A reversible, switchable pH-driven quaternary ammonium pillar[5]arene nanogate for mesoporous silica nanoparticles.

Here we describe the assembly and pH-driven operation of two nanocarriers based on non-functionalized (MCM-41) and carboxylate-functionalized (MCM-41-COOH) containers loaded with the anticancer drug doxorubicin (DOX) and capped by quaternary ammonium pillar[5]arene (P[5]A) nanogates. MCM-41 and MCM-41-COOH containers were synthesized and transmission and scanning electron microscopies showed nanoparticles with spherical morphology and dimensions of 85 ± 13 nm. The nanochannels of MCM-41 loaded with DOX were gated through the electrostatic interactions between P[5]A and the silanolate groups formed at the silica-water interface, yielding the MCM-41-DOX-P[5]A nanocarrier. The second nanocarrier was gated through the electrostatic interactions between the carboxylate groups mounted on the surface of MCM-41 and P[5]A, resulting in the MCM-41-COO-DOX-P[5]A nanocarrier. The DOX release profiles from both nanocarriers were investigated by UV-vis spectroscopy at different pH values (2.0, 5.5 and 7.4) and also in the presence of ions, such as citrate (19 mmol L) and Zn (1.2 and 50 mmol L) at 37 °C. MCM-41-COO-DOX-P[5]A can be turned on and off eight times through the formation and breaking of electrostatic interactions. In vitro studies show that MCM-41-COO-DOX-P[5]A can penetrate and release DOX in the nucleus of human breast adenocarcinoma MCF-7 cancer cells leading to a pronounced cytotoxic effect. Therefore, the fabricated nanocarrier based on a water-soluble cationic pillar[5]arene nanogate, which is reversibly opened and closed by electrostatic interactions, can be considered as a promising drug transport and delivery technique for future cancer therapy.