Effect of environmental factors on the aggregation behavior of astaxanthin in water

Molecular aggregation is a common phenomenon widely found in natural organisms, which is crucial for some specific functions of biological systems. To study the aggregating behavior of hydrophobic carotenoids in water, astaxanthin was employed and dispersed under different surroundings to induce aggregation. The results showed that astaxanthin tended to form J- or H-type aggregates when the water content was higher than 60%. Both hydrochloric acid (HCl) and sodium hydroxide (NaOH) were beneficial for the formation of astaxanthin J-aggregates, but they were not good for inducing H-aggregates. Small-molecule electrolytes, like sodium salts, mostly played an enormous hindrance role to the formation of astaxanthin H- and J-aggregates, except for sodium chloride (NaCl) which helped astaxanthin to form J-aggregates. Both sodium periodate (NaIO₄) and sodium acetate (CH₃COONa) could prevent the formation of astaxanthin H- and J-aggregates, but sodium chloride (NaCl) could only hinder the formation of H-aggregates. As for polyelectrolytes chitosan and DNA, the difference of chain structure led to different aggregation effects. The soft single chain of chitosan tended to induce J-aggregates formation, while double-stranded DNA preferred to guide the formation of H-aggregates. By choosing and integrating the advantageous environmental factors that facilitate each type of astaxanthin aggregates, J- and H-type astaxanthin aggregates were stably loaded in DNA/CS nanoparticles with distinct particle sizes. Controlled preparation of either H- or J-type aggregates is of great significance for further studies concerning the structure-activity relationship of carotenoid aggregates.