Photooxidative Bleaching of Chlorophyllin

Chlorophyllin, a water-soluble, copper-containing porphyrin, can be bleached rapidly in the light or slowly in the dark in a reaction which is oxygen dependent. Both the photo and the dark bleaching reactions are temperature dependent. Cyclic voltammetry measurements show that the copper in the bleached and nonbleached state remains in the +2 redox state and could be readily reduced. This would imply that there is no net oxidative change to the copper during the bleaching process. FT-IR absorption spectroscopy showed vibrations characteristic of a vinyl functionality disappeared upon bleaching. Aqueous solutions of chlorophyllin were not dialyzable through dialysis tubing of molecular weight cut-off, 6000-8000 molecular weight, indicative of an aggregate chlorophyllin micelle. Analysis of products by high performance liquid chromatography showed that the chlorophyllin mixture was more complex than originally anticipated and that two components were lost from the mixture upon photobleaching. One compound that is preferentially lost upon photobleaching has been identified by mass spectral analysis as Cu(II) chlorin e6.