Analysis for peptide compounds in carbonaceous chondrites and experimental simulation of abiotic peptide formation

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The Yamato-791198 and Murchison carbonaceous chondrites were analyzed for dipeptides and diketopiperazines as well as amino acids and hydantoins by gas chromatography combined with mass spectrometry. Glycylglycine (gly-gly) and cyclo (gly-gly) were detected at the concentrations of ll and 18 pmol g^<-1>, respectively, in Yamato-791198 and 4 and 23 pmol g^<-1>, respectively, in Murchison. No other dipeptide and diketopiperazine were detected. Five hydantoins were detected at 8 to 65 pmol g^<-1> in Yamato-791198 and seven in Murchison at 6 to 104 pmol g^<-1>. Total concentration of the glycine (gly) dimers is approximately four orders of magnitude less than the concentration of free gly in Yamato-791198, and three orders of magnitude less than that in Murchison. The absence of L- and LL-stereoisomers of dipeptides consisting of protein amino acids indicates that gly-gly and cyclo(gly-gly) detected are proper to the chondrites but not from terrestrial contaminants. A possibility was discussed that the gly dimers might have been formed by condensation of gly monomers but not formed through N-carboxyanhydrides of gly.We found a novel thermal polymerization of alanine, which would be likely applied to other amino acids, by taking advantage of a highly polar feature of molten urea as well as the dehydrating ability of urea. The polymer obtained by this method was revealed to have a special structure, bearing a hydantoin ring at the JV-terminal. From the viewpoint of chemical evolution, this study offered a new candidate for a dehydrating agent or a polycondensation medium that can be present on the primitive Earth.