ABSTRACT Rehydration of texturized vegetable proteins (TVPs) is decisive for their functional properties, but little is known in relation to how rehydration conditions impact their ability to absorb and retain water. The present study aimed to investigate how rehydration dynamics and intrinsic water mobility of texturized soy protein are affected by temperature, pH, and ionic strength under dynamic or equilibrium conditions. Low‐field NMR T 2 relaxation measurements were conducted dynamically on soy TVP during rehydration under different combinations of pH (5.4, 6.2, or 7.0), ionic strength (0.29, 0.46, or 0.71 M), and temperature (15, 25, or 35°C). Rehydration could be tracked from a decrease in the T 2 relaxation time constant, reflecting a reduced mobility of water protons when water molecules were immobilized in intrinsic structures. Kinetic modeling revealed a significant effect of temperature on the rate of rehydration, whereas pH and ionic strength did not affect the rate of rehydration. To evaluate equilibrium conditions, 24 h soaking experiments were conducted, which revealed significant effects of pH on the rehydration capacity and NMR T 2 relaxation. Increasing pH increased the rehydration capacity and T 2 relaxation time constants, indicating that water compartmentalization in TVPs can be modulated through pH effects on electrostatic repulsion. In conclusion, NMR relaxometry enables kinetic studies of soy TVP rehydration, and this study demonstrates that rehydration kinetics and equilibrium rehydration capacity can be decoupled. Temperature primarily governed the rate of water uptake, whereas pH influenced final rehydration capacity, while ionic strength in the range applied here did not affect rehydration capacity.
Non-hydrogenative parahydrogen-induced polarization (nh-PHIP) is an NMR sensitivity enhancement technique that is particularly suitable for studying biological samples. It can provide up to three orders of magnitude signal enhancements for a continuously expanding range of valuable analyte classes like drugs, vitamins, nucleobases, nucleosides and nucleotides, amino acids, oligopeptides, etc. The strengths of nh-PHIP lay in its modest instrumental requirements over a standard commercial NMR spectrometer, its simple operating workflow that is similar to traditional NMR spectroscopy, and its proven capability to offer quantitative information from below the sensitivity barrier of regular NMR. This tutorial will give an overview of the background, the principles, and the present application scope of nh-PHIP hyperpolarization. We provide guidelines for setting up an nh-PHIP experiment, from sample preparation to optimizing the hyperpolarization for a particular analyte class. This includes the description of the basic experimental setup and outlining the considerations for method development. An overview of different available nh-PHIP pulse sequences will be given to assist the reader in implementing nh-PHIP.
The 1 $$ {}^1 $$ H NMR relaxation dispersion (NMRD) profile of water in boehmite systems has been studied in detail. The NMRD profiles, recorded for weakly hydrated particles up to diluted suspensions, exhibit the very same shape, and a mastercurve can be obtained. 1 $$ {}^1 $$ H NMR relaxation rate R 1 $$ {R}_1 $$ strongly varies with the field indicating a slow dynamics at the surface of the boehmite particles. In addition, a bump around 0.7 MHz is observed. This characteristic feature may arise either from an interaction with a paramagnetic species or from an interaction with a quadrupolar nucleus. In the literature, this bump for aluminum hydroxide compounds has been independently attributed to one or the other interaction and a definitive answer must be provided. By decreasing the temperature, the bump increases, whereas the electron spin spectroscopy (ESR) detects a weak amount of paramagnetic species. 27 $$ {}^{27} $$ Al solid-state NMR spectrum is characterized a peak with a central transition at 9.7 ppm and quadrupolar constant equal to 2.7 MHz. The atomic force microscopy (AFM) image of individual boehmite particle evidences that the number of aluminum at the surface is high enough to be detected by solid-state NMR. Hence, the values of the 27 $$ {}^{27} $$ Al quadrupolar parameters obtained by solid-state NMR can be directly used for the calculation of the quadrupolar relaxation enhancement.
Understanding how drugs interact with metal ions is essential for predicting their stability, how well they are absorbed in the body, and possible side effects. Pravastatin is a commonly used statin to prevent cardiovascular heart disease and has several functional groups that can bind metal ions, but its interactions with transition metals and lanthanides are not well studied. This work examines the complexation process of pravastatin with transition metal ions zinc (Zn2+), nickel (Ni2+) and lanthanide gadolinium (Gd3+) using high-resolution NMR spectroscopy. It was found that the presence of ions (Ni2+, Gd3+) in an aqueous solution of pravastatin causes broadening of 1H NMR signals, leading to a change in signal intensity in the HMQC spectra and disappearance of the correlation between the 1H and 13C signals in the HMBC spectra. No significant changes were observed in the NMR spectra of similar experiments of pravastatin with zinc salt. The DOSY NMR spectrum of pravastatin in the presence of ions (Gd3+, Ni2+, and Zn2+) revealed a change in self-diffusion coefficients compared to the parent structure. An assumption about the possible centers of localization of Gd3+ and Ni2+ ions near the pravastatin molecule has been made.
An additive framework is developed to describe 17O quadrupole coupling constants (QCC's) in hydrogen-bonded water systems across isolated molecules, finite clusters, and ice-like environments. Density functional theory calculations using optimized geometries show that 17O QCC variations are primarily governed by hydrogen-bond interactions. A dimer model identifies hydrogen-bond distance as the dominant geometric factor, while angular and intramolecular distortions are minor. In ice and water clusters, first-nearest-neighbor interactions provide the largest contribution and are well captured by an additive donor-acceptor scheme, with improved accuracy upon inclusion of hydrogen bond distance dependence. Second nearest neighbor effects introduce smaller but systematic negative corrections arising from hydrogen-bond network asymmetry, restoring near-quantitative agreement with full calculations. The resulting model provides a computationally efficient and physically interpretable approach for predicting electric field gradients in aqueous environments and linking molecular simulations with 17O NMR observables.
NMR relaxation of liquids in the presence of solid interfaces, such as silica gel or porous glass, is affected by slowed-down and anisotropic molecular reorientations compared to the bulk, but also by the presence of spins as potential relaxation partners on or close to the surface. The latter contribution is predominantly considered as unpaired electrons in metal centers or surface radicals, but dipolar interactions with spin-bearing nuclei such as 29Si or 1H may also contribute to relaxation of adsorbed species. In this study, an attempt is made at identifying the most relevant relaxation contributions by either adding or removing relaxation sinks: While immobilized stable radicals (TEMPO) on the surface shorten relaxation times of adsorbed liquids, the replacement of 1H nuclei by 2H in hydroxyl groups is expected to remove the dominating part of nuclear dipolar spin-spin relaxation. In both cases, it is assumed that surface chemistry, which is the decisive parameter for spin relaxation mechanisms at interfaces, remains unchanged. Longitudinal and transverse relaxation, 2d T1-T2 maps, and frequency-dependent relaxation measurements of a number of homogeneous liquid phases as well as binary mixtures in the pore space of silica gel and porous glass are discussed in terms of the presence of radicals, whereas the replacement of OH by OD is observed to reduce relaxation rates in the systems under study.
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 (C i SE), which employs 1 J 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 1 J 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%.
The NMR interaction tensors of 9 Be and 11 B of hambergite, BeBOOH, 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 , with atoms pairwise related by inversion symmetry. This leads to four magnetically independent 9 Be and 11 B 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 9 Be– 1 H dipolar coupling effects, which could be detected in some of the 9 Be 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 and isotropic chemical shifts are as follows: for 9 Be[1] kHz and 1.6 ppm, for 9 Be[2] kHz and 1.4 ppm and for 11 B[1] MHz and 18.1 ppm.
The ability to observe transient intermediates and determine precise kinetic parameters is fundamental to understanding catalysis. This study demonstrates a methodology for the in situ investigation of photochemical ligand exchange and oxidative addition using a benchtop NMR spectrometer equipped with a through-bore UV irradiation system. To overcome the inherent sensitivity limitations of benchtop NMR, parahydrogen-induced polarisation (PHIP) was employed, providing significant signal enhancements for hydride-containing products. Specifically, the addition of pH 2 $$ {}_2 $$ to trans-[IrCl(CO)(PPh 3 $$ {}_3 $$ ) 2 $$ {}_2 $$ ], that proceeds over 10 min, was monitored yielding a second-order rate constant, 1.36 ± $$ \pm $$ 0.02 M - 1 $$ {}^{-1} $$ s - 1 $$ {}^{-1} $$ . To resolve faster catalytic processes, pump-probe synchronisation between the UV pulse and NMR detection was implemented. A spin-lock pulse was also added to preserve the singlet state of the pH 2 $$ {}_2 $$ -derived hydride ligands in the reaction products, enabling the observation of coherent magnetic oscillations after reaction in the corresponding 2D pump-probe NMR spectra. Following optimisation on diagnostic zero-quantum correlations for cis-[Ru(H) 2 $$ {}_2 $$ (dppe) 2 $$ {}_2 $$ ], a set of iodo-derivatives of Vaska's complex were explored. For these systems two photochemical pathways were effectively mapped, enabling the identification of several ligand-exchange products. These results establish that the combination of hyperpolarisation and synchronised in situ irradiation makes benchtop NMR a powerful tool for the study of reactivity.
Accurate NOE/ROE-based distance determination is a crucial tool in stereochemistry and conformational analysis of both protein and small molecule structure elucidation. Despite being widely used in countless fields of chemistry and biology, the factors determining the accuracy of the obtained distances are sometimes neglected. Herein, we present the systematic analysis of the performance of six commonly used NOESY and ROESY pulse programmes for quantitative NOE/ROE analysis, evaluating the quality of the data based on the number of quantifiable correlations and the accuracy of the corresponding NOE-derived interproton distances. The effect of two solvent suppression schemes on the NOE/ROE quantitativity is assessed. We found that the total number of quantifiable correlations and the errors of the derived distances depend on the pulse programme used, and the error increases drastically when two or more spectra are removed from the build-up curves for the generation of NOE/ROE build-up rates, using the initial-rate approximation. Solvent suppression using excitation sculpting results in the underestimation of the NOE-derived distances. EASY ROESY run without solvent suppression shows a bias towards overestimated NOE-derived distances. The obtained data suggest that the determination of quantitative interproton distances necessitates the careful selection of pulse programme.
NMR can be used to monitor reactions in situ, typically by acquiring a series of standard one-dimensional spectra at regular intervals. However, the experimental setup is more demanding than for stable, nonreacting samples. For example, the usual pre-acquisition correction of magnetic field homogeneity, known as shimming, can sometimes be too time-consuming to be repeated before each spectrum in a series. This results in a gradual increase in spectral lineshape distortions during the reaction. Fortunately, the spectra can be improved to some extent by applying post-acquisition corrections. We propose replacing the standard semi-manual reference deconvolution method with a neural network called ShimNetV2-RM. Our method, previously developed under the name ShimNet for standard nonreacting samples, can be tailored for reaction monitoring by constraining training parameters using well-shimmed pre- and post-monitoring spectra. To demonstrate the applicability of the proposed approach under realistic and demanding conditions, we applied ShimNetV2-RM to two representative copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions.
Isodon rubescens is a widely used traditional folk medicine in China. In this study, 13 natural products were isolated using a two-step ethanol extraction. Notably, flavonoid glycosides 2 and 4, and polymeric caffeic acids 7 and 8, were identified for the first time from the secondary extraction residues, highlighting the continued presence of bioactive compounds with potential for further development. Oridonin (9), the major active compound, was quantified in nine commercial preparations using quantitative NMR (qNMR). Its concentration in the drop pill (0.92 mg/g) was comparable to that in the raw extract (0.90 mg/g). The three tablet samples showed varying levels: Tablet 3 (2.66 mg/g) > Tablet 1 (1.22 mg/g) > Tablet 2 (1.09 mg/g). Capsule, tea bag, and syrup samples could not be quantified due to low concentrations.
Characterizing protein-drug interactions at the atomic level is challenging partly because small molecules can be difficult to detect within large biomolecular complexes. We have developed a strategy to introduce NMR-active isotopic 15N labels into derivatives of bevirimat (BVM), a triterpenoid inhibitor of HIV-1 maturation. Isotopically labeled compounds were synthesized through concise and efficient routes using commercially available, isotopically enriched building blocks. Three 15N-labeled BVM derivatives were prepared to be used as molecular probes to investigate HIV-1 protein interactions. These labeled compounds enable site-specific 15N detection of the inhibitor in both solution and solid-state NMR experiments, which will be useful to obtain molecular-level insight into the interactions between BVM derivatives and its target HIV-1 Gag protein. Synthetic incorporation of NMR-active isotopes produces chemical probes for atomic-level analysis of next-generation HIV-1 therapeutics derived from BVM and can be applied to other derivatives of betulinic acid with various medical applications.
To clarify the correlation between the V4+ doping and the structure of DUT-5(Al), this study establishes a theoretical calculation model for the electron paramagnetic resonance (EPR) parameters of V4+ with a 3d1 electron configuration in orthorhombically compressed octahedrons. After verifying the rationality of the model by fitting with experimental data, the local structural distortion of [VO6] clusters, the regulation mechanism of electronic states, and the essence of EPR components (lp, np, BL, and Blp) were systematically analyzed. The findings reveal that, due to the Jahn-Teller distortion, the [VO6] units adopt an orthorhombically distorted octahedral structure, quantified by an axial compression parameter ρ ranging from 5.6% to 6.4%, and in-plane bond-length variation rate τ spanning 6.0% to 6.8%. The theoretical method adopted in this study can clarify the doping mechanism of transition metal ions in metal-organic frameworks (MOFs), provide theoretical support for interpreting the EPR phenomena of V4+-doped DUT-5(Al), and offer guidance for the rational design and performance optimization of transition metal-doped MOF materials.
Field-cycling (FC) NMR relaxometry is an ideal tool to investigate multiscale polymer dynamics since it can give access to longitudinal relaxation rates (R1(ω)) over a broad Larmor frequency range, which can be further extended by employing the frequency-temperature superposition principle. Applications of FC NMR on elastomers of interest for tire industry (i.e., cis-1,4-polyisoprene, cis-1,4-polybutadiene, and co-poly [styrene-butadiene]), aimed to obtain information on segmental and polymer dynamics over different regimes as a function of chain length in polymer melts and in dependence on cross-linking degree and addition of fillers or additives in rubbers, are here reviewed for the first time. After a brief presentation of theoretical tools used in data analysis, studies on polymer melts at variable temperature are reported allowing theories for polymer dynamics, such as tube reptation and renormalized Rouse models, to be tested in the entanglement regime through characteristic dependences of R1(ω) on Larmor frequency. Then, studies on rubbers and elastomer compounds are illustrated, highlighting the effects of curing conditions (i.e., temperature, concentration of sulfur and accelerant), and the presence of reinforcing fillers and additives (e.g., tackifying resins) on segmental dynamics, related to macroscopic properties as glass transition temperature, and on collective polymer dynamics. Issues connected with the application of FC NMR relaxometry to polymeric systems with increasing structural and compositional complexity are critically discussed.
We present CEEN (coupled electrochemistry, EPR, and NMR), a Python package designed for coupled and integrated control of Bruker benchtop NMR, benchtop EPR, and Gamry electrochemical workstations. The software enables synchronized acquisition and real-time visualization of electrochemical, NMR, and EPR data, simplifying operando measurements that traditionally require three independent control interfaces. We demonstrate CEEN through practical applications relevant to aqueous organic and inorganic redox flow battery (RFB) and electrochemical synthesis research. The same setup can be readily used to study any (electrochemical) flow process using magnetic resonance. CEEN streamlines the data acquisition workflow, enabling robust and information-rich operando NMR and EPR studies.
The off-center displacement of the Cu2+ ion in Pb5Ge3O11 (PGO) crystal is theoretically investigated by analyzing the electron paramagnetic resonance (EPR) parameters, g-factors gi (i = x, y, z), and hyperfine structure constants Ai based on the high-order perturbation formulas of 3d9 ions in orthorhombically elongated octahedral crystal-fields. The doped Cu2+ was assumed to substitute the host Pb(8) site in the PGO lattice, with a different local environment from the original Pb2+ due to the Jahn-Teller (JT) effect. Based on the calculation, the off-center displacement Δz of impurity Cu2+ is about 0.19 Å, and the planar Cu2+-O2- bonds are found to experience the relative bond length variation δR (≈0.013 Å) along the x and y axes. The theoretical EPR parameters based on the above local structure parameters show good agreement with the experimental values.
