Toxicity and dyeing properties of dyes obtained through laccase-mediated synthesis

The use of enzymes in textile processes has many advantages as far as environmentally friendly processes are concerned. These advantages include water and energy savings, the use of lower amounts of chemicals, and mild and more sustainable production processes. Several orange-red colored bio-dyes were synthesized during laccase-mediated homomolecular or heteromolecular transformations of simple aromatic precursors. Due to the presence of many various substituents in the structure of these precursors, ensuring their laccase-mediated transformation into colored products, the dyes obtained were tested for their toxicity effect against humans and the environment. The evaluation of environmental toxicity employed the bioluminescent marine bacterium (Vibrio fischeri) as a test organism according to the Microtox® basic test protocol. The effect of dyes on human cells was tested in culture of normal human colon epithelial cells, using two independent tests. Despite the presence of the reactive amino group in the structure of precursors, a majority of the dyes obtained were non-toxic. The presence of a carboxylic and/or sulfonic group in the formula of the precursors ensures a good solubility of the dyes in water. The dyes obtained possess good dyeing activity towards natural and synthetic fibers. Mild conditions of synthesis thereof, as well as a lack of toxic by-products and effluents, constitute advantages of the application of laccase-mediated biocatalysis in the synthesis of textile dyes. Due to the environmental impact associated with the production of textile dyes, the potential application of fungal laccase as a biocatalyst for the synthesis of valuable colorants has been demonstrated in this paper.