A Chemical Theory of Spontaneous Generation 257 



volatilize byproduct water. HufFman had shown in 1942 [8] that the production 

 of dipeptides from amino acids at 298 °K by any route, requires an input of 

 2000-4000 cal. per mole of dipeptide formed (Table i). 



Table i 



Free-energy change accompanying formation of dipeptides from 

 amino acids 

 Alanine + Glycine = Alanylglycine + water 



A F°298 = 3730 cal. 

 Glycine + Glycine = Glycylglycine + water 



A F°298 = 3230 cal. 



Leucine + Glycine = Leucylglycine + water 



A F°298 = 2960 cal. 



Benzoic acid + Glycine = Hippuric acid + water 



A F°298 = 2260 cal. 



(From H. M. Huffman, J. phys. Chem., 46, 890, 1942) 



One can calculate that the AF value is more favourable at higher temperatures 

 for the dry reaction in the forward direction, but a destructively high tempera- 

 ture is nevertheless indicated for an energetically spontaneous reaction. One can 

 visualize, however, ,an overcoming of the energetic barrier by the occurrence 

 of a temperature sufficient to remove water in the gaseous state : 



H2N CHRCOOH + H2N CHR'COOH 



= H2N CHR CONHCHR'COOH + H2O f 



When experiments of this sort were first performed, unexpected indications of 

 the production of more amino acids than those taken for the reactions were 

 found. From this begiiming, experimental results often paralleled by thermal 

 experiments described in the early literature, led to a picture of thermal pathways. 

 Some of these results are depicted in Figs, i and 2. 



1 234567 89 10 11 



Fig. I. Tracing of chromatogram of products from ammoniimi salts 

 of Krebs-cycle acids. 



(i) 10 ix\. of aspartic acid standard^ (2) 10 fx\. of alanine standard^ (3) 10 //I. of 

 leucine standard, to permit comparisons of i?Fj (4) 10 ^1. of unheated mono- 

 ammonium fumarate; (5) 10 [A. of tmheated monoammonium malate; (6) 10 [x\. of 

 heated monoammonium fumarate : (7) 2 /^l. of hydrolysed heated monoammonium 

 fumarate (2 ixl.); (8) 10 [A. of heated monoammonium malate; (9) i /<1. of hydro- 

 lysed heated monoammonium malate showing faint spot with Rp of alanine; 

 (10) 10 /zl. of hydrolysed heated monoammonium succinate i (11) 10 /d. of hydro- 

 lysed heated ammonium citrate showing non-ninhydrin spot at origin. Solutions 

 were from i-o g of reactant made up to 15 ml. with water. Standards contained 

 I • o mg amino acid per ml. Chromatogram coloured with ninhydrin. 



17 



