Toward optimisation of electrolytic reduction of solid chromium oxide to chromium powder in molten chloride salts

Electrochemical reduction of solid Cr₂O₃, in the form of an assembled cathode of porous pellets attached to a current collector, to chromium powder was investigated in molten CaCl₂ and a molten equimolar mixture of CaCl₂ and NaCl. The study focused on the influence of pellets preparation conditions, cell voltages and temperatures on the reduction process. Analyses were reported of the characteristics of the current-time plots of the constant voltage electrolysis under different conditions, cyclic voltammograms of solid Cr₂O₃ in the molten equimolar mixture of CaCl₂ and NaCl, the microstructures and elemental compositions of the reduced pellets. Particularly, attention was given to the intermediate product of the electrolysis, calcium chromites of various stoichiometries, aiming to achieve a better understanding and optimisation of the reduction process.     

Investigation of the collapse of bubbles after the impact of a piston on a liquid free surface

A novel technique based on the impact of a piston on a liquid confined in a vessel is described. Pressure measurements reveal that strong pressure variations (up to 100 atmospheres) with a rich content of frequencies are efficiently transmitted to the liquid. High‐speed camera visualizations show that pre‐existing millimetric bubbles always collapse during the first instants of the impact whereas the behavior of submillimetric bubbles depends on the features of the pressure evolution in the system. In addition to the impact velocity, the amount of gas/vapor trapped between the piston and the liquid's surface plays an important role on how pressure evolves. Only when negative pressure occurs tiny bubbles grow significantly and collapse. The violent collapse of bubbles promote turbulence and mixing at very small length‐scales which renders this technique interesting to intensify processes limited by heat and mass diffusion. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2483–2495, 2017     

Tuning morphology of mesoporous titanium oxides through fluorinated surfactants-based systems

Four different fluorinated surfactant-based systems were used as template for the synthesis of highly ordered TiO₂ mesoporous materials with large-pore wormhole structures. The calcined materials exhibit large pore diameters (up to 5.9 nm), high surface areas (900–1,180 m² g^?1), pore volumes (0.90–1.25 cm³ g^?1) and thick pore walls (4.6–7.7 nm) depending of the synthesis route. It is established that the self-aggregation behavior of fluorinated amphiphile systems can be manipulate and provides a rich phase behavior to obtain well-organized titania sieves with adjustable pore size and surface topography. By comparison to titania and silica sieves obtained by the same procedure, it can be established that there is a deep interaction between head groups of fluorinated surfactants and Ti(IV)(iPrO)₄ showing that the inorganic precursor has a great influence on the properties of the final materials.     

Amino acid composition of some Mexican foods

Knowledge of the amino acid composition of foods is essential to calculate their chemical score, which is used to predict protein quality of foods and diets. Though amino acid composition of many foods is reasonably well established, better knowledge is needed on native foods consumed in different regions and countries. This paper presents the amino acid composition of different presentations of raw and processed foods produced and consumed in Mexico. The amino acid composition was determined using Beckman amino acid analyzers (models 116 and 6300). Tryptophan was determined using the Spies and Chambers method. Of the different foods analyzed, some comments are made on native or basic foods in Mexico: Spirulin, where lysine is the limiting amino acid, with a chemical score of 67%, is a good source of tryptophan (1.16g/16 gN); amaranth contains high levels of sulphur amino acids (4.09 to 5.34 g/16gN), with a protein content of 15 g/100g; and pulque, a Pre-Hispanic beverage that contains high levels of tryptophan (2.58 g/16 gN) and sulphur amino acids (2.72 g/16 gN). Finally, insects are good sources of sulphur amino acids and lysine.     

Effects of microwave radiation on electrodeposition processes at tin-doped indium oxide (ITO) electrodes

In situ microwave activation is investigated for the electrodeposition of a metal (gold) and for a metal oxide (hydrous Ti(IV) oxide) onto tin-doped indium oxide (ITO) film electrodes. It is demonstrated that localized microwave heating of the ITO film can be exploited to affect electrodeposition processes.The electrochemically reversible and temperature sensitive one-electron redox system Fe(CN)₆^3−/4− was employed in aqueous solution in order to calibrate the average surface temperature at the ITO film electrode. In the presence of microwave radiation the average electrode surface temperature reached ca. 363 K whereas under the same conditions the bulk solution temperature reached ca. 313 K. Therefore localized heating of the ITO film appears to be important.The rate of electrodeposition of gold from an aqueous 1 mM tetrachloroaurate(III) solution in 0.1 M KCl (adjusted to pH 2) is enhanced by microwave activation. However, the morphology of deposits remains un-effected. Hydrous titanium (IV) oxide films were electrodeposited from an aqueous solution of 1 mM TiCl₃ in 0.1 M acetate buffer pH 4.7. Dense films with blocking character were obtained with conventional heating but a fibrous more open deposit forms in the presence of microwaves.     

Antibody library selection by the {beta}-lactamase protein fragment complementation assay

Protein fragment complementation assay (PCA) is based on the interaction between two protein partners (e.g. target antigen and antibody), which are genetically fused to the two halves of a dissected marker protein. Binding of the two partners reassembles the marker protein and hence reconstitutes its activity. In this work we have developed the first application of beta-lactamase-based PCA for the isolation of single chain Fv fragments (scFvs) binding to the human receptor RON from a na?ve library. Specific scFvs with the ability to immunoprecipitate could be isolated after a single round of PCA selection from an scFv repertoire previously pre-selected by phage display. Furthermore, the PCA was used to successfully map the epitopes recognized by the selected scFvs by screening them against a small library of random RON fragments.     

Electrocatalytic reduction of nitrate on copper electrode in alkaline solution

This work is devoted to the study of the kinetics and reaction mechanism of nitrate reduction on a copper electrode in 0.1 M NaOH, which acts as the supporting electrolyte. The experimental methods include cyclic voltammetry (CV), cronoamperometry (CA), controlled-potential electrolysis (CPE), and coulometry. In CV, there are three potential regions where charge transfer reactions take place, reactions which are associated with NO₃⁻ and/or intermediates reduction. Two isopotential points observed in CV indicate the existence of some competitive adsorption processes at the electrode surface.The three charge transfer steps were also made evident in the CA, CPE and coulometry studies. The correlation of the experimental results with the literature data led to the conclusion that NO₃⁻ reduction on a copper electrode in 0.1 M NaOH has an intermediate (N₂O₂²⁻) species, which reduces to N₂ at a potential of about −1.3 V and to NH₄OH at potential values lower than −1.4 V (both values are vs. SCE).     

Using chemistry and microfluidics to understand the spatial dynamics of complex biological networks

Understanding the spatial dynamics of biochemical networks is both fundamentally important for understanding life at the systems level and also has practical implications for medicine, engineering, biology, and chemistry. Studies at the level of individual reactions provide essential information about the function, interactions, and localization of individual molecular species and reactions in a network. However, analyzing the spatial dynamics of complex biochemical networks at this level is difficult. Biochemical networks are nonequilibrium systems containing dozens to hundreds of reactions with nonlinear and time-dependent interactions, and these interactions are influenced by diffusion, flow, and the relative values of state-dependent kinetic parameters. To achieve an overall understanding of the spatial dynamics of a network and the global mechanisms that drive its function, networks must be analyzed as a whole, where all of the components and influential parameters of a network are simultaneously considered. Here, we describe chemical concepts and microfluidic tools developed for network-level investigations of the spatial dynamics of these networks. Modular approaches can be used to simplify these networks by separating them into modules, and simple experimental or computational models can be created by replacing each module with a single reaction. Microfluidics can be used to implement these models as well as to analyze and perturb the complex network itself with spatial control on the micrometer scale. We also describe the application of these network-level approaches to elucidate the mechanisms governing the spatial dynamics of two networkshemostasis (blood clotting) and early patterning of the Drosophila embryo. To investigate the dynamics of the complex network of hemostasis, we simplified the network by using a modular mechanism and created a chemical model based on this mechanism by using microfluidics. Then, we used the mechanism and the model to predict the dynamics of initiation and propagation of blood clotting and tested these predictions with human blood plasma by using microfluidics. We discovered that both initiation and propagation of clotting are regulated by a threshold response to the concentration of activators of clotting, and that clotting is sensitive to the spatial localization of stimuli. To understand the dynamics of patterning of the Drosophila embryo, we used microfluidics to perturb the environment around a developing embryo and observe the effects of this perturbation on the expression of Hunchback, a protein whose localization is essential to proper development. We found that the mechanism that is responsible for Hunchback positioning is asymmetric, time-dependent, and more complex than previously proposed by studies of individual reactions. Overall, these approaches provide strategies for simplifying, modeling, and probing complex networks without sacrificing the functionality of the network. Such network-level strategies may be most useful for understanding systems with nonlinear interactions where spatial dynamics is essential for function. In addition, microfluidics provides an opportunity to investigate the mechanisms responsible for robust functioning of complex networks. By creating nonideal, stressful, and perturbed environments, microfluidic experiments could reveal the function of pathways thought to be nonessential under ideal conditions.     

Sandwiched-Beam Procedure for Precracking Brittle Materials

A technique for precracking brittle materials is presented. This procedure, which is called the sandwiched-beam (SB) technique, allows the production of sharp through-thickness cracks with predetermined length in specimens with a rectangular section. A bar, in which an initial notch is produced by using a conventional saw, is inserted between two supporting beams and the sandwich assembly is loaded in three-point bending. Conditions can be defined that allow the stable propagation of a sharp flaw from the notch as the applied load is increased. Then, the cracked bar can be used to determine the fracture toughness. The SB technique is applied to different brittle materials, including soda-lime-silica glass, alumina, Si₃N₄, a SiC _w -Si₃N₄ composite, graphite, a Ti-Al intermetallic, and Carrara marble.