Photosystem heterogeneity

The combination of surface-associated reactants with surface-bound H-atoms, occasionally leads to poor photoinduced hydrogenation of the reactant and parallelly to inhibition of H2-evolution. For such systems, tailored bifunctional heterogeneous catalysts have been developed [141], where cooperative catalytic effects are observed in the photohydrogenation reactions. Substitution of ethylene by acetylene, C2H2, in the photosystem composed of Ru(bpy) +/MV2+/Na2EDTA and the Pt colloid results in inefficient hydrogenation of acetylene to ethylene,

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Fig. 22. Photoinduced hydrogenation of phenylacetylene in an organized water-oil two phase system. The photosystem is localized in the aqueous phase and the heterogeneous catalyst is present in the oil phase. Electron transfer communication between the two phases is mediated by C8V +...

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

The study of heterogeneous photosystems, involving u.v. or visible light irradiation of aqueous suspensions of semiconductor powders or colloids, has increased steadily over the past five years. Many studies are aimed at development of systems capable of cyclic water cleavage, although, as mentioned earlier, Ti02 doped with iron functions as a photocatalyst for reduction of N2 to The most popular semiconductor materials continue to be TiOj... 

Several interesting papers have appeared that involve somewhat unconventional heterogeneous photosystems. Thus, the photo-oxidation of water to O2 is said to occur with AgCl colloids whilst others have found that Agl is capable of the photofixation of N2. Nitrogen reduction has been reported to occur with multifarious mixed oxides and with desert sands. In fact, if all... 

Lavergne J and Briantais J-M. (1996). Photosystem-II heterogeneity. In Ort DR and Yocum CF (Eds), Oxygenic photosynthesis The Light Reactions, pp. 265-287. Kluwer Academic Publishers,... 

B Andersson and JM Anderson (1980) Lateral heterogeneity in the distribution of chlorophyll-protein complexes of the thylakoid membranes of spinach chloroplasts. Biochim Biophys Acta 593 427-440 P-" Albertsson (1985) Partition of Cell Particles and Macromolecules (3rd edition) John Wiley H-E "kerlund, B Andersson and P-" Albertsson (1976) Isolation of photosystem II enriched membrane vesicles from spinach chloroplasts by phase partition. Biochim Biophys Acta 449 525-535 P Grber, A Zickler and H-E "kerlund (1978) Electric evidence for the isolation of inside-out vesicles from spinach chloroplasts. FEES Lett 96 233-237... 

Fig. 3. (A) Absorbance changes at 820 nm induced by a sequence of 20-ns, 600-nm laser flashes in PS-1 particles at 10 K (B) left EPR spectra of reduced iron-sulfur centers induced by increasing numbers of flashes (B) right values of A[AA](820 nm) after the nth flash and the g=1.94 and g=1,896 EPR signals plotted against the number of flashes applied. The final segment beyond the maximum number of flashes refers to the corresponding values after continuous Illumination. Figure source Setif, Mathis and VanngSrd (1984) Photosystem t photochemistry at low temperatures. Heterogeneity in pathways for electron transfer to the secondary acceptors and for recombination processes. Biochim Biophys Acta 767 407,408.

P SOtif, P Mathis and T V nng rd (1984) Photosystem I photochemistry at low temperature. Heterogeneity in pathways for electron transfer to the secondary acceptors and for recombination processes. Biochim Biophys Acta 767 404-414... 

Photolysis of organic materials has also been accomplished by the oxidative ET quenching route of excited states [86]. A photosystem that includes Ru(bpy)3 as photosensitizer, JV,JV -dimethyl-4,4 -bipyridinium, MV, and NADH as electron donor, leads to MV and NAD through the sequence of reactions outlined in Eqs. (45) to (47). The reduced photoproduct, MV, mediates H2 evolution at a heterogeneous catalytic site of Pt [Eq. (48)], while NAD" " mediates the two electron oxidation of ethanol [Eq. (43)] or lactic acid [Eq. (49)]. 

Photosensitized hydrogenation of ethylene, C2H4, and acetylene, CjHj, in the presence of Pt, Rh, or Ru as heterogeneous catalysts represent photosynthetic transformations mimicking cofactor-enzyme systems [122]. In a photosystem composed of Rufbpy) as photosensitizer, (29) as... 

Photohydrogenation of various other organic substrates (i.e., 3-hexyne, 1,1-diphenylethylene, 3-pentanone, and butyraldehyde) was accomplished in similar photosystems in the presence of different heterogeneous metal colloids [123]. Also, organization of photosynthetic multiphase assemblies for photoinduced hydrogenation of water-insoluble alkenes and alkanes have been reported using multifunctional heterogeneous catalysts [124]. 

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