A solid state NMR study of layered double hydroxides intercalated with para-amino salicylate, a tuberculosis drug

Para-amino salicylate (PAS), a tuberculosis drug, was intercalated in three different layered double hydroxides (MgAl, ZnAl, and CaAl-LDH) and the samples were studied by multi-nuclear (H-1, C-13, and Al-27) solid state NMR (SSNMR) spectroscopy in combination with powder X-ray diffraction (PXRD), elemental analysis and IR-spectroscopy to gain insight into the bulk and atomic level structure of these LDHs especially with a view to the purity of the LDH-PAS materials and the concentration of impurities. The intercalations of PAS in MgAl-, ZnAl-, and CaAl-LDH's were confirmed by C-13 SSNMR and PXRD. Moreover, C-13 MAS NMR and infrared spectroscopy show that PAS did not decompose during synthesis. Large amounts (20-41%) of amorphous aluminum impurities were detected in the structure using Al-27 single pulse and 3QMAS NMR spectra, which in combination with H-1 single and double quantum experiments also showed that the M(II):Al ratio was higher than predicted from the bulk metal composition of MgAl-PAS and ZnAl-PAS. Moreover, the first high-resolution H-1 SSNMR spectra of a CaAl LDH is reported and assigned using H-1 single and double quantum experiments in combination with Al-27{H-1} HETCOR. (C) 2016 Elsevier Inc. All rights reserved.