Determination of the structure of quinolone-γ-cyclodextrin complexes and their binding constants by means of UV

The host–guest inclusion complex structure and binding ability of two different quinolones with γ-cyclodextrin (γ-CD) were investigated in solution by means of UV–Vis and 1H NMR spectroscopy. Competition of oxolinic and nalidixic acid molecules for the γ-CD cavity was evaluated by determination of association constants. Both quinolones form 1:1 inclusion complexes, their binding constants at room temperature (25 °C) under acidic and basic conditions were calculated using Benesi–Hildebrand equation. The stability of the complexes was dependent on the structure of the quinolone. In general, the weaker binding constants were observed for oxolinic acid-γ-CD complexes (1616 and 1765 M−1) and the larger binding constants were obtained for nalidixic acid-γ-CD complexes (3760 and 3840 M−1). 1H NMR studies in D2O were performed to elucidate the structure of each inclusion complex, nalidixic acid molecule penetrates more deeply into the γ-CD cavity and an intermolecular hydrogen bond is formed. Knowledge about structure and relative stability of quinolone-γ-CD complexes will be useful for future applications of these antimicrobial agents in medicinal chemistry. © 2018, Springer Nature B.V.

VIVO