Effect of fluoride anions on gramicidin photoinactivation sensitized by sulfonated aluminum phthalocyanines

Interaction of potent photodynamic agents, sulfonated aluminum phthalocyani nes (AlPcSn where n is a number of sulfonic groups), with biological membra nes was studied here using model systems: sensitized photoinactivation of g ramicidin channels in planar lipid bilayers and adsorption on lipid monolay ers, Fluoride anions known to form complexes with aluminum were found to in hibit both the adsorption of aluminum phthalocyanines on lipid monolayers, as measured with a Langmuir trough by surface pressure and surface potentia l changes, and photodynamic efficacy of the dyes, as studied by gramicidin channel photoinactivation, The similar effects were caused by the alkaliniz ation of the medium. Fluoride anions appeared to be much more effective in the case of AlPcS4 as compared to AlPcS3. The suppression of the photodynam ic potency of aluminum phthalocyanines was attributed to desorption of the dyes from lipid bilayers induced by fluoride or hydroxyl ions. With AlPcS4 an enhancement of the dye aggregation leading to a decrease in the sensitiz ing activity was probably involved in the fluoride effect as revealed by ab sorption and fluorescence spectral measurements. Capillary electrophoresis was employed to understand the mechanism of the dye desorption, The results of these experiments indicated that the reduction in the membrane affinity was associated with an increase in the negative charge of the dye molecule s due to the binding of fluoride or hydroxyl ions.