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In order to efficiently explore and use woody biomass,six lignin fractions were isolated from dewaxed Caragana sinica via successive extraction with organic solvents and alkaline solutions.The lignin structures were characterized by Fourier transform infrared spectroscopy(FT-IR) and 1D and 2D Nuclear Magnetic Resonance(NMR).FT-IR spectra revealed that the “core” of the lignin structure did not significantly change during the treatment under the conditions given.The results of 1H and 13C NMR demonstrated that the lignin fraction L2,isolated with 70% ethanol containing 1% NaOH,was mainly composed of β-O-4 ether bonds together with G and S units and trace p-hydroxyphenyl unit.Based on the 2D HSQC NMR spectrum,the ethanol organosolv lignin fraction L1,extracted with 70% ethanol,presents a predominance of β-O-4′ aryl ether linkages(61% of total side chains),and a low abundance of condensed carbon-carbon linked structures(such as ββ′,β-1′,and β-5′) and a lower S/G ratio.Furthermore,a small percentage(ca.9%) of the linkage side chain was found to be acylated at the γ-carbon.
In order to efficiently explore and use woody biomass, six lignin fractions were isolated from dewaxed Caragana sinica via successive extraction with organic solvents and alkaline solutions. Lignin structures were characterized by Fourier transform infrared spectroscopy (FT-IR) and 1D and 2D Nuclear Magnetic Resonance (NMR). FT-IR spectra revealed that the “core” of the lignin structure did not change change during the treatment under the conditions given. The results of 1H and 13C NMR showed that the lignin fraction L2, isolated with 70 % ethanol containing 1% NaOH, was mainly composed of β-O-4 ether bonds together with G and S units and trace p-hydroxyphenyl unit. Based on the 2D HSQC NMR spectrum, the ethanol organosolv lignin fraction L1, extracted with 70% ethanol, presents a predominance of β-O-4 ’aryl ether linkages (61% of total side chains), and a low abundance of condensed carbon-carbon linked structures (such as ββ’, β-1 ’, and β-5 ’) And a lower S / G ratio. Furth ermore, a small percentage (ca.9%) of the linkage side chain was found to be acylated at the γ-carbon.