Preliminary Free Energy Map of Prebiotic Compounds Formed from CO2, H2 and H2S

Abstract

What kinds of CHOS compounds might be formed in a prebiotic milieu by reducing CO2 in the presence of H2 and H2S? How might the presence of sulfur influence the chemical composition of the mixture? We explore these questions by using first-principles quantum chemistry to calculate the free energies of CHOS compounds in aqueous solution, by first generating a thermodynamic map of one- and two-carbon species. We find that while thiols are thermodynamically favored, thioesters, thioacids, and thiones are less favorable than their non-sulfur counterparts. We then focus on the key role played by mercaptoacetaldehyde in sulfur analogs of the autocatalytic formose reaction, whereby the thiol group introduces asymmetry and potential thermodynamic selectivity of some compounds over others.