Formation of cyclodextrin inclusion complexes with doxycyclin-hyclate: NMR investigation of their characterisation and stability

The solubility of cyclodextrin (CD) can be notably improved when it is included in a polymeric structure. CD was reacted with citric acid, yielding a water-soluble polymer whose inclusion properties towards doxycyclin-hyclate (DOX) as guest molecule were investigated by NMR. The new DOSY (Diffusion Ordered SpectroscopY) method, based on diffusion coefficient measurements is convenient study complexes made of large molecules and it was applied to determine the association constants between DOX and parent beta and gamma-CD and their polymerised forms. The association constant obtained by DOSY was compared with that determined more classically by the chemical shift variation measurement using Scott's plot.