Different Types Of Paramagnetic Centers Research Articles

ИЗУЧЕНИЕ МЕТОДОМ ЭЛЕКТРОННОГО ПАРАМАГНИТНОГО РЕЗОНАНСА ВЛИЯНИЯ ФИЗИКО-ХИМИЧЕСКИХ И СТРУКТУРНЫХ ХАРАКТЕРИСТИК КОСТНОЙ ТКАНИ НА ПРОЦЕССЫ ОСТЕОИНТЕГРАЦИИ ДЕНТАЛЬНЫХ ИМПЛАНТАТОВ С РАЗЛИЧНОЙ МИКРОСТРУКТУРОЙ ПОВЕРХНОСТИ

Aim. Study by the method of electronic paramagnetic resonance (EPR) physical- chemical and structural features of bone tissue and their effect on the processes of osseointegration during dental implantation using implants with different macro-microstructure of the surface.
 Material and methods. The experimental study was conducted on 7 Vietnamese visobryu-pig mini-pigs. Under anesthesia, implants with different macro-microstructures of the surface (SLA, RBM, ) were installed under the methods of direct and delayed implantation. At different dates of the experiment, after the appropriate anesthesia, the gentle method was to remove implants with small fragments of periemplant bone tissue. Macro-drugs of bone tissue of the jaws after sawing on blocks and extraction of implants, as well as appropriate preparation, were investigated by the method of stationary electronic paramagnetic resonance.
 Results. As a result of the study it was revealed that the insertation of the implant into the jaw bone leads to structural changes in the surrounding bone implant. After prior exposure, the EPR spectrums, caused by different types of paramagnetic centers, were observed in the samples studied. Two types of centers, , have been identified. and F is the center. The spectrum of the second type reflects the presence in hydroxiapatites of lattice defects associated with isomorphism, and, . The findings suggest that one of the reasons for the higher content of free radicals (SR) in bone tissue derived from radiation, after dental implantation is the weakening of chemical bonds, greater mobility of fragments that make up its structure. It must be assumed that the high content of SR in the bone in the postoperative period is nothing but a result of the disruption of the mineralization process, which is accompanied by the replacement of phosphate groups with carbonate ions that are free-radicalized. It has also been revealed that the structural integrity of the bone depends to a large extent on the degree of orderliness of microcrystals of hydroxyapatite. According to EPR, the most favorable bone recovery (the process of osseointegration) occurs when using implants with a surface, .
 Conclusions. EPR research of native and carbonate radicals is a unique tool for studying the physical and chemical and structural features of bone tissue and their role in the process of osseointegration of implants. The speed of osseointegration for implants with different microstructures of the surface varies. EPR can be used as an additional method to control the integration of implants into bone tissue.

Formation of different types of paramagnetic centers in the alanine dosimeters exposed to alpha and gamma radiation - Study by EPR spectroscopy

EPR spectra of alanine dosimeters irradiated by gamma-rays and by alpha-particles were measured at different microwave power. The spectra were decomposed into three components corresponding to different stable radiation-induced radicals. Different ratio of the components was obtained for gamma- and alpha-irradiated alanine. The observed effect can be used for discrimination of the contribution of alpha- and gamma-radiation in mixed radiation field. That may be useful for control of dose at phantom experiments with neutron boron capture therapy, performed in mixed neutron-gamma field in which alpha-particles are emitted through neutrons capture reaction with boron.

EPR Spectroscopic Examination of Different Types of Paramagnetic Centers in the Blood in the Course of Burn Healing.

The multicomponent electron paramagnetic resonance spectra of the blood during healing of skin burned wounds treated with a new generation biodegradable dressings containing poly(lactide-co-glycolide) were analysed. The evolution of different types of paramagnetic centers in the blood with time of healing was determined. The EPR spectra of the blood samples at 230 K temperature were measured at 1, 10, and 21 days after burning of the pig skin. The EPR lines of the following paramagnetic centers: the high-spin Fe3+ in methemoglobin (line I), high-spin Fe3+ in transferrin (line II), and Cu2+ in ceruloplasmin and free radicals (line III) were observed in the X-band (9.3 GHz) spectra of the blood. The multicomponent structure of the EPR spectra of the tested blood samples depended on the time of the healing of the burned wounds. The amount of the high-spin Fe3+ in methemoglobin (line I) in the blood decreased after 21 days of the healing of the burned wounds. The amount of the high-spin Fe3+ in transferrin (line II) slightly increased after 21 days of therapy with the basis. The amount of Cu2+ in ceruloplasmin and free radicals (line III) in the blood was very high after 10 days of therapy. At the first day of the healing of the burned wounds, the highest amount of the high-spin Fe3+ in methemoglobin (line I), the relatively lower amounts of the high-spin Fe3+ in transferrin (line II), and Cu2+ in ceruloplasmin and free radicals (line III) existed in the blood. In the medium phase (after 10 days) of the healing of the burned wounds, the extremely higher amounts of Cu2+ in ceruloplasmin and free radicals (line III) appeared in the blood. In the last phase (after 21 days), only the low differences between the amounts of the high-spin Fe3+ in methemoglobin (line I), the high-spin Fe3+ in transferrin (line II), and Cu2+ in ceruloplasmin and free radicals (line III) were observed. The present study may serve as a starting point for the development of a new technique for monitoring molecular complexes containing iron Fe3+ (methemoglobin, transferrin) or copper Cu2+ ions (ceruloplasmin) and free radicals in the blood during wound healing.

Synthesis of TiO2/ZrO2/SiO2 powders and their structural, optical and photocatalytic properties

Ternary oxide powders based on titania, zirconia and silica have been synthesized by the sol–gel method. The characterization of the powders was performed using UV–Vis spectroscopy, EPR, X-ray diffraction and Raman spectroscopy. The XRD study indicated the formation of TiO2 nanocrystals in anatase phase and titanium zirconate as srilankite phase. The band gap energy values of ternary powders are in the range of 3.2–3.3 eV. It is found that different types of paramagnetic centers were formed depending on silica sources after high-energy irradiation. As shown by the electron paramagnetic resonance study, the stability of SiO2 against β-irradiation is observed only for TiO2/ZrO2/SiO2 powder obtained from tetraethoxysilane as well as the formation of oxygen vacancies in TiO2 structure. Photocatalytic activity of TiO2/ZrO2/SiO2 powders is investigated in the process of photoreduction of Cr(VI) ions to Cr(III). As shown, the efficiency of photocatalyst depended on the nature of defect sites of the nanocomposites’ surface. It is found that the TiO2/ZrO2/SiO2 system obtained using tetraethoxysilane exhibited the highest photocatalytic activity as a result of the certain defect sites formation after high-energy irradiation.

Pulsed EPR Methods to Study Biomolecular Interactions.

Orthogonal site-directed spin labelling in combination with pulsed EPR spectroscopy is a powerful approach to study biomolecular interactions on a molecular level. Following a surge in pulse EPR method development, it is now possible to access distance distributions in the nanometre range in systems of complex composition. In this article we briefly outline the necessary considerations for measurements of distance distributions in macromolecular systems labelled with two or more different types of paramagnetic centres. We illustrate the approach with two examples: an application of the Double Electron-Electron Resonance (DEER) method on a triple spin-labelled protein dimer labelled with nitroxide and Gd(<small>III</small>), and an optimisation study of the Relaxation Induced Dipolar Modulation Enhancement (RIDME) experiment for the orthogonal spin pair Cu(<small>II</small>)-nitroxide.

EPR and optical spectroscopy of Yb3+ ions in hexagonal perovskite RbMgF3 crystals

EPR and optical spectroscopy of trigonal Yb3+ centers in RbMgF3 are reported. The results of these experiments make it possible to conclude that Yb3+ ions replace Mg2+ host cations at two different sites forming three different types of paramagnetic centers. The empirical schemes of the energy levels for trigonal paramagnetic centers of Yb3+ ions have been established and parameters of the corresponding crystal fields have been determined. Structural models of the observed centers are proposed.

Enhancement of room temperature ferromagnetism in tin oxide nanocrystal using organic solvents

The effect of organic solvents (ethanol & ethylene glycol) on the room temperature ferromagnetism in nanocrystalline tin oxide has been studied. The samples were synthesized using sol-gel method with the mixture of water & organic liquid as solvent. It is found that pristine SnO2 nanocrystal contain two different types of paramagnetic centres over their surface:(i) surface chemisorbed oxygen species and (ii) Sn interstitial & oxygen vacancy defect pair. The magnetic moment induced in the as-prepared samples is mainly contributed by the alignment of local spin moments resulting from these defects. These surface defect states are highly activated by the usage of ethylene glycol solvent rather than ethylene in tin oxide nanostructure synthesis. Powder X-ray diffraction, transmission electron microscope imaging, energy dispersive spectrometry, Fourier transformed infrared spectroscopy, UV–vis absorption spectroscopy, photoluminescence spectroscopy, vibrating sample magnetometer measurement and electron spin resonance spectroscopy were employed to characterize the nanostructured tin oxide materials.

Anomalous Phases in Cavity-Free 240 GHz Pulsed ENDOR Spectra of 1.44 GeV Xe-Irradiated LiF

Paramagnetic centers generated by swift heavy ion irradiation of LiF crystals could be identified as electrons trapped at regular anion vacancy sites (F centers). Well-resolved electron-nuclear double resonance (ENDOR) spectra resulting from the hyperfine interaction with 7Li and 19F nuclei located in six different shells could be recorded. In order to preserve the millimeter-sized crystals, a cavity-free setup was used for the ENDOR experiments at an electronic Larmor frequency of 240 GHz. Apparently even under conditions of extremely high local energy loss in the ion track, the local density of persistent F centers is still sufficiently low to prevent distortions of the ionic crystal. The spread of hyperfine coupling constants was less than 5 %. Neither in electron paramagnetic resonance (EPR) nor in ENDOR spectra there was evidence for different types of paramagnetic centers. When performing ENDOR by applying the radiofrequency pulse directly after the 3-pulse Mims-type microwave sequence, an anomalous ENDOR effect was observed. The observed “positive” and “negative” ENDOR response can be attributed to efficient hole and anti-hole formation in the inhomogeneously broadened EPR spectrum and can be used to determine the sign of hyperfine coupling constants.

Investigation of Paramagnetic Centers in Fullerides A2MC60 and AM2C60 (A = K, Rb, M = Mg, Be)

Paramagnetic centers in heterofullerides with the composition A2MC60 and AM2C60 (A = K, Rb, M = Mg, Be) were investigated by the electron spin resonance (ESR) method. It was found that the ESR signal can be interpreted as a composition of two lines with different temperature dependence of ESR absorption magnitude. This gives an evidence of the presence of at least two different types of paramagnetic centers. Centers of the first type behave as localized spins, while the rest can be interpreted as conduction electrons.

Formation of a solid solution of ZnO : Mn 2+ during mechanical treatment of oxides mixture

Electron paramagnetic-resonance measurements were carried out to study the structure of paramagnetic centres in ZnO+1% MnO 2 powder mixtures, processed by a ball-milling technique during different treatment times, t MT . Initiation of five different types of paramagnetic centres, I– V, was revealed. The electron-hole centres I (V Zn −:Zn i 0), II (V Zn −), and III ((V Zn −) 2 −) in ZnO first appear and then disappear with the mechanical treatment (different times t MT for different centres). It indicates that the formation of vacancies and other defects in ZnO have various reaction energies and that on annealing at higher temperatures, T MT , the defects having smaller activation energies are not stable. The formation of intermediate IV type centre is associated with diffusion of Mn 2+ ions into a superficial Zn(OH) 2 environment. The subsequent formation of spectrum V associated with the solid solution ZnO:Mn 2+, begins at t M T > 90 min .

About opportunities of the directed modification a set of defects in the surface region of ZnO particles

Using of EPR the laws of formation of various defects during mechanical treatment (MT) of powders of zinc oxide were considered. Formation of six different types of paramagnetic centers was established. The quantitative analysis of the changes of intensity (concentration of the centers in the sample) of EPR signals I– VI depending on conditions of MT (speed of rotation of jars of a mill, duration of MT, amount of entered additives, etc.) has allowed to establish interrelation between defects formation and temperature processes, which develop during MT. In the work the opportunities of an obtaining of samples with a necessary set of surface defects are discussed.

Trapped molecular species in N-doped TiO2

Nitrogen-doped TiO2, a novel photocatalyst active in the decomposition of organic pollutants using visible light, contains several different types of paramagnetic centers. These are molecular species, such as NO and NO2 radicals and other species, deeply interacting with the TiO2 structure. All or part of these species is related to specific properties of the solid. Electron paramagnetic resonance has been employed to characterize the N-containing paramagnetic species present in N-doped anatase TiO2 powders obtained via sol-gel synthesis. In the present work attention is focused on molecular species generated during the synthesis process and segregated in cavities of the TiO2 structure.

The nature of paramagnetic species in nitrogen doped TiO2 active in visible light photocatalysis

Nitrogen doped TiO2, a novel photocatalyst active in the decomposition of organic pollutants using visible light, contains two different types of paramagnetic centres (neutral NO radicals and NO2(2-) type radical ions respectively) which are likely related to specific properties of the solid.

Structure and formation mechanism of the Eα′ center in amorphous SiO2

We provide a possible formation mechanism for one of the Si-related paramagnetic centers in amorphous silica, Eα′, which is stable only below 200 K, on the basis of the quantum-chemical calculations. We show that the divalent Si defect can trap a hole, resulting in two different types of paramagnetic centers that are consistent with the experimental spectral features for Eα′. The highly anisotropic symmetry and the isotropic hyperfine coupling constants observed for one of the Eα′- center variants are reproduced by the present model.

Electron spin resonance of MO5+ in KTiOPO4

The ESR spectra from Mo5+ ions in KTiOPO4 single crystal were studied at 77 K. The ESR spectra reveal two different types of paramagnetic centers, one due to Mo5+ which occupy the Ti(1) position in the crystal and the other, due to Ti3+, formed at position Ti(2) in the crystal. The principal values and direction cosines of the g tensor are reported for the former center.

Radiation energy transfer and trapping in single crystals of hemihydrate and hydrochloride of 5-methylcytosine doped with 5-methylthiocytosine—An EPR study

Two different crystals of 5-methylcytosine with 5-methylthiocytosine as impuritiy, irradiated with ionising radiation, exhibit quite different types of paramagnetic centres associated with thio impurities. In 5-methylcytosine hemihydrate there are two types of radicals with the unpaired spin located mainly on sulphur. Both are of thiyl structure, presumably derived by a loss of an electron from 5-methylthiocytosine. In doped 5-methylcytosine hydrochloride two distinct paramagnetic species with high spin density on chlorine have been detected. One of them has been spectroscopically characterised and assigned to an electron-deficient species with the unpaired electron shared by a sulphur and a chlorine atom, with some delocalization over the pyrimidine ring. Both crystal lattices of 5-methylcytosine support migration of electrons/holes. In the hemihydrate lattice, the base stacking interaction, although weak in comparison to that in DNA or some other molecular crystals of the nucleic-acid bases, might be responsible for that. In the hydrochloride lattice, the chlorine-ion strings or layers might provide the means for the hole transport. Both neutral and positively charged 5-methylcytosine is a good radiation energy trap (hole trap).

E.p.r. studies of interactions between paramagnetic centres of exinite, vitrinite and inertinite during thermal decomposition

Electron paramagnetic resonance in the X-band (9.3 GHz) was used for investigations of petrographically complex coal samples (densities 1.24–1.28 and 1.30–1.36 g cm −3) from Polish medium-rank coal (85.6 wt% C) heated in an inert atmosphere at 300–650°C. A strong increase in total concentration of paramagnetic centres in the sample of lower density at 300–350 and 450–550°C was measured. Relatively smaller changes in the total amount of paramagnetic centres in the heavier sample at 300–650°C were observed. There are three different types of paramagnetic centres in both samples, and their e.p.r. spectra are a superposition of one broad Gauss and two Lorentz (broad and narrow) lines. The most active group in the thermal decomposition of the two coal samples is formed by paramagnetic centres responsible for the broad Lorentz lines. Mainly dipolar interactions of unpaired electrons influence the linewidths of the e.p.r. signals. The microwave saturation power of all the e.p.r. lines detected increases with temperature. According to the e.p.r. results for pure macerals and the complex coal samples, the hypothesis of independent progress of reactions in individual macerals during the thermal decomposition of coal can be rejected.

Distribution of paramagnetic defects formed in silicon by MeV ion implantations

Two different types of paramagnetic centers in silicon, Si-P3 (neutral {110} planar tetravacancies) in a well defined crystalline structure and point defects with poorly defined local structure in substantially damaged crystalline environments, formed by 3 MeV phosphorus and silicon ion implantations up to a dose of 1 × 10 14 cm −2 have been compared both in the dose dependence of area densities and in depth profiles. When the dose reaches to 1 × 10 14 cm −2, the area density of Si-P3 starts to saturate while that of “indefinite” point defects keeps increasing. Also at this dose, the mean concentration of Si-P3 decreases as a function of depth from the surface whereas that of “indefinite” point defects increases. These results are discussed in terms of a damage overlap model in conjunction with a Monte Carlo simulation of lattice disorder.

Electron spin resonance investigation of oxygen interaction with V 2O 5MoO 3 catalysts

The changes in reduction degree of V 2O 5MoO 3 catalysts occurring in the course of oxygen adsorption were investigated by electron spin resonance and chemical analysis. Two different types of paramagnetic centers, involving reduced vanadium ions stabilized by oxygen vacancies and substitutional Mo 6+ ions, have been found in partially reduced catalysts. The kinetics of oxidation of such catalysts investigated by electron spin resonance revealed a delay in oxidation of the centers stabilized by Mo 6+. The role of segregation processes occurring upon redox treatment of the V 2O 5MoO 3 catalysts in determination of the stability of particular centers has been discussed.

Different types of paramagnetic centres in polymers containing conjugated bonds

Different types of paramagnetic centres in polymers containing conjugated bonds