Characterization of fucoxanthin aggregates in mesopores of silica gel: Electronic absorption and circular dichroism spectroscopies

• We prepared the conjugates of fucoxanthin in silica gel that has nano-scale pores.
• In the conjugates, H- and J-aggregated fucoxanthin were observed by electronic absorption spectroscopy.
• The aggregation type was controlled by adjusting the amount of fucoxanthin relative to the silica gel.
• H-aggregated fucoxanthin showed the exciton chirality in its CD spectrum.
• We calculated the molecular arrangement of H-aggregated fucoxanthin based on the point-dipole approximation.

Fucoxanthin shows a large bathochromic shift of its absorption band when it is bound to photosynthetic antenna pigment–protein complexes derived in brown algae (fucoxanthin–chlorophyll a/c binding protein; FCP). In order to try to understand the intermolecular interactions of fucoxanthin responsible for this shift, we attempted to create a system that can control intermolecular interactions of carotenoids. In this study, we prepared the fucoxanthin–silica gel (CARiACT Q-6, mesoporous material) conjugates by adsorbing fucoxanthin molecules into the mesopores of CARiACT, and investigated their spectroscopic properties by recording electronic absorption and circular dichroism spectra. Fucoxanthin in the pores of CARiACT showed spectra that suggested the formation of H- or J-aggregates. The form of the aggregate could be controlled by adjusting the ratio of fucoxanthin to CARiACT. The exciton chirality of H-aggregated fucoxanthin was detected by circular dichroism spectroscopy. Based on the point-dipole approximation we were able to determine the molecular arrangement of H-aggregated fucoxanthin in the pores of CARiACT.

Figure optionsDownload as PowerPoint slide