Adsorptive anodic stripping voltammetry of zirconium(IV)-alizarin red S complex at a carbon paste electrode

A sensitive adsorptive anodic stripping procedure for the determination of trace zirconium at a carbon paste electrode (CPE) has been developed. The method is based on adsorptive accumulation of the Zr(IV)-alizarin red S(ARS) complex onto the surface of the CPE, followed by oxidation of adsorbed species. The optimal experimental conditions include the use of 0.10 mol · L⁻¹ ammonium acetate buffer (pH 4.3), ARS, an accumulation potential of 0.20 V (versus SCE), an accumulation time of 2 min, a scan rate of 200 mV · s⁻¹ and a second-order derivative linear scan mode. The oxidation peak for the complex appears at 0.69 V. The peak current is proportional to the concentration of Zr(IV) over the range of 1.0 × 10⁻⁹–2.0 × 10⁻⁷ mol · L⁻¹, and the detection limit is 3 × 10⁻¹⁰ mol · L⁻¹ for a 2 min adsorption time. The relative standard deviations (n = 8) for 5.0 × 10⁻⁸ and 5.0 × 10⁻⁹ mol · L⁻¹ Zr(IV) are 3.3 and 4.8%, respectively. The proposed method was applied to the determination of zirconium in ore samples with satisfactory results.     

Silver(I)-selective electrode based on [Bz2Oxo4(18)dieneS4] tetrathia macrocyclic carrier

A polystyrene-based membrane of 7,8:16,17-dibenzo-6,9,15,18-tetraoxo-1,5,10,14-tetrathiacyclooctadeca-7,16-diene [Bz₂Oxo₄(18)dieneS₄] was fabricated using sodium tetraphenylborate (NaTPB) and dioctyl phthalate (DOP) as anion excluder and plasticizing agent. The best performance was obtained from the membrane with the composition ionophore [Bz₂Oxo₄(18)dieneS₄]:polystyrene:DOP:NaTPB, 5:100:150:10 (w/w). The response of the electrode was linear over a wide range of concentration, 1.26×10^–6–1.00×10^–1 mol L⁻¹ for silver ion with a Nernstian slope of 58.4±0.1 mV per decade and a detection limit of 1.0×10⁻⁶ mol L⁻¹. The electrode was found to be chemically inert and of adequate stability with a response time of 10 s and could be used for a period of 3 months without change of potential. It worked satisfactorily in mixtures containing up to 35% (v/v) non-aqueous content. The proposed membrane sensor had good selectivity for Ag⁺ over a wide variety of metal ions in the pH range 2.2–8.5. It was successfully used as an indicator electrode in potentiometric titration of silver ion. The electrode was also useful for determination of Ag⁺ in waste from photographic films.     

Determination of thiocyanate ions at nanolevel in real samples using coated graphite electrode based on synthesised macrocyclic Zn(II) complex

The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating the newly synthesized zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N₂-1,5-O₂ (I ₁ ) and zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N₂-1,5-O₂ (I ₂ ) are reported here. The best response was observed with the membrane having a composition of I₂:PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with detection limit of 2.2 × 10⁻⁷ mol L⁻¹. The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics w.r.t Nernstian slope 59.0 ± 0.2 mV decade⁻¹ activity, wide concentration range of 8.9 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹ and detection limit of 6.7 × 10⁻⁸ mol L⁻¹. The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in potentiometric titration of SCN⁻ ion.     

Catalytic adsorptive stripping voltammetric determination of copper(II) on a carbon paste electrode

A catalytic adsorptive stripping voltammetric method for the determination of copper(II) on a carbon paste electrode (PCE) in an alizarin red S (ARS)-K₂S₂O₈ system is proposed. In this method, copper(II) is effectively enriched by both the formation and adsorption of a copper(II)-ARS complex on the PCE, and is determined by catalytic stripping voltammetry. The catalytic enhancement of the cathodic stripping current of the Cu(II) in the complex results from a redox cycle consisting of electrochemical reduction of Cu(II) ion in the complex and subsequent chemical oxidation of the Cu(II) reduction product by persulfate, which reduces the contamination of the working electrode from Cu deposition and also improves analytical sensitivity. In Britton-Robinson buffer (pH 4.56±0.1) containing 3.6×10⁻⁵ mol L⁻¹ ARS and 1.6×10⁻³ mol L⁻¹ K₂S₂O₈, with 180 s of accumulation at −0.2 V, the second-order derivative peak current of the catalytic stripping wave was proportional to the copper(II) concentration in the range of 8.0×10⁻¹⁰ to ∼3.0×10⁻⁸ mol L⁻¹. The detection limit was 1.6×10⁻¹⁰ mol L⁻¹. The proposed method was evaluated by analyzing copper in water and soil.     

Novel cyclohexyl‐substituted salicylaldiminato–nickel(II) complex as a catalyst for ethylene homopolymerization and copolymerization

The cyclohexyl‐substituted salicylaldiminato–Ni(II) complex [O? (3‐C₆H₁₁)(5‐CH₃)C₆H₂CH?N‐2,6‐C₆H₃ⁱPr₂]Ni(PPh₃)(Ph) ( 4 ) has been synthesized and characterized with ¹H NMR and X‐ray structure analysis. In the presence of phosphine scavengers such as bis(1,5‐cyclooctadiene)nickel(0) [Ni(COD)₂], triisobutylaluminum (TIBA), and triethylaluminum (TEA), 4 is an active catalyst for ethylene polymerization and copolymerization with the polar monomers tert‐butyl‐10‐undecenoate, methyl‐10‐undecenoate, and 4‐penten‐1‐ol under mild conditions. The polymerization parameters affecting the catalytic activity and viscosity‐average molecular weight of polyethylene, such as the temperature, time, ethylene pressure, and catalyst concentration, are discussed. A polymerization activity of 3.62 × 10⁵ g of PE (mol of Ni h)^?1 and a weight‐average molecular weight of polyethylene of 5.73 × 10⁴ g^.mol^?1 have been found for 10 μmol of 4 and a Ni(COD)₂/ 4 ratio of 3 in a 30‐mL toluene solution at 45 °C and 12 × 10⁵ Pa of ethylene for 20 min. The polydispersity index of the resulting polyethylene is about 2.04. After the addition of tetrahydrofuran and Et₂O to the reaction system, 4 exhibits still high activity for ethylene polymerization. Methyl‐10‐undecenoate (0.65 mol %), 0.74 mol % tert‐butyl‐10‐undecenoate, and 0.98 mol % 4‐penten‐1‐ol have been incorporated into the polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6071–6080, 2004     

Electrocatalytic oxidation of nitrite at a terpyridine manganese(II) complex modified carbon past electrode

A carbon past electrode modified with [Mn(H₂O)(N₃)(NO₃)(pyterpy)], ( \textpyterpy = 4￠- ( 4 - \textpyridyl ) - 2,2￠:\text6￠,\text2￠￠- \textterpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and nitrite can be determined in the ranges of 5.00 × 10⁻⁶ to 1.55 × 10⁻² mol L⁻¹, with a detection limit of 8 × 10⁻⁷ mol L⁻¹. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10⁻², 0.56× 10⁻⁶, and 7.99 × 10⁻⁶ cm² s⁻¹, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed. This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior, anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical purposes.     

Highly active three-component catalytic systems based on dialkylzirconocenes, triisobutylaluminum, and perfluorophenyl borates for synthesis of low-molecular-weight polyethylene

The catalytic properties of the zirconium complex with “constrained geometry” Me₂SiCp^*NBu¹ZrX₂ (Cp^*=C₅Me₄, X=Cl (1a), Me (1b)) and bridged bis(cyclopentadienyl)zirconocene Me₂SiCp₂ZrX₂ (X=Cl (2a), Me (2b)) during their activation with triisobutylaluminum/perfluorophenyl borates (TIBA/LB(C₆F₅)₄, L=CPh₃ (3), Me₂HNPh (4)) in ethylene polymerization under a monomer pressure of 2–20 atm were studied by comparison. Both dichloride complexes exhibit moderate activity under the action of the combined TIBA/3 activating agent and give linear high-molecular-weight polyethylene (PE). The interaction of the dimethyl complexes with TIBA/3(4) afford active sites in which the growing polymeric chain is intensely transferred to the monomer, due to which low-molecular-weight PE is formed. The dichloride complexes affected by TIBA/4 also afford low-molecular-weight PE. Analysis of the structure of the polymeric products (¹H NMR spectrometry, IR spectroscopy), molecular-weight parameters of the PE samples (gel permeation chromatography (GPC)), and kinetics of polymerization suggested that the active site contains AlBuⁱ ₃ as a heteronuclear bridged cationic complex. The influence of various basic substrates (the products of chain transfer with the terminal vinyl groups, the dimethylaniline fragment of borate4 or other amine specially introduced into the reaction mixture) on the catalytic properties of the Zr−Al site was revealed. The polymerization rate and molecular-weight parameters of PE as functions of the reaction temperature, ethylene pressure, and modifying additives were studied. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1189–1198, July, 2000.     

Adsorption of Cu(II), Cd(II), Pb(II), Cr(VI) by double hydroxides on the basis of Al oxide and Zr, Sn, and Ti oxides

It was studied the equilibrium adsorption and adsorption kinetics of Cu(II), Cd(II), Pb(II), and Cr(VI) by composite hydroxides formed by Me _x O _y · nH₂O and Me_0.4–0.7Al_0.6–0.3O _y · nH₂O, where Me = Zr, Sn and Ti. It was estimated the values of the diffusion coefficients of adsorbed ions Cu(II) and Cr(VI) from kinetic values. It was established that the estimated diffusion coefficients of adsorbed ions Cu(II) are in the range 0.4 × 10⁻¹²–2.5 × 10⁻¹² m²/s for individual hydroxides and 1.2 × 10⁻¹²–2.8 × 10⁻¹² m²/s for double hydroxides. The obtained values of diffusion coefficients Cr (VI) for double hydroxides are 0.1 × 10⁻¹⁰–0.4 × 10⁻¹⁰ m²/s.     

Effect of substituents on the catalytic properties of bis(cyclopentadienyl)zirconium dichloride complexes with polymethylaluminoxane and AlBu1 3/CPh3B(C6F5)4 cocatalysts in ethylene polymerization

The catalytic properties of the complexes (RCp)₂ZrCl₂ (R=H, Me, Prⁱ, Buⁿ, Buⁱ, Me₃Si,cyclo-C₆H₁₁), and Me₂SiCp^*NBuⁱZrCl₂ (Cp^*=C₅(CH₃)₄) combined with the AlBuⁱ ₃−CPh₃B(C₆F₅)₄ cocatalyst in ethylene polymerization were studied. The specific activity of the substituted bis-cyclopentadienyl complexes decreases in the sequence: Me>Prⁱ>Buⁿ>Buⁱ>Me₃Si>cyclo-C₆H₁₁, which corresponds to the activity sequence for these complexes activated by polymethylaluminoxane (MAO) but is 4–20 times lower in absolute value. Comparison of the polyethylene samples obtained in the presence of the same complexes with MAO and AlBuⁱ ₃−CPh₃B(C₆F₅)₄ cocatalysts showed that polyethylene with much higher molecular mass, melting point, and crystallinity is formed in the presence of the ternary catalytic systems, and this indicates a different nature of the active sites of the catalytic systems. The effective activation energy of polymerization (≈3.6 kcal mol⁻¹), first order with respect to monomer and ≈0.4 order with respect to organoaluminum component, was found for the (PrⁱCo)₂ZrCl₂−AlBuⁱ ₃−CPh₃B(C₆F₅)₄ catalytic system. It was proposed on the basis of the kinetic data that AlⁱBu₃ enters into the composition of the active site to form a bridged heteronuclear cationic complex. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp 301–307, February, 2000.     

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

The kinetics of the reactions between Fe(phen) ₃ ²⁺ [phen = tris–(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm⁻³ (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H⁺] = 0.01 mol dm⁻³) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm³ mol⁻¹ s⁻¹. Ion-pair constants K _ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 10⁴, 3.00 × 10² and 4.02 × 10⁴ mol⁻¹ dm⁻³ for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K⁻¹ mol⁻¹) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K⁻¹) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E _a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm³ mol⁻¹ s⁻¹) = (7.079 ± 0.035) × 10¹⁶, (1.413 ± 0.011) × 10¹⁷, and (9.772 ± 0.027) × 10²⁰ for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions.     

Determination of Zirconium (IV) and Aluminium (III) in Waste Water

 Zirconium (IV) was determined spectrophotometrically by reaction with quercetin as primary ligand and oxalate as secondary ligand. Polyvinylpyrrolidone (PVP) was used as protective colloid to solubilize the formed zirconium quercetin oxalate ternary complex. The molar absorptivity of the 1:3:1 (zirconium–quercetin–oxalate) complex is 7.31 × 10⁴ L·mol⁻¹ cm⁻¹ at 430 nm with a stability constant of 8.2 × 10²⁰ and its detection limit is 0.16 mg/L. Beer’s law is rectilinear up to 1.46 mg/L of zirconium (IV). The sensitivity index is 1.25 ng cm⁻². The reaction of aluminium (III) with quercetin in presence of PVP as a surfactant has been studied spectrophotometrically. The molar absorptivity of the 1:3 (aluminium–quercetin) complex is 8.09 × 10⁴ × L·mol⁻¹·cm⁻¹ at 433 nm, its stability constant is 2.6 × 10¹³ with sensitivity index of 0.33 ng·cm⁻² and its detection limit is 0.08 mg/L. The optimal conditions for the quantitative determination of zirconium and aluminium were studied. The proposed methods are examined by statistical analysis of the experimental data. The methods are free from interference of most cations and anions. The proposed methods have been used to determine zirconium and aluminium in industrial waste water. Received May 30, 2001; accepted November 2, 2001; published online July 15, 2002     

Synthesis and characterization of poly(styrene/α-t-butoxy-ω-vinylbenzyl-polyglycidol) microspheres

Polystyrene microspheres with polyglycidol (polyGL) in a surface layer were synthesized in batch radical emulsifier-free emulsion copolymerizations of styrene and surfmers, α-t-butoxy-ω-vinylbenzyl-polyGL macromonomers (VB-polyGL). Macromonomers with number-average molecular weight Mˉ _n=950 (VB-polyGL950) and Mˉ _n=2700 (VB-polyGL2700) were used for these polymerizations. In all syntheses the initial concentrations of styrene and initiator (K₂S₂O₈) were constant. The initial macromonomer-to-styrene ratios were varied from 1.10 × 10⁻³ to 1.64 × 10⁻² mol/mol and from 3.46 × 10⁻⁴ to 3.47 × 10⁻³ mol/mol for VB-polyGL950 and VB-polyGL2700, respectively. The diameters of microspheres obtained were smaller for the syntheses with higher concentrations of macromonomers. Syntheses with VB-polyGL950 yielded microspheres with number-average diameters (Dˉ _n) from 216 to 900 nm and with a bimodal diameter distribution. The number-average diameters of microspheres obtained with VB-polyGL2700 varied from 220 to 650 nm, depending on the initial concentration of macromonomer. Their diameter distributions were monomodal, with a diameter polydispersity parameter (ratio of weight-average and number-average diameters) in the range 1.007≤Dˉ _w/Dˉ _n≤1.022. For each type of microsphere the fraction of polyGL in a surface layer and the surface concentration of sulfate anions were determined. The fraction of polyGL in the surface layer was related to the initial monomer composition in the polymerizing mixture. Adsorption of human serum albumin onto surfaces of some poly(styrene/VB-polyGL) microspheres was up to 10 times lower than for the polystyrene microspheres obtained in a similar emulsifier-free emulsion polymerization of styrene. Received: 26 September 2000/Accepted: 19 February 2001     

Mass Spectrometric Determination of Association Constants of Bovine Serum Albumin (BSA) with para-Sulphonato-Calix[n]arene Derivatives

Electrospray Ionization Mass Spectrometry (ESI/MS) has been used to determine the association constants (K_As) and binding stoichiometries for parent para-Sulphonato-calix[n]arenes and their derivatives with bovine serum albumin (BSA). K_A values were determined by titration experiments using a constant concentration of protein. K_A measurements were carried out in a methanol–formic acid solution. 5,11,17,23–tetra-Sulphonato-calix[4]arene (1a) and 25-mono-(2-aminoethoxy)-5,11,17,23-tetra-Sulphonato-calix[4]arene (1d) interact strongly with BSA showing 3 non-equivalent binding sites with K_A1 = 7.69 × 10⁵ M⁻¹, K_A2 = 3.85 × 10⁵ M⁻¹, K_A3 = 0.33 × 10⁵ M⁻¹ and K_A1 = 1.69 × 10⁵ M⁻¹, K_A2 = 2.94 × 10⁵ M⁻¹, K_A3 = 0.60 × 10⁵ M⁻¹, respectively. The strength of the interactions between the calixarene and BSA is inversely proportional to the size of macrocyclic ring: n = 4 > n=6>>n=8.     

Electrocatalytic oxidation of pyridoxine (vitamin B<Subscript>6</Subscript>) on aluminum electrode modified by metallic palladium particles/iron (III) hexacyanoferrate (II) film

The electrocatalytic activity of a Prussian blue (PB) film on the aluminum electrode by taking advantage of the metallic palladium characteristic as an electron-transfer bridge (PB/Pd–Al) for electrooxidation of 2-methyl-3-hydroxy-4,5-bis (hydroxyl–methyl) pyridine (pyridoxine) is described. The catalytic activity of PB was explored in terms of Fe^III [Fe^III (CN)₆]/Fe^III [Fe^II (CN)₆]¹⁻ system. The best mediated oxidation of pyridoxine (PN) on the PB/Pd–Al-modified electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 6 at scan rate of 20 mV s⁻¹. The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The charge transfer-rate limiting reaction step is found to be a one-electron abstraction, whereas a two-electron charge transfer reaction is the overall oxidation reaction of PN by forming pyridoxal. The value of α, k, and D are 0.5, 1.2 × 10² M⁻¹ s⁻¹, and 1.4 × 10⁻⁵ cm² s⁻¹, respectively. Further examination of the modified electrodes shows that the modifying layers (PB) on the Pd–Al substrate have reproducible behavior and a high level of stability after posing it in the electrolyte or Pyridoxine solutions for a long time.     

Syntheses, Crystal Structures and Third-order Nonlinear Optical Properties of Coordination Polymers {[Et4N][Ag2I3]}n and [CuBr(C10H8N2S2)]n

Coordination polymers {[Et₄N][Ag₂I₃]}_n (1) and [CuBr(C₁₀H₈N₂S₂)]_n (2) were prepared by standard Schlenk techniques. Their X-ray measurements indicate that polymer (1) crystallizes in the orthorhombic space group Pnma, and polymer (2) crystallizes in the monoclinic space group P21/n. Complex (1) has a hanging ladder-like polymeric chain which can also be described as a helical chain bridged by Ag–Ag edges. Complex (2) exhibits a monoclinic crystal system with a slightly distorted tetrahedron. The nonlinear optical (NLO) properties of (1) and (2) were investigated by using Z-scan techniques with an 8 ns pulsed laser at 532 nm. These two coordination polymers exhibit NLO absorption and an effective self-focusing effect. The effective α₂ and n₂ values of cluster (1) are 3.04×10⁻¹¹ m W⁻¹ and 7.6×10⁻¹⁸ m² w⁻¹ and the effective α₂ and n₂ values of compound (2) are 1.08×10⁻¹¹ m W⁻¹ and 3.1×10⁻¹⁸ m² w⁻¹ when measured in CH₂Cl₂ solution.     

Solid state voltammetric characterization of iron hexacyanoferrate encapsulated in silica

We describe a sol-gel approach by which iron hexacyanoferrate is immobilized in silica in a manner suited to investigation by electrochemistry in the absence of a contacting liquid phase. Such physicochemical parameters as concentration of redox sites (C _o) and apparent (effective) diffusion coefficient (D _app) are estimated by performing cyclic voltammetric and potential step experiments in two time regimes, which are characterized by linear and spherical diffusional patterns, respectively. Values of D _app and C _o thereby obtained are 2.0 × 10⁻⁶ cm² s⁻¹ and 1.4 × 10⁻² mol dm⁻³. The D _app value is larger than expected for a typical solid redox-conducting material. Analogous measurements done in iron(III) hexacyanoferrate(III) solutions of comparable concentrations, 1.0 × 10⁻² and 5.0 × 10⁻³ mol dm⁻³, yield D _app on the level of 5–6 × 10⁻⁶ cm² s⁻¹. Thus, the dynamics of charge propagation in this sol-gel material is almost as high as in the liquid phase. The residual water in the silica, along with the pore structure, are important to the overall mechanism of charge transport, which apparently is limited by physical diffusion rather than electron self-exchange. Under conditions of a solid state voltammetric experiment which utilizes an ultramicroelectrode, encapsulated iron hexacyanoferrate redox centers seem to be in the dispersed colloidal state rather than in a form of the rigid polymeric film. Received: 8 April 1999 / Accepted: 13 August 1999     

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

The reactions between Fe(Phen)₃²⁺[phen = tris-(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm⁻³ (NaCl/HCl). Plots of k₂ versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (Z_AZ_B) for the reactions of Fe(Phen)₃²⁺ with the chloro-, bromo- and iodo- complexes respectively. Z_AZ_B of ≈ −2 suggests that the charge on these Co^III complexes cannot be −3 but is −1. This suggests the possibility of protonation of these Co^III complexes. Protonation was investigated over the range [H⁺] = 0.0001 −0.06 mol dm⁻³ and the protonation constants K_a obtained are 1.22 × 10³, 7.31 × 10³ and 9.90 × 10² dm⁶ mol⁻³ for X = Cl, Br and I, respectively.     

Polymerization of 1-octene and determination of markhouwink constants of poly(1-octene)

The polymerization of 1-octene initiated by methylalumoxane（MAO）-activated Ni（Ⅱ）-based-α-diimine complexes[（2,6-i-Pr）₂C₆H₃-DAB（An）]NiBr₂ was investigated.Using this catalyst,poly（1-octene）s with molecular weight between 100×10³ and 400×10³ and polydispersity（M_w/M_n） between 1.3 and 1.5 were synthesized successfully by varying reaction time at room temperature.The poly（1-octene）s were amorphous polymers and could be well soluble in tetrahydrofuran（THF）.After fractional precipitation,poly（1-octene）s with narrow molecular weight distributions（M_w/M_n≤1.12） were obtained.Their weight-average molecular weights were measured by gel permeation chromatography（GPC） in conjunction with online model BI-MwA multiangle laser light scattering（MALLS）,and their intrinsic viscosities were measured by Maron’s single-point method.The k and a values in Mark-Houwink equation[η]= KM^αin THF at 40℃were 0.089 mL/g and 0.61 respectively.     

Solvent/substrate effects on the micelle-catalyzed aquation reactions of some iron(II) phenanthroline complexes, I. Influence of water and acid on the aquation of Fe(Ph2Phen)32+ in acetone

The effects of a substrate additive, H⁺ and solvents (water and acetone), on the micelle-catalyzed aquation of tris-(4,7-diphenyl-1, 10-phenanthroline)iron(II), Fe(Ph₂Phen)₃ ²⁺, have been investigated using^#Triton X-100 micelles. The k₀ vs. [TX-100] profiles at fixed [H₂O] are structured, exhibiting maxima. Catalytic factors of 46.6–171.7 are observed for 5.56×10⁻²≤[H₂O] 55.60×10⁻² mol dm⁻³. On the other hand, at fixed [H⁺], the k₀ vs. [TX-100] exhibit broad maxima. The aquation reaction is inhibited by H⁺ and catalytic factors decrease rapidly and exponentially from 422.5 to 20.9 for 0.20×10⁻³≤[H⁺]≤2.00×10⁻³ mol dm⁻³. The aquation is found to be faster (ca. 160–1200 fold) in acetone than in the aqueous medium depending on the added [H₂O]. These observations are rationalized on the basis of a proposed modified lamellar structure for the Triton X-100 (TX-100) micelles in which direct substitution of water molecules into the coordination sphere of the complex occurs.     

Electrogenerated Chemiluminescence (ECL) Determination of Ephedrine with a Self-Assembly Multilayer Ni(II)-Polyluminol Modified Electrode

By combining the layer-by-layer (LBL) self-assembly technique with the electrochemical polymerization method, multilayer Ni(II)-polyluminol films were modified on the surface of a vaseline-impregnated graphite electrode. It was found that, compared with an electrode modified by direct electrochemical polymerization, this modified electrode offered a suitable ECL reaction micro-environment created by the special multilayer films, which was beneficial to the ephedrine hydrochloride enhancing effect for luminol ECL intensity. The ECL enhancing effect of ephedrine hydrochloride on the electro-oxidation luminol was improved on this modified electrode. Based on this finding, a new sensitive ECL method was developed for ephedrine hydrochloride determination under the optimal conditions. At the same time, a new idea is proposed for improving the analytical performance of the luminol ECL system by modifying the ECL reaction micro-environment with the layer-by-layer self- assembly method. Under the optimum experimental conditions, the ephedrine hydrochloride concentration in the range of 2.0 × 10⁻⁸–7.0 × 10⁻⁶ mol L⁻¹ was proportional to the enhanced ECL signal, and it offered an 8.0 × 10⁻⁹ mol L⁻¹ detection limit for ephedrine hydrochloride.