Heterogeneous distribution of paramagnetic radicals in insoluble organic matter from the Orgueil and Murchison meteorites

Abstract

An electron paramagnetic resonance (EPR) investigation was performed on the insoluble organic matter from the Orgueil and Murchison meteorites and on terrestrial coals with similar elemental composition. A complementary electron nuclear double resonance (ENDOR) study was also carried out. The measured g-factors of the observed paramagnetic radicals in the meteoritic organic matter exhibit a similar correlation with the chemical composition as for the type III (i.e., hydrogen-poor) terrestrial coals. The main result, obtained from EPR saturation and 1H ENDOR enhancement measurements, showed that the effective local concentration in radicals of about 3 to 4 × 10 19 spin.g −1 in the meteoritic organic matter is much higher than the average concentration, hence the occurrence of radical-rich regions accounting for 5% and 20% of the total volume for Murchison and Orgueil, respectively. This heterogeneity of concentration seems to be unique among natural organic macromolecules. It is proposed that these radical-rich regions correspond to pristine parts of the organic matter synthesized in conditions close to those prevailing in the interstellar medium, and which have survived the hydrothermal process on the parent body.