Oro: Experimental Organic Cosmochemistry 467 



The yield of total amino acids in these experiments was usually less than 5 

 per cent of the theoretical and the relative yield of each individual amino acid 

 was approximately inversely proportional to the number of carbon atoms in the 

 molecule. When methane was used the amino acids formed contained almost 

 exclusively from 2 to 4 carbon atoms. When methane was replaced partially 

 by ethane or higher hydrocarbons, valine and leucines were formed in addition 

 to the other amino acids. ^^ Aside from these and other small variations, the 

 overall qualitative composition of amino acids obtained in different experiments 

 by several investigators is very similar, if not identical. 



Although the mechanisms of synthesis have not been studied in detail, it 

 seems that the first phase of one of the possible mechanisms involves the forma- 

 tion of radicals which recombine to form many compounds including hydrogen 

 cyanide, aldehydes, amines, nitriles, and aliphatic hydrocarbons. The primary 

 formation of methyl radicals has been suggested by the experiments of Franck,^^ 

 with either isooctane or methanol in the presence of ammonia and water. 

 When methanol was used, the observed amino acid yield was increased more 

 than 50 per cent as compared to that obtained from methane. This is in 

 line with the fact that 20 per cent less energy is required to form a methyl 

 radical from methanol than from methane. ^^ That methyl radicals are formed 

 can also be deduced from a study of the products formed by the action of 

 electrical discharges upon methane, ^^ and upon mixtures of methane and 

 ammonia. ^^ Because of the high thermal stability of the triple bonded radical 

 C2H derived from acetylene®* one would expect that this radical should act as a 

 trap for other radicals giving rise to the formation of methyl, ethyl, vinyl, and 

 ethynyl derivatives of acetylene. In fact, these compounds were precisely 

 the products identified in the aforementioned experiments.*® In a similar 

 manner the nitrile analogues of the above compounds, namely, acetonitrile, 

 propionitrile, acrylonitrile, and cyanogen should also be expected to be formed 

 from the thermally stable triple bonded CN radical derived from hydrogen 

 cyanide. And in fact some of these compounds were detected by Sagan and 

 Miller" in model experiments with Jovian atmospheres. 



The second phase of this mechanism of amino acid synthesis does not seem to 

 occur in the gas phase, but rather in aqueous solution. It involves a Strecker 

 condensation of aldehydes with hydrogen cyanide in the presence of 

 ammonia.^® '^^ The resulting a-amino acid nitriles which can be detected during 

 the first hours®'* are progressively hydrolyzed into the corresponding amides 

 and acids. 



In addition to a-amino nitriles, (8-aminonitriles have also been detected in the 

 reaction product. In particular, |S-aminopropionitrile which is a precursor of 

 /3-alanine and of pyrimidines has been detected by paper chromatography,®^ 

 This nitrile gives a characteristic green derivative when it reacts with ninhydrin. 



An alternative mechanism for the formation of amino acids in the experiments 

 with electrical discharges is suggested by the presence in the reaction product of 

 polymers of hydrogen cyanide which are known to be converted into amino 

 acids (section (4)). 



(2) By ultraviolet light. Studies on the photochemical synthesis of amino 

 acids in aqueous systems were reported some time ago by several investigators. 

 Baudisch®^ claimed the formation of amino acids from potassium nitrite, carbon 



