Silylation Protocol for the Analysis of Meteoritic Amides

Abstract:

Carbonaceous chondrite meteorites are fragments of asteroids or comets, that have remained relatively unaltered since the formation of the Solar System. This extraterrestrial material contains a variety of organic compounds including amino acids, carboxylic acids, and nucleobases, among others. It has been suggested that carbonaceous chondrites may have been essential in the chemical processes that led to the origin of life on Earth (and possibly elsewhere), serving as delivery vehicles of important organic matter during Earth’s early history. Based on the observed relative abundances and the different alteration processes (i.e., thermal metamorphism or aqueous alteration), many synthetic mechanisms have been proposed for the origins of the organic compounds found within carbonaceous chondrites.

Among these synthetic routes, there is one mechanism involving the family of aliphatic amides, a class of substrate, with a chemical composition that includes four of the common elements required for life (C, H, O, N) which have been proposed to be important for prebiotic chemistry. The simplest, formamide, has been found in the galactic center, the interstellar medium, and comets. Experimental approaches using formamide with metal oxides, clays, phosphates, or meteorites as catalysts have formed nucleobases, carboxylic acids, amino acids, and amines. Surprisingly, neither formamide nor any other amide have been reported in meteorites. Therefore, we have developed a silylation derivatization method suitable for the identification and quantification of amides in meteoritic samples via gas chromatography mass spectrometry GC-QqQMS.

The derivatization protocol was developed using N-methyl-trimethylsilyl trifluoroacetamide (MSTFA) as the silylating agent for the derivatization of eleven C₁ to C₆ aliphatic amides and urea. Different temperatures, times of derivatization, solvents, volume of solvents, and acid and basic catalysts were evaluated to optimize our protocol. Finally, the optimized method was tested using pyrolyzed Allende meteorite impregnated with the amide standards as a control, and a fragment of Murchison meteorite as an analytical sample. The Allende/standard samples showed no decomposition of the tested compounds nor significant byproduct formation. In the sample of the Murchison meteorite, none of the aliphatic amides could be clearly identified, possibly due to the presence of water in the sample which could have hydrolyzed the amides during extraction or derivatization. Further studies are needed to firmly assess the presence of amides in carbonaceous chondrites either using our silylation protocol with precautions to eliminate water or with a new protocol that is less sensitive to the presence of water.