Lenzinger Berichte 87 (2009) 88-97 88 COUPLING OF FUNCTIONAL MOLECULES ONTO LIGNIN MODEL COMPOUND DIBENZODIOXOCIN Tukayi Kudanga 1 , Endry Nugroho Prasetyo 1 , Jussi Sipilä 2 , Gibson S. Nyanhongo 1 , and Georg M. Guebitz 1 1 Graz University of Technology, Institute of Environmental Biotechnology, Petersgasse 12/1, A-8010, Graz, Austria 2 University of Helsinki, Department of Chemistry, P. O. Box 55 (A. I. Virtasen aukio 1), 00140, Helsinki, Finland Phone: +43316 873 8404; Fax: +433168738819; E-mail: g.nyanhongo@tugraz.at Laccase-mediated grafting of functional molecules presents an eco-friendly approach to functionalise lignocellulose materials. In this study functional molecules in the form of reactive phenolic amines, hydrophobicity enhancing fluorophenols and selected wood preservatives were successfully coupled onto lignin model compound dibenzodioxocin as demonstrated by HPLC analysis. This work therefore presents for the first time a model for functionalizing lignocellulose using the lignin model dibenzodioxocin. Keywords: Coupling, laccase, Dibenzodioxocin __________________________________________________ Introduction Lignin is the most abundant form of aromatic carbon in the biosphere and one of the three major components of wood which include cellulose and hemicellulose. In nature, it provides mechanical strength to wood by binding fibres together; is involved in water transport in plants and forms a barrier against microbial destruction by protecting the readily hydrolysable polysaccharides (Hofrichter, 2002). It is a three dimensional optically inactive polymer formed by the dehydrogenative polymerization of three p-hydroxycinnamyl alcohol precursor molecules coumaryl alcohol, coniferyl alcohol and sinapyl alcohol linked together in an irregular manner (Sjöström, 1993; Boudet, 2000; Martínez et al., 2008). Polymerisation of the precursor molecules is initiated by laccase and/or peroxidase oxidation of the phenylpropanoid units to form radicals. These radicals undergo resonance stabilisation forming different mesomeric forms that can couple in many possibilities forming inter-unit linkages which include β-O-4, β-5, 5-5, β-β, 5-O-4 and the more recently discovered dibenzodioxocin 5-5-O-4 (Karhunen et al. 1995a;b). These inter-unit linkages are globally classified as non-condensed (mainly aryl-alkyl-β-O-4 ether bonds) and condensed lignin (mainly C-C bonds) (Kukkola et al. 2003). The dibenzodioxocin linkage involves the formation of α, β ethers on the same 5-5' biphenyl structures (Argyropoulos et al. 2002; Brunow et al. 1998). Recently, there has been an increase in the number of studies aimed at improving properties of wood using enzymes. Lignin has been the target polymeric unit as it can be modified with minimal effect on the structural integrity of the wood. The process usually involves targeted modification of wood fibre surfaces using oxidative enzymes to create a reactive surface which can be used to functionalise the wood. The main oxidative enzymes which are able to modify lignin are laccases and peroxidases. However, laccase is usually