Search results for "surface"
showing 10 items of 9345 documents
Potential energy surface for the decomposition of mandelic acid
1997
Abstract The decomposition of mandelic acid has been studied by ab initio calculations at the MP2/6-31G ∗∗ level. Three competitive reaction pathways have been characterized, two are stepwise processes with the formation of an α-lactone intermediate, achieved by the nucleophilic attack of either the carbonylic oxygen atom (mechanism A) or the hydroxylic oxygen atom (mechanism B) of the carboxyl group, followed by a ring opening; the third pathway (mechanism C) is a one-step process. The calculated rate coefficient agrees with experimental data. The decomposition is energetically favourable along mechanism A.
New developments in immunochemical water analysis down to 30 mul sample volume.
1999
Abstract The determination of trace levels of pesticides like atrazine in water samples of small, restricted volumes is one of the future demands of environmental analysis. In a brief review existing chromatographic and immunochemical methods for atrazine are critically discussed. Then a simple rapid enzyme-linked immunosorbent assay (ELISA) using the tip of an inoculation needle as a solid surface is presented. The sample volume could be reduced to 30 μl. The assay had a centre of the test IC50 of 0.12 μg l−1 and permitted the characterisation of atrazine at levels of 0.022–2.90 μg l−1. A first outlook for automatisation is given. The new method was compared with an ELISA using 96 well mic…
Functionalization with silyl enol ethers, VI Zinc chloride mediated alkoxyalkylation of O-methyl-O-trimethylsilyl) keten acetals with 2-alkoxy-1,3-di…
1987
O-Methyl-O-(trimethylsilyl) keten acetals2 were regioselectively alkoxyalkylated by 2-alkoxy-1,3-dioxolanes1 in the presence of zinc chloride. This method represents a good way for synthesis of α-protected β-keto carbonic esters4.
Synthesis of chemisorbed imidazolium and phosphonium cations by reaction of ionic liquid precursors with silica.
2010
The reaction of four different basic ionic liquid precursors with Aerosil®300 is presented. Chemisorbed imidazolium and phosphonium cations, with silanolate anions as part of the silicatic support, were obtained and investigated with various solid state NMR techniques.
ChemInform Abstract: Approaches for the Introduction of Fluorinated Substituents into [1,2,3]Triazolo[1,5-a]pyridines.
2014
Functionalization of [1,2,3]triazolo[1,5-a]pyridines with a trifluoromethyl group is achieved for the first time.
Recent Advances in the Synthesis of Piperidines: Functionalization of Preexisting Ring Systems
2018
Abstract The present review focuses on strategies for the construction of piperidines which have appeared in the literature since 2003 through mid-2017. In a preceding chapter ( 2017AHC191 ), we summarized synthetic methods involving the construction of the piperidine ring from essentially acyclic starting materials in an intra- or intermolecular manner. The present chapter aims at giving a general overview of decoration or modification of previously generated pyridines or piperidines. The hydrogenation of preformed pyridine or pyridinium rings and introduction of substituents into fully saturated piperidines as well as ring expansion of pyrrolidines to piperidines are the most prevalent me…
Photoinduced functionalization of the C-20 methyl group of the nor-diterpene atractyligenin
2001
Abstract Irradiation of the nor-diterpene atractyligenin at λ =254 nm in methanol gave, on one hand, the decarboxylation product, and provided, on the other hand, the transformation of the C-20 angular methyl into a methylene-carbomethoxy group. A photochemical pathway involving formation of C-19/C-20 bond is suggested.
Surface modification of graphite+polymer composite and ITO electrodes by Nafion®+cupromeronic phthalocyanine films
1999
Abstract The surface of indium tin oxide (ITO) and graphite+polymer composite electrodes can be modified by Nafion ® films containing a little amount of dispersed electroactive substances, such as phthalocyanines. This procedure allows the recovery of electroanalytical information on the electroactive deposited substance. The preparation methods for these types of modified electrodes are discussed from the voltammetric results obtained in this work. The Nafion ® net acts as a permeable membrane to the hydrogen ions. Furthermore, the presence of methylviologen within the Nafion ® film makes the electron transport throughout this membrane easy.
Recognition and sensing of fluoride anion.
2009
Fluoride anion recognition is attracting a mounting interest in the scientific community due to its duplicitous nature. It is a useful chemical for many industrial applications, and it has been used in human diet, but, recently it has been accused for several human pathologies. Here we describe the ample panorama of different approaches the chemists world-wide have employed to face the challenge of fluoride binding, and we outline some of the research which in our view can contribute to the development of this field, especially when fluoride binding has to be achieved in highly competitive protic solvents and water.
An efficient synthesis of new fluorinated uracil derivativesElectronic supplementary information (ESI) available: general procedures for the preparat…
2003
A series of potentially biologically active fluorinated uracil derivatives has been prepared in three steps from oxazolines and fluorinated nitriles with good chemical yields.