Solution-state 2D NMR of ball-milled plant cell wall gels in DMSO-d6/pyridine-d5

Abstract

NMR fingerprinting of the components of finely divided plant cell walls swelled in DMSO has been recently described. Cell wall gels, produced directly in the NMR tube with perdeutero-dimethylsulfoxide, allowed the acquisition of well resolved/dispersed 2D 13C–1H correlated solution-state NMR spectra of the entire array of wall polymers, without the need for component fractionation. That is, without actual solubilization, and without apparent structural modification beyond that inflicted by the ball milling and ultrasonication steps, satisfactorily interpretable spectra can be acquired that reveal compositional and structural details regarding the polysaccharide and lignin components in the wall. Here, the profiling method has been improved by using a mixture of perdeuterated DMSO and pyridine (4:1, v/v). Adding pyridine provided not only easier sample handling because of the better mobility compared to the DMSO-d6-only system but also considerably elevated intensities and improved resolution of the NMR spectra due to the enhanced swelling of the cell walls. This modification therefore provides a more rapid method for comparative structural evaluation of plant cell walls than is currently available. We examined loblolly pine (Pinus taeda, a gymnosperm), aspen (Populus tremuloides, an angiosperm), kenaf (Hibiscus cannabinus, an herbaceous plant), and corn (Zea mays L., a grass, i.e., from the Poaceae family). In principle, lignin composition (notably, the syringyl : guaiacyl : p-hydroxyphenyl ratio) can be quantified without the need for lignin isolation. Correlations for p-coumarate units in the corn sample are readily seen, and a variety of the ferulate correlations are also well resolved; ferulates are important components responsible for cell wall cross-linking in grasses. Polysaccharide anomeric correlations were tentatively assigned for each plant sample based on standard samples and various literature data. With the new potential for chemometric analysis using the 2D NMR fingerprint, this gel-state method may provide the basis for an attractive approach to providing a secondary screen for selecting biomass lines and for optimizing biomass processing and conversion efficiencies.

Tandem Catalytic Depolymerization of Lignin by Water‐Tolerant Lewis Acids and Rhodium Complexes

“…In addition, 16 per 100 aromatic units of p ‐hydroxybenzoate units were observed. This value is typical for poplar,17 but the actual content is likely lower as such units are systematically overestimated by 2 D NMR methods. Interestingly, Hibbert's ketone structures could be detected in the starting lignin, in line with previous organosolv lignin analyses 2b, 18…”

“…HSQC NMR analysis of the BSP lignin revealed a β‐O‐4 content of 42 per 100 aromatic units, an S/G/H ratio of 0.5:1.0:0.1 as well as p ‐coumarate, ferulate, and tricin units, common in grasses (Figure S4, Table S2) 17. Incomplete solubility in THF precluded GPC analysis for this lignin.…”

Substrate-Specific Development of Thermophilic Bacterial Consortia by Using Chemically Pretreated Switchgrass

“…Plant cell wall samples from passage 4 replicates were extracted with water-ethanol and ball milled as previously described (20,21). Gels were formed using dimethyl sulfoxide d 6 (DMSO-d 6 ) and 1-ethyl-3-methylimidazolium acetate as a cosolvent (22,23) and homogenized by sonication in a Branson 2510 tabletop cleaner (Branson Ultrasonic Corporation, Danbury, CT).…”

Chemical Pulping Advantages of Zip‐lignin Hybrid Poplar

“…The central DMSO solvent peak was used as an internal reference ( δ C =39.5, δ H =2.49 ppm). Peak assignments were made by comparison with previously assigned spectra 17d, 18…”