468 Annals New York Academy of Sciences 



monoxide, and ferric chloride. Dhar and Mukherjee observed the formation of 

 glycine from glycol, and of arginine from glucose. Nitrates were used as a 

 source of nitrogen and titanium dioxide or ferrous sulfate as catalyst. More 

 recently, Bahadur ef a/.,^^"'^ also with the use of nitrates and ferric chloride 

 have observed the formation of serine, aspartic acid, and asparagine from 

 paraformaldehyde. Other amino acids formed in these experiments as detected 

 by paper chromatography (without previous separation from other ninhydrin 

 positive compounds by ion exchange) were glycine, alanine, and threonine and 

 in particular C5 and Ce amino acids which are formed with difficulty in the 

 experiments with electric discharges. These include valine, ornithine, arginine, 

 proline, glutamic acid, histidine, leucine, isoleucine, and lysine. The above 

 amino acids comprise essentially all the building blocks of proteins with the 

 exception of the aromatic and sulfur containing amino acids. 



It would be difficult to visualize the presence of nitrates in a primitive Earth 

 environment or in a cosmic body. However, the nitrate ion per se should not 

 be considered as the immediate precursor of the amino group of amino acids. 

 It is clear that the nitrates must be reduced at the expense of the oxidation of 

 part of the carbon compounds, such as formaldehyde, which are always present 

 in a large excess in these experiments. In fact it is known that in the presence 

 of metallic ions and partiahy reduced carbon compounds, nitrates,'^^ and ni- 

 trites^^ are rapidly reduced by the action of light to some nitrogen compound of 

 a lower oxidation level. 



Hydroxylamine was suggested by Oro et al.^^ as one of the nitrogen com- 

 pounds which may be involved more directly in the formation of amino acids. 

 In fact, this could also be deduced from the synthesis of amino acids from 

 formhydroxamic acid and formaldehyde by Baly et alP The preferred partici- 

 pation of hydroxylamine in the comparative photochemical synthesis of amino 

 acids from formaldehyde and either nitrates, nitrites, hydroxylamine hydro- 

 chloride, or ammonium chloride has been coniirmed in our laboratory .^^ The 

 same conclusion has been arrived at by Ferrari^^ •^'' from similar comparative 

 photochemical experiments but with more complex carbon compounds instead 

 of formaldehyde. 



From a conceptual point of view, ammonia and ammonium chloride are 

 perhaps the most logical precursors of the amino group of amino acids in a 

 primitive Earth environment. Experiments carried out by Miller,^** and by 

 Groth and von Weyssenhoff ,*i '^^ have given evidence that the amino acids 

 glycine and alanine can be synthesized by irradiating wjth short wave ultra- 

 violet light (Krypton 1165, 1235 A, Xenon 1295, 1470 A, and mercury vapor 

 1850 A), aqueous mixtures containing ammonia as the nitrogen source and 

 either methane or ethane as the carbon source. A higher amino acid yield was 

 obtained when ethane was used instead of methane. On exposing a mixture 

 of methane, ammonia, carbon monoxide, and water to the radiation of a hy- 

 drogen lamp through a thin LiF window, Terenin**^ observed the formation of 

 the alanines and of several other amino acids. 



On the basis of the experimental quantum yields obtained by Groth and 

 recent theories of solar evolution, Sagan^'' has calculated that the synthesized 

 organic compounds in the contemporary atmospheres of the Jovian planets. 



