Characterization of Milled Wood Lignins and Dehydrogenative Polymerisates from Monolignols by Carbon-13 NMR Spectroscopy

Chen, Chen-Loung

doi:10.1021/bk-1998-0697.ch018

Cited by 32 publications

(50 citation statements)

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“…1 A and B, respectively. The assignments of signals were done using a literature precedent and model compounds (Chen 1998;Villaverde et al 2009;Del Rio et al 2012). Although signals of some inter-unit linkages were overlapped in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Molecular Changes in Corn Stover Lignin Resulting from Pretreatment Chemistry

et al. 2017

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Lignin is an amorphous polymer that limits the enzymatic conversion of polysaccharides to fermentable sugars. Thus, a pretreatment that can enhance the accessibility of carbohydrates is a key step of successful biofuel conversion schemes. In this study, corn stover was fractioned into stem, cob, and leaf because their lignin is different. To elucidate the lignin changes, autohydrolysis, diluted acid, and alkali pretreatments were applied on the samples, followed by the isolation of cellulolytic enzyme lignin preparations. Alkaline nitrobenzene oxidation, 13 C-Nuclear Magnetic Resonance (NMR), and 1 H-13 C heteronuclear single quantum coherence NMR were used to profile the lignin changes. The results indicated that corn stover lignin is a p-hydroxyphenyl-guaiacyl-syringyltype lignin that incorporates p-coumarate and ferulate esters. The β-arylether was the most abundant inter-unit linkage, followed by condensed linkages, e.g. pino-/syringaresinol, phenylcoumaran, and spirodienone. As for the non-pretreated samples, leaf lignin was more condensed than stem lignin and cob lignin. More lignin was removed by the alkali pretreatment due to more cleavage of β-aryl-ether linkages. As a comparison, more condensed linkages were generated by the acidic pretreatments. The decrease of the syringyl/guaiacyl ratio indicated that the residual lignin became more condensed and confirmed that guaiacyl and p-hydroxyphenyl units were more stable than syringyl units during the pretreatment.

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Section: Resultsmentioning

confidence: 99%

“…The signals in this range encompass those from 6.12 of aromatic and alkenyl carbons (Chen 1998). Thus, it follows that the integral value divided by 6.12 is equivalent to one aromatic ring.…”

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confidence: 94%

Molecular Changes in Corn Stover Lignin Resulting from Pretreatment Chemistry

et al. 2017

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“…Table 3 lists the corresponding peak assignments identified for the lignin preparations (21,22). The 13 C NMR spectra can be broken into structural unit regions and integrated to obtain structural information.…”

Section: Resultsmentioning

confidence: 99%

Solution-State Nuclear Magnetic Resonance Study of the Similarities between Milled Wood Lignin and Cellulolytic Enzyme Lignin

Holtman

Chang

Kadla

2004

J. Agric. Food Chem.

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The structures of milled wood lignin (MWL) and cellulolytic enzyme lignin (CEL) have been analyzed using traditional chemical methods and solution-state NMR techniques. Comparisons of the results obtained reveal that subtle differences exist between the two lignin preparations. Thioacidolysis produced higher monomer yields from CEL than MWL, suggesting MWL has a more condensed structure. Quantitative (13)C NMR determined the degree of condensation in MWL to be 0.43 unit per aromatic moiety as compared to 0.36 in CEL. The MWL also contained a lower amount of beta-O-4' substructures per aromatic ring than CEL, 0.41 versus 0.47, respectively. Carbohydrate analysis revealed that the MWL may contain a higher proportion of middle lamella material as compared to the CEL. Because the middle lamella is considered to have a more condensed lignin structure, on the basis of the bulk polymerization theory, these results could explain the differences in beta-O-4' and degree of condensation.

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“…2). In native lignins, 8-O-4-linkages are the most abundant, whereas for lignins formed in vitro by mixing coniferyl alcohol, hydrogen peroxide, and peroxidase, higher percentages of 8-8-and 8-5-linkages are found (Nimz and Ludemann, 1976;Terashima et al, 1996;Chen, 1998). How is this apparent specificity in chemical bonds between lignin subunits controlled?…”

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confidence: 99%