Electron- and energy-transfer properties of hydrophilic carotenoids.
The antioxidant activities-expressed as the electron-donating properties-of five hydrophilic carotenoids (carotenoid surfactants) and three related hydrophobic carotenoids were investigated by flash photolysis. The electron-transfer rates of the carotenoids to the triplet state of the sensitizer 2-nitronaphthalene and the energy transfer rates of triplet 2-nitronaphthalene to the carotenoids were determined. The results demonstrate that the electron-donating effects of the hydrophilic and hydrophobic carotenoids were comparable when evaluated in acetonitrile. In the presence of water, however, electron transfer (i.e., antioxidant efficiency) was enhanced by a factor of four for the hydrophilic carotenoids. The increased hydrophilicity of carotenoids, therefore, could expand their antioxidant properties, thus facilitating their use as aqueous-phase radical scavengers. At the same time, it was shown that supramolecular assembly ("aggregation") of the amphiphilic carotenoids prevented electron transfer, thus deactivating the antioxidant function. Modulation of the biophysical properties of carotenoids through synthetic modification is capable of increasing the biological and medical utility of this natural class of predominantly hydrophobic antioxidant compound.
Sliwka
Hans-Richard
HR
Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway. hrs@nvg.ntnu.no
Melø
Thor-Bernt
TB
Foss
Bente Jeanette
BJ
Abdel-Hafez
Shams H
SH
Partali
Vassilia
V
Nadolski
Geoff
G
Jackson
Henry
H
Lockwood
Samuel F
SF
D000975:Antioxidants / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry*; D004579:Electron Transport; D004735:Energy Transfer; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D015394:Molecular Structure; D010777:Photochemistry; D010782:Photolysis; D013997:Time Factors
D000975:Antioxidants; D002338:Carotenoids