Rapid and Sensitive Determination of Hg(II) Using Polarographic Technique and Application to <Emphasis Type="Italic">Chlorophytum comosum</Emphasis>

A differential pulse polarographic (DPP) method has been used for the indirect determination of Hg(II). With a known amount of cyanuric acid (CA) in polarography cell (B–R buffer, pH 10.5) was added an unknown Hg(II) sample and the Hg(II) concentration is calculated simply from the decrease in the CA peak after reaction with Hg(II). The linear concentration range was between 20 and 120 μM and limit of detection was calculated to be 6.7 μM. The proposed method was successfully applied to the dried leave samples belong to C. comosum plant. The method was extended to the indirect determination of mercury(II) in C. comosum plant and results were in agreement with that obtained by a spectrometric comparison method (ICP-MS). The sufficiently good recoveries and low standard deviations reflect the high accuracy of developed method.     

Glassy carbon electrode modified with organic�Cinorganic pillared montmorillonites for voltammetric detection of mercury

A glassy carbon electrode modified with organic?Cinorganic pillared montmorillonite was used for voltammetric detection of mercury(II) in water. High sensitivity is obtained due to the use of the montmorillonites which displays outstanding capability in terms of adsorbing mercury ion due to its high specific surface and the presence of multiple binding sites. The experimental parameters and the effect of a chelating agent were optimized to further enhance sensitivity and selectivity. Linear calibration curves were obtained over the Hg(II) concentration range from 10 to 800???g?L^?1 for 5?min accumulation, with a detection limit of 1???g?L^?1. Simultaneous determination of Hg(II) and Cu(II) was also studied, and no interference was observed.

Square wave anodic stripping voltammetric determination of lead(II) using a glassy carbon electrode modified with a lead ionophore and multiwalled carbon nanotubes

We report on a glassy carbon electrode (GCE) modified with a lead ionophore and multiwalled carbon nanotubes. It can be applied to square wave anodic stripping voltammetric determination of Pb(II) ion after preconcentration of Pb(II) at ?1.0?V (vs. SCE) for 300?s in pH?4.5 acetate buffer containing 400?μg?L^?1 of Bi(III). The ionophore-MWCNTs film on the GCE possesses strong and highly selective affinity for Pb(II) as confirmed by quartz crystal microbalance experiments. Under the optimum conditions, a linear response was observed for Pb(II) ion in the range from 0.3 to 50?μg?L^?1. The limit of detection (at S/N?=?3) is 0.1?μg?L^?1. The method was applied to the determination of Pb(II) in water samples with acceptable recovery.

Coordination chemistry of anticrowns. Complexation of cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 with the cyanoborohydride anion [H3BCN]− and triethylamineborane Et3NBH3

As was shown by IR spectroscopy, the reaction of the three-mercury anticrown (o-C₆F₄Hg)₃ (1) with the [H₃BCN]ion in THF affords the complexes {[(o-C₆F₄Hg)₃][H₃BCN](5) and [(o-C₆F₄Hg)₃]₂[H₃BCN](6). Complex 6 was isolated from solution in the analytically pure state. According to X-ray diffraction data, complex 6 has a double-decker sandwich structure, in which the borohydride group of the [H₃BCN]^? anion is bound to one anticrown molecule by three B-H-Hg bridges, whereas the cyanide group is cooperatively coordinated by three mercury centers of another molecule 1 through the nitrogen atom. The reaction of compound 1 with triethylamineborane Et₃NBH₃ in THF affords the 1: 1 complex ～[(o-C₆F₄Hg)₃][Et₃NBH₃]～ (7). In this adduct, the binding of the aminoborane to the mercury anticrown is also accomplished by B-H-Hg bridges. The stability constants of complexes 5 and 6 in THF were determined.     

Highly sensitive SERS probe for mercury(II) using cyclodextrin-protected silver nanoparticles functionalized with methimazole

We have developed a surface-enhanced Raman scattering (SERS) probe for the determination of mercury(II) using methimazole-functionalized and cyclodextrin-coated silver nanoparticles (AgNPs). These AgNPs in pH 10 solution containing sodium chloride exhibit strong SERS at 502 cm^?1. Its intensity strongly decreases in the presence of Hg(II). This effect serves as the basis for a new method for the rapid, fast and selective determination of trace Hg(II). The analytical range is from 0.50 μg L^?1 to 150 μg L^?1, and the limit of detection is 0.10 μg L^?1. The influence of 11 metal ions commonly encountered in environmental water samples was found to be quite small. The method was applied to the determination of Hg(II) in spiked water samples and gave recoveries ranging from 98.5 to 105.2 % and with relative standard deviations of <3.5 % (n?=?5). The total analysis time is <10 min for a single sample.

Coordination compounds with the general formula trans-[M(18-crown-6)(C5HO2F6)2] as structural-thermochemical analogs. The complexes trans-[Pb(18-crown-6)(C5HO2F6)2] and trans-[Ba(18-crown-6)(C5HO2F6)2]

The molecular geometries of the complexes trans-[M(18-crown-6)(C₅HO₂F₆)₂] (where M = Ca, Sr, Ba (I), Zn, Cd, Sn, Pb (II), Fe, Co, Eu, and Yb) were modeled by the molecular mechanics method with fixed R(M-O) distances. The shielding degrees of the central metal atom in these complexes were calculated and the number and types of possible intermolecular contacts between their molecules in the structure were determined. The intermolecular interactions involve identical fragments (atoms) of the ligands: the CF₃ groups of the hexafluoroacetylacetonate ligands and the methylene fragments of the crown ether. Previously unknown complex II and complex I were synthesized according to an original procedure. The structure and thermochemical properties (including sublimation by the Knudsen method) of complex II were studied. As in complex I, the metal cation in complex II is in the cavity of the macrocycle of the crown ether; the hexafluoroacetylacetonate ligands are trans relative to that cation. The presumed similarity of complexes I and II in thermochemical characteristics was confirmed experimentally. Both the complexes melt in close temperature intervals and sublime at the same temperature (～10^?2 mm Hg) without decomposition. The enthalpies of sublimation of complexes I and II, as well as the entropy contributions to their volatilities, are equal to within the experimental error.     

Carbon dots-based fluorescent probes for sensitive and selective detection of iodide

We report on a simple method for the determination of iodide in aqueous solution by exploiting the fluorescence enhancement that is observed if the complex formed between carbon dots and mercury ion is exposed to iodide. Fluorescent carbon dots (C-dots) were treated with Hg(II) ion which causes quenching of the emission of the C-dots. On addition of iodide, the Hg(II) ions are removed from the complex due to the strong interaction between Hg(II) and iodide. This causes the fluorescence to be restored and enables iodide to be determined in the 0.5 to 20 μM concentration range and with a detection limit of ~430 nM. The test is highly selective for iodide (over common other anions) and was used for the determination of iodide in urine.

Coordination modes of 3-hydroxypicolinic acid: Synthesis and structural characterization of polymeric mercury(II) complexes

Novel mercury(II) compounds of 3-hydroxypicolinic acid (HpicOH; IUPAC name: 3-hydroxy-2-pyridinecarboxylic acid) were synthesized and characterized. HgCl(picOH) (1) and HgBr₂(HpicOH) (2) were obtained as reaction products from the reaction of the corresponding mercury(II) halide with HpicOH, irrespective of the molar ratio of the reactants. From the reaction of HpicOH and mercury(II) acetate, Hg(picOH)₂ (3) was obtained, while mercury(II) nitrate monohydrate gave the 1/1 solvate with water Hg(picOH)₂ · H₂O (3a). Infrared, ¹H and ¹³C NMR spectroscopic data were analyzed for complexes 1, 2 and 3. X-ray crystal structure analysis of 1 and 2 revealed their polymeric nature and different coordination modes of HpicOH. In 1 the deprotonated picolinic acid is N,O-chelating and bridging, while in 2 HpicOH is a O-monodentate weakly bound ligand. Compound 1 consists of HgCl(picOH) moieties with two linear covalent bonds, Hg–N 2.143(4) and Hg–Cl 2.298(1) Å, and four additional Hg?O contacts (2.460(3)–2.904(3) Å) in which both oxygen atoms from the carboxylic group are bridging and involved in coordination to three neighboring mercury atoms, thus forming infinite layers. The coordination of mercury is 2 + 4. 2 consists of {HgBr₂(HpicOH)} moieties, which are linked into chains by means of mercury to bromine secondary long range interactions. The coordination sphere of mercury can be described as irregular 2 + 3 formed by two covalently bonded bromine atoms (Hg–Br 2.277(1) and 2.366(1) Å), two bridging bromine atoms (Hg?Br 3.309(1) and 3.247(1) Å) and by the HpicOH ligand attached to mercury in the zwitterionic form via the carboxylic oxygen atom (Hg?O 2.602(7) Å).     

Diiodo{N,N′-Bis(2,3,4-trimethoxybenzaldehyde)-ethylenediimine}mercury(II): Synthesis and crystal structure

Mononuclear mercury(II) complex [Hg((2,3,4-MeO-Ba)₂En)I₂] (I), where (2,3,4-MeO-Ba)₂En = N,N′-bis(2,3,4-trimethoxybenzaldehyde)ethylenediimine, has been synthesized and characterized by elemental analysis (C, H, and N) and confirmed by single-crystal X-ray diffraction analysis. The complex I crystallizes in the monoclinic system, with space group C2/c, having one symmetry-independent Hg²⁺ ion coordinated in distorted tetrahedral geometry by two N atoms of the Schiff base ligand and by two I atoms. The Schiff base ligand (2,3,4-MeO-Ba)₂En acts as a chelating ligand and coordinates via two N atoms to the mercury center and adopts an (E,E) conformation.     

New molecular complexes of trimeric perfluoro-ortho-phenylene mercury with heterocyclic compounds

Slow evaporation in air of the solution of trimeric perfluoro-ortho-phenylene mercury (1) and 2,1,3-benzothiadiazole (2) in THF affords a complex l.2 ₂·H₂O_0.59 (3). A complex of 1 with di(tetrahydrofur-2-yl) ether (4; probably, a THF oxidation product) with a composition of 1.4 ₂ (5) is detected as a minor admixture to 3. The structure of complexes 3 and 5 is determined by single crystal XRD. In complex 3, a molecule of 1 participates in Hg…N and π_F…H—C interactions with one molecule of 2 and in the π_F…π_H stacking interaction with another. Complex 5 is formed by Hg…O interactions with the participation of both heterocycles of a molecule of 4.     

Bulk polymer nanoparticles containing a tetrakis(3-hydroxyphenyl)porphyrin for fast and highly selective separation of mercury ions

We report on the synthesis of polymeric nanoparticles (PNPs) containing a tetrakis(3-hydroxyphenyl)porphyrin, and their use for the separation of mercury(II) ion. The PNPs were prepared by bulk polymerization from methacrylic acid (the monomer), ethyleneglycol dimethacrylate (the cross-linker), 2,2′-azobisisobutyronitrile (the radical initiator) and the mercury(II) complex of 5,10,15,20-tetrakis(3-hydroxyphenyl)-porphyrin. The Hg(II) ion was then removed by treatment with dilute hydrochloric acid. The PNPs were characterized by colorimetry, FT-IR spectroscopy, and scanning electron microscopy. The material is capable of binding Hg(II) from analyte samples. Bound Hg(II) ions can be eluted with dilute nitric acid and then quantified by cold vapor AAS. The extraction efficiency, the effects of pH, preconcentration and leaching times, sample volume, and of the nature, concentration and volume of eluent were investigated. The maximum adsorption capacity of the PNPs is 249 mg g^?1, the relative standard deviation of the AAS assay is 2.2 %, and the limit of detection (3σ) is 8 ng.L^?1. The nanoparticles exhibit excellent selectivity for Hg(II) ion over other metal ions and were successfully applied to the selective extraction and determination of Hg(II) ion in spiked water samples.

Two novel metal organic frameworks of Sn(II) and Pb(II) with Pyridine-2,6-dicarboxylic Acid and 4,4′-Bipyridine: syntheses, crystal structures and solution studies

Two novel compounds with formulae [Sn₂(pydcH)₂(H₂O)₂O]_n, 1, and (4,4′-bpyH₂)_0.5[Pb(pydc)₂(4,4′-bpyH)].4,4′-bpy.4H₂O, 2, were obtained from a one-pot reaction between pyridine-2,6-dicarboxylic acid (pydcH₂) and 4,4′-bipyridine (4,4′-bpy) with corresponding Sn(II) and Pb(II) salts. In compound 1 with a polymeric structure, each Sn(II) atom is six-coordinated by one water molecule, two (pydcH)^? groups and one oxide group resulted in a coordination polymer. Compound 2 has a seven-coordinated environment around Pb(II) atom by two (pydc)^2? groups and one (4,4′-bpyH). The anionic complex is balanced by half a (4,4′- bpyH₂)²⁺ as counter ion. There are four uncoordinated water molecules and one 4,4′-bpy in the crystal lattice. Therefore, in compound 2, we have neutral, mono- and biprotonated forms of 4,4′-bipyridine, simultaneously. Several interactions including O-H??? O, O-H???EN and C-H???O hydrogen bonds, ion pairing, C-O???π (O???Cg 3.324(3) Å and 3.381(3) Å in 1 and O???Cg 3.346(4) Å in 2), C-H???π (C???Cg 3.618(4) Å in 2), and π???π stackings (with Cg ??? Cg distances of 3.613(2) and 3.641 (2) Å in 2) are present to expand and stabilize the structure. The complexation reactions of bpy and pydc-bpy with Sn²⁺ and Pb²⁺ ions in aqueous solution were investigated by potentiometric pH titrations, and the resulting equilibrium constants and species distributions at various pHs for major formed complexes are described.     

Solid-phase extraction of mercury(II) with magnetic core-shell nanoparticles, followed by its determination with a rhodamine-based fluorescent probe

Magnetic Fe₃O₄@SiO₂ core shell nanoparticles containing diphenylcarbazide in the shell were utilized for solid phase extraction of Hg(II) from aqueous solutions. The Hg(II) loaded nanoparticles were then separated by applying an external magnetic field. Adsorbed Hg(II) was desorbed and its concentration determined with a rhodamine-based fluorescent probe. The calibration graph for Hg(II) is linear in the 60 nM to 7.0 μM concentration range, and the detection limit is at 23 nM. The method was applied, with satisfying results, to the determination of Hg(II) in industrial waste water.

Hydrothermal syntheses, crystal structures and fluorescent properties of five transition metal–organic hybrids incorporating an unsymmetrical benzotriazole carboxylate ligand

The hydrothermal reactions of nitrate or chloride salts of Co(II), Zn(II), Cd(II), Hg(II) and Ag(I) with an unsymmetrical benzotriazole derivative 1H-1,2,3-benzotriazole-1-propionic acid (Hbtap) afforded five new metal–organic coordination polymers with formula of [M(btap)₂(H₂O)₂] _n (M = Co 1, Zn 2, Cd 3), [Hg(btap)Cl] _n (4) and {[Ag(btap)]·H₂O} _n (5), which were characterized by X-ray diffraction and spectroscopic methods. The anionic btap^? ligands in these complexes assume the same anti conformation, but show different coordination behaviors toward transition metal ions. Complexes 1, 2 and 3 are isostructural and reveal infinite one-dimensional (1D) looped-chain structures constructed by hexacoordinated metal centers and 2-connected btap^? bridges. Complex 4 features 1D zigzag polymeric arrays, which are interlinked with each other resulting in a chiral three-dimensional (3D) 4-connected framework. In complex 5, the 3-connected ligands join Ag(I) atoms into a 1D ribbon motif. The photoluminescence spectra of three d¹⁰ metal complexes 2, 3 and 4 were measured at room temperature. The emission peaks of these complexes resemble that of the free ligand and can be ascribed to the intraligand π–π* transitions.     

Aptamer based test stripe for ultrasensitive detection of mercury(II) using a phenylene-ethynylene reagent on nanoporous silver as a chemiluminescence reagent

We describe a paper-based chemiluminescence (CL) test for the determination of mercury(II) ion. A single-stranded DNA aptamer was first covalently immobilized via its amino groups to the hydroxy groups on the surface of cellulosic paper. The aptamer probes can capture Hg(II) ions due to their specific interaction with thymine. The CL reagent (a caboxylated phenylene-ethynylene referred to as P-acid) was immobilized on nanoporous silver (NPS@P-acid) and used a CL label on the aptamer. The stripe is then contacted with a sample containing Hg(II) ions and CL is induced by the addition of permanganate. CL intensity depends on the concentration of Hg(II) because Hg(II) increases the quantity of the P-acid-conjugated aptamer. The highly active surface of the NPS@P-acid composites results in an 8-fold higher CL intensity compared to the use of pure P-acid. This enables Hg(II) ion to be quantified in the 20 nM to 0.5 μM concentration range, with a limit of detection as low as 1 pM. This CL aptasensor is deemed to represent a promising tool for simple, rapid, and sensitive detection of Hg(II).

The conditions of formation of heterometallic complexes in the GeCl4 (SnCl4)-citric acid-M(CH3COO)2-H2O systems. The crystal and molecular structures of [M(H2O)6][Ge(HCit)2] · 4H2O (M = Mg, Mn, Co, Cu, Zn) and [M(H2O)6][Sn(HCit)2] · 4H2O (M = Mg, Co, Ni)

Fourteen bis(citrato)germanates(IV) and bis(citrato)stannates(IV) were prepared, in particular, [M(H₂O)₆][Ge(HCit)₂] · 4H₂O (M = Mg (I), Mn (II), Fe (III), Co (IV), Ni (V), Cu (VI), Zn (VII)) and [M(H₂O)₆][Sn(HCit)₂] · nH₂O (M = Mg, n = 4 (VIII); Mn, n = 2 (IX); Fe, n = 4 (X); Co, n = 4 (XI); Ni, n = 4 (XII); Cu, n = 4 (XIII); Zn, n = 3 (XIV)) (H₄Cit is citric acid). The purity and the composition of the products were determined by a set of physicochemical methods including elemental analysis, thermogravimetry, and IR spectroscopy. The structures of I, II, IV, VI, VII, VIII, XI, and XII were determined by X-ray diffractometry. All eight crystals composed of centrosymmetrical octahederal [M(H₂O)₆]²⁺ cations, [Ge(HCit)₂]^2? (or [Sn(HCit)₂]^2?) anions, and crystal water molecules are isostructural. The structural units in I, II, IV, VI, VII, VIII, XI, and XII are connected by systems of hydrogen bonds to form a three-dimensional framework.     

Separation and preconcentration of mercury in water samples by ionic liquid supported cloud point extraction and fluorimetric determination

We have developed a cloud point extraction procedure based on room temperature ionic liquid for the preconcentration and determination of mercury in water samples. Mercury ion was quantitatively extracted with tetraethyleneglycol-bis(3- methylimidazolium) diiodide in the form of its complex with 5,10,15,20-tetra-(4-phenoxyphenyl)porphyrin. The complex was back extracted from the room temperature ionic liquid phase into an aqueous media prior to its analysis by spectrofluorimetry. An overall preconcentration factor of 45 was accomplished upon preconcentration of a 20?mL sample. The limit of detection obtained under the optimal conditions is 0.08?μg mL^?1, and the relative standard deviation for 10 replicate assays (at 0.5?g mL^?1 of Hg) was 2.4%. The method was successfully applied to the determination of mercury in tap, river and mineral water samples.

Colorimetric detection of lead (II) based on silver nanoparticles capped with iminodiacetic acid

We report on a colorimetric probe for the determination of Pb(II). It is based on the use of silver nanoparticles that have been functionalizd with iminodiacetic acid (IDA-Ag NPs). The absorption spectrum and solution color of IDA-Ag NPs undergo dramatic changes on exposure to Pb(II) with a new absorption peak appearing at 650 nm and a concomitant color change from yellow to green. This is assumed to result from the aggregation of IDA-Ag NPs induced by Pb(II). Under optimum conditions, there is a linear relationship between the ratio of the absorbances at 650 and 396 nm, respectively, and the concentration of Pb(II) in the 0.4 to 8.0 μM concentration range, with a detection limit of 13 nM. The method was applied to the determination of Pb(II) in tap water and urea samples, and recoveries ranged from 93.7 % to 98.6 %.

Hydrothermal synthesis of a nano-rod mercury(ii) metal-ligand coordination compound

A novel nano-rod mercury(II) coordination compound [Hg (BINH)I₂] (1), (BINH is the abbreviation of benzylideneisonicotinohydrazide) is synthesized by a hydrothermal method that produces the coordination compound at a nanosize level. The new nanostructure is characterized by scanning electron microscopy, powder X-ray diffraction, elemental analysis, and IR spectroscopy. Compound 1 was structurally characterized by single crystal X-ray diffraction and the single-crystal structure of this complex shows that each mercury(II) center is four-coordinated with two N-donor atoms from tow BINH ligands and tow iodo anions. Self-assembly of this complexes is pereformed by CH?I and π-π stacking interactions. The supramolecular features in these complexes are controlled by weak directional intermolecular interactions.     

Construction of a new one-dimensional Hg(II) coordination polymer [Hg4(Chbz)4(4,4′-Bipy)2(NO3)4 · H2O] n involving in situ chlorobenzene synthesis

A new 1D Hg(II) coordination polymer, [Hg₄(Chbz)₄(4,4′-Bipy)₂(NO₃)₄ · H₂O] _n (I) (Chbz = 2-chlorophenyl, 4,4′-Bipy = 4,4′-bipyridine), has been synthesized by the in situ synthesis of 2-chlorophenyl from the reaction of 2-chlorobenzoic acid, 4,4′-Bipy and mercury salt under hydrothermal conditions and characterized by elemental analysis, IR, TGA and single-crystal X-ray diffraction. Complex I exhibits an interesting 1D infinite zigzag polymeric chain along the x axis. The photoluminescent measurements reveal that complex I exhibits fluorescent emission in the solid state at room temperature.