The Structure of Porphyrin a, Cryptoporphyrin a and Chlorin di^ 355 



mesoporphyrin, that of the hydriodic acid reaction monoethyl-monohydroxy- 

 ethyl-deuteroporphyrin, porphyrins which are also obtained from proto- 

 porphyrin under these conditions. This evidence would not exclude that 

 chlorin a, is protochlorin with two vinyl side chains, perhaps with an 

 additional large alkyl group. The presence of one vinyl group, possibly two, 

 can be demonstrated by diazoacetic ester addition; the shift of the main 

 absorption band in the red to the blue was like that of phaeophorbide a 

 (with one vinyl), but also like that of protoporphyrin with two. The position 

 of the absorption bands of chlorin a, resemble those of pyrrochlorin (with one 

 vinyl) rather than those of mesochlorin or mesopyrrochlorin (with none), 

 except that the whole absorption spectrum is somewhat contracted. 



However, the presence of an a-hydroxyethyl (or a-hydroxyalkyl) group is 

 indicated by the low Rp values of chlorin a^ in kerosene-chloroform (0-32) 

 and kerosene-propanol (0-55) compared with those of mesochlorin (0-89 and 

 0-88) and by the fact that acetylation in pyridine-acetic anhydride increased 

 the Rp. It is therefore most hkely that chlorin a^ is a monovinyl-mono- 

 hydroxyethyl-deuterochlorin, differing from protochlorin by the hydration 

 of one vinyl group as well as by addition of a large alkyl group to one or the 

 other (or both) of these side chains. 



Table 6. Absorption bands of haem a^ compounds and of chlorin oj 

 (Barrett, 1956) 



The absorption maxima of haem a.^, chlorin a.^ and some of their compounds 

 are given in Table 6. The ferrous cyanide compound of haem a.^ is more 

 stable than its very unstable pyridine haemochrome. Since the position of the 

 band of cytochrome a^ from Acetohacter suboxidans (Chin, 1952) coincides 

 with that of pyridine haemochrome a^, cytochrome a^ may stand to cytochrome 

 flg in the same relation as cytochrome a^ to cytochrome a, but the haemochrome 

 of the Acetobacter peroxidans cytochrome has not yet been studied. 



Being an iron-dihydroporphyrin complex, haem a^ is an interesting 

 intermediate between chlorophylls and haem compounds, a new type of 



