Formamide-based prebiotic chemistry
Formamide-based prebiotic chemistry is an hypothesis about the abiogenesis of life on Earth from non-living chemical precursors which assumes that the chemical compound formamide (NH2CHO), the simplest naturally occurring amide, could have accumulated in sufficiently high amounts to serve as a building block and reaction medium for the synthesis of the first biogenic molecules.
Formamide contains all of the elements required for the synthesis of basic biomolecules (hydrogen, carbon, oxygen, and nitrogen) and is a ubiquitous molecule in the universe. It has been detected in galactic centers, star-forming regions of dense molecular clouds, high-mass young stellar objects, the interstellar medium, comets, and satellites. In particular, dense clouds containing formamide, with sizes on the order of kiloparsecs, have been observed in the vicinity of the Solar System.
Formamide forms under a variety of conditions corresponding to both terrestrial environments and interstellar media: e.g., upon high-energy particle irradiation of binary mixtures of ammonia (NH3) and carbon monoxide (CO), or from the reaction of formic acid (HCOOH) with NH3. It has been suggested that formamide may accumulate in hydrothermal vents in sufficiently high concentrations to enable synthesis of biogenic molecules. Ab initio molecular dynamics simulations suggest that formamide may have been a key intermediate of the Miller–Urey experiment as well.
The combinatorial power of carbon is manifested in the composition of the molecular populations detected in circum- and interstellar media. The number and the complexity of carbon-containing molecules are significantly higher than those of inorganic compounds, presumably all over the universe. One of the most abundant C-containing three-atom molecules observed in space is hydrogen cyanide (HCN). The chemistry of HCN has thus attracted attention in origin of life studies since the earliest times, and the laboratory synthesis of adenine from HCN under presumptive prebiotic conditions was reported as early as 1961. The intrinsic limit of HCN stems from its high reactivity, which leads in turn to instability and the difficulty associated with its concentration and accumulation in unreacted form. The “Warm Little Pond” in which life is supposed to have started, as imagined by Charles Darwin and re-elaborated by Alexander Oparin, had most likely to reach sufficiently high concentrations to start creating the next levels of complexity. Hence the necessity of a derivative of HCN that is sufficiently stable to survive for time periods extended enough to allow its concentration in the actual physico-chemical settings, but that is also sufficiently reactive to originate new compounds in prebiotically plausible environments. Ideally, this derivative should be able to undergo reactions in various directions, without prohibitively high energy barriers, thus allowing the production of different classes of potentially prebiotic compounds. Formamide fulfills all these requirements and, due to its significantly higher boiling point (210 °C), enables chemical synthesis in a much broader temperature range than water.