Structure and Properties of Sacran, One of Supergiant Polysaccharides, and Its Biomimetic Functionalization

Abstract

Cyanobacteria, which live in the rivers and sea, produce and secrete polysaccharides with functional groups such as carboxylic acid, sulfates, phosphates and amines that are responsible for ionic adsorption. Aphanothece sacrum, whose extracellular polysaccharide creates a jelly-like materialgelswhich protects the cells, is mass cultured in fresh water only in Japan, and is grown with adsorbing metal ions from groundwater. The fact motivated us in the bio-mimetics concept to develop a metal-recycle material of the extracellular polysaccharide, which was here extracted by a successful alkaline elution method. The extracted polysaccharide was a new product and then it was named as sacran. Sacran adsorbed various multivalent metals as expected and formed the gels whose structure was formed a fibrous nanostructural network containing water revealed by cryogenic-TEM images. Freeze-drying of sacran formed spongy materials capable of In 3 preferential adsorption to form hydrogels from the mixed solution of In 3 and Sn 4 with concentrations below 40 mM. Electrolytic refinement of indium was made using the ion-complex hydrogels at room temperature to obtain indium metal foil at a pure grade over 99.9%. Thus epochal energy-saving methods for indium refinement were established using spongy hydrogels of cyanobacterial polyanions.