Cyclodextrin Supramacromolecules: Unexpected Formation in Aqueous Phase under Ambient Conditions

Micellar-type aggregates of HP-β-CD/GML inclusion complex: Increased water-solubility and effective antibacterial capabilities

The inclusion complex (IC) was successfully obtained by encapsulating glycerol monolaurate (GML) into the cavity of hydroxypropyl-β-cyclodextrin (HP-β-CD). Compared with solubility of pure GML <80 μg/mL in water, and the water-solubility of encapsulated GML was significantly improved and reached to 270,000 μg/mL. IC can form nanoparticles by self-assembly, probably assigned to its strong capability to form micellar-type aggregates. A Higuchi's AL-type phase-solubility diagram indicated the strong interaction between host and guest molecules with the formation of 1:1 GML/HP-β-CD complex and the stability constant at 6248 L/mol. Compared with pure GML, encapsulated GML at the same concentration can also show good antibacterial capabilities against S. aureus and E. coli in sterile water, and the effective preservative capabilities towards beef meatballs. The boosted enhancement in water-solubility of GML and the effective antibacterial capabilities endowed IC with potential in the application of food decontamination.

Do Cyclodextrins Aggregate in Water? Insights from NMR Experiments

One decade ago Bonini et al. [Langmuir 2006, 22, 1478-1484] reported the occurrence of aggregates of β-cyclodextrin in aqueous solutions with sizes in the range from 90 nm to a few micrometers. The experimental technique used was cryo-TEM. This work followed a number of previous studies involving other physical parameters, such as viscosities and activity coefficients, the results of which were interpreted in terms of self-aggregation of cyclodextrins. Since then, the ability of cyclodextrins to self-assemble were often used to explain and rationalize the supramolecular mechanisms involving cyclodextrins. Here, the question of aggregation of native cyclodextrins (α-, β-, and γ-) in aqueous solutions is addressed by using (1)H NMR techniques, including NMR diffusometry, relaxometry, and proton peak intensities. Within the detection limit of the NMR experiments, no aggregates of cyclodextrin were observed. If aggregates are present, the fraction of cyclodextrin in aggregates is quite small-less than 1%. However, we cannot exclude the presence of transient clusters involving several cyclodextrin molecules where the lifetime of the cluster is short.

β-CD assisted dissolution of quaternary ammonium permanganates in aqueous medium

The non-polar internal cavity of β-cyclodextrin (β-CD) has been exploited for the entrapment of the hydrophobic tails of two water insoluble quaternary ammonium permanganates (QAPs): cetyltrimethylammonium permanganate (CTAP) and tetrabutylammonium permanganate (TBAP), for solubilization in aqueous medium. The solubilization and organizational behavior of the QAPs in aqueous β-CD solution have been determined from the comparison of their rates of self-oxidation in presence and in absence of β-CD. Effect of QAP concentration on their observed rate constants (k(obs)) at a fixed β-CD concentration, phase solubility analysis in varying β-CD concentration, impact of quaternary ammonium bromides (QABs) on the kobs values of CTAP and TBAP at fixed QAP and β-CD concentrations, and the temperature effect have been reported. A scheme to explain the solvation of QAPs in aqueous β-CD has been proposed based on dynamic light scattering (DLS) analysis of the samples.

Cyclodextrins as functional excipients: methods to enhance complexation efficiency

Cyclodextrins have gained currency as useful solubilizing excipients with an ever increasing list of beneficial properties and functionalities. Although their use in liquid dosage forms including oral and parenteral solutions is straightforward, their application to solids can be confounded by the added bulk that is contributed to the formulation. This factor has limited the use of cyclodextrin in tablets and relates systems mainly to potent drug substances. Increasing the ability of cyclodextrins to complex with drug through a manipulation of their complexation efficiency (CE) may expand the use of these materials to the increasing list of drug candidates and marketed drugs who may benefit from this technology. This brief review assesses tools and materials that have been suggested for increasing the CE for pharmaceutically useful cyclodextrins and drugs. The relative importance of impacting the drug solubility (S(0) ) and phase-solubility isotherm slope is discussed in the context of drug ionization and salt use; the impact of polymers, charge interactions, and charge shielding; and the coincidental formation of other complex types in the media. The influence of drug form as well as supersaturation is also discussed in the context of the responsible mechanisms along with aggregation, inclusion, and noninclusion complex formation.