Formation of cross-linked nitrile hydratase aggregates in the pores of tannic-acid-templated magnetic mesoporous silica: Characterization and catalytic application

Tannic-acid-templated magnetic mesoporous silica nanoparticles (TA-MMSNs) were synthesized for the first time. The TA-MMSNs were monodisperse spherical particles with a diameter of around 250   nm and a magnetization saturation value of 35.26 emu/g. The specific surface area of TA-MMSNs was 423.4   m 2 /g, and the diameter and cumulative volume of the pores were 9.349   nm and 1.071   cm 3 /g, respectively. The TA-MMSNs were used to prepare immobilized NHase (CLNHAs@TA-MMSNs) by forming cross-linked nitrile hydratase aggregates (CLNHAs) in pores of TA-MMSNs using glutaraldehyde as a cross-linker. CLNHAs@TA-MMSNs and free NHase had the same optimum pH (pH 7), and the optimum temperature of CLNHAs@TA-MMSNs (40   °C) was higher than that of free NHase (30   °C). Compared with free NHase, CLNHAs@TA-MMSNs exhibited improved thermal, pH, mechanical and storage stability. Furthermore, CLNHAs@TA-MMSNs was applied in production of nicotinamide, and yield of nicotinamide could reach more than 98%. The tolerance of CLNHAs@TA-MMSNs to high concentration of substrate was better than that of free NHase, and yield of nicotinamide could still reach 29.74% after seven cycles of reaction. The kinetic parameters were investigated and the results indicated a lower substrate affinity and catalytic efficiency of CLNHAs@TA-MMSNs in comparison with free NHase. This work demonstrated that TA-MMSNs could be efficiently employed as supports for enzyme immobilization.