188 LIGHT AND LIFE 



agent or a transition metal is present. The second observation which 

 seemed to many authors to demand a "regeneration" of luminol 

 was first made by Albrecht (1) . Albrecht, and later workers (18, 27), 

 showed that the fluorescence spectrum of limiinol (in acidic solu- 

 tions) was a rather good match for the chemiluminescence spectrum 

 (in basic solutions!) . This match of the spectra does not warrant 

 identification of linninol as the light emitter, however. The cor- 

 respondence which was observed holds only when the fluorescence is 

 measured in neutral or acidic solutions. In the basic solutions used 

 for chemiluminescence, luminol exists only as the mono anion, and 

 the fluorescence efficiency of this species is essentially zero (22, 23) . 

 That is, there is no luminol as such in the chemiluminescent sys- 

 tems. A far better case can be made for the 3-aminophthalate ion as 

 the light emitter. There is not only a close match between the fluores- 

 cence spectrum of this compound and the chemiluminescence spec- 

 trum of luminol, but in addition, the pH-fluorescence efficiency 

 profile is essentially the same as the pH-chemiluminescence profile 

 (22). 



A number of detailed mechanisms have been projDosed for the 

 luminol chemiluminescence by various workers (1, 5, 8, 18, 26) . 

 In general, the mechanisms are variations of two types, based on the 

 key intermediates XV and XVII (Fig. 4) . The evidence for the 

 peroxide XV consisted solely of an elementary analysis (8) . It has been 

 suggested that XV is in reality a salt of limiinol in which the metal 

 ion is solvated by hydrogen peroxide (6b) (i.e., structure XVI) . Our 

 evidence is in agreement with this view, since the infrared spectrum 

 of this salt (M z= barium) , prepared according to the directions 

 of Drew (8) , showed the normal carbonyl frequencies of the simple 

 salts of luminol. If structure XV were correct, no absorption would 

 have occurred in this region of the spectrum. Also, the addition of 

 peroxide ion or oxygen to form compounds such as XV has little 

 or no analogy in organic chemistry. 



-H 



t. ^'^^°^'' 



NH-, O-H NH^ O 



"2 



XV XVI XVII 



Fig. 4. 



