Chapter 16 - Racemization of Amino Acids in Hydrothermal Environments: A Contribution of Temperature Gradient

Abstract

Despite that hydrothermal environments in the primitive ocean might have played a significant role for prebiotic chemical evolution, there could have been some deleterious side effects. One such effect is the degradation of optical purity of amino acid molecules available near hydrothermal vents through racemization driven by heat energy from the vents, let alone their dehydration, deamination, and decarboxylation. This chapter presents an investigation on how the degradation of optical purity of amino acids would proceed in an experimental setup simulating a hydrothermal environment focusing on the role of salt ions available. In a simulated hydrothermal environment allowing fluid circulation between hot and cold regions repeatedly, L- and D-alanine molecules were racemized differently depending on the quantities of salt ions available. When there were no added salt ions, the rate of racemization starting with pure L-alanine was slightly greater than that starting with pure D-alanine. On the other hand, when there were added salt ions present, the rate of racemization starting with L-alanine was slightly less than that starting with D-alanine. Hydrothermal environments in the primitive ocean could have maintained the capacity of selectively retaining the enantiomeric excess in favor of either L-amino acids or D-amino acids depending on the quantities of salt ions available there.