Interaction between ATP, metal ions, glycine, and several minerals

The adsorption of ATP and ADP on montmorillonite, kaolinite, and A1(OH)3 was studied as a function of pH and, for montmorillonite and kaolinite, as a function of the ionic composition of the system. The three minerals exhibit different adsorption characteristics. Mg2+- and Zn2+-montmorillonite adsorb ATP and ADP more than Na+-montmorillonite, presumably because of complex formation. In kaolinite, the effect of these divalent cations is small. Pure ATP decomposes upon heating, and the rate of the decomposition is accelerated by the presence of glycine. Drying and heating glycine to 70 degrees C under vacuum in the presence of ATP results in abiotic peptide formation with yields up to 0.25%. This peptide formation also occurs when kaolinite or montmorillonite is added to the system. The presence of kaolinite, Mg2+- or Zn2+-kaolinite, or Mg2+-montmorillonite results in a reduction in the rate of the ATP decomposition in the abiotic peptide synthesizing system. These results suggest that one role for clays and metal ions in chemical evolution may have been the stabilization of nucleotides during prebiotic peptide synthesis.