The giant anionic polysaccharide "sacran", which is composed of 6-deoxyhexoses, pentoses, uronic acids as well as hexoses, showed hydrophobization and insolubilization phenomena in response to ultraviolet light irradiation. The sacran solution became turbid, and microparticles were formed by photo-irradiation. To visualize the results of this photoreaction, anionic polysaccharide gels cross-linked by metal cations were used. As a result, we observed that sacran-gels with trivalent metal ions gradually contracted depending on the photo-irradiation energy. In contrast, alginate gels used as a comparison degraded instead of contracting. This photoshrinkage of the sacran gels may be attributed to the hydrophobization of uronic acid based on photodecarboxylation. We propose that sacran-metal ion gels can function as effective, photoresponsive gels.
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