Membrane biomimetic

FIG. 14 Schematic illustration of an archaeal cell envelope structure (a) composed of the cytoplasmic membrane with associated and integral membrane proteins and an S-layer lattice, integrated into the cytoplasmic membrane, (b) Using this supramolecular construction principle, biomimetic membranes can be generated. The cytoplasmic membrane is replaced by a phospholipid or tetraether hpid monolayer, and bacterial S-layer proteins are crystallized to form a coherent lattice on the lipid film. Subsequently, integral model membrane proteins can be reconstituted in the composite S-layer-supported lipid membrane. (Modified from Ref. 124.)... 

Kolusheva S, Kafri R, Katz M, Jelinek R. Rapid colorimetric detection of antibody-epitope recognition at a biomimetic membrane interface. J Am Chem Soc 2001 123 417-422. 

Prosegment inhibition of peptide association with biomimetic membranes. J Biol Chem 2003 278 13838-13846. 

Self-assembled and spontaneously adsorbed monolayers offer a facile means of controlling the chemical composition and physical structure of a surface. As discussed later in Chapter 5, applications of these monolayers include modeling election transfer reactions, biomimetic membranes, nano-scale photonic devices, solar energy conversion, catalysis, chemical sensing and nano-scale lithography. 

Beyond the complete assembly of biomimetic membranes, interfacial supramolec-ular assemblies which incorporate biocomponents represent an important approach to replicating the biological functions outside of living systems. For example, the ability to link or wire otherwise electro-inactive enzymes to electrodes so that they can efficiently transport electrons allows sensitive and selective sensors to be developed for important bioactive molecules, e.g. glucose, lactate, urea, etc. 

The transport of molecules across biological cell membranes and biomimetic membranes, including planar bilayer lipid membranes (BLMs) and giant liposomes, has been studied by SECM. The approaches used in those studies are conceptually similar to generation-collection and feedback SECM experiments. In the former mode, an amperometric tip is used to measure concentration profiles and monitor fluxes of molecules crossing the membrane. In a feedback-type experiment, the tip process depletes the concentration of the transferred species on one side of the membrane and in this way induces its transfer across the membrane. 

The biomimetic membranes represent a special group of carrier membranes. They are artificial membranes based on biomembrane mimicking, i.e., imitation of the essential features bio membranes use for separation. Nitrocellulose filters impregnated with fatty acids, their esters, and other lipid-like substances may be used— in other words, an imitation of many nonspecific barrier properties of biomembranes. The transport of gas through these membranes will essentially be according to facilitated transport (see Section 4.2). Biomimetic membranes for CO2 capture will transport the gas as HCO3. Development of these materials may be expected for selected applications. 

Biomimetic membrane-enclosed compartments have numerous advantages when it comes to model biological systems. However, at shorter length scales, surface properties become increasingly important. In applications where the length scales are of the order of micrometers to submicrometers, the chemistry can be completely dominated by surface interactions [31]. This fact and... 

Figure 2.9a shows the lipid molecule DMPC. Two layers contacted via the hydrophobic tails lead to spontaneous formation of a double-layer biomimetic membrane that can be transferred to a single-crystal ultraplanar electrochemical Au(lll) surface. The hydrophilic head groups contact the electrode surface via an intermediate water film. Due to the structurally very well-defined assembly, not only AFM and in situ STM but also neutron reflectivity. X-ray diffraction, and infrared reflection absorption spectroscopy (IRRAS) have been employed to support the direct visual in situ STM. Electrochemically controlled structural changes, phase transitions, and the effects of the common membrane component cholesterol (Figure 2.9b) and peptide drugs have been investigated in this way. 

Lipkowski, J. (2010) Building biomimetic membrane at a gold electrode surface. Physical Chemistry Chemical Physics, 12, 13874-13887. 

The purpose of a scattering-based experiment is to determine the spatial and/or temporal correlation of the atomic or molecular components of the object under study. If one wishes to extract spatial information pertaining to collections of atoms or molecules it is expected that the probe chosen for a scattering experiment must have wavelengths comparable in magnitude to the distance between the constituent units. Similarly, in order to study temporal correlations, the incident radiation should have comparable energies to those associated with atomic or molecular motions. Beyond these criteria, there are several other requirements of the probe which are particularly relevant to the study of thin organic films such as biomimetic membranes. 

With only a few exceptions, metal-supported biomimetic membranes consist of a more or less complex architecture that includes a lipid bilayer. In order of increasing complexity, they can be classified into solid-supported bilayer lipid membranes (sBLMs), tethered bilayer lipid membranes (tBLMs), polymer-cushioned bilayer lipid membranes (pBLMs), S-layer stabilized bilayer lipid membranes (ssBLMs), and protein-tethered bilayer hpid membranes (ptBLMs). 

Apart from hpid molecules, the molecules that are most commonly employed for the fabrication of biomimetic membranes are hydrophilic spacers and thi-olipids. Hydrophihc spacers consist of a hydrophihc chain (e.g., a polyethyleneoxy or oligopeptide chain) terminated at one end with an anchor group for tethering to a support and, at the other end, with a hydrophihc functional group (e.g., a... 

Many membrane proteins are electrogenic, that is, translocate a net charge across a membrane. Consequently, it is possible to monitor their function directly by measuring the current flowing along an external electrical circuit upon their activahon. The techniques of choice for these measurements are EIS and potenhal-step chronoamperometry or chronocoulometry, because the limited volume of the ionic reservoir created by a hydrophilic spacer in solid-supported biomimetic membranes cannot sustain a steady-state current. 

Methodologies for the fabrication of biomimetic membranes vary somewhat from one biomimetic membrane to another. However, a number of experimental procedures for the formation of lipid monolayers and bilayers on solid supports are common to several biomimetic membranes. The most popular procedures are vesicle fusion, Langmuir-Blodgett and Langmuir-Schaefer transfers, and rapid solvent exchange. The formation of lipid monolayers and bilayers on gold and... 

Biomimetic membranes comprising a hpid bilayer are discussed here in the order of approximately increasing complexity. 

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