Characterizing some photophysical, photochemical and photobiological properties of photosensitizing anthraquinones

Abstract

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 −) and singlet molecular oxygen ( 1O 2) by three of the nine AQs, namely heterophylline, pustuline and 5,5′-bisoranjidiol was evaluated. Whereas the O 2 − production (Type I photosensitization mechanism) was examined in vitro using human leukocyte suspensions and measuring the reduction of NBT, the 1O 2 generation (Type II photosensitization mechanism) was studied in an organic solvent through the measurement of the quantum yield of 1O 2 ( ϕ Δ). 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, damnacanthal 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 1O 2. The ability of natural AQs to deactivate the 1O 2 generated during the photosensitization process as well as their fluorescence (as competitive mechanisms to the generation of ROS) was studied.