Persistence length for a model semirigid polyelectrolyte as seen by small angle neutron scattering: a relevant variation of the lower bound with ionic strength

In a SANS experiment, we have directly determined for the first time the conformation of hyaluronan, a model semirigid polyelectrolyte. At high ionic strength, this is completely possible, where the scattered intensity crosses over (when decreasing $q$) from a $q^{-1}$ rod variation to a $q^{-2}$ and, where fitting to the “wormlike” chain model gives the backbone, intrinsic, persistence length: $L_0=86.5$ Å. At low ionic strength, we can safely check that the measured persistence length appears increased by at least the amount predicted by Odijk for the electrostatic contribution, $L_{\rm e}$ (~$\kappa^{-2}$, square of the Debye screening length). However, the intensity at the lowest $q$ is not only due to the single chain, since it crosses over from a $q^{-1}$ to a $q^{-4}$ variation, characteristic of polymer associations