Multi-stable isotope systematics of individual organic compounds in cosmogeochemical samples

化合物特异性多同位素对碳质陨石等宇宙化学样品和海洋、湖泊沉积物等环境样品中的有机物进行了碳、氢同位素的测定，以了解其来源、形成和降解机制。相对<13>于水溶性乙酸，δ^<13>C-δD图表明，CM陨石的7个MOM可分为3组，其同位素变化可能与陨石母体的蚀变过程有关。沉积<13>物生物标志物的δ^ C-δD变化对判别其来源和迁移过程具有重要意义，本文进一步测定了乙酸、甲醇和苯等有机小分子在紫外光照射下的碳、氢同位素分馏，以了解它们在自然环境中的同位素变化。随着紫外降解的进行，分子的δ^<13>C和OD值都增加。动力学过程和同位素交换反应可能是控制同位素变化的因素，由于本研究项目的主要研究者从东京首都大学转移到冈山大学，一些研究计划无法在拟定的研究期限内完成。然而，大多数研究计划已经成功完成，21篇同行评议的英文论文和40篇国际和国内科学会议上的报告。

Compound-specific multi-isotope (especially carbon and hydrogen isotopes) measurement has been carried out for individual organic compounds in cosmochemical samples such as carbonaceous meteorites and in environmental samples such as marine and lacustrine sediments in order to understand their origins and sources as well as formation and degradation mechanisms.Acetic acid generated by hydrous pyrolysis of meteoritic macromolecular organic matter (MOM) is more depleted in ^<13>C relative to the water-soluble acetic acid. A δ^<13>C-δD plot indicates that seven MOMs of CM chondrites are divided into 3 groups, where the isotope variation could relate to alteration processes of the meteorite parent bodies. The δ^<13>C-δD variation of sedimentary biomarkers is very useful to discriminate their origins as well as transport processes.We further determined carbon and hydrogen isotope fractionations of small organic molecules such as acetic acid, methanol and benzene during the UV light irradiation to understand their isotope variations in natural environment. As the UV degradation proceeds, both δ^<13>C and OD values of the molecules increase. Kinetic process and isotope exchange reaction may be factors to control the isotope variations.Because the principal investigator move from Tokyo Metropolitan University to Okayama University during this research project, a few research plan could not be completed within the proposed research period. However, most research plans have been successfully accomplished with the 21 peer-reviewed English papers and 40 presentations at international and domestic scientific meetings.