Membranes gates

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. 

The SR membrane contains a very efficient calcium uptake transporter, which maintains free cytoplasmic calcium at very low levels during diastole by pumping calcium into the SR. The amount of calcium sequestered in the SR is thus determined, in part, by the amount accessible to this transporter. This in turn is dependent on the balance of calcium influx (primarily through the voltage-gated membrane calcium channels) and calcium efflux, the amount removed from the cell (primarily via the sodium-calcium exchanger, a transporter in the cell membrane). 

In addition, temperature-responsive properties of PNIPAAm have also been used in fabricating molecular ion gating membranes.37 38 In these studies, the concept of an ion gating molecular recognition membrane using synthetic host substances and a thermosensitive polymer was proposed. Figure 15.1038 illustrates the concept. The membrane was prepared by plasma graft copolymerization, which filled the pores of a porous polyethylene him with a copolymer of A -isopropyl... 

Figure 15.10 Schematic representation of a molecular recognition ion gating membrane. The copolymer of thermosensitive polymer fV-isopropylacrylamide, and crown ether polymer, BCAm, is grafted on the pore surface. The membrane senses a specific ion Mn+, by the crown receptor, and closes its pores rapidly.38 (Reprinted with permission from T. Ito et al., J. Am. Chem. Soc. 2002,124,7840—7846. Copyright 2002 American Chemical Society.)...

Lamas JA, Selyanko AA, Brown DA (1997) Effects of a cognition-enhancer, linopir-dine (DuP 996), on M-type potassium currents (IK(M)) and some other voltage-and ligand-gated membrane currents in rat sympathetic neurons. Eur J Neurosci 9(3) 605-616... 

When the gel used as a gating membrane to control the release of solute these will have two competing effects on flux ... 

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). 

K. Kontturi, L. Murtomaki, P. Pentti, and G. Sundholm, Preparation and properties of a pyrrole-based ion-gate membrane as studied by the EQCM, Synth. Met., M(2), 179-185 (1998). 

With local membrane depolarization caused by some stimulus, the longitudinal membrane conduction causes the local rise in TMP to spread along the adjacent regiims of the memlnane. Adjacent voltage-gated membrane channels are driven above threshold, propagating the depolarization event. This effect on adjacent membrane is illustrated in Fig. 17.11 for a nerve axcm. By diis mechanism, bioelectric action events spread outward from the point of stimulus, move along the cell membrane, and cease when the entire membrane is depolarized. 

Characteristic curves for separative extended gate. Id vs Vgs. are shown in Fig. 4.4a, which also contains the linear response of Vqs as a function of pH. The sensitivity of the gate membrane can be calculated from the slope in the linear range, for a constant Id value (see Fig. 4.4b). The Nemstian expected value for the sensitivity is 59.2 mV. pH" at 25 °C. 

The benefits of modifying EIS structures with LbL films to achieve biosensors with improved performance was also reported by Abouzar et al., who observed an amplification of the signal response upon alternating layers of polyelectrolytes and enzymes as gate membranes on the p-Si-Si02 EIS structure [99]. A new variant of EIS sensors has been produced, which comprised an array of individually addressable nanoplate field-effect capacitive biochemical sensors with an SOI (silicon-on-insulator) stmcture to determine pH and detect penicillin. It also allows for the label-free electrical monitoring of formation of polyelectrolyte multilayers and DNA (deoxyribonucleic acid)-hybridization event [100]. 

Fernandes, E.G.R., Vieira, N.C.S., de Queiroz, A.A.A., Guimaraes, F.E.G. Immobilization of poly(propylene imine) dendrimer/Nickel phthalocyanine as nanostructured multilayer films to be used as gate membranes for SEGEET pH sensors. J. Phys. Chem. C 114, 6478-6483 (2010)... 

Ito, T. Yamaguchi, T. Osmotic pressure control in response to a specific ion signal at physiological temperature using a molecular recognition ion gating membrane. J. Am. Chem. Soc. 2004,126, 6202-6203. 

Typical valinomycin cocktails contain 65-70 mass % of mediator which provides an ideally flexible PVC membrane for macro ISEs but shows poor adhesion characteristics for loading gates of ion-sensitive field effect transistor (ISFET) devices. Attempts have thus been made to improve adhesion by lowering the solvent content of the sensor cocktails without unduly compromising the usual electrode performances. Cocktails with 50 mass % solvent gave usable ISFETs but no improvement in adhesion. An ISFET with a gate membrane of 35.2 mass % solvent was noisy and showed no real response (43). 

As basic sensor a pH-l FET chip was developed which can be used for different ISM depositions. It contains a dual ISFET structure (n-channel FET, LP-CVD Si3N4 gate membrane, gate size 16 x 400 pm) and a temperature sensitive diode. The chip is fabricated in a standard MOS>production line. For using the chip in a ISFET difference measuring mode without a conventional reference electrode an integrated pseudo reference electrode has been designed too. 

Yamaguchi et al. demonstrated the multi-sensitive behavior of the ternary copolymer 8 of [3-(methacryloylamino)propyl]trimethylammonium chloride, acrylic acid, and benzo[18]crown-6-acrylamide. This system controlling thermosensitivity by cation recognition of the crown ether was applied to an ion gating membrane. 

Conductive polymers have been proposed as matrices for the controlled release of chemicals. In this application, advantage is taken of the fact that the counterions in p-type (oxidized) conducting polymers are released into solution when the polymer is electrochemically reduced. Ton gate membranes have been proposed, employing conductive polymers to vary the permeability of the membrane to ions. This exploits the fact that certain neutral undoped polymers are hydrophobic whereas their doped forms are polar salts. 

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