Electrochemical evidence of catalysis of oxygen reduction at the polarized liquid–liquid interface by tetraphenylporphyrin monoacid and diacid

Cyclic voltammetry is used to study the role of 5,10,15,20-tetraphenyl-21H,23H-porphine (H₂TPP) in the reduction of molecular oxygen by decamethylferrocene (DMFc) at the polarized water|1,2-dichloroethane (DCE) interface. It is shown that this rather slow reaction proceeds remarkably faster in the presence of tetraphenylporphyrin monoacid (H₃TPP⁺) and diacid (H₄TPP²⁺), which are formed in DCE by the successive transfer of two protons from the acidified aqueous phase. A mechanism is proposed, which includes the formation of adduct between H₃TPP⁺ or H₄TPP²⁺ and O₂ that is followed by electron transfer from DMFc to the adduct leading to the observed production of DMFc⁺ and to the regeneration of H₂TPP or H₃TPP⁺, respectively.     

Perfluoro anion-exchange polymeric films on glassy carbon electrodes

Solutions of the perfluoro anion-exchange membrane TosHex® in a solvent mixture composed of methanol + isopropanol + water (1:1:1) were prepared and applied in coating glassy carbon electrodes. The evaporated films were used to accumulate the Fe(CN) ₆ redox couple on the electrode surface. The magnitude of the electrochemical response of the loaded films is comparable with that for Nafion® incorporated cationic redox species. The multicharged Fe(CN) ₆ couple accumulated in Tosflex® film causes an ion cross-linking of the polymeric backbone, thus decreasing ion transport in the film substantially.     

Synthesis,Optical Properties,and Electronic Structures of Fully Core‐Modified Porphyrin Dications and Isophlorins

The synthesis, structures, optical properties, and electronic structures of the tetraphenyltetrathiaporphyrin dication (S₄TPP²⁺, 6 ) and tetrakis(pentafluorophenyl)tetrathiaisophlorin (S₄F₂₀TPP, 7 ) are reported. S₄TPP²⁺ ( 6 ) and S₄F₂₀TPP ( 7 ) were synthesized by acid‐catalyzed condensation of the corresponding hydroxylmethylthiophene, followed by oxidation. The electronic structures of S₄TPP²⁺ ( 6 ) and S₄F₂₀TPP ( 7 ) were analyzed by using UV/Vis‐absorption spectroscopy and by magnetic circular dichroism (MCD) spectroscopy and the bands were assigned by using time‐dependent density functional theory (TD‐DFT) and ZINDO/s calculations. A red‐shift of the Q bands of S₄TPP²⁺ ( 6 ) is observed relative to the spectra of tetraphenylporphyrins because a destabilization of the HOMO leads to a narrower HOMO–LUMO band‐gap. Michl′s perimeter model was used to assign the absorption bands and MCD spectra of S₄F₂₀TPP ( 7 ). Current‐density maps and nucleus‐independent chemical‐shift (NICS) calculations of S₄TPP²⁺ ( 6 ) and of a model compound predict marked modification to the diamagnetic ring current, whilst nonaromatic character is predicted for S₄F₂₀TPP ( 7 ).     

Modification of a Nafion® ion exchange membrane by a plasma polymerization process

An ultra-thin anionic exchange layer was deposited on the surface of a Nafion® membrane. This layer was deposited from ethylene and ammonia using a glow–discharge plasma polymerization technique. The scanning electron microscopy (SEM), Fourier transform infrared attenuated total reflection (FTIR-ATR) spectra and X-ray photoelectron spectroscopy (XPS) showed that the resulting plasma film containing amine and amide was about 0.5 μm thick. The ion selectivity coefficient for H⁺ of the plasma modified Nafion® membrane was measured and the results showed that a linear Nernst response was exhibited and the selectivity of proton was enhanced. The resistance of modified Nafion® was only slightly higher than that of the Nafion® membrane.     

Identification of the cobalt(II) chloride ‘mixed’ solvate Co4Cl8(H2O)4(MeCN)6: the ionic structure trans-[Co(H2O)2(MeCN)4] trans-[Co(H2O)2(MeCN)2(CoCl4)2]

The structure of the title compound features mononuclear octahedral Co^II cations, trans-[Co(H₂O)₂(MeCN)₄]²⁺, and trinuclear anions, trans-[Co(H₂O)₂(MeCN)₂(CoCl₄)₂]^2–; the latter centrosymmetric units contain a central octahedral Co(H₂O)₂(MeCN)₂ moiety with two tetrahedral [CoCl₄]^2– ligands. These two large ions are held in a network of intra- and inter-molecular hydrogen bonding.     

Some Electrochemical Characteristics of Boron‐ and Phosphorus‐Doped Glassy Carbon Electrodes

Three glassy carbon (GC) samples: undoped and doped with boron or phosphorus, prepared at 1000 °C, were compared in respect to hydrodynamic current‐potential curves in acidic medium, cyclic voltammograms for Fe^3+/2+ and Fe(CN)₆^3?/4? and argentometric titrations of halides. Some experiments were also carried out using standard Tokai and Sigri GC and Ag electrode. It appeared that GC doped with boron and phosphorus exhibited significant increase in hydrogen evolution overpotential. As for the electrode kinetics (ΔE_p criterion), no significant difference was observed between doped and undoped electrodes. In the potentiometric titrations the phosphorus‐doped electrode was advantageous over the other GC and Ag electrodes as it enabled more precise end‐point detection.     

Synthesis,Crystal Structure,and Spectral Properties of a Cobalt(II) Complex with N‐Salicylidene‐p‐Toluidine

The complex Co(C₁₄H₁₃NO)₂Cl₂ with the protonated N‐salicylidene‐p‐toluidine ligand was synthesized from an ethanolic solution of CoCl₂·6H₂O and N‐salicylidene‐p‐toluidine. The crystal structure was determined from X‐ray single crystal data (monoclinic, space group Cc, a = 1496.2(3) pm, b = 1257.4(4) pm, c = 1544.6(3) pm, β = 115.01(1)°, Z = 4). Co²⁺ adopts a distorted tetrahedral geometry. The UV‐Vis and IR spectra of the complex are discussed.     

Metals and alloys bonded on solid polymer electrolyte for electrochemical reduction of pure benzaldehyde without liquid supporting electrolyte

Metals and alloys bonded on the solid polymer electrolyte (SPE) Nafion® 117 were studied as both the electrodes and electrolyte for the electrochemical reduction of pure benzaldehyde without liquid supporting electrolyte. The results indicated that SPE electrodes modified with metals such as Pt, Ni, Pb, Cu and Ag by the ion exchange chemical deposition method had a more stable structure and could provide a larger electrochemical active surface area than those prepared by other methods. The composition of reducing agents and the pH value have a significant effect on the characteristics of the prepared SPE electrodes. In this study a novel method was developed to prepare a Pt+Pb/Nafion® electrode which formed a protective Pt layer on the surface of Pb/Nafion®. The results of scanning electron microscopy further confirmed that Pt+Pb/Nafion® electrodes had obvious advantages for the electrochemical reduction of benzaldehyde. The results also revealed that the current efficiencies of benzylalcohol production at various SPE electrodes decreased in the order Pt+Pb/Nafion® > Pb/ Nafion® > Ni/Nafion® > Cu/Nafion® > Ag+Cu/Nafion® > Ag/Nafion® > Pt/Nafion®.     

Synthesis,characterization, and mechanism of trans-dichlorido-bis-(ethylenediamine)cobalt(III) with L-cystine in the presence of chloride

Substitution reactions of trans-[CoCl₂(en)₂]Cl (where en?=?ethylenediamine) with L-cystine has been studied in 1.0?×?10^?1?mol?dm^?3 aqueous perchlorate at various temperatures (303–323?K) and pH (4.45–3.30) using UV-Vis spectrophotometer on various [Cl^?] from 0.05 to 0.01?mol?L^?1. The products have been characterized by their physico-chemical and spectroscopic data. Trans-[CoCl(en)₂(H₂O)]²⁺, from the hydrolysis of trans-[CoCl₂(en)₂]⁺ in the presence of Cl^?, formed a complex with L-cystine at all temperatures in 1?:?1 molar ratio. L-cystine is bidentate to Co(III) through Co–N and Co–S bonds. Product formation and reversible reaction rate constants have been evaluated. The rate constants for SN_i mechanism have been evaluated and activation parameters E _a, ΔH ^#, and ΔS ^# are determined.     

Immobilization of Enzymes on the Nano‐Au Film Modified Glassy Carbon Electrode for the Determination of Hydrogen Peroxide and Glucose

A new enzyme‐based amperometric biosensor for hydrogen peroxide was developed relying on the efficient immobilization of horseradish peroxidase (HRP) to a nano‐scaled particulate gold (nano‐Au) film modified glassy carbon electrode (GC). The nano‐Au film was obtained by a chitosan film which was first formed on the surface of GC. The high affinity of chitosan for nano‐Au associated with its amino groups resulted in the formation of nano‐Au film on the surface of GC. The film formed served as an intermediator to retain high efficient and stable immobilization of the enzyme. H₂O₂ was detected using hydroquinone as an electron mediator to transfer electrons between the electrode and HRP. The HRP immobilized on nano‐Au film maintained excellent electrocatalytical activity to the reduction of H₂O₂. The experimental parameters such as the operating potential of the working electrode, mediator concentration and pH of background electrolyte were optimized for best analytical performance of amperometry. The linear range of detection for H₂O₂ is from 6.1×10^?6 to 1.8×10^?3 mol L^?1 with a detection limit of 6.1 μmol L^?1 based on signal/noise=3. The proposed HRP enzyme sensor has the features of high sensitivity (0.25 Almol^?1cm^?2), fast response time (t_90%≤10 s) and a long‐term stability (>1 month). As an extension, glucose oxidase (GOD) was chemically bound to HRP‐modified electrode. A GOD/HRP bienzyme‐modified electrode formed in this way can be applied to the determination of glucose with satisfactory performance.     

Catalysis of dioxygen reduction at soluble polyaniline modified electrode

A reflux-treatment of soluble polyaniline (SPA) in dimethylformamide (DMF) containing CoCl₂ yields an active catalyst for dioxygen reduction which can be adsorbed on the electrode surface firmly. The catalytic reduction of dioxygen at the glassy carbon (GC) electrode modified by the catalyst was studied with cyclic voltammetry (CV), rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE). The kinetic process of dioxygen reduction at the modified electrode was analyzed with a new RRDE theory dealing with a nondiffusion-controlled process on ring electrode. The rate constants for each scheme of dioxygen reduction were calculated, showing that only 2-electron reduction to H₂O₂ was conducted at the modified electrode. The effect of solution acidity on the electrocatalytic behaviour for dioxygen reduction was investigated. A possibility of initiating catalytic activity for dioxygen reduction was explored with ESCA method.     

富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种,也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoO_x物种中钴离子可还原能力增强,C₃H₈选择性催化还原NO_x的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C₃H₈的氧化燃烧,使C₃H₈选择性催化还原NO_x的活性降低。     

Metal Halide Regulated Photophysical Tuning of Zero-Dimensional Organic Metal Halide Hybrids: From Efficient Phosphorescence to Ultralong Afterglow

The photophysical tuning is reported for a series of tetraphenylphosphonium (TPP) metal halide hybrids containing distinct metal halides, TPP₂MX_n (MX_n=SbCl₅, MnCl₄, ZnCl₄, ZnCl₂Br₂, ZnBr₄), from efficient phosphorescence to ultralong afterglow. The afterglow properties of TPP⁺ cations could be suspended for the hybrids containing low band gap emissive metal halide species, such as SbCl₅²⁻ and MnCl₄²⁻, but significantly enhanced for the hybrids containing wide band gap non-emissive ZnCl₄²⁻. Structural and photophysical studies reveal that the enhanced afterglow is attributed to stronger π–π stacking and intermolecular electronic coupling between TPP⁺ cations in TPP₂ZnCl₄ than in the pristine organic ionic compound TPPCl. Moreover, the afterglow in TPP₂ZnX₄ can be tuned by controlling the halide composition, with the change from Cl to Br resulting in a shorter afterglow due to the heavy atom effect.     

Bacterial activity of cobalt(III) complexes. Part IV: Diethylenetriaminemonoacetatocobalt(III) complexes

Summary The activities of the diethylenetriaminemonoacetatocobalt(III) complexes, [Co(en)(DTMA)]I₂, [CoX₂(DTMA)] and [CoCO₃(DTMA)]·H₂O (DTMA=diethylenetriaminemonoacetato or formally 3-amino-3, 6-diazaoctanato; en=ethylenediamine, X=Cl^–, NO ₂ ^– , NCS^–) were studied onEscherichia coli B growing in a minimal glucose medium in both lag- and log-phases. Activities decrease in the order: [Co(NCS)₂(DTMA)]> [Co(NO₂)₂(DTMA)]>[Co(en)(DTMA)]I₂>[CoCl₂(DTMA)] >[CoCO₃(DTMA)]·H₂O. The antagonistic activities of the complexes were also studied.     

A Study of Different Doped Metal Cations on the Physicochemical Properties and Catalytic Activities of Ce20M1Ox (M=Zr,Cr, Mn,Fe, Co,Sn) Composite Oxides for Nitric Oxide Reduction by Carbon Monoxide

This work is mainly focused on investigating the effects of different doped metal cations on the formation of Ce₂₀M₁O_x (M=Zr, Cr, Mn, Fe, Co, Sn) composite oxides and their physicochemical and catalytic properties for NO reduction by CO as a model reaction. The obtained samples were characterized by using N₂ physisorption, X‐ray diffraction, laser Raman spectroscopy, UV/Vis diffuse reflectance spectroscopy, inductively coupled plasma atomic emission spectroscopy, X‐ray photoelectron spectroscopy, temperature‐programmed reduction by hydrogen and by oxygen (H₂‐TPR and O₂‐TPD), in situ diffuse reflectance infrared Fourier transform spectroscopy, and the NO+CO model reaction. The results imply that the introduction of M^x+ into the lattice of CeO₂ increases the specific surface area and pore volume, especially for variable valence metal cations, and enhances the catalytic performance to a great extent. In this regard, increases in the oxygen vacancies, reduction properties, and chemisorbed O₂^? (and/or O^?) species of these Ce₂₀M₁O_x composite oxides (M refers to variable valence metals) play significant roles in this reaction. Among the samples, Ce₂₀Cr₁O_x exhibited the best catalytic performance, mainly because it has the best reducibility and more chemisorbed oxygen, and significant reasons for these attributes may be closely related to favorable synergistic interactions of the vacancies and near‐surface Ce³⁺ and Cr³⁺. Finally, a possible reaction mechanism was tentatively proposed to understand the reactions.     

Experimental Determination of an Isolated trans-Dinitrosyl Manganese(II) Heme Analogue

The lack of direct proof in either natural or synthetic systems for trans-dinitrosyl hemes, a key intermediate in the reactions of heme proteins (e.g. soluble guanylate cyclase (sGC), cytochrome c′ and So H-NOX) with nitric oxide (NO), has hampered understanding of the exact reaction mechanisms, such as the formation of the five-coordinate heme complex with NO at the proximal side (5c NO_P). Herein, we report the first isolation of a dinitrosyl metalloporphyrin complex, the six-coordinate, low-spin {Mn(NO)₂}⁷ species [Mn(TPP)(NO)₂] (TPP²⁻=meso-tetraphenylporphyrin dianion). The complex shows distinct features, such as an elongated axial bond (1.877(9) vs. 1.641(5) Å), a higher NO stretching bond position (1760 vs. 1735 cm⁻¹) and an isotropic resonance at g = 2.0, in sharp contrast to those of five-coordinate mononitrosyl analogues. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and EPR studies provided deep insight into the reaction processes, demonstrating different responses of porphyrinates to NO.     

Reaction of small molecules O2, NO,CO, and the Naldini salt (PPh3)2MnBr2: Characterized by infrared spectroscopy,elemental analysis,and single-crystal X-ray diffraction

Addition of 2 equiv. of PPh₃ to MnBr₂ in tetrahydrofuran (THF) solution under N₂ atmosphere results in the formation of Naldini salt (PPh₃)₂MnBr₂ ( 1 ). Reaction of Complex 1 and O₂, NO, and CO (with reducing agent) leads to Complex (OPPh₃)₂MnBr₂ ( 2 ), (PPh₃)₂Mn(NO)Br₂ ( 3 ), and (PPh₃)₂Mn(CO)₃Br ( 4 ), respectively. Both Complexes 2 and 4 crystallize in the triclinic space group P-1 with a = 9.94 Å, b = 10.11 Å, c = 10.53 Å; α = 65.42°, β = 63.16°, and γ = 89.22° of 2 and a = 10.23 Å, b = 12.26 Å, c = 14.44 Å and α = 97.03°, β = 104.34°, and γ = 106.33° of 4 . The isoelectronic replacement of 3CO with 2NO yields the {Mn(NO)₂}⁸ species (PPh₃)₂Mn(NO)₂Br ( 5 ). The single crystal of 5 is in the monoclinic space group C2/c with a = 23.17 Å, b = 9.62 Å, c = 15.92 Å, and β = 114.91°. In the THF solution, Complex 5 serves as an NO source in the presence of NO trapping, Co(TPP), Co(TPP) = 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II).     

Glassy carbon and boron doped glassy carbon electrodes for voltammetric determination of linuron herbicide in the selected samples

In this study the application of home-made unmodified (GC) and bulk modified boron doped glassy carbon (GCB) electrodes for the voltammetric determination of the linuron was investigated. The electrodes were synthesized with a moderate temperature treatment (1000°C). Obtained results were compared with the electrochemical determination of the linuron using a commercial glassy carbon electrode (GC-Metrohm). The peak potential (E _p ) of linuron oxidation in 0.1 mol dm⁻³ H₂SO₄ as electrolyte was similar for all applied electrodes: 1.31, 1.34 and 1.28 V for GCB, GC and GC-Metrohm electrodes, respectively. Potential of linuron oxidation and current density depend on the pH of supporting electrolyte. Applying GCB and GC-Metrohm electrodes the most intensive electrochemical response for linuron was obtained in strongly acidic solution (0.1 mol dm⁻³ H₂SO₄). Applying the boron doped glassy carbon electrode the broadest linear range (0.005–0.1 μmol cm⁻³) for the linuron determination was obtained. The results of voltammetric determination of the linuron in spiked water samples showed good correlation between added and found amounts of linuron and also are in good agreement with the results obtained by HPLC-UV method. This appears to be the first application of a boron doped glassy carbon electrode for voltammetric determination of the environmental important compounds.      

铁氰化锰修饰玻碳电极的制备及其电化学性能

A thin film of manganese hexacyanoferrate （MnHCF） was electrochemically formed on a glassy carbon （GC） electrode to prepare a chemically modified electrode （CME）. The mechanism of film formation of MnHCF and its growth process were investigated in detail by cyclic voltammetry. The results show that the stoichiometric composition of MnHCF is Mn^ⅢFe^Ⅲ（CN）6, an analogue of prussian yellow. There exist three clear-cut stages in the whole modification process and the last stage is indispensable to the fabrication of homogenized, stable MnHCF film and must last for an appropriate time. The surface morphology of MnHCF/GC electrode was characterized by scanning electron microscopy （SEM）, which further verified the effective deposition of MnHCF film on GC. The kinetic constants of MnHCF/GC electrode process were also evaluated. The resulting MnHCF film modified electrode presented good stability and high electrocatalytic activity toward the oxidation of H2O2, indicating that MnHCF film possesses function of catalase and can be expected for analytical purposes.     

Electrocatalytic and adsorption properties of platinum microparticles electrodeposited onto glassy carbon and into Nafion® films

A comparative investigation of electrocatalytic and adsorption properties of platinum microparticles electrodeposited onto a glassy carbon surface (Pt/GC) and within a thin Nafion® film formed on a GC electrode (Pt/Nf/GC) is described. As test reaction the methanol oxidation in sulfuric acid solutions is used. Dependences of the steady-state specific reaction rates upon potential and methanol concentration were established, as well as those of the platinum surface coverage with methanol chemisorption products upon concentration. It was shown that at higher platinum loadings (above 60 μg cm⁻²) the specific activities of Pt/GC and Pt/Nf/GC are nearly the same and close to that of smooth platinum. At such loadings the surface coverage of the platinum deposit surface with organic particles does not differ from that of smooth platinum. At very low platinum loadings in the polymeric matrix (10–30 μg cm⁻²) a considerable decrease in the adsorption of strongly chemisorbed methanol particles is observed. These deposits are characterized by a low specific activity, which may be caused by the decrease of the platinum particle’s size, leading to a decrease in the amount of weakly bound methanol particles participating in the limiting reaction step.