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PubMed1999

Potential carcinogenicity of the synthetic 1,3,6-triazine (6-azapyrimidine) nucleic acid analogues determined by DC polarography. II. Nucleosides of 6-azauracil.

The polarographic reduction of six synthetic 1,3,6-triazine (6-aza) nucleosides with 6-azauracil as the nucleoside base in the strictly anhydrous solutions was studied in the absence and presence of alpha-lipoic acid. The values of the half-wave potentials E1/2 and the parameter of potential carcinogenicity tg alpha were compared for six nucleosides of 6-azauracil and two nucleosides of 4-thio-6-azauracil. The current value of the first diffuse polarographic wave or a new diffuse polarographic wave belonging to the nucleoside-alpha-lipoic acid complex increased with the increase of the alpha-lipoic acid concentration for the all compounds only marginally. Although this diffuse current increase was linear and dependent on the alpha-lipoic acid concentration in anhydrous solutions, the determined index tg alpha values ranged between 0.027 and 0.114. This is an indication of a very low potential carcinogenicity of the all nucleoside analogues investigated.

Azauridine↗
PubMedDate not supplied

Preconcentration of bismuth(III) and copper(II) by solid-phase extraction and subsequent determination by differential pulse polarography.

A differential pulse polarographic method is proposed for the trace determination of bismuth and copper from large volumes of aqueous samples after adsorption of their 1-(2-thiazolylazo)-2-naphthol complexes onto microcrystalline naphthalene in the pH ranges of 7.2-9.0 and 4.0-7.8, respectively. Bismuth and copper are desorbed from microcrystalline naphthalene with 9 mL 1M HCl. Well-defined peaks are obtained at Ep = -0.09 and -0.20 V versus a saturated calomel electrode, in an HCl-isoquinoline medium as the supporting electrolyte, for bismuth and copper, respectively. Bismuth is reduced reversibly with a 3-electron change, whereas copper is reduced irreversibly under these conditions. The detection limits are 55 ng/mL for bismuth and 91 ng/mL for copper. Linearity is maintained in the concentration ranges of 0.18-13.5 and 0.30-17.3 microg/mL for bismuth and copper, respectively, with corresponding correlation coefficients of 0.9996 and 0.9885. The relative standard deviations are 1.0% for bismuth at 2.0 microg/mL and 1.4% for copper at 5.0 microg/mL. Various parameters were optimized to develop conditions for the determination of these metal ions in various samples.

Adsorption↗
PubMedDate not supplied

Determination of nitrite in foods by single-sweep polarography.

In an acid medium, nitrite diazotized with p-rosaniline and then coupled with 8-hydroxyquinoline in a weak alkaline medium produces azo compounds. The azo compounds produce a very sensitive polarographic wave at -0.70 V (versus the saturated calomel electrode). The height of the peak is linear with the concentration of nitrite in the range of 5 x 10(-9) to 5 x 10(-7) g/mL. The detection limit is 3 x 10(-9) g/mL. The electrochemical characteristics of the polarographic wave are also discussed. The method was used to determine nitrite in sausage. The results agree well with those obtained by spectrophotometry.

Food Analysis↗
PubMed2002

Determination of atovaquone in tablets by differential pulse polarography.

A differential pulse polarographic method is presented for the determination of atovaquone in its pharmaceutical formulations. The polarographic behaviour of atovaquone was examined in various buffer systems over the pH range 3.0-10.0. In Britton Robinson buffer/methanol solution (1:1; v/v; pH 8.5) the differential pulse polarograms exhibited reproducible peaks at Ep--0.43 V vs. silver/silver chloride/potassium chloride (3M). Under these conditions, strict linearity between atovaquone concentration and peak height was observed in the 2.7 x 10(-6)-3.5 x 10(-5) M concentration range. The detection limit was calculated to be 0.41 microgram/ml. The polarographic method was applied to the determination of the content of atovaquone in various pharmaceutical preparations. For the polarographic analysis of atovaquone in Wellvone and Malarone tablets no separation step was necessary. In order to evaluate the concentration of atovaquone, the standard addition method was applied. The analysis of Wellvone tablets led to a mean value of 250.4 mg with a relative standard deviation (Srel) of +/- 2.1% and of Malarone tablets 252.3 mg with a Srel of +/- 2.4%.

Antimalarials↗
PubMed2003

Comparison of the carcinogenic potential of streptozotocin by polarography and alkaline elution.

The carcinogenic potential of streptozotocin (STZ) was evaluated by the polarographic determination of its reduction potential in the presence of alpha-lipoic acid and detection of DNA single-strand brakes by alkaline elution. After STZ electrochemical reduction in an anhydrous solvent, the half-wave potential (E1/2 ) was determined to be -1.340 V. The parameter of the carcinogenic potential (tg alpha) for STZ was 0.400. This is in good agreement with WHO data regarding STZ carcinogenicity. Additionally, it is in the good agreement with the tg alpha value determined for the positive control used, N-nitroso-N-methylurea (NMU), which was found to be 0.459. The 3 hours exposure of A549 human lung tumor cells to 250, 500, and 1000 nmol/ml STZ was followed by DNA single-strand brakes detection using the alkaline elution method. NMU, the positive control, was tested under identical experimental conditions at the same concentrations. Without metabolic activation, NMU induced a significant formation of DNA single-strand brakes only at 1000 nmol/ml. In the presence of the metabolic activation, NMU caused a significant, concentration-dependent formation of DNA single-strand brakes. In the absence of metabolic activation, STZ induced no significant formation of DNA single-strand brakes at any concentration used. In the presence of metabolic activation, STZ caused a significant, concentration-dependent formation of DNA single-strand brakes. The results of this study underline the crucial role of using a metabolic activation system when carcinogenic potential of drugs and chemicals is investigated in vitro studies. Results of polarographic experiments and alkaline elution correlate well with each other and they indicate that these methods are useful to early predict the carcinogenic potential of STZ and other xenobiotics.

Carcinogens↗