RESUMEN
Zein, a naturally biocompatible and biodegradable macromolecule, is widely used as plastic film material; however, the poor water solubility limits its other applications. In this study, we aimed to obtain carboxymethyl zein (CM-zein) by modifying it with sodium monochloroacetate in weakly basic environment. CM-zein showed a new FTIR peak of C-O-C bond at 1080 cm(-1), with a new signal region appearing at 4.0-4.05 ppm that assigned to the protons of the CH2 group from a carboxymethyl on (1)H NMR and a Tg of 168.0 °C by thermal analysis. Compared with the -12.3 mV of zeta potential of unmodified zein, CM-zein increased it significantly to -23.9 mV as a consequence of carboxymethylation. 5-Fluorouracil (5-FU), a model drug used in CM-zein-based tablet, was rarely detected in 0.1 mol/L HCl (pH 1.0) but it was released massively and quickly in phosphates buffer (pH 6.8) in vitro assays. The unmodified zein-based tablet illustrated much lower release level in these two fluids. Furthermore, the pharmacokinetic study of rats showed that CM-zein released 5-FU in intestine but not in stomach after dissolving. These findings indicated that CM-zein has the potential to be used for enteric preparation as a novel pH-selective biomaterial.
