Curcumin Incorporation into Zn3Al Layered Double Hydroxides—Preparation, Characterization and Curcumin Release

Octavian D Pavel,Elena Bacalum,Ariana Şerban,Ruxandra Bîrjega,Rodica Zăvoianu

doi:10.3390/cryst10040244

Abstract

Curcumin (CR) is a natural antioxidant compound extracted from Curcuma longa (turmeric). Until now, researches related to the incorporation of CR into layered double hydroxides (LDHs) were focused only on hybrid structures based on a MgxAl-LDH matrix. Our studies were extended towards the incorporation of CR in another type of LDH-matrix (Zn3Al-LDH) which could have an even more prolific effect on the antioxidant activity due to the presence of Zn. Four CR-modified Zn3Al-LDH solids were synthesized, e.g., PZn3Al-CR(Aq), PZn3Al-CR(Et), RZn3Al-CR(Aq) and RZn3Al-CR(Et) (molar ratio CR/Al = 1/10, where P and R stand for the preparation method (P = precipitation, R = reconstruction), while (Aq) and (Et) indicate the type of CR solution, aqueous or ethanolic, respectively). The samples were characterized by XRD, Attenuated Total Reflectance Fourier Transformed IR (ATR-FTIR) and diffuse reflectance (DR)-UV–Vis techniques and the CR-release was investigated in buffer solutions at different pH values (1, 2, 5, 7 and 8). XRD results indicated a layered structure for PZn3Al-CR(Aq), PZn3Al-CR(Et), RZn3Al-CR(Aq) impurified with ZnO, while RZn3Al-CR(Et) contained ZnO nano-particles as the main crystalline phase. For all samples, CR-release revealed a decreasing tendency towards the pH increase, and higher values were obtained for RZn3Al-CR(Et) and PZn3Al-CR(Et) (e.g., 45% and 25%, respectively at pH 1).

Highlights

Turmeric (Curcuma longa) is a notorious spice, highly esteemed by the scientific world and by gastronomes as it is the primary source of curcumin (CR) or (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione, a renowned natural antioxidant polyphenol that can scavenge free radicals undergoing electron transfer or abstract H-atoms either from the phenolic OH groups or the CH2 group of the β-diketone moiety [1,2,3,4]
The results obtained by atomic absorption spectrometry (AAS) for the determination of Zn and Al content and the content of carbonate and CR in the samples calculated from the determination of the carbon content
The X-ray diffraction (XRD) patterns of the powders prepared by coprecipitation reveal that the precipitation in the presence of curcumin generates the formation of a zincite-phase (ZnO, ICDD card no. 36-1451) as by-product alongside with the layered structure

Summary

Introduction

Turmeric (Curcuma longa) is a notorious spice, highly esteemed by the scientific world and by gastronomes as it is the primary source of curcumin (CR) or (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione, a renowned natural antioxidant polyphenol that can scavenge free radicals undergoing electron transfer or abstract H-atoms either from the phenolic OH groups or the CH2 group of the β-diketone moiety [1,2,3,4]. The activity of of this this natural natural polyphenol polyphenol is is aa controversy controversy for for the the scientific scientific world. Some consider that the enol tautomer characterized by a better conjugation between the two aromatic. Some consider that the enol tautomer characterized by a better conjugation between the two rings containing the phenolic. OH groups holds the main for the of the aromatic rings containing the phenolic. OH groups holds the responsibility main responsibility forpresence the presence of antioxidant activity highlighted as an inhibition of superoxide radicals, hydrogen peroxide and the antioxidant activity highlighted as an inhibition of superoxide radicals, hydrogen peroxide and nitric better the the keto keto form form due due to nitric oxide oxide radical radical [3,5],.

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