Formazans of the pyrimidine series

Karavaeva, E. S.; Bednyagina, N. P.; Sharkova, T. A.; Mudretsova, I. I.

doi:10.1007/bf00667624

Cited by 4 publications

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Section: Methodsmentioning

confidence: 99%

“…The working solutions of manganese of different concentrations (10 -2 to 10 -4 mg/mL) were prepared by diluting the solution of the Certified Reference Materials of Mn(II) (GSO 7266-96) containing 1 mg/mL manganese(II) with a 0.1 M HCl solution. The formazans used were synthesized using known procedures [15,16].Voltammetric measurements were carried out in a three-electrode cell with working, auxiliary (a glassy-ARTICLES Abstract -A mercury-free thick-film graphite-containing electrode modified with formazan is proposed for determining manganese(II) by cathodic stripping voltammetry. The detection limit for manganese(II) found with this electrode is 0.04 µ g/L at a preconcentration time of 60 s. The analytical signal from manganese(II) is a linear function of its concentration in the range 0.1 to 30 µ g/L.…”

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A thick-film graphite-containing electrode modified with formazan for determining manganese in natural and drinking waters by stripping voltammetry

Golovei

Tkach

2005

J Anal Chem

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Manganese is an essential element capable of activating many enzymes involved in the metabolism of humans, animals, and plants. Manganese enters living organisms from the environment, in which it is present mainly as hydrated Mn 2+ . The latter can be oxidized under aerobic conditions to give Mn 3+ or Mn 4+ , which form soluble and insoluble compounds. The concentration of manganese in natural water varies from 0.0001 to 1 mg/L and may attain 50 mg/L in contaminated water [1]. The maximum permissible concentration (MPCs) for manganese is 0.01 mg/L in fresh water and 0.05 mg/L in sea water [2].Spectrophotometry and atomic-absorption spectrometry are used for determining trace manganese(II) in environmental samples. These methods require the preconcentration of manganese, which complicates and prolongs analysis. Stripping voltammetry (SVA) is the most acceptable method for determining trace amounts of metals in natural waters, especially in on-site and online modes. Two versions of this method, one with an anodic sweep of potential (ASVA) [3][4][5], the other with an cathodic sweep of potential (CSVA) [5][6][7][8][9][10][11][12] are used for determining manganese(II). In the first version of SVA, stationary mercury and mercury-film electrodes are used, whereas the second version of SVA employs both mercury and carbon-containing electrodes (impregnated graphite, glassy-carbon, composite carbon-containing, or modified with polymeric film). The determination of manganese(II) by ASVA is associated with a number of problems that restrict its wide use. Among these are the high negative accumulation potential of manganese (-1.7 V), which lies in the region of hydrogen liberation; the low solubility of manganese in mercury; and the formation of intermetallic compounds at mercury electrodes. On the whole, these problems may result in random and systematic errors and deteriorate the sensitivity of analysis. CSVA offers greater promise, because it can be performed without mercury and eliminates the effect of dissolved oxygen and elements forming intermetallic compounds with manganese. Ligands forming complexes with manganese(II) are introduced into the supporting electrolyte or into the indicator electrode to reduce the detection limit for manganese and enhance the reversibility of its Red/Ox system [13,14]. Diphenylcarbazone has been found to be very promising. The detection limit for manganese(II) found with the use of this electrode modified with diphenylcarbazone was 5 × 10 − 9 M at an accumulation time of 600 s [14].In our opinion, continuation of the work devoted to the further investigation and use of a wider spectrum of formazans in the mercury-free voltammetric determination of metals is of particular scientific and practical interest. This work is dedicated to the development of a procedure for determining manganese(II) by CSVA using new mercury-free electrodes modified with formazans with the aim of lowering the detection limit for manganese and enhancing the rapidity of analysis. EXPERIMENTALThe reagents used were...

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

A thick-film graphite-containing electrode modified with formazan for determining manganese in natural and drinking waters by stripping voltammetry

Golovei

Tkach

2005

J Anal Chem

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“…The formazans used were synthesized using known procedures [15,16]. All solutions were prepared with triply distilled water.…”

Section: Methodsmentioning

confidence: 99%

A thick-film graphite-containing electrode modified with formazan for determining manganese in natural and drinking waters by stripping voltammetry

et al. 2005

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A mercury-free thick-film graphite-containing electrode modified with formazan is proposed for determining manganese(II) by cathodic stripping voltammetry. The detection limit for manganese(II) found with this electrode is 0.04 µ g/L at a preconcentration time of 60 s. The analytical signal from manganese(II) is a linear function of its concentration in the range 0.1 to 30 µ g/L. The results of determining manganese in natural and drinking waters are presented.

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“…1) and its derivatives [1] are water-insoluble azo compounds with a wide variety of applications in chemistry [2] and biology [3]. Preparation of formazan was done by various methods such as reduction of tetrazolium salts and coupling diazonium salts [4,5]. Interestingly, the reduction of nitrotetrazolium blue to formazan is one of the current test methods for the estimation of anti-and pro-oxidant activity of different compounds [6,7].…”

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DFT and MP2 study of isomery scheme in Formazan and intermolecular and intramolecular proton transfer between its tautomers

Tavakol

2011

Int J of Quantum Chemistry

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DFT and Moller Plesset (MP2) calculations were applied to study of isomery scheme in formazan. Formazan that can be presented by three tautomers and eight isomers has various applications in dyes, complexes, and biochemistry. The structures of its isomers and related transition states were optimized, and important molecular parameters, IR frequencies, and energetic results were extracted. The relative stabilities of formazan isomers in the gas phase were found to be as 1EZ >1ZZ >1EE >1ZE >2EE > 3 >2EZ >2ZZ >TS1 >TS3 >TS2. Thermodynamic data confirms that tautomer 1 is major tautomer, and all possible tautomerism interconversions have small rates at room temperature. Then, relative stabilities were calculated in different solvents (chloroform, tetrahydrofuran, acetone, and water). The relative stabilities and thermodynamic data in solvents are nearly similar to those in the gas phase, but the rate constants are slightly more than that in the gas phase. Moreover, relative stabilities of formazan isomers and intermolecular proton transfer in presence of one to three molecules of water have been studied. The results showed that activation barriers in water-assisted tautomerisms are in general lower than those in the gas phase, but the relative energies of isomers do not change importantly by water clusters.

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Formazans of the pyrimidine series

Cited by 4 publications

References 2 publications

A thick-film graphite-containing electrode modified with formazan for determining manganese in natural and drinking waters by stripping voltammetry

A thick-film graphite-containing electrode modified with formazan for determining manganese in natural and drinking waters by stripping voltammetry

A thick-film graphite-containing electrode modified with formazan for determining manganese in natural and drinking waters by stripping voltammetry

DFT and MP2 study of isomery scheme in Formazan and intermolecular and intramolecular proton transfer between its tautomers

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