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

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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.