Thermal analysis and spectroscopic characterization of interactions between a naphthoquinone derivative with HP-β-CD or PVP

The purpose of the present study was to investigate the interaction between both hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and PVP-K30 with 2-hydroxy-N-(3-methyl-5-ethyl-4-isoxazolyl)-1,4-naphthoquinone-4-imina (I), asynthetic derivative of isoxazolylnaphthoquinones that has demonstrated to exhibit important biological activity against S. aureus and T. cruzi. The continuous variation plot for I-HP-beta-CD system showed a 1:1 stoichiometry for the complex. Ultraviolet absorption spectroscopy indicates that the isoxazole moiety of I is preferably incorporated in the cavity. Furthermore, proton nuclear magnetic resonance spectroscopy suggests that this incorporation is made from the primary hydroxyl group side of the cyclodextrin. The validation of this incorporation is further evidenced by thermal analysis (DSC and TGA) and infrared spectroscopy. I-PVP-K30 interactions in solid state were demonstrated by combining the infrared spectroscopy data with the results of thermal analysis (DSC, TGA). These methods suggest that drug-polymer interaction probably occurs via intermolecular hydrogen bonding between the drug hydroxyl and polymer carbonyl groups.