Xanthan conformational properties

Milas, M. and Rinaudo, M., Investigation on conformational properties of xanthan in aqueous solutions, in Solution Properties of Polysaccharides, Brant, D. A., Ed., ACS Symp. Ser., No. 150, American Chemical Society, Washington, D.C., 1981, 25-30. 

Xanthan gum was shown to be stiffer than CMC and alginate all three are ionic polysaccharides, with CMC having slightly more flexibility than alginate under identical conditions (R. C. Clark, 1992). The invariant nature of xanthan dispersion properties is attributed to the stability of the tertiary structure. The indifference of this gum to salt is explained by its already rigid conformation (Morris, 1976). 

Investigation on Conformational Properties of Xanthan in Aqueous Solutions... 

The unusual properties of xanthan undoubtedly result from its stmctural rigidity, which in turn is a consequence of its Linear, ceUulosic backbone that is stiffened and shielded by the trisaccharide side chains. The conformation of xanthan in solution is a matter of debate. It does appear that the conformation changes with conditions. 

The usefulness of xanthan in polymer flooding for enhanced oil recovery is based on its ability to yield large increase in viscosity at low polymer concentrations under high-temperature and high salinity conditions. This important property of xanthan is determined both by its molecular weight and by the conformation adopted in solution (1). 

In this study we use electron microscopy (EM) to study xanthan strandedness and topology both in the ordered and disordered conformation. Correlation of data obtained from electron micrographs to physical properties of dilute aqueous solution on the same sample will be used to provide a working hypothesis of the solution configuration of xanthan. Electron micrographs obtained from xanthan of different origins will be compared to assess similarities and differences in secondary structure at the level of resolution in the used EM technique. 

The possibilities of the double helical structures of xanthan were re-examined thoroughly. Among the several possibilities, only parallel and antiparallel 5 double helices could be built and packed into a unit cell. The conformation of single chains in the parallel and antiparallel chains are very similar to each other. These double helical structures are compatible with several properties of xanthan in solution. 

Young, S., and Torres, J. A. (1989). Xanthan effect of molecular conformation on surface tension properties. Food Hydrocoll. 3 365-377. 

The latex adsorption work is the only recent study examining the surface properties of xanthan gum. However, it must be stressed that it was carried out on solid particles and not on liquid interfaces. The reports claiming that the gum has surface activity and that it can stabilize emulsions did not consider the adsorption properties of the gum. The surface activity of the gum is not very clear from its structure, but it is possible that some of it is derived from conformational changes induced by heat treatment [176]. 

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