Diastereoselective Heterogeneous Catalytic Hydrogenation of Aromatic or Heteraromatic Compounds

The diastereoselective hydrogenation catalyzed by heterogeneous metallic catalysts uses a covalently bound chiral auxiliary to induce the chirality. It remains an active synthetic methodology in the asymmetric synthesis of chiral products and may proceed with high diastereoselectivity. This review describes recent examples using this method, such as hydrogenation of C=C, C=O, and C=N bonds. The use of a chiral auxiliary group has also been successfully applied to the hydrogenation of aromatic and heteroaromatic rings. The choice of the chiral auxiliary was found to play a key role in the asymmetric hydrogenation. The results could be explained in terms of steric effect, with a preferred conformation of the adduct substrate and the addition occurring from the less bulky side. The catalytic metal, the support and the presence of additives were also found to have a significant influence.     

A study about the effect of the temperature of hydrogen treatment on the properties of Ru/Al2O3 and Ru/C and their catalytic behavior during 1-heptyne semi-hydrogenation

The 1-heptyne selective hydrogenation carried out at 150 kPa, and at 283 and 303 K using Ru/Al₂O₃ and Ru/C as catalysts, was studied. Catalysts were prepared by the incipient wetness impregnation technique using RuCl₃ as precursor. Ru/Al₂O₃ was treated in hydrogen at 373 or 573 K and Ru/C only at the last temperature. Catalysts were characterized by hydrogen chemisorption, TPR and XPS. Ru dispersion after treatment in hydrogen at the highest temperature is similar for both catalysts. Ru is present as Ru⁰ in Ru/C, while Ru⁰ and Ru electron-deficient species are present on the catalysts surface after hydrogen treatment at the two temperatures using Al₂O₃ as support. The best catalytic behavior was observed for the highest temperature of hydrogen treatment and for 303 K reaction temperature. As a consequence of a shape selectivity effect of the C support, the best conversion is obtained with the alumina supported catalyst.     

Interaction between dietary protein and fat in triglyceride metabolism in the rat: Effects of soy protein and menhaden oil

The objective of the present study was to determine the mechanisms by which dietary proteins interact with dietary lipids in the regulation of triglyceridemia in rats. Male Sprague-Dawley rats (n=56) were subjected to 28-d experimental diets containing different combinations of proteins (20% w/w) and lipid sources (14% w/w): (i) casein-menhaden oil, (ii) casein-beef tallow, (iii) soy protein-menhaden oil, and (iv) soy protein-beef tallow. Significant protein-lipid interactions were observed on triglyceridemia and hepatic cholesterol in fasted rats. The combination of casein and beef tallow was associated with high plasma TG and hepatic cholesterol concentrations, which were reduced by substitution either of soy for casein or of menhaden oil for beef tallow. Therefore, triglyceridemia and liver cholesterol remained low with soy protein feeding, independently of the lipid source, as well as with menhaden oil feeding, regardless of the protein source. The menhaden oil diets reduced plasma cholesterol, hepatic TG, and TG secretion compared with beef tallow diets independently of the dietary protein source. Modifying the source of dietary proteins and lipids had no effect on post-heparin plasma lipoprotein lipase activity. These results demonstrate that soy protein can lower rat triglyceridemia relative to casein when associated with beef tallow consumption, whereas menhaden oil can attenuate hypertriglyceridemia when rats are fed casein. The data further suggest that part of the hypotriglyceridemic effect of soy protein in the rat may be mediated by reduced hepatic lipid synthesis, as is the case for menhaden oil.     

Toxicokinetics of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) in the European corn borer,Ostrinia nubilalis (Hübner)

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), the major hydroxamic acid present in corn, and its tritiated derivative, were prepared synthetically for use in the determination of the toxicokinetics of this insect deterrent in the European corn borer (ECB),Ostrinia nubilalis. In growth studies with DIMBOA (0, 0.05, 0.2, and 0.5 mg/g diet), the mean time to pupation and adult emergence were significantly lengthened by an increase in concentration. Pupal and adult weights, for both female and male, decreased with an increase in concentration. Increased larval and pupal mortality occurred at the highest concentration of DIMBOA. DIMBOA, at concentrations of 0.2 and 0.5 mg/g diet, resulted in a decrease in the number of egg masses produced per female, and at 0.5 mg/g diet, in a decrease in the number of eggs per egg mass. Larvae fed from the neonate stage on a diet containing 0.2 mg [³H]- + [¹H]DIMBOA/g diet showed an increase in the content of label from fourth to fifth instar, but levels declined at pupation and emergence. A large amount of the labeled compounds was excreted by the insect in the pupal case. In dose-related studies, both uptake and excretion increased with an increase in concentration of DIMBOA (0.05, 0.2, 0.4 mg/g diet), while a body burden (concentration in the tissues/concentration in the frass) of approximately 0.25 was maintained for all concentrations. At the highest dose of DIMBOA (0.4 mg/g), the ECB increased consumption, possibly to compensate for the toxic effects of the compound. In topical application studies, elimination of the labeled compound in the frass was rapid, reaching 65% by 4 hr and 88% by 48 hr. Accumulation of label in tissues other than hemolymph was low. The results show that the ECB does possess adaptive mechanisms to deal with the effects of this host-derived compound.     

Thermodynamic Modeling of Alkali Metal Oxide-Silica Binary Melts

The evaluation of the thermodynamic properties as well as the phase diagrams for the binary Na₂O–SiO₂, K₂O–SiO₂, and Li₂O–SiO₂ systems are carried out with a structural model for silicate melts and glasses. This thermodynamic model is based on the assumption that each metallic oxide produces the depolymerization reaction of silica network with a characteristic free-energy change. A least squares optimization program permits all available thermodynamic and phase diagram data to be optimized simultaneously. In this manner, data for these binary systems have been analyzed and represented with a small number of parameters. The resulting equations represent the thermodynamic and phase diagram data for these alkali metal oxide–silica systems within experimental error limits. In particular, the measured limiting liquidus slope at     is well reproduced.     

When does personalization work on social media? a posteriori segmentation of consumers

The aim of this research is to find a segment of consumers of fashion products based on their personal visions of personalization of shoppable ads on mobile social media. To meet this objective, three operational objectives are defined. First, a theoretical model is evaluated based on the stimulus-organism-response framework (S–O–R). This examines, with a PLS-SEM approach, how the stimulation of personalization will affect consumers' internal cognitive state (perceived usefulness) and consequently generates a behavioral response (intention to buy). Second, we look for fashion consumer segments based on their perception of personalization through prediction-oriented segmentation (PLS-POS). Third, the segments are explained based on three constructs that were considered important in fashion consumption through mobile social networks: purchase intention, concern for privacy, and perception of trend. The inclusion of personalization and the perception of usefulness of advertisements can greatly help the intention to purchase clothing to be understood. The application of a posterior segmentation helps to better understand the different types of users exposed to shoppable ads on mobile social networks and their relationship with the purchase intention, concern for privacy and trend. While the measures and scales were tested in a context of mobile clothing trade, the methodology can be applied to other types of products or services.

     

Iron recovery from zinc mine tailings by magnetic separation followed by carbothermal reduction of self‐reducing briquettes

The volume of tailings produced by the extractive industry has been increasing due to the processing of the low‐grade ore. This issue can cause environmental accidents and require significant investment to control the disposal of tailings. Therefore, this study aims to recover iron from zinc mine tailings by wet magnetic separation followed by the carbothermal reduction of self‐reducing briquettes. Two magnetic separation routes were investigated to concentrate iron. Zinc mine tailings were processed by route I, in a rougher stage followed by a scavenger stage; and route II, in a rougher stage followed by a cleaner stage. The carbothermal reductions were performed using self‐reducing briquettes composed of Fe concentrate from the route with high Fe content and charcoal. The products were analyzed by scanning electron microscopy with energy dispersive spectroscopy (SEM‐EDS), x‐ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP‐OES), and volumetric chemical analysis. Magnetic separation route II provided the highest‐grade Fe concentrate, 52% Fe, while route I provided 33% Fe. In the carbothermal reductions, a metallization degree of 98% in the Fe concentrate briquette, 97% in the briquette with a 10% replacement of its raw material by Fe concentrate, and 99% in the hematite briquette was reached. The replacement of raw material by Fe concentrate showed no significant change in Fe recovery. Considering the whole process, magnetic separation and carbothermal reduction, the recovery of Fe from the zinc mine tailings was 67%. Therefore, the process route suggested in this study will not only reduce tailings disposal and consequently the risk of environmental accidents, but it will also provide profitable raw material for the steel industry.     

Biodegradability and improved mechanical performance of polyhydroxyalkanoates/agave fiber biocomposites compatibilized by different strategies

In this work, biocomposites made of polyhydroxyalkanoates (PHA) with natural fibers were produced via compression molding. In particular, polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-hydroxyvalerate (PHBV) were reinforced with 20 wt% of agave fibers. Different compatibilization strategies were investigated to improve the fiber-matrix interaction: fiber surface treatment in PHA solution, fiber surface treatment in maleated PHA solution, fiber propionylation, and extrusion with maleated PHA. The biocomposites were characterized in terms of morphology, mechanical properties, water absorption, and biodegradability by CO₂ production tracking. In general, fiber propionylation was the best strategy for mechanical properties enhancement and water uptake decreasing. Biocomposites with propionylated fibers showed improved flexural strength (170% for PHB and 84% for PHBV). The flexural modulus was also enhanced with propionylated fibers up to 19% and 18% compared to uncompatibilized biocomposites (PHB and PHBV, respectively). Tensile strength increased by 16% (PHB) and 14% (PHBV), and the water absorption was reduced using propionylated fibers going from 6.6% to 4.4% compared with biocomposites with untreated fibers. Most importantly, the impact strength was also improved for all biocomposites by up to 96% compared with the neat PHA matrices. Finally, it was found that the compatibilization did not negatively modify the PHA biodegradability.     

Relationship between microstructure and mechanical properties of polyether block amide foams

The mechanical behaviors of five polyether block amide foams, obtained by mold-opening foam injection process, were investigated with regard to their microstructures. The materials vary in mass ratios of hard versus soft segments, and/or in process packing time. The resulting microstructures have been characterized in terms of cavity size and shape ratios, by analyzing scanning electron microscope images after careful sample preparation. The foam mechanical responses have been characterized in compression at small and large strain. At small strain, the initial linear part of the stress–strain curve is enhanced firstly by the hard segment mass ratio and secondly by the fineness of the microstructure. Similar results have been obtained at large strain. The foam viscoelasticity at large strain has been characterized by stress relaxation and strain recovery tests, relevant for foam applications. Reduced packing time and pressure have been shown to lead to the presence of undesired large cavities. The morphological defects appear to have a negligible impact on the macroscopic mechanical behavior of the foams at infinitesimal strain, but lead to critical inconsistency at large strain. Furthermore, the mechanical behavior of the tested polyether block amide foams is controlled first by hard versus soft segments ratio, and second by the microstructure fineness.     

Influence of the corrosion products of copper on its atmospheric corrosion kinetics in tropical climate

In the present paper, the identification of the corrosion product phases formed on copper under different atmospheres of Cuban tropical climate is reported. Cuprite (Cu₂O), paratacamite (Cu₂Cl(OH)₃), posnjakite (Cu₄SO₄(OH)₆ · 2H₂O) and brochantite (Cu₄SO₄(OH)₆) were the main phases identified by X-ray diffraction (XRD) analysis and Fourier transform infrared spectroscopy (FTIR).Copper corrosion products are known to have a protective effect against corrosion. However, a different behaviour was obtained under sheltered coastal conditions. This can be due to the corrosion products morphology and degree of crystallisation, rather than their phase composition. A higher time of wetness and the accumulation of pollutants not washed away from the metal surface can also play an important role.