Spectral Properties of Chlorophyllin a

The infrared and visible absorption spectra and the fluorescence spectrum of chlorophyllin a were determined and compared with those of chlorophyll a. The infrared spectrum showed the absence of a carbonyl group except when chlorophyllin b was present as an impurity. This provides the basis of a convenient method of analysis of the chlorophyll b content of a given chlorophyll preparation. Since the cyclopentanone ring is absent in chlorophyllin, the observed infrared bands help to clarify those observed in the case of chlorophyll. The visible absorption spectrum of chlorophyllin a has features in common with that of chlorophyll a. In particular, the formation of colloidal aggregates is shown by the appearance of an absorption band at 735 mμ just as is observed for microcrystals of chlorophyll a. The appearance of a pronounced absorption maximum at 688 attributed to dimer formation is analogous to that observed by difference spectra in the case of concentrated solutions of chlorophyll a. In stretched polymer films chlorophyllin a and chlorophyll a exhibit a positive dichroism which is greater for the blue absorption maximum than for the red. The fluorescence spectrum of chlorophyllin a is markedly dependent on the wave length of excitation.