| Summary: | To elucidate the chemical linkages between lignin and carbohydrates in ginkgo cell walls, <sup>13</sup>C-<sup>2</sup>H-enriched cell wall-dehydrogenation polymers (CW-DHP) were selectively prepared with cambial tissue from <i>Ginkgo biloba</i> L. by feeding D-glucose-[6-<sup>2</sup>H<sub>2</sub>], coniferin-[α-<sup>13</sup>C], and phenylalanine ammonia-lyase (PAL) inhibitor. The abundant detection of <sup>13</sup>C and <sup>2</sup>H confirmed that D-glucose-[6-<sup>2</sup>H<sub>2</sub>] and coniferin-[α-<sup>13</sup>C] were involved in the normal metabolism of ginkgo cambial cells that had been effectively labelled with dual isotopes. In the ginkgo CW-DHP, ketal and ether linkages were formed between the C-α of lignin side chains and carbohydrates, as revealed by solid state CP/MAS <sup>13</sup>C-NMR differential spectroscopy. Furthermore, the DMSO/TBAH ionic liquids system was used to fractionate the ball-milled CW-DHP into three lignin-carbohydrate complex (LCC) fractions: glucan–lignin complex (GL), glucomannan–lignin complex (GML), and xylan–lignin complex (XL). The XRD determination indicated that the cellulose type I of the GL was converted into cellulose type II during the separation process. The molecular weight was in the order of Ac-GL > Ac-GML > XL. The <sup>13</sup>C-NMR and <sup>1</sup>H-NMR differential spectroscopy of <sup>13</sup>C-<sup>2</sup>H-enriched GL fraction indicated that lignin was linked with cellulose C-6 by benzyl ether linkages. It was also found that there were benzyl ether linkages between the lignin side chain C-α and glucomannan C-6 in the <sup>13</sup>C-<sup>2</sup>H-enriched GML fraction. The formation of ketal linkages between the C-α of lignin and xylan was confirmed in the <sup>13</sup>C-<sup>2</sup>H-enriched XL fraction.
|
|---|