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Sample records for lytb epr metallacycles

  1. LytB1 and LytB2 of Mycobacterium tuberculosis Are Not Genetically Redundant

    PubMed Central

    Brown, Amanda Claire; Kokoczka, Rachel; Parish, Tanya

    2015-01-01

    Mycobacterium tuberculosis synthesises isoprenoid precursors via the MEP/DOXP pathway and at least five enzymes in the pathway (Dxs1, Dxr/IspC, IspD, IspF, and GcpE/IspG) are required for growth in vitro. We investigated the role of LytB (IspH) in M. tuberculosis; M. tuberculosis is unusual in that it has two homologs–LytB1 and LytB2. We were unable to delete the lytB2 gene unless we provided an additional copy elsewhere, demonstrating that this is the essential homolog. We expressed lytB1 from the lytB2 promoter and confirmed that this could not complement for loss of function of lytB2, despite LytB1 possessing all the previously described conserved critical residues. Interestingly the sole LytB homolog of Mycobacterium smegmatis was able to compensate for loss of LytB2 in M. tuberculosis. We tested translational fusions of LytB1 and LytB2 for functionality in M. tuberculosis, but only a fusion with 90% N-terminal LytB2 and 10% C-terminal LytB1 was functional. In order to identify the key difference between the two proteins, site directed mutagenesis was used to change LytB2 residues into their counterparts in LytB1. None of these amino acid substitutions was essential for function and all lytB2 mutant alleles were functional. In contrast, mutation of the key residues for [Fe4S4] cluster formation, as well as a catalytic residue in LytB1 did not result in functional complementation. Thus, although LytB1 and LytB2 are not genetically redundant, this is not dependent on small amino acid changes, but is likely to be a result of major overall structural differences. PMID:26309039

  2. Chiral NH-Controlled Supramolecular Metallacycles.

    PubMed

    Dong, Jinqiao; Tan, Chunxia; Zhang, Kang; Liu, Yan; Low, Paul J; Jiang, Jianwen; Cui, Yong

    2017-02-01

    Chiral NH functionalities-based discrimination is a key feature of Nature's chemical armory, yet selective binding of biologically active molecules in synthetic systems with high enantioselectivity poses significant challenges. Here we report the assembly of three chiral fluorescent Zn6L6 metallacycles from pyridyl-functionalized Zn(salalen) or Zn(salen) complexes. Each of these metallacycles has a nanoscale hydrophobic cavity decorated with six, three, or zero chiral NH functionalities and packs into a three-dimensional supramolecular porous framework. The binding affinity and enantioselectivity of the metallacycles toward α-hydroxycarboxylic acids, amino acids, small molecule pharamaceuticals (l-dopa, d-penicillamine), and chiral amines increase with the number of chiral NH moieties in the cyclic structure. From single-crystal X-ray diffraction, molecular simulations, and quantum chemical calculations, the chiral recognition and discrimination are attributed to the specific binding of enantiomers in the chiral pockets of the metallacycles. The parent metallacycles are fluorescent with the intensity of emission being linearly related to the enantiomeric composition of the chiral biorelevant guests, which allow them to be utilized in chiral sensing. The fact that manipulation of chiral NH functionalities in metallacycles can control the enantiorecognition of biomolecular complexes would facilitate the design of more effective supramolecular assemblies for enantioselective processes.

  3. Occurrence of homologs of the Escherichia coli lytB gene in gram-negative bacterial species.

    PubMed

    Potter, S; Yang, X; Boulanger, M J; Ishiguro, E E

    1998-04-01

    The Escherichia coli LytB protein regulates the activity of guanosine 3',5'-bispyrophosphate synthetase I (RelA). A Southern blot analysis of chromosomal DNA with the E. coli lytB gene as a probe revealed the presence of lytB homologs in all of the gram-negative bacterial species examined but not in gram-positive species. The lytB homologs from Enterobacter aerogenes and Pseudomonas fluorescens complemented the E. coli lytB44 mutant allele.

  4. Substrate recognition and catalysis by LytB, a pneumococcal peptidoglycan hydrolase involved in virulence

    PubMed Central

    Rico-Lastres, Palma; Díez-Martínez, Roberto; Iglesias-Bexiga, Manuel; Bustamante, Noemí; Aldridge, Christine; Hesek, Dusan; Lee, Mijoon; Mobashery, Shahriar; Gray, Joe; Vollmer, Waldemar; García, Pedro; Menéndez, Margarita

    2015-01-01

    Streptococcus pneumoniae is a major cause of life-threatening diseases worldwide. Here we provide an in-depth functional characterization of LytB, the peptidoglycan hydrolase responsible for physical separation of daughter cells. Identified herein as an N-acetylglucosaminidase, LytB is involved also in colonization and invasion of the nasopharynx, biofilm formation and evasion of host immunity as previously demonstrated. We have shown that LytB cleaves the GlcNAc-β-(1,4)-MurNAc glycosidic bond of peptidoglycan building units. The hydrolysis occurs at sites with fully acetylated GlcNAc moieties, with preference for uncross-linked muropeptides. The necessity of GlcN acetylation and the presence of a single acidic moiety (Glu585) essential for catalysis strongly suggest a substrate-assisted mechanism with anchimeric assistance of the acetamido group of GlcNAc moieties. Additionally, modelling of the catalytic region bound to a hexasaccharide tripentapeptide provided insights into substrate-binding subsites and peptidoglycan recognition. Besides, cell-wall digestion products and solubilisation rates might indicate a tight control of LytB activity to prevent unrestrained breakdown of the cell wall. Choline-independent localization at the poles of the cell, mediated by the choline-binding domain, peptidoglycan modification, and choline-mediated (lipo)teichoic-acid attachment contribute to the high selectivity of LytB. Moreover, so far unknown chitin hydrolase and glycosyltransferase activities were detected using GlcNAc oligomers as substrate. PMID:26537571

  5. Inhibition of Plasmodium falciparum ispH (lytB) gene expression by hammerhead ribozyme.

    PubMed

    Vinayak, Sumiti; Sharma, Yagya D

    2007-01-01

    The nonmevalonate pathway of isoprenoid biosynthesis in the apicoplast of the human malaria parasite Plasmodium falciparum is distinct from the mevalonate-dependent pathway of humans and thus a good drug target. We describe here the hammerhead ribozyme based cleavage of the ispH (lytB) gene transcript involved in the last step of this nonmevalonate pathway. Using RNA folding program, three hammerhead ribozymes named as RZ(876), RZ(1260), and RZ(1331) were predicted against ispH (lytB) mRNA. Messenger walk screening (RNaseH) assay confirmed the target accessibility for these ribozymes. All three ribozymes cleaved the target RNA in vitro but RZ(876) exhibited the highest catalytic potential (62.92%). Therefore, RZ(876) was chemically synthesized with appropriate chemical modifications to protect it from nuclease attack while using it for in vitro parasite growth inhibition assay. This ribozyme RZ(876) was able to inhibit 87.36% parasite growth at 30 microM concentration compared to the untreated culture. However, an absolute inhibition of 29.41% was achieved compared to the control ribozyme (RZ(ctrl)). Nonetheless, the growth inhibition effect was found to be sequence-specific as indicated by the decreased level of ispH (lytB) transcript after ribozyme treatment. In conclusion, we have identified the ispH (lytB) as a potential target whose transcript can be cleaved by a ribozyme RZ(876).

  6. Immunization with LytB protein of Streptococcus pneumoniae activates complement-mediated phagocytosis and induces protection against pneumonia and sepsis.

    PubMed

    Corsini, Bruno; Aguinagalde, Leire; Ruiz, Susana; Domenech, Mirian; Antequera, María Luisa; Fenoll, Asunción; García, Pedro; García, Ernesto; Yuste, Jose

    2016-12-07

    The cell wall glucosaminidase LytB of Streptococcus pneumoniae is a surface exposed protein involved in daughter cell separation, biofilm formation and contributes to different aspects of the pathogenesis process. In this study we have characterized the antibody responses after immunization of mice with LytB in the presence of alhydrogel as an adjuvant. Enzyme-linked immunosorbent assays measuring different subclasses of immunoglobulin G, demonstrated that the antibody responses to LytB were predominantly IgG1 and IgG2b, followed by IgG3 and IgG2a subclasses. Complement-mediated immunity against two different pneumococcal serotypes was investigated using sera from immunized mice. Immunization with LytB increased the recognition of S. pneumoniae by complement components C1q and C3b demonstrating that anti-LytB antibodies trigger activation of the classical pathway. Phagocytosis assays showed that serum containing antibodies to LytB stimulates neutrophil-mediated phagocytosis against S. pneumoniae. Animal models of infection including invasive pneumonia and sepsis were performed with two different clinical isolates. Vaccination with LytB increased bacterial clearance and induced protection demonstrating that LytB might be a good candidate to be considered in a future protein-based vaccine against S. pneumoniae.

  7. Gondola-shaped tetra-rhenium metallacycles modified evanescent wave infrared chemical sensors for selective determination of volatile organic compounds.

    PubMed

    Huang, Genin Gary; Lee, Chung-Jay; Tsai, Bo-Chan; Yang, Jyisy; Sathiyendiran, Malaichamy; Lu, Kuang-Lieh

    2011-07-15

    Water-stable and cavity-contained rhenium metallacycles were synthesized, and their ability to selectively interact with volatile organic compounds (VOCs) systematically studied using attenuated total reflection infrared (ATR-IR) spectroscopy. Integrating the unique properties of rhenium metallacycles into optical sensing technologies significantly improves selectivity in detecting aromatic compounds. To explore the interaction of rhenium metallacycles with VOCs, the surface of ATR sensing elements was modified with the synthesized rhenium metallacycles and used to detect VOCs. The results indicate that rhenium metallacycles have crown ether-like recognition sites, which can selectively interact with aromatic compounds, especially those bearing polar functional groups. The IR absorption bands of rhenium metallacycles shift significantly upon adsorption of aromatic VOCs, revealing a strong interaction between the tetra-rhenium metallacycles and guest aromatic compounds. Optimizing the thickness of the metallacycles coated on the surface of the sensing element led to rapid response in detection. The dynamic range of response was generally up to 30 mg/L with detection limits ca. 30 μg/L. Further studies of the effect of interferences indicate that recovery can be higher than 95% for most of the compounds tested. The results on the flow-cell device indicated that the performances were similar to a static detection system but the detection of VOCs can be largely simplified.

  8. Luminescent charge-transfer platinum(II) metallacycle.

    PubMed

    Hua, Fei; Kinayyigit, Solen; Rachford, Aaron A; Shikhova, Elena A; Goeb, Sébastien; Cable, John R; Adams, Christopher J; Kirschbaum, Kristin; Pinkerton, A Alan; Castellano, Felix N

    2007-10-15

    The photophysical and electrochemical properties of a platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine] (1), are compared with two reference compounds, Pt(dbbpy)(C[triple bond]CPh)(2) (2) and Pt(dppp)tda [dppp = 1,3-bis(diphenylphosphino)propane] (3), respectively. The X-ray crystal structure of 1 is reported, which illustrates the nearly perfect square planarity exhibited by this metallacycle. Chromophore 2 possesses low-lying charge-transfer excited states analogous to 1, whereas structure 3 lacks such excited states but features a low-lying platinum-perturbed tda intraligand triplet manifold. In CH(2)Cl(2), 1 exhibits a broad emission centered at 562 nm at ambient temperature, similar to 2, but with a higher photoluminescence quantum yield and longer excited-state lifetime. In both instances, the photoluminescence is consistent with triplet-charge-transfer excited-state parentage. The rigidity imposed by the cyclic diacetylide ligand in 1 leads to a reduction in nonradiative decay, which enhances its room-temperature photophysical properties. By comparison, 3 radiates highly structured tda-localized triplet-state phosphorescence at room temperature. The 77 K emission spectrum of 1 in 4:1 EtOH/MeOH becomes structured and is quantitatively similar to that measured for 3 under the same conditions. Because the 77 K spectra are nearly identical, the emissions are assigned as (3)tda in nature, implying that the charge-transfer states are raised in energy, relative to the (3)tda levels in 1 in the low-temperature glass. Nanosecond transient absorption spectrometry and ultrafast difference spectra were determined for 1-3 in CH(2)Cl(2) and DMF at ambient temperature. In 1 and 2, the major absorption transients are consistent with the one-electron reduced complexes, corroborated by reductive spectroelectrochemical measurements performed at room temperature. As 3

  9. Fluorescent metallacycle-cored polymers via covalent linkage and their use as contrast agents for cell imaging

    PubMed Central

    Zhang, Mingming; Li, Shuya; Yan, Xuzhou; Zhou, Zhixuan; Saha, Manik Lal; Wang, Yu-Cai; Stang, Peter J.

    2016-01-01

    The covalent linkage of supramolecular monomers provides a powerful strategy for constructing dynamic polymeric materials whose properties can be readily tuned either by the selection of monomers or the choice of functional linkers. In this strategy, the stabilities of the supramolecular monomers and the reactions used to link the monomers are crucial because such monomers are normally dynamic and can disassemble during the linking process, leading to mixture of products. Therefore, although noncovalent interactions have been widely introduced into metallacycle structures to prepare metallosupramolecular polymers, metallacycle-cored polymers linked by covalent bonds have been rarely reported. Herein, we used the mild, highly efficient amidation reaction between alkylamine and N-hydroxysuccinimide-activated carboxylic acid to link the pendent amino functional groups of a rhomboidal metallacycle 10 to give metallacycle-cored polymers P1 and P2, which further yielded nanoparticles at low concentration and transformed into network structures as the concentration increased. Moreover, these polymers exhibited enhanced emission and showed better quantum yields than metallacycle 10 in methanol and methanol/water (1/9, vol/vol) due to the aggregation-induced emission properties of a tetraphenylethene-based pyridyl donor, which serves as a precursor for metallacycle 10. The fluorescence properties of these polymers were further used in cell imaging, and they showed a significant enrichment in lung cells after i.v. injection. Considering the anticancer activity of rhomboidal Pt(II) metallacycles, this type of fluorescent metallacycle-cored polymers can have potential applications toward lung cancer treatment. PMID:27647900

  10. Metallacycles or coexistence of isomeric metallacycle and chain: Anion-dependent luminescent Ag complexes of a flexible diaminotriazine-imidazole ligand

    NASA Astrophysics Data System (ADS)

    Mei, Hong-Xin; Zhang, Ting; Wang, Dan-Feng; Huang, Rong-Bin; Zheng, Lan-Sun

    2015-07-01

    Reaction of a flexible ligand 2,4-diamino-6-[2-(2-methyl-1-imidazolyl) ethyl]-1,3,5-triazine (L) with Ag(I) in the presence of different counteranions afforded five complexes, namely, 2[Agn(L)n(NH3)n] · n[Ag2(L)2(NH3)2] · 2n(nds) (1, H2nds = 1,5-naphthalenedisulfonic acid), 2[Agn(L)n] · n[Ag2(L)2(CF3CO2)2] · nCF3CO2 (2), [Ag2(L)2(NH3)2] · 2(ClO4) (3), [Ag2(L)2] · 2(NO3) (4), [Ag2(L)2] · 2(ClO3) (5), which were characterized by element analysis, IR, PXRD and X-ray single-crystal diffraction. Structural analysis reveals that the L ligand take the same bidentate coordination mode in these complexes. The nds anion and the CF3 CO2- anion lead to the coexistence of isomeric metallacycle and helical chain (ring-opening isomers) in the crystals of 1 and 2, while ClO4-, NO3- and ClO3- anions afford dimeric metallacycles in complexes 3-5. Moreover, thermal gravity analysis (TGA) and emissive behaviors of these complexes were investigated.

  11. Studies on the nonmevalonate terpene biosynthetic pathway: Metabolic role of IspH (LytB) protein

    PubMed Central

    Rohdich, Felix; Hecht, Stefan; Gärtner, Katrin; Adam, Petra; Krieger, Cornelia; Amslinger, Sabine; Arigoni, Duilio; Bacher, Adelbert; Eisenreich, Wolfgang

    2002-01-01

    Isopentenyl diphosphate and dimethylallyl diphosphate serve as the universal precursors for the biosynthesis of terpenes. Although their biosynthesis by means of mevalonate has been studied in detail, a second biosynthetic pathway for their formation by means of 1-deoxy-d-xylulose 5-phosphate has been discovered only recently in plants and certain eubacteria. Earlier in vivo experiments with recombinant Escherichia coli strains showed that exogenous 1-deoxy-d-xylulose can be converted into 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate by the consecutive action of enzymes specified by the xylB and ispCDEFG genes. This article describes the transformation of exogenous [U-13C5]1-deoxy-d-xylulose into a 5:1 mixture of [U-13C5]isopentenyl diphosphate and [U-13C5]dimethylallyl diphosphate by an E. coli strain engineered for the expression of the ispH (lytB) gene in addition to recombinant xylB and ispCDEFG genes. PMID:11818558

  12. Dendronized organoplatinum(II) metallacyclic polymers constructed by hierarchical coordination-driven self-assembly and hydrogen-bonding interfaces.

    PubMed

    Yan, Xuzhou; Jiang, Bo; Cook, Timothy R; Zhang, Yanyan; Li, Jinying; Yu, Yihua; Huang, Feihe; Yang, Hai-Bo; Stang, Peter J

    2013-11-13

    We describe the efficient preparation of rhomboidal metallacycles that self-assemble upon mixing a donor decorated with 2-ureido-4-pyrimidinone (UPy) with acceptors containing pendant [G1]-[G3] dendrons. The formed rhomboids subsequently polymerize into dendronized organoplatinum(II) metallacyclic polymers through H-bonding UPy interfaces, which possess the structural features of conventional dendronized polymers as well as the dynamic reversibility of supramolecular polymers. Preservation of both properties in a single material is achieved by exploiting hierarchical self-assembly, namely the unification of coordination-driven self-assembly with H-bonding, which provides facile routes to dendronized metallacycles and subsequent high ordering. The supramolecular polymerization defined here represents a novel method to deliver architecturally complex and ordered polymeric materials with adaptive properties.

  13. Dinuclear Metallacycles with Single M-X-M Bridges (X = Cl(-), Br(-); M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)): Strong Antiferromagnetic Superexchange Interactions.

    PubMed

    Reger, Daniel L; Pascui, Andrea E; Foley, Elizabeth A; Smith, Mark D; Jezierska, Julia; Wojciechowska, Agnieszka; Stoian, Sebastian A; Ozarowski, Andrew

    2017-03-06

    A series of monochloride-bridged, dinuclear metallacycles of the general formula [M2(μ-Cl)(μ-L)2](ClO4)3 have been prepared using the third-generation, ditopic bis(pyrazolyl)methane ligands L = m-bis[bis(1-pyrazolyl)methyl]benzene (Lm), M = Cu(II), Zn(II), and L = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*), M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II). These complexes were synthesized from the direct reactions of M(ClO4)2·6H2O, MCl2, and the ligand, Lm or Lm*, in the appropriate stoichiometric amounts. Three analogous complexes of the formula [M2(μ-Cl)(μ-L)2](BF4)3, L = Lm, M = Cu(II), and L = Lm*, M = Co(II), Cu(II), were prepared from the reaction of [M2(μ-F)(μ-L)2](BF4)3 and (CH3)3SiCl. The bromide-bridged complex [Cu2(μ-Br)(μ-Lm*)2](ClO4)3 was prepared by the first method. Three acyclic complexes, [Co2(μ-Lm)μ-Cl4], [Co2(μ-Lm*)Cl4], and [Co2(μ-Lm*)Br4], were also prepared. The structures of all [M2(μ-X)(μ-L)2](3+) (X = Cl(-), Br(-)) complexes have two ditopic bis(pyrazolyl)methane ligands bridging two metals in a metallacyclic arrangement. The fifth coordination site of the distorted trigonal bipyramidal metal centers is filled by a bridging halide ligand that has an unusual linear or nearly linear M-X-M angle. The NMR spectra of [Zn2(μ-Cl)(μ-Lm*)2](ClO4)3 and especially [Cd2(μ-Cl)(μ-Lm*)2](ClO4)3 demonstrate that the metallacycle structure is maintained in solution. Solid state magnetic susceptibility data for the copper(II) compounds show very strong antiferromagnetic exchange interactions, with -J values of 536 cm(-1) for [Cu2(μ-Cl)(μ-Lm)2](ClO4)3·xCH3CN, 720 cm(-1) for [Cu2(μ-Cl)(μ-Lm*)2](ClO4)3, and 945 cm(-1) for [Cu2(μ-Br)(μ-Lm*)2](ClO4)3·2CH3CN. Smaller but still substantial antiferromagnetic interactions are observed with other first row transition metals, with -J values of 98 cm(-1) for [Ni2(μ-Cl)(μ-Lm*)2](ClO4)3, 55 cm(-1) for [Co2(μ-Cl)(μ-Lm*)2](ClO4)3, and 34 cm(-1) for [Fe2(μ-Cl)(μ-Lm*)2](ClO4

  14. Broadband transmission EPR spectroscopy.

    PubMed

    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.

  15. Rapid frequency scan EPR.

    PubMed

    Tseitlin, Mark; Rinard, George A; Quine, Richard W; Eaton, Sandra S; Eaton, Gareth R

    2011-08-01

    In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x, y plane decays to baseline at the end of the scan, which typically is about 5T(2) after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5T(2). However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded with a total scan period of 5T(2), even if some spins are excited later in the scan. This scan time is similar to polyphase excitation methods. The peak power required for either polyphase excitation or rapid frequency scans is substantially smaller than for pulsed EPR. The use of an arbitrary waveform generator (AWG) and cross loop resonator facilitated implementation of the rapid frequency scan experiments reported here. The use of constant continuous low B(1), periodic excitation waveform, and constant external magnetic field is similar to polyphase excitation, but could be implemented without the AWG that is required for polyphase excitation.

  16. Rapid Frequency Scan EPR

    PubMed Central

    Tseitlin, Mark; Rinard, George A.; Quine, Richard W.; Eaton, Sandra S.; Eaton, Gareth R.

    2011-01-01

    In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x,y plane decays to baseline at the end of the scan, which typically is about 5 T2 after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5 T2. However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded with a total scan period of 5 T2, even if some spins are excited later in the scan. This scan time is similar to polyphase excitation methods. The peak power required for either polyphase excitation or rapid frequency scans is substantially smaller than for pulsed EPR. The use of an arbitrary waveform generator (AWG) and cross loop resonator facilitated implementation of the rapid frequency scan experiments reported here. The use of constant continuous low B1, periodic excitation waveform, and constant external magnetic field is similar to polyphase excitation, but could be implemented without the AWG that is required for polyphase excitation. PMID:21664848

  17. EPR study of porous silicon

    NASA Astrophysics Data System (ADS)

    Jishi, Fu; Jinchang, Mao; En, Wu; Yongqiang, Jia; Borui, Zhang; Lizhu, Zhang; Guogang, Qin; Yuhua, Zhang; Genshuan, Wui

    1994-12-01

    An anisotropic EPR signal was observed in porous Si. According to its symmetry and g value, the EPR signal can be attributed to silicon dangling bonds located on the surface of a porous Si skeleton. The evolution of the EPR signal at room temperature in air was measured. The annealing temperature dependence of the EPR and the PL of porous Si in oxygen and the effects of gamma irradiation on the EPR and the PL spectra of porous Si were studied. The changes of the EPR signal and the PL intensity induced in atmosphere by ethyl alcohol and acetone were discovered. The dangling bond is only one of the factors which affect the PL.

  18. Self-assembly of dinuclear Pd(ii)/Pt(ii) metallacyclic receptors incorporating N-heterocyclic carbene complexes as corners.

    PubMed

    Marcos, Ismael; Domarco, Olaya; Peinador, Carlos; Fenández, Alberto; Fernández, Jesús J; Vázquez-García, Digna; García, Marcos D

    2017-03-07

    We report herein the self-assembly of a series of new square and rectangular-shaped dinuclear M2L2 metallacycles (M = Pd(ii)/Pt(ii)), receptors self-assembled in water from four different N-monoalkyl-4,4'-bipyridinium derivatives as ligands and square-planar Pd(ii) and Pt(ii) metal centers having the chelating N-heterocyclic carbene 1,1'-di(methyl)-3,3'-methylene-4-diimidazolin-2,2'-diylidene. The concentration-dependent Pd2L2 metallacycles were successfully obtained and characterized by means of NMR experiments in aqueous media. Due to the strong trans effect exerted by the carbene ligands, the synthesis of the Pt2L2 receptors was achieved as well by self-assembly of the components at room temperature in a few hours, in clear contraposition to the harsh reaction conditions usually required for the labilization of other kinetically inert Pt(ii)-N(pyridine) bonds. X-ray diffraction studies of suitable single crystals of two of the obtained receptors offered additional information on the structure of the obtained supramolecules, whose ability as receptors has been explored by the preparation and study of the corresponding inclusion complexes in water with 1,5-dihydroxynaphthalene as the model substrate.

  19. Retrocausal models for EPR

    NASA Astrophysics Data System (ADS)

    Corry, Richard

    2015-02-01

    This paper takes up Huw Price's challenge to develop a retrocausal toy model of the Bell-EPR experiment. I develop three such models which show that a consistent, local, hidden-variables interpretation of the EPR experiment is indeed possible, and which give a feel for the kind of retrocausation involved. The first of the models also makes clear a problematic feature of retrocausation: it seems that we cannot interpret the hidden elements of reality in a retrocausal model as possessing determinate dispositions to affect the outcome of experiments. This is a feature which Price has embraced, but Gordon Belot has argued that this feature renders retrocausal interpretations "unsuitable for formal development", and the lack of such determinate dispositions threatens to undermine the motivation for hidden-variables interpretations in the first place. But Price and Belot are both too quick in their assessment. I show that determinate dispositions are indeed consistent with retrocausation. What is more, I show that the ontological economy allowed by retrocausation holds out the promise of a classical understanding of spin and polarization.

  20. On Cartwright's models for EPR

    NASA Astrophysics Data System (ADS)

    Cachro, Jacek; Placek, Tomasz

    We assess Cartwright's models for probabilistic causality and, in particular, her models for EPR-like experiments of quantum mechanics. Our first objection is that, contrary to econometric linear models, her quasi-linear models do not allow for the unique estimation of parameters. We next argue that although, as Cartwright proves, Reichenbach's screening-off condition has only limited validity, her generalized condition is not empirically applicable. Finally, we show that her models for the EPR are mathematically incorrect and physically implausible.

  1. EPR, Biology, and Consciousness

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2006-03-01

    It seems that Darwin, in his concluding remark (1859, p490) ruled out the possibility of cosmic connection to evolution based on the fixed law of gravity, known then. More recent Dirac’s Large Number Hypothesis as described in http://www.arXiv.org/pdf/physics/0210040 v1 raises a possibility that the universal constant of gravity is decreasing and all coupling constants are increasing with time, so reported by some observations. Deeper investigation of the connection between evolution and the variation of the universal constant of gravity seems worthwhile to see if it impacts the passage of time in a stronger (gravitational according to the spirit of the above archive) field and affects the aging process, and explains locality and causality in random evolutionary mutations. If there is no physical locality and causality consistent with the special theory of relativity, there must be some spiritual locality and causality at superluminal speeds to explain the implicit hidden variables. Then there is a question of how to test spiritual locality and causality. Psychic effects and dream signals look promising, if they exist and can be tested with space age technology. This is neither about religion nor about Einstein’s orthodoxy in light of the spirit of EPR. This is about frontiers of science of the new millennium: biology, and consciousness.

  2. Self-assembled copper(II) metallacycles derived from asymmetric Schiff base ligands: efficient hosts for ADP/ATP in phosphate buffer.

    PubMed

    Kumar, Amit; Pandey, Rampal; Kumar, Ashish; Gupta, Rakesh Kumar; Dubey, Mrigendra; Mohammed, Akbar; Mobin, Shaikh M; Pandey, Daya Shankar

    2015-10-21

    Novel asymmetric Schiff base ligands 2-{[3-(3-hydroxy-1-methyl-but-2-enylideneamino)-2,4,6-trimethylphenylimino]-methyl}-phenol (H2L(1)) and 1-{[3-(3-hydroxy-1-methyl-but-2-enylideneamino)-2,4,6-trimethylphenylimino]-methyl}-naphthalen-2-ol (H2L(2)) possessing dissimilar N,O-chelating sites and copper(ii) metallacycles (CuL(1))4 (1) and (CuL(2))4 (2) based on these ligands have been described. The ligands and complexes have been thoroughly characterized by satisfactory elemental analyses, and spectral (IR, (1)H, (13)C NMR, ESI-MS, UV/vis) and electrochemical studies. Structures of H2L(2) and 1 have been unambiguously determined by X-ray single crystal analyses. The crystal structure of H2L(2) revealed the presence of two distinct N,O-chelating sites on dissimilar cores (naphthalene and β-ketoaminato groups) offering a diverse coordination environment. Metallacycles 1 and 2 having a cavity created by four Cu(ii) centres coordinated in a homo- and heteroleptic fashion with respective ligands act as efficient hosts for adenosine-5'-diphosphate (ADP) and adenosine-5'-triphosphate (ATP) respectively, over other nucleoside polyphosphates (NPPs). The disparate sensitivity of these metallacycles toward ADP and ATP has been attributed to the size of the ligands assuming diverse dimensions and spatial orientations. These are attuned for π-π stacking and electrostatic interactions suitable for different guest molecules under analogous conditions, metallacycle 1 offers better orientation for ADP, while 2 for ATP. The mechanism of the host-guest interaction has been investigated by spectral and electrochemical studies and supported by molecular docking studies.

  3. The marriage of metallacycle transfer chemistry with Suzuki-Miyaura cross-coupling to give main group element-containing conjugated polymers.

    PubMed

    He, Gang; Kang, Le; Torres Delgado, William; Shynkaruk, Olena; Ferguson, Michael J; McDonald, Robert; Rivard, Eric

    2013-04-10

    A versatile and general synthetic route for the synthesis of conjugated main group element-based polymers, previously inaccessible by conventional means, is reported. These polymers contain five-membered chalcogenophene rings based on S, Se, and Te, and we demonstrate that optoelectronic properties can be readily tuned via controlled atom substitution chemistry. In addition, regioregular hybrid thiophene-selenophene-tellurophene and selenophene-fluorene copolymers were synthesized to provide a further illustration of the scope of the presented metallacycle transfer/cross-coupling polymerization method.

  4. A cryogenic receiver for EPR.

    PubMed

    Narkowicz, R; Ogata, H; Reijerse, E; Suter, D

    2013-12-01

    Cryogenic probes have significantly increased the sensitivity of NMR. Here, we present a compact EPR receiver design capable of cryogenic operation. Compared to room temperature operation, it reduces the noise by a factor of ≈2.5. We discuss in detail the design and analyze the resulting noise performance. At low microwave power, the input noise density closely follows the emission of a cooled 50Ω resistor over the whole measurement range from 20K up to room temperature. To minimize the influence of the microwave source noise, we use high microwave efficiency (≈1.1-1.7mTW(-1/2)) planar microresonators. Their efficient conversion of microwave power to magnetic field permits EPR measurements with very low power levels, typically ranging from a few μW down to fractions of nW.

  5. EPR in B physics and elsewhere

    SciTech Connect

    Lipkin, H.J. ||

    1997-09-01

    The application of Einstein-Podolsky-Rosen correlations in {Upsilon}(4s) {yields} B{anti B} decays to research in CP violation is the first and probably only use of EPR as a technique for research in new physics. Elsewhere highly sophisticated EPR projects question EPR and test its predictions to look for violations of quantum mechanics, hidden variables, Bell`s inequalities, etc.

  6. EPR-based material modelling of soils

    NASA Astrophysics Data System (ADS)

    Faramarzi, Asaad; Alani, Amir M.

    2013-04-01

    In the past few decades, as a result of the rapid developments in computational software and hardware, alternative computer aided pattern recognition approaches have been introduced to modelling many engineering problems, including constitutive modelling of materials. The main idea behind pattern recognition systems is that they learn adaptively from experience and extract various discriminants, each appropriate for its purpose. In this work an approach is presented for developing material models for soils based on evolutionary polynomial regression (EPR). EPR is a recently developed hybrid data mining technique that searches for structured mathematical equations (representing the behaviour of a system) using genetic algorithm and the least squares method. Stress-strain data from triaxial tests are used to train and develop EPR-based material models for soil. The developed models are compared with some of the well-known conventional material models and it is shown that EPR-based models can provide a better prediction for the behaviour of soils. The main benefits of using EPR-based material models are that it provides a unified approach to constitutive modelling of all materials (i.e., all aspects of material behaviour can be implemented within a unified environment of an EPR model); it does not require any arbitrary choice of constitutive (mathematical) models. In EPR-based material models there are no material parameters to be identified. As the model is trained directly from experimental data therefore, EPR-based material models are the shortest route from experimental research (data) to numerical modelling. Another advantage of EPR-based constitutive model is that as more experimental data become available, the quality of the EPR prediction can be improved by learning from the additional data, and therefore, the EPR model can become more effective and robust. The developed EPR-based material models can be incorporated in finite element (FE) analysis.

  7. Background removal procedure for rapid scan EPR.

    PubMed

    Tseitlin, Mark; Czechowski, Tomasz; Quine, Richard W; Eaton, Sandra S; Eaton, Gareth R

    2009-01-01

    In rapid scan EPR the changing magnetic field creates a background signal with components at the scan frequency and its harmonics. The amplitude of the background signal increases with scan width and is more significant for weak EPR signals such as are obtained in the presence of magnetic field gradients. A procedure for distinguishing this background from the EPR signal is proposed, mathematically described, and tested for various experimental conditions.

  8. 3-Rhoda-1,2-diazacyclopentanes: a series of novel metallacycle complexes derived from C-N functionalization of ethylene.

    PubMed

    Drover, Marcus W; Beh, Daniel W; Kennepohl, Pierre; Love, Jennifer A

    2014-10-06

    Rh-containing metallacycles, [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NR)2-]Cl; TPA = N,N,N,N-tris(2-pyridylmethyl)amine have been accessed through treatment of the Rh(I) ethylene complex, [(TPA)Rh(η(2)-CH2CH2)]Cl ([1]Cl) with substituted diazenes. We show this methodology to be tolerant of electron-deficient azo compounds including azo diesters (RCO2N=NCO2R; R = Et [3]Cl, R = iPr [4]Cl, R = tBu [5]Cl, and R = Bn [6]Cl) and a cyclic azo diamide: 4-phenyl-1,2,4-triazole-3,5-dione (PTAD), [7]Cl. The latter complex features two ortho-fused ring systems and constitutes the first 3-rhoda-1,2-diazabicyclo[3.3.0]octane. Preliminary evidence suggests that these complexes result from N-N coordination followed by insertion of ethylene into a [Rh]-N bond. In terms of reactivity, [3]Cl and [4]Cl successfully undergo ring-opening using p-toluenesulfonic acid, affording the Rh chlorides, [(TPA)Rh(III)(Cl)(κ(1)-(C)-CH2CH2(NCO2R)(NHCO2R)]OTs; [13]OTs and [14]OTs. Deprotection of [5]Cl using trifluoroacetic acid was also found to give an ethyl substituted, end-on coordinated diazene [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NH)2-](+) [16]Cl, a hitherto unreported motif. Treatment of [16]Cl with acetyl chloride resulted in the bisacetylated adduct [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NAc)2-](+), [17]Cl. Treatment of [1]Cl with AcN=NAc did not give the Rh-N insertion product, but instead the N,O-chelated complex [(TPA)Rh(I)(κ(2)-(O,N)-CH3(CO)(NH)(N=C(CH3)(OCH=CH2))]Cl [23]Cl, presumably through insertion of ethylene into a [Rh]-O bond.

  9. EPR techniques for space biodosimetry

    SciTech Connect

    Haskell, E.; Hayes, R.; Kenner, G.; Sholom, S.; Chumak, V.

    1996-12-31

    Retrospective dosimetry of tooth enamel has become an increasingly complex and difficult discipline to undertake while still attaining accuracy. The paper provides a review of the major obstacles, advances and pertinent phenomenon associated with low level retrospective dosimetry of human tooth enamel. Also covered is the many sources of error in EPR dosimetry, their potential solutions, as well as the different analysis and scanning techniques in use with their prospective pros and cons. Prospective directions for new approaches, methods, and instruments are also reviewed.

  10. Overview of LBB implementation for the EPR

    SciTech Connect

    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.

  11. EPR dosimetry in chemically treated fingernails

    Technology Transfer Automated Retrieval System (TEKTRAN)

    By using EPR measurements of radiation-induced radicals it is possible to utilize human fingernails to estimate radiation dose after-the-fact. One of the potentially limiting factors in this approach is the presence of artifacts due to mechanically induced EPR signals (MIS) caused by mechanical str...

  12. In Vivo EPR For Dosimetry

    PubMed Central

    Swartz, Harold M.; Burke, Greg; Coey, M.; Demidenko, Eugene; Dong, Ruhong; Grinberg, Oleg; Hilton, James; Iwasaki, Akinori; Lesniewski, Piotr; Kmiec, Maciej; Lo, Kai-Ming; Nicolalde, R. Javier; Ruuge, Andres; Sakata, Yasuko; Sucheta, Artur; Walczak, Tadeusz; Williams, Benjamin B.; Mitchell, Chad; Romanyukha, Alex; Schauer, David A.

    2007-01-01

    As a result of terrorism, accident, or war, populations potentially can be exposed to doses of ionizing radiation that could cause direct clinical effects within days or weeks. There is a critical need to determine the magnitude of the exposure to individuals so that those with significant risk have appropriate procedures initiated immediately, while those without a significant probability of acute effects can be reassured and removed from the need for further consideration in the medical/emergency system. In many of the plausible scenarios there is an urgent need to make the determination very soon after the event and while the subject is still present. In vivo EPR measurements of radiation-induced changes in the enamel of teeth is a method, perhaps the only such method, which can differentiate among doses sufficiently for classifying individuals into categories for treatment with sufficient accuracy to facilitate decisions on medical treatment. In its current state, the in vivo EPR dosimeter can provide estimates of absorbed dose with an error approximately ± 50 cGy over the range of interest for acute biological effects of radiation, assuming repeated measurements of the tooth in the mouth of the subject. The time required for acquisition, the lower limit, and the precision are expected to improve, with improvements in the resonator and the algorithm for acquiring and calculating the dose. The magnet system that is currently used, while potentially deployable, is somewhat large and heavy, requiring that it be mounted on a small truck or trailer. Several smaller magnets, including an intraoral magnet are under development, which would extend the ease of use of this technique. PMID:18591988

  13. Time-resolved pulsed EPR: microwave and optical detection

    SciTech Connect

    Trifunac, A.D.; Smith, J.P.

    1981-01-01

    Time-resolved pulsed EPR spectrometers are described. EPR spectra, kinetic profiles, and relaxation studies are used to illustrate some capabilities of the pulsed EPR experiment. Optical detection of time-resolved EPR spectra of radical ion pairs is used to study radical-ion recombination kinetics, recombination pathways, and the structure of radical anions and cations. 17 figures.

  14. Homogeneity and EPR metrics for assessment of regular grids used in CW EPR powder simulations

    NASA Astrophysics Data System (ADS)

    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.

  15. Theoretical EPR study of 6-Mercaptopurine

    NASA Astrophysics Data System (ADS)

    Tasdemir, Halil Ugur; Türkkan, Ercan

    2017-02-01

    6-Mercaptopurine is important antineoplastics agent and it is used for immuno - suppressive and anti - inflammatory. Experimental EPR parameters of 6-Mercaptopurine molecules powder were studied in the literature. The aim of this study EPR parameters of 6 - Mercaptopurine molecules were calculated with theoretical calculations and define the possible radicals of 6 - Mercaptopurine molecules. Firstly the X-ray structure of 6-Mercaptopurine molecules were found in the literature (1). EPR parameters and possible radicals of 6 - Mercaptopurine molecules were calculated from this X-ray structure. Possible radicals of gamma-irradiated 6-Mercaptopurine molecules were constituted. EPR parameters of possible radicals were calculated with B3LYP/6-311++ G (d,p) basis set in DFT methods for 6 - Mercaptopurine molecules.

  16. Protocol for emergency EPR dosimetry in fingernails.

    PubMed

    Trompier, F; Kornak, L; Calas, C; Romanyukha, A; Leblanc, B; Mitchell, C A; Swartz, H M; Clairand, I

    2007-08-01

    There is an increased need for after-the-fact dosimetry because of the high risk of radiation exposures due to terrorism or accidents. In case of such an event, a method is needed to make measurements of dose in a large number of individuals rapidly and with sufficient accuracy to facilitate effective medical triage. Dosimetry based on EPR measurements of fingernails potentially could be an effective tool for this purpose. This paper presents the first operational protocols for EPR fingernail dosimetry, including guidelines for collection and storage of samples, parameters for EPR measurements, and the method of dose assessment. In a blinded test of this protocol application was carried out on nails freshly sampled and irradiated to 4 and 20 Gy; this protocol gave dose estimates with an error of less than 30%.

  17. Investigation of radical locations in various sesame seeds by CW EPR and 9-GHz EPR imaging.

    PubMed

    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. Monitoring enzymatic ATP hydrolysis by EPR spectroscopy.

    PubMed

    Hacker, Stephan M; Hintze, Christian; Marx, Andreas; Drescher, Malte

    2014-07-14

    An adenosine triphosphate (ATP) analogue modified with two nitroxide radicals is developed and employed to study its enzymatic hydrolysis by electron paramagnetic resonance spectroscopy. For this application, we demonstrate that EPR holds the potential to complement fluorogenic substrate analogues in monitoring enzymatic activity.

  19. Investigation of EPR signals on tooth enamel

    NASA Astrophysics Data System (ADS)

    Pavlenko, A.; Mironova-Ulmane, N.; Polakov, M.; Riekstina, D.

    2007-12-01

    Calcified tissues are involved in continues metabolic process in human organism exchanging a number of chemical elements with environment. The rate of biochemical reactions is tissue dependent and the slowest one at the tooth enamel, the most mineralized tissue of human organism. The long time stability and unique chemical composition make tooth enamel suitable for number of application. The assessment of individual radiation dose by Electron Paramagnetic Resonance (EPR) and evaluations of elemental composition by Instrumentation Neutron Activation Analysis (INAA) are the well known procedures where properties of tooth enamel intensively used. The current work is focused on investigation of EPR signals and determination of chemical composition on several teeth samples having different origin. The EPR spectra and INAA element content of milk tooth, caries tooth, and paradantose tooth have been compared to each other. The results showed that the intensity of EPR signal is much higher for the caries tooth than the for paradantose tooth that is in agreement with depleted Ca content.

  20. Teaching the EPR Paradox at High School?

    ERIC Educational Resources Information Center

    Pospiech, Gesche

    1999-01-01

    Argues the importance of students at university and in the final years of high school gaining an appreciation of the principles of quantum mechanics. Presents the EPR gedanken experiment (thought experiment) as a method of teaching the principles of quantum mechanics. (Author/CCM)

  1. Preparation of EPR/silica filler by a co-irradiation method forming PP/EPR/silica nanocomposites

    NASA Astrophysics Data System (ADS)

    Qian, Jun; Dang, Shuaiying; Huang, Zhijuan; Xu, Yongshen

    2012-01-01

    This paper presents a novel approach to prepare ethylene-propylene rubber (EPR)/silica filler by co-irradiation method forming polypropylene (PP)/EPR/silica nanocomposites. The grafting of maleic anhydride (MAH) on EPR was first studied by co-irradiation in the micro-suspension without any chemical initiator, and the effects of MAH concentration and the total co-irradiation dose on the graft degree of MAH were investigated. Then PP/EPR/silica nanocomposites were successfully prepared by blending of PP matrix and EPR/silica filler, which was obtained by co-irradiation using a mixture of EPR/MAH microsuspension in xylene and tetraethoxysilane/KH560 sol in formic acid. FTIR and SEM results showed that the reactions between MAH on EPR chains and KH560 surrounding silica particles were adopted to form the EPR/silica filler with strong bonding and well silica dispersion. Mechanical properties of PP/EPR/silica nanocomposites with different silica contents and the comparisons with PP, PP/EPR and PP/silica films were studied. The rigid silica particles were trapped in EPR shell and well dispersed in PP/EPR/silica nanocomposites with good compatibility and strong interfacial adhesion, achieving overall improvements in stiffness, strength and toughness compared with pure PP.

  2. Structural, photoluminescence, and theoretical DFT studies of gold(I) and silver(I) metallacycle dinuclear complexes of 1-methylbenzimidazolediphenyl phosphine (MBDP) ligand

    NASA Astrophysics Data System (ADS)

    Jenkins, Darkus E.; Assefa, Zerihun

    2017-04-01

    The synthesis and structural characterization of the bridging ligand, 1-methyl benzimidazole diphenylphosphine (MBDP) and its coordination with Au(I) and Ag(I) metal ions is reported. Two ligands coordinate to the metal ions in head to tail fashion forming a metallacycle coordination consisting of strong M-M bonding interaction with Ausbnd Au = 2.808 and Agsbnd Ag = 3.017 Å. Linear coordination is observed for the gold, while the silver shows distorted tetrahedral arrangement. X-ray crystal data of [(MBDP)2Au2](CH3CN)(BF4)2 (2) crystallizes in the monoclinic system with the space group of P21/n with cell constants of a = 8.9993 (8) Å, b = 19.6166 (18) Å, c = 13.4484 (12) Å, β = 100.966 (2)°, R = 0.026, and Rw = 0.064. The structure of [(MBDP)2(CH3CN)4Ag2](BF4)2, (3) crystallizes in the P (-)1 space group and the unit cell is a = 10.5423 (10) Å, b = 10.7638 (10) Å, c = 12.3530 (12) Å; α = 88.592 (3)°, β = 73.097 (3)°, γ = 84.422 (3)°, V = 1334.8 (2) Å3 with Z = 1, R = 0.034 and Rw = 0.093. The coordinating ligand as well as both dinuclear compounds reported here are luminescent in the near UV region. As supported by the DFT theoretical work, the emission is suggested to be primarily ligand based π- π* transition.

  3. EPR spectroscopy of nitrite complexes of methemoglobin.

    PubMed

    Schwab, David E; Stamler, Jonathan S; Singel, David J

    2010-07-19

    The chemical interplay of nitrogen oxides (NO's) with hemoglobin (Hb) has attracted considerable recent attention because of its potential significance in the mechanism of NO-related vasoactivity regulated by Hb. An important theme of this interplay-redox coupling in adducts of heme iron and NO's-has sparked renewed interest in fundamental studies of FeNO(x) coordination complexes. In this Article, we report combined UV-vis and comprehensive electron paramagnetic resonance (EPR) spectroscopic studies that address intriguing questions raised in recent studies of the structure and affinity of the nitrite ligand in complexes with Fe(III) in methemoglobin (metHb). EPR spectra of metHb/NO(2)(-) are found to exhibit a characteristic doubling in their sharper spectral features. Comparative EPR measurements at X- and S-band frequencies, and in D(2)O versus H(2)O, argue against the assignment of this splitting as hyperfine structure. Correlated changes in the EPR spectra with pH enable complete assignment of the spectrum as deriving from the overlap of two low-spin species with g values of 3.018, 2.122, 1.45 and 2.870, 2.304, 1.45 (values for samples at 20 K and pH 7.4 in phosphate-buffered saline). These g values are typical of g values found for other heme proteins with N-coordinated ligands in the binding pocket and are thus suggestive of N-nitro versus O-nitrito coordination. The positions and shapes of the spectral lines vary only slightly with temperature until motional averaging ensues at approximately 150 K. The pattern of motional averaging in the variable-temperature EPR spectra and EPR studies of Fe(III)NO(2)(-)/Fe(II)NO hybrids suggest that one of two species is present in both of the alpha and beta subunits, while the other is exclusive to the beta subunit. Our results also reconfirm that the affinity of nitrite for metHb is of millimolar magnitude, thereby making a direct role for nitrite in physiological hypoxic vasodilation difficult to justify.

  4. EPR Steering inequalities with Communication Assistance

    NASA Astrophysics Data System (ADS)

    Nagy, Sándor; Vértesi, Tamás

    2016-02-01

    In this paper, we investigate the communication cost of reproducing Einstein-Podolsky-Rosen (EPR) steering correlations arising from bipartite quantum systems. We characterize the set of bipartite quantum states which admits a local hidden state model augmented with c bits of classical communication from an untrusted party (Alice) to a trusted party (Bob). In case of one bit of information (c = 1), we show that this set has a nontrivial intersection with the sets admitting a local hidden state and a local hidden variables model for projective measurements. On the other hand, we find that an infinite amount of classical communication is required from an untrusted Alice to a trusted Bob to simulate the EPR steering correlations produced by a two-qubit maximally entangled state. It is conjectured that a state-of-the-art quantum experiment would be able to falsify two bits of communication this way.

  5. Deconvolution of sinusoidal rapid EPR scans.

    PubMed

    Tseitlin, Mark; Rinard, George A; Quine, Richard W; Eaton, Sandra S; Eaton, Gareth R

    2011-02-01

    In rapid scan EPR the magnetic field is scanned through the signal in a time that is short relative to electron spin relaxation times. Previously it was shown that the slow-scan lineshape could be recovered from triangular rapid scans by Fourier deconvolution. In this paper a general Fourier deconvolution method is described and demonstrated to recover the slow-scan lineshape from sinusoidal rapid scans. Since an analytical expression for the Fourier transform of the driving function for a sinusoidal scan was not readily apparent, a numerical method was developed to do the deconvolution. The slow scan EPR lineshapes recovered from rapid triangular and sinusoidal scans are in excellent agreement for lithium phthalocyanine, a trityl radical, and the nitroxyl radical, tempone. The availability of a method to deconvolute sinusoidal rapid scans makes it possible to scan faster than is feasible for triangular scans because of hardware limitations on triangular scans.

  6. EPR Steering inequalities with Communication Assistance

    PubMed Central

    Nagy, Sándor; Vértesi, Tamás

    2016-01-01

    In this paper, we investigate the communication cost of reproducing Einstein-Podolsky-Rosen (EPR) steering correlations arising from bipartite quantum systems. We characterize the set of bipartite quantum states which admits a local hidden state model augmented with c bits of classical communication from an untrusted party (Alice) to a trusted party (Bob). In case of one bit of information (c = 1), we show that this set has a nontrivial intersection with the sets admitting a local hidden state and a local hidden variables model for projective measurements. On the other hand, we find that an infinite amount of classical communication is required from an untrusted Alice to a trusted Bob to simulate the EPR steering correlations produced by a two-qubit maximally entangled state. It is conjectured that a state-of-the-art quantum experiment would be able to falsify two bits of communication this way. PMID:26880376

  7. EPR Investigation of Irradiated Curry Powder

    SciTech Connect

    Duliu, O. G.; Ali, S. I.; Georgescu, R.

    2007-04-23

    Gamma-ray irradiated curry powder, a well priced oriental spice was investigated in order to establish the ability of EPR to detect the presence and time stability of free irradiation free-radicals. Accordingly, curry powder aliquots were irradiated with gradually increasing absorbed doses up to 11.3 kGy. The EPR spectra of all irradiated samples show the presence of al last two different species of free radicals, whose concentration increased monotonously with the absorbed doses. A 100 deg. C isothermal annealing of irradiated samples has shown a differential reduction of amplitude of various components of the initial spectra, but even after 3.6 h of thermal treatment, the remaining amplitude represents no less then 30% of the initial ones. The same peculiarities have been noticed after more than one year storage at room temperature, all of them being very useful in establishing the existence of any previous irradiation treatment.

  8. Core Monitoring System for TSN EPR Reactors

    SciTech Connect

    Pfeiffer, Maxime

    2015-07-01

    In the context of Chinese (TSN) EPR reactors project, a new on-line support system was introduced to give information, either continuously or upon request, to the plant operators about some advanced physics parameters corresponding to the current state of the nuclear core. This document provides a description of the functions that are available and the advantages provided by using their results. For each function the Human Machine Interface (HMI) is illustrated. (authors)

  9. Seventy Years of the EPR Paradox

    NASA Astrophysics Data System (ADS)

    Kupczynski, Marian

    2006-11-01

    In spite of the fact that statistical predictions of quantum theory (QT) can only be tested if large amount of data is available a claim has been made that QT provides the most complete description of an individual physical system. Einstein's opposition to this claim and the paradox he presented in the article written together with Podolsky and Rosen in 1935 inspired generations of physicists in their quest for better understanding of QT. Seventy years after EPR article it is clear that without deep understanding of the character and limitations of QT one may not hope to find a meaningful unified theory of all physical interactions, manipulate qubits or construct a quantum computer.. In this paper we present shortly the EPR paper, the discussion, which followed it and Bell inequalities (BI). To avoid various paradoxes we advocate purely statistical contextual interpretation (PSC) of QT. According to PSC a state vector is not an attribute of a single electron, photon, trapped ion or quantum dot. A value of an observable assigned to a physical system has only a meaning in a context of a particular physical experiment PSC does not provide any mental space-time picture of sub phenomena. The EPR paradox is avoided because the reduction of the state vector in the measurement process is a passage from a description of the whole ensemble of the experimental results to a particular sub-ensemble of these results. We show that the violation of BI is neither a proof of the completeness of QT nor of its non-locality. Therefore we rephrase the EPR question and ask whether QT is "predictably "complete or in other words does it provide the complete description of experimental data. To test the "predictable completeness" it is not necessary to perform additional experiments it is sufficient to analyze more in detail the existing experimental data by using various non-parametric purity tests and other specific statistical tools invented to study the fine structure the time-series.

  10. W-Band Frequency-Swept EPR

    PubMed Central

    Hyde, James S.; Strangeway, Robert A.; Camenisch, Theodore G.; Ratke, Joseph J.; Froncisz, Wojciech

    2010-01-01

    This paper describes a novel experiment on nitroxide radical spin labels using a multiarm EPR W-band bridge with a loop-gap resonator (LGR). We demonstrate EPR spectroscopy of spin labels by linear sweep of the microwave frequency across the spectrum. The high bandwidth of the LGR, about 1 GHz between 3 dB points of the microwave resonance, makes this new experiment possible. A frequency-tunable yttrium iron garnet (YIG) oscillator provides sweep rates as high as 1.8 × 105 GHz/s, which corresponds to 6.3 kT/s in magnetic field-sweep units over a 44 MHz range. Two experimental domains were identified. In the first, linear frequency sweep rates were relatively slow, and pure absorption and pure dispersion spectra were obtained. This appears to be a practical mode of operation at the present level of technological development. The main advantage is the elimination of sinusoidal magnetic field modulation. In the second mode, the frequency is swept rapidly across a portion of the spectrum, and then the frequency sweep is stopped for a readout period; FID signals from a swept line oscillate at a frequency that is the difference between the spectral position of the line in frequency units and the readout position. If there is more than one line, oscillations are superimposed. The sweep rates using the YIG oscillator were too slow, and the portion of the spectrum too narrow to achieve the full EPR equivalent of Fourier transform (FT) NMR. The paper discusses technical advances required to reach this goal. The hypothesis that trapezoidal frequency sweep is an enabling technology for FT EPR is supported by this study. PMID:20462775

  11. CW-EPR Spectral Simulations: Solid State.

    PubMed

    Stoll, Stefan

    2015-01-01

    This chapter summarizes the core concepts underlying the simulation of EPR spectra from biological samples in the solid state, from a user perspective. The key choices and decisions that have to be made by a user when simulating an experimental EPR spectrum are outlined. These include: the choice of the simulation model (the network of spins and the associated spin Hamiltonian), the dynamic regime (solid, liquid, slow motion), the level of theory used in the simulation (matrix diagonalization, perturbation theory, etc.), the treatment of orientational order and disorder (powder, crystal, partial ordering), the inclusion of the effects of structural disorder (strains), the effects of other line broadening mechanisms (unresolved hyperfine couplings, relaxation), and the inclusion of experimental distortions (field modulation, power saturation, filtering). Additionally, the salient aspects of utilizing least-squares fitting algorithms to aid the analysis of experimental spectra with the help of simulations are outlined. Although drawing from the experience gained from implementing EasySpin and from interacting with EasySpin's user base, this chapter applies to any EPR simulation software.

  12. Use of the Frank sequence in pulsed EPR.

    PubMed

    Tseitlin, Mark; Quine, Richard W; Eaton, Sandra S; Eaton, Gareth R; Halpern, Howard J; Ardenkjaer-Larsen, J-H

    2011-04-01

    The Frank polyphase sequence has been applied to pulsed EPR of triarylmethyl radicals at 25 6 MHz (9.1 mT 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. 1.5 mW in the application reported here) relative to standard pulsed EPR. A 0.2 mM aqueous solution of a triarylmethyl radical was studied using a 16 mm diameter cross-loop resonator to isolate the EPR signal detection system from the incident pulses.

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

    NASA Astrophysics Data System (ADS)

    Yordanov, N. D.; Aleksieva, K.

    2007-06-01

    The shape and time stability of the electron paramagnetic resonance (EPR) spectra of non- and γ-irradiated papaya, melon, cherry and fig samples dehydrated via osmosis are reported. It is shown that non-irradiated samples are generally EPR silent whereas γ-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.

  14. EPR: what has it taught us

    SciTech Connect

    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.

  15. Case Studies in e-RPL and e-PR

    ERIC Educational Resources Information Center

    Cameron, Roslyn; Miller, Allison

    2014-01-01

    The use of ePortfolios for recognition of prior learning (e-RPL) and for professional recognition (e-PR) is slowly gaining in popularity in the VET sector however their use is sporadic across educational sectors, disciplines, educational institutions and professions. Added to this is an array of purposes and types of e-RPL and e-PR models and…

  16. EPR Assembly of Microgel for FRET Imaging of Breast Cancer

    DTIC Science & Technology

    2008-04-01

    AD_________________ Award Number: W81XWH-05-1-0342 TITLE: EPR Assembly of Microgel for FRET...4. TITLE AND SUBTITLE EPR Assembly of Microgel for FRET Imaging of Breast Cancer 5a. CONTRACT NUMBER 5b. GRANT NUMBER W81XWH-05-1-0342 5c

  17. Three key concerns for a successful EPR deployment and usage.

    PubMed

    Janols, Rebecka; Gôrranson, Bengt; Sandblad, Bengt

    2011-01-01

    The health care environment is unique because of the large and complex organisation with a traditional hierarchic structure that is governed by laws and regulations. This paper examines how a large Swedish health care organisation work with usability issues regarding Electronic Patient Record (EPR) deployment and usage. EPR systems have great impact on work environment and clinical work routines will not be performed in the same way as before. This paper analyse how the EPR management and core business understand their EPR responsibilities and work with usability aspects at different levels in the organisations. The paper reveals that there is a conflict about responsibility between EPR management and core business management. The reasons for the confusion are contradictive understanding of what an EPR system is, an IT system or a tool for the core business to perform better health care work. This leads to that care staff's experience regarding the EPR system's usability, is not being listened to within the organisation. Three key concerns for a successful EPR deployment and usage are identified and further analysed; education, evaluation and support & improvement ideas.

  18. EPR investigation of some gamma-irradiated excipients

    NASA Astrophysics Data System (ADS)

    Aleksieva, Katerina; Yordanov, Nicola D.

    2012-09-01

    The results of electron paramagnetic resonance (EPR) studies on some excipients: lactose, microcrystalline cellulose (avicel), starch, dioxosilane (aerosil), talc and magnesium stearate before and after gamma-irradiation are reported. Before irradiation, all samples are EPR silent except talc. After gamma-irradiation, they show complex spectra except magnesium stearate, which is EPR silent. Studies show the influence of gamma-irradiation on EPR spectra and stability of gamma-induced radicals. Analysis of the EPR spectrum of gamma-irradiated talc shows that this material is radiation insensitive. Only lactose forms stable-free radicals upon gamma sterilization and can be used for identification of radiation processing for a long time period thereafter.

  19. Identification of gamma-irradiated fruit juices by EPR spectroscopy

    NASA Astrophysics Data System (ADS)

    Aleksieva, K. I.; Dimov, K. G.; Yordanov, N. D.

    2014-10-01

    The results of electron paramagnetic resonance (EPR) study on commercially available juices from various fruits and different fruit contents: 25%, 40%, 50%, and 100%, homemade juices, nectars and concentrated fruit syrups, before and after gamma-irradiation are reported. In order to remove water from non- and irradiated samples all juices and nectars were filtered; the solid residue was washed with alcohol and dried at room temperature. Only concentrated fruit syrups were dried for 60 min at 40 °C in a standard laboratory oven. All samples under study show a singlet EPR line with g=2.0025 before irradiation with exception of concentrated fruit syrups, which are EPR silent. Irradiation of juice samples gives rise to complex EPR spectra which gradually transferred to "cellulose-like" EPR spectrum from 25% to 100% fruit content. Concentrated fruit syrups show typical "sugar-like" spectra due to added saccharides. All EPR spectra are characteristic and can prove radiation treatment. The fading kinetics of radiation-induced EPR signals were studied for a period of 60 days after irradiation.

  20. EPR paradox, quantum nonlocality and physical reality

    NASA Astrophysics Data System (ADS)

    Kupczynski, M.

    2016-03-01

    Eighty years ago Einstein, Podolsky and Rosen demonstrated that instantaneous reduction of wave function, believed to describe completely a pair of entangled physical systems, led to EPR paradox. The paradox disappears in statistical interpretation of quantum mechanics (QM) according to which a wave function describes only an ensemble of identically prepared physical systems. QM predicts strong correlations between outcomes of measurements performed on different members of EPR pairs in far-away locations. Searching for an intuitive explanation of these correlations John Bell analysed so called local realistic hidden variable models and proved that correlations consistent with these models satisfy Bell inequalities which are violated by some predictions of QM and by experimental data. Several different local models were constructed and inequalities proven. Some eminent physicists concluded that Nature is definitely nonlocal and that it is acting according to a law of nonlocal randomness. According to these law perfectly random, but strongly correlated events, can be produced at the same time in far away locations and a local and causal explanation of their occurrence cannot be given. We strongly disagree with this conclusion and we prove the contrary by analysing in detail some influential finite sample proofs of Bell and CHSH inequalities and so called Quantum Randi Challenges. We also show how one can win so called Bell's game without violating locality of Nature. Nonlocal randomness is inconsistent with local quantum field theory, with standard model in elementary particle physics and with causal laws and adaptive dynamics prevailing in the surrounding us world. The experimental violation of Bell-type inequalities does not prove the nonlocality of Nature but it only confirms a contextual character of quantum observables and gives a strong argument against counterfactual definiteness and against a point of view according to which experimental outcomes are produced

  1. Macromolecular therapeutics in cancer treatment: the EPR effect and beyond.

    PubMed

    Maeda, Hiroshi

    2012-12-10

    In this review, I have discussed various issues of the cancer drug targeting primarily related to the EPR (enhanced permeability and retention) effect, which utilized nanomedicine or macromolecular drugs. The content goes back to the development of the first polymer-protein conjugate anticancer agent SMANCS and development of the arterial infusion in Lipiodol formulation into the tumor feeding artery (hepatic artery for hepatoma). The brief account on the EPR effect and its definition, factors involved, heterogeneity, and various methods of augmentation of the EPR effect, which showed remarkably improved clinical outcomes are also discussed. Various obstacles involved in drug developments and commercialization are also discussed through my personal experience and recollections.

  2. EPR of radiation defects in lithium-oxyfluoride glass ceramics

    NASA Astrophysics Data System (ADS)

    Fedotovs, A.; Rogulis, U.; Sarakovskis, A.; Dimitrocenko, L.

    2010-11-01

    We studied oxyfluoride composites based on lithium silicate glasses with yttrium fluorides and rare-earth dopants. The electron paramagnetic resonance (EPR) has been used to obtain information about radiation induced defects in these materials. Spectra have been measured before and after X-ray irradiation at room temperature and at liquid nitrogen temperature. Fluoride crystallites within samples were created by means of thermal treatment at specific temperatures. EPR spectra of radiation induced defects in oxyfluoride glass ceramics, in which crystallites have not been yet created, show no explicit hfs interaction of fluorine nuclei. However, in glass ceramics, which already contains fluoride crystallites, the hfs characteristic to fluorine nuclei appears in the EPR spectra. EPR hyperfine structure could be explained within a model of an F-type centre in YF3 crystalline phase.

  3. Software for evaluation of EPR-dosimetry performance.

    PubMed

    Shishkina, E A; Timofeev, Yu S; Ivanov, D V

    2014-06-01

    Electron paramagnetic resonance (EPR) with tooth enamel is a method extensively used for retrospective external dosimetry. Different research groups apply different equipment, sample preparation procedures and spectrum processing algorithms for EPR dosimetry. A uniform algorithm for description and comparison of performances was designed and implemented in a new computer code. The aim of the paper is to introduce the new software 'EPR-dosimetry performance'. The computer code is a user-friendly tool for providing a full description of method-specific capabilities of EPR tooth dosimetry, from metrological characteristics to practical limitations in applications. The software designed for scientists and engineers has several applications, including support of method calibration by evaluation of calibration parameters, evaluation of critical value and detection limit for registration of radiation-induced signal amplitude, estimation of critical value and detection limit for dose evaluation, estimation of minimal detectable value for anthropogenic dose assessment and description of method uncertainty.

  4. High-frequency EPR study of crude oils

    NASA Astrophysics Data System (ADS)

    Volodin, M. A.; Mamin, G. V.; Izotov, V. V.; Orlinskii, S. B.

    2013-12-01

    Four different samples of crude oil were studied by means of high-frequency W-band (94 GHz) electron paramagnetic resonance (EPR) spectroscopy with the aim to develop new methods of crude oil quality control. High spectral resolution of W-band allowed to avoid an overlap of spectra contributors. The ratio K between the integral intensity of the low-field EPR component of the vanadyl complexes to that of free radical line was chosen as an attribute of each sample. Using the K-parameters and EPR spectra simulations the crude oil leaking between adjacent horizons is shown. Pulsed EPR experiments allowed detecting free radicals signals only. It is demonstrated that the extracted transverse relaxation time could be used as an additional parameter which characterizes the origin of the crude oil and nature of the oil paramagnetic centers.

  5. EPR Assembly of Microgel for FRET Imaging of Breast Cancer

    DTIC Science & Technology

    2006-04-01

    W81XWH-05-1-0342 TITLE: EPR Assembly for Microgel for FRET Imaging of Breast Cancer PRINCIPAL INVESTIGATOR: Stanley Stein, Ph.D...Annual 3. DATES COVERED (From - To) 1 Apr 05 – 31 Mar 06 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER EPR Assembly of Microgel for FRET Imaging...administered. This second conjugate will chemoselectively interact with the first conjugate to form insoluble microgels only in tumors. Alternating

  6. Simultaneous acquisition of pulse EPR orientation selective spectra

    NASA Astrophysics Data System (ADS)

    Kaminker, Ilia; Florent, Marc; Epel, Boris; Goldfarb, Daniella

    2011-01-01

    High resolution pulse EPR methods are usually applied to resolve weak magnetic electron-nuclear or electron-electron interactions that are otherwise unresolved in the EPR spectrum. Complete information regarding different magnetic interactions, namely, principal components and orientation of principal axis system with respect to the molecular frame, can be derived from orientation selective pulsed EPR measurements that are performed at different magnetic field positions within the inhomogeneously broadened EPR spectrum. These experiments are usually carried out consecutively, namely a particular field position is chosen, data are accumulated until the signal to noise ratio is satisfactory, and then the next field position is chosen and data are accumulated. Here we present a new approach for data acquisition of pulsed EPR experiments referred to as parallel acquisition. It is applicable when the spectral width is much broader than the excitation bandwidth of the applied pulse sequence and it is particularly useful for orientation selective pulse EPR experiments. In this approach several pulse EPR measurements are performed within the waiting (repetition) time between consecutive pulse sequences during which spin lattice relaxation takes place. This is achieved by rapidly changing the main magnetic field, B0, to different values within the EPR spectrum, performing the same experiment on the otherwise idle spins. This scheme represents an efficient utilization of the spectrometer and provides the same spectral information in a shorter time. This approach is demonstrated on W-band orientation selective electron-nuclear double resonance (ENDOR), electron spin echo envelope modulation (ESEEM), electron-electron double resonance (ELDOR) - detected NMR and double electron-electron resonance (DEER) measurements on frozen solutions of nitroxides. We show that a factors of 3-6 reduction in total acquisition time can be obtained, depending on the experiment applied.

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Accelerated dynamic EPR imaging using fast acquisition and compressive recovery

    NASA Astrophysics Data System (ADS)

    Ahmad, Rizwan; Samouilov, Alexandre; Zweier, Jay L.

    2016-12-01

    Electron paramagnetic resonance (EPR) allows quantitative imaging of tissue redox status, which provides important information about ischemic syndromes, cancer and other pathologies. For continuous wave EPR imaging, however, poor signal-to-noise ratio and low acquisition efficiency limit its ability to image dynamic processes in vivo including tissue redox, where conditions can change rapidly. Here, we present a data acquisition and processing framework that couples fast acquisition with compressive sensing-inspired image recovery to enable EPR-based redox imaging with high spatial and temporal resolutions. The fast acquisition (FA) allows collecting more, albeit noisier, projections in a given scan time. The composite regularization based processing method, called spatio-temporal adaptive recovery (STAR), not only exploits sparsity in multiple representations of the spatio-temporal image but also adaptively adjusts the regularization strength for each representation based on its inherent level of the sparsity. As a result, STAR adjusts to the disparity in the level of sparsity across multiple representations, without introducing any tuning parameter. Our simulation and phantom imaging studies indicate that a combination of fast acquisition and STAR (FASTAR) enables high-fidelity recovery of volumetric image series, with each volumetric image employing less than 10 s of scan. In addition to image fidelity, the time constants derived from FASTAR also match closely to the ground truth even when a small number of projections are used for recovery. This development will enhance the capability of EPR to study fast dynamic processes that cannot be investigated using existing EPR imaging techniques.

  9. Novel EPR characterization of the antioxidant activity of tea leaves

    NASA Astrophysics Data System (ADS)

    Morsy, M. A.; Khaled, M. M.

    2002-04-01

    Electron paramagnetic resonance (EPR) spectroscopy is utilized to investigate several categories of green and black tea: Twining green tea (TGT), Chinese green tea (CGT), Red-labels black tea (RBT). Basically, two EPR signals from all the studied samples are observed: One of them is a very weak sharp EPR signal with Δ Hpp≅10 G and g-factor=2.00023 superimposed on the other broad signal with Δ Hpp≅550 G and g-factor=2.02489. The broad signal is a characteristic one of manganese(II) complex, while the sharp signal is related to a stable radical of aromatic origin exist in a powder condition. The feature of the manganese EPR signal is attributed to manganese(II) complex and reflected the molecular behavior of Mn(II) in the protein system of the natural leaves. The sharp signal, which is most probably due to a semiquinones radicals, is observed at room temperature and its intensity is remarkably affected by photo degradation of the studied samples. The intensity of manganese(II) EPR signal is found to be related to ageing and disintegration of the tea leaves. Moreover, direct relation between the relative intensity of the semiquinones radical signal and antioxidant activity of the studied samples was also correlated.

  10. Characterizing rhodopsin signaling by EPR spectroscopy: from structure to dynamics.

    PubMed

    Van Eps, Ned; Caro, Lydia N; Morizumi, Takefumi; Ernst, Oliver P

    2015-09-26

    Electron paramagnetic resonance (EPR) spectroscopy, together with spin labeling techniques, has played a major role in the characterization of rhodopsin, the photoreceptor protein and G protein-coupled receptor (GPCR) in rod cells. Two decades ago, these biophysical tools were the first to identify transmembrane helical movements in rhodopsin upon photo-activation, a critical step in the study of GPCR signaling. EPR methods were employed to identify functional loop dynamics within rhodopsin, to measure light-induced millisecond timescale changes in rhodopsin conformation, to characterize the effects of partial agonists on the apoprotein opsin, and to study lipid interactions with rhodopsin. With the emergence of advanced pulsed EPR techniques, the stage was set to determine the amplitude of structural changes in rhodopsin and the dynamics in the rhodopsin signaling complexes. Work in this area has yielded invaluable information about mechanistic properties of GPCRs. Using EPR techniques, receptors are studied in native-like membrane environments and the effects of lipids on conformational equilibria can be explored. This perspective addresses the impact of EPR methods on rhodopsin and GPCR structural biology, highlighting historical discoveries made with spin labeling techniques, and outlining exciting new directions in the field.

  11. Accelerated dynamic EPR imaging using fast acquisition and compressive recovery.

    PubMed

    Ahmad, Rizwan; Samouilov, Alexandre; Zweier, Jay L

    2016-12-01

    Electron paramagnetic resonance (EPR) allows quantitative imaging of tissue redox status, which provides important information about ischemic syndromes, cancer and other pathologies. For continuous wave EPR imaging, however, poor signal-to-noise ratio and low acquisition efficiency limit its ability to image dynamic processes in vivo including tissue redox, where conditions can change rapidly. Here, we present a data acquisition and processing framework that couples fast acquisition with compressive sensing-inspired image recovery to enable EPR-based redox imaging with high spatial and temporal resolutions. The fast acquisition (FA) allows collecting more, albeit noisier, projections in a given scan time. The composite regularization based processing method, called spatio-temporal adaptive recovery (STAR), not only exploits sparsity in multiple representations of the spatio-temporal image but also adaptively adjusts the regularization strength for each representation based on its inherent level of the sparsity. As a result, STAR adjusts to the disparity in the level of sparsity across multiple representations, without introducing any tuning parameter. Our simulation and phantom imaging studies indicate that a combination of fast acquisition and STAR (FASTAR) enables high-fidelity recovery of volumetric image series, with each volumetric image employing less than 10 s of scan. In addition to image fidelity, the time constants derived from FASTAR also match closely to the ground truth even when a small number of projections are used for recovery. This development will enhance the capability of EPR to study fast dynamic processes that cannot be investigated using existing EPR imaging techniques.

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

    SciTech Connect

    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.

  13. Radiation accident dosimetry on plastics by EPR spectrometry.

    PubMed

    Trompier, F; Bassinet, C; Clairand, I

    2010-02-01

    In case of acute exposure to ionizing radiation, the dose absorbed by the victims has to be rapidly and accurately assessed in order to choose an appropriate medical treatment. Tooth enamel and bone biopsies measured by EPR spectrometry are often used as dose indicators, due to the good radiation sensitivity and the stability of EPR radiation-sensitive signals. Nevertheless, the invasive sampling of teeth and bones limits the application of this technique to retrospective dosimetry. Therefore, we have investigated an alternative non-invasive methodology. We have surveyed with EPR spectrometry the dosimetric properties of the plastics that can be found in personal effects such as glasses (CR-39, polycarbonate), mobile phones (PMMA, polycarbonate), watches and buttons. Dose response, signal stability and effects of storage conditions were investigated. Significant signal fading limits the use for radiation accident dosimetry. Few plastics present the required characteristics to be used in case of a radiation accident.

  14. Free radicals and antioxidants at a glance using EPR spectroscopy.

    PubMed

    Spasojević, Ivan

    2011-01-01

    The delicate balance between the advantageous and detrimental effects of free radicals is one of the important aspects of human (patho)physiology. The controlled production of reactive oxygen and nitrogen species has an essential role in the regulation of various signaling switches. On the other hand, imbalanced generation of radicals is highly correlated with the pathogenesis of many diseases which require the application of selected antioxidants to regain the homeostasis. In the era of growing interest for redox processes, electron paramagnetic resonance (EPR) spectroscopy is arguably the best-suited technique for such research due to its ability to provide a unique insight into the world of free radicals and antioxidants. Herein, I present the principles of EPR spectroscopy and the applications of this method in assessing: (i) the oxidative status of biological systems, using endogenous long-lived free radicals (ascorbyl radical (Asc(•)), tocopheroxyl radical (TO(•)), melanin) as markers; (ii) the production of short-lived radicals (hydroxyl radical (OH(•)), superoxide radical anion (O(2)(•-)), sulfur- and carbon-centered radicals), which are implicated in both, oxidative stress and redox signaling; (iii) the metabolism of nitric oxide (NO(•)); (iv) the antioxidative properties of various drugs, compounds, and natural products; (v) other redox-relevant parameter. Besides giving a comprehensive survey of up-to-date literature, I also provide illustrative examples in sufficient detail to provide a means to exploit the potential of EPR in biochemical/physiological/medical research. The emphasis is on the features and characteristics (both positive and negative) relevant for EPR application in clinical sciences. My aim is to encourage fellow colleagues interested in free radicals and antioxidants to expand their base knowledge or methods used in their laboratories with data acquired by EPR or some of the EPR techniques outlined in this review, in order to

  15. Comparison of Continuous Wave, Spin Echo, and Rapid Scan EPR of Irradiated Fused Quartz.

    PubMed

    Mitchell, Deborah G; Quine, Richard W; Tseitlin, Mark; Meyer, Virginia; Eaton, Sandra S; Eaton, Gareth R

    2011-09-01

    The E' defect in irradiated fused quartz has spin lattice relaxation times (T(1)) about 100 to 300 μs and spin-spin relaxation times (T(2)) up to about 200 μs, depending on the concentration of defects and other species in the sample. These long relaxation times make it difficult to record an unsaturated continuous wave (CW) electron paramagnetic resonance (EPR) signal that is free of passage effects. Signals measured at X-band (~9.5 GHz) by three EPR methods: conventional slow-scan field modulated EPR, rapid scan EPR, and pulsed EPR, were compared. To acquire spectra with comparable signal-to-noise, both pulsed and rapid scan EPR require less time than conventional CW EPR. Rapid scan spectroscopy does not require the high power amplifiers that are needed for pulsed EPR. The pulsed spectra, and rapid scan spectra obtained by deconvolution of the experimental data, are free of passage effects.

  16. Nonlinear Simulation of the Tooth Enamel Spectrum for EPR Dosimetry

    NASA Astrophysics Data System (ADS)

    Kirillov, V. A.; Dubovsky, S. V.

    2016-07-01

    Software was developed where initial EPR spectra of tooth enamel were deconvoluted based on nonlinear simulation, line shapes and signal amplitudes in the model initial spectrum were calculated, the regression coefficient was evaluated, and individual spectra were summed. Software validation demonstrated that doses calculated using it agreed excellently with the applied radiation doses and the doses reconstructed by the method of additive doses.

  17. Metamorphic modifications and EPR dosimetry in tooth enamel.

    PubMed

    Brik, A; Radchuk, V; Scherbina, O; Matyash, M; Gaver, O

    1996-01-01

    It is shown that metamorphic modifications in tooth enamel have an essential influence on the results of EPR dosimetry. The metamorphic modifications in minerals of biological origin proceed more quickly than in usual natural minerals. The approaches which at present are applied for reconstruction of doses connected with Chernobyl accident need additional investigation.

  18. Quantitative rapid scan EPR spectroscopy at 258 MHz.

    PubMed

    Quine, Richard W; Rinard, George A; Eaton, Sandra S; Eaton, Gareth R

    2010-07-01

    Experimental data obtained with an electron paramagnetic resonance (EPR) rapid scan spectrometer were translated through the reverse transfer functions of the spectrometer hardware to the sample position. Separately, theoretical calculations were performed to predict signal and noise amplitudes at the sample position for specified experimental conditions. A comparison was then made between the translated experimental values and the calculated values. Excellent agreement was obtained.

  19. Shaped optimal control pulses for increased excitation bandwidth in EPR.

    PubMed

    Spindler, Philipp E; Zhang, Yun; Endeward, Burkhard; Gershernzon, Naum; Skinner, Thomas E; Glaser, Steffen J; Prisner, Thomas F

    2012-05-01

    A 1 ns resolution pulse shaping unit has been developed for pulsed EPR spectroscopy to enable 14-bit amplitude and phase modulation. Shaped broadband excitation pulses designed using optimal control theory (OCT) have been tested with this device at X-band frequency (9 GHz). FT-EPR experiments on organic radicals in solution have been performed with the new pulses, designed for uniform excitation over a significantly increased bandwidth compared to a classical rectangular π/2 pulse of the same B(1) amplitude. The concept of a dead-time compensated prefocused pulse has been introduced to EPR with a self-refocusing of 200 ns after the end of the pulse. Echo-like refocused signals have been recorded and compared to the performance of a classical Hahn-echo sequence. The impulse response function of the microwave setup has been measured and incorporated into the algorithm for designing OCT pulses, resulting in further significant improvements in performance. Experimental limitations and potential new applications of OCT pulses in EPR spectroscopy will be discussed.

  20. Exploiting EPR in polymer drug conjugate delivery for tumor targeting.

    PubMed

    Modi, Sweta; Prakash Jain, Jay; Domb, A J; Kumar, Neeraj

    2006-01-01

    Treatment of tumor tissue without affecting normal cells has always been formidable task for drug delivery scientists and this task is effectively executed by polymer drug conjugate (PDC) delivery. The novelty of this concept lies in the utilization of a physical mechanism called enhanced permeability and retention (EPR) for targeting tumors. EPR is a physiological phenomenon that is customary for fast growing tumor and solves the problem of targeting the miscreant tissue. PDCs offer added advantages of reduced deleterious effects of anticancer drugs and augmentation of its formulation capability (e.g. Solubility). There are now at least eleven PDCs that have entered phase I/II/III clinical trial as anticancer drugs. PDCs once entered into the tumor tissue, taking advantage of EPR, are endocytosed into the cell either by simple or receptor mediated endocytosis. Various polymeric carriers have been used with hydrolyzable linker arm for conjugation with bioactive moiety. The hydrolyzable linkages of PDC are broken down by acid hydrolyses of lysosomes and releases the drug. High concentrations of the chemotherapeutic agent are maintained near the nucleus, the target site. Passive targeting by PDCs is due to the physiological event of EPR, which is becoming one of the major thrust areas for targeting solid tumors.

  1. A hand-held EPR scanner for transcutaneous oximetry

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  2. EPR/PTFE dosimetry for test reactor environments

    SciTech Connect

    Vehar, D.W.; Griffin, P.J.; Quirk, T.J.

    2011-07-01

    The use of Electron Paramagnetic Resonance (EPR) spectroscopy with materials such as alanine is well established as a technique for measurement of ionizing radiation absorbed dose in photon and electron fields such as Co-60, high-energy bremsstrahlung and electron-beam fields [1]. In fact, EPR/Alanine dosimetry has become a routine transfer standard for national standards bodies such as NIST and NPL. In 1992 the Radiation Metrology Laboratory (RML) at Sandia National Laboratories implemented EPR/Alanine capabilities for use in routine and calibration activities at its Co-60 and pulsed-power facilities. At that time it also investigated the usefulness of the system for measurement of absorbed dose in the mixed neutron/photon environments of reactors such as the Sandia Pulsed Reactor and the Annular Core Research Reactor used for hardness testing of electronics. The RML concluded that the neutron response of alanine was a sufficiently high fraction of the overall dosimeter response that the resulting uncertainties in the photon dose would be unacceptably large for silicon-device testing. However, it also suggested that non-hydrogenous materials such as polytetrafluoroethylene (PTFE) would exhibit smaller neutron response and might be useful in mixed environments. Preliminary research with PTFE in photon environments indicated considerable promise, but further development was not pursued at that time. Because of renewed interest in absorbed dose measurements that could better define the individual contributions of photon and neutron components to the overall dose delivered to a test object, the RML has re-initiated the development of an EPR/PTFE dosimetry system. This effort consists of three stages: 1) Identification of PTFE materials that may be suitable for dosimetry applications. It was speculated that the inconsistency of EPR signatures in the earlier samples may have been due to variability in PTFE manufacturing processes. 2) Characterization of dosimetry in

  3. EPR Imaging at a Few Megahertz Using SQUID Detectors

    NASA Technical Reports Server (NTRS)

    Hahn, Inseob; Day, Peter; Penanen, Konstantin; Eom, Byeong Ho

    2010-01-01

    An apparatus being developed for electron paramagnetic resonance (EPR) imaging operates in the resonance-frequency range of about 1 to 2 MHz well below the microwave frequencies used in conventional EPR. Until now, in order to obtain sufficient signal-to-noise radios (SNRs) in conventional EPR, it has been necessary to place both detectors and objects to be imaged inside resonant microwave cavities. EPR imaging has much in common with magnetic resonance imaging (MRI), which is described briefly in the immediately preceding article. In EPR imaging as in MRI, one applies a magnetic pulse to make magnetic moments (in this case, of electrons) precess in an applied magnetic field having a known gradient. The magnetic moments precess at a resonance frequency proportional to the strength of the local magnetic field. One detects the decaying resonance-frequency magnetic- field component associated with the precession. Position is encoded by use of the known relationship between the resonance frequency and the position dependence of the magnetic field. EPR imaging has recently been recognized as an important tool for non-invasive, in vivo imaging of free radicals and reduction/oxidization metabolism. However, for in vivo EPR imaging of humans and large animals, the conventional approach is not suitable because (1) it is difficult to design and construct resonant cavities large enough and having the required shapes; (2) motion, including respiration and heartbeat, can alter the resonance frequency; and (3) most microwave energy is absorbed in the first few centimeters of tissue depth, thereby potentially endangering the subject and making it impossible to obtain adequate signal strength for imaging at greater depth. To obtain greater penetration depth, prevent injury to the subject, and avoid the difficulties associated with resonant cavities, it is necessary to use lower resonance frequencies. An additional advantage of using lower resonance frequencies is that one can use

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

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

    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. 50 days, 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=2.0023±0.0003 and g⊥=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 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.

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

    PubMed

    Abdel-Fattah, A A

    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.

  6. A transferability study of the EPR-tooth-dosimetry technique.

    PubMed

    Sholom, S; Chumak, V; Desrosiers, M; Bouville, A

    2006-01-01

    The transferability of a measurement protocol from one laboratory to another is an important feature of any mature, standardised protocol. The electron paramagnetic resonance (EPR)-tooth dosimetry technique that was developed in Scientific Center for Radiation Medicine, AMS, Ukraine (SCRM) for routine dosimetry of Chernobyl liquidators has demonstrated consistent results in several inter-laboratory measurement comparisons. Transferability to the EPR dosimetry laboratory at the National Institute of Standards and Technology (NIST) was examined. Several approaches were used to test the technique, including dose reconstruction of SCRM-NIST inter-comparison samples. The study has demonstrated full transferability of the technique and the possibility to reproduce results in a different laboratory environment.

  7. The Chernobyl accident: EPR dosimetry on dental enamel of children.

    PubMed

    Gualtieri, G; Colacicchi, S; Sgattoni, R; Giannoni, M

    2001-07-01

    The radiation dose on tooth enamel of children living close to Chernobyl has been evaluated by EPR. The sample preparation was reduced to a minimum of mechanical steps to remove a piece of enamel. A standard X-ray tube at low energy was used for additive irradiation. The filtration effect of facial soft tissue was taken into account. The radiation dose for a group of teeth slightly exceeds the annual dose, whereas for another group the dose very much exceeds the annual dose. Since the higher dose is found in teeth whose enamel have much lower EPR sensitivity to the radiation, it can be suggested that for these teeth the native signal could alter the evaluation of the smaller radiation signal.

  8. Electron beam radiation effects on UHMWPE: an EPR study.

    PubMed

    Brunella, Valentina; Paganini, Maria Cristina

    2011-09-01

    Electron paramagnetic resonance (EPR) technique has been employed to detect and characterise a series of different radical species generated in ultra-high molecular weight polyethylene (UHMWPE) via electron beam irradiation. Three different radical species have been found and assigned on the basis of their EPR spectra and of the related computer simulations. A secondary alkyl species, the prevalent one, is present immediately after irradiation, an allyl species appears only 24 h after irradiation when the alkyl species disappears.The third species, clearly visible at high microwave power only, has been observed for the first time and assigned to a tertiary alkyl carbon radical, whose formation is strictly connected with a Y-shape crosslink and a migration of the unpaired electron on a carbon atom localised in an adjacent position.

  9. On the computer simulation of the EPR-Bohm experiment

    SciTech Connect

    McGoveran, D.O.; Noyes, H.P.; Manthey, M.J.

    1988-12-01

    We argue that supraluminal correlation without supraluminal signaling is a necessary consequence of any finite and discrete model for physics. Every day, the commercial and military practice of using encrypted communication based on correlated, pseudo-random signals illustrates this possibility. All that is needed are two levels of computational complexity which preclude using a smaller system to detect departures from ''randomness'' in the larger system. Hence the experimental realizations of the EPR-Bohm experiment leave open the question of whether the world of experience is ''random'' or pseudo-random. The latter possibility could be demonstrated experimentally if a complexity parameter related to the arm length and switching time in an Aspect-type realization of the EPR-Bohm experiment is sufficiently small compared to the number of reliable total counts which can be obtained in practice. 6 refs.

  10. Kinetic measurements using EPR imaging with a modulated field gradient.

    PubMed

    Herrling, Thomas; Fuchs, Jürgen; Groth, Norbert

    2002-01-01

    EPR imaging with modulated field gradient was applied for the investigation of fast diffusion processes. Three different imaging methods are possible: spectral-temporal, spatio-temporal, and spectral-spatial imaging. The time resolution is on the order of seconds and the spatial resolution is in the micrometer region. The efficiency of this imaging technique is demonstrated for the penetration of the spin probe Tempol in the skin of hairless mice biopsies. The skin is normally protected against the penetration of water soluble substances by the horny layer, a resistive thin lipophilic layer. Overcoming this horny layer for water soluble ingredients is one of the main practical problems for the topical application of pharmaceutics which could be investigated by EPR imaging. Different images represent the penetration behavior of the water soluble Tempol in the skin after treatment with the penetration enhancer DMSO (Dimethylsulfoxide) and after removing the horny layer.

  11. Kinetic Measurements Using EPR Imaging with a Modulated Field Gradient

    NASA Astrophysics Data System (ADS)

    Herrling, Thomas; Fuchs, Jürgen; Groth, Norbert

    2002-01-01

    EPR imaging with modulated field gradient was applied for the investigation of fast diffusion processes. Three different imaging methods are possible: spectral-temporal, spatio-temporal, and spectral-spatial imaging. The time resolution is on the order of seconds and the spatial resolution is in the micrometer region. The efficiency of this imaging technique is demonstrated for the penetration of the spin probe Tempol in the skin of hairless mice biopsies. The skin is normally protected against the penetration of water soluble substances by the horny layer, a resistive thin lipophilic layer. Overcoming this horny layer for water soluble ingredients is one of the main practical problems for the topical application of pharmaceutics which could be investigated by EPR imaging. Different images represent the penetration behavior of the water soluble Tempol in the skin after treatment with the penetration enhancer DMSO (Dimethylsulfoxide) and after removing the horny layer.

  12. EPR and electronic absorption spectra of copper bearing turquoise mineral

    NASA Astrophysics Data System (ADS)

    Sharma, K. B. N.; Moorthy, L. R.; Reddy, B. J.; Vedanand, S.

    1988-10-01

    Electron paramagnetic resonance and optical absorption spectra of turquoise have been studied both at room and low temperatures. It is concluded from the EPR spectra that the ground state of Cu 2+ ion in turquoise is 2A g(d x2- y2) and it is sited in an elongated rhombic octahedron (D 2π). The observed absorption bands at 14970 and 18354 cm -1 are assigned at 2A g→ 2B 1 g( dx2- y2→ xy) and 2A g→[ su2B 3g(d x 2-y 2→d yz) respectively assuming D 2π symmetry which are inconsistent with EPR studies. The three bands in the NIR region are attributed to combinations of fundamental modes of the H 2O molecule present in the sample.

  13. EPR dosimetry in a mixed neutron and gamma radiation field.

    PubMed

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

    2004-01-01

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

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

    PubMed

    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.

  15. EPR Assembly of Microgel for FRET Imaging of Breast Cancer

    DTIC Science & Technology

    2007-04-01

    AD_________________ Award Number: W81XWH-05-1-0342 TITLE: EPR Assembly of Microgel for FRET...The selection of polymer with optimum molecular size/weight is crucial in accomplishing our aim of forming intermolecular polymer network ( microgel ) of...chemoselectivity) and spontaneously form a network ( microgel ) in the tumors (Figure 1). The host and guest copolymer will each have a donor and an acceptor

  16. Noble Gas Polarimetry Using Rb EPR Frequency Shifts

    NASA Astrophysics Data System (ADS)

    Ma, Z. L.; Jeong, K.; Houghtby, E.; Paskvan, T.; Limes, M. E.; Saam, B.

    2014-05-01

    EPR frequency shifts of optically polarized alkali-metal atoms can be exploited for polarimetry of noble-gas nuclei polarized by spin-exchange optical pumping. Our group recently measured the enhancement factor κ0 = 493 for Rb-129Xe, which characterizes the electron wave-function overlap during collisions and is crucial to the calibration of the frequency-shift for 129Xe polarimetry. This type of polarimetry is useful in several applications involving optically polarized 129Xe; our particular motivation is an in situ measurement of absolute 129Xe polarization within the optical pumping cell of a flow-through 129Xe polarizer. This application has some particular challenges, and we have initially observed some unexpected shifts in the 87Rb EPR frequency measurement on board the polarizer. In effort to disentangle these apparent systematic effects, we have constructed a separate experiment to characterize Rb EPR shifts for both 3He and 129Xe in sealed cells. We present results and analysis of these experiments and discuss implications for using this method in flow-through polarizers. NSF PHY-0855482

  17. EPR investigation of some traditional oriental irradiated spices

    NASA Astrophysics Data System (ADS)

    Duliu, Octavian G.; Georgescu, Rodica; Ali, Shaban Ibrahim

    2007-06-01

    The 9.50 GHz electron paramagnetic resonance (EPR) spectra of unirradiated and 60Co γ-ray irradiated cardamom ( Elettaria cardamomum L. Maton, Zingiberaceae), ginger (( Zingiber officinale Rosc., Zingiberaceae), and saffron ( Crocus sativus L., Iridaceae) have been investigated at room temperature. All unirradiated spices presented a weak resonance line with g-factors around free-electron ones. After γ-ray irradiation at an absorbed dose of up to 11.3 kGy, the presence of EPR spectra whose amplitude increase monotonously with the absorbed dose has been noticed with all spices. A 100 °C isothermal annealing of 11.3 kGy irradiated samples has shown a differential reduction of amplitude of various components that compose initial spectra, but even after 3.6 h of thermal treatment, the remaining amplitude represents no less then 30% of the initial ones. The same peculiarities have been noticed after 83 days storage at room temperature but after 340 days storage at ambient conditions only irradiated ginger displays a weak signal that differs from those of unirradiated sample. All these factors could be taken into account in establishing at which extent the EPR is suitable to evidence any irradiation treatment applied to these spices.

  18. Physical, Optical absorption and EPR studies on fluoro- bismuthate glasses

    NASA Astrophysics Data System (ADS)

    Srinivasu, Ch; Samee, M. A.; Edukondalu, A.; Laxmi Kanth, C.; Rahman, Syed

    2015-02-01

    Glasses of the xLiF-(50-x)Li2O-20SrO-30Bi2O3 system, with 0 <= x <= 20 mole % were studied by EPR and Optical measurements. The changes in both density and molar volume indicate structural modifications occur due to addition of LiF. The glass transition temperatures are observed to decrease with an increase in LiF content in the compositions. The local structure around Cu2+ ions has been examined by means of electron paramagnetic resonance and optical absorption measurements. It is observed that the spin-Hamiltonian parameters calculated from the EPR spectra are influenced by the glass composition. The Cu2+ ions are in well-defined axial sites but subjected to small distortion leading to the broadening of the spectra. The spin-Hamiltonian parameter values indicate that the ground state of Cu2+ is and the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad band corresponding to the d-d transition bands of Cu2+ ion. By correlating EPR and optical absorption data, the bond parameters are evaluated.

  19. Implementing Diffie-Hellman key exchange using quantum EPR pairs

    NASA Astrophysics Data System (ADS)

    Mandal, Sayonnha; Parakh, Abhishek

    2015-05-01

    This paper implements the concepts of perfect forward secrecy and the Diffie-Hellman key exchange using EPR pairs to establish and share a secret key between two non-authenticated parties and transfer messages between them without the risk of compromise. Current implementations of quantum cryptography are based on the BB84 protocol, which is susceptible to siphoning attacks on the multiple photons emitted by practical laser sources. This makes BB84-based quantum cryptography protocol unsuitable for network computing environments. Diffie-Hellman does not require the two parties to be mutually authenticated to each other, yet it can provide a basis for a number of authenticated protocols, most notably the concept of perfect forward secrecy. The work proposed in this paper provides a new direction in utilizing quantum EPR pairs in quantum key exchange. Although, classical cryptography boasts of efficient and robust protocols like the Diffie-Hellman key exchange, in the current times, with the advent of quantum computing they are very much vulnerable to eavesdropping and cryptanalytic attacks. Using quantum cryptographic principles, however, these classical encryption algorithms show more promise and a more robust and secure structure for applications. The unique properties of quantum EPR pairs also, on the other hand, go a long way in removing attacks like eavesdropping by their inherent nature of one particle of the pair losing its state if a measurement occurs on the other. The concept of perfect forward secrecy is revisited in this paper to attribute tighter security to the proposed protocol.

  20. A Wire Crossed-Loop-Resonator for Rapid Scan EPR.

    PubMed

    Rinard, George A; Quine, Richard W; Biller, Joshua R; Eaton, Gareth R

    2010-04-09

    A crossed-loop (orthogonal mode) resonator (CLR) was constructed of fine wire to achieve design goals for rapid scan in vivo EPR imaging at VHF frequencies (in practice, near 250 MHz). This application requires the resonator to have a very open design to facilitate access to the animal for physiological support during the image acquisition. The rapid scan experiment uses large amplitude magnetic field scans, and sufficiently large resonator and detection bandwidths to record the rapidly-changing signal response. Rapid-scan EPR is sensitive to RF/microwave source noise and to baseline changes that are coherent with the field scan. The sensitivity to source noise is a primary incentive for using a CLR to isolate the detected signal from the RF source noise. Isolation from source noise of 44 and 47 dB was achieved in two resonator designs. Prior results showed that eddy currents contribute to background problems in rapid scan EPR, so the CLR design had to minimize conducting metal components. Using fine (AWG 38) wire for the resonators decreased eddy currents and lowered the resonator Q, thus providing larger resonator bandwidth. Mechanical resonances at specific scan frequencies are a major contributor to rapid scan backgrounds.

  1. EPR and magnetism of the nanostructured natural carbonaceous material shungite

    NASA Astrophysics Data System (ADS)

    Augustyniak-Jabłokow, Maria Aldona; Yablokov, Yurii V.; Andrzejewski, Bartłomiej; Kempiński, Wojciech; Łoś, Szymon; Tadyszak, Krzysztof; Yablokov, Mikhail Y.; Zhikharev, Valentin A.

    2010-04-01

    The X-band EPR and magnetic susceptibility in the temperature range 4.2-300 K study of the shungite-I, natural nanostructured material from the deposit of Shunga are reported. Obtained results allow us to assign the EPR signal to conduction electrons, estimate their number, N P, and evaluate the Pauli paramagnetism contribution to shungite susceptibility. A small occupation (~5%) of the localized nonbonding π states in the zigzag edges of the open-ended graphene-like layers and/or on σ ( sp 2+ x ) orbitals in the curved parts of the shungite globules has been also revealed. The observed temperature dependence of the EPR linewidth can be explained by the earlier considered interaction of conduction π electrons with local phonon modes associated with the vibration of peripheral carbon atoms of the open zigzag-type edges and with peripheral carbon atoms cross-linking different nanostructures. The relaxation time T 2 and diffusion time T D are found to have comparable values (2.84 × 10-8 and 1.73 × 10-8 s at 5.2 K, respectively), and similar dependence on temperature. The magnetic measurements have revealed the suppression of orbital diamagnetism due to small amount of large enough fragments of the graphene layers.

  2. Peptide-membrane Interactions by Spin-labeling EPR

    PubMed Central

    Smirnova, Tatyana I.; Smirnov, Alex I.

    2016-01-01

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

  3. Tetrabromidocuprates(II)—Synthesis, Structure and EPR

    PubMed Central

    Zabel, André; Winter, Alette; Kelling, Alexandra; Schilde, Uwe; Strauch, Peter

    2016-01-01

    Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several “onium” cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g‖ and g⊥) of the tensors could be determined and information on the structural changes in the [CuBr4]2− anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids. PMID:27104522

  4. Thermally stimulated luminescence and EPR studies on topaz.

    PubMed

    Souza, Divanizia N; de Lima, José Fernandes; Valerio, Mário Ernesto G; Caldas, Linda V E

    2006-08-01

    In the present work, electron paramagnetic resonance (EPR) spectra and thermoluminescence (TL) emission of colourless natural topaz from Santo Antônio do Jacinto, Brazil, was studied as a function of thermal treatment and gamma irradiation dose, focussing on the use of this material as a radiation dosimeter. EPR measurements on "as-received" samples at room temperature provided signals in the region of about 500 at 5,000 G. The signal located around g approximately equal to 2, frequently attributed to (AlO(4))(0), increased with additional gamma dose and disappeared after thermal treatment at 500 degrees C for 1h. Irradiation after thermal treatment recovered this signal. The decay promoted by isochronal thermal treatment showed the (AlO(4))(0) defects to be directly related to the TL glows peaks. The variation of EPR spectrum with annealing temperature prior to irradiation showed that the variation of TL sensitivity is a consequence of the variation of the (AlO(4))(0) population.

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

    Cancer.gov

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

  6. Effect of aging on EPR cable electrical performance during LOCA simulations. [Ethylene propylene rubber

    SciTech Connect

    Bustard, L.D.

    1984-01-01

    When exposed to a LOCA environment, some ethylene propylene rubber (EPR) cable materials experience substantial moisture absorption and dimensional changes. These phenomena may contribute to mechanical damage of the cable insulation resulting in electrical degradation. Recent experiments illustrate that the extent of moisture absorption and dimensional changes during an accident simulation are dependent on the EPR product, the accelerated age, and the aging technique employed to achieve that age. Results for several commercial EPR materials are summarized.

  7. Implementing a new EPR lineshape parameter for organic radicals in carbonaceous matter

    PubMed Central

    2013-01-01

    Background Electron Paramagnetic Resonance (EPR) is a non-destructive, non-invasive technique useful for the characterization of organic moieties in primitive carbonaceous matter related to the origin of life. The classical EPR parameters are the peak-to-peak amplitude, the linewidth and the g factor; however, such parameters turn out not to suffice to fully determine a single EPR line. Results In this paper, we give the definition and practical implementation of a new EPR parameter based on the signal shape that we call the R10 factor. This parameter was originally defined in the case of a single symmetric EPR line and used as a new datation method for organic matter in the field of exobiology. Conclusion Combined to classical EPR parameters, the proposed shape parameter provides a full description of an EPR spectrum and opens the way to novel applications like datation. Such a parameter is a powerful tool for future EPR studies, not only of carbonaceous matter, but also of any substance which spectrum exhibits a single symmetric line. Reproducibility The paper is a literate program—written using Noweb within the Org-mode as provided by the Emacs editor— and it also describes the full data analysis pipeline that computes the R10 on a real EPR spectrum. PMID:23866970

  8. Dependencies of the radiation sensitivity of human tooth enamel in EPR dosimetry.

    PubMed

    Wieser, A; El-Faramawy, N; Meckbach, R

    2001-05-01

    The EPR dose response of tooth enamel was determined for human molars collected in Egypt. The influence of age, gender and residence of the tooth donors as well as tooth position and sample preparation on EPR sensitivity and its variability over the enamel samples was investigated. The EPR sensitivity and its variability were found to depend only on the sample preparation procedure. The variability in EPR sensitivity of enamel from Egyptian teeth was maximally 10% and the mean sensitivity was in good agreement with that of German teeth.

  9. An advanced EPR stopped-flow apparatus based on a dielectric ring resonator

    NASA Astrophysics Data System (ADS)

    Lassmann, Günter; Schmidt, Peter Paul; Lubitz, Wolfgang

    2005-02-01

    A novel EPR stopped-flow accessory is described which allows time-dependent cw-EPR measurements of rate constants of reactions involving paramagnetic species after rapid mixing of two liquid reagents. The EPR stopped-flow design represents a state-of-the-art, computer controlled fluid driving system, a miniresonant EPR structure with an integrated small ball mixer, and a stopping valve. The X-band EPR detection system is an improved version of that reported by Sienkiewicz et al. [Rev. Sci. Instr. 65 (1994) 68], and utilizes a resonator with two stacked ceramic dielectric rings separated by a variable spacer. The resonator with the mode TE( H) 011 is tailored particularly for conditions of fast flowing and rapidly stopped aqueous solutions, and for a high time resolution. The short distance between the ball mixer and the small EPR active volume (1.8 μl) yields a measured dead time of 330 μs. A compact assembly of all parts results in minimization of disturbing microphonics. The computer controlled driving system from BioLogic with two independent stepping motors was optimized for EPR stopped-flow with a hard-stop valve. Performance tests on the EPR spectrometer ESP 300E from BRUKER using redox reactions of nitroxide radicals revealed the EPR stopped-flow accessory as an advanced, versatile, and reliable instrument with high reproducibility.

  10. EPR investigation of libration motion of spin labeled hemerythrin

    NASA Astrophysics Data System (ADS)

    Takacs, Istvan Mihaly; Mot, Augustin; Silaghi-Dumitrescu, Radu; Damian, Grigore

    2014-09-01

    Reported here are room-temperature continuous wave X-band Electron Paramagnetic Resonance (EPR) spectra of the non-heme di-iron protein hemerythrin (Hr), spin labeled at position 51C in different viscous media, illustrating the mobility and oligomeric recombination tendency of the Phascolopsis gouldii Hr. The mobility of a spin labeled Hr depends on the local viscosity and its connectivity to the nature of the molecular environment (glycerol, PEG4000 and BSA). This provides the basis for a tool useful in directly monitoring Hr in ex vivo samples upon injection within the bloodstream of test animals, for blood substitute research.

  11. A signal-to-noise standard for pulsed EPR.

    PubMed

    Eaton, Gareth R; Eaton, Sandra S; Quine, Richard W; Mitchell, Deborah; Kathirvelu, Velavan; Weber, Ralph T

    2010-07-01

    A 2 mm diameter by 10mm long cylinder of fused SiO2 (quartz) gamma-irradiated to 1 kGy with 60Co contains about 2x10(16) spins/cm3. It is proposed as a standard for monitoring signal-to-noise (S/N) performance of X-band pulsed EPR spectrometers. This sample yields S/N of about 25 on modern spin echo spectrometers, which permits measurement of both signal and noise under the same conditions with an 8-bit digitizer.

  12. EPR identification of irradiated Monascus purpureus red pigment

    NASA Astrophysics Data System (ADS)

    Duliu, Octavian G.; Ferdes, Mariana; Ferdes, Ovidiu S.

    2000-01-01

    Fresh red alimentary pigment extracted from Monascus purpureus fungus exhibits an intense EPR line consisting of a single, narrow line, attributed to a quinone radical. When irradiated with 7 MeV electrons or 60Co γ-rays, the amplitude of this line increased with the absorbed dose following a saturation exponential dependency up to 10 kGy. During annealing treatment (isothermal heating at 100°C) the irradiation centers decay exponentially with a half-life time of 2.30 min.

  13. Mn distribution in natural sphalerites: a micronalytical and EPR study

    NASA Astrophysics Data System (ADS)

    di Benedetto, F.; Bernardini, G. P.; Cipriani, C.; Plant, D.; Romanelli, M.; Vaughan, D. J.

    2003-04-01

    Electron Paramagnetic Resonance (EPR) has been successfully applied to determine the local coordination and distribution of transition metal cations in sulphides and sulphosalts (Di Benedetto et al., 2002). Due to its enhanced sensitivity and element-specificity it is one of the best tools to monitor Mn(II) behaviour down to very low concentrations. In order to reach a fuller understanding of the spectroscopic results, a microanalytical study has also been undertaken by means of Electron Microprobe Analysis. Operating conditions were chosen to achieve the lowest possible detection limits, taking into account that Mn can replace Zn in the sphalerite lattice both as a minor and trace element, and that EPR can detect Mn(II) below the ppm range. Six natural samples from the Museo di Storia Naturale, Università di Firenze, were selected to have pure single crystals and avoid magnetically active phases associated with the sphalerite. The Mn concentration determined ranges between 30 and 14300 ppm and Mn content varies considerably within the same sample, leading to differences up to the 50% as compared to the mean value. X-ray images confirm Mn to be distributed with an unusual pattern, unrelated to the other common Zn-replacing cations, Fe and Cd, present in the samples. Powder EPR spectra reveal at least three different Mn(II) signals: two sextets, overlapping in all samples containing Mn as trace element, and a single line, present only in the more concentrated samples. While the latter have been attributed to an inhomogeneous Mn distribution, due to an enhanced Mn-Mn superexchange interaction, the difference between the two sextets, observed by means of EEPR investigations in a synthetic sphalerite (Di Benedetto et al., 2002), appears unrelated to the Mn concentration and may be attributed to small differences in the local coordination of Mn(II) ions. This, in turn, may be explained by the segregation of small amounts of Mn into polytypic domains, features which

  14. Optical absorption near infrared and EPR studies of mottramite

    NASA Astrophysics Data System (ADS)

    Lakshmi Reddy, S.; Reddy, K. N. M.; Siva Reddy, G.; Endo, Tamio; Frost, R. L.

    2010-06-01

    Mottramite mineral from Tsumeb Corporation Mine, Tsumeb, Otavi, Namibia, is investigated in this present work. The mineral contains vanadium and copper contents of 22.73% and 16.84% by weight, respectively, as V2O5 and CuO. An electron paramagnetic resonance (EPR) study confirmed the presence of Cu(II) with g = 2.2. The optical absorption spectrum of mottramite indicates that Cu(II) is present in a rhombic environment. Near infrared results are due to water fundamentals.

  15. Geochemical constraints on the source of EPR MORBs

    NASA Astrophysics Data System (ADS)

    Tian, L.; Wang, Z.

    2015-12-01

    Geochemical variations of mid-ocean ridge basalts (MORBs) have long been attributed to the presence of compositionally distinct crustal and mantle components in their sources. The oxygen isotope composition of MORBs was proposed to be a valuable tracer of subducted crustal materials [1] since 18O/16O ratios are strongly fractioned during low-temperature water-rock interactions (e.g. seafloor alteration). Here, we present a study of combined oxygen isotopes, radiogenic isotopes, and trace elements on volcanic lavas sampled at both ridge axes and off-axis seamounts in the northern East Pacific Rise (EPR; 5-15°N). The chemical composition of these lavas ranges from normal-MORB to enriched-MORB, and the newly analyzed 18O/16O ratios of hand-picked fresh glasses from these 53 lavas were measured using laser-fluorination technique, with a typical precision of ±0.08‰ (1σ). Our results show that the δ18OSMOW values of EPR glasses span ~0.64‰ (from 5.08‰ to 5.72‰), with an average value of 5.53(±0.12, 1σ) ‰, which is comparable to results from previous survey of global MORBs (5.52±0.11‰) [1]. Two andesitic glasses show unusually lower δ18O values (5.08‰ and 5.27‰, respectively) and exhibit excess Cl addition ([Cl]>3000ppm), probably indicating an assimilation of seawater-derived component (e.g., saline brines or altered oceanic crust). Previous studies [2, 3, 4, 5] have shown the correlated variations of trace element ratios (e.g. La/Sm, and K2O/TiO2 element ratios) and radiogenic isotope compositions (e.g. 87Sr/86Sr, 143Nd/144Nd, Pb isotope ratios), suggesting the presence of at least two components in the source of EPR MORBs, an enriched component and depleted component. Our results show that δ18O values of these glasses lack statistically-significant correlations with other geochemical indicies in the same sample, suggesting that (1) the source of EPR MORBs has a uniform oxygen isotope composition, (2) the enriched components in the sources

  16. 75 FR 4882 - Meeting of the ACRS Subcommittee on EPR; Notice of Meeting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-29

    ... COMMISSION Advisory Committee On Reactor Safeguards (ACRS) Meeting of the ACRS Subcommittee on EPR; Notice of Meeting The ACRS U.S. Evolutionary Power Reactor (EPR) Subcommittee will hold a meeting on February 18-19... inconvenience. Dated: January 25, 2010. Antonio F. Dias, Chief, Reactor Safety Branch B, Advisory Committee...

  17. Use of Rapid-Scan EPR to Improve Detection Sensitivity for Spin-Trapped Radicals

    PubMed Central

    Mitchell, Deborah G.; Rosen, Gerald M.; Tseitlin, Mark; Symmes, Breanna; Eaton, Sandra S.; Eaton, Gareth R.

    2013-01-01

    The short lifetime of superoxide and the low rates of formation expected in vivo make detection by standard continuous wave (CW) electron paramagnetic resonance (EPR) challenging. The new rapid-scan EPR method offers improved sensitivity for these types of samples. In rapid-scan EPR, the magnetic field is scanned through resonance in a time that is short relative to electron spin relaxation times, and data are processed to obtain the absorption spectrum. To validate the application of rapid-scan EPR to spin trapping, superoxide was generated by the reaction of xanthine oxidase and hypoxanthine with rates of 0.1–6.0 μM/min and trapped with 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO). Spin trapping with BMPO to form the BMPO-OOH adduct converts the very short-lived superoxide radical into a more stable spin adduct. There is good agreement between the hyperfine splitting parameters obtained for BMPO-OOH by CW and rapid-scan EPR. For the same signal acquisition time, the signal/noise ratio is >40 times higher for rapid-scan than for CW EPR. Rapid-scan EPR can detect superoxide produced by Enterococcus faecalis at rates that are too low for detection by CW EPR. PMID:23870255

  18. Photodegradation of hyaluronic acid: EPR and size exclusion chromatography study.

    PubMed

    Lapcík, L; Chabrecek, P; Stasko, A

    1991-10-15

    Photochemically induced radical reactions involving the lateral sequences and the end macromolecular chain groups of hyaluronic acid in aqueous solutions at 293K were studied by EPR spin trapping technique with DMPO (5,5-dimethylpyrroline-1-oxide). In the first 1-10 minutes of irradiation EPR indicates spin adducts of two carbon centered radicals with the splitting constants of aN = 1.60 mT, aH = 2.51 mT and aN = 1.56 mT, aH = 2.28 mT. After longer irradiation time (over 10 minutes) dominate two further DMPO adducts of radicals centered on hetero-atoms with splitting constants of aN = 1.44 mT, aH = 1.60 mT and of aN = 1.49 mT, aH = 1.49 mT. Simultaneously, molecular weight followed by SEC decreases, suggesting that UV irradiation leads to the breaking of interglycosidic bonds of hyaluronic acid main macromolecular chain.

  19. Radiation induced EPR centers in foodstuffs and inorganic materials.

    PubMed

    Pilbrow, J R; Troup, G J; Hutton, D R; Rosengarten, G; Zhong, Y C; Hunter, C R

    1993-01-01

    EPR investigations of a variety of irradiated materials have provided the potential for useful dosimetry applications. Herbs and spices imported into Australia have been investigated to establish whether or not they have been irradiated. Post-irradiation studies have shown that there is more than one free radical species in most cases which decay rapidly with time. Changes to transition metal ion signals, e.g., Cu2+ or Fe3+, appear to be permanent against further irradiation. Thus if these signals change upon irradiation, the material almost certainly has not previously been irradiated. Power saturation studies of alanine, a favored dosimetry material, suggest two distinguishable types of behavior consistent with the presence of spin-flip transitions. Irradiation of vanadium doped beryl yields stable VO2+ ions which may provide a useful dosimetry material. Dosimetry applications would appear to demand low cost, user friendly, automated EPR spectrometers. A patented option based on a 2.5 GHz microstrip microwave bridge will be described briefly.

  20. EPR Spectroscopic Studies of [FeFe]-Hydrogenase Maturation.

    PubMed

    Suess, Daniel L M; Britt, R David

    2015-09-01

    Proton reduction and H2 oxidation are key elementary reactions for solar fuel production. Hydrogenases interconvert H(+) and H2 with remarkable efficiency and have therefore received much attention in this context. For [FeFe]-hydrogenases, catalysis occurs at a unique cofactor called the H-cluster. In this article, we discuss ways in which EPR spectroscopy has elucidated aspects of the bioassembly of the H-cluster, with a focus on four case studies: EPR spectroscopic identification of a radical en route to the CO and CN(-) ligands of the H-cluster, tracing (57)Fe from the maturase HydG into the H-cluster, characterization of the auxiliary Fe-S cluster in HydG, and isotopic labeling of the CN(-) ligands of HydA for electronic structure studies of its Hox state. Advances in cell-free maturation protocols have enabled several of these mechanistic studies, and understanding H-cluster maturation may in turn provide insights leading to improvements in hydrogenase production for biotechnological applications.

  1. EPR evidence for maghemitization of magnetite in a tropical soil

    NASA Astrophysics Data System (ADS)

    Fischer, H.; Luster, J.; Gehring, A. U.

    2007-06-01

    Electron paramagnetic spectroscopy (EPR) was used in combination with standard rock magnetic methods to study magnetic minerals in a tropical soil. The susceptibility and hysteresis measurements showed magnetite grains with a Curie temperature near 850 K as the dominant magnetic remanence carriers in the soil. A minor Ti content in the magnetite was found by energy dispersive X-ray analysis. In order to get insight into the weathering status of the magnetite, different chemical treatments, including oxalate and citrate-bicarbonate-dithionite (CBD) extraction, were applied to the soil samples. The hysteretic properties exhibited no significant differences between the untreated and the CBD or oxalate treated samples. By contrast, the comparison of the EPR spectra revealed a significant broadening of the linewidth (δB) and a shift of the g-values (geff) to lower fields after the CBD treatment. Furthermore, the spectral parameters geff and δB exhibited an angular dependence. At low temperature, the CBD treated samples showed a jump in δB between 120 and 100 K, the temperature range characteristic for the Verwey transition in magnetite. The changes in the spectral properties after the CBD treatment, which dissolves ferric oxides, were attributed to the removal of maghemite formed by the oxidation of magnetite, that is, during the maghemitization of the magnetite grains.

  2. EPR properties of synthetic apatites, deorganified dentine, and enamel.

    PubMed

    Kenner, G H; Haskell, E H; Hayes, R B; Baig, A; Higuchi, W I

    1998-05-01

    Electron paramagnetic resonance spectroscopy (EPR) was used to study synthetic hydroxyapatite and approximately 1, 2, and 6% synthetic carbonated apatites, deorganified dentine, and enamel. The carbonated apatites were synthesized by hydrolysis of dicalcium phosphate. Comparisons were made with spectra from enamel and deorganified dentine. Microwave power saturation and dose responses were determined for the synthetic materials. The Marquardt version of the Levenberg decomposition method was used to extract individual signals from the apatite data. Two samples of dentine were irradiated with 25 and 100 Gy, respectively, from a 60Co source. The first sample was then deorganified at 200 degreesC using the Soxhlet extraction technique. A third sample was irradiated with 100 Gy after deorganification. The resulting EPR spectra were then compared. It was determined that the dosimetric signal of 2% synthetic carbonated apatite was approximately the same as that of enamel. It was also verified that the dosimetric signal saturates at about 2% in synthetic carbonated apatites. The study established that the precenters responsible for the dosimetric signal (g perpendicular = 2.0018, g parallel = 1.9985) are preferentially concentrated in the surface-accessible region of the mineral component, as shown by the approximately 80% attenuation of the dosimetric signal in dentine following deorganification. The precenters responsible are not destroyed by the deorganification since the magnitude of the dosimetric signal from the dentine specimen irradiated following deorganification was approximately twice that of the comparable untreated, irradiated sample. Finally, the dose response of 2 and 6% synthetic carbonated apatites was determined.

  3. Alcoholic extraction enables EPR analysis to characterize radiation-induced cellulosic signals in spices.

    PubMed

    Ahn, Jae-Jun; Sanyal, Bhaskar; Akram, Kashif; Kwon, Joong-Ho

    2014-11-19

    Different spices such as turmeric, oregano, and cinnamon were γ-irradiated at 1 and 10 kGy. The electron paramagnetic resonance (EPR) spectra of the nonirradiated samples were characterized by a single central signal (g = 2.006), the intensity of which was significantly enhanced upon irradiation. The EPR spectra of the irradiated spice samples were characterized by an additional triplet signal at g = 2.006 with a hyperfine coupling constant of 3 mT, associated with the cellulose radical. EPR analysis on various sample pretreatments in the irradiated spice samples demonstrated that the spectral features of the cellulose radical varied on the basis of the pretreatment protocol. Alcoholic extraction pretreatment produced considerable improvements of the EPR signals of the irradiated spice samples relative to the conventional oven and freeze-drying techniques. The alcoholic extraction process is therefore proposed as the most suitable sample pretreatment for unambiguous detection of irradiated spices by EPR spectroscopy.

  4. Tooth enamel EPR dosimetry: optimization of EPR spectra recording parameters and effect of sample mass on spectral sensitivity.

    PubMed

    Zhumadilov, Kassym; Ivannikov, Alexander; Skvortsov, Valeriy; Stepanenko, Valeriy; Zhumadilov, Zhaxybay; Endo, Satoru; Tanaka, Kenichi; Hoshi, Masaharu

    2005-12-01

    In order to improve the accuracy of the tooth enamel EPR dosimetry method, EPR spectra recording conditions were optimized. The uncertainty of dose determination was obtained as the mean square deviation of doses, determined with the use of a spectra deconvolution program, from the nominal doses for ten enamel samples irradiated in the range from 0 to 500 mGy. The spectra were recorded at different microwave powers and accumulation times. It was shown that minimal uncertainty is achieved at the microwave power of about 2 mW for a used spectrometer JEOL JES-FA100. It was found that a limit of the accumulation time exists beyond which uncertainty reduction is ineffective. At an established total time of measurement, reduced uncertainty is obtained by averaging the experimental doses determined from recorded spectra following intermittent sample shaking and sample tube rotation, rather than from one spectrum recorded at longer accumulation time. The effect of sample mass on the spectrometer's sensitivity was investigated in order to find out how to make appropriate corrections.

  5. Carotenoid cation radicals: electrochemical, optical, and EPR study

    SciTech Connect

    Grant, J.L.; Kramer, V.J.; Ding, R.; Kispert, L.D.

    1988-03-30

    The general aim of this investigation is to determine whether carotenoid cation radicals can be produced, and stabilized, electrochemically. Hence, the authors have undertaken a detailed study of the electrooxidation of various carotenoids (..beta..-carotene (I), ..beta..-apo-8'-carotenal (II), and canthaxanthin (III) using the techniques of cyclic voltammetry, controlled-potential electrolysis (cpe) in conjunction with optical spectroscopy, and EPR spectroscopy coupled with in situ electrolysis. They report the successful generation of carotenoid cation radicals via electrochemical oxidation and, furthermore, the stabilization of these radicals for several minutes in CH/sub 2/Cl/sub 2/ and C/sub 2/H/sub 4/Cl/sub 2/ solvents.

  6. DLTS and EPR study of defects in H implanted silicon

    NASA Astrophysics Data System (ADS)

    Mikšić, V.; Pivac, B.; Rakvin, B.; Zorc, H.; Corni, F.; Tonini, R.; Ottaviani, G.

    2002-01-01

    Single crystal CZ Si samples were implanted with hydrogen ions to the dose of 2E16 He ions/cm 2 at room temperature and subsequently annealed in vacuum in the temperature interval from 100 to 900 °C. The aim of the experiment was to determine the conditions for bubble formation within the solid film, which may have important technological application. Defects produced in such samples were studied by deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR) spectroscopy. It is shown that high dose hydrogen implantation produces vacancy-related and silicon selfinterstitial clusters. The latter are thought to be responsible for the formation of the weak displacement field. The annealing at higher temperatures creates multivacancy-related clusters responsible for the strong displacement field formation.

  7. EPR pairing dynamics in Hubbard model with resonant U

    PubMed Central

    Zhang, X. Z.; Song, Z.

    2016-01-01

    We study the dynamics of the collision between two fermions in Hubbard model with on-site interaction strength U. The exact solution shows that the scattering matrix for two-wavepacket collision is separable into two independent parts, operating on spatial and spin degrees of freedom, respectively. The S-matrix for spin configuration is equivalent to that of Heisenberg-type pulsed interaction with the strength depending on U and relative group velocity vr. This can be applied to create distant EPR pair, through a collision process for two fermions with opposite spins in the case of |vr/U| = 1, without the need for temporal control and measurement process. Multiple collision process for many particles is also discussed. PMID:26728282

  8. EPR imaging of diffusional processes in biologically relevant polymers

    NASA Astrophysics Data System (ADS)

    Berliner, Lawrence J.; Fujii, Hirotada

    Diffusion processes in biological tissue are important problems for noninvasive investigation. As a model study, this work addresses the diffusion of an electrolyte buffer (Krebs) solution containing a nitroxide spin probe into a cylindrical polyacrylamide gel rod. The nitroxide spin density distribution was imaged at 1.6 GHz in gel cross sections at various time intervals for both homogeneous radial diffusion and inhomogeneous diffusion. A one-dimensional radial diffusion constant was calculated for the nitroxide spin probe, TEMPOL, of 3.7 ± 0.7 × 10 -6 cm 2/s at ambient temperature. The EPR spectrometer, using low-field flat-loop surface coils (H. Nishikawa, H. Fujii, and L. J. Berliner, J. Magn. Reson.62, 79 (1985)), showed minimal dielectric or magnetic losses in sensitity for electrolyte vs nondielectric samples.

  9. Nuclear spin-lattice relaxation in nitroxide spin-label EPR.

    PubMed

    Marsh, Derek

    2016-11-01

    Nuclear relaxation is a sensitive monitor of rotational dynamics in spin-label EPR. It also contributes competing saturation transfer pathways in T1-exchange spectroscopy, and the determination of paramagnetic relaxation enhancement in site-directed spin labelling. A survey shows that the definition of nitrogen nuclear relaxation rate Wn commonly used in the CW-EPR literature for (14)N-nitroxyl spin labels is inconsistent with that currently adopted in time-resolved EPR measurements of saturation recovery. Redefinition of the normalised (14)N spin-lattice relaxation rate, b=Wn/(2We), preserves the expressions used for CW-EPR, whilst rendering them consistent with expressions for saturation recovery rates in pulsed EPR. Furthermore, values routinely quoted for nuclear relaxation times that are deduced from EPR spectral diffusion rates in (14)N-nitroxyl spin labels do not accord with conventional analysis of spin-lattice relaxation in this three-level system. Expressions for CW-saturation EPR with the revised definitions are summarised. Data on nitrogen nuclear spin-lattice relaxation times are compiled according to the three-level scheme for (14)N-relaxation: T1n=1/Wn. Results are compared and contrasted with those for the two-level (15)N-nitroxide system.

  10. Active cancellation - A means to zero dead-time pulse EPR

    NASA Astrophysics Data System (ADS)

    Franck, John M.; Barnes, Ryan P.; Keller, Timothy J.; Kaufmann, Thomas; Han, Songi

    2015-12-01

    The necessary resonator employed in pulse electron paramagnetic resonance (EPR) rings after the excitation pulse and creates a finite detector dead-time that ultimately prevents the detection of signal from fast relaxing spin systems, hindering the application of pulse EPR to room temperature measurements of interesting chemical or biological systems. We employ a recently available high bandwidth arbitrary waveform generator (AWG) to produce a cancellation pulse that precisely destructively interferes with the resonant cavity ring-down. We find that we can faithfully detect EPR signal at all times immediately after, as well as during, the excitation pulse. This is a proof of concept study showcasing the capability of AWG pulses to precisely cancel out the resonator ring-down, and allow for the detection of EPR signal during the pulse itself, as well as the dead-time of the resonator. However, the applicability of this approach to conventional EPR experiments is not immediate, as it hinges on either (1) the availability of low-noise microwave sources and amplifiers to produce the necessary power for pulse EPR experiment or (2) the availability of very high conversion factor micro coil resonators that allow for pulse EPR experiments at modest microwave power.

  11. Active cancellation - A means to zero dead-time pulse EPR.

    PubMed

    Franck, John M; Barnes, Ryan P; Keller, Timothy J; Kaufmann, Thomas; Han, Songi

    2015-12-01

    The necessary resonator employed in pulse electron paramagnetic resonance (EPR) rings after the excitation pulse and creates a finite detector dead-time that ultimately prevents the detection of signal from fast relaxing spin systems, hindering the application of pulse EPR to room temperature measurements of interesting chemical or biological systems. We employ a recently available high bandwidth arbitrary waveform generator (AWG) to produce a cancellation pulse that precisely destructively interferes with the resonant cavity ring-down. We find that we can faithfully detect EPR signal at all times immediately after, as well as during, the excitation pulse. This is a proof of concept study showcasing the capability of AWG pulses to precisely cancel out the resonator ring-down, and allow for the detection of EPR signal during the pulse itself, as well as the dead-time of the resonator. However, the applicability of this approach to conventional EPR experiments is not immediate, as it hinges on either (1) the availability of low-noise microwave sources and amplifiers to produce the necessary power for pulse EPR experiment or (2) the availability of very high conversion factor micro coil resonators that allow for pulse EPR experiments at modest microwave power.

  12. Nuclear spin-lattice relaxation in nitroxide spin-label EPR

    NASA Astrophysics Data System (ADS)

    Marsh, Derek

    2016-11-01

    Nuclear relaxation is a sensitive monitor of rotational dynamics in spin-label EPR. It also contributes competing saturation transfer pathways in T1-exchange spectroscopy, and the determination of paramagnetic relaxation enhancement in site-directed spin labelling. A survey shows that the definition of nitrogen nuclear relaxation rate Wn commonly used in the CW-EPR literature for 14N-nitroxyl spin labels is inconsistent with that currently adopted in time-resolved EPR measurements of saturation recovery. Redefinition of the normalised 14N spin-lattice relaxation rate, b = Wn/(2We), preserves the expressions used for CW-EPR, whilst rendering them consistent with expressions for saturation recovery rates in pulsed EPR. Furthermore, values routinely quoted for nuclear relaxation times that are deduced from EPR spectral diffusion rates in 14N-nitroxyl spin labels do not accord with conventional analysis of spin-lattice relaxation in this three-level system. Expressions for CW-saturation EPR with the revised definitions are summarised. Data on nitrogen nuclear spin-lattice relaxation times are compiled according to the three-level scheme for 14N-relaxation: T1n = 1/Wn. Results are compared and contrasted with those for the two-level 15N-nitroxide system.

  13. X-band rapid-scan EPR of nitroxyl radicals.

    PubMed

    Mitchell, Deborah G; Quine, Richard W; Tseitlin, Mark; Eaton, Sandra S; Eaton, Gareth R

    2012-01-01

    X-band rapid-scan EPR spectra were obtained for dilute aqueous solutions of nitroxyl radicals (15)N-mHCTPO (4-hydro-3-carbamoyl-2,2,5,5-tetra-perdeuteromethyl-pyrrolin-1-(15)N-oxyl-d(12)) and (15)N-PDT (4-oxo-2,2,6,6-tetra-perdeuteromethyl-piperidinyl-(15)N-oxyl-d(16)). Simulations of spectra for (15)N-mHCTPO and (15)N-PDT agreed well with the experimental spectra. As the scan rate is increased in the rapid scan regime, the region in which signal amplitude increases linearly with B(1) extends to higher power and the maximum signal amplitude increases. In the rapid scan regime, the signal-to-noise for rapid-scan spectra was about a factor of 2 higher than for unbroadened CW EPR, even when the rapid scan spectra were obtained in a mode that had only 4% duty cycle for data acquisition. Further improvement in signal-to-noise per unit time is expected for higher duty cycles. Rapid scan spectra have higher bandwidth than CW spectra and therefore require higher detection bandwidths at faster scan rates. However, when the scan rate is increased by increasing the scan frequency, the increase in noise from the detection bandwidth is compensated by the decrease in noise due to increased number of averages per unit time. Because of the higher signal bandwidth, lower resonator Q is needed for rapid scan than for CW, so the rapid scan method is advantageous for lossy samples that inherently lower resonator Q.

  14. N-player quantum games in an EPR setting.

    PubMed

    Chappell, James M; Iqbal, Azhar; Abbott, Derek

    2012-01-01

    The N-player quantum games are analyzed that use an Einstein-Podolsky-Rosen (EPR) experiment, as the underlying physical setup. In this setup, a player's strategies are not unitary transformations as in alternate quantum game-theoretic frameworks, but a classical choice between two directions along which spin or polarization measurements are made. The players' strategies thus remain identical to their strategies in the mixed-strategy version of the classical game. In the EPR setting the quantum game reduces itself to the corresponding classical game when the shared quantum state reaches zero entanglement. We find the relations for the probability distribution for N-qubit GHZ and W-type states, subject to general measurement directions, from which the expressions for the players' payoffs and mixed Nash equilibrium are determined. Players' N x N payoff matrices are then defined using linear functions so that common two-player games can be easily extended to the N-player case and permit analytic expressions for the Nash equilibrium. As a specific example, we solve the Prisoners' Dilemma game for general N ≥ 2. We find a new property for the game that for an even number of players the payoffs at the Nash equilibrium are equal, whereas for an odd number of players the cooperating players receive higher payoffs. By dispensing with the standard unitary transformations on state vectors in Hilbert space and using instead rotors and multivectors, based on Clifford's geometric algebra (GA), it is shown how the N-player case becomes tractable. The new mathematical approach presented here has wide implications in the areas of quantum information and quantum complexity, as it opens up a powerful way to tractably analyze N-partite qubit interactions.

  15. Differential regulation of the Epr3 receptor coordinates membrane-restricted rhizobial colonization of root nodule primordia

    PubMed Central

    Kawaharada, Yasuyuki; Nielsen, Mette W.; Kelly, Simon; James, Euan K.; Andersen, Kasper R.; Rasmussen, Sheena R.; Füchtbauer, Winnie; Madsen, Lene H.; Heckmann, Anne B.; Radutoiu, Simona; Stougaard, Jens

    2017-01-01

    In Lotus japonicus, a LysM receptor kinase, EPR3, distinguishes compatible and incompatible rhizobial exopolysaccharides at the epidermis. However, the role of this recognition system in bacterial colonization of the root interior is unknown. Here we show that EPR3 advances the intracellular infection mechanism that mediates infection thread invasion of the root cortex and nodule primordia. At the cellular level, Epr3 expression delineates progression of infection threads into nodule primordia and cortical infection thread formation is impaired in epr3 mutants. Genetic dissection of this developmental coordination showed that Epr3 is integrated into the symbiosis signal transduction pathways. Further analysis showed differential expression of Epr3 in the epidermis and cortical primordia and identified key transcription factors controlling this tissue specificity. These results suggest that exopolysaccharide recognition is reiterated during the progressing infection and that EPR3 perception of compatible exopolysaccharide promotes an intracellular cortical infection mechanism maintaining bacteria enclosed in plant membranes. PMID:28230048

  16. Optimal strategies for tests of EPR-Steering with no detection loophole

    NASA Astrophysics Data System (ADS)

    Evans, David A.; Wiseman, Howard M.

    2014-12-01

    It has been shown in earlier works that the vertices of Platonic solids are good measurement choices for tests of EPR-Steering. Such measurements are regularly spaced, and measurement diversity is a good feature for making EPR-Steering inequalities easier to violate with entangled states. However, such measurements are provably suboptimal. By scrutinising not only the average results, but also the measurement statistics of cheating strategies in a Local Hidden State model, we outline a method for devising optimal strategies for EPR-Steering tests with no detection loophole.

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Migration from a prototype ePR for IA-MISS system to alpha version

    NASA Astrophysics Data System (ADS)

    Documet, Jorge R.; Le, Anh; Liu, Brent J.

    2010-03-01

    Last year we presented a paper that describes the design and clinical implementation of an ePR (Electronic Patient Record) system for Image-Assisted Minimally Invasive Spinal Surgery (IA-MISS). The goal of this ePR is to improve the workflow efficiency by providing all the necessary data of a surgical procedure from the preparation stage until the recovery stage. The mentioned ePR has been implemented and installed clinically and it has been in use for more than 16 months. In this paper, we will describe the migration process from a prototype version of the system to a more stable and easily-to-replicate alpha version.

  19. EPR tooth dosimetry as a tool for validation of retrospective doses: an end-user perspective.

    PubMed

    Bhat, Mohandas

    2005-02-01

    The US Department of Energy (DOE) is co-funding several studies on health effects of radiation in Southern Urals in Russia and on Chernobyl liquidators in Ukraine. Obtaining dose-response relationships is central to all these studies. In order to validate retrospective doses estimated by various methods, Electron paramagnetic Resonance (EPR) tooth dosimetry, considered by many as a gold standard, was attempted. The EPR technique, however, has some limitations. This paper discusses the potential pitfalls of using EPR tooth dosimetry, and some potential solutions.

  20. EPR as an analytical tool in assessing the mineral nutrients and irradiated food products-vegetables

    NASA Astrophysics Data System (ADS)

    Prasuna, C. P. Lakshmi; Chakradhar, R. P. S.; Rao, J. L.; Gopal, N. O.

    2008-12-01

    EPR spectral investigations of some commonly available vegetables in south India, which are of global importance like Daucus carota (carrot), Cyamopsis tetragonoloba (cluster beans), Coccinia indica (little gourd) and Beta vulgaris (beet root) have been carried out. In all the vegetable samples a free radical corresponding to cellulose radical is observed. Almost all the samples under investigation exhibit Mn ions in different oxidation states. The temperature variation EPR studies are done and are discussed in view of the paramagnetic oxidation states. The radiation-induced defects have also been assessed by using the EPR spectra of such irradiated food products.

  1. Spin dynamics effects in submillimeter EPR spectroscopy of impurity thulium ions in synthetic forsterite

    NASA Astrophysics Data System (ADS)

    Solovarov, N. K.; Tarasov, V. F.; Zharikov, E. V.

    2016-07-01

    The specific features of the EPR spectra of Tm3+ impurity ions in synthetic forsterite have been studied by continuous-wave EPR spectroscopy in the frequency range of 270-310 GHz at a temperature of 4.2 K in weak magnetic fields. Narrow resonance signals unrelated to the modulation of the resonance conditions of EPR under the modulation of the external magnetic field have been discovered in measurements at frequencies corresponding to the zero field splitting between the ground and first excited singlet electron states of Tm3+ ions in zero magnetic field. The origin of these narrow lines is discussed.

  2. Wormhole and entanglement (non-)detection in the ER=EPR correspondence

    NASA Astrophysics Data System (ADS)

    Bao, Ning; Pollack, Jason; Remmen, Grant N.

    2015-11-01

    The recently proposed ER=EPR correspondence postulates the existence of wormholes (Einstein-Rosen bridges) between entangled states (such as EPR pairs). Entanglement is famously known to be unobservable in quantum mechanics, in that there exists no observable (or, equivalently, projector) that can accurately pick out whether a generic state is entangled. Many features of the geometry of spacetime, however, are observables, so one might worry that the presence or absence of a wormhole could identify an entangled state in ER=EPR, violating quantum mechanics, specifically, the property of state-independence of observables. In this note, we establish that this cannot occur: there is no measurement in general relativity that unambiguously detects the presence of a generic wormhole geometry. This statement is the ER=EPR dual of the undetectability of entanglement.

  3. Study of dose-response and radical decay curves of gamma irradiated norfloxacin using EPR spectroscopy

    NASA Astrophysics Data System (ADS)

    Sütçü, Kerem; Osmanoǧlu, Yunus Emre

    2017-02-01

    In this study, Electron Paramagnetic Resonance (EPR) spectra of unirradiated and γ-irradiated at doses of 1, 5, 10, 12 and 15 kGy norfloxacin (NOF) were investigated. Before irradiation no EPR signal were observed. After irradiation a weak singlet signal at g = 2.0039 were obtained at room temperature. In order to describe the variation of EPR signal intensity with absorbed radiation dose, several mathematical equations were tried. Increasing irradiation dose up to 15 kGy has increased the signal intensity of the central signal however, no significant changes were observed in g spectroscopic splitting factor. The stability of signal intensity of irradiated NOF was studied over a storage period of 200 days. According to analyses conducted, EPR spectroscopy can be used to distinguish irradiated and unirradiated samples from each other.

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

    PubMed

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

    2011-10-01

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

  5. Radical ions and excited states in radiolysis. Optically detected time resolved EPR

    SciTech Connect

    Trifunac, A.D.; Smith, J.P.

    1981-01-01

    Excited-state production and radical-ion recombination kinetics in pulse-irradiated solutions of aromatic solutes in cyclohexane are studied by a new method of optical detection of time-resolved electron paramagnetic resonance (EPR) spectra. 7 figures.

  6. EPR Paradox, Locality and Completeness of Quantum Theory

    NASA Astrophysics Data System (ADS)

    Kupczynski, M.

    2007-12-01

    The quantum theory (QT) and new stochastic approaches have no deterministic prediction for a single measurement or for a single time-series of events observed for a trapped ion, electron or any other individual physical system. The predictions of QT being of probabilistic character apply to the statistical distribution of the results obtained in various experiments. The Copenhagen interpretation (CI) of QT acknowledged the abstract and statistical character of the predictions of QT but at the same time claimed that a state vector Ψ provided complete description of each individual physical system. The assigning the state vector to an individual physical system together with a postulate of its instantaneous reduction in the measurements was shown by Einstein Podolski and Rosen to lead to so called EPR paradox for the experiments with the entangled pairs of the particles. EPR concluded that a state vector could not provide a complete description of the individual systems and the question arose whether the probabilistic predictions of QT could be derived from some more fundamental spatio-temporal deterministic description of the invisible sub-phenomena by introduction of supplementary parameters. The experimental violation of the Bell inequalities in the spin polarization correlation experiments (SPCE) which were the implementations of Bohm and EPR gedanken experiments eliminated so called local and realistic models of the sub-phenomena. Quite often the violation of these inequalities has been incorrectly interpreted as a proof of the completeness of QT or as the violation of the locality and causality in the micro-world. The local and realistic models overlooked the fact that an experimental outcome is only the information about a particular system-system or system-instrument interaction. Namely the quantum phenomena are described in terms of the probabilities. It is well known that the probability distribution is not an attribute of a dice but it is a characteristic

  7. Transport de paires EPR dans des structures mesoscopiques

    NASA Astrophysics Data System (ADS)

    Dupont, Emilie

    Dans cette these, nous nous sommes particulierement interesses a la propagation de paires EPR1 delocalisees et localisees, et a l'influence d'un supraconducteur sur le transport de ces paires. Apres une introduction de cette etude, ainsi que du cadre scientifique qu'est l'informatique quantique dans lequel elle s'inscrit, nous allons dans le chapitre 1 faire un rappel sur le systeme constitue de deux points quantiques normaux entoures de deux fils supraconducteurs. Cela nous permettra d'introduire une methode de calcul qui sera reutilisee par la suite, et de trouver egalement le courant Josephson produit par ce systeme transforme en SQUID-dc par l'ajout d'une jonction auxiliaire. Le SQUID permet de mesurer l'etat de spin (singulet ou triplet), et peut etre forme a partir d'autres systemes que nous etudierons ensuite. Dans le chapitre 2, nous rappellerons l'etude detaillee d'un intricateur d'Andreev faite par un groupe de Bale. La matrice T, permettant d'obtenir le courant dans les cas ou les electrons sont separes spatialement ou non, sera etudiee en detail afin d'en faire usage au chapitre suivant. Le chapitre 3 est consacre a l'etude de l'influence du bruit sur le fonctionnement de l'intricateur d'Andreev. Ce bruit modifie la forme du courant jusqu'a aboutir a d'autres conditions de fonctionnement de l'intricateur. En effet, le bruit present sur les points quantiques peut perturber le transport des paires EPR par l'intermediaire des degres de liberte. Nous montrerons que, du fait de l'"intrication" entre la charge de la paire et le bruit, la paire est detruite pour des temps longs. Cependant, le resultat le plus important sera que le bruit perturbe plus le transport des paires delocalisees, qui implique une resonance de Breit-Wigner a deux particules. Le transport parasite n'implique pour sa part qu'une resonance de Breit-Wigner a une particule. Dans le chapitre 4, nous reviendrons au systeme constitue de deux points quantiques entoures de deux fils

  8. Low-temperature EPR spectra of synthetic diamond and type Ib nanodiamond

    NASA Astrophysics Data System (ADS)

    Vaisnoras, R.; Kulbickas, A.; Kobets, M.; Dergachev, K.; Khatsko, E.

    2013-11-01

    Low-frequency resonance studies of single crystal diamond and type Ib nanodiamond (powder) unirradiated and irradiated by protons at temperatures of 300 and 500 K are reported. EPR spectra typical of paramagnetic nitrogen centers are observed. It is shown that when synthetic diamond crystals are irradiated by protons, additional lines appear in the EPR spectra which can be attributed to radiation induced nitrogen-vacancy centers (NV defects).

  9. The EPR detection of foods preserved with the use of ionizing radiation

    NASA Astrophysics Data System (ADS)

    Stachowicz, W.; Burlińska, G.; Michalik, J.; Dziedzic-Gocławska, A.; Ostrowski, K.

    1995-02-01

    Solid constituents extracted from irradiated foods have been examined by the epr (esr) spectroscopy. It has been proved that some epr active species produced by radiation in foods are specific and stable enough to be used for the detection of irradiation treatment. The most promising results have been obtained with bones extracted from frozen raw meat (beef, pork, poultry and fish), with seeds of fruits (dates and figs), with dried mushrooms, gelatin and macaroni.

  10. EPR spectra induced by gamma-irradiation of some dry medical herbs

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Yordanov, Nicola D.; Aleksieva, Katerina

    2009-03-01

    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 °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.

  12. Photosynthetic reaction center of green sulfur bacteria studied by EPR

    SciTech Connect

    Nitschke, W.; Rutherford, A.W. ); Fieler, U. )

    1990-04-24

    Membrane preparations of two species of the green sulfur bacteria Chlorobium have been studied be EPR. Three signals were detected which were attributed to iron-sulfur centers acting as electron acceptors in the photosynthetic reaction center. (1) A signal from a center designated F{sub B}, was photoinduced at 4K. (2) A similar signal, F{sub A}, was photoinduced in addition to the F{sub B} signal upon a short period of illumination at 200 K. (3) Further illumination at 200 K resulted in the appearance of a broad feature at g=1.78. This is attributed to the g{sub x} component of an iron-sulfur center designated F{sub X}. The designations of these signals as F{sub B}, F{sub A}, and F{sub X} are based on their spectroscopic similarities to signals in photosystem I (PS I). The orientation dependence of these EPR signals in ordered Chlorobium membrane multilayers is remarkably similar to that of their PS I homologues. A magnetic interaction between the reduced forms of F{sub B} and F{sub A} occurs, which is also very similar to that seen in PS I. The triplet state of P{sub 840}, the primary electron donor, could be photoinduced at 4 K in samples which had been preincubated with sodium dithionite and methyl viologen and then preilluminated at 200 K. The preillumination reduces the iron-sulfur centers while the preincubation is thought to result in the inactivation of an earlier electron acceptor. Orientation studies of the triplet signal in ordered multilayers indicate that the bacteriochlorophylls which act as the primary electron donor in Chlorobium are arranged with a structural geometry almost identical with that of the special pair in purple bacteria. The Chlorobium reaction center appears to be similar in some respects to both PS I and to the purple bacterial reaction center. This is discussed with regard to the evolution of the different types of reaction centers from a common ancestor.

  13. In vitro Ca(2+)-dependent maturation of milk-clotting recombinant Epr: minor extracellular protease: from Bacillus licheniformis.

    PubMed

    Ageitos, José Manuel; Vallejo, Juan Andrés; Serrat, Manuel; Sánchez-Pérez, Angeles; Villa, Tomás G

    2013-06-01

    The minor extracellular protease (Epr) is secreted into the culture medium during Bacillus licheniformis, strain USC13, stationary phase of growth. Whereas, B. subtilis Epr has been reported to be involved in swarming; the B. licheniformis protease is also involved in milk-clotting as shown by the curd forming ability of culture broths expressing this protein. The objectives of this study are the characterization of recombinant B. licheniformis Epr (minor extracellular protease) and the determination of its calcium-dependent activation process. In this work, we have cloned and expressed B. licheniformis Epr in Escherichia coli. We were also able to construct a tridimensional model for Epr based on its homology to Thermococcus kodakarensis pro-tk-subtilisin 2e1p, fervidolysin from Fervidobacterium pennivorans 1rv6, and B. lentus 1GCI subtilisin. Recombinant Epr was accumulated into inclusion bodies; after protein renaturation, Epr undergoes an in vitro calcium-dependent activation, similar to that described for tk protease. The recombinant Epr is capable of producing milk curds with the same clotting activity previously described for the native B. licheniformis Epr enzyme although further rheological and industrial studies should be carried out to confirm its real applicability. This work represents for the first time that Epr may be successfully expressed in a non-bacilli microorganism.

  14. Alanine-EPR as a transfer standard dosimetry system for low energy X radiation

    NASA Astrophysics Data System (ADS)

    Khoury, H. J.; da Silva, E. J.; Mehta, K.; de Barros, V. S.; Asfora, V. K.; Guzzo, P. L.; Parker, A. G.

    2015-11-01

    The purpose of this paper is to evaluate the use of alanine-EPR as a transfer standard dosimetry system for low energy X radiation, such as that in RS-2400, which operates in the range from 25 to 150 kV and 2 to 45 mA. Two types of alanine dosimeters were investigated. One is a commercial alanine pellets from Aérial-Centre de Ressources Technologiques, France and one was prepared in our laboratory (LMRI-DEN/UFPE). The EPR spectra of the irradiated dosimeters were recorded in the Nuclear Energy Department of UFPE, using a Bruker EMX10 EPR spectrometer operating in the X-band. The alanine-EPR dosimetry system was calibrated in the range of 20-220 Gy in this X-ray field, against an ionization chamber calibrated at the relevant X-ray energy with traceability to PTB. The results showed that both alanine dosimeters presented a linear dose response the same sensitivity, when the EPR signal was normalized to alanine mass. The total uncertainty in the measured dose was estimated to be about 3%. The results indicate that it is possible to use the alanine-EPR dosimetry system for validation of a low-energy X ray irradiator, such as RS-2400.

  15. EPR and IR spectral investigations on some leafy vegetables of Indian origin

    NASA Astrophysics Data System (ADS)

    Prasuna, C. P. Lakshmi; Chakradhar, R. P. S.; Rao, J. L.; Gopal, N. O.

    2009-09-01

    EPR spectral investigations have been carried out on four edible leafy vegetables of India, which are used as dietary component in day to day life. In Rumex vesicarius leaf sample, EPR spectral investigations at different temperatures indicate the presence of anti-ferromagnetically coupled Mn(IV)-Mn(IV) complexes. EPR spectra of Trigonella foenum graecum show the presence of Mn ions in multivalent state and Fe 3+ ions in rhombic symmetry. EPR spectra of Basella rubra indicate the presence of Mn(IV)-O-Mn(IV) type complexes. The EPR spectra of Basella rubra have been studied at different temperatures. It is found that the spin population for the resonance signal at g = 2.06 obeys the Boltzmann distribution law. The EPR spectra of Moringa oliefera leaves show the presence of Mn 2+ ions. Radiation induced changes in free radical of this sample have also been studied. The FT-IR spectra of Basella rubra and Moringa oliefera leaves show the evidences for the protein matrix bands and those corresponding to carboxylic C dbnd O bonds.

  16. EPR and IR spectral investigations on some leafy vegetables of Indian origin.

    PubMed

    Prasuna, C P Lakshmi; Chakradhar, R P S; Rao, J L; Gopal, N O

    2009-09-15

    EPR spectral investigations have been carried out on four edible leafy vegetables of India, which are used as dietary component in day to day life. In Rumex vesicarius leaf sample, EPR spectral investigations at different temperatures indicate the presence of anti-ferromagnetically coupled Mn(IV)-Mn(IV) complexes. EPR spectra of Trigonella foenum graecum show the presence of Mn ions in multivalent state and Fe(3+) ions in rhombic symmetry. EPR spectra of Basella rubra indicate the presence of Mn(IV)-O-Mn(IV) type complexes. The EPR spectra of Basella rubra have been studied at different temperatures. It is found that the spin population for the resonance signal at g=2.06 obeys the Boltzmann distribution law. The EPR spectra of Moringa oliefera leaves show the presence of Mn(2+) ions. Radiation induced changes in free radical of this sample have also been studied. The FT-IR spectra of Basella rubra and Moringa oliefera leaves show the evidences for the protein matrix bands and those corresponding to carboxylic CO bonds.

  17. EPR, thermo and photoluminescence properties of ZnO nanopowders.

    PubMed

    Jagannatha Reddy, A; Kokila, M K; Nagabhushana, H; Rao, J L; Shivakumara, C; Nagabhushana, B M; Chakradhar, R P S

    2011-10-15

    Nanocrystalline ZnO powders have been synthesized by a low temperature solution combustion method. The photoluminescence (PL) spectrum of as-formed and heat treated ZnO shows strong violet (402, 421, 437, 485 nm) and weak green (520 nm) emission peaks respectively. The PL intensities of defect related emission bands decrease with calcinations temperature indicating the decrease of Zn(i) and V(o)(+) caused by the chemisorptions of oxygen. The results are correlated with the electron paramagnetic resonance (EPR) studies. Thermoluminescence (TL) glow curves of gamma irradiated ZnO nanoparticles exhibit a single broad glow peak at ∼343°C. This can be attributed to the recombination of charge carriers released from the surface states associated with oxygen defects, mainly interstitial oxygen ion centers. The trapping parameters of ZnO irradiated with various γ-doses are calculated using peak shape method. It is observed that the glow peak intensity increases with increase of gamma dose without changing glow curve shape. These two characteristic properties such as TL intensity increases with gamma dose and simple glow curve structure is an indication that the synthesized ZnO nanoparticles might be used as good TL dosimeter for high temperature application.

  18. EPR, thermo and photoluminescence properties of ZnO nanopowders

    NASA Astrophysics Data System (ADS)

    Jagannatha Reddy, A.; Kokila, M. K.; Nagabhushana, H.; Rao, J. L.; Shivakumara, C.; Nagabhushana, B. M.; Chakradhar, R. P. S.

    2011-10-01

    Nanocrystalline ZnO powders have been synthesized by a low temperature solution combustion method. The photoluminescence (PL) spectrum of as-formed and heat treated ZnO shows strong violet (402, 421, 437, 485 nm) and weak green (520 nm) emission peaks respectively. The PL intensities of defect related emission bands decrease with calcinations temperature indicating the decrease of Zn i and V o+ caused by the chemisorptions of oxygen. The results are correlated with the electron paramagnetic resonance (EPR) studies. Thermoluminescence (TL) glow curves of gamma irradiated ZnO nanoparticles exhibit a single broad glow peak at ˜343 °C. This can be attributed to the recombination of charge carriers released from the surface states associated with oxygen defects, mainly interstitial oxygen ion centers. The trapping parameters of ZnO irradiated with various γ-doses are calculated using peak shape method. It is observed that the glow peak intensity increases with increase of gamma dose without changing glow curve shape. These two characteristic properties such as TL intensity increases with gamma dose and simple glow curve structure is an indication that the synthesized ZnO nanoparticles might be used as good TL dosimeter for high temperature application.

  19. Implementation of GPU-accelerated back projection for EPR imaging.

    PubMed

    Qiao, Zhiwei; Redler, Gage; Epel, Boris; Qian, Yuhua; Halpern, Howard

    2015-01-01

    Electron paramagnetic resonance (EPR) Imaging (EPRI) is a robust method for measuring in vivo oxygen concentration (pO2). For 3D pulse EPRI, a commonly used reconstruction algorithm is the filtered backprojection (FBP) algorithm, in which the backprojection process is computationally intensive and may be time consuming when implemented on a CPU. A multistage implementation of the backprojection can be used for acceleration, however it is not flexible (requires equal linear angle projection distribution) and may still be time consuming. In this work, single-stage backprojection is implemented on a GPU (Graphics Processing Units) having 1152 cores to accelerate the process. The GPU implementation results in acceleration by over a factor of 200 overall and by over a factor of 3500 if only the computing time is considered. Some important experiences regarding the implementation of GPU-accelerated backprojection for EPRI are summarized. The resulting accelerated image reconstruction is useful for real-time image reconstruction monitoring and other time sensitive applications.

  20. Boron dose determination for BNCT using Fricke and EPR dosimetry

    SciTech Connect

    Wielopolski, L.; Ciesielski, B.

    1995-02-01

    In Boron Neutron Capture Therapy (BNCT) the dominant dose delivered to the tumor is due to {alpha} and {sup 7}Li charged particles resulting from a neutron capture by {sup 10}B and is referred to herein as the boron dose. Boron dose is directly attributable to the following two independent factors, one boron concentration and the neutron capture energy dependent cross section of boron, and two the energy spectrum of the neutrons that interact with boron. The neutron energy distribution at a given point is dictated by the incident neutron energy distribution, the depth in tissue, geometrical factors such as beam size and patient`s dimensions. To account for these factors can be accommodated by using Monte Carlo theoretical simulations. However, in conventional experimental BNCT dosimetry, e.g., using TLDs or ionization chambers, it is only possible to estimate the boron dose. To overcome some of the limitations in the conventional dosimetry, modifications in ferrous sulfate dosimetry (Fricke) and Electron Paramagnetic Resonance (EPR) dosimetry in alanine, enable to measure specifically boron dose in a mixed gamma neutron radiation fields. The boron dose, in either of the dosimeters, is obtained as a difference between measurements with boronated and unboronated dosimeters. Since boron participates directly in the measurements, the boron dosimetry reflects the true contribution, integral of the neutron energy spectrum with boron cross section, of the boron dose to the total dose. Both methods are well established and used extensively in dosimetry, they are presented briefly here.

  1. Wave Detection Beyond the Standard Quantum Limit via EPR Entanglement

    NASA Astrophysics Data System (ADS)

    Ma, Yiqiu; Miao, Haixing; Pang, Belinda; Evans, Matthew; Zhao, Chunnong; Harms, Jan; Schnabel, Roman; Chen, Yanbei

    2017-01-01

    The Standard Quantum Limit in continuous monitoring of a system is given by the trade-off of shot noise and back-action noise. In gravitational-wave detectors, such as Advanced LIGO, both contributions can simultaneously be squeezed in a broad frequency band by injecting a spectrum of squeezed vacuum states with a frequency-dependent squeeze angle. This approach requires setting up an additional long base-line, low-loss filter cavity in a vacuum system at the detector's site. Here, we show that the need for such a filter cavity can be eliminated, by exploiting EPR-entangled signal and idler beams. By harnessing their mutual quantum correlations and the difference in the way each beam propagates in the interferometer, we can engineer the input signal beam to have the appropriate frequency dependent conditional squeezing once the out-going idler beam is detected. Our proposal is appropriate for all future gravitational-wave detectors for achieving sensitivities beyond the Standard Quantum Limit.

  2. CW- and pulsed-EPR of carbonaceous matter in primitive meteorites: solving a lineshape paradox.

    PubMed

    Delpoux, Olivier; Gourier, Didier; Binet, Laurent; Vezin, Hervé; Derenne, Sylvie; Robert, François

    2008-05-01

    Insoluble organic matter (IOM) of Orgueil and Tagish Lake meteorites are studied by CW-EPR and pulsed-EPR spectroscopies. The EPR line is due to polycyclic paramagnetic moieties concentrated in defect-rich regions of the IOM, with concentrations of the order of 4x10(19) spin/g. CW-EPR reveals two types of paramagnetic defects: centres with S=1/2, and centres with S=0 ground state and thermally accessible triple state S=1. In spite of the Lorentzian shape of the EPR and its narrowing upon increasing the spin concentration, the EPR line is not in the exchange narrowing regime as previously deduced from multi-frequency CW-EPR [L. Binet, D. Gourier, Appl. Magn. Reson. 30 (2006) 207-231]. It is inhomogeneously broadened as demonstrated by the presence of nuclear modulations in the spin-echo decay. The line narrowing, similar to an exchange narrowing effect, is the result of an increasing contribution of the narrow line of the triplet state centres in addition to the broader line of doublet states. Hyperfine sublevel correlation spectroscopy (HYSCORE) of hydrogen and (13)C nuclei indicates that IOM* centres are small polycyclic moieties that are moderately branched with aliphatic chains, as shown by the presence of aromatic hydrogen atoms. On the contrary the lack of such aromatic hydrogen in triplet states suggests that these radicals are most probably highly branched. Paramagnetic centres are considerably enriched in deuterium, with D/H approximately 1.5+/-0.5x10(-2) of the order of values existing in interstellar medium.

  3. CW- and pulsed-EPR of carbonaceous matter in primitive meteorites: Solving a lineshape paradox

    NASA Astrophysics Data System (ADS)

    Delpoux, Olivier; Gourier, Didier; Binet, Laurent; Vezin, Hervé; Derenne, Sylvie; Robert, François

    2008-05-01

    Insoluble organic matter (IOM) of Orgueil and Tagish Lake meteorites are studied by CW-EPR and pulsed-EPR spectroscopies. The EPR line is due to polycyclic paramagnetic moieties concentrated in defect-rich regions of the IOM, with concentrations of the order of 4 × 10 19 spin/g. CW-EPR reveals two types of paramagnetic defects: centres with S = 1/2, and centres with S = 0 ground state and thermally accessible triple state S = 1. In spite of the Lorentzian shape of the EPR and its narrowing upon increasing the spin concentration, the EPR line is not in the exchange narrowing regime as previously deduced from multi-frequency CW-EPR [L. Binet, D. Gourier, Appl. Magn. Reson. 30 (2006) 207-231]. It is inhomogeneously broadened as demonstrated by the presence of nuclear modulations in the spin-echo decay. The line narrowing, similar to an exchange narrowing effect, is the result of an increasing contribution of the narrow line of the triplet state centres in addition to the broader line of doublet states. Hyperfine sublevel correlation spectroscopy (HYSCORE) of hydrogen and 13C nuclei indicates that IOM rad centres are small polycyclic moieties that are moderately branched with aliphatic chains, as shown by the presence of aromatic hydrogen atoms. On the contrary the lack of such aromatic hydrogen in triplet states suggests that these radicals are most probably highly branched. Paramagnetic centres are considerably enriched in deuterium, with D/H ≈ 1.5 ± 0.5 × 10 -2 of the order of values existing in interstellar medium.

  4. Uncertainty analysis for absorption and first-derivative EPR spectra.

    PubMed

    Tseitlin, Mark; Eaton, Sandra S; Eaton, Gareth R

    2012-11-01

    Electron paramagnetic resonance (EPR) experimental techniques produce absorption or first-derivative spectra. Uncertainty analysis provides the basis for comparison of spectra obtained by different methods. In this study it was used to derive analytical equations to relate uncertainties for integrated intensity and line widths obtained from absorption or first-derivative spectra to the signal-to-noise ratio (SNR), with the assumption of white noise. Predicted uncertainties for integrated intensities and line widths are in good agreement with Monte Carlo calculations for Lorentzian and Gaussian lineshapes. Conservative low-pass filtering changes the noise spectrum, which can be modeled in the Monte Carlo simulations. When noise is close to white, the analytical equations provide useful estimates of uncertainties. For example, for a Lorentzian line with white noise, the uncertainty in the number of spins obtained from the first-derivative spectrum is 2.6 times greater than from the absorption spectrum at the same SNR. Uncertainties in line widths obtained from absorption and first-derivative spectra are similar. The impact of integration or differentiation on SNR and on uncertainties in fitting parameters was analyzed. Although integration of the first-derivative spectrum improves the apparent smoothness of the spectrum, it also changes the frequency distribution of the noise. If the lineshape of the signal is known, the integrated intensity can be determined more accurately by fitting the first-derivative spectrum than by first integrating and then fitting the absorption spectrum. Uncertainties in integrated intensities and line widths are less when the parameters are determined from the original data than from spectra that have been either integrated or differentiated.

  5. EPR/alanine dosimetry for two therapeutic proton beams

    NASA Astrophysics Data System (ADS)

    Marrale, Maurizio; Carlino, Antonio; Gallo, Salvatore; Longo, Anna; Panzeca, Salvatore; Bolsi, Alessandra; Hrbacek, Jan; Lomax, Tony

    2016-02-01

    In this work the analysis of the electron paramagnetic resonance (EPR) response of alanine pellets exposed to two different clinical proton beams employed for radiotherapy is performed. One beam is characterized by a passive delivery technique and is dedicated to the eyes treatment (OPTIS2 beam line). Alanine pellets were irradiated with a 70 MeV proton beam corresponding to 35 mm range in eye tissue. We investigated how collimators with different sizes and shape used to conform the dose to the planned target volume influence the delivered dose. For this purpose we performed measurements with varying the collimator size (Output Factor) and the results were compared with those obtained with other dosimetric techniques (such as Markus chamber and diode detector). This analysis showed that the dosimeter response is independent of collimator diameter if this is larger than or equal to 10 mm. The other beam is characterized by an active spot-scanning technique, the Gantry1 beam line (maximum energy 230 MeV), and is used to treat deep-seated tumors. The dose linearity of alanine response in the clinical dose range was tested and the alanine dose response at selected locations in depth was measured and compared with the TPS planned dose in a quasi-clinical scenario. The alanine response was found to be linear in the dose in the clinical explored range (from 10 to 70 Gy). Furthermore, a depth dose profile in a quasi-clinical scenario was measured and compared to the dose computed by the Treatment Planning System PSIPLAN. The comparison of calibrated proton alanine measurements and TPS dose shows a difference under 1% in the SOBP and a "quenching" effect up to 4% in the distal part of SOBP. The positive dosimetric characteristics of the alanine pellets confirm the feasibility to use these detectors for "in vivo" dosimetry in clinical proton beams.

  6. Radiation sensitivity and EPR dosimetric potential of gallic acid and its esters

    NASA Astrophysics Data System (ADS)

    Tuner, Hasan; Oktay Bal, M.; Polat, Mustafa

    2015-02-01

    In the preset work the radiation sensitivities of Gallic Acid anhydrous and monohydrate, Octyl, Lauryl, and Ethyl Gallate (GA, GAm, OG, LG, and EG) were investigated in the intermediate (0.5-20 kGy) and low radiation (<10 Gy) dose range using Electron Paramagnetic Resonance (EPR) spectroscopy. While OG, LG, and EG are presented a singlet EPR spectra, their radiation sensitivity found to be very different in the intermediate dose range. At low radiation dose range (<10 Gy) only LG is found to be present a signal that easily distinguished from the noise signals. The intermediate and low dose range radiation sensitivities are compared using well known EPR dosimeter alanine. The radiation yields (G) of the interested material were found to be 1.34×10-2, 1.48×10-2, 4.14×10-2, and 6.03×10-2, 9.44×10-2 for EG, GA, GAm, OG, and LG, respectively at the intermediate dose range. It is found that the simple EPR spectra and the noticeable EPR signal of LG make it a promising dosimetric material to be used below 10 Gy of radiation dose.

  7. [Effect of ascorbic acid (vitamin C) on the EPR spectra from the black and red hair].

    PubMed

    Chikvaidze, E; Miminoshvili, A; Gogoladze, T; Kiparoidze, S

    2012-02-01

    The EPR spectra of melanin's free radicals in natural black and red hair have been investigated. It is show that the EPR spectrum of black hair is slightly asymmetric singlet with g=2,0035 and ΔH=0,5 mTl. The EPR spectrum of red hair with g=2,0053 differs from the spectrum of black hair. Under the influence of visible (blue with λ(max)=450 nm) in both types of hair (black and red), the protoinduced free radicals appear, which indicates an increase in the intensity of already existing EPR spectrum of hair. It should be noted that the EPR spectra of red hair from various donors are different. The antioxidant ascorbic acid has the different effect on the photoinduced free radicals. In particular, in the case of black hair, the concentration of photoinduced free radicals is slightly reduced, whereas in red hair, the disappearance of the triplet in the spectrum is observed, and at the same time, the spectrum becomes a singlet, the intensity of which increases sharply.

  8. The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis.

    PubMed

    Wieser, A; Debuyst, R; Fattibene, P; Meghzifene, A; Onori, S; Bayankin, S N; Brik, A; Bugay, A; Chumak, V; Ciesielski, B; Hoshi, M; Imata, H; Ivannikov, A; Ivanov, D; Junczewska, M; Miyazawa, C; Penkowski, M; Pivovarov, S; Romanyukha, A; Romanyukha, L; Schauer, D; Scherbina, O; Schultka, K; Sholom, S; Skvortsov, V; Stepanenko, V; Thomas, J A; Tielewuhan, E; Toyoda, S; Trompier, F

    2006-01-01

    The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.

  9. New developed cylindrical TM010 mode EPR cavity for X-band in vivo tooth dosimetry.

    PubMed

    Junwang, Guo; Qingquan, Yuan; Jianbo, Cong; Lei, Ma; Guofu, Dong; Guoshan, Yang; Ke, Wu

    2014-01-01

    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.

  10. Rapid Freeze-Quench EPR Spectroscopy: Improved Collection of Frozen Particles.

    PubMed

    Nami, Faezeh; Gast, Peter; Groenen, Edgar J J

    Rapid freeze-quench (RFQ) in combination with electron paramagnetic resonance (EPR) spectroscopy at X-band is a proven technique to trap and characterize paramagnetic intermediates of biochemical reactions. Preparation of suitable samples is still cumbersome, despite many attempts to remedy this problem, and limits the wide applicability of RFQ EPR. We present a method, which improves the collection of freeze-quench particles from isopentane and their packing in an EPR tube. The method is based on sucking the particle suspension into an EPR tube with a filter at the bottom. This procedure results in a significant reduction of the required volume of reactants, which allows the economical use of valuable reactants such as proteins. The approach also enables the successful collection of smaller frozen particles, which are generated at higher flow rates. The method provides for a reproducible, efficient and fast collection of the freeze-quench particles and can be easily adapted to RFQ EPR at higher microwave frequencies than X-band.

  11. New Developed Cylindrical TM010 Mode EPR Cavity for X-Band In Vivo Tooth Dosimetry

    PubMed Central

    Junwang, Guo; Qingquan, Yuan; Jianbo, Cong; Lei, Ma; Guofu, Dong; Guoshan, Yang; Ke, Wu

    2014-01-01

    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. PMID:25222483

  12. Continuous microwave saturation of EPR spectra of melanin complexes at different temperatures

    NASA Astrophysics Data System (ADS)

    Zdybel, Magdalena; Pilawa, Barbara; Buszman, Ewa; Wrzesniok, Dorota; Krzyminiewski, Ryszard; Kruczynski, Zdzislaw

    2011-01-01

    Paramagnetic centers in DOPA-melanin and complexes of DOPA-melanin with netilmicin and Cu(II) were studied by the use of an X-band (9.3 GHz) electron paramagnetic resonance (EPR) spectroscopy. Measurements of continuous microwave saturation of EPR spectra at temperatures: 125 K, 175 K, 225 K, 275 K, were performed. Homogeneous broadening of all the examined EPR spectra was observed. EPR spectra of DOPA-melanin-Cu(II) complexes saturated at higher microwave powers than the others tested melanin samples. Fast spin-lattice relaxation exists in DOPA-melanin-Cu(II) complexes. Slow spin-lattice relaxation processes exist in melanin's paramagnetic centers of DOPA-melanin and its complexes with netilmicin, and its complexes with both netilimicin and Cu(II). EPR spectra of all the tested samples saturated at higher microwave powers with increasing of the measuring temperature. Faster spin-lattice relaxation processes occurs in DOPA-melanin and its complexes with netilmicin and Cu(II) at higher temperature.

  13. Determination of methemoglobin in human blood after ionising radiation by EPR

    NASA Astrophysics Data System (ADS)

    Polakovs, M.; Mironova-Ulmane, N.; Pavlenko, A.; Aboltins, A.

    2015-03-01

    In the present work presents results of investigations of radiation influence on blood of patients examined by radio-isotopes diagnosis (Tc99m), blood of Chernobyl clean-up workers and human blood irradiated by LINAC using Electron Paramagnetic Resonance (EPR). The EPR spectroscopy reveals information on electronic states of transition metal ions, particularly Fe3+ in different spin states. It is shown that EPR spectra of blood of patients before examination has signal from metal-protein transferrin (g=4.3) and after administration of radioisotope proves signal of Fe3+ (methemaglobin) in the high spin state (g=6.0). The EPR spectra of Chernobyl liquidator display number of signals including low and high state of ion Fe3+ (g = 2.0 and g=6.0), and transferrin (g=4.3). The EPR spectra of irradiated human blood by LINAC (linear accelerator) have only signal Fe3+ (methemaglobin) in low-spin state with g = 2.0.

  14. Optimization of bicelle lipid composition and temperature for EPR spectroscopy of aligned membranes

    NASA Astrophysics Data System (ADS)

    McCaffrey, Jesse E.; James, Zachary M.; Thomas, David D.

    2015-01-01

    We have optimized the magnetic alignment of phospholipid bilayered micelles (bicelles) for EPR spectroscopy, by varying lipid composition and temperature. Bicelles have been extensively used in NMR spectroscopy for several decades, in order to obtain aligned samples in a near-native membrane environment and take advantage of the intrinsic sensitivity of magnetic resonance to molecular orientation. Recently, bicelles have also seen increasing use in EPR, which offers superior sensitivity and orientational resolution. However, the low magnetic field strength (less than 1 T) of most conventional EPR spectrometers results in homogeneously oriented bicelles only at a temperature well above physiological. To optimize bicelle composition for magnetic alignment at reduced temperature, we prepared bicelles containing varying ratios of saturated (DMPC) and unsaturated (POPC) phospholipids, using EPR spectra of a spin-labeled fatty acid to assess alignment as a function of lipid composition and temperature. Spectral analysis showed that bicelles containing an equimolar mixture of DMPC and POPC homogeneously align at 298 K, 20 K lower than conventional DMPC-only bicelles. It is now possible to perform EPR studies of membrane protein structure and dynamics in well-aligned bicelles at physiological temperatures and below.

  15. Photoionization of phenothiazine: EPR detection of reactions of the polarized solvated electron

    SciTech Connect

    Turro, N.J.; Khudyakov, I.V.; Willigen, H. van

    1995-12-13

    Photoionization of phenothiazine (PTH) and reactions of the solvated electron with some electron acceptors were studied with steady state and time-resolved EPR and transient optical absorption techniques. Time-resolved EPR spectra from the phenothiazine cation radical (PTH{sup .+}) and hydrated electron (e{sub aq}{sup -}) formed in sodium 1-dodecylsulfate (SDS) micellar solution were observed in emission. By contrast, PTH{sup .+} formed by photoionization of PTH in alcohols gives absorptive EPR signals. The spin polarization carried by the hydrated electron in SDS solutions can be transferred effectively to a stable nitroxyl free radical 3-carboxy-2,2,5, 5-tetramethyl-1-pyrrolidinyloxyl (N{sup .-}) present in the bulk aqueous phase. EPR and flash photolysis measurements show that this electron spin polarization transfer process proceeds with a rate which is approximately five times faster than the chemical reaction between e{sub aq}{sup -} and N{sup .-}. The marked difference in rates is attributed to differences in spin-statistical factors and difference in reaction radii for spin exchange compared to reaction. In alcohol solutions of PTH and a nitroxyl stable radical (2,2,6, 6-tetramethylpyperidin-1-oxyl, TEMPO), excitation of PTH also results in emissive polarization of the EPR spectrum of the stable radical. 46 refs., 12 figs.

  16. EPR/alanine pellets with low Gd content for neutron dosimetry.

    PubMed

    Marrale, M; Brai, M; Longo, A; Panzeca, S; Carlino, A; Tranchina, L; Tomarchio, E; Parlato, A; Buttafava, A; Dondi, D; Zeffiro, A

    2014-10-01

    This paper reports on results obtained by electron paramagnetic resonance (EPR) measurements and Monte Carlo (MC) simulation on a blend of alanine added with low content of gadolinium oxide (5 % by weight) to improve the sensitivity to thermal neutron without excessively affecting tissue equivalence. The sensitivity is enhanced by this doping procedure of more an order of magnitude. The results are compared with those obtained with the addition of boric acid (50 % by weight) where boron is in its natural isotopic composition in order to produce low-cost EPR dosemeters. The gadolinium addition influences neutron sensitivity more than the boron addition. The presence of additives does not substantially change the fading of the EPR signal induced by neutrons. The MC simulations agree the experimental results in case of gadolinium addition.

  17. EPR investigation of the gamma radiation response of different types of glasses.

    PubMed

    Gancheva, Veselka; Yordanov, Nicola D; Karakirova, Yordanka

    2006-03-13

    Several types of laboratory glasses such as: "Jena", "Rasotherm", "Thüring" as well as window and windscreen glasses were studied by the method of EPR spectroscopy as possible emergency radiation dosimeters for gamma-ray irradiation. The most appropriate values of modulation amplitude and microwave power were found to obtain best sensitivity for the measured signals. Dose measurements have shown a linear dependence between the EPR signal intensity of radiation created defects in glasses and applied dose in the dose range 50-500 Gy. "Thüring" glass was found to be the most sensitive sample to radiation. The magnitude of window glass absorbed dose was evaluated as the difference between the intensity of its EPR signal recorded after irradiation and the background signal, obtained after thermal relaxation of the former.

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

    PubMed

    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.

  19. Post-annealing effects on EPR response of irradiated nano-structure hydroxyapatite

    NASA Astrophysics Data System (ADS)

    Dowlatshah, F.; Ziaie, F.; Hajiloo, N.; Amraie, R.; Fathollahi, H.

    2012-12-01

    In this work, the nano-structure hydroxyapatite was synthesized via the hydrolysis method. The produced powders were thermally treatment at different temperatures from 400 to 1200°C. The morphological and chemical analyses were carried out using the Fourier transmission infrared spectroscopy, transmission electron microscopy, and X-ray diffraction system. Then, the samples were irradiated at different absorbed doses from 1 to 80 kGy using 60Co γ -ray. Electron paramagnetic resonance (EPR) responses of the samples were measured at room temperature in air. Subsequently, the variations of EPR signal intensities were constructed as the peak-to-peak signal amplitude and results were compared with those of non-annealed samples. The results show that the EPR responses of non-annealed samples are higher rather than other samples and also are saturated at higher doses in comparison with the others.

  20. Genetically Encoded Spin Labels for In Vitro and In-Cell EPR Studies of Native Proteins.

    PubMed

    Schmidt, M J; Fedoseev, A; Summerer, D; Drescher, M

    2015-01-01

    Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) is a powerful approach to study the structure, dynamics, and interactions of proteins. The genetic encoding of the noncanonical amino acid spin-labeled lysine 1 (SLK-1) eliminates the need for any chemical labeling steps in SDSL-EPR studies and enables the investigation of native, endogenous proteins with minimal structural perturbation, and without the need to create unique reactive sites for chemical labeling. We report detailed experimental procedures for the efficient synthesis of SLK-1, the expression and purification of SLK-1-containing proteins under conditions that ensure maximal integrity of the nitroxide radical moiety, and procedures for intramolecular EPR distance measurements in proteins by double electron-electron resonance.

  1. A reinvestigation of EXAFS and EPR spectroscopic measurements of chromium(VI) reduction by coir pith.

    PubMed

    Suksabye, Parinda; Worasith, Niramon; Thiravetyan, Paitip; Nakajima, Akira; Goodman, Bernard A

    2010-08-15

    New measurements using extended X-ray absorption fine structure (EXAFS) and electron paramagnetic resonance (EPR) techniques are consistent with Cr in the Cr(III) oxidation state as the main product from the adsorption of Cr(VI) on coir pith. These confirm the previous X-ray measurements, but differ from the results of previous EPR studies, which indicated that Cr(V) was the main form of Cr. The reason for this discrepancy is the presence of a broad signal from Cr(III) in an unsymmetrical environment that was missed previously; the Cr(V) component is in fact only a minor reaction product. As a result of this problem with spectral acquisition and interpretation, some simple recommendations are presented for conducting EPR investigations on natural systems.

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

    SciTech Connect

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

    2015-07-28

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

  3. Navigating membrane protein structure, dynamics, and energy landscapes using spin labeling and EPR spectroscopy

    PubMed Central

    Claxton, Derek P; Kazmier, Kelli; Mishra, Smriti; Mchaourab, Hassane S

    2017-01-01

    A detailed understanding of the functional mechanism of a protein entails the characterization of its energy landscape. Achieving this ambitious goal requires the integration of multiple approaches including determination of high resolution crystal structures, uncovering conformational sampling under distinct biochemical conditions, characterizing the kinetics and thermodynamics of transitions between functional intermediates using spectroscopic techniques, and interpreting and harmonizing the data into novel computational models. With increasing sophistication in solution-based and ensemble-oriented biophysical approaches such as electron paramagnetic resonance (EPR) spectroscopy, atomic resolution structural information can be directly linked to conformational sampling in solution. Here, we detail how recent methodological and technological advances in EPR spectroscopy have contributed to the elucidation of membrane protein mechanisms. Furthermore, we aim to assist investigators interested in pursuing EPR studies by providing an introduction to the technique, a primer on experimental design, and a description of the practical considerations of the method towards generating high quality data. PMID:26477257

  4. Radiation effects on microstructure and EPR signal of yttrium oxide rods

    NASA Astrophysics Data System (ADS)

    Santos, S. C.; Rodrigues, O., Jr.; Campos, L. L.

    2017-02-01

    Designing nanostructured materials with high dosimetric efficiency is a great challenge in radiation dosimetry research. From rare-earth series, yttrium oxide is considered as excellent host matrix for rare-earth ions, leading to formation of advanced functional materials with optical, mechanical, chemical, and thermal properties notably improved. Nevertheless, there is a lack of information which correlates microstructural characteristics and performance of rare earths. This work aims to evaluate the radiation effects on microstructure and EPR signal of Y2O3 rods produced by colloidal processing followed by sintering at 1600°C/4h in air. Ceramic rods were exposed to gamma radiation with doses up to 100kGy. Microstructural and dosimetric characterizations were performed by XRD, SEM and EPR techniques. Yttrium oxide rods as sintered exhibited dense microstructure (96.6% theoretical density) and linear EPR dose response behaviour for wide dose range. These results reveal that yttrium oxide is a promising material for radiation dosimetry.

  5. A password-based user authentication scheme for the integrated EPR information system.

    PubMed

    Wu, Zhen-Yu; Chung, Yufang; Lai, Feipei; Chen, Tzer-Shyong

    2012-04-01

    With the rapid development of the Internet, digitization and electronic orientation are required in various applications of our daily life. For e-medicine, establishing Electronic patient records (EPRs) for all the patients has become the top issue during the last decade. Simultaneously, constructing an integrated EPR information system of all the patients is beneficial because it can provide medical institutions and the academia with most of the patients' information in details for them to make correct decisions and clinical decisions, to maintain and analyze patients' health. Also beneficial to doctors and scholars, the EPR system can give them record linkage for researches, payment audits, or other services bound to be developed and integrated into medicine. To tackle the illegal access and to prevent the information from theft during transmission over the insecure Internet, we propose a password-based user authentication scheme suitable for information integration.

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

    PubMed

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

    2016-10-01

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

  7. EPR oxygen images predict tumor control by a 50 percent tumor control radiation dose

    PubMed Central

    Elas, Martyna; Magwood, Jessica M.; Butler, Brandi; Li, Chanel; Wardak, Rona; Barth, Eugene D.; Epel, Boris; Rubinstein, Samuel; Pelizzari, Charles A.; Weichselbaum, Ralph R.; Halpern, Howard J.

    2013-01-01

    Clinical trials to ameliorate hypoxia as a strategy to relieve the radiation resistance it causes have prompted a need to assay the precise extent and location of hypoxia in tumors. Electron Paramagnetic Resonance oxygen imaging (EPR O2 imaging) provides a non-invasive means to address this need. To obtain a preclinical proof of principle that EPR O2 images could predict radiation control, we treated mouse tumors at or near doses required to achieve 50 percent control (TCD50). Mice with FSa fibrosarcoma or MCa4 carcinoma were subjected to EPR O2 imaging and immediately radiated to a TCD50 or TCD50 ±10 Gy.. Statistical analysis was permitted by collection of ~ 1300 tumor pO2 image voxels, including the fraction of tumor voxels with pO2 less than 10 mm Hg (HF10). Tumors were followed for 90 days (FSa) or 120 days (MCa4) to determine local control or failure. HF10 obtained from EPR images showed statistically significant differences between tumors that were controlled by the TCD50 and those that were not controlled for both FSa and MCa4. Kaplan-Meier analysis of both types of tumors showed ~90% of mildly hypoxic tumors were controlled (HF10<10%), and only 37% (FSA) and 23% (MCa4) tumors controlled if hypoxic. EPR pO2 image voxel distributions in these ~0.5 ml tumors provide a prediction of radiation curability independent of radiation dose. These data confirm the significance of EPR pO2 hypoxic fractions. The ~90% control of low HF10 tumors argue that ½ ml subvolumes of tumors may be more sensitive to radiation and may need less radiation for high tumor control rates. PMID:23861469

  8. High-field EPR study of carotenoid and chlorophyll cation radicals in photosystem II.

    SciTech Connect

    Lakshmi, K. V.; Reifler, M. J.; Brudvig, G. W.; Poluektov, O. G.; Wagner, A. M.; Thurnuaer, M. C.; Chemistry; Yale Univ.

    2000-11-16

    In photosystem II (PS II), chlorophyll, {beta}-carotene, and cytochrome b{sub 559} are alternate electron donors that may be involved in a photoprotection mechanism. The present study describes the use of high-field EPR spectroscopy to characterize the low-temperature photooxidation of Chl{sub z} and Car cofactors in PS II. The EPR signals of the individual species, previously not resolved at X-band frequency (9 GHz), are resolved at higher D-band frequency (130 GHz) in deuterated Synechococcus lividus PS II. Deuteration of PS II results in significant narrowing of the EPR lines, yielding well-resolved EPR spectra of the Car{sup +} and Chl{sub z}{sup +} radicals at 130 GHz. The g tensors of the individual species were determined by EPR spectral simulations. The g tensor determined for the Car{sup +} radical (g{sub xx} = 2.00335, g{sub yy} = 2.00251, g{sub zz} = 2.00227) is similar to that previously observed for a canthaxanthin cation radical but with a slightly rhombic tensor. The Chl{sub z}{sup +} g tensor (g{sub xx} = 2.00312, g{sub yy} = 2.00263, g{sub zz} = 2.00202) is similar to that of a chlorophyll a cation radical. This study shows that both the carotenoid and chlorophyll radicals are generated in PS II by illumination at temperatures from 6 to 190 K and that there is no interconversion of Car{sup +} and Chl{sub z}{sup +} radicals upon dark annealing at temperatures up to 160 K. This study also establishes the feasibility of using deuteration and high-field EPR to resolve previously unresolvable cofactor signals in PS II.

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

    PubMed

    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.

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

    SciTech Connect

    Haskell, E.H.; Kenner, G.H.; Hayes, R.B.; Chumak, V.; Shalom, S.

    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.

  11. EPR lineshape of Mn in BCCD single crystals in the incommensurate phase

    NASA Astrophysics Data System (ADS)

    Heidler, R.; Metz, H.; Windsch, W.

    1994-10-01

    For the interpretation of the Electron Paramagnetic Resonance (EPR) lineshape of incommensurate phases there exist many theoretical models. We suppose a simple physical model to interpret the lineshape of the Mn(2+) EPR spectrum of the first incommensurate phase of betaine calcium chloride dihydrate (BCCD) and discuss it in comparison with other models. Furthermore, we investigate the critical behavior of BCCD at the normal to incommensurate phase transition on the basis of our model. The influence of the Mn(2+) impurities on the phase sequence of BCCD is investigated by dielectric measurements.

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

    PubMed

    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.

  13. EPR study of the effect of terahertz radiation on the albumin conformation dynamics

    NASA Astrophysics Data System (ADS)

    Nemova, Eugenia F.; Cherkasova, Olga P.; Fedorov, Vyacheslav I.

    2010-09-01

    Effect of the preliminary irradiation of bovine serum albumin (BSA) in the terahertz spectral range on the conformation changes revealed with the help of EPR spectroscopy was investigated using the spin probing technique. The formation of the spin probe occurs directly in the aqueous solution of BSA from a nitrone compound (dihydropyrazine dioxide). It was shown that irradiation causes changes in the parameters of the EPR spectrum of the spin probe. An approach to linking the observed changes with the structural characteristics of reaction centres - the functional groups of amino acids comprising BSA - was outlined.

  14. Use of polyphase continuous excitation based on the Frank sequence in EPR.

    PubMed

    Tseitlin, Mark; Quine, Richard W; Eaton, Sandra S; Eaton, Gareth R

    2011-08-01

    Polyphase continuous excitation based on the Frank sequence is suggested as an alternative to single pulse excitation in EPR. The method allows reduction of the source power, while preserving the excitation bandwidth of a single pulse. For practical EPR implementation the use of a cross-loop resonator is essential to provide isolation between the spin system and the resonator responses to the excitation. Provided that a line broadening of about 5% is acceptable, the cumulative turning angle of the magnetization vector generated by the excitation sequence can be quite large and can produce signal amplitudes that are comparable to that achieved with a higher power 90° pulse.

  15. Application of jade samples for high-dose dosimetry using the EPR technique.

    PubMed

    Teixeira, Maria Inês; Melo, Adeilson P; Ferraz, Gilberto M; Caldas, Linda V E

    2010-01-01

    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.

  16. EPR study of free radicals in some drugs γ-irradiated in the solid state

    NASA Astrophysics Data System (ADS)

    Ambroż, H. B.; 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 γ-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 — 4.5×10 17 spins per gram and the lowest for nimodipine — 2.1×10 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.

  17. EPR study of VO2+ doped glycine zinc sulphate single crystal

    NASA Astrophysics Data System (ADS)

    Prabakaran, R.; Subramanian, P.

    2015-06-01

    Single crystals Of GZS:VO2+ were grown by slow evaporation of solvent at room temperature. The EPR study was carried out at room temperature. Single crystal rotations in each of the three mutually orthogonal planes indicate single site occupation of VO2+ in the lattice. g and A tensors were calculated from the recorded EPR spectra. The principal values of g and A indicates existence of rhombic symmetry around the VO2+ ion. From the direction cosines of the g and A tensors, the locations of VO2+ in the lattice have been identified as substitutional site.

  18. A secure and efficient password-based user authentication scheme using smart cards for the integrated EPR information system.

    PubMed

    Lee, Tian-Fu; Chang, I-Pin; Lin, Tsung-Hung; Wang, Ching-Cheng

    2013-06-01

    The integrated EPR information system supports convenient and rapid e-medicine services. A secure and efficient authentication scheme for the integrated EPR information system provides safeguarding patients' electronic patient records (EPRs) and helps health care workers and medical personnel to rapidly making correct clinical decisions. Recently, Wu et al. proposed an efficient password-based user authentication scheme using smart cards for the integrated EPR information system, and claimed that the proposed scheme could resist various malicious attacks. However, their scheme is still vulnerable to lost smart card and stolen verifier attacks. This investigation discusses these weaknesses and proposes a secure and efficient authentication scheme for the integrated EPR information system as alternative. Compared with related approaches, the proposed scheme not only retains a lower computational cost and does not require verifier tables for storing users' secrets, but also solves the security problems in previous schemes and withstands possible attacks.

  19. Fusinite: A coal-derived EPR probe for O[sub 2]. Mechanism and application in vivo and in vitro. [EPR (electron paramagnetic resonance)

    SciTech Connect

    Vahidi, N.

    1993-01-01

    Fusinite, an inertinite coal maceral, exhibits a symmetric and exchange-narrowed electron paramagnetic resonance (EPR) line (g = 2.00276), with a first derivative peak-to-peak linewidth ([Delta]B) which is reversibly broaded by molecular O[sub 2]. To explain the mechanism of this type of broadening, pulse and multifrequency EPR measurements (0.25-250 GHz) were carried out in conjunction with O[sub 2] adsorption isotherm studies. The data suggest that, at ambient temperatures, homogeneous broadening of the EPR line of fusinite probably occurs by the exchange modulation of a group of delocalized unpaired electrons at the surface of fusinite by physical adsorbed O[sub 2]. At temperatures below 260[degrees] K, dipole-dipole mechanism begin to contribute more to the broadening of this component. The possibility of two different classes of sites for interaction with O[sub 2] is discussed. The extent of broadening per unit concentration of molecular oxygen is unusually large. This paramagnetic property of fusinite, combined with its very table physiochemical properties and low toxicity, is of utility for the measurement of the concentration of oxygen or [O[sub 2

  20. EPRS is a critical mTORC1-S6K1 effector that influences adiposity in mice.

    PubMed

    Arif, Abul; Terenzi, Fulvia; Potdar, Alka A; Jia, Jie; Sacks, Jessica; China, Arnab; Halawani, Dalia; Vasu, Kommireddy; Li, Xiaoxia; Brown, J Mark; Chen, Jie; Kozma, Sara C; Thomas, George; Fox, Paul L

    2017-02-16

    Metabolic pathways that contribute to adiposity and ageing are activated by the mammalian target of rapamycin complex 1 (mTORC1) and p70 ribosomal protein S6 kinase 1 (S6K1) axis. However, known mTORC1-S6K1 targets do not account for observed loss-of-function phenotypes, suggesting that there are additional downstream effectors of this pathway. Here we identify glutamyl-prolyl-tRNA synthetase (EPRS) as an mTORC1-S6K1 target that contributes to adiposity and ageing. Phosphorylation of EPRS at Ser999 by mTORC1-S6K1 induces its release from the aminoacyl tRNA multisynthetase complex, which is required for execution of noncanonical functions of EPRS beyond protein synthesis. To investigate the physiological function of EPRS phosphorylation, we generated Eprs knock-in mice bearing phospho-deficient Ser999-to-Ala (S999A) and phospho-mimetic (S999D) mutations. Homozygous S999A mice exhibited low body weight, reduced adipose tissue mass, and increased lifespan, similar to S6K1-deficient mice and mice with adipocyte-specific deficiency of raptor, an mTORC1 constituent. Substitution of the Eprs(S999D) allele in S6K1-deficient mice normalized body mass and adiposity, indicating that EPRS phosphorylation mediates S6K1-dependent metabolic responses. In adipocytes, insulin stimulated S6K1-dependent EPRS phosphorylation and release from the multisynthetase complex. Interaction screening revealed that phospho-EPRS binds SLC27A1 (that is, fatty acid transport protein 1, FATP1), inducing its translocation to the plasma membrane and long-chain fatty acid uptake. Thus, EPRS and FATP1 are terminal mTORC1-S6K1 axis effectors that are critical for metabolic phenotypes.

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

    PubMed

    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.

  2. Emergency Preservation and Resuscitation for Cardiac Arrest from Trauma (EPR-CAT)

    DTIC Science & Technology

    2014-12-01

    TITLE: Emergency Preservation and Resuscitation for Cardiac Arrest from Trauma (EPR-CAT) PRINCIPAL INVESTIGATOR...SUBTITLE Emergency Preservation and Resuscitation for Cardiac Arrest 5a. CONTRACT NUMBER From Trauma 5b. GRANT NUMBER W81XWH-07-1-0682...an emergency department (ED) thoracotomy and open chest CPR, results in unacceptably low survival rates. Emergency Preservation and Resuscitation

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

    ERIC Educational Resources Information Center

    Eastman, Michael P.

    1982-01-01

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

  4. Application of EPR retrospective dosimetry for large-scale accidental situation.

    PubMed

    Skvortsov, V G; Ivannikov, A I; Stepanenko, V F; Tsyb, A F; Khamidova, L G; Kondrashov, A E; Tikunov, D D

    2000-05-01

    Above 3000 tooth enamel samples, collected at population of radioactive contaminated territories after Chernobyl accident, the Chernobyl liquidators, the retired military of high radiation risk and the population of control radiation free territories were investigated by EPR spectroscopy method in order to obtain accumulated individual exposure doses. Results of EPR spectra measurements are stored in data bank; enamel samples are also stored in order to provide the possibility to repeat the measurements in future. Statistical analysis of results has allowed to detect the contribution into EPR signal in tooth enamel due to the action of the natural background radiation, and the radioactive contamination of territory. In general, the average doses of external exposure of the population obtained with EPR spectroscopy of teeth enamel are consistent with results based on other methods of direct and retrospective dosimetry. Essential exceeding of the individual doses above the average level within the population groups was observed for some persons. That gave the possibility to detect the individuals with overexposure, which were included into groups for medical monitoring.

  5. Manifestation of Strong Coupling Between Microwave Photons and Spins in the epr Spectrum of Anthracite

    NASA Astrophysics Data System (ADS)

    Fedaruk, R.; Adashkevich, S. V.

    2014-07-01

    The change of the anthracite EPR signal shape that was caused by increasing the sample size was observed by continuous-wave EPR with automatic frequency control locked to the measuring cavity. For large samples (>10 mm3), hysteresis (a difference in the resonant magnetic flux densities when the magnetic field was scanned upwards or downwards) and a bistability (a sharp amplitude change) were observed. A two-peak spectrum for a strongly coupled system formed by an electron-spin ensemble and the cavity microwave field was found by changing the frequency of the microwave oscillator during recording of the EPR signals. The difference in the frequencies of these peaks (Rabi splitting) was a measure of the coupling strength between the spins and the microwave field and increased with increasing sample size. The simultaneous increase of the hysteresis and bistability of the EPR signals provided evidence that these peculiarities were caused by the Rabi splitting. Use of the Rabi splitting to determine the number of electron spins in a sample was proposed.

  6. Four-channel surface coil array for sequential CW-EPR image acquisition

    NASA Astrophysics Data System (ADS)

    Enomoto, Ayano; Emoto, Miho; Fujii, Hirotada; Hirata, Hiroshi

    2013-09-01

    This article describes a four-channel surface coil array to increase the area of visualization for continuous-wave electron paramagnetic resonance (CW-EPR) imaging. A 776-MHz surface coil array was constructed with four independent surface coil resonators and three kinds of switches. Control circuits for switching the resonators were also built to sequentially perform EPR image acquisition for each resonator. The resonance frequencies of the resonators were shifted using PIN diode switches to decouple the inductively coupled coils. To investigate the area of visualization with the surface coil array, three-dimensional EPR imaging was performed using a glass cell phantom filled with a solution of nitroxyl radicals. The area of visualization obtained with the surface coil array was increased approximately 3.5-fold in comparison to that with a single surface coil resonator. Furthermore, to demonstrate the applicability of this surface coil array to animal imaging, three-dimensional EPR imaging was performed in a living mouse with an exogenously injected nitroxyl radical imaging agent.

  7. Simple group password-based authenticated key agreements for the integrated EPR information system.

    PubMed

    Lee, Tian-Fu; Chang, I-Pin; Wang, Ching-Cheng

    2013-04-01

    The security and privacy are important issues for electronic patient records (EPRs). The goal of EPRs is sharing the patients' medical histories such as the diagnosis records, reports and diagnosis image files among hospitals by the Internet. So the security issue for the integrated EPR information system is essential. That is, to ensure the information during transmission through by the Internet is secure and private. The group password-based authenticated key agreement (GPAKE) allows a group of users like doctors, nurses and patients to establish a common session key by using password authentication. Then the group of users can securely communicate by using this session key. Many approaches about GAPKE employ the public key infrastructure (PKI) in order to have higher security. However, it not only increases users' overheads and requires keeping an extra equipment for storing long-term secret keys, but also requires maintaining the public key system. This investigation presents a simple group password-based authenticated key agreement (SGPAKE) protocol for the integrated EPR information system. The proposed SGPAKE protocol does not require using the server or users' public keys. Each user only remembers his weak password shared with a trusted server, and then can obtain a common session key. Then all users can securely communicate by using this session key. The proposed SGPAKE protocol not only provides users with convince, but also has higher security.

  8. Estimation of the absorbed dose in radiation-processed food. 4. EPR measurements on eggshell

    SciTech Connect

    Desrosiers, M.F.; Le, F.G. ); Harewood, P.M.; Josephson, E.S. ); Montesalvo, M. )

    1993-09-01

    Fresh whole eggs treated with ionizing radiation for Salmonellae control testing. The eggshell was then removed and examined by electron paramagnetic resonance (EPR) spectroscopy to determine if EPR could be used to (1) distinguish irradiated from unirradiated eggs and (2) assess the absorbed dose. No EPR signals were detected in unirradiated eggs, while strong signals were measurable for more than 200 days after irradiation. Although a number of EPR signals were measured, the most intense resonance (g = 2.0019) was used for dosimetry throughout the study. This signal was observed to increase linearly with dose (up to [approximately]6 kGy), which decayed [approximately]20% within the first 5 days after irradiation and remained relatively constant thereafter. The standard added-dose method was used to assess, retrospectively, the dose to eggs processed at 0.2, 0.7, and 1.4 kGy. Relatively good results were obtained when measurement was made on the day the shell was reirradiated; with this procedure estimates were better for shell processed at the lower doses.

  9. Increasing sensitivity of pulse EPR experiments using echo train detection schemes

    NASA Astrophysics Data System (ADS)

    Mentink-Vigier, F.; Collauto, A.; Feintuch, A.; Kaminker, I.; Tarle, V.; Goldfarb, D.

    2013-11-01

    Modern pulse EPR experiments are routinely used to study the structural features of paramagnetic centers. They are usually performed at low temperatures, where relaxation times are long and polarization is high, to achieve a sufficient Signal/Noise Ratio (SNR). However, when working with samples whose amount and/or concentration are limited, sensitivity becomes an issue and therefore measurements may require a significant accumulation time, up to 12 h or more. As the detection scheme of practically all pulse EPR sequences is based on the integration of a spin echo - either primary, stimulated or refocused - a considerable increase in SNR can be obtained by replacing the single echo detection scheme by a train of echoes. All these echoes, generated by Carr-Purcell type sequences, are integrated and summed together to improve the SNR. This scheme is commonly used in NMR and here we demonstrate its applicability to a number of frequently used pulse EPR experiments: Echo-Detected EPR, Davies and Mims ENDOR (Electron-Nuclear Double Resonance), DEER (Electron-Electron Double Resonance|) and EDNMR (Electron-Electron Double Resonance (ELDOR)-Detected NMR), which were combined with a Carr-Purcell-Meiboom-Gill (CPMG) type detection scheme at W-band. By collecting the transient signal and integrating a number of refocused echoes, this detection scheme yielded a 1.6-5 folds SNR improvement, depending on the paramagnetic center and the pulse sequence applied. This improvement is achieved while keeping the experimental time constant and it does not introduce signal distortion.

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

    PubMed Central

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

    2015-01-01

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

  11. EPR policies for electronics in developing Asia: an adapted phase-in approach.

    PubMed

    Akenji, Lewis; Hotta, Yasuhiko; Bengtsson, Magnus; Hayashi, Shiko

    2011-09-01

    The amount of e-waste is growing rapidly in developing countries, and the health and environmental problems resulting from poor management of this waste have become a concern for policy makers. In response to these challenges, a number of Asian developing countries have been inspired by policy developments in OECD countries, and have drafted legislations based on the principle of extended producer responsibility (EPR). However, the experiences from developed countries show that a successful implementation of EPR policies requires adequate institutions and sufficient administrative capacity. Even advanced countries are thus facing difficulties. This paper concludes from existing literature and from the authors' own observations that there seems to be a mismatch between the typical policy responses to e-waste problems in developing Asia and the capacity for successful implementation of such policies. It also notes that the e-waste situation in developing Asian countries is further complicated by a number of additional factors, such as difficulties in identifying producers, import of used electronic products and e-waste (sometimes illegal), and the existence of a strong informal waste sector. Given these challenges, the authors conclude that comprehensive EPR policy schemes of the kind that have been implemented in some advanced countries are not likely to be effective. The paper therefore proposes an alternative phase-in approach whereby developing Asian countries are able to move gradually towards EPR systems. It argues that this approach would be more feasible, and discusses what could be the key building blocks of each implementation stage.

  12. A rapid freeze-quench setup for multi-frequency EPR spectroscopy of enzymatic reactions.

    PubMed

    Pievo, Roberta; Angerstein, Brigitta; Fielding, Alistair J; Koch, Christian; Feussner, Ivo; Bennati, Marina

    2013-12-16

    Electron paramagnetic resonance (EPR) spectroscopy in combination with the rapid freeze-quench (RFQ) technique is a well-established method to trap and characterize intermediates in chemical or enzymatic reactions at the millisecond or even shorter time scales. The method is particularly powerful for mechanistic studies of enzymatic reactions when combined with high-frequency EPR (ν≥90 GHz), which permits the identification of substrate or protein radical intermediates by their electronic g values. In this work, we describe a new custom-designed micro-mix rapid freeze-quench apparatus, for which reagent volumes for biological samples as small as 20 μL are required. The apparatus was implemented with homemade sample collectors appropriate for 9, 34, and 94 GHz EPR capillaries (4, 2, and 0.87 mm outer diameter, respectively) and the performance was evaluated. We demonstrate the application potential of the RFQ apparatus by following the enzymatic reaction of PpoA, a fungal dioxygenase producing hydro(pero)xylated fatty acids. The larger spectral resolution at 94 GHz allows the discernment of structural changes in the EPR spectra, which are not detectable in the same samples at the standard 9 GHz frequency.

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

    PubMed Central

    Fischer, Axel W.; Alexander, Nathan S.; Woetzel, Nils; Karakaş, Mert; Weiner, Brian E.; Meiler, Jens

    2016-01-01

    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 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 protein-size-normalized root-mean-square-deviation (RMSD100) value of the most accurate model is better than 8 Å for twenty-seven, better than 6 Å for twenty-two, and better than 4 Å for fifteen out of twenty-nine proteins, demonstrating the algorithm’s ability to sample the native topology. The average enrichment could be improved from 1.3 to 2.5, showing the improved discrimination power by using EPR data. PMID:25820805

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

    PubMed

    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.

  15. EPR Methods for Biological Cu(II): L-Band CW and NARS

    PubMed Central

    Bennett, Brian; Kowalski, Jason

    2016-01-01

    Copper has many roles in biology that involve the change of coordination sphere and/or oxidation state of the copper ion. Consequently, the study of copper in heterogeneous environments is an important area in biophysics. EPR is a primary technique for the investigation of paramagnetic copper, which is usually the isolated Cu(II) ion, but sometimes as Cu(II) in different oxidation states of multi-transition ion clusters. The gross geometry of the coordination environment of Cu(II) can often be determined from a simple inspection of the EPR spectrum, recorded in the traditional X-band frequency range (9 – 10 GHz). Identification and quantitation of the coordinating ligand atoms, however, is not so straightforward. In particular, analysis of the superhyperfine structure on the EPR spectrum, to determine the number of coordinated nitrogen atoms, is fraught with difficulty at X-band, despite the observation that the overwhelming number of EPR studies of Cu(II) in the literature have been carried out at X-band. Greater reliability has been demonstrated at S-band (3 – 4 GHz), using the low-field parallel (gz) features. However, analysis relies on clear identification of the outermost superhyperfine line, which has the lowest intensity of all the spectral features. Computer simulations have subsequently indicated that the much more intense perpendicular region of the spectrum can be reliably interpreted at L-band (2 GHz). The present work describes the development of L-band EPR of Cu(II) into a routine method, that is applicable to biological samples. PMID:26478491

  16. Concentration of Cu, EPR-detectable Cu, and formation of cupric-ferrocyanide in membranes with pMMO.

    PubMed

    Yuan, H; Collins, M L; Antholine, W E

    1998-12-01

    EPR spectra were obtained for the type 2 Cu(2+) site in particulate methane monooxygenase, pMMO, from membrane fractions of Methylomicrobium album BG8. In addition to the EPR signal with g parallel = 2.24 and A parallel = 185 G found in both cells and membrane fractions, a second EPR signal with g parallel = 2.29 and A parallel = 146 G was found in membrane fractions and attributed to oxidation of cuprous sites. Comparison of EPR-detectable Cu(2+) with total copper determined by atomic absorption suggests that there are two or three EPR-silent coppers for every EPR-detectable copper and that there are approximately four coppers per enzyme composed of the 47, 27, and 25 kDa subunits. Treatment of membrane fractions loaded with pMMO with Fe(CN)6(3-) results in a new EPR signal that is attributed to CuFe(CN)6(2-), not to an intrinsic trimeric copper cluster as previously reported in studies with a related bacterium.

  17. A combined EPR and MD simulation study of a nitroxyl spin label with restricted internal mobility sensitive to protein dynamics

    NASA Astrophysics Data System (ADS)

    Oganesyan, Vasily S.; Chami, Fatima; White, Gaye F.; Thomson, Andrew J.

    2017-01-01

    EPR studies combined with fully atomistic Molecular Dynamics (MD) simulations and an MD-EPR simulation method provide evidence for intrinsic low rotameric mobility of a nitroxyl spin label, Rn, compared to the more widely employed label MTSL (R1). Both experimental and modelling results using two structurally different sites of attachment to Myoglobin show that the EPR spectra of Rn are more sensitive to the local protein environment than that of MTSL. This study reveals the potential of using the Rn spin label as a reporter of protein motions.

  18. Digitally generated excitation and near-baseband quadrature detection of rapid scan EPR signals

    PubMed Central

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

    2014-01-01

    The use of multiple synchronized outputs from an AWG provides the opportunity to perform EPR experiments differently than by conventional EPR. We report a method for reconstructing the quadrature EPR spectrum from periodic signals that are generated with sinusoidal magnetic field modulation such as continuous wave (CW), multiharmonic, or rapid scan experiments. The signal is down-converted to an intermediate frequency (IF) that is less than the field scan or field modulation frequency and then digitized in a single channel. This method permits use of a high-pass analog filter before digitization to remove the strong non-EPR signal at the IF, that might otherwise overwhelm the digitizer. The IF is the difference between two synchronized X-band outputs from a Tektronix AWG 70002A arbitrary waveform generator (AWG), one of which is for excitation and the other is the reference for down-conversion. To permit signal averaging, timing was selected to give an exact integer number of full cycles for each frequency. In the experiments reported here the IF was 5 kHz and the scan frequency was 40 kHz. To produce sinusoidal rapid scans with a scan frequency eight times IF, a third synchronized output generated a square wave that was converted to a sine wave. The timing of the data acquisition with a Bruker SpecJet II was synchronized by an external clock signal from the AWG. The baseband quadrature signal in the frequency domain was reconstructed. This approach has the advantages that (i) the non-EPR response at the carrier frequency is eliminated, (ii) both real and imaginary EPR signals are reconstructed from a single physical channel to produce an ideal quadrature signal, and (iii) signal bandwidth does not increase relative to baseband detection. Spectra were obtained by deconvolution of the reconstructed signals for solid BDPA (1,3-bisdiphenylene-2-phenylallyl) in air, 0.2 mM trityl OX63 in water, 15N perdeuterated tempone, and a nitroxide with a 0.5 G partially

  19. Digitally generated excitation and near-baseband quadrature detection of rapid scan EPR signals

    NASA Astrophysics Data System (ADS)

    Tseitlin, Mark; Yu, Zhelin; Quine, Richard W.; Rinard, George A.; Eaton, Sandra S.; Eaton, Gareth R.

    2014-12-01

    The use of multiple synchronized outputs from an arbitrary waveform generator (AWG) provides the opportunity to perform EPR experiments differently than by conventional EPR. We report a method for reconstructing the quadrature EPR spectrum from periodic signals that are generated with sinusoidal magnetic field modulation such as continuous wave (CW), multiharmonic, or rapid scan experiments. The signal is down-converted to an intermediate frequency (IF) that is less than the field scan or field modulation frequency and then digitized in a single channel. This method permits use of a high-pass analog filter before digitization to remove the strong non-EPR signal at the IF, that might otherwise overwhelm the digitizer. The IF is the difference between two synchronized X-band outputs from a Tektronix AWG 70002A, one of which is for excitation and the other is the reference for down-conversion. To permit signal averaging, timing was selected to give an exact integer number of full cycles for each frequency. In the experiments reported here the IF was 5 kHz and the scan frequency was 40 kHz. To produce sinusoidal rapid scans with a scan frequency eight times IF, a third synchronized output generated a square wave that was converted to a sine wave. The timing of the data acquisition with a Bruker SpecJet II was synchronized by an external clock signal from the AWG. The baseband quadrature signal in the frequency domain was reconstructed. This approach has the advantages that (i) the non-EPR response at the carrier frequency is eliminated, (ii) both real and imaginary EPR signals are reconstructed from a single physical channel to produce an ideal quadrature signal, and (iii) signal bandwidth does not increase relative to baseband detection. Spectra were obtained by deconvolution of the reconstructed signals for solid BDPA (1,3-bisdiphenylene-2-phenylallyl) in air, 0.2 mM trityl OX63 in water, 15N perdeuterated tempone, and a nitroxide with a 0.5 G partially

  20. Digitally generated excitation and near-baseband quadrature detection of rapid scan EPR signals.

    PubMed

    Tseitlin, Mark; Yu, Zhelin; Quine, Richard W; Rinard, George A; Eaton, Sandra S; Eaton, Gareth R

    2014-10-30

    The use of multiple synchronized outputs from an arbitrary waveform generator (AWG) provides the opportunity to perform EPR experiments differently than by conventional EPR. We report a method for reconstructing the quadrature EPR spectrum from periodic signals that are generated with sinusoidal magnetic field modulation such as continuous wave (CW), multiharmonic, or rapid scan experiments. The signal is down-converted to an intermediate frequency (IF) that is less than the field scan or field modulation frequency and then digitized in a single channel. This method permits use of a high-pass analog filter before digitization to remove the strong non-EPR signal at the IF, that might otherwise overwhelm the digitizer. The IF is the difference between two synchronized X-band outputs from a Tektronix AWG 70002A, one of which is for excitation and the other is the reference for down-conversion. To permit signal averaging, timing was selected to give an exact integer number of full cycles for each frequency. In the experiments reported here the IF was 5kHz and the scan frequency was 40kHz. To produce sinusoidal rapid scans with a scan frequency eight times IF, a third synchronized output generated a square wave that was converted to a sine wave. The timing of the data acquisition with a Bruker SpecJet II was synchronized by an external clock signal from the AWG. The baseband quadrature signal in the frequency domain was reconstructed. This approach has the advantages that (i) the non-EPR response at the carrier frequency is eliminated, (ii) both real and imaginary EPR signals are reconstructed from a single physical channel to produce an ideal quadrature signal, and (iii) signal bandwidth does not increase relative to baseband detection. Spectra were obtained by deconvolution of the reconstructed signals for solid BDPA (1,3-bisdiphenylene-2-phenylallyl) in air, 0.2mM trityl OX63 in water, (15)N perdeuterated tempone, and a nitroxide with a 0.5G partially-resolved proton

  1. EPR and NMR detection of transient radicals and reaction products. [Radiolysis of methanol and aqueous potassium acetate

    SciTech Connect

    Trifunac, A.D.

    1981-01-01

    Magnetic resonance methods in radiation chemistry are illustrated. The most recent developments in pulsed EPR and NMR studies in pulse radiolysis are outlined with emphasis on the study of transient radicals and their reaction products. 12 figures.

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

    PubMed

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

    2016-12-01

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

  3. Vhf EPR quantitation and speciation of organic sulfur in coal. [Quarterly] technical report, December 1, 1993--February 28, 1994

    SciTech Connect

    Clarkson, R.B.; Belford, R.I.

    1994-06-01

    The existence of free electrons in coals` natural site offers a great attraction for Electron Paramagnetic Resonance (EPR) analysis to aid in the study of the structure and composition of coal. This direct and non-destructive approach to coal analysis has been hindered by the problem of resolution using the conventional 9.5 GHz EPR spectrometers. In the past few years, we have developed techniques including W-band Very High Frequency EPR spectroscopy as a means of determining the quantity and structure of organic sulfur in native and desulfurized coals. The state of the art 95 GHz (W-band) EPR spectrometer which we have constructed shows a well resolved spectrum including the interaction between unpaired electrons and the heteroatom like sulfur. The spectra also provide quantitative as well as qualitative information regarding different sulfur species. In collaboration with researchers at the University of Kentucky, we are also analyzing the result of desulfurization techniques on the presence of various sulfur species in coal. In the past, we have tried to synthesize various model compounds comparing their W-band spectra with other models, the predictions of theoretical models, and with the W-band spectra of coal specimens. In this quarter, we have been concentrating our efforts on developing a new standard protocol in handling and preparing the coal samples for EPR measurements to provide a quantitative comparison between the EPR spectra of coal in the natural state and desulfurized. Ten coal samples, both native and desulfurized, have been provided to us. These samples have been run in both laboratories. The simulation of coal EPR spectra has been carried out using several mathematical models. EPR results now are being compared with XANES data.

  4. EPR study of phenolic radical stabilization by grafting on SiO 2

    NASA Astrophysics Data System (ADS)

    Panagiota, Stathi; Louloudi, Maria; Deligiannakis, Yiannis

    2009-04-01

    A hybrid [SiO 2-GA] material has been synthesized by grafting Gallic acid (3,4,5-trihydroxybenzoic acid, GA) on SiO 2 via formation of amide bonds between amine groups on aminopropyl-silica and the carboxyl group of GA. The spatial fixation of GA prevents polymerization effects. EPR spectroscopy shows that GA radicals on [SiO 2-GA] show remarkable stability, comparable to that previously observed only for radicals in biological matrices on in soil organic matter. EPR reveals a bundle-like organization of the GA molecules on [SiO 2-GA] material. The relation of these factors to the enhanced radical stability is discussed.

  5. Optical and EPR spectroscopy studies on haem arginate, a new compound used for treatment of porphyria.

    PubMed

    Sievers, G; Häkli, H; Luhtala, J; Tenhunen, R

    1987-01-01

    A protohaem compound, used for treatment of porphyrias, has been studied to elucidate its state of aggregation. EPR and absorption spectroscopy measurements reveal that 38.3 mM protohaem, dissolved in 40% 1,2-propanediol/10% ethanol/water solution, also containing 153 mM arginine, is partly EPR silent. It exists as high molecular weight aggregates and probably also as mu-oxo-dimers. Dilution in the aqueous alcohol solution dissolves the aggregates first to oligomers and dimers, and finally to monomers (Kdiss = 24 X 10(-6)M). When haem is diluted in 0.9% sodium chloride, a fully monomeric state is not reached even at 1 microM concentration. At 3.5 microM concentration, that used for infusion in patients, the haem is still totally aggregated.

  6. EPR spectroscopy of chlorpromazine-induced free radical formation in normal human melanocytes.

    PubMed

    Otręba, Michał; Zdybel, Magdalena; Pilawa, Barbara; Beberok, Artur; Wrześniok, Dorota; Rok, Jakub; Buszman, Ewa

    2015-07-01

    The purpose of this study was to estimate the effect of chlorpromazine on free radical concentration in HEMn-DP melanocytes using electron paramagnetic resonance (EPR) spectroscopy. It was found that chlorpromazine at concentrations of 1 × 10(-7) and 1 × 10(-6) M contributed to the formation of free radicals (g values ~2) in a dose-dependent manner. The increase in free radical formation was accompanied by an increase in cytotoxicity, as shown by a tetrazolium assay. Homogeneous broadening of EPR lines, slow spin-lattice relaxation processes, and strong dipolar interactions characterized all the tested cellular samples. The performed examination of free radical formation in cells exposed to different chlorpromazine concentrations confirmed the usefulness of electron paramagnetic resonance spectroscopy to determine the effect of a drug on free radical production in a cellular model system in vitro.

  7. Cyanide inhibition of cytochrome c oxidase. A rapid-freeze e.p.r. investigation.

    PubMed Central

    Jensen, P; Wilson, M T; Aasa, R; Malmström, B G

    1984-01-01

    The inhibition of cytochrome c oxidase by cyanide, starting either with the resting or the pulsed enzyme, was studied by rapid-freeze quenching followed by quantitative e.p.r. It is found that a partial reduction of cytochrome oxidase by transfer of 2 electron equivalents from ferrocytochrome c to cytochrome a and CuA will induce a transition from a closed to an open enzyme conformation, rendering the cytochrome a3-CuB site accessible for cyanide binding, possibly as a bridging ligand. A heterogeneity in the enzyme is observed in that an e.p.r. signal from the cytochrome a3 3+-HCN complex is only found in 20% of the molecules, whereas the remaining cyanide-bound a3-CuB sites are e.p.r.-silent. PMID:6098268

  8. EPR investigation on radiation-induced graft copolymerization of styrene onto polyethylene: Energy transfer effects

    NASA Astrophysics Data System (ADS)

    Salih, M. A.; Buttafava, A.; Ravasio, U.; Mariani, M.; Faucitano, A.

    2007-08-01

    In this paper, energy transfer phenomena concerning the in-source graft copolymerization of styrene onto LDPE were investigated through the EPR analysis of the radical intermediates. The model solution experiments have shown a substantial deviation of the experimental G (radicals) values with respect to the additivity law, which reflect the negative effect of the styrene monomer concentration on the initiation rate of the graft copolymerization. The EPR measurements performed on polyethylene- co-styrene graft copolymers of various composition following low-temperature vacuum gamma irradiation have confirmed the decrease of the total radical yields with increasing the styrene concentration. The effect was partly attributed to the heterogeneity of the graft copolymer matrix and to the lack of molecular mobility in the solid state at low temperature, which prevents the attainment of the favourable geometrical configurations in intermolecular energy and charge transfer events.

  9. High precision EPR dosimetry as a reference tool for validation of other techniques.

    PubMed

    Chumak, V V; Sholom, S V; Bakhanova, E V; Pasalskaya, L F; Musijachenko, A V

    2005-02-01

    We present here a particular application area for EPR dosimetry with teeth--use as a source of reference dose values for validation/verification of other retrospective dosimetry techniques and existing dose records. The conditions of application of EPR dosimetry in this role as well as practical design of such studies are shown. Particular attention is given to the requirements to the techniques in terms of precision and throughput, as well as to the issue of availability of samples for analysis and practical solution of this problem. Practical application of this approach is illustrated by several examples of completed validation sub-studies, which were performed in the framework of large-scale post-Chernobyl epidemiological studies.

  10. Deep level defects in sublimation-grown 6H silicon carbide investigated by DLTS and EPR

    NASA Astrophysics Data System (ADS)

    Irmscher, K.; Pintilie, I.; Pintilie, L.; Schulz, D.

    2001-12-01

    6H-SiC bulk single crystals grown by physical vapor transport (PVT) were investigated by deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). One of the observed deep level defects was identified as isolated tungsten on Si sites by EPR. The electron spin of {1}/{2} could be explained by W 5+ (5d 1). This is equivalent to the single positive charge state of a double donor when taking into account the Fermi level position in the n-type samples. The interpretation is also consistent with the DLTS detection of a W related deep level which showed a behavior of the capture of electrons and holes that hints at a double donor. In addition a tantalum related deep level is tentatively discussed. W and Ta were incorporated on electrically active sites in 6H-SiC only in low concentrations (2-4×10 14 cm -3) during crystal growth by PVT.

  11. Electron paramagnetic resonance (EPR) investigations of lichens - 1: effects of air pollution

    NASA Astrophysics Data System (ADS)

    Jezierski, Adam; Bylinska, Ewa; Seaward, Mark R. D.

    Electron paramagnetic resonance (EPR) investigations were carried out on more than 800 samples of lichens from Lower Silesia, southwest Poland. A statistically confirmed correlation between annual average concentration of sulphur dioxide in the atmosphere and concentration of semiquinone radicals in Hypogymnia physodes thalli was found. Similar results were obtained for Umbilicaria species from the Karkonosze Mountains. Distribution of semiquinone radicals in lichen thalli was also investigated. The action of nitrogen dioxide on Umbilicaria species resulted in the synthesis of iminoxy radicals in the thalli. The intensification of the semiquinone free radical production in lichen thalli from atmospherically polluted environments and the degradation of lichen acids to β-diketone compounds would appear to be parallel processes. The properties of the iminoxyls derived from β-diketones in the lichen matrix (anisotropic spectra at room temperature) and in organic solutions after extraction procedure were also examined by EPR.

  12. Solid-state NMR and EPR Spectroscopy of Mn(2+) -Substituted ATP-Fueled Protein Engines.

    PubMed

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

    2017-02-13

    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 Mg(2+) / Mn(2+) substitution and the resulting information contents for two different ATP:Mg(2+) -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.

  13. EPR experiment and 2-photon interferometry: Report of a 2-photon interference experiment

    NASA Technical Reports Server (NTRS)

    Shih, Y. H.; Rubin, M. H.; Sergienko, A. V.

    1992-01-01

    After a very brief review of the historical Einstein, Podolsky, and Rosen (EPR) experiments, a new two-photon interference type EPR experiment is reported. A two-photon state was generated by optical parametric down conversion. Pairs of light quanta with degenerate frequency but divergent directions of propagation were sent to two independent Michelson interferometers. First and second order interference effectors were studied. Different than other reports, we observed that the second order interference visibility vanished when the optical path difference of the interferometers were much less than the coherence length of the pumping laser beam. However, we also observed that the second order interference behaved differently depending on whether the interferometers were set at equal or different optical path differences.

  14. Improving Conventional Enhanced Permeability and Retention (EPR) Effects; What Is the Appropriate Target?

    PubMed Central

    Kobayashi, Hisataka; Watanabe, Rira; Choyke, Peter L.

    2014-01-01

    Nano-sized therapeutic agents have several advantages over low molecular weight agents such as a larger loading capacity, the ability to protect the payload until delivery, more specific targeting due to multivalency and the opportunity for controlled/sustained release. However, the delivery of nano-sized agents into cancer tissue is problematic because it mostly relies on the enhanced permeability and retention (EPR) effect that depends on the leaky nature of the tumor vasculature and the prolonged circulation of nano-sized agents, allowing slow but uneven accumulation in the tumor bed. Delivery of nano-sized agents is dependent on several factors that influence the EPR effect; 1. Regional blood flow to the tumor, 2. Permeability of the tumor vasculature, 3. Structural barriers imposed by perivascular tumor cells and extracellular matrix, 4. Intratumoral pressure. In this review, these factors will be described and methods to enhance nano-agent delivery will be reviewed. PMID:24396516

  15. Analysis of two-player quantum games in an EPR setting using Clifford's geometric algebra.

    PubMed

    Chappell, James M; Iqbal, Azhar; Abbott, Derek

    2012-01-01

    The framework for playing quantum games in an Einstein-Podolsky-Rosen (EPR) type setting is investigated using the mathematical formalism of geometric algebra (GA). The main advantage of this framework is that the players' strategy sets remain identical to the ones in the classical mixed-strategy version of the game, and hence the quantum game becomes a proper extension of the classical game, avoiding a criticism of other quantum game frameworks. We produce a general solution for two-player games, and as examples, we analyze the games of Prisoners' Dilemma and Stag Hunt in the EPR setting. The use of GA allows a quantum-mechanical analysis without the use of complex numbers or the Dirac Bra-ket notation, and hence is more accessible to the non-physicist.

  16. EPR study of gamma irradiated DL-methionine sulfone single crystals

    NASA Astrophysics Data System (ADS)

    Karabulut, Bünyamin; Yıldırım, İlkay

    2015-12-01

    Electron paramagnetic resonance (EPR) study of gamma irradiated dl-2-amino-4-(Methylsulfonyl) butyric acid (dl-methionine sulfone, hereafter dl-ABA) single crystals and powder was performed at room temperature. It has been found that this compound indicates the existence of C. O2- and N. H2 radicals after γ-irradiation. While g and hyperfine splitting values for the N. H2 radical were observed, for the C. O2- radical, only the g factor was measured. The EPR spectra have shown that N. H2 radical has two groups each having two distinct sites and C. O2- radical has one site. The principal g and hyperfine values for all sites were analyzed.

  17. Identification and dose assessment of irradiated cardamom and cloves by EPR spectrometry

    NASA Astrophysics Data System (ADS)

    Beshir, W. B.

    2014-03-01

    The use of electron paramagnetic resonance spectroscopy to accurately distinguish irradiated from unirradiated cardamom and cloves and assesses the absorbed dose to radiation processed cardamom and cloves are examined. The results were successful for identifying both irradiated and unirradiated cardamom and cloves. Additive reirradiation of cardamom and cloves produces reproducible dose-response functions, which can be used to assess the initial dose by back-extrapolation. Third degree polynomial function was used to fit the EPR signal/dose curves. It was found that this 3rd degree polynomial function provides satisfactory results without correction of decay for free radicals. The stability of the radiation induced EPR signal of irradiated cardamom and cloves were studied over a storage period of almost 8 months.

  18. AC susceptibility and EPR investigations of superspin dynamics in magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Price, Alex D.

    In this investigation we use two complementary techniques to distinguish between superparamagnetic blocking (SPB) and superspin-glass (SSG) freezing phenomena in magnetite nanoparticles. While these manifestations of the superspin dynamics are fundamentally different, they have similar "signatures", especially in dc-magnetization experiments. Even if ac-susceptibility measurements are employed, careful use of mathematical models to analyze the data are needed to uncover which type of phenomena (SPB or SSG freezing) occurs within the material. Yet, by utilizing electron paramagnetic resonance (EPR) on a 10 nm Fe3O4 nano-powder as well as on a ferrofluid (based on the same nanoparticle ensemble) we found a very distinct difference in the absorption spectra between the two samples, which indicates markedly different EPR signatures from SPB and SSG freezing behaviors.

  19. Performance of reduced wall EPR insulated medium voltage power cables. Part 2: Mechanical characteristics

    SciTech Connect

    Wen, Y.; Cinquemani, P.L.

    1997-04-01

    For the replacement of paper insulated lead covered cables (PILC) reduced insulation wall designs have been developed. They provide a reliable lower diameter cable design for installation in existing PILC conduits. Representing Part 2 of the investigation, this paper presents the results of mechanical testing conducted on both reduced and full wall EPR insulated cables. Both jacketed and non-jacketed cable designs have been subjected to mechanical pulling forces which greatly exceed recommended industry limitations, followed by electrical testing to ascertain cable performance. The results of this study conclude that reduced wall EPR insulated cables can safely withstand the same pulling forces as recommended for conventional walls and can be designed for installation under the same pulling limitations.

  20. EPR and optical absorption studies on Gd 3+ ions in ammonium hydrogen malonate single crystals

    NASA Astrophysics Data System (ADS)

    Kripal, Ram; Mishra, Indrajeet

    2010-01-01

    X-Band electron paramagnetic resonance (EPR) studies of Gd 3+ ions in ammonium hydrogen malonate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of four physically equivalent but magnetically inequivalent sites. The zero-field splitting parameters and g factor are determined. The Gd 3+ ion is in 8S state; its levels are split by the action of the crystalline electric field of monoclinic symmetry. The optical absorption spectra of Gd 3+ ions in single crystals of ammonium hydrogen malonate are also recorded at room temperature. The energy levels of the 4f 7 configuration are calculated and compared with those observed experimentally. The values of E1=5854±11, E2=31±0.36, E3=592±3.3 and ζ 4f=1595±25 cm -1 are found to give the best over-all agreement between experimentally observed and calculated levels.

  1. EPR spectroscopy solutions for assessment of decellularization of intrathoracic organs and tissues.

    PubMed

    Gubareva, E A; Kuevda, E V; Dzhimak, S S; Basov, A A; Sotnichenko, A S; Bolotin, S N; Gilevich, I V; Gumenyuk, I S; Macchiarini, P

    2016-03-01

    Using EPR spectroscopy it was established that the determination of the concentration of paramagnetic centers in lyophilized tissues allows indirect evaluation of the quality of decellularization of intrathoracic organs (diaphragm, heart, and lungs), since the content of paramagnetic particles in them can serve as a criterion of cell viability and points to the necessity to repeat decellularization. Experiments in rats showed that the EPR spectra of the native thoracic organs contained paramagnetic centers with g-factor values ranging from 2.007 to 2.011 at a concentration of 10(-8) to 6.62 × 10(-7) mol/g of lyophilized tissue, whereas in all decellularized tissues of the same organs paramagnetic particles were not detected.

  2. Manifestation of the Hanle effect in submillimeter EPR spectroscopy of thulium impurity ions in synthetic forsterite

    NASA Astrophysics Data System (ADS)

    Tarasov, V. F.; Solovarov, N. K.; Zharikov, E. V.

    2016-10-01

    A signal related to the spin level crossing in a zero magnetic field—the Hanle effect—has been registered for the first time in the EPR spectrum. It has been shown that, in the general case, the shape of the signal is determined by two qualitatively different mechanisms: (i) the interference of unsteady-state contributions to the dynamics of atomic coherences (electric or magnetic quantum transition moments with certain phases) with close frequencies ("beats at a zero frequency") and (ii) the summation of resonant signals determined by the steady-state dynamics of the same atomic coherences. The relaxation time of spin coherences has been determined for the EPR transition of Tm3+ ions in synthetic forsterite.

  3. Investigation of signal fading in lithium formate EPR dosimeters using a new sensitive method

    NASA Astrophysics Data System (ADS)

    Adolfsson, Emelie; Karlsson, Mattias; Alm Carlsson, Gudrun; Carlsson Tedgren, Åsa; Lund, Eva; Olsson, Sara; Gustafsson, Håkan

    2012-04-01

    The aim of this study was to investigate signal fading in lithium formate electron paramagnetic resonance (EPR) dosimeters used for clinical applications in radiotherapy. A new experimental method for determination of signal fading, designed to resolve small changes in signal from slowly decaying unstable radicals, was used. Possible signal fading in lithium formate due to different storage temperatures was also tested. Air humidity was kept at a constant level of 33% throughout the experiments. The conclusion drawn from the investigations was that the EPR signal from lithium formate is stable during at least 1 month after irradiation and is not sensitive to variations in storage temperature <40 °C when kept at a relative air humidity of 33%. This makes lithium formate a suitable dosimeter for transfer dosimetry in clinical audits.

  4. Theoretical investigation of the optical and EPR parameters for VO 2+ion in some complexes

    NASA Astrophysics Data System (ADS)

    Kalfaoğlu, Emel; Karabulut, Bünyamin

    2012-04-01

    The molecular orbital coefficients and the EPR parameters of trisodium citrate dihydrate, sodium hydrogen oxalate monohydrate, potassium d-gluconate monohydrate and L-Alanine vanadyl complexes are calculated theoretically. Two d-d transition spectra and EPR parameters for the VO2+ complex are calculated theoretically by using crystal-field theory. The calculated g and A paramaters have indicated that paramagnetic center is axially symmetric. Having the relations of g∥A⊥ for VO2+ ions, it can be concluded that VO2+ ions are located in distorted octahedral sites (C4v) elongated along the z-axis and the ground state of the paramagnetic electron is dxy.

  5. EPR Study of Vanadium Ion in Zinc-Boro-Vanadate Glasses

    SciTech Connect

    Renuka, C.; Gowda, V. C. Veeranna; Chakradhar, R. P. S.; Reddy, C. Narayana

    2011-07-15

    This paper describes EPR studies on x V{sub 2}O{sub 5}-(40-x)ZnO-60B{sub 2}O{sub 3}(where x 5, 10, 15 and 20 mol %) glass system. These studies indicate a strong compositional dependent trend and existence of characteristic boro-vanadate groups in these glasses. The EPR spectra show a distinct hyperfine structure of {sup 51}V. Spectral analysis shows that the vanadium is present in the glass as vanadyl ion [VO]{sup 2+} at tetragonally distorted octahedral site. The decrease of A{sub ||} and A{sub perpendicular} with increase of V{sub 2}O{sub 5} concentration suggests an increase in the covalence between the central atom and the surrounding oxygen ligands.

  6. Influence of Pb(II) Ions on the EPR Properties of the Semiquinone Radicals of Humic Acids and Model Compounds: High Field EPR and Relativistic DFT Studies

    NASA Astrophysics Data System (ADS)

    Witwicki, Maciej; Jerzykiewicz, Maria; Jaszewski, Adrian R.; Jezierska, Julia; Ozarowski, Andrzej

    2009-11-01

    X-band (9.76 GHz) and high field (416.00 GHz) electron paramagnetic resonance spectroscopy (EPR) was used to study the interactions between Pb(II) ions and semiquinone radicals of natural humic acids and their simple models. The EPR experiments were performed on powder samples. The formation of Pb(II) complexes with the radicals was accompanied by a significant decrease of g parameters as compared to those observed for parent radicals. Two types of complexes were identified depending on the initial concentration of Pb(II) ions. For one of them the anisotropic hyperfine coupling with the 207Pb nucleus was observed. Systematic DFT calculations were carried out for complexes with different forms of radical ligands (L2-•, HL-•, and H2L•) derived from 3,4-dihydroxybenzoic acid representing different ligation schemes. The g parameters calculated for the structure characterized by a significant accumulation of spin density on the Pb atom are strongly deviated from the values observed experimentally. Moreover, a decrease of the spin population on all oxygen atoms as a result of complexation of Pb(II) via carboxyl oxygens and protonation of hydroxyl oxygens is required to reproduce the experimental g parameters.

  7. Emergency Preservation and Resuscitation for Cardiac Arrest from Trauma (EPR-CAT)

    DTIC Science & Technology

    2013-10-01

    hypothermia 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON USAMRMC a. REPORT...Emergency Preservation and Resuscitation (EPR) was developed to rapidly preserve the organism during ischemia, using hypothermia , drugs, and fluids, to “buy...time” for transport and resuscitative surgery. The purpose of this study is to test the feasibility of rapidly inducing profound hypothermia

  8. Managing integration work in an NHS electronic patient record (EPR) project.

    PubMed

    Martin, David; Mariani, John; Rouncefield, Mark

    2007-03-01

    This article uses an ethnographic study of the design and deployment of an electronic patient record (EPR) system in the UK NHS to document some of the difficulties of integrating new IT systems with existing and developing practices, technologies and regulatory requirements. It highlights that 'integration' in this situation produces a variety of different but connected and potentially competing requirements that create difficulties in achieving artful and successful system deployment.

  9. Antiviral properties against HIV of water soluble copper carbosilane dendrimers and their EPR characterization.

    PubMed

    Galan, M; Sanchez-Rodriguez, J; Cangiotti, M; Garcia-Gallego, S; Jimenez, J L; Gomez, R; Ottaviani, M F; Munoz-Fernandez, M A; de la Mata, F J

    2012-01-01

    We describe here the use of anionic carbosilane dendrimers to obtain new copper complexes. UV-Vis and a computer aided analysis of the EPR spectra provided information about the coordination modes of copper depending on the nature of the dendrimer and about the geometry and structure of the complexes in solution. Some of these metallo-dendrimers have been tested "in vitro" as antiviral compounds in the inhibition of HIV infection in pre and post-infection treatment.

  10. [Documentation of electronic patient records (EPRS) in German general practices: a telephone survey].

    PubMed

    Heidenreich, Regine; Himmel, Wolfgang; Böckmann, Harro; Hummers-Pradier, Eva; Kochen, Michael M; Niebling, Wilhelm; Rogausch, Anja; Sigle, Jörg; Wetzel, Dirk; Scheidt-Nave, Christa

    2005-01-01

    In Germany, use and contents of EPRs are largely unknown and expected to be highly variable, due to missing standards. We conducted a telephone survey to describe and compare computer documentation habits in general practices. Specifically, we were interested in: (1) the type of medical data recorded; and (2) which factors influence the extent to which doctors used the EPR while seeing their patients. The sampling frame consisted of family physicians participating in a general practice research project: 32% (145/452) of family physicians in the district of Göttingen, Lower Saxony, and 63% (52/83) of physicians from a quality assurance network of family practices in the district of Freiburg, Baden-Württemberg. With the exception of two practices in Göttingen, all practices (n = 165 of 167) took part in this survey. Diagnoses, digital codes for service fees, and prescriptions were computerized in nearly all practices, although doctors were significantly more involved in Freiburg than in Göttingen. Clinical symptoms and findings were recorded in 80% of Freiburg and 52% of Göttingen practices (p = 0.008). Overall, in 74% of Freiburg and 51% of Göttingen practices, the physicians opened the EPR while seeing patients (p = 0.022). Nearly half of the Göttingen practices (49%) and 24% of the Freiburg practices (p < 0.05) entered digital codes for service fees and diagnoses on paper before entering them electronically. In multivariate models adjusting for sex, target group and training specialty, internet access in the office was independently predictive of 'EPR-activity' (OR: 2.23; 95%-confidence interval: 1.12-4.43). There seems to be room for improvement in terms of degree and intensity of recording of clinically-relevant data. Technical interest, i.e., internet access in the office, seems to enhance electronic documentation activities.

  11. EPR and ENDOR studies of Fe(II) hemoproteins reduced and oxidized at 77 K.

    PubMed

    Davydov, Roman; Hoffman, Brian M

    2008-03-01

    gamma-irradiation of frozen solutions of Fe(II) hemoproteins at 77 K generates both electron paramagnetic resonance (EPR) active singly reduced and oxidized heme centers trapped in the conformation of the Fe(II) precursors. The reduction products of pentacoordinate (S = 2) Fe(II) globins, peroxidases and cytochrome P450cam show EPR and electron-nuclear double resonance (ENDOR) spectra characteristic of (3d 7) Fe(I) species. In addition, cryoreduced Fe(II) alpha-chains of hemoglobin and myoglobin exhibit an S = 3/2 spin state produced by antiferromagnetic coupling between a porphyrin anion radical and pentacoordinate (S = 2) Fe(II). The spectra of cryoreduced forms of Fe(II) hemoglobin alpha-chains and deoxymyoglobin reveal that the Fe(II) precursors adopt multiple conformational substates. Reduction of hexacoordinate Fe(II) cytochrome c and cytochrome b5 as well as carboxy complexes of deoxyglobins produces only Fe(II) porphyrin pi-anion radical species. The low-valent hemoprotein intermediates produced by cryoreduction convert to the Fe(II) states at T > 200 K. Cryogenerated Fe(III) cytochrome c and cytochrome b5 have spectra similar to these for the resting Fe(III) states, whereas the spectra of the products of cryooxidation of pentacoordinate Fe(II) globins and peroxidases are different. Cryooxidation of CO-Fe(II) globins generates Fe(III) hemes with quantum-mechanically admixed S = 3/2, 5/2 ground states. The trapped Fe(III) species relax to the equilibrium ferric states upon annealing at T > 190 K. Both cryooxidized and reduced centers provide very sensitive EPR/ENDOR structure probes of the EPR-silent Fe(II) state.

  12. Ionizable Nitroxides for Studying Local Electrostatic Properties of Lipid Bilayers and Protein Systems by EPR

    PubMed Central

    Voinov, Maxim A.; Smirnov, Alex I.

    2016-01-01

    Electrostatic interactions are known to play one of the major roles in the myriad of biochemical and biophysical processes. In this Chapter we describe biophysical methods to probe local electrostatic potentials of proteins and lipid bilayer systems that is based on an observation of reversible protonation of nitroxides by EPR. Two types of the electrostatic probes are discussed. The first one includes methanethiosulfonate derivatives of protonatable nitroxides that could be used for highly specific covalent modification of the cysteine’s sulfhydryl groups. Such spin labels are very similar in magnetic parameters and chemical properties to conventional MTSL making them suitable for studying local electrostatic properties of protein-lipid interfaces. The second type of EPR probes is designed as spin-labeled phospholipids having a protonatable nitroxide tethered to the polar head group. The probes of both types report on their ionization state through changes in magnetic parameters and a degree of rotational averaging, thus, allowing one to determine the electrostatic contribution to the interfacial pKa of the nitroxide, and, therefore, determining the local electrostatic potential. Due to their small molecular volume these probes cause a minimal perturbation to the protein or lipid system while covalent attachment secure the position of the reporter nitroxides. Experimental procedures to characterize and calibrate these probes by EPR and also the methods to analyze the EPR spectra by least-squares simulations are also outlined. The ionizable nitroxide labels and the nitroxide-labeled phospholipids described so far cover an exceptionally wide pH range from ca. 2.5 to 7.0 pH units making them suitable to study a broad range of biophysical phenomena especially at the negatively charged lipid bilayer surfaces. The rationale for selecting proper electrostatically neutral interface for calibrating such probes and example of studying surface potential of lipid bilayer is

  13. EPR study of a vinyl-type radical in X-irradiated. beta. -carotene

    SciTech Connect

    Joseph, J.; Samskog, P.O.; Lee, S.H.; Kispert, L.D.

    1985-05-09

    A vinyl-type radical with proton EPR couplings of 68 and 72 G has been observed at -40/sup 0/C as a secondary radical formed when a sample of trans-..beta..-carotene powder is X-ray irradiated at 77 K in the dark and warmed. An INDO/CI calculation suggests that it is due to the loss of a proton from the 15 or 15' position. 22 references, 3 tables.

  14. Effects of Ammonium Dinitramide in Human Liver Slices: An EPR/Spin Trapping Study.

    DTIC Science & Technology

    1995-09-01

    dessicator at ambient temperature protected from light until analyzed. It was very important to keep the samples dry because moisture increases molecular...free radicals such as Superoxide , (02~). The control samples were viable for the period of the study but the ADN treated samples were oxidized by... Superoxide produces tributylstannyl superoxo radicals proposed initiateors of lipid peroxidation: An EPR model system Chem Res. Toxicol. 5: 698 Steel

  15. EPR Studies of Cu2+ in dl-Aspartic Acid Single Crystals

    NASA Astrophysics Data System (ADS)

    Karabulut, B.; Tapramaz, R.; Bulut, A.

    1999-04-01

    EPR studies of Cu2+ doped dl-Aspartic Acid [NH2CH(CH2COOH)COO] powder and single crystal have been carried out at 113 and 300 K. The principal hyperfine and g values, covalancy parameter, mixing coefficients and Fermi-contact term of the complex were obtained, and the ground-state wavefuntion of the Cu2+ ion in the lattice has been constructed.

  16. Increasing sensitivity of pulse EPR experiments using echo train detection schemes.

    PubMed

    Mentink-Vigier, F; Collauto, A; Feintuch, A; Kaminker, I; Tarle, V; Goldfarb, D

    2013-11-01

    Modern pulse EPR experiments are routinely used to study the structural features of paramagnetic centers. They are usually performed at low temperatures, where relaxation times are long and polarization is high, to achieve a sufficient Signal/Noise Ratio (SNR). However, when working with samples whose amount and/or concentration are limited, sensitivity becomes an issue and therefore measurements may require a significant accumulation time, up to 12h or more. As the detection scheme of practically all pulse EPR sequences is based on the integration of a spin echo--either primary, stimulated or refocused--a considerable increase in SNR can be obtained by replacing the single echo detection scheme by a train of echoes. All these echoes, generated by Carr-Purcell type sequences, are integrated and summed together to improve the SNR. This scheme is commonly used in NMR and here we demonstrate its applicability to a number of frequently used pulse EPR experiments: Echo-Detected EPR, Davies and Mims ENDOR (Electron-Nuclear Double Resonance), DEER (Electron-Electron Double Resonance|) and EDNMR (Electron-Electron Double Resonance (ELDOR)-Detected NMR), which were combined with a Carr-Purcell-Meiboom-Gill (CPMG) type detection scheme at W-band. By collecting the transient signal and integrating a number of refocused echoes, this detection scheme yielded a 1.6-5 folds SNR improvement, depending on the paramagnetic center and the pulse sequence applied. This improvement is achieved while keeping the experimental time constant and it does not introduce signal distortion.

  17. Applications of in vivo electron paramagnetic resonance (EPR) spectroscopy: measurements of pO2 and NO in endotoxin shock.

    PubMed

    Jackson, S K; Madhani, M; Thomas, M; Timmins, G S; James, P E

    2001-03-31

    Recent developments of EPR instrumentation that allow the use of large tissue samples or whole animals and the ability to image spatially resolved EPR signals has led to novel applications of EPR spectroscopy in vivo. Utilising a 1 GHz EPR spectrometer with a 3.4-cm birdcage resonator, it was possible to detect and measure nitric oxide and oxygen in the livers of mice with lipopolysaccharide (LPS)-induced septic shock. Nitric oxide was detected as the nitric oxide (NO) complex of Fe-diethyldithiocarbamic acid (Fe-DETC) while pO2 was measured from the EPR linewidth of the oxygen-sensitive coal material 'gloxy'. LPS treatment stimulated the production of nitric oxide in the liver and the general circulation and the oxygenation of liver tissue was decreased. Selective placement of the EPR probes allowed images of nitric oxide and oxygen to be obtained in the liver. The spectral and spatial information obtained with this technique will allow improved understanding of the pathophysiology of such diseases.

  18. Scope and limitations of the TEMPO/EPR method for singlet oxygen detection: the misleading role of electron transfer.

    PubMed

    Nardi, Giacomo; Manet, Ilse; Monti, Sandra; Miranda, Miguel A; Lhiaubet-Vallet, Virginie

    2014-12-01

    For many biological and biomedical studies, it is essential to detect the production of (1)O2 and quantify its production yield. Among the available methods, detection of the characteristic 1270-nm phosphorescence of singlet oxygen by time-resolved near-infrared (TRNIR) emission constitutes the most direct and unambiguous approach. An alternative indirect method is electron paramagnetic resonance (EPR) in combination with a singlet oxygen probe. This is based on the detection of the TEMPO free radical formed after oxidation of TEMP (2,2,6,6-tetramethylpiperidine) by singlet oxygen. Although the TEMPO/EPR method has been widely employed, it can produce misleading data. This is demonstrated by the present study, in which the quantum yields of singlet oxygen formation obtained by TRNIR emission and by the TEMPO/EPR method are compared for a set of well-known photosensitizers. The results reveal that the TEMPO/EPR method leads to significant overestimation of singlet oxygen yield when the singlet or triplet excited state of the photosensitizer is efficiently quenched by TEMP, acting as electron donor. In such case, generation of the TEMP(+) radical cation, followed by deprotonation and reaction with molecular oxygen, gives rise to an EPR-detectable TEMPO signal that is not associated with singlet oxygen production. This knowledge is essential for an appropriate and error-free application of the TEMPO/EPR method in chemical, biological, and medical studies.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  20. Entanglement conservation, ER=EPR, and a new classical area theorem for wormholes

    NASA Astrophysics Data System (ADS)

    Remmen, Grant N.; Bao, Ning; Pollack, Jason

    2016-07-01

    We consider the question of entanglement conservation in the context of the ER=EPR correspondence equating quantum entanglement with wormholes. In quantum mechanics, the entanglement between a system and its complement is conserved under unitary operations that act independently on each; ER=EPR suggests that an analogous statement should hold for wormholes. We accordingly prove a new area theorem in general relativity: for a collection of dynamical wormholes and black holes in a spacetime satisfying the null curvature condition, the maximin area for a subset of the horizons (giving the largest area attained by the minimal cross section of the multi-wormhole throat separating the subset from its complement) is invariant under classical time evolution along the outermost apparent horizons. The evolution can be completely general, including horizon mergers and the addition of classical matter satisfying the null energy condition. This theorem is the gravitational dual of entanglement conservation and thus constitutes an explicit characterization of the ER=EPR duality in the classical limit.

  1. EPR and impedance spectroscopic investigations on lithium bismuth borate glasses containing nickel and vanadium ions

    NASA Astrophysics Data System (ADS)

    Yadav, Arti; Khasa, Satish; Hooda, Ashima; Dahiya, Manjeet S.; Agarwal, Ashish; Chand, Prem

    2016-03-01

    Glasses having composition 7NiO • 23Li2O • 20Bi2O3 • 50B2O3, 7V2O5 • 23Li2O • 20Bi2O3 • 50B2O3 and x(2NiO • V2O5) • (30 - x)Li2O • 50B2O3 • 20Bi2O3 (with x = 0, 2, 5, 7 & 10 mol%) prepared through melt-quench route are explored by analyzing density, impedance spectroscopy and electron paramagnetic resonance (EPR). It is found that both density and molar volume increase with an increase in substitution of 2NiO • V2O5 in the base glass matrix. Different dielectric parameters viz. dielectric loss (ε), electrical modulus (M), loss tangent (tanδ) etc. are evaluated and their variations with frequency and temperature are analyzed which reveals that these glasses exhibit a non-Debye relaxation behavior. A phenomenal description of the capacitive behavior is obtained by considering the circuitry as a parallel combination of bulk resistance (Rb) and constant phase element (CPE). The conduction mechanism is found to follow Quantum Mechanical Tunneling (QMT) model. Spin Hamiltonian Parameters (SHPs) and covalency rates are calculated from the EPR spectra of vanadyl ion. The observed EPR spectra confirmed that V4 + ion exists as vanadyl ion in the octahedral coordination with tetragonal compression.

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

    SciTech Connect

    Andrews, J.C. |

    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.

  3. Aging predictions in nuclear power plants: Crosslinked polyolefin and EPR cable insulation materials

    SciTech Connect

    Gillen, K.T.; Clough, R.L.

    1991-06-01

    In two earlier reports, we derived a time-temperature-dose rate superposition methodology, which, when applicable, can be used to predict cable degradation versus dose rate, temperature and exposure time. This methodology results in long-term predictive capabilities at the low dose rates appropriate to ambient nuclear power plant aging environments. The methodology was successfully applied to numerous important cable materials used in nuclear applications and the extrapolated predictions were verified by comparisons with long-term (7 to 12 year) results for similar or identical materials aged in nuclear environments. In this report, we test the methodology on three crosslinked polyolefin (CLPO) and two ethylene propylene rubber (EPR) cable insulation materials. The methodology applies to one of the CLPO materials and one of the EPR materials, allowing predictions to be made for these materials under low dose-rate, low temperature conditions. For the other materials, it is determined that, at low temperatures, a decrease in temperature at a constant radiation dose rate leads to an increase in the degradation rate for the mechanical properties. Since these results contradict the fundamental assumption underlying time-temperature-dose rate superposition, this methodology cannot be applied to such data. As indicated in the earlier reports, such anomalous results might be expected when attempting to model data taken across the crystalline melting region of semicrystalline materials. Nonetheless, the existing experimental evidence suggests that these CLPO and EPR materials have substantial aging endurance for typical reactor conditions. 28 refs., 26 figs., 3 tabs.

  4. Accelerated cable life testing of EPR-insulated medium voltage distribution cables

    SciTech Connect

    Walton, M.D. ); Bernstein, B.S. ); Smith, J.T. III ); Thue, W.A. , Stuart, FL ); Groeger, J.H. )

    1994-07-01

    This paper presents results aimed at developing a reliable accelerated aging tank test for EPR-insulated cables. Aging was performed at 2 to 4 times rated voltage on load cycling to temperatures of 45 C, 60 C, 75 C, and 90 C at the conductor with water in the conductor strands and outside the cable. Results show that cable failure is more rapid at the highest electrical stress and lowest conductor load cycle temperature. Cables aged at higher temperatures and various levels of electrical stress rarely failed and retained in excess of 40% of their original breakdown strength after 1,500+ days of aging. Aging performed at 90 C load cycle temperature and 4 times rated voltage with air on the outside and water at the conductor of the cable showed more rapid loss of life than with water outside. Results indicate the optimum aging conditions for EPR-insulated cables in the accelerated cable life test (ACLT) differ significantly from those previously observed for XLPE-insulated cables, and that the appropriate test methodology for EPR-insulated cables requires additional study.

  5. Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries. Two sample holders have been commissioned and built by polytetrafluoroethylene (PTFE) extrusion techniques: a 1 mm O.D. capillary with a septum down the middle, named DoubleDee, and a 3.5 mm O.D. star shaped sample holder, named AquaStar. Simulations and experimental results at X-band show that the EPR signal intensity increases by factors of 1.43 and 3.87 in the DoubleDee and AquaStar respectively, over the current TPX 0.9 mm O.D. sample tube in a two-loop-one-gap LGR. Finally, combining the insight gained from the constructed sample holders and finite-element solutions, a third multi-lumen sample holder for a cylindrical TE011 cavity is optimized, named AquaSun, where simulations show an EPR signal intensity increase by a factor of 8.2 over a standard 1 mm capillary.

  6. An EPR Study on VO2+ and Mn2+ Ions in Some Zeolites

    NASA Astrophysics Data System (ADS)

    Ucun, F.; Köksal, F.

    1996-02-01

    The electron paramagnetic resonance (EPR) of hydrated VOSO4 ·3H2O and MnCl2 · 2H2O, adsorbed on the synthetic zeolites 3A, 4A, 5A and 13X of pore diameters 0.3, 0.4, 0.5, and 1.0 nm, respectively, and the natural zeolites heulandite and clinoptilolite was investigated. The spectra indicated that the coordination structures are VO(H2O)52+ and Mn(H2O)62+ , and that their EPR line widths vary with the pore diameters and the surface areas of the zeolites. The spectra of VO(H2O)52+ in natural zeolites at room temperature display an isotropic behavior and therefore indicate that the water ligands are mobile. The EPR spin Hamiltonian parameters, the molecule orbital constant ß2*2 , and the Fermi contact term Keff were determined and are discussed. The spectra of Mn(H2O)62+ for narrow-pore zeolites indicate the existence of mobile and immobile water, whereas for wide-pore and natural zeolites they indicated the existence of only mobile water. The obtained Mn(H2O)62+ spectra are discussed.

  7. EPR study of Cu(2+) ion doped orotato(nicotinamid)cobalt(II) single crystal.

    PubMed

    Yıldırım, I; Karabulut, B; Büyükgüngör, O

    2016-01-05

    We have studied the Cu(2+) ion doped orotato(nicotinamid)cobalt(II) complex by using EPR spectroscopy and X-ray diffraction. The single crystal is triclinic with the space group P1‾. The unit cell dimensions of the crystal are a=7.2785(4)Å, b=10.2349(5)Å, c=12.7372(6)Å, α=69.297(4)°, β=74.791(4)° and γ=76.995(4)°, with Z=2. We analyzed the EPR spectra of both single crystal and powder of the complex at room temperature. EPR analysis indicates the presence of only one Cu(2+) site. We obtained the spin Hamiltonian parameters from the single crystal data for the complex. The spin Hamiltonian parameters are gx=2.032, gy=2.116, gz=2.319, Ax=28G, Ay=66G, Az=126G. These data indicate that the symmetry of paramagnetic center is rhombic. We constructed the ground state wave function of the Cu(2+) ion.

  8. Radiation-induced defects in strontium carbonate rod for EPR dosimetry applications

    NASA Astrophysics Data System (ADS)

    Rushdi, M. A. H.; Abdel-Fattah, A. A.; Soliman, Y. S.

    2017-02-01

    The radiation-induced defects in strontium carbonate (SrCO3) rod dosimeter in the dose range of 2.5 Gy-25 kGy was investigated using electron paramagnetic resonance (EPR) technique. The EPR spectra of γ-irradiated strontium carbonate (SC) rods exhibit a strong EPR signal with the spectroscopic splitting g-factor 2.008 and a weak signal at g-factor 2.003. This signal increases with increasing irradiation dose. The dose-response function has a good linearity in the low dose range of 2.5-500 Gy and slight sub-linearity in the high dose range of 0.5-25 kGy. The dosimeter is nearly humidity independent in the level of 33-77% relative humidity during irradiation. The temperature coefficient of the dose-response function is 0.22% per °C in the temperature range of 20-40 °C. The rod dosimeter exhibits a maximum deviation from water equivalency by 7% in the energy range of 0.3-5 MeV. The overall uncertainty of dose determination using SC dosimeter is 5.2% and 4.54% (2σ) for low and high dose range, respectively.

  9. UV effects in tooth enamel and their possible application in EPR dosimetry with front teeth.

    PubMed

    Sholom, S; Desrosiers, M; Chumak, V; Luckyanov, N; Simon, S L; Bouville, A

    2010-02-01

    The effects of ultraviolet (UV) radiation on ionizing radiation biodosimetry were studied in human tooth enamel samples using the technique of electron paramagnetic resonance (EPR) in X-band. For samples in the form of grains, UV-specific EPR spectra were spectrally distinct from those produced by exposure to gamma radiation. From larger enamel samples, the UV penetration depth was determined to be in the 60-120 mum range. The difference in EPR spectra from UV exposure and from exposure to gamma radiation samples was found to be a useful marker of UV equivalent dose (defined as the apparent contribution to the gamma dose in mGy that results from UV radiation absorption) in tooth enamel. This concept was preliminarily tested on front teeth from inhabitants of the region of the Semipalatinsk Nuclear Test Site (Kazakhstan) who might have received some exposure to gamma radiation from the nuclear tests conducted there as well as from normal UV radiation in sunlight. The technique developed here to quantify and subtract the UV contribution to the measured tooth is currently limited to cumulative dose measurements with a component of UV equivalent dose equal to or greater than 300 mGy.

  10. Tetrachloridocuprates(II)—Synthesis and Electron Paramagnetic Resonance (EPR) Spectroscopy

    PubMed Central

    Winter, Alette; Zabel, André; Strauch, Peter

    2012-01-01

    Ionic liquids (ILs) on the basis of metal containing anions and/or cations are of interest for a variety of technical applications e.g., synthesis of particles, magnetic or thermochromic materials. We present the synthesis and the results of electron paramagnetic resonance (EPR) spectroscopic analyses of a series of some new potential ionic liquids based on tetrachloridocuprates(II), [CuCl4]2−, with different sterically demanding cations: hexadecyltrimethylammonium 1, tetradecyltrimethylammonium 2, tetrabutylammonium 3 and benzyltriethylammonium 4. The cations in the new compounds were used to achieve a reasonable separation of the paramagnetic Cu(II) ions for EPR spectroscopy. The EPR hyperfine structure was not resolved. This is due to the exchange broadening, resulting from still incomplete separation of the paramagnetic Cu(II) centers. Nevertheless, the principal values of the electron Zeemann tensor (g║ and g┴) of the complexes could be determined. Even though the solid substances show slightly different colors, the UV/Vis spectra are nearly identical, indicating structural changes of the tetrachloridocuprate moieties between solid state and solution. The complexes have a promising potential e.g., as high temperature ionic liquids, as precursors for the formation of copper chloride particles or as catalytic paramagnetic ionic liquids. PMID:22408411

  11. EPR and AM1 study of the structure of the radical anion of {beta}-ionone

    SciTech Connect

    Kruppa, A.I. Leshina, T.V.; Konovalov, V.V.; Kispert, L.D.

    1999-03-11

    The structure of the radical anion of {beta}-ionone has been investigated by EPR and AM1 molecular modeling methods as a part of a study to determine the structure and magnetic properties of intermediates of one-electron transfer reactions of carotenoids. Analysis of the temperature dependence of the EPR spectrum of the radical anion shows that the largest hyperfine coupling of 16 G previously assigned to the 7-H proton should be assigned to the 4-H proton in the axial orientation. The previous assignment failed to account for rate of the cyclohexene ring inversion. Comparing the resolved EPR spectra at various temperatures indicates that the coupling of 7-H proton equals {approx}9.5 G. The structure of the radical anion predicted by AM1 molecular modeling is in agreement with this analysis. From the temperature dependence the rate of the cyclohexene ring inversion in the radical anion at room temperatures is approximately 6 {times} 10{sup 7} s{sup {minus}1} with an activation energy of about 7 kcal/mol.

  12. Are entangled particles connected by wormholes? Evidence for the ER =EPR conjecture from entropy inequalities

    NASA Astrophysics Data System (ADS)

    Gharibyan, Hrant; Penna, Robert F.

    2014-03-01

    If spacetime is built out of quantum bits, does the shape of space depend on how the bits are entangled? The ER =EPR conjecture relates the entanglement entropy of a collection of black holes to the cross sectional area of Einstein-Rosen (ER) bridges (or wormholes) connecting them. We show that the geometrical entropy of classical ER bridges satisfies the subadditivity, triangle, strong subadditivity, and Cadney-Linden-Winter inequalities. These are nontrivial properties of entanglement entropy, so this is evidence for ER =EPR. We further show that the entanglement entropy associated with classical ER bridges has nonpositive tripartite information. This is not a property of entanglement entropy, in general. For example, the entangled four qubit pure state |GHZ4⟩=(|0000⟩+|1111⟩)/√2 has positive tripartite information, so this state cannot be described by a classical ER bridge. Large black holes with massive amounts of entanglement between them can fail to have a classical ER bridge if they are built out of |GHZ4⟩ states. States with nonpositive tripartite information are called monogamous. We conclude that classical ER bridges require monogamous EPR correlations.

  13. Entanglement conservation, ER=EPR, and a new classical area theorem for wormholes

    DOE PAGES

    Remmen, Grant N.; Bao, Ning; Pollack, Jason

    2016-07-11

    We consider the question of entanglement conservation in the context of the ER=EPR correspondence equating quantum entanglement with wormholes. In quantum mechanics, the entanglement between a system and its complement is conserved under unitary operations that act independently on each; ER=EPR suggests that an analogous statement should hold for wormholes. We accordingly prove a new area theorem in general relativity: for a collection of dynamical wormholes and black holes in a spacetime satisfying the null curvature condition, the maximin area for a subset of the horizons (giving the largest area attained by the minimal cross section of the multi-wormhole throatmore » separating the subset from its complement) is invariant under classical time evolution along the outermost apparent horizons. The evolution can be completely general, including horizon mergers and the addition of classical matter satisfying the null energy condition. In conclusion, this theorem is the gravitational dual of entanglement conservation and thus constitutes an explicit characterization of the ER=EPR duality in the classical limit.« less

  14. Entanglement conservation, ER=EPR, and a new classical area theorem for wormholes

    SciTech Connect

    Remmen, Grant N.; Bao, Ning; Pollack, Jason

    2016-07-11

    We consider the question of entanglement conservation in the context of the ER=EPR correspondence equating quantum entanglement with wormholes. In quantum mechanics, the entanglement between a system and its complement is conserved under unitary operations that act independently on each; ER=EPR suggests that an analogous statement should hold for wormholes. We accordingly prove a new area theorem in general relativity: for a collection of dynamical wormholes and black holes in a spacetime satisfying the null curvature condition, the maximin area for a subset of the horizons (giving the largest area attained by the minimal cross section of the multi-wormhole throat separating the subset from its complement) is invariant under classical time evolution along the outermost apparent horizons. The evolution can be completely general, including horizon mergers and the addition of classical matter satisfying the null energy condition. In conclusion, this theorem is the gravitational dual of entanglement conservation and thus constitutes an explicit characterization of the ER=EPR duality in the classical limit.

  15. UV EFFECTS IN TOOTH ENAMEL AND THEIR POSSIBLE APPLICATION IN EPR DOSIMETRY WITH FRONT TEETH

    PubMed Central

    Sholom, S.; Desrosiers, M.; Chumak, V.; Luckyanov, N.; Simon, S.L.; Bouville, A.

    2009-01-01

    The effects of ultraviolet (UV) radiation on ionizing radiation biodosimetry were studied in human tooth enamel samples using the technique of electron paramagnetic resonance (EPR) in X-band. For samples in the form of grains, UV-specific EPR spectra were spectrally distinct from that produced by exposure to gamma radiation. From larger enamel samples, the UV penetration depth was determined to be in the 60–120 μm range. The difference in EPR spectra from UV exposure and from exposure to gamma radiation samples was found to be a useful marker of UV equivalent dose (defined as the apparent contribution to the gamma dose in mGy that results from UV radiation absorption) in tooth enamel. This concept was preliminarily tested on front teeth from inhabitants of the region of the Semipalatinsk Nuclear Test Site (Kazakhstan) who might have received some exposure to gamma radiation from the nuclear tests conducted there as well as from normal UV radiation in sunlight. The technique developed here to quantify and subtract the UV contribution to the measured tooth is currently limited to cumulative dose measurements with a component of UV equivalent dose equal to or greater than 300 mGy. PMID:20065706

  16. Simulation of multi-frequency EPR spectra for a distribution of the zero-field splitting.

    PubMed

    Azarkh, Mykhailo; Groenen, Edgar J J

    2015-06-01

    We present a numerical procedure called 'grid-of-errors' to extract the distribution of magnetic interactions from continuous-wave electron-paramagnetic-resonance (EPR) spectra at multiple microwave frequencies. The approach is based on the analysis of the lineshape of the spectra and explicitly worked out for high-spin systems for which the lineshape is determined by a distribution of the zero-field splitting. Initial principal values of the zero-field splitting tensor are obtained from the EPR spectrum at a microwave frequency in the high-field limit, and the initial distribution is taken Gaussian. Subsequently, the grid-of-errors procedure optimizes this distribution, without any restriction to its shape, taking into account spectra at various microwave frequencies. The numerical procedure is illustrated for the Fe(III)-EDTA complex. An optimized distribution of the zero-field splitting is obtained, which provides a proper description of the EPR spectra at 9.5, 34, 94, and 275 GHz. The proposed approach can be used as well for distributions of magnetic interactions other than the zero-field splitting.

  17. Pulsed EPR Determination of Water Accessibility to Spin-Labeled Amino Acid Residues in LHCIIb

    PubMed Central

    Volkov, A.; Dockter, C.; Bund, T.; Paulsen, H.; Jeschke, G.

    2009-01-01

    Membrane proteins reside in a structured environment in which some of their residues are accessible to water, some are in contact with alkyl chains of lipid molecules, and some are buried in the protein. Water accessibility of residues may change during folding or function-related structural dynamics. Several techniques based on the combination of pulsed electron paramagnetic resonance (EPR) with site-directed spin labeling can be used to quantify such water accessibility. Accessibility parameters for different residues in major plant light-harvesting complex IIb are determined by electron spin echo envelope modulation spectroscopy in the presence of deuterated water, deuterium contrast in transversal relaxation rates, analysis of longitudinal relaxation rates, and line shape analysis of electron-spin-echo-detected EPR spectra as well as by the conventional techniques of measuring the maximum hyperfine splitting and progressive saturation in continuous-wave EPR. Systematic comparison of these parameters allows for a more detailed characterization of the environment of the spin-labeled residues. These techniques are applicable independently of protein size and require ∼10–20 nmol of singly spin-labeled protein per sample. For a residue close to the N-terminus, in a domain unresolved in the existing x-ray structures of light-harvesting complex IIb, all methods indicate high water accessibility. PMID:19186148

  18. Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples.

    PubMed

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

    2017-04-01

    This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries. Two sample holders have been commissioned and built by polytetrafluoroethylene (PTFE) extrusion techniques: a 1mm O.D. capillary with a septum down the middle, named DoubleDee, and a 3.5mm O.D. star shaped sample holder, named AquaStar. Simulations and experimental results at X-band show that the EPR signal intensity increases by factors of 1.43 and 3.87 in the DoubleDee and AquaStar respectively, over the current TPX 0.9mm O.D. sample tube in a two-loop-one-gap LGR. Finally, combining the insight gained from the constructed sample holders and finite-element solutions, a third multi-lumen sample holder for a cylindrical TE011 cavity is optimized, named AquaSun, where simulations show an EPR signal intensity increase by a factor of 8.2 over a standard 1mm capillary.

  19. An EPR investigation of SiOx films with columnar structure

    NASA Astrophysics Data System (ADS)

    Bratus', V.; Indutnyi, I.; Shepeliavyi, P.; Torchynska, T.

    2014-11-01

    The results of electron paramagnetic resonance (EPR) study of obliquely deposited porous SiOx films before and after thermal annealing in vacuum at 950 °C are presented. The low intensity slightly asymmetrical and featureless EPR line with a g-value of 2.0044 and a linewidth of 0.77 mT has been detected in as-sputtered films and attributed to dangling bonds of silicon atoms in amorphous SiOx domains with x=0.8. Successive annealing results in decreasing this line and the appearance of an intense EPR line with g=2.0025, linewidth of 0.11 mT and a hyperfine doublet with 1.6 mT splitting. According to the parameters this spectrum has been attributed to the EX center, a hole delocalized over four non-bridging oxygen atoms grouped around a Si vacancy in SiO2. The impact of chemical treatment before annealing and duration of anneals on the defect system is discussed.

  20. Intracellular targeting delivery of liposomal drugs to solid tumors based on EPR effects.

    PubMed

    Maruyama, Kazuo

    2011-03-18

    The success of an effective drug delivery system using liposomes for solid tumor targeting based on EPR effects is highly dependent on both size ranging from 100-200 nm in diameter and prolonged circulation half-life in the blood. A major development was the synthesis of PEG-liposomes with a prolonged circulation time in the blood. Active targeting of immunoliposomes to the solid tumor tissue can be achieved by the Fab' fragment which is better than whole IgG in terms of designing PEG-immunoliposomes with prolonged circulation. For intracellular targeting delivery to solid tumors based on EPR effects, transferrin-PEG-liposomes can stay in blood circulation for a long time and extravasate into the extravascular of tumor tissue by the EPR effect as PEG-liposomes. The extravasated transferrin-PEG-liposomes can maintain anti cancer drugs in interstitial space for a longer period, and deliver them into the cytoplasm of tumor cells via transferrin receptor-mediated endocytosis. Transferrin-PEG-liposomes improve the safety and efficacy of anti cancer drug by both passive targeting by prolonged circulation and active targeting by transferrin.

  1. Assessment of quality of quartz crystals by EPR and γ-ray diffraction

    NASA Astrophysics Data System (ADS)

    Nienhaus, K.; Stegger, P.; Lehmann, G.; Schneider, J. R.

    1986-03-01

    Natural amethysts from amygdoidal cavities and from fissures as well as synthetic iron-doped quartz crystals of different origins were studied by EPR and γ-ray diffraction. Anisotropic broadening proportional to the slopes of the transitions consistent with a distribution of orientations, most likely due to a mosaic structure, was observed in the EPR spectra of Fe 3+. This broadening was considerably smaller or completely absent in natural amethysts from fissures as well as in a synthetic crystal grown from NH 4F solution. From this broadening average distributions of orientations could be evaluated for substitutional Fe 3+ in good overall agreement with those obtained for the whole crystals by γ-ray diffraction. Thus Fe 3+ is a good probe for the overall quality of the crystals, but the γ-ray diffraction experiments clearly show predominance of a few orientations rather than a random distribution. In the quartz samples of high perfection a hyperfine splitting from an alkali nucleus could be resolved in the EPR spectra of substitutional Fe 3+ at low temperatures and a contribution of vibrations to the minimum linewidths was also observed.

  2. EPR-correlated dipolar spectroscopy by Q-band chirp SIFTER.

    PubMed

    Doll, Andrin; Jeschke, Gunnar

    2016-08-17

    While two-dimensional correlation spectra contain more information as compared to one-dimensional spectra, typical spectral widths encountered in electron paramagnetic resonance (EPR) spectroscopy largely restrict the applicability of correlation techniques. In essence, the monochromatic excitation pulses established in pulsed EPR often cannot uniformly excite the entire spectrum. Here, this restriction is alleviated for nitroxide spin labels at Q-band microwave frequencies around 35 GHz. This is achieved by substitution of monochromatic pulses by frequency-swept chirp pulses tailored for uniform excitation. Unwanted interference effects brought by this substitution are analyzed for a pair of electron spins with secular dipolar coupling. Experimentally, the dipole-dipole interaction can be separated from other interactions by a constant-time Zeeman-compensated solid echo sequence called SIFTER. Such SIFTER experiments usually yield a one-dimensional dipolar spectrum. EPR-correlated dipolar spectra can be obtained when the four pulses are replaced by chirp pulses. These two-dimensional spectra encode additional information on the geometrical arrangement of the two spin labels. With the excitation parameters achieved by a home-built Q-band spectrometer capable of frequency-swept excitation, unwanted interference effects can be largely neglected for the examined model compound with a spin-spin distance of 4 nm. The experimentally obtained correlation pattern conforms to the expectation based on the inter-spin geometry of the investigated rigid model compound.

  3. Analysis of Influenza A Virus NS1 Dimer Interfaces in Solution by Pulse EPR Distance Measurements

    PubMed Central

    2014-01-01

    Pulsed electron–electron double resonance (PELDOR) is an electron paramagnetic resonance (EPR) spectroscopy technique for nanometer distance measurements between paramagnetic centers such as radicals. PELDOR has been recognized as a valuable tool to approach structural questions in biological systems. In this manuscript, we demonstrate the value of distance measurements for differentiating competing structural models on the dimerization of the effector domain (ED) of the non-structural protein 1 (NS1) of the influenza A virus. Our results show NS1 to be well amenable to nanometer distance measurements by EPR, yielding high quality data. In combination with mutants perturbing protein dimerization and in silico prediction based on crystal structures, we can exclude one of two potential dimerization interfaces. Furthermore, our results lead to a viable hypothesis of a NS1 ED:ED interface which is flexible through rotation around the vector interconnecting the two native cysteines. These results prove the high value of pulse EPR as a complementary method for structural biology. PMID:25148246

  4. Size Dependent Kinetics of Gold Nanorods in EPR Mediated Tumor Delivery

    PubMed Central

    Tong, Xiao; Wang, Zhantong; Sun, Xiaolian; Song, Jibin; Jacobson, Orit; Niu, Gang; Kiesewetter, Dale O.; Chen, Xiaoyuan

    2016-01-01

    Gold nanorods (AuNR) have been intensively used in nanomedicine for cancer diagnostics and therapy, due to their excellent plasmonic photothermal properties. Tuning the size and aspect ratio of AuNR tailors the localized surface plasmon resonance (LSPR) in the NIR spectrum at which biological tissues are transparent, thus enables specific and effective treatment. The AuNR extravasates into tumor interstitium through enhanced permeation and retention (EPR) effect. Efficient AuNR based cancer therapy requires efficient AuNR tumor delivery. However, the size of AuNR can dramatically affect its blood circulation and tumor accumulation. Here we proposed for the first time a systematic framework to investigate the size-dependent kinetics of AuNRs during EPR mediated tumor delivery. By using 64Cu-labeled AuNRs with positron emission tomography (PET) and kinetic modeling, the in vivo uptake and kinetics of 64Cu-AuNR during its blood circulation, tumor accumulation and elimination were studied both in vitro and in vivo. The results of different sized AuNRs were compared and the optimum size of AuNR was suggested for EPR mediated tumor delivery. Our study provides a better understanding of the in vivo behavior of AuNR, which can help future design of nanomaterials for cancer imaging and therapy. PMID:27698939

  5. Studying lipid organization in biological membranes using liposomes and EPR spin labeling

    PubMed Central

    Subczynski, Witold K.; Raguz, Marija; Widomska, Justyna

    2015-01-01

    Summary Electron paramagnetic resonance (EPR) spin-labeling methods provide a unique opportunity to determine the lateral organization of lipid bilayer membranes by discrimination of coexisting membrane domains or coexisting membrane phases. In some cases, the coexisting membrane domains can be characterized by profiles of alkyl chain order, fluidity, hydrophobicity, and oxygen diffusion-concentration product in situ, without the need for their physical separation. This chapter briefly explains how the EPR spin-labeling methods can be used to obtain the above mentioned profiles across the lipid bilayer membranes (liposomes) derived from the lipid extract of certain biological membranes. These procedures will be illustrated by EPR measurements performed for multilamellar liposomes made of the lipid extracts from cortical and nuclear fractions of the fiber cell plasma membranes of a cow eye lens. To elucidate better the major factors that determine membrane properties, the results for eye lens lipid membranes will be compared with those obtained for simple model membranes resembling basic lipid composition of biological membranes. PMID:20013402

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

    PubMed Central

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

    2012-01-01

    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 14N 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, while 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 sp2-hybridized nitrogens coordinating equatorially to high-valent 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. PMID:20055466

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

    NASA Astrophysics Data System (ADS)

    Alberti, Angelo; Chiaravalle, Eugenio; Fuochi, Piergiorgio; Macciantelli, Dante; Mangiacotti, Michele; Marchesani, Giuliana; Plescia, Elena

    2011-12-01

    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 60Co γ-rays. EPR could definitely identify irradiated seashells due to the presence of long-lived free radicals, primarily CO2-, CO33-, SO2- and SO3- 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.

  8. Non-invasive determination of the irradiation dose in fingers using low-frequency EPR

    NASA Astrophysics Data System (ADS)

    Zdravkova, M.; Crokart, N.; Trompier, F.; Beghein, N.; Gallez, B.; Debuyst, R.

    2004-07-01

    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 (~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.

  9. A more secure anonymous user authentication scheme for the integrated EPR information system.

    PubMed

    Wen, Fengtong

    2014-05-01

    Secure and efficient user mutual authentication is an essential task for integrated electronic patient record (EPR) information system. Recently, several authentication schemes have been proposed to meet this requirement. In a recent paper, Lee et al. proposed an efficient and secure password-based authentication scheme used smart cards for the integrated EPR information system. This scheme is believed to have many abilities to resist a range of network attacks. Especially, they claimed that their scheme could resist lost smart card attack. However, we reanalyze the security of Lee et al.'s scheme, and show that it fails to protect off-line password guessing attack if the secret information stored in the smart card is compromised. This also renders that their scheme is insecure against user impersonation attacks. Then, we propose a new user authentication scheme for integrated EPR information systems based on the quadratic residues. The new scheme not only resists a range of network attacks but also provides user anonymity. We show that our proposed scheme can provide stronger security.

  10. A Rectangular Loop Gap Resonator for EPR Studies of Aqueous Samples

    NASA Astrophysics Data System (ADS)

    Piasecki, Wojciech; Froncisz, Wojciech; Hubbell, Wayne L.

    1998-09-01

    A new rectangular geometry of the loop-gap resonator for the use with a flat cell has been developed. Maxwell's equations for the resonators with two, four, six, and eight gaps have been solved assuming the existence of only the magneticz-component. The formulas obtained were numerically solved for the electric and magnetic field distributions over the cross-sections of the resonators. The presence of a nodal plane for the electric field in the center of the resonator allows the use of a flat cell instead of a capillary for EPR measurements. Using the field distributions obtained, the quality factor and EPR signal amplitude for various shapes and gap numbers for the resonators containing a flat cell filled with water were examined numerically. This allowed finding the geometry that yields the maximum EPR signal intensity. Several X-band resonators were built in order to verify the results obtained theoretically. The experiments confirmed the ability of a novel resonant structure to accommodate a flat cell filled with an aqueous sample. It has been found that the optimum aqueous sample volume for the X-band rectangular loop-gap resonator equals 16 mm3. For a saturable aqueous sample this gives a fourfold improvement in theS/Nratio over the circular 1 mm i.d. loop-gap resonator equipped with 0.6 mm i.d. capillary.

  11. Using EPR spectroscopy to go from the Jahn-Teller effect to nuclear waste disposal

    NASA Astrophysics Data System (ADS)

    Boatner, L. A.

    2003-02-01

    Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique for elucidating the fundamental solid-state-chemical and crystal-field ground-state electronic properties of rare-earth and actinide ions that are incorporated into single-crystal host materials. In the case of rare-earth or rare-earth-like ions that are characterized by a degenerate orbital doublet ground state when placed in a cubic crystal field, EPR has proven to be an extremely valuable approach to the study of various manifestations of the Jahn-Teller (J-T) effect. The contributions of EPR spectroscopy to the study of the J-T effect in ions such as La 2+, Y 2+ and Sc 2+ include the discovery of quadrupolar effects in J-T systems and a verification of Frank Ham's theory of the dynamic J-T effect. Such basic studies can often have unforeseen consequences—like leading to the discovery of new scintillators for gamma-ray detection or the development of a matrix for the disposal of radioactive waste.

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

    SciTech Connect

    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.

  13. Response of lithium formate EPR dosimeters at photon energies relevant to the dosimetry of brachytherapy

    SciTech Connect

    Adolfsson, Emelie; Alm Carlsson, Gudrun; Grindborg, Jan-Erik; Gustafsson, Haakan; Lund, Eva; Carlsson Tedgren, Aasa

    2010-09-15

    Purpose: To investigate experimentally the energy dependence of the detector response of lithium formate EPR dosimeters for photon energies below 1 MeV relative to that at {sup 60}Co energies. High energy photon beams are used in calibrating dosimeters for use in brachytherapy since the absorbed dose to water can be determined with high accuracy in such beams using calibrated ion chambers and standard dosimetry protocols. In addition to any differences in mass-energy absorption properties between water and detector, variations in radiation yield (detector response) with radiation quality, caused by differences in the density of ionization in the energy imparted (LET), may exist. Knowledge of an eventual deviation in detector response with photon energy is important for attaining high accuracy in measured brachytherapy dose distributions. Methods: Lithium formate EPR dosimeters were irradiated to known levels of air kerma in 25-250 kV x-ray beams and in {sup 137}Cs and {sup 60}Co beams at the Swedish Secondary Standards Dosimetry Laboratory. Conversions from air kerma free in air into values of mean absorbed dose to the detectors were made using EGSnrc MC simulations and x-ray energy spectra measured or calculated for the actual beams. The signals from the detectors were measured using EPR spectrometry. Detector response (the EPR signal per mean absorbed dose to the detector) relative to that for {sup 60}Co was determined for each beam quality. Results: Significant decreases in the relative response ranging from 5% to 6% were seen for x-ray beams at tube voltages {<=}180 kV. No significant reduction in the relative response was seen for {sup 137}Cs and 250 kV x rays. Conclusions: When calibrated in {sup 60}Co or MV photon beams, corrections for the photon energy dependence of detector response are needed to achieve the highest accuracy when using lithium formate EPR dosimeters for measuring absorbed doses around brachytherapy sources emitting photons in the energy

  14. VHF EPR analysis of organic sulfur in coal. Final technical report, September 1, 1992--August 31, 1993

    SciTech Connect

    Clarkson, R.B.; Belford, R.L.

    1993-12-31

    A direct and non-destructive technique called very High Frequency Electron Paramagnetic Resonance (VHF EPR) utilizing instrumentation and application techniques developed in this laboratory, is proving to be a practical and sensitive analytical method for the organic sulfur in coal. Research during this past year (1992--1993) was very successful in terms of obtaining spectrochemical information on organic sulfur in coal both quantitatively (amount of organic sulfur) and qualitatively (form and distribution of organic sulfur). Starting in this funding year, the authors have begun to develop and use a two-species model (non-exchanging and axially symmetric) for the simulation of VHF EPR coal spectra. Such a model provides quantitative information on the total concentration of sulfur species that can be directly related to the organic sulfur content as measured by conventional chemical methods. Utilizing the newly developed method, they have analyzed the VHF EPR spectra from some sub-bituminous coals containing organic sulfur in the range from 2% to 12% and a number of maceral blends. Excellent quantitative agreement is achieved between VHF EPR results and chemical analyses. In addition, the modelling of VHF EPR spectra of coal provides detailed spectral parameters. These parameters can be related to the molecular structures of the paramagnetic species giving rise to the EPR signals, as demonstrated by our study of the model compounds. The foundation of VHF EPR analysis of aromatic sulfur radicals has been firmly established based on careful investigations of the molecular and electronic structures of the thiophenic model compounds. The results validate the theoretical soundness of the method and carry important practical implications.

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

    PubMed

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

    SciTech Connect

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

    2015-06-15

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

  17. EPR and optical studies of VO2+ doped potassium succinate-succinic acid single crystal - Substitutional incorporation

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    EPR and optical absorption studies of VO2+ doped potassium succinate-succinic acid (KSSA) single crystal has been examined at room temperature. EPR spectrum shows that well resolved hyperfine lines. The angular variation of the EPR spectra has shown that two different VO2+ complexes are located in different chemical environments. Among the number of sites, two sites have been followed and reported here. From the EPR analysis, spin Hamiltonian parameters g and A tensors and their directional cosines are evaluated. Both the sites experience rhombic crystal field symmetry around the impurity ion. The VO2+ ion entering the site location of potassium ion has coordination of eight oxygen atoms in a distorted dodecahedral arrangement. The Optical absorption spectrum studied at room temperature shows bands corresponding to C4v symmetry. The crystal field parameter and tetragonal field parameters are calculated. From the Optical and EPR data various molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.

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

    PubMed

    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.

  19. SPIDYAN, a MATLAB library for simulating pulse EPR experiments with arbitrary waveform excitation.

    PubMed

    Pribitzer, Stephan; Doll, Andrin; Jeschke, Gunnar

    2016-02-01

    Frequency-swept chirp pulses, created with arbitrary waveform generators (AWGs), can achieve inversion over a range of several hundreds of MHz. Such passage pulses provide defined flip angles and increase sensitivity. The fact that spectra are not excited at once, but single transitions are passed one after another, can cause new effects in established pulse EPR sequences. We developed a MATLAB library for simulation of pulse EPR, which is especially suited for modeling spin dynamics in ultra-wideband (UWB) EPR experiments, but can also be used for other experiments and NMR. At present the command line controlled SPin DYnamics ANalysis (SPIDYAN) package supports one-spin and two-spin systems with arbitrary spin quantum numbers. By providing the program with appropriate spin operators and Hamiltonian matrices any spin system is accessible, with limits set only by available memory and computation time. Any pulse sequence using rectangular and linearly or variable-rate frequency-swept chirp pulses, including phase cycling can be quickly created. To keep track of spin evolution the user can choose from a vast variety of detection operators, including transition selective operators. If relaxation effects can be neglected, the program solves the Liouville-von Neumann equation and propagates spin density matrices. In the other cases SPIDYAN uses the quantum mechanical master equation and Liouvillians for propagation. In order to consider the resonator response function, which on the scale of UWB excitation limits bandwidth, the program includes a simple RLC circuit model. Another subroutine can compute waveforms that, for a given resonator, maintain a constant critical adiabaticity factor over the excitation band. Computational efficiency is enhanced by precomputing propagator lookup tables for the whole set of AWG output levels. The features of the software library are discussed and demonstrated with spin-echo and population transfer simulations.

  20. Spin relaxation measurements using first-harmonic out-of-phase absorption EPR signals.

    PubMed

    Livshits, V A; Páli, T; Marsh, D

    1998-09-01

    The dependence on spin-lattice (T1) relaxation of the first-harmonic absorption EPR signal (V'1) detected in phase quadrature with the Zeeman modulation has been investigated both theoretically and experimentally for nitroxide spin labels. Spectral simulations were performed by iterative solution of the Bloch equations that contained explicitly both the modulation and microwave magnetic fields (T. Páli, V. A. Livshits, and D. Marsh, 1996, J. Magn. Reson. B 113, 151-159). It was found that, of the various non-linear EPR displays, the first-harmonic out-of-phase V'1-signal, recorded under conditions of partial saturation of the microwave absorption, is particularly favorable for determining spin-lattice relaxation enhancements because of its superior signal intensity and relative insensitivity to spin-spin (T2) relaxation. By varying the Zeeman modulation frequency it is also possible to tune the optimum sensitivity of the V'1-signal to different ranges of the T1-relaxation time. A Zeeman modulation frequency of 25 kHz appears to be particularly suited to spin label applications. Calibrations are given for the dependence on T1-relaxation time of both the amplitude and the second integral of the V'1-signal recorded under standard conditions. Experiments on different spin labels in solution and in membranes demonstrate the practical usable sensitivity of the V'1-signal, even at modulation frequencies of 25 kHz, and these are used to investigate the dependence on microwave field intensity, in comparison with theoretical predictions. The practicable sensitivity to spin-lattice relaxation enhancements is demonstrated experimentally for a spin-labeled membrane system in the presence of paramagnetic ions. The first-harmonic out-of-phase V'1-signal appears to be the non-linear CW EPR method of choice for determining T1-relaxation enhancements in spin-labeled systems.

  1. Mapping Local Protein Electrostatics by EPR of pH-Sensitive Thiol-Specific Nitroxide† ¶

    PubMed Central

    Voinov, Maxim A.; Ruuge, Andres; Reznikov, Vladimir A.; Grigor’ev, Igor A.; Smirnov, Alex I.

    2013-01-01

    A first thiol-specific pH-sensitive nitroxide spin label of the imidazolidine series -methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester (IMTSL) - has been synthesized and characterized. X- (9 GHz) and W-band (94 GHz) EPR spectral parameters of the new spin label in its free form and covalently attached to an amino acid cysteine and a tripeptide glutathione were studied as a function of pH and solvent polarity. pKa value of protonatable tertiary amino group of the spin label was found to be unaffected by other ionizable groups present in side chains of unstructured small peptides. The W-band EPR spectra were shown to allow for pKa determination from precise g-factor measurements. Is has been demonstrated that high accuracy of pKa determination for pH-sensitive nitroxides could be achieved regardless the frequency of measurements or the regime of spin exchange: fast at X-band and slow at W-band. IMTSL was found to react specifically with a model protein - iso-1-cytochrome c from yeast Saccharomyces cerevisiae - giving EPR spectra very similar to those of the most commonly employed cysteine-specific label MTSL. CD data indicated no perturbations to the overall protein structure upon IMTSL labeling. It was found that for IMTSL, giso correlates linearly with Aiso but the slopes are different for the neutral and charged forms of the nitroxide. This finding was attributed to the solvent effects on the spin density at the oxygen atom of the N–O group and on the excitation energy of the oxygen lone-pair orbital. PMID:18426227

  2. The unusual magnetic properties of kuramite-stannite pseudobinary series: a SQUID and EPR survey

    NASA Astrophysics Data System (ADS)

    di Benedetto, F.; Evstigneeva, T.; Borgheresi, M.; Caneschi, A.; Romanelli, M.

    2009-06-01

    The magnetic properties of the synthetic Cu3SnS4 (kuramite)-Cu2FeSnS4 (stannite) pseudobinary series were investigated by means of electron paramagnetic resonance (EPR) spectroscopy, at room temperature, and by magnetometry, in the range 2-300 K. The system is particularly complex, from both chemical and crystal chemical points of view, in particular with respect to the metal valence states and the local ordering in the different terms of the series. Nevertheless, recent successes in synthesising nanostructured kuramite foster the interest to ascertain the bulk magnetic properties of these important semiconducting phases. The obtained results allowed to ascertain that a variable lack of local ordering in the Cu3- x Fe x SnS4 ( x < 0.85) samples induce the raise of strong metal-sulphur-metal superexchange interactions, that result in the appearance of marked deviations from the single-ion behaviour, typical for pure stannite. Ferro- and antiferromagnetic interactions are in fact observed at relatively high temperatures (~150 K). A possible role played by Cu(I)-Fe(III) was revealed by the EPR measurements. The Cu-rich terms of the series ( x < 0.1) are characterised by dynamic resonant disorder (i.e. time-evolving delocalisation of the formally divalent valence state for Cu among the nearest neighbouring Cu-sites), in addition to the Cu-Fe-Sn static disorder verified along the whole series. Both factors concurring to a non-periodic arrangement of paramagnetic ions in the lattice have the main effect to drastically broaden the EPR lines.

  3. Water accessibility in a membrane-inserting peptide comparing Overhauser DNP and pulse EPR methods

    NASA Astrophysics Data System (ADS)

    Segawa, Takuya F.; Doppelbauer, Maximilian; Garbuio, Luca; Doll, Andrin; Polyhach, Yevhen O.; Jeschke, Gunnar

    2016-05-01

    Water accessibility is a key parameter for the understanding of the structure of biomolecules, especially membrane proteins. Several experimental techniques based on the combination of electron paramagnetic resonance (EPR) spectroscopy with site-directed spin labeling are currently available. Among those, we compare relaxation time measurements and electron spin echo envelope modulation (ESEEM) experiments using pulse EPR with Overhauser dynamic nuclear polarization (DNP) at X-band frequency and a magnetic field of 0.33 T. Overhauser DNP transfers the electron spin polarization to nuclear spins via cross-relaxation. The change in the intensity of the 1H NMR spectrum of H2O at a Larmor frequency of 14 MHz under a continuous-wave microwave irradiation of the nitroxide spin label contains information on the water accessibility of the labeled site. As a model system for a membrane protein, we use the hydrophobic α-helical peptide WALP23 in unilamellar liposomes of DOPC. Water accessibility measurements with all techniques are conducted for eight peptides with different spin label positions and low radical concentrations (10-20 μM). Consistently in all experiments, the water accessibility appears to be very low, even for labels positioned near the end of the helix. The best profile is obtained by Overhauser DNP, which is the only technique that succeeds in discriminating neighboring positions in WALP23. Since the concentration of the spin-labeled peptides varied, we normalized the DNP parameter ɛ, being the relative change of the NMR intensity, by the electron spin concentration, which was determined from a continuous-wave EPR spectrum.

  4. SPIDYAN, a MATLAB library for simulating pulse EPR experiments with arbitrary waveform excitation

    NASA Astrophysics Data System (ADS)

    Pribitzer, Stephan; Doll, Andrin; Jeschke, Gunnar

    2016-02-01

    Frequency-swept chirp pulses, created with arbitrary waveform generators (AWGs), can achieve inversion over a range of several hundreds of MHz. Such passage pulses provide defined flip angles and increase sensitivity. The fact that spectra are not excited at once, but single transitions are passed one after another, can cause new effects in established pulse EPR sequences. We developed a MATLAB library for simulation of pulse EPR, which is especially suited for modeling spin dynamics in ultra-wideband (UWB) EPR experiments, but can also be used for other experiments and NMR. At present the command line controlled SPin DYnamics ANalysis (SPIDYAN) package supports one-spin and two-spin systems with arbitrary spin quantum numbers. By providing the program with appropriate spin operators and Hamiltonian matrices any spin system is accessible, with limits set only by available memory and computation time. Any pulse sequence using rectangular and linearly or variable-rate frequency-swept chirp pulses, including phase cycling can be quickly created. To keep track of spin evolution the user can choose from a vast variety of detection operators, including transition selective operators. If relaxation effects can be neglected, the program solves the Liouville-von Neumann equation and propagates spin density matrices. In the other cases SPIDYAN uses the quantum mechanical master equation and Liouvillians for propagation. In order to consider the resonator response function, which on the scale of UWB excitation limits bandwidth, the program includes a simple RLC circuit model. Another subroutine can compute waveforms that, for a given resonator, maintain a constant critical adiabaticity factor over the excitation band. Computational efficiency is enhanced by precomputing propagator lookup tables for the whole set of AWG output levels. The features of the software library are discussed and demonstrated with spin-echo and population transfer simulations.

  5. Investigations in quantum games using EPR-type set-ups

    NASA Astrophysics Data System (ADS)

    Iqbal, Azhar

    2006-04-01

    Research in quantum games has flourished during recent years. However, it seems that opinion remains divided about their true quantum character and content. For example, one argument says that quantum games are nothing but 'disguised' classical games and that to quantize a game is equivalent to replacing the original game by a different classical game. The present thesis contributes towards the ongoing debate about quantum nature of quantum games by developing two approaches addressing the related issues. Both approaches take Einstein-Podolsky-Rosen (EPR)-type experiments as the underlying physical set-ups to play two-player quantum games. In the first approach, the players' strategies are unit vectors in their respective planes, with the knowledge of coordinate axes being shared between them. Players perform measurements in an EPR-type setting and their payoffs are defined as functions of the correlations, i.e. without reference to classical or quantum mechanics. Classical bimatrix games are reproduced if the input states are classical and perfectly anti-correlated, as for a classical correlation game. However, for a quantum correlation game, with an entangled singlet state as input, qualitatively different solutions are obtained. The second approach uses the result that when the predictions of a Local Hidden Variable (LHV) model are made to violate the Bell inequalities the result is that some probability measures assume negative values. With the requirement that classical games result when the predictions of a LHV model do not violate the Bell inequalities, our analysis looks at the impact which the emergence of negative probabilities has on the solutions of two-player games which are physically implemented using the EPR-type experiments.

  6. Single crystal EPR, optical absorption and superposition model study of Cr 3+ doped ammonium dihydrogen phosphate

    NASA Astrophysics Data System (ADS)

    Kripal, Ram; Pandey, Sangita

    2010-06-01

    The electron paramagnetic resonance (EPR) studies are carried out on Cr 3+ ion doped ammonium dihydrogen phosphate (ADP) single crystals at room temperature. Four magnetically inequivalent sites for chromium are observed. No hyperfine structure is obtained. The crystal-field and spin Hamiltonian parameters are calculated from the resonance lines obtained at different angular rotations. The zero field and spin Hamiltonian parameters of Cr 3+ ion in ADP are calculated as: | D| = (257 ± 2) × 10 -4 cm -1, | E| = (79 ± 2) × 10 -4 cm -1, g = 1.9724 ± 0.0002 for site I; | D| = (257 ± 2) × 10 -4 cm -1, | E| = (77 ± 2) × 10 -4 cm -1, g = 1.9727 ± 0.0002 for site II; | D| = (259 ± 2) × 10 -4 cm -1, | E| = (78 ± 2) × 10 -4 cm -1, g = 1.9733 ± 0.0002 for site III; | D| = (259 ± 2) × 10 -4 cm -1, | E| = (77 ± 2) × 10 -4 cm -1, g = 1.973 ± 0.0002 for site IV, respectively. The site symmetry of Cr 3+ doped single crystal is discussed on the basis of EPR data. The Cr 3+ ion enters the lattice substitutionally replacing the NH 4+ sites. The optical absorption spectra are recorded in 195-925 nm wavelength range at room temperature. The energy values of different orbital levels are determined. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The calculated values of Racah interelectronic repulsion parameters ( B and C), cubic crystal-field splitting parameter ( Dq) and nephelauxetic parameters ( h and k) are: B = 640, C = 3070, Dq = 2067 cm -1, h = 1.44 and k = 0.21, respectively. ZFS parameters are also determined using Bkq parameters from superposition model.

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

    PubMed Central

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

    2015-01-01

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

  8. Cooper-pair splitter: towards an efficient source of spin-entangled EPR pairs

    NASA Astrophysics Data System (ADS)

    Schonenberger, Christian

    2011-03-01

    In quantum mechanics the properties of two and more particles can be entangled. In basic science pairs of entangled particles, so called Einstein-Podolsky-Rosen (EPR) pairs, play a special role as toy objects for fundamental studies. They provide such things as ``spooky interaction at distance,'' but they also enable secure encoding and teleportation and are thus important for applications in quantum information technology. Whereas EPR pairs of photons can be generated by parametric down conversion (PDC) in a crystal, a similar source for EPR pairs of electrons does not exists yet. In several theory papers, it has been suggested to use a superconductor for this purpose. The superconducting ground state is formed by a condensate of Cooper-pairs which are electron pairs in a spin-singlet state. Since there are many Cooper pairs in a metallic superconductor like Al, the main tasks are to extract Cooper pairs one by one and to split them into different arms. A controlled and efficient splitting is possible if one makes use of Coulomb interaction. This has recently be demonstrated by two groups [2-4] using hybrid quantum-dot devices with both superconducting and normal metal contacts. In the present talk, I will discuss the Cooper-pair splitter results from the Basel-Budapest-Copenhagen team and compare with the other experiments. As an outlook we discuss approaches that aim at entanglement detection. The Cooper pair splitter holds great promises because very large splitting efficiencies approaching 100% and large pair current rates appear feasible. This work has been done by L. Hofstetter, S. Csonka, A. Geresdi, M. Aagesen, J. Nygard and C. Schönenberger

  9. An EPR study on a new triclinic symmetry defect in neutron-irradiated FZ-silicon

    NASA Astrophysics Data System (ADS)

    En, Wu; Shu-xian, Wu; Jin-Chang, Mao; Mao-Xun, Yan; Guo-gang, Qin

    1987-01-01

    A new defect, labled as Si-PK1, has been observed with EPR (Electron Paramagnetic Resonance) in neutron irradiated FZ-Si grown in argon, hydrogen and vacuum. Its symmetry has been determined to be triclinic symmetry, the lowest possible symmetry. Si-PK1 has not been observed in CZ-Si. It is not related to any common impurities in Si, like oxygen, carbon, phosphorus and boron, and it should be an intrinsic defect. Combining with the empirical classification of g tensor, it is concluded that Si-PK1 may be a multi-vacancy cluster.

  10. Nursing documentation with NANDA and NIC in a comprehensive HIS/EPR system.

    PubMed

    Flø, Kåre

    2006-01-01

    DIPS nursing documentation system facilitates that nurses can write several types of notes into the EPR. Within these notes the nurses can register NANDA diagnoses and NIC interventions with nursing activities. To choose NANDA and NIC the nurse can use a search engine, or she can choose a relevant Care plan guideline and pick the suggested diagnoses and interventions from there. Diagnoses and interventions with nursing activities registered are presented in a Care plan. When a nurse writes a note for a patient she will always be presented the Care plan and she can easy evaluate and update the Care plan.

  11. Pentachlorooxotechnetate(VI) anion, (TcOCl/sub 5/): an EPR study

    SciTech Connect

    Kirmse, R.; Stach, J.; Abram, U.

    1985-07-03

    The anion pentachlorooxotechnetate(VI), TcOCl/sub 5//sup -/, has been prepared by reduction of TcO/sub 4//sup -/ with HCl in concentrated H/sub 2/SO/sub 4/ and investigated by means of the EPR technique. The axial symmetric spectrum suggests an in-plane ..pi..-type ground state of the MO of the unpaired electron. The Tc-Cl/sub eq/ bonding properties have been discussed in terms of MO theory, and a comparison has been given to the bonding properties in likely complexes of neighboring elements of Tc.

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

    PubMed

    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.

  13. Chemical process to separate iron oxides particles in pottery sample for EPR dating.

    PubMed

    Watanabe, S; Farias, T M B; Gennari, R F; Ferraz, G M; Kunzli, R; Chubaci, J F D

    2008-12-15

    Ancient potteries usually are made of the local clay material, which contains relatively high concentration of iron. The powdered samples are usually quite black, due to magnetite, and, although they can be used for thermoluminescene (TL) dating, it is easiest to obtain better TL reading when clearest natural or pre-treated sample is used. For electron paramagnetic resonance (EPR) measurements, the huge signal due to iron spin-spin interaction, promotes an intense interference overlapping any other signal in this range. Sample dating is obtained by dividing the radiation dose, determined by the concentration of paramagnetic species generated by irradiation, by the natural dose so as a consequence, EPR dating cannot be used, since iron signal do not depend on radiation dose. In some cases, the density separation method using hydrated solution of sodium polytungstate [Na6(H2W12O40).H2O] becomes useful. However, the sodium polytungstate is very expensive in Brazil; hence an alternative method for eliminating this interference is proposed. A chemical process to eliminate about 90% of magnetite was developed. A sample of powdered ancient pottery was treated in a mixture (3:1:1) of HCl, HNO(3) and H(2)O(2) for 4h. After that, it was washed several times in distilled water to remove all acid matrixes. The original black sample becomes somewhat clearer. The resulting material was analyzed by plasma mass spectrometry (ICP-MS), with the result that the iron content is reduced by a factor of about 9. In EPR measurements a non-treated natural ceramic sample shows a broad spin-spin interaction signal, the chemically treated sample presents a narrow signal in g=2.00 region, possibly due to a radical of (SiO(3))(3-), mixed with signal of remaining iron [M. Ikeya, New Applications of Electron Spin Resonance, World Scientific, Singapore, 1993, p. 285]. This signal increases in intensity under gamma-irradiation. However, still due to iron influence, the additive method yielded too

  14. Chemical process to separate iron oxides particles in pottery sample for EPR dating

    NASA Astrophysics Data System (ADS)

    Watanabe, S.; Farias, T. M. B.; Gennari, R. F.; Ferraz, G. M.; Kunzli, R.; Chubaci, J. F. D.

    2008-12-01

    Ancient potteries usually are made of the local clay material, which contains relatively high concentration of iron. The powdered samples are usually quite black, due to magnetite, and, although they can be used for thermoluminescene (TL) dating, it is easiest to obtain better TL reading when clearest natural or pre-treated sample is used. For electron paramagnetic resonance (EPR) measurements, the huge signal due to iron spin-spin interaction, promotes an intense interference overlapping any other signal in this range. Sample dating is obtained by dividing the radiation dose, determined by the concentration of paramagnetic species generated by irradiation, by the natural dose so as a consequence, EPR dating cannot be used, since iron signal do not depend on radiation dose. In some cases, the density separation method using hydrated solution of sodium polytungstate [Na 6(H 2W 12O 40)·H 2O] becomes useful. However, the sodium polytungstate is very expensive in Brazil; hence an alternative method for eliminating this interference is proposed. A chemical process to eliminate about 90% of magnetite was developed. A sample of powdered ancient pottery was treated in a mixture (3:1:1) of HCl, HNO 3 and H 2O 2 for 4 h. After that, it was washed several times in distilled water to remove all acid matrixes. The original black sample becomes somewhat clearer. The resulting material was analyzed by plasma mass spectrometry (ICP-MS), with the result that the iron content is reduced by a factor of about 9. In EPR measurements a non-treated natural ceramic sample shows a broad spin-spin interaction signal, the chemically treated sample presents a narrow signal in g = 2.00 region, possibly due to a radical of (SiO 3) 3-, mixed with signal of remaining iron [M. Ikeya, New Applications of Electron Spin Resonance, World Scientific, Singapore, 1993, p. 285]. This signal increases in intensity under γ-irradiation. However, still due to iron influence, the additive method yielded too

  15. Investigations of EPR parameters for the trigonal Ti3+-Ti3+ pair in beryl crystal.

    PubMed

    Wang, Fang; Zheng, Wen-Chen

    2007-08-01

    By using the complete diagonalization of energy matrix of 3d1 ions in trigonal symmetry, the EPR parameters (g factors g( parallel), g( perpendicular) and zero-field splitting D) of the trigonal Ti3+-Ti3+ pair in beryl crystal are calculated. In the calculations, the exchange interaction in the Ti3+-Ti3+ pair is taken as the perturbation and the local trigonal distortion in the defect center is considered. The results (which are in agreement with the experimental values) are discussed.

  16. Surface loop resonator design for in vivo EPR tooth dosimetry using finite element analysis.

    PubMed

    Pollock, Jennifer D; Williams, Benjamin B; Sidabras, Jason W; Grinberg, Oleg; Salikhov, Ildar; Lesniewski, Piotr; Kmiec, Maciej; Swartz, Harold M

    2010-02-01

    Finite element analysis is used to evaluate and design L-band surface loop resonators for in vivo electron paramagnetic resonance (EPR) tooth dosimetry. This approach appears to be practical and useful for the systematic examination and evaluation of resonator configurations to enhance the precision of dose estimates. The effects of loop positioning in the mouth are examined, and it is shown that the sensitivity to loop position along a row of molars is decreased as the loop is moved away from the teeth.

  17. 2'-Alkynylnucleotides: A Sequence- and Spin Label-Flexible Strategy for EPR Spectroscopy in DNA.

    PubMed

    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.

  18. Applicability of EPR/alanine dosimetry for quality assurance in proton eye radiotherapy.

    PubMed

    Michalec, B; Mierzwinska, G; Ptaszkiewicz, M; Sowa, U; Stolarczyk, L; Weber, A

    2014-06-01

    A new quality assurance and quality control method for proton eye radiotherapy based on electron paramagnetic resonance (EPR)/alanine dosimetry has been developed. It is based on Spread-Out Bragg Peak entrance dose measurement with alanine detectors. The entrance dose is well correlated with the dose at the facility isocenter, where, during the therapeutic irradiation, the tumour is placed. The unique alanine detector features namely keeping the dose record in a form of stable radiation-induced free radicals trapped in the material structure, and the non-destructive read-out makes this type of detector a good candidate for additional documentation of the patient's exposure over the therapy course.

  19. Structure of the upper mantle under the EPR from waveform inversion of regional events

    PubMed

    Webb; Forsyth

    1998-05-22

    Waveform inversions of seismograms recorded at the Mantle Electromagnetic and Tomography (MELT) Experiment ocean bottom seismometer array from regional events with paths following the East Pacific Rise (EPR) require that low shear velocities (<3.7 km/s) extend to depths of more than 100 km below the rise axis. Velocities increase with average crustal age along ray paths. The reconciliation of Love and Rayleigh wave data requires that shear flow has aligned melt pockets or olivine crystals, creating an anisotropic uppermost mantle.

  20. Application of EPR dosimetry in bone for ex vivo measurements of doses in radiotherapy patients.

    PubMed

    Krefft, K; Drogoszewska, B; Kaminska, J; Juniewicz, M; Wołąkiewicz, G; Jakacka, I; Ciesielski, B

    2014-11-01

    In the present study, bone samples from three patients treated in radiotherapy facilities in Poland were used for the determination of doses absorbed during radiotherapy. The samples were obtained during surgical treatments of patients performed due to medical indications. For the purpose of retrospective dosimetry, sensitivity of the radiation-induced EPR signal was individually calibrated in the samples by re-irradiation of the samples with known doses. The doses reconstructed in bones extracted within 6 months after irradiation were consistent with those calculated by treatment planning systems. The dose reconstructed in the bone removed 6 y after radiotherapy was ∼14% lower than the calculated one.

  1. EPR and optical absorption study of Cu2+ doped lithium sulphate monohydrate (LSMH) single crystals

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    EPR study of Cu2+ doped NLO active Lithium Sulphate monohydrate (Li2SO4.H2O) single crystals were grown successfully by slow evaporation method at room temperature. The principal values of g and A tensors indicate existence of orthorhombic symmetry around the Cu2+ ion. From the direction cosines of g and A tensors, the locations of Cu2+ in the lattice have been identified as interstitial site. Optical absorption confirms the rhombic symmetry and ground state wave function of the Cu2+ ion in a lattice as dx2-y2.

  2. In situ EPR studies of reaction pathways in Titania photocatalyst-promoted alkylation of alkenes.

    PubMed

    Rhydderch, Shona; Howe, Russell F

    2015-03-03

    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.

  3. Saturation recovery EPR and ELDOR at W-band for spin labels

    NASA Astrophysics Data System (ADS)

    Froncisz, Wojciech; Camenisch, Theodore G.; Ratke, Joseph J.; Anderson, James R.; Subczynski, Witold K.; Strangeway, Robert A.; Sidabras, Jason W.; Hyde, James S.

    2008-08-01

    A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE 011 cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW -1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T1e previously reported for these molecules in the range of 2-35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T 1 values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524-9529]. The values of T1e decrease at 94 GHz relative to values at 35 GHz.

  4. Saturation recovery EPR and ELDOR at W-band for spin labels.

    PubMed

    Froncisz, Wojciech; Camenisch, Theodore G; Ratke, Joseph J; Anderson, James R; Subczynski, Witold K; Strangeway, Robert A; Sidabras, Jason W; Hyde, James S

    2008-08-01

    A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE(011) cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW(-1/2) with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T(1e) previously reported for these molecules in the range of 2-35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T(1) values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524-9529]. The values of T(1e) decrease at 94 GHz relative to values at 35 GHz.

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

    SciTech Connect

    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.

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

    SciTech Connect

    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.

  7. EPR assessment of protein sites for incorporation of Gd(III) MRI contrast labels

    PubMed Central

    Lagerstedt, Jens O.; Petrlova, Jitka; Hilt, Silvia; Marek, Antonin; Chung, Youngran; Sriram, Renuka; Budamagunta, Madhu S.; Desreux, Jean F.; Thonon, David; Jue, Thomas; Smirnov, Alex I.; Voss, John C.

    2013-01-01

    We have engineered Apolipoprotein A-I (apoA-I), a major protein constituent of high-density lipoprotein (HDL), to contain DOTA-chelated Gd(III) as an MRI contrast agent for the purpose of imaging reconstituted HDL (rHDL) biodistribution, metabolism, and regulation in vivo. This protein contrast agent was obtained by reacting the thiol-reactive Gd[MTS-ADO3A] label with Cys engineered at four distinct positions (52, 55, 76 and 80) in apoA-I. MRI of infused mice previously showed that the Gd-labeled apoA-I migrates to both the liver and the kidney, the organs responsible for HDL catabolism; however, the contrast properties of apoA-I are superior when the ADO3A moiety is located at position 55, compared to the protein labeled at positions 52, 76 or 80. It is shown here that continuous wave X-band (9 GHz) EPR spectroscopy is capable of detecting differences in the Gd(III) signal when comparing the labeled protein in the lipid-free to the rHDL state. Furthermore, the values of NMR relaxivity obtained for labeled variants in both the lipid-free and rHDL states correlate to the product of the X-band Gd(III) spectral width and the collision frequency between a nitroxide spin label and a polar relaxation agent. Consistent with its superior relaxivity measured by NMR, the rHDL-associated apoA-I containing the Gd[MTS-ADO3A] probe attached to position 55 displays favorable dynamic and water accessibility properties as determined by X-band EPR. While room temperature EPR requires >1 mM Gd(III)-labeled and only >10 μM nitroxide-labeled protein to resolve the spectrum, the volume requirement is exceptionally low (~5μL). Thus, X-band EPR provides a practical assessment for the suitability of imaging candidates containing the site-directed ADO3A contrast probe. PMID:23606429

  8. EPR and ENDOR Studies of Point Defects in Lithium Tetraborate Crystals

    DTIC Science & Technology

    2012-12-14

    Thermoluminescence (TL), photoluminescence (PL), photoluminescence excitation (PLE), and optical absorption (OA) are also used. An intrinsic hole trap associated...with lithium vacancies is characterized with EPR and ENDOR and its thermal stability is determined using thermoluminescence . A “perturbed” hole...Tetraborate…………... 40 3.1. Introduction……………………………………………………………… 40 3.2. Thermoluminescence Results…………………………………………… 41 3.3. Electron Paramagnetic

  9. Splitting spacetime and cloning qubits: linking no-go theorems across the ER=EPR duality

    NASA Astrophysics Data System (ADS)

    Bao, Ning; Pollack, Jason; Remmen, Grant N.

    2015-11-01

    We analyze the no-cloning theorem in quantum mechanics through the lens of the proposed ER=EPR (Einstein-Rosen = Einstein-Podolsky-Rosen) duality between entanglement and wormholes. In particular, we find that the no-cloning theorem is dual on the gravity side to the no-go theorem for topology change, violating the axioms of which allows for wormhole stabilization and causality violation. Such a duality between important no-go theorems elucidates the proposed connection between spacetime geometry and quantum entanglement.

  10. Fault-tolerant controlled deterministic secure quantum communication using EPR states against collective noise

    NASA Astrophysics Data System (ADS)

    Kao, Shih-Hung; Yang, Chun-Wei; Hwang, Tzonelih

    2016-11-01

    This paper proposes two new fault-tolerant controlled deterministic secure quantum communication (CDSQC) protocols based only on Einstein-Podolsky-Rosen (EPR) entangled states. The proposed protocols are designed to be robust against the collective-dephasing noise and the collective-rotation noise, respectively. Compared to the existing fault-tolerant controlled quantum communication protocols, the proposed protocols not only can do without a quantum channel between the receiver and the controller as the state-of-the-art protocols do, but also have the advantage that the number of quantum particles required in the CDSQC protocols is reduced owing to the use of the simplest entangled states.

  11. Robust EPR-pairs-based quantum secure communication with authentication resisting collective noise

    NASA Astrophysics Data System (ADS)

    Chang, Yan; Zhang, ShiBin; Li, Jian; Yan, LiLi

    2014-10-01

    This work presents two robust quantum secure communication schemes with authentication based on Einstein-Podolsky-Rosen (EPR) pairs, which can withstand collective noises. Two users previously share an identity string representing their identities. The identity string is encoded as decoherence-free states (termed logical qubits), respectively, over the two collective noisy channels, which are used as decoy photons. By using the decoy photons, both the authentication of two users and the detection of eavesdropping were implemented. The use of logical qubits not only guaranteed the high fidelity of exchanged secret message, but also prevented the eavesdroppers to eavesdrop beneath a mask of noise.

  12. Comparison of local and global angular interpolation applied to spectral-spatial EPR image reconstruction.

    PubMed

    Ahn, Kang-Hyun; Halpern, Howard J

    2007-03-01

    Spectral-spatial images reconstructed from a small number of projections suffer from streak artifacts that are seen as noise, particularly in the spectral dimension. Interpolation in projection space can reduce artifacts in the reconstructed images. The reduction of background artifacts improves lineshape fitting. In this work, we compared the performances of angular interpolation implemented using linear, cubic B-spline, and sinc methods. Line width maps were extracted from 4-D EPR images of phantoms using spectral fitting to evaluate each interpolation method and its robustness to noise. Results from experiment and simulation showed that the cubic B-spline, angular interpolation was preferable to either sinc or linear interpolation methods.

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

    PubMed

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

    2011-11-09

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

  14. Gadolinium-Activated CaZr4O9 Ultraviolet-B-Emitting Phosphor: A Luminescence and EPR Study

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Singh, N.; Watanabe, S.; Gundu Rao, T. K.; Pathak, M. S.; Srivastava, A. K.; Singh, P. K.; Dhoble, S. J.

    2017-04-01

    Gadolinium-activated CaZr4O9 ultraviolet-B-emitting phosphor has been prepared by a solution combustion method and characterized using powder x-ray diffraction analysis, electron paramagnetic resonance (EPR), and photoluminescence (PL) spectroscopic techniques. Upon excitation at 274 nm, the emission spectrum exhibits a well-defined ultraviolet B emission band with maximum at 313 nm, corresponding to 6P7/2 → 8S7/2 transition. A characteristic "U"-type EPR spectrum is observed for the powder samples. Doped Gd3+ ion appears to occupy calcium sites in the phosphor lattice. EPR and PL analyses of the sample confirm presence of Gd3+ in the CaZr4O9 host.

  15. EPR adoption and dual record maintenance in the U.S.: assessing variation in medical systems infrastructure.

    PubMed

    Lorence, Daniel P; Spink, Amanda; Richards, Michael C

    2002-10-01

    The growing adoption of evidence-based medicine in the United States is acting to cause fundamental changes in the delivery of healthcare management services. With the increasing incorporation of electronic patient records (EPRs) into the day-to-day practice of medicine, it necessitates greater dependence on adequate functioning of such resources, as they become more frequently used as a clinical complement in the practice of medicine. Assessing the patterns of adoption of EPRs is likewise of increasing importance, with the recent imposition of uniform government data collection and management requirements. The medium of data storage and maintenance within many organizations is a critical factor in the ultimate delivery of service, with a like need for an integrated, designated medium for the management of data becoming paramount. This study examines, on a nationwide basis, variation in reported adoption of EPRs within U.S. healthcare organizations, and the related maintenance of dual electronic/paper record systems.

  16. EPR studies of 5-bromouracil crystal after irradiation with X rays in the bromine K-edge region.

    PubMed

    Yokoya, Akinari; Takakura, Kaoru; Watanabe, Ritsuko; Akamatsu, Ken; Ito, Takashi

    2004-10-01

    Radicals induced in a single crystal of 5-bromouracil (BrUra) by synchrotron soft X rays in the bromine K-edge region (13.461-13.482 keV) were investigated using the X-band EPR method. The crystal was irradiated at three peak energies of the absorption spectrum at room temperature or at 80 K. A hydrogen abstraction radical derived from N1 of the pyrimidine ring was commonly observed for all of the energies used, though with some variation in quantity. Similar characteristics were also observed in the EPR signal for the off-K-edge low-energy (13.42 keV) and (60)Co gamma rays used for comparison. When irradiated at 80 K, a much larger exposure (roughly 10 times) of soft X rays was needed to obtain the same signal intensity as that observed at room temperature. EPR signals were not detectable with gamma irradiation at liquid nitrogen temperature.

  17. Tailored sinc pulses for uniform excitation and artifact-free radio frequency time-domain EPR imaging.

    PubMed

    Devasahayam, N; Murugesan, R; Matsumoto, K; Mitchell, J B; Cook, J A; Subramanian, S; Krishna, M C

    2004-05-01

    A method to generate shaped radiofrequency pulses for uniform excitation of electron spins in time-domain radio frequency (RF) electron paramagnetic resonance (EPR) imaging is presented. A commercial waveform generator was integrated with the transmit arm of the existing time-domain RF-EPR spectrometer to generate tailored excitation pulses with sub-nano second resolution for excitation with a 90 degrees flip-angle. A truncated sinc [sin(x)/x] pulse, tailored to compensate for the Q-profile (RF frequency response) of the resonator, was shown to yield images from phantom objects as well as in vivo images, with minimal distortion. These studies point to the advantages in using shaped sinc pulses to achieve improved uniform excitation over a relatively wide bandwidth region in time-domain RF-EPR imaging (RF-FT-EPRI).

  18. Theoretical studies of the local structure and EPR parameters for Cu2+ centers in disodium malonate trihydrate single crystal

    NASA Astrophysics Data System (ADS)

    Chao-Ying, Li; Ying, Huang; Xue-Mei, Zheng

    2015-01-01

    The electron paramagnetic resonance (EPR) parameters (g factors gxx, gyy, gzz and hyperfine structure constants Axx, Ayy, Azz) of the two Cu2+ centers in disodium malonate trihydrate (DSMT) single crystal are theoretically interpreted using the high order perturbation formulas of these parameters for a 3d9 ions in rhombically elongated octahedra. In the calculation, the rhombic crystal-field parameters are determined from the superposition model and the admixture of d-orbitals in the ground state wave function are taking account, the results show that although the admixture of the | d z 2 > state to the ground state wave function is small, it should not be neglected in calculations of the EPR parameters. The theoretical EPR parameters show good agreement with the observed values. The results are discussed.

  19. A Hash Based Remote User Authentication and Authenticated Key Agreement Scheme for the Integrated EPR Information System.

    PubMed

    Li, Chun-Ta; Weng, Chi-Yao; Lee, Cheng-Chi; Wang, Chun-Cheng

    2015-11-01

    To protect patient privacy and ensure authorized access to remote medical services, many remote user authentication schemes for the integrated electronic patient record (EPR) information system have been proposed in the literature. In a recent paper, Das proposed a hash based remote user authentication scheme using passwords and smart cards for the integrated EPR information system, and claimed that the proposed scheme could resist various passive and active attacks. However, in this paper, we found that Das's authentication scheme is still vulnerable to modification and user duplication attacks. Thereafter we propose a secure and efficient authentication scheme for the integrated EPR information system based on lightweight hash function and bitwise exclusive-or (XOR) operations. The security proof and performance analysis show our new scheme is well-suited to adoption in remote medical healthcare services.

  20. Comparison of antioxidants for combined radiation and thermal aging and superposition of radiation and thermal aging for EPR and XLPE

    NASA Astrophysics Data System (ADS)

    Reynolds, A. B.; Wlodkowski, P. A.

    Thermal and combined thermal and radiation aging of low voltage EPR and XLPE cable insulation with Agerite MA antioxidant and with the ZMTI/Aminox antioxidant system was examined to compare the relative effectiveness of the antioxidant and polymer systems. All provided significant stability with no clear choice of any particular combination being superior to the others. A comparison of degradation from thermal and radiation aging with degradation from combined thermal/radiation aging showed that the damage from the individual aging effects was superposable. This indicates that synergistic effects have little importance for the EPRs and XLPEs tested under the aging conditions observed.

  1. An EPR investigation of X-irradiated cyanoguanidine single crystals at -60°C and at room temperature

    NASA Astrophysics Data System (ADS)

    Pace, M. D.; Moniz, W. B.

    An EPR experiment on X-irradiated cyanoguanidine single crystals at -60°C and at room temperature indicates that the temperature-dependent fine broadening of the spectra is completely reversible over this temperature range. The experimental hyperfine coupling tensors determined at -60°C and at room temperature support a radical with structure H 2NC(NH 2NCHN. An EPR spectrum of a crystal grown from D 2O and X-irradiated, as well as an INDO calculation, supports this radical assignment.

  2. Zigzagging causility model of EPR correlations and on the interpretation of quantum mechanics

    SciTech Connect

    de Beauregard, O.C.

    1988-09-01

    Being formalized inside the S-matrix scheme, the zigzagging causility model of EPR correlations has full Lorentz and CPT invariance. EPR correlations, proper or reversed, and Wheeler's smoky dragon metaphor are respectively pictured in a spacetime or in the momentum-energy space, as V-shaped, anti LAMBDA-shaped, or C-shaped ABC zigzags, with a summation at B over virtual states absolute value B>

  3. Sensitization behavior of alloy 800H as characterized by the electrochemical potentiokinetic reactivation (EPR) technique

    SciTech Connect

    Edgemon, G.L.; Marek, M. ); Wilson, D.F. ); Bell, G.E.C. )

    1994-12-01

    The need for a nondestructive test to evaluate levels of sensitization in alloy 800H (UNS N08810) led to modification of the electrochemical potentiokinetic reactivation (EPR) test technique previously developed for type 304 (UNS S30400) stainless steel (SS). Results of testing on alloy 800H specimens aged at temperatures between 450 C and 700 C for 0 h to 5,000 h indicated that sensitized materials exhibited a peak in measured current density resulting from activation of grain boundaries at [minus]30 mV[sub SCE] in addition to a general surface activation peak at [minus]150 mV[sub SCE]. Unsensitized material exhibited only the general surface activation peak. It was shown that methods of data analysis previously used for type 304 SS utilizing the integrated area under the reactivation curve cannot be applied to alloy 800H because of the dual peak nature of the EPR curve. Instead, i[sub pn] (current density normalized to grain boundary area at a specimen potential of [minus]30 mV[sub SCE]) must be used. A i[sub pn] value > [approximately] 1.6 [times] 10[sup 4] [mu]A/cm[sup 2] of grain boundary area corresponded to complete grain encirclement and grain boundary ditching. Using this criterion and the aging conditions investigated, a time-temperature sensitization profile was generated for alloy 800H.

  4. Integrity of the reactor coolant boundary of the European pressurized water reactor (EPR)

    SciTech Connect

    Goetsch, D.; Bieniussa, K.; Schulz, H.; Jalouneix, J.

    1997-04-01

    This paper is an abstract of the work performed in the frame of the development of the IPSN/GRS approach in view of the EPR conceptual safety features. EPR is a pressurized water reactor which will be based on the experience gained by utilities and designers in France and in Germany. The reactor coolant boundary of a PWR includes the reactor pressure vessel (RPV), those parts of the steam generators (SGs) which contain primary coolant, the pressurizer (PSR), the reactor coolant pumps (RCPs), the main coolant lines (MCLs) with their branches as well as the other connecting pipes and all branching pipes including the second isolation valves. The present work covering the integrity of the reactor coolant boundary is mainly restricted to the integrity of the main coolant lines (MCLs) and reflects the design requirements for the main components of the reactor coolant boundary. In the following the conceptual aspects, i.e. design, manufacture, construction and operation, will be assessed. A main aspect is the definition of break postulates regarding overall safety implications.

  5. Evaluation of Partial k-space strategies to speed up Time-domain EPR Imaging

    PubMed Central

    Subramanian, Sankaran; Chandramouli, Gadisetti VR; McMillan, Alan; Gullapalli, Rao P; Devasahayam, Nallathamby; Mitchell, James B.; Matsumoto, Shingo; Krishna, Murali C

    2012-01-01

    Narrow-line spin probes derived from the trityl radical have led to the development of fast in vivo time-domain EPR imaging. Pure phase-encoding imaging modalities based on the Single Point Imaging scheme (SPI) have demonstrated the feasibility of 3D oximetric images with functional information in minutes. In this paper, we explore techniques to improve the temporal resolution and circumvent the relatively short biological half-lives of trityl probes using partial k-space strategies. There are two main approaches: one involves the use of the Hermitian character of the k-space by which only part of the k-space is measured and the unmeasured part is generated using the Hermitian symmetry. This approach is limited in success by the accuracy of numerical estimate of the phase roll in the k-space that corrupts the Hermiticy. The other approach is to measure only a judicially chosen reduced region of k-space (a centrosymmetric ellipsoid region) that more or less accounts for >70% of the k-space energy. Both of these aspects were explored in FT-EPR imaging with a doubling of scan speed demonstrated by considering ellipsoid geometry of the k-space. Partial k-space strategies help improve the temporal resolution in studying fast dynamics of functional aspects in vivo with infused spin probes. PMID:23045171

  6. HYSCORE and DEER with an upgraded 95GHz pulse EPR spectrometer.

    PubMed

    Goldfarb, Daniella; Lipkin, Yaakov; Potapov, Alexey; Gorodetsky, Yehoshua; Epel, Boris; Raitsimring, Arnold M; Radoul, Marina; Kaminker, Ilia

    2008-09-01

    The set-up of a new microwave bridge for a 95 GHz pulse EPR spectrometer is described. The virtues of the bridge are its simple and flexible design and its relatively high output power (0.7 W) that generates pi pulses of 25 ns and a microwave field, B(1)=0.71 mT. Such a high B(1) enhances considerably the sensitivity of high field double electron-electron resonance (DEER) measurements for distance determination, as we demonstrate on a nitroxide biradical with an interspin distance of 3.6 nm. Moreover, it allowed us to carry out HYSCORE (hyperfine sublevel-correlation) experiments at 95 GHz, observing nuclear modulation frequencies of 14N and 17O as high as 40 MHz. This opens a new window for the observation of relatively large hyperfine couplings, yet not resolved in the EPR spectrum, that are difficult to observe with HYSCORE carried out at conventional X-band frequencies. The correlations provided by the HYSCORE spectra are most important for signal assignment, and the improved resolution due to the two dimensional character of the experiment provides 14N quadrupolar splittings.

  7. Digital Detection and Processing of Multiple Quadrature Harmonics for EPR Spectroscopy

    PubMed Central

    Ahmad, R.; Som, S.; Kesselring, E.; Kuppusamy, P.; Zweier, J.L.; Potter, L.C.

    2010-01-01

    A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramér-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration. PMID:20971667

  8. Influence of crushing and additive irradiation procedures on EPR dosimetry of tooth enamel

    SciTech Connect

    Shalom, S.V.; Chumak, V.V.; Haskell, E.H.; Hayes, R.B.; Kenner, G.H.

    1996-01-01

    The effect of the crushing and additive dose procedures used in EPR dosimetry of enamel was studied on the signals with g-factors of 2. 0045 and g, = 2.0018, g. = 1.9975. Eight fractions, ranging in size from <75 micrometers to 2 mm, were prepared from one tooth. Two cases were investigated: crushing of a non-irradiated sample and of a sample previously irradiated (6 Gy from `Co gamma ray source). In the non-irradiated study, the intensity of the native signal at 2.0045 in by circa 1.75 times as the grain size decreased from maximum to minimum. A small in radiation sensitivity (< 8%) was also observed with decreasing grain size. In the irradiated samples, crushing resulted in slight variations of reconstructed doses from expected values, but the worst possible case (grain sizes < 75 micron) showed that additional errors were less than 10%. The radiation sensitivity of enamel measured immediately after exposure is underestimated. It increases by about 15% in the first month. Based on the decomposition of the observed spectra, a new interpretation of transient signals 1108 is proposed which explains the above phenomena. Recommendations about how to use this interpretation in retrospective EPR dosimetry are given.

  9. Effect of thermal treatment on potato starch evidenced by EPR, XRD and molecular weight distribution.

    PubMed

    Bidzińska, Ewa; Michalec, Marek; Pawcenis, Dominika

    2015-12-01

    Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification.

  10. Development of in vivo tooth EPR for individual radiation dose estimation and screening.

    PubMed

    Williams, Benjamin B; Dong, Ruhong; Kmiec, Maciej; Burke, Greg; Demidenko, Eugene; Gladstone, David; Nicolalde, Roberto J; Sucheta, Artur; Lesniewski, Piotr; Swartz, Harold M

    2010-02-01

    The development of in vivo EPR has made it feasible to perform tooth dosimetry measurements in situ, greatly expanding the potential for using this approach for immediate screening after radiation exposures. The ability of in vivo tooth dosimetry to provide estimates of absorbed dose has been established through a series of experiments using unirradiated volunteers with specifically irradiated molar teeth placed in situ within gaps in their dentition and in natural canine teeth of patients who have completed courses of radiation therapy for head and neck cancers. Multiple measurements in patients who have received radiation therapy demonstrate the expected heterogeneous dose distributions. Dose-response curves have been generated using both populations and, using the current methodology and instrument, the standard error of prediction based on single 4.5-min measurements is approximately 1.5 Gy for inserted molar teeth and between 2.0 and 2.5 Gy in the more irregularly shaped canine teeth. Averaging of independent measurements can reduce this error significantly to values near 1 Gy. Developments to reduce these errors are underway, focusing on geometric optimization of the resonators, detector positioning techniques, and optimal data averaging approaches. In summary, it seems plausible that the EPR dosimetry techniques will have an important role in retrospective dosimetry for exposures involving large numbers of individuals.

  11. Surface modification of TiO{sub 2} nanoparticles with carotenoids. EPR study

    SciTech Connect

    Konovalova, T.A.; Kispert, L.D.; Konovalov, V.V.

    1999-06-03

    Among the semiconductors, titanium dioxide is the most suitable for many environmental applications. EPR measurements demonstrate efficient charge separation on carotenoid-modified titanium dioxide nanoparticles (7 nm). Strong complexation of carotenoids containing terminal carboxy groups ({minus}CO{sub 2}H) with the TiO{sub 2} surface leads to electron transfer from the adsorbed carotenoid molecule to the surface trapping site. For these systems, EPR signals of the carotenoid radical cations Car{sup {sm_bullet}+} and the electrons trapped on the TiO{sub 2} are observed before irradiation (77 K). Their UV-visible spectra show an absorption band with a maximum near 650 nm that is characteristic of the trapped electrons. Surface modification of the TiO{sub 2} by other carotenoids results in the formation of a complex with an optical absorption band near 545 nm. These systems form charge-separated pairs [Car{sup {sm_bullet}+}{hor_ellipsis}TiO{sub 2}(e{sup {minus}}{sub tr}){sub surf}. TiO{sub 2}(e{sup {minus}}{sub tr}){sub latt}] only upon 365--600 nm illumination at 77 K. Complexation of the TiO{sub 2} colloids with carotenoids enhances spatial charge separation, shifts the absorption threshold into the visible region, and thus greatly improves the reducing ability of the semiconductor. Photoreduction of acceptor molecules such as 2,5-dichloro-1,4-benzoquinone, nitrobenzene, and oxygen is demonstrated.

  12. (39)K NMR and EPR study of multiferroic K(3)Fe(5)F(15).

    PubMed

    Blinc, R; Zalar, B; Cevc, P; Gregorovič, A; Zemva, B; Tavčar, G; Laguta, V; Scott, J F; Dalal, N

    2009-01-28

    (39)K NMR spectra and relaxation times of polycrystalline K(3)Fe(5)F(15) have been used as a microscopic detector of the local magnetic fields at the magnetic transition at T(N) = 123 K. The NMR lineshape widens abruptly upon crossing T(N) due to the onset of internal magnetic fields, while we find no significant lineshift. The paraelectric to ferroelectric transition at T(c) = 490 K and the magnetic transition at T(N) have also been studied using X-band EPR (electron paramagnetic resonance). An increase and subsequent decrease in the EPR susceptibilities is observed on approaching T(N) from above. There is also a significant increase in the linewidth. At the same time the g-factor first decreases and then increases with decreasing temperature. The local magnetic field is different at different K sites and is much smaller than the magnetic field around the Fe sites. This seems to be consistent with the behaviour of a weak ferrimagnet. The ferrimagnetism does not seem to be due to spin canting as the lattice is disordered, but may arise from thermal blocking of superparamagnetic percolation clusters. The ferroelectric transition at T(c) shows no electronic anomaly, demonstrating that we are dealing with a classical phonon anomaly as found in conventional oxides rather than an electronic transition.

  13. Use of aspartame-based sweetener tablets in emergency dosimetry using EPR.

    PubMed

    Maghraby, A; Salama, E

    2010-06-01

    Accident dosimetry aims to evaluate the unplanned radiation doses delivered to individuals through one of the objects exist in the area of the accident. The gamma dose response of free radicals generated in irradiated aspartame tablets and its usability for emergency dosimetry was studied. EPR spectra of unirradiated and irradiated aspartame-based sweetener were recorded. Two signals arise after irradiating, S(1) at g (S(1)) = 2.00229 +/- 0.00097 and S(2) at g (S(2)) = 2.00262 +/- 0.00088. Some EPR parameters were studied for radiation-induced radicals in aspartame sweeteners tablets, such as the microwave saturation behaviour, the effect of magnetic field modulation amplitude on the peak-to-peak height and peak-to-peak line width for both of S(1) and S(2). Responses of S(1) and S(2) to different radiation doses were studied and resulted in linear relationships, radicals persistence curves were plotted over a 49-d storage period. It was found that Aspartame sweeteners tablets are useful in the range from 0.96 to 39.96 Gy. Radiation-induced radicals possess reasonable stability.

  14. Dielectric behavior, conduction and EPR active centres in BiVO4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Venkatesan, Rajalingam; Velumani, Subramaniam; Tabellout, Mohamed; Errien, Nicolas; Kassiba, Abdelhadi

    2013-12-01

    Bismuth vanadate (BiVO4) nanomaterials were synthesized by mechano-chemical ball milling method and complementary investigations were devoted to their structures, nanoparticle morphologies and electronic active centres. The dielectric and conductivity behaviour were analysed systematically in wide temperature and frequency ranges to correlate such physical responses with the peculiarities of the samples. Large interfacial polarisations favoured by high specific surfaces of nanoparticles account for a drastic enhancement of the dielectric function in the quasi-static regime. Exhaustive analyses of the dielectric experiments were achieved and account for the main features of dielectric functions and their related relaxation mechanisms. The electrical conductivity is thermally activated with energies in the range 0.1-0.6 eV depending on the sample features. DC conductivity up to 10-3 S/cm was obtained in well crystallized nanoparticles. Vanadium ions reduction was revealed by EPR spectroscopy with higher concentrations of the active centres (V4+) in more agglomerated and amorphous nanopowders. The EPR spectral parameters of V4+ were determined and correlated with the local environments of reduced vanadium ions and the characteristics of their electronic configurations. An insight is also made on the role of active electronic centres (V4+) on the conduction mechanism in nanostructured BiVO4.

  15. A Bridged Loop-Gap S-Band Surface Resonator for Topical EPR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Petryakov, Sergey; Chzhan, Michael; Samouilov, Alexandre; He, Guanglong; Kuppusamy, Periannan; Zweier, Jay L.

    2001-07-01

    The design and structure of a bridged loop-gap surface resonator developed for topical EPR spectroscopy and imaging of the distribution and metabolism of spin labels in in vivo skin is reported. The resonator is a one-loop, one-gap bridged structure. A pivoting single loop-coupling coil was used to couple the microwave power to the loop-gap resonant structure. A symmetric coupling circuit was used to achieve better shielding and minimize radiation. The frequency of the resonator can be easily adjusted by trimming the area of the capacitive foil bridge, which overlaps the gap in the cylindrical loop. The working frequency set was 2.2 GHz and the unloaded Q was 720. The B1 field of this resonator was measured and spatially mapped by three-dimensional EPR imaging. The resonator is well suited to topical measurements of large biological subjects and is readily applicable for in vivo measurements of free radicals in human skin.

  16. Development of In Vivo Tooth EPR for Individual Radiation Dose Estimation and Screening

    PubMed Central

    Williams, Benjamin B.; Dong, Ruhong; Kmiec, Maciej; Burke, Greg; Demidenko, Eugene; Gladstone, David; Nicolalde, Roberto J; Sucheta, Artur; Lesniewski, Piotr; Swartz, Harold M

    2009-01-01

    The development of in vivo EPR has made it feasible to perform tooth dosimetry measurements in situ, greatly expanding the potential for using this approach for immediate screening after radiation exposures. The ability of in vivo tooth dosimetry to provide estimates of absorbed dose has been established through a series of experiments using unirradiated volunteers with specifically irradiated molar teeth placed in situ within gaps in their dentition and in natural canine teeth of patients who have completed courses of radiation therapy for head and neck cancers. Multiple measurements in patients who have received radiation therapy demonstrate the expected heterogeneous dose distributions. Dose response curves have been generated using both populations and, using the current methodology and instrument, the standard error of prediction based on single 4.5 minute measurements is approximately 1.5 Gy for inserted molar teeth and between 2.0 and 2.5 Gy in the more irregularly shaped canine teeth. Averaging of independent measurements can reduce this error significantly to values near 1 Gy. Developments to reduce these errors are underway, focusing on geometric optimization of the resonators, detector positioning techniques, and optimal data averaging approaches. In summary, it seems plausible that the EPR dosimetry techniques will have an important role in retrospective dosimetry for exposures involving large numbers of individuals. PMID:20065702

  17. Combination of EPR measurements and DFT calculations to study nitrate impurities in the carbonated nanohydroxyapatite.

    PubMed

    Biktagirov, Timur; Gafurov, Marat; Mamin, Georgy; Klimashina, Elena; Putlayev, Valery; Orlinskii, Sergei

    2014-02-27

    We demonstrate the application of the combined experimental-computational approach for studying the anionic impurities in hydroxyapatite (HAp). Influence of the carbonation level (x) on the concentration of the NO3(2-) radicals in the HAp nanocrystals of Ca10-xNax(PO4)6-x(CO3)x(OH)2 with x in the range 0 < x < 2 and average sizes of 30 nm is investigated by different analytical methods including electron paramagnetic resonance (EPR). Stable NO3(2-) radicals are formed under X-ray irradiation of nano-HAp samples from NO3(-) ions incorporated in trace amounts during the wet synthesis process. Density functional theory (DFT) based calculations show energetic preference for the PO4 group substitution by NO3(-) ions. Comparison of the calculated and experimental spectroscopic parameters (g and hyperfine tensors) reveals that EPR detects the NO3(2-) radicals located in the positions of the PO4 group only. It is shown that with the increase in x, the carbonate ions substitute the NO3(2-)/NO3(-) ions. DFT calculations confirm that carbonate incorporation in HAp structure is energetically more favorable than the formation of the nitrate defect.

  18. A 140 GHz pulsed EPR/212 MHz NMR spectrometer for DNP studies.

    PubMed

    Smith, Albert A; Corzilius, Björn; Bryant, Jeffrey A; DeRocher, Ronald; Woskov, Paul P; Temkin, Richard J; Griffin, Robert G

    2012-10-01

    We described a versatile spectrometer designed for the study of dynamic nuclear polarization (DNP) at low temperatures and high fields. The instrument functions both as an NMR spectrometer operating at 212 MHz ((1)H frequency) with DNP capabilities, and as a pulsed-EPR operating at 140 GHz. A coiled TE(011) resonator acts as both an NMR coil and microwave resonator, and a double balanced ((1)H, (13)C) radio frequency circuit greatly stabilizes the NMR performance. A new 140 GHz microwave bridge has also been developed, which utilizes a four-phase network and ELDOR channel at 8.75 GHz, that is then multiplied and mixed to obtain 140 GHz microwave pulses with an output power of 120 mW. Nutation frequencies obtained are as follows: 6 MHz on S=1/2 electron spins, 100 kHz on (1)H, and 50 kHz on (13)C. We demonstrate basic EPR, ELDOR, ENDOR, and DNP experiments here. Our solid effect DNP results demonstrate an enhancement of 144 and sensitivity gain of 310 using OX063 trityl at 80 K and an enhancement of 157 and maximum sensitivity gain of 234 using Gd-DOTA at 20 K, which is significantly better performance than previously reported at high fields (≥3 T).

  19. Association of Copper to Riboflavin Binding Protein; Characterization by EPR and XAS

    SciTech Connect

    Smith,S.; Bencze, K.; Wasiukanis, K.; Stemmler, T.; Benore-Parsons, M.

    2008-01-01

    The association of copper to Riboflavin Binding Protein (RBP) from egg white has been studied by electron paramagnetic resonance (EPR) and X-ray absorption (XAS) spectroscopies. The type II site contains a mix of copper I and II in an oxygen rich environment. The association of copper to Riboflavin Binding Protein (RBP) from egg white has been studied by electron paramagnetic resonance (EPR) and X-ray absorption (XAS) spectroscopies in order to provide insight into how this essential protein may transport and store copper in avian embryos. Riboflavin Binding Protein, RBP, purified from avian egg white, has been shown to bind copper in a 1:1 molar ratio when dialyzed against copper(II) [1]. While the egg is a unique environment and quite rich in copper, the mechanisms by which this copper is delivered during development and stored for eventual use remain unclear [2]. Since RBP is already identified in the active transport of the cofactor riboflavin to the egg, evidence of its copper binding ability may suggest an additional role for RBP in the transport and storage of copper.

  20. EPR and magnetic susceptibility investigation of iron-zinc-phosphate glass ceramics

    SciTech Connect

    Popa, A.; Stefan, R.; Bosca, M.; Dan, V.; Pop, V.; Pascuta, P.

    2013-11-13

    (Fe{sub 2}O{sub 3}){sub x}⋅(P{sub 2}O{sub 5}){sub 40}⋅(ZnO){sub 60−x} glass ceramics containing different concentrations of Fe{sub 2}O{sub 3} ranging from 1 to 20 mol% were obtained by heat treatment of glass samples at 650 °C for 2 h. The structural and magnetic properties of these glass ceramics were investigated by means of electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The EPR spectra of the studied samples revealed absorptions centered at g ≈ 2.0 and 4.3. The compositional variations of the intensity and line width of these absorption lines was interpreted in terms of the variation in Fe{sup 3+} and Fe{sup 2+} ions concentration in the glass ceramics as well as the interaction between the iron ions. The magnetic susceptibility data evidenced the presence of both Fe{sup 3+} and Fe{sup 2+} ions, with their relative content depending on the Fe{sub 2}O{sub 3} concentration. Dipolar and superexchange interactions involving iron ions were revealed depending on the iron content of the sample.

  1. Transverse interference peaks in chirp FT-EPR correlated three-pulse ESEEM spectra.

    PubMed

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

    2016-11-01

    Fourier transform (FT) electron paramagnetic resonance (EPR) correlation spectroscopy usually requires broader excitation bandwidth than can be achieved by monochromatic rectangular pulses. Replacement of such pulses by frequency-swept pulses affords the correlation spectra, which, however, may not look the same as those that would be obtained with sufficiently broad-banded monochromatic rectangular pulses. This was recently observed for correlating nuclear frequencies to FT-EPR spectra by a three-pulse electron spin echo envelope modulation experiment. Here we analyze the origin of the additional cross peaks, whose position depends on the direction of the frequency sweep. We find that such peaks arise if coherence or polarization is transferred to an electron spin transition already before this transition is actually passed during the frequency sweep. This happens by excitation of a chain of transitions that connect levels of the source transition, where coherence resides before mixing, and the target transition, where it resides after mixing. The correlation spectra can be simplified by combining data from frequency up and down sweeps.

  2. A 140 GHz pulsed EPR/212 MHz NMR spectrometer for DNP studies

    NASA Astrophysics Data System (ADS)

    Smith, Albert A.; Corzilius, Björn; Bryant, Jeffrey A.; DeRocher, Ronald; Woskov, Paul P.; Temkin, Richard J.; Griffin, Robert G.

    2012-10-01

    We described a versatile spectrometer designed for the study of dynamic nuclear polarization (DNP) at low temperatures and high fields. The instrument functions both as an NMR spectrometer operating at 212 MHz (1H frequency) with DNP capabilities, and as a pulsed-EPR operating at 140 GHz. A coiled TE011 resonator acts as both an NMR coil and microwave resonator, and a double balanced (1H, 13C) radio frequency circuit greatly stabilizes the NMR performance. A new 140 GHz microwave bridge has also been developed, which utilizes a four-phase network and ELDOR channel at 8.75 GHz, that is then multiplied and mixed to obtain 140 GHz microwave pulses with an output power of 120 mW. Nutation frequencies obtained are as follows: 6 MHz on S = 1/2 electron spins, 100 kHz on 1H, and 50 kHz on 13C. We demonstrate basic EPR, ELDOR, ENDOR, and DNP experiments here. Our solid effect DNP results demonstrate an enhancement of 144 and sensitivity gain of 310 using OX063 trityl at 80 K and an enhancement of 157 and maximum sensitivity gain of 234 using Gd-DOTA at 20 K, which is significantly better performance than previously reported at high fields (⩾3 T).

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

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

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

  4. EPR Study of H and D Atoms in Quench-Condensed Solid D $_{2}$ 2

    NASA Astrophysics Data System (ADS)

    Dmitriev, Yu. A.

    2015-08-01

    We present an experimental study of H and D atoms trapped in a solid D matrix. The samples were prepared by quench condensing gaseous D with small (0.15 %) admixture of molecular H on a substrate at 1.3-4.2 K. An EPR observation revealed two types of H and D atoms: with narrow- and broad-line spectra. In order to elucidate the origin of the centers we performed an analysis that included comparing the matrix shifts of the hyperfine structure constants, considering the saturation and spin-relaxation times, estimation of the superhyperfine broadening, and evaluation of an effect which the tunneling isotope exchange reaction has on the H and D atoms relative EPR intensities. As a result, the broad-line H and D spectra were attributed to atoms at the substitutional positions in the regular D lattice, while the narrow-line spectra were due to atoms trapped at the one-dimensional structure imperfections (like dislocations). These trapped atoms are capable of moving quickly along the defects with a diffusion coefficient cm/s. The results were compared to earlier observations which allowed us to build a suggestion about the nature of previously found atomic centers in D not explained in the literature.

  5. Temperature effects on EPR spectra of a linear chain copper complex-copper calcium acetate hexahydrate

    NASA Astrophysics Data System (ADS)

    De, D. K.

    1981-03-01

    The observed angular dependence of the electron paramagnetic resonance linewidth in the ab and ac planes of CuCa(AC)2, 6H2O in the temperature interval 77K-12K was explained by considering dipolar interactions along with hyperfine and isotropic exchange interactions in these two planes. It was found that this so called linear-chain copper compound can be better described by a three dimensional paramagnet. The exchange interaction is very nearly isotropic with values Jab = 0.0098 cm-1 and Jc = 0.0103 cm-1. The values of the A⊥ derived from the linewidth fit in the ab plane are 14G at 77K and 60.5G at 1.2K. Due to insufficiency of data in the ac plane, the fit was done with the measured value of A∥. Although the exchange interaction has been found to be temperature independent the hyperfine interaction increases very much at low temperatures. The high temperature (300-460K) EPR spectra are quite different from the low temperature spectra. High temperature differential thermal analyses and thermogravimetric analyses have been carried out and corroborated with the EPR findings.

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

    PubMed

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

    2014-09-01

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

  7. Identification of radiation-induced radical structure in azocalix[4]arene: an EPR study.

    PubMed

    Usta, Keziban; Ozen Karakus, Ozlem; Usta, Ayhan; Deligoz, Hasalettin

    2013-10-01

    A macrocyclic azocalix[4]arene (1) based ester derivative was synthesized. The single crystals of azocalix[4]arene were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to (60) Co gamma rays with a dose rate of 0.980 kGy h(-1) for 48 and 72 h to produce a stable free radical. Electron paramagnetic resonance (EPR) measurements were performed in three mutually perpendicular planes of the single crystal in the magnetic field, in addition, temperature dependence of the EPR signal was studied between 120 K and 450 K. The spectra were found to be temperature and angular dependent. Analysis based on the spectra recorded showed that a free radical was formed by fission of a C-H bond. This radical is described as (•) Ca HCb H3 The averages of the principal values of the hyperfine parameters and g-factor are: g = 2.0034, AHa  = 1.28 mT, AH1=H2  = 1.00 mT, and AH3  = 0.49 mT.

  8. Photogenerated triplet states in supramolecular porphyrin ladder assemblies: an EPR study.

    PubMed

    Richert, Sabine; Peeks, Martin D; Tait, Claudia E; Anderson, Harry L; Timmel, Christiane R

    2016-09-21

    Introducing bridging ligands such as DABCO to solutions of linear zinc porphyrin oligomers has previously been shown to lead to the formation of ladder-type assemblies in which the single porphyrin units in each strand adopt a predominantly co-planar conformation. Here, we employ transient Electron Paramagnetic Resonance (EPR) to study photogenerated triplet states of these complexes in frozen solution with a particular focus on the extent of spin delocalisation. We make use of two different techniques: (i) the zero-field splitting parameters D and E are determined using transient continuous wave (cw) EPR spectroscopy and (ii) the hyperfine coupling constants, which directly reveal the extent of spin delocalisation, are quantified by orientation-selective proton Electron Nuclear DOuble Resonance (ENDOR) spectroscopy. It is found that ladder formation does not encourage triplet state delocalisation either across the bridging ligand DABCO or along the individual porphyrin strands despite their co-planar conformation, which was previously shown to allow increased electronic delocalisation.

  9. The characteristic photoluminescence and EPR features of superdeep diamonds (São-Luis, Brazil)

    NASA Astrophysics Data System (ADS)

    Yuryeva, Olga P.; Rakhmanova, Mariana I.; Nadolinny, Vladimir A.; Zedgenizov, Dmitry A.; Shatsky, Vladislav S.; Kagi, Hiroyuki; Komarovskikh, Andrey Yu.

    2015-10-01

    Photoluminescence (PL) spectroscopy and electron paramagnetic resonance (EPR) were used for the first time to characterize properties of superdeep diamonds from the São-Luis alluvial deposits (Brazil). The infrared measurements showed the low nitrogen content (>50 of 87 diamonds from this locality were nitrogen free and belonged to type IIa) and simultaneously the extremely high level of nitrogen aggregation (pure type IaB being predominant), which indicates that diamonds under study might have formed under high pressure and temperature conditions. In most cases, PL features excited at various wavelengths (313, 473, and 532 nm) were indicative of different growth and post-growth processes during which PL centers could be formed via interaction between vacancies and nitrogen atoms. The overall presence of the 490.7 nm, H3, and H4 centers in the luminescence spectra attests to strong plastic deformations in these diamonds. The neutral vacancy known as the GR1 center has probably occurred in a number of crystals due to radiation damage in the post-growth period. The 558.5 nm PL center is found to be one of the most common defects in type IIa samples which is accompanied by the EPR center with g-factor of 2.00285. The 536 and 576 nm vibronic systems totally dominated the PL spectra of superdeep diamonds, while none of "normal" diamonds from the Mir pipe (Yakutia) with similar nitrogen characteristics showed the latter three PL centers.

  10. Hydrogen at zinc vacancy of ZnO: An EPR and ESEEM study

    SciTech Connect

    Son, N. T.; Ivanov, I. G.; Janzén, E.; Isoya, J.; Ohshima, T.

    2014-02-21

    An electron paramagnetic resonance (EPR) spectrum, labeled S1, with small-splitting doublet accompanied by weak satellites is observed in ZnO irradiated with 2 MeV electrons. The obtained structure is shown to be the hyperfine structure due to the dipolar interaction between an unpaired electron spin and a nuclear spin of hydrogen (H). The observation of the nuclear Zeeman frequency of H in electron spin echo envelope modulation experiments further confirmed the presence of a hydrogen atom in S1. From the observed spin-Hamiltonian parameters, S1 is identified to be the partly H-passivated Zn vacancy, V{sub Zn}{sup −}H{sup +}, with the H{sup +} ion making a short O-H bond with only one nearest O neighbor of V{sub Zn} in the basal plane, being off the substitutional site, while the unpaired electron spin, which gives rise to the observed EPR signal, is localized on the p orbital of another O neighbor also in the basal plane.

  11. Automatic fitting to `powder' EPR spectra of coupled paramagnetic species employing Feynman's theorem

    NASA Astrophysics Data System (ADS)

    Lund, Anders; Gustafsson, Håkan; Maruani, Jean; Shiotani, Masaru

    2006-03-01

    A previous automatic fitting procedure of EPR spectra has been extended with the purpose to characterise coupled paramagnetic complexes in powders and frozen solutions. The theoretical EPR spectra were obtained by matrix diagonalization of a general spin Hamiltonian. A least-squares fitting procedure using analytical derivatives of the calculated spectrum with respect to the spectroscopic, fine structure, nuclear quadrupole, electron-electron, and hyperfine coupling tensors was used to refine those parameters. The powder spectra of matrix isolated rad CF 3 and RCF 2CF 2rad radicals, previously measured at low temperature, were reanalysed with this method. A theoretically modeled complex consisting of a Cu 2+ ion, featuring an axially symmetric g-tensor and 63Cu hyperfine structure anisotropy, and a free radical located at different orientations, with respect to the symmetry axis of the Cu 2+ ion, was examined in order to investigate the possibility to recover the magnetic parameters of the separate units and the magnetic couplings between them.

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

    NASA Astrophysics Data System (ADS)

    Bıyık, Recep; Tapramaz, Recep

    2009-10-01

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

  13. On the "negative utility" of Ernst Cassirer's philosophy of physics: An application to the EPR argument

    NASA Astrophysics Data System (ADS)

    Stamenkovic, Philippe

    2016-08-01

    This paper tries to reconstruct Ernst Cassirer's potential reception of the EPR argument, as exposed by Einstein in his letter to Cassirer of March 1937. It is shown that, in conformity with his transcendental epistemology taking the conditions of accessibility as constitutive of the quantum object, Cassirer would probably have rejected the argument. Indeed, Cassirer would probably not have subscribed to its separability/local causality presupposition (which goes against his interpretation of the quantum formalism as a self-sufficient condition constitutive of the quantum object, without any reliance on spatial intuition), nor to its completeness requirement (as his partial endorsement of Bohr's complementarity, and his rejection of the Kantian "idea of complete determination", illustrate). By rejecting both of its premises, Cassirer's philosophy of physics thus enables to escape the EPR dilemma, and exhibits what, in Kantian terms, might be called a "negative utility" with respect to physical science. A further investigation of the anti-reductionist utility of Cassirer's systematic philosophy with respect to physics and other "symbolic forms" is finally suggested.

  14. Fast dynamic electron paramagnetic resonance (EPR) oxygen imaging using low-rank tensors

    NASA Astrophysics Data System (ADS)

    Christodoulou, Anthony G.; Redler, Gage; Clifford, Bryan; Liang, Zhi-Pei; Halpern, Howard J.; Epel, Boris

    2016-09-01

    Hypoxic tumors are resistant to radiotherapy, motivating the development of tools to image local oxygen concentrations. It is generally believed that stable or chronic hypoxia is the source of resistance, but more recent work suggests a role for transient hypoxia. Conventional EPR imaging (EPRI) is capable of imaging tissue pO2in vivo, with high pO2 resolution and 1 mm spatial resolution but low imaging speed (10 min temporal resolution for T1-based pO2 mapping), which makes it difficult to investigate the oxygen changes, e.g., transient hypoxia. Here we describe a new imaging method which accelerates dynamic EPR oxygen imaging, allowing 3D imaging at 2 frames per minute, fast enough to image transient hypoxia at the "speed limit" of observed pO2 change. The method centers on a low-rank tensor model that decouples the tradeoff between imaging speed, spatial coverage/resolution, and number of inversion times (pO2 accuracy). We present a specialized sparse sampling strategy and image reconstruction algorithm for use with this model. The quality and utility of the method is demonstrated in simulations and in vivo experiments in tumor bearing mice.

  15. Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy.

    PubMed

    Ahmad, R; Som, S; Kesselring, E; Kuppusamy, P; Zweier, J L; Potter, L C

    2010-12-01

    A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramér-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration.

  16. Decision support tools for proton therapy ePR: intelligent treatment planning navigator and radiation toxicity tool for evaluating of prostate cancer treatment

    NASA Astrophysics Data System (ADS)

    Le, Anh H.; Deshpande, Ruchi; Liu, Brent J.

    2010-03-01

    The electronic patient record (ePR) has been developed for prostate cancer patients treated with proton therapy. The ePR has functionality to accept digital input from patient data, perform outcome analysis and patient and physician profiling, provide clinical decision support and suggest courses of treatment, and distribute information across different platforms and health information systems. In previous years, we have presented the infrastructure of a medical imaging informatics based ePR for PT with functionality to accept digital patient information and distribute this information across geographical location using Internet protocol. In this paper, we present the ePR decision support tools which utilize the imaging processing tools and data collected in the ePR. The two decision support tools including the treatment plan navigator and radiation toxicity tool are presented to evaluate prostate cancer treatment to improve proton therapy operation and improve treatment outcomes analysis.

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

    PubMed

    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

  18. Epr Hyperfine Structure Of Radiation Defect In Oxyfluoride Glass Ceramics/ Radiācijas Defekta Epr Hipersīkstruktūra Oksifluorīdu Stikla Keramikā

    NASA Astrophysics Data System (ADS)

    Běrziņš, D.; Fedotovs, A.; Rogulis, U.

    2012-12-01

    We have investigated the samples of thermally treated oxyfluoride glass ceramics 50SiO2-25LiO2-20YF3-3ErF3-2YbF2 by means of electron paramagnetic resonance (EPR) techniques. After irradiation of the samples with X-rays, in the EPR spectra a hyperfine structure characteristic of F-centres could be observed in different fluoride crystals. The structure of F-centre in the oxyfluoride glass ceramics containing LiYF4 crystallites is discussed. Oksifluorīdu stiklu keramikas 50SiO2-25LiO2-20YF3-3ErF3-2YbF2 radiācijas defektu īpašības pētītas, izmantojot elektronu paramagnētiskās rezonanses (EPR) metodi. Pēc paraugu apstarošanas ar rentgen stariem, EPR spektros tika novērota vairāku fluorīdu kristālu F-centriem raksturīga hipersīkstruktūra. Šajā darbā apskatīta F-centra struktūra oksifluorīdu stiklu keramikā, kura satur LiYF4 kristalītus.

  19. From PACS to Web-based ePR system with image distribution for enterprise-level filmless healthcare delivery.

    PubMed

    Huang, H K

    2011-07-01

    The concept of PACS (picture archiving and communication system) was initiated in 1982 during the SPIE medical imaging conference in New Port Beach, CA. Since then PACS has been matured to become an everyday clinical tool for image archiving, communication, display, and review. This paper follows the continuous development of PACS technology including Web-based PACS, PACS and ePR (electronic patient record), enterprise PACS to ePR with image distribution (ID). The concept of large-scale Web-based enterprise PACS and ePR with image distribution is presented along with its implementation, clinical deployment, and operation. The Hong Kong Hospital Authority's (HKHA) integration of its home-grown clinical management system (CMS) with PACS and ePR with image distribution is used as a case study. The current concept and design criteria of the HKHA enterprise integration of the CMS, PACS, and ePR-ID for filmless healthcare delivery are discussed, followed by its work-in-progress and current status.

  20. VHF EPR quantitation and speciation of organic sulfur in coal. Technical report, September 1, 1993--November 30, 1993

    SciTech Connect

    Clarkson, R.B.; Belford, R.L.

    1993-12-31

    Over the last few years, we have developed a non-destructive technique called Very High Frequency Electron Paramagnetic Resonance (VHF-EPR) that is proving to be a practical and very sensitive analytical method for the organic sulfur in coal. Already, although still under development, the technique rapidly can quantify organic sulfur, and perhaps provide information on organic oxygen and nitrogen, in typical Illinois coals. At this stage, the precision is not well enough calibrated, and specificity for particular species needs more development. This year`s proposal outlined a 12 month work plan designed to improve and extend the utility of VHF-EPR. Two main goals of the work are: (1) refinement and calibration of organic sulfur analysis, in coals of differing rank, over a concentration range from 0.1% to 5%, and (2) better utilization of VHF-EPR coal spectral data for sulfur speciation. This quarter, goal (1) is being pursued; results will be ready to describe in a future report. Meanwhile, work toward goal (2) has produced detailed information about the VHF-EPR spectral behavior of several comparison compounds -- sulfur -- containing thiophenic fused-ring molecules.

  1. Testing and linearity calibration of films of phenol compounds exposed to thermal neutron field for EPR dosimetry.

    PubMed

    Gallo, S; Panzeca, S; Longo, A; Altieri, S; Bentivoglio, A; Dondi, D; Marconi, R P; Protti, N; Zeffiro, A; Marrale, M

    2015-12-01

    This paper reports the preliminary results obtained by Electron Paramagnetic Resonance (EPR) measurements on films of IRGANOX® 1076 phenols with and without low content (5% by weight) of gadolinium oxide (Gd2O3) exposed in the thermal column of the Triga Mark II reactor of LENA (Laboratorio Energia Nucleare Applicata) of Pavia (Italy). Thanks to their size, the phenolic films here presented are good devices for the dosimetry of beams with high dose gradient and which require accurate knowledge of the precise dose delivered. The dependence of EPR signal as function of neutron dose was investigated in the fluence range between 10(11) cm(-2) and 10(14) cm(-2). Linearity of EPR response was found and the signal was compared with that of commercial alanine films. Our analysis showed that gadolinium oxide (5% by weight) can enhance the thermal neutron sensitivity more than 18 times. Irradiated dosimetric films of phenolic compound exhibited EPR signal fading of about 4% after 10 days from irradiation.

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

    PubMed

    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.

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

    PubMed

    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.

  4. EPR studies on copper(II) complexes of 2,2',2″-triamino-triethylamine and its hexamethyl derivative

    NASA Astrophysics Data System (ADS)

    Sastry, B. A.; Chary, M. N.; Ponticelli, G.; Pinna, R.

    1980-09-01

    This paper presents EPR, and optical absorption studies on [Cu(tren)NCS]SCN and [Cu(Me 6tren)NCS]SCN in solutions. Expressions derived by Barbucci and Bencini are evaluated. It is shown that the molecular motion of the complexes is anisotropic and nondiffusional.

  5. 3D printed sample holder for in-operando EPR spectroscopy on high temperature polymer electrolyte fuel cells.

    PubMed

    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.

  6. 3D printed sample holder for in-operando EPR spectroscopy on high temperature polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    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.

  7. Insights into EPR effect versus lectin-mediated targeted delivery: biodegradable polycarbonate micellar nanoparticles with and without galactose surface decoration.

    PubMed

    Ebrahim Attia, Amalina Binte; Oh, Pamela; Yang, Chuan; Tan, Jeremy Pang Kern; Rao, Nithya; Hedrick, James L; Yang, Yi Yan; Ge, Ruowen

    2014-11-12

    Polymeric micelles with and without galactose are synthesized to study liver targeting ability in an orthotopic HCC rat model. Micelles with galactose accumulate more in the healthy liver tissue instead of HCC, while micelles without galactose amass in HCC by the EPR effect. These micelles show great potential as drug delivery carriers to target either the liver or HCC.

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

    NASA Astrophysics Data System (ADS)

    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%.

  9. Reconstruction of the first derivative EPR spectrum from multiple harmonics of the field-modulated continuous wave signal

    PubMed Central

    Tseitlin, Mark; Eaton, Sandra S.; Eaton, Gareth R.

    2011-01-01

    Selection of the amplitude of magnetic field modulation for continuous wave electron paramagnetic resonance (EPR) often is a trade-off between sensitivity and resolution. Increasing the modulation amplitude improves the signal-to-noise ratio, S/N, at the expense of broadening the signal. Combining information from multiple harmonics of the field-modulated signal is proposed as a method to obtain the first derivative spectrum with minimal broadening and improved signal-to-noise. The harmonics are obtained by digital phase-sensitive detection of the signal at the modulation frequency and its integer multiples. Reconstruction of the first derivative EPR line is done in the Fourier conjugate domain where each harmonic can be represented as the product of the Fourier transform of the 1st derivative signal with an analytical function. The analytical function for each harmonic can be viewed as a filter. The Fourier transform of the 1st derivative spectrum can be calculated from all available harmonics by solving an optimization problem with the goal of maximizing the S/N. Inverse Fourier transformation of the result produces the 1st derivative EPR line in the magnetic field domain. The use of modulation amplitude greater than linewidth improves the S/N, but does not broaden the reconstructed spectrum. The method works for an arbitrary EPR line shape, but is limited to the case when magnetization instantaneously follows the modulation field, which is known as the adiabatic approximation. PMID:21349750

  10. Role of excited singlet state in the photooxidation of carotenoids: A time-resolved Q-band EPR study

    SciTech Connect

    Jeevarajan, A.S.; Kispert, L.D.; Avdievich, N.I.; Forbes, M.D.E.

    1996-01-11

    Spin-polarized 35 GHz time-resolved EPR (TREPR) spectra were obtained for the first time of the cation radicals of {beta}-carotene (I), 15,15`-didehydro-{beta}-carotene (II), 7`,7`-dicyano-7`-apo-{beta}-carotene (III), and 7`-cyano-7`- ethoxycarbonyl-7`-apo-{beta}-carotene (IV) and the anion radical of the solvent which were formed by 308 nm photoexcitation of the carotenoids in carbon tetrachloride solution. Although the EPR spectra are weak in intensity due to the small dimensions of the 35 GHz quartz flat cell and have very broad line widths, it was possible to positively determine from the polarization pattern that the electron transfer to the solvent occurs from the excited singlet state of the carotenoids. The 35 GHz EPR spectra consist of two resolved EPR lines (one absorption and one emission) from which it has been possible to measure the g factor and {Delta}H{sub pp} of the solvent-separated radical ion pair that was formed; measurements were not possible at 9 GHz. 25 refs., 2 figs., 1 tab.

  11. Two Copies of the Einstein-Podolsky-Rosen State of Light Lead to Refutation of EPR Ideas

    NASA Astrophysics Data System (ADS)

    Rosołek, Krzysztof; Stobińska, Magdalena; Wieśniak, Marcin; Żukowski, Marek

    2015-03-01

    Bell's theorem applies to the normalizable approximations of original Einstein-Podolsky-Rosen (EPR) state. The constructions of the proof require measurements difficult to perform, and dichotomic observables. By noticing the fact that the four mode squeezed vacuum state produced in type II down-conversion can be seen both as two copies of approximate EPR states, and also as a kind of polarization supersinglet, we show a straightforward way to test violations of the EPR concepts with direct use of their state. The observables involved are simply photon numbers at outputs of polarizing beam splitters. Suitable chained Bell inequalities are based on the geometric concept of distance. For a few settings they are potentially a new tool for quantum information applications, involving observables of a nondichotomic nature, and thus of higher informational capacity. In the limit of infinitely many settings we get a Greenberger-Horne-Zeilinger-type contradiction: EPR reasoning points to a correlation, while quantum prediction is an anticorrelation. Violations of the inequalities are fully resistant to multipair emissions in Bell experiments using parametric down-conversion sources.

  12. EPR and ENDOR studies of point defects in lithium triborate and beta-barium borate

    NASA Astrophysics Data System (ADS)

    Hong, Wei

    Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (EN-DOR) have been used to identify and characterize point defects in nonlinear optical crystals of lithium triborate (LiB3O5) and beta barium borate (beta-BaB2O4). Two similar hole centers, one (Hole Center A) stable below approximately 130 K and the other one (Hole Center B) stable below approximately 170 K, were observed in LiB3O 5. For both centers, there is a major hyperfine interaction with only one 11B nucleus. The g matrix and the 11B hyperfine and nuclear quadrupole matrices have been determined for each hole center. I suggest Hole Center A is a self-trapped hole with the hole localized on an oxygen ion between a threefold-bonded boron and a fourfold-bonded boron. The self-trapping occurs because of a significant relaxation of the neighboring fourfold boron away from the hole. A similar model is suggested for Hole Center B, except a neighboring lithium vacancy is included to provide the increased thermal stability. For undoped beta-BaB2O4, the dominant electron center is an oxygen vacancy on a bridging oxygen site. The EPR spectrum of this center exhibits a 16-line hyperfine pattern from two boron nuclei. The dominant hole center in beta-BaB2O4 exhibits a four-line hyperfine pattern due to one boron, and is assigned to a hole localized on a nonbridging oxygen ion with no other defects nearby. Warming the crystal to approximately 80 K destroys the dominant hole spectrum and introduces other perturbed hole centers. For silver-doped beta-BaB 2O4, after room temperature irradiation of the sample, EPR reveals a Ag2+ center (formed when a hole is trapped by a Ag + substituting on a Ba2+ site) and two distinct interstitial Ag0 centers (formed when an electron is trapped by a Ag + on interstitial sites). The g and A matrices of the Ag2+ center have been determined. These centers in LiB3O5 and beta-BaB2O 4 are of interest because of their possible role in the unwanted transient optical

  13. RADICAL SITES IN M. TUBERCULOSIS KATG IDENTIFIED USING EPR SPECTROSCOPY, THE 3-D CRYSTAL STRUCTURE AND ELECTRON-TRANSFER COUPLINGS†

    PubMed Central

    Ranguelova, Kalina; Girotto, Stefania; Gerfen, Gary J.; Yu, Shengwei; Suarez, Javier; Metlitsky, Leonid; Magliozzo, Richard S.

    2007-01-01

    Catalase-peroxidase (KatG) from Mycobacterium tuberculosis, a Class I peroxidase, exhibits high catalase activity and peroxidase activity with various substrates, and is responsible for activation of the commonly used antitubercular drug, isoniazid (INH). KatG readily forms amino acid based radicals during turnover with alkyl peroxides and this work focuses on extending the identification and characterization of radicals forming on the millisecond to seconds time scale. Rapid freeze- quench electron paramagnetic resonance spectroscopy (RFQ-EPR) reveals a change in the structure of the initially formed radical in the presence of INH. Heme-pocket binding of the drug, and knowledge that KatG[Y229F] lacks this signal provides evidence for radical formation on residue Y229. High-field RFQ-EPR spectroscopy confirmed a tryptophanyl radical signal and new analyses of X-band RFQ-EPR spectra also established its presence. High-field EPR spectroscopy also confirmed that the majority radical species is a tyrosyl radical. Site-directed mutagenesis, along with simulations of EPR spectra based on X-ray structural data for particular tyrosine and tryptophan residues enabled assignments based on predicted hyperfine coupling parameters. KatG mutants W107F, Y229F and the double mutant W107F/Y229F showed alteration in type and yield of radical species. Results are consistent with formation of a tyrosyl radical reasonably assigned to residue Y229 within the first few milliseconds of turnover. This is followed by a mixture of tyrosyl and tryptophanyl radical species, and finally to only a tyrosyl radical on residue Y353, which lies more distant from the heme. Radical processing of enzyme lacking the Trp107-Tyr229-Met255 adduct, found as a unique structural feature of catalase-peroxidases, is suggested to be a reasonable assignment of the phenomena. PMID:17204474

  14. Membrane fluidity profiles as deduced by saturation-recovery EPR measurements of spin-lattice relaxation times of spin labels.

    PubMed

    Mainali, Laxman; Feix, Jimmy B; Hyde, James S; Subczynski, Witold K

    2011-10-01

    There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate (T(1)(-1)) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T(1)(-1) can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T(1)(-1) profiles obtained for 1-palmitoyl-2-(n-doxylstearoyl)phosphatidylcholine (n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R(⊥), obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T(1)(-1) and R(⊥) profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz).

  15. Elucidating the design principles of photosynthetic electron-transfer proteins by site-directed spin labeling EPR spectroscopy.

    PubMed

    Ishara Silva, K; Jagannathan, Bharat; Golbeck, John H; Lakshmi, K V

    2016-05-01

    Site-directed spin labeling electron paramagnetic resonance (SDSL EPR) spectroscopy is a powerful tool to determine solvent accessibility, side-chain dynamics, and inter-spin distances at specific sites in biological macromolecules. This information provides important insights into the structure and dynamics of both natural and designed proteins and protein complexes. Here, we discuss the application of SDSL EPR spectroscopy in probing the charge-transfer cofactors in photosynthetic reaction centers (RC) such as photosystem I (PSI) and the bacterial reaction center (bRC). Photosynthetic RCs are large multi-subunit proteins (molecular weight≥300 kDa) that perform light-driven charge transfer reactions in photosynthesis. These reactions are carried out by cofactors that are paramagnetic in one of their oxidation states. This renders the RCs unsuitable for conventional nuclear magnetic resonance spectroscopy investigations. However, the presence of native paramagnetic centers and the ability to covalently attach site-directed spin labels in RCs makes them ideally suited for the application of SDSL EPR spectroscopy. The paramagnetic centers serve as probes of conformational changes, dynamics of subunit assembly, and the relative motion of cofactors and peptide subunits. In this review, we describe novel applications of SDSL EPR spectroscopy for elucidating the effects of local structure and dynamics on the electron-transfer cofactors of photosynthetic RCs. Because SDSL EPR Spectroscopy is uniquely suited to provide dynamic information on protein motion, it is a particularly useful method in the engineering and analysis of designed electron transfer proteins and protein networks. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

  16. A multimedia Electronic Patient Record (ePR) system for Image-Assisted Minimally Invasive Spinal Surgery

    PubMed Central

    Documet, Jorge; Le, Anh; Liu, Brent; Chiu, John; Huang, HK

    2009-01-01

    Purpose This paper presents the concept of bridging the gap between diagnostic images and image-assisted surgical treatment through the development of a one-stop multimedia electronic patient record (ePR) system that manages and distributes the real-time multimodality imaging and informatics data that assists the surgeon during all clinical phases of the operation from planning Intra-Op to post-care follow-up. We present the concept of this multimedia ePR for surgery by first focusing on Image-Assisted Minimally Invasive Spinal Surgery as a clinical application. Methods Three clinical Phases of Minimally Invasive Spinal Surgery workflow in Pre-Op, Intra-Op, and Post Op are discussed. The ePR architecture was developed based on the three-phased workflow, which includes the Pre-Op, Intra-Op, and Post-Op modules and four components comprising of the input integration unit, fault-tolerant gateway server, fault-tolerant ePR server, and the visualization and display. A prototype was built and deployed to a Minimally Invasive Spinal Surgery clinical site with user training and support for daily use. Summary A step-by step approach was introduced to develop a multi-media ePR system for Imaging-Assisted Minimally Invasive Spinal Surgery that includes images, clinical forms, waveforms, and textual data for planning the surgery, two real-time imaging techniques (digital fluoroscopic, DF) and endoscope video images (Endo), and more than half a dozen live vital signs of the patient during surgery. Clinical implementation experiences and challenges were also discussed. PMID:20033507

  17. Single crystal EPR study of the Ni center of NiFe hydrogenase

    NASA Astrophysics Data System (ADS)

    Geßner, Ch.; Trofanchuk, O.; Kawagoe, K.; Higuchi, Y.; Yasuoka, N.; Lubitz, W.

    1996-07-01

    EPR spectra of single crystals of NiFe hydrogenase from Desulfovibrio vulgaris Miyazaki F were evaluated and yielded the g-tensors of the Ni center for two different states of enzyme. The g-values associated with these states are identical to those measured in frozen solutions for the ready (NiB) and the unready (NiA) form of the Ni center. Directions of the g-tensor axes were determined relative to the crystal symmetry axes. The obtained changes of g-values and tensor axes orientations between NiA and NiB can be explained by a structural difference involving modification of a cysteine sulfur ligand.

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

    SciTech Connect

    Haskell, E.; Kenner, G.; Hayes, R.; Chumak, V.; Shalom, S.

    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.

  19. VHF EPR determination of the chemical forms of organic sulfur in coal

    SciTech Connect

    Clarkson, R.B.

    1991-01-01

    This program addresses the need for innovative approaches to characterize the organic sulfur in Illinois Basin coals. We have developed a very high frequency electron paramagnetic resonance (EPR) spectrometer operating at the W-band of microwave frequencies (96 GHz). This instrument has shown unique sensitivity to heteroatoms in coal, and we believe the technique can be successfully applied for the non-destructive, direct determination of organic sulfur in coal. Preliminary data from Illinois coals and separated macerals indicate that the method also may be able to distinguish aromatic from aliphatic sulfur, and may be useful in assessing the extent of conjugation in aromatic portions of the coal. These high energy spectroscopic techniques, however invariably suffer from the fact that they are not truly non-destructive. By contrast, the low powers and relatively low energy radiation used in magnetic resonance techniques have virtually no effect on the physical structure or chemical composition of coal.

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

    PubMed

    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.

  1. The use of simulation in the EPR spin probe technique for detection of irradiated seeds.

    PubMed

    Sünnetçioğlu, M M; Dadaylı, D

    2000-10-02

    An electron paramagnetic resonance (EPR) spin probe study of irradiated wheat seeds was performed depending on irradiation dose. The structural changes in the membrane integrity were followed using aqueous solutions of 4-hydroxy-TEMPO (TANOL) spin probe and a line broadening material. In the studies dry seed embryos were kept in these solutions for 150 min. The spectra were recorded at various times of air drying process. The simulation of these spectra indicated a decrease in the water content of the embryos depending on the increasing irradiation dose. This indicates the increase in the permeability of the membranes as a result of the radiation damage. From the decay curves it is possible to determine about irradiation dose, however, this approach is not very successful at close irradiation doses.

  2. EPR investigation of the trivalent chromium complexes in SrTiO3

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  3. Attacks and Improvement of Quantum Sealed-Bid Auction with EPR Pairs

    NASA Astrophysics Data System (ADS)

    Liu, Wen-Jie; Wang, Fang; Ji, Sai; Qu, Zhi-Guo; Wang, Xiao-Jun

    2014-06-01

    Recently, an experimentally feasible three-party quantum sealed-bid auction protocol based on EPR pairs [Z.Y. Wang, Commun. Theor. Phys. 54 (2010) 997] was proposed. However, this study points out Wang's protocol cannot resist some internal bidders' attacks, such as the Twice-CNOT attack, the collusion attack. A malicious bidder can launch the Twice-CNOT attack to obtain the other's bid, or the dishonest auctioneer may collude with one bidder and help him/her win the action by changing his/her bid. For preventing against these attacks, a simple solution by using the QKD-based message encryption and a post-confirmation mechanism by adopting the hash function are proposed.

  4. Combined approaches of EPR and NMR illustrate only one transmembrane helix in the human IFITM3

    PubMed Central

    Ling, Shenglong; Zhang, Chengwei; Wang, Wei; Cai, Xiaoying; Yu, Lu; Wu, Fangming; Zhang, Longhua; Tian, Changlin

    2016-01-01

    Interferon-inducible transmembrane protein IFITM3 was known to restrict the entry of a wide spectrum of viruses to the cytosol of the host. The mechanism used by the protein to restrict viral entry is unclear given the unavailability of the membrane topology and structures of the IFITM family proteins. Systematic site-directed spin labeling (SDSL) and electron paramagnetic resonance (EPR) studies of IFITM3 in detergent micelles identified a single, long transmembrane helix in the C-terminus and an intramembrane segment in the N-terminal hydrophobic region. Solution NMR studies of the same sample verified the secondary structure distribution and demonstrated two rigid regions interacting with the micellar surface. The resulting membrane topology of IFITM3 supports the mechanism of an enhanced restricted membrane hemi-fusion. PMID:27046158

  5. Some comments on the EPR (The reasons why experiments should still be done)

    SciTech Connect

    Piccioni, O.; Wright, B.

    1993-10-01

    The authors believe that much of the contradiction they hear about the Einstein Podoisky Rosen Paradox (EPR), can be framed into the diverse ways of using or misusing the principle of ``collapse,`` (a principle, which according to Wigner, is very attractive, but not very informative). To make their points, they will mainly use the model [Lamehi-Rachti, Mittig, Phys. Rev. D14 (1976)] of two free protons scattering in the well known state of singlet, ud-du = SS, according to the Pauli Principle. (An equivalent description can be done with the polarization of photons.) The authors ask the important question whether, on separation, the two fermions will remain in the state SS, where neither proton has a definite state and the whole two fermion system has exactly zero component in any direction.

  6. EPR and optical absorption studies of copper ions in diglycine calcium chloride tetrahydrate

    NASA Astrophysics Data System (ADS)

    Kripal, Ram; Bajpai, Manisha

    2009-04-01

    EPR study of copper ions in diglycine calcium chloride tetrahydrate (DGCCT), [(NH 2CH 2COOH) 2·CaCl 2·4H 2O] single crystals at room temperature is carried out. The spin Hamiltonian parameters of copper ions are determined as: gx = 2.0238 ± 0.0002, gy = 2.1122 ± 0.0002, gz = 2.2250 ± 0.0002, Ax = (83 ± 2) × 10 -4 cm -1, Ay = (86 ± 2) × 10 -4 cm -1 and Az = (118 ± 2) × 10 -4 cm -1. The optical study of the single crystals at room temperature is also done and the bands are assigned to d-d and charge transfer transitions. Using above data, the nature of bonding in the complex is discussed.

  7. Deterministic and Monte-Carlo calculation schemes of the EPR core and its heavy steel reflector

    SciTech Connect

    Golfier, H.; Poinot-Salanon, C.; Nicolas, A.; Taieb, J.; Enderle, R.

    2006-07-01

    The aim of this work is to study an EPR core and its heavy reflector with the objective to quantify both the methodological biases within three calculation schemes and the impact on the core neutronic behaviour of the heavy reflector. To reach this, three different calculation schemes are presented here: - A reference calculation using the pointwise Monte-Carlo TRIPOLI4 code - A deterministic one, fully heterogeneous, based on the method of Characteristics - implemented in the APOLLO2 code - A diffusion approach using the mixed-dual finite elements with the CRONOS2 code. The first part of the paper gives the main characteristics of the core configuration chosen for the analyses. In a second part, the three different models and schemes are described and the third part is dedicated to the analysis of the results. (authors)

  8. The Formation Mechanism of Mesoporous Materials studied by EPR Spectroscopy and Cryo-TEM

    NASA Astrophysics Data System (ADS)

    Ruthstein, Sharon

    Ordered mesoporous materials raised a wide interest in the scientific community due to their unique structural properties which encompasses nanosize ordered channels. These materials have potential applications in diverse technological fields such as catalysis, membranes, microelectronics and sensors. The formation of these materials is initiated by the interaction of micelle of surfactant molecules with precursors of an inorganic oxide, usually silica, which further polymerizes to form solids with a well defined pore structure and amorphous walls. The aim of this study is to explore the details of this intriguing reaction mechanism on two types of materials, hexagonal and cubic, prepared with Pluronic block-copolymers as surfactants. The Pluronic micelles are characterized by a hydrophobic polypropylene oxide core and a hydrophilic polyethylene oxide corona. Examples of questions we address are: How does a homogeneous micellar solution transforms into an ordered phase? What kinds of interactions are responsible to this transformation? Our work focused on processes that take place on two levels, the molecular one and the mesoscale, which were investigated by combining electron paramagnetic resonance (EPR) and cryogenic transmission electron microscopy (cryo-TEM) techniques. The molecular level studies combine in-situ and freeze quench EPR spectroscopic techniques applied to nitroxide spin-probes introduced (at minute quantities) into the reaction mixtures. The nitroxide radicals serve as paramagnetic probes in the reaction mixture. They do not react or affect the reaction product but they sense in-situ the changes that occur in their environment during the reaction. The EPR spectrum provides information regarding the dynamic of the probe, which is affected by its surrounding, and the polarity of its environment. Fine structural details, such as the distribution of water and additives within the micelle, can be obtained from Electron Spin Echo Envelope Modulation

  9. Photocatalytic removal of soot: unravelling of the reaction mechanism by EPR and in situ FTIR spectroscopy.

    PubMed

    Smits, Marianne; Ling, Yun; Lenaerts, Silvia; Van Doorslaer, Sabine

    2012-12-21

    Photocatalytic soot oxidation is studied on P25 TiO(2) as an important model reaction for self-cleaning processes by means of electron paramagnetic resonance (EPR) and Fourier transform infrared (FTIR) spectroscopy. Contacting of carbon black with P25 leads on the one hand to a reduction of the local dioxygen concentration in the powder. On the other hand, the weakly adsorbed radicals on the carbon particles are likely to act as alternative traps for the photogenerated conduction-band electrons. We find furthermore that the presence of dioxygen and oxygen-related radicals is vital for the photocatalytic soot degradation. The complete oxidation of soot to CO(2) is evidenced by in situ FTIR spectroscopy, no intermediate CO is detected during the photocatalytic process.

  10. Molecular structure and the EPR calculation of the gas phase succinonitrile molecule

    NASA Astrophysics Data System (ADS)

    Kepceoǧlu, A.; Kılıç, H. Ş.; Dereli, Ö.

    2017-02-01

    Succinonitrile (i.e. butanedinitrile) is a colorless nitrile compound that can be used in the gel polymer batteries as a solid-state solvent electrolytes and has a plastic crystal structure. Prior to the molecular structure calculation of the succinonitrile molecule, the conformer analysis were calculated by using semi empirical method PM3 core type Hamiltonian and eight different conformer structures were determined. Molecular structure with energy related properties of these conformers having the lowest energy was calculated by using DFT (B3LYP) methods with 6-311++G(d,p) basis set. Possible radicals, can be formed experimentally, were modeled in this study. EPR parameters of these model radicals were calculated and then compared with that obtained experimentally.

  11. EPR study of the stable radical in a γ-irradiated single crystal of progesterone

    NASA Astrophysics Data System (ADS)

    Krzyminiewski, R.; Masiakowski, J.; Pietrzak, J.; Szyczewski, A.

    The molecular structure of free radicals formed in a γ-irradiated single crystal of progesterone was investigated by EPR spectroscopy. Two different types of radicals with different rates of recombination were observed. It is proposed that the stable radical is formed by the loss of a hydrogen atom in position 6 of the molecule, leaving an unpaired electron in the 2 pz orbital of the carbon atoms in positions 6 and 4. The hyperfine spectrum of this radical originates from the interaction of the unpaired electron with the two equivalent a protons in positions 4 and 6 and with the two non-equivalent β protons in position 7. The hyperfine tensors of the couplings are given together with the g tensor of this radical.

  12. An EPR and optical absorption study of Cu(2+) doped in disodium malonate trihydrate single crystal.

    PubMed

    Yarbaşi, Zeynep; Karabulut, Bünyamin; Karabulut, Abdulhalik

    2009-03-01

    Single crystals and powder electron paramagnetic resonance (EPR) studies of Cu(2+)-doped disodium malonate trihydrate [C(3)H(2)O(4)Na(2).3H(2)O] have been carried out at room temperature. The angular variation of the disodium malonate trihydrate single crystal have shown that two different Cu(2+) complexes are located in different chemical environments, and each environment contains one magnetically inequivalent Cu(2+) sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The principal values of the g and the hyperfine tensors were determined and were found to be in agreement with the literature values. Crystal field around the Cu(2+) ion is nearly rhombic. The optical absorption studies show two bands at 603nm (16584cm(-1)) and 890nm (11236cm(-1)) which confirm the rhombic symmetry. The crystals field parameters and than the wave function are determined.

  13. An EPR and optical absorption study of Cu 2+ doped in disodium malonate trihydrate single crystal

    NASA Astrophysics Data System (ADS)

    Yarbaşı, Zeynep; Karabulut, Bünyamin; Karabulut, Abdulhalik

    2009-03-01

    Single crystals and powder electron paramagnetic resonance (EPR) studies of Cu 2+-doped disodium malonate trihydrate [C 3H 2O 4Na 2·3H 2O] have been carried out at room temperature. The angular variation of the disodium malonate trihydrate single crystal have shown that two different Cu 2+ complexes are located in different chemical environments, and each environment contains one magnetically inequivalent Cu 2+ sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The principal values of the g and the hyperfine tensors were determined and were found to be in agreement with the literature values. Crystal field around the Cu 2+ ion is nearly rhombic. The optical absorption studies show two bands at 603 nm (16584 cm -1) and 890 nm (11236 cm -1) which confirm the rhombic symmetry. The crystals field parameters and than the wave function are determined.

  14. Digital EPR with an arbitrary waveform generator and direct detection at the carrier frequency.

    PubMed

    Tseitlin, Mark; Quine, Richard W; Rinard, George A; Eaton, Sandra S; Eaton, Gareth R

    2011-12-01

    A digital EPR spectrometer was constructed by replacing the traditional bridge with an arbitrary waveform generator (AWG) to produce excitation patterns and a high-speed digitizer for direct detection of the spin system response at the carrier frequency. Digital down-conversion produced baseband signals in quadrature with very precise orthogonality. Real-time resonator tuning was performed by monitoring the Fourier transforms of signals reflected from the resonator during frequency sweeps generated by the AWG. The capabilities of the system were demonstrated by rapid magnetic field scans at 256 MHz carrier frequency, and FID and spin echo experiments at 1 and 10 GHz carrier frequencies. For the rapid scan experiments the leakage through a cross-loop resonator was compensated by adjusting the amplitude and phase of a sinusoid at the carrier frequency that was generated with another AWG channel.

  15. The influence of additives on beer stability investigated by EPR spectroscopy

    NASA Astrophysics Data System (ADS)

    Brezová, Vlasta; Polovka, Martin; Staško, Andrej

    2002-04-01

    In thermally-accelerated aging followed by EPR spectroscopy of beer samples of various stabilities, free radical 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPOL) was shown to be an effective indicator of the breakdown of a sample's stability, comparable to the commonly used spin trapping agent α-phenyl- N- tert-butylnitrone (PBN). Both indicators were then employed to investigate the influence of additives on beer stability. The addition of L-ascorbic acid (ASC) to the beer samples accelerated the radical processes and a lower stability was found. DL-α-tocopherol (α-TOC) did not influence beer stability significantly (probably due to its limited solubility). Na 2SO 3, described as a very effective stabilizer in experiments with the PBN spin trap, was found not to be effective using the TEMPOL indicator. This is probably due to inhibition in the formation of spin adducts or their degradation by Na 2SO 3.

  16. The influence of additives on beer stability investigated by EPR spectroscopy.

    PubMed

    Brezová, Vlasta; Polovka, Martin; Stasko, Andrej

    2002-04-01

    In thermally-accelerated aging followed by EPR spectroscopy of beer samples of various stabilities, free radical 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPOL) was shown to be an effective indicator of the breakdown of a sample's stability, comparable to the commonly used spin trapping agent alpha-phenyl-N-tert-butylnitrone (PBN). Both indicators were then employed to investigate the influence of additives on beer stability. The addition of L-ascorbic acid (ASC) to the beer samples accelerated the radical processes and a lower stability was found. DL-alpha-tocopherol (alpha-TOC) did not influence beer stability significantly (probably due to its limited solubility). Na2SO3, described as a very effective stabilizer in experiments with the PBN spin trap, was found not to be effective using the TEMPOL indicator. This is probably due to inhibition in the formation of spin adducts or their degradation by Na2SO3.

  17. Deterministic Joint Remote Preparation of Arbitrary Four-Qubit Cluster-Type State Using EPR Pairs

    NASA Astrophysics Data System (ADS)

    Li, Wenqian; Chen, Hanwu; Liu, Zhihao

    2017-02-01

    Using four Einstein-Podolsky-Rosen (EPR) pairs as the pre-shared quantum channel, an economic and feasible scheme for deterministic joint remote preparation of the four-particle cluster-type state is presented. In the scheme, one of the senders performs a four-qubit projective measurement based on a set of ingeniously constructed vectors with real coefficients, while the other performs the bipartite projective measurements in terms of the imaginary coefficients. Followed with some appropriate unitary operations and controlled-NOT operations, the receiver can reconstruct the desired state. Compared with other analogous JRSP schemes, our scheme can not only reconstruct the original state (to be prepared remotely) with unit successful probability, but also ensure greater efficiency.

  18. Internal in vitro dosimetry for fish using hydroxyapatite-based EPR detectors.

    PubMed

    Ivanov, D V; Shishkina, E A; Osipov, D I; Razumeev, R A; Pryakhin, E A

    2015-08-01

    A number of aquatic ecosystems were exposed to ionizing radiation as a result of the activities of the Mayak Production Association in the Southern Urals, former Soviet Union, in the 1950s. Currently, fishes inhabiting contaminated lakes are being actively studied. These investigations need dosimetric support. In the present paper the results of a pilot study for elaborating an EPR dosimeter which can be used for internal dosimetry in vitro are described. Biological hydroxyapatite is proposed here to be used as a detecting substance. More specifically, small hydroxyapatite grains are proposed for use as point detectors fixed in a solid matrix. After having been pelletized, the detectors were covered by Mylar and placed in the body of a fish to be stored in the fridge for several months. Application of the detectors for internal fish dosimetry demonstrated that the enamel sensitivity is sufficient for passive detection of ionizing radiation in fishes inhabiting contaminated lakes in the Southern Urals.

  19. Thermally generated radicals as indicators of the starch modification studied by EPR spectroscopy: a review.

    PubMed

    Bidzińska, Ewa

    2015-06-25

    The results compiled and discussed in the present review have been published by the research group of the Chemistry Faculty, Jagiellonian University or by other Authors, as given in References. Relatively stable and short-lived radicals generated thermally in starches of various botanic origin were used as indicators of the changes in the starch structure and properties occurring upon chemical and physical modifications. The number of radicals was determined by electron paramagnetic resonance (EPR) spectroscopy. Distribution of water and accessibility of different zones in the starch granule for reagents were tested by using paramagnetic Cu(2+) ions as a probe molecule. Relatively stable radicals generated in starch at 300°C revealed protective properties against ionizing radiation. Thermally induced short-lived radicals exhibited sensitivity to the degree of the starch structure ordering.

  20. An EPR study on wastewater disinfection by peracetic acid, hydrogen peroxide and UV irradiation.

    PubMed

    Bianchini, Roberto; Calucci, Lucia; Caretti, Cecilia; Lubello, Claudio; Pinzino, Calogero; Piscicelli, Michela

    2002-09-01

    EPR spectroscopy was applied to obtain qualitative and quantitative information on the radicals produced in disinfection processes of wastewater for agricultural reuse. The DEPMPO spin trap was employed to detect hydroxyl and carbon-centered short living radicals in two different peracetic acid solutions and a hydrogen peroxide solution used for water disinfection either in the absence or in the presence of UV-C irradiation. Moreover, three different kinds of water (wastewater, demineralized water, distilled water) were analysed in order to assess the contribution of Fenton reactions to the radical production. The spectroscopic results were discussed in relation to the efficiency of the different oxidizing agents and UV irradiation in wastewater disinfection evaluated as Escherichia Coli, Faecal and Total Coliforms inactivation.

  1. Hf isotope systematics of seamounts near the East Pacific Rise (EPR) and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Meng, Fanxue; Niu, Yaoling

    2016-10-01

    We report new Hf isotopic data for basaltic glasses from seamounts flanking the East Pacific Rise (EPR) between 5° and 15°N that have been previously analyzed for Sr-Nd-Pb isotopes as well as major and trace elements. The Hf isotopic data offer new perspectives on the petrogenesis of these samples in a broader context on mantle dynamics. The Hf isotope compositions show significant correlations with Sr-Nd-Pb isotopes and with both abundances and ratios of incompatible elements. The seamount lavas are thus best interpreted as products of melting-induced mixing in a two-component mantle. The range in composition of EPR seamount lavas cannot be generated by simple mixing of melt and melting of variably heterogeneous mantle in which enriched and depleted materials contribute equally to melting (source mixing). Instead, the trace element and isotope compositions of seamount lavas can be reproduced by melting models in which more enriched, fertile mantle component are preferentially melted during mantle upwelling. At progressively lower degrees of melting, erupted lavas are thus more enriched in incompatible trace elements, have higher 87Sr/86Sr, 208Pb/204Pb ratios and lower 143Nd/144Nd, 176Hf/177Hf ratios. The "EM1" and "pyroxenite" endmember might be the suitable enriched component. The Hf-Nd isotopic variations on global scale might result from the variations in amounts of residual continental lithospheric mantle that detached into upper mantle during continental rifting. The significant correlations of Rb/Sr vs 87Sr/86Sr, Sm/Nd vs 143Nd/144Nd and Lu/Hf vs 176Hf/177Hf give pseudochron ages of 182 ± 33 Ma, 276 ± 50 Ma and 387 ± 93 Ma, respectively. These different "ages" have no significance, but result from melting-induced mixing with the pseudochron slopes controlled by the compositions of enriched component and depleted end-member.

  2. Synthesis and EPR studies of 2'-deoxyuridines with alkynyl, rodlike linkages.

    PubMed

    Sniady, Adam; Sevilla, Michael D; Meneni, Srinivasarao; Lis, Tadeusz; Szafert, Slawomir; Khanduri, Deepthi; Finke, John M; Dembinski, Roman

    2009-08-03

    Sonogashira coupling of diacetyl 5-ethynyl-2'-deoxyuridine with diacetyl 5-iodo-2'-deoxyuridine gave the acylated ethynediyl-linked 2'-deoxyuridine dimer (3 b; 63%), which was deprotected with ammonia/methanol to give ethynediyl-linked 2'-deoxyuridines (3 a; 79%). Treatment of 5-ethynyl-2'-deoxyuridine (1 a) with 5-iodo-2'-deoxyuridine gave the furopyrimidine linked to 2'-deoxyuridine (78%). Catalytic oxidative coupling of 1 a (O(2), CuI, Pd/C, N,N-dimethylformamide) gave butadiynediyl-linked 2'-deoxyuridines (4; 84 %). Double Sonogashira coupling of 5-iodo-2'-deoxyuridine with 1,4-diethynylbenzene gave 1,4-phenylenediethynediyl-bridged 2'-deoxyuridines (5; 83%). Cu-catalyzed cycloisomerization of dimers 4 and 5 gave their furopyrimidine derivatives. One-electron addition to 1 a, 3 a, and 4 gave the anion radical, the EPR spectra of which showed that the unpaired electron is largely localized at C6 of one uracil ring (17 G doublet) at 77 K. The EPR spectra of the one-electron-oxidized derivatives of ethynediyl- and butadiynediyl-linked uridines 3 a and 4 at 77 K showed that the unpaired electron is delocalized over both rings. Therefore, structures 3 a and 4 provide an efficient electronic link for hole conduction between the uracil rings. However, for the excess electron, an activation barrier prevents coupling to both rings. These dimeric structures could provide a gate that would separate hole transfer from electron transport between strands in DNA systems. In the crystal structure of acylated dimer 3 b, the bases were found in the anti position relative to each other across the ethynyl link, and similar anti conformation was preserved in the derived furopyrimidine-deoxyuridine dinucleoside.

  3. DAC-board based X-band EPR spectrometer with arbitrary waveform control

    PubMed Central

    Kaufmann, Thomas; Keller, Timothy J.; Franck, John M.; Barnes, Ryan P.; Glaser, Steffen J.; Martinis, John M.; Han, Songi

    2013-01-01

    We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8–10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles “seen” by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ≤250 ps resolution. The implications and potential applications of these capabilities will be discussed. PMID:23999530

  4. DAC-board based X-band EPR spectrometer with arbitrary waveform control

    NASA Astrophysics Data System (ADS)

    Kaufmann, Thomas; Keller, Timothy J.; Franck, John M.; Barnes, Ryan P.; Glaser, Steffen J.; Martinis, John M.; Han, Songi

    2013-10-01

    We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8-10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles "seen" by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ⩽250 ps resolution. The implications and potential applications of these capabilities will be discussed.

  5. DAC-board based X-band EPR spectrometer with arbitrary waveform control.

    PubMed

    Kaufmann, Thomas; Keller, Timothy J; Franck, John M; Barnes, Ryan P; Glaser, Steffen J; Martinis, John M; Han, Songi

    2013-10-01

    We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8-10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles "seen" by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ≤ 250 ps resolution. The implications and potential applications of these capabilities will be discussed.

  6. Effects on detection of radical formation in skin due to solar irradiation measured by EPR spectroscopy.

    PubMed

    Albrecht, Stephanie; Ahlberg, Sebastian; Beckers, Ingeborg; Kockott, Dieter; Lademann, Jürgen; Paul, Victoria; Zastrow, Leonhard; Meinke, Martina C

    2016-10-15

    In various research projects, oxidative stress in irradiated skin was investigated by measuring the production of free radical using EPR spectroscopy. However, comparison of the obtained measuring results proved to be difficult as different preparation parameters were used for those measurements. In the present study the influence of the preparation parameters on the detected radical production was methodically investigated. For this purpose, porcine skin was exposed in situ to UV and VIS-NIR radiation, respectively, while being measured in an X band EPR spectrometer. Prior to the measurements, the skin had been treated with the spin trap N-tert-Butyl-α-phenylnitrone (PBN) and the spin marker 3-(Carboxyl)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA). The two methods were investigated for quantitative comparability, for advantages and disadvantages and for errors potentially affecting the evaluation of the results. A significant influence of the preparation parameters (concentration and amount of substance) on the detected radical formations could be found. This influence had a nonlinear effect on the detected radical production. 120μl of incubated amount for 1M PBN and for PCA at a concentration of 0.6 and 1.5mM were determined to be the optimum parameters. The incubated skin samples were 1cm in diameter and 300μm thick. Between 22 and 37°C the incubation temperature showed no significant influence on the detected radical production. For the first time it could be demonstrated for PCA-incubated skin that the radiation-induced radical production depends exclusively on the irradiation dose, provided the preparation parameters and the spectral region are kept constant. In addition, the radical production in the UVB-UVA and VIS-NIR spectral regions was measured in PCA- and PBN-treated excised porcine skin. It was found that PBN and PCA provide comparable results for the relative quantity and kinetics of radical production.

  7. An image-intensive ePR for image-guided minimally invasive spine surgery applications including real-time intra-operative image acquisition, archival, and display

    NASA Astrophysics Data System (ADS)

    Documet, Jorge R.; Le, Anh; Liu, Brent; Huang, H. K.; Chiu, John

    2009-02-01

    Recent developments in medical imaging informatics have improved clinical workflow in Radiology enterprise but gaps remain in the clinical workflow from diagnosis to surgical treatment through post-operative follow-up. One solution to bridge this gap is the development of an electronic patient record (ePR) that integrates key imaging and informatics data during the pre, intra, and post-operative phases of clinical workflow. We present an ePR system based on standards and tailored to the clinical application for image-guided minimally invasive spinal surgery (MISS). The ePR system has been implemented in a clinical environment for a half-year.

  8. Melt spreading code assessment, modifications, and application to the EPR core catcher design.

    SciTech Connect

    Farmer, M. T .; Nuclear Engineering Division

    2009-03-30

    The Evolutionary Power Reactor (EPR) is under consideration by various utilities in the United States to provide base load electrical production, and as a result the design is undergoing a certification review by the U.S. Nuclear Regulatory Commission (NRC). The severe accident design philosophy for this reactor is based upon the fact that the projected power rating results in a narrow margin for in-vessel melt retention by external cooling of the reactor vessel. As a result, the design addresses ex-vessel core melt stabilization using a mitigation strategy that includes: (1) an external core melt retention system to temporarily hold core melt released from the vessel; (2) a layer of 'sacrificial' material that is admixed with the melt while in the core melt retention system; (3) a melt plug in the lower part of the retention system that, when failed, provides a pathway for the mixture to spread to a large core spreading chamber; and finally, (4) cooling and stabilization of the spread melt by controlled top and bottom flooding. The overall concept is illustrated in Figure 1.1. The melt spreading process relies heavily on inertial flow of a low-viscosity admixed melt to a segmented spreading chamber, and assumes that the melt mass will be distributed to a uniform height in the chamber. The spreading phenomenon thus needs to be modeled properly in order to adequately assess the EPR design. The MELTSPREAD code, developed at Argonne National Laboratory, can model segmented, and both uniform and nonuniform spreading. The NRC is thus utilizing MELTSPREAD to evaluate melt spreading in the EPR design. MELTSPREAD was originally developed to support resolution of the Mark I containment shell vulnerability issue. Following closure of this issue, development of MELTSPREAD ceased in the early 1990's, at which time the melt spreading database upon which the code had been validated was rather limited. In particular, the database that was utilized for initial validation consisted

  9. A prototype of image-guided outcome analysis for prostate proton therapy patients based on DICOM-RT ePR

    NASA Astrophysics Data System (ADS)

    Le, Anh; Documet, Jorge; Sullivan, Ashley; Liu, Brent

    2009-02-01

    Last year, we presented the infrastructure for a medical imaging informatics DICOM-RT based ePR system for patients treated with Proton Therapy (PT). The ePR has functionality to integrate patients' imaging and informatics data and perform outcomes analysis with patient and physician profiling in order to provide clinical decision support and suggest courses of treatment. In this paper, we present the development of a prototype for the image-guided outcomes analysis for prostate cancer patient based on DICOM-RT ePR. This ePR system, using DICOM-RT and DICOM-ION objects as well as clinical and biological parameters, provides tools to evaluate treatment plans and assess the outcomes of the patient's treatment; hence, it promotes more successful treatment planning for new prostate cancer patients treated with proton therapy.

  10. Site-directed spin-labeling of nucleotides and the use of in-cell EPR to determine long-range distances in a biologically relevant environment.

    PubMed

    Azarkh, Mykhailo; Singh, Vijay; Okle, Oliver; Seemann, Isabelle T; Dietrich, Daniel R; Hartig, Jörg S; Drescher, Malte

    2013-01-01

    Double electron-electron resonance (DEER) is an electron paramagnetic resonance (EPR) technique used to determine distance distributions in the nanometer range between spin labels by measuring their dipole-dipole interactions. Here we describe how in-cell DEER can be applied to spin-labeled DNA sequences to unravel their conformations in living cells by long-range distance measurements in cellula. As EPR detects unpaired electron spins only, diamagnetic molecules provide no background and do not reduce detection sensitivity of the specific signal. Compared with in-cell NMR spectroscopy, low concentrations of spin-labeled molecules can be used owing to the higher sensitivity of EPR per spin. This protocol describes the synthesis of the spin labels, their introduction in DNA strands, the injection of labeled DNA solutions in cells and the performance of in-cell EPR measurements. Completion of the entire protocol takes ~20 d.

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

    DTIC Science & Technology

    2008-06-17

    biodosimetry, fluorescence in situ hybridization (FISH), thermoluminescence (TL), and optically stimulated luminescence (OSL) [1]. EPR retrospective studies...Gammacell 40 Cesium 137 irradiator. C-2. EXPERIMENTAL DESIGN: 1) Several thermoluminescent detectors (TLDs), DT-702/PD, were irradiated at

  12. CARRIER-LATTICE RELAXATION FOR BROADENING EPR LINEWIDTH IN Nd0.55Sr0.45MnO3

    NASA Astrophysics Data System (ADS)

    Fan, Jiyu; Zhang, Xiyuan; Tong, Wei; Zhang, Lei; Zhang, Weichun; Zhu, Yan; Shi, Yangguang; Hu, Dazhi; Hong, Bo; Ying, Yao; Ling, Langsheng; Pi, Li; Zhang, Yuheng

    2013-12-01

    In this paper, we report the electron paramagnetic resonance (EPR) study of perovskite manganite Nd0.55Sr0.45MnO3. Experimental data reveal that the EPR linewidth broadens with a quasilinear manner up to 480 K. The broadening of the EPR linewidth can be understood in terms of the shortening of carrier-lattice relaxation time due to the occurrence of strong carrier-phonon interactions. Two same activation energies obtained respectively from the temperature dependence of EPR intensity and resistivity indicate that the linewidth variation is correlated to the small polaron hopping. Therefore, the carrier-lattice coupling play a major role for deciding its magnetism in the present system.

  13. Structural studies of marine exoskeletons: redox mechanisms observed in the Cu-supported CaCO3 surfaces tudied by EPR.

    PubMed

    Linga Raju, C H; Narasimhulu, K V; Gopal, N O; Rao, J L; Reddy, B C V

    2003-11-01

    Electron Paramagnetic Resonance (EPR), optical and infrared (IR) spectral studies have been performed on the pure and Cu-adsorbed exoskeletons of marine environment. The EPR spectrum of exoskeletons at room temperature exhibits a sharp signal at g approximately 1.9970. The possible redox mechanisms have been noticed on heating these exoskeletons in which the low spin Mn(3+) reduces to Mn(2+). The optical absorption spectra also give the evidence of the presence of Mn(3+) ions. The effects of thermal sintering on the EPR spectra have been studied and discussed in detail. The Cu-adsorbed samples clearly showed the adsorption of the Cu(2+) ions over CaCO(3) and the redox mechanism in these samples have been monitored by EPR.

  14. EPR, ELDOR, and ENDOR studies of alkali metal- o-dimesitoylbenzene radical complexes in solution. II. The lithium and sodium complexes

    NASA Astrophysics Data System (ADS)

    van der Drift, E.; Smidt, J.

    A combined EPR-ELDOR-ENDOR study on ion pairs of o-dimesitoylbenzene anions with Li or Na cations provides a unique description of the alkali relaxation pattern in terms of dipolar and quadrupolar relaxation resulting from molecular tumbling. Internal motions in the chelating ring structure appear to be of minor importance. From the EPR and ELDOR results a variety of structural information is obtained: spectral densities, rotational correlation time of the complex, and anisotropic magnetic interactions of the alkali nucleus.

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

    PubMed

    Bartoszek, Mariola; Polak, Justyna

    2016-01-15

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

  16. Multi-frequency, multi-technique pulsed EPR investigation of the copper binding site of murine amyloid β peptide.

    PubMed

    Kim, Donghun; Bang, Jeong Kyu; Kim, Sun Hee

    2015-01-26

    Copper-amyloid peptides are proposed to be the cause of Alzheimer's disease, presumably by oxidative stress. However, mice do not produce amyloid plaques and thus do not suffer from Alzheimer's disease. Although much effort has been focused on the structural characterization of the copper- human amyloid peptides, little is known regarding the copper-binding mode in murine amyloid peptides. Thus, we investigated the structure of copper-murine amyloid peptides through multi-frequency, multi-technique pulsed EPR spectroscopy in conjunction with specific isotope labeling. Based on our pulsed EPR results, we found that Ala2, Glu3, His6, and His14 are directly coordinated with the copper ion in murine amyloid β peptides at pH 8.5. This is the first detailed structural characterization of the copper-binding mode in murine amyloid β peptides. This work may advance the knowledge required for developing inhibitors of Alzheimer's disease.

  17. Investigations of the EPR Parameters and Local Lattice Structure for the Rhombic Cu2+ Centre in TZSH Crystal

    NASA Astrophysics Data System (ADS)

    Li, Chao-Ying; Liu, Shi-Fei; Fu, Jin-Xian

    2016-03-01

    The electron paramagnetic resonance (EPR) parameters [i.e. g factors gi (i=x, y, z) and hyperfine structure constants Ai] and the local lattice structure for the Cu2+ centre in Tl2Zn(SO4)2·6H2O (TZSH) crystal were theoretically investigated by utilising the perturbation formulae of these parameters for a 3d9 ion under rhombically elongated octahedra. In the calculations, the admixture of d orbitals in the ground state and the ligand orbital and spin-orbit coupling interactions are taken into account based on the cluster approach. The theoretical EPR parameters show good agreement with the observed values, and the Cu2+-H2O bond lengths are obtained as follows: Rx≈1.98 Å, Ry≈2.09 Å, Rz≈2.32 Å. The results are discussed.

  18. Primary Reactions of Photosynthesis: Photoreduction of a Bound Chloroplast Ferredoxin at Low Temperature as Detected by EPR Spectroscopy

    PubMed Central

    Malkin, R.; Bearden, Alan J.

    1971-01-01

    An electron paramagnetic resonance signal was observed at 25°K in whole spinach chloroplasts after illumination at 77°K. The light-induced epr spectrum had g-values (gx = 1.86, gy = 1.94, gz = 2.05) and a temperature dependence that were characteristic of the reduced state of a plant-type ferredoxin. The light-induced epr spectrum was also observed in broken spinach chloroplasts from which soluble ferredoxin was removed. Chemical analyses showed that both whole and broken spinach chloroplasts contained amounts of nonheme iron and “acid-labile sulfide” consistent with the presence of a bound iron-sulfur protein, at a level of about one molecule per 75 chlorophyll molecules. These results support the conclusion that chloroplasts contain a bound ferredoxin that may serve as a primary low-potential electron acceptor in photosynthesis. PMID:4322259

  19. EPR characteristics of free radicals in DOPA-melanin-moxifloxacin complexes at ambient level of UVA radiation

    NASA Astrophysics Data System (ADS)

    Beberok, Artur; Zdybel, Magdalena; Pilawa, Barbara; Buszman, Ewa; Wrześniok, Dorota

    2014-01-01

    EPR studies pointed out that o-semiquinone free radicals with g-values 2.0038-2.0040 take part in moxifloxacin-melanin complex formation. The process contributed to increase in free radicals concentration in nonirradiated complexes. This effect was observed for the complexes with 1 × 10-4 M, 1 × 10-3 M and 4 × 10-3 M drug concentrations. UV irradiation contributed to decrease in free radicals concentration in DOPA-melanin complexes with moxifloxacin, besides the complexes with the drug concentration of 1 × 10-4 M. The strongest decrease was observed for DOPA-melanin-moxifloxacin complexes with the drug concentration of 1 × 10-3 M. Homogeneous broadening of EPR lines, strong dipolar interactions and slow spin-lattice relaxation processes characterized all the tested melanin samples.

  20. Rapid-scan coherence signals in X-band EPR spectra of semiquinones with small hyperfine splittings.

    PubMed

    Elajaili, Hanan; Rinard, George A; Yu, Zhelin; Mitchell, Deborah G; Quine, Richard W; Eaton, Sandra S; Eaton, Gareth R

    2015-10-01

    Rapid-scan EPR signals for semiquinones with very-small well-resolved hyperfine splittings exhibit coherence signals at a time after passing through the EPR line that is proportional to the reciprocal of the hyperfine splitting. Such coherences are a general phenomenon due to constructive interference of the responses to transient excitation of spins by rapid scan of the magnetic field across equally spaced spin packets. Examples are shown for 2,3,5,6-tetramethoxy-1,4-benzosemiquinone with aH=46 mG for 12 protons and for 2,5-di-t-butyl-1,4-benzosemiquinone with aH=59 mG for 18 protons.

  1. Rapid-scan coherence signals in X-band EPR spectra of semiquinones with small hyperfine splittings

    PubMed Central

    Elajaili, Hanan; Rinard, George A.; Yu, Zhelin; Mitchell, Deborah G.; Quine, Richard W.; Eaton, Sandra S.; Eaton, Gareth R.

    2015-01-01

    Rapid-scan EPR signals for semiquinones with very-small well-resolved hyperfine splittings exhibit coherence signals at a time after passing through the EPR line that is proportional to the reciprocal of the hyperfine splitting. Such coherences are a general phenomenon due to constructive interference of the responses to transient excitation of spins by rapid scan of the magnetic field across equally spaced spin packets. Examples are shown for 2,3,5,6-tetramethoxy-1,4-benzosemiquinone with aH = 46 mG for 12 protons and for 2,5-di-t-butyl-1,4-benzosemiquinone with aH = 59 mG for 18 protons. PMID:26277376

  2. X-Band EPR Spectrometer with Customizable Arbitrary Waveform Generator based on a 1 GHz DAC Board

    NASA Astrophysics Data System (ADS)

    Kaufmann, Thomas

    We present an electron paramagnetic resonance (EPR) spectrometer featuring an arbitrary waveform generator (AWG) operating at 8-10 GHz (X-band) and based on a 1 GHz digital-to-analog converter (DAC) board with a 42 dB (i.e. 14-bit) dynamic range, which was developed to widen the scope of pulsed EPR and enable new experiments. This spectrometer generates shaped pulses with precise amplitude and phase control and can specify pulse lengths and delays with a time resolution of ≤250 ps. We demonstrate the capabilities of the spectrometer by presenting spin-echo measurements that implement an entirely digitally controlled and calibrated 16-step phase cycle and by measuring the excitation profiles seen by the spins in the microwave resonator as they respond to various pulse shapes, including rectangular, triangular, Gaussian, sinc and adiabatic rapid passage waveforms. Potential applications of these capabilities, and their implementation in commercial instrumentation will be discussed.

  3. Operando X-ray absorption and EPR evidence for a single electron redox process in copper catalysis

    SciTech Connect

    Lu, Qingquan; Zhang, Jian; Peng, Pan; Zhang, Guanghui; Huang, Zhiliang; Yi, Hong; Miller, Jeffrey T.; Lei, Aiwen

    2015-05-26

    An unprecedented single electron redox process in copper catalysis is confirmed using operando X-ray absorption and EPR spectroscopies. The oxidation state of the copper species in the interaction between Cu(II) and a sulfinic acid at room temperature, and the accurate characterization of the formed Cu(I) are clearly shown using operando X-ray absorption and EPR evidence. Further investigation of anion effects on Cu(II) discloses that bromine ions can dramatically increase the rate of the redox process. Moreover, it is proven that the sulfinic acids are converted into sulfonyl radicals, which can be trapped by 2-arylacrylic acids and various valuable β-keto sulfones are synthesized with good to excellent yields under mild conditions.

  4. Characteristics of the Mn2+ EPR spectra in the oxyfluoride glass ceramics containing SrF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Fedotovs, A.; Berzins, Dz; Kiselova, O.; Sarakovskis, A.

    2012-08-01

    Characteristics of the electron paramagnetic resonance (EPR) spectra of the Mn2+ ion in the oxyfluoride glass ceramics containing SrF2 crystalline counterpart has been investigated. Explicit superhyperfine structure (SHF) has been observed in the X-Band EPR spectra taken at 77 K after thermal treatment of the glass precursor. Such SHF structure is characteristic to Mn2+ ion in the fluorine coordinated nearest environment which is characteristic to cubic structure of the alkaline earth fluorides. Manganese replaces strontium in the SrF2 lattice where it has pronounced SHF interaction with surrounding fluorine nuclei. Thus Mn2+ ion provides information about crystalline structure of the particular oxyfluoride glass ceramics.

  5. Evidence for disorder in L-alanine lattice detected by Pulsed-EPR spectroscopy at cryogenic temperatures.

    PubMed

    Maltar-Strmecki, N; Rakvin, B

    2006-03-13

    The unusual behavior of lattice dynamics of L-alanine has been assigned to intermolecular dynamics and localization of vibrational energy. Recent heat capacity and Pulsed-EPR measurements support presence of thermally activated dynamic orientational disorder in the L-alanine lattice below 20 K. In the present study, the additional evidence for possible thermally activated disordered behavior of L-alanine lattice have been obtained by investigating dependences of longitudinal relaxation time of first stable L-alanine radical, SAR1, on sample cooling rates for the same low temperature interval. The obtained relaxation time by Pulsed-EPR shows clear dependence on cooling rates and this behavior can be explained within two types of suggested spin-lattice relaxation mechanisms for the paramagnetic centers in the hydrogen-bonded organic crystal.

  6. Operando X-ray absorption and EPR evidence for a single electron redox process in copper catalysis

    DOE PAGES

    Lu, Qingquan; Zhang, Jian; Peng, Pan; ...

    2015-05-26

    An unprecedented single electron redox process in copper catalysis is confirmed using operando X-ray absorption and EPR spectroscopies. The oxidation state of the copper species in the interaction between Cu(II) and a sulfinic acid at room temperature, and the accurate characterization of the formed Cu(I) are clearly shown using operando X-ray absorption and EPR evidence. Further investigation of anion effects on Cu(II) discloses that bromine ions can dramatically increase the rate of the redox process. Moreover, it is proven that the sulfinic acids are converted into sulfonyl radicals, which can be trapped by 2-arylacrylic acids and various valuable β-keto sulfonesmore » are synthesized with good to excellent yields under mild conditions.« less

  7. Metal binding studies and EPR spectroscopy of the manganese transport regulator MntR.

    PubMed

    Golynskiy, Misha V; Gunderson, William A; Hendrich, Michael P; Cohen, Seth M

    2006-12-26

    Manganese transport regulator (MntR) is a member of the diphtheria toxin repressor (DtxR) family of transcription factors that is responsible for manganese homeostasis in Bacillus subtilis. Prior biophysical studies have focused on the metal-mediated DNA binding of MntR [Lieser, S. A., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2003) Biochemistry 42, 12634-12642], as well as metal stabilization of the MntR structure [Golynskiy, M. V., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2005) Biochemistry 44, 3380-3389], but only limited data on the metal-binding affinities for MntR are available. Herein, the metal-binding affinities of MntR were determined by using electron paramagnetic resonance (EPR) spectroscopy, as well as competition experiments with the fluorimetric dyes Fura-2 and Mag-fura-2. MntR was not capable of competing with Fura-2 for the binding of transition metal ions. Therefore, the metal-binding affinities and stoichiometries of Mag-fura-2 for Mn2+, Co2+, Ni2+, Zn2+, and Cd2+ were determined and utilized in MntR/Mag-fura-2 competition experiments. The measured Kd values for MntR metal binding are comparable to those reported for DtxR metal binding [Kd from 10(-)7 to 10(-4) M; D'Aquino, J. A., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 18408-18413], AntR [a homologue from Bacillus anthracis; Sen, K. I. et al. (2006) Biochemistry 45, 4295-4303], and generally follow the Irving-Williams series. Direct detection of the dinuclear Mn2+ site in MntR with EPR spectroscopy is presented, and the exchange interaction was determined, J = -0.2 cm-1. This value is lower in magnitude than most known dinuclear Mn2+ sites in proteins and synthetic complexes and is consistent with a dinuclear Mn2+ site with a longer Mn...Mn distance (4.4 A) observed in some of the available crystal structures. MntR is found to have a surprisingly low binding affinity (approximately 160 microM) for its cognate metal ion Mn2+. Moreover, the results of DNA binding studies in

  8. In vivo evidence of methamphetamine induced attenuation of brain tissue oxygenation as measured by EPR oximetry

    SciTech Connect

    Weaver, John; Yang, Yirong; Purvis, Rebecca; Weatherwax, Theodore; Rosen, Gerald M.; Liu, Ke Jian

    2014-03-01

    Abuse of methamphetamine (METH) is a major and significant societal problem in the US, as a number of studies have suggested that METH is associated with increased cerebrovascular events, hemorrhage or vasospasm. Although cellular and molecular mechanisms involved in METH-induced toxicity are not completely understood, changes in brain O{sub 2} may play an important role and contribute to METH-induced neurotoxicity including dopaminergic receptor degradation. Given that O{sub 2} is the terminal electron acceptor for many enzymes that are important in brain function, the impact of METH on brain tissue pO{sub 2}in vivo remains largely uncharacterized. This study investigated striatal tissue pO{sub 2} changes in male C57BL/6 mice (16–20 g) following METH administration using EPR oximetry, a highly sensitive modality to measure pO{sub 2}in vivo, in situ and in real time. We demonstrate that 20 min after a single injection of METH (8 mg/kg i.v.), the striatal pO{sub 2} was reduced to 81% of the pretreatment level and exposure to METH for 3 consecutive days further attenuated striatal pO{sub 2} to 64%. More importantly, pO{sub 2} did not recover fully to control levels even 24 h after administration of a single dose of METH and continual exposure to METH exacerbates the condition. We also show a reduction in cerebral blood flow associated with a decreased brain pO{sub 2} indicating an ischemic condition. Our findings suggests that administration of METH can attenuate brain tissue pO{sub 2}, which may lead to hypoxic insult, thus a risk factor for METH-induced brain injury and the development of stroke in young adults. - Highlights: • Explored striatal tissue pO{sub 2}in vivo after METH administration by EPR oximetry. • pO{sub 2} was reduced by 81% after a single dose and 64% after 3 consecutive daily doses. • pO{sub 2} did not recover fully to control levels even 24 h after a single dose. • Decrease in brain tissue pO{sub 2} may be associated with a decrease in

  9. Coupling of Waveguide and Resonator by Inductive and Capacitive Irises for EPR Spectroscopy

    PubMed Central

    Mett, R.R.; Sidabras, J.W.; Hyde, J.S.

    2009-01-01

    An analytic circuit model for slot coupling from a waveguide to a loop-gap resonator (LGR) in a context of electron paramagnetic resonance (EPR) spectroscopy is presented. The physical dimensions of the waveguide, iris, LGR, and aqueous sample are transformed into circuit values of inductance, capacitance, and resistance. These values are used in a solution of circuit equations that results in a prediction of the rf currents, magnitude and phase, frequency, and magnetic and electric stored energies near critical coupling. The circuit geometry reflects magnetic flux conservation between the iris and LGR as well as modification of the outer loop LGR currents by the iris. Unlike conventional models, coupling is not explicitly based on a mutual inductance between the iris and LGR. Instead, the conducting wall high frequency rf boundary condition is used to define surface currents, regions, and circuit topology with lumped-circuit values of self-inductance, capacitance, and resistance. Match is produced by a combination of self-inductive and capacitive circuit coupling. Two conditions must be met to achieve match. First, the equivalent resistance of the LGR as seen by the iris must be transformed into the waveguide characteristic impedance. This transformation is met at a particular frequency relative to the natural LGR resonance frequency. The frequency shift magnitude is largely determined by the LGR properties, weakly dependent on iris length and placement, and independent of other iris dimensions. The second condition for match is that the iris reactance at this frequency shift must cancel the residual reactance of the LGR. This second condition is sensitive to the iris dimensions. If both conditions are not simultaneously satisfied, overcoupling or undercoupling results. A slotted iris of equal length to the size of the large dimension of the waveguide is found to have many properties opposite to a conventional iris of shorter length. Notably, the magnetic field

  10. High-frequency dynamic nuclear polarization using biradicals: a multifrequency EPR lineshape analysis.

    PubMed

    Hu, Kan-Nian; Song, Changsik; Yu, Hsiao-Hua; Swager, Timothy M; Griffin, Robert G

    2008-02-07

    To date, the cross effect (CE) and thermal mixing (TM) mechanisms have consistently provided the largest enhancements in dynamic nuclear polarization (DNP) experiments performed at high magnetic fields. Both involve a three-spin electron-electron-nucleus process whose efficiency depends primarily on two electron-electron interactions--the interelectron distance R and the correct electron paramagnetic resonance (EPR) frequency separation that matches the nuclear Larmor frequency, /omega(e2)-omega(e1)/ = omega(n). Biradicals, for example, two 2,2,6,6-tetramethyl-piperidine-1-oxyls (TEMPOs) tethered with a molecular linker, can in principle constrain both the distance and relative g-tensor orientation between two unpaired electrons, allowing these two spectral parameters to be optimized for the CE and TM. To verify this hypothesis, we synthesized a series of biradicals--bis-TEMPO tethered by n ethylene glycol units (a.k.a. BTnE)--that show an increasing DNP enhancement with a decreasing tether length. Specifically at 90 K and 5 T, the enhancement grew from approximately 40 observed with 10 mM monomeric TEMPO, where the average R approximately 56 A corresponding to electron-electron dipolar coupling constant omega(d)2 pi = 0.3 MHz, to approximately 175 with 5 mM BT2E (10 mM electrons) which has R approximately 13 A with omega(d)2 pi = 24 MHz. In addition, we compared these DNP enhancements with those from three biradicals having shorter and more rigid tethers-bis-TEMPO tethered by oxalyl amide, bis-TEMPO tethered by the urea structure, and 1-(TEMPO-4-oxyl)-3-(TEMPO-4-amino)-propan-2-ol (TOTAPOL) TOTAPOL is of particular interest since it is soluble in aqueous media and compatible with DNP experiments on biological systems such as membrane and amyloid proteins. The interelectron distances and relative g-tensor orientations of all of these biradicals were characterized with an analysis of their 9 and 140 GHz continuous-wave EPR lineshapes. The results show that the

  11. EPR and optical absorption studies of Cu{sup 2+} ions in alkaline earth alumino borate glasses

    SciTech Connect

    Ramesh Kumar, V.; Rao, J.L. . E-mail: jlrao46@yahoo.co.in; Gopal, N.O.

    2005-08-11

    Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu{sup 2+} ions in alkaline earth alumino borate glasses doped with different concentrations of CuO have been studied. The EPR spectra of all the glasses exhibit the resonance signals, characteristic of Cu{sup 2+} ions present in axially elongated octahedral sites. The number of spins participating in the resonance has been calculated as a function of temperature for calcium alumino borate (CaAB) glass doped with 0.1 mol% of CuO. From the EPR data, the paramagnetic susceptibility ({chi}) was calculated at different temperatures (T) and from the 1/{chi}-T graph, the Curie temperature of the glass has been evaluated. The optical absorption spectra of all the glasses show a single broad band, which has been assigned to the {sup 2}B{sub 1g} {yields} {sup 2}B{sub 2g} transition of the Cu{sup 2+} ions. The variation in the intensity of optical absorption with the ionic radius of the alkaline earth ion has been explained based on the Coulombic forces. By correlating the EPR and optical absorption spectral data, the nature of the in-plane {sigma} bonding between Cu{sup 2+} ion and the ligands is estimated. From the fundamental ultraviolet absorption edges of the glasses, the optical energy gap (E {sub opt}) and the Urbach energy ({delta}E) are evaluated. The variation in E {sub opt} and {delta}E is explained based on the number of defect centers in the glass.

  12. EPR dosimetry of cortical bone and tooth enamel irradiated with X and gamma rays: Study of energy dependence

    SciTech Connect

    Schauer, D.A.; Links, J.M. ); Desrosiers, M.F.; Le, F.G.; Seltzer, S.M. )

    1994-04-01

    Previous investigators have reported that the radiation-induced EPR signal intensity in compact or cortical bone increases up to a factor of two with decreasing photon energy for a given absorbed dose. If the EPR signal intensity was dependent on energy, it could limit the application of EPR spectrometry and the additive reirradiation method to obtain dose estimates. We have recently shown that errors in the assumptions governing conversion of measured exposure to absorbed dose can lead to similar [open quotes]apparent[close quotes] energy-dependence results. We hypothesized that these previous results were due to errors in the estimated dose in bone, rather than the effects of energy dependence per se. To test this hypothesis we studied human adult cortical bone from male and female donors ranging in age from 23 to 95 years, and bovine tooth enamel, using 34 and 138 keV average energy X-ray beams and [sup 137]Cs (662 keV) and [sup 60]Co (1250 keV) [gamma] rays. In a femur from a 47-year-old male (subject 1), there was a difference of borderline significance at the [alpha] = 0.05 level in the mean radiation-induced hydroxyapatite signal intensities as a function of photon energy. No other statistically significant differences in EPR signal intensity as a function of photon energy were observed in this subject, or in the tibia from a 23-year-old male (subject 2) and the femur from a 75-year-old female (subject 3). However, there was a trend toward a decrease (12-15%) in signal intensity at the lowest energy compared with the highest energy in subjects 1 and 3. Further analysis of the data from subject 1 revealed that this trend, which is in the opposite direction of previous reports but is consistent with theory, is statistically significant. There were no efforts of energy dependence in the tooth samples. 16 refs., 7 figs., 5 tabs.

  13. Superhyperfine structure in the EPR spectra and optical spectra of impurity f ions in dielectric crystals: A review

    NASA Astrophysics Data System (ADS)

    Aminov, L. K.; Kurkin, I. N.; Malkin, B. Z.

    2013-07-01

    The results of observation and simulation of the superhyperfine (ligand hyperfine) structure (SHFS) of the electron paramagnetic resonance (EPR) spectra of rare-earth and uranium impurity ions in dielectric crystals have been systematized. The resolved SHFS of the EPR spectra of doped cubic crystals (with the fluorite and perovskite structures) has been observed for orientations of a constant magnetic field along the crystallographic axes. Most attention has been paid to tetragonal double fluorides Li RF4 ( R = Y, Lu, Tm), in which the SHFS of the EPR spectra has also been found for intermediate orientations of the magnetic field. For the LiYF4: Nd3+ single crystal, the splitting of optical spectral lines due to the interaction of Nd3+ ions with nuclear magnetic moments of the nearest neighbor fluorine ions has been observed for the first time. The Van Vleck paramagnet LiTmF4: U3+ is characterized by the SHFS with clearly distinguishable components due to the interaction of uranium ions both with nuclei of the fluorine ions and with enhanced magnetic moments of the thulium nuclei. The SHFS envelopes of the EPR spectra of Yb3+, Ce3+, Nd3+, and U3+ ions in LiYF4 and LiLuF4 crystals are well reproduced by numerical calculations based on the microscopic model using only three fitting parameters: the width of transitions between the electron-nuclear sublevels of the complex containing the paramagnetic ion and nuclei of the ligands and two constants of covalent bonding of the f electrons with 2 s and 2 p electrons of the nearest neighbor fluorine ions.

  14. Bypassing the EPR effect with a nanomedicine harboring a sustained-release function allows better tumor control.

    PubMed

    Shen, Yao An; Shyu, Ing Luen; Lu, Maggie; He, Chun Lin; Hsu, Yen Mei; Liang, Hsiang Fa; Liu, Chih Peng; Liu, Ren Shyan; Shen, Biing Jiun; Wei, Yau Huei; Chuang, Chi Mu

    2015-01-01

    The current enhanced permeability and retention (EPR)-based approved nanomedicines have had little impact in terms of prolongation of overall survival in patients with cancer. For example, the two Phase III trials comparing Doxil(®), the first nanomedicine approved by the US Food and Drug Administration, with free doxorubicin did not find an actual translation of the EPR effect into a statistically significant increase in overall survival but did show less cardiotoxicity. In the current work, we used a two-factor factorial experimental design with intraperitoneal versus intravenous delivery and nanomedicine versus free drug as factors to test our hypothesis that regional (intraperitoneal) delivery of nanomedicine may better increase survival when compared with systemic delivery. In this study, we demonstrate that bypassing, rather than exploiting, the EPR effect via intraperitoneal delivery of nanomedicine harboring a sustained-release function demonstrates dual pharmacokinetic advantages, producing more efficient tumor control and suppressing the expression of stemness markers, epithelial-mesenchymal transition, angiogenesis signals, and multidrug resistance in the tumor microenvironment. Metastases to vital organs (eg, lung, liver, and lymphatic system) are also better controlled by intraperitoneal delivery of nanomedicine than by standard systemic delivery of the corresponding free drug. Moreover, the intraperitoneal delivery of nanomedicine has the potential to replace hyperthermic intraperitoneal chemotherapy because it shows equal efficacy and lower toxicity. In terms of efficacy, exploiting the EPR effect may not be the best approach for developing a nanomedicine. Because intraperitoneal chemotherapy is a type of regional chemotherapy, the pharmaceutical industry might consider the regional delivery of nanomedicine as a valid alternative pathway to develop their nanomedicine(s) with the goal of better tumor control in the future.

  15. Actin-binding cleft closure in myosin II probed by site-directed spin labeling and pulsed EPR.

    PubMed

    Klein, Jennifer C; Burr, Adam R; Svensson, Bengt; Kennedy, Daniel J; Allingham, John; Titus, Margaret A; Rayment, Ivan; Thomas, David D

    2008-09-02

    We present a structurally dynamic model for nucleotide- and actin-induced closure of the actin-binding cleft of myosin, based on site-directed spin labeling and electron paramagnetic resonance (EPR) in Dictyostelium myosin II. The actin-binding cleft is a solvent-filled cavity that extends to the nucleotide-binding pocket and has been predicted to close upon strong actin binding. Single-cysteine labeling sites were engineered to probe mobility and accessibility within the cleft. Addition of ADP and vanadate, which traps the posthydrolysis biochemical state, influenced probe mobility and accessibility slightly, whereas actin binding caused more dramatic changes in accessibility, consistent with cleft closure. We engineered five pairs of cysteine labeling sites to straddle the cleft, each pair having one label on the upper 50-kDa domain and one on the lower 50-kDa domain. Distances between spin-labeled sites were determined from the resulting spin-spin interactions, as measured by continuous wave EPR for distances of 0.7-2 nm or pulsed EPR (double electron-electron resonance) for distances of 1.7-6 nm. Because of the high distance resolution of EPR, at least two distinct structural states of the cleft were resolved. Each of the biochemical states tested (prehydrolysis, posthydrolysis, and rigor), reflects a mixture of these structural states, indicating that the coupling between biochemical and structural states is not rigid. The resulting model is much more dynamic than previously envisioned, with both open and closed conformations of the cleft interconverting, even in the rigor actomyosin complex.

  16. Influence of free radicals signal from dental resins on the radio-induced signal in teeth in EPR retrospective dosimetry.

    PubMed

    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.

  17. Efficiency of PBN to Trap 3-CAR in B6C3F1 Mouse Liver Slices: An EPR Study.

    DTIC Science & Technology

    1995-09-01

    AL/OE-TR-1995-0139 UNITED STATES AIR FORCE ARMSTRONG LABORATORY EFFICIENCY OF PBN TO TRAP 3-CAR IN B6C3F1 MOUSE LIVER SLICES: AN EPR STUDY...and Eckstein, JM. 1993 Comparative intestinal and testes toxicity of 4 aminothiols in irradiated and non-irradiated mice . Ann Clin and Lab Sei 23 (6...Air Force Armstrong Laboratory. Additional copies may be purchased from: National Technical Information Service 5285 Port Royal Road Springfield

  18. EPR characterization of the molybdenum(V) forms of formate dehydrogenase from Desulfovibrio desulfuricans ATCC 27774 upon formate reduction.

    PubMed

    Rivas, María G; González, Pablo J; Brondino, Carlos D; Moura, José J G; Moura, Isabel

    2007-11-01

    The EPR characterization of the molybdenum(V) forms obtained on formate reduction of both as-prepared and inhibited formate dehydrogenase from Desulfovibrio desulfuricans ATCC 27774, an enzyme that catalyzes the oxidation of formate to CO(2), is reported. The Mo(V) EPR signal of the as-prepared formate-reduced enzyme is rhombic (g(max)=2.012, g(mid)=1.996, g(min)=1.985) and shows hyperfine coupling with two nuclear species with I=1/2. One of them gives an anisotropic splitting and is not solvent exchangeable (A(max)=11.7, A(mid)=A(min)=non-detectable, A-values in cm(-1)x10(-4)). The second species is exchangeable with solvent and produces a splitting at the three principal g-values (A(max)=7.7, A(mid)=10.0, A(min)=9.3). The hyperfine couplings of the non-solvent and solvent exchangeable nuclei are assigned to the hydrogen atoms of the beta-methylene carbon of a selenocysteine and to a Mo ligand whose nature, sulfydryl or hydroxyl, is still in debate. The Mo(V) species obtained in the presence of inhibitors (azide or cyanide) yields a nearly axial EPR signal showing only one detectable splitting given by nuclear species with I=1/2 (g(max)=2.092, g(mid)=2.000, g(min)=1.989, A(max)=non-detectable, A(mid)=A(min)=7.0), which is originated from the alpha-proton donated by the formate to a proximal ligand of the molybdenum. The possible structures of both paramagnetic molybdenum species (observed upon formate reduction in presence and absence of inhibitors) are discussed in comparison with the available structural information of this enzyme and the structural and EPR properties of the closely related formate dehydrogenase-H from Escherichia coli.

  19. A DICOM-RT radiation oncology ePR with decision support utilizing a quantified knowledge base from historical data

    NASA Astrophysics Data System (ADS)

    Documet, Jorge R.; Liu, Brent; Le, Anh; Law, Maria

    2008-03-01

    During the last 2 years we have been working on developing a DICOM-RT (Radiation Therapy) ePR (Electronic Patient Record) with decision support that will allow physicists and radiation oncologists during their decision-making process. This ePR allows offline treatment dose calculations and plan evaluation, while at the same time it compares and quantifies treatment planning algorithms using DICOM-RT objects. The ePR framework permits the addition of visualization, processing, and analysis tools, which combined with the core functionality of reporting, importing and exporting of medical studies, creates a very powerful application that can improve the efficiency while planning cancer treatments. Usually a Radiation Oncology department will have disparate and complex data generated by the RT modalities as well as data scattered in RT Information/Management systems, Record & Verify systems, and Treatment Planning Systems (TPS) which can compromise the efficiency of the clinical workflow since the data crucial for a clinical decision may be time-consuming to retrieve, temporarily missing, or even lost. To address these shortcomings, the ACR-NEMA Standards Committee extended its DICOM (Digital Imaging & Communications in Medicine) standard from Radiology to RT by ratifying seven DICOM RT objects starting in 1997 [1,2]. However, they are not broadly used yet by the RT community in daily clinical operations. In the past, the research focus of an RT department has primarily been developing new protocols and devices to improve treatment process and outcomes of cancer patients with minimal effort dedicated to integration of imaging and information systems. Our attempt is to show a proof-of-concept that a DICOM-RT ePR system can be developed as a foundation to perform medical imaging informatics research in developing decision-support tools and knowledge base for future data mining applications.

  20. Solid-state EPR strategies for the structural characterization of paramagnetic NO adducts of frustrated Lewis pairs (FLPs).

    PubMed

    de Oliveira, Marcos; Wiegand, Thomas; Elmer, Lisa-Maria; Sajid, Muhammad; Kehr, Gerald; Erker, Gerhard; Magon, Claudio José; Eckert, Hellmut

    2015-03-28

    Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and (11)B, (14)N, and (31)P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that different from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to (14)N and (31)P, the ESEEM and HYSCORE spectra contain important information about the (11)B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.

  1. Solid-state EPR strategies for the structural characterization of paramagnetic NO adducts of frustrated Lewis pairs (FLPs)

    NASA Astrophysics Data System (ADS)

    de Oliveira, Marcos; Wiegand, Thomas; Elmer, Lisa-Maria; Sajid, Muhammad; Kehr, Gerald; Erker, Gerhard; Magon, Claudio José; Eckert, Hellmut

    2015-03-01

    Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and 11B, 14N, and 31P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that different from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to 14N and 31P, the ESEEM and HYSCORE spectra contain important information about the 11B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.

  2. Luminescence sensitivity changes in natural quartz induced by high temperature annealing: a high frequency EPR and OSL study

    NASA Astrophysics Data System (ADS)

    Poolton, N. R. J.; Smith, G. M.; Riedi, P. C.; Bulur, E.; Bøtter-Jensen, L.; Murray, A. S.; Adrian, M.

    2000-04-01

    Quartz undergoes very significant luminescence sensitivity changes after high temperature annealing (0-1200 °C), with particular enhancement occurring between the phase transition temperatures 573 and 870 °C. In order to understand why this occurs, high frequency electron paramagnetic resonance (EPR), operating at 90 GHz, has been used to monitor the structure and population of defects in natural sedimentary quartz, following annealing and icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/> -irradiation. The results are compared with the optically stimulated luminescence (OSL) data of the same samples. It is shown that: (i) the structure and population of the dominant [AlO4 ]0 recombination centres are largely unaffected by the annealing process; (ii) the oxygen vacancy E´ centres are destroyed when annealed at temperatures between the phase transitions and; (iii) the numbers of both [TiO4 /H+ ]0 and [TiO4 /Li+ ]0 donors increase between 400 and 700 °C. Photo-EPR spectra are presented, providing evidence that both the Ti associated donors and Al acceptors are directly involved in the OSL process. The heat-induced changes in the population of these EPR defects is mirrored in part by the change in the luminescence sensitivity of several OSL components. Evidence is also presented suggesting that E´ may act as non-radiative centres competing in the OSL process.

  3. Low frequency EPR of Pseudomonas aeruginosa azurin. Analysis of ligand superhyperfine structure from a type 1 copper site.

    PubMed Central

    Antholine, W E; Hanna, P M; McMillin, D R

    1993-01-01

    The type 1 copper in Pseudomonas aeruginosa azurin was studied by electron paramagnetic resonance (EPR) spectroscopy at low microwave frequencies. Partially resolved ligand hyperfine structure was observed in the perpendicular region of the spectra at both S-band (2.4 GHz) and L-band (1.1 GHz). A trial and error method, requiring several hundred simulations, has been used to simulate the low frequency EPR data and yield an optimum value of 30 MHz for ACUx, more than one half that previously reported. The fit between the simulated and experimental data is sensitive to changes in the Euler angles and, in particular, to the angle alpha which rotates the Cu A-tensor about the z-axis. Thus, the A- and g-tensors for copper in P. aeruginosa azurin do not appear to be coincident. A value for the Euler angle beta of at least 10 degrees does not disturb the fit between the simulated and experimental data. These studies demonstrate the advantage of evaluating EPR parameters from simulations at more than one frequency, especially at low frequencies where ligand superhyperfine structure may be resolved for type 1 copper. PMID:8381679

  4. High-frequency, spin-label EPR of nonaxial lipid ordering and motion in cholesterol-containing membranes.

    PubMed

    Gaffney, B J; Marsh, D

    1998-10-27

    The EPR spectra of spin-labeled lipid chains in fully hydrated bilayer membranes of dimyristoyl phosphatidylcholine containing 40 mol % of cholesterol have been studied in the liquid-ordered phase at a microwave radiation frequency of 94 GHz. At such high field strengths, the spectra should be optimally sensitive to lateral chain ordering that is expected in the formation of in-plane domains. The high-field EPR spectra from random dispersions of the cholesterol-containing membranes display very little axial averaging of the nitroxide g-tensor anisotropy for lipids spin labeled toward the carboxyl end of the sn-2 chain (down to the 8-C atom). For these positions of labeling, anisotropic 14N-hyperfine splittings are resolved in the gzz and gyy regions of the nonaxial EPR spectra. For positions of labeling further down the lipid chain, toward the terminal methyl group, the axial averaging of the spectral features systematically increases and is complete at the 14-C atom position. Concomitantly, the time-averaged element of the 14N-hyperfine tensor decreases, indicating that the axial rotation at the terminal methyl end of the chains arises from correlated torsional motions about the bonds of the chain backbone, the dynamics of which also give rise to a differential line broadening of the 14N-hyperfine manifolds in the gzz region of the spectrum. These results provide an indication of the way in which lateral ordering of lipid chains in membranes is induced by cholesterol.

  5. Use of epr spin-trapping techniques to detect radicals from rat lung lavage fluid following sulfur mustard vapor exposure

    SciTech Connect

    Anderson, D.R.; Yourick, J.J.; Arroyo, C.M.; Young, G.D.; Harris, L.W.

    1993-05-13

    Although well known for skin vesicating properties, pulmonary damage and associated infections account for most of the mortality associated with sulfur mustard (HD). We have employed an in vivo HD vapor exposure model, bronchoalveolar lavage and histopathology in conjunction with electron paramagnetic resonance (EPR) techniques to provide evidence for HD-induced (free radical/lipid peroxidation associated) lung injury. Anesthetized rats were intratracheally intubated and exposed to 0.35 mg HD vapor over 50 min. Immediately, 1 hr or 24 hr after exposure, lungs were lavaged with the spin trap, alpha-phenyl-t-butyl nitrone (PBN; 0.35 mg/ml). Recovered lavage fluid was assayed by EPR spectroscopy for radical spin adducts. Airway lipid extracts were assayed for thiobarbituric acid reactive products (TBARs); while separate groups of rats were used to evaluate histopathology. EPR results show the presence of an ascorbyl radical at 1 and 24 hr, and a carbon centered PBN spin adduct at 24 hr, both indicative of lipid peroxidation. TBAR (A532nm) formation was also detected at 24 hr. Histopathology revealed multifocal separation of the bronchial epithelium from the submucosa with little or no alveolar involvement at 24 hrs. These studies provide evidence that HD may affect lungs by a free radical mechanism which produces membrane and other tissue damage.

  6. EPR and DFT analysis of biologically relevant chromium(V) complexes with d-glucitol and d-glucose.

    PubMed

    Van Doorslaer, Sabine; Beirinckx, Quinten; Nys, Kevin; Mangiameli, María Florencia; Cuypers, Bert; Callens, Freddy; Vrielinck, Henk; González, Juan Carlos

    2016-09-01

    1,2-diolato ligands, such as carbohydrates and glycoproteins, tend to stabilize chromium(V), thus forming important intermediates that have been implicated in the genotoxicity of Cr(VI). Since many years, room-temperature continuous-wave electron paramagnetic resonance (EPR) at X-band microwave frequencies has been used as a standard characterization tool to study chromium(V) intermediates formed during the reduction of Cr(VI) in the presence of biomolecules. In this work, the added value is tested of using a combination of pulsed and high-field EPR techniques with density functional theory computations to unravel the nature of Cr(V) complexes with biologically relevant chelators, such as carbohydrates. The study focuses on the oxidochromium(V) complexes formed during reduction of potassium dichromate with glutathione in the presence of the monosaccharide d-glucose or the polyalcohol d-glucitol. It is shown that although the presence of a multitude of Cr(V) intermediates may hamper a complete structural determination, the combined EPR and DFT approach reveals unambiguously the effect of freezing on the location of the counterions, the gradual replacement of water ligands by the diols, and the preference of Cr(V) to bind certain conformers.

  7. Prion domain of yeast Ure2 protein adopts a completely disordered structure: a solid-support EPR study.

    PubMed

    Ngo, Sam; Chiang, Vicky; Ho, Elaine; Le, Linh; Guo, Zhefeng

    2012-01-01

    Amyloid fibril formation is associated with a range of neurodegenerative diseases in humans, including Alzheimer's, Parkinson's, and prion diseases. In yeast, amyloid underlies several non-Mendelian phenotypes referred to as yeast prions. Mechanism of amyloid formation is critical for a complete understanding of the yeast prion phenomenon and human amyloid-related diseases. Ure2 protein is the basis of yeast prion [URE3]. The Ure2p prion domain is largely disordered. Residual structures, if any, in the disordered region may play an important role in the aggregation process. Studies of Ure2p prion domain are complicated by its high aggregation propensity, which results in a mixture of monomer and aggregates in solution. Previously we have developed a solid-support electron paramagnetic resonance (EPR) approach to address this problem and have identified a structured state for the Alzheimer's amyloid-β monomer. Here we use solid-support EPR to study the structure of Ure2p prion domain. EPR spectra of Ure2p prion domain with spin labels at every fifth residue from position 10 to position 75 show similar residue mobility profile for denaturing and native buffers after accounting for the effect of solution viscosity. These results suggest that Ure2p prion domain adopts a completely disordered structure in the native buffer. A completely disordered Ure2p prion domain implies that the amyloid formation of Ure2p, and likely other Q/N-rich yeast prion proteins, is primarily driven by inter-molecular interactions.

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

    PubMed

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

    2010-01-13

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

  9. EPR studies on the kinetics of the α-hydroxyethyl radical generated by Fenton-like chemistry

    NASA Astrophysics Data System (ADS)

    Schubert, Erik; Hett, Tobias; Schiemann, Olav; NejatyJahromy, Yaser

    2016-04-01

    Flow systems, either stopped or continuous, have long been at the core of kinetic studies of chemical reactions. Such flow systems need to be coupled with appropriate spectroscopic or otherwise techniques for the detection of the chemical species studied. If paramagnetic species are formed or consumed during the investigated reaction, electron paramagnetic resonance (EPR) with its nanomolar sensitivity can be the spectroscopic method of choice. However, not much literature is available on the application of EPR to quantitatively study kinetics of chemical reactions in the liquid state. Herein, we report the characterisation of the commercially available mixing resonator ER 4117 MX from BRUKER using the TEMPO-dithionite reaction as a standard. Furthermore, this setup was used to study the kinetics of the Fenton-like system of TiCl3/H2O2 and ethanol forming the α-hydroxyethyl radical. Potential contributions of reactions with O2, H2O2, Ti3+/4+, and self-recombination in the decay of the α-hydroxyethyl radical were investigated and the bimolecular decay was shown to be the dominant decay pathway, with a decay rate constant of 6.6 ×108 M-1 s-1. This study shows the effectiveness and capabilities of EPR as a direct, sensitive and in-situ method in kinetic studies.

  10. Non-invasive measurement of melanin-derived radicals in living mouse tail using X-band EPR

    PubMed Central

    Ogawa, Yukihiro; Ueno, Megumi; Sekine-Suzuki, Emiko; Nakanishi, Ikuo; Matsumoto, Ken-ichiro; Fujisaki, Shingo

    2016-01-01

    The aim of this experiment is to measure in vivo generation of melanin-derived radicals non-invasively, as a quantifiable index of radio-biological effect. Melanin-derived radicals in a living intact mouse tail tip were non-invasively measured in very simple way using an X-band electron paramagnetic resonance spectrometer. Colored mouse strains, C57BL/6NCr, BDF1, and C3H/He, have clear EPR signal corresponding to melanin-derived radicals in the tail tip; however, albino mouse strains, BALB/cCr, ddY, ICR, have no EPR signals. An X-ray fraction of 2 Gy/day (1 Gy/min) was repeatedly irradiated to a C3H/He mouse tail skin every Monday to Friday for 4 weeks. In comparison to before starting irradiation, the C3H/He mouse tail skin became darker, like a suntan. The melanin-derived radicals in C3H/He mouse tail skin were increased in association with X-ray fractions. Melanin-derived radicals in mouse tail skin can be readily and chronologically measurable by using X-band EPR spectrometer, and can be a marker for a radiobiological effect in the skin. PMID:27895382

  11. Toward increased concentration sensitivity for continuous wave EPR investigations of spin-labeled biological macromolecules at high fields

    NASA Astrophysics Data System (ADS)

    Song, Likai; Liu, Zhanglong; Kaur, Pavanjeet; Esquiaqui, Jackie M.; Hunter, Robert I.; Hill, Stephen; Smith, Graham M.; Fanucci, Gail E.

    2016-04-01

    High-field, high-frequency electron paramagnetic resonance (EPR) spectroscopy at W-(∼94 GHz) and D-band (∼140 GHz) is important for investigating the conformational dynamics of flexible biological macromolecules because this frequency range has increased spectral sensitivity to nitroxide motion over the 100 ps to 2 ns regime. However, low concentration sensitivity remains a roadblock for studying aqueous samples at high magnetic fields. Here, we examine the sensitivity of a non-resonant thin-layer cylindrical sample holder, coupled to a quasi-optical induction-mode W-band EPR spectrometer (HiPER), for continuous wave (CW) EPR analyses of: (i) the aqueous nitroxide standard, TEMPO; (ii) the unstructured to α-helical transition of a model IDP protein; and (iii) the base-stacking transition in a kink-turn motif of a large 232 nt RNA. For sample volumes of ∼50 μL, concentration sensitivities of 2-20 μM were achieved, representing a ∼10-fold enhancement compared to a cylindrical TE011 resonator on a commercial Bruker W-band spectrometer. These results therefore highlight the sensitivity of the thin-layer sample holders employed in HiPER for spin-labeling studies of biological macromolecules at high fields, where applications can extend to other systems that are facilitated by the modest sample volumes and ease of sample loading and geometry.

  12. The Crystal Structure of Micro- and Nanopowders of ZnS Studied by EPR of Mn2+ and XRD

    NASA Astrophysics Data System (ADS)

    Nosenko, Valentyna; Vorona, Igor; Grachev, Valentyn; Ishchenko, Stanislav; Baran, Nikolai; Becherikov, Yurii; Zhuk, Anton; Polishchuk, Yuliya; Kladko, Vasyl; Selishchev, Alexander

    2016-11-01

    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, and ZnS:Eu with the particle sizes of 5-7 μm, 50-200 nm, 7-10 μm, and 5-7 nm, respectively, were studied. Manganese was incorporated in the crystal lattice of all the samples as uncontrolled impurity or by doping. The Mn2+ ions were used as EPR structural probes. It is found that the ZnS:Cu has the cubic structure, the ZnS:Mn has the hexagonal structure with a rhombic distortion, the ZnS:Co is the mixture of the cubic and hexagonal phases in the ratio of 1:10, and the ZnS:Eu has the cubic structure and a distorted cubic structure with stacking defects in the ratio 3:1. The EPR technique is shown to be a powerful tool in the determination of the crystal structure for mixed-polytype ZnS powders and powders with small nanoparticles. It allows observation of the stacking defects, which is revealed in the XRD spectra.

  13. EPR and DFT study on the stabilization of radiation-generated methyl radicals in dehydrated Na-A zeolite.

    PubMed

    Danilczuk, Marek; Pogocki, Dariusz; Lund, Anders; Michalik, Jacek

    2006-12-07

    Electron paramagnetic resonance (EPR) spectroscopy was applied to study paramagnetic species stabilized in Na-A zeolite exposed to gaseous methane and gamma-irradiated at 77 K. Two types of EPR spectra were recorded during thermal annealing of zeolite up to room temperature. Owing to the results for the zeolite exposed to (13)CH(4) the multiplet observed at 110 K was assigned to a (.-)CH(3)...Na(+) complex. After decay of the multiplet, the isotropic quartet of methyl radical was recorded in the temperature range of 170-280 K. On the basis of the EPR parameters it is postulated that (.-)CH(3) radicals in this temperature region are able to freely rotate inside the zeolite cage. The structures of the (.-)CH(3)...Na(+) adsorption complex and respective hyperfine coupling constants were calculated by applying DFT quantum chemical methods. Two different models were applied to represent the zeolite framework: the 6T structure of one six-membered ring and the 3T cluster. The hyperfine coupling constants calculated for the (.-)CH(3)...Na(+) adsorption complex for both applied models show very good agreement with those obtained experimentally.

  14. Solid-state EPR strategies for the structural characterization of paramagnetic NO adducts of frustrated Lewis pairs (FLPs)

    SciTech Connect

    Oliveira, Marcos de; Magon, Claudio José; Wiegand, Thomas; Elmer, Lisa-Maria; Sajid, Muhammad; Kehr, Gerald; Erker, Gerhard; Eckert, Hellmut

    2015-03-28

    Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and {sup 11}B, {sup 14}N, and {sup 31}P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that different from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to {sup 14}N and {sup 31}P, the ESEEM and HYSCORE spectra contain important information about the {sup 11}B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.

  15. In Situ Determination of Manganese(II) Speciation in Deinococcus radiodurans by High Magnetic Field EPR

    PubMed Central

    Tabares, Leandro C.; Un, Sun

    2013-01-01

    High magnetic field high frequency electron paramagnetic resonance techniques were used to measure in situ Mn(II) speciation in Deinococcus radiodurans, a radiation-resistant bacteria capable of accumulating high concentrations of Mn(II). It was possible to identify and quantify the evolution of Mn(II) species in intact cells at various stages of growth. Aside from water, 95-GHz high field electron nuclear double resonance showed that the Mn(II) ions are bound to histidines and phosphate groups, mostly from fructose-1,6-bisphosphate but also inorganic phosphates and nucleotides. During stationary growth phase, 285-GHz continuous wave EPR measurements showed that histidine is the most common ligand to Mn(II) and that significant amounts of cellular Mn(II) in D. radiodurans are bound to peptides and proteins. As much as 40% of the total Mn(II) was in manganese superoxide dismutase, and it is this protein and not smaller manganese complexes, as has been suggested recently, that is probably the primary defense against superoxide. PMID:23303180

  16. X- and Q-band EPR Studies of the Tetraheme Cytochrome c554 from Nitrosomonas europaea

    NASA Astrophysics Data System (ADS)

    Petasis, Doros; Culver, Caleb; Hendrich, Michael

    2001-04-01

    Cytochrome c554 (cyt c554) is a tetraheme cytochrome from the bacteria Nitrosomonas europaea that participate in the assimilation of nitrogen into plants from industrially fixed Nsub2 by oxidizing ammonia to nitrite. These autotrophic bacteria metabolize ammonia as the sole source of energy through a two-step process. In the first step, the membrane-bound enzyme ammonia monooxygenase (AMO) catalyzes the oxidation of ammonia to hydroxylamine (NH3+O2+2e-+2H+ä_NH2OH+H2O). In the second step, hydroxylamine oxidoreductase (HAO) oxidizes hydroxylamine to nitrite (NH2OH+H2Oä_NO2-+4e-+5H+). Cyt c554 accepts electrons from HAO and transports them to either AMO or the ubiquinone pool. HAO is one of the most complicated heme systems known, consisting of 24 hemes in a circular arrangement. A large region of HAO matches the tertiary structure of cyt c554, so determining the electronic structure of the simpler protein cyt c554 will help in understanding the electronic structure of the active site of the more complex HAO enzyme. We have collected perpendicular and parallel mode EPR data at X- and Q-band frequencies (9 and 34 GHz respectively) of the native cyt c554 protein and a series of reduced samples in an effort to understand the role of each heme in electron transport. The novel features of these spectra were simulated using techniques developed at CMU and will be discussed.

  17. MOX recycling in GEN 3 + EPR Reactor homogeneous and stable full MOX core

    SciTech Connect

    Arslan, M.; Villele, E. de; Gauthier, J.C.; Marincic, A.

    2013-07-01

    In the case of the EPR (European Pressurized Reactor) reactor, 100% MOX core management is possible with simple design adaptations which are not significantly costly. 100% MOX core management offers several highly attractive advantages. First, it is possible to have the same plutonium content in all the rods of a fuel assembly instead of having rods with 3 different plutonium contents, as in MOX assemblies in current PWRs. Secondly, the full MOX core is more homogeneous. Thirdly, the stability of the core is significantly increased due to a large reduction in the Xe effect. Fourthly, there is a potential for the performance of the MOX fuel to match that of new high performance UO{sub 2} fuel (enrichment up to 4.95 %) in terms of increased burn up and cycle length. Fifthly, since there is only one plutonium content, the manufacturing costs are reduced. Sixthly, there is an increase in the operating margins of the reactor, and in the safety margins in accident conditions. The use of 100% MOX core will improve both utilisation of natural uranium resources and reductions in high level radioactive waste inventory.

  18. DANCING WITH THE ELECTRONS: TIME-DOMAIN AND CW IN VIVO EPR IMAGING

    PubMed Central

    Subramanian, Sankaran; Krishna, Murali C.

    2009-01-01

    The progress in the development of imaging the distribution of unpaired electrons in living systems and the functional and the potential diagnostic dimensions of such an imaging process, using Electron Paramagnetic Resonance Imaging (EPRI), is traced from its origins with emphasis on our own work. The importance of EPR imaging stems from the fact that many paramagnetic probes show oxygen dependent spectral broadening. Assessment of in vivo oxygen concentration is an important factor in radiation oncology in treatment-planning and monitoring treatment-outcome. The emergence of narrow-line trairylmethyl based, bio-compatible spin probes has enabled the development of radiofrequency time-domain EPRI. Spectral information in time-domain EPRI can be achieved by generating a time sequence of T2* or T2 weighted images. Progress in CW imaging has led to the use of rotating gradients, more recently rapid scan with direct detection, and a combination of all the three. Very low field MRI employing Dynamic Nuclear polarization (Overhauser effect) is also employed for monitoring tumor hypoxia, and re-oxygenation in vivo. We have also been working on the co-registration of MRI and time domain EPRI on mouse tumor models at 300 MHz using a specially designed resonator assembly. The mapping of the unpaired electron distribution and unraveling the spectral characteristics by using magnetic resonance in presence of stationary and rotating gradients in indeed ‘dancing with the (unpaired) electrons’, metaphorically speaking. PMID:22025900

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

    PubMed

    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.

  20. The 3rd international intercomparison on EPR tooth dosimetry: Part 1, general analysis.

    PubMed

    Wieser, A; Debuyst, R; Fattibene, P; Meghzifene, A; Onori, S; Bayankin, S N; Blackwell, B; Brik, A; Bugay, A; Chumak, V; Ciesielski, B; Hoshi, M; Imata, H; Ivannikov, A; Ivanov, D; Junczewska, M; Miyazawa, C; Pass, B; Penkowski, M; Pivovarov, S; Romanyukha, A; Romanyukha, L; Schauer, D; Scherbina, O; Schultka, K; Shames, A; Sholom, S; Skinner, A; Skvortsov, V; Stepanenko, V; Tielewuhan, E; Toyoda, S; Trompier, F

    2005-02-01

    The objective of the 3rd International Intercomparison on Electron Paramagnetic Resonance (EPR) Tooth Dosimetry was the evaluation of laboratories performing tooth enamel dosimetry below 300 mGy. Participants had to reconstruct the absorbed dose in tooth enamel from 11 molars, which were cut into two halves. One half of each tooth was irradiated in a 60Co beam to doses in the ranges of 30-100 mGy (5 samples), 100-300 mGy (5 samples), and 300-900 mGy (1 sample). Fourteen international laboratories participated in this intercomparison programme. A first analysis of the results and an overview of the essential features of methods applied in different laboratories are presented. The relative standard deviation of results of all methods was better than 27% for applied doses in the range of 79-704 mGy. In the analysis of the unirradiated tooth halves 8% of the samples were identified as outliers with additional absorbed dose above background dose.

  1. Simultaneous 280 MHz EPR imaging of rat organs during nitroxide free radical clearance.

    PubMed Central

    Alecci, M; Ferrari, M; Quaresima, V; Sotgiu, A; Ursini, C L

    1994-01-01

    A radio frequency (RF) (280 MHz) electron paramagnetic resonance (EPR) spectroscopy and imaging apparatus has been used to localize a pyrrolidine nitroxide free radical in the rat abdomen and thorax. The nitroxide 2,2.5.5,-tetramethylpyrrolidine-1-oxyl-3- carboxylic acid (PCA) had a whole body monoexponential decay with half-life of 13.3 +/- 0.7 (n = 4), 19.4 +/- 0.2 (n = 3), and 23 +/- 2 (n = 6) min for 1, 2, and 3 mmol/kg PCA, respectively. Up to seven one-dimensional longitudinal projections were collected on six rats in the presence of a 8 mT/m field gradient. With an injection dose of 3 mmol/kg, PCA half-lives were 19 +/- 1, 17 +/- 2, and 22 +/- 2 min (n = 6) in the lower abdomen, in the liver, and in the thorax, respectively. Thorax half-life was significantly longer than liver half-life. Sequential two-dimensional images of PCA distribution in a plane longitudinal to the rat body were obtained from eight spectra in the presence of a gradient of 12 mT/m (acquisition time 5 min; spatial resolution 8 mm). After 7 min, the nitroxide was detectable in the left side of the thorax area, but it was mostly localized in the liver. PCA was more uniformly distributed in the image collected after 17 min. Images FIGURE 4 PMID:7811942

  2. EPR study of the surface basicity of calcium oxide. 3. Surface reactivity and nonstoichiometry.

    PubMed

    Paganini, Maria Cristina; Chiesa, Mario; Dolci, Francesco; Martino, Paola; Giamello, Elio

    2006-06-22

    High surface area polycrystalline calcium oxide forms ozonide O3- ions upon O2 adsorption and NO3(2-) anions under low pressures of NO. Both radical anions, detected by electron paramagnetic resonance (EPR), are not observed in the case of the homologous magnesium oxide. This behavior reveals the presence, in CaO, of anomalies with respect to the ideal composition of an ionic oxide which are identified in terms of two main types of defects. The first type consists of positive holes dispersed in the bulk and originated by the unavoidable presence of Na+ ions in the composition of the solid. The decomposition of the surface ozonide shows the formation of a transient surface stabilized O- (the chemical notation of a positive hole associated to an oxide ion) which is for the first time reported at the surface of CaO. The second type of defect consists of surface peroxide groups (present at particular surface sites where they are formed by pairing of two distinct O-) which react with nitric oxide (NO) yielding NO3(2-) radical anions. The presence of peroxide is not related to the presence of impurities but, rather, to a certain propensity of the solid to form such ions at the surface along the dehydration process.

  3. Irradiation free radicals in freshwater crayfish Astacus leptodactylus Esch investigated by EPR spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    The free radicals of irradiated crayfish Astaculs leptodactylus cuticle were studied by X-band electron paramagnetic resonance. The kinetic behaviour as well as the thermal stability of the radiation-induced free radicals in crayfish cuticle were investigated by means of both isothermal and isochronal annealing. Both short, presumable juvenile and long, mature exemplars of freshwater crayfish were investigated. Only the long exemplars cuticle displayed the presence of Mn2+ ions, very similar to those reported for Mn2+ ions in calcite. The 200 °C isothermal annealing studies attested the existence of a multitude of radical species, some of them being generated during the first minutes of thermal treatment and then partially of totally vanishing. Regardless these peculiarities, the EPR spectrum of 15 kGy irradiated cuticle showed remarkable time stability, its amplitude decreasing with about 18% after more than 16 months of storage at room temperature. The implications of these observations regarding the diversity of irradiation free radicals as well as their suitability to identify gamma radiation decontamination treatment are discussed.

  4. Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions. A Combined EPR and DFT Study

    SciTech Connect

    Mardis, Kristy L.; Webb, J.; Holloway, Tarita; Niklas, Jens; Poluektov, Oleg G.

    2015-12-03

    Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advanced electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM.

  5. Improved Deterministic N-To-One Joint Remote Preparation of an Arbitrary Qubit via EPR Pairs

    NASA Astrophysics Data System (ADS)

    Liu, Wen-Jie; Chen, Zheng-Fei; Liu, Chao; Zheng, Yu

    2015-02-01

    Recently, Bich et al. (Int. J. Theor. Phys. 51: 2272, 2012) proposed two deterministic joint remote state preparation (JRSP) protocols of an arbitrary single-qubit state: one is for two preparers to remotely prepare for a receiver by using two Einstein-Podolsky-Rosen (ERP) pairs; the other is its generalized form in the case of arbitrary N ( N > 2) preparers via N ERP pairs. While examining these two protocols, we find that the success probability for the receiver achieving the desired state is not deterministic, i.e., , for N > 2 preparers in the second protocol. Through constructing two sets of adaptive projective measurement bases for both the real space and the complex space, an improved deterministic N-to-one JRSP protocol for an arbitrary single-qubit state is presented. Analysis shows our protocol can truly achieve the unit success probability, i.e., . What is more, the receiver can be randomly assigned even after the distribution of the qubits of EPR pairs, so it is more flexible and applicable in the network situation.

  6. Evidence for Alkene cis-Aminocupration, an Aminooxygenation Case Study: Kinetics, EPR Spectroscopy, and DFT Calculations

    PubMed Central

    Paderes, Monissa C.; Belding, Lee; Fanovic, Branden; Dudding, Travis; Keister, Jerome B.

    2012-01-01

    Alkene difunctionalization reactions are important in organic synthesis. We have recently shown that copper(II) complexes can promote and catalyze intramolecular alkene aminooxygenation, carboamination, and diamination reactions. In this contribution, we report a combined experimental and theoretical examination of the mechanism of the copper(II)-promoted olefin aminooxygenation reaction. Kinetics experiments revealed a mechanistic pathway involving an equilibrium reaction between a copper(II) carboxylate complex and the γ-alkenyl sulfonamide substrate and a rate-limiting intramolecular cis-addition of N–Cu across the olefin. Kinetic isotope effect studies support that the cis-aminocupration is the rate-determining step. UV/Vis spectra support a role for the base in the break-up of copper(II) carboxylate dimer to monomeric species. Electron paramagnetic resonance (EPR) spectra provide evidence for a kinetically competent N–Cu intermediate with a CuII oxidation state. Due to the highly similar stereochemical and reactivity trends among the CuII-promoted and catalyzed alkene difunctionalization reactions we have developed, the cis-aminocupration mechanism can reasonably be generalized across the reaction class. The methods and findings disclosed in this report should also prove valuable to the mechanism analysis and optimization of other copper(-II) carboxylate promoted reactions, especially those that take place in aprotic organic solvents. PMID:22237868

  7. Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions. A Combined EPR and DFT Study

    DOE PAGES

    Mardis, Kristy L.; Webb, J.; Holloway, Tarita; ...

    2015-12-03

    Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advancedmore » electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM.« less

  8. EPR Spin Trapping of an Oxalate-Derived Free Radical in the Oxalate Decarboxylase Reaction

    PubMed Central

    Imaram, Witcha; Saylor, Benjamin T.; Centonze, Christopher P.; Richards, Nigel G. J.; Angerhofer, Alexander

    2011-01-01

    EPR spin trapping experiments on bacterial oxalate decarboxylase from Bacillus subtilis under turn-over conditions are described. The use of doubly 13C-labeled oxalate leads to a characteristic splitting of the observed radical adducts using the spin trap N-tert-butyl-α-phenylnitrone linking them directly to the substrate. The radical was identified as the carbon dioxide radical anion which is a key intermediate in the hypothetical reaction mechanism of both decarboxylase and oxidase activities. X-ray crystallography had identified a flexible loop, SENS161-4, which acts as a lid to the putative active site. Site directed mutagenesis of the hinge amino acids, S161 and T165 was explored and showed increased radical trapping yields compared to the wild type. In particular, T165V shows approximately ten times higher radical yields while at the same time its decarboxylase activity was reduced by about a factor of ten. This mutant lacks a critical H-bond between T165 and R92 resulting in compromised control over its radical chemistry allowing the radical intermediate to leak into the surrounding solution. PMID:21277974

  9. Extracting order parameters from powder EPR lineshapes for spin-labelled lipids in membranes

    NASA Astrophysics Data System (ADS)

    Schorn, Karl; Marsh, Derek

    1997-10-01

    The corrections that must be made to the spectral separations of the hyperfine extrema in the pseudo-powder EPR lineshapes from lipid spin labels in randomly oriented membranes have been investigated by spectral simulations that include slow motional components. Using simulation parameters that are able to describe the corresponding experimental spectra rather well, it is found that any correction required to the outer hyperfine splitting, 2 Amax, is small, but that the correction to the inner splitting, 2 Amin, differs from that obtained previously from motional narrowing theory. Both Amax and Amin deduced from the simulated spectra are found to vary almost linearly with the molecular-frame order parameter, Szz. The corrections to Amin are used to obtain order parameters from the experimental line splittings. These are found to be in reasonable agreement with the order parameters derived from direct spectral simulation. The inclusion of slow motional components in the simulations represents an improvement over the correction to Amin that is routinely used for membrane systems and which is based on motional narrowing theory.

  10. EPR investigation of UV light effect on calcium carbonate powders with different grain sizes.

    PubMed

    Kabacińska, Zuzanna; Krzyminiewski, Ryszard; Dobosz, Bernadeta

    2014-06-01

    This study is based on investigation of calcium carbonate powders with different grain sizes exposed to UV light. Calcium carbonate is widely used in many branches of industry, e.g. as a filler for polymer materials; therefore, knowing its properties, among them also its reaction to UV light, is essential. Samples of powdered calcium carbonate with average grain sizes of 69 and 300 nm and 2.1, 6, 16, 25 µm were used in this investigation. Measurements were performed at room temperature using EPR X-band spectrometer, and they have shown the additional signals induced by the light from Hg lamp. The effect of annealing of the micro-grain samples was also studied. The spectra of four micro-grain samples after irradiation are similar, but there are differences between them and the other two powders, which could be related to the different sizes of their grains. Further studies based on these preliminary results may prove useful in research of photodegradation of CaCO3-filled materials, as well as helpful in increasing the accuracy of dating of archaeological and geological objects.

  11. Radical production from peroxide and peracid tumour promoters: EPR spin trapping studies.

    PubMed

    Greenley, T L; Davies, M J

    1993-05-07

    EPR spin trapping using the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 3,5-dibromo-4-nitrosobenzene sulphonic acid (DBNBS) has been employed to examine the generation of radicals from a number of organic peroxides and peracids which are known or suspected tumour promoters. All of the compounds when incubated with rat liver microsomal fractions in the presence of NADPH or NADH are metabolised to radical species which can be detected, and in most cases identified definitively, as the corresponding spin adducts; the assignment of particular signals to certain spin adducts has been confirmed by photolytic experiments. In the majority of cases, the predominant species are the arenecarbonyloxyl [RC(O)O.] and hydroxyl radical adducts. The mechanism of formation of the former species is shown to be enzymatic and cytochrome P-450 dependent and requires the presence of reducing equivalents. This type of radical is shown to undergo ready decarboxylation to give aryl radicals in agreement with previous chemical studies. The detection of these radical species, which are known to cause DNA strand breaks and be cytotoxic, with all the compounds tested, provides strong supportive evidence for the theory that it is the generation of radical species from these compounds which is the cause of their tumour-promoting activity.

  12. Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions: A Combined EPR and DFT Study

    PubMed Central

    Webb, Jeremy N.; Holloway, Tarita; Niklas, Jens

    2016-01-01

    Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of the electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density Functional Theory (DFT) calculations characterize the electronic structures of the fullerene anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advanced EPR spectroscopy allows the validation of the DFT calculations. Thus, for the first time the directions of the main g-tensors axis were determined in the molecular frame. For both systems, no spin density is present on the PCBM side chain and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM. PMID:26569578

  13. 9 GHz CW-EPR molecular dynamics study of polycrystalline 1-benzyl 4-hydroxy piperidine

    NASA Astrophysics Data System (ADS)

    Krzyminiewski, R.; Pawlicka, M.; Kruczynski, Z.; Kudynska, J.; Buckmaster, H. A.

    1998-07-01

    This paper reports the results of a 9.4 GHz CW-EPR study of the molecular dynamics in a polycrystalline sample of 1-benzyl 4-hydroxy piperidine which was γ-irradiated with a 150 kGy dose at 293 K. The temperature dependence of the hyperfine splitting (HFS) and spectral line width was measured in this acceptor-bridge-donor molecular structure from 123-273 K. A model evaluation procedure was used to determine the best-fit simulation of the observed spectrum. It was concluded that the ionizing radiation generates a free radical (I) by removal of one hydrogen from the CH 2 group in the bridge connecting the benzene and piperidine rings and another free radical (II) by breaking the bond between the carbon and hydrogen atoms in the piperidine ring. The HFS parameters and the unpaired electron densities were determined. The line width for radical (I) was found to be temperature dependent with an anomaly near 190 K indicative of either a solid-solid structural phase transition or conformational changes and did not saturate at microwave cavity input power levels up to 7 mW. The HFS parameter for radical (I) was also found to be temperature dependent between 123 and 273 K with an anomalous peak near 190 K in agreement with that observed for the line width.

  14. Solid-state NMR and EPR study of fluorinated carbon nanofibers

    SciTech Connect

    Zhang Wei Dubois, Marc Guerin, Katia Hamwi, Andre Giraudet, Jerome Masin, Francis

    2008-08-15

    Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF{sub 4} during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF){sub n} structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C{sub 2}F){sub n} type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O{sub 2}), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined. - Graphical abstract: Scheme of the fluorination process using F{sub 2} and TbF{sub 4} as fluorinating agent.

  15. Effects of phloretin on lipid organization in the erythrocyte membrane as measured by EPR

    NASA Astrophysics Data System (ADS)

    Abumrad, Nada A.; Perkins, Ray C.; Dalton, Larry R.; Park, Charles R.; Park, Jane H.

    Phloretin is a lipophilic compound which has been widely studied as a broad spectrum effector of metabolite transport in red blood cells (RBC). Phloretin effects on the organization of lipids in the RBC membrane are investigated using the spin-labeled fatty acids, 5 and 16-nitroxyl stearate (5-NS and 16-NS, respectively). Phloretin at different concentrations produced biphasic effects on the lineshape of the EPR response from 16-NS-labeled RBC. The dependence of these changes on the flat cell orientation with respect to the magnetic field suggested that phloretin promoted lipid order at low concentrations (5 to 40 μ M) and disorder at high concentrations (40 to 250 μ M). The biphasic effects of phloretin occurred at concentrations which parallel its dual actions on metabolite transfer. Phloretin generally inhibits transport (protein-mediated) and stimulates diffusion (lipid-mediated) processes. The spectroscopic effects were best characterized through second-harmonic, in-phase detection. The possible contribution of other factors to the spectroscopic changes is discussed. When RBC were spin labeled with 5-NS, higher concentrations of the probe were required for adequate detection and only monophasic effects of phoretin were observed. The results suggest that membrane lipids are important in phloretin effects on transport and diffusion processes.

  16. Using spin-label W-band EPR to study membrane fluidity profiles in samples of small volume

    NASA Astrophysics Data System (ADS)

    Mainali, Laxman; Hyde, James S.; Subczynski, Witold K.

    2013-01-01

    Conventional and saturation-recovery (SR) EPR at W-band (94 GHz) using phosphatidylcholine spin labels (labeled at the alkyl chain [n-PC] and headgroup [T-PC]) to obtain profiles of membrane fluidity has been demonstrated. Dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol have been studied, and the results have been compared with similar studies at X-band (9.4 GHz) (L. Mainali, J.B. Feix, J.S. Hyde, W.K. Subczynski, J. Magn. Reson. 212 (2011) 418-425). Profiles of the spin-lattice relaxation rate (T1-1) obtained from SR EPR measurements for n-PCs and T-PC were used as a convenient quantitative measure of membrane fluidity. Additionally, spectral analysis using Freed's MOMD (microscopic-order macroscopic-disorder) model (E. Meirovitch, J.H. Freed J. Phys. Chem. 88 (1984) 4995-5004) provided rotational diffusion coefficients (R⊥ and R||) and order parameters (S0). Spectral analysis at X-band provided one rotational diffusion coefficient, R⊥. T1-1, R⊥, and R|| profiles reflect local membrane dynamics of the lipid alkyl chain, while the order parameter shows only the amplitude of the wobbling motion of the lipid alkyl chain. Using these dynamic parameters, namely T1-1, R⊥, and R||, one can discriminate the different effects of cholesterol at different depths, showing that cholesterol has a rigidifying effect on alkyl chains to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. The nondynamic parameter, S0, shows that cholesterol has an ordering effect on alkyl chains at all depths. Conventional and SR EPR measurements with T-PC indicate that cholesterol has a fluidizing effect on phospholipid headgroups. EPR at W-band provides more detailed information about the depth-dependent dynamic organization of the membrane compared with information obtained at X-band. EPR at W-band has the potential to be a powerful tool for studying membrane fluidity in samples of small volume, ˜30 n

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

    PubMed

    Zdybel, Magdalena; Chodurek, Ewa; Pilawa, Barbara

    2014-01-01

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

  18. 1D magnetic interactions in Cu(II) oxovanadium phosphates (VPO), magnetic susceptibility, DFT, and single-crystal EPR.

    PubMed

    Venegas-Yazigi, Diego; Spodine, Evgenia; Saldias, Marianela; Vega, Andrés; Paredes-García, Verónica; Calvo, Rafael; de Santana, Ricardo Costa

    2015-04-20

    We report the crystal face indexing and molecular spatial orientation, magnetic properties, electron paramagnetic resonance (EPR) spectra, and density functional theory (DFT) calculations of two previously reported oxovanadium phosphates functionalized with Cu(II) complexes, namely, [Cu(bipy)(VO2)(PO4)]n (1) and [{Cu(phen)}2(VO2(H2O)2)(H2PO4)2 (PO4)]n (2), where bipy = 2,2'-bipyridine and phen = 1,10-phenanthroline, obtained by a new synthetic route allowing the growth of single crystals appropriate for the EPR measurements. Compounds 1 and 2 crystallize in the triclinic group P1̅ and in the orthorhombic Pccn group, respectively, containing dinuclear copper units connected by two -O-P-O- bridges in 1 and by a single -O-P-O- bridge in 2, further connected through -O-P-O-V-O- bridges. We emphasize in our work the structural aspects related to the chemical paths that determine the magnetic properties. Magnetic susceptibility data indicate bulk antiferromagnetism for both compounds, allowing to calculate J = -43.0 cm(-1) (dCu-Cu = 5.07 Å; J defined as Hex(i,j) = -J Si·Sj), considering dinuclear units for 1, and J = -1.44 cm(-1) (dCu-Cu = 3.47 Å) using the molecular field approximation for 2. The single-crystal EPR study allows evaluation of the g matrices, which provide a better understanding of the electronic structure. The absence of structure of the EPR spectra arising from the dinuclear character of the compounds allows estimation of weak additional exchange couplings |J'| > 0.3 cm(-1) for 1 (dCu-Cu = 5.54 Å) and a smaller value of |J'| ≥ 0.15 cm(-1) for 2 (dCu-Cu = 6.59 Å). DFT calculations allow evaluating two different exchange couplings for each compound, specifically, J = -36.60 cm(-1) (dCu-Cu = 5.07 Å) and J' = 0.20 cm(-1) (dCu-Cu =5.54 Å) for 1 and J = -1.10 cm(-1) (dCu-Cu =3.47 Å) and J' = 0.01 cm(-1) (dCu-Cu = 6.59 Å) for 2, this last value being in the range of the uncertainties of the calculations. Thus, these values are in good agreement

  19. Conformation and dynamics of nucleotides in bulges and symmetric internal loops in duplex DNA studied by EPR and fluorescence spectroscopies

    SciTech Connect

    Cekan, Pavol; Sigurdsson, Snorri Th.

    2012-04-13

    Highlights: Black-Right-Pointing-Pointer Bulges and loops were studied by both EPR and fluorescence spectroscopies using the probe C/C{sup f}. Black-Right-Pointing-Pointer One-base bulge was in a temperature-dependent equilibrium between looped-out and stacked states. Black-Right-Pointing-Pointer Bases in two- and three-base bulges were stacked at all temperatures, resulting in DNA bending. Black-Right-Pointing-Pointer Bases were stacked in symmetrical two- to five-base internal loops, according to EPR data. Black-Right-Pointing-Pointer Unexpectedly high fluorescence for the smaller loops indicated local structural perturbations. -- Abstract: The dynamics and conformation of base bulges and internal loops in duplex DNA were studied using the bifunctional spectroscopic probe C, which becomes fluorescent (C{sup f}) upon reduction of the nitroxide functional group, along with EPR and fluorescence spectroscopies. A one-base bulge was in a conformational equilibrium between looped-out and stacked states, the former favored at higher temperature and the latter at lower temperature. Stacking of bulge bases was favored in two- and three-base bulges, independent of temperature, resulting in DNA bending as evidenced by increased fluorescence of C{sup f}. EPR spectra of C-labeled three-, four- and five-base symmetrical interior DNA bulges at 20 Degree-Sign C showed low mobility, indicating that the spin-label was stacked within the loop. The spin-label mobility at 37 Degree-Sign C increased as the loops became larger. A considerable variation in fluorescence between different loops was observed, as well as a temperature-dependence within constructs. Fluorescence unexpectedly increased as the size of the loop decreased at 2 Degree-Sign C. Fluorescence of the smallest loops, where a single T{center_dot}T mismatch was located between the stem region and the probe, was even larger than for the single strand, indicating a considerable local structural deformation of these loops

  20. Using spin-label W-band EPR to study membrane fluidity profiles in samples of small volume

    PubMed Central

    Mainali, Laxman; Hyde, James S.; Subczynski, Witold K.

    2012-01-01

    Conventional and saturation-recovery (SR) EPR at W-band (94 GHz) using phosphatidylcholine spin labels (labeled at the alkyl chain [n-PC] and headgroup [T-PC]) to obtain profiles of membrane fluidity has been demonstrated. Dimyristoyl-phosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol have been studied, and the results have been compared with similar studies at X-band (9.4 GHz) (L. Mainali, J.B. Feix, J.S. Hyde, W.K. Subczynski J. Magn. Reson. 212:418-425 [2011]). Profiles of the spin-lattice relaxation rate (T1−1) obtained from SR EPR measurements for n-PCs and T-PC were used as a convenient quantitative measure of membrane fluidity. Additionally, spectral analysis using Freed’s MOMD (microscopic-order macroscopic-disorder) model (E. Meirovitch, J.H. Freed J. Phys. Chem. 88:4995-5004 [1984]) provided rotational diffusion coefficients (R⊥ and R∥) and order parameters (S0). Spectral analysis at X-band provided one rotational diffusion coefficient, R. T1−1, R⊥, and R∥ profiles reflect local membrane dynamics of the lipid alkyl chain, while the order parameter shows only the amplitude of the wobbling motion of the lipid alkyl chain. Using these dynamic parameters, namely T1−1, R⊥, and R∥, one can discriminate the different effects of cholesterol at different depths, showing that cholesterol has a rigidifying effect on alkyl chains to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. The nondynamic parameter, S0, shows that cholesterol has an ordering effect on alkyl chains at all depths. Conventional and SR EPR measurements with T-PC indicate that cholesterol has a fluidizing effect on phospholipids headgroups. EPR at W-band provides more detailed information about the depth-dependent dynamic organization of the membrane compared with information obtained at X-band. EPR at W-band has the potential to be a powerful tool for studying membrane fluidity in samples of small volume