Solid-supported polymer bilayers as membrane mimics

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

Amphiphilic polymers at interfaces

Self-assembly phenomena in block copolymer systems are attracting considerable interest from the scientific community and industry alike. Particularly interesting is the behavior of amphiphilic copolymers, which can self-organize to nanoscale-sized objects such as micelles, vesicles, or tubes in solution, and which form well-defined assemblies at interfaces such as air–liquid, air–solid, or liquid–solid. Depending on the polymer chemistry and architecture, various types of organization at interfaces can be expected, and further exploited for applications in nanotechnology, electronics, and biomedical sciences. In this article, we discuss the formation and characterization of Langmuir monolayers from various amphiphilic block copolymers, including chargeable and thus pH-responsive materials. Solid-supported polymer films are reviewed in the context of alteration of surface properties by ultrathin polymer layers and the possibilities for application in tissue engineering, sensors and biomaterials. Finally, we focus on how organic and polymer monolayers influence the growth of inorganic materials. This is a truly biomimetic approach since Nature uses soft interfaces to control the nucleation, growth, and morphology of biominerals such as calcium phosphate, calcium carbonate, and silica

Biomimetic supported membranes from amphiphilic block copolymers

A unique combination of surface chem. and self-assembly of amphiphilic block copolymers was employed to obtain-for the first time-solid-supported biomimetic polymer bilayers. An organized monolayer from sulfur-functionalized poly(butadiene)-b-poly(ethylene oxide) was covalently attached to ultrasmooth gold upon Langmuir-Blodgett transfer. Hydrophobic interactions, on the other hand, were exploited to attach the second monolayer. As a result, we obtained a homogeneous hydrophilic-hydrophobic-hydrophilic structure, similar to supported lipid bilayers by architecture, stability and fluidity. Our polymer bilayers, however, outperform such lipid membranes with regard to tunability of thickness and stability in gaseous environments.As characterized by surface anal. tools (AFM, SPR), solid-supported polymer membranes are smooth with a thickness of ca. 11 nm, resistant to rinsing with aq. solns. and stable upon drying and rehydration. These properties could be attractive for nanotechnol. applications, such as immobilization of functional mols. or nanoparticles, sensor development or prepn. of chem. responsive functional surfaces. [on SciFinder (R)

pH-Dependent Immobilization of Proteins on Surfaces Functionalized by Plasma-Enhanced Chemical Vapor Deposition of Poly(acrylic acid)- and Poly(ethylene oxide)-like Films

The interaction of the proteins bovine serum albumin (BSA), lysozyme (Lys), lactoferrin (Lf), and fibronectin (Fn) with surfaces of protein-resistant poly(ethylene oxide) (PEO) and protein-adsorbing poly(acrylic acid) (PAA) fabricated by plasma-enhanced chemical vapor deposition has been studied with quartz crystal microbalance with dissipation monitoring (QCM-D). We focus on several parameters which are crucial for protein adsorption, i.e., the isoelectric point (pI) of the proteins, the pH of the solution, and the charge density of the sorbent surfaces, with the -potential as a measure for the latter. The measurements reveal adsorption stages characterized by different segments in the plots of the dissipation vs frequency change. PEO remains protein-repellent for BSA, Lys, and Lf at pH 4-8.5, while weak adsorption of Fn was observed. On PAA, different stages of protein adsorption processes could be distinguished under most experimental conditions. BSA, Lys, Lf, and Fn generally exhibit a rapid initial adsorption phase on PAA, often followed by slower processes. The evaluation of the adsorption kinetics also reveals different adsorption stages, whereas the number of these stages does not always correspond to the structurally different phases as revealed by the D-f plots. The results presented here, together with information obtained in previous studies by other groups on the properties of these proteins and their interaction with surfaces, allow us to develop an adsorption scenario for each of these proteins, which takes into account electrostatic protein-surface and protein-protein interaction, but also the pH-dependent properties of the proteins, such as shape and exposure of specific domains.JRC.I.4-Nanotechnology and Molecular Imagin

Efficient Two-Step Synthesis of 11,11'-Dithiobis[1-(2-bromo-2-methylpropionyloxy)undecane], a Conventional Initiator for Grafting Polymer Brushes from Gold Surfaces via ATRP

11,11'-Dithiobis[1-(2-bromo-2-methylpropionyloxy)undecane], a conventional initiator for grafting polymers from gold surfaces, was synthesized in two steps from 11-mercapto-1-undecanol in 88-92% overall yield. Oxidative dimerization of 11-mercapto-1-undecanol with a catalytic amt. of sodium iodide and 30% hydrogen peroxide in Et acetate proceeded in 96% yield. Esterification with 2-bromoisobutyryl bromide in dichloromethane was clean and almost quant. (92% yield) with pyridine used as base, whereas triethylamine gave a messy reaction (64% yield). Alternatively, esterification with 2-bromo-2-methyl-propanoic acid in dichloromethane occurred readily under Steglich's conditions with N,N'-dicyclohexylcarbodiimide (DCC) and a catalytic amt. of dimethylaminopyridine (DMAP; 88% yield). [on SciFinder(R)