Electrochemical characteristics of the n+-type GaAs substrate in HCl electrolyte and the morphology of the obtained structure

The anodic etching of n⁺-type GaAs (1 0 0) substrate in HCl aqueous solution has been investigated experimentally using an in situ current–voltage J (V) and capacitance–voltage C (V) measurements. In situ current–voltage, J (V), characteristics of the n⁺-GaAs/HCl interface exhibit the presence of three potential regions, which are attributed to different reaction mechanisms between HCl and n⁺-type GaAs surface. Also, current peaks appear in the J (V) characteristics which delimit the different potential regions. According to the Mott–Schottky relation, the characteristic C^?2 (V) exhibits the presence of two linear regions separated by a shoulder at about 1.15 V. This shoulder indicates the formation of porous GaAs/HCl interface. Scanning electron microscopy (SEM) images shows that GaAs etched in HCl can produce various surface morphologies depending on the anodization current density. Reasonable assumptions on the dissolution mechanisms according to the variety of morphologies are given.     

Prediction of permselectivity of nitrate and acetate ions in the electrodialysis of aqueous solutions

Electrodialysis of aqueous solutions of acetic and nitric acids encountered in the industrial practice of deacidification of raw glyoxal solutions has been carried out to investigate the permselectivity of the system. The dependence of the permselectivity coefficient τ on experimental parameters such as flow velocity (V), current density (I), concentration of anions (C_i), etc. has been evaluated. A correlation between τ and the critical parameters has been obtained. Well-known theoretical equations have been used to calculate τ at limiting current density I_lim and as I approaches zero. Calculated results are compared with observed values. Limitations of theoretical procedures when applied to a system containing a weak acid are explained.     

478—Theory of Brdička current and the dependence of the current on cobalt ion concentration

An equation of Brdi?ka current and its experimental verification are presented, in which Brdi?ka current is expressed by a function of the surface concentration of protein, the bulk concentration of cobalt ion and two parameters, n_ck_c and k_f/k_d, characterizing the protein-zero-valent cobalt complex which is to catalize the hydrogen evolution, where n_c is the total number of sites on which the complex can be formed in a protein molecule, and k_c and k_d are the (average) constants representing the intrinsic catalytic activity and the lifetime respectively, of the complex.     

Application of the rotated dropping mercury electrode to the analysis of mixtures of electroactive substances

The use of poylacrylamide is recommended instead of gelatin as an ideal maximum suppressor to be employed with both the rotated dropping mercury electrode (RODE) and conventional dropping electrode (DME). It is retained at the mercury surface over the entire potential range and does not combine with heavy metals. Reproducibility of the measurement of the residual current and that of the limiting current at the RDME were studied, and it was found that accurate determinations of a single constituent (±2%) are possible at concentrations as low as 1 to 2.10^-5M. The variation of the limiting current with potential is much greater at the RDME than at the DME. This effect must be considered in the analysis of a mixture of electroactive species at the RDME. Method have been discussed for making the proper correction for a preceding wave when a limiting current of a mixture of constituents is measured. Because of its high sensitivity and good reproducibility of results, the RDME is recommended for the analysis of solutions containing one or more electroactive species at concentrations less than 10^-4M.     

Interplay of thermochemistry and structural chemistry, the journal (volume 24, 2013, issues 1–2) and the discipline

The contents of issues 1 and 2 for the calendar year 2013 are summarized in the current review of the journal Structural Chemistry. In addition, a brief thermochemical commentary is added to the summary of each paper.     

Theoretical and experimental aspects of the response of stripping voltammetry in flow injection systems

The coupling of stripping voltammetry with flow injection systems offers significant advantages over conventional stripping methods. Equations solved for conventional stripping voltammetry, with steady-state deposition current, are not applicable to flow injection systems. Theoretical equations for the peak current under flow injection conditions are derived. As the total charge passed during the deposition step, ∫i dt, is independent of the shape of the sample plug, the stripping peak current is independent of the degree of dispersion. As a result, precise control of the dispersion or deposition period may not be required. The peak current is predicted to be directly proportional to the sample volume. Experimental results are incorporated to support the theoretical conclusions. The effects of experimental variables such as flow rate, length of tubing, deposition period, or sample volume are presented using cadmium ion as test species.     

Use of ring-disc electrodes and viologens for the titration of cytochrome C and oxygen and for the study of their reduction kinetics

The use of ring-disc electrodes enable the electrogeneration of viologen cation radicals V⁺ when the disc potential is controlled in the range ?0.3 to ?0.65 and ?0.2 to ?0.45 V/NHE respectively in MV²⁺ and BV²⁺ solutions. We confirmed the occurrence of very fast reactions between V^.+ and horse-heart cytochrome c or oxygen and of slow or no reaction between V^.+ and β-nicotinamide adenine dinucleotide with xanthine oxidase, riboflavine and ferricyanide. Ring current versus dise current curves enable the titration of cytochrome c and oxygen and the estimation of the reaction rate between cytochrome c and MV^.+ [(6.2±2)10⁵M^?1 s^?1].     

Pyroelectric effect in crystals of the bis-toluene sulphonate diacetylene monomer and polymer

The pyroelectric properties of the monomer and partially and fuly polymerized crystals of the bis(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol (TS) were measured along their b axes from 100 to 300 K. Two peaks in the pyroelectric current of monomer crystals were found at 192 and 151 K. It is concluded that these crystals lack a centre of symmetry.     

Magneto-electrical cyclic voltammetry for visualization of current distribution in the electrolyte

Cyclic voltammetry is widely used in electrochemistry. To visualize the current distribution in the electrolyte, we developed a two-dimensional magnetic imaging system, combining the electric measurement component used in conventional cyclic voltammetry with a pair of MR (magnetic resistive) sensors to detect the x- and y-magnetic components. The resulting system allows simultaneous measurement of the electronic current of the working electrode and the magnetic field resulting from the transport of ions by migration in the bulk electrolyte. The current distribution in the electrolyte was reconstructed using the magnetic field strength data obtained at multiple points. Consequently, we could observe the change in current distribution when changing the length of the working electrode immersed in the electrolyte.     

Determination of limiting current density for different electrodialysis modules

Limiting current density of ammonium nitrate solution in laboratory-, pilot-, and industrial-scale electrodialysis modules were determined to provide a method for the prediction of the limiting current density of ammonium nitrate solutions at any conditions. The current-voltage curve was measured in each case and the limiting current density was evaluated using the dependence of the derivative, dI/dU, on the electric current, I. The limiting current was determined as a current at which the derivative dI/dU equals zero. The developed method enables not only the prediction of the limiting current density but the limiting cut and limiting flux can be determined concurrently at any linear flow velocity of the diluate and inlet ammonium nitrate concentration. It could help to prevent working in the overlimiting region and to avoid undesirable decrease of current efficiency and pH changes. The limiting cut is the maximal cut that can be obtained at certain linear flow velocity and module geometry irrespective of the inlet ammonium nitrate concentration and it is very useful information when designing a new electrodialysis unit for specific application.     

Influence of the electrode boundary motion on the determination of the interdiffusion coefficient by electrochemical techniques

A mathematical analysis is developed to take into account the motion of the electrolyte/electrode boundary during electrolysis at constant current or at constant potential. The change in volume of the electrode is deduced from the partial molal volume of the electroactive component, which is supposed to be constant during the experiment.The applicability of this treatment is discussed. It is shown that, after a potential step, the decrease of the current density is a linear function of t^{?$\text{1}\text{2}$}, as for the Cottrell law, but the proportionality factor is changed. During the passage of a constant current the surface concentration remains nearly a linear function of t^{$\text{1}\text{2}$}, as for the Sand law when the concentration of the electroactive component is small. In general, very large departures from the standard equations appear at high concentrations of electroactive component. Applications are given for measuring solid state interdiffusion coefficients from electrochemical techniques. This study can be used to determine the kinetics of electrolyte diffusion coating and surface alloying.     

Investigation of the anodic processes on platinum in perchlorate and chlorate solutions by linear sweep voltammetry using the rotating double-ring electrodes

The polarographic behavior of chloramine-T has been investigated over a wide pH range. Chloramine-T gives two waves at low concentration. In acidic solution, the second wave is due to the formation of mercurous chloride, whereas, in alkaline solution, the second wave is due to the formation of the mercuric salt of p-toluenesulfonamide. The diffusion current of the total wave is due to a two-electron reduction, is proportional to the concentration and is stable, particularly in alkaline solution. The polarographic behavior of the anodic wave of p-toluenesulfonamide has also been investigated.     

Development of an electrochemical method for the rapid determination of microbial concentration and evidence for the reaction mechanism

A rapid amperometric method for the determination of microbial concentration is described. The micro-organisms reduce the redox mediator, potassium hexacyanoferrate(III), which is reoxidized to yield a current proportional to the microbial concentration. Escherichia coli gave a linear response (standard error (S_YX)=0.17, r=0.9999, n=5, P>99.9%) over the concentration range 10⁶–10⁸ cells ml^?1 with a response time of less than 1 min. The effect of varying temperature showed that the electrochemical response of the bacteria was linked to respiration rate. Studies with respiratory inhibitors suggested that hexacyanoferrate (III) is reduced by the segment of the respiratory chain between nicotinamide adenine dinucleotide (NADH) dehydrogenase and the terminal oxidases.     

Charge transfer between two immiscible electrolyte solutions: Part VI. Polarographic and voltammetric study of picrate ion transfer across the water/nitrobenzene interface

The transfer of the picrate ion across the interface between two immiscible electrolyte solutions, 0.05 M LiCl in water and 0.05 M tetrabutylammonium tetraphenylborate in nitrobenzene was investigated by electrolysis with the electrolyte dropping electrode and by cyclic voltammetry. Under the conditions of the experiments the charge-transfer process is controlled solely by diffusion. The maximum which appears on the polarogram of the picrate ion close to the limiting current can be suppressed by the addition of a surface-active substance (gelatine). The diffusion coefficients of the picrate ion in the aqueous and nitrobenzene phase were determined from the limiting polarographic current and from the peak current on the cyclic voltammogram. The value of the formal potential of the charge-transfer reaction, which was calculated from the half-wave potential or from the peak potential, is in good agreement with that inferred from the extraction data.     

Enhancement and quenching of photoionization in rare gas mixtures

Admixing a sufficient amount of a light rare gas to a heavier rare gas effects the photoionization current measured at the absorption lines of the latter. This current is enhanced if hv > E_c and quenched if hv <E_c where hv is the energy of the exciting photons. E_c is approximately equal to the ionization potential of the corresponding heteronuclear van der Waals molecule. Both homonuclear and heteronuclear dimer ion formation are discussed.     

Interplay of thermochemistry and structural chemistry,the journal (volume 24, 2013, issues 3–4) and the discipline

The contents of issues 3 and 4 for the calendar year 2013 are summarized in the current review of the journal Structural Chemistry. A brief thermochemical commentary is added to the summary of each paper.     

Interplay of thermochemistry and Structural Chemistry, the journal (volume 23, 2012, issues 4–6) and the discipline

In the current review of the journal Structural Chemistry, the contents of the issues 4–6 for the calendar year 2012 are related to thermochemistry. A brief thermochemical commentary is added to the summary of each paper.     

Current-induced switching of a single magnetic molecule with an arbitrary orientation of the magnetic easy axis

Magnetic switching of a single-molecule magnet (SMM) due to spin-polarized current is considered theoretically. The system under investigation consists of a single magnetic molecule attached to two ferromagnetic leads. Magnetic moments of the leads are assumed to be collinear, whereas the magnetic anisotropy axis of the molecule forms an arbitrary angle with the moments. The current flowing through the system as well as the average z-component of the molecule's spin is calculated within the perturbative approach (Fermi golden rule). The mechanism of molecule's spin reversal due to current flowing directly through the molecule is discussed.     

In vitro bioassays for the study of endocrine-disrupting food additives and contaminants

Endocrine-disrupting chemicals (EDCs) are capable of interfering with normal hormone homeostasis by acting on several targets and through a wide variety of mechanisms. Unwanted exposure to EDCs can lead to a wide spectrum of adverse health effects, especially when exposure is during critical windows of development. Feed and food are considered to be among the main routes of inadvertent exposure to EDCs, so there is an important need for efficient detection of EDCs in these matrices.We describe in vitro bioassays that can complement current analytical chemistry in order to detect unwanted EDCs and describe their action, emphasizing assays that can measure effects on nuclear receptor signaling or hormone production. We outline both validated and unvalidated in vitro assays currently available in the scientific community for detecting and studying the effects of EDCs, and discuss their possible role in the food-safety context. We conclude by identifying gaps in the current battery of in vitro assays available for EDCs and suggest future possibilities for development and validation.     

Rotating-disc electrode studies of the anodic oxidation of iodide in concentrated iodine + iodide solutions

The anodic oxidation of iodide on platinum in concentrated iodine + iodide solutions has been investigated using a rotating disc electrode. The conventional limiting diffusion current, which is produced by the diffusion of iodide ions towards the electrode, was not observed due to the formation of an iodine film on the electrode. On the other hand, the steady-state anodic current after a current/time transient is the genuine limiting diffusion current in the anodic oxidation due to diffusion of iodine species from the electrode surface towards the bulk solution. Thus, the dissolution-diffusion control mechanism of the iodine film is confirmed. This is interesting as a typical example of an anodic process in a redox system governed by diffusion of the anodic product species from the electrode surface towards the bulk solution. When an iodine film is formed on the electrode, the maximum driving force of the iodine species is Δm_I2,max, which is defined as the extent of unsaturation of the iodine, and the limiting current of the anodic oxidation of iodide is always directly proportional to Δm_I2,max, regardless of the forms of iodine species in the solution, which may be I₂, I⁻₃, i₅⁻, etc. δm_I2,max is clearly determined by the solution composition and temperature, and it is different in definition and value from the usual degree of unsaturation of iodine.