Biomimetic Membranes based on N-Heterocyclic Carbenes

Biological membranes are selective dividing layers that separate the intracellular compartments from the external environment. Integral membrane proteins allow the transport of ions and chemical compounds across the cell membrane. The complexity in structure and function of natural membranes render the research of protein-lipid-interactions difficult. The study of such interactions can be realized using immobilized biomimetic membranes. Although such membrane model systems have been developed to study protein- lipid-interactions, disadvantages such as low and inconsistent surface coverage resulting in heterogeneity as well as the low mobility of the immobilized lipids hamper their application in life science as well as nanoelectronics. These disadvantages may be circumvented by the introduction of more robust and chemically well-defined interfaces between nanostructures and lipid bilayer membranes. In the framework of this project, biomimetic membranes with high membrane fluidity will be developed allowing the integration of transmembrane proteins. For this purpose, self- assembled monolayers based on N-heterocyclic carbenes (NHC) will be synthesized, which allow the spontaneous formation of lipid bilayers. The design of NHC-based membrane precursors will aim for high stability, high mobility and tunable surface density of the resulting biomimetic membranes on metal surfaces to serve as a matrix for the incorporation of functional membrane proteins. Exemplarily, an ion channel protein, a -hemolysin, will be used to study its activity in these artificial membranes. This project aims to broaden the molecular toolkit to facilitate the systematic modification of lipid bilayer molecules and may contribute to the study of protein-lipid-interactions as well as to the development of protein-based bioelectronic systems.

Biological membranes are selective dividing layers that separate the intracellular compartments from the external environment. Integral membrane proteins allow the transport of ions and chemical compounds across the cell membrane. The complexity in structure and function of natural membranes render the research of protein-lipid-interactions difficult. The study of such interactions can be realized using immobilized biomimetic membranes. Although such membrane model systems have been developed to study protein-lipid-interactions, disadvantages such as low and inconsistent surface coverage resulting in heterogeneity as well as the low stability of the immobilized lipids hamper their application in life science as well as nanoelectronics. These disadvantages may be circumvented by the introduction of more robust and chemically well-defined interfaces between nanostructures and lipid bilayer membranes. Within this project, biomimetic membranes with high stability were developed allowing the prolonged function of membrane model systems. The basis for this is provided by synthetic self-assembling monolayers, which spontaneously arrange themselves in the form of a lipid layer on a biologically inert gold surface. The choice of newly designed N-heterocyclic carbenes (NHCs) as anchor groups contributes to the durability of these immobilized biomimetic systems on gold supports and thus minimizes disadvantages of previous anchor groups. Furthermore, the design of the NHC-based membrane building blocks proposed crucially determines the lateral surface mobility and density of the lipid bilayer formed. In this project, materials were developed that allow the surface mobility of such self-organizing monolayers to be reduced through cross-linking, which contributes to the stability of the nanostructures on gold surfaces. For this purpose, a strategy for two-dimensional click networking on the surface was developed. Optimization of the architecture of the biomimetic membranes in composition and organization allowed the integration of the ionophore valinomycin, which allowed the reversible selective potassium ion transport through the prepared biomimetic membranes. This project broadens the molecular toolkit to facilitate the systematic modification of lipid bilayer molecules and contributes to the study of protein-lipid-interactions as well as to the development of protein-based bioelectronic systems.