title: Molecular energy and electron transfer assemblies made of self-organized lipid-porphyrin bilayer vesicles.
abstract: Novel molecular energy and electron transfer assemblies in vesicular form, which are made of self-organized amphiphilic porphyrins bearing phospholipid-like substituents (lipid-porphyrins), have been photochemically characterized. Tetraphenylporphyrin (TPP) derivatives with four dialkylphosphocholine groups [free-base (1 a), Zn(2+) complex (1 b), and Fe(3+) complex (1 c)] are spontaneously associated in water to form spherical unilamellar vesicles with a diameter of 100-150 nm. Exciton calculations based on the bilayered sheet model of 1 b, which has a porphyrin packing similar to that seen in the triclinic unit cell of the Zn(2+)TPP crystals, reproduced the Soret band bathochromic shift appearing in the aqueous solution of 1 b well. The UV/Vis absorption spectrum of the 1 a/1 b hybrid vesicles (molar ratio: 1/1) showed no electronic interaction between the two porphyrin chromophores in the ground state, but efficient intermolecular singlet-singlet energy transfer took place from the excited 1 b donors to the 1 a acceptor within the vesicle. Near-field scanning optical microspectroscopy of the 1 a/1 b vesicles on a graphite surface also showed only free-base porphyrin fluorescence. The efficiency of the energy transfer was 0.81 and the rate constant was 3.1 x 10(9) s(-1). On the other hand, protoporphyrin IX bearing two alkylphosphocholine propionates (2) was incorporated into the 1 a or 1 c bilayer vesicles (ca. 100 nm phi, molar ratio: 1 a/2 or 1 c/2=10). The UV/Vis absorption spectrum showed that 2 was successfully anchored into the fluid alkylene region of the membrane without stacking. Photoirradiation (lambda(ex): 390 nm) of the 1 c/2 vesicles in the presence of triethanolamine led a vectorial electron transfer from the outer aqueous phase to the membrane center, which allowed reduction of the ferric ion of the Fe(3+)TPP platform.
authors.affiliation: Advanced Research Institute for Science and Engineering Waseda University, Tokyo 169-8555, Japan.
authors.forename: Teruyuki
authors.initials: T
authors.lastname: Komatsu
authors.forename: Miho
authors.initials: M
authors.lastname: Moritake
authors.forename: Eishun
authors.initials: E
authors.lastname: Tsuchida
mesh_terms: D004579:Electron Transport; D004735:Energy Transfer; D005290:Ferric Compounds / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000737:chemistry*; D010777:Photochemistry; D011166:Porphyrins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D008051:Lipid Bilayers; D008081:Liposomes; D010743:Phospholipids; D011166:Porphyrins; C409084:tetraphenylporphyrin; D015032:Zinc