S. Roy Caplan

Charge-Mosaic Membranes: Enhanced Permeability and Negative Osmosis with a Symmetrical Salt

Charge-mosaic membranes are prepared by embedding a single layer of alternating cation and anion exchange beads in silicone resin. Membranes made in an identical manner but containing only one type of exchanger serve as controls. The mosaic membranes are 50 to 100 times more permeable to potassium chloride than the controls; and furthermore they give rise to net volume flow from concentrated to dilute solutions of potassium chloride in the absence of a pressure gradient (negative osmosis), whereas the controls exhibit normal osmotic behavior. The negative reflection coefficients of the mosaics suggest potential applications in desalination.

An experimental enzyme-membrane oscillator

Abstract Periodic behavior has been observed in a synthetic membrane bearing papain activity. A membrane-coated glass pH electrode is exposed to a solution containing benzoyl- l -arginine ethyl ester at high pH. If the pH and substrate levels in the outer solution lie within a well-defined range, and if the rate of stirring is appropriate, spontaneous oscillations of the inner pH occur with a period of about 20 s. The oscillation depends on both the autocatalytic character of the enzymatic reaction and the feedback effect due to structural diffusion limitations. Certain relevant parameters of the cross-linked papain-albumin membrane used are reported.

Transport properties of charge-mosaic membranes I. Theoretical models

Abstract Charge-mosaic membranes are currently being considered for a number of practical applications, most notably “piezodialysis“ desalination. In Part I of this series the properties of the charge-mosaic are subjected to a nonequilibrium thermodynamic analysis, with emphasis on the role of the electrical resistance in the solutions bathing the membrane. Four regimes of operation are delineated by the analysis: (i) membrane control, (ii) solution control, (iii) co-ion leakage control, and (iv) polarization control. For a charge-mosaic operating in the regime of membrane control, the “complete” phenomenological coefficients are essentially concentration-independent, hence the flows may be expressed as linear functions of the global forces. If the membrane operates instead in the regime of solution control, the relationships are not linear but the coefficients are still directly calculable.

Charge-Mosaic Membranes: Dialytic Separation of Electrolytes from Nonelectrolytes and Amino Acids

Charge-mosaic membranes were used for dialytic separations of potassium chloride from low-molecular-weight nonelectrolytes and neutral amino acids. The permeability ratio (potassium chloride to uncharged species) ranged from about 6 in the case of methanol to about 86 in that of mannitol. A theoretical model predicts that optimum rates of dialysis should be achieved by dialyzing against salt concentrations other than zero; this prediction was confirmed by experiment. These observations suggest potential applications of mosaics in laboratory separations, industrial processing, and hemodialysis.

Nonequilibrium Thermodynamics and Its Application to Bioenergetics

Publisher Summary Nonequilibrium thermodynamics or the thermodynamics of irreversible processes extends and complements the classical method by the explicit introduction of time. It enables one to formulate a description of real processes rather than idealizations that happen in well-defined equilibrium states; the correlations it provides are between kinetic parameters. The most tractable processes are those that occur when the system is in a steady state. However, under stationary conditions, the state parameters of the system give no information about the processes occurring; to study these processes, it is necessary to look at their effects on the surroundings and indeed this is the essence of the approach. The resulting analysis immediately determines the number and nature of the degrees of freedom involved. The thermodynamic considerations lead to criteria that may help to distinguish between models of oxidative phosphorylation. These criteria neither depend on the isolation of an intermediate nor is it necessary to observe a component of hydrogen ion flow used for phosphorylation. It is necessary to determine the electrochemical potential difference of hydrogen and possibly of potassium across the mitochondrial membrane; however, the remaining parameters are evaluated externally. It is possible in principle to envisage conditions in which the flow of hydrogen ion across the membrane may be maintained non-zero and constant for brief periods

Transport properties of charge-mosaic membranes II. Experimental studies

Abstract The nonequilibrium thermodynamic analysis developed in Part I of this series is here subjected to experimental test. Experiments were performed to evaluate a set of six independent transport coefficients characterizing the individual anion and cation exchange elements. The results were used in conjunction with calculated values of the solution conductances to predict the transport properties of the charge-mosaic as a whole.

Oxygen consumption rate in vascular smooth muscle: Relation to isometric tension

Abstract Advances in muscle energetics require knowledge of the rates of the driving chemical reaction. Vascular smooth muscle, 2–3 orders of magnitude slower than amphibian skeletal muscle, permits continuous measurement of reaction rates. Oxygen consumption rates in the steady state appear to be a valid measure of the rate of the driving chemical reaction. The relation between isometric force and oxygen consumption rate is linear, and thus consistent with nonequilibrium thermodynamic analysis.

Transport properties of charge-mosaic membranes III. Piezodialysis

Abstract A nonequilibrium thermodynamic analysis of piezodialysis is presented. The expressions derived in Part I for the flows as linear functions of the global forces are used to predict the fractional recovery and rate of production of potable water in desalination by piezodialysis. An illustrative calculation is performed for a cylindrical tube (or hollow fiber) made from a hypothetical mosaic membrane whose properties have been calculated from those of Zeo-karb 315 cation exchange membrane. Perfect radial mixing and the absence of concentration polarization are assumed in order to focus attention on the role played by the membrane elements and circulating currents. For a 1 mm thick membrane under an applied pressure difference of 100 atmospheres, the calculation shows an 81% recovery of potable water of 350 ppm from a brackish water feed of 1500 ppm, the rate of production being 23 gpd/ft 2 . A thinner mosaic with a correspondingly reduced pattern size would give a proportionately higher production rate with no loss in recovery, provided that significant polarization could be prevented. This calculation sets upper limits on the performance of a given membrane by assuming that its properties, rather than the hydrodynamic conditions, are rate controlling. The analysis suggests ways of changing membrane properties to improve performance.

A comparison of the effects of ouabain and 2-deoxy-d-glucose on the thermodynamic variables of the frog skin

Previous studies support the validity of a linear thermodynamic formalism relating the rates of active Na-+ transport and oxygen consumption Jr to the electrical potential difference delta-psi and the affinity A (negative free energy) of the metabolic driving reaction. The formulation was further tested in paired control and experimental hemiskins by the use of two inhibitors of Na-+ transport. Ouabain, a specific inhibitor of the Na-+ pump, might be expected to diminish the dependence of Jr on delta-psi without affecting A, whereas 2-deoxy-D-glucose, a competitive inhibitor of glucose metabolism should be expected to diminish A. Both inhibitors were used at concentrations adequate to depress Na-+ transport (i.e. short-circuit current Io) to some 50% of control level. Measurements were made of Io and dJr/d(delat-psi), and the apparent value of the affinity Aapp was calculated according to the thermodynamic formulation. Ouabain depressed minus dJr/d(delta-psi) without affecting Aapp whereas 2-deoxy-D-glucose depressed Aapp without affecting minus dJr/d(delta-psi). The demonstration of these effects indicated the utility of the formalism.

Symmetry and the stationary state behavior of enzyme membranes

Abstract An analysis of the stationary state behavior of model enzyme (or catalytic) membranes is considered. In particular, membrane functional symmetry is shown to be of critical importance in deriving a unique set of global linear phenomenological relations from their local counterparts. Indeed the appropriate transformation of the dissipation function, based on the correct identification of the “transport plane” within the membrane, leads to a global analog of the Curie Principle. By extending the argument from the near-equilibrium regime to the pseudo-first-order kinetic regime a set of practical equations can be derived. These make it possible to obtain local transport and reaction parameters from global measurements. The facilitation of transport by reaction is discussed.