Effect of Fluoride Anions on Gramicidin Photoinactivation Sensitized by Sulfonated Aluminum Phthalocyanines¶

Abstract

Interaction of potent photodynamic agents, sulfonated aluminum phthalocyanines (AlPcSn where n is a number of sulfonic groups), with biological membranes was studied here using model systems: sensitized photoinactivation of gramicidin channels in planar lipid bilayers and adsorption on lipid monolayers. Fluoride anions known to form complexes with aluminum were found to inhibit both the adsorption of aluminum phthalocyanines on lipid monolayers, as measured with a Langmuir trough by surface pressure and surface potential changes, and photodynamic efficacy of the dyes, as studied by gramicidin channel photoinactivation. The similar effects were caused by the alkalinization of the medium. Fluoride anions appeared to be much more effective in the case of AlPcS4 as compared to AlPcS3. The suppression of the photodynamic 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 sensitizing activity was probably involved in the fluoride effect as revealed by absorption 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 molecules due to the binding of fluoride or hydroxyl ions.

Light-Triggered Liposomal Release: Membrane Permeabilization by Photodynamic Action

“…It can be proposed that AlPcS 3 efflux was incomplete due to effective binding of AlPcS 3 to membranes of liposomes either on inner or outer surface of vesicles. In fact, it was found previously that AlPcS 3 has high affinity to phosphatidylcholine membranes. , In line with this, control experiments showed that addition of liposomes to a solution of AlPcS 3 led to the increase in τ D from 0.9 ms up to 50 ms, i.e., binding of the dye to liposomes (data not shown).…”

“…In fact, it was found previously that AlPcS 3 has high affinity to phosphatidylcholine membranes. 29,34 In line with this, control experiments showed that addition of liposomes to a solution of AlPcS 3 led to the increase in τ D from 0.9 ms up to 50 ms, i.e., binding of the dye to liposomes (data not shown).…”

“…Here the inhibiting effect of sodium azide on the photosensitized liposome leakage is seen more distinctly (e.g., the CF fluorescence level achieved in 360 s after the end of illumination was 90% in the absence of azide as compared to 50% in its presence). The light-induced CF leakage of liposomes observed in the presence of AlPcS 3 was also suppressed by potassium fluoride (curve 5), which is known to inhibit the binding of AlPcS 3 to membranes. ,, Thus it can be concluded that the membrane binding of a sensitizer is a prerequisite for photosensitized liposome permeabilization. The action of AlPcS 3 was compared to that of other photosensitizers: neutral ZnPcGlyc 4 (curve 6) and chlorin e6 (curve 7).…”

“…The lightinduced CF leakage of liposomes observed in the presence of AlPcS 3 was also suppressed by potassium fluoride (curve 5), which is known to inhibit the binding of AlPcS 3 to membranes. 33,29,34 Thus it can be concluded that the membrane binding of a sensitizer is a prerequisite for photosensitized liposome permeabilization. The action of AlPcS 3 was compared to that of other photosensitizers: neutral ZnPcGlyc 4 (curve 6) and chlorin e6 (curve 7).…”

Electrochemistry of Aluminum Phthalocyanine: Solvent and Anion Effects on UV−Visible Spectra and Reduction Mechanisms

“…Aluminum porphyrins and phthalocyanines are of interest because of their possible applications in the area of new functional materials. − The Al(III) form of these compounds has a high binding affinity with the fluoride ion, − and a highly selective optical fluoride ion sensor based on aluminum(III) octaethylporphyrin has been described in a recent communication . The development of new applications for the use of aluminum phthalocyanines in material science requires, in many cases, a detailed knowledge of the compounds' electrochemical reactivity, but only a few studies of aluminum phthalocyanine electrochemistry in nonaqueous media have been reported, − none of which presents a detailed mechanistic study of the electron-transfer reactions.…”