Chain persistence length and structure in hyaluronan solutions:: Ionic strength dependence for a model semirigid polyelectrolyte

In this study, we have directly determined for the first time the structure and the chain conformation of hyaluronan, a model semirigid polyelectrolyte polysaccharide. At high ionic strength, detailed information on the chain flexibility has been obtained from combined light and small-angle neutron scattering experiments by applying different fitting methods based upon expressions for a single-chain scattering function of a wormlike chain without excluded volume. Particular attention has been given to the determination of the intrinsic persistence length, L-0, and a value close to 90 Angstrom was found using the different fitting procedures. Without screening (i.e., at low ionic strength), the measured total persistence length appears increased by at least the amount predicted by Odijk for the electrostatic contribution, L-e (similar tokappa(-2), square of the Debye-Huckel screening length). This would mean this model was checked using classical polyelectrolytes. At high ionic strength the scattered intensity crosses over, with decreasing q, from a q(-1) rod to a q(-2) coil variation as predicted for a wormlike chain. Conversely, at low ionic strength it crosses over from a q(-1) to a q(-4) (or q(-3)) variation, characteristic of polymer associations. These associations are also observed in our dynamic light scattering measurements, with a behavior very similar to that of flexible polyelectrolytes.