Intercalation of an antibacterial photoactive ruthenium(II) Polypyridyl complex onto montmorillonite clay

Abstract

Antibiotic resistance is one of the most serious public health problems. Photoactive ruthenium (II) polypyridyl complex, [RuCl(MePhtpy)(dpp)](PF₆) (where, MePhtpy = 4′ -(4-methylphenyl)-2,2′:6′,2′′-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine), has shown promise as an antibacterial agent in the dark and upon photoirradiation. Montmorillonite (MMT) clay has shown potential as a drug delivery system due to its high drug adsorption capacity. In the current study, antibacterial ruthenium(II) polypyridyl complex, [RuCl(MePhtpy)(dpp)]⁺ intercalated MMT clay mineral (Ru-Clay) was synthesized and characterized. The ruthenium metal complex was intercalated into the MMT clay by the addition of an acetonitrile solution of metal complex to an aqueous colloidal solution of MMT solution, followed by centrifugation, filtration, and air drying. In 40 min, 128 mg of [RuCl(MePhtpy)(dpp)]⁺ complex was found to be adsorbed onto 1.0 g of calcinated MMT clay. The newly synthesized mineral was characterized by electronic absorption spectroscopy, infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and X-ray diffraction studies. The kinetics of metal complex adsorption and desorption on the MMT clay was evaluated by electronic absorption spectroscopy. The rate of intercalation of the metal complex on MMT clay was found to be much higher than the rate of the release of metal complex from the clay. Preliminary studies indicated that the metal complex adsorbed clay mineral had no effects on bacterial cell growth, attributed to slow desorption of metal complex from the clay. Work is currently underway to modify the clay surface in order to enhance the desorption rate.