Study On The Structures Ofpectin-lignin Complexes And The Synlfiesis Of Pectin Percursor

The view of Lignin-carbohydrate complexes has been accepted. The compositionof carbohydrates in the wood are cellulose, hemicellulose, besides, there is a amount ofpectin. Pectin is bonding material between the cells in the plant cell wall layer in theintercellular. The main component of pectin is galacturonic acids, which can reactionwith lignin and form PLC(Pectin-Lignin Complexes, PLC). After years of researchingon the superstructure unit of Lignin, the deposition process of lignin is clear, but thedeposit of pectin and the reaction between pectin and lignin without more reserch. Sothe structure of PLC has an important research in the field of wood chemistry and pulpand paper chemistry.In order to study the structure of PLC, simulated the lignification process of thewood in the presence of pectin precursors α-D-galacturonic acid. GDHPC(Galacturonicacid-Dehydrogenation Polymer complex, GDHPC) were prepared from galacturonicacid and coniferin in the presences of enzyme. The FT-IR and¹³C-NMR spectra showedthat, β-O-4, β-β, β-5and β-1structures were the main substructures of DHP in GDHPC,in addition, coniferyl alcohol/aldehyde structure, vanillin structure, and Ar-C_αH₂-andetherified5-5' structures were formed. In GDHPC, Cαof structure unit of lignin andα-D-galacturonic acid were connected with ester bond, acetal bond and benzyl etherbond.This paper studied the change of LC bonds after treating the GDHPC withpectinase and NaOH respectively, explained the splitting of the LC bond in soda pulpingprocess and reason of pectin treatment could improve properties of pulp from theoreticalaspect. The FT-IR and¹³C-NMR spectra showed that the content of D-galacturonic aciddecreased after the two kinds of treatments. It was found that the benzyl ether bondcould not be degraded, however, the ester bonds was degraded completely afterdegradation by sodium hydroxide solution. None of the two kinds of LC bonds wasdegraded after treatment with pectinase. So, when treat fiber material contained lots ofpectin, the ester LC bond was degradated, lignin and pectin was seprated and dissoluted.When with pectinase only, pectin was degrated and dissoluted, the molecular weightbecame lower, the material became loose, and then the reaction of between chemicalsand materials was performanced. So, pectinase pretreatment could improve theefficiency of the alkali treatment, but could not seprate the pectin and lignin.α-D-glucuronic acid can form pectin after supersession in plants, soα-D-glucuronic acid can be used as precursor for isotope tracer in plants, to research thedeposit mechanism of pectin and the reaction between pectin and lignin. In order tolable pectin in the plant by α-D-glucuronic acid-¹³C, we needed to explore the synthesisroute of α-D-glucuronic acid by using α-D-glucose as the starting material. Thesynthesis step was as follows: In the first step, C₁position of α-D-glucose was blankedwith methyl, then the primary alcohols hydroxyl groups was catalytically oxidized by TEMPO/NaClO/NaBr system to be carboxyl groups. In the third step, methylα-D-glucuronide was hydrolyzed to obtain α-D-glucuronic acid in diluted hydrochloricacid. In the first two-steps, the reactions had high selectivity and yield, however, thereaction of hydrolysis was relatively slow with poor selectivity. Therefore, thehydrolysis condition was optimized. Methyl α-D-glucuronide was hydrolyzed in dilutedhydrochloric acid for15h,30h,45h,58h,65h, respectively. HPLC analysis showed thatbefore hydrolysis for58h, the yield of α-D-glucuronic acid was increased with theextension of hydrolysis time, but the continuing hydrolysis reduced the yield. HPLCanalysis showed that the yield was38.4%,50.40%,64.90%,3.9%, respectively afterqualitative and quantitative analysis. Methyl α-D-glucuronide was hydrolyzedcompletely after reaction for58h with the highest yield of64.90%, but the byproductincreased, so45h was the best hydrolysis condition. The total yield on the basis ofα-D-glucose was45.2%.