The Interactions Between Protein And Hydrophobic Modified Poly (Allylamine)s

Protein is the basis of life, which is a kind of non-periodical polymer. The interactions inside and outside protein such as hydrogen bonding, van der Waals force, disulfide bonds, electrostatic and hydrophobic interactions are very important to maintain the native structure and physiological activity. The interactions can also involve in proteins and polyelectrolytes. The complexation via the electrostatic interaction between the protein and polyelectrolyte can reserve the native structure and activity of the protein but shows poor stability, which is easy to dissociate when the pH and ionic strength change. Hydrophobic interaction can improve the stability of the complexes. However, if the hydrophobicity is too strong, polyelectrolyte aggregates by itself which decreases the binding with protein. On the other hand, too strong hydrophobic interactions between polymer and protein will cause more serious destruction and also inhibit the release of the protein. In this thesis, we used hydrophobic modified poly(allylamine)s of which hydrophobicity can be adjusted by altering the alkyl chain length and modified degree to investigate the factors that influence the binding ability with protein in details.The first part of the thesis studied the binding and release of lysozyme with butylated poly(allylamine)s at different pH and temperatures conditions, as well as the structure and activity changes of the protein in the process. The lower critical solution temperature (LCST) of poly(allylamine)s decreases with the increase of butylated degree. The hydrophobicity of butylated poly(allylamine)s measured by pyrene fluorescence does not change significantly with the change of the solution pH, but increases with the increase of temperature. At lower pH, the poly(allylamine)s with higher butylated degree have single molecular aggregation structure. The binding of native lysozyme with the butylated poly(allylamine)s depends on pH, temperature and butylated degree. In some extent, the increase of polymer hydrophobicity can increase the binding with lysozyme, but the self-aggregation of the polymer decreases the binding. The denatured lysozyme which exposed the hydrophobic residues can form more stable complex nanoparticles with the butylated poly(allylamine)s that prevent the protein from precipitation.The second part of the thesis studied the interactions between hydrophobic modified poly(allylamine)s and superoxide dismutase(SOD). The electrostatic interaction play the main role in the combination of SOD with butylated poly(allyamine)s. More than 90% SOD can bind with dodecyl-modified poly(allyllamine)s at pH 5.5 and pH 7.4 through electrostatic and hydrophobic interactions. When the pH was adjusted to 10.0, the bound SOD released completely. In PBS, the release rate of SOD can be controlled by adjusting the mass ratio of SOD to polymer:the more C12-14 involved, the slower SOD release rate. The structure and activity of SOD remained completely after release. The introduction of organic solvents can reduce the self-aggregation of the polymer and then enhance the hydrophobic interaction between SOD and the polymer to improve the stability of the complex particles.Our research reveals that the combination and release of protein can be controlled by adjusting the hydrophobic interaction between protein and polymers through choosing the appropriate conditions. The structure and activity of the protein remain completely after release from the complexes. This conclusion is helpful for the applications of polymer in protein separation and purification, protein immobilization and stabilization, as well as protein encapsulation and controlled release.