Lignin is a macromolecule that most people don't like. It gets in the way of animals when they are trying to digest plant polysaccharides, and it gets in our way when we are trying to make wood cells into paper. Its structure is unpleasantly complex and varies in an awkward statistical manner from one location to another. Because lignin is polymerised not by enzymes but by a statistically controlled chemical process (after enzymic generation of the monomer free radicals), it cannot be dismantled enzymatically in the organised way that we expect of other biopolymers, that is by reversal of the synthetic route. It follows that a lignin molecule cannot be made soluble without destroying at least some of its characteristic structural features. Since most classical methods of structure determination work in solution, that's a problem.
With a grant from the BBSRC IBTI Club we are looking at the structure of wood, grass and straw lignin, at ways of solubilising it as pre- or post-treatments for biofuel production and ways of converting the soluble lignin fragments to saleable products.