Indigenous aliphatic amines in the aqueously altered Orgueil meteorite

Abstract

The CI1 Orgueil meteorite is a highly aqueously altered carbonaceous chondrite. It has been extensively studied, and despite its extensive degree of aqueous alteration and some documented instances of contamination, several indigenous organic compounds including amino acids, carboxylic acids, and nucleobases have been detected in its carbonrich matrix. We recently developed a novel gas chromatographic method for the enantiomeric and compound-specific isotopic analyses of meteoritic aliphatic monoamines in extracts and have now applied this method to investigate the monoamine content in Orgueil. We detected 12 amines in Orgueil, with concentrations ranging from 1.1 to 332 nmol g À1 of meteorite and compared this amine content in Orgueil with that of the CM2 Murchison meteorite, which experienced less parent-body aqueous alteration. Methylamine is four times more abundant in Orgueil than in Murchison. As with other species, the amine content in Orgueil extracts shows less structural diversity than that in Murchison extracts. We measured the compound-specific stable carbon isotopic ratios (d 13 C) for 5 of the 12 monoamines detected in Orgueil and found a range of d 13 C values from -20 to +59&. These d 13 C values fall into the range of other meteoritic organic compounds, although they are 13 C-depleted relative to their counterparts extracted from the Murchison meteorite. In addition, we measured the enantiomeric composition for the chiral monoamines (R)-and (S)-sec-butylamine in Orgueil, and found it was racemic within experimental error, in contrast with the L-enantiomeric excess found for its amino acid structural analog isovaline. The racemic nature of sec-butylamine in Orgueil was comparable to that previously observed in Murchison, and to other CM2 and CR2 carbonaceous chondrites measured in this work (ALH 83100 [CM1/2], LON 94101 [CM2], LEW 90500 [CM2], LAP 02342 [CR2], and GRA 95229 [CR2]). These results allow us to place some constraints on the effects of aqueous alteration observed over the monoamine concentrations in Orgueil and Murchison, and to evaluate the primordial synthetic relationships between meteoritic monoamines and amino acids.

Distribution of aliphatic amines in CO, CV, and CK carbonaceous chondrites and relation to mineralogy and processing history

“…The amine content of the CO meteorites DOM 08006 and MIL 05013 is very low (1.3 to 4.0 nmol g −1 of meteorite), consistent with the values observed for the CV and CK meteorites, and 2–3 orders of magnitude lower than those observed in CM, CI, and CR meteorites (Aponte et al. , , ) (Fig. ).…”

“…For comparison, amine abundances in CI 1, CM 1/2, CM 2, and CR 2 meteorites have been included in the graph (values taken from Aponte et al. , , ).…”

“…We have analyzed the amine content in a limited set of samples belonging to various carbonaceous chondrite subtypes (Aponte et al. , , ) and can now add examples from CO, CV, and CK meteorites to this data set. Although the number of analyzed samples remains small, we observe some variations within each group of meteorites (Fig.…”

“…Analyses of amines were performed according to previously published methods (Aponte et al. , , ). The meteorite samples were powdered and homogenized by mixing using a mortar and pestle in a positive pressure ISO 5 HEPA‐filtered laminar flow hood, and separated into ~500 mg portions.…”

“…We have previously investigated the molecular abundance and distributions of aliphatic monoamines (hereafter called “amines”) in the CI, CM, and CR meteorites and have evaluated their potential synthetic relationships with their structurally analogous amino acids (Aponte et al. , , ). CV, CK, and CO meteorites contain much less carbon than CI and CM meteorites (e.g., Pearson et al.…”