Permeability hydroxyl ion

A stopped-flow rapid-reaction apparatus was used to measure the time course of pH changes in human erythrocyte suspensions. In one set of experiments a red cell suspension at pH 72 was mixed with an isotonic saline solution whose pH had been adjusted to a value between 2.1 and 10.4. Analysis of the results enabled computation of erythrocyte hydroxyl ion permeability as a function of pH. Further experiments were then performed in which erythrocyte suspensions at low pco2 were mixed with bicarbonate solutions at high pco2- Analysis revealed that C02 equilibrium in the mixture was reached quickly, but pH equilibrium was delayed. Evaluation of the results indicates that variation in red cell OH permeability with pH is not compatible with a simple fixed-charge hypothesis of membrane permselectivity, and the uncatalyzed hydration-dehydration of C02 in extracellular fluid is required to produce pH equilibration after blood-gas exchange. 

We present first the equipment developed for the study of rapid pH changes in cell suspensions, and we then discuss the use of this equipment in studies of the hydroxyl ion permeability (Poh-) of the human erythrocyte membrane and in studies of pH equilibration between red cells and their environment during blood-gas exchanges. Finally, the implications of these studies, relative to previously presented hypotheses about anionic and blood-gas exchanges, are critically examined. 

Estimates of the hydroxyl ion permeability (Poh-) of human erythrocytes were calculated from observations of rapid pH changes in red cell suspensions under conditions where only chloride and hydroxyl ion fluxes were significant. The experimental design used was similar to procedures reported previously by Maizels (17) Wilbrandt (IS), and others. 

One effect of the electrochemical reactions in an aqueous system is a local pH change around the electrodes. By water electrolysis, hydronium ions (H30+) are generated at the anode, while hydroxyl ions (OH ) are produced at the cathode. These changes have been utilized for controlling the permeability of polyelectrolyte gel membrane or on-off solute release via ion exchange or surface erosion of interpolymer complex gels. 

The separator used in silver—zinc cells should be permeable to water and hydroxyl ions, stable in strong alkaline solutions, and not oxidized by the solid silver oxide or dissolved silver ions and should retard the migration of dissolved ions to the anode. 

In order to avoid this undesirable effect and to promote metal ion accumulation in the liquid phase, Ryss and Goldberg (1973) developed a special element-collector. This consists of a vessel containing a metallic electrode and a semi-permeable membrane, on one side of which is a solution of nitric acid (Fig. 2-17). The semi-permeable membrane prevents egress of the acid solution and allows ionic exchange between the element-collector and the surrounding environment. The acid neutralises the hydroxyl ions and thereby maintains the solubility of metal ions in the vicinity of the cathode. 

The study of the fixed-charge hypothesis is ideally carried out by steady-state isotopic permeability experiments. These conditions are impossible to meet in the study of hydroxyl ion movements. Furthermore, net OH" movements necessarily involve pH changes by their nature. Nevertheless, the experiments reported here can be used to determine the effects of external pH on OH" permeability since temperature and... 

Paint the cathodic material. This provides a barrier against electrolyte contact with the cathode however, this is not simply accomplished in many cases due to the permeability of coatings by moisture combined with the generation of hydrogen and hydroxyl ion on the cathode surface. The combined effect is to strip all but the most alkali-resistant coatings. 

As ion-semipermeable membranes, which - despite good permeability to hydroxyl ions - hinder the transfer of zincate and silver ions, essentially only regenerated cellulose is being used in alkaline batteries. In a complex conversion process, a pulp of wood cellulose, primarily from eucalyptus trees, is dissolved... 

The role of an AEM is to conduct hydroxyl ions from cathode to anode at match-able rates to the foreign current, as well as the separation of fuels and oxidants. In addition, its integration with the catalytic electrodes forms the heart, MEA, of the AEM fuel cell system. The basic requirements for an AEM are summarized in Section 11.2. To evaluate the performance of a developed AEM material, the fundamental physicochemical properties, including lEC, water absorbing and dimensional swelling, mechanical and thermal properties, membrane morphology, and methanol permeability, are usually investigated. The physical properties of some selected aromatic AEMs are summarized in Table 11.1. 

An alternate procedure used in a few specialty applications is the cuprammonium process. This involves stabilization of cellulose in an ammonia solution of cupric oxide. Solubilization occurs by complex formation of cupric ion with ammonia and the hydroxyl groups of cellulose. Regeneration of cellulose, after formation of the desired products, is accomplished by treatment with acid. The main application of the cuprammonium process is for the synthesis of films and hollow fibers for use in artificial kidney dialysis machines. The cuprammonium process yields products with superior permeability and biocompatibility properties compared to the xanthation process. Less than 1% of all regenerated cellulose is produced by the cuprammonium process. 

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