There is a major need for light-activated materials for the release of sensitizers and drugs. Considering the success of chiral columns for the separation of enantiomer drugs, we synthesized an S,S-chiral linker system covalently attached to silica with a sensitizer ethene near the silica surface. First, the silica surface was modified to be aromatic rich, by replacing 70% of the surface groups with (3-phenoxypropyl)silane. We then synthesized a 3-component conjugate [chlorin sensitizer, S,S-chiral cyclohexane and ethene building blocks] in 5 steps with a 13% yield, and covalently bound the conjugate to the (3-phenoxypropyl)silane-coated silica surface. We hypothesized that the chiral linker would increase exposure of the ethene site for enhanced O -based sensitizer release. However, the chiral linker caused the sensitizer conjugate to adopt a U shape due to favored 1,2-diaxial substituent orientation; resulting in a reduced efficiency of surface loading. Further accentuating the U shape was π-π stacking between the (3-phenoxypropyl)silane and sensitizer. Semiempirical calculations and singlet oxygen luminescence data provided deeper insight into the sensitizer's orientation and release. This study has lead to insight on modifications of surfaces for drug photorelease and can help lead to the development of miniaturized photodynamic devices.
Intralipid is a lipid emulsion used in photodynamic therapy (PDT) for its light scattering and tissue-simulating properties. The purpose of this study is to determine whether or not Intralipid undergoes photooxidation, and we have carried out an Intralipid peroxide trapping study using a series of phosphines [2'-dicyclohexylphosphino-2,6-dimethoxy-1,1'-biphenyl-3-sulfonate, 3-(diphenylphosphino)benzenesulfonate, triphenylphosphine-3,3',3''-trisulfonate and triphenylphosphine]. Our new findings are as follows: (1) An oxygen atom is transferred from Intralipid peroxide to the phosphine traps in the dark, after the photooxidation of Intralipid. 3-(Diphenylphosphino)benzenesulfonate is the most suitable trap in the series owing to a balance of nucleophilicity and water solubility. (2) Phosphine trapping and monitoring by P NMR are effective in quantifying the peroxides in H O. An advantage of the technique is that peroxides are detected in H O; deuterated NMR solvents are not required. (3) The percent yield of the peroxides increased linearly with the increase in fluence from 45 to 180 J cm based on our trapping experiments. (4) The photooxidation yields quantitated by the phosphines and P NMR are supported by the direct H NMR detection using deuterated NMR solvents. These data provide the first steps in the development of Intralipid peroxide quantitation after PDT using phosphine trapping and P NMR spectroscopy.
Photodynamic treatment is often thought to produce reactive oxygen species (ROS) that directly induce killing; the nomenclature and phrases revolve around such notions of light-dependency. Few studies reference the possible existence of oxidation products formed in secondary reactions, which bear cytotoxicity competitive to their ROS precursors. Here, we highlight the paper by Girotti and Korytowski in this issue of Photochemistry and Photobiology, which does just that. In this paper, they report on cholesterol hydroperoxides, which are formed after photosensitized oxidation and yield cytotoxic mixtures in dark reactions after the light's turned off. Some of the hydroperoxides are transported by protein carriers and damage tissue outside their site of origin. A similar dark cytotoxicity may be anticipated for biological peroxides from in vivo photodynamic therapy.
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