Latex and hollow particles of reactive polypyrrole: preparation, properties, and decoration by gold nanospheres

Polypyrrole-coated polystyrene latex particles bearing reactive N-amino functional groups (PS-PPyNH2) were prepared by the in-situ copolymerization of pyrrole (Py) and the active amino-functionalized pyrrole (PyNH2) in the presence of 1.33 microm-diameter polystyrene (PS) latex particles. These particles were prepared by dispersion polymerization of styrene using poly(N-vinylpyrrolidone), PNVP, as a steric stabilizer. The functionalized polypyrrole-coated PS particles (PS-PPyNH2) were characterized in terms of their particle size and surface morphology using transmission electron microscopy (TEM). Infrared and X-ray photoelectron spectroscopy (XPS) detected pyrrole-NH2 repeat units at the surface of the latex particles, indicating that this monomer had indeed copolymerized with pyrrole. The core-shell structure of the PS-PPyNH2 particles was confirmed by etching the polystyrene core in THF, leading to the formation of hollow conducting polymer capsules. The PS-PPyNH2 particles were then decorated with citrate-stabilized gold nanoparticles via electrostatic interactions. Furthermore, etching of the polystyrene core resulted in the formation of gold-decorated PPyNH2 hollow capsules.     

Development of a radiochemical separation for selenium with the aim of measuring its isotope 79 in low and intermediate nuclear wastes by ICP-MS

Selenium (Se) 79 is a beta emitter produced from ²³⁵U fission thus occurring as one of the fission products found in nuclear reactors. Due to its long half life (about 10⁵ years), ⁷⁹Se is one of the radionuclides of interest for the performance of assessment studies of waste storage or disposal. Thus, the National Radioactive Waste Management Agency (Andra, France) requests its monitoring in wastes packages before their disposal in specific sites.Measurement of ⁷⁹Se is difficult owing to its trace level concentration and its low activity in nuclear wastes. A radiochemical procedure has to be carried out in order to separate selenium from the matrix and to concentrate it before the measurement with a mass spectrometric or a nuclear technique. The beginning of the development is presented in this paper. The optimised protocol firstly developed in view of an ICP-MS measurement, includes five steps based on microwave digestion, evaporation and separations on ion exchange resins. It was tested first on synthetic solutions and was optimised in order to be applicable to a large number of sample types. The recoveries of the whole procedure were evaluated using natural ⁸²Se or the gamma emitter ⁷⁵Se as a radioactive spiker. Then, the protocol was applied to two solid samples spiked with natural selenium, a glass microfiber filter and an ion exchange resin, and two liquid samples spiked with ⁷⁵Se, a synthetic solution and an effluent. The yields obtained for both samples ranged from 70 up to 80%.     

Determination of carbon monoxide with palladium chloride

The gas sample transfer apparatus, as shown in Fig. 1, was designed to facilitate the analysis of several carbon monoxide samples during a normal work day. With this apparatus, gas samples were accurately transferred from the Tedlar bags leak free through the system to the reaction flask. Changing from one gas concentration to another was greatly simplified by using the quick-connect fittings; gas volumes were readily calculated from direct readings taken from the differential pressure gauge.Tests were conducted to assess the performance of the PdCl₂ method and the sampling system with various gas mixtures. The proposed PdCl₂ method utilizing this particular sampling scheme is capable of successfully measuring carbon monoxide in nitrogen cylinder gas at levels of 0.1, 0.05, and 0.01% with expected average recoveries of 96, 96, and 93%, respectively.     

Modelling the Epidemiological Consequences of HIV Infection and AIDS: A Contribution from Operational Research

As part of the worldwide effort involved in modelling the spread of AIDS, nothing has been heard from the operational research community. Yet OR, with its client-oriented modelling philosophy, patently has a role to play in assisting clinicians, epidemiologists and health planners to obtain greater understanding of this staggering threat to public health. Using the methods of system dynamics, a model of the spread of AIDS in the UK homosexual population has been developed. It is implemented on a personal computer, and possesses the capability to capture complex virological and behavioural features of the epidemic whilst portraying the consequences in an easily digested graphical form. Some examples of these results are presented. The model's structure and parameters are also fully described, together with sensitivity tests on the crucial incubation time distribution.     

An Expeditious Synthesis of Methyl Jasmonate

We present an efficient three‐step, two‐pot synthesis of methyl jasmonate (trans‐ 1 ) based on Diels–Alder cycloaddition of cyclopent‐2‐enone ( 2 ) and chloroprene (= 2‐chlorobuta‐1,3‐diene; 3d ) in either CHCl₃ or CH₂Cl₂, catalyzed by SnCl₄ (0.2 mol‐equiv.) at 20° (75% yield). Subsequent ozonolysis of a cis/trans 55 : 45 mixture of the cycloadduct 4d in either CH₂Cl₂ or AcOEt at ? 78°, followed by addition of Me₂S and MeOH in the presence of NaHCO₃, afforded, in 64% yield, a cis/trans 40 : 60 mixture of the known aldehyde 5c . The latter was reacted at ? 50° under salt‐free conditions with the propyl Wittig reactant to furnish 1 as a cis/trans 20 : 80 mixture ((E/Z) 3 : 97). Alternatively, a cis/trans 7 : 93 mixture ((E/Z) 4 : 96) was obtained in 88% yield from epimerized 5c (AcOH, H₂O, 40°; 99%) under usual Wittig conditions at ? 20°.     

Strategies for developing NADH detectors based on Meldola Blue and screen-printed electrodes: a comparative study

Three strategies have been compared to produce screen-printed amperometric detectors for NADH: mixing Meldola Blue (MB) in the screen-printing ink, incorporation of MB-Reinecke salt (MBRS) in the graphite ink and electrodeposition of films of MB-derived polymer (poly (MB)) on electrode surface. Following modification of graphite electrodes the mediators displayed values of the formal potential E°′ from −0.129 to −0.160 V vs. Ag/AgCl and pK_as of 5.09-6.02. A second redox couple with E°′=−0.450 V vs. Ag/AgCl was observed in cyclic voltammetry experiments with poly (MB) sensors or with old electrodes obtained according to the other two strategies. Electropolymerisation of MB allowed to achieve the best operational stability and best detection limit, 2×10⁻⁶ M, for amperometric detection of NADH, while the most extended linear range, 1×10⁻⁵-7.5×10⁻⁴ M, corresponds to sensors with MBRS. MB and MBRS electrodes were compared with a similar NADH detector produced by Gwent Electronic Materials, England. Several characteristics of the modified-electrodes induced by the fabrication by screen-printing were also highlighted.     

Engineering an obligate domain-swapped dimer of cyanovirin-N with enhanced anti-HIV activity

The anti-HIV cyanobacterial protein cyanovirin-N can undergo domain swapping to form an intertwined dimer. The dimeric form is stable at low pH and millimolar concentrations. By deleting an amino acid from the hinge linker about which domain swapping occurs, we have constructed an obligate domain-swapped dimer of cyanovirin-N that represents a new tetravalent carbohydrate binding protein that is stable over a large range of pH values. This obligate dimer displays enhanced anti-HIV activity relative to the wild-type cyanovirin-N monomer with an observed 3.5-fold decrease in IC(50) (9nM for the dimer vs 32 nM for the monomer) for inhibition of HIV-1 envelope-mediated cell fusion and, when expressed in Escherichia coli, can be rapidly obtained in >98% purity in a single chromatographic step.     

Qualitative and Quantitative Studies of Neodymium Doped Silica Gel-Glasses

The effect of neodymium ions on establishment of the sol-gel matrix and of the sol-gel matrix on the metal ion chemistry has been investigated by spectroscopic techniques including FTIR, FTNIR and UV/Vis. Materials were prepared by the pre-doping method and contained metal ions added as the chloride in either the aqueous or alcoholic phase at initial solution concentrations between 10–7 M and 1 M. The presence of the metal ions affects the rate of drying of the gel-silicas and can reduce the time required for weight stabilization by ca. 50%. Irrespective of the solvent system used for metal ion incorporation, the metal ions are found in 9-fold coordination sites in the as-prepared gels, in 8-fold coordination sites in gels where solvent has been removed by evacuation and for gels heated to 800°C, a highly symmetric environment (concentrations of 0.01 M and below) or 8-fold solid-state coordination where there is a degree of covalent character between the liganding atoms and the metal ions. Metal ion concentration and absorbance are related for gel-silicas prepared with dopants at initial concentrations of 0.01–1 M, although the absorbances measured depend on the solvent used for incorporation of the metal ion. Experimental data suggest that the matrix and metal ions interact at various stages in the formation of the doped gel-silica, however, we do not presently know if these interactions are transitory or permanent in nature.     

A New Mechanism of Thermochromism for Silica Sol-gel Materials

Summary.  In this contribution we provide evidence for thermochromic colour changes unique to silica based materials formed at low temperature by the sol-gel process. The mechanism requires the matrix and the dopant to interact in order to produce the observed colour changes. The materials formed have potential application as temperature sensitive light filters, visual temperature indicators, self-diagnostic labels for electronic devices and infrared recording media. Corresponding author. E-mail: carole.perry@ntu.ac.uk Received June 28, 2002; accepted July 30, 2002