Interaction between myoglobin and hyaluronic acid in their layer-by-layer assembly: Quartz crystal microbalance and cyclic voltammetry studies

Myoglobin (Mb), with different net surface charges at different pH in buffers and negatively charged hyaluronic acid (HA) at pH 5.0 in solutions were alternately adsorbed onto various solid surfaces and successfully assembled into {Mb/ HA} n layer- by- layer films. The Mb in {Mb/ HA} n films showed a quasi- reversible cyclic voltammetry ( CV) response for its heme FeIII/ FeII redox couple. Quartz crystal microbalance ( QCM) and CV were used to confirm the film growth and characterize the films. The interaction between Mb and HA and the influencing factors for Mb adsorption on HA surface, such as pH, Mb concentration, and ionic strength, were investigated in detail. The assembly driving force for {Mb/ HA} n films, especially for the films assembled with like- charged Mb and HA, was found to be of electrostatic origin, while the secondary interaction such as hydrophobic interaction also plays an important role in some circumstances. Although the growth of {Mb( pH 7.0)/ HA} n and {Mb( pH 9.0)/ HA} n films was linear with the adsorption step, the exponential growth of {Mb( pH 5.0)/ HA} n films was observed, especially when the films became thick. This exponential increase of mass and thickness with deposition step for {Mb( pH 5.0)/ HA} n films was most probably attributed to the diffusion mechanism in which some HA molecules could diffuse in to and out of the whole films during the film assembly. Atomic force microscopy ( AFM) results supported this speculation. UV- vis and IR spectroscopies of {Mb/ HA} n films, combined with the comparative CV experiments of {Mb/ HA} n and {catalase/ HA} n films, suggest that Mb in the {Mb/ HA} n multilayer films retains its near- native structure.