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PORPHYRIN‐LIPOSOME INTERACTIONS: INFLUENCE OF THE PHYSICO‐CHEMICAL PROPERTIES OF THE PHOSPHOLIPID BILAYER
Author(s) -
Ricchelli* Fernanda,
Stevanin Daniela,
Jori Giulio
Publication year - 1988
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1988.tb02780.x
Subject(s) - chemistry , liposome , hematoporphyrin , phosphatidylcholine , monolayer , phospholipid , porphyrin , lipid bilayer , quenching (fluorescence) , vesicle , bilayer , micelle , photochemistry , fluorescence , membrane , organic chemistry , biochemistry , aqueous solution , physics , photodynamic therapy , quantum mechanics
— The quenching of the fluorescence emitted by hematoporphyrin incorporated into unilamellar liposomes of dipalmitoyl‐phosphatidylcholine and dimyristoyl‐phosphatidylcholine, was studied by using methylviologen, 9,10‐anthraquinone‐2,6‐disulfonate and 9,10‐anthraquinone‐2‐sulfonate as quenchers, in order to assess how the distribution of the porphyrin and the interaction mode of the various quenchers with the porphyrin is affected by the physico‐chemical properties of the vesicles. The results obtained indicate that, below the critical temperature for the phase transition of the lipids, hematoporphyrin is preferentially distributed in the outer lipid monolayer of liposomes of dipalmitoyl‐phosphatidylcholine while most hematoporphyrin molecules are located in the inner monolayer in liposomes of dimyristoyl‐phosphatidylcholine. This distribution is only slightly changed when the external mean radius of liposomes increases from 26 to 50 nm. The rise of temperature above the critical value for the liquid‐gel phase transition causes a shift of the hematoporphyrin molecules toward the inner phospholipid monolayer. This shift is more pronounced in liposomes of dimyristoyl‐phosphatidylcholine. Studies on model systems, i.e. neutral and ionic micelles, indicate that methylviologen and anthra‐quinone‐type quenchers drastically differ in their interaction mechanism with hematoporphyrin. In particular, methylviologen is the only quencher which can discriminate different hematoporphyrin populations in liposomes of dimyristoyl‐phosphatidylcholine and dipalmitoyl‐phosphatidylcholine in both the liquid and gel phase. Anthraquinone‐type quenchers interact with both hematoporphyrin populations when the lipids are in the gel phase. When the lipids are in a fluid state, the quenching occurs only on the external hematoporphyrin population in liposomes of dipalmitoyl‐phosphatidylcho‐line while in liposomes of dimyristoyl‐phosphatidylcholine no discrimination is observed. The influence of the liposomal structure at different temperatures and of the length of the hydrocarbon chains is discussed.