Supramolecular Structure, Thermal Property and Sustained-release of Captopril-intercalated Zn/Al-layered Double Hydroxides

The antihypertensive compound captopril (Cpl) anion pillared Zn-Al layered double hydroxides were assembled by coprecipitation and anion exchange methods. The samples thereby obtained were characterized by XRD, FTIR, UV-Vis, TG-DTA and ICP measurements. The results show that the original interlayer nitrate anions of the hydrotalcite can be replaced by captopril anions to obtain captopril intercalated Zn-Al layered double hydroxides with good crystallinity. XRD analyses indicated that the interlayer spaces of as-synthesized Cpl-LDHs are 1.955 nm to 2.053 nm. The comparison was made between the above results and three-dimensional molecular size of Cpl ion calculated from the PM3 semi-empirical molecular orbital method. The captopril guests were arranged with alternately and bilayer tilted (along the long axis orientation in proper angle) between layers. It was found that the interaction of the host layers and the guests is through hydrogen bonding and electrostatic attraction, confirming that the intercalated hydrotalcite has a supramolecular structure. The thermal stability, and sustained-release of captopril anion-pillared hydrotalcite were enhanced to a considerable extent, comparing with that of captopril. The release profiles were fitted by the theoretical models of Higuchi and Korsmeyer-Peppas, the fitting data primarily agree with the experimental results, indicating that the release of Cpl ion from Cpl-LDHs is based on Fickian diffusion mechanism.