On the Possibility That Cyclodextrins' Chiral Cavities Can Be Available on AOT n-Heptane Reverse Micelles. A UV−Visible and Induced Circular Dichroism Study

Abstract

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.

Cyclodextrin modified niosomes to encapsulate hydrophilic compounds

“…The wavelength of MO maximum absorption shis from 467 nm in water to lower wavelength (l ¼ 425 nm) in niosomes media. This hypsochromic shi indicates that in niosomes, MO is sensing a less polar environment 41 and suggest that it resides in the polar region of interphase but we cannot discard the presence of MO in the entrapped aqueous. In presence of CDs, the results show that the MO absorption band shis to lower wavelengths, i.e., l max ¼ 457 nm in b-CD aqueous solution and l max ¼ 445 nm in niosomes with b-CD (or Mod-b-CD), in comparison with that obtained in water.…”

“…These features were attributed to the interaction between MO and CDs by the formation of an inclusion complex. 41 On the other hand, the electronic band of the complex MO:CDs in niosomes is quite different, in position and in shape, when they were compared with the spectrum of the complex MO:b-CD in aqueous solution. We interpret our results considering that in niosomes systems, the inclusion process occurs preferably in lower polarity regions such as the interphases.…”

“…Mod-b-CD has been synthetized and studied in our laboratory 38,39 and it was demonstrated that it can form aggregates in aqueous and organic media, and in both systems, the cavity is available to interact with external guests. [40][41][42] It is worth to mention that all the molecules used in this work for the synthesis of the carriers are fatty acids and sugar derivated. They are biodegradable, food grade, and their production is sustainable.…”

Spectral characterization and colloidal properties of 1-hexadecylpyridinium chloride in aqueous binary mixtures of different glycols

“…Due to their amphiphilic nature, surfactants have applications in a wide variety of fields [1,2]. Surfactants are used as additives in pharmaceutical formulations [3], to enhance the solubilization of hydrophobic compounds [4], as catalysts [5], as detergents [6], etc.…”

Reversible vesicles based on one and two head supramolecular cyclodextrin amphiphile induced by methanol

“…24,25 However, the 2:1 stoichiometry for the complexation of HPbCD with piroxicam ( reported. 26 This may be due to the two hydrophobic heads of the relatively linear molecule of piroxicam, as well as the different substitution degree for the HPbCD used.…”