Building on recent findings that have uncovered awaruite’s ability to convert CO2 under hot, pressurized, alkaline aqueous conditions, the team explored the hydrogenation reactivity of synthetic Ni3Fe nanoparticles under milder conditions — 25 °C and pH 6 — and observed the formation of millimolar concentrations of formate, acetate and pyruvate. Unlike previous investigations, activity is detected for conditions that are closer to those of biological fixation.
Pyruvate is an important intermediate in a variety of metabolic pathways; therefore, the authors were interested in further potential transformations of this crucial α-keto-carboxylate in the presence of Ni3Fe. Interestingly, experiments with a 13C-labelled reactant in combination with 13C-based NMR analysis and electron spray ionization mass spectroscopy revealed that pyruvate can be converted into citramalate (pictured; asterisks in figure indicate 13C isotopic labelling). A series of control experiments further allowed to shed light on the path leading to the formation of this important C5 scaffold, and suggests that citramalate is generated via homoaldol condensation of pyruvate into parapyruvate, while the condensation of acetate and pyruvate does not occur. Thus, parapyruvate decarboxylates yielding citramalate. Both steps require the presence of the Ni3Fe catalyst. All in all, the speciation of the products formed during the reaction allows to conclude that Ni3Fe replicates the function of enzymes associated with the acetyl coenzyme A pathway as well as of citramalate synthase.
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