The effect of ions on the enzymatically induced synthesis of lignin graft copolymers

The effect of different ions which are constituents of technical lignin sul fonates (LS) on chemo-enzymatic graft co-polymerization was determined. The application of the iron chelator desfenioxamine in the initial reaction mi xture revealed that iron impurities of LS which catalyzed a Fenton-like rea ction were crucial for the initiation of grafting, whereas calcium or chlor ide ions showed no such effect. The addition of laccase (ATCC 11235) to the reaction mixture which contained desferrioxamine caused a significantly hi gher yield compared to the control; this indicates a crucial effect of lacc ase with regard to the initiation of copolymerization. The involvement of l accase in the initiation of the graft copolymerization was additionally con firmed by the application of low molecular weight phenolics instead of LS. In the presence of the lignin-like substrates, 3,4-dihydroxybenzoic acid an d guaiacol, the rare of the decomposition of t-butylhydroperoxide was signi ficantly enhanced by laccase. It can be assumed that the enzymatically gene rated phenoxy radicals mediate the production of oxygen centered radicals ( alkoxy or peroxy) which initiate grafting. (C) 2001 Elsevier Science Inc. A ll rights reserved.