The Analysis of Carbonaceous Meteorites: Unusual Mirror-Image Properties Of Organic Compounds From The Early Solar System
Carbonaceous meteorites contain several classes of organic compounds including amino acids, amines, nucleobases (components of RNA and DNA), and sugar derivatives. Many of these compounds are thought to have formed in water solutions by the reactions of small precursor interstellar molecules (ammonia, cyanide, formaldehyde, etc.) on meteorite parent bodies, asteroids and comets. The chemistry of formaldehyde, a ubiquitous molecule in interstellar space, is thought to have led to the meteoritic sugar derivatives. In current biology, sugars are critical components of membranes, DNA and RNA. Could ancient (~ 4.6 billion year-old) chemistry have eventually led to such molecules?
Many of the above meteoritic compounds are "chiral", i.e., their two mirror images cannot be superposed (often called "superimposed"). A useful analogy is trying to fit a left hand into a right-hand glove. Scientifically, each of these mirror images is referred to as an "enantiomer". Such molecules are important in life because the central compound in biological polymers such as RNA and proteins are built exclusively from only one of two enantiomers. In the case of RNA, only the "right handed" enantiomer of a sugar (ribose) is present. It is still a mystery as to how such mirror-image preferences originated but meteorites might offer clues. One of the unusual properties of meteorites is that several of their compounds also contain unequal amounts of their left and right hand enantiomers. The analyses of meteoritic enantiomers were pioneered at ASU. I will describe the latest general results in the analysis of meteoritic organic compounds including the analysis of enantiomer ratios of individual compounds.
Technical Talk: Attempts At the Abiotic Production of Mirror-Image Excesses in Organic Compounds
Our current project involves the utilization of formaldehyde reactions to produce chiral compounds, i.e., compounds that are composed of two non-superposable mirror images or "enantiomers", analogous to a left and right hand. Such molecules are important in contemporary biology because biological polymers (proteins, nucleic acids, etc.) are homochiral - their monomers consist exclusively of one of the two enantiomers (an "enantiomer excess"). I will describe our methods in attempts at creating enantiomer excesses in sugar derivatives: these procedures are thought to be prebiotically plausible. The analytical methods consist of gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and various methods of sample preparation.