2:40 PM - 2:55 PM
[MIS08-04] Reconstruction of Bioorganic Compounds in Early Solar System Bodies: Formation and Alteration of Organic Compounds in Meteorite Parent Bodies
Keywords:Carbonaceous chondrites, Amino acids, Nucleic acid bases, Meteorite parent bodies, gamma rays, Origins of life
A wide variety of organic compounds, including amino acids and nucleobases, have been detected in extraterrestrial bodies such as meteorites [1] and asteroids [2]. Extraterrestrial organic materials may have been delivered to Earth by meteorites and cosmic dust approximately 4 billion years ago (Ga). However, the organic compounds found in present-day meteorites and asteroids have undergone alteration due to prolonged exposure to various energy sources, including radiation from radioactive nuclides in asteroids.
Previous studies have demonstrated that amino acid precursors (AAPs) can be produced in laboratory simulations of the icy mantles of interstellar dust particles in molecular clouds [3]. Such interstellar-derived organic materials, along with small molecules such as H2O, NH3, and HCHO, could have been incorporated into small bodies as ice mixtures during the formation of the solar system. These interstellar ices would have undergone aqueous alteration due to heat and radiation from the decay of short-lived radionuclides, such as 26Al, within meteorite parent bodies. This process likely facilitated the formation of various organic compounds, including amino acids [4] and sugars [5]. However, these organics would have continued to be exposed to middle- and long-lived radionuclides such as 40K, leading to further alterations. The meteoritic organic compounds observed today have thus been shaped by long-term chemical evolution.
To reconstruct the nature of extraterrestrial organics delivered to early Earth 4 Ga, we conducted experiments simulating reactions occurring within meteorite parent bodies.
Experimental Methods: Interstellar amino acid precursor analogs were synthesized via proton irradiation of a mixture of CO, NH3 and H2O, yielding a complex organic mixture referred to as CAW [6]. CAW contained a variety of organic compounds and, upon acid hydrolysis, primarily produced glycine.
To assess the stability of organic compounds in meteorite parent bodies, free amino acids, amino acid precursors (CAW), and nucleobases were subjected to gamma irradiation in aqueous environments (ammonia water or a mixture of HCHO, CH3OH, NH3, and H2O). The resulting products were analyzed using high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC/MS).
Results and Discussion: The results indicated that glycine yields from CAW (following acid hydrolysis) were higher than those of free glycine after gamma irradiation. Among free amino acids, glycine was the most stable, and amino acids lacking an α-hydrogen were more resistant to degradation than their isomeric counterparts containing α-hydrogens. Among nucleobases, purine bases exhibited significantly greater stability than pyrimidine bases.
When formaldehyde and methanol were added to the reaction mixture, various amino acids were newly synthesized by gamma irradiation, alongside the degradation of existing amino acids and their precursors. The yield and diversity of newly formed amino acids increased significantly when CAW was included in the reaction system. This suggests that interstellar organic matter, including AAPs, imported into asteroids could have contributed to the formation of the wide variety of organic compounds found in asteroids and meteorites.
Notably, in present-day carbonaceous chondrites, purine bases are sometimes more abundant than pyrimidine bases, and amino acids lacking an α-hydrogen (e.g., α-aminoisobutyric acid) are among the predominant amino acids [1]. In contrast, prebiotic synthesis experiments have shown that amino acids lacking an α-hydrogen are not typically among the most abundant amino acids, and pyrimidine bases are more readily formed [7]. These differences likely stem from variations in stability under extraterrestrial conditions, including prolonged exposure to radiation within meteorite parent bodies.
Understanding these stability-driven alterations is crucial for reconstructing the nature of organic compounds in carbonaceous chondrites as they were when delivered to early Earth before the emergence of life.
References
[1] D. P. Glavin et al. (2020) Chemical Reviews 120, 4660–4689.
[2] H. Naraoka et al. (2023) Science 379, 6634.
[3] T. Kasamatsu et al. (1997) Bulletin of the Chemical Society of Japan 70, 1021–1026.
[4] Y. Kebukawa et al. (2022) ACS Central Science 8, 1664–1671.
[5] S. Abe et al. (2024) ACS Earth and Space Chemistry 8, 1737–1744.
[6] T. Takano et al. (2004) Applied Physics Letters 84, 1410–1412.
[7] H. Yamanashi et al. (2001) Analytical Sciences 17 Suppl, i1639–1642.
Previous studies have demonstrated that amino acid precursors (AAPs) can be produced in laboratory simulations of the icy mantles of interstellar dust particles in molecular clouds [3]. Such interstellar-derived organic materials, along with small molecules such as H2O, NH3, and HCHO, could have been incorporated into small bodies as ice mixtures during the formation of the solar system. These interstellar ices would have undergone aqueous alteration due to heat and radiation from the decay of short-lived radionuclides, such as 26Al, within meteorite parent bodies. This process likely facilitated the formation of various organic compounds, including amino acids [4] and sugars [5]. However, these organics would have continued to be exposed to middle- and long-lived radionuclides such as 40K, leading to further alterations. The meteoritic organic compounds observed today have thus been shaped by long-term chemical evolution.
To reconstruct the nature of extraterrestrial organics delivered to early Earth 4 Ga, we conducted experiments simulating reactions occurring within meteorite parent bodies.
Experimental Methods: Interstellar amino acid precursor analogs were synthesized via proton irradiation of a mixture of CO, NH3 and H2O, yielding a complex organic mixture referred to as CAW [6]. CAW contained a variety of organic compounds and, upon acid hydrolysis, primarily produced glycine.
To assess the stability of organic compounds in meteorite parent bodies, free amino acids, amino acid precursors (CAW), and nucleobases were subjected to gamma irradiation in aqueous environments (ammonia water or a mixture of HCHO, CH3OH, NH3, and H2O). The resulting products were analyzed using high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC/MS).
Results and Discussion: The results indicated that glycine yields from CAW (following acid hydrolysis) were higher than those of free glycine after gamma irradiation. Among free amino acids, glycine was the most stable, and amino acids lacking an α-hydrogen were more resistant to degradation than their isomeric counterparts containing α-hydrogens. Among nucleobases, purine bases exhibited significantly greater stability than pyrimidine bases.
When formaldehyde and methanol were added to the reaction mixture, various amino acids were newly synthesized by gamma irradiation, alongside the degradation of existing amino acids and their precursors. The yield and diversity of newly formed amino acids increased significantly when CAW was included in the reaction system. This suggests that interstellar organic matter, including AAPs, imported into asteroids could have contributed to the formation of the wide variety of organic compounds found in asteroids and meteorites.
Notably, in present-day carbonaceous chondrites, purine bases are sometimes more abundant than pyrimidine bases, and amino acids lacking an α-hydrogen (e.g., α-aminoisobutyric acid) are among the predominant amino acids [1]. In contrast, prebiotic synthesis experiments have shown that amino acids lacking an α-hydrogen are not typically among the most abundant amino acids, and pyrimidine bases are more readily formed [7]. These differences likely stem from variations in stability under extraterrestrial conditions, including prolonged exposure to radiation within meteorite parent bodies.
Understanding these stability-driven alterations is crucial for reconstructing the nature of organic compounds in carbonaceous chondrites as they were when delivered to early Earth before the emergence of life.
References
[1] D. P. Glavin et al. (2020) Chemical Reviews 120, 4660–4689.
[2] H. Naraoka et al. (2023) Science 379, 6634.
[3] T. Kasamatsu et al. (1997) Bulletin of the Chemical Society of Japan 70, 1021–1026.
[4] Y. Kebukawa et al. (2022) ACS Central Science 8, 1664–1671.
[5] S. Abe et al. (2024) ACS Earth and Space Chemistry 8, 1737–1744.
[6] T. Takano et al. (2004) Applied Physics Letters 84, 1410–1412.
[7] H. Yamanashi et al. (2001) Analytical Sciences 17 Suppl, i1639–1642.