The formation of host–guest complexes between surfactants and cyclodextrins

Abstract

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.

Interactions between Bio-Based Compounds and Cyclodextrins

“…The beneficial modification of guest molecular properties after the formation of the inclusion complex leads to a large number of applications in areas as diverse as encapsulation of active substances (i.e., flavoring agents, metallic cations, fragrances, and pesticides), enzymatic synthesis, catalysis, and energy transfer studies [3,4]. Additionally, CDs also find important uses in cosmetics, environment protection, bioconversion, packing, textiles, and food domain [1,5].…”

“…The effect of the length of the alkyl chain and surfactant head group on the association constant of APGs with different CDs was studied by 1 H NMR spectroscopy, NMR selfdiffusion, and surface tension ( Table 1) [58][59][60]. Although the comparison between association constants computed on the basis of different physical parameters is a difficult task [5], the analysis of the data allowed concluding that by increasing the alkyl chain length and decreasing the CD cavity volume (from β-toα-CD), the association constant increases. Furthermore, some authors stated that no interactions were observed when γ-CD was used [59,58].…”

“…Also from group II, surface tension has also been used to follow the effect of CDs on the aggregation and interfacial properties of surfactants in CD-surfactant-containing solutions [74] Phase solubility studies Cabreuva essential oil + HP-β-CD [74] Phase solubility studies β-caryophyllene + HP-β-CD [76] UV-vis Black pepper essential oil + HP-β-CD [76] Phase solubility studies CDs 1 + PPs 2 [77] Phase solubility studies, NMR, TGA, DSC β-CD + estragole [78] NMR β-CD + eugenol [27] NMR β-CD + rosmarinic acid [75] NMR Cyclohexylacetic acid + β-CD Phase solubility studies, NMR, HPLC Polymethoxyflavones + HP-β-CD [93] GC, total organic carbon, phase-solubility studies SBE-β-CD, SBE-γ-CD and HP-β-CD + EOS 6 [94,95] 1 CDs: alpha-cyclodextrin (α-CD), beta-cyclodextrin (β-CD), gamma-cyclodextrin (γ-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), randomly methylated-beta-cyclodextrins (RAMEB), low methylated beta-cyclodextrin (CRYSMEB), and sulfobutylether β-cyclodextrin (SBE-β-CD) 2 PPs: trans-anethole, estragole, eugenol, isoeugenol (phenylpropenes), caffeic acid, p-coumaric acid, and ferulic acid (hydroxycinnamic acids) 3 UAS: ultrasonic attenuation spectroscopy APGs: glucopyranosides (octyl G8, decyl G10, dodecyl G12, tetradecyl G14) and two maltosides (decyl M10, dodecyl M12) 5 EOs: essential oils of cedarwood, clove, eucalyptus, and peppermint 6 EOS: essential oils of Artemisia dracunculus, Citrus reticulata Blanco, Citrus aurantifolia, Melaleuca alternifolia, Melaleuca quinquenervia, and Rosmarinus officinalis cineoliferum Table 2. Compilation of the most relevant techniques used to study the interactions between CDs and bio-based compounds.…”

Supramolecular Catalytic System Based on β-Cyclodextrin, Sodium Dodecyl Sulfate and Pralidoxime for the Hydrolysis of Paraoxon

“…The mixed cyclodextrin-surfactants systems combine the characteristics of composing species and also have many features compared to conventional single systems. [15] Therefore, in this paper we would like to construct the supramolecular systems based on β-cyclodextrin (β-CD) and ionic surfactant with oxime-counterion for effective hydrolysis of paraoxon (POX) being one of the most potent acetylcholinesterase-inhibiting pesticides. Since the cationic oxime pralidoxime (2-PAM) was taken as a surfactant counterion, the anionic sodium dodecyl sulfate (SDS) was chosen as a surfactant.…”

Triton X-100/β-Cyclodextrin Cloud Point Extraction for Removal of Phenol Using Different of Sodium Salts as Inducing Phase Separation Agent

“…The solutions undergo micellar growth and micelle to vesicle transitions. Moreover, β-cyclodextrin is also important towards controlling the thicknesses of hydropho-bically modified polymers, e.g., ethyl(hydroxyl ethyl) cellulose and modified poly(ethylene glycol) in water by decoupling hydrophobic-hydrophobic intermolecular interactions [22,23]. Hence, the orientation of the β-cyclodextrin-surfactant com-plexes in the CPE is suitable towards the cooperative binding of the analyte recoveries.…”