10:45 〜 11:00
[PCG22-07] Detection of nucleobases and other N-heterocycles in the sample returned from asteroid (101955) Bennu
★Invited Papers
キーワード：小惑星、核酸塩基
Samples collected at the B-type asteroid (101955) Bennu by NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft [1] were delivered to Earth on 24 September 2023. Because the samples returned by OSIRIS-REx are among the most primitive and least contaminated extraterrestrial samples currently available for laboratory analyses [2], they should possess decisive information on the chemical processes that occurred before and during the early stages of solar system formation. Various organic molecules have been identified in other extraterrestrial materials such as meteorites and samples of asteroid (162173) Ryugu, which has stimulated discussion of their role in prebiotic chemistry on early Earth. We hypothesized [3] that Bennu contains prebiotic organic molecules, such as nucleobases, that could have contributed to the emergence of life on Earth. To test this, we searched for nitrogen (N)–heterocyclic molecules, including nucleobases, as a part of coordinated analyses of samples from Bennu [3].
We used two parallel techniques on three separate aggregate samples of Bennu. One was pyrolysis–gas chromatography–triple-quadrupole mass spectrometry with wet chemistry pyrolysis after reacting with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide and N,N-dimethylformamide to derivatize and semi-quantitatively detect soluble organic matter [4,5]. The MS scanned for multiple reaction monitoring (MRM) transitions targeting N-heterocycles. Compound identification was conducted via comparison with retention time and three MRM transitions of targeted standards. Analysis was conducted on a 1 mg subsample of fine particles (parent OREX-500002-0) recovered from spillover outside the OSIRIS-REx sample collector and a 1 mg subsample of fine- to intermediate-sized particles (parent OREX-800031-0) from inside the collector. The other technique was high-performance liquid chromatography with high-resolution Orbitrap mass spectrometry (HPLC-HRMS) [6,7], where the HCl extract from a 17.75 mg of fine- to intermediate-sized particles of the Bennu sample OREX-800044-101 was analyzed.
We identified all five canonical nucleobases—cytosine (C), uracil (U), thymine (T), guanine (G), and adenine (A), as well as some of their structural isomers—in the Bennu samples, with a wider diversity of N-heterocycles than previously has been found in Ryugu samples and the Murchison meteorite (Table 1). We also identified other N-heterocyclic molecules such as xanthine, hypoxanthine, and nicotinic acid (B3 vitamer). The concentration of the pyrimidine nucleobases (C, U, and T) was in the range of 50 to 100 parts per billion (ng/g), which was a few times higher than that of the purine nucleobases (G and A). The diversity of structural isomers in the nucleobase molecule group supports an extraterrestrial origin of these compounds in the Bennu samples. These results demonstrate that asteroids like Bennu may have delivered a wide variety of nucleobases that could have served as the building blocks of nucleic acids on the early Earth.
References
[1] Lauretta, D. et al. Science, 377, 285–291 (2022).
[2] Oba, Y. et al. Nature Communications, 14, Article number: 3107(2023).
[3] Lauretta D.S. et al. OSIRIS-REx Sample Analysis Plan. 10.48550/arXiv.2308.11794 (2023).
[4] Mahaffy P.R. et al. (2012) Space Sci. Rev. 170, 401-478
[5] Mojarro A. et al. LPSC 55 #2019 (2024).
[6] Oba, Y. et al. Nature Communications, 14, Article number: 1292 (2023).
[7] Koga, T. et al. Geochimica et Cosmochimica Acta, 365, 253-265 (2024).
[8] Oba, Y. et al. Nature Communications, 13:2008 (2022).
[9] Callahan et al. Proceedings of the National Academy of Science, 108, 13995-13998 (2011).
We used two parallel techniques on three separate aggregate samples of Bennu. One was pyrolysis–gas chromatography–triple-quadrupole mass spectrometry with wet chemistry pyrolysis after reacting with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide and N,N-dimethylformamide to derivatize and semi-quantitatively detect soluble organic matter [4,5]. The MS scanned for multiple reaction monitoring (MRM) transitions targeting N-heterocycles. Compound identification was conducted via comparison with retention time and three MRM transitions of targeted standards. Analysis was conducted on a 1 mg subsample of fine particles (parent OREX-500002-0) recovered from spillover outside the OSIRIS-REx sample collector and a 1 mg subsample of fine- to intermediate-sized particles (parent OREX-800031-0) from inside the collector. The other technique was high-performance liquid chromatography with high-resolution Orbitrap mass spectrometry (HPLC-HRMS) [6,7], where the HCl extract from a 17.75 mg of fine- to intermediate-sized particles of the Bennu sample OREX-800044-101 was analyzed.
We identified all five canonical nucleobases—cytosine (C), uracil (U), thymine (T), guanine (G), and adenine (A), as well as some of their structural isomers—in the Bennu samples, with a wider diversity of N-heterocycles than previously has been found in Ryugu samples and the Murchison meteorite (Table 1). We also identified other N-heterocyclic molecules such as xanthine, hypoxanthine, and nicotinic acid (B3 vitamer). The concentration of the pyrimidine nucleobases (C, U, and T) was in the range of 50 to 100 parts per billion (ng/g), which was a few times higher than that of the purine nucleobases (G and A). The diversity of structural isomers in the nucleobase molecule group supports an extraterrestrial origin of these compounds in the Bennu samples. These results demonstrate that asteroids like Bennu may have delivered a wide variety of nucleobases that could have served as the building blocks of nucleic acids on the early Earth.
References
[1] Lauretta, D. et al. Science, 377, 285–291 (2022).
[2] Oba, Y. et al. Nature Communications, 14, Article number: 3107(2023).
[3] Lauretta D.S. et al. OSIRIS-REx Sample Analysis Plan. 10.48550/arXiv.2308.11794 (2023).
[4] Mahaffy P.R. et al. (2012) Space Sci. Rev. 170, 401-478
[5] Mojarro A. et al. LPSC 55 #2019 (2024).
[6] Oba, Y. et al. Nature Communications, 14, Article number: 1292 (2023).
[7] Koga, T. et al. Geochimica et Cosmochimica Acta, 365, 253-265 (2024).
[8] Oba, Y. et al. Nature Communications, 13:2008 (2022).
[9] Callahan et al. Proceedings of the National Academy of Science, 108, 13995-13998 (2011).