| 1. |
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| 2. |
- Andreasson, Joakim, 1973, et al.
(författare)
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The gold porphyrin first excited singlet state
- 2002
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Ingår i: Photochemistry and Photobiology. - 0031-8655 .- 1751-1097. ; 76:1, s. 47-50
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Tidskriftsartikel (refereegranskat)abstract
- Gold porphyrins are often used as electron-accepting chromophores in artificial photosynthetic constructs. Because of the heavy atom effect, the gold porphyrin first-excited singlet state undergoes rapid intersystem crossing to form the triplet state. The lowest triplet state can undergo a reduction by electron donation from a nearby porphyrin or another moiety. In addition, it can be involved in triplet-triplet energy transfer interactions with other chromophores. In contrast, little has been known about the short-lived singlet excited state. In this work, ultrafast time-resolved absorption spectroscopy has been used to investigate the singlet excited state of Au(III) 5,15-bis(3,5-di-t-butylphenyl)-2,8,12,18,-tetraethyl-3,7,13,17-tetrameth ylporphyrin in ethanol solution. The excited singlet state is found to form with the laser pulse and decay with a time constant of 240 fs to give the triplet state. The triplet returns to the ground state with a lifetime of 400 ps. The lifetime of the singlet state is comparable with the time constants for energy and photoinduced electron transfer in some model and natural photosynthetic systems. Thus, it is kinetically competent to take part in such processes in suitably designed supermolecular systems.
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| 3. |
- Billsten, Helena, et al.
(författare)
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Photophysical Properties of Xanthophylls in Carotenoproteins from Human Retina.
- 2003
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Ingår i: Photochemistry and Photobiology. - 0031-8655. ; 78:2, s. 138-145
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Tidskriftsartikel (refereegranskat)abstract
- The macula of the human retina contains high amounts of the xanthophyll carotenoids lutein and zeaxanthin [a mixture of (3R,3′R)-zeaxanthin and (3R,3′S-meso)-zeaxanthin]. Recently, it was shown that the uptake and the stabilization of zeaxanthin and lutein into the retina are likely to be mediated by specific xanthophyll-binding proteins (XBP). Here, we have used femtosecond pump–probe spectroscopy to study the dynamics of the S1 state of these xanthophylls in xanthophyll-enriched and native XBP. The results from the native XBP and the enriched XBP were then compared with those for carotenoids in organic solvents and in detergent micelles. Steady-state and transient absorption spectra show that the incorporation of xanthophylls into the protein causes a redshift of the spectra, which is stronger for lutein than for zeaxanthin. The transient absorption spectra further indicate that a part of the xanthophylls remains unbound in the xanthophyll-enriched XBP. The transient absorption spectra of the native XBP prove the presence of both xanthophylls in native XBP. Although the S1 lifetime of lutein does not exhibit any changes when measured in solution, micelles or XBP, we have observed the influence of the environment on the S1 lifetime of meso-zeaxanthin, which has a longer (12 ps) lifetime in XBP than in solution (9 ps). The most pronounced effect was found for vibrational relaxation in the S1 state, which is significantly slower for xanthophylls in XBP compared with micelles and solution. This effect is more pronounced for meso-zeaxanthin, suggesting a specific site of binding of this carotenoid to XBP.
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| 4. |
- 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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| 5. |
- Durbeej, Bo, et al.
(författare)
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On the formation of cyclobutane pyrimidine dimers in UV-irradiated DNA : why are thymines more reactive?
- 2003
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Ingår i: Photochemistry and Photobiology. - : John Wiley & Sons. - 0031-8655 .- 1751-1097. ; 78:2, s. 159-167
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Tidskriftsartikel (refereegranskat)abstract
- The reaction pathways for thermal and photochemical formation of cyclobutane pyrimidine dimers in DNA are explored using density functional theory techniques. Although it is found that the thermal [2+2] cycloadditions of thymine + thymine (T + T T<>T), cytosine + cytosine (C + C C<>C) and cytosine + thymine (C + T C<>T) all are similarly unfavorable in terms of energy barriers and reaction energies, the excited-state energy curves associated with the corresponding photochemical cycloadditions display differences that – in line with experimental findings – unanimously point to the predominance of T<>T in UV-irradiated DNA. It is shown that the photocycloaddition of thymines is facilitated by the fact that the S1 state of the corresponding reactant complex lies comparatively high in energy. Moreover, at a nuclear configuration coinciding with the ground-state transition structure, the excited-state energy curve displays an absolute minimum only for the T + T system. Finally, the T + T system is also associated with the most favorable excited-state energy barriers and has the smallest S2–S0 energy gap at the ground-state transition structure.
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| 6. |
- von Beckerath, Mathias, 1966-, et al.
(författare)
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The influence of UV exposure on 5-aminolevulinic acid-induced protoporphyrin IX production in skin
- 2001
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Ingår i: Photochemistry and Photobiology. - 0031-8655 .- 1751-1097. ; 74:6, s. 825-828
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Tidskriftsartikel (refereegranskat)abstract
- The skin of nude mice was exposed to erythemogenic doses of UV radiation, which resulted in erythema with edema. An ointment containing 5-aminolevulinic acid (ALA) was topically applied on mouse and human skin. Differences in the kinetics of protoporphyrin accumulation were investigated in normal and UV-exposed skin. At 24 and 48 h after UV exposure, skin produced significantly less protoporphyrin IX (PpIX) than skin unexposed to UV. Human skin on body sites frequently exposed to solar radiation (the lower arm) also produced less PpIX than skin exposed more rarely to the sun (the upper arm). It is concluded that UV radiation introduces persisting changes in the skin, relevant to its capability of producing PpIX from ALA. The observed differences in ALA-induced PpIX fluorescence may be the result of altered penetration of ALA through the stratum corneum or altered metabolizing ability of normal and UV-exposed skin (or both).
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| 7. |
- DaCosta, R. S., et al.
(författare)
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Molecular fluorescence excitation-emission matrices relevant to tissue spectroscopy
- 2003
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Ingår i: Photochemistry and Photobiology. - 0031-8655 .- 1751-1097. ; 78:4, s. 384-392
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Tidskriftsartikel (refereegranskat)abstract
- In vivo and ex vivo studies of fluorescence from endogenous and exogenous molecules in tissues and cells are common for applications such as detection or characterization of early disease. A systematic determination of the excitation-emission matrices (EEM) of known and putative endogenous fluorophores and a number of exogenous fluorescent photodynamic therapy drugs has been performed in solution. The excitation wavelength range was 250-520 nm, with fluorescence emission spectra collected in the range 260-750 nm. In addition, EEM of intact normal and adenomatous human colon tissues are presented as an example of the relationship to the EEM of constituent fluorophores and illustrating the effects of tissue chromophore absorption. As a means to make this large quantity of spectral data generally available, an interactive database has been developed. This currently includes EEM and also absorption spectra of 35 different endogenous and exogenous fluorophores and chromophores and six photosensitizing agents. It is intended to maintain and extend this database in the public domain, accessible through the Photochemistry and Photobiology website (http://www.aspjournal.com/).
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| 8. |
- Andersson-Engels, Stefan, et al.
(författare)
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Fluorescence Imaging and Point Measurements of Tissue - Applications To the Demarcation of Malignant-tumors and Atherosclerotic Lesions From Normal Tissue
- 1991
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Ingår i: Photochemistry and Photobiology. - 0031-8655. ; 53:6, s. 807-814
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Tidskriftsartikel (refereegranskat)abstract
- The possibilities of using laser-induced fluorescence for tissue diagnostics are discussed. The tissue types investigated are malignant tumors and atherosclerotic lesions. Studies with natural autofluorescence as well as with fluorescent tumor markers are included in this paper. Fluorescence emission and decay data are presented for some tissue chromophores contributing to tissue autofluorescence. Optical spectroscopic characteristics of fluorescent malignant tumor markers are analyzed and instrumental designs for clinical applications are discussed. Images recorded with a multicolor fluorescence imaging system developed in Lund are presented.
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| 9. |
- Andersson-Engels, Stefan, et al.
(författare)
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Laser-induced Fluorescence In Malignant and Normal Tissue of Rats Injected With Benzoporphyrin Derivative
- 1993
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Ingår i: Photochemistry and Photobiology. - : Wiley. - 0031-8655 .- 1751-1097. ; 57:6, s. 978-983
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced fluorescence was used to characterize the localization of intravenously administered benzoporphyrin derivative-monoacid (BPD-MA) 3 h postinjection in different rat tissue types, including an induced experimental malignant tumor. A comparison of the fluorescence properties and the demarcation potential between the newer sensitizer BPD-MA and four other substances, hematoporphyrin (HP), polyhematoporphyrin ester (PHE), tetrasulfonated phthalocyanine (TSPc) and the commercially available Photofrin earlier investigated, is included. The fluorescence light was induced with a nitrogen laser, emitting at 337 nm. The fluorescence spectrum in the region 380-750 nm was analyzed by a polychromator equipped with a diode array detector. The demarcation potential between tumor and surrounding tissue in terms of fluorescence signal for the tumor model used was 2:1 for BPD-MA. In comparison with the other drugs, HP shows about the same demarcation potential, whereas Photofrin and PHE exhibit about 3 times better and TSPc about 1.5 times better demarcation. By also employing the endogenous tissue fluorescence signature the contrast was enhanced by a factor of about 2 for each of the five drugs.
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| 10. |
- Andersson, PA, et al.
(författare)
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Photophysical characterization of natural cis-carotenoids
- 2001
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Ingår i: PHOTOCHEMISTRY AND PHOTOBIOLOGY. - 0031-8655. ; 74:4, s. 549-57
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Tidskriftsartikel (refereegranskat)abstract
- By means of steady-state fluorescence spectroscopy we explore the photophysics of two lowest lying singlet excited states in two natural 15-cis-carotenoids, namely phytoene and phytofluene, possessing three and five conjugated double bonds (N), respectively. The results are interpreted in relation to the photophysics of all-trans-carotenoids with varying N. The fluorescence of phytofluene is more Stokes-shifted relative to that of phytoene, and is ascribed to the forbidden S-1 --> S-0 transition, with its first excited singlet state (S-1) lying 3340 cm(-1) below the dipole allowed second excited singlet state (S-2), at 77 K. For phytoene the S-2 and S-1 potential surfaces are closer in energy, probably giving rise to the mixed S-2 and S-1 fluorescence characteristics. The origin of phytoene fluorescence is discussed and is suggested to be due to the S-1 --> S-0 transition; with the S-1 state located 1100 cm(-1) below S-2 at 77 K. The dependence of the fluorescence quantum yield on temperature and viscosity shows that large amplitude molecular motions are involved in the radiationless relaxation process of phytoene. The transition dipole moment of absorption and emission are parallel in phytoene and nonparallel in phytofluene.
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