論文 / 著書情報
Article / Book Information
題目(和文)
Title(English)

Atmospheric synthesis of NH3 and Amino Acids from N2O and its
implication for the prebiotic chemistry

著者(和文)

藏暁鳳

Author(English)

XIAOFENG ZANG

出典(和文)

学位:博士(理学),学位授与機関:東京工業大学,
報告番号:甲第12506号,授与年月日:2023年9月22日,
学位の種別:課程博士,
審査員:上野 雄一郎,横山 哲也,関根 康人,尾﨑 和海,石川 晃

Citation(English)

Degree:Doctor (Science),
Conferring organization: Tokyo Institute of Technology,
Report number:甲第12506号,
Conferred date:2023/9/22,
Degree Type:Course doctor,Examiner:,,,,

学位種別(和文)

博士論文

Category(English)

Doctoral Thesis

種別(和文)

要約

Type(English)

OutlinePowered by T2R2 (Tokyo Institute Research Repository)

Doctoral Thesis

Atmospheric synthesis of NH3 and Amino Acids from N2O
and its implication for the prebiotic chemistry

Xiaofeng Zang

Department of Earth and Planetary Sciences
Tokyo Institute of Technology

2023

Outline

Nitrous oxide(N2O), which is produced from N2 atmosphere by lightning discharges, is thesecond most abundant nitrogen compound in the atmosphere, and is expected to be an essential
nitrogen source for prebiotic synthesis. However, abiotic sink of N2O has been largely unknown.
There are few experimental studies on N2O, and its chemical processes in the reducing earlyterrestrial atmospheres are completely unknown especially. In this study, experimental study on
abiotic synthesis of organic compounds from nitrous oxide(N2O) under a reducing atmosphere areconducted. The discovery of this study reveals a new aspect of the role of N2O in prebiotic
chemistry on primitive Earth, and expand our current acknowledge on nitrogen cycle on primitive
Earth as well as planetary atmospheric chemistry.
In Chapter 2, a series of UV-irradiation experiments are conducted. The results showed thatNH3 can be synthesized from N2O under reducing atmospheric containing CO or H2. Furthermore,
several amino acids can be synthesized from N2O and CO even without metal catalysts. This work
demonstrated, for the first time, that N2O could be an important nitrogen source and provide a
new process for synthesizing ammonia and organic nitrogen species.
In Chapter 3, the potential formation mechanisms of amino acids were investigated throughfurther analysis. Acid hydrolysis of the aqueous samples of UV experiment resulted 50 times moreamino acids than free amino acids, indicating that amino acids precursors may be synthesized
through the photochemical process. Analysis of unhydrolyzed samples by MALDI-TOF-MS andHPLC-Orbitrap MS/MS revealed that a variety of nitrogen containing heterocyclic compounds
such as imidazole and hexamethylenetetetramine (HMT) were present in the sample. The latter isknown to produce amino acids after hydrolysis, indicating that these heterocyclic compounds areformed by UV irradiation to N2O and become precursors. Furthermore, uracil was detected intrace amounts, suggesting that photochemical reactions in atmospheres including N2O and CO are
crucial synthetic processes since they provide both amino acids and nucleobases simultaneously.
In Chapter 4, electric discharge experiments into a simulated atmosphere containing N2O andCO were conducted. As a result, nitrite NO2− and nitrate NO3−, which were not produced by UV
irradiation, are the main products. Although the discharge process also produced NH3 and aminoacids, the varieties and yields of the organic compounds from the reacted N2O were much lower
compared to UV irradiation. The results showed that N2O and CO also have the potential togenerate NH3 as well as amino acids at the same time by corona discharge. However, the main
pathway for amino acids synthesis from N2O is atmospheric chemical reaction by solar UV light.
In Chapter 5, the supply flux of NH3 and glycine to the surface from atmospheric N2O were
estimated according to the experimental results from Chapter 2~4. Photochemical supply of freeglycine from the atmosphere is calculated to be 4 × 107 kg/year, assuming an early Earthatmosphere (CO2: 0.1%, CO: 1%, N2O: 3ppm) composed mainly of N2 (1 bar). The value could
reach to 108 kg yr-1 after fully hydrolyzed. This flux is comparable to the previously estimatedproduction rate. Therefore, the photochemical process of N2O in a reduced atmosphere may havebeen the primary pathway for amino acid supply processes on the early Earth before the arose of
the first life.