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Sökning: WFRF:(Stenhagen G)

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1.
  • Bergström, Gunnar, 1934, et al. (författare)
  • Floral scent chemistry within the genus Linnaea (Caprifoliaceae)
  • 2018
  • Ingår i: Nordic Journal of Botany. - 0107-055X .- 1756-1051. ; 36:3
  • Tidskriftsartikel (refereegranskat)abstract
    • ‘Beauty bush’ and ‘twin flower’ are common names attributed to two well-recognizable species belonging to the genus Linnaea (16 spp.) – L. amabilis and L. borealis – long admired by botanists and gardeners for their perfumed paired bell-shaped flowers. In the present study, we investigated their floral scent compositions through gas chromatography – mass spectrometry (GC-MS) analysis of dynamic headspace samples. Because the flowers of L. borealis in wild populations are fragrant both during the day and in the evening, circadian variation of scent emission was also assessed for this species. In total, 26 chemical compounds comprise the floral scent bouquets of L. amabilis and L. borealis, identified as monoterpenes (14), benzenoids and phenylpropanoids (5), aliphatics (3), sesquiterpenes (3) and irregular terpenes (1). Whereas monoterpenes, notably (-)-α- and β-pinene, dominated the scent of L. amabilis (over 82% relative abundance), benzene derivates: 1,4 dimethoxybenzene, anisaldehyde, 2-phenylethanol, benzaldehyde and nicotinaldehyde were exclusive to analysed headspace samples of L. borealis, accounting for 52% to 100% of their relative compositions, in three Swedish populations. A southwestern Finnish population was characterized by the four first mentioned benzenoid compounds and large amounts of (-)-α- and β-pinenes plus two aliphatic substances. The scent compounds identified for both species are ubiquitous and may serve as generalist attractants/stimulants for a broad assortment of anthophilous insects. The basic work on the flower scent of L. amabilis and L. borealis should inspire studies of their pollination biology, primarily the behaviour-guiding roles of the characteristic emitted volatiles. © 2017 The Authors
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2.
  • Sun, Licheng, et al. (författare)
  • Towards an artificial model for Photosystem II : A manganese(II,II) dimer covalently linked to ruthenium(II) tris-bipyridine via a tyrosine derivative
  • 2000
  • Ingår i: Journal of Inorganic Biochemistry. - : Elsevier. - 0162-0134 .- 1873-3344. ; 78:1, s. 15-22
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to model the individual electron transfer steps from the manganese cluster to the photooxidized sensitizer P680+ in Photosystem II (PS II) in green plants, the supramolecular complex 4 has been synthesized. In this complex, a ruthenium(II) tris-bipyridine type photosensitizer has been linked to a manganese(II) dimer via a substituted L-tyrosine, which bridges the manganese ions. The trinuclear complex 4 was characterized by electron paramagnetic resonance (EPR) and electrospray ionization mass spectrometry (ESI-MS). The excited state lifetime of the ruthenium tris-bipyridine moiety in 4 was found to be about 110 ns in acetonitrile. Using flash photolysis in the presence of an electron acceptor (methylviologen), it was demonstrated that in the supramolecular complex 4 an electron was transferred from the excited state of the ruthenium tris-bipyridine moiety to methylviologen, forming a methylviologen radical and a ruthenium(III) tris-bipyridine moiety. Next, the Ru(III) species retrieved the electron from the manganese(II/II) dimer in an intramolecular electron transfer reaction with a rate constant kET > 1.0 x 10(7) s(-1), generating a manganese(II/III) oxidation state and regenerating the ruthenium(II) photosensitizer. This is the first example of intramolecular electron transfer in a supramolecular complex, in which a manganese dimer is covalently linked to a photosensitizer via a tyrosine unit, in a process which mimics the electron transfer on the donor side of PS II.
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  • Sun, L C, et al. (författare)
  • Binuclear ruthenium-manganese complexes as simple artificial models for photosystem II in green plants
  • 1997
  • Ingår i: Journal of the American Chemical Society. - : The American Chemical Society (ACS). - 1520-5126. ; 119:30, s. 6996-7004
  • 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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