Interaction of nicotine with magnesium aluminum silicate at different pHs: characterization of flocculate size, zeta potential and nicotine adsorption behavior

The purposes of this study were to prepare dispersions in various ratios of nicotine (NCT) and magnesium aluminum silicate (MAS) at different pHs and to investigate interaction of NCT with MAS by characterizing microscopic morphology, particle size and zeta potential of MAS-NCT flocculates. Moreover, the NCT adsorption onto MAS at different pHs were also investigated. At basic medium, incorporating NCT into MAS dispersion brought about a small decrease in the zeta potential of MAS, leading to a loose flocculate formation of MAS. This is likely to be due to an adsorption of unionized form of NCT onto MAS via intermolecular hydrogen bonding. The lower zeta potential, denser matrix structure and larger size of the flocculates was found at neutral and acidic media because the protonated species of NCT could interact with the negatively charged MAS by electrostatic force. In addition the flocculates formed at pH 4 possibly possessed a higher density than those formed at pH 7, suggesting that the diprotonated species of NCT at pH 4 caused stronger interaction with MAS. The adsorption isotherms of NCT onto MAS at different pHs can be described not only using the Langmuir model, but also using the Freundlich model. The higher affinity of NCT adsorption onto MAS at neutral and acidic media was found. However, the adsorption capacity to form NCT monolayer reduced with decreasing the pH of the dispersions because of an adsorption of hydronium ions and a decrease in surface area of adsorption site by flocculation. These findings suggested that the flocculation of MAS dispersion could be induced by incorporation of NCT. The characteristics, such as particle size and zeta potential, of the NCT-MAS flocculates and the adsorption isotherms of NCT onto MAS were depended upon pH of dispersion, in which the different charged species of NCT were formed.     

Alginate-magnesium aluminum silicate films for buccal delivery of nicotine

Sodium alginate-magnesium aluminum silicate (SA-MAS) dispersions with nicotine (NCT) were prepared at different pHs and characterized for the particle size and zeta potential, NCT adsorbed by MAS, and flow behavior before film casting. The physicochemical properties, NCT content, in vitro bioadhesive property, and NCT release and permeation of the NCT-loaded SA-MAS films were investigated. This study showed that incorporation of NCT into the SA-MAS dispersions caused a change in particle size and flow behavior and that NCT could be adsorbed by MAS. The formation of protonated NCT at acidic and neutral pHs could interact with negatively charged MAS via an electrostatic force, resulting in the formation of NCT-MAS flocculates/complexes that could act as microreservoirs in the films. The NCT-loaded SA-MAS films prepared at pH 5 yielded the highest NCT content due to non-significant loss of NCT during drying. Moreover, pH of the preparation also affected the crystallinity and thermal properties of the films. The NCT release and permeation across the mucosal membrane of the films could be described using a matrix diffusion controlled mechanism. In addition, the NCT-loaded SA-MAS films also possessed a bioadhesive property for adhesion to the mucosal membrane. This finding suggests that the NCT-loaded SA-MAS films composed of numerous NCT-MAS complexes as microreservoirs demonstrated a strong potential for use as a buccal delivery system.     

Growth Inhibition of Thermotolerant Yeast,Kluyveromyces marxianus,in Hydrolysates from Cassava Pulp

In this study, we report the inhibition of Kluyveromyces marxianus TISTR5925 growth and ethanol fermentation in the presence of furan derivatives and weak acids (acetic acid and lactic acid) at high temperatures. Cassava pulp, obtained as the waste from starch processing, was collected from 14 starch factories located in several provinces of Thailand. At a high temperature (42 °C), the cassava pulp hydrolysate from some starch factories strongly inhibited growth and ethanol production of both K. marxianus (strain TISTR5925) and Saccharomyces cerevisiae (strain K3). HPLC detected high levels of lactic acid and acetic acid in the hydrolysates, suggesting that these weak acids impaired the growth of K. marxianus at high temperature. We isolated Trp-requiring mutants that had reduced tolerance to acetic acid compared to the wild-type. This sensitivity to acetic acid was suppressed by supplementation of the medium with tryptophan.