474 



S. S. Brody and M. Brody 



cells, none of the Z x Z matrices vanished completely at either temperature. 

 For some of the experiments made at room temperature, all the possible 

 3x3 matrices vanished - but for other experiments at room temperature 

 there were 3x3 matrices which did not vanish. It remains to be seen under 

 which conditions only two emission bands are possible at room temperature. 

 Since, with the experiments made at 77°K, none of the 3x3 matrices 

 vanished completely, there exist more than Z fluorescent components at this 

 temperature. Although our preliminary experiments indicate that all the 

 possible 4x4 matrices vanish completely at both temperatures (implying the 

 existance of no more than three emission bands) we wish to re-confirm these 

 data. 



One of the three fluorescing components corresponds to the chlorophyll 

 monomer. If one of the other bands corresponds to a dimer, then the third 

 remaining band would have to be a tetramer - since our calculations (in 

 section III -C) indicate that the chlorophyll aggregate increases until it attains 

 an effective size of 3.8 chlorophyll molecules. We must assume, therefore, 

 that either a trimer exists - but is nonfluorescent, or that it does not exist - 

 the formation of larger aggregates involving condensation of dinners to form 

 tetramers. 



E. Low Temperature Emission Spectroscopy of Dilute Chlorophyll Solutions 



Low -temperature emission spectroscopy of dilute solutions of specially 

 prepared chlorophyll a reveals the presence of three bands(l 1 , 61 ). In Fig. 18 

 curve II, may be seen the emission spectrum of this chlorophyll, 10" M in 

 acetone, excited with blue light (436 m|j.); in addition to the anticipated maxima 

 at 671 and 7Z5 mp., there is another band with maximum at 698 m|j.. At room 

 temperature this new band is not observed, and the emission spectrum is 

 similar to others previously reported for chlorophyll a (19). 



We have found that crystalline chlorophyll a, prepared according to 

 either the method of Jacobs, Vatter and Holt (35), or Anderson and Calvin (Z ) 

 yields upon excitation only two emission bands at 77°K. (See curve I in 

 Fig. 18). The chlorophyll with which we have observed the additional band 

 is obtained by washing the crystalline chlorophyll-prepared by either of the 

 above methods - exhaustively with petroleum ether. Preliminary measure- 

 ments of the emission lifetime of the new band show it to be shorter than 

 10 sec. 



There are no appreciable differences that one can observe at room temper- 

 ature in the absorption spectra or extinction coefficients of the chlorophyll 

 preparations which do and do not show emission at 698 m(j.. This third band 

 with maximum at about 698 mfj, has been observed in the following solvents 

 at 77°K: acetone, benzene, ethanol, ethyl ether, and pyridine. At this point 

 it might be well to recall the third emission band seen in young Chlorella , 

 at 77'-'K (See Fig. 4)', its maximum at 697 mp. (uncorrected) is close to the 



