Intercalation of Apocarotenoids from Annatto (Bixa orellana L.) into Layered Double Hydroxides

Synthetic conditions were evaluated to intercalate norbixin into layered double hydroxides (LDH). Norbixin was isolated from a hydrosoluble commercial annatto extract. LDH samples comprising M2+/Al3+ (M = Mg, Zn) were synthesized by coprecipitation and characterized by X-ray diffraction, thermal analysis coupled to mass spectrometry, vibrational spectroscopies, and solid-state C-13 nuclear magnetic resonance. Radical scavenging activity of LDH hybrids was monitored by electron paramagnetic resonance towards the stable radical DPPH (1,1-diphenyl-2-picrylhydrazyl). LDH hosts presented more than 50 wt.% of norbixin and d-spacing (003) values of about 2.5 or 3.0 nm depending of the cation LDH composition. Vibrational spectra assignment (supported by density functional theory calculations) confirmed the chemical integrity of norbixin after intercalation into LDH. The inorganic layers were found to enhance the thermal stability of norbixin upon intercalation. The free radical scavenging capacity of norbixin was retained when immobilized into LDH. Considering that zinc and magnesium-LDH matrices are biocompatible and that norbixin presents biological activity, the hybrid materials appear as promising systems for biomedical assessment.