Elektrochemische untersuchung von bis(diphenyldithiophosphin) disulfid

The electrochemical behaviour of bis(diphenyldithiophosphine)disulphide (RSSR) and mercuric diphenyldithiophosphinate [(RS)₂Hg] in ethanol-lithium perchlorate and ethanol-sulphuric acid media was studied by the methods of classical polarography, and electrolysis at controlled-potential and at a rotating disc platinum electrode. The data obtained show that RSSR is not reduced directly on the dropping mercury electrode but is adsorbed. It then undergoes a rapid chemical reaction causing the formation of (RS)₂Hg, which is electroactive. The electrolysis at controlled potential proves that (RS)₂Hg undergoes a two-electron reduction, giving diphenyldithiophosphinic acid (RSH) as a main product, whereas the oxidation of RSH leads to the production of (RS)₂Hg. Regardless of the fact that the chemical and adsorption equilibria during reduction of RSSR and (RS)₂Hg are complex, the coulometric generation of RSH is not difficult to achieve, and permits the use of RSSR as a coulometric reagent.     

The electrochemistry of proteins and related substances: Part II. Insulin

The electroreduction of insulin in pH 7.4 solution was studied at the hanging mercury drop electrode by cyclic voltammetry and at a mercury pool electrode by controlled potential coulometry. The proposed mechanism involves reduction of an adsorbed monolayer of insulin (maximum coverage of 10 μC cm^?2) in a four-electron reaction at about ?0.6 V vs. SCE resulting in breakage of two of the three disulfide bonds in the molecule. Fast reoxidation leads to recovery of much of the reduced species. At longer time (ca. 100 s) a steady state is reached where the reductions and reoxidation involve reversible two-electron reactions.     

The electrochemistry of proteins and related substances part III. Bovine serum albumin

The electroreduction of bovine serum albumin (BSA) in pH 7.4 solution was studied at the hanging mercury drop electrode by double potential step chronocoulometry and cyclic voltammetry, and at a mercury pool electrode by controlled potential coulometry. The proposed mechanism involves reduction of an adsorbed monolayer of BSA (maximum coverage 3.3 μC^?2); at short times 3 or 4 disulfide bonds are reduced, the product remains adsorbed and may be reoxidized. On the coulometric time scale (hours) 8 or 9 of the total 17 disulfide bonds are broken and an insoluble product which cannot be oxidized is formed.     

Adsorption of succinonitrile at the mercury-aqueous solution interface: Unusual role of a fixed dipole in the adsorbed molecule

The adsorption of succinonitrile (SN) on a polarized Hg electrode has been studied from 0.25 M NaF aqueous solutions by means of both capacity and electrocapillary curves. Adsorption isotherms have been found to be strictly congruent with respect to both charge and potential. The charge of maximum adsorption is at ?4.6 μC cm^?2 and ΔG_ads⁰, the free energy of adsorption at zero coverage, decreases more rapidly as the charge is made positive with respect to O_max^M than on the other side. The adsorption obeys a Frumkin isotherm with a=?1.87 corresponding to attraction and saturation concentration of 4.8×10^?10 mol cm^?2 corresponding to an area per molecule of about 34.5 Ų. Experimental results suggest that SN adsorbs flat on the surface but, unlike acetonitrile and propionitrile, the CN groups are slightly turned towards the solution. This is responsible for the absence of electronic interaction of the CN groups with the metal at positive charges, which is apparent with the other two nitriles. Implications of the particular structure of the adsorbed molecule on the other adsorption parameters are discussed in detail.     

Preliminary Study on Reverse Pulse Amperometric Detection in Capillary Electrophoresis for Simultaneous Determination of Cysteine and Cystine

Simultaneous determination of cysteine (RSH) and cystine (RSSR), two important sulfur-containing amino acids, in capillary electrophoresis (CE) has been an analytical task. Dual-microelectrode amperometric detection seems to be a good scheme, but significant difficulty in electrode construction and poor detection limit for RSSR determination remain major short-comings. In reverse pulse amperometric (RPA) detection, the applied potentials are repeatedly pulsed back and forth between the reducing initial potential (e.g., E_i = ?1.4 V) and the oxidizing final potential (e.g., E_f = 0.0 V) at a single, gold-mercury amalgam (Au/Hg) microelectrode. At E_i, RSSR is reduced to RSH which causes catalytical oxidation of the Au/Hg amalgam microelectrode when the potential is pulsed to E_f. The resulting anodic current is then recorded. Therefore, by using RPA detection after CE separation, RSH and RSSR can be simultaneously determined.     

Cyclic voltammetry of FAD adsorbed on graphite,glassy carbon,platinum and gold electrodes

The electrochemical properties of FAD adsorbed on graphite were studied with cyclic voltammetry. A film with a surface coverage of up to 2×10^?8 mol cm^?2 was formed after 4 h. The film-covered electrodes were stable for long times and they were investigated in buffers without any FAD. A single well-behaved wave was observed, k⁰≌1 s^?1. The pH dependence of E_1/2 was studied. On glassy carbon, platinum and gold much less FAD was adsorbed and it was removed with one rinse.     

Voltammetric Behavior of Antileukemia Drug Glivec. Part II – Redox Processes of Glivec Electrochemical Metabolite

Glivec is a newly developed drug that belongs to the class of 2‐phenylaminopyrimidine. It is a potent inhibitor of ABL‐kinase, the main clinical manifestation of chronic myelogenous leukemia (CML). Based on its activity on CML, glivec is undergoing extensive evaluation for its activity against other tumor types. Detection and quantitation of glivec in biological fluids or cells is thus very important. The antileukemia drug glivec undergoes oxidation at glassy carbon electrodes and involves the formation of an oxidation product, P_glivec. The adsorption of P_glivec at the GCE surface yields a compact monolayer allowing an electrochemical study of this compound adsorbed at the GCE surface. The reversible redox reaction of the adsorbed P_glivec is pH dependent and occurs with the transfer of 2 electrons and 2 protons. The surface standard potential and the rate constant of the heterogeneous electrochemical reaction were calculated using cyclic voltammetry to be E^θ′=+180 mV and k=15.5 s^?1, respectively. The total surface concentration of adsorbed P_glivec is 2.5×10^?12 mol cm^?2. The analytical determination of glivec was carried out by differential pulse voltammetric measurement of the anodic peak current corresponding to either the oxidation peak of glivec or the oxidation peak of P_glivec adsorbed on the GCE surface. The limits of detection of glivec and adsorbed P_glivec based on three times the noise level are 3.3×10^?8 M and 2.9×10^?10 M, respectively.     

Amperometric argentimetric and mercurimetric titration of sulfhydryl: Mercurimetric titration

The ampero-mercurimetric titration of cysteine (RSH), glutathione (GSH), thioglycolic acid (TSH) and 2-mercaptoethanol (ESH) at the RMPE at pH 9 yields a sharply defined end-point corresponding to the composition (XS)₂Hg. Under the same conditions with the KPtWK two lirciiks an; (ibst'rvc-d in the titration lines with RSH and GSH, corresponding to compositions (RS)₂Hg and (RS)₂Hg₂ respectively. On the other hand, with TSHl and ESH only one clear break is found at the RPtWE corresponding to ('l'S)₂Hg or (ES)₂Hg Conditions liave been describcd for the accurate mercurimetric titration of the thiol compnunds at pH 2 in the pesence of 0.01 M sulfur dioxide at the RMPE, use of this can be made in the determination of disufides and in the determination of the equilibrium concentrations of the reaction betwcen a disulfide and a sulfite at varying pH.     

Prediction of semiconducting SiP_2 monolayer with negative Possion's ratio,ultrahigh carrier mobility and CO_2 capture ability

Using particle swarm optimization(PSO) methodology for crystal structure prediction,we predicted a novel two-dimensional(2 D) monolayer of silicide diphosphorus compound:SiP_2,which exhibits good stability as examined via cohesive energy,mechanical criteria,molecular dynamics simulation and all positive phonon spectrum,respectively.The SiP_2 monolayer is an indirect semiconductor with the band gap as 1.8484 eV(PBE) or 2.681 eV(HSE06),which makes it more advantageous for high-frequencyresponse optoelectronic materials.Moreover,the monolayer is a relatively hard auxetic material with negative Possion's ratios,and also possesses a ultrahigh carrier mobility(1.069 × 10~5 cm~2 V~1 s~1) which is approximately four times the maximum value in phosphorene and comparable to the value of graphene and CP monolayers.Furthermore,the effects of strains on band structures and optical properties of SiP2 monolayer have been studied,as well as CO_2 molecules can be strongly chemically adsorbed on the SiP_2 monolayer.A semiconductor-to-metal transition for-9.5% strain ratio case and a huge optical absorption capacity on the order of 106 cm ~1 in visible region present.These theoretical findings endow SiP2 Monolayer to be a novel 2 D material holding great promises for applications in highperformance electronics,optoelectronics,mechanics and CO_2 capturing material.     

[RuIII(EDTA)(H2O)]− catalyzed oxidation of biologically important thiols by H2O2

[Ru^III(EDTA)(H₂O)]^? (EDTA^4? = ethylenediaminetetraacetate) catalyzes the oxidation of biological thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, penicillamine) using H₂O₂ as precursor oxidant. The kinetics of the oxidation process were studied spectrophotometrically as a function of [Ru^III(EDTA)(H₂O)]^?, [H₂O₂], [RSH], and pH (4–8). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with [Ru^III(EDTA)] catalyst complex to form [Ru^III((EDTA)(SR)]^2? intermediate species. In the subsequent reaction step the oxidant, H₂O₂, reacts directly with the coordinated S of the [Ru^III((EDTA)(SR)]^2? intermediate leading to formation of the disulfido (RSSR) oxidation product (identified by HPLC and ESI-MS studies) of thiols (RSH). Based on the experimental results, a working mechanism involving oxo-transfer from H₂O₂ to the coordinated thiols is proposed for the catalytic oxidation.     

Theoretical studies of thiols and disulfides. Conformations,barriers and proton affinities

Results from an ab-initio MO LCAO SCF study of RSSR, RSH and RS^? (R = H, CH₃) in a minimal and a double zeta basis and cysteine [COO^?CH(NH⁺₃)CH₂SH] and cysteine anion in a minimal basis are reported. The barriers and conformational preference of the disulfides are discussed and it is suggested that their origin is more confined to the disulfide region than previously believed. The proton affinities of the different RS^? ions are calculated, whereas the protonation of the disulfide bond is studied by use of the molecular electrostatic potential. The good agreement of the results in the minimal and the double zeta basis is discussed.     

Bioactive Hydrogel Layers on Microdisk Electrode Arrays: Cyclic Voltammetry Experiments and Simulations

Poly(hydroxyethylmethacrylate)‐based hydrogel membranes were applied to microfabricated, microdisk electrode arrays (MDEAs) of 50 μm (5184 disks), 100 μm (1296 disks) and 250 μm (207 disks) (d/r=4; A= 0.1 cm²) and studied by cyclic voltammetry (CV) in 1.0 mM ferrocene monocarboxylic acid (FcCO₂H). The membrane produced an order of magnitude decrease in current densities and a shift to quasi reversibility due to a decrease in the D_appt of FcCO₂H, from 4.51×10^?6 cm² s^?1 to 1.42×10^?8 cm² s^?1, (2.18×10^?8 cm² s^?1 from release experiments). The MDEA050 (comprising 50 μm disks) maintained its enhanced current density attributes confirming its value as an effective electrode for biosensors. Finite element modeling (FEM) simulations successfully replicated the voltammograms of the MDEAs.     

Electrosorption of β-naphthol on graphite

Isotherms for the adsorption of β-naphthol from a buffered aqueous solution of 0.5 M K₂SO₄ onto graphite were detemrined over a range of potential of 1.27 V. The adsorbent was a packed bed of ?100 + 120 mesh graphite powder. Sufficient surface area was available to calculate accurately the amount adsorbed by measuring spectrophotometrically the change in adsorbate concentration in the bulk solution.At all potentials, a Langmuir adsorption isotherm, modified for the displacement of solvent molecules, was followed up to 60–65% of monolayer coverage. The ratio of projected areas of β-naphthol and water molecules was consistent with the experimentally derived number of solvent molecules displaced, six. The largest amount of adsorption observed, 2.5×10^?10 mol cm^?2, agreed with the calculated monolayer coverage of β-naphthol molecules lying in flat orientation on the graphite surface. Adsorption increased at more positive potentials. Over the range of potential investigated, the adsorbability constant increased sixfold. Desorption was only partially reversible.     

A study of the gold/aqueous electrolyte interphase by modulated reflection spectroscopy

The admittance and differential reflectivity of an electrode of polycrystalline gold in contact with aqueous 0.02 M NaF, KClO₄, 0.01 M Na₂SO₄ and KCl have been measured in the range of potential where the electrode is ideally polarized (?0.7 V to 0.8 V NHE). In NaF and KClO₄ evidence was obtained for the compression of the adsorbed layer of water. The increase of the number of water molecules, with respect to the number in the least original state (at?4μC cm^?2), is 3% at +8 μC cm^?2 and at?17 μC cm^?2. At the potential of zero charge the water dipoles are oriented preferentially with the oxygen towards the metal. In KCl the optical measurements confirm the existence of two types of Au?Cl^? interaction and the covalent character of the bond at the most positive charges.     

Na+ transport across the beta alumina-propylene carbonate interface

Interfacial Na⁺ ion transport between polycrystalline beta alumina and propylene carbonate has been studied using a galvanostatic transient technique which separates interfacial overpotential from bulk resistivity effects. No interfacial polarization is detected during ion entry into beta alumina and exit from beta alumina across a dry interface from 30–1000 μA cm^?2. Transport across an interface contaminated with adsorbed water follows Tafel-type i/E behavior with a transition coefficient (α) of 0.24 and exchange current (i₀) of 3.0×10^?6 A cm^?2 at 23°C. Interfacial transport appears to take place through an intermediate state in which the mobile ion is adsorbed on the interface. Large increases in interfacial polarization occur at both dry and hydrated interfaces for ionic currents exceeding the rate of adsorption or desorption.     

Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes: Part VIII. Cu2+ reduction and Cu°(Hg) oxidation in perchloric acid

The effect of the specific adsorption of the ClO₄^? ion upon the kinetics of Cu²⁺ reduction and Cu⁰(Hg) oxidation in aqueous solutions of HClO₄ was investigated using chronocoulometry, d.c., normal pulse, and a.c. polarography. For this purpose three different sets of data for ClO₄^? adsorption were used. In the first set the absolute surface excess of water as reckoned at the outer Helmholtz plane (o.H.p.) was disregarded, in the second set it was accounted for by postulating a complete adsorbed monolayer of water molecules [32], whereas in the third set partial displacement of water molecules from this monolayer by adsorbed ClO₄^? ions was accounted for. Kinetic data were found to the compatible with the latter set, indicating that ClO₄^? adsorption affects the rate-determining step Cu²⁺+e→Cu⁺ only by altering the average electric potential σ_d-effect). The absence of any additional electrostatic effect points out that, in the transition state for Cu²⁺ reduction to Cu⁺, the centre of charge of the reacting particle falls in the proximity of the o.H.p.     

Two-stage mechanism of the dicarbollyliron redox-reaction at electrode coated with a monolayer of behenic acid and hemin

The dicarbollyliron (Cb₂Fe^-) redox reaction is studied at an amalgamated platinum electrode coated with a monolayer of behenic acid on top of which hemin is adsorbed. The redox reaction of Cb₂Fe^- involves two stages. First, an electrochemical reaction of adsorbed hemin proceeds, which involves the electron transfer through the dielectric monolayer; it is followed by the hemin’s chemical redox reaction with dissolved Cb₂Fe^-. It is shown that the adsorbed hemin transformation, no matter how small, is sufficient for the stimulation of the Cb₂Fe^- redox reaction.     

Die Kristallstruktur des SrHg(SCN)4 · 3 H2O

Crystal Structure of SrHg(SCN)₄ · 3 H₂O SrHg(SCN)₄ · 3 H₂O is orthorhombic, space group Pcca, with a = 19.476(7), b = 8.150(1), c = 8.991(3) Å, V = 1427.1 ų, Z = 4, d_c = 2.67 g · cm^?3, μ(AgKα) = 77.95 cm^?1. The salt consists of nearly tetrahedral Hg(SCN)₄ groups, Sr has a tricapped trigonal prismatic coordination: four N and five O atoms. The thiocyanate groups form end-to-end bridges and connect the Hg and Sr coordination polyhedra.     

High‐Performance Amperometric Sensors Using Catalytic Platinum Nanoparticles‐Thionine‐Multiwalled Carbon Nanotubes Nanocomposite

Thionine (TH) adsorbed on multiwalled carbon nanotubes (MWCNTs) increases the load and dispersion of platinum nanoparticles (PtNPs) generated by chemical reduction of H₂PtCl₆ with NaBH₄. Under the optimum conditions, the PtNPs‐TH‐MWCNTs/Au electrode electrocatalyzed the reduction and oxidation of H₂O₂ with high sensitivity, and after glucose oxidase (GOx) adsorption it responded to glucose concentration with a sensitivity of 0.14 A M^?1 cm^?2. The cyclic voltammetric cathodic peak current for NO₂^? reduction on PtNPs‐TH‐MWCNTs/Au responded linearly to NO₂^? concentration from 0.5 to 150 µM, with a sensitivity of 5.52 A M^?1 cm^?2 and a detection limit of 0.2 µM.