PHOTOSENSITIZED OXIDATION OF TYROSINE DERIVATIVES IN PRESENCE OF ALGINATE .1. REACTION UNDER HOMOGENEOUS CONDITIONS

The rates of dye-sensitized photooxidation of tyrosine and tyramine to brown products were compared in the presence and the absence of the anionic polysaccharide, alginate. The polyelectrolyte did not affect the reaction when it was sensitized by monochromatic light absorbed mainly by the monomeric form of the dye. In white light the rate of oxidation sensitized by thionine or phenosafranine was increased in the presence of alginate for tyramine but not for tyrosine. In the thionine sensitized reaction, the ratio of brown product formation to tyramine consumption increased with decreasing wavelength of monochromatic excitation. These and other phenomena are believed related to the formation of complexes between the dyes and some of the oxidation products, and to association between some of the oxidation products and alginate. A mechanism for oxidation of phenols is proposed, based on the addition of O2 (1.DELTA.g) across a double bond ortho to the phenolate O. Dyes bind to alginate in monomeric and in aggregated forms: only the monomeric forms of thiazine dyes are photochemically active, but both the monomeric and the aggregated forms of crystal violet are active.