Li Gai-yun, Sun Qi-ning, Qin Te-fu, Huang Luo-hua
Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2010 Jul;30(7):1930-3.
The FTIR, UV-Visible, 1H NMR and GPC were used to study structural changes of brown-rotted lignin after sodium borohydride reduction. FTIR spectra showed that, after reduction, the band at 1,677 cm(-1) attributed to the conjugated carbonyl groups disappeared, and the band intensity at 1,715 cm(-1) attributed to the nonconjugated carbonyl groups decreased. On the other hand, the band at 1,509 and 1,603 cm(-1) attributed to aromatic skeletal vibration remained almost unchanged. UV spectra showed the decreased absorptions at 288 nm and 300-400 nm after reduction. 1H NMR spectra showed that, after reduction, the number of aromatic methoxyl and aromatic hydroxyls decreased, the number of aliphatic hydroxyls and the proton number attributed to many linkage structures connecting the phenylpropane units increased. GPC results showed that the molecular weight of reduced brown-rotted lignin increased and the molecular distribution got wider, as a consequence of the large molecular weight molecules generated during the reduction reaction. Our results suggest that the conjugated carbonyl groups can be totally reduced to the hydroxyl groups, but only some nonconjugated carbonyl groups can be reduced to the hydroxyl groups. The chemical structure of the brown-rotted lignin changed, but the benzyl ring kept stable. The condensation reaction took place during the sodium borohydride reduction process.
采用傅里叶变换红外光谱（FTIR）、紫外可见光谱（UV-Visible）、核磁共振氢谱（1H NMR）和凝胶渗透色谱（GPC）研究硼氢化钠还原后褐腐木质素的结构变化。FTIR光谱表明，还原后，归属于共轭羰基的1677 cm-1处的谱带消失，而归属于非共轭羰基的1715 cm-1处的谱带强度降低。另一方面，归属于芳环骨架振动的1509和1603 cm-1处的谱带几乎保持不变。紫外光谱表明，还原后288 nm以及300 - 400 nm处的吸收降低。1H NMR光谱表明，还原后，芳环甲氧基和芳环羟基的数量减少，脂肪族羟基的数量以及归属于连接苯丙烷单元的许多连接结构的质子数增加。GPC结果表明，还原后褐腐木质素的分子量增加且分子分布变宽，这是还原反应过程中生成大分子的结果。我们的结果表明，共轭羰基可完全还原为羟基，但只有部分非共轭羰基可还原为羟基。褐腐木质素的化学结构发生了变化，但苄基环保持稳定。硼氢化钠还原过程中发生了缩合反应。
