A New Ent-Kaurane from the Roots of Lasianthaea aurea

Chemistry of Natural Compounds - A known kaurenoic acid (1), together with a new kaurane derivative named 3α-isobutyryloxykaurenoic acid (2), was isolated from the roots of Lasianthaea aurea,...     

Interactions between cellulose nanofibers and retention systems in flocculation of recycled fibers

Although the positive effect that cellulose nanofibers (CNF) can have on paper strength is known, their effect on flocculation during papermaking is not well understood, and most relevant studies have been carried out in presence of only cationic starch. Flocculation is the key to ensuring retention of fibers, fines, and fillers, and furthermore floc properties have a great influence on paper quality. The aim of this research is to study the interactions between CNF and flocculants by assessing the effect of two types of CNF, from eucalyptus and corn, on the flocculation process induced by three different retention systems [a dual system, polyvinylamine (PVA), and cationic starch as reference]. The results showed that CNF interacted with the flocculants in different ways, affecting flocculation efficiency and floc properties. In general, addition of CNF increased floc stability and minimized overdosing effects. Moreover, presence of CNF increased floc size for given PVA dose; therefore, CNF addition could contribute to improve the wet end in the paper machine if combined with the optimal flocculant and dose.     

Tetragonal to monoclinic phase transition observed during Zr anodisation

Plasma electrolytic oxidation (PEO) is a coating procedure that utilises anodic oxidation in aqueous electrolytes above the dielectric breakdown voltage to produce oxide coatings that have specific properties. These conditions facilitate oxide formation under localised high temperatures and pressures that originate from short-lived microdischarges at sites over the metal surface and have fast oxide volume expansion. Anodic ZrO₂ films were prepared by subjecting metallic zirconium to PEO in acid solutions (H₂C₂O₄ and H₃PO₄) using a galvanostatic DC regime. The ZrO₂ microstructure was investigated in films that were prepared at different charge densities. During the anodic breakdown, an important change in the amplitude of the voltage oscillations at a specific charge density was observed (i.e., the transition charge density (Q ^T)). We verified that this transition charge is a monotonic function of both the current density and temperature applied during the anodisation, which indicated that Q ^T is an intrinsic response of this system. The oxide morphology and microstructure were characterised using SEM and X-ray diffraction experiments (XRD) techniques. X-ray diffraction analysis revealed that the change in voltage oscillation was correlated with oxide microstructure changes during the breakdown process.     

Kinetic study of template removal of Al-MCM-41 synthesized at room temperature

The Al-MCM-41 molecular sieve with Si/Al = 20 molar ratio was synthesized at room temperature and characterized by X-ray diffractometry, surface area, thermogravimetry, and infrared spectroscopy. The kinetic study was conducted by Vyazovkin and Ozawa method, in order to verify the activation energy during the Hofmann degradation between 130 and 370 °C, in which most of surfactant removal occurs. The results suggest that the activation energy for template removal is close to 80 kJ mol^?1 lower in Al-MCM-41 synthesized at room temperature, when compared to results obtained for mesopores Al-MCM-41 and MCM-41 synthesized by hydrothermal method. This lower activation energy may be understood as consequence of textural properties, such as higher pore size.     

Optimal post-stratification for the study of the sustainability: An application to the monitoring of diversity in Sierra de Guerrero

The need of designing a monitoring network in Sierra de Guerrero motivated this paper. The study of the effect of deforestation of the forest needs of monitoring in the diversity. A quantitative evaluation of diversity is measured by estimating an index. Commonly the monitoring of biodiversity is based on the periodical selection of samples for evaluating the diversity. We propose to use sample information for determining post strata. They must constitute homogeneous zones in the forest. A stochastic program is developed for determining the post strata to be used for sampling. The procedure seems to be a good alternative with respect to the use of a heuristic procedure. The results presented are based on the data obtained in a research developed at one of the most important forest diversity reservoirs of Mexico     

Synthesis and characterization of organic–inorganic hybrid materials prepared by sol–gel and containing CdS nanoparticles prepared by a colloidal method using poly(N-vinyl-2-pyrrolidone)

This paper describes the synthesis and characterization of CdS nanoparticles (NPs) stabilized with poly(N-vinyl-2-pyrrolidone) and their further immobilization on a hybrid organic–inorganic matrix produced by the sol–gel process. The production of the hybrid matrix doped with CdS NPs was carried out in two steps. In the first step a precursor, designated diureasil precursor, was synthesized from the reaction between the terminal amine groups of α,ω-diamine-poly(oxyethylene-co-oxypropylene) and the isocyanate group of 3-isocyanatopropyltriethoxysilane. The next step involved the hydrolysis and condensation reactions of ethoxy groups attached to silicon, this step resulting in the formation of a crosslinked siliceous network linked through urea bonds to a poly(oxyethylene)/poly(oxypropylene) chain. The NPs were added to the diureasil precursor before the gelation process to allow a homogeneous dispersion of the NPs within the matrix. The developed method allowed the transfer of colloidal NPs to a solid matrix without the need of exchange the capping agents or the solvent. The materials were characterized by absorption, steady-state photoluminescence spectroscopy and by TEM. The results obtained showed the presence of CdS NPs with quantum size effect dispersed within the diureasil matrix. The obtained nanocomposites show a high transparency in the visible range accounting for the good dispersion of the NPs within the matrix. The TEM analysis confirmed that the NPs are uniformly dispersed within the diureasil matrix.     

Chemical composition,antioxidant and cytotoxic activities of extracts from the leaves of Smilax brasiliensis Sprengel (Smilacaceae)

The antioxidant and cytotoxic activities of petroleum ether and methanol extracts, fatty acids and methyl esters from leaves of Smilax brasiliensis were evaluated, and the composition of the extracts was determined. Palmitic, linoleic and linolenic acids were major components of the extracts. For antioxidant activity, all samples exhibited IC₅₀ values lower than BHT (2,6-di-tert-butyl-4-methylphenol). The extracts, fatty acids and methyl esters from S. brasiliensis presented no toxicity to larvae of the brine shrimp, Artemia salina. Among the purified substances, only methyl linolenate showed toxicity (LD₅₀ = 21.47 μg/mL). This study showed, for the first time, the composition of petroleum ether and methanol extracts from S. brasiliensis leaves, as well as the antioxidant and cytotoxic activities of extracts, fatty acids and methyl esters.