1H Magic Angle Spinning Research Articles

Metabolomics of Small Intestine Neuroendocrine Tumors and Related Hepatic Metastases.

To assess the metabolomic fingerprint of small intestine neuroendocrine tumors (SI-NETs) and related hepatic metastases, and to investigate the influence of the hepatic environment on SI-NETs metabolome. Ninety-four tissue samples, including 46 SI-NETs, 18 hepatic NET metastases and 30 normal SI and liver samples, were analyzed using 1H-magic angle spinning (HRMAS) NMR nuclear magnetic resonance (NMR) spectroscopy. Twenty-seven metabolites were identified and quantified. Differences between primary NETs vs. normal SI and primary NETs vs. hepatic metastases, were assessed. Network analysis was performed according to several clinical and pathological features. Succinate, glutathion, taurine, myoinositol and glycerophosphocholine characterized NETs. Normal SI specimens showed higher levels of alanine, creatine, ethanolamine and aspartate. PLS-DA revealed a continuum-like distribution among normal SI, G1-SI-NETs and G2-SI-NETs. The G2-SI-NET distribution was closer and clearly separated from normal SI tissue. Lower concentration of glucose, serine and glycine, and increased levels of choline-containing compounds, taurine, lactate and alanine, were found in SI-NETs with more aggressive tumors. Higher abundance of acetate, succinate, choline, phosphocholine, taurine, lactate and aspartate discriminated liver metastases from normal hepatic parenchyma. Higher levels of alanine, ethanolamine, glycerophosphocholine and glucose was found in hepatic metastases than in primary SI-NETs. The present work gives for the first time a snapshot of the metabolomic characteristics of SI-NETs, suggesting the existence of complex metabolic reality, maybe characteristic of different tumor evolution.

Evidence of proton beam irradiation compared to isotope effect

In this study, we obtained experimental results similar to the isotope substitution effect by using the proton irradiation of K(H0.47D0.53)2PO4 (DKDP) ferroelectric single crystals. Temperature dependence of dielectric constants showed that the ferroelectric phase to paraelectric phase transition temperature increased from 175 K to 195 K of approximately 20 K after the proton beam irradiation. It was observed that the vibration mode P(OD)2 was changed from 893 to 884 cm−1 in Raman spectroscopy. In 1H Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, the isotropic chemical shift after proton irradiation decreased from 14.46 to 14.32 ppm, which is indicative of the change of the O–H…O the equilibrium distance of hydrogen bonds estimated as 1.60066 Å and 1.62228 Å before and after the proton irradiation, respectively. It was observed that the Full width at half maximum (FWHM) line width also decreased from 563 to 244 Hz in 1H MAS spectral line shape, which is indicative of obeying the displacive phase transition model.

The composition and structure of n-hexane insoluble-hot benzene soluble fraction and hot benzene insoluble fraction from low temperature coal tar

The composition and structure analysis of coal tar is a very important basic issue. In the process of preparing asphaltenes (insoluble in C5-C7 n-alkanes but soluble in hot benzene, HIBS) according to the definition, it was found that hot benzene insoluble (HIBI) components still exist in the coal tar. It is necessary to carry out in-depth analysis and identification of their compositions and structures, in order to obtain detailed information, which provides a certain guiding significance for the deep processing of coal tar. Their compositions and structures were studied by means of physical and thermo-chemical analysis, including Fourier transform infrared spectroscopy (FTIR), Uv-fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), 1H magic angle spinning nuclear magnetic resonance spectroscopy (1H-MAS-NMR), 13C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS-NMR), thermogravimetric analysis (TG) and pyrolysis gas chromatography-mass spectroscopy (PY-GC/MS). The results show that: HIBS and HIBI are mainly composed of aromatic compounds, phenolic compounds and heteroatomic compounds, but the forms of these compounds are different. The ring number of the aromatic structure in HIBI is larger than that in HIBS. The main bonding ways of oxygen in HIBS and HIBI include CO, C–O, C–OH, C–O–C and COO–, but the peak positions of those functional groups are slightly offset. There are more COO– in the structure of the latter. Compared with HIBS, HIBI contains more carboxyl hydrogen and more oxygen-bonded hydrogen, thus inferring that HIBI contains more oxygenated compounds. In addition, HIBI has more shorter alkyl side chains.

Various morphologies of hydrogen-substituted graphynes: The importance of reaction solvents

Hydrogen-substituted graphyne (HsGY) composed of alternative phenylene and ethynylene units were synthesized with organic solvents and deep eutectic solvents as reaction solvents by cross-coupling polymerization of 1, 3, 5- triethynylbenzene and 1, 3, 5-tribromobenzene. The microstructure and properties of HsGYs were analyzed by various characterization methods. Sphere, reticular, irregular massive, claws-like, fibrous structures were observed by scanning electron microscope using the mesitylene, N, N-dimethylformamide and three DESs, respectively. The results showed that the morphologies of five HsGYs were greatly affected by the choice of solvents. The chemical structure of the HsGYs was confirmed by Fourier transform infrared spectroscopy and solid-state 1H magic-angle spinning nuclear magnetic resonance. Moreover, HsGYs with different morphologies had chemical stability, high thermal stability, super-hydrophobic, and semiconductor properties. Studies had shown that HsGY-D (N, N-dimethylformamide as solvent) with the largest specific surface area (1453.16 m2 g−1) and average pore diameter (40.10 Å) had the strongest adsorption performance for carbendazim and thiabendazole by static adsorption test in dried jujube sample. This work was expected to provide useful guidance to rationally design alkynyl carbon materials in adsorption of organic chemical pollutants.

Catalytic arene alkylation over H-Beta zeolite: Influence of zeolite shape selectivity and reactant nucleophilicity

Renewable arenes and aromatic alcohols can be derived from lignocellulose by biorefineries, which has been considered as a sustainable alternative to replace petrochemical feedstocks in the synthesis of monobenzylation products, key industrial intermediates, via benzylation reactions. Zeolites with micropores are the most widely used catalysts in the benzylation of arenes, however, their performance suffers from diffusion limitations in converting large arenes. In this work, mesoporous and microporous H–Beta zeolites were prepared and applied in the systematic study of benzylation of arenes (benzene, toluene, p-xylene and mesitylene) with benzyl alcohol (BA). The porous structure of these zeolites has been confirmed by XRD, BET and TEM techniques. The catalytically active Brønsted acid sites (BAS) were determined by quantitative 1H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) experiments. The benzylation studies have shown that introducing mesopores into H–Beta zeolites can significantly increase the diffusion/access of arenes to surface sites, particularly for bulky arenes (e.g. mesitylene), while micropores are mainly selective for the conversion of small arenes (e.g. benzene). Increasing the nucleophilicity of arenes with more alkyl groups can enhance their catalytic performance in mesopores, however, the increase hinders their conversion in micropores because of the shape selectivity due to their increasing molecular size. Compared to mesopores, micropores promote the conversion of small arenes (e.g. benzene), which can be additionally enhanced by a high Brønsted acidity. Therefore, introducing a suitable porosity balanced with acidity are keys in the tailoring of the catalytic performance of H-Beta zeolites for target benzylation reactions.

Investigating the Dynamic Behavior of Zinc Oxide Discharge Product in Rechargeable Zinc Electrodes

Rechargeable zinc-alkaline batteries are attractive alternatives to established battery technologies such as lithium-ion and lead-acid in certain applications because of their inherent low cost, safety, and environmental friendliness. Commercialization of zinc-alkaline batteries has been largely unsuccessful because of the limited cycle life of zinc electrodes at high depth of discharge. At high depths of discharge, dissolved zinc precipitates from the electrolyte as solid zinc oxide. Zinc oxide buildup causes passivation of zinc metal particles, which increases resistance within the battery and results in eventual cell death. It can also electrically isolate metal particles from the current collector, resulting in loss of active zinc mass. Zinc oxide in alkaline batteries has been studied for decades, but an understanding of the properties of the material and effects on battery performance is still not complete. A complete understanding of the discharge products of zinc electrodes is a necessary step toward wide-spread commercialization of zinc metal electrodes. We demonstrate in this work that zinc oxide produced during discharge undergoes chemical changes as a function of electrode potential. In operando optical microscopy shows that the oxide reversibly changes color from blue at more negative zinc electrode potentials to white at more positive zinc electrode potentials. In operando Raman spectroscopy shows differences in Raman scattering between the blue and the white oxide species, indicating that additional bonds are present in the blue material, which are not observed in the white material. Solid-state 1H magic angle spinning NMR spectroscopy on extracted oxide material suggests that changes to electrode potential result in simultaneous insertion or disinsertion of protons and electrons into the oxide material. More immobile species are present in the blue material compared to the white, indicating inserted protons may be more abundant in the blue oxide. Additionally, two-dimensional 1H-1H exchange spectroscopy shows more chemical exchange between sites in the white material compared to the blue, indicating protons may be more strongly bound in the blue oxide. The behavior observed in these studies is similar to that observed for electrochromic materials. In electrochromic materials, inserted electrons can increase the electrical conductivity of the oxide by orders of magnitude. At more positive zinc potentials, an increase in the electrical resistance of the oxide may result in conductivity losses between zinc metal particles. Additionally, when protons are disinserted from the oxide, they result in a local pH decrease in the electrolyte surrounding the oxide, which affects the ionic conductivity of the electrolyte. The work outlined in this study demonstrates the effects of this behavior on electrode performance and explores avenues for controlling the behavior through electrode additives and operation controls. Figure 1

Negative Knight Shift in Ba-Ti Oxyhydride: An Indication of the Multiple Hydrogen Occupation

Multiple hydrogen occupation in Ba-Ti oxyhydride is demonstrated by a negative Knight shift in the 1H magic-angle spinning (MAS) NMR spectra combined with hydrogen concentration and X-ray photoelec...

Membrane Localization and Lipid Interactions of Common Lipid-Conjugated Fluorescence Probes.

Lateral segregation of lipids in model and biological membranes has been studied intensively in the last decades using a comprehensive set of experimental techniques. Most methods require a probe to report on the biophysical properties of a specific molecule in the lipid bilayer. Because such probes can adversely affect the results of the measurement and perturb the local membrane structure and dynamics, a detailed understanding of probe behavior and its influence on the properties of its direct environment is important. Membrane phase-selective and lipid-mimicking molecules represent common types of probes. Here, we have studied how the fluorescent probes trans-parinaric acid (tPA), diphenylhexatriene (DPH), and 1-oleoyl-2-propionyl[DPH]-sn-glycero-3-phosphocholine (O-DPH-PC) affect the membrane properties of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) bilayers using 2H and 31P NMR spectroscopy in the solid state. In addition, using 2D 1H magic-angle spinning (MAS) nuclear Overhauser enhancement spectroscopy (NOESY) NMR, we have determined the distribution of the probe moieties in the POPC membrane parallel to the membrane normal. We found that the different probes exhibit distinct membrane localizations and distributions, e.g. tPA is located parallel to the membrane normal while DPH predominantly exist in two orientations. Further, tPA was conjugated to sphingomyelin (tPA-SM) as a substitute for the acyl chain in the SM. 1H NOESY NMR was used to probe the interaction of the tPA-SM with cholesterol as dominant in liquid ordered membrane domains in comparison to POPC-cholesterol interaction in membranes composed of ternary lipid mixtures. We could show that tPA-SM exhibited a strong favorable and very temperature-dependent interaction with cholesterol in comparison to POPC. In conclusion, the NMR techniques can explain probe behavior but also be used to measure lipid-specific affinities between different lipid segments and individual molecules in complex bilayers, relevant to understanding nanodomain formation in biological membranes.

Study on Paramagnetic Interactions of (CH3NH3)2CoBr4 Hybrid Perovskites Based on Nuclear Magnetic Resonance (NMR) Relaxation Time.

The thermal properties of organic–inorganic (CH3NH3)2CoBr4 crystals were investigated using differential scanning calorimetry and thermogravimetric analysis. The phase transition and partial decomposition temperatures were observed at 460 K and 572 K. Nuclear magnetic resonance (NMR) chemical shifts depend on the local field at the site of the resonating nucleus. In addition, temperature-dependent spin–lattice relaxation times (T1ρ) were measured using 1H and 13C magic angle spinning NMR to elucidate the paramagnetic interactions of the (CH3NH3)+ cations. The shortening of 1H and 13C T1ρ of the (CH3NH3)2CoBr4 crystals are due to the paramagnetic Co2+ effect. Moreover, the physical properties of (CH3NH3)2CoBr4 with paramagnetic ions and those of (CH3NH3)2CdBr4 without paramagnetic ions are reported and compared.

Molecular dynamics of hybrid halide perovskite (CH3NH3)2CuX4 (X = Br and Cl) determined by nuclear magnetic resonance relaxation processes

The thermal stability of hybrid halide perovskite (CH3NH3)2CuBr4 crystals are investigated using differential scanning calorimetry and thermogravimetric analysis. To elucidate the local environment of the cations, temperature-dependent chemical shifts and spin-lattice relaxation times are measured using 1H magic angle spinning nuclear magnetic resonance (MAS NMR) and 13C cross-polarization/MAS NMR techniques. The chemical shifts of 1H and 13C decrease with increasing temperature, which indicates that the environment around 1H and 13C changes with temperature. Moreover, the 1H and 13C spin-lattice relaxation times T1ρ increase significantly at high temperatures. These T1ρ results reveal that the cations are subject to high mobility at high temperatures. A comparison of the molecular dynamics of (CH3NH3)2CuX4 (X = Br, Cl) crystals is made, together with a discussion of the effect of substituting Cl ions for the Br ions in the structure.

Interpretation of the crystal growth, phase transition, and molecular dynamics of [N(CH3)4]2ZnBr4 crystals by replacing partially the Zn2+ ions with Co2+ ions

The effects on the physical properties of [N(CH3)4]2Zn1-xCoxBr4 (x = 0, 0.5, 0.7, and 1) crystal due to the partial substitution of Zn2+ ions with paramagnetic Co2+ ions were discussed. The crystal structures and phase transition temperature (287 K) of layered perovskite-type [N(CH3)4]2Zn1-xCoxBr4 were nearly unaffected by the partial doping of Co2+ ions, as revealed by X-ray diffraction and differential scanning calorimetry experiments. The environments surrounding the 1H and 13C in [N(CH3)4]2Zn1-xCoxBr4 mixed systems were determined from the chemical shifts and the spin-lattice relaxation time T1ρ of 1H magic angle spinning nuclear magnetic resonance (MAS NMR) and 13C cross-polarization (CP)/MAS NMR. The molecular motions by the T1ρ for 13C nuclei were nearly unaffected when Zn2+ ions were substituted with Co2+ ions, whereas those for 1H nuclei were influenced by doping Co2+ ions. A comparison of the molecular dynamics of TMA-Zn1-xCoxBr4 studied in this paper with the previously reported TMA-Zn1-xCoxCl4 was made to understand the effects of Cl and Br ions.

Polymorphic Transformation of Drugs Induced by Glycopolymeric Vesicles Designed for Anticancer Therapy Probed by Solid-State NMR Spectroscopy.

Understanding the nature of the drug-polymer interactions in micellar drug delivery systems and what happens with the drug and the polymer once the complex has formed is essential for the rational design of the polymeric matrices suitable for a particular drug. In this work, glycopolymeric vesicles-a block copolymer, poly(1-O-methacryloyl-β-d-fructopyranose)-b-poly(methyl methacrylate), (PFru36-PMMA160),-designed to target tumor cells loaded with two drugs, ellipticine and curcumin, were characterized. Advanced solid-state NMR spectroscopy and single-crystal/powder X-ray diffraction (XRD) combined with CASTEP calculations shed light on the nature of the drug, the polymer, and their interactions. While the low drug loading (ca. 5%) ensured that the structure, size, and shape of the polymeric vesicles did not change significantly, the solid-state forms of the drugs changed markedly. Upon loading into the vesicles, ellipticine favored a highly ordered form distinctly different from the bulk drug as indicated by 13C solid-state NMR spectroscopy. A detailed analysis of the CASTEP-calculated 13C spectra derived from crystallographic data based on the lowest mean absolute error showed the best match with form I. Moreover, ellipticine before loading was found as a new polymorph and was described by single-crystal XRD as a new orthorhombic Form III. Likewise, curcumin, originally present in monoclinic Form I was found to recrystallize as metastable orthorhombic Form II inside the vesicles. Intermolecular interactions between the polymeric vesicles and the drugs, ellipticine as well as curcumin, were detected using 2D 1H magic angle spinning experiments, indicating that the drugs are localized in the hydrophobic layer of the vesicles.

Transition in Longgu Surface Associated with Decoction Process of Keishikaryukotsuboreito.

We aim to attain the sustainable use of longgu and have investigated the significance of longgu in Keishikaryukotsuboreito (KRB) decoction. We have already reported that longgu alters compound profiles in KRB decoction and hypothesized that it does so by adsorbing foreign organic compounds into its superficial pores. In the present study, we focused on the adsorbability of organic materials onto longgu surface as the cause of component profile alteration. We analyzed the physical changes in longgu through the decoction process by measuring the adsorbed water on longgu surface. 1H magic angle spinning NMR (1H-MASNMR) spectroscopic analysis revealed that raw longgu (R-raw) as well as decocted longgu [whether single (R-r) or KRB (R-krb) decoction] adsorbed water. However, the amount of adsorbed water in R-krb was smaller than that in R-raw and R-r. The nitrogen adsorption isotherms of longgu samples indicated that longgu was macroporous. The Brunauer-Emmett-Teller (BET) surface area of R-krb was smaller than that of R-raw and R-r. Further, thermogravimetric analysis of longgu samples showed that R-krb adsorbed matter that R-raw and R-r did not adsorb. The above findings and the 1H-MASNMR analysis of heated longgu samples suggested that longgu adsorbed organic compounds into the pores. We considered that longgu adsorbed organic compounds during KRB decoction into its superficial pores through the decoction process.

Understanding the Effect of UV-Induced Cross-Linking on the Physicochemical Properties of Highly Performing PEO/LiTFSI-Based Polymer Electrolytes.

We report a thorough, multitechnique investigation of the structure and transport properties of a UV-cross-linked polymer electrolyte based on poly(ethylene oxide), tetra(ethylene glycol)dimethyl ether (G4), and lithium bis(trifluoromethane)sulfonimide. The properties of the cross-linked polymer electrolyte are compared to those of a non-cross-linked sample of same composition. The effect of UV-induced cross-linking on the physico/chemical characteristics is evaluated by X-ray diffraction, differential scanning calorimetry, shear rheology, 1H and 7Li magic angle spinning nuclear magnetic resonance (NMR) spectroscopy, 19F and 7Li pulsed field gradient stimulated echo NMR analyses, electrochemical impedance spectroscopy, and Fourier transform Raman spectroscopy. Comprehensive analysis confirms that UV-induced cross-linking is an effective technique to suppress the crystallinity of the polymer matrix and reduce ion aggregation, yielding improved Li+ transport number (>0.5) and ionic conductivity (>0.1 mS cm?1) at ambient temperature, by tailoring the structural/morphological characteristics of the polymer matrix. Finally, the polymer electrolyte allows reversible operation with stable profile for hundreds of cycles upon galvanostatic test at ambient temperature of LiFePO4-based lithium-metal cells, which deliver full capacity at 0.05 or 0.1C current rate and keep high rate capabilities up to 1C. This enforces the role of UV-induced cross-linking in achieving excellent electrochemical characteristics, exploiting a practical, easy up-scalable process.

Wet chemical extraction of silicon from natural palygorskite for preparing a mesoporous molecular sieve of Al-SBA-16

Three-dimensional mesoporous molecular sieve, Al-SBA-16, was successfully prepared via a wet chemical route, which involved co-condensation of silicon source from natural palygorskite by alkali-melting extraction, and acidic mixture of templating agent F127 and aluminum sulfate. XRF and Raman spectra confirmed quantitative incorporation of aluminum into ordered cubic mesostructure. Pyridine-probed Fourier transformed infrared spectroscopy and 1H magic-angle spinning nuclear magnetic resonance showed a doubling of the Bronsted and Lewis acidity after aluminum activation. At neutral pH, the Al-SBA-16 was used as an adsorbent for the removal of aniline and basic fuchsin with the maximum adsorption capacities of 46.22 and 70.08 mg g−1, respectively. Adsorption kinetics and isotherm indicated that adsorption of aniline and basic fuchsin was occurred by their lone pair electrons on N atom interacting with the Bronsted and Lewis acid sites of Al-SBA-16. The adsorbed material could be easily regenerated by a simple process of acid washing. It was reused for five times with basic fuchsin removal rate still up to above 90%.

Solid-state 1H and 13C NMR of corn starch plasticized with glycerol and urea

1H and 13C NMR spectroscopy was used for the study of corn starch plasticized with urea and/or glycerol. The information on the interactions between plasticizers and starch macromolecules as well as the arrangement of starch macromolecules depending on the storage time (from 1 day to 52 weeks), were obtained from the broad-line and magic-angle spinning 1H NMR spectra measured at 22 °C and within the range from 30 to 140 °C and the cross-polarization magic-angle spinning (CP MAS) 13C NMR spectra measured at 30 °C. The 1H chemical shifts for the groups of the plasticizer molecules enabled characterization of the interactions between urea and glycerol molecules in starch plasticized with a mixture of urea and glycerol. With increasing temperature, the signal related to water molecules gradually vanished due to water evaporation, and resolved 1H peaks associated with starch macromolecules were detected above 100 °C. The free water amount in the thermoplastic starch samples was also estimated using MAS 1H NMR spectra. Formation of double helices due to sample ageing was observed through the CP MAS 13C NMR spectra.

Structures and Brønsted acidity features for titanoniobates with different laminate composition

Surface acidity is one of the important features for the layered titanoniobates. However, the effects of the laminate composition on the structure and acidity of titanoniobates are not clear. Herein, a series of layered solid acids including HTiNbO5, HTi2NbO7 and H3Ti5NbO14 are prepared through the high temperature calcination and proton exchange process. Their structures and physicochemical properties are investigated by the means of X-ray diffraction (XRD), thermal gravimetric–differential thermal gravimetric (TG-DTG), laser Raman spectroscopy (LRS) and 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR) spectra. The esterification of acetic acid and n-butanol is used to evaluate the acid catalytic properties of the as-prepared layered solid acids. The results show that the Brønsted acid sites on the as-prepared samples are derived from different hydroxyl species and the strength is obviously affected by its laminate composition, phase structure and hydroxyl species feature, especially the possible hydrogen bonding. More TiOH and TiOHTi bonds will be formed in those layered compounds with an increasing Ti/Nb atomic ratio, due to more exposure of the terminal TiO or TiOTi bonds on the laminate surface. The compound H3Ti5NbO14 possesses the strongest Brønsted intensity and acid catalytic activity among the investigated samples.

Integrated analysis of modified Japanese cypress using solid-state NMR spectra and nuclear magnetic relaxation times

Acetylation and resin impregnation of Japanese cypress and subsequent heating of these modified cypresses were examined using an integrated analysis of solid-state NMR spectra and relaxation times. The 1H magic angle spinning NMR showed altered moisture balance after chemical and thermal modifications because of changed hydrophobicity. The 13C cross-polarization/magic angle spinning (CP-MAS) NMR spectra showed that acetylation predominately occurred for carbohydrates while phenol formaldehyde (PF) and melamine formaldehyde (MF) resins permeated all biomass constituents in cypress samples. Spin–lattice relaxation times in the laboratory frame, T1H and T1C, increased with chemical modifications although T1C decreased with the curing of both resins. In contrast, 1H spin–lattice relaxation in the rotation frame, T1ρH, increased with the curing as well as acetylation. The tendencies of relaxation times with curing suggested that faster molecular motions were suppressed in the MHz frequency range, and slower molecular motions were enhanced in the kHz frequency range, which generally matched with the signal changes in the 13C pulse saturation transfer/magic angle spinning NMR spectra. Scanning electron microscope observation showed different adhesion distribution between PF and MF resins, affecting the cellulose signals of 13C CP-MAS NMR and T1H change due to the curing.

Capping Structure of Ligand-Cysteine on CdSe Magic-Sized Clusters.

Ligand molecules capping on clusters largely affect the formation and stabilization mechanism and the property of clusters. In semiconductor CdSe clusters, cysteine is used as one of the ligands and allows the formation of ultrastable (CdSe)34 magic-sized clusters. Cysteine has sulfhydryl, amine, and carboxylate groups, all of which have coordination ability to the CdSe surface, and the bonding states of the three functional groups of ligand–cysteine on the CdSe core have not been determined. In this work, the capping structure of ligand–cysteine is examined by performing Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and multinuclear solid-state nuclear magnetic resonance (NMR) spectroscopy. FT-IR, XPS, and 1H, 13C, and 23Na magic-angle spinning NMR show that the sulfhydryl group of ligand–cysteine forms a sulfur–cadmium bond with a cadmium atom at the CdSe surface, while the carboxylate group does not contribute to the protection of the CdSe core and binds to a sodium ion contained as a counterion. 15N–{77Se} through-bond J-single quantum filtered NMR experiment reveals that the amine group of ligand–cysteine has no coordination to selenium atoms. By considering the N–Cd bond forming ratio (∼43%) revealed in our previous work, which is confirmed in this work by analyzing 13Cα signal intensity (∼42%), we concluded that cysteine capping on (CdSe)34 occurs in two ways: one involves both the sulfur–cadmium and nitrogen–cadmium bonds, and the other bears only the sulfur–cadmium bond.

Hydration and Hydroxylation of MgO in Solution: NMR Identification of Proton-Containing Intermediate Phases.

Magnesium oxide (MgO)-engineered barriers used in subsurface applications will be exposed to high concentration brine environments and may form stable intermediate phases that can alter the effectiveness of the barrier. To explore the formation of these secondary intermediate phases, MgO was aged in water and three different brine solutions and characterized with X-ray diffraction (XRD) and 1H magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. After aging, there is ∼4% molar equivalent of a hydrogen-containing species formed. The 1H MAS NMR spectra resolved multiple minor phases not visible in XRD, indicating that diverse disordered proton-containing environments are present in addition to crystalline Mg(OH)2 brucite. Density functional theory (DFT) simulations for the proposed Mg–O–H-, Mg–Cl–O–H-, and Na–O–H-containing phases were performed to index resonances observed in the experimental 1H MAS NMR spectra. Although the intermediate crystal structures exhibited overlapping 1H NMR resonances in the spectra, Mg–O–H intermediates were attributed to the growth of resonances in the δ +1.0 to 0.0 ppm region, and Mg–Cl–O–H structures produced the increasing contributions of the δ = +2.5 to 5.0 ppm resonances in the chloride-containing brines. Overall, 1H NMR analysis of aged MgO indicates the formation of a wide range of possible intermediate structures that cannot be observed or resolved in the XRD analysis.