title: Enhancing intersystem crossing in phenotiazinium dyes by intercalation into DNA.
abstract: Phenothiazinium dyes are used as photosensitizers in photodynamic therapy. Their mode of action is related to the generation of triplet excited states by intersystem crossing. Therefore, rationalizing the factors that influence intersystem crossing is crucial to improve the efficacy of photodynamic therapy. Here we employ quantum mechanics/molecular mechanics calculations to investigate the effect of aqueous and nucleic acid environments on the intersystem crossing mechanism in methylene blue. We find that the mechanism by which the triplet states are generated depends strongly on the environment. While intersystem crossing in water is mediated exclusively by vibronic spin-orbit coupling, it is enhanced in DNA due to a second pathway driven by electronic spin-orbit coupling. Competing charge-transfer processes, which are also possible in the presence of DNA, can therefore be suppressed by a suitable structural functionalization, thereby increasing the efficacy of photodynamic therapy.
authors: Institute of Theoretical Chemistry, University of Vienna, Währinger Strasse 17, 1090 Wien (Austria) http://www.theochem.univie.ac.at. nogueira.perez.juanjose@univie.ac.at.
authors: Juan J
authors: JJ
authors: Nogueira
authors: Markus
authors: M
authors: Oppel
authors: Leticia
authors: L
authors: González
mesh_terms: D004396:Coloring Agents / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D007364:Intercalating Agents / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D004396:Coloring Agents; D007364:Intercalating Agents; D004247:DNA
keywords: QM/MM; hydrogen bonds; intersystem crossing; photochemistry; photodynamic therapy