784 



FLUORESCENCE OF PIGMENTS IN VITRO 



CHAP. 23 



clear that oxidants (quinones, diazo dyes, nitro and nitroso compounds, and 

 oxygen) are strong quenchers, while redudants (such as amines) are at best 

 only weak quenchers. Among compounds listed in Table 23. HID, only 

 phenylhydroxyamine showed any measurable quenching at all, at concen- 

 trations up to 0.1 mole/1. See also footnote b to Table 23. HID. 



1.00 j 



0.02 

 [O], mole/liter 



0.04 



P^ig. 23.8. Quenching of fluorescence of chlorophyll a in methanol by different 

 quenchers (after Livingston and Ke, 1949). For convenience, a separate zero point of 

 ordinates is used for each compound. Each curve begins with Ft^/F = 1 . 1 , chloranil ; 2, 

 methyl red; 3, quinone; 4, trinitrotoluene; 5, duroquinone; 6, ?«-dinitrobenzene; 

 7, |8-nitroso-a-naphtho] ; 8, /3-nitrostyrene ; 9, nitric oxide; 10, nitric o.xide; 11, oxy- 

 gen. Dotted lines, empirical; broken lines, eqs. (23.1b-c). 



As shown by figure 23.8, where F^/F is plotted as function of \Q\ for a 

 number of true quenchers, the quenching follows approximately the Stern- 

 Volmer equation (eq. 23.16B), which we have repeatedly used before. (It 

 applies to all cases of competition between a monomolecular process such 

 as fluorescence, and a bimolecular process, such as quenching, by kinetic 

 encounters) : 



(23.1GA) 

 (23.1GB) 



F = /'V(l + k\Q\) or 



F,IF = 1 + A-[Q1 



