Permeability control, electrochemical

Y. Okahata, G. Enna, K. Taguchi, and T. Seki, Electrochemical permeability control through a redox bilayer film. J. Am. Chem. Soc. 107, 5300-5301 (1985). 

Electrochemical permeability control of organic molecules by a bilayer-immobilized film containing redox sites has been reported 1 Bilayer-forming amphiphiles 37) and sodium poly(styrene sulfonate) (PSSNa) were mixed in water, and the resulting precipitates were dissolved in CHCI3 and cast on a Pt minigrid. The amphiphiles form extended lamellae parallel to the film plane in polyion complexes with polystyrene sulfonate (PSS ). The 57-PSS and the reduced 57-PSS" film showed phase transition temperatures T at 24° and 38 °C, respectively. When the 37 group... 

Okahata Y, Enna G (1988) Permeability-controllable membranes. 7. Electrochemical responsive gate membranes of a multibilayer film containing a viologen group as redox sites. J Phys Chem 92 4546 551... 

Horizontal Touch Cyclic Voltammetry with a Condensed Monolayer of a Cyclodextrin Derivative. To obtain experimental evidence supporting that such a mode of permeability control is possible, an approach based on horizontal touch cyclic voltammetry was carried out for a condensed monolayer of 4, which was formed at the air/water interface in a Langmuir trough 14), This technique, first used by Fujihira (25) and recently sophisticated by Bard (2d, 27), enables the investigation of the electrochemical properties of oriented monolayers at varying packing densities under an appropriately controlled surface pressure. 

One effect of the electrochemical reactions in an aqueous system is a local pH change around the electrodes. By water electrolysis, hydronium ions (H30+) are generated at the anode, while hydroxyl ions (OH ) are produced at the cathode. These changes have been utilized for controlling the permeability of polyelectrolyte gel membrane or on-off solute release via ion exchange or surface erosion of interpolymer complex gels. 

P Burgmayer, RW Murray. An ion gate membrane Electrochemical control of ion permeability through a membrane with an embedded electrode. J Am Chem Soc 104 6139-6140, 1982. 

As can be seen from Figure 27.13, the permeability measurements of Nafion-like membranes do vary considerably, probably because the state of the membranes is difficult to control (e.g., the dryness of the membrane). There is a pronounced difference in the permeabilities for wet and dry membranes, but the method of measurement does not yield consistent variation in the measured values. It can therefore be concluded that the electrochemical method is equivalent to the gas analysis method, even though the measurement conditions are different from those in fuel cell applications. 

A novel principle for increasing the selectivity is the use of an ion gate membrane. Here, the ion permeability is controlled by electrochemical regulation of the redox state of the membrane material. For example, a polypyrrole film has to be in the reduced state to become permeable for anions. If the film is oxidized, no anion can permeate (Burgmayer and Murray, 1982). 

Efforts to stabilize BLMs by the use of polymerizable lipids have been successful, but the electrochemical properties of these membranes were greatly compromised and ion channel phenomena could not be observed [21]. Microfiltration and polycarbonate filters, polyimide mesh, and hydrated gels have been used successfully as stabilizing supports for the formation of black lipid films [22-25] and these systems were observed to retain their electrical and permeability characteristics [24]. Poly(octadec-l-ene-maleic anhydride) (PA-18) was found to be an excellent intermediate layer for interfacing phospholipids onto solid substrates, and is sufficiently hydrophilic to retain water for unimpeded ion transfer at the electrode-PA-18 interface [26]. Hydrostatic stabilization of solventless BLMs has been achieved by the transfer of two lipid monolayers onto the aperture of a closed cell compartment however, the use of a system for automatic digital control of the transmembrane pressure difference was necessary [27]. 

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