2.3.3. 2D-HSQC NMR spectroscopy analysis

The accurately detail structural information of the isolated lignin samples was characterized by 2D-HSQC NMR (400 MHz, Bruker, Germany) at 25 °C.²⁰ Specifically, 60 mg of the acetylated lignin was dissolved in 500 μL of dimethyl sulfoxide (DMSO-d6) and placed into a 5 mm NMR tube for NMR analysis. The NMR assay conditions were: The number of acquisition points was 2048 and 256 for 1TD and 2TD, respectively. The scanning time (NS) was 64, the spectrum width (SW) was 15.9794 ppm (with 1SW and 2SW values of 259.9935 and 15.9794 ppm, respectively), and the center frequencies were 4.7 and 100 ppm for O1P and O2P, respectively.