Chloroaniline/lignin conjugates as model system for nonextractable pesticide residues in crop plants

In vitro lignins formed by the peroxidase/H2O2-mediated polymerization of coniferyl alcohol in the presence of 3,4-dichloroaniline or [N-15]aniline were studied by H-1, C-13 and N-15 NMR spectroscopy. The anilines were >95% bound to the benzylic a-position of lignin side chains. Mild acid hydrolysis under simulated stomach conditions (0.1 M HCl, 37 degrees C) was studied as a first estimate of animal bioavailability. The two extremes,of facile or slow acid hydrolysis that are known for chloroaniline/lignin-comelexes could be reproduced by using low or high incorporation ratios of aniline to coniferyl alcohol (10 or 40 mol %, respectively). The case of facile a cid hydrolysis and high animal bioavailability may be due to the high; mole ratios used and may not be relevant for pesticidal crop plant residue levels of 3,4-dichloroaniline. The latter are typically in the parts per million range. On the basis of N-15 NMR spectre I fine structure; we propose that the acid-labile linkage may be due to anchimeric assistance in conformers formed at the high aniline molar ratio. The;optimized methods represented here allow the use; of in vitro lignin copolymers as a reference system for the structural features. and the bioavailability of nonextractable pesticide residues in crop plants.