Solid-state Cross-polarization Magic Angle Spinning Research Articles

Direct oxidation of alcohols to carboxylic acids using simple and economical Pd@Glu-HTC catalyst: Practical and scalable approach towards biomass based value added chemicals

Sustainable catalytic transformation of bio-based alcohols to high value-added fine chemicals is an important topic of research. This work described preparation of simple and economical Pd@Glu-HTC catalyst from biomass derived low cost d-glucose. Hydrothermal carbonization of glucose was carried out in first step to synthesize Glu-HTC support in a simpler, greener, economical and efficient manner followed by incorporation of palladium metal on surface of the catalyst in second step. The catalyst was characterized using techniques such as Fourier Transform Infrared Spectroscopy (FT-IR), Solid-state Cross-Polarization Magic Angle Spinning Carbon-13 (13C CPMAS), Energy-dispersive X-ray spectroscopy (EDAX), Powder X-ray diffraction (P-XRD), X-ray photoelectron spectroscopy (XPS), Thermogravimetric/Differential Thermal Analyzer (TG-DTA), Field emission scanning electron microscopy (FE-SEM) and High-resolution transmission electron microscopy (HR-TEM). The catalyst was evaluated for direct oxidation of alcohols to yield carboxylic acids and exhibited very good catalytic activity for wider substrate scope. Oxidation of alcohols was carried out using milder base, molecular oxygen and water as a solvent to achieve 92–99 % excellent yields. The practical utility of current strategy was also studied for gram scale synthesis of bio-based value added industrially important chemicals such as furoic acid (flavouring agent and preservative in industry), 2, 5-furan-dicarboxylic acid (monomer to 100 % fossil-free, recyclable polymer polyethylene furanoate (PEF), tetrahydro-2-furoic acid (production of many drugs) and vanillin (important product of flavor and fragrance industry). Pd@Glu-HTC catalyst was found to be reusable for four recycles and the catalytic performance was retained without any loss in its activity after four cycles.

Solid-State NMR Characterization of Mefloquine Resinate Complexes Designed for Taste-Masking Pediatric Formulations.

Mefloquine (MQ) is an antimalarial medication prescribed to treat or malaria prevention.. When taken by children, vomiting usually occurs, and new doses of medication frequently need to be taken. So, developing pediatric medicines using taste-masked antimalarial drug complexes is mandatory for the success of mefloquine administration. The hypothesis that binding mefloquine to an ion-exchange resin (R) could circumvent the drug's bitter taste problem was proposed, and solid-state 13C cross-polarization magic angle spinning (CPMAS) NMR was able to follow MQ-R mixtures through chemical shift and relaxation measurements. The nature of MQ-R complex formation could then be determined. Impedimetric electronic tongue equipment also verified the resinate taste-masking efficiency in vitro. Variations in chemical shifts and structure dynamics measured by proton relaxation properties (e.g., T1ρH) were used as probes to follow the extension of mixing and specific interactions that would be present in MQ-R. A significant decrease in T1ρH values was observed for MQ carbons in MQ-R complexes, compared to the ones in MQ (from 100-200 ms in MQ to 20-50 ms in an MQ-R complex). The results evidenced that the cationic resin interacts strongly with mefloquine molecules in the formulation of a 1:1 ratio complex. Thus, 13C CPMAS NMR allowed the confirmation of the presence of a binding between mefloquine and polacrilin in the MQ-R formulation studied.

A new route of production of the meso-porous chitosan with well-organized honeycomb surface microstructure from shrimp waste without destroying the original structure of native shells: Extraction, modification and characterization study

The highly active bio-polysaccharide based compound namely chitin and chitosan have been extracted from shrimp shell which usually expelled out extensively from food processing industries and considered as waste materials. However, by conducting demineralization, de-proteinization and deacetylation on it which could be a new route of production of valuable meso-porous chitosan that possesses a noteworthy well-organized honeycomb like surface microstructure which undoubtedly capable to form sustainable bio-composites. Whereas the honeycomb like microstructures showed a well-defined pore canals (Pc) and pore canal tubes (Pct) onto their surface. The samples were characterized via ATR-FTIR spectroscopy, High resolution SEM, AFM, EDX, XRD and 13C solid-state Cross-Polarization Magic Angle Spinning (CPMAS) NMR. The molecular weight(M‾v) of isolated chitin and chitosan were determined by viscosity and the values were 1.06 × 106(DPv = 5228), 1.8 × 104(DPv = 116) respectively besides degree of deacetylation (DDA) were measured by ATR-FTIR spectroscopy, CPMAS NMR, pH-metric titration and the values were 24&21 for chitin and 84&82 for chitosan. The results suggest that the shrimp shell waste is an attractive source of well-organized honeycomb like meso-porous chitin and chitosan with regular surface microstructures which might have a significant/potential application into the sustainable bio-composite formulation due to various industrial and biomedical sector indeed.

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.

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.

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.

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.

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.

Trash into treasure: Converting waste polyester into C3N4-based intramolecular donor-acceptor conjugated copolymer for efficient visible-light photocatalysis

Carbon nitride (C3N4) is regarded as one of the most prospective photocatalysts for environmental remediation. The design of intramolecular donor-acceptor (D-A) conjugated structure has aroused particular interest for improving visible-light photocatalytic activity of C3N4, but remains a huge challenge. Herein, a novel C3N4-based D-A conjugated copolymer is synthesized by incorporating aromatic ring into the C3N4 skeleton by copolymerization of melamine with terephthalic acid from the in-situ controlled degradation of recycled poly(ethylene terephthalate) catalyzed by ZnO at 360 °C. The results of X-ray diffraction, solid-state 13C cross-polarization magic-angle spinning nuclear magnetic resonance, thermodynamics analysis, and X-ray photoelectron spectroscopy confirm the structure of C3N4-based D-A conjugated system, consisting of terminal amino group of the tri-s-triazine unit as electron-donating group and aromatic ring as acceptor. Notably, the C3N4-based D-A conjugated copolymer displays shorter lifetime of light-induced charge carriers, lower photoluminescence emission, and larger photocurrent response than pristine C3N4, certifying that the D-A conjugated system significantly promotes the separation efficiency of light-induced charge carriers. As such, the C3N4-based D-A conjugated copolymer displays high performance in the photocatalytic degradation of Amido black 10B upon visible light illumination, of which the kinetic constant is 101 times that of unmodified C3N4. Lastly, reactive oxygen species including ·OH, ·O2- and 1O2 are proved to be the main active sites. This work not only offers new insights into the synthesis of efficient C3N4-based D-A conjugated copolymers, but also will inspire new paradigms toward sustainable transformation of waste plastics into value-added products for environmental remediation.

Phenoloxidase activity and organic carbon dynamics in historic Anthrosols in Scotland, UK.

Phenolic compounds are chemical precursor building blocks of soil organic matter. Their occurrence can be inhibitory to certain enzymes present in soil, thereby influencing the rate of decomposition of soil organic matter. Microbe-derived phenoloxidases (laccases) are extracellular enzymes capable of degrading recalcitrant polyphenolic compounds. In this study, our aim was to investigate the relationships between phenoloxidase enzyme activity, organic carbon content and microbial abundance in the context of long-term anthropogenically amended soils. To achieve this, we used a series of complementary biochemical analytical methods including gas chromatography, enzyme assays and solid-state Carbon-13 Cross Polarisation Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy (13C CPMAS NMR). Using several anthrosols found in St Andrews (Scotland, UK) that had been subjected to intense anthropogenic modification since the medieval period (11th century AD) to present-day, we were able to scope the impact of past waste disposal on soils. The long-term anthropogenic impact led to organic matter-rich soils. Overall, phenoloxidase activity increased by up to 2-fold with soil depth (up to 100 cm) and was inversely correlated with microbial biomass. Solid-state 13C NMR characterisation of carbon species revealed that the observed decline in soil organic matter with depth corresponded to decreases in the labile organic carbon fractions as evidenced by changes in the O/N-alkyl C region of the spectra. The increase in phenoloxidase activity with depth would appear to be a compensatory mechanism for the reduced quantities of organic carbon and lower overall nutrient environment in subsoils. By enzymatically targeting phenolic compounds, microbes can better utilise recalcitrant carbon when other labile soil carbon sources become limited, thereby maintaining metabolic processes.

Dinuclear Copper Complex Immobilized on a Janus-Type Material as an Interfacial Heterogeneous Catalyst for Green Synthesis.

We herein describe a rational design of a heterogeneous catalyst composed of a dinuclear cuprate anion being immobilized electrostatically on one surface of Janus-type nanosheets while the other surface is decorated with highly hydrophobic octyl groups. The catalyst was found to be well dispersible in the organic phase of a biphasic aqueous/organic mixture. It was characterized by means of elemental analysis, atomic absorption spectroscopy, mass spectrometry, N2 absorption-desorption analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and solid-state 13C and 29Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy. The Janus nature of the catalyst was investigated by employing a selective surface labeling method and by means of SEM. The catalyst shows higher activity compared to a non-Janus analogue in a biphasic synthesis. It was successfully used for the azide-alkyne cycloaddition and the Chan-Lam C-N coupling reaction. In addition, new and simple ways have been established for the production of a coumarin-triazole derivative and for the synthesis of the biologically active compound Monastrol via a solvent-free Biginelli reaction. The role of the dinuclear copper centers is discussed mechanistically.

An additive-free silicon anode in nanotube morphology as a model lithium ion battery material

Ordered arrays of parallel, cylindrical silicon nanotubes are obtained by aluminothermic reduction of SiO2 nanotubes generated by atomic layer deposition (ALD) on nanoporous aluminum oxide templates. The reduction to amorphous Si (a-Si) is characterized by a combination of X-ray diffraction (XRD), solid-state cross-polarization magic-angle spinning nuclear magnetic resonance (29Si CP-MAS NMR), ultraviolet-visible spectroscopy, attenuated total reflectance infrared spectroscopy (ATR-IR), and X-ray photoelectron spectroscopy (XPS). These a-Si nanotube arrays are electrochemically active in a lithium-ion battery environment when prepared on Cu current collectors without any additives. The absence of the traditional additive carbon black, which is an electrochemically inert conductor, increases the proportion of capacity associated with faradaic reactions (Li incorporation) with respect to the capacitive component. Electrochemical impedance spectroscopy (EIS) and charge-discharge tests demonstrate that the nanotube morphology yields an improved tolerance to fast cycling.

Decomposition of woody debris in Mediterranean ecosystems: the role of wood chemical and anatomical traits

Data about woody debris (WD) decomposition are very scarce for the Mediterranean basin. The specific aim of this work is to explore the relationships between WD traits with the decay rate. We carried out a three-year litterbag decomposition experiment using ten WD types incubated in two plant communities (i.e. shrubland and woodland) and in laboratory conditions. WD was characterized for 31 chemical and anatomical traits, including macro- and micronutrients, lignin, and cellulose as well as organic chemistry by Solid-state Cross-Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (13C CPMAS NMR) and Fourier transform infrared spectroscopy/ Attenuated Total Reflection (FT-IR/ATR spectroscopy). WD decay rate was negatively associated with di-O-alkyl, lignin/N and C/N ratios, but positively with N concentration. Less consistent but positive correlations were recored for K, Mn, and Na concentration. The alkyl C and carboxylic C regions, associated with aliphatic and amide compounds, was positively correlated with WD decomposition. Conversely, di-O-alkyl C and O-alkyl C fractions, largely associated with cellulose and hemicellulose, were negatively correlated with WD decay rate. Finally, the positive correlation between Na concentration and WD mass loss in field conditions suggest a role of this neglected micronutrient for wood decomposition. WD specific density and anatomical features, have a minor capability to explain decomposition rate. Our findings demonstrate a major role of WD chemical traits in explaining the variability of decomposition in Mediterranean ecosystems.

13C CP/MAS NMR Can Discriminate Genetic Backgrounds of Rice Starch

Solid-state cross-polarization magic-angle spinning carbon-13 nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy is used to analyze starch derived from plants including wheat, maize, and potato, but few reports have described its application to rice starch. Here, we combined 13C CP/MAS NMR with deconvolution and subtraction methods to analyze rice lines including mutants that are deficient in at least one enzyme involved in amylose and/or amylopectin biosynthesis. We found that differences in the content of ordered structures between rice lines could be evaluated using C1 signal deconvolution and subtraction. The content of the V-type ordered structure increased with increasing amylose content. Furthermore, starch derived from a starch synthase (SS) IIIa/starch branching enzyme (BE) IIb-deficient mutant formed B- and V-type ordered structures and significantly more nonordered structures than the other rice lines. These data indicate that 13C CP/MAS NMR analysis is useful for discriminating the genetic backgrounds of starch derived from different rice cultivars.

Physical aspects of the biopolymer matrix in wheat bran and its dissected layers

The objectives of this work were to 1) determine the physical structure of untreated wheat bran and the differences in physical structure between its dissected layers; 2) evaluate how bran hydration affected bran crystallinity and polymer order; and 3) determine how enzymatic treatment of wheat bran affected its physical structure. For the first time, X-ray diffraction (XRD), small angle X-ray scattering (SAXS), solid-state 13C cross-polarization magic-angle spinning nuclear magnetic resonance (13C CP/MAS NMR), and polarized light microscopy with a waveplate were used to study the physical structure of wheat bran and its dissected layers. The XRD and solid-state 13C CP/MAS NMR both confirmed the presence of crystalline cellulose in untreated bran, enzymatically treated bran, and dissected bran layers. The outer pericarp had the highest crystallinity of the dissected bran layers and showed negative birefringence. The aleurone layer was low in cellulose content and completely amorphous, yet the cell walls in the aleurone layer showed strong positive birefringence. The treatment of destarched and deproteinated bran with the Updegraff reagent removed amorphous material, leaving its crystalline cellulose structure intact. Hydration of the outer pericarp increased its crystallinity index and CP/MAS NMR resonance intensity, which indicated a possible increase in polymer order. The SAXS also confirmed that cell wall polymers, possibly aggregated cellulose microfibrils, increased in order as a result of hydration.

Structure of a Luminescent MOF-2 Derivative with a Core of Zn(II)-Terephthalate-Isoquinoline and Its Application in Sensing of Xylenes

A new blue photoluminescent 2D metal–organic framework, 1, with formula {[Zn2(μ2-BDC)2(iQ)2]}∞ has been synthesized in a high yield under solvothermal conditions by reacting Zn(II) ions with 1,4-benzenedicarboxylic acid (H2BDC) and isoquinoline (iQ) in DMF. Compound 1 was thoroughly characterized by single-crystal X-ray diffraction, solid-state cross-polarization magic-angle spinning 13C NMR, X-ray powder diffraction, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and thermoanalysis. The crystal structure of 1 showed interpenetrated 2D frameworks consisting of dinuclear paddle-wheel cores Zn2; moreover, this material possessed thermostability up to 310 °C. The CPMAS 13C-NMR spectrum of 1 is consistent with the symmetry of the crystal structure. Luminescence studies showed that 1 strongly enhances its fluorescence emission in the presence of xylene isomers with a pronounced selectivity to p-xylene.

Dynamic Covalent Synthesis of Crystalline Porous Graphitic Frameworks

Summary Porous graphitic framework (PGF) is a two-dimensional (2D) material that has emerging energy applications. An archetype contains stacked 2D layers, the structure of which features a fully annulated aromatic skeleton with embedded heteroatoms and periodic pores. Due to the lack of a rational approach in establishing in-plane order under mild synthetic conditions, the structural integrity of PGF has remained elusive and ultimately limited its material performance. Here, we report the discovery of the unusual dynamic character of the C=N bonds in the aromatic pyrazine ring system under basic aqueous conditions, which enables the successful synthesis of a crystalline porous nitrogenous graphitic framework with remarkable in-plane order, as evidenced by powder X-ray diffraction studies and direct visualization using high-resolution transmission electron microscopy. The crystalline framework displays superior performance as a cathode material for lithium-ion batteries, outperforming the amorphous counterparts in terms of capacity and cycle stability.

Molecular characterization of particulate organic matter in full scale anaerobic digesters: An NMR spectroscopy study

This study assesses the molecular characteristics of particulate organic matter (POM) in agricultural and food waste digesters and elucidates the molecular properties of the recalcitrant POM fraction, which remains in the digestate after AD process. Molecular properties of POM in influent (substrate) and effluent (digestate) of seven full-scale AD plants (three agricultural waste and four food waste digesters) were characterized and compared using solid-state 13C cross-polarization magic angle spinning (CP-MAS) and solution-state 1H,13C heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectroscopy. Comparison of the POM structural compositions of substrate and digestate from each AD plant revealed an enrichment of protein structures relative to the carbohydrates in most cases, implying a preferential degradation of the carbohydrates over proteins and/or increase of microbial biomass upon AD of agricultural and food wastes. Distinctive molecular structures of labile and recalcitrant fractions of POM, subjected to AD, were identified by comparing the NMR spectra of all substrate and digestate POM. Accordingly, the labile POM fraction in food and agricultural solid wastes is characterized by structural entities of lipids and starch-like carbohydrates, whereas recalcitrant POM structures resemble alkyl and aromatic subunits of amino acids, lignin, and polysaccharides with β-glycosidic linkages. This information serves as a basis to further explore optimization approaches for improving AD of the underutilized POM and the fate of organic matter in digestate-amended arable lands.

Porous Crystalline Olefin-Linked Covalent Organic Frameworks.

The first unsubstituted olefin-linked covalent organic framework, termed COF-701, was made by linking 2,4,6-trimethyl-1,3,5-triazine (TMT) and 4,4'-biphenyldicarbaldehyde (BPDA) through Aldol condensation. Formation of the unsubstituted olefin (-CH═CH-) linkage upon reticulation is confirmed by Fourier transform infrared (FT-IR) spectroscopy and solid-state 13C cross-polarization magic angle spinning (CP-MAS) NMR spectroscopy of the framework and of its 13C-isotope-labeled analogue. COF-701 is found to be porous (1715 m2 g-1) and to retain its composition and crystallinity under both strongly acidic and basic conditions. The high chemical robustness is attributed to the unsubstituted olefin linkages. Immobilization of the strong Lewis acid BF3·OEt2 in the pores of the structure yields BF3⊂COF-701. In the material, the catalytic activity of the guest is retained, as evidenced in a benchmark Diels-Alder reaction.