Applied Magnetic Resonance最新文献

It is acknowledged that a solid-state foundation for qubit implementation can be found in optically active high-spin vacancy-type defects (color centers) in semiconductors. Silicon carbide (SiC) crystals serve as a reliable host for defects, positioning them as strong competitors to the well-known nitrogen vacancy ({NV}^{-}) centers in diamond. This paper reports on photoinduced electron paramagnetic resonance (W-band, 94 GHz) spectroscopy measurements on 4H and 6H polytype SiC crystals which exhibit distinct optically polarizable color centers due to their unique structural and electronic properties. Spin defects such as negatively charged nitrogen vacancy centers and divacancies excited at 532 nm, are present in 4H-SiC. By contrast, only ({NV}^{-}) centers excited at 980 nm are found in 6H-SiC across a wide temperature range. These features make the 6H-SiC color centers promising for quantum technologies because of their excitation and luminescence in the near-infrared telecommunications range, as well as their ability to selectively target the resonant excitation of individual-based qubits.

The local ordering and features of the molecular mobility of water confined in voids of a pure silica mordenite were studied using the molecular dynamics simulation over a temperature range from 298 to 163 K. The simulated system was a fragment of mordenite consisted of 2 × 2 × 4 unit cells filled with 384 water molecules. Three different water models: SPCE, SPCF, and TIP5P were considered. To study the effect of nanoconfinment, the results were compared with bulk water. The modeling suggests that at room temperature, a 2D (in c and b directions of the mordenite cell) water diffusion takes place, while upon cooling, the diffusion in b direction essentially slows down. The analysis of microstructure shows that the pores prevent the formation of a full tetrahedral structure of water environment that results in formation of several water substructures. A detailed analysis of water reorientational motion was carried out and the activation energies were determined from temperature dependences of the correlation times. Of the three water models considered, SPCE demonstrated the best performance. The results obtained can be helpful for interpretation of experimental temperature dependences of NMR relaxation rates for water molecules confined in porous media with complex topology.

Schiff bases allow the creation of compounds with a wide variety of architectures and properties and have been of interest to researchers for many years. This mini-review describes some of the possibilities of the EPR method, which we use to study Fe(III) complexes with polydentate Schiff bases, many of which have been synthesized for the first time. Obtaining information at the local level using EPR spectroscopy allows us to grasp the molecular structure–property relationship and to adjust the synthesis strategy to create multifunctional substances with predetermined properties.

A more detailed insight into the chemical kinetics and dynamics of chemical exchanges within a molecule or between molecules in liquids is made possible by the NMR CPMG method, which, in addition to the exchange rate, gives its power spectrum, which contains information about the underlying processes of chemical exchange. The applicability of the method is demonstrated by measuring the chemical exchange in an aqueous solutions of sucrose, whose rate spectra have shapes that cannot be explained as transitions in a double potential well, but after interpretation using the chemical Langevin equations, it can be explained as a cascading chemical transition across several intermediate potential walls.

We celebrate 80 years of EPR with a special issue of Applied Magnetic Resonance featuring both reviews and regular research articles. The focus is new opportunities for application of EPR and new directions for development of EPR. This introduction concisely surveys the scope of EPR and hints at future developments.

We examine the electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy of three quite distinct high-spin Mn(II) systems and describe experimental techniques and methods of analysis that are useful in their study. We demonstrate that this S = 5/2 metal center provides useful orientation-selection through the Zero-Field Splitting (ZFS) tensor that enables determination of a ¹³C hyperfine-coupling tensor with extremely small hyperfine interaction. We also demonstrate that Mims suppression effects can be used in concert with orientation-selection to edit complex ^[1,2]H ENDOR patterns that can be produced by even a ‘simple’ center with a single Mn(II). We develop a perturbation-based approach to understanding second-order shifts in Mn(II) ENDOR responses that occur in systems with intermediate ZFS values, and show that these shifts can be used to estimate the values of the ZFS tensors.

Lignin is the second most abundant biological polymer on Earth with a complex chemical structure. A large amount of different technical lignins are produced as a waste product of the pulp and paper industry and are not used rationally. The study of the structure of such lignins is relevant due to their potential applications. It is important to obtain comprehensive knowledge about the structure of lignin macromolecule and to classify lignins based on it. High-resolution nuclear magnetic resonance (NMR) experiments for dissolved samples are widely used to study this biopolymer. However, this approach does not allow researching insoluble technical lignins. Solid-state NMR spectroscopy may become a solution to this problem. In this paper, we propose an approach to classify the degree of lignin alteration by clustering of solid-state spectra with hierarchical cluster analysis method. This approach is important because of the lack of direct correlations between the NMR spectra of lignins in the dissolved and solid states, which is based on experimental data.

Respiratory diseases are the leading cause of death and disabilities worldwide. Current clinical approaches are based on computed tomography and positron emission tomography which use harmful ionizing radiation and cannot be used often. Because of that, proton MRI is a promising tool for functional lung assessment. PREFUL MRI method was shown to yield promising results for future clinical use, however, no standard imaging protocols or computer programs which do not require human supervision exist. Therefore, the purpose of this study was to make a step toward automating and improving robustness of the PREFUL method. Several algorithms were designed including phase sorting for respiratory and heart cycles, image registration and lung segmentation. Ten healthy volunteers underwent PREFUL MRI study and maps of fractional ventilation (FV) and perfusion (Q_quant) were calculated. The maps showed no sign of any pathology and among all healthy volunteers the mean values of FV and Q_quant were 0.21 ± 0.08 and 460 ± 140 ml/min/100 ml, respectively. The obtained results are well agreed with known research data. Thus, our designed automated algorithms for PREFUL MRI can be implemented for assessing ventilation and perfusion of the lung.

With a view to developing a procedure for the differentiation of cinchonine derivatives from cinchonidine derivatives by NMR analysis, experimental data on cinchonine and cinchonidine, after their dissolution in different solvents (CDCl₃, CD₃OD and DMSO-d₆), were compared with theoretical data, originating from different methodologies: DP4, DP4+ , J-DP4 and ANN. Taking into account the lower computational consumption, as well as the greater efficiency in differentiation, the method selected was the trained artificial neural networks (ANN), which considered only the ¹³C data from the quinuclidine ring. The method successfully differentiated derivatives originating from OH group protection in ester and ether forms; replacement of the OH group by F and NH₂; insertions of N₃, 1H-1,2,3-triazol-1-yl and CH₃O groups, linked to the quinoline ring; conversion of the vinyl group to the 1-benzyl-1H-1,2,3-triazol-4-yl; and of hydrogenation, dehydrogenation, and bromination of the vinyl group. In all cases the application of the ANN method succeeded in differentiation of cinchonine from cinchonidine derivatives.

Properties of two lowest electron levels of the Fe²⁺ impurity ion in a natural amethyst are studied by continuous wave electron paramagnetic resonance spectroscopy in the Q-band. It is established that the these levels present quasi-doublet (left| { pm 2} rightrangle)with zero-field splitting of 30.9 ± 0.2 GHz. Orientation of principal magnetic axes and value of g-factor of this paramagnetic center are determined.