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

采用气相色谱-质谱联用技术对Yamato-791198和Murchison碳质球粒陨石进行了二肽、二酮哌嗪、氨基酸和氢酮酮的分析。在Yamato-791198和Murchison中分别检测到1和18 pmol g^<-1>和4和23 pmol g^<-1>的甘氨酸（gly-gly）和环氨酸（gly-gly）。未检出其他二肽和二酮哌嗪。在Yamato-791198和Murchison中分别检测到8 ~ 65 pmol g^<-1>和7 pmol g^<-1>。在yamata -791198中，甘氨酸（gly）二聚体的总浓度比游离gly的浓度低约4个数量级，比Murchison低3个数量级。由蛋白质氨基酸组成的二肽的L-和ll -立体异构体的缺失表明，检测到的gly-gly和环（gly-gly）是球粒陨石特有的，而不是来自陆地污染物。讨论了gly二聚体可能是由gly单体缩合形成的，而不是由gly的n -羧基氢化物形成的。我们发现了一种新的丙氨酸热聚合方法，这种方法很可能应用于其他氨基酸，利用了熔融尿素的高度极性特征以及尿素的脱水能力。通过这种方法得到的聚合物具有一种特殊的结构，在jv末端有一个氢酰脲环。从化学进化的角度来看，该研究为原始地球上可能存在的脱水剂或缩聚介质提供了新的候选物。

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.