Electrochemical potential difference

Mitchell s chemiosmotic theory postulates that the energy from oxidation of components in the respiratory chain is coupled to the translocation of hydrogen ions (protons, H+) from the inside to the outside of the inner mitochondrial membrane. The electrochemical potential difference resulting from the asymmetric dis-... 

Each of the respiratory chain complexes I, III, and IV (Figures 12-7 and 12-8) acts as a proton pump. The inner membrane is impermeable to ions in general but particularly to protons, which accumulate outside the membrane, creating an electrochemical potential difference across the membrane (A iH )-This consists of a chemical potential (difference in pH) and an electrical potential. 

The electrochemical potential difference is used to drive a membrane-located ATP synthase which in the presence of P + ADP forms ATP (Figure 12-8). Scattered over the surface of the inner membrane are the phos-phorylating complexes, ATP synthase, responsible for the production of ATP (Figure 12-1). These consist of several protein subunits, collectively known as F, which project into the matrix and which contain the phosphorylation mechanism (Figure 12-8). These sub-... 

A strong electric field is formed in very thin films (with a thickness of about 10 5 cm) during current flow. If the average electrochemical potential difference between two neighbouring ions in the lattice is comparable with their energy of thermal motion, kTy then Ohm s law is no longer valid for charge transport in the film. Verwey, Cabrera, and Mott developed a theory of ion transport for this case. 

The rate of the active transport of sodium ion across frog skin depends both on the electrochemical potential difference between the two sides of this complex membrane (or, more exactly, membrane system) and also on the affinity of the chemical reaction occurring in the membrane. This combination of material flux, a vector, and chemical flux (see Eq. 2.3.26), which is scalar in nature, is possible according to the Curie principle only when the medium in which the chemical reaction occurs is not homogeneous but anisotropic (i.e. has an oriented structure in the direction perpendicular to the surface of the membrane or, as is sometimes stated, has a vectorial character). 

It is assumed that the chloride ion is transported passively across the membrane. Using an approach similar to the formulation of Eqs (2.1.2), (2.3.26) and (2.5.23), relationships can be written for the material fluxes of sodium and chloride ions, /Na+ and Jcr (the driving force is considered to be the electrochemical potential difference), and for the flux of the chemical reaction, Jch ... 

Thus, the electrochemical potential difference between an electron in the solution and in the electrode is related to the absolute electrode potential. If the solution composition is assumed to be constant with potential, the chemical potential and dipole potential of the solution are constant. Thus, the ability of an electron to transfer across the interface for a given solution composition is controlled exclusively by the electrode potential. 

Additionally, other reference electrodes are used which are easier to maintain at standard conditions. These include the silver/silver chloride electrode and the saturated calomel electrode (SCE). The voltage difference between the working electrode and the reference electrode is proportional to the electrochemical potential difference between them. This is written... 

As electrons move through complexes I, III, and IV, protons are taken up from the matrix and released on the cytosolic side of the membrane. This raises the pH of the matrix and leaves the matrix negatively charged relative to the cytosol, creating an electrochemical potential difference that tends to pull protons from the cytosol back into the matrix. 

From the earliest proposal for Na+-coupled transport, it was considered likely that K+ participated in the overall reaction (Crane, 1965). With the use of membrane vesicles where the internal and external K+ levels could be manipulated and replaced by other ions (Colombini and Johnstone, 1974 Murer and Hopfer, 1974 Sigrist-Nelson et al., 1975 Hopfer, 1978), it became clear that the apparent K+ requirement in intact cell systems was likely indirect and due to its requirement by the Na+/K+ ATPase to maintain the electrochemical potential difference for Na+. 

Thus, local corrosion (and the term local may imply a size of a few atoms up to that of a millimeter) occurs whenever a region of a material surface, a, is connected electrically (through a flow of electrons in the underlying metal region, p, at which there are interfacial reactions exhibiting an electrochemical potential different from that at a. The different constituents of an alloy would tend to provoke such a situation or, for example, S inclusions in steel. 

The electrochemical potential difference between ( ) and E corresponds to a free energy difference ... 

Since the corrosion of iron in copper sulfate solution involves an oxidation and reduction reactions with exchange of electrons, the reaction must involve an electrochemical potential difference, related to the equilibrium constant. This relationship may be written as ... 

Corrosion is due to electrochemical potential differences (galvanic corrosion) between the HAZ/fusion line and the parent material, attributed to the unstable MnS inclusions produced during the welding cycle. It was observed that enhanced corrosion of the weld metal was due to electrochemical potential differences between the weld metal and the base metal, such that the weld metal is anodic in the galvanic couple. The potential difference may only be of the order of perhaps 30-70 mV, but the low surface area ratio of anode to cathode results in high corrosion rates (1-10 mm). (Bond)5... 

Galvanic Cell Formation. When dissimilar metals are in contact and with the presence of electrolyte, a so-called galvanic cell will be established due to the electrochemical potential difference.2 The result of the galvanic cell is corrosion of the metal that is less noble. For instance, when copper is in contact with iron in the presence of electrolyte... 

The translocator moves the two nucleotides in either direction. However, ATT is transported as ATP4- and ADP as ADP3-. Thus the equilibrium position of the exchange is dependent on the electrochemical potential difference across the membrane. When the electrical potential difference is 160 mV, the ratio of ATP/ADP in the medium outside the mitochondrion is 125/1. 

Equations (10.152) and (10.153) can be used to analyze sodium flow in frog skin. The flow of sodium chloride across the skin comprises the flow of sodium ions. /Na, which is coupled to the metabolic process Jrtot, while the flow of the chloride ions JC may be assumed to be passive transport. The driving forces for the ionic flows are the electrochemical potential differences, and are given for a component i in a simple system as follows ... 

Potassium leaves the cell, while the net flow of sodium is inward. A nonequilibrium stationary state for the cell at rest is maintained by the sodium and potassium pumps, which pump out the entering sodium ions and pump the leaking potassium ions back into the cell interior, using a certain metabolic output. The sodium transfer is coupled with the chemical reaction. The electrochemical potential difference for sodium ions is expressed as... 

The above model is useful however, biological membranes, which transport various substances, are complex systems. Such membranes are close to composite membranes with series and parallel elements. A value of q < 1 shows an incomplete coupling, where a metabolic energy must be expended to maintain an electrochemical potential difference of sodium even in the absence of active transport, that is (./, )y =0 A0. 

Here, the subscripts P, H, and O refer to phosphorylation, the H+ flow, and substrate oxidation, respectively, and A/uh is the electrochemical potential difference of protons. We consider only systems at steady state. The dissipation function can be transformed as... 

Lu and L1 are the straight and cross-coefficients, respectively. By Onsager s reciprocal rules, we have LtJ = L. The electrochemical potential differences between internal i and external e regions are defined by... 

Alternatively, a potentiometer connected across the open circuit is found to register a potential difference that renders the Cu electrode positive relative to the Zn electrode the magnitude of the open—circuit electrochemical potential difference, which later will be shown to be identical with the electromotive force (emf), symbolized by fS, is approximately 1.1 volts. 

The electrochemical potential differs from the chemical potential by a term which depends on the electrical potential, a, of the phase... 

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