Activated alumina as an energy source for peptide bond formation: consequences for mineral-mediated prebiotic processes.

The catalytic properties of various forms of alumina were tested for alanine dimerization reaction. The catalytic efficiency of alumina depends on the structure, as well as on acid/base properties of the catalyst. The highest yields of Ala2 were achieved on activated alumina with surface of neutral pH (about 3% conversion after 2 weeks). Thermal analysis of Ala + alumina reaction systems shows that the thermal behavior of amino acid changes substantially in contact with the activated surface of the alumina catalyst. The reaction of Ala is detected as being strongly endothermic by differential thermal analysis of pure amino acid (above 250 degrees C). The alanine endothermic reaction is shifted substantially to lower values (below 200 degrees C) and hardly detectable if activated alumina is present. The reaction mechanism of amino acid activation on alumina surface and its significance for mineral-catalyzed prebiotic peptide bond formation are discussed.