The origin of biomolecular asymmetry – Insights from cometary and meteoritic matter

Abstract

Abstract. The chemistry of life is purely stereospecific. The fundamental biopolymers -proteins and nucleic acids -are intrinsically chiral due to their molecular building blocks, namely L-amino acids and D-sugars. Hypotheses for the evolutionary origin of that strict stereochemical selection include the asymmetric photochemistry model by which circularly polarized (CP) photons induced an enantiomeric excess in chiral organic molecules via asymmetric photolysis. The transfer of a distinct chirality from chiral photons to organic molecules is assumed to have occurred in environments of interstellar molecular clouds. This model is strengthened by the observation of CP light in the star-forming region of Orion. Due to our laboratory experiments mimicking cometary ice evolution, we show that molecules of prebiotic interest such as amino and diamino acids are formed in inter/protostellar environments and might have been subjected to CP vacuum-UV radiation before and during their space journey to the early Earth. How did Life originate?The goal is to understand the scenarios by which extraterrestrial organic matter has seeded the surface of the primitive Earth and propose an astrophysical explanation for the origin of asymmetry in chiral protein and nucleotide precursors that may have led later to homochirality an assumed prerequisite for Life on Earth [1].Why were left-handed amino acids selected for its architecture? Topical research reasons that circularly polarized light (CPL) -observed in star-forming regions -might induce an enantiomeric excess (ee) in chiral organic molecules via asymmetric interstellar photon-molecule interactions [2,3]. A major challenge of our research is to shed some light on the asymmetric mechanism for the formation of chiral prebiotic molecules based on their interaction with UV-CPL as an external chiral force with particular emphasis on absolute asymmetric photolysis and synthesis. Therefore, we are identifying various chiral organic molecules and quantifying any small ee in carbonaceous chondrites by using the highly increased resolution power of novel multidimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS) [4]. Detected ees are compared with those produced under controlled asymmetric photolysis experiments using circularly polarized synchrotron radiation (CPSR) at the synchrotron radiation source SOLEIL (France). First promising