A squaraine-based colorimetric and "turn on" fluorescent sensor for selective detection of Hg2+ in an aqueous medium

A novel squaraine-based chemosensor SQ-1 has been synthesized, and its sensing behavior toward various metal ions was investigated by UV-vis and fluorescence spectroscopies. In AcOH-H(2)O (40:60, v/v) solution, Hg(2+) ions coordinate with SQ-1 causing a deaggregation which induces a visual color and absorption spectral changes as well as strong fluorescence. In contrast, the addition of other metals (e.g., Pb(2+), Cd(2+), Cu(2+), Zn(2+), Al(3+), Ni(2+), Co(2+), Fe(3+), Ca(2+), K(+), Mg(2+), Na(+), and Ag(+)) does not induce these changes at all. Thus SQ-1 is a specific Hg(2+) sensing agent due to the inducing deaggregation of the dye molecule by Hg(2+).     

Oxidative cyclization of thiosemicarbazone: an optical and turn-on fluorescent chemodosimeter for Cu(II)

A weakly fluorescent thiosemicabazone (L(1)H) was found to be a selective optical and "turn-on" fluorescent chemodosimeter for Cu(2+) ion in aqueous medium. A significant fluorescence enhancement along with change in color was only observed for Cu(2+) ion; among the other tested metal ions (viz. Na(+), K(+), Mg(2+), Ca(2+), Cr(3+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), Ag(+), Ni(2+), Co(2+), Fe(3+) and Mn(2+)). The Cu(2+) selectivity resulted from an oxidative cyclization of the weak fluorescent L(1)H into highly fluorescent rigid 4,5-dihydro-5,5-dimethyl-4-(naphthalen-5-yl)-1,2,4-triazole-3-thione (L(2)). The signaling mechanism has been confirmed by independent synthesis with detail characterization of L(2).     

Hg2+-sensing system based on structures of complexes

The first example of a new Hg(2+)-sensing system based on the structures of complexes is reported. The system uses a combination of a new chiral bidentate ligand and CD spectroscopy. Significant CD spectral changes are observed when Hg(2+) is added, whereas no CD spectral changes are observed in the cases of Li(+), Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Rb(+), Ag(+), Cd(2+), La(3+), Gd(3+), and Pb(2+).     

A BODIPY-based colorimetric and fluorometric chemosensor for Hg(II) ions and its application to living cell imaging

A new monostyryl boron dipyrromethene derivative (MS1) appended with two triazole units indicates the presence of Hg(2+) among other metal ions with high selectivity by color change and red emission. Upon Hg(2+) binding, the absorption band of MS1 is blue-shifted by 29 nm due to the inhibition of the intramolecular charge transfer from the nitrogen to the BODIPY, resulting in a color change from blue to purple. Significant fluorescence enhancement is observed with MS1 in the presence of Hg(2+); the metal ions Ag(+), Ca(2+), Cd(2+), Co(2+), Cu(2+), Fe(2+), Fe(3+), K(+), Mg(2+), Mn(2+), Ni(2+), Pb(2+), and Zn(2+) cause only minor changes in the fluorescence of the system. The apparent association constant (K(a)) of Hg(2+) binding in MS1 is found to be 1.864 × 10(5) M(-1). In addition, fluorescence microscopy experiments show that MS1 can be used as a fluorescent probe for detecting Hg(2+) in living cells.     

Development and applications of fluorescent indicators for Mg2+ and Zn2+

In a study of the spectroscopic behavior of two Schiff base derivatives, salicylaldehyde salicylhydrazone (1) and salicylaldehyde benzoylhydrazone (2), Schiff base 1 has high selectivity for Zn(2+) ion not only in abiotic systems but also in living cells. The ion selectivity of 1 for Zn(2+) can be switched for Mg(2+) by swapping the solvent from ethanol-water to DMF (N,N-dimethylformamide)-water mixtures. Imine 2 is a good fluorescent probe for Zn(2+) in ethanol-water media. Many other ions tested, such as Li(+), Na(+), Al(3+), K(+), Ca(2+), Cr(3+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Ag(+), Cd(2+), Sn(2+), Ba(2+), Hg(2+), and Pb(2+), failed to induce any spectral change in various solvents. The selectivity mechanism of 1 and 2 for metal ions is based on a combinational effect of proton transfer (ESPT), C═N isomerization, and chelation-enhanced fluorescence (CHEF). The coordination modes of the complexes were investigated.     

A naphthalene-based Al3+ selective fluorescent sensor for living cell imaging

An efficient fluorescent Al(3+) receptor, N-(2-hydroxy-1-naphthalene)-N'-(2-(2-hydroxy-1-naphthalene)amino-ethyl)-ethane-1,2-diamine (L) has been synthesized by the condensation reaction between 2-hydroxy naphthaldehyde and diethylenetriamine. High selectivity and affinity of L towards Al(3+) in ethanol (EtOH) as well as in HEPES buffer at pH 7.4, makes it suitable to detect intracellular Al(3+) with fluorescence microscopy. Metal ions, viz. Li(+), Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Ag(+), Cd(2+), Hg(2+) and Pb(2+) do not interfere. The lowest detection limit for Al(3+) is 3.0 × 10(-7) M and 1.0 × 10(-7) M in EtOH and HEPES buffer respectively.     

A chelation enhanced selective fluorescence sensing of Hg2+ by a simple quinoline substituted tripodal amide receptor

Two tris(2-aminoethyl)amine (tren) based tripodal amide fluoroionophores, 1 and 2, functionalized with quinoline (chelating fluorophore) and naphthalene (non-chelating fluorophore) respectively, are synthesized in good yields. Fluoroionophore 1 shows a selective UV-Vis spectral shift in the case of Hg(2+) in acetonitrile among different metal ions like Li(+), Na(+), Ca(2+), Mg(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+). On the other hand, fluoroionophore 2 shows no selectivity towards any of the above metal ions in the UV-Vis study. Furthermore, 1 shows a selective chelation induced fluorescence enhancement in the presence of Hg(2+) whereas 2 shows the enhancement of fluorescence with most of the metal ions via a photoinduced charge transfer mechanism. The naked eye detection of Hg(2+) in an acetonitrile solution of 1 shows a greenish fluorescence upon UV light irradiation. The isolated Hg(2+) complex of 1, 3, shows a similar UV-Vis and fluorescence spectral output as observed from in situ spectroscopic studies of 1 in the presence of Hg(2+). Infra-red (IR) and (1)H- NMR studies also reveal the interaction of Hg(2+) with the quinoline nitrogen atoms as well as with the amide functionality.     

Determination of lead in phosphate ore and phosphogypsum

Laser induced breakdown spectroscopy (LIBS) is applied to analyze aqueous solutions of Li(+), Na(+), Ca(2+), Ba(2+), Pb(2+), Cd(2+), Hg(2+) and Er(3+) and suspensions of ErBa(2)Cu(3)O(x) particles (d=0.2 microm). An excimer (308 nm) pumped dye laser with laser pulse at 500 nm and pulse energy at 22+/-2 mJ is used to produce plasma in aqueous solution. Plasma emission lines of the elements are detected by a photodiode array detector. Detection limits of the metal ions are 500 mg/l for Cd(2+), 12.5 mg/l for Pb(2+), 6.8 mg/l for Ba(2+), 0.13 mg/l for Ca(2+), 13 microg/l for Li(+) and 7.5 microg/l for Na(+). No mercury and erbium emission can be detected, even at Hg(2+) and Er(3+) concentrations of up to the g/l range. On the other side, for Er in suspensions of ErBa(2)Cu(3)O(x) particles a more than 10(3) times higher sensitivity is found than for dissolved Er(3+). This result gives a possibility to analyze colloid-borne metal ions with an increased sensitivity.     

A highly selective on/off fluorescence sensor for cadmium(II)

A polypyridyl ligand, 2,3,6,7,10,11-hexakis(2-pyridyl)dipyrazino[2,3-f:2',3'-h]quinoxaline (HPDQ), was found to have excellent fluorescent selectivity for Cd(2+) over many other metal ions (K(+), Na(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Ni(2+), Co(2+), Cu(2+), Ag(+), Hg(2+), Zn(2+), and Cr(3+)) based on the intramolecular charge-transfer mechanism, which makes HPDQ a potential fluorescence sensor or probe for Cd(2+). An obvious color change between HPDQ and HPDQ + Cd(2+) can be visually observed by the naked eye. The structure of the complex HPDQ-Cd has been characterized by X-ray crystallography. Density functional theory calculation results on the HPDQ and HPDQ-Cd complexes could explain the experimental results.     

2,1,3-Benzoxadiazole-based selective chromogenic chemosensor for rapid naked-eye detection of Hg2+ and Cu2+

We report a simple twisted intramolecular charge transfer (TICT) chromogenic chemosensor for rapid and selective detection of Hg(2+) and Cu(2+). The sensor was composed of an electron-acceptor 4-fluoro moiety and an electron-donor 7-mercapto-2,1,3-benzoxadiazole species where the S together with the 1-N provided the soft binding unit. Upon Hg(2+) and Cu(2+) complexation, remarkable but different absorbance spectra shifts were obtained in CH(3)CN-H(2)O mixed buffer solution at pH 7.6, which can be easily used for naked-eye detection. The sensor formed a stable 2:1 complex with Cu(2+), and both 2:1 and 3:1 complexes with Hg(2+). While alkali-, alkaline earth- and other heavy and transition metal ions such as Na(+), Mg(2+), Mn(2+), Co(2+), Ni(2+), Ag(+), Zn(2+), Pb(2+) and Cd(2+) did not cause any significant spectral changes of the sensor. This finding is not only a supplement to the detecting methods for Hg(2+) and Cu(2+), but also adds new merits to the chemistry of 4,7-substituted 2,1,3-benzoxadiazoles.     

Incorporation of triazole into a quinoline-rhodamine conjugate imparts iron(iii) selective complexation permitting detection at nanomolar levels

Two new rhodamine based probes 1 and 2 for the detection of Fe(3+) were synthesized and their selectivity towards Fe(3+) ions in the presence of other competitive metal ions tested. The probe 1 formed a coloured complex with Fe(3+) as well as Cu(2+) ions and revealed the lack of adequate number of coordination sites for selective complexation with Fe(3+). Incorporation of a triazole unit to the chelating moiety of 1 resulted in the probe 2, that displayed Fe(3+) selective complex formation even in the presence of other competitive metal ions like Li(+), Na(+), K(+), Cu(2+), Mg(2+), Ca(2+), Sr(2+), Cr(3+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+). The observed limit of detection of Fe(3+) ions (5 × 10(-8) M) confirmed the very high sensitivity of 2. The excellent stability of 2 in physiological pH conditions, non-interference of amino acids, blood serum and bovine serum albumin (BSA) in the detection process, and the remarkable selectivity for Fe(3+) ions permitted the use of 2 in the imaging of live fibroblast cells treated with Fe(3+) ions.     

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.     

Selective colorimetric sensing of Cu2+ using triazolyl monoazo derivative

Although the high sensitivity, high selectivity and fast response make emission (fluorescence) based technique as one of the most promising tool for developing the chemosensors for metal ions, the past few years have witnessed a demand for the absorption based chemosensors for paramagnetic heavy metal ions, especially Cu(2+). Being paramagnetic, Cu(2+) leads to the low signal outputs ("turn-off") caused by decreased emission which may sometimes give false positive response, rendering the emission based technique less reliable for analytical purposes. Herein, we report synthesis and characterization of a hetarylazo derivative, characterized by a strong charge-transfer band which gets attenuated convincingly in the presence of Cu(2+) leading to distinct naked-eye color change (yellow to purple), and to a lesser extent in the presence of Cd(2+), Zn(2+), Co(2+), Pb(2+), Fe(2+), Ni(2+), Fe(3+) and Hg(2+) for which the naked eye sensitivity was comparatively (w.r.t. Cu(2+)) much less. No response was observed for the other metal ions including Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+), Mn(2+), Ag(+), Zn(2+), Cd(2+), Pb(2+), and lanthanides Ce(3+), La(3+), Pr(3+), Eu(3+), Nd(3+), Lu(3+), Yb(3+), Tb(3+), Sm(3+), Gd(3+). The proposed sensing mechanism has been ascribed to the stabilization of LUMO after complexation with Cu(2+) and a 1:1 stoichiometry has been deduced.     

Silver(I) ion selective PVC membrane based on bis-pyridine tetramide macrocycle

A PVC membrane based on bis-pyridine tetramide macrocycle exhibits a good response for silver ion over a wide concentration range (1.0x10(-1)-4.0x10(-5) mol l(-1)). The electrode has a relatively fast response time and can be used for more than 5 months without observing any divergence. High selectivity for Ag(+) ions over that of Na(+), K(+), Ca(2+), Sr(2+), Pb(2+) and Hg(2+) have been observed.     

Label-free emission assay of mercuric ions using DNA duplexes of poly(dT)

In this study, an assay to quantify the presence of mercuric ions and methyl mercury by double-stranded DNA containing a poly(dT) sequence was developed using a light switch compound, Ru(phen)(2)(dppz)(2+) (1), which is known to intercalate into double-stranded DNA. Upon treatment with mercuric ions, the metal-to-ligand charge transfer (MLCT) emission derived from the intercalation of 1 was reduced due to the formation of DNA duplexes containing T-Hg(2+)-T base pairs by the dehybridization of poly(dT)-poly(dA) duplexes at room temperature. As the concentration of Hg(2+) was increased, the emission of 1 gradually decreased. This label-free method had a detection limit of 5 nM. Other metal ions, such as K(+), Ag(+), Ca(2+), Mg(2+), Zn(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Cd(2+), Cr(3+), Fe(3+), had no significant effect on reducing emission. This emission method can differentiate matched and mismatched poly(dT) sequences based on the dehybridization rate of dsDNA and the rate decreased in the order of T(10)C·A(11)～ T(10)A·A(11) > T(10)G·A(11) > T(11)·A(11).     

Competitive cesium-133 NMR spectroscopic study of complexation of different metal ions with dibenzo-21-crown-7 in acetonitrile-dimethylsulfoxide and nitromethane-dimethylsulfoxide mixtures

(133)Cs NMR spectroscopy was used to determine the stoichiometry and stability of the Cs(+) ion complex with dibenzo-21-crown-7 (DB21C7) in acetonitrile-dimethylsulfoxide (96.5:3.5, w/w) and nitromethane-dimethylsulfoxide (96.5:3.5, w/w) mixtures. A competitive (133)Cs NMR technique was also employed to probe the complexation of Na(+), K(+), Rb(+), Ag(+), Tl(+), NH(4)(+), Mg(2+), Ba(2+), Hg(2+), Pb(2+) and UO(2)(2+) ions with DB21C7 in the same solvent systems. All the resulting 1:1 complexes in nitromethane-dimethylsulfoxide were more stable than those in acetonitrile-dimethylsulfoxide solution. In both solvent systems, the stability of the resulting complexes was found to vary in the order Rb(+)>K(+) approximately Ba(2+)>Tl(+)>Cs(+)>NH(4)(+) approximately Pb(2+)>Ag(+)>UO(2)(2+)>Hg(2+)>Mg(2+)>Na(+).     

New masking procedure for selective complexometric determination of copper(II)

A study has been made of a new masking procedure for highly selective complexometric determination of copper(II), based on decomposition of the copper-EDTA complex at pH 5-6. Among the various combinations of masking agents tried, ternary masking mixtures comprising a main complexing agent (thiourea), a reducing agent (ascorbic acid) and an auxiliary complexing agent (thiosemicarbazide or a small amount of 1,10-phenanthroline or 2,2'-dipyridyl) have been found most suitable. An excess of EDTA is added and the surplus EDTA is back-titrated with lead (or zinc) nitrate with Xylenol Orange as indicator (pH 5-6). A masking mixture is then added to decompose the copper-EDTA complex and the liberated EDTA is again back-titrated with lead (or zinc) nitrate. The following cations do not interfere: Ag(+), Hg(2+), Pb(2+), Ni(2+), Bi(3+), As(3+), Al(3+), Sb(3+), Sn(4+), Cd(2+), Co(2+), Cr(3+) and moderate amounts of Fe(3+) and Mn(2+). The notable feature is that consecutive determination of Hg(2+) and Cu(2+) can be conveniently carried out in the presence of other cations.     

Lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene: synthesis, characterization, and selective recognition of Hg2+ and its sensitivity toward pyrimidine bases

The structurally characterized lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene (L) exhibits high selectivity toward Hg(2+) among other biologically important metal ions, viz., Na(+), K(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+) as studied by fluorescence, absorption, and ESI MS. L acts as a sensor for Hg(2+) by switch-off fluorescence and exhibits a lowest detectable concentration of 1.87 ± 0.1 ppm. The complex formed between L and Hg(2+) is found to be 1:1 on the basis of absorption and fluorescence titrations and was confirmed by ESI MS. The coordination features of the mercury complex of L were derived on the basis of DFT computations and found that the Hg(2+) is bound through an N(2)O(2) extending from both the arms to result in a distorted octahedral geometry with two vacant sites. The nanostructural features such as shape and size obtained using AFM and TEM distinguishes L from its Hg(2+) complex and were different from those of the simple mercuric perchlorate. L is also suited to sense pyrimidine bases by fluorescence quenching with a minimum detection limit of 1.15 ± 0.1 ppm in the case of cytosine. The nature of interaction of pyrimidine bases with L has been further studied by DFT computational calculations and found to have interactions through a hydrogen bonding and NH-π interaction between the host and the guest.     

Separation and gravimetric determination of cerium and lanthanum with N-m-tolyl-m-nitrobenzohydroxamic acid

Cerium and lanthanum were determined gravimetrically by selective precipitation with N-m-tolyl-m-nitrobenzohydroxamic acid and separated from several metal ions such as Ag(+), Be(2+) , Pb(2+) , Mn(2+) , Cu(2+), Zn(2+) , Cd(2+) , Hg(2+) , Pd(2+) , Ga(3+) A1(3+) , Bi(3+) , Sb(3+), Sn(4+), Ce(3+) , Pr(3+) , Nd(3+) , Ti(4+), Zr(4+), Th(4+), V(5+) , Mo(6+) and U(6+) . The precipitates were weighted directly after drying at 110 degrees . The analytical results indicated the composition of the complexes to be (C(14)H(11)N(2)O(4))(n)M.     

Salicylimine-based fluorescent chemosensor for aluminum ions and application to bioimaging

In this study, an assay to quantify the presence of aluminum ions using a salicylimine-based receptor was developed utilizing turn-on fluorescence enhancement. Upon treatment with aluminum ions, the fluorescence of the sensor was enhanced at 510 nm due to formation of a 1:1 complex between the chemosensor and the aluminum ions at room temperature. As the concentration of Al(3+) was increased, the fluorescence gradually increased. Other metal ions, such as Na(+), Ag(+), K(+), Ca(2+), Mg(2+), Hg(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), Cr(3+), Fe(3+), and In(3+), had no such significant effect on the fluorescence. In addition, we show that the probe could be used to map intracellular Al(3+) distribution in live cells by confocal microscopy.