Polyelectroyte behavior of a bacterial polysaccharide from Xanthomonas campestris: Comparison with carboxymethylcellulose

The main physicochemical properties of the polysaccharide called Xanthan produced by Xanthomonas compestris are discussed: the activity coefficient of the counter-ion, the pK(α), and the ionic selectivity are investigated and compared to those of a carboxymetholcellulose. The weight-average molecular weight (M _w = 2 × 10⁶), the intrinsic viscosity and the constant of sedimentation are determined as a function of the ionic strength. It is proved that in dilute solution, there is no intermolecular association, whatever the ionic strength. The conformation is proposed to be a rigid rodlike molecule whose length is 6000 Å, independent of ionic strength > 10^?2N.