Application Of NMR Research Articles

Tritium NMR: A compilation of data and a practical guide.

The present review is focused on experimental methods and structural applications of tritium NMR. It consists of five parts covering accordingly, introduction, brief overview, early (based on the papers appearing before 2000), more recent (based on the papers appeared in the interim of 2000 to 2015), and recent (based on the papers that appeared after 2015) reports. A special interest in this review is focused on practical aspects of tritium NMR spectroscopy, which is thoroughly illustrated by its numerous applications in chemistry and biochemistry.

Unravelling the mechanisms of drugs partitioning phenomena in micellar systems via NMR spectroscopy

Despite extensive use of micelles in materials and colloidal science, their supramolecular organization as well as host–guest interactions within these dynamic assemblies are poorly understood. Small guest molecules in the presence of micelles undergo constant exchange between a micellar aggregate and the surrounding solution, posing a considerable challenge for their molecular level characterisation. In this work we reveal the interaction maps between small guest molecules and surfactants forming micelles via novel applications of NMR techniques supported with state-of-the-art analytical methods used in colloidal science. Model micelles composed of structurally distinct surfactants (block non-ionic polymer Pluronic® F-127, non-ionic surfactant Tween 20 or Tween 80, and ionic surfactant sodium lauryl sulphate, SLS) were selected and loaded with model small molecules of biological relevance (i.e. the drugs fluconazole, FLU or indomethacin, IMC) known to have different partition coefficients. Molecular level organization of FLU or IMC within hydrophilic and hydrophobic domains of micellar aggregates was established using the combination of NMR methods (1D 1H NMR, 1D 19F NMR, 2D 1H–1H NOESY and 2D 1H-19F HOESY, and the multifrequency-STD NMR) and corroborated with molecular dynamics (MD) simulations. This is the first application of multifrequency-STD NMR to colloidal systems, enabling us to elucidate intricately detailed patterns of drug/micelle interactions in a single NMR experiment within minutes. Importantly, our results indicate that flexible surfactants, such as block copolymers and polysorbates, form micellar aggregates with a surface composed of both hydrophilic and hydrophobic domains and do not follow the classical core–shell model of the micelle. We propose that the magnitude of changes in 1H chemical shifts corroborated with interaction maps obtained from DEEP-STD NMR and 2D NMR experiments can be used as an indicator of the strength of the guest-surfactant interactions. This NMR toolbox can be adopted for the analysis of broad range of colloidal host–guest systems from soft materials to biological systems.

Ligand-observed in-tube NMR in natural products research: A review on enzymatic biotransformations, protein–ligand interactions, and in-cell NMR spectroscopy

Natural product-observed NMR methods have considerably expanded the potentialities for in-tube NMR monitoring of complex enzymatic biotransformations and investigation of protein-natural product interactions even in living cells. We review, herein, the significant advantages of ligand-observed in-situ NMR monitoring of enzymatic biotransformations without restoring to laborious and time-consuming chromatographic methods. Emphasis will be given to the potentialities of the use of the NMR bioreactor: (i) to investigate through saturation transfer difference (STD), the capacity of natural products to serve as enzyme substrates, (ii) to monitor multiple biotransformation products of natural products with the use of immobilized enzymes and (iii) to investigate interactions of biotransformed products with protein targets. The use of STD and its variants, transfer effect Noes for PHArmacophore Mapping (INPHARMA) NMR, in conjunction with computational methods, can provide excellent tools in investigating competitive binding modes even in proteins with multiple binding sites. The method has been successfully applied in the study of unsaturated free fatty acids (UFFAs)-serum albumin complexes in which the location and conformational states of UFFAs could not be determined accurately, despite numerous X-ray structural studies, due to conformational averaging. This combined method, thus, may find promising applications in the field of protein-natural product recognition research. The emerging concept of in-cell NMR and recent applications will be discussed since they can provide atomic level insights into natural product-protein interactions in living cells without the need of isotope labelled techniques.

Non-Steady State NMR Effect and Application on Time-Varying Magnetic Field Measurement.

The measurement of a time-varying magnetic field is different from a constant magnetic field, due to its field intensity variation with time. Usually, the time-varying magnetic field measurement converts the solution of the magnetic induction intensity into the calculation of the induced electromotive force (EMF); then, the magnetic induction intensity is obtained by the time integration of the EMF, but the process is vulnerable to external interference. In this paper, a non-steady state nuclear magnetic resonance (NSS-NMR) scheme for the measurement of a time-varying magnetic field is proposed. In a time-varying magnetic field environment, an RF excitation signal with a certain frequency bandwidth is applied to excite the nuclear spin system. The NSS-NMR signal, which varies with time in the frequency range corresponding to the frequency bandwidth of the RF excitation, could finally be obtained after a series of processing of the probe output signal. During the NSS-NMR experiment, an orthogonal dual-coil probe is adopted to synchronously generate the RF excitation and induce the probe output signal. Moreover, a directional coupler that utilized in the experiment outputs a reference signal from the coupling port for the subsequent signal processing. The experimental results show that the weak NSS-NMR signal is indeed observed. The longitudinal time-varying magnetic field ranges from 0.576 T to 0.582 T, which is inverted by the Larmor precession relationship, have been successfully detected based on the so-called NSS-NMR effect.

Enhancing 19F Benchtop NMR Spectroscopy by Combining para-Hydrogen Hyperpolarization and Multiplet Refocusing.

Benchtop NMR spectrometers provide a promising alternative to high-field NMR for applications that are limited by instrument size and/or cost. 19F benchtop NMR is attractive due to the larger chemical shift range of 19F relative to 1H and the lack of background signal in most applications. However, practical applications of benchtop 19F NMR are limited by its low sensitivity due to the relatively weak field strengths of benchtop NMR spectrometers. Here we present a sensitivity-enhancement strategy that combines SABRE (Signal Amplification By Reversible Exchange) hyperpolarization with the multiplet refocusing method SHARPER (Sensitive, Homogeneous, And Resolved PEaks in Real time). When applied to a range of fluoropyridines, SABRE-SHARPER achieves overall signal enhancements of up to 5700-fold through the combined effects of hyperpolarization and line-narrowing. This approach can be generalized to the analysis of mixtures through the use of a selective variant of the SHARPER sequence, selSHARPER. The ability of SABRE-selSHARPER to simultaneously boost sensitivity and discriminate between two components of a mixture is demonstrated, where selectivity is achieved through a combination of selective excitation and the choice of polarization transfer field during the SABRE step.

11B and 1H-11B HMBC NMR as a Tool for Identification of a Boron-Containing Nucleoside Dimer.

Boron-containing compounds are commonly used in synthetic chemistry and are known to play important roles in biology. Despite the widespread relevance of boronated compounds, there have been limited methods to discover, characterize, and study them. Here, we describe the use of 11B NMR, including 1H-11B HMBC, for the isolation and characterization of the boron-containing natural product diadenosine borate. Utilizing synthetic standards, we optimized coupling parameters for 1H-11B HMBC experiments to allow for the analysis of small quantities (∼1 mg) of boron-containing compounds. This work can facilitate the broader application of 11B NMR to the study of boron in a range of applications, from synthetic chemistry to the role of boron in naturally occurring systems.

First Occurrence of Megastigmane Glucosides in a Plant of Retama Genus.

Chemical investigation of Retama sphaerocarpa collected in Algeria resulted in the isolation of two megastigmane glucosides, compounds 1 and 2, along with a series of isoflavones and phenol derivatives. Compound 1, named retamoside, was new and its structure was determined by extensive application of spectroscopic methods, including HRMS, 1D and 2D NMR and CD. The anti-inflammatory properties of co-occurring main megastigmane, saurobaccioside B (2) and structurally related vomifoliol (3) on LPS-stimulated murine macrophages RAW 274.7 have been evaluated.

Novel application of 1H NMR spectroscopy coupled with chemometrics for the authentication of dark chocolate

The applicability of 1H NMR spectroscopy coupled with chemometric in the quality control of dark chocolate was investigated for the first time to detect cocoa-butter equivalents (CBEs) above the allowed limit by European regulation. Blends of chocolate-fats with CBEs in the range 0–50 % were prepared and analyzed by 1H NMR spectroscopy. Datasets composed of peaks’ areas or spectral variables (fingerprinting) in glycerol region were tested for the creation of multivariate statistical models. Partial least-squares discriminant analysis (PLS-DA) and regression (PLS-R) methods were used to correctly identify the type of CBE and quantify its concentration respectively. The performances of the models created on the two datasets were evaluated in terms of chemometric indicators and compared. The robustness of models was investigated through the analysis of test sets and random permutation tests. Fingerprinting models revealed fruitful results in classifying and quantifying CBEs in blends demonstrating the applicability of NMR in chocolate quality control.

19F fast MAS (60–111 kHz) dipolar and scalar based correlation spectroscopy of organic molecules and pharmaceutical formulations

19F magic angle spinning (MAS) NMR spectroscopy is a powerful tool for characterization of fluorinated solids. The recent development of 19F MAS NMR probes, operating at spinning frequencies of 60–111 kHz, enabled analysis of systems spanning from organic molecules to pharmaceutical formulations to biological assemblies, with unprecedented resolution. Herein, we systematically evaluate the benefits of high MAS frequencies (60–111 kHz) for 1D and 2D 19F-detected experiments in two pharmaceuticals, the antimalarial drug mefloquine and a formulation of the cholesterol-lowering drug atorvastatin calcium. We demonstrate that 1H decoupling is essential and that scalar-based, heteronuclear single quantum coherence (HSQC) and heteronuclear multiple quantum coherence (HMQC) correlation experiments become feasible and efficient at the MAS frequency of 100 kHz. This study opens doors for the applications of high frequency 19F MAS NMR to a wide range of problems in chemistry and biology.

NMR applications to find and progress TREX1 binders

Inhibition of the exonuclease activity of Three-prime Repair EXonuclease 1 (TREX1) has emerged as a potential novel immunotherapeutic strategy. Herein we describe our screening approach to find initial low-affinity fragment hits for TREX1 from our 19F library and the use of both ligand- and target-based NMR methods for hit confirmation and validation. In a further step to support the early hit expansion stage we describe our setup of a 19F competition assay for KI determination of analogs.

Deformation Analysis of No-Insulation REBCO Coils Considering Turn-to-Turn Contact Configuration

In recent year, there has been remarkable progress in the use of high-field rare-earth barium copper oxide (REBCO) coils in NMR, MRI, and accelerator applications. No-insulation (NI) winding techniques are adopted to achieve high thermal stability and high current density. Thus, each winding in a non-impregnated NI REBCO coil can deform separately and move freely because of the thermal strain and electromagnetic force. The additional force and stress due to a screening current has also become an issue in REBCO coils. The screening current leads to a non-uniform force distribution in REBCO tapes and forces exceeding an acceptable value. It has been reported that REBCO coils have experienced mechanical deterioration or damage when operating under high magnetic fields. However, the detailed mechanism for this damage or deterioration has not been clarified. In order to clarify the detailed mechanism of this damage to a REBCO coil, the stress and strain during the winding, cooling down, charging, and discharging processes need to be evaluated. Furthermore, in NI REBCO coils, the turn-to-turn contact configurations are very important for the current bypassing, the thermal and mechanical stability. In previous studies, we have developed the numerical simulation code on the electromagnetic behavior of screening current and mechanical behavior of the turn-to-turn contact state. This study numerically evaluated the deformation and stress in REBCO tape and the turn-to-turn contact in NI REBCO coils.

Frontiers of NMR

This article is the content of the closing lecture delivered at the XIVth Manuel Rico Advanced NMR Course, held in Jaca (Spain) in June 2022. It is my personal impression on the technical frontiers where I expect new advances to expand even further the fields of NMR application, especially in the fields of biomedicine and biotechnology. It is dedicated to Robert Konrat on the occasion of his 60th birthday as an acknowledgement of his wide range of interest and vast scientific culture.

Scalable and Tunable Diamond Nanostructuring Process for Nanoscale NMR Applications.

Nanostructuring of a bulk material is used to change its mechanical, optical, and electronic properties and to enable many new applications. We present a scalable fabrication technique that enables the creation of densely packed diamond nanopillars for quantum technology applications. The process yields tunable feature sizes without the employment of lithographic techniques. High-aspect-ratio pillars are created through oxygen-plasma etching of diamond with a dewetted palladium film as an etch mask. We demonstrate an iterative renewal of the palladium etch mask, by which the initial mask thickness is not the limiting factor for the etch depth. Following the process, 300–400 million densely packed 100 nm wide and 1 μm tall diamond pillars were created on a 3 × 3 mm2 diamond sample. The fabrication technique is tailored specifically to enable applications and research involving quantum coherent defect center spins in diamond, such as nitrogen-vacancy (NV) centers, which are widely used in quantum science and engineering. To demonstrate the compatibility of our technique with quantum sensing, NV centers are created in the nanopillar sidewalls and are used to sense 1H nuclei in liquid wetting the nanostructured surface. This nanostructuring process is an important element for enabling the wide-scale implementation of NV-driven magnetic resonance imaging or NV-driven NMR.

Coils for large standoff relaxometry with unilateral magnets

Maximizing standoff distance by direct placement of probe coils on magnet bodies, while maximizing signal-to-noise is critical to the successful application of unilateral NMR. Two types of radio frequency (rf) coils for linear array, unilateral magnets are described: “simple fringe” and “split fringe coils.” These coils are designed to fully exploit the standoff distance of the unilateral magnet by placement directly on the magnet surface. Such placement fails for normal surface coils used for magnetic resonance due to eddy current induced shielding by the conductive magnet surface. The coil design strategy includes a rectangular cross section solenoid coil, either continuous or split in the center, mounted with the center axis of the coil parallel to the magnet surface. These geometries, when placed on a conducting surface, enhance the rf field produced in the sample region, outside of the solenoid coil. The spatial homogeneity of both rf coils are characterized using the ANSYS™ finite element modelling software. ANSYS™ modeled coil geometries led to homogeneous, surface displaced rf fields. These coils were then constructed and characterized with magnetic resonance imaging. Finally, two experiments that use these coils to perform large standoff relaxation measurements are described.

A simple protocol for the production of highly deuterated proteins for biophysical studies

Highly deuterated protein samples expand the biophysics and biological tool kit by providing, among other qualities, contrast matching in neutron diffraction experiments and reduction of dipolar spin interactions from normally protonated proteins in magnetic resonance studies, impacting both electron paramagnetic resonance and NMR spectroscopy. In NMR applications, deuteration is often combined with other isotopic labeling patterns to expand the range of conventional NMR spectroscopy research in both solution and solid-state conditions. However, preparation of deuterated proteins is challenging. We present here a simple, effective, and user-friendly protocol to produce highly deuterated proteins in Escherichia coli cells. The protocol utilizes the common shaker flask growth method and the well-known pET system (which provides expression control via the T7 promotor) for large-scale recombinant protein expression. One liter expression typically yields 5 to 50 mg of highly deuterated protein. Our data demonstrate that the optimized procedure produces a comparable quantity of protein in deuterium (2H2O) oxide M9 medium compared with that in 1H2O M9 medium. The protocol will enable a broader utilization of deuterated proteins in a number of biophysical techniques.

Current limitations of solid-state NMR in carbohydrate and cell wall research

High-resolution investigation of cell wall materials has emerged as an important application of biomolecular solid-state NMR (ssNMR). Multidimensional correlation experiments have become a standard method for obtaining sufficient spectral resolution to determine the polymorphic structure of carbohydrates and address biochemical questions regarding the supramolecular organization of cell walls. Using plant cellulose and matrix polysaccharides as examples, we will review how the multifaceted complexity of polysaccharide structure is impeding the resonance assignment process and assess the available biochemical and spectroscopic approaches that could circumvent this barrier. We will emphasize the ineffectiveness of the current methods in reconciling the ever-growing dataset and deriving structural information. We will evaluate the protocols for achieving efficient and homogeneous hyperpolarization across the cell wall material using magic-angle spinning dynamic nuclear polarization (MAS-DNP). Critical questions regarding the line-broadening effects of cell wall molecules at cryogenic temperature and by paramagnetic biradicals will be considered. Finally, the MAS-DNP method will be placed into a broader context with other structural characterization techniques, such as cryo-electron microscopy, to advance ssNMR research in carbohydrate and cell wall biomaterials.

A helical grid equivalent circuit model for an intra-layer no-insulation coil

The intra-layer no-insulation (LNI) coil, which has the advantages of self-protection and high magnetic field homogeneity, is of great potential in HTS NMR and MRI applications. Compared to the more commonly-used double-pancake coils, the transient characteristics are more complex due to additional axial current. While the present circuit model cannot accurately describe the geometry of the LNI coil and the internal characteristics of each turn of the coil, a helical grid equivalent circuit model with consideration of types of mutual inductances is proposed in this paper. In the circuit model, details of the coil are characterized with subdivided helical surface elements in each turn, and each helical surface element can be equivalent to corresponding circuit parameters. The circuit model is verified by a comparison experiment with an intra-layer insulation coil. And elaborate current distributions in each turn of the LNI coil can be obtained with this circuit model. Analysis results demonstrate that the azimuthal current and the axial current are always symmetrically distributed about the middle plane, and the radial current is always anti-symmetrically distributed about the midplane. The circuit model can be used to simulate the quench electromagnetic characteristics of the LNI coil in the future.

Review on Chemometrics Techniques for Detection of Edible Fats and Oils Using NMR


 The assessment and authentication of edible fats using NMR spectroscopy and several techniques in chemometrics for the determination of the compounds that are present in the mixture of edible fats and oils were reviewed. NMR spectroscopy was used to determine the compound in edible fats and Principal Component Analysis (PCA) was performed on the NMR data for compound grouping. Meanwhile, Partial Least Square (PLS) was used to predict the amount of adulteration that present in the sample with high accuracy. The application of NMR and these chemometrics techniques have speed up the analysis of fats and oils, and given good results in the detection of compound in the edible fats and the determination of adulterant in the fats mixtures that can be a potential techniques for halal authentication. 

Active shim coils design for Halbach magnet based on inverse boundary element method

With advantages of small volume, high field strength, and compact stray field, the Halbach array magnet is of great potential in desktop NMR applications. However, field inhomogeneity poses a main obstacle to its applications. Active shimming is necessary for improving the field homogeneity. An active shim coil design method for cylindrical Halbach magnet based on inverse boundary element method (iBEM) is introduced in this work. Shim coils targeting 1st∼3rd and Z4/Z5/Z6 spherical harmonic (SH) terms were designed with constraints of field accuracy, resistance, inductance, and current density. Wire loops and symmetric property influence were discussed to further improve the performance of high-order shim coils. Finally, with the prototype of the shim coils constructed, field pattern and SH transformation proved that the coils designed could fit the target SH distribution, though contamination from low-order components existed in high-order terms. A practical shimming experiment on the Halbach magnet has improved the homogeneity from 40.3 ppm to 3.8 ppm in radius 2.5 mm, height 5 mm cylindrical sample space, verifying the coils' compensation ability. This work provides a flexible inverse coil design method for cylindrical Halbach magnet and discusses the high-order shim coil design and implementation, which is potential in nuclear magnetic resonance applications based on Halbach magnet arrays.

Quality Assessment of Medicinal Plants via Chemometric Exploration of Quantitative NMR Data: A Review

Since ancient times, herbal medicines (HM) have played a vital role in worldwide healthcare systems. It is therefore critical that a thorough evaluation of the quality and control of its complicated chemical makeup be conducted, in order to ensure its efficacy and safety. The notion of HM chemical prints, which aim to acquire a full characterization of compound chemical matrices, has become one of the most persuasive techniques for HM quality evaluation during the last few decades. The link between NMR and chemometrics is discussed in this article. The chemometric latent variable technique has been shown to be extremely valuable in inductive studies of biological systems as well as in solving industrial challenges. The results of unsupervised data exploration utilizing main component analysis as well as the multivariate curve resolution, were various. On the other hand, many contemporary NMR applications in metabolomics and quality control are based on supervised regression or classification analyses.