Ion concentration gradient

Unfortunately, in the presence of detectable polyions in the solution a strong potential drift is normally observed due to the instability of the ion concentration gradients. Moreover, the main disadvantage of polyion-selective potentiometric electrodes lies in the intrinsic irreversibility of the underlying response mechanism. The target polyions eventually displace the counter-ions in the membrane phase and consequently the sensor loses its response. 

Microresearch Diffusion control in constant potential mode. The ion concentration gradient in proximity to an electrode surface depends on how the electrode potential state is manipulated by an external electronic device, either... 

Consider now the situation when a counter ion concentration gradient that exactly balances the metal ion concentration gradient is established, so no flux of either ion across the membrane occurs. Under this condition, [MR ]o(m) = [MR ]f(ffl) and RH "./h, = [RH] (m), producing the expression... 

Equations (11.1)—(11.10) provide a basis for rationalizing the principal features of coupled transport membranes. It follows from Equation (11.8) that coupled transport membranes can move metal ions from a dilute to a concentrated solution against the metal ion concentration gradient, provided the gradient in the second coupled ion concentration is sufficient. A typical experimental result demonstrating this unique feature of coupled transport is shown in Figure 11.7. The process is counter-transport of copper driven by hydrogen ions, as described in Equation (11.1). In this particular experiment, a pH difference of 1.5 units is... 

Mitchell based his concept on the suggestion that as electron is transported along the respiratory chain, H+ ions are ejected to cytoplasm (the mitochondrion environment). As a consequence, a gradient of H+ ion concentration occurs in external and internal mitochondrial spaces. Of course, this H+ ion concentration gradient is supported by electron transfer free energy decrease and in the case of membrane impermeability for H+ ions. 

The respiration process produces electric potential difference on the membrane, and then H+ ion concentration gradient is formed on the membrane sides, which plays the important role in H+ ion transport. 

Gibb, L.E. Eddy, A.A. (1972). An electrogenic sodium pump as a possible factor leading to the concentration of amino acids by mouse ascites-tumour cells with reversed sodium ion concentration gradients. Biochem. J. 129, 979-981. 

Figure 1.3 Illustration of a potassium ion concentration gradient across a cell membrane. The concentration gradient and the electrostatic potential oppose and balance one another in thermodynamic equilibrium.

For 1300K a switch to 0 ions is involved. Superheated steam is produced at the anode. The O ion concentration gradient climbs from the oxygen cathode to hydrogen anode, to achieve migration/diffusion balance. Thus... 

Figure 4.1. Major membrane ion transport systems that shape the ion concentration gradients across the cytoplasmic membrane. Top Na /K -ATPase left NaTCa Nexchanger bottom Ion chaimels for and Na, and KTCf-cotransporter right Na -amino acid cotransporter.

K, too), so that the potential is essentially a function of the ion concentration gradient alone. However, this simple relationship will hold only when there is only one diffusible ion species. In a cell, we have several ion species, and finite permeabilities for several of them. The two dominant cations, Na and K, have roughly opposite distributions across the plasma membrane. Application of the Nemst equation to Na and would yield membrane potentials of -1-60 mV and -90 mV, respectively. Yet, the actual resting... 

A hydrogen ion concentration gradient of 1 to 1000 may be estabhshed across tubular cell membranes of... 

Potentiometric transducers measure the potential under conditions of constant current. This device can be used to determine the analytical quantity of interest, generally the concentration of a certain analyte. The potential that develops in the electrochemical cell is the result of the free-energy change that would occur if the chemical phenomena were to proceed until the equilibrium condition is satisfied. For electrochemical cells containing an anode and a cathode, the potential difference between the cathode electrode potential and the anode electrode potential is the potential of the electrochemical cell. If the reaction is conducted under standard-state conditions, then this equation allows the calculation of the standard cell potential. When the reaction conditions are not standard state, however, one must use the Nernst equation to determine the cell potential. Physical phenomena that do not involve explicit redox reactions, but whose initial conditions have a non-zero free energy, also will generate a potential. An example of this would be ion-concentration gradients across a semi-permeable membrane this can also be a potentiometric phenomenon and is the basis of measurements that use ion-selective electrodes (ISEs). 

A chemical baseline for snow at Palmer Station was preliminarily assessed (67). Samples were collected on a sheet of clean polyethylene. Standard EPA protocols were strictly adhered to and clean polyethylene gloves were used throughout. Ionic composition in Br , inorganic and organic carbon, Ca, Cl", F , K, Mg, Na", NH4, NOj" and S04 was ascertained by means of IC and ETA-AAS. No particular wind direction appears to influence pH and ion concentration gradients. Concurrent aerosol and snowfall along with meteorological data would be necessary to substantiate preliminary assumptions on the chemical baseline. 

Weak organic acids that destroy the hydrogen ion concentration gradient between the two sides of the membrane... 

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