SELF-ASSEMBLED LIPIDPORPHYRIN BILAYER VESICLES, MICROSTRUCTURE AND DIOXYGEN BINDING IN AQUEOUS-MEDIUM

An amphiphilic tetraphenylporphyrinatometal (Zn, Fe) derivative having four dialkylglycerophosphocholine groups on one side of the ring plan e (lipidporphyrin) was easily dispersed in an aqueous medium to give a red, stable dispersion. Based on electron microscopy, lipidporphyrins themselves produced spherical unilamellar vesicles with a diameter of ca. 100 nm. The thickness of the membrane (9.5 +/- 0.5 nm) correspond ed to a bilayer of the lipidporphyrin (4.6 nm); the ratio of the lipid porphyrin molecules in the outer and inner layers was 1.57. The lipidp orphyrinatozinc(II) vesicle displayed some characteristics of a J-aggr egate: (i) a red-shifted Soret band (425 --> 438 nm), (ii) no fluoresc ence quenching, and (iii) a reduced triplet-state lifetime. Simple exc iton calculations indicate that the porphyrin squares located in the o uter and inner layers formed a J-aggregate with an average angle of 47 degrees. A vesicle composed of the lipidporphyrinatoiron(II) coordina ted with an alkylimidazole reversibly formed a stable dioxygen adduct. The O-2-binding equilibrium and kinetic parameters were determined. T his vesicle has the ability to act as a totally synthetic O-2 carrier under physiological conditions (pH 7.4, 37 degrees C).