Cigarette smoke is suspected to cause diverse illnesses in smokers and people breathing second- and third-hand smoke. Although diﬀerent studies have been done to elucidate the impact on health due to smoking, there is a lack of kinetic information regarding the degradation of nicotine under diﬀerent environmental conditions. As a consequence, currently it is not possible to determine thoroughly the risk due to exposure to nicotine and the compounds derived from its decomposition.
With the aim of contributing to clarify the diﬀerent degradation paths followed by nicotine during and after the consumption of cigarettes, this work presents a theoretical study of the hydrogen atom abstraction reaction by hydroxyl radical at four sites in the nicotine molecule in a broad range of temperature, speciﬁcally be-tween 200-3000 K. The site-speciﬁc kinetic rate constants were computed by means of the multi-structural torsional variational transition state theory with small curvature tunneling contribution, performing ab initio calculations at the level M06-2X/aug-cc-pVQZ//M06-2X/cc-pVTZ.
According to our computations, the dependence on temperature of the studied rate constants exhibited a non-Arrhenius fashion, with a minimum at 873 K. A negative temperature dependence was observed at temperatures lower than 873 K, indicating more prolonged exposure to nicotine in warmer environments. On the other hand, the opposite behavior was observed at higher temperatures; this non-Arrhenius be-havior results of interest in tobacco cigarette combustion, inducing diﬀerent reaction mechanisms depending on the burning conditions of the diﬀerent smoking devices.
The results indicate that multi-structural and torsional anharmonicity is an im-portant factor in the computation of accurate rate constants, especially at high tem-peratures where the higher-energy conformers of the diﬀerent species exert a larger inﬂuence. The anharmonicity factors suggest that disregarding the anharmonic de-viations leads to overestimation of the rate constant coeﬃcients, by a factor between four and six. Our computed overall kinetic rate constant at 298 K exhibited very good agreement with the only experimental value meausred by Borduas et al. , af-fording certainty about our calculated site-speciﬁc rate constants, which are currently inaccessible to experiments. However, further experimental studies are necessary to validate our kinetic studies at other temperatures.
|Date of Award||Nov 2020|
|Original language||English (US)|
- Physical Science and Engineering
|Supervisor||Mani Sarathy (Supervisor)|
- Nicotine degradation
- Kinetic study
- Atmospheric oxidation