Oro: Experimental Organic Cosmochemistry 469 



and in the primitive reducing atmospheres of the terrestrial planets is of the 

 order of 1000 g. per cm.^ of planetary surface. 



Experiments carried out by Pavlovskaya and Pasynskii"- and also in this 

 laboratory/^ have shown that several amino acids can be synthesized by irradia- 

 tion with ultraviolet light of aqueous mixtures containing formaldehyde and 

 ammonium salts. The synthesized amino acids, which were separated by ion 

 exchange resins and detected by paper chromatography, include glycine, serine, 

 alanine, and glutamic acid. The Russian investigators found also vaUne, 

 isoleucine, phenylalanine, and basic amino acids. 



With regard to the mechanism of photochemical synthesis of amino acids it 

 has been pointed out previously, that the amino group may be derived from 

 either ammonia or hydroxylamine. However, very little is known about the 

 mechanism of formation of the hydrocarbon chain. Perhaps monosaccharides 

 of 2 to 6 carbons are lirst formed photochemically and then transformed by 

 redox processes into a-keto acids which upon transamination are converted into 

 amino acids. 



That hexoses and hydroxy acids or their lactides are formed by the irradiation 

 of formaldehyde solutions with ultraviolet light was shown by Baly^^ and Irvine 

 and Francis.'^'' Moreover, when the syrupy product, thus obtained, was 

 heated with a trace of acid at 100° C. it was found to resinify into a polymeric 

 material. This suggested the additional presence in the reaction product of 

 furfuryl alcohols or polyhydroxyphenols. If phenolic compounds were formed 

 from formaldehyde these compounds may be the precursors of the aromatic 

 amino acids. 



That hydroxy acids and also keto acids and dicarboxylic acids react photo- 

 chemically with ammonia, ammonium salts, or other nitrogen compounds to 

 produce amino acids has been shown by Deschreider*^ and by Cultrera and 

 Ferrari.^^'*^ Nonphotochemical transamination reactions are also well known. 



The synthesis of amino acids containing straight chains with 5 or 6 carbon 

 atoms could be explained by the intermediate formation of Cs or Ce mono- 

 saccharides, respectively. These compounds become stabilized by the forma- 

 tion of furanose and pyranose cyclic structures, stopping the growth of the 

 monosaccharide chain by preventing the condensation of additional formalde- 

 hyde molecules. Therefore, essentially no monosaccharides and amino acids 

 with a linear chain of more than 6 carbon atoms are formed. Branched chain 

 amino acids could be derived from branched chain monosaccharides such as 

 dendroketose. 



It is of interest that the same maximal amino acid chain length is observed in 

 these photochemical experiments as in the experiments with electric discharges. 

 Whereas in the present case the maximal chain length may be determined by 

 the stability of cyclic structures, in the experiments with electrical discharges it 

 may be the result of the decreased probability of formation of long chains by 

 processes of methyl radical recombination. 



(3) By ionizing radiations. The synthesis of organic compounds by ionizing 

 radiation was reviewed by Swallow.'^* After the pioneering investigations in this 

 area by Garrison et al.,-^ the formation of amino acids by the action of ionizing 

 radiations has been studied by several investigators. Hasselstrom et al.,^^ 



