Electrocatalytic Nitrite Reduction to Nitrogen Oxide by a Synthetic Analogue of the Active Site of Cu‐Containing Nitrite Reductase Incorporated in Nafion Film

The electrocatalytic reduction of nitrite to NO by [CuMe₂bpa(H₂O)(ClO₄)]⁺ ( 1 ), which is a model for the active site of copper‐containing nitrite reductase, incorporated in Nafion film was investigated. The Cu complex in the Nafion matrix exhibits an intense band at 267 nm and a broad band around 680 nm, assigned to d–d and ligand field transitions, respectively. The 77‐K EPR spectrum of 1 in the Nafion matrix reveals the typical axial signals (g_//=2.28, g =2.08, A_//=13.3 mT) of a tetragonal Cu²⁺ chromophore. The redox potential, which is related to the Cu⁺/Cu²⁺ couple, was ?146 mV (ΔE=72 mV) at pH 5.5. The redox reaction of 1 in Nafion was not dependent on pH and was a diffusion‐controlled process. The electronic structure and redox properties of 1 in the negatively charged polymer matrix were almost the same as those in aqueous solution. In the presence of nitrite, an increase in the cathodic current was observed in the cyclic voltammogram of 1 in the Nafion matrix. The current increase was dependent on the nitrite concentration and pH in solution. Upon reaching ?400 mV, a linear generation of NO was observed for the 1 /Nafion film coated electrode. The relationship between the rate of NO generation and the nitrite concentration in solution was analyzed with the Michaelis–Menten equation, where V_max=45.1 nM s^?1 and K_m=15.8 mM at pH 5.5. The Cu complex serves the function of both the catalyst and electron transport in the Nafion matrix. The sensitivity of the electrode was estimated to be 3.23 μA mM^?1 in the range of 0.1–0.4 mM nitrite.     

Cu(II) Hexacyanoferrate(III) Modified Carbon Paste Electrode; Application for Electrocatalytic Detection of Nitrite

Copper hexacyanoferrate (CuHCF) film‐modified carbon paste electrode (CPE) has been prepared from various electrolytic aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms showed the direct deposition of CuHCF films from the mixing of Cu²⁺ and Fe(CN)₆^3? ions and each time with one of the six cations: H⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, and Al³⁺. The CuHCF film showed a single redox couple that exhibited a cation effect (Na⁺, K⁺, Mg²⁺, and NH₄⁺) and anion effect (Cl^?, NO₃^?, SO₄^2?, ClO₄^?, and BrO₃^?) in the cyclic voltammograms. Voltammetric studies have indicated that in presence of nitrite, the cathodic peak current of CuHCF increases, followed by a decrease in the corresponding anodic current. This indicated that nitrite was reduced by the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. The process of reduction and its kinetics were investigated by using cyclic voltammetry, differential pulse voltammetry, chronoamperometry and chronocoulometry techniques. The electrocatalytic ability about 800 mV can be seen. The rate constant of the catalytic reduction of nitrite was found to be 7.9×10⁵ cm³ mol^?1 s^?1. Linearity range obtained was 5×10^?5?8.4×10^?3 by cyclic voltammetry and 8×10^?6?1.3×10^?3 and 4×10^?3?2×10^?2 by differential pulse voltammetry.     

Electrochemical Probe of the Reduced Graphene Oxide Modified by Bare Gold Nanoparticles Functionalized Zr(IV)-based Metal-organic Framework for Detecting Nitrite

Widely presented nitrite in drinking water, food and even physiological system endangers human health. Here,bare gold nanoparticles functionalized Zr-based metal-organic framework modified reduced graphene oxide (GNPs/UiO-66-NH₂/rGO) nanocomposites were prepared by hydrothermal method. This experiment studies the morphology, composition, structure and electrochemical behavior of the sensor. The experimental results show that the sensor has a peak potential of 0.9 V, the concentration range of NO₂⁻ is 5.0 μM to 768 μM, the linear regression equation of the calibration curve is I_pa=0.3646+0.00642 C (R²=0.9998), and the LOD is as low as 3.7 μM (S/N=3). Therefore, an electrochemical sensor platform for trace detection of NO₂⁻ was successfully constructed.     

Structurally Simple Osmium(II) Polypyridyl Complexes as Photosensitizers for Photodynamic Therapy in the Near Infrared**

Five osmium(II) polypyridyl complexes of the general formula [Os(4,7-diphenyl-1,10-phenanthroline)₂ L ]²⁺ were synthesized as photosensitizers for photodynamic therapy by varying the nature of the ligand L . Thanks to the pronounced π-extended structure of the ligands and the heavy atom effect provided by the osmium center, these complexes exhibit a high absorption in the near-infrared (NIR) region (up to 740 nm), unlike related ruthenium complexes. This led to a promising phototoxicity in vitro against cancer cells cultured as 2D cell layers but also in multicellular tumor spheroids upon irradiation at 740 nm. The complex [Os(4,7-diphenyl-1,10-phenanthroline)₂(2,2′-bipyridine)]²⁺ was found to be the most efficient against various cancer cell lines, with high phototoxicity indexes. Experiments on CT26 tumor-bearing BALB/c mice also indicate that the Os^II complexes could significantly reduce tumor growth following 740 nm laser irradiation. The high phototoxicity in the biological window of this structurally simple complex makes it a promising photosensitizer for cancer treatment.     

Electrochemical Investigation of the Role of Reducing Agents in Copper‐Catalyzed Nitric Oxide Release from S‐Nitrosoglutathione

Studies of nitric oxide (NO) release from S‐nitrosoglutathione (GSNO) decomposition by Cu²⁺ in the presence of reducing agents were performed using a nickel porphyrin and Nafion‐coated microsensor in order to compare the efficiency of sodium hydrosulfite (Na₂S₂O₄) and sodium borohydride (NaBH₄) to that of the most abundant endogenous reducer, glutathione (GSH). When it was mixed to Cu(NO₃)₂ and added to equimolar concentration of GSNO, each reducing agent caused a NO release (measured in terms of oxidation current) but only NaBH₄ induced a proportional rise if its concentration doubled and that of Cu²⁺ remained constant. For Na₂S₂O₄, there was a mild increase and for GSH, no change. Furthermore, when Cu²⁺ concentrations ranging from 0.5 to 5 μM were mixed with 2 μM reducing agent and added to 2 μM GSNO_, the NO oxidation current linearly increased with NaBH₄ and was constant with Na₂S₂O₄. Concerning GSH, Cu²⁺ dose‐dependently increased the NO release from GSNO only if the Cu²⁺‐to‐reducer ratio was ≤1. However, GSH formed the catalytic species Cu⁺ even in excess of Cu²⁺ and GSNO as indicated by suppression of the Cu²⁺/GSH‐induced NO release when the Cu⁺ chelator neocuproine was added to GSNO. This work shows that, among the 3 reducing agents, only NaBH₄ allows Cu²⁺ to dose‐dependently increase the NO release from GSNO for Cu²⁺‐to‐reducer ratios ranging from 0.25 to 2.5. Despite this good effectiveness, excess of NaBH₄ compared to both Cu²⁺ and GSNO seems to be required for optimal NO release.     

Construction of Mononuclear Copper(II) and Trinuclear Cobalt(II) Complexes Based on Asymmetric Salamo‐Type Ligands

Mononuclear copper(II) and trinuclear cobalt(II) complexes, namely [Cu(L¹)]₂ · CH₂Cl₂ and [{Co(L²)(EtOH)}₂Co(H₂O)] · EtOH {H₂L¹ = 4,6‐dichloro‐6′‐methyoxy‐2,2′‐[1,1′‐(ethylenedioxydinitrilo)dimethylidyne]diphenol and H₃L² = 6‐ethyoxy‐6′‐hydroxy‐2,2′‐[1,1′‐(ethylenedioxydinitrilo)dimethylidyne]diphenol}, were synthesized and characterized by elemental analyses, IR and UV/Vis spectroscopy, and single‐crystal X‐ray diffraction. In the Cu^II complex, the Cu^II atom is four‐coordinate, with a N₂O₂ coordination sphere, and has a slightly distorted square‐planar arrangement. Interestingly, the obtained trinuclear Co^II complex is different from the common reported 2:3 (L:Co^II) salamo‐type Co^II complexes. Infinite 2D layer supramolecular structures are formed via abundant intermolecular hydrogen bonding and π ··· π stacking interactions in the Cu^II and Co^II complexes.     

Structural and Spectroscopic Characterization of a Mononuclear Hydroperoxo–Copper(II) Complex with Tripodal Pyridylamine Ligands

A model for the key intermediate in copper oxygenase reactions, the Cu(II )–OOH complex, was prepared with the novel tripodal pyridylamine ligand, bis(6-pivalamide-2-pyridylmethyl)(2-pyridylmethyl)amine. The HOO⁻ moiety is stabilized by hydrogen bonding to two amine H atoms (see structure on the right).     

Investigation of Copper(II) Interference on the Anodic Stripping Voltammetry of Lead(II) and Cadmium(II) at Bismuth Film Electrode

The bismuth‐coated electrode is known to be prone to errors caused by copper(II). This study investigates copper(II) interference at bismuth film electrode for the detection of lead(II) and cadmium(II). It was conducted using glassy carbon electrode, while the bismuth film was plated in situ simultaneously with the target metal ions at ? 1200 mV. Copper(II) presented in solution significantly reduced the sensitivity of the electrode, for example there was an approximately 70 % and 90 % decrease in peak signals for lead(II) and cadmium(II), respectively, at a 10‐fold molar excess of copper(II). The decrease in sensitivity was ascribed to the competition between copper and bismuth or the metal ions for surface active sites. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) analysis suggested a large decrease in the amount of bismuth nanoparticles formed on the electrode surface in the presence of copper(II) occurred, validating the competition between copper and bismuth ions for surface active sites. Recovery of the stripping signal of lead(II) and cadmium(II) was obtained by adding ferrocyanide ion to the solution. Finally, the proposed method was successfully applied to determine lead(II) and cadmium(II) in water samples and the method was validated by ICP‐MS technique.     

Disposable Screen‐Printed Edge Band Ultramicroelectrodes for Use as Nitric Oxide Gas Sensor in Designing an Easily Applicable Method for Real Sample Analysis of Nitrite with Superior Selectivity and Sensitivity

We report here an easily applicable method for the quantification of nitrite (NO₂^?) in real samples. This approach simplified the two steps of sample preparation and detection into a 2‐in‐1 single step process. Samples were digested in sulfuric acid and the as‐generated nitric oxide (NO) was detected by an electrochemical sensor in the gas phase. It eliminated almost all of the interferents in the solution phase and hence resulted in a highly selective determination of nitrite suitable for food samples with complicated matrix. We successfully demonstrated the determination of nitrite in sausage and vegetables and further validated the results with an AOAC official reference method.     

聚四氨基酞菁铜微型传感器及其在一氧化氮测定中的应用

利用电化学聚合的方法制备了聚四氨基酞菁酮微型传感器，并探讨了微型传感器对一氧化氮（ＮＯ）的电化学响应。结果表明，电化学聚合Ｃｕ（ＴＡＰｃ）微型传感器对ＮＯ具有良好的催化氧化作用。     

Physicochemical Insight into Coordination Systems Obtained from Copper(II) Bromoacetate and 1,10-Phenanthroline

Two different coordination compounds of copper were synthesized from the same building blocks (1,10-phenanthroline, bromoacetate anions, and copper cations). The synthesis parameters were carefully designed and evaluated to allow the change of the resulting compounds molecular structure, i.e., formation of mononuclear (bromoacetato-O,O’)(bromoacetato-O)aqua(1,10-phenanthroline-N,N’)copper(II) and dinuclear (μ-bromido-1:2κ²)bis(μ-bromoacetato-1κO,2κO’)bis(1,10-phenanthroline-N,N’)dicopper(II) bromoacetate bromoacetic acid solvate. The crystal, molecular and supramolecular structures of the studied compounds were determined and evaluated in Hirshfeld analysis. The UV-Vis-IR absorption and thermal properties were studied and discussed. For the explicit determination of the influence of compounds structure on radiation absorption in UV-Vis range, density functional theory and time-dependent density functional theory calculations were performed.     

Sensitive Spectrophotometric Determination of Copper(II) in the Presence of Manganese

Abstract

This paper recommends a simple and convenient procedure for the determination of copper(II) in the presence of large amounts of manganese. An aqueous solution of hydroxylamine hydrochloride and diluted sulphuric acid was used for dissolution and reduction of MnO₂. The copper(II) was complexed with an ethanolic 0.05% PAN solution in the pH range of 2 - 3 in aqueous medium. The absorbances of copper-PAN complexes are measured at 550 nm where molar absorptivity is 2.10 L.mol^?1.cm^?1.

The complex obeys Beer's Law from 0.1 to 4 ppm. of copper. Manganese(II) up to 1000 ppm. doesn't interfere. The method is sensitive and reproducible.

It has been applied to the analysis of samples containing 0.01 to 5% of copper on manganese dioxide catalysts.     

The Stability of the Copper(II)-Eriochrome Red B Complex and the Compleximetric Titration of Copper(II) Ion

Abstract

Values of the conditional stability constant of the copper(II)-Eriochrome Red B complex in aqueous solutions of pH 3–6 have been determined employing a cupric ion electrode. When the ionic strength of the solution is 0.01, the value of the second acidity constant (pk₂) of Eriochrome Red B is 6.28 and the logarithm of the stability constant of the copper complex, log k_CuHI, about 8.2. The complex can be used as an indicator in the ocapleximetric titration of cupric ion with EDTA at pH values from 4 to 8.     

Cyclic Voltammetry and Structural Studies of Nitric Oxide Monolayers Adsorbed on Pt(111)

The structural analysis of the adsorption of NO monolayers on Pt(111) from solution has been explored by cyclic voltammetry (CV) and X‐ray photoelectron spectroscopy (XPS) techniques. The monolayers were formed from acid solutions saturated with NO gas as well and from nitrite solutions in sulfuric acid. Results by both techniques indicate a maximum coverage of 0.2 monolayers as well as the presence of NO molecularly adsorbed on the surface with different orientations. The voltammetric oxidation of NO gives rise to two peaks separated in the voltammogram by 50 mV. This value is in agreement with the theoretical value of 9 kJ corresponding to the difference between different adsorption sites. A mechanism for the surface mediated oxidation process from adsorbed NO to NO₂ under potential control is proposed.     

Copper(II) complexes of the antihypertensive drug nadolol

The complexation of the non-selective β-blocker nadolol, HL, 1 with copper(II) leads to formation of mono-and dinuclear complexes depending mainly on the metal-to-ligand molar ratio. The mononuclear violet complex CuL₂·2Solv, 2, was obtained in a soluble form at metal-to-ligand molar ratio Cu(II): HL ≤ 1: 10 in methanolic or slightly alkaline aqueous solutions. The dinuclear green complex Cu₂L₂Cl₂·H₂O, 3 was synthesized at Cu(II): HL ≥ 1: 2 molar ratio in methanolic solutions. The complexes were studied using spectral (UV-Vis, FT-IR, EPR), magnetochemical, thermogravimetric methods and elemental analysis. In the complexes nadolol acts as a monoanionic bidentate ligand coordinated to copper(II) through the NH-and the deprotonated OH-groups of its aminoalcohol fragment.      

Supramolecular Stuctures from Mononuclear,Binuclear and 2D Net of Copper(II) Complexes with 6‐Hydroxypicolinic Acid

First examples of transition metal complexes with HpicOH [Cu(picOH)₂(H₂O)₂] ( 1 ), [Cu(picO)(2,2′‐bpy)]·2H₂O ( 2 ), [Cu(picO)(4,4′‐bpy)_0.5(H₂O)]_n ( 3 ), and [Cu(picO)(bpe)_0.5(H₂O)]_n ( 4 ) (HpicOH = 6‐hydroxy‐picolinic acid; 2,2′‐bpy = 2,2′‐bipyridine; 4,4′‐bpy = 4,4′‐bipyridine; bpe = 1,2‐bis(4‐pyridyl)ethane) have been synthesized and characterized by single‐crystal X‐ray diffraction. The results show that HpicOH ligand can be in the enol or ketonic form, and adopts different coordination modes under different pH value of the reaction mixture. In complex 1 , HpicOH ligand is in the enol form and adopts a bidentate mode. While in complexes 2 – 4 , as the pH rises, HpicOH ligand becomes in the ketonic form and adopts a tridentate mode. The coordination modes in complexes 1 – 4 have not been reported before. Because of the introduction of the terminal ligands 2,2′‐bpy, complex 2 is of binuclear species; whereas in complexes 3 and 4 , picO ligands together with bridging ligands 4,4′‐bpy and bpe connect Cu^II ions to form 2D nets with (12³)₂(12)₃ topology.     

Antimony Film Microelectrode for Anodic Stripping Measurement of Cadmium(II), Lead(II) and Copper(II)

The antimony film microelectrode (SbFME) is presented for measuring trace heavy metal ions in combination with anodic stripping voltammetry. The SbFME was tested in model solutions of 0.01 M HCl containing Cd(II) and Pb(II) in the presence of dissolved oxygen. The microsensor exhibited good linear behavior in the examined concentration range 20 μg L⁻¹ to 100 μg L⁻¹ and LoD of 1.9 and 3.1 μg L⁻¹ for Cd(II) and Pb(II), respectively. The suitability of SbFME for measuring trace levels of Cu(II) was demonstrated using the standard reference material of natural water exploiting the sensor's specific characteristic of low re‐oxidation signal for antimony.     

Graphene Oxide as a Platform for Copper Pentacyanonitrosylferrate Nanoparticles and their Behavior in the Electro‐oxidation of N‐Acetylcysteine

This work describes the preparation of graphene oxide by the Modified Hummers Method and the chemical modification of its surface with nanoparticles of copper pentacyanonitrosylferrate(III) (GOCuNP). The materials obtained were characterized by Raman spectroscopy, x‐ray photoelectron spectroscopy and transmission electron microscopy. The GOCuNP was characterized by cyclic voltammetry using a graphite paste electrode that presented electrocatalytic response for N‐acetylcysteine with detection limit of 2.97×10^?5 mol L^?1 at concentration range of 3.00×10^?5 to 6.00×10^?3 mol L^?1 of N‐acetylcysteine. By this way, the bimetallic complex formed is included in the list of materials obtained as potential candidates for the construction of electrochemical sensors for N‐acetylcysteine detection.     

Copper(II) complexes of a biphenyl-based ligand: Tuning the needs of the metal with those of the ligand

The novel pyrazole-containing tetradentate ligand 2,2′-bis[[(3,5-dimethylpyrazol-1-yl)methyl]amino]-1,1′-biphenyl (N₄-mpz), 1, was synthesized and three Cu(II) complexes, 2–4, were prepared from this compound. These complexes were characterized by a combination of elemental analysis, FAB-MS and electrochemistry and were shown to have the structure of [Cu(N₄-mpz)(Pz)]X₂ where X = BF₄ or ClO₄ or [Cu(N₄-mpz)(Cl)]Cl. The X-ray structure of [Cu(N₄-mpz)(Pz)] (ClO₄)₂ · CH₃OH, 2, was determined and it showed the Cu(II) coordinated by the four nitrogen donors from the ligand along with an exogenous pyrazole donor that had been extracted from another molecule of the ligand. Cyclic voltammetry studies indicated that the complexes undergo quasi-reversible one-electron reductions in acetonitrile at potentials between 396 and 422 mV versus Ag/AgCl.     

Cis-and Trans-Coordination Assembly of Nitrogen Heterocycle with Copper(II) and Silver(I)

After the preparation of 1,4-bis(4,5-dihydro-1H-imidazol-2-yl)benzene(bdib),a nitrogen heterocycle with potential coordination manners of both cis-and tram-configuration forms,three complexes,including successfully self-assembled.Complexes 1 and 2 crystallized in the monoclinic system with P21/n space group and complex 3 in the triclinic system with P1 space group.