Abstract
Chirality is a central feature in the evolution of biological systems, but the reason for biology’s strong preference for specific chiralities of amino acids, sugars, and other molecules remains a controversial and unanswered question in origins of life research. Biological polymers tend toward homochiral systems, which favor the incorporation of a single enantiomer (molecules with a specific chiral configuration) over the other. There have been numerous investigations into the processes that preferentially enrich one enantiomer to understand the evolution of an early, racemic, prebiotic organic world. Chirality can also be a property of minerals; their interaction with chiral organics is important for assessing how post-depositional alteration processes could affect the stereochemical configuration of simple and complex organic molecules. In this paper, we review the properties of organic compounds and minerals as well as the physical, chemical, and geological processes that affect organic and mineral chirality during the preservation and detection of organic compounds. We provide perspectives and discussions on the reactions and analytical techniques that can be performed in the laboratory, and comment on the state of knowledge of flight-capable technologies in current and future planetary missions, with a focus on organics analysis and life detection.
Highlights
Enantiomeric Excess as a BiosignatureEnantiomeric excess (ee) of organic molecules has been proposed as a biosignature based on our observations and knowledge of molecular biochemistry on Earth [17,47,48,49]
We highlight the importance of continued instrument development (Section 9.2), contamination control (Section 9.3), and multidisciplinary collaboration (Section 9.4) in order to further the study of chirality in organic and mineral systems that is geared towards understanding the origins and contexts of how life evolved on Earth and where and how to find it elsewhere
Homochirality is of great interest and importance to prebiotic chemistry as well as those researching the origins of life
Summary
Enantiomeric excess (ee) of organic molecules has been proposed as a biosignature based on our observations and knowledge of molecular biochemistry on Earth [17,47,48,49]. To expand on the fourth point, it remains possible for extraterrestrial life to rely on homochiral polymers of various chiralities; for example, perhaps it could use a protein composed of D-amino acids for one function and another composed of L-amino acids for another. The difference between R and S involves assigning priority to the different substituents and determining whether the identified lowest to highest priority groups follows a clockwise direction (designated R) or counterclockwise direction (designated S). This method is called the Cahn–Ingold–Prelog rules in organic nomenclature [55]. While the majority of chirality discussed in the context of origins of life is point/molecular chirality, there are other types of chirality that organics can possess, including axial, helical, and planar chirality, which we discuss below
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