G. Scibona

Extraction selectivity of organic solutions of a cyclic polyether with respect to the alkali cations

Abstract The extraction of alkali cations (Li+, Na+, K+, Rb+, Cs+) by the neutral cyclic polyether dibenzo-18-crown-6 dissolved in various nitrobenzene-toluene mixtures has been studied. Thermodynamic data have been so obtained regarding the alkali cation-cyclic polyether reaction. The affinity of the cyclic polyether for the alkali cations has been found to vary in the order K+ > Rb+ > Cs+ > Na+ > Li+ for all the diluents compositions. Moreover the independence of the selectivity constant, defined as the equilibrium constant of the reaction: Cs + + MSX ⇌ Cs SX + M + (where M is the alkali cation, S the cyclic polyether, X the picrate ion and the bar indicates organic species) on the diluent composition seem to indicate that the complexes formed with the cyclic polyether are isosteric, i.e. with size, shape and external electronic distribution independent of the chemical nature of the cation.

Liquid ion exchange selectivity of dinonylnaphthalenesulfonic acid (HD) with respect to some lanthanide and actinide ions

Abstract The liquid ion exchange selectivity of dinonylnaphthalenesulfonic acid (HD) dissolved in a series of organic diluents covering the dielectric constant range 2·38-34·8 with respect to the cations Ce3+, Eu3+, Gd3+, Tm3+, Am3+, Cm3+, Cf3+ in perchloric solutions has been studied at 25°C. The extent of aggregation of HD in the different diluents and the equilibrium constants of the exchange reactions have been evaluated. As far as the dependence of the ion exchange selectivity on the diluent nature is concerned, a decrease of the selectivity with the increase of the diluent dielectric constant has been evidenced only in the case of M33+H-+ exchange. The reasons of this behaviour are discussed together with literature data concerning other liquid ion exchange systems.

Liquid anion exchange of thiocyanate-nitrate actinide and lanthanide complexes

Abstract The liquid-liquid biphasic chemistry of the system quaternary alkylammonium salt- o -xylene-water-trivalent metal cation (actinide or lanthanide)-thiocyanate-nitrate anions has been studied with the purpose to obtain both information on the aqueous complex formation constants of these elements and parametric equations useful to process chemistry design. The aqueous equilibrium constants between Eu +3 , Ce +3 , Am +3 , Cm +3 , Cf +3 and SCN − and NO 3 − have been obtained at the constant ionic strength of 2·01 M and 25°C, by using a liquid anion exchanger (tricaprylmethylammonium thiocyanate in o -xylene). In the case of the SCN − anion the actinide series shows a tendency to form complexes greater than the lanthanides, while this is approximately the same with the NO 3 − anion. For the actinide elements the tendency to form complexes is greater for SCN − than for NO 3 − . As far as the technological applications are concerned the possibility of performing actinides-lanthanides separation appears promising.

Enthalpy and entropy variations in the liquid cation exchange of some lanthanide ions by dinonylnaphthalenesulfonic acid(HD) and bis(2-ethyl-hexyl)phosphoric acid (HDEHP)

Abstract Free energy, enthalpy and entropy variations concerning the liquid ion exchange reactions of some lanthanides between aqueous perchloric acid solutions and organic solutions of the liquid cation exchangers dinonylnaphthalenesulfonic acid (HD) and bis(2-ethyl-hexyl) phosphoric acid (HDEHP) have been determined. The meaning of the experimentally obtained thermodynamic quantities is discussed on the basis of structural considerations regarding both the aqueous and the organic phase.

The meaning of slope analysis in solvent extraction chemistry: The case of zinc extraction by trilaurylammonium chloride

Abstract By using suitable equations, which are derived by treating the extraction of a metal complex in the general form pMY n + q RY ⇌ (RY) q (MY n ) p (with MYn extractable species, RY extracting agent, (RY) q (MY n ) p complex formed by the extraction reaction, with the bar indicating organic phase species), the physical meaning obtained by the slope analysis of extraction data (logarithmic plot of distribution coefficient vs. extractant concentration) has been discussed. The experimental case of distribution data obtained by extracting ZnCl2 with a benzene solution of trilaurylammonium chloride in a wide range of metal and extractant concentration has been treated.

Stability constants of nitrate and chloride complexes of Np(IV), Np(V) and Np(VI) ions

Abstract The formation constants of NpO22+ and Np4+ ions with the Cl− and NO3− ligands have been determined by the TTA extraction method in a 4M constant ionic medium. The complexes between NpO2+ and Cl− and NO3− have been evaluated by studying the potential variations of the Np(VI)/NP(V) couple at a platinum electrode as function of the ligand concentration. The data have been analyzed by using a suitable computer least squares program. The following formation constants have been determined at μ = 4M and T = 25°C: Np4+ +Cl− ⇋NpCl3+ β 1 = 0·77 ± 0·06 Np4+ +2Cl− ⇋NpCl22+ β 0.79 = ± 0·06 Np4+ + 2Cl− ⇋NpCl22+ β 2 = 0·79 ± 0·06 Np4+ + NO3− ⇋ NpNO33+ β 1 = 0·07 ± 0·2 Np4+ + 2NO3− ⇋Np(NO3)22+ β 2 = 0·18 ± 0·05 NpO22+ + Cl− ⇋ NpO2Cl+ β 1 = 0·69 ± 0·05 NpO22+ NO3− ⇋ NpO2NO3+ β 1 = 0·21 ± 0·03 NpO2+ + Cl− ⇋ NpO2Cl β 1 = 0·003 ± 0·003 NpO2+ + Cl− ⇋ NpO2Cl β 1 = 0·003 ± 0·003 NpO2+ + 2Cl− ⇋ NpO2Cl2− β 2 = 0·028 ± 0·003 NpO2+ + NO3− ⇋ NpO2NO3 β 1 = 0·025 ± 0·001 NpO2+ + 2NO3− ⇋ NpO2 (NO3)2− β 2 = 0·043 ± 0·001

Non-isothermal potential of phospholipid bilayer films Influence of cholesterol and macrocyclic carrier effects

The effect of cholesterol on the ion selective behavior of phoshpolipid (phosphatidylcholine or phosphatidylethanolamine) bilayer films is studied through the measurement of the membrane non-isothermal potential. It is shown how the mixed phosphatidylcholine-cholesterol membrane can be either cation of anion permselective according to the film composition (cationic behavior is met in the 0--10% cholesterol composition range while anionic selectivity appears in the 20--50% range). On the contrary, mixed phosphatidylethanolamine-cholesterol membranes show the absence of ionic selectivity already met with pure phosphatidylethanolamine films. The presence of a cationic carrier as Dibenzo-18-crown-6 in the film transforms all the studied films (cationic, anionic and no selective bilayers) into ideally cationic selective membranes. These results are discussed on the basis of the current ideas on the charge distribution through the bilayer membranes. Moreover, the role of the permeating ions as potential determining species is stressed.

Cation and anion responses of zwitterion phospholipid bilayers

Abstract The electrochemical behavior of zwitterion phospholipid bilayers as determined with the help of membrane potential data, is examined. The synthetic DL-β,γ-dipalmitoyl-α-phosphatidylcoline bilayer shows at 30°C nernstian and sub-nernstian anion responses which depend on the cation present in the electrolytes (LiCl, NaCl, KCl, CsCl, CaCl2, CeCl3), and in some cases on the concentration of the solutions considered. On the other hand, nernstian cation responses have been observed in non-isothermal membrane-potential measurements performed on the same lipidic films. These experimental results are explained on the assumption that, from a potentiometric viewpoint the phospholipid membrane behaves as a neutral carrier membrane electrode. Accordingly, the form of the potential equations, and then the anion response of the bilayer, follows from the chemistry of the phospholipid molecules.

Distribution equilibria involving plutonium(III) between organic trilaurylammonium nitrate solutions and aqueous nitric acid solutions

Abstract In the partition of plutonium between organic solutions of long chain tertiary alkylammonium salts and aqueous nitric solutions containing reducing agents, the small value of the distribution coefficient has been attributed to the partition of plutonium(III). In this paper a different point of view is presented. The main assumption is that the plutonium present in the organic phase is in the four valence state. The small D values are therefore explained by considering all the equilibria that take place in the plutonium distribution process. An expression of D capable to account for the oxidation-reduction equilibria is derived. The comparison between experimental (in presence of iron(II) sulphamate as reducing agent) and calculated D values, and spectophotometric measurements agree with the suggested mechanism.