Chemical Structure and Heterogeneity Differences of Two Lignins from Loblolly Pine As Investigated by Advanced Solid-State NMR Spectroscopy

摘要

Advanced solid-state NMR was employed to investigate differences in chemical structure and heterogeneity between milled wood lignin (MWL) and residual enzyme lignin (REL). Wiley and conventional milled woods were also studied. The advanced NMR techniques included ~(13)C quantitative direct polarization, various spectral-editing techniques, and two-dimensional ~1H-~(13)C heteronuclear correlation NMR with ~1H spin, diffusion. The ~(13)C chemical shift regions between 110 and 160 ppm of two lignins were quite similar to those of two milled woods. REL contained much more residual carbohydrates than MWL, showing that MWL extraction more successfully separated lignin from cellulose and hemicellu-loses than REL extraction; REL was also of higher COO, aromatic C-C, and condensed aramatics but of lower aromatic C-H. At a spin diffusion time of 0.55 ms, the magnetization was equilibrated through the whole structure of MWL lignin, but not through that of REL, indicating that REL is more heterogeneous than MWL.