Made available in DSpace on 2014-06-11T19:29:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-03-18Bitstream added on 2014-06-13T19:17:32Z : No. of bitstreams: 1 pereira_rp_me_arafo.pdf: 718418 bytes, checksum: e3bb9ad8e88ee0f369f92dd6e3ca7045 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Vários protocolos de desinfecção podem ser usados para romper a cadeia de infecção cruzada entre o consultório odontológico e o laboratório de prótese. A inclusão de agentes antimicrobianos à composição do gesso ou a manipulação do gesso com soluções desinfetantes podem ser usados com esta finalidade. O propósito deste estudo foi avaliar a atividade antimicrobiana de dois agentes desinfetantes (digluconato de clorexidina 2% e cloridrato de clorexidina 98%) incorporados ao gesso IV (FujiRock - GC Europe, Leuven, Bélgica) durante sua manipulação. No teste microbiológico de difusão em Agar foram uti l izados os seguintes microorganismos: Escherichia coli, Staphylococcus aureus, Bacilus subtilis e Candida albicans. Amostras com 5 mm de diâmetro e 3 mm de espessura foram separadas em quatro grupos: 1) gesso manipulado com água destilada esterilizada (controle positivo); 2) discos de papel embebidos com solução de digluconato de clorexidina 2% (controle negativo); 3) gesso manipulado com solução de digluconato de clorexidina 2%; 4) gesso com a incorporação de cloridrato de clorexidina 98% em pó, na proporção de 1% da massa do gesso, e manipulado com água destilada esterilizada. Após 1 hora e 24 horas do vazamento do gesso, as amostras foram posicionadas em placas de Petri com meios de cul tura específicos inoculados com as suspensões microbianas. A atividade antimicrobiana dos desinfetantes foi avaliada pelo diâmetro médio dos halos de inibição do crescimento microbiano. Os valores foram analisados pela ANOVA Aninhada (p<0,05) e teste de Tukey para comparações específicas. Os resultados encontrados demonstraram que os agentes desinfetantes analisados apresentaram atividade antimicrobiana quando misturados ao gesso, com exceção para Candida albicans, na qual não houve efeito da solução de clorexidina nos dois períodos de análise... / Many protocols for disinfection procedures can be used to break the chain of cross-contamination between dental office and dental laboratory. The inclusion of antimicrobial agent to the composition of gypsum or the manipulat ion of gypsum with disinfectant substances can be used to that aim. The purpose of this study was to evaluate the antimicrobial activity of two disinfectant agents (2% chlorhexidine digluconate and 98% chlorhexidine hydrochloride) incorporated into type IV dental stone (FujiRock - GC Europe, Leuven, Belgium) at the time of mixing. The microbiological test used was the Agar diffusion test to the following microorganisms: Escherichia coli, Staphylococcus aureus, Bacilus subtilis and Candida albicans. Samples of 5 mm in diameter and 3 mm in length were separated in four groups: 1) dental stone mixed wi th steri le distilled water (positive control); 2) paper disk soaked wi th solution of 2% chlorhexidine digluconate (negative control); 3) dental stone mixed with solution of 2% chlorhexidine digluconate; 4) dental stone wi th incorporation of chlorhexidine hydrochloride 98% powder, in proportion of 1% of the dental stone mass, and mixed with sterile distilled water. The samples were placed, 1 hour and 24 hours after pouring of dental stone, in Petri plates with specific cul ture medium wich were inoculated with the microbial suspensions. The antimicrobial activity of disinfectant was evaluated by the average diameter of microbial growth inhibi tion zones. The data were analyzed with a Nested ANOVA (p<0,05) and Tukey test for specific comparisons. The disinfectant agents analyzed demonstrated antimicrobial effect against microorganisms used in this study, in exception to Candida albicans, against wich there was not effect from chlorhexidine digluconate at two periods of analysis. Significant difference between disinfectantes were found to all microrganisms... (Complete abstract click electronic access below)

This project studied the production of barium sulphate nanoparticles through inhibition of crystal growth, during precipitation, by different surfactants. Barium sulphate is the pure form of the ore baryte, which due to its high density and softness, is the most commonly used additive used to increase the density of drilling fluids. A non-agglomerating, stable nano-scale dispersion of barium sulphate particles would have significant technical and commercial impact in the drilling fluids industry. This thesis tested the possibility of precipitating barium sulphate and restricting its crystal growth with inhibitors, creating nanoparticles. Six inhibitors were tested; dodecanoic acid, palmitic acid, stearic acid, adamantane carboxylic acid, methylnonanoic acid and a mixture of phosphate esters known commercially as Fazewet. Precipitated, inhibited barium sulphate was characterised using powder XRD, DRIFT FTIR and solid-state NMR (SSNMR). All inhibitors were shown to form single-phase, orthorhombic barium sulphate crystals proving that the inhibitors affect only the surfaces of precipitated crystals and do not enter the crystal lattice. FTIR allowed the relative adsorbed concentration of each inhibitor to be assessed. The results indicate that adsorbed inhibitor increases with increasing inhibitor concentrations but that their attachment is not proportional to the concentration. In most cases concentrations of 0.1mol l-1 of inhibitor were sufficient to saturate the crystal surface. SSNMR also agreed with this although the sample size was too small, due to equipment restrictions, to make definitive conclusions. Through the use of the Debye-Scherrer equation, the crystallite size was calculated and showed that at concentrations of 0.2mol l-1 all inhibitors other than palmitic acid produced nano-scale (< 100nm) crystallites. Further analysis showed that further reductions could be achieved through precipitation in an alkaline pH environment, with the application of mechanical shear and by using adding 50% v/v of ethanol. iv Laser diffraction particle size analysis showed that the dominant factor in reducing particle size distribution was inhibitor concentration. The volume-based PSD used by the laser diffraction system was considered to distort excessively the particle sizes present and so analysis switched to dynamic light scattering. DLS showed that dodecanoic acid, palmitic acid and stearic acid, despite forming nano-scale crystallites, could not produce a nano-scale dispersion of barium sulphate and as such were unsuitable for use in drilling fluids. Stable nano-scale dispersions were found to have been formed when inhibited with adamantane carboxylic acid, methylnonanoic acid and Fazewet. DLS also confirmed that dispersed particle size rather than simply crystallite size could be reduced with an alkaline pH and high mechanical shear. Concentration was still the dominant effect, however with the smallest particles sizes (ZAvg) being observed at concentrations of 0.6mol l-1. The particle sizes for the three modifiers were approaching that of the crystallite size, suggesting that some further reduction is possible, but large reductions are unlikely. All three inhibitors produced sub 100nm ZAvgs, with the smallest produced by methylnonanoic acid of 43nm. Spherical nanoparticles were observed through the use of ESEM and TEM. Due to equipment time restrictions only 0.2mol l-1 treatment levels could be examined, but ESEM showed apparent nanoparticle clusters, later confirmed using pixel count and SFDA methods. TEM analysis showed discrete particles as small as 3nm, indicating that the lower limit for achievable particle size may be lower than PSD measurements would suggest. The results indicate that adamantane carboxylic acid, methylnonanoic acid and Fazewet sufficiently inhibit crystal growth to be potential candidates for the production of barium sulphate nanoparticles. These three inhibitors produce a barium sulphate dispersion that is stable and nano-scale even after drying and redispersion.

No description available.

Efforts to discover an efficient yet environmentally friendly mode of metal nanoparticle (NP) synthesis are increasing rapidly. A ‘green’ route that avoids the high costs, toxic wastes and complicated protocols associated with chemical synthesis methods is therefore highly sought after. A biologically based protocol will provide the possibility of gaining control over the mechanism merely by manipulating the experimental conditions of the system. Given that the properties of nanoparticles are highly dependant on the morphology of the particles themselves, this mechanistic control will provide significant industrial advantages with regards to tailoring specific properties of the nanoparticles produced. The key objectives of this study were to: a) determine whether a consortium of sulfate-reducing bacteria was capable of platinum nanoparticle synthesis, b) elucidate the bioreductive, enzymatic mechanism responsible, and c) attempt to control the morphologies of the particles produced. A consortium of sulfate-reducing bacteria (SRB), isolated from sewage sludge, was used in these investigations due to the advantages a consortium provides in comparison to pure cultures. The syntrophic relationships established within the constituent species not only prevent the growth of contaminant microbes, but increases the oxygen-tolerance of the system as a whole. The sulfate-reducing consortium was shown to possess an aerobic mechanism for Pt(IV) reduction which, though different from the anaerobic bioreductive mechanism previously identified in literature, did not require an exogenous electron donor. It was demonstrated that the Pt(IV) ion becomes reduced to Pt(0) via a two-cycle mechanism involving Pt(II) as the intermediate. Further investigation elucidated the reduction of Pt(IV) to Pt(II) to be dependant on a novel Pt(IV) reductase which becomes upregulated in the presence of Cu(II), while the reduction of Pt(II) to Pt(0) occurred by means of a periplasmic hydrogenase. To our knowledge, this is the first time a coupled mechanism for Pt(IV) reduction by micro-organisms has been proposed. A cell-free, crude protein solution from the consortium produced both geometric and irregular platinum nanoparticles. The wavelength of 334 nm was chosen as a nonquantitative indicator of Pt(0) nanoparticle formation over time. The optimum conditions for nanoparticle synthesis were pH 9.0, 65 ˚C and 0.75 mM Pt(IV) as H2PtCl6 salt. In the absence of a buffer a Pt(IV) concentration > 1 mM resulted in the precipitation of protein-nanoparticle bioconjugates, due to unfavourable acidic conditions. This demonstrated that the nanoparticles were binding to and becoming stabilised by general protein in the cell-free solution. Upon addition of a sodium-bicarbonate buffer, a general increase in Pt(IV) reduction to Pt(II) was observed. The addition of the buffer also resulted in an unexplained change in particle morphology and for this reason was not used in subsequent investigations. Polyvinylpyrrolidone (PVP) was shown to compromise the reduction rate of the Pt(IV) ion by SRB cells. The presence of extracellular NP’s was suggested by the colour of the supernatant turning brown and the A334 increasing over time. Attempts to visualise the particles by transmission electron microscopy (TEM) resulted in an unexpected phenomenon where nanoparticles could be observed to form dynamically upon irradiation by the electron beam. Extended irradiation by the electron beam also resulted in structural changes of the particles occurring during observation. An increase in temperature was shown to increase the reduction rate which in turn resulted in particles decreasing in size. The starting pH was shown to have a significant effect on the reduction rate and particle morphology although specific trends could not be identified. In conclusion, the cell-soluble extract from the sulfate-reducing consortium investigated, is capable of Pt(0) nanoparticle synthesis. Precise control over the particle morphology was not attained although the mechanism was further clarified and optimal conditions for nanoparticle synthesis were determined.

No description available.

No description available.

No description available.

As stagnant water contacts copper pipe and lead solder (simulated soldered joints), a corrosion cell is formed between the metals in solder (Pb, Sn) and copper. If the resulting galvanic current exceeds about 2 µA/cm², a highly corrosive microenvironment can form at the solder surface, with pH <2.5 and chloride concentrations 11 times higher than bulk water levels. Waters with relatively high chloride tend to sustain high galvanic currents, preventing passivation of the solder surface and contributing to lead contamination of potable water. If the concentration of sulfate increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced, and solder surfaces were readily passivated. Mechanistically, at the relatively high concentrations of lead and low pH values that might be present at lead surfaces, sulfate forms precipitates while chloride forms soluble complexes with lead. Considering net transport of anions in water, a chloride-to-sulfate mass ratio (CSMR) above 0.77 results in more chloride than sulfate transported to the lead anode surface, whereas the converse occurs below this CSMR. Bicarbonate can compete with chloride transport and buffer the pH, providing benefits to lead corrosion. Although orthophosphate is often an effective corrosion inhibitor, tests revealed cases in which orthophosphate increased lead and tin release from simulated soldered joints in potable water. Phosphate tended to increase the current between lead-tin and copper when the water contained less than 10 mg/L SO₄²⁻ or the percentage of the anodic current carried by SO₄²- ions was less than 30%. Additionally, nitrate in the potable water range of 0-10 mg/L N dramatically increased lead leaching from simulated soldered pipe joints. Chloramine decay and the associated conversion of ammonia to nitrate during nitrification could create much higher lead contamination of potable water from solder in some cases. In practical bench-scale studies with water utilities, the CSMR was affected by the coagulant chemical, blending of desalinated seawater, anion exchange, and sodium chloride brine leaks from on-site hypochlorite generators. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from lead-tin solder connected to copper. / Ph. D.

Thesis (M.S.)--Chemical Engineering, Georgia Institute of Technology, 2005. / Empie, Jeff, Committee Chair ; Banerjee, Sujit, Committee Member ; Deng, Yulin, Committee Member. Includes bibliographical references.

The increased risk of atherothrombosis in chronic kidney disease (CKD) has been under extensive examination for decades now. However, a treatment tailored for CKD patients is yet to be found. Current management plans can only tackle comorbidities and mostly fail. This thesis study examines the current literature related to CKD and thrombosis. The aim is to find a target suitable for therapeutic exploration. Normalizing the risk of thrombosis in CKD patients could curb a huge margin of their morbidity and mortality. In recent years, molecular biology studies attributed the extreme thrombogenicity in CKD to the retained uremic toxins. Indolic compounds are uremic toxins with a well described point of thrombotic activation. Of them, indoxyl sulfate is to be highlighted since it was shown to that it is one of the strongest pro-thrombotic uremic toxin. It is possible to therapeutically target this CKD specific cause of hyperthrombogenicity. Further research is very much needed in this area.