Ultrafast excitation relaxation dynamics and energy transfer in the siphonaxanthin-containing green alga Codium fragile

Structurally flexible macro-organization of the pigment–protein complexes of the diatom Phaeodactylum tricornutum

“…Further details of the molecular organization of this long-wavelength absorbing Fx might be possible to gain from Starkspectroscopy (Palacios et al 2004). It is interesting to note that a similar, weak, CD-silent long-wavelength (*535 nm) absorbing band was identified in a marine green alga, and was assigned to originate from a new electronic excited state, S x between S 1 and S 2 , of siphonaxanthin, which appears to transfer to a specific Chl a molecule(s) (Akimoto et al 2004(Akimoto et al , 2007. This state arises only in pigment-protein complexes, probably due to a specific interaction with amino acids (Akimoto et al 2007), and resembles the long wavelength absorbance band of Fx in diatoms (Gillbro et al 1993).…”

Application of Time‐Resolved Polarization Fluorescence Spectroscopy in the Femtosecond Range to Photosynthetic Systems†

“…When carotenoids in solution were excited to the S 2 state, the anisotropy of the S 2 fluorescence did not change with time and showed a constant value of approximately 0.4, which is the theoretical limit: r ( t ) = 0.4 for β‐carotene (15), r ( t ) = 0.38 for lutein (16) and r ( t ) = 0.39 for siphonaxanthin (17). This indicates that the carotenoids fluoresced from the initially excited state.…”

“…In order to analyze the time evolution of the fluorescence anisotropy of carotenoids in A. thaliana LHC II complexes, the time constants for I // ( t ), I ⊥ ( t ), and r ( t ) were globally evaluated as follows: where f ( t ) is an instrumental response function, and A i and B i are pre‐exponential factors for τ i in I // ( t ) and I ⊥ ( t ), respectively. For the instrumental response function, a Gaussian function of 220 fs FWHM was used (17). Here, t’ in is introduced to convolute the Gaussian function and an exponential decay function.…”

“…In pigment–protein complexes, carotenoids containing the keto‐carbonyl group, i.e. siphonaxanthin and fucoxanthin, exhibit an absorption band at approximately 535 nm (17). This is explained by the strong interaction between the keto‐carbonyl group and the proteins (17).…”

“…siphonaxanthin and fucoxanthin, exhibit an absorption band at approximately 535 nm (17). This is explained by the strong interaction between the keto‐carbonyl group and the proteins (17). As lutein has no group that could strongly interact with proteins in its conjugation system, the carotenoid–protein interaction should not be significant for lutein, at least not enough to make the S x – S 0 transition occur.…”