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

Javier E Chavarrio Cañas,S Mani Sarathy,E Grajales-González,M Monge-Palacios

doi:10.1021/acs.jpca.1c01650

Javier E Chavarrio Cañas, S Mani Sarathy + Show 2 more

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https://doi.org/10.1021/acs.jpca.1c01650

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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.

Highlights

IntroductionCigarette smoke causes more than 8 million of fatalities per year worldwide, with ∼86% of deaths owing to direct use of tobacco and the remaining to exposure to second-hand smoke (inhalation in the presence of a smoker) and third-hand smoke (inhalation close to surfaces previously exposed to cigarette smoke).[1,2] Tobacco smoke is a complex matrix of more than 3800 harmful species such as free radicals, heavy metals,[3] and organic compounds.[4] The effect of free radicals and toxic chemicals over health has been documented, attributing them an active role in development and progression of multiple ailments including cardiovascular and pulmonary disorders, asthma, and cancer.[5] People continue smoking tobacco due to addiction to nicotine,[6] which is the predominant alkaloid in tobacco leaves.[5,7]
Cigarette smoke causes more than 8 million of fatalities per year worldwide, with ∼86% of deaths owing to direct use of tobacco and the remaining to exposure to second-hand smoke and third-hand smoke.[1,2] Tobacco smoke is a complex matrix of more than 3800 harmful species such as free radicals, heavy metals,[3] and organic compounds.[4]
We found eight distinguishable conformers for nicotine by rotating the dihedrals C1-C2-C6-N2 and N2-C6-C7-C8, which are the pseudorotation within the pyrrolidine ring responsible for its envelope conformation,[53,54] and by changing the orientation of the methyl group bonded to the atom N2, which may display axial or equatorial orientation

Summary

Introduction

Cigarette smoke causes more than 8 million of fatalities per year worldwide, with ∼86% of deaths owing to direct use of tobacco and the remaining to exposure to second-hand smoke (inhalation in the presence of a smoker) and third-hand smoke (inhalation close to surfaces previously exposed to cigarette smoke).[1,2] Tobacco smoke is a complex matrix of more than 3800 harmful species such as free radicals, heavy metals,[3] and organic compounds.[4] The effect of free radicals and toxic chemicals over health has been documented, attributing them an active role in development and progression of multiple ailments including cardiovascular and pulmonary disorders, asthma, and cancer.[5] People continue smoking tobacco due to addiction to nicotine,[6] which is the predominant alkaloid in tobacco leaves.[5,7]. Nicotine reacts with indoor oxidants either in the gas phase or on surfaces, producing more toxic and carcinogenic compounds such as nitrosamines.[12,13] Undoubtedly, nicotine compromises the health of smokers and that of second- and third-hand smokers even once the cigarette is extinguished

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