Synthesis and characterization of novel ion-imprinted polymeric nanoparticles for very fast and highly selective recognition of copper(II) ions

This work reports the preparation of new Cu²⁺ ion-imprinted polymeric nanoparticles using 1-hydroxy-4-(prop-2′-enyloxy)-9,10-anthraquinone (AQ) as a vinylated chelating agent. The Cu²⁺ ion found to form a stable 1:1 complex with AQ in methanol solution. The resulting Cu²⁺-AQ complex was copolymerized with ethyleneglycol dimethacrylate, as a cross-linking monomer, via precipitation polymerization method. The imprint copper ion was removed from the polymeric matrix using a 0.1 mol L⁻¹ HNO₃ solution. The Cu²⁺-imprinted polymeric nanoparticles were characterized by IR spectroscopy, scanning electron microscopy (SEM) and N₂ adsorption-desorption isotherms. The SEM micrographs showed colloidal nanoparticles of 60-100 nm in diameter and slightly irregular in shape. Optimum pH for maximum sorption was 7.0. Sorption and desorption of Cu²⁺ ion on the IIP nanoparticles were quite fast and achieved completely over entire investigated time periods of 2-30 min. Maximum sorbent capacity and enrichment factor of the prepared IIP for Cu²⁺ were 73.8 μmol g⁻¹ and 56.5, respectively. The relative standard deviation and limit of detection (C_LOD = 3S_b/m) of the method were evaluated as 2.6% and 0.1 ng mL⁻¹, using inductively coupled plasma-atomic emission spectrometry, respectively. It was found that the imprinting technology results in increased affinity of the prepared material toward Cu²⁺ ion over other metal ions with the same charge and close ionic radius. The relative standard deviations for six and twenty replicates with the same nanoparticles were found to be 1.7% and 2.1%, respectively.     

Adsorption of copper(II) ions by keratin/PA6 blend nanofibres

Mats of randomly oriented nanosized filaments, prepared by electrospinning wool keratin/polyamide 6 blends in formic acid, were evaluated as adsorbents of Cu²⁺ ions. The adsorption capacity was evaluated as a function of the nanofibre composition, specific surface area, initial metal ion concentration, contact time and pH of the solution. The adsorption tests revealed that keratin-based nanofibres highly adsorb Cu²⁺ ions and the adsorption capacity increases with increasing the specific surface area of the nanofibre mats. The maximum adsorption capacities for nanofibre mats containing 50%, 70% and 90% (wt.%) of keratin were found to be 61.7 (mg/g), 90 (mg/g) and 103.5 (mg/g), respectively. The Cu²⁺adsorption onto the keratin rich nanofibres is highly pH-dependent and the optimum pH was found above the isoelectric point of keratin. The experimental data fit the pseudo second-order kinetic model. Infrared analysis demonstrated the formation of complexes between Cu²⁺ ions and keratin that involve terminal free carboxyl groups of the protein.     

A highly selective and sensitive fluorescein-based chemodosimeter for Hg2+ ions in aqueous media

A new fluorescein-based chemodosimeter (II) for Hg²⁺ ion was designed and synthesized, and it displayed excellent selective and sensitive toward Hg²⁺ ion over other commonly metal ions in aqueous media. II was a colorless, non-fluorescent compound. Upon addition of Hg²⁺ to the solution of II, the thiosemicarbazide moiety of II would undergo an irreversible desulfurization reaction to form its corresponding oxadiazole (IV), a colorful and fluorescent product. During this process, the spirocyclic ring of II was opened, causing instantaneous development of visible color and strong fluorescence emission in the range of 500-600 nm. Based on the above mechanism, a fluorogenic Hg²⁺-selective chemodosimeter was developed. The fluorescence increase is linearly with Hg²⁺ concentration up to 1.0 μmol L⁻¹ with a detection limit of 8.5 × 10⁻¹⁰ mol L⁻¹ (3σ). Compared with the rhodamine-type chemodosimeter, II is more stable in aqueous media and exhibits higher sensitivity toward Hg²⁺. The findings suggest that II will serve as a practical chemodosimeter for rapid detection of Hg²⁺ concentrations in realistic media.     

A simple click generated probe for highly selective sequential recognition of Cu(II) and pyrophosphate

A click generated quinoline derivative (1) has been synthesized and used as a fluorescent probe for sequential recognition of Cu²⁺ and pyrophosphate (PPi) in DMSO/H₂O (1:1, v/v, HEPES 20 mM, pH = 7.4) solution. Probe 1 displays high selectivity to Cu²⁺ ions, and the in-situ prepared probe 1-Cu²⁺ exhibits high selectivity toward pyrophosphate (PPi) with emission recovery of probe 1. Therefore, 1-Cu²⁺ complex can be applied as a fluorescence turn-on probe for PPi with high selectivity and sensitivity.     

Removal of copper(II) from aqueous solution with rape stalk modified by citric acid

In this paper, rape stalk was modified with citric acid (CA) to prepare copper ion biosorbent. The modified rape stalk (MRS) was characterized by Fourier transforms infrared (FTIR), zeta potential, and thermogravimetric analysis (TGA). The effects of various parameters like initial Cu²⁺ concentration, contact time, initial pH, and temperature on adsorption capacity were studied. The adsorption capacity of MRS at 298 K was 69.84 mg/g, far higher than 18.24 mg/g for native rape stalk (NRS). The adsorption mechanism was also evaluated in terms of kinetics and thermodynamics. The adsorption equilibrium data was well described by the Langmuir isotherm model. The adsorption process followed the pseudo-second-order rate kinetics. Thermodynamic study showed spontaneous and endothermic nature of the adsorption process. The ion exchange of the adsorption mechanism was affirmed. MRS could be a potentially low-cost and green adsorbent for removal of Cu²⁺ from aqueous solution.     

A fluorescence reagent for the highly selective recognition and separation of lead ion (II) from aqueous solutions

A new fluorescence reagent, N,N-bi[4(1-pyrene)-butyroyl]-lysine (1) was synthesized. The new fluorescence sensor showed high sensitivity (detection limit up to 20.7 μg L⁻¹) and specific selectivity for Pb²⁺ over other metal ions examined in aqueous solutions. It could also be used to remove Pb²⁺ from aqueous solutions by filtering the insoluble 1–Pb²⁺ complex with sufficient reversibility.     

Characterization of rhodamine B hydroxylamide as a highly selective and sensitive fluorescence probe for copper(II)

Rhodamine B hydroxylamide (1) is characterized as a highly selective and sensitive fluorescence probe for Cu²⁺. Under the optimized conditions, the probe exhibits specific absorbance-on and fluorescence-on responses to Cu²⁺ only. This remarkable property may allow Cu²⁺ to be detected directly in the presence of the other transition metal ions, and such an application has been demonstrated to human serum. The reaction mechanism is also investigated and proposed as that the hydroxylamide group of 1 binds Cu²⁺, and the subsequent complexation of Cu²⁺ displays a high catalytic activity for the hydrolytic cleavage of the amide bond, causing the release of fluorophore (rhodamine B) and thereby the retrievement of absorbance and fluorescence. The recovered fluorescence intensity is proportional to the concentration of Cu²⁺ in the range 1-20 μM. The detection limit for Cu²⁺ is 33 nM (k = 3). The reaction mechanism described here may be useful for developing excellent spectroscopic probes with cleavable active bonds for other analytes.     

Application of artificial neural network to simultaneous potentiometric determination of silver(I), mercury(II) and copper(II) ions by an unmodified carbon paste electrode

The response characteristics and selectivity coefficients of an unmodified carbon paste electrode (CPEs) towards Ag⁺, Cu²⁺ and Hg²⁺ were evaluated. The electrode was used as an indicator electrode for the simultaneous determination of the three metal ions in their mixtures via potentiometric titration with a standard thiocyanate solution. A three-layered feed-forward artificial neural network (ANN) trained by back-propagation learning algorithm was used to model the complex non-linear relationship between the concentration of silver, copper and mercury in their different mixtures and the potential of solution at different volumes of the added titrant. The network architecture and parameters were optimized to give low prediction errors. The optimized networks were able to precisely predict the concentrations of the three cations in synthetic mixtures.     

Novel calix[4]arene based metallo-supramolecular complex for recognition of cyanide ions in aqueous medium

A novel bis-naphthalimidocalix[4]arene-Cu(II) supramolecular complex has been observed to provide an efficient recognition system for CN^? ions in aqueous medium. The binding stoichiometry of bis-naphthalimidocalix[4]arene and copper ion has been found to be 1:1 while that for bis-naphthalimidocalix[4]arene-Cu(II) and cyanide ion it has been determined to be 1:2.     

Novel naphthalene-based fluorescent chemosensors for Cu2+ and Fe3+ in aqueous media

Three novel compounds bearing 2,7-dihydroxylnaphthalene capable of detecting Cu²⁺ or Fe³⁺ have been synthesised based on photoinduced electron transfer. The ability of these compounds for complex transition metal ions has been studied, and complex stoichiometry for Cu²⁺ and Fe³⁺ complex has been determined in the Tris–HCl (0.01 M DMSO/H₂O (v/v) 1:1, buffer, pH 7.4) solution system by fluorescence titration experiments. These chemosensors form a 1:1 complex with Cu²⁺ or Fe³⁺ and show a fluorescent quenching with a binding constant of (4.46 ± 0.29) × 10³ and (8.04 ± 0.26) × 10⁴, respectively.     

Selective solid-phase extraction of trace cadmium(II) with an ionic imprinted polymer prepared from a dual-ligand monomer

A novel dual-ligand reagent (2Z)-N,N′-bis(2-aminoethylic)but-2-enediamide, was synthesized and applied to prepare metal ion-imprinted polymers (IIPs) materials by ionic imprinted technique for selective solid-phase extraction (SPE) of trace Cd(II) from aqueous solution. In the first step, Cd(II) formed coordination linkage with the two ethylenediamine groups of the synthetic monomer. Then the complex was copolymerized with pentaerythritol triacrylate (crosslinker) in the presence of 2,2′-azobisisobutyronitrile as initiator. Subsequently, the imprinted Cd(II) was completely removed by leaching the dried and powdered materials particles with 0.5 M HCl. The obtained IIPs particles exhibited excellent selectivity for target ion. The distribution ratio (D) values of Cd(II)-IIPs for Cd(II) were greatly larger than that for Cu(II), Zn(II) and Hg(II). The relative selective factor (α_r) values of Cd(II)/Cu(II), Cd(II)/Zn(II) and Cd(II)/Hg(II) were 25.5, 35.3 and 62.1. The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Cd(II) was 32.56 and 6.30 mg g⁻¹, respectively. Moreover, the times of adsorption equilibration and complete desorption were remarkably short. The prepared Cd(II)-IIPs were shown to be promising for solid-phase extraction coupled with inductively coupled plasma atomic emission spectrometry (ICP-AES) for the determination of trace Cd(II) in real samples. The precision (R.S.D.) and detection limit (3σ) of the method were 2.4% and 0.14 μg L⁻¹, respectively. The column packed with Cd(II)-IIPs was good enough for Cd(II) separation in matrixes containing components with similar chemical behaviour such as Cu(II), Zn(II) and Hg(II).     

Highly selective ratiometric fluorescent sensor for Cu(II) with two urea groups

A new Naphthalene derivative with two urea groups, 1,8-bis[N-(o-methoxyphenyl)ureido]naphthalene (BMPUN), was synthesized for detecting Cu(II) ratiometrically. Complexation between urea groups of BMPUN and Cu(II) with high selectivity gives rise to a great red-shift from 380 to 440 nm in the emission spectra. The introduction of electron donating groups is helpful to increase the electron density of the nitrogen atom of urea groups and then enhance the ability of complexation for Cu(II).     

Flow-injection chemiluminescence simultaneous determination of cobalt(II) and copper(II) using partial least squares calibration

A flow-injection chemiluminescence (CL) system is proposed for simultaneous determination of Co²⁺ and Cu²⁺ using partial least squares (PLS) calibration. This method is based on the fact that both Co²⁺ and Cu²⁺ catalyse the CL reaction of luminol-H₂O₂, and that their kinetic characteristics of Co²⁺ and Cu²⁺ are significantly different in the luminol-H₂O₂ system. The CL intensity was measured and recorder at different reaction times of luminol-H₂O₂Co²⁺Cu²⁺, and the obtained data were processed by the chemometric approach of partial least squares. The experimental calibration set was composed of 16 sample solutions using an orthogonal calibration design for two component mixtures. The proposed method offers the potential advantages of high sensitivity, simplicity and rapidity for Co²⁺ and Cu²⁺ determination, and was successfully applied to the simultaneous determination of both analytes in real water sample. The present paper demonstrated that the simultaneous determination of two metal ions without any prior separation has been possible using flow-injection CL system.     

Preparation of ethambutol-copper(II) complex and fabrication of PVC based membrane potentiometric sensor for copper

Copper(II) complex of ethambutol (I) was prepared and used in the fabrication of Cu(2+) selective ISE membrane. The membrane having Cu(II)-ethambutol complex (I) as electroactive material, along with sodium tetraphenylborate (NaTPB) as anion discriminator, dioctylphthalate (DOP) as plasticizer in poly(vinyl chloride) (PVC) matrix in the percentage ratio 6:2:190:200 (I:NaTPB:DOP:PVC) (w/w) gave a linear response in the concentration range 7.94x10(-6) to 1.0x10(-1) M of Cu(2+) with a slope of 29.9+/-0.2 mV per decade of activity and a fast response time of 11+/-2 s. The sensor works well in the pH range 2.1-6.3 and could be satisfactorily used in presence of 40% (v/v) methanol, ethanol and acetone and is selective for copper over a large number of cations with slight interference from Na(+) and Co(2+) if present at a level 1.5x10(-5) and 6.5x10(-5) M, respectively. It works well over a period of 6 months and can also be used as indicator electrode for the end point determination in the potentiometric titration of Cu(2+) against EDTA as well as in the determination of Cu(2+) in real samples.     

EPR studies of Cu2+ in tetraaqua-di(nicotinamide) Zn(II)-saccharinate single crystals

Electron paramagnetic resonance (EPR) studies of copper ions, Cu(II), as paramagnetic impurity in tetraaqua-di(nicotinamide) Zn(II)-saccharinates single crystals [Zn(nic)2(H2O)4](sac)2, have been investigated at ambient temperature. The detailed EPR analysis shows the only one site and the copper ion entered the lattice substitutionally in place of Zn(II). The spin-Hamiltonian parameters were obtained from the single crystal EPR analysis. By using the EPR data, molecular bonding coefficient and the Fermi contact interaction terms have been evaluated. Superhyperfine splittings were observed.     

Novel potentiometric copper (II) selective membrane sensors based on cyclic tetrapeptide derivatives as neutral ionophores

Two novel membrane sensors sensitive and reasonably selective for Cu²⁺ ions are described. These are based on the use of newly synthesized cyclic tetrapeptide derivatives as neutral ionophores and sodium tetraphenylborate (NaTPB) as an anionic excluder in plasticized PVC membranes. The sensors exhibit fast and stable near-Nernstian response over the concentration range 1.0 × 10⁻⁶ mol l⁻¹ to 1.0 × 10⁻² mol l⁻¹ Cu²⁺ with a cationic slope of 30.2-25.9 mV per decade at pH 4.5-7 with a lower detection limit of 0.05-0.13 μg ml⁻¹. Effects of plasticizers, lipophilic salts and various foreign common ions are tested. The sensors display long life-span, long term stability, high reproducibility, and short response time. Selectivity of both sensors is significantly high for Cu²⁺ over Fe³⁺, Al³⁺, Zn²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Co²⁺, Mn²⁺, alkaline earth and alkali metal ions. The sensors are used for direct measurement of copper content in different rocks and industrial wastewater samples from electroplating factories. The results agree fairly well with data obtained using atomic absorption spectrometry.     

A highly selective molecularly imprinted electrochemiluminescence sensor for ultra-trace beryllium detection

A new molecularly imprinted electrochemiluminescence (ECL) sensor was proposed for highly sensitive and selective determination of ultratrace Be²⁺ determination. The complex of Be²⁺ with 4-(2-pyridylazo)-resorcinol (PAR) was chosen as the template molecule for the molecularly imprinted polymer (MIP). In this assay, the complex molecule could be eluted from the MIP, and the cavities formed could then selectively recognize the complex molecules. The cavities formed could also work as the tunnel for the transfer of probe molecules to produce sound responsive signal. The determination was based on the intensity of the signal, which was proportional to the concentrations of the complex molecule in the sample solution, and the Be²⁺ concentration could then be determined indirectly. The results showed that in the range of 7 × 10⁻¹¹ mol L⁻¹ to 8.0 × 10⁻⁹ mol L⁻¹, the ECL intensity had a linear relationship with the Be²⁺ concentrations, with the limit of detection of 2.35 × 10⁻¹¹ mol L⁻¹. This method was successfully used to detect Be²⁺ in real water samples.     

Azo 8-hydroxyquinoline benzoate as selective chromogenic chemosensor for Hg and Cu

Azo 8-hydroxyquinoline benzoate (2) was synthesized and studied to detect metal ions. Distinct color change was found for compound 2 in the presence of transition metal ions Hg²⁺ or Cu²⁺ in CH₃CN, respectively, which makes it possible for distinguishing Hg²⁺ and Cu²⁺ from other metal ions by the ‘naked eye’.     

Cu(II)-triggered release of paclitaxel from a supramolecular complex

The research on the stimuli-responsive property of biological or synthetic macromolecules in a wide range of scientific fields is a crucial subject for the achievements of the targeted drug release and the precise control of the functions of the supramolecules at a molecular level. We used an anthraquinone-functioned cyclodextrin (1) bridged by an aza-arm to solubilise paclitaxel (PTX) by forming a supramolecular complex (1/PTX). The possible inclusion mode was given based on the experimental results of ultraviolet–visible spectroscopy, Fourier transform infrared, X-ray diffraction, fluorescence spectra, nuclear magnetic resonance, transmission electron microscope, scanning electron microscope and dynamic light scattering characterisations. The controlled release of PTX can be achieved by adding Cu²⁺ to the solution. This study provides useful references in developing stimuli-responsive drug-carrying and drug-releasing materials.     

Synthesis of Cu-mediated nano-sized salbutamol-imprinted polymer and its use for indirect recognition of ultra-trace levels of salbutamol

Cu²⁺-mediated salbutamol-imprinted polymer nanoparticles, synthesized by precipitation polymerization, were mixed with graphite powder and n-eicosane in order to fabricate a modified carbon paste electrode. This electrode was then applied for indirect differential pulse voltammetry determination of salbutamol. In the presence of Cu²⁺ ions, the formed Cu²⁺–salbutamol complex was adsorbed in to the pre-designed cavities of the MIP particles, situated on the electrode surface. Since the electrochemical signal of salbutamol was intrinsically small, the oxidation peak of the participant Cu²⁺, after reduction step, was recorded and used as an indication of salbutamol amount, adsorbed in the electrode. Different variables influencing the sensor performance were studied and the best conditions were chosen for the determination purpose. Correlation between the sensor response to salbutamol and its concentration was linear in the range of 1.0 × 10⁻⁹–5.5 × 10⁻⁸ M. Detection limit was calculated equal to 6.0 × 10⁻¹⁰ M (S/N). Five replicated determination of salbutamol (1 × 10⁻⁸ M) resulted in standard error of 3.28%, meaning a satisfactory precision of the determination method. The prepared sensor was applied for real sample analysis. In order to minimize the interference effect, the synthesized polymer was successfully used as a solid phase sorbent for salbutamol extraction, before analysis of real samples by the developed sensor.