Applied Magnetic Resonance最新文献

NMR diffusion measurements have the promise to provide deep insight into chemical reactions and processes including self-assembly, reaction kinetics, crystallization, and binding. However, when the chemical system alters on the timescale of the diffusion measurement, great care must be taken in both the performance and interpretation of the data. This paper considers the various NMR diffusion timescales, some of the problems that arise with time-variant systems, and various ways that the problems can be removed or at least reduced.

The magnetization process of the (S=1/2) distorted diamond spin chain with the Dzyaloshinsky–Moriya interaction is investigated using the numerical diagonalization of the finite-size cluster. Although the spin gap cannot be observed by ESR because of the spin conservation law, it is sometimes possible to detect due to the Dzyaloshinsky–Moriya interaction. When the spin gap at the 1/3 magnetization plateau of the natural mineral azurite is possibly observed by ESR, the selection rules with respect to the relative angle between the external magnetic field and the Dzyaloshinsky–Moriya interaction are theoretically predicted.

A method of secondary quantization with a non-orthogonal basis for calculating the electronic structure of paramagnetic fragments in a crystal lattice is described. The method is applicable to fragments of arbitrary symmetry. The main stages of the calculation are illustrated using the example of a LaMnO₃ crystal. The splitting of the ground state of the Mn³⁺ ion is calculated beyond approximation of the axial symmetry of individual Mn³⁺–O²⁻ pairs. Multicenter integrals within the MnO6 cluster are calculated on the Hartie–Fock wave functions of free ions. An original method of accounting for electrostatic fields from remote lattice ions is used.

The two sites water exchange model (2SWEM) and the three sites exchange model (3SEM) were properly used to describe proton (¹H) magnetic relaxation dispersion (¹HMRD) in human serum albumin (HSA) solutions at 310 K. Lyophilized HSA was obtained from Sigma-Aldrich and diluted in phosphate buffered saline (PBS, pH 7.4) to obtain 10 samples with a concentration of 50 g/l. The ¹HMRD profiles (20–60 MHz) were obtained using a fast field cycling nuclear magnetic resonance relaxometry facility (Stelar FFC 2000 Spinmaster) and two Minispec (Mq20, Mq60) relaxometry facilities from Bruker. The longitudinal ¹H magnetic relaxation time (T₁) was measured employing the inversion recovery pulse sequence and the 1/T₁ was plotted as a function of the frequency of resonance to create the ¹HMRD profiles. The 2 sites water exchange model considering ellipsoidal geometry is the best option to fit the ¹HMRD profiles in diluted HSA solutions, which allows to update the physical model previously presented to describe the theoretical dependence between the transverse proton magnetic relaxation rate and the protein dynamic viscosity in blood plasma and blood serum solutions. The physical parameters obtained from the fit, using this model, describe properly the diluted HSA solutions in comparison with previous experimental reports and theoretical estimations. This result can be improved taking into consideration all the proton–proton dipolar interactions of the protons belonging to the bound water molecules.

In this work, we investigate the effect of gold nanoparticles of different shapes on the structural and dynamic properties of l-tyrosine in aqueous solution. Using ¹H NMR spectroscopy, NOESY, and ¹H NMR relaxation methods, we studied the interactions between l-tyrosine and gold nanoparticles of spherical shaped, star shaped, and rod shaped focusing on their effects on the molecular conformation. Particular attention was paid to the extent to which particles of different shapes affect the structural and dynamic properties of the l-tyrosine molecule. Based on the ¹H NMR spectroscopy data, T₁ relaxation studies, and NOESY cross-peak intensities, we conclude that gold nanoparticles of different shapes exert diverse effects on conformational behavior of the l-tyrosine in aqueous solution. Different changes in interproton distances were found depending on the nanoparticle shape. The presence of nanoparticles in an aqueous l-tyrosine solution induces a reorientation of the –CH₂–CH–COOH chain relative to the aromatic ring. Understanding the processes of conformational changes in AST under the influence of AuNPs, as well as the role of their functional groups binding to AuNPs, has important practical applications for the development of therapeutic agents against Alzheimer’s and Parkinson’s and cardiovascular deceases, associated with aggregation processes and its inhibition.

It is generally accepted that the resonant homogeneously broadened line of the EPR spectrum has a Lorentz shape. However, in the presence of the spin exchange process, this is not the case. The resonant line of the spectrum has a mixed shape. It can be represented as the sum of two Lorentzian curves: absorption and dispersion. This follows from the solution of kinetic equations for ensembles of magnetizations. These equations take into account the processes of coherence transfer and decoherence that arise in the presence of spin exchange and dipole–dipole interaction. From the concentration dependences of the absorption and dispersion contributions, one can obtain the rate constants due to the spin exchange and dipole–dipole interaction. In this work, we present decomposition of experimental spectra of nitroxide radical [15N]-4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl in toluene. From this decomposition, the values of the rate constants were found. All presented experimental spectra were obtained in the linear response conditions.

We report the Heisenberg spin-exchange of electro-neutral and negatively charged spin probes in the room-temperature ionic liquids (RTILs) investigations in a wide temperature range. The contributions of spin-exchange and dipole–dipole interactions of radicals into EPR spectrum line shape were separated by analyzing the temperature dependence of the concentration line broadening. Translational diffusion coefficients and effective activation energy of translational mobility were determined and compared with rotational correlation times and effective activation energy of rotational mobility. Formation of charged and uncharged domains in RTILs was clearly demonstrated by comparing the dynamic parameters for charged and uncharged probes. The influence of repeated collisions of radicals in the matrix cage on spin exchange was specially studied.

Several physical processes produce similar effects in electron paramagnetic resonance (EPR) spectroscopy that are often collectively characterized as exchange. One common description of the exchange effects is based on stochastic changes in the EPR frequency. This general treatment has been adapted and modified for each specific type of exchange. But the general treatment can provide insights into the mechanisms and appearance of exchange.

Quantum magnonics is an emerging field of research with great potential for applications in quantum technologies, including quantum computing, information processing, and coding. Of particular interest is magnon Bose–Einstein condensation, which can occur even at room temperature due to the small mass of magnons and their weak interaction even at high concentrations. The article describes unique experimental results obtained in the study of the phase transition from magnon gas to Bose condensation with increasing magnon density. It is shown that the properties of a magnon gas are well described by the quasi-classical Landau–Lifshitz–Gilbert equations. However, upon transition to the quantum state of Bose–Einstein condensation, the properties of magnetization precession change dramatically. Instead of spin waves formation outside of the magnon generation region, coherent precession of magnetization occurs. In this paper, attention is drawn for the first time to the change in the direction of phase gradients at the boundary of the magnon excitation region and an explanation of this effect is given. The experiments were carried out in a Yttrium Iron Garnet film under the continuous RF pumping.