by Mark E. Griffin (Great Lakes Bioenergy Research Center) … “Bacteria and fungi break down plants through a number of different ways. When you see mushrooms growing on dead logs in a forest, they are breaking down the plant cell wall into small pieces that they ‘eat’ so that they can grow,” says Klinger, who works with Eric Hegg and James “Ned” Jackson at MSU.
In a new paper, Klinger and her colleagues in the Great Lakes Bioenergy Research Center (GLBRC) mimicked this natural approach to deconstructing lignin, an abundant but tough substance that makes up about a third of most plants. Their paper appears in a special issue of ChemSusChem focused on lignin valorization. Lignin’s complex molecular structure make it a potential source of an array of platform chemicals—molecular building blocks that can be used to make plastics, fabrics, pharmaceuticals and more. But that same complexity also makes lignin hard to break down, requiring harsh and expensive conditions. Here, Klinger describes the group’s efforts to find a more efficient and cost-effective way to turn the tough-to-manage substance into valuable molecules.
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What was the focus of this study?
Because lignin is so complicated, we focused on an enzymatic process that cleaves the most common lignin bond, called beta-O-4. We chemically mimicked this process with thiols, which are simple organic compounds containing sulfur.
Previously, we published a proof-of-concept using this approach on simpler versions of lignin—small fragments like dimers and trimers, which have two or three lignin subunits linked together. In this newest publication, we moved on to polymer systems—larger, more complex lignin models that contain different kinds of chemical bonds. We found that our thiol-based process can do the same chemistries seen in the bacteria, not only on small lignin fragments but also on large lignin polymers.
Testing on small fragments lets us understand what is chemically happening to make sure we are mimicking the bacteria correctly. Then it was important to see if we could cleave bulky polymers that are more like real lignin. In future work, we are also hoping to increase the efficiency of our process by using electrochemistry to recycle the thiol compounds to decrease costs and increase yields.
How might this process be useful in industry?
Many manufacturing processes can’t deal effectively with large polymers, so breaking lignin into fragments, like monomers, dimers, trimers, etc., is important for moving toward industrial use. Then these smaller products can be converted into basically anything that fossil fuels can be converted into. Petroleum is distilled into various fractions for manufacturing, and the idea is that if fragmented lignin can be as well, we might be able to replace a petro-barrel with a bio-barrel. READ MORE
Klinger, G.E., Zhou, Y., Foote, J.A., Wester, A.M., Cui, Y., Alherech, M., Stahl, S.S., Jackson, J.E. and Hegg, E.L., “Nucleophilic Thiols Reductively Cleave Ether Linkages in Lignin Model Polymers and Lignin,” ChemSusChem (2020). [DOI: 10.1002/cssc.202001238]
Mimicking wood-eaters to cleave lignin for biofuels (Great Lakes Bioenergy Research Center)
