Platinum nanoparticle-modified electrodes, morphologic, and electrochemical studies concerning electroactive materials deposition

The present work describes the synthesis of platinum nanoparticles followed by their electrophoretic deposition onto transparent fluorine-doped tin oxide electrodes. The nano-Pt-modified electrodes were characterized by voltammetric studies in acidic solutions showing a great electrocatalytic behavior towards H⁺ reduction being very interesting for fuel cell applications. Morphological characterization was performed by atomic force microscopy on different modified electrodes showing a very rough surface which can be tuned by means of time of deposition. Also, nickel hydroxide thin films were galvanostatically grown onto these electrodes showing an interesting electrochemical behavior as sharper peaks, indicating a faster ionic exchange from the electrolyte to the film.     

An acrylic acid modified polypropylene as a compatibilizing agent for the intercalation/exfoliation of an organically modified montmorillonite in polypropylene

This work dealt with the effect of using an acrylic acid modified polypropylene (PP‐g‐AA) as a compatibilizing agent for the intercalation/exfoliation of an organically modified montmorillonite (o‐MMT) in a polypropylene matrix (PP). Two PP‐g‐AA containing the same AA content (6 wt %) and having different molar masses were used. The o‐MMT content was 0, 1, or 5 wt % of total mass and the PP‐g‐AA/o‐MMT mass ratio was 0/1, 1/1, 2/1, or 5/1. Results of wide angle X‐ray scattering (WAXS) and transmission electronic microscopy (TEM) showed that without the PP‐g‐AA, the o‐MMT was dispersed in the PP/o‐MMT in a micrometer scale, similar to a conventional microcomposite. With the PP‐g‐AA, the o‐MMT was much better dispersed and its interlayers were intercalated and partly exfoliated by the polymer chains. Compared with the neat PP, some PP/PP‐g‐AA/o‐MMT systems exhibited higher G′ values and a yield stress at low frequencies, indicating that the PP‐g‐AA promoted the intercalation/exfoliation of the o‐MMT. The compatibilizing efficiency of those two PP‐g‐AA was very similar. Generally speaking, the higher the PP‐g‐AA/o‐MMT mass ratio, the better the state of dispersion and the degree of intercalation/exfoliation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1811–1819, 2008     

Antitrypanasomal activity of novel benzaldehyde-thiosemicarbazone derivatives from kaurenoic acid

A series of new thiosemicarbazones derived from natural diterpene kaurenoic acid were synthesized and tested against the epimastigote forms of Trypanosoma cruzi to evaluate their antitrypanosomal potential. Seven of the synthesized thiosemicarbazones were more active than kaurenoic acid with IC?? values between 2-24.0 mM. The o-nitro-benzaldehyde-thiosemicarbazone derivative was the most active compound with IC?? of 2.0 mM. The results show that the structural modifications accomplished enhanced the antitrypanosomal activity of these compounds. Besides, the thiocyanate, thiosemicarbazide and the p- methyl, p-methoxy, p-dimethylamine, m-nitro and o-chlorobenzaldehyde-thiosemicarbazone derivatives displayed lower toxicity for LLMCK? cells than kaurenoic acid, exhibing an IC?? of 59.5 mM.     

Bead-injection determination of total mercury in river water samples.

A bead-injection system is proposed for total mercury determination in river-water samples. The procedure is based on the introduction of a defined quantity of a resin suspension in the flow system. The selected beads are packed inside of a flow cell and the formed resin mini-column constitutes the optical path. The sample volume is then selected, and its passage by the mini-column allows retention of the mercury ions on the surfaces of the beads. The introduction of a spectrophotometric reagent in the flow system leads to the formation of a colored Hg-dithizone complex on the surface of the bead, which is spectrophotometricaly monitored. The spent beads are directed to waste, allowing the system to become ready to process another sample. The proposed system handles about 20 measurements per hour, consuming 1000 microl of the sample, 1 mg of Chelex 100 resin and 1.25 microg of Dithizone per determination. When 1000 microl of the sample is injected, a linear analytical curve is obtained (A = 0.0052[Hg] + 0.1028, from 0 up to 30 microg l(-1), R2 = 0.995); the detection limit is estimated to be 0.9 microg l(-1). The results are precise, r.s.d. < 9%; spiked sample recoveries within 91.2 and 109% are found.     

Resveratrol-derived stilbenoids and biological activity evaluation of seed extracts of Cenchrus echinatus L

A phytochemical study of the ethyl acetate fractions from the partition of seeds and roots methanol extracts of Cenchrus echinatus L. led to the isolation of three resveratrol-derived stilbenoids: pallidol (1), carasiphenol C (2) and nepalensinol B (3). The results of a topic anti-inflammatory evaluation, DPPH assay and antiproliferative activity against adenocarcinoma cells (Caco 2) are described.     

Electrochromic properties of a metallo-supramolecular polymer derived from tetra(2-pyridyl-1,4-pyrazine) ligands integrated in thin multilayer films

The electrochromic behavior of iron complexes derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) and a hexacyanoferrate species in polyelectrolytic multilayer adsorbed films is described for the first time. This complex macromolecule was deposited onto indium-tin oxide (ITO) substrates via self-assembly, and the morphology of the modified electrodes was studied using atomic force microscopy (AFM), which indicated that the hybrid film containing the polyelectrolyte multilayer and the iron complex was highly homogeneous and was approximately 50 nm thick. The modified electrodes exhibited excellent electrochromic behavior with both intense and persistent coloration as well as a chromatic contrast of approximately 70%. In addition, this system achieved high electrochromic efficiency (over 70 cm(2) C(-1) at 630 nm) and a response time that could be measured in milliseconds. The electrode was cycled more than 10(3) times, indicating excellent stability.     

“On line” mass spectrometric detection of ammonia oxidation products generated by polypyrrole based amperometric sensors

Polypyrrole (PPy) is the conducting polymer most widely employed in electrochemical sensors for ammonia detection in the last decade. Although sensors have been described in depth in the literature, the mechanism of ammonia detection by polypyrrole is still a matter of controversy. The differential electrochemical mass spectrometry (DEMS) technique, together with UV-Vis spectroscopy, gives direct and conclusive evidence with respect to the ammonia oxidation products formed in NaOH solution (pH=10) at polyrrole or N-methyl polypyrrole film sensors polarized at 0.35 V (Ag/AgCl). Monitoring of the different possible ammonia oxidation products by on-line DEMS measurements indicates that only NO is formed and that other species such as N₂ or N₂O are absent. UV-Vis absorption spectroscopy also showed that ionic products such as nitrate or nitrite are not formed.