Carlos A. Ferreira

Application of polypyrrole/TiO2 composite films as corrosion protection of mild steel

This work is a study of the anticorrosion protection of polypyrrole (PPy) on AISI 1010 steel (mild steel) by the incorporation of TiO2 pigment into the PPy matrix during electrochemical synthesis. The influence of parameters such as stirring, concentration, pH and nature of the electrolyte were investigated. The degree of pigment incorporation into the polymeric matrix with respect to time and current densities of the electrodeposition process were also investigated. The influence on the current efficiencies of the process was evaluated. The morphology of the composite film was studied by scanning electron microscopy (SEM) and the distribution of the pigment within the polymeric matrix by X-ray photoelectron spectroscopy (XPS). The PPy/TiO2 composite showed a considerable improvement in anticorrosion properties with respect to PPy films after being submitted to salt spray and weight loss tests. These composite films can be applied as a primary coating replacing the phosphatized layers on mild steel. # 2002 Published by Elsevier Science B.V.

Synthesis and characterization of polypyrrole/TiO2 composites on mild steel

The anodic codeposition of polypyrrole and TiO2 on AISI 1010 steel substrates in oxalic acid medium was studied from the standpoint of their use as protective coatings against corrosion. The influence of surface treatment, pH, stirring and current density (j) on the current efficiency (γ) and pigment concentration incorporated in the polymer (Cc) were investigated. The highest Cc values (7.5%) were found at j = 5 mA cm−2, pH 4 and stirred baths. The composites were characterized by adherence and surface roughness tests, XPS, EDX, SEM, FTIR and cyclic voltammetry.

Cloning and partial characterization of a Boophilus microplus (Acari: Ixodidae) calreticulin☆

We report the cloning, sequence characterization and expression analysis of a calreticulin (CRT) coding cDNA of Boophilus microplus. CRT is a calcium-binding protein involved in multiple cell functions and possibly implicated in parasites host immune system evasion. The CRT cDNA sequence and its molecular characterization are described. Sequence similarity and phylogenetic analyses indicate a close relationship to other arthropod CRT sequences. The CRT cDNA was also expressed in a procariotic system and the recombinant protein (rBmCRT) was used to raise antibodies in a rabbit. Expression analyses of the corresponding gene in different developmental stages and tissues were performed by RT-PCR and Western-blot, which indicated a ubiquitous expression of the B. microplus calreticulin gene and demonstrated its presence in saliva. Sera of tick-infested bovines suggested that this protein may not be able to induce an IgG-based humoral response in its natural host.

Measuring the Proton Conductivity of Ion-Exchange Membranes Using Electrochemical Impedance Spectroscopy and Through-Plane Cell

The role of the incorporation of conducting polymer (CP), doped with different sulfonic acid organic molecules, in polystyrene (PS) and high-impact polystyrene (HIPS) with poly(styrene-ethylene-butylene) (SEBS) triblock copolymer has been investigated. Two factors associated with this model membrane system are addressed: (i) the influence of the presence of a low concentration of doped conducting polymer and (ii) the influence of the membrane preparation method. Membrane characterization and bulk conductivity measurements allowed the conclusion that proton conductivity has been promoted by the addition of CP; the best results were achieved for PAni-CSA, in either PS/SEBS or HIPS/SEBS blends. Additionally, the water uptake only decreased with the addition of PAni-doped molecules compared to the pure copolymer, without loss of ion-exchange capacity (IEC). Electrodialysis efficiency for HIPS/SEBS (before annealing) is higher than that for HIPS/SEBS (after annealing), indicating that membrane preparation method is crucial. Finally, through-plane cell arrangement proved to be an effective, quick, and time-saving tool for studying the main resistance parameters of isolating polymers, which is useful for application in industry and research laboratories working with membranes for electrodialysis or fuel cells.

Thermal and dynamic-mechanical characterization of rice-husk filled polypropylene composites

Natural fiber-filled polymer composites have attracted great interest due to increasing environmental concerns and their low costs. In this study, the properties of rice husk flour-filled polypropylene (PP) were analysed in view of the large quantities of this agricultural product available as residue in Brazil. The rice husk flour (RHF) was characterized by SEM and particle size distribution. The properties of the composites were studied by MFI, DMA, DSC and TGA analyses. A commercial PP modified with maleic anhydride (MAPP) was used as coupling agent. It was verified that RHF decreased the MFI of the composites and that the coupling agent decreased it even more. The efficiency of MAPP was confirmed by the high storage modulus and high loss factor of the coupled composites.

cDNA cloning, expression and characterization of a Boophilus microplus paramyosin.

The tick Boophilus microplus is a 1-host tick that causes important losses to bovine herds, and protective antigens are being investigated in order to develop vaccines that avoid the use of acaricides. Paramyosins are multi-functional invertebrate muscle proteins, whose roles may include host immunomodulation, and seem to be a prominent candidate in a schistosomiasis vaccine. We report here the cloning, expression and characterization of a B. microplus paramyosin (BmPRM). Sequence analysis of the full length coding sequence cDNA shows high identity to other arthropod paramyosin sequences, and the predicted molecular weight, pI and secondary structure are consistent with a typical paramyosin. Western-blot expression analysis indicates the presence of BmPRM in all tissues and developmental stages tested, but not in saliva. The recombinant protein (rBmPRM) was shown to bind both IgG and collagen. Possible implications of these activities with host evasion mechanisms are discussed.

Heterogeneous Persister Cells Formation in Acinetobacter baumannii

Bacterial persistence is a feature that allows susceptible bacteria to survive extreme concentrations of antibiotics and it has been verified in a number of species, such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus spp., Mycobacterium spp. However, even though Acinetobacter baumannii is an important nosocomial pathogen, data regarding its persistence phenotype are still lacking. Therefore, the aim of this study was to evaluate the persistence phenotype in A. baumannii strains, as well as its variation among strains after treatment with polymyxin B and tobramycin. Stationary cultures of 37 polymyxin B-susceptible clinical strains of A. baumannii were analyzed for surviving cells after exposure to 15 µg/mL of polymyxin B for 6 h, by serial dilutions and colony counting. Among these, the 30 tobramycin-susceptible isolates also underwent tobramycin treatment at a concentration of 160 µg/mL and persister cells occurrence was evaluated equally. A high heterogeneity of persister cells formation patterns among isolates was observed. Polymyxin B-treated cultures presented persister cells corresponding from 0.0007% to 10.1% of the initial population and two isolates failed to produce detectable persister cells under this condition. A high variability could also be observed when cells were treated with tobramycin: the persister fraction corresponded to 0.0003%–11.84% of the pre-treatment population. Moreover, no correlation was found between persister subpopulations comparing both antibiotics among isolates, indicating that different mechanisms underlie the internal control of this phenotype. This is the first report of persister cells occurrence in A. baumannii. Our data suggest that distinct factors regulate the tolerance for unrelated antibiotics in this species, contrasting the multi-drug tolerance observed in other species (eg. dormancy-mediated tolerance). Supporting this observation, polymyxin B – an antibiotic that is believed to act on non-dividing cells as well – failed to eradicate persister cells in the majority of the isolates, possibly reflecting a disconnection between persistence and dormancy.

Poly(3,4-ethylenedioxythiophene) on self-assembled alkanethiol monolayers for corrosion protection

Self-assembled monolayers (SAMs) of octanethiol and dodecanethiol were used to modify the stainless steel substrates for electrodepositing poly(3,4-ethyledioxythiophene) (PEDOT), a well known polythiophene derivative. Although the influence of the alkanethiol monolayers on the morphology and topology of micrometric (thickness: 2.25–2.35 μm) PEDOT films is practically negligible, they increase significantly the ability to store charge and the adherence. In contrast, treated substrates not only enhance the electrochemical properties of ultra-thin PEDOT films (thickness: 150–350 nm) but also affect significantly the thickness, roughness, porosity, morphology and topology. Such changes depend on both the length of the alkyl chain in the alkanethiol and the incubation period used for the preparation of the SAMs. Finally, the protection against corrosion imparted by PEDOT films deposited on treated substrates has been examined and compared with that obtained using PEDOT deposited on bare stainless steel electrodes. Inhibition of the corrosion in a 3.5% NaCl solution was found to be considerably higher when PEDOT is deposited on treated electrodes, which has been attributed, in addition to the barrier effect produced by the SAMs, to the structural changes induced at the first stages of the electropolymerization.

Distribution analysis of TiO2 and commercial zinc phosphate in polypyrrole matrix by XPS

Abstract TiO2 as well as a commercial zinc phosphate pigment were incorporated to the PPy matrix during its electropolymerisation on mild steel. Their distribution in the composite films (PPy/TiO2 and PPy/zinc phosphate) was examined by X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy (SEM). Chemical and electrochemical factors had different influences on their distribution within the PPy matrix. XPS analysis showed that TiO2 is found throughout the PPy films and it is uniformly distributed onto the surface, conversely to zinc phosphate. The latter is present in two heterogeneously distributed forms; (1) a conductive soluble minority and (2) a non-conductive non-soluble majority. The minority form is probably inserted from the soluble species in a complexed form and plays a counter-ion role.

Identification of Candida spp. by phenotypic tests and PCR

The correct identification of Candida species is of great importance, as it presents prognostic and therapeutical significance, allowing an early and appropriate antifungical therapy. The purpose of this study was to identify isolates of Candida spp. from oral mucosa of 38 patients with oral candidosis evaluated in 2004 by phenotypic methods and PCR, discriminating C. albicans from the other Candida species. The tests used for phenotypic analysis were germ-tube and chlamydoconidia production, culture in CHROMAgar™ Candida, carbohydrate assimilation test, growth at 45ºC and culture in Tween 80 agar. Genotypic confirmation was performed by PCR. Phenotypic tests showed that 63.2% strains formed germ-tubes, 73.7% produced chlamydoconidia, and 63.2% showed green colonies in chromogenic medium, presumptively indicating C. albicans or C. dubliniensis. The carbohydrate assimilation test confirmed these results. A total of 21% strains were identified as C. krusei and 13.2% were indicative of C. tropicalis. Of these later strains, three produced chlamydoconidia. The association of other phenotypic tests with culture in Tween 80 agar identified 95.8% of strains as C. albicans and 4.2% as C. dubliniensis. All 24 strains indicative of C. albicans and C. dubliniensis were confirmed by PCR as C. albicans.