The electrochemical properties of a platinum electrode in functionalized room temperature imidazolium ionic liquids

The electrochemical behavior of a platinum electrode in a set of 1-alkyl ether (and 1-alkyl)-3-methylimidazolium room-temperature ionic liquids (RTILs) 1–3 ([C_xO_yMim]⁺[Anion]⁻ or [C_xMim]⁺[Anion]⁻, where Mim = 3-methylimidazolium; C_xO_y = 1-alkyl ether; C₇O₃ = -(CH₂)₂O(CH₂)₂O(CH₂)₂OCH₃; C₃O₁ = -(CH₂)₂OCH₃; C_x = 1-alkyl; C₁₀ = C₁₀H₂₁; C₄ = C₄H₉; and ) was studied by cyclic voltammetry and electrical conductivity. This complementary set of imidazolium RTILs allowed us to explore the effect of the imidazolium cation and the counter-ion, both of which affected the electrochemical window of these RTILs. Various electrochemical events with low current values were observed, which diminished the electrochemical windows. Interestingly, RTILs 2b [1-(2-methoxyethyl)-3-methylimidazolium tetrafluoroborate] and 2d [1-butyl-3-methylimidazolium tetrafluoroborate] showed quasireversible charge transfer processes. The length of the functional group attached to the imidazolium cation was shown to be of great influence as larger electrochemical windows, as well as lower electrical conductivities, were obtained with the longer C₇O₃ and C₁₀ functional groups. The largest electrochemical window of 2.0 V was achieved with RTIL 2c, 1-decyl-3-methylimidazolium tetrafluoroborate. Dedicated to the memory of Prof. Francisco Nart.     

Characterization of hierarchical porosity in novel composite monoliths with adsorption studies

Two different and novel composite monolithic materials with multimodal hierarchical porosity were prepared. The composites were prepared by immobilizing porous clay hetrostructure (PCH) and aluminum pillared clay (PILC), individually, into highly porous framework of a foam like monolith zeolite (MZ). The MZ was prepared hydrothermally, by following a polyurethane foam (PUF) based induced-template procedure and, consists of ZSM-5 framework. The MZ was fabricated into different composite materials through a simple dip coating method. Characterization of these materials with X-ray, SEM, and low temperature nitrogen adsorption techniques shows that composites materials are the morphological mixture (hybrid) of constituting materials. It also show that PCH based composites are meso and microporous, where as PILC based composites are essentially microporous in nature. The materials were further characterized for their hierarchical porosities by adsorption of two VOCs, which were toluene and n-hexane, under ambient conditions. The difference in adsorption of various sized (small to large) molecules was considered to work out the hierarchy of pores in these materials. With help of adsorption data, the hierarchical porosity was established into three size ranges, based on pore volumes of certain pore size ranges (>0.36 nm–<0.49 nm, >0.49 nm–<0.66 nm, and ≥0.66 nm). Water adsorption studies on these materials confirm that the coating of zeolite monolith with clay based adsorbents can also modify the hydrophobicity of original zeolite structure.     

Nutritional value of the Chilean seaweeds Cryptonemia obovata and Rhodymenia corallina

Some nutritional components of the edible seaweeds Cryptonemia obovata and Rhodymenia corallina were determined. The amino acid content ranged from 1.0 +/- 0.3 to 4174.2 +/- 14.2 mg 100 g(-1) dry wt in C. obovata and between 0.9 +/- 0.3 and 2657.0 +/- 13.5 mg 100 g(-1) dry wt in R. corallina. The most abundant fatty acid in C. obovata was palmitic acid, reaching a value of 36.5 +/- 0.2%, while in Rhodymenia corallina the main fatty acid was oleic acid, reaching a value of 24.7 +/- 0.07%. Both seaweeds showed an important content of EPA (C20:5omega3). In C. obovata, alpha-tocopherol was the principal tocol (138.5 +/- 4.9 mg kg(-1) lipid), while in R. corallina, it was gamma-tocotrienol (850.3 +/- 9.4 mg kg(-1) lipid). Furthermore, beta-carotene was the main carotenoid pigment found in C. obovata.     

Ruthenium-catalyzed (2 + 2) intramolecular cycloaddition of allenenes

We report a ruthenium-catalyzed (2 + 2) intramolecular cycloaddition of allenes and alkenes. We have found that the use of the ruthenium complex RuH(2)Cl(2)(P(i)Pr(3))(2), which has previously gone unnoticed in catalytic applications, is crucial for the observed reactivity. The reaction proceeds under mild conditions and is fully diastereoselective, providing a practical entry to a variety of bicyclo[3.2.0]heptane skeletons featuring cyclobutane rings.     

Catalysis by metallic nanoparticles in aqueous solution: model reactions

Catalysis by metallic nanoparticles is certainly among the most intensely studied problems in modern nanoscience. However, reliable tests for catalytic performance of such nanoparticles are often poorly defined, which makes comparison and benchmarking rather difficult. We tackle in this tutorial review a subset of well-studied reactions that take place in aqueous phase and for which a comprehensive kinetic analysis is available. Two of these catalytic model reactions are under consideration here, namely the reduction of (i) p-nitrophenol and (ii) hexacyanoferrate (iii), both by borohydride ions. Both reactions take place at the surface of noble metal nanoparticles at room temperature and can be accurately monitored by UV-vis spectroscopy. Moreover, the total surface area of the nanoparticles in solution can be known with high precision and thus can be directly used for the kinetic analysis. Hence, these model reactions represent cases of heterogeneous catalysis that can be modelled with the accuracy typically available for homogeneous catalysis. Both model reactions allow us to discuss a number of important concepts and questions, namely the dependence of catalytic activity on the size of the nanoparticles, electrochemistry of nanoparticles, surface restructuring, the use of carrier systems and the role of diffusion control.     

First evidence of simultaneous different kinetic behaviors at the interface and the continuous medium of w/o microemulsions

A study was carried out on the butylaminolysis reaction of 4-nitrophenyl caprate in AOT/chlorobenzene/water microemulsions, with the observed rate constant, kobs, showing both first- and second-order dependence on butylamine concentration. The first-order term in [BuNH2] is due to the reaction occurring at the interface of the microemulsion while the second-order term is due to the reaction in the continuous medium. The different kinetic behavior is accounted for by the mechanism by which the reaction proceeds: at the interface of the microemulsion, the rate-determining step is the formation of the addition intermediate, T+/-, whereas in the continuous medium the slow step is the base-catalyzed decomposition of this intermediate. The application of the pseudophase formalism allows the observed kinetic behavior to be explained and to obtain the rate constants at the interface, ki2=0.13 M-1 s-1, and in the continuous medium, ko2KT=2.46x10(-2) M-2 s-1. These values indicate that the reaction rate decreases approximately 23 times upon going from the aqueous medium to the interface of the microemulsion, whereas the rate constant in the continuous medium is consistent with that obtained in pure chlorobenzene, ko2KT=2.09x10(-2) M-2 s-1.     

Thermal emission of macroporous silicon chirped photonic crystals

In this Letter we report on the thermal properties of macroporous silicon photonic crystals with the unit cell gradually varied along the pore axis. We show experimentally that arbitrarily large omnidirectional total-reflectance bands can be produced with such structures. We also demonstrate that those bands can be effectively used to reduce thermal radiation in large spectral bands.     

Novel catalytic effects in ester aminolysis in chlorobenzene

The mechanism of glyme catalyzed ester aminolysis in chlorobenzene should be modified by including a new reaction pathway that shows a first-order dependence on the concentration of the phase transfer catalyst and a second-order dependence on butylamine.     

Flow-injection determination of phenylephrine hydrochloride in pharmaceutical dosage forms with on-line solid-phase extraction and spectrophotometric detection

A flow injection method is proposed for the determination of phenylephrine hydrochloride in pharmaceutical dosage forms. The method involves the use of on-line solid-phase extraction by means of a microcolumn containing Dowex 50W X8 ion-exchange resin for the separation of the analyte prior to colour development and spectrophotometric detection in the visible region.

The influence of preconcentration flow, preconcentration pH and elution volume was studied.

The method exhibits appropriate linearity (r² = 0.9999) which was proved statistically by means of the “F”-test. When applied to commercial samples containing several active ingredients and excipients, a significant reduction of interferences was found. Accuracy, evaluated by means of the spike recovery method was in the range 99.7–100.8%, with precision (R.S.D., %) better than 1%.

In order to achieve the automation the system was controlled from a notebook computer by means of a program written in QuickBASIC language. Under these conditions, a sampling frequency of 40 samples per hour could be attained.     

On the low-lying excited states of sym-triazine-based herbicides.

We report a joint computational and luminescence study on the low-lying excited states of sym-triazines, namely, 1,3,5-triazine (1) and the ubiquitous herbicides atrazine [6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (2)] and ametryn [6-methylthio-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (3)]. Geometrical structures, energetics, and transition and state properties of I and 2 were computed at the TD-DFT, CASSCF, and CASPT2 levels of theory. The fluorescence and phosphorescence emission spectra, lifetimes, and fluorescence quantum yields were measured for the three compounds, and from these, the energies of the lowest excited states and their corresponding radiative rates were determined. The predictions from CASPT2 calculations are in good agreement with the experimental results obtained from the luminescence studies and allow the interpretation of different absorption and emission features.