Reinaldo C. Bazito

Visualization of Cathode Activity for Fe-Rich and Cu-Rich Intermetallic Particles via Cathodic Corrosion from Dioxygen Reduction at Aluminum Alloy 2024-T3

A wall-jet flow cell was used to study O 2 reduction at AA2024-T3. In buffered O 2 -saturated solution the current density was 2% of the diffusion-limited value and relatively stable with time. In unbuffered solution the current density was 25-50% of the diffusion-limited value. The higher currents under unbuffered conditions are attributed to production of OH - via O 2 reduction at the intermetallic particles (IPs) at AA2024-T3. Trenching was observed around both Cu-rich and Fe-rich IPs. This cathodic corrosion was observed in the absence of chloride and when the alloy was held potentiostatically at open-circuit potential demonstrating that both types of IPs can act as cathodes toward O 2 reduction under these conditions.

Sugar-based anionic surfactants: synthesis and micelle formation of sodium methyl 2-acylamido-2-deoxy-6-O-sulfo-d-glucopyranosides

The following sequence of reactions has been employed to synthesize the title anionic surfactants: [chemical reaction: see text] where R=C7H15; C11H23; and C15H31, respectively, and Py refers to pyridine. Aggregation of the surfactants synthesized (predominantly alpha anomers) in water was studied at 40 degrees C by conductivity measurements. Increasing the chain length of R decreases the critical micelle concentration (CMC) and the degree of counter-ion dissociation. The dependence of the Gibbs free energy of micellization and CMC on the length of R is similar to other ionic surfactants, but the head-group, i.e., the sulfated sugar moiety is less hydrophilic than the structurally related group -(OCH2-CH2)2-OSO3-Na+, most probably because of intermolecular H-bonding in the micellar pseudo-phase

Cellular internalization and transport of biodegradable polyester dendrimers on a model of the pulmonary epithelium and their formulation in pressurized metered-dose inhalers

The purpose of this study was to evaluate the effect of generation and surface PEGylation of degradable polyester-based dendrimers nanocarriers on their interactions with an in vitro model of the pulmonary epithelium as well as to assess the ability to formulate such carriers in propellant-based, portable oral-inhalation devices to determine their potential for local and systemic delivery of drugs to and through the lungs. Hydroxyl (-OH) terminated polyester dendrimers of generation 3 and 4 (G3, and G4) were synthesized using a divergent approach. G4 was surface-modified with PEG (1,000Da). All dendrimers and their building blocks were determined to be highly compatible with the model pulmonary epithelium, with toxicity profiles much more favorable than non-degradable polyamidoamine dendrimers (PAMAM). The transport of the species from the apical to basolateral side across polarized Calu-3 monolayers showed to be generation and surface-chemistry (PEGylation) dependent. The extent of the transport is modulated by their interaction with the polarized epithelium and their transient opening of the tight junctions. G3 was the one most efficiently internalized by the epithelium, and had a small impact on the integrity of the monolayer. On the other hand, the PEGylated G4 was the one least internalized by the polarized epithelium, and at the same time had a more pronounced transient impact on the cellular junctions, resulting in more efficient transport across the cell monolayer. PEGylation of the dendrimer surface played other roles as well. PEGylation modulated the degradation profile of the dendrimer, slowing the process in a step-wise fashion - first the PEG layer is shed and then the dendrimer starts degrading. PEGylation also helped increase the solvation of the nanocarriers by the hydrofluoroalkane propellant used in pressurized metered-dose inhalers, resulting in formulations with excellent dispersibility and aerosol quality (deep lung deposition of 88.5%), despite their very small geometric diameter. The combined in vitro and formulation performance results shown here demonstrated that degradable, modified polyester dendrimers may serve as a valuable platform that can be tailored to target the lung tissue for treating local diseases, or the circulation, using the lungs as pathway to the bloodstream.

Dioxygen Reduction Affects Surface Oxide Growth and Dissolution on AA2024-T3

The influence of dioxygen reduction on oxide growth and dissolution at the surface of AA2024-T3 has been investigated in near-neutral, unbuffered conditions. Dioxygen reduction at Fe and Cu also was examined to compare with the behavior of intermetallic particles in AA2024-T3. Electrodes were exposed alternately to N 2 -saturated or O 2 -saturated 0.1 M Na 2 SO 4 solution in a characterized wall-jet flow cell. Limiting current densities associated with O 2 reduction on Fe and Cu range between 1.5 and 2.0 mA cm -2 , whereas AA2024-T3 displays significantly lower values. AA2024-T3 samples also display potential-dependent current density transients when the solution is alternated between N 2 -saturated and O 2 -saturated supporting electrolyte. The data show that the current density transient behavior is due to competition between interfacial etching of oxide due to high local pH, which is a result of the cathodic oxygen reduction reaction (ORR) at intermetallic particles, and anodic oxide growth on the alloy, which is driven by the electric field produced at a given potential. Scanning electron microscopy shows significant differences in oxide thickness with radial distance from the center of the jet impingement region. Energy-dispersive spectroscopic imaging reveals an increase in near-surface Cu and Fe in areas that experience high current densities.

Support Functionalization with a Phosphine‐Containing Hyperbranched Polymer: A Strategy to Enhance Phosphine Grafting and Metal Loading in a Hydroformylation Catalyst

We present the design of a hydroformylation catalyst through the immobilization of air‐stable Rh nanoparticles (NPs) on a magnetic support functionalized with a hyperbranched polymer that bears terminal phosphine groups. The catalyst modification with the hyperbranched polymer improved the metal–support interaction, the metal loading, and the catalytic activity. The catalyst was active for the hydroformylation of natural products, such as estragole, and could be used in successive reactions with negligible metal leaching. The phosphine grafting played a key role in the recyclability of Rh NPs under hydroformylation conditions. The catalytic activity was maintained in successive reactions, even if the catalyst was exposed to air during each recovery procedure. The modification of the support with hyperbranched polyester allowed us either to increase the number of Rh active species or to obtain more active Rh species on the catalyst surface.

Proline derivatives as organocatalysts for the aldol reaction in conventional and non-conventional reaction media

Abstract Different l-proline derivatives were investigated as organocatalysts for the aldol condensation reaction between acetone and 4-nitrobenzaldehyde, in a conventional organic solvent (DMSO), in supercritical carbon dioxide, and in mixtures of this solvent and 1-allyl-3-alkyllimidazolium chlorides ionic liquids. The catalysts evaluated were: (S)-pyrrolidine-2-carboxylic acid (l-proline), (R)-thiazolidine-4-carboxylic acid (l-thioproline), (2S,4R)-4-[dimethyl(phenyl)silyl]oxy-pyrrolidine-2-carboxylic acid (dimethylphenylsilyloxy-l-proline), (2S,4R)-4-(tert-butyldimethylsilyl)oxy-pyrrolidine-2-carboxylic acid (butyldimethylsilyloxy-l-proline), and (2S,3R,4R,5S,6R)-6-(acetoxymethyl)-3-[(S)-pyrrolidine-2-carboxamido]-tetrahydro-2H-pyran-2,4,5-triyl triacetate (peracetylated glucosamine-l-proline). One of the catalysts tested, the tert-butyldimethylsilyloxy-l-proline, was very effective, allowing lower reaction times, resulting in better yields and enantiomeric excesses than l-proline itself, both in organic solvent (DMSO) and in sc-CO2 or a mixture of sc-CO2 and ionic liquids. The use of the ionic liquid resulted in better yields and enantiomeric excesses in sc-CO2. The other catalysts tested were not as effective, resulting in yields and enantiomeric excesses similar or inferior to the ones obtained with l-proline.