English Abstract

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

School of Materials Science, The Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan
Nippon Gomu Kyokaishi,(2014),87(4),146-152 General Review in Japanese

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 materialigelsjwhich 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 biomimetics 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 In3{ preferential adsorption to form hydrogels from the mixed solution of In3{ and Sn4{ 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.

Keywords: Cyanobacterium, Polysaccharides, Hydrogels, Metal Recycles