Study On The Chemical Connection Of Lienin-xylan Complexes By Isotopic Tracer Technique

Lignin fibers are important source of resources used for pulp and paper makingwhich account for about80%percentage of earth biomass and are mainly consisted ofplant cytoskeleton of cellulose, hemicelluloses, lignin and other components. Theessence of pulp and paper making industry is to remove lignin from plant cell walls,however, the existed lignin-carbohydrate complexes make problems for completelyremoval of lignin which may cause significant effluence for paper physical propertiesduring paper making process. Earlier researchers have confirmed that there is chemicalbonding between cellulose and lignin which can be concluded as benzyl ether linkage,benzyl ester linkage and acetal linkage in which acetal linkage may be the main type.For the linkage of lignin and hemicelluloses, Bj rkman found that half of the lignin isfree and other half is linked with hemicelluloses, With years of studies, researchersfound that¹³C labeled lignin precursor applied in the studies of structure analysis canmore accurately infer the bonding position of polysaccharides on lignin side chainwhich importantly promoted the process of the studies of lignin-hemicellulosesstructures. However it can’t infer the bonding position of lignin side chain onpolysaccharides unite. Therefore, this thesis adopted the¹³C isotopic tracer technique torealized the isotopic label of xylan precursor in plant hemicelluloses, combined withCP/MAS,¹³C-NMR and high resolution liquid¹³C-NMR technique to discuss theconnection of xylan in hemicelluloses and lignin，which is important research directionof wood chemistry and field of pulp and paper making.In this thesis,¹³C labeled precursor of xylan myo-inositol was synthesized bybiochemical method with D-¹³C₆-glucose as raw material and was characterized withFT-IR spectra and1H-NMR spectra. Precursors of xylan, the precursor of ligninconiferin-β-D-glucoside were injected to the rice stalk as well as PAL inhibitorL-2-amino-3-phenyl-propionic acid. After one month of natural training it showed noabnormal growth of rice.¹³C isotope abundance analysis of rice stalks were taken withVario cube element analyzer, results showed that rice were successfully labeled. Withhigh resolution CP/MAS¹³C-NMR preliminarily test the rice stalk and found thatobvious enhanced peak were obtained by applying¹³C labeled precursor which can beinfered that lignin in rice stalk were connected by β-O-4、β-1、β-5and β-β linkage. C1ofxylan may connected with lignin in the forms of acetal and ether linkage respectively.With targged rice stalk with raw material, hemicelluloses and milled wood lignin （MWL）were extracted for¹³C isotope abundance test, results showed that precursor of xylanwere metabolized to hemicelluloses.Lignin-carbohydrate complexes （LCC） is extracted grom¹³C labeling rice stalkxylem by the method of Bj rkman, combined with FT-IR and high resolution liquid¹³C-NMR detection analysis it was found that the bonds between lignin and xylan wasacetal and ester linkage on C1of xylan unit, In order to find the highly efficient enzymeseparate lignin and hemicellulose, prepared LCC is enzymed by cellulose, hemicellulaseand xylanase. The Enzymatic hydrolysis product is detected by high resolution liquid ¹³C NMR which made it more confirmed that the bond between hemicellulose and α-Cof lignin was acetal and ester linkage.In order to better simulate the deposit and copolymerization of cell wallcarbohydrate, this study used¹³C labeled xylose and coniferin as raw material, with thefunction of mixed enzyme, a model complex of DHP-xylose were achieved, to keep thenatural structure and completeness of the complex, high resolution¹³C-NMR analysiswere taken to clarify the bonding position of lignin on xylose. And the followingconclusion were reached: The¹³C-xylose were incorporated into DHP-xylose complexwhile slight difference exist between water soluable and water insoluable fraction; The¹³C-NMR sprctra of¹³C-enriched DHP-xylose provide definite information on structureof LCC; Two kinds of lignin-carbohydrate linkage（ester and benzyl ether linkage） werefound in DHP-xylose-WS while in DHP-xylose-IS only found benzyl ether linkage;LCC lingkage was most possiblely occur on C1position of D-xylose; In the presence ofD-xylose, the lignin units were mainly linked in the forms of β-O-4, β-β，β-1and β-5structures.