Submitted to: Journal of Wood Chemistry and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2004
Publication Date: 3/15/2006
Citation: Zhang, L., Gellerstedt, G., Ralph, J., Lu, F. 2006. NMR studies on the occurrence of spirodienone structures in lignins. Journal of Wood Chemistry and Technology. 26(1):65-79. Interpretive Summary: The polymer, lignin, that holds plant fibers together (as well as serving in defense and water transport), still holds many mysteries. Unlocking them provides crucial clues to its biosynthesis and structure to provide the basis for targeted approaches toward improved utilization of plant fibers in processes ranging from natural ruminant digestion to industrial chemical pulping. One long-standing mystery is the appearance of substantial amounts in so-called beta-1 structures in products from various degradative analytical methods, but an inability to detect these structures in the whole lignin polymer by non-destructive methods, such as with nuclear magnetic resonance (NMR) spectroscopy. It is now recognized that these structures are present not in the conventionally described form but as precursors with novel structures. Here, we have garnered complete NMR evidence for such structures in a small range of plants, and at particularly high levels in kenaf. The data allows researchers to identify and quantify these components in plant fibers and to begin to determine their role in lignification (the biological process of making the lignin polymer), and their effect on lignin properties. Such studies are ultimately aimed at improving the sustainable utilization of our plant fiber resources.
Technical Abstract: Spirodienone structures have been detected in spruce, birch and kenaf lignin isolates. NMR signals corresponding to guaiacyl and syringyl spirodienones were fully identified and assigned based on 13C, QUAT, HSQC, HSQC-TOCSY and HMBC NMR data. Spruce lignin contains spirodienone structures of the guaiacyl type. Syringyl spirodienones dominate in kenaf and birch lignins. Each type of spirodienone was found to be present in two different stereoisomeric forms, with one of the isomers being more prevalent. Signal integrations indicate that about three spirodienones per 100 phenylpropanoid units are present in the spruce and birch lignins and about four in the kenaf lignin.