Biblioteca Digital

Using a water activity instrument meter, water activity in aqueous solutions of DL-alanine, glycine, or L-serine, with potassium chloride, molality ranging from 0.0 to 3.0, has been measured at 298.15 K. The reliability of the method was checked comparing the experimental data with literature values. The method proved to be accurate, and the water activities measured for water + amino acid systems are reproducible when compared to the data reported using the isopiestic method. Additionally, a simple theoretical approach applied to those binary systems enabled the calculation of unsymmetric molal amino acid activity coefficients in high agreement with the values found using the isopiestic measurements. Finally, the usefulness of the ternary data to extend the capabilities of thermodynamic models to higher salt and amino acid concentrations was briefly discussed.

This research reports kinetic modeling studies concerning the synthesis of PAAm and acrylamide/N,N’-methylenebisacrylamide (AAm/BAAm) hydrogels, in a 2.5 L batch reactor, considering aqueous solution and water in oil inverse suspension polymerizations.

The kinetics of the solution free radical polymerization of N-vinylcaprolactam, in 1,4-dioxane and under various polymerization conditions was studied. Azobisisobutyronitrile and 3-mercaptopropionic acid were used as initiator and as chain transfer agent (CTA), respectively. The influence of monomer and initiator concentrations and polymerization temperature on the rate of polymerizations (R(p)) was investigated. In general, high conversions were obtained. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to the monomer was greater than unity. The overall activation energy of 53.6 kJ mol(-1) was obtained in the temperature range 60-80 degrees C. The decreasing of the absolute molecular weights when increasing the CIA concentration was confirmed by GPC/SEC/LALS analyses. It was confirmed by UV-visible analyses the effect of molecular weights on the lower critical solution temperature of the polymers. It was also verified that the addition of the CTA influenced the kinetic of the polymerizations. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 229-240, 2010; CAPES; CNPq; FAPESP

The Jacobsen catalyst, Mn(salen), was immobilized in chitosan membrane. The obtained Mn(salen)-Chit was characterized by thermogravimetric analysis (TC), differential thermal analysis (DTA), differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), degree of N-acetylation by (1)H NMR, and UV-vis spectroscopy. The UV-vis absorption spectrum of the encapsulated catalyst displayed the typical bands of the Jacobsen catalyst, and the FT-IR presented an absorption band characteristic of the imines present in the Jacobsen catalyst. The chitosan membranes were available, in a biphasic system, as a catalytic barrier between two different phases: an organic substrate phase (cyclooctene or styrene) and an aqueous solution of either m-CPBA, t-BuOOH or H(2)O(2), and dismissing the need for phase transfer agents and leading to better product yields compared with the catalyst in homogeneous medium. This new catalyst did not leach from the support and was reused many times, leading to high turnover frequencies. (C) 2009 Elsevier B.V. All rights reserved.; FAPESP; CAPES; CNPq

In this work, native xyloglucan was extracted from Tamarindus indica seeds (XGT), and its properties in phosphate buffer solution (PBS) were evaluated in comparison with a commercial tamarind kernel powder (TKP). The physico-chemical characteristics of the polysaccharides such as molar mass, critical concentration and intrinsic viscosity were determined. Furthermore, using spectroscopic and microscopy techniques, it was observed that the XGs tested can be considered macromolecules able to aggregate as nano-entities of 60-140 nm. The XGT tended to an ordered and compact spherical conformation determined by the Huggins constant, circular dichroism, atomic force microscopy and transmission electron microscopy. After the determination of the properties in PBS the XGs, at concentrations of 25% above their critical aggregation concentration, were used to encapsulate camptothecin, an anti-cancer drug. The XGT sample showed an encapsulation efficiency of 42% and first-order drug delivery kinetics. These results demonstrated the importance of knowledge of the physico-chemical properties of polysaccharides, for example, to better conduct their biotechnological applications as drug carriers. (C) 2010 Elsevier Ltd. All rights reserved.; CNPq (Conselho Nacional de Pesquisa); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES-Brasil; Fundação Araucária; Fundacao Araucaria

Stoichiometric CaWO4 and SrWO4 thin films were synthesized using a chemical solution processing, the so-called polymeric precursor method. In this soft chemical method, soluble precursors such as strontium carbonate, calcium carbonate and tungstic acid, as starting materials, were mixed in an aqueous solution. The thin films were deposited on glass substrates by means of the spinning technique. The surface morphology and crystal structure of the thin films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Nucleation stages and surface morphology evolution of the thin films on glass substrates were studied by atomic force microscopy. The films nucleate at 300 degreesC, after the coalescence of small nuclei into larger grains yielding a homogeneous dense surface. XRD characterization of these films showed that the CaWO4 and SrWO4 phases crystallize at 400 degreesC from an inorganic amorphous phase. No intermediate crystalline phase was identified. The optical properties were also studied. It was found that CaWO4 and SrWO4 thin films have an optical band gap, E-gap=5.27 and 5.78 eV, respectively, of a direct transition nature. The excellent microstructural quality and chemical homogeneity confirmed that this soft solution processing provides an inexpensive and environmentally friendly route for the preparation of CaWO4 and SrWO4 thin films. (C) 2003 Elsevier B.V. All rights reserved.

This work describes the efficiency of photoelectrocatalysis based on Ti/TiO2 nanotubes in the degradation of the azo dyes Disperse Red 1, Disperse Red 13 and Disperse Orange 1 and to remove their toxic properties, as an alternative method for the treatment of effluents and water. For this purpose, the discoloration rate, total organic carbon (TOC) removal, and genotoxic, cytotoxic and mutagenic responses were determined, using the comet, micronucleus and cytotoxicity assays in HepG2 cells and the Salmonella mutagenicity assay. In a previous study it was found that the surfactant Emulsogen could contribute to the low mineralization of the dyes (60% after 4h of treatment), which, in turn, seems to account for the mutagenicity of the products generated. Thus this surfactant was not added to the chloride medium in order to avoid this interference. The photoelectrocatalytic method presented rapid discoloration and the TOC reduction was ≥87% after 240min of treatment, showing that photoelectrocatalysis is able to mineralize the dyes tested. The method was also efficient in removing the mutagenic activity and cytotoxic effects of these three dyes. Thus it was concluded that photoelectrocatalysis was a promising method for the treatment of aqueous samples. © 2013 Elsevier Ltd.

The effectiveness of ozone in aqueous solution treatment on microbial inactivation was studied for three combinations microorganism/food: Listeria innocua/red bell peppers (artificially inoculated), total mesophiles/strawberries, and total coliforms/watercress, with two concentrations (0.3 and 2.0 ppm). Blanching treatments (50–60 C) were also individually applied and in combination with ozone, for studying possible synergistic effects. In relation to ozone treatments, the highest microbial reductions were obtained for the highest concentration with the highest treatment time (3 min). Under those conditions, L. innocua/peppers, total mesophiles/strawberries and total coliforms/watercress were reduced respectively 2.8 ± 0.5, 2.3 ± 0.4 and 1.7 ± 0.4 log-cycles. However, a substantial portion of the microbial populations were reduced by water washing alone, and the presence of ozone generally added an additional reduction of 0.5–1.0 log-cycles. If ozone at the highest concentration is used, the treatment impacts on L. innocua/peppers and total mesophiles/strawberries load reductions were equivalent to a blanching at 50 C (for the same treatment times). Combining blanching and ozone did not generate synergistic effects, and in some situations microbial reductions were lower than the ones observed when treatments were applied independently.

Spirulina platensis microalgae (SP) and commercial activated carbon (AC) were compared as adsorbents to remove Reactive Red 120 (RR-120) textile dye from aqueous effluents. The batch adsorption system was evaluated in relation to the initial pH, contact time, initial dye concentration and temperature. An alternative kinetic model (general order kinetic model) was compared with the traditional pseudo-first order and pseudo-second order kinetic models. The equilibrium data were fitted to the Langmuir, Freundlich and Liu isotherm models, and the thermodynamic parameters were also estimated. Finally, the adsorbents were employed to treat a simulated dye-house effluent. The general order kinetic model was more appropriate to explain RR-120 adsorption by SP and AC. The equilibrium data were best fitted to the Liu isotherm model. The maximum adsorption capacities of RR-120 dye were found at pH 2 and 298 K, and the values were 482.2 and 267.2 mg g−1 for the SP and AC adsorbents, respectively. The thermodynamic study showed that the adsorption was exothermic, spontaneous and favourable. The SP and AC adsorbents presented good performance for the treatment of simulated industrial textile effluents, removing 94.4–99.0% and 93.6–97.7%, respectively...

The development of numerical modeling of reactive transport relies on the availability of thermodynamic properties for the solid, surface, aqueous, and vapor species stable at the conditions of interest. The lack of experimental studies and comprehensive

Clorexidina (CHX) é um antisséptico com amplo espectro de ação utilizada em muitos tipos de preparações farmacêuticas para uso tópico. Uma vez que não há na literatura ensaio microbiológico oficial para quantificar a clorexidina, este trabalho objetivou o desenvolvimento e validação de um ensaio microbiológico simples, sensível, exato e reprodutível, por difusão em ágar, para doseamento de digliconato de clorexidina (CHX-D) em solução aquosa. O ensaio é baseado no efeito da inibição de Staphylococcus aureus ATCC 25923, utilizado como microorganismo teste, pela CHX-D. Utilizou-se o delineamento 3x3. Os resultados foram verificados estatisticamente pela análise de variância (ANOVA) e apresentaram excelente linearidade (r = 0,9999), demonstrando que o método segue o modelo linear com regressão significativa entre o diâmetro da zona de inibição e o lagaritmo da concentração no intervalo de 0,5 a 4,5%. Os resultados obtidos foram precisos apresentando desvio padrão relativo (DPR) para precisão intra-dia de 2,03% e DPR para precisão inter-dias de 2,94%. A exatidão foi 99,03%. O método provou ser muito útil e apropriado para doseamento microbiológico da CHX-D em formas farmacêuticas e pode ser empregado para análise desta substância no controle de qualidade em indústrias farmacêuticas.; Chlorhexidine (CHX) is a broad-spectrum antiseptic that is used in many topical pharmaceutical formulations. Because there is no official microbiological assay reported in the literature that is used to quantify CHX...

Realizou-se estudo sobre a associação da N-hexil-2-metil-4-nitroimidazol, fármaco modelo, aos agregados formados por polieletrólitos aniônicos em solução aquosa. Os copolímeros alternados de anidrido maléico e N-vinil-2-pirrolidona foram sintetizados e, em seguida, modificados pela reação dos grupos de anidrido com aminas e álcoois alifáticos de duração variável da cadeia alquílica. A partição do fármaco modelo entre a água e os microdomínios hidrofóbicos fornecido pelos copolímeros foi estudada usando o modelo de pseudo-fase, a fim de determinar a distribuição do coeficiente K S e a energia livre padrão de transferência ∆µ°t. Os resultados indicam que todos os copolímeros avaliados são potenciais reservatórios farmacêuticos do fármaco. No entanto, a solubilidade do N-hexil-2-metil-4-nitroimidazol sobre as soluções poliméricas é independente do comprimento da cadeia alquílica do copolímero.; This study evaluated the association of N-hexyl-2-methyl-4-nitroimidazol, a model drug, to aggregates formed by anionic polyelectrolytes on aqueous solution. The alternating copolymers of maleic anhydride and N-vinyl-2-pyrrolidone were synthesized and then modified by reaction of the anhydride groups with aliphatic amines and alcohols of varying length of the alkyl chain. The partition of the model drug between water and the hydrophobic microdomains provided by the copolymers was studied using the pseudo-phase model to determinate the distribution coefficient K S...

Regioisomeric pairs of isoxazolines were prepared through reaction of nitrile oxides with ethyl trans-cinnamate. The effect of β -cyclodextrin on the solubility of these compounds in aqueous ethanol and their extraction into chloroform has been examined.

The equilibrium and kinetic aspects of the adsorption of alkyltrimethylammonium surfactants at the silica-aqueous solution interface have been investigated using optical reflectometry. The effect of added electrolyte, the length of the hydrocarbon chain,

Møller-Plesset perturbation theory at the level of third order (MP3) is used to compute two-electron reduction potentials for some substituted benzoquinones in aqueous solution. The calculations are carried out at the MP2 and MP3 levels with the use of c

We describe a method to retrieve hazardous dye from aqueous solution that employs magnetic nanoparticles with strong affinity to dyes. Ionic liquids with stronger affinity to the magnetic particles promote up to 99% dye recovery.

H/D isotope effect on the circular dichroism spectrum of methyl α-D-glucopyranoside in aqueous solution has been analyzed by multicomponent density functional theory calculations using the polarizable continuum model. By comparing the computational spectra with the corresponding experimental spectrum obtained with a vacuum-ultraviolet circular dichroism spectrophotometer, it was demonstrated that the isotope effect provides insights not only into the isotopic difference of the intramolecular interactions of the solutes, but also into that of the solute–solvent intermolecular interaction.

Atrazine is a highly used herbicide and it has been found in both deep and superficial waters. Its solubility in water is reduced and is relatively stable in humid environments, where it has a half-life of one hundred days. Atrazine can be degraded by oxidative photolysis or by microorganisms. It is moderately toxic in humans, animals and plants, because it can be absorbed by inhalation, ingestion or through the skin. In this work, we study the degradation of atrazine in aqueous solution using current controlled electrolysis at a platinum electrode. The effects of pH, current magnitude and direction, and temperature, were evaluated. The atrazine decomposition was monitored during electrolysis by UV-Vis spectrophotometry; quantification of atrazine was done by GC/MS, and quantification of cyanuric acid was done by HPLC. It was found that at 25 ºC in acid media, atrazine is degraded partially to cyanuric acid with formation of persistent intermediate compounds, but at 60 ºC atrazine is completely degraded to cyanuric acid. The TOC results indicate no electrochemical combustion and no mineralization was observed under the experimental conditions studied.

The adsorption capacity of hebba clay and activated carbon towards (Fe3+, Cu2+, Zn2+, Pb2+, Cr3+, Cd2+) metal ions was studied. The adsorption capacity was investigated by batch experiment. The effect of weight of hebba was studied and the results showed that the removal percentages increased as the weight of sorbent increased. The effect of contact time was also studied and the results showed that the removal percentages increased as the contact time increased. The effect of pH of the solution was also studied and the removal percentages for (Cu2+, Zn2+ and Cd2+) were affected slightly by changing the pH value, but for (Fe3+, Pb2+ and Cr3+) the effect was higher. Also, the effect of initial concentration of metal ions was studied at four different concentrations (5, 10, 30, 50 mg/L); in case of metal ions (Cu2+, Zn2+ and Cd2+), the removal percentages increased by increasing initial concentration. But for the other metal ions it decreased. The order of increasing removal percentages of metal ions at pH=4.86, concentration of metal ions 30 mg/L, and after four hours of shaking, was (Pb2+ < Cu2+ < Cd2+ < Cr3+ < Zn2+ < Fe3+). But in the case of activated carbon, the order was Cd2+ < Zn2+ < Cu2+ < Pb2+ < Cr6+ < Fe3+.