同位素标记法用于植物纤维中LCC蒸煮过程中结构变化的研究

Tracking structural change of LCC in plant by isotopic tracer technique

为了研究植物纤维原料中的木素-碳水化合物复合体(lignin-carbohydrate complexes,LCCs)在硫酸盐法蒸煮过程中的结构变化,向天然植物稻秆中投入带13 C同位素标记的松柏醇葡萄糖苷,用Bjrkman的方法将木素-碳水化合物复合体从稻秆粉末中分离出来,结合红外光谱和高分辨率的液态13 C NMR检测分析发现木素与糖类主要是通过苯甲醚键、酯键和缩醛键连接。其中,在LCC中木素的主要结构为β-O-4结构。将分离出来的带标记的LCC模拟硫酸盐法蒸煮,分离得到木素-碳水化合物复合体的硫酸盐木素。通过对天然稻秆LCC硫酸盐木素和稻秆LCC硫酸盐木素-[α-13 C]的红外光谱和高分辨率13 C NMR分析,证实了在稻秆LCC硫酸盐蒸煮后,产物中还存在少量以苯甲醚键和缩醛键连接的LC结构。另外,所得硫酸盐木素主要以β-O-4结构为主,含有少量的β-β、β-5和β-1结构。

To understand structure change of lignin-carbohydrate complexes （LCCs） in kraft cooking process, it was separated firstly out from the powder of rise straw by Bjorkman procedure, into which coniferyl alcohol glucoside with xaC-label had been rejected, and its structure was determined by 13C NMR and FT-IR spectra. The result showed that lignin was linked to carbohydrate by benzyl ether, ester and a- ketal bonds, and β-0-4 structure was the main structure of lignin in LCC. Then, the LCC obtained with and without 13C-label was cooked by kraft method and isolated respectively, to get lignin-carbohydrate complex-kraft lignins （LCC-KLs）. The LCC-KLs structures were determined by 13C NMR and FT-IR spectra, and the intensities of a-carbons increased markedly for the sample with a-13 C-label. The result showed that most of benzyl ether bonds and ketal linkage between lignin and carbohydrate were broken in pulping, but there still were bits of ketal linkage. Main structures of LCC-KL were found to be β-0-4 units, with a small number of phenylcoumaran units, pinoresinol units and β-1 units.