Chronopotentiometric study of a Nafion membrane in presence of glucose

Chronopotentiometric and swelling experiments have been conducted to characterize the behavior of a Nafion membrane in NaCl and KCl aqueous solutions without and with glucose. A mixture solution with similar composition to the cerebrospinal fluid and blood plasma has also been studied. From the chronotentiograms, current-voltage curves have been obtained, and the values of the limiting current density, diffusion boundary layer thickness, difference between counter-ion transport number in membrane and free solution, and transition times have been determined for the investigated membrane systems. The obtained results indicate that the presence of glucose affects the ion transport through the membrane depending on the electrolyte and glucose concentrations. At low electrolyte concentration, experimental transition times are found to be smaller in presence of glucose, which has been related to an effective membrane area reduction in presence of glucose. The membrane system corresponding to the mixture solution shows a behavior similar to the single high concentration NaCl membrane system, indicating that the observed behavior is mainly associated to the Na^+ ions transport in higher proportion. In this case, the glucose presence does not affect significantly the investigated properties of the membrane, which is interesting for its utilization in a glucose fuel cell.

Swelling properties of alkali-metal doped polymeric anion-exchange membranes in alcohol media for application in fuel cells

Swelling properties of four commercial anion-exchange membranes with different structure have been analyzed in several hydro-organic media. With this target, the liquid uptake and the surface expansion of the membranes in contact with different pure liquids, water and alcohols (methanol, ethanol and 1-propanol), and with water alcohol mixtures with different concentrations have been experimentally determined in presence and in absence of an alkaline medium (LiOH, NaOH and KOH of different concentrations). The alkali-metal doping effect on the membrane water uptake has also been investigated, analyzing the influence of the hydroxide concentration and the presence of an alcohol in the doping solution. The results show that the membrane structure plays an essential role in the influence that alcohol nature and alkaline media has on the selective properties of the membrane. The heterogeneous membranes, with lower density, show higher liquid uptakes and dimensional changes than the homogeneous membranes, regardless of the doping conditions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Role of the Tryptophan Residues in the Specific interaction of the Sea Anemone Stichodacty la helianthus’s Actinoporin Sticholysin II with Biological Membranes

Actinoporins are pore-forming toxins from sea anemones. Upon interaction with sphingomyelin-containing bilayers, they become integral oligomeric membrane structures that form a pore. Sticholysin II from Stichodactyla helianthus contains five tryptophans located at strategic positions; its role has now been studied using different mutants. Results show that W43 and W115 play a eterminant role in maintaining the high thermostability of the protein, while W146 provides specific interactions for protomer−protomer assembly. W110 and W114 sustain the hydrophobic effect, which is one of the major driving forces for membrane binding in the presence of Chol. However, in its absence, additional interactions with sphingomyelin are required. These conclusions were confirmed with two sphingomyelin analogues, one of which had impaired hydrogen bonding properties. The results obtained support actinoporins’ Trp residues playing a major role in membrane recognition and binding, but their residues have an only minor influence on the diffusion and oligomerization steps needed to assemble a functional pore.