Effect of calcium ions on the organization of iota-carrageenan helices: an X-ray investigation

摘要

X-ray fiber diffraction analysis confirms that calcium #iota#-carrageenan forms a threefold, right-handed, half-staggered, parallel, double helix of pitch 26.42 A stabilized by interchain hydrogen bonds. According to the detailed structural results, three helices are peacked in a trigonal unit cell (a = 23.61 and c = 13.21 A). Strong interactions between the sulfate groups of neighboring helices, mediated by calcium ions and water molecules, are responsible for stabilizing the three-dimensional structure.