Evidence for complexes of different stoichiometries between organic solvents and cyclodextrins

Host-Guest Complexes

Host-guest complexes, also known as inclusion complexes, are supramolecular structures [...].

Spectroscopic methods for aqueous cyclodextrin inclusion complex binding measurement for 1,4-dioxane, chlorinated co-contaminants, and ozone

Recalcitrant organic contaminants, such as 1,4-dioxane, typically require advanced oxidation process (AOP) oxidants, such as ozone (O₃), for their complete mineralization during water treatment. Unfortunately, the use of AOPs can be limited by these oxidants' relatively high reactivities and short half-lives. These drawbacks can be minimized by partial encapsulation of the oxidants within a cyclodextrin cavity to form inclusion complexes. We determined the inclusion complexes of O₃ and three common co-contaminants (trichloroethene, 1,1,1-trichloroethane, and 1,4-dioxane) as guest compounds within hydroxypropyl-β-cyclodextrin. Both direct (ultraviolet or UV) and competitive (fluorescence changes with 6-p-toluidine-2-naphthalenesulfonic acid as the probe) methods were used, which gave comparable results for the inclusion constants of these species. Impacts of changing pH and NaCl concentrations were also assessed. Binding constants increased with pH and with ionic strength, which was attributed to variations in guest compound solubility. The results illustrate the versatility of cyclodextrins for inclusion complexation with various types of compounds, binding measurement methods are applicable to a wide range of applications, and have implications for both extraction of contaminants and delivery of reagents for treatment of contaminants in wastewater or contaminated groundwater.

Host-Guest-Mediated DNA Templation of Polycationic Supramolecules for Hierarchical Nanocondensation and the Delivery of Gene Material

Only a few examples of monodisperse molecular entities that can compact exogenous nucleic acids into nanocomplexes, protect the cargo from the biological environment, facilitate cell internalization, and promote safe transfection have been reported up to date. Although these species open new venues for fundamental studies on the structural requirements that govern the intervening processes and their application in nonviral gene-vector design, the synthesis of these moieties generally requires a relatively sophisticated chemistry, which hampers further development in gene therapy. Herein, we report an original strategy for the reversible complexation and delivery of DNA based on the supramolecular preorganization of a β-cyclodextrin-scaffolded polycationic cluster facilitated by bisadamantane guests. The resulting gemini-type, dual-cluster supramolecules can then undergo DNA-templated self-assembly at neutral pH value by bridging parallel DNA oligonucleotide fragments. This hierarchical DNA condensation mechanism affords transfectious nanoparticles with buffering capabilities, thus facilitating endosomal escape following cell internalization. Protonation also destabilizes the supramolecular dimers and consequently the whole supramolecular edifice, thus assisting DNA release. Our advanced hypotheses are supported by isothermal titration calorimetry, NMR and circular dichroism spectroscopic analysis, gel electrophoresis, dynamic light scattering, TEM, molecular mechanics, molecular dynamics, and transfection studies conducted in vitro and in vivo.

Cyclodextrin-Surfactant Mixed Systems as Reaction Media

In recent years our reseach group has investigated the chemical behaviour of β-cyclodextrin (CD)/surfactant mixed systems and their characteristics as reaction media. The results have been interpreted in terms of a pseudophase model that takes into account the formation of both CD-surfactant and CD-substrate complexes and also, in some cases, the exchange of X- and OH- ions between the micellar and aqueous pseudophases. from the experimental results it was concluded that the presence of CD has no effect on existing micelles but raises the critical micellar concentration (cmc). on the other hand, at surfactant concentrations above the cmc, competition between the micellisation and complexation processes leads to the existence of a significant concentration of free CD in equilibrium with the micellar aggregates. The percentage of uncomplexed β-CD in equilibrium with the micellar system increases on increasing the hydrophobicity of the surfactant molecule. This behaviour was justified taking into account the existence of two simultaneous processes: complexation of surfactant monomers by CD and the process of self-assembly to form micellar aggregates. The autoaggregation of surfactant monomers is more important than the complexation process in this mixed system. Varying the hydrophobicity of the surfactant monomer enabled us to determine that the percentages of uncomplexed CD in equilibrium with the micellar system were in the range of 5-95%. When the surfactant self-assembly structure is a vesicle, the free CD in the CD/surfactant mixed system yields a percentage of 100%.

The influence of cosolvent on the complexation of HP-beta-cyclodextrins with oleanolic acid and ursolic acid

The present work was aimed at the influence of ethanol on the complex formation of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) with oleanolic acid (OA) and ursolic acid (UA), two insoluble isomeric triterpenic acids. Phase solubility studies were carried out to evaluate the solubilizing power of HP-beta-CD, in association with ethanol, toward OA and UA. A mathematical model was applied to explain and predict the solubility of OA and UA influenced by HP-beta-CD and ethanol. The solid complexes were prepared by evaporating the filtrate of samples which was prepared in different complexing media. The solubility of OA is much higher than that of UA in all the tested aqueous solutions. The solubility of OA and UA can be increased over 900 and 200 times, respectively, by forming complex with HP-beta-CD. Ethanol (0.5%, v/v) can help the formation of OA-HP-beta-CD complex, but is harmful to the formation of UA-HP-beta-CD complex. Increasing solubility in water can be achieved by adding ethanol into the complexing media, but the concentration of ethanol should be optimized. The ring E of the chemical compounds has a great influence on the complexing process.