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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #91953
Title: PREPARATION OF SYNTHETIC LIGNINS WITH SUPERIOR NMR CHARACTERISTICS VIA ISOTOPICALLY LABELED MONOLIGNOLS

Author
item Ralph, John
item ZHANG, YINGSHENG - UNIV OF WISCONSIN-MADISON
item EDE, RICHARD - UNIV OF WAIKATO-NZ

Submitted to: Journal of the Chemical Society Perkin Transactions 1
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: A major component in all terrestrial plants, lignin is a polymer that limits digestion of plants by animals, and must be removed from wood to make paper. Efforts at improved utilization of fiber require methods to look at the complex structure of lignin. One of the most powerful methods is Nuclear Magnetic Resonance spectroscopy (NMR). Recent advances in NMR have provided a huge and welcome sensitivity gain, but at the cost of annoying artifacts that are detrimental to clearly interpreting structures in the lignin. Most of the artifacts come from a single substituent in the lignin. Here we describe a way to make that substituent NMR-invisible. The result is beautifully detailed and produces interpretable NMR spectra almost completely devoid of artifacts. These spectra allow us to make more detailed interpretation of lignin NMR spectra, allowing us to quickly elucidate new structures that are formed in lignin by chemical or physical treatments, or by genetic engineering of plants. Such studies are at the heart of efforts to improve agricultural sustainability and maximize our plant resources.

Technical Abstract: Synthetic lignins are particularly valuable for studying aspects of lignification, plant cell wall cross-linking, and lignin structure. If they are not too highly polymeric, they are soluble in normal lignin solvents and amenable to solution-state NMR studies. However, in the application of inverse-detected correlation experiments, particularly the popular HMQC and dHMBC experiments, the spectra have annoying T1-noise ridges. These artifacts make it difficult to locate correlation peaks that are near the methoxyl signal in the proton dimension. One solution is to use gradient- enhanced NMR but that requires additional hardware that is not yet ubiquitous. An alternative is to produce monolignols in which the atoms of the methoxyl group are NMR-invisible. We have accomplished this by preparing coniferyl and sinapyl alcohols using 13C-depleted deuterated methyl iodide (12C-2H3-I). The methods, which incorporate steps simpler than have been used previously for labeled monolignols, are sufficiently low cost and straightforward that these monomers can be utilized for any synthetic lignins destined for NMR studies. The NMR spectra of lignins derived from these "methoxyl-less" monomers are markedly superior to their normal-monomer counterparts. Several popular NMR experiments are illustrated for synthetic lignins derived from normal vs isotopically labeled coniferyl alcohol, along with some useful experiments that have not been seen in lignin-related publications to date.