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121.
Piperidine was stereoselectively alpha-alkynylated in a four-step sequence made up of transformation to a chiral nonracemic N-sulfinylpiperidine, anodic oxidation to N-sulfinyliminium ion equivalent, alkynylation through addition of a mixed organoaluminum derivative, and final acidic deprotection of the sulfoxide. Overall yields are around 50%, and the diastereoselectivity of the nucleophilc addition was between 92 and 99% de, allowing isolation of the final product with 99% enantiomeric purity. 相似文献
122.
Sandström MC Johansson E Edwards K 《Langmuir : the ACS journal of surfaces and colloids》2007,23(8):4192-4198
Polyethylene glycol (PEG)-conjugated lipids are commonly employed for steric stabilization of liposomes. When added in high concentrations PEG-lipids induce formation of mixed micelles, and depending on the lipid composition of the sample, these may adapt either a discoidal or a long threadlike shape. The factors governing the type of micellar aggregate formed have so far not been investigated in detail. In this study we have systematically varied the lipid composition in lipid/PEG-lipid mixtures and characterized the aggregate structure by means of cryo-transmission electron microscopy (cryo-TEM). The effects caused by adding sterols, phosphatidylethanolamines, and phospholipids with saturated acyl chains to egg phosphatidylcholine/1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000 (EPC/DSPE-PEG2000) mixtures with a fixed amount (25 mol %) of DSPE-PEG2000 was studied. Further, the aggregate structure in 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine/1,2-dimyristoyl-sn-glycero-3-phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000] (DMPC/DMPE-PEG2000) samples above and below the gel to liquid crystalline phase transition temperature (TC) was investigated. Our results revealed that lipid components, as well as environmental conditions, that reduce the lipid spontaneous curvature and increase the monolayer bending modulus tend to promote formation of discoidal micelles. At temperatures below the gel-to-liquid crystalline phase transition temperature reduced lipid/PEG-lipid miscibility, furthermore, likely contribute to the observed formation of discoidal rather than threadlike micelles. 相似文献
123.
Emma Davies 《Nachrichten aus der Chemie》2004,52(6):721-724
The German Chemical Society (GDCh) and the Royal Society of Chemistry (RSC) have worked closely together for many years. David Giachardi, chief executive of the RSC, and Wolfram Koch, GDCh's chief executive, discuss the issues faced by the societies today. 相似文献
124.
Liquid crystalline products of oligomeric p-phenylenevinylene derivates were prepared metathetically using a stable molybdenum carbene complex (Mo(NArMe2)(CHCMe2Ph)[OCMe(CF3)2]2). The synthesis was conducted via two steps: 1. Metathesis polycondensation of 2, 5-dialkyl-1, 4-divinylbenzenes to oligo-(2, 5-dialkyl-1, 4-phenylenevinylene)s, 2. Endcapping of the vinyl groups via cross-metathesis using 3-hexene. The products were characterized by1H-NMR and UV/Vis spectroscopy, as well as by DSC. 相似文献
125.
Emma Wikstad Mikael Kritikos 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(3):m87-m89
The title novel vanadium borophosphate compound, bis(1,4‐diazonia[2.2.2]octane) μ3‐oxo‐oxopenta‐μ‐phosphato‐diboronvanadium monohydrate phosphoric acid solvate, containing the cluster anion [VO(PO3OH)5B2O]4−, has been synthesized under mild hydrothermal conditions. Extensive O—H⃛O and N—H⃛O hydrogen bonding is observed between the molecular units. 相似文献
126.
127.
Dr. Milan Pramanik Michael G. Guerzoni Dr. Emma Richards Prof. Dr. Rebecca L. Melen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(9):e202316461
The development of new methods for enantioselective reactions that generate stereogenic centres within molecules are a cornerstone of organic synthesis. Typically, metal catalysts bearing chiral ligands as well as chiral organocatalysts have been employed for the enantioselective synthesis of organic compounds. In this review, we highlight the recent advances in main group catalysis for enantioselective reactions using the p-block elements (boron, aluminium, phosphorus, bismuth) as a complementary and sustainable approach to generate chiral molecules. Several of these catalysts benefit in terms of high abundance, low toxicity, high selectivity, and excellent reactivity. This minireview summarises the utilisation of chiral p-block element catalysts for asymmetric reactions to generate value-added compounds. 相似文献
128.
A catalyst screening programme has revealed that a combination of Pd(0) and the N-heterocyclic carbene ligand SIPr forms a particularly robust and efficient catalyst for the formation of important quaternary 3-aminooxindoles via intramolecular enolate arylation. Catalyst loadings of 0.1 mol % give complete conversion in under 4 h. 相似文献
129.
Serena Silvi Dr. Edwin C. Constable Prof. Catherine E. Housecroft Prof. Jonathon E. Beves Dr. Emma L. Dunphy Dr. Massimiliano Tomasulo Dr. Françisco M. Raymo Prof. Alberto Credi Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(1):178-185
Molecular logic gates process physical or chemical “inputs” to generate “outputs” based on a set of logical operators. We report the design and operation of a chemical ensemble in solution that behaves as integrated AND, OR, and XNOR gates with optical input and output signals. The ensemble is composed of a reversible merocyanine‐type photoacid and a ruthenium polypyridine complex that functions as a pH‐controlled three‐state luminescent switch. The light‐triggered release of protons from the photoacid is used to control the state of the transition‐metal complex. Therefore, the two molecular switching devices communicate with one another through the exchange of ionic signals. By means of such a double (optical–chemical–optical) signal‐transduction mechanism, inputs of violet light modulate a luminescence output in the red/far‐red region of the visible spectrum. Nondestructive reading is guaranteed because the green light used for excitation in the photoluminescence experiments does not affect the state of the gate. The reset is thermally driven and, thus, does not involve the addition of chemicals and accumulation of byproducts. Owing to its reversibility and stability, this molecular device can afford many cycles of digital operation. 相似文献
130.
José M. Marín Emma Gracia-LorJuan V. Sancho Francisco J. LópezFélix Hernández 《Journal of chromatography. A》2009,1216(9):1410-1420
An ultra-high-pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method for the determination of 37 pesticides (herbicides, insecticides and fungicides) in environmental and wastewater has been developed. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple quadrupole mass analyzer was used. This analyzer (minimum dwell time, 5 ms) allows acquiring up to three simultaneous transitions in the selected reaction monitoring mode for each compound assuring a reliable identification without resolution or sensitivity losses. A pre-concentration step based on solid-phase extraction using Waters Oasis HLB cartridges (0.2 g) was applied with a 100-fold pre-concentration factor along the whole analytical procedure. The method was validated based on European SANCO guidelines using surface, ground, drinking and treated water (from an urban solid residues treatment plant) spiked at two concentration levels (0.025 and 0.1 μg/L), the lowest having been established as the limit of quantification objective. The method showed excellent sensitivity, with instrumental limits of detection ranging from 0.1 to 7 pg. It was applied to environmental water samples (ground and surface water) as well as to samples of urban solid waste leachates (raw leachate and treated leachate after applying reversed osmosis) collected from a municipal treatment plant. Matrix effects have been studied in the different types of water samples analyzed, and several isotope-labelled internal standards have been evaluated as a way to compensate the signal suppression observed for most of the compounds studied, especially in wastewater samples. As a general remark, only those pesticides which response was corrected using their own isotope-labelled molecule, could be satisfactorily corrected in all type of samples, assuring in this way the accurate quantification in all matrix samples. 相似文献