Heikkinen Harri, Elder Thomas, Maaheimo Hannu, Rovio Stella, Rahikainen Jenni, Kruus Kristiina, Tamminen Tarja
VTT Technical Research Centre of Finland , Biologinkuja 7, Espoo, FI-02044 VTT, Finland.
J Agric Food Chem. 2014 Oct 29;62(43):10437-44. doi: 10.1021/jf504622j. Epub 2014 Oct 15.
Chemical changes of lignin induced by the steam explosion (SE) process were elucidated. Wheat straw was studied as the raw material, and lignins were isolated by the enzymatic mild acidolysis lignin (EMAL) procedure before and after the SE treatment for analyses mainly by two-dimensional (2D) [heteronuclear single-quantum coherence (HSQC) and heteronuclear multiple-bond correlation (HMBC)] and (31)P nuclear magnetic resonance (NMR). The β-O-4 structures were found to be homolytically cleaved, followed by recoupling to β-5 linkages. The homolytic cleavage/recoupling reactions were also studied by computational methods, which verified their thermodynamic feasibility. The presence of the tricin bound to wheat straw lignin was confirmed, and it was shown to participate in lignin reactions during the SE treatment. The preferred homolytic β-O-4 cleavage reaction was calculated to follow bond dissociation energies: G-O-G (guaiacyl) (69.7 kcal/mol) > G-O-S (syringyl) (68.4 kcal/mol) > G-O-T (tricin) (67.0 kcal/mol).
阐明了蒸汽爆破（SE）过程引起的木质素化学变化。以小麦秸秆为原料，在SE处理前后通过酶促温和酸解木质素（EMAL）方法分离木质素，主要通过二维（2D）[异核单量子相干（HSQC）和异核多键相关（HMBC）]以及（31）P核磁共振（NMR）进行分析。发现β-O-4结构发生均裂，随后重新偶联形成β-5键。还通过计算方法研究了均裂/重新偶联反应，证实了其热力学可行性。证实了与小麦秸秆木质素结合的小麦黄素的存在，并表明其在SE处理过程中参与木质素反应。计算得出，均裂β-O-4裂解反应的优先顺序遵循键解离能：G-O-G（愈创木基）（69.7千卡/摩尔）> G-O-S（紫丁香基）（68.4千卡/摩尔）> G-O-T（小麦黄素）（67.0千卡/摩尔）。
