NMR Measurements Research Articles

One-Year Water-Stable and Porous Bi(III) Halide Semiconductor with Broad-Spectrum Antibacterial Performance.

Hybrid metal halide semiconductors are a unique family of materials with immense potential for numerous applications. For this to materialize, environmental stability and toxicity deficiencies must be simultaneously addressed. We report here a porous, visible light semiconductor, namely, (DHS)Bi2I8 (DHS = [2.2.2] cryptand), which consists of nontoxic, earth-abundant elements, and is water-stable for more than a year. Gas- and vapor-sorption studies revealed that it can selectively and reversibly adsorb H2O and D2O at room temperature (RT) while remaining impervious to N2 and CO2. Solid-state NMR measurements and density functional theory (DFT) calculations verified the incorporation of H2O and D2O in the molecular cages, validating the porous nature. In addition to porosity, the material exhibits broad band-edge light emission centered at 600 nm with a full width at half-maximum (fwhm) of 99 nm, which is maintained after 6 months of immersion in H2O. Moreover, (DHS)Bi2I8 exhibits bacteriocidal action against three Gram-positive and three Gram-negative bacteria, including antibiotic-resistant strains. This performance, coupled with the recorded water stability and porous nature, renders it suitable for a plethora of applications, from solid-state batteries to water purification and disinfection.

Synthesis, Characterization, and Catalytic Activity of a Cubic [Mo3S4Pd] Cluster Bearing Bulky Cyclopentadienyl Ligands

AbstractA cubic metal‐sulfur cluster containing three Mo ions and a Pd ion, [CpSiEt33Mo3S4Pd]Cl (Mo3Pd, CpSiEt3=C5Me4SiEt3), was synthesized by the incorporation of the Pd ion into a Mo3S4 cluster [CpSiEt33Mo3S4] (Mo3). Mo3Pd was characterized by 1H NMR, UV‐vis, X‐ray crystallography, and cyclic voltammetry measurements. The electrochemical measurements demonstrated reversible one‐ and two‐electron reduction processes for Mo3Pd, which suggested potential catalytic activity for two‐electron substrate reductions such as hydrogen evolution reaction. Controlled potential electrolysis in the presence of Mo3Pd and trifluoroethanol in THF solvent displayed H2 formation with a constant current over 60 min. The amount of generated H2 by Mo3Pd was two times higher than Mo3, indicating the catalytic activity facilitated by the Pd center. The mechanism of the catalytic cycle was determined by density functional theory.

Preparation and Characterization of Silica-Based Ionogel Electrolytes and Their Application in Solid-State Lithium Batteries.

In this study, tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) were used as precursors for silica, combined with the ionic liquid [BMIM-ClO4]. Lithium perchlorate was added as the lithium-ion source, and formic acid was employed as a catalyst to synthesize silica ionogel electrolytes via the sol-gel method. FT-IR and NMR identified the self-prepared ionic liquid [BMIM-ClO4], and its electrochemical window was determined using linear sweep voltammetry (LSV). The properties of the prepared silica ionogel electrolytes were further investigated through FT-IR, DSC, and 29Si MAS NMR measurements, followed by electrochemical property measurements, including conductivity, electrochemical impedance spectroscopy (EIS), LSV, and charge-discharge tests. The experimental results showed that adding methyltriethoxysilane (MTES) enhanced the mechanical strength of the silica ionogel electrolyte, simplifying its preparation process. The prepared silica ionogel electrolyte exhibited a high ionic conductivity of 1.65 × 10-3 S/cm. In the LSV test, the silica ionogel electrolyte demonstrated high electrochemical stability, withstanding over 5 V without oxidative decomposition. Finally, during the discharge-charge test, the second-cycle capacity reached 108.7 mAh/g at a discharge-charge rate of 0.2 C and a temperature of 55 °C.

Interactions of Mono- and Divalent Host Molecules with Multi- and Divalent Guest Molecules

Abstract The interactions of mono- and divalent host molecules with multi- and divalent guest molecules in aqueous media were investigated by steady-state fluorescence or NMR measurements. The multivalent and two-step interactions were observed depending on the combination of the host and guest molecules.

Bulk NMR Measurements of Spray Dynamics

Bulk NMR Measurements of Spray Dynamics

Investigation of ethylene-propylene-diene monomer (EPDM) ageing behaviour in PMDIs environment by surface NMR

Pressurized Metered Dose Inhalers (PMDIs) are mostly used for the treatment of respiratory diseases. The long-term durability of Pressurized Metered Dose Inhalers heavily depends on the functionality of the elastomeric gaskets they contain. The mechanical, chemical, and morphological stability of those elastomeric gaskets is of a great concern to the overall performance of PMDIs. Elastomers used as sealing materials ethylene-propylene-diene monomer (EPDM), have been investigated in this work, during an accelerated ageing study. The evolution of two formulation of EPDM has been reported via standard characterization techniques. Optical microscopy was used to determine any topographic changes on the surface impacted by chemical or mechanical stress. Attenuated total reflection Fourier transform infrared (ATR-FTIR), swelling tests, and thermogravimetric analysis (TGA) were performed to assess the chemical and structural modification of the materials before and after ageing. Surface NMR measurement were conducted to study the degradation as a function of the thickness of the elastomeric gaskets. In the presence of chemical constraints, degradations were observed compared to mechanical constraints which did not lead to significant changes.

Preparation, properties and formation mechanism of hydroxyl-silicone oil coating on the surface of kaolin/ TiO2 composites

A simple and effective preparation method of the powder surface coating was found. Namely, spraying hydroxyl-silicone oil (HSO) ethanol solution on the surface of calcined kaolin and nano-TiO2 composite (CKT) powder and formed the HSO layer due to the volatilization of ethanol. Subsequently, the samples were heated at 250 ℃ to form the HSO cure coating. The FT-IR, MAS NMR, XPS and SEM measure results indicate that the surface modification reaction occur between the OH groups in HSO molecules and HO-AlVI in the calcined kaolin. No any chemical reaction carry out on the Si, Ti sites on the surface of CKT composites. The performance testings show the HSO modification reaction dramatically improve the hydrophobicity of the CKT composites. The modification coating has no any negative effect on the whiteness, but the oil absorption values slightly reduce. Interestingly, it increases again after curing because the HSO layer releases a large great of lipophilic groups such as CH3 and CH2 during the curing process. The comparison of performances with nano-TiO2 and calcined kaolin shows that the CKT composites are expected to replace nano-TiO2 in many fields.

The Impact of Intergrain Phases on the Ionic Conductivity of the LAGP Solid Electrolyte Material Prepared by Spark Plasma Sintering.

Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is a promising oxide solid electrolyte for all-solid-state batteries due to its excellent air stability, acceptable electrochemical stability window, and cost-effective precursor materials. However, further improvement in the ionic conductivity performance of oxide solid-state electrolytes is hindered by the presence of grain boundaries and their associated morphologies and composition. These key factors thus represent a major obstacle to the improved design of modern oxide based solid-state electrolytes. This study establishes a correlation between the influence of the grain boundary phases, their 3D morphology, and compositions formed under different sintering conditions on the overall LAGP ionic conductivity. Spark plasma sintering has been employed to sinter oxide solid electrolyte material at different temperatures with high compacity values, whereas a combined potentiostatic electrochemical impedance spectroscopy, 3D FIB-SEM tomography, XRD, and solid-state NMR/materials modeling approach provides an in-depth analysis of the influence of the morphology, structure, and composition of the grain boundary phases that impact the total ionic conductivity. This work establishes the first 3D FIB-SEM tomography analysis of the LAGP morphology and the secondary phases formed in the grain boundaries at the nanoscale level, whereas the associated 31P and 27Al MAS NMR study coupled with materials modeling reveals that the grain boundary material is composed of Li4P2O7 and disordered Li9Al3(P2O7)3(PO4)2 phases. Quantitative 31P MAS NMR measurements demonstrate that optimal ionic conductivity for the LAGP system is achieved for the 680 °C SPS preparation when the disordered Li9Al3(P2O7)3(PO4)2 phase dominates the grain boundary composition with reduced contributions from the highly ordered Li4P2O7 phases, whereas the 27Al MAS NMR data reveal that minimal structural change is experienced by each phase throughout this suite of sintering temperatures.

Nuclear Magnetic Resonance Study of CO2 Capture by Fluoroalkylamines: Ammonium Ion pKa Depression via Fluorine Modification and Thermochemistry of Carbamylation.

We are developing energy-efficient and reversible carbon capture and release (CCR) systems that mimic the Lys201 carbamylation reaction in the active site of ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO). The multiequilibria scenario ammonium ion Xa ⇌ amine Xb ⇌ carbamic acid Xc ⇌ carbamate Xd requires the presence of both free amine and CO2 for carbamylation and is affected by the pKa(Xa). Two fluorination strategies aimed at ammonium ion pKa depression and low pH carbamylation were analyzed with (2,2,2-trifluoroethyl)butylamine 2b and 2,2-difluoropropylamine 3b and compared to butylamine 1b. The determination of K1 and ΔG1 of the carbamylation reactions requires the solution of multiequilibria systems of equations based on initial conditions, 1H NMR measurements of carbamylation yields over a wide pH range, and knowledge of K2-K5 values. K2 and K3 describe carbonic acid acidity, and ammonium ion acidities K4 were measured experimentally. We calibrated carbamic acid acidities K5 based on the measured value K6 of aminocarbamic acid using isodesmic reactions. The proton exchange reactions were evaluated with ab initio computations at the APFD/6-311+G* level in combination with continuum solvation models and explicit solvation. The utilities of 1-3 will be discussed as they pertain to the development of fluorine-modified RuBisCO-mimetic reversible CCR systems.

Dynamic Structure of Organic Compounds in Solution by Dynamic NMR Measurements and Quantum Molecular Dynamics Calculations: IV. Benzamide

Dynamic Structure of Organic Compounds in Solution by Dynamic NMR Measurements and Quantum Molecular Dynamics Calculations: IV. Benzamide

Supramolecular chemistry enables vat photopolymerization 3D printing of novel water-soluble tablets

Vat photopolymerization has garnered interest from pharmaceutical researchers for the fabrication of personalised medicines, especially for drugs that require high precision dosing or are heat labile. However, the 3D printed structures created thus far have been insoluble, limiting printable dosage forms to sustained-release systems or drug-eluting medical devices which do not require dissolution of the printed matrix. Resins that produce water-soluble structures will enable more versatile drug release profiles and expand potential applications. To achieve this, instead of employing cross-linking chemistry to fabricate matrices, supramolecular chemistry may be used to impart dynamic interaction between polymer chains. In this study, water-soluble drug-loaded printlets (3D printed tablets) are fabricated via digital light processing (DLP) 3DP for the first time. Six formulations with varying ratios of an electrolyte acrylate monomer, [2-(acryloyloxy)ethyl]trimethylammonium chloride (TMAEA), and a co-monomer, 1-vinyl-2-pyrrolidone (NVP), were prepared to produce paracetamol-loaded printlets. 1H NMR spectroscopy analysis confirmed the integration of TMAEA and NVP in the polymer, and residual TMAEA monomers were found to be present only in trace amounts (0.71 – 1.37 %w/w). The apparent molecular mass of the photopolymerised polymer was found to exceed 300,000 Da with hydrodynamic radii of 15 – 20 nm, estimated based on 1H DOSY NMR measurements The loaded paracetamol was completely released from the printlets between 45 minutes to 5 hours. In vivo single-dose acute toxicity studies in rats suggest that the printlets did not cause any tissue damage. The findings reported in this study represent a significant step towards the adoption of vat photopolymerization-based 3DP to produce personalised medicines.

The effects of daptomycin on cell wall biosynthesis in Enterococcal faecalis

Daptomycin is a cyclic lipodepsipeptide antibiotic reserved for the treatment of serious infections by multidrug-resistant Gram-positive pathogens. Its mode of action is considered to be multifaceted, encompassing the targeting and depolarization of bacterial cell membranes, alongside the inhibition of cell wall biosynthesis. To characterize the daptomycin mode of action, 15N cross-polarization at magic-angle spinning NMR measurements were performed on intact whole cells of Staphylococcus aureus grown in the presence of a sub-inhibitory concentration of daptomycin in a chemically defined media containing l-[ϵ-15N]Lys. Daptomycin-treated cells showed a reduction in the lysyl-ε-amide intensity that was consistent with cell wall thinning. However, the reduced lysyl-ε-amine intensity at 10 ppm indicated that the daptomycin-treated cells did not accumulate in Park’s nucleotide, the cytoplasmic peptidoglycan (PG) precursor. Consequently, daptomycin did not inhibit the transglycosylation step of PG biosynthesis. To further elucidate the daptomycin mode of action, the PG composition of daptomycin-susceptible Enterococcus faecalis grown in the presence of daptomycin was analyzed using liquid chromatography-mass spectrometry. Sixty-nine muropeptide ions correspond to PG with varying degrees of modifications including crosslinking, acetylation, alanylation, and 1,6-anhydrous ring formation at MurNAc were quantified. Analysis showed that the cell walls of daptomycin-treated E. faecalis had a significant reduction in PG crosslinking which was accompanied by an increase in lytic transglycosylase activities and a decrease in PG-stem modifications by the carboxypeptidases. The changes in PG composition suggest that daptomycin inhibits cell wall biosynthesis by impeding the incorporation of nascent PG into the cell walls by transpeptidases and maturation by carboxypeptidases. As a result, the newly formed cell walls become highly susceptible to degradation by the autolysins, resulting in thinning of the cell wall.

Removal of Acid Orange G Azo Dye by Polycation-Modified Alpha Alumina Nanoparticles.

Highly positively charged poly(vinyl benzyl trimethylammonium chloride) (PVBMA) was successfully synthesized with approximately 81.8% of yield. The PVBMA was characterized by the molecular weight (Mw) of 343.45 g·mol-1 and the molecular weight distribution, (Đ) of 2.4 by 1H NMR and SEC measurements. The PVBMA was applied as an effective agent for α-Al2O3 surface modification in the adsorptive removal of the azo dye acid orange G (AOG). The AOG removal performance was significantly enhanced at all pH compared to without surface modification. The experimental parameters were optimal at pH 8, free ionic strength, 15 min of adsorption time, and 5 mg·mL-1 α-Al2O3 adsorbents. The AOG adsorption which was mainly controlled by the PVBMA-AOG electrostatic attractions was better applicable to Langmuir isotherm and pseudo-second kinetic model. The PVBMA-modified α-Al2O3 demonstrates a high-performance and highly reusable adsorbent with great AOG performances of approximately 90.13 % after 6 reused cycles.

Microemulsions supported by octyl monoglucoside and geraniol. 3. Microstructure & general pattern

This paper completes previous studies on the phase behaviour and microstructure of the quaternary microemulsion water – cyclohexane – n-octyl-β-D-glucoside (β-C8G1) – geraniol. The properties of this system are almost insensitive to temperature, while they can be tuned easily by adding an alcohol as co-surfactant. The addition of the alcohol changes the composition of the interfacial film, which, in turn, is the tuning parameter for the quaternary system. Studies of the phase behaviour together with SANS and NMR measurements allow drawing a quantitative picture of how the domain size ξ, the curvature H, and the interfacial tension σab depend on the composition of the interfacial film. The SANS data of both oil-in-water and water-in-oil droplet microemulsions recorded near the emulsification failure boundary were evaluated with the Generalised Indirect Fourier Transformation (GIFT), revealing a growth towards cylindrical structures when approaching the respective critical end point. We will show that the general behaviour of ternary and quaternary systems is equal if the appropriate tuning parameters are chosen. In addition, we will show that it is possible to apply the scaling description derived for temperature-dependent ternary systems to composition-dependent quaternary systems: plotting the reduced domain size, the reduced curvature and the reduced interfacial tension against the proper reduced tuning parameter, i.e., either the reduced temperature or the reduced interfacial composition, leads to one master curve for all systems.

Self‐Diffusion of a Chemical Warfare Agent Simulant and Water in Nafion by Pulsed Field Gradient NMR

AbstractPulsed field gradient (PFG) NMR at high magnetic field was used to study microscopic diffusion of dimethyl methyl phosphonate (DMMP), a common chemical warfare agent (CWA) simulant, and water in Nafion membranes. PFG NMR measurements were performed for a broad range of molecular displacements. The self‐diffusivities were measured as a function of the DMMP concentration for several fixed water concentrations. The measured data suggest that DMMP and water diffuse in different regions of Nafion. While water mostly diffuses in hydrophilic regions of the membrane, viz. water channels, DMMP diffusion is mostly limited to interfacial perfluoroether regions between these water channels and the semi‐crystalline matrix.

Torsion Angle Analysis of a Thermally Activated Delayed Fluorescence Emitter in an Amorphous State Using Dynamic Nuclear Polarization Enhanced Solid-State NMR.

The torsion angle between donor and acceptor segments of a thermally activated delayed fluorescence (TADF) molecule is one of the most critical factors in determining the performance of TADF-based organic light-emitting diodes (OLEDs) because the torsion angle affects not only the energy gap between the singlet and triplet but also the oscillator strength and spin-orbit coupling. However, the torsion angle is difficult to analyze, because organic molecules are in an amorphous state in OLEDs. Here, we determined the torsion angle of a highly efficient TADF emitter, DACT-II, in an amorphous state by dynamic nuclear polarization enhanced solid-state NMR measurements. From the experimentally obtained chemical shift principal values of 15N on carbazole, we determined the average torsion angle to be 52°. Such quantification of the torsion angles in TADF molecules in amorphous solids will provide deep insight into the TADF mechanism in amorphous OLEDs.

Clay-induced permeability decline in sandstone reservoirs: Insights from a coupled NMR-SEM experimental approach

The blockage induced by solid particles transport and deposition is one of the main causes of injectivity decline in geothermal sandstone reservoirs during reinjection. This paper investigates clay-induced clogging mechanisms to provide a better understanding to formation damage problems encountered in geothermal fields. In-depth NMR measurements were carried out during core-flooding experiments where illite clay particles (120 nm) were injected in sand-packed columns. SEM imaging was performed to compare the porous space before and after damage and study the morphology and distribution of the deposited particles in the sand column. Pressure drop measurements and NMR T2 relaxation time distributions revealed that clogging occurs in two stages: surface deposition and pore bridging. This was further confirmed by SEM images showing that pore-blocking illite ribbons were formed in the porous space.

Investigation into the Hydration Behavior of K2CO3 Packed Beds: An NMR Study

K2CO3 is seen as a promising heat storage material, available for applications in the domestic sector. For practical purposes, the material is hereby often employed in a packed bed containing millimeter-sized particles. To gain more insight into the hydration behavior of these packed beds, quantitative NMR measurements, capable of following the in-situ hydration behavior, are presented for the first time. It is found that hydration behavior varies significantly, depending on the specific hydration conditions that are chosen. At low airflows hydration is found to proceed via a hydration front, while higher airflows cause the hydration front to widen. Since an increase in flow rate coincided with an increase in the supplied water vapor, hydration is eventually found to proceed in a uniform manner. A comparison between TGA and NMR measurements shows that the overall packed bed hydration kinetics hereby transition to the reaction kinetics of single K2CO3 particles.Graphical

Assigning the Absolute Configuration of Inositol Poly- and Pyrophosphates by NMR Using a Single Chiral Solvating Agent.

Inositol phosphates constitute a family of highly charged messenger molecules that play diverse roles in cellular processes. The various phosphorylation patterns they exhibit give rise to a vast array of different compounds. To fully comprehend the biological interconnections, the precise molecular identification of each compound is crucial. Since the myo-inositol scaffold possesses an internal mirror plane, enantiomeric pairs can be formed. Most commonly employed methods for analyzing InsPs have been geared towards resolving regioisomers, but they have not been capable of resolving enantiomers. In this study, we present a general approach for enantiomer assignment using NMR measurements. To achieve this goal, we used 31P-NMR in the presence of L-arginine amide as a chiral solvating agent, which enables the differentiation of enantiomers. Using chemically synthesized standard compounds allows for an unambiguous assignment of the enantiomers. This method was applied to highly phosphorylated inositol pyrophosphates, as well as to lowly phosphorylated inositol phosphates and bisphosphonate analogs. Our method will facilitate the assignment of biologically relevant isomers when isolating naturally occurring compounds from biological specimens.

Entrapping aliphatic and heterocyclic gaseous amines on copper-exchanged montmorillonite: A straight and green process to reduce air pollution

The capture of a number of aliphatic (APAs) and heterocyclic (HCAs) amines, known as widespread pollutants, by Cu2+-exchanged montmorillonite (Mt-Cu) was studied through elemental analysis diffuse-reflectance ultraviolet-visible and infra-red spectroscopies, X-rays diffraction, thermal analysis coupled with mass spectrometry of the evolved gases, XANES and EXAFS spectroscopy, and solid-state NMR. The investigated APAs and HCAs were: ethylamine (EtNH2), triethylamine (Et3N), ethylenediamine (En) and morpholine (Morph), piperidine (Piper), and pyridine (Py), respectively. Mt-Cu saturation occurred within 25 h at worst, the immobilized amount was relevant and involved the binding of the amino nitrogen to the interlayer Cu2+ ions. While for APAs the entrapped amount changed with the structure of the molecule, for HCAs it did not. The EXAFS and XANES studies showed that the interlayer Cu2+ ions are strongly coordinated to the amino groups. This resulted in the coordination number changing from four to five coordination, with the exception of En for which the CuII ions remained tetra-coordinated as in pristine Mt-Cu. Residual water molecules were found to be bound to the copper also after exposure to the amines. For EtNH2, En, Morph, and Piper the coordination to CuII occurred without the deprotonation of the amino group. NMR measurements showed the presence of physisorbed amines whose amount depended on the structure: while En was mostly bound to CuII (physisorption was negligible), for EtNH2, Et3N, Morph, and Piper the physisorbed amount ranged from 55 to 30% and for Py it was even the 70%. In addition, En was found to be the amine entrapped with the highest strength and covalent character. The obtained results supported the effectiveness of Cu2+-modified layered silicates as an air/gas purification system. The exploitation of devices based on Cu2+-exchanged montmorillonite could therefore become a very appealing future challenge as the interlayer modification was very simple and fast and the entire process turned out to be green and economic.