Peróxido de hidrogênio: importância e determinação

A brief discussion about the hydrogen peroxide importance and its determination is presented. It was emphasized some consideration of the H2O2 as reagent (separated or combined), uses and methods of analysis (techniques, detection limits, linear response intervals, sensor specifications). Moreover, it was presented several applications, such as in environmental, pharmaceutical, medicine and food samples.

Teor e composição do óleo essencial de cinco acessos de mentrasto

This study aimed to analyse the content and the composition of the essential oil of five accesses of mentrasto (Ageratum conyzoides). Five accesses of mentrasto with three repetitions were used. The accesses were obtained in Mariana-MG (AMA), Piranga-MG (API), Visconde do Rio Branco (ARB) and Viçosa-MG (AVB and AVP). The essential oil was obtained by hydrodistillation and the identification of the oil components by CG and GC/MS. The ARB access presented the higher essential oil content, that is 0.70% (P < 0.05). Eleven chemical compounds were identified. The precocene I was the main constituent in the access API, and the precocene II was the main constituent in the accesses AMA, ARB, AVB and AVP.

O pKa de indicadores ácido-base e os efeitos coloidais

An experiment is proposed that can be included in undergraduate courses of chemistry. The subject is the acidity of organic compounds, which are employed as pH indicators, particularly in acid-base titrations. The indicators used are methyl orange, bromophenol blue and bromocresol green in aqueous medium. The influence of colloidal systems on the equilibrium is evaluated by the pKa. The colloids employed are surfactants like sodium dodecyl sulfate, cetyl-trimethylammonium bromide and a polymeric non-ionic F127 (pluronics). The effect of stabilization promoted by the system on the acidic or basic structureof the indicator establishes the action mechanism of the colloid on the pKa values.

Um aparato para monitorar reações rápidas: um "stopped-flow" artesanal de baixo custo

The modern stopped-flow reaction analyzer has shown high efficiency and flexibility, which provides outstanding sample economy with a dead-time of less than 1 ms. However the cost of the equipment imposes a serious restriction to many Brazilian scientists and teachers. In this work we describe the construction of a low-cost stopped-flow system coupled to a UV-Vis spectrophotometer. The performance of the system was checked by monitoring the kinetics of two reactions: the fading of phenolphthalein in aqueous alkaline solution and the chlorophyll a demetallation in acid medium. The apparatus showed reasonable efficiency with a dead-time of 0.3 to 0.5 s. The very good results obtained in these two illustrative processes show that the system is satisfactory for determining rate constants with mean reaction times ranging from seconds to minutes.

Pilhas a combustível de óxido sólido: materiais, componentes e configurações

In this paper the current status of fuel cells is described with particular emphasis on high (T > 800 ºC) and intermediate (T < 800 ºC) temperature solid oxide fuel cells. Also the importance of the fuel cell technology is shown. Reviewed are the fundamental features, the basic principles, types of fuel cell, fabrication methods, cell configurations and the development of components (cathodes, anodes, electrolytes, interconnect) and materials.

Caracterização e propriedades do material coloidal nanoestruturado β-FeOOH/bentonita

A new mixed material was obtained through the combination of the suspensions of iron oxy-hydroxide and bentonite clay, denoted BFe. Analysis of its structure (XRD, Mossbauer and TGA) and composition (AAS) suggests the maintenance of the layer structure of the clay and an increase in the thermal stability of the BFe. Electrochemical studies performed in different electrolytes show that only in an alkaline medium it is possible to observe the redox peaks relative to the processes involving Fe+2/Fe+3 pair. Tests that evaluated the potential use of the photo-Fenton process showed an efficient degradation process of the dyes in significantly reduced reaction times.

Development of dissolution method for benznidazole tablets

The aim of this work was the development of a dissolution method for benznidazole (BNZ) tablets. Three different types of dissolution media, two stirring speeds and apparatus 2 (paddle) were used. The accomplishment of the drug dissolution profiles was compared through the dissolution efficiency. The assay was performed by spectrophotometry at 324 nm. The better conditions were: sodium chloride\hydrochloride acid buffer pH 1.2 with stirring speed of 75 rpm, volume of 900 mL and paddle as apparatus. Ahead of the results it can be concluded that the method developed consists in an efficient alternative for assays of dissolution for benznidazole tablets.

Construção e aplicação de um minissensor de filme de bismuto utilizando materiais de baixo custo para determinações voltamétricas in loco

The construction of a low cost mini sensor containing a bismuth-film electrode (BiFE), as work electrode, a silver electrode as pseudo reference electrode, and copper as counter electrode is proposed. The application of this mini sensor using a low cost electrochemical cell for in loco voltammetric determinations of inorganic and organic analytes is also described.

Atividade antibacteriana in vitro e toxicidade frente à Artemia salina Leach. de alguns compostos triazenos

Bacterial resistance to antibacterial agents is currently a major concern. We report the synthesis, in vitro antibacterial activity and toxicity toward Artemia salina of six diaryltriazene compounds bearing different substituent groups. Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) values against standard strains (ATCC) and clinical isolates (including ESBL, MBL and AmpC strains) were good to very good, in the range 8 to 128 mg mL-1. Results suggest that hydroxyl, 4-carboxyl and 4-phenyldiazenil groups attached to the diaryltriazenes provide enhanced activity. Toxicity results showed very low LC50 values for three compounds (10-fold lower than DTIC).

A quimiometria nos cursos de graduação em química: proposta do uso da análise multivariada na determinação de pkª

An experiment was proposed applying the Chemometric approach of Multivariate Analysis for inclusion in undergraduate Chemistry courses to promote and expand the use of this analytical-statistical tool. The experiment entails the determination of the acid dissociation constant of dyes via UV-Vis electronic spectrophotometry. The dyes used show from simple equilibrium to very complex systems involving up to four protolytic species with high spectral overlap. The Chemometric methodology was more efficient than univariate methods. For use in classes, it is up to the teacher to decide which systems should be utilized given the time constraints and laboratory conditions.

Influência de meios de cultura e da interação carbono-nitrogênio no crescimento e esporulação de Penicillium sclerotigenum

A podridão verde do inhame é uma doença de grande expressão econômica no estado de Pernambuco. Foram realizados estudos fisiológicos visando avaliar a influência de seis meios de cultura (BDA, Aveia, V-8, Czapeck, Cenoura e Inhame) sobre o crescimento micelial, esporulação e peso seco de dois isolados de Penicillium sclerotigenum (IB1 e IPR2). Os meios BDA e Inhame induziram maior crescimento micelial e, a maior produção de conídios foi obtida no Czapeck e Aveia, para ambos isolados utilizados. O meio de Aveia propiciou maior peso seco para o IB1 e IPR2. Foi estudado o efeito de diferentes combinações de fontes de carbono (maltose, dextrose, sacarose, amido) e nitrogênio (asparagina, peptona, nitrato de sódio, nitrato de potássio) sobre o desenvolvimento de P. sclerotigenum. O nitrato de sódio foi menos favorável ao crescimento micelial e esporulação. A combinação sacarose x peptona proporcionou o melhor crescimento micelial para ambos isolados. Para o IB1, a maior produção de conídios foi obtida com a sacarose x nitrato de potássio e para o IPR2 com a sacarose x peptona.