SPECTRUM AND STRUCTURE OF PORPHIN DERIVATIVES 



619 



alcoholic extracts from ChJorcUa (green alga), Chlorobium limicola (green 

 bacteria) and Oscillatoria (blue alga). The difference between the curves 

 1 and 3 can be attributed to the absence of chlorophyll h in blue algae; 

 while the larger difference between the curves 3 and 2 indicates a chemical 

 distinction between chlorophyll a and bacterioviridin. The absorption 

 peak of the latter pigment in ethanol lies at 668 m/x, while that of the former 

 one is situated at about 662 m/x. 



The absorption spectrum of protochlorophyU (from squash seeds) was 

 described by Noack and Kiessling (1929, 1930, 1931) as well as by Rudolph 

 (1933), Seybold (1937) and Koski and Smith (1948). The long-wave 

 bands are listed in Table 21.IV; the whole spectrum is shown in figure 

 21.8. 



Table 21. IV 

 Absorption Bands of Protochlorophyll 



3. Relation between Absorption Spectrum and Molecular Structure 



of Porphin Derivatives 



To understand the role of chlorophyll in photosynthesis, it would be 

 important to have a detailed knowledge of the nature of the lowest excited 

 state of the chlorophyll molecule, since sensitization must be due to the 

 interaction of chlorophyll in this excited state with the primary sensitiza- 

 tion substrate or substrates (e. g., with the C02-acceptor complex {CO2}, 

 or with the oxidant {H2O} ; cf. Vol. I, chapter 7). If this interaction is in 

 the nature of a reversible oxidation-reduction (which is probable) analysis 

 of the nature of the excited state may permit conclusions as to the type of 

 oxidations (or reductions) most likely to be involved. Theoretical analy- 

 sis of porphin spectra was initiated too late for use in the following discus- 

 sion, which is based on empirical relationships only. The papers by Kuhn 

 (1949), Simpson (1949), and Piatt and co-workers (1950) will be summar- 

 ized in the last chapter. 



