Control of Zeolite Local Polarity toward Efficient Xenon/Krypton Separation.

The inherent inertness and striking physicochemical similarities of krypton and xenon pose significant challenges to their separation. Reported herein is the efficient xenon capture and xenon/krypton adsorptive separation by transition metal-free zeolites under ambient conditions. The polarized environment of zeolite, denoted as local polarity, can be tuned by changing the topology, framework composition, and counter-cations, which in turn correlates with the guest-host interaction and separation performance. Chabazite zeolite with a framework Si/Al ratio of 2.5 and Ca2+ as the counter-cations, namely, Ca-CHA-2.5, is developed as a state-of-the-art zeolite adsorbent, showing remarkable performance, i.e., high dynamic xenon uptake, high xenon/krypton separation selectivity, and good recyclability, in the adsorptive separation of the xenon/krypton mixture. Grand Canonical Monte Carlo simulation reveals that extraframework Ca2+ cations act as the primary binding sites for xenon and can stabilize xenon molecules together with the chabazite framework, whereas krypton molecules are stabilized by weak guest-host interaction with the zeolite framework.

Zeolite-encaged mononuclear copper centers catalyze CO2 selective hydrogenation to methanol.

The selective hydrogenation of CO2 to methanol by renewable hydrogen source represents an attractive route for CO2 recycling and is carbon neutral. Stable catalysts with high activity and methanol selectivity are being vigorously pursued, and current debates on the active site and reaction pathway need to be clarified. Here, we report a design of faujasite-encaged mononuclear Cu centers, namely Cu@FAU, for this challenging reaction. Stable methanol space-time-yield (STY) of 12.8 mmol gcat-1 h-1 and methanol selectivity of 89.5% are simultaneously achieved at a relatively low reaction temperature of 513 K, making Cu@FAU a potential methanol synthesis catalyst from CO2 hydrogenation. With zeolite-encaged mononuclear Cu centers as the destined active sites, the unique reaction pathway of stepwise CO2 hydrogenation over Cu@FAU is illustrated. This work provides a clear example of catalytic reaction with explicit structure-activity relationship and highlights the power of zeolite catalysis in complex chemical transformations.

Stable and Uniform Extraframework Cations in Faujasite Zeolites.

Extraframework transition metal ions (TMIs) in zeolites can serve as active sites for adsorption and catalysis. However, due to the complexity and mobility of extraframework cation sites, their applications are significantly limited and the structure-performance relationship is poorly understood. In this Perspective, stable and uniform TMIs in zeolites are exemplified and their characteristics are discussed. A series of TMIs can be introduced to specific cation sites of faujasite via a ligand-protected in situ synthesis route to construct uniform TMIs in the zeolite matrix, namely, TMI@FAU (TMI= Co, Ni, Cu, Rh, and Pt). Coordinatively unsaturated TMIs within faujasite are active for small-molecule adsorption and activation, and therefore, TMI@FAU zeolites show unique properties in adsorption and catalysis. TMI@FAU zeolites appear to be ideal model systems, and the well-defined structure of TMI@FAU greatly facilitates the mechanism studies by spectroscopic investigations and theoretical simulations.

Regulating Extra-Framework Cations in Faujasite Zeolites for Capture of Trace Carbon Dioxide.

The development of cost-effective sorbents for direct capture of trace CO2 (<1 %) from the atmosphere is an important and challenging task. Natural or commercial zeolites are promising sorbents, but their performance in adsorption of trace CO2 has been poorly explored to date. A systematic study on capture of trace CO2 by commercial faujasite zeolites reveals that the extra-framework cations play a key role on their performance. Under dry conditions, Ba-X displays high dynamic uptake of 1.79 and 0.69 mmol g-1 at CO2 concentrations of 10000 and 1000 ppm, respectively, and shows excellent recyclability in the temperature-swing adsorption processes. K-X exhibits perfect moisture resistance, and >95 % dry CO2 uptake can be preserved under relative humidity of 74 %. In situ solid-state NMR spectroscopy, synchrotron X-ray diffraction and neutron diffraction reveal two binding sites for CO2 in these zeolites, namely the basic framework oxygen atoms and the divalent alkaline earth metal ions. This study unlocks the potential of low-cost natural zeolites for applications in direct air capture.

Confinement in a Zeolite and Zeolite Catalysis.

ConspectusZeolites, accompanied by their initial discovery as natural mines and the subsequent large-scale commercial production, have played indispensable roles in various fields such as petroleum refining and the chemical industry. Understanding the characteristics of zeolites, in contrast to their counterparts with similar chemical compositions and the origin thereof, is always a hot and challenging topic. Zeolites are known as intrinsic confined systems with ordered channels on the molecular scale, and structural confinement has been proposed to explain the unique chemical behaviors of zeolites. Generally, the channels of zeolites can regulate the diffusion of molecules, leading to a visible difference in molecular transportation and the ultimate shape-selective catalysis. On the other hand, the local electric field within the zeolite channels or cages can act on the guest molecules and change their energy levels. Confinement can be simply interpreted from both spatial and electronic issues; however, the nature of zeolite confinement is ambiguous and needs to be clarified.In this Account, we make a concise summary and analysis of the topics of confinement in a zeolite and zeolite catalysis from two specific views of spatial constraint and a local electric field to answer two basic questions of why zeolites and what else can we do with zeolites. First, it is shown how to construct functional sites including Brønsted acid sites, Lewis acid sites, extraframework cation sites, and entrapped metal or oxide aggregates in zeolites via confinement and how to understand the specific role of confinement in their reactivity. Second, the multiple impacts of confinement in zeolite-catalyzed reactions are discussed, which rationally lead to several unique processes, namely, Brønsted acid catalysis confined in zeolites, Lewis acid catalysis confined in zeolites, catalysis by zeolite-confined coordinatively unsaturated cation sites, and a cascade reaction within the confined space of zeolites. Overall, confinement effects do exist in zeolite systems and have already played extremely important roles in adsorption and catalysis. Although confinement might exist in many systems, the confinement by zeolites is more straightforward thanks to their well-ordered and rigid structure, deriving unique chemical behaviors within the confined space of zeolites. A zeolite is a fantastic scaffold for constructing isolated sites spatially and electrostatically confined in its matrix. Furthermore, zeolites containing well-defined transition-metal sites can be treated as inorganometallic complexes (i.e., a zeolite framework as the ligand of transition-metal ions) and can catalyze reactions resembling organometallic complexes or even metalloenzymes. The local electric field within the confined space of zeolites is strong enough to induce or assist the activation of small molecules, following the working fashion of frustrated Lewis pairs. The tactful utilization of structural confinement, both spatially and electronically, becomes the key to robust zeolites for adsorption and catalysis.

Efficient Separation of Acetylene and Carbon Dioxide in a Decorated Zeolite.

The almost identical molecular sizes and volatilities of acetylene and carbon dioxide make their separation extremely challenging in industry. Reported here is the efficient separation of acetylene and carbon dioxide (v/v=2/1, which is relevant to that in the industrial cracking stream) in faujasite zeolites decorated with atomically-dispersed copper(II) sites under ambient conditions. In situ neutron powder diffraction and inelastic neutron scattering confirm that the confined copper(II) site displays chemoselective yet reversible binding to acetylene, whereas adsorbed carbon dioxide molecules are stabilized by weak host-guest supramolecular interactions with the framework oxygen centers, thus resulting in the efficient separation of these two gases under flow conditions. A designed adsorption-purging-desorption system based upon Cu@FAU is established for the recovery of high purity acetylene (98-99 %) from the mixture of acetylene and carbon dioxide, offering an unprecedented separation factor of 22.2 with an effective dynamic uptake of acetylene of 1.51 mmol g-1 at 298 K.

Control of zeolite pore interior for chemoselective alkyne/olefin separations.

The efficient removal of alkyne impurities for the production of polymer-grade lower olefins remains an important and challenging goal for many industries. We report a strategy to control the pore interior of faujasite (FAU) zeolites by the confinement of isolated open nickel(II) sites in their six-membered rings. Under ambient conditions, Ni@FAU showed remarkable adsorption of alkynes and efficient separations of acetylene/ethylene, propyne/propylene, and butyne/1,3-butadiene mixtures, with unprecedented dynamic separation selectivities of 100, 92, and 83, respectively. In situ neutron diffraction and inelastic neutron scattering revealed that confined nickel(II) sites enabled chemoselective and reversible binding to acetylene through the formation of metastable [Ni(II)(C2H2)3] complexes. Control of the chemistry of pore interiors of easily scalable zeolites has unlocked their potential in challenging industrial separations.

Determination of fucoidan in rat plasma by HPLC and its application in pharmacokinetics.

This is a new expanded method of determining the characterisation of fucoidan from Laminaria japonica (kelp) in rat plasma by high-performance liquid chromatography (HPLC) with fluorescence detection. We tagged fucoidan by fluoresce in isothiocyanate (FITC) for tracking and treated the plasma samples via protein precipitation with 10% trichloroacetic acid and methanol. Column chromatography separation was on a TSK-G4000sw column (7.8 mm × 300 mm, 5 mm) by elution with 0.15 M NaCl. The quantification of fucoidan was performed by HPLC with fluorescence detection. The results suggested that the calibration curve for fucoidan concentration was linear dependent in the limits of 0.5-100µg/mL. The lower limit of quantitation (LLOQ) was 0.5µg/mL and the lower limit of detection (LLOD) was 0.15µg/mL. The intra-day and inter-day precision values were less than 13%and the accuracy ranged from 96.83 to 100.03% at 3 different concentrations. The fucoidan stability of rat plasma at different temperatures and time-points was estimated. The extraction efficiencies ranged from 93.33 to 96.53%and the matrix effect ranged from 92.67 to 95.83%. Method selectivity was evaluated as well. We successfully studied the pharmacokinetic of fucoidan in rat plasma after oral by the validated method. Fucoidan was administered to rats intravenously at a dose of 6 mg/kg and orally at a dose of 20 mg/kg. The Cmax was 7.33µg/mL within 2 h by oral administration; The initial Cmax was 75.59µg/mL. The bioavailability of fucoidan after oral administration to rats was 8.91%.

Noble Metal Particles Confined in Zeolites: Synthesis, Characterization, and Applications.

Noble metal nanoparticles or subnanometric particles confined in zeolites, that is, metal@zeolite, represent an important type of functional materials with typical core-shell structure. This type of material is known for decades and recently became a research hotspot due to their emerging applications in various fields. Remarkable achievements are made dealing with the synthesis, characterization, and applications of noble metal particles confined in zeolites. Here, the most representative research progress in metal@zeolites is briefly reviewed, aiming to boost further research on this topic. For the synthesis of metal@zeolites, various strategies, such as direct synthesis from inorganic or ligand-assisted noble metal precursors, multistep postsynthesis encapsulation and ion-exchange followed by reduction, are introduced and compared. For the characterization of metal@zeolites, several most useful techniques, such as electron microscopy, X-ray based spectroscopy, infrared and fluorescence emission spectroscopy, are recommended to check the successful confinement of noble metal particles in zeolite matrix and their unique physiochemical properties. For the applications of metal@zeolites, catalysis and optics are involved with an emphasis on catalytic applications including the size-dependent catalytic properties, the sintering-resistance properties, the substrate shape-selective catalysis, and catalysis modulation by zeolite microenvironment.

Acetylene-Selective Hydrogenation Catalyzed by Cationic Nickel Confined in Zeolite.

The selective hydrogenation of alkynes to alkenes is an important type of organic transformation with large-scale industrial applications. This transformation requires efficient catalysts with precise selectivity control, and palladium-based metallic catalysts are currently employed. Here we show that four-coordinated cationic nickel(II) confined in zeolite can efficiently catalyze the selective hydrogenation of acetylene to ethylene, a key process for trace acetylene removal prior to the polymerization process. Under optimized conditions, 100% acetylene conversion and an ethylene selectivity up to 97% are simultaneously achieved. This catalyst system also exhibits good stability and recyclability for potential applications. Spectroscopy investigations and density functional theory calculations reveal the heterolytic dissociation of hydrogen molecules and the importance of hydride and protons in the selective hydrogenation of acetylene to ethylene. This work provides an efficient strategy toward active and selective zeolite catalysts by utilizing the local electrostatic field within the zeolite confined space for small-molecule activation and by linking heterogeneous and homogeneous catalysis.

Purification and characterization of a novel fibrinolytic enzyme from Whitmania pigra Whitman.

A fibrinolytic enzyme was purified from the dry body of Whitmania pigra Whitman. The fibrinolytic enzyme was purified to homogeneity with a yield of 0.003% and a purification of 630.7 fold. The molecular weight of the enzyme was estimated to be 26.7 kDa by reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme was tested by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) and it showed that the enzyme was a novel fibrinolytic enzyme. The optimal pH and temperature of the enzyme were 8.5 and 55°C, respectively. Enzyme activity was enhanced by Na+, Mg2+, and K+. On the contrary, the proteolytic activity was significantly inhibited by Mn2+, Fe2+, Fe3+, ethylenediaminetetraacetic acid (EDTA), and ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA). Fibrinolytic and fibrinogenolytic assays showed that the enzyme preferentially hydrolyzed fibrinogen Aα-chains, followed by Bß- and γ-chains. The α-, ß-, and γ-γ-chains of fibrin were also degraded by the enzyme.

Synthesis and fluorescence properties of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazol derivatives and their terbium complexes.

Eight novel 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazol derivatives have been designed and synthesized, and their corresponding Tb(3+) complexes were also prepared successfully. The fluorescence properties and fluorescence quantum yields of the target complexes were investigated, the results showed that the ligands were an efficient sensitizer for Tb(3+) luminescence, and the target complexes exhibited characteristic fluorescence emissions of Tb(3+) ion. The fluorescence intensity of the complex substituted by chlorine was stronger than that of other complexes. The substituents' nature has a great effect upon the electrochemical properties of the target complexes. The results showed that the introduction of the electron-withdrawing groups tended to decrease the oxidation potential and highest occupied molecular orbital energy levels of the target Tb(3+) complexes; however, introduction of the electron-donating groups can increase the corresponding complexes' oxidation potential and highest occupied molecular orbital energy levels.

Natural variation in the sequence of PSY1 and frequency of favorable polymorphisms among tropical and temperate maize germplasm.

Provitamin A (Pro-VA) is necessary for human vision and immune system health, especially in growing children. The first committed step in the maize carotenoid biosynthesis pathway is catalyzed by phytoene synthase 1 (encoded by PSY1) which controls the flux of substrates into the pathway. The flow of these substrates could be directed into production of the ß-branch carotenoids (the step controlled largely by the lycopene epsilon cyclase gene), but terminated after the production of ß-carotene, rather than allowing it to be converted into the next metabolite (the step controlled largely by the ß-carotenoid hydroxylase gene). In this study, PSY1 was subjected to association mapping in two diverse maize populations, quantitative trait loci (QTL) mapping in one segregating population, and expression analysis of lines polymorphic for sites within PSY1. The results indicated that a 378-bp InDel upstream of the transcription start site and a SNP in the fifth exon resulting in a Thr to Asn substitution, explaining 7 and 8 % of the total carotenoid variation, respectively, may be functional sites associated with total carotenoid levels in maize grain. Analysis of the evolution of PSY1 strongly suggests that there was positive selection for these polymorphic sites after the divergence of yellow maize from white maize.

Genome-wide association study dissects the genetic architecture of oil biosynthesis in maize kernels.

Maize kernel oil is a valuable source of nutrition. Here we extensively examine the genetic architecture of maize oil biosynthesis in a genome-wide association study using 1.03 million SNPs characterized in 368 maize inbred lines, including 'high-oil' lines. We identified 74 loci significantly associated with kernel oil concentration and fatty acid composition (P < 1.8 × 10(-6)), which we subsequently examined using expression quantitative trait loci (QTL) mapping, linkage mapping and coexpression analysis. More than half of the identified loci localized in mapped QTL intervals, and one-third of the candidate genes were annotated as enzymes in the oil metabolic pathway. The 26 loci associated with oil concentration could explain up to 83% of the phenotypic variation using a simple additive model. Our results provide insights into the genetic basis of oil biosynthesis in maize kernels and may facilitate marker-based breeding for oil quantity and quality.

A highly efficient TiO2@ZnO n-p-n heterojunction nanorod photocatalyst.

Shell@core-nanostructured TiO(2)@ZnO n-p-n heterojunction nanorods with diameter of 30 nm were successfully fabricated via a hydrothermal method. The photodegradation rate of the TiO(2)@ZnO n-p-n nanorods evaluated by photodegrading methyl orange has been demonstrated to increase three times compared to that of wurtzite hexagonal ZnO. Anatase TiO(2) and Ti(2)O(3) grow along ZnO crystal lattices, which forms p-type Zn(2+) doped Ti(2)O(3) in the interface of TiO(2)/ZnO and therefore numerous n-p-n heterojunctions owing to the substitution of Ti(3+) by Zn(2+). Under the drive of inner electric field, the photogenerated electrons are both injected to the conduction band of Zn(2+) doped Ti(2)O(3) from conduction bands of ZnO and TiO(2), which efficiently enhances the separation of photogenerated electron-hole pairs and accelerates the transport of charges. The results suggest that TiO(2)@ZnO n-p-n heterojunction nanorods are very promising for enhancing the photocatalytic activity of photocatalysts.

An 11-bp insertion in Zea mays fatb reduces the palmitic acid content of fatty acids in maize grain.

The ratio of saturated to unsaturated fatty acids in maize kernels strongly impacts human and livestock health, but is a complex trait that is difficult to select based on phenotype. Map-based cloning of quantitative trait loci (QTL) is a powerful but time-consuming method for the dissection of complex traits. Here, we combine linkage and association analyses to fine map QTL-Pal9, a QTL influencing levels of palmitic acid, an important class of saturated fatty acid. QTL-Pal9 was mapped to a 90-kb region, in which we identified a candidate gene, Zea mays fatb (Zmfatb), which encodes acyl-ACP thioesterase. An 11-bp insertion in the last exon of Zmfatb decreases palmitic acid content and concentration, leading to an optimization of the ratio of saturated to unsaturated fatty acids while having no effect on total oil content. We used three-dimensional structure analysis to explain the functional mechanism of the ZmFATB protein and confirmed the proposed model in vitro and in vivo. We measured the genetic effect of the functional site in 15 different genetic backgrounds and found a maximum change of 4.57 mg/g palmitic acid content, which accounts for ∼20-60% of the variation in the ratio of saturated to unsaturated fatty acids. A PCR-based marker for QTL-Pal9 was developed for marker-assisted selection of nutritionally healthier maize lines. The method presented here provides a new, efficient way to clone QTL, and the cloned palmitic acid QTL sheds lights on the genetic mechanism of oil biosynthesis and targeted maize molecular breeding.

Genetic analysis and characterization of a new maize association mapping panel for quantitative trait loci dissection.

Association mapping based on the linkage disequilibrium provides a promising tool to identify genes responsible for quantitative variations underlying complex traits. Presented here is a maize association mapping panel consisting of 155 inbred lines with mainly temperate germplasm, which was phenotyped for 34 traits and genotyped using 82 SSRs and 1,536 SNPs. Abundant phenotypic and genetic diversities were observed within the panel based on the phenotypic and genotypic analysis. A model-based analysis using 82 SSRs assigned all inbred lines to two groups with eight subgroups. The relative kinship matrix was calculated using 884 SNPs with minor allele frequency > or = 20% indicating that no or weak relationships were identified for most individual pairs. Three traits (total tocopherol content in maize kernel, plant height and kernel length) and 1,414 SNPs with missing data < 20% were used to evaluate the performance of four models for association mapping analysis. For all traits, the model controlling relative kinship (K) performed better than the model controlling population structure (Q), and similarly to the model controlling both population structure and relative kinship (Q + K) in this panel. Our results suggest this maize panel can be used for association mapping analysis targeting multiple agronomic and quality traits with optimal association model.

[Measuring fatty acid concentration in maize grain by near-infrared reflectance spectroscopy].

The fatty acid concentrations in maize grain were analyzed with a set of 294 samples including normal inbred lines, high-oil inbred lines and high-oil recombinant inbred lines (RIL). The method of partial least squares (PLS) regression with internal cross validation was employed to develop the measuring models of near-infrared reflectance spectroscopy (NIRS) for concentrations of four major fatty acids, palmitic, stearic, oleic and linoleic acids, as well as oil concentration in maize grain. The NIRS models were accurate for oleic acid, linoleic acid and oil concentrations. The determination coefficients of these models in cross validation were 0.89, 0.88 and 0.91, respectively; the determination coefficients in external validation were 0.86, 0.84 and 0.92, respectively; and the ratio of standard deviation (SD) to root mean square error of validation (RMSEV) in both calibration and external validation sets (RSC(P)) was higher than 2.5. But the models for palmitic and stearic acid concentrations were not accurate enough with determination coefficients in cross validation and external validation lower than 0.80, and RSC(P) lower than 2.5. Further practical validation showed that the predicted results by using NIRS models for oleic acid, linoleic acid and oil concentrations were accurate and reliable, which will be a useful approach to the measurement of a large number of breeding samples during genetic improvement of oil quality and quantity in maize.