Nuclear Magnetic Resonance Experiments Research Articles

Molecular Dynamics Simulation of Methane Adsorption and Diffusion

To study the adsorption and diffusion mechanism of low-rank coal at the microscopic level, samples of Fukang low-rank coal were collected, and the elemental composition, carbon type distribution and functional group type of the Fukang low-rank coal structure were determined by elemental analysis (Ea), Fourier-transform interferometric radiometer (FTIR), X-ray photoelectron spectroscopy (XPS) and 13C nuclear magnetic resonance (13C NMR) experiments to construct a 2D molecular structure of the coal and a 3D macromolecular structure model. The adsorption and diffusion characteristics of methane were researched by giant regular Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The results showed that the excess adsorption amount of methane increased and then decreased with the increase in pressure. The diffusion of methane showed two stages with increasing pressure: a sharp decrease in the diffusion coefficient from 0.5 to 5.0 MPa and a slow decrease in the diffusion coefficient from 5.0 to 15.0 MPa. The lower the pressure, the larger the effective radius of the CH4 and C atoms, and the higher the temperature, the more pronounced the diffusion and the larger the effective radius.

New Monoterpenoid as the Sex Pheromone of Spanish Populations of the Longtailed Mealybug Pseudococcus Longispinus (Hemiptera: Pseudococcidae).

Pseudococcus longispinus (Targioni-Tozzetti) (Hemiptera: Coccoidea: Pseudococcidae), a polyphagous and cosmopolitan pest native to Australia, is a highly damaging pest for numerous crops of economic importance. The sex pheromone of this species (2-(1,5,5-trimethylcyclopent-2-en-1-yl)ethyl acetate), currently used for pest monitoring purposes, was not attractive to males in field experiments conducted in Spanish persimmon orchards infested with this mealybug. The virgin and mated female volatile profiles of these P. longispinus populations were studied by the volatile collection of effluvia in Porapak-Q. The resulting extracts were analyzed by gas chromatography coupled to mass spectrometry (GC-MS), revealing a new compound specific to virgin females and different from the previously described sex pheromone. Based on GC-MS data and nuclear magnetic resonance experiments, we envisaged monoterpene 2-(1,5-dimethyl-4-methylenecyclopent-2-en-1-yl)ethyl acetate as the new sex pheromone candidate, which was synthesized and shown to be attractive in the field to P. longispinus males of the Spanish population.

Single-Scan Heteronuclear 13C-15N J-Coupling NMR Observations Enhanced by Dissolution Dynamic Nuclear Polarization.

Heteronuclear 13C-15N couplings were measured in single-scan nuclear magnetic resonance (NMR) experiments for a variety of nitrogen-containing chemical compounds with varied structural characteristics, by using a one-dimensional (1D) 13C-15N multiple-quantum (MQ)-filtered experiment. Sensitivity limitations of the MQ filtering were overcome by the combined use of 15N labeling and dissolution dynamic nuclear polarization (dDNP), performed at cryogenic conditions and followed by quick and optimized sample melting and transfer procedures. Coupling information could thus be obtained from nucleotide bases, amino acids, urea, and aliphatic and aromatic amides, including the measurement of relatively small J-couplings directly from the 1D filtered spectra. This experiment could pave the way for NMR-based analytical applications that investigate structural and stereochemical insights into nitrogen-containing compounds, including dipeptides and proteins, while relying on heteronuclear couplings and nuclear hyperpolarization.

Determination of Acetylamantadine by γ-Cyclodextrin-Assisted α-HL Nanopore for Potential Cancer Prediagnosis.

The high expression of Spermidine/spermine N1-acetyltransferase (SSAT-1) is an important indicator in early cancer diagnosis. Here, we developed a nanopore-based methodology with γ-cyclodextrin as an adaptor to detect and quantify acetylamantadine, the specific SSAT-1-catalyzed product from amantadine, to accordingly reflect the activity of SSAT-1. We employ γ-cyclodextrin and report that amantadine cannot cause any secondary signals in γ-cyclodextrin-assisted α-HL nanopore, while its acetylation product, acetylamantadine, does. This allows γ-cyclodextrin to practically detect acetylamantadine in the interference of excessive amantadine, superior to the previously reported β-cyclodextrin. The quantification of acetylamantadine was not interfered with even a 50-fold amantadine and displayed no interference in artificial urine sample analysis, which indicates the good feasibility of this nanopore-based methodology in painless cancer prediagnosis. In addition, the discrimination mechanism is also explored by 2-D nuclear magnetic resonance (NMR) and nanopore experiments with a series of adamantane derivatives with different hydrophilic and hydrophobic groups. We found that both the hydrophobic region matching effect and hydrophilic interactions play a synergistic effect in forming a host-guest complex to further generate the characteristic signals, which may provide insights for the subsequent design and study of drug-cyclodextrin complexes.

The Molecular Mechanism of FABP4 Inhibition Effects of GAS and 4-HBA in Gastrodia elata Blume Was Discussed Based on NMR and Molecular Docking.

To isolate gastrodin (GAS), 4-hydroxybenzyl alcohol (4-HBA), and phenolic compounds from Chinese medicine Gastrodia elata Blume, and to explore the binding mode of fatty acid binding protein 4 (FABP4/aP2) that is closely related to macrophage inflammation, we study their anti-inflammatory targets. After the ultrasonic extraction of the main active components with 70% ethanol, three resins and three eluents were selected, and eight phenolic monomers with similar structures, such as gastrodin and 4-hydroxybenzyl alcohol, were isolated from Gastrodia elata by AB-8 macroporous resin and silica gel column chromatography and eluted with the CHCl3-MeOH gradient. Their structures were identified by HPLC and nuclear magnetic resonance (NMR). The FABP4 protein was added to GAS and 4-HBA, and the NMR experiment was performed to observe ligand binding. Finally, according to the spectral information of STD-NMR and molecular docking technology, the interaction between ligands and protein was studied. The fluorescence competition experiment confirmed that both GAS and 4-HBA were in the binding cavity of FABP4. Moreover, 3-phenoxy-2-phenylbenzoic acid (PPA) is a possible inhibitor of FABP4, reducing macrophage-related inflammation and endoplasmic reticulum stress. This work provides a new basis for the anti-inflammatory mechanism of Gastrodia elata, paving the way for the research and development of FABP4 inhibitor drugs.

Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure.

Exploration of compositional disorder using conventional diffraction-based techniques is challenging for systems containing isoelectronic ions possessing similar coherent neutron scattering lengths. Here, we show that a multinuclear solid-state Nuclear Magnetic Resonance (NMR) approach provides compelling insight into the Ga3+/Ge4+ cation distribution and oxygen anion transport in a family of solid electrolytes with langasite structure and La3Ga5-xGe1+xO14+0.5x composition. Ultrahigh field 71Ga Magic Angle Spinning (MAS) NMR experiments acquired at 35.2 T offer striking resolution enhancement, thereby enabling clear detection of Ga sites in different coordination environments. Three-connected GaO4, four-connected GaO4 and GaO6 polyhedra are probed for the parent La3Ga5GeO14 structure, while one additional spectral feature corresponding to the key (Ga,Ge)2O8 structural unit which forms to accommodate the interstitial oxide ions is detected for the Ge4+-doped La3Ga3.5Ge2.5O14.75 phase. The complex spectral line shapes observed in the MAS NMR spectra are reproduced very accurately by the NMR parameters computed for a symmetry-adapted configurational ensemble that comprehensively models site disorder. This approach further reveals a Ga3+/Ge4+ distribution across all Ga/Ge sites that is controlled by a kinetically governed cation diffusion process. Variable temperature 17O MAS NMR experiments up to 700 °C importantly indicate that the presence of interstitial oxide ions triggers chemical exchange between all oxygen sites, thereby enabling atomic-scale understanding of the anion diffusion mechanism underpinning the transport properties of these materials.

A Joint Inversion Method Algorithm for T2-Pc two Dimensional NMR based on Logistic Functions

Data processing is a key step in the analysis of nuclear magnetic resonance (NMR) experimental data, and efficient and accurate computer inversion algorithms are the core of the T2-Pc two-dimensional NMR experiment. T2-Pc two-dimensional NMR experiment is an advanced experimental method that characterizes reservoir connectivity through two dimensions: relaxation time and capillary pressure, and can obtain irreducible water saturation under different pressure differences. However, the algorithm currently used for T2-Pc two-dimensional spectrum inversion uses a mutation kernel function, resulting in low accuracy of calculation results. This paper uses the Logistic function as the two-dimensional inversion kernel function, rewrites the inversion algorithm, and obtains more accurate inversion results. Numerical simulations have proven that the T2-Pc two-dimensional map obtained by this method not only has higher resolution, but also has greater applicability in the case of low signal-to-noise ratio and a small number of centrifugal echo groups. Practice has found that the proposed method can reduce the number of centrifugations during the experiment and significantly improve the efficiency of T2-Pc two-dimensional nuclear magnetic resonance experiments.

Mechanism analysis of injection technique of water composition modification for enhanced oil recovery

ABSTRACT By adjusting the composition of injection water, including ionic type and strength, the goal of enhance oil recovery rate can be achieved. However, there is no clear understanding of which factor, ionic type or strength, has a greater impact. In this paper, based on the formation water of the offshore G oilfield, various brines with different ionic strengths and types were prepared. By measuring the zeta potential of rock powder and oil droplets, three-phase contact angle, interfacial tension between oil and water, emulsification properties of brines, and film strength of oil-water interface, the variation rules of the core wettability and emulsification performance of brine were systematically analyzed when the ionic strength and ionic type were changed. The experimental results showed that ionic strength has a greater impact than that of ionic type. For the oil-water-solid (rock) system of the G oilfield, an ionic strength of 82 mM/kg is the threshold for low salinity effect. Reducing ionic strength resulted in an increase in the hydrophilicity of rock and the ability of water flooding to emulsify oil droplets, which contribute to the improvement of oil displacement efficiency. Theoretically, water flooding to enhance oil recovery can be achieved by only reducing the ionic strength. This understanding was verified by dual polarization interferometry (DPI) experiments and low-field nuclear magnetic resonance experiments, which showed that reducing the salinity of the injection water from 42,000 mg/L (ionic strength of 820 mM/kg) to 4200 mg/L (ionic strength of 82 mM/kg) enhanced the oil recovery by 7.9%.

Experimental investigation of geometric quantum speed limits in an open quantum system

The quantum speed limit (QSL) is a fundamental lower bound on the evolution time for quantum systems, and its tightness has been observed to be dependent on the properties of the physical process. However, experimental studies exploring the QSL in open quantum systems are still missing. Here, we studied geometric quantum speed limits of a qubit subject to decoherence in an ensemble of chloroform molecules in a Nuclear Magnetic Resonance experiment. We controlled the system-reservoir interaction and the spin relaxation rates by adding a paramagnetic salt, allowing the observation of both Markovian and non-Markovian open system dynamics for the qubit. We used two distinguishability measures of quantum states to assess the speed of the qubit evolution: the quantum Fisher information (QFI) and Wigner-Yanase skew information (WY). For non-Markovianity and low salt concentrations, we found crossovers between QSLs related to those metrics. The WY metric sets the tighter QSL for high concentrations and Markovian dynamics. We also show that QSLs are sensitive even to small fluctuations in spin magnetization.

Chemical reaction driven self-assembly of a nucleobase functionalized molecule

Molecular self-assembly is an important aspect in the nano technology and nano science which is exploited to produce complex supramolecular nanoarchitectures. Different strategies are used to achieve the molecular self-assembly in the laboratory. Here, the methylation reaction is used to induce the supramolecular order in the synthesized guanine functionalized molecules. Methylation is an important biological process which is used for DNA methylation. The methylation reaction driven formation of higher order self-assembly is discussed. The formation of the activated building blocks is studied using high-performance liquid chromatography. The N7 methylation is observed majorly. The pH of the medium is decreased with the progress of the reaction. The progress of self-assembly upon the addition of dimethyl sulphate is monitored by fluorescence, circular dichroism spectroscopy, 1H nuclear magnetic resonance and turbidity experiments. Additionally, Thioflavin T dye binding, wide-angle powder X-ray diffraction, circular dichroism spectroscopy experiments are performed to establish the formation of the chemical reaction driven self-assembled hydrogel. The formation of the nanofiber inside the hydrogel is confirmed by performing various microscopic experiments.

Making 1H-1H Couplings More Accessible and Accurate with Selective 2DJ NMR Experiments Aided by 13C Satellites.

1H-1H coupling constants are one of the primary sources of information for nuclear magnetic resonance (NMR) structural analysis. Several selective 2DJ experiments have been proposed that allow for their individual measurement at pure shift resolution. However, all of these experiments fail in the not uncommon case when coupled protons have very close chemical shifts. First, the coupling between protons with overlapping multiplets is inaccessible due to the inability of a frequency-selective pulse to invert just one of them. Second, the strong coupling condition affects the accuracy of coupling measurements involving third spins. These shortcomings impose a limit on the effectiveness of state-of-the-art experiments, such as G-SERF or PSYCHEDELIC. Here, we introduce two new and complementary selective 2DJ experiments that we coin SERFBIRD and SATASERF. These experiments overcome the aforementioned issues by utilizing the 13C satellite signals at natural isotope abundance, which resolves the chemical shift degeneracy. We demonstrate the utility of these experiments on the tetrasaccharide stachyose and the challenging case of norcamphor, for the latter achieving measurement of all JHH couplings, while only a few were accessible with PSYCHEDELIC. The new experiments are applicable to any organic compound and will prove valuable for configurational and conformational analyses.

A modular library for fast prototyping of solution-state nuclear magnetic resonance experiments

Abstract. We present a framework library (Modular Elements, ME) for the development of pulse sequences for Bruker spectrometers. It implements a two-level abstraction approach – the lower level comprises basic functional elements of pulse sequences and the higher one often-reused blocks comprising several evolution periods. The low-level abstractions reduce code duplication between variants of experiments such as hard-pulse and selective variants of individual NMR experiments. The high-level modules enable further reuse of pulse program code and aid in the construction of complex experiments. We show the library's functionality by presenting pulse programs that can be switched between standard and TROSY variants as well as hard and shaped pulses and that can seamlessly incorporate real-time homodecoupling. Adaptability is further demonstrated in a configurable 4D NOESY program.

Exploring long-range fluorine–carbon J-coupling for conformational analysis of deoxyfluorinated disaccharides: A combined computational and NMR study

In this study, we investigated the potential of long-range fluorine–carbon J-coupling for determining the structures of deoxyfluorinated disaccharides. Three disaccharides, previously synthesized as potential galectin inhibitors, exhibited through-space fluorine–carbon J-couplings. In our independent conformational analysis of these disaccharide derivatives, we employed a combination of density functional theory (DFT) calculations and nuclear magnetic resonance (NMR) experiments. By comparing the calculated nuclear shieldings with the experimental carbon chemical shifts, we were able to identify the most probable conformers for each compound. A model comprising fluoromethane and methane molecules was used to study the relationship between molecular arrangements and intermolecular through-space J-coupling. Our study demonstrates the important effect of internuclear distance and molecular orientation on the magnitude of fluorine–carbon coupling. The experimental values for the fluorine–carbon through-space couplings (TSCs) of the disaccharides corresponded with values calculated for the most probable conformers identified by the conformational analysis. These results unlock the broader application of fluorine–carbon TSCs as powerful tools for conformational analysis of flexible molecules, offering valuable insights for future structural investigations.

Spontaneous Formation of 1D/3D Perovskite Heterojunctions for Efficient Inverted Perovskite Solar Cells

AbstractInterfacial modification is a key strategy for improving the performance of perovskite photovoltaic devices. While the modification of the top surface of the perovskite active layer is well established, engineering of the buried interface is highly challenging. Here, the spontaneous formation of a 1D/3D perovskite heterojunction at the buried interface of a perovskite active layer by incorporating choline acetate alongside the perovskite precursors is reported. Importantly, extensive spectroscopic and microscopic characterization and solid‐state nuclear magnetic resonance experiments demonstrate the formation of phase‐pure 1D and 3D domains. The 1D/3D junction results in a suppression of the defect states and an improved energetic level alignment at the buried interface, leading to a maximum power conversion efficiency of >24% when incorporated in inverted architecture perovskite solar cells. This work introduces a versatile approach to the modification of the buried interface of the perovskite active layer.

Rapid simulation of two-dimensional spectra with correlated anisotropic dimensions.

A new algorithm has been developed to simulate two-dimensional (2D) spectra with correlated anisotropic frequencies faster and more accurately than previous methods. The technique uses finite-element numerical integration on the sphere and an interpolation scheme based on the Alderman-Solum-Grant algorithm. This method is particularly useful for numerical calculations of joint probability distribution functions involving quantities with a parametric orientation dependence. The technique's efficiency also allows for practical least-squares fitting of experimental 2D solid-state nuclear magnetic resonance (NMR) datasets. The simulation method is illustrated for select 2D NMR methods, and a least-squares analysis is demonstrated in the extraction of paramagnetic shift and quadrupolar coupling tensors and their relative orientation from the experimental shifting-d echo 2H NMR spectrum of a NiCl2 · 2D2O salt.

Identification of potential C1-binding sites in the immunoglobulin CL domains.

IgG molecules that bind antigen on the membrane of target cells spontaneously form hexameric rings, thus recruiting C1 to initiate the complement pathway. However, our previous report indicated that a mouse IgG mutant lacking the Cγ1 domain activates the pathway independently of antigen presence through its monomeric interaction with C1q via the CL domain, as well as Fc. In this study, we investigated the potential interaction between C1q and human CL isoforms. Quantitative single molecule observations using high-speed atomic force microscopy revealed that human Cκ exhibited comparable C1q binding capabilities with its mouse counterpart, surpassing the Cλ types, which have a higher isoelectric point than the Cκ domains. Nuclear magnetic resonance and mutation experiments indicated that the human and mouse Cκ domains share a common primary binding site for C1q, centered on Glu194, a residue conserved in the Cκ domains but absent in the Cλ domains. Additionally, the Cγ1 domain, with its high isoelectric point, can cause electrostatic repulsion to the C1q head and impede the C1q-interaction adjustability of the Cκ domain in Fab. The removal of the Cγ1 domain is considered to eliminate these factors and thus promote Cκ interaction with C1q with the potential risk of uncontrolled activation of the complement pathway in vivo in the absence of antigen. However, this research underscores the presence of potential subsites in Fab for C1q binding, offering promising targets for antibody engineering to refine therapeutic antibody design.

Nuclear magnetic resonance experiments on the time-varying law of oil viscosity and wettability in high-multiple waterflooding sandstone cores

A simulated oil viscosity prediction model is established according to the relationship between simulated oil viscosity and geometric mean value of T2 spectrum, and the time-varying law of simulated oil viscosity in porous media is quantitatively characterized by nuclear magnetic resonance (NMR) experiments of high multiple waterflooding. A new NMR wettability index formula is derived based on NMR relaxation theory to quantitatively characterize the time-varying law of rock wettability during waterflooding combined with high-multiple waterflooding experiment in sandstone cores. The remaining oil viscosity in the core is positively correlated with the displacing water multiple. The remaining oil viscosity increases rapidly when the displacing water multiple is low, and increases slowly when the displacing water multiple is high. The variation of remaining oil viscosity is related to the reservoir heterogeneity. The stronger the reservoir homogeneity, the higher the content of heavy components in the remaining oil and the higher the viscosity. The reservoir wettability changes after water injection: the oil-wet reservoir changes into water-wet reservoir, while the water-wet reservoir becomes more hydrophilic; the degree of change enhances with the increase of displacing water multiple. There is a high correlation between the time-varying oil viscosity and the time-varying wettability, and the change of oil viscosity cannot be ignored. The NMR wettability index calculated by considering the change of oil viscosity is more consistent with the tested Amott (spontaneous imbibition) wettability index, which agrees more with the time-varying law of reservoir wettability.

Core Analysis Using Nuclear Magnetic Resonance

Core analysis is critical for oil and gas exploration and recovery. Nuclear magnetic resonance (NMR) has been widely applied to the petroleum industry for many years, and NMR core analysis plays an important role in supporting borehole NMR formation evaluation and understanding the mechanisms of petrophysics and petrochemistry. It’s unfortunate, however, that there has been a lack of commented descriptions of the basic procedures for NMR rock core analysis in the literature, which has led to issues of comparability and repeatability of NMR measurements between different laboratories. In this paper, we present a brief guideline for NMR rock core analysis of conventional T2, T1, T1-T2, and D-T2 measurements. As an established procedure in daily laboratory work, NMR core analysis includes three sophisticated steps: rock sample preparation, an NMR experiment, and data analysis. The acquisition and saturation of rock samples are described, and corresponding solutions are also considered. Detailed NMR experimental measurements, data setting, and calibration are addressed. Laplace inversion for different NMR experiments and models for estimation of porosity, irreducible water, permeability, pore structure, and oil saturation are included. The aim of this paper is to try to standardize general NMR experiments for rock core analysis.

Microscopic occurrence and distribution of oil and water in situ shale: Evidence from nuclear magnetic resonance

Characterizing the microscopic occurrence and distribution of in-situ pore water and oil is crucial for resource estimation and development method selection of shale oil. In this paper, a series of nuclear magnetic resonance (NMR) experiments were conducted on shales from the Gulong Sag, Songliao Basin, China, at AR, WR-AR, WOR-AR, Dry, SO, and WR states. In-situ pore water and oil were reconstructed after WOR-AR. An improved T1–T2 pattern for shale oil reservoirs comprising water and oil was proposed to classify and quantitatively detect pore fluids at different occurrence states. The total and free oil contents derived from NMR T1–T2 spectra at AR states were found to correlate well with those from multistage Rock-Eval. Moreover, the NMR-calculated total and free oil are generally larger than those measured from multistage Rock-Eval, whereas adsorbed oil is the opposite, which implies that adsorbed, bound, and movable oils in shale pores can be accurately and quantitatively detected via NMR, without absorbed hydrocarbons in kerogen. As per the NMR T2 and T1–T2 spectra at WOR-AR state, the microdistributions of in-situ pore water and oil were clearly demonstrated. Adsorbed, bound, and movable oils primarily occur in the micropores (<100 nm), mesopores (100–1000 nm), and macropores (>1000 nm), respectively, whereas capillary-bound water is primarily correlated with micropores. Thus, the microscopic occurrence and distribution of adsorbed oil are remarkably affected by pore water, followed by bound oil, and movable oil is hardly affected. This study would be helpful in further understanding the microscopic occurrence characteristics of pore fluids in-situ shale oil reservoirs.

NMR diffusion in restricted environment approached by a fractional Langevin model

The diffusion motion of spin-bearing molecules is considerably affected in confined environments. In Nuclear Magnetic Resonance (NMR) experiments, under the presence of magnetic field gradients, this movement can be encoded in spin phase and the NMR signal attenuation due to diffusion can be evaluated. This paper considered this effect in both normal and anomalous diffusion by means of the Langevin stochastic model within the Gaussian phase approximation (GPA) for a constant gradient temporal profile. The phenomenological approach illustrates the emergence of fractional order exponential decay in the NMR signal and retrieves the classical result from Hanh echo.