Chlorophyll triplet quenching by fucoxanthin in the fucoxanthin–chlorophyll protein from the diatom Cyclotella meneghiniana

In this work we present an optically detected magnetic resonance (ODMR) study on the triplet states populated under illumination in the isolated fucoxanthin–chlorophyll light-harvesting complex from the diatom Cyclotella meneghiniana. Evidence for the quenching of chlorophyll triplet states by fucoxanthin is provided, showing that this carotenoid is able to perform the photoprotective role. For the first time, the magnetic parameters characterizing the fucoxanthin triplet state have been determined.The results reveal analogies but also differences with respect to the triplet–triplet energy transfer process, which involves chlorophylls a and carotenoids in the LHC complex from dinoflagellates and LHCII from higher plants. The degree of efficiency of the photoprotection mechanism, in these light harvesting complexes, is discussed in terms of pigment–protein structure.

► Fucoxanthin plays a photoprotective role in FCP by quenching Chl a triplet states.
► “Unquenched” triplet states belong to the red-most Chls in the complex.
► FCP’s structure shows a general similarity with LHCII of higher plants.
► Differences exist in the local geometry of the Cars and the nearby Chls.