Study of host–guest interaction between ß-cyclodextrin and alkyltrimethylammonium bromides in water

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• 作者：Anja Petek ; Majda Krajnc ; Aljana Petek
• 关键词：Inclusion complex ; Cyclodextrin ; Alkyltrimethylammonium bromides ; Micelles ; Conductivity
• 刊名：Journal of Inclusion Phenomena and Macrocyclic Chemistry
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：86
• 期：3-4
• 页码：221-229
• 全文大小：628 KB
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Organic Chemistry
  Food Science
  Crystallography
  
• 出版者：Springer Netherlands
• ISSN：1573-1111
• 卷排序：86

文摘

Cyclodextrins were found to play important roles in self-assembly systems of surfactants. The interactions between host molecule ß-cyclodextrin (CD) and model cationic surfactants, alkyltrimethylammonium bromides with different alkyl chain length: dodecyl-(C₁₂TAB), tetradecyl-(C₁₄TAB) and hexadecyl-(C₁₆TAB) are studied by means of conductivity measurements at 313.2 K. The data obtained indicate that inclusion complexes (CD:S+) had formed, and apparent critical micelle concentration (CMC*) is equivalent to the combined concentrations of surfactant monomers complexed with the CD and that of a free dissolved monomer in equilibrium with the micellized surfactant without CD. Inclusion complexes were characterized by an equilibrium binding constant K₁₁, which value increases as the length of alkyl chains, and consequently the hydrophobicity, increases. From mathematical model the concentrations of the uncomplexed cyclodextrin, uncomplexed surfactant ion, and inclusion complex in the submicellar, as well as in the micellar range were calculated. The competition between the micellization and complexation processes leads to the existence of a significant concentration of free CD in equilibrium with the micellar aggregates. The percentage of uncomplexed cyclodextrin in equilibrium with the micelles is independent on cyclodextrin concentration for a particular ternary system and is 31, 37, and 34 % for C₁₂TAB/water/ß-CD, C₁₄TAB/water/ß-CD and C₁₆TAB/water/ß-CD, respectively. By using standard Gibbs free energy for micellization and surfactant complexation by CD, we can explain the observed behavior.