Structural Elucidation Of Lignin And Lignin-carbohydrate Complex(LCC) From Eucalyptus Grandis × E.urophylla

Lignin and lignin-carbohydrate complex(LCC)have complex and heterogeneous structures which are neither absolutely definable nor determinable.Thereinto,the main question is how to isolate lignin and LCC from plant cell wall with unaltered forms.Therefore,lignin and LCC were isolated from Eucalyptus grandis × E.urophylla under mild conditions in this thesis.The structure of lignin and LCC were characterizd by chemical and other methods.(1)Eucalyptus grandis × E.urophylla LCC were extracted by neutral and acidic dioxane(0.05 M HCl),then precipitated sequentially by 70%ethanol and 100%ethanol.It was found that the acidic dioxane treatment signifcantly improved the yield of LCC(66.4%based on Klason lignin),and LCC structures and linkages were relatively complete.Moreover,the 2D-HSQC spectra showed that the main LCC linkages of Eucalyptus were phenyl glycoside(PhGlc)and benzyl ether(BE)bonds.(2)A combined method based on alkaline dioxane(0.05 M NaOH)extraction and gradient acid precipitation was used to separate lignin from Eucalyptus.In addition,the residual lignin was also characterized to evaluate the whole lignin structure which was obtained after extraction.Results showed that the yield of lignin extracted by alkaline dioxane was relatively high and the content of carbohydrates was lower than that of MWL.The structure of isolated lignin was similar to that of MWL.The molecular weight of lignin fractions decreased with the decline of the pH of acid water,while the contents of total phenolic-OH present trend of increasing.Moreover,the Eucalyptus grandis × E.urophylla lignin was typical "G-S" lignin.(3)Milled wood lignin(MWL),lignin-carbohydrate complex(LCC),celluloytic enzyme lignin(CEL),and enzymatic hydrolysis residual lignin(EHRL)were sequentially isolated from Eucalyptus grandis × E.urophylla with different ages(2,3 and 4 years old)under mild conditions,and the variations of LCC linkages and lignin structures during the Eucalyptus growth were investigated.The 2D-HSQC analysis showed that the amounts of ?-O-4 in the MWL and LCC fractions increased tendency with the Eucalyptus growth,while those in the CEL and EHRL fractions had no obvious variation.The S/G ratios of the MWL,LCC,and CEL fractions increased first and then decreased,whereas those of the EHRL fractions decreased with the growth of the tree.Moreover,the PhGlc was only detected in the LCC fractions and the trends of PhGlc amount in the LCC fractions were consistent with the S/G ratio.The variation of the amount of BE in the MWL fractions was parallel to the S/G ratio,while that in the CEL fractions was contrary to it.