ABSTRACT
The central structural feature of all carotenoids, a linear conjugated chain, makes carotenoids highly hydrophobic molecules. Since pioneering work carried out on carotenoids more than 40 years ago (Buchwald and Jencks 1968), it has been known that this hydrophobicity promotes the formation of carotenoid aggregates when dissolved in hydrated solvents and that aggregation is characterized by dramatic changes in absorption spectra (Ruban et al. 1993, Gruszecki 1999, Simonyi et al. 2003). A number of studies carried out since the observation of astaxanthin aggregation (Buchwald and Jencks 1968) demonstrates that two types of carotenoid aggregates can be distinguished according to their absorption spectra. The rst type is termed an H-aggregate and is characterized by a large blueshift of the absorption spectrum. The H-aggregate consists of molecules whose conjugated chains are oriented parallel to each other and are closely packed (the card-pack arrangement). The second aggregation type, the J-aggregate, is characterized by a redshift of the absorption spectrum, and results from a head-to-tail organization of conjugated chains (Simonyi et al. 2003).
