  The conformation of polyelectrolytes in the solution state has long been of
interest in polymer science. Herein we utilize all atom molecular dynamics
simulations (MD) and small-angle x-ray scattering experiments (SAXS) to
elucidate the molecular structure of the model polyelectrolyte
homogalacturonan. Several degrees of polymerization were studied and in
addition partial methylesterification of the otherwise charge-carrying carboxyl
groups was used in order to generate samples with varying intra-chain charge
distributions. It is shown that at length scales above around 1 nm the
conformation of isolated chains has surprisingly little dependence on the
charge distribution or the concentration of attendant monovalent salts,
reflective of the intrinsic stiffness of the saccharide rings and the dynamical
constraints of the glycosidic linkage. Indeed the conformation of isolated
chains over all accessible length-scales is well described by the atomic
co-ordinates available from fibre diffraction studies. Furthermore, in more
concentrated systems it is shown that, after careful analysis of the SAXS data,
the form of the inter-particle effects heralded by the emergence of a so-called
polyelectrolyte peak, can be extracted, and that this phenomena can be
reproduced by multiple chain MD simulations.

Soft Condensed Matter