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981.
Yufang Hu Zhaohui Zhang Huabin Zhang Lijuan Luo Minglei Zhang Xiao Yang Shouzhuo Yao 《中国化学》2012,30(2):377-385
A novel sensor for detection of trace gallium ion [Ga(III)] was created by stepwise modification of a gold electrode with β‐cyclodextrin (β‐CD)/multi‐walled carbon nanotubes (MWCNTs) and an ion imprinted polymer (IIP). The sensor surface morphology was characterized by scanning electron microscopy. The electrochemical performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The sensor displayed excellent selectivity towards the target Ga(III) ion. Meanwhile, the introduced MWCNTs displayed noticeable catalytic activity, and β‐CD demonstrated significant enrichment capacity. A linear calibration curve was obtained covering the concentration range from 5.0×10?8 to 1.0×10?4 mol·L?1, with a detection limit of 7.6×10?9 mol·L?1. The proposed sensor was successfully applied to detect Ga(III) in real urine samples. 相似文献
982.
Dr. Michal Lejkowski Prof. Dr. Prabal Banerjee Dipl.‐Chem. Sabine Schüller Dipl.‐Chem. Alexander Münch Dr. Jan Runsink Cornelia Vermeeren Prof. Dr. Hans‐Joachim Gais 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(12):3529-3548
An asymmetric synthesis of densely functionalized 7–11‐membered carbocycles and 9–11‐membered lactones has been developed. Its key steps are a modular assembly of sulfoximine‐substituted C‐ and O‐tethered trienes and C‐tethered dienynes and their Ru‐catalyzed ring‐closing diene and enyne metathesis (RCDEM and RCEYM). The synthesis of the C‐tethered trienes and dienynes includes the following steps: 1) hydroxyalkylation of enantiomerically pure titanated allylic sulfoximines with unsaturated aldehydes, 2) α‐lithiation of alkenylsulfoximines, 3) alkylation, hydroxy‐alkylation, formylation, and acylation of α‐lithioalkenylsulfoximines, and 4) addition of Grignard reagents to α‐formyl(acyl)alkenylsulfoximines. The sulfoximine group provided for high asymmetric induction in steps 1) and 4). RCDEM of the sulfoximine‐substituted trienes with the second‐generation Ru catalyst stereoselectively afforded the corresponding functionalized 7–11‐membered carbocyles. RCDEM of diastereomeric silyloxy‐substituted 1,6,12‐trienes revealed an interesting difference in reactivity. While the (R)‐diastereomer gave the 11‐membered carbocyle, the (S)‐diastereomer delivered in a cascade of cross metathesis and RCDEM 22‐membered macrocycles. RCDEM of cyclic trienes furnished bicyclic carbocycles with a bicyclo[7.4.0]tridecane and bicyclo[9.4.0]pentadecane skeleton. Selective transformations of the sulfoximine‐ and bissilyloxy‐substituted carbocycles were performed including deprotection, cross‐coupling reaction and reduction of the sulfoximine moiety. Esterification of a sulfoximine‐substituted homoallylic alcohol with unsaturated carboxylic acids gave the O‐tethered trienes, RCDEM of which yielded the sulfoximine‐substituted 9–11‐membered lactones. RCEYM of a sulfoximine‐substituted 1,7‐dien‐10‐yne showed an unprecedented dichotomy in ring formation depending on the Ru catalyst. While the second‐generation Ru catalyst gave the 9‐membered exo 1,3‐dienyl carbocycle, the first‐generation Ru catalyst furnished a truncated 9‐membered 1,3‐dieny carbocycle having one CH2 unit less than the dienyne. 相似文献
983.
Chongnan Zhang Haijun Yang Guangying Lü Cailin Liu Yun Tang Laibao Liu 《Helvetica chimica acta》2012,95(6):1026-1032
The novel 8,14‐secoursatriene derivative 6 was synthesized starting from ursolic acid ( 1 ) via methyl esterification of the 17‐carboxylic acid group and benzoylation of the 3‐hydroxy group (→ 2 ; Scheme 1), ozone oxidation of the C(12)?C(13) bond (→ 3 ), dehydrogenation with Br2/HBr (→ 4 ), enol acetylation of the resulting carbonyl group (→ 5 ; Scheme 2), and ring‐C opening with the aid of UV light (→ 6 ). Ring‐C‐opened dienone derivative 7 of ursolic acid was also obtained via selective hydrolysis of 6 (Scheme 2). Both compounds 6 and 7 are key intermediates for the preparation of chiral decalin synthons from ursolic acid. 相似文献
984.
Several 2‐alkylquinolizinium‐1‐olates 9 , i.e., heterobetaines, were prepared from ketone 11 , the latter being readily available either from pyridine‐2‐carbaldehyde via a Grignard reaction, followed by oxidation with MnO2, or from 2‐picolinic acid (=pyridine‐2‐carboxylic acid) via the corresponding Weinreb amide and subsequent Grignard reaction. Mesoionic heterobetaines such as quinolizinium derivatives have the potential to undergo cycloaddition reactions with double and triple bonds, e.g., 1,3‐dipolar cycloadditions or Diels? Alder reactions. We here report on the scope and limitations of cycloaddition reactions of 2‐alkylquinolizinium‐1‐olates 9 with electron‐poor acetylene derivatives. As main products of the reaction, 5‐oxopyrrolo[2,1,5‐de]quinolizines (=‘[2.3.3]cyclazin‐5‐ones’) 19 were formed via a regioselective [2+3] cycloaddition, and cyclohexadienone derivatives, formed via a Diels? Alder reaction, were obtained as side products. The structures of 2‐benzylquinolizinium‐1‐olate ( 9a ) and two ‘[2.3.3]cyclazin‐5‐ones’ 19i and 19l were established by X‐ray crystallography. 相似文献
985.
Dr. Kerim Samedov Dr. Yilmaz Aksu Prof. Dr. Matthias Driess 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(25):7766-7779
The syntheses and structural elucidation of dimeric [Sn(OCyHex)2] ( 1 ), its corresponding (cyclohexoxy)alkalistannates(II) [{M(OCyHex)3Sn}2] (M=Li ( 2 ), Na ( 3 ), K ( 4 )), and of the first heteroleptic heterotermetallic Li/In/Sn–haloalkoxide clusters [X2In{LiSn2(OCyHex)6}] (X=Br ( 5 ), Cl ( 6 )) with a double seco‐norcubane core are reported. They represent suitable precursors for new amorphous indium tin oxide (ITO) materials as transparent conducting oxides with drastically reduced concentrations of expensive indium, while maintaining their high electrical performance. In fact, compounds 5 and 6 were successfully degraded under dry synthetic air at relatively low temperature, resulting in new semiconducting tin‐rich ITOs homogeneously dispersed in a tin oxide/lithium oxide matrix. The obtained particles were investigated and characterised by different analytical techniques, such as powder XRD, IR spectroscopy, SEM, TEM and energy‐dispersive X‐ray spectroscopy (EDX). The analytical data confirm that the final materials consist of tin‐containing indium oxide embedded in an amorphous tin oxide matrix. The typical broadening and shift of the observed indium oxide reflections to higher 2θ values in the powder XRD pattern clearly indicated that tin centres were successfully incorporated into the In2O3 lattice and partially occupied In3+ sites. Investigations by EDX mapping proved that Sn was homogeneously distributed in the final materials. Thin‐film field‐effect transistors (FETs) were fabricated by spin‐coating of silicon wafers with solutions of 5 in toluene and subsequent calcination under dry air (25–700 °C). The FETs prepared with precursor 5 exhibited excellent performances, as shown by a charge‐carrier mobility of 6.36×10?1 cm2 V?1 s (calcination at 250 °C) and an on/off current ratio of 106. 相似文献
986.
Prof. Dr. Toshiaki Mori Takayuki Kodera Hiroshi Yoshimine Prof. Dr. Yoshimitsu Kakuta Prof. Dr. Nobuo Sugiura Prof. Dr. Koji Kimata Prof. Dr. Yoshio Okahata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(24):7388-7393
Using a highly sensitive flow‐type 27 MHz quartz crystal microbalance, we could detect a small mass change during stepwise and alternating one‐sugar transfer of glucuronic acid (GlcA) and N‐acetylgalactosamine (GalNAc) to an acceptor, catalyzed by chondroitin polymerase from Escherichia coli strain K4 (K4CP), and analyze the elongation mechanism of K4CP. K4CP was found to bind strongly to a chondroitin acceptor (Kd=0.97 μM ). Although the binding affinity and the catalytic rate constant for each monomer were considerably different, the apparent catalytic efficiency (kcat/Km) was similar (6.3×104 M ?1 s?1 for GlcA transfer and 3.4×104 M ?1 s?1 for the GalNAc transfer). This is reasonable for the smooth alternating elongation of GlcA and GalNAc on the acceptor. This is the first study to report the determination of kinetic parameters for enzymatic, alternated, sugar elongation. 相似文献
987.
Jia‐Qi Li Xu Quan Prof. Dr. Pher G. Andersson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10609-10616
α,β‐Unsaturated esters have been employed as substrates in iridium‐catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic‐ and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. 相似文献
988.
Gideon Fraenkel Albert Chow Yulan Liang Jinhua Song Judith Gallucci 《Helvetica chimica acta》2012,95(11):2063-2071
In a one‐pot process without isolation of intermediates, (but‐3‐en‐1‐yl)pyridine ( 13 ) is treated sequentially with dicyclohexylborane, trimethylaluminium, and ethyl carbonochloridate yielding ethyl 1,4‐dihydro‐4,4‐(tetramethylene)pyridine‐1‐carboxylate (=ethyl 8‐azaspiro[4.5]deca‐6,9‐diene‐8‐carboxylate; 2 ) in 46% yield based on starting alkenylpyridine 13 (Scheme 5). 相似文献
989.
A new strategy was explored to generate pure gold cluster ions, Aun+/?, from gold films deposited on solid substrates via a matrix‐assisted laser ablation technique. The gold films deposited on SiO2‐particle‐assembled photonic crystals were demonstrated to be the most ideal compared with the films deposited on various glass slides. Dropped with a matrix of 2‐(4‐hydroxyphenylazo) benzoic acid and bombarded by nitrogen pulse laser (355 nm), they could release a series of Aun+ with n more than 110 or Aun? with n more than 60 according to the data obtained by inline time‐of‐flight mass spectrometry. The gold‐deposited photonic crystal substrates could be stored at room temperature for at least 6 months. The method is hence steady and convenient in use. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
990.
An accurate and fast method for simultaneous determination of small organic acids and much larger humic acids was developed using high performance size exclusion chromatography. Two small organic acids, i.e. salicylic acid and 2,3‐dihydroxybenzoic acid, and one purified humic acid material were used in this study. Under the experimental conditions, the UV peaks of salicylic acid and 2,3‐dihydroxybenzoic acid were well separated from the peaks of humic acid in the chromatogram. Concentrations of the two small organic acids could be accurately determined from their peak areas. The concentration of humic acid in the mixture could then be derived from mass balance calculations. The measured results agreed well with the nominal concentrations. The detection limits are 0.05 mg/L and 0.01 mg/L for salicylic acid and 2,3‐dihydroxybenzoic acid, respectively. Applicability of the method to natural samples was tested using groundwater, glacier, and river water samples (both original and spiked with salicylic acid and 2,3‐dihydroxybenzoic acid) with a total organic carbon concentration ranging from 2.1 to 179.5 mg C/L. The results obtained are promising, especially for groundwater samples and river water samples with a total organic carbon concentration below 9 mg C/L. 相似文献