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 high two-photon absorption cross-section values within the therapeutic window and significant transition probabilities, making it an efficient two-photon photosensitizer. Excited-state dynamics analysis revealed a triplet state quantum yield of 0.51 for the neutral species and around 0.88–0.89 for the anionic species, with triplet lifetimes of 26.0 s and 0.66 s, respectively. Both species exhibit similar Type I photoreactivity, but the neutral form more effectively oxidizes biomolecules during Type III photoreactivity. Additionally, the neutral species intercalates into DNA, particularly 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.