Antibacterial nitrogen-containing mesostructured SBA-15-type materials: insight into functional groups and surface polarity

Abstract

Several nitrogen-containing organofunctionalized SBA-15-type materials have been successfully prepared and characterized. Besides the well-known aminopropyl-modified silica, propyl-dimethyl-octadecyl-ammonium and propyl-pyridyl-pyridinium have also been used for tethering the framework through Pluronic-templated sol–gel hydrolysis and co-condensation. Regardless of the nature of the starting precursors, their functionalities and/or their bulkiness, well-ordered silica mesostructures with high surface areas, pore sizes and pore volumes were obtained, with the flexibility or rigidity fingerprint of the precursor being transcribed at the mesoscale. The accessibility to nitrogen functionalities has been assessed through adsorption of the anionic helianthine dye pollutant. Their antibacterial activity was next evaluated against Gram negative Escherichia coli and Gram positive Staphylococcus aureus, revealing primary dependence on the loading of ammonium and pyridinium groups and correlating well with their accessibility. A substantial increase in the antibacterial activity was noticed through trimethylsilylation of residual surface silanols, providing consequently an easy route towards more potent antibacterial materials, through switching surface polarity, without introducing any metal additive that could add cost and compromise their sustainability. We also demonstrate the utility of these nitrogen-containing solids to uptake and release pharmaceuticals, as exemplified by the entrapment of the well-established quercetin antioxidant, opening the way towards synergistic biomaterials.