Forest Sciences Institute (ICIFOR-INIA), CSIC, Ctra. de la Coruña Km 7.5, 28040 Madrid, Spain.
Department of Biomedicine and Biotechnology, University of Alcalá, 28805 Alcalá de Henares, Spain.
Int J Mol Sci. 2023 Jan 25;24(3):2359. doi: 10.3390/ijms24032359.
The usage of laccases is a sustainable and environmentally friendly approach to modifying the Kraft lignin structure for use in certain applications. However, the inherent structure of Kraft lignin, as well as that resulting from laccase modification, still presents challenges for fundamental comprehension and successful lignin valorization. In this study, bacterial and fungal laccases were employed to modify eucalypt Kraft lignin. To evaluate the type and range of the chemical and structural changes of laccase-treated lignins, different NMR techniques, including solution H and 2D NMR (heteronuclear single quantum correlation (HSQC)), and solid-state C NMR, were applied. Size exclusion chromatography and infrared spectroscopy were also used. Interestingly, HSQC analysis showed substantial changes in the oxygenated aliphatic region of lignins, showing an almost complete absence of signals corresponding to side-chains due to laccase depolymerization. Simultaneously, a significant loss of aromatic signals was observed by HSQC and H NMR, which was attributed to a deprotonation of the lignin benzenic rings due to polymerization/condensation by laccase reactions. Then, condensed structures, such as α-5', 5-5', and 4-O-5', were detected by HSQC and C NMR, supporting the increment in molecular weight, as well as the phenolic content reduction determined in lignins.
漆酶的使用是一种可持续且环保的方法，可以改变 Kraft 木质素的结构，以用于某些应用。然而，Kraft 木质素的固有结构以及漆酶修饰所产生的结构，仍然对基本理解和成功的木质素增值带来挑战。在这项研究中，使用细菌和真菌漆酶来修饰桉木 Kraft 木质素。为了评估漆酶处理木质素的化学和结构变化的类型和范围，应用了不同的 NMR 技术，包括溶液 H 和二维 NMR（异核单量子相关 (HSQC)）以及固态 C NMR。还使用了尺寸排阻色谱法和红外光谱法。有趣的是，HSQC 分析显示木质素中含氧脂肪族区域发生了重大变化，由于漆酶解聚，几乎完全没有侧链对应的信号。同时，HSQC 和 H NMR 观察到芳环信号的显著损失，这归因于漆酶反应的聚合/缩合导致木质素苯环的去质子化。然后，通过 HSQC 和 C NMR 检测到缩合结构，如 α-5'、5-5'和 4-O-5'，这支持了分子量的增加，以及木质素中酚含量的降低。
