Prebiotic photoredox synthesis from carbon dioxide and sulfite

Carbon dioxide (CO 2 ) is the major carbonaceous component of many planetary atmospheres, which includes the Earth throughout its history. Carbon fixation chemistry—which reduces CO 2 to organics, utilizing hydrogen as the stoichiometric reductant—usually requires high pressures and temperatures, and the yields of products of potential use to nascent biology are low. Here we demonstrate an efficient ultraviolet photoredox chemistry between CO 2 and sulfite that generates organics and sulfate. The chemistry is initiated by electron photodetachment from sulfite to give sulfite radicals and hydrated electrons, which reduce CO 2 to its radical anion. A network of reactions that generates citrate, malate, succinate and tartrate by irradiation of glycolate in the presence of sulfite was also revealed. The simplicity of this carboxysulfitic chemistry and the widespread occurrence and abundance of its feedstocks suggest that it could have readily taken place on the surfaces of rocky planets. The availability of the carboxylate products on early Earth could have driven the development of central carbon metabolism before the advent of biological CO 2 fixation. Carbon dioxide is a substantial component of many planetary atmospheres, but reduction of carbon dioxide requires conditions and substrates that are rare on planetary surfaces. Now, the reduction of carbon dioxide to organic species with biological relevance has been photochemically coupled to the oxidation of sulfite, suggesting that prebiotic carbon fixation could take place on the surfaces of rocky planets.