Anderson-type polyoxometalate-based metal-organic framework as an efficient heterogeneous catalyst for selective oxidation of benzylic C-H bonds

Oxidative transformation of benzylic C-H bonds into functional carbonyl groups under mild conditions represents an efficient method for the synthesis of aromatic carboxylic acids and ketones. Here we report a high-efficiency catalyst system constructed from an Anderson-type polyoxometalate-based metal-Organic framework (POMOF-1) and N-hydroxyphthalimide (NHPI) for selective oxidation of methylarenes and alkylarenes under 1 atm O2 atmosphere. POMOF-1 exerted a synergistic effect originating from the well-aligned Anderson {CrMo6} clusters and Cu centers within the framework, and this entailed good cooperation with NHPI to catalyze the selective oxidation. Accordingly, the reactions exhibit good tolerance and chemical selectivity for a wide range of substrates bearing diverse substituent groups, and the corresponding carboxylic acids and ketones were harvested in good yields under mild conditions. Mechanism study reveals that POMOF-1 worked synergistically with NPHI to activate the benzylic C-H bonds of substrates, which are sequentially oxidized by oxygen and HOO˙ to give rise to the products. This work may pave a way to design high-efficiency catalysts by integration of polyoxometalate-based materials with NPHI for challenging C-H activation.

A porous Anderson-type polyoxometalate-based metal-organic framework as a multifunctional platform for selective oxidative coupling with amines

Incorporating catalytic units into a crystalline porous matrix represents a facile way to build high-efficiency heterogeneous catalysts, and by rational design of the porous skeleton with appropriate building blocks the catalytic performance can be significantly enhanced for a series of organic transformations owing to the synergistic effect from the multicomponent and confined porous microenvironment around catalytically active sites. Herein, we demonstrate that the design and synthesis of a porous polyoxometalate-based metal-organic framework YL2(H2O)2[CrMo6O18(PET)2]·4H2O (POMOF-1) constructed from Anderson-type [CrMo6O18(PET)2] (PET = pentaerythritol), which can be employed as a multifunctional platform for synthesis of N-containing compounds via selective oxidative coupling with amines. POMOF-1 features microporous 1D channels defined by Y3+ and L, with [CrMo6O18(PET)2] arranged orderly between adjacent Lvia electrostatic interactions. Upon using POMOF-1 as a catalyst and H2O2 as an oxidant, a variety of amines could be effectively converted to value-added amides, imines and azobenzenes via the oxidative cross-coupling with alcohols or homo-coupling. In particular, POMOF-1 showed dramatically improved activity for the N-formylation reaction owing to the synergistic and confinement effect, with the yield of amides up to 95% and 4 times higher than that of homogeneous [CrMo6O18(PET)2]. Meanwhile, the oxidative homo-coupling of arylmethylamines and arylamines can be facilely tuned by adjustment of the amount of oxidant, solvent and additive, affording imines and azobenzenes in high selectivity and yield, respectively. POMOF-1 is robust and can be reused for 5 cycles with little loss of catalytic activity and structural integrity. The work demonstrates that the combination of catalytically active POMs with crystalline porous MOFs holds great potential to build robust and recyclable heterogeneous systems with enhanced activity and selectivity for multifunctional catalysis.

Copper(I)-Catalyzed Direct Oxidative Annulation of 1,3-Dicarbonyl Compounds with Maleimides: Access to Polysubstituted Dihydrofuran Derivatives

An efficient annulation method for the synthesis of polysubstituted dihydrofurans from 1,3-dicarbonyl compounds and maleimides is described. The reactions can afford furo[2,3-c]pyrrole derivatives with satisfactory yields. The developed strategy realizes the direct oxidative double C(sp³)-H functionalization in the presence of copper(I) salts and 2-(tert-butylperoxy)-2-methylpropane. Meanwhile, this protocol features a mild reaction condition and simple catalytic system. A reaction mechanism involving a single electron oxidation is also proposed.

Iodine-Promoted C(sp 2)–H Thiolation of Maleimides with Dimethyl Sulfoxide and Thiols

Iodine-promoted C(sp 2)–H methylthiolation of maleimides using DMSO as synthon has been developed to afford 3-methylthiomaleimides in moderate yields under metal-free conditions. In addition, 3-thiomaleimides were synthesized from maleimides and thiols in the presence of iodine and triethylamine. The methods are simple and efficient for the formation of C–S bond.

Poly(ferrocenylsilane) electrolytes as a gold nanoparticle foundry: "two-in-one" redox synthesis and electrosteric stabilization, and sensing applications

Gold nanoparticles (AuNPs) coated with responsive polymers gained considerable interest due to their controllable size, good stability, and fast environmental response suitable for biological applications and sensing. Here we report on a simple and efficient method for the synthesis of stable and redox responsive AuNPs using organometallic polyelectrolytes in aqueous solutions of HAuCl₄. In the redox reaction, positively or negatively charged poly(ferrocenylsilanes) (PFS⁺/PFS^-) served as reducing agents, and also as stabilizing polymers. Due to their unique tunable electrostatic and electrosteric protection, AuNPs coated with PFS^-, (PFS⁺)@AuNPs, possess high redox sensitivity, with reversible, repetitive, sustainable color switching between the assembled (purple color) and disassembled (red color) states as evidenced by UV-Vis absorption and TEM measurements. Feasibility studies reported here indicate that the particles described can be applied as a colorimetric probe for the detection of redox molecules, e.g. vitamin C, in a controlled and facile manner.

Flumethrin residue levels in honey from apiaries of China by high-performance liquid chromatography

A method for detection of flumethrin residue in honey by high-performance liquid chromatography was established. After n-hexane-dichloromethane (4:6, vol/vol) extraction, the honey samples were concentrated by rotary evaporation, purified by an Oasis HLB solid-phase extraction column, and detected using a UV detector at 267 nm. The interference of the matrix was greatly reduced by optimizing pretreatment conditions; thus, the minimal detection limit of cyhalothrin was 0.005 mg/kg, the average recovery was 80.8 to 96.8%, and the coefficient of variation was 0.6 to 1.5%. The precision and reproducibility of this method was suitable and applicable for detecting flumethrin residue in honey. With this method, 135 honey samples from seven locations in the People's Republic of China were tested; 77 samples tested positive for flumethrin residue, resulting in a detection rate of 75.3%. Samples from the Guangdong province had the highest flumethrin residue level (0.122 mg/kg) of the locations tested. On the basis of analytical validation, the high-performance liquid chromatography has been shown to be a promising alternative for the analysis of flumethrin residue in honey samples.

Enhanced tribological, corrosion, and microstructural properties of an ultrathin (<2 nm) silicon nitride/carbon bilayer overcoat for high density magnetic storage

An ultrathin bilayer overcoat of silicon nitride and carbon (SiNx/C) providing low friction, high wear resistance, and high corrosion resistance is proposed for future generation hard disk media. The 16 Å thick SiNx/C overcoat consists of an atomically thin SiNx underlayer (4 Å) and a carbon layer (12 Å), fabricated by reactive magnetron sputtering and filtered cathodic vacuum arc (FCVA), respectively. When compared with monolithic overcoats of FCVA-deposited carbon (16 Å) and sputtered SiNx (16 Å), the SiNx/C bilayer overcoat demonstrated the best tribological performance with a coefficient of friction < 0.2. Despite showing marginally less electrochemical corrosion protection than monolithic SiNx, its ability to protect the magnetic media from corrosion/oxidation was better than that of an ∼27 Å thick commercial hard disk overcoat and 16 Å thick monolithic FCVA-deposited carbon. From X-ray photoelectron spectroscopy and Raman spectroscopy analyses, it was found that the introduction of the 4 Å SiNx underlayer facilitated higher sp(3) hybridization within the carbon layer by acting as a barrier and promoted the formation of strong bonds at the SiNx/C and the SiNx/media interfaces by acting as an adhesion layer. The higher sp(3) carbon content is expected to improve the thermal stability of the overcoat, which is extremely important for future hard disk drives employing heat assisted magnetic recording (HAMR).

Synthesis and phase evolutions in layered structure of Ga2S3 semiconductor thin films on epiready GaAs (111) substrates

We report on synthesis and properties of p-type Ga2S3 semiconductor thin films that were prepared by sulfurizing epiready n-type GaAs (111) surface at elevated temperatures. Comparisons of structural and optical properties among the thin films, peeling-off resulted microtubes, and the remains after peeling-off give a clear clue to the crystal growth and phase evolutions of Ga2S3. Three layers of Ga2S3 are clearly identified in the thin films. They are layer i, cubic Ga2S3 epitaxially grown on the GaAs (111) substrate; layer ii, polycrystalline cubic Ga2S3 on top of layer-i; and layer iii, monoclinic and/or hexagonal Ga2S3 on top of layer ii. The onset of peeling-off occurred in layer i and/or at the interface between layer i and ii. Both the phase evolutions and the location of peeling-off are associated with a Ga out diffusion growth mechanism. Absorption spectroscopy revealed a direct bandgap of 3.0 eV, whereas photoluminescence spectra showed defects (excited Ga vacancies) related red (1.62 eV) and green (2.24 eV) emissions of the Ga2S3 films; both are qualitatively consistent with those reported values obtained at lower sample temperatures from Ga2S3 single crystals. These results, together with a large on/off current ratio (i.e., ∼14 at a bias of 4.0 V) of the resultant hetero p-Ga2S3/n-GaAs junction under a blue laser (405 nm, 3.0 mW) illumination, shed light on consequent integrations of Ga2S3- and GaAs-based optoelectronic devices, e.g., high-power laser radiation sensors.

Polystyrene-microsphere-assisted patterning of ZnO nanostructures: growth and characterization

In this work, periodic arrays of various ZnO nanostructures were fabricated on both Si and GaN substrates via a facile hydrothermal process. To realize the site-specific growth, two kinds of masks were introduced. The polystyrene (PS) microsphere self-assembled monolayer (SAM) was employed as the mask to create a patterned seed layer to guide the growth of ZnO nanostructures. However, the resulting ZnO nanostructures are non-equidistant, and the diameter of the ZnO nanostructures is uncontrollable. As an alternative, TiO2 sol was used to replicate the PS microsphere SAM, and the inverted SAM (ISAM) mask was obtained by extracting the PS microspheres with toluene. By using the ISAM mask, the hexagonal periodic array of ZnO nanostructures with high uniformity were readily produced. Furthermore, the effect of the underlying substrates on the morphology of ZnO nanostructures has been investigated. It is found that the highly ordered and vertically aligned ZnO nanorods epitaxially grow on the GaN substrate, while the ZnO nanoflowers on Si substrates are random oriented.

Surface passivation and interface properties of bulk GaAs and epitaxial-GaAs/Ge using atomic layer deposited TiAlO alloy dielectric

High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices.

α-Fe2O3 nanotubes-reduced graphene oxide composites as synergistic electrochemical capacitor materials

We present a facile approach for the fabrication of a nanocomposite comprising α-Fe(2)O(3) nanotubes (NTs) anchored on reduced graphene oxide (rGO) for electrochemical capacitors (ECs). The hollow tubular structure of the α-Fe(2)O(3) NTs presents a high surface area for reaction, while the incorporation of rGO provides an efficient two-dimensional conductive pathway to allow fast, reversible redox reaction. As a result, the nanocomposite materials exhibit a specific capacitance which is remarkably higher (~7 times) than α-Fe(2)O(3) NTs alone. In addition, the nanocomposites show excellent cycling life and large negative potential window. These findings suggest that such nanocomposites are a promising candidate as negative electrodes in asymmetrical capacitors with neutral electrolytes.

Controllable growth of highly ordered ZnO nanorod arrays via inverted self-assembled monolayer template

This article presents a facile and effective approach to the controllable growth of highly ordered and vertically aligned ZnO nanorod arrays on the GaN substrate via a hydrothermal route by using the TiO(2) ring template deriving from the polystyrene microsphere self-assembled monolayer. The size of TiO(2) ring template can be flexibly tuned from 50 to 400 nm for the 500 nm polystyrene microspheres by varying the time of reactive ion etching and the concentration of TiO(2) sol. As a result, the diameter of the individual ZnO nanorods can be potentially tuned over a wide range. The combination of several characterization techniques has demonstrated that the ordered ZnO nanorods are highly uniform in diameter and height with perfect alignment and are epitaxially grown along [0001] direction. This work provides a novel and accessible route to prepare oriented and aligned ZnO nanorod arrays with high crystalline quality.

Low-rate sputter-deposited Fe3Si thin films on Si substrates: structural and ferromagnetic properties

Fe3Si thin films were sputter-deposited on Si(001) substrates. Structural investigations show that Fe3Si was deposited poly-crystalline with a Si-containing layer at the Fe3Si/Si interface. The formation of the layer was attributed to the influence of low deposition rates used in this study on the grain nucleation in Fe3Si. This layer helps to stabilize the ferromagnetic properties of the subsequent annealed films at 350 degrees C with 5 Oe obtained for coercive field H(c), approximately 920 emu/cm3 for saturation magnetization M(s) and approximately 0.9M(s) for remnant magnetization M(r).

[Cloning and function of sanJ--a gene involved in nikkomycins biosynthesis of Streptomyces ansochromogenes]

A 7.5 kb DNA fragment was identified from the cosmid library of Streptomyces ansochromogenesus using a partial DNA fragment involved in the nikkomycin biosynthesis as a probe. It was cloned into pBluescript M13- and the resulting recombinant plasmid was designated as pNL2200. The nucleotide sequence of 2.3 kb Sal I -BamH I DNA fragment was determined and analysed. The result indicated that the fragment contains one complete open reading frame (ORF); The start codon is GTG at 271 position and the stop codon is TGA at 1,954 position. It contains 1,686 base pairs and encodes a protein with 561 amino acids. The deduced product has 44% identity with the ligase belong to the superfamily of adenylate-forming enzyme. The experiment of gene disruption showed that the sanJ gene was closely related to nikkomycins biosynthesis of Streptomyces ansochromogenes. It was designated as sanJ.

[Effects of isoprenaline on apoptosis related gene expression in rat myocardium cells]

AIM

To study the relationship between acute myocardial ischemia rat induced by isoprenaline (Iso) and expression of some apoptosis related genes in myocardium.

METHODS

Acute myocardial ischemic rat model was induced by subcutaneous injection of large doses of Iso. The myocardial expression of apoptosis related genes, Fas, CPP32, Bcl-2 and Bax, were detected with RT-PCR method. The influences of aloperine (Alo, 20 mg.kg-1) and propranolol (Prop, 2 mg.kg-1) on apoptosis related genes were also investigated by the same method.

RESULTS

Myocardial expression of Fas, CPP32 and Bcl-2 were increased in acute myocardial ischemic rats, but no significance was detected in Bax expression. Both Alo and Prop were shown to decrease the expression of Fas and CPP32, and increase expression of Bcl-2. Prop also showed down regulated effect on expression of Bax.

CONCLUSION

Subcutaneous injection of large doses of Iso was shown to induce expressions of apoptosis related genes in rat myocardium, which were also influences by Alo and Prop.

[Progress on studies of nikkomycin structure and some genes related to nikkomycin biosynthesis]

Nikkomycin is a kind of new antifungal antibiotics. More than 20 biologically active nikkomycin structures have been isolated and the main active structures are nikkomycins X, Z, I, J. Here, we introduce the progress on the studies of nikkomycin structures, the relationships between nikkomycin structure and biological activity, and genes related to nikkomycin biosynthesis.

[Cloning and expression of human Cu/Zn superoxide dismutase gene in Lactococcus lactis]

The cDNA encoding human Cu/Zn SOD was amplified by RT-PCR using the total RNA of human liver as the template, and was cloned into an E. coli expression vector pET23b. After the DNA sequence was determined, the recombinant plasmid pET23bsod was introduced into E. coli BL21(DE3)/pLysS. SDS-PAGE analysis revealed that the recombinant E. coli expressed the predicted 19 kDa human Cu/Zn SOD, and its amount was over 50% of total proteins. The Cu/Zn SOD cDNA was then subcloned into a lactococcal expression vector pMG36e, and resulting pMG36esod was introduced into L. lactis MG1363 by electroporation. The human Cu/Zn-SOD was expressed up to 5% of the soluble proteins, and the enzymatic activity was also observed by SOD activity dying.