Gibbs energies membrane

The voltammetric information given here suggests that the transfer of an objective cation from Wl to LM can be achieved under a smaller membrane potential when an anion for which the Gibbs transfer energy at the LM/W2 interface is smaller is added into W2. In the case of the above-mentioned membrane system, the transfer of K+ from Wl to LM in the presence of 0.01 M MgBr2 in W2 is expected to be attained even at the membrane potential 0.19 V (which corresponds to the Gibbs energy of transfer of 18.3... 

It is apparent that the deviation from Nemstian behaviour depends on the activity of the determinand and anion B in the studied solution. It decreases with increasing magnitude of the sum of the standard Gibbs energies of transfer of ions J and B " from water into the membrane phase. The effect of the interfering anion is suppressed by increasing the concentration of the ion-exchanger ion in the membrane. 

The use of ISEs in non-aqueous media(for a survey see [125,128]) is limited to electrodes with solid or glassy membranes. Even here there are further limitations connected with membrane material dissolution as a result of complexation by the solvent and damage to the membrane matrix or to the cement between the membrane and the electrode body. Silver halide electrodes have been used in methanol, ethanol, n-propanol, /so-propanol and other aliphatic alcohols, dimethylformamide, acetic acid and mixtures with water [40, 81, 121, 128]. The slope of the ISE potential dependence on the logarithm of the activity decreases with decreasing dielectric constant of the medium. With the fluoride ISE, the theoretical slope was found in ethanol-water mixtures [95] and in dimethylsulphoxide [23], and with PbS ISE in alcohols, their mixtures with water, dioxan and dimethylsulphoxide [134]. The standard Gibbs energies for the transfer of ions from water into these media were also determined [27, 30] using ISEs in non-aqueous media. 

In contrast to ISEs with neutral ion carriers in the membrane, not even qualitative rules have been formulated for the solvent effect on the behaviour of ISEs with ion-exchanger ions in a liquid membrane. A basic condition for the ion-exchanger ions is that they be strongly hydrophobic. It must hold for the standard Gibbs energy of transfer of the ion-exchanger ion X and the deter-minand Y that... 

The DEFC transforms directly the Gibbs energy of combustion of ethanol into electricity, without a fuel processor. This greatly simplifies the system, reducing its volume and cost [22, 23]. The important development of DEFCs is due to the use of a proton exchange membrane as electrolyte, instead of a liquid add electrolyte, as done previously. 

It is not immediately obvious why K+ is the preferred counterion within tissues, but a fundamental reason may lie in the differences in hydration between Na+ and K+ (Chapter 6). On the other hand, the relationship of these ions to the excitability of membranes (Chapter 30) may be of paramount importance, even in bacteria. The concentration differences in the two ions across membranes represent a readily available source of Gibbs energy for a variety of membrane-associated activities. Cells actively pump Na+ out and K+ into cells (Chapter 8). 

The mitochondrial membrane potential Em (or Ay) is the potential difference measured across a membrane relative to a reference electrode present in the surrounding solution.176 For both mitochondria and bacteria Em normally has a negative value. The Gibbs energy change AyH+ for transfer of one mole of H+ from the inside of the mitochondrion to the outside, against... 

Transformed Gibbs Energy of a Two-Phase System with a Chemical Reaction and a Membrane Permeable by a Single Ion... 

Consider an aqueous two-phase system containing A, B, C, and solvent H20 in which the reaction A + B = C occurs. The two phases are separated by a membrane, and the membrane is permeable to all four species. The fundamental equation for the Gibbs energy of the a phase is... 

TRANSFORMED GIBBS ENERGY OF A TWO-PHASE SYSTEM WITH A CHEMICAL REACTION AND A MEMBRANE PERMEABLE BY A SINGLE ION... 

When a system at specified T and P contains two species and one of them is in equilibrium with that species in a reservoir through a semipermeable membrane, the transformed Gibbs energy of the system is calculated from the semigrand partition function F(7( P, /q, N2) by use of... 

Use has here been made in steps 2 through 4 of the fact that there is no change in the Gibbs energy for processes carried out under conditions of membrane and chemical-reaction equilibrium. This explains why the value of AG° is related directly to the ratios of the equilibrium-state and standard-state fugacities (ft = 1). 

If the electron transfer chain in the membrane is inhibited and an amount of ATP is made available, the ATP synthase would attempt to hydrolyze the ATP and pump protons across the membrane. This process would not continue indefinitely, since the ATP concentration would fall, and that of ADP and P would rise, lowering the Gibbs energy for the ATP hydrolysis. At the same time a would build up... 

An ionophore, from the Greek words ion and/ero (carry), is a compound (organic or organometallic) which can selectively and reversibly coordinate to a specific ion and can thus, based on differences in Gibbs energy, transport the ion from the aqueous solution into a membrane. Up-to-date knowledge in the area of ionophores suggests that there are some very important physicochemical characteristics that a compound must have in order to be a candidate for use as an ionophore in ISEs. The most important of these are ... 

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