Utilization of an Hg(2+)-sensitive membrane-electrode in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+)

The paper reports the results obtained in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+) by using an Hg(2+)-sensitive membrane-electrode for the end-point indication. The determination of Bi(3+) and Fe(3+) is performed after addition of mercuric complexonate from which these cations release Hg(2+) by means of which the electrode senses the equivalence point. In the case of Cr(3+) an excess of complexone is added and the surplus is titrated with a standard solution of Hg(2+) in the presence of the Hg(2+)-sensitive membrane-electrode.     

Highly sensitive multiresponsive chemosensor for selective detection of Hg2+ in natural water and different monitoring environments

A new chemosensor RF1 that combines a ferrocene unit and a rhodamine block via the linkage of a carbohydrazone binding unit was designed and prepared for the highly selective detection of Hg (2+) in natural water. This chemosensor displays great brightness and fluorescence enhancement following Hg (2+) coordination within the limit of detection for Hg (2+) at 1 parts per billion (ppb). The fluorescence intensities are nearly proportional to the amount of Hg (2+) at the ppb level. It is capable of distinguishing between the safe and the toxic levels of inorganic mercury in drinking water. Hg (2+)-binding also arouses the absorption of the rhodamine moiety in RF1 significantly with the chromogenic detection limit for Hg (2+) at 50 ppb. The conventional UV-vis spectroscopic method thus has the potential to provide the critical information about the mercury hazard assessment for industrial wastewater discharging. The obvious and characteristic color change of the titration solution from colorless to pink upon the addition of Hg (2+) demonstrates that RF1 can be used for "naked-eye" detection of Hg (2+) in water. The Hg (2+) complexation also causes a significant shift of the redox potential about the ferrocene/ferrocenium couple. The electrochemical responses provide the possibility to quantitative analysis of Hg (2+) at the parts per million (ppm) level. Preliminary investigations in natural water samples including seawater and freshwater indicate that RF1 offers a direct and immediate Hg (2+) detection in complex media, pointing out its potential utility in environment monitoring and assessment. The responses of RF1 are Hg (2+) specific, and the chemosensor exhibits high selectivity toward Hg (2+) over other Group 12 metals, alkali, alkaline earth metals, and most of the divalent first-row transition metals. The RF1-Hg (2+) complex is successfully isolated and the Hg (2+)-binding is reversible. The crystal structure and spectral properties of its congener RF2 that contains one ferrocene group and two rhodamine 6G moieties were also investigated for a comparison.     

A theoretical study of the large Hg-Hg spin-spin coupling constants in Hg(2)(2+), Hg(3)(2+), and Hg(2)(2+)-crown ether complexes

Nuclear spin-spin coupling constants (1)J(Hg-Hg) in the systems Hg(2)(2+) and Hg(3)(2+) represent the largest coupling constants so far observed in NMR experiments. We have performed a computational study on these ions, on Hg(2)(2+) complexes with 18-crown-6 and 15-crown-5, and on Hg(3)(2+) with solvent molecules and counterions. The results obtained with our recently developed program for the density functional computation of heavy nucleus spin-spin coupling constants are in good agreement with experiments. The data reveal that the bare ions Hg(2)(2+) and Hg(3)(2+) would afford much larger coupling constants than those experimentally observed, with an upper limit of approximately 0.9 MHz for Hg(2)(2+). This limit is much larger than that previously estimated by Hückel theory. It is demonstrated that in solution or due to complexation the experimentally determined values are much smaller than the free ion's coupling constants. With the help of intuitive MO arguments, it is illustrated how the environment strongly reduces the coupling constants in Hg(2)(2+) and Hg(3)(2+). The two-bond coupling constant (2)J(Hg-Hg) in Hg(3)(2+) is also examined.     

Cyclic control of the surface properties of a monolayer-functionalized electrode by the electrochemical generation of Hg nanoclusters

Hg(2+) ions are bound to a 1,4-benzenedimethanethiol (BDMT) monolayer assembled on a Au electrode. Electrochemical reduction of the Hg(2+)-BDMT monolayer to Hg(+)-BDMT (at E degrees =0.48 V) and subsequently to Hg(0)-BDMT (at E degrees =0.2 V) proceeds with electron-transfer rate constants of 8 and 11 s(-1), respectively. The Hg(0) atoms cluster into aggregates that exhibit dimensions of 30 nm to 2 microm, within a time interval of minutes. Electrochemical oxidation of the nanoclusters to Hg(+) and further oxidation to Hg(2+) ions proceeds with electron-transfer rate constants corresponding to 9 and 43 s(-1), respectively, and the redistribution of Hg(2+) on the thiolated monolayer occurs within approximately 15 s. The reduction of the Hg(2+) ions to the Hg(0) nanoclusters and their reverse electrochemical oxidation proceed without the dissolution of mercury species to the electrolyte, implying high affinities of Hg(2+), Hg(+), and Hg(0) to the thiolated monolayer. The electrochemical transformation of the Hg(2+)-thiolated monolayer to the Hg(0)-nanocluster-functionalized monolayer is characterized by electrochemical means, surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact-angle measurements. The Hg(0)-nanocluster-modified surface reveals enhanced hydrophobicity (contact angle 76 degrees ) as compared to the Hg(2+)-thiolated monolayer (contact angle 57 degrees ). The hydrophobic properties of the Hg(0)-nanocluster-modified electrode are further supported by force measurements employing a hydrophobically modified AFM tip.     

Chromofluorescent indicator for intracellular Zn2+/Hg2+ dynamic exchange

The fluorescence of NABQ increases remarkably in the presence of Zn(2+) and is quenched by Hg(2+). As shown by confocal imaging, NABQ-Zn(2+) can penetrate cells, where the bound Zn(2+) is exchanged for Hg(2+). This results in the concomitant export of Hg(2+) from the cells, showing that NABQ can act as a Zn(2+) carrier and as a Hg(2+) extracting agent in living cells.     

Ratiometric sensing of Hg2+ based on the calix[4]arene of partial cone conformation possessing a dansyl moiety

A new fluorescent chemosensor based on the calix[4]arene of partial cone conformation possessing a dansyl moiety has been synthesized. The chemosensor demonstrates selective optical recognition of Hg(2+) and Cu(2+) in two contrasting modes. The receptor exhibited ratiometric sensing of Hg(2+) and "ON-OFF" type of fluorescence behavior in the presence of Cu(2+). The compound behaves as a fluorescent molecular switch upon chemical inputs of Hg(2+) and Cu(2+) ions.     

A novel cationic triazatetrabenzcorrole: selective detection of mercury(II) by nucleic acid-induced aggregation

In the present work, a novel water-soluble cationic triazatetrabenzcorrole compound was synthesised. Its aggregation and fluorescence quenching properties are demonstrated by serval methods, such as UV-vis and fluorescence spectroscopic studies and naked-eye visualization. Unlike the traditional Hg(2+) sensor based on thymine-Hg(2+)-thymine, we use a novel approach, exploiting the high affinity of Hg(2+) for sulfur in phosphorothioate DNA. Based on the S-Hg(2+)-S pairs, we designed the phosphorothioate DNA T4G4-S3 as an Hg(2+) sensor, which can detect Hg(2+) sensitively and selectively in aqueous solution. And this sensing system is fairly fast and convenient.     

A simple and label-free sensor for mercury(II) detection in aqueous solution by malachite green based on a resonance scattering spectral assay

Mercury ions (Hg(2+)) can specifically interact with the thymine-rich Hg(2+) aptamer and malachite green (MG) to form the Hg(2+) aptamer-MG-Hg(2+) complex, inducing the increase of resonance scattering (RS) intensity at 611 nm, which enables the label-free detection of Hg(2+) in aqueous solution with high selectivity and a detection limit of 1.7 nM.     

An efficient rhodamine thiospirolactam-based fluorescent probe for detection of Hg2+ in aqueous samples

This paper described the optimized design, synthesis and application of a novel rhodamine thiospirolactam derivative as an 'off-on' fluorescent probe for the detection of Hg(2+) in aqueous samples. The 'off-on' fluorescence and color signal change of the probe is based on an Hg(2+)-triggered domino reaction which brings on the opened-ring form of the rhodamine spirolactam to regain the conjugated system of the rhodamine skeleton. In the well designed probe, the thiospirolactam serves as both Hg(2+) binding unit and electron-defect carbon centre, a phenolic hydroxyl with very strong nucleophilicity after deprotonation is chosen as the attacking unit, and a benzene ring is introduced on the linker to afford steric effects, which benefits an efficient nucleophilic reaction, with a high sensitivity towards Hg(2+). It exhibits a stable response for Hg(2+) from 1.0 × 10(-8) to 1.0 × 10(-6) M, with a detection limit of 3.0 × 10(-9) M. The response of the probe to Hg(2+) is highly selective and pH-insensitive, with a fast response time. All these unique features make it particularly favorable for cellular Hg(2+) imaging applications. It has been preliminarily used for highly sensitive monitoring of Hg(2+) levels in living cells with satisfying resolution.     

Highly sensitive, selective, and rapid fluorescence Hg2+ sensor based on DNA duplexes of poly(dT) and graphene oxide

Coupling T base with Hg(2+) to form stable T-Hg(2+)-T complexes represents a new direction in detection of Hg(2+). Here a graphene oxide (GO)-based fluorescence Hg(2+) analysis using DNA duplexes of poly(dT) that allows rapid, sensitive, and selective detection is first reported. The Hg(2+)-induced T(15)-(Hg(2+))(n)-T(15) duplexes make T(15) unable to hybridize with its complementary A(15) labelled with 6'-carboxyfluorescein (FAM-A(15)), which has low fluorescence in the presence of GO. On the contrary, when T(15) hybridizes with FAM-A(15) to form double-stranded DNA because of the absence of Hg(2+), the fluorescence largely remains in the presence of GO. A linear range from 10 nM to 2.0 μM (R(2) = 0.9963) and a detection limit of 0.5 nM for Hg(2+) were obtained under optimal experimental conditions. Other metal ions, such as Al(3+), Ag(+), Ca(2+), Ba(2+), Mg(2+), Zn(2+), Mn(2+), Co(2+), Pb(2+), Ni(2+), Cu(2+), Cd(2+), Cr(3+), Fe(2+), and Fe(3+), had no significant effect on Hg(2+) detection. Moreover, the sensing system was used for the determination of Hg(2+) in river water samples with satisfactory results.     

Colorimetric assay for mercury (II) based on mercury-specific deoxyribonucleic acid-functionalized gold nanoparticles

A colorimetric nanoprobe-mercury-specific DNA-functionalized gold nanoparticles (Au-MSD) was developed for sensing Hg(2+). The new mercury-sensing concept relies on measuring changes in the inhibition of "non-crosslinking" aggregation of Au-MSD-induced by the folding of mercury-specific DNA strand through the thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination. In the absence of Hg(2+), a high concentration of MgCl(2) (50 mM) results in a rapid aggregation of Au-MSD because of the removal of charge repulsion. When Hg(2+) is present, the particles remain stable due to the folding of MSD functionalized on the particle surface. The assay enables the colorimetric detection of Hg(2+) in the concentration range of 0.1-10 μM Hg(2+) ions with a detection limit of 60 nM, and allows for the selective discrimination of Hg(2+) ions from the other competitive metal ions. Toward the goal for practical applications, the sensor was further evaluated by monitoring Hg(2+) in fish tissue samples.     

Reduction of the host cationic framework charge by isoelectronic substitution: synthesis and structure of Hg7Ag2P8X6 (X = Br, I) and Hg6Ag4P8Br6

The first compounds, Hg(7)Ag(2)P(8)X(6) (X = Br, I) and Hg(6)Ag(4)P(8)Br(6), featuring the partial isoelectronic substitution of Hg(2+) for Ag(1+) in mercury-pnicogen frameworks have been obtained and structurally characterized. The new compounds are the supramolecular assemblies built of the covalently bonded metal-pnicogen frameworks trapping guests of different complexity. The frameworks feature the perfect ordering of Hg(2+) and Ag(1+) cations and contain P(2)(4)(-) and P(6)(6)(-) phosphorus clusters. The substitution of Hg(2+) with Ag(1+) leads to the reduction in charge of the host cluster-containing cationic matrix and concomitant replacement of the monatomic X(-) guest by a lesser amount of the AgBr(3)(2)(-) anions.     

Molecular assembly directed by metal-aromatic interactions: control of the aggregation and photophysical properties of Zn-salen complexes by aromatic mercuration

There is widespread interest in non-covalent bonding and weak interactions, such as electrostatic interactions, hydrogen bonding, solvophobic/hydrophobic interactions, metal-metal interactions, and π-π stacking, to tune the molecular assembly of planar π-conjugated organic and inorganic molecules. Inspired by the roles of metal-aromatic interaction in biological systems, such as in ion channels and metalloproteins, herein, we report the first example of the use of Hg(2+) -aromatic interactions to selectively control the assembly and disassembly of zinc-salen complexes in aqueous media; moreover, this process exhibited significant "turn on" fluorescent properties. UV/Vis and fluorescence spectroscopic analysis of the titration of Hg(2+) ions versus complex ZnL(1) revealed that the higher binding affinity of Hg(2+) ions (compared to 13 other metal ions) was ascribed to specific interactions between the Hg(2+) ions and the phenyl rings of ZnL(1); this result was also confirmed by (1)H NMR spectroscopy and HRMS (ESI). Further evidence for this type of interaction was obtained from the reaction of small-molecule analogue L(1) with Hg(2+) ions, which demonstrates the proximity of the N-alkyl group to the aromatic protons during Hg(2+)-ion binding, which led to the consequential H/D exchange reaction with D(2) O. DFT modeling of such interactions between the Hg(2+) ions and the phenyl rings afforded calculated distances between the C and Hg atoms (2.29 ?) that were indicative of C-Hg bond-formation, under the direction of the N atom of the morpholine ring. The unusual coordination of Hg(2+) ions to the phenyl ring of the metallosalen complexes not only strengthened the binding ability but also increased the steric effect to promote the disassembly of ZnL(1) in aqueous media.     

Reversible "off-on" fluorescent chemosensor for Hg2+ based on rhodamine derivative

A novel and simple fluorescent chemosensor based on rhodamine was designed and synthesized to detect Hg(2+) with high selectivity. The structure of chemosensor 1 was characterized by IR, (1)H NMR, and HRMS spectroscopies. Chemosensor 1 exhibited distinct fluorescent and colorimetric changes toward Hg(2+) in an ethanol/water (80/20, v/v) solution, which resulted in the formation of 1/Hg(2+) complex with the Hg(2+)-induced ring opening of the spirolactam ring in rhodamine. The reversibility of chemosensor 1 was verified through its spectral response toward Hg(2+) ions and TBAI (tetrabutylammonium iodide) titration experiments.     

Multisignaling detection of Hg2+ based on a phosphorescent iridium(III) complex

A multisignaling chemosensor for Hg(2+) based on the iridium(III) complex Ir(thq)(2)(acac) was realized through UV-Vis absorption, phosphorescent emission and electrochemical measurements. Upon addition of Hg(2+), an obvious blue-shift in absorption spectra and a strong decrease of emission intensity were measured for Ir(thq)(2)(acac), which could be observed by the naked eye. Hg(2+) is coordinated to Ir(thq)(2)(acac), forming a 1 : 1 complex. Because Hg(2+) is a thiophilic metal ion, the interaction between Hg(2+) and the sulfur atom of cyclometalated ligands is responsible for the significant variations in optical and electrochemical signals.     

Single sensor for two metal ions: colorimetric recognition of Cu2+ and fluorescent recognition of Hg2+

The first novel rhodamine B based sensor, rhodamine B hydrazide methyl 5-formyl-1H-pyrrole-2-carboxylate Schiff base (2) capable of detecting both Cu(2+) and Hg(2+) using two different detection modes has been designed and synthesized. The metal ion induced optical changes of 2 were investigated in MeOH:H(2)O (3:1) HEPES buffered solution at pH 7.4. Sensor 2 exhibits selective colorimetric recognition of Cu(2+) and fluorogenic recognition of Hg(2+) with UV-vis and fluorescence spectroscopy, respectively. Moreover, both of the Cu(2+) and Hg(2+) recognition processes are proven to be hardly influenced by other coexisting metal ions.     

Dual functional rhodamine-immobilized silica toward sensing and extracting mercury ions in natural water samples

A reversible solid optical sensor (SGIR) for Hg(2+) based on silica gel was designed and synthesized. The binding and adsorption abilities of SGIR for metal cations were investigated with fluorophotometry and cold vapor atomic absorption spectrometry, respectively. The SGIR exhibits high selectivity for sensing Hg(2+) over other metal cations in aqueous media because the Hg(2+) ion selectively induces a ring opening of the rhodamine fluorophores, and the SGIR was also found to adsorb 72% of Hg(2+) ion. The determination of Hg(2+) in both tap and lake water samples displays satisfactory results, and the SGIR can also be easily recovered by treatment of a solution of TBA(+)OH(-).     

Control over surface DNA density on gold nanoparticles allows selective and sensitive detection of mercury(II)

We have developed a new highly selective and sensitive technique for the detection of Hg(2+) using DNA-functionalized gold nanoparticles (Au NPs) and OliGreen. This system is the first that allows the detection of Hg(2+) based on the release of DNA molecules, induced by conformational changes on Au NP surfaces, and its sensitivity is highly dependent upon surface DNA density. When Hg(2+) ions interact with the thymidine units of the DNA molecules bound to the Au NPs through Au-S bonds, the conformations of these DNA derivatives change from linear to hairpin structures, causing the release of some of the DNA molecules from the surface of the Au NPs into the bulk solution to react with OliGreen. The fluorescence of OliGreen-DNA complexes increased with increasing concentration of Hg(2+), and Hg(2+) could be detected at concentrations as low as 25 nM. A linear correlation existed between the fluorescence intensity and the concentration of Hg(2+) over the range 0.05-2.5 microM (R(2) = 0.98). This simple and cost-effective probe was applied to determine the spiked Hg(2+) in the pond samples; the recoveries (96-102%) suggested low matrix interference and high sensitivity.     

Novel hemicyanine dye as colorimetric and fluorometric dual-modal chemosensor for mercury in water

A novel water soluble Hg(2+)-selective chemosensor 1 with hemicyanine as fluorescent reporting group and NO(2)Se(2) chelating unit as ion binding site was reported. Chemosensor 1 shows a specific Hg(2+) selectivity and discrimination between Hg(2+) and chemically similar ions in conjunction with a visible colorimetric change from red to colorless, potentially leading to both "naked-eye" and fluorometric detection of Hg(2+) cations.     

Uptake and effect of mercury on amino acid losses from the gills of the bivalve mollusks Mytilus californianus and Anodonta californiensis

Inorganic mercury (Hg(2+)) and herbicides are important contaminants of world water systems with effects on aquatic organisms and humans. The uptake of Hg(2+) and glycine by the gills of the bivalve mollusks Mytilus californianus and Anodonta californiensis was determined. Additionally, the effects of glycine, 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4-dinitrophenol (DNP) on the uptake of Hg(2+) were also determined. The loss of primary amines from the excised gills of both species was measured in the presence and absence of Hg(2+) or MeHg(+). The results indicate that (1) the uptake of Hg(2+) is approximately equivalent in both species; (2) comparison of the uptakes with that of inulin, which occupies only extracellular space, shows that Hg(2+) is taken up; (3) the uptake of Hg(2+) is slightly altered by the presence of glycine and herbicides such as 2,4-D and DNP; (4) the rate of loss of primary amines was highly increased relative to the control by the presence of Hg(2+) and to a lesser extent MeHg(+) for both species. These results showed that both inorganic and MeHg(+) are effective in disrupting the permeability of cell membranes, causing leakage of essential amino acids from the cell. This could result in discharge of potential gradients, reduced efficiency of energy coupling, and consequently cell death.