Physicochemical characterizations and release studies of nicotine–magnesium aluminum silicate complexes

Nicotine (NCT), a volatile strongly alkaline liquid, is widely used in smoking cessation therapy for relieving addiction symptoms. Magnesium aluminum silicate (MAS) is a mixture of montmorillonite and saponite and thus may adsorb an amine drug. In this study, NCT–MAS complexes were prepared at different pHs in order to improve NCT stability and to use as drug carriers. Physicochemical properties and in vitro NCT release of the complexes were studied. The molecular interaction between NCT and MAS was investigated using FTIR and solid-state 29Si NMR spectroscopy. The results indicated that the complexation of NCT and MAS was formed not only via non-ionic electrostatic interaction, hydrogen bonding and water bridging mechanisms, but also via ionic electrostatic interaction, a cation exchange mechanism that was dependent on the pH of the preparation medium. The intercalation of NCT was revealed by PXRD. DSC and TGA studies indicated that the complexes could reduce evaporation and enhance the stability of NCT at high temperature. The complexes prepared at pH 4 and 7 had higher thermal stability than the complex prepared at pH 10. The complexes presented a sustained release of NCT after a burst release in pH 6 phosphate buffer. The NCT release kinetics could be described using the particle diffusion-controlled and Higuchi's models. The findings suggest that the NCT–MAS complexes could enhance the thermal stability of NCT and have good potential for use as drug reservoirs or drug carriers in NCT delivery systems intended for sustained release.