Modified quantum mechanical approach for the estimation of single-electron reduction potential of nitroaromatic compounds in aqueous medium

Abstract

The midpoint single-electron reduction potential of nitroaromatic compounds in aqueous medium at pH 7.0 (potential of ArNO₂/ArNO₂·^– couple, E_m7) frequently determines their therapeutic and/or toxic properties. However, its estimation remains a complex problem. We propose a modified method of E_m7 estimation by quantum mechanical calculations, based on the use of the dielectric continuum model together with a certain number of H₂O molecules at the vicinity of nitro group. The optimal number of H₂O molecules corresponds to a minimal difference between the experimentally determined and calculated values of E_m7, and/or the most negative value of calculated E_m7. This enabled us to calculate the E_m7 values for a number of ArNO₂ (n = 19) with the average deviation of 0.027 V from the experimentally determined ones. Apart from nitrobenzene derivatives, the application of this approach for the representatives of nitropyridines, nitrofurans, nitrothiophenes, and nitrothiazoles was demonstrated. In this case, nitroimidazole derivatives are an exception, evidently due to a strong proton accepting properties of N3 atom of their free radicals.

Keywords:

• Nitroaromatic compounds
• redox reactions
• free radicals
• single-electron reduction
• redox potential

Acknowledgements

The authors are grateful to the Information Technology Research Center of Vilnius University for the use of supercomputer system, Dr. Jonas Šarlauskas (Institute of Biochemistry) for his generous gift of nitroaromatic compounds, and Dr. Mindaugas Lesanavičius for checking the stylistics of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the European Social Fund (Measure No. 09.33-LMT-K-712, Grant No. DOTSUT-43/09.3.3.-LMT-K71201-0058/LSS-600000-58).