Enantioselective Synthesis of Quaternary Carbon Stereocenters: Addition of 3‐Substituted Oxindoles to Vinyl Sulfone Catalyzed by Pentanidiums

A pentanidium‐catalyzed highly enantioselective conjugate addition of 3‐alkyloxindoles to phenyl vinyl sulfone has been demonstrated. This approach allows the construction of 3,3‐dialkyl‐substituted oxindole frameworks with high yield and excellent enantioselectivity (up to 99 %) under simple phase‐transfer conditions. A variety of oxindoles bearing all‐carbon quaternary stereogenic centers were obtained in the presence of 0.25 mol % pentanidium. Meanwhile, practicality was illustrated by a gram‐scale asymmetric synthesis of two 3,3‐dialkyl‐substituted oxindoles. The resulting adduct can be smoothly transformed to the natural product analogue in a short synthetic route.     

多金核二氧化铈空心球用于硝基苯酚催化加氢

催化剂的微观结构在催化还原反应、有机物氧化反应及有机物转化反应中起着关键作用。本文利用无模板方法合成了多金核中空二氧化铈微球催化剂。将制备好的二氧化铈中空微球浸渍到一定浓度的氯金酸溶液中,然后多次洗涤除去表面吸附的氯金酸离子,最后通过硼氢化钠还原制成中空氧化铈微球包覆的多金核的核壳结构催化剂。将该核壳结构材料用于硝基苯酚加氢反应与金纳米粒子及氧化铈微球相比,多金核中空二氧化铈核壳结构表现出优越的活性和稳定性。通过这种浸渍洗涤再还原的简单方法合成的多金核二氧化铈催化剂有望应用于生物医药和能源环境等领域。     

齐次分数次积分算子在变指标函数空间上的有界性

本文得到了齐次分数次积分算子在变指标Lebesgue空间、变指标Hardy空间和变指标Herz型Hardy空间上的一些有界性结果.     

Direct determination of mercury in cosmetic samples by isotope dilution inductively coupled plasma mass spectrometry after dissolution with formic acid

A new method was proposed for the accurate determination of mercury in cosmetic samples based on isotopic dilution (ID)-photochemical vapor generation (PVG)-inductively coupled plasma mass spectrometry (ICP MS) measurement. Cosmetic samples were directly dissolved in formic acid solution and subsequently subjected to PVG for the reduction of mercury into vapor species following by ICP MS detection. Therefore, the risks of analyte contamination and loss were avoided. Highly enriched ²⁰¹Hg isotopic spike is added to cosmetics and the isotope ratios of ²⁰¹Hg/²⁰²Hg were measured for the quantitation of mercury. With ID calibration, the influences originating from sample matrixes for the determination of mercury in cosmetic samples have been efficiently eliminated. The effects of several experimental parameters, such as the concentration of the formic acid, and the flow rates of carrier gas and sample were investigated. The method provided good reproducibility and the detection limits were found to be 0.6 pg mL⁻¹. Finally, the developed method was successfully applied for the determination of mercury in six cosmetic samples and a spike test was performed to verify the accuracy of the method.     

Copper-free click conjugation of methotrexate to a PAMAM dendrimer platform

The synthesis of a generation 5 (G5) poly(amidoamine) (PAMAM) dendrimer platform having cyclooctyne ligands that were subsequently be used for a copper-free Huisgen 1,3-dipolar cycloaddition (click reaction) with azido modified methotrexate is described. The G5 PAMAM dendrimer was first partially (70%) acetylated and then coupled with 20 cyclooctyne ligands through amide bonds. The remaining primary amine groups on the dendrimer surface were neutralized by acetylation. The platform was then ‘clicked’ with different numbers (5, 10, and 17) of γ-azido functionalized methotrexate. The copper-free click reactions were stoichiometric with excellent yields.     

Simultaneous analysis of citrulline and arginine in serum and tissue

We developed a method for simultaneously determining l-citrulline and l-arginine levels in serum and tissue samples using RP-HPLC with ultraviolet (UV) detection. The serum was deproteinized by trichloroacetic acid and heat; the tissue was homogenized by trichloroacetic acid and deproteinized as the same as serum. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out. The linearity for l-arginine and l-citrulline ranged from 0 to at least 1000 μmol/L. R² values were above 0.9999 for both. LODs for l-arginine and l-citrulline were 0.0462 μmol/L and 0.0195 μmol/L, respectively, while LOQs were 0.530 μmol/L and 0.417 μmol/L, respectively. Intra- and inter-day CVs were less than 3.5% and 7.5% in serum, respectively. The average recovery was from 85.5% to 116.5% in serum. Intra-assay CVs were 3.8% and 10.3%, and inter-assay CVs were 13.7% and 10.7% for l-arginine and l-citrulline respectively in tissue. The average recovery was from 92.8% to 113.5% in tissue. This is a reliable and convenient analytical method which is suitable for most clinical laboratories.     

Crystal facet dependence of water oxidation on BiVO4 sheets under visible light irradiation

Monoclinic BiVO(4) crystals with preferentially exposed (040) facets were hydrothermally synthesized by using a trace amount of TiCl(3) as the directing agent; this function was confirmed by X-ray diffraction patterns (XRD) and high-resolution transmission electron microscopy (HRTEM). The effects of the directing agent TiCl(3) and the pH values applied during synthesis have been studied, and the optimized BiVO(4) sample with highly exposed (040) facet could be obtained by using 1.2 at.% of TiCl(3) as the directing agent at a pH value of 2. Some complementary techniques were also applied to exclude the effects of the structural and physical property changes, such as surface area and hydrophilicity. The photocatalytic activity of oxygen evolution on BiVO(4) is found to be proportionally correlated with the exposed surfaces of the (040) facet. It is assumed that the active sites with a BiV(4) structure on the exposed (040) facet is assigned to be responsible for the high activity of O(2) evolution.     

离子液体/多壁碳纳米管/壳聚糖修饰电极同时检测多巴胺、抗坏血酸及尿酸的研究

将水溶性离子液体([ BMIM] N(CN)2)、多壁碳纳米管(MWCNTs)和壳聚糖(CS)三者结合,修饰在玻碳电极上制备MWCNTs - IL - CS修饰玻碳电极,并研究了多巴胺(DA)、抗坏血酸(AA)、尿酸(UA)在该修饰电极上的电化学行为.扫描电子显微镜图显示,MWCNTs在IL - CS中能良好分散,并形...     

Atom transfer radical polymerization with activators regenerated by electron transfer of acrylonitrile from silica nanoparticles,and adsorption properties of the resin for Hg2+ after amidoximation with hydroxylamine

Polyacrylonitrile (PAN) was grafted from surfaces of chloro‐modified silica‐gel with their surface chlorines as initiation sites, using an iron (III)‐mediated surface‐initiated atom transfer radical polymerization (ATRP) with activators regenerated by electron transfer (SI‐ARGET ATRP) method. The graft reaction exhibits first‐order kinetics with respect to the polymerization time in the low‐monomer‐conversion stage. The conversion of monomer (C%) and the percentage of grafting (PG%) increased with increasing of the polymerizing time and reached 23 and 730% after a polymerizing time of 24 hr, respectively. Hydroxylamine (NH₂OH·HCl) was used to modify the cyano groups of SG‐g‐PAN to obtain amidoxime (AO) groups. The AO SG‐g‐PAN was used to remove Hg²⁺. The adsorption kinetics indicated that the pseudo‐second‐order model was more suitable to describe the adsorption kinetics of AO SG‐g‐PAN for Hg²⁺. The adsorption isotherms demonstrated that Langmuir model was much better than Freundlich model to describe the isothermal process. Copyright © 2010 John Wiley & Sons, Ltd.