New DTPA-derived bis-naphthalenophanes: fluorescence,protonation, and complexation with aromatic amines

Two fluorescent, water-soluble bis-naphthalenophane isomers with six carboxylate arms, abbreviated as (bis-dtpa14nap)H₆ and (bis-dtpa15nap)H₆, were synthesized, which consist of two 1,4- or 1,5-substituted naphthalene rings interlinked by two diethylenetriaminepentaacetic (DTPA) chains through amide-linkages. Both DTPA-based macrocycles exhibit intense excimer and monomer emission bands, which sensitively respond to pH in three protonation steps; more sensitive is the 1,4-naphthyl isomer. The full pH-emission profiles have confirmed that the mono-protonated anion (bis-dtpanap)H₅ ^? is the major protonation species at the physiological pH. Fluorometric titrations at pH 7.2 have proven that the 1,4-naphthalenophane anion forms 1:1-complexes with cationic phenethylamine (formation constant, 5700 M^?1) and histamine (3000 M^?1), excluding tryptamine cation, whereas the 1,5-isomer does not react with any of the three amines. The primary binding forces are electrostatic interactions between the CH₂CO₂ ^? arms of 1,4-naphthalenophane and the CH₂CH₂NH₃ ⁺ chain of an aromatic amine. The resulting ion-pair is stabilized by encapsulation of the guest molecule in 1,4-napthalenophane cavity, while the 1,5-isomer cannot encapsulate. NMR studies have demonstrated that 1,4-napthalenophane has a higher freedom in reorientation of naphthalene rings. Such geometrical properties controlled by selection of naphthalene units are the feature of the new naphthalenophanes, and are responsible for the pH?emission profiles and the complexation.     

Chromatographic Framework to Determine the Memantine Binding Mechanism on Human Serum Albumin Surface

In this work, the interaction of memantine with human serum albumin (HSA) immobilized on porous silica particles was studied using a biochromatographic approach. The determination of the enthalpy change at different pH values suggested that the protonated group in the memantine–HSA complex exhibits a heat protonation with a magnitude around 65 kJ mol^?1. This value agrees with the protonation of a guanidinium group, and confirmed that an arginine group may become protonated in the memantine–HSA complex formation. The thermodynamic data showed that memantine–HSA binding, for low temperature (<293 K), is dominated by a positive entropy change. This result suggests that dehydration at the binding interface and charge–charge interactions contribute to the memantine–HSA complex formation. Above 293 K, the thermodynamic data ΔH and ΔS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface. The temperature dependence of the free energy of binding is weak because of the enthalpy–entropy compensation caused by a large heat capacity change, ΔC _p = ? 3.79 kJ mol^?1 K^?1 at pH = 7. These results were used to determine the potential binding site of this drug on HSA.     

Bichromophoric naphthalene derivatives of diethylenetriaminepentaacetate (DTPA): fluorescent response to H+, Ca2+, Zn2+, and Cd2+

As an effort to design selective fluorescent sensors toward Ca²⁺, Zn²⁺ and Cd²⁺, synthetic and fluorometric studies were performed on four bichromophores, each of which consists of two naphthyl or methynaphthyl units (1- and 2-isomers) linked with a diethylenetriaminepentaacetate (DTPA) chain. Every bichromophore exhibits naphthalene-monomer emission at 370 nm and excimer emission at 405 nm. Emission intensities show sensitive pH dependence, from which protonation constants were determined. Fluorometric titrations with the metal ions were performed at the physiological pH and the conditional formation constants were determined. Naphthyl rings define the stoichiometry and stability of the complexes. The insertion of CH₂ spacer intensifies the emission and enhances the selective response to metal ions: the excimer emission is strengthened by 70?100 % with Cd²⁺ coordination, weakened by 60 % with Zn²⁺, and insensitive to Ca²⁺. The high response of methylnaphthyl bichromophores to Cd²⁺ is advantageous in fluorometric analyses.     

Investigation of the protonation of triethylenetetramine by means of a glass electrode

A quantitative study by means of a glass pH electrode was made of the successive protonation of triethylenetramine(trien), in the pH range 2.0–12.0 at 25°C for unit ionic strength (KNO₃). The successive acidity constants of fully protonated H₄ trien⁴⁺ were found to be 10^?3.97, 10^?7.12, 10^?9.49 and 10^?10.14.     

A screw-shaped alignment of pyrene using m-calix[3]amide

m-Calix[3]amide bearing three pyrenes (1a) was prepared by the condensation reaction of 3-nonylaminobenzoic acid derivative using Ph₃PCl₂. Pyrenyl groups were found to be aligned in the screw-like fashion by m-calix[3]amide as confirmed by the X-ray crystallography. Aromatic proton signals observed at the up-field region in the ¹H NMR spectrum at low temperature indicated that pyrenyl groups in 1a are aligned in close proximity in THF solution. UV–vis absorption and fluorescence emission spectra did not show marked peak shift nor concentration fluorescence quenching compared with reference compounds implying no significant electronic interaction between pyrenyl groups. These results can be explained by the steric effect of the m-calix[3]amide platform. On the other hand, an excimer emission was observed for m-calix[3]amide having a flexible spacer between pyrene and m-calix[3]amide (1b).     

Speciation and Stability of Dioxovanadium(V) Complexes with Diethylenetriaminepentaacetic Acid at Different Ionic Strengths

UV spectroscopic measurements have been used to determine the binding ability of diethylenetriaminepentaacetic acid (DTPA) ligand towards the $ {\text{VO}}_2^+ $ ion at different ionic strengths of sodium chloride (0.11–0.95 mol·dm^?3) and at T = 298 K. Dissociation constants of DTPA have been gathered from the literature. Calculations allowed us to identify the formation of three species VO₂H₃L, VO₂H₂L^? and VO₂HL^2? in the pH range of about 1.00–2.50. All of these complexes were characterized in terms of their stability constants on the basis of two different thermodynamic models (extended Debye–Hückel type and specific ion interaction theory) for the investigation of the ionic strength dependence of the stability and dissociation constants. Comparison with literature data is also reported.     

Anion binding by fluorescent Fmoc-protected amino acids

Two non-natural amino acids with fluorescent urea side-chains were prepared from Fmoc-protected aspartic and glutamic acids. In acetonitrile solution, the emission of the Asp derivative is strongly quenched by HCO₃^?  or H₂PO₄^?  (K ≥ 10⁴ M^? 1) but not by less-basic Cl^?  or NO₃^? . Solutions containing excess bicarbonate ion appear peach-colored, with λ_abs at 394 and 495 nm ascribed to the anion complex and urea-deprotonated sensor, respectively. Corresponding fluorescence bands are observed at 475 and 579 nm. Dihydrogenphosphate is not sufficiently basic to remove H⁺ from the ground state of the fluorophore. However, deprotonation of the excited state occurs in the presence of>1 equiv of H₂PO₄^?  (λ_em = 578 nm). According to ¹H NMR in DMSO-d₆, recognition of H₂PO₄^?  occurs at the urea N–H groups and the amino acid backbone N–H. DFT techniques further predict that the backbone C = O group accepts an H-bond from the anion. The Glu derivative has lower affinity for anions; the additional CH₂ group in its side-chain apparently sets the backbone N–H and C = O too far from the urea to contribute significantly to binding. To demonstrate suitability for standard Fmoc-based solid-phase peptide synthesis, the Asp derivative was incorporated into a 12-residue peptide.     

[RuIII(EDTA)(H2O)]− catalyzed oxidation of biologically important thiols by H2O2

[Ru^III(EDTA)(H₂O)]^? (EDTA^4? = ethylenediaminetetraacetate) catalyzes the oxidation of biological thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, penicillamine) using H₂O₂ as precursor oxidant. The kinetics of the oxidation process were studied spectrophotometrically as a function of [Ru^III(EDTA)(H₂O)]^?, [H₂O₂], [RSH], and pH (4–8). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with [Ru^III(EDTA)] catalyst complex to form [Ru^III((EDTA)(SR)]^2? intermediate species. In the subsequent reaction step the oxidant, H₂O₂, reacts directly with the coordinated S of the [Ru^III((EDTA)(SR)]^2? intermediate leading to formation of the disulfido (RSSR) oxidation product (identified by HPLC and ESI-MS studies) of thiols (RSH). Based on the experimental results, a working mechanism involving oxo-transfer from H₂O₂ to the coordinated thiols is proposed for the catalytic oxidation.     

Kinetics and mechanism of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) by N-bromosuccinimide in aqueous acidic medium

The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H₂O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm^?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H₂O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed.     

Kinetics of oxidation of glutathione by an octahedral cobalt(III) complex with phenolate–amide–amine coordination

The reduction of the octahedral cobalt(III) complex Co^III(HL)·9H₂O, H₄L = 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane by glutathione (GSH) has been studied by conventional spectrophotometry at 25.0 ≤ t/°C ≤ 45.0, 0.02 ≤ [H⁺]/mol dm^?3 ≤ 0.20 and I = 0.3 mol dm^?3 (NaClO₄). The reaction is biphasic. The fast initial phase is attributed to the H⁺-induced formation of the mixed ligand complex, [Co^III(H₂L)GSH]⁺, for which the rate-limiting step is the chelate ring opening via Co^III–NH (amide–N) bond cleavage of the protonated species, [Co^III(H₂L)]⁺. Outer-sphere association equilibria between GSH/GSH₂ ⁺ and [Co^III(H₂L)]⁺ substantially retard the ring opening process and consequently the mixed ligand complex formation. This is then followed by a slow phase involving reduction of [Co^III(H₂L)GSH]⁺ by both GSH and GSH₂ ⁺. The final products are the corresponding Co(II) complex and the oxidized form of GSH, GS–SG. The kinetic data and activation parameters for the redox process are interpreted in terms of an outer-sphere electron transfer mechanism.     

Acid–Base Properties, Solubility, Activity Coefficients and Na+ Ion Pair Formation of Complexons in NaCl(aq) at Different Ionic Strengths

The protonation constants and solubilities of three complexons [ethylenediamine-N,N′-disuccinic acid (EDDS), ethylene glycol bis(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) and 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CDTA)] are reported in aqueous solutions of NaCl with different ionic strength values (0 ≤ I ≤ 4.8 mol·L^?1) and, in the case of CDTA, in (CH₃)₄NCl (0.1 ≤ I ≤ 2.7 mol·L^?1). The dependence on ionic strength of the protonation constants of these three complexons and four other complexons that were previously reported (NTA, EDTA, DTPA and TTHA), is analyzed in NaCl solution; the ionic strength influences quite strongly the protonation constants (as an example for CDTA, log₁₀ K ₁ = 10.54 and 9.25 at I = 0.1 and 1 mol·L^?1, respectively), while the effect of (CH₃)₄NCl concentration is lower. Based on the total solubility S ^T and the protonation constant data at different salt concentrations, the solubility of the neutral species S ⁰ and the solubility products K _S0 are obtained. The Setschenow coefficients k _m and the solubility values S ₀ ⁰ in pure water are also reported (S ₀ ⁰  = 0.55, 0.21 and 0.75 mmol·kg^?1 for EDDS, EGTA and CDTA, respectively). The dependence of the protonation constants on ionic strength is also interpreted in terms of ion pair formation, and the formation constants of Na⁺ species are reported.     

Two-step one-electron transfer reaction of chromium(III) complex containing levodopa and uridine with N-bromosuccinimide

[Cr^III(LD)(Urd)(H₂O)₄](NO₃)₂?·?3H₂O (LD?=?Levodopa; Urd?=?uridine) was prepared and characterized. The product of the oxidation reaction was examined using HPLC. Kinetics of the oxidation of [Cr^III(LD)(Urd)(H₂O)₄]²⁺ with N-bromosuccinimide (NBS) in an aqueous solution was studied spectrophotometrically, with 1.0–5.0?×?10^?4?mol?dm^?3 complex, 0.5–5.0?×?10^?2?mol?dm^?3 NBS, 0.2–0.3?mol?dm^?3 ionic strength (I), and 30–50°C. The reaction is first order with respect to [Cr^III] and [NBS], decreases as pH increases in the range 5.46–6.54 and increases with the addition of sodium dodecyl sulfate (SDS, 0.0–1.0?×?10^?3?mol?dm^?3). Activation parameters including enthalpy, ΔH*, and entropy, ΔS*, were calculated. The experimental rate law is consistent with a mechanism in which the protonated species is more reactive than its conjugate base. It is assumed that the two-step one-electron transfer takes place via an inner-sphere mechanism. A mechanism for this reaction is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* for some Cr^III complexes. Formation of [Cr^III(LD)(Urd)(H₂O)₄]²⁺ in vivo probably occurs with patients who administer the anti-Parkinson drug (Levodopa), since Cr^III is a natural food element. This work provides an opportunity to identify the nature of such interactions in vivo similar to that in vitro.     

Synergetic effect of Prussian blue film with gold nanoparticle graphite–wax composite electrode for the enzyme-free ultrasensitive hydrogen peroxide sensor

Enzyme-free amperometric ultrasensitive determination of hydrogen peroxide (H₂O₂) was investigated using a Prussian blue (PB) film-modified gold nanoparticles (AuNPs) graphite–wax composite electrode. A stable PB film was obtained on graphite surface through 2-aminoethanethiol (AET)-capped AuNPs by a simple approach. Field emission scanning electron microscope studies results in formation of PB nanoparticle in the size range of 60–80 nm. Surface modification of PB film on AET–AuNPs–GW composite electrode was confirmed by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy studies. Highly sensitive determination of H₂O₂ at a peak potential of ?0.10 V (vs. SCE) in 0.1 M KCl PBS, pH?=?7.0) at a scan rate of 20 mVs^?1 with a sensitivity of 23.58 μA/mM was observed with the modified electrode using cyclic voltammetry. The synergetic effect of PB film with AuNPs has resulted in a linear range of 0.05 to 7,800 μM with a detection limit of 0.015 μM for H₂O₂ detection with the present electrode. Chronoamperometric studies recorded for the successive additions of H₂O₂ with the modified electrode showed an excellent linearity (R ²?=?0.9932) in the range of 4.8?×?10^?8 to 7.4?×?10^?8 M with a limit of detection of 1.4?×?10^?8 M. Selective determination of H₂O₂ in presence of various interferents was successfully demonstrated. Human urine samples and stain remover solutions were also investigated for H₂O₂ content.     

Acid Dissociation Constants and Rare Earth Stability Constants for DTPA

Diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) is an octadentate aminopolycarboxylate complexing agent whose f-element complexes find important practical applications in nuclear medicine and in advanced nuclear fuel reprocessing. This investigation focuses primarily on the latter application, specifically on characterization of lanthanide–DTPA complexes of relevance to the Trivalent Actinide–Lanthanide Separations by Phosphorus reagent Extraction and Aqueous Komplexants (TALSPEAK) process. To function acceptably, the TALSPEAK process requires the presence of moderate concentrations (0.5–2.0 mol·L^?1) of a (Na⁺/H⁺) lactate (or citrate) buffer. Competition between DTPA, lactate, and the extractant bis(2-ethylhexyl)phosphoric acid (HDEHP) for the lanthanides and trivalent actinides governs the course of the extraction process. To facilitate modeling and to support process improvements, the acid dissociation constants and stability constants for rare earth complexes with DTPA have been determined in 2.0 mol·L^?1 ionic strength (NaClO₄) media. The acid dissociation constants for DTPA and the stability constant for [Eu(DTPA)]^2? also were determined in sodium trifluoromethanesulfonate at 2.0 mol·L^?1 ionic strength to evaluate the potential impact of changing the nature of the electrolyte. The thermodynamic data are compared with earlier reports of similar data at lower ionic strength and used to complete calculations exploring the relative stability of lanthanide–DTPA and lactate complexes under TALSPEAK extraction conditions. Lanthanide–DTPA stability trends are discussed in comparison with literature data on a variety of other metal ions.     

Kinetics of hydrogen peroxide decomposition with complexed and “free” iron catalysts

The hydrogen peroxide decomposition kinetics were investigated for both “free” iron catalyst [Fe(II) and Fe(III)] and complexed iron catalyst [Fe(II) and Fe(III)] complexed with DTPA, EDTA, EGTA, and NTA as ligands (L). A kinetic model for free iron catalyst was derived assuming the formation of a reversible complex (Fe–HO₂), followed by an irreversible decomposition and using the pseudo‐steady‐state hypothesis (PSSH). This resulted in a first‐order rate at low H₂O₂ concentrations and a zero order rate at high H₂O₂ concentrations. The rate constants were determined using the method of initial rates of hydrogen peroxide decomposition. Complexed iron catalysts extend the region of significant activity to pH 2–10 vs. 2–4 for Fenton's reagent (free iron catalyst). A rate expression for Fe(III) complexes was derived using a mechanism similar to that of free iron, except that a L–Fe–HO₂ complex was reversibly formed, and subsequently decayed irreversibly into products. The pH plays a major role in the decomposition rate and was incorporated into the rate law by considering the metal complex specie, that is, EDTA–Fe–H, EDTA–Fe–(H₂O), EDTA–Fe–(OH), or EDTA–Fe–(OH)₂, as a separate complex with its unique kinetic coefficients. A model was then developed to describe the decomposition of H₂O₂ from pH 2–10 (initial rates = 1 × 10⁻⁴ to 1 × 10⁻⁷ M/s). In the neutral pH range (pH 6–9), the complexed iron catalyzed reactions still exhibited significant rates of reaction. At low pH, the Fe(II) was mostly uncomplexed and in the free form. The rate constants for the Fe(III)–L complexes are strongly dependent on the stability constant, K_ML, for the Fe(III)–L complex. The rates of reaction were in descending order NTA > EGTA > EDTA > DTPA, which are consistent with the respective log K_MLs for the Fe(III) complexes. Because the method of initial rates was used, the mechanism does not include the subsequent reactions, which may occur. For the complexed iron systems, the peroxide also attacks the chelating agent and by‐product‐complexing reactions occur. Accordingly, the model is valid only in the initial stages of reaction for the complexed system. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 24–35, 2000     

Complex Formation Equilibria of Unusual Seven-Coordinate Fe(EDTA) Complexes with DNA Constituents and Related Bio-relevant Ligands

Seven-coordinate Fe(EDTA)?CL complexes, where L represents a DNA constituent (uracil, uridine, thymine, thymidine and inosine), methylamine, ammonium chloride or imidazole, were investigated to resolve the solution chemistry of this system. The results show formation of 1:1 complexes with DNA constituents and the other ligands, supporting the hepta-coordination mode of Fe(III) ion. Stability constants of the complexes were measured by potentiometric titration at 25?°C and ionic strength 0.1 mol?L^?1 NaNO₃. The hydrolysis constant of [Fe(EDTA)(H₂O)]^? and the formation constants of the complexes formed in solution were calculated using the non-linear least-squares program MINIQUAD-75. The concentration distributions of the various complex species were evaluated as a function of?pH. The thermodynamic parameters ??H ⁰ and ??S ⁰, calculated from the temperature dependence of the equilibrium constants, were determined for the Fe(EDTA)?Curacil complex. The effect of dioxane as a solvent on the protonation constant of uracil, hydrolysis constants of [Fe(EDTA)(H₂O)]^?, and the formation constants of the Fe(EDTA)?Curacil complex are discussed.     

Synthesis of Two Derivatives of 3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic Acid and the Stabilities of Their Complexes with Ca2+, Cu2+, Zn2+, Dy3+ and Gd3+

Two N‐2‐hydroxy‐1‐phenylethyl and N‐2‐hydroxy‐2‐phenylethyl derivatives of DTPA (3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic acid), DTPA‐H1P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐1‐phenylethyl‐3,6,9‐triazaundecanedioic acid, and DTPA‐H2P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐2‐phenylethyl‐3,6,9‐triazaundecanedioic acid were synthesized. Their protonation constants were determined by Potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1°C. The formations of lanthanide(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constant for Gd(III) complex is larger than those for Ca(II), Zn(II) and Cu(II) complexes with these two ligands. The selectivity constants and modified selectivity constants of the DTPA‐H1P and DTPA‐H2P for Gd(III) over endogenously available metal ions were calculated. Comparing pM values at physiological pH 7.4 assesses effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media. The observed water proton relaxivity values of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? became constant with respect to pH changes over the range of 4‐10. ¹⁷O NMR shifts showed that the [Dy(DTPA‐H1P)]^? and [Dy(DTPA‐H2P)]^? complexes at pH 6.30 had 1.91 and 2.28 inner‐sphere water molecules, respectively. Water proton spin‐lattice relaxation rates of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? complexes were also consistent with the inner‐sphere Gd(III) coordination.     

Theoretical and experimental study of the catalytic cathodic stripping square-wave voltammetry of chromium species

The electrocatalytic mechanism of Cr(III) reduction in the presence of diethylenetriaminepentaacetic acid (DTPA) and nitrate ions is studied theoretically and experimentally by using stripping square-wave voltammetry (SWV). Experimental curves are in excellent agreement with theoretical profiles corresponding to a catalytic reaction of second kind. This type of mechanism is equivalent to a CE mechanism, where the chemical reaction produces the electroactive species. Accordingly, the reaction of Cr(III)–H₂O–DTPA and \( {\mathrm{NO}}_3^{-} \) would produce the electroactive species Cr(III)–NO₃–DTPA and this last species would release \( {\mathrm{NO}}_2^{-} \) to the solution during the electrochemical step. In this regard, the complex of Cr(III)–DTPA would work as the catalyzer that allows the reduction of \( {\mathrm{NO}}_3^{-} \) to \( {\mathrm{NO}}_2^{-} \). Furthermore, it was found that the electrochemical reaction is quite irreversible, with a constant of k _s?=?9.4?×?10^?5 cm s^?1, while the constant for the chemical step has been estimated to be k _chem?=?1.3?×?10⁴ s^?1. Considering that the equilibrium constant is K?=?0.01, it is possible to estimate the kinetic constants of the chemical reaction as k ₁?=?1?×?10² s^?1 and k _?1?=?1.29?×?10⁴ s^?1. These values of k ₁ and k _?1 indicate that the exchange of water molecules by nitrate is fast and that the equilibrium favors the complex with water. Also, a value for the formal potential E°’?≈??1.1 V was obtained. The model used for simulating experimental curves does not consider the adsorption of reactants yet. Accordingly, weak adsorption of reagents should be expected.     

Switchable Spherical-Wormlike Micelle Transition in Sodium Oleate/N-(3-(Dimethylamino)propyl)-Octanamide Aqueous System Induced by Carbon Dioxide Stimuli and pH Regulation

The structure transitions of the aggregates in the sodium oleate (NaOA)/N-(3-(dimethylamino)propyl)-octanamide (DPOA) aqueous system was investigated upon CO₂ stimuli. During the process of bubbling of CO₂, three appearance states of sol, gel, and emulsion with little white precipitate were observed continuously. The cryo-transmission electron microscope characterization and rheological measurements exhibited that the sol–gel transition was attributed to a spherical-wormlike micelle transition. Moreover, this transition was switchable at least three cycles in the pH range of 10.91–9.56 by CO₂ stimuli and pH regulation (adding NaOH), which could be explained by the protonation of DPOA and deprotonation of DPOA · H⁺. Bubbling of CO₂ resulted in protonation of DPOA, which not only inserted into the OA^– as a co-surfactant but also screened the electrostatic repulsion among OA^–, corporately leading to the spherical-wormlike micelle transition. Adding NaOH caused the deprotonation of DPOA · H⁺ and hence reversed this transition. This surfactant system with switchable micelle transition not only displays tremendous application potential in various fields but also is of key importance in cyclic utilization of surfactant.     

Radiochemical precipitation studies for separation of iodine from tellurium and other trace impurities

Precipitation of radiotellurium, containing trace radioimpurities, has been carried out from sulfate media at different pH-values. The highest precipitation yield was achieved at the region of pH ~4–6. Quantitative uptake by the formed precipitate was noticed for (i) ⁵⁴Mn, ^110mAg and ¹²⁵Sb over all the pH-range of study (pH 1.7–9.2), (ii) for ⁶⁵Zn and ⁶⁰Co in the regions of pH ~6–8 and pH 6–8.8, respectively, and (iii) for ¹³⁴Cs in the region of pH 1.7–2.8, while its percent uptake fluctuated around 60.5 % in the region of pH 4.4–6.4. Further precipitation studies have been conducted for a mixture of ¹²⁵I and radiotellurium from sulfate, nitrate and chloride media at pH-values of 6.0 and 7.5. The highest ¹²⁵I recovery yield in the obtained supernatant was 95.0 ± 1.3 %, which was achieved with sulfate medium at pH 6.0 with percent uptake values of 5.0 ± 1.3, 98.9 ± 0.9 and 62.0 ± 4.6 % of ¹²⁵I, ^123mTe and ¹³⁴Cs, respectively, and quantitative uptake of ⁵⁴Mn, ^110mAg, ¹²⁵Sb, ⁶⁰Co and ⁶⁵Zn by the precipitated tellurium. Thereafter, the supernatant was further acidified with H₂SO₄ and boiled, after adding H₂O₂, for 3 h. >99 % of ¹²⁵I was distilled off from the acidified supernatant. The distilled of ¹²⁵I was received in 0.1 M NaOH + 1 % Na₂S₂O₃ solution, with a radionuclidic purity of >99.99 %, radiochemical purity of >99.8 % as I^? and pH ~13.