A Prebiotic Surface Catalysed Photochemically Activated Synthesis of L-Methionine and L-Homocysteine

Abstract: Alkynes such as propyne nitrile and propynimine form weak charge-transfer, ?^2 -alkynyl complexes, with surface catalysts such as Mg.porphin in which the alkynyl group is positively charged and the porphin has a negative charge. The enthalpy changes are -0.024 and -0.040 h, respectively. Addition of methyl thiol to the complexes allows the formation of Mg.1,N-3-methylsulfanyl propenyl nitril-1yl.porphin and Mg.1,N-3-methylsulfanyl propenylimin-1yl.porphin. When the imine is bound to a Mg.porphin complex in which carbon monoxide has been oriented by exciting radiation an aziridine-2one complex is formed hydrolysable and reducible to the amino acid L-methionine. With hydrogen sulphide addition an analogous set of reactions yields L-homocysteine. The reactions have been shown to be feasible from the overall enthalpy changes in the ZKE approximation at the HF and MP2 /6-31G* level.