Binding of ³O₂ and ¹O₂ to dyes used in photodynamic therapy in gas phase and aqueous media

Abstract

Density functional theory (DFT) was employed at the B3LYP/6-31ϩG* level to study complexes of 1 O 2 and 3 O 2 with the dye molecules proflavine, methylene blue, and acridine orange, which are useful in photodynamic therapy. It was found that the most stable complex between 1 O 2 and proflavine are formed when 1 O 2 is located above the central ring, while the most stable complex between 1 O 2 and methylene blue is formed when 1 O 2 is located above the molecular plane, but not above any of the rings, near the sulfur atom.1 O 2 can make a stable complex with acridine orange, as it is located above the outer ring of the dye. The binding energies of the complexes of 1 O 2 with all three dyes are enhanced considerably in going from gas phase to aqueous media. The complexes of 3 O 2 with the dyes will be unstable in all cases, while those of 1 O 2 with the same will be quite stable and will not be dissociated due to thermal fluctuations at room temperature. In the complexes of 1 O 2 and 3 O 2 with the dyes, charge transfer occurs from the dyes to the O 2 moiety, the amount of charge transfer being much more to 1 O 2 than to 3 O 2 in each case.