Solid state NMR characterization of zeolite beta based drug formulations containing Ag and sulfadiazine

Abstract

In this study we present a detailed characterization of zeolite beta-based drug formulations with antibacterial properties, containing Ag and sulfadiazine (SD). Solid state NMR spectroscopy (¹H, ¹³C, ²⁹Si, ²⁷Al and ¹H–²⁹Si CP-HETCOR experiments) was applied to address some important questions concerning the changes in zeolite structure as a result of the simultaneous presence of both drugs SD and silver sulfadiazine (AgSD). A mechanism for transformation of octahedral defect framework Al sites and encapsulation of the extraframework Al (EFAl) present in the parent beta material into framework tetrahedral species as a result of the drug loading procedure is proposed. The analysis of ¹H spectra suggested that an ion exchange process between the zeolite protons and Ag ions occurred upon the solid-state procedure of silver introduction by AgNO₃ or AgSD. Suggestions about the location of the drug molecules inside the pores and/or on the crystallite surface are made and the nature of the drug–carrier interactions is discussed. Comparison of ¹H spin-lattice (T₁) and spin–spin (T₂) relaxation times of pure drugs and drug loaded formulations indicate amorphization of the drug incorporated into the zeolite pores.