Pt–Sn/C electrocatalysts for methanol oxidation synthesized by reduction with formic acid

Carbon supported Pt–Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid, and their electrocatalytic activity for methanol oxidation was compared with commercial Pt/C and Pt₇₅Sn₂₅/C electrocatalysts. By X-ray diffraction analysis it was found that the Pt lattice parameter increases with the addition of Sn, indicative of alloy formation. It was confirmed that Sn exhibits cocatalytic activity for CO oxidation. The onset potential for the methanol oxidation reaction of the Pt–Sn electrode was approximately 0.1 V smaller than that on Pt both at room temperature and at 90 °C. The best performance in a direct methanol fuel cell was obtained using the Pt₇₅Sn₂₅/C alloy catalyst prepared by the formic acid method as the result of an optimal balance of Sn content, degree of alloying and metal particle size.     

Electron transfer to sulfides:: Heterogeneous kinetics, CS bond cleavage, and self-protonation

The problem of characterizing the steps associated with the dissociative reduction of sulfides has been addressed. The electrochemical reduction of diphenylmethyl para-methoxyphenyl sulfide in N,N-dimethylformamide, on both glassy carbon and mercury electrodes, was chosen as a test system. The electrode process involves the slow heterogeneous outer-sphere electron transfer to the sulfide, the fast cleavage of the CS bond, the reduction of the ensuing carbon radical, and the self-protonation triggered by the generation of the strong base Ph₂CH⁻. The latter reaction is rather slow, in agreement with the large intrinsic barriers characterizing proton transfers between CH-acids and carbon bases. The dissociative reduction was studied in the presence of an exogenous acid. The results, obtained by convolution analysis, point to a stepwise DET mechanism in which the ET step is accompanied by rather large reorganization energy. Similar results were obtained on both electrode materials. Analysis of the heterogeneous electron transfer and associated CS bond cleavage indicate that the reduction of this and other sulfides lies between the stepwise dissociative electron transfers leading to the formation of stiff π^* radical anions and those going through the intermediacy of loose σ^* radical anions.     

Guide Cells Support Muscle Regeneration and Affect Neuro-Muscular Junction Organization

Muscular regeneration is a complex biological process that occurs during acute injury and chronic degeneration, implicating several cell types. One of the earliest events of muscle regeneration is the inflammatory response, followed by the activation and differentiation of muscle progenitor cells. However, the process of novel neuromuscular junction formation during muscle regeneration is still largely unexplored. Here, we identify by single-cell RNA sequencing and isolate a subset of vessel-associated cells able to improve myogenic differentiation. We termed them ‘guide’ cells because of their remarkable ability to improve myogenesis without fusing with the newly formed fibers. In vitro, these cells showed a marked mobility and ability to contact the forming myotubes. We found that these cells are characterized by CD44 and CD34 surface markers and the expression of Ng2 and Ncam2. In addition, in a murine model of acute muscle injury and regeneration, injection of guide cells correlated with increased numbers of newly formed neuromuscular junctions. Thus, we propose that guide cells modulate de novo generation of neuromuscular junctions in regenerating myofibers. Further studies are necessary to investigate the origin of those cells and the extent to which they are required for terminal specification of regenerating myofibers.     

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> electrodes

The generation of active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L⁻¹) and a low current density (5 mA cm⁻²) it was possible to produce up to 60 mg L⁻¹ of active chlorine on a Ti/Sn_0.99Ir_0.01O₂ anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm⁻² and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 × 10⁻⁴ mol L⁻¹. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.     

Kinetic Studies of Mullite Synthesis from Alumina Nanoparticles and a Preceramic Polymer

The crystallization kinetics of mullite formation in a diphasic precursor consisting of a silicone resin filled with commercial γ-alumina nanoparticles (15 nm mean particle size, specific surface area of 100 m²/g), heated in air from 1250° to 1350°C, was studied by X-ray diffraction. Transitional γ-alumina and amorphous silica from the pyrolysis of the preceramic polymer exhibited a remarkable reactivity, as demonstrated by a very low incubation time (from 500 s at 1250°C to 20 s at 1350°C), a high mullite yield (about 80 vol%, after 100 s at 1350°C), and a low activation energy for nucleation (677±60 kJ/mol). The activation energy values found were lower than those reported previously for other diphasic systems, including sol–gel precursors. Besides the high specific surface of nanosized γ-alumina particles, the low energy barrier could be attributed to the highly reactive silica deriving from the oxidation of Si–CH₃ bonds in the silicone and to the homogeneous dispersion of the nanosized filler inside the preceramic polymer. Furthermore, the possibility of applying plastic shaping processing methods to the mixture of a preceramic polymer and nanosized filler makes this approach particularly valuable, in comparison, for instance, with sol–gel based alternatives.     

Density functional computational studies on the intermediate stage of the ribose and glycine Maillard reaction: Formation of deoxyosones in aqueous solution

Mechanisms in an aqueous solution of the Maillard reaction are proposed under several pH conditions for the interaction of glycine with cyclic ribose (c-Rib) and open-chain ribose (Rib). According to the Gibbs free energy relationships as well as internal energies values derived from our density functional theory calculations, the c-Rib/Rib + DGly (glycine) are the most favourable reaction pathways for the formation of deoxyosones under basic conditions, where Rib is more reactive than c-Rib. The intermediate stage of the Maillard reaction leads to the formation of deoxyosones.     

The effect of surface treatments on the mechanical properties of basalt‐reinforced epoxy composites

Basalt fiber is an emerging alternative reinforcement to glass or carbon depending upon the application. An important contributing parameter to ultimate performance of any composite is the fiber–‐matrix interface, to which toughness and compressive strength are intimately related. To better understand this matrix fiber interaction in controlling properties, we compared different modification strategies and the impact upon the properties of composites. Strategies focussing upon mechanical interlocking through increased surface roughness and covalent chemical bonding using sol/get methods were explored. Combined methods were also used to explore synergistic behavior as well as the use of aliphatic triethylenetetramine (TETA) to react with any covalently attached epoxy groups. Results from single ply composites showed that when the properties were fiber or fiber/matrix dominated, the sol/gel or epoxy silane method gave the largest improvement in ultimate tensile strength increasing 66% and 27% for uni‐weave 0° and 45° laminas. The combined surface modification methods exhibited increases of 45% and 13% for the same laminas. When properties were matrix dominated, the combined strategies produced the highest improvements in ultimate tensile strength of about 55% compared with 37% for sol/gel modification. For 16‐ply plain weave laminates, epoxy silane surface treatments produced the greatest improvements in compressive and interlaminar shear strengths, increasing 52% and 21%, respectively. This correlated with fiber‐ and fiber/matrix‐dominated results from single ply laminas. The combined treatment using TETA however decreased shear and compressive strength by about 20%, while scanning electron microscopy (SEM) evaluation and dynamic mechanical thermal analysis (DMTA) attributed this to increased resin ductility and plasticization. © 2013 Society of Plastics Engineers