Studies On Calcined Hydrotalcites As A "Biomolecular Vessel" For Bromelain And Orientation Study On Interlayer O-NBA In ZnAl-hydrotalcite

Calcined layered double hydroxide (LDO) has been used as the novel blomclecular vessel for the immobilization, storage as well as release of bromeiain. Tne immobilization is attributed to physical adsorption without affecting the structure of LDO, and the optimum initial amount of bromelain was 20 ml of 4 mg/ml for 1 g LDO and the immobilized enzyme activity express was 33．4% at pH 6．5．Tne adsorption isotherm of bromeiain / LDO can be well described with the Langmuir model with a R~2 of 0．9946, a maximum adsorption amount of 157 mg/g and the Langmuir adsorption equilibrium constant of 0．07 ml/mg. Significant improvements have been found in the stability of immobilized bromeiain upon heat treatment (increase in residual activity and denaturation temperature) as well as storage time compared with those of free bromeiain. In addition, the release maximum of bromeiain reached to 70% and the residual activity maintained 81% in water solution at pH 7．O-nitrobenzoic acid (o-NBA), naphthyl acetic acid (NAA) and fluorescein (FLU) have been intercalated into Zn-Al layered double hydroxides (LDHs) by ion-exchange method, respectively. The structure and composition of the intercalated materials have been characterized by XRD and FT-IR. The schematic models of three intercalation structures were proposed. Furthermore, the fluorescence polarization method has been used to investigate the preferential orientation of o-NBA intercalated ZnAl-LDHs. For this purpose, the fluorescence spectra for the horizontal and vertical directions of the emission polarizer were recorded for a common horizontally polarized excitation light as a function of the twist angle ofδof the film with respect to the excitation (emission) beam. The orientation of the o-NBA in the interlayer region of LDH was evaluated from the linear relationship between the fluorescence dichroic ratio and the twist angleδ. The results show that o-NBA molecules are intercalated into the LDH sheets as monomeric units with a tiltδangle of 39°with respect to the LDH layer.