1780 CHEMISTRY OF CHLOEOPLAST PIGMENTS CHAP. 37B 



pearance of fluorescence; the shape of the final absorption spectrum could 

 be explained by assuming the presence of a mixture of Zn pheophytin with 

 unchanged Cu pheophytin. 



In all cases, the "cycle" led to the destruction of a considerable fraction 

 of the pigment (50% in the case of chlorophyll a, 80% in that of phthalo- 

 cyanin). 



The order of increasing velocities of reduction was phthalocyanin, 

 chlorophyll a, chlorophyll 6, Zn pheophytin, pheophytiti. Reoxidation 

 required 1.5-2 hours at room temperature with chlorophyll a, and up to 10 

 hours with phthalocyanin. 



The general conclusion was that Timiriazev's reaction is irreversible 

 because it leads to the replacement of magnesium by zinc, and not because it 

 causes hydrogenation of the vinyl group in ring I (as tentatively suggested in 

 Vol. I, p. 457). 



Godnev (1939) applied Timiriazev's method to protochlorophyll, 

 and found similar results — decoloration with zinc and acetic acid, restora- 

 tion of green color upon admission of air. Marked differences between 

 the absorption spectra before and after the experiment were noted by 

 Godnev and Kalishevish (1944). 



The experiments of Linschitz and co-workers on 'photochemical oxida- 

 tion, and of Krasnovsky and co-workers on photochemical reduction of 

 chlorophyll and its analogues, and the reversals of these reactions in the 

 dark, have been described in chaptei- 35. 



The abnormal position of chlorophyll a baud in piperidine was noted on 

 p. 642. More recent studies (Weigl and Livingston 1952; Holt, unpub- 

 lished) showed that this band shift is caused by an irreversible reaction of 

 the pigment ^\dth this strongly basic solvent. Similar reactions occur 

 with other strong bases, e. g., parabenzoyl amine (cf. Chapter 37C, section 

 2a). A peculiar behavior was noted by Freed and Saucier (1954) also 

 when chlorophyll b was dissolved in a solvent containing a secondary 

 amine (e. g., diisopropylamine). At — 188° C. this solution showed a sharp 

 double band (430 and 480 m/x) in place of the single band (at 450 m/x) 

 which characterizes chlorophyll b solutions at room temperature; in other 

 solvents only a broad absorption at 450-480 m^ appeared at low tempera- 

 tures, indicating the formation of solvates. Upon warming of the solution 

 of diisopropylamine, an irreversible transformation of chlorophyll b took 

 place. 



Weller and Li^'ingston (1954) pointed out that a clea^'age of i-ing 

 V by amines was observed in 1936 by Fischer and Gobel in methyl pheo- 

 phorbide, and that the product was identified by them as chlorin-6-acet- 

 amide. The bond between the C-atoms 9 and 10 is broken in this reaction, 

 the H-atom being added in position 10 and the amide residue in position 9. 



