Sulfate and Functional Groups Modify the Helical Conformation of Iota ‐Carrageenan Insight Difference in the Biological Activities

Abstract The biological activity of seaweed sulfated polysaccharides depends on chain length, functional groups, and molecular weight, but their structural dynamics in solution projecting functional groups for bioactivity remain unexplored. This study evaluated the biological activity of ι ‐carrageenan fractions extracted from red seaweed, Solieria robusta , based on sulfate content and helical conformation. The extracted ι ‐carrageenan was dialyzed into three fractions (<3.5, 3.5–14, and >14 kDa), with the >14 kDa fraction further hydrolyzed into sub‐fractions. Sulfate content was highest in the extracted <3.5 kDa, followed by >14 kDa and 3.5–14 kDa, while bioactivity was highest in 3.5–14 kDa. HeLa cell cytotoxicity was also highest in extracted 3.5–14 kDa, with the lowest IC 50 value. FTIR confirmed ι ‐carrageenan and sulfate groups (830 cm − ¹) in all fractions. AFM showed high bioactivity in sulfate‐rich fractions with packed helices, while hydrolyzed fractions had irregular folding and low bioactivity. This study concludes that the bioactivity of carrageenan fractions depends on chain length, sulfate, and functional group intactness, and their associated dynamic helical conformation. The 3.5–14 kDa fractions of ι ‐carrageenan, with high sulfate content and distinct helical conformation with regular average folding, showed good cytotoxicity against HeLa cells, making it a promising material for biomedical applications.