Síntese, caracterização e estudo das propriedades magnéticas de um polímero de coordenação contendo cobalto(II) e cobre(II)

This work describes the synthesis and characterization of two new compounds with ligand opy (N-(2-pyridyl)oxamate): the copper(II) precursor [Me4N]2[Cu(opy)2].5H2O and CoII CuII coordination polymer {[CoCu(opy)2]}n×4nH2O. This latter compound was obtained by reaction of [Me4N]2[Cu(opy)2].5H2O and CoCl2.6H2O in water. The heterobimetallic CoII CuII chain was characterized by elemental analysis, IR spectroscopy, thermogravimetry and magnetic measurements. Magnetic characterization revealed typical behavior of one-dimensional (1D) ferrimagnetic chain as shown in the curves of temperature (T) dependence of magnetic susceptibility (χM), in the form of χMT versus T, and dependence of magnetization (M) with applied field (H).

Síntese e caracterização de hidrogéis compósitos a partir de copolímeros acrilamida-acrilato e caulim: efeito da constituição de diferentes caulins do nordeste brasileiro

Superabsorbent hydrogels based on poly (acrylamide-co-acrylate) and different kaolins, were prepared by free-radical aqueous copolymerization. FTIR and WAXS techniques were employed for characterization of a series of hydrogels, obtained by varying the percentage of clay, crosslinking and constitution of kaolin. The water absorbency at equilibrium (Weq) decreased with increasing clay content and the amount of crosslinking agent. Superabsorbent hydrogel (Weq > 1084 g H2O/g gel) was obtained as 10 wt% of white kaolin and 0.05 mol% of crosslinking agent were used. The hydrogel proved sensitive to pH variation and the presence of salts.

Influência do pH nas propriedades físico-químicas, térmicas e mecânicas de filmes de poli(vinil álcool)/poli(ácido acrílico)/aciclovir

Drug-loaded films represent an alternative method for the treatment of skin lesions caused by Herpes simplex, since they facilitate delivery of the drug directly at the site of lesion. The objective of this work was to prepare PVA/PAA films containing AC at pH 2.0 and 4.0. The results show that the pH of the film preparations influences the polymer¾drug interaction kinetic order and the degree of swelling. The mechanism of release of AC from the films obtained at pH 4.0 was anomalous, whereas for the films prepared at pH 2.0 the release followed zero-order kinetics.

Síntese, caracterização e estudo das propriedades de um novo complexo mononuclear contendo quercetina e íon Ga(III)

Flavonoids are one of the most important compound groups applied as medicine given their antioxidant properties, but several intrinsic properties can be improved through structural modifications to their molecules. Here, the synthesis and characterization of a new gallium (III) complex with quercetin is described. Electrochemical properties, as well as antioxidant and cytotoxic activities, were investigated and compared to the free flavonoid molecule. The mononuclear complex obtained, [Ga(C15H9O7)3].2H2O.2CH3OH.CH3CH2OH, seems more active as a DPPH radical scavenger given its lower oxidation potential compared to quercetin. The new complex cytotoxic responses have shown to be more effective than those of the free flavonoid and of lapachol used as a control.

Compósitos biodegradáveis de amido de mandioca e resíduos da agroindústria

The objectives of this work were to produce biodegradable composites using starch and different agro-industrial wastes (coconut fiber, soy bran and sugarcane bagasse) using a baking process, and to study the effects of these components on the resultant composite properties. The addition of different residues yielded trays with different properties. Samples manufactured with soy bran showed the highest density and water uptake at relative humidities ≥ 60%. The addition of sugarcane bagasse resulted in less dense and resistant samples whereas coconut fiber composites showed the highest breaking stress. The samples fabricated in this study represent an alternative packaging option for foods with low water content.

Biossurfactantes: propriedades anticorrosivas, antibiofilmes e antimicrobianas

Due to the importance of biofilms in the food industry, new products are being developed to enhance the efficiency of cleaning food-contact surfaces. Biosurfactants could be an alternative to synthetic products. The major advantages of biosurfactants over synthetic detergents are their low toxicity and highly biodegradable nature. Biosurfactants may also exhibit antimicrobial, anti-adhesive and anticorrosive activity concomitantly. In this review, we emphasize the potential application of biosurfactants as surface coating agents to prevent corrosion and decrease planktonic and sessile microbial growth.

Hemocidinas derivadas da hemoglobina: estruturas, propriedades e perspectivas

The increasing incidence of microbial infections, high toxicity, and high level of resistance associated with conventional antibiotics has created a need for new drugs. Antimicrobial peptides (AMPs) constitute a promising alternative and/or an important source of knowledge given their ability to inhibit the growth and/or to kill bacteria, fungi, parasites and/or viruses through mechanisms of action different from those of non-peptide drugs. This review focused on this important class of organic compounds that includes hemocidins resulting from hemoglobin proteolysis in vivo and in vitro or from chemical synthesis, subject of research in foreign and Brazilian laboratories.

Frações da matéria orgânica e propriedades redox de substâncias húmicas em sedimentos de oceanos profundos

Previous studies have verified that free radicals such as quinone moieties in organic matter participate in the redox reactions in natural systems. These functional groups were positively correlated with the increase in aromaticity and hydrophobicity of the humic substances. As an alternative to relatively complex and expensive spectroscopic methods, the redox properties of the humic substances, determined by potentiometric titrations, have been used to evaluate organic carbon stability in soil and sediments. The present study aimed to perform organic matter fractionation and isolation of humic substances from deep oceans in different isobaths (750; 1,050; 1,350; 1,650; 1,950 m) to determine their redox properties by iodimetric titrations under an inert atmosphere and specified conditions of pH and ionic strength. Sediment samples were collected to the North and South of platforms of petroleum exploration located in the North of Rio de Janeiro State, Brazil. Fractions of organic carbon and redox properties of humic substances varied with origin and depth of the samples and with position North and South of the petroleum exploration area.

Acúmulo de cargas elétricas em propelente sólido compósito com matriz de polibutadieno líquido hidroxilado

Composite solid propellants prepared with HTPB prepolymer - Hydroxyl Terminated Polybutadiene, AP - Ammonium Perchlorate as oxidizer and aluminum particles as an additive metal, have characteristics of high electrical resistivity. The loading process of the polymer matrix did not obtain homogeneity, resulting in clusters, mainly of metal particles. The effect of clustering in the composite was studied and observed experimentally, and this effect was one of the factors explaining the phenomenon of electrical charging of the composite. This electrical potential, when discharged abruptly, can generate an electric spark with sufficient energy for sustained ignition of a solid rocket motor.

Efeito da adição de TIO2 nas propriedades térmicas e na cristalinidade do copolímero de etileno/acetato de vinila

We investigated the effect of adding titanium dioxide nanoparticles (TiO2) to ethylene vinyl acetate (EVA) copolymer, containing 28% vinyl acetate groups, on the crystallinity and miscibility of the copolymer. Films of EVA/TiO2 containing 0.25%-1% TiO2, relative to the total weight of EVA, were prepared from their solution. The obtained films were characterized by X-ray diffraction, low-field nuclear magnetic resonance, and differential scanning calorimetry. The addition of TiO2 to the EVA copolymer was proved to cause changes in the crystallinity and mobility of the polymer chains of EVA, due to new intermolecular interactions and nanostructure organization.

Propriedades relacionadas à acidez e basicidade a partir da abordagem em química computacional

Analytical Chemistry books lack a clear link between thermodynamic and equilibrium approaches involving acids and bases. In this work, theoretical calculations were performed to search for these relations. An excellent relationship was found between difference in Gibbs free energy, ∆G of acid dissociation reaction and ∆G of hydrolysis reaction of the corresponding conjugate base. A relationship between ∆G of hydrolysis reaction of conjugate acids and their corresponding atomic radius was also identified, showing that stability plays an important role in hydrolysis reactions. Finally, the importance of solvation in acid/base behavior was demonstrated when comparing the corresponding theoretical and experimental ∆G´s.

Estudo da liberação controlada do herbicida ametrina em compósitos à base de PVA: carvão ativado

Herbicides have great importance in agricultural productivity for weed control, given their competition with crops. However, inadequate application of herbicides may lead to environmental problems, which can be minimized through controlled release of the active compounds. This may be achieved by protecting the herbicide in a structure with adequate porosity, where the diffusional behavior can determine release. Thus, in this study we evaluated a novel structure, a composite based on activated carbon bonded by polyvinyl alcohol (PVA) as pellets, to deliver a triazine herbicide. The product obtained was shown to be adequate for its purpose, since it was possible to process regular pellets, where the PVA percentage determined the properties.

Propriedades estruturais e eletrônicas de nanofilmes de TiO2 anatase: cálculos B3LYP-D* em sistemas periódicos bidimensionais

Structural and electronic properties of titanium dioxide (TiO2) thin films, in anatase phase, were investigated using periodic 2D calculations at density functional theory (DFT) level with B3LYP hybrid functional. The Grimme dispersion correction (DFT/B3LYP-D*) was included to better reproduce structural features. The electronic properties were discussed based on the band gap energy, and proved dependent on surface termination. Surface energies ranged from 0.80 to 2.07 J/m², with the stability orders: (101) > (100) > (112) > (110) ~ (103) > (001) >> (111), and crystal shape by Wulff construction in accordance with experimental data.

Desenvolvimento de reator tipo "dip catalyst" para filmes poliméricos contendo nanopartículas de metais de transição

This article describes the development of a new catalytic reactor designed to operate with nanoparticle-embedded polymer thin films. Stabilization of metal nanoparticles in films that serve as catalysts in organic reactions is relatively new; therefore, the development of reactors to facilitate their use is necessary. We describe in detail the preparation of the GDCR reactor-type "dip catalyst" and its evaluation in the Suzuki - Miyaura cross-coupling reaction of phenylboronic acid and 4-bromoanisole catalyzed by palladium nanoparticle-embedded cellulose acetate thin film (CA/PD(0)). Compared with earlier prototypes, GDCR reactor showed excellent results when operating with CA/PD(0) thin films.

Efeitos da rugosidade superficial nas propriedades de passivação de monocamadas orgânicas automontadas

Precise surface area is needed for accurate characterization of self-assembled monolayers (SAMs) on metallic surfaces. The aim of this manuscript was to emphasize that miscalculation of surface area is the major source of errors in SAM electrochemical characterization. Limitations are discussed and recommendations given for beginners in analyses of SAM functionalized electrodes. The electrochemical measurements and examples were based on bare gold electrode immobilized with dodecanethiol. The degree of compression of the monolayer properties of formation and reproducibility of the electrochemical response depends on roughness factor, with values closer to the unit being better.