Kosmotropic and chaotropic behavior of hydrated ions in aqueous solutions in terms of expansibility and compressibility parameters

Hydrated ions have fundamental applications in chemical and biological processes. Kosmotropic and chaotropic nature of hydrated ions affect the water structure in solutions depending upon their hydrophobicity or hydrophilicity nature. In present study Kosmotropic and chaotropic behavior of hydrated ions have been explained in terms of volumetric and acoustic parameters like apparent molar volume (V_ϕ), expansibility and compressibility factors for aqueous electrolytic solutions provide useful information about interactions among ions and water molecules. Results of V_ϕ showed that SO₄²⁻ ions due to stronger H-bonding with water molecules are termed as kosmotropes while Cl⁻ and HCO₃^– are chaotropes due to their weaker H-bonding with water molecules. More compressible structure of solutions in the presence of SO₄²⁻ ions indicated its kosmotropic behavior and comparatively less compressible structure of solutions in the presence of Cl⁻¹ and HCO₃^– ions renders them chaotropes. Results obtained from expansibility factor showed the dominance of electrostatic interactions over hydrophobic hydration of ions at higher temperatures. Greater values of expansibility factor for SO₄²⁻ ions as compared to Cl⁻¹ and HCO₃^– ions renders them kosmotropic ion while later are termed as chaotropes. Hence, thermo-acoustic parameters could be effectively used to describe the hydrogen bonding character of ionic solutions in terms of kosmotropic and chaotropic behavior of solutions.     

The Role of Substitutional Defects in Order/Disorder Phenomena of OH− Ions in Hydroxyapatite

We report on density functional quantum mechanical calculations of hydroxyapatite. The central focus is dedicated to the local arrangement of hydroxide ions in proximity of defects originating from substituting OH^? by F^? or O^2? ions. At ambient conditions the preferred structure of bulk hydroxyapatite exhibits an ordering of OH^? ions oriented in rows along the [001] direction. From zero Kelvin geometry optimizations the orientation inversion of a hydroxide ion was found to be disfavored by 0.165 eV. This picture changes dramatically when replacing one of the OH^? ions by a fluoride ion. The preferred hydroxide ion arrangement next to the F^? defect was identified as an OH^?··F^?··HO^? constellation, which implies the orientation inversion of one of the neighboring hydroxide ions. An analogous phenomenon was observed for O^2? defects.     

Effect of Cs+ ions on the electrochemical nanogravimetric response of platinum electrode in acid media

Platinum electrodes have been investigated in sulfuric acid solutions in the presence and absence of Cs⁺ ions by electrochemical quartz crystal nanobalance (EQCN). An unusual potential dependence of the quartz crystal frequency response has been observed in the presence of Cs⁺ ions. The frequency decrease is more pronounced in the region of the underpotential deposition of hydrogen, and the frequency decrease in the double layer region diminishes as the concentration ratio of Cs⁺ and H⁺ ions increases. After immersion in Cs₂SO₄ solutions the frequency change was higher than that expected taking into account the density and viscosity. The effects observed can be explained by the specific adsorption of Cs⁺ ions on the Pt surface, which competes with the hydrogen adsorption. At more positive potentials than the potential of zero charge (pzc) a desorption of the Cs⁺ ions starts. In this potential region both Cs⁺ and HSO₄^? ions are adsorbed at the platinum surface. In the double layer region the mass change caused by the desorption of Cs⁺ ions and the starting adsorption of sulfate ions compensates each other.     

Desorption due to charge exchange in low-energy collisions of organofluorine ions at solid surfaces

Collisions of organofluorine ions at a metal surface result in efficient emission of adsorbate species as gas-phase ions. The experiments are done at 120° scattering angle in a hybrid (BQ) mass spectrometer; the primary ions, mass-selected by a magnetic sector (B), are allowed to collide with a target at a selected kinetic energy in the tens of eV range and the emitted ions are mass-analyzed using a quadrupole mass filter (Q). It is proposed that the impinging ions undergo neutralization accompanied by desorption of hydrocarbon ions and that the amount of internal energy deposited in the desorbed ions is strongly dependent on the collision energy and affects their degree of fragmentation. Competing processes include reflection and fragmentation of the colliding particle, along with such ion/adsorbate reactions as hydrogen atom abstraction by the fluorinated ion. Small even-electron ions, such as [CHF₂]⁺ and [C₂H₂F]⁺ are more effective in promoting chemical sputtering of the surface adsorbate as compared to larger ions (e.g. [C₃F₅]⁺) and odd-electron ions (e.g. [C₂F₄]⁺˙ and [C₂HF₂]⁺˙). At low energies some odd-electron fluorinated ions undergo collision without any secondary ions being emitted from the surface. In these cases the parent ions are apparently neutralized, but without sufficient energy transfer to cause hydrocarbon ion desorption. Non-fluorinated organic ions yield fragment ions and ion/surface reaction products under the condition of these experiments, but do not cause significant desorption of hydrocarbon ions.     

Isomerization and fragmentation of methylfuran ions and pyran ions in the gas phase

The mutual interconversion of the molecular ions [C₅H₆O]⁺ of 2-methylfuran (1), 3-methylfuran (2) and 4H-pyran (3) before fragmentation to [C₅H₅O]⁺ ions has been studied by collisional activation spectrometry, by deuterium labelling, by the kinetic energy release during the fragmentation, by appearance energles and by a MNDO calculation of the minimum energy reaction path. The electron impact and collisional activation mass spectra show clearly that the molecular ions of 1–3 do not equilibrate prior to fragmentation, but that mostly pyrylium ions [C₅H₅O]⁺ arise by the loss of a H atom. This implies an irreversible isomerization of methylfuran ions 1 and 2 into pyran ions before fragmentation, in contrast to the isomerization of the related systems toluene ions/cycloheptatriene ions. Complete H/D scrambling is observed in deuterated methylfuran ions prior to the H/D loss that is associated with an iostope effect k_H/k_D = 1.67–2.16 for metastable ions. In contrast, no H/D scrambling has been observed in deuterated 4H-pyran ions. However, the loss of a H atom from all metastable [C₅H₅O]⁺ ions gives rise to a flat-topped peak in the mass-analysed ion kinetic energy spectrum and a kinetic energy release (T₅₀) of 26 ± 1.5 kJ mol^?1. The MNDO calculation of the minimum energy reaction path reveals that methylfuran ions 1 and 2 favour a rearrangement into pyran ions before fragmentation into furfuryl ions, but that the energy barrier of the first rearrangement step is at least of the same height as the barrier for the dissociation of pyran ions into pyrylium ions. This agrees with the experimental results.     

Substitution reactions in the secondary ion mass spectrometry of N-methylpyridinium halides

Secondary ion mass spectra of N-methylpyridinium halides (C⁺X^?, where C⁺ is a pyridinium cation and X^? is a halogen anion) exhibit the C⁺ ions, a series of cluster ions ((C⁺)_n(X^?)_n–1) and, furthermore, remarkable [CX – R]⁺ ions (R = H or Me). The mechanism of the formation of [CX – R]⁺ ions was investigated by the use of deuterated compounds and B/E and B²/E constant linked-scan measurements. A possible explanation is proposed in which the ions are produced through substitution reactions between species constituting the C₂X⁺ cluster ions in the gas phase.     

A radiochemical study of the kinetics of exchange between manganese oxides and some cations in solution

The kinetics of the exchange between⁵⁶Mn-labelled manganese dioxide and cations in aqueous solution was studied by measuring the β⁻ activity acquired by the solution. The results of the exchange between a chemical γ MnO₂ and a divalent M²⁺ ion (M=Mn, Co, Cu or Zn) or a trivalent M³⁺ ion (M=Ga, Fe, In, Rh or Al) indicate a fast initial process followed by a diffusion—controlled exchange. It is assumed that M²⁺ ions exchange with Mn²⁺ ions and M³⁺ ions exchange with Mn³⁺ ions in MnO₂. The process depends on the radii of the host and substituent ions and on consideration of crystal field stabilisation energies. It seems that the γ MnO₂ studied contains more Mn³⁺ than Mn²⁺ ions. The possibility of the exchange between Mn ions and cations of a different charge cannot be ruled out. The exchange between Co²⁺ ions and MnO₂ was enhanced in presence of pyrophosphate, which stabilises Mn(III) as a complex. The fraction of Mn in different samples of MnO₂ exchanged with a given cation depends on the type and not on the surface area of the sample.     

Metastable ion study of substituted cyclopentadienylmanganese cations in the gas phase

The behavior of some substituted cyclopentadienylmanganese ions has been studied by tandem mass spectrometry. This metastable ion study showed that only C₅H₅Mn⁺ and (C₅H₄CN)Mn⁺ ions retain their nido-cluster structure (1), which is characterized by a simple metal-ligand bond cleavage. Other substituted ions, RXC₅H₄Mn⁺, rearrange to a different extent, depending on the nature of the substituent. The first rearrangement step is R radical migration to the central metal atom, leading to RMnC₅H₄X⁺-type ions (2). These ions decompose by elimination of X (for X=CO) or with formation of RMnX⁺, but further rearrangements can also occur. These are the reverse migration of R from the metal atom to the π-ligand (for R=H, Ph) and cyclopentadienyl ring expansion (for X=CH₂). Collisional activation mass spectra contained an Mn⁺ ion peak, which can indicate the existence of stable type 1 structures for most cyclopentadienylmanganese ions. Carboxyl and hydroxymethyl derivatives exist, presumably as ions of type 2. The neutralization-reionization mass spectra of RXC₅H₄Mn⁺ ions are also discussed.     

Image analysis of the spatial distribution of paramagnetic Pr3+ ions in a polymer gel by a 1H-chemical shift NMR imaging method

¹H-chemical shift NMR imaging patterns of a poly(methacrylic acid) gel containing water with paramagnetic praseodymium ions(Pr³⁺) were successfully observed, in order to elucidate spatial distribution of Pr³⁺ ions in the gel. The ¹H chemical shift of water associated with Pr³⁺ ions in the gel moves largely downfield. By analyzing these experimental results, the immersion process of Pr³⁺ ions into the network of the polymer gel was spatially clarified. Further, it is shown that the chemical shift NMR imaging method is a useful means for determining the spatial distribution of paramagnetic metal ions in polymer gels.     

The structures of [C5H5O]+ ions formed from isomers of nitrophenol in the gaseous phase

Translational energy release measurments on metastable ions are used in the comparison of the structures of isomeric ions. Metastable ions, m₂⁺, formed from m₁⁺ ions as the result of a high energy process in the ion source are compared with isomeric metastable ions formed as daughters from fragmentation of metastable m₁⁺ ions in a field. In the case of o-, m- and p-nitrophenol the structure of the [C₅H₅O]⁺ ions formed from [C₆H₅O]⁺ ions by these two independent methods is different as verified by comparison of the behaviour of [C₅H₅O]⁺ ions formed from several other compounds.     

The problem of the irreversibility of the adsoprtion of halides on platinum

The problem of the irreversibility of the adsorption of Cl^? ions on platinum has been studied by a tracer method described previously. The mobility of adsorbed Cl^? ions has been observed in the following experiments: in the exchange of adsorbed labelled Cl^? with nonlabelled dissolved Cl^? ions; in the desorption caused by the rinsing of the electrode; in the displacement of adsorbed Cl^? ions by Br^? and I^? ions; in the simultaneous adsorption of Cl^? ions and other halide ions. In the light of these results the views based on the assumption of irreversibility have been criticized.     

Effect of silver and copper ions on the decomposition of ozone in water

Features of the kinetics of ozone decomposition in water at pH 2 are studied depending on the concentration of silver and copper ions that are present. The existence of a critical concentration of metal ions (??3?6 × 10^?6 M) is established, below which ions slow the rate of ozone decomposition and above which the accelerate the process. It is concluded that the first region is due to the capture of hydroxyl and other radicals by metal ions, inhibiting the chain of ozone decomposition in water. A further increase in the concentration of ions leads to dominance of their direct interaction with molecules of ozone. A mechanism for the process is proposed and the rate constants of reaction of ozone with silver ions and copper are calculated (0.033 and 0.06 M^?1 s^?1, respectively).     

Transport properties of vanadium ions in cation exchange membranes:: Determination of diffusion coefficients using a dialysis cell

Diffusion coefficients of vanadium ions in cation exchange membranes are of interest because they allow to calculate the ion exchange across the membrane in an all vanadium redox flow battery which leads to undesired cross contamination and energy losses in the battery system. Diffusion coefficients of V²⁺, V³⁺, VO²⁺ and VO⁺₂ ions in CMS, CMV and CMX cation exchange membranes have been determined by measuring the ion exchange fluxes of these ions with H₃O⁺ ions using a dialysis cell. The experimental data are evaluated on the basis of integrated flux equations which require also ion exchange sorption equilibria obtained already in previous work. The lowest diffusion coefficients are observed in the CMS membrane for all vanadium ions. This membrane turns out to be the most suitable one for being applied in a vanadium battery since it is expected to prevent most effectively cross contamination of vanadium ions.     

Distribution of isomorphous substitutions in silicates by NMR spectroscopy

The use of spectroscopic methods permits in certain cases to investigate the relative distribution of cations and anions in silicate structures. In particular, in micas (phyllosilicates 2:1) with very heterogeneous composition, the use of multinuclear (²⁹Si, ²⁷Al, ¹H and ¹⁹F) NMR spectroscopy has demonstrated the existence of local ordering in both the tetrahedral and octahedral sheets.From the study of NMR spectra associated to OH⁻ and F⁻ ions we have concluded that: a) the Fe⁺² ions have not any preference to occupy M1 or M2 sites in the octahedral sheet of micas, b) the F⁻ ions are located in homogeneous domains composed only by F⁻ and Mg⁺² ions, and c) the Fe⁺² are in close association with OH⁻ ions. As the content in Fe⁺² and F⁻ increases Fe⁺² ions have a net tendency to cluster around the OH groups.The analysis of ²⁹Si and ²⁷Al NMR spectra showed that in the tetrahedral sheet of micas: a) each Al is surrounded by 3Si, and b) Si, Al distribution is more dispersed that imposed by Loewenstein's rule.     

The role of the solvation shell decomposition of alkali metal ions in their selective complexation by resorcinarene and its cavitand

2-Methylresorcinarene and its methylene-bridged cavitand derivative as host compounds were investigated in selective complexation of alkali metal ions as guests in methanol media by photoluminescence measurements. These host molecules possess either flexible (2-methylresorcinarene) or rigid (cavitand) molecular skeleton. The Benesi–Hildebrand method and the van't Hoff theory have been applied to determine the stability constants and the thermodynamic parameters, respectively. Considerable interactions between 2-methylresorcinarene and Li⁺ or Na⁺ ions have been observed while the rigid cavitand derivative can interact only with K⁺ or Cs⁺ ions. Neither the complexes of 2-methylresorcinarene with K⁺ or Cs⁺ nor those of the cavitand derivative with Li⁺ or Na⁺ ions are stable at room temperature in methanol media. Quantum-chemical investigations justified that only solvated Li⁺ and Na⁺ ions can form stable complexes with 2-methylresorcinarene while unsolvated K⁺ and Cs⁺ ions form stable complexes with the methylene-bridged cavitand. These results highlight that the stability of the guest solvation shell and its size could play a key role in the selectivity behaviour of host molecules.     

Diffusion coefficients of ions through ion excange membrane in Donnan dialysis using ions of different valence

Donnan dialysis with an ion exchange membrane was investigated for ions of different valence. The effective diffusion coefficients (D_e) of various kinds of ions in the membrane were obtained by fitting of the equation derived from the Nernst–Planck equation to three or more sets of experimental data for Donnan dialysis. It became apparent that the value of D_e/D_s of monovalent ions (e.g., K⁺ or Na⁺ ions) at z_A=1 and z_B=2 (feed ions are monovalent ones and driving ions are bivalent ones) remained constant at ca. 1/210 and that of bivalent ions (e.g., Ca²⁺, Cu²⁺, or Mg²⁺ ions) remained constant at ca. 1/526 where D_s denotes the diffusion coefficient of ions at infinite dilution in water calculated from the Nernst–Einstein equation, and z_A and z_B represent the valences of the feed and driving ions, respectively. D_e/D_s of monovalent ions (e.g., H⁺, K⁺, or Na⁺ ions) at z_A=2 and z_B=1 (feed ions are bivalent ones and driving ions are monovalent ones) was constant at ca. 1/23.3 and that of bivalent ions remained constant at ca. 1/58.4. It was proved that D_e/D using D_e at z_A=1 and z_B=2 was constant at 1/3.0 and that at z_A=2 and z_B=1 remained constant at 3.0 where D represents the diffusion coefficient of ions in the membrane at z_A=z_B (the valences of both feed and driving ions are equal). Therefore, it was found that a large flux of ions could be obtained using the monovalent driving ions in Donnan dialysis. On the other hand, the small flux can be obtained using bi- or higher-valent driving ions.     

Evidence for stepwise processes in the charge reversal of negative ions

Various processes during the charge reversal of the simple negative ions OH⁻, Cl^−·₂, CN⁻ and C₂H⁻ have been revealed by application of a voltage to the collision cell in the second field-free region of a VG Micromass ZAB-2F mass spectrometer. It is shown for all these ions that the two-electron stripping process required for charge reversal can take place not only in one step, but also in two steps. Moreover, for the Cl^−·₂ ions, it has been found that they can fragment to Cl⁻ ions prior to the two-electron stripping process. In the charge reversal of the OH⁻ and CN⁻ ions, some processes have been found which strongly indicate that even a one-step three-electron stripping is possible in addition to a stepwise process of two- and one-electron stripping. Many of the electron stripping processes are accompanied at some stage by fragmentation.     

A ‘turn-on’ fluorescent sensor for the selective detection of cobalt and nickel ions in aqueous media

Two newly designed turn-on fluorescein-based chemosensors are highly sensitive and selective for Co²⁺ and Ni²⁺ in both absorption and emission modes, normally difficult to achieve with these paramagnetic ions. Binding to both ions is reversible, as indicated by the bleaching of the color when the metal is extracted with EDTA. Given the difficulty of designing enhanced fluorescent sensors for paramagnetic Co²⁺ and Ni²⁺ ions, the fluorescein compounds may inspire the further development of more sophisticated sensing constructs for the detection of these ions.     

The application of ion-exchanger foils in the determination of trace amounts of some metals in water by means of the non-dispersive X-ray fluorescence method

Preliminary enrichment by means of strong acid ion-exchanger foils has been used to determine trace amounts of metals in water. The kinetics of the exchange reaction between the hydrogen ions in the cation-exchanger foil and metal ions in the solution has been studied. The time needed for the attainment of equilibrium and the values of the distribution coefficients have been determined for Fe²⁺, Zn²⁺, Pb²⁺, Ca²⁺, Cd²⁺ and Ba²⁺ ions. The metal contents in the cation-exchanger foil were determined by means of non-dispersive X-ray fluorescence. The feasibility of the method was determined on the examples of Pb, Zn and Cd ions. The method permits trace amounts of these elements to be determined above 0.01 ppm in the solution. No significant matrix effect due to the presence of Ca and Ba was found for concentration in the solution below 60 ppm.     

Green synthesis of fluorescent carbon dots from Kumquat (Fortunella margarita) for detection of Fe3+ ions in aqueous solution

In this study, kumquat was first time used for synthesizing carbon dot structures (CDs) with the hydrothermal method. These newly synthesized CDs was characterized structurally and optically. The ion sensor application of the new CDs was carried out using 20 different metal ions. It was observed that CDs have high selectivity only for Fe³⁺ ions among the metal ions studied. Detection limit for Fe³⁺ ions was calculated as 0.70 µM. The results showed that these new CDs are highly selective against Fe³⁺ ions and have a very short response time such as 0.5 min. The Fe³⁺ ions selectivity of CDs was tested on real (tap water) samples. The results exhibited that this new CDs, obtained with green synthesis from Kumquat fruit without using chemical agents in one-pot simple and economical process, can be used as fluorometric sensor for detection of Fe³⁺ ions with high selectivity and sensitivity, low detection limit and rapid response time.