CO2 reduction driven by a pH gradient

[BillTre]

TL;DR

A proposed method in which organic molecules could be produced abiotically has been demonstrated in a lab.

In the world of Origin of Life hypothesizing, there now seem to be two main competing approaches. Life originating at alkaline hydrothermal vents and an origin in intermittent terrestrial pools (exposed to periods of drying) getting outflow from volcanically heated water sources.

The alkaline hydrothermal vent hypothesis depends upon particular reactions dependent on electrochemical potential between ocean water and the outflow of the alkaline hydrothermal vents. To my knowledge, until now these reactions have not been demonstrated.

Here is a abstract of a paper I found on https://www.researchgate.net/publication/339699873_CO2_reduction_driven_by_a_pH_gradient:

All life on Earth is built of organic molecules, so the primordial sources of reduced carbon are a major open question in studies of the origin of life. A variant of the alkaline-vent theory suggests that organics could have been produced by the reduction of CO₂ via H₂ oxidation, facilitated by geologically sustained pH gradients. The process would be an abiotic analog—and proposed evolutionary predecessor—of the modern Wood-Ljungdahl acetyl-Co-A pathway of extant archaea and bacteria. The first energetic bottleneck of the pathway involves the endergonic reduction of CO₂ with H₂ to formate, which has proven elusive in low-temperature abiotic settings. Here we show the reduction of CO₂ with H₂ at moderate pressures (1.5 bar), driven by microfluidic pH gradients across inorganic Fe(Ni)S precipitates. Isotopic labelling with ¹³ C confirmed production of formate. Separately, deuterium ( ² H) labelling indicated that electron transfer to CO₂ did 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, or removing either H₂ or the precipitate, yielded no detectable product. Our work demonstrates the feasibility of spatially separated, yet electrically coupled geochemical reactions as drivers of otherwise endergonic processes. Beyond corroborating the ability of early-Earth alkaline hydrothermal systems to couple carbon reduction to hydrogen oxidation through geologically plausible and biologically relevant mechanisms, these results may also be of significance for industrial and environmental applications, where other redox reactions could be facilitated using similarly mild approaches.

Still waiting to get a copy of the full paper, but it sounds exciting to me.

 

[Ygggdrasil]

Still waiting to get a copy of the full paper, but it sounds exciting to me.

You can download the (non-peer-reviewed) pre-print for free on bioRxiv: https://www.biorxiv.org/content/10.1101/2020.03.02.973982v1