Tethered membranes, lateral mobility

Deverall MA, Gindl E, Sinner EK, Besir H, Ruche J, Saxton MJ, Naumann CA. Membrane lateral mobility obstructed by 57. polymer-tethered lipids studied at the single molecule level. Biophys. J. 2005 88 1875-1886. 

In the case of PEMs, the situation is more complicated because the sulfonate counter-ions (in the case of a PEM such as Nafion ) are bound to the polymer chain and are thus relatively immobile, in contrast to the free counter-ion in a small molecule acid such as sulfuric or acetic acid. Tethering of the sulfonate group can be considered to be an impediment to the mobility of the proton as it traverses the membrane. Proton mobility is also affected by the effective mean-free path of connectivity of the conduction pathway as shown in Figure 3.2. In situation (a), the increased number of dead ends and tortuosity of the aqueous domains through which proton transport occurs over the situation in (b) leads to lower overall mobility. This has been demonstrated by Kreuer and will be discussed later in this section. 

For some of these polymer-tethered lipid bilayers a few key performance indicators are discussed. In particular, we describe structural parameters obtained from surface plasmon resonance spectroscopy and compare those to important functional features, i.e., the electrical capacitance and resistance of the membrane. Furthermore, the ability of the polymer tethers to swell in water and evidence for the resulting lateral mobility of the lipid molecules in the membrane as an indicator for the fluid nature of the tethered bilayers are presented. 

Lateral Mobility of Lipids in a Tethered Bilayer Membrane. 102... 

Among the various membrane properties that might need to be optimized for a particular application of the tethered membrane architecture and/or of any incorporated proteins we discuss only two key performance parameters, i.e., (1) the ability of the tethering system to swell by the up-take of a sufficient amount of water into the interstitial space between the lipid bilayer and the solid support, and (2) the high lateral mobility of the individual lipid molecules in the two opposing leaflets of the bilayer membrane. 

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