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| 2. |
- Johansson, Jonas, et al.
(författare)
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Time-Resolved Studies of Light Propagation in Crassula and Phaseolus Leaves
- 1999
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Ingår i: Photochemistry and Photobiology. - 0031-8655. ; 69:2, s. 242-247
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved transmittance was used to extract in vivo optical properties of leaves of green plants experimentally. In time-resolved transmittance measurements an ultrashort light pulse is directed onto the surface of the object and the transmitted light is measured with a time resolution in the range of picoseconds. A table-top terawatt laser was used to generate 200 fs light pulses at 790 nm with a repetition rate of 10 Hz. The light pulses were focused through a cuvette filled with water to produce white light pulses and optical filters were placed in the beam path to select the wavelength of the light focused onto the leaf surface. The time profiles of the light transmitted through the leaves was recorded with a streak camera having a time resolution of about 2.5 ps. Results from Crassula falcata and Phaseolus vulgaris studied at 550, 670 and 740 nm are reported. The three selected wavelength regions represent medium, high and a low absorption of light, respectively. A library of curves was generated using Monte Carlo simulation, and the absorption and scattering coefficients were extracted by comparison of experimental curves with this library. Our results suggest that in the case of the thin (200 μm) Phaseolus leaves and certainly in the case of the thick (4 mm) Crassula leaves, light scattering plays an important role in light transport through the leaf and should also affect light flux in these leaves.
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| 4. |
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| 5. |
- Olsson, Roger, et al.
(författare)
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Endocyclic cleavage of glycosides. VI. Substituent effects of the alkylative endocyclic cleavage of glycosides
- 1998
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Ingår i: Tetrahedron. - 0040-4020. ; 54:15, s. 3935-3954
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Tidskriftsartikel (refereegranskat)abstract
- A number of pentopyranoside derivatives were treated with Me 3 Al in order to investigate the influence of structural parameters on the methyl group transfer in the endocyclic alkylative cleavage reaction of these substrates. A cyclic CH ··· O hydrogen bonded model is suggested as an intermediate, which is used to explain the stereoselectivities for different substrates. In several, cases the diastereoselectivities were better than 9:1.
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| 6. |
- Olsson, Roger, et al.
(författare)
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Is a hydrogen bonded carbene an intermediate in the organoaluminum-induced ring opening of pyranosides?
- 1997
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Ingår i: Tetrahedron Letters. - 0040-4039. ; 38:32, s. 5701-5704
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Tidskriftsartikel (refereegranskat)abstract
- Semiempirical and ab initio quantum chemical computations indicate that the intermediate formed prior to the selectivity-determining methyl transfer step in the reaction between glycosides and trimethylaluminum is a strongly hydrogen-bended equilibrium OH...C = O-H...C, which is proposed to be an important selectivity promoting factor in the alkyl transfer reaction.
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