Binding of {{\textless}SUP{\textgreater}{\textless}FONT} {SIZE='-1'{\textgreater}3{\textless}/FONT{\textgreater}{\textless}/SUP{\textgreater}O{\textless}SUB{\textgreater}{\textless}FONT} {SIZE='-1'{\textgreater}2{\textless}/FONT{\textgreater}{\textless}/S

Abstract

Density functional theory {(DFT)} was employed at the {B3LYP/6-31+G*}level to study complexes of {1O2} and {3O2} with the dye moleculesproflavine, methylene blue, and acridine orange, which are usefulin photodynamic therapy. It was found that the most stable complexbetween {1O2} and proflavine are formed when {1O2} is located abovethe central ring, while the most stable complex between {1O2} andmethylene blue is formed when {1O2} is located above the molecularplane, but not above any of the rings, near the sulfur atom. {1O2}can make a stable complex with acridine orange, as it is locatedabove the outer ring of the dye. The binding energies of the complexesof {1O2} with all three dyes are enhanced considerably in going fromgas phase to aqueous media. The complexes of {3O2} with the dyeswill be unstable in all cases, while those of {1O2} with the samewill be quite stable and will not be dissociated due to thermal fluctuationsat room temperature. In the complexes of {1O2} and {3O2} with thedyes, charge transfer occurs from the dyes to the O2 moiety, theamount of charge transfer being much more to {1O2} than to {3O2}in each case. � 2006 Wiley Periodicals, Inc. Int J Quantum Chem,2006