Streamlined access to 2,3-dihydropyrazino[1,2-a]indole-1,4-diones via Ugi reaction followed by microwave-assisted cyclization

An efficient method is developed to construct drug-like 2,3-dihydropyrazino[1,2-a]indole-1,4-diones from 1H-indole-2-carboxylic acids, ethyl pyruvate, isocyanides, and primary amines via a one-pot, two-step procedure involving Ugi reaction and microwave-assisted cyclization.     

NaCl-MgCl_2-H_2O体系低温拉曼光谱研究

通过在低温下进行大量的最优生成条件的实验探索,得到了NaCl-H2O体系和MgCl2-H2O体系水合物生成的最优实验条件——迅速降温至-180℃然后缓慢升温至观察到水合物生成过程结束(即视野突然变暗),最后快速降温至-180℃。对NaCl-MgCl2-H2O体系进行了定性和半定量尝试,并得到结论:3 537cm-1可以指示NaCl的存在,3 514 cm-1可以指示MgCl2的存在;3 537和3 514 cm-1峰的相对高低可以大致判断出NaCl和MgCl2的相对多少。这一发现为天然包裹体液相成分拉曼光谱原位定性、定量分析奠定了良好的基础。对于历史上亚稳低共熔混合物形成过程的模式的争议,实验结果初步赞同了Samson等的观点,即冰在最初的冷却中形成,在冰之间的空隙中剩余过饱和的盐溶液,再次升温时,盐的水合物从这个液体中结晶出来。     

Kinetics Studies on a Multicomponent Knoevenagel−Michael Domino Reaction by an Automated Flow Reactor

The optimization of complex chemical reaction systems is often a troublesome and time-consuming process. The application of modern technologies, including automated reactors and analytics, opens the avenue for generating large data sets on chemical reaction processes in a short period of time. In this work, an automated flow reactor is used to present detailed kinetics and mechanistic studies about an amine-catalyzed Knoevenagel−Michael domino reaction to yield tetrahydrochromene derivatives. High-performance monoliths as catalyst supports and online coupled HPLC analysis allow for time-efficient data generation. We show that the two-step multicomponent domino reaction does not follow the kinetics of consecutive reaction steps proceeding independently from each other. Instead, the starting materials of both individual reactions compete for the active sites on the heterogeneous catalyst, which lowers the rate constants of both steps. This knowledge was used to implement a more efficient experimental setup which increased the turnover numbers of the catalyst, without adjusting common reaction parameters like temperature, reaction time, and concentrations.     

Identifiability of causal effects on a binary outcome within principal strata

Principal strata are defined by the potential values of a post-treatment variable, and a principal effect is a causal effect within a principal stratum. Identifying the principal effect within every principal stratum is quite challenging. In this paper, we propose an approach for identifying principal effects on a binary outcome via a pre-treatment covariate. We prove the identifiability with single post-treatment intervention under the monotonicity assumption. Furthermore, we discuss the local identifiability with multicomponent intervention. Simulations are performed to evaluate our approach. We also apply it to a real data set from the Improving Mood-Promoting Access to Collaborate Treatment program.     

同步荧光分析法的应用及其新进展

同步荧光技术是解决多组分荧光物质同时测定的良好手段之一.本文从恒波长同步荧光法、恒能量同步荧光法、可变角同步荧光法、恒基体同步荧光法以及它们与导数技术、低温技术、化学计量学方法的联用等方面对同步荧光技术领域出现的新技术及应用作一评述.     

Proposal for Fourier-Transform Phase-Modulation Fluorometer

I propose a concept of a novel Fourier-transform phase-modulation fluorometer by which a fluorescence decay waveform can be obtained. In the fluorometer, the modulation frequency of the excitation light source is swept continuously from a start frequency f_min to an end frequency f_max with a time duration T. The resultant fluorescence signal waveform is Fourier-transformed to obtain amplitude and phase spectra. The ratio of the amplitude spectrum and the difference of the phase spectrum over those of the reference spectra that are obtained from a non-fluorescent material are calculated, respectively, and the pair of both spectral data is inverse-Fourier-transformed again to obtain the fluorescence decay waveform. To verify and demonstrate the effectiveness of the concept, I carried out (1) numerical simulations, (2) determination of a time constant of a passive resistor-capacitor (RC) differential circuit, and (3) measurement of a fluorescent decay waveform of YAG materials packed in Nichia’s white LED.     

多组分颗粒稠密气固两相流动的数值模拟

基于气体分子运动理论和颗粒动理学方法，建立多组分颗粒气固两相流等温流动模型。模型考虑了颗粒相各组分颗粒温度的差异、气相与颗粒相以及颗粒相各组分之间的动量和能量的传递和耗散，以及相间作用。建立颗粒相粘性系数、颗粒相压力等物性参数计算模型。模拟计算颗粒相浓度、粒径分布等参数与实测值相吻合。     

Micelle-stabilized liquid room-temperature phosphorimetry for metals: The micellar reaction of gallium with 7-iodo-hydroxyquinoline-5-sulfonic acid and its application to the metal determination

The Ga(III)-7-iodo-8-hydroxyquinoline-5-sulfonic acid complex in the presence of suitable micelles and with sodium sulfite as oxygen scavenger exhibited strong phosphorescence at room temperature in aqueous solutions. This micellar reaction provides the basis for a convenient phosphorimetric determination of traces of gallium. Different types of micelles showed their maximum enhancing effects at different pH ranges, affording greater convenience for various analytical purposes. A phosphorimetric procedure with surfactant cetyltrimethylammonium bromide as enhancing agent is proposed. The detection limit for gallium was 5 ng/ml and the calibration graph was rectilinear in the range of 5 to 600 ng/ml. The relative standard deviation was 4% at 50 ng/ml level. The applicability of this room-temperature phosphorimetric procedure to multi-component analyses for the group III elements, Al(III), Ga(III), and In(III), was demonstrated. Kalman filtering was used to deconvolute the phosphorescence spectra of mixtures of aluminium and gallium allowing the simultaneous determination of both metals with satisfactory results.     

Direct and Simultaneous Determination of Phenol, Hydroquinone and Nitrophenol at Boron-Doped Diamond Film Electrode

The electrochemical characteristics of multi-component phenolic pollutants, such as phenol （Ph）, hydroquinone （HQ） and 4-nitrophenol （4-NP）, were investigated on boron-doped diamond （BDD） film electrode by differential pulse voltammetry （DPV） technique. A simple and feasible platform was accordingly established for the direct and simultaneous determination of these three phenolic pollutants. Results showed that, Ph, HQ and 4-NP gave obvious oxidation peaks on BDD electrode at the potential of 1.24, 0.76 and 1.52 V, respectively. Each of them displayed good linear relationship between their oxidation peak currents and their corresponding concentrations in a rather wide range coexisting with one or two of the other phenolic pollutants. The detection limits of Ph, HQ and 4-NP were estimated to be as low as 1.82×10^-6, 1.67×10^-6 and 1.44×10^-6 mol·L^-1, respectively. Therefore, a promising direct and simultaneous electrochemical determination method of multi-component phenolic pollutants in wastewater samples was constructed successfully on BDD electrode with advantages being rapid, simple, convenient, sensitive, in situ and inexpensive.     

Efficient synthesis of 3-cyano-6-(2-hydroxyphenyl)pyridines by multi-component condensations on beads

An efficient procedure to perform pyridine ring closure reactions has been developed on beads. A certain number of hydroxyacetophenones were immobilized on Wang resin and condensed with a variety of aldehydes and malononitrile in the presence of ammonium acetate to give 3-cyano-6-(2-hydroxyphenyl)pyridines in a suitable manner for a good example of combinatorial approaches. Chemical yields were better than the corresponding solution-phase chemistry except only a few examples and the best use of inherent advantage of solid-phase chemistry was successfully demonstrated.