Studying the transfer process of a gemini surfactant from water to β-cyclodextrin at a molecular level

A volumetric and NMR study of cyclodextrin-inhalation anesthetic complexes in aqueous solutions

The apparent molar volumes (Vϕ) of two anesthetics (halothane and forane) have been determined in water and in binary solvent (H2O + cyclodextrin) systems at 25 °C. The results show that the magnitudes of Vϕ are greater in ternary solutions than in the binary aqueous systems. The apparent molar volumes at infinite dilution (Vϕo) of halothane in ternary solutions are observed to depend on the following factors: (i) the magnitude of the binding constant (K1:1), (ii) the lipophilicity of the anesthetic, (iii) the mole ratio of the host/halothane system, and (iv) the topology (i.e., facial vs. inclusion) of the host/guest complex. The volumetric properties of the ternary systems have been analyzed in terms of the complexed and uncomplexed species by application of Young’s rule. The formation of 1:1 CD–halothane complexes was successfully modeled using a two-state model. The binding affinity of the various cyclodextrins toward halothane is listed in descending order as follows: DM-β-CD > HP-β-CD > β-CD > α-CD > TM-β-CD.

Complexation of β-cyclodextrin with a gemini surfactant studied by isothermal titration microcalorimetry and surface tensiometry

We report on the inclusion complex formation of β-cyclodextrin (βCD) with a cocogem surfactant (counterion-coupled gemini surfactant; (bis(4-(2-alkyl)benzenesulfonate)-Jeffamine salt, abbreviated as ABSJ), studied by isothermal titration calorimetry (ITC) and surface tension (SFT) measurements. We measured the critical micelle concentration (cmc) of ABSJ in water by the two experimental techniques in the temperature range 283-343 K, and determined the thermodynamic parameters of the complex formation directly by ITC and indirectly by the SFT. The stoichiometry (N), the binding constant (K), and the enthalpy of complexation were determined, and the Gibbs free energy and the entropy term were calculated from the experimental data. A novel method is presented for the determination of N and K by using surface tensiometry.

The formation of host-guest complexes between surfactants and cyclodextrins

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host-guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host-guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD-surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature. In general, the surfactant-cyclodextrin association is treated without reference to the kinetics of the process. However, there are several examples where the kinetics of the process can be investigated, in particular those where volumes of the CD cavity and surfactant (either the tail or in special cases the head group) are similar in magnitude. This will also be critically reviewed.