Molecular Modeling of Lignin β-O-4 Model Compounds. Comparative Study of the Computed and Experimental Conformational Properties for a Guaiacyl β-O-4 Dimer

S. Besombes, D. Robert, J.-P. Utille, F. R. Taravel,  and K. Mazeau


The conformational preferences of the threo and erythro diastereomeric forms of a guaiacyl β-O-4 dimer have been investigated by molecular modeling using the CHARMM force field. Many low energy conformations have been identified for each diastereomer, showing that β-O-4 dimers can adopt a large variety of shapes. A consistent structural model has emerged that indicates different conformational behavior for the threo and erythro forms, corresponding to a preferential extended overall shape for the threo form. All the low energy conformers are stabilized by intramolecular H-bonds. In particular, the highly directional H-bond between the α or γ hydroxyl hydrogen and the aromatic methoxy oxygen governs the B aromatic ring orientation. However, it has appeared that the conformational preferences are predominantly governed by local steric interactions rather than by differences in the H-bonding pattern. From the satisfactory agreement between computed data (geometries and the Boltzmann distribution of the low energy conformers) and the experimental data reported in the literature (X-ray crystal structures and 3JHαHβ NMR coupling constant), the CHARMM force field has been validated for the study of β-O-4 structures. Clearly, the molecular modeling calculations have led to an improved rationalization of the conformational data collected by experimental techniques.

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Holzforschung is an international scholarly journal that publishes cutting-edge research on the biology, chemistry, physics and technology of wood and wood components. High quality papers about biotechnology and tree genetics are also welcome. Rated year after year as one of the top scientific journals in the category of Pulp and Paper (ISI Journal Citation Index), Holzforschung represents innovative, high quality basic and applied research.