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Molecular Energy and Electron Transfer Assemblies Made of Self‐Organized Lipid‐Porphyrin Bilayer Vesicles
Author(s) -
Komatsu Teruyuki,
Moritake Miho,
Tsuchida Eishun
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305013
Subject(s) - porphyrin , vesicle , tetraphenylporphyrin , chemistry , bilayer , bathochromic shift , photochemistry , crystallography , electron acceptor , chromophore , lipid bilayer , fluorescence , membrane , biochemistry , physics , quantum mechanics
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 3.1×10 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 ϕ , 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 ( λ 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.