Nitrosobenzene: electrochemical, UV-visible and EPR spectroscopic studies on the nitrosobenzene free radical generation and its interaction with glutathione
Introduction
Nitroso compounds are among the most potent chemical carcinogens and are widely distributed in the environment. These compounds are also recognized as potentially reactive metabolites of a variety of toxicologically interesting compounds, which after covalent binding to proteins and DNA, become carcinogenic and/or mutagenic [1], [2].
Many nitroso compounds are reduced nonenzymatically by several endobiotic compounds, such as, NAD (P) H, glutathione, cysteine and hemoglobin with formation of free radical derivatives, as confirmed by their corresponding ESR spectra [3], [4]. On the other hand, several studies using electron spin resonance [5], [6], [7] have established the presence of radicals in chemical and electrochemical reduction of nitrosobenzene in aqueous and non-aqueous solvent systems.
Several studies [8], [9], [10] using cyclic voltammetry and EPR, have demonstrated that thiol compounds, such as glutathione significantly scavenged nitro radicals. However, the interaction between nitroso radical species and thiol compounds has not received an adequate attention up-to date.
In this paper, we examine the interaction between radical species generated from nitrosobenzene and glutathione. From these studies, the electrochemical generation of nitroso radical species from nitrosobenzene has been used. Cyclic voltammetry, UV-Visible and ESR spectroscopy were used to follow the interaction of radical species and glutathione.
Section snippets
Chemicals
Nitrosobenzene (NB), glutathione (GSH), anhydrous dimethylsulfoxide (DMSO), spectroscopic grade and anhydrous acetonitrile for UV spectroscopy were purchased from Merck. Solutions of NB were prepared in the different solvents, which were presaturated under a pure nitrogen stream. Tetrabutylammonium hexafluorophosphate (TBAHFP) was purchased from Aldrich.
Drug solutions
Stock solutions of 10 mM NB both in DMSO or acetonitrile were prepared and protected from daylight. Aliquots to obtain final concentrations
Results and discussion
The main goal of this paper was to assess the possible scavenging effect of the radical’s species from nitrosobenzene by glutathione. For this purpose electrochemical, UV-Visible and ESR spectroscopic techniques were used. Because the reduction mechanism is strongly affected by the solvent, studies were performed in two different solvents, i.e. DMSO and acetonitrile.
Concluding remarks
Our study provides experimental data that demonstrated the nitro radical anion electrochemical generated from nitrosobenzene is scavenged by GSH and could support the view that under hypoxic or anaerobic conditions, is not possible to discard the reactivity of this thiol molecule with this type of species and at least, partially could explain the significant loss of GSH under the above experimental conditions. On the other hand, the generated nitroso radical anion reacted with O2 (as was
Acknowledgements
This work was supported by Grants from FONDECYT (Project 8970023) and D.I.D. (U. de Chile). Also, the collaboration of CEPEDEQ is acknowledged.
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