Prebiotic chemistry: chemical evolution of organics on the primitive Earth under simulated prebiotic conditions.
A series of prebiotic mixtures of simple molecules, sources of C, H, N, and O, were examined under conditions that may have prevailed during the Hadean eon (4.6-3.8 billion years), namely an oxygen-free atmosphere and a significant UV radiation flux over a large wavelength range due to the absence of an ozone layer. Mixtures contained a C source (methanol, acetone or other ketones), a N source (ammonia or methylamine), and an O source (water) at various molar ratios of C : H : N : O. When subjected to UV light or heated for periods of 7 to 45 days under an argon atmosphere, they yielded a narrow product distribution of a few principal compounds. Different initial conditions produced different distributions. The nature of the products was ascertained by gas chromatographic-mass spectral analysis (GC-MS). UVC irradiation of an aqueous methanol-ammonia-water prebiotic mixture for 14 days under low UV dose (6 x 10(-2) Einstein) produced methylisourea, hexamethylenetetramine (HMT), methyl-HMT and hydroxy-HMT, whereas under high UV dose (45 days; 1.9 x 10(-1) Einstein) yielded only HMT. By contrast, the prebiotic mixture composed of acetone-ammonia-water produced five principal species with acetamide as the major component; thermally the same mixture produced a different product distribution of four principal species. UVC irradiation of the CH(3)CN-NH(3)-H(2)O prebiotic mixture for 7 days gave mostly trimethyl-s-triazine, whereas in the presence of two metal oxides (TiO(2) or Fe(2)O(3)) also produced some HMT; the thermal process yielded only acetamide.
Dondi
Daniele
D
Dipartimento di Chimica Generale, Università di Pavia, via Taramelli 12, Pavia, 27100, Italy. dondi@unipv.it
Merli
Daniele
D
Pretali
Luca
L
Fagnoni
Maurizio
M
Albini
Angelo
A
Serpone
Nick
N
D000097:Acetonitriles / Q000737:chemistry; D018534:Earth, Planet; D019143:Evolution, Molecular; D018559:Exobiology; D006358:Hot Temperature; D007659:Ketones / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D008954:Models, Biological; D009930:Organic Chemicals / Q000737:chemistry*; D000069497:Origin of Life; D018462:Photobiology; D010777:Photochemistry; D014466:Ultraviolet Rays
D000097:Acetonitriles; D007659:Ketones; D009930:Organic Chemicals; D000432:Methanol; C032159:acetonitrile