Effect of ion-exchanged alkali metal cations on the photolysis of 2-pentanone included within ZSM-5 zeolite cavities: a study of ab initio molecular orbital calculations

The Norrish Type I and Type II reactions in the photolysis of 2-pentanone included within the alkali metal cation-exchanged ZSM-5 zeolite have been investigated by experimental and theoretical approaches. Changes in the molecular environment of the zeolite cavities by exchanging the cations had significant effects not only on the adsorption state but also on the photochemical reactions of the ketones included within the zeolite cavities. The yields of the photolysis decreased and the ratio of the Type I/Type II reactions increased, respectively, by changing the ion-exchanged cations from Cs⁺ to Li⁺. The observed IR and phosphorescence spectra of the adsorbed ketones and the ab initio molecular orbital calculations of this host-guest system indicate that the ketones interact with two different adsorption sites, i.e. the surface OH groups and alkali metal cations, while the interaction between the ketones and cations increased by changing the cations from Cs⁺ to Li⁺. Molecular orbital calculations were also carried out and indicated that the zeolite framework promotes the delocalization of the charge density of the alkali metal cations which can modify the interaction between the adsorbed ketones and cations, resulting in significant changes in the photolysis of these ketones.     

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.     

An Imine‐Based Molecular Cage with Distinct Binding Sites for Small and Large Alkali Metal Cations

The synthesis of a cylindrical, imine‐based cage composed of two trimeric metallamacrocycles is described. The cage acts as a heterotopic receptor for alkali metal cations. The small cations Li⁺, Na⁺, and K⁺ bind to the outside of the cage with good selectivity for Li⁺, whereas the larger cations Rb⁺ and Cs⁺ are bound inside the cage to form unusual π complexes with a good selectivity for Cs⁺. Negative heterotopic cooperativity between the two binding sites is observed. The complexation of Cs⁺ is associated with a color change, which enables the cage to be used as a specific sensor for Cs⁺.     

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.     

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.     

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.     

Co‐adsorption of Cations as the Cause of the Apparent pH Dependence of Hydrogen Adsorption on a Stepped Platinum Single‐Crystal Electrode

The successful deployment of advanced energy‐conversion systems depends critically on our understanding of the fundamental interactions of the key adsorbed intermediates (hydrogen *H and hydroxyl *OH) at electrified metal–aqueous electrolyte interfaces. The effect of alkali metal cations (Li⁺, Na⁺, K⁺, Cs⁺) on the non‐Nernstian pH shift of the step‐related voltammetric peak of the Pt(553) electrode is investigated over a wide pH window (1 to 13) by means of experimental and computational methods. The co‐adsorbed alkali cations along the step weaken the OH adsorption at the step sites, causing a positive shift of the potential of the step‐related peak on Pt(553). Density functional calculations explain the observations on the identity and concentration of alkali cations on the non‐Nernstian pH shift, and demonstrate that cation–hydroxyl co‐adsorption causes the apparent pH dependence of “hydrogen” adsorption in the step sites of platinum electrodes.     

Physicochemical properties of alkali-metal exchanged type X zeolites

The changes in the physicochemical properties of a series of faujasite type X zeolites cation exchanged with K⁺, Rb⁺ and Cs⁺ have been studied by XRD, IR, thermoanalytical methods and sorption measurements. As a consequence of the enhanced scattering of X-rays by larger alkali metal cations, the percent relative intensity of the XRD peaks of cation exchanged zeolites was found to have decreased considerably. The framework IR spectra also showed analogous changes. The alkali metal exchange was found to enhance the thermal stability of the parent zeolite. The available void volume and specific surface area (obtained by low temperature nitrogen sorption) also decreased with the increase in the degree of exchange and cationic size. Equilibrium sorption capacities (298 K andP/P ₀=0.5) for water,n-hexane, cyclohexane and 1,3,5-trimethylbenzene also exhibited the same trend.NCL communication no. 6056.     

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.     

The influence of alkali metal cations on the rate of the Fe(CN)64−/Fe(CN)63− electrode process

The rate of the hexacyanoferrate redox system shows a first order dependence on the concentration of the cationic component of the supporting electrolyte. The catalytic influence of the alkali metal cations on the electrode process increases in the order Li⁺<Na⁺<K⁺～Cs⁺. The temperature dependence of the rate constant of the electrode process in KF and LiNO₃ has been measured and the results show that the activated complex is formed by the collision or association of a cation of the supporting electrolyte with the reactant anion, which may already be paired with one cation. It is suggested that this mechanism may be applicable to other electrode reactions involving highly charged species.     

Ruthenium(II)−Bipyridine/NanoC3N4 Hybrids: Tunable Photochemical Properties by Using Exchangeable Alkali Metal Cations

A series of nanoporous carbon nitrides that contained a range of alkali metal cations (M@nanoC₃N₄: M=Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) have been successfully synthesized from as‐synthesized g‐C₃N₄ by delamination with concentrated sulfuric acid, followed by neutralization with aqueous solutions of the corresponding alkali metal hydroxides. Tris(2,2′‐bipyridine)ruthenium(II) complexes, [Ru(bpy)₃]²⁺, were grafted onto the carbon nitrides in an effort to explore the physicochemical properties of the deposited [Ru(bpy)₃]²⁺, as well as its photocatalytic activity in the aerobic photooxidation of phenylboronic acid and H₂ production from aqueous media in the presence of a Pt co‐catalyst under visible‐light irradiation. Highly porous nanoC₃N₄ could significantly enhance photocatalytic activity, because of its high surface area, owing to its unique porous structure. More interestingly, the photoluminescence intensities of [Ru(bpy)₃]²⁺ complexes that were associated with M@nanoC₃N₄ increased in the presence of lighter alkali metal cations, which correlated with increased photocatalytic activities for both reactions. This study demonstrates that M@nanoC₃N₄ are fascinating supports, in which the local environment of an immobilized metal complex can be precisely controlled by varying the alkali metal cation from Li⁺ to Cs⁺.     

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.     

Calix[4]arene-based fluorescent probe and the adsorption capacity of its electrospun nanofibrous film for the cesium cation as an adsorbent

Calix[4]arene-based cation receptor 1 has been synthesised by following a multi-step synthetic procedure. The fluorescence properties of 1 upon the addition of various metal ions were investigated by fluorescence spectroscopy. As a result, it was revealed that 1 displayed dramatic quenching effect upon the exposure to Cs⁺. In contrast, no significant quenching effects were observed upon the addition of other metal ions such as Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ag⁺, Zn²⁺ and Ni²⁺. Compound 1 was also found by Job plot to form a 1:1 complex with Cs⁺. In addition, we also prepared 1-embedded electrospun nanofibrous film (NF-1) as an adsorbent for Cs⁺. NF-1 is proved to adsorb Cs⁺ effectively from an aqueous solution, indicating that it would be usefully utilised as an adsorbent to remove Cs⁺.     

Cation exchange, interlayer spacing, and thermal analysis of Na/Ca-montmorillonite modified with alkaline and alkaline earth metal ions

Na-montmorillonites were exchanged with Li⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra²⁺ and Ca²⁺. Montmorillonites with interlayer cations Li⁺ or Na⁺ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs⁺?>?Rb⁺?>?K⁺?>?Na⁺?>?Li⁺ and Ba²⁺?>?Sr²⁺?>?Ca²⁺?>?Mg²⁺. The cation exchange capacity with single ion exchange capacity illustrates that Mg²⁺ and Ca²⁺ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d ₀₀₁ depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d ₀₀₁ value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36?C84?°C), the dehydration of interlayer water and the chemical-adsorption water (47?C189?°C) and dehydration of bound water of interlayer metal cation (108?C268?°C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg²⁺-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.     

Selective Complexation of S‐block Cations with Nanotubular Silk Type Cyclopeptides: A DFT Study

Density functional theory (DFT) was used to study the interaction of alkali metal cations (Li⁺, Na⁺ and K⁺) with cyclic peptides constructed from silk type macrocycles ( Silk1, Silk2, Silk3, Silk4, Silk5 and Silk6 ). The calculated binding energies were used as a base for investigating the selectivity of the cyclic peptides in biniding to considered metals ions. The highest cation selectivity for Li⁺ compared to the other alkali metal ions was observed. The orbital nature of different interactions between the metal cations and the cyclic peptides was analyzed using NBO analysis. The main types of driving force for host‐guest interactions was investigated and it was found that the electron‐donating O offers lone pair electrons to the contacting LP* of alkali metal cations     

Synthesis of macrocyclic tetraamides derived from α-amino acids and their investigations using ESI-MS technique

Chiral α,ω-diesters react under high-pressure conditions (10 kbar) with α,ω-diamines to give chiral cyclic tetraamides of C₂-symmetry. The complexation properties of tetraamides towards alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) were estimated on the basis of ESI-MS spectra.     

Solvent effect on complexation reactions

The inclusion complexation of aromatic amines with cucurbit[6]uril (CB[6]) capped with alkali metal cations was studied spectrophotometrically. We showed that CB[6] capped with alkali metal cations forms a 1:1 inclusion complex with the aromatic amine guests (neutral organic molecules), independent of the length of guest molecules. The effects of salts on the inclusion constants of CB[6] in the presence of different alkali salts were examined and it was found that the inclusion constants increased in the order of alkali cation Cs⁺ < Na⁺ < K⁺, suggesting the interaction of amine guests with the capped alkali metal cation. Further, the structures of the inclusion complexation of aromatic amines with CB[6] were characterized by ¹H NMR measurements. Based on the results, the inclusion abilities of CB[6] capped with alkali metal cations are discussed.     

Selective substitution of alkali cations in mixed alkali glass by solid-state electrochemistry

Electrosubstitution of alkali cations in mixed-alkali glass containing both Na₂O and K₂O for other monovalent metal cations (M⁺=Li⁺, Ag⁺, and Cs⁺) was investigated using a solid-state electrochemical method. The fundamental electrolysis system consists of anode/M⁺-conducting microelectrode/glass/Na-β″-Al₂O₃/cathode, where M⁺ is substituted for the alkali metal ions in the glass under an applied electric field. Li⁺ ions attacked only Na⁺ sites, and Ag⁺ ions replaced Na⁺ sites more readily than K⁺. In contrast, Cs⁺ ions simultaneously substituted for both Na⁺ and K⁺ sites. The substitution behavior appears to depend on the difference in ionic conductivity between K⁺ and Na⁺ and the radius of the dopant. This mechanism was discussed qualitatively.     

Cations in a Molecular Funnel: Vibrational Spectroscopy of Isolated Cyclodextrin Complexes with Alkali Metals

The benchmark inclusion complexes formed by α‐cyclodextrin (αCD) with alkali‐metal cations are investigated under isolated conditions in the gas phase. The relative αCD‐M⁺ (M=Li⁺, Na⁺, K⁺, Cs⁺) binding affinities and the structure of the complexes are determined from a combination of mass spectrometry, infrared action spectroscopy and quantum chemical computations. Solvent‐free laser desorption measurements reveal a trend of decreasing stability of the isolated complexes with increasing size of the cation guest. The experimental infrared spectra are qualitatively similar for the complexes with the four cations investigated, and are consistent with the binding of the cation within the primary face of the cyclodextrin, as predicted by the quantum computations (B3LYP/6‐31+G*). The inclusion of the quantum‐chemical cation disrupts the C₆ symmetry of the free cyclodextrin to provide the optimum coordination of the cations with the ‐CH₂OH groups in C₁, C₂ or C₃ symmetry arrangements that are determined by the size of the cation.     

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