Prebiotic synthesis of the major classes of iron-sulfur clusters

Conditions that led to the synthesis of iron-sulfur clusters coordinated to tripeptides with a single thiolate ligand were investigated by UV-vis, NMR, EPR, and Mössbauer spectroscopies and by electrochemistry. Increasing concentrations of hydrosulfide correlated with the formation of higher nuclearity iron-sulfur clusters from mononuclear to [2Fe-2S] to [4Fe-4S] and finally to a putative, nitrogenase-like [6Fe-9S] complex. Increased nuclearity was also associated with decreased dynamics and increased stability. The synthesis of higher nuclearity iron-sulfur clusters is compatible with shallow, alkaline bodies of water on the surface of the early Earth, although other niche environments are possible. Because of the plasticity of such complexes, the type of iron-sulfur cluster formed on the prebiotic Earth would have been greatly influenced by the chemical environment and the thiolate containing scaffold. The discovery that all the major classes of iron-sulfur clusters easily form under prebiotically reasonable conditions broadens the chemistry accessible to protometabolic systems.