Types of paramagnetic centers in Cu2+ complexes with model neuromelanins

Electron paramagnetic resonance (EPR) spectroscopy was used to examine free radical properties of model neuromelanins obtained by oxidative polymerization of noradrenaline, adrenaline and dopamine. We compared the lineshape of the experimental spectra, type and concentration of free radicals in the analyzed samples. The effect of different concentrations of Cu²⁺ on free radicals in melanins was studied. The total concentration of free radicals (about 10¹⁸ to 10¹⁹ spin/g) in the studied melanins increases as follows: adrenaline-melanin < dopamine-melanin < noradrenaline-melanin. EPR spectra of dopamine-melanin and adrenaline-melanin were a single EPR line (ΔB _pp, 0.50 and 0.55 mT, respectively). o-Semiquinone free radicals with the characteristicg-value of 2.0040 exist in these melanins. EPR spectra of noradrenaline-melanin were a superposition of two lines (ΔB _pp, 0.45 and 0.81 mT). o-Semiquinone free radicals were responsible for the narrower component. Nitrogen free radicals with ag-factor of 2.0030 were probably responsible for the broader component. Paramagnetic copper ions quenched the EPR signals of melanin free radicals in the studied samples. For melanin-Cu²⁺ complexes, broad EPR lines (ΔB _pp, 10–32 mT) of copper ions with ag-value of about 2.1 appeared. The influence of the microwave power on the EPR spectra of these complexes demonstrated the fast spin-lattice relaxation in the copper system in melanins.     

Effect of reduction and butylation on coal: Application of microwave saturation of two-component EPR spectra

Changes in individual groups of paramagnetic centers after reduction and reductive butylation of Polish flame coal (70.8 wt.% C) were studied by electron paramagnetic resonance (EPR) spectroscopy. The modern method of reductive butylation of coal in a potassium-liquid ammonia system was used. This process increases the solubility of coal in organic solvents. Microwave saturation of EPR spectra was applied to test the spin-lattice relaxation in coal. The measured EPR spectra were a superposition of broad (ΔB _pp, 0.42–0.49 mT) and narrow (ΔB _pp, 0.09–0.13 mT) Lorentz lines. Paramagnetic centers located in simple and multiring aromatic structures were responsible for the broad and narrow lines, respectively. Microwave saturation indicates that slow and fast spin-lattice relaxation processes are characteristic for these two types of structures in the original coal. A decrease of the microwave power saturation of the broad Lorentz line after a single reduction of coal was observed. It increased for both 4 times reduced coal and reductively butylated coal. As the result of multiple reduction and butylation, spin-lattice relaxation processes in simple coal aromatic units were fastened. The narrow Lorentz lines of both 4 times reduced and reductively butylated coal were saturated and the spin-lattice relaxation time increased.     

Low temperature one-step synthesis of cobalt nanowires encapsulated in carbon

The one-step method of carbon nanotubes filled with continuous cobalt nanowires (CoF-CNT) synthesis is presented. Co/ZSM-5 (8 wt% Co) was used as catalyst for CoF-CNT production by methane decomposition at the temperature of 400 °C and 800 °C at atmospheric pressure in a conventional gas-flow system. The average diameter of the CoF-CNT is about 25 and 40 nm for products obtained at 400 °C and at 800 °C, respectively. The average size of coherently scattering domains along the normal to graphite layers L _c , the interlayer spacing d ₀₀₂, the graphitization degree of carbon, and the relative intensities of the G and D bands in Raman spectroscopy were determined to characterize the quality of carbon. It was proved that cobalt-filled carbon nanotubes can be produced by a simple method. The results of XRD, FE-SEM, and TEM show that CoF-CNT can be obtained even at 400 °C by catalytic decomposition of methane. On the basis of XRD, TEM, Raman spectroscopy was found that at a temperature of 800 °C, a better quality of carbon was produced.     

Carbonaceous deposits on alumina as catalysts and supports

Studies of carbonaceous deposits, intercalated within alumina pores, were carried out from the point of view of their catalytic activity for a number of reactions of alkyl-substituted benzenes. Alumina was not active for ammoxidation of ethylbenzene and m-xylene as well as oxidative dehydrogenation of ethylbenzene until certain amount of the deposit was generated on acid sites of alumina surface. Carbonaceous deposits formed during reactions of decomposition of 2-propanol and hexafluoro-2-propanol were used as supports for platinum catalysts for hydrosilylation of allyl chloride and 1-octene to result in excellent selectivity. Precursor of carbonaceous deposit formed from hexafluoro-2-propanol has been identified and scheme of the deposit formation was proposed.     

Application of EPR spectroscopy to examination of gentamicin and kanamycin binding to DOPA-melanin

Electron paramagnetic resonance (EPR) spectroscopy was applied to measure the influence of two aminoglycoside antibiotics: gentamicin and kanamycin on free radical propertis of DOPA-melanin. DOPA-melanin was formed by oxidative polymerization of 3,4-dihydroxyphenylalanine. Different concentrations of gentamicin and kanamycin (from 1·10⁻⁴ to 1·10⁻² M) were used. o-Semiquinone free radicals with ag factor of 2.0043 were found in all studied melanin samples. Their concentrations in the DOPA-melanin-drug complexes were higher than in DOPA-melanin, and increased with the increase of gentamicin and kanamycin concentration. A single EPR line of the analyzed samples (ΔB _pp, 0.48-0.52 mT) indicates that aminoglycoside antibiotics do not create a new type of free radicals in DOPA-melanin. Microwave saturation behavior of the experimental lines indicates the homogeneous broadening of resonance absorption curves for DOPA-melanin and its complexes with aminoglycosides. The EPR lines saturate at low microwave powers. Slow spin-lattice relaxation processes were characteristic for all studied melanin samples.     

Simultaneous electrochemical and electron paramagnetic resonance studies of fullerene anion radicals C 60 1− and C 60 3−

Simultaneous electrochemical and electron paramagnetic resonance experiments have been carried out on the reduced C₆₀ fullerene to examine theg-factor assignment of the radical species. C ₆₀ ^1? and C ₆₀ ^3? show the following EPR characteristics at room temperature: C ₆₀ ^1? :g _1?=2.0002±0.0001, 2ΔB _1s=0.17 mT, and C ₆₀ ^3? :g _{3?=2.0008±0.0002}, 2ΔB _1s=0.07 mT. EPR linewidths are apparently narrower compared to those in most of the spectra previously reported. Variable temperature EPR study on solution containing C ₆₀ ^1? has shown thatg _1? value is not while the linewidth is only slightly temperature dependent.     

Mössbauer and magnetic studies on nanocrystalline NiFe2O4 particles prepared by ethylene glycol route

NiFe₂O₄ nanoparticles have been synthesized by co-precipitation method at 145°C in N₂ atmosphere using ethylene glycol as solvent and capping agent. This gives the promising synthesis route for nanoparticles at low temperature. The as-synthesized NiFe₂O₄ is subsequently heated at 400°C, 500°C, 700°C and 800°C. Crystallite size increases with the heat treatment temperature. The heat treatment temperature has direct effect on the electron paramagnetic resonance and intrinsic magnetic properties. The room temperature Mössbauer spectrum of the 800°C heated sample shows the two sextets pattern indicating that the sample is ferrimagnetic and Fe^3?+? ions occupy both tetrahedral and octahedral sites of spinel structure.     

EPR study of radical anions of C60 and C70

Utilizing highly polar solvents for the stabilization of Fullerene anions, electrochemical and chemical reduction resulted in narrow single line EPR spectra for the monoanions of C₆₀ and C₇₀ being characterized byg=2.0001(1), ΔB=0.075 mT,g=2.0019(1), ΔB=0.016 mT, respectively. Apparently, the orbital degeneracy of the C₆₀ monoanion is lifted under these conditions to such an extent, that the abnormal large spin lattice relaxation rate believed to be responsible for the approximately 5 mT line width of the monoanion is sufficiently reduced.¹³C enrichment resulted in noticeable line broadening, allowing an estimate of the average¹³C hyperfine coupling constanta _ave=0.1 mT.     

Characterisation of the Ru/MgF2 catalyst with adsorbed O2, NO, CO probe molecules by EPR and IR spectroscopy

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst during O₂, NO, and CO adsorption at room temperature on 1 wt% Ru/MgF₂ catalysts prepared from Ru₃(CO)₁₂ . Both EPR and IR results provided clear evidence for the interaction between surface ruthenium and probe molecules. No EPR signals due to ruthenium (Ru) species were recorded at 300 and 77 K after H₂-reduction of the catalyst at 673 K. However, at 4.2 K a very weak EPR spectrum due to low-spin (4d⁵) Ru³⁺ complexes was detected. A weak anisotropic O₂^- radicals signal with g_∣∣=2.017 and g_⊥=2.003 superimposed on a broad (ΔB_pp=120 mT), slightly asymmetric line at g=2.45(1) was identified after O₂ admission to the reduced sample. Adsorption of NO gives only a broad, Gaussian-shaped EPR line at g=2.43(1) indicating that the admission of NO, similarly to O₂ adsorption, brings about an oxidation of Ru species in the course of the NO decomposition reaction. Introduction of NO over the CO preadsorbed catalyst leads to EPR spectrum with parameters g_⊥=1.996, g_∣∣=1.895, and A_⊥^N=2.9 mT assigned to surface NO species associated with Ru ions. The IR spectra recorded after adsorption of NO or CO probe molecules showed the bands in the range of frequency characteristic of ruthenium nitrosyl, nitro, and nitrate/nitrite species and the bands characteristic of ruthenium mono-and multicarbonyls, respectively. Addition of CO after NO admission to the catalyst leads to appearance in the IR spectrum, beside the ones characteristic of NO adsorption, the bands which can be attributed to Ru-CO₂ and Ru-NCO species, indicating that the reaction between NO and CO occurs. These species were also detected after CO adsorption followed by NO adsorption, additionally to the band at 1850 cm⁻¹ being due to cis-type species.     

Sol–gel synthesized powder and pulsed laser deposited film of amorphous indium zinc oxides doped with Fe

Chemical co-precipitation method was used to synthesize nano-structured α-Fe₂O₃-CeO₂ composite by calcination of the goethite–cerium hydroxide precursor. It was observed that the precursor contained goethite matrix doped with cerium. Calcination of the precursor at 400°C showed the formation of nanosize hematite. Mössbauer spectra show the presence of a paramagnetic component in the precursor but not in the samples calcined at 400°C to 800°C temperatures. Our study shows that Ce precipitated as CeO₂ and stuck on the surface of hematite particles. The precipitation of Ce as CeO₂ is independent of the concentration of Ce in the Ce–Fe–O composite.     

Paramagnetic centers in nonmetallic amorphous polyphthalocyanines

Electron paramagnetic resonance (EPR) spectra of nonmetallic amorphous polyphthalocyanines are investigated in the temperature range 295–500 K. The EPR spectrum of nonmetallic amorphous polyphth-alocyanine samples at room temperature prior to heating is a narrow singlet of approximately Lorentzian shape with a linewidth ΔH_pp ≈ 1.7 Oe, a splitting factor g=2.00, and an intensity I_EPR ≈ 10¹⁷ spins/g. It is found that the intensity and linewidth of the EPR spectrum increase with increasing temperature. Beginning with a characteristic temperature T₁, both parameters, ΔH_pp and I_EPR, become dependent on time (under isothermal conditions). Computer calculations of the spectra demonstrate that the EPR spectrum can be represented as a superposition of two lines with substantially differing parameters whose dependences on the temperature and micro-wave power also differ significantly. The possible reasons for the existence of electron paramagnetic resonance centers of two types with different degrees of delocalization of a charge carrier with a magnetic moment in nonmetallic amorphous polyphthalocyanines are discussed.     

Structural transformations in NANOPERM-type alloys studied by Mössbauer spectrometry and diffraction of synchrotron radiation

As-quenched Fe_91???x Mo₈Cu₁B _x NANOPERM-type alloys (x?=?12, 15, 17, 20) were exposed to continuous heat treatment up to 800°C. During the temperature increase (ramp of 10 K/min), an in situ acquisition of diffracted synchrotron radiation intensities was performed. The obtained data are correlated with those derived from the volume and surface Mössbauer effect experiments. The onset of individual crystallization steps as well as identification of the crystalline phases created is discussed.     

Effect of pre-annealing on NO32- centers in synthetic hydroxyapatite

Effect of pre-annealing of synthetic hydroxyapatite (HAP) on properties of γ- and UV- induced NO₃^2- centers was studied by electron paramagnetic resonance (EPR). Nitrate-containing hydroxyapatite powders ((N)HAP)) and the powders with an admixture of carbonate and nitrate ions ((C,N)HAP) were annealed in the temperature range T_ann = 20 °C ? 600 °C before irradiation. It was found that pre-annealing of (N)HAP samples changes the parameters of NO₃^2- centers while no changes took place in (C,N)HAP. Moreover, at the pre-annealing temperatures T_ann > 200 °C two new NO₃^2- centers were observed in (N)HAP samples; they are characterized by larger value of A_⊥ (3.67 and 4.41 mT) as compared to the known centers. It was also found that the dependence of NO₃^2- centers amount on T_ann is non-monotonous in both types of samples. Presumably this is caused by the escape of water molecules from HAP during the annealing and essential modification of the defect subsystem of HAP.     

M?ssbauer study of carbon coated iron magnetic nanoparticles produced by simultaneous reduction/pyrolysis

Magnetic iron nanoparticles immersed in a carbon matrix were produced by a combined process of controlled dispersion of Fe^3?+? ions in sucrose, thermal decomposition with simultaneous reduction of iron cores and the formation of the porous carbonaceous matrix. The materials were prepared with iron contents of 1, 4 and 8 in %wt in sucrose and heated at 400, 600 and 800°. The samples were analyzed by XRD, Mössbauer spectroscopy, magnetization measurements, TG, SEM and TEM. The materials prepared at 400° are composed essentially of Fe₃O₄ particles and carbon, while treatments at higher temperatures, e.g. 600 and 800° produced as main phases Fe⁰ and Fe₃C. The Mössbauer spectra of samples heated at 400° showed two sextets characteristic of a magnetite phase and other contributions compatible with Fe^3?+? and Fe^2?+? phases in a carbonaceous matrix. Samples treated at temperatures above 600° showed the presence of metallic iron with concentrations between 16?C43%. The samples heated at 800° produced higher amounts of Fe₃C (between 20% and 58%). SEM showed for the iron 8% sample treated at 600?C800°C particle sizes smaller than 50 nm. Due to the presence of Fe⁰ particles in the carbonaceous porous matrix the materials have great potential for application as magnetic adsorbents.     

Self-organization of the structure in the Cu60Fe40 composite during deformation-thermal treatment

The deformation-thermal stability of a clusterized amorphous-crystalline structure prepared from a Cu₆₀Fe₄₀ powder mixture at a logarithmic strain e = 4.6 and subjected to isochronous (40 min) annealings at T _a = 200–800°C has been investigated. Periodic changes (ΔT = 300°C) in the order and disorder with a maximum ordering at T _a = 300 and 600°C and a maximum disordering at T _a = 400 and 700°C have been observed. The periodicity of the dominant crystallographic order with a period ΔT = 400°C in the annealing temperature has been revealed for face-centered cubic copper phase planes separated by a singular point at T = 500°C characterized by the dominant body-centered cubic iron phase ordering. It has been shown that the sawtooth shape of the size distribution of strain clusters formed within the crystal structure of deformed samples slowly changes with increasing annealing temperature from exponential (T _a = 200–700°C) to linear (T _a = 800°C). This indicates a high density of internal local distortions in structural units.     

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

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.     

Strangeness production in AA collisions at SIS18

Aluminium oxides doped with 1% ⁵⁷Fe were prepared by sol-gel method, and annealed for 3 hours at various temperatures between 550°C and 1100°C. Amorphous phases were obtained below 1000°C, and crystalline α–Al₂O₃ was formed at 1100°C. Although Al₂O₃ itself shows diamagnetism, the light doping of Fe ions into aluminium oxide induced a very weak ferromagnetism, but the ferromagnetism disappeared by longer annealing. M?ssbauer spectra were composed of paramagnetic Fe^2?+? and Fe^3?+? species for samples heated below 750°C, and of paramagnetic Fe^3?+? above 850°C, in addition to a magnetic sextet and relaxation peaks of Fe^3?+?. The magnetic and quadrupole interactions of the sextet and the relaxation peaks and the density functional calculations suggest that the lightly doped Fe^3?+? ions are substituted at Al sites in the Al₂O₃ lattice.     

Spectral study of reactions involving organic vapours and the pink afterglow of nitrogen

Chemiluminescent reactions resulting from addition of C₂H₂ and BrCN to nitrogen showing a pink afterglow have been investigated. The spectra show CN(B→A), CN(B→X), CN(A→X), and N₂(IIP) bands. The CN(B→X) bands are intense and exhibit abnormal rotational distributions with two rotational temperatures (T₁ = 2400°K, T₂ = 400°K). New perturbations and high-J rotational lines are reported. Comparisons of intensities of bands of the CN(B→A) and (B→X) systems yield 1:80 as the ratio of electronic transition probabilities for the two systems.     

Magnetic properties after irradiation of tetrakis[4-(α-diazobenzyl)pyridine]copper(II) in a frozen solution

The molecular structure of tetrakis[4-(α-diazobenzyl)pyridine]copper(II) bis(hexafluorophosphate) was revealed by X-ray structure analysis. The magnetic properties after irradiation of a 1∶4 mixture of Cu(NO₃)₂ and 4-(α-diazobenzyl)pyridine in frozen ethanol solutions were investigated by electron paramagnetic resonance (EPR) spectrometry and magneto/susceptometry. In a randomly oriented X-band EPR spectrum, new signals appeared in the field range of 0–500 mT at the expense of the signals due to the isolated copper(II) after irradiation. All signal intensities gradually decreased on warming and new signals disappeared over 60 K. The field dependence of difference magnetizationM at 2 and 5 K was measured under a condition similar to that for the EPR experiment. Fitting experiments toM vs.H/T plots by use of theoretical equations for two components suggested that a mixture of high-spin species withS=9/2 and 7/2 in a ratio of 0.18∶0.82 formed under a frozen condition.     

On the equilibrium of peroxy radicals in the oxidation of 2-propanol by molecular oxygen

Based on kinetic data, it is demonstrated that the 1-hydroxy-1-methylethylperoxyl and hydroperoxy radicals are at equilibrium in the oxidation of 2-propanol at 323°C initiated by azobisisobutyronitrile. It is shown that the equilibrium of between the peroxy radicals is not disturbed within the covered range of alcohol concentrations. The rate constants of the reaction of the hydroperoxy radical with 2-propanol is determined: k _2.2 = (0.13 ± 0.04) L mol^?1 s^?1.