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Solid state NMR studies of timber

Understanding the molecular architecture of timber using solid state NMR

 

              Solid state NMR

                             

Researchers from Cambridge lab led by Prof Paul Dupree (Department of Biochemistry, University of Cambridge) together with researchers led by his father, Prof Ray Dupree, from University of Warwick are gaining insight into the molecular architecture of wood. Their research uses solid state NMR to analyse the structure of timber. The work was recently published in Nature Communications and Nature Plants and provides novel insights into how components of timber come together to form the strong and resistant material. 

Timber is mainly composed of plant secondary cell walls - an intricate material of polysaccharides and phenolic compounds which surround wood cells. Due to the abundance of trees, plant secondary cell walls are the largest renewable resource of bioenergy on the planet. Sugars extracted from wood can be converted to biofuels. In addition, timber can be a sustainable source of advanced biomaterials such as nanocellulose with applications in food, medicicines and electronics.

Traditionally, wood is studied using biochemical analysis of individual components. Polysaccharides constituting the plant cell walls are isolated and looked at independently of the other components of biomass. This approach allowed characterisation of chemical composition of timber. However, it does not allow for analysis and understanding of the interaction between polysaccharides, or their structure, within an intact piece of wood.

OMT

To gain an understanding of the intact wood structure, researchers working at the University of Cambridge and University of Warwick are developing ways to use solid state Nuclear Magnetic Resonance (NMR). Similarly to magnetic resonance imaging (MRI) used by medical doctors, solid state NMR uses magnetic fields and radio-waves which can be used to decipher the structure of a material. The insights gained with the solid state NMR studies of a model plant Arabidopsis thaliana enabled the Cambridge and Warwick researchers to propose a model of wood molecular architecture.

 

                 cellulose-xylan

Model of cell wall molecular architecture. Xylan (green molecule) can interact with the cellulose microfibril (pink molecule).

 

The key wood components investigated by the group are cellulose and xylan. Cellulose is a crystalline, rod like structure, formed from a linear chain (called a polymer) of glucose and providing mechanical strength to wood. The key discovery from this work came when the group looked at xylan, a polymer of xylose sugars with branches of other sugars. The scientists were surprised to observe that xylan adapts a specific shape within wood. The in-depth analysis of solid state NMR data enabled them to conclude that xylan only binds one, surface of the cellulose crystal that has a suitable shape to stick to the xylan.

In the recent work published in Nature Plants the group has demonstrated that by altering the biosynthesis of xylan its structure can be changed. This led to formation of xylan molecules which are no longer able to interact with cellulose.  “This study is the first demonstration that the structure of xylan in the cell wall affects the xylan-cellulose interaction.” says Oliver Terrett, a PhD student and contributor to the publication, “Rather than being a random mixture of polysaccharides, there are specific interactions in the cell wall. These determine the properties we are interested in, such as strength.”

This opens the way for generation of improved timber, by better wood treatments and perhaps by plant breeding, to suit the needs of both bioenergy and advanced material industries.

Key publications:

Grantham N. et al., An even pattern of xylan substitution is critical for interaction with cellulose in plant cell walls. Nature Plants, 2017, DOI: 10.1038/s41477-017-0030-8

Simmons T. et al., Folding of xylan onto cellulose fibrils in plant cell walls revealed by solid-state NMR. Nature Communications, 2016, 7 (13902); DOI:10.1038/ncomms13902

Dupree R. et al., Probing the Molecular Architecture of Arabidopsis thaliana Secondary Cell Walls Using Two- and Three-Dimensional 13C Solid State Nuclear Magnetic Resonance Spectroscopy. Biochemistry2015, 54 (14), pp 2335–2345; DOI: 10.1021/bi501552k

 

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