Early Chemistry of Nicotine Degradation in Heat-Not-Burn Smoking Devices and Conventional Cigarettes: Implications for Users and Second- and Third-Hand Smokers

Abstract
Nicotine exposure results in health risks not only for smokers but also for second- and third-hand smokers. Unraveling nicotine's degradation mechanism and the harmful chemicals that are produced under different conditions is vital to assess exposure risks. We performed a theoretical study to describe the early chemistry of nicotine degradation by investigating two important reactions that nicotine can undergo: hydrogen abstraction by hydroxyl radicals and unimolecular dissociation. The former contributes to the control of the degradation mechanism below 800 K due to a non-Arrhenius kinetics, which implies an enhancement of reactivity as temperature decreases. The latter becomes important at higher temperatures due to its larger activation energy. This change in the degradation mechanism is expected to affect the composition of vapors inhaled by smokers and room occupants. Conventional cigarettes, which operate at temperatures higher than 1000 K, are more prone to yield harmful pyridinyl radicals via nicotine dissociation, while nicotine in electronic cigarettes and vaporizers, with operating temperatures below 600 K, will be more likely degraded by hydroxyl radicals, resulting in a vapor with a different composition. Although low-temperature nicotine delivery devices have been claimed to be less harmful due to their nonburning operating conditions, the non-Arrhenius kinetics that we observed for the degradation mechanism below 873 K suggests that nicotine degradation may be more rapidly initiated as temperature is reduced, indicating that these devices may be more harmful than it is commonly assumed.

Citation
Chavarrio Cañas, J. E., Monge-Palacios, M., Grajales-González, E., & Sarathy, S. M. (2021). Early Chemistry of Nicotine Degradation in Heat-Not-Burn Smoking Devices and Conventional Cigarettes: Implications for Users and Second- and Third-Hand Smokers. The Journal of Physical Chemistry A. doi:10.1021/acs.jpca.1c01650

Acknowledgements
The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST).
We express thanks for the resources of the Supercomputing Laboratory at KAUST. We are grateful to Marcus Hanwell, Chris Harris, and Alessandro Genova for kindly releasing their Open Chemistry Python package and open source scripts to build our molecular structures.

Publisher
American Chemical Society (ACS)

Journal
The Journal of Physical Chemistry A

DOI
10.1021/acs.jpca.1c01650

PubMed ID
33834773

Additional Links
https://pubs.acs.org/doi/10.1021/acs.jpca.1c01650

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