Cascade cyclization intermolecular dipolar cycloaddition by multi-component couplings—synthesis of indolizidines and pyrrolizidines

A three-component coupling reaction of a primary amine (an amino-acid or amino-ester or hydroxylamine), an alkene or alkyne dipolarophile and an aldehyde bearing a halide as a leaving group has been developed. Condensation of the amine with the aldehyde and cyclization (intramolecular N-alkylation) provides, after decarboxylation or deprotonation, a cyclic azomethine ylide (or nitrone) that undergoes intermolecular dipolar cycloaddition with the dipolarophile. This sets up, in a single step, the bicyclic indolizidine or pyrrolizidine ring system, depending on the length of the tether between the aldehyde and the halide. The reaction is successful with stabilized and non-stabilized azomethine ylides that result from using primary amino-esters or amino-acids, respectively.     

Electron impact mass spectral fragmentation of 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]benzothia zepin-1-ones

The mass spectrometric behaviour of nine 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]b enzothiazepin-1-ones has been studied with the aid of mass-analysed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a neutral chlorine atom, or a chloroketene, or neutral propene, or styrene or substituted styrene molecule, plus Cl and/or H (or Cl) atom(s), to yield [M-Cl]+ ions, 2,3-dihydro-1,5-benzothiazepine derivative ions, 4,5-dihydro-5H-1,5-benzothiazepin-4-one ions which can further lose CO to give 1,4-benzothiazine ions. Both molecular ions and [M-Cl]+ ions show a tendency to eliminate an ethyl or benzyl/substituted benzyl radical to produce 2,2a-dihydro-1H-azeto[2,1-c][1,4]benzothiazin-1-one ions. The [M-Cl]+ ions could undergo rearrangement to yield 2,2a-dihydro-1H-azeto[2,1-d][1,5]benzothiazepin-1-one ions, 2,2a,3,4-tetrahydro-1H-azeto[1,2-a]quinoline ions or 1,1a,2,3-tetrahydro-azirino[2,1-d][1,5]benzothiazepine ions by loss of an ethane or a benzene/substituted benzene, a SH radical or a CO molecule. The molecular ions could also undergo rearrangement reactions to form other small fragment ions.     

Structural evolution of anionic silicon clusters SiN (20 <or= N <or= 45)

Results of a combined photoelectron spectroscopy and first-principles density-functional study of SiN- clusters in the size range 20 or= 20. For 28 相似文献   

Patterned deposition at moving contact lines

When a simple or complex liquid recedes from a smooth solid substrate it often leaves a homogeneous or structured deposit behind. In the case of a receding non-volatile pure liquid the deposit might be a liquid film or an arrangement of droplets depending on the receding speed of the meniscus and the wetting properties of the system. For complex liquids with volatile components as, e.g., polymer solutions and particle or surfactant suspensions, the deposit might be a homogeneous or structured layer of solute — with structures ranging from line patterns that can be orthogonal or parallel to the receding contact line via hexagonal or square arrangements of drops to complicated hierarchical structures. We review a number of recent experiments and modelling approaches with a particular focus on mesoscopic hydrodynamic long-wave models. The conclusion highlights open question and speculates about future developments.     

Nucleic acid biosensors for environmental pollution monitoring

Nucleic acid-based biosensors are finding increasing use for the detection of environmental pollution and toxicity. A biosensor is defined as a compact analytical device incorporating a biological or biologically-derived sensing element either integrated within or intimately associated with a physicochemical transducer. A nucleic acid-based biosensor employs as the sensing element an oligonucleotide, with a known sequence of bases, or a complex structure of DNA or RNA. Nucleic acid biosensors can be used to detect DNA/RNA fragments or either biological or chemical species. In the first application, DNA/RNA is the analyte and it is detected through the hybridization reaction (this kind of biosensor is also called a genosensor). In the second application, DNA/RNA plays the role of the receptor of specific biological and/or chemical species, such as target proteins, pollutants or drugs. Recent advances in the development and applications of nucleic acid-based biosensors for environmental application are reviewed in this article with special emphasis on functional nucleic acid elements (aptamers, DNAzymes, aptazymes) and lab-on-a-chip technology.     

Roughness induced surface acoustic resonances

The vibrational and electronic spectra of a semi-infinite crystal with a planar surface is modified in presence of surface inhomogeneities or roughness such as ridges or grooves, quantum wires or tips… Using a Green's function formalism, we present an exact numerical method for obtaining the variation of the density of states associated with the adsorption of a ridge on a flat surface or with a groove cut into an otherwise planar surface. This general method is applied to the determination of the acoustic resonances of shear horizontal polarization associated with such deterministic surface protuberances or indentations. The positions and widths of the peaks in the total or local densities of states give the frequencies and lifetimes of the resonances, which may be more or less pronounced features depending on the relative parameters of the substrate and ridge materials. We also investigate the modifications of these acoustic surface shape resonances due to the interaction between two such defects. This calculation can also be transposed to the study of electronic structure of a wire near a flat surface, in the framework of an effective mass model.     

Organic-inorganic nanohybrids through the direct tailoring of semiconductor nanocrystals with conjugated polymers

Two main synthetic strategies are used to prepare conjugated oligomer- or polymer-nanocrystal nanohybrids. In the first strategy ligand exchange is invoked to either replace with a bifunctional ligand, which contains a second functional group for coupling with conjugated oligomers or polymers (COs or CPs), or exchange for the functionalized COs or CPs in a "grafting-onto" process. Alternatively, in the second strategy the nanocrystal (NC) is passivated with functional ligands from which COs or CPs are directly grown in the absence of ligand exchange. The well-defined interface between the COs or CPs and NCs facilitates an efficient charge-transfer between them.     

On the transition between a heterogeneous and homogeneous corona in mixed polymeric micelles

Two-dimensional NMR and small-angle neutron scattering experiments were performed on comicelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO, and poly(acrylic acid)-block-poly(acryl amide), PAA-b-PAAm, in aqueous solutions to study whether a transition between a heterogeneous (Janus-type) and homogeneous corona can be observed upon a variation of parameters that are anticipated to affect the miscibility of the PEO and PAAm coronal blocks. Investigated were the effect of a salt-induced decrease in micellar aggregation number, P agg for 1相似文献   

Mécanismes de Formation d'α-Aminophosphonates

When di-n-decylphosphonate 1a or di-benzylphosphite 1b are reacted with furan imine 2a or thiophenic imine 2b , the reaction leads to an f -aminophosphonate: 3a , 3b , or 3c following an ion- or radical-based reaction.     

Electrokinetic Separation Methods

Electrophoresis is the transport of dissolved molecules or suspended particles in a homogeneous polar liquid (such as water) under the influence of an electric field. Most molecules or particles acquire a surface electric charge when dissolved or suspended in buffered water (or other polar liquids), owing to ionization or adsorption of ions present in the water. The sign of the surface charge of molecules or particles determines whether they will migrate towards the positive or the negative electrode of the applied electric field, and the velocity of migration depends on the surface potential of the molecules or particles, as well as on the potential of the electric field.     

Tox-match/pharm-match prediction of toxicological and pharmacological features by using optimal substructure coding and retrieval systems

The computer program TOX-MATCH/PHARM-MATCH allows prediction of toxicological or pharmacological features based on a reverse search strategy. The program has a library of model chemical structure toxicophores or pharmacophores in a tree structure using a special chemical coding method (based on topology, topography, and graph theory). Graph theory has proven particularly efficient for coding and retrieval of polynuclear aromatic hydrocarbons. The library of model pharmacophores or toxicophores is then followed by a library of the toxicological or pharmacological triggering events (usually biochemical) caused by each model toxicophore or pharmacophore, the subsequent physiological events (also usually biochemical) and the observed physiological signs and symptoms of each species. An unknown sample is input (also in the special chemical coding), and the model toxicophore or pharmacophore is compared with the sample compound to see how close the match is (reverse search). This program is open-ended and extremely versatile and can be used for any toxicological or pharmacological problem.     

The effect of radiation on the physical and chemical properties of polyethylene containing an antioxidant and/or other additives

This paper describes the effect of an antioxidant, a monomer and fillers (silica or carbon black), alone or in certain combinations with each other, on the mechanical and chemical response of a low density polyethylene to exposure to ionizing radiation. If chain scission is a significant factor in the radiolysis of a polymer, then the relation between sol fraction and Young's modulus or ultimate elongation (both at 160°C) should change depending on whether an additive inhibits or enhances crosslinking. Such additives do not significantly or consistently alter the relation between these properties in a low density polyethylene, indicating that chain scission is not a significant feature of the radiolysis of this polymer.     

Linear or cross-shaped di(cyclopentadienyltitanium) compounds with aryl or heteroaryl spacers

The preparation of hexamethylated and hexabenzylated arylene or heteroarylene bridged dinuclear di(cyclopentadienyltitanium) compounds from the reaction of the corresponding hexachlorides with methyllithium or benzylmagnesium chloride is described. The spacers between the cyclopentadienyl rings consist of one, two or three phenylene groups, a dioctyloxyphenylene group or a 2,2'-bithienylene group. The corresponding hexachlorides and hexaisopropoxides have also been prepared.     

Bridged Ferrocenes : XIII. Friedel—crafts reactions of ferrocene and alkylferrocenes with α,β-unsaturated acid chlorides

The reactions of ferrocene, butylferrocenes, and [3] ferrocenophane with α,β-unsaturated acid chlorides give mixtures of ketonic products reuslting from introduction of either a propanoyl or a propenoyl substituent or a homo- or a hetero-annular three-carbon bridge.     

Water-soluble phosphines. 17.(1) novel water-soluble secondary and tertiary phosphines with disulfonated 1,1'-biphenyl backbones and dibenzophosphole moieties

Reaction of 2,2'-difluoro-1,1'-biphenyl with chlorosulfonic acid and subsequent hydrolysis followed by neutralization with potassium or sodium hydroxide affords disodium or dipotassium 5,5'-disulfonato-2,2'-difluoro-1,1'-biphenyl (1a, 1b). On treatment of 1b with diphenyl- or phenylphosphine in the superbasic medium DMSO/KOH, phosphine ligand 2 or 3 with a disulfonated 1,1'-biphenyl backbone or a dibenzophosphole moiety is formed. The structure of the oxide of 5-phenyldibenzophosphole 3, which crystallizes as 4.2.5H(2)O in the monoclinic space group P2(1)/n with a = 13.799(3) A, b = 19.246(4) A, c = 17.764(4) A, beta = 105.63(3) degrees, and Z = 4, has been determined by X-ray analysis. Nucleophilic phosphination of 1a with NaPH(2) in liquid ammonia yields the sodium phosphide 5a which on protonation gives the water-soluble 5H-dibenzophosphole 5. Reaction of 1b with PH(3) in the superbasic medium DMSO/KOtBu affords 5b in addition to the oxidation product 6a. On oxidation of 5a or 5b with H(2)O(2), the sodium or potassium salts of the sulfonated phosphinic acids 6a or 6b, respectively, are formed. Alkylation of the sodium dibenzophospholide 5a with 2,2'-bis(chloromethyl)-1,1'-biphenyl or 1,4-di-O-p-toluenesulfonyl-2,3-O-isopropylidene-D-threitol yields the chiral water-soluble bidentate phosphine ligands 8 and 9, respectively.     

New In Situ Trapping Metalations of Functionalized Arenes and Heteroarenes with TMPLi in the Presence of ZnCl2 and Other Metal Salts

The addition of TMPLi to a mixture of an aromatic or heteroaromatic substrate with a metal salt such as MgCl₂, ZnCl₂, or CuCN at ?78 °C first leads to lithiation of the arene followed by transmetalation with the metal salt to afford functionalized organometallic compounds of Mg, Zn, or Cu. This in situ trapping method allows an expedited metalation (?78 °C, 5 min) of a range of sensitive pyridines (bearing a nitro, ester, or cyano group) and allows the preparation of kinetic regioisomers of functionalized aromatic compounds or heterocycles not otherwise available by standard metalating agents, such as TMPMgCl?LiCl or TMPZnCl?LiCl.     

High-efficiency passive elution of bacterial lipopolysaccharides from polyacrylamide gels

We recently described a method for recovering polyacrylamide-gel-separated bacterial lipopolysaccharides (LPS) based on the sensitive on-gel LPS detection (1-10 ng/band) with zinc-imidazole followed by passive elution from 32 microm average size gel microparticles into water. With this procedure, the recovery of rough- or semismooth-type LPS after 3 h elution is about 70-80%, while that of smooth LPS is only about 10%. Here we evaluated whether a simple replacement of water with other eluents would enhance the passive diffusion of LPS. We found that solutions of the detergents sodium dodecyl sulfate (SDS), sodium deoxycholate (DOC) and Triton X-100, or mixtures of the organic solvents acetonitrile and triethylamine and water, increased the recovery of a smooth LPS band from Vibrio cholerae O1 in a concentration-dependent manner. Furthermore, a quantitative recovery of rough or smooth LPS from V. cholerae O1, Escherichia coli O111:B4, E. coli K-235, or Serratia marcescens was feasible in 1% SDS or DOC after 3 h or in 5% triethylamine after only 2 min. A simple dilution of SDS or DOC or evaporation of triethylamine rendered the eluted LPS preparations compatible with biochemical activity determination, as tested by Limulus amebocyte lysate assay. Thus, this improved micropurification method may be a suitable interface between analytical gel electrophoresis and further characterization or use of LPS.     

A two-component pericyclic reaction for synthesis of substituted benzofurans and aryl-quaternary carbon bonds

The reaction shown is presumed to be a new [3,3]-sigmatropic rearrangement involving an O-arylsulfoxonium species or related sulfurane. It allows a sulfoxide and a phenol to be joined and rearranged in one operation at or below room temperature, coupling an aromatic to a quaternary carbon and creating benzofurans or articulated dihydrobenzofurans in a number of examples.     

Cine Substitution in 2-Oxabicyclo[4.2.0]octanones and Subsequent Unusual Rearrangements(1)

Reaction of 2-chlorooxabicyclo[4.2.0]octanone 5 with several nucleophiles was examined and found to differ significantly from those of carbon analog 1. MeO(-) and PhS(-) led either to products of cine substitution 9 or of ring opening to cyclobutenones 8. With most enolates cine substitution occured via C-alkylation of the intermediate oxidoallyl cation in spite of formation of a new C-C bond between two quaternary carbons; with nitroalkanes O-alkylation was preferred. With azide as a nucleophile, further transformations occurred, among them an oxy-promoted electrocyclic cyclobutane opening, with incorporation of a phenyl triazole unit and final formation of the unusual product 19a. Evidence for a mechanism explaining formation of 19a was obtained by isolation of intermediates. Thermolysis or photolysis of 8e or9b led via electrocyclic ring opening to a vinyl ketene which was trapped by MeOH, alkenes, dienes, or oxygen to produce polyfunctional unsaturated esters 29 and 30 or 8-membered ring lactone 31, fused cyclobutanones 33 and 34, pyranone 38, or gamma-lactone 39, respectively.     

Stabilization of zwitterions in solution: GABA analogues

The solution-phase structures of a number of conformationally restricted gamma-aminobutyric acid (GABA) analogues are investigated at the MP2/6-31+G* level of theory, using both explicit water molecules and the conductor-like screening solvation model (COSMO) to model solvation. GABA analogues constrained in a cis conformation by either a double bond or cyclopropane ring have the potential to attain either folded, intramolecularly hydrogen-bonded, or partially folded conformations in solution. Systems constrained in a cis conformation by a cyclopentane or cyclopentene ring are more conformationally restricted and exist only in a folded, intramolecularly hydrogen-bonded form. GABA analogues constrained in a trans conformation by either a double bond or cyclopropane ring have the potential to adopt either partially folded or fully extended conformations in solution. Due to a lack of conformational flexibility, analogues that are constrained in a trans conformation by a cyclopentane or cyclopentene ring attain only partially folded conformations. Like GABA, conformationally flexible GABA analogues possess a large number of stable rotamers, and may exist in any or all of these conformations in aqueous solution. The structures of these analogues provide an essential foundation for subsequent structure-activity analysis of ligand binding at GABA receptors and transporters. This work is therefore expected to facilitate the design and development of new biologically active GABA analogues to treat GABA-related neurological disorders.