Chloroaniline/Lignin Conjugates as Model System for Nonextractable Pesticide Residues in Crop Plants

In vitro lignins formed by the peroxidase/H 2 O 2 -mediated polymerization of coniferyl alcohol in the presence of 3,4-dichloroaniline or [ 15 N]aniline were studied by 1 H, 13 C, and 15 N NMR spectroscopy. The anilines were >95% bound to the benzylic α-position of lignin side chains. Mild acid hydrolysis under simulated stomach conditions (0.1 M HCl, 37 °C) was studied as a first estimate of animal bioavail ability. The two extremes of facile or slow acid hydrolysis that are known for chloroaniline/lignin complexes could be reproduced by using low or high incorporation ratios of aniline to coniferyl alcohol (10 or 40 mol %, respectively). The case of facile acid 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 15 N NMR spectral 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 presented 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.