A nonenzymatic biosensor based on gold electrodes modified with peptide self-assemblies for detecting ammonia and urea oxidation.

We have developed a nonenzymatic biosensor for the detection of ammonia and urea oxidation based on the deposition of peptide microstructures onto thiolated gold electrodes. FF-MNSs/MCP/Au assemblies were obtained by modifying gold substrates with 4-mercaptopyridine (MCP), followed by coating with l,l-diphenylalanine micro/nanostructures (FF-MNSs) grown in the solid-vapor phase. Benzene rings and amide groups with peptide micro/nanostructures interact with synthetic NH4(+) receptors through cation-π and hydrogen bonding. AuOH clusters on the Au surface provided the catalytic sites. The application of a predetermined concentration of analytes at the peptide interfaces activated the catalytic sites. We observed a relationship between the stability of films and the crystal structure of peptides, and we organized the FF-MNSs into an orthorhombic symmetry that was the most suitable assembly for creation of our biosensors. At 0.1 mol L(-1) NaOH, these FF-MNSs/MCP/Au electrodes have electrocatalytic properties regarding ammonia and urea oxidation that are comparable to those of enzyme-based architectures. Under optimal conditions, the electrocatalytic response is proportional to the ammonia and urea concentration in the range 0.1-1.0 mmol L(-1). The sensitivity was calculated as 2.83 and 81.3 µA mmol L(-1) cm(-2) for ammonia and urea, respectively, at +0.40 V (vs SCE). Our detection method is easy to follow, does not require a mediator or enzyme, and has strong potential for detecting urea via nonenzymatic routes.

Lipase production by Botryosphaeria ribis EC-01 on soybean and castorbean meals: optimization, immobilization, and application for biodiesel production.

The effects of soybean and castorbean meals were evaluated separately, and in combinations at different ratios, as substrates for lipase production by Botryosphaeria ribis EC-01 in submerged fermentation using only distilled water. The addition of glycerol analytical grade (AG) and glycerol crude (CG) to soybean and castorbean meals separately and in combination, were also examined for lipase production. Glycerol-AG increased enzyme production, whereas glycerol-CG decreased it. A 2(4) factorial design was developed to determine the best concentrations of soybean meal, castorbean meal, glycerol-AG, and KH2PO4 to optimize lipase production by B. ribis EC-01. Soybean meal and glycerol-AG had a significant effect on lipase production, whereas castorbean meal did not. A second treatment (2(2) factorial design central composite) was developed, and optimal lipase production (4,820 U/g of dry solids content (ds)) was obtained when B. ribis EC-01 was grown on 0.5 % (w/v) soybean meal and 5.2 % (v/v) glycerol in distilled water, which was in agreement with the predicted value (4,892 U/g ds) calculated by the model. The unitary cost of lipase production determined under the optimized conditions developed ranged from US$0.42 to 0.44 based on nutrient costs. The fungal lipase was immobilized onto Celite and showed high thermal stability and was used for transesterification of soybean oil in methanol (1:3) resulting in 36 % of fatty acyl alkyl ester content. The apparent K m and V max were determined and were 1.86 mM and 14.29 µmol min(-1) mg(-1), respectively.

Study of the influence of pigments in the polymerization and mechanical performance of commercial dental composites / Estudo sobre a influência dos pigmentos na polimerização e no desempenho mecânico dos compósitos dentais comerciais

Objective: The aim of this study was to analyze the influence of the amount of shade pigment and opacifying components inthe polymerization and mechanical properties in two brands of Brazilian dental resin composites. Material and Methods: Master Fill microhybrid resin for enamel (colorless and shades A2, A4), and Opallis for enamel and dentine, both shades A2. Thecomposite resins were photopolymerized by a LED device at 19.7 J. The mechanical properties were obtained through flexuralresistance (FR), compression strength (CS) and Vickers microhardness (VM); the degree of conversion (DC) was obtainedby FTIR and translucence was obtained by sphere espectrometer. Conclusion: The analysis indicated that resin with more colorpigments (MA4) or more opacity components (ODA2) hadlow polymerization and poor mechanical properties than clearer(M) or more translucent (OEA2) resins, indicating that betterperformance can be obtained by increasing the radiation dose.

Objetivo: O objetivo deste estudo era analisar a influênciada quantidade de pigmentos de cor e de componentes opacificantesna polimerização e nas propriedades mecânicas em duasmarcas Brasileiras de resinas compostas dentárias. Material e Métodos: Resina Master Fill, microhíbrida, para esmalte (incolore nas cores A2 e A4) e Opallis para esmalte e dentina, ambas na cor A2. As resinas foram fotoativadas por um aparelho diodo emissor de luz (LED) a 19.7 J. As propriedades mecânicas foram obtidas por resistência flexural, força de compressão, microdureza Vickers; o grau de conversão foi obtido por FTIR e a translucidez foi obtida por meio do Espectrômetro de Esfera. Conclusões: As análises indicaram que resinas com mais pigmentos decor (MA4) ou mais componentes opacificantes (ODA2) mostrarambaixa polimerização e pobre qualidade mecânica quandocomparadas às mais claras e/ou mais translúcidas, indicando que a dose de irradiação deve ser aumentada para obter melhor performance.