The surface behavior of monoacylated beta-cyclodextrins, with hydrocarbon chains of 16, 14, and 10 carbons, has been assessed by the measurement of the surface pressure, surface (dipole) potential, optical reflectivity, and surface topography in monolayers at the air-water interface. For all the derivatives studied, the intermolecular organization adopted along compression-decompression isotherms reveals a rich variety of packing states which imply profound reorganization of the hydrophobic and hydrophilic moieties of the beta-cyclodextrin derivatives in the film, depending on the lateral surface pressure. The intermolecular arrangements are consistent with the adoption of a different and defined orientation of the cyclic oligosaccharide unit, relative to the interfacial plane and the aqueous subphase. This is different from the behavior of the per-substituted derivatives, and none of the changes exhibited by the monosubstituted forms are consistent with the oligosaccharide ring remaining in a fixed orientation along the interface when the surface pressure is varied.

A cyclodextrin derivative (Mod-CD) was synthesized through the monoesterification of beta-cyclodextrin (beta-CD) with 3-((E)-dec-2-enyl)-dihydrofuran-2,5-dione. The compound is an interesting surfactant that can form large aggregates not only through the interaction of the hydrophobic tails as in common amphiphilic compounds but also through the inclusion of the alkenyl chain into the cavity of another Mod-CD molecule. The self-inclusion of the chain in the cavity of cyclodextrin as well as the intermolecular inclusion was demonstrated by 1H NMR measurements that were able to detect methyl groups in three different environments. Besides, in the aggregates of Mod-CD, the cavity is available to interact with external guests such as phenolphthalein, 1-amino adamantane, and Prodan. Phenolphthalein has the same binding constant with Mod-CD and beta-CD, but the equilibrium constant for the interaction with Prodan is about 2 times larger for Mod-CD than for beta-CD. The latter result is attributed to the fact that this probe interacts with the micelle in two binding sites: the cavity of the cyclodextrin and the apolar heart of the micelle as evidenced by the spectrofluorimetric behavior of Prodan in solutions containing different concentrations of Mod-CD.

The formation of reverse micelles (RMs) of sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT) in n-heptane including two different beta-cyclodextrin (beta-CD) derivatives (hydroxypropyl-beta-CD, hp-beta-CD, and decenyl succinyl-beta-CD, Mod-beta-CD) is reported. Both cyclodextrins can be incorporated into AOT RMs in different zones within the aggregate, while beta-CD cannot. Using UV-vis and induced circular dichroism (ICD) spectroscopy and different achiral molecular probes (some azo dyes, p-nitroaniline and ferrocene), it was possible to determine that Mod-beta-CD is located with its cavity at the oil side of the AOT RM interface, while for hp-beta-CD the cavity is inside the RM water pool. Among the molecular probes used, methyl orange (MO) was the only one which gave the ICD signal when dissolved in the AOT RMs with hp-beta-CD, so a detailed study of MO behavior in homogeneous media was also performed to compare with the microheterogeneous media. The solvatochromic behavior of the dye depends not only on the polarity of the media but also on other specific solvent properties. A Kamlet-Taft analysis shows that the MO absorption spectrum shifts to longer wavelength with an increase in the solvent polarity-polarizability (pi*) and the hydrogen donor ability (alpha) of the medium. MO appears to be almost 3 times more sensitive to the pi* parameter than to the alpha parameter. In addition, from the MO absorption spectral changes with the hp-beta-CD concentration, the association equilibrium constants in pure water (K11W) and inside the RMs (K11RM) were computed. The results show that K11W is almost 10 times larger than the value inside the RMs. The latter can be explained considering that MO resides anchored to the RM interface through hydrogen bond interaction with the hydration bound water. This study shows for the first time that the cyclodextrin chiral cavity is available for a guest in an organic medium such as the RMs; therefore, we have created a potentially powerful nanoreactor with two different confined regions in the same aggregate: the polar core of the RMs and the chiral hydrophobic cavity of cyclodextrin.