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961.
Yu-Yang Zhang Huixuan Chen Xiaoding Jiang Hao Liang Xuefeng He Yaqi Zhang Xiangmeng Chen Wenhuan He Yongsu Li Liqin Qiu 《Tetrahedron》2018,74(18):2245-2250
A Ni-catalyzed addition of arylboronic acids to isatins was first developed. The reaction, driven by Ni(acac)2 and dppp as the phosphine ligand, gave 3-aryl-3-hydroxy-2-oxindoles in up to 97% yield. Scopes of benzyl-protected isatins and arylboronic acids were examined. Substituted phenylboronic acids along with fused-ring and heterocyclic boronic acids reacted with isatins smoothly. Preliminary asymmetric catalysis was investigated as well, showing moderate enantioselectivity. The mechanism was also described. 相似文献
962.
Huicong Yang Prof. Lichang Yin Dr. Ji Liang Dr. Zhenhua Sun Yuzuo Wang Hucheng Li Kuang He Lipo Ma Prof. Zhangquan Peng Siyao Qiu Chenghua Sun Prof. Hui‐Ming Cheng Prof. Feng Li 《Angewandte Chemie (International ed. in English)》2018,57(7):1898-1902
The electrochemical performance of the aluminum‐sulfur (Al‐S) battery has very poor reversibility and a low charge/discharge current density owing to slow kinetic processes determined by an inevitable dissociation reaction from Al2Cl7? to free Al3+. Al2Cl6Br? was used instead of Al2Cl7? as the dissociation reaction reagent. A 15‐fold faster reaction rate of Al2Cl6Br? dissociation than that of Al2Cl7? was confirmed by density function theory calculations and the Arrhenius equation. This accelerated dissociation reaction was experimentally verified by the increase of exchange current density during Al electro‐deposition. Using Al2Cl6Br? instead of Al2Cl7?, a kinetically accelerated Al‐S battery has a sulfur utilization of more than 80 %, with at least four times the sulfur content and five times the current density than that of previous work. 相似文献
963.
Pyrrolidine enones, derived from 3-oxo pyrrolidine 2-phosphonates and a HWE reaction with aldehydes, on Luche reduction give pyrrolidine allylic alcohols. The alcohols on hydrogenation (Pd/H2) give cis-2,5-disubstituted pyrrolidines and on treatment with TFA-NaBH3CN undergo a hydroxy directed reduction to trans-2,5-disubstituted pyrrolidines. 相似文献
964.
Ultra-performance LC/TOF MS analysis of medicinal Panax herbs for metabolomic research 总被引:1,自引:0,他引:1
Xie G Plumb R Su M Xu Z Zhao A Qiu M Long X Liu Z Jia W 《Journal of separation science》2008,31(6-7):1015-1026
In this study, metabolite profiling of five medicinal Panax herbs including Panax ginseng (Chinese ginseng), Panax notoginseng (Sanchi), Panax japonicus (Rhizoma Panacis Majoris), Panax quinquefolium L. (American ginseng), and P. ginseng (Korean ginseng) were performed using ultra-performance LC-quadrupole TOF MS (UPLC-QTOFMS) and multivariate statistical analysis technique. Principal component analysis (PCA) of the analytical data showed that the five Panax herbs could be separated into five different groups of phytochemicals. The chemical markers such as ginsenoside Rf, 20(S)-pseudoginsenoside F11, malonyl gisenoside Rb1, and gisenoside Rb2 accountable for such variations were identified through the loadings plot of PCA, and were identified tentatively by the accurate mass of TOFMS and partially verified by the available reference standards. Results from this study indicate that the proposed method is reliable for the rapid analysis of a group of metabolites present in herbal medicines and other natural products and applicable in the differentiation of complex samples that share similar chemical ingredients. 相似文献
965.
Comprehensive 2-D GC (GC x GC) coupled with TOF MS or flame ionization detector (FID) was employed to characterize and quantify the chemical composition of volatile oil in the radixes of Panax ginseng C. A. Mey. (ginseng) at different ages. Thirty-six terpenoids were tentatively identified based on the MS library search and retention index in a ginseng sample at the age of 3 years. An obvious group-type separation was obtained in the GC x GC-TOF MS chromatogram. The data collected by GC x GC-FID were processed using a principal component analysis (PCA) method to classify the samples at different ages. The compounds responsible for the significant differentiation among samples were defined. It was found that the relative abundances of alpha-cadinol, alpha-bisabolol, thujopsene, and n-hexadecanoic acid significantly rise with the increase in age. 相似文献
966.
Three-phase hollow fiber-mediated liquid-phase microextraction followed by HPLC was used for the determination of three synthetic estrogens, namely diethylstilbestrol, dienestrol, and hexestrol, in wastewater. Extraction conditions including organic solvent, volume ratio between donor solution and acceptor phase, extraction time, stirring rate, donor phase and acceptor phase were optimized. The target compounds were extracted from a 10 mL aqueous sample at pH 1.5 (donor solution) through a 45 mm in length hollow polypropylene fiber that was immersed in 1-octanol in advance, and then the hollow fiber was filled with 10 microL 0.5 mol/L sodium hydroxide solution (acceptor phase). After a 40 min extraction, the acceptor phase was directly injected into an HPLC system for detection. Under the optimized extraction conditions, a large enrichment factor (more than 300-fold) was achieved for the three estrogens. The determination limit at an S/N of 3 ranged from 0.25 to 0.5 microg/L for the estrogens. The recovery ratio was more than 86% in the determination of these estrogens in wastewater. 相似文献
967.
A new self-assembling bolaamphiphilic peptide has been designed and synthesized using only natural amino acids. This simple peptide is composed of two lysines connected by 4-8 alanines to maintain the characteristics of the traditional bolaamphiphiles. Based on an irregular secondary structure, it can self-assemble into nanospheres, nanorods, or nanofibers with lengths up to micrometers. The long nanofibers can be broken into smaller fragments by sonication, however, they could reassemble into nanofibers after incubation. Furthermore, the nanostructures were shown to have considerable thermostability. This new bolaamphiphilic peptide differs from any other self-assembling peptides or bolaamphiphiles, and possibly provides a new approach to fabricate nanomaterials. 相似文献
968.
There is a natural tendency in science to prefer straightforward, logical classification systems. The use of mobile phase-stationary phase combinations that do not fit neatly into the standard "normal phase" or "reversed-phase" categories has been going on for over 50 years. The term "hydrophilic interaction chromatography" (HILIC) is sometimes being used as a general category for these "other" separations. In some cases, it may be appropriate and in others, not. Indeed the mechanistic constrains used to define the method seem to be varying with time. Given the name HILIC, it is assumed that water is not only present in the mobile phase, but also plays an essential role in the retention mechanism. However, there is residual water present in all organic solvents. Regardless, the number of reported separations in this alternative mode has increased tremendously in the last two decades. This is due to the advent of new stationary phases and an emphasis on polar, biologically important molecules. We discuss the relationships between HILIC and other chromatographic modes. We then examine two classes of stationary phases that have played a major role in these separations. These particular stationary phases can be used to provide appreciable mechanistic information as well. 相似文献
969.
Tao X Liu Y Wang Y Qiu Y Lin J Zhao A Su M Jia W 《Analytical and bioanalytical chemistry》2008,391(8):2881-2889
An optimized method based on GC-MS with ethyl chloroformate derivatization has been developed for the comprehensive analysis
of endogenous metabolites in serum. Twenty-two reference standards and serum samples were used to validate the proposed method.
The correlation coefficient was higher than 0.9900 for each of the standards, and the LOD varied from 125 to 300 pg on-column.
The analytical equipment exhibited good repeatability (RSD<10%) for all of the standards. Both the repeatability and the within-48-h
stability of the analytical method were satisfactory (RSD<10%) for the 18 metabolites identified in the serum samples. Mean
recovery was acceptable for the 18 metabolites, ranging from 70% to 120% with RSDs of less than 10%. Using the optimized protocol
and a subsequent multivariate statistical technique, complete differentiation was achieved between the metabolic profile of
uremic patients and that of age- and sex-matched normal subjects. Significantly decreased levels of valine, leucine, and isoleucine
and increased levels of myristic acid and linoleic acid were observed in the patient group. This work demonstrated that this
method is suitable for serum-based metabolic profiling studies. 相似文献
970.
Ionic liquids (ILs) are being increasingly studied in many different chemical application areas, particularly in green solvent applications that are extending into microemulsion applications. We summarize herein these initial microemulsion formulations and applications where ILs are used as oil substitutes, water substitutes, co-surfactants (additives), and surfactants. 相似文献