Determinação espectrofotométrica de hexametilenotetramina (HMT) em medicamentos, utilizando ácido cromotrópico e forno de micro-ondas

This paper proposes a methodology for spectrophotometric determination of hexamethylenetetramine (HMT) by using chromotropic acid in a phosphoric acid media employing a domestic microwave oven as a source of heating. The reddish-purple soluble product is quantitatively formed after 30 s of irradiation and obeys the Beer´s law in the range between 0.1-1.2 mg L-1 HMT (r = 0.99925). The method was applied successfully in commercial pharmaceutical preparations containing dyes in their composition. The results showed that the method proposed is feasible for simplicity, speed, low cost, precision and accuracy when compared with United States Pharmacopeia official method.

Desenvolvimento de métodos analíticos para determinação de agrotóxicos em sedimentos por cromatografia gasosa monodimensional e bidimensional abrangente com micro detector de captura de elétrons

The development of analytical methods for determination of eight pesticides of different chemical classes (trichlorfon, propanil, fipronil, propiconazole, trifloxystrobin, permethrin, difenoconazole and azoxystrobin) in sediments with gas chromatography-micro-electron capture detector (GC/µECD) and comprehensive two-dimensional gas chromatography with micro-electron capture detector (GCxGC/µECD) is described. These methods were applied to real sediment samples, and the best results were obtained using a 5% diphenyl-methylpolysiloxane column for 1D-GC. For GCxGC the same column was employed in the first dimension and a 50%-phenyl-methylpolysiloxane stationary phase was placed in the second dimension. Due to the superior peak capacity and selectivity of GCxGC, interfering matrix peaks were separated from analytes, showing a better performance of GCxGC.

O uso de aparelhos de micro-ondas domésticos em aulas experimentais de química orgânica: nitração de salicilaldeído

The use of microwave in chemistry has known benefits over conventional heating methods, e.g. reduced reaction times, chemical yield improvement and the possibility if reducing or eliminating the use of organic solvents. We describe herein a procedure for the nitration of salicylaldehyde in water using a domestic microwave oven, which can be used as an experiment in the undergraduate chemistry laboratory. The experiment involves safe and rapid preparation and identification of the position isomers by thin layer chromatography and 1H NMR, or by their melting points.

Aspectos coloidais da adesão de micro-organismos

The ability of bacteria to attach to surface and develop into a biofilm has been of considerable interest to food industry. Electrostatic, Lifhistz-van der Waals and Lewis acid-base forces are usually considered responsible for the interactions at the interface of the bacterial adhesion. The study of microbial adhesion thermodynamic is important because it represents the reflection of microbial surface and food processing surface physicochemical characteristics. This review examines the most important aspects involved in bacterial attachment to a surface with emphases in thermodynamics of adhesion process.

Isolamento e seleção de micro-organismos resistentes e capazes de volatilizar mercúrio

Mercury (Hg) occurs in the environment as a natural and anthropogenic element, and through the years the accumulation of mercury has affected the integrity of ecosystems and human health. This study presents a screening of microorganisms resistant to organic and inorganic mercury, the determination of the minimum inhibitory concentration of Hg, the estimation of the mercury volatilization by selected microorganisms and the dynamics of volatilization. Eight Gram-negative bacteria resistant to high concentrations of mercury (60 to 210 mg L-1) were selected, and these isolates showed ability to volatilize the metal. The dynamics of the volatilization of the Proteus mirabilis M50C demonstrated that in only 4 h of incubation it was possible to volatilize 72% of the mercury present in the culture. The results showed promising application for bioremediation strategies.

Síntese hidrotermal assistida por micro-ondas como metodologia sintética eficiente para obtenção da rede metalorgânica [ZN(BDC)(H2O)2]n

This work presents the optimization of the microwave-assisted hydrothermal synthesis of [Zn(BDC)(H2O)2]n . The reactions were carried out at the fixed temperature of 120 ºC for 10, 20, 30 and 40 min. Pure crystalline [Zn(BDC)(H2O)2]n was obtained in high yield (ca. 90%) with a reaction time of 10 min. The phase obtained and its purity was confirmed by Rietveld refinement, with a final value for Rwp/Rexp equal to 1.48. Increased reaction times (20, 30 and 40 min) favored the formation of unwanted by products, resulting in mixtures of several crystalline phases.

Irradiação de micro-ondas aplicada à síntese orgânica: uma história de sucesso no Brasil

This review article shows the publications in the field of microwave irradiation published by Brazilian researchers over the past 10 years. In South America, Brazil leads the publication of articles with the use of microwave irradiation possessing a large advantage in number of articles published over the others countries. The works were divided into four major areas: Catalysis, Reactions without Solvent, Heterocycles Chemistry, Natural Products and Other, and some could be classified in more than one category.

Um exemplo de aplicação da Microscopia Raman na autenticação de obras de arte

In the present work, Raman Microscopy was employed in the characterization of the pigments used in a drawing assigned to Tarsila do Amaral, one of the most important Brazilian artists. The work (colored pencil on paper), supposedly produced in the 1920 decade, is of a very simple composition, where blue, green and brown were the colors used. Prussian Blue was found as the blue pigment, whereas green was a mixture of copper phthalocyanine and a yellow dye, probably a diarylide; the brown pigment was a carbonaceous compound. Prussian Blue was replaced by phthalocyanine as pigment since the end of the 1930's and the possibility that it could have been used as pigment in the 1920's can be ruled out.

Análise de pinturas rupestres do Abrigo do Janelão (Minas Gerais) por microscopia raman

Rock art paintings from Abrigo do Janelão (Minas Gerais, Brazil) were non-destructively investigated by Raman Microscopy, aiming at the identification of materials used, their interaction and degradation. This technique is particularly tailored for heterogeneous samples and allows unequivocal identification of the substances present in the investigated sample. Pigments, were identified together with products of microbiological degradation; no binders were detected. White pigment was identified as calcite (CaCO3), whereas charcoal was used as black, goethite (α-FeOOH) as yellow and hematite (α-Fe2O3) as red. Whewellite (CaC2O4.H2O) and weddelite (CaC2O4.2H2O) were detected and their origin was assigned to degradation products from microbiological activity.

Desenvolvimento de um algoritmo para identificação e correção de spikes em espectroscopia Raman de imagem

Raman imaging spectroscopy is a highly useful analytical tool that provides spatial and spectral information on a sample. However, CCD detectors used in dispersive instruments present the drawback of being sensitive to cosmic rays, giving rise to spikes in Raman spectra. Spikes influence variance structures and must be removed prior to the use of multivariate techniques. A new algorithm for correction of spikes in Raman imaging was developed using an approach based on comparison of nearest neighbor pixels. The algorithm showed characteristics including simplicity, rapidity, selectivity and high quality in spike removal from hyperspectral images.

Síntese da fenitoína assistida por micro-ondas: proposta de aula prática para alunos de graduação

Microwave synthesis is considered a breakthrough in the field of chemistry due to its benefits over conventional heating methods. We describe, for the first time, the total synthesis of phenytoin adapted for a microwave reactor, proposed as an experiment for undergraduate courses. When carried out with microwaves, the synthetic route provided phenytoin in 6 min and 30 s, while for conventional heating the total time was 170 min. The experiment also involves rapid identification of compounds by TLC, ¹H NMR, FT-IR and melting points determination.

Síntese e hidrólise de azalactonas de Erlenmeyer-Plöchl mediadas por radiação micro-ondas em aparelhos doméstico e dedicado: experimentos de química orgânica para a graduação

This work describes a green chemistry experiment for the synthesis of Erlenmeyer-Plöchl azalactones mediated by microwave irradiation, employing both dedicated and domestic equipment. Hippuric acid was reacted with equimolar amounts of benzaldehyde, p-chloro-benzaldehyde or p-N,N-dimethyl-benzaldehyde in acetic anhydride as the solvent. Acid hydrolysis of obtained 4-benzylidene-2-phenyloxazol-5(4H)-one under microwave and convectional heating afforded Z-α-(benzoylamino)cinnamic acid at a 51-61.5% yield. The UV-Vis molecular spectra of 4-benzylidene-2-phenyloxazol-5(4H)-one and 4-(4'-N,N-dimethylbenzylidene)-2-phenyloxazol-5(4H)-one were obtained in ethanol, CH2Cl2 and DMSO and bathochromic shift was observed for the latter azalactone.

Miniprojeto para ensino de Química Orgânica Experimental baseado no acoplamento catalítico N-C promovido por micro-ondas

This paper describes a three-week mini-project for an Experimental Organic Chemistry course. The activities include N-C cross-coupling synthesis of N-(4-methoxyphenyl) benzamide in an adapted microwave oven by a copper catalyst (CuI). Abilities and concepts normally present in practical organic chemistry courses are covered: use of balances, volumetric glassware, separation of mixtures (liquid-liquid extraction and filtration), chromatographic techniques, melting point determination and stoichiometric calculations.

Cromatografia gasosa-espectrometria de massas e derivatização assistida por micro-ondas na identificação de isômeros de glicose: uma prática para o ensino avançado em análise e caracterização de compostos orgânicos

This work reports a practical case based on the use of microwave-assisted derivatization and GC-MS for the analysis of glucose. Using two different methods for derivatization, one reference compound and the calculated dipole moment, all the isomers of glucose were identified. Identification was corroborated for the assignment of structures using the mass spectra. With this work, students are expected to associate different types of information to solve the complex problem of the analysis of glucose.