Highly efficient synthesis of linear pyrrole oligomers by twofold Heck reactions

The twofold Heck reaction of the vinylpyrroles 3a and 3b with the iodobenzenes 4a-c led to the linear pyrrole oligomers 5, 6, and 7. The synthesis of both symmetrical and unsymmetrical oligomers, such as 10a and 10b, was also accomplished by a Heck reaction of 8 and 9 and by a Heck reaction of 3a and 11 followed by a Wittig reaction and a second Heck reaction with 8. The pentacyclic oligomers 14 and 19 were prepared by a twofold Heck reaction of 13 with 4 and by a twofold Heck reaction of 15 with 16 followed by a Wittig reaction and a twofold Heck reaction with 8.     

Synthesis of the glivocarcin-M aglycone

The synthesis of the agylcone of the antibiotic Gilvocardin-M by a sequential Meerwein Diels-Alder route is reported. The D-ring of the agylcone is attached by a halogen atom directed Meerwein arylation reaction and the A-ring is attached by a halogen atom directed Diels-Alder reaction. In the key step the directing chlorine atom is removed by a new thiophenylation reduction sequence.     

The use of radioactive bacteriophage proteins as X-Y markers for silver stained two-dimensional electrophoresis gels and quantification of the patterns.

We have demonstrated the feasibility of using bacteriophage ghost proteins, tritiated by metabolic labeling, as a set of standard markers for two-dimensional gels in which the proteins are to be detected by silver staining. The results indicate that a 2.5 microgram load of phage proteins yields a reproducible silver pattern of 48 spots. The spots can also be readily identified by radioautography and radiofluorography, establishing their value as a standard constellation of markers. Quantification of these patterns by computerized densitometry indicates a general agreement between detection by silver staining and detection by radiofluorography.     

Back-electron transfer suppresses the periodic length dependence of DNA-mediated charge transport across adenine tracts

DNA-mediated charge transport (CT) is exquisitely sensitive to the integrity of the bridging pi-stack and is characterized by a shallow distance dependence. These properties are obscured by poor coupling between the donor/acceptor pair and the DNA bridge, or by convolution with other processes. Previously, we found a surprising periodic length dependence for the rate of DNA-mediated CT across adenine tracts monitored by 2-aminopurine fluorescence. Here we report a similar periodicity by monitoring N 2-cyclopropylguanosine decomposition by rhodium and anthraquinone photooxidants. Furthermore, we find that this periodicity is attenuated by consequent back-electron transfer (BET), as observed by direct comparison between sequences that allow and suppress BET. Thus, the periodicity can be controlled by engineering the extent of BET across the bridge. The periodic length dependence is not consistent with a periodicity predicted by molecular wire theory but is consistent with a model where multiples of four to five base pairs form an ideal CT-active length of a bridging adenine domain.     

Enantiomer systems of carnitinamide inorganic salts: introductory studies to a successful entrainment resolution

The ready availability of (R)-carnitinamide, an immediate synthetic precursor of (R)-carnitine, is an ambitious goal and resolutions, due to the very low cost of racemic carnitinamide, can be the most convenient technology to achieve it. Before developing a new advantageous resolution of carnitinamide chloride by entrainment, we characterized the enantiomer systems formed by the chloride, nitrate and sulfate of carnitinamide, mainly by DSC and IR analyses, proving that a different type of racemate is produced by each of these salts: a conglomerate by the chloride, a racemic compound by the nitrate and a solid solution, a very rare type of enantiomer system, by the sulfate.     

Controlled release by polyelectrolyte microcapsule membranes

Polyelectrolyte submicron microcapsules were prepared by interfacial crosslinking of an aqueous salt solution of poly(ethyleneimine) and a toluene solution of brominated poly-(2,6-dimethylphenylene oxide). The two solutions were brought together and mixed by sonication. As a result, a stable emulsion was obtained, which was subsequently cast into a membrane in which the microcapsules were embedded. The salt solution contained in the microcapsules could be released under controlled conditions. The rates of release were measured. They could be controlled by applying osmotic pressures, by additional quaternization of the membrane, or by modification of the structure of the capsule wall by introduction of a surfactant.     

Synthesis of cationic porphyrin modified amino acids

Derivatives of amino acids bearing a porphyrin moiety on a side chain were synthesized by coupling a porphyrin to a glutamic acid side chain; the utility of these compounds was demonstrated by their use in solid-phase synthesis of a peptide bearing a cationic porphyrin and by studying its DNA-binding properties.     

Standards and GC-MS analysis: An answer to the requirement of compound confirmation

Summary The attribution of an unknown GC-MS chromatographic peak to a specific substance should be confirmed whenever possible by comparison with a standard compound analysed under the same experimental conditions. The range of chemicals supplied by various companies is very wide but can never be completely comprehensive. This paper proposes two simple ways by which a reference compound may be obtained. Firstly, it may occur as an impurity in a commercial sample as a synthesis by-product. Alternatively, the compound may be synthesized by a simple procedure, preferably a single step one, by putting small amounts of reagents in a sealed glass vial placed in a programmable oven. Examples of these two approaches are described.     

Magnetic targeting and cellular uptake of polymer microcapsules simultaneously functionalized with magnetic and luminescent nanocrystals

By using a flow channel system for modeling the bloodstream in the circulatory system and by locally creating a magnetic field gradient caused by a permanent magnet, we demonstrate specific trapping of polymer capsules simultaneously functionalized with two types of nanoparticles--magnetic and luminescent nanocrystals. In the regions where the capsules were trapped by the magnetic field, drastically increased uptake of capsules by cells has been observed. The uptake of capsules by cells could be conveniently monitored with a fluorescence microscope by the luminescence of CdTe nanocrystals that had been embedded into the shells of the capsules. Our experiments envisage the feasibility of magnetic targeting of polymer capsules loaded by pharmaceutical agents to pathogenic parts of a tissue.     

Application of Polymer-Embedded Tris(2,2′ Bipyridine-Ruthenium(II) to Photodetection of Oxygen

A Nafion film containing tris(2,2′-bipyridine)ruthenium(II) as a luminescence probe was applied to photodetection of oxygen in a gas by utilizing the luminescence quenching by dioxygen. The linear Stern-Volmer plots of the emission intensity with respect to the oxygen concentration allowed quantitative determination of the oxygen. From the emission decay studied by a single-photon counting method, it was concluded that the quenching of the excited state Ru complex by oxygen proceeds by a conventional dynamic mechanism.     

微孔板发光二极管诱导荧光-表面活性剂增敏法测定盐酸小檗碱

研制了微孔板发光二极管诱导荧光分析仪,以发光二极管为激发光源,Y形光纤束传导激发光和荧光,采用平面型光敏二极管接收荧光.采用二维定位器移动微孔板,可实现对多个样品快速连续的测定.利用弱碱性介质中阴离子表面活性剂十二烷基苯磺酸钠(SDBS)对盐酸小檗碱荧光的增敏作用,在pH 9.0的Britton-Robinson缓冲溶...     

A Total Synthesis of FK-506(1)

A total synthesis of FK-506 (1) is presented. The synthesis features a highly convergent approach utilizing a block coupling strategy. Top and bottom half sections of the molecule are coupled by addition of a vinyl cuprate with a spiroenone. The alpha-allyl aldol functionality is revealed by a reductive opening of the spiroenone system. The labile alpha,beta-diketoamide hemiketal portion of the molecule is prepared by a late stage generation and oxidation of a masked enediol. Top and bottom half segments are themselves derived by coupling of smaller subunits, resulting in a very convergent route.     

Microphase separation during the concurrent formation of two polymer networks

As a rule, interpenetrating polymer networks (IPNs) are multiphase systems, and the degree of microphase separation is determined by the competition between the chemical kinetics of reaction and the physical kinetics of phase separation. For semi-IPNs of crosslinked polyurethane and linear polystyrene obtained by a one-step process, the development of the morphology has been followed by light transmission measurements and by optical microscopy, and finally examined by scanning electron microscopy. When phase separation takes place after gelation, the rather short elastic chains of polyurethane limit the growth of the styrenic phase at a submicroscopic level and the materials thus formed are transparent. On the contrary, when the reaction medium can phase-separate before gelation of polyurethane, the final morphology results from a superposition of two levels of phase separation: i) a fine dispersion of the components and ii) a gross phase separation of polystyrene noduli surrounded by a polyurethane-rich shell.     

A nanocatalyst-based assay for proteins: DNA-free ultrasensitive electrochemical detection using catalytic reduction of p-nitrophenol by gold-nanoparticle labels

This communication reports a nanocatalyst-based electrochemical assay for proteins. Ultrasensitive detection has been achieved by signal amplification combined with noise reduction: the signal is amplified both by the catalytic reduction of p-nitrophenol to p-aminophenol by gold-nanocatalyst labels and by the chemical reduction of p-quinone imine to p-aminophenol by NaBH4; the noise is reduced by employing an indium tin oxide electrode modified with a ferrocenyl-tethered dendrimer and a hydrophilic immunosensing layer.     

Novel photodegradation of the antifungal antibiotic pyrrolnitrin in anhydrous and aqueous aprotic solvents

The UV irradiation of pyrrolnitrin (1a), which is an antibiotic clinically useful against dermatophytosis and possesses a unique 2-(pyrrol-3-yl)nitrobenzene moiety in the molecule, in an anhydrous aprotic solvent resulted in the exclusive formation of transient 7,4'-dichlorospiro[1,3-dihydrobenzo(c)isoxazole-3,3'-pyrrolin-2'-one] (2a) via the intramolecular oxidation of the juxtaposed pyrrole ring by the triplet-excited nitro group. The irradiation in an aqueous aprotic solvent, however, allowed the concurrent occurrence of intramolecular cyclization by the singlet-excited nitro group in 1a and the hydroxylation at the 2-position of the pyrrole ring by water to afford 3,7-dichloro-8-hydroxy-8,8a-dihydropyrrolo[2,3-b]indol-2-one (3a), accompanied by the formation of 2a. Elongation of the irradiation time in these photoreactions caused a rapid consumption of the products, 2a and 3a, to give undetermined polar polymeric products. The present results indicate that the photodegradation of 1a is significantly influenced by the presence of water in the reaction media and by the nature of its excited state. Thus, the loss of the antifungal activities by the photosensitive antibiotic 1a was chemically proved.     

Direct Combination of a High Performance Liquid Chromatograph and a Circular Dichroism Spectrometer for Separation and Structural Analysis of Proteins

Abstract

Basic studies of the combined system of a high performance liquid chromatograph (HPLC) and a circular dichroism (CD) spectrometer for separation and analysis of proteins are described. The HPLC-CD measurement of standard protein mixture was easily carried out by using a micro flow-cell device with a beam condenser and with a thin cell of a 1 mm-optical path. The effluent was firstly monitored at 280 nm by using an UV detector and subsequently monitored at 220 nm by using a CD spectrometer. The CD spectrum at each chromatographic peak by CD was measured in the wavelength region of 250–195 nm by a stopped flow method.     

Localized Deposition of Chitosan as Matrix for Enzyme Immobilization

A local electrodeposition method was developed for chitosan by exploiting a pH gradient between a macroscopic electrode (the support) and a much smaller counter electrode. The deposition was confined either by using the direct mode of scanning electrochemical microscopy (SECM) or by performing the deposition in channels of a microfluidic network. The roughness was characterized by noncontact scanning force microscopy. The availability of amino groups at the surface of the microstructures was visualized after labeling by confocal laser scanning microscopy. The enzyme glucose oxidase could be entrapped during the electrochemical deposition and showed activity as seen by SECM images.     

Comparison of monolithic approaches for enantioselective capillary electrochromatography involving cyclodextrins

The access to CD-modified monoliths for enantiomeric separation by CEC can be divided into two main approaches. (i) Silica-based monoliths, prepared by either a sol-gel process or by sintering of silica particles, are modified after fabrication by coating with a CD selector. Alternatively the fusion of CD functionalized silica particle via gluing is feasible. (ii) Rigid or homogeneous organic polymer-based monoliths, prepared by polymerization of organic monomers in the presence of a porogen, are modified with the CD selector either by copolymerization or by physical incorporation into the continuous bed.     

Effect of the temperature on the kinetics of the chemisorption of atmospheric oxygen by a sodium dithionite solution

Properties of a 0.0316 mol/l sodium hydroxide solution and the reactivity of reactants involved in the reaction of aerobic oxidation of sodium dithionite are studied over a temperature range of 283–353 K, and changes in motive forces of the rate-limiting, multistage interphase transfer of atmospheric oxygen are estimated. It is established that heating accelerates the adsorption of the gas by the liquid surface by a factor of 18, decreases the solubility of oxygen by a factor of 2, increases the rate of diffusion of oxygen molecules by a factor of 5, and, as a result, increases the absorption of the oxidizer from the air by a factor of 8.     

Patterning biomolecules with a water-soluble release and protection interlayer

We report on a general lithography method for high-resolution biomolecule patterning with a bilayer resist system. Biomolecules are first immobilized on the surface of a substrate and covered by a release-and-protection interlayer of water-soluble polymer. Patterns can then be obtained by lithography with a spin-coated resist layer in a conventional way and transferred onto the substrate by reactive ion etching. Afterward, the resist layer is removed by dissolution in water. To demonstrate a high-resolution patterning, soft UV nanoimprint lithography has been used to produce high-density dot arrays of poly-(L-lysine) molecules on a glass substrate. Both fluorescence images and cell proliferation behaviors on such a patterned substrate have shown evidence of improved stability of biomolecule immobilization comparing to that obtained by microcontact printing techniques.