Membrane phosphatidylserine regulates surface charge and protein localization

Electrostatic interactions with negatively charged membranes contribute to the subcellular targeting of proteins with polybasic clusters or cationic domains. Although the anionic phospholipid phosphatidylserine is comparatively abundant, its contribution to the surface charge of individual cellular membranes is unknown, partly because of the lack of reagents to analyze its distribution in intact cells. We developed a biosensor to study the subcellular distribution of phosphatidylserine and found that it binds the cytosolic leaflets of the plasma membrane, as well as endosomes and lysosomes. The negative charge associated with the presence of phosphatidylserine directed proteins with moderately positive charge to the endocytic pathway. More strongly cationic proteins, normally associated with the plasma membrane, relocalized to endocytic compartments when the plasma membrane surface charge decreased on calcium influx.     

十二烷基苯磺酸钠对重氮偶合反应催化作用的研究

本文以十二烷基苯磺酸钠(简称为NaDBS)为阴离子相转移催化剂(anionic—PTC),对其在偶合反应中的催化性能进行了初步的研究。结果表明NaDBS确能使一些较难发生的重氮偶合反应顺利进行。本文使用一系列的苯胺衍生物作为重氮组份,以咔唑、二苯胺作为偶合组份,合成了九种偶氮化合物,其中有六种未见文献报道。最后对结果进行了详细的讨论。     

A powerful chiral counterion strategy for asymmetric transition metal catalysis

Traditionally, transition metal-catalyzed enantioselective transformations rely on chiral ligands tightly bound to the metal to induce asymmetric product distributions. Here we report high enantioselectivities conferred by a chiral counterion in a metal-catalyzed reaction. Two different transformations catalyzed by cationic gold(I) complexes generated products in 90 to 99% enantiomeric excess with the use of chiral binaphthol-derived phosphate anions. Furthermore, we show that the chiral counterion can be combined additively with chiral ligands to enable an asymmetric transformation that cannot be achieved by either method alone. This concept of relaying chiral information via an ion pair should be applicable to a vast number of metal-mediated processes.     

Asymmetric catalysis of the transannular Diels-Alder reaction

Transannular chemical reactions are unparalleled in their ability to generate high degrees of stereochemical and architectural complexity in a single transformation. However, the successful application of this approach in synthesis depends on the ability to predict and control the outcome of the transannular reaction. Use of a chiral catalyst in this context represents an attractive, yet unused, strategy. This report describes a catalytic, asymmetric transannnular Diels-Alder (TADA) reaction that affords polycyclic products in high enantiomeric excess. This catalyst system can also alter the inherent diastereoselectivity of cyclizations with substrates containing chiral centers. Additionally, the catalytic enantioselective TADA has been used as the key step in a total synthesis of the sesquiterpene 11,12-diacetoxydrimane; this route may provide a general approach to the polycyclic carbon framework shared by many terpene natural products.     

Metals and DNA: molecular left-handed complements

Chiral metal complexes provide unique molecular probes for DNA. Chiral reagents that "recognize" different local structures along the DNA strand have been designed by a process in which the asymmetry in shape and size of the complex is matched to that of the DNA helical groove. As a result, the chiral metal complexes provide very sensitive probes for local helical structure, both left- and right-handed. Direct coordination of chiral complexes to the DNA bases adds an element of sequence selectivity to the probe design. With a suitable reactive metal center, reagents that target chemically specific sites along the strand may be developed. One such chiral reagent, which cleaves left-handed DNA sites with photoactivation, has been useful in mapping this distinct conformation and examining its biological role. The conformation-specific molecular cleaver, much like a DNA-binding enzyme, recognizes and reacts at discrete sites along the DNA strand. These site-specific chiral metal complexes provide exciting new tools for probing the local variations in DNA structure and its role in the regulation of gene expression.     

新手性吡啶类配体的合成及其不对称诱导性能研究

以2,6-二甲基吡啶和2,6-二溴吡啶为原料,经锂试剂分别与光学活性的樟脑、薄荷酮和3-甲酰基蒎烷反应合成了4个新的手性吡啶类化合物。测定了它们在苯甲醛和二乙基锌加成反应中的不对称诱导性能。     

Helical polyacetylene synthesized with a chiral nematic reaction field

Helical polyacetylene was synthesized under an asymmetric reaction field consisting of chiral nematic (N*) liquid crystals (LCs). The chiral nematic LC was prepared by adding a chiroptical binaphthol derivative as a chiral dopant to a mixture of two nematic LCs. Acetylene polymerizations were carried out using the catalyst titanium tetra-n-butoxide-triethylaluminum dissolved in the chiral nematic LC solvent. The polyacetylene film was shown by scanning electron microscopy to consist of clockwise or counterclockwise helical structure of fibrils. A Cotton effect was observed in the region of the pi --> pi* transition of the polyacetylene chain in circular dichroism spectra. The high electrical conductivities of approximately 1500 to 1800 siemens per centimeter after iodine doping and the chiral helicity of these films may be exploited in electromagnetic and optical applications.     

Dynamic control of chiral space in a catalytic asymmetric reaction using a molecular motor

Enzymes and synthetic chiral catalysts have found widespread application to produce single enantiomers, but in situ switching of the chiral preference of a catalytic system is very difficult to achieve. Here, we report on a light-driven molecular motor with integrated catalytic functions in which the stepwise change in configuration during a 360° unidirectional rotary cycle governs the catalyst performance both with respect to activity and absolute stereocontrol in an asymmetric transformation. During one full rotary cycle, catalysts are formed that provide either racemic (R,S) or preferentially the R or the S enantiomer of the chiral product of a conjugate addition reaction. This catalytic system demonstrates how different molecular tasks can be performed in a sequential manner, with the sequence controlled by the directionality of a rotary cycle.     

丙酸香叶酯的催化合成(英文)

[目的]进行丙酸香叶酯的合成并优化合成条件。[方法]在敞开体系中合成中孔分子筛Al-MCM-41。通过X射线衍射(XRD)、红外光谱(FT-IR)、NH3程序升温脱附(NH3-TPD)、N2吸附-脱附和气相色谱(GC)等方法对所合成样品的结构和催化性能进行表征分析。用其催化合成丙酸香叶酯,考察了反应时间、反应温度、催化剂用量、反应物配比及催化剂再生对香叶醇酯化反应结果的影响。[结果]合成的样品具有中孔分子筛的六方介孔结构以及良好的长程有序性和结晶度,属于典型的中孔材料,分子筛表面有弱酸中心。最佳的反应条件是n(香叶醇)/n(丙酸)=1.0∶1.5,反应温度为120℃,反应时间为8h,但香叶醇的转化率仅为40.01%,丙酸香叶酯的选择性为70.01%。催化剂使用到第5次时有失活现象,可通过焙烧除去掩盖酸中心的积碳,使催化剂的活性和选择性得到恢复。[结论]得到了丙酸香叶酯的合成优化条件,为进一步研究奠定基础。     

Spontaneous vesicle formation in aqueous mixtures of single-tailed surfactants

Spontaneous, single-walled, equilibrium vesicles can be prepared from aqueous mixtures of simple, commercially available, single-tailed cationic and anionic surfactants. Vesicle size, surface charge, or permeability can be readily adjusted by varying the ratio of anionic to cationic surfactant. Vesicle formation apparently results from the production of anion-cation surfactant pairs that then act as double-tailed zwitterionic surfactants. These vesicles are quite stable in comparison to conventional vesicles prepared by mechanical disruption of insoluble liquid crystalline dispersions.     

Green, catalytic oxidation of alcohols in water

Alcohol oxidations are typically performed with stoichiometric reagents that generate heavy-metal waste and are usually run in chlorinated solvents. A water-soluble palladium(II) bathophenanthroline complex is a stable recyclable catalyst for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic water-alcohol system. The use of water as a solvent and air as the oxidant makes the reaction interesting from both an economic and environmental point of view.     

α-·β-·γ-环糊精对Temazepam手性识别的分子模拟筛选

在相同的模拟条件下,采用α-、β-和γ-CD作为手性拆分试剂,对Temazepam手性拆分进行了模拟研究。结果表明,不同大小的环糊精在识别Temazepam对映体分子时有不同的手性识别能力：α-CD〉γ-CD〉β-CD。说明在这3种环糊精中,α-CD最适合作为溶剂对Temazepam对映异构体进行拆分,计算机模拟筛选为今后合理选用手性拆分试剂提供了理论依据。     

Deeply inverted electron-hole recombination in a luminescent antibody-stilbene complex

The blue-emissive antibody EP2-19G2 that has been elicited against trans-stilbene has unprecedented ability to produce bright luminescence and has been used as a biosensor in various applications. We show that the prolonged luminescence is not stilbene fluorescence. Instead, the emissive species is a charge-transfer excited complex of an anionic stilbene and a cationic, parallel pi-stacked tryptophan. Upon charge recombination, this complex generates exceptionally bright blue light. Complex formation is enabled by a deeply penetrating ligand-binding pocket, which in turn results from a noncanonical interface between the two variable domains of the antibody.     

壳聚糖对酸性染料的吸附作用

壳聚糖是一种用途广泛的天然高分子阳离子型吸附剂，具有吸附分离水溶液中酸性染料的能力。研究结果表明，壳聚糖对酸性染料的吸附能力受到吸附剂的脱乙酸化度、颗粒直径、吸附时间以及溶液中乙酸含量等因素的严重影响。在最佳吸附条件下，壳聚糖对酸性红Ａ和酸性湖蓝Ｖ的吸附回收率可达９５％以上。     

木粉多元醇液化残余物的结构表征

为了探究木粉多元醇液化过程中缩聚反应阶段液化残余物的化学基团、结晶度以及微观形态的变化,进而探明缩聚反应机理,以聚乙二醇和丙三醇为液化剂、H2SO4为催化剂,对桦木木粉液化,并用FTIR、XRD和SEM对液化残余物进行分析.结果表明:1)在O～180 min液化时间内,缩聚反应约发生在70 min以后.2)与木粉相比,...     

Synthesis of biaryls via catalytic decarboxylative coupling

We present a safe and convenient cross-coupling strategy for the large-scale synthesis of biaryls, commercially important structures often found in biologically active molecules. In contrast to traditional cross-couplings, which require the prior preparation of organometallic reagents, we use a copper catalyst to generate the carbon nucleophiles in situ, via decarboxylation of easily accessible arylcarboxylic acid salts. The scope and potential economic impact of the reaction are demonstrated by the synthesis of 26 biaryls, one of which is an intermediate in the large-scale production of the agricultural fungicide Boscalid.     

土壤中苯系物在表面活性剂溶液中的解吸研究

选用阴离子表面活性剂十二烷基苯磺酸钠和十二烷基硫酸钠(LAS和SDS)，阳离子表面活性剂十六烷基三甲基氯化铵(CTAB)和非离子表面活性剂(AEO-9和SA-20)对污染土壤进行解析试验。研究了用表面活性剂解吸土壤中的苯系物，从而为淋滤冲洗被石油污染的农田提供理论依据。试验表明，阴离子表面活性剂对苯系物的去除效率达95％，非离子表面活性剂对苯系物的去除率达85％，而阳离子表面活性剂无明显去除效果。     

有机锌试剂对亚胺的催化不对称加成反应研究进展

亚胺的催化不对称加成反应是近年来不对称催化反应中的热点研究领域,从手性配体类型的角度总结了近10余年来有机锌试剂在亚胺不对称加成反应中的应用进展.     

A microfluidic device for conducting gas-liquid-solid hydrogenation reactions

We have developed an efficient system for triphase reactions using a microchannel reactor. Using this system, we conducted hydrogenation reactions that proceeded smoothly to afford the desired products quantitatively within 2 minutes for a variety of substrates. The system could also be applied to deprotection reactions. We could achieve an effective interaction between hydrogen, substrates, and a palladium catalyst using extremely large interfacial areas and the short path required for molecular diffusion in the very narrow channel space. This concept could be extended to other multiphase reactions that use gas-phase reagents such as oxygen and carbon dioxide.     

Oscillating stereocontrol: a strategy for the synthesis of thermoplastic elastomeric polypropylene

A strategy has been developed for the synthesis of thermoplastic elastomeric polypropylene based on the catalytic activity of the unbridged metallocene bis(2-phenylindenyl)zirconium dichloride [(2-PhInd)(2)ZrCl(2)]. This catalyst was designed to isomerize between achiral and chiral coordination geometries during the polymerization reaction to produce atactic-isotactic stereoblock polymers. The metallocene precursor (2-PhInd)(2)ZrCl(2) in the presence of methylaluminoxane polymerizes propylene to yield rubbery polypropylene. The isotacticity of the polymer, described by the isotactic pentad content, increases with increasing propylene pressure and decreasing polymerization temperature to produce polypropylenes with an isotactic pentad content ranging from 6.3 to 28.1 percent.