The formation of amino acids by the action of electric discharges on a mixture of methane, nitrogen, and water with traces of ammonia was studied in detail. The presence of glycine, alanine, a-amino-n-butyric acid, a-aminoisobutyric acid, valine, norvaline, isovaline, leucine, isoleucine, alloisoleucine, norleucine, proline, aspartic acid, glutamic acid, serine, threonine, allothreonine, a-hydroxy---aminobutyric acid, and a,-y-diaminobutyric acid was confirmed by ion-exchange chromatography and gas chromatography-mass spectrometry. All of the primary a-amino acids found in the Murchison Meteorite have been synthesized by this electric discharge experiment.Most prebiotic syntheses that start with the primitive atmospheric constituents give substantial yields of glycine, alanine, and a-amino-n-butyric acid (1). Prebiotic syntheses of the higher aliphatic amino acids have been claimed, for example, by the action of electric discharges on CH4 + NH3 + H20 (2-6), by heating CH4 + NH3 + H20 to 900-1200°(7, 8), and by the action of shock waves on CH4, C2H6, NH3, and H20 (9). The amino acids were identified only by an amino-acid analyzer (2-4, 6, 7, 9), only by paper electrophoresis (8), or only by gas chromatography (5). However, these techniques are not sufficient by themselves to identify an amino acid.In the original synthesis of amino acids by electric discharges (10-12), only glycine, alanine, a-amino-t-butyric acid, a-aminoisobutyric acid, and ,B-alanine, of the simple aliphatic amino acids, were synthesized in sufficient yield to obtain identification by a melting point of a derivative. Recently developed techniques permit the identification of compounds found in lower yield by this synthesis.The synthesis under prebiotic conditions of aspartic and glutamic acid (2-8, 12-14), serine (2, 5, 6-8, 13), threonine (2, 3, 5-7), and proline (3, 4, 7, 8, 13) have been reported but they have not been properly identified [except for aspartic acid (14) ]. The synthesis of these amino acids (except proline) has also been reported from the polymerization of HCN (1), but again without proper identification. A prebiotic synthesis of threonine should also yield allothreonine, but this amino acid has never been reported. In addition, several investigators have reported the appearance of a large peak at the isoleucine position on the amino-acid analyzer (2, 4-6, 13). The identification of this peak as isoleucine has been questioned (4, 13). It is evident that this compound cannot be isoleucine, since a corresponding peak for alloisoleucine is not observed.Most electric-discharge experiments have been done with a large amount of ammonia present. Use of nitrogen instead of ammonia in such experiments does not change the major products, although the yield of amino acids is lower (12).The use of a higher concentration of ammonia in such experiments has been criticized (15), and it is now thought that the ammonia concentration in the prebiotic atmosphere was not likely to have been greater than 10-5 atm (16,17). Although this i...
Phenylacetylene can be synthesized in substantial yields from various hydrocarbons by high temperatures, electric discharges, and ultraviolet light. Phenylacetylene is hydrated to phenylacetaldehyde by way of both nucleophilic and radical additions of H(2)S followed by hydrolysis of the thtioaldehyde. The addition of NH(3) and HCN to phenylacetaldehyde yields phenylalanine nitrile which is hydrolyzed to phenylalanine. A small yield of tyrosine is obtained from the radical addition of H(2)S to phenylacetylene. This sequence of reactions is a possible mechanism for the synthesis of these amino acids on the primitive earth.
Nicotinonitrile, 2-cyanopyridine, and 4-cyanopyridine can be synthesized under primitive earth conditions by the action of electric discharges on ethylene and ammonia. The electric discharge first synthesizes pyridine and hydrogen cyanide, which react in the discharge to form the cyanopyridines. Nicotinonitrile would have hydrolyzed in the primitive ocean to nicotinamide and nicotinic acid.
The pyrolysis of nine hydrocarbons at 1200°has been studied. The main products, which were the same for all hydrocarbons studied, were 1,3-cyclopentadiene, benzene, toluene, phenylacetylene, styrene, indene, and naphthalene. Twenty-three minor products were identified. The distribution of products can be accounted for in terms of polymerization of acetylene, produced by the pyrolysis of the hydrocarbon, and the addition of CH2 or CH3 to some of the acetylene polymers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.