46 ORIGIN AND MAINTEN. OF OPT. ACTIVITY 



the non-iitilizable isomer appears only in insignificant con- 

 centrations in the first stages of synthesis. A large value 

 of the constant of equilibrium K, on the other hand, as- 

 sures a more lasting stability of the active state. Both 

 these factors contribute toward having the system 

 "evade" for a time the effects of inevitable racemization. 

 h ) Langenbeck and Triem's IVIechan- 

 i s m . Recently, Langenbeck and Triem (1936) have 

 shown that an increase of optical purity can be obtained 

 in interrupted reactions between two optically impure 

 substances. If an optically impure enzyme is acting upon 

 an optically impure substance and if the reaction is not 

 allowed to proceed to the end, the optical purity of the 

 system may be increased. Let us suppose that two sub- 

 stances, optically active but not optically pure, A and B, 

 combine to form AB. Let us assume also that the 

 laevorotatory isomers, Ai and Bi, predominate over their 

 antipodes. A,, and B^. The following partial reactions 

 will take place 



A. + B,->A,B. 



A, + B, ^ A,B, 



A, + Ba -^ A.Ba 



A, + B,^A,Bi 



Since [A.] > [AJ and [B,] > [BJ, we shall have, if 

 we interrupt the reaction before it is completed, 

 1A3J [AJ [A.B,] rB.] 



[A,B,] ^ [AJ "^'^^ [A,BJ ^ [BJ ' 



If, for instance, the concentrations of the initial sub- 

 stances, Ai and A,,, are in the ratio 2 : 1, and if the concen- 

 trations of Bi and B,, are identical respectively to those of 

 Ai and A,,, i.e., are also in the ratio 2: 1, a time will come 

 at which the ratio of the concentrations of the enantio- 

 morphic products, AjB, and A^B,,, will be the product of 



2 X 2 

 the ratios, tttTj that is, 4 : 1. If the reaction is inter- 

 rupted at that time, the optical purity of the transformed 

 material will be increased. (It is certain that, simultan- 



