Conformational study of a guaiacyl β-O-4 lignin model compound by NMR.: Examination of intramolecular hydrogen bonding interactions and conformational flexibility in solution

被引:27
作者
Besombes, S [1 ]
Utille, JP [1 ]
Mazeau, K [1 ]
Robert, D [1 ]
Taravel, FR [1 ]
机构
[1] Univ Grenoble 1, CNRS, Ctr Rech Macromol Vegetales, F-38041 Grenoble 9, France
关键词
H-1; NMR; C-13; lignin; beta-O-4 model compound; hydroxyl protons; H-bonding; conformational flexibility;
D O I
10.1002/mrc.1317
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Intramolecular H-bonding interactions were investigated in solution for the threo and erythro diastereomeric forms of a guaiacyl beta-O-4 lignin model compound by using the NMR data obtained from hydroxyl protons. Temperature coefficients of the chemical shifts (ddelta/dT) and coupling constants ((3)J(HCOH)) were measured in aprotic and protic solutions: DMSO-d(6), acetone-d(6) and acetone-d(6)-water. The NMR parameters do not support the existence of strong and persistent intramolecular H-bonds that could participate in the stabilization of the guaiacyl beta-O-4 structure in solution, but instead indicate that intermolecular H-bonds to solvent predominate. 1D NOE experiments nevertheless revealed the presence of a direct chemical exchange between the hydroxyl protons, suggesting the possible existence of weak and transient intramolecular H-bonding interactions. The conformational flexibility of the threo structure was also investigated in acetone solution from the measurement of long-range H-1, H-1 and H-1, C-13 coupling constants and from NOESY experiments. The NMR data are not consistent with any single conformation, indicating that different conformers co-exist in solution. The experimental results support the conformational flexibility predicted by molecular dynamics simulations performed in a previous study. Finally, both experimental and theoretical approaches indicate that weak intramolecular H-bonds can exist transiently in solution, breaking and reforming as the beta-O-4 molecule undergoes conformational interconversion, but cannot be invoked as possible means of conferring rigidity to the beta-O-4 structure. Copyright (C) 2004 John Wiley Sons, Ltd.
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页码:337 / 347
页数:11
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