Solar energy photosystems

The water-plastoquinone photo-oxidoreductase, also known as photosystem II (PSII), embedded in the thylakoid membrane of plants, algae and cyanobacteria, uses solar energy to power the oxidation of water to dioxygen by a special centre containing four Mn ions. The overall reaction catalysed by PSII is outlined below ... 

Finally it is worthwhile noting that MV2+ (also known as paraquat) is an effective herbicide which operates by intercepting an electron from photoexcited chlorophyll in photosystem I, preventing the plant from utilizing solar energy. There then exists an obvious parallel between the behaviour of MV2+ as a herbicide and its behaviour as an electron-transfer reagent in model systems for photochemical water decomposition. 

The capture of solar energy occurs in photosystems. Each photosystem consists of an antenna complex and a photosynthetic reaction center. The... 

Serra, J.L., Llama, M.J., Rao, K.K. and Hall, D.O. 1986. B-5 Hydrogen photoproduction using photosystem I-enriched particles from Phormidium laminosum. Book of Abstracts 6th International Conference on Photochemical Conversion and Storage of Solar Energy, Lab. Biophysique, INSERM, Paris. 

Turning to photobiological schemes for producing H2 (Chapter 8), a complex reaction scheme uses solar energy to convert H2O into O2 and reducing equivalents which appear as NADPH. In photosystem 1, the reducing equivalents in NADPH are used to reduce CO2 to carbohydrates ... 

The bacterial photosystem functions without dioxygen production which simplifies the task at hand. Namely, electrons are obtained from more easily oxidized terminal electron donors such as H2S instead of water. Nonetheless, the basic design needed to transform solar energy into stored chemical energy is present. The protein subunits and cofactors that comprise the photosystem in purple bacteria, such as Rhodobacter (Rb.) sphaeroides and Rhodopseudomonas (Rps.) viridis,33 are shown schematically in Fig. 1 which is based on a crystal structure of this assembly.34... 

Photosystem 11 (PS II) within higher plants represents a solar-energy-driven process that removes hydrogen atoms from water to form molecular oxygen (O2, dioxygen) through an overall four-electron transfer reaction (equation 20), ... 

The electrons that are provided by photosystem I are finally used to reduce CO2 to carbohydrates, while in photosystem II, water is oxidized to oxygen. Intense research over many decades has partially revealed the extremely complicated mechanism of natural photosynthesis. It follows that it is obviously rather difficult to imitate this in an artificial photosynthesis that is intended to convert and store solar energy in simple but energy-rich chemicals. Different approaches have been developed to solve this problem (i). It has been suggested to facilitate artificial photosynthesis by the assistance of redoxactive metal complexes in homogeneous systems. Generally, photoredox reactions of metal... 

Photochemical Aspects of Solar Energy Conversion 3 Heterogeneous Photosystems... 

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