The implication of mediators for enhancement of laccase oxidation of sulfonamide antibiotics.

In this study, the transformation of sulfonamide antibiotics (SAs, 50 mg L(-1)) was investigated in systems consisting of a fungal laccase (6 IU) and six mediators (1mM). The results illustrate that the laccase had limited effect on the removal of sulfadimethoxine and sulfamonomethoxine. However, laccase oxidation with the mediators (LMS) led to significant declines of the SAs. Two mediators, 2-2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) and violuric acid, provided the fastest transformations of SAs in LMS, with t(1/2)s of 1.8-4.1 min; slower transformations in syringaldehyde and 4-hydroxybenzyl alcohol, with t(1/2)s of 19.0-131 min; and the slowest or no significant decline in 4-hydroxyacetophenone and 4-cyanophenol, with t(1/2)s > 330 min. The decline of the re-added SAs in LMS was slower than that of the first addition. De-aniline and oxidative coupling are the two detectable pathways for the transformation of SAs. The results indicated that some mediators enhanced laccase oxidation of the SAs.