Adsorção de Cr(VI) em esferas reticuladas de quitosana: novas correlações cinéticas e termodinâmicas utilizando microcalorimetria isotérmica contínua

The synthesis and characterization of crosslinked chitosan microbeads and their application in the removal of Cr(VI) are described. New kinetic and thermodynamic parameters of Cr(VI) adsorptions processes were found using continuous isothermal calorimetry. All adsorption processes are exothermic in nature. However, a multivariate statistical analysis have pointed out that adsorption enthalpies were affected by important binary interactions of the initial Cr(VI) in solution and temperature. The adsorption energetic data were well fitted to a kinetic exponential model, which have indicated fractionary adsorption kinetic orders.

Adsorção e propriedades de volume de misturas binárias água álcool: um experimento didático com base em medidas de tensão superficial

An undergraduate physical chemistry experiment based on the drop counting method for surface tension measurements is proposed to demonstrate adsorption isotherms of binary aqueous solutions of ethanol, n-propanol, and n-butanol. Excess surface is obtained by the derivative of surface tension taken with respect to alcohol activity, after this activity calculation using van Laar equation. Laboratory class contents are surface tension, excess surface, percolation of hydrogen bonds, micelle, activity, and ideal solution.

Autoassociação de misturas dos Surfactantes Dodecanoato de Sódio (SDoD) e Decanoato de Sódio (SDeC) com o Polímero Hidrofobicamente Modificado Etil(Hidroxietil)Celulose (EHEC)

In this work, the interactions between the non-ionic polymer of ethyl(hydroxyethyl)cellulose (EHEC) and mixed anionic surfactant sodium dodecanoate (SDoD)-sodium decanoate (SDeC) in aqueous media, at pH 9.2 (20 mM borate/NaOH buffer) were investigated by electric conductivity and light transmittance measurements at 25 ºC. The parameters of the surfactant to polymer association processes such as the critical aggregation concentration and saturation of the polymer by surfactants were determined from plots of specific conductivity vs total surfactant concentration, [surfactant]tot = [SDoD] + [SDeC]. Through the results was not observed a specific link of polymer with the surfactant, implying therefore a phenomenon only cooperative association.

Uso da cromatografia gasosa bidimensional abrangente (GC×GC) na caracterização de misturas biodiesel/diesel: aplicação ao biodiesel de sebo bovino

The growth of biodiesel market and the implementation of regulations related to biodiesel production and biodiesel/diesel blending has encouraged the development of appropriate analytical methods to control the composition of this type of mixture. In this study, an evaluation of the potential of GC×GC for the characterization of samples of beef tallow biodiesel and the composition of blends of biodiesel/diesel is presented. The methodology was applied to beef tallow biodiesel and its mixtures with petrodiesel, ranging from B2 to B50. Results allowed not only the identification and quantification of the biodiesel esters, but also the biodiesel percentage in biodiesel/diesel blends.

Abordagem teórico-experimental da teoria do campo cristalino na disciplina de síntese inorgânica

We describe herein the synthesis and characterization of the complexes KNiF3, [Ni(en)3]I2, [Ni(en)3]Cl2, [Ni(acac)2(H2O)2], [Ni(en)2(H2O)2]Cl2 and [Ni(NH3)6](BF4)2 (en = ethylenediamine, acac- = acetylacetonate) performed in the inorganic synthesis major course at the Chemistry Institute of UFRGS (Universidade Federal do Rio Grande do Sul). The compounds were characterized by infrared and electronic spectroscopy and the electrolytic conductivity was measured. The parameters 10Dq and B were obtained from the electronic spectra and the nefelauxetic and spectrochemical series were determined. The obtained spectrochemical series was F- < acac- < NH3 < en and the nefeulaxetic series was en < NH3 < acac- < F-.

Uso de redes neurais recorrentes na determinação das constantes de acidez para a 7-epiclusianona em misturas etanol-água

This work propose a recursive neural network to solve inverse equilibrium problem. The acidity constants of 7-epiclusianone in ethanol-water binary mixtures were determined from multiwavelength spectrophotmetric data. A linear relationship between acidity constants and the %w/v of ethanol in the solvent mixture was observed. The proposed method efficiency is compared with the Simplex method, commonly used in nonlinear optimization techniques. The neural network method is simple, numerically stable and has a broad range of applicability.

Modelos ridge em planejamentos de misturas: uma aplicação na extração da polpa de pequi

Mixture Models can be used in experimental situations involving areas related to food science and chemistry. Some problems of a statistical nature can be found, such as effects of multicollinearity that result in uncertainty in the optimization of a dependent variable. This study proposes the application of the ridge model adapted for mixture planning considering the Kronecker (K-model) and Scheffe (S-Model) methods applied to response surfaces. The method determined the proportions of hexane, acetone and alcohol proportions that resulted in the maximum response of percentage of extracted pequi (Caryocar brasiliense) pulp oil.

O centenário da Teoria de Bohr

The year 2013 marks the centennial of that wondrous year in which Niels Bohr proposed a novel theory about the constitution of atoms and small molecules after which the way we regard atoms and their behaviour began to be drastically altered. Bohr drew on several sources for his original description of the atoms, most importantly on spectroscopy and Balmer's equation thereof, the new quantum hypothesis advanced a few years earlier by Planck, and the planetary atom proposed by Rutherford. Although Bohr's ideas were to be eventually overtaken by the advent of quantum mechanics, his theory was the basis of a new thinking about atoms and molecules which constitutes an invaluable asset in the development of science ever since.

Contextualizando reações ácido-base de acordo com a teoria protônica de Brönsted-Lowry usando comprimidos de propranolol e nimesulida

This paper reports the use of alternative materials for teaching experimental chemistry. In this context, nimesulide and propranolol tablets were used to teach chemical concepts about acid-base reactions according to Brönsted-Lowry protonic Theory. Important topics of Organic, Analytical and Pharmaceutical Chemistry were discussed, such as purification by acid-base extraction, solubility of organic compounds in aqueous solutions, buffers, the dissociation constant (pKa), potentiometric titration and ionization of drugs in biological fluids. The purification of propranolol and nimesulide from tablets produced yields of 75% and 90%, respectively. The experimental values of pKa for both drugs were in agreement with those from the literature.

A teoria de pearson para a disciplina de química orgânica: um exercício prático e teórico aplicado em sala de aula

We report a didactic experience in teaching Pearson's theory (HSAB) to graduate students in organic chemistry. This approach was based on teaching students how to use computer programs to calculate frontier orbitals (HOMO-LUMO). The suggested level of calculation was a semi-empiric PM3, proving to be efficient for obtaining robust and fast numerical results that can be performed easily in the classroom. We described a practical computational exercise and asked students to compare these numerical data with qualitative analysis using valence bond theory. A comprehensive solution of this exercise is presented, aiming to support teachers in their lessons.

Otimização da etapa de extração do ácido clavulânico presente no caldo de fermentação utilizando misturas de solventes

The purpose of this work was to study four different solvent mixtures intended to increase the yield of the extraction stage of clavulanic acid (CA), which is one of the steps in the purification process. Four central composite rotatable designs (CCRD) were utilized to optimize the solvent mixtures. The variables selected for the factorial design were solvent mixture ratio (mL/mL) and temperature (ºC). The results showed that the yield of CA extracted from fermentation broth with the solvent mixtures of methyl-ethyl-ketone and ethyl acetate, and methyl-isobutyl-ketone and ethyl acetate (44.7 and 50.0%, respectively) was higher than that of the individual ethyl acetate alone (36.5%).

DESENVOLVIMENTO DE ENSAIO PARA ANÁLISE QUALITATIVA DE BIODIESEL EM MISTURAS DIESEL-BIODIESEL PARA APLICAÇÃO EM POSTOS REVENDEDORES DE COMBUSTÍVEIS

In this study, we developed a method for the visual detection of biodiesel in petrodiesel-biodiesel (BX) blends through the aminolysis of the methyl or ethyl esters of fatty acids that are found in biodiesel and that are absent from diesel and vegetable oils. This method is based on three reactional stages, which produce a dark red and easily visualized complex in the presence of biodiesel. In the absence of biodiesel, there is no dark red coloring, whereas in the presence of diesel or vegetable oil, there is a light red to yellow coloring. This simple, practical, inexpensive, and effective procedure may be applied by petrol stations to guarantee to consumers and resellers the presence of biodiesel in diesel blends, regardless of the BX blend's initial coloring or of the sulfur found in the diesel. In short, it ensures a safe fuel tank fill-up with BX blend.

Dinâmica molecular: teoria e aplicações em planejamento de fármacos

Dinâmica Molecular (DM) é uma ferramenta computacional poderosa usada em Química Medicinal para o planejamento racional de fármacos. DM é uma extensão da Mecânica Molecular, onde o comportamento dinâmico de um sistema molecular é simulado através da integração numérica das equações de movimento. Esta técnica tem sido usada extensivamente para auxiliar e complementar o planejamento de novos ligantes de um alvo terapêutico, bem como estimar a sua potência. Este artigo enfoca a teoria básica da DM clássica e suas importantes aplicações no planejamento racional de potenciais compostos bioativos, particularmente compostos com atividade anti-HIV.

Sobre a natureza da teoria moral de Hume

Este artigo discute duas variedades de interpretação para a teoria moral de Hume. De um lado, ela é representada como uma forma de subjetivismo e, de outro, como uma forma de realismo. Ao final, é proposto que esta filosofia pode ser melhor descrita como uma forma de intersubjetivismo.