Photophysical and photochemical processes in zeolite cavities: The effects of ion-exchanged alkalimetal cations on the excited states of xanthone and the photolysis of 2-pentanone

The characteristics properties of xanthone phosphorescence and of 2-pentanone photolysis in alkali metal cation-exchanged zeolites have been investigated to clarify the effect of the micro-environment of host-adsorbents on the photophysical and photochemical properties of guest-molecules in restricted void spaces. The enhancement of the phosphorescence yields of xanthone included in zeolites is observed by changing the exchangeablealkali metal cation from Li⁺ to Cs⁺. Simultaneously, the phosphorescence lifetimes were observed to continuously shorten by changing the cation from Li⁺ to Cs⁺. These results suggest that the external heavy-atom effect deriving from the alkali metal cations on the singlet-triplet transitions of xanthone molecules stabilized on alkali metal cations in the order of Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. The yields for the photolysis of 2-pentanone included in zeolites increase with changing the alkali metal cation from Li⁺ to Cs⁺. IR investigations of the adsorption state of 2-pentanone indicate that strength of the interaction between the alkali metal cations and 2-pentanones decreases by changing the cation from Li⁺ to Cs⁺, which results in a longer lifetime of 2-pentanone. The selectivity of propylene formation is dramatically increased by changing the cation from Li⁺ to Cs⁺. The enhanced formation of propylene is asociated with the hydrogen absorption from propyl radicals by lattice oxygen, their basicity increasing by changing the cation from Li⁺ to Cs⁺. Thus, these changes in the zeolite cavities modified by exchanging cations caused significant effects not only on the excited state but also on the following chemical reactions of ketones.     

Quantum simulation on donor and acceptor II calix[4]arene substrate and alkali metal ions: the driven inclusion

The energetic and structural optimized of a calix[4]arene with and without alkali-metal cations are presented with performance of various quantum chemical methods such as Hartree--Fock, second order Møller-Plesset perturbation theory, and density functional theory. The geometry optimizations have been carried out with the 3-21G (Li⁺--Cs⁺) and 3-21G(d,p) (Li⁺--K⁺) and the 3-21G basis sets for Cs⁺ and Rb⁺. Additional single-point energy ab initio calculations for Li⁺–K⁺ were carried out at HF/6--31G, HF/6-31G (d,p), HF/6--311G(d,p) for complexes of Li⁺ and Na⁺. The calculations were carried out to analyze the complexation of calix[4]arene with alkali metal cationic species (Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺). Assumption to isolate the effects of the aromatic core and cation-π interactions. Particular emphasis has been on conformational binding selectivity and the structural characterization of the complexes, the smaller cation as Li⁺ and Na⁺ has been placed in the lower rim's of the calix[4]arene's cavity. The large cations like K⁺, Rb⁺, and Cs⁺ take placed in upper rim and the endo (inclusive) complexation is driven by cation-π interactions, that reflect a superior interaction with two phenol rings. The endo complexation of Cs⁺ with calix[4]arene is in agreement with X-ray diffraction data. The binding modes of calixarene-cation systems are studied to involve cooperative effects between cation-π and electrostatic forces.     

Selective complexation of alkali metal ions and nanotubular cyclopeptides: a DFT study

A density functional theory based on interaction of alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) with cyclic peptides constructed from 3 or 4 alanine molecule (CyAla3 and CyAla4), has been investigated using mixed basis set (C, H, O, Li⁺, Na⁺ and K⁺ using 6-31+G(d), and the heavier cations: Rb⁺ and Cs⁺ using LANL2DZ). The minimum energy structures, binding energies, and various thermodynamic parameters of free ligands and their metal cations complexes have been determined with B3LYP and CAM-B3LYP functionals. The order of interaction energies were found to be Li⁺ > K⁺ > Na⁺ > Rb⁺ > Cs⁺ and Li⁺ > Na⁺ > K⁺ ? Rb⁺ > Cs⁺, calculated at CAM-B3LYP level for the M/CyAla3 and M/CyAla4 complexes, respectively. Their selectivity trend shows that the highest cation selectivity for Li⁺ over other alkali metal ions has been achieved on the basis of thermodynamic analysis. The main types of driving force host–guest interactions are investigated, the electron-donating O offers lone pair electrons to the contacting LP* of alkali metal cations.     

Factors Influence Complexing Selectivity of Lariat Crown Ethers Toward Alkali Metal Ions in Electrospray Ionization Mass Spectrometry

The selectivity of eight lariat crown ethers in the sym‐dibenzo‐16‐crown‐5 series toward alkali metal ions was studied with electrospray ionization mass spectrometry under different conditions. With the exception of 2g , which is equally selective toward Na⁺ and Li⁺, all other lariat crown ethers show the best selectivity toward Li⁺ in methanol. Factors that influence the selectivity include the water content, counterions, nature of the side arms, and the externally added cations. Iodide gives the best Na⁺ selectivity with R_I > R_Br > R_Cl. Increased water content profoundly increases the Na⁺ selectivity when the side arm is hydrophilic and the steric hindrance is small. Externally added cations (Cs⁺ and/or Rb⁺) enhance the Na⁺ selectivity by exchanging the smaller Li⁺ from the cavity.     

Cation transport at 25°c from binary Na+Mn+, Cs+Mn+ and Sr2+Mn+ nitrate mixtures in a H2OCHCl3H2O liquid membrane system containing a series of macrocyclic carriers

Cation fluxes from binary mixtures of either Na⁺, Cs⁺ or Sr²⁺ with other alkali metal cations, alkaline earth metal cations, and Pb²⁺ through a H₂OCHCl³H₂O bulk liquid membrane system containing one of several macrocyclic carriers have been determined Nitrate salts were used in all cases. The most selective transport of Na⁺ over all other cations studied was found with the carrier cryptand [2.2.1]. Selective transport of Na⁺ relative to Li⁺, Cs⁺ and the alkaline earth cations was found with cryptand [2.2.2B] and cryptand [2.2.2D]. The ligands 21-crown-7 and dibenzo-24-crown-8 showed selective transport of Cs⁺ over the second cation in all cases. Several macrocycles showed selectivity for Sr²⁺ over the second cation with the macrocycle 1,10-diaza-18-crown-6 showing the highest selectivity for this cation of all ligands studied. Relative fluxes from binary cation mixtures are rationalized in terms of macrocycle cavity size, donor atom type and ring substituents.     

Spectrophotometric studies of alkali and alkali earth metal ions complexes of mono amino derivative of calix[4]arene

The synthesis and complexive abilities of 5,11,17-tris(tert-butyl)-23 amino-25,26,27,28-tetra-propoxycalix[4]arene towards alkali cations Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and alkali earth cations Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ in methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed that the ligand is capable to complex with all the cations by 1: 1 metal to ligand ratios. The selectivity presented considering the calculated formation constants are in the order Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺ and Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ with the ligand.     

Synthesis and adsorption investigations of zeolites MCM-22 and MCM-49 modified by alkali metal cations

Ion exchange was made on MCM-22 and MCM-49 zeolites with different Si/Al molar ratios, with Li⁺, Na⁺, K⁺, and Cs⁺ ions and the study of the influence of alkali metal cations on CO₂ adsorption properties was performed. The degree of ion-exchange decreased for larger cations (Cs⁺) apparently due to steric hindrances. The exchange with different cations led to a decrease in the surface area and the micropore volume. Our study shows that the adsorption capacity of the tested zeolites depends significantly on the nature and the concentration of the charge-compensating cations. The highest CO₂ adsorption capacity was obtained on the MWW zeolites with the lowest Si/Al molar ratio and the Li⁺ or K⁺ cations.     

Hydration forces between mica surfaces in electrolyte solutions

The forces between two molecularly smooth mica surfaces were measured over a range of concentrations in aqueous Li⁺, Na⁺, K⁺ and Cs⁺ chloride solutions. Deviations from DLVO forces in the form of additional short-range repulsive “Hydration” forces were observed only above some critical bulk concentration, which was different for each electrolyte. These observations are interpreted in terms of the corresponding ion exchange properties at the mica surface. “hydration” forces apparently arise when hydrated cations adsorbed on mica are prevented from desorbing as two interacting surfaces approach. dehydration of the cations leads to a repulsive hydration force. A simple site-binding model was successfully applied to describe the charging behavior of interacting mica surfaces . By subtraction of the DLVO-regulation theory from the total measured force the net hydration force was obtained for mica surfaces apparently fully covered with adsorbed cations. The magnitude of this extra force followed the series Na⁺ > Li⁺ > K⁺ > Cs⁺ and, in each case, could be described by a double-exponential decay.     

Polymerization and molecular recognition in the monolayers of the surface-active derivatives of crown-ethers

The four surface-active derivatives of crown-ethers with a variety of fatty alkyl chains were synthesized and studied in monolayers at various conditions. The areas per crown-ether molecule in monolayers are increasing significantly in the presence of various alkali metal cations in the aqueous subphase. These effects can be explained as complex formation between crown-ethers in the monolayers and cations from aqueous subphase, causing a change in the conformation of the polyether ring of the molecule at the interface. This is accompanied with the change in the cation selectivity (Na⁺ > Li⁺ > K⁺ > Cs⁺) as compared with the series in volume (K⁺ > Cs⁺ > Na⁺ > Li⁺). Polymerization of the crown-ether monolayer allows to stabilize the conformation of the molecule at the interface as if tuned to the definite cation.     

Mobility of water molecules in Li+, Na+ and Cs+ ionic forms of Nafion membrane studied by NMR

Correlation times and diffusion coefficients of water molecules were measured for the first time by ¹H spin relaxation and pulsed field gradient NMR in Li⁺, Na⁺ and Cs⁺ ionic forms of Nafion 117 membrane. Hydration numbers of Li⁺, Na⁺ and Cs⁺ cations were calculated. It was shown that at high humidity macroscopic transfer is controlled by the local translational motion of water molecules.     

Selectivity ratios of cation-sensitive glass electrodes in ethanol-water mixtures

Summary The response of cation-sensitive glass electrodes to univalent cations in ethanol-water mixtures shows increasing e.m.f. values with increasing fractions of ethanol for Na⁺, K⁺, Cs⁺, Rb⁺, Li⁺, and NH₄ ⁺, but anomalous behavior for H⁺. The calculated selectivity of the glass electrode for metal ions over the hydrogen ion thus increases sharply over the range of 10–70 weight % ethanol. It is suggested that sodium rather than hydrogen ion may be adopted as the reference ion for the definition of selectivity ratios in mixed solvents.

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Zusammenfassung Die Ansprechbarkeit von kation-empfindlichen Glaselektroden auf einwertige Kationen (Na⁺, K⁺, Cs⁺, Rb⁺, Li⁺, NH₄ ⁺) in Äthanol-Wassergemischen weist mit steigendem Äthanolgehalt steigende E.M.K.-Werte auf; H⁺ zeigt ein abweichendes Verhalten. Die berechnete SelektivitÄt der Glaselektrode für Metallionen nimmt daher im Bereich von 10–70% Äthanol stark zu. Es wird empfohlen, für die Definition von SelektivitÄtsverhÄltnissen in Lösungsmittelgemischen Na⁺ an Stelle von H⁺ als Bezugsion zu verwenden.

     

Enhancement of Oxygen Evolution Activity of Nickel Oxyhydroxide by Electrolyte Alkali Cations

Herein, the effect of the alkali cation (Li⁺, Na⁺, K⁺, and Cs⁺) in alkaline electrolytes with and without Fe impurities is investigated for enhancing the activity of nickel oxyhydroxide (NiOOH) for the oxygen evolution reaction (OER). Cyclic voltammograms show that Fe impurities have a significant catalytic effect on OER activity; however, both under purified and unpurified conditions, the trend in OER activity is Cs⁺ > Na⁺ > K⁺ > Li⁺, suggesting an intrinsic cation effect of the OER activity on Fe‐free Ni oxyhydroxide. In situ surface enhanced Raman spectroscopy (SERS), shows this cation dependence is related to the formation of superoxo OER intermediate (NiOO^?). The electrochemically active surface area, evaluated by electrochemical impedance spectroscopy (EIS), is not influenced significantly by the cation. We postulate that the cations interact with the Ni?OO^? species leading to the formation of NiOO^??M⁺ species that is stabilized better by bigger cations (Cs⁺). This species would then act as the precursor to O₂ evolution, explaining the higher activity.     

Host-guest complexes of the Beer-Can-cryptand: prediction of ion selectivity by quantum chemical calculations XI

Abstract

Based on DFT calculations (B3LYP/LANL2DZp) and the application of model equations, as well as a comparison of M-N-donor length with an unstrained reference ([M(solvent)₆]ⁿ⁺), the selectivity of the alkali and alkaline earth cations (Li⁺ – Cs⁺ and Be²⁺ – Ba²⁺) for the recently synthesized cryptand bis-triazacyclononane tris-pyridyl N₉-azacryptand (Beer-Can) was investigated. The host can bind the alkali cation K⁺ best, followed by the alkaline earth cations Ca²⁺ and Sr²⁺, and by Na⁺ and Ba²⁺. This selectivity pattern is identical to the selectivity of the Lehn-type cryptand [phen.phen.phen], which suggests a similar cavity size. The good flexibility of the Beer-Can is provided by the aza-crown-like top and bottom of the “can,” and the pyridines on the “can-wall.”     

Cover Feature: Are the Accompanying Cations of Doping Anions Influential in Conducting Organic Polymers? The Case of the Popular PEDOT (Chem. Eur. J. 63/2019)

Conducting organic polymers (COPs) are made of a conjugated polymer backbone supporting a certain degree of oxidation. These positive charges are compensated by the doping anions that are introduced into the polymer synthesis along with their accompanying cations. In this work, the influence of these cations on the stoichiometry and physicochemical properties of the resulting COPs have been investigated, something that has previously been overlooked, but, as here proven, is highly relevant. As the doping anion, metallacarborane [Co(C₂B₉H₁₁)₂]⁻ was chosen, which acts as a thistle. This anion binds to the accompanying cation with a distinct strength. If the binding strength is weak, the doping anion is more prone to compensate the positive charge of the polymer, and the opposite is also true. Thus, the ability of the doping anion to compensate the positive charges of the polymer can be tuned, and this determines the stoichiometry of the polymer. As the polymer, PEDOT was studied, whereas Cs⁺, Na⁺, K⁺, Li⁺, and H⁺ as cations. Notably, with the [Co(C₂B₉H₁₁)₂]⁻ anions, these cations are grouped into two sets, Cs⁺ and H⁺ in one and Na⁺, K⁺, and Li⁺ in the second, according to the stoichiometry of the COPs: 2:1 EDOT/[Co(C₂B₉H₁₁)₂]⁻ for Cs⁺ and H⁺, and 3:1 EDOT/[Co(C₂B₉H₁₁)₂]⁻ for Na⁺, K⁺, and Li⁺. The distinct stoichiometries are manifested in the physicochemical properties of the COPs, namely in the electrochemical response, electronic conductivity, ionic conductivity, and capacitance.     

Amperometric detection studies of Nafion/indium hexacyanoferrate film for the determination of electroinactive cations in ion chromatography

An amperometric detector based on the chemical modification of Nafion and indium (III) hexacyanoferrate (II, III) thin film (Nafion/In-CN-Fe) onto a glassy carbon (GC) electrode, was first successfully used for the determination of electroinactive cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺) in single column ion chromatography (IC). A set of well-defined peaks of electroinactive cations was obtained. The detection limits of the cations are 8.9 × 10^–6 mol/L for Li⁺, 2.3 × 10^–6 mol/L for Na⁺, 5.2 × 10^–6 mol/L for K⁺, 4.8 × 10^–6 mol/L for Rb⁺, 4.0 ׶10^–6 mol/L for Cs⁺ and 5.3 × 10^–6 mol/L for NH₄ ⁺ at a single-to-noise ratio of 3. The proposed method was quick, sensitive and simple. The cations in rainwater and mineral water were successfully analyzed by this method.     

Counterion mixing effects on the conformational transitions of polyelectrolytes. II. Counterion binding as measured by NMR spectroscopy of alkali metal poly(acrylate)s

Bound states of counterions during the coil‐globule transition of poly(acrylic acid) in water/organic solvent mixtures were investigated by NMR spectroscopy of alkali metal cations (Li⁺, Na⁺, Cs⁺). Accompanying the transition, the line widths of the respective NMR peaks significantly increased with increasing the organic solvent composition in the medium. Although this line width broadening suggests that some specific counterion binding with desolvation is involved with the coil‐globule transition, the most marked broadening was observed in higher organic solvent compositions than those of the coil‐globule transition region detected by the viscometry. Namely, the specific counterion binding with desolvation proceeds even after the polymer chain collapsed. This means in turn that such a strong counterion binding is not a prerequisite for the coil‐globule transition, at least at the stage of the onset. For the Li⁺/Cs⁺ mixed counterion system in 60 vol % DMSO, where our previous conductivity data suggested that the specific counterion binding occurred only for Cs⁺ during the coil‐globule transition induced on mixing with Li⁺, a significant increase in the line width was also observed only for Cs⁺. The coincidence between the conductivity and the NMR results for the Li⁺/Cs⁺ mixed counterion system strongly supports a working hypothesis, “size‐fitting effect,” that has been proposed to determine the counterion specificity observed for the conformational transitions of polyelectrolytes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2132–2139, 2009     

Preparation of Thallium Hexacyanoferrate Film and Mixed‐Film Modified Electrodes with Cobalt(II) Hexacyanoferrate

Thallium hexacyanoferrate films have been prepared from various aqueous electrolyte solutions using consecutive cyclic voltammetry. The cyclic voltammograms recorded the direct deposition of thallium hexacyanoferrate films from the mixing of Tl³⁺ and [Fe(CN)₆]^3? ions from solutions of seven cations: Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, H⁺, and Tl⁺. An electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of the thallium hexacyanoferrate films. The thallium hexacyanoferrate film shows a single redox couple with a formal potential between +0.6 V and +1.2 V, and shows a cation effect (H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and Tl⁺). A mixed film and a two‐layered modified electrodes composed of a thallium hexacyanoferrate film with cobalt(II) hexacyanoferrate film were prepared.     

Effect of the Alkali-Metal Cations On the Protonation Constants of Myo-Inositol Hexakis(Phosphate)

Abstract

Values for the protonation constants of myo-inositol hexakis(phosphate) have been determined at 25°C and 0.1 M ionic strength by potentiometry in media containing two different concentrations of Li⁺, Na⁺, K⁺ and Cs⁺ salts.

The Alog K_yHM values, which correspond to the differences between the constants obtained with and without alkali-metal cations, are considered as being related to the binding ability of the ligand towards these cations.

Their relative behaviour is then analysed and some conclusions are drawn about the conformations which might be adopted by the complexes in different pH regions.     

Ion transport membranes based on conducting polymers

Polypyrrole membranes containing four different dopant ions were prepared galvanostatically from aqueous solutions of pyrrole (0.1 M) and the appropriate counter ion salt (0.1 M). The transport of mono-valent cations through each membrane was achieved by applying a potential gradient across the membranes. The influence of a number of set up parameters on the flux of K⁺ ions across a PPy/pTS membrane was assessed, as well as the relative selectivities of the four membrane types for the mono-valent cations; Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺.     

Cs+ and Ba2+ Selective Transport by a Novel Self-Assembled Isoguanosine Ionophore Through Polymer Inclusion and Bulk Liquid Membranes

5'-(Tert-butyldimethylsilyl)-2',3'-O-isopropylidene isoguanosine(isoG 1) serves as a selective Cs⁺ carrier in liquid membrane transport. IsoG~1 is a lipophilic nucleoside that self-assembles via hydrogen bonds and cation-dipole interactions to form a stable decamer sandwich complex with Cs⁺. Using an acidic receiving phase, Cs⁺ transport through polymer inclusion membranes (PIMs) was observed at concentrations of isoG 1 below 21 mM. When isoG 1 was precomplexed with Cs⁺ to give the (isoG 1)₁₀-Cs⁺decamer, flux was observed above 21 mM carrier. The Cs⁺ flux increased with increasing carrier concentration of the precomplexed (isoG 1)₁₀-Cs⁺ decamer. The Cs⁺ transport selectivity by isoG 1 was investigated in the presence of sodium salt solutions of high concentration. Excellent Cs⁺ flux and selectivity over the other alkali metal cations was observed in PIMs and bulk liquid membranes (BLMs). In the absence of Cs⁺, this ionophore exhibitsgood Ba²⁺ selectivity in BLMs.