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The manuscript focuses on the demixing of hyaluronan and alginate in the hydrogel state. Binary solutions of the two polysaccharides have been treated with Ca2+ as the alginate cross-linking ion and the radial distribution of the two components in the hydrogels was measured by means of 1H NMR. These results revealed the presence of alginate-enriched and hyaluronan-enriched domains stemming from a polysaccharide demixing. The hydrogels were characterized by means of uniaxial compression and creep-compliance measurements which showed that the demixing increased the overall resistance of the hydrogel to stress. In addition, due to the viscoelastic properties of hyaluronan, a marked increase of the Newtonian viscosity of the constructs was noticed. The peculiarity of the effect of hyaluronan was demonstrated by the use of an alginate unable to form gel by binding non-calcium binding alginate, i.e. mannuronan, ruling out the effect of viscosity over the time-dependent behavior of the mixed hyaluronan-alginate hydrogels.

This paper reports some physicochemical properties of the capsular polysaccharide produced by Klebsiella pneumoniae serotype K40 (K40-CPS) in aqueous solution. The polymer has a linear hexasaccharide repeating unit containing one glucuronic acid residue as the only ionizable group. Potentiometric, viscometric, chiro-optical and rheological measurements have been carried out over a range of ionic strength, pH and temperature, with the aim of characterizing the conformational state of the polysaccharide in aqueous solution. All the data reported indicate that the K40-CPS does not undergo a cooperative conformational transition under the investigated experimental conditions. Furthermore, the viscosity data and the viscoelastic spectra suggest that the K40-CPS is rather flexible and adopts a random coil conformation in solution.

The solution properties of the capsular polysaccharide produced by Klebsiella pneumoniae SK1, SK1-CPS, were investigated by various methods. The SK1-CPS repeating unit is a branched pentasaccharide containing one glucuronic acid as single unit side chain; acetyl groups are present as non-carbohydrate substituents on the uronic acid residue in non-stoichiometric amounts. Chiro-optical, potentiometric, viscometric and rheological measurements have been performed in order to characterize the conformational behaviour of the polymer in water and in aqueous salt solutions. Under the investigated experimental conditions, changes of temperature, ionic strength and pH were shown not to induce any cooperative conformational transition. All the results obtained suggest that the solution conformation of SK1-CPS is a random coil with a certain degree of chain flexibility. The removal of the acetyl substituents apparently does not modify the overall conclusions drawn for the native polymer, except for an incipient tendency to aggregation revealed for high salt conditions.

The thermodynamic properties of the dissociation of natural polyuronic acids in dilute aqueous solution at 25°C are reported. The investigation concerns polygalacturonic acid and alginic acids from different sources, including highly homogeneous mannuronic and guluronic fractions and involved potentiometry, isothermal calorimetry, dilatometry and circular dichroism measurements. The dissociation of polyuronic acids was studied as a function of degree of dissociation, concentration of the polymer and ionic strength. Abnormal behaviour upon dissociation was observed only in polyguluronic and polygalacturonic acids and attributed to a pH-induced conformational transition and/or to an interchain disaggregation. Direct molecular weight evidence supports the proposed intramolecular transition of polygalacturonate chain.

A statistical model is presented in which an ionic polymer is taken as a linear arrangement of flexible segments (similar to the spring-bead model). This model is used to represent semi-flexible linear ionic polysaccharides in solution. The distribution of end-to-end distances is taken from Monte Carlo calculations of the amylosic chain conformation and combined with Manning's counterion condensation theory of linear polyelectrolytes. The excess thermodynamic properties are then calculated as a function of the degree of ionization and of a number of physical variables. The results show that the statistical average of thermodynamic functions taken over the conformational states is not equivalent to the thermodynamic function of the average conformation. This has important implications for the correct comparison of theoretical prediction with the experimental results.