SPECTRUM AND STRUCTURE OF rORPITIN DERIVATIVES 



020 



spect to conjugation, the role of nucleus I is similar to that of nucleus III — 

 and this points to structure B as the tme structure of chlorophyll, in prefer- 

 ence to structure A, advocated by Fischer (page 443). (As mentioned on 

 page 444, Vol. I, structure B also has the advantage of providing a direct 

 link to bacteriochlorophyll.) 



If this interpretation of the spectroscopic data is correct, it means 

 that the introduction of a carbonyl group has a stronger effect on the spec- 



7.0 



60 



Dihydropheophorbide 

 Pheoporphyrin 05 



30000 25000 20000 



60 



5.0 



4.0 



3.0 



6.0 



Chlorophyll a 

 Pheophorbide a 



30000 25000 20000 ^' 



_i L 



■ [ ■ ■ ■ I ■ • r • I ■ r ■! ■ I' 

 350 400 450 500 600 



WAVE LENGTH, m/i 



4.0- 



' ' 'I ' ■ ■ I ■ ■ I' ■ I ■ r 'I — r- 



350 400 450 500 600 

 WAVE LENGTH, m^ 



Fig. 2 1.1 9 A. Effect of porphin -> chlo- 

 rin transition on the visible and ultraviolet 

 spectrum (after Hagenbach, Auerbacher 

 and Wiedemann 1936). 



3.0 



Chlorophyll b 

 Pheophorbide b 



30000 

 __i i_ 



25000 20000 



-I I ■ ' ■ ■ 1 ■ ■ ' . ' * 



-1 1 1 1 • ]• '\ • \ 



350 400 450 500 600 

 WAVE LENGTH, m^ 



Fig. 21.19B. Extinction curves of 

 chlorophyll and pheophorbides in the 

 visible and near ultraviolet (after 

 Hagenbach, Auerbacher and Wiede- 

 mann 1936). 



trum if this group comes into conjugation with a C=^C bond, which is 

 merely in one-sided conjugation with the "aromatic" system, than if it is 

 attached directly to the latter system. 



Introduction of magnesium, into the molecule (transition from phorbin 

 to phyllin) has the effect of enhancing further the main red absorption 

 band, and of weakening the bands in the green, as illustrated by figure 21.18. 

 The result is the beautiful pure green color of chlorophyll — so different 

 from the dull olive-green of pheophytin. 



While the porphyrins, chlorins, phorbins and rhodins differ in their 

 absorption spectra in the green, yellow, orange and red, their spectra in the 



