Envelhecimento acelerado em diásporos de Oenocarpus bacaba (Arecaceae)

O objetivo do presente trabalho foi adequar o teste de envelhecimento acelerado para avaliar a qualidade fisiológica de diásporos de Oenocarpus bacaba Mart. (bacaba). Inicialmente, os diásporos foram expostos às temperaturas de 41; 43 e 45 ºC, durante 3; 6; 12; 24; 36; 48 e 72 h, com cerca de 100% de umidade relativa do ar. Foram considerados dois critérios de germinação: emissão da primeira bainha igual ou superior a 1cm e plântula normal. o teste de germinação foi realizado com 6 repetições de 20 diásporos, em temperatura de 30 ºC e fotoperíodo de 12 h. Pelos resultados preliminares, observou-se que os lotes de diásporos de bacaba podem ser separados em níveis de vigor por meio do envelhecimento acelerado, em 43ºC e com cerca de 100% de umidade relativa do ar, por 48 h. os quatro lotes de diásporos foram então submetidos, num segundo experimento, a 43 ºC por 24; 48 e 72 h, sendo adotada como critério de germinação a emissão de primeira bainha. Em 45 ºC, a porcentagem de germinação foi drasticamente reduzida após 12 h. Não houve diferenças significativas entre os critérios de germinação utilizados. Os lotes de diásporos foram separados em diferentes níveis de vigor após 48 e 72 h de exposição a 43 ºC. De acordo com os resultados obtidos, sugere-se o uso de primeira bainha como critério de germinação e período de envelhecimento de 48 h a 43 ºC, para a avaliação da qualidade fisiológica de diásporos de bacaba.

Íon Be H+ em campo elétrico uniforme intenso

The influence of a strong external electric field in chemical bonding is not extensively studied. In this work, the behavior of the potential energy curves of the BeH+ ion in an external electric field is investigated by means of variational calculations using molecular orbitals. For simplicity we consider the case where the external field is parallel to the molecular axis, in the direction of the dipole moment, which raises the polarization of the ion. The effects on dissociation are investigated.

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

Chloride poisoning is known as having an inhibitor effect in the activity of metal catalysis. In this work in situ infrared spectroscopy (FTIR) of adsorbed carbon monoxide and x-ray photoelectron spectroscopy (XPS) were used to investigate the effect of chloride presence in the electronic metal density in the d subshell of palladium dispersed on alumina. The chloride poisoning effect was interpreted as an electronic effect since a weak back-bonded Pd-CO was formed due to the decrease in the electronic density of the d subshell of palladium, which could be also detected by the higher Pd 3d5/2 binding energy in the chloride presence. A similar poisoning effect was also observed for chloride free Pd/Al2O3 reduced at 500 ºC, and it was interpreted based on the interaction of metal with the alumina surface. The use of molybdena/alumina binary system as support, yield a contrary effect due to the metal-support interaction.

Decomposição do NO sobre Cu suportado em zeólitas

Direct decomposition of NO on copper supported on zeolite catalysts such as MCM-22 and Beta was compared with that on the thoroughly studied Cu-ZSM-5. The catalysts were prepared by ion-exchange in basic media. They were characterized by atomic absorption, surface area, nitrogen adsorption at 77K, X-ray diffraction and temperature programmed reduction. The products of the reaction were analyzed by Fourier transform infrared spectroscopy using a gas cell. Catalytic activity tests indicated that zeolite catalysts, like Beta and MCM-22, lead to NO conversion values comparable to ZSM-5.

Síntese e emprego do ciclometalado [Pd(dmba)(N3)(PPh3)] em processos catalíticos envolvendo a n-carbonilação redutiva de nitroarenos a carbamatos e na síntese de derivados da uréia

This work deals with the use of the cyclometallated compound [Pd(dmba)(N3)(PPh3)] in homogeneous catalytic processes comprising the reductive N-carbonylation of nitrobenzene and p-nitrotoluene to ethyl-phenylcarbamate and ethyl-4-methylphenylcarbamate, respectively. The cyclopalladated compound was also employed in the synthesis of urea derivatives by reacting p-nitrotoluene and m-nitrotoluene, respectively, with p-toluidine and and m-chloroaniline.

Compósitos magnéticos baseados em hidrotalcitas para a remoção de contaminantes aniônicos em água

In this work the adsorption features of hydrotalcites (Al, Mg- CO3) and the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbents for anionic contaminants in water and subsequently removed from the medium by a simple magnetic process. The magnetic hydrotalcites were characterized by XRD, magnetization measurements, N2 adsorption isotherms and Mössbauer spectroscopy. These magnetic adsorbents show remarkable adsorption capacity for anionic contaminants in water.

As secretarias regionais e as divisões científicas da Sociedade Brasileira de Química

This article offers an overview on the historical facts and the recent state of the Regional Secretaries and the Scientific Divisions in the course of 30 years of SBQ.

Avaliação da estabilidade do marcador plasmático do estresse oxidativo: malondialdeído

Malondialdehyde (MDA) is one of the lipid peroxidation products widely used as indicator of cellular injury. However, the short-term and the long-term stability of this biomarker remain unclear. The objective of this work was to evaluate the stability of plasmatic MDA at -20 ºC, utilizing thiobarbituric acid (TBA) as derivative in spectrophotometric and chromatographic analysis. The results showed that MDA was stable for 24 h after blood collection, was not stable when stored after alkaline hydrolysis, remained stable for 30 days after TBA derivatization and was stable for 3 days when stored after n-butanol extraction, all at -20 ºC.

Determinação voltamétrica de metais em águas e fluidos biológicos empregando mineralização de amostras com radiação ultravioleta

This work describes the optimization of pretreatment steps for the destruction of organic matter in samples of waters and biological fluids, by using an UV irradiation system with a high power UV radiation source (400 W). The efficiency of the system constructed for the photo-decomposition of samples of model waters, natural waters and biological fluids was investigated by performing recovery experiments of the metallic species Zn(II), Cd(II), Pb(II), Cu(II), Al(III) and Fe(III). The use of UV irradiation allowed the liberation of metals bound to the organic matrix and the determination of the total content of elements in the samples.

Quantificação simultânea de indicadores biológicos de exposição a solventes orgânicos por cromatografia líquida de alta eficiência

Biological monitoring is very important to guarantee health to workers. This method was developed for simultaneous determination of xylene, toluene, styrene and ethylbenzene metabolites. It involves only dilution and centrifugation of urine samples and improved chromatographic conditions. Analyses show recovery > 95%; r² > 0.99; intermediate precision CV% < 6% and % bias < ±10. Exposed subjects presented at least three metabolites in urine. The method proved to be feasible, reliable and important in biological monitoring, especially in exposure to organic solvent mixtures.

Materiais híbridos à base de sílica obtidos pelo método sol-gel

This review deals with silica based hybrid materials obtained by the sol-gel method. It involves concepts, classifications and important definitions regarding the sol-gel method that allows obtaining materials with organic and inorganic components dispersed in a molecular or nanometric level. We discuss the properties and characteristics of hybrid materials related to experimental synthesis conditions. We devote a special attention to the nanostructured materials, where the self-organization is imposed by the organic component. Finally, we present some important applications of these materials based on their specific properties.

Degradação fotocatalítica do fungicida tebuconazole em solução aquosa

The tebuconazole photocatalytic degradation kinetics was studied in a batch reactor using TiO2 (P25-Degussa) as catalyst and a high pressure mercury lamp. The photolysis, adsorption and irradiation effects in the reaction rate were evaluated. Afterward, the suspension catalyst concentration and initial pH to the maximum reaction rate was determined. It was observed that the reaction rate can be approached by a pseudo-first order, with a maximum kinetics constant at 260 mg L-1catalyst concentration and pH 7.7.

Nanotubos de TiO2 dopados com nitrogênio: comparação das atividades fotocatalíticas de materiais obtidos através de diferentes técnicas

TiO2 nanotubes were synthesized by hydrothermal method and doped with three nitrogen compounds to enhance photocatalytic activity under visible light. Catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and specific surface area and pore volume determined by BET and BJH methods, respectively. Photocatalytic activity was evaluated by photodegradation of rhodamine B under visible and UV radiations. Results showed doped-nanotubes were more efficient under visible light. The best photocatalytic activity was for sample NTT-7-600/NH3I, being 30% higher than the non-doped sample.

Síntese, caracterização e atividade fotocatalítica de catalisadores nanoestruturados de TiO2 dopados com metais

Titanium dioxide nanostructured catalysts (nanotubes) doped with different metals (silver, gold, copper, palladium and zinc) were synthesized by the hydrothermal method in order to promote an increase in their photocatalytic activity under visible light. The catalysts were characterized by X-ray diffraction, diffuse reflectance spectroscopy, transmission electron microscopy and specific area and pore volume determination. The materials' photocatalytic activity was evaluated by rhodamine B decomposition in a glass batch reactor. Under UV radiation, only nanotubes doped with palladium were more active than the TiO2 P25, but the samples doped with silver, palladium and gold exhibited better results than the undoped samples under visible light.

A FTIR study of the metal-support interactions and hydrogen spillover on Pd/TiO2 and Ni/TiO2

Nickel and palladium dispersed on titania support were submitted to reductive treatment, under hydrogen, at 200 and 500 ºC. After the reductive thermal treatment the materials were exposed to carbon monoxide (10 Torr) and analyzed in the infrared region. The increasing of the electronic density in the metallic d subshell, produced by the reductive thermal treatment, was monitored by the infrared stretching band shift of carbon monoxide adsorbed and it was interpreted as a consequence of the metal-support interactions. The highest effect was observed for Pd/TiO2 system. From the FTIR spectra was also observed that the hydrogen spillover was stronger on Pd/TiO2 than Ni/TiO2 system.