Efeito da concentração do catalisador acetilacetonato férrico na cura de poliuretano à base de polibutadieno líquido hidroxilado (PBLH) e diisocianato de isoforona (IPDI)

The reaction between hydroxy-terminated polybutadiene and isophorone diisocyanate constitutes the base of the curing process of the most composite solid propellant used in the propulsion of solid rocket propellant. In this work, differential scanning calorimetry and viscosity measurements were used to evaluate the effect of the ferric acetylacetonate catalyst concentration on the reaction between HTBR and IPDI. These analyses show one exotherm, which shifts to lower temperatures as the catalyst concentration increases. The viscosity analyses show that the increase of temperature causes, at first, a reduction in the mixture viscosity, reaching a minimum range called gelification region (increasing the crosslinking density).

Estudo de algumas reações oxoacidobásicas no solvente NaCl fundido entre 1100K e 1200K

Equilibrium constants (K) of some oxoacidbasic reactions in molten NaCl in the temperature range of 1100K to 1200K, have been measured potentiometrically with a calcia stabilized zirconia oxide ion (O2-) indicator electrode. In molten NaCl at 1100K the pKs values (in molality scale) for HCl/H2O and HO-/H2O are respectively 11.0 ± 0.3; 1.6 ± 0.3 and the pKs for CaO is 4.3 ± 0.3. The results have been compared with those determined previously by Combes for the molten equimolar NaCl-KCl mixture and are in good agreement with literature data and gives some qualitative explanation of the comparison of oxoacidbasic properties between molten NaCl and NaCl-KCl.

Validação lateral em relações quantitativas entre estrutura e atividade farmacológica, QSAR

The comparative QSAR is a tool for validating any statistical model that seems to be reasonable in describing an interaction between a bioactive new chemical entity, BIONCE, and the biological system. In order to deeper the understanding of the relationships and the meaning of parameters within the model it is necessary some kind of lateral validation. This validation can be accomplished by chemical procedures using physicochemical organic reactions and by means of biological systems. In this paper we review some of such comparisons and also present a lateral validation between the same set of antimicrobial hydrazides acting against Saccharomyces cerevisiae yeast and Escherichia coli bacterium cells. QSARs are presented to shed light in this important way of stating that the QSAR model is not the endpoint, but the beginning.

Constituintes químicos isolados de simira glaziovii (K. schum) steyerm. e a atribuição dos deslocamentos químicos dos átomos de carbono e hidrogênio do alcalóide ofiorina e seus derivados

Chromatographic fractionation of bark extracts from Simira glaziovii (Rubiaceae) afforded the steroids beta-sitostenone, stigmastenone, beta-sitosterol and stigmasterol, methyl trans-4-hidroxy-3-methoxycinamate (1), the alkaloids harmane (2) and the new stereoisomer of ophiorine B (3). The structures were established by ¹H and 13C NMR, including 2D techniques and mass spectral analysis, of the natural products and pentaacetyllyalosidic acid (4a) and beta-carboline monoterpene tetraacetylglucoside (5, 1,22-lactamlyaloside) derivatives obtained by chemical transformations.

Emprego de planejamento fatorial para a otimização das temperaturas de pirólise e atomização de Al, Cd, Mo e Pb por ETAAS

This work describes a factorial design for the optimization of pyrolysis and atomization temperatures in ETAAS. As examples, Cd and Pb were determined using lower pyrolysis and atomization temperatures and Al and Mo with higher pyrolysis and atomization temperatures. Good results were obtained for Cd employing Rh (m o = 1.4 pg) as a permanent modifier with pyrolysis and atomization temperatures of 640 and 1500 °C, respectively. For Zr, W or Zr+W, the Cd pyrolysis and atomization temperatures were 500 and 1500 °C, respectively, with m o = 1.4 pg using Zr or W and 1.5 pg using Zr+W. The best results for Pb were those using Rh, Zr, W and Zr+Rh, obtaining characteristic masses of 42, 37, 34 and 36 pg, respectively. Pyrolysis and atomization temperatures of 910 and 1850 °C, respectively, were achieved for this metal. For Al, the best results were obtained when Zr or Zr+W were used. Mo was also tested as a possible permanent modifier for Al, but the results were not satisfactory. The results obtained for Mo without modifier were similar to those with conventional modifiers (Mg or Pd+Mg) and the results obtained using permanent chemical modifiers were not satisfactory. In all situations, the experiments were performed faster than those using the univariate procedure.

Emprego de reagente em suspensão em sistema de injeção em fluxo: determinação espectrofotométrica de sulfato em águas naturais

This paper presents an automatic procedure employing a reagent in the form of a slurry in a flow-injection system. The feasibility of the proposal is demonstrated by sulphate determination in water using the Barium Chloranilate method, which is based on the precipitation of barium sulphate. The release of a stoichiometric amount of highly colored chloranilic ions is monitored at 528 nm. The reaction is carried out in alcoholic medium in order to reduce the solubility of the reagent. A considerable improvement in the sensitivity is attained by adding ferric ions to the released chloranilic ions. An on-line filtration step to separate the excess reagent from the released chloranilic ions was necessary. In addition, a column containing a cation exchange resin was included in the manifold to remove potentially interfering ions. The proposed procedure is suitable for 30 determinations per hour and the relative standard deviation is less than 2%. The analytical curve is linear between 0.0 and 40 mg L-1 and the determination limit is about 2.0 mg L-1SO4(2-). Accuracy was confirmed by running several samples already analysed by a standard turbidimetric procedure.

Química atmosférica do enxofre (IV): emissões, reações em fase aquosa e impacto ambiental

The oxidation process of sulfur(IV) species by oxygen, ozone and nitrogen oxides, catalysed by trace metal ions, can play an important role in atmospheric chemistry processes like acid rain, visibility degradation and health hazard. An overview of the more relevant investigations on emissions sources, aqueous phase conversion process and environmental impact is presented.

O gênero copaifera L.

This review details the history, chemistry and pharmacology of the Copaifera L. genus (Leguminosae - Caesalpinoideae), including copaiba oils.

Materiais para cátodos de baterias secundárias de lítio

In this work, cathodes employed in secondary lithium batteries are reviewed. These cathodes have great technologic and scientific importance, specifically, materials for cathodes as electronic conductor polymers (ECP), transition metal oxides (TMO) and nanocomposites of ECP/TMO. The use of a specific cathodic material is based in some intrinsic characteristics that improve the performance of the battery. Thus, some vantages and disvantages of these insertion compounds are discussed, as lithium insertion capacity, energy density, and the ciclability of these materials.

Redução de amidas por boranos

Despite the fact that boranes are frequently used in amide reductions, the reaction mechanisms of the involved are note well known. This work presents the results of a bibliographic search on probable amide reduction mechanisms and an analysis of the existing literature. Steric and electronic effects were considered in light of reactivity since it could be concluded that the formation of intermediates and products depends mainly on the substitution patterns of both the boron and nitrogen atoms. Otherwise, results described in the literature for the reactions of boranes, sodium borohydride, lithium aluminum hydride, alkylboranes or haloboranes with others functional groups such as carboxylic acids, esters, ketones and alkenes were analysed with the aim to obtain something about the N-substituted amide reactions employing boranes.

Reciclagem de cobre proveniente de analisador automático de carbono e nitrogênio

Isotopic and elemental analysis of N, C and S in liquid and solid samples has been simplified with the advent of automated systems. The simplest method of automation for this kind of analysis involves an elemental analyzer interfaced directly to the ion source of an IRMS (Isotope Ratio Mass Spectrometry). In the analyzer reduction system, an expressive amount of oxidized copper is generated as solid residue. This material is normally imported and the price is very high. A methodology was proposed for the recovery of metallic copper in order to recycle this reagent in the reduction system of a GC-IRMS, using the hydrogen gas in the vacuum line. Results show that it is possible to obtain a recycle of about 95 % of the initial metallic copper used in the reduction system.

Imunossensor amperométrico

The reaction between antigen and antibody has been widely used in many strategies for the development of analytical methodology, due to its high specificity. The immuno-reaction has been successfully employed for the biosensor development. A focus on biosensor based on immunoassay coupled to amperometric transducer is presented.

Própolis: 100 anos de pesquisa e suas perspectivas futuras

Propolis is a multifunctional material used by bees in the construction and maintenance of their hives. The chemical composition and pharmacological properties have been studied for centuries. Today they represent an important raw material for many health products and constitute a new interdisciplinary area for research. Among others they show important antimicrobial and cytotoxic activities and various pharmacological properties. This paper presents an overview of the scientific literature and patents concerning propolis.

Técnica para seleção de variáveis aplicada à separação de gases

This paper describes an experimental design technique, known as variables search, developed to expose the critical variables and screen out the irrelevant ones. It is easy to learn and use and clearly dissociates the main and interactions effects from each other. An example of air separation process by pressure swing adsorption was used to demonstrate how the variables search technique works. The phases of identification of the critical variables is shown, step by step,.

O estado vítreo dentro da perspectiva do curso de graduação em química (físico-química)

We consider the relevance of the study of the glassy state properties and the glass transition as important topics of the physical chemistry for undergraduate courses of Chemistry. Two of the most important theoretical approaches for the description of the glassy state, the thermodynamic and the kinetic models, are summarized with emphasis on the physical chemistry aspects. Examples illustrating the glass transition of some materials are also presented.