The mediated adsorption (cosorption) of anionic drugs by cationic surfactants onto silica

Abstract

The mediated adsorption (coadsorption) of anionic drugs — genetisic acid (GA) ethylene diaminotetraacetic acid (EDTA) — and cationic surfactants — alkylpyridinium chlorides (C₁₀–C₁₆), tetradecylpyridiniumsalicylate and nitrate — on silicas with different structures and on Escherichia coli was studied. The anionic drugs are not adsorbed to silica from their pure aqueous solutions. In the presence of cationic surfactants, however, they are coadsorbed, accompanying the surfactant cations as counterions in their corresponding adsorbates. The establishment of these coadsorbates is hampered by narrow pores (d ⁻_pore < 6 nm) of the silicas. This mediated adsorption depends on the aggregation behavior of the surfactants and, consequently, on their hydrocarbon chain length. The coadsorbed drug anions can be rapidly exchanged by other ions, demonstrating that the surfactant adsorbates on silica act as anion exchanger. — From mixtures of cationic surfactants with EDTa the same mediated adsorption was confirmed on E. coli bacteria, explaining the enhanced antimicrobial action of these mixtures.