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We have constructed a fiber optic device that internally flows triplet oxygen and externally produces singlet oxygen, causing a reaction at the (Z)‐1,2‐dialkoxyethene spacer group, freeing a pheophorbide sensitizer upon the fragmentation of a reactive dioxetane intermediate. The device can be operated and sensitizer photorelease observed using absorption and fluorescence spectroscopy. We demonstrate the preference of sensitizer photorelease when the probe tip is in contact with octanol or lipophilic media. A first‐order photocleavage rate constant of 1.13 h−1 was measured in octanol where dye desorption was not accompanied by readsorption. When the probe tip contacts aqueous solution, the photorelease was inefficient because most of the dye adsorbed on the probe tip, even after the covalent ethene spacer bonds have been broken. The observed stability of the free sensitizer in lipophilic media is reasonable even though it is a pyropheophorbide‐a derivative that carries a p‐formylbenzylic alcohol substituent at the carboxylic acid group. In octanol or lipid systems, we found that the dye was not susceptible to hydrolysis to pyropheophorbide‐a, otherwise a pH effect was observed in a binary methanol‐water system (9:1) at pH below 2 or above 8.
A fiber optic device was developed that externally produced 1O2, in turn, freeing sensitizer from the probe tip upon fragmentation of a dioxetane intermediate. The maneuverable probe tip was placed in octanol and water solutions, as well as liposomes. The release of sensitizer was quantitative in octanol solution, but was inefficient in water where the hydrophobic dye remained adsorbed on the probe tip. The photocleaved sensitizer was found to partition into 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine and L‐α‐phosphatidylcholine liposomes.<!--Unmatched element: w:blockFixed-->
|Authors:||Adaickapillai Mahendran; Yasemin Kopkalli; Goutam Ghosh; Ashwini Ghogare; Mihaela Minnis; Bonnie I. Kruft; Matibur Zamadar; David Aebisher; Lesley Davenport; Alexander Greer|
|Journal:||Photochemistry and Photobiology|
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