Model systems for photosynthetic energy conversion

Conference · Thu Sep 23 04:00:00 EDT 1976 · J. Phys. Chem.; (United States)

OSTI ID:7246095

Tollin, G

Energy conversion in photosynthesis is known to proceed via light-induced one-electron-transfer-reactions involving chlorophyll and electron donors and acceptors. Although the chemical identities of all of the components have not as yet been elucidated, considerable evidence has been accumulated which points to quinones (Q) as primary electron acceptors in both green plants and bacterial photosynthesis. Furthermore, it has been established that the initial photoprocess leads to the formation of a chlorophyll cation radical (C./sup +/). The research reported attempted to elucidation of the molecular--electronic mechanism of chlorophyll participation in photosynthesis. Model photoreactions in solution (mainly in alcohols) which lead to quinone reduction and chlorophyll oxidation were investigated. Electron spin resonance spectroscopy and laser flash photolysis have been the major techniques utilized in these studies. The following reactions have been observed: (a) Photoproduction of C./sup +/ in solution in the absence of added electron acceptors, a low quantum yield reaction which proceeds via the lowest excited singlet state and (b) one-electron phototransfer between the chlorophyll lowest triplet state and quinones to yield a radical pair (C./sup +/--Q./sup -/). This may either recombine or separate. The C./sup +/ formed upon separation is unstable and either undergoes reverse electron transfer with Q./sup -/ orreacts with hydroxylic compounds to regenerate chlorophyll. The excess Q./sup -/ species disproportionates. The quenching of the chlorophyll lowest singlet state by quinones does not, however, lead to detectable radical formation. These reactions seem to provide acceptable models for certain aspects of photosynthetic energy conversion, and thus elucidation of their detailed mechanisms should lead to useful insights into the nature of the biological process. (BLM)

• Research Organization: Univ. of Arizona, Tucson
• OSTI ID: 7246095
• Conference Information: Journal Name: J. Phys. Chem.; (United States) Journal Volume: 80:20
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
140504 -- Solar Energy Conversion-- Biomass Production & Conversion-- (-1989)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AROMATICS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CHLOROPHYLL
CONVERSION
DECOMPOSITION
ELECTRON SPIN RESONANCE
ENERGY CONVERSION
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
LASERS
MAGNETIC RESONANCE
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PHOTOSYNTHESIS
PHYTOCHROMES
PIGMENTS
PORPHYRINS
QUINONES
RESONANCE
SYNTHESIS