The Chameleon-Like Nature of Zwitterionic Micelles: Effect of Cation Binding

Addition of salts, especially perchlorates, to zwitterionic micelles of SB3-14, C(14)H(29)NMe(2)(+)(CH(2))(3)SO(3)(-), induces anionic character and uptake of H(3)O(+) by SB3-14 micelles. Thus, the addition of alkali metal perchlorates accelerates the acid hydrolysis of 2-(p-heptoxypheny1)-1,3-dioxolane, HPD, in the presence of SB3-14 micelles, which depends on the local proton concentration at the micelle surface. The addition of metal chlorides to solutions of such perchlorate-modified SB3-14 micelles decreases both the negative zeta potential of the micelles and the observed rate constant for acid hydrolysis of HPD. The effect of the monovalent cations Li(+), Na(+), and K(+) is smaller than that of the divalent cations Be(2+), Mg(2+), and Ca(2+), and much smaller than that of the trivalent cations Al(3+), La(3+), and Er(3+). The major factor responsible for this cation valence dependence of these effects is shown to be electrostatic in nature, reflecting the strong dependence of the micellar surface potential on the cation valence. The fact that the salt effects are not identical after correction for the electrostatic effects indicates that additional secondary nonelectrostatic effects may contribute as well.

Oxygen reduction reaction on a Pt/carbon fuel cell catalyst in the presence of trace quantities of ammonium ions: An RRDE study

The effect of trace quantities of ammonia on oxygen reduction reaction (ORR) on carbon-supported platinum catalysts in perchloric acid solutions is assessed using rotating ring disk electrode (RRDE) technique. The study demonstrates that ammonia has detrimental effects on ORR. The most significant effect takes place in the potential region above 0.7 V vs RHE. The effect is explained by the electrochemical oxidation of ammonia, which blocks Pt active sites and increases the formation of H2O2. This leads to losses in the disk currents and increments in the ring currents. The apparent losses in ORR currents may occur in two ways, namely, through the blocking of the active sites for ORR as well as by generating a small anodic current, which is believed to have a lower contribution. In addition, a detrimental effect of sodium cations in the potential range below 0.75 V vs RHE was demonstrated. This effect is most likely due to the co-adsorption of sodium cations and perchlorate anions on the Pt surface. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Iodide treatment acutely increases pendrin (SLC26A4) mRNA expression in the rat thyroid and the PCCl3 thyroid cell line by transcriptional mechanisms

Iodine is a critical element involved in thyroid hormone synthesis. Its efflux into the follicular lumen is thought to occur, in part, through pendrin at the apical membrane of thyrocytes. This study attempted to investigate whether iodide administration affects SLC26A4 mRNA expression in rat thyroid and in PCCl3 cells. Rats and cells were treated or not with Nal from 30 min up to 48 h. One group was concomitantly treated with sodium perchlorate. SLC26A4 mRNA expression was also investigated in PCCl3 cells treated with actinomycin D prior to Nal treatment. Iodide administration significantly increased SLC26A4 mRNA content in both models. The simultaneous administration of Nal and perchlorate, as well as the treatment of PCCl3 cells with actinomycin D prevented this effect, indicating that intracellular iodide is essential for this event, which appears to be triggered by transcriptional mechanisms. These data show that intracellular iodide rapidly upregulates SLC26A4 mRNA expression. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

New insights about the posttranscriptional mechanisms triggered by iodide excess on sodium/iodide symporter (NIS) expression in PCCl3 cells

Iodide excess acutely downregulates NIS mRNA expression, as already demonstrated. PCCl3 cells treated or not with Nal, Nal + NaClO4 or Nal + Methimazole, for 30 min to 24 h, were used to further explore how iodide reduces NIS gene expression. NIS mRNA expression was evaluated by Real-Time PCR; its poly(A) tail length, by RACE-PAT; its translation rate, by polysome profile; total NIS content, by Western blotting. NIS mRNA decay rate was evaluated in actinomycin-D-treated cells, incubated with or without Nal for 0-6 h. Iodide treatment caused a reduction in NIS mRNA expression, half-life, poly(A) tail length, recruitment to ribosomes, as well as NIS protein expression. Perchlorate, but not methimazole, prevented these effects. Therefore, reduced poly(A) tail length of NIS mRNA seems to be related to its decreased half-life, in addition to its translation impairment. These data provide new insights about the molecular mechanisms involved in the rapid and posttranscriptional inhibitory effect of iodide on NIS expression. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

Sodium Alginate-Based Ionic Conducting Membranes

The present study investigates gel polymer electrolytes (GPEs) based on sodium alginate plasticized with glycerol containing either CH3COOH or LiClO4. The membranes showed ionic conductivity results of 3.1 x 10(-4) S/cm for the samples with LiClO4 and 8.7x10(-5) S/cm for the samples with CH3COOH at room temperature. The samples also showed thermal stability up to 160 degrees C, transparency of up to 90%, surface uniformity and adhesion to glass and steel. Moreover, Dynamic Mechanical Analysis revealed two relaxations for both samples and the Ea values were between 18 and 36 kJ/mol. All the results obtained indicate that alginate-based GPEs can be used as electrolytes in electrochemical devices.