Calix[4]pyrroles bearing quinolinium moiety for halide sensing in aqueous solution

Sensing of chloride in aqueous solution with high selectivity is a challenging task and has a great potential for cellular imaging and analytical applications in food chemistry. Supramolecular binding motif calix[4]pyrrole has been conjugated with a known fluorescent probe for chloride – a quinolinium dye - through conformationally flexible and rigid linkers. Effects of the supramolecular host on the properties of the fluorescent dye and vice versa have been investigated by NMR, X-ray crystallographic and spectroscopic methods. New fluorescent probes have demonstrated better binding and quenching properties towards chloride, bromide and iodide in a 1:1 water-methanol mixture as compared to free calix[4]pyrrole and the quinolinium dye.     

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.     

Structural parameters of the nearest surrounding of halide ions in the aqueous electrolyte solutions

Literature data and own experimental results on structural characteristics of the halide ions nearest surrounding in the aqueous electrolyte solutions under standard conditions has been summarized. Structural parameters like coordination number, interparticle distance, and ion association type have been discussed. It has been shown that in the halide ions series, from fluoride to iodide, the coordination number gradually increases from 6 to 8. In the same row, the coordination sphere stability decreases, this is reflected in more asymmetrical arrangement of water molecules of the nearest surrounding.     

On the electrolytic accumulation of halide ions at hanging mercury drop electrodes

The process of electrolytic accumulation of halide ions as Hg(2)X(2), at the hanging mercury drop electrode is considered theoretically. The efficiency of this process is explained by considering various chemical reactions of mercury ions with halogens, and the adsorption of Hg(2)X(2). The agreement of these considerations with experimental results obtained by other authors is found to be satisfactory.     

Stability in solution of indolium heptamethine cyanines and related pH‐sensitive systems

Relative stabilities of methanolic solutions of dyes that are potentially important for labeling of biological macromolecules with a visible‐red or near‐infrared fluorophore were evaluated in the presence of molecular oxygen under dark and light conditions.     

Reduction of nitroaromatics to arylnitrenium ions by vinyl halide cations

The title reduction of nitroaromatics ArNO(2) by vinyl halide radical cations CH(2)[double bond]CH-X(+*)(X = Cl or Br) to form arylnitrenium ions ArNH(+) involves a change in oxidation number of nitrogen from +3 to -1. This novel reaction provides a new route for the generation of arylnitrenium ions, a highly selective method for the detection of explosives in mixtures, and offers clues to the carcinogenic activity of nitroaromatics in vivo.     

Electroreduction of cerium ions on silver electrode in halide melts at 973 K

The mechanism of electroreduction of cerium ions in equimolar KCl-NaCl melt is explored at 973 K. The effect of the anionic composition of the melt on the electroreduction of cerium ions is studied. It is shown that the electrodeposition of metal cerium from halide melts on a silver electrode is the primary electrochemical process that occurs at potentials more positive than those corresponding to the supporting-electrolyte decomposition. The electroreduction of chloride complexes of cerium on a silver electrode in the melt in both steady-and non-steady-state polarization modes at rates below V ≤ 0.5 V/s is limited by the diffusion delivery; at higher polarization rates, the charge-transfer stage predominates.     

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 MA₂+MB₂⇌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.     

A highly selective and sensitive fluorescein-based chemodosimeter for Hg2+ ions in aqueous media

A new fluorescein-based chemodosimeter (II) for Hg²⁺ ion was designed and synthesized, and it displayed excellent selective and sensitive toward Hg²⁺ ion over other commonly metal ions in aqueous media. II was a colorless, non-fluorescent compound. Upon addition of Hg²⁺ to the solution of II, the thiosemicarbazide moiety of II would undergo an irreversible desulfurization reaction to form its corresponding oxadiazole (IV), a colorful and fluorescent product. During this process, the spirocyclic ring of II was opened, causing instantaneous development of visible color and strong fluorescence emission in the range of 500-600 nm. Based on the above mechanism, a fluorogenic Hg²⁺-selective chemodosimeter was developed. The fluorescence increase is linearly with Hg²⁺ concentration up to 1.0 μmol L⁻¹ with a detection limit of 8.5 × 10⁻¹⁰ mol L⁻¹ (3σ). Compared with the rhodamine-type chemodosimeter, II is more stable in aqueous media and exhibits higher sensitivity toward Hg²⁺. The findings suggest that II will serve as a practical chemodosimeter for rapid detection of Hg²⁺ concentrations in realistic media.     

Spectroscopic studies of solvated hydrogen and hydroxide ions at aqueous surfaces

Measuring the molecular properties of the surface of acidic and basic aqueous solutions is essential to understanding a wide range of important biological, chemical, and environmental processes on our planet. In the present studies, vibrational sum-frequency spectroscopy (VSFS) is employed in combination with isotopic dilution experiments at the vapor/water interface to elucidate the interfacial water structure as the pH is varied with HCl and NaOH. In acidic solutions, solvated proton species are seen throughout the interfacial region, and they alter the hydrogen bonding between water molecules in ways that reflect their depth in the interfacial region. At the higher frequencies of the OH stretch region, there is spectral evidence for solvated proton species residing in the topmost layers of the interfacial region. As reported in previous VSF studies, more strongly bound solvated proton species are observed at lower OH stretching frequencies. The solvated proton species that have stronger hydrogen bonding are similar in structure to those found in bulk acid solutions and likely reside somewhat deeper in the interfacial region. There is also evidence of OH stretching from solvated protons and relatively strong hydrogen bonding in the solvation sphere that is similar to other solvated ions. In contrast, water molecules solvating OH(-) ions show relatively weak hydrogen bonding and significantly less interfacial order. VSF spectra are acquired under multiple polarizations to provide crucial information for the interpretation of the spectra and for the determination of interfacial structure.     

Investigation of the aqueous lithium and magnesium halide systems

The solubilities of the system LiBr–MgBr₂–H₂O have been investigated at 25°C and 50°C. It is established that the system is of a simple eutonic type. Pitzer's model is used for calculating the thermodynamic functions needed for plotting the solubility isotherms of the systems LiX–MgX₂–H₂O (X=Cl, Br) at 25°C. According to calculations made, the Gibbs energy of formation of LiCl·MgCl₂·7H₂O from simple salts is _rG°_m=–2.01 kJ-mol^–1, while the value _fG°_m=–2748 kJ-mol^–1 corresponds to formation from the elements.     

A polystyrene-based membrane electrode sensitive to molybdate ions

A polystyrene-based zirconium oxide membrane has been used to determine the concentration of molybdate ions in the range 0.5-10(-3)M and pH range 7-11. The response time is about 20 sec and the electrode remains usable for at least 6 months. It can also be used as an indicator electrode for titrations involving molybdate ions. Univalent anions interfere more strongly than bivalent and multivalent anions.     

Gas-phase protonation and methyl cation transfer from methyl halide ions

The ion-molecule reactions between [CH₃X]⁺˙ [CH₃XH] ⁺, [CH₃XCH₃]⁺ ions (X = F, Cl, Br, I) and a number of nucleophiles have been studied by ion cyclotron resonance techniques. Protonation of the nucleophiles is observed to occur from both the molecular ions [CH₃]X⁺˙ and protonated species [CH₃XH]⁺ whereas dimethylhalonium ions [CH₃XCH₃]⁺ react principally by methyl cation transfer. A notable exception occurs in methyl iodide where the molecular ions [CH₃I]⁺˙ act both as proton and methyl cation donors, whereas dimethyliodonium ions are found unreactive. The results are discussed with reference to the use of alkyl halides as reagent gases in chemical ionization experiments.     

Hydrogen bonds in gas-phase clusters between halide ions and olefins

Gas-phase clustering reactions of halide ions (X- = F-, Cl-, Br-, and I-) with ethylene (C2H4) and propylene (C3H6) were studied with a pulsed electron beam mass spectrometer. Bonding energies of all cluster ions were found to be less than 10 kcal/mol, i.e., no anion-initiated polymerization of C2H4 and C3H6 took place. For the cluster F-(C2H4)n, a small gap in the binding energy is observed between n = 4 and 5 suggesting that the first shell is completed with n = 4. For larger halide ions, the bond energies for the clusters X-(C2H4)n were found to be nearly n independent. For Cl-(C3H6)n a steep decrease in binding energies was observed between n = 2 and 3 and n = 3 and 4. The structure of the cluster ions was investigated by ab initio calculations. X-(C2H4)n complexes were calculated to have hydrogen-bond geometries regardless of the identity of the halide ions, and bidentate (chelate) type geometries of X-(C3H6)1 were found.     

Three-dimensional printed knotted reactors enabling highly sensitive differentiation of silver nanoparticles and ions in aqueous environmental samples

Whether silver nanoparticles (AgNPs) persist or release silver ions (Ag⁺) when discharged into a natural environment has remained an unresolved issue. In this study, we employed a low-cost stereolithographic three-dimensional printing (3DP) technology to fabricate the angle-defined knotted reactors (KRs) to construct a simple differentiation scheme for quantitative assessment of Ag⁺ ions and AgNPs in municipal wastewater samples. We chose xanthan/phosphate-buffered saline as a dispersion medium for in situ stabilization of the two silver species, while also facilitating their extraction from complicated wastewater matrices. After method optimization, we measured extraction efficiencies of 54.5 and 32.3% for retaining Ag⁺ ions and AgNPs, respectively, in the printed KR (768-turn), with detection limits (DLs) of 0.86 and 0.52 ng L⁻¹ when determining Ag⁺ ions and AgNPs, respectively (sample run at pH 11 without a rinse solution), and 0.86 ng L⁻¹ when determining Ag⁺ ions alone (sample run at pH 12 with a 1.5-mL rinse solution). The proposed scheme is tolerant of the wastewater matrix and provides more reliable differentiation between Ag⁺/AgNPs than does a conventional filtration method. The concept and applicability of adopting 3DP technology to renew traditional KR devices were evidently proven by means of these significantly improved analytical performance. Our analytical data suggested that the concentrations of Ag⁺ ions and AgNPs in the tested industrial wastewater sample were both higher than those in domestic wastewater, implying that industrial activity might be a main source of environmental silver species, rather than domestic discharge from AgNP-containing products.     

Thermosolvatochromism of betaine dyes revisited: theoretical calculations of the concentrations of alcohol-water hydrogen-bonded species and application to solvation in aqueous alcohols

Solvatochromic data of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (RB) in aqueous methanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol at 25 degrees C were recalculated by employing a recently introduced model that explicitly considers the presence of 1:1 alcohol-water hydrogen-bonded species, ROH-W, in bulk solution and their exchange equilibria with water and alcohol in the probe solvation microsphere. The thermosolvatochromic behavior of RB in aqueous ethanol was measured in the temperature range from 10 to 60 degrees C; the results thus obtained were treated according to the same model. All calculations require reliable values of Kdissoc, the dissociation constant of the ROH-W species. This was previously calculated from the dependence of the density of the binary solvent mixture on its composition. Through the use of iteration, the volume of the hydrogen-bonded species, VROH-W, and Kdissoc are obtained simultaneously from the same set of experimental data. This approach may be potentially problematic because Kdissoc and VROH-W are highly correlated. Therefore, we introduced the following approach: (i) VROH-W was obtained from ab initio calculations, (ii) these volumes were corrected for the nonideal behavior of the binary solvent mixtures at different temperatures, (iii) corrected VROH-W values were employed as a constant in the equation used to calculate Kdissoc (from density vs binary solvent mixture composition). VROH-W calculated by the COSMO-RS solvation model fitted the density data better than those calculated by the IEFPCM model. In all aqueous alcohols, solvation by ROH-W is favored over that by the two precursor solvents. In aqueous ethanol, a temperature increase resulted in a gradual desolvation of RB, due to a decrease in the hydrogen-bonding of both components of the mixture. The microscopic polarities of ROH-W are much closer to those of the precursor alcohols.