Abstract
A green alga Codium fragile contains a specific carotenoid siphonaxanthin (Sxn). This carotenoid has a keto-carbonyl group conjugating with a conjugated double-bond. In pigment-protein complexes, an absorption maximum of Sxn is red-shifted and energy transfer from Sxn to chlorophyll (Chl) is known to be very efficient. We analyzed this transfer process by the femto-second fluorescence up-conversion system, and also considered the origin of the 530-nm absorption band.
The 530-nm absorption band is assigned to the S2 state based on the fluorescence lifetime, and energy transfer occurred only from the S1 state of Sxn, as similar to the case of fucoxanthin. The degree of fluorescence polarization of Sxn was approximately 0.29 in the complex and 0.38 in solution. This suggests that the 530-nm band arise from an interaction between Sxn molecules. Together with the optical properties of the complex, the origin will be discussed.
