An improved 13C-tracer method for the study of lignin structure and reactions : differential 13C-NMR

Abstract

The technique of selective 13C-enrichment of specific carbons in lignin combined with 13C-NMR differential spectrometry between spectra of 13C-enriched and unenriched lignins (Ä13C-NMR) provides definitive information on the structure of the lignin macromolecule. Improvements were made on, (1) specific 13C-enrichment of almost all carbons involved in inter-unit bonds and functional groups in lignin, (2) estimation of the frequencies of bonds and functional groups using Ä13CNMR under quantitative conditions, and (3) detection of specifically 13C-labeled carbons by 2D- ifference spectra. A softwood lignin model, guaiacyl-type 13C-DHP, was prepared from specifically 13C-enriched coniferin. Based on the Ä13C-NMR, the structure of the DHP is proposed. Specifically 13C-enriched MWLs were prepared from ginkgo wood fed with 13C-enriched coniferins. Qualitative and quantitative differences in structure between MWL and DHP were shown by the comparison of Ä13C-NMR determined under the same quantitative conditions. Despite a large difference in the structure of DHP from that of MWL, the 13C-enriched DHP can be used as a model of lignin for a variety of studies on formation, structure and reactions of lignin in combination with the Ä13C-NMR technique.

Citation

Terashima, Noritsugu; Evtuguin, Dmitry; Neto, Carlos Pascoal; Parkas, Jim; Paulsson, Magnus; Westermark, Ulla; Ralph, Sally; Ralph, John. 2003. An improved 13C-tracer method for the study of lignin structure and reactions : differential 13C-NMR. 12th ISWPC International Symposium on Wood and Pulping Chemistry : Madison, Wisconsin, June 9-12, 2003, proceedings. Volume 1, Oral presentations. [Madison, WI : University of Wisconsin--Madison, Dept. of Forest Ecology and Management, 2003]: Pages 175-178