Controlled Radical Release with Iron Oxide Nanoparticles Grafted with Thermosensitive Alkoxyamine Triggered by External Stimuli

Abstract

We report an investigation of a controlled radical release produced by iron oxide nanoparticles (IONP) of ca. 25 nm covalently grafted through phosphonic groups with a thermosensitive alkoxyamine, 6-(4-(1-((di-tert-butylamino)oxy)ethyl)benzamido)hexyl)phosphonic acid having a relatively low homolysis temperature (kd = 2.43 10-2 s-1 at 89.5 °C, Ea = 117.8 kJ.mol-1). Action of an alternating current magnetic field (AMF) or a light irradiation at 808 nm produces a rapid heating of the nanoparticles’ surface, which induces the homolysis of the C-ON bond of alkoxyamines providing the efficient formation of free radicals. The kinetic of homolysis investigated by Electronic Paramagnetic Resonance (EPR) spectroscopy indicates almost total homolysis after 20 min of AMF exposure (16 kA.m-1) and 60 min of irradiation (2.6 W.cm-2), respectively. These findings underscore the critical importance of localized nanoscale effects, demonstrating that the homolysis rate at the nanoparticle surface under external stimuli is significantly higher compared to bulk solution heating, with this enhancement being even more pronounced under light irradiation.