Search

Electron spin resonance spectroscopy and mass spectrometry are two analytical methods that are very rarely used in combination. In this paper, we will show that the methods complement one another in the example of the distribution of stable nitroxide radicals in human skin, including the spatial resolution of these distribution processes. There are many ESR investigations dealing with this subject, but unfortunately, they are all limited to the detection of paramagnetic species. The combination with MS allows the successful examination of the distribution profile of the main biotransformation product of the nitroxide radicals, the respective 'ESR-silent' hydroxylamines. In order to maintain the biological state of the sample material as far as possible, atmospheric pressure matrix-assisted laser desorption/ionization with ion trap detection has been used for the mass spectrometric investigations. The results validate the former findings of the strong reduction of stable free radicals by biological material; moreover, the diamagnetic species formed during these processes have been identified. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Co-milling of AlO(OH) xerogels with various iron(III) compounds such as α-Fe2O3 or K3[Fe(CN)6] has been used for mechanochemical activation leading to Fe/Al oxide phases in coexistence with the activated main component. The results obtained allow a deeper insight into the chemical processes occurring during activation, doping, and thermal treatment in atmospheres of different chemical activity (H2O; N2; O2/N2; H2/N2). Evidence will be given for Fe3 + species being able to form suitable crystallization germs and to lower the crystallization temperature. One can distinguish between the incorporation of Fe3 + ions into the alumina matrix at the crystallite growth (e.g. on Fe2O3-like seeds) and the incorporation of Fe3 + ions during the last steps of crystallization. These last-mentioned Fe3 + ions are provided by coexisting Fe/Al oxide phases. In contrast to alumina matrices equilibrated at high temperatures (e.g. at 1,200–1,500°C), the matrices formed in situ are able to incorporate Fe3 + ions by diffusion at temperatures of ∼900–1,100°C in a short time regime. [ABSTRACT FROM AUTHOR]

The spectral–spatial electron spin resonance (ESR) imaging experiment provides information about the spatial and spectral properties of the examined sample, as well as the intensity distribution. Obtaining quantitative statements of the respective sample requires the usage of reference standards such as diphenylpicrylhydrazyl (DPPH) or charcoal. By means of ultraviolet-visible spectroscopy a DPPH sample has been quantified to become the reference DPPH standard for the following experiments. Moreover, charcoal together with DPPH serves as a standard to determine the spatial dimension. An ESR tomographic device has been modified concerning the sample shaping and arranging in a TE102 resonator to allow the spatially resolved quantitative determination of spin concentrations of spin probes ( S = 1/2) with an acceptable error. Only standard ESR equipment has been used except the additional gradient coils and their computer-aided controls for recording the tomogram. The presented results, i.e., the spatially resolved determination of spin concentrations, seem to be useful to describe, e.g., transport processes in biological objects. As a first application of the developed method, the spatial resolution of the effect of ultraviolet irradiation on the concentration of a spin probe in human skin could be determined. Altogether, the newly introduced method widens the field of applications of ESR spectroscopy and tomography. [ABSTRACT FROM AUTHOR]

Copyright of Erwerbs-Obstbau is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Focussed on the understanding of the complex Fe3+ electron spin resonance (ESR) spectra in crystalline and amorphous systems, the simulation program ESR-MAKRO-1 was developed, which allows the calculation of powder spectra of paramagnetic centers with 1/2 ≤ S ≤7/2. For the reproduction of the ESR spectra of amorphous systems Gaussian distributions of the zero-field-splitting parameters of second and fourth order ( D, E, a, F) were implemented into the program. Applications of ESR-MAKRO-l are given both for crystalline powders and for glassy systems. A stepwise analysis of the ESR spectra, allowing an approach to Fe3+ ESR spectra of amorphous matrices and showing the influence of D, E, a, and F as well as their distributions, is given. [ABSTRACT FROM AUTHOR]

Searching for a microscopic description of structural phase transitions in AlF3, these transitions were followed by electron paramagnetic resonance (EPR) in situ measurements in X-band in the temperature range 290 K ≤ T ≤ 800 K with Cr3+ — and Fe3+-doped powder samples of α-AlF3. For each temperature the zero-field splitting (zfs) parameters of the paramagnetic transition metal ions were determined by simulation. Starting from the axial zfs parameters b ( T) and bearing in mind the trigonal symmetry, the application of the superposition model allowed the calculation of the angle θ( T) (θ: <( c-axis, Al-F)) with b ( T) = 3 b 2( R)(3cos2θ( T) − 1) ( c-axis ∥ 3-fold axis). Direct relations between θ and the rotational angle ω of the matrix in dependence on temperature could be obtained by geometrical considerations. Local displacements of the anions were taken into account in terms of the parameter x characterizing their lattice position in the hexagonal cell of aluminium fluoride. [ABSTRACT FROM AUTHOR]

Two-frequency continuous-wave and pulse EPR (electron paramagnetic resonance) spectroscopical techniques are applied to determine static and dynamic EPR parameters of Cu2+ ions in oxide and fluoride glasses. The investigations are focussed on the analysis of strain effects in the glassy matrices, the identification of the magnetic nuclei in the vicinity of Cu2+ ions as well as the determination of the dependence of the phase memory time T M on temperature and resonance field. The results obtained by X-band continuous-wave EPR, X- and S-band echo-detected EPR, and X- and S-band electron spin echo envelope modulation studies of Cu2+-doped inorganic glasses yield information on the local symmetry of the Cu2+ coordination polyhedra, the chemical nature of the atoms in the second and higher coordination spheres, the distribution of the parameters of the static spin Hamiltonian and the low-temperature motions of the dopant-containing structural units. Special techniques like 2-D Mims ENDOR (electron nuclear double resonance) and hyperfine-correlated ENDOR are applied for the first time to doped inorganic glasses. From the spin relaxation measurements a stronger tendency of the Cu2+ ions to aggregate is found for fluoride glasses in comparison to aluminosilicate and phosphate glasses. [ABSTRACT FROM AUTHOR]

Coprecipitates of CdII, KI and FeIII with hexacyanoferrate ions [Fe(CN)6]4− have been studied by solid-state electrochemistry (voltammetry of immobilized microparticles), magnetic susceptibility measurements, X-ray powder diffraction, electron spin resonance, Mössbauer and diffuse reflectance spectroscopy. Most suprisingly, all experimental results point to the formation of a continuous series of complex mixed phases without the formation of phase mixtures. Although CdII and FeIII ions differ too much in their ionic radii to allow the formation of simple substitution mixed hexacyanoferrates, they are capable of forming different kinds of complex insertion and substitution mixed crystals because of the zeolitic structure of both the iron and the cadmium hexacyanoferrate. Low cadmium concentrations can be found in the zeolitic cavities of iron hexacyanoferrate (Prussian blue), and they start to widen the lattice and facilitate, at higher concentrations, the direct substitution of high-spin iron(III) ions by cadmium ions. In cases of an excess of cadmium, the formation of cadmium hexacyanoferrate with iron(III) ions in the interstitials of the zeolitic structure is observed. These mixed phases show strong charge transfer bands in the visible range and have the appearance of “diluted” Prussian blue. For the first time, this indicates that the charge transfer between the carbon-coordinated low-spin iron(II) ions and the high-spin iron(III) ions can also occur when the latter are situated in the cavities of a host hexacyanoferrate. In Prussian blue the interstitial iron(III) ions are responsible for a very strong charge transfer interaction between the low-spin iron(II) ions and the nitrogen-coordinated high-spin iron(III) ions. Upon substitution of the very small amount of interstitial iron(III) ions in Prussian blue by potassium and cadmium ions the Kubelka-Munk function diminishes by more than 30%, indicating a tremendous decrease in iron(III)-iron(II) interaction. [ABSTRACT FROM AUTHOR]

Stepwise amorphization of a low-level doped α-Al2O3 single crystal yielded powders without changes of the concentration and chemical nature of the dopants. Kind and degree of disturbances could be unambiguously monitored by the allowed and forbidden transitions of the Fe3+-cw-EPR in X-band using a Bruker bimodal cavity. Based on simulations diagonalizing the spin Hamiltonian for S = 5/2 it was possible to discriminate between regions as well as samples of structural order and disorder. The spectral pattern of the allowed and forbidden transitions of Fe3+ ions together with the field-position-dependent saturation behaviour (4.2 K) allowed us to differentiate between crystalline and amorphous components or regions of a sample. [ABSTRACT FROM AUTHOR]

ESR spectroscopy was used to study order/disorder phenomena in paramagnetically doped solids. The dehydration process of aluminium fluoride and oxide hydrates and aluminosilicates was examined by ESR in situ measurements as well as using thermoanalytically quenched samples. Two types of amorphous states of solids have been studied: inorganic glasses in the conventional sense and amorphous states of solids which have not passed the liquid state. The complete ESR fine structure pattern of Fe3+ ions is susceptible with respect to order/disorder processes of the actual host matrix. Dehydration processes bear some model character in this field. A quantitative description of the disorder effects on the Fe3+ ESR could be given on the basis of a complete spin Hamiltonian using distributions of the fourth order spin coupling parameters. [ABSTRACT FROM AUTHOR]

2-Chloroethylphosphonic acid (CEPA) facilitates the separation of the fruit from the pedicel significantly. The application of 2,000 and 4,000 ppm CEPA in four sweet cherry varieties during maturation resulted in the formation of a complete abscission layer in the transition zone between pedicel and fruit. In contrast, in the untreated fruit no abscission layer was evident at maturity. The walls of the cells in the abscission layer contained less total polysaccharides than adjacent cells. Cellulose was partially broken down, and the pectins were degraded. The Ca and Mg content in the cell walls decreased. Thus the same histochemical changes are involved in natural and CEPA induced abscission. [ABSTRACT FROM AUTHOR]

Abscission layer formation in the sour cherry ( Prunus cerasus L.) during fruit maturation occurred in the transition zone between the fruit and the pedicel. The abscission layer, consisting of 5-8 rows of cells, was first identified by its low affinity for haematoxylin. The walls of cells in the abscission layer contained less total polysaccharides than adjacent cells. The pectins were degraded and the cellulose was partially broken down resulting in cell separation. The Ca level in the abscission zone decreased and Ca and Mg were lost from the walls of cells in the layer during abscission. After the abscission layer formed, cells associated with the layer had a lower capacity to bind Ca than cells distal or proximal to the layer. [ABSTRACT FROM AUTHOR]