Halide Concentration Research Articles

Glancing-angle Raman spectroscopic probe for reaction kinetics at water surfaces

We report glancing-angle Raman spectra acquired at the surface of aqueous dimethyl sulfoxide solutions and demonstrate that this technique can be used to measure the surface concentration of solutes. The presence of some solute molecules at the surface suppresses the intensity of the OH-stretching band of water there. We used this phenomenon to study the interfacial reaction of gas-phase ozone with aqueous NaX solutions (X = Br, I) by monitoring the decrease in intensity of the OH-stretching band of water over time. UV-VIS analysis of the product solutions indicates that X(3)(-), formed from X(2) evolved in the ozonation reaction, is the species most likely responsible for the decrease in OH-stretching intensity at the surface. The dependence of the rate of OH-Raman signal loss at the water surface on the bulk halide concentration is well described by a Langmuir-Hinshelwood kinetic model. The Langmuir-Hinshelwood parameters indicated that iodide has a approximately 50 times greater propensity for the surface compared to bromide.

Contrasting Effects of Halides on the Structure and Function of A Multimeric Allosteric Protein

We have used two halide salts, namely, sodium chloride and sodium iodide, and studied their impact on the oxygenation characteristics of adult human hemoglobin (Hb). Previous studies in our group showed that both the halide salts exerted similar effects on the Hb function at concentrations below 0.1 M, i.e., an overall decrease in the affinity for oxygen, as a result of a decrease in the affinity at low oxygenation levels. However, as the halide concentrations increased, while chloride continued producing a progressive but rather diminished effect, iodide reverted its effects on Hb: the overall affinity for oxygen rather increased. Careful analysis of the oxygenation curves revealed that while the affinity for oxygen decreased at high oxygen saturation levels, the affinity at low oxygen concentration increased markedly. These effects reached a plateau at a concentration of 2 M, but even more surprisingly, cooperativity was never canceled. The results hinted at the possibility that iodide ions were splitting the tetrameric Hb molecules into asymmetric dimers. Dimers have been and still are considered non-cooperative, high oxygen-affinity systems. Yet, our present data clearly contrast with the previous tenet since cooperativity index showed values as high as 1.6 in the presence of 2 M NaI. Determination of molecular weight by size exclusion chromatography, and the study of oxygenation characteristics of symmetric nickel-iron Hb hybrids in the presence of sodium iodide showed that in fact the tetrameric Hb splits into two dimers that, strikingly, remain allosterically functional.

Acetaminophen (paracetamol) inhibits myeloperoxidase-catalyzed oxidant production and biological damage at therapeutically achievable concentrations

The heme peroxidase enzyme myeloperoxidase (MPO) is released by activated neutrophils and monocytes, where it uses hydrogen peroxide (H 2O 2) to catalyze the production of the potent oxidants hypochlorous acid (HOCl), hypobromous acid (HOBr) and hypothiocyanous acid (HOSCN) from halide and pseudohalide (SCN −) ions. These oxidants have been implicated as key mediators of tissue damage in many human inflammatory diseases including atherosclerosis, asthma, rheumatoid arthritis, cystic fibrosis and some cancers. It is shown here that acetaminophen (paracetamol), a phenol-based drug with analgesic and antipyretic actions, is an efficient inhibitor of HOCl and HOBr generation by isolated MPO–H 2O 2–halide systems. With physiological halide concentrations, acetaminophen concentrations required for 50% inhibition of oxidant formation (IC 50) were 77 ± 6 μM (100 mM Cl −) and 92 ± 2 μM (100 mM Cl − plus 100 μM Br −), as measured by trapping of oxidants with taurine. The IC 50 for inhibition of HOCl generation by human neutrophils was ca. 100 μM. These values are lower than the maximal therapeutic plasma concentrations of acetaminophen (≤150 μM) resulting from typical dosing regimes. Acetaminophen did not diminish superoxide generation by neutrophils, as measured by lucigenin-dependent chemiluminescence. Inhibition of HOCl production was associated with the generation of fluorescent acetaminophen oxidation products, consistent with acetaminophen acting as a competitive substrate of MPO. Inhibition by acetaminophen was maintained in the presence of heparan sulfate and extracellular matrix, materials implicated in the sequestration of MPO at sites of inflammation in vivo. Overall, these data indicate that acetaminophen may be an important modulator of MPO activity in vivo.

Distributions and fluxes of methyl chloride and methyl bromide in the East China Sea and the Southern Yellow Sea in autumn

We determined the distributions and fluxes of methyl chloride and methyl bromide in the East China Sea (ECS) and the Southern Yellow Sea (SYS) in November 2007. Methyl chloride and methyl bromide concentrations in the surface waters ranged from 47.1 to 163 pmol L − 1 and from 0.70 to 9.82 pmol L − 1 , with average values of 87.6 and 2.97 pmol L − 1 , respectively. The distributions of the two methyl halides were clearly influenced by the Yangtze (Changjiang) River effluent and Kuroshio water, with high concentrations appearing in the coastal zone and low values occurring in the open waters. A positive linear correlation was observed between methyl chloride and methyl bromide concentration anomalies in the surface waters, suggesting that they may share some origins in this coastal area. However, no correlation was found between the two methyl halide concentration anomalies and chlorophyll a in the surface waters. The vertical profiles of the two methyl halides were characterized by the maxima in the upper mixed layer. Both gases were generally supersaturated in the surface seawater, with mean sea-to-air fluxes of methyl chloride and methyl bromide of 391 and 20.0 nmol m − 2 d − 1 , respectively.

Influence of lithium chloride, lithium bromide and lithium fluoride additives on performance of polyethersulfone membranes and its application in the treatment of palm oil mill effluent

In this study three different types of lithium halides; lithium bromide (LiBr), lithium chloride (LiCl) and lithium fluoride (LiF) were used as additives in the making of polyethersulfone (PES) membranes. The concentration of PES is kept constant at 20 wt.% throughout the study, and the lithium halide concentration is varied in the range of 1–5 wt %. The solvent used is N, N-dimethylformamide and the PES asymmetric membrane was prepared by the dry/wet phase inversion process. Membrane performance was characterized in terms of pure water permeation (PWP), permeation rate (PR) and solute separation of polyethylene glycol (PEG) solution of various molecular weights ranging from 600 to 35,000 Da. The molecular weight cut off (MWCO) and mean pore size distribution were subsequently determined. Results revealed that the 3 wt.% LiBr exhibits the best performance with MWCO at 90% rejection in the range of 2.83 kDa and high flux range of 117.69 L m − 2 h − 1 . Hollow fibers spun from the dope solutions containing LiBr revealed that they are capable of treating palm oil mill effluent (POME) with reduction in turbidity, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of 96.7%, 53.12% and 76.7% respectively.

Hypothiocyanous acid reactivity with low-molecular-mass and protein thiols: absolute rate constants and assessment of biological relevance

MPO (myeloperoxidase) catalyses the oxidation of chloride, bromide and thiocyanate by H(2)O(2) to HOCl (hypochlorous acid), HOBr (hypobromous acid) and HOSCN (hypothiocyanous acid, also know as cyanosulfenic acid) respectively. Specificity constants indicate that thiocyanate, SCN-, is a major substrate for MPO. HOSCN is also a major oxidant generated by other peroxidases including salivary, gastric and eosinophil peroxidases. Whereas HOCl and HOBr are powerful oxidizing agents, HOSCN appears to be a less reactive, but more thiol-specific oxidant. Although it is established that HOSCN selectively targets thiols, absolute kinetic data for the reactions of thiols with HOSCN are absent from the literature. This study shows for the first time that the reactions of HOSCN with low-molecular-mass thiol residues occur with rate constants in the range from 7.3 x 10(3) M(-1).s(-1) (for N-acetyl-cysteine at pH 7.4) to 7.7 x 10(6) M(-1).s(-1) (for 5-thio-2-nitrobenzoic acid at pH 6.0). An inverse relationship between the rate of reaction and the pKa of the thiol group was observed. The rates of reaction of HOSCN with thiol-containing proteins were also investigated for four proteins (creatine kinase, BSA, beta-lactoglobulin and beta-L-crystallins). The values obtained for cysteine residues on these proteins are in the range 1 x 10(4)- 7 x 10(4) M(-1).s(-1). These second-order rate constants indicate that HOSCN is a major mediator of thiol oxidation in biological systems exposed to peroxidase/H(2)O(2) systems at (patho)physiological concentrations of halide and SCN- ions, and that HOSCN may play an important role in inflammation-induced oxidative damage.

Effect of alkali halides on the emission properties in Tm‐doped chalcogenide glasses

AbstractPhotoluminescence properties and local structure of Tm ions in Ge‐Ga‐Se glasses with the addition of alkali halides were investigated. The range of halide concentrations in the glass of composition (Ge26Ga9(Se+S)65)100‐x (Halide)x)99Tm1 (where x = 0–12 mol%, Halide = CsBr, CsI) were prepared by melt quenching methods. The luminescence lifetime of Tm3+ ions at 1780 nm band (3F4→3H6) increased with increasing alkali halide concentration. When the CsBr content is 10 mol%, the PL lifetime of the 1780 nm band increased about 4 times compared with that in the glass without CsBr. The 1460 nm band PL lifetime did not increase as much. The glass transition temperature decreased with increasing CsBr content. The effect of CsI addition is almost the same as the addition of CsBr. The addition of Br ions into the glass would result in the formation of Ga‐Br bonding. These phenomena in Ge‐Ga‐Se glasses are similar to those in Ge‐Ga‐S glasses with CsBr (Y.B. Shin et al., J. Mater. Res. 16, 1318 (2001) [1]). It is supposed that a complex such as a tetrahedral [GaSe3/2Br]– subunit is formed. The structure could be coordinated to Tm3+ ions. The local structure plays an important role in the emission properties of excited Tm3+ ions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A spectrophotometric study of aqueous Au(III) halide–hydroxide complexes at 25–80 °C

The mobility and transport of gold in low-temperature waters and brines is affected by the aqueous speciation of gold, which is sensitive in particular to pH, oxidation and halide concentrations. In this study, we use UV–Vis spectrophotometry to identify and measure the thermodynamic properties of Au(III) aqueous complexes with chloride, bromide and hydroxide. Au(III) forms stable square planar complexes with hydroxide and halide ligands. Based on systematic changes in the absorption spectra of solutions in three binary systems NaCl–NaBr, NaCl–NaOH and NaBr–NaOH at 25 °C, we derived log dissociation constants for the following mixed and end-member halide and hydroxide complexes: [AuCl 3Br] −, [AuCl 2Br 2] −, [AuBr 3Cl] − and [AuBr 4] −; [AuCl 3(OH)] −, [AuCl 2(OH) 2] −, [AuCl(OH) 3] − and [Au(OH) 4] −; and [AuBr 3(OH)] −, [AuBr 2(OH) 2] − and [AuBr(OH) 3] −. These are the first reported results for the mixed chloride–bromide complexes. Increasing temperature to 80 °C resulted in an increase in the stability of the mixed chloride–bromide complexes, relative to the end-member chloride and bromide complexes. For the [AuCl (4− n )(OH) n ] − series of complexes ( n = 0–4), there is an excellent agreement between our spectrophotometric results and previous electrochemical results of Chateau et al. [Chateau et al. (1966)]. In other experiments, the iodide ion (I −) was found to be unstable in the presence of Au(III), oxidizing rapidly to I 2(g) and causing Au to precipitate. Predicted Au(III) speciation indicates that Au(III) chloride–bromide complexes can be important in transporting gold in brines with high bromide–chloride ratios (e.g., >0.05), under oxidizing (atmospheric), acidic (pH < 5) conditions. Native gold solubility under atmospheric oxygen conditions is predicted to increase with decreasing pH in acidic conditions, increasing pH in alkaline conditions, increasing chloride, especially at acid pH, and increasing bromide for bromide/chloride ratios greater than 0.05. The results of our study increase the understanding of gold aqueous geochemistry, with the potential to lead to new methods for mineral exploration, hydrometallurgy and medicine.

Correlations of Water Quality Parameters with Mutagenicity of Chlorinated Drinking Water Samples

Adverse health effects that may result from chronic exposure to mixtures of disinfection by-products (DBPs) present in drinking waters may be linked to both the types and concentrations of DBPs present. Depending on the characteristics of the source water and treatment processes used, both types and concentrations of DBPs found in drinking waters vary substantially. The composition of a drinking-water mixture also may change during distribution. This study evaluated the relationships between mutagenicity, using the Ames assay, and water quality parameters. The study included information on treatment, mutagenicity data, and water quality data for source waters, finished waters, and distribution samples collected from five full-scale drinking water treatment plants, which used chlorine exclusively for disinfection. Four of the plants used surface water sources and the fifth plant used groundwater. Correlations between mutagenicity and water quality parameters are presented. The highest correlation was observed between mutagenicity and the total organic halide concentrations in the treated samples.

Evaluation of a Microfluidic Device for the Electrochemical Determination of Halide Content in Ionic Liquids

A microfluidic device designed for electrochemical studies on a microliter scale has been utilized for the examination of impurity levels in ionic liquids (ILs). Halide impurities are common following IL synthesis, and this study demonstrates the ability to quantify low concentrations of halide in a range of ILs to levels of approximately 5 ppm, even in ILs not currently measurable using other methods such as ion chromatography. To validate the mixer device, the electrochemistry of ferrocene was also examined and compared with spectroscopic and bulk electrochemistry measurements. An automated "sample preparation, delivery, and calibration" method was developed, and the chip successfully used for linear sweep, cyclic voltammetry (under both quiescent and steady-state flowing conditions), square wave voltammetry, and differential pulse voltammetry. An effective method of electrochemically cleaning the electrodes is also presented.

Quantitative FRET Analysis With the E0GFP‐mCherry Fluorescent Protein Pair

Fluorescence resonance energy transfer (FRET) between fluorescent proteins (FPs) is a powerful tool to investigate protein-protein interaction and even protein modifications in living cells. Here, we analyze the E(0)GFP-mCherry pair and show that it can yield a reproducible quantitative determination of the energy transfer efficiency both in vivo and in vitro. The photophysics of the two proteins is reported and shows good spectral overlap (Förster radius R(0) = 51 A), low crosstalk between acceptor and donor channels, and independence of the emission spectra from pH and halide ion concentration. Acceptor photobleaching (APB) and one- and two-photon fluorescence lifetime imaging microscopy (FLIM) are used to quantitatively determine FRET efficiency values. A FRET standard is introduced based on a tandem construct comprising donor and acceptor together with a 20 amino acid long cleavable peptidic linker. Reference values are obtained via enzymatic cleavage of the linker and are used as benchmarks for APB and FLIM data. E(0)GFP-mCherry shows ideal properties for FLIM detection of FRET and yields high accuracy both in vitro and in vivo. Furthermore, the recently introduced phasor approach to FLIM is shown to yield straightforward and accurate two-photon FRET efficiency data even in suboptimal experimental conditions. The consistence of these results with the reference method (both in vitro and in vivo) reveals that this new pair can be used for very effective quantitative FRET imaging.

Kinetic effects of halide ions on the morphological evolution of silver nanoplates

Time-resolved extinction spectroscopy is employed to study the reaction kinetics in the shape-conversion reaction involving halide ions (including Cl(-), Br(-) and I(-)) etching (sculpturing) silver nanoplates. A series of time-resolved extinction spectra are obtained during the in situ etching process and the evolution of surface plasmon resonance (SPR) of the silver nanoparticles is analyzed. Spectral analysis indicates that the conversion of nanoprisms starts simultaneously with the emergence of nanodisks when the halide ions are added. The etching rate of different halide ions is evaluated through the in-plane dipole resonance peak intensity of silver nanoplates vs. the reaction time (dI/dt). The relationship between the etching rate and the halide ion concentration shows that the halide ion etching reaction can be considered as a pseudo-first-order reaction. The effect of different halide ions on the shape-conversion of silver nanoplates is compared in detail. The activation energy of the etching reaction is calculated, which indicates that the etching ability of different halide ions is on the order of Cl(-) < I(-) < Br(-).

Bond character, optical properties and ionic conductivity of Li 2O/B 2O 3/SiO 2/Al 2O 3 glass: Effect of structural substitution of Li 2O for LiCl

A glass of composition (20 − x)Li 2O– xLiCl–65B 2O 3–10SiO 2–5Al 2O 3 where 0 ⩽ x ⩽ 12.5 wt% is prepared using the normal melt-quenching technique. The optical constants and electrical conductivity and their correlation are investigated, furnished and discussed with the substitution of Li 2O for LiCl. The mechanism of the optical absorption and the calculated Urbach energy follow the rule of phonon-assisted transitions. The ionic conduction mechanism is determined by activation energy process. Substitution up to 10 wt% LiCl provides high ionic conductivity (1.9 × 10 −2 Ω −1 m −1) due to the high average electronegativity of LiCl which increases the polarizability of lithium ions. The small cation–anion distance approach confirmed the enhancement in ionic conductivity of LiCl containing glass compared to that of Li 2O. Due to the large size of Cl − ions, there is an expansion of the lattice which in turn broadens the available path windows. For 12.5 wt% LiCl, anomalous density behavior is observed and a reduction in conductivity is occurred, σ = 5.4 × 10 −3 Ω −1 m −1. Owing to the model of bond fluctuation, the reduction is attributed to the increase in the alkali halide concentration which creates bottlenecks that hinder the motion of Li + ions. The ionic conductivity character is strongly supported by the behavior of the glass ionicity factor, density, molar volume, refractive index, average boron–boron separation, molar refraction, metallization criterion and non-bridging oxygen concentration of the studied glass.

The dynamic interfacial tension between HPAM/C17H33COONa mixed solution and crude oil in the presence of sodium halide

Abstract The dynamic interfacial tension between crude oil and the partially hydrolyzed polyacrylamide (HPAM)/sodium oleate (C 17 H 33 COONa) mixed solution in the presence of sodium halide (NaX: X = F, Cl, Br, I) was investigated by TX500C interfacial tensiometer, and the viscosity of the mixed solution was investigated by DV-iii ultra programmable rheometer. It is shown that the addition of sodium halide results in the lowering of the interfacial tension between HPAM/C 17 H 33 COONa system and crude oil. When the concentration of sodium halide reaches 0.50 mol L −1 , the minimum interfacial tension can reach the magnitude of 10 −4 mN m −1 . When the addition of sodium halide varies from NaF to NaCl, NaBr and NaI, the time to reach the minimum interfacial tension becomes shorter and shorter. In addition, NaI has the biggest influence on the decrease of the interfacial tension between HPAM/C 17 H 33 COONa system and crude oil. Also it is shown that the addition of sodium halide can decrease the viscosity of the mixed solution, both NaCl and NaI have the same effects.

Chloride and iodide mediated oxidation of antimony(III) by cerium(IV) in aqueous sulphuric acid medium

The micro amounts of iodide (10−7) (mol dm−3) and chloride (10−2) (mol dm−3) mediated oxidation of antimony(III) by cerium(IV) in an aqueous sulphuric acid medium have been studied spectrophotometrically at 25 °C and μ = 3.10 mol dm−3. The stoichiometry is 1:2 in chloride and iodide mediated reactions. i.e. one mole of antimony(III) requires two moles of cerium(IV). In the case of chloride mediated reaction, the reaction was first order in cerium(IV) and halide concentrations, whereas in the case of iodide mediated reaction the order with respect to [cerium(IV)] was unity and with respect to iodide concentrations was more than unity (ca. 1.4). In both chloride and iodide mediated reactions the order with respect to antimony(III) concentrations was less than unity. Increase in sulphuric acid concentration increased the rate. The order with respect to H+ ion concentration was less than unity. Added products, cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant was understood to be $$\hbox{H}_{3}\hbox{Ce}(\hbox{SO}_{4})_{4}^{-}$$ , whereas that of reductant as SbCl3 in the case of chloride and SbI2+ in case of iodide mediated reactions. The possible reaction mechanisms were proposed and the activation parameters were determined and discussed.

Direct Oxidation of Hydrogen to Hydrogen Peroxide over Pd (or PdO)/Al2O3 in Aqueous Reaction Medium: Influence of Different Acids and Halide Anions in Reaction Medium on Formation and Destruction of H2O2

Effects of different mineral acids (viz. H 2 SO 4 , H 3 PO 4 , HNO 3 , HCl, HBr, and HI), acid (H 3 PO 4 ) concentration, different halide anions (viz. F - , Cl-, Br - , and I - ), and halide anion concentration in aqueous reaction medium on the H 2 O 2 formation (in H 2 -to-H 2 O 2 oxidation) and/or on the H 2 O 2 destruction (by H 2 O 2 decomposition and hydrogenation) activities of Pd (or PdO)/Al 2 O 3 catalyst (at 300 K and atmospheric pressure) have been thoroughly investigated. Among the different halide anions, Br - anions are most effective for promoting the H 2 O 2 formation and inhibiting the H 2 O 2 destruction by both the H 2 O 2 decomposition and/or hydrogenation. The cations associated with the halide anions, however, have only a little or no influence on both the H 2 O 2 formation and destruction. The concentration of the different halide anions has a strong influence on the H 2 conversion and H 2 O 2 formation and destruction activities of the Pd/Al 2 O 3 . The H 2 O 2 formation activity in the presence of Br - or Cl- anions is highest at the optimum concentration of halide (about 1.0 mmol/dm 3 ). It is also highest at the optimum concentration of phosphoric acid (between 0.1 and 0.3 mol/dm 3 ). In general, the H 2 O 2 formation is increased with decreasing the H 2 O 2 destruction activity of the catalyst, indicating a close relationship between the two. Br - anions act as an excellent catalyst promoter for Pd/Al 2 O 3 catalyst, but they show only a small promoting effect for PdO/Al 2 O 3 catalyst. The next choice for halide promoter for Pd/ Al 2 O 3 catalyst is Cl- anions. F - and I - anions are, however, catalyst inhibitor and strong poison, respectively, for the H 2 O 2 formation. At the same concentration, Br - anions are more effective than Cl- anions for inhibiting the H 2 O 2 destruction reactions over Pd/Al 2 O 3 catalyst. For both halide promoters (Cl - and Br - ), the net H 2 O 2 formation is controlled by the H 2 O 2 hydrogenation rather than by the H 2 O 2 decomposition.

Mechanisms of Photoinitiated Cleavage of DNA by 1,8-Naphthalimide Derivatives¶

Using water-soluble 1,8-naphthalimide derivatives, the mechanisms of photosensitized DNA damage have been elucidated. Specifically, a comparison of rate constants for the photoinduced relaxation of supercoiled to circular DNA, as a function of dissolved halide, oxygen and naphthalimide concentration, has been carried out. The singlet excited states of the naphthalimide derivatives were quenched by chloride, bromide and iodide. In all cases the quenching products were naphthalimide triplet states, produced by induced intersystem crossing within the collision complex. Similarly, the halides were found to quench the triplet excited state of the 1,8-naphthalimide derivatives by an electron transfer mechanism. Bimolecular rate constants were <105M−1 s−1 for quenching by bromide and chloride. As expected from thermodynamic considerations quenching by iodide was 6.7 × 109 and 8.8 × 109M−1 s−1 for the two 1,8-naphthalimide derivatives employed. At sufficiently high ground-state concentration self-quenching of the naphthalimide triplet excited state also occurs. The photosensitized conversion of supercoiled to circular DNA is fastest when self-quenching reactions are favored. The results suggest that, in the case of 1,8-naphthalimide derivatives, radicals derived from quenching of the triplet state by ground-state chromophores are more effective in cleaving DNA than reactive oxygen species or radicals derived from halogen atoms.

Kinetics of the Heck reactions of styrene with bromobenzene and iodobenzene in the presence of ligandless catalytic systems: A comparative study

The comparative kinetic study of the Heck reactions of styrene with iodobenzene and bromobenzene has revealed specific features of these reactions that should necessarily be taken into account for the observed data to be interpretable in the framework of a unified mechanistic conception. It has been proved for the styrene-bromobenzene reaction that benzene forms as a by-product via a heterogeneous route and catalytically active Pd(0) undergoes aggregation via an autocatalytic mechanism. The kinetics of the styrene-iodobenzene reaction indicates that benzene in this reaction forms via a homogeneous route, biphenyl forms as another by-product by a bimolecular mechanism, and excessive aryl halide concentration reduces the catalyst formation rate. A nonlinear-law mechanism is suggested for the conjugation of palladium reduction, aggregation, and oxidation in the Heck reaction. This mechanism allows the existence of a “critical” Pd(0) concentration and a “critical” formation rate of this catalytic species above which the catalytic activity begins to decrease.

The Partition Behavior of Zn(II) using Halide Ions Extractants in Aqueous Peg‐Based Two‐Phase Systems

The partition behavior of Zn(II) has been studied in aqueous polyethylene glycol PEG(1550) – (NH4)2SO4 two‐phase system using halide ions (Cl−, Br− and I−) as extracting agents, at two different values of salt stock solution pH. The efficiency of extractants increase in this order: Cl−>Br−>I−. The extracted species were estimated from the distribution coefficients' values determined as a function of halide ions concentration, and the “conditional extraction constants” were calculated. The experimental results suggest that the Zn(II) partition in presence of halide ions in such systems is the result of two competitive processes. The IR spectra of solidified PEG‐rich phases show that the passing of metal species into PEG‐rich phases bring a supplementary water contribution, which makes the extraction process to occurs until it reaches an “equilibrium state”, dependent on the hydrophobicity of these phases and not on the type of extracted metal species.

Understanding the Oxidative Stability of Gold Monolayer-Protected Clusters in the Presence of Halide Ions under Ambient Conditions

We report on the oxidative stability of thiol-passivated Au monolayer-protected clusters (MPCs) made via a modified Brust-Schiffrin method. A sequential oxidation of the anchored thiol groups to disulfide and sulfonate groups and the oxidation of Au atoms to Au3+ species is observed upon exposure of Au MPCs to air in the presence of halide anions. In addition, the average nanoparticle size grows via aggregation of the MPCs, leading eventually to partial oxidation of the Au MPCs and precipitation of the remaining nanoparticles from solution or to complete oxidation of the gold atoms at high halide concentrations. These results show that Au MPCs are prone to oxidation in air in the presence of halide anions, and therefore, particles made using phase transfer reagents such as tetraoctylammonium bromide must be thoroughly removed to avoid particle size growth, oxidation, and precipitation of the Au MPCs. In addition, for biological applications involving Au MPCs, care must be taken to ensure that oxidation of MPCs in air is not problematic when working in media containing halide anions.