Conformational Dynamics of Hyaluronan in Solution. 2. Mode-Coupling Diffusion Approach to Oligomers

A detailed study of structure and dynamics of hyaluronan oligomers (UA)4 and (UA)2 is presented. Recent advances in macromolecule diffusion theory are applied to second order in the mode-coupling expansion to derive second-rank time-correlation functions of the C-H vectors along the chains. The required equilibrium averages are approximated by time averages along an atomistic molecular dynamics simulation. The results are compared with experimental 13C-NMR relaxation parameters of different nuclei in the molecule. The pronounced structure in the relaxation pattern found in the experiments for (UA)4 can be qualitatively interpreted in terms of rotational diffusion anisotropy with partially screened hydrodynamic interactions. Inter-residue hydrogen bonds concerning the side chains are weak and do not have significant local effects while O5(i)- HO3/4(i+1) hydrogen bonds can play a significant role in coupling conformational degrees of freedom with solvation. The implications of this study on the knowledge of the hyaluronan polymer structure and dynamics are addressed.