Nuclear Magnetic Resonance Detection Research Articles

Cumulative damage characteristics of rock samples under cyclic low energy inclined plane impact

The ore pass wall in underground mines is often damaged by the impact and wear caused by unloaded ores. Studying the mechanisms of rock damage and failure under different impact angles can provide technical insights for the design and maintenance of the ore passes. This study employed an inclined impact experimental device along with a drop hammer loading test machine to perform cyclic low-energy impact tests on sandstone samples at five different inclined plane angles. The porosity of the rock samples was measured using a nuclear magnetic resonance (NMR) detection system, which provided data on porosity, T2 spectrum distribution, and NMR images of the samples after different numbers of impacts at different slope angles. The results indicate that: (1) Under cyclic inclined plane impact loading, an increase in the inclination angle, leads to reduced damage to the rock sample. The rock sample impacted at a 45° inclined plane exhibited the most severe damage. Rock samples with large inclination angles are more prone to experience rupture fractures at the tip of the inclined plane, primarily due to shear-tensile failure. The porosity changes dramatically at initially slope angles, resulting in greater damage. (2) As the number of impacts increases, the porosity of the samples first decreases, then increases, and subsequently decreases again. This progression corresponds to the closure of large pores following the first impact, followed by the expansion of micropores into macropores after 5 impacts, ultimately leading to gradual degradation of the samples until failure. (3) As the number of impacts increases, new cracks form within the rock sample and small cracks expand. Despite an increase in the number of micropores, the macropores still exert a significant influence on the rock samples, with the macropore spectrum area accounting for over 95%.

Real‐Time Nuclear Magnetic Resonance Detection Using Maximum Likelihood Estimation with Single‐Shallow‐Nitrogen‐Vacancy Centers in Quantum Heterodyne Measurements

Single‐nitrogen‐vacancy (NV) centers in diamond are highly promising quantum nuclear magnetic resonance (NMR) sensors. However, their exposure to many sources of noise, such as surface impurities, shot noise from avalanche photodiode overlaps, and spin‐state projection errors inherent in quantum systems, limits their usefulness. Often, long measurement durations are required to accumulate sufficient data for NMR signal detection via fast Fourier transform spectrometry. For practical reasons, methods to shorten the necessary accumulation time for NMR signal detection are greatly desired. In this article, an on‐line formulation of maximum likelihood estimation (MLE) signal processing for quantum heterodyne NMR measurements is presented as a step toward this goal. This MLE method reduces the required data accumulation time by orders of magnitude and provides good estimates of target frequency locales in real time. These results are significant to practitioners of NMR detection with single‐NV centers in diamond who require a quick litmus test for potential signals when probing a wide area.

Direct Chiral Discrimination with NMR.

Unaided nuclear magnetic resonance (NMR) spectroscopy is considered incapable of distinguishing enantiomers. However, as first derived by A.D. Buckingham, the tensor coupling the electric and magnetic dipoles is space-dependent, which varies according to the molecular structure, hence, would be different for two enantiomers. Exploiting the odd-parity coupling tensor, a new variant of a double-resonant radiofrequency (RF) NMR detector is developed, which is sensitive to both electric and magnetic dipoles. Using the detector, a new method for liquid-state NMR is developed and elaborated, with which two enantiomers are successfully discriminated.

Crown ethers: Small organic molecules unexpectedly hidden in nuclear magnetic resonance

The new class of ten macrocyclic compounds, lactic acid derived crown ethers, was designed and synthesized. They mainly composed of lactic acid and benzene or iodobenzene skeletons, and the introduction of iodine on the benzene ring was crucial to the formation of more regular crown ether conformation, starting from the diacid precursor. They possessed stable and larger cavities than classical macrocycles such as cyclodextrins. These crown ethers were discovered hiding function onto small molecules such as ethyl lactate, methanol, ethanol, aniline and phenol in nuclear magnetic resonance detection.

200 GHz single chip microsystems for dynamic nuclear polarization enhanced NMR spectroscopy

Dynamic nuclear polarization (DNP) is one of the most powerful and versatile hyperpolarization methods to enhance nuclear magnetic resonance (NMR) signals. A major drawback of DNP is the cost and complexity of the required microwave hardware, especially at high magnetic fields and low temperatures. To overcome this drawback and with the focus on the study of nanoliter and subnanoliter samples, this work demonstrates 200 GHz single chip DNP microsystems where the microwave excitation/detection are performed locally on chip without the need of external microwave generators and transmission lines. The single chip integrated microsystems consist of a single or an array of microwave oscillators operating at about 200 GHz for ESR excitation/detection and an RF receiver operating at about 300 MHz for NMR detection. This work demonstrates the possibility of using the single chip approach for the realization of probes for DNP studies at high frequency, high field, and low temperature.

Rapid Non-Destructive Detection Technology in the Field of Meat Tenderness: A Review.

Traditionally, tenderness has been assessed through shear force testing, which is inherently destructive, the accuracy is easily affected, and it results in considerable sample wastage. Although this technology has some drawbacks, it is still the most effective detection method currently available. In light of these drawbacks, non-destructive testing techniques have emerged as a preferred alternative, promising greater accuracy, efficiency, and convenience without compromising the integrity of the samples. This paper delves into applying five advanced non-destructive testing technologies in the realm of meat tenderness assessment. These include near-infrared spectroscopy, hyperspectral imaging, Raman spectroscopy, airflow optical fusion detection, and nuclear magnetic resonance detection. Each technology is scrutinized for its respective strengths and limitations, providing a comprehensive overview of their current utility and potential for future development. Moreover, the integration of these techniques with the latest advancements in artificial intelligence (AI) technology is explored. The fusion of AI with non-destructive testing offers a promising avenue for the development of more sophisticated, rapid, and intelligent systems for meat tenderness evaluation. This integration is anticipated to significantly enhance the efficiency and accuracy of the quality assessment in the meat industry, ensuring a higher standard of safety and nutritional value for consumers. The paper concludes with a set of technical recommendations to guide the future direction of non-destructive, AI-enhanced meat tenderness detection.

Evaluating lumbar disc degeneration by MRI quantitative metabolic indicators: the perspective of factor analysis

PurposeThis study aimed to investigate an early diagnostic method for lumbar disc degeneration (LDD) and improve its diagnostic accuracy.MethodsQuantitative biomarkers of the lumbar body (LB) and lumbar discs (LDs) were obtained using nuclear magnetic resonance (NMR) detection technology. The diagnostic weights of each biological metabolism indicator were screened using the factor analysis method.ResultsThrough factor analysis, common factors such as the LB fat fraction, fat content, and T2* value of LDs were identified as covariates for the diagnostic model for the evaluation of LDD. This model can optimize the accuracy and reliability of LDD diagnosis.ConclusionThe application of biomarker quantification methods based on NMR detection technology combined with factor analysis provides an effective means for the early diagnosis of LDD, thereby improving diagnostic accuracy and reliability.

Gradient-based surface nuclear magnetic resonance for groundwater investigation

In medical magnetic resonance imaging, spatial localization (imaging) is based upon the application of controlled magnetic field gradients on top of the main magnetic field to spatially modulate the frequency and/or phase of the nuclear magnetic resonance (NMR) signal across the volume of investigation. In this work, we have applied similar physical principles to produce controlled magnetic field gradients during surface NMR-based groundwater investigations. In this approach, a gradient pulse of variable amplitude or duration is applied immediately after the excitation pulse to cause predictable phase encoding of the NMR signal as a function of depth. This approach is also applicable to emerging surface NMR detection methods that use a prepolarization field with fast nonadiabatic turn-off to generate detectable NMR signals from the shallow subsurface. In this case, the gradient pulse is applied after terminating the prepolarization field and provides a heretofore unavailable means of localizing the NMR response as a function of depth. The application of gradients can also be combined with tip-angle-based modulation to yield higher imaging resolution than can be achieved through either gradient- or tip-angle-based imaging alone. We implemented this new gradient-based capability into a surface NMR gradient generation accessory that is compatible with the GMR-Flex instrument and developed surface NMR-specific forward modeling and linear inverse models. We validated the accuracy of this novel gradient-based sNMR technology using computer simulations, experiments using a small pool filled with a discrete layer of bulk water, and field experiments at well-characterized groundwater test sites along Ebey Island, WA, and Larned, KS. The gradient-based sNMR imaging observations were compared with high-resolution direct push NMR results observed at these sites. The results of computer simulations and field experiments indicate improvements in both the detection (signal-to-noise ratio) and spatial resolution of shallow subsurface water content using gradient-based surface NMR, compared with traditional surface NMR imaging methods.

Contribution of protein conformational heterogeneity to NMR lineshapes at cryogenic temperatures

While low-temperature Nuclear Magnetic Resonance (NMR) holds great promise for the analysis of unstable samples and for sensitizing NMR detection, spectral broadening in frozen protein samples is a common experimental challenge. One hypothesis explaining the additional linewidth is that a variety of conformations are in rapid equilibrium at room temperature and become frozen, creating an inhomogeneous distribution at cryogenic temperatures. Here, we investigate conformational heterogeneity by measuring the backbone torsion angle (Ψ) in Escherichia coli Dihydrofolate Reductase (DHFR) at 105 K. Motivated by the particularly broad N chemical shift distribution in this and other examples, we modified an established NCCN Ψ experiment to correlate the chemical shift of Ni+1 to Ψi. With selective 15N and 13C enrichment of Ile, only the unique I60-I61 pair was expected to be detected in 13C'-15N correlation spectrum. For this unique amide, we detected three different conformation basins based on dispersed chemical shifts. Backbone torsion angles Ψ were determined for each basin: 114 ± 7° for the major peak and 150 ± 8° and 164 ± 16° for the minor peaks as contrasted with 118° for the X-ray crystal structure (and 118° to 130° for various previously reported structures). These studies support the hypothesis that inhomogeneous distributions of protein backbone torsion angles contribute to the lineshape broadening in low-temperature NMR spectra.

Phase Change Study of a New Two-Phase Absorbent Based on DAP.

In order to overcome the drawbacks of conventional absorbents, which exhibit slow absorption rates and low absorption loads, this study suggests enhancing the absorbent system for CO2 absorption by incorporating a nonaqueous solvent into 1,3-propanediamine (DAP) and tetramethylethylenediamine (TMEDA), resulting in a two-phase system. The mechanism of solvent absorption of CO2 was investigated using nuclear magnetic resonance (NMR) carbon spectroscopy. By comparing the absorption load, fraction ratio, and viscosity of different absorbents after absorbing carbon dioxide, the two-phase absorbents with good performance were selected. The poor water absorbent consisting of the DAP/TMEDA system exhibited an absorption load of 3.8 mol/kg, surpassing that of the conventional 30% ethanolamine solution. A nonaqueous solvent is added to the system to replace some of the water to reduce the fraction. After adding different nonaqueous solvents, the phase separation system was screened after 2 h of CO2 absorption. The system with good performance was tested for the absorption of the solution under different amine concentration and water concentration tests. It is found that the absorption load of the DAP/TMEDA/diglyme system is 3.2 mol/kg, but the fraction can be reduced to 38%. The significant reduction in rich phase volume is beneficial for reducing the size and cost of regeneration tower. According to NMR detection and quantum chemical calculations, it was found that DAP/TMEDA absorbs carbon dioxide to form carbamate. DAP acts as the main absorbent, while TMEDA and nonaqueous solvents do not participate in the absorption reaction. Nonaqueous solvents were found to accelerate the solution phase separation due to the salt precipitation reaction.

Pore-pressure and stress-coupled creep behavior in deep coal: Insights from real-time NMR analysis

Understanding the variations in microscopic pore-fracture structures (MPFS) during coal creep under pore pressure and stress coupling is crucial for coal mining and effective gas treatment. In this manuscript, a triaxial creep test on deep coal at various pore pressures using a test system that combines in-situ mechanical loading with real-time nuclear magnetic resonance (NMR) detection was conducted. Full-scale quantitative characterization, online real-time detection, and visualization of MPFS during coal creep influenced by pore pressure and stress coupling were performed using NMR and NMR imaging (NMRI) techniques. The results revealed that seepage pores and microfractures (SPM) undergo the most significant changes during coal creep, with creep failure gradually expanding from dense primary pore fractures. Pore pressure presence promotes MPFS development primarily by inhibiting SPM compression and encouraging adsorption pores (AP) to evolve into SPM. Coal enters the accelerated creep stage earlier at lower stress levels, resulting in more pronounced creep deformation. The connection between the micro and macro values was established, demonstrating that increased porosity at different pore pressures leads to a negative exponential decay of the viscosity coefficient. The Newton dashpot in the ideal viscoplastic body and the Burgers model was improved using NMR experimental results, and a creep model that considers pore pressure and stress coupling using variable-order fractional operators was developed. The model’s reasonableness was confirmed using creep experimental data. The damage-state adjustment factors ω and β were identified through a parameter sensitivity analysis to characterize the effect of pore pressure and stress coupling on the creep damage characteristics (size and degree of difficulty) of coal.

Quantitative Analysis in Continuous-Flow ^1H Benchtop NMR Spectroscopy by Paramagnetic Relaxation Enhancement

Nuclear magnetic resonance (NMR) spectroscopy is an excellent tool for reaction and process monitoring. Process monitoring is often carried out online, where the analytic device is operated in flow mode. Benchtop NMR spectrometers are especially well-suited for these applications because they can be installed close to the studied process. However, quantitative analysis of a fast-flowing liquid with NMR spectroscopy is challenging because short residence times in the magnetic field of the spectrometer result in inefficient polarization buildup and thus poor signal intensity. This is particularly problematic for benchtop NMR spectrometers, where it severely limits the flow velocity in quantitative measurements. One method for increasing polarization in continuous-flow NMR spectroscopy is paramagnetic relaxation enhancement (PRE). Here, the interaction of the studied liquid with a PRE agent significantly accelerates the buildup of nuclear polarization prior to NMR detection, which enables quantitative measurements at high flow velocities. For process monitoring applications, the synthesis of robust and chemically inert immobilized PRE agents is mandatory. This was accomplished in the present work, where a new PRE agent is tested on 12 common solvents including water, acetonitrile, 1,4-dioxane, and binary mixtures with quantitative benchtop ^1H NMR spectroscopy at 1 Tesla. The results show that the flow regime for quantitative measurements can be greatly extended by the use of the synthesized PRE agent.

High-resolution nanoscale NMR for arbitrary magnetic fields

Nitrogen vacancy (NV) centers are a major platform for the detection of nuclear magnetic resonance (NMR) signals at the nanoscale. To overcome the intrinsic electron spin lifetime limit in spectral resolution, a heterodyne detection approach is widely used. However, application of this technique at high magnetic fields is yet an unsolved problem. Here, we introduce a heterodyne detection method utilizing a series of phase coherent electron nuclear double resonance sensing blocks, thus eliminating the numerous Rabi microwave pulses required in the detection. Our detection protocol can be extended to high magnetic fields, allowing chemical shift resolution in NMR experiments. We demonstrate this principle on a weakly coupled 13C nuclear spin in the bath surrounding single NV centers, and compare the results to existing heterodyne protocols. Additionally, we identify the combination of NV-spin-initialization infidelity and strong sensor-target-coupling as linewidth-limiting decoherence source, paving the way towards high-field heterodyne NMR protocols with chemical resolution.

Dead Time-Free Detection of NMR Signals Using Voltage-Controlled Oscillators

In this paper, we introduce voltage-controlled oscillators (VCOs) as a new type of nuclear magnetic resonance (NMR) detector, enabling dead time-free detection of NMR signals after an excitation pulse as well as the real-time inductive detection of Rabi oscillations during the pulse. Together with the theory of operation, we present the details of a custom-designed prototype implementation of a VCO-based NMR detector with an operating frequency around 62 MHz. The proof-of-concept measurements obtained with this prototype clearly demonstrate the possibility of performing dead time-free NMR experiments with coherent spin manipulation. Moreover, we also experimentally verified the capability of VCO-based detectors for performing real-time inductive detection of Rabi oscillations during the excitation pulse.

Large cross-effect dynamic nuclear polarisation enhancements with kilowatt inverting chirped pulses at 94 GHz

Dynamic nuclear polarisation (DNP) is a process that transfers electron spin polarisation to nuclei by applying resonant microwave radiation, and has been widely used to improve the sensitivity of nuclear magnetic resonance (NMR). Here we demonstrate new levels of performance for static cross-effect proton DNP using high peak power chirped inversion pulses at 94 GHz to create a strong polarisation gradient across the inhomogeneously broadened line of the mono-radical 4-amino TEMPO. Enhancements of up to 340 are achieved at an average power of a few hundred mW, with fast build-up times (3 s). Experiments are performed using a home-built wideband kW pulsed electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz, integrated with an NMR detection system. Simultaneous DNP and EPR characterisation of other mono-radicals and biradicals, as a function of temperature, leads to additional insights into limiting relaxation mechanisms and give further motivation for the development of wideband pulsed amplifiers for DNP at higher frequencies.

High-speed countercurrent chromatography with offline detection by electrospray mass spectrometry and nuclear magnetic resonance detection as a tool to resolve complex mixtures: A practical approach using Coffea arabica leaf extract.

Many secondary metabolites isolated from plants have been described in the literature owing to their important biological properties and possible pharmacological applications. However, the identification of compounds present in complex plant extracts has remained a great scientific challenge, is often laborious, and requires a long research time with high financial cost. The aim of this study was to develop a method that allows the identification of secondary metabolites in plant extracts with a high degree of confidence in a short period of time. In this study, an ethanolic extract of Coffea arabica leaves was used to validate the proposed method. Countercurrent chromatography was chosen as the initial step for extraction fractionation using gradient elution. Resulting fractions presented a variation of compounds concentrations, allowing for statistical total correlation spectroscopy (STOCSY) calculations between liquid chromatography coupled with high-resolution tandem mass spectrometry (LC-HRMS/MS) and NMR across fractions. The proposed method allowed the identification of 57 compounds. Of the annotated compounds, 20 were previously described in the literature for the species and 37 were reported for the first time. Among the inedited compounds, we identified flavonoids, alkaloids, phenolic acids, coumarins, and terpenes. The proposed method presents itself as a valid alternative for the study of complex extracts in an effective, fast, and reliable way that can be reproduced in the study of other extracts.

Noncontact Evaluation of HTS Cylinder for Compact Cryogen-Free NMR

Herein, a compact cryogen-free nuclear magnetic resonance (NMR) system is developed using a stacked high-temperature superconducting (HTS) bulk system. To compensate for magnetic field uniformity, an HTS cylinder is installed inside the measurement space. The cylinder is wound with REBCO tapes placed on the surface of a copper cylinder. The uniformity of its critical current density is important for NMR signal detection. Such an operation requires an examination of the quality of the critical-current-density distribution of the cylinder. A noncontact measurement method is required for such an examination. When a magnetic field is applied, the superconductor exhibits a demagnetization effect. Moreover, if any defect exists in any part of the superconducting tape, that particular part would contain no demagnetization, thus disturbing the relevant magnetic field distribution. In this study, this phenomenon is investigated using DC and AC magnetic fields. The magnets and sensor are placed inside the HTS cylinder, and magnetic fields are applied to the HTS cylinder surface. The results confirm that the proposed method is effective and applicable for evaluating the critical-current distribution.

Magnetic relaxation switching biosensor for one-step detection of Vibrio parahaemolyticus based on click chemistry-mediated sol-gel system

In this study, a magnetic relaxation switching (MRS) biosensor was developed for one-step detection of pathogenic bacteria Vibrio parahaemolyticus (VP). The biosensor is based on a click chemistry-mediated sol-gel system and utilizes low-field nuclear magnetic resonance (LF NMR) detection. VP aptamer (Apt)-coated hollow mesoporous silica microspheres (HMSMs) with saturated sodium ascorbate (SAA) solution sealed inside, HMSMs@SAA&Apt, are designed as the signal unit. When the target VP is present, the Apt binds to VP and releases SAA from the signal unit. The released SAA reduces Cu2+ in the test solution to Cu+, which catalyzes the click chemistry reaction between azide-modified polyethylene glycol (PEG-Azide) and acetylene-modified polyacrylic acid (PAA-Alkyne). The sol-gel transition is triggered, a large amount of "free" water is converted into "bound" water, resulting in the decrease of transverse relaxation time (T2). Under the optimal experimental conditions, the variation of T2 (ΔT2) was linearly related to the logarithm of VP concentration in the range of 10 ∼ 1.0 × 108 CFU/mL, with a limit of detection of 5 CFU/mL. The assay demonstrated good selectivity, stability, and reproducibility. It is completed in one step, holding promising applications in the rapid field detection of pathogenic bacteria.

Planar Waveguide NMR Gradients (B0 and B1) for spatiotemporal Investigations of Anticancer Drug Concentration in 3D Cancer Cell Cultures

Despite the progression in cancer therapeutic approaches, cancer is still the leading cause of death worldwide with a steadily increasing incidence rate. In Jordan, CRC is the most common type of cancer among men and the second most common among women, while being one of the most accruing cancers in Germany.
 The difficulties in cancer treatments arise from the poor correlation between in vivo and in in vitro anti-cancer drug testing results and cancer cells resistance to chemotherapy, which are attributed to the heterogeneity of cancer cells, and the interaction of cancer cells with non-cancerous cells in the tumor microenvironment (TME). In addition to, the several mechanisms, that governs DNA damages repair, epigenetics, epithelial to mesenchymal transition (EMT).
 Cell culture techniques have been developed to construct in vitro multicellular cancer spheroids (MTCS) that mimic cell-cells interaction and the cellular organization in the TME. They also illustrate the proliferation gradient of solid tumors, and the nutrition and gas supply to cancer cells at different depth in the spheroid. Therefore, they are considered an excellent in vitro cancer model to study the efficiency and to investigate the penetration depth of the anti-cancer materials.
 Nuclear Magnetic Resonance (NMR) spectroscopy is a reliable analytical method that gives comprehensive and rich chemical information, along with high speciation performance. It is one of the major noninvasive tools for metabolomics, therefore it has been utilized to study the metabolic profiling of freshly isolated- non-destructed tissues, and living in vitro cellular models.
 A micro-imaging technique for real-time NMR investigations is developed to study the penetration depth, rate, and effective diffusion coefficients of anti-cancer materials through cancer spheroids. This technique is based on our patented invention of planar waveguide micro slot NMR detector with on board thermal regulator integrated and a microfluidic device. Based on this innovative development, we are able to perform real-time magnetic resonance spectroscopic imaging (MRSI) on a living synthetic tissue constructed in micrometer scale to monitor drug penetration and diffusion, while providing spectroscopic information about the production and degradation of metabolites in picomoles concentrations.

Nuclear Magnetic Resonance Detection of Hydrogen Bond Network in a Proton Pump Rhodopsin RxR and Its Alteration during the Cyclic Photoreaction.

Hydrogen bond formation and deformation are crucial for the structural construction and functional expression of biomolecules. However, direct observation of exchangeable hydrogens, especially for oxygen-bound hydrogens, relevant to hydrogen bonds is challenging for current structural analysis approaches. Using solution-state NMR spectroscopy, this study detected the functionally important exchangeable hydrogens (i.e., Y49-ηOH and Y178-ηOH) involved in the pentagonal hydrogen bond network in the active site of R. xylanophilus rhodopsin (RxR), which functions as a light-driven proton pump. Moreover, utilization of the original light-irradiation NMR approach allowed us to detect and characterize the late photointermediate state (i.e., O-state) of RxR and revealed that hydrogen bonds relevant to Y49 and Y178 are still maintained during the photointermediate state. In contrast, the hydrogen bond between W75-εNH and D205-γCOO- is strengthened and stabilizes the O-state.