Solid-supported polymer bilayers as membrane mimics

Abstract

Membranes are one of Nature’s most remarkable designs. Due to their importance in numerous cellular processes, they are prominent subjects of biochemical and biophysical fundamental research. In particular, it is crucial to understand the membrane morphology, the role of individual membrane components, and also to correlate the membrane structure to its various functions. Besides, systems inspired by natural membranes are of high interest for technological applications, such as water purification, drug screening, or sensing. However, the complexity and fragility of natural membranes often limit their direct use. For that reason, the development of membrane models is indispensable. Suitable building blocks for model systems could be lipids or amphiphilic polymers. In this thesis, robust solid-supported membrane models from amphiphilic diblock copolymers were designed by combining different methods of polymer synthesis, membrane preparation, and surface analytics. Anionic polymerization yielded a well-defined poly(butadiene)-b-poly(ethylene oxide) polymer in terms of overall molecular weight and individual block length. Through a chemical modification procedure, a sulfur-functionalized derivate of the polymer was obtained, which served for covalent immobilization of the polymer monolayers on ultrasmooth gold surfaces. For membrane preparation two different procedures were employed: on the one hand, individual polymeric monolayers were deposited on the gold supports by a combination of the well-controllable Langmuir film transfer techniques. On the other hand, in a one-step procedure, polymer superstructures were spread either on gold or on glass surfaces to yield solid-supported polymer membranes. The membranes with a covalently immobilized proximal leaflet by sulfur/gold chemistry possess high mechanical stability, and at the same time, a certain degree of mobility resulting from the non-covalent coupling of the individual sheets. The membranes were characterized by surface-sensitive techniques such as atomic force microscopy and surface plasmon resonance spectroscopy to gain insights into morphology, homogeneity, and thickness of the layers. To demonstrate the membranes’ biomimetic potential, they were incubated with peptides, polymyxin B and -haemolysin. Occurring interactions were detected by electrochemical impedance spectroscopy. In summary, this thesis might impact fundamental membrane science as well as prospective biotechnological applications.