Kinetic and molecular modeling of selected tobacco alkaloids in mainstream cigarette smoke

Abstract

Consensus of opinion in literature regarding tobacco use has shown that cigarette smoking can cause irreparable damage to the genetic material, cell injury, and the general respiratory landscape. The alkaloid family of tobacco has been implicated in a series of ailments including addiction, mental illnesses, psychological disorders, and mental deficits. Accordingly, this study describes the kinetic and molecular modelling of the major tobacc alkaloids in mainstream cigarette smoke; nicotine, β-nicotyrine, and 3,5-dimethyl-1- phenylpyrazole with the principal focus of understanding their energetics, their environmental fate, and the formation of intermediates considered harmful to tobacco users. Two commercial cigarette brands coded SM1 and ES1 were explored for the evolution of major tobacco alkaloids over a modest temperature range of 200 – 700 ℃ for a total pyrolysis time of 3 minutes using a tubular quartz reactor, typically in increments of 100 ℃ using nitrogen as the pyrolysis gas. The heating rate was ~ 20 ℃ s-1. The pyrolysate was analysed using a Gas-Chromatography hyphenated to a mass spectrometer (GC-MS) fitted with a mass selective detector (MSD). Analysis of pyrolysate using GC-MS showed that nicotine was the major alkaloid in both cigarettes, reaching a maximum at ~ 400 ℃ (8.0 x 108 GC-Area counts) for ES1 cigarette and about 2.7 x 108 GC-Area counts for SM1 cigarette (at 500 ℃). Moreover, β-nicotyrine and 3, 5-dimethyl-1-phenylpyrazole were also detected in significant amounts. Chemissian computational code was used to generate the electron density contour maps in order to determine the neucleophilicity of these alkaloids in relation to how they interact with biological molecules to cause toxicity and cell impairment. The density functional theory calculations were conducted with B3LYP correlation function and established that the scission of the phenyl C-C bond in nicotine and β-nicotyrine, and C-N phenyl bond in 3,5-dimethyl-1-phenylpyrazole were respectively 365.33, 507.37, and 494.24 kJmol-1. Clearly, the value of the bond dissociation energy is dependent on the π – π interactions which play a primary role in stabilizing the phenyl bonds. A kinetic model on the destruction of nicotine was proposed using pseudo-first order rate law and found that the rate constan KI for the destruction of nicotine at 673 K was 0.31s-1 and 0.74 s-1 for ES1 and SM1 cigarettes respectively. It was noted that the rate constant for the destruction of nicotine in SM1 is ~2 times the rate constant for the destruction of nicotine in ES1. Based on nicotine information obtained from this study, it is clear that ES1 cigarette is more addictive than SM1 cigarette.