Functionalization of the benzobicyclo[3.2.1]octadiene skeleton via photocatalytic and thermal oxygenation of a furan derivative

A simple and efficient protocol is utilized for the synthesis of novel functionalized benzobicyclo[3.2.1]octadiene derivatives by photocatalytic oxygenation of a furan derivative using an anionic free-base porphyrin as well as cationic and anionic manganese(III) porphyrins under different reaction conditions. The course and yields of these reactions were compared to those of the thermal reaction using m-chloroperbenzoic acid as the oxidizing agent. The deviating reaction pathways with anionic and cationic metalloporphyrins may be attributed to simultaneous electronic and steric effects. Application of free-base and metalated water-soluble porphyrins for photocatalytic oxygenation of the furan ring fused to the rigid methano-bridged skeleton proved to be regioselective and flexible compared to the thermal reactions with mCPBA, giving at the same time novel potentially biologically active bicyclo[3.2.1]octenes with the basic skeleton of which is incorporated in many natural compounds.     

Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn²⁺ or Cd²⁺ is a worldwide concern. Developing an inexpensive and facile detection method for Zn²⁺ and Cd²⁺ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn²⁺ and Cd²⁺ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S²⁻). The presence of Zn²⁺ (or Cd²⁺) can “turn-on” the weak fluorescence of QDs quenched by S²⁻ due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn²⁺ (or Cd²⁺) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd²⁺). The limit of detection (LOD) for Zn²⁺ and Cd²⁺ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn²⁺ and Cd²⁺ over other metal ions and was successfully used in the detection of Zn²⁺ or Cd²⁺ in real water samples.     

GC-MS法测定发酵食品中氨基甲酸乙酯的含量

建立了发酵食品中氨基甲酸乙酯的GC-MS测定方法.样品经饱和NaCl溶液溶解,超声提取,提取液经硅藻土固相萃取小柱净化,二氯甲烷洗脱,以氨基甲酸丁酯作为内标物,使用GC-MS联用仪选择离子监测模式对其定性定量测量.氨基甲酸乙酯在21 ～ 846ng/mL范围内线性关系良好,相关系数r=0.9999.最低检出限为5.0n...     

Preparation and characterization of Bi0.75Er0.25O1.5 and Bi0.75Er0.125Y0.125O1.5 nanocrystalline ceramics by SPS

Nanopowders of Bi_0.75Er_0.25O_1.5 and Bi_0.75Er_0.125Y_0.125O_1.5 were prepared by a reverse titration chemical coprecipitation method under controlled pH conditions. After calcination at 500 °C for 3 h, powders with grain size in the order of 10 nm were obtained. In order to keep the nanosize of grains, these powders were densified by spark plasma sintering. Samples with relative density higher than 96% were prepared in only 10 min up to 500 °C with an average grain size of 15 and 11 nm for Bi_0.75Er_0.25O_1.5 and Bi_0.75Er_0.125Y_0.125O_1.5, respectively. Impedance spectroscopy revealed slightly higher conductivity for the Bi_0.75Er_0.125Y_0.125O_1.5 composition compared to Bi_0.75Er_0.25O_1.5 nanoceramic, but performances remained lower than the corresponding Bi_0.75Er_0.25O_1.5 microcrystalline sample. However, mechanical properties of both nanocrystalline ceramics are improved when compared to microcrystalline samples.     

Preparation,characterization and catalytic applications of ZrO<Subscript>2</Subscript> supported on low cost SBA-15

This work presents some applications of ZrO₂ supported over SBA-15 silica as promoter of sulfated zirconia and as support from CuO/CeO₂ catalytic system for preferential oxidation of CO to CO₂ in hydrogen rich streams, used as feed for proton exchange membrane fuel cells (PEMFC). Different amounts of ZrO₂, from 10 to 30 wt.% were incorporated. These prepared materials were characterized by powder XRD, adsorption-desorption of N₂ at 77 K, transmission and scanning electron microscopy (TEM and SEM) and X-rays photoelectron spectroscopy (XPS). The acidity was studied by thermo-programmed desorption of ammonia (NH₃-TPD). These materials were tested, after treatment with H₂SO₄, by 2-propanol dehydration and 1-butene isomerization catalytic tests. The samples were found quite good catalyst with strong acid sites, the sample with 20 wt.% of ZrO₂ being the better performing sample. Finally this material was successfully used as support for a CuO/CeO₂ system, with 6 wt.% of Cu and 20 wt.% of Ce. The resulting catalyst was tested in the preferential oxidation of CO (CO-PROX) attaining conversions close to 100% and high selectivity to CO₂.     

Gas-Phase Alkylation of Pyridine and Phenol with Alcohols Over Halide Clusters of Group 5–7 Transition Metals as Solid Acid Catalysts

Pyridine is allowed to react with methanol under a hydrogen stream in the presence of (H₃O)₂[(W₆Cl₈)Cl₆]·6H₂O supported on silica gel. When the temperature is raised above 200 °C, the catalytic activity of the cluster appears. Methylation of pyridine proceeds yielding 2-methylpyridine in 61% selectivity at 400 °C. The corresponding hexanuclear chloride clusters of niobium, molybdenum, and tantalum also catalyze the reaction. Ethanol affords the corresponding 2-ethylpyridine. When phenol is allowed to react with methanol in the presence of (H₃O)₂[(Mo₆Cl₈)Cl₆]·6H₂O supported on silica gel in the same manner, selective O-methylation proceeds yielding anisole in 57% selectivity at 150–200 °C. Above 250 °C, C-methylation predominates and provides o-cresol with 67% selectivity at 300 °C. The corresponding clusters of niobium, tantalum, and tungsten also catalyze the reaction. Ethanol and 1-propanol afford the corresponding 2-alkylphenols. Alkyl cations produced over weak Brønsted acid sites (H ₀ ≈ +1.3) developed on the clusters are assumed as intermediates for both reactions.     

Pd-catalyzed ligand-free C(5)–H arylation of 1,4-disubstituted 1,2,3-triazoles promoted by microwaves

Pd(OAc)₂-catalyzed regioselective C(5)–H arylation of 1,4-disubstituted 1,2,3-triazoles was achieved without ligand under microwave conditions in 1?h, generating 1,4,5-trisubstituted 1,2,3-triazoles with good to excellent yields. The obtained molecules can be easily converted into 4,5-disubstituted 1,2,3-triazoles through the debenzylation process with one-pot manipulation.     

Preparation and methane adsorption of two-dimensional carbide Ti<Subscript>2</Subscript>C

Here a novel material for methane adsorption was synthesized and studied, which is a graphene-like two-dimensional (2D) carbide (Ti₂C, a member of MXenes), formed by exfoliating Ti₂AlC powders in a solution of lithium fluoride (LiF) and hydrochloric acid (HCl) at 40 °C for 48 h. Based on first-principles calculation, theoretically perfect Ti₂C with O termination has a specific surface area (SSA) of 671 m² g^?1 and methane storage capacity is 22.9 wt%. Experimentally, 2.85 % exfoliated Ti₂C with mesopores shown methane capacity of 11.58 cm³ (STP: 0 °C, 1 bar) g^?1 (0.82 wt%) under 5 MPa and the SSA was 19.1 m² g^?1. For Ti₂C sample intercalated with NH₃·H₂O, the adsorbed amount was increased to 16.81 cm³ (STP) g^?1 at same temperature. At the temperature of 323 K, the adsorbed amount of as-prepared Ti₂C was increased to 52.76 cm³ (STP) g^?1. For fully exfoliated Ti₂C, the methane capacity was supposed to be 28.8 wt% or 1148 V (STP)v^?1. Ti₂C theoretically has much larger volume methane capacity than current methane storage materials, though its SSA is not very high.     

Peroxy radicals as motional probes at the end of isolated polystyrene chains and on the cellulose surfaces in vacuum

The isolated polystyrene chains spin-labeled with peroxide radical at the free end (IPSOO) in which the chain roots were covalently bonded to the surface of microcrystalline cellulose (MCC) powder were produced by mechanochemical polymerization of styrene initiated by MCC mechanoradicals. The IPSOO was used as motional probes at the ends of isolated polystyrene chains tethered on the surface of MCC powder. Two modes for the molecular motion of IPSOO were observed. One was a tumbling motion of IPSOO on the MCC surface, defined as a train state, and another was a free rotational motion of IPSOO protruding out from the MCC surface, defined as a tail state. The temperature of tumbling motion (T _tum ) of IPSOO at the train state was at 90 K with anisotropic correlation times. T _tum (90 K) is extremely low compared to the glass transition temperature (T _g ^b ; 373 K) of polystyrene in the bulk. At temperatures above 219 K, the IPSOO was protruded out from the MCC surface, and freely rotated at the tail state. The train–tail transition temperature (T _train–tail ) was estimated to be 222 K. T _tum (90 K) and T _train–tail (222 K) are due to the extremely low chain segmental density of IPSOO on the MCC surface under vacuum. The interaction between IPSOO and the MCC surface is a minor contributing factor in the mobility of IPSOO on the surface under vacuum. It was found that peroxy radicals are useful probes to characterize the chain mobility reflecting their environmental conditions.