Enantioselective epoxidation of conjugated cis-enynes by chiral dioxirane

This paper describes a highly chemo- and enantioselective epoxidation of conjugated cis-enynes using readily available glucose-derived ketone 2 as catalyst and Oxone as oxidant to form cis-propargyl epoxides in high ee's. The interaction between the alkyne group of the substrate and the oxazolidinone moiety of the ketone catalyst as well as the interactions between the substituents on enynes and the oxazolidinone moiety of the ketone catalyst are important for the stereodifferentiation.     

New reactivity of oxaziridine: Pd(II)-catalyzed aromatic C-H ethoxycarbonylation via C-C bond cleavage

A novel Pd(II)-catalyzed aromatic C-H ethoxycarbonylation with oxaziridine involving C-C bond cleavage is described. Various aromatic 2-phenylpyridines and related compounds as well as aryl ureas can be effectively ethoxycarbonylated. A catalytic cycle involving Pd(II) and Pd(IV) is proposed.     

Chitosan-g-poly(acrylic acid) hydrogel with crosslinked polymeric networks for Ni recovery

In this study, chitosan-g-poly(acrylic acid) (CTS-g-PAA) hydrogel with crosslinked polymeric networks was prepared from an aqueous dispersion polymerization and then used as the adsorbent to recover a valuable metal, Ni²⁺. The adsorption capacity of CTS-g-PAA for Ni²⁺ was evaluated and the adsorption kinetics was investigated using Voigt-based model and pseudo-second-order model. In addition, the effects of pH values and coexisting heavy metal ions such as Cu²⁺ and Pb²⁺ on the adsorption capacity were studied. The results indicate that the as-prepared adsorbent has faster adsorption rate and higher adsorption capacity for Ni²⁺ recovery, with the maximum adsorption capacity of 161.80 mg g⁻¹. In a wide pH range of 3–7, the adsorption capacity keeps almost the same, and even under competitive conditions, the adsorption capacity of CTS-g-PAA for Ni²⁺ is observed to be as high as 54.47 mg g⁻¹. Finally, the adsorption performance of CTS-g-PAA for Ni²⁺ in real water sample and the reusability of the as-prepared adsorbent were evaluated, and also the controlled adsorption mechanism was proposed.     

FeCl3/NaI-catalyzed allylic C-H oxidation of arylalkenes with a catalytic amount of disulfide under air

This paper describes a FeCl(3)/NaI-catalyzed formal allylic C-H oxidation of arylalkenes using a catalytic amount of disulfide with BnOH and 4-nitroaniline as nucleophiles and air as oxidant to form the corresponding allyl ethers and amines. A possible reaction mechanism has been proposed.     

Self-assembled monolayers induced inter-conversion of crystal structure by vertical to lateral growth of aluminium doped zinc oxide thin films

In this communication, we demonstrate the inter-conversion of crystal structure of aluminium doped zinc oxide (AZO) thin films from highly (002) plane oriented vertical growth to (103) plane oriented lateral growth by adjusting the polarity of the self-assembled monolayers (SAMs) on glass substrates at room temperature.     

Asymmetric epoxidation of 1,1-disubstituted terminal olefins by chiral dioxirane via a planar-like transition state

Various 1,1-disubstituted terminal olefins have been investigated for asymmetric epoxidation using chiral ketone catalysts. Up to 88% ee has been achieved with a lactam ketone, and a planar transition state is likely to be a major reaction pathway.     

A novel class of tunable cyclopropanation reagents (RXZnCH2Y) and their synthetic applications

The Simmons-Smith cyclopropanation is a widely used method to synthesize cyclopropanes from alkenes using methylene iodide and a zinc reagent. A novel class of organozinc species, RXZnCH(2)Y, has been found to efficiently cyclopropanate alkenes, including traditionally unreactive unfunctionalized alkenes. The reactivity and selectivity of this class of organozinc reagents can be regulated by tuning the electronic and/or steric nature of the RX group attached to Zn. During recent years, this class of organozinc reagent has been widely used in organic synthesis as a reagent for cyclopropanation and other useful synthetic transformations. Catalytic, asymmetric versions of this reaction have been developed providing high enantiomeric excess for unfunctionalized olefins.     

The influence of the Al pre-deposition on the properties of AlN buffer layer and GaN layer grown on Si (1 1 1) substrate

The influence of Al pre-deposition on the properties of AlN buffer layer and GaN layer grown on Si (1 1 1) substrate by metalorganic chemical vapor deposition (MOCVD) has been systematically studied. Compared with the sample without Al pre-deposition, optimum Al pre-deposition time could improve the AlN buffer layer crystal quality and reduce the root mean square (RMS) roughness. Whereas, overlong Al-deposition time deteriorated the AlN crystal quality and Al-deposition patterns could be found. Cracks and melt-back etching patterns appeared in the GaN layer grown without Al pre-deposition. With suitable Al-deposition time, crack-free 2.0 μm GaN was obtained and the full-width at half-maximum (FWHM) of (0 0 2) plane measured by double crystal X-ray diffraction (DCXRD) was as low as 482 arcsec. However, overlong Al-deposition time would result in a great deal of cracks, and the crystal quality of GaN layer deteriorated. The surface of GaN layer became rough in the region where the Al-deposition patterns were formed due to overlong Al-deposition time.     

High-Efficiency Extraction of Pantoea alhagi Exopolysaccharides Driven by pH-Related Changes in the Envelope Structure

Increasing numbers of exopolysaccharides and their properties have been explored. However, the difficulty of extracting high-viscosity exopolysaccharides has hindered their further industrialization. In this research, we explored a strategy based on encapsulated structure control under different pH to efficiently extract Pantoea alhagi exopolysaccharides (PAPS). Results showed that at pH levels of 6, 12, and 13, the extraction efficiency of PAPS was elevated, and the yield did not decrease. The rheological properties of the pH−12-treated PAPS were better than those of PAPS treated at pH 7, while the pH−6-treated PAPS decreased. The effects of pH−12-treated PAPS on soil macroaggregates and soil’s water evaporation rate were similar to those of PAPS treated at pH 7. In addition, we observed that treatment at pH 12 produced a significantly reduced encapsulated structure compared with treatment at pH 7. The proportion of unsaturated fatty acids after treatment at pH 12 was higher than after treatment at pH 7, which may result in reduced encapsulated structure in pH−12 conditions. These results enrich the understanding of the effect that alters pH conditions on the encapsulated structure to improve the extraction efficiency of exopolysaccharides and provide a theoretical basis for the extraction of exopolysaccharides with extreme viscosity.