Application of localized reactivity index in combination with periodic DFT calculation to rationalize the swelling mechanism of clay type inorganic material

Clays are layered alumino-silicates. Clays swell and expand in aqueous solution. This property governs the usage of these materials in synthesis of nano-composites and is a source of many of its catalytic applications. We used both localized and periodic calculations within the realm of density functional theory (DFT) on a series of monovalent (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺), and divalent (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) cations, to monitor their effect on the swelling of clays. The activity order obtained for the exchangeable cations among all the monovalent and divalent series studied is: Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺ > K⁺. We have studied two types of clays, montmorillonite and beidellite, with different surface structures and with/without water using periodic calculations. We have calculated the layer spacing at the first, second and third hydration shells of exchangeable cation, to compare with the experimentald-spacing values to correlate with humidity. A novel quantitative scale is proposed in terms of the intermolecular relative nucleophilicity of the active cation sites in their hydrated state through Fukui functions using hard-soft acid base (HSAB) principle. Finally, a swelling mechanism is proposed. This is a unique study where a combination of periodic and localized calculations has been performed to validate the capability of reactivity index calculations in material designing.     

Formability and properties of self-standing clay film by montmorillonite with different interlayer cations

Influences of exchangeable interlayer cations were investigated on self-standing film formability, film morphology, and properties of the clay films such as flexibility and gas barrier property. Ion-exchanged montmorillonite samples were prepared by a cation exchange from naturally bearing cation, mostly Na⁺, to Li⁺, Mg²⁺, Ca²⁺, Al³⁺, and Fe^{2+, 3+}. Self-standing films were prepared from aqueous colloidal dispersions of these montmorillonite samples with no additives. The montmorillonite samples with monovalent or divalent cation formed flat self-standing films while the Al-montmorillonite sample produced a distorted film. The Fe-montmorillonite sample formed many separated reddish-brown rod-shaped pieces. Clay film microstructures were different with interlayer cations. The films with monovalent interlayer cations were constructed by the stacking of units with delicately waved thin clay sheets in the whole film, but other films show different morphologies between the upper side and lower side; the upper side is laminated with thin sheets; the lower side is laminated with large thick sheets.The self-standing films’ flexibility and gas barrier property differed according to the interlayer cations. These properties were good in cases of samples with monovalent cations. The innumerable short wave and sheet thinness are considered to foster good flexibility and gas barrier properties. The differences in film formability and properties of the films are attributable to different swellability among samples with different interlayer cations. The montmorillonite samples with monovalent cations swell sufficiently by water, but those with polyvalent cations swell poorly. In the latter case, clay crystals aggregate in water, then the aggregate grows into large particles, creating a film with large particles.     

Affinity capillary electrophoresis employed for determination of stability constants of antamanide complexes with univalent and divalent cations in methanol

Affinity capillary electrophoresis (ACE) and pressure‐assisted ACE were employed to study the noncovalent molecular interactions of antamanide (AA), cyclic decapeptide from the deadly poisonous fungus Amanita phalloides, with univalent (Li⁺, Na⁺, K⁺, and NH₄⁺) and divalent (Mg²⁺ and Ca²⁺) cations in methanol. The strength of these interactions was quantified by the apparent stability constants of the appropriate AA‐cation complexes. The stability constants were calculated using the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of AA on the concentration of the above ions in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, pH_MeOH 7.8, containing 0–50 mM concentrations of the above ions added in the form of chlorides). Prior to stability constant calculation, the AA effective mobilities measured at actual temperature inside the capillary and at variable ionic strength of the BGEs were corrected to the values corresponding to the reference temperature of 25°C and to the constant ionic strength of 10 mM. From the above ions, sodium cation interacted with AA moderately strong with the stability constant 362 ± 16 L/mol. K⁺, Mg²⁺, and Ca²⁺ cations formed with AA weak complexes with stability constants in the range 37–31 L/mol decreasing in the order K⁺ > Ca²⁺ > Mg²⁺. No interactions were observed between AA and small Li⁺ and large NH₄⁺ cations.     

CO<Subscript>2</Subscript> adsorption and dehydration behavior of LiNaX,KNaX, CaNaX and CeNaX zeolites

In this study, NaX synthetic zeolite was modified by following the conventional cation exchange method at 70°C. 82, 81, 79 and 48% of sodium were exchanged with Li⁺, K⁺, Ca2⁺ and Ce3⁺, respectively. Thermal analysis data obtained by TG/DSC was used to evaluate the dehydration behavior of the zeolites. The strongest interaction with water and the highest dehydration enthalpy (ΔH) value were found for Li-exchanged form and compared with the other forms. The temperature required for complete dehydration increased with decreasing cation size (cation size: K⁺>Ce³⁺>Ca2⁺>Na⁺>Li⁺). CO₂ adsorption at 5 and 25°C was also studied and the virial model equation was used to analyze the experimental data to calculate the Henry’s law constant, K _o and isosteric heat of adsorption at zero loading Q _st. K _o values decreased with increasing temperature and the highest Qst was obtained for K rich zeolite. It was observed that both dehydration and CO₂ adsorption properties are related to cation introduced into zeolite structure.     

New ICT probes: synthesis and photophysical studies of N-phenylaza-15-crown-5 aryl/heteroaryl oxadiazoles under acidic condition and in the presence of selected metal ions

Molecular probes 6 and 7, incorporating N-phenylaza-15-crown-5 and aryl/heteroaryl oxadiazole have been designed to function as the new intramolecular charge transfer (ICT) probes. Photophysical properties have been studied under acidic condition as well as in the presence of selected metal ions, Ca²⁺, Ba²⁺, Mg²⁺, Na⁺, K⁺, and Li⁺. The changes in the ICT character of the probes, following the addition of trifluoroacetic acid, were interpreted in terms of site and degree of protonations. Based on the cation affinity, the ICT bands in both UV-vis and emission spectra experienced varying degrees of blue shifts due to removal of the aza-crown ether nitrogen from conjugation. The cation-induced spectral shifts and the stability constants revealed binding strength in the order Ca²⁺>Ba²⁺?Li⁺>Na⁺>K⁺>Mg²⁺. Competitive experiments performed in a matrix of ions also indicated superior interaction of 6 and 7 with Ca²⁺. The excited state decay profiles remained largely unperturbed in the presence of metal ions. The studied probes displayed positive solvatochromism and the Stokes shifts and excited state lifetimes increased with increasing solvent polarity. These findings can be rationalized by invoking highly polar nature of the emittive states. The chemoionophores 6 and 7 constitute potentially interesting Ca²⁺ sensitive probes due to their relatively high binding interaction for Ca²⁺ (log K_s=3.55-3.10) vis-a-vis that of biologically interfering Mg²⁺ (log K_s=1.67-1.30).     

Emanation thermal analysis study of Na-montmorillonite and montmorillonite saturated with various cations

Emanation thermal analysis (ETA) and thermogravimetry measured in the range 20–1000°C was used to characterize the thermal behaviour of Na-montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite samples prepared by saturation with cations Li⁺ , Mg²⁺ , Al³⁺ , respectively. It was confirmed that the presence of cations used for montmorillonite saturation (Li⁺ , Mg²⁺ , Al³⁺ ) influenced the thermal behaviour of the samples. The results that indicated the decrease of radon release rate corresponding to a collapse of the interlayer space between the silicate sheets after water release and the crystallization of meta-montmorillonite in the respective temperature intervals were compared. From the ETA results it followed that the thermal stability of intermediate microstructure depends on the type of exchanged cation. A mathematical model was used to evaluate the ETA data.     

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.     

An active transport mimetic system based on thioctic acid as carrier for alkaline earth metal ions

Liquid membranes incorporating thioctic acid as a carrier to mimic an active transport system for alkaline earth metals has been described. A transport cell, operating on the same principle as the Schulman Bridge was used. It has been demonstrated that such a system is capable of transporting alkaline earth metals against a proton gradient, as driving force. The potential of thioctic acid to complex and transport these metal ions particularly Mg²⁺, Ca²⁺, and Ba²⁺ was verified. Furthermore, this transport phenomenon was extended to some different barium salts (Cl^?, Br^? NO₃ ^?, and SCN^?) to determine the effect of nature of anion on the transport of the Ba²⁺ ions. The order of the transport rate was found to be Ba²⁺ > Ca²⁺ > Mg²⁺ which is inconsistent with the stability of coordination to the carboxyl group. The rate of transport of Ba²⁺ ions were found to decrease with the anion type in the order SCN^? > Br^? > NO₃ ^? > Cl^? which is related to the extent of hydration of the anions.     

New PCT probes featuring N-phenylmonoaza-18-crown-6 and aryl/pyridyl oxadiazoles: optical spectral studies of solvent effects and selected metal ions

Aryl/pyridyl oxadiazole chromophores 6, 8 and 10, carrying N-phenyl aza-18-crown-6 have been synthesized as new photo-induced charge transfer (PCT) probes. While, the absorption spectra of the hosts experienced a slight negative solvatochromism, however the emission bands were dramatically red shifted (Stokes shifts up to 178 nm) in solvents of increasing polarity. Among the metal ions tested, Li⁺, Na⁺, K⁺ and Mg²⁺ did not appreciably perturbed the optical properties of the hosts. On the other hand, Ba²⁺ and to a lesser extent Ca²⁺ induced marked blue shifts in both the absorption and emission spectra of the hosts. The magnitude of cation induced spectral blue shifts corresponded with the increasing acceptor strength of the attached aryl/pyridyl groups in the host molecules. The blue shifts and the stability constants were found to follow the order Ba²⁺ > Ca²⁺ ? Mg²⁺ > Na⁺ > Li⁺ > K⁺. Competitive experiments performed with a matrix of ions also revealed superior binding affinity of Ba²⁺ with all the hosts examined. Noteworthily, the deep yellow solution (λ_max, 386 nm) of the host 10 was completely bleached (λ_max, 320 nm), in the company of Ba²⁺ thereby allowing the naked eye detection of this ion.     

Thermal characterization of montmorillonite clays saturated with various cations

Emanation thermal analysis (ETA), thermogravimetry and high temperature XRD were used to characterize the thermal behavior during dehydration of natural Na montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite (MMT) samples saturated with different cations, i.e. Li⁺, Cs⁺, NH₄⁺, Mg²⁺ and Al³⁺. ETA results characterized radon mobility and microstructure changes that accompanied the mass loss of the samples due to dehydration on heating in air. A collapse of interlayer space between the silicate sheets after water release from the MMT samples was characterized by a decrease of the radon release rate, ΔE. Decreases in c-axis basal spacing (d ₀₀₁) values determined from XRD patterns for the different montmorillonite samples follow the sequence:

Interaction energies of histidine with cations (H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>)

The imidazol side group of histidine has two nitrogen atoms capable of being protonated or participating in metal binding. Hence, histidine can take on various metal-bound and protonated forms in proteins. Because of its variable structural state, histidine often functions as a key amino acid residue in enzymatic reactions. Ab initio (HF and MP2) calculations were done in modeling the cation (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺) interaction with side chain of histidine. The region selectivity of metal ion complexation is controlled by the affinity of the side of attack. In the imidazol unite of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity. The complexation energies with the model systems decrease in the following order: Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.     

Determination of alkali, alkaline earth and transition metal ions in UO2, ThO2 powders and sintered (Th,U)O2 pellets by ion chromatography

An ion chromatographic method has been developed for the determination of traces of Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Fe³⁺, Cu²⁺, Ni^2+, Co²⁺, Zn²⁺, Cd²⁺, Mn²⁺ in UO₂, ThO₂ powders and sintered (Th,U)O₂ pellets. This new method utilizes poly-(butadiene-maleic acid) (PBDMA) coated silica cation exchange column and mixed functionality column of anion and cation exchange to achieve the separation of alkali, alkaline earths and transition metal ions, respectively. It involves matrix separation after sample dissolution by solvent extraction with TBP (tri butyl phosphate)-TOPO (tri octyl phosphine oxide)/CCl₄. Interference of transition metal ions in the determination of alkali, alkaline earth metal ions are removed by using pyridine 2,6-dicarboxylic acid (PDCA) in the tartaric acid mobile phase. Mobile phase composition is optimized for the base line separation of alkali, alkaline earth and transition metal ions. Linear calibration graphs in the range 0.01–20 μg mL⁻¹ were obtained with regression coefficients better than 0.999. The respective relative standard deviations were also determined. Recoveries of the spiked samples are within ±10% of the expected value. The developed method is authenticated by comparison with certified standards of UO₂ and ThO₂ powders.     

SPECTROPHOTOMETRIC STUDY OF COMPLEX FORMATION BETWEEN SOME ALKALI AND ALKALINE EARTH CATIONS AND SEVERAL CONVENTIONAL (N,N), (N,O) AND (O,O) LIGANDS IN 95% ETHANOL

Abstract

The complexation of Li⁺, Na⁺, Mg²⁺ and Ca²⁺ with 1,10-phenanthroline, 2,2′-bipyridine, 1,2-phenylenediamine, 2-aminopyridine, 8-hydroxyquinoline, catechol and ethylene glycol was studied in 95% ethanol by means of a competitive spectrophotometric method using murexide as indicator. Formation constants of 1:1 conplexes were determined. In the case of all ligands used, the stability of the complexes was found to vary in the order Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺. It was found that the structure influences the formation and stability of resulting complexes. Effects of various parameters on complexation are discussed.     

Calix[4]pyrrole‐Based Heteroditopic Ion‐Pair Receptor That Displays Anion‐Modulated,Cation‐Binding Behavior

A new ditopic ion‐pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl₃. Treatment of the halide‐ion complexes of 1 with Group I and II metal ions (Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, and Ca²⁺; studied as their perchlorate salts in CD₃CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [ 1? F]^? (preformed as the tetrabutylammonium (TBA⁺) complex), little evidence of interaction with the K⁺ ion was seen. In contrast, when this same complex (i.e., [ 1? F]^? as the TBA⁺ salt) was treated with the Li⁺ or Na⁺ ions, complete decomplexation of the receptor‐bound fluoride ion was observed. In sharp contrast to what was seen with Li⁺, Na⁺, and K⁺, treating complex [ 1? F]^? with the Cs⁺ ion gave rise to a stable, receptor‐bound ion‐pair complex [Cs ?1? F] that contains the Cs⁺ ion complexed within the cup‐like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [ 1? Cl]^?. In this case, no appreciable interaction was observed with Na⁺ or K⁺. In addition, treating [ 1? Cl]^? with Li⁺ produces a tightly hydrated dimeric ion‐pair complex [ 1? LiCl(H₂O)]₂ in which two Li⁺ ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [ 1? F]^?, exposure of [ 1? Cl]^? to the Cs⁺ ion gives rise to an ion‐pair complex [Cs ?1? Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts.     

Effect of ring annelation on cations [M = H+, Li+, Na+, K+, Be2+, Mg2+, and Ca2+]…benzene interaction: A density functional theory investigation

Density functional theory calculation was carried out on cation‐π complexes formed by cations [M = H⁺, Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺] and π systems of annelated benzene. The cation‐π bonding energy of Be²⁺ or Mg²⁺ with annelated benzene is very strong in comparison with the common cation‐π intermolecular interaction, and the bonding energies follow the order Be²⁺ > Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. Similarly, the interaction energies follow the trend 1‐M < 2‐M < 3‐M for all the metal cations considered. These outcomes may be due to the weak interactions of the metal cations with C? H and the interactions of metal cations with π in addition to the nature of a metal cation. We have also investigated on all the possible substituted sites, and find that the metal ion tends to interact with all ring atoms while proton prefers to bind covalently to one of the ring carbons. The binding of metal cations with annelated benzenes has striking effect on nuclear magnetic resonance chemical shifts using the gauge independent atomic orbital method. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Chromium uptake from tricomponent solution in zeolite fixed bed

Removal of Cr³⁺,Ca²⁺,Mg²⁺ and K⁺ in equilibrium isotherms and in tricomponent solutions (Cr/Ca/K, Cr/Ca/Mg and Cr/Mg/K) were investigated in NaX and NaY packed beds at 30^∘C. The equilibrium selectivity was obtained as Cr⁺³ > Mg²⁺ > Ca²⁺≈K⁺ for zeolite NaY and Ca^{2 +}≫Cr^{3 +} > Mg^{2 +}≈K⁺ for zeolite NaX. The breakthrough curves showed sequential ion exchange where chromium ions are able to replace the competing cations. Some mass transfer parameters, such as length of unused bed and overall mass transfer coefficient, were investigated. Chromium retention was also investigated through a mass balance. Based on the breakthrough results, it was concluded that chromium-uptake mechanism was hardly influenced by the competition and interaction between the entering ions. NaY showed a higher affinity towards Cr³⁺ for both equilibrium and dynamic systems and its sites were more efficiently used in the ion exchange process. Chromium was less retained in NaX due to the high selectivity towards calcium ions.     

Estimation of Li+, K+ and Ca2+ Complexation with [12] crown-4, [15] crown-5 and [18] crown-6 Using a Na+ ISE in Dioxane-Water, Part IV*

 The (1:1) Na⁺ equilibrium constants, Ke1, of macrocyclic ethers of [12]crown-4, [12]crown-5 and [18]crown-6 were determined with a Na⁺ ISE in the presence of a second cation e.g. Li⁺, K⁺ and Ca²⁺ in dioxane/water (50/50). We estimated the (1:1) equilibrium constants, K e2 of the macrocyclic ethers with Li⁺, K⁺ and Ca²⁺ by this way. The binding selectivity of a macrocyclic ether between two cations was estimated in the same binary solvent mixture where the water hydration role is diminished. Results showed clearly the effect of macrocyclic size and cation radii in a solution. Received October 27, 1998. Revision March 22, 1999.     

Thermodynamics of cationic substitutions on titanyl hydrogen phosphate

Heterophasic substitution of Group I and Group II metal cations for hydrogen ions of titanyl hydrogen phosphate in aqueous solutions has been studied by a potentiometric method. The thermodynamic parameters of the process have been determined. The exchange constants depend on the degree of cation hydration and increase in the following orders: Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺ and Mg²⁺ < Ca²⁺ < Sr²⁺ < Ba²⁺. Our results make it possible to determine conditions for the efficient deactivation of high-salt liquid radioactive wastes and for the synthesis of stoichiometric compounds of the KTP family.     

Modification of sulfonated polyphenylquinoxaline by alkali and alkaline earth metal cations

Salts of sulfonated polyphenylquinoxaline (SPPQ) containing alkaline earth metal ions—Mg²⁺, Ca²⁺, and Ba²⁺—were synthesized. The paper considers their solubilities, the properties of solutions, and thermal stability in comparison with analogous characteristics of SPPQ salts with alkali metals. The introduction of alkaline earth metal cations into SPPQ affords soluble polymeric salts having high thermal stability. Solutions of SPPQ salts in N-methylpyrrolidone (N-MP) containing Mg²⁺, Ca²⁺, and Ba²⁺ ions do not exhibit polyelectrolyte properties, unlike solutions of SPPQ salts in which the counterions are Li⁺, Na⁺, and K⁺. Solutions of SPPQ and its salts in N-MP can be converted to water-soluble form by dialysis. This opens up new prospects for using the polymeric salts.     

Water transference through nickel hydroxide precipitate membrane

The transference of water that results from ion migration through the nickel hydroxide precipitate membrane was studied in chloride, perchlorate, nitrate, and sulphate solutions to estimate the transference number of water and the co-ion transport. In the systems of univalent anions, the moles of water transported per mole of electrons in 0.1 N solutions is almost identical to the hydration number of each anion. This water flow decreases gradually as the concentration of external solution increases, because of increase in the co-ion (cation) transport with increasing concentration of the solution. In the system of sulphate solutions the co-ion transport is remarkable, the transport number of Na⁺ ions being 0.03 in 0.01 N, 0.27 in 0.10 N, and 0.50 in 0.5 N Na₂SO₄ solution. This large co-ion transport in Na₂SO₄ solution is attributed to the partical replacement of hydroxyl groups on the membrane by SO^2?₄ ions, which then acts as a negative fixed charge. The order of the selectivity for co-ion transport is K⁺ > Na⁺ > Li⁺ > Ni²⁺ ? Mg²⁺ in sulphate solutions and also in chloride solutions, although the transport number of the cations is much smaller in chloride solution than in sulphate solution.