Oligomerization of 3-substituted quinolines by catalytic activity of soybean peroxidase as a wastewater treatment. Product formation and computational studies

Although heterocyclic aromatics make up a vast group of water contaminants, the effect of enzyme on this class of recalcitrant compounds is largely unknown. Here, the feasibility of treatment of selected quinolines with soybean peroxidase is demonstrated and the effects of the most important parameters; pH, enzyme concentration, and peroxide concentration are optimized for each compound. 3-hydroxy and 3-aminoquinoline were found to be substrates amenable to >= 94% removal with pH optima of 8.6 and 5.6, respectively. In order to identify the transformation products of such treatment, the solution and precipitate after enzymatic treatment were analyzed by mass spectrometry to find that the dominant products were dimers and trimers from oxidative radical coupling. In addition, for 3-aminoquinoline azo-linked dimers and trimers were found. Computational techniques used to investigate the influence of redox potential and ionization energy of pollutants on their treatability by SBP showed a possible threshold between substrates and non-substrates. Computed spin densities were used to predict the regiochemistry of the radical coupling reaction.