1784 



CHEMISTRY OF CHLOKOPLAST PIGMEXTS 



CHAP. 37b 



bacteriochlorophyllide shows no evidence of a three-fold screw axis, sug- 

 gesting that the successive layers may be oriented in parallel (or rotated by 

 90°, instead of by 120°, as in chlorophylHde; compare the shapes of the 

 conjugated ring systems in Fig. 37C.1!). The diffraction pattern of the 



CHLOROPHYLL 



14.8 7.6 



CHLOH)PHniL b 



7.6 4 



MCTERIOCHLOBOPHYLL 



CHLOROPHYLL a (Hanson) 



Fig. 37B.7. X-ray diffraction patterns of microcrystals of chlorophyll a and b and 

 of bacteriochlorophyll (after Jacobs, Vatter and Holt 1954). 



o o 



pheophorbides shows a spacing of 16 A, instead of 12.8 A as in the chloro- 

 phyllides, suggesting that the molecules in each layer may be standing up 

 vertically, instead of being inclined by 55° (16 = 12.8/sin 55°) (Jacobs 

 1954). 



The absorption spectrum of crystalline chlorophyll will be described in 

 Chapter 37C, together with that of the crystalline chlorophyllides (cf. 

 Figs. 37C.16to 18). 



