The formation of inclusion compounds of alginic acid in aqueous solution

From the microscopic visualization of metal alginates, the alginate fine structure was found to be a regularly arranged network having many host spaces in its fiber net. Under acid solution such a fiber net took the rounded, buckled and twisted form as much as possible and finally changed to a porous cluster form. Then the binding properties of sodium alginate, calcium or cadmium alginate and granular alginic acid obtained from the treatment with hydrochloric acid to iodine, cholesterol and dyes were investigated. Sodium alginate and calcium or cadmium alginate formed adducts with iodine, cholesterol and dyes; accordingly the amount of these materials in solution was reduced by the addition of alginates. The high uptake of alginates by these materials were cleary observed under acid solution giving inclusion compounds. Granular alginic acid also showed high uptake of iodine and dyes, but not of cholesterol. The blue stained alginate-iodine compound formed at pH about 1 having maximum absorption at 587nm was found to be an inclusion compound judging from the distance of 3.13 Å for included iodine I-I and the number of uronic residues bound to the iodine molecule in the granular alginic acid-iodine compound. The binding mechanism for the high uptake behavior of alginic acid was clarified with the observation of inclusion compounds by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).