Thiacalixarenes with Sulfur Functionalities at Lower Rim: Heavy Metal Ion Binding in Solution and 2D-Confined Space

Sulfur-containing groups preorganized on macrocyclic scaffolds are well suited for liquid-phase complexation of soft metal ions; however, their binding potential was not extensively studied at the air–water interface, and the effect of thioether topology on metal ion binding mechanisms under various conditions was not considered. Herein, we report the interface receptor characteristics of topologically varied thiacalixarene thioethers (linear bis-(methylthio)ethoxy derivative L², O₂S₂-thiacrown-ether L³, and O₂S₂-bridged thiacalixtube L⁴). The study was conducted in bulk liquid phase and Langmuir monolayers. For all compounds, the highest liquid-phase extraction selectivity was revealed for Ag⁺ and Hg²⁺ ions vs. other soft metal ions. In thioether L² and thiacalixtube L⁴, metal ion binding was evidenced by a blue shift of the band at 303 nm (for Ag⁺ species) and the appearance of ligand-to-metal charge transfer bands at 330–340 nm (for Hg²⁺ species). Theoretical calculations for thioether L² and its Ag and Hg complexes are consistent with experimental data of UV/Vis, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffractometry of Ag–thioether L² complexes and Hg–thiacalixtube L⁴ complex for the case of coordination around the metal center involving two alkyl sulfide groups (Hg²⁺) or sulfur atoms on the lower rim and bridging unit (Ag⁺). In thiacrown L³, Ag and Hg binding by alkyl sulfide groups was suggested from changes in NMR spectra upon the addition of corresponding salts. In spite of the low ability of the thioethers to form stable Langmuir monolayers on deionized water, one might argue that the monolayers significantly expand in the presence of Hg salts in the water subphase. Hg²⁺ ion uptake by the Langmuir–Blodgett (LB) films of ligand L³ was proved by X-ray photoelectron spectroscopy (XPS). Together, these results demonstrate the potential of sulfide groups on the calixarene platform as receptor unit towards Hg²⁺ ions, which could be useful in the development of Hg²⁺-selective water purification systems or thin-film sensor devices.     

Photochemical Synthesis of Silver Hydrosol Stabilized by Carbonate Ions and Study of Its Bactericidal Impact on Escherichia coli: Direct and Indirect Effects

The great attention paid to silver nanoparticles is largely related to their antibacterial and antiviral effects and their possible use as efficient biocidal agents. Silver nanoparticles are being widely introduced into various areas of life, including industry, medicine, and agriculture. This leads to their spreading and entering the environment, which generates the potential risk of toxic effect on humans and other biological organisms. Proposed paper describes the preparation of silver hydrosols containing spherical metal nanoparticles by photochemical reduction of Ag⁺ ions with oxalate ions. In deaerated solutions, this gives ~10 nm particles, while in aerated solutions, ~20 nm particles with inclusion of the oxide Ag₂O are obtained. Nanoparticles inhibit the bacterium Escherichia coli and suppress the cell growth at concentrations of ~1 × 10⁻⁶–1 × 10⁻⁴ mol L⁻¹. Silver particles cause the loss of pili and deformation and destruction of cell membranes. A mechanism of antibacterial action was proposed, taking into account indirect suppressing action of Ag⁺ ions released upon the oxidative metal dissolution and direct (contact) action of nanoparticles on bacterial cells, resulting in a change in the shape and destruction of the bacteria.     

Two Calix-Crown Based Stationary Phases. Synthesis,Chromatographic Performance and X-ray Photoelectron Spectroscopy Investigation

Two chromatographic stationary phases, obtained by covalently linking two suitably derivatized calix[4]crown-6 and calix[4]crown-5 receptors onto silica gel, are described here. A study of their chromatographic behaviour as well as their surface composition is reported. The packing materials exhibit high selectivity toward alkali metal ions. Complete separations of Cs⁺ from K⁺ and Na⁺ were obtained when using a water/methanol mixture (80:20) as the mobile phase. In these conditions, a selectivity factor Cs⁺/Na⁺=4.10 was achieved with the silica gel-bound calix[4]crown-6. The degree of coverage of the activated silica-gel surface following the covalent attachment of the macrocycle was estimated by mean of X-ray photoelectron spectroscopy (XPS). This technique allows the first few monolayers of the material to be analysed and thus is to be preferred to conventional Elemental Analysis for similar studies. Three methods for an adequate correction of the XP signals for the presence of organic contaminants are suggested and critically compared.     

Hydrazine Radiolysis by Gamma-Ray in the N2H4–Cu+–HNO3 System

Radiolysis of chemical agents occurs during the decontamination of nuclear power plants. The γ-ray irradiation tests of the N₂H₄–Cu⁺–HNO₃ solution, a decontamination agent, were performed to investigate the effect of Cu⁺ ion and HNO₃ on N₂H₄ decomposition using a Co-60 high-dose irradiator. After the irradiation, the residues of N₂H₄ decomposition were analyzed by Ultraviolet-visible (UV) spectroscopy. NH₄⁺ ions generated from N₂H₄ radiolysis were analyzed by ion chromatography. Based on the results, the decomposition mechanism of N₂H₄ in the N₂H₄–Cu⁺–HNO₃ solution under γ-ray irradiation condition was derived. Cu⁺ ions form Cu⁺N₂H₄ complexes with N₂H₄, and then N₂H₄ is decomposed into intermediates. H⁺ ions and H^● radicals generated from the reaction between H⁺ ion and e_aq⁻ increased the N₂H₄ decomposition reaction. NO₃⁻ ions promoted the N₂H₄ decomposition by providing additional reaction paths: (1) the reaction between NO₃⁻ ions and N₂H₄^●+, and (2) the reaction between NO^● radical, which is the radiolysis product of NO₃⁻ ion, and N₂H₅⁺. Finally, the radiolytic decomposition mechanism of N₂H₄ obtained in the N₂H₄–Cu⁺–HNO₃ was schematically suggested.     

Chromogenic sensing of Cu(II) by imino linked thiacalix[4]arene in mixed aqueous environment

Thiacalix[4]arene based imino receptors 4–5 carrying azophenol appendage have been synthesized and studied for their binding abilities towards different metal ions (Li⁺, Na⁺, K⁺, Cd²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺ and Hg²⁺). Receptor 4 showed selective chromogenic sensing for Cu²⁺ ions in mixed aqueous conditions (THF:H₂O, 9:1 v/v).     

Ag+ ions imprinted cryogels for selective removal of silver ions from aqueous solutions

ABSTRACT

The removal of heavy metal ions from aquatic media or any conditions is crucial. Silver ions turn out to be the important example of this problem on earth when these are released to the environment. In the present study, silver ions (Ag⁺) imprinted poly(hydroxyethyl methacrylate) (PHEMA)-based cryogels were prepared using N-methacryloyl-L-cysteine as functional monomer, to be chelated with Ag⁺ ions. The maximum adsorption capacity of Ag⁺-imprinted polymeric cryogel was found to be 49.27 mg/g from aqueous solutions. To investigate the affinity of Ag⁺-imprinted PHEMAC cryogel column, photographic film material from the natural silver ion source was used. The recovery results were 72.8% for the Ag⁺-imprinted PHEMAC cryogel and 0.62% for the non-imprinted PHEMAC cryogels. These values clearly showed the selectivity of the Ag⁺-imprinted PHEMAC cryogel column. The adsorption–desorption cycle was performed more 10 times with use of the same Ag⁺-imprinted PHEMAC cryogel for the determination of reuse. These molecularly imprinted cryogels were used in adsorption process for a long time with no significant loss.     

NEW NITROGEN-CONTAINING MACROCYCLIC LIGANDS COVALENTLY ATTACHED TO SILICA GEL AND THEIR USE IN SEPARATING METAL CATIONS

Several polyaza-crowns and cyclams, each containing an allyl-oxymethyl or other monofunctional group capable of further reaction to attach it to silica gel, have been prepared. As an example of an attachment of a crown to silica gel, allyloxymethyl-substituted diaza-18-crown-6 was reacted with triethoxysilane to form the crown-substituted triethoxysilane This crown-silane material was heated on silica gel to effect a covalent attachment of the crown. The silica gel-bound macrocyclic ligands were found to interact with various metal cations with log K ( H2O) values similar to those of the same cations with unbound macrocycles. A tetraaza-crown bound to silica gel was found to quantitatively remove toxic heavy metal ions, such as Pb²⁺, Hg²⁺ Cd²⁺ Ag⁺and others at the ppb level, from large volumes of aqueous solutions containing those metal ions and much larger amounts of Na⁺Mg²⁺and Ca²⁺ions     

Complexation studies of some newly synthesized precursors for substituted dibenzo and dibenzodiaza crown ethers

This study represents the synthesis of dibenzo and dibenzodiaza crown ether precursors with various functional groups in good yield by employing four different methods using polar protic and aprotic solvents with high boiling points. Also the complexation abilities of all synthesized ligands with Cu²⁺, Zn²⁺, and Ag⁺ were studied by conductometry; thus the conductometric behavior of Cu(NO₃)₂, ZnCI₂, and AgNO₃ in 80% dioxane–water mixture was investigated in the presence of these ligands. The order of formation constant for complexes of the ligands with Cu²⁺, Zn²⁺, and Ag⁺ ions was found to be: Cu²⁺ > Zn²⁺ > Ag⁺ for the ligands of VI , VII , XI , and XII ; Cu²⁺ > Ag⁺ > Zn²⁺ for the ligands of III and VIII ; and Zn²⁺ > Cu²⁺ > Ag⁺ for the ligands of I , II , IV , V , IX , and X . © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2497–2501, 2004     

Oxidase Reactivity of CuII Bound to N-Truncated Aβ Peptides Promoted by Dopamine

The redox chemistry of copper(II) is strongly modulated by the coordination to amyloid-β peptides and by the stability of the resulting complexes. Amino-terminal copper and nickel binding motifs (ATCUN) identified in truncated Aβ sequences starting with Phe4 show very high affinity for copper(II) ions. Herein, we study the oxidase activity of [Cu–Aβ_4−x] and [Cu–Aβ_1−x] complexes toward dopamine and other catechols. The results show that the Cu^II–ATCUN site is not redox-inert; the reduction of the metal is induced by coordination of catechol to the metal and occurs through an inner sphere reaction. The generation of a ternary [Cu^II–Aβ–catechol] species determines the efficiency of the oxidation, although the reaction rate is ruled by reoxidation of the Cu^I complex. In addition to the N-terminal coordination site, the two vicinal histidines, His13 and His14, provide a second Cu-binding motif. Catechol oxidation studies together with structural insight from the mixed dinuclear complexes Ni/Cu–Aβ_4−x reveal that the His-tandem is able to bind Cu^II ions independently of the ATCUN site, but the N-terminal metal complexation reduces the conformational mobility of the peptide chain, preventing the binding and oxidative reactivity toward catechol of Cu^II bound to the secondary site.     

Physicochemical investigation of radiation‐grafted poly(acrylic acid)‐graft‐poly(tetrafluoroethylene–ethylene) copolymer membranes and their use in metal recovery from aqueous solution

ET‐g‐PAAc membranes were obtained by radiation grafting of acrylic acid onto poly(tetrafluoroethylene–ethylene) copolymer films using a mutual technique. The ion selectivity of the grafted membranes was determined toward K⁺, Ag⁺, Hg²⁺, Co²⁺, and Cu²⁺ in a mixed aqueous solution. The ion‐exchange capacity of the grafted membranes was measured by back titration and atomic absorption spectroscopy. The Hg²⁺ ion content of the membrane was more than that of either the K⁺ or Ag⁺ ions. The presence of metal ions in the membranes was studied by infrared and energy‐dispersive spectroscopy measurements. Scanning electron microscopy of the grafted and metal‐treated grafted membranes showed modification of the morphology of the surface due to the adsorption of K⁺ and Ag⁺ ions. No change was observed for the surface of the membrane that was treated with Hg²⁺ ions. The thermal stability of different membranes was improved more with Ag⁺ and Hg²⁺ ions than with K⁺ ions. It was found that the modified grafted membranes possessed good hydrophilicity, which may make them promising candidates for practical applications, such as for cation‐exchange membranes in the recovery of metals from an aqueous solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2692–2698, 2002     

Thioether‐Functionalized Corn Oil Biosorbents for the Removal of Mercury and Silver Ions from Aqueous Solutions

Heavy‐metal contamination is one of the most important environmental problems faced in the world, particularly in developing countries. Metals such as silver and mercury from drinking water, food, and air sources can accumulate in living organisms and present significant health concerns. Meanwhile, the demand for these metals in many industries continues to increase. In the present study, thioether‐functionalized corn oil (TFCO) from a photoinitiated thiol‐ene synthesis was utilized to remove Ag⁺ and Hg²⁺ ions from an aqueous solution. An aqueous solution containing AgNO₃ and Hg[NO₃]₂ was prepared and contacted directly with TFCO. After vortex mixing for 60 s, the experiment ran for 351 min with the aqueous phase being periodically sampled for the analysis of metal ions (M ⁿ⁺). Results showed that 88.9% of Ag⁺ and 99.6% of Hg²⁺ ions were removed from the aqueous phase by the TFCO. Mass balances indicated that the total M ⁿ⁺ concentration in the oil phase was 13.890 g kg^?1 under the conditions studied. TFCO exhibited higher selectivity for removing Hg²⁺ than for Ag⁺ ions. Analysis of the adsorption kinetics showed that a pseudosecond‐order model may be used to determine the rate of Ag⁺ ion sorption by the oil phase. The presence of the Hg²⁺ ions interfered with the adsorption of Ag⁺ ions from the aqueous solution.     

Competitive Adsorption of Ag+, Pb2+, Ni2+, and Cd2+ Ions on Vermiculite

Competitive adsorption of Ag⁺, Pb²⁺, Ni²⁺, and Cd² ions on vermiuculite in a binary, ternary, and quaternary mixture was investigated in batch experiments. The effects of the presence of Ag⁺, Ni²⁺, and Cd²⁺ ions on the adsorption of Pb²⁺ ions were investigated in terms of the equilibrium isotherm. Experimental results indicated that Pb²⁺ ions always favorably adsorbed on vermiculite over Ag⁺, Ni²⁺, and Cd²⁺ ions. The adsorption equilibrium data of Pb²⁺ ions better fitted the Langmuir model than the Freundlich model. The results showed that the pseudo-second-order kinetics model was in good agreement with the experimental results for all metal ions, and the adsorption rate among the metal ions followed Ag⁺ > Pb²⁺ > Ni²⁺ > Cd²⁺. The desorption and regenration study indicated that vermiculite can be used repeatedly and be suitable for the design of a continuous process.     

The synthesis and complexation study of some novel 3-methoxyphenyl chromenone crown ethers using conductometry

7,8-Dihydroxy-3-(3,4-dimethoxyphenyl)-2H-chromenones, 7,8-dihydroxy-3-(3,5-dimethoxyphenyl)-2H-chromenones and 7,8-dihydroxy-3-(3,4,5-trimethoxyphenyl)-2H-chromenones, o-dihydroxy-3-methoxyphenylcoumarins, were prepared from 2,3,4-trihydroxybenzaldehyde and corresponding methoxyphenylacetic acid in NaOAc/Ac₂O, respectively. 3-Methoxyphenyl-7,8-dihydroxy-2H-chromenone reacted with the polyethylene glycol ditosylate or dichloride in CH₃CN/alkali carbonate to afford [12]crown-4, [15]crown-5 and [18]crown-6-chromonones.The chromatographically purified novel chromenone crown ethers were identified with IR, ¹H NMR, ¹³C NMR and low and high resolution mass spectroscopy and elemental analysis.Stability constants for the 1:1 complexes of Na⁺ and K⁺ with different substituted methoxyphenyl derivatives of coumarino[12]crown-4, coumarino[15]crown-5 and coumarino[18]crown-6 (5a–5i) have been determined by conductometry at 25 °C in a binary solvent, dioxane/water. For all the coumarino crown ether derivatives, the stability constant decreases for K⁺ ion compared to Na⁺ ion.The selectivity sequence of these crown ethers in dioxane/water has showed an irregular order with respect to their cavity size.     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.     

Inclusion and exclusion complexes of cucurbit[7]uril with silver cations

We describe a strategy to prepare cucurbit [7]uril(Q [7])-M^n + complexes in an ammonia medium, in which a competitive coordination of metal ions to ammonia molecules or Q [7] molecules occurs. Using this strategy, a novel compound consisting of Q [7] and a metal Ag⁺ ion was obtained. The X-ray crystal structure of this compound showed an infinite 2D network comprising three-Q [7] units and with a cavity size of around 11.0 Å × 5.5 Å. Moreover, a Q [7]-based host-guest inclusion Ag⁺ aquo complex was observed. Considering the generality of the behavior shown in the complexes described, this phenomenon may well deserve further study.     

Etude potentiometrique de la stabilite de complexes Ag(I)-pyridines substituees et de complexes mixtes Ag(I)-bipyridine-pyridines substituees dans le carbonate de propylene

The formation of Ag^IL⁺_n (L = substituted pyridines, n = 1,2) and Ag^I(bipy)L⁺ (bipy = 2,2 bipyridine) complexes has been investigated using potentiometry in propylene carbonate. This study, required by the investigation of the reactivity of Ag(II)/Ag(I)-bipyridine system towards pyridine-type substrates, allows the determination of the nature and distribution of the species in solutions containing Ag⁺ ions and both types of ligands; bipyridine and substituted pyridines.     

Rate and Product Studies with 1-Adamantyl Chlorothioformate under Solvolytic Conditions

A study was carried out on the solvolysis of 1-adamantyl chlorothioformate (1-AdSCOCl, 1) in hydroxylic solvents. The rate constants of the solvolysis of 1 were well correlated using the Grunwald–Winstein equation in all of the 20 solvents (R = 0.985). The solvolyses of 1 were analyzed as the following two competing reactions: the solvolysis ionization pathway through the intermediate (1-AdSCO)⁺ (carboxylium ion) stabilized by the loss of chloride ions due to nucleophilic solvation and the solvolysis–decomposition pathway through the intermediate 1-Ad⁺Cl⁻ ion pairs (carbocation) with the loss of carbonyl sulfide. In addition, the rate constants (k_exp) for the solvolysis of 1 were separated into k_1-Ad⁺Cl⁻ and k_{1-AdSCO⁺Cl⁻} through a product study and applied to the Grunwald–Winstein equation to obtain the sensitivity (m-value) to change in solvent ionizing power. For binary hydroxylic solvents, the selectivities (S) for the formation of solvolysis products were very similar to those of the 1-adamantyl derivatives discussed previously. The kinetic solvent isotope effects (KSIEs), salt effects and activation parameters for the solvolyses of 1 were also determined. These observations are compared with those previously reported for the solvolyses of 1-adamantyl chloroformate (1-AdOCOCl, 2). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions calculated using Gaussian 03.     

Silver Nanostructures: Limited Sensitivity of Detection,Toxicity and Anti-Inflammation Effects

Nanosilver with sizes 1–100 nm at least in one dimension is widely used due to physicochemical, anti-inflammatory, anti-angiogenesis, antiplatelet, antifungal, anticancer, antibacterial, and antiviral properties. Three modes of the nanosilver action were suggested: “Trojan horse”, inductive, and quantum mechanical. The Ag⁺ cations have an affinity to thiol, amino, phosphate, and carboxyl groups. Multiple mechanisms of action towards proteins, DNA, and membranes reduce a risk of pathogen resistance but inevitably cause toxicity for cells and organisms. Silver nanoparticles (AgNP) are known to generate two reactive oxygen species (ROS)-superoxide (•O₂⁻) and hydroxyl (•OH) radicals, which inhibit the cellular antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) and cause mechanical damage of membranes. Ag⁺ release and replacement by electrolyte ions with potential formation of insoluble AgCl result in NP instability and interactions of heavy metals with nucleic acids and proteins. Protein shells protect AgNP core from oxidation, dissolution, and aggregation, and provide specific interactions with ligands. These nanoconjugates can be used for immunoassays and diagnostics, but the sensitivity is limited at 10 pg and specificity is restricted by binding with protective proteins (immunoglobulins, fibrinogen, albumin, and others). Thus, broad implementation of Ag nanostructures revealed limitations such as instability; binding with major blood proteins; damage of proteins, nucleic acids, and membranes; and immunosuppression of the majority of cytokines.     

Adsorption of metal cations on wool carbonising waste. Part 1. Adsorption isotherms

The adsorption of various metal ions (Hg²⁺, Ag⁺, Ni²⁺, Cr³⁺, Al³⁺, Zn²⁺ and Pb²⁺) on wool carbonising waste has been investigated to assess its possible use as an adsorbent in water pollution control. Isotherms show that few metal ions (Hg²⁺, Ag⁺ and Ni²⁺) are adsorbed satisfactorily by this material. Moreover, the adsorption capacity of the plant material within the carbonising waste is higher than that of the keratin fraction. Equations fitting the experimental data can be used for the design of processing units.