Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: October 25, 1999
Publication Date: N/A
Technical Abstract: Studies of lignin structure and reactivity have been re-energized by the emergence of modern technologies, new analytical methods, and by exciting recent findings. The structural aspects which were considered complex but well understood some years back have seen revisions that add to the complexity in some ways but are clarified by the logical chemistry in others. One of the most significant recent findings has been the elucidation of dibenzodioxocins as significant components of natural lignins. Another new structural unit, aryl-isochromans, expose a logical new pathway following beta-1-coupling. These new structures and others have been revealed by modern analytical and instrumental methods, particularly NMR. The now common use of 2D and 3D NMR, using pulsed field gradients, inverse detection, and modern digital instruments allows ever more sensitive detection and, more importantly, diagnostic interpretation. Studying lignins from non-woody plants has also provided significant new knowledge. Acylated lignins are now better understood, and cell wall cross- linking in grasses by ferulates has also recently been clarified. Mutant and transgenic plants in which steps in the monolignol biosynthetic pathway are down- or up-regulated are also providing a rich source of insight into the processes of lignification. Massive compositional shifts, significantly beyond traditional bounds, are found in a variety of mutants/transgenics. In some cases, units that are minor in "normal" lignins become major components. This facilitates their identification and may elucidate their radical-coupling reactions. Pathways interacting with lignification become identified, and the very definition of lignin itself becomes clouded or simplified depending on ones perspective.