EPR Study of Iron Ion Complexes in Human Blood

Electronic states of iron ion complexes in human blood from patients with melanoma have been investigated by electron paramagnetic resonance (EPR). The measurements were performed at liquid nitrogen temperature (77 K) on an X-band EPR spectrometer. Numerous types of iron paramagnetic centers have been identified. In several kinds of protein complexes exemplified by methemoglobin, transferrin or ferritin, various forms of trivalent iron have been found. Three groups of patients with typical EPR spectra have been individualized. These groups differed in types and concentration of paramagnetic centers in peripheral blood. A good correlation has been found between the EPR results, the total iron ion complexes concentration and transferrin saturation.     

Intramolecular Dynamics of the 1,2,4-Trifluorobenzene Radical Anion: An Optically Detected EPR and Quantum Chemistry Study

A previously unknown electron paramagnetic resonance (EPR) spectrum of the 1,2,4-trifluorobenzene radical anion in liquid solution in nonpolar solvent has been obtained by means of the optically detected EPR technique. On the basis of quantum chemical calculations, the observed fluorine hyperfine coupling values and their temperature dependence have been interpreted as a consequence of fast conformational exchange among different nonplanar structures.     

<Superscript>29</Superscript>Si nuclear spin relaxation in microcrystals of plastically deformed Si: B samples

Single crystals and microcrystals Si: B enriched with ²⁹Si isotopes have been studied using nuclear magnetic resonance and electron paramagnetic resonance (EPR) in the temperature range from 300 to 800 K. It has been found that an increase in the temperature from 300 to 500 K leads to a change in the kinetics of the relaxation of the saturated nuclear spin system. At 300 K, the relaxation kinetics corresponds to direct electron–nuclear interaction with inhomogeneously distributed paramagnetic centers introduced by the plastic deformation of the crystals. At 500 K, the spin relaxation occurs through the nuclear spin diffusion and electron–nuclear interaction with an acceptor impurity. It has been revealed that the plastic deformation affects the EPR spectra at 9 K.     

Influence of carbonic nanostructure formation on EPR line parameters during carbonization of wheat bran

Carbonized wheat bran samples were studied by electron paramagnetic resonance (EPR) spectroscopy, elemental analysis and electron microscopy. The carbonization was performed in the temperature range from 250 to 800 °C in argon medium. The carbon content increased with temperature. At high temperatures a sharp decrease in the concentration of free radicals takes place. It is shown that at high temperatures the EPR line width reduces from 0.87 (initial) to 0.11 mT. This phenomenon is explained by the fact that at high temperatures there occurs the formation not only of graphitelike structures (classical interpretation) but also of different nanosize structures. The electron microscopy data verify the formation of different forms of nanostructures in the carbonized wheat bran samples. Presented at the 5th Asia-Pacific EPR/ESR Symposium, August 24–27, 2006, Novosibirsk, Russian Federation.     

YAG晶体色心的EPR谱

本文描述了8种YAG样品的室温和77K的EPR谱.从这些谱的参数与光谱的实验数据对照,认为晶体中有三种顺磁性的色心,其中g～2.00和g～1.98两条顺磁谱相应于光谱2×10~4cm~(-1)～3.4×10~4cm~(-1)的吸收带,为YAG基质晶体中的缺陷俘获一个电子构成的电子型缺陷中心;而 g～30.60的顺磁谱线与氧空位和掺杂的金属离子Mg~(2+) 、Cr~(3+)有关,推测为氧空位团或氧空位与金属离子构成的S>1/2的复合顺磁中心缺陷.YAG晶体随着在大气氛中高温退火,氧的进入和金属离子的掺入,造成电子和空间体积的不平衡,从而使晶体色心浓度加大.     

Conformational dynamics of some short-chain biradicals in solutions

Intramolecular electron spin exchange, as a function of temperature and the solvent nature, has been studied by X-band electron paramagnetic resonance (EPR) spectroscopy in five short-chain flexible nitroxide biradicals. Certain thermodynamic parameters of the conformational rearrangements were calculated from the EPR spectra. The process of spin exchange in short flexible biradicals has some peculiarities in comparison with that in long-chain molecules.     

Gamma-radiolysis of deaerated cysteine solutions

The electron paramagnetic resonance (EPR) spectra of gamma-irradiated single crystals of phenidone (fenidon C₉H₁₀N₂O) have been studied for different orientations of crystals in a magnetic field. Phenidone single crystals have been irradiated with ⁶⁰Co-γ rays at room temperature. The EPR spectra have been investigated at temperatures between 125 and 450 K. The spectra have been found to be temperature independent. The spin-Hamiltonian parameters have been obtained from the single-crystal EPR analysis. The principal values of the hyperfine coupling tensor of the unpaired electron and the principal values of the g-tensor have been determined.     

Magnetic properties of crystals of the molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl)

The EPR and static magnetic susceptibility of the crystalline molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl) (BTX) have been measured as functions of temperature. At temperatures T above 130 K, the samples exhibit anomalously high magnetic susceptibility exceeding the values calculated under the assumption that each molecule bears one paramagnetic spin 1/2. A very intense magnetic resonance signal is also observed in the samples in the region of high g factors (g>4.5). This allows the suggestion that the samples under study possess ferromagnetism (or superparamagnetism). The EPR signal and magnetic susceptibility sharply decay almost to zero as the temperature decreases below 100–120 K. It is supposed that electron transfer from donor molecules BTX to C60 molecules takes place at temperatures above 110 K. This electron transfer generates electron spins in the system, whereas the anomalously high magnetism is due to ferromagnetic correlations in the system of these spins.     

Detection of vortex excitations in a Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10</Subscript> crystal at temperatures above the critical temperature by EPR of the surface layer

Vortex excitations have been detected at temperatures both below and above the critical temperature when investigating local magnetic fields on the surface of a Bi₂Sr₂Ca₂Cu₃O₁₀ single crystal by means of an electron paramagnetic resonance (EPR) probe. A thin layer of a diphenyl picrylhydrazyl organic radical deposited on the crystal surface is used as the EPR probe. A narrow EPR signal makes it possible to detect weak distortions of the magnetic field appearing at T ≿ T _c. The analysis of the temperature dependences of the resonance field and the EPR linewidth is thebasis of the assumption of the vortex nature of magnetic excitations in this temperature range.     

Spectroscopic studies on vanadyl ion in rubidium magnesium sulphate hexahydrate

The optical absorption spectrum of VO²⁺ ion in a single crystal of Rb₂Mg(SO₄)₂6H₂O has been investigated both at laboratory and liquid nitrogen temperatures. The electron paramagnetic resonance (EPR) spectrum of the polycrystalline sample has also been investigated at the laboratory temperature. Both optical absorption and EPR spectra are characteristic of the VO²⁺ ion in tetragonal symmetry. Molecular orbital coefficients have been evaluated by correlating the optical absorption and EPR data.     

Cyclic Voltammetry and Electron Paramagnetic Resonance Study of the Electrochemical Reduction of P-Nitrobenzyl Bromide in Aprotic Solvents

EPR has been used to investigate the radicals postulated as intermediates in the intramolecular electron transfer and dehalogenation of p-nitrobenzyl bromide (p-NBBr) in DMSO and DMFA at room temperature. The electrochemical behavior has been studied through the use of cyclic voltammetry. According to the postulated reaction mechanism, the one-electron reduction of p-nitrobenzyl bromide generates an anion radical which undergoes breakage of the C-Br bond followed by intramolecular electron transfer. The free radical obtained is finally transformed into p-nitrotoluene.     

EPR investigation of two types of Syrian's natural zeolites

Two different samples of natural zeolite have been investigated by X-band electron paramagnetic resonance (EPR) spectroscopy. The observed EPR spectra are typical to those observed for Fe³⁺ and Mn²⁺ ions. The lines, related to the iron, are observed, respectively at g≈4.3 and g≈2. The observed six lines, at g≈2, are the hyperfine structure due to the Mn²⁺ ions. The simulation of the experimental EPR spectra suggests that both of the manganese and the iron are present in more one site. The temperature dependence of the EPR spectra has been also investigated. The nature of the different sites involved in the EPR absorption is discussed.     

The dynamical transition in proteins of bacterial photosynthetic reaction centers observed by echo-detected EPR of specific spin labels

An echo-detected electron paramagnetic resonance (ED EPR) approach was used to study molecular dynamics in photosynthetic reaction centers (RCs) fromRhodobacter sphaeroides R26, employing the specific spin label methanethiosulfonate and 3-maliemido proxyl. ED EPR has recently been shown to be sensitive to so-called dynamical transition in disordered media, which is characterized by the transition from a harmonic-like librational motion of a molecule to an anharmonic one or to a stochastic wobbling motion. ED EPR line shapes studied over a wide temperature range reveal a sharp transition occurring above 180 K. The possible relation of the found transition to the temperature dependence of electron transfer reactions in RC is discussed.     

Study of Stable L-Alanine Radicals by W-Band EPR Spectroscopy

Stable L-alanine radicals, SAR1 and SAR2, induced by γ-irradiation of the L-alanine crystal have been investigated by electron paramagnetic resonance (EPR) technique at W-band (94 GHz) frequency. The study provides assignment of radical centers detected by continuous-wave EPR, saturation transfer mode and echo-detected field-swept EPR at W-band frequencies. The phase memory time, T _m, which was measured simultaneously at X-band (9.5 GHz) and W-band frequencies for different spectral components has been employed to estimate rotation correlation times of CH₃ protons and an effective correlation time related to the local dynamics of the entire SAR1 center at room temperature.     

EPR study of monomeric and dimeric vanadyl ions in SbVO 5

A new compound, SbVO 5 , formed in the V-Sb-O system, has been synthesized and investigated using the electron paramagnetic resonance (EPR) technique. SbVO 5 has been prepared by two methods: by heating equimolar mixtures of V 2 O 5 and f -Sb 2 O 4 in air and by oxidation of the known phase (SbVO 4.5 ) of rutile type obtained in pure argon at temperatures between 550 v C and 650 v C. At room temperature only a weak EPR signal from the powder sample of SbVO 5 was detected corroborating the absence of bulk V(IV) ions in the structure. Comparison with the CuSO 4 reference sample revealed that only 0.02% vanadium ions are EPR active. Intense EPR spectra obtained in the low temperature range, below 100 v K, showed a well resolved hyperfine structure typical of isolated vanadium ions in axial symmetry, present as VO 2+ species, and a broad line attributed to V 4+ -O-V 5+ bonds. The hyperfine structure lines could be analyzed by an axial spin Hamiltonian with g =1.9311, g =1.9425 and A =181 ‐ 10 m 4 v cm m 1 , A =54 ‐ 10 m 4 v cm m 1 . The spectrum recorded at the lowest obtainable temperature T=3.65 v K contains yet another component which is typical of a triplet state indicating the presence of two interacting VO 2+ nuclei with spin 1/2 giving a singlet S=0 and a triplet S=1 state. The appearance of a low-field line (B～1600 v Gs at g , 4) is another diagnostic for the presence of dimeric species and is attributed to the forbidden j M S = - 2 transition.     

EPR study of radiation damage in gamma-irradiated 3-nitroacetophenone single crystal

This paper presents the results of the electron paramagnetic resonance (EPR) study of the anion radical formed from 3-nitroacetophenone (C₈H₇NO₃) (3NAP) single crystal, by gamma irradiation. The EPR spectra of gamma-irradiated single crystals of 3NAP have been recorded at 10-degree intervals for different orientations of crystals in a magnetic field, at room temperature. The EPR analysis of gamma-irradiated crystals of 3NAP has shown that the radiation damage center produced by gamma irradiation is the carbon-centered 3NAP anion radical. One-electron reduction of 3NAP results in general bond loosening. The single crystals have been investigated between 120 and 450?K. The spectra have been found to be temperature-dependent. The EPR parameters of the 3NAP anion radical have been evaluated.     

EPR study of some rare-earth ions (Dy3+, Tb3+, and Nd3+) in YBa2Cu3O6-compound

We investigate the low temperature X-band electron paramagnetic resonance (EPR) of YBa(2)Cu(3)O(x) compounds with x congruent with 6.0 doped with Dy(3+), Tb(3+), and Nd(3). The EPR spectra of Dy(3+) and Tb(3+) have been identified. The EPR of Tb(3+) is used also to study the effect of suppression of high T(c) superconductivity by doping with Tb(3+). The EPR of Nd(3+) is probably masked by the intense resonance of Cu(2+). All experimental EPR results compare well with theoretical estimations.     

Mechanisms of TL for production of the 230 °C peak in natural sodalite

The thermoluminescence (TL) peak in natural sodalite near 230 °C, which appears only after submitted to thermal treatments and to gamma irradiation, has been studied in parallel with electron paramagnetic resonance (EPR) spectrum appearing under the same procedure. This study revealed a full correlation between the 230 °C TL peak and the eleven hyperfine lines from EPR spectrum. In both case, the centers disappear at the same temperature and are restored after gamma irradiation. A complete model for the 230 °C TL peak is presented and discussed. In addition to the correlation and TL model, specific characteristics of the TL peaks are described.     

Special aspects of the temperature dependence of EPR absorption of chemically carbonized polyvinylidene fluoride derivatives

The temperature dependences of electron paramagnetic resonance (EPR) absorption of two samples of chemically carbonized derivatives of polyvinylidene fluoride (PVDF) synthesized under different conditions have been measured in the range of 100–300 K. It has been found that the temperature dependence of the integrated intensity of the EPR signal of both samples is nonmonotonic and does not obey the classical Curie dependence characteristic of free radicals. An analytical expression that is consistent with experimental data and suggests the presence of an activation component of paramagnetism in the test samples has been obtained. The presence of a term independent of temperature in this equation also indicates the paramagnetic contribution of free electrons. The magnitude of the activation energy of the singlet–triplet transitions has been evaluated: δ = 0.067 eV. The HYSCORE spectra of chemically carbonized PVDF derivatives have been obtained for the first time.     

On reasons for the hysteresis of melting and crystallization of nanoparticles

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.