Estimation of thermodynamic and physicochemical properties of the alkali astatides: On the bond strength of molecular astatine (At2 ) and the hydration enthalpy of astatide (At- )

The recent accurate and precise determination of the electron affinity (EA) of the astatine atom At0 warrants a re-investigation of the estimated thermodynamic properties of At0 and astatine containing molecules as this EA was found to be much lower (by 0.4 eV) than previous estimated values. In this contribution we estimate, from available data sources, the following thermodynamic and physicochemical properties of the alkali astatides (MAt, M = Li, Na, K, Rb, Cs): their solid and gaseous heats of formation, lattice and gas-phase binding enthalpies, sublimation energies and melting temperatures. Gas-phase charge-transfer dissociation energies for the alkali astatides (the energy requirement for M+ At- ➔ M0  + At0 ) have been obtained and are compared with those for the other alkali halides. Use of Born-Haber cycles together with the new AE (At0 ) value allows the re-evaluation of ΔHf (At0 )g (=56 ± 5 kJ/mol); it is concluded that (At2 )g is a weakly bonded species (bond strength <50 kJ/mol), significantly weaker bonded than previously estimated (116 kJ/mol) and much weaker bonded than I2 (148 kJ/mol), but in agreement with the finding from theory that spin-orbit coupling considerably reduces the bond strength in At2 . The hydration enthalpy (ΔHaq ) of At- is estimated to be -230 ± 2 kJ/mol (using ΔHaq [H+ ] = -1150.1 kJ/mol), in good agreement with molecular dynamics calculations. Arguments are presented that the largest alkali halide, CsAt, like the smallest, LiF, will be only sparingly soluble in water, following the generalization from hard/soft acid/base principles that "small likes small" and "large likes large."

Donor Strength Determination of Anionic Ligands

14 new gold(I) NHC complexes of the type [AuX(iPr2-bimy)] (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene) have been prepared and fully characterized. These complexes and their reported analogues were used to systematically compare and rank the donating abilities of overall 34 anionic X-type donors by 13C NMR spectroscopy. Specifically, the carbene chemical shift of the iPr2-bimy ligand was found to be responsive to the ligand X spanning an overall range Δδ > 37 ppm between the strongest and weakest donor in this study.

The Ionic Composition and Chemistry of Nanopore-Confined Solutions

There is increasing interest in understanding the properties of solutions confined within nanotubes and synthetic or biological nanopores. How the ionic content of a nanopore-confined solution differs from that of a contacting bulk salt solution is of particular importance, for example, to water desalinization, industrial electrolysis, and all living systems. This paper explores ionic content, ionic interactions, and ion-transport properties of solutions confined within the 10 nm diameter pores of a synthetic polymer membrane. The membrane has a fixed negative pore-wall and surface charge due to ionizable carbonate groups. As a result, under some conditions, the nanopore-confined solution contains only cations and no anions or salt present in a contacting solution, ideal cation permselectivity. This anion- and salt-rejecting ability varies greatly with the cation of the salt, a result that is in contradiction to the prevailing model for permselectivity in nanopores. The extant model fails because it does not account for specific chemical interactions between the cation and the carbonate groups. The nature of these ion-selective interactions is discussed here.

Unipolar stroke, electroosmotic pump carbon nanotube yarn muscles

Success in making artificial muscles that are faster and more powerful and that provide larger strokes would expand their applications. Electrochemical carbon nanotube yarn muscles are of special interest because of their relatively high energy conversion efficiencies. However, they are bipolar, meaning that they do not monotonically expand or contract over the available potential range. This limits muscle stroke and work capacity. Here, we describe unipolar stroke carbon nanotube yarn muscles in which muscle stroke changes between extreme potentials are additive and muscle stroke substantially increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate is overwhelmed by a notable increase in effective ion size. Enhanced muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles.

Catalytic Activity of Alkali Metal Cations for the Chemical Oxygen Reduction Reaction in a Biphasic Liquid System Probed by Scanning Electrochemical Microscopy

Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane-based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H2 O2 detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H2 O2 , which varies systematically with the acidity of the transferred alkali metal ions in the organic phase.

Adaptable DNA-Interactive Probe Proficient at Selective Turn-On Sensing for Al3+: Insight from the Crystal Structure, Photophysical Studies, and Molecular Logic Gate

The synthesized Schiff base ligand 3-hydroxy-N'-(2-hydroxy-3-methoxybenzylidene)-2-naphthohydrazide (H₂NPV) is structurally characterized by single-crystal X-ray diffraction (XRD) and exhibits weak fluorescence in the excited state owing to the effect of excited-state-induced proton transfer (ESIPT). However, in the presence of Al³⁺, the ESIPT is blocked and chelation-enhanced fluorescence (CHEF) is induced because of complexation with the cations, resulting in turn-on emission for Al³⁺. The probe H₂NPV selectively detects Al³⁺ among the various metal ions, and the detection limit is found to be 1.70 μM. The composition and modes of complex coordination were determined by spectroscopic, theoretical studies and molecular logic gate applications. Finally, DNA binding studies were performed by spectroscopic and calorimetric methods to elucidate possible bioactivity of H₂NPV.

Adaptable DNA-Interactive Probe Proficient at Selective Turn-On Sensing for Al3+: Insight from the Crystal Structure, Photophysical Studies, and Molecular Logic Gate

The synthesized Schiff base ligand 3-hydroxy-N'-(2-hydroxy-3-methoxybenzylidene)-2-naphthohydrazide (H2NPV) is structurally characterized by single-crystal X-ray diffraction (XRD) and exhibits weak fluorescence in the excited state owing to the effect of excited-state-induced proton transfer (ESIPT). However, in the presence of Al3+, the ESIPT is blocked and chelation-enhanced fluorescence (CHEF) is induced because of complexation with the cations, resulting in turn-on emission for Al3+. The probe H2NPV selectively detects Al3+ among the various metal ions, and the detection limit is found to be 1.70 μM. The composition and modes of complex coordination were determined by spectroscopic, theoretical studies and molecular logic gate applications. Finally, DNA binding studies were performed by spectroscopic and calorimetric methods to elucidate possible bioactivity of H2NPV.

Solution chemistry in the surface region of aqueous solutions

Solution chemistry is commonly regarded as the physical chemistry of reactions and chemical equilibria taking place in the bulk of a solvent, and between solutes in solution, and solids or gases in contact with the solution. Our knowledge about such reactions and equilibria in aqueous solution is very detailed such as their physico–chemical constants at varying temperature, pressure, ionic medium and strength. In this paper the solution chemistry in the surface region of aqueous solutions, down to ca. 10 Å below the water–air interface, will be discussed. In this region, the density and relative permittivity are significantly smaller than in the aqueous bulk strongly affecting the chemical behaviour of solutes. Surface sensitive X-ray spectroscopic methods have recently been applicable on liquids and solutions by use of liquid jets. This allows the investigation of the speciation of compounds present in the water–air interface and the surface region, a region hardly studied before. Speciation studies show overwhelmingly that neutral molecules are accumulated in the surface region, while charged species are depleted from it. It has been shown that the equilibria between aqueous bulk, surface region, solids and/or air are very fast allowing effective transport of chemicals over the aqueous surface region.

Effects of fixed charge group physicochemistry on anion exchange membrane permselectivity and ion transport

Understanding the effects of polymer chemistry on membrane ion transport properties is critical for enabling efforts to design advanced highly permselective ion exchange membranes for water purification and energy applications. Here, the effects of fixed charge group type on anion exchange membrane (AEM) apparent permselectivity and ion transport properties were investigated using two crosslinked AEMs. The two AEMs, containing a similar acrylonitrile, styrene and divinyl benzene-based polymer backbone, had either trimethyl ammonium or 1,4-dimethyl imidazolium fixed charge groups. Membrane deswelling, apparent permselectivity and ion transport properties of the two AEMs were characterized using aqueous solutions of lithium chloride, sodium chloride, ammonium chloride, sodium bromide and sodium nitrate. Apparent permselectivity measurements revealed a minor influence of the fixed charge group type on apparent permselectivity. Further analysis of membrane swelling and ion sorption, however, suggests that less hydrophilic fixed charge groups more effectively exclude co-ions compared to more hydrophilic fixed charge groups. Analysis of ion diffusion properties suggest that ion and fixed charge group enthalpy of hydration properties influence ion transport, likely through a counter-ion condensation, ion pairing or binding mechanism. Interactions between fixed charge groups and counter-ions may be stronger if the enthalpy of hydration properties of the ion and fixed charge group are similar, and suppressed counter-ion diffusion was observed in this situation. In general, the hydration properties of the fixed charge group may be important for understanding how fixed charge group chemistry influences ion transport properties in anion exchange membranes.

Aqueous Cathodic Exfoliation Strategy toward Solution-Processable and Phase-Preserved MoS2 Nanosheets for Energy Storage and Catalytic Applications

The production of MoS₂ nanosheets by electrochemical exfoliation routes holds great promise as a means to access this two-dimensional material in large quantities for different practical applications. However, the use of electrolytes based on synthetic organic salts and solvents, as well as issues related to the unwanted oxidation and/or phase transformation of the exfoliated nanosheets, constitute significant obstacles that hinder the industrial adoption of the electrochemical approach. Here, we introduce a safe and sustainable method for the cathodic delamination of MoS₂ that makes use of aqueous solutions of very simple and widely available salts, mainly KCl, as the electrolyte. Combined with an appropriate biomolecule-based solvent transfer protocol, such an electrolytic exfoliation route is shown to afford colloidally dispersed, oxide-free, and phase-preserved MoS₂ nanosheets of high structural quality in considerable yields. The mechanisms behind the efficient aqueous delamination of the bulk MoS₂ cathode are also discussed and rationalized on the basis of the penetration of hydrated cations from the electrolyte between its layers and the immediate reduction of the accompanying water molecules. An asymmetric supercapacitor assembled with a cathodic MoS₂ nanosheet-single walled carbon nanotube hybrid as the positive electrode and activated carbon as the negative electrode delivered energy densities (e.g., 26 W h kg^-1 at 750 W kg^-1 in 6 M KOH) that were competitive with those of other MoS₂-based asymmetric devices. When used as a catalyst for the reduction of nitroarenes, the present cathodically exfoliated nanosheets exhibited one of the highest activities reported so far with MoS₂ nanostructures, the origin of which is accounted for as well. Overall, by facilitating access to this two-dimensional material through a particularly simple, efficient, and cost-effective technique, these results should expedite the practical implementation of MoS₂ nanosheets in energy storage, catalysis, and beyond.

Theoretical study on the ability of bicyclic cryptands to separate alkali-metal isotopes by ion exchange

Cryptand [2.2.2] collects heavier isotope ¹³⁷Cs more readily than [3.2.2] that gives a potential minimum at d = d_e.

Unveiling Cs-adsorption mechanism of Prussian blue analogs: Cs+-percolation via vacancies to complete dehydrated state

Metal hexacyanoferrates (MHCF) or Prussian blue analogs are excellent Cs⁺-adsorbents used for radioactive Cs-decontamination. However, the adsorption mechanism is controversial. To clarify the issue, we quantitatively investigated the Cs-adsorption behaviors of potassium copper hexacyanoferrate (KCuHCF) and A_yCu[Fe(CN)₆]_1−x·zH₂O. To obtain samples having homogeneous chemical composition and particle size, flow systems were used for both synthesis and purification. After sufficient rinsing with water, the range of x stable in aqueous solution in time appropriate for Cs-adsorption was 0.25 < x < 0.50. The relations y = 4 − 2x and z = 10x were also found independent of x, indicating complete dehydration of K⁺ in the crystal. We concluded that the excellent Cs-selectivity of MHCF was not due to difference in free energy of the adsorbed state between K⁺ and Cs⁺ but because of the hydrated state in aqueous solution. We also found that the guiding principle for determining the maximum capacity depended on the chemical composition. In particular, for the range 0.25 < x < 0.35, we propose a new model to understand the suppression of the maximum capacity. In our model, we hypothesize that Cs⁺ could migrate in the crystal only through [Fe(CN)₆]⁴⁻ vacancies. The model reproduced the observed maximum capacity without fitting parameters. The model would also be applicable to other MHCFs, e.g. a little adsorption by soluble Prussian blue. The ion exchange between Cs⁺ and H⁺ occurred only when the implemented K⁺ was small.

Cs⁺ adsorption selectivity caused by hydration energy and percolation theory to evaluate the ion-exchangeable site ratio.