On the Photosensitizing Properties of Aloe-Emodin in Photodynamic Therapy: Insights from the Molecular Modeling

The photosensitizing properties of aloe-emodin were investigated under physiological conditions using computational chemistry tools. The neutral and monoanionic species were found to coexist in a 98:2 ratio, with dissociation causing a redshift in the absorption spectrum. Aloe-emodin exhibits a two-photon absorption cross-section not smaller than 77 GM and high transition probabilities, making it an efficient photosensitizer. Excited-state dynamics analysis revealed a triplet state quantum yield of 0.51 for the neutral species and 0.79 for the anionic species (0.29 without S2 involvement), with triplet lifetimes of 47.1 s and 0.77 s, respectively. Both species show similar type I photoreactivity, but the neutral form oxidizes biomolecules more effectively during type III photoreactivity. The neutral species also intercalates DNA, especially at the AT–TA site, inducing absorption changes and structural nucleotide rearrangements. The computational results align closely with available experimental data, further confirming their reliability.