Scope and Post‐Transformations for the Borane‐Isocyanide Multicomponent Reactions: Concise Access to Structurally Diverse Heterocyclic Compounds

A recently described family of multicomponent reactions (MCRs) involving isocyanides, aldehydes, dipolarophiles and alkylboranes that yield highly substituted aziridines, oxazolidines and pyrrolidines has been studied in detail. In this work the scope of these processes is significantly increased by preparing the borane input through hydroboration of alkenes or organometallic processes, in tandem with the MCR. The aldehyde range is also expanded, and indole‐3‐carbaldehydes yield reactive imines and bis‐indolyloxazolidines, depending on the electron density of the heterocycle. Finally, the obtained adducts constitute an ideal platform to generate structurally diverse compounds using simple post‐condensation modifications. In this way, indole imines undergo stereoselective hydrocyanation and oxazolidines are reductively opened to give amino alcohols. Additionally, palladium‐, ruthenium‐ and gold‐catalyzed processes lead to a variety of complex heterocycles. The methodology is simple, efficient and highly divergent, leading to an array of interesting scaffolds for medicinal chemistry.

     

Ethanol steam reforming kinetics of a Pd–Ag membrane reactor

The ethanol steam reforming reaction carried out in a Pd-based tubular membrane reactor has been modelled via a finite element code. The model considers the membrane tube divided into finite volume elements where the mass balances for both lumen and shell sides are carried out accordingly to the reaction and permeation kinetics. Especially, a simplified “power law” has been applied for the reaction kinetics: the comparison with experimental data obtained by using three different kinds of catalyst (Ru, Pt and Ni based) permitted defining the coefficients of the kinetics expression as well as to validate the model. Based on the Damkohler–Peclet analysis, the optimization of the membrane reformer has been also approached.     

Boosting the photocatalytic hydrogen production of TiO2 by using copper hexacyanocobaltate as co-catalyst

The development of cheap and efficient co-catalysts is crucial to improve the performance of well-known photocatalysts towards the hydrogen evolution reaction. Here, copper hexacyanocobaltate was evaluated for the first time as a potential candidate to be used as co-catalyst coupled with conventional TiO₂. Copper hexacyanocobaltate was formed by chemical precipitation in the presence of TiO₂, without needing further treatments. The composite exhibited paramount performance towards hydrogen generation, surpassing by up to 16 times the behavior reached with bare TiO₂. This composite also overcome the performance of conventional TiO₂ modified with copper and cobalt oxides derived from copper hexacyanocobaltate. The enhanced behavior of TiO₂/Cu₃[Co(CN)₆]₂ composite was promoted by the efficient separation of photogenerated charge carries, and the faster charge transfer from photocatalyst towards species in solution, as it was proved by the photoelectrochemical characterization of the materials. Furthermore, the composite experienced a slight detriment (15%) in its hydrogen production rate after four consecutive photocatalyst tests. This variation was attributed to the slow leaching of copper in the co-catalyst caused by its partial transformation into metal hydroxides, as it was suggested by the ex-situ XPS characterization. Nevertheless, the structural characterization evinced the presence of the Cu₃[Co(CN)₆]₂ in the composite after long-term use. This study should be considered a proof of concept on a reliable route to obtain appropriate composites for hydrogen production using light as primary energy source.     

Study of the reactivity of Double-perovskite type oxide La1−xMxNiO4 (M = Ca or Sr) for chemical looping hydrogen production

La_2-xM_xNiO₄ perovskite oxygen carriers (OC) doped with Ca and Sr (x = 0.05 and 0.20) in the site La were prepared by microwave assisted combustion method and calcined at 800 °C for 2 h. A reactivity study was carried out applying pulses of H₂, O₂ and CH₄. The reactions involved in each step, as well as H₂ production, were studied to evaluate the redox properties of each OC. The crystalline structure, morphology, reduction and oxidation profiles were determined by XRD, SEM and TPR/TPO cycles, respectively. The results indicate that the dopant (Ca or Sr) strongly affect the structure and reactivity of the OC. The increase in dopant concentration increased the degree of crystallinity and the amount of the A₂BO₄ phase formed. The increase in dopant concentration decreased the reducibility of the perovskite. OCs doped with Ca showed higher conversion percentages, and also higher H₂ production. In carriers doped with Sr no coke formation was observed.     

Factors affecting smoking of elementary and high school children from Chile

The outcome of orthodontic treatment involving early extraction of 4 second molars was evaluated in 52 patients (29 girls, 23 boys). Computer-assisted analysis of cephalograms, casts and panoramic X-rays was performed at the start (T1, mean age 11.5 years) and at the end (T2, mean age 14.4 years) of treatment. Following treatment, mesial migration of upper and lower first molars was counteracted; however, treatment only moderately influenced normal development of the position of the incisors and the profile. At the end of treatment, the third molars had erupted in only 3 patients. Nevertheless, on average a significant mesial movement of these teeth was observed. In addition, there was a significant improvement in the axial inclination of the third molars, especially in the upper arch. This improvement was correlated with the original position of the teeth. All patients needed a longer follow-up period and it seems reasonable that some of them might require a second treatment phase to adjust the position of the third molars.     

Lipid metabolism of the yellow clam,Mesodesma mactroides: 2-Polyunsaturated fatty acid metabolism

The fate of labeled linoleic, α-linolenic, and higher homologs of α-linolenic acid administered to the yellow clam,Mesodesma mactroides, was investigated. It was found that the clam incorporated the acids dissolved in sea water and converted 18∶2 (n−6) into 20∶2 (n−6) and 18∶3 (n−3) into 18∶4 (n−3) and 20∶3 (n−3). The addition of casein hydrolysate to the sea water increased the desaturation capacity of the clam and allowed the conversion of 18∶2 (n−6) into 18∶3 (n−6) to be demonstrated. An enhanced desaturation of 18∶3 (n−3) into 18∶4 (n−3) was also demonstrated. After 12 hr administration of the acid, no radioactivity was found in arachidonic, 20∶5 (n−3), or 22∶6 (n−3). Feeding the clams a culture ofPhaeodactylum tricornutum previously incubated with 1-¹⁴C-α-linolenic acid demonstrated that all the homologs of the α-linolenic series were found in the clam without any important changes. Six hour administration of labeled linolenic acid resulted in the incorporation of the acid into diglycerides and phospholipids. Member of the carrera del Investigador Cientifico of the Consejo Nacional de Investigaciones Cientificas y Tecnicas     

Sterol composition of two freshwater molluscs of genusDiplodom

The sterol composition of two taxonomically related freshwater species,Diplodom patagonicus andDiplodom variabilis, respectively, from Lake Nahuel Huapi and the Río de la Plata river were studied by gas liquid chromatography and mass spectrometry. Cholesterol was the main sterol in both species and it was followed by 24-methylcholesta-5, 22-dien-3β-ol, 24-methylcholest-5-en-3β-ol, 24-ethylcholesta-5,22-dien-3β-ol and 24-ethylcholest-5-en-3β-ol. The river species collected within the proximity of marine influence showed less cholesterol and more 24-methylcholesta-5,22-dienol, 24-methylcholest-5-enol and 24-ethylcholesta-5,22-dienol than the lake species.