Polarographische Untersuchungen an Solochromviolett RS in Pufferlösungen in Abwesenheit und in Gegenwart oberflächenaktiver Stoffe (SAS)

The polarographic behaviour of solochrome violet RS is investigated in buffer solutions of varying pH in the absence and presence of surfactants (triton 100-X and dodecylbenzene-sulphonate). The reduction proceeds irreversibly along a single wave in acid solutions and two waves in alkaline ones. The electrode reaction corresponds to four electrons in media of pH<2.5 and pH>8.0; in media of pH 4 5.5 two electrons are consumed. In solution of pH 2.5 4 or 5.5–8.0, both reactions contribute in varying magnitudes. The addition ofSAS causes the inhibition of reduction beyond the 2-electrons stage in acid solutions; the polarograms comprise one wave in case ofDBS and two waves of equal height in presence of triton. In alkaline media the polarogram comprises three waves due to the splitting of the main reduction wave. The kinetic parameters of the electrode reaction are also determined.     

Polarographic Behaviour of some Triazol Derivatives

Abstract

The polarographic behavior of some organic dyes such as nitro-benzo-triazol, amino-nitro-benzo-triazol, benzo-triazol azo thionaphthene carboxylic acid and 5-methyl imidazol 2-methyl benzo-triazol in aqueous buffered media has been studied. The results reveal that the reduction reactions occurred irreversibly under diffusion-control. The reduction mechanism of nitro-benzo-triazol and amino-nitro-benzo-triazol involve the consumption of six electrons in the form of one wave in acid and two waves in alkaline media. The electro-reduction of benzo-triazol azo thionsphthene carboxylic acid consumes four electrons. The mechanism proposed for that compound indicates that the triazol centre forms a radical as an intermediate state in alkaline medium. The reduction process of 5-methyl imidazole 2-methyl benzo-triazol contains two consumed electronic in acid media while four electrons are consumed in alkaline media.     

Polarography of Molybdenum (VI)—Gallic Acid Complexes in Perchlorate Media

Polarographic and spectrophotometric studies were carried out on Mo (VI)—gallic acid (G) complexes in aqueous solution of perchlorate media. It was found that the number of waves of Mo (VI) depends on gallic acid concentration as well as on the pH of solution. Only a single well-defined irreversible wave is obtained at pH 8.0 for the reduction of Mo (VI) to Mo (III), proportional to Mo (VI) concentration in presence of 20 mM gallic acid with E_1/2=?1.22 V vs SCE. The composition of the formed complexes depends on the pH of solution as revealed from spectrophotometric studies, a 1:1 Mo/G complex is formed at pH 3.0 and 1:2 complex at higher pH′s-NMR study of the isolated 1:2 complex proves that the complexation occurs through—OH groups of gallic acid.     

Polarography of 4-Nitrophthalic Acid

The–NO₂ group reduction in 4-nitrophthalic acid (NPA) at dropping mercury electrode over a wide range of _PH, is irreversible and diffusion controlled. Ill defined waves preceded the —NO₂ group wave, were observed between _PH 7 and 12 whereas at _PH 5.0, a rounded maximum appears. The a. c. reduction of NPA at _PH 12.0, provides two peaks, first peak corresponds to d. c. pre-step, is essentially due to adsorption phenomena whereas other peak is the reduction wave. Using McBain Down cell and King-cathcart equation the diffusion coefficient of NPA is 0.713×10^-3 cm²sec^-1. Six electrons are being involved in nitro group reduction and mechanism of the reduction was suggested. The kinetic parameters in absence and presence of ionic and non-ionic surfactants were determined. The reduction process becomes more and more irreversible as surface activity of organic compounds increases. Ionic surfactants are effective in increasing the value of —log K° than the non-ionic surfactants. The value of ana decreases regularly by the presence of compounds having regular increase of surface activity.     

克拉霉素的电化学反应机理研究与应用

应用线性扫描伏安法、循环伏安法、常规脉冲伏安法等电化学手段并结合紫外吸收光谱研究了药物克拉霉素(clarithromycin, CAM)在pH 1.8～9.2 Britton-Robinson缓冲溶液和0.05 mol•L^－1 NaOH溶液中的电化学行为. 在所研究的pH范围, CAM分别产生P₁, P₂, P₃, P₄四个还原波, 其中P₁, P₂, P₄三个波均为其药效活性基团C-9位羰基的还原所产生. 实验结果表明: 在pH 1.8～5.7的B-R缓冲溶液条件下所获得的P₁波为两电子不可逆弱吸附还原波; 在6.0＜pH＜9.2的B-R缓冲溶液中, CAM产生P₂和P₃两个波, 其中P₂为两电子不可逆还原波, P₃为催化氢波. 在0.05 mol• L^－1 NaOH溶液中, CAM产生的P₄波是一个单电子的不可逆吸附还原波. 根据P₄波的峰电流i_P与CAM浓度的线性关系, 建立了CAM含量测定的新方法.     

Solitonic waves in polyene dications and principles of charge carrier localization in π‐conjugated organic materials

The quantum‐chemical investigations by ab initio method (restricted Hartree–Fock/6‐31G**) have been performed for a series of unsubstituted, monosubstituted, and disubstituted neutral polyenes and their double charged cations. The waves of charge alternation (characterized by the difference in the electron densities at the nearest carbon atoms or Δq function) and bond length alternation (characterized by the lengths difference of the nearest carbon–carbon bonds or Δl function) are reported. Comparisons are made with the corresponding monocationic polymethine molecules. We found that ionization by two electrons results in formation of two solitonic waves of charge alternation, rather than superposition of two overlapping solitonic waves into one. These waves behave similar to two independent elastic particles, which do not penetrate into each other despite the special confinement by the length of chromophore π‐system. In monosubstituted polyene dication, Δq and Δl functions contain two waves each; however, only one wave is mobile and sensitive to a change of the chemical nature of the terminal group, whereas the second wave remains practically unchanged. The introduction of one oxymethyl or phenyl terminal groups leads to a relatively small shift of the mobile wave from the center to a direction of the terminal group. The effect of the amino or tropilium terminal groups is much more pronounced and leads to a shift of the mobile wave to the end of the molecule. In disubstituted polyene dication, both solitonic waves become mobile and shift symmetrically to both ends. The general principles of the charge localization described in this study may be used in molecular design and fine‐tuning of the charge transport properties in plastic photovoltaics and other organic semiconducting materials. © 2012 Wiley Periodicals, Inc.     

The Polarographic Behaviour of Bromate Ions in Buffered and Unbuffered Solutions and the Effect of Surface Active Substances

The polarographic behaviour of bromate ions in buffered and unbuffered solutions has been studied in the absence and presence of cationic, anionic and nonionic surfactants. The mechanism for the reduction in acid media is discussed. The adsorption effects of electrochemically inactive surfactants on the polarographic waves of BrO₃^? has been investigated. The values of the kinetic parameters for the electrode reaction at different pH values have been computed.     

Electrochemical reduction of secnidazole and its determination in tablets

The electrochemical reduction of secnidazole has been carried out in aqueous solution in the pH range of 2.0–12.0 by DC polarography, AC polarography and cyclic voltammetry. Two well-defined reduction waves appear in acidic media, whereas at higher pHs the two waves overlap. The variation of E_1/2 or E_p and I_lim or I_p with pH was studied. The diffusion-controlled nature of the waves was established and the irreversibility of the electrode process was verified by different criteria. The mechanism of reduction was discussed. A method for the detemination of secnidazole by DC polarography at pH 8.5 which allows quantitation over the 1 × 10⁻⁵ M-4 × 10⁻⁴ M range was proposed and applied to the determination of secnidazole in tablets. The mean recovery was 99.67% and the relative standard deviation was 0.89%. Excipients did not interfere in the determination.     

Electrode Kinetics and Activation Energy of Uranyl-Ferron Chelate by Polarography

The uranyl chelate of ferron was investigated polarographically over the pH range 1.98–10.00 and ligand concentration 0.005–0.060.M. A reversible and diffusion controlled reduction wave was obtained, however, when ferron concentration below 0.02M and pH below 5.0, it became irreversible. The chelate species identified were UO₂(HA) ₂ at pH range 2.5–7.1 and UO₂(OH) (A) ₂^?3 over pH 7.1. The electron-transfer coefficient, rate constant, diffusion coefficient and activation energy of the reduction process were determined.     

Electrochemical reduction of 4-thienylquinazoline in dimethylformamide

Electrochemical reduction of 4-thienylquinazoline (4-TQ) at the dropping mercury electrode in dimethylformamide solutions containing 0.1 M tetrabutyl ammonium iodide supporting electrolyte gave two well-defined diffusion-controlled waves. The first wave was found to be quasi-reversible and the second irreversible, on the basis of the usual criteria. The controlled potential electrolysis experiments carried out at the limiting regions of the frist and the total waves of 4-TQ yielded the same number of electrons, namely two, in both cases. Mechanisms corresponding to the total wave and the first wave were proposed based on the results obtained.     

Quinaldic Acid Complexes with Some Trivalent Rare Earth Metals

The Polarographic behaviour of quinaldic acid in the presence of lanthanide cations (Kd³⁺, Gd³⁺, Er³⁺) is studied at pH=4.5 and 0.1 M HClO₄ as supporting electrolyte. The polarographic reduction gives two waves at lower concentrations of quinaldic acid and three waves at higher concentrations. The nature of the waves was investigated. The dissociation constant of quinaldic acid as well as the stability constants of some lanthanide cation complexes with quinaldic acid were determined potentiometrically in 75% (v/v) dioxane-water at 25°C and 0.1 M KNO₃. The solid complexes of Nd, Gd and Er were isolated and studied by ir, differential thermal analysis (DTA) and thermogravimetric analysis (TGA) techniques.     

The Effect of an Electric Field on Reaction Fronts in Autocatalytic Systems

The effects of applying a constant electric field E to an ionic autocatalytic reaction with a general power p (p≥1) are discussed through a consideration of the equations for the corresponding travelling waves. It is shown that, when the ratio of diffusion coefficients D of autocatalyst and substrate is less than some value D₀ (which depends on p), the effect of a negative electric field is to increase the wave speed of the reaction front over its field-free value. This is in contrast to previous results for cubic autocatalysis (p=2) [J.H. Merkin and H. Ševčíková. J. Math. Chem. 25 (1999) 111.] for D>D₀, where the effect is to decrease the wave speed. This feature, seen in the numerical solutions of the travelling wave equations, is confirmed by an expansion for small E and in an asymptotic analysis for p large     

pH effects on the reduction of bilirubin in aqueous media

The electrochemical reduction of bilirubin at the mercury electrode was studied in aqueous media embracing an extended pH range; a variety of electrochemical techniques was used. Reduction in neutral solution results in three waves—the first a reversible adsorption prewave, followed by a pH dependent, reversible, two electron wave and finally by a one electron irreversible wave. In basic solution, only two waves are discernable: the reversible adsorption prewave, followed by a three electron wave resulting from the coalescence of the second and third waves seen in neutral solution. Familiarity with the detailed electrochemistry of bilirubin reduction provides the prerequisite basis for developing a sensitive analytical method for its determination.     

Electrode Kinetics of Lead in N-(3-Aminopropyl)-Diethanolamine Solution at the Dropping Mercury Electrode

The lead complex of N-(3-Aminopropyl)-Diethanolamine (APDEA) was investigated polarographically over the pH range 10.40-12-85 and ligand concentration 0.0227-1.002M. A quasi-reversible and diffusion-controlled reduction wave was obtained at pH≥10.40. The electron-transfer coefficient and rate constants were determined as 0.11-0.34 and 10^?4 cmsec^?1, respectively.     

Polarographic Behaviour and Determination of Stability Constants of Uranyl-Ascorbate Complex

The complex species of UO₂(HA)(H₂A)⁺ and UO₂(HA)₂ were identified in the ascorbic acid solution of uranyl ion at pH<2.1 and pH>2.1, respectively. Polarographic wave was proved to be the simultaneous reduction of UO₂⁺² and UO₂(HA)(H₂A)⁺ at pH <2.1. However, at pH>2.1, the wave is due to the reduction of U0₂(HA)₂ The stability constants of the two complex species were found to be 5.1×10⁺ and 1.0×10⁵, respectively. The hydrolysis constant of uranyl ion in the solution of ascorbic acid was determined.     

白杨素在汞电极上的电化学行为及其消除超氧阴离子自由基能力研究

The electrochemical behavior of chrysin in pH 2.0-9.0 Britton-Robinson （B-R） buffer solutions was studied by the means of linear sweep voltammetry and cyclic voltammetry at a static mercury drop electrode. In different pH range of B-R buffer solutions, chrysin could cause four reduction waves. In pH 2.0-5.8 B-R buffer solutions, wave P1 yielded by chrysin is a one-electron reduction wave, and wave P1 caused by further reduction of the products of wave P1 in pH〈3.0 B-R buffer solution is also a one-electron reduction wave. But in 3.0〈pH〈5.8 B-R buffer solution wave P1 was overlapped by the hydrogen wave. Between pH 5.8 and 9.0, chrysin could yield two reduction waves P2 and P3- The former is an irreversible adsorptive wave of ionized chrysin involving one electron and the latter is also an irreversible adsorptive wave of reduction intermediate radical of chrysin involving one electron and one proton. And a linear relationship between ip3 and the concentration of chrysin can be established from 1.0×10^-6 to 4.0×10^-5 mol·L^-1 （r=0.9924） with the detection limit of 5×10^-7 mol·L^-1. In addition, the antioxidant ability of chrysin was investigated by linear sweep voltammetry （LSV）. The determination result of IC50 of chrysin showed that chrysin is a good antioxidant.     

Effects of proton donors on the electrochemical reduction of benzo[c]cinnoline in acetonitrile

The polarographic behaviour of benzo[c]cinnoline in acetonitrile in the presence of various proton donors (water, phenol, benzoic acid and perchloric acid) is reported. In aprotic medium benzo[c]cinnoline is reduced in two one-electron waves, followed by one two-electron wave. The most probable final reduction product is 2,2′-diaminobiphenyl. The addition of proton donors causes a shift and/or appearance of new polarographic waves, which can be related to the reduction of various protonated species.     

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.     

Effect of the leaving group on the electrodic reduction mechanism of anti-Helicobacter pylori metronidazole derivatives, in aprotic and protic media

Because redox properties are central to bioreductive drug activity and selectivity, six 2-methyl-5-nitroimidazole, substituted at the N1-ethyl side chain with I, Br, Cl, OAc, OMs and NH(3)(+) were synthesized and submitted to cyclic voltammetry and electrolyses, in order to define their electrodic reduction mechanism, in aprotic [dimethylsulphoxide (DMSO)+0.1 mol l(-1) tetrabuthylammonium perchlorate (TBAP)] and phosphate-buffered media, on glassy carbon electrode, in comparison with metronidazole. Three of these compounds, namely, the iodo, bromo and ammonium salt derivatives showed significant anti-Helicobacter pylori (strain resistant to metronidazole) activity. All the cyclic voltammograms (CV), in aprotic medium, are similar to the one for metronidazole, except for -I, -Br and -NH(3)(+) derivatives. The CV of the N1-ethylhalide (-I, -Br) 5-nitroimidazole showed more intense and irreversible first waves, even at faster sweep rates (nu<2 V s(-1)). The absence of the first wave anodic counterpart, along with analysis of the dependence of E(p), I(p) and other parameters with nu, and results from electrolysis (consumption of two electrons) showed the process to be an ECE system, with halide release, after uptake of two electrons. This behaviour represents a case of dissociative electron transfer (ET). For the ammonium salt, self-protonation mechanism was evident. The facility of reduction represented by the first wave potential and concerning the substituents is NH(3)(+)>Br>I>Cl>OMs>OH>OAc. In aqueous phosphate-buffered medium, the electrochemical behaviour of all the compounds is similar to the one of metronidazole, represented by a unique and irreversible 4e(-)/4H(+) wave. The order of reduction ease is NH(3)(+)>Br approximately OMs>I>OH>OAc. Aprotic medium allows a better discrimination between the substituents. Concerning biological activity, despite the impossibility of establishing a correlation, it has been observed that the more electrophilic compounds showed better anti-H. pylori activity.