resumo
In the structural analysis of lignins by C-13-NMR, signal overlap limits definitive assignment and accurate intensity measurement. Selective labeling by C-13-enrichment of a specific carbon in lignin enhances its signal intensity in the spectrum. Further enhancement of the specifically labeled carbons can be realized via difference spectra created from the enriched and unenriched samples. Difference 2D C-13-H-1 correlation (HSQC) NMR spectra, derived from the spectra of specifically C-13-enriched lignin model polymers (so-called dehydrogenation polymers) and their unenriched counterparts, take advantage of the enhanced dispersion afforded by both C-13 and H-1 chemical shifts, diminishing the difficulties arising from the signal-overlap problem and aiding in definitive signal assignments. In this research, protolignin in xylem cell walls was specifically C-13-enriched at all of the individual phenylpropanoid side-chain carbons by feeding C-13-enriched coniferins to growing stems of Ginkgo biloba. The whole xylem fractions containing C-13-enriched and unenriched protolignins were dissolved in a mixture of N-methylimidazole and DMSO, and then acetylated. Solution state 2D-NMR (HSQC) spectra of the acetylated whole cell wall were acquired. Difference spectra between the walls containing C-13-enriched and unenriched lignins afforded simplified 2D spectra in which well-separated signals were assigned exclusively to the specifically enriched carbons. This novel NMR technique provides a useful tool for elucidation of entire protolignin in the cell wall of ginkgo xylem.
palavras-chave
NUCLEAR-MAGNETIC-RESONANCE; SIDE-CHAIN CARBONS; LIGNIN BIOSYNTHESIS; NMR-SPECTROSCOPY; PART 1; LIGNIFICATION; GLUCOSIDES; ENRICHMENT; CONIFERIN; SPRUCE
categoria
Forestry; Materials Science
autores
Terashima, N; Akiyama, T; Ralph, S; Evtuguin, D; Neto, CP; Parkas, J; Paulsson, M; Westermark, U; Ralph, J
nossos autores
Carlos Pascoal Neto
Diretor do Raiz
Dmitry Evtyugin
Professor Associado com Agregaçãoagradecimentos
The authors wish to acknowledge financial support from FCT, Portugal and Stiftelsen Nils och Dorthi Troedssons Forsknings-fond, Sweden, and through the DOE Energy Biosciences program (# DE-AI02-00ER15067 to J. R.). NMR experiments on the Bruker DMX-500 cryoprobe system availed of the use of the National Magnetic Resonance Facility at the University of Wisconsin-Madison (www.nmrfam.wisc.edu).