The relation between structure, function and properties of hemicelluloses is still not fully understood. Further knowledge about the heterogeneous molecular structure of hemicelluloses is needed in order to improve the utilization of polymeric hemicelluloses. The two main hemicelluloses in woody tissues are xylans, with a backbone consisting of D-xylose units, and glucomannans where the backbone contains both D-glucose and D-mannose, all linked by 1,4-β-glycosidic bonds in equatorial configuration. One important structural characteristic is the glycosidic bond and how it can affect the flexibility of the polymer. This could potentially be correlated to the hydrogen bonding possibilities over the linkage. In figure 1 we hypothesize three different types of glycosidic bond stabilizations. In this study all the disaccharides and tetrasaccharides mimicking the backbone of hemicelluloses were studied in aqueous solution by molecular dynamic simulations. Although the conformation of the glycosidic bond is also stabilized by steric interactions, there is a clear correlation with the hydrogen bonding possibilities. It was shown that tetrasaccharides show essentially the same phi/psi behavior as their corresponding disaccharides. Thus disaccharides seem to be a good starting point for analyzing the behavior of the glycosidic bonds in hemicellulose. To validate the results the modelled disaccharide systems are also being evaluated by NMR spectroscopy. According to preliminary results the three different glycosidic bond types show similarities, but they still have some varying properties. Type C is the stiffest, Type X the most flexible, and Type M can form hydrogen bonds around the glycosidic bond in the largest variety of conformations. The implications of these findings with regard to the properties of hemicelluloses will be discussed.

How the flexibility properties of hemicelluloses are affected by the glycosidic bonds between different backbone sugars – A molecular dynamics study

251st National Meeting (2016)

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