Model Studies on the Formation and Reactions of Solid Glycine Complexes at the Coasts of a Primordial Salty Ocean

Laboratory experiments pertinent to the prebiotic hot-volcanic-coast scenario are described. When artificial primordial seawater which contained NaCl, KCl, MgCl2, CaCl2, and a small amount of glycine (Hgly) was evaporated to dryness, it was found that in the remaining solid salt mixture the amino acid was exclusively present as CaCl2(Hgly)center dot H2O(1). The coordination compound 1 was also obtained by controlled efflorescence of the corresponding trihydrate CaCl2(Hgly)center dot 3H(2)O (2). A characteristic structural feature of crystalline 2 is [CaCl(Hgly)(H2O)(3)](+) units that are interconnected to form one-dimensional coordination polymers. On thermolysis at 350 degrees C in a nitrogen atmosphere, compound 1 yielded, inter alia, 15 different methylated and ethylated pyrroles. In contrast, the artificial sea salt-glycine mixtures, despite containg 1, produced no detectable amounts of organics under the same conditions. Hydrochloric acid from thermal hydrolysis of the sea salt component MgCl2 center dot 6H(2)O may be responsible for this different behavior. 1, 2, and the related compounds CaCl2(Hgly)(2)center dot 4H(2)O (3), and MgCl2(Hgly)(2)center dot 2H(2)O (4) have been prepared in analytically pure form on a multi-gram scale. Methods used in this study were single-crystal and powder X-ray diffraction, infrared and Raman spectroscopy, thermogravimetric and differential thermal analysis, and gas chromatography-mass spectrometry.