New pyrolytic and spectroscopic data on Orgueil and Murchison insoluble organic matter: A different origin than soluble?

Abstract

Pyrolysis with and without tetramethylammonium hydroxide (TMAH), vacuum pyrolysis, and solid state 15 N nuclear magnetic resonance (NMR) were used to examine the macromolecular insoluble organic matter (IOM) from the Orgueil and Murchison meteorites. Conventional pyrolysis reveals a set of poorly functionalized aromatic compounds, ranging from one to four rings and with random methyl substitutions. These compounds are in agreement with spectroscopic and pyrolytic results previously reported. For the first time, TMAH thermochemolysis was used to study extraterrestrial material. The detection of aromatics bearing methyl esters and methoxy groups reveals the occurrence of ester and ether bridges between aromatic units in the macromolecular network.No nitrogen-containing compounds were detected with TMAH thermochemolysis, although they are a common feature in terrestrial samples. Along with vacuum pyrolysis results, thermochemolysis shows that nitrogen is probably sequestered in condensed structures like heterocyclic aromatic rings, unlike oxygen, which is mainly located within linkages between aromatic units. This is confirmed by solid state 15 N NMR performed on IOM from Orgueil, showing that nitrogen is present in pyrrole, indole, and carbazole moieties.These data show that amino acids are neither derived from the hydrolysis of IOM nor from a common precursor. In order to reconcile the literature isotopic data and the present molecular results, it is proposed that aldehydes and ketones (1) originated during irradiation of ice in space and (2) were then mobilized during the planetesimal hydrothermalism, yielding the formation of amino acids. If correct, prebiotic molecules are the products of the subsurface chemistry of planetesimals and are thus undetectable through astronomical probes.

Organic material and gases in the early Solar System : the meteorite record

“…On the other hand, hydrothermal alteration may induce oxidation of some functional groups like O and S containing groups. In the IOM, oxidized moieties like ether and ester groups are more abundant in more altered carbonaceous chondrites (Remusat et al 2005). The S-containing groups show a higher degree of oxidation in the more altered carbonaceous chondrites (Orthous-Daunay et al 2010).…”

Organic materials in planetary and protoplanetary systems: nature or nurture?

“…molecules released with organic solvents or water -has been attributed to the effects of hydrothermal processes in the parent body (Alexander et al 1998;Yabuta et al 2005), in which SOM could be the hydrolysis product of IOM. An alternative view considers SOM as a component of the ices that were accreted along with refractory phases, and therefore with no connection with IOM (Remusat et al 2005).…”

Organic and volatile elements in the solar system

“…But this reaction can not produce the non -amino acids and other mechanisms like hydrolysis of lactams and Michael addition has been proposed to account for the and amino acids [53]. Molecular properties and isotopic ratios of both the IOM and the amino acids fraction rule out an origin from the hydrolysis of the macromolecule [54]. Molecular and isotopic data on extraterrestrial amino acids thus indicate a complex origin for this fraction.…”