Characterizing some photophysical, photochemical and photobiological properties of photo sensitizing anthraquinones

Some photophysical, photochemical and photobiological properties of nine anthraquinones (AQs) isolated from a phototoxic plant, Heterophyllaea pustulata, were studied. The photosensitized generation of superoxide anion radical (O-2(center dot-)) and singlet molecular oxygen (O-1(2)) by three of the nine AQs, namely heterophylline, pustuline and 5,5'-bisoranjidiol was evaluated. Whereas the O-2(center dot-) production (Type I photosensitization mechanism) was examined in vitro using human leukocyte suspensions and measuring the reduction of NBT, the O-1(2) generation (Type II photosensitization mechanism) was studied in an organic solvent through the measurement of the quantum yield of O-1(2) (phi(Delta)). It was established that these three AQs possess photosensitizing properties as do the other AQ derivatives present in this vegetable species, soranjidiol, soranjidiol 1-methyl ether, rubiadin, rubiadin 1-methyl ether, dammacanthal and damnacanthol, acting both by Type I and Type II mechanisms. Furthermore, nordamnacanthal, a species synthesized in the laboratory from one of the natural AQs, showed the highest production of O-1(2). The ability of natural AQs to deactivate the O-1(2) generated during the photosensitization process as well as their fluorescence (as competitive mechanisms to the generation of ROS) was studied. (C) 2006 Elsevier B.V. All rights reserved.