The Role of Submarine Hydrothermal Systems in the Synthesis of Amino Acids

Abstract

There is little consensus regarding the plausibility of organic synthesis in submarine hydrothermal systems (SHSs) and its possible relevance to the origin of life. The primary reason for the persistence of this debate is that most experimental high temperature and high-pressure organic synthesis studies have neglected important geochemical constraints with respect to source material composition. We report here the results of experiments exploring the potential for amino acid synthesis at high temperature from synthetic seawater solutions of varying composition. The synthesis of amino acids was examined as a function of temperature, heating time, starting material composition and concentration. Using very favorable reactant conditions (high concentrations of reactive, reduced species), small amounts of a limited set of amino acids are generated at moderate temperature conditions ( approximately 125-175 degrees C) over short heating times of a few days, but even these products are significantly decomposed after exposure times of approximately 1 week. The high concentration dependence observed for these synthetic reactions are demonstrated by the fact that a 10-fold drop in concentration results in orders of magnitude lower yields of amino acids. There may be other synthetic mechanisms not studied herein that merit investigation, but the results are likely to be similar. We conclude that although amino acids can be generated from simple likely environmentally available precursors under SHS conditions, the equilibrium at high temperatures characteristic of SHSs favors net amino acid degradation rather than synthesis, and that synthesis at lower temperatures may be more favorable.

Concentrations and distributions of dissolved amino acids in fluids from Mid-Atlantic Ridge hydrothermal vents

“…Apart from the biotic origin of DFAA, several experimental studies have demonstrated that the conditions at hydrothermal vent sites may be favourable for the abiotic synthesis of amino acids (e.g., Hennet et al, 1992;Marshall, 1994;Simoneit et al, 2007). However, recent experiments by Aubrey et al (2009) suggest that lower temperatures are more favourable than high temperatures for abiotic synthesis. Theoretical calculations suggest that synthesis of the primary AAs is energetically favourable under hot (100°C) reducing conditions (Amend and Shock, 1998).…”

Foldamer hypothesis for the growth and sequence differentiation of prebiotic polymers

“…1A). Prebiotic monomer concentrations are thought to have been in the range of micromolar to millimolar (36,(42)(43)(44)(45). Given micromolar concentrations of monomers and given l = 2, the concentration of 40-mers would be ≈ 10 −19 mol/L.…”

The energetics of organic synthesis inside and outside the cell

“…Purines can be synthesized by heating aqueous solutions of cyanides [97,100,101], and pyrimidines by including compounds such as malic acid or cyanoacetylene in addition to cyanides [102,103] or by heating solutions of formamide [104,105]. It should be noted that although these studies demonstrate that biomolecules can be synthesized abiotically in hydrothermal solutions, the relevance of the experimental conditions to those of natural hydrothermal systems has been questioned (see, for instance, [106][107][108][109]). Most of these experiments are performed with highly reactive reactants such as HCN and formamide that are present in concentrations many orders of magnitude higher than could reasonably be expected to occur in natural environments.…”