Magnetic Resonance in Chemistry最新文献

Two new sesquiterpenoids, neopinguisane-2β,5β-diol (1) (pinguisane-type) and isoseiricardine B (2) (seiricardine-type), along with two known compounds, pentalenic acid (3) and nakienone C (4), were isolated from the culture broth of Streptomyces argenteolus derived from Pantholops hodgsoni feces. Structures of new compounds 1 and 2 were elucidated through comprehensive analysis of 1D and 2D NMR spectroscopic data. The stereochemistry at C-10 of compound 2 could not be determined due to insufficient sample quantity. This study represents the first reported isolation of both pinguisane-type and seiricardine-type sesquiterpenoids from Streptomyces species. In addition, the antimicrobial activities of all isolated compounds were evaluated.

The structure, dynamics, and reaction kinetics exhibited by molecules in the solution state are essentially governed by their interactions with the solvents. Solvents influence solute structure, stability, aggregation, and binding through noncovalent solute–solvent interactions. Hence, understanding solute–solvent interactions is essential for elucidating the molecular behavior in solution. Traditionally, solute–solvent interactions are studied experimentally via solute properties, while theory examines both solute and solvent behavior. Nuclear magnetic resonance (NMR) spectroscopy offers a gamut of experimental methods for probing molecular interactions in condensed phase. Solvent-based NMR methods have become powerful tools to experimentally detect and quantify solute–solvent interactions. The present review highlights the solvent-detected as well as solvent-mediated NMR approaches discussed in literature in the past two decades portraying the dynamicity of solvents in shaping solute behavior—affecting structure, conformational flexibility, and intermolecular interactions. Solvents used in solution NMR experiments offer a plethora of NMR active nuclei both dipolar and quadrupolar in nature that can be efficiently probed to unveil molecular dynamics and interactions. NMR solvent-based methods, from simple to complex systems, are more efficient than other spectroscopic techniques. Solvent relaxation, magnetization transfer, and dynamic nuclear polarization effectively capture subtle solute–solvent interaction changes. These methods are reviewed in specifics to emphasize the potential of solvent-based NMR.

CO₂ flooding is commonly employed for enhanced oil recovery in tight reservoirs. However, asphaltene deposition-induced pore blockage occurs during injection. Conventional studies primarily neglect pore-scale impairment mechanisms. To accurately characterize asphaltene precipitation patterns and quantify microscopic pore blockage, this study integrates static miscibility experiments with dynamic flooding tests. The methodology investigates parametric influences on asphaltene precipitation volumes, evaluates deposition dynamics across pore-size distributions, and employs NMR to quantify pore blockage ratios. Experimental results demonstrated that the Chang-8 Block crude oil in the Ordos Basin exhibited a minimum miscibility pressure (MMP) of 18.58 MPa at 60°C, with the system being identified as asphaltene-unstable. Post-CO₂ miscibility, asphaltene precipitation increases progressively with both rising temperature and pressure, reaching maximum escalation rates at pressures approaching the MMP. However, this escalation rate moderated when pressure exceeded the MMP. Formation damage and pore blockage ratios increased progressively with CO₂ injection volumes, reaching 14.27% at 6 PV. Initial blockage occurred preferentially in macropores, followed by concurrent impairment in both macropores and micropores. Elevated displacement temperatures enhanced CO₂ dissolution. Below CO₂ critical conditions (T > 31.6°C, p > 7.38 MPa), limited displacement efficiency resulted in macropore blockage. Upon exceeding the critical temperature, pore blockage escalation intensified, achieving 25.22% at 60°C. This study systematically investigates asphaltene precipitation characteristics within tight reservoir cores during CO₂ flooding, clarifies the precipitation law of asphaltene in the core under the influence of different factors, and provides operational guidelines for enhancing recovery efficiency and optimizing field-scale CO₂ injection strategies in tight reservoirs.

These studies are intended to be a step towards the identification of characteristic markers of relaxation processes in tissues, with the aim of revealing the extent to which they are tissue and/or cancer specific, and thus to consider the potential of NMR relaxometry for diagnostic purposes. ¹H spin–lattice and spin–spin relaxation studies were carried out on 20 samples of endometrial cancer tissue. The spin–lattice relaxation experiments were performed in the frequency range from 10 kHz to 10 MHz and complemented by spin–lattice and spin–spin relaxation measurements at 18.7 MHz. It was shown that the spin–lattice relaxation data can be reproduced in the form of a power-law function with the exponent of about 0.35 over the whole frequency range, while the spin–spin relaxation process was found to be bi-exponential in all cases. The relaxation scenario has been described quantitatively, leading to a number of parameters such as the ratio between the spin–spin relaxation rates and their contributions to the total relaxation process, or the relative decay of the spin–lattice relaxation rates in the low frequency range (from 10 to 100 kHz). As a result of ¹H spin–lattice and spin–spin relaxation studies several characteristic relaxation features of endometrial cancer tissue have been revealed. The relaxation markers include the characteristic values of the relaxation rates, the shapes of the frequency dependencies of the spin–lattice relaxation rates and bi-exponentiality of the relaxation processes. The relaxation features have been compared with those for proteins and polymers.

Coumarin and benzimidazole are widely preferred pharmacophores in drug design due to their broad spectrum of biological activities, and hybrid molecules formed by the combination of these two structures are thought to possess improved pharmacokinetic and pharmacodynamic properties. In this study, four coumarin-substituted benzimidazolium salts were synthesized, three of which are reported here for the first time. Structural characterization was performed using NMR spectroscopy, FTIR, and elemental analysis. To assess their acid–base properties, the pK_a values of all compounds were determined using three complementary approaches: a signal intensity-based NMR method (pK_aNMRI), classical potentiometric titration (pK_aPTS), and the ERETIC2-assisted quantitative NMR method (pK_aNMRE), which is applied for the first time in the literature for this purpose. Comparison of the obtained pK_a values showed that the pK_aNMRE method yielded values in the range of 10.7–11.4, the pK_aNMRI method provided values between 10.0 and 11.2, and the pK_aPTS method resulted in values ranging from 12.1 to 12.8. All compounds displayed intermediate acidity, attributed to the formation of resonance-stabilized anionic species upon deprotonation by tetrabutylammonium hydroxide. The consistency between the acidity rankings obtained by ERETIC2 and potentiometric titration highlights the robustness of combining advanced NMR-based quantification with classical techniques for reliable and comparative pK_a determination.

NMR spectroscopy has been widely used for the identification and structural elucidation of key components found in essential oils. For many years, the combination of NMR spectroscopy with other analytical techniques, such as gas chromatography (GC) and mass spectrometry (MS), has allowed researchers to identify and quantify a wide variety of terpenes, terpenoids, aldehydes, and other very low-level components present in various essential oils. Importantly, however, whereas GC continues to be the most widely used technique for the quantification of these components, NMR spectroscopy is still mostly reserved for structural elucidation purposes. In this work, we demonstrate how benchtop NMR spectroscopy can also be used for the quantification of key species in various essential oils, increasing accessibility to this technique by decreasing the costs associated with traditional high-field NMR instrumentation and lowering the expertise barriers required for accessing this technique.

Cocrystallization is of fundamental importance in active pharmaceutical ingredients in order to enhance their physicochemical properties, particularly solubility, stability, and bioavailability, without altering the pharmacological activity. While crystal engineering has provided key principles for designing cocrystals, detailed experimental insights into the specific intermolecular interactions governing cocrystallization remain important for structurally complex APIs. We investigate the cocrystallization of an antileukemia drug, venetoclax, with fumaric acid as a coformer. The formation of a new cocrystalline phase is confirmed through powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC). Solid-state nuclear magnetic resonance (NMR) spectroscopy provides key insights into the cocrystallization mechanism, revealing specific hydrogen-bonding interactions between the aromatic amine and pyrrole groups of venetoclax and the carboxylic groups of fumaric acid. These results not only demonstrate a successful case of cocrystallization but also highlight the value of complementary solid-state characterization techniques, PXRD, DSC, and solid-state NMR, in probing cocrystal formation and elucidating the underlying supramolecular interactions in complex pharmaceutical systems.

The series of new 2-substituted-5,7-di(het)aryl-6-nitro-4,5,6,7-tetrahydroazolo[1,5-a]pyrimidines were synthesized by reaction between imine and 1-substituted 2-nitroethylene derivatives. The structure of the obtained compounds including stereochemical configuration was confirmed by NMR techniques such as ¹H, ¹³C, 2D ¹H-¹H (gNOESY), ¹H-¹³C (gHSQC, gHMBC) 2D ¹H-¹⁵N gHMBC and XRD method, additionally. For the obtained compounds, the signals of all hydrogen, carbon, and nitrogen nuclei in the NMR spectra were associated using two-dimensional NMR experiments. Based on the analysis of the spin–spin coupling constants (SSCC), it was found that the target compounds were obtained in the form of trans-trans isomers.