# Heat Triggered Release Behavior of Eugenol from Tobacco Leaf
## 3 Results  
Eugenol, giving out the odor of cloves, is a commonly used fragrance with weak acidity. Eugenol was selected as the model fragrance for this investigation due to its importance in food chemistry. Eugenol was loaded onto commercial tobacco leaf by injection of the eugenol solution onto the tobacco leaf. The amount of loaded eugenol was controlled to be 0.005 mg mg\({}^{-1}\) in all experiments. Successful loading of eugenol on tobacco leaf was demonstrated with FT-IR measurements. Tobacco leaf is a complex mixture mainly composed of cellulose, monosaccharide, starch, lignin, etc. A group of characteristic vibration peaks from these main components were clearly observed in the FT-IR spectra of tobacco leaf. For example, peaks associated with stretching vibrations of the C=O group in the acetyl group of cellulose, stretching vibration of the phenyl group in lignin and stretching vibration of C=O group in aryl ether compounds of lignin were observed at 1737, 1543 and 1240 cm\({}^{-1}\)[14; 15], respectively. Other characteristic peaks of tobacco leaf were also labeled in Figure 2. In the FT-IR spectra of eugenol, peaks from the stretching vibration of C-O in -OCH (1428 cm\({}^{-1}\)), stretching vibration of -C-O (1261 cm\({}^{-1}\)) and in-plane wagging vibration of phenyl hydroxyl groups (1235 cm\({}^{-1}\)) could be identified. These characteristic peaks of eugenol were also observed in the spectra of eugenol-loaded tobacco leaf, suggesting successful loading of eugenol onto the tobacco leaf. Next, the interaction of eugenol with the tobacco leaf was investigated with theoretical calculations. Since the main component of tobacco leaf is cellulose (-6-25%), monosaccharides (e.g., glucose, -10-25%), starch (-10-30%) and lignin (-1-13%), the adsorption configurations of eugenol on these components were calculated to give an insight into the adsorption mechanism of eugenol on a tobacco leaf. The optimized molecular configuration of the adsorption is shown in Figure 3. The adsorption energy of eugenol on cellulose, monosaccharide (D-glucose), starch and lignin was calculated to be \(-\)0.06, \(-\)0.125, \(-\)0.202 and \(-\)0.288 eV, respectively. The negative adsorption energy suggests that the eugenol adsorption on tobacco leaf is thermodynamically favorable. In addition, the low adsorption energy indicates that the adsorption of eugenol on tobacco leaves is weak physical adsorption. The thermal stability of eugenol, tobacco and eugenol-loaded tobacco leaf was evaluated with thermogravimetry (TG) analysis in argon (Figure 4). The tobacco leaf exhibited a four-stage weight loss. At a temperature below 130 \({}^{\circ}\)C (state I), the weight loss mainly resulted from the loss of physically adsorbed water and volatile species in the sample. In the temperature range of 150 to 270 \({}^{\circ}\)C (stage II), the weight loss of tobacco leaf was largely from the heat-induced release of glycerol (a common additive in tobacco leaf), nicotine and initial decomposition of cellulose and lignin. Further increases in the temperature led to the thermolysis and carbonization of cellulose and lignin, which caused rapid weight loss (stage IV). As a volatile solution, eugenol evaporated quickly as temperature increased. Eugenol completely evaporated at 220 \({}^{\circ}\)C. Compared with pristine tobacco leaf, tobacco leaf loaded with eugenol experienced a faster weight loss with temperature increase due to the incorporation of eugenol. The TG results above show the release of eugenol at a high rate above 200 \({}^{\circ}\)C. Considering that the working temperature of the fragrance release system in heat, not burn, cigarettes is normally between 200 \({}^{\circ}\)C to 260 \({}^{\circ}\)C, the release of eugenol from tobacco leaf loaded with eugenol was investigated in this temperature range. The released eugenol was collected sequentially (time interval 30 s) at eight different spots of the sampling chamber. The amount of collected eugenol was quantified with GC analysis.