Naslov
Oxidation of ascorbic acid and compounds containing sulfur (RSH) with iron(III) phenanthroline complex: thermodinamic approach and kinetic experiment

Autori
Radić, Njegomir ; Martinović, Anita

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
1st European Chemistry Congress / Naray-Szabo, Gabor - Budimpešta : European Association for Chemical and Molecular Sciences, 2006

Skup
1st European Chemistry Congress

Mjesto i datum
Budimpešta, Mađarska, 27.08.2006. - 31.08.2006

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Kinetic spectrophotometric experiment; Thiols; Ascorbic acid

Sažetak
Compounds containing sulfur, RSH, (N-Acetyl-L-Cysteine, NAC ; Cysteine, cys ; Penicillamine, pen ; Glutathione, glu), and Ascorbic acid (AA) are important cellular antioxidant and detoxicant. They are the cells premier resource for protection against damaging molecules commonly called “ free radicals” . Thiols (RSH) are also chelating agents, which are used to aid the elimination of excess heavy metal ions. The cumulative damaging effects of “ free radicals” and heavy metal ions are contributors to degenerative diseases and to the progressive aging. Therefore, many pharmaceutical and cosmetic preparations contain thiols and AA. Many analytical methods for RSH and AA determination are based on oxidation of these compounds with Fe(III) in the presence of phenantroline. For analytical purpose equilibrium constants of these redox reactions are important parameter. Although knowing the equilibrium constant is very valuable the determination of the constant is often difficult. However, if the formal reduction potential for each couple in the proposed redox reaction can be calculated, we are able to determine the equilibrium constant. The formal reduction potential for Fe(III)-phenantroline complex, RSH compounds and AA have been calculated for the large pH range. In acidic solution (pH: 0-5) the calculated reduction potential for Fe(III)-phenantroline/Fe(II)-phenantroline couple was much more positive then for Fe(III)/Fe(II) couple. When pH of reaction solution decreases the formal reduction potentials of RSH and AA becomes larger and reduction activity of these compounds decreases. Calculated values indicate that cys and glu are stronger reductant then AA. Also, the calculated equilibrium constants for redox reaction when cys or glu are examined as reductant were higher then equilibrium constant for redox reaction between Fe(III)-phenantroline complex and AA. According to this, one can conclude that analytical signal, absorbance in spectrophotometric experiment, obtained for RSH compounds would be larger then for AA. In the kinetic spectrophotometric experiment rectilinear calibration graph was obtained by plotting absorbance versus concentration in the AA concentration range from 4.0 x 10-6 to 4.0 x 10-5 M. In the proposed kinetic experiment, at a same experimental condition, the recorded absorbance for AA was higher then for cys and glu. The entire redox process and formation of colored Fe(II)-phenantroline complex for AA was faster then for cys. In addition, in the time of proposed kinetic spectrophotometric experiment (15 min) glu, up to concentration 8 x 10-5 M, do not produce measured quantity of colored complex.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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