Tetramethylguanidine catalyzed transesterification of fats and oils: A new method for rapid determination of their composition

A new method for the rapid preparation of methyl esters from vegetable oils and fats, using tetramethylguanidine as catalyst, has been developed. This method is compared with the traditional method (Ce 2–66, using 20% BF₃ in methanol) and that proposed by Hartman and Lago (using NH₄Cl/H₂SO₄ in methanol). It is shown that the new method produces the methyl esters in quantitative yields and has certain advantages, as it is simpler, cheaper and does not result in isomerization of the fatty acids.     

Role of the composition and preparation method in the activity of hydrotalcite-derived Ru catalysts in the catalytic partial oxidation of methane

Hydrotalcite-derived Ru catalysts were tested in the catalytic partial oxidation of CH₄ to produce syngas. The effect of Ru content, oxidic matrix composition, and preparation procedure on chemical–physical properties and performances of catalysts was studied. Bulk catalysts (0.25 and 0.50 wt.% Ru) were obtained via Ru/Mg/Al hydrotalcite-type (HT) precursors with carbonates or silicates as interlayer anions. A supported catalyst was prepared by impregnation on a calcined Mg/Al–CO₃ HT. Ru/γ-Al₂O₃ was evaluated for comparison. Both the Ru dispersion and the interaction with the support decreased as the Ru loading increased and when silicates were present due to RuO₂ segregation. Regardless of the Ru loading, carbonate-derived catalysts performed better than those containing silicates. The increased Ru loading improved the initial activity, but deactivation occurred after high temperature tests. Stability tests for shorter contact times over a 0.25 wt.% bulk sample obtained from Ru/Mg/Al HT with carbonates showed a tendency to deactivate at 750 °C.     

COMPCHEM: Progress Towards GEMS a Grid Empowered Molecular Simulator and Beyond

Foundations and structure of the building blocks of GEMS, the ab initio molecular simulator designed for implementation on the EGEE computing Grid, are analyzed. The impact of the computational characteristics of the codes composing its blocks (the calculation of the ab initio potential energy values, the integration of the dynamics equations of the nuclear motion, and the statistical averaging of microscopic information to evaluate the relevant observable properties) on their Grid implementation when using rigorous ab initio quantum methods are discussed. The requests prompted by this approach for new computational developments are also examined by considering the present implementation of the simulator that is specialized in atom diatom reactive exchange processes.     

Alkaline extraction conditions determine gelling properties of corn bran arabinoxylans

Alkali treatment is used for extraction of arabinoxylans (AXs) from cereal brans. Our objective was to determine the effect of alkali treatment conditions on oxidative gelling of corn bran AXs. AXs extracted through mild alkali treatment formed strong gels through ferulic acid (FA) crosslinking by the action of laccase. Increasing harshness of alkali treatment caused a decrease in average FA content of AXs and elasticity of gels. However, gelling capacity of the AX samples was not predicted well by average FA content. We hypothesize that this is due to the presence of AX molecules with different FA contents within a sample. AX molecules rich in FA would form crosslinks and participate in the network, while those with low FA contents would not. The proportion of participating molecules would be the factor deciding the gelling capacity of the sample. This concept of participating molecules was tested by establishing the presence of crosslinks in non-gelling samples through HPSEC and rheological measurements pertaining to the Cox–Merz rule. The study provides an approach to design of gels with different strengths, textures and colonic fermentation properties.     

Protein adsorption on titanium dioxide: Effects on double layer and semiconductor space charge region studied by EIS

The semiconductor properties of an n-type TiO₂ oxide surface and its modification by protein adsorption using electrochemical impedance spectroscopy (EIS) were studied. Impedance spectra under steady state conditions were obtained as a function of electrode potential and human serum albumin (HSA) concentration in solution. The effect of the adsorption potential on the EIS response was also analyzed (E_ads −0.70, −0.50 and −0.080 V vs. saturated calomel electrode). The impedance spectra were modeled using different equivalent circuits, and data analysis were performed by data fitting in the whole frequency range, as well as in the low and high frequency ranges. The electric representation that better fit experimental data consisted of two equivalent subcircuits composed by a combination of constant phase elements (cpe₁ and cpe₂) and resistances (R_s and R₁). The cpe₁ element represented the distributed capacity in the semiconductor oxide. The cpe₂ element was associated with diffusional processes. We have analyzed EIS data based on a theoretical calculation of interface apparent capacitance (C_app) from the cpe₁ parameters (Q₁ and ?₁) and resistance elements. The changes in capacitance, produced by the presence of HSA, were associated to changes in the space charge layer capacitance of the semiconductor, as a result of the energy band bending near the surface. The values obtained for the R₁ element from the theoretical fitting procedures (in the high and whole frequency range) were correlated to the electric resistance inherent to the semiconductor properties having a value of 6.10³ Ω cm².