Paramagnetic centers in tumor cells

Free radical properties of different types of tumor cells were compared. Electron paramagnetic resonance (EPR) studies were performed for human (BM, IGR and SK) and mouse (B16 and S91) melanoma cells. In contrast to melanotic melanoma IGR, BM and B16 cells, amelanotic S91 cells contained only a trace amount of melanin. No EPR signals were detected for Caco2 cells and only a very weak EPR line was measured for fibroblast cells. Melanin does not exist in these cells. The aim of this work was the application of EPR spectroscopy to the determination of the kind of melanin (eu- or pheomelanin) in melanotic tumor cells. Microwave saturation of EPR spectra of tumor cells with high and low melanin content was compared. Eumelanin was identified in human BM, IGR, SK, and B16 melanoma cells. Single asymmetrical EPR lines were detected for these samples. The EPR spectra of human BM melanoma cells had the highest intensity. Paramagnetic centers in amelanotic S91 melanoma cells were also found. Trace amounts of eumelanin free radicals and the other free radicals in cells were responsible for their very weak EPR lines. The obtained results indicate that EPR spectroscopy is a very useful technique for the identification of melanin in tumor cells. Strong differences of microwave saturation of EPR lines for cells with high and low melanin content were observed. EPR lines of tumor cells with a low melanin content did not saturate at the used range of microwave power. Saturation was observed for melanotic BM melanoma cells.     

EPR Studies of DOPA–Melanin Complexes with Netilmicin and Cu(II) at Temperatures in the Range of 105–300?K

The application of electron paramagnetic resonance (EPR) spectroscopy in pharmacy of melanin complexes with netilmicin and Cu(II) was presented. The continuous microwave saturation of EPR spectra of DOPA–melanin and the complexes was performed. EPR spectra were measured on an X-band (9.3?GHz) spectrometer at temperatures in the range of 105–300?K. Paramagnetic copper ions decrease the intensity of the EPR lines of melanin’s free radicals. It was found that fast spin–lattice relaxation characterizes DOPA–melanin–Cu(II) complexes. Slow spin–lattice relaxation processes exist in melanin’s paramagnetic centers of DOPA–melanin and DOPA–melanin–netilmicin, [DOPA–melanin–netilmicin]–Cu(II), [DOPA–melanin–Cu(II)]–netilmicin complexes. Spin–lattice relaxation processes are faster at higher temperatures. The homogeneous broadening of EPR lines for melanin complexes was observed. The practical consequences of differences between paramagnetic properties of melanin complexes with netilmicin and the complexes with Cu(II) were discussed.     

Effect of Zn2+ and Cu2+ on free radical properties of melanin fromCladosporium cladosporioides

Effect of metal ions on free radical properties of natural melanin produced by soil fungiCladosporium cladosporioides was studied. The electron paramagnetic resonance (EPR) spectrum of the studied melanin consists mainly of a single line of eumelanin, and only a very weak signal of pheomelanin was observed. o-Semiquinone free radicals form paramagnetic centers in melanin. Diamagnetic Zn²⁺ ions produce an increase in the free radical concentration in melanin. Quenching of melanin EPR lines was obtained for melanin and paramagnetic Cu²⁺ ion complexes. Slow spin-lattice relaxation processes are characteristic for the free radicals in melanin samples and fast spin-lattice relaxation was observed for Cu²⁺ ions. The EPR lines of copper ions saturate at higher microwave powers than the EPR lines of melanin.     

Influence of the regime of plastic deformation on the magnetic properties of single-crystal silicon Cz-Si

A variation has been revealed in electron paramagnetic resonance spectra of single-crystal silicon Cz-Si plates plastically deformed by bending and torsion. The plastic deformation of the silicon plates is accompanied by the introduction of dislocations (∼10⁷ cm⁻²) and leads to the appearance of new lines in the electron paramagnetic resonance spectrum of the sample. The paramagnetic centers introduced during bending and torsion, as well as their electron paramagnetic resonance spectra, differ from those previously studied under conditions of uniaxial deformation. The plastic deformation results in a significant increase in the diamagnetic component of the magnetic susceptibility, which exceeds the increase in the paramagnetic component for the magnetic susceptibility of the Cz-Si crystals.     

EPR Studies of DOPA–Melanin Complexes with Fe(III)

Paramagnetic centers in 3,4-dihydroxyphenylalanine–melanin and its complexes with Fe(III) were examined by electron paramagnetic resonance (EPR) spectroscopy. Paramagnetic centers of melanin play an important role in detoxification of environment and they reveal high activity in binding of metal ions. Two different signals were observed in EPR spectra: lines of o-semiquinone free radicals and lines of paramagnetic Fe(III). Amplitudes of EPR lines of both free radicals and iron ions decrease with increasing Fe(III) content in melanin–metal ion complexes. Free radical concentrations in the melanin samples, g-factors, amplitudes and line widths of EPR spectra were determined. It was stated that fast spin–lattice relaxation processes exist in both free radical system and paramagnetic iron ions in melanin complexes.     

Electron paramagnetic resonance in YbNiAl<Subscript>2</Subscript> single crystals with strong magnetic anisotropy

Anisotropy in the magnetic properties of YbNiAl₂ intermetallide has been studied. Electron paramagnetic resonance (EPR) signals assigned to the localized magnetic moments of trivalent ytterbium have been detected at temperatures below 20 K. Spin–lattice relaxation processes like the Orbach–Aminov process with participation of the first excited Stark sublevel of the Yb³⁺ ion with an energy of 96 K govern electron–spin dynamics and the disappearance of spectrum lines with a further increase in temperature. Strong magnetic anisotropy effects are discussed as a main reason for the appearance of electron paramagnetic resonance.     

Instability of Fabry-Perot interferometer with a multilayered paramagnetic filling

The results of the analysis of the stability of stationary solutions of wave equations discribing a behavior of the nonlinear Fabry-Perot interferometer with a saturated paramagnetic filling are presented in this paper. The cases when paramagnetic medium is characterized by a homogeneously and nonhomogeneously broadened line of the magnetic resonance have been considered. Areas of unstable behavior of these characteristics of the resonance structure have been found.     

Magnetic Resonance Studies of Intrinsic Defects in ZnO: Oxygen Vacancy

Electron paramagnetic resonance (EPR), photo-EPR, and optical detection of magnetic resonance (ODMR) investigations of paramagnetic centers related to the oxygen vacancy in ZnO are reviewed. Main attention is paid to problems of identification of different EPR spectra related to the oxygen vacancy. The experimental photo-EPR and ODMR results, concerning the energy levels formed by the oxygen vacancy in the ZnO gap, are summarized and analyzed.     

A review of characterization and physical property studies of metallic nanoparticles

In this survey, the characterization of metallic nanoparticles prepared by various methods and the physical properties including the theory and measurements of linear and nonlinear optics, electric and magnetic properties are reviewed. Technical results involving linear optical absorption, optical second harmonic generation, temperature dependence of resistivity, electron paramagnetic resonance and magnetic susceptibility measurements were portrayed. A number of fascinating and provocative results have been developed that lead our perspective understanding of quantum size confinements.     

Magnetic resonance of paramagnetic ion-nuclei in metals and superconductors

The magnetic resonance lineshape of paramagnetic ion-nuclei in metals is calculated using the temperature Green functions method and is analyzed for limiting cases of fast and slow spin lattice relaxation of localized moments. The longitudinal spin lattice relaxation rate for paramagnetic ion-nuclei in type II superconductors due to the hyperfine coupling with local moments is calculated. The influence of the fluctuation coupling of electrons on relaxation of paramagnetic ion-nuclei in “dirty” type II superconductors is investigated in magnetic field slightly above the upper critical field H_c2.     

ESR microscopy

New spatial imaging methods to determine the microscopic concentration of unpaired electron spins or paramagnetic ions (ESR microscopy methods) have been developed (a) with an intense magnetic field gradient method based on conventional magnetic resonance imaging (MRI) using field gradient coils in a cavity, (b) by scanning the localized magnetic field or modulation field mechanichally or electronically, and (c) by use of the scanning localized microwave field. Some examples of fossil imaging and of microdosimetry in this laboratory are reviewed briefly.     

Combined Magneto-Electric Spin Resonance of Impurity Ho Ions in Synthetic Forsterite

Continuous-wave electron paramagnetic resonance spectra of impurity holmium ions in synthetic forsterite have been studied on an ELEXSYS E580 spectrometer equipped with a cylindrical dielectric resonator ER4118MD5-W1 of the Flexline series. Resonance lines of the anomalous shape demonstrating the absorption contour instead of its derivative were observed at the conventional operation mode with the magnetic field modulation. The conditions of the appearance of anomalous signals and their characteristics have been studied. The anomalous lines shape effect was explained by the simultaneous excitation of magnetic dipole and electric quadrupole transitions between electron–nuclear spin sublevels of the holmium ions.     

EPR/FMR, FTIR, X-Ray and Raman Investigations of Fe-Doped SiCN Ceramics

SiCN magnetic ceramics doped with Fe ions were synthesized at different pyrolysis temperatures in the range from 600 to 1600°C. Several phases of ceramics were detected using the techniques of electron paramagnetic resonance/ferromagnetic resonance, Raman, Fourier-transform infrared and X-ray diffractometry, listed as follows: (a) transformation to the ceramic state from the polymer state, where the Fe ions are in the paramagnetic state, as the temperature is increased from 600 to 800°C; (b) formation of two different Fe species in the range of 950–1150°C: nanocrystalline particles in the ferromagnetic state and Fe ions incorporated into the free-carbon state in the superparamagnetic state; (c) diminution of the free-carbon content above 1150°C, and, as a consequence, diminution of the intensity of the broad Fe signal related to this phase; (d) appearance of a new Fe phase at about 1200°C; (e) disappearance of the ferromagnetic phase at about 1400°C; (f) disappearance of all Fe ions above 1530°C. The samples exhibiting superparamagnetic behavior are potentially useful in developing high-temperature magnetic sensor devices.     

Study of interparticle interaction in conjugates of magnetic nanoparticles injected into mice

In this work the first fast stage of the biodegradation in vivo of magnetic ferrofluid was investigated. The appearance of a paramagnetic doublet was observed in M?ssbauer spectra of mouse liver within 2?h after intravenous injection of the ferrofluid. It was shown that nanosized superparamagnetic particles were combined into groups in the initial magnetic beads of the ferrofluid and were connected inside each group by magnetic dipole interaction. It was found that the appearance of a paramagnetic doublet in the spectrum of mouse liver is caused by the decrease of the magneto-dipole interaction between the superparamagnetic nanoparticles.     

Specific features of the EPR line shape of dimers due to spin-lattice relaxation

The magnetization relaxation in a coupled system of two spins has been shown to induce magnetization transfer between the observed transitions. In the degeneracy region of the transitions, the magnetization transfer becomes most effective and leads to the collapse of the magnetic resonance lines. In the electron paramagnetic resonance (EPR) spectra calculated for a polycrystal, this effect manifests itself in the form of additional peaks in the absorption line. The effect of anisotropy of the g factors of the dimer spins and misalignment of the axes of the g tensor and the interaction tensor on the appearance of additional lines in the EPR spectra has been analyzed.     

Magnetic resonance in Kazan and in Oxford

A general survey is given of magnetic resonance measurements in Kazan and in Oxford, starting with the first experiments of Zavoisky, and ending with contemporary research. In addition to electron paramagnetic resonance relevant aspects of nuclear magnetic resonance and enhanced nuclear magnetic resonance are included.     

Paranasal sinus mucocele: unusual MR manifestations at 1.5 T

The classic MR appearance of paranasal sinus mucoceles is due to its cystic composition. We present two cases of paranasal sinus mucocele that exhibit atypical signal characteristics. The morphology of this lesion, rather than its signal intensity, is paramount in establishing this diagnosis.     

Phase domain structures in cylindrical magnets under conditions of a first-order magnetic phase transition

The magnetic and resonance properties of cylindrical magnets at first-order phase transition from paramagnetic to ferromagnetic state were theoretically studied. It has been shown that in the external magnetic field directed perpendicularly to the rotation axis, formation of a specific domain structure of paramagnetic and ferromagnetic layers can be energetically favorable. The parameters of cylindrical phase domains as well as their dependences on temperature, magnetic field and material characteristics have been calculated. Peculiarities of the magnetic resonance spectra appearing as a result of the phase domain formation have been considered. Dependence of the resonance field of the system of ferromagnetic domains on magnetization and temperature has been obtained.     

EPR and ENDOR Studies of Shallow Donors in SiC

Recent progress in the investigation of the electronic structure of the shallow nitrogen (N) and phosphorus (P) donors in 3C–, 4H– and 6H–SiC is reviewed with focus on the applications of magnetic resonance including electron paramagnetic resonance (EPR) and other pulsed methods such as electron spin echo, pulsed electron nuclear double resonance (ENDOR), electron spin-echo envelope modulation and two-dimensional EPR. EPR and ENDOR studies of the ²⁹Si and ¹³C hyperfine interactions of the shallow N donors and their spin localization in the lattice are discussed. The use of high-frequency EPR in combination with other pulsed magnetic resonance techniques for identification of low-temperature P-related centers in P-doped 3C–, 4H– and 6H–SiC and for determination of the valley–orbit splitting of the shallow N and P donors are presented and discussed.