Factors Contributing to Solubility Synergism of Some Basic Drugs with β-Cyclodextrin in Ternary Molecular Complexes

Cyclodextrin-enhanced photo-induced fluorescence of tau-fluvalinate, molecular modelling of inclusion complexes and determination in natural waters

The effect of adding organized supramolecular systems such as β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) on the photochemically-induced fluorescence (PIF) spectral properties of tau-fluvalinate (TFV) in aqueous solutions was examined. The influence of pH, UV irradiation time and photoproduct stability on the cyclodextrin-enhanced photochemically-induced fluorescence intensity was also investigated. The spectral changes associated with the inclusion process yielded values for the formation constants of TFV inclusion complexes between 450 and 640 M-1, which were calculated using the nonlinear iterative regression approach least squares. In addition, host-guest interaction was clearly determined by PIF enhancement and a 1 : 1 stoichiometry was found for the β-CD and HP-β-CD complexes formed with TFV. The negative free energy (ΔG°) value indicated that the reaction of TFV with cyclodextrins was thermodynamically favorable. Furthermore, the structures of inclusion complexes of TFV with cyclodextrins were elucidated by 3-21G ab initio calculations. The limits of detection and quantification obtained ranged between 1.3 and 4.0 ng mL-1 and from 4.4 to 13.0 ng mL-1 in β-CD and HP-β-CD media, respectively. The analytical application in tap and river water samples yielded satisfactory mean recoveries ranging from 98.12 to 102.97%. Due to its sensitivity and ease of use, this method can be reliably applied to routine analysis.

Solubility of Cyclodextrins and Drug/Cyclodextrin Complexes

Cyclodextrins (CDs), a group of oligosaccharides formed by glucose units bound together in a ring, show a promising ability to form complexes with drug molecules and improve their physicochemical properties without molecular modifications. The stoichiometry of drug/CD complexes is most frequently 1:1. However, natural CDs have a tendency to self-assemble and form aggregates in aqueous media. CD aggregation can limit their solubility. Through derivative formation, it is possible to enhance their solubility and complexation capacity, but this depends on the type of substituent and degree of substitution. Formation of water-soluble drug/CD complexes can increase drug permeation through biological membranes. To maximize drug permeation the amount of added CD into pharmaceutical preparation has to be optimized. However, solubility of CDs, especially that of natural CDs, is affected by the complex formation. The presence of pharmaceutical excipients, such as water-soluble polymers, preservatives, and surfactants, can influence the solubilizing abilities of CDs, but this depends on the excipients' physicochemical properties. The competitive CD complexation of drugs and excipients has to be considered during formulation studies.