[P-PS24_1PM2] 宇宙における物質の形成と進化

[PPS24-12] Murchison隕石中の極性有機化合物の多様性

*奈良岡 浩¹、山下 陽平¹、三田 肇² (1.九州大学理学研究院地球惑星科学部門、2.福岡工業大学工学部)

キーワード：polar organic compounds, carbonaceous meteorite, Murchison, high-resolution mass spectrometry

Various organic compounds have been found in carbonaceous chondrites, in which water-soluble bio-related organic compounds such as amino acids and carboxylic acids are fully studied mainly because of their great interests to origins of life in the universe and standards available for the analyses. The concentrations of these acids increase significantly after acid hydrolysis of the water extract. Even though a few studies attempted to identify the chemical structures of their precursors (Cooper and Cronin, 1995), the original structures remain largely unclear. The aqueous activity on the meteorite parent body also could proceed in a chemical oxidation (i.e. incorporation of oxygen by hydrous reaction), resulting in the alteration of original organic matter (Oba and Naraoka, 2009). The large abundance of carboxylic acids in the water extract may be attributable to such oxidation processes. In contrast to the water extract, less polar methanol extract of chondrites has not been characterized well in spite of relatively high content of organic matter with the D- and 15N enrichment. Recently, ultrahigh-resolution mass spectral analysis on various solvent extracts of the Murchison meteorite (CM2) was performed by electrosplay ionization (ESI) using Fourier transform-ion cyclotron resonance/mass spectrometry (FT-ICR/MS) to reveal significant chemical diversity to tens of thousands of different mass peaks having CHO, CHOS, CHNO and CHNOS elemental compositions (Schmitt-Kopplin et al., 2010). With the assumption for molecular formulae calculation and no chromatographic separation, however, the detailed chemical structures of the compounds cannot be determined. In particular, the organic compounds with their elemental compositions of CH and CHN were not discussed. In this study, we performed high-performance liquid chromatography/high resolution mass spectrometry (HPLC/HRMS) analysis of organic compounds in polar solvent extracts of the Murchison meteorite. Homologous series of alkylpyridines have been identified in the polar solvent extracts of the Murchison meteorite by liquid chromatography/high- resolution mass spectrometry. The wide range of saturated- and unsaturated-alkylated (C1 to C21) pyridines is more diverse relative to that previously found, which could be produced by aldehydes and NH3 through aldol condesation and Chichibabin-type synthesis on the meteorite parent body. This finding implies a high aldehyde activity under an alkaline condition with ammonia for the chemical evolution of organic matters in carbonaceous meteorites. In addition to the compound distribution of alkylpyridines, the occurrence of other compounds in the water extract will be also discussed with respect to their formation mechanisms in carbonaceous meteorites.