Magnetic Resonance in Chemistry最新文献

1D and 2D NMR spectra of amide 3 and benzimidazole 4 were unequivocally assigned. Moreover, the aminolysis of D-glycero-D-gulo-heptono-1,4-lactone 1 with o-phenylenediamine 2 was explored using different methodologies. Results indicated that focused ultrasound selectively yielded the amide 3. Studies demonstrated that intensive cavitation can exceed the activation energy without disrupting the thermodynamic equilibrium. Thus, the kinetic product (amide 3) was favored over the thermodynamic product (benzimidazole 4). In contrast, the ultrasonic cleaner led to an incomplete and unselective reaction. On the other hand, thermal induction favored the synthesis of benzimidazole 4, while the mechanochemical synthesis was inefficient in promoting the aminolysis of the γ-lactone 1 with compound 2.

Propolis from Apis mellifera and cerumen from Tetragonula carbonaria are complex mixtures of beeswax, plant resins, and bee secretions whose composition varies with geography and species. Understanding these differences is important for exploring their bioactive potential. This study employs untargeted quantitative ¹H NMR metabolomics to characterize A. mellifera propolis from Scandinavia (Denmark and Norway) and Australia, as well as cerumen from T. carbonaria in Australia. Hydrophilic and hydrophobic extracts were analyzed to assess compositional differences across geographical origin and bee species, and to link specific metabolites to radical scavenging activity (RSA). Principal component analysis (PCA) of the ¹H NMR spectra showed a marked separation between Scandinavian and Australian propolis. Hydrophilic extracts showed that Scandinavian propolis contains higher levels of aromatic compounds, whereas Australian propolis is richer in carbohydrates. In contrast, cerumen from T. carbonaria exhibits higher amounts of terpenoids. Hydrophobic extracts revealed that Australian propolis has the highest wax content, with shorter chains and more free fatty acids, while Scandinavian propolis samples display uniform wax structures and the highest aromatic content. Multivariate regression using recursive weighted partial least squares (rPLS) to RSA prediction highlighted signals attributable to ferulic acid and p-coumaric acid, which were confirmed by statistical total correlation spectroscopy (STOCSY). These findings demonstrate the utility of quantitative ¹H NMR metabolomics for distinguishing botanical and geographic chemotypes of propolis and cerumen. The findings further show that Scandinavian propolis is more consistent with respect to metabolite composition compared to Australian samples, presumably reflecting differences in resin sources for foraging.

The NMR interaction tensors of ⁹Be and ¹¹B of hambergite, Be ${}_2$ BO ${}_3$ OH, were derived from single-crystal NMR experiments. In the orthorhombic crystal structure of hambergite (which we redetermined by single-crystal XRD, confirming the results of previous studies), both beryllium and boron atoms occupy Wyckoff position $8c$ , with atoms pairwise related by inversion symmetry. This leads to four magnetically independent ⁹Be and ¹¹B atoms per site, which are observable in the NMR spectra. Unequivocal assignment of these resonances to atomic positions in the unit cell is generally impossible, as an analysis of the symmetry relations shows. For the hambergite system, this assignment ambiguity could be resolved with the help of DFT calculations using the VASP code, with the resulting eigenvectors compared with the experimental ones. Examination of ⁹Be-¹H dipolar coupling effects, which could be detected in some of the ⁹Be spectra, in combination with XRD experiments to confirm the goniometer axis orientation, provided further spatial information and confirmed the assignment. The thus determined numerical values for the quadrupolar coupling constants $\chi$ and isotropic chemical shifts ${\delta }_{iso}$ are as follows: for ⁹Be[1] $222.6\pm 0.6$  kHz and 1.6 ppm, for ⁹Be[2] $-121.2\pm 0.4$  kHz and 1.4 ppm and for ¹¹B[1] $2.648\pm 0.004$  MHz and 18.1 ppm.

Stereochemical elucidation of synthetic and natural compounds is a rate-determining step in the structure determination process. In the present work, we introduce a method called Chirality In Silico Structure Elucidation (CiSE), which employs ¹J_CC coupling constants to determine the correct stereochemistry of natural products. To determine the correct stereochemistry, the proposed method assigns a probability to all possible structures of a compound in question. For calculating these probabilities, the errors between the experimental and density functional theory (DFT) computed ¹J_CC couplings of a large number of compounds are fitted into Student's t-distribution, from which statistical parameters such as mean, standard deviation, and degrees of freedom are determined. Afterward, the probabilities for all possible candidate structures are calculated using Bayes's theorem, with the correctly assigned stereoisomer typically exhibiting a probability exceeding 95%.

Nuclear magnetic resonance (NMR) is a powerful analytical tool for wine analysis to identify and quantify a metabolite composition. However, a limiting factor of 1D ¹H NMR spectroscopy is the overlap of signals in complex mixtures. While conventional 2D NMR methods disperse the signals over two dimensions, they are associated with long experiment times. In the case of wine, interesting metabolites are also often masked by the large water and ethanol peaks. To improve wine analysis by NMR, a method that uses the advantages of 2D NMR while suppressing solvent signals and being within the timeframe of 1D NMR is highly desirable. Interleaved ultrafast COSY (iuf-COSY) offers a possibility for fast acquisition of a 2D spectrum and has been demonstrated as a powerful tool in metabolomics studies, as a complement to 1D NMR methods. Here, the iuf-COSY experiment has been adapted to suppress water and ethanol signals by using a shaped pulse and a NOESY block. This approach efficiently suppresses solvent signals and gives a 2D COSY spectrum of wine in approximately 20 min. Important metabolites that originally were covered by solvent signals could be annotated, while minimal interleaving artefacts were observed. This is an efficient method to acquire a COSY spectrum of a wine sample, which can aid with the identification and discrimination of metabolites in future wine studies through additional cross peaks, while working within a high-throughput time scale. This might be particularly interesting in the field of wine metabolomics, quality control, authenticity and fraud.

NMR and MRI provide a variety of customizable methods for process monitoring. A selection was applied to monitor structural and compositional changes in hazelnuts during thermal treatment, with particular focus on the roasting and aging behavior of hazelnut oil. Hazelnuts contain a high oil fraction stored in subcellular oleosomes, whose stability is crucial for product quality and shelf life. Thermal stress can alter these microscopic oil-containing structures, affecting oil mobility and oxidative stability. In situ MRI measurements were combined with pulsed field gradient stimulated echo (PFG-STE) NMR diffusion experiments to investigate structural changes across multiple length scales. MRI detected mesostructural alterations in the hazelnut matrix from ~50 μm to several millimeters, corresponding to features above the cellular level. At roasting temperatures below 150°C, only minor structural changes occurred, whereas at 200°C, pronounced void formation and cellular collapse were observed. A dedicated experimental setup enabled in situ measurements during roasting under controlled temperature, allowing spatially resolved monitoring of oil redistribution in coarse nut structure. Complementary PFG-STE NMR diffusion measurements provided insight into the microstructure (100 nm-10 μm), revealing subcellular structural changes and oil mobility. These results showed that oleosomes were largely destroyed already at 100°C. Furthermore, NMR spectroscopy demonstrated temperature-dependent oxidation kinetics of unsaturated fatty acids in hazelnut oil on a molecular level, with clear formation of oxidation products upon heating, whereas ambient storage caused only minor chemical changes. The combined use of MRI and NMR enables quasi-nondestructive, in situ monitoring of molecular, microstructural, and mesostructural transformations in hazelnuts and their oil under controlled thermal processing conditions.

The drying of egg yolk tempera paint in the dark has been investigated from 24 h up to 2 years by nuclear magnetic resonance (NMR) relaxometry and spectroscopy. Variations around a reference recipe have been carried out to investigate several aspects: the amount of added water to the binder, the nature of the minerals or the pigments and the drying time. The ¹H signal measured here corresponds to the ¹H contained in the fatty acids of the egg yolk (EY). The $R_1$ NMR dispersion (NMRD) profile increases when the added water in the preparation of the tempera is above 50 wt% linked to a destructuration of egg yolk high- and low-density lipoproteins (HDL and LDL). In addition to the chemical nature of the minerals, the shape and the surface area also play an important role in the destructuration of egg yolk HDL and LDL. The most striking result is the discontinuous evolution of the NMRD with time with the appearance of a step around 1 or 2 months. Depending on the water content in the initial tempera, a steep change in $R_1$ is observed while before and after only a weak evolution occurs.

The presence of radicals in fluids can significantly influence the ¹H longitudinal nuclear magnetic resonance relaxation processes. The field-cycling nuclear magnetic relaxometry technique provides a unique approach to study these interactions within a broad Larmor frequency range. The situation is quite common in fluid systems subjected to oxidative stress, such as lubricants in internal combustion engines. Our previous studies in lubricant degradation did not consider in detail specific effects of radicals on the ¹H longitudinal relaxation. In the present work, we focus on a simplified system in which TEMPOL radicals are introduced in controlled concentrations into ethylene glycol samples. The system's behavior is evaluated at different radical concentrations to elucidate the influence of the paramagnetic species on the relaxation dispersion profile. We propose the inclusion of an additional relaxation term to account for intermolecular proton-electron interactions. We observe that, for radical concentrations exceeding approximately 2 × 10¹⁷ radicals/cm³, paramagnetic interactions dominate the relaxation dispersion at Larmor frequencies below 1 MHz. Moreover, we show that both the diffusion constants of ethylene glycol and TEMPOL molecules can be estimated from a single experiment. The consistency of our results with existing literature suggests an in-depth analysis of the paramagnetic contribution in the relaxometric characterization of degraded lubricants.

Liquid state processes often involve mixing of process streams. With the development of microfluidics in chemical engineering, questions arise about analytical tools which are capable of monitoring the processes spatially and time-resolved. Optical techniques are widely spread, which, however, require optical transparency. MRI techniques are explored to elucidate the possibilities of measuring hydrodynamic parameters and monitoring mixing with molecular, chemical information.

Drug development is a risky endeavour with a high failure rate, often caused by the limited ability to predict the efficacy and interactions of candidate drugs in a native cellular environment. In this context, in-cell NMR spectroscopy is a promising tool for assessing drug-target binding directly in living cells, thereby improving the screening and development of new molecules. In this study, we used real-time in-cell ¹⁹F NMR spectroscopy in a flow bioreactor to observe competitive binding of fluorinated benzenesulfonamide derivatives to three cytosolic isoforms of carbonic anhydrase. Quantitative measurement of the dissociation constants relative to a spy ligand allowed an accurate ranking of the compounds based on their intracellular affinities for each isoform. The use of two fluorinated ligands allowed simultaneous observation of spy ligand displacement and test ligand binding, as well as estimation of the effective ratio of free ligand concentrations under poor solubility conditions. We also show that signal saturation caused by short repetition times, which can significantly impact the analysis, can be easily corrected a posteriori. Overall, we show that real-time in-cell ¹⁹F NMR spectroscopy can reliably quantify drug-target binding in the cellular environment, paving the way for future applications in drug discovery.