Chitosan oxalate gel

This paper describes a novel thermally reversible chitosan oxalate gel, a thermally irreversible chitosan gel, and a thermally irreversible chitin gel (N-acetylchitosan gel or regenerated chitin). An intramolecular conversion of the chitosan oxalate gel into the chitin gel via the chitosan gel is discussed. The chitin gel may play a role of the structural processing of crab and shrimp shells and insect cuticle. A sheet of transparent film has been prepared from the gel slice by air-drying, 2 and a sheet of non-transparent porous by freeze-drying. The gel may be usable as a digestible material for drug delivery systems and as media for the immobilization of enzymes and cells. 

Chitosan (0.97 g. d.s. 0.10 for NAc) was dissolved in aqueous oxalic acid solution (30 mL, 0.97 g, 1.8 mol./GlcN) on a boiling water bath, and a transparent gel was obtained by cooling for 18 hrs. The gel was dialyzed in distilled water at room temperature for 3 days, and a transparent chitosan oxalate gel was obtained. The gel was composed of about 5% chitosan oxalate (1.0 for oxalic acid/GlcN) and about 95% water. A portion of the gel was homogenized, washed with distilled water, and dried to give the xerogel (1.3 g). 1740 (COOH), and 2600, 1620 and 1400... 

Chitosan oxalate gel (20 g by wet weight) was treated with IN NaOH... 

Gelation of Chitosan Chitosan Oxalate Gel, Chitosan Gel and Chitin Gel... 

The gel did not undergo syneresis, and it was stable in water and in 2% aqueous acetic acid solution at room temperature for several months. The excess of oxalic acid present in the gel was removed by dialysis in distilled water to give the chitosan oxalate gel. Its elemental analysis data proved that the chitosan oxalate xerogel is composed of one mol. equiv. of oxalic acid per D-glucosaminyl residue, indicating the absence of the cross-linking of oxalic acid in chitosan chains. The structure was... 

Figure 1. Effect of chitosan concentration on the elastic hardness of the chitosan oxalate gel at a molar ratio of GlcN oxalic acid = 1.0 1.5...

The gel shape was little changed, even after the complete removal of oxalic acid by treating the gel with aqueous NaOH solution however, the gel turned opaque (Figure 4). The opaque xerogel was identified as chitosan on the basis of its IR and CP/MAS-NMR spectra, and on the elemental analysis data. The elastic hardness and the breaking point of the chitosan gel were about two times higher than that of the chitosan oxalate gel (Table 1). 

Figure 4. A view of the chitosan oxalate gel (right) and the chitosan gel (left).

In conclusion, this is the first report dealing with a basic polysaccharide gel that is thermally reversible and dealing with an intramolecular conversion of one gel to another gel in the solid phase. The chitin gels, which were produced by N-acetylation of the chitosan gel via the chitosan oxalate gel, and by 0-deacetylation of the partial 0-acetylated... 

Table 2), and on a scanning electron microscopic observation of the xerogel.The present study strongly indicates the presence of a common solid phase among the chitosan oxalate, chitosan, and N-acetylchitosan gels. 

Chitosan was also crosslinked with epichlorhydrin, diisocyanate or 1,4,-butanediol diglycidyl ether [112-114] a naturally occurring crosslinker, genepin, was recently studied. [115] Different gels were obtained by reaction of polycarboxylic acids, such as citric acid and oxalic acid. [116-118]... 

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