Laccase-mediator system assembling co-immobilized onto functionalized calcium alginate beads and its high-efficiency catalytic degradation for acridine.

A heterogeneous bead-shaped biocatalyst was prepared by assembling co-immobilization of encapsulating mediator 2,2'-Azino-bis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) into the functionalized calcium alginate composite beads by grafting glycidyl methacrylate and dopamine and then immobilizing laccase covalently onto beads. The enzyme-catalyzed degradation for acridine in water was systematically studied for the first time, and it was found that the co-immobilized laccase-mediator system has excellent capability to degrade acridine in water. Treating 30 mg/L acridine aqueous solution for 8 h with the biocatalyst, the degradation rate of acridine reached 100 %. In contrast, the degradation of acridine by free laccase under the same treatment conditions was low and difficult to observe. Its outstanding catalytic activity could be attributed to the effective assembling co-immobilization of laccase and the mediator so that the catalytic activity of the enzyme and the synergistic promoting action of the mediator have been given full play in the process of acridine degradation. The beaded biocatalyst about 3 mm in diameter could be easily recovered and reused several times without obvious deterioration in catalytic activity. Furthermore, according to the test results of electron paramagnetic resonance and the identified intermediates, the possible biocatalytic mechanism and reaction pathways for acridine degradation have been proposed.