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EPR Spectra (epr + spectrum)

Distribution by Scientific Domains

Chemistry	52%
Physics and Astronomy	26%
Medical Sciences	9%
Polymers and Materials Science	7%
2 Other Domains	6%

Selected Abstracts

Binuclear Mixed Valence Oxovanadium(IV/V) Complexes Containing a [OVIV(,-Ooxo)(,-Ophen)VVO]2+ Core: Synthesis, EPR Spectra, Molecular and Electronic Structure

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2006
Amrita Mondal
Abstract Binuclear mixed valence oxovanadium(IV/v) complexes of general formula [V2O3L] containing a [OVIV(,-Ooxo)(,-Ophen)VVO]2+ core have been synthesised using conformationally labile N4O3 -coordinating heptadentate ligands (H3L). The X-ray structure of one complex has been examined. Solution EPR spectra revealed that the unpaired electron of the complexes is delocalised between the two vanadium centres. The simulated EPR spectrum of one complex confirms this experimental observation. DFT studies have been performed using crystallographic coordinates in order to obtain further insight into the electronic structure of this type of molecule. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Exchange Interactions at the Supramolecular Level , Synthesis, Crystal Structure, Magnetic Properties, and EPR Spectra of [Mn(MAC)(TCNQ)2] (MAC = Pentaaza Macrocyclic Ligand; TCNQ·, = Radical Anion of 7,7,8,8-Tetracyano- p -quinodimethane)

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003
Augustin M. Madalan
Abstract The reaction between [Mn(MAC)(H2O)2]Cl2·4H2O and LiTCNQ (MAC = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene) affords a complex with the formula [Mn(MAC)(TCNQ)2] (1), whose crystal structure has been determined. Its structure consists of neutral mononuclear entities. The manganese(II) ion is heptacoordinated, with a pentagonal bipyramidal geometry. The apical positions are occupied by the TCNQ·, radicals, while the macrocyclic ligand is coordinated at the equatorial positions. The seven Mn,N distances range from 2.273(3) to 2.301(6) Å. The strong intermolecular ,,, stacking interactions between the TCNQ radicals (3.2 Å) leads to weave-like infinite chains, which propagate along the crystallographic c axis. The cryomagnetic investigation of 1 revealed a weak intermolecular antiferromagnetic coupling of the Mn2+ ions (J = ,0.18 cm,1), which is mediated by the diamagnetic (TCNQ)22, pairs resulting from the stacking interactions in the crystal. The intermolecular exchange interaction between the Mn2+ ions was further confirmed by variable temperature EPR spectroscopic measurements [|J| = 0.15(5) cm,1], which have been carried out in both the X and Q bands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Single-Line EPR Spectra from Radicals Encapsulated in Aggregates of Amphiphilic Block Copolymers with Hydrophobic Dendritic Pendants in Water

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2006
Kana Tamano
Abstract Summary: A water-insoluble organic 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical is solubilized in aqueous solutions of aggregates of amphiphilic block copolymers with hydrophobic dendritic pendants. The number (100,200) of DPPH molecules solubilized in an aggregate, which is evaluated from UV-visible absorption spectra, is in agreement with that of the DPPH radicals determined from electron paramagnetic resonance (EPR) spectroscopy. The DPPH radicals are stably solubilized without decomposition in the polymer aggregates. The radicals exhibit a single-line EPR absorption, which is narrowed by the interspin interaction, and indicates the assembly formation of DPPH radicals in polymer aggregates. These results suggest the effective utilization of the DPPH radical as a spin-probe indicator in aqueous solutions. When DPPH is solubilized in aqueous solutions of NaAMPS- b -G2(n3), the polymer solutions become purple colored, which is characteristic of the DPPH radical. [source]

Thermal and EPR investigations of thallium gallium disulphide single crystal

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2009
M. Acikgoz
Abstract In this research, the results of the differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) investigations of TlGaS2 single crystal are presented. Specific heat capacity (Cp) anomalies of layered TlGaS2 have been obtained by using a new DSC technique for such crystals. Remarkable heat capacity anomalies have been revealed at the temperatures of 137.7 K, 174.5 K and 238.5 K. It is found that the anomalies appear at maximum with a small deviation (by 3-4%) from the regular values, and Cp discontinuity amounted to approximately 5%. Additionally, EPR spectra of Fe doped TlGaS2 single crystals have been recorded at various temperatures down to 6 K for different orientations of the applied magnetic field. Transformations of present EPR spectra are not sufficient for the confirmation of structural phase transitions, in contrast to the cases in iso structural TlInS2 and TlGaSe2 compounds. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis and Characterization of CuII Complexes with Amino Acid Substituted Di(2-pyridyl)amine Ligands

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2007
ko I. Kirin
Abstract The two-step syntheses of the substituted di(2-pyridyl)amine ligands (dpa), dpa-CH2CO2H (1) and dpa-PhCO2H (2), are described. Ligands 1 and 2 are successfully coupled to the amino acid phenylalanine, yielding the derivatives 4 and 6, respectively. Four CuII(dpa)2 complexes, [Cu(dpa-CH2CO2tBu)2(NO3)2] (3Cu), [Cu(dpa-CH2CO-PheOMe)2(H2O)2](NO3)2·2MeOH (4Cu), [Cu(dpa-PhCO2Me)2 (MeOH)2](ClO4)2 (5Cu) and [Cu(dpa-PhCO-PheOMe)2(ClO4)2] (6Cu) have been prepared and characterized, including their single crystal X-ray structures. Fluorescence emission at UV (for 3 and 4) or blue (for 5 and 6) wavelengths of the free ligands is preserved in the corresponding Cu complexes, although with lower intensity. X-band EPR spectra of 4Cu and 6Cu both revealed one axial CuII signal with hyperfine and superhyperfine splittings. Complexes 4Cu and 6Cu are chiral inorganic complexes with amino acid bioconjugates that may serve as nucleoside analogs in modified peptide nucleic acids (PNA). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Chemical and Electrochemical Behaviours of a New Phenolato-Bridged Complex [(L)MnIIMnII(L)]2+.

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006
Dinuclear Mono-µ-Oxido [(L)MnIII(µ-O)MnIII/IV(L)]2+/3+ Species, Pathways to Mononuclear Chlorido [(L)MnII/III/IVCl]0/1/2+
Abstract The X-ray structure of a new dinuclear phenolato-bridged Mn2II complex abbreviated as [(L)MnMn(L)]2+ (1), where LH is the [N4O] phenol containing ligand N,N -bis(2-pyridylmethyl)- N, -salicylidene-ethane-1,2-diamine ligand, is reported. A J value of ,3.3 cm,1 (H = ,J,1·,2) was determined from the magnetic measurements and the 9.4 GHz EPR spectra of both powder and frozen acetonitrile solution samples were analyzed with temperature. The cyclic voltammetry of 1 displays a reversible anodic wave at E1/2 = 0.46 V vs. SCE associated with the two-electron oxidation of 1 yielding the dinuclear Mn2III complex [(L)MnMn(L)]4+ (2). The easy air oxidation of 1 gives the mono-,-oxido Mn2III complex [(L)Mn(, - O)Mn(L)]2+ (3). A rational route to the formation of the mixed-valence Mn2III,IV complex [(L)Mn(, - O)Mn(L)]3+ (4) starting from 1 by bulk electrolysis at EP = 0.75 V vs. SCE in the presence of one equiv. of base per manganese ion is also briefly reported. Addition of chloride ions to 1 led to the cleavage of the phenolato bridges to give the mononuclear MnII complex [(L)MnCl] (5). Cyclic voltammetry of 5 displays two reversible anodic waves at E1/2 = 0.21 and E1/2 = 1.15 V vs. SCE, assigned to the two successive one-electron abstractions giving the MnIII and MnIV species [(L)MnCl]+ (6) and [(L)MnCl]2+ (7), respectively. The electronic signatures from UV/Visible and EPR spectroscopy of the electrochemically prepared samples of 6 and 7 confirmed the respective oxidation states. For instance, 7 displays a broad and intense absorption band characteristic of a phenolato to MnIV charge-transfer transition at 690 nm (2000 M,1,cm,1) and its 9.4 GHz EPR spectrum shows a strong transition at g = 5.2 consistent with a rhombically distorted S = 3/2 system with a zero-field splitting dominating the Zeeman effect. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Binuclear Mixed Valence Oxovanadium(IV/V) Complexes Containing a [OVIV(,-Ooxo)(,-Ophen)VVO]2+ Core: Synthesis, EPR Spectra, Molecular and Electronic Structure

Cobalt(II) Complexes with Substituted Salen-Type Ligands and Their Dioxygen Affinity in N,N -Dimethylformamide at Various Temperatures

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005
Andreas Huber
Abstract Several unsymmetrically substituted salen-type cobalt(II) Schiff-base complexes CoL [H2L = 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-hexadiene (1); 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (2); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-(2-hydroxyphen-yl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (3); 1-(2-hydroxyphenyl)-6-methyl-2,5-diaza-1,5-nonadien-8-one (4); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-methyl-2,5-di-aza-1,5-nonadien-8-one (5); 1-(2-hydroxyphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (6); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (7)] were prepared and characterized by their UV/Vis absorption spectra, magnetic moments, and oxidation potentials. Except for complex 4 (irreversible oxidation with t½ , 3 h), complexes 1,3 and 5,7 are remarkably resistant against irreversible auto-oxidation in air-saturated N,N -dimethylformamide (DMF) at ambient temperature. To characterize the Lewis acidity of the cobalt center in 1,7, the equilibrium constant Kpy was determined for monoadduct formation with pyridine (CoL + pyCoL·py). An O2 -sensitive optode was used to determine the Henry constant, KH, for the system O2/DMF in the temperature range 298,228 K. The formation of 1:1 adducts of complexes 1,7 with O2 in DMF, as characterized by the equilibrium constant K, was followed spectrophotometrically in the temperature range 298,228 K. The parameters ,Ho, ,So, and K are reported. At 298 K, K ranges from 21.9 M,1 (5) to 155 M,1 (7). The overall spectroscopic information, including EPR spectra obtained with frozen solutions of 3 and 7 in O2 -saturated DMF, confirm that the 1:1 adducts CoL·O2 are cobalt(III) superoxo compounds. The symmetrically substituted salen complex8 [H2L = 1,6-bis(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,4,4-tetramethyl-2,5-diaza-1,5-hexadiene in 8] is shown to catalyze the oxidation of triphenylphosphane and 2,6-di- tert -butylphenol by O2 in DMF at ambient temperature. The correlation of the data obtained for K, Kpy, and the oxidation potential E½ is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Studies of Pyridinyl-Containing 14-Membered Macrocyclic Copper(II) Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2003
Sabrina Autzen
Abstract Six copper(II) complexes of tetracoordinating, pyridinyl-containing 14-membered macrocycles with varying ratios of nitrogen and oxygen donor atoms were prepared and characterized by IR, UV/Vis, and EPR spectroscopy and cyclic voltammetry. A distorted tetragonal coordination of the copper center in the solid-state was established by X-ray crystallography for the tetraazamacrocyclic complex Cu-3 carrying a methoxybenzyl pendent arm and the trioxaaza complex Cu-6. The superoxide dismutase-like activity of the CuII complexes was investigated by inhibition of NADH oxidation. Although the UV/Vis and EPR spectra of the complexes were strongly affected when the coordinating nitrogen atoms were successively replaced by oxygen atoms, no significant change in their reactivity towards superoxide was observed. In all cases a 1:1 or 1:2 stoichiometry for the reaction with superoxide was found, with the exception of the methoxybenzyl-substituted tetraaza complex, which showed a low catalytic activity with a turnover number of about 10. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Oxidation of oleuropein studied by EPR and spectrophotometry

EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 2 2008
Evaggelia D. Tzika
Abstract The autoxidation at alkaline pH and enzymatic oxidation by mushroom tyrosinase of oleuropein, the dominant biophenol present in the fruits and leaves of Olea europea, was followed by both electron paramagnetic resonance (EPR) and absorption spectroscopy. For comparison, the same oxidation processes were applied to 4-methylcatechol, a simple polyphenol present in olive mill wastewaters. EPR spectra of stable o -semiquinone radicals produced during autoxidation at pH,12 and short-lived o -semiquinone free radicals produced during autoxidation at pH,9.0 or tyrosinase action and stabilized by chelation with a diamagnetic metal ion (Mg2+) were recorded for both polyphenols, and the corresponding hyperfine splitting constants were determined. The UV-Vis spectral characteristics of the oxidation of polyphenols were highly dependent on the type of polyphenol, oxidant type and the pH of the reaction. The kinetic behavior of tyrosinase in the presence of oleuropein and 4-methylcatechol was followed by recording spectral changes at 400,nm (absorption maximum) over time. The tysosinase activity with oleuropein showed a pronounced pH optimum at pH,6.5 and a minor one around pH,8. From the data analysis of the initial rate at pH,6.5, the kinetic parameters Km = 0.34,±,0.03,mM and Vmax = 0.029,±,0.002 ,A400,min,1 were determined for oleuropein. [source]

Assignment of the [4Fe-4S] clusters of Ech hydrogenase from Methanosarcina barkeri to individual subunits via the characterization of site-directed mutants

FEBS JOURNAL, Issue 18 2005
Lucia Forzi
Ech hydrogenase from Methanosarcina barkeri is a member of a distinct group of membrane-bound [NiFe] hydrogenases with sequence similarity to energy-conserving NADH:quinone oxidoreductase (complex I). The sequence of the enzyme predicts the binding of three [4Fe-4S] clusters, one by subunit EchC and two by subunit EchF. Previous studies had shown that two of these clusters could be fully reduced under 105 Pa of H2 at pH 7 giving rise to two distinct S½ electron paramagnetic resonance (EPR) signals, designated as the g = 1.89 and the g = 1.92 signal. Redox titrations at different pH values demonstrated that these two clusters had a pH-dependent midpoint potential indicating a function in ion pumping. To assign these signals to the subunits of the enzyme a set of M. barkeri mutants was generated in which seven of eight conserved cysteine residues in EchF were individually replaced by serine. EPR spectra recorded from the isolated mutant enzymes revealed a strong reduction or complete loss of the g = 1.92 signal whereas the g = 1.89 signal was still detectable as the major EPR signal in five mutant enzymes. It is concluded that the cluster giving rise to the g = 1.89 signal is the proximal cluster located in EchC and that the g = 1.92 signal results from one of the clusters of subunit EchF. The pH-dependence of these two [4Fe-4S] clusters suggests that they simultaneously mediate electron and proton transfer and thus could be an essential part of the proton-translocating machinery. [source]

Blue Luminescence of ZnO Nanoparticles Based on Non-Equilibrium Processes: Defect Origins and Emission Controls

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010
Haibo Zeng
Abstract High concentrations of defects are introduced into nanoscale ZnO through non-equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420,nm (2.95,eV,<,Eg,=,3.26,eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488,nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial-zinc-related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in as-prepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co-emission of blue and green emissions and peak adjustment from blue to yellow. [source]

Proton-Coupled Electron Transfer of Unsaturated Fatty Acids and Mechanistic Insight into Lipoxygenase

HELVETICA CHIMICA ACTA, Issue 10 2006
Shunichi Fukuzumi
Abstract A proton-coupled electron transfer (PCET) process plays an important role in the initial step of lipoxygenases to produce lipid radicals which can be oxygenated by reaction with O2 to yield the hydroperoxides stereoselectively. The EPR spectroscopic detection of free lipid radicals and the oxygenated radicals (peroxyl radicals) together with the analysis of the EPR spectra has revealed the origin of the stereo- and regiochemistry of the reaction between O2 and linoleyl (=,(2Z)-10-carboxy-1-[(1Z)-hept-1-enyl]dec-2-enyl) radical in lipoxygenases. The direct determination of the absolute rates of H-atom-transfer reactions from a series of unsaturated fatty acids to the cumylperoxyl (=,(1-methyl-1-phenylethyl)dioxy) radical by use of time-resolved EPR at low temperatures together with detailed kinetic investigations on both photoinduced and thermal electron-transfer oxidation of unsaturated fatty acids provides the solid energetic basis for the postulated PCET process in lipoxygenases. A strong interaction between linoleic acid (=,(9Z,12Z)-octadeca-9,12-dienoic acid) and the reactive center of the lipoxygenases (FeIIIOH) is suggested to be involved to make a PCET process to occur efficiently, when an inner-sphere electron transfer from linoleic acid to the FeIII state is strongly coupled with the proton transfer to the OH group. [source]

Structure, Characterization, and Metal-Complexation Properties of a New Tetraazamacrocycle Containing Two Phenolic Pendant Arms

HELVETICA CHIMICA ACTA, Issue 10 2004
Xiuling Cui
The new tetraazamacrocycle 2 (=2,2,-[[7-Methyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene-3,11-diyl]bis(methylene)]bis(4-bromophenol)) was synthesized and used as a ligand for different metal-ion complexes. The X-ray crystal structures of the complexes of the general formula [M(H- 2)]+NO,MeOH (M=Ni2+, Zn2+), in which only one of the two pendant phenolic OH groups of 2 is deprotonated, were determined. In both complexes, the coordination environment is of the [5+1] type, the four N-atoms of the macrocyclic framework defining a square-planar arrangement around the metal center, with similar NiN and ZnN distances of 1.961(9) to 2.157(9),Å and 2.021(9) to 2.284(8),Å, respectively. In contrast, the MO distances are markedly different, 2.060(6) and 2.449(8),Å in the NiII complex, and 2.027(7) and 2.941(9),Å in the ZnII complex. The UV/VIS spectra of the NiII and CuII complexes with ligand 2, and the EPR spectra of the CuII system, suggest the same type of structure for the complexes in solution as in the solid state. Theoretical studies by means of density functional theory (DFT) confirmed the experimental structures of the NiII and ZnII complexes, and led to a proposal of a similar structure for the corresponding CuII complex. The calculated EPR parameters for the latter and comparison with related data support this interpretation. The singly occupied molecular orbital (SOMO) in these systems is mainly made of a d orbital of Cu, with a strong antibonding (,*) contribution of the axially bound phenolate residue. [source]

Radical annihilation of ,-ray-irradiated contact lens blanks made of a 2-hydroxyethyl methacrylate copolymer at elevated temperatures

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010
Young-Shang Lin
Abstract The annihilation of the radicals in irradiated 2-hydroxyethyl methacrylate copolymer was analyzed by the use of electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra were deconvoluted into three radicals: a quartet (Ra), a triplet (Rb), and a broad singlet (Rc). Radical Ra was attributed to coupling with a methyl radical and/or a doublet or triplet with about the same hyperfine coupling due to a methylene radical. Radical Rb was due to a methylene radical produced by main-chain scission. Radical Rc was attributed to various free radicals without coupling to protons. By comparing the EPR spectra of radicals Ra, Rb, and Rc with the spectrum of a 2,2-diphenyl-1-picrylhydrazyl (DPPH) standard with a known spin number, we calculated the spin numbers of the radicals, which decreased with time in the temperature range 25,45°C, regardless of the irradiation dose. The annealing of Ra and Rb and the annealing of Rc at longer times followed second-order kinetics; these were different from the kinetics for the color formation and defect-controlled hardening of polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Matrix isolation and magnetic parameters of septet 3,5-dicyanopyridyl-2,4,6-trinitrene

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2010
Sergei V. Chapyshev
Abstract Septet 3,5-dicyanopyridyl-2,4,6-trinitrene was synthesized together with quintet 2-azido-3,5-dicyanopyridyl-4,6-dinitrene, quintet 4-azido-3,5-dicyanopyridyl-2,6-dinitrene, triplet 2,6-diazido-3,5-dicyanopyridyl-4-nitrene, and triplet 2,4-diazido-3,5-dicyanopyridyl-6-nitrene by photolysis of 2,4,6-triazido-3,5-dicyanopyridine in solid argon at 4,K. The electronic and magnetic properties of the matrix-isolated nitrenes were studied using electron paramagnetic resonance (EPR) spectroscopy in combination with density functional theory (DFT) calculations. The fine-structure parameters of the nitrenes were determined with high accuracy from spectral simulations. All signals in the EPR spectra of the nitrenes, randomly oriented in the solid phase, were unambiguously assigned based on eigenfield calculations of the Zeeman energy levels and angular dependences of resonance fields. Copyright © 2009 John Wiley & Sons, Ltd. [source]

EPR studies of the dynamics and phase behaviour of dithiadiazolyl radicals derived from mesogenic precursors

MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2009
Jeremy M. Rawson
Abstract A series of liquid-crystalline materials based on 4-substituted cyanobiphenyls, RC6H4C6H4CN (R = C5H11, C6H13, C7H15, C8H17 and C12H25, commonly referred to as 5CB, 6CB, 7CB, 8CB and 12CB, respectively) were functionalised to give the corresponding dithiadiazolyl organic radicals RC6H4C6H4CNSSN, (compounds 1,, 2,, 3,, 4, and 5,, respectively). EPR spectra of n -C12H25C6H4C6H4CNSSN, (5,) reveal that it adopts a dimeric diamagnetic structure in the solid state with a small number of paramagnetic defect sites. Variable temperature electron paramagnetic resonance (EPR) studies reveal a thermally activated rotation about the molecular long axis at temperatures above 314 K. The energy barrier to rotation about the phenylene,dithiadiazolyl bond was estimated as 25 kJ mol,1 using density functional theory (DFT). At elevated temperatures thermal annealing was also observed, quenching the sample's paramagnetism. Copyright © 2008 John Wiley & Sons, Ltd. [source]

EPR study of nitroxides formed from the reaction of nitric oxide with photolyzed amides

MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2003
Fan Wang
Abstract Free radicals generated from UV irradiation of simple aliphatic amides in anaerobic and nitric oxide (NO)-saturated liquid mixtures or solutions gave EPR spectra of nitroxides. The application of isotopic effects to EPR spectra and the generation of radicals by transient radical attack on substrate molecules or by photolysing amine or acetoin were used to help identify photochemically produced radicals from the amides. The aliphatic amides used were formamide, acetamide and their N -methyl- or deuterium-substituted derivatives. Transient radicals used to attack the amides via hydrogen-atom abstraction were generated from the initiator AIBN or AAPH. The observation of various nitroxides indicates the reactivity of NO for trapping acyl, carbamoyl and other carbon-centered radicals. Possibly mechanistic pathways diagnosed with this trap are proposed. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Spectral fitting: The extraction of crucial information from a spectrum and a spectral image

MAGNETIC RESONANCE IN MEDICINE, Issue 6 2003
Colin Mailer
Abstract A highly accurate line-width simulation computer program is used that can account for both high amplitude and frequency of the Zeeman modulation in an electron paramagnetic resonance (EPR) experiment. This allows for the overmodulation of EPR lines to increase signal-to-noise ratio (SNR) in EPR spectra and spectroscopic images, without any sacrifice in the determination of the intrinsic line width (1/, · T2e). The technique was applied to continuous-wave EPR spectroscopic images of a narrow, single-line trityl spin probe wherein a full EPR spectrum was extracted from each 3D spatial voxel. Typical improvements are a three- to fivefold increase in SNR in the high-gradient projections in the image and a reduction in the standard deviation (SD), by a factor of 3, of the line widths in the low-gradient domain. This method is a general one that is also applicable to the analysis of conventional 14N or 15N nitroxide spin probes. Magn Reson Med 49:1175,1180, 2003. © 2003 Wiley-Liss, Inc. [source]

EPR study of Ni distribution in LaNiy Co1,yO3 solid solutions (0 , y , 0.25)

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2008
S. Ivanova
Abstract The distribution of Ni in LaNiy Co1,yO3 solid solutions was examined by means of EPR spectroscopy. For the assignment of the EPR signals, La1,xSrx CoO3 oxides were used as reference for Co3+,Co4+ magnetic clusters. For the oxides heated at 600 °C, the EPR spectra of LaNiy Co1,yO3 consist of a signal due to magnetic Ni clusters, while the oxides prepared at 700 °C display an EPR signal due to ferromagnetic coupled Co3+ and Co4+ impurity ions that do not form magnetic clusters. LaNiy Co1,yO3 samples prepared at T > 700 °C are EPR "silent". The effect of the preparation method and the preparation temperature on the formation of Ni clusters is discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Theoretical investigation of the optical and EPR spectra for ytterbium(III) in strontium tungstate crystal

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010
Y. C. Zhong
Abstract A theoretical method for studying the optical spectra and electron paramagnetic resonance (EPR) parameters of Yb3+ ions in SrWO4 crystal is presented. Using the crystal-field theory, the formulas relating the optical spectra and EPR parameters are derived. Based on the theoretical formulas, the 14×14 full energy matrices for 4f13 configuration ions in a D2d point symmetry are constructed. By diagonalizing the full energy matrices, the optical spectra and EPR data of Yb3+ in SrWO4 crystal have been investigated. The theoretical results are in good agreement with the experimental values. Furthermore, the crystal-field parameters for SrWO4 have been determined in this work. [source]

SWNT probed by multi-frequency EPR and nonresonant microwave absorption

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008
B. Corzilius
Abstract In addition to g = 2.00 signals seen frequently in EPR spectra of SWNT, signals at g = 2.07 of SWNT prepared by CVD were detected, exhibiting a Pauli susceptibility temperature dependence. This Pauli magnetism in combination with the large g shift is taken as evidence that these signals originate from itinerant electrons of metallic nanotubes. At temperatures below 150 K, a dominant narrow signal develops at g = 2.00. By applying multifrequency EPR up to 319 GHz, its inhomogeneous nature was confirmed. This signal is assigned to defects of the carbon network of the tubes. Comparing room temperature EPR spectra of CVD and arc-grown SWNT, we found a much lower concentration of metallic tubes in arc material. No g = 2.07 signals of itinerant spins could be observed, which might be also caused by the high amount of residing catalyst. A drastic increase in nonresonant microwave absorption is observed below 10 K for both types of samples, if a threshold microwave power level is passed. In the same temperature range a drop in EPR intensity is also detected. These observations are taken as evidence for a transition into a superconducting phase of part of the sample. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Investigations of the optical and EPR spectra of V3+ ions in C(NH2)3Al(SO4)2 · 6H2O crystal

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006
Wen-Lin Feng
Abstract By means of the diagonalization of the complete energy matrix of 3d2/d8 ions in trigonal symmetry and in consideration of the covalency reduction effect, the optical and EPR spectra of V3+ ions in C(NH2)3Al(SO4)2 · 6H2O crystal are calculated. The results are in agreement with the observed values. The difficulty about the too-large spin,orbit coupling parameter in the explanation of EPR parameters from the Abragam and Pryce model is removed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spectroscopic studies of 2H-PbI2(Mn) layered crystals

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2005
F. V. Motsnyi
Abstract For the first time we studied Raman, exciton and EPR spectra of PbI2 layered crystals of 2H polytype doped with high concentration of Mn impurity. A novel type of Fermi resonance was found. The anomalous temperature shift of the exciton band n = 1 was registered. It was shown that this shift can be explained by means of anharmonic vibrations of layered lattice at T < 40 K and low-frequency optical phonons at T > 40 K. The manifestation of single and exchange-bound Mn2+ ions in EPR spectra was observed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

EPR of anatase titanium dioxide under uv light irradiation

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006
T. Sekiya
Abstract EPR spectra on a colorless single crystal of anatase titanium dioxide have sextuplet signals under irradiation of ultra violet (uv) light at temperatures of 100-40 K. The sextuplet is assigned to a paramagnetic species of S = 1/2 interacting with I = 5/2. The angular dependence of the sextuplet signals reveals anisotropic g -values of gxx = 2.026, gyy = 2.002 and gzz = 2.015. The intensities of the sextuplets reduce gradually with decrease in temperature. Only one signal can be observed at temperatures lower than 30K. This signal will originate from Ti3+ in bulk. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

EPR study of Fe3+ centers in ternary layered TlInS2 single crystal

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004
F.A. Mikailov
Abstract An iron doped TlInS2 single crystal has been studied at room temperature by Electron Paramagnetic Resonance (EPR) technique. The fine structure of EPR spectra of the paramagnetic Fe3+ ions was observed. The spectra were interpreted to correspond to the transitions among the spin multiplets (S=5/2, L=0) of the Fe3+ ion, which is split in the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe3+ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe3+ site and the CF parameters were determined. It was established that the symmetry axis of the axial component in the CF is making an angle of about 48 degree with the (ab) plane of TlInS2 crystal. Experimental results indicate that Fe ions substitute for In ions at the center of the InS4 tetrahedrons, and the rhombic distortion of the CF is caused by Tl ions located in the trigonal cavities between the tetrahedral complexes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis, Crystal Structures, and Properties of Oxovanadium(IV),Lanthanide(III) Heteronuclear Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2005
Wei Shi
Abstract A new series of oxovanadium(IV),lanthanide(III) heteronuclear complexes [Yb(H2O)8]2[(VO)2(TTHA)]3,21,H2O (1), {[Ho(H2O)7(VO)2(TTHA)][(VO)2(TTHA)]0.5}, 8.5,H2O (2), {[Gd(H2O)7(VO)2(TTHA)][(VO)2(TTHA)]0.5},8.5,H2O (3), {[Eu(H2O)7][(VO)2(TTHA)]1.5}, 10.5,H2O (4), and [Pr2(H2O)6(SO4)2][(VO)2(TTHA)] (5) (H6TTHA=triethylenetetraaminehexaacetic acid) were prepared by using the bulky flexible organic acid H6TTHA as structure-directing agent. X-ray crystallographic studies reveal that they contain the same [(VO)2(TTHA)]2, unit as building block, but the Ln3+ ion lies in different coordination environments. Although the lanthanide ions always exhibit similar chemical behavior, the structures of the complexes are not homologous. Compound 1 is composed of a [Yb(H2O)8]3+ ion and a [(VO)2(TTHA)]2, ion. Compounds 2 and 3 are isomorphous; both contain a trinuclear [Ln(H2O)7(VO)2(TTHA)]+ (Ln=Ho for 2 and Gd for 3) ion and a [(VO)2(TTHA)]2, ion. Compound 4 is an extended one-dimensional chain, in which each Eu3+ ion links two [(VO)2(TTHA)]2, ions. For 5, the structure is further assembled into a three-dimensional network with an interesting framework topology comprising V2Pr2 and V4Pr2 heterometallic lattices. Moreover, 4 and 5 are the first oxovanadium(IV),lanthanide(III) coordination polymers and thus enlarge the realm of 3d,4f complexes. The IR, UV/Vis, and EPR spectra and the magnetic properties of the heterometallic complexes were studied. Notably, 2 shows unusual ferromagnetic interactions between the VO2+ and Ho3+ ions. [source]

Synthesis, Crystal Structure of Cis -dioxo-catecholatotungsten(VI) Complex and Its NMR Studies on the Interaction with ATP

CHINESE JOURNAL OF CHEMISTRY, Issue 6 2003
Lu Xiao-Ming
Abstract Cis -dioxo-catecholatotungsten(VI) complex anion [W(VI)O2 -(OC6H2O)]2- was obtained with discrete protonated ethylene-diamine (NH2CH2CH2NH3)+ cations by the reaction of tetra-butyl ammonium decatungstate with catechol in the mixed solvent of CH3OH, CH3CN and ethylenediamine, and compared with its molybdenum analogue [Mo(v)O2(OC6H4O)2]3- by crystal structure, UV, EPR. The results of the UV and EPR spectra show that tungsten is less redox active than molybdenum since the molybdenum is reduced from Mo(VI) to Mo(V) but tungsten stays in the original highest oxidized state Mo (VI) when they are crystallized from the solution above. It is worthy to note that [W(VI)O2(OC6H4O2)]2- shows the same coordination structure as its molybdenum analogue in which the metal center exhibits distorted octahedral coordination geometry with two cis -dioxocatecholate ligands and might have the related coordination structure feature with the cofactor of flavoenzyme because [Mo(v)O2(OC6H4O)2]3- presented essentially the same EPR spectra as flavoenzyme. The NMR studies on the interaction of the title complex with ATP reveal that the reduction of W(VI) to W(V) occurs when the title complex is dissolved in D2O and the W (V) is oxidized again when ATP solution is mixed with original solution and the hydrolysis of the catechola-to ligand take places at mean time being monitored by 1H NMR and 13C NMR spectra. [source]

Effects of mild aerobic physical exercise on membrane fluidity of erythrocytes in essential hypertension

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 5-6 2003
Kazushi Tsuda
Summary 1.,The present study was undertaken to investigate the effects of aerobic physical exercise on membrane function in mild essential hypertension. 2.,Hypertensive patients were divided into an exercise group (n = 8) and a non-exercise (control) group (n = 8). Physical exercise within the intensity of the anaerobic threshold level was performed twice a week for 6 months. Membrane fluidity of erythrocytes was examined by means of electron paramagnetic resonance (EPR) and spin-labelling methods before and after the trial period in both groups. 3.,After physical exercise, blood pressure decreased significantly. 4.,Compared with the non-exercise group, in the exercise group both the order parameter (S) and the peak height ratio (ho/h -1) in the EPR spectra of erythrocytes were significantly reduced (S, 0.717 ± 0.004 vs 0.691 ± 0.008, respectively (n = 8), P < 0.05; ho/h -1, 5.38 ± 0.06 vs 4.89 ± 0.06, respectively (n = 8), P < 0.05). These findings indicated that exercise increased membrane fluidity and improved the membrane microviscosity of erythrocytes. 5.,There was no direct correlation between blood pressure reduction and the exercise-induced increase in membrane fluidity of erythrocytes. 6.,In the non-exercise (control) group, blood pressure and membrane fluidity were not changed after a 6 month follow-up period. 7., The results show that aerobic physical exercise increased erythrocyte membrane fluidity and improved the rigidity of cell membranes in hypertensive patients. The improvement of rheological properties of erythrocytes may explain, in part, the cellular mechanisms for the beneficial effects of physical exercise in hypertension. [source]

Bioaccumulation and ROS generation in liver of freshwater fish, goldfish Carassius auratus under HC Orange No. 1 exposure

ENVIRONMENTAL TOXICOLOGY, Issue 3 2007
Yuanyuan Sun
Abstract HC Orange No. 1 (CAS No. 54381-08-7, 2-nitro-4,-hydroxydiphenylamine) is used as a color additive in hair dyes. In this study, laboratory experiment was carried out to determine HC Orange No. 1 bioaccumulation and oxidative stress in the liver of freshwater fish, goldfish Carassius auratus. Fish were exposed to different concentrations (0.05, 0.1, 0.2, 0.5, and 1.0 mg/L) of HC Orange No. 1 for 10 days, with one group assigned as control. The accumulation of HC Orange No. 1 in liver increased with the exposure concentration (R2 = 0.94). A secondary spin trapping technique was used followed by electron paramagnetic resonance (EPR) analysis to study the reactive oxygen species (ROS) production. On the basis of the hyperfine splitting constants and shape of the EPR spectrum, the ROS generated in fish liver after exposure was identified as hydroxyl radical (,OH). There is a good correlation between the exposure concentrations and ,OH generation (R2 = 0.92). The ,OH signal intensity of the EPR spectrum showed a significant increase (P < 0.05) when the HC Orange No. 1 concentration was 1.0 mg/L, compared with that of the control. A good positive relationship (R2 = 0.95) was found between the ,OH formation and accumulation level of HC Orange No. 1 in liver. The changes of the activities of catalase (CAT), superoxide dismutase (SOD), glutathione S -transferase (GST), and contents of reduced glutathione (GSH) were also detected. These observations indicated a possible mechanism of oxidative stress induced by HC Orange No. 1 on fish. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 256,263, 2007. [source]