Amino acid compositions in heated carbonaceous chondrites and their compound-specific nitrogen isotopic ratios

Queenie Hoi Shan Chan, Yoshito Chikaraishi, Yoshinori Takano, Nanako O.Ogawa, Naohiko Ohkouchi

Earth, Planets and Space
December 2016, 68:7

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“A novel method has been developed for compound-specific nitrogen isotope compositions with an achiral column which was previously shown to offer high precision for nitrogen isotopic analysis. We applied the method to determine the amino acid contents and stable nitrogen isotopic compositions of individual amino acids from the thermally metamorphosed (above 500 °C) Antarctic carbonaceous chondrites Ivuna-like (CI)1 (or CI-like) Yamato (Y) 980115 and Ornans-like (CO)3.5 Allan Hills (ALH) A77003 with the use of gas chromatography/combustion/isotope ratio mass spectrometry. ALHA77003 was deprived of amino acids due to its extended thermal alteration history. Amino acids were unambiguously identified in Y-980115, and the δ15N values of selected amino acids (glycine +144.8 ‰; α-alanine +121.2 ‰) are clearly extraterrestrial. Y-980115 has experienced an extended period of aqueous alteration as indicated by the presence of hydrous mineral phases. It has also been exposed to at least one post-hydration short-lived thermal metamorphism. Glycine and alanine were possibly produced shortly after the accretion event of the asteroid parent body during the course of an extensive aqueous alteration event and have abstained from the short-term post-aqueous alteration heating due to the heterogeneity of the parent body composition and porosity. These carbonaceous chondrite samples are good analogs that offer important insights into the target asteroid Ryugu of the Hayabusa-2 mission, which is a C-type asteroid likely composed of heterogeneous materials including hydrated and dehydrated minerals.”

Supplementary material (DOCX):
“Additional file 1: Figure S1. GC/C/IRMS chromatogram of the 12 M HCl-hydrolyzed hot-water extracts of the Piv/iPr amino acid esters in Y-980115. The subgraph (a) shows the magnified region with the alanine and glycine peaks. The single-ion traces GC/MS chromatograms of (b) Y-980115 and (c) amino acid standard mixture of the same region as shown in (a) indicate that no coeluting compounds were present that could have interfered the IRMS analysis of Y-980115 and that only alanine and glycine are the main nitrogen-bearing compounds in the region. ”