固相萃取-高效液相色谱/串联质谱法测定食醋中的3种甜味剂

建立了食醋中3种甜味剂的固相萃取-高效液相色谱/串联质谱分析方法。样品经酸性水稀释,弱阴离子固相萃取柱净化,Pursuit C18色谱柱分离,10 mmol/L醋酸铵(含0.1%氨水)和乙腈为流动相梯度洗脱,电喷雾负离子模式下多反应监测(MRM)模式检测。糖精钠、安赛蜜、甜蜜素的定量限分别为10、5、5 μg/kg,回收率为72.1%～96.8%,相对标准偏差小于15%。该方法准确、灵敏度高,可用于食醋中甜味剂的定性定量检验。     

ZrO2-SiO2复合物表面酸性的调控及催化四氢呋喃聚合性能研究

采用醇-水溶液加热法制备了复合均匀的ZrO2-SiO2复合氧化物,通过调整复合物中ZrO2含量及焙烧温度对ZrO2-SiO2复合氧化物表面酸量及酸类型进行精细调控,并将其应用于催化四氢呋喃(THF)开环聚合反应.结果表明,当ZrO2含量小于30 mol%时,随着ZrO2含量的增加,复合物总酸量显著增加,且B酸与L酸酸量...     

Unexpected Adsorption Capacity of Ca-deficient Hydroxyapatite in Oil/water System

Symmetrical diynes were synthesized by ligand‐free copper‐catalyzed homocoupling reaction of 1,1‐dibromo‐1‐alkenes using a DBU/DMSO system at room temperature in good to excellent yields dot.^?1.     

Electrocatalysis Oxidation of GMP Based on Layered Double Hydroxide Functionalized with Anionic Surfactant and Room Temperature Ionic Liquid Modified Glassy Carbon Electrode

The electrocatalysis oxidation of guanosine‐5′‐monophosphate (GMP) was investigated on Mg‐Al layered double hydroxide (LDH) functionalized with sodium dodecyl sulfate (SDS) and room temperature ionic liquid (RTIL) modified glass carbon electrode (GCE). The cyclic voltammogram of GMP on the modified electrode (RTIL/ LDH‐SDS/GCE) exhibited a well defined anodic peak at 1.091 V in 0.2 mol·L^?1 pH 4.4 acetate buffer solution. The GMP oxidation was enhanced in the presence of anionic surfactant in the ?lms. The results suggest that the surfactant molecules intercalate the LDH layers to preconcentrate GMP molecules and the RTIL showed good ionic conductivity. The experimental parameters were optimized, the kinetic parameters were investigated and the probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to GMP concentration in the range from 5.0×10^?7 to 1.0×10^?4 mol·L^?1 with the correlation coefficient of 0.9987 and the detection limit was 1.0×10^?7 mol·L^?1. The RTIL/LDH‐SDS/GCE showed a good electrochemical response to the oxidation of GMP and would be developed into a new biosensor.     

Mechanism of Gold(I)‐Catalyzed Conia‐ene Reaction of β‐Ketoesters with Alkynes: A DFT Study

Density functional calculations have been performed to comparatively investigate two possible pathways of Au(I)‐catalyzed Conia‐ene reaction of β‐ketoesters with alkynes. Our studies find that, under the assistance of trifluoromethanesulfonate (TfO), the β‐ketoester is the most likely to undergo Model II to isomerize into its enol form, in which TfO plays a proton transfer role through a 6‐membered ring transition state. The coordination of the Au(I) catalyst to the alkynes triple bond can enhance the eletrophilic capability and reaction activity of the alkynes moiety, which triggers the nucleophilic addition of the enol moiety on the alkynes moiety to give a vinyl‐Au intermediate. This cycloisomerizaion step is exothermal by 21.3 kJ/mol with an energy barrier of 56.0 kJ/mol. In the whole catalytic process, the protonation of vinyl‐Au is almost spontaneous, and the formation of enol is a rate‐limiting step. The generation of enol and the activation of Au(I) catalyst on the alkynes are the key reasons why the Conia‐ene reaction can occur in mild condition. These calculations support that Au(I)‐catalyzed Conia‐ene reactions of β‐ketoesters with alkynes go through the pathway 2 proposed by Toste.     

A low dielectric constant polyimide/polyoxometalate composite

A silane‐modified mono‐lacunary Keggin‐type polyoxometalate (POM), (Bu₄N)₄[SiW₁₁O₃₉{(CH₂?CH? Si)₂O}] (SiW₁₁? CH?CH₂), was obtained by reaction of vinyltrimethoxysilane with K₈(SiW₁₁O₃₉) in acidic MeCN/H₂O mixed solutions. Then, the modified polyoxometalate was physically blended with the pyromellitic dianhydride (PMDA)‐4,4′‐oxydianiline (ODA) poly(amic acid) and the blends were thermally imidized to form polyimide/ polyoxometalate composites. The X‐ray diffraction (XRD) analysis indicates that the polyoxometalate clusters cannot form crystalline structures in the composite, suggesting that the blending leads to improved compatibility between the polymer matrix and the modified polyoxometalate. The EDS (W‐mapping) studies on the composite films reveal that the polyoxometalate clusters are well dispersed in the polyimide matrix. The physical incorporation of modified POM into polyimide remarkably reduced the dielectric constant of the latter from 3.29 to 2.05 when 20 wt% of SiW₁₁? CH?CH₂ was used. Besides, the addition of the modified POM into polyimide increased the storage modulus of polyimide without severely affecting its thermal properties. Copyright © 2009 John Wiley & Sons, Ltd.     

A novel ion‐imprinted hydrogel for recognition of potassium ions with rapid response

A novel ion‐imprinted strategy is developed for synthesizing responsive hydrogels with rapid response to potassium ions. With potassium ions as templates, ion‐imprinted poly(N‐isopropylacrylamide‐co‐benzo‐15‐crown‐5‐acrylamide) (P(NIPAM‐co‐B15C5Am)) hydrogels are synthesized with 15‐crown‐5 crown ethers mounted on the polymer networks in pairs; therefore, it is very easy and fast for the crown ethers to capture potassium ions again by their Venus flytrap action and form stable 2:1 “host–guest” complexes with potassium ions in the ion‐recognition process. As a result, the response rate of the ion‐imprinted hydrogels to potassium ions is significantly faster than that of normal P(NIPAM‐co‐B15C5Am) hydrogels in which 15‐crown‐5 crown ethers are randomly pendent on the polymeric networks. Copyright © 2010 John Wiley & Sons, Ltd.     

3,4‐Dihydroxy‐L‐phenylalanine for Preparation of Gold Nanoparticles and as Electron Transfer Promoter in H2O2 Biosensor

3,4‐Dihydroxy‐L ‐phenylalanine (dopa) and 2‐(3,4‐dihydroxyphenyl)ethylamine (dopamine) were investigated as reducing agent and stabilizer for synthesis of gold nanoparticles (AuNPs) by one‐pot heating of a solution of HAuCl₄/dopa or dopamine. AuNPs with different sizes were obtained by controlling the mass ratios of HAuCl₄/dopa or dopamine. The formation mechanism for AuNPs was also proposed. Immobilization of horseradish peroxidase (HRP) and promotion of its electron transfer by polydopa film were investigated for preparation of H₂O₂ biosensor. Alkaline dopa solution was dropped onto a gold electrode for the formation of polydopa film. HRP was immobilized on the polydopa film through interactions between heme centre of HRP and the amine and carboxyl groups in polydopa. The AuNPs embedded in the polydopa film improved the electron transfer efficiency. These two factors allowed successful development of a H₂O₂ sensor with HRP@polydopa‐AuNPs electrode. Due to its biocompatibility, the polydopa‐AuNPs film provided good retention of enzyme activity and long‐term stability of the sensor. A rapid catalytic response (3 s) and a linear range from 0.006 to 5.0 mmol L^?1 were obtained for H₂O₂. This facile preparation strategy can be extended to other enzyme‐based biosensors.     

High throughput identification of components from traditional Chinese medicine herbs by utilizing graphene or graphene oxide as MALDI-TOF-MS matrix

In this work, graphene or graphene oxide was utilized, for the first time, to identify small molecular components from traditional Chinese medicine (TCM) herbs, by acting as matrix of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Due to the large surface area of graphene or graphene oxide, the analytes were trapped tightly to the matrix, which avoids the contamination of the ion source and vacuum system. Besides, their excellent electronic, thermal and mechanical properties make them desired matrices for MALDI-TOF-MS. Stable analysis was achieved with no background inference even at the concentration of 100 nM. Moreover, the limit of detection (LOD) could be greatly lowered by utilizing graphene or graphene oxide as a pre-enrichment adsorbent. In summary, the promoted MALDI-TOF-MS methodology was demonstrated to be simple, sensitive, fast, cost effective and, most importantly, high throughput.     

Pseudoceramines A-D, new antibacterial bromotyrosine alkaloids from the marine sponge Pseudoceratina sp

Bioassay-guided fractionation of the CH(2)Cl(2)/MeOH extract of the Australian marine sponge Pseudoceratina sp. resulted in the purification of four new bromotyrosine alkaloids, pseudoceramines A-D (1-4), along with a known natural product, spermatinamine (5). The structures of 1-5 were determined by spectroscopic methods. Pseudoceramines A (1) and B (2) feature a rare bromotyrosyl-spermine-bromotyrosyl sequence, and pseudoceramine C (3) is the first example of bromotyrosine coupled with an N-methyl derivative of spermidine. Compounds 1-5 were screened for inhibition of toxin secretion by the type III secretion (T3S) pathway in Yersinia pseudotuberculosis. Compounds 2 and 5 inhibited secretion of the Yersinia outer protein YopE (IC(50) = 19 and 6 μM, respectively) and the enzyme activity of YopH (IC(50) = 33 and 6 μM, respectively).