Surfactant mediated intercalation of a hydrophobic drug into layered double hydroxides: Probing the structural features by the photophysical behaviour of piroxicam

Abstract

Piroxicam (PIR), a hydrophobic drug with ionisable properties, can adopt various prototropic forms and conformations, which make its structural and dynamic properties highly dependent on its environment. In this study, PIR was, for the first time, incorporated into Zn²⁺/Al³⁺ layered double hydroxides using a surfactant-mediated intercalation method (Zn₂Al-DS_@%PIR), which first involved the encapsulation of PIR within dodecyl sulfate (DS) micelles. A comprehensive investigation of the DS-PIR assembly within the interlayer space of the LDH is proposed, particularly emphasizing the utilization of the optical properties of PIR as a structural probe. The structural and chemical properties of the Zn₂Al-DS_@%PIR samples prepared with different PIR contents (0.16, 0.90 and 2.06 wt%) were assessed by X-ray diffraction, Fourier transform infrared (FTIR) and thermal analysis. By exploiting PIR's photochemical properties in both solid-state and solution, it was gained deeper insights into PIR molecular arrangement within the LDH interlayer space. FTIR results showed the stabilization of the ZZZ conformation form for intercalated PIR, while thermal analyses revealed an improved thermal stability of PIR of 80 °C for the sample with a maximum PIR loading content of 2.06 wt%. Interestingly, fluorescence results clearly confirmed the intercalation of PIR in LDH, both as global neutral and anionic forms, and allowed to infer their location in the interlayer space. A protective effect against photodegradation was also observed. This work can contribute to advancements in the challenging intercalation of other hydrophobic drugs.