The mechanisms of ROS-photogeneration by berberine, a natural isoquinoline alkaloid

Abstract

The reactive oxygen species (ROS)-photogenerating mechanisms of berberine (BER) have been elucidated based on the time-dependent density functional theory calculated triplet excited ( T 1) state characters in explicit solvent models. The lowest triplet excitation energy of BER is obtained for the first time. Mechanistic analysis reveals the strong dependence of 1O 2 and O 2 · − generation on the solvent polarity. Through direct energy transfer pathway from T 1 state BER to 3O 2, 1O 2 can be photogenerated both in benzene and ethanol. Nevertheless, O 2 · − can be given birth to only in ethanol through two pathways, i.e., direct electron transfer from T 1 state BER and electron transfer from BER ·− (formed through autoionization reactions) to 3O 2. The findings also provide clues to explaining the much higher 1O 2-yield of BER in nonpolar than in polar solvents.