13C Cross-polarization Magic Angle Spinning Research Articles

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.

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.

Identification of a Novel Pyruvyltransferase Using 13C Solid-State Nuclear Magnetic Resonance To Analyze Rhizobial Exopolysaccharides.

The alphaproteobacterium Sinorhizobium meliloti secretes two acidic exopolysaccharides (EPSs), succinoglycan (EPSI) and galactoglucan (EPSII), which differentially enable it to adapt to a changing environment. Succinoglycan is essential for invasion of plant hosts and, thus, for the formation of nitrogen-fixing root nodules. Galactoglucan is critical for population-based behaviors such as swarming and biofilm formation and can facilitate invasion in the absence of succinoglycan on some host plants. The biosynthesis of galactoglucan is not as completely understood as that of succinoglycan. We devised a pipeline to identify putative pyruvyltransferase and acetyltransferase genes, construct genomic deletions in strains engineered to produce either succinoglycan or galactoglucan, and analyze EPS from mutant bacterial strains. EPS samples were examined by 13C cross-polarization magic-angle spinning (CPMAS) solid-state nuclear magnetic resonance (NMR). CPMAS NMR is uniquely suited to defining chemical composition in complex samples and enables the detection and quantification of distinct EPS functional groups. Galactoglucan was isolated from mutant strains with deletions in five candidate acyl/acetyltransferase genes (exoZ, exoH, SMb20810, SMb21188, and SMa1016) and a putative pyruvyltransferase (wgaE or SMb21322). Most samples were similar in composition to wild-type EPSII by CPMAS NMR analysis. However, galactoglucan produced from a strain lacking wgaE exhibited a significant reduction in pyruvylation. Pyruvylation was restored through the ectopic expression of plasmid-borne wgaE. Our work has thus identified WgaE as a galactoglucan pyruvyltransferase. This exemplifies how the systematic combination of genetic analyses and solid-state NMR detection is a rapid means to identify genes responsible for modification of rhizobial exopolysaccharides. IMPORTANCE Nitrogen-fixing bacteria are crucial for geochemical cycles and global nitrogen nutrition. Symbioses between legumes and rhizobial bacteria establish root nodules, where bacteria convert dinitrogen to ammonia for plant utilization. Secreted exopolysaccharides (EPSs) produced by Sinorhizobium meliloti (succinoglycan and galactoglucan) play important roles in soil and plant environments. The biosynthesis of galactoglucan is not as well characterized as that of succinoglycan. We employed solid-state nuclear magnetic resonance (NMR) to examine intact EPS from wild-type and mutant S. meliloti strains. NMR analysis of EPS isolated from a wgaE gene mutant revealed a novel pyruvyltransferase that modifies galactoglucan. Few EPS pyruvyltransferases have been characterized. Our work provides insight into the biosynthesis of an important S. meliloti EPS and expands the knowledge of enzymes that modify polysaccharides.

Stoichiomorphic halogen-bonded cocrystals: a case study of 1,4-diiodotetrafluorobenzene and 3-nitropyridine

The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Single-crystal X-ray diffraction analysis reveals key differences between each of the nominally similar cocrystals. For instance, the 1:1 cocrystal crystallizes in the P21/n space group and features a single chemically and crystallographically unique halogen bond between iodine and the pyridyl nitrogen. The 2:1 cocrystal crystallizes in the [Formula: see text] space group and features a halogen bond between iodine and one of the nitro oxygens in addition to an iodine–nitrogen halogen bond. The 1:2 cocrystal crystallizes with a large unit cell (V = 9896 Å3) in the Cc space group and features 10 crystallographically distinct iodine-nitrogen halogen bonds. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. 1H → 13C and 19F → 13C cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. Carbon-13 chemical shifts in the cocrystals are shown to change only very subtly relative to pure solid 1,4-diiodotetrafluorobenzene, but the shift of the carbon directly bonded to iodine nevertheless increases, consistent with halogen bond formation (e.g., a shift of +1.6 ppm for the 2:1 cocrystal). This work contributes new examples to the field of variable stoichiometry cocrystal engineering with halogen bonds.

The Boltzmann-Monte-Carlo-Percolation (BMCP) model on pyrolysis of coal: The quantitative correction on CP/MAS 13C solid-state NMR spectra and insight on structural evolution during coalification

Because of the Nuclear Overhauser Effect (NOE), the quantitative bonds’ population can hardly be obtained directly from Cross-polarization Magic Angle Spinning (CP/MAS) 13C solid-state Nuclear Magnetic Resonance (NMR) spectra. Thus, correction must be carried out to obtain the bonds’ population with high precision. In this work, the correction factor was derived from Solomon equation, and the previously developed Boltzmann-Monte-Carlo-Percolation (BMCP) model was employed reversely to the calculate correction factor from the tar yields of coal pyrolysis. The results showed that correction on the bonds’ population from tar yields improved the prediction results both on the bonds’ population and product distribution; the correction factor showed an abrupt trend corresponding to coalification jumps. Furthermore, an empirical equation for calculating the correction factor was obtained. The success of the correction indicates that the pyrolysis behaviors of coals under moderate conditions are governed by the bonds’ population, and BMCP model is a proper way to describe the structure–activity relationship quantitatively.

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.

Direct Preparation of *MRE Zeolites with Ultralarge Mesoporosity: Strategy and Working Mechanism.

Introduction of mesopore is critical for applications where mass-transport limitations within microporous networks, especially for zeolite with one-dimensional microporous network, hinder their performance. Generally, the creation of mesopore in zeolite through a direct synthesis route is strongly dependent on complex and expensive organic molecules, which limits their commercial application. Here, we successfully developed a facile synthesis route for preparing ZSM-48 zeolite (*MRE topology) with ultralarge mesoporosity in which typical 1,6-hexylenediamine worked as an organic structure-directing agent, innovatively assisted by a simple crystal growth modifier (tetraethylammonium bromide, TEABr). The working mechanism of TEABr during crystallization was revealed and proposed on the basis of TEM, thermal gravimetric mass spectrum, and 13C cross-polarization magic angle spinning NMR characterization results. In the process, TEA+ ions preferentially interacted with the solid during the induction period, which effectively suppressed the aggregation of ZSM-48 primary nanorods. As a result, ultralarge mesoporosity of 0.97 cm3·g-1 was constructed through the stacking of the nanorods. Interestingly, TEA+ ions only took part in the crystallization process and did not occlude in the pores of the final zeolites indicating its potential in recyclability. Moreover, similar synthesis strategy could be applied for the preparation of hierarchical ferrierite zeolites, implying the universality of this strategy. Compared with a conventional sample, ZSM-48 zeolite with ultralarge mesoporosity showed superior catalytic stability in the m-xylene isomerization reaction due to its significantly enhanced diffusion and mass transfer capability, which will greatly promote the practical application of ZSM-48 zeolite.

Alizarin Grafting onto Ultrasmall ZnO Nanoparticles: Mode of Binding, Stability, and Colorant Studies.

The demand is rising for colorants that are obtained from natural resources, tolerant to industrial processing methods, and meet color quality demands. Herein, we report how relevant properties such as thermal stability and photostability of the natural colorant alizarin can be improved by grafting it onto ZnO nanoparticles (NPs), allowing application in a warm extrusion process for the fabrication of polyamide fibers. For this study, ZnO NPs (diameter 2.0 ± 0.6 nm) were synthesized and subsequently functionalized with alizarin. The alizarin-coated ZnO NPs (i.e., dyed nanoparticles, DNPs) were characterized. Thermogravimetric analysis and ultraviolet–visible (UV–vis) studies revealed that alizarin coating accounts for ∼65% (w/w) of the total mass of the DNPs. A subsequent detailed characterization with Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), 13C cross-polarization magic angle spinning (CP-MAS) NMR, X-ray photoelectron spectroscopy (XPS), and quantum chemistry studies using various density functional theory (DFT) functionals and basis sets indicated that binding onto the ZnO NPs occurred predominantly via the catechol moiety of alizarin. Importantly, this grafting increased the thermal stability of alizarin with >100 °C, which allowed the processing of the DNPs into polyamide fibers by warm extrusion at 260 °C. Evaluation of the lightfastness of the DNP-dyed nylon fibers revealed that the changes in color quantified via the distance metric ΔE* of alizarin when embedded in a hybrid material were 2.6-fold better compared to nylon fibers that were directly dyed with alizarin. This reveals that the process of immobilization of a natural dye onto ZnO nanoparticles indeed improves the dye properties significantly and opens the way for a wide range of further studies into surface-immobilized dyes.

An indirect CO2 utilization for the crystallization control of CaCO3 using alkylcarbonate

Carbon mineralization into calcium carbonate (CaCO3) has been widely studied as a promising CO2 resource utilization pathway. In this work, CO2 was fixed to alkylcarbonate through phase change absorption in polyethylene glycol 200 (PEG) plus ethanediamine (EDA) system at ambient conditions. This alkylcarbonate was identified by FTIR and 13C cross-polarization magic-angle spinning (CP-MAS) NMR spectra. It was used as both CO32− source and crystal modifier to induce crystallization of CaCO3 particles. The CaCO3 microsphere with uniform morphology and vaterite crystal phase was acquired by adjusting quality of alkylcarbonate, concentration of Ca2+ concentration, and crystallization period without any additives. Furthermore, a plausible self-assembly formation mechanism toward inducing crystallization of vaterite CaCO3 microsphere also was proposed. This synthesis strategy is environmentally friendly and offers an alternative strategy for indirect utilization of CO2.

Structural Evaluation of the Choline and Geranic Acid/Water Complex by SAXS and NMR Analyses

Recently, choline and geranic acid (CAGE), an ionic liquid (IL), has been recognized to be a superior biocompatible material for oral and transdermal drug delivery systems (DDS). When CAGE is administered, CAGE would be exposed to various types of physiological fluids, such as intestinal and intradermal fluids. However, the effect of physiological fluids on the structure of CAGE remains unclear. In the present study, molecular structures of CAGE with different ratios of water were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance (NMR). The SAXS pattern of CAGE showed an IL-specific broad peak derived from nanoscale aggregation until 17 vol % water. Meanwhile, narrow peaks were observed in samples with 25-50 vol % water, showing a transition to the lamellar phase. With more than 67 vol % water, CAGE was found to exist as micelles in water. The 1H NMR spectra indicated that protons of H2O, OH in choline (CH), and COOH in geranic acid (GA) were observed as only one peak up to 17 vol % water. This peak shifted to a high magnetic field, and the integral values increased with the water content, speculating that water is localized close to the COOH and OH groups to allow proton exchange. The 13C NMR spectra showed that peaks related to the carboxyl group shifted with adding water. Moreover, only GA peaks were observed in the lamellar phase through 13C cross-polarization magic-angle spinning NMR, suggesting that the main rigid component of the lamellar phase was GA. Taken together, this study suggested that CAGE still maintained its IL structure up to 17 vol % water, then transitioned to the lamellar phase with 25-50 vol % water, and finally changed to the micellar phase with more than 67 vol % water. This information would be useful in the formulation and development of DDS using CAGE.

Silica Nanopowder Supported Frustrated Lewis Pairs for CO2 Capture and Conversion to Formic Acid.

Treatment of hydroxylated silica nanopowders S1 and allyl-functionalized silica nanopowders S2 with 3-(diphenylborano)- or 3-bis(pentafluorophenylborano)propyltrimethoxysilane or 2-(diphenylphosphino)- or 2-(dicyclohexylphosphino)ethyltriethoxysilane generates silica nanopowder supported Lewis acids S3 and silica nanopowder supported Lewis bases S4. These surfaces were characterized by 13C, 11B, and 31P cross-polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR), X-ray photoelectron spectroscopy (XPS), and attenuated total reflection Fourier transform infrared (ATR FTIR). When S3 is combined with solution-phase Lewis bases PR3 (R = C6F5, C6H5, mesityl), six associated silica nanopowder supported frustrated Lewis pairs (FLPs) are formed. In another set of six reactions, the interactions between the supported Lewis bases S4 and solution-phase Lewis acids BR3 with R = C6F5, C6H5, mesityl produced six more associated supported FLPs. The capture of CO2 by these FLPs producing FLP-CO2 Lewis pair adducts S5 and S6 were highlighted by ATR FTIR, and it was found that FLP S5e with R = C6H5 on both the supported Lewis acid and solution-phase Lewis base trapped the largest quantities of CO2 on the silica nanopowder supports. Conversion of CO2 to HCOOH was achieved by first activating H2 to generate activated FLP-H2 surfaces S7 and S9. Addition of CO2 then generated HCOOH via the silica nanopowder supported FLP-HCOOH adducts S8 and S10. Qualitative identification of HCOOH generation was achieved by ATR FTIR measurements, and surface 10b with R = C6H5 proved to be the most successful silica nanopowder surface bound FLP in HCOOH generation. In some cases, diborano formates (-BO(CH)OB-) S11 and S12 were also identified as side products during HCOOH formation. Spectroscopic characterization of purposefully synthesized S11 and S12 included 11B and 31P CP MAS NMR.

Solid state NMR investigation of the roman Acqualadroni rostrum: tenth year assessment of the consolidation treatment of the wooden part

This work follows a previous one dealing with the state of conservation study of the wooden part of the roman Acqualadroni rostrum soon after its finding in the seabed of Acqualadroni (Messina, Italy). The archaeological survey and recovery were particularly relevant since this artefact is one of the two rostrums, nowadays known, found together with its wooden part. Following the recovery, it was consolidated by immersion in a melamine-formaldehyde resin (Kauramin) aqueous solution for eight months at the “Centro di Restauro del Legno Bagnato” (Pisa, Italy). The present investigation is aimed to determine at microscopic scale the wood state of conservation and to highlight interactions of the consolidant with wood components, by using solid-state NMR spectroscopy ten years after the consolidation treatment. Sampling by coring was exceptionally authorized, and the wood core was divided into seven aliquots as a function of depth. 13C cross-polarization magic angle spinning (13C{1H} CP-MAS NMR) spectra and variable contact time (VCT) experiments have been carried out to determine the cellulose crystallinity index, the lignin condensation degree and the holocellulose-lignin ratio. The interactions between the resin and the wood components were highlighted by T1ρH relaxation times determination and two-dimensional 13C–1H correlation (FSLG CP HETCOR) NMR experiments. Findings revealed specific interactions between the aromatic part of the resin and the lignin, as well as a network of hydrogen bonds involving all components of the system.

Molecular Crystal Forms of Antitubercular Ethionamide with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study.

We report on the preparation, characterization, and bioavailability properties of three new crystal forms of ethionamide, an antitubercular agent used in the treatment of drug-resistant tuberculosis. The new adducts were obtained by combining the active pharmaceutical ingredient with three dicarboxylic acids, namely glutaric, malonic and tartaric acid, in equimolar ratios. Crystal structures were obtained for all three adducts and were compared with two previously reported multicomponent systems of ethionamide with maleic and fumaric acid. The ethionamide-glutaric acid and the ethionamide-malonic acid adducts were thoroughly characterized by means of solid-state NMR (13C and 15N Cross-Polarization Magic Angle Spinning or CPMAS) to confirm the position of the carboxylic proton, and they were found to be a cocrystal and a salt, respectively; they were compared with two previously reported multicomponent systems of ethionamide with maleic and fumaric acid. Ethionamide-tartaric acid was found to be a rare example of kryptoracemic cocrystal. In vitro bioavailability enhancements up to a factor 3 compared to pure ethionamide were assessed for all obtained adducts.

Improving the compatibility, surface strength, and dimensional stability of cellulosic fibers using glycidyl methacrylate grafting

The graft copolymerization of lignocellulosic fibers with glycidyl methacrylate (GMA) using a Fe2+–thiourea dioxide–H2O2 redox system (Fe2+–TD–H2O2) was studied to overcome the problems of poor compatibility and low surface strength when cellulosic fibers are composited with synthetic polymers. The results show that cellulose–poly(GMA) (CPGMA) was successfully synthesized from GMA and bleached Eucalyptus cellulosic fibers by Fe2+–TD–H2O2 in a mild aqueous solution. CPGMA had high graft rate (244%), high content of epoxy group, and high stability in water. X-ray diffraction patterns and 13C cross-polarization magic angle spinning nuclear magnetic resonance spectra analyses showed that graft copolymerization did not change the crystalline structure of the CPGMA fiber backbone cellulose, but the crystallinity of the CPGMA fiber decreased with an increase in amorphous PGMA grafting. Scanning electron microscopy confirmed that the grafting reaction occurred both inside and outside the fiber. The specific surface area and pore diameter of the grafted fibers were significantly affected by the grafting. The hydrophobicity of the fibers was significantly enhanced by graft copolymerization. PGMA grafting can enhance the compatibility between the modified fiber and synthetic polymer matrix, improving the processing runnability and product properties of composite materials. A high intensity focused ultrasound method was used to analyze the fiber surface strength. It was confirmed that graft copolymerization significantly improved the surface strength of the grafted fibers. Graft copolymerization can significantly improve the dimensional stability of cellulosic fibers.

Synthesis and Solid-State Dynamics of a Crystalline Steroid Molecular Rotor without the Alkyne Axle: Steroid Dimers Based on a 1,4-Di(1,3-dioxan-2-yl)benzene Moiety.

Two diastereomeric crystalline steroid dimers were obtained by acid-catalyzed double acetalization of (20S)-5α-pregnan-3β,16β,20-triol 3-monoacetate with terephtalaldehyde. These compounds were characterized by NMR in solution, MS, single-crystal X-ray diffraction, and variable-temperature solid-state NMR by 13C cross-polarization magic angle spinning (CPMAS). While the phenylene rotator in the SR diastereomer remains static even at 373 K, the RR isomer shows a slow rotational process of the phenylene ring at temperatures above room temperature and thus may be considered the first crystalline steroid molecular rotor without the alkyne axle.

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.

Carboxylated Cellulose Nanocrystals Developed by Cu-Assisted H2O2 Oxidation as Green Nanocarriers for Efficient Lysozyme Immobilization.

Cellulose nanocrystals (CNCs), having a high specific surface area and versatile surface chemistry, provide considerable potential to interact by various mechanisms with enzymes for nano-immobilization purposes. However, engineering chemically safe CNCs, suitable for edible administrations, presents a significant challenge. A reliable carboxylate form of H-CNCs was formed using H2O2 oxidation of softwood pulp under mild thermal conditions. Negatively charged carboxyl groups (∼0.9 mmol g-1) played a key role in lysozyme immobilization via electrostatic interactions and covalent linkages, as evidenced by Fourier transform infrared and 13C cross-polarization magic angle spinning nuclear magnetic resonance spectroscopies. Adsorption isotherms showed a high loading capacity of H-CNCs (∼240 mg g-1), and fitting the data to the Langmuir model confirmed monolayer coverage of lysozyme on their surface. Using a non-toxic coupling agent, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, lysozyme-conjugated H-CNCs were developed with an immobilization yield of ∼65% and relative catalytic activity of ∼60%, similar to lysozyme adsorption on H-CNCs. These H-CNC-lysozyme nanohybrids, rationally processed via safe and green strategies, are specifically exploitable as catalytically active emulsifiers in food and pharmaceutical sectors.

2-Mercaptopyrimidine-functionalized mesostructured silicas to develop electrochemical sensors for a rapid control of scopolamine in tea and herbal tea infusions

Mesostructured silicas were synthesized and chemically functionalized with a 2-mercaptopyrimidine (MPY)-derivative. Bare and functionalized silicas (MSU-2, HMS, SBA-15, MSU-2-MPY, HMS-MPY and SBA-15-MPY) were characterized by powder X-ray diffraction, nitrogen adsorption-desorption isotherms, transmission electron and scanning electron microscopy, 29Si and 13C cross-polarization magic-angle spinning NMR spectroscopy and elemental analysis, and used to prepare modified carbon paste electrodes (CPEs). The electrodes properties were studied using potassium ferrocyanide and scopolamine as probes employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Results proved that MPY groups on the silica surface were necessary to improve the sensitivity in the voltammetric determination of scopolamine. CPE modified with HMS-MPY exhibited higher peak current toward the oxidation of scopolamine, with a well-defined oxidation peak at + 1.1 V (vs. Ag/AgCl) in DPV. This fact can be attributed to the high electroactive area of this material, with 3 D wormhole-like channel structure that favored the scopolamine diffusion. Under optimum conditions, HMS-MPY-CPE exhibited a wider linearity range, from 0.9 to 200 μM, with a detection limit of 0.3 μM and good reproducibility by DPV. The developed sensor was successfully applied for a rapid determination of scopolamine in spiked tea and herbal tea infusion samples with good recoveries (between 83 ± 5 and 101 ± 1%).