MEASUREMENTS OF ABSORPTION SPECTRA OF PIGMENTS 



1805 



of Strain (c/. chapter 37B, section 4), that "allomerized chlorophyll" is 

 not a single compound, but can be separated chromatographically into 

 at least three fractions. Fig. 37C.9 shows the visible absorption spectra, 

 in ether, of the three fractions of allomerized ethyl chlorophyllide a. The 

 most abundant one of them (No. 2) has the spectrum shown in fig. 21.4A; 

 another (No. 3) a spectrum very similar to that of chlorophyllide itself; 

 the third one (No. 1) an absorption band further to the red, near 680 mju. 

 Evstigneev and Gavrilova (1953) made the first quantitative study of 

 the absorption spectrum of photochemically reduced chlorophijUs a and b. 



600 



500 



400 



Fig. 37C.10. Absorption spectra of 

 reduced chlorophyll a (after Evstigneev 

 and Gavrilova 1953). Curve 1: before 

 reduction. Curve 2: after reduction. 

 Curves 3, 4: same after 30 and 160 

 min. of reoxidation in darkness with- 

 out air. Curves 5, 6: same after 100 

 additional min. and 1 day in air. Cui"ve 7: 

 absorption curve of reduced pheophytin 

 a (larger scale). 



700 



600 



500 400 



XiTi m)x. 



Fig. 37C.11. Absorption spectra of 

 reduced chlorophyll b (after Evstigneev 

 and Gavrilova 1953). Curve 1: before 

 reduction. Curve 2: after reduction. 

 Curves 3 and 4: different stages of re- 

 oxidation, 25 min. in darkness without 

 air and same plus 60 min. in air. Curve 

 5: shift of red peak after 24 hr. 



As described in chapter 35 (part A), chlorophyll can be reduced by illumi- 

 nation in the presence of ascorbic acid in basic medium ("Krasnovsky 

 reaction"). The product has been desciibed as "pink," with an ab- 

 sorption band at about 530 m^ (fig. 35.3); but its rapid re-oxidation after 

 the cessation of illumination had prevented a quantitative study of the 

 spectrum. Evstigneev and Gavrilova found that if the reaction is carried 

 out in toluene (instead of pyridine), and with phenyl hydrazine serving as 

 both the reductant and the basic ingredient, the back reaction is slowed 

 down so much that a comparatively cojicentrated chlorophyll solution 

 can be completely reduced, and the absorption spectrum of the product 

 can be measured before re-oxidation occurs. Figs. 37C.10 and 11 show the 

 results for the chlorophylls a and 6, respectively. The different behavior 



