Step-up synthesis of amidoxime-functionalised periodic mesoporous organosilicas with an amphoteric ligand in the framework for drug delivery

Abstract

The step-up synthesis of amidoxime-functionalised periodic mesoporous organosilicas (PMOs) with an ordered hexagonal structure was achieved in two steps: (i) direct co-condensation of diaminomaleonitrile and 3-isocyanatopropyltriethoxysilane (IPTES) and (ii) chemical modification of bridged nitrile into amidoxime using a hydroxylamine hydrochloride (NH₂OH·HCl) reagent. The synthesis approach allowed a high loading of amidoxime functional groups in the pore wall framework of the mesoporous materials with controlled regular morphologies. The resulting materials with various diureylenemaleonitrile contents (up to 40 mol%) contained ordered hexagonal mesopores. The highly ordered hexagonal arrangement of the pores with a high degree of uniformity of amidoxime-functionalised PMOs was confirmed by low-angle X-ray diffraction (XRD), N₂ adsorption isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composition of the mesoporous organosilica was further characterised by Fourier transform infrared (FT-IR) spectroscopy, ²⁹Si magic angle spinning (MAS) and ¹³C cross-polarization (CP) MAS nuclear magnetic resonance (NMR) spectroscopy. The synthesised materials with an amphoteric ligand in the framework were found to be suitable carrier materials for controlled drug delivery systems in a phosphate buffer solution at pH 6.0, 7.4 and 9.0 for both hydrophobic (ibuprofen) and hydrophilic drugs (5-fluorouracil).