This paper aimed to study the mode of inclusion for 7-hydroxyflavone (7HF) in β-cyclodextrin (β-CD) complex in basic (pH 12) and acid (pH 4.5) media. The thermodynamic parameters of the complexation of 7HF with β-CD were evaluated by means of steady-state fluorescence and solubility measurements at several temperatures. The 7HF-β-CD inclusion complex was spontaneously formed at 1:1 stoichiometry in both basic and acid media. The high number of hydrogen bonds formed between the host and the guest molecules favored complexation in the basic medium, with a ground-state equilibrium constant (K) of 990 ± 130 mol-1 L, at 25 ºC. The quantum-mechanics calculations showed that complexation of 7HF (neutral or anionic form) with β-CD occurred mainly via the phenyl group of the flavonoid. This result agreed with the induced circular dichroism signal of 7HF complexed with β-CD.
Keywords:
7-hydroxyflavone; β-cyclodextrin; fluorescence; solubility; quantum-mechanics calculations
