Effect of Trivalent Metal Cations on the Gelation of Carboxymethylchitin Aqueous Solution

Abstract

The 6-O-carboxymethylchitin (CM-chitin) is a chelating polymer. Rheological properties of CM-chitin solution are varied by chelating with metal ions and also depend on the affinity between metal ions and CM-chitin. CM-chitin aqueous solution forms a gel by introducing some kind of trivalent metal cations. The gel attracts attentions for high potential of medical polymer, but the effects of added metal cations on the gelation are not clear. In the present study, these effects are investigated through the rheological properties of the systems. The rheological properties of the CM-chitin aqueous solution added various concentrations of AlCl3, GaCl3, or InCl3 are measured using a cone-and-plate type rheometer at 25 °C. It is revealed that the salt concentration required for gelation of CM-chitin aqueous solution increases in the following order; InCl3>AlCl3>GaCl3. This result is likely attributed to the fact that the constraint in the molecular motion of CM-chitin by In3+, Al3+, or Ga3+ ions in the aqueous solution is decreasing in the following order; In3+