Vol 47, No 6 (2016)

Samples of individual and mixed vanadium-molybdenum (V:Mo) oxides xV₂O₅:(1-x)MoO₃, 0 ≤ x ≤ 1, were prepared by the method of mechanochemical activation (MCA). The samples have been characterized by X-ray diffraction (XRD) and X-band electron paramagnetic resonance (EPR) spectroscopy. Prolongation of the treatment duration time in mills led to considerable increase in the V(IV) paramagnetic centers content as well as after additional high temperature annealing at 600 °C. Paramagnetic Mo(V) centers were recorded only in the case of MCA of individual MoO₃ oxide. Complexity of the composition of mechanically activated mixed oxides was confirmed with the XRD data. It is shown that in the case of all individual and mixed oxides the content of paramagnetic species increases noticeably with the increase in milling time. The annealing at 600 °C after MCA of mixed oxides forms a new mixed phase of MoV₂O₈ composition.

The bioavailability of many soil contaminants depends on their interaction with the soil organic matter. The paper presents a new approach of using stable paramagnetic spin labels for investigating the kinetics of covalent binding of specific xenobiotic functional groups with humic acids, a major organic matter fraction. Leonardite humic acid (LHA) was incubated with the nitroxide spin labels amino-TEMPO (4-amino-2,2,6,6-Tetramethylpiperidin-1-oxyl) and anilino-NO (2,5,5-Trimethyl-2-(3-aminophenyl)pyrrolidin-1-oxyl), respectively, which contain an aliphatic or aromatic functionality susceptible to interaction with LHA. Electron spin resonance spectra of LHA samples without and with the enzyme laccase were recorded at X-band frequency (9.43 GHz) at room temperature and neutral pH. Binding was detected by a pronounced broadening of the spectral lines after incubation of LHA for both spin labels. The development of a broad signal component in the spectrum of anilino-NO indicated the immobilization due to strong binding of the aniline group. The reorientational correlation time of bound anilino-NO is more than two orders of magnitude greater than that of the free label. The ratio of the amount of bound to the unbound species was used to determine the kinetics of the covalent bond formation. Reaction rate constants of 0.16 and 0.01 min⁻¹ were determined corresponding to half-times of 4.3 and 69.3 min, respectively. Treatment of LHA with laccase enhanced the amount of the reacting anilino-NO species by a factor of 7.6, but left the reaction rate unaltered. Oxidative radical coupling was excluded using the spin trap agent n-tert-butyl-alpha-phenylnitrone.

In this paper, a Fourier analytical method to calculate temperature distribution of uniplanar gradient coils for unilateral nuclear magnetic resonance (NMR) magnet is presented. A model of uniplanar gradient coils used for unilateral NMR magnet is presented. Fourier analysis reveals the structure of the spatial filters that solve the two-dimensional screened Poisson equation and shows the temperature distribution to be a well-defined sharpen filter of the dissipated power. Subsequently, target field method is used for the gradient coil design for unilateral magnet and the hot spot temperature of the uniplanar gradient coils with different sharpen filters are compared through simulation. Practical measurement has shown that the structure of the spatial filters made a great contribution to the distribution of the hot spot temperature.