Reversible supramolecular modification of surfaces

Enzymes are biocatalysts widely used in a large number of industrial biotech processes as they offer clear advantages over their chemical counterparts. Indeed, enzymes often show high substrate selectivity along with elevated turnover rates. Enzymatic catalysis usually functions under mild conditions of temperature, pressure and acidity. However, the industrial application of enzymes is often limited by their limited stability under operational conditions. Moreover, due to high water solubility of enzymes it is challenging to confined them in a flow reactor system. In order to circumvent these limitations, we have developed a supramolecular strategy that allows the reversible immobilization of active enzyme-polymer conjugates at the surface of filtration membranes. It is based on multivalent host-guest inclusion interactions between the membrane surface and a soluble enzyme-polymer conjugate. Cyclodextrins (CDs) as "host" molecules are covalently attached at the surface of polyethersulfone membranes and a multivalent water-soluble polymer is synthesized as a "guest" molecule. We demonstrate that while this supramolecular surface modification is stable under operational conditions and allows for efficient bio-catalysis, it can be straightforwardly reverse by competitive host-guest interactions. The first part of this manuscript is dedicated to a literature review on selected topics. As the supramolecular strategy we have developed in the course of this PhD research work is based on the use of cyclodextrins as supramolecular host molecules, the first part of this literature review focuses on the physico-chemical characteristics of this class of macrocycles. A special emphasis is done on their ability to form host-guest multivalent inclusion complexes. In this context, we describe the concept of multivalency and the underpinning essential thermodynamic principles, which can be apply to design controllable, directional, and selective self-assemblies. In the second part of this manuscript, we present our strategy to bio-functionalize polymeric membrane surfaces using multivalent reversible inclusion reactions. In more details, the chemical strategy to introduce CD macrocycles, in a covalent fashion, at the surface of the polymeric material is discussed. The synthesis and characterization of an enzyme-polymer conjugate, possessing multiple chemical functional groups (i.e. adamantyl) able to form inclusion complexes with CDs, is presented. It is demonstrated that this supramolecular strategy could be applied to the reversible immobilization of an active enzyme at the surface of polyethersulfone membranes. A similar strategy is applied to the reversible bio-functionalization of gold surfaces and used to prepare sensor chips for surface plasmon resonance (SPR) experiments. Self-assembled monolayers of CDs derivatives are prepared on the surface of a gold sensor chip. A water-soluble protein-polymer conjugate, possessing multiple adamantyl moieties, is synthesized. The supramolecular reversible binding of this new conjugate on the chemically modified SPR chip is demonstrated. The possibility to use this system for antigen/antibody biosensing experiment is successfully confirmed.