Magnetic Resonance in Chemistry最新文献

Spinocerebellar ataxia 12 (SCA12) is a progressive degenerative neurological disorder, primarily characterized by impaired coordination and balance. To investigate the correlation between proton (¹H) magnetic resonance spectroscopy (MRS) and structural imaging indices in patients with SCA12. T1-weighted MRI, DTI, and single voxel MRS point resolved spectroscopy (PRESS) in the left hemispheric cerebellum were acquired using a 3-T MR scanner in 40 SCA12 patients and 25 healthy controls. Correlations between metabolites, gray and white matter volume of lobules, fractional anisotropy (FA), and clinical, nonclinical, and genetic data were examined. Three machine learning algorithms (KNN, LDA, and SVM) were used to analyze the metabolic feature differences between SCA12 and HC groups. Significant decreases in choline (Cho [GPC (glycerophosphocholine) + PCh (phosphocholine)]) and N-acetyl aspartate (NAA) levels, along with increases in myo-inositol ratios to creatine, FA, and white matter volume values (p < 0.05), were observed in the cerebellum of the SCA12 group compared to healthy controls. Positive correlations were observed between NAA levels and cerebellar lobule volume, the SPM IQ score with the right crus II in the SCA12 group. The International Cooperative Ataxia Rating Scale (ICARS) score showed a negative correlation with white matter and specific cerebellar lobules. Disease duration and cytosine, adenine, and guanine (CAG) repeat length were negatively correlated with right lobule VIIIB, lobule IX, and left lobule X. Machine learning algorithms achieved an accuracy of over 95% in MRS data, and 88.89% in volumetric data. MRS, VBM, and DTI techniques reveal neuronal degeneration in SCA12 compared to healthy individuals.

The spin Hamiltonian parameters (SHPs) (g factors g_// and g_⊥ and hyperfine structure constants A_// and A_⊥) and their concentration (x) dependences for Cu²⁺ in xNaI·(30–x)·Na₂O·70B₂O₃ (5 ≤ x ≤ 25) glasses are theoretically investigated in a consistent way. The [CuO₆]¹⁰⁻ complexes are subject to the Jahn–Teller effect, leading to the relative elongations of about 7%. The concentration dependences of the SHPs are suitably attributed to the nonmonotonic piecewise relationships of cubic field parameter, covalency factor, relative tetragonal elongation ratio, and core polarization constant with NaI concentration x due to the modifications of local crystal fields and electron cloud distribution around impurity Cu²⁺. The calculated cubic field splittings E₁, g factors, and A_// at various concentrations x agree well with the measured results, and the values of corresponding A_⊥ are also predicted. The properties of optical and EPR spectra are discussed, and the microscopic mechanisms of the concentration dependences of the related quantities are also analyzed.

A chemical investigation of the 95% EtOH extract of Dendrobium nobile Lindl. led to the isolation of one new sesquiterpene component (1), together with one known compound (2). Its structure was completely and unambiguously assigned by 1D and 2D NMR spectra (¹H NMR, ¹³C NMR, HSQC, HMBC, COSY, and NOESY), and HR-ESI-MS spectroscopic analysis and the absolute configuration was confirmed by ECD calculation.

The hydroethanolic extract obtained from the seeds of Annona diversifolia Saff (Annonaceae) fruits was analyzed to obtain a new cycloheptapeptide, called papaucin (1) or cyclo(-Pro¹-Val²-Ile³-Thr⁴-Asn⁵-Leu⁶-Gly⁷-). Its molecular structure was determined using 1D and 2D NMR spectroscopic techniques (¹H, ¹³C, HSQC, COSY, HMBC, and TOCSY) and MALDI-TOF mass spectrometry. Additionally, the antiprotozoal activity was evaluated. Papaucin (1) showed moderate positive activity compared with in vitro assays of Entamoeba histolytica and Giardia lamblia, with IC₅₀ values of 63.07 and 67.62 μg mL⁻¹ respectively. On the other hand, in silico studies revealed a higher affinity of papaucin for the PFOR enzyme compared with metronidazole, as evidenced by a greater number of polar interactions. Regarding the ALR enzyme, papaucin also showed affinity, although at a binding site different from the main catalytic site. These results suggest that papaucin could exert its antiprotozoal effect through multiple mechanisms.

NMR spectroscopy under magic angle spinning (MAS) conditions can be employed to study the freezing of aqueous solutions and gel-like systems without the need for specialized equipment. This is attractive as one sample can be studied in its liquid and solid form without changing the experimental setup. There are multiple areas that benefit from such an analysis. Here, we will thoroughly study the freezing process of various aqueous systems containing multiple NMR-active nuclei (¹H, ¹¹B, ¹³C, ²³Na, and ⁷⁹Br) to gain detailed insights into what the prerequisites are, what problems one must be aware of and what limitations arise, how reproducible the measurements are, and what additional information can be gained from them for different sample types. As a further aspect it will be shown how the described setup can be used for the study of aqueous systems in solution at subfreezing conditions.

The local structures and the electron paramagnetic resonance (EPR) g factors of Cu²⁺ centers in GdBa₂Cu₃O_7-Δ and La_0.5Gd_0.5Ba₂Cu₃O_y are theoretically studied by using the perturbation formulas of the g factors for an orthorhombically elongated octahedral 3d⁹ cluster. In these formulas, the crystal-field parameters (CFPs) are determined from the superposition model and the local distortions due to the Jahn–Teller (JT) effect. Based on the calculations, the Cu-O bond lengths are found to experience the axial elongations δz (≈0.052 and 0.055 Å) along the c-axis and the planar bond length variations δr (≈0.061 and 0.128 Å) in the perpendicular (ab) plane for the orthorhombic Cu²⁺ centers in GdBa₂Cu₃O_7-Δ and La_0.5Gd_0.5Ba₂Cu₃O_y, respectively. The calculated g factors are in good agreement with the experimental data. The local structures of both Cu²⁺ centers are discussed.

Peptide-based supramolecular hydrogels are well known for their biocompatibility and the various range of applications in biotechnologies. The grafting of nucleobases along with the multicomponent approach allows a fine tuning of the hydrogel properties to match new uses. Such adjustments rely on a precise understanding of the material at the atomic level, and nuclear magnetic resonance (NMR) spectroscopy is a tool of choice for soft matter study. High-resolution NMR and fast-field cycling NMR relaxation can be used to investigate the hydrogel gelation process through the study of the gelator signal and the water dynamical behavior along the gelation time. NMR dispersion profiles can also bring insights into the presence of different water pools and their mobility inside the hydrogel matrix by modeling dispersion curves and extracting correlation times. Measurements were performed at two different temperatures, 295 K and 313 K. Examining the effect of temperature provides insight into the mechanism underlying the transition from solution to gel. This approach highlights not only how an increase in temperature influences the gelation process but also how it affects solvent dynamics within the gelator structure.