Protoporphyrins, photooxidation

Finally superoxide radicals can also be generated photochemically in chloroplasts in the presence of ascorbate or of paraquat. The formation was demonstrated by spin trapping on illumination of spinach chloroplasts in the presence of oxygen and paraquat Superoxide radicals are formed, moreover, in the near-ultraviolet photooxidation of tryptophan, as indicated by the increase of the HjO production in the presence of SOD and on irradiation in aerated solutions of protoporphyrin at 400 nm and of melanin with light of 320—600nmas shown by spintrapping. 

These studies also indicate that singlet oxygen generated in either the aqueous phase or in a micelle can diffuse in and out of micelles easily. Therefore, a reaction of singlet oxygen can occur in a micelle other than the one in which it was generated. In the photooxidation of protoporphyrin IX, where the sensitizer is also... 

Berthomieu C, Boussac A, Mantele W, Breton J, Nabedryk E. (1992) Molecular changes following oxidoreduction of cytochrome b559 characterized by Fourier transform infrared difference spectroscopy and electron paramagnetic resonance Photooxidation in photosystem II and electrochemistry of isolated cytochrome b559 and iron protoporphyrin IX-bisimidazole model compounds. Biochemistry 31 11460-11471. 

Bifenox, fluoroglycofen-ethyl, HC-252, lactofen, and oxyfluorfen have analogous structures and modes of action. The carboxyl group may be replaced by an ether group or an ester, and many other herbicides with related structures have been developed. Tetrapyrrol and protoporphyrin accumulate, act as photosensitizers, and cause photooxidation and necrosis. They are contact herbicides and are more active in strong sunlight. 

Krieg, M. and Whitten, D.G. (1984a) Self-sensitized photo-oxidation of protoporphyrin IX and related porphyrins in erythrocyte ghosts and microemulsions a novel photooxidation pathway involving singlet oxygen, J. Photochem., 25 235-252. 

Trytek M, Lipke A, Majdan M, Pisarek S, Gryko D (2013) Homo- and heterogeneous a-pinene photooxidation using a protoporphyrin-derived amide. Eur J Org Chem 9 1653-1658... 

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