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To elucidate the chemical linkages between lignin and carbohydrates in ginkgo cell walls, 13 C- 2 H-enriched cell wall-dehydrogenation polymers (CW-DHP) were selectively prepared with cambial tissue from Ginkgo biloba L. by feeding D-glucose-[6- 2 H 2 ], coniferin-[α- 13 C], and phenylalanine ammonia-lyase (PAL) inhibitor. The abundant detection of 13 C and 2 H confirmed that D-glucose-[6- 2 H 2 ] and coniferin-[α- 13 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 13 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 13 C-NMR and 1 H-NMR differential spectroscopy of 13 C- 2 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 13 C- 2 H-enriched GML fraction. The formation of ketal linkages between the C-α of lignin and xylan was confirmed in the 13 C- 2 H-enriched XL fraction.

The results showed that o-quinone and q-quinone had strong absorption while vanillin had nearly no absorption in the 800-900 nm range of near-infrared spectroscopy through the comparison of their near-infrared absorption spectra. It was proved that quinone structure of alkali lignin had strong absorption in the 800-900 nm range of near-infrared spectroscopy. The change in the absorbency of oleander milled wood lignin treated with NaOH and Na2 S before and after is greater than that in the absorbency of ginkgo milled wood lignin treated with NaOH and Na2 S before and after because more quinone structure was formed in the process of oleander milled wood lignin treated with NaOH and Na2 S. The finding well explained that cooking liquor of hardwood was much stronger than that of softwood while their pulp kappa number was very near.