Nuclear Magnetic Resonance Studies Research Articles

An alternative approach for conditioning wood samples in nuclear magnetic resonance studies

An alternative approach for conditioning wood samples in nuclear magnetic resonance studies

Fast anion reorientations in ammine yttrium borohydride compounds Y(BH4)3·xNH3 (x = 3 and 7): a nuclear magnetic resonance study

Fast anion reorientations in ammine yttrium borohydride compounds Y(BH4)3·xNH3 (x = 3 and 7): a nuclear magnetic resonance study

Percarbonate mediated advanced oxidation of irbesartan: A suitable alternative to chlorination?

This study aims to investigate the environmental fate of irbesartan when subjected to activated percarbonate treatment. The investigation delves into the formation of disinfection byproducts (DBPs) and evaluates their toxicity, and it seeks to draw comparisons with outcomes from treatment with sodium hypochlorite, already characterized in previous findings. The proposed treatment indicates the formation of at least 11 DBPs - eight identified for the first time - which have been isolated by various chromatographic techniques, identified by Nuclear Magnetic Resonance and Mass Spectrometry studies and for which a mechanism has been proposed to elucidate their formation. To evaluate irbesartan's biological impact during treatment with sodium percarbonate (SPC), a toxicity study of the DBPs was conducted using Daphnia magna, Aliivibrio fischeri, and Raphidocelis subcapitata, three model organisms. The ecotoxicity was evaluated using the Ecological Structure-Activity Relationships (ECOSAR) computer program and compared with experimental results. Compared to chlorination treatment, a lower mineralization percentage (−43 %) and amount of DBPs at least twice higher were observed. Toxicity assessment highlighted that DBPs formed during SPC treatment were more toxic than those from chlorination. ECOSAR predicted toxicity aligned with experimental findings. Additionally, the DBPs exhibited varying levels of toxicity, primarily attributable to the presence of aromatic and hydroxyl groups in their chemical structure, indicating that SPC treatment is not suitable for treatment of irbesartan polluted waters.

Characterization and Dissolution Mechanism of Low-Molecular-Weight Organic Acids or Inorganic Mesoporous Particle-Based Piperine Amorphous Solid Dispersions.

The objective of the current study is to prepare amorphous solid dispersions (ASDs) containing piperine (PIP) by utilizing organic acid glycyrrhizic acid (GA) and inorganic disordered mesoporous silica 244FP (MSN/244FP) as carriers and to investigate their dissolution mechanism. The physicochemical properties of ASDs were characterized with scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC). Fourier transform infrared spectroscopy (FTIR) and one-dimensional proton nuclear magnetic resonance (1H NMR) studies collectively proved that strong hydrogen-bonding interactions formed between PIP and the carriers in ASDs. Additionally, molecular dynamic (MD) simulation was conducted to simulate and predict the physical stability and dissolution mechanisms of the ASDs. Interestingly, it revealed a significant increase in the dissolution of amorphous PIP in ASDs in in vitro dissolution studies. Rapid dissolution of GA in pH 6.8 medium resulted in the immediate release of PIP drugs into a supersaturated state, acting as a dissolution-control mechanism. This exhibited a high degree of fitting with the pseudo-second-order dynamic model, with an R2 value of 0.9996. Conversely, the silanol groups on the outer surface of the MSN and its porous nanostructures enabled PIP to display a unique two-step drug release curve, indicating a diffusion-controlled mechanism. This curve conformed to the Ritger-Peppas model, with an R2 > 0.9. The results obtained provide a clear evidence of the proposed transition of dissolution mechanism within the same ASD system, induced by changes in the properties of carriers in a solution medium of varying pH levels.

Aluminum Alkyl Induced Isomerization of Group IV meso Metallocene Complexes

The synthesis of group IV metallocene precatalysts for the polymerization of propylene generally yields two different isomers: The racemic isomer that produces isotactic polypropylene (iPP) and the meso isomer that produces atactic polypropylene (aPP). Due to its poor physical properties, aPP has very limited applications. To avoid obtaining blends of both polymers and thus diminish the mechanical and thermal properties of iPP, the meso metallocene complexes need to be separated from the racemic ones tediously –rendering the metallocene‐based polymerization of propylene industrially far less attractive than the Ziegler/Natta process. To overcome this issue, we established an isomerization protocol to convert meso metallocene complexes into their racemic counterparts. This protocol increased the yield of iPP by 400% while maintaining the polymer’s excellent physical properties and was applicable to both hafnocene and zirconocene complexes, as well as different precatalyst activation methods. Through targeted variation of the ligand frameworks, methoxy groups at the indenyl moieties were found to be the structural motifs responsible for an isomerization to take place –this experimental evidence was confirmed by density functional theory calculations. Liquid injection field desorption ionization mass spectrometry, as well as 1H and 29Si nuclear magnetic resonance studies, allowed the proposal of an isomerization mechanism.

Aluminum Alkyl Induced Isomerization of Group IV meso Metallocene Complexes.

The synthesis of group IV metallocene precatalysts for the polymerization of propylene generally yields two different isomers: The racemic isomer that produces isotactic polypropylene (iPP) and the meso isomer that produces atactic polypropylene (aPP). Due to its poor physical properties, aPP has very limited applications. To avoid obtaining blends of both polymers and thus diminish the mechanical and thermal properties of iPP, the meso metallocene complexes need to be separated from the racemic ones tediously -rendering the metallocene-based polymerization of propylene industrially far less attractive than the Ziegler/Natta process. To overcome this issue, we established an isomerization protocol to convert meso metallocene complexes into their racemic counterparts. This protocol increased the yield of iPP by 400% while maintaining the polymer's excellent physical properties and was applicable to both hafnocene and zirconocene complexes, as well as different precatalyst activation methods. Through targeted variation of the ligand frameworks, methoxy groups at the indenyl moieties were found to be the structural motifs responsible for an isomerization to take place -this experimental evidence was confirmed by density functional theory calculations. Liquid injection field desorption ionization mass spectrometry, as well as 1H and 29Si nuclear magnetic resonance studies, allowed the proposal of an isomerization mechanism.

Hypertrophic Pachymeningitis, Associated with Eosinophilic Granulomatosis with Polyangiitis, and ANCA-Negative Serology.

Hypertrophic pachymeningitis (HP) is a disease with diverse aetiologies, including the autoimmune one, either associated with antineutrophil cytoplasmic antibodies or immunoglobulin G4. A 65-year-old woman with a history of systemic arterial hypertension, presented with intense progressive headaches. HP and hemispheric vasogenic oedema were observed by nuclear magnetic resonance (NMR) study. During the six months before the headache, she had developed progressive hearing loss which she attributed to age. A biopsy of dura mater showed necrotising vasculitis with peripheral inflammatory infiltrate, made up of accumulations of epithelioid cells and multinucleated giant cells, and abundant eosinophils. A final diagnosis of HP with eosinophilic granulomatosis with polyangiitis (EGPA) was made. The patient had eosinophilic granulomatosis with polyangiitis (EGPA) histology, ANCA-negative serology and HP. This case is important because it shows that EGPA seems to have a spectrum of clinical diseases, including HP with negative serology, and bilateral sensorineural hearing loss. We are facing a wide spectrum of EGPA, breaking the paradigm of only systemic involvement. Hypertrophic pachymeningitis (HP) has several aetiologies; if the systemic investigation is not contributory to a diagnosis, a meningeal biopsy is necessary.This is the first case report of HP, associated with eosinophilic granulomatosis with polyangiitis (EGPA), and ANCA-negative serology.EGPA is probably a spectrum of diseases with predominant systemic involvement, but there may be cases where there is histological evidence, without the systemic context or positive serology.

NMR and X-ray diffraction conformational study of guanidines

Leishmaniasis is a neglected disease that affects regions such as South Asia, South Africa, and Latin America, less developed regions. The research proposed the conformational study of brominated guanidine compounds with potential antileishmanial activity using Nuclear Magnetic Resonance (NMR) and X-ray diffraction (XRD) techniques. The present study involves the brominated molecules LQOF-G2, LQOF-G30, LQOF-G35 and LQOF-G35-Br. The latter was synthesized by the reaction of LQOF-G35 with NBS under IR irradiation at 120 Watts of potency and dichloromethane as solvent by 12 h of exposition. The obtained results demonstrated the efficiency of the bromination method, since two bromine atoms entered the molecule. Furthermore, NMR analysis showed a conformational change from Z to E when compound LQOF-G35 was brominated to LQOF-G35-Br. This behavior was confirmed by a comparative XRD study of the LQOF-G35 and LQOF-G35-Br compounds. The antileishmanial activity of LQOF-G2 e LQOF-G35 motivated the synthesis of new brominated compounds LQOF-G30 e LQOF-G35-Br.

Nuclear magnetic resonance studies in a model transverse field Ising system

The suppression of ferroquadrupolar order in TmVO4 in a magnetic field is well-described by the transverse field Ising model, enabling detailed studies of critical dynamics near the quantum phase transition. We describe nuclear magnetic resonance measurements in pure and Y-doped single crystals. The non-Kramers nature of the ground state doublet leads to a unique form of the hyperfine coupling that exclusively probes the transverse field susceptibility. Our results show that this quantity diverges at the critical field, in contrast to the mean-field prediction. Furthermore, we find evidence for quantum critical fluctuations present near Tm-rich regions in Y-doped crystals at levels beyond which long-range order is suppressed, suggesting the presence of quantum Griffiths phases.

Organic Solvent-Induced Structural Changes in a Protein Confined in a Giant Coordination Cage

Abstract We investigate the molecular mechanism of acetonitrile-induced structural changes in a cutinase-like enzyme in a giant coordination cage using molecular dynamics (MD) simulations. As the acetonitrile content within the cage increases, significant conformational changes of the caged protein occur due to acetonitrile binding to the specific sites, in line with protein denaturation events observed in previous nuclear magnetic resonance (NMR) studies. Accordingly, employing MD simulations on caged proteins represents an effective strategy for investigating the dynamics of unstable protein structures.

Heat-induced structural and chemical changes to a computationally designed miniprotein.

The de novo design of miniprotein inhibitors has recently emerged as a new technology to create proteins that bind with high affinity to specific therapeutic targets. Their size, ease of expression, and apparent high stability makes them excellent candidates for a new class of protein drugs. However, beyond circular dichroism melts and hydrogen/deuterium exchange experiments, little is known about their dynamics, especially at the elevated temperatures they seemingly tolerate quite well. To address that and gain insight for future designs, we have focused on identifying unintended and previously overlooked heat-induced structural and chemical changes in a particularly stable model miniprotein, EHEE_rd2_0005. Nuclear magnetic resonance (NMR) studies suggest the presence of dynamics on multiple time and temperature scales. Transiently elevating the temperature results in spontaneous chemical deamidation visible in the NMR spectra, which we validate using both capillary electrophoresis and mass spectrometry (MS) experiments. High temperatures also result in greatly accelerated intrinsic rates of hydrogen exchange and signal loss in NMR heteronuclear single quantum coherence spectra from local unfolding. These losses are in excellent agreement with both room temperature hydrogen exchange experiments and hydrogen bond disruption in replica exchange molecular dynamics simulations. Our analysis reveals important principles for future miniprotein designs and the potential for high stability to result in long-lived alternate conformational states.

NMR study of nitrate ionic liquids confined between micrometer-spaced plates

This review paper presents the results of a study conducted using nuclear magnetic resonance (NMR) methods to investigate the dynamic behaviour of ionic liquid-based compositions in micrometre-spaced confinement. Ethylammonium nitrate (EAN) and other ionic liquid (IL) systems with nitrate anion in glass or quartz spaced confinement demonstrate anomalous cation dynamics that differ from those observed in bulk and in nano-confinement. It was demonstrated that the principal axis of the nitrate anion exhibits preferential orientation to the surface, akin to that in liquid crystals. It was shown that the cation translational mobility reversibly changes during exposure to a static magnetic field. This phenomenon was interpreted as a result of intermolecular structure transformations occurring in the confined ILs. The mechanisms of these transformations were discussed.

Investigation of Aging Mechanism of Pt‐ZSM‐5 Catalysts for Non‐Oxidative Propane Dehydrogenation

AbstractA Pt‐ZSM5 catalyst, coked during propane dehydrogenation and regenerated with lean air, was studied by various in‐situ and ex‐situ methods. A newly developed isothermal ceramic flat‐bed reactor with inert surfaces is described and used in the experiments. Comparative measurements successfully demonstrated that temperature alone has no effect on the catalyst and that changes in conversion and selectivity are due to coke formation. Nuclear magnetic resonance (NMR) studies using triphenylphosphine probe molecules of activated and deactivated samples showed the localization of the Pt clusters inside and outside the zeolite pores. It was shown that the Pt clusters are mainly located inside the zeolites and that the mobilization of Pt by contact with oxygen leads to permanent aging.

Capturing of neurotoxins causing diabetes stress and nervous breakdown in the aqueous medium by naphthazarin esters.

The fear of an increase in blood sugar can be very traumatic. Being diabetic either type I or type II leads to a disorder called diabetes distress having traits of stress, depression, and anxiety. Among risk factors of diabetes mellitus heavy and trace metal toxicity emerges as new risk factors reported in many studies. In this study we target toxic metals, viz., Ni2+, Zn2+, and Cu2+, involved in the pathogenesis of diabetes and diabetic stress with naphthazarin esters. The compounds C1-C3 isolated from the leaves and roots of Arnebia guttata were tested for their metal-binding ability in an aqueous medium in UV-Visible and nuclear magnetic resonance (NMR) studies. These probes are well-known naphthoquinones present in the Arnebia species. In the UV-Visible titrations of compounds C1-C3 with Na2+, K2+, Zn2+, Ca2+, Cu2+, Mg2+, Co2+, and Ni2+ ions, significant binding was observed with Ni2+, Cu2+, and Zn2+ ions in MeOH/H2O. There occurs a beautiful formation of red-shifted bands between the 520 to 620 nm range with a synergistic increase in absorbance. Also, the disappearance of proton peaks in the 1H NMR spectrum on addition of metal ions confirmed binding. Compounds C1-C3 isolated from A. guttata came out as potent Ni2+, Zn2+, and Cu2+ sensors that are reportedly involved in islet function and induction of diabetes.

The critical importance of conditions: Reconciling GPCR functionality and biophysical findings

G-protein-coupled receptor (GPCR) activation relies on conformational sampling, a nuanced but functionally key behavior well suited to elucidation by nuclear magnetic resonance (NMR) spectroscopy. In this issue of Structure, Thakur etal.1 demonstrate that judicious choice of experimental conditions for 19F NMR studies of a GPCR enables rationalization of functional and pharmacological behavior, leading to testable hypotheses correlating structure, dynamics, and function.

Saponins from seeds of Zizyphus jujuba Mill. var. spinosa exhibit vasorelaxant effects on rat isolated aorta

AbstractAimThe vasorelaxant saponins jujuboside A(1), A1(2), B(3), and acetyljujuboside B(4) were isolated from 50% MeOH extracts of seeds of Zizyphus jujuba Mill. var. spinosa Hu ex H.F. Chou (Rhamnaceae), and their effects were studied using isolated rat aortic rings.MethodDried jujube seeds were crushed and extracted with 50% MeOH, and the extracts were concentrated under reduced pressure. Vasorelaxant effects of this extracts were assessed on rat isolated aorta rings. The aorta rings were placed in a well‐oxygenated bath of modified Krebs–Henseleit solution and the mechanical tension was measured isometrically.ResultsThe crude extract was fractionated by chromatographic methods with the guidance of vasorelaxant activity, and four saponins (1~4) were isolated. These compounds were identified using nuclear magnetic resonance (NMR) studies. Compounds 1~4 showed slow relaxation activity against norepinephrine (NE)‐induced contractions of rat aorta with/without endothelium. Treatment with 1~4 did not significantly inhibit NE‐induced vasoconstrictions. Compounds 1~4 inhibited vasoconstriction induced by high‐concentration potassium (60 mM) and NE in the presence of nicardipine but did not affect phorbol 12‐myristate 13‐acetate‐induced vasoconstriction.ConclusionThese results suggest that inhibition of NE‐induced vasoconstriction by 1~4 is due to the inhibition of receptor‐operated Ca2+ channels and voltage‐dependent Ca2+ channels or inhibition of intracellular calcium modulations.

Randomly Methylated β-Cyclodextrin Inclusion Complex with Ketoconazole: Preparation, Characterization, and Improvement of Pharmacological Profiles.

As a powerful imidazole antifungal drug, ketoconazole's low solubility (0.017 mg/mL), together with its odor and irritation, limited its clinical applications. The inclusion complex of ketoconazole with randomly methylated β-cyclodextrin was prepared by using an aqueous solution method after cyclodextrin selection through phase solubility studies, complexation methods, and condition selection through single factor and orthogonal strategies. The complex was confirmed by FTIR (Fourier-transform infrared spectroscopy), DSC (differential scanning calorimetry), TGA (thermogravimetric analysis), SEM (scanning electron microscope images), and NMR (Nuclear magnetic resonance) studies. Through complexation, the water solubility of ketoconazole in the complex was increased 17,000 times compared with that of ketoconazole alone, which is the best result so far for the ketoconazole water solubility study. In in vitro pharmacokinetic studies, ketoconazole in the complex can be 100% released in 75 min, and in in vivo pharmacokinetic studies in dogs, through the complexation, the Cmax was increased from 7.56 μg/mL to 13.58 µg/mL, and the AUC0~72 was increased from 22.69 μgh/mL to 50.19 μgh/mL, indicating that this ketoconazole complex can be used as a more efficient potential new anti-fungal drug.

Beyond the permeability barriers: Unveiling the potential of dual-crosslinking hydrogel nanofiltration membranes for high-performance molecular/ion sieving

Membrane separation technology has shown great potential in resource recovery, energy utilization, and environmental protection, attracting extensive attention for the various practical applications. The alginate-based hydrogel membrane, derived from natural biomass, possesses sustainability and anti-fouling properties, effectively reducing the burden of waste membrane disposal. However, the limitations of alginate hydrogel include its high swelling ability, low permeability, and poor mechanical properties. In this study, we propose a straightforward method to fabricate orderliness hydrogels by employing lanthanide ion via dual cross-linking with CaAlg, resulting in the formation of lanthanum calcium alginate (La-CaAlg) hydrogel membrane. The La-CaAlg membrane exhibits superior mechanical performance and anti-swelling properties compared to LaAlg and CaAlg membranes. Additionally, through small-angle scattering and low-field nuclear magnetic resonance studies on the membrane's spatial orientation, and pore size distribution, we gained the comparable results into its internal structure for the design insight. Notably, the La-CaAlg membrane demonstrates outstanding performance in dye/salt separation, showcasing high selectivity and permeability. We propose the strategy that enhances the orderliness and durability of the alginate hydrogel membrane, providing the separation design insight to overcome the limitations associated with the permeability and rejection trade-off.

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.

Coupling of source rock gas expulsion intensity and reservoir quality in time and space-a key to determine gas accumulation in Upper Paleozoic tight sandstones of the Mugua gas field, Ordos Basin, China

Research on gas accumulation mechanisms and variations in gas saturation is limited in the newly established Mugua gas field in the Ordos Basin. Understanding these aspects is vital for reduce drilling uncertainty and exploration risk. This study employed a variety of methods, including: (1) the use of organic geochemical examinations to determine the gas expulsion intensity of hydrocarbon source rocks; (2) fluid inclusion analyses to determine the time of gas accumulation; (3) a combination of optical microscopy, scanning electron microscopy observations, pore-simulation and permeability tests, mercury-intrusion capillary pressure experiments, and nuclear magnetic resonance studies to assess the properties of the reservoir quality and identify the tight sandstone rock type; (4) wireline logging and interpretive data analyses to research the gas saturations features; and (5) establish reservoir quality evolution model to systematically study this problem. Integrating fluid inclusion homogenization temperatures with burial and thermal histories indicates that gas accumulation in the Mugua gas fields occurred throughout the Early Jurassic to Late Cretaceous period. Five diagenetic facies have been identified: dissolution, quartz-cemented, clay mineral filling, tightly compacted, and carbonate-cemented facies. The reservoir quality evolution model reveals that the five diagenetic facies experienced densification before the period of gas accumulation. Therefore, for gas accumulation in tight sandstones, it is essential that mature and gas-generating source rocks, provide sufficient expulsion forces to drive gas into the rocks. The mechanism of gas accumulation in the Mugua gas field's tight gas sandstone reservoirs involves the process occurring in sandstones that are either near or interbedded with source rocks, under high pore-fluid pressure generated by gas production. Compared to other Upper Paleozoic gas fields in the Ordos Basin, the gas expulsion intensity in the Mugua gas field is lower, ranging from 6.12–8.39 × 108 m3/km2. Due to the low gas expulsion intensity, the Shihezi 8 Member's tight sandstone reservoirs, situated away from the source rock, typically show low gas saturation. Conversely, the dissolution and quartz-cemented facies within the Benxi, Taiyuan, and Shanxi Formations, intimately interbedded with hydrocarbon source rocks, exhibit good reservoir quality. They offer ideal conditions for gas accumulation, making them prime candidates for exploration and development.