Co-Authors:
Rosenthal, I., Department of Food Science, The Volcani Institute, PO Box 6, Bet Dagan, 50250, Israel
Ben-Hur, E., New York Blood Center, 310 E. 67th St, New York, NY, 10021, United States
Abstract:
The presence of molecular oxygen is a determinant in the phototoxicity of phthalocyanines, and photosensitized oxidation is the accepted chemical mechanism for photodynamic action. However, it is difficult to establish whether the process is initiated by a type I electron transfer, or by a type II energy transfer reaction to form singlet oxygen. Usually, the involvement of singlet oxygen in photodamage has been indicated by the inhibition of the biological effect by a competitive physical or chemical singlet oxygen quencher, or by a rate increase in D2O, in which singlet oxygen has a longer lifetime than in H2O. Unfortunately, these techniques are not completely specific for singlet oxygen. Moreover, thermodynamic considerations suggest that photoinduced electron abstraction from appropriate biomaterials could compete with singlet oxygen production under in vivo conditions. This likely source of one electron-oxidized primary radicals, which can provide the precursors of the oxidative damage in phthalocyanine photosensitization, suggests the possibility of modulated toxicity by interaction with chemical additives. Examples of such additives recently studied are ascorbate, tocopherol and quercetin, all of which are natural antioxidants. © 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.
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