Effects of lysophosphatidylcholine micelle and phosphatidylcholine liposome on photoreduction of methylviologen.
Photoinduced reduction of methylviologen (MV2+) by ethylenediaminetetraacetate (EDTA3-), which was sensitized by thiacarbocyanine dyes having long alkyl chains (C+m-n) embedded in palmitoyl lysophosphatidylcholine micelle and dipalmitoyl phosphatidylcholine liposomal membrane, was carried out. The formation rate of reduced methylviologen cation radical (MV+.) decreased with the time of irradiation with visible light, and the deceleration was more pronounced in the micellar solution. In kinetic studies, we found that the sensitizer divalent cation radical (C2+.m-n) is formed through the reaction of photoexcited sensitizer (C+*m-n) with MV2+ as an intermediate in this reaction, and that the reduction of C2+.m-n with EDTA3- inhibits the back reaction of MV+. with C2+.m-n. The inhibition was greater in the liposomal solution than in the micellar solution. This was ascribed to a higher concentration of EDTA3- on the liposomal surfaces through the electrostatic interaction between EDTA3- and the liposomal surfaces, the charge of which is attributed to the univalent cation sensitizer embedded in the liposomal membrane. The difference in the positive charge density of the surface of these lipid aggregates was due to the difference in the curvature of the micelle and the liposome. These results suggest that the dipalmitoyl phosphatidylcholine liposome is a more effective carrier than the palmitoyl lysophosphatidylcholine micelle for the production of MV+. in the photoreduction studied here.
D004492:Edetic Acid; D008081:Liposomes; D008244:Lysophosphatidylcholines; D008433:Mathematics; D008567:Membranes, Artificial; D008823:Micelles; D008956:Models, Chemical; D010084:Oxidation-Reduction / Q000528:radiation effects; D010269:Paraquat / Q000528:radiation effects*; D010713:Phosphatidylcholines; D010777:Photochemistry
D008081:Liposomes; D008244:Lysophosphatidylcholines; D008567:Membranes, Artificial; D008823:Micelles; D010713:Phosphatidylcholines; D004492:Edetic Acid; D010269:Paraquat