The role of spin-phonon coupling in enhanced desorption kinetics of antioxidant flavonols from magnetic nanoparticles aggregates

An important criterion in the evaluation of drug delivery systems based on nanoparticles is the drug release kinetics. From numerous published works, it is obvious that the fraction of the released drug as a function of time shows qualitatively the same behaviour, even when the release is assisted by an external force. In this study a series of experiments has been performed on a system that can be considered as the simplest drug delivery system. It consists only of uncoated/unprotected superparamagnetic magnetite nanoparticles in the form of mesoporous aggregates and adsorbed flavonols (quercetin, myricetin, or myricitrin). The simultaneous utilization of external permanent and oscillating magnetic fields remarkably accelerated the flavonol release. There is no a specific pulling force that eventually causes the rupture of the bonds between the molecules and the particle surface, i.e. the detachment of an individual molecule is thermally activated. The adsorption of molecules onto nanoparticles follows almost without delay quick changes in the field-induced motion of the nanoparticles, and they are subject to more frequent collisions with the surrounding solvent molecules. The barrier fluctuations occur due to the magnetic field dependence of the nanoparticle phonon spectra, to which the adsorbed flavonol molecule vibrations are strongly coupled. The phonon frequencies and phonon damping of a ferromagnetic nanoparticle are actually affected by the magnetic field through the spin-phonon coupling. The rate of release (spontaneous or forced) is invariably a first-order process, which can be considered a basic property of a broad class of drug nanodelivery systems.