Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn²⁺ or Cd²⁺ is a worldwide concern. Developing an inexpensive and facile detection method for Zn²⁺ and Cd²⁺ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn²⁺ and Cd²⁺ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S²⁻). The presence of Zn²⁺ (or Cd²⁺) can “turn-on” the weak fluorescence of QDs quenched by S²⁻ due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn²⁺ (or Cd²⁺) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd²⁺). The limit of detection (LOD) for Zn²⁺ and Cd²⁺ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn²⁺ and Cd²⁺ over other metal ions and was successfully used in the detection of Zn²⁺ or Cd²⁺ in real water samples.     

In Situ Hydrogenation and Crystal Chemistry Studies of Co2Si Type Compounds MgPd2 and Pd2Zn

The hydrogenation properties of the intermetallic compounds MgPd₂ and Pd₂Zn, crystallizing in the Co₂Si type, were studied by in situ thermal analysis (DSC) under hydrogen pressure. Pd₂Zn does not show any reaction with hydrogen while MgPd₂ reversibly forms the hydride MgPd₂H. Neutron diffraction on the deuterides reveals the compositions MgPd₂D_0.861(6) (ambient) and MgPd₂D_0.97(1) [308(2) K, 2.56(5) MPa deuterium] with hydrogen (deuterium) occupying distorted [MgPd₅] octahedral voids. Quantum mechanical calculations support the structure models and show the hydrogenation to be exergonic for MgPd₂ and endergonic for Pd₂Zn. MgPd₂H releases hydrogen under normal conditions or vacuum. Heating under hydrogen pressure leads first reversibly to MgPd₂H_≈0.2 and subsequently irreversibly to MgPd₃H_≈1 and MgH₂. MgPd₂, Pd₂Zn, and MgPd₂H were classified in a structure map. Trends of axial ratio changes upon hydrogenation of TiNiSi type and ZrBeSi type compounds are discussed.     

Capillary gas chromatographic analysis of pyrrolidinedithiocarbamate metal chelates

Pyrrolidinedithiocarbamate (PDTC) chelates of Zn(II), Cu(II), Ni(II), Co(III), Fe(III), Mn(II), Cr(III), and VO(II) were analysed by capillary GC on a DB-1701 column (30 m x 0.25 mm id) with flame ionisation detection (FID). Linear calibrations were attained within "1-30 microg/mL" for Ni(II), Fe(III), Mn(II), Cr(III), Cu(II), and VO(II), and within "2-50 microg/mL" for Co(III) and Zn(II). The limits of detection were in the "150-500 ng/mL" range, corresponding to 15-50 pg amounts reaching the FID system. The optimised method was applied to the determination of Cu(II) and Ni(II) in coins, and that of Zn(II), Cu(II), Ni(II), Fe(III), Mn(II), Cr(III), and VO(II) in pharmaceutical preparations with relative standard deviations within 1.1-5.2%. The results obtained are in good agreement with sewage water samples and the declared values for the pharmaceutical formulations, or with the results of AAS of metal contents in coins, pharmaceutical preparations, and sewage water samples.     

A Novel Reduction of Azides to Amines with Tellurium Metal in Near-Critical Water

Tellurium metal in near-critical water (275°;C) provides a novel and efficient method for the reduction of azides, producing amines in good yields.     

Thermo-kinetic Investigation of Optimum Growth Temperature of Petroleum Bacteria

The power-time curves of the growth of three strains of petroleum bacteria at different temperatures have been determined. A novel equation of a power-time curve has been proposed in this paper. The general formula to calculate the rate constant of the bacterial growth has been derived. The rate constants of the bacterial growth at different temperatures, the heat production per newly formed bacterium, the bacterial number at the end of the bacterial growth and the deceleration rate constant of the bacterial growth at 50.00°C, have been calculated. The optimum growth temperatures of the three strains have been obtained.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nickel nanoparticles and solids using organic solvents

Nickel colloids were prepared by codeposition of the metal with several organic solvents: acetone, ethanol, 2-propanol, 2-methoxyethanol and 1,2-dimethoxyethane at 77 K. The stabilities of the colloids and fine powders were measured. The metallic films and active solids were obtained by evaporation under vacuum at room temperature. The Ni-2-methoxyethanol colloids are stable over three months at room temperature, and the UV-VIS absorption spectra of the most stable colloids were obtained. A chemical characterization of Ni solids was carried out by several techniques such as elemental analysis, FT-IR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry (TGA). The IR studies show the presence of the solvent in the solids, which was confirmed by microanalysis. From TGA, DSC, and TGA-FTIR the metal-solvent was studied. From TGA, the kinetic parameters of decomposition reaction were calculated using the Freeman and Carroll equations. Received: 6 June 2000 Accepted: 6 September 2000     

Reactions of bis(diphenylphosphine)acetylene with metal carbonyl complexes

The reaction of [Co₂(CO)₈] with DPPA at room temperature yields a diphosphine bridged product [Co₄(CO)₁₂(μ-Ph₂-P-C≡C-P-Ph₂)₂] 1. Heating of 1 at 45°C promoted cleavage of the P-C_sp bond with the formation of binuclear, phosphido-bridged σ-π-acetylide isomer complexes [Co₂(CO)₅(μ-PPh₂) (μ-σ-π-C≡C-PPh₂ )] 2a, 2b. Heating (60°C) of the complex [CpFe(CO)₂CH₃] and DPPA affords mono and binuclear acetyl, P-coordinated diphenylphosphinoalkyne metal complexes [CpFe(Ph₂P-C≡C-PPh₂)CO(COCH₃)] 3, [CpFeCO(COCH₃)]₂-μ-(Ph₂P-C≡C-PPh₂) 4.     

The chemical identity of “[Ag(py)2]MnO4” organic solvent soluble oxidizing agent and new synthetic routes for the preparation of [Ag(py)n]XO4 (X = Mn,Cl, and Re,n = 2–4) complexes

Abstract

A widely used oxidizing agent in organic chemistry with an assumed structure of “[Ag(py)₂]MnO₄” and its perchlorate and perrhenate analogues are studied. Their synthesis in pure form is challenging. In order to clarify the chemical nature of the known compounds and find routes to new derivatives, a systematic study is presented for the synthesis of [Ag(py)_n]XO₄ (X?=?Mn, Cl, and Re, n?=?2–4) complexes. Ten complexes including four new derivatives, [Ag(py)₄]MnO₄, [Ag(py)₄]MnO₄·4[Ag(py)₂]MnO₄, [Ag(py)₂]ClO₄·0.5 py, and [Ag(py)₂]ReO₄, are synthesized and characterized. The chemical identity of “Ag(py)₂MnO₄” is also clarified. A novel route to prepare [Ag(py)₂]MnO₄ is developed. The reaction of AgXO₄ salts with neat pyridine followed by various crystallization techniques is used to prepare [Ag(py)₂]XO₄, [Ag(py)₄]XO₄, [Ag(py)₄]XO₄·4[Ag(py)₂]XO₄, and [Ag(py)₂]XO₄·0.5py (X?=?Cl, Mn) complexes. The solid phase structure of [Ag(py)₂]MnO₄·0.5py is determined (a?=?19.410 Å, b?=?7.788 Å, c?=?21.177 Å, β?=?104.20°, C2/c (15), Z?=?4 (3a)). [Ag(py)₂]⁺ cations in the crystal form dimeric units where silver ions are connected by oxygen atoms of two MnO₄^– anions. The Ag…Ag distance is indicative of argentophilic interactions. The pyridine ring π…π interactions contribute to the stability of the crystal lattice.     

Synthesis,characterization, and biological activity of metal complexes of 4-ethyl vanillideneamino-3-methyl-5-mercapto-1,2,4-triazole

A series of transition metal–triazole derivatives have been synthesized and characterized by microanalytical, thermal, magneto-chemical, and spectral studies. The synthesized complexes were screened for biological activities. The complexes of Co(II) and Ni(II) emerged as a good antibacterial agent against Gram-negative bacteria such as Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Bacillus subtilis, and Shigella flexneri.     

Studies on oxovanadium(IV), Cr(III), Co(II), Ni(II), and Cu(II) chelates of some bisketimino ligands

The oxovanadium(IV), Cr(III), Ni(II), Co(II), and Cu(II) chelates of some bisketimino Schiff-base ligands (H₂L) obtained by condensation of 4-butyryl-3-methyl-1-phenyl-(or-1,3-diphenyl)-2-pyrazolin-5-ones with thiourea were synthesized and characterized by elemental analyses and thermogravimetric analyses, molar conductivities, magnetic susceptibility measurements, mass, infrared, and electronic spectroscopies. Ligand field parameters, such as splitting energy, Racah parameter, spin–orbit coupling constant, and covalency parameter of the Cr(III), Ni(II), and Co(II) chelates were calculated by band-fitting methods. Based on these studies, tetragonally distorted octahedral environment around OV(IV) and Cu(II) and octahedral Cr(III), Ni(II), and Co(II) have been proposed.