(;. WEBER 



85 



OCCURRENCE OF PEAKS IN 

 ALKALINE QUENCHING CURVES 



0.6 r 



RYPTOPHAN 



TRYPTAMINE 



pH 



Fig. 2. Elictl ol 1>V\ ii|)oii I he lliioicsceiuc ol iiululc and phenol (lcri\;Ui\cs 



(alkaline range). 



it is possible to observe quenching ot the fluorescence of indole and 

 phenol by the addition of such simple substances as acetic acid and 

 hydroxylamine (Fig. 3), and the interpretation of their quenching 

 effects seems, in most cases at least, to be that of a straightforward 

 proton transfer to the excited ring. Finally, tryptophan and indole 

 show quenching of the fluorescence in alkaline solution (NaOH, 

 0.01 M and higher) . In accordance with ideas developed by Boaz 

 and Rollefson (1) and by Forster (6), we have looked upon this as 

 a reaction of the excited molecule with hydroxyl ion to yield the N- 

 compound, which undergoes a radiationless transition to the groimd 

 state before recombining with water to regenerate the uncharged in- 

 dole and a hydroxyl ion. The postulated series of reactions is as 

 follows: 



