EFFECT OF ANIONS ON THERMODYNAMICS OF EXTRACTION OF Am(III) AND Eu(III) WITH OCTYL(PHENYL)-N,N-DIISOBUTYL-CARBAMOYLMETHYLPHOSPHINE OXIDE

The extraction of Am(III) and Eu(III) by octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in xylene from aqueous media containing 1.0 M NH₄NO₃, NH₄SCN, NH₄ClO₄ or a mixture of 0.3 M NH₄NO₃ + 0.7 M NH₄ClO₄ at pH 2.70 and at the temperatures of 15, 25, 35 and 45±0.1 °C has been studied. At all the temperatures, the species extracted were ML₃ · 3CMPO (M = Am(III) or Eu(III), L = NO₃ ^?, SCN^? or ClO₄ ^?) and M(NO₃)(ClO₄)₂ · 3CMPO. The thermodynamic parameters of the extraction reactions have been evaluated using the temperature coefficient method. The ?ΔG values follow the order SCN^? > NO₃ ^? + ClO₄ ^? > NO₃ ^? ≈ ClO₄ ^?, whereas the ?ΔH values an order NO₃ ^? + ClO₄ ^? > SCN^? > NO₃ ^? ≈ ClO₄ ^?. The effect of these anions on the thermodynamic parameters have been discussed employing compensation effects and also on the basis of the energy associated with the transfer of these anions from aqueous to the extractant phase.     

13C and 1H n.m.r. dynamic study of poly(γ-benzyl-l-glutamate) poly(β-benzyl-l-aspartate) and poly(l-alanine) in solution

¹H T₁ relaxation times were measured in solutions of poly (γ-benzyl-l-glutamate), PBLG, and poly(β-benzyl-^l-aspartate), PBLA, and ¹³C T₁ relaxation times, NOE factors and line widths in solutions of the two polypeptides and of poly(l-alanine), PLA, over a broad range of solvent composition (CDCI₃—trifluoroacetic acid) including the helix—coil transition. PBLG was also studied through temperature-induced inverted helix—coil transition. Most relaxation parameters change smoothly over the studied range, and the observed changes correspond to increase of mobility with increasing content of trifluoroacetic acid and with increasing temperature except for PBLG which undergoes an inverted helix—coil transition with temperature. Analysis of experimental data by means of the isotropic model yielded, for the backbone carbons of all three polypeptides, τ_eff ～ 2 × 10^?8 sec in the helix and τ_eff ～ 1 × 10^?9 sec in the coil form. For the side-chain carbons, τ_eff decreases in the range 10^?9 ? 10^?10 sec with increasing distance from the backbone, with τ_eff values consistently lower in the coil form. Results of analysis by means of a model with two correlation times are discussed.     

EXTRACTION OF INDIUM( III) FROM BROMIDE AND THIOCYANATE MEDIA WITH 1-PHENYL-3-HETHYL-1-BENZOYLPYRAZOL-5-ONE; EFFECT OF LIPOPHILIC AMMONIUM SALTS

1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HL) in toluene extracts In(III) from ClO₄ ^?, (Br^?, CIO ClO₄ ^?, ) and Br^? media according to the extraction equilibria (1) and (2). Tri-n-octylmethylammonium bromide (B⁺Br^?) induces a medium synergic effect for Br^? and (Br^?,NO₃ ^?) media, which is cancelled in ClO₄ ^?medium. It corresponds to the extraction of (B⁺InBr_xL_4-x) ion pairs. On the contrary, from SCN^? or (SCN^?,ClO₄ ^?) media, In is extracted by HL according to only (1) and no synergism is obtained with tri-n-octylammonium salt.

These results are compared with those obtained with Cl^? and (C1^?,ClO₄ ^?) aqueous media. They are to a great extent explained by taking into account the complexing of In³⁺ by aqueous inorganic anions, the lipophilicity of the diverse species and the anionic exchanges in the B⁺X^? ion pairs.     

The enthalpies of formation and of dehydration of some AFm phases with singly charged anions

The enthalpies of formation of some AFm phases of the type Ca₂Al (OH) ₆X.xH₂O (X = Cl^?, Br^?, I^?, NO₃^?, ClO₄^?, ClO₃^?,BrO₃^?and IO₃^?) were determined by measuring the heats of solution in hydrochloric or perchloric acid. From the differences between the heats of solution of the compounds and their dehydration products, the enthalpies of dehydration were established. They increase with increasing enthalpies of hydration of the individual anions X in aqueous solution. However, this relationship is not the same for halide ions as for oxy-anions.     

Salt effects on the conformation of a ‘statistical’ copolymer of l-leucine and l-lysine

For studying the influence of water structure breaking and making anions on the conformation of poly(α-amino acids) containing hydrophobic and ionic side chains, c.d. measurements on ‘statistical copolymers of l-leucine and l-lysine were carried out in LiClO₄, NaClO₄, Li₂SO₄, Na₂SO₄, KF, NaF, and NaCl solutions and also in salt-free water. Copolymers with 50 mol% l-leucine do not form α-helices in pure water at pH 7 (20°C); however LiClO₄ and NaClO₄ at concentrations as low as 0.003 moll^?1 induce α-helix formation almost independent of cation. Surprisingly, not only ClO^?₄ but also SO^2?₄ has an α-helix inducing effect in this case, in contrast with basic homopoly (α-amino acids), where such an effect of SO^2?₄ was not observed. Therefore the presence of l-leucyl residues seems to be responsible for this α-helix inducing effect of sulphate anions. This agrees with the fact that sulphate stabilizes the ordered periodic conformation of native proteins as the increase of denaturing temperature shows. It can be assumed that the results of these measurements support the assumptions on the influence of water structure in making SO₄ anions on hydrophobic interactions, as well as of water structure breaking ClO₄ anions.     

Salt effect on the conformation of an alternating copolymer of l-leucine and l-lysine

The ‘statistical’ copoly(l-leucyl-l-lysine) is shown to undergo a coil to α-helix transition by either adding salt or raising the pH. However, the corresponding alternating copolymer undergoes a conformational transition from a coil to a b-structure, which is accomplished by adding various salts or by raising the pH. The b-structure fraction of the alternating copoly(l-leucyl—l-lysine) is especially enhanced by either water structure, breaking or making anion (e.g., ClO^?₄ or SO^2?₄), in which the β-structure may be induced by a different molecular mechanism. As a consequence of the strong shielding effect due to the specific binding of ClO^?₄ with charged side chain as well as its electrochemical monovalency, an intramolecular cross-β-structure is formed at lower salt concentration (e.g., 0.10 moll^?1). However, in the presence of SO^2?₄, due to its divalency, intermolecular β-pleated sheet structure occurs even at very low salt concentration (e.g., 0.002 moll^?1). Furthermore, in both cases the resulting β-structure is stable up to 90°C.     

Ion interaction chromatography of anions in alkaline solutions: effect of temperature and the kind of stationary phase

Effect of temperature (5°–65°C) on the separation of 11 inorganic anions by ion interaction chromatography (IIC) was studied employing RP C₁₈ and C _PhenylHexyl columns and aqueous mobile phase: 2.8 mM NaHCO₃ + 0.7 mM TBAOH (tetra-n-butylammonium hydroxide). The apparent enthalpy changes, ΔH for hydrophobic ions like I^?, SCN^?, and ClO₄ ^? largely exceeded 3 kcal/mole suggesting that added to ion exchange they are retained by hydrophobic adsorption. Unlike conventional strongly basic anion exchangers, our system can be used at elevated temperatures with alkaline eluents without irreversible damaging the column.     

Counter‐ion‐specific helix formation of poly(γ‐methyl L‐glutamate) derivatives containing sulfonate group in aqueous alcohols

Charged polypeptides containing sulfonate groups were prepared by transesterification of poly(γ‐methyl L ‐glutamate) with isethionic acid. The coil–helix transition of the sulfonated polypeptides was investigated in aqueous alcohols. Marked counter‐ion specificity was observed for helix formation: Li⁺ < Na⁺ < Cs⁺ ≦ Rb⁺ ≦ K⁺; this was different to that for poly(L ‐glutamate) (PLG): Cs⁺ ? K⁺ < Li⁺ < Na⁺. Specific helix stabilization by counter‐ion mixing, which has been found for the PLG system, was not observed for the sulfonated polypeptides. The counter‐ion‐ and solvent‐specific helix formation is discussed and compared with that in PLG. © 2001 Society of Chemical Industry     

Conformational Versatility of Open-Chain Polyethers: Crystal and Molecular Structures of the Ba(SCN)2 Complexes of Two Heptaethyleneglycol Diaryl Ethers

The crystal structures of the Ba(SCN)₂ complexes of two linear octaethers, heptaethyleneglycol diphenylether (HGPE; 1,20-bis(phenyloxy)-3,6,9,12,15,18-hexaoxaicosane) and heptaethyleneglycol dinaphthylether (HGNE; 1,20-bis(naphthyloxy)-3,6,9,12,15,18-hexaoxaicosane), are reported. In spite of their close similarity, the ligands adopt quite different conformations in their Ba(SCN)₂ complexes. HGPE wraps around the metal ion in a discontinuous helix providing seven of its eight ether oxygens for coordination. 10-fold coordination of Ba²⁺ is completed by the nitrogens of the SCN⁻ ions and by a water molecule for which an occupancy of 0.37(5) was determined. In contrast, HGNE behaves as a hexadentate only. The barium ion is 9-fold coordinated to six ether oxygens, to a water molecule, to one SCN⁻ ion via its nitrogen atom and to a symmetry-related thiocyanate ion via its sulphur atom. The second SCN⁻ ion does not contact the metal ion but is hydrogen-bonded to two symmetry-generated water molecules. HGNE displays some unusual conformational features never found before for open-chain polyethers.     

THERMODYNAMICS OF EXTRACTION OF Am(III) AND Eu(III) FROM NITRATE AND THIOCYANATE MEDIA WITH OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE

ABSTRACT

The extraction of Am(III) and Eu(III) from 1.0 M NH₄NO₃ and NHS₄SCN at pH 2.60 into octyl(pheriyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in n-dodecane has been studied in the temperature range 15.0 to 45.0°C. Under all conditions, the species ML₃·CMPO is the dominant extracted complex. The extraction equilibrium constants are at least 10₃ higher in the SCN^- systems than in the NO₃ ^- systems. This difference is attributed to the relative energy associated with transfer of the anions from the aqueous to the: extractant phase. Extraction enthalpies and entropies have been calculated in each system from the temperature dependence of K_ex. Enthalpies are considerably more exothermic in the thiocyanate system for both metal ions. Comparison of ΔH_Am ^SCN with ΔH_EU ^SCN gives a possible indication of enhanced Am-SCN bond strength in the extracted complex.     

Adsorption of perchlorate onto raw and oxidized carbon nanotubes in aqueous solution

Perchlorate (ClO₄^?) is an emerging trace contaminant. The adsorption of ClO₄^? on raw and oxidized carbon nanotubes (CNTs) was investigated to elucidate the affinity mechanism of CNTs with anion pollutants. The adsorption of ClO₄^? into different CNTs increased in the order multi-walled CNTs < single-walled CNTs < double-walled CNTs (DWCNTs). Co-existing anions (SO₄^2?, NO₃^?, Cl^?) significantly weakened ClO₄^? adsorption, while the co-existence of Fe³⁺ and cetyltrimethylammonium cations increased ClO₄^? adsorption 2- to 3-fold. ClO₄^? adsorption was promoted by oxidized DWCNTs due to the introduction of more oxygen-containing functional groups, which served as additional adsorption sites. The pH values significantly affected the zeta potential of raw and oxidized DWCNTs and thus ClO₄^? adsorption. The pH-dependent curves of ClO₄^? adsorption on CNTs were distinct from those of conventional sorbents (e.g., activated carbon and resin). Maximum ClO₄^? adsorption occurred at pH = the isoelectric point (pH_IEP) + 0.85 rather than at pH < pH_IEP, which cannot be explained by electrostatic interactions alone. Hydrogen bonding is proposed to be a dominant mechanism at neutral pH for the interaction of ClO₄^? with CNTs, and variations of ClO₄^? affinity with CNTs in different pH ranges are illustrated.     

Effects of dopants and copolymerization on Schottky barriers of polypyrrole and polyindole/metal interfaces

Schottky-barrier diode devices were fabricated in a sandwich configuration with poly(pyrrole-co-indole) copolymer semiconducting films prepared by electropolymerization. Effect of different dopants of ClO₄ ^?, BF₄ ^?, C₇H₇SO₃ ^? and [Fe(CN)₆]^3? on the electronic properties of the fabricated devices was followed using Ag, In, Al and Cu metal junctions. Current?Cvoltage and capacitance?Cvoltage characteristics were recorded for making a comparative evaluation of the electronic and junction properties of the devices. The electrical characteristics of the junctions were analyzed based on the standard thermionic emission theory. Polymer doped by ClO₄ ^? showed lower reverse saturation currents and ideality factor but higher potential barriers and rectification ratios. Effect of dopant ions and copolymerization on the optical band gaps (E _g) of the films were investigated and the optical transmissions of the doped copolymer films were measured in the wavelength range of 250?C900?nm. It was shown that the energy gap of copolymers laid between those of corresponding homopolymers and polyindole (PIN) doped by [Fe(CN₆)]^?3 had E _g less than that of polymer doped by other anions whereas E _g of polypyrrole was independent of dopant ions. Also, the morphology of the polymeric films revealed the surface of the PIN doped with ClO₄ ^? was very smooth which created a good contact with indium metal.     

Electrode reactions of nickel(II) at mercury electrodes in aqueous solutions of pyridine at high ionic strengths

At high ionic strength the ion pair (NiPy²⁺₄, nX^?) or complex (NiPy₄X₂), n = 0, 1, 2; X^? = Cl^?, Br^?, SCN^?, N^?₃, F^?, NO^?₃, ClO^?₄; is adsorbed at the surface of mercury electrode. Under specified conditions in chloride, bromide, and thiocyanates solutions the electroreduction is preceded by a crystallization of a complex on the electrode surface. The inductive role of specifically coadsorbed Cl^? ions is discussed.     

Polypyrrole–poly(heptamethylene p,p′-bibenzoate) conducting materials. Synthesis and characterization

Polypyrrole–poly(heptamethylene p,p′-bibenzoate) conducting materials, PPy–P7MB/ClO₄, were obtained by anodic coupling of pyrrole into a polybibenzoate inert matrix, using perchlorate anions as dopant agent. P7MB is a main-chain liquid crystalline polybibenzoate with adequate mechanical properties and elastic modulus of 1.4GPa at room temperature. The method of synthesis, galvanostatic or potentiostatic electrodeposition, is responsible for differences in the PPy–P7MB/ClO₄ films electrochemical response. FTIR spectra show the complex structures of P7MB and the composite conducting material. The conductivity of PPy–P7MB/ClO₄ films maintains a relatively high value, σ = 13.74Scm^?1, in spite of the insulating effect of polybibenzoate. Film micrographs reveal the typical cauliflower morphology exhibited by polypyrrole and the evolution of film growth with time.     

Effects of anions on the photocatalytic and photoelectrocatalytic degradation of reactive dye in a packed‐bed reactor

The effects of various anions, Cl^?, ClO₄^?, SO₄^2?, NO₃^?, HCO₃^?, H₂PO₄^? and C₂O₄^2?, on the photocatalytic and photoelectrocatalytic degradation of reactive Brilliant Orange K‐R have been investigated in a packed‐bed photoelectrocatalytic reactor. It was found that the nature and concentrations of these inorganic anions significantly affected the photocatalytic and photoelectrocatalytic degradation performance of the reactive dye. The results indicated that the external electric field was successfully applied to improve the photocatalytic efficiency of reactive Brilliant Orange K‐R in the presence of Cl^?, especially at higher concentrations, while other inorganic anions displayed more or less negative effects on the degradation of the dye. The strongest inhibition effect on photocatalytic and photoelectrocatalytic degradation of the dye was observed in the presence of HCO₃^? ions. Copyright © 2004 Society of Chemical Industry     

Influence of Some Hofmeister Anions on the Krafft Temperature and Micelle Formation of Cetylpyridinium Bromide in Aqueous Solution

In this work, the effect of some Hofmeister anions on the Krafft temperature (T_K) and micelle formation of cetylpyridinium bromide (CPB) have been studied. The results show that more chaotropic anions increase, while the less chaotropic ones lower the T_K of the surfactant. More chaotropic I^? and SCN^? form contact ion pairs with the cetylpyridinium ion and reduce the electrostatic repulsion between the CPB molecules. As a result, these ions show salting‐out behavior, with a consequent increase in the T_K. In contrast, less chaotropic Cl^? and NO₃^? increase the activity of free water molecules and enhance hydration of CPB molecules, showing a decrease in the T_K. A rather unusual behavior was observed in the case of SO₄^2? and F^?. These strong kosmotropes shift from their usual position in the Hofmeister series and behave like moderate chaotropes, lowering the T_K of the surfactant. Because of the high charge density and the strong tendency for hydration these ions preferentially remain in the bulk. Rather than forming contact ion pairs, these ions stay away from the CPB molecules, decreasing the T_K of the surfactant. In term of decreasing the T_K, the ions follow the order NO₃^? > SO₄^2? > Cl^? > F^? > Br^? > SCN^? > I^?. The critical micelle concentration (CMC) of the surfactant decreases significantly in the presence of these ions due to the screening of the micelle surface charge by the excess counterions. The decreasing trend of the CMC in the presence of the salts follows the order SCN^? > I^? > SO₄^2? > NO₃^? > Br^? > Cl^? > F^?.     

Effect of tris(methoxy diethylene glycol) borate on ionic conductivity and electrochemical stability of ethylene carbonate-based electrolyte

The effect of tris(methoxy diethylene glycol) borate (TMDGB) on the coordination structure between ethylene carbonate (EC) solvents with high permittivity and ClO₄⁻ anions has been investigated by using a Fourier transform infrared (FT-IR) spectroscopy. The results of FT-IR analyses manifested that the boron atom of TMDGB anion receptor forms the complex with ClO₄⁻ anions. Even though Lewis acid-base interaction between the TMDGB anion receptor and ClO₄⁻ anions in the electrolyte solution lead to the prominent enhancement of both the dissociation degree of lithium salts and the lithium ion transference number, the ionic conductivity of the EC-based electrolyte solution decreased due to the trap of ClO₄⁻ anions by introducing the TMDGB anion receptor.The electrochemical stability of gel polymer electrolyte based on semi-interpenetrating network (IPN) structure with tris(pentafluoro phenyl) borane (TPFPB) or TMDGB anion receptor was obviously improved.     

Strong effects of counterions on the electrochemistry of poly(N‐methylaniline) thin films

Poly(N‐methylaniline) thin films show different cyclic voltammetric behaviour when cycled in HClO₄, HBF₄, HCl or HNO₃. While in the first two acids the film shows profiles peak potentials similar to those of polyaniline, profiles in HCl and HNO₃ show higher peak potentials for oxidation and a different shape. The free energy for the process, calculated from the oxidation peak potential, shows a linear correlation with the free energy of hydration of the anions present in the test solution. An energy cycle for the oxidation process is proposed to explain the results. The reaction mechanism assumes that anions have to lose their hydration shell to form the polymer salt during electrochemical oxidation of the films. Electropolymerization also depends on the anion present in the solution. While this is possible with low hydration energy anions (ClO₄^?, BF₄^?), it is difficult or impossible when the electrolyte solution contains other anions (Cl^?, NO₃^?) where a higher oxidation potential of the preformed polymer is observed. © 2002 Society of Chemical Industry     

Electrically controllable perchlorate removal based on poly(aniline‐co‐o‐aminophenol) doped with p‐toluene sulfonate

Poly(aniline‐co‐o‐aminophenol) (PANOA) was synthesized via electrochemical copolymerization of o‐aminophenol and aniline using p‐toluene sulfonate (TSA^?) as the counterion. The redox transformation of PANOA is accompanied by the exchange of anions into and out of the copolymer, and the feasibility of perchlorate (ClO₄^?) removal via an electrically switched ion exchange process was evaluated in this study. The results of electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared spectroscopy (FTIR) demonstrated the successful release of TSA^? upon reduction and uptake of ClO₄^? upon reoxidation of the copolymer. Also, in this work, the possible ion‐exchange mechanism of PANOA was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41895.     

Influence of ionic thiocyanate on growth of cabbage,bean, and tobacco

Plant weight and contents of chlorophyll, ionic thiocyanate (SCN^?), and hydrogen cyanide (HCN) were determined in cabbage (Brassica oleracea var.capitula L. cv. Early Greenball), bean (Phaseolus vulgaris L. cv. Contender), and tobacco (Nicotiana tabacum L. cv. Delhi 76) grown hydroponically in modified Hoagland's nutrient solution with six concentrations of SCN^? (supplied as KSCN) (0, 5, 25, 50, 100, and 200 mg/liter). Whereas tobacco plants did not grow with any level of SCN^? in the culture solution, beans grew with 5 mg/liter and cabbages grew with between 5 and 50 mg/ liter. Increasing levels of SCN^? in the culture solution resulted in decreased growth and chlorophyll content, accompanied by consistently increasing amounts of SCN^? in cabbage. Small amounts of HCN found only in tissues of cabbage were not influenced by levels of SCN^?. The greater insensitivity of cabbages to the presence of SCN^? compared with beans is apparently related to the presence of endogenous glucosinolates which are capable of being degraded into SCN^?. Accumulation of SCN^? and occurrence of leaf chlorosis in cabbage and beans and death of tobacco plants supplied with SCN^? in hydroponic culture confirm the capacity of SCN^? as an allelopathic agent, but its effect mechanism in ecology needs to be demonstrated.