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This article is the first one in a series dedicated to the study of hyaluronan as observed by IR spectrometry. The goal is to determine its hydration mechanism and the structural changes this mechanism implies. Hyaluronan is a natural polysaccharide that is widely used in biomedical applications and cosmetics. Its macroscopic properties are significantly dependent on its degree of hydration. In this article we record the IR spectrum of a several micron thick dried film and deduce that four or five residual H 2 O molecules remain around each disaccharide repeat unit in the dried film. We then compare the spectra of sodium hyaluronan and its acid form to assign vibrational bands linked to the carboxylate group. We proceed with a qualitative analysis of the spectral changes induced by changes of temperature and hygroscopicity, two independent parameters that act by modifying the hydrogen bond network of the sample. This enables us to assign most of the vibrational bands of the hydrophilic groups and to distinguish the bands that are due to these hydrophilic groups when they are or are not hydrogen bonded. It constitutes a prerequisite for the quantitative analysis of hydration spectra that will be described in the following articles of this series.

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In this paper, we present some results on the dimensions-radius of gyration (p2)1/2 and persistence length Lp-and the intrinsic viscosity [tj] of different molecular weights of hyaluronate samples using light scattering and viscosity experiments. Particular attention has been given to the salt concentration effects. Extension of Odijk's model and application of the Yamakawa-Fujii theory lead to a good description of electrostatic expansion of the molecule assumed as a wormlike chain. A good agreement has been found between calculated and experimental values and allows the determination of the intrinsic persistence length Lp s 80 A. In addition, the Mark-Houwink exponent o, relating intrinsic viscosity with molecular weight and its dependence with ionic strength is predicted. A good agreement between calculated and experimental data is found, and the usually high value of a" measured on this polymer is confirmed and justified.

This paper concerns the rheological behavior of an unpasteurized sample of xanthan as a function of the polymer concentration and of the conformation of the polysaccharide. The evidence of critical concentrations (C* and C**) is discussed from steady shear and dynamic experiments. The behavior of the xanthan solutions is characteristic of polymeric solutions without any evidence of gellike character in contrast with the results obtained previously on commercial samples.

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This paper concerns the behavior in dilute and demidilute solutions of deacetylated gellan. The conformational transition, controlled by temperature and ionic strength, is investigated. It corresponds to a double-helix single-chain transition. Large ionic selectivity is observed in the helical conformation th at controls the degree of aggregation upon gelation. Potentiometry and conductivity measurements are interpreted in terms of the Manning polyelectrolyte theory in the sol state.

Hyaluronan (HA) is a linear charged polysaccharide whose structure is made up of repeating disaccharide units. Apparently conflicting reports have been published about the nature of the helical structure of HA in the solid state. Recent developments in the field of molecular modeling of polysaccharides offer new opportunities to reexamine the structural basis underlying the formation and stabilization of ordered structures and their interactions with counterions. The conformational spaces available and the low energy conformations for the disaccharide, trisaccharide, and tetrasaccharide segments of HA were investigated via molecular mechanics calculations using the MM3 force field. First, the results were used to access the configurational statistics of the corresponding polysaccharide. A disordered chain having a persistence length of 75 A at 25 degrees C is predicted. Then, the exploration of the stable ordered forms of HA led to numerous helical conformations, both left- and right-handed, having comparable energies. Several of these conformations correspond to the experimentally observed ones and illustrate the versatility of the polysaccharide. The double stranded helical forms have also been explored and theoretical structures have been compared to experimentally derived ones.