AFM Vision of Carrageenan Structures
The structural conformations of the anionic carrageenan polysaccharides in the presence of monovalent salt close to physiological conditions are studied by atomic force microscopy. Iota-carrageenan undergoes a coil–helix transition at high ionic strength, whereas lambda-carrageenan remains in the coiled state. Polymer statistical analysis reveals an increase in persistence length from 22.6 (0.2) nm in the random coil, to 26.4 (0.2) nm in the ordered helical conformation, indicating an increased rigidity of the helical iota-carrageenan chains.
The many decades-long debated issue on whether the ordered state can exist as single or double helix is conclusively resolved.The present work corroborates the model of a single helix ordered state, although this does not preclude the possibility of superhelical formation or a mechanism changing from intramolecular single to intermolecular dimeric double helices when increasing the polymer concentration.