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

The reactive oxygen species (ROS)-photogenerating mechanisms of berberine (BER) have been elucidated based on the time-dependent density functional theory calculated triplet excited (T1) 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 1O2 and O 2 · − generation on the solvent polarity. Through direct energy transfer pathway from T1 state BER to 3O2, 1O2 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 T1 state BER and electron transfer from BER·− (formed through autoionization reactions) to 3O2. The findings also provide clues to explaining the much higher 1O2-yield of BER in nonpolar than in polar solvents.