An assessment of stoichiometric autocatalysis across element groups

Autocatalytic chemical reaction systems have been proposed to play critical roles during the transition from an abiotic world to one that contains living systems. These proposals are at odds with a limited number of known examples of abiotic (and in particular, inorganic) autocatalytic systems that might reasonably function in a prebiotic environment. In this study, we broadly assess the occurrence of stoichiometries that can support autocatalytic chemical systems through comproportionation reactions. If the product of a comproportionation process can be coupled with an auxiliary oxidation or reduction pathway that furnishes a reactant, then a candidate comproportionation-based autocatalytic cycle (CompAC) structure can exist. Using this strategy, we surveyed the literature and chemical databases for reactions that can be organized into CompACs that consume some chemical species as food to synthesize more autocatalysts. 226 CompACs and 44 Broad-sense CompACs were documented, and it was found that each of the 18 groups, lanthanoid series, and actinoid series in the periodic table has at least two CompACs. Our findings demonstrate that stoichiometric relationships underpinning abiotic autocatalysis could broadly exist across a range of geochemical and cosmochemical conditions, some of which are substantially different from the modern Earth. At the same time, the observation of some autocatalytic systems requires effective spatial or temporal separation between the food chemicals while allowing comproportionation and auxiliary reactions to proceed, which may explain why naturally occurring autocatalytic systems are not frequently observed. The collated CompACs and the conditions in which they might plausibly support complex, “life-like” chemical dynamics, can directly aid an expansive assessment of life’s origins and provide a compendium of alternative hypotheses concerning false-positive biosignatures.