Complex compounds of ferrocene in a biacceptor system

Summary Three-component systems of ferrocene (FcH): carbon tetrachloride: tetranitromethane have been investigated spectrally in the 290–800 nm range. Quantitative relationships were investigated between electron-donor acceptor (EDA) complexes of ferrocene and CCl₄ (FcH · CCl₄) and C(NO₂)₄ [FcH · C(NO₂)₄] and the ferricenium cation (FcH⁺) which is formed as a result of dissociation of complexes and which depends upon the initial concentration of C(NO₂)₄ and duration the reaction. The results prove the destabilizing influence of C(NO₂)₄ on the EDA complex of ferrocene and CCl₄.     

Solvent effects on the electron donor acceptor complex properties of ferrocene and tetranitromethane

Summary Spectral investigations in the 350–800 nm range of ferrocene (FcH) and tetranitromethane [C(NO₂)₄] solutions in cyclohexane and carbon tetrachloride at concentration-constant (FcH) and variable (tetranitromethane) were made. The electron donor acceptor (EDA) complex of ferrocene and tetranitromethane and its dissociation to the ferricenium cation (FcH⁺) were studied as a function of the solvent, the initial C(NO₂)₄ concentration and reaction time.     

Effect of microheterogeneous environments of CTAB,Triton X-100, and Tween 20 on the oxidative degradation of d-fructose by nanoparticles of MnO2

The kinetics of the oxidative degradation of d -fructose by nanoparticles of MnO₂ has been studied in dilute sulfuric acid medium and also in the presence of surfactants of cetyl trimethyl ammonium bromide (CTAB), Triton X-100 (TX-100), and Tween 20. Amorphous nanoparticles of MnO₂ in the form of spherical particulates of size 50–200 nm, as detected by a transmission electron microscope, have been found to exist, supported on two-dimensional gum acacia sheets. The reaction is first order in MnO₂ but complex order with respect to fructose and H⁺. The reaction is inhibited due to adsorption of reaction products on the surface of MnO₂ nanoparticles. The reaction takes place through an intermediate complex formation between β-d -fructopyranose and protonated MnO₂. A one-step two-electron transfer reaction ultimately leads to the formation of an aldonic acid and formic acid. The entropy of activation plays the key role for the reaction in the absence of surfactants. In the surfactant-mediated reaction, partitioning of both the reactants takes place between the aqueous and micellar pseudophases and reaction occurs following Berezin's model. Binding of fructose with the surfactants in the Stern/palisade layer takes place through the ion–dipole interaction and H-bonding while protonated MnO₂ remains at the outer side of the Stern/palisade layer within the micelle. Both the enthalpy and entropy changes associated with the fructose–water interaction, fructose–micelle interaction, and micelle–water interaction finally control the fructose–micelle binding.     

Remarkable Electrochemical Responses of Ferrocene/NaY Zeolite Composite modified Electrode Based on Hydrophobic Ionic Liquid

The ferrocene/NaY zeolite composites (Fc/NaY) are introduced on the surface of a glassy carbon electrode together with the hydrophobic ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆). The modified electrode thus constructed exhibits a pair of reversible redox peaks corresponding to ferrocene. Additionally the peak separation remains almost constant (58–75 mV) and the value of the ratio i_pa/i_pc is close to 1 for scan rates in the range from 10 to 1000 mV s^?1. The effects of the scan rate, aqueous supporting electrolytes, hydrophobic ionic liquid and the contents of ferrocene encapsulated by electrochemistry are investigated. The extrazeolite electron transfer process is discussed. Furthermore, the Fc/NaY/IL‐modified electrode shows good mediation towards oxidation of ascorbic acid, dopamine, hydroquinone, and catechol.     

New Strategy for Dehydrogenase Amperometric Biosensors Using Surfactant to Enhance the Sensitivity of Diaphorase/Ferrocene Modified Carbon Paste Electrodes for Electrocatalytic Oxidation of NADH

A carbon paste electrode (CPE) modified with diaphorase (DAP) and ferrocene (FcH) has been developed for determination of NADH at low working potential. The sensitivity and operational stability, towards the detection of the reduced form of the nicotinamide adenine dinucleotide (NADH) in flow injection analysis (FIA), were greatly improved (5 times) upon adding Tween 20 into the electrode matrix. The magnitude of the amperometric signal was dependent on DAP, FcH and surfactant loading, into the modified carbon paste electrode. A rapid and repeatable response was observed to the variation of NADH concentration in the vicinity of the electrode surface. Such advantages of the DAP/FcH/Tween 20 modified carbon paste were successfully used in the construction of L ‐lactate dehydrogenase modified electrodes. The use of this new approach can be generalized to other dehydrogenases and represents a decisive step for a versatile preparation method of amperometric biosensors.     

The electrocatalytic reactions of adenine, guanine, H2O, H2O2, N2H4, and l -cysteine catalyzed by poly(Ni(4-TMPyP)) film-modified electrodes

Electrochemical preparation of poly(nickel tetrakis(N-methyl-4-pyridyl)porphyrin) tetratosylate (poly-Ni(4-TMPyP)) produces stable and electrochemically active films in strong and weak basic aqueous solutions. These films were produced on glassy carbon and gold electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of poly(Ni(4-TMPyP)) films. The electrochemical properties of poly(Ni(4-TMPyP)) films indicate that the redox process was confined in to the immobilized film. The electrochemical quartz crystal microbalance results showed an ion exchange reaction for the redox couple. The polymer films showed one new redox couple when transferred to strong and weak basic aqueous solutions and the formal potential was found to be pH dependent. The electrocatalytic oxidation of H₂O by a nickel tetrakis(N-methyl-4-pyridyl)porphyrin film-modified electrode was also performed. The mechanism of oxygen evolution was determined by cyclic voltammetry, chronoamperometry and rotating ring disc electrode methods. The oxygen evolution was determined by a bicatalyst system using hemoglobin, and iron tetrakis (N-methyl-2-pyridyl)porphyrin as catalyst to detect the oxygen by electrocatalytic reduction. The electrocatalytic oxidations of adenine, guanine, H₂O₂, N₂H₄, NH₂OH, and l-cysteine by the film-modified electrode obtained from water-soluble nickel porphyrin were also investigated.     

Hydrogen peroxide biosensor based on the immobilization of horseradish peroxidase on ��-Al2O3 nanoparticles/chitosan film-modified electrode

An amperometric biosensor based on horseradish peroxidase (HRP) and ??-Al₂O₃/chitosan composite film at a glassy carbon electrode has been developed. Hydrogen peroxide (H₂O₂) was detected with the aid of ferrocene monocarboxylic acid mediator to transfer electrons between the electrode and HRP. The morphology and composition of the modified electrode were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and amperometry. The effects of HRP concentration, the applied potential, and the pH values of the buffer solution on the response of the sensor were investigated for optimum analytical performance. The proposed biosensor showed high sensitivity (0.249?A M^?1?cm^?2) and a fast response (<5?s) to H₂O₂ with the detection limit of 0.07???M. The linear response range of the enzyme electrode to H₂O₂ concentration was from 0.5 to 700???M with a correlation coefficient of 0.9998. The apparent Michaelis-Menten constant of the biosensor was calculated to be 0.818?mM, exhibiting a high enzymatic activity and affinity for H₂O₂.     

Micellar effects upon electron transfer from ferrocenes

The oxidations of ferrocene (FcH) and n-butylferrocene (FcBu) by ferric salts (nitrate or bromide) are strongly inhibited by aqueous cetyltrimethylammonium bromide and nitrate (CTABr and CTANO₃, respectively). The kinetics of inhibition fit a model in which the substrates are distributed between water, and the micelles and binding constants K_s to the micelle can be estimated. The oxidations are strongly catalyzed by micelles of sodium lauryl sulfate (NaLS), and the kinetics can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase and the rate constants in that pseudophase, which for both substrates are very similar to those in water. Some added salts reduce the micellar catalysis by excluding ferric ions from the micelle. The oxidations of FcH and FcBu by ferricyanide ions are too fast to be followed in water, but they are inhibited by anionic micelles of NaLS. By analyzing the rate surfactant profiles using independently measured values of K_s the second-order rate constants in water have been estimated.     

Ferrocene-functionalized graphene electrode for biosensing applications

A novel ferrocene-functionalized reduced graphene oxide (rGO)-based electrode is proposed. It was fabricated by the drop casting of ferrocene-functionalized graphene onto polyester substrate as the working electrode integrated within screen-printed reference and counter electrodes. The ferrocene-functionalized rGO has been fully characterized using FTIR, XPS, contact angle measurements, SEM and TEM microscopy, and cyclic voltammetry. The XPS and EDX analysis showed the presence of Fe element related to the introduced ferrocene groups, which is confirmed by a clear CV signal at ca. 0.25 V vs. Ag/AgCl (0.1 KCl). Mediated redox catalysis of H₂O₂ and bio-functionalization with glucose oxidase for glucose detection were achieved by the bioelectrode providing a proof for potential biosensing applications.     

Preparation,Characterization and Electrochemical Application of ZnS/ZnAl2S4 Nanocomposite for Voltammetric Determination of Methionine and Tryptophan Using Modified Carbon Paste Electrode

ZnS/ZnAl₂S₄ nanocomposite and 2‐chlorobenzoyl ferrocene, were synthesized and used to construct a modified carbon paste electrode. The electrooxidation of methionine at the surface of the modified electrode was studied. Under the optimized conditions, the square wave voltammetric (SWV) peak current of methionine increased linearly with methionine concentration in the range of 5.0×10^?8 to 8.0×10^?4 M and detection limit of 10.0 nM was obtained for methionine. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of methionine and tryptophan which makes it suitable for the detection of methionine in the presence of tryptophan in real samples.     

The effect of arylferrocene ring substituents on the synthesis of multi-walled carbon nanotubes

The synthesis of shaped carbon nanomaterials (SCNMs) such as carbon nanotubes (CNTs), amorphous carbon, carbon fibres (CFs) and carbon spheres (CSs) was achieved using para-substituted arylferrocenes, FcPhX (X = H, OH, Br, COCH₃) or a mixture of ferrocene (FcH) and substituted benzenes (PhX; X = H, OH, Br, COCH₃). The reactions were carried out by an injection chemical vapour deposition (CVD) method using toluene solutions (carrier gas: 5% H₂ in Ar at a flow rate of 100 ml/min) in the temperature range of 800-1000 °C. In most instances multi-walled CNTs (MWCNTs) were produced. Variations in the concentrations of precursor catalysts, the injection rate and temperature affected the type, distribution and dimensions of the SCNMs produced. The overall finding is that the presence of Br and O in these studies significantly reduces CNT growth. A comparative study on the effect of FcPhX versus FcH/PhX mixtures was investigated. The SCNMs were characterized by transmission electron microscopy (TEM), Raman spectroscopy and thermal gravimetric analysis (TGA).     

Electrocatalytic oxidation of ascorbate by heme-FeIII/heme-FeII redox couple of the HRP and its effect on the electrochemical behaviour of an L-lactate biosensor

The measurements of L-lactate using the carbon paste electrode modified with lactate oxidase (LOD), horseradish peroxidase (HRP) and ferrocene (FcH) operating at low working potential in flow injection mode showed that the intensity as well as the shape of peaks were dependent on the concentration of the reducing species present in samples (e.g. ascorbate) even at low operating potentials (-200 to 0 mV vs. Ag/AgCl). The mechanism of the electrochemical contribution of ascorbate to the L-lactate response was examined by using cyclic voltammetry, hydrodynamic voltammetry and FIA results. Comparative studies showed that HRP was catalytically active for the oxidation of ascorbate leading to a decrease in the cathodic electrochemical signal of L-lactate. The results of our investigation postulated that the direct electron transfer from the HRP-Fe(III)/HRP-Fe(II) redox couple to the electrode surface was involved in the electrocatalytic oxidation of ascorbate at the electrode surface.     

Electrochemical determination of iodide by poly(3-aminophenylboronic acid) film electrode at moderately low pH ranges

A new potentiometric sensor for the determination of iodide based on poly(3-aminophenylboronic acid) (PAPBA) film electrode was constructed. Poly(3-Aminophenylboronic acid) films were synthesized electrochemically on platinum electrode by cyclic voltammetry. The effect of film thickness, pH, and preconditioning parameters on the electrode performance were examined. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 10⁻⁶ to 10⁻¹ M iodide ion. The limit of detection was found to be 8 × 10⁻⁷ M. The response time of the sensor was 5 s and its lifetime is about one week. To check the selectivity of the PAPBA film for iodide ion, potential interferences such as Cl⁻, Br⁻, F⁻, CN⁻, IO₃⁻, Ca²⁺, and Mg²⁺ were tested. The PAPBA electrode was also employed as a sensing platform for the determination of iodide ions in commercial table salt.     

Effect of Poly(amine)s on the Redox Properties of Carboxymethylcellulose and Ferrocene‐modified Poly(amine) Layer‐by‐Layer Films

Multilayer films consisting of carboxymethylcellulose (CMC) and ferrocene‐modified poly(ethyleneimine) (Fc‐PEI) or poly(allylamine hydrochloride) (Fc‐PAH) were successfully prepared on a gold electrode to examine their redox properties. The redox current of (Fc‐PEI/CMC)_n film‐coated electrodes increased with the number of layers, while the (Fc‐PAH/CMC)_n film‐coated electrodes exhibited increased response only for the first eight bilayers. The (Fc‐PEI/CMC)_n and (Fc‐PAH/CMC)_n films deposited on the surface of Fc‐free multilayer film‐coated electrodes also showed a redox response. The (PEI/CMC)₅ film‐coated electrode showed redox responses in Fc‐PEI and Fc‐PAH solutions, confirming the uptake of the Fc‐polymers in the inner film. In contrast, the uptake of the Fc‐polymers in the (PAH/CMC)₅ film was severely suppressed, suggesting that different permeability of (PEI/CMC)₅ and (PAH/CMC)₅ films.     

Renewable Surface Sol‐gel Derived Carbon Ceramic Electrode Modified with Copper Complex and Its Application as an Amperometric Sensor for Bromate Detection

A sol‐gel technique was used for the preparation of a three dimensional carbon composite electrode modified with [Cu(bpy)₂]Br₂ complex. A reversible redox couple of Cu(II)/Cu(I) is observed at the electrode surface. The electrochemical behavior and stability of the modified electrode was characterized by cyclic voltammetry. The charge transfer coefficient (α) and charge transfer rate constant (K_s) for the modified electrode were determined by cyclic voltammetry, which were found to be 0.46 and 14.2 s^?1, respectively. The modified electrode showed excellent catalytic activity toward bromate reduction at significantly reduced overpotentials and can be used successfully for amperometric detection of bromate. Under the optimized conditions, the calibration plots are linear in the concentration range 0.5 μM ?200μM. Detection limit (signal to noise is 3) and sensitivity were found to be 0.1 μM and 20 nA / μM, respectively. These analytical parameters compare favorably with those obtained with modern analytical techniques. The modified carbon ceramic electrode doped with Cu‐Complex shows a good reproducibility, a short response time (t<2 s), remarkable long term stability (>4 months) and especially good surface renewability by simple mechanical polishing (RSD for 6 successive polishing is 1.5%).     

取代二茂铁多碘化合物的合成`表征和穆斯堡尔谱研究

合成了一系列新的取代二茂铁多碘化合物,通式为[(RC_5H_4)(R′C_5H_4)Fe]·I_x。元素分析表明,取代基不同时,二茂铁与碘可以整比或非整比结合。~(57)Fe穆斯堡尔谱和红外光谱的研究表明,因取代基不同,二茂铁可以完全地或部分地被碘氧化。     

A Molybdenum Carbide Nanotubes Modified Electrode as the Functionalized Sensing Platform for Electrochemical Detection of Dopamine

In this work, molybdenum carbide (Mo₂C) nanotubes were prepared via the self‐degradable template method and high‐temperature calcination, and then were successfully used to modify glassy carbon electrode (CGE) for the high‐sensitivity determination of dopamine (DA) without the inference of ascorbic acid(AA) and uric acid (UA). The surface morphology of Mo₂C nanotubes has been investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). Owing to the enhanced electron transfer rate and high surface area of Mo₂C, the modified electrode not only exhibits very excellent electrochemical performance for DA, but also has good analytical performance for DA in the mixture with AA and UA through differential pulse voltammetry (DPV), which can be applied for DA detection with wide linear range(0.005–50 μ mol L^?1) and low detection limit 0.001 μ mol L^?1. The modified electrode has been applied to detect DA in DA hydrochloride injection by using standard adding method with satisfactory results.     

Comparative studies of the behavior of neutral and ionic ferrocene derivatives under different conditions of electrospray ionization

We have studied the behavior of ferrocene CpFeCp (FcH), ferrocenium triiodide [FcH]⁺I₃⁻, dimethylaminomethylferrocene FcCH₂NMe₂ and its trimethylammonium salt [FcCH₂NMe₃]⁺I⁻ under the conventional conditions of electrospray ionization (ESI), when the substance solution is subjected to spraying, and in two versions of desorption electrospray ionization (DESI), when the sprayed solvent bombards the surface of solid or liquid samples. In addition to these techniques, the behavior of neutral compounds under conditions of electrospray ionization of vapors of the studied compounds in a gas phase (ESI_V) has been investigated. It has been shown using the examples of ferrocene and its dimethylaminomethyl derivative that the detection limits for these compounds occurring in a gas phase are comparable within an order of magnitude with their detection limits under the ESI and DESI conditions of solid and liquid samples. The high effectiveness of ionization of analyte vapors makes it possible to use the ESI method not only in combination with liquid (conventional ESI technology) and thin layer chromatography (DESI), but also with gas liquid chromatography (ESI_V). Thus, the electrospray ionization becomes a universal method allowing studies of a compound under the natural conditions in any state of aggregation, that is, solid, liquid, and gas. With the help of statistical methods for designing experiments (complete factorial experiment), quantitative evaluation of the influence of experimental parameters on the ion-formation processes under different ESI conditions has been carried out, which makes it possible to purposefully select the optimal conditions to record the ESI mass spectra with a minimum number of experiments. Moreover, analysis of the dependences of the mass spectra on the experimental parameters can serve as an instrument for studying the details of the ion-formation mechanisms depending upon different ways of ionization.     

Intermolecular Interactions in Mixed Self‐Assembled Monolayers of Ferrocene

Electrochemical characterization of mixed self‐assembled monolayers (SAMs) of 6‐ferrocenyl‐1‐hexanethiol (FcH) and mercaptoundecanoic acid tyrosinamide (MUATyr) on gold is reported. Single‐component SAMs of FcH presented repulsive intermolecular interactions (vGθ_T=?1.12), while mixed SAMs of FcH/MUATyr (1 : 1) exhibited attractive interactions (vGθ_T=+0.20), with a homogeneous distribution of both components. Electrochemical kinetic determinations on mixed SAMs of FcH/MUATyr, indicated a secondary electron transfer pathway between the redox centers of both components. Higher amounts of FcH in the mixed SAMs lowered the observed rate of electron transfer of MUATyr. The oxidation of FcH caused an anodic shift of 160 mV in the voltammetric wave of MUATyr.     

Titanium Dioxide/Multi-walled Carbon Nanotubes Composite Modified Pencil Graphite Sensor for Sensitive Voltammetric Determination of Propranolol in Real Samples

A very effective electrochemical sensor for the analysis of propranolol was constructed using TiO₂/MWCNT film deposited on the pencil graphite electrode as modifier. The modified electrode represented excellent electrochemical properties such as fast response, high sensitivity and low detection limit. The proposed sensor showed an excellent selective response to propranolol in the presence of foreign species and other drugs. The electrochemical features of the modified electrode were investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) technique which indicated a decrease in resistance of the modified electrode versus bare PGE and MWCNT/PGE. The surface morphology for the modified electrode was determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT-IR). Differential pulse technique (DPV) was used to determine propranolol which showed a good analytical response in the linear range of 8.5×10⁻⁸-6.5×10⁻⁶ M with a limit of detection 2.1×10⁻⁸ M. The TiO₂/MWCNT/PGE sensor was conveniently applied for the measurement of propranolol in biological and pharmaceutical media.