Photochemical energy conversion by membrane-bound photoredox systems
We have developed a system for carrying out chlorophyll (chl)- photosensitized vectorial transbilayer electron transfer from reduced cytochrome c (cyt) in the inner aqueous compartment of negatively charged unilamellar lipid bilayer vesicles to oxidized ferridoxin (fd) in the outer aqueous phase, with the viologen analog propylene diquat in the outer phase as a mediator. This was investigated using both laser flash and steady state photolysis techniques. The results demonstrate that triplet chl is initially quenched by viologen at the outer membrane surface to form chl cation radical and viologen radical, followed by a biphasic recombination. The slow phase represents reverse electron transfer and could be suppressed by reduction of the chl radical by reduced cyt at the inner vesicle surface, following transbilayer electron transfer, and by electron transfer from viologen radical to oxidized fd. These reactions lead to charge separation across the vesicular membrane. The yields are limited by the formation of the transmembrane potential and accumulation of oxidized cyt in the lumen of the vesicle. Addition of the ionophore valinomycin will diminish the membrane potential, and double the reaction yield. It is important to note that this system mimics one of the key events in photosynthesis (Photosystem 1) and results in appreciable energy storage in the reaction products (about 0.7 V). Reduction of cyt has been investigated at a Pt electrode modified with a lipid bilayer membrane with immobilized vinyl ferrocene as a mediator. The current-voltage curves show that the direct reduction of cyt at the electrode occurs quite efficiently, allowing us to calculate an absorption equilibrium constant and an electron transfer rate constant. These results suggest that biomembrane-like'' electrode surfaces have potential for metalloprotein electrochemistry, as well as the development of biosensors.
- Research Organization:
- Arizona Univ., Tucson, AZ (USA). Dept. of Biochemistry
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (USA)
- DOE Contract Number:
- FG02-86ER13631
- OSTI ID:
- 5684841
- Report Number(s):
- DOE/ER/13631-T1; ON: DE91012171
- Country of Publication:
- United States
- Language:
- English
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Photochemical energy conversion by membrane-bound photoredox systems
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
CYTOCHROMES
PHOTOCHEMICAL REACTIONS
BIOCHEMICAL REACTION KINETICS
PHOTOSYNTHETIC MEMBRANES
ELECTRON TRANSFER
CHLOROPHYLL
ELECTROCHEMISTRY
LIPOSOMES
PHOTOCHEMICAL ENERGY STORAGE
PHOTOCHEMISTRY
PHOTOSENSITIVITY
PROGRESS REPORT
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHEMICAL REACTIONS
CHEMISTRY
DOCUMENT TYPES
ENERGY STORAGE
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
MEMBRANES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOIDS
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PROTEINS
REACTION KINETICS
SENSITIVITY
STORAGE
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)
550200 - Biochemistry