Curdlan gels

There are several reports on the coating of bone-like hydroxyapatite onto natural polymer substrates. Kawashita et at. [57] reported that carboxymethylated chitin and gellan gum gels, which have carboxyl groups, can form hydroxyapatite on their surfaces in SBF if they are treated with a saturated Ca(OH)2 solution in advance, while curdlan gel, which has no carboxyl group, does not form hydroxyapatite in SBF, even if it is treated with Ca(OH)2 solution. These results support the hypothesis that carboxyl groups induce hydroxyapatite nucleation. Kokubo et at. [58,59] reported that non-woven fabrics of carboxymethylated chitin and alginate fibers also form hydroxyapatite on their surfaces in SBF if they are treated with Ca(OH)2 solution. 

Figure 8. A model for the ultrastructure of curdlan gel at room temperature.

A wide and 1000-1500 A long (Fig. 11D), in which striat-ions are not so clear as in the renatured and 60°C-set preparations. X-ray studies of the oriented curdlan gels showed that the heat treatment at temperatures above 120°C(autoclaving) caused a... 

We have examined the X-ray results from various oriented curdlan gels and report our findings and calculations on a number of models. In addition we have investigated the behaviour of curdlan gels in a series of deuterium exchange experiments monitored with infra-red spectroscopy. 

Figure 3. X-ray fiber diffraction photograph obtained from a dry, annealed-oriented fiber of curdlan gel (fiber axis vertical)...

Table II. The band assignment for the infra-red absorption spectrum of a curdlan gel film (1A).

The X-ray evidence favours a model for the curdlan gel based on triple-stranded molecules. This structure is present in both the gel prepared from aqueous suspension and from alkali solution. The alkali gel contains the proposed seven-fold triple-stranded model (Figs. 7 and 14a) which converts to the more symmetric six-fold triple helix by annealing (Figs. 6 and 14b). This... 

Curdlan gel formation is heat dependent. This polysaccharide is not soluble in water, but when an aqueous suspension is heated it becomes dear at about 54°C. Furdier heating leads to gel fonnation. The gels are stable over a wide range of pH (3 to 95) and do not melt at temperatures below 100°C. Curdlan gels are formed by cross-linldng, involvii conformational ordering of the exopolysaccharide molecules to give a triple helical structure. 

Fig. 24.6. C NMR spectra of curdlan gel recorded by a variety of experimental conditions [21].

The properties of the curdlan gel have been shown to be intermediate between those of the elastic gelatin gel and the brittle agar gel. The relationship between the breaking strength and the elastic modulus of agar, curdlan, and gelatin is shown in Figure 9. 

The melting points and heats of junction formation of curdlan gels depend on the concentration and DP of the polysaccharide [a (1 3)-P-D-glucan from Alcaligenes faecalis. The junction zones of the gels appear to form in regions of aggregation of intertwined helices. X-Ray diffraction studies have revealed that curdlan assumes a triple-helical structure. ... 

Fig. 3 Comparison of NMR spectra of (b) Curdlan gel and (a) its low molecular weight oligomer [123].

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