13C Cross-polarization Magic Angle Spinning Research Articles

Carbon-13 chemical shift tensor measurements for nitrogen-dense compounds.

This paper reports the principal values of the 13 C chemical shift tensors for five nitrogen-dense compounds (i.e., cytosine, uracil, imidazole, guanidine hydrochloride, and aminoguanidine hydrochloride). Although these are all fundamentally important compounds, the majority do not have 13 C chemical shift tensors reported in the literature. The chemical shift tensors are obtained from 1 H→13 C cross-polarization magic-angle spinning (CP/MAS) experiments that were conducted at a high field of 18.8T to suppress the effects of 14 N-13 C residual dipolar coupling. Quantum chemical calculations using density functional theory are used to obtain the 13 C magnetic shielding tensors for these compounds. The best agreement with experiment arises from calculations using the hybrid functional PBE0 or the double-hybrid functional PBE0-DH, along with the triple-zeta basis sets TZ2P or pc-3, respectively, and intermolecular effects modeled using large clusters of molecules with electrostatic embedding through the COSMO approach. These measurements are part of an ongoing effort to expand the catalog of accurate 13 C chemical shift tensor measurements, with the aim of creating a database that may be useful for benchmarking the accuracy of quantum chemical calculations, developing nuclear magnetic resonance (NMR) crystallography protocols, or aiding in applications involving machine learning or data mining. This work was conducted at the National High Magnetic Field Laboratory as part of a 2-week school for introducing undergraduate students to practical laboratory experience that will prepare them for scientific careers or postgraduate studies.

Effects of dual modification by cationization and acetylation on the physicochemical and structural characteristics of glutinous rice starch

In this research, the effects of cationization, acetylation and dual modification by cationization and acetylation on the physicochemical and structural characteristics of glutinous rice starches were investigated. The rapid viscosity analyzer revealed a substantial increased paste viscosity post modification. Particularly, for dually modified starch, the peak viscosity increased from 3071.67 to 4082.00 cP. The freeze-thaw stability substantially enhanced, with both single cationic and dually-modified starches standing out by exhibiting no water syneresis even at 21 freeze-thaw cycles, while native starch exhibited higher syneresis, up to 74.55 %. Both single cationization and cationization-acetylation destroyed the starch granules, characterized by the roughness and cracks. But, for single acetylation, there was no notable changes on granules' morphology. Fourier transform infrared spectroscopy exhibited notable shifts after modification, both acetylation and dual modification, resulting in a new peak at 1728 cm−1. 13C cross-polarization magic angle spinning nuclear magnetic resonance spectra displayed new peaks at 52–55 and 19–22 ppm following cationization and acetylation, respectively. These structural alterations indicate the successful incorporation of functional groups during modification. Overall, this study provides valuable insights for the industrial utilization of these three modified glutinous rice starches.

Reticular Synthesis of Highly Crystalline Three-Dimensional Mesoporous Covalent-Organic Frameworks for Lipase Inclusion.

The synthesis and application of three-dimensional (3D) mesoporous covalent-organic frameworks (COFs) are still to be developed. Herein, two mesoporous 3D COFs with an stp topology were synthesized in a highly crystalline form with aniline as the modulator. The chemical composition of these COFs was confirmed by Fourier transform infrared (FT-IR) and 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopies. These 3D mesoporous COFs were highly crystalline and exhibited permanent porosity and good chemical stability in both aqueous and organic media. The space group and unit cell parameters of COF HFPTP-TAE were verified by powder X-ray diffraction (PXRD), small-angle X-ray scattering, and three-dimensional electron diffraction (3D ED). The appropriate pore size of the COF HFPTP-TAE facilitated the inclusion of enzyme lipase PS with a loading amount of 0.28 g g-1. The lipase⊂HFPTP-TAE (⊂ refers to "include in") composite exhibited high catalytic activity, good thermal stability, and a wide range of solvent tolerance. Specifically, it could catalyze the alcoholysis of aspirin methyl ester (AME) with high catalytic efficiency. Oriented one-dimensional (1D) channel mesopores in HFPTP-TAE accommodated lipase, meanwhile preventing them from aggregation, while windows on the wall of the 1D channel favored molecular diffusion; thus, this COF-enzyme design outperformed its amorphous isomer, two-dimensional (2D) mesoporous COF, 3D mesoporous COF with limited crystallinity, and mesoporous silica as an enzyme host.

NMR spectroscopy-based analysis of gallstones of cancerous and benign gallbladders from different geographical regions of the Indian subcontinent.

Analysis of the chemical composition of gallstones is vital for the etiopathogenesis of gallstone diseases that can ultimately help in the prevention of its formation. In the present study, gallstones from seven different regions of India were analyzed to highlight the major difference in their composition. Also, gallstones of different pathological conditions i.e., benign (chronic cholecystitis, CC) and malignant gallbladder disease (gallbladder cancer GBC) were characterized. The type of polymorphs of cholesterol molecules was also studied to provide insight into the structure of gallstones. 1H solution state NMR spectroscopy 1D experiments were performed on a total of 94 gallstone (GS) samples collected from seven different geographical regions of India. Solid-State NMR spectroscopy 13C cross-polarization magic angle spinning (CPMAS) experiments were done on the 20 CC GS samples and 20 GBC GS samples of two regions. 1H NMR spectra from the solution state NMR of all the stones reveal that cholesterol was a major component of the maximum stones of the north India region while in south Indian regions, GS had very less cholesterol. 13C CPMAS experiments reveal that the quantity of cholesterol was significantly more in the GS of CC in the Lucknow region compared with GBC stones of Lucknow and Chandigarh. Our study also revealed that GS of the Lucknow region of both malignant and benign gallbladder diseases belong to the monohydrate crystalline form of cholesterol while GS of Chandigarh region of both malignant and benign gallbladder diseases exists in both monohydrate crystalline form with the amorphous type and anhydrous form. Gallstones have a complicated and poorly understood etiology. Therefore, it is important to understand the composition of gallstones, which can be found in various forms and clinical conditions. Variations in dietary practices, environmental conditions, and genetic factors may influence and contribute to the formation of GS. Prevention of gallstone formation may help in decreasing the cases of gallbladder cancer.

In Situ Multinuclear Magic-Angle Spinning NMR: Monitoring Crystallization of Molecular Sieve AlPO4-11 in Real Time.

Molecular sieves are crystalline three-dimensional frameworks with well-defined channels and cavities. They have been widely used in industry for many applications such as gas separation/purification, ion exchange, and catalysis. Obviously, understanding the formation mechanisms is fundamentally important. High-resolution solid-state NMR spectroscopy is a powerful method for the study of molecular sieves. However, due to technical challenges, the vast majority of the high-resolution solid-state NMR studies on molecular sieve crystallization are ex situ. In the present work, using a new commercially available NMR rotor that can withhold high pressure and high temperature, we examined the formation of molecular sieve AlPO4-11 under dry gel conversion conditions by in situ multinuclear (1H, 27Al, 31P, and 13C) magic-angle spinning (MAS) solid-state NMR. In situ high-resolution NMR spectra obtained as a function of heating time provide much insights underlying the crystallization mechanism of AlPO4-11. Specifically, in situ 27Al and 31P MAS NMR along with 1H → 31P cross-polarization (CP) MAS NMR were used to monitor the evolution of the local environments of framework Al and P, in situ 1H → 13C CP MAS NMR to follow the behavior of the organic structure directing agent, and in situ 1H MAS NMR to unveil the effect of water content on crystallization kinetics. The in situ MAS NMR results lead to a better understanding of the formation of AlPO4-11.

Design of β-Alanine-Derived Novel C18 Stationary Phase Containing Embedded Urea and Amide Groups for the Separation of Versatile Analytes.

Novel stationary phases have been emerging recently. A β-alanine-derived embedded urea and amide group-containing C18 phase (Sil-Ala-C18) was prepared for the first time. The media were packed into a 150 × 2.1 mm HPLC column, and the newly designed column was evaluated with the Tanaka and Neue test protocols in reversed-phase liquid chromatography (RPLC) separation mode. Moreover, it was characterized by the Tanaka test protocol in hydrophilic interaction chromatography (HILIC) separation mode. The new phase was characterized by elemental analysis, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and solid-state 13C cross-polarization magic angle spinning (CP/MAS) NMR spectroscopy at variable temperatures. The chromatographic evaluation involved very good separation of nonpolar shape-constrained isomers, polar and basic compounds in RPLC, and highly polar compounds in HILIC compared to the commercial reference columns. The Sil-Ala-C18 phase was able to separate the challenging β- and γ-isomers of tocopherol. The phase was also successfully applied for the separation of the isomers of tocopherol (vitamin E) and capsaicinoids from real samples of chili peppers (Capsicum spp.) in RPLC and ascorbic acid (vitamin C) in HILIC.

Potentially Health-Promoting Spaghetti-Type Pastas Based on Doubly Modified Corn Starch: Starch Oxidation via Wet Chemistry Followed by Organocatalytic Butyrylation Using Reactive Extrusion.

Extruded spaghetti-type pasta systems were obtained separately either from native or oxidized starch prepared via wet chemistry with the aim of evaluating the effect of oxidation modification of starch. In addition to this, the butyrylation reaction (butyrate (Bu) esterification-short-chain fatty acid) using native or oxidized starch was analyzed under reactive extrusion (REx) conditions with and without the addition of a green food-grade organocatalyst (l(+)-tartaric acid) with the purpose of developing potentially health-promoting spaghetti-type pasta systems in terms of increasing its resistant starch (RS) values. These would be due to obtaining organocatalytic butyrylated starch or not, or the manufacture of a doubly modified starch (oxidized-butyrylated-starch oxidation followed by organocatalytic butyrylation) or not. To this end, six pasta systems were developed and characterized by solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR) spectroscopy, degree of substitution (DS), attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), pancreatic digestion, free Bu content analysis and in vitro starch digestibility. The results obtained here suggest that starch oxidation hydrolytically degrades starch chains, making them more susceptible to enzymatic degradation by α-amylase. However, the oxidized starch-based pasta systems, once esterified by Bu mainly on the amylose molecules (doubly modified pasta systems) increased their RS values, and this was more pronounced with the addition of the organocatalyst (maximum RS value = ~8%). Interestingly, despite the checked chemical changes that took place on the molecular structure of starch upon butyrylation or oxidation reactions in corn starch-based spaghetti-type pasta systems, and their incidence on starch digestibility, the orthorhombic crystalline structure (A-type starch) of starch remained unchanged.

Synthesis, characterization, and application of starch-based adhesives modified with itaconic acid and N-hydroxyethyl acrylamide

A renewable, biodegradable, formaldehyde-free starch-based adhesive was prepared by grafting itaconic acid (IA) and N-hydroxyethyl acrylamide (HEAA) onto corn starch. The adhesive exhibits excellent performance for particleboard and low viscosity (251 mPas, 62 s measured by flow cup viscometer) using 8% addition of IA (w/w, dry starch basis), and 10% addition of HEAA (w/w, dry starch basis). The thickness swelling of the particleboard was decreased to 10%. When unmodified starch-based adhesive was used, the particleboard soaked in water disintegrated completely. The data obtained from the Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), confocal Raman microscopy (CRM), and 13C cross-polarization magic-angle spinning (CPMAS) showed that IA wrapped and covered the surface of starch granules. HEAA is unevenly distributed on the surface of starch as a cross-linked backbone. After the hot-pressing process, IA and HEAA are self-cross-linked and inter-cross-linked, respectively, to form a complex network structure, which can inhibit the disintegration caused by excessive expansion during the soaking process of the board, thus improving the water resistance of the starch adhesive.

Studies of Organic Matter in Composting, Vermicomposting, and Anaerobic Digestion by 13C Solid-State NMR Spectroscopy

Composting, vermicomposting, and anaerobic digestion are three commonly applied processes for the transformation of organic waste into valuable products for soil amendment. The application of compost, vermicompost, and digestate to soil requires specific properties, such as maturity and stability, strongly related to the composition of organic matter. 13C solid-state Nuclear Magnetic Resonance (SSNMR) has often been applied to follow the transformation of organic matter during waste treatment processes, as well as to assess the quality of the produced amendments and the effectiveness of the treatments. Thanks to the possibility of associating the 13C chemical shift to different functional groups of biomacromolecules present in the waste feedstocks and in the final products, thorough characterizations of organic matter have been performed exploiting 13C cross-polarization magic angle spinning experiments, and semiquantitative descriptions of the evolution of the different groups during composting, vermicomposting and anaerobic digestion have been reported. Here, these studies are reviewed with the aim of highlighting the potential of the application of 13C SSNMR to these complex materials, as well as the critical issues and perspectives.

Zwitterionic or Not? Fast and Reliable Structure Determination by Combining Crystal Structure Prediction and Solid-State NMR.

When it comes to crystal structure determination, computational approaches such as Crystal Structure Prediction (CSP) have gained more and more attention since they offer some insight on how atoms and molecules are packed in the solid state, starting from only very basic information without diffraction data. Furthermore, it is well known that the coupling of CSP with solid-state NMR (SSNMR) greatly enhances the performance and the accuracy of the predictive method, leading to the so-called CSP-NMR crystallography (CSP-NMRX). In this paper, we present the successful application of CSP-NMRX to determine the crystal structure of three structural isomers of pyridine dicarboxylic acid, namely quinolinic, dipicolinic and dinicotinic acids, which can be in a zwitterionic form, or not, in the solid state. In a first step, mono- and bidimensional SSNMR spectra, i.e., 1H Magic-Angle Spinning (MAS), 13C and 15N Cross Polarisation Magic-Angle Spinning (CPMAS), 1H Double Quantum (DQ) MAS, 1H-13C HETeronuclear CORrelation (HETCOR), were used to determine the correct molecular structure (i.e., zwitterionic or not) and the local molecular arrangement; at the end, the RMSEs between experimental and computed 1H and 13C chemical shifts allowed the selection of the correct predicted structure for each system. Interestingly, while quinolinic and dipicolinic acids are zwitterionic and non-zwitterionic, respectively, in the solid state, dinicotinic acid exhibits in its crystal structure a "zwitterionic-non-zwitterionic continuum state" in which the proton is shared between the carboxylic moiety and the pyridinic nitrogen. Very refined SSNMR experiments were carried out, i.e., 14N-1H Phase-Modulated (PM) pulse and Rotational-Echo Saturation-Pulse Double-Resonance (RESPDOR), to provide an accurate N-H distance value confirming the hybrid nature of the molecule. The CSP-NMRX method showed a remarkable match between the selected structures and the experimental ones. The correct molecular input provided by SSNMR reduced the number of CSP calculations to be performed, leading to different predicted structures, while RMSEs provided an independent parameter with respect to the computed energy for the selection of the best candidate.

Evolution of the Cellulose Microfibril through Gamma-Valerolactone-Assisted Co-Solvent and Enzymatic Hydrolysis

Biomass recalcitrance during deconstruction remains a key bottleneck to affordable biomass processing technologies. A clear connection between the cell wall structure and biomass deconstruction is necessary to understand how lignocellulosic material is broken down to valuable monomeric components. Here, we monitor changes in the cellulose microfibril domains of poplar, sorghum, and switchgrass throughout gamma-valerolactone (GVL)–water co-solvent pretreatment and enzymatic hydrolysis using solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C-NMR) and wide-angle X-ray scattering (WAXS). Spectral fitting of NMR peaks corresponding to different cellulose microenvironments at the C4 carbon center suggests that a mildly acidic GVL–water co-solvent pretreatment of poplar leads to nearly full removal of xylan–cellulose linkages, which primes the cellulose for enzymatic attack. The spectral fitting also suggests that the pretreatment causes significant depletion of the inaccessible fibril surface domains with an increase in more thermally stable crystalline resonances (Iβ). WAXS confirmed a decrease in the lattice spacing between (200) crystalline planes with increasing co-solvent pretreatment severity. These results are interpreted as an opening of bound microfibril surfaces previously inaccessible to the co-solvent system, which leaves behind a more thermally stable, crystalline domain that is potentially prone to relaxation and recrystallization. Full conversion of residual GVL-pretreated biomass was achieved after the GVL co-solvent pretreatment at 140 °C using a commercial enzyme cocktail, CTec2, which contains different cellulases and other enzymes. Spectral fitting of enzymatically hydrolyzed samples by a single engineered cellulase, CelR, suggests that the residual cellulose recalcitrance is mainly due to the inability of CelR to digest the Iβ crystalline domain present in pretreated samples. This work helps to provide new information regarding the structure of the cell wall and recalcitrance throughout GVL–water mild acidolysis and CelR enzymatic biomass deconstruction by tracking the evolution of structural domains within the cellulose microfibril. This work further directs recommendations for improving the conversion and sugar yields in future studies. Our findings inform inquiry into larger questions of cellulose recalcitrance through GVL pretreatment and CelR enzymatic hydrolysis and give insight into subsequent required steps for full cellulose conversion with attention to the most recalcitrant cellulose structures.

Dynamic nuclear polarization – nuclear magnetic resonance for analyzing surface functional groups on carbonaceous materials

Dynamic nuclear polarizing (DNP) technique in nuclear magnetic resonance (NMR) is a powerful tool for a microanalysis. Nevertheless, it has not been applied to analyses of carbon materials such as graphene oxide (GO) and amorphous carbon effectively because of the electroconductivity and microwave absorption of the carbon, which attenuate the enhancement effect of DNP. For this study, we applied DNP-NMR to analyses of surface functional groups on GO and sucrose-derived carbon to evaluate the method. The 1H–13C cross-polarization magic-angle spinning (CP/MAS) DNP-NMR of a GO sample with AMUPol (polarizing agent) showed 2.2-times-enhanced peaks of 13C in epoxide, bonding to hydroxyl group, and in the graphene plane. Signal enhancement was raised by AMUPol radicals neighboring the surface functional groups and the graphene planes on GO particles, although attenuation by temperature rise must be considered. Furthermore, additional new peaks assigned to CH3 group on the GO particle surface were highly enhanced and were observed clearly only by the accumulations of 64 scans. For sucrose-derived carbon, DNP-NMR clearly revealed the –OH group on the carbon surface or carbon edge by heat treatment, which was not possible using conventional CP/MAS experiments. Cross Effect was found to be dominant in signal enhancements of the functional groups on GO and sucrose-derived carbon samples, except for the CH3 groups on GO. The CH3 enhancement is ascribed mainly to the Overhauser effect or solid effect.

Identifying the Point of Attachment in the Hypercrosslinking of Benzene for the Synthesis of a Nanoporous Polymer as a Superior Adsorbent for High-Pressure CO2 Capture Application

The point of attachment in the hypercrosslinking of benzene using formaldehyde dimethyl acetal as the crosslinker, anhydrous ferric chloride as the catalyst, and 1,2 dichloroethane as the solvent for the synthesis of poly-benz is reported. A fast microwave-assisted synthesis, within a reaction time of 60 min, resulted in the formation of nanoporous poly-benz having a specific surface area of 1168 m2 g–1. A thorough analysis of poly-benz using 13C cross-polarization magic angle spinning nuclear magnetic resonance and X-ray photoelectron spectra has revealed the hypercrosslinking at the meta position of the benzene ring. The synthesized poly-benz further shows a high CO2 capture capacity of 65.3 wt % at 298 K and 30 bar. Various adsorption isotherm models have been fitted at different temperatures up to 30 bar to represent the equilibrium CO2 adsorption data.

Influence of Air Humidity Level on the Structure and Mechanical Properties of Thermoplastic Starch-Montmorillonite Nanocomposite during Storage.

Thermoplastic starch (TPS) consisting of corn starch and glycerol as a plasticizer, and TPS-montmorillonite (MMT) nanocomposite were stored at room temperature in the air with relative humidities (RH) of 11, 55 and 85% for seven weeks. Mechanical testing and dynamic mechanical thermal analysis (DMTA) were performed to detect changes in their mechanical properties. Solid-state NMR spectroscopy monitoring the changes in molecular mobility in the samples provided an insight into relations between mechanical properties and local structure. The results of mechanical testing indicated that the addition of MMT results in the increase in the tensile strength and Young's modulus while elongation at break decreased, indicating the reinforcing effect of MMT. DMTA experiments revealed a decrease in glass transition temperature of starch-rich phase below room temperature for samples stored at higher RH (55 and 85%). This indicates that absorbed water molecules had additional plasticizing effect on starch resulting in higher mobility of starch chain segments. Recrystallization in these samples was deduced from the shape of cross-polarization magic-angle spinning 13C NMR spectra. The shape of broad-line 1H NMR spectra reflected changes in molecular mobility in the studied samples during seven weeks of storage and revealed that a high amount of water molecules impacts the starch intermolecular hydrogen bond density.

Circular adsorptive utilization of benzalkonium chloride via construction of ionic microenvironment in dopamine quinone-functionalized acrylic fiber surface

A novel dopamine quinone-functionalized acrylic fiber (PANdpqF) was successfully synthesized, which adsorbed the disinfectant dodecyl dimethyl benzyl ammonium chloride (DDBAC) to in-situ construct a highly efficient catalyst (DDBAC@PANdpqF) for the cyclization of CO2 with epoxide. The successful preparation of PANdpqF was proved by 13C Cross Polarization-Magic Angle Spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, Fourier transform infrared, and scanning electron microscopy. High adsorption capacity of DDBAC on PANdpqF has been demonstrated by ultraviolet analysis, and the theoretical maximum adsorption capacity was calculated as 666.67 mg/g. Based on comprehensive analysis, the corresponding adsorption mechanism is proposed in which chloride ion of DDBAC is added to o-quinone moiety through Michael addition, followed by the formation of phenoxy and quaternary ammonium ion pair. DDBAC@PANdpqF was well applicable to catalyze the cyclization of CO2, and the yield could reach 93.7% even with a low catalyst loading. The possible cooperatively catalytic mechanism was proposed correspondingly, in which phenolic hydroxyl helps to activate CO2 and epoxide, phenoxy anion attacks CO2 as a nucleophile, and quaternary ammonium cation stabilizes the anionic intermediates. Overall, the functionalized acrylic fiber adsorbed environmentally harmful disinfectant DDBAC to furnish a highly active catalyst for the transformation of greenhouse gas CO2 into useful carbonates, which provides a new method for advanced environmental pollution control.

The Photodegradation of Lignin Methoxyl C Promotes Fungal Decomposition of Lignin Aromatic C Measured with 13C-CPMAS NMR.

Solar radiation has been regarded as a driver of litter decomposition in arid and semiarid ecosystems. Photodegradation of litter organic carbon (C) depends on chemical composition and water availability. However, the chemical changes in organic C that respond to solar radiation interacting with water pulses remain unknown. To explain changes in the chemical components of litter organic C exposed to UV-B, UV-A, and photosynthetically active radiation (PAR) mediated by water pulses, we measured the chemistry of marcescent Lindera glauca leaf litter by solid-state 13C cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) over 494 days of litter decomposition with a microcosm experiment. Abiotic and biotic factors regulated litter decomposition via three pathways: first, photochemical mineralization of lignin methoxyl C rather than aromatic C exposed to UV radiation; second, the biological oxidation and leaching of cellulose O-alkyl C exposed to PAR and UV radiation interacts with water pulses; and third, the photopriming effect of UV radiation on lignin aromatic C rather than cellulose O-alkyl C under the interaction between radiation and water pulses. The robust decomposition index that explained the changes in the mass loss was the ratio of aromatic C to O-alkyl C (AR/OA) under radiation, but the ratio of hydrophobic to hydrophilic C (hydrophobicity), the carbohydrate C to methoxyl C ratio (CC/MC), and the alkyl C to O-alkyl C ratio (A/OA) under radiation were mediated by water pulses. Moreover, the photopriming effect and water availability promoted the potential activities of peroxidase and phenol oxidase associated with lignin degradation secreted by fungi. Our results suggest that direct photodegradation of lignin methoxyl C increases microbial accessibility to lignin aromatic C. Photo-oxidized compounds might be an additional C pool to regulate the stability of the soil C pool derived from plant litter by degrading lignin methoxyl and aromatic C.

Organic amendments and gypsum reduce dispersion and increase aggregation of two sodic Vertisols

Sodic soils are widespread in semi-arid and arid regions of the world, with agricultural production on these soils constrained due to structural instability resulting from high concentration of exchangeable sodium (Na). The structural instability results in clay dispersion, reduced infiltration, crust formation and poor seed germination. One way to decrease undesirable effects of Na on soil structure is to apply gypsum (G) and organic amendments. We evaluated the effect of G and four organic amendments [polyacrylamide (PAM), feedlot manure (FLM), chicken manure (CM), and lucerne pellets (LP)] on two sodic soils. These amendments differed in their chemical nature as assessed by 13C cross-polarisation magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy after amended soils were incubated for 60 d at field water capacity. Gypsum reduced dispersion but had no effect on macroaggregates or aggregate mean weight diameter (MWD). Using principal component analysis, we found that aryl C and O-aryl C functional groups were positively correlated with microaggregates and the silt + clay fraction, and O-alkyl C and di-O alkyl C were positively correlated with soil dispersion after 1 d of soil incubation. The CM reduced dispersion more than FLM, LP, or PAM, although LP increased the proportion of large macroaggregates and MWD. We also found that large macroaggregates and MWD were positively correlated with microbial respiration and dissolved organic carbon. Except for the G + LP amendment, G had no synergistic effect with other organic amendments on macroaggregates and MWD of the two sodic soils. This study demonstrates that the functional groups of organic amendments and microbial activity play important roles in aggregation and dispersion of sodic soils. This study also demonstrates that a combination of gypsum and organic amendments will be a better option to ameliorate sodic soils by decreasing dispersion and increasing aggregate formation.

Controlling the Nucleation Process to Prepare a Family of Crystalline Tribenzimidazole-Based Covalent Organic Frameworks

Covalent organic frameworks (COFs) are at the forefront of porous material research due to their crystallinity and topological diversity. However, most COFs are connected by reversible chemical bonds, which limit their applications under harsh conditions. Herein, we develop a novel synthetic method to lock the imine bond using amino groups via a precursor-involved cascade reaction. We experimentally demonstrated that the nucleation process of COFs can be controlled by precursor hydrolysis. A family of crystalline two-dimensional tribenzimidazole-based COFs (2D BI-COFs) was prepared by the condensation of o-phenylenediamine derivative and aryl aldehydes. Their structures were confirmed by powder X-ray diffraction, Fourier-transform infrared spectroscopy, and solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP/MAS NMR) spectroscopy. They showed high surface areas, good CO2 uptake capacities, excellent CO2/N2 selectivities, and high chemical stabilities. Of these materials, BI-COF-1 was an efficient photocatalyst for the visible-light-driven photocatalytic oxidation of sulfides, which displayed high conversion (∼100%) and excellent selectivity (>90%). We believe that our study can provide new insights into the synthesis of 2D chemical-stable COFs.

A method to quantify composition, purity, and cross-link density of the active polyamide layer in reverse osmosis composite membranes using 13C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy

A method for harvesting and purifying the thin polyamide (PA) active layer from thin-film composite (TFC) reverse osmosis (RO) membranes was developed, enabling quantitative nuclear magnetic resonance (NMR) measurements of the composition and cross-linking in the PA layer that can be directly related to membrane performance. Using our chemical separation process, we report on four trimesoyl chloride (TMC)/isophthaloyl chloride (IPC)/ m -phenylene diamine (MPD)-based TFC membranes in which the cross-link density was intentionally reduced by replacing trifunctional cross-linking TMC monomers with their linear IPC difunctional analog. While the NMR results show a two-fold decrease in cross-linking that causes a 30% increase in salt passage, the addition of the difunctional analog leads to increased polar amine groups that reduce water permeance due to tighter binding of water in the PA membrane. Our results demonstrate that 13 C cross polarization magic angle spinning (CPMAS) is a powerful method for quantitatively monitoring the purity, cross-linking, and chemical composition in PA membranes and will be an essential tool in ascertaining atomistic models of PA structure. • A method for purifying the polyamide layer from TFC RO membranes was developed. • 13 C CPMAS quantifies composition and crosslinking in harvested polyamide TFC RO films. • Crosslinking is controlled by IPC/TMC ratio. • With a two-fold decrease in crosslinking, a 30% increase in salt passage. • With a two-fold increase of amine content, a 30% decrease in water permeance.

Assessment of halogen-bond induced cocrystallization of 1,3,5-trihalo-2,4,6-trifluorobenzenes with 2,3,5,6-Tetramethylpyrazine

Cocrystallization of each of 1,3,5-trichloro-2,4,6-trifluorobenzene, 1,3,5-tribromo-2,4,6-trifluorobenzene, and 1,3,5-triiodo-2,4,6-trifluorobenzene with 2,3,5,6-tetramethylpyrazine via selected mechanochemical and solution methods is assessed. In lieu of single crystals of suitable quality for structure determination via single-crystal X-ray diffraction, powder X-ray diffraction and 13C cross-polarization magic-angle spinning solid-state NMR spectroscopy are used to qualitatively assess halogen-bond induced cocrystal formation. The results suggest a rich polymorphic landscape worthy of further study.