Polarographic investigations of 7-methylguanosine

The mechanism of reduction of 7-methylguanosine (7-MeGuo) in buffered solution was studied by electrochemical methods. The polarographic reduction involves complex processes due to the presence of maxima (maximum of the first kind and maximum of catalytic reduction of protons). Consequently other techniques are required such as u.v. and n.m.r. spectroscopies, and chromatography for the identification of the reduction product.A mechanism of reduction is suggested in acid medium, the reduction saturates the imidazolium ring by fixation of two electrons and one proton.     

Polarographic investigations of some copper chelates of 3-arylazopentane-2,4-diones

The polarographic curves of the copper chelates of twelve substituted 3-arylazopentane-2, 4-diones exhibit single 4e diffusion-controlled irreversible waves between pH 2 and 11. The two azo groups in the compound are equivalent so that only a single 4e wave is obtained; no copper reduction wave is observed. The polarographic behaviour differs from that of p-bisazobenzene. There is a linear correlation between the E$\text{1}\text{2}$ values and the Hammett substituent constants.     

Polarographic and voltammetric investigations of new catalytic systems of iron for application in trace analysis

New catalytic systems consisting of complexes of Fe(III)-ions with ligands such as nitrilotriacetic acid, N-(2-hydroxyethyl)iminodiacetic acid, N,N-bis(2-hydroxyethyl)glycine, triisopropanolamine, 2-hydroxy-1,3-diaminopropanetetraacetic acid, tris-(hydroxymethyl)aminomethane, bis-(2-hydroxymethyl) iminotris-(hydroxymethyl)methane, 1,3-bis/tris(hydroxymethyl)methylamino/propane in ammonia buffer and 1,2-dihydroxybenzene in tris-(hydroxymethyl) amino-methane-HCl buffer and ClO^-₂-ions as the oxidizing agent were studied by pulse polarography and voltammetry. Optimal conditions such as kind and concentration of the ligand, the composition of supporting electrolyte and concentration of NaClO₂ for the determination of traces of iron in the presence of a large excess of other electrochemically active ions were examined. Examples of acceleration and inhibition of catalytic reactions between Fe(II)L and ClO^-₂-ions by electrochemically inactive ions have been found.     

Polarographic and voltammetric investigations in N-methylpyrrolidinone(2) and N-methylthiopyrrolidinone(2)

Polarographic and voltammetric methods were employed to study the influence of N-methylpyrrolidinone(2) (NMP) and N-methylthiopyrrolidinone(2) (NMTP) towards a series of cations. In NMP reversible electrode reactions were observed for Na⁺, K⁺, Tl⁺, Zn²⁺, Cd²⁺, Cu²⁺, Ag⁺ and irreversible reductions for Ba²⁺, Mn²⁺, Co²⁺ and Ni²⁺. 0.1 mol l^?1 tetraethylammoniumperchlorate solutions served as supporting electrolytes. Li⁺ was not electroactive in the supporting electrolyte mentioned, but yielded an irreversible cathodic wave in tetra-n-butylammonium perchlorate. In NMTP, Li⁺, Na⁺, Tl⁺, Zn²⁺, Cd²⁺, Cu⁺ and Ag⁺ gave reversible cathodic waves on the DME, while Mn²⁺, Co²⁺ and Ni²⁺ were reduced in an irreversible electrode process. Bisbiphenylchromium iodide serving as a reference system throughout this study showed reversible behaviour in both solvents. A comparison of E_1/2 for given ions in both solvents showed a shift of about 0.5 V to more positive values in the case of a typically hard cation such as Na⁺ whereas soft cations such as Ag⁺ and Cu⁺ shifted by more than 0.8 V to more negative values. The effects of these two solvents on the cations studied is discussed in terms of donor acceptor interactions between the cation and the solvent molecules with special respect to the changes caused by replacing the oxygen atom in NMP by a sulphur atom.     

Polarographic determination of semicarbazones

Acetone, methyl isobutyl ketone, acetaldehyde, formaldehyde, cyclohexanone, butyraldehyde, crotonaldehyde, and acrolein semicarbazones all give polarographic waves suitable for quantitative analysis in an acetate buffer at pH 4.6 .The half-wave potentials are —1.3, —1.3, —1.16 —1.05, —1.2,—1.11, —1.06,–0.99 V vs. S.C.E., respectively, for the compounds listed above. The diffusion current constants of these compounds average approximately 7 in the concentration range of 10^-2 to 10^-1 mM, giving an extremely sensitive method of carbonyl compound analysis. A supporting electrolyte that is 0.1M each in acetic acid, sodium acetate, sodium chloride, and semicarbazide, and 0.0016% in Triton X-100, is satisfactory both for polarograph analysis and for the quantitative absorption of acetone, acetaldehyde, cyclohexanone, and crotonaldehyde from air samples by means of a scrubber.     

Polarographic reduction of germanium

In a previous note the authors had reported the polarographic reduction of ravalent germanium. These observations were confirmed, and full data are presented here which show the two-step reduction of tetravalent germanium under the dropping mercury electrode, from ammoniacal-ammonium chloride solutions.     

Polarographic determination of nitramide

Nitramide gives two cathodic polarographic waves with half-wave potentials varying with pH, and having minimum values − 1·22 V at pH 4·5 and − 1·58 V at pH 8·8. Nitramide is fist reduced to nitrosamine in a two-electron reduction. In the second step, hydroxy-hydrazine may be formed in a two-electron reduction, or hydrazine itself in a four-electron step. For the polarographic determination of nitramide the first wave is used, and the supporting electrolyte is a Britton—Robinson buffer 0·1 M in KCl, at pH < 5 and at 0–2°.     

Polarographic determination of pirimicarb

A sensitive and selective polarographic method for the determination of pirimicarb is proposed. Linear calibration graphs were obtained by differential-pulse polarography in the 3.0 × 10^?7–9.0 × 10^?5 mol l^?1 range, the limit of determination being 2.8 × 10^?7 mol l^?1. No interferences were observed from other carbamate pesticides such as aminocarb, bendiocarb or carbaryl and only a matrix effect occurs in the presence of methiocarb. The method was applied to the determination of Pirimicarb in water samples with good recoveries.     

Polarographic determination of thiabendazole

Summary Polarographic Determination of Thiabendazole Thiabendazole is used as a fungistat on citrus fruit to protect it from decay.In order to work out a polarographic determination the electrochemical behaviour of thiabendazole was investigated by sampledd c polarography and differential pulse polarography. Thiabendazole shows one wave or peak in the polarogram, when a short drop time (0.4 s) is used. Detection is most sensitive at pH 8. The current measured is proportional to the concentration. The detection limit is 0.5 ppm.By evaluating further experimental data it was possible to conclude, that mercury is first oxidised. Thereby two electrons are exchanged. Then mercury(II) ions formed in this way react with two molecules thiabendazole. Two protons are involved in this chemical process.Applying drop times greater than 0.4 s and concentrations higher than 1.5·10^–4 M a polarogram with two peaks is formed. This is due to the adsorption of the reaction product.For quantitative determination several citrus fruits were peeled and the peels were extracted with ethylacetate. After removing interfering substances by shaking with sodium hydroxide solution, thiabendazole was extracted by diluted hydrochloric acid and quantitatively determined by differential pulse polarography. The recovery of thiabendazole is 70.0% with a relative standard deviation of 2.9%. For all samples investigated the thiabendazole concentrations were below the permitted value.Cordially dedicated to Univ.-Prof. Dr. Dr. h. c. K. Kratzl on the occasion of his 70th birthday.     

Polarographic oxidation of triarylimidazoles

Ten series of triarylimidazoles were subjected to polarographic oxidation. It was found that electron-donor substituents facilitate polarographic oxidation, while electron-acceptor substituents hinder it. Correlation equations in coordinates of E_1/2 and ⁺ were found for all of the investigated series.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 387–390, March, 1973.The synthesis and characteristics of the investigated imidazoles were described in [7–10].     

Polarographic behaviour of phenothiazine

Summary Phenothiazine oxidizes at the dropping mercury electrode in waterethanolic solutions, containing 7 N sulphuric acid, giving a wave corresponding to the formation of free cation radicals.The normal potential of the system phenothiazine/radical, against the reference electrode formed from mercuric sulphate in the presence of 10 N H₂SO₄ and 30% ethanol, is –240±20 mV.In alkaline solutions of pH 12.5 phenothiazine also gives a polarographic wave. This wave corresponds to the insoluble anions of compounds formed with mercury. The conditions for the quantitative polarographic determination of phenothiazine are also given.

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Zusammenfassung Es wurde bewiesen, daß in äthanolisch-wäßrigen Lösungen, die 7 n H₂SO₄ enthalten, Phenothiazin an der Quecksilber-Tropfelektrode oxydiert wird. Als Reaktionsprodukt entsteht ein freies Kation-Radikal. Das Normalpotential des Systems Phenothiazin/Radikal gegen die gesättigte Quecksilbersulfatelektrode, die 10 n H₂SO₄ und 30% C₂H₅OH enthält, beträgt –240 ± 20 mV.In alkalischen Lösungen bei pH 12,5 konnte man eine polarographische Welle registrieren, deren Eigenschaften schwerlöslichen Anionen einer Quecksilberverbindung entsprechen.Die Bedingungen für eine quantitative polarographische Phenothiazinbestimmung werden angegeben.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.     

Polarographic determination of deltamethrin

The electrochemical characteristics of deltamethrin have been determined by means of electrochemical techniques such as d.c. polarography, cyclic voltammetry and differential pulse polarography over a wide range of pH from 2.0-12.0. The title compound exhibits a single well defined peak due to the reduction of the CC moiety present in deltamethrin. The overall reduction process is diffusion-controlled and adsorption free in nature. The variation of half-wave potential with the pH, concentration of the title compound, and other experimental conditions is described. A possible mechanism for the reduction is suggested. The number of electrons involved in the electrode reduction is two. Investigation was also undertaken for the determination of deltamethrin in vegetables and in storage bags of rice and wheat under FCI's storage system.