Structural considerations and reactivity of peroxocomplexes of V(V), Mo(VI) and W(VI)

In this perspective we will discuss recent results on structural aspects of peroxocomplexes of transition metals having the d(0) configuration (V(V), Mo(VI), W(VI)), and show how these may be related to the reactivity of these species in both chemical and biological systems. In addition, we will consider the relevance of structural properties to their involvement as important intermediates in industrial and enzymatic catalysis. These will be related to the behaviour of peroxocomplexes of other diamagnetic transition metals, such as those with d(8) (Pd(II), Pt(II)) configurations.     

Comparison of different types of stationary phases for the analysis of soy isoflavones by HPLC

Nowadays, there are new technologies in high-performance liquid chromatography columns available enabling faster and more efficient separations. In this work, we compared three different types of columns for the analysis of main soy isoflavones. The evaluated columns were a conventional reverse phase particle column, a fused-core particle column, and a monolithic column. The comparison was in terms of chromatographic parameters such as resolution, asymmetry, number of theoretical plates, variability of retention time, and peak width. The lower column pressure was provided by the monolithic column, although lower chromatographic performance was achieved. Conventional and fused-core particle columns presented similar pressure. Results also indicate that direct transfer between particle and monolithic columns is not possible requiring adjustment of conditions and a different method optimization strategy. The best chromatographic performance and separation speed were observed for the fused-core particle column. Also, the effect of sample solvent on the separation and peak shape was evaluated and indicated that monolithic column is the most affected especially when using higher concentrations of acetonitrile or ethanol. Sample solvent that showed the lowest effect on the chromatographic performance of the columns was methanol. Overall evaluation of methanol and acetonitrile as mobile phase for the separation of isoflavones indicated higher chromatographic performance of acetonitrile, although methanol may be an attractive alternative. Using acetonitrile as mobile phase resulted in faster, higher resolution, narrower, and more symmetric peaks than methanol with all columns. It also generated the lower column pressure and flatter pressure profile due to mobile phase changes, and therefore, it presents a higher potential to be explored for the development of faster separation methods.     

Shear horizontal wave in multilayered piezoelectric structures: Effect of frequency,incidence angle and constructive parameters

In this paper, the global matrix method is applied to find the behavior of transmission coefficients for shear horizontal (SH) wave propagation with oblique incidence in piezocomposite layered systems. The elemental periodic cells of these piezocomposites are formed by two types of components: a piezoelectric PZT material and an Araldite polymer. The behavior of the transmission coefficient with respect to the frequency, incidence angle and piezoelectric volume fraction is studied. Some numerical calculations for different configurations of the composite are shown. The influence of the bonding films made of polymeric material is also studied. These results could be used to versatile transducers design.     

Estimating the norm of conformal maps in Korenblum-Orlicz spaces

We use Young’s functions to define the Korenblum-Orlicz spaces as a generalization of the Korenblum spaces and we establish some of its properties. We show that the norm of the conformal maps in Korenblum-Orlicz spaces can be dominated by a certain expression involving the supremum over the inverse image of certain sectors. This extend a result of J. Ramos Fernández in (C. R. Math. Acad. Sci. Paris, 344(5):291–294, 2007) for α-Bloch spaces.     

Voltammetric study of a sulfur contaminant of aviation biokerosene

Journal of Solid State Electrochemistry - Butanethiol is a contaminant of aviation biokerosene, and its monitoring is of great importance to evaluate the quality of this biofuel. In this work, the...     

Catalytic Activity of Alkali Metal Cations for the Chemical Oxygen Reduction Reaction in a Biphasic Liquid System Probed by Scanning Electrochemical Microscopy

Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane-based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H₂O₂ detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H₂O₂, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase.     

“Three-in-one” Complexes Formed by Anionic Guests and Monosubstituted Cationic Alkyldiamino β-Cyclodextrin Derivatives

The effect of electrostatic interactions on the complexation of ionic guests by charged β-cyclodextrin (βCD) derivatives is reviewed. Special attention is paid to the numerous studies concerning the effect of electrostatic interactions on (i) the complexation of fluorescent and UV probes; (ii) the catalytic and chiral recognition properties of βCD derivatives; and (iii) the complexation of two bile salts (sodium cholate, NaC, and sodium deoxycholate, NaDC). The formation of three-in-one complexes between NaC and alkyldiamino βCD derivatives is also presented.     

Thermal and quality evaluation of vegetable oils used in ruminant feed

Dairies add fat supplements to the diets of small ruminants to increase energy production and consequently the production and quality nutritional and sensorial of the milk. This study investigated the thermal and oxidative stability of babassu, castor, faveleira, and sesame oils by TG/DTA and PDSC. The profile of the fatty oils studied was determined by GC–MS as well as physicochemical characteristics. The thermogravimetric profile of the oils indicated that mass loss was caused by the decomposition or volatility of the triacylglycerides. Faveleira and sesame oils showed a high percentage of polyunsaturated fatty acids, especially C18:2. From a nutritional standpoint, unsaturated oils are more suitable supplements for animals because they promote biochemical changes beneficial to human health.     

Investigation of thermal behavior of Heliotropium indicum L. lyophilized extract by TG and DSC

Thermogravimetric (TG) techniques and differential scanning calorimetry (DSC) used for the study of pre-formulation or drug–adjuvant compatibility have been gaining importance in Brazil. These techniques are being used for the verification of possible interactions between drugs and adjuvants. Aiming at studying the behavior of a plant extract and its mixture with adjuvants, using these thermoanalytical techniques the plant species Heliotropium indicum L. was used. This plant which is originally from India and has been well acclimatized in Brazil has healing and anti-inflammatory properties. The methodology for obtaining the extract followed the Brazilian Pharmacopoeia methodology. And the incorporation of the extract with adjuvants was through binary mixtures (1:1 w/w). The TG and DSC curves were obtained under nitrogen atmosphere (25 mL min^?1) at a heating rate of 5 °C min^?1; TG tests were analyzed within a temperature range from 25 to 600 °C and DSC from 25 to 300 °C. The TG curves show good thermal stability of the extract and its mixtures with adjuvants up to 150 °C, except the propylene glycol (PLG). The DSC curves revealed an incompatibility of the extract with methylparaben and PLG mixture.     

On the mechanism responsible of Raman enhancement on carbon allotropes surfaces: the role of molecule‐surface vibrational coupling in SERS

The ability of different carbon allotropes surfaces as potential substrates for enhanced Raman spectroscopy is analysed theoretically and the factors responsible of the Raman‐enhancing mechanism deeply scrutinised. Our analysis is based on the partition of the Raman tensor into molecule and surface terms, which leads to three different contributions to the Raman activity (‘molecule’, ‘surface’ and ‘intermolecular’). Both static and pre‐ resonance conditions are considered in our analysis of the Raman spectra of pyridine adsorbed on model planar and curved surfaces and the three contributions to the Raman activity obtained separately. At static conditions, there is a general decrease in the Raman activity of vibrational modes associated to the molecule, proportional to the strength of the molecule–surface interaction. This stems from a reduction of the polarizability of pyridine upon its adsorption on the carbon surface. Under pre‐resonance conditions, the surface contributes significantly to the Raman activity of the pyridine vibrational modes, even if the electronic transition involves exclusively energy levels from the surface. This is because of small vibrational couplings between molecular and surface modes which are negligible in metallic surface‐like silver. It suggests also the possibility of finding similar effects in metallic surface built from lighter atoms like silicon or aluminium. Copyright © 2015 John Wiley & Sons, Ltd.