Theoretical study of hypericin

Electronic properties and phototoxic reactions of the hypericin molecule are explored by the use of density functional theory, integral equation formalism polarised continuum model (to include solvent effects) and a time-dependent formalism for the study of singlet and triplet excited states. Our structural and vibrational data are in very good agreement with previous calculated and experimental results. The results suggest a hypericin (triplet state) reduction and subsequent electron transfer from the drug to molecular oxygen in aqueous solution. The most probable source of singlet molecular oxygen is a transfer of triplet excitation energy from hypericin to molecular oxygen. Direct radiation induced electron transfer between hypericin and oxygen is also explored, as well as the effect of triplet excitation on hypericin auto ionization reactions. (c) 2004 Elsevier B.V. All rights reserved.