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Sample records for epr spectroscopy studies

  1. Biomolecular EPR spectroscopy

    CERN Document Server

    Hagen, Wilfred Raymond

    2008-01-01

    Comprehensive, Up-to-Date Coverage of Spectroscopy Theory and its Applications to Biological SystemsAlthough a multitude of books have been published about spectroscopy, most of them only occasionally refer to biological systems and the specific problems of biomolecular EPR (bioEPR). Biomolecular EPR Spectroscopy provides a practical introduction to bioEPR and demonstrates how this remarkable tool allows researchers to delve into the structural, functional, and analytical analysis of paramagnetic molecules found in the biochemistry of all species on the planet. A Must-Have Reference in an Intrinsically Multidisciplinary FieldThis authoritative reference seamlessly covers all important bioEPR applications, including low-spin and high-spin metalloproteins, spin traps and spin lables, interaction between active sites, and redox systems. It is loaded with practical tricks as well as do's and don'ts that are based on the author's 30 years of experience in the field. The book also comes with an unprecedented set of...

  2. Broadband transmission EPR spectroscopy.

    Directory of Open Access Journals (Sweden)

    Wilfred R Hagen

    Full Text Available EPR spectroscopy employs a resonator operating at a single microwave frequency and phase-sensitive detection using modulation of the magnetic field. The X-band spectrometer is the general standard with a frequency in the 9-10 GHz range. Most (biomolecular EPR spectra are determined by a combination of the frequency-dependent electronic Zeeman interaction and a number of frequency-independent interactions, notably, electron spin - nuclear spin interactions and electron spin - electron spin interactions, and unambiguous analysis requires data collection at different frequencies. Extant and long-standing practice is to use a different spectrometer for each frequency. We explore the alternative of replacing the narrow-band source plus single-mode resonator with a continuously tunable microwave source plus a non-resonant coaxial transmission cell in an unmodulated external field. Our source is an arbitrary wave digital signal generator producing an amplitude-modulated sinusoidal microwave in combination with a broadband amplifier for 0.8-2.7 GHz. Theory is developed for coaxial transmission with EPR detection as a function of cell dimensions and materials. We explore examples of a doublet system, a high-spin system, and an integer-spin system. Long, straigth, helical, and helico-toroidal cells are developed and tested with dilute aqueous solutions of spin label hydroxy-tempo. A detection limit of circa 5 µM HO-tempo in water at 800 MHz is obtained for the present setup, and possibilities for future improvement are discussed.

  3. Broadband Transmission EPR Spectroscopy

    Science.gov (United States)

    Hagen, Wilfred R.

    2013-01-01

    EPR spectroscopy employs a resonator operating at a single microwave frequency and phase-sensitive detection using modulation of the magnetic field. The X-band spectrometer is the general standard with a frequency in the 9–10 GHz range. Most (bio)molecular EPR spectra are determined by a combination of the frequency-dependent electronic Zeeman interaction and a number of frequency-independent interactions, notably, electron spin – nuclear spin interactions and electron spin – electron spin interactions, and unambiguous analysis requires data collection at different frequencies. Extant and long-standing practice is to use a different spectrometer for each frequency. We explore the alternative of replacing the narrow-band source plus single-mode resonator with a continuously tunable microwave source plus a non-resonant coaxial transmission cell in an unmodulated external field. Our source is an arbitrary wave digital signal generator producing an amplitude-modulated sinusoidal microwave in combination with a broadband amplifier for 0.8–2.7 GHz. Theory is developed for coaxial transmission with EPR detection as a function of cell dimensions and materials. We explore examples of a doublet system, a high-spin system, and an integer-spin system. Long, straigth, helical, and helico-toroidal cells are developed and tested with dilute aqueous solutions of spin label hydroxy-tempo. A detection limit of circa 5 µM HO-tempo in water at 800 MHz is obtained for the present setup, and possibilities for future improvement are discussed. PMID:23555819

  4. EPR spectroscopy of spices

    Directory of Open Access Journals (Sweden)

    R. T. Тimakova

    2016-01-01

    Full Text Available From 01 January 2017 you enter the interstate standard GOST 33271-2015 “Dry Spices, herbs and vegetable seasonings. Manual exposure in order to combat pathogens and other microorganisms” which States that the absorbed dose of radiation to the spices should be from 3 to 30 kGy. The study found that before the introduction of permissive legislative framework in the consumer market of Russia there are irradiated food products (chili, ground chili, ground spicy chili, black pepper. For radiation monitoring of food safety, we used the method of electron paramagnetic resonance (EPR, which allows quickly and with a high degree of reliability to establish the fact of irradiation. It is established that all samples of spices irradiated with dose of 12 kGy (technology radappertization gave typical spectra of the signals established by the method of electron paramagnetic resonance in the domestic EPR spectrometer, the intensity, amplitude and peak width of the EPR signal of samples of spices with the increase of irradiation dose increases. It is proven that repeated exposure no effect accumulation. Integration with 2017 Russia in the global practi ce of using radiation technologies of processing of food products and food raw materials with the purpose of extending shelf life confirms the need for a data Bank on the radiation sensitivity of various food products to determine the optimal doses and the eff ect of radiation doses on the shelf life and quality of products.

  5. EPR Spectroscopy in Environmental Lichen-Indication

    Science.gov (United States)

    Bondarenko, P. V.; Nguyet, Le Thi Bich; Zhuravleva, S. E.; Trukhan, E. M.

    2017-09-01

    The paramagnetic properties of lichens were investigated using EPR spectroscopy and Xanthoria parietina (L.) Th. Fr. as a case study. It was found that the concentration of paramagnetic centers in lichen thalli increased as the air-pollution level increased. Possible formation mechanisms of the paramagnetic centers in lichens were discussed. The efficiency of using EPR spectroscopy to study lichens as environmental quality indicators was demonstrated.

  6. Model compounds of humic acid and oxovanadium cations. Potentiometric titration and EPR spectroscopy studies

    Directory of Open Access Journals (Sweden)

    Mercê Ana Lucia Ramalho

    1999-01-01

    Full Text Available The stability constants and the isotropic EPR parameters Ao (hyperfine splitting constant and g o (g value were obtained by potentiometric titrations and EPR spectroscopy, respectively, of 85%v/v aqueous solutions of model compounds of humic acids - salicylic acid (SALA - and both nitrohumic acids, a laboratory artifact - nitrosalicylic acids, 3-nitrosalicylic acid (3-NSA, 5-nitrosalicylic acid (5-NSA and 3,5-dinitrosalicylic acid (3,5-DNSA and oxovanadium cations. It was possible to record EPR spectra of those model compounds and the ion VO2+ (V(IV, and the stability constants were obtained from a solution of VO3+ (V(V, the values for the logarithms of the stability constants ranging from 12.77 ± 0.04 to 7.06 ± 0.05 for the species ML, and from 9.90 ±0.04 to 4.06 ± 0.05 for the species ML2 according to the decrease in the acidity of the carboxylic and the hydroxyl groups in the aromatic ring of the model compounds studied as the -NO2 substituents were added. Species distribution diagrams were also obtained for the equilibria studied. The EPR parameters showed that as the logarithm of the overall stability constants increase, g o values also increase, while Ao values show a tendency to decrease.

  7. Applications of pulsed EPR spectroscopy to structural studies of sulfite oxidizing enzymes

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Eric L.; Astashkin, Andrei V.; Raitsimring, Arnold M.; Enemark, John H.

    2013-01-01

    Sulfite oxidizing enzymes (SOEs), including sulfite oxidase (SO) and bacterial sulfite dehydrogenase (SDH), catalyze the oxidation of sulfite (SO32-) to sulfate (SO42-). The active sites of SO and SDH are nearly identical, each having a 5-coordinate, pseudo-square-pyramidal Mo with an axial oxo ligand and three equatorial sulfur donor atoms. One sulfur is from a conserved Cys residue and two are from a pyranopterindithiolene (molybdopterin, MPT) cofactor. The identity of the remaining equatorial ligand, which is solvent-exposed, varies during the catalytic cycle. Numerous in vitro studies, particularly those involving electron paramagnetic resonance (EPR) spectroscopy of the Mo(V) states of SOEs, have shown that the identity and orientation of this exchangeable equatorial ligand depends on the buffer pH, the presence and concentration of certain anions in the buffer, as well as specific point mutations in the protein. Until very recently, however, EPR has not been a practical technique for directly probing specific structures in which the solvent-exposed, exchangeable ligand is an O, OH-, H2O, SO32-, or SO42- group, because the primary O and S isotopes (16O and 32S) are magnetically silent (I = 0). This review focuses on the recent advances in the use of isotopic labeling, variable-frequency high resolution pulsed EPR spectroscopy, synthetic model compounds, and DFT calculations to elucidate the roles of various anions, point mutations, and steric factors in the formation, stabilization, and transformation of SOE active site structures.

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

    Energy Technology Data Exchange (ETDEWEB)

    Andrews, J.C. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States). Structural Biology Div.

    1995-08-01

    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 II 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.

  9. EPR spectroscopy of spices

    OpenAIRE

    R. T. Тimakova; S. L. Tikhonov; A. N. Tararkov; D. O. Vakhnin

    2016-01-01

    From 01 January 2017 you enter the interstate standard GOST 33271-2015 “Dry Spices, herbs and vegetable seasonings. Manual exposure in order to combat pathogens and other microorganisms” which States that the absorbed dose of radiation to the spices should be from 3 to 30 kGy. The study found that before the introduction of permissive legislative framework in the consumer market of Russia there are irradiated food products (chili, ground chili, ground spicy chili, black pepper). For radiation...

  10. Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

    Directory of Open Access Journals (Sweden)

    Nikolay O. Chalkov

    2016-11-01

    Full Text Available The chemical oxidation and reduction processes of deprotonated, direduced o-quinone-exTTF-o-quinone in protic solvents were studied by EPR spectroscopy. The formation of relatively stable paramagnetic protonated redox forms of the parent triad was very surprising. The character of spin-density distribution in the semiquinone–quinone and semiquinone–catechol redox forms indicates that the p-phenylene-extended tetrathiafulvalene connector provides a quite effective electronic communication channel between dioxolene coordination sites. It was found that the deprotonated, direduced o-quinone-exTTF-o-quinone is capable to reduction of the metal copper in solution. The radical anion species formed in this reaction exists in solution as a solvent-separated ion pair with a copper cation. A character of spin-density distribution in a radical anion species leads to the conclusion that the ligand corresponds to type III of the Robin–Day classification.

  11. Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study.

    Science.gov (United States)

    Chalkov, Nikolay O; Cherkasov, Vladimir K; Abakumov, Gleb A; Starikov, Andrey G; Kuropatov, Viacheslav A

    2016-01-01

    The chemical oxidation and reduction processes of deprotonated, direduced o-quinone-exTTF-o-quinone in protic solvents were studied by EPR spectroscopy. The formation of relatively stable paramagnetic protonated redox forms of the parent triad was very surprising. The character of spin-density distribution in the semiquinone-quinone and semiquinone-catechol redox forms indicates that the p-phenylene-extended tetrathiafulvalene connector provides a quite effective electronic communication channel between dioxolene coordination sites. It was found that the deprotonated, direduced o-quinone-exTTF-o-quinone is capable to reduction of the metal copper in solution. The radical anion species formed in this reaction exists in solution as a solvent-separated ion pair with a copper cation. A character of spin-density distribution in a radical anion species leads to the conclusion that the ligand corresponds to type III of the Robin-Day classification.

  12. CONFORMATIONAL EQUILIBRIA OF BULGED SITES IN DUPLEX DNA STUDIED BY EPR SPECTROSCOPY

    OpenAIRE

    Smith, Alyssa L.; Cekan, Pavol; Brewood, Greg P.; Okonogi, Tamara M.; Alemayehu, Saba; Hustedt, Eric J.; Benight, Albert S.; Sigurdsson, Snorri Th.; Robinson, Bruce H.

    2009-01-01

    Conformational flexibility in nucleic acids provides a basis for complex structures, binding, and signaling. One-base bulges directly neighboring single-base mismatches in nucleic acids can be present in a minimum of two distinct conformations, complicating the examination of the thermodynamics by calorimetry or UV-monitored melting techniques. To provide additional information about such structures, we demonstrate how electron paramagnetic resonance (EPR) active spin-labeled base analogues, ...

  13. EPR spectroscopy of the manganese cluster of photosystem II.

    Science.gov (United States)

    Haddy, Alice

    2007-06-01

    Electron paramagnetic resonance (EPR) spectroscopy is a valuable tool for understanding the oxidation state and chemical environment of the Mn4Ca cluster of photosystem II. Since the discovery of the multiline signal from the S2 state, EPR spectroscopy has continued to reveal details about the catalytic center of oxygen evolution. At present EPR signals from nearly all of the S-states of the Mn4Ca cluster, as well as from modified and intermediate states, have been observed. This review article describes the various EPR signals obtained from the Mn4Ca cluster, including the metalloradical signals due to interaction of the cluster with a nearby organic radical.

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

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    Makoto Chikira

    2015-09-01

    Full Text Available 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.

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

    Science.gov (United States)

    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

  16. EPR spectroscopy applied to the study of the TEMPO mediated oxidation of nanocellulose.

    Science.gov (United States)

    Buffa, Juan M; Grela, María Alejandra; Aranguren, Mirta I; Mucci, Verónica

    2016-01-20

    Two different methods of pH control were used in the synthesis of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanocrystals (CNC) and the reaction kinetics and degree of oxidation were investigated. In method I the media pH was controlled by addition of NaOH solution. The effect of the oxidant concentration (sodium hypochloride, NaClO) on the final degree of oxidation and crystallinity of the samples was investigated. Conditions for obtaining an optimum balance between high crystallinity and degree of oxidation were selected from those results. In method II, pH was fixed by using a buffer solution. Electron spin resonance (ESR) spectroscopy offered direct information of the decay of TEMPO concentration under these conditions. The kinetics of the reaction was determined, finding a direct correlation between these results and those corresponding to the decay of the NaClO concentration and the advance of the CNC degree of oxidation. Differences found between the two methods were analyzed. Copyright © 2015 Elsevier Ltd. All rights reserved.

  17. EPR and NMR spectroscopy on spin-labeled proteins

    NARCIS (Netherlands)

    Finiguerra, Michelina Giuseppina

    2011-01-01

    Spin labeling and electron paramagnetic resonance (EPR) have been employed to study structure and dynamics of proteins. The surface polarity of four single cysteine mutants of the Zn-azurin in frozen solution were studied using 275 GHz EPR (J-band), with the advantage compared to 9 GHz (X-band) and

  18. Cysteine, thiourea and thiocyanate interactions with clays: FT-IR, Mössbauer and EPR spectroscopy and X-ray diffractometry studies.

    Science.gov (United States)

    de Santana, Henrique; Paesano, Andrea; da Costa, Antonio C S; di Mauro, Eduardo; de Souza, Ivan G; Ivashita, Flávio F; de Souza, Cláudio M D; Zaia, Cássia T B V; Zaia, Dimas A M

    2010-04-01

    The present study examined the adsorption of cysteine, thiourea and thiocyanate on bentonite and montmorillonite at two different pHs (3.00, 8.00). The conditions used here are closer to those of prebiotic earth. As shown by FT-IR, Mössbauer and EPR spectroscopy and X-ray diffractometry, the most important finding of this work is that cysteine and thiourea penetrate into the interlayer of the clays and reduce Fe(3+) to Fe(2+), and as consequence, cystine and c,c'-dithiodiformamidinium ion are formed. This mechanism resembles that which occurs with aconitase. This is a very important result for prebiotic chemistry; we should think about clays not just sink of molecules, but as primitive vessels of production of biomolecules. At pH 8.00, an increasing expansion was observed in the following order for both minerals: thiourea > thiocyanate > cysteine. At pH 3.00, the same order was not observed and thiourea had an opposite behavior, being the compound producing the lowest expansion. Mössbauer spectroscopy showed that at pH 8.00, the proportion of Fe(2+) ions in bentonite increased, doubling for thiourea, or more than doubling for cysteine, in both clays. However, at pH 3.00, cysteine and thiourea did not change significantly the relative amount of Fe(2+) and Fe(3+) ions, when compared to clays without adsorption. For thiocyanate, the amount of Fe(2+) produced was independent of the pH or clay used, probably because the interlayers of clays are very acidic and HSCN formed does not reduce Fe(3+) to Fe(2+). For the interaction of thiocyanate with the clays, it was not possible to identify any potential compound formed. For the samples of bentonite and montmorillonite at pH 8.00 with cysteine, EPR spectroscopy showed that intensity of the lines due to Fe(3+) decreased because the reaction of Fe(3+)/cysteine. Intensity of EPR lines did not change when the samples of bentonite at pH 3.00 with and without cysteine were compared. These results are in accordance with those

  19. Electronic Structure of ZnO Quantum Dots studied by High-frequency EPR, ESE, ENDOR and ODMR Spectroscopy

    NARCIS (Netherlands)

    Baranov, P.G.; Romanov, N.G.; Bundakova, A.P.; de Mello-Donega, Celso; Schmidt, J.

    2016-01-01

    High-frequency electron paramagnetic resonance (EPR), electron spin echo (ESE), electron-nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) were applied for the investigation of the electronic properties of ZnO colloidal quantum dots (QDs) which consist of a ZnO

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

    Science.gov (United States)

    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.

  1. A special JMR issue: Methodological advances in EPR spectroscopy and imaging

    Science.gov (United States)

    2017-07-01

    Since about five decades, EPR spectroscopy provides important insights into the electronic structure of metalloproteins and transition-metal based catalysts. Somewhat later this spectroscopy was also applied to the study of electron transfer processes, often in radical enzymes. The study of diamagnetic proteins and nucleic acids with site-directed spin labeling (SDSL) techniques became really popular in the 1990s and early in the new millennium. The same applies to applications of pulsed EPR techniques to metalloproteins, although the pioneering work in this field by Mims and Peisach dates back to the early 1970s. Pulsed dipolar spectroscopy for the measurement of distance distributions in the nanometer range has become the major EPR-based tool in structural biology during the past 15 years and is still expanding its scope. EPR (or ESR) imaging may appear to be overshadowed by (nuclear) MRI, as it has not yet found clinical application. However, development of EPR-based imaging modalities has recently gained much momentum as they can provide information that is inaccessible by any established imaging technology.

  2. Aggregation behavior of amphiphilic p(HPMA)-co-p(LMA) copolymers studied by FCS and EPR spectroscopy.

    Science.gov (United States)

    Hemmelmann, Mirjam; Kurzbach, Dennis; Koynov, Kaloian; Hinderberger, Dariush; Zentel, Rudolf

    2012-12-10

    A combined study of fluorescence correlation spectroscopy and electron paramagnetic resonance spectroscopy gave a unique picture of p(HPMA)-co-p(LMA) copolymers in aqueous solutions, ranging from the size of micelles and aggregates to the composition of the interior of these self-assembled systems. P(HPMA)-co-p(LMA) copolymers have shown high potential as brain drug delivery systems, and a detailed study of their physicochemical properties can help to elucidate their mechanism of action. Applying two complementary techniques, we found that the self-assembly behavior as well as the strength of hydrophobic attraction of the amphiphilic copolymers can be tuned by the hydrophobic LMA content or the presence of hydrophobic molecules or domains. Studies on the dependence of the hydrophobic lauryl side chain content on the aggregation behavior revealed that above 5 mol % laury side-chain copolymers self-assemble into intrachain micelles and larger aggregates. Above this critical alkyl chain content, p(HPMA)-co-p(LMA) copolymers can solubilize the model drug domperidone and exhibit the tendency to interact with model cell membranes.

  3. Organic matter transformation in the environment investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy: studies on lignins

    Science.gov (United States)

    Czechowski, Franciszek; Golonka, Iwona; Jezierski, Adam

    2004-05-01

    The lignins separated from angiosperm and gymnosperm trees, peat and xylitic brown coal were investigated by quantitative EPR. Observed free radicals in lignins are sensitive to alkaline environment. Gaseous ammonia interacting with solid lignins in resonance cavity shifts quinone-hydroquinone equilibria towards formation of semiquinone anions. Complexation of copper(II) by lignins causes drastic decrease of the semiquinones in the matrices. Formation of lignin-Pb(II) complexes yielded radicals characterised by unusually low g-value (1.9999-2.0003). Monomeric structural units of the investigated lignins were recognised by pyrolysis with in situ methylation by tetramethylammonium hydroxide. Although for the natural lignins the mixture of normal semiquinone signals at g about 2.0034 and signals at g 1.9999 were observed, some monomeric components of lignins (e.g., caffeic acid, pyrogallol) gave pure lines at g=1.9999. The bacterial oxidative biodegradation of lignin monomeric components and their Pb(II) complexes resulted in increase of the radical signals.

  4. Organic matter transformation in the environment investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy: studies on lignins

    Energy Technology Data Exchange (ETDEWEB)

    Czechowski, F.; Golonka, I.; Jezierski, A. [University of Wroclaw, Wroclaw (Poland). Faculty of Chemistry

    2004-05-01

    The lignins separated from angiosperm and gymnosperm trees, peat and xylitic brown coal were investigated by quantitative EPR. Observed free radicals in lignins are sensitive to alkaline environment. Gaseous ammonia interacting with solid lignins in resonance cavity shifts quinone-hydroquinone equilibria towards formation of semiquinone anions. Complexation of copper(II) by lignins causes drastic decrease of the semiquinones in the matrices. Formation of lignin-Pb(II) complexes yielded radicals characterised by unusually low g-value (1.9999-2.0003). Monomeric structural units of the investigated lignins were recognised by pyrolysis with in situ methylation by tetramethylammonium hydroxide. Although for the natural lignins the mixture of normal semiquinone signals at g about 2.0034 and signals at g 1.9999 were observed, some monomeric components of lignins (e.g., caffeic acid, pyrogallol) gave pure lines at g = 1.9999. The bacterial oxidative biodegradation of lignin monomeric components and their Pb(II) complexes resulted in increase of the radical signals.

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

    Science.gov (United States)

    1978-12-12

    Preliminary Interpretation of Spectra 60 sUltrafiltration eStudy of Cu(II)-IgGoSystems 74 < CONCLUSIONS 79 i Findings 79 Significance 79 Directions... cases , purchased standards, and making dilutions as required for the concentration (in ppm) range desired. By making solutions of standard concentration...hydration content in several cases , specifically chromium, iron, and nickel, the stock metal solutions were prepared by adding solid metal chloride to

  6. Platinum species in the pores of NaX, NaY and NaA zeolites studied using EPR, XAS and FTIR spectroscopies.

    Science.gov (United States)

    Akdogan, Yasar; Vogt, Christina; Bauer, Matthias; Bertagnolli, Helmut; Giurgiu, Liviu; Roduner, Emil

    2008-05-28

    The results of X-band EPR, X-ray absorption and Fourier transform infrared spectroscopy on Pt(NH(3))(4)(2+) exchanged NaX, NaY and NaA zeolites reveal after oxygen calcination at 573 K that diamagnetic Pt(2+) is not the only product. Calcination provides Pt(3+) cations, but depending on the heating rate, the decomposition of amino groups during calcination also produces hydrogen that reduces Pt(3+) to Pt(2+) and Pt(+). NaX (Si/Al = 1.23) has a more negative framework charge than NaY (Si/Al = 2.31), so Pt(3+) can be stabilized only in NaX, whereas lower oxidation states of Pt such as Pt(+) can be stabilized in both, NaX and NaY, and neither of the paramagnetic Pt cations are stabilized in NaUSY (Si/Al = 3). The autoreduction process allows controlling the number of Pt(3+) and Pt(+) in the NaX zeolite by changing the calcination heating rate: a heating rate of 1.25 K min(-1) gives only Pt(+), but 0.5 K min(-1) gives a Pt(3+)/Pt(+) ratio close to 1. The structure of the support is also important for the synthesis of Pt species. While isolated paramagnetic Pt ions were stabilized in faujasite zeolites (NaX and NaY), a paramagnetic Pt dimer was obtained in a Linde type A zeolite (LTA, Si/Al = 1) by applying the same preparation methods. The fraction of paramagnetic Pt species which were characterized by X-band EPR spectroscopy amounts to 2-18% of the total Pt in the zeolites, the remaining Pt must be diamagnetic.

  7. Application of EPR spectroscopy to the examination of pro-oxidant activity of coffee.

    Science.gov (United States)

    Krakowian, Daniel; Skiba, Dominik; Kudelski, Adam; Pilawa, Barbara; Ramos, Paweł; Adamczyk, Jakub; Pawłowska-Góral, Katarzyna

    2014-05-15

    Free radicals present in coffee may be responsible for exerting toxic effects on an organism. The objectives of this work were to compare free radicals properties and concentrations in different commercially available coffees, in solid and liquid states, and to determine the effect of roasting on the formation of free radicals in coffee beans of various origins. The free radicals content of 15 commercially available coffees (solid and liquid) was compared and the impact of processing examined using electron paramagnetic resonance (EPR) spectroscopy at X-band (9.3 GHz). First derivative EPR spectra were measured at microwave power in the range of 0.7-70 mW. The following parameters were calculated for EPR spectra: amplitude (A), integral intensity (I), and line-width (ΔBpp); g-Factor was obtained from resonance condition. Our study showed that free radicals exist in green coffee beans (10(16) spin/g), roasted coffee beans (10(18) spin/g), and in commercially available coffee (10(17)-10(18) spin/g). Free radical concentrations were higher in solid ground coffee than in instant or lyophilised coffee. Continuous microwave saturation indicated homogeneous broadening of EPR lines from solid and liquid commercial coffee samples as well as green and roasted coffee beans. Slow spin-lattice relaxation processes were found to be present in all coffee samples tested, solid and liquid commercial coffees as well as green and roasted coffee beans. Higher free radicals concentrations were obtained for both the green and roasted at 240 °C coffee beans from Peru compared with those originating from Ethiopia, Brazil, India, or Colombia. Moreover, more free radicals occurred in Arabica coffee beans roasted at 240 °C than Robusta. EPR spectroscopy is a useful method of examining free radicals in different types of coffee. Copyright © 2013 Elsevier Ltd. All rights reserved.

  8. A comparative study of the effect of cholesterol on bicelle model membranes using X-band and Q-band EPR spectroscopy.

    Science.gov (United States)

    Ghimire, Harishchandra; Inbaraj, Johnson J; Lorigan, Gary A

    2009-08-01

    X-band and Q-band electron paramagnetic resonance (EPR) spectroscopic techniques were used to investigate the structure and dynamics of cholesterol containing phospholipid bicelles based upon molecular order parameters (S(mol)), orientational dependent hyperfine splittings and line shape analysis of the corresponding EPR spectra. The nitroxide spin-label 3-beta-doxyl-5-alpha-cholestane (cholestane) was incorporated into DMPC/DHPC bicelles to report the alignment of bicelles in the static magnetic field. The influence of cholesterol on aligned phospholipid bicelles in terms of ordering, the ease of alignment, phase transition temperature have been studied comparatively at X-band and Q-band. At a magnetic field of 1.25 T (Q-band), bicelles with 20 mol% cholesterol aligned at a much lower temperature (313 K), when compared to 318 K at a 0.35 T field strength for X-band, showed better hyperfine splitting values (18.29 G at X-band vs. 18.55 G at Q-band for perpendicular alignment and 8.25 G at X-band vs. 7.83 G at Q-band for the parallel alignment at 318 K) and have greater molecular order parameters (0.76 at X-band vs. 0.86 at Q-band at 318 K). Increasing cholesterol content increased the bicelle ordering, the bicelle-alignment temperature and the gel to liquid crystalline phase transition temperature. We observed that Q-band is more effective than X-band for studying aligned bicelles, because it yielded a higher ordered bicelle system for EPR spectroscopic studies.

  9. Detection of free radicals formed by in vitro metabolism of fluoride using EPR spectroscopy.

    Science.gov (United States)

    Pawłowska-Góral, Katarzyna; Pilawa, Barbara

    2011-10-01

    In many parts of the globe, where water contains large amount of fluoride, fluorosis is a serious public health problem. It is accompanied by many changes, not only in the bones, but practically in all organs of the body. Since it was discovered that oxidation stress, together with the peroxidation of lipids which accompanies it, results in many diseases, research has been carried out on this aspect of fluorosis. The findings, however, are incomplete and divergent. The aim of our study was to determine the presence of free radicals in hepatocytes exposed to fluoride in concentrations which do not lead to changes in the concentrations of calcium and magnesium ions. Free radical properties of hepatocytes incubated with fluoride were studied by an X-band electron paramagnetic resonance (EPR) spectroscopy. Hepatocytes are paramagnetic and broad unsymmetrical EPR spectra were obtained for them. Oxygen free radicals with g-factor of 2.0032 exist in hepatocytes. The effect of fluoride concentration and the time of incubation on free radicals amount in cells were examined. The amount of free radicals in hepatocytes increases with the increase of fluoride concentration for all the incubation times (10, 30, and 60 min). The amount of free radicals in hepatocytes decreases with the increase of time of incubation for all the used fluoride concentrations (0.002, 0.082, and 0.164 mmol/l). EPR spectra of the studied cells are homogeneously broadened. Continuous microwave saturation of EPR lines indicates that slow spin-lattice relaxation processes exist in the studied cells. Strong dipolar interactions responsible for the broadening (ΔB(pp): 1.45-1.87 mT) of the EPR spectra exist in the hepatocytes. Copyright © 2011 Elsevier Ltd. All rights reserved.

  10. Camel molar tooth enamel response to gamma rays using EPR spectroscopy.

    Science.gov (United States)

    El-Faramawy, N A; El-Somany, I; Mansour, A; Maghraby, A M; Eissa, H; Wieser, A

    2017-10-12

    Tooth enamel samples from molar teeth of camel were prepared using a combined procedure of mechanical and chemical tooth treatment. Based on electron paramagnetic resonance (EPR) spectroscopy, the dose response of tooth enamel samples was examined and compared to that of human enamel. The EPR dose response of the tooth enamel samples was obtained through irradiation to gamma doses from 1 Gy up to 100 kGy. It was found that the radiation-induced EPR signal increased linearly with gamma dose for all studied tooth enamel samples, up to about 15 kGy. At higher doses, the dose response curve leveled off. The results revealed that the location of the native signal of camel tooth enamel was similar to that of enamel from human molars at 2.00644, but different from that of enamel from cows and goats. In addition, the peak-to-peak width (ΔH pp) for human and camel molar teeth was similar. It was also found that the response of camel enamel to gamma radiation was 36% lower than that of human enamel. In conclusion, the results indicate the suitability of camel teeth for retrospective gamma dosimetry.

  11. Application of EPR Spectroscopy to Examination of the Effect of Sterilization Process on Free Radicals in Different Herbs

    OpenAIRE

    Paw?owska-G?ral, Katarzyna; Ramos, Pawe?; Pilawa, Barbara; Kurzeja, Ewa

    2013-01-01

    Free radicals in the original and sterilized caraway, curry, curcuma and cardamom were studied. An X-band (9.3?GHz) electron paramagnetic resonance (EPR) spectroscopy was the experimental technique. Effect of microwave power in the range of 2.2?70?mW on amplitudes, linewidths, and lineshape parameters of the EPR spectra was tested. Free radicals concentrations in the non- and sterilized herb samples were compared. The aim of this work was to determine properties and concentration of free radi...

  12. 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).

    Science.gov (United States)

    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".

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

    Science.gov (United States)

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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  16. Thermodynamic basis of electron transfer in dihydroorotate dehydrogenase B from Lactococcus lactis: analysis by potentiometry, EPR spectroscopy, and ENDOR spectroscopy.

    Science.gov (United States)

    Mohsen, Al-Walid A; Rigby, Stephen E J; Jensen, Kaj Frank; Munro, Andrew W; Scrutton, Nigel S

    2004-06-01

    Dihydroorotate dehydrogenase B (DHODB) is a complex iron-sulfur flavoprotein that catalyzes the conversion of dihydroorotate to orotate and the reduction of NAD(+). The enzyme is a dimer of heterodimers containing an FMN, an FAD, and a 2Fe-2S center. UV-visible, EPR, and ENDOR spectroscopies have been used to determine the reduction potentials of the flavins and the 2Fe-2S center and to characterize radicals and their interactions. Reductive titration using dithionite indicates a five-electron capacity for DHODB. The midpoint reduction potential of the 2Fe-2S center (-212 +/- 3 mV) was determined from analysis of absorption data at 540 nm, where absorption contributions from the two flavins are small. The midpoint reduction potentials of the oxidized/semiquinone (E(1)) and semiquinone/hydroquinone (E(2)) couples for the FMN (E(1) = -301 +/- 6 mV; E(2) = -252 +/- 8 mV) and FAD (E(1) = -312 +/- 6 mV; E(2) = -297 +/- 5 mV) were determined from analysis of spectral changes at 630 nm. Corresponding values for the midpoint reduction potentials for FMN (E(1) = -298 +/- 4 mV; E(2) = -259 +/- 5 mV) in the isolated catalytic subunit (subunit D, which lacks the 2Fe-2S center and FAD) are consistent with the values determined for the FMN couples in DHODB. During reductive titration of DHODB, small amounts of the neutral blue semiquinone are observed at approximately 630 nm, consistent with the measured midpoint reduction potentials of the flavins. An ENDOR spectrum of substrate-reduced DHODB identifies hyperfine couplings to proton nuclei similar to those recorded for the blue semiquinone of free flavins in aqueous solution, thus confirming the presence of this species in DHODB. Spectral features observed during EPR spectroscopy of dithionite-reduced DHODB are consistent with the midpoint reduction potentials determined using UV-visible spectroscopy and further identify an unusual EPR signal with very small rhombic anisotropy and g values of 2.02, 1.99, and 1.96. This unusual

  17. Oxidation processes in Sicilian olive oils investigated by a combination of optical and EPR spectroscopy.

    Science.gov (United States)

    Ricca, Mariaelena; Foderà, Vito; Vetri, Valeria; Buscarino, Gianpiero; Montalbano, Maria; Leone, Maurizio

    2012-10-01

    Extra virgin olive oil (EVOO) is recognized as one of the healthiest foods for its high content of antioxidants, which forestall and slow down radical formation. Free radical-initiated oxidation is considered one of the main causes of rancidity in fats and oils. As a consequence, reliable protocols for the investigation of oil oxidation based on selective, noninvasive, and fast methods are highly desirable. Here we report an experimental approach based on UV-Vis absorbance, steady-state fluorescence, and electron paramagnetic resonance (EPR) spectroscopy for studying oxidation processes induced by temperature for a period up to 35 d on Sicilian EVOO samples. We followed the decrease in β-carotene content during incubation time and observed changes in polyphenols and tocopherols during the oxidation processes, focusing on the time scale of those changes. Using EPR spectroscopy, the free radical formation in different oil samples is reported, providing a fingerprint for both the antioxidant content and temporal features of the oxidation process at its early stage. We monitor β-carotene and chlorophyll in an auto-oxidation process. A protocol based on spectroscopic measurements is presented and can be used for the quality control process of commercial olive oil. © 2012 Institute of Food Technologists®

  18. EPR spectroscopy of a family of Cr(III) 7M(II) (M = Cd, Zn, Mn, Ni) "wheels": studies of isostructural compounds with different spin ground states

    DEFF Research Database (Denmark)

    Piligkos, Stergios; Weihe, Høgni; Bill, Eckhard

    2009-01-01

    spin states is observed.We present highly resolved multifrequency (X-, K-, Q- and W-band) continous wave EPR spectra of the heterooctametalic "wheels", [(CH(3))(2)NH(2)][Cr(III) (7)M(II)F(8)((CH(3))(3)CCOO)(16)], hereafter Cr(7)M, where M=Cd, Zn, Mn, and Ni. These experimental spectra provide rare...

  19. High-field EPR spectroscopy of thermal donors in silicon

    DEFF Research Database (Denmark)

    Dirksen, R.; Rasmussen, F.B.; Gregorkiewicz, T.

    1997-01-01

    Thermal donors generated in p-type boron-doped Czochralski-grown silicon by a 450 degrees C heat treatment have been studied by high-field magnetic resonance spectroscopy. In the experiments conducted at a microwave frequency of 140 GHz and in a magnetic field of approximately 5 T four individual...

  20. EPR study on gamma-irradiated fruits dehydrated via osmosis

    Energy Technology Data Exchange (ETDEWEB)

    Yordanov, N.D. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)]. E-mail: ndyepr@bas.bg; Aleksieva, K. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)

    2007-06-15

    The shape and time stability of the electron paramagnetic resonance (EPR) spectra of non- and {gamma}-irradiated papaya, melon, cherry and fig samples dehydrated via osmosis are reported. It is shown that non-irradiated samples are generally EPR silent whereas {gamma}-irradiated exhibit 'sugar-like' EPR spectra. The recorded EPR spectra are monitored for a period of 7 months after irradiation (stored at low humidity and in the dark). The results suggest longer period of unambiguous identification of the radiation processing of osmose dehydrated fruits. Therefore, the Protocol EN 13708,2001 issued by CEN is fully applicable for the studied fruit samples.

  1. EPR spectroscopy of a family of Cr(III) 7M(II) (M = Cd, Zn, Mn, Ni) "wheels": studies of isostructural compounds with different spin ground states.

    Science.gov (United States)

    Piligkos, Stergios; Weihe, Høgni; Bill, Eckhard; Neese, Frank; El Mkami, Hassane; Smith, Graham M; Collison, David; Rajaraman, Gopalan; Timco, Grigore A; Winpenny, Richard E P; McInnes, Eric J L

    2009-01-01

    Spinning wheels: The presented highly resolved multifrequency continuous wave EPR spectra (e.g., see figure) of the heterooctametalic "wheels" Cr(7)M provide rare examples of high nuclearity polymetallic systems where detailed information on the spin-Hamiltonian parameters of the ground and excited spin states is observed.We present highly resolved multifrequency (X-, K-, Q- and W-band) continous wave EPR spectra of the heterooctametalic "wheels", [(CH(3))(2)NH(2)][Cr(III) (7)M(II)F(8)((CH(3))(3)CCOO)(16)], hereafter Cr(7)M, where M=Cd, Zn, Mn, and Ni. These experimental spectra provide rare examples of high nuclearity polymetallic systems where detailed information on the spin-Hamiltonian parameters of the ground and excited spin states is observed. We interpret the EPR spectra by use of restricted size effective subspaces obtained by the rigorous solution of spin-Hamiltonians of dimension up to 10(5) by use of the Davidson algorithm. We show that transferability of spin-Hamiltonian parameters across complexes of the Cr(7)M family is possible and that the spin-Hamiltonian parameters of Cr(7)M do not have sharply defined values, but are rather distributed around a mean value.

  2. High-frequency EPR and ENDOR spectroscopy on semiconductor quantum dots

    NARCIS (Netherlands)

    Baranov, P.G.; Orlinskii, S.B.; de Mello Donega, C.|info:eu-repo/dai/nl/125593899; Schmidt, J.

    2010-01-01

    It is shown that high-frequency electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy are excellent tools for the investigation of the electronic properties of semiconductor quantum dots (QDs). The great attractions of these techniques are that, in contrast

  3. Identification of irradiated food by EPR-spectroscopy and tomography

    Energy Technology Data Exchange (ETDEWEB)

    Groth, N. (KAI e.V., Tomographie-Labor, Berlin (Germany)); Anders, B. (Technische Fachhochschule Berlin (Germany). Fachbereich Mathematik/Physik); Maerzke, A. (Forschungsstelle fuer Ortsaufloesende Messtechnik e.V., Berlin (Germany)); Nitschke, S. (KAI e.V., Tomographie-Labor, Berlin (Germany)); Schlawe, R. (Forschungsstelle fuer Ortsaufloesende Messtechnik e.V., Berlin (Germany)); Herrling, T. (KAI e.V., Tomographie-Labor, Berlin (Germany))

    1993-01-01

    Food irradiation is used to kill harmful microorganisms (e.g. salmonella), this improving food safety and extending the shelf-life. The electron paramagnetic resonance (EPR) detection of stable, radiation-induced free radicals within the matrix of calcified tissue is well established. An extention of this technique to food provides in suitable cases one of the most promissing methods for detecting that irradiation has been performed. It provides an excellent method for the identification of irradiated foods containing bones or calcified cuticle even in the absence of unirradiated controls. Bones of chicken, pepper grains and lentils were also identified as irradiated some weeks after radiation treatment. The method is rapid and can detect very low doses. With EPR - Tomography the 2D spatial distribution of the irradiation induced stable radicals in the cross section of a chicken bone was measured. The use of ionising radiation to treat certain foodstuffs is increasingly of interest and there is a need to determine wether irradiation has occured, and to what extent. (orig.)

  4. EPR study on tomatoes before and after gamma-irradiation

    Science.gov (United States)

    Aleksieva, K.; Georgieva, L.; Tzvetkova, E.; Yordanov, N. D.

    2009-09-01

    The results from the EPR studies on fresh, air-dried and lyophilized tomato samples before and after gamma-irradiation are reported. Before irradiation fresh and air-dried tomatoes exhibit one singlet EPR line characterized with common g-factor of 2.0048±0.0005, whereas freeze-dried tomato does not show any EPR spectrum. After irradiation, a typical "cellulose-like" triplet EPR spectrum appears in all samples, attributed to cellulose free radicals, generated by gamma-irradiation. It consists of intense central line with g=2.0048±0.0005 and two weak satellite lines separated ca. 3 mT left and right of it. In air-dried and lyophilized tomatoes the "cellulose-like" EPR spectrum is superimposed by an additional partly resolved carbohydrate spectrum. Fading measurements of the radiation-induced EPR signals indicate that the intensity of the EPR spectra of air-dried and freeze-dried tomato are reduced to about 50% after 50 days, whereas those of fresh irradiated tomatoes kept at 4 °C fade completely in 15 days. The reported results unambiguously show that the presence of two satellite lines in the EPR "cellulose-like" spectra of tomato samples can be used for identification of radiation processing.

  5. Application of EPR Spectroscopy to Examination of the Effect of Sterilization Process on Free Radicals in Different Herbs.

    Science.gov (United States)

    Pawłowska-Góral, Katarzyna; Ramos, Paweł; Pilawa, Barbara; Kurzeja, Ewa

    2013-03-01

    Free radicals in the original and sterilized caraway, curry, curcuma and cardamom were studied. An X-band (9.3 GHz) electron paramagnetic resonance (EPR) spectroscopy was the experimental technique. Effect of microwave power in the range of 2.2-70 mW on amplitudes, linewidths, and lineshape parameters of the EPR spectra was tested. Free radicals concentrations in the non- and sterilized herb samples were compared. The aim of this work was to determine properties and concentration of free radicals in steam sterilized caraway, curry, curcuma and cardamom. It was pointed out that free radicals (~10(18) spin/g) exist in both the original and sterilized herbs. Complex free radical system with oxygen and carbon paramagnetic centers characterizes the examined herbs. Homogeneously dipolar broadened EPR spectra were measured for all the tested herbs. Slow spin-lattice relaxation processes exist in the examined samples. Practical usefulness of EPR method in food technology was discussed.

  6. Irradiated bivalve mollusks: Use of EPR spectroscopy for identification and dosimetry

    Energy Technology Data Exchange (ETDEWEB)

    Alberti, Angelo, E-mail: aalberti@isof.cnr.it [CNR-ISOF, Area della Ricerca di Bologna, Via P. Gobetti 101, Bologna I-40129 (Italy); Chiaravalle, Eugenio [Istituto Zooprofilattico Sperimentale della Puglia e Basilicata, Via Manfredonia 20, Foggia I-71100 (Italy); Fuochi, Piergiorgio; Macciantelli, Dante [CNR-ISOF, Area della Ricerca di Bologna, Via P. Gobetti 101, Bologna I-40129 (Italy); Mangiacotti, Michele, E-mail: michelemangiacotti@libero.it [Istituto Zooprofilattico Sperimentale della Puglia e Basilicata, Via Manfredonia 20, Foggia I-71100 (Italy); Marchesani, Giuliana [Istituto Zooprofilattico Sperimentale della Puglia e Basilicata, Via Manfredonia 20, Foggia I-71100 (Italy); Plescia, Elena [CNR-ISOF, Area della Ricerca di Bologna, Via P. Gobetti 101, Bologna I-40129 (Italy)

    2011-12-15

    High energy radiation treatment of foodstuff for microbial control and shelf-life extension is being used in many countries. However, for consumer protection and information, the European Union has adopted the Directives 1999/2/EC and 1999/3/EC to harmonize the rules concerning the treatment and trade of irradiated foods in EU countries. Among the validated methods to detect irradiated foods the EU directives also include Electron Paramagnetic Resonance (EPR/ESR) spectroscopy. We describe herein the use of EPR for identification of four species of bivalve mollusks, i.e. brown Venus shells (Callista chione), clams (Tapes semidecussatus), mussels (Mytilus galloprovincialis) and oysters (Ostrea edulis) irradiated with {sup 60}Co {gamma}-rays. EPR could definitely identify irradiated seashells due to the presence of long-lived free radicals, primarily CO{sub 2}{sup -}, CO{sub 3}{sup 3-}, SO{sub 2}{sup -} and SO{sub 3}{sup -} radical anions. The presence of other organic free radicals, believed to originate from conchiolin, a scleroprotein present in the shells, was also ascertained. The use of one of these radicals as a marker for irradiation of brown Venus shells and clams can be envisaged. We also propose a dosimetric protocol for the reconstruction of the administered dose in irradiated oysters. - Highlights: > EPR spectroscopy is confirmed a valuable identification tool for irradiated mollusks. > A conchiolin-derived radical can be used as irradiation marker for some mollusks. > A reliable protocol is outlined for dose reconstruction of irradiated oysters.

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

    Directory of Open Access Journals (Sweden)

    Daniel eNohr

    2015-09-01

    Full Text Available 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.

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

    Science.gov (United States)

    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.

  9. Wideband frequency-swept excitation in pulsed EPR spectroscopy

    Science.gov (United States)

    Doll, Andrin; Jeschke, Gunnar

    2017-07-01

    Excitation of electron spins with monochromatic rectangular pulses is limited to bandwidths that are smaller than the spectral widths of most organic radicals and much smaller than the spectral widths of transition and rare earth metal ions. With frequency-swept pulses, bandwidths of up to 800 MHz have previously been attained for excitation and detection of spin packets at frequencies of about 9.6 GHz and bandwidths of up to 2.5 GHz in a polarization transfer experiment at frequencies of about 34 GHz. The remaining limitations, mainly due to resonator bandwidth and due to pulse length restrictions are discussed. Flip angles for state-space rotations on passage of a transition can generally be computed from the critical adiabaticity by the Landau-Zener-Stückelberg-Majorana expression. For hyperbolic secant pulses, the Demkov-Kunike model describes excitation for spin packets within and outside the sweep range. Well within the sweep range, the Bloch-Siegert phase shift is proportional to critical adiabaticity to a very good approximation. Because of the dependence of both flip angle and coherence phase on critical adiabaticity, it is advantageous to use pairs of amplitude and frequency modulation functions that provide such offset-independent adiabaticity. Compensation for the resonator response function should restore offset-independent adiabaticity. Whereas resonance offsets and Bloch-Siegert phase can be refocused at certain pulse length ratios, phase dispersion in coupled spin systems cannot generally be refocused. Based on the bandwidth limitations that arise from spin dynamics, requirements are derived for a spectrometer that achieves precise spin control over wide bands. The design of such a spectrometer and hardware characterization by EPR experiments are discussed.

  10. Investigating fatty acids inserted into magnetically aligned phospholipid bilayers using EPR and solid-state NMR spectroscopy

    Science.gov (United States)

    Nusair, Nisreen A.; Tiburu, Elvis K.; Dave, Paresh C.; Lorigan, Gary A.

    2004-06-01

    This is the first time 2H solid-state NMR spectroscopy and spin-labeled EPR spectroscopy have been utilized to probe the structural orientation and dynamics of a stearic acid incorporated into magnetically aligned phospholipid bilayers or bicelles. The data gleaned from the two different techniques provide a more complete description of the bilayer membrane system. Both methods provided similar qualitative information on the phospholipid bilayer, high order, and low motion for the hydrocarbon segment close to the carboxyl groups of the stearic acid and less order and more rapid motion at the end towards the terminal methyl groups. However, the segmental order parameters differed markedly due to the different orientations that the nitroxide and C-D bond axes transform with the various stearic acid acyl chain conformations, and because of the difference in dynamic sensitivity between NMR and EPR over the timescales examined. 5-, 7-, 12-, and 16-doxylstearic acids spin-labels were used in the EPR experiments and stearic acid-d 35 was used in the solid-state NMR experiments. The influence of the addition of cholesterol and the variation of temperature on the fatty acid hydrocarbon chain ordering in the DMPC/DHPC phospholipid bilayers was also studied. Cholesterol increased the degree of ordering of the hydrocarbon chains. Conversely, as the temperature of the magnetically aligned phospholipid bilayers increased, the order parameters decreased due to the higher random motion of the acyl chain of the stearic acid. The results indicate that magnetically aligned phospholipid bilayers are an excellent model membrane system and can be used for both NMR and EPR studies.

  11. EPR and NMR studies of amorphous aluminum borates

    NARCIS (Netherlands)

    Simon, S.; Pol, A. van der; Reijerse, E.J.; Kentgens, A.P.M.; Moorsel, G.J.M.P. van; Boer, E. de

    1994-01-01

    Amorphous aluminium borates, Al2(1–x)B2xO3 with O [less-than-or-eq]x[less-than-or-eq] 0.5, prepared from mixtures of aluminium nitrate, boric acid and glycerol, have been studied by EPR and 27Al MASNMR as a function of composition and heat-treatment temperature (Tt[less-than-or-eq] 860 °C). EPR

  12. EPR spectroscopy as a tool in homogeneous catalysis research

    NARCIS (Netherlands)

    Goswami, M.; Chirila, A.; Rebreyend, C.; de Bruin, B.

    2015-01-01

    In the context of homogeneous catalysis, open-shell systems are often quite challenging to characterize. Nuclear magnetic resonance (NMR) spectroscopy is the most frequently applied tool to characterize organometallic compounds, but NMR spectra are usually broad, difficult to interpret and often

  13. EFFECT OF CADMIUM(II) ON FREE RADICALS IN DOPA-MELANIN TESTED BY EPR SPECTROSCOPY.

    Science.gov (United States)

    Zdybel, Magdalena; Pilawa, Barbara; Chodurek, Ewa

    2015-01-01

    Electron paramagnetic resonance (EPR) spectroscopy may be applied to examine interactions of melanin with metal ions and drugs. In this work EPR method was used to examination of changes in free radical system of DOPA-melanin--the model eumelanin after complexing with diamagnetic cadmium(II) ions. Cadmium(II) may affect free radicals in melanin and drugs binding by this polymer, so the knowledge of modification of properties and free radical concentration in melanin is important to pharmacy. The effect of cadmium(II) in different concentrations on free radicals in DOPA-melanin was determined. EPR spectra of DOPA-melanin, and DOPA-melanin complexes with cadmium(II) were measured by an X-band (9.3 GHz) EPR spectrometer produced by Radiopan (Poznań, Poland) and the Rapid Scan Unit from Jagmar (Krak6w, Poland). The DOPA (3,4-dihydroxyphenylalanine) to metal ions molar ratios in the reaction mixtures were 2:1, 1:1, and 1: 2. High concentrations of o-semiquinone (g ~2.0040) free radicals (~10(21)-10(22) spin/g) characterize DOPA-melanin and its complexes with cadmium(II). Formation of melanin complexes with cadmium(II) increase free radical concentration in DOPA-melanin. The highest free radical concentration was obtained for DOPA-melanin-cadmium(II) (1:1) complexes. Broad EPR lines with linewidths: 0.37-0.73 mT, were measured. Linewidths increase after binding of cadmium(II) to melanin. Changes of integral intensities and linewidths with increasing microwave power indicate the homogeneous broadening of EPR lines, independently on the metal ion concentration. Slow spin-lattice relaxation processes existed in all the tested samples, their EPR lines saturated at low microwave powers. Cadmium(II) causes fastening of spin-lattice relaxation processes in DOPA-melanin. The EPR results bring to light the effect of cadmium(II) on free radicals in melanin, and probably as the consequence on drug binding to eumelanin.

  14. EPR study on non- and gamma-irradiated herbal pills

    Science.gov (United States)

    Aleksieva, K.; Lagunov, O.; Dimov, K.; Yordanov, N. D.

    2011-06-01

    The results of EPR studies on herbal pills of marigold, hawthorn, yarrow, common balm, tutsan, nettle and thyme before and after gamma-irradiation are reported. Before irradiation all samples exhibit one weak singlet EPR line with a g-factor of 2.0048±0.0005. After irradiation herbal pills could be separated in two groups according to their EPR spectra. Radiation-induced free radicals in pills of marigold, yarrow, nettle, tutsan and thyme could be attributed mainly to saccharide excipients. Tablets of hawthorn and common balm show "cellulose-like" EPR spectrum, superimposed on partly resolved carbohydrate spectrum, due to the active part (herb) and inulin, which is present in the pills as an excipient. Fading study of the radiation-induced EPR signals confirms that sugar radicals are more stable than cellulose species. The reported results show that the presence of characteristic EPR spectra of herbal pills due to excipients or active part can be used as unambiguous proof of radiation processing within 35 or more days after irradiation.

  15. EPR study on non- and gamma-irradiated herbal pills

    Energy Technology Data Exchange (ETDEWEB)

    Aleksieva, K., E-mail: katerina_bas@abv.b [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Lagunov, O. [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Dimov, K. [Institute of Cryobiology and Food Technologies, 1162 Sofia (Bulgaria); Yordanov, N.D. [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)

    2011-06-15

    The results of EPR studies on herbal pills of marigold, hawthorn, yarrow, common balm, tutsan, nettle and thyme before and after gamma-irradiation are reported. Before irradiation all samples exhibit one weak singlet EPR line with a g-factor of 2.0048{+-}0.0005. After irradiation herbal pills could be separated in two groups according to their EPR spectra. Radiation-induced free radicals in pills of marigold, yarrow, nettle, tutsan and thyme could be attributed mainly to saccharide excipients. Tablets of hawthorn and common balm show 'cellulose-like' EPR spectrum, superimposed on partly resolved carbohydrate spectrum, due to the active part (herb) and inulin, which is present in the pills as an excipient. Fading study of the radiation-induced EPR signals confirms that sugar radicals are more stable than cellulose species. The reported results show that the presence of characteristic EPR spectra of herbal pills due to excipients or active part can be used as unambiguous proof of radiation processing within 35 or more days after irradiation.

  16. Determination of the Antioxidant Status of the Skin by In Vivo-Electron Paramagnetic Resonance (EPR Spectroscopy

    Directory of Open Access Journals (Sweden)

    Silke Barbara Lohan

    2015-08-01

    Full Text Available Organisms produce free radicals which are essential for various metabolic processes (enzymatic oxidation, cellular respiration, signaling. Antioxidants are important chemical compounds that specifically prevent the oxidation of substances by scavenging radicals, especially reactive oxygen species (ROS. Made up of one or two unpaired electrons, ROS are free radicals that are highly reactive and can attack other metabolites. By using electron paramagnetic resonance (EPR spectroscopy, it is possible to measure paramagnetic substances such as free radicals. Therefore the dermal antioxidant activity can be determined by applying semi-stable radicals onto the skin and measuring the antioxidant-induced radical scavenging activity in the skin. In recent years, EPR has been developed as a spectroscopic method for determining the antioxidant status in vivo. Several studies have shown that an additional uptake of dietary supplements, such as carotenoids or vitamin C in physiological concentrations, provide a protective effect against free radicals. Using the EPR technique it could be demonstrated that the radical production in stress situations, such as irradiation with infrared and visible light, was reduced with time. However, not only the oral uptake of antioxidants, but also the topical application of antioxidants, e.g., a hyperforin-rich cream, is very useful against the development of oxidative stress. Regular application of a hyperforin-rich cream reduced radical formation. The skin lipids, which are very important for the barrier function of the skin, were also stabilized.

  17. Characterization of Bifunctional Spin Labels for Investigating the Structural and Dynamic Properties of Membrane Proteins Using EPR Spectroscopy.

    Science.gov (United States)

    Sahu, Indra D; Craig, Andrew F; Dunagum, Megan M; McCarrick, Robert M; Lorigan, Gary A

    2017-10-05

    Site-directed spin labeling (SDSL) coupled with electron paramagnetic resonance (EPR) spectroscopy is a very powerful technique to study structural and dynamic properties of membrane proteins. The most widely used spin label is methanthiosulfonate (MTSL). However, the flexibility of this spin label introduces greater uncertainties in EPR measurements obtained for determining structures, side-chain dynamics, and backbone motion of membrane protein systems. Recently, a newer bifunctional spin label (BSL), 3,4-bis(methanethiosulfonylmethyl)-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-1-yloxy, has been introduced to overcome the dynamic limitations associated with the MTSL spin label and has been invaluable in determining protein backbone dynamics and inter-residue distances due to its restricted internal motion and fewer size restrictions. While BSL has been successful in providing more accurate information about the structure and dynamics of several proteins, a detailed characterization of the spin label is still lacking. In this study, we characterized BSLs by performing CW-EPR spectral line shape analysis as a function of temperature on spin-labeled sites inside and outside of the membrane for the integral membrane protein KCNE1 in POPC/POPG lipid bilayers and POPC/POPG lipodisq nanoparticles. The experimental data revealed a powder pattern spectral line shape for all of the KCNE1-BSL samples at 296 K, suggesting the motion of BSLs approaches the rigid limit regime for these series of samples. BSLs were further utilized to report for the first time the distance measurement between two BSLs attached on an integral membrane protein KCNE1 in POPC/POPG lipid bilayers at room temperature using dipolar line broadening CW-EPR spectroscopy. The CW dipolar line broadening EPR data revealed a 15 ± 2 Å distance between doubly attached BSLs on KCNE1 (53/57-63/67) which is consistent with molecular dynamics modeling and the solution NMR structure of KCNE1 which yielded a

  18. Characterization of KCNE1 inside Lipodisq Nanoparticles for EPR Spectroscopic Studies of Membrane Proteins.

    Science.gov (United States)

    Sahu, Indra D; Zhang, Rongfu; Dunagan, Megan M; Craig, Andrew F; Lorigan, Gary A

    2017-06-01

    EPR spectroscopic studies of membrane proteins in a physiologically relevant native membrane-bound state are extremely challenging due to the complexity observed in inhomogeneity sample preparation and dynamic motion of the spin-label. Traditionally, detergent micelles are the most widely used membrane mimetics for membrane proteins due to their smaller size and homogeneity, providing high-resolution structure analysis by solution NMR spectroscopy. However, it is often difficult to examine whether the protein structure in a micelle environment is the same as that of the respective membrane-bound state. Recently, lipodisq nanoparticles have been introduced as a potentially good membrane mimetic system for structural studies of membrane proteins. However, a detailed characterization of a spin-labeled membrane protein incorporated into lipodisq nanoparticles is still lacking. In this work, lipodisq nanoparticles were used as a membrane mimic system for probing the structural and dynamic properties of the integral membrane protein KCNE1 using site-directed spin labeling EPR spectroscopy. The characterization of spin-labeled KCNE1 incorporated into lipodisq nanoparticles was carried out using CW-EPR titration experiments for the EPR spectral line shape analysis and pulsed EPR titration experiment for the phase memory time (Tm) measurements. The CW-EPR titration experiment indicated an increase in spectral line broadening with the addition of the SMA polymer which approaches close to the rigid limit at a lipid to polymer weight ratio of 1:1, providing a clear solubilization of the protein-lipid complex. Similarly, the Tm titration experiment indicated an increase in Tm values with the addition of SMA polymer and approaches ∼2 μs at a lipid to polymer weight ratio of 1:2. Additionally, CW-EPR spectral line shape analysis was performed on six inside and six outside the membrane spin-label probes of KCNE1 in lipodisq nanoparticles. The results indicated significant

  19. Multifrequency EPR Studies of Manganese Catalases Provide a Complete Description of Proteinaceous Nitrogen Coordination

    OpenAIRE

    Stich, Troy A.; Whittaker, James W.; Britt, R. David

    2010-01-01

    Pulse electron paramagnetic resonance (EPR) spectroscopy is employed at two very different excitation frequencies, 9.77 and 30.67 GHz, in the study of the nitrogen coordination environment of the Mn(III)Mn(IV) state of the dimanganese-containing catalases from Lactobacillus plantarum and Thermus thermophilus. Consistent with previous studies, the lower-frequency results reveal one unique histidine nitrogen-Mn cluster interaction. For the first time, a second, more strongly hyperfine-coupled 1...

  20. Simultaneous EPR and optical spectroscopy of pure and Rh-doped barium calcium titanate crystals

    Science.gov (United States)

    Grachev, Valentin; Malovichko, Galina; Schirmer, Ortwin

    2003-03-01

    The large electro-optic coefficients and high holographic sensitivity of barium calcium titanate (Ba0.77Ca0.23TiO3, BCT) make it promising candidate for various applications, since it has no drawback related to the phase transition at 280 K like barium titanate. The nominally pure and Rh doped BCT crystals were investigated with the help of optical absorption spectroscopy, light induced absorption change measurements and electron paramagnetic resonance (EPR) in the temperature range between 4.2 and 300 K. Analyzing angular dependencies of the EPR lines we succeed to identify low-symmetry and nearly cubic centers of iron trace impurity. Four other paramagnetic defects were found after illumination: Ti3+, Rh2+, O- and Pt3+. All these defects are participants of charge transfer processes. At the light energy E about 1.3 eV the holes abandon Ti4+ creating the paramagnetic electronic Ti3+. At E > 2.3 eV O2- ions capture the holes and create hole O- centers and simultaneously Ti3+ concentration increases. Nearly located non-controlled or intentionally introduced impurities (Sr, K, Na, Ca...) may serve as pins for the fixation of the electrons and holes. Additional correlated changes were found at E > 3.2 eV (band-band transition), when EPR lines of Rh2+, Pt3+ appear and intensities of Ti3+, O- and Fe3+ essentially increase. Models of defects involved in these light induced processes are proposed.

  1. EPR and optical absorption spectral studies on sphalerite mineral

    Science.gov (United States)

    Seshamaheswaramma, K.; Reddy, G. Udayabhaskara; Reddy, A. Varada; Lakshmi Reddy, S.; Frost, R. L.; Endo, Tamio

    2011-10-01

    The mineral sphalerite (Zn,Fe)S has been characterized by a combination of X-ray diffraction, EPR and NIR spectroscopy. The optical absorption spectrum of mineral sphalerite is due to an iron impurity only, which is in a distorted octahedral environment. The g = 2.2 is attributed to iron and g and A value observed in the spectrum 1.999 and 6.0 mT are assigned to Mn(II) impurity in the mineral. These results indicate that iron and Mn(II) impurity have entered the lattice by substitution. The EPR results confirm the presence of manganese in a distorted octahedral environment. It is evident from the chemical analysis that iron is present in higher concentrations. NIR results are due to the presence of water and sulphide fundamentals which also support the formula of the mineral. No sulphate in the sphalerite mineral was observed.

  2. 2'-Alkynylnucleotides: A Sequence- and Spin Label-Flexible Strategy for EPR Spectroscopy in DNA.

    Science.gov (United States)

    Haugland, Marius M; El-Sagheer, Afaf H; Porter, Rachel J; Peña, Javier; Brown, Tom; Anderson, Edward A; Lovett, Janet E

    2016-07-27

    Electron paramagnetic resonance (EPR) spectroscopy is a powerful method to elucidate molecular structure through the measurement of distances between conformationally well-defined spin labels. Here we report a sequence-flexible approach to the synthesis of double spin-labeled DNA duplexes, where 2'-alkynylnucleosides are incorporated at terminal and internal positions on complementary strands. Post-DNA synthesis copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions with a variety of spin labels enable the use of double electron-electron resonance experiments to measure a number of distances on the duplex, affording a high level of detailed structural information.

  3. Adsorption of adenine and thymine on zeolites: FT-IR and EPR spectroscopy and X-ray diffractometry and SEM studies.

    Science.gov (United States)

    Baú, João Paulo T; Carneiro, Cristine E A; de Souza Junior, Ivan G; de Souza, Cláudio M D; da Costa, Antonio C S; di Mauro, Eduardo; Zaia, Cássia T B V; Coronas, Joaquin; Casado, Clara; de Santana, Henrique; Zaia, Dimas A M

    2012-02-01

    The interactions of adenine and thymine with and adsorption on zeolites were studied using different techniques. There were two main findings. First, as shown by X-ray diffractometry, thymine increased the decomposition of the zeolites (Y, ZSM-5) while adenine prevented it. Second, zeolite Y adsorbed almost the same amount of adenine and thymine, thus both nucleic acid bases could be protected from hydrolysis and UV radiation and could be available for molecular evolution. The X-ray diffractometry and SEM showed that artificial seawater almost dissolved zeolite A. The adsorption of adenine on ZSM-5 zeolite was higher than that of thymine (Student-Newman-Keuls test-SNK pzeolite, when compared to other zeolites (SNK pzeolites was not statistically different (SNK p>0.05). The adsorption of adenine and thymine on zeolites did not depend on pore size or Si/Al ratio and it was not explained only by electrostatic forces; rather van der Waals interactions should also be considered.

  4. Magnetic, catalytic, EPR and electrochemical studies on binuclear ...

    Indian Academy of Sciences (India)

    Unknown

    Spectral, catalytic, magnetic, EPR and electrochemical studies have been ... attention in recent years, particularly to understand the redox function of copper ... Binuclear Cu(II) complexes with 3,4-disubstituted phenol. 3. 2.2 Materials. All solvents and reagents were obtained from commercial source. Ethanol and methanol.

  5. Electrical transport and EPR investigations: A comparative study for ...

    Indian Academy of Sciences (India)

    A detailed comparative study of electron paramagnetic resonance (EPR) in conjunction with d.c. electrical conductivity has been undertaken to know about the charge transport mechanism in polyaniline (PANI) doped with monovalent and multivalent protonic acids. This work is in continuation of our previous work for further ...

  6. [Laser flash photolysis, EPR and Raman studies of liquids at elevated pressures

    Energy Technology Data Exchange (ETDEWEB)

    Eyring, E.M.

    1992-01-01

    The proposed research will solve a number of analytical chemical problems in solutions with measurement techniques that benefit from the use of elevated hydrostatic pressures: stopped-flow spectrophotometry (Gd[sup 3+] + L(ligand), [RuL[sub 5]H[sub 2]O][sup 2+], laser flash photolysis of Mo(CO)[sub 6] + L, flash photolysis of binuclear metalloproteins), EPR spectroscopy (Gd[sup 3+] ion-exchanged into ETS-10 and ETAS-10 molecular sieves), laser flash photolysis kinetic studies of Mo(CO)[sub 6]-2,2'-bipyridine, and electrochemical studies of metalloporphyrins using resonance Raman spectroscopy.

  7. [Laser flash photolysis, EPR and Raman studies of liquids at elevated pressures

    Energy Technology Data Exchange (ETDEWEB)

    Eyring, E.M.

    1992-10-01

    The proposed research will solve a number of analytical chemical problems in solutions with measurement techniques that benefit from the use of elevated hydrostatic pressures: stopped-flow spectrophotometry (Gd{sup 3+} + L(ligand), [RuL{sub 5}H{sub 2}O]{sup 2+}, laser flash photolysis of Mo(CO){sub 6} + L, flash photolysis of binuclear metalloproteins), EPR spectroscopy (Gd{sup 3+} ion-exchanged into ETS-10 and ETAS-10 molecular sieves), laser flash photolysis kinetic studies of Mo(CO){sub 6}-2,2`-bipyridine, and electrochemical studies of metalloporphyrins using resonance Raman spectroscopy.

  8. Multifrequency EPR studies of manganese catalases provide a complete description of proteinaceous nitrogen coordination.

    Science.gov (United States)

    Stich, Troy A; Whittaker, James W; Britt, R David

    2010-11-18

    Pulse electron paramagnetic resonance (EPR) spectroscopy is employed at two very different excitation frequencies, 9.77 and 30.67 GHz, in the study of the nitrogen coordination environment of the Mn(III)Mn(IV) state of the dimanganese-containing catalases from Lactobacillus plantarum and Thermus thermophilus. Consistent with previous studies, the lower-frequency results reveal one unique histidine nitrogen-Mn cluster interaction. For the first time, a second, more strongly hyperfine-coupled (14)N atom is unambiguously observed through the use of higher frequency/higher field EPR spectroscopy. The low excitation frequency spectral features are rationalized as arising from the interaction of a histidine nitrogen that is bound to the Mn(IV) ion, and the higher excitation frequency features are attributed to the histidine nitrogen bound to the Mn(III) ion. These results allow for the computation of intrinsic hyperfine coupling constants, which range from 2.2 to 2.9 MHz, for sp(2)-hybridized nitrogens coordinating equatorially to high-valence Mn ions. The relevance of these findings is discussed in the context of recent results from analogous higher frequency EPR studies of the Mn cluster in photosystem II and other exchange-coupled, transition metal-containing systems.

  9. Solid-state NMR and EPR Spectroscopy of Mn2+ -Substituted ATP-Fueled Protein Engines.

    Science.gov (United States)

    Wiegand, Thomas; Lacabanne, Denis; Keller, Katharina; Cadalbert, Riccardo; Lecoq, Lauriane; Yulikov, Maxim; Terradot, Laurent; Jeschke, Gunnar; Meier, Beat H; Böckmann, Anja

    2017-03-13

    Paramagnetic metal ions deliver structural information both in EPR and solid-state NMR experiments, offering a profitable synergetic approach to study bio-macromolecules. We demonstrate the spectral consequences of Mg2+ / Mn2+ substitution and the resulting information contents for two different ATP:Mg2+ -fueled protein engines, a DnaB helicase from Helicobacter pylori active in the bacterial replisome, and the ABC transporter BmrA, a bacterial efflux pump. We show that, while EPR spectra report on metal binding and provide information on the geometry of the metal centers in the proteins, paramagnetic relaxation enhancements identified in the NMR spectra can be used to localize residues at the binding site. Protein engines are ubiquitous and the methods described herein should be applicable in a broad context. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Delocalisation of photoexcited triplet states probed by transient EPR and hyperfine spectroscopy

    Science.gov (United States)

    Richert, Sabine; Tait, Claudia E.; Timmel, Christiane R.

    2017-07-01

    Photoexcited triplet states play a crucial role in photochemical mechanisms: long known to be of paramount importance in the study of photosynthetic reaction centres, they have more recently also been shown to play a major role in a number of applications in the field of molecular electronics. Their characterisation is crucial for an improved understanding of these processes with a particular focus on the determination of the spatial distribution of the triplet state wavefunction providing information on charge and energy transfer efficiencies. Currently, active research in this field is mostly focussed on the investigation of materials for organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). As the properties of triplet states and their spatial extent are known to have a major impact on device performance, a detailed understanding of the factors governing triplet state delocalisation is at the basis of the further development and improvement of these devices. Electron Paramagnetic Resonance (EPR) has proven a valuable tool in the study of triplet state properties and both experimental methods as well as data analysis and interpretation techniques have continuously improved over the last few decades. In this review, we discuss the theoretical and practical aspects of the investigation of triplet states and triplet state delocalisation by transient continuous wave and pulse EPR and highlight the advantages and limitations of the presently available techniques and the current trends in the field. Application of EPR in the study of triplet state delocalisation is illustrated on the example of linear multi-porphyrin chains designed as molecular wires.

  11. Redox reactions and the influence of natural Mn oxides on Cr oxidation in a contaminated site in northern Italy: evidence from Cr stable-isotopes and EPR spectroscopy

    OpenAIRE

    Marafatto F. F.; Petrini R.; Pinzino C.; Pezzetta E.; Slejko F.; Lutman A.

    2013-01-01

    Hexavalent chromium-contaminated groundwaters and sediments in northern Italy have been studied using the Cr stable-isotope systematics and electron spin resonance spectroscopy (ESR), in order to explore redox changes and soil-groundwater interactions. The isotopic data indicate a possible Cr(VI) source released into the environment from an industrial plant. EPR spectra on the sediments which constitute the aquifers show a broad asymmetric absorption due to coupled Fe(III) and coupled Cr(III)...

  12. Structure and dynamics of a conformationally constrained nitroxide side chain and applications in EPR spectroscopy.

    Science.gov (United States)

    Fleissner, Mark R; Bridges, Michael D; Brooks, Evan K; Cascio, Duilio; Kálai, Tamás; Hideg, Kálmán; Hubbell, Wayne L

    2011-09-27

    A disulfide-linked nitroxide side chain (R1) is the most widely used spin label for determining protein topology, mapping structural changes, and characterizing nanosecond backbone motions by site-directed spin labeling. Although the internal motion of R1 and the number of preferred rotamers are limited, translating interspin distance measurements and spatial orientation information into structural constraints is challenging. Here, we introduce a highly constrained nitroxide side chain designated RX as an alternative to R1 for these applications. RX is formed by a facile cross-linking reaction of a bifunctional methanethiosulfonate reagent with pairs of cysteine residues at i and i + 3 or i and i + 4 in an α-helix, at i and i + 2 in a β-strand, or with cysteine residues in adjacent strands in a β-sheet. Analysis of EPR spectra, a crystal structure of RX in T4 lysozyme, and pulsed electron-electron double resonance (ELDOR) spectroscopy on an immobilized protein containing RX all reveal a highly constrained internal motion of the side chain. Consistent with the constrained geometry, interspin distance distributions between pairs of RX side chains are narrower than those from analogous R1 pairs. As an important consequence of the constrained internal motion of RX, spectral diffusion detected with ELDOR reveals microsecond internal motions of the protein. Collectively, the data suggest that the RX side chain will be useful for distance mapping by EPR spectroscopy, determining spatial orientation of helical segments in oriented specimens, and measuring structural fluctuations on the microsecond time scale.

  13. High-frequency EPR on high-spin transition-metal sites

    NARCIS (Netherlands)

    Mathies, Guinevere

    2012-01-01

    The electronic structure of transition-metal sites can be probed by electron-paramagnetic-resonance (EPR) spectroscopy. The study of high-spin transition-metal sites benefits from EPR spectroscopy at frequencies higher than the standard 9.5 GHz. However, high-frequency EPR is a developing field. In

  14. Multifrequency EPR study on freeze-dried fruits before and after X-ray irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Yordanov, N.D. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)]. E-mail: ndyepr@bas.bg; Aleksieva, K. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Dimitrova, A. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Georgieva, L. [Institute of Cryobiology and Food Technologies, 1162 Sofia (Bulgaria); Tzvetkova, E. [Institute of Cryobiology and Food Technologies, 1162 Sofia (Bulgaria)

    2006-09-15

    X-, K- and Q-band EPR studies on lyophilized whole pulp parts of blue plum, apricot, peach, melon as well as achens and pulp separately of strawberry before and after X-ray irradiation are reported. Before irradiation all samples show in X band a weak singlet EPR line with g=2.0030+/-0.0005, except melon, which is EPR silent. Immediately after irradiation all samples exhibit complex fruit-depending spectra, which decay with time and change to give, in ca. 50days, an asymmetric singlet EPR line with g=2.0041+/-0.0005. Only apricot pulp gave a typical ''sugar-like'' EPR spectrum. Singlet EPR lines recorded after irradiation in X -band are K- and Q-band resolved as typical anisotropic EPR spectra with g{sub ||}=2.0023+/-0.0003 and g{sub -}bar =2.0041+/-0.0005. In addition, K- and Q-band EPR spectra of all samples show a superposition with the six EPR lines of Mn{sup 2+} naturally present in the fruits. The saturation behavior of the EPR spectra of achens of lyophilized and fresh strawberry is also studied. The differences in g factors of samples before and after X-ray irradiation might be used for the identification of radiation processing of fruits in the case of pulp and the differences in the EPR saturation behavior might be used for the achens of strawberry.

  15. Examination by EPR spectroscopy of free radicals in melanins isolated from A-375 cells exposed on valproic acid and cisplatin.

    Science.gov (United States)

    Chodurek, Ewa; Zdybel, Magdalena; Pilawa, Barbara; Dzierzewicz, Zofia

    2012-01-01

    Drug binding by melanin biopolymers influence the effectiveness of the chemotherapy, radiotherapy and photodynamic therapy. Free radicals of melanins take part in formation of their complex with drugs. The aim of this work was to determine the effect of the two compounds: valproic acid (VPA) and cisplatin (CPT) on free radicals properties of melanin isolated from A-375 melanoma cells. Free radicals were examined by an X-band (9.3 GHz) electron paramagnetic resonance (EPR) spectroscopy. EPR spectra were measured for the model synthetic eumelanin - DOPA-melanin, the melanin isolated from the control A-375 cells and these cells treated by VPA, CPT and both VPA and CPT. For all the examined samples broad EPR lines (deltaBpp: 0.48-0.68 mT) with g-factors of 2.0045-2.0060 characteristic for o-semiquinone free radicals were observed. Free radicals concentrations (N) in the tested samples, g-factors, amplitudes (A), integral intensities (I) and linewidths (deltaBpp) of the EPR spectra, were analyzed. The EPR lines were homogeneously broadened. Continuous microwave saturation of the EPR spectra indicated that slow spin-lattice relaxation processes existed in all the tested melanin samples. The relatively slowest spin-lattice relaxation processes characterized melanin isolated from A-375 cells treated with both VPA and CPT. The changes of the EPR spectra with increasing microwave power in the range of 2.2-70 mW were evaluated. Free radicals concentrations in the melanin from A-375 cells were higher than in the synthetic DOPA-melanin. The strong increase of free radicals concentration in the melanin from A-375 cells was observed after their treating by VPA. CPT also caused the increase of free radicals concentrations in the examined natural melanin. The free radicals concentration in melanin isolated from A-375 cells treated with both VPA and CPT was slightly higher than those in melanin from the control cells.

  16. EPR studies of free radicals decay and survival in gamma irradiated aminoglycoside antibiotics: sisomicin, tobramycin and paromomycin.

    Science.gov (United States)

    Wilczyński, Sławomir; Pilawa, Barbara; Koprowski, Robert; Wróbel, Zygmunt; Ptaszkiewicz, Marta; Swakoń, Jan; Olko, Paweł

    2012-02-14

    Radiation sterilization technology is more actively used now that any time because of its many advantages. Gamma radiation has high penetrating power, relatively low chemical reactivity and causes small temperature rise. But on the other hand radiosterilization can lead to radiolytic products appearing, in example free radicals. Free radicals in radiative sterilized sisomicin, tobramycin and paromomycin were studied by electron paramagnetic resonance (EPR) spectroscopy. Dose of gamma irradiation of 25kGy was used. Concentrations and properties of free radicals in irradiated antibiotics were studied. EPR spectra were recorded for samples stored in air and argon. For gamma irradiated antibiotics strong EPR lines were recorded. One- and two-exponential functions were fitted to experimental points during testing and researching of time influence of the antibiotics storage to studied parameters of EPR lines. Our study of free radicals in radiosterilized antibiotics indicates the need for characterization of medicinal substances prior to sterilization process using EPR values. We propose the concentration of free radicals and other spectroscopic parameters as useful factors to select the optimal type of sterilization for the individual drug. The important parameters are i.a. the τ time constants and K constants of exponential functions. Time constants τ give us information about the speed of free radicals concentration decrease in radiated medicinal substances. The constant K(0) shows the free radicals concentration in irradiated medicament after long time of storage. Copyright © 2011 Elsevier B.V. All rights reserved.

  17. EPR characterization of Mn(ii) complexes for distance determination with pulsed dipolar spectroscopy.

    Science.gov (United States)

    Keller, Katharina; Zalibera, Michal; Qi, Mian; Koch, Vanessa; Wegner, Julia; Hintz, Henrik; Godt, Adelheid; Jeschke, Gunnar; Savitsky, Anton; Yulikov, Maxim

    2016-09-14

    The four Mn(ii) complexes Mn-DOTA, Mn-TAHA, Mn-PyMTA, and Mn-NO3Py were characterized by electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and relaxation measurements, to predict their relative performance in the EPR pulse dipolar spectroscopy (PDS) experiments. High spin density localization on the metal ions was proven by ENDOR on 1H, D, 14N, and 55Mn nuclei. The transverse relaxation of the Mn(ii) complexes appears to be slow enough for PDS-based spin-spin distance determination. Rather advantageous ratios of T1/Tm were measured allowing for good relaxation induced dipolar modulation enhancement (RIDME) performance and, in general, fast shot repetitions in any PDS experiment. Relaxation properties of the Mn(ii) complexes correlate with the strengths of their zero field splitting (ZFS). Further, a comparison of Mn(ii)-DOTA and Gd(iii)-DOTA based spin labels is presented. The RIDME technique to measure nanometer-range Mn(ii)-Mn(ii) distances in biomolecules is discussed as an alternative to the well-known DEER technique that often appears challenging in cases of metal-metal distance measurements. The use of a modified kernel function that includes dipolar harmonic overtones allows model-free computation of the Mn(ii)-Mn(ii) distance distributions. Mn(ii)-Mn(ii) distances are computed from RIDME data of Mn-rulers consisting of two Mn-PyMTA complexes connected by a rodlike spacer of defined length. Level crossing effects seem to have only a weak influence on the distance distributions computed from this set of Mn(ii)-Mn(ii) RIDME data.

  18. High-field EPR spectroscopy applied to biological systems: characterization of molecular switches for electron and ion transfer.

    Science.gov (United States)

    Möbius, K; Savitsky, A; Schnegg, A; Plato, M; Fuchst, M

    2005-01-07

    The last decade witnessed a tremendous growth in combined efforts of biologists, chemists and physicists to understand the dominant factors determining the specificity and directionality of transmembrane transfer processes in proteins. A large variety of experimental techniques is being used including X-ray and neutron diffraction, but also time-resolved optical, infrared and magnetic resonance spectroscopy. This is done in conjunction with genetic engineering strategies to construct site-specific mutants for controlled modification of the proteins. As a general perception of these efforts, the substantial influence of weak interactions within the protein and its membrane interfaces is recognized. The weak interactions are subject to subtle changes during the reaction cycle owing to the inherent flexibility of the protein-membrane complex. Specific conformational changes accomplish molecular-switch functions for the transfer process to proceed with optimum efficiency. Characteristic examples of time varying non-bonded interactions are specific H-patterns and/or polarity effects of the microenvironment. The present perception has emerged from the coupling of newly developed spectroscopic techniques - and advanced EPR certainly deserves credit in this respect - with newly developed computational strategies to interpret the experimental data in terms of protein structure and dynamics. By now, the partners of this coupling, particularly high-field EPR spectroscopy and DFT-based quantum theory, have reached a level of sophistication that applications to large biocomplexes are within reach. In this review, a few large paradigm biosystems are surveyed which were explored lately in our laboratory. Taking advantage of the improved spectral and temporal resolution of high-frequency/high-field EPR at 95 GHz/3.4 T and 360 GHz/12.9 T, as compared to conventional X-band EPR (9.5 GHz/0.34 T), three biosystems are characterized with respect to structure and dynamics: (1) Light

  19. Application of EPR spectroscopy to examine free radicals evolution during storage of the thermally sterilized Ungentum ophthalmicum.

    Science.gov (United States)

    Ramos, Paweł; Pilawa, Barbara

    2016-06-24

    Free radicals formed during thermal sterilization of the Ungentum ophthalmicum were examined by an X-band EPR spectroscopy. The influence of storage time (15 min; 1, 2 and 3 days after heating) on free radical properties and concentrations in this sample was determined. Thermal sterilization was done according to the pharmaceutical norms. The first-derivative EPR spectra with g-values about 2 were measured with magnetic modulation of 100 kHz in the range of microwave power 2.2-70 mW. The changes of amplitudes (A) and linewidths (ΔBpp) with microwave powers were evaluated. Free radicals in concentration ∼10(17) spin/g were formed during heating of the tested Ungentum. Free radical concentration decreased with increase in storage time, and reached values ∼10(17) spin/g after 3 days from sterilization. The tested U. ophthalmicum should not be sterilized at a temperature of 160 °C because of the free radicals formation, or it should be used 3 days after heating, when free radicals were considerably quenched. Free radical properties remain unchanged during storage of the Ungentum. The EPR lines of the U. ophthalmicum were homogeneously broadened and their linewidths (ΔBpp) increased with increase in microwave power. EPR spectroscopy is useful to examine free radicals to optimize sterilization process and storage conditions of ophthalmologic samples.

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

    Energy Technology Data Exchange (ETDEWEB)

    Bahar, N; Roberts, K; Stabile, F; Mongillo, N; Decker, RD; Wilson, LD; Husain, Z; Contessa, J; Carlson, DJ [Yale University School of Medicine, New Haven, Connecticut (United States); Williams, BB; Flood, AB; Swartz, HM [Geisel Medical School at Dartmouth University, Hanover, New Hampshire (United States)

    2015-06-15

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

  1. EPR study on copper- and vanadium complexes with substituted phthalocyanines

    Energy Technology Data Exchange (ETDEWEB)

    Shklyaev, A.A.; Selyutin, G.E.; Shakot' ko, N.I.; Mikhalenko, S.A. (Nauchno-Issledovatel' skij Inst. Organicheskikh Poluproduktov i Krasitelej, Moscow (USSR))

    1984-06-01

    The structure of binuclear associates of substituted vanadyl- and copper-phthalocyanines is investigated. The EPR study has shown that metal phthalocyanine protonation in acid media (CH/sub 2/Cl/sub 2/, Py, H/sub 2/SO/sub 4/, toluence, etc) is accompanied by destabilization of bonds of the central ion with a polycyclic ligand. Substituted copper- and vanadyl phthalocyanines form dimerized associates where M-M interatmic distance varies in a wide range from 4.1 to 12 A.

  2. Utilizing NMR and EPR spectroscopy to probe the role of copper in prion diseases

    KAUST Repository

    Emwas, Abdul-Hamid M.

    2013-02-24

    Copper is an essential nutrient for the normal development of the brain and nervous system, although the hallmark of several neurological diseases is a change in copper concentrations in the brain and central nervous system. Prion protein (PrP) is a copper-binding, cell-surface glycoprotein that exists in two alternatively folded conformations: a normal isoform (PrPC) and a disease-associated isoform (PrPSc). Prion diseases are a group of lethal neurodegenerative disorders that develop as a result of conformational conversion of PrPC into PrPSc. The pathogenic mechanism that triggers this conformational transformation with the subsequent development of prion diseases remains unclear. It has, however, been shown repeatedly that copper plays a significant functional role in the conformational conversion of prion proteins. In this review, we focus on current research that seeks to clarify the conformational changes associated with prion diseases and the role of copper in this mechanism, with emphasis on the latest applications of NMR and EPR spectroscopy to probe the interactions of copper with prion proteins. Copyright © 2013 John Wiley & Sons, Ltd.

  3. Fe (III - Galactomannan Solid and Aqueous Complexes: Potentiometric, EPR Spectroscopy and Thermal Data

    Directory of Open Access Journals (Sweden)

    Mercê Ana L. R.

    2001-01-01

    Full Text Available Galactomannans can be employed in food industries to modify the final rheological properties of the products. Since they are not absorbed by the living organisms they can also be used in dietary foods. The equilibria involving the interactions of Fe(III and galactomannans and arabinogalactan of several leguminous plants were characterized by potentiometric titrations and EPR spectroscopy. The log of the equilibrium constants for the formation of ML species, where M is the metal ion and L is the monomeric unit of the biopolymers, were 15.4, 14.1 and 18.5, for the galactomannans of C. fastuosa, L. leucocephala and S. macranthera, respectively. Log K values for protonated species (MHL were 3.1, 3.3, and were not detected for the galactomannan of S. macranthera. The log K values for the formation of ML2 were 14.1, 13.3 and 15.2, respectively. Early formation of insoluble products in the equilibrium with arabinogalactan and Fe(III prevented acquisition of reliable data. The solid complexes assays showed a great dipolar interaction between two Fe(III ions in the inner structure of the biopolymer which increased as the degree of substitution of the galactomannan decreased, and also showed the resulting thermal stability. The complexes impart a new possibility of providing essential metal ions in dietary foods since decomplexation of the complexes can occur at different pH values existing in the human body.

  4. Non-invasive in vivo evaluation of in situ forming PLGA implants by benchtop magnetic resonance imaging (BT-MRI) and EPR spectroscopy.

    Science.gov (United States)

    Kempe, Sabine; Metz, Hendrik; Pereira, Priscila G C; Mäder, Karsten

    2010-01-01

    In the present study, we used benchtop magnetic resonance imaging (BT-MRI) for non-invasive and continuous in vivo studies of in situ forming poly(lactide-co-glycolide) (PLGA) implants without the use of contrast agents. Polyethylene glycol (PEG) 400 was used as an alternative solvent to the clinically used NMP. In addition to BT-MRI, we applied electron paramagnetic resonance (EPR) spectroscopy to characterize implant formation and drug delivery processes in vitro and in vivo. We were able to follow key processes of implant formation by EPR and MRI. Because EPR spectra are sensitive to polarity and mobility, we were able to follow the kinetics of the solvent/non-solvent exchange and the PLGA precipitation. Due to the high water affinity of PEG 400, we observed a transient accumulation of water in the implant neighbourhood. Furthermore, we detected the encapsulation by BT-MRI of the implant as a response of the biological system to the polymer, followed by degradation over a period of two months. We could show that MRI in general has the potential to get new insights in the in vivo fate of in situ forming implants. The study also clearly shows that BT-MRI is a new viable and much less expensive alternative for superconducting MRI machines to monitor drug delivery processes in vivo in small mammals. Copyright 2009 Elsevier B.V. All rights reserved.

  5. Comparative EPR studies of free radicals in melanin synthesized by Bacillus weihenstephanensis soil strains

    Science.gov (United States)

    Zdybel, Magdalena; Pilawa, Barbara; Drewnowska, Justyna M.; Swiecicka, Izabela

    2017-07-01

    EPR spectroscopy was used to examine the properties of and free radical concentrations in atypical water-soluble melanin-like pigments from Bacillus weihenstephanensis strains. The same EPR spectral shape was observed in bacterial melanins as in eumelanin. The EPR lines were homogeneously broadened. Continuous microwave saturation of the EPR lines indicated slow spin-lattice relaxation processes in the samples. Strong dipolar interactions characterized the tested melanin samples. Higher free radical concentrations were found in bacterial melanin than in synthetic melanin. The free radical concentrations in melanin from B. weihenstephanensis increased in the following order: strain JAS 81/4 < JAS 83/3 < JAS 86/1 < JAS 39/1.

  6. FPGA based digital signal processing for EPR spectroscopy with an application to MRI

    OpenAIRE

    Duraiswamy, Punithavathi

    2011-01-01

    Electron Paramagnetic Resonance (EPR), a magnetic resonance technique similar to nuclear magnetic resonance, detects paramagnetic species such as free radicals. Like Magnetic Resonance Imaging (MRI), EPR can be implemented as an imaging technique for small animals and potentially human applications both in pulsed and continuous wave mode. Typical frequencies used for in vivo applications are about 300 MHz with a corresponding static magnetic field of about 100 G (10mT). As demonstrated with h...

  7. 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.

    Science.gov (United States)

    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

  8. 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

    Directory of Open Access Journals (Sweden)

    Maria Filek

    2017-05-01

    Full Text Available 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

  9. Lipid peroxidation and water penetration in lipid bilayers: a W-band EPR study.

    Science.gov (United States)

    Conte, Elena; Megli, Francesco Maria; Khandelia, Himanshu; Jeschke, Gunnar; Bordignon, Enrica

    2013-02-01

    Lipid peroxidation plays a key role in the alteration of cell membrane's properties. Here we used as model systems multilamellar vesicles (MLVs) made of the first two products in the oxidative cascade of linoleoyl lecithin, namely 1-palmitoyl-2-(13-hydroperoxy-9,11-octadecanedienoyl)-lecithin (HpPLPC) and 1-palmitoyl-2-(13-hydroxy-9,11-octadecanedienoyl)-lecithin (OHPLPC), exhibiting a hydroperoxide or a hydroxy group at position 13, respectively. The two oxidized lipids were used either pure or in a 1:1 molar ratio mixture with untreated 1-palmitoyl-2-linoleoyl-lecithin (PLPC). The model membranes were doped with spin-labeled lipids to study bilayer alterations by electron paramagnetic resonance (EPR) spectroscopy. Two different spin-labeled lipids were used, bearing the doxyl ring at position (n) 5 or 16: γ-palmitoyl-β-(n-doxylstearoyl)-lecithin (n-DSPPC) and n-doxylstearic acid (n-DSA). Small changes in the acyl chain order in the sub-polar region and at the methyl-terminal induced by lipid peroxidation were detected by X-band EPR. Concomitantly, the polarity and proticity of the membrane bilayer in those regions were investigated at W band in frozen samples. Analysis of the g(xx) and A(zz) parameters revealed that OHPLPC, but mostly HpPLPC, induced a measurable increase in polarity and H-bonding propensity in the central region of the bilayer. Molecular dynamics simulation performed on 16-DSA in the PLPC-HpPLPC bilayer revealed that water molecules are statistically favored with respect to the hydroperoxide groups to interact with the nitroxide at the methyl-terminal, confirming that the H-bonds experimentally observed are due to increased water penetration in the bilayer. The EPR and MD data on model membranes demonstrate that cell membrane damage by oxidative stress cause alteration of water penetration in the bilayer. Copyright © 2012 Elsevier B.V. All rights reserved.

  10. Preliminary study for precision dosimetry using electron paramagnetic resonance (EPR) in radiotherapy applications

    Energy Technology Data Exchange (ETDEWEB)

    Shehzadi, N. N.; Kim, I. J.; Yi, C. Y. [Center for Ionizing Radiation, Korea Research for Standards and Science, Daejeon (Korea, Republic of)

    2015-10-15

    EPR (Electron paramagnetic resonance) dosimetry for radiotherapy dose range (1-10 Gy) is still being established.Alanine is an important material for EPR dosimetry because in terms of density and radiation absorption properties, it is water equivalent. High repeatability and high reproducibility of alanine spectrum measurement makes it possible to estimate the irradiation dose accurately. This baseline study has been carried out to establish precision EPR dosimetry in therapeutic photon range. For that purpose, an EPR dosimetry system has been setup and repeatability as well as reproducibility of measurements using alanine dosimeter have been evaluated. Effect of anisotropy of alanine dosimeter in spectrometer cavity has also been observed. EPR dosimetry system is set up at KRISS. It is found that reproducibility of the system at therapeutic photon range is 1.5 % - 6.6 %.

  11. EPR and ENDOR spectroscopic study of the reactions of aromatic azides with gallium trichloride.

    Science.gov (United States)

    Bencivenni, Giorgio; Cesari, Riccardo; Nanni, Daniele; El Mkami, Hassane; Walton, John C

    2010-11-21

    The reactions of gallium trichloride with phenyl and deuterio-phenyl azides, as well as with 4-methoxyphenyl azide and deuterium isotopomers, were examined by product analysis, CW EPR spectroscopy and pulsed ENDOR spectroscopy. The products included the corresponding anilines together with 4-aminodiphenylamine type dimers, and polyanilines. Complex CW EPR spectra of the radical cations of the dimers [ArNHC(6)H(4)NH(2)](+)˙ and trimers [ArNHC(6)H(4)NHC(6)H(4)NH(2)](+)˙ were obtained. These EPR spectra were analysed with the help of data from the deuterium-substituted analogues as well as the pulse Davies ENDOR spectra. DFT computations of the radical cations provided corroborating evidence and suggested the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposed.

  12. Clinical Electron Paramagnetic Resonance (EPR) Oximetry using India Ink

    OpenAIRE

    Williams, Benjamin B.; Khan, Nadeem; Zaki, Bassem; Hartford, Alan; Ernstoff, Marc S.; Swartz, Harold M.

    2010-01-01

    Electron paramagnetic resonance (EPR) oximetry can be used to provide direct absolute measurements of pO2 in living tissue using India ink as an O2 reporter. In vivo measurements are made using low frequency (1.2GHz) EPR spectroscopy and surface loop resonators, which enable measurements to be made at superficial sites through a non-invasive (after placing the ink in the tissues) and repeatable measurement procedure. Ongoing EPR oximetry studies in human subjects include measurement of subcut...

  13. EPR Spectroscopy of Different Sol Concentration Synthesized Nanocrystalline-ZnO Thin Films

    Directory of Open Access Journals (Sweden)

    Manju Arora

    2015-01-01

    Full Text Available Nanocrystalline zinc oxide (nc-ZnO thin films were grown on p-type silicon substrate through spin coating by sol-gel process using different sol concentrations (10 wt.%, 15 wt.%, and 25 wt.%. These films were characterized by high resolution nondestructive X-ray diffraction (XRD, scanning electron microscopy (SEM with energy dispersive X-ray analysis (EDS attachment, and electron paramagnetic resonance (EPR techniques to understand variations in structural, morphological, and oxygen vacancy with respect to sol concentration. The film surface morphology changes from nanowall to nanorods on increasing sol concentration. EPR spectra revealed the systematic variation from ferromagnetic to paramagnetic nature in these nc-ZnO films. The broad EPR resonance signal arising from the strong dipolar-dipolar interactions among impurity defects present in nc-ZnO film deposited from 10 wt.% sol has been observed and a single strong narrow resonance signal pertaining to oxygen vacancies is obtained in 25 wt.% sol derived nc-ZnO film. The concentrations of impurity defects and oxygen vacancies are evaluated from EPR spectra, necessary for efficient optoelectronic devices development.

  14. An EPR line shape study of anisotropic rotational reorientation and slow tumbling in liquid and frozen jojoba oil

    Science.gov (United States)

    Hwang, J. S.; Al-Rashid, W. A.

    Spin probe investigation of jojoba oil was carried out by electron paramagnetic rresonance (EPR) spectroscopy. The spin probe used was 2,2,6,6-tetramethyl-4-piperidone- N-oxide. The EPR line shape studies were carried out in the lower temperature range of 192 to 275 K to test the applicability of the stochastic Liouville theory in the simulation of EPR line shapes where earlier relaxation theories do not apply. In an earlier study, this system was analysed by employing rotational diffusion at the fast-motional region. The results show that PD-Tempone exhibits asymmetric rotational diffusion with N = 3.3 at an axis z'= Y in the plane of the molecule and perpendicular to the NO bond direction. In this investigation we have extended the temperature range to lower temperatures and observed slow tumbling EPR spectra. It is shown that the stochastic Liouville method can be used to simulate all but two of the experimentally observed EPR spectra in the slow-motional region and details of the slow-motional line shape are sensitive to the anisotropy of rotation and showed good agreement for a moderate jump model. From the computer simulation of EPR line shapes it is found that the information obtained on τ R, and N in the motional-narrowing region can be extrapolated into the slow-tumbling region. It is also found that ln (τ R) is linear in 1/ T in the temperature range studied and the resulting activation energy for rotation is 51 kJ/mol. The two EPR spectra at 240 and 231 K were found to exhibit the effects of anisotropic viscosity observed by B IRELL for nitroxides oriented in tubular cavities in inclusion crystals in which the molecule is free to rotate about the long axis but with its rotation hindered about the other two axes because of the cavity geometry. These results proved that the slow-tumbling spectra were very sensitive to the effects of anisotropy in the viscosity.

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

    Science.gov (United States)

    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.

  16. An EPR Primer

    Indian Academy of Sciences (India)

    IAS Admin

    electron paramagnetic resonance (EPR) is given to help the uninitiated reader to get prepared to appreciate the following article. Electron paramagnetic resonance (EPR), also known as electron spin resonance, (ESR) is a form of spectroscopy dealing with electronic spin-state transitions. These transitions are caused.

  17. Thermodynamic Basis of Electron Transfer in Dihydroorotate Dehydrogenase B from Lactococcus lactis:  Analysis by Potentiometry, EPR Spectroscopy, and ENDOR Spectroscopy

    DEFF Research Database (Denmark)

    Mohnsen, Al-Walid A.; Rigby, Stephen E. J.; Jensen, Kaj Frank

    2004-01-01

    for the FMN couples in DHODB. During reductive titration of DHODB, small amounts of the neutral blue semiquinone are observed at 630 nm, consistent with the measured midpoint reduction potentials of the flavins. An ENDOR spectrum of substrate-reduced DHODB identifies hyperfine couplings to proton nuclei......-visible spectroscopy and further identify an unusual EPR signal with very small rhombic anisotropy and g values of 2.02, 1.99, and 1.96. This unusual signal is assigned to the formation of a spin interacting state between the FMN semiquinone species and the reduced 2Fe-2S center. Reduction of DHODB using an excess...

  18. Multifrequency Pulsed EPR Studies of Biologically Relevant Manganese(II) Complexes

    OpenAIRE

    Stich, T. A.; Lahiri, S.; Yeagle, G.; Dicus, M.; Brynda, M.; Gunn, A; Aznar, C.; DeRose, V.J.; Britt, R. D.

    2007-01-01

    Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different fre...

  19. Bismuth germanate as a perspective material for dielectric resonators in EPR spectroscopy

    Science.gov (United States)

    Ivanov, Mikhail Y.; Nadolinny, Vladimir A.; Bagryanskaya, Elena G.; Grishin, Yuriy A.; Fedin, Matvey V.; Veber, Sergey L.

    2016-10-01

    High purity bismuth germanate (Bi4(GeO4)3, BGO) is proposed and implemented as an alternative material for dielectric EPR resonators. A significant improvement of the absolute sensitivity can be readily achieved by substituting the alumina insert (ring) by BGO-made one in commercially available X-band EPR probeheads. Four BGO dielectric inserts of 2, 3, 4 and 5 mm inner diameter (ID) were made for comparison with standard 5 mm inner diameter alumina insert. All inserts were introduced into commercial Bruker EPR resonator ER 4118X-MD-5W1, and their performance was investigated. The Q-values of empty resonators, B1 saturation curves and continuous wave EPR spectra of DPPH (2,2-diphenyl-1-picrylhydrazyl) were measured and analyzed in a temperature range 6-300 K. BGO-made resonators were found superior in several important aspects. The background signals arising from BGO are much weaker compared to those of alumina at B = 0-0.6 T and T = 6-300 K; this is especially useful for measuring weak signals in the half-field region, as well as those near the central field. Moreover, mechanical properties of BGO allow easy fabrication of dielectric bodies having various shapes and sizes; in particular, small BGO resonators (e.g. ID = 2 or 3 mm) strongly enhance sensitivity for small samples due to increase of the filling factor. All these advantages have been also inspected in the pulse mode, proving that higher B1 fields and better filling factors can be achieved, contributing to the overall enhancement of the performance.

  20. Characterization of Oxygen Bridged Manganese Model Complexes Using Multifrequency (17)O-Hyperfine EPR Spectroscopies and Density Functional Theory.

    Science.gov (United States)

    Rapatskiy, Leonid; Ames, William M; Pérez-Navarro, Montserrat; Savitsky, Anton; Griese, Julia J; Weyhermüller, Thomas; Shafaat, Hannah S; Högbom, Martin; Neese, Frank; Pantazis, Dimitrios A; Cox, Nicholas

    2015-10-29

    Multifrequency pulsed EPR data are reported for a series of oxygen bridged (μ-oxo/μ-hydroxo) bimetallic manganese complexes where the oxygen is labeled with the magnetically active isotope (17)O (I = 5/2). Two synthetic complexes and two biological metallocofactors are examined: a planar bis-μ-oxo bridged complex and a bent, bis-μ-oxo-μ-carboxylato bridge complex; the dimanganese catalase, which catalyzes the dismutation of H2O2 to H2O and O2, and the recently identified manganese/iron cofactor of the R2lox protein, a homologue of the small subunit of the ribonuclotide reductase enzyme (class 1c). High field (W-band) hyperfine EPR spectroscopies are demonstrated to be ideal methods to characterize the (17)O magnetic interactions, allowing a magnetic fingerprint for the bridging oxygen ligand to be developed. It is shown that the μ-oxo bridge motif displays a small positive isotropic hyperfine coupling constant of about +5 to +7 MHz and an anisotropic/dipolar coupling of -9 MHz. In addition, protonation of the bridge is correlated with an increase of the hyperfine coupling constant. Broken symmetry density functional theory is evaluated as a predictive tool for estimating hyperfine coupling of bridging species. Experimental and theoretical results provide a framework for the characterization of the oxygen bridge in Mn metallocofactor systems, including the water oxidizing cofactor of photosystem II, allowing the substrate/solvent interface to be examined throughout its catalytic cycle.

  1. Redox reactions and the influence of natural Mn oxides on Cr oxidation in a contaminated site in northern Italy: evidence from Cr stable-isotopes and EPR spectroscopy

    Directory of Open Access Journals (Sweden)

    Marafatto F. F.

    2013-04-01

    Full Text Available Hexavalent chromium-contaminated groundwaters and sediments in northern Italy have been studied using the Cr stable-isotope systematics and electron spin resonance spectroscopy (ESR, in order to explore redox changes and soil-groundwater interactions. The isotopic data indicate a possible Cr(VI source released into the environment from an industrial plant. EPR spectra on the sediments which constitute the aquifers show a broad asymmetric absorption due to coupled Fe(III and coupled Cr(III ions and a well resolved hyperfine structure due to manganese ions, resulting from Mn(IV and Mn(II. The isotopic and EPR data support the hypothesis of Cr(III being oxidized by Mn oxides which are widespread in the aquifer, possibly related to the oscillation of the phreatic level. The obtained results highlight the usefulness of chromium stable isotopes as environmental tracers and support the observations that naturally occurring Mn oxides in soils may catalize Cr oxidation from the stable Cr(III form to the toxic Cr(VI soluble form, yielding valuable information in planning remediation interventions.

  2. Single crystals of DPPH grown from diethyl ether and carbon disulfide solutions - crystal structures, IR, EPR and magnetization studies.

    Science.gov (United States)

    Zilić, Dijana; Pajić, Damir; Jurić, Marijana; Molčanov, Krešimir; Rakvin, Boris; Planinić, Pavica; Zadro, Krešo

    2010-11-01

    Single crystals of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) obtained from diethyl ether (ether) and carbon disulfide (CS₂) were characterized by the X-ray diffraction, IR, EPR and SQUID magnetization techniques. The X-ray structural analysis and IR spectra showed that the DPPH form crystallized from ether (DPPH1) is solvent free, whereas that one obtained from CS₂ (DPPH2) is a solvate of the composition 4DPPH·CS₂. Principal values of the g-tensor were estimated by the X-band EPR spectroscopy at room and low (10 K) temperatures. Magnetization studies revealed the presence of antiferromagnetically coupled dimers in both types of crystals. However, the way of dimerization as well as the strength of exchange couplings are different in the two DPPH samples, which is in accord with their crystal structures. The obtained results improved parameters accuracy and enabled better understanding of properties of DPPH as a standard sample in the EPR spectrometry. Copyright © 2010 Elsevier Inc. All rights reserved.

  3. EPR study of spermine interaction with multilamellar phosphatidylcholine liposomes.

    Science.gov (United States)

    Momo, F; Wisniewska, A; Stevanato, R

    1995-11-22

    The interaction of spermine with egg-yolk phosphatidylcholine liposomes was investigated. The EPR spin labeling technique evidenced that spermine induces modifications of some membrane functions of biological interest like water permeability and is a possible modulator of diffusion processes for charged and polar molecules. The association constant for a hypothesized complex between spermine and the phosphate group of phosphatidylcholine was evaluated by enzymatic methods.

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

    Science.gov (United States)

    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 (Pi) 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.

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

    Science.gov (United States)

    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.

  6. EPR and UV spectral study of gamma-irradiated white and burned sugar, fructose and glucose

    Science.gov (United States)

    Yordanov, Nicola D.; Georgieva, Elka

    2004-05-01

    The EPR and UV spectral properties of γ-irradiated white and burned sugar, fructose and glucose are studied with the accent on their suitability as dosimetric materials. It is shown that γ-irradiation of solid samples of white sugar and fructose yields stable EPR spectra whereas glucose signal remains time-dependent even 11 months later. Sugar and glucose exhibit linear EPR dose response in the region 0.44-21 kGy and fructose only up to ca. 10 kGy. The relative radiation sensitivity obtained for sugar and fructose is up to 10 kGy and slightly lower for glucose. Burned saccharides provide 2-3 orders of magnitude lower EPR radiation sensitivity making them not suitable for the proposed designation. According to the UV spectra water solutions of γ-irradiated solid white saccharides show well pronounced absorption bands at 267 and 286 nm for sugar and fructose with time-dependent intensities reaching steady values ca. 11 days after dissolution. The intensities of these absorption bands are in linear relation with the absorbed dose of γ-radiation. Glucose shows low sensitively because irradiation with 5.5 kGy yields only a shoulder at about 260-280 nm with decreasing to ca. 40% intensity in the first few days after dissolution. Excellent correlation between the intensities of the EPR- and UV-absorbed dose response is found for sugar and fructose in the region 0.44-10 kGy. This opens new possibilities for independent calibration the EPR dose response. Finally, the comparison suggests sugar as the best, universal material for EPR- and/or UV-dosimetry in the region 0.44-160 kGy.

  7. EPR study of deoxygenated high-temperature superconductors

    Indian Academy of Sciences (India)

    Abstract. High-Tc superconductors are EPR silent but on a little deoxygenation of the high-Tc materials and their constituents, they yield rich but complex spectra. Spectra of (1) CuO, (2) BaCuO2,. (3) CaCuO2, (4) Y2Cu2O5, (5) La2CuO4, (6) La2−x Mx CuO4 (M = Sr, Ba), (7) Y based-123, (8) Bi based-2201, 2212, 2223, ...

  8. EPR spectroscopy and catalase activity of manganese-bound DNA-binding protein from nutrient starved cells.

    Science.gov (United States)

    Hayden, Joshua Allen; Hendrich, Michael P

    2010-06-01

    DNA-binding proteins from nutrient-starved cells (DPS) protect cells from oxidative stress by removing H(2)O(2) and iron. A new class of DPS-like proteins has recently been identified, with DPS-like protein from Sulfolobus solfataricus (SsDPS) being the best characterized to date. SsDPS protects cells from oxidative stress and is upregulated in response to H(2)O(2) but also in response to iron depletion. The ferroxidase active site of SsDPS is structurally similar to the active sites of manganese catalase and rat liver arginase. The present work shows that the ferroxidase center in SsDPS binds two Mn(2+) ions with K (D) = (1/K (1) K (2))(1/2) = 48(3) microM. The binding constant of the second Mn(2+) is significantly higher than that of the first, inducing dinuclear Mn(II) cluster formation for all but the lowest concentrations of added Mn(2+). In competition experiments, equimolar amounts of Fe(2+) were unable to displace the bound manganese. EPR spectroscopy of the Mn(2) (2+) cluster showed signals comparable to those of other characterized dimanganese clusters. The exchange coupling for the cluster was determined, J = -1.4(3) cm(-1) (H = -2JS (1) S (2)), and is within the range expected for a mu(1,1)-carboxylato bridge between the manganese ions. Manganese-bound SsDPS showed catalase activity at a rate 10-100 times slower than for manganese catalases. EPR spectra of SsDPS after addition of H(2)O(2) showed the appearance of an intermediate in the reaction with H(2)O(2).

  9. Harmonization of dosimetric information obtained by different EPR methods: Experience of the Techa river study

    Energy Technology Data Exchange (ETDEWEB)

    Volchkova, A. [Urals Research Center for Radiation Medicine, 68A, Vorovsky Str., 454076 Chelyabinsk (Russian Federation); Shishkina, E.A., E-mail: ElenaA.Shishkina@gmail.com [Urals Research Center for Radiation Medicine, 68A, Vorovsky Str., 454076 Chelyabinsk (Russian Federation); Ivanov, D. [Institute of Metal Physics, Russian Academy of Sciences, 18, S. Kovalevskoy Str., 620041 Yekaterinburg (Russian Federation); Timofeev, Yu. [Urals Research Center for Radiation Medicine, 68A, Vorovsky Str., 454076 Chelyabinsk (Russian Federation); Fattibene, P.; Della Monaca, S. [Istituto Superiore di Sanita and Istituto Nazionale di Fisica Nucleare, Viale Regina Elena 299, 00161 Rome (Italy); Wieser, A. [Helmholtz Zentrum Muenchen, German Research Centre for Environmental Health, D-85764 Neuherberg (Germany); Degteva, M.O. [Urals Research Center for Radiation Medicine, 68A, Vorovsky Str., 454076 Chelyabinsk (Russian Federation)

    2011-09-15

    Between 1949 and 1956 the Techa River (Southern Urals, Russia) was contaminated as a result of releases of radioactive waste by the Mayak Production Association. EPR dosimetry with tooth enamel has been used to estimate the external exposure of Techa riverside residents over the last 17 years. The database 'Tooth' of the Urals Research Center for Radiation Medicine (URCRM) has accumulated about 1000 EPR measurements of tooth enamel from the rural population of the Urals region. The teeth were investigated by laboratories of Russia, USA, Germany and Italy. Most of the enamel samples were measured several times in different laboratories. Each laboratory used different equipment and its own methods for sample preparation and EPR spectra analysis. Even measurements performed at the same laboratory over 10-15 years may not be assumed as uniform: methods change with time, and equipment is subject to aging. These two factors influenced EPR performance. The purpose of this study is, therefore, the harmonization of EPR data accumulated during long-term dosimetric investigations in the Southern Urals for further pooled analysis. The results will be used for external dose evaluation in the Techa River region.

  10. 2D FTIR correlation spectroscopy and EPR analysis of Urtica dioica leaves from areas of different environmental pollution.

    Science.gov (United States)

    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.

  11. 2D FTIR correlation spectroscopy and EPR analysis of Urtica dioica leaves from areas of different environmental pollution

    Science.gov (United States)

    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.

  12. EPR and optical absorption studies on VO 2+ ions in calcium fumarate trihydrate single crystals

    Science.gov (United States)

    Kripal, Ram; Mishra, Indrajeet; Gupta, S. K.; Arora, Manju

    2010-01-01

    Electron Paramagnetic Resonance (EPR) studies of VO 2+ ions in calcium fumarate trihydrate single crystals have been done at room temperature. EPR analysis indicates the presence of two magnetically inequivalent VO 2+ sites. For the two sites the spin Hamiltonian parameters are, Site I: g x = 1.9689 ,g y = 2.0087 ,g z = 1.9344, A x = 73 ,A y = 88 ,A z = 202; Site II: g x = 1.9675 ,g y = 2.0100 ,g z = 1.9346 ,A x = 75 ,A y = 90, A z = 206 (×10 -4) cm -1. The optical absorption study is also carried out at room temperature. By correlating EPR and optical data the nature of bonding in the crystal is discussed. The three-line superhyperfine structure has been attributed to two protons.

  13. Electrochemical behaviour of gold modified with contaminated TMP amine adlayers studied by STM, CV, EPR

    Energy Technology Data Exchange (ETDEWEB)

    Krukowski, P. [Division of Physics and Technology of Nanometric Structures, Solid State Physics Department, University of Lodz, Pomorska 149/153, 90-236 Lodz (Poland)], E-mail: pkrukowski@std2.phys.uni.lodz.pl; Kowalczyk, P.J. [Division of Physics and Technology of Nanometric Structures, Solid State Physics Department, University of Lodz, Pomorska 149/153, 90-236 Lodz (Poland); Krzyczmonik, P. [Department of General and Inorganic Chemistry, University of Lodz, Narutowicza 68, 90-136 Lodz (Poland); Olejniczak, W.; Klusek, Z.; Puchalski, M. [Division of Physics and Technology of Nanometric Structures, Solid State Physics Department, University of Lodz, Pomorska 149/153, 90-236 Lodz (Poland); Gwozdzinski, K. [Department of Molecular Biophysics, University of Lodz, Banacha 12/16, 90-237 Lodz (Poland)

    2009-01-15

    Scanning tunnelling microscopy (STM), cyclic voltammetry (CV) and electron paramagnetic resonance spectroscopy (EPR) were used to investigate the influence of the TMP amine derivative on Au (1 1 1). The STM results show that the gold surface covered by the adlayer of the TMP derivative is easily modified (holes formation) after increasing the bias voltage to 0.5 V. The CV and EPR results show the electrochemical origin of observed STM topography changes. It is suggested that TMP could be oxidized to the nitroxyl TEMPO radical which adsorbs on Au in the form of an oxoammonium cation. Such an oxoammonium cation at the potential of 0.5 V forms a permanent complex of gold and the nitroxyl radical which could be easily desorbed during STM imaging.

  14. EPR studies of carbonaceous compounds deposited on Al-MCM-41

    Energy Technology Data Exchange (ETDEWEB)

    Nowak, L.; Lezanska, M.; Rozwadowski, M.; Rozploch, F.; Marciniak, W

    2002-11-30

    Electron paramagnetic resonance (EPR) spectroscopy was used to investigate carbonaceous compounds deposited on aluminosilicate mesoporous molecular sieves of the MCM-41 type during conversion of cyclohexene at various temperatures. The amount of the deposited coke grew with the increasing Al content of the catalysts and with the decreasing reaction temperature. The deposits caused a reduction in both the surface area and pore volume of the Al-MCM-41 materials. The measurements showed that the EPR lines were complex. The performed analysis revealed a hyperfine structure the envelope of which was of the Gaussian shape. It was found that the spin concentration increased and the peak-to-peak width ({delta}B{sub pp}) decreased with the increasing reaction temperature.

  15. Mechanistic implications for the formation of the diiron cluster in ribonucleotide reductase provided by quantitative EPR spectroscopy.

    Science.gov (United States)

    Pierce, Brad S; Elgren, Timothy E; Hendrich, Michael P

    2003-07-23

    The small subunit of Escherichia coli ribonucleotide reductase (R2) is a homodimeric (betabeta) protein, in which each beta-peptide contains a diiron cluster composed of two inequivalent iron sites. R2 is capable of reductively activating O(2) to produce a stable tyrosine radical (Y122*), which is essential for production of deoxyribonucleotides on the larger R1 subunit. In this work, the paramagnetic Mn(II) ion is used as a spectroscopic probe to characterize the assembly of the R2 site with EPR spectroscopy. Upon titration of Mn(II) into samples of apoR2, we have been able to quantitatively follow three species (aquaMn(II), mononuclear Mn(II)R2, and dinuclear Mn(2)(II)R2) and fit each to a sequential two binding site model. As previously observed for Fe(II) binding within apoR2, one of the sites has a greater binding affinity relative to the other, K(1) = (5.5 +/- 1.1) x 10(5) M(-)(1) and K(2) = (3.9 +/- 0.6) x 10(4) M(-)(1), which are assigned to the B and A sites, respectively. In multiple titrations, only one dinuclear Mn(2)(II)R2 site was created per homodimer of R2, indicating that only one of the two beta-peptides of R2 is capable of binding Mn(II) following addition of Mn(II) to apoR2. Under anaerobic conditions, addition of only 2 equiv of Fe(II) to R2 (Fe(2)(II)R2) completely prevented the formation of any bound MnR2 species. Upon reaction of this sample with O(2) in the presence of Mn(II), both Y122* and Mn(2)(II)R2 were produced in equal amounts. Previous stopped-flow absorption spectroscopy studies have indicated that apoR2 undergoes a protein conformational change upon binding of metal (Tong et al. J. Am. Chem. Soc. 1996, 118, 2107-2108). On the basis of these observations, we propose a model for R2 metal incorporation that invokes an allosteric interaction between the two beta-peptides of R2. Upon binding the first equiv of metal to a beta-peptide (beta(I)), the aforementioned protein conformational change prevents metal binding in the adjacent beta

  16. EPR and optical absorption studies on manganese ion doped in mixed alkali cadmium phosphate glasses

    Science.gov (United States)

    Giridhar, G.; Rangacharyulu, M.; Ravikumar, R. V. S. S. N.; Sambasiva Rao, P.

    2009-07-01

    Electron paramagnetic resonance (EPR) spectra of Mn(II) ions in cadmium phosphate glasses are presented with mixed alkali variation as xLi2O + (20 - x) Na2O + 20 CdO + 59.5 P2O5 + 0.5 MnO glass system with 5 EPR spectra of Mn(II) ions doped samples exhibit a sextet centered at g = 2·0. The optical absorption spectrum at room temperature shows three bands for Mn(II) ions in octahedral symmetry. The crystal field (Dq) and Racah parameters (B and C) are evaluated. From EPR and optical spectral studies reveals the nature of the bonding is dominantly ionic and its site symmetry is octahedral. At equal composition of alkali content, i.e. for x = 10 the glass system shows the mixed alkali effect.

  17. Applying the conventional moving average filter for estimation of low radiation doses using EPR spectroscopy: Benefits and drawbacks

    Science.gov (United States)

    Maghraby, Ahmed M.

    2014-02-01

    Alanine/EPR is the most common dosimetry system for high radiation doses because of its high stability and wide linear response, however, use of alanine in most of medical applications still require special sophisticated methodologies and techniques in order to extend alanine detection limit to low levels of radiation doses. One of these techniques is the use of digital processing of acquired alanine spectra for enhancing useful components in spectra while useless features are suppressed. Simple moving average filter (MA) impacts on alanine EPR spectra have been studied in terms of peak-to-peak height, peak-to-peak line width, and associated uncertainty. Three types of the used filter were investigated: upward MA, central MA, and downward MA filters, effects of each on the peak position for different values of filter width were studied. It was found that MA filter always lead to the reduction in signal intensity and the increase of line width of the central peak of alanine spectrum. Peak position also changes in cases of the upward MA and downward MA filters while no significant changes were observed in the case of central MA. Uncertainties associated to the averaging process were evaluated and plotted versus the filter width resulting in a linear relationship. Filter width value should be carefully selected in order to avoid probable distortion in processed spectra while gaining less noisy spectra with less associated uncertainties.

  18. Probing topology and dynamics of the second transmembrane domain (M2δ) of the acetyl choline receptor using magnetically aligned lipid bilayers (bicelles) and EPR spectroscopy.

    Science.gov (United States)

    Sahu, Indra D; Mayo, Daniel J; Subbaraman, Nidhi; Inbaraj, Johnson J; McCarrick, Robert M; Lorigan, Gary A

    2017-08-01

    Characterizing membrane protein structure and dynamics in the lipid bilayer membrane is very important but experimentally challenging. EPR spectroscopy offers a unique set of techniques to investigate a membrane protein structure, dynamics, topology, and distance constraints in lipid bilayers. Previously our lab demonstrated the use of magnetically aligned phospholipid bilayers (bicelles) for probing topology and dynamics of the membrane peptide M2δ of the acetyl choline receptor (AchR) as a proof of concept. In this study, magnetically aligned phospholipid bilayers and rigid spin labels were further utilized to provide improved dynamic information and topology of M2δ peptide. Seven TOAC-labeled AchR M2δ peptides were synthesized to demonstrate the utility of a multi-labeling amino acid substitution alignment strategy. Our data revealed the helical tilts to be 11°, 17°, 9°, 17°, 16°, 11°, 9°±4° for residues I7TOAC, Q13TOAC, A14TOAC, V15TOAC, C16TOAC, L17TOAC, and L18TOAC, respectively. The average helical tilt of the M2δ peptide was determined to be ∼13°. This study also revealed that the TOAC labels were attached to the M2δ peptide with different dynamics suggesting that the sites towards the C-terminal end are more rigid when compared to the sites towards the N-terminus. The dynamics of the TOAC labeled sites were more resolved in the aligned samples when compared to the randomly disordered samples. This study highlights the use of magnetically aligned lipid bilayer EPR technique to determine a more accurate helical tilt and more resolved local dynamics of AchR M2δ peptide. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. Optical and EPR studies of iron bearing phosphate minerals: satterlyite and gormanite from Yukon Territory, Canada

    Science.gov (United States)

    Chandrasekhar, A. V.; Ramanaiah, M. Venkata; Reddy, B. J.; Reddy, Y. P.; Rao, P. S.; Ravikumar, R. V. S. S. N.

    2003-07-01

    The iron phosphate minerals satterlyite and gormanite have been investigated by EPR and optical absorption studies. The optical results indicate the presence of ferrous and ferric ions in both minerals. In gormanite the site symmetry of Fe(III) is near octahedral whereas in satterlyite it is tetragonally distorted. On the other hand, the Fe(II) ions are in tetragonally distorted octahedral site in both minerals. In satterlyite the EPR results indicate the presence of the ferric ion in a tetragonally distorted state together with a small percentage of Mn(II). Crystal field (Dq) and interelectronic parameters (B and C) are evaluated.

  20. Investigation of the cutaneous penetration behavior of dexamethasone loaded to nano-sized lipid particles by EPR spectroscopy, and confocal Raman and laser scanning microscopy.

    Science.gov (United States)

    Lohan, Silke B; Saeidpour, Siavash; Solik, Agnieszka; Schanzer, Sabine; Richter, Heike; Dong, Pin; Darvin, Maxim E; Bodmeier, Roland; Patzelt, Alexa; Zoubari, Gaith; Unbehauen, Michael; Haag, Rainer; Lademann, Jürgen; Teutloff, Christian; Bittl, Robert; Meinke, Martina C

    2017-07-01

    An improvement of the penetration efficiency combined with the controlled release of actives in the skin can facilitate the medical treatment of skin diseases immensely. Dexamethasone (Dx), a synthetic glucocorticoid, is frequently used for the treatment of inflammatory skin diseases. To investigate the penetration of nano-sized lipid particles (NLP) loaded with Dx in comparison to a commercially available base cream, different techniques were applied. Electron paramagnetic resonance (EPR) spectroscopy was used to monitor the penetration of Dx, which was covalently labeled with the spin probe 3-(Carboxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA). The penetration into hair follicles was studied using confocal laser scanning microscopy (CLSM) with curcumin-loaded NLP. The penetration of the vehicle was followed by confocal Raman microscopy (CRM). Penetration studies using excised porcine skin revealed a more than twofold higher penetration efficiency for DxPCA into the stratum corneum (SC) after 24h incubation compared to 4h incubation when loaded to the NLP, whereas when applied in the base cream, almost no further penetration was observed beyond 4h. The distribution of DxPCA within the SC was investigated by consecutive tape stripping. The release of DxPCA from the base cream after 24h in deeper SC layers and the viable epidermis was shown by EPR. For NLP, no release from the carrier was observed, although DxPCA was detectable in the skin after the complete SC was removed. This phenomenon can be explained by the penetration of the NLP into the hair follicles. However, penetration profiles measured by CRM indicate that NLP did not penetrate as deeply into the SC as the base cream formulation. In conclusion, NLP can improve the accumulation of Dx in the skin and provide a reservoir within the SC and in the follicular infundibula. Copyright © 2017 Elsevier B.V. All rights reserved.

  1. NMR and EPR Studies of Free-Radical Intermediates from Experiments Mimicking the Winds on Mars

    DEFF Research Database (Denmark)

    Jakobsen, Hans J.; Song, Likai; Gan, Zhehong

    2016-01-01

    -enriched methane ((CH4)-C-13 and CD4), carbon dioxide ((CO2)-C-13), hydrogen (H-2(2)) and oxygen (O-17(2)). The solid-state Si free-radical intermediate and gas reaction and silicate products are formed in a specially designed rotating apparatus, which by mechanical tumbling mimics the winds and collision......A new kind of solid gas chemical reactions has been investigated using solid-state powder H-2, C-13, and Si-29 NMR and EPR spectroscopies. These studies involve reactions between a silicate-created Si free-radical intermediate and a few ordinary gases such as isotopically H-2-, C-13-, and O-17...... speed of the mineral particles on Mars. It is shown that the "hard" quartz (SiO2) or corundum (alpha-AL(2)O(3)) grain particles, used to simulate the collision particles in a rotating Pyrex (borosilicate) reaction flask, act as an abrasive on the "soft" Pyrex flask and thereby create a silicate Si free...

  2. Characterization by epr spectroscopy of the chiral catalysts bis(oxazoline-Cu supported in laponites

    Directory of Open Access Journals (Sweden)

    Alonso, P. J.

    2000-08-01

    Full Text Available An Electron Paramagnetic Resonance study of a chiral Bis(oxazoline-Cu(II supported in laponite (synthetic hectorite is presented. It is concluded that the complex is incorporated into the interllamellar space of the clay giving out isolated Cu(II entities in which the metal is co-ordinated to oxygen or nitrogen atoms with a symmetry practically planar-square, regardless the solvent used. That point out that the chlorine ligands in the complex are exchanged in the incorporation process in agreement with the previous X-ray absorption spectroscopy data, so that the oxygen atoms of the interlayers and clay surface act as counterions.

    Se presenta un estudio mediante Resonancia Paramagnética Electrónica del complejo quiral Bis(oxazolina-Cu(II soportado en laponita (hectorita sintética (libre de hierro. Del mismo se concluye que el complejo se incorpora en el espacio interlamelar de la arcilla dando lugar a entidades de Cu(II aisladas en las cuales el metal se coordina a átomos de oxígenos y nitrógenos con una simetría prácticamente planocuadrada, independientemente del disolvente empleado. Ello indica, de acuerdo con los datos previos de espectroscopia de absorción de rayos-X, que los ligandos cloruro del complejo son intercambiados en el proceso de incorporación de forma que los oxígenos de la superficie interlaminar y externa de la arcilla actúan como contraiones.

  3. Identification of Fe3+-Li+ complexes in ZnO by means of high-frequency EPR/ENDOR spectroscopy

    Science.gov (United States)

    Kutin, Yu. S.; Mamin, G. V.; Orlinskii, S. B.

    2013-12-01

    Theoretical prediction of a high Curie temperature in ZnO doped with Mn, Fe, and other transition metals has stimulated the investigation of these materials by many research groups. Although charge-compensated Fe3+ centers in ZnO:Fe have been observed by means of EPR and have been known for decades, conclusions on the chemical nature of these defects are still contradictory. Originally, these centers were treated as Fe3+-Li+ complexes with both ions occupying adjacent cationic sites. Recently, however, the centers were interpreted as a substitutional Fe3+ ion with a vacancy at an adjacent zinc or oxygen site (Fe-VZn or Fe-VO). In order to determine the chemical nature of the impurity associated with Fe3+, electron-nuclear double resonance (ENDOR) spectroscopy was used. ENDOR measurements reveal NMR transitions corresponding to nuclei with g-factor gN = 2.171 and spin I = 3/2. This unambiguously shows presence of Li as a charge compensator and also resolves contradictions with the theoretical prediction of the Fe-VO formation energy. The electric field gradients at the 7Li nuclei (within the Fe3+-Li+ complexes) were estimated to be significantly lower than the gradient at undistorted Zn sites.

  4. Single crystal EPR studies of Mn (II) doped into zinc ammonium ...

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 62; Issue 1. Single crystal EPR studies of Mn(II) doped into zinc ammonium phosphate hexahydrate (ZnNH4PO4⋅6H2O): A case of interstitial site for bio-mineral analogue. H Anandalakshmi K Velavan I Sougandi Venkatesan P Sambasiva Rao. Research Articles ...

  5. single crystal EPR studies of Mn(II) doped into zinc ammonium ...

    Indian Academy of Sciences (India)

    -sulphato-aquotris(imidazole) cadmium(II), the paramagnetic ion enters substi- tutionally into the host lattice giving rise to two magnetically inequivalent sites. [9]. single crystal EPR study of Mn(II)-doped magnesium bis(hydrogen maleate) hexahydrate confirms that the impurity ion not only occupies the magnesium site.

  6. Single crystal EPR study of VO (II)-doped cadmium potassium ...

    Indian Academy of Sciences (India)

    Single crystal EPR studies of VO(II)-doped cadmium potassium phosphate hexahydrate (CPPH) have been carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice only substitutionally in place of Cd(II). Spin Hamiltonian ...

  7. Multifrequency Pulsed EPR Studies of Biologically Relevant Manganese(II) Complexes.

    Science.gov (United States)

    Stich, T A; Lahiri, S; Yeagle, G; Dicus, M; Brynda, M; Gunn, A; Aznar, C; Derose, V J; Britt, R D

    2007-03-01

    Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different frequencies (9, 31, and 130 GHz) on [Mn(II)(H(2)O)(6)](2+), Mn(II) adducts with the nucleotides ATP and GMP, and the Mn(II)-bound form of the hammerhead ribozyme (MnHH). Through line shape analysis and interpretation of the zero-field splitting values derived from successful simulations of the corresponding continuous-wave and field-swept echo-detected spectra, these data are used to exemplify the ability of the MF EPR approach in distinguishing the nature of the first ligand sphere. A survey of recent results from pulsed EPR, as well as pulsed electron-nuclear double resonance and electron spin echo envelope modulation spectroscopic studies applied to Mn(II)-dependent systems, is also presented.

  8. Two-dimensional Pulsed EPR Studies of Vanadium-Exchanged ZSM-5

    Energy Technology Data Exchange (ETDEWEB)

    Woodworth, James F.; Bowman, Michael K.; Larsen, Sarah C.

    2004-10-14

    The pulsed electron paramagnetic resonance (EPR) technique of hyperfine sublevel correlation spectroscopy (HYSCORE) was used to obtain structural information about vanadium(VO2+) exchanged ZSM-5. HYSCORE spectra were obtained for vanadium exchanged ZSM-5 before and after dehydration and after adsorption of ammonia. For the hydrated samples, proton hyperfine coupling constants were measured and assigned to equatorial water ligands with orientations perpendicular and parallel to the equatorial plane. Nitrogen hyperfine coupling constants for adsorbed ammonia were also determined from the HYSCORE spectra. The results were compared with previous density functional theory (DFT) calculations of hyperfine coupling constants for vanadyl model complexes.

  9. In Situ EPR Studies of Reaction Pathways in Titania Photocatalyst-Promoted Alkylation of Alkenes

    Directory of Open Access Journals (Sweden)

    Shona Rhydderch

    2015-03-01

    Full Text Available In situ EPR spectroscopy at cryogenic temperatures has been used to observe and identify paramagnetic species produced when titania is irradiated in the presence of reactants used in the photocatalytic alkylation of maleimide with t-butyl carboxylic acid or phenoxyacetic acid. It is shown that maleimide acts as an acceptor of conduction band electrons. Valence band holes oxidise t-butyl carboxylic acid to the t-butyl radical and phenoxyacetic acid to the phenoxyacetic acid radical cation. In the presence of maleimide, the phenoxymethyl radical is formed from phenoxyacetic acid. The relevance of these observations to the mechanisms of titania photocatalyst-promoted alkylation of alkenes is discussed.

  10. Use of the Frank sequence in pulsed EPR

    DEFF Research Database (Denmark)

    Tseitlin, Mark; Quine, Richard W.; Eaton, Sandra S.

    2011-01-01

    The Frank polyphase sequence has been applied to pulsed EPR of triarylmethyl radicals at 256MHz (9.1mT magnetic field), using 256 phase pulses. In EPR, as in NMR, use of a Frank sequence of phase steps permits pulsed FID signal acquisition with very low power microwave/RF pulses (ca. 1.5m......W in the application reported here) relative to standard pulsed EPR. A 0.2mM aqueous solution of a triarylmethyl radical was studied using a 16mm diameter cross-loop resonator to isolate the EPR signal detection system from the incident pulses. Keyword: Correlation spectroscopy,Multi-pulse EPR,Low power pulses...

  11. Emulsion Polymerization of Butyl Acrylate: Spin Trapping and EPR Study

    Science.gov (United States)

    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.

  12. High-frequency and -field EPR spectroscopy of tris(2,4-pentanedionato)manganese(III): investigation of solid-state versus solution Jahn-Teller effects.

    Science.gov (United States)

    Krzystek, J; Yeagle, Gregory J; Park, Ju-Hyun; Britt, R David; Meisel, Mark W; Brunel, Louis-Claude; Telser, Joshua

    2003-07-28

    High-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy of a classical coordination complex, Mn(acac)(3) (Hacac = 2,4-pentanedione), has been performed on both solid powder and frozen solution (in CH(2)Cl(2)/toluene, 3:2 v/v) samples. Parallel mode detection X-band EPR spectra exhibiting resolved (55)Mn hyperfine coupling were additionally obtained for frozen solutions. Magnetic susceptibility and field-dependent magnetization measurements were also made on powder samples. Analysis of the entire EPR data set for the frozen solution allowed extraction of the relevant spin Hamiltonian parameters: D = -4.52(2); |E| = 0.25(2) cm(-1); g(iso) = 1.99(1). The somewhat lower quality solid-state HFEPR data and the magnetic measurements confirmed these parameters. These parameters are compared to those for other complexes of Mn(III) and to previous studies on Mn(acac)(3) using X-ray crystallography, solution electronic absorption spectroscopy, and powder magnetic susceptibility. Crystal structures have been reported for Mn(acac)(3) and show tetragonal distortion, as expected for this Jahn-Teller ion (Mn(3+), 3d(4)). However, in one case, the molecule exhibits axial compression and, in another, axial elongation. The current HFEPR studies clearly show the negative sign of D, which corresponds to an axial (tetragonal) elongation in frozen solution. The correspondence among solution and solid-state HFEPR data, solid-state magnetic measurements, and an HFEPR study by others on a related complex indicates that the form of Mn(acac)(3) studied here exhibits axial elongation in all cases. Such tetragonal elongation has been found for Mn(3+) and Cr(2+) complexes with homoleptic pseudooctahedral geometry as well as for Mn(3+) in square pyramidal geometry. This taken together with the results obtained here for Mn(acac)(3) in frozen solution indicates that axial elongation could be considered the "natural" form of Jahn-Teller distortion for octahedral high-spin 3d(4

  13. VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques.

    Science.gov (United States)

    Prakash, P Giri; Rao, J Lakshmana

    2005-09-01

    Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites.

  14. EPR study of thermally treated Archean microbial mats analogues and comparison with Archean cherts: towards a possible marker of oxygenic photosynthesis?

    Science.gov (United States)

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

    2012-04-01

    The datation of photosynthesis apparition remains an open question nowadays: did oxygenic photosynthesis appear just before the Great Oxidation Event (GOE) of the atmosphere, 2.3 to 2.4 Gyr ago, or does it originate much earlier? It is therefore of uttermost interest to find markers of oxygenic photosynthesis, applicable to samples of archean age. In order to handle this problem, Microcoleus Chtonoplastes cyanobacteria and Chloroflexus-like non-oxygenic photosynthetic bacteria, were studied using Electron Paramagnetic Resonance (EPR) spectroscopy, a high sensitivity technique for the study of organic radicals in mature geological samples (coals, cherts, meteorites...). M. chtonoplastes and Chloroflexus-like bacteria were sampled in mats from the hypersaline lake "La Salada de Chiprana" (Spain), an analogue to an Archean environment, and were submitted to accelerated ageing through cumulative thermal treatments. For thermal treatment temperatures higher than 620° C, a drastic increase in the EPR linewidth of the oxygenic photosynthetic bacteria (M. chtonoplastes) occurred, as compared with the anoxygenic photosynthetic one (Chloroflexus-like). The EPR study of a thermally treated mixture of the two bacteria evidences that this linewidth increase is driven by catalytic reaction at high temperatures on an element selectively fixed by M. chtonoplastes. Based on comparative EDS analyses, Mg is a potential candidate for this catalytic activity but its precise role and the nature of the reaction are still to be determined. The EPR study of organic radicals in chert rocks of ages ranging from 0.42 to 3.5 Gyr, from various localities and that underwent various metamorphisms, revealed a dispersion of the signal width for the most mature samples. This comparative approach between modern bacterial samples and Precambrian cherts leads to propose the EPR linewidth of mature organic matter in cherts as a potential marker of oxygenic photosynthesis. If confirmed, this marker

  15. Structural differences between the closed and open states of channelrhodopsin-2 as observed by EPR spectroscopy.

    Science.gov (United States)

    Krause, Nils; Engelhard, Christopher; Heberle, Joachim; Schlesinger, Ramona; Bittl, Robert

    2013-10-11

    Channelrhodopsin is a cation channel with the unique property of being activated by light. To address structural changes of the open state of the channel, two variants, which contain either 1 or 2 wild-type cysteines, were derivatised with nitroxide spin label and subjected to electron paramagnetic resonance spectroscopy. Both variants contained the C128T mutation to trap the long-lived P3(520) state by illumination. Comparison of spin-spin distances in the dark state and after illumination reflect conformational changes in the conductive P3(520) state involving helices B and F. Spin distance measurements reveal that channelrhodopsin forms a dimer even in the absence of intermolecular N-terminal cysteines. Copyright © 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  16. High-field (high-frequency) EPR spectroscopy and structural characterization of a novel manganese(III) corrole

    OpenAIRE

    Bendix, Jesper; Gray, Harry B.; Golubkov, Galina; Gross, Zeev

    2000-01-01

    The X-ray structure, magnetic susceptibility, and high-field (high-frequency) EPR spectrum of manganese 5,10,15-tris(pentafluorophenyl) corrole unambiguously establish that the complex contains an isolated, slightly rhombic, manganese(III) center.

  17. Reactions of superoxide dismutases with HS(-)/H2S and superoxide radical anion: An in vitro EPR study.

    Science.gov (United States)

    Bolić, Bojana; Mijušković, Ana; Popović-Bijelić, Ana; Nikolić-Kokić, Aleksandra; Spasić, Snežana; Blagojević, Duško; Spasić, Mihajlo B; Spasojević, Ivan

    2015-12-01

    Interactions of hydrogen sulfide (HS(-)/H2S), a reducing signaling species, with superoxide dimutases (SOD) are poorly understood. We applied low-T EPR spectroscopy to examine the effects of HS(-)/H2S and superoxide radical anion O2.- on metallocenters of FeSOD, MnSOD, and CuZnSOD. HS(-)/H2S did not affect FeSOD, whereas active centers of MnSOD and CuZnSOD were open to this agent. Cu(2+) was reduced to Cu(1+), while manganese appears to be released from MnSOD active center. Untreated and O2.- treated FeSOD and MnSOD predominantly show 5 d-electron systems, i.e. Fe(3+) and Mn(2+). Our study provides new details on the mechanisms of (patho)physiological effects of HS(-)/H2S. Copyright © 2015 Elsevier Inc. All rights reserved.

  18. Membrane remodeling by amyloidogenic and non-amyloidogenic proteins studied by EPR

    Science.gov (United States)

    Varkey, Jobin; Langen, Ralf

    2017-07-01

    The advancement in site-directed spin labeling of proteins has enabled EPR studies to expand into newer research areas within the umbrella of protein-membrane interactions. Recently, membrane remodeling by amyloidogenic and non-amyloidogenic proteins has gained a substantial interest in relation to driving and controlling vital cellular processes such as endocytosis, exocytosis, shaping of organelles like endoplasmic reticulum, Golgi and mitochondria, intracellular vesicular trafficking, formation of filopedia and multivesicular bodies, mitochondrial fusion and fission, and synaptic vesicle fusion and recycling in neurotransmission. Misregulation in any of these processes due to an aberrant protein (mutation or misfolding) or alteration of lipid metabolism can be detrimental to the cell and cause disease. Dissection of the structural basis of membrane remodeling by proteins is thus quite necessary for an understanding of the underlying mechanisms, but it remains a formidable task due to the difficulties of various common biophysical tools in monitoring the dynamic process of membrane binding and bending by proteins. This is largely since membranes generally complicate protein structure analysis and this problem is amplified for structural analysis in the presence of different types of membrane curvatures. Recent EPR studies on membrane remodeling by proteins show that a significant structural information can be generated to delineate the role of different protein modules, domains and individual amino acids in the generation of membrane curvature. These studies also show how EPR can complement the data obtained by high resolution techniques such as X-ray and NMR. This perspective covers the application of EPR in recent studies for understanding membrane remodeling by amyloidogenic and non-amyloidogenic proteins that is useful for researchers interested in using or complimenting EPR to gain better understanding of membrane remodeling. We also discuss how a single

  19. EPR, optical and superposition model study of Mn2+ doped L+ glutamic acid

    Science.gov (United States)

    Kripal, Ram; Singh, Manju

    2015-12-01

    Electron paramagnetic resonance (EPR) study of Mn2+ doped L+ glutamic acid single crystal is done at room temperature. Four interstitial sites are observed and the spin Hamiltonian parameters are calculated with the help of large number of resonant lines for various angular positions of external magnetic field. The optical absorption study is also done at room temperature. The energy values for different orbital levels are calculated, and observed bands are assigned as transitions from 6A1g(s) ground state to various excited states. With the help of these assigned bands, Racah inter-electronic repulsion parameters B = 869 cm-1, C = 2080 cm-1 and cubic crystal field splitting parameter Dq = 730 cm-1 are calculated. Zero field splitting (ZFS) parameters D and E are calculated by the perturbation formulae and crystal field parameters obtained using superposition model. The calculated values of ZFS parameters are in good agreement with the experimental values obtained by EPR.

  20. Resonance Raman and EPR spectroscopic studies on heme-heme oxygenase complexes.

    Science.gov (United States)

    Sun, J; Wilks, A; Ortiz de Montellano, P R; Loehr, T M

    1993-12-28

    The binding of ferrous and ferric hemes and manganese(II)- and manganese(III)-substituted hemes to heme oxygenase has been investigated by optical absorption, resonance Raman, and EPR spectroscopy. The results are consistent with the presence of a six-coordinate heme moiety ligated to an essential histidine ligand and a water molecule. The latter ionizes with a pKa approximately 8.0 to give a mixture of high-spin and low-spin six-coordinate hydroxo adducts. Addition of excess cyanide converts the heme to a hexacoordinate low-spin species. The resonance Raman spectrum of the ferrous heme-heme oxygenase complex and that of the Mn(II)protoporphyrin-heme oxygenase complex shows bands at 216 and 212 cm-1, respectively, that are assigned to the metal-histidine stretching mode. The EPR spectrum of the oxidized heme-heme oxygenase complex has a strongly axial signal with g parallel of approximately 6 and g perpendicular approximately 2. 14NO and 15NO adducts of ferrous heme-heme oxygenase exhibit EPR hyperfine splittings of approximately 20 and approximately 25 Gauss, respectively. In addition, both nitrosyl complexes show additional superhyperfine splittings of approximately 7 Gauss from spin-spin interaction with the proximal histidine nitrogen. The heme environment in the heme-heme oxygenase enzyme-substrate complex has spectroscopic properties similar to those of the heme in myoglobin. Hence, there is neither a strongly electron-donating fifth (proximal) ligand nor an electron-withdrawing network on the distal side of the heme moiety comparable to that for cytochromes P-450 and peroxidases. This observation has profound implications about the nature of the oxygen-activating process in the heme-->biliverdin reaction that are discussed in this paper.

  1. Characterization of Monomeric MnII/III/IV–Hydroxo Complexes from X- and Q-Band Dual Mode Electron Paramagnetic Resonance (EPR) Spectroscopy

    Science.gov (United States)

    Gupta, Rupal; Taguchi, Taketo; Borovik, A. S.; Hendrich, Michael P.

    2013-01-01

    Manganese–hydroxo species have been implicated in C–H bond activation performed by metalloenzymes, but the electronic properties of many of these intermediates are not well characterized. The present work presents a detailed characterization of three Mnn–OH complexes (where n = II, III, and IV) of the tris[(N′-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3−) ligand using X- and Q-band dual mode electron paramagnetic resonance (EPR). Quantitative simulations for the [MnIIH3buea(OH)]2− complex demonstrated the ability to characterize similar MnII species commonly present in the resting states of manganese-containing enzymes. The spin states of the MnIII and MnIV complexes determined from EPR spectroscopy are S = 2 and 3/2, respectively, as expected for the C3 symmetry imposed by the [H3buea]3− ligand. Simulations of the spectra indicated the constant presence of two MnIV species in solutions of [MnIVH3buea(OH)] complex. The simulations of perpendicular- and parallel-mode EPR spectra allow determination of zero-field splitting and hyperfine parameters for all complexes. For the MnIII and MnIV complexes, density functional theory calculations are used to determine the isotropic Mn hyperfine values, to compare the excited electronic state energies, and to give theoretical estimates of the zero-field energy. PMID:24156406

  2. Characterization of monomeric Mn(II/III/IV)-hydroxo complexes from X- and Q-band dual mode electron paramagnetic resonance (EPR) spectroscopy.

    Science.gov (United States)

    Gupta, Rupal; Taguchi, Taketo; Borovik, A S; Hendrich, Michael P

    2013-11-04

    Manganese-hydroxo species have been implicated in C-H bond activation performed by metalloenzymes, but the electronic properties of many of these intermediates are not well characterized. The present work presents a detailed characterization of three Mn(n)-OH complexes (where n = II, III, and IV) of the tris[(N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea](3-)) ligand using X- and Q-band dual mode electron paramagnetic resonance (EPR). Quantitative simulations for the [Mn(II)H3buea(OH)](2-) complex demonstrated the ability to characterize similar Mn(II) species commonly present in the resting states of manganese-containing enzymes. The spin states of the Mn(III) and Mn(IV) complexes determined from EPR spectroscopy are S = 2 and 3/2, respectively, as expected for the C3 symmetry imposed by the [H3buea](3-) ligand. Simulations of the spectra indicated the constant presence of two Mn(IV) species in solutions of [Mn(IV)H3buea(OH)] complex. The simulations of perpendicular- and parallel-mode EPR spectra allow determination of zero-field splitting and hyperfine parameters for all complexes. For the Mn(III) and Mn(IV) complexes, density functional theory calculations are used to determine the isotropic Mn hyperfine values, to compare the excited electronic state energies, and to give theoretical estimates of the zero-field energy.

  3. EPR Oximetry Sensor-Developing a TAM Derivative for In Vivo Studies.

    Science.gov (United States)

    Boś-Liedke, Agnieszka; Walawender, Magdalena; Woźniak, Anna; Flak, Dorota; Gapiński, Jacek; Jurga, Stefan; Kucińska, Małgorzata; Plewiński, Adam; Murias, Marek; Elewa, Marwa; Lampp, Lisa; Imming, Peter; Tadyszak, Krzysztof

    2017-09-04

    Oxygenation is one of the most important physiological parameters of biological systems. Low oxygen concentration (hypoxia) is associated with various pathophysiological processes in different organs. Hypoxia is of special importance in tumor therapy, causing poor response to treatment. Triaryl methyl (TAM) derivative radicals are commonly used in electron paramagnetic resonance (EPR) as sensors for quantitative spatial tissue oxygen mapping. They are also known as magnetic resonance imaging (MRI) contrast agents and fluorescence imaging compounds. We report the properties of the TAM radical tris(2,3,5,6-tetrachloro-4-carboxy-phenyl)methyl, (PTMTC), a potential multimodal (EPR/fluorescence) marker. PTMTC was spectrally analyzed using EPR and characterized by estimation of its sensitivity to the oxygen in liquid environment suitable for intravenous injection (1 mM PBS, pH = 7.4). Further, fluorescent emission of the radical was measured using the same solvent and its quantum yield was estimated. An in vitro cytotoxicity examination was conducted in two cancer cell lines, HT-29 (colorectal adenocarcinoma) and FaDu (squamous cell carcinoma) and followed by uptake studies. The stability of the radical in different solutions (PBS pH = 7.4, cell media used for HT-29 and FaDu cells culturing and cytotoxicity procedure, full rat blood and blood plasma) was determined. Finally, a primary toxicity test of PTMTC was carried out in mice. Results of spectral studies confirmed the multimodal properties of PTMTC. PTMTC was demonstrated to be not absorbed by cancer cells and did not interfere with luciferin-luciferase based assays. Also in vitro and in vivo tests showed that it was non-toxic and can be freely administrated till doses of 250 mg/kg BW via both i.v. and i.p. injections. This work illustrated that PTMTC is a perfect candidate for multimodal (EPR/fluorescence) contrast agent in preclinical studies.

  4. 240 GHz EPR Studies of Intrinsic Defects in 4H SiC

    Science.gov (United States)

    Konovalov, V. V.; Zvanut, M. E.; van Tol, J.; Brunel, L.-C.

    2002-03-01

    Intrinsic defects may strongly influence the conductivity and optical behavior of SiC. Several groups have reported 9.5 GHz EPR studies of a carbon vacancy in electron irradiated p-type and as-grown nominally semi-insulating SiC. Recently, Son et al. interpreted two lines in a 95 GHz EPR spectrum as a carbon vacancy and silicon antisite. We report 240 GHz EPR studies of intrinsic defects in as-grown 4H SiC provided by Cree Inc. The ID-1 line we observed earlier at 9.5 GHz and assigned to a carbon vacancy was resolved at 240 GHz into two lines, ID-1a and ID-1b. As the temperature decreased from 80 to 4 K, with H//c-axis the g-value of ID-1a remained constant at 2.00307, but the g-value of ID-1b decreased from 2.00272 to 2.00235. Concomitantly, the intensity of ID-1a decreased while that of ID-1b increased. Although our data are close to Son’s 95 GHz spectrum, preliminary interpretation of the highly resolved lines obtained at 240 GHz does not suggest a silicon antisite. Illumination with IR light quenches both ID-1a and ID-1b simultaneously, indicating close defect levels. The work is supported by the ONR.

  5. EPR study of gamma-irradiated amphi-phenylglyoxime single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Dereli, O., E-mail: odereli@selcuk.edu.t [A. Kelesoglu Education Faculty, Department of Physics, Selcuk University, Meram, 42090, Konya (Turkey); Tuerkkan, E. [A. Kelesoglu Education Faculty, Department of Physics, Selcuk University, Meram, 42090, Konya (Turkey); Ozmen, A.; Yueksel, H. [Science Faculty, Department of Physics, Selcuk University, Selcuklu, 42079, Konya (Turkey)

    2011-06-15

    Gamma-irradiated single crystals of Amphi-phenylglyoxime (APGO) were investigated using electron paramagnetic resonance (EPR) at different orientations in a magnetic field at room temperature (298 K). Considering the chemical structure and the experimental spectra of the irradiated single-crystals of APGO, we assumed that two different paramagnetic species, labeled as R{sup *} and R{sup **}, are either two iminoxy radicals formed by the abstraction of a H atom from different oxime branches or are different conformations of an iminoxy radical. Pursuant to this assumption, RA- and RB-type iminoxy radicals were modeled by the abstraction of H atoms from different oxime branches, and conformational analysis of these modeled radicals was performed using the semi-empirical AM1 and B3LYP/6-31+G(d,p) methods. EPR parameters were calculated for the modeled radicals using the B3LYP method and EPR-III basis set. Theoretically calculated values of the most stable conformers (RA-1 and RB-1) of the modeled radicals are in good agreement with the experimental EPR parameters determined from the spectra (differences in isotropic hyperfine coupling constant values <5%, and differences in isotropic g values fall into 1 ppt). Thus, from the findings of the present study, we strongly suggest that the experimentally observed R{sup *} and R{sup **} radicals in the single crystal of amphi-phenylglyoxime are the most stable conformers of RA- and RB-type modeled iminoxy radicals, respectively. The experimental g factors and hyperfine coupling constants were found to be anisotropic, with average values of g=2.0052, A({sup 14}N)=29.50 G, A({sup 1}H)=25.30 G for R{sup *}, and g=2.0057, A({sup 14}N)=34.50 G for R{sup **}.

  6. Photochemistry of naphthalene diimides: EPR study of free radical formation via photoredox process.

    Science.gov (United States)

    Reszka, Krzysztof J; Takayama, Masami; Sik, Robert H; Chignell, Colin F; Saito, Isao

    2005-01-01

    Earlier studies have shown that on exposure to UVA, hydroperoxynaphthalene diimide (IA) generates hydroxyl radicals, induces DNA strand scission, and kills cells. Here we employed electron paramagnetic resonance (EPR) and spin trapping to investigate the free radical photochemistry of IA and that of related naphthalene diimides, which are devoid of the hydroperoxyl moiety (N,N'-bis[2-methyl]-1,4,5,8-naphthaldiimide [IB], N,N'-bis[2-thiomethyl-2-methoxyethyl]-1,4,5,8-naphthaldiimide [IC]) and therefore are unable to generate hydroxyl radicals. It is shown that on UV irradiation (>300 nm) in air-free methanol or ethanol solutions all these naphthalene diimides undergo one-electron reduction to corresponding anion radicals, positively identified by EPR. With EPR and a spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), we found that the photogeneration of the naphthalene diimide radicals is concomitant with the formation of radicals from the solvents, presumably through electron/hydrogen atom abstraction by photoactivated diimides. Irradiation of IA, IB or IC in the presence of oxygen generates superoxide, which was detected as a DMPO adduct. The high photoreactivity of IB and IC supports the notion that hydroperoxide IA can induce oxidative damage via photoprocesses that are independent of *OH generation. These observations could be pertinent to the application of naphthalene diimides as selective photonucleases, PDT anticancer agents or both.

  7. EPR study of the formation of radicals in PP with antioxidants irradiated with gamma rays

    Energy Technology Data Exchange (ETDEWEB)

    Silva, P. [Instituto Venezolano de Investigaciones Cientificas, Centro de Fisica, Carretera Panamericana Km. 11, Caracas 1020-A (Venezuela)], E-mail: silva@ivic.ve; Albano, C. [Instituto Venezolano de Investigaciones Cientificas, Centro de Quimica, Universidad Central de Venezuela, Facultad de Ingenieria (Venezuela); Perera, R. [Departamento de Mecanica, Universidad Simon Bolivar (Venezuela)

    2007-12-15

    The behavior of different compounds of polypropylene (PP) with stabilizers such as buthyl-hydroxy-toluene (BHT), Chimassorb 944 (Hals) (CHIM), and a copolymer of styrene-butadiene-styrene (SBS) was studied using electron paramagnetic resonance (EPR). A characteristic spectra for pure PP irradiated in air was obtained for all the samples just after being irradiated [M. Dole, The Radiation Chemistry of Macromolecules, Vol. 2, Academic Press, 1973]. A change in the lineshape of the spectra from a pure PP's EPR signal to that of nitroxyl radical as a function of time was observed. The total free radical concentration (TFRC) decayed until approximately 800 h in the PP-HALS and until around 2000 h in all other cases, when the TFRC began to increase in all the cases, except in that of PP-BHT. In this last case, the EPR signal was not detectable after 4000 h. The BHT and the SBS diluted the free radical concentrations, being them smaller when they are present. The behavior observed in all the samples is consistent with the formation of nitroxyl radicals by gamma rays.

  8. Highly-Efficient Charge Separation and Polaron Delocalization in Polymer-Fullerene Bulk-Heterojunctions: A Comparative Multi-Frequency EPR & DFT Study

    Science.gov (United States)

    Niklas, Jens; Mardis, Kristy L.; Banks, Brian P.; Grooms, Gregory M.; Sperlich, Andreas; Dyakonov, Vladimir; Beaupré, Serge; Leclerc, Mario; Xu, Tao; Yu, Luping; Poluektov, Oleg G.

    2016-01-01

    The ongoing depletion of fossil fuels has led to an intensive search for additional renewable energy sources. Solar-based technologies could provide sufficient energy to satisfy the global economic demands in the near future. Photovoltaic (PV) cells are the most promising man-made devices for direct solar energy utilization. Understanding the charge separation and charge transport in PV materials at a molecular level is crucial for improving the efficiency of the solar cells. Here, we use light-induced EPR spectroscopy combined with DFT calculations to study the electronic structure of charge separated states in blends of polymers (P3HT, PCDTBT, and PTB7) and fullerene derivatives (C60-PCBM and C70-PCBM). Solar cells made with the same composites as active layers show power conversion efficiencies of 3.3% (P3HT), 6.1% (PCDTBT), and 7.3% (PTB7), respectively. Under illumination of these composites, two paramagnetic species are formed due to photo-induced electron transfer between the conjugated polymer and the fullerene. They are the positive, P+, and negative, P-, polarons on the polymer backbone and fullerene cage, respectively, and correspond to radical cations and radical anions. Using the high spectral resolution of high-frequency EPR (130 GHz), the EPR spectra of these species were resolved and principal components of the g-tensors were assigned. Light-induced pulsed ENDOR spectroscopy allowed the determination of 1H hyperfine coupling constants of photogenerated positive and negative polarons. The experimental results obtained for the different polymer-fullerene composites have been compared with DFT calculations, revealing that in all three systems the positive polaron is distributed over distances of 40 - 60 Å on the polymer chain. This corresponds to about 15 thiophene units for P3HT, approximately three units PCDTBT, and about three to four units for PTB7. No spin density delocalization between neighboring fullerene molecules was detected by EPR. Strong

  9. 3D printed sample holder for in-operando EPR spectroscopy on high temperature polymer electrolyte fuel cells

    Science.gov (United States)

    Niemöller, Arvid; Jakes, Peter; Kayser, Steffen; Lin, Yu; Lehnert, Werner; Granwehr, Josef

    2016-08-01

    Electrochemical cells contain electrically conductive components, which causes various problems if such a cell is analyzed during operation in an EPR resonator. The optimum cell design strongly depends on the application and it is necessary to make certain compromises that need to be individually arranged. Rapid prototyping presents a straightforward option to implement a variable cell design that can be easily adapted to changing requirements. In this communication, it is demonstrated that sample containers produced by 3D printing are suitable for EPR applications, with a particular emphasis on electrochemical applications. The housing of a high temperature polymer electrolyte fuel cell (HT-PEFC) with a phosphoric acid doped polybenzimidazole membrane was prepared from polycarbonate by 3D printing. Using a custom glass Dewar, this fuel cell could be operated at temperatures up to 140 °C in a standard EPR cavity. The carbon-based gas diffusion layer showed an EPR signal with a characteristic Dysonian line shape, whose evolution could be monitored in-operando in a non-invasive manner.

  10. Structural investigation of a high-affinity MnII binding site in the hammerhead ribozyme by EPR spectroscopy and DFT calculations. Effects of neomycin B on metal-ion binding.

    Science.gov (United States)

    Schiemann, Olav; Fritscher, Jörg; Kisseleva, Natalja; Sigurdsson, Snorri Th; Prisner, Thomas F

    2003-10-06

    Electron paramagnetic resonance spectroscopy and density functional theory methods were used to study the structure of a single, high-affinity Mn(II) binding site in the hammerhead ribozyme. This binding site exhibits a dissociation constant Ke of 4.4 microM in buffer solutions containing 1 M NaCl, as shown by titrations monitored by continuous wave (cw) EPR. A combination of electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) experiments revealed that the paramagnetic manganese(II) ion in this binding site is coupled to a single nitrogen atom with a quadrupole coupling constant kappa of 0.7 MHz, an asymmetry parameter eta of 0.4, and an isotropic hyperfine coupling constant of Aiso(14N)=2.3 MHz. All three EPR parameters are sensitive to the arrangement of the Mn(II) ligand sphere and can therefore be used to determine the structure of the binding site. A possible location for this binding site may be at the G10.1, A9 site found to be occupied by Mn(II) in crystals (MacKay et al., Nature 1994, 372, 68 and Scott et al., Science 1996, 274, 2065). To determine whether the structure of the binding site is the same in frozen solution, we performed DFT calculations for the EPR parameters, based on the structure of the Mn(II) site in the crystal. Computations with the BHPW91 density function in combination with a 9s7p4d basis set for the manganese(II) center and the Iglo-II basis set for all other atoms yielded values of kappa(14N)=+0.80 MHz, eta=0.324, and Aiso(14N)=+2.7 MHz, in excellent agreement with the experimentally obtained EPR parameters, which suggests that the binding site found in the crystal and in frozen solution are the same. In addition, we demonstrated by EPR that Mn(II) is released from this site upon binding of the aminoglycoside antibiotic neomycin B (Kd=1.2 microM) to the hammerhead ribozyme. Neomycin B has previously been shown to inhibit the catalytic activity of this ribozyme (Uhlenbeck et al., Biochemistry

  11. Phenylbutazone Oxidation via Cu,Zn-SOD Peroxidase Activity: An EPR Study.

    Science.gov (United States)

    Aljuhani, Naif; Whittal, Randy M; Khan, Saifur R; Siraki, Arno G

    2015-07-20

    We investigated the effect of Cu,Zn-superoxide dismutase (Cu,Zn-SOD)-peroxidase activity on the oxidation of the nonsteroidal anti-inflammatory drug phenylbutazone (PBZ). We utilized electron paramagnetic resonance (EPR) spectroscopy to detect free radical intermediates of PBZ, UV-vis spectrophotometry to monitor PBZ oxidation, oxygen analysis to determine the involvement of C-centered radicals, and LC/MS to determine the resulting metabolites. Using EPR spectroscopy and spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), we found that the spin adduct of CO3(•-) (DMPO/(•)OH) was attenuated with increasing PBZ concentrations. The resulting PBZ radical, which was assigned as a carbon-centered radical based on computer simulation of hyperfine splitting constants, was trapped by both DMPO and MNP spin traps. Similar to Cu,Zn-SOD-peroxidase activity, an identical PBZ carbon-centered radical was also detected with the presence of both myeloperoxidase (MPO/H2O2) and horseradish peroxidase (HRP/H2O2). Oxygen analysis revealed depletion in oxygen levels when PBZ was oxidized by SOD peroxidase-activity, further supporting carbon radical formation. In addition, UV-vis spectra showed that the λmax for PBZ (λ = 260 nm) declined in intensity and shifted to a new peak that was similar to the spectrum for 4-hydroxy-PBZ when oxidized by Cu,Zn-SOD-peroxidase activity. LC/MS evidence supported the formation of 4-hydroxy-PBZ when compared to that of a standard, and 4-hydroperoxy-PBZ was also detected in significant yield. These findings together indicate that the carbonate radical, a product of SOD peroxidase activity, appears to play a role in PBZ metabolism. Interestingly, these results are similar to findings from heme peroxidase enzymes, and the context of this metabolic pathway is discussed in terms of a mechanism for PBZ-induced toxicity.

  12. The nature of the exchange coupling between high-spin Fe(III) heme o3 and CuBII in Escherichia coli quinol oxidase, cytochrome bo3: MCD and EPR studies.

    Science.gov (United States)

    Cheesman, Myles R; Oganesyan, Vasily S; Watmough, Nicholas J; Butler, Clive S; Thomson, Andrew J

    2004-04-07

    Fully oxidized cytochrome bo3 from Escherichia coli has been studied in its oxidized and several ligand-bound forms using electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopies. In each form, the spin-coupled high-spin Fe(III) heme o3 and CuB(II) ion at the active site give rise to similar fast-relaxing broad features in the dual-mode X-band EPR spectra. Simulations of dual-mode spectra are presented which show that this EPR can arise only from a dinuclear site in which the metal ions are weakly coupled by an anisotropic exchange interaction of J 1 cm-1. A variable-temperature and magnetic field (VTVF) MCD study is also presented for the cytochrome bo3 fluoride and azide derivatives. New methods are used to extract the contribution to the MCD of the spin-coupled active site in the presence of strong transitions from low-spin Fe(III) heme b. Analysis of the MCD data, independent of the EPR study, also shows that the spin-coupling within the active site is weak with J approximately 1 cm-1. These conclusions overturn a long-held view that such EPR signals in bovine cytochrome c oxidase arise from an S' = 2 ground state resulting from strong exchange coupling (J > 10(2) cm-1) within the active site.

  13. Structural characterization, thermoluminescence and EPR studies of Nd{sub 2}O{sub 3}:Co{sup 2+} nanophosphors

    Energy Technology Data Exchange (ETDEWEB)

    Umesh, B. [Department of Humanities, PVP Polytechnic, Dr. AIT Campus, Bangalore 560 056 (India); Department of Physics, Bangalore University, Bangalore 560 056 (India); Eraiah, B., E-mail: eraiah@rediffmail.com [Department of Physics, Bangalore University, Bangalore 560 056 (India); Nagabhushana, H., E-mail: bhushanvlc@gmail.com [Prof. C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumkur 572 103 (India); Sharma, S.C.; Sunitha, D.V. [Prof. C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumkur 572 103 (India); Nagabhushana, B.M. [Department of Chemistry, M.S. Ramaiah Institute of Technology, Bangalore 560 054 (India); Rao, J.L. [Department of Physics, Sri Venkateswara University, Tirupati 517 502 (India); Shivakumara, C. [Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012 (India); Chakradhar, R.P.S., E-mail: sreechakra72@yahoo.com [CSIR – National Aerospace Laboratories, Bangalore 560 017 (India)

    2013-02-15

    Graphical abstract: Display Omitted Highlights: ► Nd{sub 2}O{sub 3}:Co{sup 2+} (1–4 mol%) nanophosphors have been prepared at much lower temperatures. ► Phosphors are well characterized by PXRD, SEM, TEM, FTIR, Raman, UV–vis spectroscopy. ► EPR and thermoluminescence properties were also reported. ► TL intensity increases linearly with γ dose suggesting usage in radiation dosimetry. -- Abstract: Nd{sub 2}O{sub 3}:Co{sup 2+} (1–4 mol%) nanophosphors (15–25 nm) have been prepared via low temperature solution combustion method. Scanning electron micrograph (SEM) shows that the product is highly porous in nature. The stokes line in the Raman spectrum at ∼2000 cm{sup −1} is assigned to F{sub g} mode and the anti-stokes lines are assigned to a combination of A{sub g} + E{sub g} modes. With increase of Co{sup 2+} concentration, the intensity of F{sub g} mode decreases, whereas the combination of A{sub g} + F{sub g} modes completely disappears. Electron paramagnetic resonance (EPR) spectrum exhibits two resonance signals with effective g values at g = 2.25 and g = 2.03. Thermoluminescence (TL) response of Nd{sub 2}O{sub 3}:Co{sup 2+} nanopowders with γ dose 0.23–2.05 kGy was studied. The activation energy (E) and frequency factor (s) are estimated using Chen's glow peak shape method and obtained to be in the range 0.45–1.67 eV and 1.8 × 10{sup 4} to 4.0 × 10{sup 12} s{sup −1}, respectively. It is observed that the TL glow peak intensity at 430 K increases linearly with γ dose which is suitable for radiation dosimetry.

  14. Synthesis and room temperature single crystal EPR studies of a ...

    Indian Academy of Sciences (India)

    Unknown

    Optical and electron paramagnetic spectral data have been used to obtain the parameters Dq, B and C. Keywords. Hsalamp; cyclic voltammetry; electron paramagnetic resonance; spin-. Hamiltonian parameters. 1. Introduction. Biological activity of complexes derived from hydrazones has been widely studied and.

  15. EPR and 55Mn cw-ENDOR study of an antiferrogmagnetically coupled dinuclear manganese (Mn III Mn IV) complex

    Science.gov (United States)

    Zweygart, W.; Bittl, R.; Wieghardt, K.; Lubitz, W.

    1996-10-01

    X- and Q-band EPR and 55Mn cw-ENDOR experiments are reported on a binuclear oxo-bridged dimanganese Mn III Mn IV complex. Consistent simulations of spectra from both frequency bands using one parameter set for the orthorhombic g tensor and Mn III and Mn IV hyperfine tensors are achieved. Information on the manganese hyperfine couplings is independently obtained from 55Mn cw-ENDOR spectroscopy performed on both ions.

  16. EPR Spectroscopy of catalytic systems based on nickel complexes of 1,4-diaza-1,3-butadiene (α-diimine) ligands in hydrogenation and polymerization reactions

    Science.gov (United States)

    Titova, Yu. Yu.; Belykh, L. B.; Schmidt, F. K.

    2015-01-01

    EPR spectroscopy is used to study catalytic hydration and polymerization reaction systems based on α-diimine complexes of Ni(0) and Ni(II) with the general formula NiBr2(DAD-R) (R = -C3H7 or -CH3) or Ni(DAD-CH3)2 (DAD(-C3H7) = 1,4-bis(2,6-diiso-propylphenyl)-2,3-(dimethyl-1,4-diazabuta-1,3-diene, DAD(-CH3) = 1,4-bis(2,6-dimethylphenyl)-2,3-dimethyl-1,4-diazabuta-1,3-diene)), in combination with Lewis acids (AlEt3, AlEt2Cl, AlEtCl2, B(F5C6)3, BF3.OEt2). Ni(I) complexes of the form (DAD-R)NiX2AlX'y(C2H5)3-y composition (an aluminum atom can be replaced by a boron atom) were identified, where R = -CH3 or -C3H7, X = Br, and X' = Cl or -C2H5 and α-diimine anion radicals are included in derivatives of aluminum or boron. Oxidation reactions of the Ni(DAD-CH3)2 complex with aluminum alkyl halides and boron derivatives with formation of paramagnetic nickel complexes are observed. It is found that there is no direct relationship between the polymerization activity of ethylene or hydration of the alkenes and the concentration of paramagnetic particles.

  17. Study of dental enamel and synthetic hydroxyapatite irradiated by EPR at K-band

    Energy Technology Data Exchange (ETDEWEB)

    Santos, A.B. [Departamento Fisica e Matematica, FFCLRP, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, SP (Brazil); Universidade Federal do Tocantins, 77020-120 Palmas, Tocantins (Brazil)]. E-mail: adevailton@uft.edu.br; Rossi, A.M. [Centro Brasileiro de Pesquisas Fisicas, 22290 180 Rio de Janeiro, RJ (Brazil); Baffa, O. [Departamento Fisica e Matematica, FFCLRP, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, SP (Brazil)

    2005-02-01

    In this preliminary work the EPR spectra of a small dental enamel block and a synthetic B-type hydroxyapatite in powder form, both irradiated with gamma rays, were analyzed in K-band. The spectra of the dental enamel block allow the analysis of independent components with different angular orientations, while the study of the dosimetric properties of the synthetic hydroxyapatites showed good performance of this spectrometer. K-band spectra show better resolution when compared to X-band, while using significantly less sample material.

  18. Study of dental enamel and synthetic hydroxyapatite irradiated by EPR at K-band.

    Science.gov (United States)

    Santos, A B; Rossi, A M; Baffa, O

    2005-02-01

    In this preliminary work the EPR spectra of a small dental enamel block and a synthetic B-type hydroxyapatite in powder form, both irradiated with gamma rays, were analyzed in K-band. The spectra of the dental enamel block allow the analysis of independent components with different angular orientations, while the study of the dosimetric properties of the synthetic hydroxyapatites showed good performance of this spectrometer. K-band spectra show better resolution when compared to X-band, while using significantly less sample material.

  19. Free radical formation in chloramphenicol heated at different temperatures and the best thermal sterilization conditions - application of EPR spectroscopy and UV spectrophotometry.

    Science.gov (United States)

    Ramos, Paweł; Pilawa, Barbara

    2016-12-12

    Free radicals in thermally treated chloramphenicol were examined by electron paramagnetic resonance (EPR) spectroscopy. The parameters and shape of EPR spectra were analysed and free radical concentrations were obtained in the tested drug samples. Chloramphenicol was thermally sterilized at pharmacopeia conditions: 100 °C (120 min). Sterilization was also carried out at different conditions, 110 °C (60 min) and 120 °C (30 min), for comparison with pharmacopeia settings. Microbiological analysis was performed on the samples to confirm sterility. The aim of this work was to determine the concentration of free radicals in chloramphenicol following thermal sterilization at pharmacopeia conditions and compare this with other sets of conditions [110 °C (60 min) and 120 °C (30 min)]. The best conditions of thermal sterilization are determined as those that kill microorganisms and produce the lowest amounts of free radicals in this drug. It was concluded that the optimal temperatures and times for the thermal sterilization of chloramphenicol are 100 °C and 120 min and 110 °C and 60 min. A temperature of 120 °C coupled with a heating time of 30 min was rejected for thermal sterilization because of the high amount of free radicals produced by the drug samples.

  20. Continuous wave W- and D-Band EPR spectroscopy offer “sweet-spots” for characterizing conformational changes and dynamics in intrinsically disordered proteins

    Energy Technology Data Exchange (ETDEWEB)

    Casey, Thomas M.; Liu, Zhanglong; Esquiaqui, Jackie M.; Pirman, Natasha L.; Milshteyn, Eugene; Fanucci, Gail E., E-mail: fanucci@chem.ufl.edu

    2014-07-18

    Highlights: • W- and D-Band line shapes are sensitive to motions in the 0.1–2 ns time regime. • These frequencies effectively report on conformational dynamics of IDPs. • W-band spectra reflecting helical formation in IA{sub 3} is experimentally demonstrated. - Abstract: Site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for characterizing conformational sampling and dynamics in biological macromolecules. Here we demonstrate that nitroxide spectra collected at frequencies higher than X-band (∼9.5 GHz) have sensitivity to the timescale of motion sampled by highly dynamic intrinsically disordered proteins (IDPs). The 68 amino acid protein IA{sub 3}, was spin-labeled at two distinct sites and a comparison of X-band, Q-band (35 GHz) and W-band (95 GHz) spectra are shown for this protein as it undergoes the helical transition chemically induced by tri-fluoroethanol. Experimental spectra at W-band showed pronounced line shape dispersion corresponding to a change in correlation time from ∼0.3 ns (unstructured) to ∼0.6 ns (α-helical) as indicated by comparison with simulations. Experimental and simulated spectra at X- and Q-bands showed minimal dispersion over this range, illustrating the utility of SDSL EPR at higher frequencies for characterizing structural transitions and dynamics in IDPs.

  1. Synthesis, redox properties, and EPR spectroscopy of manganese(III) complexes of the ligand N,N-bis(2-hydroxybenzyl)-N'-2-hydroxybenzylidene-1,2-diaminoethane: formation of mononuclear, dinuclear, and even higher nuclearity complexes.

    Science.gov (United States)

    Schmitt, Heimo; Lomoth, Reiner; Magnuson, Ann; Park, Jonathan; Fryxelius, Jacob; Kritikos, Mikael; Mårtensson, Jerker; Hammarström, Leif; Sun, Licheng; Akermark, Björn

    2002-08-16

    The synthesis and characterization of the title trisphenolate ligand are described. From its reaction with manganese(III) three complexes were isolated. The crystal structures revealed one pentacoordinate monomer and two similar dimers with different solvents of crystallization. In the dimers the metal ions are hexacoordinate and connected through bridging of two phenolates. A combination of electrochemistry and EPR spectroscopy showed that, in acetonitrile, the isolated batches were all identical and mainly monomeric, indicating that the mononuclear complex is in equilibrium with the dimer and perhaps also with complexes of higher nuclearity, as suggested by the detection of both the trimer and the tetramer by electrospray ionization mass spectrometry (ESI-MS). The successful use of the monomer batch as an epoxidation catalyst indicated that a high-valent manganese-oxo species can be formed, although it is probably short-lived. This is also suggested by EPR studies of the species formed by electrochemical oxidation of the complex. Upon one-electron oxidation, a manganese(IV) species was formed, which was at least partly converted to another species containing a phenoxy radical.

  2. Contribution of major lipophilic antioxidants to the antioxidant activity of basil extracts: an EPR study.

    Science.gov (United States)

    Sgherri, Cristina; Pinzino, Calogero; Navari-Izzo, Flavia; Izzo, Riccardo

    2011-04-01

    The present research analyses the contribution of some lipid antioxidants to the antioxidant activity of lipophilic extracts from basil by an electron paramagnetic resonance (EPR) study using the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). DPPH assay is considered an easy and accurate method with regard to measuring the antioxidant activity of plant extracts and EPR has already been employed to determine antioxidant activities of lipophilic plant extracts. Lipid extracts were obtained from basil grown hydroponically for 20 or 35 days from sowing and in soil for 35 days from sowing. Fast and slow rate constants were distinguishable in the decay kinetics of DPPH mixture added with lipid extract. Antioxidants with kinetics characterized by a fast decay rate were tocopherols and chlorophylls, whereas those characterized by a slow decay rate were carotenoids, among which were β-carotene, lutein, β-apo-8'-carotenal and zeaxanthin. The 20-day hydroponically grown sample, which showed higher contents of tocopherol, chlorophyll and carotenoid molecules, was the sample endowed with the higher content of fast lipophilic antioxidants (FLA) and slow lipophilic antioxidants (SLA). The three samples showed different compositions of FLA and SLA, giving rise to different decay kinetics. Despite the differences, in all samples tocopherol contributed about 0.3% to the bulk of FLA, whereas the figure for chlorophyll was about 40%, evidencing the relevant but little-studied role of chlorophyll as an antioxidant. Copyright © 2011 Society of Chemical Industry.

  3. Synthesis, XRD, TEM, EPR, and Optical Absorption Spectral Studies of CuZnO2 Nanocompound

    Directory of Open Access Journals (Sweden)

    T. Ravindra Reddy

    2014-01-01

    Full Text Available Synthesis of nano CuZnO2 compound is carried out by thermal decomposition method. The crystalline phase of the material is characterized by XRD. The calculated unit cell constants are a=3.1 Å and c=3.4786 Å and are of tetragonal structure. The unit cell constants are different from wurtzite (hexagonal which indicate that a nanocompound is formed. Further TEM images reveal that the metal ion is in tetragonal structure with oxygen ligands. The prepared CuZnO2 is then characterized for crystallite size analysis by employing transmission electron microscopy (TEM. The size is found to be 100 nm. Uniform bright rings are noticed in the TEM picture suggesting that the nanocrystals have preferential instead of random orientations. The selected-area electron diffraction (SAED pattern clearly indicates the formation of CuO-ZnO nanocompound. The nature of bonding is studied by electron paramagnetic resonance (EPR. The covalency character is about 0.74 and thus the compound is electrically less conductive. Optical absorption spectral studies suggest that Cu(II is placed in tetragonal elongation crystal field. The spin-orbit coupling constant, λ, is calculated using the EPR and optical absorption spectral results suggest some covalent bond between metal and ligand. Near infrared (NIR spectra are due to hydroxyl and water fundamentals.

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

    Science.gov (United States)

    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.

  5. Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy

    OpenAIRE

    Hogg, Neil

    2010-01-01

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

  6. Gamma-irradiated ExtraVit M nutritive supplement studied by electron paramagnetic resonance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Petrisor, Dina [Faculty of Physics, Babes-Bolyai University, 1A Kogalniceanu Street, 400084 Cluj-Napoca (Romania)], E-mail: dinapetrisor@yahoo.co.uk; Damian, Grigore; Simon, Simion [Faculty of Physics, Babes-Bolyai University, 1A Kogalniceanu Street, 400084 Cluj-Napoca (Romania)

    2008-04-15

    An unirradiated and {gamma}-irradiated nutritive supplement named ExtraVit M was studied by electron paramagnetic resonance (EPR) spectroscopy in order to detect stable paramagnetic species following improvement of hygienic quality by {gamma}-radiation. Free radicals were induced by {gamma}-radiation in the studied samples from low absorbed doses, showing a certain sensibility of these samples to the radiation treatment. The EPR spectrum of irradiated ExtraVit M is typical for drugs or nutritive supplements containing high levels of sugars, vitamin C and cellulose.

  7. EPR study of positive holes on phenylene vinylene chains : from dimer to polymer

    NARCIS (Netherlands)

    Zezin, AA; Feldman, [No Value; Warman, JM; Wildeman, J; Hadziioannou, G

    2004-01-01

    Isolated radical cations of substituted oligomers and polymers of phenylene vinylenes (PV) produced by irradiation in glassy toluene solutions were characterized by EPR. It was shown that the linewidth of the EPR signal from radical cations in oligomers decreased with increasing the number of repeat

  8. Assessing the RAFT equilibrium constant via model systems: an EPR study.

    Science.gov (United States)

    Meiser, Wibke; Buback, Michael

    2011-09-15

    Reversible addition-fragmentation chain transfer (RAFT) equilibrium constants, K(eq), for the model system cyano-iso-propyl dithiobenzoate (CPDB) - cyano-iso-propyl radical (CIP) have been deduced via electron paramagnetic resonance (EPR) spectroscopy. The CIP species is produced by thermal decomposition of azobis-iso-butyronitrile (AIBN). In solution of toluene at 70 °C, K(eq) has been determined to be (9 ± 1) L · mol(-1). Measurement of K(eq) = k(ad)/k(β) between 60 and 100 °C yields ΔE(a) = (-28 ± 4) kJ · mol(-1) as the difference in the activation energies of k(ad) and k(β). The data measured on the model system are indicative of fast fragmentation of the intermediate radical produced by addition of CIP to CPDB. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Slow Relaxation of Magnetization in an Isostructural Series of Zinc-Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study.

    Science.gov (United States)

    Amjad, Asma; Madalan, Augustin M; Andruh, Marius; Caneschi, Andrea; Sorace, Lorenzo

    2016-08-26

    We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Light-induced EPR study of charge transfer in P3HT/bis-PCBM bulk heterojunctions

    National Research Council Canada - National Science Library

    Krinichnyi, Victor I; Yudanova, Eugenia I

    2011-01-01

    ... – 2.73 eV in bulk heterojunctions formed by poly(3-hexylthiophene) (P3HT) with bis(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6.6]C62 (bis-PCBM) fullerene derivative have been studied by direct light-induced EPR...

  11. EPR and optical absorption studies of VO{sup 2+} ion doped magnesium citrate decahydrate single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Dwivedi, Prashant [Department of Physics, Kali Charan Nigam Institute of Technology, Banda 210001, UP (India); Kripal, Ram, E-mail: ram_kripal2001@rediffmail.co, E-mail: prashant_kcnit@rediffmail.co [EPR Laboratory, Department of Physics, University of Allahabad, Allahabad 211002 (India)

    2010-10-15

    An X-band electron paramagnetic resonance (EPR) study of VO{sup 2+} ions in magnesium citrate decahydrate single crystals was done at room temperature. Detailed EPR analysis indicated the presence of two magnetically inequivalent VO{sup 2+} sites. Both the vanadyl complexes were found to take up substitutional positions. The angular variation of the EPR spectra in three planes a{sup *}b, bc and ca{sup *} were used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are site I: g{sub x}=2.0976, g{sub y}=1.9093, g{sub z}=1.9505, |A{sub x}|=73, |A{sub y}|=115, |A{sub z}|=237x10{sup -4} cm{sup -1}; site II: g{sub x}=2.0735, g{sub y}=1.9235, g{sub z}=1.9699, |A{sub x}|=72, |A{sub y}|=111, |A{sub z}|=233x10{sup -4} cm{sup -1}. An optical absorption study was also performed at room temperature, and absorption bands were assigned to various transitions. The theoretical band positions were estimated using energy expressions, and good agreement with experimental values was found. By correlating EPR and optical data, different molecular orbital coefficients were evaluated; the nature of the bonding in the crystal is discussed.

  12. EPR and optical absorption studies of paramagnetic molecular ion (VO2+) in Lithium Sodium Acid Phthalate single crystal

    Science.gov (United States)

    Subbulakshmi, N.; Kumar, M. Saravana; Sheela, K. Juliet; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.

    2017-12-01

    Electron Paramagnetic Resonance (EPR) spectroscopic studies of VO2+ ions as paramagnetic impurity in Lithium Sodium Acid Phthalate (LiNaP) single crystal have been done at room temperature on X-Band microwave frequency. The lattice parameter values are obtained for the chosen system from Single crystal X-ray diffraction study. Among the number of hyperfine lines in the EPR spectra only two sets are reported from EPR data. The principal values of g and A tensors are evaluated for the two different VO2+ sites I and II. They possess the crystalline field around the VO2+ as orthorhombic. Site II VO2+ ion is identified as substitutional in place of Na1 location and the other site I is identified as interstitial location. For both sites in LiNaP, VO2+ are identified in octahedral coordination with tetragonal distortion as seen from the spin Hamiltonian parameter values. The ground state of vanadyl ion in the LiNaP single crystal is dxy. Using optical absorption data the octahedral and tetragonal parameters are calculated. By correlating EPR and optical data, the molecular orbital bonding parameters have been discussed for both sites.

  13. EPR and optical absorption studies of Cu{sup 2+} ions doped magnesium citrate decahydrate single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Dwivedi, Prashant, E-mail: prashant_kcnit@rediffmail.co [Department of Physics, Kali Charan Nigam Institute of Technology, Banda (U.P.) 210001 (India); Kripal, Ram, E-mail: ram_kripal2001@rediffmail.co [EPR Laboratory, Department of Physics, University of Allahabad, 22/5A Katra Road, Allahabad, 211002 (India); Misra, Madan Gopal [EPR Laboratory, Department of Physics, University of Allahabad, 22/5A Katra Road, Allahabad, 211002 (India)

    2010-06-04

    X-band electron paramagnetic resonance (EPR) studies of Cu{sup 2+} ions in magnesium citrate decahydrate single crystals are done at room temperature. Detailed EPR analysis indicates the presence of only one Cu{sup 2+} site. Cu{sup 2+} is found to take up substitutional position at Mg site. The angular variation of the EPR spectra in three planes a*b, bc and ca* are used to determine principal g and A tensors. The spin Hamiltonian parameters are: g{sub x} = 2.0346, g{sub y} = 2.1400, g{sub z} = 2.3874, A{sub x} = 57, A{sub y} = 76, A{sub z} = 99 (x10{sup -4}) cm{sup -1}. The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are estimated using energy expressions and a good agreement is obtained with the experimental values. By correlating EPR and optical data, different molecular orbital coefficients are evaluated and the nature of bonding in the complex is discussed.

  14. EPR and ligand field studies of iron superoxide dismutases and iron-substituted manganese superoxide dismutases: relationships between electronic structure of the active site and activity.

    Science.gov (United States)

    Renault, J P; Verchère-Béaur, C; Morgenstern-Badarau, I; Yamakura, F; Gerloch, M

    2000-06-12

    The problem of metal selectivity of iron/manganese superoxide dismutases (SODs) is addressed through the electronic structures of active sites using electron paramagnetic resonance and ligand field calculations. Studies of wild-type iron(III) SOD (FeSOD) from Escherichia coli and from Methanobacterium thermoautotrophicum and iron-substituted manganese(III) SOD (Fe(sub)MnSOD) from E. coli and from Serratia marcescens are reported. EPR spectroscopy of wild-type enzymes shows transitions within all three Kramers doublets identified by their g values. From the temperature dependence of the observed transitions, the zero-field splitting is found to be negative, D = -2 +/- 0.2 cm-1. The electronic structure is typical of a distorted trigonal bipyramid, all the EPR features being reproduced by ligand field analysis. This unique and necessary electronic structure characterizes wild-type enzymes whatever their classification from the amino acid sequence into iron or manganese types, as E. coli FeSOD or M. thermoautotrophicum FeSOD. In iron-substituted manganese SODs, reduced catalytic activity is found. We describe how inhomogeneity of all reported substituted MnSODs might explain the activity decrease. EPR spectra of substituted enzymes show several overlapping components. From simulation of these spectra, one component is identified which shares the same electronic structure of the wild-type FeSODs, with the proportion depending on pH. Ligand field calculations were performed to investigate distortions of the active site geometry which induce variation of the excitation energy of the lowest quartet state. The corresponding coupling between the ground state and the excited state is found to be maximum in the geometry of the native SODs. We conjecture that such coupling should be considered in the electron-transfer process and in the contribution of the typical electronic structure of FeSOD to the activity.

  15. Redox intermediates of the Mn-Fe Site in subunit R2 of Chlamydia trachomatis ribonucleotide reductase: an X-ray absorption and EPR study.

    Science.gov (United States)

    Voevodskaya, Nina; Lendzian, Friedhelm; Sanganas, Oliver; Grundmeier, Alexander; Gräslund, Astrid; Haumann, Michael

    2009-02-13

    The R2 protein of class I ribonucleotide reductase (RNR) from Chlamydia trachomatis (Ct) can contain a Mn-Fe instead of the standard Fe-Fe cofactor. Ct R2 has a redox-inert phenylalanine replacing the radical-forming tyrosine of classic RNRs, which implies a different mechanism of O(2) activation. We studied the Mn-Fe site by x-ray absorption spectroscopy (XAS) and EPR. Reduced R2 in the R1R2 complex (R2(red)) showed an isotropic six-line EPR signal at g approximately 2 of the Mn(II)Fe(II) state. In oxidized R2 (R2(ox)), the Mn(III)Fe(III) state exhibited EPR g values of 2.013, 2.009, and 2.015. By XAS, Mn-Fe distances and oxidation states of intermediates were determined and assigned as follows: approximately 4.15 A, Mn(II)Fe(II); approximately 3.25 A, Mn(III)Fe(II); approximately 2.90 A, Mn(III)Fe(III); and approximately 2.75 A, Mn(IV)Fe(III). Shortening of the Mn/Fe-ligand bond lengths indicated formation of additional metal bridges, i.e. microO(H) and/or peroxidic species, upon O(2) activation at the site. The structural parameters suggest overall configurations of the Mn-Fe site similar to those of homo-metallic sites in other R2 proteins. However, the approximately 2.90 A and approximately 2.75 A Mn-Fe distances, typical for di-microO(H) metal bridging, are shorter than inter-metal distances in any R2 crystal structure. In diffraction data collection, such bridges may be lost due to rapid x-ray photoreduction of high-valent metal ions, as demonstrated here for Fe(III) by XAS.

  16. Effect of microwave power on EPR spectra of natural and synthetic dental biocompatible materials

    Directory of Open Access Journals (Sweden)

    Adamczyk Jakub

    2015-07-01

    Full Text Available Paramagnetic centers in the two exemplary synthetic and natural dental biocompatible materials applied in implantology were examined by the use of an X-band (9.3 GHz electron paramagnetic resonance (EPR spectroscopy. The EPR spectra were measured in the range of microwave power 2.2–70 mW. The aims of this work were to compare paramagnetic centers concentrations in different dental biocompatible materials and to determine the effect of microwave power on parameters of their EPR spectra. It is the very first and innovatory examination of paramagnetic centers in these materials. It was pointed out that paramagnetic centers existed in both natural (~1018 spin/g and synthetic (~1019 spin/g dental biocompatible materials, but the lower free radical concentration characterized the natural sample. Continuous microwave saturation of EPR spectra indicated that faster spin-lattice relaxation processes existed in synthetic dental biocompatible materials than in natural material. Linewidths (ΔBpp of the EPR spectra of the natural dental material slightly increased for the higher microwave powers. Such effect was not observed for the synthetic material. The broad EPR lines (ΔBpp: 2.4 mT, 3.9 mT, were measured for the natural and synthetic dental materials, respectively. Probably strong dipolar interactions between paramagnetic centers in the studied samples may be responsible for their line broadening. EPR spectroscopy is the useful experimental method in the examination of paramagnetic centers in dental biocompatible materials.

  17. Single Crystal X- and Q-Band EPR Spectroscopy of a Binuclear Mn2(III,IV) Complex Relevant to the Oxygen-Evolving Complex of Photosystem II

    OpenAIRE

    Yano, Junko; Sauer, Kenneth; Girerd, Jean-Jacques; Yachandra, Vittal K.

    2004-01-01

    The anisotropic g and hyperfine tensors of the Mn di-μ-oxo complex, [Mn2(III,IV)O2(phen)4](PF6)3·CH3CN, were derived by single-crystal EPR measurements at X- and Q-band frequencies. This is the first simulation of EPR parameters from single-crystal EPR spectra for multinuclear Mn complexes, which are of importance in several metalloenzymes; one of them is the oxygen-evolving complex in photosystem II (PS II). Single-crystal [Mn2(III,IV)O2(phen)4](PF6)3·CH3CN EPR spectra showed distinct resolv...

  18. Stable radicals and biochemical compounds in embryos and endosperm of wheat grains differentiating sensitive and tolerant genotypes--EPR and Raman studies.

    Science.gov (United States)

    Kurdziel, Magdalena; Dłubacz, Aleksandra; Wesełucha-Birczyńska, Aleksandra; Filek, Maria; Łabanowska, Maria

    2015-07-01

    The aim of this study was to uncover the specific species in grains that might differentiate the wheat genotypes according to their tolerance to oxidative stress. Measurements by EPR and Raman spectroscopy techniques were used to examine whole grains and their parts (embryo, endosperm, seed coat) originating from four wheat genotypes with differing tolerance to drought stress. Raman spectra showed that, in spite of the similar amounts of proteins in whole grains from tolerant and sensitive genotypes, in tolerant ones they were accumulated mainly in embryos. Moreover, in embryos from these grains, a higher content of unsaturated fatty acids was observed. Endosperm of grains from the tolerant genotype, richer with starch than that of sensitive one, exhibited higher content of amylopectin. Detailed analysis of EPR signals and simulation procedures of the spectra allowed the estimation of the nature of interactions of Fe(III) and Mn(II) with organic and inorganic structures of grains and the character of organic stable radicals. Three types of these radicals: carbohydrate, semiquinone and phenoxyl, were identified. The amounts of these radicals were higher in grains of sensitive genotypes, mostly because of differences in carbohydrate radical content in endosperm. Taking into account the level of radical concentration and greater capacity for radical formation in grains from plants of lower tolerance to stress, the content of radicals, especially of a carbohydrate nature, was considered as a marker of the plant resistance to stress conditions. Copyright © 2015 Elsevier GmbH. All rights reserved.

  19. Reactive oxygen species generation by copper(II) oxide nanoparticles determined by DNA damage assays and EPR spectroscopy.

    Science.gov (United States)

    Angelé-Martínez, Carlos; Nguyen, Khanh Van T; Ameer, Fathima S; Anker, Jeffrey N; Brumaghim, Julia L

    2017-03-01

    Copper(II) oxide nanoparticles ((NP)CuO) have many industrial applications, but are highly cytotoxic because they generate reactive oxygen species (ROS). It is unknown whether the damaging ROS are generated primarily from copper leached from the nanoparticles, or whether the nanoparticle surface plays a significant role. To address this question, we separated nanoparticles from the supernatant containing dissolved copper, and measured their ability to damage plasmid DNA with addition of hydrogen peroxide, ascorbate, or both. While DNA damage from the supernatant (measured using an electrophoresis assay) can be explained solely by dissolved copper ions, damage by the nanoparticles in the presence of ascorbate is an order of magnitude higher than can be explained by dissolved copper and must, therefore, depend primarily upon the nanoparticle surface. DNA damage is time-dependent, with shorter incubation times resulting in higher EC50 values. Hydroxyl radical ((•)OH) is the main ROS generated by (NP)CuO/hydrogen peroxide as determined by EPR measurements; (NP)CuO/hydrogen peroxide/ascorbate conditions generate ascorbyl, hydroxyl, and superoxide radicals. Thus, (NP)CuO generate ROS through several mechanisms, likely including Fenton-like and Haber-Weiss reactions from the surface or dissolved copper ions. The same radical species were observed when (NP)CuO suspensions were replaced with the supernatant containing leached copper, washed (NP)CuO, or dissolved copper solutions. Overall, (NP)CuO generate significantly more ROS and DNA damage in the presence of ascorbate than can be explained simply from dissolved copper, and the (NP)CuO surface must play a large role.

  20. The measurement of oxygen in vivo using EPR techniques

    Energy Technology Data Exchange (ETDEWEB)

    Swartz, Harold M. [Dartmouth Medical School, Hanover, NH 03755 (United States); Clarkson, Robert B. [College of Veterinary Medicine, University of Illinois, Urbana, IL 61801 (United States)

    1998-07-01

    The measurement of pO{sub 2} in vivo using EPR has some features which have already led to very useful applications and this approach is likely to have increasingly wide and effective use. It is based on the effect of oxygen on EPR spectra which provides a sensitive and accurate means to measure pO{sub 2} quantitatively. The development of oxygen-sensitive paramagnetic materials which are very stable, combined with instrumental developments, has been crucial to the in vivo applications of this technique. The physical basis and biological applications of in vivo EPR oximetry are reviewed, with particular emphasis on the use of EPR spectroscopy at 1 GHz using particulate paramagnetic materials for the repetitive and non-invasive measurement of pO{sub 2} in tissues. In vivo EPR has already produced some very useful results which have contributed significantly to solving important biological problems. The characteristics of EPR oximetry which appear to be especially useful are often complementary to existing techniques for measuring oxygen in tissues. These characteristics include the capability of making repeated measurements from the same site, high sensitivity to low levels of oxygen, and non-invasive options. The existing techniques are especially useful for studies in small animals, where the depth of measurements is not an overriding issue. In larger animals and potentially in human subjects, non-invasive techniques seem to be immediately applicable to study phenomena very near the surface (within 10 mm) while invasive techniques have some very promising uses. The clinical uses of EPR oximetry which seem especially promising and likely to be undertaken in the near future are long-term monitoring of the status and response to treatment of peripheral vascular disease and optimizing cancer therapy by enabling it to be modified on the basis of the pO{sub 2} measured in the tumour. (author)

  1. Evidence for the stabilization of manganese ion as Mn (II) and Mn (IV) in α-Zn{sub 2}P{sub 2}O{sub 7}: Probed by EPR, luminescence and electrochemical studies

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Santosh K., E-mail: santufrnd@gmail.com [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Kadam, R.M. [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Gupta, R. [Fuel Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Sahu, Manjulata [Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Natarajan, V. [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)

    2014-05-01

    Zn{sub 2}P{sub 2}O{sub 7}: Mn was synthesized by wet chemical route and characterized by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and photoluminescence (PL) techniques. EPR spectroscopic studies confirmed the presence of both Mn{sup 2+} and Mn{sup 4+} ions in zinc pyrophosphate. The presence of EPR signal at g = 2 is attributed to Mn{sup 2+} at Zn{sup 2+} site having octahedral coordination of oxygen whereas the presence of an EPR signal at g = 1.998 is attributed to Mn{sup 4+} at Zn{sup 2+} site having considerably lower symmetry due to the presence of extra interstitial oxygen ions required for charge compensation or due to the substitution of manganese at distorted 5-coordinated zinc site. Photoluminescence spectrum also shows two bands, one at 500 nm (green emission), which is attributed to the {sup 4}T{sub 1} ({sup 4}G)–{sup 6}A{sub 1} ({sup 6}S) transition of Mn{sup 2+} and the other centered at 686 nm (red emission), which is attributed to the electronic transition between {sup 2}E and {sup 4}A{sub 2} of Mn{sup 4+}. - Graphical abstract: Display Omitted - Highlights: • Stabilization of manganese as Mn{sup 2+} and Mn{sup 4+} in the same host. • EPR spectroscopy has shown the presence of Mn{sup 2+} and Mn{sup 4+} in 6-coordinated and 5-coordinated Zn{sup 2+} sites, respectively. • Emission spectrum also shows green emission from Mn{sup 2+} and red emission from Mn{sup 4+}.

  2. EPR safety. Consideration of the internal and external hazards in the safety studies; Surete du reacteur EPR. Prise en compte des agressions internes et externes dans les etudes de surete EPR

    Energy Technology Data Exchange (ETDEWEB)

    Gueguin, H. [Electricite de France (EDF-DIN), Centre National d' Equipement Nucleaire, Service Controle Commande, 92 - Montrouge (France)

    2008-04-15

    The author presents the main points of the Preliminary Safety Report of EDF on the EPR reactor safety. It concerns the considerations of the internal (fire, flood, explosions, pipes failures) and external (earthquakes, airplane falls, explosions, exceptional natural disasters, extreme meteorological conditions) damages. It presents how the safety report takes into account the aggression. (A.L.B.)

  3. HF-EPR, Raman, UV/VIS light spectroscopic, and DFT studies of the ribonucleotide reductase R2 tyrosyl radical from Epstein-Barr virus.

    Directory of Open Access Journals (Sweden)

    Ane B Tomter

    Full Text Available Epstein-Barr virus (EBV belongs to the gamma subfamily of herpes viruses, among the most common pathogenic viruses in humans worldwide. The viral ribonucleotide reductase small subunit (RNR R2 is involved in the biosynthesis of nucleotides, the DNA precursors necessary for viral replication, and is an important drug target for EBV. RNR R2 generates a stable tyrosyl radical required for enzymatic turnover. Here, the electronic and magnetic properties of the tyrosyl radical in EBV R2 have been determined by X-band and high-field/high-frequency electron paramagnetic resonance (EPR spectroscopy recorded at cryogenic temperatures. The radical exhibits an unusually low g₁-tensor component at 2.0080, indicative of a positive charge in the vicinity of the radical. Consistent with these EPR results a relatively high C-O stretching frequency associated with the phenoxyl radical (at 1508 cm⁻¹ is observed with resonance Raman spectroscopy. In contrast to mouse R2, EBV R2 does not show a deuterium shift in the resonance Raman spectra. Thus, the presence of a water molecule as a hydrogen bond donor moiety could not be identified unequivocally. Theoretical simulations showed that a water molecule placed at a distance of 2.6 Å from the tyrosyl-oxygen does not result in a detectable deuterium shift in the calculated Raman spectra. UV/VIS light spectroscopic studies with metal chelators and tyrosyl radical scavengers are consistent with a more accessible dimetal binding/radical site and a lower affinity for Fe²⁺ in EBV R2 than in Escherichia coli R2. Comparison with previous studies of RNR R2s from mouse, bacteria, and herpes viruses, demonstrates that finely tuned electronic properties of the radical exist within the same RNR R2 Ia class.

  4. EPR and optical absorption study of Mn 2+-doped zinc ammonium phosphate hexahydrate single crystals

    Science.gov (United States)

    Kripal, Ram; Govind, Har; Gupta, S. K.; Arora, Manju

    2007-04-01

    EPR study of Mn 2+-doped zinc ammonium phosphate hexahydrate (ZAPH) is done at room temperature. The Mn 2+ spin Hamiltonian parameters are evaluated employing a large number of resonant line positions observed for different orientations of the external magnetic field. The evaluated value of g-factor is 1.9527±0.0002 and the values of other parameters D, E, a, A and B (in 10 -4 cm -1) are, 175±2, 58±2, 10±1, 92±2 and 86±2, respectively. The optical absorption study of the crystal is also done. The observed bands are assigned as transitions from the 6A 1g(S) ground state to various excited quartet levels of Mn 2+ ion in a cubic crystal field. These bands are fitted with four parameters: inter-electronic repulsion parameters ( B and C), cubic crystal field splitting parameter ( Dq), and Tree's correction ( α). The values obtained for the parameters are B=917, C=2254, Dq=756 and α=76 cm -1. From the data obtained the surrounding crystal field and the nature of metal-ligand bonding are discussed. The considerable decrease in the values of B and C from their free ion values indicates the existence of a fair amount of covalent bonding between the central metal ion and the ligand. On the basis of the deviations Δ g= g-2.0023, the transfer of electrons to or from the central metal ion for bond formation is ascertained.

  5. Magnetic properties of single crystal alpha-benzoin oxime: An EPR study

    Science.gov (United States)

    Sayin, Ulku; Dereli, Ömer; Türkkan, Ercan; Ozmen, Ayhan

    2012-02-01

    The electron paramagnetic resonance (EPR) spectra of gamma irradiated single crystals of alpha-benzoinoxime (ABO) have been examined between 120 and 440 K. Considering the dependence on temperature and the orientation of the spectra of single crystals in the magnetic field, we identified two different radicals formed in irradiated ABO single crystals. To theoretically determine the types of radicals, the most stable structure of ABO was obtained by molecular mechanic and B3LYP/6-31G(d,p) calculations. Four possible radicals were modeled and EPR parameters were calculated for the modeled radicals using the B3LYP method and the TZVP basis set. Calculated values of two modeled radicals were in strong agreement with experimental EPR parameters determined from the spectra. Additional simulated spectra of the modeled radicals, where calculated hyperfine coupling constants were used as starting points for simulations, were well matched with experimental spectra.

  6. EPR study of Mn-implanted single crystal TiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Gueler, S; Rameev, B [Department of Physics, Gebze Institute of Technology, 41400 Gebze-Kocaeli (Turkey); Khaibullin, R I; Aktas, B [Lab. of Radiation Physics, Kazan Physical-Technical Institute, 420029 Kazan (Russian Federation); Lopatin, O N, E-mail: sumeyra@gyte.edu.t [Faculty of Geology, Kazan State University, 420008 Kazan (Russian Federation)

    2009-03-01

    Single crystals of manganese-implanted TiO{sub 2} rutile have been investigated by electron paramagnetic resonance (EPR) technique at room temperature. ESR spectra have been interpreted to correspond to the transitions among the spin multiplet (S=3/2) of the paramagnetic Mn{sup 4+} ion. Characteristic six-line hyper-fine splitting of the ESR spectra resulting from the spin I=5/2 of the Mn{sup 55} nucleus has been observed. Analysis of EPR spectra shows that manganese in TiO{sub 2} rutile host substitutes for Ti{sup 4+} ions. Two equivalent Mn{sup 4+} centers have been observed in the EPR spectra in correspondence with two equivalent octahedral positions of Ti ions in the rutile structure. Parameters of the crystal field of orthorhombic symmetry on the Mn{sup 4+} centers have been obtained as result of computer modelling.

  7. EPR study of Mn-implanted single crystal TiO2

    Science.gov (United States)

    Güler, S.; Rameev, B.; Khaibullin, R. I.; Lopatin, O. N.; Aktaş, B.

    2009-03-01

    Single crystals of manganese-implanted TiO2 rutile have been investigated by electron paramagnetic resonance (EPR) technique at room temperature. ESR spectra have been interpreted to correspond to the transitions among the spin multiplet (S=3/2) of the paramagnetic Mn4+ ion. Characteristic six-line hyper-fine splitting of the ESR spectra resulting from the spin I=5/2 of the Mn55 nucleus has been observed. Analysis of EPR spectra shows that manganese in TiO2 rutile host substitutes for Ti4+ ions. Two equivalent Mn4+ centers have been observed in the EPR spectra in correspondence with two equivalent octahedral positions of Ti ions in the rutile structure. Parameters of the crystal field of orthorhombic symmetry on the Mn4+ centers have been obtained as result of computer modelling.

  8. "Assessing the RAFT equilibrium constant via model systems: an EPR study"--response to a comment.

    Science.gov (United States)

    Meiser, Wibke; Buback, Michael

    2012-08-14

    We have presented an EPR-based approach for deducing the RAFT equilibrium constant, K(eq), of a dithiobenzoate-mediated system [Meiser, W. and Buback M. Macromol. Rapid Commun. 2011, 32, 1490]. Our value is by four orders of magnitude below K(eq) from ab initio calculations for the identical monomer-free system. Junkers et al. [Macromol. Rapid Commun. 2011, 32, 1891] claim that our EPR approach would be model dependent and our data could be equally well fitted by assuming slow addition of radicals to the RAFT agent and slow fragmentation of the so-obtained intermediate radical as well as high cross-termination rate. By identification of all side products, our EPR-based method is shown to be model independent and to provide reliable K(eq) values, which demonstrate the validity of the intermediate radical termination model. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. EPR study of complex formation between copper (II) ions and sympathomimetic amines in aqueous solution

    Energy Technology Data Exchange (ETDEWEB)

    Preoteasa, E.A. [Inst. of Atomic Physics, IFIN, Bucharest (Romania); Duliu, O.G.; Grecu, V.V. [Bucharest, Univ. (Romania). Dept. of Atomic and Nuclear Physics

    1997-07-01

    The complex formation between sympathomimetic amines (SA): adrenaline (AD), noradrenaline (NA), dopamine (DA), ephedrine (ED) and p-tyramine (pTA), and Cu(II) ion in aqueous solution has been studied by X-band EPR at room temperature. Excepting pTA, all investigated SA yielded two types of complexes in different pH domains. All complexes consistent with a ligand fields having a distorted octahedral symmetry, i.e., hexacoordination of Cu(II). The covalence coefficient calculated from the isotropic g and A values has shown strong ionic sigma-type ligand bonds. A structural model with the Cu(II) ion bound by four catecholic O(hydroxy) atoms for the low pH complexes of AD, NA and DA is proposed. For the high pH complexes of the former compounds as well as for both Ed complexes, the authors suppose Cu(II) bound by two N (amino) and two O (hydroxy) atoms. The spectra are consistent to water binding on the longitudinal octahedron axis in all compounds excepting the high pH complex of Ed, where OH2- ions are bound. Possible implications for the SA-cell receptors interactions are discussed.

  10. Revealing model dependencies in "Assessing the RAFT equilibrium constant via model systems: an EPR study".

    Science.gov (United States)

    Junkers, Thomas; Barner-Kowollik, Christopher; Coote, Michelle L

    2011-12-01

    In a recent article (W. Meiser, M. Buback, Assessing the RAFT Equilibrium Constant via Model Systems: An EPR Study, Macromol. Rapid Commun. 2011, 18, 1490-1494), it is claimed that evidence is found that unequivocally proves that quantum mechanical calculations assessing the equilibrium constant and fragmentation rate coefficients in dithiobenzoate-mediated reversible addition fragmentation transfer (RAFT) systems are beset with a considerable uncertainty. In the present work, we show that these claims made by Meiser and Buback are beset with a model dependency, as a critical key parameter in their data analysis - the addition rate coefficient of the radicals attacking the C=S double bond in the dithiobenzoate - induces a model insensitivity into the data analysis. Contrary to the claims made by Meiser and Buback, their experimental results can be brought into agreement with the quantum chemical calculations if a lower addition rate coefficient of cyanoisopropyl radicals (CIP) to the CIP dithiobenzoate (CPDB) is assumed. To resolve the model dependency, the addition rate coefficient of CIP radicals to CPDB needs to be determined as a matter of priority. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. EPR study of free radicals in some drugs {gamma}-irradiated in the solid state

    Energy Technology Data Exchange (ETDEWEB)

    Ambroz, H.B. E-mail: ambroz@orange.ichtj.waw.pl; Kornacka, E.M.; Marciniec, B.; Ogrodowczyk, M.; Przybytniak, G.K

    2000-06-01

    A range of drugs in the form of microcrystalline powder was exposed to {gamma}-radiation. EPR measurements proved that all of them contained various paramagnetic species after 4 and 8 weeks of storage. We observed following radical concentrations, stable up to 4 weeks: the highest for ifosfamide -- 4.5x10{sup 17} spins per gram and the lowest for nimodipine -- 2.1x10{sup 16} spins per gram. Three drugs exhibited very weak EPR signals before irradiation, not detectable quantitatively. Some spectroscopic properties and suggestions concerning possible structure of the radicals are given in our paper. (author)

  12. EPR study of VO/sup 2 +/ in some paramagnetic Tutton salt single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Upreti, G.C. (Indian Inst. of Tech., Kanpur. Dept. of Physics); Saraswat, R.S. (Indian Inst. of Tech., Kharagpur. Dept. of Physics)

    1984-04-01

    The EPR spectra of VO/sup 2 +/ in single crystals of some paramagnetic salts Me(II)(NH/sub 4/)/sub 2/(SO/sub 4/)/sub 2/x6H/sub 2/O (Me = Co, Fe, or Ni) and NiK/sub 2/(SO/sub 4/)/sub 2/x6H/sub 2/O have been recorded and analyzed. The vanadyl ions doped in Co and Fe double salt crystals showed sharp and well resolved EPR spectra consisting in two sets of eight-line hyperfine patterns. The spin-Hamiltonian parameters and the molecular orbital coefficients are given and the bonding in vanadyl complexes is discussed.

  13. EPR study of concentration dependence in Ce, Ce : La and Ce:Y doped SrF2

    NARCIS (Netherlands)

    Dankert, O.; Vainchtein, David; Datema, H.C.; den Hartog, Hendrik

    1995-01-01

    Experimental results of an EPR-study of the concentration dependence of the doubly integrated intensity and linewidth of the signals associated with tetragonal Ce3+-F--dipoles in Sr1-xCexF2+x, Sr-1-0.005-x Ce0.005LaxF2+0.005+x and Sr-1-0.005-x Ce0.005YxF2+0.005+x are presented. Both show a nonlinear

  14. High temperature EPR study of the M3Fe4V6O24 (M = Cu, Zn, Mg and Mn

    Directory of Open Access Journals (Sweden)

    Guskos Niko

    2016-09-01

    Full Text Available Electron paramagnetic resonance (EPR spectra of M3Fe4V6O24 (M = Cu, Zn, Mg and Mn compounds in high temperature range (293 K to 493 K have been investigated. The role of magnetic (Cu, Mn and non-magnetic (Zn, Mg ions in M3Fe4V6O24 structure in formation of magnetic resonance spectra was studied. Temperature dependence of EPR parameters: resonance field, linewidth and integrated intensity were examined. Similarities and differences in temperature behavior of these parameters has been discussed in terms of different relaxation mechanisms and magnetic interactions in the spin systems. An important role of additional magnetic ions (M = Mn or Cu in the M3Fe4V6O24 structure has been identified and its consequences considered.

  15. Optical and EPR studies of Gd2Zr2O7 phosphors prepared via solution combustion method

    Science.gov (United States)

    Singh, Vijay; Sivaramaiah, Gobburu; Rao, J. L.; Hwan Kim, Sang

    2013-05-01

    Phosphor powder of Gd2Zr2O7 has been prepared by the urea combustion route. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) technique. The structural environment between the Gd3+ and the zirconium oxide lattice has been investigated using electron paramagnetic resonance (EPR), diffuse reflectance and photoluminescence (PL) studies. The EPR spectrum of Gd2Zr2O7 phosphor exhibits a broad and intense signal at g≈2.0 and this has been attributed to Gd3+ ions in octahedral symmetry with strong dipolar interactions between Gd3+ ions. The intensity of the spectrum increases with temperature lowering from 296 to 110 K following the usual Boltzmann law. The g value is invariant with temperature variation. The diffuse reflectance spectrum exhibits two sharp and weak bands characteristic of Gd3+ ions in octahedral symmetry. The photoluminescence spectrum exhibits several bands characteristic of Gd3+ ions in octahedral symmetry.

  16. Investigating the structure and properties of hydrated hydroxypropyl methylcellulose and egg albumin matrices containing carbamazepine: EPR and NMR study.

    Science.gov (United States)

    Katzhendler, I; Mäder, K; Azoury, R; Friedman, M

    2000-10-01

    The present study was conducted in order to investigate the correlation between the hydration properties of HPMC and EA matrices, gel microstructure and mobility, crystalline changes occurring in the gel and CBZ release kinetics. The influence of HPMC and EA erosion modes on CBZ release kinetics was interpreted in terms of gel microstructures. NMR technique was used to determine the T1 and T2 relaxation rates of water in hydrated matrices. PFGSE NMR technique was employed to determine the SDC of water in the gels. EPR technique was used to determine the rotational correlation time of PCA in the hydrated matrices, gel microviscosity, mobile compartment, alpha, beta, gamma parameters and lorentzian/ gaussian ratio. These parameters are indicative of matrix microstructure. CBZ release mechanism from HPMC and EA matrices was markedly different. This behavior was related to the different structures of the polymer and protein. T2 relaxation studies and SDC measurements by NMR revealed higher chain hydration for HPMC compared to EA. Using the EPR technique it has been shown that the microviscosity and mobile compartment of matrices containing HPMC are lower than matrices containing EA. The microviscosity, mobile compartment and S-parameter values of hydrated matrices containing different EA/CBZ ratios were in correlation with the crystallization properties of CBZ in the gels, matrix erosion properties and CBZ release kinetics from the matrices. Characterization of matrix structures using EPR and NMR techniques supported our hypothesis concerning the mechanism involved in HPMC-CBZ interaction. EA/CBZ matrix microstructure features, analyzed by NMR and EPR techniques, were in correlation with the crystalline changes occurring in the gel and drug release kinetics.

  17. The structural flexibility of the human copper chaperone Atox1: Insights from combined pulsed EPR studies and computations.

    Science.gov (United States)

    Levy, Ariel R; Turgeman, Meital; Gevorkyan-Aiapetov, Lada; Ruthstein, Sharon

    2017-08-01

    Metallochaperones are responsible for shuttling metal ions to target proteins. Thus, a metallochaperone's structure must be sufficiently flexible both to hold onto its ion while traversing the cytoplasm and to transfer the ion to or from a partner protein. Here, we sought to shed light on the structure of Atox1, a metallochaperone involved in the human copper regulation system. Atox1 shuttles copper ions from the main copper transporter, Ctr1, to the ATP7b transporter in the Golgi apparatus. Conventional biophysical tools such as X-ray or NMR cannot always target the various conformational states of metallochaperones, owing to a requirement for crystallography or low sensitivity and resolution. Electron paramagnetic resonance (EPR) spectroscopy has recently emerged as a powerful tool for resolving biological reactions and mechanisms in solution. When coupled with computational methods, EPR with site-directed spin labeling and nanoscale distance measurements can provide structural information on a protein or protein complex in solution. We use these methods to show that Atox1 can accommodate at least four different conformations in the apo state (unbound to copper), and two different conformations in the holo state (bound to copper). We also demonstrate that the structure of Atox1 in the holo form is more compact than in the apo form. Our data provide insight regarding the structural mechanisms through which Atox1 can fulfill its dual role of copper binding and transfer. © 2017 The Protein Society.

  18. Study of Thermal Properties of Mixed (PP/EPR/ABS with Five Model Compatibilizers

    Directory of Open Access Journals (Sweden)

    Pierre Marcel Anicet Noah

    2016-01-01

    Full Text Available The influences of incorporating compatibilizers E-EA-MAH, E-MA-GMA, E-AM, SEBS KRATON G, or PP-g-MAH on the thermal properties of mixed (polypropylene/ethylene propylene rubber/acrylonitrile butadiene styrene (PP/EPR/ABS have been investigated. DSC investigations have revealed that the incorporation of 5% of ABS in the copolymer (PP/EPR does not fundamentally affect the thermal properties of the basic copolymer; additionally, the addition of 1.5% of each of the compatibilizers in the basic mixture does not significantly alter the crystallization temperature values and the melting of the -P- sequences. There is a variation of melting enthalpy values of the -P- sequences of 18.23% using SEBS KRATON G and of 10.38% using E-AM-GMA. When the rate of each of the compatibilizers increases to 5%, overall crystallization enthalpies of -P- sequences are almost kept unchanged, except for the case of using the compatibilizer E-AM-GMA with a variation of 8.42%. There is a minor variation of the melting enthalpy of -P- sequences with higher levels of compatibilizer. The incorporation of 5% ABS copolymer in the PP/EPR does not significantly alter the thermal properties of the basic structure of (PP/EPR/ABS.

  19. EPR and photoluminescence study of irradiated anion-defective alumina single crystals

    Science.gov (United States)

    Kortov, V. S.; Ananchenko, D. V.; Konev, S. F.; Pustovarov, V. A.

    2017-09-01

    Electron paramagnetic resonance (EPR) and photoluminescence (PL) spectra of anion-defective alumina single crystals were measured. Exposure to a dose 10 Gy-1 kGy causes isotropic EPR signal of a complex form, this signal contains narrow and broad components. At the same time, in the PL spectrum alongside with a band of F+-centers (3.8 eV) an additional emission band with the maximum of 2.25 eV is registered. This band corresponds to aggregate F22+-centers which were create under irradiation. By comparing measurements in EPR and PL spectra with further stepped annealing in the temperature range of 773-1473 K of the samples exposed to the same doses, we were able to conclude that a narrow component of isotropic EPR signal is associated with the formation of paramagnetic F22+-centers under irradiation. A wide component can be caused by deep hole traps which are created by a complex defect (VAl2- - F+) with a localized hole.

  20. Pulsed EPR Spin-probe study of intracellular glasses in seed and pollen

    NARCIS (Netherlands)

    Buitink, J.; Dzuba, S.A.; Hoekstra, F.A.; Tsvetkov, Y.D.

    2000-01-01

    EPR spectra of 3-carboxy-proxyl (CP) in dry biological tissues exhibited a temperature-dependent change in the principal value A′zz of the hyperfine interaction tensor. The A′zz value changed sharply at a particular temperature that was dependent on water content. At elevated water contents, the

  1. The analogy in the formation of hardness salts and gallstones according to the EPR study

    Science.gov (United States)

    Pichugina, Alina; Tsyro, Larisa; Unger, Felix

    2017-11-01

    The article shows that the hardness salts contain the same crystalline phases as the bile stone pigment. The identity of EPR spectra of hardness salts and pigment of gallstones containing calcium carbonate was established. An analogy between the processes of formation of hardness salts and gallstones is played, in which particles with open spin-orbitals (fermions) play a decisive role.

  2. The effects of short-term selenium stress on Polish and Finnish wheat seedlings-EPR, enzymatic and fluorescence studies.

    Science.gov (United States)

    Łabanowska, Maria; Filek, Maria; Kościelniak, Janusz; Kurdziel, Magdalena; Kuliś, Ewa; Hartikainen, Helina

    2012-02-15

    Biochemical analyses of antioxidant content were compared with measurements of fluorescence and electron paramagnetic resonance (EPR) to examine the alteration of radicals in wheat seedlings exposed to 2 days of selenium stress. Two genotypes of Polish and one of Finnish wheat, differing in their tolerance to long-term stress treatment, were cultured under hydroponic conditions to achieve the phase of 3-leave seedlings. Afterwards, selenium (sodium selenate, 100 μM concentration) was added to the media. After Se-treatment, all varieties showed an increase in carbohydrates (soluble and starch), ascorbate and glutathione content in comparison to non-stressed plants. These changes were more visible in Finnish wheat. On the basis of lipid peroxidation measurements, Finnish wheat was recognized as the genotype more sensitive to short-term Se-stress than the Polish varieties. The antioxidant enzyme activities (superoxide dismutase, ascorbate peroxidase and glutathione reductase) increased in Polish genotypes, whereas they decreased in Finnish wheat plants cultured on Se media. The action of reactive oxygen species in short-term action of Se stress was confirmed by the reduction of PSII and PSI system activities (measured by fluorescence parameters and EPR, respectively). EPR studies showed changes in redox status (especially connected with Mn(II)/Mn(III), and semiquinone/quinone ratios) in wheat cell after Se treatment. The involvement of the carbohydrate molecules as electron traps in production of long-lived radicals is postulated. Copyright © 2011 Elsevier GmbH. All rights reserved.

  3. EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II) and bis(octyldithiocarbonato)copper(II)

    Science.gov (United States)

    Yordanov, Nicola D.; Dimitrova, Anna

    2006-03-01

    EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II), Cu(Et 2dsc) 2, and bis(octyldithiocarbonato)copper(II), Cu(octxant) 2, in CH 2Cl 2, CHCl 3, CCl 4, C 6H 6 and C 6H 5·CH 3 is reported for the first time. Mixing of equimolar amounts of the parents (chromophores CuSe 4 and CuS 4, respectively) in C 6H 6, C 6H 5·CH 3 and CH 2Cl 2 makes EPR signals of both parents superimposed by the spectrum of a mixed-chelate Cu(xant)(dsc) complex (chromophore CuS 2Se 2). A new additional EPR spectrum appears in CHCl 3 or CCl 4 due to a five-coordinate mixed-ligand complex with the chromophore Cu(S 3Se)S as follows by comparing the g-values of parents and mixed-ligand complexes. The appearance of this complex could be explained having in mind donor-acceptor properties of complexes, solvents and the resultant reaction of Cu(octxant) 2 with the ester of diselenocarbamic acid yielded in Cu(Et 2dsc) 2 destruction by CCl 4 or CHCl 3.

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

    Science.gov (United States)

    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.

  5. Study on radiation-induced radicals giving rise to stable EPR signal suitable for the detection of irradiation in L-sorbose-containing fruits

    Directory of Open Access Journals (Sweden)

    Guzik Grzegorz P.

    2016-12-01

    Full Text Available The stable and complex EPR signals produced by the action of ionizing radiation on crystalline L-sorbose (C6H12O6 separated from rowan berries (Sorbus aucuparia were studied. Isothermal heating of the samples at the temperature close to the melting point of L-sorbose (140°C results in the modification and simplification of the EPR signal involved. In the EPR signal of heated L-sorbose, the isotropic quartet was distinguished. In the differential spectrum obtained by subtraction of normalized spectra of unheated and heated L-sorbose, the isotropic doublet was identified in addition. The DFT fitting offers the probable assignment of the EPR signals to specific radical structures.

  6. The influence of genistein on free radicals in normal dermal fibroblasts and keloid fibroblasts examined by EPR spectroscopy.

    Science.gov (United States)

    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.

  7. In situ IR, NMR, EPR, and UV/Vis Spectroscopy: Tools for New Insight into the Mechanisms of Heterogeneous Catalysis.

    Science.gov (United States)

    Hunger, M; Weitkamp, J

    2001-01-01

    The development of new solid catalysts for use in industrial chemistry has hitherto been based to a large extent upon the empirical testing of a wide range of different materials. In only a few exceptional cases has success been achieved in understanding the overall, usually very complex mechanism of the chemical reaction through the elucidation of individual intermediate aspects of a heterogeneously catalyzed reaction. With the modern approach of combinatorial catalysis it is now possible to prepare and test much more rapidly a wide range of different materials within a short time and thus find suitable catalysts or optimize their chemical composition. Our understanding of the mechanisms of reactions catalyzed by these materials must be developed, however, by spectroscopic investigations on working catalysts under conditions that are as close as possible to practice (temperature, partial pressures of the reactants, space velocity). This demands the development and the application of new techniques of in situ spectroscopy. This review will show how this objective is being achieved. By the term in situ (Lat.: in the original position) is meant the investigation of the chemical reactions which are taking place as well as the changes in the working catalysts directly in the spectrometer. Copyright © 2001 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.

  8. High-spin chloro mononuclear MnIII complexes: a multifrequency high-field EPR study.

    Science.gov (United States)

    Mantel, Claire; Chen, Hongyu; Crabtree, Robert H; Brudvig, Gary W; Pécaut, Jacques; Collomb, Marie-Noëlle; Duboc, Carole

    2005-03-01

    The isolation, structural characterization, and electronic properties of two six-coordinated chloromanganese (III) complexes, [Mn(terpy)(Cl)3] (1) and [Mn(Phterpy)(Cl)3] (2), are reported (terpy = 2,2':6'2"-terpyridine, Phterpy = 4'-phenyl-2,2':6',2"-terpyridine). These complexes complement a series of mononuclear azide and fluoride Mn(lll) complexes synthesized with neutral N-tridentate ligands, [Mn(L)(X)3] (X = F- or N3 and L = terpy or bpea [N,N-bis(2-pyridylmethyl)-ethylamine)], previously described. Similar to these previous complexes, 1 and 2 exhibit a Jahn-Teller distortion of the octahedron, characteristic of a high-spin Mn(III) complex (S = 2). The analysis of the crystallographic data shows that, in both cases, the manganese ion lies in the center of a distorted octahedron characterized by an elongation along the tetragonal axis. Their electronic properties were investigated by multifrequency EPR (190-475 GHz) performed in the solid state at different temperatures (5-15 K). This study confirms our previous results and further shows that: i) the sign of D is correlated with the nature of the tetragonal distortion; ii) the magnitude of D is not sensitive to the nature of the anions in our series of rhombic complexes, contrary to the porphyrinic systems; iii) the [E/D] values (0.124 for 1 and 0.085 for 2) are smaller compared to those found for the [Mn(L)(X)3] complexes (in the range of 0.146 to 0.234); and iv) the E term increases when the ligand-field strength of the equatorial ligands decreases.

  9. The use of high field/frequency EPR in studies of radical and metal sites in proteins and small inorganic models

    Science.gov (United States)

    Andersson, K. Kristoffer; Barra, Anne-Laure

    2002-04-01

    Low temperature electron paramagnetic resonance (EPR) spectroscopy with frequencies between 95 and 345 GHz and magnetic fields up to 12 T have been used to study radicals and metal sites in proteins and small inorganic model complexes. We have studied radicals, Fe, Cu and Mn containing proteins. For S=1/2 systems, the high frequency method can resolve the g-value anisotropy. It was used in mouse ribonucleotide reductase (RNR) to show the presence of a hydrogen bond to the tyrosyl radical oxygen. At 285 GHz the type 2 Cu(II) signal in the complex enzyme laccase is clearly resolved from the Hg(II) containing laccase peroxide adduct. For simple metal sites, the systems over S=1/2 can be described by the spin Hamiltonian: HS= BgS+ D[ Sz2- S( S+1)/3+ E/ D ( Sx2- Sy2)]. From the high frequency EPR the D-value can be determined directly by, (I) shifts of geff for half-integer spin systems with large D-values as observed at 345 GHz on an Fe(II)NOEDTA complex, which is best described as S=3/2 system with D=11.5 cm -1, E=0.1 cm -1 and gx= gy= gz=2.0; (II) measuring the outermost signal, for systems with small D values, distant of (2 S-1)*∣ D∣ from the center of the spectrum as observed in S=5/2 Fe(III)EDTA. In Mn(II) substituted mouse RNR R2 protein the weakly interacting Mn(II) at X-band could be observed as decoupled Mn(II) at 285 GHz.

  10. Synthesis and EPR studies of the first water-soluble N@C60 derivative.

    Science.gov (United States)

    Cornes, Stuart P; Zhou, Shen; Porfyrakis, Kyriakos

    2017-11-28

    The first water-soluble derivative of the paramagnetic endohedral fullerene N@C60 has been prepared through the covalent attachment of a single addend containing two permethylated β-cyclodextrin units to the surface of the carbon cage. The line width of the derivative's EPR signal is highly sensitive to both the nature of the solvent and the presence of Cu(ii) ions in solution.

  11. Effects of clary sage oil and its main components, linalool and linalyl acetate, on the plasma membrane of Candida albicans: an in vivo EPR study.

    Science.gov (United States)

    Blaskó, Ágnes; Gazdag, Zoltán; Gróf, Pál; Máté, Gábor; Sárosi, Szilvia; Krisch, Judit; Vágvölgyi, Csaba; Makszin, Lilla; Pesti, Miklós

    2017-02-01

    The effects of clary sage (Salvia sclarea L.) oil (CS-oil), and its two main components, linalool (Lol) and linalyl acetate (LA), on cells of the eukaryotic human pathogen yeast Candida albicans were studied. Dynamic and thermodynamic properties of the plasma membrane were investigated by electron paramagnetic resonance (EPR) spectroscopy, with 5-doxylstearic acid (5-SASL) and 16-SASL as spin labels. The monitoring of the head group regions with 5-SASL revealed break-point frequency decrease in a temperature dependent manner of the plasma membrane between 9.55 and 13.15 °C in untreated, in CS-oil-, Lol- and LA-treated membranes. The results suggest a significant increase in fluidity of the treated plasma membranes close to the head groups. Comparison of the results observed with the two spin labels demonstrated that CS-oil and LA induced an increased level of fluidization at both depths of the plasma membrane. Whereas Lol treatment induced a less (1 %) ordered bilayer organization in the superficial regions and an increased (10 %) order of the membrane leaflet in deeper layers. Acute toxicity tests and EPR results indicated that both the apoptotic and the effects exerted on the plasma membrane fluidity depended on the composition and chemical structure of the examined materials. In comparison with the control, treatment with CS-oil, Lol or LA induced 13.0, 12.3 and 26.4 % loss respectively, of the metabolites absorbing at 260 nm, as a biological consequence of the plasma membrane fluidizing effects. Our results confirmed that clary sage oil causes plasma membrane perturbations which leads to cell apoptosis process.

  12. Synthesis, magnetism, and high-frequency EPR spectroscopy of a family of mixed-valent cuboctahedral Mn13 complexes with 1,8-naphthalenedicarboxylate ligands.

    Science.gov (United States)

    Lampropoulos, Christos; Koo, Changhyun; Hill, Stephen O; Abboud, Khalil; Christou, George

    2008-12-01

    Four mixed-valent (Mn(IV)Mn(III)(6)Mn(II)(6)) tridecanuclear Mn clusters [Mn(13)O(8)(OH)(6)(ndc)(6)] (1), [Mn(13)O(8)(OEt)(5)(OH)(ndc)(6)] (2), [Mn(13)O(8)(O(2)CPh)(12)(OEt)(6)] (3), and [Mn(13)O(8)(OMe)(6)(ndc)(6)] (4) are reported, where ndcH(2) is 1,8-naphthalenedicarboxylic acid. This is the first use of the latter in Mn chemistry. Complexes 1-3 are essentially isostructural and possess a central core composed of three layers. The middle layer consists of a Mn(II)(6) hexagon containing a central Mn(IV) atom, and above and below this are Mn(III)(3) triangular units. These core Mn atoms are held together by a combination of O(2-), RO(-), or HO(-) bridging groups. The overall metal topology is an unusual one, with the overall geometry being a metal-centered cuboctahedron (heptaparallelohedron). Variable-temperature, solid-state dc, and ac magnetization studies were carried out on complexes 1-4 in the 5.0-300 K range. Compound 1 was found to possess an S = 9/2 ground-state spin, whereas 2, 3, and 4 have an S = 11/2 ground state. Fitting of the magnetization (M) versus field (H) and temperature (T) data by matrix diagonalization and including only axial zero-field splitting, D, gave D = -0.14 cm(-1) for 1. High-frequency EPR studies were carried out on single crystals of 1.xDMF, and these confirmed D to be very small, that is, 1 is essentially isotropic. The combined work demonstrates the ligating ability of 1,8-naphthalenedicarboxylate, notwithstanding its robust organic backbone and the restricted parallel disposition of its two carboxylate moieties, and its usefulness in the synthesis of new polynuclear Mn(x) clusters. The work also demonstrates a sensitivity of the ground-state spin in this Mn(13) family of complexes to relatively small structural perturbations, while the high-frequency EPR study demonstrated the magnetically isotropic nature of the Mn(13) core.

  13. Single crystal X- and Q-band EPR spectroscopy of a binuclear Mn(2)(III,IV) complex relevant to the oxygen-evolving complex of photosystem II.

    Science.gov (United States)

    Yano, Junko; Sauer, Kenneth; Girerd, Jean-Jacques; Yachandra, Vittal K

    2004-06-23

    The anisotropic g and hyperfine tensors of the Mn di-micro-oxo complex, [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN, were derived by single-crystal EPR measurements at X- and Q-band frequencies. This is the first simulation of EPR parameters from single-crystal EPR spectra for multinuclear Mn complexes, which are of importance in several metalloenzymes; one of them is the oxygen-evolving complex in photosystem II (PS II). Single-crystal [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN EPR spectra showed distinct resolved (55)Mn hyperfine lines in all crystal orientations, unlike single-crystal EPR spectra of other Mn(2)(III,IV) di-micro-oxo bridged complexes. We measured the EPR spectra in the crystal ab- and bc-planes, and from these spectra we obtained the EPR spectra of the complex along the unique a-, b-, and c-axes of the crystal. The crystal orientation was determined by X-ray diffraction and single-crystal EXAFS (Extended X-ray Absorption Fine Structure) measurements. In this complex, the three crystallographic axes, a, b, and c, are parallel or nearly parallel to the principal molecular axes of Mn(2)(III,IV)O(2)(phen)(4) as shown in the crystallographic data by Stebler et al. (Inorg. Chem. 1986, 25, 4743). This direct relation together with the resolved hyperfine lines significantly simplified the simulation of single-crystal spectra in the three principal directions due to the reduction of free parameters and, thus, allowed us to define the magnetic g and A tensors of the molecule with a high degree of reliability. These parameters were subsequently used to generate the solution EPR spectra at both X- and Q-bands with excellent agreement. The anisotropic g and hyperfine tensors determined by the simulation of the X- and Q-band single-crystal and solution EPR spectra are as follows: g(x) = 1.9887, g(y) = 1.9957, g(z) = 1.9775, and hyperfine coupling constants are A(III)(x) = |171| G, A(III)(y) = |176| G, A(III)(z) = |129| G, A(IV)(x) = |77| G, A

  14. Vanadium(IV/V) speciation of pyridine-2,6-dicarboxylic acid and 4-hydroxy-pyridine-2,6-dicarboxylic acid complexes: potentiometry, EPR spectroscopy and comparison across oxidation states.

    Science.gov (United States)

    Jakusch, Tamás; Jin, Wenzheng; Yang, Luqin; Kiss, Tamás; Crans, Debbie C

    2003-05-01

    Evaluation of stability of vanadium(IV) and (V) complexes under similar conditions is critical for the interpretation and assessment of bioactivity of various vanadium species. Detailed understanding of the chemical properties of these complexes is necessary to explain differences observed their activity in biological systems. These studies are carried out to link the chemistry of both vanadium(IV) and (V) complexes of two ligands, 2,6-pyridinedicarboxylic acid (dipicolinic acid, H(2)dipic) and 4-hydroxy-2,6-pyridinedicarboxylic acid (H(2)dipic-OH). Solution speciation of the two 2,6-pyridinedicarboxylic acids with vanadium(IV) and vanadium(V) ions was determined by pH-potentiometry at I=0.2 M (KCl) ionic strength and at T=298 K. The stability and the metal affinities of the ligands were compared. Vanadium(V) complexes were found to form only tridentate coordinated 1:1 complexes, while vanadium(IV) formed complexes with both 1:1 and 1:2 stoichiometries. The formation constant reflects hindered coordination of a second ligand molecule, presumably because of the relatively small size of the metal ion. The most probable binding mode of the complexes was further explored using ambient and low temperature EPR spectroscopy for vanadium(IV) and 51V NMR spectroscopy for vanadium(V) systems. Upon complex formation the pyridinol-OH in position 4 deprotonates with pK approximately 3.7-4.1, which is approximately 6 orders of magnitude lower than that of the free ligand. The deprotonation enhances the ligand metal ion affinity compared to the parent ligand dipicolinic acid. In the light of the speciation and stability data of the metal complexes, the efficiency of the two ligands in transporting the metal ion in the two different oxidation states are assessed and discussed.

  15. Radical model of arsenic(III) toxicity: theoretical and EPR spin trapping studies.

    Science.gov (United States)

    Zamora, Pedro L; Rockenbauer, Antal; Villamena, Frederick A

    2014-05-19

    Arsenic is one of the most environmentally significant pollutants and a great global health concern. Although a growing body of evidence suggests that reactive oxygen species (ROS) mediate the mechanism of arsenic toxicity, the exact mechanism remains elusive. In this study, we examine the capacity of trivalent arsenic species arsenous acid (iAs(III)), monomethylarsonous acid (MMA(III)), and dimethylarsinous acid (DMA(III)) to generate ROS through a theoretical analysis of their structures, redox properties, and their reactivities to various ROS using a density functional theory (DFT) approach at the B3LYP/6-31+G**//B3LYP/6-31G* level of theory and by employing electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap. Results show that the oxidized forms (As(IV)) are structurally more stable compared to the reduced forms (As(II)) that impart elongated As-O bonds leading to the formation of As(III) and hydroxide anion. Enthalpies of one-electron reduction and oxidation indicate that increasing the degree of methylation makes it harder for As(III) to be reduced but easier to be oxidized. The order of increasing favorability for arsenical activation by ROS is O2 redox pathways with concomitant generation of radicals. This is followed by MMA(III) and by iAs(III) being the least favorable. Spin trapping studies showed a higher propensity for methylated arsenicals to generate radicals than iAs(III) upon treatment with H2O2. However, in the presence of Fe(II,III), all showed radical generation where MMA(III) gave predominantly C-centered adducts, while acidified iAs (III) and DMA(III) gave primarily HO-adducts, and their formation was affected in the presence of SOD suggesting a As(III)-OO/OOH radical intermediate. Therefore, our results suggest a basis for the increased redox activity of methylated arsenicals that can be applied to the observed trends in arsenic methylation and toxicity in biological systems.

  16. BCL::MP-Fold: membrane protein structure prediction guided by EPR restraints

    CERN Document Server

    Fischer, Axel Walter; Woetzel, Nils; Karakas, Mert; Weiner, Brian; Meiler, Jens

    2015-01-01

    For many membrane proteins the determination of their topology remains a challenge for methods like X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy. Electron paramagnetic resonance (EPR) spectroscopy has evolved as an alternative technique to study structure and dynamics of membrane proteins. The present study demonstrates the feasibility of membrane protein topology determination using limited EPR distance and accessibility measurements. The BCL::MP-Fold (BioChemical Library membrane protein fold) algorithm assembles secondary structure elements (SSEs) in the membrane using a Monte Carlo Metropolis (MCM) approach. Sampled models are evaluated using knowledge-based potential functions and agreement with the EPR data and a knowledge-based energy function. Twenty-nine membrane proteins of up to 696 residues are used to test the algorithm. The RMSD100 value of the most accurate model is better than 8{\\AA} for twenty-seven, better than 6{\\AA} for twenty-two and better than 4{\\AA} for fifte...

  17. Force spectroscopy in studying infection

    CERN Document Server

    Zhou, Zhaokun

    2016-01-01

    Biophysical force spectroscopy tools - for example optical tweezers, magnetic tweezers, atomic force microscopy, - have been used to study elastic, mechanical, conformational and dynamic properties of single biological specimens from single proteins to whole cells to reveal information not accessible by ensemble average methods such as X-ray crystallography, mass spectroscopy, gel electrophoresis and so on. Here we review the application of these tools on a range of infection-related questions from antibody-inhibited protein processivity to virus-cell adhesion. In each case we focus on how the instrumental design tailored to the biological system in question translates into the functionality suitable for that particular study. The unique insights that force spectroscopy has gained to complement knowledge learned through population averaging techniques in interrogating biomolecular details prove to be instrumental in therapeutic innovations such as those in structure-based drug design.

  18. Spectroscopic characterization and EPR spectral studies on transition metal complexes with a novel tetradentate, 12-membered macrocyclic ligand

    Science.gov (United States)

    Gupta, Lokesh Kumar; Chandra, Sulekh

    2006-11-01

    Complexes of Cr(III), Mn(II), Co(II), Ni(II) and Cu(II) containing a tetradentate macrocyclic N-donor ligand have been prepared via template reaction of 2,3-pentanedione, ethylene-di-ammine and transition metal ions. The complexes have been characterized on the basis of the elemental analysis, molar conductance, magnetic moment susceptibility, IR, electronic and EPR spectral studies. The complexes are of high spin type and possess four coordinate tetrahedral five coordinate square pyramidal and six coordinated octahedral/tetragonal geometry.

  19. Free radicals in virgin olive oil: a spin trapping EPR study

    OpenAIRE

    Avramiotis, S.; Georgalaki, M.; Cazianis, C.T.; Sotiroudis, Theodore G.; Xenakis, Aristotelis

    2008-01-01

    The spin trap 5.5-dimethyl-1-pyrroline-N-oxide (DMPO) has been used as a probe for monitoring the oxidation properties of virgin olive oil and the detection of free radicals produced in the oil during storage. When DMPO is added in an olive oil sample (or in oxidised triolein) a 12-line Electron Paramagnetic Resonance (EPR) signal is recorded suggesting the trapping of alkoxyl radicals In presence of ethanol the formation of hydroxyl radicals is also detected. The 12-line spectrum changes gra...

  20. Light-induced EPR study of a direct light conversion by polymer/fullerene bulk heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Krinichnyi, V.I.; Yudanova, E.I. [Institute of Problems of Chemical Physics, Chernogolovka (Russian Federation)

    2010-07-01

    Paramagnetic charge carriers photoinduced in poly(3-alkylthiophene)s modified by 6,6-phenyl-C{sub 61}-butanoic acid methyl ester (PCBM) and bis-PCBM by photons with the energy of 1.98 - 2.73 eV were investigated by X-band Light-Induced EPR (LEPR) method. LEPR spectra were attributed to non-interacting polarons and methanofullerene anion-radicals with different magnetic and relaxation parameters. A part of these charge carriers was proved to be trapping in a polymer matrix. The number of mobile charge carriers and their relaxation follow activation law. (orig.)

  1. Preparation and applicability of fresh fruit samples for the identification of radiation treatment by EPR

    Energy Technology Data Exchange (ETDEWEB)

    Yordanov, Nicola D. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)], E-mail: ndyepr@bas.bg; Aleksieva, Katerina [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)

    2009-03-15

    The results of electron paramagnetic resonance (EPR) study on fresh fruits (whole pulp of pears, apples, peaches, apricots, avocado, kiwi and mango) before and after gamma-irradiation are reported using two drying procedures before EPR investigation. In order to remove water from non-irradiated and irradiated samples of the first batch, the pulp of fresh fruits is pressed, and the solid residue is washed with alcohol and dried at room temperature. The fruits of the second batch are pressed and dried in a standard laboratory oven at 40 deg. C. The results obtained with both drying procedures are compared. All samples under study show a singlet EPR line with g=2.0048{+-}0.0005 before irradiation. Irradiation gives rise to typical 'cellulose-like' EPR spectrum featuring one intensive line with g=2.0048{+-}0.0005 and two very weak satellite lines situated 3 mT at left and right of the central line. Only mango samples show a singlet line after irradiation. The fading kinetics of radiation-induced EPR signal is studied for a period of 50 days after irradiation. When the irradiated fruit samples are stored in their natural state and dried just before each EPR measurement, the satellite lines are measurable for less than 17 days of storage. Irradiated fruit samples, when stored dried, lose for 50 days ca. 40% of their radiation-induced radicals if treated with alcohol or ca. 70% if dried in an oven. The reported results unambiguously show that the presence of the satellite lines in the EPR spectra could be used for identification of radiation processing of fresh fruits, thus extending the validity of European Protocol EN 1787 (2000). Foodstuffs-Detection of Irradiated Food Containing Cellulose by EPR Spectroscopy. European Committee for Standardisation. Brussels for dry herbs.

  2. Kinetics of elimination and distribution in blood and liver of biocompatible ferrofluids based on Fe{sub 3}O{sub 4} nanoparticles: An EPR and XRF study

    Energy Technology Data Exchange (ETDEWEB)

    Gamarra, L.F. [Instituto de Ensino e Pesquisa, Hospital Israelita Albert Einstein, Sao Paulo 05651-901 (Brazil); Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo 05315-970 (Brazil)], E-mail: lgamarra@if.usp.br; Pontuschka, W.M. [Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo 05315-970 (Brazil); Amaro, E. [Instituto de Ensino e Pesquisa, Hospital Israelita Albert Einstein, Sao Paulo 05651-901 (Brazil); Instituto de Radiologia, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo 05403-001 (Brazil); Costa-Filho, A.J. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Sao Carlos 13560-970 (Brazil); Brito, G.E.S. [Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo 05315-970 (Brazil); Vieira, E.D. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Sao Carlos 13560-970 (Brazil); Carneiro, S.M. [Laboratorio de Biologia Celular, Instituto Butantan, Sao Paulo 05503-900 (Brazil); Escriba, D.M. [Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo 05315-970 (Brazil); Falleiros, A.M.F. [Centro de Ciencias Biologicas, Universidade Estadual de Londrina 86051-990 (Brazil); Salvador, V.L. [Centro de aplicacoes e Lasers, IPEN, Sao Paulo 05508-000 (Brazil)

    2008-05-01

    In this study, we evaluated the biodistribution and the elimination kinetics of a biocompatible magnetic fluid, Endorem{sup TM}, based on dextran-coated Fe{sub 3}O{sub 4} nanoparticles endovenously injected into Winstar rats. The iron content in blood and liver samples was recorded using electron paramagnetic resonance (EPR) and X-ray fluorescence (XRF) techniques. The EPR line intensity at g = 2.1 was found to be proportional to the concentration of magnetic nanoparticles and the best temperature for spectra acquisition was 298 K. Both EPR and XRF analysis indicated that the maximum concentration of iron in the liver occurred 95 min after the ferrofluid administration. The half-life of the magnetic nanoparticles (MNP) in the blood was (11.6 {+-} 0.6) min measured by EPR and (12.6 {+-} 0.6) min determined by XRF. These results indicate that both EPR and XRF are very useful and appropriate techniques for the study of kinetics of ferrofluid elimination and biodistribution after its administration into the organism.

  3. New Amino-Acid-Based β-Phosphorylated Nitroxides for Probing Acidic pH in Biological Systems by EPR Spectroscopy.

    Science.gov (United States)

    Thétiot-Laurent, Sophie; Gosset, Gaëlle; Clément, Jean-Louis; Cassien, Mathieu; Mercier, Anne; Siri, Didier; Gaudel-Siri, Anouk; Rockenbauer, Antal; Culcasi, Marcel; Pietri, Sylvia

    2017-02-01

    There is increasing interest in measuring pH in biological samples by using nitroxides with pH-dependent electron paramagnetic resonance (EPR) spectra. Aiming to improve the spectral sensitivity (ΔaX ) of these probes (i.e., the difference between the EPR hyperfine splitting (hfs) in their protonated and unprotonated forms), we characterized a series of novel linear α-carboxy, α'-diethoxyphosphoryl nitroxides constructed on an amino acid core and featuring an (α or α')-C-H bond. In buffer, the three main hfs (aN , aH , and aP ) of their EPR spectra vary reversibly with pH and, from aP or aH titration curves, a two- to fourfold increase in sensitivity was achieved compared to reference imidazoline or imidazolidine nitroxides. The crystallized carboxylate 10 b (pKa ≈3.6), which demonstrated low cytotoxicity and good resistance to bioreduction, was applied to probe stomach acidity in rats. The results pave the way to a novel generation of highly sensitive EPR pH markers. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. SOM assembly of hydroxynaphthoquinone and its oxime: Polymorphic X-ray structures and EPR studies

    Science.gov (United States)

    Todkary, Ashwini V.; Dalvi, Rupali; Salunke-Gawali, Sunita; Linares, Jorge; Varret, François; Marrot, Jérôme; Yakhmi, Jatinder V.; Bhadbhade, Mohan; Srinivas, D.; Gejji, Shridhar P.; Rane, Sandhya Y.

    2006-01-01

    Investigation on solvent-induced polymorphism in X-ray structures of 2-hydroxy-1,4-naphthoquinone (Lawsone) 1, is carried out. In protic methanol, 1 crystallizes in monoclinic space group P21/c (1a) comprising of 2D hydrogen bonded network via cyclic dimers. In aprotic solvent such as acetone on the other hand, 1 exhibits orthorhombic space group Pna 21 (1b) and emerges with 1D catemeric chain. Solvent-induced topological isomerism of cyclic dimers and helical catemeric chains arising from (i) bifurcated intra- and inter molecular hydrogen bondings viz. Osbnd H ⋯Odbnd C interactions between C(2) hydroxyl and C(1), C(4) carbonyls, (ii) Csbnd H ⋯O interactions viz. C(3)sbnd H ⋯O(1)C(1) have been discussed. A signal for radical in 1 at g = 2.0058 is signatured by EPR spectrum and it's oxime derivative viz. 2-hydroxy-4-naphthoquinone-1-oxime 2, in solid state shows biradical and monoradical formation with aggregation of dimer and monomer due to non-covalent hydrogen bonds. Zero field split parameters for 2 are estimated to be D = 215 G, Ex = 13 G, Ey = 47 G at 298 K. A half field signal at 77 K indicates triplet ground state. Frozen glass EPR of 2 resolves as regioregular dimeric-monomeric species showing hyperfine interactions with 1-oximino nitrogen in dimer Abar(14N) = 15.5 G].

  5. Radical Intermediates in Photoinduced Reactions on TiO2 (An EPR Spin Trapping Study

    Directory of Open Access Journals (Sweden)

    Dana Dvoranová

    2014-10-01

    Full Text Available The radical intermediates formed upon UVA irradiation of titanium dioxide suspensions in aqueous and non-aqueous environments were investigated applying the EPR spin trapping technique. The results showed that the generation of reactive species and their consecutive reactions are influenced by the solvent properties (e.g., polarity, solubility of molecular oxygen, rate constant for the reaction of hydroxyl radicals with the solvent. The formation of hydroxyl radicals, evidenced as the corresponding spin-adducts, dominated in the irradiated TiO2 aqueous suspensions. The addition of 17O-enriched water caused changes in the EPR spectra reflecting the interaction of an unpaired electron with the 17O nucleus. The photoexcitation of TiO2 in non-aqueous solvents (dimethylsulfoxide, acetonitrile, methanol and ethanol in the presence of 5,5-dimethyl-1-pyrroline N-oxide spin trap displayed a stabilization of the superoxide radical anions generated via electron transfer reaction to molecular oxygen, and various oxygen- and carbon-centered radicals from the solvents were generated. The character and origin of the carbon-centered spin-adducts was confirmed using nitroso spin trapping agents.

  6. Growth, optical and EPR studies of {sup 151}Eu{sup 2+}:YAG single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Petrosyan, A.G., E-mail: pet@ipr.sci.am [Institute for Physical Research, National Academy of Sciences, Ashtarak, 0203 (Armenia); Asatryan, H.R. [Ioffe Physical-Technical Institute, Politekhnicheskaya ul. 26, St. Petersburg, 194021 (Russian Federation); Hovhannesyan, K.L.; Derdzyan, M.V. [Institute for Physical Research, National Academy of Sciences, Ashtarak, 0203 (Armenia); Feofilov, S.P. [Ioffe Physical-Technical Institute, Politekhnicheskaya ul. 26, St. Petersburg, 194021 (Russian Federation); Eganyan, A.V.; Sargsyan, R.S. [Institute for Physical Research, National Academy of Sciences, Ashtarak, 0203 (Armenia)

    2017-01-01

    Single crystals of {sup 151}Eu:YAG were grown by the vertical Bridgman method using Eu{sub 2}O{sub 3} with isotopic enrichment of {sup 151}Eu of 97.5%. Additional Hf{sup 4+}or Si{sup 4+} ions were introduced to favor a high concentrations of Eu{sup 2+}. As compared to Eu:YAG with natural isotope composition, the EPR spectra of YAG doped with {sup 151}Eu isotope show a reduced number of hyperfine structure components and a well-resolved structure of a bigger number of electronic transitions. Optical properties of obtained crystals and the effects of heat treatments under oxidizing and reducing conditions are reported. Based on the analysis of Eu{sup 3+} distribution in oxidized Eu,Hf:YAG, in comparison to that in Eu:YAG, the concentration of Eu{sup 2+} in as-grown Eu,Hf:YAG is determined. - Highlights: • YAG:Eu,Hf single crystals containing only {sup 151}Eu isotopes were prepared. • isotopic enriched crystals gave a well-resolved EPR hyperfine structure of Eu{sup 2+} centers. • the redox ratio was followed through the Eu{sup 2+} associated absorption band at 250 nm. • the band intensities at 378 nm correlate with the Eu{sup 2+} concentration.

  7. SOM assembly of hydroxynaphthoquinone and its oxime: polymorphic X-ray structures and EPR studies.

    Science.gov (United States)

    Todkary, Ashwini V; Dalvi, Rupali; Salunke-Gawali, Sunita; Linares, Jorge; Varret, François; Marrot, Jérôme; Yakhmi, Jatinder V; Bhadbhade, Mohan; Srinivas, D; Gejji, Shridhar P; Rane, Sandhya Y

    2006-01-01

    Investigation on solvent-induced polymorphism in X-ray structures of 2-hydroxy-1,4-naphthoquinone (Lawsone) 1, is carried out. In protic methanol, 1 crystallizes in monoclinic space group P2(1)/c (1a) comprising of 2D hydrogen bonded network via cyclic dimers. In aprotic solvent such as acetone on the other hand, 1 exhibits orthorhombic space group Pna 2(1) (1b) and emerges with 1D catemeric chain. Solvent-induced topological isomerism of cyclic dimers and helical catemeric chains arising from (i) bifurcated intra- and inter molecular hydrogen bondings viz. O-H...O=C interactions between C(2) hydroxyl and C(1), C(4) carbonyls, (ii) C-H...O interactions viz. C(3)-H...O(1)C(1) have been discussed. A signal for radical in 1 at g = 2.0058 is signatured by EPR spectrum and it's oxime derivative viz. 2-hydroxy-4-naphthoquinone-1-oxime 2, in solid state shows biradical and monoradical formation with aggregation of dimer and monomer due to non-covalent hydrogen bonds. Zero field split parameters for 2 are estimated to be D = 215 G, Ex = 13 G, Ey = 47 G at 298 K. A half field signal at 77 K indicates triplet ground state. Frozen glass EPR of 2 resolves as regioregular dimeric-monomeric species showing hyperfine interactions with 1-oximino nitrogen in dimer A (14N) = 15.5 G].

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

    Science.gov (United States)

    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 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.

  9. EPR study of the production of OH radicals in aqueous solutions of uranium irradiated by ultraviolet light

    Directory of Open Access Journals (Sweden)

    MARKO DAKOVIĆ

    2009-06-01

    Full Text Available The aim of the study was to establish whether hydroxyl radicals (•OH were produced in UV-irradiated aqueous solutions of uranyl salts. The production of •OH was studied in uranyl acetate and nitrate solutions by an EPR spin trap method over a wide pH range, with variation of the uranium concentrations. The production of •OH in uranyl solutions irradiated with UV was unequivocally demonstrated for the first time using the EPR spin-trapping method. The production of •OH can be connected to speciation of uranium species in aqueous solutions, showing a complex dependence on the solution pH. When compared with the results of radiative de-excitation of excited uranyl (*UO22+ by the quenching of its fluorescence, the present results indicate that the generation of hydroxyl radicals plays a major role in the fluorescence decay of *UO22+. The role of the presence of carbonates and counter ions pertinent to environmental conditions in biological systems on the production of hydroxyl radicals was also assessed in an attempt to reveal the mechanism of *UO22+ de-excitation. Various mechanisms, including •OH production, are inferred but the main point is that the generation of •OH in uranium containing solutions must be considered when assessing uranium toxicity.

  10. Identification of slow relaxing spin components by pulse EPR techniques in graphene-related materials

    Directory of Open Access Journals (Sweden)

    Antonio Barbon

    2017-01-01

    Full Text Available Electron Paramagnetic Resonance (EPR is a powerful technique that is suitable to study graphene-related materials. The challenging ability requested to the spectroscopy is its capability to resolve the variety of structures, relatively similar, that are obtained in materials produced through different methods, but that also coexist inside a single sample. In general, because of the intrinsic inhomogeneity of the samples, the EPR spectra are therefore a superposition of spectra coming from different structures. We show that by pulse EPR techniques (echo-detected EPR, ESEEM and Mims ENDOR we can identify and characterize species with slow spin relaxing properties. These species are generally called molecular states, and are likely small pieces of graphenic structures of limited dimensions, thus conveniently described by a molecular approach. We have studied commercial reduced graphene oxide and chemically exfoliated graphite, which are characterized by different EPR spectra. Hyperfine spectroscopies enabled us to characterize the molecular components of the different materials, especially in terms of the interaction of the unpaired electrons with protons (number of protons and hyperfine coupling constants. We also obtained useful precious information about extent of delocalization of the molecular states.

  11. Quantitative EPR study on free radicals in the natural polyphenols interacting with metal ions and other environmental pollutants

    Science.gov (United States)

    Jezierski, Adam; Czechowski, Franciszek; Jerzykiewicz, Maria; Golonka, Iwona; Drozd, Jerzy; Bylinska, Ewa; Chen, Yona; Seaward, Mark R. D.

    2002-04-01

    Quantitative electron paramagnetic resonance (EPR) method was applied to characterise radicals stabilised in polyphenolic matrices of various biogenic materials: lichens, mosses, composts, soils, peats, brown coals and sewage sludge sediments. The investigations were carried out on raw materials and extracted fractions of humic acids (HA). General trends of g value and spin concentration changes were found. These parameters in lichens strongly depend on lichen species and air pollution. Determination of the g value and semiquinone spin concentration allows to assess degree of transformation of organic matter in compost, soil, peat and lignite. Application of gaseous ammonia as a base penetrating the organic matrices extends the possibilities and usefulness of the method. Interaction of metal ions with humic materials is illustrated by interaction of VO 2+ ion with peat and lignite HA as well as demineralised (raw and carbonised) brown coal. Our investigations demonstrate that quantitative EPR is a rapid and effective monitoring method to study the influence of various environmental factors on substances containing polyphenolic matrices.

  12. EPR interpretation, magnetism and biological study of a Cu(II) dinuclear complex assisted by a schiff base precursor.

    Science.gov (United States)

    Das, Kuheli; Patra, Chiranjit; Sen, Chandana; Datta, Amitabha; Massera, Chiara; Garribba, Eugenio; El Fallah, Mohamed Salah; Beyene, Belete B; Hung, Chen-Hsiung; Sinha, Chittaranjan; Askun, Tulin; Celikboyun, Pinar; Escudero, Daniel; Frontera, Antonio

    2017-06-01

    A new Cu(II) dinuclear complex, Cu2L2 (1) was afforded employing the potentially pentatentate Schiff base precursor H2L, a refluxed product of o-vanillin and diethylenetriamine in methanol. Complex 1 was systematically characterized by FTIR, UV-Vis, emission and EPR spectrometry. The single crystal X-ray diffraction analysis of 1 reveals that the copper atom exhibits a distorted square planar geometry, comprising two pairs of phenolato-O and imine-N donors from two different H2L ligands. The temperature dependent magnetic interpretation agrees with the existence of weak antiferromagnetic interactions between the bridging dinuclear Cu(II) ions. A considerable body of experimental evidence has been accumulated to elucidate the magneto-structural relationship in this dinuclear Cu(II) complex by DFT computation. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy on M. tuberculosis H37Ra (ATCC 25177) and M. tuberculosis H37Rv (ATCC 25618) strains. The practical applicability of the ligand and complex 1 has been examined in living cells (African Monkey Vero Cells). The MTT assay proves the non-toxicity of the probe up to 100 mg mL-1. A new homometallic dinuclear Cu(II) complex is afforded with a tetradentate Schiff base precursor. EPR interpretation and temperature dependent magnetic studies show that complex 1 has weak antiferromagnetic coupling and DFT computation is governed to explain the magneto-structural correlation.

  13. EPR studies of chromium(V) intermediates generated via reduction of chromium(VI) by DOPA and related catecholamines

    DEFF Research Database (Denmark)

    Pattison, D I; Lay, P A; Davies, Michael Jonathan

    2000-01-01

    The reductions of K2Cr2O7 by catecholamines, DOPA, DOPA-beta,beta-d2, N-acetyl-DOPA, alpha-methyl-DOPA, dopamine, adrenaline, noradrenaline, catechol, 1,2-dihydroxybenzoic acid (DHBA), and 4-tert-butylcatechol (TBC), produce a number of Cr(V) electron paramagnetic resonance (EPR) signals. These s......The reductions of K2Cr2O7 by catecholamines, DOPA, DOPA-beta,beta-d2, N-acetyl-DOPA, alpha-methyl-DOPA, dopamine, adrenaline, noradrenaline, catechol, 1,2-dihydroxybenzoic acid (DHBA), and 4-tert-butylcatechol (TBC), produce a number of Cr(V) electron paramagnetic resonance (EPR) signals...... previously but have been reassigned as octahedral Cr(V) species with mixed catechol-derived ligands, [CrV(semiquinone)2(catecholate)]+. Experiments with excess K2Cr2O7 show complex behavior with the catecholamines and TBC. Several weak Cr(V) signals are detected after mixing, and the spectra evolve over time...... to yield relatively stable substrate-dependent signals at g(iso) approximately 1.980. These signals have been attributed to [Cr(O)L2](L = diolato) species, in which the Cr is coordinated to two cyclized catecholamine ligands and an oxo ligand. Isotopic labeling studies with DOPA (ring or side chain...

  14. Direct synthesis, crystal structures, high-field EPR, and magnetic studies of heterometallic polymers containing manganese(II) carboxylates interconnected by [Cu(en)2]2+.

    Science.gov (United States)

    Makhankova, Valeriya G; Beznischenko, Asya O; Kokozay, Vladimir N; Zubatyuk, Roman I; Shishkin, Oleg V; Jezierska, Julia; Ozarowski, Andrew

    2008-06-02

    Two heterometallic polymers containing cations [Cu(en)2]2+ and either the [Mn(mal)2(H2O)2]2- (1) or [Mn2(succ)2Cl2]n2n- (2) anions (mal=malonate and succ=succinate) were investigated by X-ray crystallography, high-field electron paramagnetic resonance (EPR) spectroscopy, and magnetic susceptibility measurements. Magnetic susceptibility and EPR spectra characteristic of antiferromagnetically coupled Mn2+-Mn2+ pairs were observed in 2, and the exchange integral J=31 cm(-1) (H=JS1S2) as well as the zero-field-splitting parameter D=-3.046 cm(-1) in the triplet state of the dimanganese entity was determined.

  15. High resolution EPR applications to metalloenzymes and metals in medicine

    CERN Document Server

    Berliner, Lawrence

    2009-01-01

    EPR spectroscopy has an important role in the geometric structural characterization of the redox cofactors in metalloproteins and their electronic structure, as this is crucial for their reactivity. This title covers high-resolution EPR methods, iron proteins, nickel and copper enzymes, and metals in medicine.

  16. Effect of Ca2+/Sr2+ substitution on the electronic structure of the oxygen-evolving complex of photosystem II: a combined multifrequency EPR, 55Mn-ENDOR, and DFT study of the S2 state.

    Science.gov (United States)

    Cox, Nicholas; Rapatskiy, Leonid; Su, Ji-Hu; Pantazis, Dimitrios A; Sugiura, Miwa; Kulik, Leonid; Dorlet, Pierre; Rutherford, A William; Neese, Frank; Boussac, Alain; Lubitz, Wolfgang; Messinger, Johannes

    2011-03-16

    The electronic structures of the native Mn(4)O(x)Ca cluster and the biosynthetically substituted Mn(4)O(x)Sr cluster of the oxygen evolving complex (OEC) of photosystem II (PSII) core complexes isolated from Thermosynechococcus elongatus, poised in the S(2) state, were studied by X- and Q-band CW-EPR and by pulsed Q-band (55)Mn-ENDOR spectroscopy. Both wild type and tyrosine D less mutants grown photoautotrophically in either CaCl(2) or SrCl(2) containing media were measured. The obtained CW-EPR spectra of the S(2) state displayed the characteristic, clearly noticeable differences in the hyperfine pattern of the multiline EPR signal [Boussac et al. J. Biol. Chem.2004, 279, 22809-22819]. In sharp contrast, the manganese ((55)Mn) ENDOR spectra of the Ca and Sr forms of the OEC were remarkably similar. Multifrequency simulations of the X- and Q-band CW-EPR and (55)Mn-pulsed ENDOR spectra using the Spin Hamiltonian formalism were performed to investigate this surprising result. It is shown that (i) all four manganese ions contribute to the (55)Mn-ENDOR spectra; (ii) only small changes are seen in the fitted isotropic hyperfine values for the Ca(2+) and Sr(2+) containing OEC, suggesting that there is no change in the overall spin distribution (electronic coupling scheme) upon Ca(2+)/Sr(2+) substitution; (iii) the changes in the CW-EPR hyperfine pattern can be explained by a small decrease in the anisotropy of at least two hyperfine tensors. It is proposed that modifications at the Ca(2+) site may modulate the fine structure tensor of the Mn(III) ion. DFT calculations support the above conclusions. Our data analysis also provides strong support for the notion that in the S(2) state the coordination of the Mn(III) ion is square-pyramidal (5-coordinate) or octahedral (6-coordinate) with tetragonal elongation. In addition, it is shown that only one of the currently published OEC models, the Siegbahn structure [Siegbahn, P. E. M. Acc. Chem. Res.2009, 42, 1871-1880, Pantazis

  17. An investigation of the chromium oxidation state of a monoanionic chromium tris(catecholate) complex by X-ray absorption and EPR spectroscopies

    DEFF Research Database (Denmark)

    Pattison, D I; Levina, A; Davies, Michael Jonathan

    2001-01-01

    The well-known monoanionic Cr tris(3,5-di-tert-butylcatecholato) complex, [Cr(DTBC)3]-, has been studied by X-ray absorption spectroscopy. The multiple-scattering fit to the XAFS gave good correlation (R = 19.8%) and good values for all of the bond lengths, angles, and Debye-Waller factors. The p...

  18. EPR dosimetry of teeth in past and future accidents: a prospective look at a retrospective method

    Energy Technology Data Exchange (ETDEWEB)

    Haskell, E.H.; Kenner, G.H.; Hayes, R.B. [Utah Univ., Salt Lake City, UT (United States). Center for Applied Dosimetry; Chumak, V.; Shalom, S. [All-Union Scientific Centre of Radiation Medicine, Kiev (Ukraine)

    1996-01-01

    Electron paramagnetic resonance spectroscopy (EPR) of tooth enamel is a relatively new technique for retrospective dosimetry that in the past two years has seen increasing effort towards its development and evaluation. Efforts have centered on determining the accuracy which may be achieved with current measurement techniques as well as the minimum doses detectable. The study was focused on evaluating some factors which influence the accuracy of EPR dosimetry of enamel. Reported are studies on sample intercomparisions, instrumental considerations, and effects of dental x-rays, environmental sunlight and ultraviolet radiation.

  19. Solute distribution and stability in emulsion-based delivery systems: an EPR study.

    Science.gov (United States)

    Yucel, Umut; Elias, Ryan J; Coupland, John N

    2012-07-01

    Oil-in-water emulsions and related systems are often used to deliver hydrophobic solutes in foods, personal care products, and pharmaceuticals. Recent work has considered the use of crystalline lipid carrier particles (i.e., solid lipid nanoparticles, SLN) to control the availability of the solute; however, there is little direct evidence for the localization of small molecules in these systems. Alkanes (10 wt.% tetradecane or eicosane) containing the spin probe 4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl (PTMIO, 200 ppm) were homogenized into sodium caseinate solution (1 wt.%) to produce fine or coarse droplets (0.2 μm or 1.3 μm, respectively) and cooled to 21.5 °C where eicosane is crystalline and tetradecane is liquid. Analysis of the resulting EPR spectra revealed populations of probe in two discrete environments (i.e., aqueous and lipid). PTMIO is largely hydrophobic with 77% and 70% present in the coarse and fine liquid lipid droplets (i.e., tetradecane droplets), respectively. In the solid droplets (i.e., eicosane), all of the probe was excluded from the droplets into the aqueous environment. In all cases, the mobility of the probe in both lipid and aqueous environments was affected by the droplet surface; thus, we hypothesize that the majority of the probe molecules are associated with the droplet interface. The PTMIO was reduced to an EPR-silent form by the addition of iron/ascorbate to the aqueous phase, and the apparent rate constant of the reaction was proportional to the fraction of the spin probe in the aqueous phase. Based on these findings, we propose that droplet crystallization excludes solute molecules from the droplet core to the aqueous environment where they interact with the droplet surface. Copyright © 2012 Elsevier Inc. All rights reserved.

  20. Linking Cr₃ triangles through phosphonates and lanthanides: synthetic, structural, magnetic and EPR studies.

    Science.gov (United States)

    Zangana, Karzan H; Pineda, Eufemio Moreno; Vitorica-Yrezabal, Iñigo J; McInnes, Eric J L; Winpenny, Richard E P

    2014-09-21

    The preparation and structural characterisation of five 3d-4f mixed metal phosphonate cages with general formula [Cr(III)6Ln(III)2(μ3-O)2(H2O)2(O3P(t)Bu)4(O2C(t)Bu)12(HO(i)Bu)2((i)PrNH2)2] where Ln(III) = La, 1; Tb, 3; Dy, 4; Ho, 5 and [Cr(III)6Gd(III)2(μ3-O)2(H2O)2(O3P(t)Bu)4(O2C(t)Bu)12(HO(i)Bu)4] (2) are reported. The structure contains two oxo-centred {Cr3} triangles, bridged by phosphonates and lanthanides. The magnetic behaviour of 1 has been modelled as two non-interacting isosceles triangles, involving two antiferromagnetic interactions (J1 = -8.8 cm(-1)) with a smaller ferromagnetic interaction for the unique edge of the triangle (J2 = +1.3 cm(-1)) giving an isolated S = 3/2 ground state per triangle. The quartet ground state has been proven through simulation of electron paramagnetic resonance (EPR) spectra obtained at the X- and Q-band. EPR simulations have also resulted in the introduction of small single-ion Zero Field Splitting (ZFS) parameters D = ±0.19 cm(-1) and rhombic term E = ±0.02 cm(-1), which are consistent with strong exchange limit calculations for an isolated S = 3/2 (D = ±0.22 and E = ±0.018 cm(-1)).

  1. EPR, UV-Visible, and Near-Infrared Spectroscopic Characterization of Dolomite

    Directory of Open Access Journals (Sweden)

    S. Lakshmi Reddy

    2008-01-01

    Full Text Available Dolomite mineral samples having white and light green colors of Indian origin have been characterized by EPR, optical, and NIR spectroscopy. The optical spectrum exhibits a number of electronic bands due to presence of Fe(III ions in the mineral. From EPR studies, the parameters of g for Fe(III and g,A, and D for Mn(II are evaluated and the data confirm that the ions are in distorted octahedron. Optical absorption studies reveal that Fe(III is in distorted octahedron. The bands in NIR spectra are due to the overtones and combinations of water molecules. Thus EPR and optical absorption spectral studies have proven useful for the study of the solid state chemistry of dolomite.

  2. Identification and dose assessment of irradiated cumin by EPR spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Fattah, A.A. E-mail: atef_fattah@hotmail.com

    2002-03-01

    The use of electron paramagnetic resonance spectroscopy to accurately distinguish irradiated from unirradiated cumin and assess the absorbed dose to radiation-processed cumin is examined. The results were successful for identifying both irradiated and unirradiated cumin. Additive reirradiation of the cumin produces a reproducible dose response function, which can be used to assess the initial dose by back-extrapolation. Third-degree polynomial and exponential functions were used to fit the EPR signal/dose curves. It was found that the 3rd degree polynomial function provides satisfactory results without correction for decay of free radicals. The exponential fit to the data cannot be used without correction of decay of free radicals. The stability of the radiation-induced EPR signal of irradiated cumin was studied over a storage period of 6 months. The additive reirradiation of some samples was carried out at different storage times (10, 20 and 30 days) after initial irradiation.

  3. Does aspartate 170 of the D1 polypeptide ligate the manganese cluster in photosystem II? An EPR and ESEEM Study.

    Science.gov (United States)

    Debus, Richard J; Aznar, Constantino; Campbell, Kristy A; Gregor, Wolfgang; Diner, Bruce A; Britt, R David

    2003-09-16

    Aspartate 170 of the D1 polypeptide provides part of the high-affinity binding site for the first Mn(II) ion that is photooxidized during the light-driven assembly of the (Mn)(4) cluster in photosystem II [Campbell, K. A., Force, D. A., Nixon, P. J., Dole, F., Diner, B. A., and Britt, R. D. (2000) J. Am. Chem. Soc. 122, 3754-3761]. However, despite a wealth of data on D1-Asp170 mutants accumulated over the past decade, there is no consensus about whether this residue ligates the assembled (Mn)(4) cluster. To address this issue, we have conducted an EPR and ESEEM (electron spin-echo envelope modulation) study of D1-D170H PSII particles purified from the cyanobacterium Synechocystis sp. PCC 6803. The line shapes of the S(1) and S(2) state multiline EPR signals of D1-D170H PSII particles are unchanged from those of wild-type PSII particles, and the signal amplitudes correlate approximately with the lower O(2) evolving activity of the mutant PSII particles (40-60% compared to that of the wild type). These data provide further evidence that the assembled (Mn)(4) clusters in D1-D170H cells function normally, even though the assembly of the (Mn)(4) cluster is inefficient in this mutant. In the two-pulse frequency domain ESEEM spectrum of the 9.2 GHz S(2) state multiline EPR signal of D1-D170H PSII particles, the histidyl nitrogen modulation observed at 4-5 MHz is unchanged from that of wild-type PSII particles and no significant new modulation is observed. Three scenarios are presented to explain this result. (1) D1-Asp170 ligates the assembled (Mn)(4) cluster, but the hyperfine couplings to the ligating histidyl nitrogen of D1-His170 are too large or anisotropic to be detected by ESEEM analyses conducted at 9.2 GHz. (2) D1-Asp170 ligates the assembled (Mn)(4) cluster, but D1-His170 does not. (3) D1-Asp170 does not ligate the assembled (Mn)(4) cluster.

  4. Mass, IR, electronic and EPR spectral studies on transition metal complexes with a new tetradentate 12-membered new macrocyclic ligand

    Science.gov (United States)

    Chandra, Sulekh; Gupta, Lokesh Kumar

    2004-11-01

    Complexes of Cr(III), Co(II), Ni(II) and Cu(II) containing a novel macrocyclic tetradentate nitrogen donor (N 4) ligand prepared via reaction of 2,3-hexanedione and ethylenediamine has been prepared and characterized. The newly synthesized ligand (L) and its complexes have been characterized on the basis of elemental analysis, molar conductance, magnetic moment susceptibility, EI-Mass, IR, Electronic and EPR spectral studies. The complexes are of high-spin type and four coordinated tetrahedral, five coordinated square pyramidal and six coordinated octahedral/tetragonal geometries. The ligand (L) and its soluble transition metal complexes have also been screened against different bacteria and plant pathogenic fungi in vitro.

  5. EPR study of gamma and neutron irradiation effects on KU1, KS-4V and Infrasil 301 silica glasses

    Energy Technology Data Exchange (ETDEWEB)

    Lagomacini, Juan C., E-mail: jc.lagomacini@uam.es [Dept. Fisica de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Bravo, David [Dept. Fisica de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Leon, Monica; Martin, Piedad; Ibarra, Angel [Materiales para Fusion, CIEMAT, Avda. Complutense 22, E-28040 Madrid (Spain); Martin, Agustin [Dept. Fisica e Instalaciones, ETS Arquitectura UPM, E-28040 Madrid (Spain); Lopez, Fernando J. [Dept. Fisica de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain)

    2011-10-01

    Electron paramagnetic resonance (EPR) studies have been carried out on KU1 and KS-4V high purity quartz glasses and commercial silica Infrasil 301, irradiated with gamma rays up to a dose of 11.6 MGy and neutron fluences of 10{sup 21} and 10{sup 22} n/m{sup 2}. Gamma irradiations produce a much higher concentration of defect centres (mainly E', POR and NBOHC) for KU1 and I301 than for KS-4V silica. In contrast, neutron irradiation at the highest fluence produces similar concentrations in all silica types. These results agree to a good extent with those obtained in previous optical absorption measurements. Moreover, oxygen-related centres (POR and NBOHC) have been well characterized by means of electron paramagnetic resonance.

  6. Study of EPR/ESR Dosimetry in Fingernails as a Method for Assessing Dose of Victims of Radiological Accidents/Incidents

    Science.gov (United States)

    2008-06-17

    factor, μB is the Bohr magneton, equal to 9.2740 E-24 J T-1, and B0 is the magnetic field strength [37]. The separation between the two energy states...use of EPR biodosimetry in calcified tissues (teeth and bones) as an accurate method for retrospective radio -epidemiological studies. It recommended

  7. Multi-frequency and high-field EPR study of manganese(III) protoporphyrin IX reconstituted myoglobin with an S=2 integer electron spin.

    Science.gov (United States)

    Horitani, Masaki; Yashiro, Haruhiko; Hagiwara, Masayuki; Hori, Hiroshi

    2008-04-01

    We investigate the electronic state of Mn(III) center with an integer electron spin S=2 in the manganese(III) protoporphyrin IX reconstituted myoglobin, Mn(III)Mb, by means of multi-frequency electron paramagnetic resonance (MFEPR) spectroscopy. Using a bimodal cavity resonator, X-band EPR signal from Mn(III) center in the Mn(III)Mb was observed near zero-field region. The temperature dependence of this signal indicates a negative axial zero-field splitting value, DEPR analysis shows that this signal is attributed to the transition between the closely spaced M(s)=+/-2 energy levels for the z-axis, corresponding to the heme normal. To determine the zero-field splitting (ZFS) parameters, EPR experiments on the Mn(III)Mb were performed at various temperatures for some frequencies between 30GHz and 130GHz and magnetic fields up to 14T. We observed several EPR spectra which are analyzed with a spin Hamiltonian for S=2, yielding highly accurate ZFS parameters; D=-3.79cm(-1) and |E|=0.08cm(-1) for an isotropic g=2.0. These ZFS parameters are compared with those in some Mn(III) complexes and Mn(III) superoxide dismutase (SOD), and effects on these parameters by the coordination and the symmetry of the ligands are discussed. To the best of our knowledge, these EPR spectra in the Mn(III)Mb are the very first MFEPR spectra at frequencies higher than Q-band in a metalloprotein with an integer spin.

  8. CW-EPR study of 2,2,4,4-tetramethyl-3-pentanone oxime single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Sayin, Ulku; Yuksel, Huseyin; Ozmen, Ayhan [Physics Department, Selcuk University, Konya (Turkey); Birey, Mehmet, E-mail: birey@science.ankara.edu.t [Physics Department, Ankara University, Ankara (Turkey)

    2010-12-15

    The electron paramagnetic resonance (EPR) spectra of gamma irradiated single crystals of 2,2,4,4-tetramethyl-3-pentanone oxime (TPO) have been examined between temperatures of 125 and 450 K. The spectra were found to be both dependent on temperature and orientation of single crystals with magnetic field. We attributed radiation damage centers to iminoxy radicals (RC=N{sup {center_dot}}O). There are two similar group of splitting in the spectra because of conformational isomers (R1, R2) of iminoxy radicals produced by gamma irradiation of TPO. Determined g-factor and hyperfine coupling constants for R1 and R2 conformers were found anisotropic with the average values (g{sub iso}){sub R1}=2.01057, (g{sub iso}){sub R2}=2.009337, [(a{sub N}){sub iso}]{sub R1}=28.09 G, [(a{sub N}){sub iso}]{sub R2}=36.34 G, [(a{sub H}){sub iso}]{sub R2}=9.15 G, respectively.

  9. EPR, TEM and cell viability study of asbestiform zeolite fibers in cell media.

    Science.gov (United States)

    Cangiotti, Michela; Salucci, Sara; Battistelli, Michela; Falcieri, Elisabetta; Mattioli, Michele; Giordani, Matteo; Ottaviani, Maria Francesca

    2018-01-01

    Human monocyte U937 cell line was used as a model to verify the toxicity of erionite and offretite asbestiform zeolite fibers. As a presumed non-toxic reference, a fibrous scolecite zeolite was also used. To analyze the process of fiber ingestion into cells and the cells-fibers interactions, a spin-probe electron paramagnetic resonance (EPR) analysis was performed supported by transmission electron microscopy (TEM) and cell viability measurements as a function of the incubation time. Erionite fibers were fast internalized in the membrane mainly as aggregates with radical-solution drops trapped inside, and were found in the cytosol and at the nucleus. In 24h, first erionite fibers rich in sodium and potassium, and then calcium-rich erionite fibers, induced cell necrosis. The offretite fibers formed rounding electron-dense filaments which transformed in curved filaments, initially perturbing the cell structure and interacting at the external surface more than erionite fibers. Such interactions probably diminished the toxic effect of offretite on cells. Interestingly, the presumed non-toxic scolecite fibers were partially internalized, inducing formation of swollen mitochondria and squared cells. Overall, the toxic effect of the fibrous zeolites was related to fiber morphology, chemical distribution of sites, structural variations and formation of aggregates. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, Hal

    1968-01-01

    This booklet discusses spectroscopy, the study of absorption of radiation by matter, including X-ray, gamma-ray, microwave, mass spectroscopy, as well as others. Spectroscopy has produced more fundamental information to the study of the detailed structure of matter than any other tools.

  11. Characterization of Monomeric MnII/III/IV–Hydroxo Complexes from X- and Q-Band Dual Mode Electron Paramagnetic Resonance (EPR) Spectroscopy

    OpenAIRE

    Gupta, Rupal; Taguchi, Taketo; Borovik, A. S.; Hendrich, Michael P.

    2013-01-01

    Manganese–hydroxo species have been implicated in C–H bond activation performed by metalloenzymes, but the electronic properties of many of these intermediates are not well characterized. The present work presents a detailed characterization of three Mnn–OH complexes (where n = II, III, and IV) of the tris[(N′-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3−) ligand using X- and Q-band dual mode electron paramagnetic resonance (EPR). Quantitative simulations for the [MnIIH3buea(OH)]2− comp...

  12. An EPR study of the intramolecular dynamics in o-semiquinonic nickel complexes with a diphosphorous pincer ligand.

    Science.gov (United States)

    Kozhanov, Konstantin A; Bubnov, Michael P; Cherkasov, Vladimir K; Fukin, Georgy K; Abakumov, Gleb A

    2003-10-21

    Square pyramidal o-semiquinonic nickel complexes with 2,6-bis(diphenylphosphinomethyl)phenyl have a flexible coordination sphere and exist in solution as the mixture of tautomers rapidly, according to EPR time scale, interconverting at room temperature.

  13. Identification of irradiated crab using EPR

    Energy Technology Data Exchange (ETDEWEB)

    Maghraby, A. [Radiation Dosimetry Department, National Institute for Standards (NIS), Ministry of Scientific Research, Haram, 12211- Giza, P.O. Box: 136 (Egypt)]. E-mail: maghrabism@yahoo.com

    2007-02-15

    EPR spectroscopy is a fast and powerful technique for the identification of irradiated food. Crab exoskeleton was divided into six parts: dactyl, cheliped, carapace, apron, swimming legs, and walking legs. Samples of the exoskeleton were prepared and irradiated to Cs-137 gamma radiation in the range (1.156-5.365 kGy). EPR spectra of unirradiated as well as irradiated samples were recorded and analyzed. Response to gamma radiation was plotted for each part of the exoskeleton, dactyl was found to be the most sensitive part, followed by the apron (38%), cheliped (37%), walking legs (30%), swimming legs (24%), and carapace (21%) relative to the dactyl response.

  14. Monitoring local redox processes in LiNi0.5Mn1.5O4 battery cathode material by in operando EPR spectroscopy.

    Science.gov (United States)

    Niemöller, Arvid; Jakes, Peter; Eurich, Svitlana; Paulus, Anja; Kungl, Hans; Eichel, Rüdiger-A; Granwehr, Josef

    2018-01-07

    Despite the multitude of analytical methods available to characterize battery cathode materials, identifying the factors responsible for material aging is still challenging. We present the first investigation of transient redox processes in a spinel cathode during electrochemical cycling of a lithium ion battery by in operando electron paramagnetic resonance (EPR). The battery contains a LiNi0.5Mn1.5O4 (LNMO) spinel cathode, which is a material whose magnetic interactions are well understood. The evolution of the EPR signal in combination with electrochemical measurements shows the impact of Mn3+ on the Li+ motion inside the spinel. Moreover, state of charge dependent linewidth variations confirm the formation of a solid solution for slow cycling, which is taken over by mixed models of solid solution and two-phase formation for fast cycling due to kinetic restrictions and overpotentials. Long-term measurements for 480 h showed the stability of the investigated LNMO, but also small amounts of cathode degradation products became visible. The results point out how local, exchange mediated magnetic interactions in cathode materials are linked with battery performance and can be used for material characterization.

  15. Study of light-induced MscL gating by EPR spectroscopy

    NARCIS (Netherlands)

    Yilmaz, Duygu; Dimitrova, Anna I.; Walko, Martin; Kocer, Armagan

    2015-01-01

    A number of techniques developed to investigate protein structure and function depend on chemically modifying and/or labeling of proteins. However, in the case of homooligomeric proteins, the presence of multiple identical subunits obstructs the introduction of residue-specific labels to only one or

  16. EPR and Fluorescence Spectroscopy in the Photodegradation Study of Arabian and Colombian Crude Oils

    Directory of Open Access Journals (Sweden)

    Carmen L. B. Guedes

    2006-01-01

    W/m2. The reduction in the linewidth of the free radical of 9.8% in Arabian oil and 18.5% in Colombian oil, as well as the decrease in radical numbers, indicated photochemical degradation, especially in Colombian oil. The linewidth narrowing corresponding to free radicals in the irradiated oils occurred due to the rearrangement among radicals and aromatic carbon consumption. The irradiated oils showed a reduction in the relative intensity of fluorescence of the aromatics with high molecular mass, polar aromatics, and asphaltene. The fluorescent fraction was reduced by 61% in Arabian oil and 72% in Colombian oil, corresponding to photochemical degradation of crude oil aromatic compounds.

  17. Multi-photon transitions and Rabi resonance in continuous wave EPR.

    Science.gov (United States)

    Saiko, Alexander P; Fedaruk, Ryhor; Markevich, Siarhei A

    2015-10-01

    The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines. Copyright © 2015 Elsevier Inc. All rights reserved.

  18. Kinetics of chromium(V) formation and reduction in fronds of the duckweed Spirodela polyrhiza--a low frequency EPR study.

    Science.gov (United States)

    Appenroth, K J; Bischoff, M; Gabryś, H; Stoeckel, J; Swartz, H M; Walczak, T; Winnefeld, K

    2000-02-01

    The uptake of chromate by the duckweed Spirodela polyrhiza was investigated with atomic absorption spectroscopy and the reduction of Cr(VI) to Cr(V) was measured using low frequency EPR spectroscopy. The biphasic kinetics of the uptake was fitted to parameters of a proposed kinetic model. Another model was developed to simulate chromate reduction. The first step of chromate reduction was found to be much faster than the uptake of Cr(VI) from the free space. Most probably, this step occurs already in the cell wall or on the cell membrane surface. Further reduction of Cr(V) to Cr(III) was estimated to be slower. The disappearance of the Cr(V) signal, following transfer of the plants into a Cr-free solution, lasted several tens of hours; the kinetics was mono- or biexponential depending on the length of Cr loading. The rate constants for Cr reduction in living plants were determined for the first time.

  19. Biodistribution and Bioimaging Studies of Hybrid Paclitaxel Nanocrystals: Lessons Learned of the EPR Effect and Image-Guided Drug Delivery

    Science.gov (United States)

    Hollis, Christin P.; Weiss, Heidi L.; Leggas, Markos; Evers, B. Mark; Gemeinhart, Richard A.; Li, Tonglei

    2013-01-01

    Paclitaxel (PTX) nanocrystals (200 nm) were produced by crystallization from solution. Antitumor efficacy and toxicity were examined through a survival study in a human HT-29 colon cancer xenograft murine model. The antitumor activity of the nanocrystal treatments was comparable with that by the conventional solubilization formulation (Taxol®), but yielded less toxicity as indicated by the result of survival study. Tritium-labeled PTX nanocrystals were further produced with a near infrared (NIR) fluorescent dye physically integrated in the crystal lattice. Biodistribution and tumor accumulation of the tritium-labeled PTX nanocrystals were determined immediately after intravenous administration and up to 48 hours by scintillation counting. Whole-body optical imaging of animals was concurrently carried out; fluorescent intensities were also measured from excised tumors and major organs of euthanized animals. It was found that drug accumulation in the tumor was less than 1% of 20 mg/kg intravenous dose. Qualitatively correlation was identified between the biodistribution determined by using tritium-labeled particles and that using optical imaging, but quantitative divergence existed. The divergent results suggest possible ways to improve the design of hybrid nanocrystals for cancer therapy and diagnosis. The study also raises questions of the general role of the enhanced permeability and retention (EPR) effect in tumor targeting and the effectiveness of bioimaging, specifically for hybrid nanocrystals, in tracking drug distribution and pharmacokinetics. PMID:23920039

  20. Clinical electron paramagnetic resonance (EPR) oximetry using India ink.

    Science.gov (United States)

    Williams, Benjamin B; Khan, Nadeem; Zaki, Bassem; Hartford, Alan; Ernstoff, Marc S; Swartz, Harold M

    2010-01-01

    Electron paramagnetic resonance (EPR) oximetry can be used to provide direct absolute measurements of pO(2) in living tissue using India ink as an O(2) reporter. In vivo measurements are made using low frequency (1.2 GHz) EPR spectroscopy and surface loop resonators, which enable measurements to be made at superficial sites through a non-invasive (after placing the ink in the tissues) and repeatable measurement procedure. Ongoing EPR oximetry studies in human subjects include measurement of subcutaneous pO(2) in the feet of healthy volunteers to develop procedures that could be used in the treatment of peripheral vascular disease and oximetry in tumors during courses of radiation and chemotherapy, to follow pO(2) so oxygen-dependent therapies can be optimized. In each case, we aim to provide quantitative measurements of tissue pO(2) which will aid physicians in the characterization of disease status and the effects of therapeutic measures, so that treatments can be applied with optimal effectiveness by taking into account the oxygen-dependent aspects of the therapy. The overall goal is to enhance clinical outcomes. Oximetry measurements of subcutaneous tissue on dorsal and plantar foot surfaces have been made in 9 volunteers, with measurements ongoing for each and the longest set of measurements carried out successfully over the last 5 years. Tumor oximetry measurements have been performed in tumor tissues of 10 patients during courses of radiation and chemotherapy. Tumor types include melanoma, basal cell, soft tissue sarcoma, and lymphoma, and measurement sites have ranged from the feet to the scalp. These studies demonstrate the feasibility of EPR oximetry in a clinical setting and the potential for more widespread use in the treatment of these and other oxygen-dependent diseases.

  1. Unprecedented access of phenolic substrates to the heme active site of a catalase: substrate binding and peroxidase-like reactivity of Bacillus pumilus catalase monitored by X-ray crystallography and EPR spectroscopy.

    Science.gov (United States)

    Loewen, Peter C; Villanueva, Jacylyn; Switala, Jacek; Donald, Lynda J; Ivancich, Anabella

    2015-05-01

    Heme-containing catalases and catalase-peroxidases catalyze the dismutation of hydrogen peroxide as their predominant catalytic activity, but in addition, individual enzymes support low levels of peroxidase and oxidase activities, produce superoxide, and activate isoniazid as an antitubercular drug. The recent report of a heme enzyme with catalase, peroxidase and penicillin oxidase activities in Bacillus pumilus and its categorization as an unusual catalase-peroxidase led us to investigate the enzyme for comparison with other catalase-peroxidases, catalases, and peroxidases. Characterization revealed a typical homotetrameric catalase with one pentacoordinated heme b per subunit (Tyr340 being the axial ligand), albeit in two orientations, and a very fast catalatic turnover rate (kcat  = 339,000 s(-1) ). In addition, the enzyme supported a much slower (kcat  = 20 s(-1) ) peroxidatic activity utilizing substrates as diverse as ABTS and polyphenols, but no oxidase activity. Two binding sites, one in the main access channel and the other on the protein surface, accommodating pyrogallol, catechol, resorcinol, guaiacol, hydroquinone, and 2-chlorophenol were identified in crystal structures at 1.65-1.95 Å. A third site, in the heme distal side, accommodating only pyrogallol and catechol, interacting with the heme iron and the catalytic His and Arg residues, was also identified. This site was confirmed in solution by EPR spectroscopy characterization, which also showed that the phenolic oxygen was not directly coordinated to the heme iron (no low-spin conversion of the Fe(III) high-spin EPR signal upon substrate binding). This is the first demonstration of phenolic substrates directly accessing the heme distal side of a catalase. © 2015 Wiley Periodicals, Inc.

  2. Light-induced EPR study of charge transfer in P3HT/bis-PCBM bulk heterojunctions

    Directory of Open Access Journals (Sweden)

    Victor I. Krinichnyi

    2011-06-01

    Full Text Available Radical pairs, polarons and fullerene anion radicals photoinduced by photons with energy of 1.98 – 2.73 eV in bulk heterojunctions formed by poly(3-hexylthiophene (P3HT with bis(1-[3-(methoxycarbonylpropyl]-1-phenyl-[6.6]C62 (bis-PCBM fullerene derivative have been studied by direct light-induced EPR (LEPR method in a wide temperature range. A part of photoinduced polarons are pinned in trap sites which number and depth are governed by an ordering of the polymer/fullerene system and energy of initiating photons. It was shown that dynamics and recombination of mobile polarons and counter fullerene anion radicals are governed by their exchange- and multi-trap assisted diffusion. Relaxation and dynamics parameters of both the charge carriers were determined separately by the steady-state saturation method. These parameters are governed by structure and conformation of the carriers’ microenvironment as well as by the energy of irradiating photons. Longitudinal diffusion of polarons was shown to depend on lattice phonons of crystalline domains embedded into an amorphous polymer matrix. The energy barrier required for polaron interchain hopping is higher than that its intrachain diffusion. Pseudorotation of fullerene derivatives in a polymer matrix was shown to follow the activation Pike model.

  3. An EPR spin-probe and spin-trap study of the free radicals produced by plant plasma membranes

    Directory of Open Access Journals (Sweden)

    GORAN BACIC

    2005-02-01

    Full Text Available Plant plasma membranes are known to produce superoxide radicals, while the production of hydroxyl radical is thought to occur only in the cell wall. In this work it was demonstrated using combined spin-trap and spin-probe EPR spectroscopic techniques, that plant plasma membranes do produce superoxide and hydroxyl radicals but by kinetically different mechanisms. The results show that superoxide and hydroxyl radicals can be detected by DMPO spin-trap and that the mechanisms and location of their production can be differentiated using the reduction of spin-probes Tempone and 7-DS. It was shown that the mechanism of production of oxygen reactive species is NADH dependent and diphenylene iodonium inhibited. The kinetics of the reduction of Tempone, combined with scavengers or the absence of NADH indicates that hydroxyl radicals are produced by a mechanism independent of that of superoxide production. It was shown that a combination of the spin-probe and spin-trap technique can be used in free radical studies of biological systems, with a number of advantages inherent to them.

  4. Theoretical studies of the optical and EPR spectra for VO^{2+} in Na_3C_6H_5O_7·2H_2O single crystal

    Directory of Open Access Journals (Sweden)

    Ch.-Y. Li

    2015-06-01

    Full Text Available On the basis of the perturbation formulas for a d^1 configuration ion in a tetragonal crystal field, the three optical absorption bands and electron paramagnetic resonance (EPR parameters (g factors g_i and hyperfine structure constants A_i for i = || and ⊥, respectively of VO^{2+} in Na_3C_6H_5O_7·2H_2O (TSCD single crystals were studied using the perturbation theory method. By simulating the calculated optical and EPR spectra to the observed values, local structure parameters and negative signs of the hyperfine structure constants A_i of the octahedral (VO_6^{8-} cluster in TSCD single crystal can be obtained.

  5. Multi-frequency EPR studies of a mononuclear holmium single-molecule magnet based on the polyoxometalate [Ho(III)(W5O18)2]9-.

    Science.gov (United States)

    Ghosh, Sanhita; Datta, Saiti; Friend, Lisa; Cardona-Serra, Salvador; Gaita-Ariño, Alejandro; Coronado, Eugenio; Hill, Stephen

    2012-11-28

    Continuous-wave, multi-frequency electron paramagnetic resonance (EPR) studies are reported for a series of single-crystal and powder samples containing different dilutions of a recently discovered mononuclear Ho(III) (4f(10)) single-molecule magnet (SMM) encapsulated in a highly symmetric polyoxometalate (POM) cage. The encapsulation offers the potential for applications in molecular spintronics devices, as it preserves the intrinsic properties of the nanomagnet outside of the crystal. A significant magnetic anisotropy arises due to a splitting of the Hund's coupled total angular momentum (J = L + S = 8) ground state in the POM ligand field. Thus, high-frequency (50.4 GHz) EPR studies reveal a highly anisotropic eight line spectrum corresponding to transitions within the lowest m(J) = ±4 doublet, split by a strong hyperfine interaction with the I = 7/2 Ho nucleus (100% natural abundance). X-band EPR studies reveal the presence of an appreciable tunneling gap between the m(J) = ±4 doublet states having the same nuclear spin projection, leading to a highly non-linear field-dependence of the spectrum at low-frequencies.

  6. Incorporation of Mn into the vacant T-atom sites of a BEA zeolite as isolated, mononuclear Mn: FTIR, XPS, EPR and DR UV-Vis studies.

    Science.gov (United States)

    Baran, R; Valentin, L; Dzwigaj, S

    2016-04-28

    A MnSiBEA zeolite has been prepared via a two-step postsynthesis procedure which consisted, in the first step, of the treatment of a tetraethylammonium BEA zeolite with nitric acid for the formation of vacant T-atom sites and then, in the second step, of the incorporation of Mn ions into the framework, resulting in a SiBEA zeolite, through their reaction with the silanol group of the vacant T-atom sites. The incorporation of Mn ions into the framework of the SiBEA zeolite has been evidenced using XRD. The formation of isolated mononuclear Mn(ii) and Mn(iii) in a MnSiBEA zeolite has been shown using FTIR, diffuse reflectance UV-Vis, EPR and XPS. The acidic properties of the mononuclear manganese species have been investigated via FTIR spectroscopy using pyridine as the probe molecule. The changes in the oxidation state of the Mn species under various treatments have been proven using EPR.

  7. Synthesis and characterization of mono- and dinuclear phenanthroline-extended tetramesitylporphyrin complexes as well as UV-Vis and EPR studies on their one-electron reduced species.

    Science.gov (United States)

    Matlachowski, Corinna; Schwalbe, Matthias

    2013-03-14

    The syntheses of mononuclear compounds based on the fused porphyrin phenanthroline ligand (H(2)-1) and their corresponding dinuclear porphyrin bis-bipyridine ruthenium complexes are reported. The extended π-system of the ligand is able to store electron equivalents as could be proven by the single electron reduction with KC(8) (and/or Na(Hg)) followed by subsequent UV-Vis and EPR analysis. Electron reduction could also be achieved under light illumination in a dichloromethane-triethylamine mixture. The two coordination spheres of the ligand are different so that mononuclear or (hetero)dinuclear complexes can be isolated depending on the reaction conditions. We could successfully introduce Zn, Cu and Pd into the porphyrinic unit leading to a series of mononuclear (M-1) compounds. Further, we could attach the bis-(4,4'-di-tert-butyl-2,2'-bipyridine) ruthenium fragment (Ru(tbbpy)(2)(2+)) to obtain dinuclear (M-1-Ru) metal complexes. In the case of Zn-1 an X-ray crystal structure could be obtained confirming the selective metallation in the porphyrinic unit. All metal complexes were isolated and characterized with standard analytical tools (elemental analysis, mass spectrometry and NMR (or EPR) spectroscopy).

  8. EPR-based distance measurements at ambient temperature

    Science.gov (United States)

    Krumkacheva, Olesya; Bagryanskaya, Elena

    2017-07-01

    Pulsed dipolar (PD) EPR spectroscopy is a powerful technique allowing for distance measurements between spin labels in the range of 2.5-10.0 nm. It was proposed more than 30 years ago, and nowadays is widely used in biophysics and materials science. Until recently, PD EPR experiments were limited to cryogenic temperatures (T biomolecules, the influence of a linker between the spin probe and biomolecule, and future opportunities.

  9. Recent pulsed EPR studies of the photosystem II oxygen-evolving complex: implications as to water oxidation mechanisms.

    Science.gov (United States)

    Britt, R David; Campbell, Kristy A; Peloquin, Jeffrey M; Gilchrist, M Lane; Aznar, Constantino P; Dicus, Michelle M; Robblee, John; Messinger, Johannes

    2004-04-12

    The pulsed electron paramagnetic resonance (EPR) methods of electron spin echo envelope modulation (ESEEM) and electron spin echo-electron nuclear double resonance (ESE-ENDOR) are used to investigate the structure of the Photosystem II oxygen-evolving complex (OEC), including the paramagnetic manganese cluster and its immediate surroundings. Recent unpublished results from the pulsed EPR laboratory at UC-Davis are discussed, along with aspects of recent publications, with a focus on substrate and cofactor interactions. New data on the proximity of exchangeable deuterons around the Mn cluster poised in the S(0)-state are presented and interpreted. These pulsed EPR results are used in an evaluation of several recently proposed mechanisms for PSII water oxidation. We strongly favor mechanistic models where the substrate waters bind within the OEC early in the S-state cycle. Models in which the O-O bond is formed by a nucleophilic attack by a Ca(2+)-bound water on a strong S(4)-state electrophile provide a good match to the pulsed EPR data.

  10. STRUCTURAL AND DYNAMIC PROPERTIES OF SOLID-SOLUTIONS OF BAF2 AND GDF3 - AN EPR STUDY

    NARCIS (Netherlands)

    DENHARTOG, HW

    Results of EPR experiments on solid solutions of barium and gadolinium fluoride in the temperature range 300 to 900 K are presented. At room temperature the Gd-ions are located predominantly at trigonal sites. If the temperature is increased, the interstitial fluoride ions are found to dissociate

  11. EPR study of free radicals in non- and gamma-irradiated nutritive supplements containing anthocyanins concentrate from lyophilized red wine

    Science.gov (United States)

    Mladenova, Ralitsa B.; Firzov, Cyril; Yordanov, Nicola D.

    2010-09-01

    Nutritive supplements Enoviton, Enoviton C and Enoviton CE containing standardized anthocyanins from lyophilized red wine, vitamins (some of them) and excipients were investigated by EPR spectrometry before and after gamma-irradiation. Non-irradiated samples exhibit one singlet line with g=2.0039±0.0002, most probably due to free radicals from anthocyanins. After irradiation with 10 kGy gamma-rays, tablets of Еnoviton, Еnoviton С and Еnoviton СЕ, all exhibit complex EPR signals centered at a g-value of g=2.0034. The EPR spectrum of irradiated Enoviton is different from that of Еnoviton С or Еnoviton СЕ due to the overlap of the spectra of microcrystalline cellulose and the background singlet spectrum present in all tablets with the EPR resonance due to irradiated ascorbic acid (in Еnoviton С and Еnoviton СЕ). Gamma-induced free radicals exhibit long time stability—for a six months period the intensity of central peak decrease with 30-40%.

  12. EPR study of free radicals in non- and gamma-irradiated nutritive supplements containing anthocyanins concentrate from lyophilized red wine

    Energy Technology Data Exchange (ETDEWEB)

    Mladenova, Ralitsa B., E-mail: ralitsa@ic.bas.b [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Firzov, Cyril [Institute of Cryobiology and Food Technology, 1162 Sofia (Bulgaria); Yordanov, Nicola D. [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)

    2010-09-15

    Nutritive supplements Enoviton, Enoviton C and Enoviton CE containing standardized anthocyanins from lyophilized red wine, vitamins (some of them) and excipients were investigated by EPR spectrometry before and after gamma-irradiation. Non-irradiated samples exhibit one singlet line with g=2.0039{+-}0.0002, most probably due to free radicals from anthocyanins. After irradiation with 10 kGy gamma-rays, tablets of Enoviton, Enoviton S and Enoviton SE, all exhibit complex EPR signals centered at a g-value of g=2.0034. The EPR spectrum of irradiated Enoviton is different from that of Enoviton S or Enoviton SE due to the overlap of the spectra of microcrystalline cellulose and the background singlet spectrum present in all tablets with the EPR resonance due to irradiated ascorbic acid (in Enoviton S and Enoviton SE). Gamma-induced free radicals exhibit long time stability-for a six months period the intensity of central peak decrease with 30-40%.

  13. Laser spectroscopy studies on nobelium

    Science.gov (United States)

    Block, Michael

    2017-11-01

    Laser spectroscopy of the heaviest elements provides high-precision data on their atomic and nuclear properties. For example, atomic level energies and ionization potentials allow us to probe the influence of relativistic effects on their atomic structure and to benchmark state-of-the-art atomic structure calculations. In addition, it offers an alternative route to determine nuclear properties like spins, magnetic moments and quadrupole moments in a nuclear model-independent way. Recently, a sensitive method based on resonant laser ionization has been applied to nobelium isotopes around N = 152 at GSI Darmstadt. In pioneering experiments, several atomic states have been identified extending the reach of laser spectroscopy beyond fermium. In this contribution, the main achievements and future perspectives are briefly summarized.

  14. Vesicle to micelle transition in the ternary mixture of L121/SDS/D2O: NMR, EPR and SANS studies.

    Science.gov (United States)

    Prameela, G K S; Phani Kumar, B V N; Reddy, R Ravikanth; Pan, A; Subramanian, J; Kumar, Sugam; Aswal, V K; Kohlbrecher, Joachim; Mandal, A B; Moulik, S P

    2017-12-06

    Subtle changes in the microstructure and dynamics of the triblock copolymer L121, (ethylene oxide) 5 (propylene oxide) 68 (ethylene oxide) 5 i.e., E 5 P 68 E 5 , and sodium dodecylsulfate (SDS) system in aqueous medium were investigated using high-resolution nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and small-angle neutron scattering (SANS) methods. NMR self-diffusion measurements helped us to understand the nature of binding of SDS with L121, and the formation of their mixed aggregates. These results showed that even at low [SDS] (∼2 mM), the addition of L121 stabilized the dynamics of SDS. Furthermore, the increase in [SDS] resulted in progressive changes in the diffusion behavior of both SDS and L121. 13 C chemical shift analysis revealed that preferential binding of L121 occurred on the SDS micelle surface. Deuterium ( 2 H) NMR spin-relaxation data evidenced that the formed mixed aggregates were non-spherical in terms of relaxation rate changes, and slowed the dynamics. The rotational correlation times of mixed aggregates were estimated from EPR analysis. A SANS study indicated the presence of uni- and multi-lamellar vesicles of L121 at low [SDS]. The vesicles transformed to mixed L121-SDS micelles in the presence of a higher [SDS]. This was supported by the measurements of 2 H NMR spin-relaxation and EPR rotational correlation times.

  15. Dual-mode EPR study of Mn(III) salen and the Mn(III) salen-catalyzed epoxidation of cis-beta-methylstyrene.

    Science.gov (United States)

    Campbell, K A; Lashley, M R; Wyatt, J K; Nantz, M H; Britt, R D

    2001-06-20

    Dual-mode electron paramagnetic resonance (EPR), in which an oscillating magnetic field is alternately applied parallel or perpendicular to the static magnetic field, is a valuable technique for studying both half-integer and integer electron spin systems and is particularly useful for studying transition metals involved in redox chemistry. We have applied this technique to the characterization of the Mn(III) salen (salen = N,N'-ethylene bis(salicylideneaminato)) complex [(R,R)-(-)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III)], with an S = 2 integer electron spin system. Furthermore, we have used dual-mode EPR to study the Mn salen complex during the Mn(III) salen-catalyzed epoxidation of cis-beta-methylstyrene. Our study shows that the additives N-methylmorpholine N-oxide (NMO) and 4-phenylpyridine-N-oxide (4-PPNO), which are used to improve epoxidation yields and enantioselection, bind to the Mn(III) center prior to the epoxidation reaction, as evidenced by the alteration of the Mn(III) parallel mode EPR signal. With these additives as ligands, the axial zero-field splitting values and (55)Mn hyperfine splitting of the parallel mode signal are indicative of an axially elongated octahedral geometry about the Mn(III) center. Since the dual-mode EPR technique allows the observation of both integer and half-integer electron spin systems, Mn oxidation states of II, III, IV, and potentially V can be observed in the same sample as well as any radical intermediates or Mn(III,IV) dinuclear clusters formed during the Mn(III) salen-catalyzed epoxidation reaction. Indeed, our study revealed the formation of a Mn(III,IV) dinuclear cluster in direct correlation with expoxide formation. In addition to showing the possible reaction intermediates, dual-mode EPR offers insight into the mechanism of catalyst degradation and formation of unwanted byproducts. The dual-mode technique may therefore prove valuable for elucidating the mechanism of Mn

  16. Competitive sorption and selective sequence of Cu(II) and Ni(II) on montmorillonite: Batch, modeling, EPR and XAS studies

    Science.gov (United States)

    Yang, Shitong; Ren, Xuemei; Zhao, Guixia; Shi, Weiqun; Montavon, Gilles; Grambow, Bernd; Wang, Xiangke

    2015-10-01

    Heavy metal ions that leach from various industrial and agricultural processes are simultaneously present in the contaminated soil and water systems. The competitive sorption of these toxic metal ions on the natural soil components and sediments significantly influences their migration, bioavailability and ecotoxicity in the geochemical environment. In this study, the competitive sorption and selectivity order of Cu(II) and Ni(II) on montmorillonite are investigated by combining the batch experiments, X-ray diffraction (XRD), electron paramagnetic resonance (EPR), surface complexation modeling and X-ray Absorption Spectroscopy (XAS). The batch experimental data show that the coexisting Ni(II) exhibits a negligible influence on the sorption behavior of Cu(II), whereas the coexisting Cu(II) reduces the Ni(II) sorption percentage and changes the shape of the Ni(II) sorption isotherm. The sorption species of Cu(II) and Ni(II) on montmorillonite over the acidic and near-neutral pH range are well simulated by the surface complexation modeling. However, this model cannot identify the occurrence of surface nucleation and the co-precipitation processes at a highly alkaline pH. Based on the results of the EPR and XAS analyses, the microstructures of Cu(II) on montmorillonite are identified as the hydrated free Cu(II) ions at pH 5.0, inner-sphere surface complexes at pH 6.0 and the surface dimers/Cu(OH)2(s) precipitate at pH 8.0 in the single-solute and the binary-solute systems. For the Ni(II) sorption in the single-solute system, the formed microstructure varies from the hydrated free Ni(II) ions at the pH values of 5.0 and 6.0 to the inner-sphere surface complexes at pH 8.0. For the Ni(II) sorption in the binary-solute system, the coexisting Cu(II) induces the formation of the inner-sphere complexes at pH 6.0. In contrast, Ni(II) is adsorbed on montmorillonite via the formation of Ni phyllosilicate co-precipitate/α-Ni(OH)2(s) precipitate at pH 8.0. The selective sequence

  17. Ligation of D1-His332 and D1-Asp170 to the manganese cluster of photosystem II from Synechocystis assessed by multifrequency pulse EPR spectroscopy.

    Science.gov (United States)

    Stich, Troy A; Yeagle, Gregory J; Service, Rachel J; Debus, Richard J; Britt, R David

    2011-08-30

    Multifrequency electron spin-echo envelope modulation (ESEEM) spectroscopy is used to ascertain the nature of the bonding interactions of various active site amino acids with the Mn ions that compose the oxygen-evolving cluster (OEC) in photosystem II (PSII) from the cyanobacterium Synechocystis sp. PCC 6803 poised in the S(2) state. Spectra of natural isotopic abundance PSII ((14)N-PSII), uniformly (15)N-labeled PSII ((15)N-PSII), and (15)N-PSII containing (14)N-histidine ((14)N-His/(15)N-PSII) are compared. These complementary data sets allow for a precise determination of the spin Hamiltonian parameters of the postulated histidine nitrogen interaction with the Mn ions of the OEC. These results are compared to those from a similar study on PSII isolated from spinach. Upon mutation of His332 of the D1 polypeptide to a glutamate residue, all isotopically sensitive spectral features vanish. Additional K(a)- and Q-band ESEEM experiments on the D1-D170H site-directed mutant give no indication of new (14)N-based interactions.

  18. Comparative 5-doxylstearoyllecithin and 3-doxylcholestane EPR spin labeling study of phospholipid bilayer perturbation by different oxidized lecithin species.

    Science.gov (United States)

    Megli, Francesco M; Conte, Elena; Russo, Luciana

    2010-10-01

    A 3-doxylcholestane spin label was employed in addition to 5-doxylstearoyl lecithin for a more detailed study of the different effects exerted by variously oxidized lecithins on fatty acid alignment in phospholipid planar bilayers. Either spin label was enclosed in oriented PLPC planar samples also containing in turn a variety of conjugated-dienes lecithins and cleaved chain lecithins, in order to monitor EPR spectral angular dependence loss. Data obtained by use of arachidonoyl-hydroxystearoyl-PC and palmitoyl-hydroxylinoleoyl-PC confirm that the 5-DSPC nitroxide ring almost completely retains its orientation in CD-PCs-containing planar membranes, in contrast with angular dependence loss observed in the presence of the CC-PC molecular species palmitoyl-oxononanoyl-PC and palmitoyl-oxovaleroyl-PC, already seen with cleaved-chain palmitoyl-glutaroyl-PC and palmitoyl-azelaoyl-PC. However, the 3-DC nitroxide ring also loses its orientation with CD-PCs, in addition to being disoriented by cleaved chain-lecithins, similarly to 5DSPC. Joint information from the two spin labels will help to clarify whether OXPC-related disordering involved the whole bilayer structure or only the hydrophobic core. In addition, the propensity of different OXPCs to form bilayer vesicles in water suspension was also determined by Sepharose 4B gel-chromatography. The results suggest that CD-PCs might yield SPB bilayer structures with a disordered hydrophobic core, while pure CC-PC more probably forms non-bilayer disordered structures, possibly micelles or mixed micelle/bilayers. Copyright © 2010 Elsevier B.V. All rights reserved.

  19. Structural, magnetic, EPR, and electrochemical characterizations of a spin-frustrated trinuclear Cr(III) polyoxometalate and study of its reactivity with lanthanum cations.

    Science.gov (United States)

    Compain, Jean-Daniel; Mialane, Pierre; Dolbecq, Anne; Mbomekallé, Israël Martyr; Marrot, Jérôme; Sécheresse, Francis; Duboc, Carole; Rivière, Eric

    2010-03-15

    The asymmetric Cr(III) polyoxometalate complex Cs(10)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)] x 17 H(2)O (1) has been synthesized in water under atmospheric pressure from the trinuclear precursor [Cr(3)(CH(3)COO)(7)(OH)(2)] and the divacant ligand [gamma-SiW(10)O(36)](8-). Complex 1 is built up of two [gamma-SiW(10)O(36)](8-) Keggin units sandwiching a trinuclear {(Cr(III)(OH)(H(2)O))(3)} fragment where the paramagnetic centers are bridged by three mu-OH ligands forming a nearly isosceles triangle. The magnetic properties of this spin-frustrated system have thus been interpreted considering a 2-J Hamiltonian showing that the Cr(III) ions are antiferromagnetically coupled and that 1 possesses an S = 3/2 ground state with an S = 1/2 first excited state located at 11 cm(-1). These results have been confirmed by EPR spectroscopy measurements (Q-band), which have also enabled the quantification of the electronic parameters characterizing the quadruplet spin ground state. The magnitude of the magnetic exchange interactions and the nature of the ground state are discussed in light of previously reported isosceles triangular S = 3/2 clusters. UV-visible and electrochemical studies have shown that 1 is stable in aqueous media in a 1-7 pH range. This stability is chemically confirmed by the study of the reactivity of 1 with La(III) cations, which has allowed the isolation of the Cs(4)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)(La(H(2)O)(7))(2)] x 20 H(2)O compound (2). Indeed, during the synthetic process of this 3d-4f system, the integrity of the [(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)](10-) building unit constituting 1 is maintained despite the high oxophilic character of the La(III) ions. The single crystal X-ray diffraction study of 2 has revealed that in the solid state the rare earth cations connect these subunits, affording a 3d-4f double-chain monodimensional system.

  20. N-hydroxyguanidines as new heme ligands: UV-visible, EPR, and resonance Raman studies of the interaction of various compounds bearing a C=NOH function with microperoxidase-8.

    Science.gov (United States)

    Lefevre-Groboillot, D; Dijols, S; Boucher, J L; Mahy, J P; Ricoux, R; Desbois, A; Zimmermann, J L; Mansuy, D

    2001-08-21

    Interaction between microperoxidase-8 (MP8), a water-soluble hemeprotein model, and a wide range of N-aryl and N-alkyl N'-hydroxyguanidines and related compounds has been investigated using UV-visible, EPR, and resonance Raman spectroscopies. All the N-hydroxyguanidines studied bind to the ferric form of MP8 with formation of stable low-spin iron(III) complexes characterized by absorption maxima at 405, 535, and 560 nm. The complex obtained with N-(4-methoxyphenyl) N'-hydroxyguanidine exhibits EPR g-values at 2.55, 2.26, and 1.86. The resonance Raman (RR) spectrum of this complex is also in agreement with an hexacoordinated low-spin iron(III) structure. The dissociation constants (K(s)) of the MP8 complexes with mono- and disubstituted N-hydroxyguanidines vary between 15 and 160 microM at pH 7.4. Amidoximes also form low-spin iron(III) complexes of MP8, although with much larger dissociation constants. Under the same conditions, ketoximes, aldoximes, methoxyguanidines, and guanidines completely fail to form such complexes with MP8. The K(s) values of the MP8-N-hydroxyguanidine complexes decrease as the pH of the solution is increased, and the affinity of the N-hydroxyguanidines toward MP8 increases with the pK(a) of these ligands. Altogether these results show that compounds involving a -C(NHR)=NOH moiety act as good ligands of MP8-Fe(III) with an affinity that depends on the electron-richness of this moiety. The analysis of the EPR spectrum of the MP8-N-hydroxyguanidine complexes according to Taylor's equations shows a strong axial distortion of the iron, typical of those observed for hexacoordinated heme-Fe(III) complexes with at least one pi donor axial ligand (HO(-), RO(-), or RS(-)). These data strongly suggest that N-hydroxyguanidines bind to MP8 iron via their oxygen atom after deprotonation or weakening of their O-H bond. It thus seems that N-hydroxyguanidines could constitute a new class of strong ligands for hemeproteins and iron(III)-porphyrins.

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

    Science.gov (United States)

    Nakagawa, Kouichi; Epel, Boris

    2014-10-01

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

  2. Structural and magnetic properties of Mn(III) and Cu(II) tetranuclear azido polyoxometalate complexes: multifrequency high-field EPR spectroscopy of Cu4 clusters with S = 1 and S = 2 ground states.

    Science.gov (United States)

    Mialane, Pierre; Duboc, Carole; Marrot, Jérôme; Rivière, Eric; Dolbecq, Anne; Sécheresse, Francis

    2006-02-20

    Two new azido-bridged polyoxometalate compounds were synthesized in acetonitrile/methanol media and their molecular structures have been determined by X-ray crystallography. The [[(gamma-SiW10O36)Mn2(OH)2(N3)(0.5)(H2O)(0.5)]2(mu-1,3-N3)](10-) (1 a) tetranuclear Mn(III) complex, in which an end-to-end N3- ligand acts as a linker between two [(gamma-SiW10O36)Mn2(OH)2]4- units, represents the first manganese-azido polyoxometalate. The magnetic properties have been studied considering the spin Hamiltonian H = -J1(S1S2+S1*S2*)-J2(S1S1*), showing that antiferromagnetic interactions between the paramagnetic centers (g = 1.98) occur both through the di-(mu-OH) bridge (J1 = -25.5 cm(-1)) and the mu-1,3-azido bridge (J2 = -19.6 cm(-1)). The [(gamma-SiW10O36)2Cu4(mu-1,1,1-N3)2(mu-1,1-N3)2]12- (2 a) tetranuclear Cu(II) complex consists of two [gamma-SiW10O36Cu2(N3)2]6- subunits connected through the two mu-1,1,1-azido ligands, the four paramagnetic centers forming a lozenge. The magnetic susceptibility data have been fitted. This reveals ferromagnetic interactions between the four Cu(II) centers, leading to an S=2 ground state (H = -J1(S1S2+S1*S2*)-J2(S2S2*), J1 = +294.5 cm(-1), J2 = +1.6 cm(-1), g = 2.085). The ferromagnetic coupling between the Cu(II) centers in each subunit is the strongest ever observed either in a polyoxometalate compound or in a diazido-bridged Cu(II) complex. Considering complex 2 a and the previously reported basal-basal di-(mu-1,1-N3)-bridged Cu(II) complexes in which the metallic centers are not connected by other magnetically coupling ligands, the linear correlation J1 = 2639.5-24.95*theta(av) between the theta(av) bridging angle and the J1 coupling parameter has been proposed. The electronic structure of complex 2 a has also been investigated by using multifrequency high-field electron paramagnetic resonance (HF-EPR) spectroscopy between 95 and 285 GHz. The spin Hamiltonian parameters of the S = 2 ground state (D = -0.135(2) cm(-1), E = -0

  3. Single crystal EPR study of VO(II)-doped cadmium potassium ...

    Indian Academy of Sciences (India)

    symmetry of the central metal ion and the nature of the bonding with the ligands and this has also been used as an impurity for understanding the defect, structural, phase transition and orientation properties of the host lattice 1–5. Studies of VO(II) in glasses and other systems have attracted attention very recently6–8.

  4. Spin Probe Multi-Frequency EPR Study of Unprocessed Cotton Fibers.

    Science.gov (United States)

    Marek, Antonin; Voinov, Maxim A; Smirnov, Alex I

    2017-06-01

    Known since the ancient times, cotton continues to be one of the essential materials for the human civilization. Cotton fibers are almost pure cellulose and contain both crystalline and amorphous nanodomains with different physicochemical properties. While understanding of interactions between the individual cellulose chains within the crystalline phase is important from a perspective of mechanical properties, studies of the amorphous phase lead to characterization of the essential transport parameters, such as solvent diffusion, dyeing, drug release, and toxin absorption, as well as more complex processes of enzymatic degradation. Here, we describe the use of spin probe electron paramagnetic resonance methods to study local polarity and heterogeneous viscosity of two types of unprocessed cotton fibers, G. hirsutum and G. barbadense, harvested in the State of North Carolina, USA. These fibers were loaded with two small molecule nitroxide probes that differ in polarity-Tempo and its more hydrophilic derivative Tempol-using a series of polar and non-polar solvents. The electron paramagnetic resonance spectra of the nitroxide-loaded cotton fibers were analyzed both semi-empirically and by least-squares simulations using a rigorous stochastic theory of electron paramagnetic resonance spectra developed by Freed and coworkers. A software package and least-squares fitting protocols were developed to carry out automatic simulations of multi-component electron paramagnetic resonance spectra in both first-derivative and the absorption forms at multiple resonance frequencies such as X-band (9.5 GHz) and W-band (94.3 GHz). The results are compared with the preceding electron paramagnetic resonance spin probe studies of a commercial bleached cotton sheeting carried out by Batchelor and coworkers. One of the results of this study is a demonstration of a co-existence of cellulose nanodomains with different physicochemical properties such as polarity and microviscosity that

  5. Aragonite→calcite transformation studied by EPR of Mn 2+ ions

    Science.gov (United States)

    Lech, J.; Śl|zak, A.

    1989-05-01

    The irreversible transformation aragonite→calcite has been studied both at different fixed heating rates (5, 10, 15 and 20 K/min) and at different fixed temperatures. Apparent progression rates of the transformation were observed above 685 K. At 730 K the transformation became sudden and violent. Time developments of the transformation at fixed temperatures have been discussed in terms of Avrami-Lichti's approach to transitions involving nucleation processes.

  6. Photoelectron Spectroscopy Study of Quinonimides

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, Ekram [The; Deng, Shihu M. [Physical; Gozem, Samer [Department; Krylov, Anna I. [Department; Wang, Xue-Bin [Physical; Wenthold, Paul G. [The

    2017-08-03

    Structures and energetics of o-, m- and p-quinonimide anions (OC6H4N) and quinoniminyl radicals have been investigated by using negative ion photoelectron spectroscopy. Modeling of the photoelectron spectrum of the ortho isomer shows that the ground state of the anion is a triplet, while the quinoniminyl radical has a doublet ground state with a doublet-quartet splitting of 35.5 kcal/mol. The para radical has doublet ground state, but a band for a quartet state is missing from the photoelectron spectrum indicating that the anion has a singlet ground state, in contrast to previously reported calculations. The theoretical modeling is revisited here, and it is shown that accurate predictions for the electronic structure of the para quinonimide anion require both an accurate account of electron correlation and a sufficiently diffuse basis set. Electron affinities of o- and p-quinoniminyl radicals are measured to be 1.715 ± 0.010 and 1.675 ± 0.010 eV, respectively. The photoelectron spectrum of the m-quinonimide anion shows that the ion undergoes several different rearrangements, including a rearrangement to the energetically favorable para isomer. Such rearrangements preclude a meaningful analysis of the experimental spectrum.

  7. Extended defects in vanadium doped rutile. An EPR and TEM study

    Energy Technology Data Exchange (ETDEWEB)

    Otero-Diaz, L.C.; Soria, J.; Alario-Franco, M.A. (Madrid Univ. (Spain))

    1984-04-16

    Electron microscopy and diffraction coupled with electron paramagnetic resonance are used to study the system TiO/sub 2/-V/sub 2/O/sub 3/ on samples prepared at 1373 K. Substitutional and/or interstitial V/sup 4 +/ ions are detected at low concentrations of V/sub 2/O/sub 3/ together with isolated extended defects. At higher vanadium concentrations (>= 5 wt% V/sub 2/O/sub 3/) the extended defects order giving rise to a homologous occur between the paramagnetic vanadium ions which would appear to be close to the crystallographic shear planes.

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

    Science.gov (United States)

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

    2014-08-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Rocker, J.; Cornu, D.; Kieseritzky, E.; Hänsel-Ziegler, W.; Freund, H.-J. [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Seiler, A. [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Laboratorium für Applikationen der Synchrotronstrahlung, KIT Campus Süd, Kaiserstr. 12, 76131 Karlsruhe (Germany); Bondarchuk, O. [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); CIC energiGUNE, Parque Tecnologico, C/Albert Einstein 48, CP 01510 Minano (Alava) (Spain); Risse, T., E-mail: risse@chemie.fu-berlin.de [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin (Germany)

    2014-08-01

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

  10. Dose reconstruction by EPR spectroscopy of tooth enamel: application to the population of Zaborie village exposed to high radioactive contamination after the Chernobyl accident.

    Science.gov (United States)

    Ivannikov, A I; Gaillard-Lecanu, E; Trompier, F; Stepanenko, V F; Skvortsov, V G; Borysheva, N B; Tikunov, D D; Petin, D V

    2004-02-01

    Individual irradiation doses were determined by electron paramagnetic resonance spectroscopy of the tooth enamel of the inhabitants of Zaborie, the most contaminated inhabited settlement not evacuated after the Chernobyl accident. Dose determination was performed using a specially developed automatic spectrum processing procedure. Spectrum processing was carried out in different operating modes, and average results were taken in order to reduce the contribution of uncertainty in dose determination caused by spectrum processing. The absorbed doses determined in enamel were corrected to take into account the contribution of natural background radiation and to determine the individual excess dose due to radioactive contamination of the territory. Individual excess doses are compared to calculated individualized doses to teeth, estimated using the local radioactive contamination levels, dose rates, and information concerning individual behavior. The individual excess doses measured by electron paramagnetic resonance spectroscopy and the calculated individualized doses are fully independent. Mean square variation between results of two methods was found to be 34 mGy, which is consistent with error estimation for both methods. This result can validate both the methodology of signal processing presented here when using electron paramagnetic resonance dosimetry of tooth enamel for low doses and the methodology of individualized dose calculation.

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

    Science.gov (United States)

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

    1993-08-01

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

  12. Butanolic fraction of Moringa oleifera Lam. (Moringaceae) attenuates isoprotrenol-induced cardiac necrosis and oxidative stress in rats: an EPR study.

    Science.gov (United States)

    Panda, Sunanda

    2015-01-01

    The preventive effect of Moringa oleifera polyphenolic fraction (MOPF) on cardiac damage was evaluated in isoproterenol (ISO) induced cardiotoxicity model of Wistar rats. Male rats in different groups were treated with MOPF orally at the dose of 50, 100 and 150 mg/kg/day for 28 days and were subsequently administered (s.c.) with ISO (85 mg/kg body weight) for the last two days. At the end of the experiment levels of serum troponin-T, creatine kinase-MB, lactate dehydrogenase, content of malondialdehyde (MDA), activities/levels of different cellular antioxidants were estimated in control and experimental groups. Additionally, scavenging potential to the hydroxyl radical of the fraction was measured by electron paramagnetic resonance (EPR). ISO administered rats showed significant increase in the levels of serum troponin-I, creatine kinase, lactate dehydrogenase, and heart tissue MDA content. Furthermore, marked reduction in the activities of antioxidants such as superoxide dismutase, catalase, glutathione peroxidase and reduced glutathione levels were observed. EPR study showed an increase in signal intensity in ISO-induced rats. Triphenyl tetrazolium chloride (TTC) staining of heart section revealed a marked increase in infarcted area in ISO-induced rats. Histological features of the heart also indicated a disruption in the structure of cardiac myofibrils in these animals. MOPF (100 mg/kg body weight) pretreatment prevented all these adverse effects of ISO. Present results show that the rich polyphenolic content of Moringa oleifera significantly reduced the myocardial damage and decreased the oxidative stress, possibly through hydroxyl radical scavenging activity as evidenced from the EPR spectra.

  13. Substitutional and surface Mn2+ centers in cubic ZnS:Mn nanocrystals. A correlated EPR and photoluminescence study

    Science.gov (United States)

    Stefan, M.; Nistor, S. V.; Ghica, D.; Mateescu, C. D.; Nikl, M.; Kucerkova, R.

    2011-01-01

    The EPR, radioluminescence, and photoluminescence of cubic ZnS (cZnS) nanocrystals (NCs) with a narrow size distribution centered at 2 nm, doped with 0.1, 0.2, and 0.5at.% Mn2+ ions were investigated. Besides the main lines from substitutional Mn2+ ions localized in the core of the NCs next to a stacking defect, the EPR spectra exhibited two broader hyperfine sextets, attributed to the so-called Mn(II) and Mn(III) surface centers, which could be separated by adequate thermal treatments. The contribution to the photoluminescence from the Mn2+ ions at various sites was further determined from the analysis of the steady-state and time-resolved photoluminescence data from cZnS:Mn NCs subjected to thermal treatments and from cZnS:Mn single crystals. Thus, the main emission consisting of two intense overlapping bands peaking at 596 and 630 nm was attributed to the 4T1-6A1 transition of the substitutional Mn2+ ions in the core of the cZnS nanocrystals and to residual aggregated Mn2+ ions, respectively, the last ones being responsible for a broad EPR line observed in the X-band spectrum. The Mn(II) and Mn(III) centers, consisting of Mn2+ ions in the oxidized and hydrolyzed surface layer of the NCs, respectively, are only indirectly involved in the energy transfer to the substitutional Mn2+ centers, very likely through pairs interaction.

  14. Lattice Studies of Hyperon Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Richards, David G. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

    2016-04-01

    I describe recent progress at studying the spectrum of hadrons containing the strange quark through lattice QCD calculations. I emphasise in particular the richness of the spectrum revealed by lattice studies, with a spectrum of states at least as rich as that of the quark model. I conclude by prospects for future calculations, including in particular the determination of the decay amplitudes for the excited states.

  15. An improved approach to identify irradiated dog feed by electron paramagnetic resonance study and thermoluminescence measurements

    Energy Technology Data Exchange (ETDEWEB)

    Sanyal, Bhaskar, E-mail: bhaskar_sanyal@rediffmail.co [Food Technology Division, Bhabha Atomic Research Centre, Mumbai-400 085 (India); Chawla, S.P.; Sharma, Arun [Food Technology Division, Bhabha Atomic Research Centre, Mumbai-400 085 (India)

    2011-05-15

    In the present study, probably for the first time, a detailed analysis of the radiation induced radical species and thermoluminescence measurements of irradiated dog feed are reported. The EPR spectrum of non-irradiated ready-to-eat dog feed was characterized by singlet g=2.0047{+-}0.0003. Irradiated samples exhibited a complex EPR spectrum. During high power (50.0 mW) EPR spectroscopy, a visible change in the shape of the EPR spectrum was observed and characterized by EPR spectrum simulation technique. An axially symmetric anisotropic signal with g{sub ||}=2.0028 and g{sub perpendicular}=1.9976 was identified. However, a negligible change in the matrix of irradiated edible dog chew was observed using EPR spectroscopy. Therefore, thermoluminescence study of the isolated minerals from dog chew was carried out. The composition of the poly-minerals was studied using SEM and EDX analysis and a complete verdict on identification of irradiation is proposed.

  16. Assessment of an alanine EPR dosimetry technique with enhanced precision and accuracy

    CERN Document Server

    Hayes, R B; Wieser, A; Romanyukha, A A; Hardy, B L; Barrus, J K

    2000-01-01

    Dose reconstruction in the course of a series of blind tests demonstrated that an accuracy of 10 mGy for low doses and 1% for high doses can be achieved using EPR spectroscopy. This was accomplished using a combination of methodologies including polynomial filtration of the EPR spectrum, dosimeter rotation during scanning, use of an EPR standard fixed into the resonator and subtraction of all nonradiogenic signals. Doses were reconstructed over the range of 0.01-1000 Gy using this compound spectral EPR analysis. This EPR technique, being equally applicable to fractionated doses (such as those delivered during multiple radiotherapy treatments), was verified to exhibit dose reciprocity. Irradiated alanine dosimeters which were stored exhibited compound spectral EPR signal fading of ca 3% over 9 months. All error estimates given in this paper are given at the 1 standard deviation level and unless otherwise specified do not account for uncertainties in source calibration.

  17. Quantitative EPR A Practitioners Guide

    CERN Document Server

    Eaton, Gareth R; Barr, David P; Weber, Ralph T

    2010-01-01

    This is the first comprehensive yet practical guide for people who perform quantitative EPR measurements. No existing book provides this level of practical guidance to ensure the successful use of EPR. There is a growing need in both industrial and academic research to provide meaningful and accurate quantitative EPR results. This text discusses the various sample, instrument and software related aspects required for EPR quantitation. Specific topics include: choosing a reference standard, resonator considerations (Q, B1, Bm), power saturation characteristics, sample positioning, and finally, putting all the factors together to obtain an accurate spin concentration of a sample.

  18. Mn7 species with an S = 29/2 ground state: high-frequency EPR studies of a species at the classical/quantum spin interface.

    Science.gov (United States)

    Wang, Zhenxing; van Tol, Johan; Taguchi, Taketo; Daniels, Matthew R; Christou, George; Dalal, Naresh S

    2011-11-09

    A high spin (S) compound has been synthesized whose properties straddle the interface between the classical and quantum mechanical spin descriptions. The cluster [Mn(7)O(4)(pdpm)(6)(N(3))(4)](ClO(4))(2) (Mn(7)) has an unprecedented core structure comprising an octahedral [Mn(III)(6)(μ(4)-O)(μ(3)-O)(3)(μ(3)-N(3))(4)](6+) unit with one of its faces capped by a Mn(II) ion. Magnetization and susceptibility studies indicate an S = (29/2) ground state, the maximum possible. Variable-temperature, high-frequency electron paramagnetic resonance (HF-EPR) spectra on powder and single-crystal samples of Mn(7) exhibit sharp spectral features characteristic of a quantum spin that are well resolved in a certain temperature range but which transform to a continuum of peaks characteristic of a classical spin in another; these features have been well reproduced by computer simulations. A fast Fourier transform analysis of the sharp spectral features and the low temperature EPR spectra suggests that more than one spin state are involved.

  19. Optical and EPR studies of Gd{sub 2}Zr{sub 2}O{sub 7} phosphors prepared via solution combustion method

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Vijay, E-mail: vijayjiin2006@yahoo.com [Department of Chemical Engineering, Konkuk University, Seoul 143-701 (Korea, Republic of); Sivaramaiah, Gobburu [Department of Physics, Government College (M), Kadapa 516004 (India); Rao, J.L. [Department of Physics, Sri Venkateswara University, Tirupati 517502 (India); Hwan Kim, Sang, E-mail: sanghhkim@konkuk.ac.kr [Department of Chemical Engineering, Konkuk University, Seoul 143-701 (Korea, Republic of)

    2013-05-01

    Phosphor powder of Gd{sub 2}Zr{sub 2}O{sub 7} has been prepared by the urea combustion route. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) technique. The structural environment between the Gd{sup 3+} and the zirconium oxide lattice has been investigated using electron paramagnetic resonance (EPR), diffuse reflectance and photoluminescence (PL) studies. The EPR spectrum of Gd{sub 2}Zr{sub 2}O{sub 7} phosphor exhibits a broad and intense signal at g≈2.0 and this has been attributed to Gd{sup 3+} ions in octahedral symmetry with strong dipolar interactions between Gd{sup 3+} ions. The intensity of the spectrum increases with temperature lowering from 296 to 110 K following the usual Boltzmann law. The g value is invariant with temperature variation. The diffuse reflectance spectrum exhibits two sharp and weak bands characteristic of Gd{sup 3+} ions in octahedral symmetry. The photoluminescence spectrum exhibits several bands characteristic of Gd{sup 3+} ions in octahedral symmetry.

  20. Vibrational Spectroscopy in Studies of Atmospheric Corrosion

    Directory of Open Access Journals (Sweden)

    Saman Hosseinpour

    2017-04-01

    Full Text Available Vibrational spectroscopy has been successfully used for decades in studies of the atmospheric corrosion processes, mainly to identify the nature of corrosion products but also to quantify their amounts. In this review article, a summary of the main achievements is presented with focus on how the techniques infrared spectroscopy, Raman spectroscopy, and vibrational sum frequency spectroscopy can be used in the field. Several different studies have been discussed where these instruments have been used to assess both the nature of corrosion products as well as the properties of corrosion inhibitors. Some of these techniques offer the valuable possibility to perform in-situ measurements in real time on ongoing corrosion processes, which allows the kinetics of formation of corrosion products to be studied, and also minimizes the risk of changing the surface properties which may occur during ex-situ experiments. Since corrosion processes often occur heterogeneously over a surface, it is of great importance to obtain a deeper knowledge about atmospheric corrosion phenomena on the nano scale, and this review also discusses novel vibrational microscopy techniques allowing spectra to be acquired with a spatial resolution of 20 nm.

  1. The dynamics of the surface layer of lipid membranes doped by vanadium complex: computer modeling and EPR studies

    Directory of Open Access Journals (Sweden)

    Olchawa Ryszard

    2015-07-01

    Full Text Available Penetration of the liposome membranes doped with vanadium complex formed in the liquid-crystalline phase from egg yolk lecithin (EYL by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl spin probes has been investigated. The penetration process was followed by 360 hours at 24°C, using the electron spin resonance (EPR method. The spectroscopic parameter of the partition (F of this probe indicated that a maximum rigidity of the membrane was at 3% concentration of the vanadium complex. Computer simulations showed that the increase in the rigidity of the membrane corresponds to the closure of gaps in the surface layer of the membrane, and indicates the essential role of the membrane surface in transport processes.

  2. Quantitative analysis of dinuclear manganese(II) EPR spectra.

    Science.gov (United States)

    Golombek, Adina P; Hendrich, Michael P

    2003-11-01

    A quantitative method for the analysis of EPR spectra from dinuclear Mn(II) complexes is presented. The complex [(Me(3)TACN)(2)Mn(II)(2)(mu-OAc)(3)]BPh(4) (1) (Me(3)TACN=N, N('),N(")-trimethyl-1,4,7-triazacyclononane; OAc=acetate(1-); BPh(4)=tetraphenylborate(1-)) was studied with EPR spectroscopy at X- and Q-band frequencies, for both perpendicular and parallel polarizations of the microwave field, and with variable temperature (2-50K). Complex 1 is an antiferromagnetically coupled dimer which shows signals from all excited spin manifolds, S=1 to 5. The spectra were simulated with diagonalization of the full spin Hamiltonian which includes the Zeeman and zero-field splittings of the individual manganese sites within the dimer, the exchange and dipolar coupling between the two manganese sites of the dimer, and the nuclear hyperfine coupling for each manganese ion. All possible transitions for all spin manifolds were simulated, with the intensities determined from the calculated probability of each transition. In addition, the non-uniform broadening of all resonances was quantitatively predicted using a lineshape model based on D- and r-strain. As the temperature is increased from 2K, an 11-line hyperfine pattern characteristic of dinuclear Mn(II) is first observed from the S=3 manifold. D- and r-strain are the dominate broadening effects that determine where the hyperfine pattern will be resolved. A single unique parameter set was found to simulate all spectra arising for all temperatures, microwave frequencies, and microwave modes. The simulations are quantitative, allowing for the first time the determination of species concentrations directly from EPR spectra. Thus, this work describes the first method for the quantitative characterization of EPR spectra of dinuclear manganese centers in model complexes and proteins. The exchange coupling parameter J for complex 1 was determined (J=-1.5+/-0.3 cm(-1); H(ex)=-2JS(1).S(2)) and found to be in agreement with a

  3. Effect of UV irradiation on free radicals in synthetic melanin and melanin biopolymer from Sepia officinalis – EPR examination

    Directory of Open Access Journals (Sweden)

    Zdybel Magdalena

    2015-07-01

    Full Text Available Free radicals in synthetic melanin and melanin from Sepia officinalis were studied by electron paramagnetic resonance (EPR spectroscopy. The effect of time of ultraviolet (UV irradiation on free radicals in these melanins was tested. The samples were exposed to UV during 15, 30, and 60 minutes. EPR spectra were measured with microwaves from an X-band (9.3 GHz in the range of microwave power of 2.2–70 mW. The performed EPR examinations indicate that high concentrations (~1021–1022 spin/g of o-semiquinone free radicals with g factors of 2.0039–2.0045 exist in all the tested samples. For nonirradiated samples, free radical concentration was higher in natural melanin than in synthetic melanin. UV irradiation caused the increase of free radical concentrations in synthetic melanin samples and this effect depends on the time of irradiation. The largest free radical formation in the both melanins was obtained for 60 min of UV irradiation. Free radical concentrations after the UV irradiation of melanins during 30 min were lower than during irradiation by 15 min, and probably this effect was the result of recombination of the radiatively formed free radicals. EPR lines of the tested samples broadened with increasing microwave power, so these lines were homogeneously broadened. The two types of melanins differed in the time of spin-lattice relaxation processes. Slower spin-lattice relaxation processes exist in melanin from Sepia officinalis than in synthetic melanin. UV irradiation did not change the time of spin-lattice relaxation processes in the tested melanins. The performed studies confirmed the usefulness of EPR spectroscopy in cosmetology and medicine.

  4. Electronic structure of a weakly antiferromagnetically coupled Mn(II)Mn(III) model relevant to manganese proteins: a combined EPR, 55Mn-ENDOR, and DFT study.

    Science.gov (United States)

    Cox, Nicholas; Ames, William; Epel, Boris; Kulik, Leonid V; Rapatskiy, Leonid; Neese, Frank; Messinger, Johannes; Wieghardt, Karl; Lubitz, Wolfgang

    2011-09-05

    An analysis of the electronic structure of the [Mn(II)Mn(III)(μ-OH)-(μ-piv)(2)(Me(3)tacn)(2)](ClO(4))(2) (PivOH) complex is reported. It displays features that include: (i) a ground 1/2 spin state; (ii) a small exchange (J) coupling between the two Mn ions; (iii) a mono-μ-hydroxo bridge, bis-μ-carboxylato motif; and (iv) a strongly coupled, terminally bound N ligand to the Mn(III). All of these features are observed in structural models of the oxygen evolving complex (OEC). Multifrequency electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) measurements were performed on this complex, and the resultant spectra simulated using the Spin Hamiltonian formalism. The strong field dependence of the (55)Mn-ENDOR constrains the (55)Mn hyperfine tensors such that a unique solution for the electronic structure can be deduced. Large hyperfine anisotropy is required to reproduce the EPR/ENDOR spectra for both the Mn(II) and Mn(III) ions. The large effective hyperfine tensor anisotropy of the Mn(II), a d(5) ion which usually exhibits small anisotropy, is interpreted within a formalism in which the fine structure tensor of the Mn(III) ion strongly perturbs the zero-field energy levels of the Mn(II)Mn(III) complex. An estimate of the fine structure parameter (d) for the Mn(III) of -4 cm(-1) was made, by assuming the intrinsic anisotropy of the Mn(II) ion is small. The magnitude of the fine structure and intrinsic (onsite) hyperfine tensor of the Mn(III) is consistent with the known coordination environment of the Mn(III) ion as seen from its crystal structure. Broken symmetry density functional theory (DFT) calculations were performed on the crystal structure geometry. DFT values for both the isotropic and the anisotropic components of the onsite (intrinsic) hyperfine tensors match those inferred from the EPR/ENDOR simulations described above, to within 5%. This study demonstrates that DFT calculations provide reliable estimates for spectroscopic

  5. Single crystal EPR studies of paramagnetic ions doped zinc potassium phosphate hexahydrate. Part III: Mn(II)—a case of rhombic distortion

    Science.gov (United States)

    Anandalakshmi, H.; Sougandi, I.; Velavan, K.; Venkatesan, R.; Rao, P. S.

    2004-09-01

    Single crystal electron paramagnetic resonance (EPR) studies of Mn(II) doped zinc potassium phosphate hexahydrate have been carried out at room temperature. Single crystal rotations along the three orthogonal axes indicate orthorhombic symmetry with spin-Hamiltonian parameters as: gxx=1.9997; gyy=1.9538; gzz=1.9524, Dxx=15.49 mT; Dyy=0.22 mT; Dzz=-15.71 mT, Axx=11.70 mT; Ayy=10.53 mT; Azz=10.42 mT and a=0.8×10 -4 cm -1. A large E term indicates considerable distortion from axial symmetry. The impurity is found to enter the lattice substitutionally. The distortion axis for the impurity has been identified along one of the ZnO bond directions in the crystal.

  6. Single crystal EPR studies of paramagnetic ions doped zinc potassium phosphate hexahydrate; Part III: Mn(II)-a case of rhombic distortion.

    Science.gov (United States)

    Anandalakshmi, H; Sougandi, I; Velavan, K; Venkatesan, R; Rao, P S

    2004-09-01

    Single crystal electron paramagnetic resonance (EPR) studies of Mn(II) doped zinc potassium phosphate hexahydrate have been carried out at room temperature. Single crystal rotations along the three orthogonal axes indicate orthorhombic symmetry with spin-Hamiltonian parameters as: g(xx) = 1.9997; g(yy) = 1.9538; g(zz) = 1.9524, D(xx) = 15.49 mT; D(yy) = 0.22 mT; D(zz) = -15.71 mT, A(xx) = 11.70 mT; A(yy) = 10.53 mT; A(zz) = 10.42 mT and a = 0.8 x 10(-4) cm(-1). A large E term indicates considerable distortion from axial symmetry. The impurity is found to enter the lattice substitutionally. The distortion axis for the impurity has been identified along one of the Zn-O bond directions in the crystal.

  7. Structural Characterization of Polymer-Clay Nanocomposites Prepared by Co-Precipitation Using EPR Techniques

    Directory of Open Access Journals (Sweden)

    Udo Kielmann

    2014-02-01

    Full Text Available Polymer-clay nanocomposites (PCNCs containing either a rubber or an acrylate polymer were prepared by drying or co-precipitating polymer latex and nanolayered clay (synthetic and natural suspensions. The interface between the polymer and the clay nanoparticles was studied by electron paramagnetic resonance (EPR techniques by selectively addressing spin probes either to the surfactant layer (labeled stearic acid or the clay surface (labeled catamine. Continuous-wave (CW EPR studies of the surfactant dynamics allow to define a transition temperature T* which was tentatively assigned to the order-disorder transition of the surfactant layer. CW EPR studies of PCNC showed that completely exfoliated nanoparticles coexist with agglomerates. HYSCORE spectroscopy in PCNCs showed couplings within the probe −assigned with DFT computations− and couplings with nuclei of the environment, 1H and 23Na for the surfactant layer probe, and 29Si, 7Li, 19F and 23Na for the clay surface probe. Analysis of these couplings indicates that the integrity of the surfactant layer is conserved and that there are sizeable ionic regions containing sodium ions directly beyond the surfactant layer. Simulations of the very weak couplings demonstrated that the HYSCORE spectra are sensitive to the composition of the clay and whether or not clay platelets stack.

  8. Retrospective dosimetry using EPR and TL techniques: a status report

    Energy Technology Data Exchange (ETDEWEB)

    Haskell, E.H.

    1996-12-31

    Methods of retrospective dosimetry, including luminescence and electron paramagnetic resonance spectroscopy (EPR), rely on measurement of accident dose absorbed by naturally occurring materials - ceramics in the case of both thermoluminescence (TL) and optically stimulated luminescence (OSL) and organic materials and bio- minerals in the case of EPR. Each of these methods relies on measurement of radiation defects resulting from accidental exposure. Since defects also result from natural sources of radiation over the lifetime of a sample, analysis is usually restricted to materials for which the natural dose may be determined and subtracted from the measured cumulative dose. Luminescence dating techniques rely heavily on an accurate assessment of cumulative dose from natural radiation sources, and dating research has provided us with the bulk of our knowledge in this area. Virtually all of the work on natural dose determination can be directly applied to retrospective techniques. With EPR techniques the cumulative dose from diagnostic x- rays is also of importance.

  9. Membrane docking geometry of GRP1 PH domain bound to a target lipid bilayer: an EPR site-directed spin-labeling and relaxation study.

    Directory of Open Access Journals (Sweden)

    Huai-Chun Chen

    Full Text Available The second messenger lipid PIP(3 (phosphatidylinositol-3,4,5-trisphosphate is generated by the lipid kinase PI3K (phosphoinositide-3-kinase in the inner leaflet of the plasma membrane, where it regulates a broad array of cell processes by recruiting multiple signaling proteins containing PIP(3-specific pleckstrin homology (PH domains to the membrane surface. Despite the broad importance of PIP(3-specific PH domains, the membrane docking geometry of a PH domain bound to its target PIP(3 lipid on a bilayer surface has not yet been experimentally determined. The present study employs EPR site-directed spin labeling and relaxation methods to elucidate the membrane docking geometry of GRP1 PH domain bound to bilayer-embedded PIP(3. The model target bilayer contains the neutral background lipid PC and both essential targeting lipids: (i PIP(3 target lipid that provides specificity and affinity, and (ii PS facilitator lipid that enhances the PIP(3 on-rate via an electrostatic search mechanism. The EPR approach measures membrane depth parameters for 18 function-retaining spin labels coupled to the PH domain, and for calibration spin labels coupled to phospholipids. The resulting depth parameters, together with the known high resolution structure of the co-complex between GRP1 PH domain and the PIP(3 headgroup, provide sufficient constraints to define an optimized, self-consistent membrane docking geometry. In this optimized geometry the PH domain engulfs the PIP(3 headgroup with minimal bilayer penetration, yielding the shallowest membrane position yet described for a lipid binding domain. This binding interaction displaces the PIP(3 headgroup from its lowest energy position and orientation in the bilayer, but the headgroup remains within its energetically accessible depth and angular ranges. Finally, the optimized docking geometry explains previous biophysical findings including mutations observed to disrupt membrane binding, and the rapid lateral

  10. Competing interactions and dimensional crossover in (Er{sub 0.5}Y{sub 0.5}){sub 2}Cu{sub 2}O{sub 5} studied by EPR

    Energy Technology Data Exchange (ETDEWEB)

    Typek, J. [Institute of Physics, Szczecin University of Technology, Al. Piastow 17, 70-310 Szczecin (Poland)]. E-mail: typjan@ps.pl

    2007-08-16

    Copper spin dynamics in (Er{sub 0.5}Y{sub 0.5}){sub 2}Cu{sub 2}O{sub 5} solid solution has been investigated by electron paramagnetic resonance (EPR) technique. The temperature dependence of the EPR integrated intensity of the resonance line has showed a pronounced maximum at low temperatures and has vanished at the transition to the antiferromagnetic ordering at T {sub N} = 11 K. The temperature at which the EPR integrated intensity reaches maximum was different for the heating and cooling runs. Study of the product of integrated intensity and temperature has allowed determination of the dominating interactions in a particular temperature range. A model used previously to describe the AFM modes in the antiferromagnetic state of Y{sub 2}Cu{sub 2}O{sub 5} was applied to explain the observed changes in the EPR spectra. A dimensional crossover from 2D to 3D magnetic behaviour was observed at 55 K and interpreted in terms of the spin correlation length.

  11. Magnetic resonance spectroscopy studies in migraine

    Energy Technology Data Exchange (ETDEWEB)

    Montagna, P.; Cortelli, P.; Barbiroli, B. (Inst. of Medical Pathology, Univ. of Bologna (Italy))

    1994-06-01

    The authors describe the method of [sup 31]phosphorus magnetic resonance spectroscopy and review the results when it is applied to the study of brain and muscle energy metabolism in migraine subjects. Brain energy metabolism appears to be abnormal in all major subtypes of migraine when measured both during and between attacks. Impaired energy metabolism is also documented in skeletal muscle. It is suggested that migraine is associated with a generalized disorder of mitochondrial oxidative phosphorylation and that this may constitute a threshold for the triggering of migraine attacks. 47 refs., 10 figs., 3 tabs.

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

    Science.gov (United States)

    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.

  13. Electronic structure of the Mn4OxCa cluster in the S0 and S2 states of the oxygen-evolving complex of photosystem II based on pulse 55Mn-ENDOR and EPR spectroscopy.

    Science.gov (United States)

    Kulik, Leonid V; Epel, Boris; Lubitz, Wolfgang; Messinger, Johannes

    2007-11-07

    The heart of the oxygen-evolving complex (OEC) of photosystem II is a Mn4OxCa cluster that cycles through five different oxidation states (S0 to S4) during the light-driven water-splitting reaction cycle. In this study we interpret the recently obtained 55Mn hyperfine coupling constants of the S0 and S2 states of the OEC [Kulik et al. J. Am. Chem. Soc. 2005, 127, 2392-2393] on the basis of Y-shaped spin-coupling schemes with up to four nonzero exchange coupling constants, J. This analysis rules out the presence of one or more Mn(II) ions in S0 in methanol (3%) containing samples and thereby establishes that the oxidation states of the manganese ions in S0 and S2 are, at 4 K, Mn4(III, III, III, IV) and Mn4(III, IV, IV, IV), respectively. By applying a "structure filter" that is based on the recently reported single-crystal EXAFS data on the Mn4OxCa cluster [Yano et al. Science 2006, 314, 821-825] we (i) show that this new structural model is fully consistent with EPR and 55Mn-ENDOR data, (ii) assign the Mn oxidation states to the individual Mn ions, and (iii) propose that the known shortening of one 2.85 A Mn-Mn distance in S0 to 2.75 A in S1 [Robblee et al. J. Am. Chem. Soc. 2002, 124, 7459-7471] corresponds to a deprotonation of a mu-hydroxo bridge between MnA and MnB, i.e., between the outer Mn and its neighboring Mn of the mu3-oxo bridged moiety of the cluster. We summarize our results in a molecular model for the S0 --> S1 and S1 --> S2 transitions.

  14. EPR in characterization of seeds paramagnetic species

    Energy Technology Data Exchange (ETDEWEB)

    Luiz, A.P.C.; Mauro, M.F.F.L.; Portugal, K.O.; Barbana, V.M.; Guedes, C.L.B.; Mauro, E. di; Carneiro, C.E.A.; Zaia, D.A.M.; Prete, C.E.C. [Universidade Estadual de Londrina (UEL), PR (Brazil)

    2011-07-01

    Full text. In Brazil, since 1970s, renewable fuel programs has been developed in order to replace petroleum. Today a program that has been discussed is the bio diesel, which intend to replace diesel fuel, fossil oil, to bio diesel, renewal fuel. As seeds are the basis for production of oil and consequently processed into bio diesel, the goal of this work is to characterize and compare paramagnetic species present in the seeds by Electron Paramagnetic Resonance (EPR). Samples used in this study were seeds of sorghum, barley, corn, peanuts, soy beans, cotton, wheat, oats, mustard, rice, sunflower and turnip. Some paramagnetic species present in soil was also investigated as goethite (FeOOH), hematite (Fe{sub 2}O{sub 3}), magnetite (Fe{sub 3}O{sub 4}), and ferrihydrite (Fe{sub 5}HO{sub 8} {center_dot} 4H{sub 2}O), since, these species present in appreciable quantities in the soil can be present in the seeds and analyzed for comparison. The characterization of these species is essential to understand the EPR seeds spectra. Each sample is placed in a thin quartz tube 4 mm in diameter, and it is inserted into the cavity of the spectrometer at room temperature, at low temperature (77 K) and variable temperature using liquid nitrogen flow and hot flow through a compressor air. It was used as standard Mg O:Mn{sup 2+}, which is also inserted into the cavity. Shortly after the potency is regulated, frequency, amplitude and sweep the field. The spectroscopic analysis by EPR X-band ({approx} 9:5GHz), were performed at the Fluorescence and Electron Paramagnetic Resonance Laboratory, Exact Sciences Center, State University of Londrina, Parana state, Brazil, through an EPR spectrometer JEOL brand (JES-PE-3X). In the EPR spectra, spectroscopic factor or g factor and line width were determined in paramagnetic species. Studies from several seeds with EPR technique detected in all of them presence of same complex of Fe{sup 3+} present in the goethite at g {approx} 2, and in the seeds

  15. Lorentz symmetry breaking effects on relativistic EPR correlations

    Energy Technology Data Exchange (ETDEWEB)

    Belich, H. [Universidade Federal do Espirito Santo, Departamento de Fisica e Quimica, Vitoria, ES (Brazil); Furtado, C.; Bakke, K. [Universidade Federal da Paraiba, Departamento de Fisica, Caixa Postal 5008, Joao Pessoa, PB (Brazil)

    2015-09-15

    Lorentz symmetry breaking effects on relativistic EPR (Einstein-Podolsky-Rosen) correlations are discussed. From the modified Maxwell theory coupled to gravity, we establish a possible scenario of the Lorentz symmetry violation and write an effective metric for the Minkowski spacetime. Then we obtain the Wigner rotation angle via the Fermi-Walker transport of spinors and consider the WKB (Wentzel-Kramers-Brillouin) approximation in order to study the influence of Lorentz symmetry breaking effects on the relativistic EPR correlations. (orig.)

  16. Detection of nanodiamonds in biological samples by EPR spectrometry.

    Science.gov (United States)

    Inzhevatkin, E V; Baron, A V; Maksimov, N G; Volkova, M B; Puzyr, A P; Bondar, V S

    2017-11-01

    In model experiments in vitro, the applicability of the EPR spectrometry method for the detection of modified nanodiamonds (MNDs) in blood and homogenates of mouse organs has been established. A characteristic signal (g = 2.003, ΔH ≈ 10 G) is observed in the samples of biomaterials containing MNDs, the intensity of which increases linearly with the concentration of nanoparticles in the range of 1.6-200 μg MNDs per 1 mL of the sample. The EPR method in biomaterials reveals the presence of intrinsic paramagnetic centers, signals from which are superimposed on the signal from the MNDs. However, the intensity of these signals is small, which makes it possible to register the MNDs using EPR spectrometry with the necessary accuracy. The data obtained open up the prospects of using the EPR method for studies of the interorgan distribution, accumulation, and elimination of MNDs during their intravenous injection into experimental animals.

  17. Surface studies of praseodymium by electron spectroscopies

    Science.gov (United States)

    Krawczyk, Mirosław; Pisarek, Marcin; Lisowski, Wojciech; Jablonski, Aleksander

    2016-12-01

    Electron transport properties in praseodymium (Pr) foil samples were studied by elastic-peak electron spectroscopy (EPES). Prior to EPES measurements, the Pr sample surface was pre-sputtered by Ar ions with ion energy of 2-3 keV. After such treatment, the Pr sample still contained about 10 at.% of residual oxygen in the surface region, as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses. The inelastic mean free path (IMFP), characterizing electron transport within this region (4 nm-thick), was evaluated from EPES using both Ni and Au standards as a function of energy in the range of 0.5-2 keV. Experimental IMFPs, λ, were approximated by the simple function λ = kEp, where E is energy (in eV), and k = 0.1549 and p = 0.7047 were the fitted parameters. These values were compared with IMFPs for the praseodymium surface in which the presence of oxygen was tentatively neglected, and also with IMFPs resulting from the TPP-2M predictive equation for bulk praseodymium. We found that the measured IMFP values to be only slightly affected by neglect of oxygen in calculations. The fitted function applied here was consistent with the energy dependence of the EPES-measured IMFPs. Additionally, the measured IMFPs were found to be from 2% to 4.2% larger than the predicted IMFPs for praseodymium in the energy range of 500-1000 eV. For electron energies of 1500 eV and 2000 eV, there was an inverse correlation between these values, and then the resulting deviations of -0.4% and -2.7%, respectively, were calculated.

  18. Spectroscopy

    CERN Document Server

    Walker, S

    1976-01-01

    The three volumes of Spectroscopy constitute the one comprehensive text available on the principles, practice and applications of spectroscopy. By giving full accounts of those spectroscopic techniques only recently introduced into student courses - such as Mössbauer spectroscopy and photoelectron spectroscopy - in addition to those techniques long recognised as being essential in chemistry teaching - sucha as e.s.r. and infrared spectroscopy - the book caters for the complete requirements of undergraduate students and at the same time provides a sound introduction to special topics for graduate students.

  19. EPR investigation of some desiccated Ascomycota and Basidiomycota gamma-irradiated mushrooms

    Energy Technology Data Exchange (ETDEWEB)

    Bercu, V., E-mail: vbercu@gmail.co [University of Bucharest, Department of Atomic and Nuclear Physics, P.O. Box MG-11, 077125 Magurele (Ilfov) (Romania); Negut, C.D., E-mail: dnegut@nipne.r [University of Bucharest, Department of Atomic and Nuclear Physics, P.O. Box MG-11, 077125 Magurele (Ilfov) (Romania); Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Magurele (Ilfov) (Romania); Duliu, O.G., E-mail: duliu@b.astral.r [University of Bucharest, Department of Atomic and Nuclear Physics, P.O. Box MG-11, 077125 Magurele (Ilfov) (Romania)

    2010-12-15

    The suitability of the EPR spectroscopy for detection of {gamma}-irradiation in five species of dried mushroom, currently used in gastronomy: yellow morel-Morchella esculenta, (L.) Pers. (Phylum Ascomycota), button mushroom-Agaricus bisporus (J.E.Lange), Agaricus haemorrhoidarius Fr., golden chantarelle-Cantharellus cibarius Fr., as well as oyster mushroom-Pleurotus ostreatus (Jacq. ex Fr.) (Phylum Basidiomycota) is presented and discussed. Although after irradiation at doses up to 11 kGy, all specimens presented well defined EPR spectra, only A. bisporus EPR signal was enough stable to make detection possible after 18 months.

  20. EPR investigation of some desiccated Ascomycota and Basidiomycota gamma-irradiated mushrooms

    Science.gov (United States)

    Bercu, V.; Negut, C. D.; Duliu, O. G.

    2010-12-01

    The suitability of the EPR spectroscopy for detection of γ-irradiation in five species of dried mushroom, currently used in gastronomy: yellow morel— Morchella esculenta, (L.) Pers. (Phylum Ascomycota), button mushroom— Agaricus bisporus (J.E.Lange), Agaricus haemorrhoidarius Fr., golden chantarelle— Cantharellus cibarius Fr., as well as oyster mushroom— Pleurotus ostreatus (Jacq. ex Fr.) (Phylum Basidiomycota) is presented and discussed. Although after irradiation at doses up to 11 kGy, all specimens presented well defined EPR spectra, only A. bisporus EPR signal was enough stable to make detection possible after 18 months.

  1. Corrosion Study Using Electrochemical Impedance Spectroscopy

    Science.gov (United States)

    Farooq, Muhammad Umar

    2003-01-01

    Corrosion is a common phenomenon. It is the destructive result of chemical reaction between a metal or metal alloy and its environment. Stainless steel tubing is used at Kennedy Space Center for various supply lines which service the orbiter. The launch pads are also made of stainless steel. The environment at the launch site has very high chloride content due to the proximity to the Atlantic Ocean. Also, during a launch, the exhaust products in the solid rocket boosters include concentrated hydrogen chloride. The purpose of this project was to study various alloys by Electrochemical Impedance Spectroscopy in corrosive environments similar to the launch sites. This report includes data and analysis of the measurements for 304L, 254SMO and AL-6XN in primarily neutral 3.55% NaCl. One set of data for 304L in neutral 3.55%NaCl + 0.1N HCl is also included.

  2. Surface studies of praseodymium by electron spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    Krawczyk, Mirosław, E-mail: mkrawczyk@ichf.edu.pl; Pisarek, Marcin; Lisowski, Wojciech; Jablonski, Aleksander

    2016-12-01

    Highlights: • Pr foil. • EPES applied to measure the IMFPs in Pr samples after 3 keV Ar{sup +} ion etching. • Etched surfaces found to be formed by oxygen-containing Pr. • Measured IMFPs for E = 0.5–2 keV were approximated by Eq. (2). • The IMFPs were slightly affected by oxygen and agreed well with those from Eq. (3). - Abstract: Electron transport properties in praseodymium (Pr) foil samples were studied by elastic-peak electron spectroscopy (EPES). Prior to EPES measurements, the Pr sample surface was pre-sputtered by Ar ions with ion energy of 2–3 keV. After such treatment, the Pr sample still contained about 10 at.% of residual oxygen in the surface region, as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses. The inelastic mean free path (IMFP), characterizing electron transport within this region (4 nm-thick), was evaluated from EPES using both Ni and Au standards as a function of energy in the range of 0.5–2 keV. Experimental IMFPs, λ, were approximated by the simple function λ = kE{sup p}, where E is energy (in eV), and k = 0.1549 and p = 0.7047 were the fitted parameters. These values were compared with IMFPs for the praseodymium surface in which the presence of oxygen was tentatively neglected, and also with IMFPs resulting from the TPP-2M predictive equation for bulk praseodymium. We found that the measured IMFP values to be only slightly affected by neglect of oxygen in calculations. The fitted function applied here was consistent with the energy dependence of the EPES-measured IMFPs. Additionally, the measured IMFPs were found to be from 2% to 4.2% larger than the predicted IMFPs for praseodymium in the energy range of 500–1000 eV. For electron energies of 1500 eV and 2000 eV, there was an inverse correlation between these values, and then the resulting deviations of −0.4% and −2.7%, respectively, were calculated.

  3. Enzymatic and cryoreduction EPR studies of the hydroxylation of methylated N(ω)-hydroxy-L-arginine analogues by nitric oxide synthase from Geobacillus stearothermophilus.

    Science.gov (United States)

    Davydov, Roman; Labby, Kristin Jansen; Chobot, Sarah E; Lukoyanov, Dmitriy A; Crane, Brian R; Silverman, Richard B; Hoffman, Brian M

    2014-10-21

    Nitric oxide synthase (NOS) catalyzes the conversion of L-arginine to L-citrulline and NO in a two-step process involving the intermediate N(ω)-hydroxy-L-arginine (NHA). It was shown that Cpd I is the oxygenating species for L-arginine; the hydroperoxo ferric intermediate is the reactive intermediate with NHA. Methylation of the N(ω)-OH and N(ω)-H of NHA significantly inhibits the conversion of NHA into NO and L-citrulline by mammalian NOS. Kinetic studies now show that N(ω)-methylation of NHA has a qualitatively similar effect on H₂O₂-dependent catalysis by bacterial gsNOS. To elucidate the effect of methylating N(ω)-hydroxy L-arginine on the properties and reactivity of the one-electron-reduced oxy-heme center of NOS, we have applied cryoreduction/annealing/EPR/ENDOR techniques. Measurements of solvent kinetic isotope effects during 160 K cryoannealing cryoreduced oxy-gsNOS/NHA confirm the hydroperoxo ferric intermediate as the catalytically active species of step two. Product analysis for cryoreduced samples with methylated NHA's, NHMA, NMOA, and NMMA, annealed to 273 K, show a correlation of yields of L-citrulline with the intensity of the g 2.26 EPR signal of the peroxo ferric species trapped at 77 K, which converts to the reactive hydroperoxo ferric state. There is also a correlation between the yield of L-citrulline in these experiments and k(obs) for the H₂O₂-dependent conversion of the substrates by gsNOS. Correspondingly, no detectable amount of cyanoornithine, formed when Cpd I is the reactive species, was found in the samples. Methylation of the NHA guanidinium N(ω)-OH and N(ω)-H inhibits the second NO-producing reaction by favoring protonation of the ferric-peroxo to form unreactive conformers of the ferric-hydroperoxo state. It is suggested that this is caused by modification of the distal-pocket hydrogen-bonding network of oxy gsNOS and introduction of an ordered water molecule that facilitates delivery of the proton(s) to the one

  4. EPR-Spin Trapping and Flow Cytometric Studies of Free Radicals Generated Using Cold Atmospheric Argon Plasma and X-Ray Irradiation in Aqueous Solutions and Intracellular Milieu.

    Science.gov (United States)

    Uchiyama, Hidefumi; Zhao, Qing-Li; Hassan, Mariame Ali; Andocs, Gabor; Nojima, Nobuyuki; Takeda, Keigo; Ishikawa, Kenji; Hori, Masaru; Kondo, Takashi

    2015-01-01

    Electron paramagnetic resonance (EPR)-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP) in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH) radicals and hydrogen (H) atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO), and phenyl N-t-butylnitrone (PBN). The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H2O2, which is the recombination product of ·OH, and OCl- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and an

  5. EPR-Spin Trapping and Flow Cytometric Studies of Free Radicals Generated Using Cold Atmospheric Argon Plasma and X-Ray Irradiation in Aqueous Solutions and Intracellular Milieu.

    Directory of Open Access Journals (Sweden)

    Hidefumi Uchiyama

    Full Text Available Electron paramagnetic resonance (EPR-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH radicals and hydrogen (H atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO, 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO, and phenyl N-t-butylnitrone (PBN. The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H2O2, which is the recombination product of ·OH, and OCl- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and

  6. EPR studies of the vitamin K 1 semiquinone radical anion. Comparison to the electron acceptor A 1 in green plant photosystem I

    Science.gov (United States)

    Thurnauer, Marion C.; Brown, James W.; Gast, P.; Feezel, Laura L.

    Suggestions that the electron acceptor, A 1, in Photosystem I is a quinone have come from both optical and epr experiments. Vitamin K 1 (phylloquinone) is present in the PSI complex with a stoichiometry of two molecules per reaction center. In order to determine if A 1 can be identified with vitamin K 1, X-band and Q-band epr properties of the vitamin K 1 radical anion in frozen alcohol solutions are examined. The results are compared to the epr properties that have been observed for the reduced A 1 acceptor in vivo. The g-values obtained for the vitamin K 1 radical anion are consistent with identifying A 1 with vitamin K 1.

  7. Detection and characterisation of radicals using electron paramagnetic resonance (EPR) spin trapping and related methods

    DEFF Research Database (Denmark)

    Davies, Michael Jonathan

    2016-01-01

    Electron paramagnetic resonance (EPR) spectroscopy (also known as electron spin resonance, ESR, or electron magnetic resonance, EMR, spectroscopy) is often described as the “gold standard” for the detection and characterisation of radicals in chemical, biological and medical systems. The article...

  8. Alternative chitosan-based EPR dosimeter applicable for a relatively wide range of gamma radiation doses

    Science.gov (United States)

    Piroonpan, Thananchai; Katemake, Pichayada; Panritdam, Eagkapong; Pasanphan, Wanvimol

    2017-12-01

    Chitosan biopolymer is proposed as an alternative EPR dosimeter. Its ability to be EPR dosimeter was studied in comparison with the conventional alanine, sugars (i.e., glucose and sucrose), formate derivatives (i.e., lithium (Li), magnesium (Mg), and calcium (Ca) formate). Ethylene vinyl acetate (EVA) and paraffin were used as binder for the preparation of composite EPR dosimeter. Dose responses of all materials were investigated in a wide dose range of radiation doses, i.e., low-level (0-1 kGy), medium-level (1-10 kGy) and high-level (10-100 kGy). The EPR dosimeter properties were studied under different parameters, i.e., microwave power, materials contents, absorbed doses, storage conditions and post-irradiation effects. Li-formate showed a simple EPR spectrum and exhibited superior radiation response for low-dose range; whereas chitosan and sucrose exhibited linear dose response in all studied dose ranges. The EPR signals of chitosan exhibited similar stability as glucose, Li-formate and alanine at ambient temperature after irradiation as long as a year. All EPR signals of the studied materials were affected post-irradiation temperature and humidity after gamma irradiation. The EPR signal of chitosan exhibited long-term stability and it was not sensitive to high storage temperatures and humidity values after irradiation. Chitosan has a good merit as the alternative bio-based material for a stable EPR dosimeter in a wide range of radiation-absorbed doses.

  9. Study of EPR, optical properties and electrical conductivity of vanadyl doped Bi2O3.PbO.B2O3 glasses.

    Science.gov (United States)

    Gahlot, P S; Agarwal, A; Seth, V P; Sanghi, S; Gupta, S K; Arora, M

    2005-04-01

    Heavy metal based oxide glasses having composition xBi(2)O(3).(0.30 - x)PbO.0.70B(2)O(3) have been prepared (0.00 melt-quenching technique. Electron paramagnetic resonance (EPR), optical spectra and dc conductivity of these glasses have been studied. Spin Hamiltonian parameters (SHP) of VO(2+) ions, dipolar hyperfine parameter, P and Fermi contact interaction parameter, K, molecular orbital coefficients (alpha(2) and gamma(2)) and optical band gap have been calculated. It is observed that in these glasses, the tetragonal nature of V(4+)O(6) complex increases with Bi(2)O(3) content. Increase in Bi(2)O(3):PbO ratio results in the contraction of 3d(xy) orbit of the unpaired electron in the vanadium ion, and the SHP are dependent on the theoretical optical basicity, Lambda(th). In present glasses, the conductivity (activation energy) first decreases (increases) with increase in mol% of Bi(2)O(3) content upto x = 0.08 and then shows a maxima (minima) at x = 0.10 and then starts decreasing (increasing) upto x < or = 0.15 with mol% of Bi(2)O(3) content.

  10. Effect of temperature on thermal oxidation of palmitic acid studied by combination of EPR spin trapping technique and SPME-GC-MS/MS.

    Science.gov (United States)

    Chen, Hongjian; Wang, Yong; Cao, Peirang; Liu, Yuanfa

    2017-11-01

    Effect of temperatures on thermal oxidation of palmitic acid was studied by the combination of EPR and GC-MS/MS. DMPO was used as the spin trap. The experimental spectrum was simulated with alkyl and alkoxyl spin adducts. Total amount of spins, a parameter to indicate radical concentrations, detected at 180°C was nearly 10 times higher than that at 175°C. Besides, total amounts of spins detected at 180°C decreased rapidly because of the reaction between radical adducts and newly formed radicals. Signal intensities of alkyl radical adducts increased rapidly from 0.405 to 4.785 from 175°C to 180°C. Besides, more palmitic acid degraded to oxidized compounds from 175°C to 180°C than that of other temperature ranges. The C-C linkages between carbons 2 to 6 were easier to be oxidized at 180°C. The results all implied that oxidation rates of palmitic acid samples increased rapidly from 175°C to 180°C. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. EPR: the nuclear impasse; EPR: l'impasse nucleaire

    Energy Technology Data Exchange (ETDEWEB)

    Marillier, F. [Association Ecologiste Greenpeace (France)

    2008-07-01

    The questions relative to the climatic change constitute crucial challenges for the next ten years. In this context the author aims to show how the EPR project illustrates the nuclear french ''autism''. He presents and analyzes the international and environmental impacts of this obsolete technology, as a project useless and dangerous. (A.L.B.)

  12. 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.

    Science.gov (United States)

    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 (PPh4)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-: (PPh4)2[Co(SPh)4] (1) and (NEt4)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.

  13. A variable temperature EPR study of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) single crystal at 170 GHz: zero-field splitting parameter and its absolute sign.

    Science.gov (United States)

    Misra, Sushil K; Andronenko, Serguei I; Chand, Prem; Earle, Keith A; Paschenko, Sergei V; Freed, Jack H

    2005-06-01

    EPR measurements have been carried out on a single crystal of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) at 170-GHz in the temperature range of 312-4.2K. The spectra have been analyzed (i) to estimate the spin-Hamiltonian parameters; (ii) to study the temperature variation of the zero-field splitting (ZFS) parameter; (iii) to confirm the negative absolute sign of the ZFS parameter unequivocally from the temperature-dependent relative intensities of hyperfine sextets at temperatures below 10K; and (iv) to detect the occurrence of a structural phase transition at 4.35K from the change in the structure of the EPR lines with temperature below 10K.

  14. Research on EPR measurement methods of sucrose used in radiation accident dose reconstruction.

    Science.gov (United States)

    Ding, Yanqiu; Jiao, Ling; Zhang, Wenyi; Zhou, Li; Zhang, Xiaodong; Zhang, Liang'an

    2010-03-01

    Sucrose is a convenient, common, tissue-equivalent material suitable for electron paramagnetic resonance (EPR) dosimetry of ionising radiation. A number of publications have reported on the dosimetric properties of sucrose and their use in radiation accident dose reconstruction. However, previous studies did not include specially the description of measurement methods of sucrose by EPR. The aim of this work is to introduce particularly the EPR measurement methods of sucrose. In this regard, practical considerations of sample size, microwave power, modulation amplitude, EPR spectrum and signal stability are discussed.

  15. Study of clusters using negative ion photodetachment spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Yuexing [Univ. of California, Berkeley, CA (United States)

    1995-12-01

    The weak van der Waals interaction between an open-shell halogen atom and a closed-shell atom or molecule has been investigated using zero electron kinetic energy (ZEKE) spectroscopy. This technique is also applied to study the low-lying electronic states in GaAs and GaAs-. In addition, the spectroscopy and electron detachment dynamics of several small carbon cluster anions are studied using resonant multiphoton detachment spectroscopy.

  16. Characterization of Cu-exchanged SSZ-13: a comparative FTIR, UV-Vis, and EPR study with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios.

    Science.gov (United States)

    Giordanino, Filippo; Vennestrøm, Peter N R; Lundegaard, Lars F; Stappen, Frederick N; Mossin, Susanne; Beato, Pablo; Bordiga, Silvia; Lamberti, Carlo

    2013-09-21

    Cu-SSZ-13 has been characterized by different spectroscopic techniques and compared with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios and prepared by the same ion exchange procedure. On vacuum activated samples, low temperature FTIR spectroscopy allowed us to appreciate a high concentration of reduced copper centres, i.e. isolated Cu(+) ions located in different environments, able to form Cu(+)(N2), Cu(+)(CO)n (n = 1, 2, 3), and Cu(+)(NO)n (n = 1, 2) upon interaction with N2, CO and NO probe molecules, respectively. Low temperature FTIR, DRUV-Vis and EPR analysis on O2 activated samples revealed the presence of different Cu(2+) species. New data and discussion are devoted to (i) [Cu-OH](+) species likely balanced by one framework Al atom; (ii) mono(μ-oxo)dicopper [Cu2(μ-O)](2+) dimers observed in Cu-ZSM-5 and Cu-β, but not in Cu-SSZ-13. UV-Vis-NIR spectra of O2 activated samples reveal an intense and finely structured d-d quadruplet, unique to Cu-SSZ-13, which is persistent under SCR conditions. This differs from the 22,700 cm(-1) band of the mono(μ-oxo)dicopper species of the O2 activated Cu-ZSM-5, which disappears under SCR conditions. The EPR signal intensity sets Cu-β apart from the others.

  17. Spectroscopy

    DEFF Research Database (Denmark)

    Berg, Rolf W.

    This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules.......This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules....

  18. EPR studies of the water oxidizing complex in the S1 and the higher S states: the manganese cluster and Y(Z) radical.

    Science.gov (United States)

    Mino, H; Kawamori, A

    2001-01-05

    The parallel polarization electron paramagnetic resonance (EPR) method has been applied to investigate manganese EPR signals of native S1 and S3 states of the water oxidizing complex (WOC) in photosystem (PS) II. The EPR signals in both states were assigned to thermally excited states with S=1, from which zero-field interaction parameters D and E were derived. Three kinds of signals, the doublet signal, the singlet-like signal and g=11-15 signal, were detected in Ca2+-depleted PS II. The g=11-15 signal was observed by parallel and perpendicular modes and assigned to a higher oxidation state beyond S2 in Ca2+-depleted PS II. The singlet-like signal was associated with the g=11-15 signal but not with the Y(Z) (the tyrosine residue 161 of the D1 polypeptide in PS II) radical. The doublet signal was associated with the Y(Z) radical as proved by pulsed electron nuclear double resonance (ENDOR) and ENDOR-induced EPR. The electron transfer mechanism relevant to the role of Y(Z) radical was discussed.

  19. The Crystal Structure of Micro- and Nanopowders of ZnS Studied by EPR of Mn^sup 2+^ and XRD

    National Research Council Canada - National Science Library

    Valentyna Nosenko; Igor Vorona; Valentyn Grachev; Stanislav Ishchenko; Nikolai Baran; Yurii Becherikov; Anton Zhuk; Yuliya Polishchuk; Vasyl Kladko; Alexander Selishchev

    2016-01-01

      The crystal structure of micro- and nanopowders of ZnS doped with different impurities was analyzed by the electron paramagnetic resonance (EPR) of Mn2+ and XRD methods. The powders of ZnS:Cu, ZnS:Mn, ZnS:Co...

  20. Synthesis, X-ray crystal structure, and EPR study of [Na(H 2O) 2] 2[VO(H 2O) 5][SiW 12O 40]·4H 2O

    Science.gov (United States)

    Tézé, André; Marchal-Roch, Catherine; So, Hyunsoo; Fournier, Michel; Hervé, Gilbert

    2001-03-01

    The vanadyl salt [Na(H 2O) 2] 2[VO(H 2O) 5][SiW 12O 40]·4H 2O has been synthesized in mild conditions by cationic exchanges from dodecasilicotungstic acid. Structural determination and EPR study have been achieved on single crystals. They are tetragonal, space group P4/ n with a=14.7759(1), c=10.4709(2) Å, V=2286(1) Å 3 and Z=2. A three-dimensional framework built from Keggin anions [SiW 12O 40] 4- linked by sodium cations in (110) and ( 1 1¯0 ) planes generates channels along the c axis in which are localized aquo vanadyl complexes [VO(H 2O) 5] 2+ and water molecules. Single crystal EPR spectra show eight hyperfine lines of the vanadium atom ( I=7/2) which are split into 1:2:1 pattern when the magnetic field is parallel to the c axis. The triplet pattern may be attributed to weak dipolar interactions between the nearest-neighbor vanadium atoms which are 10.47 Å apart in the infinite chain. A ring model was used to simulate the spectrum, and a very small antiferromagnetic exchange interaction was determined accurately . The EPR parameters determined are gx= gy=1.980, gz=1.9336, Ax= Ay=0.0072 cm -1, and Az=0.01805 cm -1, J=-0.00025 cm -1.

  1. EPR spectral investigation of radiation-induced radicals of gallic acid

    Energy Technology Data Exchange (ETDEWEB)

    Tuner, Hasan [Balikesir University, Department of Physics, Faculty of Art and Science, Balikesir (Turkey)

    2017-11-15

    In the present work, spectroscopic features of the radiation-induced radicals of gallic acid compounds were investigated using electron paramagnetic resonance (EPR) spectroscopy. While un-irradiated samples presented no EPR signal, irradiated samples exhibited an EPR spectrum consisting of an intense resonance line at the center and weak lines on both sides. Detailed microwave saturation investigations were carried out to determine the origin of the experimental EPR lines. It is concluded that the two side lines of the triplet satellite originate from forbidden ''spin-flip'' transitions. The spectroscopic and structural features of the radiation-induced radicals were determined using EPR spectrum fittings. The experimental EPR spectra of the two gallic acid compounds were consistent with the calculated EPR spectroscopic features of the proposed radicals. It is concluded that the most probable radicals are the cyclohexadienyl-type, O(OH){sub 2}C{sub 6}H{sub 2}COOH radicals for both compounds. (orig.)

  2. Study of melanoma invasion by FTIR spectroscopy

    Science.gov (United States)

    Yang, Y.; Sulé-Suso, J.; Sockalingum, G. D.

    2008-02-01

    Compared to other forms of skin cancer, a malignant melanoma has a high risk of spreading to other parts of the body. Melanoma invasion is a complex process involving changes in cell-extracellular matrix (ECM) interaction and cell-cell interactions. To fully understand the factors which control the invasion process, a human skin model system was reconstructed. HBL (a commercially available cell line) melanoma cells were seeded on a skin model with and without the presence of keratinocytes and/or fibroblasts. After 14 days culture, the skin specimens were fixed, parafin embedded and cut into 7 µm sections. The de-parafinised sections were investigated by synchrotron Fourier transformed infrared (FTIR) microspectroscopy to study skin cell invasion behaviour. The advantage of using FTIR is its ability to obtain the fingerprint information of the invading cells in terms of protein secondary structure in comparison to non-invading cells and the concentration of the enzyme (matrix-metalloproteinase) which digests protein matrix, near the invading cells. With aid of the spectral mapping images, it is possible to pinpoint the cells in non-invasion and invasion area and analyse the respective spectra. It has been observed that the protein bands in cells and matrix shifted between non-invasive and invasive cells in the reconstructed skin model. We hypothesise that by careful analysis of the FTIR data and validation by other models, FTIR studies can reveal information on which type of cells and proteins are involved in melanoma invasion. Thus, it is possible to trace the cell invasion path by mapping the spectra along the interface of cell layer and matrix body by FTIR spectroscopy.

  3. Mössbauer, EPR, and magnetic susceptibility studies on members of a new family of cyano-bridged 3d-4f complexes. Demonstration of anisotropic exchange in a Fe-Gd complex

    Science.gov (United States)

    Stoian, Sebastian A.; Paraschiv, Carmen; Kiritsakas, Nathalie; Lloret, Francesc; Münck, Eckard; Bominaar, Emile L.; Andruh, Marius

    2010-01-01

    The synthesis and crystallographic characterization of a new family of M(μ-CN)Ln complexes are reported. Two structural series have been prepared by reacting in water rare earth nitrates (LnIII = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho) with K3[M(CN)6] (MIII = Fe, Co) in the presence of hexamethylenetetramine (hmt). The first series consists of six isomorphous heterobinuclear complexes, [(CN)5M-CNLn(H2O)8]·2hmt ([FeLa] 1, [FePr] 2, [FeNd] 3, [FeSm] 4, [FeEu] 5, [FeGd] 6), while the second series consists of four isostructural ionic complexes, [Ln(H2O)8][M(CN)6]·hmt ([FeDy] 7, [FeHo] 8, [CoEu] 9, [CoGd] 10). The hexamethylenetetramine molecules contribute to the stabilization of the crystals by participating in an extended network of hydrogen bond interactions. In both series the aqua ligands are hydrogen bonded to the nitrogen atoms from both the terminal CN groups and the hmt molecules. The [FeGd] complex has been analyzed with 57Fe Mössbauer spectroscopy, EPR, and magnetic susceptibility measurements. We have also analyzed the [FeLa] complex, in which the paramagnetic GdIII is replaced by diamagnetic LaIII, to obtain information about the low-spin FeIII site that is not accessible in the presence of a paramagnetic ion at the complementary site. For the same reason, the [CoGd] complex, containing diamagnetic CoIII, was studied with EPR and magnetic susceptibility measurements, which confirmed the S = 7/2 spin of GdIII. Prior knowledge about the paramagnetic sites in [FeGd] allows a detailed analysis of the exchange interactions between them. In particular, the question of whether the exchange interaction in [FeGd] is isotropic or anisotropic has been addressed. Standard variable-temperature magnetic susceptibility measurements provide only the value for a linear combination of Jx, Jy, and Jz but contain no information about the values of the individual exchange parameters Jx, Jy, and Jz. In contrast, the spin-Hamiltonian analysis of the variable-field, variable

  4. Analysis of EPR and FISH studies of radiation doses in persons who lived in the upper reaches of the Techa River

    Energy Technology Data Exchange (ETDEWEB)

    Degteva, M.O.; Shagina, N.B.; Shishkina, E.A.; Vozilova, A.V.; Volchkova, A.Y.; Vorobiova, M.I. [Urals Research Center for Radiation Medicine, Chelyabinsk (Russian Federation); Wieser, A. [Helmholtz Centrum Munich, Neuherberg (Germany); Fattibene, P.; Della Monaca, S. [Instituto Superiore di Sanita, Rome (Italy); Ainsbury, E.; Moquet, J. [Public Health England, Chilton, Didcot (United Kingdom); Anspaugh, L.R. [University of Utah, Salt Lake City, UT (United States); Napier, B.A. [Pacific Northwest National Laboratory, Richland, WA (United States)

    2015-11-15

    Waterborne radioactive releases into the Techa River from the Mayak Production Association in Russia during 1949-1956 resulted in significant doses to about 30,000 persons who lived in downstream settlements. The residents were exposed to internal and external radiation. Two methods for reconstruction of the external dose are considered in this paper, electron paramagnetic resonance (EPR) measurements of teeth, and fluorescence in situ hybridization (FISH) measurements of chromosome translocations in circulating lymphocytes. The main issue in the application of the EPR and FISH methods for reconstruction of the external dose for the Techa Riverside residents was strontium radioisotopes incorporated in teeth and bones that act as a source of confounding local exposures. In order to estimate and subtract doses from incorporated {sup 89,90}Sr, the EPR and FISH assays were supported by measurements of {sup 90}Sr-body burdens and estimates of {sup 90}Sr concentrations in dental tissues by the luminescence method. The resulting dose estimates derived from EPR to FISH measurements for residents of the upper Techa River were found to be consistent: The mean values vary from 510 to 550 mGy for the villages located close to the site of radioactive release to 130-160 mGy for the more distant villages. The upper bound of individual estimates for both methods is equal to 2.2-2.3 Gy. The EPR- and FISH-based dose estimates were compared with the doses calculated for the donors using the most recent Techa River Dosimetry System (TRDS). The TRDS external dose assessments are based on the data on contamination of the Techa River floodplain, simulation of air kerma above the contaminated soil, age-dependent lifestyles and individual residence histories. For correct comparison, TRDS-based doses were calculated from two sources: external exposure from the contaminated environment and internal exposure from {sup 137}Cs incorporated in donors' soft tissues. It is shown here that the

  5. ANALYSIS OF EPR AND FISH STUDIES OF RADIATION DOSES IN PERSONS WHO LIVED IN THE UPPER REACHES OF THE TECHA RIVER

    Energy Technology Data Exchange (ETDEWEB)

    Degteva, M. O.; Shagina, N. B.; Shishkina, Elena A.; Vozilova, Alexandra; Volchkova, A. Y.; Vorobiova, M. I.; Wieser, Albrecht; Fattibene, Paola; Della Monaca, S.; Ainsbury, E.; Moquet, J.; Anspaugh, L. R.; Napier, Bruce A.

    2015-07-24

    Waterborne radioactive releases into the Techa River from the Mayak Production Association in Russia during 1949–1956 resulted in significant doses to about 30,000 persons who lived in downstream settlements. The residents were exposed to internal and external radiation. Two methods for reconstruction of the external dose are considered in this paper, electron paramagnetic resonance (EPR) measurements of teeth and fluorescence in situ hybridization (FISH) measurements of chromosome translocations in circulating lymphocytes. The main issue in the application of the EPR and FISH methods for reconstruction of the external dose for the Techa Riverside residents was strontium radioisotopes incorporated in teeth and bones that served as a source of confounding local exposures. In order to estimate and subtract doses from incorporated 89,90Sr, the EPR and FISH assays were supported by measurements of 90Sr-body burdens and estimates of 90Sr concentrations in dental tissues by the luminescence method. The resulting dose estimates derived from EPR and FISH measurements for residents of the upper Techa River were found to be consistent: the mean values vary from 510 – 550 mGy for the villages located close to the site of radioactive release to 130 – 160 mGy for the more distant villages. The upper bound of individual estimates for both methods is equal to 2.2 – 2.3 Gy. The EPR- and FISH-based dose estimates were compared with the doses calculated for the donors using the Techa River Dosimetry System (TRDS). The TRDS external dose assessments were based on the data on contamination of the Techa River floodplain, simulation of ai r kerma above the contaminated soil, age-dependent life-styles and individual residence histories. For correct comparison TRDS-based doses were calculated from two sources: external exposure from the contaminated environment and internal exposure from 137Cs incorporated in donors’ soft tissues. The TRDS-based absorbed doses in tooth enamel

  6. Electron Paramagnetic Resonance Spectroscopy of Photosynthetic Systems and Inorganic Model Complexes.

    Science.gov (United States)

    Dexheimer, Susan Lynne

    1990-01-01

    This thesis discusses the application of parallel polarization electron paramagnetic resonance (EPR) spectroscopy, a technique sensitive to formally forbidden transitions in high spin states, to the study of the electronic structure of photosynthetic electron transfer centers and related inorganic model complexes. The theoretical basis for the origin of the parallel polarization transitions and the interpretation of the resulting spectra is presented, and experimental aspects of the detection of parallel polarization transitions are discussed. Parallel polarization EPR was used to study inorganic complexes of trivalent manganese that serve as models for the spectroscopic properties of biological electron transfer centers. X-band EPR spectra were detected from non-Kramers spin states of these complexes. EPR spectra of the S = 2 ground states of the mononuclear complexes Mn(III) tris -acetylacetonate and Mn(III) tris-picolinate and a low-lying excited state of the weakly antiferromagnetically coupled binuclear complex Mn_2(III,III) O(O_2CCH_3) _2 (HB(pz)_3) _2 (HB(pz)_3 = hydrotris(1-pyrazolyl)borate) are discussed. The spectra are interpreted using numerical simulations. Application of parallel polarization EPR to photosyntheic systems led to the detection of a new paramagnetic intermediate associated with photosynthetic water oxidation. The parallel polarization EPR signal is assigned to an S = 1 spin state of an exchange-coupled manganese center in the resting (S_1) state of the photosynthetic oxygen-evolving complex. The properties of the S _1 state parallel polarization EPR signal indicate that it corresponds to the reduced form of the species that gives rise to the previously established multiline conventional EPR signal in the light-induced S _2 state, and the behavior of the signal upon advancement to the S_2 state demonstrates the presence of two separate redox-active centers in the oxygen-evolving complex. The implications for the electronic structure of

  7. Identification and dosimetry of irradiated walnuts (Juglans regia) using EPR

    Science.gov (United States)

    Maghraby, A.; Salama, E.; Sami, A.; Mansour, A.; El-Sayed, M.

    2012-03-01

    Electron paramagnetic resonance (EPR) is an easy, fast, and reliable tool for identification of irradiated food. Untreated nuts may encounter hazards of carrying several pathogens or microbial contamination; walnuts are of specific importance due to their nutritional and medicinal values, and hence walnut processing via gamma irradiation is a necessary step. EPR was employed for the identification and dosimetry of Cs-137 gamma-irradiated walnuts (shells and kernels). Several important parameters were studied, such as spectral features, microwave power dependence of signal intensities, and short- and long-term time dependences. Responses of walnut shells and kernels to different radiation doses in the range 0-10 kGy were investigated. Results confirmed that EPR is a suitable tool for the identification and dosimetry of irradiated walnuts using either their shells or only kernels.

  8. EPR structure of the gamma irradiated alanine spectrum

    Energy Technology Data Exchange (ETDEWEB)

    Cabral P, A.; Jimenez D, H.; Urena N, F.; Galindo, S.; Bosch, P

    1992-03-15

    In this study is shown that the broadened five-line EPR pattern of the gamma irradiated alanine possibly decomposes into a more complex pattern when the recorded spectrum is subject to an operation of deconvolution. The EPR powder spectra of gamma irradiated DL- and L-alanine with and without binders are analysed. In all recorded spectra, each observed line is resolved into an asymmetrical triplet when a Gaussian distribution of 8.2 gauss width is removed, by deconvolution, from the observed spectrum. On the other hand, from a simple fitting analysis carried out on the original data, one encounters that some calculated relations between characteristic parameters, such as intensity ratios, deviate consistently from assumed height ratios. Both, from deconvolution and fitting results, a different structure is suggested for the observed broadened five-line EPR pattern of {gamma}-irradiated powder DL- and L-alanine. (Author)

  9. Iron oxide and pyrocatechol: a spectroscopy study of the reaction products

    OpenAIRE

    Wagner José Barreto; Sônia Regina Giancoli Barreto; Ivanira Moreira; Yoshio Kawano

    2006-01-01

    The reaction of 1,2-dihydroxy-benzene (pyrocatechol) (C6H6O2) with iron oxide (Fe2O3) and sodium thiosulfate (Na2S2O3) in aqueous medium (pH 7) was investigated. Pyrocatechol suffers autoxidation and coordinates with Fe3+ in solution. The presence of S2O3(2-) in solution was fundamental to generate and stabilize the pyrocatechol oxidation products as o-semiquinones. This compound was isolated and its structure characterized using FT-IR, EPR and UV-Vis Spectroscopy as [CTA][Fe(SQ)2(Cat)]. A th...

  10. Skeletal muscle and glioma oxygenation by carbogen inhalation in rats: a longitudinal study by EPR oximetry using single-probe implantable oxygen sensors.

    Science.gov (United States)

    Hou, Huagang; Khan, Nadeem; Lariviere, Jean; Hodge, Sassan; Chen, Eunice Y; Jarvis, Lesley A; Eastman, Alan; Williams, Benjamin B; Kuppusamy, Periannan; Swartz, Harold M

    2014-01-01

    The feasibility of EPR oximetry using a single-probe implantable oxygen sensor (ImOS) was tested for repeated measurement of pO₂ in skeletal muscle and ectopic 9L tumors in rats. The ImOS (50 mm length) were constructed using nickel-chromium alloy wires, with lithium phthalocyanine (LiPc, oximetry probe) crystals loaded in the sensor loop and coated with AF 2400(®) Teflon. These ImOS were implanted into the skeletal muscle in the thigh and subcutaneous 9L tumors. Dynamic changes in tissue pO₂ were assessed by EPR oximetry at baseline, during tumor growth, and repeated hyperoxygenation with carbogen breathing. The mean skeletal muscle pO₂ of normal rats was stable and significantly increased during carbogen inhalation in experiments repeated for 12 weeks. The 9L tumors were hypoxic with a tissue pO₂ of 12.8 ± 6.4 mmHg on day 1; however, the response to carbogen inhalation varied among the animals. A significant increase in the glioma pO₂ was observed during carbogen inhalation on day 9 and day 14 only. In summary, EPR oximetry with ImOS allowed direct and longitudinal oxygen measurements in deep muscle tissue and tumors. The heterogeneity of 9L tumors in response to carbogen highlights the need to repeatedly monitor pO₂ to confirm tumor oxygenation so that such changes can be taken into account in planning therapies and interpreting results.

  11. Theoretical studies of EPR site center for Mn{sup 2+} in potassium thiourea bromide single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Ravi, S. [Department of Physics, Gandhigram Rural University, Gandhigram 624302 (India)], E-mail: sravi_phygri@yahoo.com; Subramanian, P. [Department of Physics, Gandhigram Rural University, Gandhigram 624302 (India)], E-mail: psmanian_gri@yahoo.com

    2007-11-01

    The impurity location of Mn{sup 2+} ion in potassium thiourea bromide single crystal is theoretically studied using perturbation formulas of spin Hamiltonian (SH) for 3d{sup 5} ions on strong-field scheme. The spin Hamiltonian parameter values are calculated by this technique. The g and A factors are in reasonable agreement with the experimental results. The zero-field splitting parameter is calculated as 775x10{sup -4} cm{sup -1}. The impurity ion Mn{sup 2+} undergoes off-center displacement of about 0.38 A. The results are discussed.

  12. Influence of free radicals signal from dental resins on the radio-induced signal in teeth in EPR retrospective dosimetry.

    Science.gov (United States)

    Levêque, Philippe; Desmet, Céline; Dos Santos-Goncalvez, Ana Maria; Beun, Sébastien; Leprince, Julian G; Leloup, Gaëtane; Gallez, Bernard

    2013-01-01

    In case of radiological accident, retrospective dosimetry is needed to reconstruct the absorbed dose of overexposed individuals not wearing personal dosimeters at the onset of the incident. In such a situation, emergency mass triage will be required. In this context, it has been shown that Electron Paramagnetic Resonance (EPR) spectroscopy would be a rapid and sensitive method, on the field deployable system, allowing dose evaluation of a great number of people in a short time period. This methodology uses tooth enamel as a natural dosimeter. Ionising radiations create stable free radicals in the enamel, in a dose dependent manner, which can be detected by EPR directly in the mouth with an appropriate resonator. Teeth are often subject to restorations, currently made of synthetic dimethacrylate-based photopolymerizable composites. It is known that some dental composites give an EPR signal which is likely to interfere with the dosimetric signal from the enamel. So far, no information was available about the occurrence of this signal in the various composites available on the market, the magnitude of the signal compared to the dosimetric signal, nor its evolution with time. In this study, we conducted a systematic characterization of the signal (intensity, kinetics, interference with dosimetric signal) on 19 most widely used composites for tooth restoration, and on 14 experimental resins made with the most characteristic monomers found in commercial composites. Although a strong EPR signal was observed in every material, a rapid decay of the signal was noted. Six months after the polymerization, the signal was negligible in most composites compared to a 3 Gy dosimetric signal in a tooth. In some cases, a stable atypical signal was observed, which was still interfering with the dosimetric signal.

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

    Science.gov (United States)

    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.

  14. Photosynthetic Electron and Proton Transport in Chloroplasts: EPR Study of ΔpH Generation, an Overview.

    Science.gov (United States)

    Tikhonov, Alexander N

    2017-12-01

    This is a brief overview focused on the electron paramagnetic resonance applications to the study of the proton transport processes in chloroplasts. After brief description of structural and functional organization of the chloroplast electron transport chain, our attention is focused on the measurements of trans-thylakoid pH difference (ΔpH) with pH-sensitive spin-probes. The use of spin-probes is based either (i) on measuring the ΔpH-partitioning of spin-probes between the thylakoid lumen and external volume, or (ii) on monitoring changes in the electron paramagnetic resonance spectra of pH-sensitive nitroxide radicals located in the lumen. Along with the use of spin-probes, the intra-thylakoid pH (pHin) can be determined by the "kinetic" method, which relies on the fact that the rate-limiting step in the chain of photosynthetic electron transfer (plastoquinol oxidation by the cytochrome b 6 f complex) is controlled by pHin. The results of ΔpH determinations in chloroplasts based on the use of pH-sensitive spin-probes and measurements of post-illumination reduction of photoreaction centers of Photosystem I are discussed in the context of the problem of energy coupling in laterally heterogeneous lamellar system of chloroplasts.

  15. The impact of short-term UV irradiation on grains of sensitive and tolerant cereal genotypes studied by EPR.

    Science.gov (United States)

    Kurdziel, Magdalena; Filek, Maria; Łabanowska, Maria

    2017-10-24

    UV irradiation has ionisation character and leads to the generation of reactive oxygen species (ROS). The destructive character of ROS was observed among others during interaction of cereal grains with ozone and was caused by changes in structures of biomolecules leading to the formation of stable organic radicals. That effect was more evident for stress sensitive genotypes. In this study we investigated the influence of UV irradiation on cereal grains originating from genotypes with different tolerance to oxidative stress. Grains and their parts (endosperm, embryo and seed coat) of barley, wheat and oat were subjected to short-term UV irradiation. It was found that UV caused the appearance of various kinds of reactive species (O2-• , H2 O2 ) and stable radicals (semiquinone, phenoxyl and carbon-centred). Simultaneously, lipid peroxidation occurred and the organic structure of Mn(II) and Fe(III) complexes become disturbed. UV irradiation causes damage of main biochemical structures of plant tissues, the effect is more significant in sensitive genotypes. In comparison with ozone treatment, UV irradiation leads to stronger destruction of biomolecules in grains and their parts. It is caused by the high energy of UV light, facilitating easier breakage of molecular bonds in biochemical compounds. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

  16. High-frequency EPR study of a new mononuclear manganese(III) complex:. [(terpy)Mn(N3)3] (terpy = 2,2':6',2''-terpyridine).

    Science.gov (United States)

    Limburg, J; Vrettos, J S; Crabtree, R H; Brudvig, G W; de Paula, J C; Hassan, A; Barra, A L; Duboc-Toia, C; Collomb, M N

    2001-03-26

    The isolation and structural characterization of [(terpy)Mn(III)(N3)3], complex 1, is reported (terpy = 2,2':6',2' '-terpyridine). Complex 1, a product of the reaction between the mixed-valence dimer [(terpy)(H2O)Mn(III)(O)2Mn(IV)(OH2)(terpy)](NO3)3 and NaN3, crystallizes in a triclinic system, space group P1, a = 8.480(1) A, b = 8.9007(2) A, c = 12.109(2) A, alpha = 93.79(1) degrees, beta = 103.17(1) degrees, gamma = 103.11(1) degrees, and Z = 2. Complex 1 exhibits a Jahn-Teller distortion of the octahedron characteristic of a six-coordinated high-spin Mn(III). A vibrational spectroscopic study was performed. The nu(asym)(N3) mode of complex 1 appears in the IR as a strong band at 2035 cm(-1) with a less intense feature at 2072 cm(-1), and in the FT-Raman as a strong band at 2071 cm(-1) with a weaker broad band at 2046 cm(-1). The electronic properties of complex 1 were investigated using a high-field and high-frequency EPR study (190-475 GHz). The different spin Hamiltonian parameters have been determined (D = -3.29 (+/-0.01) cm(-1), E = 0.48 (+/-0.01) cm(-1), E '= 0.53 (+/-0.01) cm(-1), g(x) = 2.00 (+/-0.005), g(y) = 1.98 (+/-0.005), g(z) = 2.01 (+/-0.005)). These parameters are in agreement with the geometry of complex 1 observed in the crystal structure, a D < 0 related to the elongated distortion, and a value of E/D close to 0.2 as expected from the highly distorted octahedron. The two values of the E-parameter are explained by the presence of two slightly different structural forms of complex 1 in the crystal lattice. A second hypothesis was explored to explain the experimental data. The calculation for the simulation was done taking into account that the g and D tensors are not collinear due to the low symmetry of complex 1. In that case, the spin Hamiltonian parameters found are D = -3.29 (+/-0.01) cm(-1), E = 0.51 (+/-0.01) cm(-1), g(x) = 2.00 (+/-0.005), g(y) = 1.98 (+/-0.005), and g(z) = 2.01 (+/-0.005).

  17. Hyperfine interaction of Er3+ ions in Y2SiO5 : An electron paramagnetic resonance spectroscopy study

    Science.gov (United States)

    Guillot-Noël, O.; Goldner, Ph.; Du, Y. Le; Baldit, E.; Monnier, P.; Bencheikh, K.

    2006-12-01

    Electron paramagnetic resonance (EPR) spectroscopy of rare earth ions in crystals is a powerful tool to analyze the hyperfine structure of the rare earth ground state. This can be useful for coherent spectroscopy and quantum information applications where the hyperfine structure of the electronic levels is used. In this work, we give a detailed analysis of the hyperfine structure of the ground state [I15/24(0)] of Er3+ ions in Y2SiO5 . The electronic Zeeman, hyperfine, and quadrupole matrices are obtained from angular variations of the magnetic field in three orthogonal crystal planes. An excellent agreement is obtained between experimental and simulated magnetic field positions and relative intensities of EPR lines.

  18. EPR investigations of Mn 2+, Fe 3+ ions and carbonaceous radicals in atmospheric particulate aerosols during their transport over the eastern coast of the English Channel

    Science.gov (United States)

    Ledoux, Frédéric; Zhilinskaya, Elena; Bouhsina, Saâd; Courcot, Lucie; Bertho, Marie-Laure; Aboukaı̈s, Antoine; Puskaric, Emile

    Electron paramagnetic resonance (EPR) spectroscopy was used to follow the evolution of the chemical forms of manganese and study other paramagnetic species in the atmospheric particulate aerosols at Wimereux, a French station located on the eastern coast of the English Channel. In parallel, Graphite Furnace Atomic Absorption Spectrometry (GFAAS) was used to measure the metal concentrations. Fe concentration values are common in North Sea sites, but those of Mn are quite higher due to the presence of an important local source of Mn. EPR spectra have evidenced isolated Fe 3+ and Mn 2+ ions and carbonaceous products with variable intensities according to the wind directions. Amounts of paramagnetic species and carbonaceous products are maximum for continental winds and minimum for marine winds. Three Mn types were identified depending on the sampling distance from the source of emission and the size of the particles.

  19. Dosimetry of an accident in mixed field (neutrons, photons) using the spectrometry by electronic paramagnetic resonance(EPR); Dosimetrie d'accident en champ mixte (neutrons, photons) utilisant la spectrometrie par resonance paramagnetique electronique (RPE)

    Energy Technology Data Exchange (ETDEWEB)

    Herve, M.L

    2006-03-15

    In a radiological accident, the assessment of the dose received by the victim is relevant information for the therapeutic strategy. Two complementary dosimetric techniques based on physical means are used in routine practice in the laboratory: EPR spectroscopy performed on materials removed from the victim or gathered from the vicinity of the victim and Monte Carlo calculations. EPR dosimetry, has been used successfully several times in cases of photon or electron overexposures. Accidental exposure may also occur with a neutron component. The aim of this work is to investigate the potentiality of EPR dosimetry for mixed photon and neutron field exposure with different organic materials (ascorbic acid, sorbitol, glucose, galactose, fructose, mannose, lactose and sucrose). The influence of irradiation parameters (dose, dose rate, photon energy) and of environmental parameters (temperature of heating, light exposure) on the EPR signal amplitude was studied. To assess the neutron sensitivity, the materials were exposed to a mixed radiation field of experimental reactors with different neutron to photon ratios. The relative neutron sensitivity was found to range from 10% to 43% according to the materials. Prior knowledge of the ratio between the dose in samples measured by EPR spectrometry and organ or whole body dose obtained by calculations previously performed for these different configurations, makes it possible to give a first estimation of the dose received by the victim in a short delay. The second aim of this work is to provide data relevant for a quick assessment of the dose distribution in case of accidental overexposure based on EPR measurements performed on one or several points of the body. The study consists in determining by calculation the relation between the dose to the organs and whole body and the dose to specific points of the body, like teeth, bones or samples located in the pockets of victim clothes, for different external exposures corresponding

  20. Elucidating the Structures of the Low- and High-pH Mo(V) Species in Respiratory Nitrate Reductase: A Combined EPR, 14,15N HYSCORE, and DFT Study.

    Science.gov (United States)

    Rendon, Julia; Biaso, Frédéric; Ceccaldi, Pierre; Toci, René; Seduk, Farida; Magalon, Axel; Guigliarelli, Bruno; Grimaldi, Stéphane

    2017-04-17

    Respiratory nitrate reductases (Nars), members of the prokaryotic Mo/W-bis Pyranopterin Guanosine dinucleotide (Mo/W-bisPGD) enzyme superfamily, are key players in nitrate respiration, a major bioenergetic pathway widely used by microorganisms to cope with the absence of dioxygen. The two-electron reduction of nitrate to nitrite takes place at their active site, where the molybdenum ion cycles between Mo(VI) and Mo(IV) states via a Mo(V) intermediate. The active site shows two distinct pH-dependent Mo(V) electron paramagnetic resonance (EPR) signals whose structure and catalytic relevance have long been debated. In this study, we use EPR and HYSCORE techniques to probe their nuclear environment in Escherichia coli Nar (EcNar). By using samples prepared at different pH and through different enrichment strategies in 98Mo and 15N nuclei, we demonstrate that each of the two Mo(V) species is coupled to a single nitrogen nucleus with similar quadrupole characteristics. Structure-based density functional theory calculations allow us to propose a molecular model of the low-pH Mo(V) species consistent with EPR spectroscopic data. Our results show that the metal ion is coordinated by a monodentate aspartate ligand and permit the assignment of the coupled nitrogen nuclei to the Nδ of Asn52, a residue located ∼3.9 Å to the Mo atom in the crystal structures. This is confirmed by measurements on selectively 15N-Asn labeled EcNar. Further, we propose a Mo-O(H)···HN structure to account for the transfer of spin density onto the interacting nitrogen nucleus deduced from HYSCORE analysis. This work provides a foundation for monitoring the structure of the molybdenum active site in the presence of various substrates or inhibitors in Nars and other molybdenum enzymes.

  1. Characterization of Cu-exchanged SSZ-13: a comparative FTIR, UV-Vis, and EPR study with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios

    DEFF Research Database (Denmark)

    Giordanino, Filippo; Vennestrøm, Peter N. R.; Lundegaard, Lars Fahl

    2013-01-01

    Cu-SSZ-13 has been characterized by different spectroscopic techniques and compared with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios and prepared by the same ion exchange procedure. On vacuum activated samples, low temperature FTIR spectroscopy allowed us to appreciate a high concentrat......Cu-SSZ-13 has been characterized by different spectroscopic techniques and compared with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios and prepared by the same ion exchange procedure. On vacuum activated samples, low temperature FTIR spectroscopy allowed us to appreciate a high...... concentration of reduced copper centres, i.e. isolated Cu+ ions located in different environments, able to form Cu+(N2), Cu+(CO)n (n = 1, 2, 3), and Cu+(NO)n (n = 1, 2) upon interaction with N2, CO and NO probe molecules, respectively. Low temperature FTIR, DRUV-Vis and EPR analysis on O2 activated samples...

  2. {sup 13}C NMR and EPR spectroscopic evaluation of oil shale mined soil recuperation

    Energy Technology Data Exchange (ETDEWEB)

    Santos, J.V. dos, E-mail: mangrich@ufpr.br [Universidade Federal do Parana (UFPR), Curitiba, PR (Brazil); Mangrich, A.S. [Instituto Nacional de Ciencia e Tecnologia: Energia e Ambiente, Salvador, BA (Brazil); Pereira, B.F. [EMBRAPA Clima Temperado, Pelotas, RS (Brazil); Pillon, C.N. [EMBRAPA Clima Temperado, Pelotas, RS (Brazil). Estacao Experimental Cascata; Novotny, E.H. [EMBRAPA Solos, Rio de Janeiro, RJ (Brazil); Bonagamba, T.J. [Universidade de Sao Paulo (USP), Sao Carlos, SP (Brazil). Instituto de Fisica; Abbt-Braun, G.; Frimmel, F.H. [Engler-Bunte-Institut, Universitaet Karlsruhe, TH (Germany)

    2013-02-15

    In this work, native forest soil (NFS) organic matter (SOM) sample and SOM samples from a neighboring forest soil area of an oil shale mine which is being rehabilitated for thirty years (RFS) were analyzed. X-band electron paramagnetic resonance (EPR) and solid-state {sup 13}C nuclear magnetic resonance (NMR) spectroscopies were used to evaluate the soil reclamation of the Brazilian oil shale mining process. Two-dimensional heterospectral correlation studies of the results obtained from EPRand {sup 13}C NMR were used to obtain information about SOM structures and their interactions with residual paramagnetic metal ion. The signal of the residual metallic oxycation, VO{sup 2+} correlated positively with uronic acid-type hydrophilic organic structures, determined from the {sup 13}C NMR spectra, and correlated negatively with the organic free radical (OFR) signal associated with oxygen atoms (g = 2.0042). The hydrophobic aromatic structures correlate positively with the EPR OFR signal associated with carbon atoms (g = 2.0022). The data from the two spectroscopic magnetic techniques show that the used recuperation process is effective. (author)

  3. EPR of exchange coupled systems

    CERN Document Server

    Bencini, Alessandro

    2012-01-01

    From chemistry to solid state physics to biology, the applications of Electron Paramagnetic Resonance (EPR) are relevant to many areas. This unified treatment is based on the spin Hamiltonian approach and makes extensive use of irreducible tensor techniques to analyze systems in which two or more spins are magnetically coupled. This edition contains a new Introduction by coauthor Dante Gatteschi, a pioneer and scholar of molecular magnetism.The first two chapters review the foundations of exchange interactions, followed by examinations of the spectra of pairs and clusters, relaxation in oligon

  4. In vivo imaging of a stable paramagnetic probe by pulsed-radiofrequency electron paramagnetic resonance spectroscopy

    DEFF Research Database (Denmark)

    Murugesan; Cook; Devasahayam

    1997-01-01

    Imaging of free radicals by electron paramagnetic resonance (EPR) spectroscopy using time domain acquisition as in nuclear magnetic resonance (NMR) has not been attempted because of the short spin-spin relaxation times, typically under 1 μs, of most biologically relevant paramagnetic species......, Recent advances in radiofrequency (RF) electronics have enabled the generation of pulses of the order of 10-50 ns. Such short pulses provide adequate spectral coverage for EPR studies at 300 MHz resonant frequency. Acquisition of free induction decays (FID) of paramagnetic species possessing...

  5. Study of Belousov—Zhabotinsky oscillators in water—acetonitrile medium employing EMF and EPR techniques with o-vanillin, p-vanillin and adrenaline as substrates

    Science.gov (United States)

    Lalitha, P. V.; Ramaswamy, R.; Ramakrishnan, Geetha; Rao, P. Sambasiva

    1994-12-01

    The oscillatory behaviour of three substrates, ortho-vanillin, para-vanillin and adrenaline, in mixed media (water plus 20% acetonitrile) has been investigated using EPR and EMF techniques. All these substrates exhibit two types of oscillation involving Br 2/Br - and Mn(III)/Mn(II) redox couples. From the oscillatory characteristics (total time, number of oscillations and time per oscillation) obtained by employing these techniques, the reactivities of the vanillins have been correlated. The Field—Koros—Noyes mechanism, suggested for catalysed systems in pure aqueous medium, is established to be applicable even in mixed media.

  6. New developed cylindrical TM010 mode EPR cavity for X-band in vivo tooth dosimetry.

    Directory of Open Access Journals (Sweden)

    Guo Junwang

    Full Text Available EPR tooth in vivo dosimetry is an attractive approach for initial triage after unexpected nuclear events. An X-band cylindrical TM010 mode resonant cavity was developed for in vivo tooth dosimetry and used in EPR applications for the first time. The cavity had a trapezoidal measuring aperture at the exact position of the cavity's cylindrical wall where strong microwave magnetic field H1 concentrated and weak microwave electric field E1 distributed. Theoretical calculations and simulations were used to design and optimize the cavity parameters. The cavity features were evaluated by measuring DPPH sample, intact incisor samples embed in a gum model and the rhesus monkey teeth. The results showed that the cavity worked at designed frequency and had the ability to make EPR spectroscopy in relative high sensitivity. Sufficient modulation amplitude and microwave power could be applied into the aperture. Radiation induced EPR signal could be observed remarkably from 1 Gy irradiated intact incisor within only 30 seconds, which was among the best in scan time and detection limit. The in vivo spectroscopy was also realized by acquiring the radiation induced EPR signal from teeth of rhesus monkey whose teeth was irradiated by dose of 2 Gy. The results suggested that the cavity was sensitive to meet the demand to assess doses of significant level in short time. This cavity provided a very potential option for the development of X-band in vivo dosimetry.

  7. In Vivo EPR Resolution Enhancement Using Techniques Known from Quantum Computing Spin Technology.

    Science.gov (United States)

    Rahimi, Robabeh; Halpern, Howard J; Takui, Takeji

    2017-01-01

    A crucial issue with in vivo biological/medical EPR is its low signal-to-noise ratio, giving rise to the low spectroscopic resolution. We propose quantum hyperpolarization techniques based on 'Heat Bath Algorithmic Cooling', allowing possible approaches for improving the resolution in magnetic resonance spectroscopy and imaging.

  8. Overview of LBB implementation for the EPR

    Energy Technology Data Exchange (ETDEWEB)

    Cauquelin, C.

    1997-04-01

    This paper presents an overview of the use of leak-before-break (LBB) analysis for EPR reactors. EPR is an evolutionary Nuclear Island of the 4 loop x 1500 Mwe class currently in the design phase. Application of LBB to the main coolant lines and resulting design impacts are summarized. Background information on LBB analysis in France and Germany is also presented.

  9. THE ORIENTATION OF MEMBRANE BOUND RADICALS: AN EPR INVESTIGATION OF MAGNETICALLY ORDERED SPINACH CHLOROPLASTS

    Energy Technology Data Exchange (ETDEWEB)

    Dismukes, G. Charles; Sauer, Kenneth

    1978-03-01

    The orientation of membrane-bound radicals in spinach chloroplasts is examined by electron paramagnetic resonance (EPR) spectroscopy of chloroplasts oriented by magnetic fields. Several of the membrane-bound radicals which possess g-tensor anisotropy display EPR signals with a marked dependence on the orientation of the membranes relative to the applied EPR field. The fraction of oxidized and reduced plastocyanin, P-700, iron-sulfur proteins A and B, and the X center, an early acceptor of Photosystem I, can be controlled by the light intensity during steady-state illumination and can be trapped by cooling. The X center can be photoreduced and trapped in the absence of strong reductants and high pH, conditions previously found necessary for its detection. These results confirm its role as an early electron acceptor in P-700 photo-oxidation. X is oriented with its smallest principal g-tensor axis (g{sub x}) predominantly parallel to the normal to the thylakoid membrane, the same orientation as was found for an early electron acceptor based on time-resolved electron spin polarization studies. We propose that the X center is the first example of a high potential iron-sulfur protein which functions in electron transfer in its 'superreduced' state. We present evidence which suggests that iron-sulfur proteins A and B are 4Fe-4S clusters in an 8Fe-8S protein. Center B is oriented with g{sub y} predominantly normal to the membrane plane. The spectra of center A and plastocyanin do not show significant changes with sample orientation. In the case of plastocyanin, this may indicate a lack of molecular orientation. The absence of an orientation effect for reduced center A is reconcilable with a 4Fe-4S geometry, provided that the electron obtained upon reduction can be shared between any pair of Fe atoms in the center. Orientation of the 'Rieske' iron-sulfur protein is also observed. It has axial symmetry with g{parallel} close to the plane of the membrane

  10. EPR Dosimetry - Present and Future

    Energy Technology Data Exchange (ETDEWEB)

    Regulla, D.F. [GSF - National Research Centre for Environment and Health, Institute of Radiation Protection, 85764 Neuherberg (Germany)

    1999-07-01

    In the past, IAEA has played a central role in stipulating research and development in EPR high-dose standardisation as well as in coordinating and organising international dose intercomparison programs, within the Member States of the United Nations from the mid-seventies till today. The future tasks of EPR dosimetry seem to tend towards different subjects such as bio markers, biological radiation effects, post-accident dose reconstruction in the environment, and retrospective human dosimetry. The latter may be considered a promising tool for epidemiology on the way to re-define radiation risk of man for chronicle radiation exposures, based on e.g. South Ural civil population and radiation workers. There are on-going international activities in the field of standardising high-level dosimetry by the American Standards on Testing and Materials (Astm), and by the International Organisation of Standards (ISO). The International Commission on Radiation Units and Measurements (ICRU) is considering the establishment of relevant recommendations concerning industrial radiation processing, but also human dose reconstruction. (Author)

  11. Synthesis, characterization, EPR spectroelectrochemistry studies and theoretical calculations of manganese(II) complexes with the ligands H{sub 3}bpeten and H{sub 3}bnbpeten

    Energy Technology Data Exchange (ETDEWEB)

    Romanowski, Stela Maris de M.; Friedermann, Geraldo R.; Mangrich, Antonio S.; Hermann, Monique de F.; Nakagaki, Shirley, E-mail: shirley@quimica.ufpr.b [Universidade Federal do Parana (UFPR), Curitiba, PR (Brazil). Dept. de Quimica; Machado, Sergio P.; Lima, Hugo Orofino [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Quimica

    2010-07-01

    The synthesis and characterization of the manganese(II) complexes [Mn{sup II}(Hbpeten)] and [Mn{sup II}(Hbnbpeten)], where H{sub 3}bpeten and H{sub 3}bnbpeten are respectively [N,N'-bis-(2-hydroxybenzyl)- N-(2-pyridylmethyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine] and [N,N'-bis-(5-nitro-2- hydroxybenzyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine], are reported. The characterization was carried out by elemental analyses, cyclic voltammetry, spectroscopic methods (UV-Vis, FTIR, {sup 1}H NMR), electronic paramagnetic resonance spectroelectrochemistry (EPR) and theoretical DFT calculations. The electrochemistry and EPR spectroelectrochemistry data were consistent with the reduction of one of the nitro groups in free H{sub 3}bnbpeten and in the respective manganese(II) complex. These results were supported by DFT calculations, which showed that only one nitro group contributes to the LUMO. The theoretical data appear to be suitable to describe the electronic properties of the compounds. (author)

  12. Study of amorphous semiconductors doped with rare earths (Gd and Er) and conducting polymers by EPR techniques and magnetic susceptibility; Estudo de semicondutores amorfos dopados com terras raras (Gd e Er) e de polimeros condutores atraves das tecnicas de RPE e susceptibilidade magnetica

    Energy Technology Data Exchange (ETDEWEB)

    Sercheli, Mauricio da Silva

    1999-07-01

    This thesis involves the study of amorphous semiconductors and conducting polymers, which have been characterized by EPR and magnetic susceptibility measurements, and to a lesser extent by Raman spectroscopy and RBS. The semiconductors were studied using thin films of silicon doped with rare earth metals, e.g. erbium and gadolinium, which had their magnetic properties studied. Using these studies we could determine the state of valence of the rare earths as well as their concentrations in the silicon matrix. According to our results, the valence of the rare earth metal ions is 3+, and we were able to conclude that 4f electronic shells could not be used for the calculation of the conducting band in this system. Furthermore, the analysis of the data on the magnetic susceptibility of the Er{sup 3+} ion with cubic crystalline acting field, gave us the opportunity to estimate the overall splitting of their electronic states for the first time. The conducting polymers were studied using samples of poly(3-methylthiophene) doped with ClO{sub 4}{sup -}, which show a phase transition in the range of 230 K to 130 K. The electron paramagnetic resonance also gives important information on the crystallization, doping level and the presence of polarons or bipolarons in conducting polymers. (author)

  13. Quantitative Analysis of the Enhanced Permeation and Retention (EPR Effect.

    Directory of Open Access Journals (Sweden)

    Andrew D Wong

    Full Text Available Tumor vasculature is characterized by a variety of abnormalities including irregular architecture, poor lymphatic drainage, and the upregulation of factors that increase the paracellular permeability. The increased permeability is important in mediating the uptake of an intravenously administered drug in a solid tumor and is known as the enhanced permeation and retention (EPR effect. Studies in animal models have demonstrated a cut-off size of 500 nm - 1 µm for molecules or nanoparticles to extravasate into a tumor, however, surprisingly little is known about the kinetics of the EPR effect. Here we present a pharmacokinetic model to quantitatively assess the influence of the EPR effect on the uptake of a drug into a solid tumor. We use pharmacokinetic data for Doxil and doxorubicin from human clinical trials to illustrate how the EPR effect influences tumor uptake. This model provides a quantitative framework to guide preclinical trials of new chemotherapies and ultimately to develop design rules that can increase targeting efficiency and decrease unwanted side effects in normal tissue.

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

    Science.gov (United States)

    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.

  15. EPR dosimetry of teeth in past and future accidents. A prospective look at a retrospective method

    Energy Technology Data Exchange (ETDEWEB)

    Haskell, E.; Kenner, G.; Hayes, R. [Center for Applied Dosimetry, Salt Lake City, UT (United States); Chumak, V.; Shalom, S.

    1996-12-31

    Accurate assessments of doses received by individuals exposed to radiation from nuclear accidents and incidents such as those at Hiroshima and Nagasaki, the Nevada test site, Chelyabinsk and Mayak are required for epidemiological studies seeking to establish relationships between radiation dose and health effects. One method of retrospective dosimetry which allows for measurement of cumulative gamma ray doses received by exposed individuals is electron paramagnetic resonance spectroscopy (EPR) of tooth enamel. Tooth enamel stores and retains, indefinitely, information on absorbed radiation dose; and teeth are available in every population as a result of dental extraction for medical reasons including periodontal disease and impacted wisdom teeth. In the case of children, deciduous teeth, which are shed between the ages of 7 and 13, can be a very important dosimetric source if documented collection is implemented shortly following an accident. (author)

  16. EPR dosimetry teeth in past and future accidents: A prospective look at a retrospective method

    Energy Technology Data Exchange (ETDEWEB)

    Haskell, E.; Kenner, G.; Hayes, R. [Univ. of Utah, Salt Lake City, UT (United States). Center for Applied Dosimetry; Chumak, V.; Shalom, S. [Scientific Center for Radiation Medicine, Kiev (Ukraine)

    1997-03-01

    Accurate assessments of doses received by individuals exposed to radiation from nuclear accidents and incidents such as those at Hiroshima and Nagasaki, the Nevada test site, Cheliabinsk and Mayak are required for epidemiological studies seeking to establish relationships between radiation dose and health effects. One method of retrospective dosimetry which allows for measurement of cumulative gamma ray doses received by exposed individuals is electron paramagnetic resonance spectroscopy (EPR) of tooth enamel. Tooth enamel stores and retains, indefinitely, information on absorbed radiation dose. And teeth are available in every population as a result of dental extraction for medical reasons including periodontal disease and impacted wisdom teeth. In the case of children, deciduous teeth, which are shed between the ages of 7 and 13, can be a very important dosimetric source if documented collection is implemented shortly following an accident.

  17. UV/Vis, MCD and EPR Spectra of Mononuclear Manganese and Molybdenum Complexes

    OpenAIRE

    Westphal, Anne

    2012-01-01

    This PhD thesis deals with the spectroscopic characterization of the electronic structures of mononuclear manganese and molybdenum complexes. At this, in addition to UV/Vis absorption spectroscopy, electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopy were applied in this work. Additionally, new procedures for the general analysis of MCD C-term intensities were developed within the scope of this thesis. It is divided into four parts. Following a general p...

  18. FTIR and EPR spectroscopic investigation of calcium-silicate glasses with iron and dysprosium

    Science.gov (United States)

    Eniu, D.; Gruian, C.; Vanea, E.; Patcas, L.; Simon, V.

    2015-03-01

    The sol-gel derived 50SiO2ṡ30CaOṡ10Fe2O3ṡ10Dy2O3 system was subjected to heat treatments at 500, 800 and 1200 °C in order to obtain crystalline phases of interest for biomedical applications. The structural changes were investigated by Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). Both FTIR and EPR results support the development of wollastonite, hematite and magnetite crystalline phases desirable for samples bioactivity and heating possibility for hyperthermia treatment. Dysprosium addition was considered for subsequent radioactivation of the samples that could extend their application to thermoradiotherapy.

  19. Radiolysis of proteins in the solid state: an approach by EPR and product analysis.

    Science.gov (United States)

    Terryn, Hélène; Deridder, Véronique; Sicard-Roselli, Cécile; Tilquin, Bernard; Houée-Levin, Chantal

    2005-05-01

    Radio-induced modifications in proteins have been studied using several techniques. Electron paramagnetic resonance (EPR) was used to characterize free radicals, and analysis methods (high-performance liquid chromatography, capillary electrophoresis) were employed to visualize final degraded forms. Whereas EPR indicates that perthiyl radicals are formed, analysis does not detect any compound in which such bonds would be broken. Since EPR signals decay with time, it is concluded that rearrangements occur at subsequent steps, in which the solvent used during the analysis might play a role.

  20. Magnetic model for Mn{sub 2}La{sub 2} developed from spectroscopic studies with inelastic neutron scattering and frequency-domain Fourier-transform THz EPR

    Energy Technology Data Exchange (ETDEWEB)

    Milazzo, R.; Nehrkorn, J.; Stuiber, S.; Waldmann, O. [Physikalisches Institut, Universitaet Freiburg (Germany); Akhtar, M.N.; Lan, Y.; Powell, A.K. [Institut fuer Anorganische Chemie, Universitaet Karlsruhe, KIT (Germany); Mutka, H. [Institut Laue Langevin, Grenoble (France); Dreiser, J. [Swiss Light Source, Paul Scherrer Institut (Switzerland); Schnegg, A. [Helmholtz-Zentrum Berlin, Institut fuer Silizium-Photovoltaik (Germany); Holldack, K. [Helmholtz-Zentrum Berlin, Institut fuer Synchrotonstrahlung (Germany)

    2011-07-01

    Molecular nanomagnets which contain several magnetic centers with a large single-ion magnetic anisotropy are of general interest, because they could lead to interesting phenomena such as single-molecule magnet (SMM) behavior. We performed spectroscopic experiments on Mn{sub 2}La{sub 2} using inelastic neutron scattering at the direct time-of-flight disc chopper spectrometer IN5 at ILL and the newly developed frequency-domain Fourier-transform THz EPR at BESSY. Based on the experimental results a magnetic model has been developed. It is discussed why no SMM behavior was observed, even though Mn{sub 2}La{sub 2} exhibits a remarkably high energy barrier of about 37 K for spin relaxation. Furthermore our results can be applied to analogous clusters, with the diamagnetic La{sup I}II ions replaced by magnetic rare earth ions.

  1. Nitrosyl hemoglobins: EPR above 80 K

    Energy Technology Data Exchange (ETDEWEB)

    Wajnberg, E.; Bemski, G.; El-Jaick, L.J.; Alves, O.C.

    1995-03-01

    The EPR spectra of nitrosyl hemoglobin and myoglobin in different conditions (native, denatured and lyophilized), as well as of hematin-NO were obtained in the temperature range of 80 K-280 K. There is a substantial and reversible.decrease of the areas of the EPR spectra of all the hemoglobin samples above 150 K. The interpretation of the results implies the existence of two conformational states in thermal equilibrium only one of which is EPR detectable. Thermodynamical parameters are determined for the hexa and penta-coordinated cases. (author). 25 refs, 3 figs.

  2. NATO Advanced Study Institute on Low Temperature Molecular Spectroscopy

    CERN Document Server

    1996-01-01

    Molecular spectroscopy has achieved rapid and significant progress in recent years, the low temperature techniques in particular having proved very useful for the study of reactive species, phase transitions, molecular clusters and crystals, superconductors and semiconductors, biochemical systems, astrophysical problems, etc. The widening range of applications has been accompanied by significant improvements in experimental methods, and low temperature molecular spectroscopy has been revealed as the best technique, in many cases, to establish the connection between experiment and theoretical calculations. This, in turn, has led to a rapidly increasing ability to predict molecular spectroscopic properties. The combination of an advanced tutorial standpoint with an emphasis on recent advances and new perspectives in both experimental and theoretical molecular spectroscopy contained in this book offers the reader insight into a wide range of techniques, particular emphasis being given to supersonic jet and matri...

  3. Raman Spectroscopy Studies of Normal and Burned Biological Tissue

    Science.gov (United States)

    Zarnani, Faranak; Maass, David; Idris, Ahamed; Glosser, Robert

    2011-03-01

    Burn injuries are a significant medical problem, and need to be treated quickly and precisely. Burned skin needs to be removed early, within hours (less than 24 hrs) of injury, when the margins of the burn are still hard to define. Studies show that treating and excising burn wounds soon after the injury prevents the wound from becoming deeper, reduces the release of proinflammatory mediators, and reduces or prevents the systemic inflammatory reaction syndrome. Also, removing burned skin prepares the affected region for skin grafting. Raman spectroscopy could be used as an objective diagnostic method that will assist burn surgeons in removing burned skin precisely. As a first step in developing a diagnostic tool, we present Raman spectroscopy information from normal and burned ex vivo rat skin, and a comparison of our findings. Raman spectroscopy is explored for its specificity and sensitivity.

  4. Francium Spectroscopy for Weak Interaction Studies

    Science.gov (United States)

    Orozco, Luis

    2014-05-01

    Francium, a radioactive element, is the heaviest alkali. Its atomic and nuclear structure makes it an ideal laboratory to study the weak interaction. Laser trapping and cooling in-line with the superconducting LINAC accelerator at Stony Brook opened the precision study of its atomic structure. I will present our proposal and progress towards weak interaction measurements at TRIUMF, the National Canadian Accelerator in Vancouver. These include the commissioning run of the Francium Trapping Facility, hyperfine anomaly measurements on a chain of Fr isotopes, the nuclear anapole moment through parity non-conserving transitions in the ground state hyperfine manifold. These measurements should shed light on the nucleon-nucleon weak interaction. This work is done by the FrPNC collaboration: S. Aubin College of William and Mary, J. A. Behr TRIUMF, R. Collister U. Manitoba, E. Gomez UASLP, G. Gwinner U. Manitoba, M. R. Pearson TRIUMF, L. A. Orozco UMD, M. Tandecki TRIUMF, J. Zhang UMD Supported by NSF and DOE from the USA; TRIUMF, NRC and NSERC from Canada; and CONACYT from Mexico

  5. EPR and FTIR Characterization of Paramagnetic Transition Metal Ions in Fossil Fuels: Tar Sands

    Science.gov (United States)

    Shepherd, Robert Anthony

    The techniques of EPR and FTIR spectroscopy have been applied to the bitumen and mineral fractions of a tar sand sample originating from Circle Cliffs, Utah to detect and identify paramagnetic transition metal ions present, indicate whether or not they are organically bound, and determine the identities of the complexes in which they occur. An EPR spectrum of the bitumen reveals the presence of V('4+) at a site of axial symmetry. Fitting the spectrum to the second order perturbation solution of the spin Hamiltonian indicates that the spectrum originates from vanadyl etioporphyrin. An EPR spectrum characteristic of Mn('2+) in a carbonate lattice was observed for the mineral component. A quantitative analysis of the mineral components, conducted using FTIR spectroscopy, shows the tar sand mineral fraction consists of the two clays, kaolinite and illite, quartz, gypsum, and one carbonate, dolomite. A computer simulation of the EPR spectrum positively identifies the Mn('2+) host as polycrystalline dolomite, shows the ions are at two crystallographically distinct sites in the dolomite lattice, and gives the relative population at each site. A second feature observed in the EPR spectrum of the mineral fraction is a broad line at g = 4.2 which is attributed to Fe('3+) in kaolinite. A third and final feature observed in the EPR spectrum of the tar sand mineral fraction is a broad line at g = 2. The temperature-dependent behavior of this line suggests that it is due to Fe('3+) in amorphous iron oxides and wustite, two compounds that commonly coat kaolinite surfaces.

  6. Homogeneity and EPR metrics for assessment of regular grids used in CW EPR powder simulations

    Science.gov (United States)

    Crăciun, Cora

    2014-08-01

    CW EPR powder spectra may be approximated numerically using a spherical grid and a Voronoi tessellation-based cubature. For a given spin system, the quality of simulated EPR spectra depends on the grid type, size, and orientation in the molecular frame. In previous work, the grids used in CW EPR powder simulations have been compared mainly from geometric perspective. However, some grids with similar homogeneity degree generate different quality simulated spectra. This paper evaluates the grids from EPR perspective, by defining two metrics depending on the spin system characteristics and the grid Voronoi tessellation. The first metric determines if the grid points are EPR-centred in their Voronoi cells, based on the resonance magnetic field variations inside these cells. The second metric verifies if the adjacent Voronoi cells of the tessellation are EPR-overlapping, by computing the common range of their resonance magnetic field intervals. Beside a series of well known regular grids, the paper investigates a modified ZCW grid and a Fibonacci spherical code, which are new in the context of EPR simulations. For the investigated grids, the EPR metrics bring more information than the homogeneity quantities and are better related to the grids’ EPR behaviour, for different spin system symmetries. The metrics’ efficiency and limits are finally verified for grids generated from the initial ones, by using the original or magnetic field-constraint variants of the Spherical Centroidal Voronoi Tessellation method.

  7. Surface oxidation of cobalt nanoparticles studied by Mossbauer spectroscopy

    DEFF Research Database (Denmark)

    Bødker, Franz; Mørup, Steen; Charles, S.W.

    1999-01-01

    The surface oxide formed on cobalt nanoparticles has been studied by Mossbauer emission spectroscopy. Exposure of the cobalt particles to oxygen at room temperature was found to result in the formation of a relatively well-ordered surface oxide with Mossbauer parameters similar to those of CoO....

  8. Optical spectroscopy by Hantaro Nagaoka Pioneer nuclear structure study

    Science.gov (United States)

    Inamura, Takashi T.

    2000-08-01

    Hantaro Nagaoka is a Japanese physicist who made an experimental pioneer work on optical spectroscopy for nuclear structure studies in 1920s. Today much attention should be paid to this work rather than to his famous atomic model that died away long time ago along with Thomson's model.

  9. Optical spectroscopy by Hantaro Nagaoka - Pioneer nuclear structure study

    Energy Technology Data Exchange (ETDEWEB)

    Inamura, Takashi T. [Warsaw University, Heavy Ion Laboratory (Poland)], E-mail: inamura@slcj.uw.edu.pl

    2000-08-15

    Hantaro Nagaoka is a Japanese physicist who made an experimental pioneer work on optical spectroscopy for nuclear structure studies in 1920s. Today much attention should be paid to this work rather than to his famous atomic model that died away long time ago along with Thomson's model.

  10. Magnetic excitations studied with time-of-flight spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Rainford, B. [Southampton Univ. (United Kingdom). Dept. of Physics

    1996-11-01

    An introduction to time-of-flight neutron spectroscopy is presented in the context of the study of magnetic materials. Examples are taken from the class of rare earth and actinide magnetic materials known as `strongly correlated electron` systems. (author) 11 figs., 24 refs.

  11. An RNA toolbox for single-molecule force spectroscopy studies

    NARCIS (Netherlands)

    Vilfan, I.D.; Kamping, W.; Van den Hout, M.; Candelli, A.; Hage, S.; Dekker, N.H.

    2007-01-01

    Precise, controllable single-molecule force spectroscopy studies of RNA and RNA-dependent processes have recently shed new light on the dynamics and pathways of RNA folding and RNAenzyme interactions. A crucial component of this research is the design and assembly of an appropriate RNA construct.

  12. Social Perception in Infancy: A Near Infrared Spectroscopy Study

    Science.gov (United States)

    Lloyd-Fox, Sarah; Blasi, Anna; Volein, Agnes; Everdell, Nick; Elwell, Claire E.; Johnson, Mark H.

    2009-01-01

    The capacity to engage and communicate in a social world is one of the defining characteristics of the human species. While the network of regions that compose the social brain have been the subject of extensive research in adults, there are limited techniques available for monitoring young infants. This study used near infrared spectroscopy to…

  13. Charge-Transfer Complexes Studied by Dynamic Force Spectroscopy

    Directory of Open Access Journals (Sweden)

    Jurriaan Huskens

    2013-03-01

    Full Text Available In this paper, the strength and kinetics of two charge-transfer complexes, naphthol-methylviologen and pyrene-methylviologen, are studied using dynamic force spectroscopy. The dissociation rates indicate an enhanced stability of the pyrene-methylviologen complex, which agrees with its higher thermodynamic stability compared to naphthol-methylviologen complex.

  14. Orientation of the tetranuclear manganese cluster and tyrosine Z in the O(2)-evolving complex of photosystem II: An EPR study of the S(2)Y(Z)(*) state in oriented acetate-inhibited photosystem II membranes.

    Science.gov (United States)

    Lakshmi, K V; Eaton, S S; Eaton, G R; Brudvig, G W

    1999-09-28

    Inhibitory treatment by acetate, followed by illumination and rapid freezing, is known to trap the S(2)Y(Z)(*) state of the O(2)-evolving complex (OEC) in photosystem II (PS II). An EPR spectrum of this state exhibits broad split signals due to the interaction of the tyrosyl radical, Y(Z)(*), with the S = 1/2 S(2) state of the Mn(4) cluster. We present a novel approach to analyze S(2)Y(Z)(*) spectra of one-dimensionally (1-D) oriented acetate-inhibited PS II membranes to determine the magnitude and relative orientation of the S(2)Y(Z)(*) dipolar vector within the membrane. Although there exists a vast body of EPR data on isolated spins in oriented membrane sheets, the present study is the first of its kind on dipolar-coupled electron spin pairs in such systems. We demonstrate the feasibility of the technique and establish a rigorous treatment to account for the disorder present in partially oriented 1-D membrane preparations. We find that (i) the point-dipole distance between Y(Z)(*) and the Mn(4) cluster is 7.9 +/- 0.2 A, (ii) the angle between the interspin vector and the thylakoid membrane normal is 75 degrees, (iii) the g(z)()-axis of the Mn(4) cluster is 70 degrees away from the membrane normal and 35 degrees away from the interspin vector, and (iv) the exchange interaction between the two spins is -275 x 10(-)(4) cm(-)(1), which is antiferromagnetic. Due to the sensitivity of EPR line shapes of oriented spin-coupled pairs to the interspin distance, the present study imposes a tighter constraint on the Y(Z)-Mn(4) point-dipole distance than obtained from randomly oriented samples. The geometric constraints obtained from the 1-D oriented sample are combined with published models of the structure of Mn-depleted PS II to propose a location of the Mn(4) cluster. A structure in which Y(Z) is hydrogen bonded to a manganese-bound hydroxide ligand is consistent with available data and favors maximal orbital overlap between the two redox center that would facilitate

  15. Applications of EPR in radiation research

    CERN Document Server

    Lund, Anders

    2014-01-01

    Applications of EPR in Radiation Research is a multi-author contributed volume presented in eight themes: I. Elementary radiation processes (in situ and low temperature radiolysis, quantum solids); II: Solid state radiation chemistry (crystalline, amorphous and heterogeneous systems); III: Biochemistry, biophysics and biology applications (radicals in biomaterials, spin trapping, free-radical-induced DNA damage); IV: Materials science (polymeric and electronic materials, materials for treatment of nuclear waste, irradiated food); V: Radiation metrology (EPR-dosimetry, retrospective and medical

  16. Electronic, cyclic voltammetry, IR and EPR spectral studies of copper(II) complexes with 12-membered N 4, N 2O 2 and N 2S 2 donor macrocyclic ligands

    Science.gov (United States)

    Chandra, Sulekh; Kumar, Rajiv

    2005-01-01

    A new series of copper(II) complexes have been synthesized with macrocyclic ligands having three different donating atoms in the macrocyclic ring. It has been shown that the stereochemistry of complexes is dependent on the coordinated anions. These complexes are characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, IR, electronic, 1H NMR and EPR spectral studies. Cyclic voltammetric behavior of the complexes has also been discussed. The observed anisotropic g-values indicate that the chloro and acetato complexes are six-coordinate tetragonal. Whereas the sulfato and nitrato complexes are found to have five-coordinate square-pyramidal and four-coordinate square-planar geometry, respectively.

  17. Radicals as EPR probes of magnetization of gadolinium stearate Langmuir-Blodgett film

    DEFF Research Database (Denmark)

    Koksharov, Y.A.; Bykov, I.V.; Malakho, A.P.

    2002-01-01

    the Gd and Y stearate LB films. Placing the small BDPA crystal on the film surface we have found that for the Gd LB sample the effective g-value of the radical's resonance depends on the film orientation in respect to the external magnetic field direction. The relative shift of the EPR signal......In the present work we have applied the method of the EPR spin probes which allows performing simultaneously EPR and magnetization measurements to the investigation of magnetism of the Cid stearate Langmuir-Blodgett (LB) films. For this purpose we have prepared and studied by the EPR technique...... corresponded to the magnetization of the film along the field direction. Such effect has not been observed for the Y stearate LB film. The data obtained give an experimental proof for the room temperature. magnetic ordering in the! gadolinium stearate LB film....

  18. Iron oxide and pyrocatechol: a spectroscopy study of the reaction products

    Directory of Open Access Journals (Sweden)

    Wagner José Barreto

    2006-12-01

    Full Text Available The reaction of 1,2-dihydroxy-benzene (pyrocatechol (C6H6O2 with iron oxide (Fe2O3 and sodium thiosulfate (Na2S2O3 in aqueous medium (pH 7 was investigated. Pyrocatechol suffers autoxidation and coordinates with Fe3+ in solution. The presence of S2O3(2- in solution was fundamental to generate and stabilize the pyrocatechol oxidation products as o-semiquinones. This compound was isolated and its structure characterized using FT-IR, EPR and UV-Vis Spectroscopy as [CTA][Fe(SQ2(Cat]. A thermal mass loss mechanism was proposed based on Thermogravimetric Analysis (TG to support the structural characterization.

  19. Two-dimensional correlation spectroscopy in polymer study

    Science.gov (United States)

    Park, Yeonju; Noda, Isao; Jung, Young Mee

    2015-01-01

    This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted. PMID:25815286

  20. NMR spectroscopy applied to the eye: Drugs and metabolic studies

    Energy Technology Data Exchange (ETDEWEB)

    Saether, Oddbjoern

    2005-07-01

    NMR spectroscopy has been extensively applied in biomedical research during the last decades. It has proved to be an analytical tool of great value. From being mainly used in chemistry, technological developments have expanded the application of NMR spectroscopy to a great wealth of disciplines. With this method, biochemical information can be obtained by analysing tissue extracts. Moreover, NMR spectroscopy is increasingly employed for pharmacokinetic studies and analysis of biofluids. Technological progress has provided increased sensitivity and resolution in the spectra, which enable even more of the complexity of biological samples to be elucidated. With the implementation of high-resolution magic angle spinning (HR-MAS) NMR spectroscopy in biomedicine, intact tissue samples or biopsies can be investigated. Thus, NMR spectroscopy has an ever-increasing impact in metabolic screening of human samples and in animal models, and methods are also increasingly realised in vivo. The present work, NMR spectroscopy applied to eye research, consists of two main parts. Firstly, the feasibility to monitor fluorinated ophthalmic drugs directly in the eye was assessed. Secondly, HR-MAS H1 NMR spectroscopy was applied for metabolic profiling of the anterior eye segment, specifically to analyse metabolic changes in intact corneal and lenticular samples after cataractogenic insults. This work included metabonomics with the application of pattern recognition methods to analyse HR-MAS spectra of eye tissues. Optimisation strategies were explored for F19 NMR detection of fluorinated drugs in a phantom eye. S/N gains in F19 NMR spectroscopy were achieved by implementing time-share H1 decoupling at 2.35 T. The method is advantageous for compounds displaying broad spectral coupling patterns, though detection of drugs at concentrations encountered in the anterior eye segment after topical application was not feasible. Higher magnetic fields and technological improvements could enable

  1. Well-Known Mediators of Selective Oxidation with Unknown Electronic Structure: Metal-Free Generation and EPR Study of Imide-N-oxyl Radicals.

    Science.gov (United States)

    Krylov, Igor B; Kompanets, Mykhailo O; Novikova, Katerina V; Opeida, Iosip O; Kushch, Olga V; Shelimov, Boris N; Nikishin, Gennady I; Levitsky, Dmitri O; Terent'ev, Alexander O

    2016-01-14

    Nitroxyl radicals are widely used in chemistry, materials sciences, and biology. Imide-N-oxyl radicals are subclass of unique nitroxyl radicals that proved to be useful catalysts and mediators of selective oxidation and CH-functionalization. An efficient metal-free method was developed for the generation of imide-N-oxyl radicals from N-hydroxyimides at room temperature by the reaction with (diacetoxyiodo)benzene. The method allows for the production of high concentrations of free radicals and provides high resolution of their EPR spectra exhibiting the superhyperfine structure from benzene ring protons distant from the radical center. An analysis of the spectra shows that, regardless of the electronic effects of the substituents in the benzene ring, the superhyperfine coupling constant of an unpaired electron with the distant protons at positions 4 and 5 of the aromatic system is substantially greater than that with the protons at positions 3 and 6 that are closer to the N-oxyl radical center. This is indicative of an unusual character of the spin density distribution of the unpaired electron in substituted phthalimide-N-oxyl radicals. Understanding of the nature of the electron density distribution in imide-N-oxyl radicals may be useful for the development of commercial mediators of oxidation based on N-hydroxyimides.

  2. EPR Characterization of the Triheme Cytochrome from Geobacter sulfurreducens.

    Science.gov (United States)

    Ponomarenko, Nina; Niklas, Jens; Pokkuluri, Phani Raj; Poluektov, Oleg G; Tiede, David Michael

    2018-01-03

    Periplasmic cytochrome A (PpcA) is a representative of a broad class of multi-heme cytochromes functioning as protein "nanowires" for storage and extracellular transfer of multiple electrons in the δ-proteobacterium Geobacter sulfurreducens. PpcA contains three bis-His coordinated hemes held in a spatial arrangement that is highly conserved among the multi-heme cytochromes c3 and c7 families, carries low potential hemes and is notable for having one of the lowest number of amino acids utilized to maintain a characteristic protein fold and site specific heme function. Low temperature X-band EPR spectroscopy has been used to characterize the electronic configuration of the Fe(III) and the ligation mode for each heme. The three sets of EPR signals are assigned to individual hemes in the 3D crystal structure. The relative energy levels of the Fe(III) 3d orbitals for individual hemes was estimated from the principal g values. The observed g tensor anisotropy was used as a probe of electronic structure of each heme and differences were determined by specifics of axial ligation. To ensure unambiguous assignment of highly anisotropic low spin (HALS) signal to individual hemes, EPR analyses of iron atom electronic configurations have been supplemented with investigation of porphyrin macrocycles by 1D 1H NMR chemical shift patterns for the methyl substituents. Within optimized geometry of hemes in PpcA the magnetic interactions between hemes were found to be minimal, similar to c3 family of tetraheme cytochromes.

  3. EPR = ER, scattering amplitude and entanglement entropy change

    Energy Technology Data Exchange (ETDEWEB)

    Seki, Shigenori, E-mail: sigenori@hanyang.ac.kr [Research Institute for Natural Science, Hanyang University, Seoul 133-791 (Korea, Republic of); Sin, Sang-Jin, E-mail: sjsin@hanyang.ac.kr [Department of Physics, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2014-07-30

    We study the causal structure of the minimal surface of the four-gluon scattering, and find a world-sheet wormhole parametrized by Mandelstam variables, thereby demonstrate the EPR = ER relation for gluon scattering. We also propose that scattering amplitude is the change of the entanglement entropy by generalizing the holographic entanglement entropy of Ryu–Takayanagi to the case where two regions are divided in space–time.

  4. EPR spectra induced by gamma-irradiation of some dry medical herbs

    Science.gov (United States)

    Yordanov, N. D.; Lagunov, O.; Dimov, K.

    2009-04-01

    The radiation-induced EPR spectra in some medical herbs are reported. The samples studied are: (i) leaves of nettle, common balm, peppermint and thyme; (ii) stalks of common balm, thyme, milfoil, yarrow and marigold; (iii) blossoms of yarrow and marigold; (iv) blossoms and leaves of hawthorn and tutsan; and (v) roots of common valerian, nettle, elecampane (black and white), restharrows and carlina. Before irradiation all samples exhibit one weak anisotropic singlet EPR line with effective g-value of 2.0050±0.0002. The radiation-induced spectra fall into three groups. EPR spectra of irradiated blossoms of yarrow and marigold, stalks of common balm, thyme, tutsan and yarrow as well as roots of common valerian, nettle and elecampane (black and white) show "cellulose-like" EPR spectrum typical for irradiated plants. It is characterized by one intense central line with g=2.0050±0.0005 and two weak satellite lines situated ca. 30 G left and right to it. EPR spectra of gamma-irradiated restharrows and carlina are complex. They may be represented by one triplet corresponding to the "cellulose-like" EPR spectrum, one relatively intense singlet, situated in the center of the spectrum, and five weak additional satellite lines left and right to the center. The last spectrum was assigned as "carbohydrate-like" type. Only one intense EPR singlet with g=2.0048±0.0005 was recorded after irradiation of leaves of nettle and common balm. The lifetime of the radiation-induced EPR spectra was followed for a period of 3 months.

  5. EPR spectra induced by gamma-irradiation of some dry medical herbs

    Energy Technology Data Exchange (ETDEWEB)

    Yordanov, N.D. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)], E-mail: ndyepr@bas.bg; Lagunov, O. [Laboratory EPR, Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Dimov, K. [Institute of Cryobiology and Food technology, 1162 Sofia (Bulgaria)

    2009-04-15

    The radiation-induced EPR spectra in some medical herbs are reported. The samples studied are: (i) leaves of nettle, common balm, peppermint and thyme; (ii) stalks of common balm, thyme, milfoil, yarrow and marigold; (iii) blossoms of yarrow and marigold; (iv) blossoms and leaves of hawthorn and tutsan; and (v) roots of common valerian, nettle, elecampane (black and white), restharrows and carlina. Before irradiation all samples exhibit one weak anisotropic singlet EPR line with effective g-value of 2.0050{+-}0.0002. The radiation-induced spectra fall into three groups. EPR spectra of irradiated blossoms of yarrow and marigold, stalks of common balm, thyme, tutsan and yarrow as well as roots of common valerian, nettle and elecampane (black and white) show 'cellulose-like' EPR spectrum typical for irradiated plants. It is characterized by one intense central line with g=2.0050{+-}0.0005 and two weak satellite lines situated ca. 30 G left and right to it. EPR spectra of gamma-irradiated restharrows and carlina are complex. They may be represented by one triplet corresponding to the 'cellulose-like' EPR spectrum, one relatively intense singlet, situated in the center of the spectrum, and five weak additional satellite lines left and right to the center. The last spectrum was assigned as 'carbohydrate-like' type. Only one intense EPR singlet with g=2.0048{+-}0.0005 was recorded after irradiation of leaves of nettle and common balm. The lifetime of the radiation-induced EPR spectra was followed for a period of 3 months.

  6. Atomic photoelectron-spectroscopy studies using synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Kobrin, P.H.

    1983-02-01

    Photoelectron spectroscopy combined with tunable synchrotron radiation has been used to study the photoionization process in several atomic systems. The time structure of the synchrotron radiation source at the Stanford Synchrotron Radiation Laboratory (SSRL) was used to record time-of-flight (TOF) photoelectron spectra of gaseous Cd, Hg, Ne, Ar, Ba, and Mn. The use of two TOF analyzers made possible the measurement of photoelectron angular distributions as well as branching ratios and partial cross sections.

  7. Infrared Spectroscopy in the Study of Renal Lithiasis

    Science.gov (United States)

    Fernández-Almeida, Jesús; Fernández-Gacio, Ana; Marcos, Carlos F.; Fernández-Gacio, Maira

    2003-08-01

    Infrared spectroscopic analysis of urinary stones is presented as a laboratory experiment for undergraduate students studying life sciences. Infrared spectroscopy, usually combined with the observation of macroscopic and microscopic features, is the preferred tool for unequivocal determination of renal stones composition. In this paper we represent and discuss the IR spectra of some of the most common types of urinary calculi occurring in humans and domestic animals.

  8. Studies of cartilaginous tissue using Raman spectroscopy method

    Science.gov (United States)

    Timchenko, Pavel E.; Timchenko, Elena V.; Volova, Larisa T.; Dolgyshkin, Dmitry A.; Markova, Maria D.; Kylabyhova, A. Y.; Kornilin, Dmitriy V.

    2016-10-01

    The work presents the results of studies of samples of human articular surface of the knee joint, obtained by Raman spectroscopy implementedduring endoprosthesis replacement surgery . The main spectral characteristics of articular surface areas with varying degrees of cartilage damage were detected at 956 cm-1, 1066 cm-1 wavenumbers, corresponding to phosphate and carbonate, and at 1660 cm-1, 1271 cm-1 wavenumbers, corresponding to amide I and amide III. Criteria allowing to identify the degree of articular hyaline cartilage damage were introduced.

  9. Electron spectroscopy study of the oxidation of a Zr-Fe getter. Pt. 1; Core spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Bastianon, A.; Braicovich, L.; Michelis, B. de (Ist. di Fisica, Politecnico di Milano (Italy))

    1992-03-15

    The room temperature oxidation (up to 2500 L) of a Zr-Fe getter having Zr{sub 2}Fe as majority component (80% of the total volume) is studied with X-ray photoemission (h{nu}=1253.6 eV) and Auger spectroscopy. Core photoemission (Zr 3d, Fe 2p and O 1s) and ZrM{sub 45}N{sub 23}V Auger spectra have been measured for increasing oxygen exposure. The oxidation proceeds via an interface suboxide up to an oxide having about the same chemical shift as ZrO{sub 2} (4.3 eV). At saturation the reacted overlayer is about 6 monolayers thick. A small fraction of Fe is found in the reacted overlayer (concentration around 15% of the that of the substrate). (orig.).

  10. Calculation and Study of Graphene Conductivity Based on Terahertz Spectroscopy

    Science.gov (United States)

    Feng, Xiaodong; Hu, Min; Zhou, Jun; Liu, Shenggang

    2017-07-01

    Based on terahertz time-domain spectroscopy system and two-dimensional scanning control system, terahertz transmission and reflection intensity mapping images on a graphene film are obtained, respectively. Then, graphene conductivity mapping images in the frequency range 0.5 to 2.5 THz are acquired according to the calculation formula. The conductivity of graphene at some typical regions is fitted by Drude-Smith formula to quantitatively compare the transmission and reflection measurements. The results show that terahertz reflection spectroscopy has a higher signal-to-noise ratio with less interference of impurities on the back of substrates. The effect of a red laser excitation on the graphene conductivity by terahertz time-domain transmission spectroscopy is also studied. The results show that the graphene conductivity in the excitation region is enhanced while that in the adjacent area is weakened which indicates carriers transport in graphene under laser excitation. This paper can make great contribution to the study on graphene electrical and optical properties in the terahertz regime and help design graphene terahertz devices.

  11. EPR investigations of Mn{sup 2+}, Fe{sup 3+} ions and carbonaceous radicals in atmospheric particulate aerosols during their transport over the eastern coast of the English Channel

    Energy Technology Data Exchange (ETDEWEB)

    Ledoux, F.; Bouhsina, S.; Courcot, L.; Bertho, M.L.; Puskaric, E. [Universite du Littoral Cote d' Opale, Wimereaux (France). Lab. Interdisciplinaire en Sciences de l' Environnement; Zhilinskaya, E.; Aboukais, A. [Universite du Littoral Cote d' Opale, Wimereaux (France). Lab. de Catalyse et Environnement

    2002-07-01

    Electron paramagnetic resonance (EPR) spectroscopy was used to follow the evolution of the chemical forms of manganese and study other paramagnetic species in the atmospheric particulate aerosols at Wimereux, a French station located on the eastern coast of the English Channel. In parallel, Graphite Furnace Atomic Absorption Spectrometry (GFAAS) was used to measure the metal concentrations. Fe concentration values are common in North Sea sites, but those of Mn are quite higher due to the presence of an important local source of Mn. EPR spectra have evidenced isolated Fe{sup 3+} and Mn{sup 2+} ions and carbonaceous products with variable intensities according to the wind directions. Amounts of paramagnetic species and carbonaceous products are maximum for continental winds and minimum for marine winds. Three Mn types were identified depending on the sampling distance from the source of emission and the size of the particles. (Author)

  12. RosettaTMH: a method for membrane protein structure elucidation combining EPR distance restraints with assembly of transmembrane helices

    Directory of Open Access Journals (Sweden)

    Andrew Leaver-Fay

    2015-12-01

    Full Text Available Membrane proteins make up approximately one third of all proteins, and they play key roles in a plethora of physiological processes. However, membrane proteins make up less than 2% of experimentally determined structures, despite significant advances in structure determination methods, such as X-ray crystallography, nuclear magnetic resonance spectroscopy, and cryo-electron microscopy. One potential alternative means of structure elucidation is to combine computational methods with experimental EPR data. In 2011, Hirst and others introduced RosettaEPR and demonstrated that this approach could be successfully applied to fold soluble proteins. Furthermore, few computational methods for de novo folding of integral membrane proteins have been presented. In this work, we present RosettaTMH, a novel algorithm for structure prediction of helical membrane proteins. A benchmark set of 34 proteins, in which the proteins ranged in size from 91 to 565 residues, was used to compare RosettaTMH to Rosetta’s two existing membrane protein folding protocols: the published RosettaMembrane folding protocol (“MembraneAbinitio” and folding from an extended chain (“ExtendedChain”. When EPR distance restraints are used, RosettaTMH+EPR outperforms ExtendedChain+EPR for 11 proteins, including the largest six proteins tested. RosettaTMH+EPR is capable of achieving native-like folds for 30 of 34 proteins tested, including receptors and transporters. For example, the average RMSD100SSE relative to the crystal structure for rhodopsin was 6.1 ± 0.4 Å and 6.5 ± 0.6 Å for the 449-residue nitric oxide reductase subunit B, where the standard deviation reflects variance in RMSD100SSE values across ten different EPR distance restraint sets. The addition of RosettaTMH and RosettaTMH+EPR to the Rosetta family of de novo folding methods broadens the scope of helical membrane proteins that can be accurately modeled with this software suite.

  13. EPR analysis and DFT computations of a series of polynitroxides.

    Science.gov (United States)

    Ottaviani, M Francesca; Modelli, Alberto; Zeika, Olaf; Jockusch, Steffen; Moscatelli, Alberto; Turro, Nicholas J

    2012-01-12

    Polynitroxides with varying numbers of nitroxide groups (one to four) derived from different aromatic core structures show intramolecular electron spin-spin coupling. The scope of this study is to establish an easy methodology for extracting structural, dynamical, and thermodynamical information from the EPR spectra of these polynitroxides which might find use as spin probes in complex systems, such as biological and host/guest systems, and as polarizing agents in dynamic nuclear polarization (DNP) applications. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level provided information on the structural details such as bond lengths and angles in the gas phase, which were compared with the single crystal X-ray diffraction data in the solid state. Polarizable continuum model (PCM) calculations were performed to account for solvent influences. The electron paramagnetic resonance (EPR) spectra of the polynitroxides in chloroform were analyzed in detail to extract information such as the percentages of different conformers, hyperfine coupling constants a, and rotational correlation times τ(c). The temperature dependence on the line shape of the EPR spectra gave thermodynamic parameters ΔH and ΔS for the conformational transitions. These parameters were found to depend on the number and relative positions of the nitroxide and other polar groups.

  14. [Studies on Cancer Diagnosis by Using Spectroscopy Combined with Chemometrics].

    Science.gov (United States)

    Zhang, Zhuo-yong

    2015-09-01

    Studies on cancer diagnosis using various spectroscopic methods combined with chemometrics are briefly reviewed. Elemental contents in serum samples were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES), bidirectional associative memory (BAM) networks were used to establish diagnosis models for the relationships between elemental contents and lung cancer, liver cancer, and stomach cancer, respectively. Near infrared spectroscopy (NIRS) is a non-destructive detection technology. Near infrared spectra of endometrial carcinoma samples were determined and spectral features were extracted by chemoometric methods, a fuzzy rule-based expert system (FuRES) was used for establishing diagnosis model, satisfactory results were obtained. We also proposed a novel variable selection method based on particle swarm optimization (PSO) for near infrared spectra of endometrial carcinoma samples. Spectra with optimized variable were then modeled by support victor machine (SVM). Terahertz technology is an emerging technology for non-destructive detection, which has some unique characteristics. Terahertz time domain spectroscopy (THz-TDS) was used for cervical carcinoma measurement. Absorption coefficients were calculated from the measured time domain spectra and then processed with derivative, orthogonal signal correction (PC-OSC) to reduce interference components, and then fuzzy rule-based expert system (FuRES), fuzzy optimal associative memory (FOAM), support victor machine (SVM), and partial least squares discriminant analysis (PLS-DA) were used for diagnosis model establishment. The above results provide useful information for cancer occurring and development, and provide novel approaches for early stage diagnosis of various cancers.

  15. [Near infrared spectroscopy study on water content in turbine oil].

    Science.gov (United States)

    Chen, Bin; Liu, Ge; Zhang, Xian-Ming

    2013-11-01

    Near infrared (NIR) spectroscopy combined with successive projections algorithm (SPA) was investigated for determination of water content in turbine oil. Through the 57 samples of different water content in turbine oil scanned applying near infrared (NIR) spectroscopy, with the water content in the turbine oil of 0-0.156%, different pretreatment methods such as the original spectra, first derivative spectra and differential polynomial least squares fitting algorithm Savitzky-Golay (SG), and successive projections algorithm (SPA) were applied for the extraction of effective wavelengths, the correlation coefficient (R) and root mean square error (RMSE) were used as the model evaluation indices, accordingly water content in turbine oil was investigated. The results indicated that the original spectra with different water content in turbine oil were pretreated by the performance of first derivative + SG pretreatments, then the selected effective wavelengths were used as the inputs of least square support vector machine (LS-SVM). A total of 16 variables selected by SPA were employed to construct the model of SPA and least square support vector machine (SPA-LS-SVM). There is 9 as The correlation coefficient was 0.975 9 and the root of mean square error of validation set was 2.655 8 x 10(-3) using the model, and it is feasible to determine the water content in oil using near infrared spectroscopy and SPA-LS-SVM, and an excellent prediction precision was obtained. This study supplied a new and alternative approach to the further application of near infrared spectroscopy in on-line monitoring of contamination such as water content in oil.

  16. EPR (Electronic Patient Record Laboratory - Simulated Environment to Learn about a Hospital EPR System

    Directory of Open Access Journals (Sweden)

    Kazuko Yamamoto

    2011-03-01

    Full Text Available The “Electronic Patient Record (EPR Laboratory” is a computer based self-learning system developed for students to acquire practical skills and knowledge required to deal with EPRs. The system is designed to supplement conventional lectures on health information systems given as part of our undergraduate curriculum. Using the Laboratory, the students may learn not only operations of EPR systems but also the subjects connected with patient information handling, including privacy, security and health information ethics. The EPR Laboratory is composed of an eLearing system and an EPR system. The learning materials are arranged in units in the eLearning system, and in each unit, the student learns the materials and the EPR operations through practice. Tests are given at each end of unit, and if a student failed a test, the system shows which questions were answered incorrectly and indicates which parts of the unit he/she should review. For this purpose, we introduced a structure to the learning materials based on an information model. In this paper, the overview of the system, the simulated environment to learn patient flow, information flow and hospital workflow, fundamental EPR operations, and structured learning materials for the test and review cycle are described.

  17. Investigation of radical locations in various sesame seeds by CW EPR and 9-GHz EPR imaging.

    Science.gov (United States)

    Nakagawa, K; Hara, H

    2015-01-01

    We investigated the location of radical in various sesame seeds using continuous-wave (CW) electron paramagnetic resonance (EPR) and 9-GHz EPR imaging. CW EPR detected persistent radicals (single line) for various sesame seeds. The EPR linewidth of black sesame seeds was narrower than that of the irradiated white sesame seeds. A very small signal was detected for the white sesame seeds. Two-dimensional (2D) imaging using a 9-GHz EPR imager showed that radical locations vary for various sesame seeds. The paramagnetic species in black sesame seeds were located on the seed coat (skin) and in the hilum region. The signal with the highest intensity was obtained from the hilum part. A very low-intensity image was observed for the white sesame seeds. In addition, the 2D imaging of the irradiated white sesame seeds showed that free radicals were located throughout the entire seed. For the first time, CW EPR and 9-GHz EPR imaging showed the exact location of radical species in various sesame seeds.

  18. Computational and instrumental methods in EPR

    CERN Document Server

    Bender, Christopher J

    2006-01-01

    Computational and Instrumental Methods in EPR Prof. Bender, Fordham University Prof. Lawrence J. Berliner, University of Denver Electron magnetic resonance has been greatly facilitated by the introduction of advances in instrumentation and better computational tools, such as the increasingly widespread use of the density matrix formalism. This volume is devoted to both instrumentation and computation aspects of EPR, while addressing applications such as spin relaxation time measurements, the measurement of hyperfine interaction parameters, and the recovery of Mn(II) spin Hamiltonian parameters via spectral simulation. Key features: Microwave Amplitude Modulation Technique to Measure Spin-Lattice (T1) and Spin-Spin (T2) Relaxation Times Improvement in the Measurement of Spin-Lattice Relaxation Time in Electron Paramagnetic Resonance Quantitative Measurement of Magnetic Hyperfine Parameters and the Physical Organic Chemistry of Supramolecular Systems New Methods of Simulation of Mn(II) EPR Spectra: Single Cryst...

  19. EPR support for the ketyl radical-anion "triggered" [3,3]-sigmatropic rearrangement.

    Science.gov (United States)

    Enholm, Eric J; Battiste, Merle A; Gallagher, Maria; Moran, Kelley M; Alberti, Angelo; Guerra, Maurizio; Macciantelli, Dante

    2002-09-06

    New physical evidence to support a ketyl radical-anion mechanism for the [3,3]-sigmatropic rearrangement is presented. With use of EPR spectroscopy, spectra are observed that can be attributed to 8, an acyl radical-anion species resulting from a [3,3]-rearrangement; this also functions as a key intermediate in the process. The spectrum of an additional paramagnetic species resulting from further addition of tin-centered radicals to the reaction product was also observed.

  20. Assessing dimerisation degree and cooperativity in a biomimetic small-molecule model by pulsed EPR

    OpenAIRE

    Ackermann, Katrin; Giannoulis, Angeliki; Cordes, David Bradford; Slawin, Alexandra Martha Zoya; Bode, Bela Ernest

    2015-01-01

    AG acknowledges a postgraduate fellowship by the EPSRC funded doctoral training centre ‘integrated magnetic resonance’. BEB is grateful for an EaStCHEM Hirst Academic Fellowship by the School of Chemistry, St Andrews, and funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (REA 334496). Pulsed electron paramagnetic resonance (EPR) spectroscopy is gaining increasing importance as a complementary biophysical technique in structural biol...

  1. Free Radical Scavenging Activity of Drops and Spray Containing Propolis—An EPR Examination

    OpenAIRE

    Pawel Olczyk; Katarzyna Komosinska-Vassev; Pawel Ramos; Lukasz Mencner; Krystyna Olczyk; Barbara Pilawa

    2017-01-01

    The influence of heating at a temperature of 50 °C and UV-irradiation of propolis drops and spray on their free radical scavenging activity was determined. The kinetics of interactions of the propolis samples with DPPH free radicals was analyzed. Interactions of propolis drops and propolis spray with free radicals were examined by electron paramagnetic resonance spectroscopy. A spectrometer generating microwaves of 9.3 GHz frequency was used. The EPR spectra of the model DPPH free radicals we...

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

    Science.gov (United States)

    Desmet, Filip

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

  3. EPR examination of free radical properties of DOPA-melanin complexes with ciprofloxacin, lomefloxacin, norfloxacin and sparfloxacin

    Science.gov (United States)

    Beberok, Artur; Buszman, Ewa; Zdybel, Magdalena; Pilawa, Barbara; Wrześniok, Dorota

    2010-09-01

    Paramagnetic complexes of DOPA-melanin with ciprofloxacin, lomefloxacin, norfloxacin and sparfloxacin were studied by EPR spectroscopy. The aim of this work was to determine free radical concentration and properties of these complexes. Free radical concentrations in the studied complexes were ∼1019-1020 spin/g. Relatively lower and similar (5.1-6.6 × 1019 spin/g) free radical concentrations characterized DOPA-melanin complexes with ciprofloxacin, and lomefloxacin. Higher concentrations (0.8-1.2 × 1020 spin/g) were obtained for complexes of norfloxacin and sparfloxacin. Effect of the drug concentration on free radicals in melanin was observed. Strong dipolar spin-spin interactions and slow spin-lattice relaxation processes exist in all of the samples.

  4. Polarization Studies in Fast-Ion Beam Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Trabert, E

    2001-12-20

    In a historical review, the observations and the insight gained from polarization studies of fast ions interacting with solid targets are presented. These began with J. Macek's recognition of zero-field quantum beats in beam-foil spectroscopy as indicating alignment, and D.G. Ellis' density operator analysis that suggested the observability of orientation when using tilted foils. Lastly H. Winter's studies of the ion-beam surface interaction at grazing incidence yielded the means to produce a high degree of nuclear orientation in ion beams.

  5. Mast-sipping in EPR trademark plants

    Energy Technology Data Exchange (ETDEWEB)

    Langenberger, Jan [AREVA NP GmbH, Erlangen (Germany). Fuel Service; Schienbein, Marcel; Geier, Roland [AREVA NP GmbH, Erlangen (Germany). Radiochemical Lab.

    2010-05-15

    For more than 20 years, AREVA applies and develops different sipping techniques to identify fuel assemblies with leaking fuel rods. For the EPR trademark reactors a Mast Sipping System with newest developments will be implemented considering radiation protection and latest standards requirements. The innovative EPR trademark Sipping System differs from previous systems in many ways. One of the main innovations is that all the necessary processes of the Sipping system have been fully digitized. Second, several ALARA design modifications have been implemented to meet the current radiation protection requirements. An additional implementable multilingual assistance program facilitates the handling of the system and helps to prevent incorrect operation. (orig.)

  6. TL and EPR dating: some applications

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, S. [Institute of Physics, University of Sao Paulo, Sao Paulo (Brazil)

    2006-07-01

    The intensity of thermoluminescence light emitted by a crystal is a function of radiation dose. The number of defects or of radicals in a crystal or organic substances is also a function of radiation dose. Since such defects or radicals present EPR signals, the EPR intensity is also a function of radiation dose. These facts are basis for radiation dosimetry and can be applied in dating of archaeological potteries or other materials, as well as in dating geological substances such as sediments, caves speleothemes, animal teeth and bones. Recent investigation on sensitized quartz based dosimeters and dating calcite covering ancient wall painting to find early settlers in Brazil will be presented. (Author)

  7. Studies of defects and defect agglomerates by positron annihilation spectroscopy

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Singh, B.N.

    1997-01-01

    A brief introduction to positron annihilation spectroscopy (PAS), and in particular lo its use for defect studies in metals is given. Positrons injected into a metal may become trapped in defects such as vacancies, vacancy clusters, voids, bubbles and dislocations and subsequently annihilate from...... the trapped state iri the defect. The annihilation characteristics (e.g., the lifetime of the positron) can be measured and provide information about the nature of the defect (e.g., size, density, morphology). The technique is sensitive to both defect size (in the range from monovacancies up to cavities...

  8. EPR-dosimetry of ionizing radiation

    Science.gov (United States)

    Popova, Mariia; Vakhnin, Dmitrii; Tyshchenko, Igor

    2017-09-01

    This article discusses the problems that arise during the radiation sterilization of medical products. It is propose the solution based on alanine EPR-dosimetry. The parameters of spectrometer and methods of absorbed dose calculation are given. In addition, the problems that arise during heavy particles irradiation are investigated.

  9. The EPR Paradox: Einstein Scrutinises Quantum Mechanics

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 5; Issue 4. The EPR Paradox: Einstein Scrutinises Quantum Mechanics. Arvind. General Article Volume 5 Issue 4 April 2000 pp 28-36. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/005/04/0028-0036 ...

  10. EPR spin trapping of protein radicals

    DEFF Research Database (Denmark)

    Davies, Michael Jonathan; Hawkins, Clare Louise

    2004-01-01

    Electron paramagnetic resonance (EPR) spin trapping was originally developed to aid the detection of low-molecular-mass radicals formed in chemical systems. It has subsequently found widespread use in biology and medicine for the direct detection of radical species formed during oxidative stress...

  11. Rotational coherence spectroscopy at FLASH. Toward dynamic studies in nanosuperfluids

    Energy Technology Data Exchange (ETDEWEB)

    Kickermann, Andreas

    2013-07-15

    The field of molecular physics, which is focusing on molecular motion in the transition states of physical, chemical, and biological changes, is a wide-spread research area. It strives to reveal the structural and functional properties of molecules, the chemical bonds between atoms and the time evolution. Many processes occurring in nature upon electronic excitation proceed on the ultrafast femtosecond timescale and can be triggered by modern ultrashort femtosecond-laser sources under laboratory conditions. In the present thesis pump-probe studies were performed to follow molecular motion using ultrashort light pulses in the nanometer wavelength range provided by an XUV freeelectron laser (FEL). In detail, alignment of molecular species in space under field-free conditions was investigated. In the specific case of rotational wave packets in molecules the rotational dynamics shows characteristic temporal features, which contain a wealth of information on molecular structure and give insight into molecular coupling mechanisms, i.e. rotational constants and transition frequencies. Within this thesis, Rotational Coherence Spectroscopy (RCS) reveals wave-packet motion observed by subsequent Coulomb explosion of Raman excited carbon monoxide, which results in a time-dependent asymmetry of spatial fragmentation patterns. With the method presented here, the time resolution to elucidate the fast dynamics of strong couplings can be pushed toward a single rotational period even for the fastest rotors. This is due to large pump-probe delays with small subpicosecond step size. This kind of spectroscopy can also be expanded to molecular species, which are not accessible by other powerful spectroscopic methods, such as Fourier-transform microwave spectroscopy (FTMW). Furthermore, it allows to measure weak molecular couplings on a long timescale (large pump-probe delays), e.g. couplings of molecules in a solution or molecules dissolved in quantum fluids. This is valuable to

  12. UVB radiation induced effects on cells studied by FTIR spectroscopy

    CERN Document Server

    Di Giambattista, Lucia; Gaudenzi, S; Pozzi, D; Grandi, M; Morrone, S; Silvestri, I; Castellano, A Congiu; 10.1007/s00249-009-0446-9

    2010-01-01

    We have made a preliminary analysis of the results about the eVects on tumoral cell line (lymphoid T cell line Jurkat) induced by UVB radiation (dose of 310 mJ/cm^2) with and without a vegetable mixture. In the present study, we have used two techniques: Fourier transform infrared spectroscopy (FTIR) and flow cytometry. FTIR spectroscopy has the potential to provide the identiWcation of the vibrational modes of some of the major compounds (lipid, proteins and nucleic acids) without being invasive in the biomaterials. The second technique has allowed us to perform measurements of cytotoxicity and to assess the percentage of apoptosis. We already studied the induction of apoptotic process in the same cell line by UVB radiation; in particular, we looked for correspondences and correlations between FTIR spetroscopy and flow cytometry data finding three highly probable spectroscopic markers of apoptosis (Pozzi et al. in Radiat Res 168:698-705, 2007). In the present work, the results have shown significant changes ...

  13. A Mn(II)-Mn(III) EPR signal arises from the interaction of NO with the S1 state of the water-oxidizing complex of photosystem II.

    Science.gov (United States)

    Sarrou, J; Ioannidis, N; Deligiannakis, Y; Petrouleas, V

    1998-03-17

    It was shown recently [Goussias, C., Ioannidis, N., and Petrouleas, V. (1997) Biochemistry 36, 9261-9266] that incubation of photosystem II preparations with NO at -30 degrees C in the dark results in the formation of a new intermediate of the water-oxidizing complex. This is characterized by an EPR signal centered at g = 2 with prominent manganese hyperfine structure. We have examined the detailed structure of the signal using difference EPR spectroscopy. This is facilitated by the observations that NO can be completely removed without decrease or modification of the signal, and illumination at 0 degree C eliminates the signal. The signal spans 1600 G and is characterized by sharp hyperfine structure. 14NO and 15NO cw EPR combined with pulsed ENDOR and ESEEM studies show no detectable contributions of the nitrogen nucleus to the spectrum. The spectrum bears similarities to the experimental spectrum of the Mn(II)-Mn(III) catalase [Zheng, M., Khangulov, S. V., Dismukes, G. C., and Barynin, V. V. (1994) Inorg. Chem. 33, 382-387]. Simulations allowing small variations in the catalase-tensor values result in an almost accurate reproduction of the NO-induced signal. This presents strong evidence for the assignment of the latter to a magnetically isolated Mn(II)-Mn(III) dimer. Since the starting oxidation states of Mn are higher than II, we deduce that NO acts effectively as a reductant, e.g., Mn(III)-Mn(III) + NO--> Mn(II)-Mn(III) + NO+. The temperature dependence of the nonsaturated EPR-signal intensity in the range 2-20 K indicates that the signal results from a ground state. The cw microwave power saturation data in the range 4-8 K can be interpreted assuming an Orbach relaxation mechanism with an excited state at delta = 42 K. Assuming antiferromagnetic coupling, -2JS1.S2, between the two manganese ions, J is estimated to be 10 cm-1. The finding that an EPR signal from the Mn cluster of PSII can be clearly assigned to a magnetically isolated Mn(II)-Mn(III) dimer

  14. Comparison of Laurentian Fulvic Acid luminescence with that of the hydroquinone/quinone model system: Evidence from low temperature fluorescence studies and EPR spectroscopy

    NARCIS (Netherlands)

    Ariese, F.; van Assema, S.G.A.; Gooijer, C.; Bruccoleri, A.G.; Langford, C.H.

    2004-01-01

    Fluorescence techniques have been used to identify humic substances, (e.g. aquatic fulvic acids from different origins). Synchronous scans have proven adequate for distinguishing detail and differentiating samples. As well, fluorescence has often been used to probe humic interactions with metals and

  15. Review: Magnetic Resonance Spectroscopy Studies of Pediatric Major Depressive Disorder

    Directory of Open Access Journals (Sweden)

    Douglas G. Kondo

    2011-01-01

    Full Text Available Introduction. This paper focuses on the application of Magnetic Resonance Spectroscopy (MRS to the study of Major Depressive Disorder (MDD in children and adolescents. Method. A literature search using the National Institutes of Health's PubMed database was conducted to identify indexed peer-reviewed MRS studies in pediatric patients with MDD. Results. The literature search yielded 18 articles reporting original MRS data in pediatric MDD. Neurochemical alterations in Choline, Glutamate, and N-Acetyl Aspartate are associated with pediatric MDD, suggesting pathophysiologic continuity with adult MDD. Conclusions. The MRS literature in pediatric MDD is modest but growing. In studies that are methodologically comparable, the results have been consistent. Because it offers a noninvasive and repeatable measurement of relevant in vivo brain chemistry, MRS has the potential to provide insights into the pathophysiology of MDD as well as the mediators and moderators of treatment response.

  16. Structural dynamics in complex liquids studied with multidimensional vibrational spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Tokmakoff, Andrei [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

    2013-08-31

    The development of new sustainable energy sources is linked to our understanding of the molecular properties of water and aqueous solutions. Energy conversion, storage, and transduction processes, particularly those that occur in biology, fuel cells, and batteries, make use of water for the purpose of moving energy in the form of charges and mediating the redox chemistry that allows this energy to be stored as and released from chemical bonds. To build our fundamental knowledge in this area, this project supports work in the Tokmakoff group to investigate the molecular dynamics of water’s hydrogen bond network, and how these dynamics influence its solutes and the mechanism of proton transport in water. To reach the goals of this grant, we developed experiments to observe molecular dynamics in water as directly as possible, using ultrafast multidimensional vibrational spectroscopy. We excite and probe broad vibrational resonances of water, molecular solutes, and protons in water. By correlating how molecules evolve from an initial excitation frequency to a final frequency, we can describe the underlying molecular dynamics. Theoretical modeling of the data with the help of computational spectroscopy coupled with molecular dynamics simulations provided the atomistic insight in these studies.

  17. Photoluminescence and Raman Spectroscopy Studies of Carbon Nitride Films

    Directory of Open Access Journals (Sweden)

    J. Hernández-Torres

    2016-01-01

    Full Text Available Amorphous carbon nitride films with N/C ratios ranging from 2.24 to 3.26 were deposited by reactive sputtering at room temperature on corning glass, silicon, and quartz as substrates. The average chemical composition of the films was obtained from the semiquantitative energy dispersive spectroscopy analysis. Photoluminescence measurements were performed to determine the optical band gap of the films. The photoluminescence spectra displayed two peaks: one associated with the substrate and the other associated with CNx films located at ≈2.13±0.02 eV. Results show an increase in the optical band gap from 2.11 to 2.15 eV associated with the increase in the N/C ratio. Raman spectroscopy measurements showed a dominant D band. ID/IG ratio reaches a maximum value for N/C ≈ 3.03 when the optical band gap is 2.12 eV. Features observed by the photoluminescence and Raman studies have been associated with the increase in the carbon sp2/sp3 ratio due to presence of high nitrogen content.

  18. Studies in ferromagnetism using electron polarization analysis Spectroscopy

    CERN Document Server

    Saubi, B H

    2001-01-01

    Motivated by recent reports of induced ferromagnetism in non-magnetic transition metals by rare earth metals, we have modified an existing Electron Spectroscopy with Polarization Analysis (ESPA) apparatus to allow for a set of experiments on induced ferromagnetism at Pd:Gd interfaces. We have investigated a number of magnetic materials for their potential as magnetically reversible substrates on which the Gd under layer could be grown. An evaporation source for Gd. suitable for use in Ultra High Vacuum (UHV) has been developed. Auger Electron Spectroscopy (AES) has been used to characterize the growth of Gd on a CO sub 6 sub 6 Si sub 1 sub 5 B sub 1 sub 4 Fe sub 4 Ni sub 1 ribbon substrate held at 100K, by comparing the peak to background (P/B) ratios of Gd and Co Auger lines as a function of overlayer film thickness. We have established that Gd grows in a kinetically limited statistical fashion. The magnetic behaviour of the Gd films on the Co-based ribbon substrate has been studied using Spin Polarized Seco...

  19. Single crystal EPR study of the dinuclear Cu(II) complex [Cu(tda)(phen)](2)·H(2)tda (tda = thiodiacetate, phen = phenanthroline): influence of weak interdimeric magnetic interactions.

    Science.gov (United States)

    Neuman, Nicolás I; Perec, Mireille; González, Pablo J; Passeggi, Mario C G; Rizzi, Alberto C; Brondino, Carlos D

    2010-12-23

    We report powder and single crystal EPR measurements of [Cu(tda)(phen)](2)·H(2)tda (tda = thiodiacetate, phen = phenanthroline) at 9.7 GHz. This compound consists of centrosymmetric copper(II) ion dimers, weakly ferromagnetically exchange-coupled (J = +3.2 cm(-1)), in which the dimeric units are linked by hydrophobic chemical paths involving the phen molecules. EPR revealed that the triplet spectra are collapsed by interdimeric exchange interactions mediated by that chemical path. Analysis and simulation of the single crystal EPR spectra were performed using Anderson's exchange narrowing model, together with statistical arguments. This approach allowed us to interpret the spectra modulated by the interdimeric interactions in situations of weak, intermediate, and strong exchange. We evaluated an interdimeric exchange constant J' = 0.0070(3) cm(-1), indicating that hydrophobic paths can transmit weak exchange interactions between centers at relatively long distances of the order of ∼10 Å.

  20. A microwave absorption study in the thermochromic SrMnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez, G. [Departamento de Materiales Metalicos y Ceramicos, Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, 04510 Coyoacan, DF (Mexico)], E-mail: memodin@yahoo.com; Heiras, J. [Centro de Ciencias de la Materia Condensada, Universidad Nacional Autonoma de Mexico, Apartado Postal 356, 22800 Ensenada, BC (Mexico); Castellanos, M. [Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, 04510 Mexico DF (Mexico); Valenzuela, R. [Departamento de Materiales Metalicos y Ceramicos, Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, 04510 Coyoacan, DF (Mexico)

    2008-07-15

    We report electron paramagnetic resonance (EPR) and magnetically modulated microwave absorption spectroscopy (MAMMAS) studies at X-band (8.8-9.6 GHz) on powdered SrMnO{sub 3} in the 90-400 K temperature range. EPR spectrum shows one broad single-line at room temperature, which is observed only above 280.5 K, being compatible with an antiferromagnetic order. The onset of the para-antiferromagnetic transition has been determined from the temperature dependence of three main parameters extracted from the EPR spectra: resonant field (H{sub res}), peak-to-peak linewidth ({delta}H{sub pp}) and integrated intensity (I{sub EPR}). The MAMMAS response shows a change in the region 276-283 K, compatible with the para-antiferromagnetic transition, without presenting any significant change in the region of thermochromism.

  1. The study of 'microsurfaces' using thermal desorption spectroscopy

    Science.gov (United States)

    Thomas, M. E.; Poppa, H.; Pound, G. M.

    1979-01-01

    The use of a newly combined ultrahigh vacuum technique for studying continuous and particulate evaporated thin films using thermal desorption spectroscopy (TDS), transmission electron microscopy (TEM), and transmission electron diffraction (TED) is discussed. It is shown that (1) CO thermal desorption energies of epitaxially deposited (111) Ni and (111) Pd surfaces agree perfectly with previously published data on bulk (111) single crystal, (2) contamination and surface structural differences can be detected using TDS as a surface probe and TEM as a complementary technique, and (3) CO desorption signals from deposited metal coverages of one-thousandth of a monolayer should be detectable. These results indicate that the chemisorption properties of supported 'microsurfaces' of metals can now be investigated with very high sensitivity. The combined use of TDS and TEM-TED experimental methods is a very powerful technique for fundamental studies in basic thin film physics and in catalysis.

  2. [Infrared spectroscopy and XRD studies of coral fossils].

    Science.gov (United States)

    Chen, Quan-li; Zhou, Guan-min; Yin, Zuo-wei

    2012-08-01

    Coral fossil is an old remain of multicellular animal on the earth, and formed by various geological processes. The structural characteristics and compositions of the coral fossils with different color and radial texture on the surface were studied by infrared absorption spectroscopy and X-ray powder diffraction analyses. The results show that the studied coral fossils mainly are composed of SiO2, and the radial microstructure characterized by the calcareous coral cross-section is preserved. It is formed by metasomatism by SiO2. The infrared absorption spectra of the coral fossil with different color and texture are essentially the same, showing typical infrared absorption spectra of the quartz jade. XRD analysis shows that the main components of the coral fossils with different color and texture are consistent and mainly composed of SiO2 with a trace amount of other minerals and without CaCO3.

  3. Non-invasive determination of the irradiation dose in fingers using low-frequency EPR

    Energy Technology Data Exchange (ETDEWEB)

    Zdravkova, M [Laboratory of Biomedical Magnetic Resonance, Universite catholique de Louvain, UCL, Avenue Hippocrate, 10, B-1200 Brussels (Belgium); Crokart, N [Laboratory of Biomedical Magnetic Resonance, Universite catholique de Louvain, UCL, Avenue Hippocrate, 10, B-1200 Brussels (Belgium); Trompier, F [Service de Dosimetrie Externe, Departement de Radioprotection et de Protection de l' Homme, Institut de Radioprotection et de Surete Nucleaire, IRSN, BP no 17, F-92262 Fontenay-aux-Roses Cedex (France); Beghein, N [Laboratory of Biomedical Magnetic Resonance, Universite catholique de Louvain, UCL, Avenue Hippocrate, 10, B-1200 Brussels (Belgium); Gallez, B [Laboratory of Biomedical Magnetic Resonance, Universite catholique de Louvain, UCL, Avenue Hippocrate, 10, B-1200 Brussels (Belgium); Debuyst, R [Laboratory of Biomedical Magnetic Resonance, Universite catholique de Louvain, UCL, Avenue Hippocrate, 10, B-1200 Brussels (Belgium)

    2004-07-07

    Several reports in the literature have described the effects of radiation in workers who exposed their fingers to intense radioactive sources. The radiation injuries occurring after local exposure to a high dose (20 to 100 Gy) could lead to the need for amputation. Follow-up of victims needs to be more rational with a precise knowledge of the irradiated area that risks tissue degradation and necrosis. It has been described previously that X-band electron paramagnetic resonance (EPR) spectroscopy could be used to assess the dose in irradiated amputated fingers. Here, we propose the use of low-frequency EPR spectroscopy to evaluate non-invasively the absorbed dose. Low-frequency microwaves are indeed less absorbed by water and penetrate more deeply into living material ({approx}10 mm in tissues using 1 GHz spectrometers). This work presents preliminary results obtained with baboon and human fingers compared with human dry phalanxes placed inside a surface-coil resonator. The EPR signal increased linearly with the dose. The ratio of the slopes of the dry bone to whole finger linear regression lines was around 5. The detection limit achievable with the present spectrometer and resonator is around 60 Gy, which is well within the range of accidentally exposed fingers. It is likely that the detection limit could be improved in the future, thanks to further technical spectrometer and resonator developments as well as to appropriate spectrum deconvolution into native and dosimetric signals.

  4. Magnetic resonance spectroscopy and imaging for the study of fossils.

    Science.gov (United States)

    Giovannetti, Giulio; Guerrini, Andrea; Salvadori, Piero A

    2016-07-01

    Computed tomography (CT) has long been used for investigating palaeontological specimens, as it is a nondestructive technique which avoids the need to dissolve or ionize the fossil sample. However, magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) have recently gained ground as analytical tools for examination of palaeontological samples, by nondestructively providing information about the structure and composition of fossils. While MRI techniques are able to reveal the three-dimensional geometry of the trace fossil, MRS can provide information on the chemical composition of the samples. The multidimensional nature of MR (magnetic resonance) signals has potential to provide rich three-dimensional data on the palaeontological specimens and also to help in elucidating paleopathological and paleoecological questions. In this work the verified applications and the emerging uses of MRI and MRS in paleontology are reviewed, with particular attention to fossil spores, fossil plants, ambers, fossil invertebrates, and fossil vertebrate studies. Copyright © 2016 Elsevier Inc. All rights reserved.

  5. Relaxation dispersion NMR spectroscopy for the study of protein allostery.

    Science.gov (United States)

    Farber, Patrick J; Mittermaier, Anthony

    2015-06-01

    Allosteric transmission of information between distant sites in biological macromolecules often involves collective transitions between active and inactive conformations. Nuclear magnetic resonance (NMR) spectroscopy can yield detailed information on these dynamics. In particular, relaxation dispersion techniques provide structural, dynamic, and mechanistic information on conformational transitions occurring on the millisecond to microsecond timescales. In this review, we provide an overview of the theory and analysis of Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion NMR experiments and briefly describe their application to the study of allosteric dynamics in the homeodomain from the PBX transcription factor (PBX-HD). CPMG NMR data show that local folding (helix/coil) transitions in one part of PBX-HD help to communicate information between two distant binding sites. Furthermore, the combination of CPMG and other spin relaxation data show that this region can also undergo local misfolding, reminiscent of conformational ensemble models of allostery.

  6. Proton MR spectroscopy in neuroborreliosis: a preliminary study

    Energy Technology Data Exchange (ETDEWEB)

    Ustymowicz, A.; Tarasow, E.; Walecki, J. [Department of Radiology, Medical Academy, Bialystok (Poland); Zajkowska, J.; Hermanowska-Szpakowicz, T. [Department of Infectious Diseases and Neuroinfections, Medical Academy, Bialystok (Poland)

    2004-01-01

    We report results of a magnetic resonance spectroscopy (MRS) study in 12 patients with neuroborreliosis. We used a PRESS sequence, placing an 8 cm{sup 3} voxel in normal-appearing white matter of the frontal lobe. Peaks indicating N-acetylaspartate (NAA), choline (Cho), creatine (Cr), myo-inositol (mI), lipids (Lip) and lactate (Lac) were identified and ratios of NAA/Cr, Cho/Cr, mI/Cr, Lip/Cr, Lac/Cr calculated. Significant increases in Cho/Cr and Lip/Cr were noted. No abnormality was found in mean NAA/Cr and Lac/Cr, but in four patients there was a decreased NAA peak; mI/Cr ratio was slightly increased. Although the spectroscopic profile in patients with neuroborreliosis seems to be nonspecific, MRS might be useful for assessing tissue damage of the central nervous system. (orig.)

  7. Medical reference dosimetry using EPR measurements of alanine

    DEFF Research Database (Denmark)

    Helt-Hansen, Jakob; Rosendal, F.; Kofoed, I.M.

    2009-01-01

    Background. Electron spin resonance (EPR) is used to determine the absorbed dose of alanine dosimeters exposed to clinical photon beams in a solid-water phantom. Alanine is potentially suitable for medical reference dosimetry, because of its near water equivalence over a wide energy spectrum, low...... methods the proposed algorithm can be applied without normalisation of phase shifts caused by changes in the g-value of the cavity. The study shows that alanine dosimetry is a suitable candidate for medical reference dosimetry especially for quality control applications....

  8. EPR dosimetry of radiation background in the Urals region

    Energy Technology Data Exchange (ETDEWEB)

    Shishkina, E.A.; Degteva, M.O.; Shved, V.A. [Urals Research Center for Radiation Medicine, 48-A Vorovsky, Chelyabinsk 454076 (Russian Federation); Fattibene, P.; Onori, S. [Istituto Superiore di Sanita and Istituto Nazionale di Fisica Nucleare (Italy); Wieser, A. [GSF, Forschungszentrum fuer Umwelt und Gesundheit, Ingolstaedter Landstr (Germany); Ivanov, D.V.; Bayankin, S.N. [Institute of Metal Physics, Russian Academy of Sciences (Russian Federation); Knyazev, V.A.; Vasilenko, E.I.; Gorelov, M. [ZAO, Closed Corporation ' Company GEOSPETSECOLOGIA' (Russian Federation)

    2006-07-01

    Method of Electron Paramagnetic Resonance is extensively applied to individual retrospective dosimetry. The background dose is unavoidable component of cumulative absorbed dose in the tooth enamel accumulated during the lifetime of donor. Estimation of incidental radiation dose using tooth enamel needs in extraction of background dose. Moreover, the variation of background doses in the population is a limited factor for reliable detection of additional irradiation especially for low dose level. Therefore the accurate knowledge of the natural background radiation dose is a critical element of EPR studies of exposed populations. In the Urals region the method applies for such two large cohorts as the workers of Mayak (Ozersk citizens) and Techa River riverside inhabitants (rural population). Current study aimed to investigate the Urals radiation background detected by EPR spectrometry. For this aim two group of unexposed Urals residents were separated, viz: citizens of Ozersk and rural inhabitants of Chelyabinsk region. Comparison of two investigated territories has demonstrated that from the point of view of radiation background it is impossible to assume the Urals population as uniform. The reliable difference between the urban and rural residents has been found. The average background doses of Ozersk donors is in average 50 mGy higher than those detected for rural residents. The individual variability of background doses for Osersk has been higher than in the rural results. The difference in background dose levels between two population results in different limits of accidental dose detection and individualization. The doses for 'Mayak' workers (Ozyorsk citizens) can be classed as anthropogenic if the EPR measurements exceed 120 mGy for teeth younger than 40 years, and 240 mGy for teeth older than 70 years. The anthropogenic doses for Techa River residents (rural population) would be higher than 95 mGy for teeth younger than 50 years and 270 mGy for

  9. Laser Raman Spectroscopy in studies of corrosion and electrocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Melendres, C.A.

    1988-01-01

    Laser Raman Spectroscopy (LRS) has become an important tool for the in-situ structural study of electrochemical systems and processes in recent years. Following a brief introduction of the experimental techniques involved in applying LRS to electrochemical systems, we survey the literature for examples of studies in the inhibition of electrode reactions by surface films (e.g., corrosion and passivation phenomena) as well as the acceleration of reactions by electro-sorbates (electrocatalysis). We deal mostly with both normal and resonance Raman effects on fairly thick surface films in contrast to surface-enhanced Raman investigations of monolayer adsorbates, which is covered in another lecture. Laser Raman spectroelectrochemical studies of corrosion and film formation on such metals as Pb, Ag, Fe, Ni, Co, Cr, Au, stainless steel, etc. in various solution conditions are discussed. Further extension of the technique to studies in high-temperature and high-pressure aqueous environments is demonstrated. Results of studies of the structure of corrosion inhibitors are also presented. As applications of the LRS technique in the area of electrocatalysis, we cite studies of the structure of transition metal macrocyclic compounds, i.e., phthalocyanines and porphyrins, used for catalysis of the oxygen reduction reaction. 104 refs., 20 figs.

  10. EPR oximetry of tumors in vivo in cancer therapy

    Science.gov (United States)

    Šentjurc, Marjeta; Čemažar, Maja; Serša, Gregor

    2004-05-01

    The partial oxygen pressure ( pO 2) in tumors is considered to be one of important factors that affect the response of tumors to different treatment. Therefore, we anticipate that the information about the variation of oxygen concentration in tumors can be used as a guide for individualizing radiotherapy, chemotherapy, and especially the combined therapies. There is thus a need to obtain quantitative data on the effects of different therapies on tumor oxygenation under in vivo conditions. One of the methods, which enable these measurements is EPR oximetry. In this work basic principles of the method will be described as well as some examples of tumor oxygenation changes after application of chemotherapeutic drugs (vinblastine, cisplatin, bleomycin) or electric pulses in combination with cisplatin or bleomycin to fibrosarcoma SA-1 tumors in mice. A paramagnetic probe, a char of Bubinga tree, was implanted into the tumor (center and periphery) and in the muscle or subcutis. EPR spectra line-width, which is proportional to oxygen concentration, was measured with time after the treatments. Tumor oxygenation was reduced for 58% of pretreatment value 1 h after intraperitoneal injection of 2.5 mg kg -1 VLB and returned to pretreatment level within 24 h. Reduction in oxygenation of muscle and subcutis was much smaller and returned to pretreatment value faster as in tumors. With cisplatin (4 mg kg -1) and bleomicyn (1 mg kg -1) the reduction was less than 15%, but increases in combined therapy to 70%. Similar reduction was observed also with electric pulses alone (eight pulses, 1300 V cm -1, 100 μs, 1 Hz) with fast recovery of 8 h. After electrochemotherapy the recovery was slower and occurs only after 48 h. This study demonstrates that EPR oximetry is a sensitive method for monitoring changes in tissue oxygenation after different treatments, which may have implications in controlling side effects of therapy and in the planning of combined treatments.

  11. Full cycle rapid scan EPR deconvolution algorithm

    Science.gov (United States)

    Tseytlin, Mark

    2017-08-01

    Rapid scan electron paramagnetic resonance (RS EPR) is a continuous-wave (CW) method that combines narrowband excitation and broadband detection. Sinusoidal magnetic field scans that span the entire EPR spectrum cause electron spin excitations twice during the scan period. Periodic transient RS signals are digitized and time-averaged. Deconvolution of absorption spectrum from the measured full-cycle signal is an ill-posed problem that does not have a stable solution because the magnetic field passes the same EPR line twice per sinusoidal scan during up- and down-field passages. As a result, RS signals consist of two contributions that need to be separated and postprocessed individually. Deconvolution of either of the contributions is a well-posed problem that has a stable solution. The current version of the RS EPR algorithm solves the separation problem by cutting the full-scan signal into two half-period pieces. This imposes a constraint on the experiment; the EPR signal must completely decay by the end of each half-scan in order to not be truncated. The constraint limits the maximum scan frequency and, therefore, the RS signal-to-noise gain. Faster scans permit the use of higher excitation powers without saturating the spin system, translating into a higher EPR sensitivity. A stable, full-scan algorithm is described in this paper that does not require truncation of the periodic response. This algorithm utilizes the additive property of linear systems: the response to a sum of two inputs is equal the sum of responses to each of the inputs separately. Based on this property, the mathematical model for CW RS EPR can be replaced by that of a sum of two independent full-cycle pulsed field-modulated experiments. In each of these experiments, the excitation power equals to zero during either up- or down-field scan. The full-cycle algorithm permits approaching the upper theoretical scan frequency limit; the transient spin system response must decay within the scan

  12. Characterisation of prehnite by EPMA, Mössbauer, optical absorption and EPR spectroscopic methods.

    Science.gov (United States)

    Reddy, N C Gangi; Fayazyddin, S Md; Reddy, R Rama Subba; Reddy, G Siva; Reddy, S Lakshmi; Rao, P Sambasiva; Reddy, B Jagannatha

    2005-11-01

    A sample of prehnite from Rayalaseema zone of Andhra Pradesh, India containing about 2.565 wt.% Fe(2)O(3) is used in the present work. The mineral has been characterized by EPMA, optical absorption, EPR, NIR and Mössbauer techniques. Mössbauer studies confirm the presence of iron as an impurity in two sites. An EPR study on powder sample confirm the presence of Fe(III) impurity in the mineral. Optical absorption spectrum also indicates that Fe(III) impurity is present in two sites with octahedral structure. NIR results are due to water fundamentals.

  13. Hydration structure of the Ti(III) cation as revealed by pulse EPR and DFT studies: new insights into a textbook case.

    Science.gov (United States)

    Maurelli, Sara; Livraghi, Stefano; Chiesa, Mario; Giamello, Elio; Van Doorslaer, Sabine; Di Valentin, Cristiana; Pacchioni, Gianfranco

    2011-03-21

    The (17)O and (1)H hyperfine interactions of water ligands in the Ti(III) aquo complex in a frozen solution were determined using Hyperfine Sublevel Correlation (HYSCORE) and Pulse Electron Nuclear Double Resonance (ENDOR) spectroscopies at 9.5 GHz. The isotropic hyperfine interaction (hfi) constant of the water ligand (17)O was found to be about 7.5 MHz. (1)H Single Matched Resonance Transfer (SMART) HYSCORE spectra allowed resolution of the hfi interactions of the two inequivalent water ligand protons and the relative orientations of their hfi tensors. The magnetic and geometrical parameters extracted from the experiments were compared with the results of DFT computations for different geometrical arrangements of the water ligands around the cation. The theoretical observable properties (g tensor (1)H and (17)O hfi tensors and their orientations) of the [Ti(H(2)O)(6)](3+) complex are in quantitative agreement with the experiments for two slightly different geometrical arrangements associated with D(3d) and C(i) symmetries.

  14. Time-Resolved EPR Study of Electron-Hole Dissociations Influenced by Alkyl Side Chains at the Photovoltaic Polyalkylthiophene:PCBM Interface.

    Science.gov (United States)

    Miura, Taku; Aikawa, Motoko; Kobori, Yasuhiro

    2014-01-02

    Nanosecond time-resolved electron paramagnetic resonance (TREPR) spectroscopy has been utilized at T = 77 K to characterize alkyl side-chain effects on geometries and on the electronic couplings (VCR) of transient charge-separated (CS) states in the photoactive layers fabricated by the spin-coating of mixed solutions of regioregular polyalkylthiophenes (RR-P3AT) and [6,6]-C61-butyric acid methyl ester (PCBM). By increasing the alkyl side-chain number from 6 to 12 in P3AT, a highly distant and long-lived CS state has been obtained. This result is explained by a coupling of the hole dissociation to the polymer librations by the side-chains. From an exponential decay of VCR with respect to the CS distance, the attenuation factor (βe) has been determined to be βe = 0.2 Å(-1). Such a long-range tunneling feature is explained by the generations of the shallowly trapped, delocalized electron-hole pairs by the dissociation of the hole toward π-stacking directions at the organic photovoltaic interface.

  15. Crystallite arrangement of hydroxyapatite microcrystals in human tooth cementum as revealed by electron paramagnetic resonance (EPR)

    Energy Technology Data Exchange (ETDEWEB)

    Skaleric, U.; Gaspirc, B. [Univ. of Ljubljana, Jozef Stefan Inst., Center for Dental Research, Ljubljana (Slovenia); Cevc, P.; Schara, M. [Univ. of Ljubljana, Jozef Stefan Inst., EPR Center Ljubljana, Ljubljana (Slovenia)

    1998-08-01

    Human dental cementum was analyzed by electron paramagnetic resonance (EPR). The measured EPR powder spectra of {gamma}-irradiated cementum resembled those of {gamma}irradiated enamel. Both spectra were characterized by the same line shapes and g values. The position of the extreme first derivate peaks can be described by g{sub 1}=2.0023 and g{sub 2}=1.9971{+-}0.0002, and are assignable to the CO{sub 3}{sup 3-} center. The angular dependence of the cementum EPR spectra indicates a different arrangement of the hydroxyapatite microcrystals compared to that of enamel. A corresponding model of cementum micro-crystal alignment has been proposed. The methodology presented can be utilized for studying the mineralization process of root cementum and other mineralized tissues. (au) 14 refs.

  16. Infrared Heterodyne Spectroscopy and its Unique Application to Planetary Studies

    Science.gov (United States)

    Kostiuk, Theodore

    2009-01-01

    Since the early 1970's the infrared heterodyne technique has evolved into a powerful tool for the study of molecular constituents, temperatures, and dynamics in planetary atmospheres. Its extremely high spectral resolution (Lambda/(Delta)Lambda/>10(exp 6)) and highly accurate frequency measurement (to 1 part in 10(exp 8)) enabled the detection of nonthermal/natural lasing phenomena on Mars and Venus; direct measurements of winds on Venus, Mars, and Titan; study of mid-infrared aurorae on Jupiter; direct measurement of species abundances on Mars (ozone, isotopic CO2), hydrocarbons on Jupiter, Saturn., Neptune, and Titan, and stratospheric composition in the Earth's stratosphere (O3, CIO, N2O, CO2 ....). Fully resolved emission and absorption line shapes measured by this method enabled the unambiguous retrieval of molecular abundances and local temperatures and thermal structure in regions not probed by other techniques. The mesosphere of Mars and thermosphere of Venus are uniquely probed by infrared heterodyne spectroscopy. Results of these studies tested and constrained photochemical and dynamical theoretical models describing the phenomena measured. The infrared heterodyne technique will be described. Highlights in its evolution to today's instrumentation and resultant discoveries will be presented, including work at Goddard Space Flight Center and the University of Koln. Resultant work will include studies supporting NASA and ESA space missions and collaborations between instrumental and theoretical groups.

  17. 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

    Science.gov (United States)

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

    2017-12-01

    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 27Al atom and all its relevant 14N and 27Al 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 Al3+ 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 Al3+ 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.

  18. Study on Senna alata and its different extracts by Fourier transform infrared spectroscopy and two-dimensional correlation infrared spectroscopy

    Science.gov (United States)

    Adiana, M. A.; Mazura, M. P.

    2011-04-01

    Senna alata L. commonly known as candle bush belongs to the family of Fabaceae and the plant has been reported to possess anti-inflammatory, analgesic, laxative and antiplatelet-aggregating activity. In order to develop a rapid and effective analysis method for studying integrally the main constituents in the medicinal materials and their extracts, discriminating the extracts from different extraction process, comparing the categories of chemical constituents in the different extracts and monitoring the qualities of medicinal materials, we applied Fourier transform infrared spectroscopy (FT-IR) associated with second derivative infrared spectroscopy and two-dimensional infrared correlation spectroscopy (2D-IR) to study the main constituents of S. alata and its different extracts (extracted by hexane, dichloromethane, ethyl acetate and methanol in turn). The findings indicated that FT-IR and 2D-IR can provide many holistic variation rules of chemical constituents. Use of the macroscopical fingerprint characters of FT-IR and 2D-IR spectrum can identify the main chemical constituents in medicinal materials and their extracts, but also compare the components differences among similar samples. In a conclusion, FT-IR spectroscopy combined with 2D correlation analysis provides a powerful method for the quality control of traditional medicines.

  19. EPR determination of the mechanism of the oxidation of alkenyl aminophosphites

    Energy Technology Data Exchange (ETDEWEB)

    Il' yasov, A.V.; Kibardin, A.M.; Morozov, V.I.; Gryaznov, P.I.; Vafina, A.A.; Pudovik, A.N.

    1987-10-20

    Aminophosphites that contain a vinyl group on the nitrogen atom are oxidized easily by atmospheric oxygen. Since it is important to clarify the nature of this reaction in order to understand the reactivity of organic phosphites, the authors have made an EPR study of the reaction of these phosphites with oxygen. Unstable intermediate paramagnetic reaction products were trapped in the presence of 2-methyl-nitrosopropane, ..cap alpha..-phenyl-N-tert-butylnitrone, and chloroaniline, compounds that served as spin traps. The hyperfine structure of the EPR spectra can be attributed to the interaction of an unpaired electron with nuclei of hydrogen, nitrogen, and phosphorus atoms.

  20. Application of jade samples for high-dose dosimetry using the EPR technique

    Energy Technology Data Exchange (ETDEWEB)

    Teixeira, Maria Ines [Instituto de Pesquisas Energeticas e Nucleares/Comissao Nacional de Energia Nuclear Av. Prof. Lineu Prestes 2242, 05508-000, Sao Paulo (Brazil)], E-mail: miteixei@ipen.br; Melo, Adeilson P. [Instituto de Pesquisas Energeticas e Nucleares/Comissao Nacional de Energia Nuclear Av. Prof. Lineu Prestes 2242, 05508-000, Sao Paulo (Brazil); Centro Federal de Educacao Tecnologica de Sergipe, Aracaju (Brazil)], E-mail: adeilson_pessoa_melo@yahoo.com.br; Ferraz, Gilberto M. [Depto. de Fisica Nuclear, Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo (Brazil)], E-mail: gmarconf@if.usp.br; Caldas, Linda V.E. [Instituto de Pesquisas Energeticas e Nucleares/Comissao Nacional de Energia Nuclear Av. Prof. Lineu Prestes 2242, 05508-000, Sao Paulo (Brazil)], E-mail: lcaldas@ipen.br

    2010-04-15

    The dosimeter characteristics of jade samples were studied for application in high-dose dosimetry. Jade is the common denomination of two silicates: jadeite and actinolite. The EPR spectra of different jade samples were obtained after irradiation with absorbed doses of 100 Gy up to 20 kGy. The jade samples present signals that increase with the absorbed dose (g-factors around 2.00); they can be attributed to electron centers. The EPR spectra obtained for the USA jade samples and their main dosimetric properties as reproducibility, calibration curves and energy dependence were investigated.

  1. Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

    DEFF Research Database (Denmark)

    Godiksen, Anita; Vennestrøm, Peter N. R.; Rasmussen, Søren Birk

    2017-01-01

    Recent quantitative electron paramagnetic resonance spectroscopy (EPR) data on different copper species present in copper exchanged CHA zeolites are presented and put into context with the literature on other copper zeolites. Results presented herein were obtained using ex situ and in situ EPR...

  2. Early Amyloidogenic Oligomerization Studied through Fluorescence Lifetime Correlation Spectroscopy

    OpenAIRE

    Angel Orte; Lorena Varela; Fabio Castello; Elena Fernandez; Salvador Casares; Ruedas-Rama, Maria J.; Jose M. Paredes

    2012-01-01

    Amyloidogenic protein aggregation is a persistent biomedical problem. Despite active research in disease-related aggregation, the need for multidisciplinary approaches to the problem is evident. Recent advances in single-molecule fluorescence spectroscopy are valuable for examining heterogenic biomolecular systems. In this work, we have explored the initial stages of amyloidogenic aggregation by employing fluorescence lifetime correlation spectroscopy (FLCS), an advanced modification of conve...

  3. Supported organometallic complexes: Surface chemistry, spectroscopy, and catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Marks, T.J.

    1991-02-01

    Adsorbing organometallic molecules onto the surfaces of inorganic supports such as Al{sub 2}O{sub 3}, MgCl{sub 2}, SiO{sub 2}, etc. can result in dramatic enhancements in catalytic activity. The reasons for this and the structures of the resulting surface organometallic centers are not well understood. We have addressed this problem using thorium, uranium, and early transition metal complexes as model adsorbates. Characterization tools include catalytic and stoichiometric reaction chemistry, reaction kinetics and isotopic labeling, quantitative poisoning studies, model solution chemistry, and a wide array of surface-sensitive physicochemical techniques such as CPMAS, NMR, EPR, and optical spectroscopy as well as titration calorimetry.

  4. Molecular structure and single crystal EPR spectra of bis(L-Valinato)copper(II) monohydrate, Cu[H 2NCH(CH 3) 2CHCO 2] 2·H 2O

    Science.gov (United States)

    Steren, C. A.; Calvo, R.; Castellano, E. E.; Fabiane, M. S.; Piro, O. E.

    1990-09-01

    A magnetic-structural study of the title compound, Cu(L-Val) 2·H 2O, employing EPR spectroscopy and X-ray diffraction methods is presented. The complex crystallizes in the space group C2 with a = 21.314(5) Å, b = 9.586(2) Å, c = 7.417(2) Å, β = 108.89(2)°, and Z=4. The Cu(II) ions, which are in a five-fold pyramidal coordination, with two valine molecules and a water oxygen (O w), are arranged in layers parallel to (100). Neighboring Cu(L-Val) 2·H 2O molecules in a layer are linked to each other by a net of O w-H…O and N-H…O hydrogen bonds. The single EPR line observed arises from the collapse of the resonances due to the two magnetically inequivalent Cu(II) ions in the lattice caused by the exchange interaction. The obtained g⌈ = 2.254(1) and g⊥ = 2.061(1) principal values of the molecular gyromagnetic tensor point to a d( x2- y2) orbital for the unpaired electron. The orientation of this orbital was also obtained from our EPR data. The angular variation of the resonance line width has contributions arising from the dipolar interaction modulated by exchange effects in a two-dimensional magnetic lattice, and from the incomplete collapse of the hyperfine structure. The EPR results are compared to those obtained in other copper amino acid complexes.

  5. EPR-Bohr and Quantum Trajectories: Entaglement and Nonlocality

    OpenAIRE

    Floyd, Edward R.

    2010-01-01

    Quantum trajectories are used to investigate the EPR-Bohr debate in a modern sense by examining entanglement and nonlocality. We synthesize a single "entanglement molecule" from the two scattered particles of the EPR experiment. We explicitly investigate the behavior of the entanglement molecule rather than the behaviors of the two scattered particles to gain insight into the EPR-Bohr debate. We develop the entanglement molecule's wave function in polar form and its reduced action, both of wh...

  6. Josephson Effect in Graphene: a Tunneling Spectroscopy Study

    Science.gov (United States)

    Bretheau, Landry; Wang, Joel I.-Jan; Pisoni, Riccardo; Watanabe, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo

    A normal conductor placed in good contact with a superconductor can inherit its electronic properties. This proximity effect in the conductor originates from the formation of entangled electron-hole states, called Andreev states. Spectroscopic studies of Andreev states have been performed in just a handful of systems. Graphene provides a novel platform for studying Andreev physics in two dimensions because of its large mobility, ease of access and electrostatically tunable carrier density. Using a full van der Waals heterostructure, we have performed direct tunnelling spectroscopy of proximitized graphene. The measured energy spectra, which depend on the phase difference between the superconductors and on graphene carrier density, reveal a continuum of Andreev bound states. We further infer the supercurrent they carry from the phase dependence of the spectra, thus relating Andreev physics and the Josephson effect. As graphene's extended two-dimensional nature enables one to combine superconductivity and the quantum Hall effect, this platform is promising for the detection of Majorana modes, key ingredients for topologically protected quantum computation.

  7. Spectroscopy Study of Synthetic Forsterite Obtained from Zeolite Precursors

    Directory of Open Access Journals (Sweden)

    Subotić, B.

    2008-02-01

    Full Text Available Important ceramics materials are prepared from aluminosilicate based precursors using novel methods, offering at the same time a better control over many important properties. Forsterite, due to its good refractoriness with melting point at 2163 K, excellent electrical insulation properties even at high temperatures, low dielectric permittivity, thermal expansion and chemical stability, is a material of interest to engineers and designers especially as an active medium for tuneable laser and is also a material of interest to SOFC (Solid oxide fuel cells manufacturers. The aim of this study is to investigate the synthesis of crystalline forsterite using different zeolite precursors previously activated by ball milling. Synthetic forsterite was synthesized from different zeolite precursors and MgO combining highenergy ball milling and thermal treatment of the mixture under determined conditions of time and temperature for each operation. In this research are studied the solid-state phase transformations taking place at temperatures below 1273 K. The obtained products were characterized using different spectroscopy techniques in comparison with surface analysis method and X-ray diffraction.

  8. The application of near infrared spectroscopy in nutritional intervention studies

    Directory of Open Access Journals (Sweden)

    Philippa A Jackson

    2013-08-01

    Full Text Available Functional near infrared spectroscopy (NIRS is a non-invasive optical imaging technique used to monitor cerebral blood flow (CBF and by proxy neuronal activation. The use of NIRS in nutritional intervention studies is a relatively novel application of this technique, with only a small, but growing, number of trials published to date. These trials—in which the effects on CBF following administration of dietary components such as caffeine, polyphenols and omega-3 polyunsaturated fatty acids are assessed—have successfully demonstrated NIRS as a sensitive measure of change in haemodynamic response during cognitive tasks in both acute and chronic treatment intervention paradigms. The existent research in this area has been limited by the constraints of the technique itself however advancements in the measurement technology, paired with studies endeavouring increased sophistication in number and locations of channels over the head should render the use of NIRS in nutritional interventions particularly valuable in advancing our understanding of the effects of nutrients and dietary components on the brain.

  9. Variation of long-lived free radicals responsible for the EPR native signal in bone of aged or diseased human females and ovariectomized adult rats

    Energy Technology Data Exchange (ETDEWEB)

    Kenner, G.H. E-mail: gerry.kenner@m.cc.utah.edu; Brik, A.B.; Liu, G.; Haskell, E.H.; Hayes, R.B.; Knight, J.A.; Vajda, E.G.; Miller, S.C.; Jee, W.S.S.; Barrus, J.K

    2005-06-01

    The purpose of this study was to gain insights into the variations seen in the electron paramagnetic resonance (EPR) spectroscopy of the native signals of teeth and bones used for retrospective dosimetry measurements. We determined that changes occur in the long-lived free radicals responsible for the native signal of cortical bone in aging or diseased human females and aged ovariectomized rats. This was done by measuring the magnitude of the broad (BC) and narrow (NC) components of the native EPR signal of bone following chemical extraction, aging, crushing and thermal annealing. Bone from the upper midshaft of femora of young (17-34 years old, n=5) and elderly (70-92 years old, n=18) females was examined. The results showed that the elderly women had significantly higher BC than the younger women (P<0.01). A similar interpretation was made of the data from an aging female rat osteoporosis model. The results for the NC signals were similar. Finally, dramatic decreases in both NC and BC signals were seen in HIV positive and uncontrolled diabetic (one each) patients indicating the need for studying this signal for a broad spectrum of metabolic disorders. Experiments were performed which strongly indicate that iron liganded with organic molecules is the source of the BC signal. Finally, the accuracy achieved in this study indicates that resolving the dosimetric signal (g=2.0018) should be improved by subtraction of the deconvoluted NC and BC signals from the original spectrum.

  10. New Developments in Spin Labels for Pulsed Dipolar EPR

    Directory of Open Access Journals (Sweden)

    Alistair J. Fielding

    2014-10-01

    Full Text Available Spin labelling is a chemical technique that enables the integration of a molecule containing an unpaired electron into another framework for study. Given the need to understand the structure, dynamics, and conformational changes of biomacromolecules, spin labelling provides a relatively non-intrusive technique and has certain advantages over X-ray crystallography; which requires high quality crystals. The technique relies on the design of binding probes that target a functional group, for example, the thiol group of a cysteine residue within a protein. The unpaired electron is typically supplied through a nitroxide radical and sterically shielded to preserve stability. Pulsed electron paramagnetic resonance (EPR techniques allow small magnetic couplings to be measured (e.g., <50 MHz providing information on single label probes or the dipolar coupling between multiple labels. In particular, distances between spin labels pairs can be derived which has led to many protein/enzymes and nucleotides being studied. Here, we summarise recent examples of spin labels used for pulse EPR that serve to illustrate the contribution of chemistry to advancing discoveries in this field.

  11. Toward Computational Spectroscopy Studies for Large Molecular Systems

    Science.gov (United States)

    Biczysko, Malgorzata; Bloino, Julien; Barone, Vincenzo

    2013-06-01

    Integrated computational approaches built on quantum mechanical (QM) methods combined with time-independent schemes to account for nuclear motion effects are applied to the spectroscopic investigation of molecular systems, from large biomolecules to hybrid supra-molecular systems. Within the time-independent approaches, vibrational spectra are computed including anharmonicities through perturbative corrections while UV-vis line-shapes are simulated accounting for the vibrational structure; in both cases, the environmental effects are taken into account by explicit or continuum models. Extension to larger systems relies on reduced dimensionality approaches and effective schemes to select transitions of interest, available for both vibrational and vibronic spectra. Such procedures are exploited to simulate IR and UV-vis spectra leading in all cases to good agreement with experimental observations and allowing to dissect different effects underlying spectral phenomena, finally, paving a feasible route toward the state-of-the-art computational spectroscopy studies, even for relatively large molecular systems [1,2]. 1. V. Barone, A. Baiardi, M. Biczysko, J. Bloino, C. Cappelli, F. Lipparini Phys. Chem. Chem. Phys, 14, 12404, 2012 2. V. Barone, M. Biczysko, J. Bloino, M. Borkowska-Panek, I. Carnimeo, P. Panek, Int. J. Quantum Chem. 112, 2185, 2012

  12. Laser Spectroscopy Studies in the Neutron-Rich Sn Region

    CERN Multimedia

    Obert, J

    2002-01-01

    We propose to use the powerful laser spectroscopy method to determine the magnetic moment $\\mu$ and the variation of the mean square charge radius ($\\delta\\,\\langle$r$_{c}^{2}\\,\\rangle$) for ground and long-lived isomeric states of the Sn isotopes from A=125 to the doubly-magic $^{132}$Sn isotope and beyond. For these neutron-rich Sn nuclei, numerous $\\delta\\,\\langle$r$^{2}_{c}\\,\\rangle$ curves have already been calculated and the predictions depend upon the effective interactions used. Therefore, a study of the effect of the shell closure N=82 on the $\\delta\\,\\langle$r$^{2}_{c}\\,\\rangle$ values in the Z=50 magic nuclei is of great interest, especially because $^{132}$Sn is located far from the stability valley. It will help to improve the parameters of the effective interactions and make them more suitable to predict the properties of exotic nuclei. \\\\ \\\\The neutron-rich Sn isotopes produced with an uranium carbide target, are ionized using either a hot plasma ion source or the resonant ionization laser ion ...

  13. Study of gas detection based on integrated cavity output spectroscopy

    Science.gov (United States)

    Pei, Shixin; Cui, Fenping; Su, Jing; Xu, Linhua; Sun, Tingting

    2013-08-01

    A trace gases detection system based on integrated cavity output spectroscopy (ICOS) was developed, where a NIR tunable diode laser (TDL) was used as light source, an optical cavity composed by two plan-concave mirrors with reflection near 99.7% was used as the absorption cell. Trace water vapour (H2O), carbon dioxide (CO2), methane (CH4), carbon monoxide (CO) and mixture of CO2 and CO were tested by ICOS based on the characteristics absorption. The wavelength calibration, cavity transmission characteristics, quantitative measurement ability and sensitivity of the TDL-ICOS were also studied, and a evaluated minimum detectable sensitivity of 1.15 × 10-7 cm-1 was obtained when the system was used to CH4 detection. The experiment results show that TDL-ICOS is expected to be a reliable and promising system for the detection of trace gases since it has some advantages such as real-time monitoring, simple device, easy operation, high sensitivity, good stability and quantitative ability.

  14. High-field CW electron paramagnetic resonance spectroscopy with Gd(III) tags for structure-dynamics studies of proteorhodopsin

    Science.gov (United States)

    Clayton, Jessica A.; Han, Chung-Ta; Wilson, C. Blake; Qi, Mian; Godt, Adelheid; Goldfarb, Daniella; Sherwin, Mark S.; Han, Songi

    Proteorhodopsin (PR) is a seven-helical transmembrane protein that functions as a light-activated proton pump. Much of the structure of PR has been mapped by solution-state NMR and X-ray crystallography, however it remains difficult to study protein associations and conformational changes. Here we report development of 240 GHz CW electron paramagnetic resonance (EPR) as a tool to determine inter- and intra-protein distances in the range of 1-4 nm under biologically relevant conditions, using S = 7/2 Gd(III)-based complexes as an EPR-active paramagnetic tag. The dipolar coupling between Gd(III) pairs is determined via the width of the central transition in the CW EPR spectrum, allowing for the inference of an interspin distance. Proof-of-principle experiments are demonstrated on Gd-ruler molecules, from cryogenic temperatures up to room temperature. First results applying this method to inter-protein measurement of Gd(III) tagged PR oligomers reveals distances consistent with the penta- or hexameric organization determined by crystal structure. Finally, we present progress towards development of measurement methods that will enable observation of light-induced conformational changes in the EF-loop region of PR at temperatures above the protein dynamical transition. This work is supported by NSF MCB-1617025 and NSF MCB-1244651.

  15. Interactions of short-acting, intermediate-acting and pre-mixed human insulins with free radicals--Comparative EPR examination.

    Science.gov (United States)

    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.

  16. EPR dosimetric properties of nano-barium sulfate

    Science.gov (United States)

    Aboelezz, E.; Hassan, G. M.; Sharaf, M. A.; El-Khodary, A.

    2015-01-01

    Nano/micro BaSO4 were prepared through the co-precipitation method to measure ionizing radiation doses using electron paramagnetic resonance (EPR). The nano-BaSO4 sample was characterized using X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. The dose response and fading properties of nano- and micro-phase BaSO4 were compared in EPR spectra. The prepared nano- and micro-BaSO4 samples have the same hole and electron centers, which may be attributed to SO4- and SO3-, respectively. The dosimetric signals for prepared nano- and micro-BaSO4 have spectroscopic splitting factor (g) with values 2.0025±0.0006 and 2.0027±0.0006, respectively. The nanocrystalline sample has a linear γ-ray dose response over the range 0.4 Gy-1 kGy. The performance parameters which including detection limit and critical level calculated from weighted and unweighted least-squares fitting. The sensitivity of nano-BaSO4 to γ-ray is one and a half times more than alanine. The lifetime and activation energy for nano-BaSO4 were estimated by conducting a thermal stability study, and were 5.7±1.1×104 years and 0.73±0.14 eV, respectively. The combined and expanded uncertainties accompanying measurements were ±3.89% and ±7.78%, respectively.

  17. Early Amyloidogenic Oligomerization Studied through Fluorescence Lifetime Correlation Spectroscopy

    Directory of Open Access Journals (Sweden)

    Angel Orte

    2012-07-01

    Full Text Available Amyloidogenic protein aggregation is a persistent biomedical problem. Despite active research in disease-related aggregation, the need for multidisciplinary approaches to the problem is evident. Recent advances in single-molecule fluorescence spectroscopy are valuable for examining heterogenic biomolecular systems. In this work, we have explored the initial stages of amyloidogenic aggregation by employing fluorescence lifetime correlation spectroscopy (FLCS, an advanced modification of conventional fluorescence correlation spectroscopy (FCS that utilizes time-resolved information. FLCS provides size distributions and kinetics for the oligomer growth of the SH3 domain of α-spectrin, whose N47A mutant forms amyloid fibrils at pH 3.2 and 37 °C in the presence of salt. The combination of FCS with additional fluorescence lifetime information provides an exciting approach to focus on the initial aggregation stages, allowing a better understanding of the fibrillization process, by providing multidimensional information, valuable in combination with other conventional methodologies.

  18. Angle-resolved photoemission spectroscopy (ARPES) studies of cuprate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Palczewski, Ari Deibert [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    This dissertation is comprised of three different angle-resolved photoemission spectroscopy (ARPES) studies on cuprate superconductors. The first study compares the band structure from two different single layer cuprates Tl2Ba2CuO6+δ (Tl2201) Tc,max ~95 K and (Bi1.35Pb0.85)(Sr1.47La0.38)CuO6+δ (Bi2201) Tc,max 35 K. The aim of the study was to provide some insight into the reasons why single layer cuprate's maximum transition temperatures are so different. The study found two major di erences in the band structure. First, the Fermi surface segments close to ( π,0) are more parallel in Tl2201 than in Bi2201. Second, the shadow band usually related to crystal structure is only present in Bi2201, but absent in higher Tc Tl2201. The second study looks at the different ways of doping Bi2Sr2CaCu2O8+δ (Bi2212) in-situ by only changing the post bake-out vacuum conditions and temperature. The aim of the study is to systematically look into the generally overlooked experimental conditions that change the doping of a cleaved sample in ultra high vacuum (UHV) experiments. The study found two major experimental facts. First, in inadequate UHV conditions the carrier concentration of Bi2212 increases with time, due to the absorption of oxygen from CO2/CO molecules, prime contaminants present in UHV systems. Second, in a very clean UHV system at elevated temperatures (above about 200 K), the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. The final study probed the particle-hole symmetry of the pseudogap phase in high temperature superconducting cuprates by looking at the thermally excited bands above the Fermi level. The data showed a particle-hole symmetric pseudogap which symmetrically closes away from the nested FS before the node. The data is consistent with

  19. Angle-resolved photoemission spectroscopy (ARPES) studies of cuprate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Palczewski, Ari Deibert [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    This dissertation is comprised of three different angle-resolved photoemission spectroscopy (ARPES) studies on cuprate superconductors. The first study compares the band structure from two different single layer cuprates Tl2Ba2CuO6+δ (Tl2201) Tc, max ≈ 95 K and (Bi 1.35Pb0.85)(Sr1.47La0.38)CuO6+δ (Bi2201) Tc, max ≈ 35 K. The aim of the study was to provide some insight into the reasons why single layer cuprate's maximum transition temperatures are so different. The study found two major differences in the band structure. First, the Fermi surface segments close to (π,0) are more parallel in Tl2201 than in Bi2201. Second, the shadow band usually related to crystal structure is only present in Bi2201, but absent in higher Tc Tl2201. The second study looks at the different ways of doping Bi2Sr2CaCu2O8+δ (Bi2212) in-situ by only changing the post bake-out vacuum conditions and temperature. The aim of the study is to systematically look into the generally overlooked experimental conditions that change the doping of a cleaved sample in ultra high vacuum (UHV) experiments. The study found two major experimental facts. First, in inadequate UHV conditions the carrier concentration of Bi2212 increases with time, due to the absorption of oxygen from CO2/CO molecules, prime contaminants present in UHV systems. Second, in a very clean UHV system at elevated temperatures (above about 200 K), the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. The final study probed the particle-hole symmetry of the pseudogap phase in high temperature superconducting cuprates by looking at the thermally excited bands above the Fermi level. The data showed a particle-hole symmetric pseudogap which symmetrically closes away from the nested FS before the node. The data is

  20. Vibrational spectroscopy studies of formalin-fixed cervix tissues.

    Science.gov (United States)

    Krishna, C M; Sockalingum, G D; Vadhiraja, B M; Maheedhar, K; Rao, A C K; Rao, L; Venteo, L; Pluot, M; Fernandes, D J; Vidyasagar, M S; Kartha, V B; Manfait, M

    2007-02-15

    Optical histopathology is fast emerging as a potential tool in cancer diagnosis. Fresh tissues in saline are ideal samples for optical histopathology. However, evaluation of suitability of ex vivo handled tissues is necessitated because of severe constraints in sample procurement, handling, and other associated problems with fresh tissues. Among these methods, formalin-fixed samples are shown to be suitable for optical histopathology. However, it is necessary to further evaluate this method from the point of view discriminating tissues with minute biochemical variations. A pilot Raman and Fourier transform infrared (FTIR) microspectroscopic studies of formalin-fixed tissues normal, malignant, and after-2-fractions of radiotherapy from the same malignant cervix subjects were carried out, with an aim to explore the feasibility of discriminating these tissues, especially the tissues after-2-fractions of radiotherapy from other two groups. Raman and FTIR spectra exhibit large differences for normal and malignant tissues and subtle differences are seen between malignant and after-2-fractions of radiotherapy tissues. Spectral data were analyzed by principal component analysis (PCA) and it provided good discrimination of normal and malignant tissues. PCA of data of three tissues, normal, malignant, and 2-fractions after radiotherapy, gave two clusters corresponding to normal and malignant + after-2-fractions of radiotherapy tissues. A second step of PCA was required to achieve discrimination between malignant and after-2-fractions of radiotherapy tissues. Hence, this study not only further supports the use of formalin-fixed tissues in optical histopathology, especially from Raman spectroscopy point of view, it also indicates feasibility of discriminating tissues with minute biochemical differences such as malignant and after-2-fractions of radiotherapy. 2006 Wiley Periodicals, Inc.

  1. The effect of charged axial ligands on the EPR parameters in oxovanadium(IV) compounds: an unusual reduction of the Az (51V) values.

    Science.gov (United States)

    Tolis, E J; Teberekidis, V I; Raptopoulou, C P; Terzis, A; Sigalas, M P; Deligiannakis, Y; Kabanos, T A

    2001-06-18

    Two series of octahedral oxovanadium(IV) compounds, containing charged or neutral axial ligands, with the tetradentate amidate molecules Hcapca and H2capcah of the general formulae trans-[V(IV)OX(capca)]0/+ (where X = Cl- (1.CH2Cl2), SCN- (2), N3 (3), CH3COO- (4), PhCOO- (5), imidazole (6. CH3NO2), and eta-nBuNH2 (7)) and cis-[V(VI)OX(Hcapcah)]0/+ (where X = Cl- (8.0.5CH2Cl2), SCN (9), N3 (10.2CH3OH), and imidazole (11)), were synthesized and characterized by X-ray crystallography (1.CH3OH,8.CHCl3, 9.2CH3CN, 10.CH3CN and cis-[VO(imidazole)(Hcapcah)+) and continuous-wave electron paramagnetic resonance (cw EPR) spectroscopy. In addition to the synthesis, crystallographic and EPR studies, the optical, infrared and magnetic properties (room temperature) of these compounds are reported. Ab initio calculations were also carried out on compound 8 CHCl3 and revealed that this isomer is more stable than the trans isomer, in good agreement with the experimental data. The cw EPR studies of compounds 1-5, that is, the V(IV)O2+ species containing monoanionic axial ligands, revealed a novel phenomenon of the reduction of their A, components by about 10% relative to the N4 reference compounds ([V(IV)O-(imidazole)4]2+ and [V(IV)O(2,2-bipyridine)2]2+). In marked contrast, such a reduction is not observed in compounds 6. CH3NO2-11, which contain neutral axial ligands. Based on the spin-Hamiltonian formalism a theoretical explanation is put forward according to which the observed reduction of Az is due to a reduction of the electron - nuclear dipolar coupling (P). The present findings bear strong relevance to cw EPR studies of oxovanadium(IV) in vanadoproteins, V(IV)O2+-substituted proteins, and in V(IV)O2+ model compounds, since the hyperfine coupling constant, Az, has been extensively used as a benchmark for identification of equatorial-donor-atom sets in oxovanadium(IV) complexes.

  2. Free Radical Scavenging Activity of Drops and Spray Containing Propolis-An EPR Examination.

    Science.gov (United States)

    Olczyk, Pawel; Komosinska-Vassev, Katarzyna; Ramos, Pawel; Mencner, Lukasz; Olczyk, Krystyna; Pilawa, Barbara

    2017-01-13

    The influence of heating at a temperature of 50 °C and UV-irradiation of propolis drops and spray on their free radical scavenging activity was determined. The kinetics of interactions of the propolis samples with DPPH free radicals was analyzed. Interactions of propolis drops and propolis spray with free radicals were examined by electron paramagnetic resonance spectroscopy. A spectrometer generating microwaves of 9.3 GHz frequency was used. The EPR spectra of the model DPPH free radicals were compared with the EPR spectra of DPPH in contact with the tested propolis samples. The antioxidative activity of propolis drops and propolis spray decreased after heating at the temperature of 50 °C. A UV-irradiated sample of propolis drops more weakly scavenged free radicals than an untreated sample. The antioxidative activity of propolis spray increased after UV-irradiation. The sample of propolis drops heated at the temperature of 50 °C quenched free radicals faster than the unheated sample. UV-irradiation weakly changed the kinetics of propolis drops or spray interactions with free radicals. EPR analysis indicated that propolis drops and spray should not be stored at a temperature of 50 °C. Propolis drops should not be exposed to UV-irradiation.

  3. EPR: what has it taught us

    Energy Technology Data Exchange (ETDEWEB)

    Stapp, H.P.

    1985-05-01

    This symposium commemorating the fiftieth anniversary of the paper of Einstein, Podolsky, and Rosen is a fitting place to review what that work and its sequels have taught us. Prima facie, the EPR paper appears to have been exceedingly counter-productive for the following reasons: (1) The work was quickly rebutted by Bohr, and this rebuttal was apparently accepted by most workers in the field. (2) Scientists who adopted the position advocated by Bohr have produced, in the intervening fifty years, a marvelous body of useful theory, whereas those following the course suggested by EPR have produced nothing of any certified practical value. (3) It has been shown by Bell that the conclusion reached by EPR is incompatible with their assumptions. Chemists and physicists have recently begun to examine the behavior of quantum mechanical systems that are very small, yet large enough to influence their environment in ways that appreciably modify their own behavior, vis-a-vis the behavior they would have if isolated. Because these systems are neither small enough to be treated as isolated (or as residing in a classically described environment) between preparation and detection, nor large enough to be treated classically, they do not conform to the format demanded by the Copenhagen interpretation. Indeed, the behavior of these systems depends on ontological considerations that were irrelevant in the situations covered by the Copenhagen interpretation, and that were systematically ignored in that interpretation. Scientists now face the task of enlarging the scope of quantum theory to cover these new situations, and comparing the empirical consequences of various ontological assumptions. 17 refs.

  4. EPR and luminescence studies of the radiation induced Eu.sup.2+./sup. centers in the EuAl.sub.3./sub.(BO.sub.3./sub.).sub.4./sub. single crystals

    Czech Academy of Sciences Publication Activity Database

    Prokhorov, Andriy; Chernush, L.F.; Babin, Vladimir; Buryi, Maksym; Savchenko, Dariia; Lančok, Ján; Nikl, Martin; Prokhorov, A.D.

    2017-01-01

    Roč. 66, Apr (2017), s. 428-433 ISSN 0925-3467 R&D Projects: GA MŠk LO1409; GA MŠk LM2015088 Institutional support: RVO:68378271 Keywords : EPR spectra * multiferroics * rare-earth * luminescence * aluminum borates * X-ray irradiation * spin Hamiltonian parameters * superposition model Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.238, year: 2016

  5. Synthesis and EPR-spectroscopic characterization of the perchlorotriarylmethyl tricarboxylic acid radical (PTMTC) and its (13)C labelled analogue (13C-PTMTC).

    Science.gov (United States)

    Elewa, Marwa; Maltar-Strmečki, Nadica; Said, Mohamed M; El Shihawy, Hosam A; El-Sadek, Mohamed; Frank, Juliane; Drescher, Simon; Drescher, Malte; Mäder, Karsten; Hinderberger, Dariush; Imming, Peter

    2017-03-01

    A hydrophilic tris(tetrachlorotriaryl)methyl (tetrachloro-TAM) radical labelled 50% with (13)C at the central carbon atom was prepared. The mixture of isotopologue radicals was characterised by continuous wave and pulsed X-band electron paramagnetic spectroscopy (EPS). For the pharmaceutical and medical applications planned, the quantitative influence of oxygen, viscosity, temperature and pH on EPR line widths was studied in aqueous buffer, DMSO, water-methanol and water-glycerol mixtures. Under in vivo conditions, pH can be disregarded. There is a clear oxygen dependence of the width of the (12)C isotopologue single EPR line in aqueous solutions while changes in rotational motion (viscosity) are observable only in the doublet lines of the central carbon of the (13)C isotopologue. The tetrachloro-TAM proved to be very stable as a solid. Its thermal decay was determined quantitatively by thermal annealing. Towards ascorbic acid as a reducing agent and towards an oocyte cell extract it had a half-life of approx. 60 and 10 min. Thus for in vivo applications, 50% (13)C tetrachloro-TAMs are suitable for selective and simultaneous oxygen and macroviscosity measurements in a formulation, e.g. nanocapsules.

  6. A Mononuclear Mn(II) Pseudoclathrochelate Complex Studied by Multi-Frequency Electron-Paramagnetic-Resonance Spectroscopy.

    Science.gov (United States)

    Azarkh, Mykhailo; Penkova, Larysa V; Kats, Svitlana V; Varzatskii, Oleg A; Voloshin, Yan Z; Groenen, Edgar J J

    2014-03-06

    Knowledge of the correlation between structural and spectroscopic properties of transition-metal complexes is essential to deepen the understanding of their role in catalysis, molecular magnetism, and biological inorganic chemistry. It provides topological and, sometimes, functional insight with respect to the active site properties of metalloproteins. The electronic structure of a high-spin mononuclear Mn(II) pseudoclathrochelate complex has been investigated by electron-paramagnetic-resonance (EPR) spectroscopy at 9.5 and 275.7 GHz. A substantial, virtually axial zero-field splitting with D = -9.7 GHz (-0.32 cm(-1)) is found, which is the largest one reported to date for a Mn(II) complex with six nitrogen atoms in the first coordination sphere.

  7. Teaching the EPR paradox at high school?

    Science.gov (United States)

    Pospiech, Gesche

    1999-09-01

    The discovery of quantum mechanics at the beginning of our century led to a revolution of the physical world view. Modern experiments, made possible by new techniques on the border of the classical and the quantum regimes, offer new insights and better understanding of the quantum world and have an impact on new technological development. Therefore it seems important that students at university and in the final years of high school gain an appreciation of the principles of quantum mechanics. A suitable way seems to be through treatment of the EPR gedanken experiment (thought experiment).

  8. Laser light-scattering spectroscopy: a new application in the study of ciliary activity.

    Science.gov (United States)

    Lee, W I; Verdugo, P

    1976-09-01

    A uniquely precise and simple method to study ciliary activity by laser light-scattering spectroscopy has been developed and validated. A concurrent study of the effect of Ca2+ on ciliary activity in vitro by laser scattering spectroscopy and high speed cinematography has demonstrated that this new method is simpler and as accurate and reproducible as the high speed film technique.

  9. Impedance spectroscopy studies of surface engineered TiO2 ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Dielectric analysis of nanometre range size ceramic particles like TiO2 is very important in the understanding of the performance and design of their polymer nanocomposites for energy storage and other applications. In recent times, impedance spectroscopy is shown to be a very powerful tool to investigate the.

  10. Dynamics in photosynthetic transient complexes studied by paramagnetic NMR spectroscopy

    NARCIS (Netherlands)

    Scanu, Sandra

    2013-01-01

    This PhD thesis focuses on fundamental aspects of protein-protein interactions. A multidisciplinary methodology for the detection and visualization of transient, lowly-populated encounter protein complexes is described. The new methodology combined paramagnetic NMR spectroscopy with computational

  11. Phase transitions reflected in HF-EPR spectra

    NARCIS (Netherlands)

    Horst, Eric van der

    2006-01-01

    EPR is a technique limited to unpaired electrons. Current state of the art set-ups operate at frequencies of 130 GHz or higher. The benefits are increased resolution and the ability to measure large D systems. Using EPR data combined with other techniques systems in which (magnetic) phase

  12. Electron Paramagnetic Resonance Spectroscopy

    Indian Academy of Sciences (India)

    IAS Admin

    Recently, electron paramagnetic resonance (EPR) spectros- copy has emerged as a powerful tool to study the structure and dynamics of biological macromolecules such as proteins, protein aggregates, RNA and DNA. It is used in combination with molecular modelling to study complex systems such as soluble proteins ...

  13. Diagnostic study of laser-produced tungsten plasma using optical emission spectroscopy and time-of-flight mass spectroscopy

    Science.gov (United States)

    Wu, Ding; Zhang, Lei; Liu, Ping; Sun, Liying; Hai, Ran; Ding, Hongbin

    2017-11-01

    In this work, the plasma was produced by irradiating a tungsten target with an 8 ns pulsed Nd:YAG (λ = 1064 nm) laser in a vacuum chamber under the pressure of 4 × 10- 4 Pa. The optical and particle emissions were systematically investigated using laser induced breakdown spectroscopy and time-of-flight mass spectroscopy respectively. The results showed that not only there were neutral and single ionized atoms in the laser induced plasma, but also quite a number of multi-charged ions were observed. The ion charge state was even up to 6 at the laser power density of 11 GW/cm2. Time and space resolved optical spectroscopy was investigated by using a bundle of lined fibers. Meanwhile, the time-resolved mass spectrometric study of laser produced tungsten plasma was carried out. The variation in intensities of the different species with time showed that higher charged ions reached their peak intensities earlier. This demonstrated that the higher charged ions had higher velocities and the different charged ions were separated during the expansion process. The kinetic energy corresponding to the velocity of the ions was found to increase exponentially with ionic charge state which was related to the acceleration of the dynamic plasma sheath.

  14. Electron spin dynamics of Ce3 + ions in YAG crystals studied by pulse-EPR and pump-probe Faraday rotation

    Science.gov (United States)

    Azamat, D. V.; Belykh, V. V.; Yakovlev, D. R.; Fobbe, F.; Feng, D. H.; Evers, E.; Jastrabik, L.; Dejneka, A.; Bayer, M.

    2017-08-01

    The spin relaxation dynamics of Ce3 + ions in heavily cerium-doped YAG crystals is studied using pulse-electron paramagnetic resonance and time-resolved pump-probe Faraday rotation. Both techniques address the 4 f ground state, while pump-probe Faraday rotation also provides access to the excited 5 d state. We measure a millisecond spin-lattice relaxation time T1, a microsecond spin coherence time T2, and a ˜10 ns inhomogeneous spin dephasing time T2* for the Ce3 + ground state at low temperatures. The spin-lattice relaxation of Ce3 + ions is due to modified Raman processes involving the optical phonon mode at ˜125 cm-1 . The relaxation at higher temperature goes through a first excited level of the 5/2 2F term at about ℏ ω ≈228 cm-1 . Effects provided by the hyperfine interaction of the Ce3 + with the 27Al nuclei are observed.

  15. Electron paramagnetic resonance studies of magnetically aligned phospholipid bilayers utilizing a phospholipid spin label: the effect of cholesterol.

    Science.gov (United States)

    Dave, Paresh C; Nusair, Nisreen A; Inbaraj, Johnson J; Lorigan, Gary A

    2005-08-15

    X-band EPR spectroscopy has been employed to study the dynamic properties of magnetically aligned phospholipid bilayers (bicelles) utilizing a variety of phosphocholine spin labels (n-PCSL) as a function of cholesterol content. The utilization of both perpendicular and parallel aligned bicelles in EPR spectroscopy provides a more detailed structural and orientational picture of the phospholipid bilayers. The magnetically aligned EPR spectra of the bicelles and the hyperfine splitting values reveal that the addition of cholesterol increases the phase transition temperature and alignment temperature of the DMPC/DHPC bicelles. The corresponding molecular order parameter, Smol, of the DMPC/DHPC bicelles increased upon addition of cholesterol. Cholesterol also decreased the rotational motion and increased the degree of anisotropy in the interior region of the bicelles. This report reveals that the dynamic properties of DMPC/DHPC bicelles agree well with other model membrane systems and that the magnetically aligned bicelles are an excellent model membrane system.

  16. NO sub 3 , the study of molecular properties and photodissociation by ab initio method, spectroscopy, and translational spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, B.

    1990-10-01

    This report discusses the following topics: molecular structure of NO{sub 3} radical studied by laser induced fluorescence; photodissociation and fluorescence spectroscopy of NO{sub 3} in molecular beam; vertical electronic spectrum of NO{sub 3}:{sup 2}A{prime}{sub 2}, {sup 2}E{double prime}({sup 2}A{sub 2}{sup 2}B{sub 1}), and {sup 2}E{prime} states; and Ab initio study of the vibrational spectra of NO{sub 3}.

  17. CO{sub 2} doped γ-irradiated hydroxyapatite for EPR dosimetry

    Energy Technology Data Exchange (ETDEWEB)

    Ziaie, Farhood [Nuclear Science and Technology Resesarch Institute, Tehran (Iran, Islamic Republic of). Radiation Application Research School

    2014-11-15

    Synthetic nano-structure hydroxyapatite samples were doped by carbon in furnace via exposing to CO{sub 2} circulating gas in different time of 30, 120, and 360 min under 100 C and 400 C of temperatures. FTIR, TEM and XRD analyses results confirmed the doping of carbonate group to the hydroxyapatite structure. The samples were irradiated in absorbed doses of 2, 5, 10, 20, 50, and 80 kGy using a {sup 60}Co γ-ray source and subjected to EPR measurement, subsequently. The EPR signal intensities were constructed as a function of radiation dose, were compared with the results of raw sample and were studied from dosimetric point of view. The obtained results show a considerable increment in EPR signal intensities of the samples which were treated at 400 C. At the doses less than 20 kGy the carbon doped samples show a better EPR respond. This is much better for doses below 5 kGy in comparison to the raw samples and the response is quite linear.

  18. Microrheology of viscoelastic solutions studied by magnetic rotational spectroscopy

    CERN Document Server

    Berret, Jean-François

    2016-01-01

    Magnetic rotational spectroscopy is based on the use of magnetic micron-size wires for viscosity measurements. Submitted to a rotational magnetic field with increasing frequency, the wires undergo a hydrodynamic instability between a synchronous and an asynchronous regime. From a comparison between predictions and experiments, the static shear viscosity and elastic modulus of wormlike micellar solutions are here determined. The values agree with the determination by cone-and-plate rheometry.

  19. Study of an organogelator by diffusion-ordered NMR spectroscopy.

    Science.gov (United States)

    Dama, Murali; Berger, Stefan

    2013-05-09

    The low-molecular weight organogelator 2,3-di-n-decyloxyanthracene was synthezised and dissolved in dimethyl sulfoxide. With diffusion-ordered NMR spectroscopy, the temperature dependence of the diffusion coefficients was measured and a clear hysteresis of the gelation was observed between 320 and 330 K. This hysteresis was interpreted with respect to different entanglement behavior on heating and cooling. No alignment of the gelator with respect to the magnetic field was found despite its 14 π-electrons.

  20. Brain Biochemistry and Personality: A Magnetic Resonance Spectroscopy Study

    OpenAIRE

    Ryman, Sephira G.; Gasparovic, Chuck; Bedrick, Edward J.; Flores, Ranee A.; Marshall, Alison N.; Jung, Rex E.

    2011-01-01

    To investigate the biochemical correlates of normal personality we utilized proton magnetic resonance spectroscopy ((1)H-MRS). Our sample consisted of 60 subjects ranging in age from 18 to 32 (27 females). Personality was assessed with the NEO Five-Factor Inventory (NEO-FFI). We measured brain biochemistry within the precuneus, the cingulate cortex, and underlying white matter. We hypothesized that brain biochemistry within these regions would predict individual differences across major domai...