A quantitative colorimetric assay of H2O2 and glucose using silver nanoparticles induced by H2O2 and UV

A simple spectrophotometric assay of H2O2 and glucose using Ag nanoparticles has been carried out. Relying on the synergistic effect of H2O2 reduction and ultraviolet （UV） irradiation, Ag nanoparticles with enhanced absorption signals were synthesized. H2O2 served as a reducing agent in the Ag nanoparticles formation in which Ag＋ was reduced to Ago by O2- generated via the decomposition of H2O2 in alkaline media. On the other hand, photoreduction of Ag＋ to Ago under UV irradiations also contributed to the nanoparticles formation. The synthesized nanoparticles were characterized by TEM, XPS, and XRD. The proposed method could determine H2O2 with concentrations ranging from 5.0× 10^-7 to 6.0× 10^-5 tool/ L The detection limit was estimated to be 2.0 × 10^-7 mol/L. Since the conversion of glucose to gluconic acid catalyzed by glucose oxidase was companied with the formation of H2O2, the sensing protocol has been successfully utilized for the determination of glucose in human blood samples. The results were in good agreement with those determined by a local hospital. This colorimetric sensor thus holds great promises in clinical applications.     

Synthesis of metal nanoclusters within microphase-separated diblock copolymers: sodium carboxylate vs carboxylic acid functionalization

Conversion of carboxylic acid groups, within the morphologies of [MTD]₄₀₀[NORCOOH]₅₀ diblock copolymers, to the sodium carboxylate form, [MTD]₄₀₀[NORCOONa]₅₀, results in large increases in both the rate and extent of transition metal and rare earth ion uptake from metal acetates, chlorides, nitrates, and sulfates. A[MTD]₄₀₀[NORCOONa]₅₀ film was subjected to four consecutive Ag⁺ loading and reduction sequences, resulting in a cumulative loading of approximately 26 wt% Ag in the overall polymer/Ag composite. Mean crystal diameters of 37, 50, 64, and 65 Å were estimated following the first, second, third, and fourth, loading and reduction sequences, respectively. During a single loading and reduction sequence, cluster size (ca. 30 Å) within [MTD]₄₀₀[NORCOOH]₅₀ was found to be relatively insensitive to the extent of Ag⁺ uptake, for loadings between 40 and 500 mg Ag⁺/g polyNORCOOH, consistent with a nucleation-controlled cluster formation process.     

Anthroneamine based chromofluorogenic probes for Hg2+ detection in aqueous solution

Anthroneamine derivatives 1–3 (H₂O:DMSO; 9:1, HEPES buffer, pH 7.0 ± 0.1) undergo highly selective fluorescence quenching with Hg²⁺. The observed linear fluorescence intensity change allows the quantitative detection of Hg²⁺ between 200 nM/40 ppb—12 μM/2.4 ppm even in the presence of interfering metal ions viz. Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, Pb²⁺. Probes 1–3 and their Hg²⁺ complexes also show the broad pH resistance for their practical applicability.     

Spectroscopic and pH-metric studies of the complexation of 3-[2-(4-methylquinolin-2-yl)hydrazono]butan-2-one oxime compound

The electronic absorption spectra of the oximic quinolinyl hydrazone (MHQ; H₂L) and its Co(II) and Cu(II)-complexes have been studied in Britton–Rhobinson buffer solutions of varying pH's in 75% dioxane-water. The dissociation constant of the hydrazone (pK^H) as well as the stability constants (log K) of its chelates were determined spectrophotometrically and pH-metrically. The obtained data are in good agreement. Beer's law is valid in the ranges (0.64–6.99) and (2.36–6.48) μg/mL for Cu(II) and Co(II)-ions, respectively. On the other hand, the pK^H and log K were determined pH-metrically in 75% solvent-water; (solvent = dioxane, ethanol, methanol and isopropanol). The variation of pK^H or log K as a function of solvent parameters viz. 1/D, E_T, AN and π* was used to evaluate the dissociation and stability constants in the aqueous medium. Furthermore, the reaction of the oximic hydrazone (H₂L) with copper(II)-nitrate and chloride in addition to copper(I)-iodide afforded square planar mononuclear and binuclear complexes in which the oximic hydrazone showed three different modes of bonding. The obtained complexes reflect the strong bridging ability of the oximato group as well as its ambidentate and flexidentate characters.     

Experimental study of the gas phase chemistry of C3H3+ with several cyclic molecules

Rate coefficients and ion product distributions have been determined for the gas phase reactions of C₃H₃⁺ with several homocyclic and heterocyclic molecules in a selected ion flow tube (SIFT) at 298 K. The rate coefficients for both the linear and cyclic isomers of C₃H₃⁺ are given. l-C₃H₃⁺ reacts by association in the majority of the reactions. c-C₃H₃⁺ is shown to be more reactive than previously suggested by low pressure experiments. In fact, the cyclic isomer reacts at the gas kinetic rate when the reaction involves a nitrogen containing cyclic compound but is less reactive with oxygen containing cyclic compounds. It is noted this reactivity of both the cyclic and linear isomer should be included when modeling the atmosphere of Titan due to the large number of nitrogen containing molecules that are considered to be present. Currently, the models consider electron recombination to be the only loss channel for c-C₃H₃⁺.     

Electrospray ionization mass spectrometry of a cerium(III) phosphomolybdate complex: Condensed and gas-phase cluster chemistry

Electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT/MS) of the ammonium cerium(III) phosphomolybdate complex (NH₄)₁₁[Ce(III)(PMo₁₁O₃₉)₂] in aqueous media has revealed a concentration-dependent behavior. Under fixed instrumental parameters, the Ce-containing polyoxomolybdate complexes H₂Ce(III)P₂Mo₂₂O₇₅^3? and Ce(III)PMo₁₁O₃₈^2? are the primary species present at 11 mM (pH = 4.3); at 0.7 mM (pH = 3.6), Ce(III)PMo₁₀O₃₅^2? is the predominant species, Ce(III)PMo₁₁O₃₈^2? is quite diminished, and H₂Ce(III)P₂Mo₂₂O₇₅^3? is absent. As a result of the complex isotopic fingerprints from multiple molybdenums, compositions of such ions are difficult to assign—successive collision induced dissociation (CID) of large ions produced smaller ions for which calculated and experimental isotopic patterns could be compared. The oxidation state of Ce and the number of counter cations on negative complexes was discerned from spectra of ions containing ¹H⁺ and ⁷Li⁺. The overall result is an ESI method applicable to phosphomolybdate complexes containing redox sensitive f-block metal ions such as Ce(IV) and Pu(III/IV). Dissociation studies also gave insight into favored fragmentation pathways, and generated gas ions with empirical formulae similar to known condensed-phase ions. Deconvolution of concentration- and pH-dependent solution behavior via ESI/MS and ³¹P NMR spectroscopy showed speciation dependent on solution concentration, not on pH.     

Silver alkoxide and amino N-heterocyclic carbenes; syntheses and crystal structures

Silver(I) complexes of heterobidentate ligands that incorporate one or two N-heterocyclic carbene moieties coupled with an alcohol or amine group have been made by direct deprotonation of ligands of the form [HOCR¹R²CH₂(1-HC{NCHCHNR})][X], H₂L¹X (X = Br, I), [H₂NR¹CHR²CHR²(1-HC{NCHCHNR})][Br]₂ H₃L²X₂ (X = Cl, Br), and [H₂N{CH₂CH₂(1-HC[NCHCHNMes])}₂][X]₃ H₄L³X₃ (X = Cl, Br). Silver(I) oxide is sufficiently basic to deprotonate both the imidazolium and the alcohol functional groups of all but one of the L¹ ligand precursors, to afford rare examples of silver alkoxide complexes [Ag(L¹)], stabilised by the soft donor carbene. Another complex of L¹ is characterised as the carbene alcohol adduct [Ag(HL¹)₂I]. The analogous reactions of silver(I) oxide with the amino imidazolium precursors afford silver amino-carbenes [Ag(HL²)Br] with the potentially bidentate L² ligand, and [Ag(HL³)X] (X = Cl, Br) with the potentially tridentate L³ ligand. A single crystal X-ray diffraction study of the latter complex confirms that the neutral amine of the potentially tridentate L³ ligand is unco-ordinated; instead the structure contains discrete chains of T-shaped silver bis(carbene) halide moieties that bridge to form a zig-zag 2-connected polymer. Protonolysis of two of the silver alkoxide and amino adducts, [Ag(L^1a)] and [Ag(HL^2a)Br], affords imidazolium complexes salts [H₂L^1a][AgCl₂] and [Ag(H₂L^2a)Br][AgBr₂] that retain the Ag(I) centre as complex counterions. The single crystal X-ray structures of these salts have been determined and show the silver(I) cations are now incorporated into ladders or chains as silver(I) halo-anions, and a silver amine dative bond is present in the latter complex.     

Synthesis of silver nanoparticles supported on silica aerogel using gamma radiolysis

Silver clusters on SiO₂ support have been synthesized using ⁶⁰Co gamma radiation. The irradiation of Ag⁺ in aqueous suspension of SiO₂ in the presence of 0.2 mol dm⁻³ isopropanol resulted in the formation of yellow suspension. The absorption spectrum showed a band at 408 nm corresponding to typical characteristic surface plasmon resonance of Ag nanoparticles. The effect of Ag⁺ concentration on the formation of Ag cluster indicated that the size of Ag clusters vary with Ag⁺ concentration, which was varied from 4×10⁻⁴ to 5×10⁻³ mol dm⁻³. The results showed that Ag clusters are stable in the pH range of 2–9 and start agglomerating in the alkaline region at pH above 9. The effect of radiation dose rate and ratio of Ag⁺/SiO₂ on the formation of Ag clusters have also been investigated. The prepared clusters have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), which showed the particle size of Ag clusters to be in the range of 10–20 nm.     

Electrochemical characterization of common catalysts and initiators for atom transfer radical polymerization in [BMIm][OTf]

The redox properties of some largely employed ATRP initiators and copper catalysts (Cu/L/X⁻) were investigated in 1-butyl-3-methylimidazolium trifluoromethanesulfonate (L = amine ligand, X = Br or Cl). Both Cu(II) and Cu(I) complexes are stable in the IL and, as required by ATRP, X⁻ stabilizes more Cu(II) than Cu(I). The activation rate constants of initiators by [Cu^ITPMA]⁺ were measured and a good correlation between k_act and the C-X bond dissociation free energy (BDFE) was observed. Overall, the results indicated that [BMIm][OTf] behaves much like organic solvents; the reported data launch the bases for a useful database to select the appropriate catalyst/initiator couple for ATRP in ILs.     

Voltammetric study on the mechanism of ion transfer caused by weak acids in the bilayer lipid membrane

The mechanism has been investigated by cyclic voltammetry for the ion transfer from one aqueous phase (W1) to another (W2) across a bilayer lipid membrane (BLM) in the presence of a typical uncoupler, carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP). Voltammograms for the ion transfer were in steady-state and showed rotated sigmoidal and symmetrical shape about the origin (0 V, 0 A). The magnitude of the ion transfer current at a given applied potential increased linearly with the concentration of FCCP in W2 up to 10⁻⁶ M and then became saturated. The ion transfer current also showed a bell-type dependence on pH centered around pH ≅ pK_a + 1, K_a being the dissociation constant of FCCP in aqueous phase. These properties have been well explained by our proposed model that the ion transfer current is attributable to the transfers of H⁺ and Na⁺ distributed in BLM. The hydrophilic counter ions, H⁺ and Na⁺, compensate the negative charge of the dissociated FCCP in BLM. The current intensity is predominantly governed by the concentration and the ion mobility of the counter cations.     

Metal complexes of azo compounds derived from 4-acetamidophenol and substituted aniline

The Ni(II) and Cu(II) complexes of four azo compounds (H₂L^1–4), namely, 2-(p-X-phenylazo)-4-acetamidophenol (X = OCH₃, NO₂, Br, and H for H₂L¹, H₂L², H₂L³, and H₂L⁴, respectively) were prepared and characterized on the basis of their analytical, spectroscopic, magnetic, and conductance data. The isolated complexes are found to have the general formulae [M(HL^1–4)Cl(H₂O)₃] (M = Ni(II) and Cu(II)). The chelates are found to have octahedral structure. The infrared spectra show that H₂L^1–4 ligands are coordinated to the metal ions in a uninegative bidentate manner, with NO donor sites of the azo N and the deprotonated phenolic O. The ligands and their chelates are subjected to thermal analysis. The biological activity of the synthesized ligands and their metal complexes also are screened against the adult Tribolium confusum mortality. They showed remarkable biological activity.     

Synthesis,characterization and spectroscopic studies of pyrazinamide metal complexes

The present paper deals with the synthesis and characterization of Schiff base complexes of pyrazinamide an antitubercular drug. Metals selected for complexation are copper, silver, gold, zinc, mercury, iron and cobalt. The complexes have been suitably synthesized and isolated in pure powdered form. Analytical data agrees with the compositions M(L), M′(L)₂ and M″(L)₂·2H₂O, respectively where M = Ag, M′ = Cu, Au, Zn and Hg and M″ = Fe and Co, ligand metal ratios were also confirmed by monovariation method and Job’s method of continuous variation. Molar conductance values suggest the non ionic nature of the complexes. The tentative structure assigned to the complexes on the basis of stoichiometry and analytical data were further supported by spectral studies viz; IR, NMR, magnetic susceptibility and electronic spectra. A preliminary attempt has also been made to compare the potencies of metal complexes with parent drug. The Cu and Ag complexes are giving encouraging results. Particle size studies further suggest that the drug molecule undergoes reduction in size on complexation.     

Electro-reduction of cuprous chloride powder to copper nanoparticles in an ionic liquid

Cyclic voltammetry of the CuCl powder in a cavity microelectrode revealed direct electro-reduction in solid state in 1-butyl-3-methylimidazolium hexafluorophosphate. Potentiostatic electrolysis of the salt powder (attached to a current collector) in the ionic liquid produced Cu nanoparticles as confirmed by X-ray diffraction, energy dispersive X-ray analysis, scanning and transmission electron microscopy. The particle size decreased down to 10 nm when the electrode potential was shifted from −0.9 V to −1.8 V (versus Ag/Ag⁺). The electro-reduction and the nanoparticle formation mechanisms were investigated in the ionic liquid and also in aqueous 0.1 mol L⁻¹ KClO₄ in which larger Cu particles were obtained.     

Carboxylic-supported copper complexes as catalyst for the green oxidative coupling of 2,6-dimethylphenol: Synthesis,characterization and structure

Three new Cu(II) complexes with carboxylic ligand, namely {[Cu(qc)₂(py)]·4H₂O}_∞ (1), [Cu(qc)₂(4,4′-bpy)]_∞ (2) and [Cu(pc)(2,2′-bpy)(H₂O)]₂·H₂O (3) (Hqc = 3-hydroxy-2-quinoxalinecarboxylic acid, H₂pc = 4-hydroxyphthalic acid, py = pyrazine) have been synthesized and characterized. In both 1 and 2, each Cu(II) ion is coordinated by two quinoxalinecarboxylate moieties in the equatorial plane and two 4,4′-bpy or pyrazine units provide coordination in the axial positions, thus, resulting in a 1-D polymeric chain structure. Complex 3 has a dimeric structure in which two Cu(II) cations are bridged by two deprotonated pc^2? ligands and two 2,2′-bpy molecules. As heterogeneous catalysts, the title complexes showed high catalytic efficiency in the green oxidative polymerization of 2,6-dimethylphenol (DMP) to poly(1,4-phenylene ether) (PPE) in the presence of H₂O₂ as oxidant in water under mild conditions. Moreover, they allow reuse without significant loss of activity through four runs, which suggests that these catalysts are efficient, mild, and easily recyclable for the oxidative coupling of DMP. The preliminary study of the catalytic–structural correlations suggests that the coordination environment of the metal center plays an important role in the improvement of their catalytic efficiencies.     

Synthesis and crystal structure of sodium copper tetrametaphosphimate heptahydrate Na2Cu(PO2NH)4·7H2O and sodium potassium copper tetrametaphosphimate heptahydrate KxNa2−xCu(PO2NH)4·7H2O

Na₂Cu(PO₂NH)₄·7H₂O and K_xNa_2−xCu(PO₂NH)₄·7H₂O (x ≈ 0.5) were synthesized by gel crystallization in sodium silicate gels. The crystal structures were solved by single-crystal X-ray methods and found to be isotypic (Pnma, Z = 4; Na₂Cu(PO₂NH)₄·7H₂O: a = 627.5(2) pm, b = 1456.0(3) pm, c = 1900.5(4) pm, R1 = 0.0352; K_0.47Na_1.53Cu(PO₂NH)₄·7H₂O: a = 632.2(2) pm, b = 1460.0(3) pm, c = 1936.4(4) pm, R1 = 0.0345). The P₄N₄ rings of the tetrametaphosphimate anion exhibit a distorted chair-2 conformation with admixtures of saddle and crown conformation. The M⁺ ions are six- and sevenfold coordinated by oxygen atoms, the Cu²⁺ ions are fivefold coordinated, respectively. The MO₇ and the CuO₅ units form pairs of face-sharing polyhedra, which are connected by common corners forming chains and are further interconnected by tetrametaphosphimate anions, forming a three-dimensional network structure with channels along [100] and [010]. The MO₆ units form chains of face-sharing polyhedra, which are situated in the channels along [100]. Extended hydrogen bonding reinforces the three-dimensional framework structure of the compounds. ²³Na-MAS NMR experiments were conducted to verify the K/Na distribution on the M sites derived from the X-ray crystal structure refinement.     

Glass transition behaviour of the quaternary ammonium type ionic liquid, {[DEME][I] + H2O} mixtures

By a simple DTA system, the glass transition temperatures of the quaternary ammonium type ionic liquid, {N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium iodide, [DEME][I] + H₂O} mixtures after quick pre-cooling were measured as a function of water concentration (x mol% H₂O). Results were compared with the previous results of {[DEME][BF₄] + H₂O} mixtures in which double glass transitions were observed in the water concentration region of (16.5 to 30.0) mol% H₂O. Remarkably, we observed the double glass transition phenomenon in {[DEME][I] + H₂O} mixtures too, but the two-T_gs regions lie towards the water-rich side of (77.5 to 85.0) mol% H₂O. These clearly reflect the difference in the anionic effect between ${\text{BF}}_4^{-}$ and I^? on the water structure. The end of the glass-formation region of {[DEME][I] + H₂O} mixtures is around x = 95.0 mol% H₂O, and this is comparable to that of {[DEME][BF₄] + H₂O} mixtures (x = 96.0 mol% H₂O).     

Theoretical study on structures and vibrational spectra of M+(H2O)Ar (M = Cu,Ag, Au)

A theoretical study on the structures and vibrational spectra of M⁺(H₂O)Ar_0‐1 (M = Cu, Ag, Au) complexes was performed using ab initio method. Geometrical structures, binding energies (BEs), OH stretching vibrational frequencies, and infrared (IR) absorption intensities are investigated in detail for various isomers with Ar atom bound to different binding sites of M⁺(H₂O). CCSD(T) calculations predict that BEs are 14.5, 7.5, and 14.4 kcal/mol for Ar atom bound to the noble metal ion in M⁺(H₂O)Ar (M = Cu, Ag, Au) complexes, respectively, and the corresponding values have been computed to be 1.5, 1.3, and 2.1 kcal/mol when Ar atom attaches to a H atom of water molecule. The former structure is predicted to be more stable than the latter structure. Moreover, when compared with the M⁺(H₂O) species, tagging Ar atom to metal cation yields a minor perturbation on the IR spectra, whereas binding Ar atom to an OH site leads to a large redshift in OH stretching vibrations. The relationships between isomers and vibrational spectra are discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Thermodynamic study of the mixed system (CsCl + CaCl2 + H2O) by EMF Measurements at T = 298.15 K

This work reports the results of a thermodynamic investigation of the ternary mixed-electrolyte system (CsCl + CaCl₂ + H₂O). The activity coefficients of this mixed aqueous electrolyte system have been studied with the electromotive force measurement (EMF) of the cell: Cs ion-selective electrode (ISE)|CsCl(m_A), CaCl₂(m_B), H₂O|Ag/AgCl at T = 298.15 K and over total ionic strengths from (0.01 to 1.50) mol · kg^?1 for different ionic strength fractions y_B of CaCl₂ with y_B = (0, 0.2, 0.4, 0.6, and 0.8). The cesium ion-selective electrode (Cs-ISE) and the Ag/AgCl electrode used in this work were made in our laboratory and had a good Nernst response. The experimental results obey the Harned rule, and the Pitzer model can be used to describe this ternary system satisfactorily. The osmotic coefficients, excess Gibbs free energies and activities of water of the mixtures were also calculated.     

Synthesis and spectroscopic,magnetic and cyclic voltammetric characterization of some metal complexes of methionine: [(C5H10NO2S)2MII]; MII = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)

Some metal complexes of DL–methionine were prepared in aqueous medium and characterized by different physico-chemical methods. Methionine forms 1:2 complexes with metal, M(II). The general empirical formula of the complexes is proposed as [(C₅H₁₀NO₂S)₂M^II]; where M^II = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II). All the complexes are extremely stable in light and air and optically inactive. Magnetic susceptibility data of the complexes demonstrate that they are high spin paramagnetic complex except Zn(II), Cd(II) and Hg(II) complexes. The bonding pattern in the complexes are similar to each other as indicated by electronic absorption spectra and FTIR spectral analysis. The current potential data, peak separation (AE) and the peak current ratio (i_pa/i_pc) of the (Mn, Cu and Cd) complexes indicate that the charge transfer processes are irreversible, the systems are diffusion controlled and also adsorptive controlled. The charge transfer rate constant of metals in their complexes are less than those in their metal salts at identical experimental conditions due to the coordination of metal with methionine.     

Lithium Intercalation into ATi2(PS4)3 (A = Li,Na, Ag)

Comparison of the electrochemical insertion of lithium into ATi₂(PS₄)₃ with A = Li, Na, Ag and ATi₂(PO₄)₃ with Li, Ag is striking. Whereas only four lithium per formula unit (Li/f.u.) can be inserted reversibly into the phosphates, up to 7 and 10 Li/f.u. can be inserted reversibly in the thiophosphates with A = Li and Ag. Moreover, the Ag⁺ to Ag⁰ reduction in AgTi₂(PO₄)₃ is not reversible, but in AgTi₂(PS₄)₃ it is reversible. Strong hybridization of the Ag-5s and host antibonding bands stabilizes the formal valences Ag⁰, Ti⁺, and (PS₄)⁴⁻ in the discharged state of AgTi₂(PS₄)₃; but only the formal valence Ti²⁺ is accessible in LiTi₂(PS₄)₃. Unfortunately the large volume change associated with the lithium insertion renders the structure progressively more amorphous on cycling, which causes the capacity to fade quite dramatically on further cycling. The thiophosphates transform to the phosphates on heating in air.