1516 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



kcal of free energy must be accumulated, which is 40% of the energy 

 of a red quantum, or 20% of the energy of two such quanta. 



Later, Krasnovsky and Voynovskaya (1949) observed that the same 

 reaction of ascorbic acid with safranin T can be obtained also with proto- 

 chlorophyll (from pumpkin seeds) as sensitizer. 



Krasnovsky and Brin (1949) described experiments which they inter- 

 preted as indicating the sensitized reduction of the oxidized form of co- 



4 8 12 16 20 



TIME, minutes 



Fig. 35.7. Bleaching of chlorophyll (a + b)hy ascorbic acid in red light and its 

 regeneration by riboflavin (5), safranin T (4), oxygen (2), DPN (3), and without 

 added oxidant (1) (after Krasnovsky and Brin 1949). 



enzyme I (dipyridine nucleotide, DPN) by ascorbic acid, with chlorophyll 

 as sensitizer. Here, again, aqueous pyridine must be used as solvent. 



In these experiments, 1 cc. of a 5 X 10"^ M solution of DPN (a 60% 

 pure preparation) and 10 mg, crystalline ascorbic acid were added to 5 cc. 

 of a 7 X 10 ~^ M solution of chlorophyll (a + h) in a Thunberg tube. After 

 evacuation by an oil pump, the spectrum was measured by means of a 

 Beckman spectrophotometer. The tube was then illuminated for 3 min. 

 at 8° C. and the spectrum re-examined. Comparison of this spectrum after 



