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[MIS03-P02] Stability of nucleobases in small solar system bodies.
Keywords:nucleobases, small solar system bodies, γ-rays
Introduction
Abiotic synthesis of bioorganic compounds in the primitive Earth environments is unknown, since we have limited knowledge on the environments. On the other hand, the existence of organic compounds in interstellar space suggested that interstellar dust in molecular clouds could be the site where organic compounds that led to the birth of life were formed. Interstellar dust is covered with an ice mantle, in which water, carbon monoxide, and other molecules are frozen [1]. It was also shown that amino acid precursors and nucleobases are formed by irradiation of a mixture of carbon monoxide, ammonia, methanol and water with ultraviolet light or high energy particles simulating interstellar dust environments [2,3]. The presence of nucleobases in meteorites [4] suggested that the organic compounds produced in molecular clouds was once incorporated into the small bodies in early solar system, which were then delivered to Earth by meteorites.
Small bodies were formed by the gravitational collapse of molecular clouds, followed by the formation of the protoplanetary disk and the collisional growth of dust particles. Small bodies contained ice, minerals, and organic compounds derived from molecular clouds.
It was suggested that the decay heat of radionuclides such as 26Al present in small bodies and collisional heating among small bodies melted ice to form liquid water, where organic reactions proceeded. γ-rays have attracted attention as an energy source there [5]. In this study, γ-ray irradiation experiments were conducted to investigate the stability of nucleobases in small solar system bodies.
Method
Adenine, thymine, guanine, cytosine, or uracil were dissolved in a solution of 0.5% ammonia solution to simulate the interior of a small body of early solar system. They were sealed in glass tubes, and were irradiated with γ-ray from 60Co source (2.75 kGy/h, 48 h or 163 h), and were analyzed by reversed-phase HPLC. As a control experiment, similar samples left in a freezer (-25℃) without γ-ray irradiation were also analyzed.
Results and Discussion
Recovery after 48 hours’ irradiation was as follows: adenine: 64%; guanine: 22%; cytosine: 5%; uracil: 5%, thymine: 0.2 %. They were further decreased after 163 hours’ irradiation as follows: adenine: 10%; guanine: 5%; cytosine: 1% ; uracil: 0.2%; thymine: 0.2%.
These results suggest that nucleobases dissolved in ammonia water are easily decomposed by γ-rays.
In this study, nucleobases were dissolved in ammonia solution and then irradiated with γ-rays. In the actual environment of small bodies, the liquid disappeared before the decay of 26Al was mostly ceased. It was suggested that the stability of nucleobases in solution and that in solid were different. We are planning to examine the radiation stability of nucleobases in solid. It would be of interest to analyze the products after irradiation of nucleobases. We also plan to examine the formation and stability of nucleobases in a mixture of formaldehyde, ammonia, and water, which simulates the environment of interior of small bodies in the early solar system.
References
[1] J. M. Greenberg et al., Adv. Space Res., 1997, 19, 981.
[2] T. Kasamatsu et al., Bull. Chem. Soc. Jpn. 1997, 70, 1021.
[3] Y. Oba. et al., Nat Commun, 2019, 10.
[4] Y. Oba. et al., Nat Commun, 2022, 13.
[5] Y. Kebukawa et al., ACS Cent. Sci. 2022, 8, 1864.
Abiotic synthesis of bioorganic compounds in the primitive Earth environments is unknown, since we have limited knowledge on the environments. On the other hand, the existence of organic compounds in interstellar space suggested that interstellar dust in molecular clouds could be the site where organic compounds that led to the birth of life were formed. Interstellar dust is covered with an ice mantle, in which water, carbon monoxide, and other molecules are frozen [1]. It was also shown that amino acid precursors and nucleobases are formed by irradiation of a mixture of carbon monoxide, ammonia, methanol and water with ultraviolet light or high energy particles simulating interstellar dust environments [2,3]. The presence of nucleobases in meteorites [4] suggested that the organic compounds produced in molecular clouds was once incorporated into the small bodies in early solar system, which were then delivered to Earth by meteorites.
Small bodies were formed by the gravitational collapse of molecular clouds, followed by the formation of the protoplanetary disk and the collisional growth of dust particles. Small bodies contained ice, minerals, and organic compounds derived from molecular clouds.
It was suggested that the decay heat of radionuclides such as 26Al present in small bodies and collisional heating among small bodies melted ice to form liquid water, where organic reactions proceeded. γ-rays have attracted attention as an energy source there [5]. In this study, γ-ray irradiation experiments were conducted to investigate the stability of nucleobases in small solar system bodies.
Method
Adenine, thymine, guanine, cytosine, or uracil were dissolved in a solution of 0.5% ammonia solution to simulate the interior of a small body of early solar system. They were sealed in glass tubes, and were irradiated with γ-ray from 60Co source (2.75 kGy/h, 48 h or 163 h), and were analyzed by reversed-phase HPLC. As a control experiment, similar samples left in a freezer (-25℃) without γ-ray irradiation were also analyzed.
Results and Discussion
Recovery after 48 hours’ irradiation was as follows: adenine: 64%; guanine: 22%; cytosine: 5%; uracil: 5%, thymine: 0.2 %. They were further decreased after 163 hours’ irradiation as follows: adenine: 10%; guanine: 5%; cytosine: 1% ; uracil: 0.2%; thymine: 0.2%.
These results suggest that nucleobases dissolved in ammonia water are easily decomposed by γ-rays.
In this study, nucleobases were dissolved in ammonia solution and then irradiated with γ-rays. In the actual environment of small bodies, the liquid disappeared before the decay of 26Al was mostly ceased. It was suggested that the stability of nucleobases in solution and that in solid were different. We are planning to examine the radiation stability of nucleobases in solid. It would be of interest to analyze the products after irradiation of nucleobases. We also plan to examine the formation and stability of nucleobases in a mixture of formaldehyde, ammonia, and water, which simulates the environment of interior of small bodies in the early solar system.
References
[1] J. M. Greenberg et al., Adv. Space Res., 1997, 19, 981.
[2] T. Kasamatsu et al., Bull. Chem. Soc. Jpn. 1997, 70, 1021.
[3] Y. Oba. et al., Nat Commun, 2019, 10.
[4] Y. Oba. et al., Nat Commun, 2022, 13.
[5] Y. Kebukawa et al., ACS Cent. Sci. 2022, 8, 1864.