THE IRON-SULFUR WORLD AND THE ORIGINS OF LIFE - ABIOTIC THIOL SYNTHESIS FROM METALLIC IRON, H2S AND CO2 - A COMPARISON OF THE THIOL GENERATING FES HCL(H2S)/CO2-SYSTEM AND ITS FE-0/H2S/CO2-COUNTERPART/

The FeS/HCl(H2S)/CO2-system, described in a foregoing paper (Heinen an d Lauwers, 1996), was shown to operate also under more 'open' conditio ns, with a fixed amount of FeS, but varied supply of H2S. Furthermore it could be demonstrated that HCl can be replaced by several other aci ds, so that the system can he defined in a more generalized way as the 'FeS/acid/CO2-system'. The basic reaction (3 H-2 + H2S + CO2 --> CH3S H + 2H2O) has been studied in some more detail. Departing from this re action as the foundation of thiol synthesis, we had already replaced H z by the H-2 generating FeS + H2S, and H2S by FeS + HCl In the next st ep, metallic iron in water was used for the generation of Hz. The reac tion was found to be linearly correlated to the amount of Fe-0, and de pending on time and temperature. Addition of H2S to this system, with the optimal molar ratio of 1 Fe-0 : 5H(2)S, resulted in the synthesis of thiols with significantly higher yields than obtained with the FeS/ acid/CO2-system. In a following step, H2S was replaced by H2S generati ng reactions, by adding sulfides to Fe-0 in an acid environment. Intro ducing FeS as the H2S generator actually signified a combination of th e systems Fe-0/(H)2S and FeS/acid/CO2, and it could be shown that this expands the chances for thiol synthesis under varying conditions. Usi ng D2O replacing the water phase and analysing the resulting thiols by GC/MS revealed that hydrogen from water acts as the reductant. The re cognition that thiol synthesis is not confined to a singular scenario and the resulting implications are discussed in some detail.