Halide Ions In Aqueous Solutions Research Articles

Surface Propensity of Aqueous Atmospheric Bromine at the Liquid-Gas Interface.

Multiphase reactions of halide ions in aqueous solutions exposed to the atmosphere initiate the formation of molecular halogen compounds in the gas phase. Their photolysis leads to halogen atoms, which are catalytic sinks for ozone, making these processes relevant for the regional and global tropospheric ozone budget. The affinity of halide ions in aqueous solution for the liquid-gas interface, which may influence their reactivity with gaseous species, has been debated. Our study focuses on the surface properties of the bromide ion and its oxidation products. In situ X-ray photoelectron spectroscopy carried out on a liquid jet combined with classical and first-principles molecular dynamics calculations was used to investigate the interfacial depth profile of bromide, hypobromite, hypobromous acid, and bromate. The simulated core electron binding energies support the experimentally observed values, which follow a correlation with bromine oxidation state for the anion series. Bromide ions are homogeneously distributed in the solution. Hypobromous acid, a key species in the multiphase cycling of bromine, is the only species showing surface propensity, which suggests a more important role of the interface in multiphase bromine chemistry than thought so far.

Effect of interionic interactions on the structure and dynamics of ionic solvation shells in aqueous electrolyte solutions

Molecular dynamics (MD) simulations to explore the structure and dynamics of the ionic solvation shell of alkali ions and halide ions in aqueous solution.

Iodeosin-based fluorescent and colorimetric sensing for Ag+, Hg2+, Fe3+, and further for halide ions in aqueous solution

We report that common erythrosin B can be used as a dual-mode fluorescent and colorimetric sensor for Ag+, Hg2+ and Fe3+, and further for halide ions in aqueous solution based on erythrosin B complexation with the three metal ions.

Crystal lattice properties fully determine short-range interaction parameters for alkali and halide ions

Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-derived parameters for the primitive model and the Lennard-Jones model with Lorentz-Berthelot mixing rules. The resulting parameters successfully reproduce the lattice properties used to derive them and are free from the influence of any water model. To assess the transferability of the Lennard-Jones parameters to aqueous systems, we used them to estimate hydration free energies and found that the results were in quantitative agreement with experimentally measured values. These lattice-derived parameters are applicable in simulations where coupling of ion parameters to a particular solvent model is undesirable. The simplicity and low computational demands of the calibration procedure make it suitable for parametrization of crystallizable ions in a variety of force fields.

A set of molecular models for alkali and halide ions in aqueous solution

This work presents new molecular models for alkali and halide ions in aqueous solution. The force fields were parameterized with respect to the reduced liquid solution density at 293.15 K and 1 bar, considering all possible ion combinations simultaneously. The experimental target data are reproduced with a high accuracy over a wide range of salinity. The ion models predict structural properties of electrolyte solutions well, such as pair correlation functions and hydration numbers. The force fields provide good predictions of the properties studied here in combination with different models for water.

Quenching of the Luminescence of Upconverting Luminescent Nanoparticles by Heavy Metal Ions

We report that the luminescence of upconverting luminescent nanoparticles (UCLNPs) is quenched by heavy metal ions and halide ions in aqueous solution. The UCLNPs consist of hexagonal NaYF(4) nanocrystals doped with trivalent rare earth ions and were synthesized by both the oleic acid (solvothermal) method and the ethylenediaminetetraacetic acid (co-precipitation) method. Quenching was studied for the Cu(II), Hg(II), Pb(II), Cd(II), Co(II), Ag(I), Fe(III), Zn(II), bromide, and iodide ions and is found to be particularly strong for Hg(II). Stern-Volmer plots are virtually linear up to quencher concentrations of 10-25 mM, but deviate from linearity at higher quencher concentrations, because static quenching causes an additional effect. The UCLNPs display two main emission bands (blue, green, red or near-infrared), and the quenching efficiencies for these are found to be different. The effect seems to be generally associated with UCLNPs because it was observed for all UCLNPs doped with trivalent lanthanide ions including Yb(III), Er(III), Ho(III), and Tm(III). The results are discussed in terms of quenching mechanisms and with respect to potential applications such as optical sensing.

The Thermodynamics of Latent Fingerprint Corrosion of Metal Elements and Alloys

Redox reactions taking place between the surface of a metal and fingerprint residue have been expressed thermodynamically in terms of both the Nernst equation for reduction potential and the complexation constant for the formation of complex metal halide ions in aqueous solution. These expressions are used to explain experimental results for the corrosion of 10 different metal elements by fingerprint residue in air at room temperature. Corrosion of noble metals, such as silver and gold, supports the proposition that the degree of metal corrosion is enhanced by the presence of chloride ions in eccrine sweat. Extending the experiments to include 10 metal alloys enabled the construction of a fingerprint corrosion series for 20 different metals. Fingerprint corrosion on metals alloyed with > approximately 40% copper was found to display third level fingerprint detail. A comparison of both conventional ink on paper and digital (Livescan) fingerprinting techniques with fingerprints deposited on 9 Karat gold alloy has shown that gold alloy depositions are least susceptible to third level detail obliteration by poor fingerprint capturing techniques.

Ion spatial distributions at the liquid–vapor interface of aqueous potassium fluoride solutions

X-Ray photoemission spectroscopy operating under ambient pressure conditions is used to probe ion distributions throughout the interfacial region of a free-flowing aqueous liquid micro-jet of 6 M potassium fluoride. Varying the energy of the ejected photoelectrons by carrying out experiments as a function of X-ray wavelength measures the composition of the aqueous-vapor interfacial region at various depths. The F(-) to K(+) atomic ratio is equal to unity throughout the interfacial region to a depth of 2 nm. The experimental ion profiles are compared with the results of a classical molecular dynamics simulation of a 6 M aqueous KF solution employing polarizable potentials. The experimental results are in qualitative agreement with the simulations when integrated over an exponentially decaying probe depth characteristic of an APPES experiment. First principles molecular dynamics simulations have been used to calculate the potential of mean force for moving a fluoride anion across the air-water interface. The results show that the fluoride anion is repelled from the interface, consistent with the depletion of F(-) at the interface revealed by the APPES experiment and polarizable force field-based molecular dynamics simulation. Together, the APPES and MD simulation data provide a detailed description of the aqueous-vapor interface of alkali fluoride systems. This work offers the first direct observation of the ion distribution at an aqueous potassium fluoride solution interface. The current experimental results are compared to those previously obtained for saturated solutions of KBr and KI to underscore the strong difference in surface propensity between soft/large and hard/small halide ions in aqueous solution.

Ion pairs of 2,6-diphenyl-4-(4-dimethylaminostyryl)pyrylium chloride with halide ions: Physicochemical characteristics and analytical applications

The interaction of a cationic pyrylocyanine reagent, 2,6-diphenyl-4-(4-dimethylaminostyryl)pyrylium chloride, with halide ions in aqueous solutions was studied. The spectrophotometric characteristics and stability constants of the resulting ion pairs were determined, and the kinetic and thermodynamic parameters of the reactions were calculated. A procedure was developed for the photometric determination of iodides in medicinal preparations and mineral waters.

Partial Molar Volume and Compressibility of Alkali−Halide Ions in Aqueous Solution: Hydration Shell Analysis with an Integral Equation Theory of Molecular Liquids

The partial molar volume and partial molar compressibility of alkali−halide ions in aqueous solution at infinite dilution are calculated based on the RISM−Kirkwood−Buff theory. The theoretical results are in qualitative agreement with the corresponding experimental data. The volume and compressibility values are decomposed into the volume-exclusion and electrostriction contributions. The volume-exclusion effect qualitatively determines the dependence of the partial molar volume on the ion size, whereas the electrostriction effect dominates in the size dependence of the partial molar compressibility. The partial molar volume and compressibility are further analyzed by using the hydration shell model which enables us to distinguish a contribution from each hydration shell. For the primary hydration shell, we can make contact with the classical models of ion hydration proposed by Frank−Wen and Samoilov. Water molecules in the immediate vicinity of an ion always give a negative contribution to its partial molar volume. The first hydration shell makes a negative contribution to the partial molar compressibility for the ions classified with the “positive hydration” in terms of Samoilov's model and does the opposite contribution for those with the “negative hydration”. The reason the water structure around a negatively hydrated ion is more compressible is explained in terms of density fluctuations around the ions from a viewpoint of the Landau fluctuation formula for the thermodynamic response functions.

Comment on “Measurements of the hydration numbers for halide ions by the mass spectrometric method of field evaporation of ions out of solution” [Chem. Phys. Lett. 242 (1995) 390

It has been suggested by Dunsyuryun, Karpov and Morozov that two different terms should be used to describe the solvation of halide ions in aqueous solutions. The term co-ordination number gives the primary `solvation number' (ca. 6), whilst the term hydration number gives the number of water molecules that stay co-ordinated to the anions as they move through the liquid (ca. 2). Here it is suggested that since these two terms are widely used to mean the same thing, it is better not to change one of them. It is also suggested that the number of water molecules that move with ions is variable and ill defined and that it is not appropriate to specify a precise number for this.

On the possible solvation of tetraalkyl-ammonium cations and tetraphenyl-boron anions by water

Evidence of the extent of hydration of halide ions in aqueous solutions is discussed, and it is concluded that a primary solvation number of ca. 6 is correct. A recent suggestion that two different ways of describing this interaction, namely the '‘hydration number’' ca. 2–3, and the '‘coordination number’' ca. 6, does not seem to be desirable. It is suggested that neither R4N+ nor BPh4- ions are actively solvated in water. Instead, the vibrational spectral changes often associated with these ions are interpreted in terms of changes in the concentration of free O–H groups. These changes are caused by active solvation of the gegen ions.

Effective radii of alkali halide ions in aqueous solutions, crystals and in the gas phase and the interpretation of stokes radii

The effective radii of alkali halide ions have been evaluated from data on ion-water internuclear distances and equilibrium interionic distances in crystals and in the gas phase. The Stokes radius of an ion has been shown to be equal to the product of the effective molecular radius of water and the ratio of the coefficient of viscosity of water adjacent to the ions to that of pure water. The Stokes radius of a water molecule has been found to be the same as its (intrinsic) radius.

Hydrogen-Bonded Complexes between Chloral Hydrate and Halide Ions in Aqueous Solution

AbstractThe hydrogen-bonded interactions of chloral hydrate and halide ions have been investigated conductometrically at 25.00 °C in aqueous solutions. In spite of the strong competing effect of water, the 1:1 associates have relatively high stability constants, in the order of chloride > bromide > fluoride ≃ iodide. The rather low stability of the fluoride:chloral hydrate associate can be explained by the strong hydration of the small fluoride ion. Although the 1:1 association dominates, other stoichiometries cannot be excluded; the cations and the ionic strength seem to have no effect.

Spectrophotometric investigations of binary and ternary complexes of Cd(II), methylthiourea and halide ions in aqueous solution

The results of spectrophotometric investigations of mixed-complex formation equilibria of Cd(II), methylthiourea (MeTU) and halide ions (Cl −, Br − and I −) in aqueous solution have been reported. The formation of binary and ternary complexes has been found. The values of the equilibrium constants (log units) for the reaction MA 2+MB 2⇌2MAB, are 1.03±0.10, 1.17±0.12 and 1.34±0.08 for [CdMeTUCl] +, [CdMeTUBr] + and [CdMeTUI] +, respectively. It was found that the stability of ternary complexes depends on the values of the normal redox potential of halide ions.

One-electron reduction of halothane and formation of halide ions in aqueous solutions

Formation of Br − and, under certain conditions also F − ions has been observed in the radiation chemically induced one-electron reduction of the anesthetic halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) in aqueous solutions. The initial step is the release of Br − and formation of the 2-chloro-1,1,1-trifluoroethyl radical. The latter can react via competing pathways including H-atom abstraction, addition of molecular oxygen and further reduction by an antioxidant. All of these three competitive routes lead to different product patterns. High yields of F − ions are observed under anaerobic conditions in the presence of antioxidants such as ascorbate, propylgallate, etc. The fluoride elimination is strongly pH-dependent and seems to occur in various steps after initiation through reduction of the (CF 3CHCl) radical. The implication for biochemical studies on the metabolism of halothane under different oxygen concentrations is discussed.

The corrosion and passivation of iron in the presence of halide ions in aqueous solution

The anodic dissolution behaviour of iron in halide solutions has been studied with both stationary and rotating electrodes. With stationary electrodes active dissolution kinetics are observed, whereas with rotation a pronounced active/passive transition occurs. A distinct pitting potential ( E c ) was noted in each solution, the value of E c increasing in the order I>Br>Cl>F. Halide ion concentration and electrode velocity did not have any effect on the value of E c , indicating that the kinetics of pit initiation are independent of mass-transfer effects. During anodic dissolution at potentials more regative than E c , an inhibiting effect was noted, the degree of which depended on the atomic radius of the anion. A model is suggested which involves three electrode reactions of iron with the electrolyte: (1) Active dissolution involving the well-known FeOH + (ads) rate-determining step. (2) Above the passivation potential, increased reaction of the metal surface with hydroxyl ions causes passivation due to the enhanced access of OH − to the surface and accelerated removal of solvated protons caused by rotation and a thinning of the diffusion layer. (3) At the pitting potential, direct reaction of the metal with electro-adsorbed halide ions produces pit initiation and growth by a complex ion formation reaction not possible at lower electrode potentials.

The corrosion and passivation of iron in the presence of halide ions in aqueous solution

The anodic dissolution behaviour of iron in halide solutions has been studied with both stationary and rotating electrodes. With stationary electrodes active dissolution kinetics are observed, whereas with rotation a pronounced active/passive transition occurs. A distinct pitting potential ( E c ) was noted in each solution, the value of E c increasing in the order I>Br>Cl>F. Halide ion concentration and electrode velocity did not have any effect on the value of E c , indicating that the kinetics of pit initiation are independent of mass-transfer effects. During anodic dissolution at potentials more negative than E c , an inhibiting effect was noted, the degree of which depended on the atomic radius of the anion. A model is suggested which involves three electrode reactions of iron with the electrolyte: (1) Active dissolution involving the well-known FeOH + (ads) rate-determining step. (2) Above the passivation potential, increased reaction of the metal surface with hydroxyl ions causes passivation due to the enhanced access of OH − to the surface and accelerated removal of solvated protons caused by rotation and a thinning of the diffusion layer. (3) At the pitting potential, direct reaction of the metal with electro-adsorbed halide ions produces pit initiation and growth by a complex ion formation reaction not possible at lower electrode potentials.

Determination of halide ions by cathodic stripping analysis

The determination of halide ions in aqueous solution by cathodic stripping analysis is discussed. It is shown that a linear response is obtained over the concentration range 2 × 10 −5−10 −3 M for solutions containing only a single halide and that mixtures of halides can usually be analysed. Other interferences are also considered.

Concentration dependence of chemical shifts and hydration of some halide ions in aqueous solutions

Concentration dependence of chemical shifts and hydration of some halide ions in aqueous solutions