Exploring The Antimicrobial Effects Of Nitric Oxide Via Encapsulation Of A Photoactive Manganese Nitrosyl In MCM-41 Zeolite

Acinetobacter baumannii has emerged as a problematic pathogen capable of colonizing open wounds. Furthermore, it exhibits resistance to most traditional antibiotics. In this study, we report the synthesis of a zeolite-based material that photodynamically releases the antimicrobial agent nitric oxide (NO), and the material’s potent antibiotic effects against A. baumannii. The manganese nitrosyl [Mn(PaPy₃)(NO)](ClO)₄, which releases NO upon exposure to visible light, was incorporated into the sodium aluminosilicate zeolite MCM-41 by ion-exchange. The aluminosilicate matrix immobilizes the nitrosyl while still allowing photon absorption and subsequent release of photodissociated NO. The cationic [Mn(PaPy₃)(NO)]⁺ was soaked in an acetonitrile solution of MCM-41 to replace sodium ions binding the negatively-charged aluminum tetrahedral sites in the zeolite framework.  The ion-exchange method was compared to simple physisorption of [Mn(PaPy₃)(NO)]⁺ by soaking in a solution of silicate-based MCM-41. Loading capacity and NO release capabilities of both zeolites were compared by IR spectroscopy, powder x-ray diffraction, AAS and SEM-ED(X). The silicate-based zeolite exhibited loading capacity of 2 wt.% while the aluminosilicate-based zeolite demonstrated loading capacity as high as 5 wt.%, thus considerably increasing NO release. Furthermore, the ability to retain nitrosyl upon soaking in PBS buffer was also analyzed. We found that the negative charge of the aluminosilicate zeolite frame immobilized the nitrosyl within its framework with no leakage detected through ICP-MS after 4 hours of soaking; however, [Mn(PaPy₃)(NO)]⁺ was detected in the silicate zeolite solution after 1 hour of soaking. Finally, the antibiotic effects of the zeolites were demonstrated against A. baumannii by agar suspension method.