Zeolite Encapsulation of Indole as an Antibacterial with Controllable Release Property

Effective regulation of the release behavior of bactericides to avoid both too fast release and too slow release to maximize their antibacterial ability is still the face of a grand challenge. In this study, indole as a bactericide was encapsulated into three types of zeolites (denoted as indole@zeolite), including the ZSM-22 zeolite, ZSM-12 zeolite, and beta zeolite with different topologies, respectively, to obtain indole@ZSM-22, indole@ZSM-12, and indole@Beta complexes finally. Benefiting from the confinement effect of zeolites, the release rate of indole from these three zeolite encapsulation systems showed a much slower release rate than that of indole impregnated onto a counterpart zeolite (denoted as indole/zeolite), thus avoiding the too-fast and too-slow release very well. As determined by molecular dynamics simulation combined with experimental results, attributed to the unequal diffusion coefficient in these three encapsulation systems caused by different zeolite topologies, the release rate of indole within these three complexes was different from each other, hence providing an effective way to avoid a too-slow release rate through choosing different zeolite topologies. The simulation results showed that the timescale of hopping of indoles in zeolites plays an important role in the dynamics in zeolites. Taking killing Escherichia coli as an instance, compared with indole/zeolite, the corresponding indole@zeolite sample exhibited more efficient and sustainable antibacterial activity for its controlled-release behavior.