A theoretical study of cation--π interactions: Li+, Na+, K+, Be2+, Mg2+ and Ca2+ complexation with mono- and bicyclic ring-fused benzene derivatives

DFT (B3LYP functional) and MP2 methods using 6-311+G(2d,2p) basis set have been employed to examine the effect of ring fusion to benzene on the cation--π interactions involving alkali metal ions (Li⁺, Na⁺, and K⁺) and alkaline earth metal ions (Be²⁺, Mg²⁺ and Ca²⁺). Our present study indicates that modification of benzene (π-electron source) by fusion of monocyclic or bicyclic (or mixture of these two kinds of rings) strengthens the binding affinity of both alkali and alkaline earth metal cations. The strength of interaction decreases in the following order: Be²⁺ > Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺ for any considered aromatic ligand. The interaction energies for the complexes formed by divalent cations are 4–6 times larger than those for the complexes involving monovalent cations. The structural changes in the ring wherein metal ion binds are examined. The distance between ring centroid and the metal ion is calculated for all of the complexes. Strained bicyclo[2.1.1]hexene ring fusion has substantially larger effect on the strength of cation--π interactions than the monocyclic ring fusion for all of the cations due to the π-electron localization at the central benzene ring.     

Sorption of strontium on Slovak bentonites

Sorption of Sr on five Slovak bentonites of deposits has been studied with the use of batch technique. In the experiments there have been used natural, chemically modified and irradiated samples, in three different kinds of grain size. The pH influence on sorption of strontium on bentonites, pH change after sorption and influence of competitive ions have been studied. Distribution ratios have been determined for bentonite–strontium solution system as a function of contact time, pH and sorbate concentration. The data have been interpreted in term of Langmuir isotherm. The uptake of Sr has been rapid and the sorption of strontium has increased by increasing pH. The percentage sorption has decreased with increasing metal concentrations. The pH value after sorption for the natrificated forms of bentonite starts already in the alkaline area and moves to the higher values. For the natural bentonites the values occur in the neutral or in the acidic area. Sorption of Sr has been suppressed by presence of competitive cations as follows: Ba²⁺ > Ca²⁺ > Mg²⁺ > NH₄ ⁺ > K⁺ > Na⁺. By sorption on natrificated samples colloidal particles and pH value increase have been formed. The bentonite exposure as a result of interaction of γ-rays has led to expansion of the specific surface, increasing of the sorption capacity and to the change in the solubility of the clay materials.     

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.     

The use of ESI-MS to probe the binding of divalent cations to calmodulin

Proteins have evolved with distinct sites for binding particular metal ions. This allows metalloproteins to perform a myriad of specialized tasks with conformations tailor-made by the combination of its primary sequence and the effect on this of the ligated metal ion. Here we investigate the selectivity of the calcium trigger protein calmodulin for divalent metal ions. This ubiquitous and highly abundant protein exists in equilibrium between its apo and its holo form wherein four calcium ions are bound. Amongst its many functions, calmodulin modulates the calcium concentration present in cells, but this functional property renders it a target for competition from other metal ions. We study the competition posed by four other divalent cations for the calcium binding sites in calmodulin using electrospray ionization mass spectrometry (ESI-MS). We have chosen two other group II cations Mg²⁺, Sr²⁺, and two heavy metals Cd²⁺, Pb²⁺. The ease with which each of these metals binds to apo and to holo CaM[4Ca] is described. We find that each metal ion has different properties with respect to calmodulin binding and competition with calcium. The order of affinity for apo CaM is Ca²⁺ ≫ Sr²⁺ ∼ Mg²⁺ > Pb²⁺ ∼ Cd²⁺. In the presence of calcium the affinity alters to Pb²⁺ > Ca²⁺ > Cd²⁺ > Sr²⁺ > Mg²⁺. Once complexes have been formed between the metal ions and protein (CaM:[xM]) we investigate whether the structural change which must accompanies calcium ligation to allow target binding takes place for a given CaM:[xM] system. We use a 20 residue target peptide, which forms the CaM binding site within the enzyme neuronal nitric-oxide synthase. Our earlier work (Shirran et al. 2005) [1] has demonstrated the particular selectivity of this system for CaM:4Ca²⁺. We find that along with Ca²⁺ only Pb²⁺ forms complexes of the form CaM:4M²⁺:nNOS. This work demonstrates the affinity for calcium above all other metals, but also warns about the ability of lead to replace calcium with apparent ease.     

Kinetic Study of Metals Sorption on a Resin Modified with Tetrakis(carboxyphenyl)Porphyrin

 The sorption of metal ions (e.g. Cd²⁺, Cu²⁺, Ni²⁺ and Pb²⁺) from aqueous solution on the anion exchange resin Amberlite IRA-904 modified with tetrakis(4-carboxyphenyl)porphyrin (TCPP) was studied in batch equilibrium experiments. The influence of operating variables such as initial pH and contact time between solution and the resin on the equilibrium parameters was measured. The selectivity order of investigated metal ions was evaluated as follows: Pb²⁺ > Ni²⁺ > Cu²⁺ > Cd²⁺. The matrix cations, such as Mg²⁺ and Ca²⁺, exhibit very low affinity for TCPP-modified resin. The rate uptake of the sorption procedure is predominantly controlled by film diffusion. The best retention kinetic was observed for lead where half the saturation of the TCPP-modified sorbent was achieved in less than 5 min. Author for correspondence. E-mail: kryspyrz@chem.uw.edu.pl Received November 20, 2002; accepted January 26, 2003 Published online May 5, 2003     

Synthesis and sorption properties of new synthesized rare-earth-doped sodium titanate

A series of rare-earth-doped sodium titanates with the chemical formula R _x H _y Na_{4 − (x+y)}TiO₄·nH₂O (where R = Ce³⁺, Nd³⁺ and Sm³⁺) were grown employing solid-state fusion reaction technique. The physico-chemical investigations indicated that the new materials were self engineered into large particles enough to be used in sorption process and having crystalline structures containing localized Na⁺ ions. Equilibrium studies revealed that an enhancement in sorption efficiency of sodium titanate after rare-earth doping. The neodymium-rich sodium titanate exhibited a better exchange affinity for Cs⁺ compared to the other studied series. Data on the kinetics of cesium exchange fit well to pseudo-second order and intra-particle diffusion models. In a separate experiment, it was reported that the R-HNaTi series showed responsible sorption affinity toward Ce, Nd and Sm ions in their solution mixture with insignificant selectivity trend which reflects the high stability of titanate matrices.     

Interaction of Cs+, Sr2+ and Gd3+ with humin

Humin is separated from a soil sample and characterized by elemental analysis, IR and potentiometric titration. These investigations indicated that humin displayed similar characteristics as humic acid. The sorption behavior of¹³⁷Cs,⁹⁰Sr and¹⁵³Gd with humin was investigated from aqueous solution. The results indicated that the sorption process follows the order: Gd³⁺≫Sr²⁺>Cs⁺. It was time dependent and increased with pH. The sorption in the presence of humic acid or EDTA showed that both form a metal-ligand complex and consequently decrease the % uptake.     

Reactivity of molecules with nitrogen-containing functional groups toward H+ and SiMe3 + ions

The equilibrium constants of trimethylsilyl cation transfer reactions differ from those of proton transfer reactions by many orders of magnitude. The basicity of MeCN (1), MeNO₂ (2), and Et₂NH (3) in the gas phase decreases in the series3≫1>2, whereas the affinity of the same compounds for trimethylsilyl cation decreases in the series1≫3≈2. Semiempirical quantum-chemical MNDO calculations indicate that the formation of MeCN·SiMe₃ ⁺ ions is thermodynamically more favorable than that of MeNH₂·SiMe₃ ⁺ ions. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1260–1261, June, 1998.     

Affinity and removal of radionuclides mixture from low-level liquid waste by synthetic ferrierites

The affinity and removal efficiency of ¹³⁷Cs⁺, ¹³³Ba²⁺, ⁸⁵Sr²⁺ and ²⁴¹Am³⁺ mixture from aqueous solutions using two synthetic ferrierites HSZ 700KOA and 700KOD commercially used as a catalyst in oil industry were investigated. The uptake of metal ions as a function of different parameters has been studied using batch equilibrium technique. Kinetic curves showed that the equilibrium was mostly reached within 45 min for Cs⁺ and Ba²⁺ and revealed to be longer for Sr²⁺ and Am³⁺. Using Freundlich and Langmuir adsorption isotherms, the results showed that the affinity and adsorption capacity of 700KOA and 700KOD follow the order: Cs⁺ > Ba²⁺ > Sr²⁺ > Am³⁺ with higher values for first material. Both adsorbents exhibited significant high capacity for Cs⁺ relative to other cations giving q _max 1.97 and 1.78 mmol g⁻¹ for 700KOA and 700KOD, respectively. All metals uptake found to be concentration dependant and independent of the pH over 2 to 10 range except Am³⁺; this reveals that the adsorption mechanism is controlled mainly by pure ion exchange reaction for Cs⁺, Ba²⁺, Sr²⁺ and by surface complexation mechanism for Am³⁺. These simple nontoxic materials are recommended to be used for radioactive waste treatment especially fission product ¹³⁷Cs and activation product ¹³³Ba.     

Spectrophotometric study of complexation of dibenzopyridino-18-crown-6 with some transition and post-transition metal ions in DMSO solution using murexide as a metallochromic ligand

The complexation reaction of dibenzopyridino-18-crown-6 (DBPY 18C6) with Co²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Hg²⁺, and Ag⁺ have been studied in DMSO at 25°C by the spectrophotometric method. Murexide was used as a competitive colored ligand. The stoichiometry of metal ion-murexide and metal ions with DBPY18C6 complexes were estimated by mole ratio and continuous variation methods and emphasized by the KINFIT program. The stoichiometry of all the complexes was found to be 1: 1 (metal ion/ligand). The order of stability constants for the obtained metal ion-murexide complexes (1: 1) varies in the order Cu²⁺ > Cd²⁺ > Co²⁺ ∼ Pb²⁺ > Zn²⁺ > Ag⁺ > Hg²⁺. This trend shows that the transition metal ions clearly obey the Irving-Williams role. For the post-transition metal ions, the ionic radius and soft-hard behavior was the major affects in varying of this order. The dibenzopyridino-18-crown-6 complexes with the used metal ions vary as Ag⁺ > Pb²⁺ > Cu²⁺ > Cd²⁺ > Hg²⁺ > Zn²⁺ > Co²⁺. The article is published in the original.     

Sorption of cesium from water solutions on potassium nickel hexacyanoferrate-modified <Emphasis Type="Italic">Agaricus bisporus</Emphasis> mushroom biomass

In order to gain biosorbent that would have the ability to bind cesium ions from water solution effectively, potassium nickel hexacyanoferrate(II) (KNiFC) was incorporated into the mushroom biomass of Agaricus bisporus. Cesium sorption by KNIFC-modified A. bisporus biosorbent was observed in batch system, using radiotracer technique using ¹³⁷Cs radioisotope. Kinetic study showed that the cesium sorption was quite rapid and sorption equilibrium was attained within 1 h. Sorption kinetics of cesium was well described by pseudo-second order kinetics. Sorption equilibrium was the best described by Freundlich isotherm and the distribution coefficient was at interval 7,662–159 cm³ g⁻¹. Cesium sorption depended on initial pH of solution. Cesium sorption was very low at pH₀ 1.0–3.0. At initial pH 11.0, maximum sorption of cesium was found. Negative effect of monovalent (K⁺, Na⁺, NH₄ ⁺) and divalent (Ca²⁺, Mg²⁺) cations on cesium sorption was observed. Desorption experiments showed that 0.1 M potassium chloride is the most suitable desorption agent but the complete desorption of cesium ions from KNiFC-modifed biosorbent was not achieved.     

A new chelating resin containing 2-aminothiophenol: Synthesis characterization and determination of mercury in waste water using <Superscript>203</Superscript>Hg radiotracer

A new stable chelating resin was synthesized by incorporating 2-aminothiophenol into Merrifield polymer through C-N covalent bond and characterized by elemental analysis, IR and thermal study. The sorption capacity of the newly formed resin for Hg²⁺ as a function of pH has been studied using ²⁰³Hg radioisotope. The resin exhibits no affinity to alkali or alkaline earth metal ions and common anions. The separation of mercury(II) in presence of different alkali and alkaline earth metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), common anions (ClO₄ ⁻, SO₄ ²⁻) and other diverse ions (Ag⁺, Cu²⁺, Pb²⁺, Fe³⁺, Ni²⁺ and Zn²⁺) has been checked. In column operation it has been observed that Hg²⁺ content of the waste water can be removed at usual pH of natural water. Mercury was determined by isotope dilution method and the concentration of Hg²⁺ in the waste water spiked with ²⁰³Hg was found to be 0.05 to 0.09 μg/ml.     

Preparation,characterization and applications of polyurethane foam functionalized with resorcinol for quantitative separation and determination of silver(I) and mercury(II) from tap and wastewater

A stable chelating resin matrix was prepared by covalently linking resorcinol with polyurethane foam matrix through a –N=N– group. Preconcentration and determination of trace Ag⁺ and Hg²⁺ ions from samples of different origin, using Res-PUF, were studied. Various conditions influencing the sorption of these metal ions onto Res-PUF were optimized. The kinetics of sorption of the Ag⁺ and Hg²⁺ by Res-PUF were found to be fast, reached equilibrium in few minutes (5–10?min) and followed a first-order rate equation with an overall rate constant k in 0.102 and 0.267/min, respectively. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for ΔG, ΔH and ΔS of ?3.94, ?22.02 and ?58.37, respectively. The mean free sorption energy (E) computed from the Dubinin–Radushkevich (D–R) isotherm was found to be equal to 8.91 kJ/mol, which reflects the chelation sorption process. The capacities of the foam material were 0.15 and 0.07?mmol/g for Ag⁺ and Hg²⁺, respectively. Preconcentration factors of?>?50 were achieved (RSD?≈?5.99). The proposed preconcentration procedure was applied successfully to the determination of trace metal ions in natural and wastewater samples.     

Extraction and preconcentration capacity of bifunctionalized diamine-thiol polysiloxane immobilized ligand system towards some divalent cations

Porous solid bi-organofunctionalized diamine-thiol polysiloxane immobilized ligand system of the general formula P-(CH₂)₃- X, (where P represents [Si-O]_n siloxane network and X represents a mixture of diamine; -NH(CH)₂NH₂ and thiol; -SH functional groups) has been prepared by hydrolytic polycondensation of TEOS with a mixture of 3-mercaptopropyltrimethoxysilane and 3- (2-aminoethylimino)propyltrimethoxysilane agents. The ligand system was evaluated for extraction and preconcentartion of a series of divalent metal ions from aqueous solutions including: Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺. Both batch and dynamic methods were used to examine maximum sorption capacity. The maximum binding capacity followed the sequence; Cu²⁺ > Pb²⁺ > Cd²⁺ > Ni²⁺ > Zn²⁺ > Co²⁺ at pH 5.5. Measurement of variation of sorption of metal ions with temperature yielded negative values of ΔG° and positive values of ΔS° and ΔH° indicating a spontaneous and endothermic process of binding metal ions to the ligand system.     

Preparation and ion-exchange properties of zirconium tungstoarsenate

A new inorganic ion-exchanger, zirconium tugnstoarsenate, has been synthesized which has been characterized by chemical analysis, thermogravimetry, X-ray and infrared spectroscopy. The ion exchanger has been found to be stable in acids and neutral salt solutions. The K_d values for 30 metal ions have been determined at pH 3–4 which show that the exchanger has high affinity for UO ₂ ²⁺ , ZrO²⁺, Cs⁺ and Tl⁺ ions. The variation of K_d for a number of metal ions as a function of concentration of nitric acid and ammonium nitrate has been investigated to elucidate the probable exchange mechanism and to work out conditions for elution. Some binary separations, viz. Sr²⁺−Cs⁺, Sr²⁺−Rb⁺, Sr²⁺−Y³⁺, Fe³⁺−Al³⁺, Fe³⁺−Zn²⁺ and Zn²⁺−Hg²⁺ in trace amounts have been carried out on the column of the exchanger which demonstrate the utility of the exchanger in radionalytical and analytical chemistry.     

Study on complexation adsorption behavior of dibenzo-18-crown-6 immobilized on CPVA microspheres for metal ions

Dibenzo-18-crown-6 (DBC) was immobilized on crosslinked polyvinyl alcohol (CPVA) microspheres, resulting in polymer-supported crown ether DBC–CPVA. The complexation adsorption behaviors of DBC–CPVA microspheres towards diverse metal ions were investigated. The experimental results show that among alkali metal ions, the complexation adsorption ability of DBC–CPVA for K⁺ ion is the strongest, and crown ether-metal complex in 1:1 ratio is formed, exhibiting a high adsorption capacity. The adsorption capacities of alkali metal ions on DBC–CPVA are in the order: K⁺ ? Na⁺ > LI⁺ > Rb⁺ > Cs⁺. Among several divalent metal ions, DBC–CPVA exhibits stronger adsorption ability towards Zn²⁺ and Co²⁺ ions, and a “sandwich”-type complex is formed probably in a molar ratio of 2:1 between the immobilized DBC and Zn²⁺ ion as well as between the immobilized DBC and Co²⁺ ion. The adsorption capacities of the several divalent metal ions on DBC–CPVA are in the order: Zn²⁺ > Co²⁺ ? Cd²⁺ > Cu²⁺ > Ni²⁺ > Pb²⁺. The complexation adsorption is exothermic physical physisorption process, and raising temperature leads to the decrease of the adsorption capacity. At the same time, the entropy during the complexation adsorption decreases, so the adsorption process is driven by the decrease of enthalpy.     

Sorption behavior of Am<Superscript>3+</Superscript> on suspended pyrite

Sorption behavior of ²⁴¹Am (~10⁻⁹ M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11), and ionic strength (0.01–1.0 M (NaClO₄)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10⁻⁴ M CO₃ ²⁻, SO₄ ²⁻, C₂O₄ ²⁻ and PO₄ ³⁻), di- and trivalent metal ions (1 × 10⁻³ M Mg²⁺, Ca²⁺ and Nd³⁺) on sorption behavior of Am³⁺ at a fixed ionic strength (I = 0.10 M (NaClO₄)) have been studied. The sorption of ²⁴¹Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of ²⁴¹Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption of ²⁴¹Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C₂O₄ ²⁻ (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence on ²⁴¹Am sorption. The presence of Mg²⁺, Ca²⁺ ions showed marginal effect on the sorption profile of ²⁴¹Am; while the presence of Nd³⁺ ion suppressed its sorption significantly under the conditions of present study. The sorption of ²⁴¹Am on pyrite decreased with increased temperature indicating an exothermic process.     

Synthetic Crystalline Calcium Silicate Hydrate (I): Cation Exchange and Caesium Selectivity

Summary.  Solid crystalline calcium silicate hydrate (I) synthesized from equimolar amounts of Ca and Si under hydrothermal conditions at 120°C shows cation exchange properties towards divalent metal cations such as Ni, Cu, Cd, or Hg. It also exhibits caesium selectivity in the presence of Na⁺. The exchange capacity and selectivity of the solid can be increased by 10 and 28%, respectively, upon substitution of 0.01 mol of the Ca²⁺ in its structure by Na⁺. The ability of metal cation uptake by the solid was found to obey the order Ni²⁺ > Hg²⁺ > Cu²⁺ > Cd²⁺. The different affinities of calcium silicate hydrate (I) towards these ions can be used for their separation from solutions and also in nuclear waste treatment. The mechanism of the exchange reaction is discussed. Received June 11, 2001. Accepted September 10, 2001     

Selectivity of mixed zirconium-titanium phosphates toward transition metals

Mixed zirconium-titanium phosphates were synthesized by various methods and under various conditions. The effect of these conditions on the selectivity of synthetized samples toward the transition metal ions was investigated. It was found that the k_d values are independent of the metal concentration and they give the selectivity order Zn²⁺>Cu²⁺ Co²⁺, Ni²⁺>Mn²⁺.     

Analytical application of polyurethane foam functionalized with quinolin-8-ol for preconcentration and determination of trace metal ions in wastewater

Quinolin-8-ol-bonded polyurethane foam (Ox-PUF) was synthesized by coupling the polyurethane foam matrix with oxine through an azo (-N=N-) group. The chromatographic retention behavior of Ag⁺, Pb²⁺, and Al³⁺ onto the Ox-PUF was studied. The extraction of Ag⁺, Pb²⁺, and Al³⁺ was accomplished within 15–20 min at pH ranges of 1–4, 4–6, and 6–12, respectively. The kinetics and thermodynamics of the sorption of tested metal ions onto Ox-PUF have been studied. The average values of ΔH, ΔS, ΔG; k ₁, k ₋₁, k′, and t _1/2 at 298 K were −28.7 kJ/mol, 210.1 J/(mol K), −6.74 kJ/mol, 0.095, 0.01, 0.113, and 7.184 min, respectively. The sorption capacities of the Ox-PUF were 0.16, 0.07, and 0.59 mmol/g for Ag⁺, Pb²⁺, and Al³⁺, correspondingly. The proposed method has been successfully applied to the preconcentration and removal of tested metal ions from wastewater. Recoveries between 80 and 99% were obtained (RSD ∼ 7). The text was submitted by the authors in English.