Reactions of nicotine and the hydroxyl radical in the environment: Theoretical insights into the mechanism, kinetics and products

Abstract

Nicotine (NCT) is a prevalent and highly poisonous tobacco alkaloid found in wastewater discharge. Advanced oxidative processes (AOP) are radical interactions between harmful pollutants and ambient free radicals that, theoretically, result in less toxic compounds. For a better understanding of the chemical transformations and long-term environmental effects of toxic discharges, the study of these processes is crucial. Here, quantum chemical calculations are used to investigate the AOP of the NCT in aqueous and lipidic environments. It was found that NCT interacted with HO^• in polar and nonpolar media, with an overall rate constant k_overall = 10⁶ - 10¹⁰ M^-1 s^-1. The computed kinetic data are reasonably accurate as seen by the comparison with the experimental rate constant in water (pH = 7.0), which results in a k_calculated/k_experimetal ratio of 1.4. The hydrogen transfer (C7, C9, C12)-single electron transfer pathways are the main mechanisms for the HO^• + NCT reaction in pentyl ethanoate solvent to form the cations as the primary products of the two-step reaction. However, in aqueous environments, the degradation of NCT by HO^• radicals increases with increasing pH levels. It is predicted that oxidation products are less toxic than nicotine itself, especially in an aqueous environment with a pH < 7.0.

Keywords: Advanced oxidation processes; Chemical fate; DFT study; Nicotine; Structure-activity relationship.