M.Sc Thesis

M.Sc StudentMoskovitz Yevgeny
SubjectStabilization of Surface-Immobilized Enzymes Using
Grafted Polymers
DepartmentDepartment of Chemical Engineering
Supervisor ASSOCIATE PROF. Simcha Srebnik


In recent years, extensive research, both theoretical and experimental, has been directed at the behavior of polymers near surfaces and in the presence of proteins. However, a complete understanding of the phase transition accompanying protein adsorption is not yet available. Our research was carried out using statistical thermodynamics methods. Two-dimensional mean-field lattice is used to model immobilization and stabilization of an enzyme on a hydrophobic surface using grafted hydrophilic polymers. The protein is modeled as compact hydrophobic-polar polymer, designed to have a specific bulk conformation reproducing the catalytic cleft of natural enzymes. A series of solutions was examined for the immobilized protein at different distances from a clean surface (without polymer). The resulting adsorption isotherm revealed an abrupt phase transition at a critical distance from a hydrophobic surface, a phenomenon that is particular to random heteropolymers, in general, and proteins, in particular. Moreover, a metstabile conformation was observed prior to complete denaturation of the tertiary structure and its collapse into a flat globular conformation. Further two scenarios are modeled that have medical and industrial importance. While the enzyme affords biofunctionality to the surface, the grafted polymer layer imparts biocompatibility as well as stabilizes the enzyme. It is shown that short hydrophilic grafted polymers provide biocompatibility while protecting the enzyme from the denaturing effects of the hydrophobic surface. On the other hand, a combination of short hydrophilic polymers and long copolymer polymers shield the enzyme from, e.g., harmful organic solvents. The grafted polymer layer not only shields the enzyme, but also presents an energetic as well as entropic barrier to undesirable adsorption, or fouling.