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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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...     

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.     

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.     

Unidirectional redox-stimulated movement around a C-C single bond

A remarkable challenge for the design of molecular machines is the realization of a synchronized and unidirectional movement caused by an external stimulus. Such a movement can be achieved by a unidirectionally controlled change of the conformation or the configuration. Biphenol derivatives are one possibility to realize a redox-driven unidirectional molecular switch. For this reason, a 4,4'-biphenol derivative was fixed to a chiral cyclopeptidic scaffold and stimulated by chemical oxidants and reduction agents. The conformation of the switch was determined by DFT calculations by using B3LYP and the 6-31G* basis set. The switching process was observed by UV and circular dichroism (CD) spectroscopic measurements. Several oxidation agents and various conditions were tested, among which (diacetoxy)iodobenzene (DAIB) in methanol proved to be the best. In this way it was possible to synthesize a redox-stimulated molecular switch with a movement that is part of a rotation around a biaryl binding axis.     

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.     

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.     

Conditions for the onset of current oscillations at the limiting current of the iron electrodissolution in sulfuric acid solutions

The experimental conditions and parameters that control the transition from a steady to an nonsteady limiting current and vice versa in the anodic Fe dissolution are studied in sulfuric acid solutions by using a downward-facing Fe electrode. Periodic and chaotic current oscillations are observed at the beginning of the limiting current region within a fixed potential region by decreasing the sulfuric acid concentration, by increasing the Fe-disk rotation rate and by increasing a series external resistance. It is found that current oscillations emerge when theIR drop exceeds a critical value (IR)_crit. The latter depends on the hydrodynamic conditions pertaining to the system. This is realized by the differences appeared in the value of (IR)_crit on using a stationary or a rotating Fe electrode. The effect of hydrodynamic conditions is shown by additional experimental results obtained by using an upward-facing Fe electrode, by increasing the density and viscosity of the solution on addition of glycerol, and by altering the solution properties near the Fe surface on addition of halide ions. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth. This article was submitted by the authors in English.     

Paraelectric and ferroelectric order in two-state dipolar fluids

Monte Carlo simulations are used to examine the cooperative creation of a polar state in fluids of two-state particles with nonzero dipole in the excited state. With lowering temperature such systems undergo a second-order transition from nonpolar to polar, paraelectric phase. The transition is accompanied by a dielectric anomaly of polarization susceptibility increasing by three orders of magnitude. The paraelectric phase is then followed by a formation of a nematic ferroelectric which further freezes into a fcc ferroelectric crystal by a first-order transition. A mean-field model of phase transitions is discussed.     

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.     

Synthesis, characterization of dihydrolipoic acid capped gold nanoparticles, and functionalization by the electroluminescent luminol

The use of gold nanoparticles as biological probes requires the improvement of colloidal stability. Dihydrolipoic acid (DHLA), a dithiol obtained by the reduction of thioctic acid, appears therefore very attractive for the stabilization and the further functionalization of gold nanoparticles because DHLA is characterized by a carboxylic acid group and two thiol functions. The ionizable carboxylic acid groups ensure, for pH > or = 8, the water solubility of DHLA-capped gold (Au@DHLA) nanoparticles, prepared by the Brust protocol, and the stability of the resulting colloid by electrostatic repulsions. Moreover almost all DHLA, adsorbed onto gold, adopts a conformation allowing their immobilization by both sulfur ends. It is proved by sulfur K-edge X-ray absorption near edge structure spectroscopy, which appears as an appropriate tool for determining the chemical form of sulfur atoms present in the organic monolayer. Such a grafting renders the DHLA monolayers more resistant to displacement by dithiothreitol than mercaptoundecanoic acid monolayers. The presence of DHLA on gold particles allows their functionalization by the electroluminescent luminol through amine coupling reactions assisted by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. As a luminol-functionalized particle is nine times as bright as a single luminol molecule, the use of the particles as a biological probe with a lower threshold of detection is envisaged.