Ion-interaction chromatographic separation of metal cations in the presence of complexing agents

The mechanism of the separation of selected divalent metal cations (Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Mn²⁺, Fe²⁺ and Pb²⁺) by ion-interaction chromatography (IIC) in the presence of complexing agents has been investigated; the dependence of the retention of the analyte on the concentration of the complexing ligand has been studied. Separations have been obtained on an octadecyl-bonded silica column, mobile phases containing an ion-interaction agent (octane sulfonate), eluting cations (Na⁺ ions) and a complexing ligand (oxalate anions).     

A highly selective colorimetric and fluorescent chemosensor for Cr2+ in aqueous solutions

A new rhodamine-based chemosensor was synthetized through a modified copper-catalyzed [3+2]-cycloaddition of an azidocoumarin with an alkynyl-rhodamine. Its sensing properties toward various metal cations in aqueous solutions were investigated by colorimetric changes, UV–vis and fluorescence spectroscopies. The sensor exhibited a high selectivity for Cr²⁺ over Cr³⁺ and other divalent cations such as Cu²⁺, Mg²⁺, Zn²⁺, Ca²⁺, Cd²⁺, Co²⁺, Hg²⁺ and Ni²⁺. The linear range of detection by fluorescence spectroscopy is 0.07–3.5 mM, with a detection limit of ca. 64 μM. The binding mode of Cr²⁺ with the sensor was rationalized through experimental evidences.     

Layered hydrous manganese dioxide saturated with alkaline-earth cations: Synthesis and sorption properties

Layered compounds based on hydrous manganese dioxides (hereafter, Mn-phases) saturated with alkaline-earth cations were synthesized at 3–6°C. These phases are analogues of manganese minerals from oceanic iron-manganese sediments (vernadite, birnessite, buserite-I, an asbolan-like phase, and a hybrid phase). All the Mn-phases, as a rule, had poorly ordered structures. The sorption properties of these phases were studied with respect to alkali-metal cations (Na⁺, K⁺), an s-metal cation (Ba²⁺), a p-metal cation (Pb²⁺), and d-metal cations (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺). The exchange capacities of the Mn-phases were 0.45–1.06 mg-equiv/g for the alkali cations and 0.94–5.78 mg-equiv/g for the other cations. The phase composition of the Mn-phase did not affect the alkali cation sorption but affected the divalent cation sorption. The divalent cation exchange capacity increased from well-ordered birnessite to poorly ordered vernadite.     

Construction of Strontium PVC-Membrane Sensor Based on Salicylaldehyde Thiosemicarbazone

Abstract

This work introduces a unique ionophore for the selective determination of Sr²⁺ ions. The ionophore, salicylaldehyde thiosemicarbazone (ST), presented a high affinity toward the strontium cations. The demonstrated characteristics of the sensor included a linear dynamic range between 1.0 × 10^?6 and 1.0 × 10^?2 M with a near Nernstian slope of 29.4±0.5 mV per decade, a detection limit of 4.8 × 10^?7 M, and a very good selectivity for Sr²⁺ over other cations in a wide pH range (2.8–10.4). The sensor possessed the advantages of short conditioning time, fast response time (< 10 s), and, especially, good selectivity toward the transition and heavy metal ions as well as some mono, di, and trivalent cations. Concerning the electrode lifetime, no considerable potential divergence was noticed for at least 10 weeks. The developed sensor was successfully used as an indicator electrode in the Sr²⁺ titration with EDTA from binary mixtures, and the Sr²⁺ monitoring in mixtures of three and five different ions.     

Synthesis and characterization of novel silica gel supported N-pyrazole ligand for selective elimination of Hg(II)

The polar organic molecule N-(2-hydroxyethyl)-3,5-dimethylpyrazole reacted with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous way to yield the product SiPz. The epoxide group was opened yielding chelating pendant group bonded to the inorganic surface. The product was characterized through elemental analysis, infrared spectroscopy, ¹³C NMR, surface area and thermogravimetry. The binding and adsorption abilities of SiPz was investigated for Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Zn²⁺, K⁺, Na⁺ and Li⁺ cations and compared to results of classical liquid-liquid extraction with the unbound N-pyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SiPz exhibits a high selectivity toward Hg²⁺ ion with no complexation being observed towards Zinc and alkali metals. The extracted and the complexing cation percentage were determined by atomic absorption measurements.     

Complexation of di-benzyloxy ether derivatives of calix[4]arene with alkali earth metal cations

The synthesis and complexing abilities of 26,28-bis-benzyloxy-25,27-dihydroxy-5,11,17,23-tetra-tertbutyl-calix[4]arene towards alkali earth metal ions Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ in a methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed that the ligand is capable to complex all alkali earth cations by 1:1 metal to ligand ratios. The selectivity presented considering the calculated stability constants are in the order Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ towards the ligand.     

Separation and quantification of quantum dots and dissolved metal cations by size exclusion chromatography–ICP-MS

The prevalence of engineered metallic nanoparticles within electronic products has evoked a need to assess their occurrence and fate within environmental systems upon potential release of these nanoparticles. Quantum dots (QDs) are mixed-metal nanocrystals with the smallest of particle sizes (2–10 nm) that readily leach heavy metal cations in water, potentially creating a co-occurrence of nanoparticulate and dissolved metal pollutants. In this report, we develop a size exclusion chromatography–inductively coupled plasma–mass spectrometry method (SEC-ICP-MS) for the rapid separation and quantification of ~5-nm-sized CdSe/ZnS QDs and dissolved Cd²⁺ and Zn²⁺ cations in water. The SEC-ICP-MS method provided a wide chromatographic separation of CdSe/ZnS QDs and dissolved Cd²⁺ and Zn²⁺ cations only when using the smallest SEC column pore size available and an eluent composition that prevented loss of metals to column polymer surfaces by using a surfactant to ensure elution of QDs (ammonium lauryl sulfate) and a complexing ligand to ensure elution of metal cations (ethylenediaminetetraacetate). Detection limits were between 0.2 and 2 µg L^–1 for Cd²⁺ and Zn²⁺ among dissolved cation and QD phases, and ranges of linearity covered two to three orders of magnitude. Gold nanoparticles of sizes 5, 10, 20 and 50 nm were also effectively separated from dissolved Au³⁺ cations, illustrating the method applicability to a wide range of nanoparticle sizes and compositions. QD and dissolved metal concentrations measured by SEC-ICP-MS were comparable to those measured using the more conventional method of centrifuge ultrafiltration on split samples for dissolved and total metals. The applicability of the SEC-ICP-MS method to environmental systems was verified by measuring QDs and dissolved metals added to samples of natural waters. The method was also applied to monitoring CdSe/ZnS dissolution kinetics in an urban river water. The SEC-ICP-MS developed here may offer improved automation for characterising heterogeneous suspensions containing >1 µg L^–1 heavy metals.     

Thermochemistry of interaction between cellulose modified with 2-aminomethylpyridine and divalent cations

Cellulose, a biopolymer seemingly inert, was chlorinated initially by reaction with thionyl chloride and then after it becomes more reactive, reacted with 2-aminomethylpyridine molecule for increasing its capacity of removal of divalent cations from an aqueous medium. These materials were characterized by means of elemental analysis, ¹³C NMR, and FTIR techniques, which have proved that a successful modification has occurred. The final material (Celamp), after being characterized was submitted to adsorption assays to evaluate its interaction with cations, whose affinity was found to be Cu²⁺ > Co²⁺ > Ni²⁺ > Zn²⁺. The quantitative cation/base center interactions were calorimetrically determined and showed exothermic enthalpies of ?(13.25 ± 0.12), ?(15.11 ± 0.22), ?(17.23 ± 0.15), and ?(14.66 ± 0.27) kJ mol^?1; negative Gibbs energies of ?(16.3 ± 0.7), ?(14.7 ± 0.7), ?(14.4 ± 0.7), and ?(13.3 ± 0.7) kJ mol^?1; and entropies of 10 ± 2, ?1 ± 1, ?10 ± 1, and ?5 ± 1 J mol^?1 K^?1 for the same sequence of cations. These favorable thermodynamic data suggest that the synthesis involving cellulose produces a new useful material for cation removal from the environment.     

Sulfonamide and Morpholine‐Based Dual Chemosensor for Cu2+ and Ag+ in Different Solvent Media

The detection of cations has attracted considerable interest because of their importance in various physiological processes. In this study, compound 1 bearing sulfonamide and morpholine functionalities was synthesized. Its structure was well characterized by NMR spectroscopy and mass spectrometry. UV/vis absorption spectra and fluorescence spectra indicated that it displayed high sensitivity and selectivity for Cu²⁺ and Ag⁺ by switching solvent media. It means that: (1) it showed selective response to Cu²⁺ in acetonitrile, (2) whereas it exhibited high selectivity for Ag⁺ in water. The density functional theory calculations were used to clearly explain the different recognition behaviors in different solvent media. This research suggests that compound 1 bearing sulfonamide and morpholine functionalities could act as a multifunctional chemosensor for monitoring multiple cations by changing solvent media and provides an alternative approach to design novel dual cations chemosensors.     

Water soluble crown ethers: selective masking agents for improving extraction-separation of zinc and lead cations

The presence of crown ethers 12C4, 15C5 and 18C6 (CE) in aqueous phase influences extraction-separation of zinc and lead ions (M²⁺) by acidic extractant bis(2-ethylhexyl)phosphoric acid (DEHPA) in cyclohexane. In fact, higher complexing ability of the crown ethers towards lead ions causes a greater shift toward higher pH region of the extraction curves versus aqueous phase pH, and consequently an enhancement in the extraction selectivity. The order of extraction selectivity in the presence of the crown ethers varies as 18C6 > 15C5 > 12C4. The analysis of extraction data allows evaluating the stability constants of [M?CE]²⁺ complexes in the aqueous phase. It is demonstrated that the influence of aqueous crown ethers on the extraction process is deeply affected by the organic diluent used. The influence of temperature on the extraction process was studied in the range 286–302 K. This study lets estimating the thermodynamic parameters, i.e., free-energy (ΔGº), enthalpy (ΔΗº), and entropy (ΔSº) changes associated with the extraction process as well as the complexation of cations by the crown ethers in water.     

Calix[4]arenes with carboxamide and sulfonamide groups and their complexation with transition metal salts

Calix[4]arene derivatives functionalized by ester and carboxamide groups on the lower rim and sulfonamide groups on the upper rim were synthesized, and their complexing properties toward transition metal salts (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺) were studied by extraction in chloroform-water system. The presence of carboxamide and sulfonamide fragments in the ligand was shown to considerably enhance binding of transition metal cations.     

Synthesis and sorption properties of layered hydrous manganese dioxide saturated with <Emphasis Type="Italic">s</Emphasis>-, <Emphasis Type="Italic">p</Emphasis>-, and <Emphasis Type="Italic">d</Emphasis>-metal cations

Layered compounds based on hydrous manganese dioxide (hereafter, Mn-phases) saturated with s-metal (Ba²⁺), p-metal (Pb²⁺), and d-metal (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) cations, analogues of manganese minerals of oceanic ferromanganese formations (vernadite, birnessite, buserite-I, and asbolan), were prepared at 4–6°C. All Mn-phases have poorly ordered structures. The sorption properties of phase compounds were studied in relation to alkali-metal (Na⁺ and K⁺) and other s-, p-, and d-metal cations. The exchange capacities of Mn-phases for alkali cations are very low, within 0.02–0.10 mg-equiv/g; for the other cations, the exchange capacities are 0.13–4.20 mg-equiv/g. The sorption of divalent metal cations depends on the phase and chemical composition of the Mn-phase.     

Chromogenic azole diazothiacrown ethers

Azocrown ethers with sulphur atoms and pyrrole or imidazole residue as a part of macrocycle have been synthesised. Their metal complexation abilities in acetonitrile were studied using UV–vis spectrophotometry. The largest spectral changes were observed for both pyrrole- and imidazole-azothiacrown ethers on complexation with Pb^2 + , Cu^2 + , Zn^2 + , Ni^2 + , Co^2 +  and Ag⁺ ions. In the case of alkali and alkaline earth metal ions no spectral changes were found. Preliminary studies of ion-selective membrane electrodes with synthesised ionophores are presented. In the measurement for transition/heavy metal cations, only copper and lead give high responses. X-ray structure of 18-membered pyrrole azothiacrown ether is described.     

Binding of carboxylate and trimethylammonium salts to octa-acid and TEMOA deep-cavity cavitands

In participation of the fifth statistical assessment of modeling of proteins and ligands (SAMPL5), the strength of association of six guests (3–8) to two hosts (1 and 2) were measured by ¹H NMR and ITC. Each host possessed a unique and well-defined binding pocket, whilst the wide array of amphiphilic guests possessed binding moieties that included: a terminal alkyne, nitro-arene, alkyl halide and cyano-arene groups. Solubilizing head groups for the guests included both positively charged trimethylammonium and negatively charged carboxylate functionality. Measured association constants (K _a ) covered five orders of magnitude, ranging from 56 M^?1 for guest 6 binding with host 2 up to 7.43 × 10⁶ M^?1 for guest 6 binding to host 1.     

Interaction between cucurbit[8]uril and viologen derivatives

The interaction between cucurbit[8]uril (Q[8]) and a series of symmetric viologen derivatives having aliphatic substituents of variable length [N,N′-dialkyl-4,4′-bipyridinium dianions; alkyl = CH₃(CH₂) _n –, n = 0 (MV²⁺), 1 (EV²⁺), 2 (PV²⁺), 3 (BV²⁺), 4 (FV²⁺), 5 (HV²⁺) or 6 (SV²⁺); BPY²⁺ = diprotonated 4,4-bipyridine], determined by ¹H NMR and electronic absorption spectroscopy methods, is described. Some different binding models were observed in this work when compared to the interactions between cucurbit[7]uril (Q[7]) and these guests. The experimental results revealed that the binding site of the guests by Q[8] depended strongly on the length of the aliphatic substituents on the 4,4′-bipyridinium nucleus. While a 1:2 complex was observed for Q[8]-BPY²⁺ under acidic conditions, a 1:1 complex was formed for Q[8]-viologen derivatives with chains shorter than four carbon atoms. However, multiple Q[8] molecules could be threaded on the longer-chain FV²⁺, HV²⁺ or SV²⁺ molecules to form 2:1 and even possibly 3:1 complexes.     

Determination of organic acids by capillary electrophoresis with simultaneous addition of Ca and Mg as complexing agents

Summary A capillary electrophoretic method, with divalent cations as complexing agents in the electrolyte, has been developed for separation and determination of the low molecular weight organic acids most commonly found in wine, viz. formic, fumaric, succinic, oxalic, malic, tartaric, acetic, lactic, and citric acids. The separation conditions optimized were electrolyte concentration, organic flow modifier concentration, type and concentration of complexing agents in the electrolyte, and injection time. The best resolution of some of the acids studied was achieved by use of an electrolyte containing tetraborate buffer (10mm) at pH 9.3, an organic flow modifier (tetradecyltrimethylammonium hydroxide), and Ca²⁺ (10 ppm) and Mg²⁺ (10 ppm) as complexing agents. Other conditions used in the method were hydrostatic injection (10 cm height for 30 s), detection at 185 nm, and temperature 20°C. For all the acids studied detector response was linear for the concentration ranges considered. The repeatability of each point on the calibration plot for standards (n=4) was generally better than 1% the method was applied to samples of must, wine, brandy, and vinegar from the Jerez region.     

Biochemical Characterization and Antitumor Study of l-Glutaminase from Bacillus cereus MTCC 1305

l-Glutaminase (E.C.3.5.2.1) extracellularly produced by Bacillus cereus MTCC 1305 was purified to apparent homogeneity with a fine band. The molecular weight of native enzyme and its subunit were found to be approximately 140 and 35 kDa, respectively, which indicates its homotetrameric nature. The substrate specificity test of this enzyme showed its specificity for l-glutamine. The purified enzyme showed maximum activity at optimum pH 7.5 and temperature 35 °C. The enzyme retained stability up to 50 and 20 % even after treatment at 50 and 55 °C, respectively, for 30 min. Monovalent cations (Na⁺, K⁺) and phosphate ion activated the enzyme activity, while divalent cations (Mg²⁺, Mn²⁺, Zn²⁺, Pb²⁺, Ca²⁺, Co²⁺, Hg²⁺, Cd²⁺, Cu²⁺) inhibited its activity. Reducing agents (cysteine, glutathione, dithiothreitol, l-ascorbic acid, and β-mercaptoethanol) stimulated its activity, whereas thiol-binding agents (iodoacetamide, p-chloromercuribenzoic acid) resulted in the inhibition of this enzyme. Kinetic parameters, K _m, V _max, K _cat, of purified enzyme were found to be 6.25 mM, 100 μmol/min/mg protein and 2.22?×?10² M^?1s^?1, respectively. The gradual inhibition in growth of hepatocellular carcinoma (Hep-G2) cell lines was found with IC₅₀ value of 82.27 μg/ml in the presence of different doses of l-glutaminase (10–100 μg/ml).     

Quantum chemical study of the interaction between selenium analog of methimazole as an anti-thyroid drug and metal cations

Energetic and structural properties of complexes formed from interaction between selenium analog of methimazole (MSeI) as an anti-thyroid drug and M^z+ (Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺ and Ca²⁺) cations have been investigated using B3LYP, M062X, PBE1PBE, and MP2 methods with 6-311++G(d,p) and 6-311++G(2d,2p) basis sets. Two planar and perpendicular complexes were predicted from interaction of MSeI and M^z+ cations. From the Gibbs free energy difference between the planar and perpendicular forms of MSeI–M^z+ complexes, it is found that the perpendicular forms are the predominant ones. In addition, the comparison of interaction energies shows that the order of energies increases in the following order: K⁺ < Na⁺ < Li⁺ < Ca²⁺ < Mg²⁺ < Be²⁺. The results of natural bond orbital analysis showed that the charge transfer occurs from MSeI to metal cations. The atom in molecule analysis shows that the charge density and its Laplacian at the Se–M^z+ bond critical point of the MSeI–M²⁺ complexes are greater than the MSeI–M¹⁺ ones. Also, it was revealed that the Se–M^z+ interactions in perpendicular complexes of alkali and alkaline metal cations are electrostatic and partially covalent in nature, respectively.     

Comparison of upper and lower rim-functionalized,di-ionizable calix[4]arene-crown-6 structural isomers in divalent metal ion extraction

Upper rim-functionalized, di-ionizable calix[4]arene-crown-6 ligands are synthesized and compared with structural isomers having the two acidic side arms attached to the lower rim. Solvent extractions of selected divalent metal cations (alkaline earth metal cations, Pb²⁺, and Hg²⁺) from aqueous solutions into chloroform by the upper and lower rim-functionalized, di-ionizable calix[4]arene-crown-6 isomers are utilized to assess the effects of this structural modification on metal ion complexation abilities of the ligands. The observed effects are compared with those reported for analogous di-ionizable calix[4]arene-crown-5 structural isomers.     

Synthesis and extraction studies of polymeric phthalimido functionalized calix[4]arene

The article comprises synthesis and extraction studies of polymeric calix[4]arene having phthalimide groups at the lower rim. The polymeric phthalimido functionalized calix[4]arene was synthesized via radical initiated reactions involving a vinylic monomer 5,11,17,23-tetra-tert-butyl-25-[4-(acrylamido)benzyloxy]-26,28-bis-(2-phthalimido-ethoxy)-27-hydroxycalix[4]arene (5) with styrene. A five atom spacer group was incorporated between the bulky calixarene core and the acrylate moiety in order to minimize steric interactions which proved to impede the polymerization. From the liquid–liquid and solid–liquid extraction studies it has been concluded that the precursor 3 (5,11,17,23-tetra-tert-butyl-25-(4-nitro benzyloxy)-26,28-bis-(3-phthalimidoethoxy)-27-hydroxy-calix[4]arene) is selective for metal cations. The order of extractability of metal cations by the ligand 3 decreases in the sequence: Hg²⁺ > Cd²⁺ > Cu²⁺ > K⁺ > Co²⁺ whereas its polymeric derivative is selective in the sequence: Hg²⁺ > Cd²⁺ > K⁺ > Co²⁺ > Cu²⁺ for the metal cations used in the experiments.