The conformation of lignin in solvents is major key factors governing the physicochemical properties of aromatic polymers. However, the conformational changes of lignin in good and poor solvents is not clearly understood at the molecular level. In this study, short- (DP 2.77) and long-chain (DP 4.49) lignin oligomer model compounds composed solely of interunit β– O –4 bonds with a narrow polydispersity were synthesized, and their NMR spectra were recorded to evaluate the molecular structural changes induced by addition of water to an organic solvent. The spectral signals were completely assigned in DMSO- d 6 and D 2 O by applying 2D 1 H– 13 C HSQC, HMBC, and long-range heteronuclear single quantum multiple bond correlation (LR-HSQMBC). The conformation of the long- and short-chain lignin models were analyzed by 2D 1 H– 1 H ROESY. In all the solvent systems, consisting of DMSO- d 6 and containing 0–90% volume of acetic acid- d 4 buffer in D 2 O (pD 5.0), the lignin models were found to have folded conformations, but more compact structures were observed in D 2 O compared with DMSO- d 6 .

中文翻译：

---

不同含水量有机介质中完整的NMR分配和β–O–4木质素低聚物模型化合物的分子结构变化分析

木质素在溶剂中的构象是支配芳族聚合物理化性质的主要关键因素。然而，在分子水平上尚不清楚木质素在好溶剂和差溶剂中的构象变化。在这项研究中，合成了短（DP 2.77）和长链（DP 4.49）木质素低聚物模型化合物，这些化合物仅由具有窄多分散性的单元间β–O–4键组成，并记录了其NMR光谱以评估分子结构将水添加到有机溶剂中引起的变化。通过应用2D 1 H– 13 C HSQC，HMBC和远程异核单量子多键相关（LR-HSQMBC），将光谱信号完全分配到DMSO-d 6和D 2 O中。长链和短链木质素模型的构象通过2D 1 H–1 H ROESY分析。