Egil Severin; Fu, Feng

2018-01-04

Crystalline ZnO -ROH and ZnO -OR (R = Me, Et, i Pr, n Bu) nanoparticles (NPs) have been successfully synthesized by the thermal decomposition of in-situ-formed organozinc complexes Zn(OR)₂ deriving from the reaction of Zn[N(SiMe₃)₂]₂ with ROH and of the freshly prepared Zn(OR)₂ under an identical condition, respectively. With increasing carbon chain length of alkyl alcohol, the thermal decomposition temperature and dispersibility of in-situ-formed intermediate zinc alkoxides in oleylamine markedly influenced the particle sizes of ZnO -ROH and its shape (sphere, plate-like aggregations), while a strong diffraction peak-broadening effect is observed with decreasing particle size. For ZnO -OR NPs, different particle sizes and various morphologies (hollow sphere or cuboid-like rod, solid sphere) are also observed. As a comparison, the calcination of the fresh-prepared Zn(OR)₂ generated ZnO -R NPs possessing the particle sizes of 5.4~34.1 nm. All crystalline ZnO nanoparticles are characterized using X-ray diffraction analysis, electron microscopy and solid-state ¹H and 13 C nuclear magnetic resonance (NMR) spectroscopy. The size effect caused by confinement of electrons' movement and the defect centres caused by unpaired electrons on oxygen vacancies or ionized impurity heteroatoms in the crystal lattices are monitored by UV-visible spectroscopy, electron paramagnetic resonance (EPR) and photoluminescent (PL) spectroscopy, respectively. Based on the types of defects determined by EPR signals and correspondingly defect-induced probably appeared PL peak position compared to actual obtained PL spectra, we find that it is difficult to establish a direct relationship between defect types and PL peak position, revealing the complication of the formation of defect types and photoluminescence properties.

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

PubMed

Merunka, Dalibor; Peric, Mirna; Peric, Miroslav

2015-02-19

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

Using the methods of radiospectroscopy (EPR, NMR) to study the nature of the defect structure of solid solutions based on lead zirconate titanate (PZT).

PubMed

Bykov, Igor; Zagorodniy, Yuriy; Yurchenko, Lesya; Korduban, Alexander; Nejezchleb, Karel; Trachevsky, Vladimir; Dimza, Vilnis; Jastrabik, Lubomir; Dejneka, Alexander

2014-08-01

The nature of intrinsic and impurity point defects in lead zirconate titanate (PZT) ceramics has been explored. Using electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) methods, several impurity sites have been identified in the materials, including the Fe(3+)-oxygen vacancy (VO) complex and Pb ions. Both of these centers are incorporated into the PZT lattice. The Fe(3+) –VО paramagnetic complex serves as a sensitive probe of the local crystal field in the ceramic; the symmetry of this defect roughly correlates with PZT phase diagram as the composition is varied from PbTiO3 to PbZrO3. NMR spectra (207)Pb in PbTiO3, PbZrO3, and PZT with iron content from 0 to 0.4 wt% showed that increasing the iron concentration leads to a distortion of the crystal structure and to improvement of the electrophysical parameters of the piezoceramics. This is due to the formation of a phase which has a higher symmetry, but at high concentrations of iron (>0.4 wt%), it leads to sharp degradation of electrophysical parameters.

Functionalization of paramagnetic nanoparticles for protein immobilization and purification.

PubMed

Carneiro, Lara A B C; Ward, Richard J

2018-01-01

A paramagnetic nanocomposite coated with chitosan and N-(5-Amino-1-carboxy-pentyl) iminodiacetic acid (NTA) that is suitable for protein immobilization applications has been prepared and characterized. The nanoparticle core was synthesized by controlled aggregation of Fe 3 O 4 under alkaline conditions, and Transmission Electron Microscopy revealed a size distribution of 10-50 nm. The nanoparticle core was coated with chitosan and derivatized with glutaraldehyde and NTA, as confirmed by Fourier Transform Infrared Spectroscopy. The final nanoparticles were used as a metal affinity matrix to separate a recombinant polyhistidine-tagged β-galactosidase from Bacillus subtilis directly from E. coli cell lysates with high purity (>95%). After loading with Ni 2+ , nanoparticles demonstrated a binding capacity of 250 μg of a polyhistidine-tagged β-galactosidase per milligram of support. The immobilized enzyme retained 80% activity after 9 cycles of washing, and the immobilized recombinant protein could be eluted with high purity with imidazole. The applications for these nanomagnetic composites extend beyond protein purification, and can also be used for immobilizing enzymes, where the β-galactosidase immobilized on the nanomagnetic support was used in multiple cycles of catalytic reactions with no significant loss of catalytic activity. Copyright © 2017. Published by Elsevier Inc.

The role of surface/interfacial Cu{sup 2+} sites in the photocatalytic activity of coupled CuO-TiO{sub 2} nanocomposites.

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

Li, G.; Dimitrijevic, N. M.; Chen, L.

Coupled CuO-TiO{sub 2} nanocomposite photocatalysts were prepared by a deposition precipitation method and were characterized with a variety of techniques. Electron paramagnetic resonance (EPR) spectroscopy was employed to study the local structures of surface/interfacial Cu{sup 2+}+ sites using Cu{sup 2+} as a sensitive paramagnetic probe. The addition of bulk CuO to TiO{sub 2} led to decreased photocatalytic efficiency in the degradation of methylene blue. However, doping with a very small amount of CuO (0.1 wt % copper loading) significantly enhanced the photocatalytic activity of TiO{sub 2}. EPR study of the TiO{sub 2} surface revealed the presence of both highly dispersedmore » CuO clusters and substitutional Cu{sup 2+} sites (Ti-O-Cu linkages) at 0.1 wt % copper loading. The data suggest that the Ti-O-Cu linkages contributed to the improved photooxidative activity of the 0.1% CuO-TiO{sub 2} nanocomposite. In contrast, at higher loadings the bulk form of CuO created charge recombination centers lowering the photoactivity of the composites.« less

Properties of Gd{sub 2}O{sub 3} nanoparticles studied by hyperfine interactions and magnetization measurements

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

Correa, E. L., E-mail: eduardo.correa@usp.br; Bosch-Santos, B.; Cavalcante, F. H. M.

2016-05-15

The magnetic behavior of Gd{sub 2}O{sub 3} nanoparticles, produced by thermal decomposition method and subsequently annealed at different temperatures, was investigated by magnetization measurements and, at an atomic level, by perturbed γ − γ angular correlation (PAC) spectroscopy measuring hyperfine interactions at {sup 111}In({sup 111}Cd) probe nuclei. Nanoparticle structure, size and shape were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Magnetization measurements were carried out to characterize the paramagnetic behavior of the samples. XRD results show that all samples crystallize in the cubic-C form of the bixbyite structure with space group Ia3. TEM images showed that particlesmore » annealed at 873 K present particles with highly homogeneous sizes in the range from 5 nm to 10 nm and those annealed at 1273 K show particles with quite different sizes from 5 nm to 100 nm, with a wide size distribution. PAC and magnetization results show that samples annealed at 873 and 1273 K are paramagnetic. Magnetization measurements show no indication of blocking temperatures for all samples down to 2 K and the presence of antiferromagnetic correlations.« 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.

EPR study of a gamma-irradiated (2-hydroxyethyl)triphenylphosphonium chloride single crystal

NASA Astrophysics Data System (ADS)

Karakaş, E.; Türkkan, E.; Dereli, Ö.; Sayιn, Ü.; Tapramaz, R.

2011-12-01

In this study, gamma-irradiated single crystals of (2-hydroxyethyl)triphenylphosphonium chloride [CH2CH2OH P(C6H5)3Cl] were investigated with electron paramagnetic resonance (EPR) spectroscopy at room temperature for different orientations in the magnetic field. The single crystals were irradiated with a 60Co-γ-ray source at 0.818 kGy/h for about 36 h. Taking the chemical structure and the experimental spectra of the irradiated single crystal of the title compound into consideration, a paramagnetic species was produced with the unpaired electron delocalized around 31P and several 1H nuclei. The anisotropic hyperfine values due to the 31P nucleus, slightly anisotropic hyperfine values due to the 1H nuclei and the g-tensor of the radical were measured from the spectra. Depending on the molecular structure and measured parameters, three possible radicals were modeled using the B3LYP/6-31+G(d) level of density-functional theory, and EPR parameters were calculated for modeled radicals using the B3LYP/TZVP method/basis set combination. The calculated hyperfine coupling constants were found to be in good agreement with the observed EPR parameters. The experimental and theoretically simulated spectra for each of the three crystallographic axes were well matched with one of the modeled radicals (discussed in the text). We thus identified the radical C˙H2CH2 P(C 6H5)3 Cl as a paramagnetic species produced in a single crystal of the title compound in two magnetically distinct sites. The experimental g-factor and hyperfine coupling constants of the radical were found to be anisotropic, with the isotropic values g iso = 2.0032, ? G, ? G, ? G and ? G for site 1 and g iso=2.0031, ? G, ? G ? G and ? G for site 2.

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.

Single-electron transfer in palladium complexes of 1,4-naphthoquinone-containing bis(pyrazol-1-yl)methane ligands.

PubMed

Scheuermann, Sebastian; Sarkar, Biprajit; Bolte, Michael; Bats, Jan W; Lerner, Hans-Wolfram; Wagner, Matthias

2009-10-05

A 1,4-naphthoquinone-substituted bis(pyrazol-1-yl)methane ligand (N--N) has been synthesized and transformed into its corresponding Pd(II) chelate complex [(N--N)PdCl(2)]. Both N--N and [(N--N)PdCl(2)] have been fully characterized by NMR spectroscopy, spectro-electrochemistry, and X-ray crystallography. After treatment of [(N--N)PdCl(2)] with NEt(3), the signature of a 1,4-naphthosemiquinonate radical is visible in the UV-vis- and electron paramagnetic resonance (EPR) spectrum of the reaction mixture; the free ligand N--N does not react with NEt(3) under the conditions applied. It is therefore concluded that NEt(3) first reduces the Pd(II)-ion of [(N--N)PdCl(2)] to the zero-valent state and that this reaction is followed by a single-electron transfer from the metal atom to the 1,4-naphthoquinone moiety. The complex has been specifically designed to disfavor any direct Pd-to-naphthoquinone coordination. Electron transfer thus proceeds through space or, less likely, via sigma-bonds of the ligand framework.

Outer-Sphere Contributions to the Electronic Structure of Type Zero Copper Proteins

PubMed Central

Lancaster, Kyle M.; Zaballa, María-Eugenia; Sproules, Stephen; Sundararajan, Mahesh; DeBeer, Serena; Richards, John H.; Vila, Alejandro J.; Neese, Frank; Gray, Harry B.

2016-01-01

Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called “type zero” sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding. PMID:22563915

Electron beam agrobionanotechnologies for agriculture and food industry enabled by electron accelerators

NASA Astrophysics Data System (ADS)

Pavlov, Y. S.; Revina, A. A.; Souvorova, O. V.; Voropaeva, N. L.; Chekmar, D. V.; Abkhalimov, E. V.; Zavyalov, M. A.; Filippovich, V. P.

2017-12-01

Electron beam (EB) radiation technologies have been employed to increase efficiency of biologically active nanochips developed for agricultural plants seed pre-treatment with purpose of enhancing crop yield and productivity. Iron-containing nanoparticles (NPs), synthesized in reverse micelles following known radiation-chemical technique, have served as a multifunctional biologically active and phytosanitary substance of the chips. Porous chip carriers activation has been performed by EB ionization (doze 20kGy) of the active carbons (AC) prepared from agricultural waste and by-products: Jerusalem artichoke (Helianthus tuberosus) straw, rape (Brassica napus L. ssp. oleifera Metzg) straw, camelina (Camelina sativa (L.) Crantz) straw, wheat (Triticum aestivum) straw. Three methods, UV-VIS spectrophotometry, Electron Paramagnetic Resonance (EPR) spectroscopy, cyclic voltammetry (CV) have been used for process control and characterization of radiation-activated and NPs-modified ACs. The results show a notable effect of ACs activation by electron beam radiation, evidenced by FeNPs-adsorption capacity increase. Studies of the impact of Fe NPs-containing nanochip technology on enhancement of seeds germination rate and seedlings vigour suggest that reported electron beam radiation treatment techniques of the ACs from selected agricultural residues may be advantageous for industrial application.

Electron paramagnetic resonance analysis of La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) perovskite-like nanostructured catalysts.

PubMed

Oliva, Cesare; Allieta, Mattia; Scavini, Marco; Biffi, Cesare; Rossetti, Ilenia; Forni, Lucio

2012-08-06

The physical-chemical properties of some nanostructured perovskite-like catalysts of general formula La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) have been investigated, in particular by using the electron paramagnetic resonance (EPR) technique. We show that the interplay between the -O-Mn(3+)-O-Mn(4+)-O- electron double-exchange and the electron mobility is strictly dependent on the dopant nature and the annealing conditions in air. A relationship between the observed properties of these samples and their activity in the methane flameless catalytic combustion is proposed.

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.

Insights into the mechanism of X-ray-induced disulfide-bond cleavage in lysozyme crystals based on EPR, optical absorption and X-ray diffraction studies

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

Sutton, Kristin A.; Black, Paul J.; Mercer, Kermit R.

2013-12-01

Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage, to confirm a multi-track radiation-damage process and to develop a model of that process. Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV–visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5–0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. Themore » observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure.« less

Localization of dexamethasone within dendritic core-multishell (CMS) nanoparticles and skin penetration properties studied by multi-frequency electron paramagnetic resonance (EPR) spectroscopy.

PubMed

Saeidpour, S; Lohan, S B; Anske, M; Unbehauen, M; Fleige, E; Haag, R; Meinke, M C; Bittl, R; Teutloff, C

2017-07-01

The skin and especially the stratum corneum (SC) act as a barrier and protect epidermal cells and thus the whole body against xenobiotica of the external environment. Topical skin treatment requires an efficient drug delivery system (DDS). Polymer-based nanocarriers represent novel transport vehicles for dermal application of drugs. In this study dendritic core-multishell (CMS) nanoparticles were investigated as promising candidates. CMS nanoparticles were loaded with a drug (analogue) and were applied to penetration studies of skin. We determined by dual-frequency electron paramagnetic resonance (EPR) how dexamethasone (Dx) labelled with 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA) is associated with the CMS. The micro-environment of the drug loaded to CMS nanoparticles was investigated by pulsed high-field EPR at cryogenic temperature, making use of the fact that magnetic parameters (g-, A-matrices, and spin-lattice relaxation time) represent specific probes for the micro-environment. Additionally, the rotational correlation time of spin-labelled Dx was probed by continuous wave EPR at ambient temperature, which provides independent information on the drug environment. Furthermore, the penetration depth of Dx into the stratum corneum of porcine skin after different topical applications was investigated. The location of Dx in the CMS nanoparticles is revealed and the function of CMS as penetration enhancers for topical application is shown. Copyright © 2016 Elsevier B.V. All rights reserved.

Free radicals produced by the oxidation of gallic acid: An electron paramagnetic resonance study.

PubMed

Eslami, Angelique C; Pasanphan, Wanvimol; Wagner, Brett A; Buettner, Garry R

2010-08-05

Gallic acid (3,4,5-trihydroxybenzoic acid) is found in a wide variety of plants; it is extensively used in tanning, ink dyes, as well as in the manufacturing of paper. The gallate moiety is a key component of many functional phytochemicals. In this work electron paramagnetic spectroscopy (EPR) was used to detect the free radicals generated by the air-oxidation of gallic acid. We found that gallic acid produces two different radicals as a function of pH. In the pH range between 7-10, the spectrum of the gallate free radical is a doublet of triplets (aH = 1.00 G, aH = 0.23 G, aH = 0.28 G). This is consistent with three hydrogens providing hyperfine splitting. However, in a more alkaline environment, pH >10, the hyperfine splitting pattern transforms into a 1:2:1 pattern (aH (2) = 1.07 G). Using D2O as a solvent, we demonstrate that the third hydrogen (i.e. aH = 0.28 G) at lower pH is a slowly exchanging hydron, participating in hydrogen bonding with two oxygens in ortho position on the gallate ring. The pKa of this proton has been determined to be 10. This simple and novel approach permitted the understanding of the prototropic equilibrium of the semiquinone radicals generated by gallic acid, a ubiquitous compound, allowing new insights into its oxidation and subsequent reactions.

Antioxidant and radical-scavenging activities of Slovak honeys - An electron paramagnetic resonance study.

PubMed

Zalibera, Michal; Staško, Andrej; Šlebodová, Anna; Jančovičová, Viera; Čermáková, Tatiana; Brezová, Vlasta

2008-09-15

The antioxidant properties of 15 honey samples from different floral sources and various Slovak regions were investigated by means of electron paramagnetic resonance spectroscopy. Cation radical of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt), DPPH (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals generated by the photochemical decomposition of hydrogen peroxide were used as oxidants. The antioxidant activities found with ABTS(+), expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 0.15 to 1.14mmolkg(-1), and those determined with DPPH, from 0.04 to 0.32mmolkg(-1). TEAC values correlated well with results found by elimination of DPPH, and both values revealed a linear relationship with the concentration of phenolics obtained with the Folin-Ciocalteu phenol test (expressed as gallic acid equivalents, GAE). The colour coordinates (CIE L(∗)a(∗)b(∗)), as well as reflectance spectra determined for original honeys using a white background, demonstrated that the colour difference (ΔE(∗)) and coordinate b(∗) interrelate with TEAC values. The radical-scavenging capacities (RSC) of the honey samples determined in the experiments with photochemically decomposed hydrogen peroxide, generating reactive OH radicals in the presence of spin trapping agent, differ from those found with ABTS(+) and DPPH. Here, probably, the reactive OH radicals, having higher redox potential, are scavenged by a variety of compounds not effective with ABTS(+) and DPPH (e.g., saccharides, proteins). Copyright © 2008 Elsevier Ltd. All rights reserved.

Perovskite oxides: Oxygen electrocatalysis and bulk structure

NASA Technical Reports Server (NTRS)

Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, Ernest

1987-01-01

Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

Use of spin traps to detect superoxide production in living cells by electron paramagnetic resonance (EPR) spectroscopy.

PubMed

Abbas, Kahina; Babić, Nikola; Peyrot, Fabienne

2016-10-15

Detection of superoxide produced by living cells has been an on-going challenge in biology for over forty years. Various methods have been proposed to address this issue, among which spin trapping with cyclic nitrones coupled to EPR spectroscopy, the gold standard for detection of radicals. This technique is based on the nucleophilic addition of superoxide to a diamagnetic cyclic nitrone, referred to as the spin trap, and the formation of a spin adduct, i.e. a persistent radical with a characteristic EPR spectrum. The first application of spin trapping to living cells dates back 1979. Since then, considerable improvements of the method have been achieved both in the structures of the spin traps, the EPR methodology, and the design of the experiments including appropriate controls. Here, we will concentrate on technical aspects of the spin trapping/EPR technique, delineating recent breakthroughs, inherent limitations, and potential artifacts. Copyright © 2016 Elsevier Inc. All rights reserved.

Toward the fourth dimension of membrane protein structure: insight into dynamics from spin-labeling EPR spectroscopy.

PubMed

McHaourab, Hassane S; Steed, P Ryan; Kazmier, Kelli

2011-11-09

Trapping membrane proteins in the confines of a crystal lattice obscures dynamic modes essential for interconversion between multiple conformations in the functional cycle. Moreover, lattice forces could conspire with detergent solubilization to stabilize a minor conformer in an ensemble thus confounding mechanistic interpretation. Spin labeling in conjunction with electron paramagnetic resonance (EPR) spectroscopy offers an exquisite window into membrane protein dynamics in the native-like environment of a lipid bilayer. Systematic application of spin labeling and EPR identifies sequence-specific secondary structures, defines their topology and their packing in the tertiary fold. Long range distance measurements (60 Å-80 Å) between pairs of spin labels enable quantitative analysis of equilibrium dynamics and triggered conformational changes. This review highlights the contribution of spin labeling to bridging structure and mechanism. Efforts to develop methods for determining structures from EPR restraints and to increase sensitivity and throughput promise to expand spin labeling applications in membrane protein structural biology. Copyright © 2011 Elsevier Ltd. All rights reserved.

X-ray absorption spectroscopy and EPR studies of oriented spinach thylakoid preparations

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

Andrews, J.C.

In this study, oriented Photosystem II (PS II) particles from spinach chloroplasts are studied with electron paramagnetic resonance (EPR) and x-ray absorption spectroscopy (XAS) to determine more details of the structure of the oxygen evolving complex (OEC). The nature of halide binding to Mn is also studied with Cl K-edge and Mn EXAFS (extended x-ray absorption fine structure) of Mn-Cl model compounds, and with Mn EXAFS of oriented PS II in which Br has replaced Cl. Attention is focused on the following: photosynthesis and the oxygen evolving complex; determination of mosaic spread in oriented photosystem II particles from signal IImore » EPR measurement; oriented EXAFS--studies of PS II in the S{sub 2} state; structural changes in PS II as a result of treatment with ammonia: EPR and XAS studies; studies of halide binding to Mn: Cl K-edge and Mn EXAFS of Mn-Cl model compounds and Mn EXAFS of oriented Br-treated photosystem II.« less

Chitosan-based nanocarriers for antimalarials

NASA Astrophysics Data System (ADS)

Dreve, Simina; Kacso, Iren; Popa, Adriana; Raita, Oana; Bende, A.; Borodi, Gh.; Bratu, I.

2012-02-01

The objective of this research was to synthesize and characterize chitosan-based liquid and solid materials with unique absorptive and mechanical properties as carriers for quinine - one of the most used antimalarial drug. The use of chitosan (CTS) as base in polyelectrolyte complex systems, to prepare solid release systems as sponges is presented. The preparation by double emulsification of CTS hydrogels carrying quinine as anti-malarial drug is reported. The concentration of quinine in the CTS hydrogel was 0.08 mmol. Chitosan - drug loaded hydrogel was used to generate solid sponges by freeze-drying at -610°C and 0.09 atm. Structural investigations of the solid formulations were done by Fourier-transformed infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-VIS), spectrofluorimetry, differential scanning calorimetry (DSC) and X-ray diffractometry. The results indicated that the drug molecule is forming temporary chelates in CTS hydrogels and sponges. Electron paramagnetic resonance (EPR) demonstrates the presence of free radicals in a wide range and the antioxidant activity for chitosan - drug supramolecular cross-linked assemblies.

Magnetic and Mössbauer characterization of the magnetic properties of single-crystalline sub-micron sized Bi₂Fe₄O₉ cubes

DOE PAGES

Papaefthymiou, Georgia C.; Wong, Stanislaus S.; Viescas, Arthur J.; ...

2014-11-25

Magnetic and Mössbauer characterization of single crystalline, sub-micron sized Bi₂Fe₄O₉ cubes has been performed using SQUID magnetometry and transmission Mössbauer spectroscopy in the temperature range of 4.2 K ≤ T ≤ 300 K. A broad magnetic phase transition from the paramagnetic to the anti-ferromagnetic state is observed below 250 K, with the Mössbauer spectra exhibiting a superposition of magnetic, collapsed and quadrupolar spectra in the transition region of 200 K < T < 245 K. Room temperature Mössbauer spectra obtained in transmission geometry are identical to those recorded in back-scattering geometry via conversion electron Mössbauer spectroscopy, indicating the absence ofmore » strain at the surface. A small hysteresis loop is observed in SQUID measurements at 5 K, attributable to the presence of weak-ferromagnetism arising from the canting of Fe³⁺ ion sublattices in the antiferromagnetic matrix.« less

17 O MRS assesses the effect of mild hypothermia on oxygen consumption rate in tumors.

PubMed

Neveu, Marie-Aline; Joudiou, Nicolas; De Preter, Géraldine; Dehoux, Jean-Paul; Jordan, Bénédicte F; Gallez, Bernard

2017-08-01

Although oxygen consumption is a key factor in metabolic phenotyping, its assessment in tumors remains critical, as current technologies generally display poor specificity. The objectives of this study were to explore the feasibility of direct 17 O nuclear magnetic resonance (NMR) spectroscopy to assess oxygen metabolism in tumors and its modulations. To investigate the impact of hypometabolism induction in the murine fibrosarcoma FSAII tumor model, we monitored the oxygen consumption of normothermic (37°C) and hypothermic (32°C) tumor-bearing mice. Hypothermic animals showed an increase in tumor pO 2 (measured by electron paramagnetic resonance oximetry) contrary to normothermic animals. This was related to a decrease in oxygen consumption rate (assessed using 17 O magnetic resonance spectroscopy (MRS) after the inhalation of 17 O 2 -enriched gas). This study highlights the ability of direct 17 O MRS to measure oxygen metabolism in tumors and modulations of tumor oxygen consumption rate. Copyright © 2017 John Wiley & Sons, Ltd.

Perovskite-type oxides - Oxygen electrocatalysis and bulk structure

NASA Technical Reports Server (NTRS)

Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, E.

1988-01-01

Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

Caffeoylquinic acid derived free radicals identified during antioxidant reactions of bitter tea (Ilex latifolia and Ilex kudincha).

PubMed

Pirker, Katharina Franziska; Goodman, Bernard Albert

2010-12-01

In order to provide some insight into the chemical basis for the antioxidant behaviour of bitter tea, the Chinese medicinal beverage derived from leaves of Ilex kudincha or Ilex latifolia, free radicals generated during the oxidation of aqueous extracts of dried leaves have been investigated by electron paramagnetic resonance (EPR) spectroscopy. With both beverages, the major components in the EPR spectra after accelerated autoxidation under alkaline conditions or oxidation with the superoxide anion radical were comparable to those derived from reactions of caffeoylquinic acids. Thus these reaction products have sufficient stability for biological activity, and the present results suggest that such molecules contribute appreciably to the antioxidant chemistry of these beverages.

EPR study of gamma-irradiated N-methyl-L-alanine, DL-2-methyl glutamic acid hemihydrate and Di-leucine hydrochloride in solid state

NASA Astrophysics Data System (ADS)

Sütçü, Kerem; Osmanoğlu, Y. Emre

2017-12-01

In this study, it was aimed to investigate ɣ-irradiated powders of N-methyl-L-alanine (NMLA), DL-2-methyl glutamic acid hemihydrate (DL2MGAH), and Di-leucine hydrochloride (DLHCl) at room temperature by electron paramagnetic resonance spectroscopy. After the γ-irradiation the samples indicated the existence of the CH3ĊNHCH3COOH, HOOCCH3NH2CĊHCH2COOH·1/2H2O and (CH3)2ĊCH2CH NHCOOHCOCH (NH2HCl) CH2CH (CH3)2 radicals, respectively. The spectral parameters of the radicals were determined. The results were compared with the earlier studies and discussed accordingly.

Multifrequency electron paramagnetic resonance and electron-nuclear double-resonance studies of photo-hole processes in AgBr and AgCl emulsion grains

NASA Astrophysics Data System (ADS)

Eachus, R. S.; Pawlik, Th D.; Baetzold, R. C.

2000-10-01

By using a combination of multifrequency EPR spectroscopy, ENDOR spectroscopy and calculations of structure and energy, the reactivities of photo-generated holes in microcrystalline AgBr and AgCl dispersions (photographic emulsions) have been followed in detail. Progress has been facilitated by the use of both gelatin and polyvinyl alcohol (PVA) as peptizers. The initial trapped hole centres produced by band-gap excitation have been identified. In AgBr, this species is [(Br4)3-.V], a neutral complex formed from hole trapping by the four nearest neighbours of a surface Ag+ vacancy (=V). [(Br4)3-.V] reacts with gelatin to produce a transient organic radical at the grain's surface. It does not, however, react with PVA. The formation of the oxidized gelatin radical might involve atomic bromine as an intermediate. In AgCl, the well-known self-trapped hole centre (AgCl6)4- is the initial hole species. The hole diffuses by an electron exchange process until it is trapped by a silver ion on the grain's surface or within its penultimate layer of lattice ions. It is subsequently released from this Ag2+ site to be retrapped at a centre containing four equivalent Cl- ions. The precise identity of this defect has yet to be determined, but its decay also results in the oxidation of gelatin.

Iron silicide formation at different layers of (Fe/Si)3 multilayered structures determined by conversion electron Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Badía-Romano, L.; Rubín, J.; Magén, C.; Bürgler, D. E.; Bartolomé, J.

2014-07-01

The morphology and the quantitative composition of the Fe-Si interface layer forming at each Fe layer of a (Fe/Si)3 multilayer have been determined by means of conversion electron Mössbauer spectroscopy (CEMS) and high-resolution transmission electron microscopy (HRTEM). For the CEMS measurements, each layer was selected by depositing the Mössbauer active 57Fe isotope with 95% enrichment. Samples with Fe layers of nominal thickness dFe = 2.6 nm and Si spacers of dSi = 1.5 nm were prepared by thermal evaporation onto a GaAs(001) substrate with an intermediate Ag(001) buffer layer. HRTEM images showed that Si layers grow amorphous and the epitaxial growth of the Fe is good only for the first deposited layer. The CEMS spectra show that at all Fe/Si and Si/Fe interfaces a paramagnetic c-Fe1-xSi phase is formed, which contains 16% of the nominal Fe deposited in the Fe layer. The bottom Fe layer, which is in contact with the Ag buffer, also contains α-Fe and an Fe1-xSix alloy that cannot be attributed to a single phase. In contrast, the other two layers only comprise an Fe1-xSix alloy with a Si concentration of ≃0.15, but no α-Fe.

A comprehensive overview on the structure and comparison of magnetic properties of nanocrystalline synthesized by a thermal treatment method

NASA Astrophysics Data System (ADS)

Naseri, Mahmoud Goodarz; Halimah, M. K.; Dehzangi, Arash; Kamalianfar, Ahmad; Saion, Elias B.; Majlis, Burhanuddin Y.

2014-03-01

This study reports the simple synthesis of MFe2O4 (where M=Zn, Mn and Co) nanostructures by a thermal treatment method, followed by calcination at various temperatures from 723 to 873 K. Poly(vinyl pyrrolidon) (PVP) was used as a capping agent to stabilize the particles and prevent them from agglomeration. The pyrolytic behaviors of the polymeric precursor were analyzed by use of simultaneous thermo-gravimetry analyses (TGA) and derivative thermo-gravimetry (DTG) analyses. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of metal oxide bands for all the calcined samples. Magnetic properties were demonstrated by a vibrating sample magnetometer (VSM), which displayed that the calcined samples exhibited different types of magnetic behavior. The present study also substantiated that magnetic properties of ferrite nanoparticles prepared by the thermal treatment method, from viewing microstructures of them, can be explained as the results of the two important factors: cation distribution and impurity phase of α-Fe2O3. These two factors are subcategory of the preparation method which is related to macrostructure of ferrite. Electron paramagnetic resonance (EPR) spectroscopy showed the existence of unpaired electrons ZnFe2O4 and MnFe2O4 nanoparticles while it did not exhibit resonance signal for CoFe2O4 nanoparticles.

Redox properties of the nitronyl nitroxide antioxidants studied via their reactions with nitroxyl and ferrocyanide.

PubMed

Bobko, A A; Khramtsov, V V

2015-01-01

Nitronyl nitroxides (NNs) are the paramagnetic probes that are capable of scavenging physiologically relevant reactive oxygen (ROS) and nitrogen (RNS) species, namely superoxide, nitric oxide (NO), and nitroxyl (HNO). NNs are increasingly considered as potent antioxidants and potential therapeutic agents. Understanding redox chemistry of the NNs is important for their use as antioxidants and as paramagnetic probes for discriminative detection of NO and HNO by electron paramagnetic resonance (EPR) spectroscopy. Here we investigated the redox properties of the two most commonly used NNs, including determination of the equilibrium and rate constants of their reduction by HNO and ferrocyanide, and reduction potential of the couple NN/hydroxylamine of nitronyl nitroxide (hNN). The rate constants of the reaction of the NNs with HNO were found to be equal to (1-2) × 10(4) M(-1)s(- 1) being close to the rate constants of scavenging superoxide and NO by NNs. The reduction potential of the NNs and iminonitroxides (INs, product of NNs reaction with NO) were calculated based on their reaction constants with ferrocyanide. The obtained values of the reduction potential for NN/hNN (E'0 ≈ 285 mV) and IN/hIN (E' ≈ 495 mV) are close to the corresponding values for vitamin C and vitamin E, correspondingly. The "balanced" scavenging rates of the NNs towards superoxide, NO, and HNO, and their low reduction potential being thermodynamically close to the bottom of the pecking order of oxidizing radicals, might be important factors contributing into their antioxidant activity.

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.

Recent trends in the impurity profile of pharmaceuticals

PubMed Central

Pilaniya, Kavita; Chandrawanshi, Harish K.; Pilaniya, Urmila; Manchandani, Pooja; Jain, Pratishtha; Singh, Nitin

2010-01-01

Various regulatory authorities such as the International Conference on Harmonization (ICH), the United States Food and Drug administration (FDA), and the Canadian Drug and Health Agency (CDHA) are emphasizing on the purity requirements and the identification of impurities in Active Pharmaceutical Ingredients (APIs). The various sources of impurity in pharmaceutical products are — reagents, heavy metals, ligands, catalysts, other materials like filter aids, charcoal, and the like, degraded end products obtained during \\ after manufacturing of bulk drugs from hydrolysis, photolytic cleavage, oxidative degradation, decarboxylation, enantiomeric impurity, and so on. The different pharmacopoeias such as the British Pharmacopoeia, United State Pharmacopoeia, and Indian Pharmacopoeia are slowly incorporating limits to allowable levels of impurities present in APIs or formulations. Various methods are used to isolate and characterize impurities in pharmaceuticals, such as, capillary electrophoresis, electron paramagnetic resonance, gas–liquid chromatography, gravimetric analysis, high performance liquid chromatography, solid-phase extraction methods, liquid–liquid extraction method, Ultraviolet Spectrometry, infrared spectroscopy, supercritical fluid extraction column chromatography, mass spectrometry, Nuclear magnetic resonance (NMR) spectroscopy, and RAMAN spectroscopy. Among all hyphenated techniques, the most exploited techniques for impurity profiling of drugs are Liquid Chromatography (LC)-Mass Spectroscopy (MS), LC-NMR, LC-NMR-MS, GC-MS, and LC-MS. This reveals the need and scope of impurity profiling of drugs in pharmaceutical research. PMID:22247862

Speeding up NMR by in Situ Photo-Induced Reversible Acceleration of T1 -Relaxation (PIRAT).

PubMed

Stadler, Eduard; Dommaschk, Marcel; Frühwirt, Philipp; Herges, Rainer; Gescheidt, Georg

2018-03-05

Increasing the signal-to-noise ratio is one of the major goals in the field of NMR spectroscopy. In this proof of concept, we accelerate relaxation during an NMR pulse sequence using photo-generated paramagnetic states of an inert sensitizer. For the follow-up acquisition period, the system is converted to a diamagnetic state. The reversibility of the photo-induced switching allows extensive repetition required for multidimensional NMR. We thus eliminate the obstacle of line-broadening by the presence of paramagnetic species. In this contribution, we show how cycling of synchronized light/pulse sequences leads to an enhanced efficiency in multidimensional NMR. Our approach utilizes a molecular spin switch reversibly altering between a paramagnetic and diamagnetic state. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Correlation between structural and opto-electronic characteristics of crystalline Si microhole arrays for photonic light management

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

Sontheimer, Tobias, E-mail: tobias.sontheimer@helmholtz-berlin.de; Schnegg, Alexander; Lips, Klaus

2013-11-07

By employing electron paramagnetic resonance spectroscopy, transmission electron microscopy, and optical measurements, we systematically correlate the structural and optical properties with the deep-level defect characteristics of various tailored periodic Si microhole arrays, which are manufactured in an easily scalable and versatile process on nanoimprinted sol-gel coated glass. While tapered microhole arrays in a structured base layer are characterized by partly nanocrystalline features, poor electronic quality with a defect concentration of 10{sup 17} cm{sup −3} and a high optical sub-band gap absorption, planar polycrystalline Si layers perforated with periodic arrays of tapered microholes are composed of a compact crystalline structure and amore » defect concentration in the low 10{sup 16} cm{sup −3} regime. The low defect concentration is equivalent to the one in planar state-of-the-art solid phase crystallized Si films and correlates with a low optical sub-band gap absorption. By complementing the experimental characterization with 3-dimensional finite element simulations, we provide the basis for a computer-aided approach for the low-cost fabrication of novel high-quality structures on large areas featuring tailored opto-electronic properties.« less

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.

VCSEL based Faraday rotation spectroscopy at 762nm for battery powered trace molecular oxygen detection

NASA Astrophysics Data System (ADS)

So, Stephen; Wysocki, Gerard

2010-02-01

Faraday Rotation Spectroscopy (FRS) is a polarization based spectroscopic technique which can provide higher sensitivity concentration measurements of paramagnetic gases and free radicals than direct absorption spectroscopic techniques. We have developed sensor systems which require only 0.2W to perform TDLAS (tunable diode laser absorption spectroscopy), and can additionally be quickly duty cycled, enabling operation in wireless sensor networks of laser-based trace gas sensors We adapted our integrated TDLAS electronics to perform FRS in a compact and more sensitive system for quantification of molecular oxygen (O2) using a 762.3nm VCSEL in the A band. Using an AC magnetic field, we demonstrate detector noise dominated performance, achieving 2.1×10-6/Hz1/2 equivalent detectable fractional absorption and a minimum detection limit of 462 ppmv O2 in 1 second in a 15cm path. At longer paths and integration times, such a sensor will enable oxygen measurements at biotic respiration levels (<1ppmv) to measure CO2 - O2 exchange for mapping natural exchange of greenhouse gases. Potential improvement of detection limits by increasing various system performance parameters is described.

Dual emissions from MnS clusters confined in the sodalite nanocage of a chalcogenide-based semiconductor zeolite.

PubMed

Hu, Dandan; Zhang, Yingying; Lin, Jian; Hou, Yike; Li, Dongsheng; Wu, Tao

2017-03-21

A new host-guest hybrid system with MnS clusters confined in a chalcogenide-based semiconductor zeolite was for the first time constructed and its photoluminescence (PL) properties were also investigated. The existence of MnS clusters in the nanopores of the semiconductor zeolite was revealed by UV-Vis absorption spectroscopy, steady-state fluorescence analysis, Raman as well as Fourier transform infrared (FTIR) spectroscopy. The aggregation state of the entrapped MnS clusters at different measurement temperatures was probed by electron paramagnetic resonance (EPR) spectroscopy. Of significant importance is the fact that the entrapped MnS clusters displayed dual emissions at 518 nm (2.39 eV) and 746 nm (1.66 eV), respectively, and the long-wavelength emission has never been observed in other MnS-confined host-guest systems. These two emission peaks displayed tunable PL intensity affected by the loading level and measurement temperature. This can be explained by the different morphologies of MnS clusters with different aggregation states at the corresponding loading level or measurement temperature. The current study opens a new avenue to construct inorganic chalcogenide cluster involved host-guest systems with a semiconductor zeolite as the host matrix.

Reusable Oxidation Catalysis Using Metal-Monocatecholato Species in a Robust Metal–Organic Framework

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

Fei, Honghan; Shin, JaeWook; Meng, Ying Shirley

2014-04-02

An isolated metal-monocatecholato moiety has been achieved in a highly robust metal–organic framework (MOF) by two fundamentally different postsynthetic strategies: postsynthetic deprotection (PSD) and postsynthetic exchange (PSE). Compared with PSD, PSE proved to be a more facile and efficient functionalization approach to access MOFs that could not be directly synthesized under solvothermal conditions. Metalation of the catechol functionality residing in the MOFs resulted in unprecedented Fe-monocatecholato and Cr-monocatecholato species, which were characterized by X-ray absorption spectroscopy, X-band electron paramagnetic resonance spectroscopy, and ⁵⁷Fe Mössbauer spectroscopy. The resulting materials are among the first examples of Zr(IV)-based UiO MOFs (UiO = Universitymore » of Oslo) with coordinatively unsaturated active metal centers. Importantly, the Cr-metalated MOFs are active and efficient catalysts for the oxidation of alcohols to ketones using a wide range of substrates. Catalysis could be achieved with very low metal loadings (0.5–1 mol %). Unlike zeolite-supported, Cr-exchange oxidation catalysts, the MOF-based catalysts reported here are completely recyclable and reusable, which may make them attractive catalysts for ‘green’ chemistry processes.« less

Metal Complexes and Free Radical Toxins Produced by Pfiesteria piscicida

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

Moeller,P.; Beauchesne, K.; Huncik, K.

2007-01-01

Metal-containing organic toxins produced by Pfiesteria piscicida were characterized, for the first time, by corroborating data obtained from five distinct instrumental methods: nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma mass spectrometry (ICP-MS), liquid chromatography particle beam glow discharge mass spectrometry (LC/PB-GDMS), electron paramagnetic resonance spectroscopy (EPR), and X-ray absorption spectroscopy (XAS). The high toxicity of the metal-containing toxins is due to metal-mediated free radical production. This mode of activity explains the toxicity of Pfiesteria, as well as previously reported difficulty in observing the molecular target, due to the ephemeral nature of radical species. The toxins are highly labile inmore » purified form, maintaining activity for only 2-5 days before all activity is lost. The multiple toxin congeners in active extracts are also susceptible to decomposition in the presence of white light, pH variations, and prolonged heat. These findings represent the first formal isolation and characterization of a radical forming toxic organic-ligated metal complex isolated from estuarine/marine dinoflagellates. These findings add to an increased understanding regarding the active role of metals interacting with biological systems in the estuarine environment, as well as their links and implications to human health.« less

Metal Complexes And Free Radical Toxins Produced By Pfiesteria Piscicida

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

Moeller, P.D.R.; Beauchesne, K.R.; Huncik, K.M.

2009-06-03

Metal-containing organic toxins produced by Pfiesteria piscicida were characterized, for the first time, by corroborating data obtained from five distinct instrumental methods: nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma mass spectrometry (ICPMS), liquid chromatography particle beam glow discharge mass spectrometry (LC/PB-GDMS), electron paramagnetic resonance spectroscopy (EPR), and X-ray absorption spectroscopy (XAS). The high toxicity of the metal-containing toxins is due to metal-mediated free radical production. This mode of activity explains the toxicity of Pfiesteria, as well as previously reported difficulty in observing the molecular target, due to the ephemeral nature of radical species. The toxins are highly labile inmore » purified form, maintaining activity for only 2-5 days before all activity is lost. The multiple toxin congeners in active extracts are also susceptible to decomposition in the presence of white light, pH variations, and prolonged heat. These findings represent the first formal isolation and characterization of a radical forming toxic organic-ligated metal complex isolated from estuarine/marine dinoflagellates. These findings add to an increased understanding regarding the active role of metals interacting with biological systems in the estuarine environment, as well as their links and implications to human health.« less

Enhanced Photoreduction of Nitro-aromatic Compounds by Hydrated Electrons Derived from Indole on Natural Montmorillonite.

PubMed

Tian, Haoting; Guo, Yong; Pan, Bo; Gu, Cheng; Li, Hui; Boyd, Stephen A

2015-07-07

A new photoreduction pathway for nitro-aromatic compounds (NACs) and the underlying degradation mechanism are described. 1,3-Dinitrobenzene was reduced to 3-nitroaniline by the widely distributed aromatic molecule indole; the reaction is facilitated by montmorillonite clay mineral under both simulated and natural sunlight irradiation. The novel chemical reaction is strongly affected by the type of exchangeable cation present on montmorillonite. The photoreduction reaction is initiated by the adsorption of 1,3-dinitrobenzene and indole in clay interlayers. Under light irradiation, the excited indole molecule generates a hydrated electron and the indole radical cation. The structural negative charge of montmorillonite plausibly stabilizes the radical cation hence preventing charge recombination. This promotes the release of reactive hydrated electrons for further reductive reactions. Similar results were observed for the photoreduction of nitrobenzene. In situ irradiation time-resolved electron paramagnetic resonance and Fourier transform infrared spectroscopies provided direct evidence for the generation of hydrated electrons and the indole radical cations, which supported the proposed degradation mechanism. In the photoreduction process, the role of clay mineral is to both enhance the generation of hydrated electrons and to provide a constrained reaction environment in the galley regions, which increases the probability of contact between NACs and hydrated electrons.

Measurement of free radicals using electron paramagnetic resonance spectroscopy during open aorto-iliac arterial reconstruction.

PubMed

Majewski, Wacław; Krzyminiewski, Ryszard; Stanisić, Michał; Iskra, Maria; Krasiński, Zbigniew; Nowak, Marek; Dobosz, Bernadeta

2014-11-27

Aortic cross-clamping during abdominal aortic aneurysm (AAA) open repair leads to development of ischemia-reperfusion injury. Electron paramagnetic resonance spectroscopy (EPR) spin-trapping is a valuable method of direct measurement of free radicals. The objective of the study was to evaluate the results of EPR as a direct method of free radical measurement and degree of inflammatory response in open operative treatment of patients with AAA and aorto-iliac occlusive disease (AIOD). The study was performed on a group of 32 patients with AAA and 25 patients with AIOD scheduled for open repair. Peripheral venous blood for EPR spectroscopy and for SOD, GPx, ox-LDL, Il-6, TNF-alfa, CRP, and HO-1 were harvested. Selected parameters were established accordingly to specified EPR and immunohistochemical methods and analyzed between groups by Mann-Whitney U test and Wilcoxon matched-pairs signed-ranks test with Bonferroni correction. Free radicals level was correlated with the time of the aortic cross-clamping after the reperfusion of he first and second leg in AAA (r=0.7; r=0.47). ox-LDL in AAA decreased 5 min after reperfusion of the first leg (32.99 U/L, range: 14.09-77.12) and 5 min after reperfusion of the second leg (26.75 U/L, range: 11.56-82.12) and 24 h after the operation (25.85 U/L, range: 14.29-49.70). HO-1 concentration increased to above the level before intervention 24 h after surgery. The activities of GPx and SOD decreased 5 min after the first-leg reperfusion in AAA. Twenty-four hours after surgery, inflammatory markers increased in AAA to CRP was 14.76 ml/l (0.23-38.55), IL-6 was 141.22 pg/ml (84.3-591.03), TNF-alfa was 6.82 pg/ml (1.76-80.01) and AIOD: CRP was 18.44 mg/l (2.56-33.14), IL-6: 184.1 pg/ml (128.46-448.03), TNF-alfa was 7.74 pg/ml (1.74-74.74). EPR spin-trapping demonstrates temporarily elevated level of free radicals in early phase of reperfusion, leading to decrease antioxidants in AAA. Elevated free radical levels decreased 24 h after surgery due to various endogenous antioxidants and therapies.

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.

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.

High-field EPR on membrane proteins - crossing the gap to NMR.

PubMed

Möbius, Klaus; Lubitz, Wolfgang; Savitsky, Anton

2013-11-01

In this review on advanced EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR concerning the measurement of molecular interactions in large biomolecules. From these interactions, detailed information can be revealed on structure and dynamics of macromolecules embedded in solution- or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed to new horizons the limits of EPR spectroscopy and its multifrequency extensions concerning the sensitivity of detection, the selectivity with respect to interactions, and the resolution in frequency and time domains. One of the most important advances has been the extension of EPR to high magnetic fields and microwave frequencies, very much in analogy to what happens in NMR. This is exemplified by referring to ongoing efforts for signal enhancement in both NMR and EPR double-resonance techniques by exploiting dynamic nuclear or electron spin polarization via unpaired electron spins and their electron-nuclear or electron-electron interactions. Signal and resolution enhancements are particularly spectacular for double-resonance techniques such as ENDOR and PELDOR at high magnetic fields. They provide greatly improved orientational selection for disordered samples that approaches single-crystal resolution at canonical g-tensor orientations - even for molecules with small g-anisotropies. Exchange of experience between the EPR and NMR communities allows for handling polarization and resolution improvement strategies in an optimal manner. Consequently, a dramatic improvement of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Unique structural and dynamic information is thus revealed that can hardly be obtained by any other analytical techniques. Micromolar quantities of sample molecules have become sufficient to characterize stable and transient reaction intermediates of complex molecular systems - offering highly interesting applications for chemists, biochemists and molecular biologists. In three case studies, representative examples of advanced EPR spectroscopy are reviewed: (I) High-field PELDOR and ENDOR structure determination of cation-anion radical pairs in reaction centers from photosynthetic purple bacteria and cyanobacteria (Photosystem I); (II) High-field ENDOR and ELDOR-detected NMR spectroscopy on the oxygen-evolving complex of Photosystem II; and (III) High-field electron dipolar spectroscopy on nitroxide spin-labelled bacteriorhodopsin for structure-function studies. An extended conclusion with an outlook to further developments and applications is also presented. Copyright © 2013 Elsevier B.V. All rights reserved.

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).

Measurement of myocardial free radical production during exercise using EPR spectroscopy.

PubMed

Traverse, Jay H; Nesmelov, Yuri E; Crampton, Melanie; Lindstrom, Paul; Thomas, David D; Bache, Robert J

2006-06-01

Exercise is associated with an increase in oxygen flux through the mitochondrial electron transport chain that has recently been demonstrated to increase the production of reactive oxygen species (ROS) in skeletal muscle. This study examined whether exercise also causes free radical production in the heart. We measured ROS production in seven chronically instrumented dogs during rest and treadmill exercise (6.4 km/h at 10 degrees grade; and heart rate, 204 +/- 3 beats/min) using electron paramagnetic resonance spectroscopy in conjunction with the spin trap alpha-phenyl-tert-butylnitrone (PBN) (0.14 mol/l) in blood collected from the aorta and coronary sinus (CS). To improve signal detection, the free radical adducts were deoxygenated over a nitrogen stream for 15 min and extracted with toluene. The hyperfine splitting constants of the radicals were alpha(N) = 13.7 G and alpha(H) = 1.0 G, consistent with an alkoxyl or carbon-centered radical. Resting aortic and CS PBN adduct concentrations were 6.7 and 6.3 x 10(8) arbitrary units (P = not significant). Both aortic and CS adduct concentrations increased during exercise, but there was no significant difference between the aortic and CS concentrations. Thus, in contrast to skeletal muscle, submaximal treadmill exercise did not result in detectable free radical production by the heart.

Safe disposal of toxic chrome buffing dust generated from leather industries.

PubMed

Swarnalatha, S; Srinivasulu, T; Srimurali, M; Sekaran, G

2008-01-31

The high concentration of trivalent chromium along with organic/inorganic compounds in chrome buffing dust (CBD), the solid waste discharged from leather industries, causes severe groundwater contamination on land co-disposal and chronic air pollution during thermal incineration. In the present investigation, CBD was subjected to starved air incineration (SAI) at 800 degrees C in a thermal incinerator under different flow rates of oxygen to optimize the oxygen required to incinerate the organic compounds and simultaneously preventing the conversion of Cr(3+) to Cr(6+). The energy audit of SAI of buffing dust under the external supply of oxygen was carried out under different incineration conditions. The bottom ash from SAI was effectively solidified/stabilized using Portland cement and fine aggregate. The solidified blocks were tested for unconfined compressive strength and heavy metal leaching. Unconfined compressive strength of the blocks was in the range of 120-180 kg/cm(2). The stabilization of chromium(III) in the cement gel matrix was confirmed using Scanning Electron Microscopy SEM, Electron Paramagnetic Resonance spectroscopy (EPR) and X-ray diffraction spectroscopy (XRD). Leachability studies through TCLP on solidified blocks were carried out to determine the degree of leaching of chromium and organic compounds (expressed as COD) under standard conditions.

Spin conversion of positronium in NiO/Al2O3 catalysts observed by coincidence Doppler broadening technique

NASA Astrophysics Data System (ADS)

Zhang, H. J.; Chen, Z. Q.; Wang, S. J.; Kawasuso, A.; Morishita, N.

2010-07-01

High-purity NiO/Al2O3 catalysts were prepared by mixing NiO and γ-Al2O3 nanopowders. X-ray diffraction patterns were measured to characterize the grain size and crystalline phase of the nanopowders. Positron-annihilation spectroscopy was used to study the microstructure and surface properties of the pores inside the NiO/Al2O3 catalysts. The positron lifetime spectrum comprises two short and two long lifetime components. The two long lifetimes τ3 and τ4 correspond to ortho-positronium (o-Ps) annihilated in microvoids and large pores, respectively. With increasing NiO content in the NiO/Al2O3 catalysts, both τ4 and its intensity I4 show continuous decrease. Meanwhile, the para-positronium (p-Ps) intensity, obtained from coincidence Doppler broadening spectra, increases gradually with NiO content. The different variation in o-Ps and p-Ps intensity suggests the ortho-para conversion of positronium in NiO/Al2O3 catalysts. X-ray photoelectron spectroscopy shows that Ni mainly exists in the form of NiO. The electron-spin-resonance measurements reveal that the ortho-para conversion of Ps is induced by the unpaired electrons of the paramagnetic centers of NiO.

On the energy scale involved in the metal to insulator transition of quadruple perovskite EuCu3Fe4O12: infrared spectroscopy and ab-initio calculations.

PubMed

Brière, B; Kalinko, A; Yamada, I; Roy, P; Brubach, J B; Sopracase, R; Zaghrioui, M; Phuoc, V Ta

2016-06-27

Optical measurements were carried out by infrared spectroscopy on AA'3B4O12 A-site ordered quadruple perovskite EuCu3Fe4O12 (microscopic sample) as function of temperature. At 240 K (=TMI), EuCu3Fe4O12 undergoes a very abrupt metal to insulator transition, a paramagnetic to antiferromagnetic transition and an isostructural transformation with an abrupt large volume expansion. Above TMI, optical conductivity reveals a bad metal behavior and below TMI, an insulating phase with an optical gap of 125 meV is observed. As temperature is decreased, a large and abrupt spectral weight transfer toward an energy scale larger than 1 eV is detected. Concurrently, electronic structure calculations for both high and low temperature phases were compared to the optical conductivity results giving a precise pattern of the transition. Density of states and computed optical conductivity analysis identified Cu3dxy, Fe3d and O2p orbitals as principal actors of the spectral weight transfer. The present work constitutes a first step to shed light on EuCu3Fe4O12 electronic properties with optical measurements and ab-initio calculations.

On the energy scale involved in the metal to insulator transition of quadruple perovskite EuCu3Fe4O12: infrared spectroscopy and ab-initio calculations

PubMed Central

Brière, B.; Kalinko, A.; Yamada, I.; Roy, P.; Brubach, J. B.; Sopracase, R.; Zaghrioui, M.; Phuoc, V. Ta

2016-01-01

Optical measurements were carried out by infrared spectroscopy on AA′3B4O12 A-site ordered quadruple perovskite EuCu3Fe4O12 (microscopic sample) as function of temperature. At 240 K (=TMI), EuCu3Fe4O12 undergoes a very abrupt metal to insulator transition, a paramagnetic to antiferromagnetic transition and an isostructural transformation with an abrupt large volume expansion. Above TMI, optical conductivity reveals a bad metal behavior and below TMI, an insulating phase with an optical gap of 125 meV is observed. As temperature is decreased, a large and abrupt spectral weight transfer toward an energy scale larger than 1 eV is detected. Concurrently, electronic structure calculations for both high and low temperature phases were compared to the optical conductivity results giving a precise pattern of the transition. Density of states and computed optical conductivity analysis identified Cu3dxy, Fe3d and O2p orbitals as principal actors of the spectral weight transfer. The present work constitutes a first step to shed light on EuCu3Fe4O12 electronic properties with optical measurements and ab-initio calculations. PMID:27346212

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.

High Resolution Transmission Electron Microscopy (HRTEM) of nanophase ferric oxides

NASA Technical Reports Server (NTRS)

Golden, D. C.; Morris, R. V.; Ming, D. W.; Lauer, H. V., Jr.

1994-01-01

Iron oxide minerals are the prime candidates for Fe(III) signatures in remotely sensed Martian surface spectra. Magnetic, Mossbauer, and reflectance spectroscopy have been carried out in the laboratory in order to understand the mineralogical nature of Martian analog ferric oxide minerals of submicron or nanometer size range. Out of the iron oxide minerals studied, nanometer sized ferric oxides are promising candidates for possible Martian spectral analogs. 'Nanophase ferric oxide (np-Ox)' is a generic term for ferric oxide/oxihydroxide particles having nanoscale (less than 10 nm) particle dimensions. Ferrihydrite, superparamagnetic particles of hematite, maghemite and goethite, and nanometer sized particles of inherently paramagnetic lepidocrocite are all examples of nanophase ferric oxides. np-Ox particles in general do not give X-ray diffraction (XRD) patterns with well defined peaks and would often be classified as X-ray amorphous. Therefore, different np-Oxs preparations should be characterized using a more sensitive technique e.g., high resolution transmission electron microscopy (HRTEM). The purpose of this study is to report the particle size, morphology and crystalline order, of five np-Ox samples by HRTEM imaging and electron diffraction (ED).

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

Mei, Yang; Ramanathan, Arvind; Glover, Karen

BECN1 is essential for autophagy, a critical eukaryotic cellular homeostasis pathway. Here we delineate a highly conserved BECN1 domain located between previously characterized BH3 and coiled-coil domains and elucidate its structure and role in autophagy. The 2.0 angstrom sulfur-single-wavelength anomalous dispersion X-ray crystal structure of this domain demonstrates that its N-terminal half is unstructured while its C-terminal half is helical; hence, we name it the flexible helical domain (FHD). Circular dichroism spectroscopy, double electron electron resonance electron paramagnetic resonance, and small-angle X-ray scattering (SAXS) analyses confirm that the FHD is partially disordered, even in the context of adjacent BECN1 domains.more » Molecular dynamic simulations fitted to SAXS data indicate that the FHD transiently samples more helical conformations. FHD helicity increases in 2,2,2-trifluoroethanol, suggesting it may become more helical upon binding. Lastly, cellular studies show that conserved FHD residues are required for starvation-induced autophagy. Thus, the FHD likely undergoes a binding-associated disorder to-helix transition, and conserved residues critical for this interaction are essential for starvation-induced autophagy.« less

Evolution of ground-state wave function in CeCoIn5 upon Cd or Sn doping

NASA Astrophysics Data System (ADS)

Chen, K.; Strigari, F.; Sundermann, M.; Hu, Z.; Fisk, Z.; Bauer, E. D.; Rosa, P. F. S.; Sarrao, J. L.; Thompson, J. D.; Herrero-Martin, J.; Pellegrin, E.; Betto, D.; Kummer, K.; Tanaka, A.; Wirth, S.; Severing, A.

2018-01-01

We present linear polarization-dependent soft-x-ray absorption spectroscopy data at the Ce M4 ,5 edges of Cd- and Sn-doped CeCoIn5. The 4 f ground-state wave functions have been determined for their superconducting, antiferromagnetic, and paramagnetic ground states. The absence of changes in the wave functions in CeCo (In1-xCdx) 5 suggests that the 4 f -conduction-electron (c f ) hybridization is not affected by global Cd doping, thus supporting the interpretation of magnetic droplets nucleating long-range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in CeCo (In1-ySny) 5 compresses the 4 f orbitals into the tetragonal plane of these materials, suggesting enhanced c f hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the 4 f wave functions are a very sensitive probe of small changes in the hybridization of 4 f and conduction electrons, even conveying information about direction dependencies.

Organozinc Precursor-Derived Crystalline ZnO Nanoparticles: Synthesis, Characterization and Their Spectroscopic Properties

PubMed Central

Wicker, Susanne; Wang, Xiao; Erichsen, Egil Severin; Fu, Feng

2018-01-01

Crystalline ZnO-ROH and ZnO-OR (R = Me, Et, iPr, nBu) nanoparticles (NPs) have been successfully synthesized by the thermal decomposition of in-situ-formed organozinc complexes Zn(OR)2 deriving from the reaction of Zn[N(SiMe3)2]2 with ROH and of the freshly prepared Zn(OR)2 under an identical condition, respectively. With increasing carbon chain length of alkyl alcohol, the thermal decomposition temperature and dispersibility of in-situ-formed intermediate zinc alkoxides in oleylamine markedly influenced the particle sizes of ZnO-ROH and its shape (sphere, plate-like aggregations), while a strong diffraction peak-broadening effect is observed with decreasing particle size. For ZnO-OR NPs, different particle sizes and various morphologies (hollow sphere or cuboid-like rod, solid sphere) are also observed. As a comparison, the calcination of the fresh-prepared Zn(OR)2 generated ZnO-R NPs possessing the particle sizes of 5.4~34.1 nm. All crystalline ZnO nanoparticles are characterized using X-ray diffraction analysis, electron microscopy and solid-state 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The size effect caused by confinement of electrons’ movement and the defect centres caused by unpaired electrons on oxygen vacancies or ionized impurity heteroatoms in the crystal lattices are monitored by UV-visible spectroscopy, electron paramagnetic resonance (EPR) and photoluminescent (PL) spectroscopy, respectively. Based on the types of defects determined by EPR signals and correspondingly defect-induced probably appeared PL peak position compared to actual obtained PL spectra, we find that it is difficult to establish a direct relationship between defect types and PL peak position, revealing the complication of the formation of defect types and photoluminescence properties. PMID:29300343

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.

Identification of the substrate radical intermediate derived from ethanolamine during catalysis by ethanolamine ammonia-lyase.

PubMed

Bender, Güneş; Poyner, Russell R; Reed, George H

2008-10-28

Rapid-mix freeze-quench (RMFQ) methods and electron paramagnetic resonance (EPR) spectroscopy have been used to characterize the steady-state radical in the deamination of ethanolamine catalyzed by adenosylcobalamin (AdoCbl)-dependent ethanolamine ammonia-lyase (EAL). EPR spectra of the radical intermediates formed with the substrates, [1-13C]ethanolamine, [2-13C]ethanolamine, and unlabeled ethanolamine were acquired using RMFQ trapping methods from 10 ms to completion of the reaction. Resolved 13C hyperfine splitting in EPR spectra of samples prepared with [1-13C]ethanolamine and the absence of such splitting in spectra of samples prepared with [2-13C]ethanolamine show that the unpaired electron is localized on C1 (the carbinol carbon) of the substrate. The 13C splitting from C1 persists from 10 ms throughout the time course of substrate turnover, and there was no evidence of a detectable amount of a product like radical having unpaired spin on C2. These results correct an earlier assignment for this radical intermediate [Warncke, K., et al. (1999) J. Am. Chem. Soc. 121, 10522-10528]. The EPR signals of the substrate radical intermediate are altered by electron spin coupling to the other paramagnetic species, cob(II)alamin, in the active site. The dipole-dipole and exchange interactions as well as the 1-13C hyperfine splitting tensor were analyzed via spectral simulations. The sign of the isotropic exchange interaction indicates a weak ferromagnetic coupling of the two unpaired electrons. A Co2+-radical distance of 8.7 A was obtained from the magnitude of the dipole-dipole interaction. The orientation of the principal axes of the 13C hyperfine splitting tensor shows that the long axis of the spin-bearing p orbital on C1 of the substrate radical makes an angle of approximately 98 degrees with the unique axis of the d(z2) orbital of Co2+.

Paramagnetic oxotungsten(V) complexes containing the hydrotris(3,5-dimethylpyrazol-1-yl)borate ligand.

PubMed

Sproules, Stephen; Eagle, Aston A; Taylor, Michelle K; Gable, Robert W; White, Jonathan M; Young, Charles G

2011-05-16

Sky-blue Tp*WOCl(2) has been synthesized from the high-yielding reaction of Tp*WO(2)Cl with boron trichloride in refluxing toluene. Dark-red Tp*WOI(2) was prepared via thermal decarbonylation followed by aerial oxidation of Tp*WI(CO)(3) in acetonitrile. From these precursors, an extensive series of mononuclear tungstenyl complexes, Tp*WOXY [X = Cl(-), Y = OPh(-), SPh(-); X = Y = OPh(-), 2-(n-propyl)phenolate (PP(-)), SPh(-), SePh(-); XY = toluene-3,4-dithiolate (tdt(2-)), quinoxaline-2,3-dithiolate (qdt(2-)), benzene-1,2-diselenolate (bds(2-)); Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate], was prepared by metathesis with the respective alkali-metal salt of X(-)/XY(2-) or (NHEt(3))(2)(qdt). The complexes were characterized by microanalysis, mass spectrometry, electrochemistry, IR, electron paramagnetic resonance (EPR), and electronic absorption spectroscopies, and X-ray crystallography (for X = Y = OPh(-), PP(-), SPh(-); XY = bds(2-)). The six-coordinate, distorted-octahedral tungsten centers are coordinated by terminal oxo [W≡O = 1.689(6)-1.704(3) Å], tridentate Tp*, and monodentate or bidentate O/S/Se-donor ligands. Spin Hamiltonian parameters derived from the simulation of fluid-solution X-band EPR spectra revealed that the soft-donor S/Se ligand complexes had larger g values and smaller (183)W hyperfine coupling constants than the less covalent hard-donor O/Cl species. The former showed low-energy ligand-to-metal charge-transfer bands in the near-IR region of their electronic absorption spectra. These oxotungsten(V) complexes display lower reduction potentials than their molybdenum counterparts, underscoring the preference of tungsten for higher oxidation states. Furthermore, the protonation of the pyrazine nitrogen atoms of the qdt(2-) ligand has been examined by spectroelectrochemistry; the product of the one-electron reduction of [Tp*WO(qdtH)](+) revealed usually intense low-energy bands.

Fluorinated Paramagnetic Complexes: Sensitive and Responsive Probes for Magnetic Resonance Spectroscopy and Imaging

NASA Astrophysics Data System (ADS)

Peterson, Katie L.; Srivastava, Kriti; Pierre, Valérie C.

2018-05-01

Fluorine magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) of chemical and physiological processes is becoming more widespread. The strength of this technique comes from the negligible background signal in in vivo 19F MRI and the large chemical shift window of 19F that enables it to image concomitantly more than one marker. These same advantages have also been successfully exploited in the design of responsive 19F probes. Part of the recent growth of this technique can be attributed to novel designs of 19F probes with improved imaging parameters due to the incorporation of paramagnetic metal ions. In this review, we provide a description of the theories and strategies that have been employed successfully to improve the sensitivity of 19F probes with paramagnetic metal ions. The Bloch-Wangsness-Redfield theory accurately predicts how molecular parameters such as distance, geometry, rotational correlation times, as well as the nature, oxidation state, and spin state of the metal ion affect the sensitivity of the fluorine-based probes. The principles governing the design of responsive 19F probes are subsequently described in a “how to” guide format. Examples of such probes and their advantages and disadvantages are highlighted through a synopsis of the literature.

Tracing and quantification of pharmaceuticals using MR imaging and spectroscopy at clinical MRI system

NASA Astrophysics Data System (ADS)

Jeong, Eun-Kee; Liu, Xin; Shi, Xianfeng; Yu, Y. Bruce; Lu, Zeng-Rong

2012-10-01

Magnetic resonance imaging (MRI) and spectroscopy (MRS) is very powerful modality for imaging and localized investigation of biological tissue. Medical MRI measures nuclear magnetization of the water protons, which consists of 70 % of our body. MRI provides superior contrast among different soft tissues to all other existing medical imaging modalities, including ultrasound, X-ray CT, PET, and SPECT. In principle, MRI/S may be an ideal non-invasive tool for drug delivery research. However, because of its low sensitivity, a large dose is required for tracing pharmaceuticals. Therefore, its use for imaging of pharmaceuticals is very limited mostly to molecules that contain a paramagnetic metal ion, such as gadolinium (Gd3+) and manganese (Mn2+). The paramagnetic metal ion provides a large fluctuating magnetic field at the proton in the water molecule via a coordinate site. The measurement of local drug concentration is the first step for further quantification. Local concentration of the paramagnetic-ion based MRI contrast agent can be indirectly measured via the change in the water signal intensity. 19F MRI/S of fluorinated complex may be an option for drug delivery and tracing agent, because the fluorinated molecule may be directly detected due to its large magnetic moment (94 % of proton) and 100 % abundance.

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.

A hand-held EPR scanner for transcutaneous oximetry

NASA Astrophysics Data System (ADS)

Wolfson, Helen; Ahmad, Rizwan; Twig, Ygal; Blank, Aharon; Kuppusamy, Periannan

2015-03-01

Cutaneous (skin) oxygenation is an important prognostic factor for the treatment of chronic wounds, skin cancer, diabetes side effects, and limb amputation. Currently, there are no reliable methods for measuring this parameter. Oximetry, using electron paramagnetic resonance (EPR) spectroscopy, is emerging as a potential tool for clinical oximetry, including cutaneous applications. The problem with EPR oximetry, however, is that the conventional EPR design requires the use of a large magnet that can generate homogeneous field across the sample, making it unattractive for clinical practice. We present a novel approach that makes use of a miniature permanent magnet, combined with a small microwave resonator, to enable the acquisition of EPR signals from paramagnetic species placed on the skin. The instrumentation consists of a hand-held, modular, cylindrical probehead with overall dimensions of 36-mm diameter and 24-mm height, with 150-g weight. The probehead includes a Halbach array of 16 pieces (4×4×8 mm3) of Sm-Co permanent magnet and a loop-gap resonator (2.24 GHz). Preliminary measurements using a Hahn-echo pulse sequence (800 echos in 20 ms) showed a signalto- noise ratio of ~70 compared to ~435 in a homogenous magnet under identical settings. Further work is in progress to improve the performance of the probehead and to optimize the hand-held system for clinical use

EPR studies of the free radicals generated in gamma irradiated amino acid derivatives

NASA Astrophysics Data System (ADS)

Osmanoğlu, Y. Emre; Sütçü, Kerem

2017-10-01

Gamma irradiated powder forms of N-acetyl-DL-aspartic acid, N-carbamoyl-DL-aspartic acid and N-methyl-L-serine were investigated by electron paramagnetic resonance spectroscopy (EPR) at room temperature. In these compounds, the paramagnetic centers formed after irradiation were attributed to the HOOCCH2ĊHCOOH, COOHĊHCHNH and HOCH2ĊHCOOH radicals, respectively. The g values and the hyperfine coupling constants for the radical species are with values of g = 2.0038 ± 0.0005, aα = 2.15 mT, aβ(1) = 3.84 mT and aβ(2) = 2.15 for the first radical, g = 2.0039 ± 0.0005, aα = 1.7 mT, aß(1) = 0.62 mT, aß(2) = 0.54 mT, aγ = 0.53 mT for the second radical and g = 2.0039 ± 0.0005, aβ(1) = 2.40 mT, aβ(2) = 1.83 mT and aα = 1.83 mT for the third radical. The free radicals formed in three compounds were found to be stable for three months at room temperature. It was concluded that, spin density was concentrated predominantly in the 2pπ orbital of the carbon atom.

Molecular packing and magnetic properties of lithium naphthalocyanine crystals: hollow channels enabling permeability and paramagnetic sensitivity to molecular oxygen

PubMed Central

Pandian, Ramasamy P.; Dolgos, Michelle; Marginean, Camelia; Woodward, Patrick M.; Hammel, P. Chris; Manoharan, Periakaruppan T.; Kuppusamy, Periannan

2009-01-01

The synthesis, structural framework, magnetic and oxygen-sensing properties of a lithium naphthalocyanine (LiNc) radical probe are presented. LiNc was synthesized in the form of a microcrystalline powder using a chemical method and characterized by electron paramagnetic resonance (EPR) spectroscopy, magnetic susceptibility, powder X-ray diffraction analysis, and mass spectrometry. X-Ray powder diffraction studies revealed a structural framework that possesses long, hollow channels running parallel to the packing direction. The channels measured approximately 5.0 × 5.4 Å2 in the two-dimensional plane perpendicular to the length of the channel, enabling diffusion of oxygen molecules (2.9 × 3.9 Å2) through the channel. The powdered LiNc exhibited a single, sharp EPR line under anoxic conditions, with a peak-to-peak linewidth of 630 mG at room temperature. The linewidth was sensitive to surrounding molecular oxygen, showing a linear increase in pO2 with an oxygen sensitivity of 31.2 mG per mmHg. The LiNc microcrystals can be further prepared as nano-sized crystals without the loss of its high oxygen-sensing properties. The thermal variation of the magnetic properties of LiNc, such as the EPR linewidth, EPR intensity and magnetic susceptibility revealed the existence of two different temperature regimes of magnetic coupling and hence differing columnar packing, both being one-dimensional antiferromagnetic chains but with differing magnitudes of exchange coupling constants. At a temperature of ∼50 K, LiNc crystals undergo a reversible phase transition. The high degree of oxygen-sensitivity of micro- and nano-sized crystals of LiNc, combined with excellent stability, should enable precise and accurate measurements of oxygen concentration in biological systems using EPR spectroscopy. PMID:19809598

A Stable Room-Temperature Luminescent Biphenylmethyl Radical.

PubMed

Ai, Xin; Chen, Yingxin; Feng, Yuting; Li, Feng

2018-03-05

There is only one family of room-temperature luminescent radicals, the triphenylmethyl radicals, to date. Herein, we synthesize a new stable room-temperature luminescent radical, (N-carbazolyl)bis(2,4,6-tirchlorophenyl)methyl radical (CzBTM), which has improved properties compared to the triphenylmethyl radicals. X-ray crystallography, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements confirmed the radical structure. CzBTM shows room-temperature deep-red to near-infrared emission in various solutions. Both thermal and photo stability were significantly enhanced by the replacement of trichlorobenzene by the carbazole moiety. The electroluminescence results of CzBTM verify its potential application to circumvent the problem of triplet harvesting in traditional fluorescent OLEDs. A new family of stable luminescent radicals based on CzBTM is anticipated. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unraveling the chemical identity of meat pigments.

PubMed

Pegg, R B; Shahidi, F

1997-10-01

This review examines the chemistry of nitrite curing of meat and meat products as it relates to the development of cured meat color and provides a detailed account of how nitrite-free processed meats could be prepared using the preformed cooked cured-meat pigment (CCMP). Thus, a chemical description of meat color, both raw and cooked, and characterization of nitrosylheme pigments follows. Based on electron paramagnetic resonance (EPR), visible and infrared spectroscopic studies, evidence has been provided to support the hypothesis that the chemical structure of the preformed CCMP is identical to that of the pigment prepared in situ after thermal processing of nitrite-cured meat and is in fact a mononitrosylheme complex. An appendix, which describes the basic principles of EPR spectroscopy used in the context of this review, is attached.

EPR study of the effect of ionizing radiation on chromium centers in Mg2SiO4: Cr,Li laser crystals

NASA Astrophysics Data System (ADS)

Akhmetzyanov, D. A.; Dudnikova, V. B.; Zharikov, E. V.; Zhiteitsev, E. R.; Konovalov, A. A.; Tarasov, V. F.

2013-09-01

Forsterite single crystals doped with chromium and lithium and exposed to ionizing radiation have been studied using multifrequency electron paramagnetic resonance (EPR) spectroscopy. It has been found that ionizing irradiation up to a dose of 108 rad does not lead to a significant change in the concentration of single chromium impurity centers. At the same time, γ-ray irradiation of the crystal leads to a decrease in the concentration of active laser centers, which form an associate of trivalent chromium and monovalent lithium in the crystallographic positions M2 and M1, respectively, and to the formation of new centers of divalent chromium. The structure and magnetic properties of the new centers have been discussed.

Heme compounds in dinosaur trabecular bone.

PubMed

Schweitzer, M H; Marshall, M; Carron, K; Bohle, D S; Busse, S C; Arnold, E V; Barnard, D; Horner, J R; Starkey, J R

1997-06-10

Six independent lines of evidence point to the existence of heme-containing compounds and/or hemoglobin breakdown products in extracts of trabecular tissues of the large theropod dinosaur Tyrannosaurus rex. These include signatures from nuclear magnetic resonance and electron spin resonance that indicate the presence of a paramagnetic compound consistent with heme. In addition, UV/visible spectroscopy and high performance liquid chromatography data are consistent with the Soret absorbance characteristic of this molecule. Resonance Raman profiles are also consistent with a modified heme structure. Finally, when dinosaurian tissues were extracted for protein fragments and were used to immunize rats, the resulting antisera reacted positively with purified avian and mammalian hemoglobins. The most parsimonious explanation of this evidence is the presence of blood-derived hemoglobin compounds preserved in the dinosaurian tissues.

Respiratory chain components involved in the glycerophosphate dehydrogenase-dependent ROS production by brown adipose tissue mitochondria.

PubMed

Vrbacký, Marek; Drahota, Zdenek; Mrácek, Tomás; Vojtísková, Alena; Jesina, Pavel; Stopka, Pavel; Houstek, Josef

2007-07-01

Involvement of mammalian mitochondrial glycerophosphate dehydrogenase (mGPDH, EC 1.1.99.5) in reactive oxygen species (ROS) generation was studied in brown adipose tissue mitochondria by different spectroscopic techniques. Spectrofluorometry using ROS-sensitive probes CM-H2DCFDA and Amplex Red was used to determine the glycerophosphate- or succinate-dependent ROS production in mitochondria supplemented with respiratory chain inhibitors antimycin A and myxothiazol. In case of glycerophosphate oxidation, most of the ROS originated directly from mGPDH and coenzyme Q while complex III was a typical site of ROS production in succinate oxidation. Glycerophosphate-dependent ROS production monitored by KCN-insensitive oxygen consumption was highly activated by one-electron acceptor ferricyanide, whereas succinate-dependent ROS production was unaffected. In addition, superoxide anion radical was detected as a mGPDH-related primary ROS species by fluorescent probe dihydroethidium, as well as by electron paramagnetic resonance (EPR) spectroscopy with DMPO spin trap. Altogether, the data obtained demonstrate pronounced differences in the mechanism of ROS production originating from oxidation of glycerophosphate and succinate indicating that electron transfer from mGPDH to coenzyme Q is highly prone to electron leak and superoxide generation.

Electron paramagnetic resonance (EPR) dosimetry using lithium formate in radiotherapy: comparison with thermoluminescence (TL) dosimetry using lithium fluoride rods.

PubMed

Vestad, Tor Arne; Malinen, Eirik; Olsen, Dag Rune; Hole, Eli Olaug; Sagstuen, Einar

2004-10-21

Solid-state radiation dosimetry by electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) was utilized for the determination of absorbed doses in the range of 0.5-2.5 Gy. The dosimeter materials used were lithium formate and lithium fluoride (TLD-100 rods) for EPR dosimetry and TL dosimetry, respectively. 60Co gamma-rays and 4, 6, 10 and 15 MV x-rays were employed. The main objectives were to compare the variation in dosimeter reading of the respective dosimetry systems and to determine the photon energy dependence of the two dosimeter materials. The EPR dosimeter sensitivity was constant over the dose range in question, while the TL sensitivity increased by more than 5% from 0.5 to 2.5 Gy, thus displaying a supralinear dose response. The average relative standard deviation in the dosimeter reading per dose was 3.0% and 1.2% for the EPR and TL procedures, respectively. For EPR dosimeters, the relative standard deviation declined significantly from 4.3% to 1.1% over the dose range in question. The dose-to-water energy response for the megavoltage x-ray beams relative to 60Co gamma-rays was in the range of 0.990-0.979 and 0.984-0.962 for lithium formate and lithium fluoride, respectively. The results show that EPR dosimetry with lithium formate provides dose estimates with a precision comparable to that of TL dosimetry (using lithium fluoride) for doses above 2 Gy, and that lithium formate is slightly less dependent on megavoltage photon beam energy than lithium fluoride.

Electron paramagnetic resonance (EPR) dosimetry using lithium formate in radiotherapy: comparison with thermoluminescence (TL) dosimetry using lithium fluoride rods

NASA Astrophysics Data System (ADS)

Vestad, Tor Arne; Malinen, Eirik; Rune Olsen, Dag; Olaug Hole, Eli; Sagstuen, Einar

2004-10-01

Solid-state radiation dosimetry by electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) was utilized for the determination of absorbed doses in the range of 0.5-2.5 Gy. The dosimeter materials used were lithium formate and lithium fluoride (TLD-100 rods) for EPR dosimetry and TL dosimetry, respectively. 60Co ggr-rays and 4, 6, 10 and 15 MV x-rays were employed. The main objectives were to compare the variation in dosimeter reading of the respective dosimetry systems and to determine the photon energy dependence of the two dosimeter materials. The EPR dosimeter sensitivity was constant over the dose range in question, while the TL sensitivity increased by more than 5% from 0.5 to 2.5 Gy, thus displaying a supralinear dose response. The average relative standard deviation in the dosimeter reading per dose was 3.0% and 1.2% for the EPR and TL procedures, respectively. For EPR dosimeters, the relative standard deviation declined significantly from 4.3% to 1.1% over the dose range in question. The dose-to-water energy response for the megavoltage x-ray beams relative to 60Co ggr-rays was in the range of 0.990-0.979 and 0.984-0.962 for lithium formate and lithium fluoride, respectively. The results show that EPR dosimetry with lithium formate provides dose estimates with a precision comparable to that of TL dosimetry (using lithium fluoride) for doses above 2 Gy, and that lithium formate is slightly less dependent on megavoltage photon beam energy than lithium fluoride.

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.

Asphaltenes as new objects for nanoelectronics

NASA Astrophysics Data System (ADS)

Dolomatov, M. Yu; Petrov, A. M.; Bakhtizin, R. Z.; Dolomatova, M. M.; Khairudinov, I. R.; Shutkova, S. A.; Kovaleva, E. A.; Paymurzina, N. Kh

2017-05-01

Abstract. Modern carbon nanomaterials (carbon nanotubes, graphenes, fullerenes, polycyclic molecules) are products of rather complicated technologies. Therefore development of new not expensive materials on the basis of natural substances, in particular high-molecular compounds of oil - asphaltenes, is actual for nanoelectronics. Asphaltenes are complex materials that are found in crude oil, bitumen and high-boiling hydrocarbons distillates. Usually asphaltenes are composed mainly of polyaromatic carbon with a small amount of vanadium and nickel, which are in porphyrin structures. Molecules of asphaltenes may contain 5-10-member benzene and naphthenic rings in their structure and also have paramagnetic centers. A variety of techniques: electronic phenomenological spectroscopy (EPS), atomic force microscopy (AFM) and quantum chemistry calculations were used to define the structure of oil asphaltenes. It was supposed that asphaltene fraction is a strong donor (ionization potential 4.10-6.70 eV) and an acceptor (electron affinity 1.80-2.50 eV). The structures of asphaltenes fragments were calculated by RHF-6-31G** methods. AFM images of asphaltenes obtained from crude oil showed the presence of structure fragments ranged from 3 to 10 nm, disposed to strong intermolecular interactions. We used doped compounds for formation of wide band gap amorphous semiconductors from a concentrates of asphaltens. Changes of conductivity in dispersed petroleum systems (DPS) were studied during a pyrolysis at 500 K. The numerous experiments defined of conductivity testify about phase transitions dielectric - semiconductor in DPS for range of 360 - 400 K. The main conclusion is paramagnetic phase of asphaltenes is organic amorphous wide band gap semiconductor. Besides this substance can be consider as an organic spin glasses.

A mass spectrometry and electron paramagnetic resonance study of photochemical and thermal aging of triterpenoid varnishes.

PubMed

Dietemann, P; Kälin, M; Zumbühl, S; Knochenmuss, R; Wülfert, S; Zenobi, R

2001-05-01

Photochemical and thermal aging of triterpenoid dammar and mastic resins used as varnishes on paintings were studied using graphite-assisted laser desorption/ionization mass spectrometry. This extends an earlier study on similar materials (Zumbühl et al., Anal. Chem. 1998, 70, 707-715) that focused on photoaging. Progressive aging results in development of groups of signals spaced by 14 and 16 Da, indicating incorporation of oxygen as well as simultaneous loss of hydrogen. Oligomers up to tetramers are formed, while cleavage reactions lead to increased signal intensities in the mass ranges between the oligomers and below the monomers. No major differences were found between the mass spectra of samples aged in light or darkness, except that deterioration was faster in light. Electron paramagnetic resonance spectroscopy revealed similar and significant amounts of radicals in films of dammar stored either in light or in darkness. It is concluded that oxidative radical reactions also take place in darkness and that differences in light and dark aging pathways are minor, although rates may differ. These findings lead to a unified explanation for yellowing of natural resin varnishes, one of the major degenerative changes in the appearance of paintings. It is also shown that the commercially available, nominally fresh resins are already in an advanced stage of oxidation and degradation. Energy-rich substances are formed upon irradiation with sunlight and are believed to restart the autoxidative chain reactions, regardless of storage conditions. As a result, varnishes are oxidized quite quickly (months) even when kept in darkness.

EPR Investigation of Gamma-Irradiated Rapana Thomasiana (Gastropoda, Muricidae) Shell

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

Seletchi, Emilia Dana; Duliu, Octavian G.; Georgescu, Rodica

2007-04-23

The shell of Rapana Thomasiana snail, a carnivorous gastropod collected from the coasts of the Black Sea (Romania) was investigated by using Electron Paramagnetic Resonance (EPR) spectroscopy. The samples in powder form were irradiated with a 60Co gamma-ray source at ambient temperature in the dose range between 1.06 and 11.3 kGy. The measurements showed that the EPR signal intensity enhanced following saturation exponential with the absorbed dose. The estimated EPR parameters: g1 = 1.9976, g2 = 2.0006, g3 = 2.0015, g4 = 2.0030 and g5 = 2.0043 revealed a complex spectrum consisting of CO{sub 2}{sup -}, CO{sub 3}{sup 3-} andmore » CO{sub 3}{sup -} species. A very weak signal at g6 = 2.0057 was associated to SO{sub 2}{sup -} electron center. All EPR signals of gamma-irradiated samples decreased with various rate with the of 100 deg. C isothermal annealing time.« less

Spectral methods for study of the G-protein-coupled receptor rhodopsin. II. Magnetic resonance methods

NASA Astrophysics Data System (ADS)

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

2016-02-01

This article continues our review of spectroscopic studies of G-protein-coupled receptors. Magnetic resonance methods including electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) provide specific structural and dynamical data for the protein in conjunction with optical methods (vibrational, electronic spectroscopy) as discussed in the accompanying article. An additional advantage is the opportunity to explore the receptor proteins in the natural membrane lipid environment. Solid-state 2H and 13C NMR methods yield information about both the local structure and dynamics of the cofactor bound to the protein and its light-induced changes. Complementary site-directed spin-labeling studies monitor the structural alterations over larger distances and correspondingly longer time scales. A multiscale reaction mechanism describes how local changes of the retinal cofactor unlock the receptor to initiate large-scale conformational changes of rhodopsin. Activation of the G-protein-coupled receptor involves an ensemble of conformational substates within the rhodopsin manifold that characterize the dynamically active receptor.

Role of doping and CuO segregation in improving the giant permittivity of CaCu{sub 3}Ti{sub 4}O{sub 12}

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

Capsoni, D.; CNR-IENI, Sezione di Pavia, viale Taramelli 16, 27100 Pavia; Bini, M.

2004-12-01

The dopant role on the electric and dielectric properties of the perovskite-type CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) compound is evidenced. Impedance spectroscopy measurements show that the relevant permittivity value attributed to sintered CCTO is due to grain boundary (g.b.) effects. The g.b. permittivity value of the pure CCTO can be increased of 1-2 orders of magnitude by cation substitution on Ti site and/or segregation of CuO phase, while the bulk permittivity keeps values 90{epsilon}r180. Bulk and g.b. conductivity contributions are discussed: electrons are responsible for the charge transport and a mean bulk activation energy of 0.07eV is obtained at roommore » temperature for all the examined samples. The g.b. activation energy ranges between 0.54 and 0.76eV. Defect models related to the transport properties are proposed, supported by electron paramagnetic resonance measurements.« less

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

Spatially resolved nuclear spin relaxation, electron spin relaxation and light absorption in swift heavy ion irradiated LiF crystals.

PubMed

Stork, H; Dinse, K-P; Ditter, M; Fujara, F; Masierak, W; Neumann, R; Schuster, B; Schwartz, K; Trautmann, C

2010-05-12

Spatially resolved (19)F and (7)Li spin-lattice relaxation rates are measured for LiF single crystals after irradiation with two kinds of swift heavy ions ((12)C of 133 MeV and (208)Pb of 1.78 GeV incident energy). Like in earlier studies on (130)Xe and (238)U irradiated LiF crystals, we found a strong enhancement of the nuclear spin-lattice relaxation rate within the ion penetration depth and a slight--but still significant--enhancement beyond. By evaluating the nuclear relaxation rate enhancement within the ion range after irradiation with different projectiles, a universal relationship between the spin-lattice relaxation rate and the dose is deduced. The results of accompanying X-band electron paramagnetic resonance relaxation measurements and optical absorption spectroscopy are included in a physical interpretation of this relationship. Also the reason for the enhanced relaxation rate beyond the ion range is further discussed.

Structural, mechanical, and magnetic properties of ferrite-austenite mixture in evaporated 304 stainless steel thin films

NASA Astrophysics Data System (ADS)

Merakeb, Noureddine; Messai, Amel; Djelloul, Abdelkader; Ayesh, Ahmad I.

2015-11-01

In this paper, we investigate the structure, composition, magnetic, and mechanical properties of stainless steel thin films formed by thermal evaporation technique. These thin films reveal novel structural and physical properties where they were found to consist of nanocrystals that are ~90 % body-centred cubic crystal structure which holds ferromagnetic properties (α-phase), and ~10 % face-centred cubic crystal structure which is paramagnetic at room temperature (γ-phase). The presence of the above phases was quantified by X-ray diffraction, transmission electron microscopy, and conversion electron Mössbauer spectroscopy. The magnetic properties were evaluated by a superconducting quantum interference device magnetometer, and they confirmed the dual-phase crystal structure of the stainless thin films, where the presence of γ-phase reduced the magnetization of the produced thin films. In addition, the fabricated stainless steel thin films did not contain micro-cracks, and they exhibit a tensile stress of about 1.7 GPa, hardness of 7.5 GPa, and elastic modulus of 104 GPa.

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.

Silver-Zinc Redox-Coupled Electroceutical Wound Dressing Disrupts Bacterial Biofilm

PubMed Central

Roy, Sashwati; Khanna, Savita; Hemann, Craig; Deng, Binbin; Das, Amitava; Zweier, Jay L.; Wozniak, Daniel; Sen, Chandan K.

2015-01-01

Pseudomonas aeruginosa biofilm is commonly associated with chronic wound infection. A FDA approved wireless electroceutical dressing (WED), which in the presence of conductive wound exudate gets activated to generate electric field (0.3–0.9V), was investigated for its anti-biofilm properties. Growth of pathogenic P. aeruginosa strain PAO1 in LB media was markedly arrested in the presence of the WED. Scanning electron microscopy demonstrated that WED markedly disrupted biofilm integrity in a setting where silver dressing was ineffective. Biofilm thickness and number of live bacterial cells were decreased in the presence of WED. Quorum sensing genes lasR and rhlR and activity of electric field sensitive enzyme, glycerol-3-phosphate dehydrogenase was also repressed by WED. This work provides first electron paramagnetic resonance spectroscopy evidence demonstrating that WED serves as a spontaneous source of reactive oxygen species. Redox-sensitive multidrug efflux systems mexAB and mexEF were repressed by WED. Taken together, these observations provide first evidence supporting the anti-biofilm properties of WED. PMID:25803639

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.

Radiation-Induced Damage to Nucleic Acid Constituents

NASA Astrophysics Data System (ADS)

Kim, Heasook

The objective of this research was to identify the primary free radical species produced by ionizing radiation in DNA. The ultimate goal would be to use these data obtained from model compounds to analyze radiation-induced damage in DNA itself. The different single crystals were studied in detail. The first was the sodium salt of guanosine-3 ^':5^' -cyclic monophosphate (cyclic GMP). The results of studies on crystals irradiated at 4.2^ circK distinguished two species. One of these species exhibited a non-exchangeable proton coupling that was characterized by ENDOR spectroscopy and shown to be sigma proton. The spin density on C8 was deduced from the ENDOR hyperfine coupling tensor and found to be 0.15. The second species also exhibited a non-exchangeable sigma proton coupling and a beta proton coupling. The spin densities on C8 and N9 were deduced from ENDOR measurements to be 0.09 and 0.36. The former is attributed to the oxidation product and the latter to the primary reduction product. These products are respectively the guanine cation and anion. The second single crystal studied was a sodium salt of 2^'-deoxyguanosine -5^'-monophosphate tetrahydrate. The ESR and ENDOR spectra obtained from this crystal after x-irradiation at 4.2^circK were complex and the paramagnetic species were tentatively identified as ionic species. The third DNA model compound studied was thymidine. Single crystal of thymidine were irradiated at 1.6^ circK and at 4.2^circ K. The lower temperature preserved a more primitive stage of the radiation damage process. ENDOR measurements distinguished three paramagnetic species. The most interesting component of the paramagnetic absorption in crystals irradiated at 1.6^circK is attributed to trapped electron. These electrons are stabilized by the electrostatic fields generated by hydroxy dipoles. The hyperfine couplings between the trapped electron and the proton of these polar groups were deduced from ENDOR measurements. The ESR and ENDOR measurements described in this report were carried out DNA model compounds x-irradiated and measured at lower temperatures than reported previously. The experiments have demonstrated that an earlier stage of radiation damage can sometimes be stabilized and characterized in single crystals by maintaining the sample at 1.4 ^circK. (Abstract shortened with permission of author.).

Cancer detection based on Raman spectra super-paramagnetic clustering

NASA Astrophysics Data System (ADS)

González-Solís, José Luis; Guizar-Ruiz, Juan Ignacio; Martínez-Espinosa, Juan Carlos; Martínez-Zerega, Brenda Esmeralda; Juárez-López, Héctor Alfonso; Vargas-Rodríguez, Héctor; Gallegos-Infante, Luis Armando; González-Silva, Ricardo Armando; Espinoza-Padilla, Pedro Basilio; Palomares-Anda, Pascual

2016-08-01

The clustering of Raman spectra of serum sample is analyzed using the super-paramagnetic clustering technique based in the Potts spin model. We investigated the clustering of biochemical networks by using Raman data that define edge lengths in the network, and where the interactions are functions of the Raman spectra's individual band intensities. For this study, we used two groups of 58 and 102 control Raman spectra and the intensities of 160, 150 and 42 Raman spectra of serum samples from breast and cervical cancer and leukemia patients, respectively. The spectra were collected from patients from different hospitals from Mexico. By using super-paramagnetic clustering technique, we identified the most natural and compact clusters allowing us to discriminate the control and cancer patients. A special interest was the leukemia case where its nearly hierarchical observed structure allowed the identification of the patients's leukemia type. The goal of this study is to apply a model of statistical physics, as the super-paramagnetic, to find these natural clusters that allow us to design a cancer detection method. To the best of our knowledge, this is the first report of preliminary results evaluating the usefulness of super-paramagnetic clustering in the discipline of spectroscopy where it is used for classification of spectra.

New Combustion Regimes and Kinetic Studies of Plasma Assisted Combustion

DTIC Science & Technology

2012-11-01

IR Faraday Rotational Spectroscopy Method to quantify HO2 29 30 Brian Brumfield, Wenting Sun, Gerard Wysock, and Yinguang Ju, submitted...to JACS, 2012 7.1 μm Mid infra-red Faraday Rotation Spectroscopy (FRS), 1396 cm-1 Quantitative HO2 Measurement (very challenging!): 2L + 1...paramagnetic species Polarization rotation detection Linearly-polarized laser light 610 Hz oscillating magnetic field 125 Gauss rms Sub-ppm level

Charge ordering transition in GdBaCo2O5: Evidence of reentrant behavior

NASA Astrophysics Data System (ADS)

Allieta, M.; Scavini, M.; Lo Presti, L.; Coduri, M.; Loconte, L.; Cappelli, S.; Oliva, C.; Ghigna, P.; Pattison, P.; Scagnoli, V.

2013-12-01

We present a detailed study on the charge ordering transition in a GdBaCo2O5.0 system by combining high-resolution synchrotron powder/single-crystal diffraction with electron paramagnetic resonance experiments as a function of temperature. We found a second-order structural phase transition at TCO = 247 K (Pmmm to Pmma) associated with the onset of long-range charge ordering. At Tmin ≈ 1.2TCO, the electron paramagnetic resonance linewidth rapidly broadens, providing evidence of antiferromagnetic spin fluctuations. This likely indicates that, analogously to manganites, the long-range antiferromagnetic order in GdBaCo2O5.0 sets in at ≈TCO. Pair distribution function analysis of diffraction data revealed signatures of structural inhomogeneities at low temperature. By comparing the average and local bond valences, we found that above TCO the local structure is consistent with a fully random occupation of Co2+ and Co3+ in a 1:1 ratio and with a complete charge ordering below TCO. Below T ≈ 100 K the charge localization is partially melted at the local scale, suggesting a reentrant behavior of charge ordering. This result is supported by the weakening of superstructure reflections and the temperature evolution of electron paramagnetic resonance linewidth that is consistent with paramagnetic reentrant behavior reported in the GdBaCo2O5.5 parent compound.

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.

Tailoring bifunctional hybrid organic–inorganic nanoadsorbents by the choice of functional layer composition probed by adsorption of Cu2+ ions

PubMed Central

Tomina, Veronika V; Melnyk, Inna V; Zub, Yuriy L; Kareiva, Aivaras; Vaclavikova, Miroslava; Kessler, Vadim G

2017-01-01

Spherical silica particles with bifunctional (≡Si(CH2)3NH2/≡SiCH3, ≡Si(CH2)3NH2/≡Si(CH2)2(CF2)5CF3) surface layers were produced by a one-step approach using a modified Stöber method in three-component alkoxysilane systems, resulting in greatly increased contents of functional components. The content of functional groups and thermal stability of the surface layers were analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and 13C and 29Si solid-state NMR spectroscopy revealing their composition and organization. The fine chemical structure of the surface in the produced hybrid adsorbent particles and the ligand distribution were further investigated by electron paramagnetic resonance (EPR) and electron spectroscopy of diffuse reflectance (ESDR) spectroscopy using Cu2+ ion coordination as a probe. The composition and structure of the emerging surface complexes were determined and used to provide an insight into the molecular structure of the surfaces. It was demonstrated that the introduction of short hydrophobic (methyl) groups improves the kinetic characteristics of the samples during the sorption of copper(II) ions and promotes fixation of aminopropyl groups on the surface of silica microspheres. The introduction of long hydrophobic (perfluoroctyl) groups changes the nature of the surface, where they are arranged in alternately hydrophobic/hydrophilic patches. This makes the aminopropyl groups huddled and less active in the sorption of metal cations. The size and aggregation/morphology of obtained particles was optimized controlling the synthesis conditions, such as concentrations of reactants, basicity of the medium, and the process temperature. PMID:28243572

Mononuclear Sulfido-Tungsten(V) Complexes: Completing the Tp*MEXY (M = Mo, W; E = O, S) Series.

PubMed

Sproules, Stephen; Eagle, Aston A; George, Graham N; White, Jonathan M; Young, Charles G

2017-05-01

Orange Tp*WSCl 2 has been synthesized from the reactions of Tp*WOCl 2 with boron sulfide in refluxing toluene or Tp*WS 2 Cl with PPh 3 in dichloromethane at room temperature. Mononuclear sulfido-tungsten(V) complexes, Tp*WSXY {X = Y = Cl, OPh, SPh, SePh; X = Cl, Y = OPh; XY = toluene-3,4-dithiolate (tdt), quinoxaline-2,3-dithiolate (qdt); and Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate} were prepared by metathesis of Tp*WSCl 2 with the respective alkali metal salt of X - /XY 2- , or [NHEt 3 ] 2 (qdt). The complexes were characterized by microanalysis, mass spectrometry, electrochemistry, and infrared (IR), electron paramagnetic resonance (EPR) and electronic absorption spectroscopies. The molecular structures of Tp*WS(OPh) 2 , Tp*WS(SePh) 2 , and Tp*WS(tdt) have been determined by X-ray crystallography. The six-coordinate, distorted-octahedral W centers are coordinated by terminal sulfido (W≡S = 2.128(2) - 2.161(1) Å), terdentate facial Tp*, and monodentate/bidentate O/S/Se-donor ligands. The sulfido-W(V) complexes are characterized by lower energy electronic transitions, smaller g iso , and larger A iso ( 183 W) values, and more positive reduction potentials compared with their oxo-W(V) counterparts. This series has been probed by sulfur K-edge X-ray absorption spectroscopy (XAS), the spectra being assigned by comparison to Tp*WOXY (X = Y = SPh; XY = tdt, qdt) and time-dependent density functional theoretical (TD-DFT) calculations. This study provides insight into the electronic nature and chemistry of the catalytically and biologically important sulfido-W unit.

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.

Energy transfer and tunable multicolor emission and paramagnetic properties of GdF3:Dy(3+),Tb(3+),Eu(3+) phosphors.

PubMed

Guan, Hongxia; Sheng, Ye; Xu, Chengyi; Dai, Yunzhi; Xie, Xiaoming; Zou, Haifeng

2016-07-20

A series of Dy(3+), Tb(3+), Eu(3+) singly or doubly or triply doped GdF3 phosphors were synthesized by a glutamic acid assisted one-step hydrothermal method. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) spectroscopy. The results show that the synthesized samples are all pure GdF3. The obtained samples have a peanut-like morphology with a diameter of about 270 nm and a length of about 600 nm. Under UV excitation, GdF3:Dy(3+), GdF3:Tb(3+) and GdF3:Eu(3+) samples exhibit strong blue, green and red emissions, respectively. By adjusting their relative doping concentrations in the GdF3 host, the different color hues of green and red light are obtained by co-doped Dy(3+), Tb(3+) and Tb(3+), Eu(3+) ions in the GdF3 host, respectively. Besides, there exist two energy transfer pairs in the GdF3 host: (1) Dy(3+) → Tb(3+) and (2) Tb(3+) → Eu(3+). More significantly, in the Dy(3+), Tb(3+), and Eu(3+) tri-doped GdF3 phosphors, white light can also be achieved upon excitation of UV light by adjusting the doping concentration of Eu(3+). In addition, the obtained samples also exhibit paramagnetic properties at room temperature (300 K) and low temperature (2 K). It is obvious that multifunctional Dy(3+), Tb(3+), Eu(3+) tri-doped GdF3 materials including tunable multicolors and intrinsic paramagnetic properties may have potential applications in the field of full-color displays.

Microstructural Investigation, Raman and Magnetic Studies on Chemically Synthesized Nanocrystalline Ni-Doped Gadolinium Oxide (Gd1.90Ni0.10O3- δ )

NASA Astrophysics Data System (ADS)

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

2018-03-01

Nanocrystalline Ni-doped gadolinium oxide (Gd1.90Ni0.10O3- δ , GNO) is synthesized by co-precipitation method. The as-prepared sample is annealed in vacuum at 700°C for 6 h. Analyses of the x-ray diffractogram by Rietveld refinement method, transmission electron microscopy and Raman spectroscopy of GNO recorded at room temperature confirmed the pure crystallographic phase and complete substitution of Ni-ions in Gd2O3 lattice. Magnetization ( M) as a function of temperature ( T) and magnetic field ( H) is measured by a superconducting quantum interference device magnetometer, which suggests the presence of ferromagnetic/antiferromagnetic phases together with a paramagnetic phase. From the M-T curve it can be shown that the ferromagnetic phase dominates over para-/antiferromagnetic phases in the temperature range of 300-100 K, but from 100 K to 50 K, the antiferromagnetic phase dominates over ferro-/paramagnetic phases. Hysteresis loops recorded at different temperatures indicate the presence of weak ferro-/antiferromagnetism, which dominates in the low field region (˜ 4000 Oe), above which magnetization increases linearly. The sharp increase of magnetization in M-T curve observed in the temperature range of 50-5 K confirms the presence of dominating ferromagnetic plus paramagnetic phase over antiferromagnetic part. For the first time a combined formula generated from three-dimensional (3D) spin wave model and Johnston formula is proposed to analyze the coexistence of different magnetic phases in different temperature ranges. Interestingly, the combined formula successfully explains the co-existence of different magnetic phases along with their contribution at different temperatures. The onset of ferromagnetism in Gd1.90Ni0.10O3- δ is explained by oxygen vacancy mediated F-centre exchange (FCE) coupling mechanism.

Electron spin-echo techniques for the study of protein motion

NASA Astrophysics Data System (ADS)

Kar, Leela; Johnson, Michael E.; Bowman, Michael K.

Electron spin-echo (ESE) spectroscopy has been used to make the first direct measurements of spin-spin relaxation times of a spin-labeled protein at physiological temperatures. Results from experiments using maleimide-labeled deoxygenated hemoglobin (dHb) from individuals homozygous for sickle cell anemia (dHbS) have been compared with those from control experiments using dHb from normal adults (dHbA). Hb "immobilized" by ammonium sulfate precipitation and by siloxane polymer entrapment have been studied for a suitable "rigid" reference. Two-dimensional ESE (2D-ESE) experiments have been performed using all of these systems. The 2D contour plots show that 2D-ESE is sensitive to the slow motion of dHbS polymers and can differentiate it from both that of immobilized Hb and of HbA molecules in solution at the same temperature and concentration. More importantly, the 2D-ESE technique enables one to select for slower motion and thereby extract the dHbS polymer signal from the total signal generated by the heterogeneous system containing dHbS molecules in solution as well as in the polymer. Computer simulations using current slow motional theories show that detailed motional and structural information may be obtained by such studies. The considerable potential of 2D-ESE spectroscopy in the study of macromolecular motion is illustrated by comparing 2D-ESE with the nonlinear technique of saturation transfer electron paramagnetic resonance.

Electronic structure and spectroscopic properties of mononuclear manganese(III) Schiff base complexes: a systematic study on [Mn(acen)X] complexes by EPR, UV/vis, and MCD spectroscopy (X = Hal, NCS).

PubMed

Westphal, Anne; Klinkebiel, Arne; Berends, Hans-Martin; Broda, Henning; Kurz, Philipp; Tuczek, Felix

2013-03-04

The manganese(III) Schiff base complexes [Mn(acen)X] (H2acen: N,N'-ethylenebis(acetylacetone)imine, X: I(-), Br(-), Cl(-), NCS(-)) are considered as model systems for a combined study of the electronic structure using vibrational, UV/vis absorption, parallel-mode electron paramagnetic resonance (EPR) and low-temperature magnetic circular dichroism (MCD) spectroscopy. By variation of the co-ligand X, the influence of the axial ligand field within a given square-pyramidal coordination geometry on the UV/vis, EPR, and MCD spectra of the title compounds is investigated. Between 25000 and 35000 cm(-1), the low-temperature MCD spectra are dominated by two very intense, oppositely signed pseudo-A terms, referred to as "double pseudo-A terms", which change their signs within the [Mn(acen)X] series dependent on the axial ligand X. Based on molecular orbital (MO) and symmetry considerations, these features are assigned to π(n.b.)(s, a) → yz, z(2) ligand-to-metal charge transfer transitions. The individual MCD signs are directly determined from the calculated MOs of the [Mn(acen)X] complexes. The observed sign change is explained by an inversion of symmetry among the π(n.b.)(s, a) donor orbitals which leads to an interchange of the positive and negative pseudo-A terms constituting the "double pseudo-A term".

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.

Structural Changes Correlated with Magnetic Spin State Isomorphism in the S2 State of the Mn4CaO5 Cluster in the Oxygen-Evolving Complex of Photosystem II

PubMed Central

Chatterjee, Ruchira; Han, Guangye; Kern, Jan; Gul, Sheraz; Fuller, Franklin D.; Garachtchenko, Anna; Young, Iris; Weng, Tsu-Chien; Nordlund, Dennis; Alonso-Mori, Roberto; Bergmann, Uwe; Sokaras, Dimosthenis; Hatakeyama, Makoto; Yachandra, Vittal K.; Yano, Junko

2016-01-01

The Mn4CaO5 cluster in Photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (Si, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in the S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. Such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis. PMID:28044099

Structural changes correlated with magnetic spin state isomorphism in the S 2 state of the Mn 4CaO 5 cluster in the oxygen-evolving complex of photosystem II

DOE PAGES

Chatterjee, Ruchira; Han, Guangye; Kern, Jan; ...

2016-05-09

The Mn 4CaO 5 cluster in photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (S i, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in themore » S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. As a result, such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis.« less

TCNQ molecular semiconductor of the Cu(II)TAAB macrocycle: Optical and electrical properties.

PubMed

Sánchez Vergara, M E; Salcedo, R; Molina, Bertha; Carrera-Téllez, R; Álvarez-Bada, J R; Hernández-García, A; Gómez-Vidales, V

2018-07-05

The present study reports the doping of a semiconducting molecular material through the formation of hydrogen bonds between the macrocycle Cu(II)(TAAB) and the electronic acceptor TCNQ. According to density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) analysis, the doped compound has the shape of a distorted square pyramid, with four nitrogen atoms in the equatorial position and the apical oxygen atom from the water ligands. These water molecules can generate strong hydrogen bonds with TCNQ and the TAAB metallic complex. Thin films of copper molecular material were obtained through high vacuum evaporation and were structurally characterized by IR spectroscopy, EPR and scanning electron microscopy (SEM). Additionally, the absorption coefficient (α) and photon energy (hν) were calculated from UV-vis spectroscopy and used to determine the optical activation energy in each film, from which its semiconducting behavior was established. An important aspect to consider is that the presence of hydrogen bonds is essential to establish the semiconducting nature of these species; this chemical behavior, as well as the resulting electronic mobility, have been studied by DFT theoretical calculations, which reinforce the experimental conclusion of a relationship between Cu(II)TAAB and TCNQ moieties generated by a weak bond. Finally, I-V characteristics have been obtained from a glass/ITO/doped molecular semiconductor/Ag device using Ag and ITO electrodes. Results for the copper-based device show that, at low voltages, the conduction process is of an ohmic nature while, at higher voltages, space-charge-limited current (SCLC) is found. It is highly probable that the doping effect in TCNQ favors electronic transport due to the formation of conduction channels caused by dopant-favored anisotropy. Copyright © 2018 Elsevier B.V. All rights reserved.

Magnetic properties of point defects in proton irradiated diamond

NASA Astrophysics Data System (ADS)

Makgato, T. N.; Sideras-Haddad, E.; Ramos, M. A.; García-Hernández, M.; Climent-Font, A.; Zucchiatti, A.; Muñoz-Martin, A.; Shrivastava, S.; Erasmus, R.

2016-09-01

We investigate the magnetic properties of ultra-pure type-IIa diamond following irradiation with proton beams of ≈1-2 MeV energy. SQUID magnetometry indicate the formation of Curie type paramagnetism according to the Curie law. Raman and Photoluminescence spectroscopy measurements show that the primary structural features created by proton irradiation are the centers: GR1, ND1, TR12 and 3H. The Stopping and Range of Ions in Matter (SRIM) Monte Carlo simulations together with SQUID observations show a strong correlation between vacancy production, proton fluence and the paramagnetic factor. At an average surface vacancy spacing of ≈1-1.6 nm and bulk (peak) vacancy spacing of ≈0.3-0.5 nm Curie paramagnetism is induced by formation of ND1 centres with an effective magnetic moment μeff~(0.1-0.2)μB. No evidence of long range magnetic ordering is observed in the temperature range 4.2-300 K.

Spectroscopic, structural and computational analysis of [Re(CO)3(dippM)Br](n+) (dippM = 1,1'-bis(diiso-propylphosphino)metallocene, M = Fe, n = 0 or 1; M = Co, n = 1).

PubMed

Furneaux, Aliza G; Piro, Nicholas A; Hernández Sánchez, Raúl; Gramigna, Kathryn M; Fey, Natalie; Robinson, Michael J; Kassel, W Scott; Nataro, Chip

2016-03-21

While the redox active backbone of bis(phosphino)ferrocene ligands is often cited as an important feature of these ligands in catalytic studies, the structural parameters of oxidized bis(phosphino)ferrocene ligands have not been thoroughly studied. The reaction of [Re(CO)3(dippf)Br] (dippf = 1,1'-bis(diiso-propylphosphino)ferrocene) and [NO][BF4] in methylene chloride yields the oxidized compound, [Re(CO)3(dippf)Br][BF4]. The oxidized species, [Re(CO)3(dippf)Br][BF4], and the neutral species, [Re(CO)3(dippf)Br], are compared using X-ray crystallography, cyclic voltammetry, visible spectroscopy, IR spectroscopy and zero-field (57)Fe Mössbauer spectroscopy. In addition, the magnetic moment of the paramagnetic [Re(CO)3(dippf)Br][BF4] was measured in the solid state using SQUID magnetometry and in solution by the Evans method. The electron transfer reaction of [Re(CO)3(dippf)Br][BF4] with acetylferrocene was also examined. For additional comparison, the cationic compound, [Re(CO)3(dippc)Br][PF6] (dippc = 1,1'-bis(diiso-propylphosphino)cobaltocenium), was prepared and characterized by cyclic voltammetry, X-ray crystallography, and NMR, IR and visible spectroscopies. Finally, DFT was employed to examine the oxidized dippf ligand and the oxidized rhenium complex, [Re(CO)3(dippf)Br](+).

Dipicolinic Acid Derivatives as Inhibitors of New Delhi Metallo-β-lactamase-1.

PubMed

Chen, Allie Y; Thomas, Pei W; Stewart, Alesha C; Bergstrom, Alexander; Cheng, Zishuo; Miller, Callie; Bethel, Christopher R; Marshall, Steven H; Credille, Cy V; Riley, Christopher L; Page, Richard C; Bonomo, Robert A; Crowder, Michael W; Tierney, David L; Fast, Walter; Cohen, Seth M

2017-09-14

The efficacy of β-lactam antibiotics is threatened by the emergence and global spread of metallo-β-lactamase (MBL) mediated resistance, specifically New Delhi metallo-β-lactamase-1 (NDM-1). By utilization of fragment-based drug discovery (FBDD), a new class of inhibitors for NDM-1 and two related β-lactamases, IMP-1 and VIM-2, was identified. On the basis of 2,6-dipicolinic acid (DPA), several libraries were synthesized for structure-activity relationship (SAR) analysis. Inhibitor 36 (IC 50 = 80 nM) was identified to be highly selective for MBLs when compared to other Zn(II) metalloenzymes. While DPA displayed a propensity to chelate metal ions from NDM-1, 36 formed a stable NDM-1:Zn(II):inhibitor ternary complex, as demonstrated by 1 H NMR, electron paramagnetic resonance (EPR) spectroscopy, equilibrium dialysis, intrinsic tryptophan fluorescence emission, and UV-vis spectroscopy. When coadministered with 36 (at concentrations nontoxic to mammalian cells), the minimum inhibitory concentrations (MICs) of imipenem against clinical isolates of Eschericia coli and Klebsiella pneumoniae harboring NDM-1 were reduced to susceptible levels.

Reactive oxygen species mediate growth and death in submerged plants

PubMed Central

Steffens, Bianka; Steffen-Heins, Anja; Sauter, Margret

2013-01-01

Aquatic and semi-aquatic plants are well adapted to survive partial or complete submergence which is commonly accompanied by oxygen deprivation. The gaseous hormone ethylene controls a number of adaptive responses to submergence including adventitious root growth and aerenchyma formation. Reactive oxygen species (ROS) act as signaling intermediates in ethylene-controlled submergence adaptation and possibly also independent of ethylene. ROS levels are controlled by synthesis, enzymatic metabolism, and non-enzymatic scavenging. While the actors are by and large known, we still have to learn about altered ROS at the subcellular level and how they are brought about, and the signaling cascades that trigger a specific response. This review briefly summarizes our knowledge on the contribution of ROS to submergence adaptation and describes spectrophotometrical, histochemical, and live cell imaging detection methods that have been used to study changes in ROS abundance. Electron paramagnetic resonance (EPR) spectroscopy is introduced as a method that allows identification and quantification of specific ROS in cell compartments. The use of advanced technologies such as EPR spectroscopy will be necessary to untangle the intricate and partially interwoven signaling networks of ethylene and ROS. PMID:23761805

Novel homo- and heterobinuclear ball-type phthalocyanines: synthesis and electrochemical, electrical, EPR and MCD spectral properties.

PubMed

Odabaş, Zafer; Dumludağ, Fatih; Ozkaya, Ali Riza; Yamauchi, Seigo; Kobayashi, Nagao; Bekaroğlu, Ozer

2010-09-21

The mononuclear Fe(II) phthalocyanine 2 and ball-type homobinuclear Fe(II)-Fe(II) and Cu(II)-Cu(II) phthalocyanines, 3 and 4 respectively, were synthesized from the corresponding 4,4'-[1,1'-methylenebis-(naphthalene-2,1-diyl)]bis(oxy)diphthalonitrile 1, and then ball-type heterobinuclear Fe(II)-Cu(II) phthalocyanine 5 was synthesized from 2. The novel compounds 4 and 5 have been characterized by elemental analysis, UV/vis, IR and MALDI-TOF mass spectroscopies. Electron paramagnetic resonance and magnetic circular dichroism measurements of 3, 4 and 5 were also examined. The voltammetric measurements of the complexes showed the formation of various electrochemically stable ligand- and metal-based mixed-valence species, due to the intramolecular interactions between the two MPc units, especially in ball-type binuclear iron(II) phthalocyanine. Impedance spectroscopy and d.c. conductivity measurements of 4 and 5 were performed as a function of temperature (295-523 K) and frequency (40-10(5) Hz). While room temperature impedance spectra consist of a curved line, a transformation into a full semicircle with increasing temperature was observed for both compounds.

Gold atoms and clusters on MgO(100) films; an EPR and IRAS study

NASA Astrophysics Data System (ADS)

Yulikov, M.; Sterrer, M.; Risse, T.; Freund, H.-J.

2009-06-01

Single gold atoms deposited on single crystalline MgO(1 0 0) films grown on Mo(1 0 0) are characterized by electron paramagnetic resonance spectroscopy as well as IR spectroscopy using CO as probe molecules. In this article we describe the first angular dependent measurements to determine the principal hyperfine components of a secondary hyperfine interaction, namely, with 17O of the MgO. The values determined here are in perfect agreement with theoretical expectations and corroborate the previously reported binding mechanism of Au atoms on the oxygen anions of the MgO terrace. The temperature dependent EPR data reveal an onset of Au atom mobility at about 80 K while the formation of Au particles occurs only above 125 K. By an analysis of the EPR line width in combination with STM measurements it is possible to deduce an increase of the interatomic distance above 80 K. The Au/CO complexes show a somewhat smaller temperature stability as compared to the Au atoms. The observed thermal stability is in perfect agreement with theoretical predictions for CO desorption.

A Radical Pathway for Organic Phosphorylation during Schreibersite Corrosion with Implications for the Origin of Life

NASA Technical Reports Server (NTRS)

Pasek, Matthew A.; Dworkin, Jason P.; Lauretta, Dante S.

2007-01-01

Phosphorylated compounds (e.g. DNA, RNA, phospholipids, and many coenzymes) are critical to biochemistry. Thus, their origin is of prime interest to origin of life studies. The corrosion of the meteoritic mineral schreibersite ((Fe,Ni)3P) may have significantly contributed to the origin of phosphorylated biomolecules. Corrosion of synthetic schreibersite in a variety of solutions was analyzed by nuclear magnetic resonance spectroscopy, mass spectrometry, and electron paramagnetic resonance spectroscopy. These methods suggest a radical reaction pathway for the corrosion of schreibersite to form phosphite radicals (raised dot PO3 sup 2-)) aqueous solution. These radicals can form activated polyphosphates and can phosphorylate organic compounds such as acetate (3% yield). Phosphonates (O3P-C) are found in the organic P inventory of the carbonaceous meteorite Murchison. While phosphonates are rare in biochemistry, the ubiquity of corroding iron meteorites on the early Earth could have provided an accessible source of organophosphorous for the origin of life allowing the invention of the organophosphates in modern biology as a product of early evolution.

Abiotic Protein Fragmentation by Manganese Oxide: Implications for a Mechanism to Supply Soil Biota with Oligopeptides.

PubMed

Reardon, Patrick N; Chacon, Stephany S; Walter, Eric D; Bowden, Mark E; Washton, Nancy M; Kleber, Markus

2016-04-05

The ability of plants and microorganisms to take up organic nitrogen in the form of free amino acids and oligopeptides has received increasing attention over the last two decades, yet the mechanisms for the formation of such compounds in soil environments remain poorly understood. We used Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopies to distinguish the reaction of a model protein with a pedogenic oxide (Birnessite, MnO2) from its response to a phyllosilicate (Kaolinite). Our data demonstrate that birnessite fragments the model protein while kaolinite does not, resulting in soluble peptides that would be available to soil biota and confirming the existence of an abiotic pathway for the formation of organic nitrogen compounds for direct uptake by plants and microorganisms. The absence of reduced Mn(II) in the solution suggests that birnessite acts as a catalyst rather than an oxidant in this reaction. NMR and EPR spectroscopies are shown to be valuable tools to observe these reactions and capture the extent of protein transformation together with the extent of mineral response.

EPR studies of free radicals in A-2058 human melanoma cells treated by valproic acid and 5,7-dimethoxycoumarin.

PubMed

Zdybel, Magdalena; Chodurek, Ewa; Pilawa, Barbara

2014-01-01

Free radicals in A-2058 human melanoma cells were studied by the use of electron paramagnetic resonance (EPR) spectroscopy. The aim of this work was to determine the changes in relative free radical concentrations in tumor A-2058 cells after treatment by valproic acid (VPA) and 5,7-dimethoxycoumarin (DMC). The influences of VPA and DMC on free radicals in A-2058 cells were compared with those for human melanoma malignum A-375 and G-361 cells, which were tested by us earlier. Human malignant melanoma A-2058 cells were exposed to interactions with VPA, DMC, and both VPA and DMC. The tumor cells A-2058 were purchased from LGC Standards (Lomianki, Poland), and they were grown in the standard conditions: at 37°C and in an atmosphere containing 95% air and 5% CO2, in the Minimum Essential Medium Eagle (MEM, Sigma-Aldrich). The A-2058 cells were incubated with VPA (1 mM) and DMC (10 μM) for 4 days. The first-derivative EPR spectra of the control A-2058 cells, and the cells treated with VPA, DMC, and both VPA and DMC, were measured by the electron paramagnetic resonance spectrometer of Radiopan (Poznań, Poland) with microwaves from an X-band (9.3 GHz). The parameters of the EPR lines: amplitudes (A), integral intensities (I), line widths (ΔBpp), and g-factors, were analyzed. The changes of amplitudes and line widths with microwave power increasing from 2.2 to 70 mW were drawn evaluated, o-Semiquinone free radicals of melanin biopolymer are mainly responsible for the EPR lines of A-2058 melanoma malignum cells. The amounts of free radicals in A-2058 cells treated with VPA, and both VPA and DMC, were lower than in the untreated control cells. Application of the tested substances (VPA, and both VPA and DMC) as the antitumor compounds was discussed. DMC without VPA did not decrease free radicals concentration in A-2058 cells. The studies con-firmed that EPR spectroscopy may be used to examine interactions of free radicals with antitumor compounds.

Hyperoxic sheep pulmonary microvascular endothelial cells generate free radicals via mitochondrial electron transport.

PubMed Central

Sanders, S P; Zweier, J L; Kuppusamy, P; Harrison, S J; Bassett, D J; Gabrielson, E W; Sylvester, J T

1993-01-01

Free radical generation by hyperoxic endothelial cells was studied using electron paramagnetic resonance (EPR) spectroscopy and the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Studies were performed to determine the radical species produced, whether mitochondrial electron transport was involved, and the effect of the radical generation on cell mortality. Sheep pulmonary microvascular endothelial cell suspensions exposed to 100% O2 for 30 min exhibited prominent DMPO-OH and, occasionally, additional smaller DMPO-R signals thought to arise from the trapping of superoxide anion (O2-.), hydroxyl (.OH), and alkyl (.R) radicals. Superoxide dismutase (SOD) quenched both signals suggesting that the observed radicals were derived from O2-.. Studies with deferoxamine suggested that the generation of .R occurred secondary to the formation of .OH from O2-. via an iron-mediated Fenton reaction. Blocking mitochondrial electron transport with rotenone (20 microM) markedly decreased radical generation. Cell mortality increased slightly in oxygen-exposed cells. This increase was not significantly altered by SOD or deferoxamine, nor was it different from the mortality observed in air-exposed cells. These results suggest that endothelial cells exposed to hyperoxia for 30 min produce free radicals via mitochondrial electron transport, but under the conditions of these experiments, this radical generation did not appear cause cell death. PMID:8380815

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.

Paramagnetic dysprosium-doped zinc oxide thin films grown by pulsed-laser deposition

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

Lo, Fang-Yuh, E-mail: fangyuhlo@ntnu.edu.tw; Ting, Yi-Chieh; Chou, Kai-Chieh

2015-06-07

Dysprosium(Dy)-doped zinc oxide (Dy:ZnO) thin films were fabricated on c-oriented sapphire substrate by pulsed-laser deposition with doping concentration ranging from 1 to 10 at. %. X-ray diffraction (XRD), Raman-scattering, optical transmission spectroscopy, and spectroscopic ellipsometry revealed incorporation of Dy into ZnO host matrix without secondary phase. Solubility limit of Dy in ZnO under our deposition condition was between 5 and 10 at. % according to XRD and Raman-scattering characteristics. Optical transmission spectroscopy and spectroscopic ellipsometry also showed increase in both transmittance in ultraviolet regime and band gap of Dy:ZnO with increasing Dy density. Zinc vacancies and zinc interstitials were identified by photoluminescencemore » spectroscopy as the defects accompanied with Dy incorporation. Magnetic investigations with a superconducting quantum interference device showed paramagnetism without long-range order for all Dy:ZnO thin films, and a hint of antiferromagnetic alignment of Dy impurities was observed at highest doping concentration—indicating the overall contribution of zinc vacancies and zinc interstitials to magnetic interaction was either neutral or toward antiferromagnetic. From our investigations, Dy:ZnO thin films could be useful for spin alignment and magneto-optical applications.« less

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

Combining EPR spectroscopy and X-ray crystallography to elucidate the structure and dynamics of conformationally constrained spin labels in T4 lysozyme single crystals.

PubMed

Consentius, Philipp; Gohlke, Ulrich; Loll, Bernhard; Alings, Claudia; Heinemann, Udo; Wahl, Markus C; Risse, Thomas

2017-08-09

Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling is used to investigate the structure and dynamics of conformationally constrained spin labels in T4 lysozyme single crystals. Within a single crystal, the oriented ensemble of spin bearing moieties results in a strong angle dependence of the EPR spectra. A quantitative description of the EPR spectra requires the determination of the unit cell orientation with respect to the sample tube and the orientation of the spin bearing moieties within the crystal lattice. Angle dependent EPR spectra were analyzed by line shape simulations using the stochastic Liouville equation approach developed by Freed and co-workers and an effective Hamiltonian approach. The gain in spectral information obtained from the EPR spectra of single crystalline samples taken at different frequencies, namely the X-band and Q-band, allows us to discriminate between motional models describing the spectra of isotropic solutions similarly well. In addition, it is shown that the angle dependent single crystal spectra allow us to identify two spin label rotamers with very similar side chain dynamics. These results demonstrate the utility of single crystal EPR spectroscopy in combination with spectral line shape simulation techniques to extract valuable dynamic information not readily available from the analysis of isotropic systems. In addition, it will be shown that the loss of electron density in high resolution diffraction experiments at room temperature does not allow us to conclude that there is significant structural disorder in the system.

Microwave-assisted synthesis of iron oxide nanoparticles in biocompatible organic environment

NASA Astrophysics Data System (ADS)

Aivazoglou, E.; Metaxa, E.; Hristoforou, E.

2018-04-01

The development of magnetite and maghemite particles in uniform nanometer size has triggered the interest of the research community due to their many interesting properties leading to a wide range of applications, such as catalysis, nanomedicine-nanobiology and other engineering applications. In this study, a simple, time-saving and low energy-consuming, microwave-assisted synthesis of iron oxide nanoparticles, is presented. The nanoparticles were prepared by microwave-assisted synthesis using polyethylene glycol (PEG) or PEG and β-cyclodextrin (β-CD)/water solutions of chloride salts of iron in the presence of ammonia solution. The prepared nano-powders were characterized using X-Ray Diffraction (XRD), Transition Electron Microscopy (TEM), Fourier-transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, Vibrating Sample Magnetometer (VSM), X-Ray Photoelectron Spectroscopy (XPS) and Thermal analysis (TG/DSC). The produced nanoparticles are crystallized mostly in the magnetite and maghemite lattice exhibiting very similar shape and size, with indications of partial PEG coating. Heating time, microwave power and presence of PEG, are the key factors shaping the size properties of nanoparticles. The average size of particles ranges from 10.3 to 19.2 nm. The nanoparticles exhibit a faceted morphology, with zero contamination levels. The magnetic measurements indicate that the powders are soft magnetic materials with negligible coercivity and remanence, illustrating super-paramagnetic behavior.

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.

Determining the Orientation and Localization of Membrane-Bound Peptides

PubMed Central

Hohlweg, Walter; Kosol, Simone; Zangger, Klaus

2012-01-01

Many naturally occurring bioactive peptides bind to biological membranes. Studying and elucidating the mode of interaction is often an essential step to understand their molecular and biological functions. To obtain the complete orientation and immersion depth of such compounds in the membrane or a membrane-mimetic system, a number of methods are available, which are separated in this review into four main classes: solution NMR, solid-state NMR, EPR and other methods. Solution NMR methods include the Nuclear Overhauser Effect (NOE) between peptide and membrane signals, residual dipolar couplings and the use of paramagnetic probes, either within the membrane-mimetic or in the solvent. The vast array of solid state NMR methods to study membrane-bound peptide orientation and localization includes the anisotropic chemical shift, PISA wheels, dipolar waves, the GALA, MAOS and REDOR methods and again the use of paramagnetic additives on relaxation rates. Paramagnetic additives, with their effect on spectral linewidths, have also been used in EPR spectroscopy. Additionally, the orientation of a peptide within a membrane can be obtained by the anisotropic hyperfine tensor of a rigidly attached nitroxide label. Besides these magnetic resonance techniques a series of other methods to probe the orientation of peptides in membranes has been developed, consisting of fluorescence-, infrared- and oriented circular dichroism spectroscopy, colorimetry, interface-sensitive X-ray and neutron scattering and Quartz crystal microbalance. PMID:22044140

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.

Semiconductor-insulator transition in a YbB6 nanowire with boron vacancy

NASA Astrophysics Data System (ADS)

Han, Wei; Wang, Zhen; Li, Qidong; Lian, Xin; Liu, Xudong; Fan, Qinghua; Zhao, Yanming

2018-06-01

In this paper, we report the study of transport and magnetic properties of ytterbium hexaboride (YbB6) nanowires grown by a low trigger-temperature (200-240 °C) solid state method. The temperature dependence of resistivity shows that the YbB6 nanowire undergoes a semiconductor-insulator transition (SIT) below 20 K with an activation energy ΔE of 1 meV. The value of ρ at 2 K reaches 49 times the value of ρ at 300 K (ρ2 K/ρ300 K = 49). The observed non-saturating magnetoresistance (MR) has a linear relationship with B2. The anomalous electronic transport in the YbB6 nanowire can be explained by the mixed valence of Yb ions due to the boron deficiency supporting by the X-ray photoelectron spectroscopy (XPS) and paramagnetic magnetization.

Cerebral formation of free radicals during hypoxia does not cause structural damage and is associated with a reduction in mitochondrial PO2; evidence of O2-sensing in humans?

PubMed

Bailey, Damian M; Taudorf, Sarah; Berg, Ronan M G; Lundby, Carsten; Pedersen, Bente K; Rasmussen, Peter; Møller, Kirsten

2011-04-01

Cellular hypoxia triggers a homeostatic increase in mitochondrial free radical signaling. In this study, blood was obtained from the radial artery and jugular venous bulb in 10 men during normoxia and 9  hours hypoxia (12.9% O(2)). Mitochondrial oxygen tension (p(O(2))(mit)) was derived from cerebral blood flow and blood gases. The ascorbate radical (A(•-)) was detected by electron paramagnetic resonance spectroscopy and neuron-specific enolase (NSE), a biomarker of neuronal injury, by enzyme-linked immunosorbent assay. Hypoxia increased the cerebral output of A(•-) in proportion to the reduction in p(O(2))(mit), but did not affect NSE exchange. These findings suggest that neuro-oxidative stress may constitute an adaptive response.

Water Oxidation Catalysis by Co(II) Impurities in Co(III) 4O 4 Cubanes

DOE PAGES

Ullman, Andrew M.; Liu, Yi; Huynh, Michael; ...

2014-11-18

Here, the observed water oxidation activity of the compound class Co 4O 4(OAc) 4(Py–X) 4 emanates from a Co(II) impurity. This impurity is oxidized to produce the well-known Co-OEC heterogeneous cobaltate catalyst, which is an active water oxidation catalyst. We present results from electron paramagnetic resonance spectroscopy, nuclear magnetic resonance line broadening analysis, and electrochemical titrations to establish the existence of the Co(II) impurity as the major source of water oxidation activity that has been reported for Co 4O 4 molecular cubanes. Differential electrochemical mass spectrometry is used to characterize the fate of glassy carbon at water oxidizing potentials andmore » demonstrate that such electrode materials should be used with caution for the study of water oxidation catalysis.« less

Time-resolved EPR spectroscopy in a Unix environment.

PubMed

Lacoff, N M; Franke, J E; Warden, J T

1990-02-01

A computer-aided time-resolved electron paramagnetic resonance (EPR) spectrometer implemented under version 2.9 BSD Unix was developed by interfacing a Varian E-9 EPR spectrometer and a Biomation 805 waveform recorder to a PDP-11/23A minicomputer having MINC A/D and D/A capabilities. Special problems with real-time data acquisition in a multiuser, multitasking Unix environment, addressing of computer main memory for the control of hardware devices, and limitation of computer main memory were resolved, and their solutions are presented. The time-resolved EPR system and the data acquisition and analysis programs, written entirely in C, are described. Furthermore, the benefits of utilizing the Unix operating system and the C language are discussed, and system performance is illustrated with time-resolved EPR spectra of the reaction center cation in photosystem 1 of green plant photosynthesis.

Biogenic Mn-Oxides in Subseafloor Basalts

PubMed Central

Ivarsson, Magnus; Broman, Curt; Gustafsson, Håkan; Holm, Nils G.

2015-01-01

The deep biosphere of the subseafloor basalts is recognized as a major scientific frontier in disciplines like biology, geology, and oceanography. Recently, the presence of fungi in these environments has involved a change of view regarding diversity and ecology. Here, we describe fossilized fungal communities in vugs in subseafloor basalts from a depth of 936.65 metres below seafloor at the Detroit Seamount, Pacific Ocean. These fungal communities are closely associated with botryoidal Mn oxides composed of todorokite. Analyses of the Mn oxides by Electron Paramagnetic Resonance spectroscopy (EPR) indicate a biogenic signature. We suggest, based on mineralogical, morphological and EPR data, a biological origin of the botryoidal Mn oxides. Our results show that fungi are involved in Mn cycling at great depths in the seafloor and we introduce EPR as a means to easily identify biogenic Mn oxides in these environments. PMID:26107948

Chiral Spin Texture in the Charge-Density-Wave Phase of the Correlated Metallic Pb /Si (111 ) Monolayer

NASA Astrophysics Data System (ADS)

Tresca, C.; Brun, C.; Bilgeri, T.; Menard, G.; Cherkez, V.; Federicci, R.; Longo, D.; Debontridder, F.; D'angelo, M.; Roditchev, D.; Profeta, G.; Calandra, M.; Cren, T.

2018-05-01

We investigate the 1 /3 monolayer α -Pb /Si (111 ) surface by scanning tunneling spectroscopy (STS) and fully relativistic first-principles calculations. We study both the high-temperature √{3 }×√{3 } and low-temperature 3 ×3 reconstructions and show that, in both phases, the spin-orbit interaction leads to an energy splitting as large as 25% of the valence-band bandwidth. Relativistic effects, electronic correlations, and Pb-substrate interaction cooperate to stabilize a correlated low-temperature paramagnetic phase with well-developed lower and upper Hubbard bands coexisting with 3 ×3 periodicity. By comparing the Fourier transform of STS conductance maps at the Fermi level with calculated quasiparticle interference from nonmagnetic impurities, we demonstrate the occurrence of two large hexagonal Fermi sheets with in-plane spin polarizations and opposite helicities.

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

Basel, Bettina S.; Zirzlmeier, Johannes; Hetzer, Constantin

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron–hole pairs, leading to a predicted B50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state thatmore » precedes formation of the pentacene triplet excitons. In conclusion, using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.« less

Oxidation Kinetics of Bromophenols by Nonradical Activation of Peroxydisulfate in the Presence of Carbon Nanotube and Formation of Brominated Polymeric Products.

PubMed

Guan, Chaoting; Jiang, Jin; Pang, Suyan; Luo, Congwei; Ma, Jun; Zhou, Yang; Yang, Yi

2017-09-19

This work demonstrated that bromophenols (BrPs) could be readily oxidized by peroxydisulfate (PDS) activated by a commercial carbon nanotube (CNT), while furfuryl alcohol (a chemical probe for singlet oxygen ( 1 O 2 )) was quite refractory. Results obtained by radical quenching experiments, electron paramagnetic resonance spectroscopy, and Fourier transform infrared spectroscopy further confirmed the involvement of nonradical PDS-CNT complexes rather than 1 O 2 . Bicarbonate and chloride ion exhibited negligible impacts on BrPs degradation by the PDS/CNT system, while a significant inhibitory effect was observed for natural organic matter. The oxidation of BrPs was influenced by solution pH with maximum rates occurring at neutral pH. Linear free energy relationships (LFERs) were established between the observed pseudo-first-order oxidation rates of various substituted phenols and the classical descriptor variables (i.e., Hammett constant σ + , and half-wave oxidation potential E 1/2 ). Products analyses by liquid chromatography tandem mass spectrometry clearly showed the formation of hydroxylated polybrominated diphenyl ethers and hydroxylated polybrominated biphenyls on CNT surface. Their formation pathway possibly involved the generation of bromophenoxyl radicals from BrPs one-electron oxidation and their subsequent coupling reactions. These results suggest that the novel nonradical PDS/CNT oxidation technology is a good alternative for selectively eliminating BrPs with alleviating toxic byproducts in treated water effluent.

Studies on novel BiyXz-TiO2/SrTiO3 composites: Surface properties and visible light-driven photoactivity

NASA Astrophysics Data System (ADS)

Marchelek, Martyna; Grabowska, Ewelina; Klimczuk, Tomasz; Lisowski, Wojciech; Giamello, Elio; Zaleska-Medynska, Adriana

2018-03-01

A series of novel BiyXz-TiO2/SrTiO3 composites were prepared by multistep synthesis route. The as-prepared photocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR), Raman spectra and BET analysis. The photocatalytic activity test was performed in aqueous solution of phenol under the irradiation of visible light range (λ ≥ 420 nm). Obtained results revealed that the BiOI_TiO2/SrTiO3 sample exhibit the highest photocatalytic activity under visible irradiation (0.6 μmol/dm3/min). Thus, it was demonstrated that modification of the TiO2/SrTiO3 microspheres by flowers-like structure made of bismuth oxyiodide resulted in enhancement of photocatalytic activity under visible light. The role of active species during the decomposition process of organic compound was investigated using different types of active species scavengers as well as electron paramagnetic resonance analysis (EPR). The study showed that in the BiOI_TiO2/SrTiO3/Vis system the holes (h+) plays relevant role in phenol decomposition. Furthermore, the stability and recyclable properties of obtained BiOI_TiO2/SrTiO3 sample were confirmed during three consecutive processes.

Iron-containing pigment from an archaeological rupestrian painting of the Planalto Tradition in Minas Gerais, Brazil

NASA Astrophysics Data System (ADS)

Floresta, D. L.; Fagundes, M.; Fabris, J. D.; Ardisson, J. D.

2015-06-01

Archaeological rupestrian arts of the Planalto Tradition are of relatively widespread occurrence all over the land area of the state of Minas Gerais (MG), Brazil. They are typically composed by monochromic zoomorphic figures, especially of cervids, mainly in red or orange color. A fragment of a rock wall containing an archaeological painting was collected at the Itanguá site, in the municipality of Senador Modestino Gonçalves (geographical coordinates, 17° 56' 51″ S 43° 13' 22″ W), MG. The rock piece was covered with an archaeological painting with pigments of two different hues of red. The X-ray fluorescence (XRF) analysis revealed only a slight difference in Fe and P content for the two different color zones. The pigment materials on this small fragment of rock were analyzed by X-ray diffraction on the conventional incidence mode (XRD) and on grazing incidence X-ray mode (GIXRD), scanning electron microscopy with energy dispersive x-ray detector (SEM/EDS) and conversion electron Mössbauer spectroscopy (CEMS) at room temperature. Results indicated the occurrence of mainly hematite but also of diopside in the pigment. CEMS at RT reveal the presence of hematite and (super)paramagnetic ferric components. In order to confirm these results a small amount of powder from the painting pigments was also analyzed by transmission Mössbauer spectroscopy at 20 K.

H?, D? and HD adsorption upon the metal-organic framework [Cu?Zn?(btc)?]? studied by pulsed ENDOR and HYSCORE spectroscopy

NASA Astrophysics Data System (ADS)

Jee, Bettina; Hartmann, Martin; Pöppl, Andreas

2013-10-01

The adsorption of hydrogen has become interesting in terms of gas separation as well as safe and reversible storage of hydrogen as an energy carrier. In this regard, metal-organic framework compounds are potential candidates. The metal-organic framework [Cu?Zn?(btc)?]? as a partially Zn-substituted analogue of the well known compound HKUST-1 is well suited for studying adsorption geometries at cupric ions by electron paramagnetic resonance (EPR) methods due to the formation of few mixed Cu/Zn paddle wheel units with isolated S = 1/2 electron spins. The adsorption of hydrogen (H2) as well as the deuterium (D2) and HD molecules were investigated by continuous wave EPR and pulsed ENDOR and HYSCORE spectroscopy. The principal values of the proton and deuterium hyperfine coupling tensors ? and ? were determined by spectral simulations as well as of the deuterium nuclear quadrupole tensor ? for adsorbed HD and D2. The results show a side-on coordination of HD and D2 with identical Cu-H and Cu-D distances rCuX = 2.8 Å with the tensors ? and ? aligned parallel to the C4 symmetry axis of the paddle wheel unit. A thermodynamic non-equilibrium state with J = 1, mJ = ±1 is indicated by the experimental data with ? and ? averaged by rotation around C4.

Preparation and Characterization of WS2@SiO2 and WS2@PANI Core-Shell Nanocomposites

PubMed Central

Sade, Hagit

2018-01-01

Two tungsten disulfide (WS2)-based core-shell nanocomposites were fabricated using readily available reagents and simple procedures. The surface was pre-treated with a surfactant couple in a layer-by-layer approach, enabling good dispersion of the WS2 nanostructures in aqueous media and providing a template for the polymerization of a silica (SiO2) shell. After a Stöber-like reaction, a conformal silica coating was achieved. Inspired by the resulting nanocomposite, a second one was prepared by reacting the surfactant-modified WS2 nanostructures with aniline and an oxidizing agent in an aqueous medium. Here too, a conformal coating of polyaniline (PANI) was obtained, giving a WS2@PANI nanocomposite. Both nanocomposites were analyzed by electron microscopy, energy dispersive X-ray spectroscopy (EDS) and FTIR, verifying the core-shell structure and the character of shells. The silica shell was amorphous and mesoporous and the surface area of the composite increases with shell thickness. Polyaniline shells slightly differ in their morphologies dependent on the acid used in the polymerization process and are amorphous like the silica shell. Electron paramagnetic resonance (EPR) spectroscopy of the WS2@PANI nanocomposite showed variation between bulk PANI and the PANI shell. These two nanocomposites have great potential to expand the use of transition metals dichalcogenides (TMDCs) for new applications in different fields. PMID:29534426

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.

Blood free Radicals Concentration Determined by Electron Paramagnetic Resonance Spectroscopy and Delayed Cerebral Ischemia Occurrence in Patients with Aneurysmal Subarachnoid Hemorrhage.

PubMed

Ewelina, Grzywna; Krzysztof, Stachura; Marek, Moskala; Krzysztof, Kruczala

2017-12-01

Pathophysiology of delayed cerebral ischemia and cerebral vasospasm following aneurysmal subarachnoid hemorrhage is still poorly recognized, however free radicals are postulated as one of the crucial players. This study was designed to scrutinize whether the concentration of free radicals in the peripheral venous blood is related to the occurrence of delayed cerebral ischemia associated with cerebral vasospasm. Twenty-four aneurysmal subarachnoid hemorrhage patients and seven patients with unruptured intracranial aneurysm (control group) have been studied. Free radicals in patients' blood have been detected by the electron paramagnetic resonance (CMH.HCl spin probe, 150 K, ELEXSYS E500 spectrometer) on admission and at least 72 h from disease onset. Delayed cerebral ischemia monitoring was performed by daily neurological follow-up and transcranial color coded Doppler. Delayed cerebral ischemia observed in six aneurysmal subarachnoid hemorrhage patients was accompanied by cerebral vasospasm in all six cases. No statistically significant difference in average free radicals concentration between controls and study subgroups was noticed on admission (p = .3; Kruskal-Wallis test). After 72 h free radicals concentration in delayed cerebral ischemia patients (3.19 ± 1.52 mmol/l) differed significantly from the concentration in aneurysmal subarachnoid hemorrhage patients without delayed cerebral ischemia (0.65 ± 0.37 mmol/l) (p = .012; Mann-Whitney test). These findings are consistent with our assumptions and seem to confirm the role of free radicals in delayed cerebral ischemia development. Preliminary results presented above are promising and we need perform further investigation to establish whether blood free radicals concentration may serve as the biomarker of delayed cerebral ischemia associated with cerebral vasospasm.

Arsenic speciation in newberyite (MgHPO(4)·3H(2)O) determined by synchrotron X-ray absorption and electron paramagnetic resonance spectroscopies: implications for the fate of arsenic in green fertilizers.

PubMed

Lin, Jinru; Chen, Ning; Pan, Yuanming

2014-06-17

Newberyite (MgHPO4·3H2O), a biomineral and common constituent in guano deposits, is an important decomposition product of struvite that is an increasingly popular green fertilizer recovered from wastewaters. Two samples of newberyite containing 1099 and 25 ppm As have been obtained at pH = 6.4, by using Na2HAsO4·7H2O and NaAsO2 as the dopant, respectively (i.e., Synthesis 1 and Synthesis 2). Synchrotron arsenic K-edge X-ray absorption spectroscopic data of newberyite from Synthesis 1 show that As(5+) is dominant and has a local environment typical of the arsenate species. Single-crystal electron paramagnetic resonance (EPR) spectra of gamma-ray-irradiated newberyite from Synthesis 1 contain two arsenic-associated oxyradicals: [AsO3](2-) and [AsO2](2-) derived from As(5+) and As(3+), respectively, at the P site. Quantitative analyses of powder EPR spectra allow determinations of the As(5+) and As(3+) contents in newberyite from Synthesis 1 and Synthesis 2. Elevated concentrations of arsenic also occur in natural newberyite transformed from struvite in guano deposits and record the accumulation of this metalloid in the food chain. Therefore, newberyite, which sequesters As during crystallization and retains this metalloid during the transformation from struvite, can attenuate arsenic contamination from green fertilizers in moderately acidic soils. Also, the capacity for accommodating both As(5+) and As(3+) in the crystal lattice coupled with simple chemistry and easy crystallization at ambient conditions makes newberyite an attractive material for remediation of arsenic contamination in aqueous environments.

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.

Measuring “Free” Iron Levels in Caenorhabditis Elegans Using Low-Temperature Fe(III) Electron Paramagnetic Resonance Spectroscopy

PubMed Central

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

2007-01-01

Oxidative stress, caused by free radicals within the body, has been associated with the process of aging and many human diseases. As free radicals, in particular superoxide, are difficult to measure, an alternative indirect method for measuring oxidative stress levels has been successfully used in E. coli and yeast. This method is based on a proposed connection between elevated superoxide levels and release of iron from solvent exposed [4Fe-4S] enzyme clusters, which eventually leads to an increase in hydroxyl radical production. In past studies using bacteria and yeast, a positive correlation was found between superoxide production or oxidative stress due to superoxide within the organism and EPR (electron paramagnetic resonance) detectable “free” iron levels. In the present study, we have developed a reliable and an efficient method for measuring “free” iron levels in C. elegans using low temperature Fe(III) EPR at g = 4.3. This method utilizes synchronized worm cultures grown on plates, which are homogenized and treated with desferrioxamine, an Fe(III) chelator, prior to packing the EPR tube. Homogenization was found not to alter “free” iron levels, while desferrioxamine treatment significantly raised these levels, indicating presence of both Fe(II) and Fe(III) in the “free” iron pool. The correlation between free radical levels and the observed “free” iron levels was examined by using heat stress and paraquat treatment. The intensity of the Fe(III) EPR signal and thus, the concentration of the “free” iron pool, varied with the treatments that altered radical levels without changing the total iron levels. This study provides the groundwork needed to uncover the correlation between oxidative stress, “free” iron levels, and longevity in C. elegans. PMID:17010298

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.

Combined MCD/DFT/TDDFT Study of the Electronic Structure of Axially Pyridine Coordinated Metallocorroles.

PubMed

Rhoda, Hannah M; Crandall, Laura A; Geier, G Richard; Ziegler, Christopher J; Nemykin, Victor N

2015-05-18

A series of metallocorroles were investigated by UV-vis and magnetic circular dichroism spectroscopies. The diamagnetic distorted square-pyramidal main-group corrole Ga(tpfc)py (2), the diamagnetic distorted octahedral transition-metal adduct Co(tpfc)(py)2 (3), and paramagnetic distorted octahedral transition-metal complex Fe(tpfc)(py)2 (4) [H3tpfc = tris(perfluorophenyl)corrole] were studied to investigate similarities and differences in the electronic structure and spectroscopy of the closed- and open-shell metallocorroles. Similar to the free-base H3tpfc (1), inspection of the MCD Faraday B-terms for all of the macrocycles presented in this report revealed that a ΔHOMO < ΔLUMO [ΔHOMO is the energy difference between two highest energy corrole-centered π-orbitals and ΔLUMO is the energy difference between two lowest energy corrole-centered π*-orbitals originating from ML ± 4 and ML ± 5 pairs of perimeter] condition is present for each complex, which results in an unusual sign-reversed sequence for π-π* transitions in their MCD spectra. In addition, the MCD spectra of the cobalt and the iron complexes were also complicated by a number of charge-transfer states in the visible region. Iron complex 4 also exhibits a low-energy absorption in the NIR region (1023 nm). DFT and TDDFT calculations were used to elaborate the electronic structures and provide band assignments in UV-vis and MCD spectra of the metallocorroles. DFT and TDDFT calculations predict that the orientation of the axial pyridine ligand(s) has a very minor influence on the calculated electronic structures and absorption spectra in the target systems.

Charge Separation and Triplet Exciton Formation Pathways in Small-Molecule Solar Cells as Studied by Time-Resolved EPR Spectroscopy

DOE PAGES

Thomson, Stuart A. J.; Niklas, Jens; Mardis, Kristy L.; ...

2017-09-13

Organic solar cells are a promising renewable energy technology, offering the advantages of mechanical flexibility and solution processability. An understanding of the electronic excited states and charge separation pathways in these systems is crucial if efficiencies are to be further improved. Here we use light induced electron paramagnetic resonance (LEPR) spectroscopy and density functional theory calculations (DFT) to study the electronic excited states, charge transfer (CT) dynamics and triplet exciton formation pathways in blends of the small molecule donors (DTS(FBTTh 2) 2, DTS(F2BTTh 2) 2, DTS(PTTh 2) 2, DTG(FBTTh 2) 2 and DTG(F2BTTh 2) 2) with the fullerene derivative PCmore » 61BM. Using high frequency EPR the g-tensor of the positive polaron on the donor molecules was determined. The experimental results are compared with DFT calculations which reveal that the spin density of the polaron is distributed over a dimer or trimer. Time-resolved EPR (TR-EPR) spectra attributed to singlet CT states were identified and the polarization patterns revealed similar charge separation dynamics in the four fluorobenzothiadiazole donors, while charge separation in the DTS(PTTh 2) 2 blend is slower. Using TR-EPR we also investigated the triplet exciton formation pathways in the blend. The polarization patterns reveal that the excitons originate from both intersystem crossing (ISC) and back electron transfer (BET) processes. The DTS(PTTh 2) 2 blend was found to contain substantially more triplet excitons formed by BET than the fluorobenzothiadiazole blends. As a result, the higher BET triplet exciton population in the DTS(PTTh 2) 2 blend is in accordance with the slower charge separation dynamics observed in this blend.« less

Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory

NASA Astrophysics Data System (ADS)

Paul, Souvik; Iuşan, Diana; Thunström, Patrik; Kvashnin, Yaroslav O.; Hellsvik, Johan; Pereiro, Manuel; Delin, Anna; Knut, Ronny; Phuyal, Dibya; Lindblad, Andreas; Karis, Olof; Sanyal, Biplab; Eriksson, Olle

2018-03-01

Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of BiFeO3, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the LDA +U approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe 3 d states, whereas the LDA +U method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe 3 d orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe 3 d states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.

Charge Separation and Triplet Exciton Formation Pathways in Small Molecule Solar Cells as Studied by Time-resolved EPR Spectroscopy.

PubMed

Thomson, Stuart A J; Niklas, Jens; Mardis, Kristy L; Mallares, Christopher; Samuel, Ifor D W; Poluektov, Oleg G

2017-10-19

Organic solar cells are a promising renewable energy technology, offering the advantages of mechanical flexibility and solution processability. An understanding of the electronic excited states and charge separation pathways in these systems is crucial if efficiencies are to be further improved. Here we use light induced electron paramagnetic resonance (LEPR) spectroscopy and density functional theory calculations (DFT) to study the electronic excited states, charge transfer (CT) dynamics and triplet exciton formation pathways in blends of the small molecule donors (DTS(FBTTh 2 ) 2 , DTS(F 2 BTTh 2 ) 2 , DTS(PTTh 2 ) 2 , DTG(FBTTh 2 ) 2 and DTG(F 2 BTTh 2 ) 2 ) with the fullerene derivative PC 61 BM. Using high frequency EPR the g-tensor of the positive polaron on the donor molecules was determined. The experimental results are compared with DFT calculations which reveal that the spin density of the polaron is distributed over a dimer or trimer. Time-resolved EPR (TR-EPR) spectra attributed to singlet CT states were identified and the polarization patterns revealed similar charge separation dynamics in the four fluorobenzothiadiazole donors, while charge separation in the DTS(PTTh 2 ) 2 blend is slower. Using TR-EPR we also investigated the triplet exciton formation pathways in the blend. The polarization patterns reveal that the excitons originate from both intersystem crossing (ISC) and back electron transfer (BET) processes. The DTS(PTTh 2 ) 2 blend was found to contain substantially more triplet excitons formed by BET than the fluorobenzothiadiazole blends. The higher BET triplet exciton population in the DTS(PTTh 2 ) 2 blend is in accordance with the slower charge separation dynamics observed in this blend.

Charge Separation and Triplet Exciton Formation Pathways in Small-Molecule Solar Cells as Studied by Time-Resolved EPR Spectroscopy

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

Thomson, Stuart A. J.; Niklas, Jens; Mardis, Kristy L.

Organic solar cells are a promising renewable energy technology, offering the advantages of mechanical flexibility and solution processability. An understanding of the electronic excited states and charge separation pathways in these systems is crucial if efficiencies are to be further improved. Here we use light induced electron paramagnetic resonance (LEPR) spectroscopy and density functional theory calculations (DFT) to study the electronic excited states, charge transfer (CT) dynamics and triplet exciton formation pathways in blends of the small molecule donors (DTS(FBTTh 2) 2, DTS(F2BTTh 2) 2, DTS(PTTh 2) 2, DTG(FBTTh 2) 2 and DTG(F2BTTh 2) 2) with the fullerene derivative PCmore » 61BM. Using high frequency EPR the g-tensor of the positive polaron on the donor molecules was determined. The experimental results are compared with DFT calculations which reveal that the spin density of the polaron is distributed over a dimer or trimer. Time-resolved EPR (TR-EPR) spectra attributed to singlet CT states were identified and the polarization patterns revealed similar charge separation dynamics in the four fluorobenzothiadiazole donors, while charge separation in the DTS(PTTh 2) 2 blend is slower. Using TR-EPR we also investigated the triplet exciton formation pathways in the blend. The polarization patterns reveal that the excitons originate from both intersystem crossing (ISC) and back electron transfer (BET) processes. The DTS(PTTh 2) 2 blend was found to contain substantially more triplet excitons formed by BET than the fluorobenzothiadiazole blends. As a result, the higher BET triplet exciton population in the DTS(PTTh 2) 2 blend is in accordance with the slower charge separation dynamics observed in this blend.« less

1,5-Diamido-9,10-anthraquinone, a Centrosymmetric Redox-Active Bridge with Two Coupled β-Ketiminato Chelate Functions: Symmetric and Asymmetric Diruthenium Complexes.

PubMed

Ansari, Mohd Asif; Mandal, Abhishek; Paretzki, Alexa; Beyer, Katharina; Fiedler, Jan; Kaim, Wolfgang; Lahiri, Goutam Kumar

2016-06-06

The dinuclear complexes {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 ([3](ClO4)2), {(μ-H2L)[Ru(pap)2]2}(ClO4)2 ([4](ClO4)2), and the asymmetric [(bpy)2Ru(μ-H2L)Ru(pap)2](ClO4)2 ([5](ClO4)2) were synthesized via the mononuclear species [Ru(H3L)(bpy)2]ClO4 ([1]ClO4) and [Ru(H3L)(pap)2]ClO4 ([2]ClO4), where H4L is the centrosymmetric 1,5-diamino-9,10-anthraquinone, bpy is 2,2'-bipyridine, and pap is 2-phenylazopyridine. Electrochemistry of the structurally characterized [1]ClO4, [2]ClO4, [3](ClO4)2, [4](ClO4)2, and [5](ClO4)2 reveals multistep oxidation and reduction processes, which were analyzed by electron paramagnetic resonance (EPR) of paramagnetic intermediates and by UV-vis-NIR spectro-electrochemistry. With support by time-dependent density functional theory (DFT) calculations the redox processes could be assigned. Significant results include the dimetal/bridging ligand mixed spin distribution in 3(3+) versus largely bridge-centered spin in 4(3+)-a result of the presence of Ru(II)-stabilizig pap coligands. In addition to the metal/ligand alternative for electron transfer and spin location, the dinuclear systems allow for the observation of ligand/ligand and metal/metal site differentiation within the multistep redox series. DFT-supported EPR and NIR absorption spectroscopy of the latter case revealed class II mixed-valence behavior of the oxidized asymmetric system 5(3+) with about equal contributions from a radical bridge formulation. In comparison to the analogues with the deprotonated 1,4-diaminoanthraquinone isomer the centrosymmetric H2L(2-) bridge shows anodically shifted redox potentials and weaker electronic coupling between the chelate sites.

Evolution of ground-state wave function in CeCoIn 5 upon Cd or Sn doping

DOE PAGES

Chen, K.; Strigari, F.; Sundermann, M.; ...

2018-01-17

We present linear polarization-dependent soft-x-ray absorption spectroscopy data at the Ce M 4,5 edges of Cd- and Sn-doped CeCoIn 5. The 4f ground-state wave functions have been determined for their superconducting, antiferromagnetic, and paramagnetic ground states. The absence of changes in the wave functions in CeCo (In 1- xCd x) 5 suggests that the 4f-conduction-electron (c f) hybridization is not affected by global Cd doping, thus supporting the interpretation of magnetic droplets nucleating long-range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in CeCo (In 1 - ySn y) 5 compressesmore » the 4f orbitals into the tetragonal plane of these materials, suggesting enhanced c f hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the 4 f wave functions are a very sensitive probe of small changes in the hybridization of 4f and conduction electrons, even conveying information about direction dependencies.« less

Synthesis and characterization of Cu0.3Zn0.5Mg0.2Fe2O4 nanoparticles as a magnetic drug delivery system

NASA Astrophysics Data System (ADS)

Ansari, Mohammad; Bigham, Ashkan; Hassanzadeh-Tabrizi, S. A.; Abbastabar Ahangar, H.

2017-10-01

Mixed spinel ferrite nanoparticles are being applied in biomedical applications due to their biocompatibility, antibacterial activity, particular magnetic and electronic properties with chemical and thermal stabilities. The Cu0.3Zn0.5Mg0.2Fe2O4 nanoparticles are synthesized through the thermal treatment method. Polyvinyl alcohol (PVA) is used as the capping agent to stabilize the particles and prevent their agglomeration. The synthesized nanoparticles are characterized through X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption, field emission scanning electron microscopy (FESEM), and transmission electron microscope (TEM). The magnetic characterization is made on a vibrating sample magnetometer (VSM), which displayed super-paramagnetic behavior of the synthesized sample. Potential application of the Cu0.3Zn0.5Mg0.2Fe2O4 nanoparticles as a drug delivery agent is assessed in vitro by estimating their release properties. The obtained results indicate that the amount of ibuprofen (IBU) adsorbed into the nanocarrier of Cu0.3Zn0.5Mg0.2Fe2O4 is 104 mg/g and the drug release is sustained up to 72 h.

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

Coherent Raman detected electron spin resonance spectroscopy of metalloproteins: linking electron spin resonance and magnetic circular dichroism.

PubMed

Bingham, Stephen J; Wolverson, Daniel; Thomson, Andrew J

2008-12-01

The simultaneous excitation of paramagnetic molecules with optical (laser) and microwave radiation in the presence of a magnetic field can cause an amplitude, or phase, modulation of the transmitted light at the microwave frequency. The detection of this modulation indicates the presence of coupled optical and ESR transitions. The phenomenon can be viewed as a coherent Raman effect or, in most cases, as a microwave frequency modulation of the magnetic circular dichroism by the precessing magnetization. By allowing the optical and magnetic properties of a transition metal ion centre to be correlated, it becomes possible to deconvolute the overlapping optical or ESR spectra of multiple centres in a protein or of multiple chemical forms of a particular centre. The same correlation capability also allows the relative orientation of the magnetic and optical anisotropies of each species to be measured, even when the species cannot be obtained in a crystalline form. Such measurements provide constraints on electronic structure calculations. The capabilities of the method are illustrated by data from the dimeric mixed-valence Cu(A) centre of nitrous oxide reductase (N(2)OR) from Paracoccus pantotrophus.

Evolution of ground-state wave function in CeCoIn 5 upon Cd or Sn doping

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

Chen, K.; Strigari, F.; Sundermann, M.

We present linear polarization-dependent soft-x-ray absorption spectroscopy data at the Ce M 4,5 edges of Cd- and Sn-doped CeCoIn 5. The 4f ground-state wave functions have been determined for their superconducting, antiferromagnetic, and paramagnetic ground states. The absence of changes in the wave functions in CeCo (In 1- xCd x) 5 suggests that the 4f-conduction-electron (c f) hybridization is not affected by global Cd doping, thus supporting the interpretation of magnetic droplets nucleating long-range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in CeCo (In 1 - ySn y) 5 compressesmore » the 4f orbitals into the tetragonal plane of these materials, suggesting enhanced c f hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the 4 f wave functions are a very sensitive probe of small changes in the hybridization of 4f and conduction electrons, even conveying information about direction dependencies.« less

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.

Clinical EPR: Unique Opportunities and Some Challenges

PubMed Central

Swartz, Harold M.; Williams, Benjamin B.; Zaki, Bassem I.; Hartford, Alan C.; Jarvis, Lesley A.; Chen, Eunice; Comi, Richard J.; Ernstoff, Marc S.; Hou, Huagang; Khan, Nadeem; Swarts, Steven G.; Flood, Ann B.; Kuppusamy, Periannan

2014-01-01

Electron paramagnetic resonance (EPR) spectroscopy has been well established as a viable technique for measurement of free radicals and oxygen in biological systems, from in vitro cellular systems to in vivo small animal models of disease. However, the use of EPR in human subjects in the clinical setting, although attractive for a variety of important applications such as oxygen measurement, is challenged with several factors including the need for instrumentation customized for human subjects, probe and regulatory constraints. This paper describes the rationale and development of the first clinical EPR systems for two important clinical applications, namely, measurement of tissue oxygen (oximetry), and radiation dose (dosimetry) in humans. The clinical spectrometers operate at 1.2 GHz frequency and use surface loop resonators capable of providing topical measurements up to 1 cm depth in tissues. Tissue pO2 measurements can be carried out noninvasively and repeatedly after placement of an oxygen-sensitive paramagnetic material (currently India ink) at the site of interest. Our EPR dosimetry system is capable of measuring radiation-induced free radicals in the tooth of irradiated human subjects to determine the exposure dose. These developments offer potential opportunities for clinical dosimetry and oximetry, which include guiding therapy for individual patients with tumors or vascular disease, by monitoring of tissue oxygenation. Further work is in progress to translate this unique technology to routine clinical practice. PMID:24439333

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.

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

Muonium as a model for interstitial hydrogen in the semiconducting and semimetallic elements

NASA Astrophysics Data System (ADS)

Cox, S. F. J.

2009-11-01

Although the interstitial hydrogen atom would seem to be one of the simplest defect centres in any lattice, its solid state chemistry is in fact unknown in many materials, not least amongst the elements. In semiconductors, the realization that hydrogen can profoundly influence electronic properties even as a trace impurity has prompted its study by all available means—but still only in the functionally important or potentially important materials—for the elements, Si, Ge and diamond. Even here, it was not studies of hydrogen itself but of its pseudo-isotope, muonium, that first provided the much needed microscopic pictures of crystallographic site and local electronic structure—now comprehensively confirmed by ab initio computation and such data as exists for monatomic, interstitial hydrogen centres in Si. Muonium can be formed in a variety of neutral paramagnetic states when positive muons are implanted into non-metals. The simple trapped atom is commonly only metastable. It coexists with or reacts to give defect centres with the unpaired electron in somewhat more extended orbitals. Indications of complete delocalization into effective mass states are discussed for B, α-Sn, Bi and even Ge, but otherwise all the muonium centres seen in the elemental semiconductors are deep and relatively compact. These are revealed, distinguished and characterized by μSR spectroscopy—muon spin rotation and resonance informing on sites and spin-density distributions, muon spin relaxation on motional dynamics and charge-state transitions. This Report documents the progress of μSR studies for all the semiconductors and semimetals of the p-block elements, Groups III-VI of the Periodic Table. The striking spectra and originally unanticipated results for Group IV are for the most part well known but deserve summarizing and updating; the sheer diversity of muonium states found is still remarkable, especially in carbon allotropes. The interplay of crystallographic site and charge state in Si and Ge at high temperatures, or under illumination, reflects the capture and loss of charge carriers that should model the electrical activity of monatomic hydrogen but still challenges theoretical descriptions. Spin-flip scattering of conduction electrons by the paramagnetic centres is revealed in heavily doped n-type material, as well as some modification of the local electronic structures. The corresponding spectroscopy for the solid elements of Groups III, V and VI is rather less well known and is reviewed here for the first time; a good deal of previously unpublished data is also included. Theoretical expectations and computational modelling are sparse, here. Recent results for B suggest a relatively shallow centre with molecular character; P and As show deeper quasi-atomic states, but still with substantial overlap of spin density onto surrounding host atoms. Particular attention is paid to the chalcogens. Muonium centres in Te show charge-state transitions already around room temperature; the identification of those in S and Se has been complicated by unusual spin dynamics of a different character, here attributed to spin-orbit coupling and interstitial reorientation. In the metals and semimetals, muonium is not formed as a paramagnetic centre. Here the implanted muons mimic interstital protons and interest shifts to a variety of other topics, including aspects of charge screening (α-Sn, Sb, Bi), site preference and quantum mobility (Al, β-Sn, Pb). The post-transition metals receive only a brief mention, by way of contrast with the nonmetals. Systematic studies of local susceptibility via measurements of muon Knight shifts extends in favourable cases to revealing the elusive high-field Condon domains (Al, Sn, Pb, Bi). Some new information is available on the superconducting phases. Appendices include a derivation of the spin Hamiltonian for paramagnetic muonium centres or molecular radicals having varying admixtures of orbital angular momentum, including the extreme case of orbital degeneracy, and examine the consequences of significant spin-orbit coupling for μSR spectroscopy and muon spin relaxation. This is the framework for the tentative assignments made here for the muonium defect centres formed in sulphur and selenium, namely diatomic species resembling the chalcogen monohydrides. Equally, it provides guidelines for eventual solid-state detection of OMu—the elusive muoniated hydroxyl radical.

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

Hoffeditz, William L.; Katz, Michael J.; Deria, Pravas

Dye-sensitized solar cells (DSCs) are an established alternative photovoltaic technology that offers numerous potential advantages in solar energy applications. However, this technology has been limited by the availability of molecular redox couples that are both noncorrosive/nontoxic and do not diminish the performance of the device. In an effort to overcome these shortcomings, a copper-containing redox shuttle derived from 1,8-bis(2'-pyridyl)-3,6-dithiaoctane (PDTO) ligand and the common DSC additive 4-tert-butylpyridine (TBP) was investigated. Electrochemical measurements, single-crystal X-ray diffraction, and absorption and electron paramagnetic resonance spectroscopies reveal that, upon removal of one metal-centered electron, PDTO-enshrouded copper ions completely shed the tetradentate PDTO ligand andmore » replace it with four or more TBP ligands. Thus, the Cu(I) and Cu(II) forms of the electron shuttle have completely different coordination spheres and are characterized by widely differing Cu(II/I) formal potentials and reactivities for forward versus reverse electron transfer. Notably, the coordination-sphere replacement process is fully reversed upon converting Cu(II) back to Cu(I). In cells featuring an adsorbed organic dye and a nano- and mesoparticulate, TiO2-based, photoelectrode, the dual species redox shuttle system engenders performance superior to that obtained with shuttles based on the (II/I) forms of either of the coordination complexes in isolation.« less

Modeling the active site of [NiFe] hydrogenases and the [NiFeu] subsite of the C-cluster of carbon monoxide dehydrogenases: low-spin iron(II) versus high-spin iron(II).

PubMed

Weber, Katharina; Erdem, Özlen F; Bill, Eckhard; Weyhermüller, Thomas; Lubitz, Wolfgang

2014-06-16

A series of four [S2Ni(μ-S)2FeCp*Cl] compounds with different tetradentate thiolate/thioether ligands bound to the Ni(II) ion is reported (Cp* = C5Me5). The {S2Ni(μ-S)2Fe} core of these compounds resembles structural features of the active site of [NiFe] hydrogenases. Detailed analyses of the electronic structures of these compounds by Mössbauer and electron paramagnetic resonance spectroscopy, magnetic measurements, and density functional theory calculations reveal the oxidation states Ni(II) low spin and Fe(II) high spin for the metal ions. The same electronic configurations have been suggested for the Cred1 state of the C-cluster [NiFeu] subsite in carbon monoxide dehydrogenases (CODH). The Ni-Fe distance of ∼3 Å excludes a metal-metal bond between nickel and iron, which is in agreement with the computational results. Electrochemical experiments show that iron is the redox active site in these complexes, performing a reversible one-electron oxidation. The four complexes are discussed with regard to their similarities and differences both to the [NiFe] hydrogenases and the C-cluster of Ni-containing CODH.

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.

Color change of tourmaline by heat treatment and electron beam irradiation: UV-Visible, EPR, and Mid-IR spectroscopic analyses

NASA Astrophysics Data System (ADS)

Maneewong, Apichate; Seong, Baek Seok; Shin, Eun Joo; Kim, Jeong Seog; Kajornrith, Varavuth

2016-01-01

The color of pink tourmaline gemstone changed to colorless when heating at temperature of 600 °C in air. This colorless tourmaline recovered its pink color when irradiated with an electron beam (e-beam) of 800 kGy. The origin of the color change was investigated in three types of tourmaline gemstones, two pink are from Afghanistan and one green are from Nigeria, by using Ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), Electron paramagnetic resonance (EPR), and Energy Dispersive X-ray Fluorescence (EDXRF). The UV-Vis absorption spectrum of the pink tourmaline with higher Mn concentration (T2, 0.24 wt%) showed characteristic absorption peaks originating from the Mn3+ color center: two absorption bands centered at wavelength of 396 and 520 nm, respectively. Both absorption bands disappeared when heated in air at 600 °C and then reappeared when irradiated with an e-beam at 800 kGy. EPR T2 spectra showed that the color change was related to the valence change of Mn3+ to Mn2+ and vice versa. The pink tourmaline of lower MnO content (T1, 0.08 wt%) also became colorless when heated, but the color was not recovered when the gemstone underwent e-beam irradiation. Instead, a yellow color was obtained. UV-Vis and FTIR spectra indicated that this yellow color originated from a decomposition of the hydroxyl group (-OH) into O- and Ho by the e-beam irradiation. Green tourmaline did not show any color change with either heat treatment or e-beam irradiation.

Formation of Environmentally Persistent Free Radical (EPFR) in Iron(III) Cation-Exchanged Smectite Clay

PubMed Central

Nwosu, Ugwumsinachi G.; Roy, Amitava; dela Cruz, Albert Leo N.; Dellinger, Barry; Cook, Robert

2016-01-01

Environmentally persistent free radicals (EPFRs) have been found at a number of Superfund sites, with EPFRs being formed via a proposed redox process at ambient environmental conditions. The possibility of such a redox process taking place at ambient environmental conditions is studied utilizing a surrogate soil system of phenol and iron(III)-exchanged calcium montmorillonite clay, Fe(III)CaM. Sorption of phenol by the Fe(III)CaM is demonstrated by Fourier-transformed infra-red (FT-IR) spectroscopy, as evidenced by the peaks between 1345 cm−1 and 1595 cm−1, and at lower frequencies between 694 cm−1 and 806 cm−1, as well as X-ray diffraction (XRD) spectroscopy, as shown by an increase in interlayer spacing within Fe(III)CaM. The formation and characterization of the EPFRs is determined by electron paramagnetic resonance (EPR) spectroscopy, showing phenoxyl-type radical with a g-factor of 2.0034 and ΔHp-p of 6.1 G at an average concentration of 7.5 × 1017 spins/g. EPFRs lifetime data are indicative of oxygen and water molecules being responsible for EPFR decay. The change in the oxidation state of the iron redox center is studied by X-ray absorption near-edge structure (XANES) spectroscopy, showing that 23% of the Fe(III) is reduced to Fe(II). X-ray photoemission spectroscopy (XPS) results confirm the XANES results. These findings, when combined with the EPFR concentration data, demonstrate that the stoichiometry of the EPFR formation under the conditions of this study is 1.5 × 10−2 spins/Fe(II) atom. PMID:26647158

Formation of environmentally persistent free radical (EPFR) in iron(III) cation-exchanged smectite clay.

PubMed

Nwosu, Ugwumsinachi G; Roy, Amitava; dela Cruz, Albert Leo N; Dellinger, Barry; Cook, Robert

2016-01-01

Environmentally persistent free radicals (EPFRs) have been found at a number of Superfund sites, with EPFRs being formed via a proposed redox process at ambient environmental conditions. The possibility of such a redox process taking place at ambient environmental conditions is studied utilizing a surrogate soil system of phenol and iron(III)-exchanged calcium montmorillonite clay, Fe(III)CaM. Sorption of phenol by the Fe(III)CaM is demonstrated by Fourier-transformed infra-red (FT-IR) spectroscopy, as evidenced by the peaks between 1345 cm(-1) and 1595 cm(-1), and at lower frequencies between 694 cm(-1) and 806 cm(-1), as well as X-ray diffraction (XRD) spectroscopy, as shown by an increase in interlayer spacing within Fe(III)CaM. The formation and characterization of the EPFRs is determined by electron paramagnetic resonance (EPR) spectroscopy, showing phenoxyl-type radical with a g-factor of 2.0034 and ΔHP-P of 6.1 G at an average concentration of 7.5 × 10(17) spins per g. EPFRs lifetime data are indicative of oxygen and water molecules being responsible for EPFR decay. The change in the oxidation state of the iron redox center is studied by X-ray absorption near-edge structure (XANES) spectroscopy, showing that 23% of the Fe(III) is reduced to Fe(II). X-ray photoemission spectroscopy (XPS) results confirm the XANES results. These findings, when combined with the EPFR concentration data, demonstrate that the stoichiometry of the EPFR formation under the conditions of this study is 1.5 × 10(-2) spins per Fe(II) atom.

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.

How paramagnetic and diamagnetic LMOCs detect picric acid from surface water and the intracellular environment: a combined experimental and DFT-D3 study.

PubMed

Ghosh, Pritam; Banerjee, Priyabrata

2016-08-17

Diamagnetic and Paramagnetic Luminescent Metal Organic Complexes (LMOCs) have been reported for Explosive and Pollutant Nitro Aromatic (epNAC) recognition. The diamagnetic complex shows a highly intense AIE induced by NEt3H(+), which disappears after picric acid recognition and subsequently RET will quench the emission intensity. Radical stabilized paramagnetic LMOCs seem to be active but show lower sensing efficiency in comparison with diamagnetic LMOCs. Solution and solid state spectroscopy studies along with DFT-D3 have been executed to enlighten the host guest interaction. Limit of PA detection is ∼250 ppb with a binding constant of 1.2 × 10(5) M(-1). Time-stepping, i.e. intervening in the problem of picric acid recognition from surface water collected from several places of West Bengal, India, has been performed. Mutagenic picric acid has been successfully detected in an aqueous medium inside both prokaryotic and eukaryotic cells at a ppm level using fluorescence microscopy.

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.

Bulk magnetic properties of La1-xCaxMnO3 (0⩽x⩽0.14) : Signatures of local ferromagnetic order

NASA Astrophysics Data System (ADS)

Terashita, Hirotoshi; Neumeier, J. J.

2005-04-01

We report the bulk magnetic properties of hole-doped La1-xCaxMnO3 (0⩽x⩽0.14) in the paramagnetic and antiferromagnetic regions; the Mn4+ concentration was determined with chemical analysis. Significant enhancement of the effective paramagnetic moment illustrates the existence of ferromagnetic clusters (polarons). The data reveal a distinct crossover in the paramagnetic region, signifying competition between ferromagnetic clusters and antiferromagnetic correlations associated with the low-temperature magnetically ordered state. The results suggest similarity in the magnetic properties at low temperatures between hole-doped LaMnO3 and electron-doped CaMnO3 .

Neutron irradiation and damage assessment of plastic scintillators of the Tile Calorimeter

NASA Astrophysics Data System (ADS)

Mdhluli, J. E.; Mellado, B.; Sideras-Haddad, E.

2017-01-01

Following the comparative study of proton induced radiation damage on various plastic scintillator samples from the ATLAS-CERN detector, a study on neutron irradiation and damage assessment on the same type of samples will be conducted. The samples will be irradiated with different dose rates of neutrons produced in favourable nuclear reactions using a radiofrequency linear particle accelerator as well as from the SAFARI nuclear reactor at NECSA. The MCNP 5 code will be utilized in simulating the neutron transport for determining the dose rate. Light transmission and light yield tests will be performed in order to assess the radiation damage on the scintillators. In addition, Raman spectroscopy and Electron Paramagnetic Resonance (EPR) analysis will be used to characterize the samples after irradiation. The project aims to extent these studies to include radiation assessment damage of any component that processes the scintillating light and deteriorates the quantum efficiency of the Tilecal detector, namely, photomultiplier tubes, wavelength shifting optical fibres and the readout electronics. They will also be exposed to neutron irradiation and the damage assessed in the same manner.

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.

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

Mei, Yang; Ramanathan, Arvind; Glover, Karen

BECN1 is essential for autophagy, a critical eukaryotic cellular homeostasis pathway. Here in this study, we delineate a highly conserved BECN1 domain located between previously characterized BH3 and coiled-coil domains and elucidate its structure and role in autophagy. The 2.0 Å sulfur-single-wavelength anomalous dispersion X-ray crystal structure of this domain demonstrates that its N-terminal half is unstructured while its C-terminal half is helical; hence, we name it the flexible helical domain (FHD). Circular dichroism spectroscopy, double electron–electron resonance–electron paramagnetic resonance, and small-angle X-ray scattering (SAXS) analyses confirm that the FHD is partially disordered, even in the context of adjacent BECN1more » domains. Molecular dynamic simulations fitted to SAXS data indicate that the FHD transiently samples more helical conformations. FHD helicity increases in 2,2,2-trifluoroethanol, suggesting it may become more helical upon binding. Finally, cellular studies show that conserved FHD residues are required for starvation-induced autophagy. Thus, the FHD likely undergoes a binding-associated disorder-to-helix transition, and conserved residues critical for this interaction are essential for starvation-induced autophagy.« less

Growth, Crystal Structure, Theoretical Analysis and Properties of Te4+-Doped KTiOPO4

NASA Astrophysics Data System (ADS)

Liu, Lintao; Yao, Qian; Zhang, Junying; Dong, Weimin; Li, Jing; Wang, Jiyang; Boughton, Robert I.

2018-04-01

A single crystal of Te4+-doped KTiOPO4(Te:KTP) has been grown by the flux method. The electronic structure and density of states of KTiOPO4 (KTP) and Te:KTP were calculated from first principles. As the results reveal, there is no change in the space group or lattice structure of Te:KTP, but that some increase in lattice parameters occurred. The chemical composition of Te:KTP was analyzed using x-ray photoelectron spectroscopy (XPS). The possible existence of Ti3+ has been evaluated by measuring the electron paramagnetic resonance spectrum, and the results reveal that the ion is absent from this crystal. It was observed that Te4+ doping reduces the conductivity of the crystal from measurements of its conductivity at different temperatures and frequencies, indicating that Te:KTP has excellent electro-optical properties. The effect of Te4+ doping on the second harmonic generation in KTP was also studied. The thermal expansion, thermal diffusivity, thermal conductivity and specific heat capacity of KTP and Te:KTP were determined.

Colour-causing defects and their related optoelectronic transitions in single crystal CVD diamond.

PubMed

Khan, R U A; Cann, B L; Martineau, P M; Samartseva, J; Freeth, J J P; Sibley, S J; Hartland, C B; Newton, M E; Dhillon, H K; Twitchen, D J

2013-07-10

Defects causing colour in nitrogen-doped chemical vapour-deposited (CVD) diamond can adversely affect the exceptional optical, electronic and spintronic properties of the material. Several techniques were used to study these defects, namely optical absorption spectroscopy, thermoluminescence (TL) and electron paramagnetic resonance (EPR). From our studies, the defects causing colour in nitrogen-doped CVD diamond are clearly not the same as those causing similar colour in natural diamonds. The brown colour arises due to a featureless absorption profile that decreases in intensity with increasing wavelength, and a broad feature at 360 nm (3.49 eV) that scales in intensity with it. Another prominent absorption band, centred at 520 nm (2.39 eV), is ascribed to the neutral nitrogen-vacancy-hydrogen defect. The defects responsible for the brown colour possess acceptor states that are 1.5 eV from the valence band (VB) edge. The brown colour is removed by heat treatment at 1600 ° C, whereupon new defects possessing shallow (<1 eV) trap states are generated.

Surface structural reconstruction of SrVO3 thin films on SrTiO3 (001)

NASA Astrophysics Data System (ADS)

Wang, Gaomin; Saghayezhian, Mohammad; Chen, Lina; Guo, Hangwen; Zhang, Jiandi

Paramagnetic metallic oxide SrVO3>(SVO) is an itinerant system known to undergo thickness-induced metal-insulator-transition (MIT) in ultrathin film form, which makes it a prototype system for the study of the mechanism behind metal-insulator-transition like structure distortion, electron correlations and disorder-induced localization. We have grown SrVO3 thin film with atomically flat surface through the layer-by-layer deposition by laser Molecular Beam Epitaxy (laser-MBE) on SrTiO3 (001) surface. Low Energy Electron Diffraction (LEED) measurements reveal that there is a (√2X √2) R45°surface reconstruction independent of film thickness. By using LEED-I(V) structure refinement, we determine the surface structure. In combination with X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM), we discuss the implication on the MIT in ultrathin films below 2-3 unit cell thickness. This work is supported by the National Science Foundation under the NSF EPSCoR Cooperative Agreement No. EPS-1003897 with additional support from the Louisiana Board of Regents.

ESEEM of industrial quartz powders: insights into crystal chemistry of Al defects

NASA Astrophysics Data System (ADS)

Romanelli, Maurizio; Di Benedetto, Francesco; Bartali, Laura; Innocenti, Massimo; Fornaciai, Gabriele; Montegrossi, Giordano; Pardi, Luca A.; Zoleo, Alfonso; Capacci, Fabio

2012-06-01

A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H+, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H+ (hAl) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested. As a consequence, the hAl centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes.

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).

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.

Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment.

PubMed

Yang, Yang; Kao, Li Cheng; Liu, Yuanyue; Sun, Ke; Yu, Hongtao; Guo, Jinghua; Liou, Sofia Ya Hsuan; Hoffmann, Michael R

2018-05-04

TiO 2 has long been recognized as a stable and reusable photocatalyst for water splitting and pollution control. However, it is an inefficient anode material in the absence of photoactivation due to its low electron conductivity. To overcome this limitation, a series of conductive TiO 2 nanotube array electrodes have been developed. Even though nanotube arrays are effective for electrochemical oxidation initially, deactivation is often observed within a few hours. To overcome the problem of deactivation, we have synthesized cobalt-doped Black-TiO 2 nanotube array (Co-Black NTA) electrodes that are stable for more than 200 h of continuous operation in a NaClO 4 electrolyte at 10 mA cm -2 . Using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and DFT simulations, we are able to show that bulk oxygen vacancies (O v ) are the primary source of the enhanced conductivity of Co-Black. Cobalt doping both creates and stabilizes surficial oxygen vacancies, O v , and thus prevents surface passivation. The Co-Black electrodes outperform dimensionally stable IrO 2 anodes (DSA) in the electrolytic oxidation of organic-rich wastewater. Increasing the loading of Co leads to the formation of a CoO x film on top of Co-Black electrode. The CoO x /Co-Black composite electrode was found to have a lower OER overpotential (352 mV) in comparison to a DSA IrO 2 (434 mV) electrode and a stability that is greater than 200 h in a 1.0 M KOH electrolyte at a current density of 10 mA cm -2 .

Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment

PubMed Central

2018-01-01

TiO2 has long been recognized as a stable and reusable photocatalyst for water splitting and pollution control. However, it is an inefficient anode material in the absence of photoactivation due to its low electron conductivity. To overcome this limitation, a series of conductive TiO2 nanotube array electrodes have been developed. Even though nanotube arrays are effective for electrochemical oxidation initially, deactivation is often observed within a few hours. To overcome the problem of deactivation, we have synthesized cobalt-doped Black-TiO2 nanotube array (Co-Black NTA) electrodes that are stable for more than 200 h of continuous operation in a NaClO4 electrolyte at 10 mA cm–2. Using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and DFT simulations, we are able to show that bulk oxygen vacancies (Ov) are the primary source of the enhanced conductivity of Co-Black. Cobalt doping both creates and stabilizes surficial oxygen vacancies, Ov, and thus prevents surface passivation. The Co-Black electrodes outperform dimensionally stable IrO2 anodes (DSA) in the electrolytic oxidation of organic-rich wastewater. Increasing the loading of Co leads to the formation of a CoOx film on top of Co-Black electrode. The CoOx/Co-Black composite electrode was found to have a lower OER overpotential (352 mV) in comparison to a DSA IrO2 (434 mV) electrode and a stability that is greater than 200 h in a 1.0 M KOH electrolyte at a current density of 10 mA cm–2. PMID:29755829

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.

Ensemble models of proteins and protein domains based on distance distribution restraints.

PubMed

Jeschke, Gunnar

2016-04-01

Conformational ensembles of intrinsically disordered peptide chains are not fully determined by experimental observations. Uncertainty due to lack of experimental restraints and due to intrinsic disorder can be distinguished if distance distributions restraints are available. Such restraints can be obtained from pulsed dipolar electron paramagnetic resonance (EPR) spectroscopy applied to pairs of spin labels. Here, we introduce a Monte Carlo approach for generating conformational ensembles that are consistent with a set of distance distribution restraints, backbone dihedral angle statistics in known protein structures, and optionally, secondary structure propensities or membrane immersion depths. The approach is tested with simulated restraints for a terminal and an internal loop and for a protein with 69 residues by using sets of sparse restraints for underlying well-defined conformations and for published ensembles of a premolten globule-like and a coil-like intrinsically disordered protein. © 2016 Wiley Periodicals, Inc.