Silsesquioxane - Antimicrobial Silsesquioxanes

Antimicrobial Silsesquioxanes

In recent research efforts silsesquioxanes have been functionalized with biocidal groups to produce antimicrobial coatings. Such coatings have numerous applications, as there is a continually increasing demand for materials that will keep people safe and healthy. Organic ammonium salts are well known for their antimicrobial properties, meaning their ability to kill or inhibit the growth of harmful microbes. Specifically, quaternary ammonium salts (QAS) are used as disinfectants, antiseptics, and antifoulants that kill bacteria, fungi, and algae, but are not harmful to humans and animals. Several research groups have functionalized polyhedral oligomeric silsesquioxanes with QASs. The relatively small size of the silsesquioxane molecule, 2-5 nm, allows a QAS functionalized molecule to have a charge density similar to dendrimers and thus the antimicrobial efficacy is prominent. Chojnowski et al. explored the quaternization of dimethyl-n-octylamine by octa(3-chloropropylsilsesquioxane), (T-ClPr)₈, and transformed almost all eight chloropropyl groups into ionic quaternary ammonium chloride functions. The synthesis is based on a three-step hydrolytic polycondensation process of 3-chlo- ropropyltrimethoxysilane. The resulting material exhibited antimicrobial efficacy for the prevention of growth of both Gram-positive and Gram-negative bacteria.

More recently, Majumdar et al. synthesized an array of QAS functionalized polyhedral oligomeric silsesquioxanes (Q-POSS). These researchers varied the alkyl chain length from –C₁₂H₂₅ to –C₁₈H₃₇ and varied the counter ion between chloride, bromide, and iodine. The first reaction was the hydrosilylation between allydimethlamine and octasilane polyhedral oliomeric silsesquioxane via Karstedt’s catalyst to make a tertiaryamino-functinoalized silsesquioxane. The second step was the quaternization of the tertiaryamino groups with an alkyl halide. The alkyl halides used were 1-iodooctadecane, 1-bromohexadecane, and 1-chloroctadecane.