*2.7. Nuclear Magnetic Resonance (NMR) Spectroscopy*

<sup>1</sup>H NMR, <sup>13</sup>C NMR and HSQC (heteronuclear single quantum correlation) solution state analysis were performed on lignin samples (~40 mg) dissolved on 1 mL of DMSO-d6. The spectra were recorded at 25 ◦C on a Bruker Advance instrument at 500 MHz. Standard Bruker programs such as zg30 for <sup>1</sup>H NMR, zgpg60 for <sup>13</sup>C NMR, and hsqcetgp for HSQC, were used.

For <sup>31</sup>P NMR, the samples were derivatized with a phosphitylation reagent according to the procedures previously described [24–27]. Lignin (20 mg) was first dissolved in 500 µL of a mixture of pyridine and deuterated chloroform (1.6:1 *v*/*v*). Afterwards, 100 µL of cholesterol (10 mg/mL) and 100 µL of chromium (III) acetylacetonate solution (5 mg/mL) were added, as an internal standard and relaxation agent, respectively. Finally, the solution was mixed with 100 µL of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (agent of phosphitylation) for about 10 min and transferred into a 5 mm NMR tube for subsequent NMR analysis at 25 ◦C on a Bruker Avance 400 MHz instrument using the pulse program zgig (inverse gated decoupling).

In the aliphatic oxygenated region of the HSQC spectra, the relative abundance of interunit linkages were estimated using the volume integrals from the Cα–H<sup>α</sup> correlations. In the aromatic region, the C2,6–H2,6 correlations from S units and the C2–H<sup>2</sup> from G units were used to estimate the S/G ratio according with previous works [28].
