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- Sun, L C, et al.
(författare)
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Binuclear ruthenium-manganese complexes as simple artificial models for photosystem II in green plants
- 1997
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 119:30, s. 6996-7004
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Tidskriftsartikel (refereegranskat)abstract
- As part of a project aimed at developing models for photosystem II (PSII) in green plants, we have prepared a series of model compounds (7, 8, and 13). In these compounds, a photosensitizer, ruthenium(II) tris(bipyridyl) complex (to mimic the function of P-680 in PSII), was covalently linked to a manganese(II) ion through different bridging ligands. The structures of the compounds were characterized by electron paramagnetic resonance measurements and electrospray ionization mass spectrometry. The interaction between the ruthenium and manganese moieties within the complex was probed by steady-state and time-resolved emission measurements. When the binuclear complexes are exposed to flash photolysis in the presence of an electron acceptor such as methylviologen (MV2+), it could be shown that after the initial electron transfer from the excited state of Ru(II) in compound 7, forming Ru(III) and MV+., an intramolecular electron transfer from coordinated Mn(II) to the photogenerated Ru(III) occurred with a first-order rate constant of 1.8 x 10(5) s(-1), regenerating Ru(II). This is believed to be the first supramolecular system where a manganese complex has been used as an electron donor to a photo-oxidized photosensitizer, Possible extensions to develop the manganese donor, and thus to approach the function of reaction center in PSII, are indicated.
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- Swansson Vethamuthu, M, et al.
(författare)
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The hexagonal phase and cylindrical micelles in the system alkyltrimethylammonium bromide-sodium desoxycholate-water as studied by x-ray diffraction and fluorescence quenching
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 178, s. 538-548
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Tidskriftsartikel (refereegranskat)abstract
- The hexagonal (E) liquid-crystaline phase in mixtures of sodium desoxycholate (NaDOC) with the catiorwic surfactant cetyltrimethylammonium bromide (CTAB) in water has been investigated by small-angle X-ray diffraction and optical polarizing microscopy. Large proportions of the dihydroxy bile salt can be incorporated in the E phase of the detergent and lead to a decreasing average radius from 22 Å for pure CTAB to 19.5 Å at 46 mole% of NaDOC. The introduction of the bile salt in the cylinders thus increases the curvature, whereas the same bile salt induces a transition to rod-like micelles when added to spherical CTAB micelles at low surfactant concentration. The mixed E phase was identified and characterized as a hexagonal mesophase by optical polarizing microscopy. The diffusion-limited fluorescence quenching of excited state pyrene by dimethylbenzophenone was investigated in the cylindrical mixed micelles of the micellar (Ll) phase in the same system. The decay curves were evaluated using a model of excited state deactivation in infinitely long rod-like micelles without exchange of quenchers (Almgren, M., Alsins, J., Mukhtar, E., and van Stam, J., J. Phys. Chem. 92, 4479 (1988)) and gave as results the relative diffusion coefficient of the excUed probe and quencher. The addition of DOC- up to an equimolar concentration decreased the diffusion coefficient substantially, indicating an increased rigidity of the micelle.
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