A simple alternative determination of the formation constant for the inclusion complex between rutin and β-cyclodextrin

An investigation into the supramolecular structure, solubility, stability and antioxidant activity of rutin/cyclodextrin inclusion complex

The formation of supramolecular inclusion complexes between rutin and four cyclodextrins, namely β-cyclodextrin (β-CD), (2-hydroxypropyl)-α-cyclodextrin (HP-α-CD), (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) and (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD), and the effects of the complexation on the stability and antioxidant activity of rutin were investigated. Results from phase-solubility studies showed that rutin formed 1:1 stoichiometric inclusion complexes with HP-α-CD, β-CD, HP-β-CD and HP-γ-CD; the complexes formed with HP-γ-CD and HP-β-CD had the greatest stability constants, followed by β-CD and HP-α-CD. Thermodynamic studies demonstrate that the inclusion of rutin into HP-β-CD was an exothermic process which occurred spontaneously. Two-dimensional rotating-frame nuclear Overhauser effect spectroscopy (2D ROESY) (1)H NMR analyses show that the A ring of rutin was the part of the molecule that most likely inserted into the cavity of HP-β-CD, thus forming a supramolecular inclusion complex. Formation of such an inclusion complex conferred moderate degrees of protection to rutin from degradation by heat and UV radiation during storage, and significantly enhanced its antioxidant capacity as determined by three different procedures.

Studies on the interactions between some flavonols and cyclodextrins

The interactions of some natural flavonols with alpha, beta- and gamma-Cds have been investigated. Guest molecules were galangin, kaempferol and quercetin. Inclusion complexes were prepared by kneading and freeze-drying. The complexes were characterized using different physico-chemical methods based on differential scanning calorimetry (DSC), infrared spectroscopy (IR) and NMR spectroscopy. In the proton and carbon spectra the effects of complexation on the chemical shifts of the internal and external protons of Cds in the presence of each flavonoid were observed. Moreover, the water-solubility of the flavonols in the presence of Cds was also evaluated. The increased solubility of quercetin and kaempferol in the presence of beta-Cd was evidenced. For all three guests, multidimensional NMR experiments in DMSO and water are consistent with dynamic binding processes, dominated by insertion of the B ring into the wider rim of the Cd cavity.

The rutin/β-cyclodextrin interactions in fully aqueous solution: spectroscopic studies and biological assays

In the present work the feasibility of beta-cyclodextrin complexation was explored, as a tool for improving the aqueous solubility and antioxidant efficacy of rutin. By means of 1H NMR, UV-vis and circular dichroism spectroscopy the single aromatic ring of rutin was found to be inserted into the beta-cyclodextrin cavity to form a 1:1 inclusion complex. The effect of beta-cyclodextrin on the spectral features of rutin was quantitatively investigated, in fully aqueous medium, by holding the concentration of the guest constant and varying the host concentration. The associated binding constants were estimated to be 142+/-20 and 153+/-20 M(-1), respectively, on the basis of the observed UV-vis absorption and circular dichroism intensities. The antioxidant activity of rutin was also investigated, as affected by molecular encapsulation within beta-cyclodextrin (batophenanthroline test; comet assay; lipid peroxidation); the inclusion complex revealed improved antioxidant efficacy that may be in part explained by an increased solubility in the biological moiety.

Preparation and spectral investigation on inclusion complex of beta-cyclodextrin with rutin

Solid inclusion complex of rutin with beta-cyclodextrin (beta-CD) was prepared by coprecipitate method. The formation of inclusion complex was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction. The formation constant was obtained by steady-state fluorescence measurements and the result suggested the complex preferred 1:1 (rutin:CD) stoichiometry. Furthermore, the spatial configuration of the complex has been proposed based on NMR and molecular modeling.