Applied Magnetic Resonance最新文献

The study aimed to compare lipid proton concentrations across three fatty liver models, highlighting induction methods and differences in hepatic protonation identified through magnetic resonance spectroscopy (MRS) analysis to gain insights into fatty liver pathogenesis and potential therapeutic approaches. This research sought to induce various conditions of fatty liver and examine disparities in hepatic protonation patterns through meticulous MRS analysis. The models for fatty liver in mice were established using distinct methods including ethanol feeding, MCD diet, and CCl₄ injection. MRS was utilized for lipid proton analysis, with data processed using LCModel software. Statistical analyses encompassed profile comparisons via OPLS-DA, consistency evaluations using Kendal correlation, assessments of concentration differences via Mann–Whitney U test, and an exploration of lipid accumulation influences through Spearman's correlation analysis. All three fatty liver models displayed hepatic fat infiltration rates exceeding 40%, with the MCD model showing the highest rate at 52.46%. Analyzing the lipid protons, a higher concentration of methylene protons was observed in the NIAAA model compared to the other groups. Additionally, there were notable distinctions in the composition values of specific lipid protons across the models, highlighting varying trends in fatty acid deposition. The correlation and composition analysis provided insights into the different patterns of lipid accumulation in each model, with significant correlations identified among various lipid protons. Furthermore, differences in the composition values of specific lipid protons indicated distinct characteristics of fatty acid profiles in the different fatty liver models. No significant differences were found between the NIAAA and CCl₄ models, but the MCD model exhibited higher deposition of polyunsaturated bonds, specifically diallylic protons, compared to other groups.

The oligomerization of many peptides is known to be influenced by the binding of transition metal ions, with intermolecular metal–ion bridges being one possible mechanism. In the case of copper ions, it is possible to identify Cu²⁺ bridges between peptide monomers using EPR spectroscopy by analyzing the metal–ligand hyperfine structure in the spectra of a mixture of two peptides, each having the same amino acid sequence but a different isotopic content. This isotopic dilution method was previously used to show that the N-terminus of the misfolding peptide α-synuclein forms antiparallel Cu²⁺-bridged dimers, and such a quaternary structure was also proposed for the Cu²⁺-bound form of another misfolding peptide, β-amyloid (Aβ). To investigate this possibility, the isotopic dilution strategy was applied to the Aβ1–16 peptide, which contains the complete N-terminal Cu²⁺-binding domain of Aβ. Rigorous analysis of the superhyperfine structure in experimental and simulated low-frequency EPR spectra provided no conclusive evidence for Cu²⁺ bridging of Aβ monomers in the pH range 6.5–8.5.

Incorporating the effects of spin coherence transfer into the theory of spin exchange during random molecular collisions opens new perspectives for understanding the processes in this field. The elementary excitations of the collective modes - which describe the dynamics  of the average values of the transverse magnetization components in a subensemble of radicals with different resonance frequencies - can be treated as quasi-particles. Through their interaction with the microwave field, these quasi-particles hybridize to form a new type of quasi-particle: spin polaritons. Theoretical studies have predicted the formation of spin polariton sunder strong  microwave fields. This paper presents one more experimental evidence for the dependence of the spin ensemble's resonance frequencies on microwave power, obtained from studies of TEMPOL-15N nitroxide radical solution in toluene.

Sludge dewatering is a critical stage in sludge treatment, directly influencing the efficiency and environmental risks of subsequent disposal. This study systematically investigated the optimization of sludge dewatering by analyzing the matching relationship between the pore size of filter media materials and sludge particle size. The equivalent pore sizes of materials (e.g., nylon fabrics, geotextiles) were determined using nuclear magnetic resonance (NMR) and a machine learning-based image analysis method (IAM). Model experiments evaluated their dewatering performance. Results demonstrated that NMR, based on transverse relaxation time (T₂) inversion, achieved high accuracy for hydrophilic multilayer materials like geotextiles (errors < 11%), while IAM showed ± 10% error for hydrophobic single-layer materials (e.g., nylon fabrics) but up to 53.91% error for geotextiles due to complex fiber interweaving. Optimal dewatering was achieved when the filter media pore size (O95) matched the sludge’s volume-mean particle size (D[4,3]). The 400-g/m² geotextile (pore size: 65 μm) exhibited the best alignment with the sludge’s D[4,3] (63.54 μm), yielding a relatively low cake moisture content and significantly reduced filtrate turbidity. This study provides a theoretical foundation for filter media selection and highlights the importance of pore size-particle size matching in enhancing dewatering efficiency, offering practical guidance for engineering applications.

The shape of the EPR spectrum in conditions when spin exchange is an essential feature of the spin system contains peculiar information about molecular mobility. The mathematical model of such systems is the paradigm of collective modes developed by Kev Salikhov in the last 10 or more years (Molin et al., Spin Exchange: Principles and Applications in Chemistry and Biology, Springer-Verlag, New York, 1980; Salikhov, Appl. Magn. Reson. 47:1207–1227, 2016; Salikhov, UFN 189:1017–1043, 2019). Our task was to extract the quantitative parameters of this model from experimentally obtained spectra and correlate them with the physical characteristics of the environment in which the measurements were taken. Thus, our idea, if successfully developed, can be used to determine the characteristics of molecular dynamics in a wide variety of objects, such as membranes, glasses, colloidal systems, semiconductors, and superconductors.

It has been shown that the preservation of nitric oxide (NO) in the tissues of animal and human organs, despite the presence of a significant amount (up to several millimoles) of oxygen (O₂) as an oxidizer of NO, can be due to two reasons. The first, trivial one is determined by the low rate of NO oxidation by oxygen at its concentration of less than 10 μM, at which the remaining amount of NO is sufficient to implement its biological effect, for example, the ability to exert a vasodilatory effect on blood vessels. At NO concentrations of 50 μM or more, for example, in activated macrophages, an increase in the NO oxidation rate can sharply decrease the NO concentration in macrophages and thereby weaken their immune activity. In this case, NO oxidation is prevented by its inclusion in EPR-active dinitrosyl iron complexes (DNICs) with thiol-containing ligands. The formation of these complexes is determined by the competitive inclusion of a divalent weakly bound ("free") iron ion instead of an oxygen molecule into the dimeric form of NO, as a target for the oxidative action of oxygen on NO. The inclusion of NO in DNICs not only stabilizes NO, but also leads to the transformation of half of it in these complexes into nitrosonium cations (NO⁺). As a result, DNICs with thiol-containing ligands can act in the body of animals and humans not only as donors of NO molecules as positive regulators of various metabolic processes, but also as NO⁺ cations as negative, cytotoxic agents.

Spin exchange interaction between nitroxide radicals (R) and transition metal ions such as Cu(II) and Zn(II) has been studied. In this work, basing on the results obtained on the analysis of [Polymer–Cu(II)–R] systems, we demonstrate peculiarities of small molecules diffusion inside such systems in aqueous solutions of complex-forming polymers: partially alkylated poly(4-vinylpyridine) (P4VP-β), poly(2-methyl-5-vinylpyridine) (P2M5VP-β), branched (BPEI) and linear (LPEI) poly(ethylenimine). The metal ion nature, concentration, spin–lattice relaxation time, the spin probe electric charge and size manifested significant effect on the collisions between Cu–polymer complexes and R. Correct selection of the radical (probe) makes possible obtaining reliable information on the structure of polymer–metal complexes in solutions and about the fraction of the functional groups of a macromolecule involved in the formation of complexes of various types. We believe that the spin-exchange titration (SET) approach will be useful for elucidation peculiarities of small molecules intercalation into ion-exchange resins, supported catalysts based on various nano- and micro-porous organic and inorganic carriers.

Structures of two new spiro-adducts synthesized on the basis of [3 + 2]-cycloaddition reaction of stable azomethine ylide with styrene and 2,3-dihydrofuran, respectively, were defined by NMR methods. Complete signal assignments in ¹H spectra of both compounds were obtained on base analysis of COSY and NOESY experiments by determination of scalar networks in the first case and spatial interactions in the second one, respectively. The identification of aromatic proton signals of indan-1.3-dione fragment was made on base registration of long-range NOEs between them and aliphatic protons which are located at the distances up to 6 angstroms. These proton assignments were helpful for the identification of carbon signals in ¹³C NMR spectra of compounds under study which were performed by combination of HSQC and HMBC data. Thus, the results of the consistent use of homonuclear (COSY, NOESY) and heteronuclear (HSQC, HMBC) allowed us to make a complete and unambiguous NMR description of two new spiro-adducts and prove their belonging to one of the four synthetically possible regioisomers: (2'SR,7a'RS)-2'-phenyl-1',2',5',6',7',7a'-hexahydrospiro[indene-2,3'-pyrrolizine]-1,3-dione) and (3aSR,3bSR,8aSR)-2,3,3a,3b,4,5,6,8a-octahydrospiro[furo[3,2-a]pyrrolizine-8,2'-indene]-1',3'-dione). The possibility of the existence of the second regioisomer in solution in the form of a fast (in the NMR time-scale) conformational exchange associated with pseudo-rotation around the CH₂–CH₂ bond in the ethane fragment of the oxygen-containing five-membered ring was detected.