Preparation, analysis and toxicity characterisation of the redox metabolites of the azo food dye tartrazine.

Tartrazine (E102, FD&C Yellow 5) is a vibrant yellow azo dye added to many processed foods. The safety of this ubiquitous chemical has not been fully elucidated, and it has been linked to allergic reactions and ADHD in some individuals. In our study, bacterial species isolated from human stool decolourised tartrazine and, upon exposure to air, a purple compound formed. Tartrazine is known to undergo reduction in the gut to sulfanilic acid and 4-amino-3-carboxy-5-hydroxy-1-(4-sulfophenyl)pyrazole (SCAP). These metabolites and their derivatives are relevant to the toxicology of tartrazine. The toxicity of sulfanilic acid has been studied before, but the oxidative instability of SCAP has previously prevented full characterisation. We have verified the chemical identity of SCAP and confirmed that the purple-coloured oxidation derivative is 4-(3-carboxy-5-hydroxy-1-(4-sulfophenyl)-1H-pyrazol-4-yl)imino-5-oxo-1-(4-sulfophenyl)-4,5-dihydro-1H-pyrazole-3-carboxylic acid (purpurazoic acid, PPA), as proposed by Westöö in 1965. A yellow derivative of SCAP is proposed to be the hydrolysed oxidation product, 4,5-dioxo-1-(4-sulfophenyl)-4,5-dihydro-1H-pyrazole-3-carboxylic acid. SCAP and PPA are moderately toxic to human cells (IC50 89 and 78 µM against HEK-293, respectively), but had no apparent effect on Escherichia coli and Bacillus subtilis bacteria. These results prompt further analyses of the toxicology of tartrazine and its derivatives.

Room Temperature Ion Beam Synthesis of Ultra-Fine Molybdenum Carbide Nanoparticles: Toward a Scalable Fabrication Route for Earth-Abundant Electrodes.

Molybdenum carbides are promising low-cost electrocatalysts for electrolyzers, fuel cells, and batteries. However, synthesis of ultrafine, phase-pure carbide nanoparticles (diameter < 5 nm) with large surface areas remains challenging due to uncontrollable agglomeration that occurs during traditional high temperature syntheses. This work presents a scalable, physical approach to synthesize molybdenum carbide nanoparticles at room temperature by ion implantation. By tuning the implantation conditions, various molybdenum carbide phases, stoichiometries, and nanoparticle sizes can be accessed. For instance, molybdenum ion implantation into glassy carbon at 30 keV energy and to a fluence of 9 × 1016 at cm-2 yields a surface η-Mo3 C2 with a particle diameter of (10 ± 1) nm. Molybdenum implantation into glassy carbon at 60 keV to a fluence of 6 × 1016 at cm-2 yields a buried layer of ultrafine γ'-MoC/η-MoC nanoparticles. Carbon ion implantation at 20 keV into a molybdenum thin film produces a 40 nm thick layer primarily composed of ß-Mo2 C. The formation of nanoparticles in each molybdenum carbide phase is explained based on the Mo-C phase diagram and Monte-Carlo simulations of ion-solid interactions invoking the thermal spike model. The approaches presented are widely applicable for synthesis of other transition metal carbide nanoparticles as well.