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991.
Some novel cycloaddition reactions based on benzyne and olefins have been developed.These reactions were performed in the absence of a transition metal catalyst,and they displayed good yields.These cycloaddition reactions of benzyne with olefins provide effective routes for synthesizing benzocyclobutenes,biaryl compounds and 9,10-dihydrophenanthrene derivatives. 相似文献
992.
Xiaojian Shi Yelian Miao Jie Yu Chen Jun Chen Wenli Li Xun He Jining Wang 《Applied biochemistry and biotechnology》2014,172(6):3042-3053
Freeze-tolerant baker’s yeasts are required for the processing of frozen doughs. The present study was carried out to investigate the cell survival rate after frozen storage and the change of fermentability in dough due to frozen storage, and to discuss quantitatively the relationship of freeze tolerance with intracellular trehalose, amino acids, and glycerol, using six types of baker’s yeasts as the test materials. The experimental results showed that the fermentability of yeast cells in frozen dough was strongly correlated with the cell survival rate. The baker’s yeast with a higher level of cell survival rate had a larger increase in the total intracellular compound content after frozen storage, and the cell survival rate increased linearly with increasing total intracellular compound content in frozen yeast cells. Trehalose was a primary compound affecting freeze tolerance, followed by glutamic acid, arginine, proline, asparagic acid, and glycerol. The basic information provided by the present study is useful for exploring the freeze-tolerance mechanisms of baker’s yeast cells, breeding better freeze-tolerant baker’s yeast strains, and developing more effective cryoprotectants. 相似文献
993.
Jian-Fen Zhang Bo Yang Weiqing Chen Jing Chen 《Applied biochemistry and biotechnology》2014,172(8):3913-3925
A soluble glucoside 3-dehydrogenase (G3DH) was purified from a newly isolated Sphingobacterium faecium ZJF-D6 CCTCC M 2013251. The enzyme was purified to 35.71-fold with a yield of 41.91 % and was estimated by sodium dodecyl sulphate–polyacrylamide gel electrophoresis with a molecular mass of 62 kDa. The sequences of two peptides of the enzyme were all contained in a GMC family oxidoreductase (EFK55866) by mass spectrometry analysis. The optimal pH of the enzyme was around 6.2. The enzyme was stable within a pH range of 5.0–6.6 and was sensitive to heat. G3DH from S. faecium exhibited extremely broad substrate specificity and well regioselectivity to validoxylamine A. The enzyme was completely inhibited by Hg2Cl2 and partly inhibited by Cu2+, Fe2+, Ca2+, and Cd2+. The apparent K m values for D-glucose, sucrose, and validoxylamine were calculated to be 1.1, 1.7, and 2.1 mM, respectively. With this purified enzyme, 3-keto sucrose was prepared at pH 5.0, 30 °C for 10 h with a yield of 28.7 %. 相似文献
994.
Junbo Li Wenlan Wu Chen Han Shijie Zhang Huiyun Zhou Jinwu Guo 《Colloid and polymer science》2014,292(7):1657-1664
Two distinctive block copolymers protected gold nanoparticles (AuNPs) were prepared with poly(methylacrylic acid)-block-poly(N-isopropylacrylamide) (SH-PMAA64-b-PNIPAM35) and poly (N-isopropylacrylamide)-block-poly(methylacrylic acid) (SH-PNIPAM40-b- PMAA60) through strong gold-sulfur bonding. The hybrid NPs have a pH-responsive inner shell (or corona) and a thermo-responsive corona (or inner shell) due to different location relations of the PNIPAM and PMAA on the surface of AuNPs. Then, the aggregation behaviors, as well as the changes of optical properties, of two hybrid NPs were compared in response to both stimuli. The results showed the obvious inter-particle aggregation caused by the phase transition for hydrophobic coronal polymer. However, the particles of hydrophilic corona layer retained good dispersion and the pH-responsive or thermo-responsive characteristics of shell layer made relatively minor changes. 相似文献
995.
Dielectric relaxation studies were conducted on the ternary systems of the nonionic surfactant Triton X-100 (a nonionic surfactant with a polyoxyethylene chain)/toluene/water in the frequency range from 40 Hz to 110 MHz. The contents of water and toluene were varied separately while the ratios of the other two components were fixed. Remarkable dielectric relaxations were observed around 1 MHz and dielectric intensity shows different variation with the increase of the contents of water or toluene. Dielectric parameters were obtained by fitting the data using the Cole–Cole equation with one dispersion term. The reverse micelles, water-in-oil, and oil-in-water micro-regions of the microemulsions were identified by the dependence of conductivity of the dispersed phase and continuous phase on the contents of water or toluene. Hanai theory and the corresponding analysis method were used to calculate the phase parameters of the constituent phases. The analysis results suggest that the dielectric relaxation probably arises from the interfacial polarization. 相似文献
996.
Qian Sun Xi-Ping Wang Qiao-Juan Yan Wei Chen Zheng-Qiang Jiang 《Applied biochemistry and biotechnology》2014,174(1):174-185
Purification and characterization of a chymosin from Rhizopus microsporus var. rhizopodiformis were investigated in the present study. A newly isolated R. microsporus var. rhizopodiformis F518 produced a high level of milk-clotting activity (1,001 SU/mL). A chymosin from the fungus was purified 3.66-fold with a recovery yield of 33.2 %. The enzyme appeared as a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with a molecular mass of 37.0 kDa. It was optimally active at 60 °C and was stable up to 40 °C. The purified enzyme was an acid protease with an optimum pH of 5.2 and retained 80 % of residual activity within pH 2.0–8.0. The inhibition of 96 and 100 % by pepstatin A at 0.01 and 0.02 mM, respectively, revealed that the enzyme is an aspartic protease. Thus, high milk-clotting activity of the chymosin with good stability will strengthen the potential use of the chymosin as a substitute for calf rennet in cheese manufacturing. 相似文献
997.
Kang-Chieh Lo Chiao-Yin Sun Yu-Ju Ding Jen-Ning Tsai Kai-Ping Chang Yi-En Wen Wan-Ling Chang Shin C. Chang Ming-Fu Chang Yun-Hsin Wang Yau-Hung Chen 《Research on Chemical Intermediates》2014,40(6):2177-2185
Benzo(a)pyrene is a chemical produced during the process of making fried, roasted, and smoked foods. It remains unclear whether benzo(a)pyrene affects the early development of human organs. In this study, we used the transgenic zebrafish line Tg(wt1b:GFP) as a model to assess benzo(a)pyrene-induced kidney malformation. By soaking zebrafish embryos in benzo(a)pyrene at various doses (2, 20, and 200 ppb), only a minor effect on the survival rate was detected (0 ppb: 97.8 ± 1.9 %; 2–200 ppb: 89.1 ± 5.8–91.5 ± 8.3 %). However, benzo(a)pyrene significantly affected the development of the kidney (malformation rates ranges from 50.0 ± 3.5 to 77.4 ± 5.3 %). Various abnormalities, such as unusual curving of pronephric tubes, swollen glomerulus, and incomplete development of pronephric ducts, were observed. This study provides a rapid and effective protocol for the evaluation of the notable effects of benzo(a)pyrene on embryonic kidney development. 相似文献
998.
Dr. Nan Chen Dr. Yuan Liu Yuanpei Li Prof. Dr. Chu Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(37):16203-16209
Protein 4′-phosphopantetheinylation is an essential post-translational modification (PTM) in prokaryotes and eukaryotes. So far, only five protein substrates of this specific PTM have been discovered in mammalian cells. These proteins are known to perform important functions, including fatty acid biosynthesis and folate metabolism, as well as β-alanine activation. To explore existing and new substrates of 4′-phosphopantetheinylation in mammalian proteomes, we designed and synthesized a series of new pantetheine analogue probes, enabling effective metabolic labelling of 4′-phosphopantetheinylated proteins in HepG2 cells. In combination with a quantitative chemical proteomic platform, we enriched and identified all the currently known 4′-phosphopantetheinylated proteins with high confidence, and unambiguously determined their exact sites of modification. More encouragingly, we discovered, using targeted chemical proteomics, a potential 4′-phosphopantetheinylation site in the protein of mitochondrial dehydrogenase/reductase SDR family member 2 (DHRS2). 相似文献
999.
Pan-Pan Chen Dr. Jeffrey I. Seeman Prof. Dr. Kendall N. Houk 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(30):12606-12619
Rolf Huisgen explored the Diels–Alder reactions of 1,3,5-cycloheptatriene (CHT) and cyclooctatetraene (COT) with the dienophiles maleic anhydride and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) to determine the kinetics and mechanisms of various electrocyclizations and Diels–Alder reactions. These reactions have been examined with density functional theory. Modern computational chemistry has provided information not previously available by experiment. Transition states for all the reactions have been identified, and their Gibbs energies are used to explain the experimental reactivities. Zwitterionic intermediates were not found in the [4+2] cycloadditions of both CHT or COT with PTAD and are thus not involved in these reactions. [2+2+2] cycloadditions, as an alternative path to the Diels–Alder products, are highly disfavored. Rapid double nitrogen inversion was found for the cycloaddition products with PTAD. 相似文献
1000.
Meng Zhao Dr. Hong-Jie Peng Bo-Quan Li Dr. Xiao Chen Jin Xie Dr. Xinyan Liu Prof. Qiang Zhang Prof. Jia-Qi Huang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9096-9102
In situ evolution of electrocatalysts is of paramount importance in defining catalytic reactions. Catalysts for aprotic electrochemistry such as lithium–sulfur (Li-S) batteries are the cornerstone to enhance intrinsically sluggish reaction kinetics but the true active phases are often controversial. Herein, we reveal the electrochemical phase evolution of metal-based pre-catalysts (Co4N) in working Li-S batteries that renders highly active electrocatalysts (CoSx). Electrochemical cycling induces the transformation from single-crystalline Co4N to polycrystalline CoSx that are rich in active sites. This transformation propels all-phase polysulfide-involving reactions. Consequently, Co4N enables stable operation of high-rate (10 C, 16.7 mA cm−2) and electrolyte-starved (4.7 μL mgS−1) Li-S batteries. The general concept of electrochemically induced sulfurization is verified by thermodynamic energetics for most of low-valence metal compounds. 相似文献