Applied Magnetic Resonance最新文献

The EPR spectrum of the Gd³⁺ ion in the elpasolite-type Rb₂NaYF₆ crystal has been discovered and studied. It is established that the paramagnetic Gd³⁺ center has cubic symmetry at T = 295 K. The parameters of the corresponding spin Hamiltonians are calculated. A structural model of the complex is proposed. The experimental results are analyzed by comparison with those for the paramagnetic Gd³⁺ ion in other lattices.

A signal observed out-of-phase with the microwaves in continuous wave EPR, predicted by theories in the early 1960’s, changed the then-existing paradigm to study Heisenberg spin exchange of radicals in solution. This is a brief history of the importance and use of that signal, which we call DIS. Since those early days, several important paradigm changes have occurred, all requiring a role for DIS. We outline our perception of those changes.

Electron spin resonance (ESR) measurements under multi-extreme conditions are extremely useful for exploring novel physical phenomena in condensed matter physics. However, achieving high magnetic fields, high pressures, and high sensitivity simultaneously is still challenging. In this study, we have developed basic techniques separately to achieve this goal. Using a pulsed magnetic field, we have succeeded in obtaining ESR spectra of a sample in a pressure cell up to 30 T. To improve sensitivity, we used a high output power light source gyrotron, and we achieved a 10-fold improvement in sensitivity compared to previous high-pressure ESR measurements using Gunn oscillators. Because breakthrough is needed to enable reaching higher pressures without reducing sensitivity, in this study, we focused on using the optically detected magnetic resonance of the NV(^{-}) center, and we observed it successfully in a diamond-anvil cell. The combination of these techniques offer a promising direction for future ESR measurements in more extreme environments.

In this review, we present a novel technique for terahertz (THz) electron spin resonance (ESR) spectroscopy using broadband frequency-tunable photomixers. These photomixers offer unique advantages, such as continuous and broadband frequency tunability, enabling high-resolution ESR spectroscopy in the THz region. Our technique can be applied to both field- and frequency-swept ESR setups, covering a wide frequency range of up to 1.1 THz and magnetic fields of up to 10 T. We also demonstrate an application to antiferromagnetic resonance spectroscopy. A comparison is made with other frequency-domain ESR techniques using continuous-wave and pulsed THz sources to emphasize the characteristics of our technique.

The use of EPR spectroscopy for studying spin crossover (SCO) is often limited due to the fact that a large number of complexes do not have an EPR signal in X- and Q-bands. At the same time, EPR spectroscopy, being insensitive to diamagnetic impurities and having excellent sensitivity to paramagnetic centers, provides unique advantages compared to direct current magnetometry. In this paper, we propose a method for detecting the thermal spin transition in a spin crossover Fe(II)-based complex by pulsed EPR in the direct dimension with a specially designed spin-probe. The spin probe is non-contact and reusable, consisting of an ampoule of 1 mm diameter filled with a Finland triarylmethyl radical. To detect the SCO transition, the probe is surrounded by a powder of the SCO complex under investigation. In such a design, the transition can be observed through the shift of the line in the EPR spectrum of the spin probe. The latter occurs due to an addition to the external magnetic field of the spectrometer caused by the transition of the spin crossover complex to a high-spin state, in which it demonstrates paramagnetic properties. The experimental results showed that the proposed method allows one to register a transition in [FeL₂][BF₄]₂ complex, where L is 2,6-di(pyrazol-1-yl)pyridine, in the temperature range of 260–262 K with a 2 K wide hysteresis. The change in the local magnetic field at the location of the spin probe of about 0.004 mT was registered, which is in agreement with the numerical calculations performed.

In this study, several pharmaceutical compounds commonly used in the treatment of heart failure, namely, ramipril, clopidogrel, indapamide, and atorvastatin calcium in their pure powder forms, were subjected to gamma irradiation. The resulting irradiated samples were analyzed using Electron Paramagnetic Resonance (EPR) spectroscopy over the temperature range of 130–300 K. Spectroscopic parameters were determined, and the molecular structures of the radiation-induced paramagnetic species were elucidated. The radicals detected in the irradiated samples were assigned to specific molecular fragments: –CH₂CH₂ĊCOOHC₂H₅NH–, –NCH₂ĊHCH₂–, –NĊCH₃CH₂–, and –NCH₂ĊHCH–, respectively. Notably, these paramagnetic species exhibited considerable stability, persisting at room temperature for over 2 months. The experimental EPR spectra were also subjected to computer simulation to determine the g values of the identified species. The findings were compared with the existing literature and evaluated in the context of previous studies on irradiated pharmaceutical compounds.

Quantitative nuclear magnetic resonance (qNMR) is considered as a powerful tool for measuring the absolute amount of small molecules in complex mixtures. In this study, the performance of quantitative analysis on low-field NMR (LF NMR) devices was evaluated for a representative set of 33 finished medicinal products. Sample preparation, critical acquisition, and processing parameters were systematically evaluated. Recovery rates varied between 97 and 103% were achieved by signal-to-noise ratio (SNR) equal to 300 using deuterated solvents. For non-deuterated solvents, the recovery rates between 95 and 105% were observed at this SNR value. Average bias values in comparison with the reference high-field NMR were found to be 1.4% and 2.6% for deuterated and non-deuterated solvents, respectively. Erroneous results can be obtained for non-deuterated solvents when the integrated signals are situated close to solvent suppression regions. Validation results in terms of precision and reproducibility demonstrate that the LF qNMR method is fit-for-purpose for the marketed pharmaceutical products.

High-spin metallocomplexes having sizable zero-field splitting (ZFS) parameters feature in both exotic magnetic materials and many biological systems. The magnetic properties of such compounds have frequently been determined by X-band ESR spectroscopy with the help of fictitious spin-1/2 Hamiltonian approaches. The determined g^eff-values, however, never agree with those (g^true-values) of the true g-tensors, which are obtained from precise quantum chemical calculations. In this work, we have revisited the X-band ESR spectra of four important penta-coordinated cobalt(II) complexes (complex 1 and 2, A. A. Fischer, et al., Dalton Trans. 46, 13, 229 (2017); complex 3 and 4, P. Kumar, et al., J. Am. Chem. Soc. 141, 10, 984 (2019), P. Kumar, et al., Inorg. Chem. 59, 16, 178 (2020)) in their quartet states. We use the exact relationships for the g- and hyperfine tensors derived using the fictitious spin-1/2 and true spin Hamiltonian (SH). Double perturbation treatments combined with the Zeeman and hyperfine interaction perturbations have been invoked to derive the relationships, giving physical insights into the complex exact relationships. The accuracy of the simplified relationships relevant to hyperfine tensors has been examined compared with the exact ones. The full sets of the principal values of the g-, hyperfine, and rank-2 ZFS tensors of the complexes have been evaluated from the canonical peaks of the |M_S =  ± 3/2 > -dominant transitions as well as the weak peaks attributed to the |M_S =  ± 1/2 > -dominant transitions. The absolute D-values amount to ~ 10 cm^–1 (D < 0) for complexes 1–3. Quantum chemical calculations for the true magnetic tensors provide their salient electronic structures, which have not been considered in the previous works.

For the first time, the widespread model of spin exchange between paramagnetic particles in dilute solutions of paramagnetic particles is introduced as one paper. This model has served for decades as a useful tool for qualitative assessments when planning experiments and interpreting experimental results. It qualitatively interpreted peculiar manifestations of the spin exchange: the concentration broadening of the resonance lines in EPR spectra in the case of the slow rate of the spin exchange and the exchange narrowing of the EPR spectra when the fast rate of the spin exchange is realized. Here are presented results that do not agree with the widespread understanding of spin exchange in dilute solutions of paramagnetic particles. This widespread model of the spin exchange was never formally named a “paradigm”. But this set of ideas was widely accepted and shared by scientific community, functioned as one framework guiding how scientists understood and interpreted results concerning spin exchange. In light of shift to a new paradigm, which was presented in 2019, I refer to these widespread ideas and understanding of spin exchange as widespread paradigm.

Recently, Salikhov formulated a new paradigm of spin exchange. The basic statement of this paradigm is that due to the spin coherence transfer from the interaction partner in course of random bimolecular collisions of paramagnetic particles collective modes of electron spin magnetization motion in dilute solutions are formed. Here are presented some peculiar features in the concentration dependence of the EPR spectrum shape of ¹⁴N nitroxide radicals solution. Experimental results are in a good agreement with theoretical predictions of the new paradigm of spin exchange and its manifestations in EPR spectroscopy.