Hideo Kimizuka

Nonequilibrium thermodynamics of ion transport through membranes

Abstract A theory of membrane ion transport suitable for a self-consistent analysis of transport phenomena is presented on the basis of nonequilibrium thermodynamics. The theory assumes only a steady state and no volume flow across the membrane. Ion flow is expressed as a linear function of the total ion activity difference across the membrane. Coefficients of the flux equation are defined as elements of a permeability matrix. The equations for the membrane properties (e.g., potential and conductance) are derived from the equation of ion flux. The theory is applicable to any multi-ionic system containing ions of various charges. A physical representation of membrane permeability and a correlation between membrane permeability and the elements of a permeability matrix are explained. Transport phenomena are discussed with respect to the theory presented.

Effect of ionic charge on the electrical properties of an amphoteric ion exchange membrane

Abstract In order to clarify the mechanism of ion transport across an amphoteric membrane with sulfonate and N -methylpyridinium groups as exchange sites, membrane potential and membrane conductance measurements were carried out with varying valences of cations and anions of the electrolyte solution. It was shown that the membrane studied behaves as a cation exchange membrane in 1-1 valent and 2-2 valent electrolyte solutions. On the other hand, the membrane function was strongly influenced by the valence of the cation; the membrane in the LaCl 3 system in particular was preferentially anion selective. The permeability coefficients were evaluated according to the theory of nonequilibrium thermodynamics, and ion transport was discussed.

Study of bi-ionic potentials.

The bi-ionic membrane potential has been studied on a system consisting of electrolyte solutions separated from another one by an ion exchange membrane. The slope of the linear portion of the curve of potential vs. log activity ratio, log aMaN, was found to be 118(zM+zN) mv at 20°C, where aM and zM denote respectively the activity and the charge of permselective ion M present on one side of the membrane and aN and zN, those of the ion N on the other side. This was in good agreement with the theoretical prediction provided that the membrane is permselective to either cations or anions and the relative membrane permeability is a constant.

Ion current and potential across membranes

Abstract Theoretical treatments of the membrane process in the steady state were presented by using the rate equation in the preceding paper (Kimizuka & Koketsu,1964). It was shown that the equation for the ion conductance and transport number were expressed as functions of the membrane permeability, the composition and the membrane potential. The transport numbers of ions to the membrane of frogs sartorius muscle in normal Ringers solution were calculated according to the derived equation. The membrane potential calculated according to the Nernst equation by using the transport numbers and the equilibrium potentials of potassium, sodium and chloride ions was in agreement with the observed value. The membrane conductance was shown to be a function of the applied potential, by which the difference between the calculated membrane resistance at rest and the observed one, could be explained. The equation for the passive ion flux at rest was given as a function of the composition and the membrane permeability, and it was shown that the calculated passive movements of ions were consistent with the directions of the active transports. The equation for the resting potential, as well as the membrane conductance, were obtained for the case in which the external solution contains the bivalent ions. The prolonged action porential of the crustacean muscle fibers (Fatt & Ginsborg, 1958) in the presence of strontium ions could be expressed in terms of the derived equation, and the membrane permeabilities to the ions were evaluated according to the proposed relationships. It was shown that the current-voltage relation measured with the giant axon of loligo (Hodgkin, Huxley & Katz, 1952) could be expressed by the derived equations. The discussion for the states of the membrane was given in terms of the proposed theory. The current-voltage relation for the cable has also been derived.

Study of ion transport across an amphoteric ion exchange membrane — general transport properties of a simple electrolyte

Abstract Basic electrochemical properties of an amphoteric ion-exchange membrane (1.0—PA—29), in which almost equal numbers of cationic and anionic sites are distributed homogeneously over the functionalized polymer networks, were studied for a variety of concentration-cell systems. Unlike the usual uniform ion-exchange membrane, potentiometric permselectivities were demonstrated even for ions of the same charge, as shown by the result that distinctive potential responses were observed for a series of alkali metal chloride, sodium salt, and tetra-alkylammonium chloride systems. The sequence of membrane permeabilities to cations and anions calculated from the electrochemical data could well be correlated to the sequence of the hydrated radii of the respective ions. So the potentiometric responses to any electrolyte system can be predicted from the permeability data or hydrated radius values of individual cations and anions. The present results suggest that the homogeneous amphoteric ion-exchange membrane functions effectively as an ion sieve, sifting out the sizes of permeating hydrated cations and anions.

Electrokinetic phenomena in amphoteric membranes

Abstract The membrane phenomena in an amphoteric membrane-single-electrolyte or mixed-electrolyte solution systems were examined. The mobilities of the ions within the membrane were evaluated from the relation between the transport number and membrane conductance after determination of the ionic concentration within the membrane. In the single-electrolyte system, the mobilities depending on the ionic charges were observed. The facts supported that ion-transport phenomena were mainly controlled by the electrostatic interaction between the ion-exchange sites and the ions within the membrane. On the other hand, the cation with the smaller valence was always excluded out of the membrane in the mixed-electrolyte system. When comparing the ratios of mobilities in the single-electrolyte system with those in the mixed-electrolyte system, large differences between them could be observed. It is conjectured that one of the reasons may be the difference in the Donnan adsorption salt concentration within the membrane.

A physicochemical study of reverse transport system based on nonequilibrium thermodynamics

Abstract Reverse transport in a liquid membrane system was studied on the basis of nonequilibrium thermodynamics. The electrochemical affinities which drive the ion flux in the system accompanying the chemical reaction were described in the form of the dissipation function. The system was confirmed to be a typical physicohemical system. In addition, using the equations developed in this study, several membrane parameters were estimated and the correlation between the diffusional ion conductance and ion concentration within the liquid membrane was discussed.

Membrane potential and ion flux in a reverse transport system with a liquid membrane using monensin as a carrier

Abstract Reverse transport coupled to a chemical reaction was studied with a liquid membrane-electrolyte system. The liquid membrane was prepared by dissolving 10−2 mol-dm−3 monensin in 1-octanol; it was supported by a Millipore filter. The membrane showed an ideal potential response for Na+ and H+ cations. A system with the same Na+ ion concentrations in both exterior aqueous phases was chosen as the reverse transport system. The membrane potential and the ion flux of the system were measured as functions of time. The results were treated in terms of the membrane equations developed in previous papers. The membrane potential and the ion flux could be described consistently according to equations derived on the assumption of a rapid acid-base reaction taking place at the boundary. It was concluded that the acid-base reaction energy is transformed into an electrochemical potential, and, as a result, the reverse ion flux is apparently driven by the electrochemical potential gradient.

Ion transport mediated by inverted micellar aggregates across a phosphatidylcholine-octanol liquid membrane

Abstract The ionophoretic activity of dipalmitoyl-DL-α-phosphatidylcholine (DPPC) was investigated on the system in which two aqueous NaCl solutions are separated by a porous support membrane impregnated with a 1-octanol solution of DPPC. Transmembrane potential and conductance measurements were carried out with changing temperature to estimate the membrane permeability to ions. To clarify the mechanism of ion transport through an immobilized DPPC-1-ctanol membrane, differential scanning calorimetry and photon correlation spectroscopy were employed to investigate the molecular properties of DPPC in a water-saturated 1-octanol system. An endothermic peak was detected at around 18°C in the water-saturated 1-octanol system, but not in the pure 1-ctanol system. Laser light scattering study indicated that DPPC molecules form aggregates, ca. 0.1 μm in diameter, in water-saturated 1-octanol, but not in pure 1-octanol. Temperature dependences of the relaxation time estimated by the light scattering study changed above and below 18°C. The critical temperature, 18°C, correlates well with that at which modes of the temperature dependences of membrane permeability are altered. Results obtained by these three types of experiments indicate that inverted micellar aggregates of DPPC function as an ionophore.

Kinetics of permeation of nucleotide through oil/water interface in the interaction of nucleotide with octadecylamine and dodecyl guanidine

The transports of tritiated ATP, ADP and AMP from the aqueous to scintillator phase with and without octadecylamine (or dodecyl guanidine) have been studied by the layered scintillation method and a theory suitable for an explanation of the results has been presented. (1) Transport processes were all expressed by the first order kinetics. (2) For the simple partitioning of ATP, the reciprocal of the rate constant of the backward permeation was linear with respect to the square of the partition coefficient. (3) For the transport of nucleotide with chemical reaction, the reciprocal of the rate constant of the backward permeation was linear against the overall partition coefficient of nucleotide. (4) A theory was presented on the basis of a general diffusion equation by assuming the two-film model with potential energy near the interface. (5) The theory could explain the dependences of the permeation rates on the partition coefficients. (6) From the finding that the ratio of the apparent diffusion coefficient in aqueous to scintillator phase was much smaller than unity, the occurrence of an energy barrier at interface was suggested. For the simple partitioning of ATP, the energy barrier was not significant.