Analysis of the molecular association of rifampicin with hydroxypropyl-ß-cyclodextrin

Inclusion complexes of rifampicin (RP) were prepared with hydroxypropyl-ß-cyclodextrin (HPßCD). 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/HPßCD 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/HPßCD 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 HPßCD...