L.M. Yudi

Competitive transfer of H+ and Li+ ions through the water-1,2-dichloroethane interface mediated by 1,10-phenanthroline

Abstract The transfer of H + and Li + ions through the water-1,2-dichloroethane interface in the presence of 1,10-phenanthroline is studied by cyclic voltammetry. These ions compete for phenanthroline in the organic phase; the pH and the concentration of the ligand relative to that of the cation determine which predominates in the transfer. It is concluded that the transfer of H + mediated by phenanthroline occurs via a direct mechanism, whereas “facilitated” transfer is operative in the case of Li + .

Interfacial phenomena involving Fe(III)–ofloxacin complexes at the water|1,2-dichloroethane interface

Abstract When the interface formed between an aqueous solution containing ofloxacin, a fluorquinolone antibiotic complexed with Fe(III), and an organic solution of a supporting electrolyte in 1,2-dichloroethane is potentiodynamically polarized, interesting electroadsorption phenomena are observed. The narrow negative voltammetric peak observed at much lower potentials than those corresponding to the diffusional transfer of a triply charged species, the linear response of I p with v , the difference in the potentials of the positive and negative processes and the shift of this peak towards more negative potentials with sweep rate as coverage is increased, provide clear evidence of an irreversible adsorption–desorption process displaying attractive interaction between the adsorbate molecules at high coverage. These results are reinforced by the appearance of an important charge transfer resistance value in ac measurements.

Quantitative determination of erythromycin and its hydrolysis products by cyclic voltammetry at the interface between water and 1,2-dichloroethane

Abstract An electrochemical method for quantifying erythromycin (Er) salts and their hydrolysis products is described. Cyclic voltammetry at the water/1,2-dichloroethane interface in a four-electrode system was used. A linear relationship between Ip and the erythromycin concentration was obtained up to the solubility limit of the antibiotic. The various hydrolysis products which can be obtained in acid or basic solutions were characterized by their respective transfer potentials. Similar hydrolysis products were observed for aged solutions of Er lactobionate. It is concluded that the proposed method is suitable for the quantification of Er and for distinguishing it from its hydrolysis products.

Electrochemical Study of a Dendritic Family at the Water/ 1,2-Dichloroethane Interface

The transfer of six dendritric molecules, DMs, across the water/1,2-dichloroethane interface was investigated using cyclic voltammetry. From the variation of peak potential with pH, two different mechanisms of transfer were postulated depending on the nature of the molecules. Voltammetric parameters were employed to evaluate the hydrophilic/hydrophobic character and calculate the acid dissociation constant of these molecules. The results were explained taking into account the nature and multiplicity of functional surface groups.

Electrochemical study of the interaction of alkali and alkaline-earth cations with a dibehenoyl phosphatidylcholine monolayer at the water/1,2-dichloroethane interface

Abstract The transfer of alkali and alkaline-earth cations across a dibehenoyl phosphatidyl choline (DBPC) monolayer is analysed by cyclic voltammetry and capacitance measurements. A cation adsorption process at the polar head of the phospholipid was evidenced. After the adsorption an enhancement of the current or a blocking of the transfer process was produced, depending on the nature and cation concentration. This blocking arises as a consequence of the packing induced by Li + or alkaline-earth cations adsorption at high concentrations which, in addition, is responsible for the destruction of the monolayer at high positive potentials. Capacitance measurements reinforce this statement. This paper also illustrates how electrochemical measurements at ITIES are a useful methodology for studying cation interactions with lipidic membranes and the transfer processes which occur across them.

Comparative analysis of the transfer of alkaline and alkaline-earth cations across the water/1,2-dichloroethane interface

The transfer of alkaline and alkaline-earth cations across the water/1,2-dichloroethane interface in presence of 1,10-phenanthroline (phen) in the organic phase was studied using cyclic voltammetry in a concentration range wide enough to cover the following experimental conditions: CM2+(w) ⪢ Cphen(o) and Cphen(o) ⪢ CM2+(w). The results obtained (when CM2+(w) ⪢ Cphen(o)) were compared with the theoretical voltammetric criteria reported by Homolka1l] for facilitated transfer. It appears that the transfer of all these cations occurs via a facilitated mechanism. The stoichiometry of all complexes formed in the organic phase is also reported. The stability constants for Ca2+-phen and Sr2+-phen complexes were estimated and compared with the tendency observed in the transfer potentials of these cations.

Erythromycin transfer across the water ⋎ 1,2-dichloroethane interface modified by a phospholipid monolayer

Abstract The transfer of ions at the water ⋎ 1,2-dichloroethane interface mediated either by erythromycin or by its decomposition products in the presence and absence of a phospholipid monolayer was analysed by dc cyclic voltammetry and electrochemical impedance measurements in a four-electrode system. The composition of the liquid phases has an important effect on the transfer processes. Significant differences in their parameters were found depending on the phase in which the antibiotic was initially present, i.e. erythromycin as a base in the organic phase or protonated erythromycin in the aqueous phase. A dependence on pH was also noticed. These results suggest that the ion transfer mechanisms can be modified by the experimental conditions. The charge transfer resistance ( R ct ) for erythromycin and for its hydrolysis products was measured with and without the phospholipid monolayer. Except when erythromycin was in the organic phase, a general increase in R ct , more important for the hydrolysed antibiotic, was observed, indicating that the loss of the sugar units or the opening of the lactone ring hinders the transport process at the phospholipid modified interface.

Electrochemical behaviour of cationic polyelectrolytes at a polarized liquid/liquid interface

The behaviours of several cationic polyelectrolytes (chitosan; polyquaternium-4; diethylaminoethyl dextran; polyquaternium-10, and aminoacrylmethacrylate copolymer, Eudragit® E100) at a polarised liquid/liquid interface are analysed and compared in the present paper. Based on the analysis of the voltammetric results, it was possible to determine some of the relationships between polymer structure and the tendency to adsorb at the interface. It was also possible to determine the substitution degree of a polymer comprising a chitosan main chain modified with glycidyltrimethylammonium chloride, and the values obtained are in agreement with those calculated using other methodologies. Finally, we report a comparative study concerning the effect of cationic (chitosan) and anionic (dextran sulphate) polyelectrolytes on the compactness of a phospholipid film.

An Electrochemical Approach to Quantitative Analysis of Herbicides and to the Study of Their Interactions with Soils Components

R2 Fig. 1. Chemical structure of s-triazine core, substituent in R1 : Cl, SCH3 or OCH3; R2 and R3: hydrocarbons chains. These herbicides have been extensively applied to pre and post-emergence weed control. Many studies were focused on ecological and health hazards of these compounds and their toxic effects are very well known. For this reason, the use of some triazine pesticides has been banned in some countries or their permitted levels in drinking water is very low, so that analytical procedures for quantitative determination of several triazines, as well as their degradation products, at low levels are often requested. In this sense, several analytical techniques have been developed, like HPLC (Katsumata et al., 2006), CG-MS, capillary electrophoresis (Frias et al., 2004), solid-phase micro-extraction coupling with GC, LC, ion mobility spectrometry (Garcia Galan et al., 2010; Mohammadi et al., 2009; Sanchez Ortega et al., 2009; Quintana et al., 2001) and with HPLC (Zhou et al.,

Mediated electrochemical reduction of dibromonorcarane in an emulsified system using Cr(II)

High material yields were obtained in the indirect electrochemical reduction of 7,7-dibromobicyclo-[4-1-0]heptane (dibromonorcarane) to give the corresponding monobromo derivative in an ethylene chloride/water emulsion. The reducing agent was Cr(II) generated by current controlled electrolysis of aqueous chromic chloride at a silver cathode. The effect of the concentration of Cr(II) and the temperature was studied. At 0.1 M Cr(II) and at 40° C the best results were obtained (90% yield).