Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane induced by N-heterocyclic carbene and thiourea

Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane catalyzed by thiazolium A has been developed. The reaction rate and efficiency are profoundly impacted by the presence of thiourea B. The reaction affords moderate to good yields of the Stetter product. Some factors influencing yield were discussed.     

美国NGSS科学与工程实践构架与化学教学案例——影响化学反应速率的因素

美国《新一代科学标准》（NGSS）强调科学实践的重要性并提出科学与工程实践的关键要素，不仅为科学实践的具体实施提供了方向而且使科学实践的评价标准更加明确。在介绍NGSS科学与工程实践的构架基础上，以“影响化学反应速率的因素”为例分析了科学与工程实践的关键要素在教学中的反映及实施特点，并基于案例分析提出对我国中学化学教学过程设计的借鉴与启示。     

Heterogenized peroxopolyoxotungstate catalyst on the surface of clicked magnetite‐graphene oxide nanocomposite: Magnetically recoverable epoxidation catalyst

A new heterogeneous catalyst for the epoxidation of olefins was prepared by immobilization of peroxophosphotungstate anions on the surface of clicked magnetite‐graphene oxide as magnetically recoverable support. To prepare the heterogeneous catalyst, the clicked magnetite‐graphene oxide support was prepared by thiolene click reaction of thiol functionalized graphene oxide with vinyl modified magnetite nanoparticles. The tailored support was then modified with aminopropyl groups followed by electrostatic interaction with peroxophosphotungstate anions to achieve the desired heterogeneous catalyst. Characterization of the catalyst was performed by various physicochemical methods which confirmed the successful immobilization of peroxopolyoxotungstate species on the surface of clicked magnetite‐graphene oxide. Catalytic activity of the catalyst revealed its high catalytic activity and selectivity in the epoxidation of various olefins in the presence of H₂O₂ as green oxidant. This heterogeneous catalyst can be magnetically reused several times without significant loss of activity and selectivity.     

Arylhydrazones Derivatives Containing a Benzothiazole Moiety,Efficient Ligands in the Palladium‐Catalyzed Mizoroki–Heck and Suzuki–Miyaura Cross‐coupling Reactions under IR Irradiation

A simple arylhydrazone containing the benzothiazole moiety which may be used as an efficient ligand in the palladium‐catalyzed Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions, under infrared irradiation as an alternative source of energy, is presented. The reactions proceeded with extremely high efficiency under mild conditions and produced very good yields.     

Simultaneous quantification of ten Amadori compounds in tobacco using liquid chromatography with tandem mass spectrometry

Amadori compounds are aroma precursors formed in the initial phase of the Maillard reaction. Based on their similar structures, simultaneous quantification of more than six Amadori compounds in tobacco has not been reported yet. In this study, a simple and rapid method was developed to simultaneously quantify ten Amadori compounds including the isomers of Fructose‐isoleucine and Fructose‐leucine in tobacco. The separation was performed on an Atlantis T₃ column (2.1 × 250 mm, 5 μm) by gradient elution using acetonitrile and water as the mobile phases. The quantification method was systematically evaluated and proven to be sensitive and accurate. The linearity was good, with correlation coefficients of 0.9977–0.9999. The limits of detection and quantitation were 1.354–2.532 and 4.516–8.444 ng/mL, respectively. The recoveries were 84.0–119.6%, and the relative standard deviations were 1.33–5.40%. The method was used to analyze the changes in the amounts of ten Amadori compounds in tobacco before and after tobacco primary processing. The analysis shows that the Maillard reaction occurs during the short processing period.     

Effect of deuteron density distribution on the deduction of screening potential from the D(d,p)T reaction in Be metals

The D(d,p)T reaction in Be metal environments has been measured to investigate the electron screening effect in metals in an energy region of from 5.5 keV to 10 keV in a center of mass system(CMS)at a temperature of 121 K.The depth distribution of deuteron density in Be metals has an impact on the observed reaction yields.A model of deuteron density distribution in metal has been proposed to obtain the original yields.A screening energy of(116±46)eV has been obtained with the assumed deuteron density distribution model.     

Aza-Michael reaction: selective mono- versus bis-addition under environmentally-friendly conditions

Aza-Michael reactions between primary amines and methyl propenoate have been investigated under environmentally-friendly solventless heterogeneous catalysis in order to obtain the mono- or the bis-adduct. The reaction conditions can be altered so as to maximise the yields of the required product with high selectivity.     

In vivo lifetimes of the three color-sectors in bioluminescence emissions of the firefly Luciola praeusta at different temperatures

Bioluminescence emissions from fireflies have been well-studied for over a century. From the apparent features of the emitted light, conclusions have been drawn and hypotheses put forward on the characteristics of the highly efficient light emitting system. The basic emitter oxyluciferin, being chemically unstable, is difficult to study in isolation and, therefore, its analogs have been prepared and analyzed. In this letter, the lifetimes of the excited-state emitter oxyluciferin are measured, and an inference is drawn on the chemiluminescence reaction in vivo. The light from the Indian species of firefly Luciola praeusta contains three color-sectors: green, yellow, and red, and hence three optical filters are used to study time-resolved emissions from these sectors at different temperatures. All the three color-sectors are observed to be temperature sensitive in the time domain. An exponential variation of lifetime with temperature is observed for the emissions in these three regions.