Soranjidiol as a photosensitizer: Mechanistic insights into its photochemistry and photoinduced tautomerization

Abstract

This study employs computational chemistry to evaluate soranjidiol as a potential one– and two–photon photosensitizer in photodynamic therapy. Using density functional theory, its time–dependent counterpart, and molecular dynamics, the photophysical properties, phototoxicity mechanisms, and DNA intercalation were studied. The results reveal that neutral and anionic species are present in an approximate ratio of 57:43. The main one–photon absorption peaks are found in the blue–green region (446.4 nm and 564.3 nm, respectively) and correspond to nπ→π* types of excitations. High two–photon absorption cross–sections within the therapeutic window — 67.8 GM for the neutral form and 149.8 GM for the anionic form — strengthen their potential application in two–photon therapy as well. Through the network of reactions, the eventually reached lowest lying triplet have lifetime of 1.39 s (neutral form) and 1.57 μs (anionic form), both effectively harnessing type II photoactivity. In contrast, thermochemical and kinetic analyses underline that type I mechanisms are more relevant for the anionic form, while type III mechanisms dominate the activity of the neutral form. The analysis of 100 ns trajectories highlights that the neutral substance effectively intercalates DNA, while the anion is capable to bind CG–GC base pairs only. In most cases, the absorption profile alters, suggesting greater vulnerability of nucleic acids to photoexcitation after the process. The overall activity of soranjidiol is expected to be lower than that of aloe–emodin, which has been previously studied.