Induced Chirality in Canthaxanthin Aggregates Reveals Multiple Levels of Supramolecular Organization

Carotenoids tend to form supramolecular aggregates via non-covalent interactions where the chirality of individual molecules is amplified to the macroscopic level. We show that this can also be achieved for non-chiral carotenoid monomers interacting with polysaccharides. The chirality induction in canthaxanthin (CAX), caused by heparin (HP) and hyaluronic acid (HA), was monitored by chiroptical spectroscopy. Electronic circular dichroism (ECD) and Raman optical activity (ROA) spectra indicated the presence of multiple carotenoid formations, such as H- and J-type aggregates. This is consistent with molecular dynamics (MD) and density functional theory (DFT) simulations of the supramolecular structures and their spectroscopic response. Mixing chiral polysaccharides with the achiral carotenoid canthaxanthin (CAX) leads to a unique chirality induction, with strong optical activity visible in the electronic circular dichroism (ECD) and resonance Raman optical activity (RROA) spectra. Interpretation of the data using density functional theory (DFT) and molecular dynamics (MD) modelling suggests an intricate supramolecular structure with multiple carotenoid-carotenoid interactions. image