Extraterrestrial hydroxy amino acids in CM and CR carbonaceous chondrites

1Toshiki Koga,2Eric T. Parker,2,3Hannah L. McLain,2,3José C. Aponte,2Jamie E. Elsila,2Jason P. Dworkin,2Daniel P. Glavin,1Hiroshi Naraoka
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13661]
1Department of Earth and Planetary Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395 Japan
2NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
3Catholic University of America, Washington, District of Columbia, 20064 USA
Published by arrangement with John Wiley & Sons

The abundances, distributions, and enantiomeric ratios of a family of three- and four-carbon hydroxy amino acids (HAAs) were investigated in extracts of five CM and four CR carbonaceous chondrites by gas chromatography-mass spectrometry analyses. HAAs were detected in both the acid hydrolysates of the hot water extracts and the 6 M HCl extracts of all the CM and CR chondrites analyzed here with total hot water and HCl extractable HAA concentrations ranging from 6.94 to 315 nmol g−1. The HAA analyses performed in this study revealed: (1) the combined (hot water + HCl) extracts of CR2 chondrites contained greater abundances of α-HAAs than that of CM2 chondrites and (2) the combined extracts of CM and CR chondrites contained roughly similar abundances of β- and γ-HAAs. Application of the new GC-MS method developed here resulted in the first successful chromatographic resolution of the enantiomers of an α-dialkyl HAA, d,l-α-methylserine, in carbonaceous chondrite extracts. Meteoritic α-methylserine was found to be mostly racemic within error and did not show l-enantiomeric excesses correlating with the degree of aqueous alteration, a phenomenon observed in meteoritic isovaline, another α-dialkyl amino acid. The HAAs identified in CM and CR chondrite extracts could have been produced during parent body alteration from the Strecker cyanohydrin reaction (for α-HAAs) and an ammonia-involved formose-like reaction (for β-, and γ-HAAs).

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