Effect of the microenvironment on the efficiency of singlet oxygen (O-2((1)Delta(g))) production by photosensitizing anti-inflammatory drugs

The influence of the medium on the quantum yields of singlet oxygen (O-2((1 )Delta(g))) production (Phi(Delta)) by a series of photosensitizing nonster oid anti-inflammatory drugs (NSAID) derived from 2-arylpropionic acid (APA) has been investigated. Four-component oil-in-water and water-in-oil microe mulsions, based on anionic and cationic surfactants, have been employed as the simplest models to mimic more complex biological environments. Phi(Delt a) values have been determined by monitoring the singlet oxygen (O-1(2)) lu minescence at 1270 nm upon continuous excitation of the drugs under air-equ ilibrated conditions. Results indicate that Phi(Delta) values are highly af fected by the medium, being higher in microheterogeneous systems than in (h omogeneous) solution. Some of the anti-inflammatory derivatives are very ef ficient O-1(2) sensitizers: e.g., values of apparent Phi(Delta) as high as 0.86 (+/-0.04) and 0.70 (+/-0.03) have been found for tiaprofenic acid and suprofen, respectively. The location of the drugs in the interfacial region of the microemulsions combined with their high Phi(Delta) values suggest t hat type II reactions may play a significant role in the overall photodynam ic process in more complex organized media, such as biological membranes. ( C) 1998 Elsevier Science S.A. All rights reserved.