Simulation of Photosynthesis, a Resource for Energy

Willner, Itamar; Ford, William E.; Otvos, John W.; Calvin, Melvin

doi:10.1007/978-1-4613-3117-9_5

Cited by 3 publications

(3 citation statements)

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“…The net reaction, the oxidation of the Chl triplet in the membrane phase by Ru(NH3):+ in the aqueous phase, is mediated by the viologens. Electron transfer reactions of this kind that are mediated across phase boundaries are of interest because of their potential application in artificial photosynthetic solar energy devices (Willner et al, 1980;Fendler, 1982;Gratzel, 1983). At *Present address: Radiation Laboratory, University of ?To whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH₃)₆³⁺

Ford

Tollin

1986

Photochem & Photobiology

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Abstract— The kinetics of the oxidation of a homologous series of 4,4′‐di(n‐alkyl)‐bipyridinium (viologen) radicals by Ru(NH3)63+ in vesicle suspensions was studied using laser flash photolysis. The viologen radicals were produced photochemically in the bilayer membrane phase of the vesicles by electron transfer from the triplet state of chlorophyll‐α. At high concentrations of Ru(NH3)63+, the rate of oxidation of the viologen radicals in the aqueous phase was limited by the rate at which the radicals diffused from the membrane to the aqueous phase. The exit rate constant decreased from 2 × 105 s−1 for the methyl viologen radical to 4 × 103 s−1 for the pentyl viologen radical. Both the exit rate constants and the calculated values for the equilibrium association constants of the viologen radicals were unexpectedly insensitive to the length of their alkyl substituents. This, as well as other data, suggests that the radicals that diffused into the aqueous phase tended to remain associated with the membrane‐water interface.

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Section: Introductionmentioning

confidence: 99%

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH₃)₆³⁺

Ford

Tollin

1986

Photochem & Photobiology

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“…Therefore, the observation that, under these circumstances, hardly any MeVt could be detected during steady-state illumination indicates that the photochemical components of the system are rapidly exchangeable. We tried to increase the quantum yield for hydrogen production by using viologen derivatives that are known to be more efficient in quenching the excited state of the surfactant-Ru2+ complex than methyl viologen (21). For this purpose, the surfactant viologens 1, 1'-diheptyl4,4'-bipyridinium dibromide and 1-octadecyl-1'-propylsulfonate44'-bipyridinium bromide were used.…”

Section: Resultsmentioning

confidence: 99%

Photosensitized production of hydrogen by hydrogenase in reversed micelles

Hilhorst

Laane

Veeger

1982

Proc. Natl. Acad. Sci. U.S.A.

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Hydrogenase (hydrogen:ferricytochrome c3 oxidoreductase, EC 1. 12.2. 1) from Desulfovibrio vulgaris was encapsulated in reversed micelles with cetyltrimethylammonium bromide as surfactant and a chloroform/octane mixture as solvent. Reducing equivalents for hydrogenase-catalyzed hydrogen production were provided-by vectorial photosensitized electron.transfer from a donor (thiophenol) in the organic phase through a surfactant-Ru2, sensitizer located in the interphase to methyl viologen concentrated in the aqueous core ofthe reversed micelle. The results show that reversed micelies provide a microenvironment that (i) stabilizes hydrogenase against inactivation and (ii) allows an efficient vectorial photosensitized electron and proton flow from the organic phase to hydrogenase in the aqueous phase.It has been well established that surfactant molecules dissolved in organic solvents aggregate to reversed micelles in the presence of small amounts of water. Reversed micelles are of multiple interest for they create a microenvironment that provides a unique reaction medium.An area of active current research is the photochemical investigation of these organized structures with the aim of obtaining structural characteristics (1-3) and of modeling natural processes such as photosynthesis (4-6). The latter objective is of particular interest because it includes potential applications such as solar energy conversion and storage. Essential for efficient solar energy conversion and storage is the separation of photoproducts formed in photosensitized electron transfer reactions. Recently, Willner et aL (5) showed that effective separation ofphotoproducts can be achieved in a reversed micellar system by vectorial photosensitized electron transfer from a donor in the organic phase to an acceptor in the water pool and vice versa.In addition, the application of reversed micelles in enzyme catalysis increases. Reversed micelles have been shown to provide a microenvironment for enzymes that protects them from the unfavorable action of organic solvents by means of surfactants. Hence, the study of structural and catalytic properties of enzymes can be extended to organic media. To date, several enzymes, such as trypsin, a-chymotrypsin, lactate dehydrogenase, peroxidase, and lysozyme have been encapsulated in the aqueous core of reversed micelles (7-9).In this study we entrapped hydrogenase (hydrogen:ferricytochrome c3 oxidoreductase, EC 1.12.2.1) from Desulfovibrio vulgaris in a reversed cetyltrimethylammonium bromide micelle; the objective was to obtain a highly organized system for an efficient coupling between hydrogenase and a photochemical system that produces reducing equivalents and protons necessary for hydrogenase action.

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“…Therefore, it is of interest to see whether the porphyrin complexes can catalyze the oxidation of water. Since manganese-porphyrin complexes with manganese in higher oxidation states can form dimeric species by bridging two oxygen atoms obtained from water molecules, these complexes might be able to liberate oxygen from water (10). A first and necessary step in the chemical solar energystoring system is the driving of a thermodynamically unfavored reaction by absorption of photons.…”

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confidence: 99%

Photoinduced oxidation of a water-soluble manganese(III) porphyrin

Maliyackel

Otvos

Spreer

et al. 1986

Proc. Natl. Acad. Sci. U.S.A.

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The photoinduced oxidation of tetra(Nmethyl-4-pyridyl)porphyrinmanganese(III) has been achieved in homogeneous solution. The manganese porphyrin was used as an electron donor in a three-component system with tris-(2,2'-bipyridine)ruthenium(II) as the photosensitizer and chloropentaamminecobalt(III) as the electron acceptor. The photooxidized manganese porphyrin is unstable in aqueous solution, reverting to the starting manganese(HI) porphyrin. The oxidation of manganese(HI) porphyrin and the subsequent reduction of the oxidized porphyrin can be cycled repeatedly.Much attention has been given to the study of photochemical generation of hydrogen and oxygen from water as a means of collecting and storing solar energy (1-3). A practical device for such solar energy conversion should be capable of generating hydrogen and oxygen simultaneously. While considerable progress has been made in achieving the photoinduced hydrogen evolution from water (ref. 3, pp. 99-122), only few advances have been made in the photogeneration of oxygen (4-6). The basic reason for the lack of progress in oxygen evolution is that the oxidation of water to oxygen involves four electrons. Nevertheless, photochemical generation of oxygen from water has been reported with the use of heterogeneous catalysts (4-6). In these experiments, tris(2,2'-bipyridine)ruthenium(II), Ru(bpy)2+, was used as a photosensitizer and chloropentaamminecobalt(III), CoCl(NH3) +, as an electron acceptor. Our work is directed at the development of homogeneous catalysts for the evolution of oxygen.In photosynthesis, manganese complexes are involved in the oxygen-evolution process; the exact nature of these complexes is not known (7). Manganese complexes exhibit a rich variety of oxidation states, making them promising oxidation catalysts (8), and, in addition, it has been reported that manganese-porphyrin complexes catalyze the oxidation of olefinic hydrocarbons (9). Therefore, it is of interest to see whether the porphyrin complexes can catalyze the oxidation of water. Since manganese-porphyrin complexes with manganese in higher oxidation states can form dimeric species by bridging two oxygen atoms obtained from water molecules, these complexes might be able to liberate oxygen from water (10). A first and necessary step in the chemical solar energystoring system is the driving of a thermodynamically unfavored reaction by absorption of photons. In the present paper we report the photochemical oxidation of a watersoluble manganese(III) porphyrin, tetra(N-methyl-4-pyridyl)-porphyrinmanganese(III), Mn(III)Por+.As manganese(III)-porphyrin complexes are short-lived in their excited states, use of these complexes as photosensitizers to achieve their oxidation is limited (11,12). The approach taken in the present investigation is to use the manganese porphyrin as an electron donor in a threecomponent system consisting of a photosensitizer, an electron acceptor, and an electron donor. A schematic arrangement of this system is shown in Fig. 1. In this study, Ru(bpy)32 i...

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Simulation of Photosynthesis, a Resource for Energy

Cited by 3 publications

References 48 publications

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH₃)₆³⁺

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH₃)₆³⁺

Photosensitized production of hydrogen by hydrogenase in reversed micelles

Photoinduced oxidation of a water-soluble manganese(III) porphyrin

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Simulation of Photosynthesis, a Resource for Energy

Cited by 3 publications

References 48 publications

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH3)63+

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH3)63+

Photosensitized production of hydrogen by hydrogenase in reversed micelles

Photoinduced oxidation of a water-soluble manganese(III) porphyrin

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CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH₃)₆³⁺

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH₃)₆³⁺