STRUCTURAL HETEROGENEITY OF LIGNIN - CONTRIBUTION OF CARBON-CARBON BONDS

To collect information on the structural heterogeneity of lignin, diff erentiating xylem lignin of birch (Betula sp.) wood as a lignin sample representing compound middle lamella lignin was characterized in comp arison with mature xylem lignin as a further extension of our earlier studies. Differentiating xylem lignin was found to be composed mainly of p-hydroxyphenyl and guaiacyl units. The ratio of each structural un it, syringyl/guaiacyl/p-hydroxyphenyl=0.05/0.46/0.49, was quite differ ent from that of mature xylem lignin (0.33/0.67/0.00). Dioxane-chlorof orm (1 : 1) soluble fractions of acetylated periodate lignins prepared from these two xylems were characterized mainly by gel-filtration chr omatography and gel-permeation chromatography before and after iodotri methylsilane treatment. Differentiating xylem lignin was found to be r ich in the small molecular weight fraction with extended carbon-carbon bondings.