Villaverde Juan José, Li Jiebing, Ek Monica, Ligero Pablo, de Vega Alberto
Department of Physical Chemistry and Chemical Engineering, University of A Coruna, 15071 A Coruna, Spain.
J Agric Food Chem. 2009 Jul 22;57(14):6262-70. doi: 10.1021/jf900483t.
Milled wood lignin (MWL) and acetic and formic acid lignin (AL and FL) from Miscanthus x giganteus bark were produced, respectively, before and after organosolv fractionations under optimal conditions, in terms of organic and hydrochloric acid concentrations, liquid/wood ratio, and reaction time. In order to study the M. x giganteus native lignin structure and its modifications during the fractionation process, the lignins were studied by two-dimensional heteronuclear single quantum coherence (2D-(HSQC)), (13)C- and (31)P nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR), size-exclusion chromatography (SEC) both before and after thioacidolysis, and elemental analysis. In addition, chemical composition analysis was performed on ash, Klason lignin, and carbohydrate content. The analyses demonstrated that M. x giganteus native lignin (MWL) is highly acylated at the C(gamma) of the lignin side chain (46%), possibly with p-coumarate and/or acetate groups. This is newsworthy since several earlier studies showed that acylation at the gamma-carbon commonly occurs in C(3) and CAM grasses, whereas M. x giganteus is a C(4) grass. Furthermore, M. x giganteus showed a low S/G ratio (0.7) and a predominance of beta-O-4' linkages (up to 93% of all linkages). AL and FL lose part of these linkages during organosolv fractionation (up to 21 and 32%, respectively). The p-coumarate groups resist fractionation processes and are still present in high quantities in AL and FL. During the fractionation process, lignin is acetylated (acetic acid process) and condensed, with the G units condensing more than S units. M. x giganteus MWL contains a high content of carbohydrates (22.8%), suggesting that it is a lignin-carbohydrate complex (LCC). AL and FL showed low carbohydrate contents because of the breaking down of the LCC structures. AL and FL have high molecular weights and low polydispersities, and are high in phenolic content, qualities that make these suitable for different applications. These results suggest that refinement of M. x giganteus via organosolv processes could potentially turn this grass into a valuable source of both fiber and lignin.
在最佳条件下，就有机和盐酸浓度、液木比及反应时间而言，分别在有机溶剂分级分离前后，制备了芒草（Miscanthus x giganteus）树皮的磨木木素（MWL）以及乙酸和甲酸木素（AL和FL）。为了研究芒草天然木素结构及其在分级分离过程中的变化，通过二维异核单量子相干（2D-(HSQC)）、(13)C-和(31)P核磁共振（NMR）光谱、傅里叶变换红外（FTIR）、硫代酸解前后的尺寸排阻色谱（SEC）以及元素分析对木素进行了研究。此外，对灰分、克拉森木素和碳水化合物含量进行了化学成分分析。分析表明，芒草天然木素（MWL）在木素侧链的C(γ)处高度酰化（46%），可能带有对香豆酸酯和/或乙酸酯基团。这具有新闻价值，因为此前的几项研究表明，γ-碳处的酰化通常发生在C(3)和景天酸代谢（CAM）禾本科植物中，而芒草是C(4)禾本科植物。此外，芒草的S/G比值较低（0.7），且β-O-4'键占主导（占所有键的93%）。AL和FL在有机溶剂分级分离过程中失去了部分这些键（分别高达21%和32%）。对香豆酸酯基团抵抗分级分离过程，并且在AL和FL中仍大量存在。在分级分离过程中，木素被乙酰化（乙酸法）并发生缩合，其中G单元比S单元缩合得更多。芒草MWL含有高含量的碳水化合物（22.8%），表明它是一种木素-碳水化合物复合体（LCC）。由于LCC结构的分解，AL和FL的碳水化合物含量较低。AL和FL具有高分子量和低多分散性，且酚含量高，这些特性使其适用于不同的应用。这些结果表明，通过有机溶剂法对芒草进行精制有可能将这种草转化为纤维和木素的宝贵来源。
