Aug 25 – 27, 2021
Europe/Berlin timezone

Using a pH gradient to drive CO2 reduction

Aug 26, 2021, 4:00 PM


Due to unstable situation with Covid-19 the event will be held online!


Victor Sojo (New York Natural History Museum)


Carbon-based “organic” molecules are the foundational blocks of all living beings on Earth. Elucidating the primordial sources of reduced carbon at the emergence of life is therefore key to understanding the processes that gave rise to biochemistry from geochemistry. There were multiple plausible sources of reduced carbon on the early Earth, and a rich array of corresponding theories for the emergence of the first (bio)organics have been built on this knowledge. A variant of the alkaline-hydrothermal-vent theory suggests that organics could have been produced by indirect reduction of CO2 via H2 oxidation, facilitated by geologically sustained pH gradients. The process would be an abiotic analogue—and proposed evolutionary predecessor—of the Wood-Ljungdahl acetyl-Co-A pathway present in modern archaea and bacteria. I will discuss our results recreating in the lab an abiotic analogue of the first energetic bottleneck of the pathway, which involves the endergonic reduction of CO2 with H2 to formate. Using CO2 with H2 at room temperature under moderate pressures (1.5 bar), and in the presence of microfluidic pH gradients across inorganic Fe(Ni)S precipitates, we have produced small amounts of formate that open a way to explore further reactions in a possible abiotic analogue of the Wood-Ljungdahl pathway. Isotopic labelling with 13C confirms formate production, while deuterium (2H) labelling indicates that electron transfer to CO2 does not occur via direct hydrogenation with H2. Instead, freshly deposited Fe(Ni)S precipitates appear to facilitate electron transfer in an electrochemical-cell mechanism with two distinct half-reactions. Decreasing the pH gradient significantly leads to no detectable product, as does removing the H2 supply, or eliminating the precipitate. We believe our work demonstrates the feasibility of spatially separated, yet electrically coupled geochemical reactions as drivers of otherwise endergonic processes, as well as the potential for microscopic pH gradients to be one such driver of the early transition from geochemistry to biochemistry. The results may also be of significance for industrial and environmental applications, where other redox reactions could be driven using similarly mild approaches.

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