Biomimetic Lipoglycopolymer Membranes: Photochemical Surface Attachment of Supramolecular Architectures with Defined Orientation

Abstract

The assembly of defined supramolecular architectures on a molecular scale, such as biomimetic membranes, [1][2][3] requires the synthesis of multifunctional building blocks and a sophisticated combination of nanotechnological surface preparation techniques. A drawback of current tethered bilayer lipid membrane (tBLM) systems is their limited submembrane decoupling distance from the solid support. The necessity for large (6 nm and more) cytoplasma analogue compartments originates from several biological and biophysical requirements, such as accommodation of cytoplasmatic subunits of membrane proteins, [4] reduction of the Förster energy transfer [5] for the use of fluorescent or photoaffinity probes in vicinity of metal surfaces, and compensation for surface roughness of sensor surfaces often preventing good electrical tBLMs properties.[6] Current polymer-based tBLMs on gold do not achieve membranesurface decoupling distances of more than 5 nm, nor are polymer based tBLMs able to maintain sufficient electrical properties (resistance of at least several MW cm 2 ). To overcome these limitations, we have devised a new strategy to expand the existing scope of tBLMs using lipoglycopolymers (LGP). Special emphasis was placed on increasing the cytoskeleton analogue compartment size (decoupling distance from the sensor surface) whilst retaining tightly sealing membranes, which requires the careful design of the lipid moiety, the tethering polymer, and the reactive self-assembling monolayer (SAM) to immobilize the LGP. Furthermore, we introduced a new covalent immobilization procedure that utilizes photochemical surface attachment to assemble complex supramolecular architectures of defined orientation from aqueous solution. This procedure may have interesting additional applications in the design of new protein nanoarrays and in bionanotechnology in general.The idea of using macromolecules as a cushion [7] to mimic the cytsol/cytoskeleton of the cell to create a hydrophilic space between membrane and solid support was first introduced by Ringsdorf and Sackmann. [1,8] Macromolecular tethers impose several challenging features. They adopt coiled conformations, which strongly depend on the solvent, and have a range of molecular weights and lengths, whilst interchain interactions determine shape and stability of thin films. Lipid-functionalized small macromolecular tether systems with less than 100 repeating units n that have been used to date reached no more than 40 % of their maximal theoretical thickness. Examples include poly(ethyloxazoline) (n = 50, length 3-3.5 nm) [9] and PEG2000 (n = 45, length 4.9 nm).[10] The requirements for a macromolecular tether can be summarized as follows: 1) There must be complete wetting between the surface and the hydrated polymer and between the membrane and the hydrated polymer; [11,12] 2) the interaction between membrane and surface needs to be repulsive to prevent dewetting; [37] and 3) nonspecific contacts by van der Waals attraction (effective up to about 3 nm) between lipids and surfa...

Glycopolymer Brushes for Specific Lectin Binding by Controlled Multivalent Presentation ofN-Acetyllactosamine Glycan Oligomers

“…Therefore, growing glycopolymer brushes from surfaces represents an attractive alternative as the grafted glycopolymer chains adopt a stretched conformation and thus do not overlap . To date, a wide range of synthetic surface‐grafted glycopolymers has been prepared using different techniques such as Langmuir‐Blodgett, layer‐by‐layer growth or grafting from or onto polymerization . For the preparation of densely packed polymer brushes, the grafting of polymer chains from a surface using controlled/“living” polymerization techniques is particularly attractive .…”

Surface Chemoselective Phototransformation of C–H Bonds on Organic Polymeric Materials and Related High-Tech Applications

“…Tethered bilayer lipid membranes (tBLMs) have also been prepared on surfaces by using lipoglycopolymers (LGP) together with azide photochemistry (Figure 61). 244 Reactive SAMs are first formed on a gold surface where a phenyl azide group is exposed outward from the surface. Subsequently, an LB monolayer of LGP is transferred onto this surface, followed by photochemical immobilization to form a stable lipid modified surface.…”

“…Figure61. The grafting of lipoglycopolymers by phenyl azide photochemistry onto gold sensor surfaces after Langmuir−Blodgett (LB) transfer 244. …”

S-Layer Protein-Based Biosensors

“…[ 20 , 21 ]. Molecules, like polymers (in particular polyethylene glycol), glyco-polymers, peptides, and proteins are used so far to build up the hydrophilic part of the tether layers [ 22 , 23 , 24 ]. The challenge generating the intermediate layer is to combine multiple functions, including: (1) to act as immobilization layer with a suitable binding to both, the inorganic support, and the biological molecules (e.g., bioreceptors, matrix-forming lipids; (2) to allocate a binding matrix where the immobilized molecules are arranged in a well-defined spatial and directed orientation; (3) to provide a reservoir for water and ions; and, (4) to provide sufficient space and stability for the biosensing elements.…”