Magnetic Resonance in Chemistry最新文献

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.

The substitution reaction of Cl⁻ ion in the complex [IrCl₆]²⁻ with the acetone molecule was investigated in detail by CW X-band EPR and UV–Vis spectroscopy methods. An original software package for deconvolution of a series of EPR or optical spectra has been developed. Based on the all-data analysis, the most probable mechanism of the process under study is proposed, including four reactions (two reversible ones). One of the stages is the redox reactions between iridium(IV) and iridium(III).

Sickle-Cell Disease (SCD) is one of the most common autosomal recessive genetic blood disorders that manifest in abnormal behavior of the red blood cells (RBCs). The mutated Hb causes sickling of RBCs under deoxygenated conditions, reducing their flowing ability, pliability, and resulting in hemolysis. The pathophysiology observed in the Indian cohort varies regionally, with some Indian tribal populations depicting milder symptoms despite SCD being relatively prevalent among them. To understand the pathogenesis of SCD with respect to nongenetic parameters, we initiated a comparative untargeted metabolomics study of the eastern Indian cohort of SCD patients using ¹H NMR spectroscopy. In this exploratory study, we focused only on a small cohort of 26 SCD patients from the eastern part of India with relatively high prevalence of SCD. Our NMR-based metabolomics, in combination with statistical analyses, yielded 11 of the 29 identified metabolites that showed a statistically significant difference in concentrations between healthy controls and SCD patients. The dysregulated metabolites include molecules involved in glycolysis, hypoxic, and acute-stress conditions.

Deamidation, a modification of glutamine residues in host proteins, plays a key role in bacterial pathogenesis, where bacterial effectors manipulate host signaling pathways by modifying proteins like ubiquitin (Ub) and Ub-like protein NEDD8. The study uses traditional and real-time NMR-based techniques to investigate the enzymatic activity of two bacterial deamidases, cycle inhibitory factors, CIF_EC from Escherichia coli and CIF_BP from Burkholderia pseudomallei. We employed BEST-HSQC NMR spectroscopy to monitor real-time deamidation of ubiquitin, providing a robust and efficient method for quantifying enzyme activity. Our findings highlight significant differences in catalytic efficiency between CIF_EC and CIF_BP, despite their structural similarities. NMR-based rate measurements show CIF_BP has higher catalytic efficiency than CIF_EC, consistent with the previous reports, while kinetic analysis of CIF_EC indicates relatively weak substrate binding and suboptimal efficiency, suggesting a potential regulatory role during infections. While the overall globular fold of the ubiquitin remains unchanged upon deamidation, we observed changes in the local chemical environment, suggesting potential localized structural changes. This study extends the use of NMR spectroscopy to investigate irreversible posttranslational modifications (PTMs) like deamidation, offering a valuable tool for understanding the molecular mechanisms behind bacterial manipulation of host cellular processes.

Small heat shock proteins (sHSPs) are essential molecular chaperones that play a crucial role in maintaining protein homeostasis and protecting cells from stress-induced damage. HSPB8 (Small heat shock protein B8), in particular, plays a crucial role in protein folding and degradation pathways and has been associated with protein aggregation disorders. However, its structural and dynamic behavior under different environmental stress conditions remains poorly defined. In particular, the effect of pH, temperature, and concentration on its oligomeric state and structural integrity needs further investigation. In this study, we performed the biophysical characterization of full-length HSPB8 and its α-crystallin domain (ACD) using solution-state nuclear magnetic resonance (NMR) spectroscopy under different environmental perturbations. The effect on the monomer–dimer equilibrium of the ACD was characterized by monitoring changes in chemical shifts and linewidths in response to the perturbations, including protein concentration, pH, and temperature. It was observed that at low pH, reduced protein concentrations, and elevated temperatures, the ACD favored sharper resonances, reflecting a monomeric state. The relative contribution of disulfide bond and noncovalent interactions in stabilizing the dimer form of ACD was also established. These results provide NMR-based molecular insights into the dynamic monomer–dimer equilibrium, crucial for HSPB8 function in protein folding.

Simulations are essential in NMR spectroscopy for understanding and quantitatively predicting the outcomes of experiments. Dynamic NMR experiments are influenced by relaxation and chemical exchange phenomena, which complicate their interpretation. The quantum mechanical theory behind NMR simulations is well established and enables simulations under various conditions or states of the system. In particular, the representation of the spin system in terms of the density matrix, energy and pulse operators, and relaxation and chemical exchange in Liouville space is straightforward and allows for the routine simulation of dynamic NMR experiments. In fact, several advanced open-source software packages are currently available—such as Spinach, GAMMA (pyGAMMA), Simpson, ChemEx, and NMR TITAN—which users can choose from based on their simulation needs. Many of these software packages are optimized for computational speed and make use of sophisticated bases, such as the irreducible spherical tensor basis. Here, we present simulations using the direct method (spin product basis), as implemented in GAMMA, which we believe will help users better understand the underlying theory and thereby explore the other available software resources more effectively. We chose two experiments—CPMG-RD and CEST—as a case study to understand the conformational changes in proteins or macromolecules occurring in the fast and slow exchange regimes, which are frequently investigated by structural biologists.