Solid-state 13C NMR Measurements Research Articles

A putative mechanism for capture of carbon dioxide by quartz, mediated by triboelectric charging

Mechanical activation of quartz grains in a dry atmosphere causes triboelectric charging that can capture CO2 quantitatively (Thøgersen et al., https://doi.org/10.1016/j.cplett.2021.139069). Based on electron structure calculations, we propose a mechanism for this process. According to the mechanism, CO2 is inserted in the quartz lattice to form an anchored CO3 moiety. Predicted 13C chemical shifts of this product agree with solid-state 13C NMR measurements.

Cobalt Porphyrin-Cross-Linked Poly(Ionic Liquid)s as Efficient Heterogeneous Catalysts for Carbon Dioxide Conversion under Mild Conditions

The cycloaddition reaction of CO2 and epoxides to form cyclic carbonates is a promising strategy to alleviate the climate change caused by CO2 in view of its high atomic economic efficiency and solvent-free and mild conditions. Inspired by the mechanism of cycloaddition reactions catalyzed by Lewis acid/Lewis base binary systems, we explored a series of heterogeneous catalysts functionalized by cobalt porphyrin cross-linked phosphonium salt poly(ionic liquid)s. Specifically, poly(4-vinylbenzyl chloride) (PVBnCl) was used as the polymer backbone. Then, PVBnCl was cross-linked by 5,10,15,20-tetra(4-pyridyl) porphyrin (TPyP) and quaternized by triphenylphosphine (PPh3). After complexing with CoCl2 and anion exchange, the as-prepared polymers CoTPyP-c-PVBnPPh3X were characterized using FTIR, SEM, TEM, XPS, TGA, ICP, and solid-state 13C NMR measurements. The results demonstrated that CoTPyP-c-PVBnPPh3X were efficient catalysts for the cycloaddition of CO2 and epoxides under mild conditions. Almost quantitative conversion of epoxides could be achieved at 80 °C and 1 atm CO2, and CoTPyP-c-PVBnPPh3X could be easily separated and reused for four cycles only with a little decrease in the catalysis activity. The synergistic catalysis of the Lewis acid metal center and nucleophilic halogen ion addressed the excellent performance of CoTPyP-c-PVBnPPh3X. Therefore, our findings provided a new solution for the development of efficient heterogeneous catalysts with multi-centers for CO2 conversion.

Molecular-level elucidation of saccharin-assisted rapid dissolution and high supersaturation level of drug from Eudragit® E solid dispersion

In this work, the effect of saccharin (SAC) addition on the dissolution and supersaturation level of phenytoin (PHT)/Eudragit® E (EUD-E) solid dispersion (SD) at neutral pH was examined. The PHT/EUD-E SD showed a much slower dissolution of PHT compared to the PHT/EUD-E/SAC SD. EUD-E formed a gel layer after the dispersion of the PHT/EUD-E SD into an aqueous medium, resulting in a slow dissolution of PHT. Pre-dissolving SAC in the aqueous medium significantly improved the dissolution of the PHT/EUD-E SD. Solid-state 13C NMR measurements showed an ionic interaction between the tertiary amino group of EUD-E and the amide group of SAC in the EUD-E gel layer. Consequently, the ionized EUD-E could easily dissolve from the gel layer, promoting PHT dissolution. Solution-state 1H NMR measurements revealed the presence of ionic interactions between SAC and the amino group of EUD-E in the PHT/EUD-E/SAC solution. In contrast, interactions between PHT and the hydrophobic group of EUD-E strongly inhibited the crystallization of the former from its supersaturated solution. The PHT supersaturated solution was formed from the PHT/EUD-E/SAC SD by the fast dissolution of PHT and the strong crystallization inhibition effect of EUD-E after aqueous dissolution.

Powder Structure Analysis of Vapochromic Quinolone Antibacterial Agent Crystals

Vapochromic materials, or those that show a reversible color change induced by vapor, are expected to serve as valuable sensors for volatile organic compounds or humidity. Crystals of pipemidic acid (PPA), a quinolone antibacterial agent, were found to exhibit vapochromism, as they undergo a reversible color change in the presence of acetonitrile vapor. The colorless trihydrate phase transformed into a yellow anhydrous phase upon exposure to acetonitrile vapor and returned to the trihydrate phase under high humidity. Ab initio structure determination from powder diffraction and solid state 13C NMR measurements revealed that the molecule exists in its zwitterionic form in the colorless trihydrate phase, whereas it is non-zwitterionic in the anhydrous phase because of the rearrangement of hydrogen bonds, due to dehydration in the crystal state. Theoretical calculations revealed that the color change in PPA is due to the change in the molecular electronic state upon taking the non-zwitterionic form, which ge...

Crystallization of Probucol in Nanoparticles Revealed by AFM Analysis in Aqueous Solution.

The crystallization behavior of a pharmaceutical drug in nanoparticles was directly evaluated by atomic force microscopy (AFM) force curve measurements in aqueous solution. A ternary spray-dried sample (SPD) was prepared by spray drying the organic solvent containing probucol (PBC), hypromellose (HPMC), and sodium dodecyl sulfate (SDS). The amorphization of PBC in the ternary SPD was confirmed by powder X-ray diffraction (PXRD) and solid-state 13C NMR measurements. A nanosuspension containing quite small particles of 25 nm in size was successfully prepared immediately after dispersion of the ternary SPD into water. Furthermore, solution-state 1H NMR measurements revealed that a portion of HPMC coexisted with PBC as a mixed state in the freshly prepared nanosuspension particles. After storing the nanosuspension at 25 °C, a gradual increase in the size of the nanoparticles was observed, and the particle size changed to 93.9 nm after 7 days. AFM enabled the direct observation of the morphology and agglomeration behavior of the nanoparticles in water. Moreover, AFM force-distance curves were changed from (I) to (IV), depending on the storage period, as follows: (I) complete indentation within an applied force of 1 nN, (II) complete indentation with an applied force of 1-5 nN, (III) partial indentation with an applied force of 5 nN, and (IV) nearly no indentation with an applied force of 5 nN. This stiffness increase of the nanoparticles was attributed to gradual changes in the molecular state of PBC from the amorphous to the crystal state. Solid-state 13C NMR measurements of the freeze-dried samples demonstrated the presence of metastable PBC Form II crystals in the stored nanosuspension, strongly supporting the AFM results.

MgCl2·6CH3OH: A Simple Molecular Adduct and Its Influence As a Porous Support for Olefin Polymerization

A single phase molecular adduct, MgCl2·6CH3OH has been synthesized using MgCl2 and the simplest alcohol, methanol. Structural, spectroscopic, and morphological studies have been carried out for a better understanding of the single phase MgCl2·6CH3OH adduct. 13C CPMAS solid state NMR studies show all six methanol molecules are magnetically equivalent and present in a single environment around the Mg2+ center. Raman spectral analysis of the characteristic peak at 708 cm–1 substantiates octahedral coordination of six CH3OH molecules around Mg2+. Solid state 13C NMR measurements, made after heat treatment at different temperatures, have been utilized to understand the variations in CH3OH stoichiometry and coordination around Mg2+ with temperature. A titanated active catalyst, TiCl4 on MgCl2·6CH3OH, has also been synthesized and subjected to detailed characterizations. The active catalyst shows high surface area (102 m2/g) and mesoporosity. The titanated catalyst has been screened for ethylene polymerization reactions using different cocatalysts (R3Al; R= −CH3, −CH2CH3, and −CH2CH(CH3)2). A total of 7.25 kg of polyethylene per gram of catalyst has been obtained with Me3Al cocatalyst, which is six times higher in activity compared with commercial Me3Al/TiCl4/ MgCl2·6EtOH-supported catalyst. Although porosity influences the catalytic activity, other factors also seem to contribute to the total catalytic activity.

Thermodynamic Stability, Spectroscopic Identification, and Gas Storage Capacity of CO2–CH4–N2 Mixture Gas Hydrates: Implications for Landfill Gas Hydrates

Landfill gas (LFG), which is primarily composed of CH(4), CO(2), and N(2), is produced from the anaerobic digestion of organic materials. To investigate the feasibility of the storage and transportation of LFG via the formation of hydrate, we observed the phase equilibrium behavior of CO(2)-CH(4)-N(2) mixture hydrates. When the specific molar ratio of CO(2)/CH(4) was 40/55, the equilibrium dissociation pressures were gradually shifted to higher pressures and lower temperatures as the mole fraction of N(2) increased. X-ray diffraction revealed that the CO(2)-CH(4)-N(2) mixture hydrate prepared from the CO(2)/CH(4)/N(2) (40/55/5) gas mixture formed a structure I clathrate hydrate. A combination of Raman and solid-state (13)C NMR measurements provided detailed information regarding the cage occupancy of gas molecules trapped in the hydrate frameworks. The gas storage capacity of LFG hydrates was estimated from the experimental results for the hydrate formations under two-phase equilibrium conditions. We also confirmed that trace amounts of nonmethane organic compounds do not affect the cage occupancy of gas molecules or the thermodynamic stability of LFG hydrates.

Spectroscopic identification and conversion rate of gaseous guest-loaded hydroquinone clathrates

The formation of hydroquinone clathrates with CO2, CH4, N2, and H2 was investigated using X-ray diffraction, Raman spectroscopy, and solid-state 13C NMR spectroscopy. Of the hydroquinones prepared at 5.0MPa, the CH4- and CO2-loaded hydroquinones show complete conversion to β-form hydroquinone clathrates while the N2-loaded hydroquinone shows only partial conversion; there is no indication of the formation of hydroquinone clathrate with H2. The CO2-loaded hydroquinone is fully converted to the β-form hydroquinone clathrate even at 1.0MPa. Solid-state 13C NMR measurements of the hydroquinone clathrate samples prepared at different pressures reveal that the conversion rate for the formation of clathrate compounds from CH4 and N2 decreases with decreasing pressure.

Crystal transition from cellulose II hydrate to cellulose II

Samples of cellulose II hydrate were prepared by immersion of mercerized cellulose II in anhydrous hydrazine followed by washing with water. The synchrotron X-ray fiber diffraction and solid-state 13C NMR measurements showed that cellulose II hydrate had a larger unit cell that contained water molecules with lower degree of crystallinity than mercerized cellulose II, but it had basically the same molecular conformation as mercerized cellulose II. The crystal transition from cellulose II hydrate to cellulose II was monitored using synchrotron X-ray diffraction under controlled relative humidity. In the drying process, the cellulose II hydrate gradually contracted, and this decreased the distance between the hydrophobic stacking sheets of molecular chains, while maintaining its sheet structure. The absence of an obvious transition point and the irreversibility of the transition indicated a random location of the water molecules occurred in the unit cell of cellulose II hydrate. On annealing a sample in hot water, the cellulose II hydrate was converted to cellulose II. Cellulose II hydrate was unstable at high temperatures, even in water.

Improved Adsorption Behaviors of Amine-Modified Tannin Gel for Palladium and Platinum Ions in Acidic Chloride Solutions

A tannin gel (TG) synthesized from condensed tannin molecules has a remarkable ability to adsorb various metal ions in aqueous solutions. Previously, we found that the adsorbability of the TG for the palladium ion can be improved by the ammonia treatment (Chem. Lett.2007, 36, 1316). In the present study, we have performed solid-state 13C NMR measurements of the tannin gels before and after the ammonia treatment and found that some hydroxy groups in the TG are substituted by amino groups. Using this amine-modified tannin gel (ATG), we have investigated the adsorption behaviors of palladium and platinum ions, Pd(II) and Pt(IV), in acidic chloride solutions under various conditions. The adsorbability of the ATG for both precious metal ions was greatly improved compared to that of the original TG. Their adsorption amounts onto the ATG increased with increasing pH and temperature or decreasing chloride ion concentration. Under all conditions examined here, the adsorbability of the ATG for Pd(II) was much higher than that for Pt(IV), resulting in the success of the selective adsorption of Pd(II) from the solution mixture of Pd(II) and Pt(IV).

Zinc Glycolate: A Precursor to ZnO

A simple and versatile solvent-growth process using ethylene glycol has been demonstrated for the synthesis of novel faceted bipyramidal zinc glycolate. Upon thermal treatment in air, this structure can be converted into a ZnO hexagonal phase with wurtzite structure via solid-state transformation. The morphology, microstructure, and crystallinity of the products before and after thermal treatment have been characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and solid-state (13)C NMR measurements. In addition, the room-temperature photoluminescence of the resulting ZnO has also been investigated.

Radiation oxidation of polypropylene: A solid-state 13C NMR study using selective isotopic labeling

Polypropylene samples, in which the three different carbon atoms along the chain were selectively labeled with carbon-13, were subjected to radiation under inert and air atmospheres, and to post-irradiation exposure in air at various temperatures. By using solid-state 13C NMR measurements at room temperature, we have been able to identify and quantify the oxidation products. The isotopic labeling provides insight into chemical reaction mechanisms, since oxidation products can be traced back to their positions of origin on the macromolecule. The major products include peroxides and alcohols, both formed at tertiary carbon sites along the chain. Other products include methyl ketones, acids, esters, peresters, and hemiketals formed from reaction at the tertiary carbon, together with in-chain ketones and esters from reaction at the secondary chain carbon. No evidence is found of products arising from reactions at the methyl side chain. Significant temperature-dependent differences are apparent; for example much higher yields of chain-end methyl ketones, which are the indicator product of chain scission, are generated for both elevated temperature irradiation and for post-irradiation treatment at elevated temperatures. Time-dependent plots of yields of the various oxidation products have been obtained under a wide range of conditions, including the post-irradiation oxidation of a sample at room temperature in air that has been monitored for 2 years. Radiation-oxidation products of polypropylene are contrasted to products measured for 13C-labeled polyethylene in an earlier investigation: the peroxides formed in irradiated polypropylene are remarkably longer lived, the non-peroxidic products are significantly different, and the overall ratios of oxidation products in polypropylene change relatively little as a function of the extent of oxidation.

Search of structure and ligands exchange for palladium(II) complexes with N-allylimidazole; X-ray and solid-state/solution NMR studies

Two coordination compounds of palladium(II) with N-allylimidazole ( l) of the general formula [PdL 4]Cl 2 · 3H 2O ( 1) and trans-[PdL 2Cl 2] ( 2) have been synthesized. The crystal and molecular structure of complexes 1 and 2 was established by single-crystal X-ray diffraction analysis. The X-ray structural data were supplemented by solid-state 13C NMR measurements (CP MAS and PASS 2D). The 1D and 2D NMR studies in solution reveal that complex 1 is unstable at room temperature and undergoes reversible decomposition to 2. The method for how to preserve a complex with four allyl-imidazole ligands in solution is shown.

NMR determination of photorespiration in intact leaves using in vivo 13CO 2 labeling

Solid-state 13C NMR measurements of intact soybean leaves labeled by 13CO 2 lead to the conclusion that photorespiration is 17% of photosynthesis for a well-watered and fertilized plant. This is the first direct assessment of the level of photorespiration in a functioning plant. A 13C{ 31P} rotational-echo double-resonance (REDOR) measurement tracked the incorporation of 13C label into intermediates in the Calvin cycle as a function of time. For labeling times of 5 min or less, the isotopic enrichment of the Calvin cycle depends on the flux of labeled carbon from 13CO 2, relative to the flux of unlabeled carbon from glycerate returned from the photorespiratory cycle. Comparisons of these two rates for a fixed value of the 13CO 2 concentration indicate that the ratio of the rate of photosynthesis to the rate of photorespiration of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in soybean leaves is 5.7. This translates into a photorespiratory CO 2 loss that is 21% of net CO 2 assimilation, about 80% of the value estimated from Rubisco kinetics parameters. The ratio of rates is reduced at low external CO 2 concentrations, as measured by net carbon assimilation rates. The carbon assimilation was determined from 13C-label spin counts converted into total carbon by the REDOR-determined isotopic enrichments of the Calvin cycle. The net carbon assimilation rates indicate that the rate of decarboxylation of glycine is not directly proportional to the oxygenase activity of Rubisco as is commonly assumed.

Glycine Metabolism in Intact Leaves by in Vivo 13C and 15N Labeling

Solid-state (13)C NMR measurements of intact soybean leaves labeled by (13)CO(2) (at subambient concentrations) show that excess glycine from the photorespiratory C(2) cycle (i.e. glycine not part of the production of glycerate in support of photosynthesis) is either fully decarboxylated or inserted as (13)C-labeled glycyl residues in proteins. This (13)C incorporation in leaf protein, which is uniformly (15)N labeled by (15)NH(4)(15)NO(3), occurs as soon as 2 min after the start of (13)CO(2) labeling. In those leaves with lower levels of available nitrogen (as measured by leaf nitrate and glutamine-glutamate concentrations), the excess glycine is used primarily as glycyl residues in protein.

Counting of labelled tyrosine molecules in hydrophobic yoctolitre wells filled with water

Time-dependent radioactivity and solid-state 13C-NMR measurements of tyrosine entrapped in water-filled yoctolitre (10(-24) L) wells with hydrophobic walls are reported; the results indicate that such wells induce the formation of quasi solid tyrosine if they are brought in contact with 0.1 M solutions of this edge amphiphile.

Assessment of Thermal Evolution of Kerogen Geopolymers with Their Structural Parameters Measured by Solid-State 13C NMR Spectroscopy

The sidebands in the solid-state 13C NMR spectra of 13 polycyclic aromatic hydrocarbon compounds associated with kerogen structure were suppressed with cross polarization (CP), magic-angle spinning (MAS), and total sideband suppression (TOSS). The chemical shift values of these model compounds were obtained under various chemical circumstances, which were subsequently used to determine the chemical shifts of aliphatic and aromatic carbons in kerogen structure via CP/MAS/TOSS 13C NMR measurements. Dipolar dephasing (DD) was used to obtain the spectra of nonprotonated carbon, discriminating protonated and nonprotonated carbons in the aromatic cluster. Consequently, the structural parameters for different carbons were characterized. High-resolution solid-state 13C NMR measurements were conducted on a suite of kerogen macromolecules isolated from source rocks originated from the Kuqa depression, Awati River, and Kapusaliang River of the Tarim Basin in northwestern China to develop an NMR-associated method for...

Solid-State 13C NMR Study of Chiral Twisted Conformation Attributable to Chirality in Smectic Phases of Achiral Banana-Shaped Molecules

Solid-state 13C NMR measurements were made for the B2 and B4 phases of the achiral banana-shaped molecule, P-14-O-PIMB, which exhibits a direct transformation from the B2 phase to the B4 phase. In both phases, an NMR resonance signal assigned to carbonyl carbons of the ester linkages appears as doublet peaks, showing that the two carbonyl carbons are circumstanced in different electronic environments on the NMR time scale. The chemical shifts of the two peaks are 165.6 and 163.9 ppm in the B2 phase, and these values are not changed in the transformation to the low-temperature B4 phase. To explain this distinct splitting of the carbonyl carbon signal, we take three assumptions into account: (1) the molecules are accommodated in the unique phase, but the conformational exchange between two states takes place slowly; (2) the two side wings of each molecule experience fast interconformational jumps, but their “average conformer” is different, thus giving two different peaks in the spectra; and (3) the individual molecule claims the twisted conformation, where the two carbonyl carbons of the ester moieties are twisted away from each other by rotating out of the molecular core plane with different dihedral angles. From the present 13C NMR results, the first and second possibilities are ruled out, and it is concluded that the banana-shaped molecules assume the twisted conformation, which is attributable to the origin of the chirality of the B2 and B4 phases in the achiral banana-shaped molecular system.

Solid-state 13C NMR studies on the molecular motions for n-alkanethiol and α,ω-alkanedithiol crystals

Solid-state 13C NMR measurements have been carried out for the first time for the pure n-alkanethiol ( n-C n H 2 n+1 SH) and α,ω-alkanedithiol (HS–(CH 2) n –SH) crystals to characterize molecular motions in each crystal phase. The comparison of 13C spin-lattice relaxation time ( T 1C) values for n-alkanethiol and α,ω-alkanedithiol crystals determined in this work and those for n-alkane or α,ω-alkanediol crystals reported in previous works reveals that the intermolecular S⋯S interaction between SH groups is stronger than the van der Waals interaction between CH 3 groups but weaker than the hydrogen bonding between OH groups as well as the covalent bonding between CH 2 carbons. For the melt-crystallized and solution-crystallized n-tetracosanethiol ( n-C 24H 49SH) samples, which have the same side chain packing structure, remarkable changes are observed in 13C NMR line widths and T 1C values. These changes seem to reflect the difference in the monoclinic-to-rotator phase transition behavior, in accord with the results obtained by previous DSC and X-ray analyses. It is also found that the 1,20-eicosanedithiol (HS–(CH 2) 20–SH) sample forms polyethylene-like rigid long-chain crystals through the intermolecular S⋯S interaction in contrast to the case of n-alkanes in which each crystalline stem is separated by the CH 3 end groups.

Structural characterization of highly cis-1,4-polybutadiene: A comparing study in swollen and solid state using NMR technique

Commercial highly cis-1,4-polybutadiene was cured out by benzoyl peroxide from 3 to 12 phr in toluene solution. The structural characterization of resulting gel fraction or cured rubber was carried out in both swollen- and solid-state 13C-NMR measurements. The assignment of observed chemical shift proposed by using a shift factor method and empirical calculation using HOSE method.