Magnetic Resonance in Chemistry

doi: 10.1002/mrc.70086pmid: N/A

No abstract is available for this article.

Gerony, Floriane; Jaber, Maguy; Viguerie, Laurence; Rigaud, Baptiste; Michot, Laurent; Rollet, Anne‐Laure; Mériguet, Guillaume

doi: 10.1002/mrc.70079pmid: 41482655

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 R1 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 R1 is observed while before and after only a weak evolution occurs.

Delgado‐Delgadillo, Luisa Fernanda; García‐Ortiz, Miguel Ángel; Gaspar‐López, Federico Javier; Tlahuextl, Margarita; Islas‐Trejo, Eltonh; Tlahuext, Hugo; Patricio‐Rangel, Emmanuel Blas; Tapia‐Benavides, Antonio Rafael

doi: 10.1002/mrc.70081

Pathak, Swaraj; Goyary, Swrangsi; Nath, Nilamoni

doi: 10.1002/mrc.70076pmid: 41502071

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 1JCC 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 1JCC 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%.

Steinadler, Jennifer; Krach, Georg; Witthaut, Kristian; Stürzer, Tobias; Hochleitner, Rupert; Schnick, Wolfgang; Bräuniger, Thomas

doi: 10.1002/mrc.70073pmid: 41521587

The NMR interaction tensors of 9Be and 11B of hambergite, Be 2BO 3OH, 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 χ and isotropic chemical shifts δiso are as follows: for 9Be[1] 222.6±0.6 kHz and 1.6 ppm, for 9Be[2] −121.2±0.4 kHz and 1.4 ppm and for 11B[1] 2.648±0.004 MHz and 18.1 ppm.

Mayer, Pia S.; Marchand, Jérémy; Letertre, Marine P. M.; Dumez, Jean‐Nicolas; Engelsen, Søren B.; Giraudeau, Patrick

doi: 10.1002/mrc.70078pmid: 41548883

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.

Trapp, L.; Weis, N.; Karschin, N.; Schacht, H.; Nirschl, H.; Guthausen, G.

doi: 10.1002/mrc.70084pmid: 41572861

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.

Vind, Jonas; Engelsen, Søren Balling; Jørgensen, Henrik Munch; Antvorskov, Julie Christine; Josefsen, Knud; Aru, Violetta

doi: 10.1002/mrc.70082pmid: 41605461

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.