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.