Origins of life and evolution of the biosphere

, Volume 31, Issue 3, pp 221-229

First online:

Concentration by Evaporation and the Prebiotic Synthesis of Cytosine

  • Kevin E. NelsonAffiliated withDepartment of Biochemistry, University of Illinois at Urbana-Champaign
  • , Michael P. RobertsonAffiliated withDepartment of Molecular Biology, The University of Texas at Austin
  • , Matthew LevyAffiliated withDepartment of Molecular Biology, The University of Texas at Austin
  • , Stanley L. MillerAffiliated withDepartment of Chemistry and Biochemistry, University of California

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The efficient prebiotic synthesis of cytosine from urea andcyanoacetaldehyde (CA) has recently been claimed to be invalidon the basis of possible side reactions of the starting materials and the inapplicability of prebiotic syntheses usingdrying beach conditions. We therefore have investigated the synthesis of cytosine and uracil from urea and cyanoacetaldehydeat 100 °C under dry-down conditions, and in solution at 4 °C and -20 °C. We find that cytosine isproduced from the low temperature experiments more efficientlythan calculated from the Arrhenius extrapolation from highertemperatures, i.e., 60-120 °C. In addition, we findthat CA dimer is as efficient as the monomer in cytosine synthesis. We also studied whether evaporating very dilutesolutions of nonvolatile organic compounds will concentrateaccording to theory. Solutions as dilute as 10-4 M concentrate from pure water approximately according to theory.Similar solutions in 0.5 M NaCl have less than theoreticalconcentrations due to absorption, but concentrations neardryness were very high.

cyanoacetaldehyde cyanoacetaldehyde dimer cytosine dry-down conditions evaporation prebiotic synthesis uracil