摘要
采用岳阳天然荻场当年成熟获秆为代表样,经苯:乙醇(2:1V/V)及热水抽提,再用缓和亚氯酸钠法处理得到综纤维素.然后用 KOH 溶液抽提,得到三种半纤维素级份 DA、DB_1和 DB_2.用 Fehling’s 试剂纯化半纤维素级份 DA 二次,得到聚木糖(DA_2)试样,测其糖基比、数均聚合度、各糖基的摩尔比、红外光谱和气谱-质谱(GC-MS)等结果可证实获主要半纤维素聚木糖(DA_2)的化学结构,平均由104.5个 D-吡喃式木糖基以β(1→4)糖苷键构成主链,另有6.3个 L-呋喃式阿拉伯糖基和2.1个 D-吡喃式葡萄糖醛酸基作为侧链连接在主链本糖基的2-或3-位上。
This paper is concerned with the isolation,purification and chemical structural studies of hemicelluloses in Miscanthus Sacchariflorus Benth collected from Yueyang,Hunan province.The Miscanthus Sacchariflorus Benth meal(20-40mesh)was successively extracted with benzene/alcohol(2:1 by volume) and hot water.The residue was delignified by treating with sodium chlorite at room temperature;the resultant holocellulose was extracted us- ing 10% aqeous KOH solution.Three different hemicellulose fractions(DA,DB_1 and DB_2)were thus obtained. These hemicellulose fractions were subjected to acid hydrolysis,releasing arabinose,xylose,galactose,glucose and traces of mannose. Hemicellulose DA was purifieated two times with Fehling’s solution,and xylan DA,was obtained.Reseults observed in acid hydrosis and the determination of the uronic acid content indicated that arabinose,xylose,glu- curonic acids and traces of other sugars were produced from xylan DA_2.And,the molar ratios of arabinose,xylose and glucuronic acid are 0.6:10:0.2.The specific rotation of xylan DA_2 is negative([α]_D^(20)=-111.6,in 2.5% NaOH Aqueous solution),indicating that the xylan is β-linkage.IR spectrum of xylan DA_2 gave absorptions bands at 892.88cm^(-1),conforming very well with results obtained by specific rotation. Xylan DA_2 was converted to permethyl ether,its DPn determined by vapour phase osmometry was ca.113.The methylated xylan was hydrolysed with formic acid and then with dilute sulphuric acid.The hydrolysate,with some methylated sugars,were then converted into alditol acetates.GC and GC-MS analyses indicated the presence of alditol acetates existing as 2,3.5-tri-O-methylarabinose,2,3,4-tri-O-methylxylose,2,3-di-O- methylxylose and 2(3-)0-methylxylose in molar ratios of 0.30:0.06:10:0.30.A sample of the methylated xylan was reduced with LiAIH_4 and then hydrolysed.The following sugars were identified by GC and GC-MS technigues 2,3,5-tri-0-methylarabinose,2,3,4-tri-0-methylxylose,2,3-di-0-methylxylose,2(3-)0- methylxylose and 2,3,4-tri-0-methylglucose in the molar ratios of 0.29:0.05:10:0.50:0.11. Thus,it can be concluded that xylan DA_2 possessed an average of ca.104.5 contiguous β(1→4)linkage D- xylopyranosyl residues to which were attached ca.6.3 L-arabinofuranosyl residues and ca.2.1 D-glucopyra- nuronosyl residues at C-3 or C-2 positions of the xylose units.
出处
《中国造纸学报》
CAS
CSCD
北大核心
1992年第1期25-36,共12页
Transactions of China Pulp and Paper
