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.