1820 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



Table 37C.II 



Red Absorption Band of Chlorophyll Derivatives in Different States of Ag- 

 gregation (after Jacobs) 



Corrected for scattering. 



Table 37C.III 

 Optical Density of Single Monolayers (at Red Peak) 



Pigment 



Et chlorophyllide a 



Me bacteriochlorophyllide . . . . 



Chlorophyll a (Ca"*""^ present). 



(noCa ++) 



log (lo/I) 



gas 



Shift 

 monolayer 



1000 cm.-i 



of layers built and arranged as shown in fig. 49 (Vol. I). Fig. 37B.9 rep- 

 resents a model of this structure. Monolayers of chlorophyllide on water 

 have, according to Hanson, the same structure as the layers in the crystal, 

 with the plane of the porphin ring inclined by 55° to the water-air 

 interface^ — perhaps, because of the affinity of the magnesium atom for 

 water. The surface density is one molecule per 0.69 mju^. 



In colloidal chlorophyll rnonolayers, each molecule occupies 1.06 m/x^. 

 The additional 0.37 m^u^ (compared to the surface requirement of ethyl 

 chlorophyllide) is needed to accommodate the phytol chain. More pre- 

 cisely, the presence of phytol prevents the orderly arrangement charac- 

 teristic of chlorophyllide monolayers, and leaves the pigment molecules 

 more or less randomly oriented — except that their symmetry axes seem 

 to prefer the orientation parallel to the water surface also in this "com- 

 pressed gas type" monolayer; this is indicated by the fact that, as shown 



