Colorimetric assay for parallel detection of Cd2+, Ni2+ and Co2+ using peptide-modified gold nanoparticles

A colorimetric assay has been developed for parallel detection of Cd(2+), Ni(2+) and Co(2+) utilizing peptide-modified gold nanoparticles (P-AuNPs) as a sensing element based on its unique surface plasmon resonance properties. The functional peptide ligand, CALNNDHHHHHH, was self-assembled on gold nanoparticles (AuNPs) to produce P-AuNPs probe. The P-AuNPs probe could be used to simultaneously detect and showed different responses to the three ions Cd(2+), Ni(2+) and Co(2+) in an aqueous solution based on the aggregation-induced color change of AuNPs. The method showed good selectivity for Cd(2+), Ni(2+) and Co(2+) over other metal ions, and detection limit as low as 0.05 μM Cd(2+), 0.3 μM Ni(2+) or 2 μM Co(2+). To simultaneously (or parallel) detect the three metal ions coexisting in a sample, EDTA and imidazole were applied to mask Co(2+) and Ni(2+) for detecting Cd(2+), glutathione and EDTA were applied to mask Cd(2+) and Co(2+) for detecting Ni(2+), and glutathione and imidazole were applied to mask Cd(2+) and Ni(2+) for detecting Co(2+). Finally, the simple and cost-effective probe could be successfully applied for simultaneously detecting Cd(2+), Ni(2+), and Co(2+) in river water. Because this novel P-AgNPs-based probe design offers many advantages, including simplicity of preparation and manipulation compared with other methods that employ specific strategies, the sensing system shows potential application in the developing region for monitoring water quality.     

A pyrenyl-appended triazole-based calix[4]arene as a fluorescent sensor for Cd2+ and Zn2+

The synthesis and evaluation of a novel calix[4]arene-based fluorescent chemosensor 8 for the detection of Cd(2+) and Zn(2+) is described. The fluorescent spectra changes observed upon addition of various metal ions show that 8 is highly selective for Cd(2+) and Zn(2+) over other metal ions. Addition of Cd(2+) and Zn(2+) to the solution of 8 results in ratiometric measurement.     

Influence of Cd2+, Hg2+ and Pb2+ on (+)-catechin binding to bovine serum albumin studied by fluorescence spectroscopic methods

The effect of heavy metal ions, Cd(2+), Hg(2+) and Pb(2+) on (+)-catechin binding to bovine serum albumin (BSA) has been investigated by spectroscopic methods. The results indicated that the presence of heavy metal ions significantly affected the binding modes and binding affinities of (+)-catechin to BSA, and the effects depend on the types of heavy metal ion. One binding mode was found for (+)-catechin with and without Cd(2+), while two binding modes - a weaker one at low concentration and a stronger one at high concentration were found for (+)-catechin in the presence of Hg(2+) and Pb(2+). The presence of Cd(2+) decreased the binding affinities of (+)-catechin for BSA by 20.5%. The presence of Hg(2+) and Pb(2+) decreased the binding affinity of (+)-catechin for BSA by 8.9% and 26.7% in lower concentration, respectively, and increased the binding affinity of (+)-catechin for BSA by 5.2% and 9.2% in higher concentration, respectively. The changed binding affinity and binding distance of (+)-catechin for BSA in the presence of Cd(2+), Hg(2+) and Pb(2+) were mainly because of the conformational change of BSA induced by heavy metal ions. However, the quenching mechanism for (+)-catechin to BSA was based on static quenching combined with non-radiative energy transfer irrespective of the absence or presence of heavy metal ions.     

Adsorption of Pb2+, Zn2+, and Cd2+ from waters by amorphous titanium phosphate

In the current study, amorphous titanium phosphate (TiP) was prepared as an adsorbent for heavy metals from waters. Uptake of Pb(2+), Zn(2+), and Cd(2+) onto TiP was assayed by batch tests; a polystyrene-sulfonic acid exchanger D-001 was selected for comparison and Ca(2+) was chosen as a competing cation due to its ubiquitous occurrence in waters. The pH-titration curve of TiP implied that uptake of heavy metals onto TiP is essentially an ion-exchange process. Compared to D-001, TiP exhibits more preferable adsorption toward Pb(2+) over Zn(2+) and Cd(2+) even in the presence of Ca(2+) at different levels. FT-IR analysis of the TiP samples laden with heavy metals indicated that the uptake of Zn(2+) and Cd(2+) ions onto TiP is mainly driven by electrostatic interaction, while that of Pb(2+) ions is possibly dependent upon inner-sphere complex formation, except for the electrostatic interaction. Moreover, uptake of heavy metals onto TiP approaches equilibrium quickly and the exhausted TiP particles could be readily regenerated by HCl solution.     

Influence of Mg2+ and Cd2+ on the interaction between sparfloxacin and calf thymus DNA

Mg(2+) and Cd(2+) have different binding capacity to sparfloxacin, and have different combination modes with calf thymus DNA. Selecting these two different metal ions, the influence of them on the binding constants between SPFX and calf thymus DNA, as well as the related mechanism have been studied by using absorption and fluorescence spectroscopy. The result shows that Cd(2+) has weak binding capacity to SPFX in the SPFX-Cd(2+) binary system, but can decrease the binding between SPFX and DNA obviously in SPFX-DNA-Cd(2+) ternary system. Mg(2+) has strong binding capacity to SPFX. It can increase the binding between SPFX and DNA at concentrations <0.01 mM, and decrease the binding between them at concentrations >0.01 mM. Referring to the different modes of Mg(2+) and Cd(2+) binding to DNA, the mechanism of the influence of metal ions on the binding between SPFX and DNA has been proposed. SPFX can directly bind to DNA by chelating DNA base sites. If a metal ion at certain concentration mainly binds to DNA bases, it can decrease the binding constants between SPFX and DNA through competing with SPFX. While if a metal ion at certain concentration mainly binds to phosphate groups of DNA, it can increase the binding constants by building a bridge between SPFX and DNA. The influence direction of metal ions on the binding between quinolone and DNA relays on their binding ratio of affinity for bases to phosphate groups on DNA. Our result supports Palumbo's conclusion that the binding between SPFX and the phosphate groups is the precondition for the combination between SPFX and DNA, which is stabilized through stacking interactions between the condensed rings of SPFX and DNA bases.     

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.     

Colorimetric detection of Cd2+ using gold nanoparticles cofunctionalized with 6-mercaptonicotinic acid and L-cysteine

We have developed a colorimetric assay for the highly sensitive and selective detection of Cd(2+) using gold nanoparticles (AuNPs) cofunctionalized with 6-mercaptonicotinic acid (MNA) and L-Cysteine (L-Cys) through the formation of an Au-S bond. In the presence of Cd(2+), the aggregation of functionalized AuNPs occurred by means of a metal-ligand interaction that led to visible color changes. Most importantly, cofunctionalized AuNPs had better responses for Cd(2+) than that functionalized by either MNA or L-Cys. Cd(2+) could be detected by the colorimetric response of AuNPs that could be detected by the naked eye or a UV-vis spectrophotometer. The absorbance ratio (A(620)/A(523)) was linear with the Cd(2+) concentration in the range of 2.0 × 10(-7) to 1.7 × 10(-6) M. Under optimum conditions (2.0 × 10(-5) M MNA, 2.0 × 10(-6) M L-Cys and 0.020 M NaCl at pH 10.0), the detection limit (3σ) of Cd(2+) could be as low as 1.0 × 10(-7) M. Interference experiments showed that Pb(2+) and Cu(2+) caused a slight interference for Cd(2+) determination while other metal ions caused no interference. The proposed method was successfully applied to determine the concentration of Cd(2+) in environmental samples (lake water).     

Preparation, crystal structure, and thermal stability of the cadmium sulfide nanoclusters Cd6S44+ and Cd2Na2S4+in the sodalite cavities of zeolite A (LTA)

The crystal structure and thermal stability of two cadmium sulfide nanoclusters prepared in zeolite A (LTA) have been studied by XPS, TGA, and single-crystal and powder XRD. The crystal structures of Cd2.4Na3.2(Cd6S4)0.4(Cd2Na2S)0.6(H2O)> or =5.8[Si12Al12O48]-LTA (a = 12.2919(7) A, crystal 1 (hydrated)) and /Cd4Na2(Cd2O)(Na2O)/[Si12Al12O48]-LTA (a = 12.2617(4) A, crystal 2 (dehydrated)) were determined by single-crystal methods in the cubic space group Pm3m at 294(1) K. Crystal 1 was prepared by ion exchange of Na12-LTA in an aqueous stream 0.05 M in Cd2+, followed by washing in a stream of water, followed by reaction in an aqueous stream 0.05 M in Na2S. Crystal 2 was made by dehydrating crystal 1 at 623 K and 1 x 10(-6) Torr for 3 days. In crystal 1, Cd6S4(4+) nanoclusters were found in and extending out of about 40% of the sodalite cavities. Central to each Cd6S4(4+) cluster is a Cd4S4 unit (interpenetrating Cd2+ and S2- tetrahedra with near Td symmetry, Cd-S = 2.997(24) A, Cd-S-Cd = 113.8(12) degrees, and S-Cd-S = 58.1(24) degrees). Each of the two remaining Cd2+ ions bonds radially through a 6-ring of the zeolite framework to a sulfide ion of this Cd4S4 unit (Cd-S = 2.90(8) A). In each of the remaining 60% of the sodalite cavities of crystal 1, a planar Cd2Na2S4+ cluster was found (Cd-S/Na-S = 2.35(5)/2.56(14) A and Cd-S-Cd/Na-S-Na = 122(5)/92(7) degrees). Cd6S4(4+) and Cd2Na2S4+ are stable within the zeolite up to about 700 K in air. Upon vacuum dehydration at 623 K, all sulfur was lost (crystal 2). Instead as anions, only two oxide ions remain per sodalite unit. One bridges between two Cd2+ ions (Cd2O2+, Cd-O = 2.28(3) A) and the other between two Na+ ions (Na2O, Na-O = 2.21(10) A).     

1H and (113)Cd NMR Investigations of Cd(2+) and Zn(2+) Binding Sites on Serum Albumin: Competition with Ca(2+), Ni(2+), Cu(2+), and Zn(2+)

1H and (113)Cd NMR studies are used to investigate the Cd(2+) binding sites on serum albumin (67 kDa) in competition with other metal ions. A wide range of mammalian serum albumins possess two similar strong Cd(2+) binding sites (site A 113-124 ppm; site B 24-28 ppm). The two strong sites are shown not to involve the free thiol at Cys34. Ca(2+) influences the binding of Cd(2+) to isolated human albumin, and similar effects due to endogenous Ca(2+) are observed for intact human blood serum. (1)H NMR studies show that the same two His residues of human serum albumin are perturbed by Zn(2+) and Cd(2+) binding alike. Zn(2+) displaces Cd(2+) from site A which leads to Cd(2+) occupation of a third site (C, 45 ppm). The N-terminus of HSA is not the locus of the two strong Cd(2+) binding sites, in contrast to Cu(2+) and Ni(2+). After saturation of the N-terminal binding site, Cu(2+) or Ni(2+) also displaces Cd(2+) from site A to site C. The effect of pH on Cd(2+) binding is described. A common Cd(2+)/Zn(2+) binding site (site A) involving interdomain His residues is discussed.     

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.     

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.     

Effect of phosphate complexation on Cd2+ sorption by manganese dioxide (beta-MnO2)

Sorption of metal ions on oxide/hydroxide surfaces mediates the fate and transport of these ions in many natural systems. These metallic ions often exist in bulk in the aqueous phase as complexes with inorganic and organic ligands. In the present study, we investigated the sorption properties of manganese dioxide in the presence of phosphate which is thought to be one of the most important complex forming species. The surface area, point of zero charge and structural morphology of the solid manganese dioxide were determined. Cd(2+) sorption studies were carried out on manganese dioxide as a function of pH, temperature and phosphate concentration. Cd(2+) sorption increased with increasing pH, temperature and phosphate concentration. It was found that phosphate formed both outer and inner sphere complexes via metal and ligand-like adsorption. The Langmuir equation was applied to describe the data and from the constants of this equation different thermodynamic parameters such as DeltaH(0), DeltaS(0) and DeltaG(0) were evaluated.     

Dansyl-anthracene dyads for ratiometric fluorescence recognition of Cu2+

Dansyl-anthracene dyads 1 and 2 in CH(3)CN-H(2)O (7:3) selectively recognize Cu(2+) ions amongst alkali, alkaline earth and other heavy metal ions using both absorbance and fluorescence spectroscopy. In absorbance, the addition of Cu(2+) to the solution of dyads 1 or 2 results in appearance of broad absorption band from 200 nm to 725 nm for dyad 1 and from 200 nm to 520 nm for dyad 2. This is associated with color change from colorless to blue (for 1) and fluorescent green (for 2). This bathochromic shift of the spectrum could be assigned to internal charge transfer from sulfonamide nitrogen to anthracene moiety. In fluorescence, under similar conditions dyads 1 and 2 on addition of Cu(2+) selectively quench fluorescence due to dansyl moiety between 520-570 nm (for 1)/555-650 nm (for 2) with simultaneous fluorescence enhancement at 470 nm and 505 nm for dyads 1 and 2, respectively. Hence these dyads provide opportunity for ratiometric analysis of 1-50 μM Cu(2+). The other metal ions viz. Fe(3+), Co(2+), Ni(2+), Cd(2+), Zn(2+), Hg(2+), Ag(+), Pb(2+), Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+) do not interfere in the estimation of Cu(2+) except Cr(3+) in case of dyad 1. The coordination of dimethylamino group of dansyl unit with Cu(2+) causes quenching of fluorescence due to dansyl moiety between 520-600 nm and also restricts the photoinduced electron transfer from dimethylamino to anthracene moiety to release fluorescence between 450-510 nm. This simultaneous quenching and release of fluorescence respectively due to dansyl and anthracene moieties emulates into Cu(2+) induced ratiometric change.     

反相高效液相色谱法同时测定镉、铅、铜和锌

 研究了meso-四（对羟基苯基）卟啉为柱前衍生化试剂与Cd2+,Pb2+,Cu2+和Zn2+离子的配合反应条件及配合物在C18色谱柱上的分离条件,建立了反相高效液相色谱快速分离光度检测Cd2+,Pb2+,Cu2+和Zn2+的新方法。配合物和试剂在15 min内出峰完毕。4种离子的检出限为: Cd2+0.02 ng,Pb2+0.02 ng, Cu2+0.02 ng,Zn2+0.12 ng;线性范围为:Cd2+0.8 μg/L～150 μg/L,Pb2+0.8 μg/L～300 μg/L,Cu2+0.8 μg/L～500 μg/L,Zn2+5.0 μg/L～1 000 μg/L;方法的日内相对标准偏差为:2.8%～4.8%,测定低、中、高3个浓度的日间相对标准偏差为3.7%～9.7%。     

Cd2+和Ni2+在粉煤灰上的吸附特性

考察了粉煤灰对Cd2+和Ni2+的单组分吸附和双组分吸附性能。结果表明,粉煤灰可有效吸附水溶液中的Cd2+和Ni2+,去除率随pH升高而增加。吸附约60min后趋于平衡。粉煤灰对Ni2+的吸附容量高于Cd2+。单组分吸附平衡符合Freundlich模型和Redlich Peterson (R P)模型。双组分吸附时,Ni2+和Cd2+之间存在明显的竞争吸附效应;随干扰离子浓度升高,竞争吸附效应增强。不同模型拟合结果表明,双组分吸附平衡符合Freundlich竞争吸附模型。脱附实验表明,Cd2+比Ni2+易于脱附;0.1mol/L HCl、0.1mol/L HNO3 和0.05mol/L H2SO4的脱附效果接近,对Cd2+脱附率>60%,对Ni2+脱附率>35%。     

Dual-mode unsymmetrical squaraine-based sensor for selective detection of Hg2+ in aqueous media

A novel chemosensor based on unsymmetrical squaraine dye (USQ-1) for the selective detection of Hg(2+) in aqueous media is described. USQ-1 in combination with metal ions shows dual chromogenic and "turn-on" fluorogenic response selectivity toward Hg(2+) as compared to Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+), Al(3+), Cu(2+), Cd(2+), Mn(2+), Fe(3+), Ag(+), Pb(2+), Zn(2+), Ni(2+) and Co(2+) due to the Hg(2+)-induced deaggregation of the dye molecule. A recognition mechanism based on the binding mode is proposed based on the absorption and fluorescence changes, (1)H NMR titration experiments, ESI-MS study, and theoretical calculations.     

Structures of [(n-C4H9)2NH2]2Cd9Cl20.2H2O and [Cu(C14H24N4)]2Cu13Cl30(H2O)2.xH2O: perforated layer structures based on the CdCl2 layer network

The crystal structures are reported for two compounds containing novel perforated layer structures, [DBA] 2Cd 9Cl 20.2H 2O and [Cu(TIM)] 2Cu 13Cl 30(H 2O) 2. xH 2O, where [DBA] (+) = di n-butylammonium and TIM = 2,3,9,10-tetramethyl-1,3,8,10-tetraenecyclo- 1,4,8,11-tetraazatetradecane. In the former compound, single Cd (2+) ions are excised from the parent CdCl 2 layers, with water molecules hydrogen bonded to chloride ions on both sides of the excision. Lattice stability is provided by the DBA (+) cations, which have an all-trans conformation. These lie between the layers, hydrogen bonding to the adjacent [Cd 9Cl 20(H 2O) 2] n (2 n- ) sheets. In the copper compound, the modification of the parent CuCl 2 structure is much more complex. In this compound, [Cu 2Cl 2] (2+) moieties are excised in a regular fashion. In addition, at 50% of the Cu1 sites, CuCl 2 species are replaced by pairs of water molecules in a random fashion. The Cu(TIM) (2+) cations bridge the layers via the formation of two semicoordinate bonds to chloride ions at the edge of the [Cu 2Cl 2] (2+) excision sites of adjacent layers.     

Terbium hybrid particles with spherical shape as luminescent probe for detection of Cu2+ and Fe3+ in water

A novel green emissive terbium inorganic-polymeric hybrid particle was designed and this material could detect cations in water. Polyvinyl alcohol as an amphiphilic surfactant rendered the powders dispersible in water with regular round shape (10-20 μm). Interestingly, we noticed that not only Cu(2+) (detection limit 10(-4)M) but also Fe(3+) (detection limit 10(-4) M) can give rise to emission quenching to this target material in comparison with K(+), Na(+), Fe(2+), Mn(2+), Pd(2+), Cd(2+) and Co(2+) (10(-3) mol L(-1)). We regarded that the coordination interactions between ligand and metal ions resulted in these quenching processes. Additionally, it was found that the sensing material can be repeatedly used at least 5 cycles. More importantly, this novel material demonstrated higher thermal-stability in aqueous media than pure silica hybrid material.     

ToF-SIMS depth profiling analysis of the uptake of Ba2+ and Co2+ ions by natural kaolinite clay

The sorption behavior of Ba(2+) and Co(2+) ions on a natural clay sample rich in kaolinite was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling at 10-A steps was performed up to a 70-A matrix depth of the clay prior to and following sorption. The results showed that Co(2+) is sorbed in slightly larger quantities than Ba(2+), with significant numbers of ions fixed on the outermost surface of the clay. Depletion of the ions K(+), Mg(2+), and Ca(2+) from the clay lattice was observed to accompany enrichment with Co(2+) and Ba(2+) ions. The data obtained using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) indicated insignificant structural and morphological changes in the lattice of the clay upon sorption of both Ba(2+) and Co(2+) ions. Analysis using energy dispersive X-ray spectroscopy (EDS) showed that the average atomic percentage (+/-S.D.) of Ba and Co on kaolinite surface were 0.49 +/- 0.11 and 0.61 +/- 0.19 , respectively, indicating a limited uptake capacity of natural kaolinite for both ions.     

Photo-controlled metal-ion (Zn2+ and Cd2+) release in aqueous Tween-20 micelle solution

Photo-controlled metal-ion (Zn(2+) and Cd(2+)) release in aqueous micelle solution (tris-HCl, pH = 7.4) has been described using 2-((2-mercaptophenylimino)methyl) phenol as ligand. It is found that both the ligand-Zn complex (1) and the ligand-Cd complex (2) are stable in micelle solution, and Zn(2+) (Cd(2+)) can be released from the complex with 365 nm light trigger. Accompanying the metal-ion release, the ligand is photo-converted to 2-(benzothiazol-2-yl) phenol (3) as product, and the turn-on fluorescence is detected. The fluorescence intensity increases with the photo-triggered release until Zn(2+) (Cd(2+)) is completely released, which is beneficial for monitoring the process of photo-controlled metal ion release. Control experiments demonstrate that no binding occurs between 3 and Zn(2+) (Cd(2+)) in micelle solution and there is no binding between cations and micelle, either.