POLAR INTERACTIONS OF HYALURONIC ACID -EXPERIMENTS AND MOLECULAR DYNAMICS SIMULATIONS-

ABSTRACT

To study the polar interactions of the cartilage component hyaluronate (HA) contact angle measurements of polymer films of sodium hyaluronate and of the free hyaluronic acid with different probe liquids and theoretical investigations with molecular dynamics simulation (MD) on polymer segments in aqueous environment were performed. For the designation of contact angles water, formamid, glycerol and α-bromnaphthalene as probe liquids were used. The surface tension components were calculated on the basis of the theory of van Oss using the Young equation. Experimental investigations were done with air dried layers of the sodium salt of HA whose surface has been formed at the interface to the air resp. glass support. Whereas the surface polymer/air is characterized by small, but non-zero values for γ^• and γ^-the surface polymer/glass tends to have γ^-monopolar properties. In opposite to the salt form of HA a strong repulsion of chains and high γ^- monopolarity was measured for the protonated form.

The molecular dynamics simulation (MD) on HA in water were carried out employing the force field CHARMM and the water model TIP3P. MD trajectories of HA tetramer subunit surrounded by approximately 950 water molecules were produced up to 3 ns. The interaction energies of HA and water, hydrogen bonding, and the orientation of water molecules at different solute atom groups were calculated. On the basis of energy and geometry criteria, the number of hydrogen bonds between the water molecules and the polymer acceptor atoms was determined to be between 10 and 15 per dimer unit.