Inclusion complexes of rifampicin (RP) were prepared with hydroxypropyl-²-cyclodextrin (HP²CD). The aqueous solubility of RP increased linearly with cyclodextrin concentration in all range of the solubility diagram. The data was analyzed using the framework of Higuchi and Connors. The stability constant (K) values for RP/HP²CD complex at pH 6.9 were 18 and 120-125 M-1 for ionic strength 0.01 and 0.18M, respectively. The analysis of the chemical shift data of ¹H and 15N for free RP and RP/HP²CD inclusion complex reveal that only peaks of the side chain related to the piperazine ring of RP change substantially, probably due to interaction of this region of RP molecule with the hydrophobic core of HP²CD. We also postulated the optimized structure of RP/HP²CD inclusion complex using molecular modelling study. We found that the postulated structure was in agreement with ¹H and 13C-NMR and 15N-NMR spectra.
Rifampicin; Hydroxypropyl-ß-cyclodextrin; Inclusion complex; Molecular Modelling; Proton Nuclear Magnetic; Resonance
