The ability to store information is believed to have been crucial for the origin and evolution of life; however, little is known about the genetic polymers relevant to abiogenesis. Nitrogen heterocycles (N-heterocycles) are plausible components of such polymers as they may have been readily available on early Earth and are the means by which the extant genetic macromolecules RNA and DNA store information. Here, we report the reactivity of numerous N-heterocycles in highly complex mixtures, which were generated using a Miller-Urey spark discharge apparatus with either a reducing or neutral atmosphere, to investigate how N-heterocycles are modified under plausible prebiotic conditions. High throughput mass spectrometry was used to identify N-heterocycle adducts. Additionally, tandem mass spectrometry and nuclear magnetic resonance spectroscopy were used to elucidate reaction pathways for select reactions. Remarkably, we found that the majority of N-heterocycles, including the canonical nucleobases, gain short carbonyl side chains in our complex mixtures via a Strecker-like synthesis or Michael addition. These types of N-heterocycle adducts are subunits of the proposed RNA precursor, peptide nucleic acids (PNAs). The ease with which these carbonylated heterocycles form under both reducing and neutral atmospheres is suggestive that PNAs could be prebiotically feasible on early Earth.

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.

Phosphate, an essential molecule in biochemistry, is not abundant in modern oceans and would have been even less abundant in early Earth’s oceans. One possible mechanism for concentrating phosphate for prebiotic reactions is adsorption onto iron (oxy)­hydroxide minerals, which would have precipitated from interactions between iron-rich oceans of the early Earth and near neutral-alkaline hydrothermal fluids. In this work, we synthesized ferrous and ferric (oxy)­hydroxides to test their adsorptivity toward phosphate under early Earth oceanic conditions (anoxic, dissolved Fe2+, pH 6–9, and low phosphate levels). Prebiotically relevant amino acids (cysteine, histidine, and arginine) were added to test their effect on phosphate adsorption. Colorimetry techniques coupled with nuclear magnetic resonance and statistical analysis were utilized to determine how experimental conditions influenced the adsorption reaction. We observed an 80–90% reduction of ferric to ferrous iron minerals in the presence of cysteine; we hypothesize that iron and cysteine underwent a redox reaction to produce cystine. In addition, phosphate was readily adsorbed onto iron (oxy)­hydroxide minerals, but their efficacy depended on the iron redox state and pH at which the minerals were precipitated. Phosphate adsorption was the greatest with ferrous (oxy)­hydroxide minerals precipitated at pH 9, reaching a maximum average adsorption of 45%. Under these conditions, the addition of organics significantly enhanced phosphate adsorption by an additional ∼30%; differences due to the amino acid side chain were not statistically significant. This work shows how environmental conditions (redox state, pH, and presence of organics) influenced adsorption in a simulated mineral system; such systems merit further study under increasingly complex conditions in order to better understand phosphate dynamics on wet-rocky worlds such as early Earth or Mars.

No abstract