Conformations of Xanthan in Solution: Analysis by Steric Exclusion Chromatography

Clinically Relevant Insulin Degludec and its Interaction with Polysaccharides: A Biophysical Examination

Protein polysaccharide complexes have been widely studied for multiple industrial applications and are popular due to their biocompatibility. Insulin degludec, an analogue of human insulin, exists as di-hexamer in pharmaceutical formulations and has the potential to form long multi-hexamers in physiological environment, which dissociate into monomers to bind with receptors on the cell membrane. This study involved complexation of two negatively charged bio-polymers xanthan and alginate with clinically-relevant insulin degludec (PIC). The polymeric complexations and interactions were investigated using biophysical methods. Intrinsic viscosity [η] and particle size distribution (PSD) of PIC increased significantly with an increase in temperature, contrary to the individual components indicating possible interactions. [η] trend was X > XA > PIC > A > IDeg. PSD trend was X > A > IDeg > XA > PIC. Zeta (ζ)- potential (with general trend of IDeg < A < XA < X ≈ PIC) revealed stable interaction at lower temperature which gradually changed with an increase in temperature. Likewise, sedimentation velocity indicated stable complexation at lower temperature. With an increase in time and temperature, changes in the number of peaks and area under curve were observed for PIC. Conclusively, stable complexation occurred among the three polymers at 4 °C and 18 °C and the complex dissociated at 37 °C. Therefore, the complex has the potential to be used as a drug delivery vehicle.

Effect of xanthan on the molecular mobility of amorphous sucrose detected by erythrosin B phosphorescence

Molecular mobility in amorphous solids is modulated by composition and environmental conditions such as temperature. Phosphorescence of erythrosin B was used to generate a mobility map of amorphous sucrose film doped with xanthan gum at weight ratios of xanthan/sucrose ranging from 0.0001 to 0.01. On the basis of analysis of the emission energy and lifetime of erythrosin B in pure sucrose and sucrose-xanthan films over the temperature range from 5 to 100 degrees C, we conclude that xanthan influences the molecular mobility as well as the dynamic site heterogeneity of amorphous sucrose in a dose-dependent fashion. At xanthan/sucrose weight ratios below approximately 0.0005, both emission energy and lifetime decreased and k(TS0) (the nonradiative decay rate of the triplet state) increased, indicating that xanthan increased the matrix molecular mobility. At weight ratios above 0.001, both emission energy and lifetime increased and k(TS0) decreased, indicating that xanthan decreased matrix mobility, reaching a plateau at weight ratios between 0.005 and 0.01. The concentration at which the effect of xanthan switched from increasing to decreasing mobility was similar to the concentration at which polymer chains overlapped in solution, suggesting that the dynamic changeover reflected the onset of chain overlap in the amorphous solid. Systematic trends in the emission bandwidth and lifetime heterogeneity and variations in the emission lifetime vs wavelength indicated that xanthan reduced the matrix dynamic site heterogeneity except at a weight ratio of 0.01. These data illustrate the complex effects of a polymer with a rigid structure and large side chains on the mobility of an amorphous, hydrogen-bonded sugar matrix.

Polysaccharide/Surfactant complexes at the air-water interface - effect of the charge density on interfacial and foaming behaviors

The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide. Besides classical methods to investigate polymer/surfactant systems, we applied, for the first time concerning these systems, the analogy between the small angle neutron scattering by foams and the neutron reflectivity of films to measure in situ film thicknesses of foams. CTAB/pectin foam films are much thicker than the pure surfactant foam film but similar for high- and low-charged pectin/CTAB systems despite the difference in structure of complexes at interfaces. The improvement of the foam properties of CTAB bound to pectin is shown to be directly related to the formation of pectin-CTAB complexes at the air-water interface. However, in opposition to surface activity, there is no specific behavior for the highly charged pectin: foam properties depend mainly upon the bulk charge concentration, while the interfacial behavior is mainly governed by the charge density of pectin. For the highly charged pectin, specific cooperative effects between neighboring charged sites along the chain are thought to be involved in the higher surface activity of pectin/CTAB complexes. A more general behavior can be obtained at lower charge density either by using a low-charged pectin or by neutralizing the highly charged pectin in decreasing pH.

Role of Substituents on the Properties of Some Polysaccharides

This paper concerns the influence of the chemical structure on the physical properties of some polysaccharides. Especially, we proposed to discuss the role of the substituents on these properties. In some cases, non-carbohydrate substituents play a minor role on rheological properties in the presence of a salt excess as shown on xanthan and succinoglycan. The rheology of aqueous solution of these stereoregular polysaccharides is controlled by the conformation (helical conformation) whose stability is not largely influenced by these substituents. On the other hand, the interaction between galactomannan and xanthan depends on the presence of acetyl substituents on xanthan but also on the xanthan conformation. However, for polymers such as gellan, XM-6 or BEC 1615, complete deacetylation induces the ability to form physical gels in given thermodynamic conditions. The presence of carbohydrate substituents or short side chains was also examined. Especially in the gellan family, the role of position of substitution (position 3 on the glucose unit C or position 6 on the A glucose) was presented. It is concluded that the substituents giving the higher stability for the helical conformation (higher DeltaH and Tm values) also cause a lower salt sensitivity for the helical stability. The role of the substituents on the properties is also described for natural polymers and their chemically or enzymatically modified derivatives.

Polyelectrolyte and surfactant mixed solutions. behavior at surfaces and in thin films

Dilute mixed solutions of non-surface active anionic polymers (polyacrylamide and polystyrene sulfonate, xanthan) and various surfactants have been studied with several methods: surface tension, ellipsometry, X-ray and neutron reflectivity, thin film balance, surface and bulk rheology. A strong synergistic lowering of the surface tension is found with cationic surfactants in the concentration range where no appreciable complexation of surfactant and polymer occurs in the bulk solution (as seen from viscosity measurements). Despite appreciable differences between surface tension behaviour, the adsorbed layer is very similar for all the polymers: their thickness is small and the polymer chains are stretched along the surface. The surface tension behaviour of these polymers with non-ionic surfactants is also different. When the polymers are confined in thin films, the forces between surfaces are similar, and independent of surfactant nature: oscillatory forces are measured, which reflect the existence of a polymer network with a well defined mesh size. The connection of foam stability with surface and bulk complexation is far from clear.

A new bacterial polysaccharide (YAS34). I. Characterization of the conformations and conformational transition

This paper concerns the study of the conformational transition of a new exopolysaccharide (YAS34) using experimental techniques such as optical rotation, conductimetric and microcalorimetric measurements as a function of temperature. The behaviors of this polysaccharide in the acid or sodium salt form are compared; a deacetylated sample is also prepared to demonstrate the role of substituents. For the native structure (never heated), a conformational transition is observed but the deacetylated polysaccharide exhibits no ordered conformation. Multidetection size exclusion chromatography (SEC) analyses and conductimetric experiments allowed to determine the nature of each conformation and the molecular dimensions. From these results, it is suggested that the native conformation is a double helix which by heating over T(m) (temperature corresponding to half conformational transition) dissociates into disordered single chains. In the acid and sodium salt forms, by cooling below T(m), an ordered conformation is restored. This conformation seems to be an intramolecular double helix 'hairpin-like turn' (called renatured conformation). Nevertheless an irreversible denaturation is obtained progressively in the sodium salt form when the time of heating over T(m) increases. The conformation of the deacetylated polysaccharide corresponds to that of a single flexible chain (disordered conformation). The conformational transition for the native conformation was studied also in relation to the polyelectrolytic character of the polysaccharide: stability as a function of salt nature and salt and polymer concentrations was investigated for the polymer initially in the sodium and acid forms.