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Photochemical and photophysical properties of carotenoid immobilized on a surfactant micellar medium including chlorophyll as an artificial photosynthesis system

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ABSTRACT

To develop an artificial photosynthesis model, the anionic water-soluble carotenoid dye crocetin was electrostatically immobilized onto the surface of cationic surfactant cetyltrimethylammonium bromide (CTAB) micellar medium including Mg chlorophyll-a and b (MgChl-a and b) (Cro/MgChl), and its photophysical properties were studied using UV-vis absorption and fluorescence spectroscopy. The fluorescence of MgChl-a and b was observed, with the excitation wavelength attributed to the absorption band of crocetin, indicating that photo-induced energy transfer from the photoexcited state of crocetin to MgChl-a and b occurs. The photostability of MgChl-a and b in Cro/MgChl was investigated under continuous irradiation. After 60 min irradiation, the absorbance decreases at 660 nm Cro/MgChl and MgChl-a/b, without crocetin, were 3.0 and 17%, respectively. These results indicate that the photo-bleaching rate of MgChl-a/b in Cro/MgChl on irradiation is suppressed by the crocetin molecule on the surface of micelles.

No MeSH data available.


Photoinduced hydrogen production system containing an electron donor (D), a photosensitizer (S), an electron relay (C), and a hydrogen production catalyst.
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f5-2_57: Photoinduced hydrogen production system containing an electron donor (D), a photosensitizer (S), an electron relay (C), and a hydrogen production catalyst.

Mentions: Artificial photosynthesis is attractive as a solar energy conversion system. For example, photoinduced hydrogen production from water has been studied extensively by means of converting solar energy to chemical energy. Photo-induced hydrogen production systems containing an electron donor (D), a photosensitizer (S), an electron relay (C), and a hydrogen production catalyst have been widely studied, as shown in Scheme 11–3. In this system, colloidal platinum and hydrogenase from Desulfovibrio vulgaris (Miyazaki) are widely used as a catalyst4–7. We have reported some photoinduced hydrogen production with chlorophyll and colloidal platinum8,9. However, chlorophylls purified from green plants are unstable on irradiation. Thus, photosensitizer molecules with a high stability to withstand irradiation are desired for the development of photoinduced hydrogen production. On the other hand, light-harvesting sites in natural photosynthetic proteins consist of Mg chlorophyll-a and b (MgChl-a and b) and a carotenoid dye such as β-carotene10. These dye molecules play an important role in photosynthesis such as light harvesting, photoinduced electron transfer, and so on. The carotenoid dyes in these proteins absorb light in the blue-green region, in which chlorophyll has a low extinction coefficient, and transfer excitation energy to chlorophyll. Many studies on excitation energy transfer from carotenoids to chlorophylls have been reported11–14. On the other hand, carotenoid dyes also have important functions such as in the absorption of UV light, photo-protection of MgChl-a and b, photosynthetic proteins, and so on15,16. Artificial photosynthesis systems based on carotenoid and chlorophyll conjugation via covalent bonds have been reported17,18. In photosyhthetic proteins, MgChl-a and b and carotenoid dyes are assembled via hydrogen bonds, hydrophobic interactions, and coordination bonds, but not covalently to amino acid residues19–21. Moreover, to develop an artificial photosynthesis model, a small separation between energy donors (carotenoids) and acceptors (chlorophylls) is a requirement dictated by the extremely short excited state lifetimes of the carotenoids. Carotenoid dye immobilized onto the surface of a surfactant micellar medium including MgChl-a and b in the hydrophobic site as an artificial photosynthesis protein is an attractive photosensitised system, because the carotenoid dye molecule on the surface of micelles will act as a UV light cut-off filter, and so the degradation of MgChl-a/b will be suppressed.


Photochemical and photophysical properties of carotenoid immobilized on a surfactant micellar medium including chlorophyll as an artificial photosynthesis system
Photoinduced hydrogen production system containing an electron donor (D), a photosensitizer (S), an electron relay (C), and a hydrogen production catalyst.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC5036646&req=5

f5-2_57: Photoinduced hydrogen production system containing an electron donor (D), a photosensitizer (S), an electron relay (C), and a hydrogen production catalyst.
Mentions: Artificial photosynthesis is attractive as a solar energy conversion system. For example, photoinduced hydrogen production from water has been studied extensively by means of converting solar energy to chemical energy. Photo-induced hydrogen production systems containing an electron donor (D), a photosensitizer (S), an electron relay (C), and a hydrogen production catalyst have been widely studied, as shown in Scheme 11–3. In this system, colloidal platinum and hydrogenase from Desulfovibrio vulgaris (Miyazaki) are widely used as a catalyst4–7. We have reported some photoinduced hydrogen production with chlorophyll and colloidal platinum8,9. However, chlorophylls purified from green plants are unstable on irradiation. Thus, photosensitizer molecules with a high stability to withstand irradiation are desired for the development of photoinduced hydrogen production. On the other hand, light-harvesting sites in natural photosynthetic proteins consist of Mg chlorophyll-a and b (MgChl-a and b) and a carotenoid dye such as β-carotene10. These dye molecules play an important role in photosynthesis such as light harvesting, photoinduced electron transfer, and so on. The carotenoid dyes in these proteins absorb light in the blue-green region, in which chlorophyll has a low extinction coefficient, and transfer excitation energy to chlorophyll. Many studies on excitation energy transfer from carotenoids to chlorophylls have been reported11–14. On the other hand, carotenoid dyes also have important functions such as in the absorption of UV light, photo-protection of MgChl-a and b, photosynthetic proteins, and so on15,16. Artificial photosynthesis systems based on carotenoid and chlorophyll conjugation via covalent bonds have been reported17,18. In photosyhthetic proteins, MgChl-a and b and carotenoid dyes are assembled via hydrogen bonds, hydrophobic interactions, and coordination bonds, but not covalently to amino acid residues19–21. Moreover, to develop an artificial photosynthesis model, a small separation between energy donors (carotenoids) and acceptors (chlorophylls) is a requirement dictated by the extremely short excited state lifetimes of the carotenoids. Carotenoid dye immobilized onto the surface of a surfactant micellar medium including MgChl-a and b in the hydrophobic site as an artificial photosynthesis protein is an attractive photosensitised system, because the carotenoid dye molecule on the surface of micelles will act as a UV light cut-off filter, and so the degradation of MgChl-a/b will be suppressed.

View Article: PubMed Central - PubMed

ABSTRACT

To develop an artificial photosynthesis model, the anionic water-soluble carotenoid dye crocetin was electrostatically immobilized onto the surface of cationic surfactant cetyltrimethylammonium bromide (CTAB) micellar medium including Mg chlorophyll-a and b (MgChl-a and b) (Cro/MgChl), and its photophysical properties were studied using UV-vis absorption and fluorescence spectroscopy. The fluorescence of MgChl-a and b was observed, with the excitation wavelength attributed to the absorption band of crocetin, indicating that photo-induced energy transfer from the photoexcited state of crocetin to MgChl-a and b occurs. The photostability of MgChl-a and b in Cro/MgChl was investigated under continuous irradiation. After 60 min irradiation, the absorbance decreases at 660 nm Cro/MgChl and MgChl-a/b, without crocetin, were 3.0 and 17%, respectively. These results indicate that the photo-bleaching rate of MgChl-a/b in Cro/MgChl on irradiation is suppressed by the crocetin molecule on the surface of micelles.

No MeSH data available.