Heavy metal complexation by N-acyl(thio)urea-functionalized cavitands: synthesis, extraction and potentiometric studies

The synthesis and binding properties of resorcinarene-based cavitands functionalized with N-acylthiourea moieties towards different cations are described. Extraction studies with metal (Pb²⁺, Cu²⁺, Ag⁺, Hg²⁺, Cd²⁺, Eu³⁺, Fe³⁺, K⁺, Na⁺, and Ca²⁺) picrates and the incorporation in ion selective electrodes (ISEs), show that there is more than a 40% increase of the Ag⁺ extraction for N-acylthiourea ionophores (2, 3, and 8) in comparison with N-benzoyl-N′-benzylthiourea (9). Ionophore 8, which has a C₃ chain between the platform and the ionophore, extracts two times more Cu²⁺ than the more rigid one (2). Stoichiometry studies showed for ligand 2 a ligand/metal ratio of 1:1, while for model compound 9 a ratio of 1:2 was found. Potentiometric studies of electrodes revealed that cavitands 2, 3, and 8 induce a significantly different selectivity pattern compared to the cation-exchanger used, as well as model compound 9. Especially, a considerable enhancement of the selectivity towards Ag⁺ and Pb²⁺ over K⁺, Ca²⁺, and Na²⁺ ions was observed.     

Novel fluorescent sensor for Ag and Hg based on the BINOL-pyrene derivative via click reaction

A novel BINOL-pyrene derivative sensor 1 for Ag⁺ and Hg²⁺ incorporating the triazole moieties and pyrenes was synthesized via click reaction. Binding of Ag⁺ ion induces the formation of 1:1 Ag⁺-1 chelating complex, and occurs in a ratiometric manner through an enhanced monomer and declining excimer emission, which make it possible to ratiometrically detect Ag⁺. The competitive experiment shows 1 can be used as an Ag⁺ specific fluorescence sensor over a wide range of competing cations. In the meanwhile, the sensor 1 was found to be selectively quenched by only Hg²⁺ at both monomer and excimer emission. Furthermore, we obtained evidences for different fluorescence signaling behaviors with Ag⁺ and Hg²⁺ by ¹H NMR titration experiments.     

A convenient synthesis of new thiaazacrown ethers and study of their complexation reactions with some transition metal cations in binary acetonitrile–chloroform mixture using the conductometric method

Three novel thiaazacrown ethers 1, 2 and 3 were synthesized in a simple way and in high yield. The complex formation between Ag⁺, Cu²⁺, Zn²⁺, Pb²⁺, Hg²⁺ and Cd²⁺ metal cations with thiaazacrown ethers 1, 2 and 3 have been studied in acetonitrile:chloroform (1:1) binary solvent system using conductometric technique. The conductance data show that the stochiometry of the complexes with Ag⁺, Cu²⁺ and Zn²⁺ cations is 1:1 (L:M), but in the case of Pb²⁺ and Hg²⁺ cations, a 1:2 (L:M) complex is formed in solutions. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data at 25 °C. It was found that the stability constants of 1-Ag²⁺, 2-Ag⁺ and 3-Ag⁺ complexes are higher than those of their corresponding Zn²⁺ and Cu²⁺ complexes and found to vary in order 3 > 1 > 2 for Ag⁺.     

Synthesis,characterization and metal ion complexation and extraction capabilities of calix[4]arene Schiff base compounds

The syntheses, characterization and metal ion complexation and extraction capabilities of six new calix[4]arene Schiff base compounds, 5–10, are reported. The preparation of the compounds was achieved by the condensation of 5,17-diamino-11,23-di-tert-butyl-25,27-di-n-butoxy-26,28-dihydroxycalix[4]arene with the appropriate aldehyde (5-bromosalicylaldehyde for 5, 4-anisaldehyde for 6, 4-(dimethylamino)benzaldehyde for 7, 9-anthracenecarboxaldehyde for 8, 1-pyrenecarboxaldehyde for 9, and 9-fluorenecarboxaldehyde for 10) in refluxing ethanol. The compounds were characterized by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry and elemental analysis. The X-ray crystal structures of 7, 8 and 9 (as dichloromethane solvates) revealed that the calixarene molecules adopt H-bond stabilized, distorted-cone conformations and form centrosymmetric dimers in the solid state. Compounds 5–10 did not form host–guest complexes with NEt₄[(bdt)MoO₂(OSiPh₃)] (bdt^2–=benzene-1,2-dithiolate), a potential precursor for biologically relevant oxosulfido-Mo(VI/V) enzyme models; such host–guest complexes have the potential to stabilize these sought-after but highly reactive model compounds. In addition, the capabilities of 5–10 to extract selected metal ions (Ni²⁺, Co²⁺, Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺, Cd²⁺ and Hg²⁺) from an aqueous into an organic phase have been assessed by picrate extraction experiments. Compound 5 displayed exceptional selectivity towards Ni²⁺, compound 7 exhibited enhanced extraction towards all of the metal ions tested and compounds 6, 9 and 10 showed very high selectivity towards Hg²⁺. On the other hand, compound 8 exhibited negligible capacity to extract any of the metal ions tested.     

A hybrid mesoporous material functionalized by 1,8-naphthalimide-base receptor and the application as chemosensor and absorbent for Hg2+ in water

A novel hybrid material (SBA-P1) is prepared through the functionalization of mesoporous silica (SBA-15) with a 1,8-naphthalimide-based dye by sol-gel reaction. The characterization results of elemental analysis (EA), X-ray powder diffractometer (XRD) and spectroscopic methods demonstrate the fluorescence dye P1 is successfully grafted onto the inner surface of SBA-15 and the organized structure is preserved. SBA-P1 can detect Hg²⁺ with high selectivity to Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Ni²⁺, Co²⁺, Ag⁺, Cr³⁺, and Mg²⁺, Ca²⁺, Li⁺, Na⁺, K⁺ in water and sensitivity to environmentally relevant mercury in complex natural samples. The quenching fluorescence detection is also reversible by treating with EDTA/base. Furthermore, its fluorescence intensity keeps stable in the physiologically relevant pH range. The extraction ability of SBA-P1 is also estimated by inductively coupled plasma source mass spectrometer (ICP), showing that approximately 90% of the Hg²⁺ ion is extracted. These results imply that the hybrid material has potential application for sensing and removing of Hg²⁺ ions in waste water and working as toxicide for acute mercury poisoning.     

Synthesis of crownophanes possessing bipyridine moieties: bipyridinocrownophanes exhibiting perfect extractability toward Ag ion

Novel crownophanes with two bipyridine moieties (bipyridinocrownophanes 1a and 1b) were conveniently prepared by means of intramolecular [2+2] photocycloaddition of vinylbipyridine derivatives. In the liquid-liquid extraction of heavy metal cations, 1a and 1b exhibited perfect selectivity toward Ag⁺ with high efficiency. It was found that the ethereal oxygen atoms and the four nitrogen atoms in 1a and 1b acted as ligating sites, according to the high extractability and complexing stability constant for Ag⁺ compared to those of the corresponding pyridinocrownophanes 4a and 4b. ¹H NMR and ESI-MS analyses suggested that the crownophanes formed a 1:1 complexes with the Ag⁺ ion.     

Improving the use of mercury bis(phenyltellurolate) as efficient start for the synthesis of ternary clusters and polymers

Hg(TePh)₂ reacts with AgCl/PMe₂Ph and AgClO₄/PPh₃ to give the ternary clusters [(PhTe)₄Ag₂Hg₂(Cl)₂]_n (1) and [(PhTe)₁₆Ag₄Hg₆Py₄] · H₂O (2). While 1 assembles polymeric, bidimensional layers, 2 attains high symmetric moieties in which the occupational relationship is 40%/60% for the Ag⁺ and Hg²⁺ ions, respectively.     

Mesitylene based azo-coupled chromogenic tripodal receptors—a visual detection of Ag(I) in aqueous medium

A series of novel tripodal ligands 3a-d, based on a mesitylene anchor, containing aza-thioethers as donor atoms and coupled with 4-(4/3/2-nitrophenyl)azophenol or 4-(2-chlorophenyl)azophenol have been synthesized as chromogenic receptors, which are highly selective for silver(I). The complexation behavior of 3a-d with various metal ions has been evaluated by UV-vis spectrometry in dioxane/water (1:9/v:v) solution at 25 °C. The UV-vis spectra show that the complexation of 3a-c with Ag⁺ have pronounced bathochromic shifts accompanied by a unique color change in the solution from yellow to red, which is visible with the naked eye. The ligands do not show any significant change on addition of other metal ions like Li⁺, Na⁺, K⁺, Sr²⁺, Ca²⁺, Cd²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Ni²⁺, and Cu²⁺ and thus are highly specific and selective for Ag⁺ in the aqueous medium.     

Metal binding studies using spiroacetal thiacrown ethers

The binding ability of a series of spiroacetal thiacrown ethers with Li⁺, Na⁺, K⁺, Cs⁺, Co²⁺, Cd²⁺, Ag⁺ and Pb²⁺ is reported. The thiacrown ethers showed an affinity for the heavy metals. The interaction of the three thiacrown ethers 1-3 and [Al(acac)₃] 5, [Co(NH₃)₅NO₂](BPh₄)₂6 and [Co(en)₃](BPh₄)₃7 complexes is also investigated.     

Synthesis and characterization of novel indole-containing half-crowns as new emissive metal probes

Two new indole derivatives have been synthesized by a one-pot procedure and their potential as fluorescence probes for metal ions was investigated. The sensor capability of 1 and 2 toward cations such as Ag⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Hg²⁻ was studied in dichloromethane solution by absorption, fluorescence emission, and ¹H NMR titrations. Both probes showed selectivity for Ag⁺ and Hg²⁺ ions. The results suggest that these compounds may serve as promising models for future design of novel and more potent sensors.     

Novel versatile imine—enamine chemosensor based on 6-nitro-4-oxo-4H-chromene for ion detection in solution, solid and gas-phase: synthesis, emission, computational and MALDI-TOF-MS studies

A new versatile emissive molecular probe (3) derived from 1,5-bis(2-aminophenoxy)-3-oxopenthane bearing two units of 6-nitro-4-oxo-4H-chromene- has been prepared by a Schiff-base condensation method using conventional and green, ultrasound-aided, methods. The dry yellow powder was characterized as the imine species (3). These imine species, however, where found to rapidly convert to their enamine form (4) in solution, under the presence of water traces. This reaction was computationally studied through Density Functional Theory (DFT) in order to investigate the relative stability of the molecular pair 3/4. The sensing properties of the enamine (4) towards various metal ions were investigated via absorption and fluorometric titrations in solution in dichloromethane, acetonitrile and DMSO. The compound shows a fluorescent turn-off response in the presence of Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Ag⁺ over the other metal ions studied, such as Li⁺, Na⁺, K⁺, Ca²⁺, Co²⁺ and Ni²⁺, being stronger for Cu²⁺ and Hg²⁺. The gas phase chemosensing abilities of (3) were also explored suggesting (3) as new active MALDI-TOF-MS matrix by two dry methods showing a strong selectivity towards Cu²⁺ and Ag⁺. Our preliminary results show promising uses of (3) supported in PPMA films as metal ion solid chemosensor.     

Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag ion

New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag⁺ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu²⁺, and Hg²⁺ quench both the monomer and excimer emission of pyrene acutely. The ¹H NMR results indicated that Ag⁺ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene.     

Synthesis, NMR characterization and ion binding properties of 1,3-bridged p-tert-butyldihomooxacalix[4]crown-6 bearing pyridyl pendant groups

1,3-Di(2-pyridylmethoxy)-p-tert-butyldihomooxacalix[4]arene-crown-6 (2) was synthesized for the first time. 2 was isolated in a cone conformation in solution at room temperature, as established by NMR spectroscopy (¹H, ¹³C and NOESY). Complete assignment of both proton and carbon NMR spectra was achieved by a combination of COSY, HSQC and HMBC experiments. The binding properties of ligand 2 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with other dihomooxacalix[4]arene-crowns-6 and closely-related calix[4]arene-crown derivatives. 2 shows a preference for the soft heavy metal cations (except for Cd²⁺), with a very strong affinity for Ag⁺. Some transition metal cations are also well extracted. 2 forms 1:1 complexes with K⁺, Ca²⁺ and Ag⁺, and ¹H NMR titrations indicate that they should be encapsulated into the cavity defined by the crown ether unit and by the two pyridyl pendant arms. A 1:2 (ML₂) complex is formed with Zn²⁺ and two species, probably 1:1 and 1:2 complexes, are obtained with Pb²⁺.     

Luminophore-immobilized mesoporous silica for selective Hg sensing

Novel mesoporous silica-immobilized rhodamine (MSIR) and silica particle-immobilized rhodamine (SPIR) anchored by a tren (N(CH₂CH₂NH₂)₃) were synthesized. The binding and adsorption abilities of both MSIR and SPIR for metal cations were investigated with fluorophotometry and ion chromatography, respectively. Both MSIR and SPIR show selectivity for Hg²⁺ ion over other metal cations because the Hg²⁺ ion selectively induces a ring opening of the rhodamine fluorophores. The sensitivity of the MSIR for Hg²⁺ ion is greater than that of the SPIR and the MSIR adsorbs 70% of Hg²⁺ ion while the SPIR does only 40%. The MSIR can be also easily recovered by treatment of a solution of TBA⁺OH⁻. For the application of Hg²⁺ detection in the environmental field, the MSIR-coated glass plate is also developed and exhibits an excellent function in visual and fluorescence changes with Hg²⁺ ion.     

Photoactive chemosensors 4: a Cu protein cavity mimicking fluorescent chemosensor for selective Cu recognition

Fluorescent chemosensor 3 can sense Cu²⁺ ions (1-8 μM) even in the presence of elevated levels of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺, Ag⁺ and Pb²⁺ (5000 μM). 3 can also analyze for Ag⁺ ions (50-500 μM) in the presence of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺ and Pb²⁺ (5000 μM) but Cu²⁺ strongly interferes.     

Syntheses, spectroscopic and structural characterizations and metal ion binding properties of Schiff bases derived from 4′-aminobenzo-15-crown-5

A series of benzyloxybenzaldehyde derivatives (1-4) were synthesized by the reactions of 4-(bromomethyl)benzonitrile with 4-hydroxy-3-methoxybenzaldehyde (vanillin), 2-hydroxy-3-methoxybenzaldehyde (o-vanillin), 2-hydroxy-4-methoxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde. Condensation reactions among the new benzyloxybenzaldehyde derivatives (1-4) with 4′-aminobenzo-15-crown-5 yielded the new Schiff base compounds (5-8). Sodium complexes (5a-8a) and potassium complexes (5b-8b) were prepared with NaClO₄ and KI, respectively. All of these synthesized compounds were characterized on the basis of FT-IR, ¹H and ¹³C NMR, mass spectrometry and elemental analyses data. The solid state structures of compounds 8 and 5a were determined by X-ray crystallography. The extraction abilities of compounds 5-8 were also evaluated in CH₂Cl₂ by using several main group and transition metal picrates, such as Na⁺, K⁺, Pb²⁺, Cr³⁺, Ni²⁺, Cu²⁺ and Zn²⁺.     

Three different fluorescent responses to transition metal ions using receptors based on 1,2-bis- and 1,2,4,5-tetrakis-(8-hydroxyquinolinoxymethyl)benzene

The dipod 1,2-bis(8-hydroxyquinolinoxymethyl)benzene (3) and tetrapod 1,2,4,5-tetrakis(8-hydroxyquinolinoxymethyl)benzene (5) have been synthesized through nucleophilic substitution of respective 1,2-bis(bromomethyl)benzene (2) and 1,2,4,5-tetra(bromomethyl)benzene (4) with 8-hydroxyquinoline (1). For comparison, 1,3,5-tris(8-hydroxyquinolinoxymethyl)benzene derivatives (7a and 7b) have been obtained. The complexation behavior of these podands towards Ag⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺ metal ions has been investigated in acetonitrile by fluorescence spectroscopy. The sterically crowded 1,2,4,5-tetrapod 5 displays unique fluorescence ‘ON-OFF-ON’ switching through fluorescence quenching (λ_max 395 nm, switch OFF) with <1.0 equiv of Ag⁺ and fluorescence enhancement (λ_max 495 nm, switch ON) with >3 equiv Ag⁺ and can be used for estimation of two different concentrations of Ag⁺ at two different wavelengths. The addition of Cu²⁺, Ni²⁺, and Co²⁺ metal ions to tetrapod 5 causes fluorescence quenching, i.e., ‘ON-OFF’ phenomena at λ_max 395 nm for <10 μM (1 equiv) of these ions but addition of Zn²⁺ and Cd²⁺ to tetrapod 5 results in fluorescence enhancement with a gradual shift of λ_em from 395 to 432 and 418 nm, respectively. Similarly, dipod 3 behaves as an ‘ON-OFF-ON’ switch with Ag⁺, an ‘ON-OFF’ switch with Cu²⁺, and an ‘OFF-ON’ switch with Zn²⁺. The placement of quinolinoxymethyl groups at the 1,3,5-positions of benzene ring in tripod 7a-b leads to simultaneous fluorescence quenching at λ_max 380 nm and enhancement at λ_max 490 nm with both Ag⁺ and Cu²⁺. This behavior is in parallel with 8-methoxyquinoline 8. The rationalization of these results in terms of metal ion coordination and protonation of podands shows that 1,2 placement of quinoline units in tetrapod 5 and dipod 3 causes three different fluorescent responses, i.e., ‘ON-OFF-ON’, ‘ON-OFF’, and ‘OFF-ON’ due to metal ion coordination of different transition metal ions and 1, 3, and 5 placement of three quinolines in tripod 7, the protonation of quinolines is preferred over metal ion coordination. In general, the greater number of quinoline units coordinated per metal ion in 5 compared with the other podands points to organization of the four quinoline moieties around metal ions in the case of 5.     

Complexing properties of two benzocrown-ether moieties arranged at a cyclobutane ring system

Biscrown ethers 2a-c and 3a-c arranged at a cyclobutane ring were prepared by intermolecular [2+2] photocycloaddition of vinylated benzocrown ethers. The complexing behavior of 2a-c toward alkali metal cations was evaluated by ESI-MS analysis, liquid-liquid extraction, and the comparison of complexing stability constant. An intramolecular sandwich-type 1:1 (host/guest) complexation was observed by ESI-MS analysis in the competitive system where 2a-Na⁺, 2b-K⁺, and 2c-Cs⁺ were formed selectively. In the liquid-liquid extraction, however, 2a hardly extracted any cation, while both 2b and 2c efficiently extracted larger cations such as K⁺, Rb⁺, and Cs⁺. It was found that the complexing stability constant of 2a-Na⁺ is lower than that of benzo-15-crown-5-Na⁺ though extraordinarily high values were obtained for 2b-K⁺ and 2c-Cs⁺ complexes compared with those of 18-crown-6-K⁺ and dibenzo-24-crown-8-Cs⁺ complexes, respectively. Hence, the excellent complexing ability was achieved by using the cyclobutane ring, which strongly preorganized two benzocrown-ether moieties for the larger alkali metal cations.     

A highly selective turn-on fluorescent chemosensor for copper(II) ion

A new pyrene derivative (1) containing a diaminomaleonitrile moiety exhibits high selectivity for Cu²⁺ detection. Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence values for the system. The apparent association constant (K_a) of Cu²⁺ binding in chemosensor 1 was found to be 5.55×10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5-7.5.     

Spectroscopic,structure and DFT studies of copper(II) and palladium(II) complexes of pyridine-2-carboxaldehyde-2-pyridylhydrazone: A chromogenic agent for palladium(II)

A heterocyclic hydrazone ligand, pyridine-2-carboxaldehyde-2-pyridylhydrazone, HL, 1, was investigated as a new chromogenic agent for selective detection of Pd²⁺. The ligand HL, 1, undergoes 1:1 complexation with Pd²⁺ and Cu²⁺ to form complexes [Pd(L)Cl], 1a and [Cu(HL)Cl₂], 1b respectively. The complex 1a gives a characteristic absorption peak at 536 nm with distinct reddish-pink coloration. The change in color can easily be distinguished from other metal complexes by the naked eye. No obvious interference was observed in the presence of other metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Sn²⁺, Hg²⁺, Pb²⁺). The association constants, K_ass (UV–Vis), were found to be 5.52 ± 0.004 × 10⁴ for 1a and 4.94 ± 0.006 × 10⁴ for 1b at 298 K. On excitation at 295 nm, the ligand HL, 1 strongly emits at 372 nm due to an intraligand ¹(π–π^∗) transition. Upon complexation the emission peaks are blue shifted (λ_ex 295 nm, λ_em 358 nm for 1a and λ_ex 295 nm, λ_em 367 nm for 1b) along with a quenching (F/F₀ 0.32 for 1a and 0.88 for 1b) in the emission intensity. DFT and TDDFT calculations were highly consistent with the spectroscopic behavior of the ligand and complexes. The molecular structure of the complex 1b has been determined by single crystal X-ray diffraction studies.