Membrane continued potential

A particular point of interest is that the chemiosmotic theory predicts that no ATP synthesis can occur other than in membranes which form closed vesicles since no membrane potential can exist unless there is membrane continuity. Observation of ATP synthesis in the absence of... 

The simplest way of modeling the CCL performance is to consider the structure depicted in Figure 3.1 as a homogeneous medium with effective parameters for electron, proton, and oxygen transport (macrohomogeneous model, MHM). Particularly, the membrane phase potential and carbon-phase potential 4> are assumed to be continuous functions of coordinates. Physically, this means that each representative volume of the CCL contains many carbon and Pt particles, Nafion phase domains, and voids, so that one may speak about volume-averaged concentrations, potentials, transport coefficients, currents, reaction rates, and so on. 

When first developed, potentiometry was restricted to redox equilibria at metallic electrodes, limiting its application to a few ions. In 1906, Cremer discovered that a potential difference exists between the two sides of a thin glass membrane when opposite sides of the membrane are in contact with solutions containing different concentrations of H3O+. This discovery led to the development of the glass pH electrode in 1909. Other types of membranes also yield useful potentials. Kolthoff and Sanders, for example, showed in 1937 that pellets made from AgCl could be used to determine the concentration of Ag+. Electrodes based on membrane potentials are called ion-selective electrodes, and their continued development has extended potentiometry to a diverse array of analytes. 

If metallic electrodes were the only useful class of indicator electrodes, potentiometry would be of limited applicability. The discovery, in 1906, that a thin glass membrane develops a potential, called a membrane potential, when opposite sides of the membrane are in contact with solutions of different pH led to the eventual development of a whole new class of indicator electrodes called ion-selective electrodes (ISEs). following the discovery of the glass pH electrode, ion-selective electrodes have been developed for a wide range of ions. Membrane electrodes also have been developed that respond to the concentration of molecular analytes by using a chemical reaction to generate an ion that can be monitored with an ion-selective electrode. The development of new membrane electrodes continues to be an active area of research. 

In order to maintain a definite contact area, soHd supports for the solvent membrane can be introduced (85). Those typically consist of hydrophobic polymeric films having pore sizes between 0.02 and 1 p.m. Figure 9c illustrates a hoUow fiber membrane where the feed solution flows around the fiber, the solvent—extractant phase is supported on the fiber wall, and the strip solution flows within the fiber. Supported membranes can also be used in conventional extraction where the supported phase is continuously fed and removed. This technique is known as dispersion-free solvent extraction (86,87). The level of research interest in membrane extraction is reflected by the fact that the 1990 International Solvent Extraction Conference (20) featured over 50 papers on this area, mainly as appHed to metals extraction. Pilot-scale studies of treatment of metal waste streams by Hquid membrane extraction have been reported (88). The developments in membrane technology have been reviewed (89). Despite the research interest and potential, membranes have yet to be appHed at an industrial production scale (90). 

Membrane-based separation techniques constitute nowadays well-established process methods for industrial treatments of fluids. Like SMB, membrane-based separations can be performed in continuous mode. In the field of preparative-scale enan-tiodiscrimination, much effort has been invested in this subject due its high potential [154, 155]. (Chapter 5 of this book is devoted to the subject, and further discusses the advantages and applications of membrane technologies.)... 

Resting potential is a stable membrane potential in nonexcitable cells, or the most stable membrane potential between Action Potentials in excitable cells. In some excitable tissues it is impossible to define a resting potential because of continuous change in membrane potential. 

NADH and reduced substrate dehydrogenase-flavoproteins (FPH2) must be continually reoxidized for mitochondrial oxidations to proceed. This is achieved by the electron transport chain (respiratory chain) which is a series of redox carriers of graded redox potential in the inner mitochondrial membrane (Appendix 1) that catalyzes the net reactions ... 

As described above, the propagation of the action potential is sensitive to Na -K changes over the membranes. These changes are most pronounced during continu-... 

LSnnergren, J. Westerblad, H. (1986). Force and membrane potential during and after fatiguing, continuous high-frequency stimulation of single Ae/topus muscle fibers. Acta Physiol. Scand. 128, 359-368. 

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