NMR of Lignins

Ralph, John; Landucci, Larry L.

doi:10.1201/ebk1574444865-c5

Cited by 299 publications

(411 citation statements)

References 277 publications

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“…Sinapyl (73% yield) and p-coumaryl (76% yield) alcohols were synthesized analogously. The NMR data of the three obtained monolignols are consistent with those in the NMR database of lignin model compounds (Ralph et al, 2005).…”

Section: Radical Coupling Reaction Between Tricin and Monolignolssupporting

confidence: 79%

Tricin, a Flavonoid Monomer in Monocot Lignification

et al. 2015

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Tricin was recently discovered in lignin preparations from wheat (Triticum aestivum) straw and subsequently in all monocot samples examined. To provide proof that tricin is involved in lignification and establish the mechanism by which it incorporates into the lignin polymer, the 49-Ob-coupling products of tricin with the monolignols (p-coumaryl, coniferyl, and sinapyl alcohols) were synthesized along with the trimer that would result from its 49-O-b-coupling with sinapyl alcohol and then coniferyl alcohol. Tricin was also found to cross couple with monolignols to form tricin-(49-O-b)-linked dimers in biomimetic oxidations using peroxidase/hydrogen peroxide or silver (I) oxide. Nuclear magnetic resonance characterization of gel permeation chromatography-fractionated acetylated maize (Zea mays) lignin revealed that the tricin moieties are found in even the highest molecular weight fractions, ether linked to lignin units, demonstrating that tricin is indeed incorporated into the lignin polymer. These findings suggest that tricin is fully compatible with lignification reactions, is an authentic lignin monomer, and, because it can only start a lignin chain, functions as a nucleation site for lignification in monocots. This initiation role helps resolve a long-standing dilemma that monocot lignin chains do not appear to be initiated by monolignol homodehydrodimerization as they are in dicots that have similar syringyl-guaiacyl compositions. The term flavonolignin is recommended for the racemic oligomers and polymers of monolignols that start from tricin (or incorporate other flavonoids) in the cell wall, in analogy with the existing term flavonolignan that is used for the lowmolecular mass compounds composed of flavonoid and lignan moieties.Lignin, a complex phenylpropanoid polymer in the plant cell wall, is predominantly deposited in the cell walls of secondary-thickened cells (Vanholme et al., 2010). It is synthesized via oxidative radical coupling reactions from three prototypical monolignols, p-coumaryl, coniferyl, and sinapyl alcohols, differentiated by their degree of methoxylation ortho to the phenolic hydroxyl group. Considered within the context of the entire polymer, the main structural features of lignin can be defined in terms of its p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units, derived respectively from these three monolignols (Ralph, 2010). Several novel monomers, all deriving from the monolignol biosynthetic pathway, have been found to incorporate into lignin in wild-type and transgenic plants. For example, monolignol acetate, p-hydroxybenzoate, and p-coumarate ester conjugates have all been shown to incorporate into lignin polymers and are the source of naturally acylated lignins (Ralph et al., 2004;Lu and Ralph, 2008); lignins derived solely from caffeyl alcohol were found in the seed coats of both monocot and dicot plants (Chen et al., 2012a(Chen et al., , 2012b; lignins derived solely from 5-hydroxyconiferyl alcohol were found in a cactus (for example, in a member of the genera Astrop...

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Section: Radical Coupling Reaction Between Tricin and Monolignolssupporting

confidence: 79%

Tricin, a Flavonoid Monomer in Monocot Lignification

et al. 2015

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“…2D-NMR HSQC cross-signals were assigned after comparison with data from literature [17,[21][22][23][24][25]. A semi-quantitative analysis of the volume integrals of the HSQC correlation peaks was performed using Bruker's Topspin 3.1 processing software.…”

Section: D-nmr Spectroscopymentioning

confidence: 99%

“…Py-GC/MS is a reproducible and sensitive technique for the characterization of the composition of the lignin polymer, in terms of their phydroxyphenyl (H), guaiacyl (G), and syringyl (S) units [13][14][15]. 2D-NMR complements the information obtained by pyrolysis and provides useful information regarding the lignin units and lignin interunit linkages [16,17]. Finally, DFRC is a chemical degradative method that can give information on the occurrence of acylated γ-OH units.…”

Section: Introductionmentioning

confidence: 99%

Isolation and Structural Characterization of Lignin from Cardoon (Cynara cardunculus L.) Stalks

et al. 2015

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The lignin from Cynara cardunculus stalks was isolated by the classical Björkman method and characterized by pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR), and derivatization followed by reductive cleavage (DFRC). The milled Cynara lignin (MCyL) was constituted mainly by guaiacyl (G) and syringyl-units(S) (S/G molar ratio of 0.7), with the complete absence of p-hydroxyphenyl (H) units. The 2D-NMR analysis indicated a predominance of alkyl-aryl ether linkages (70 % of all inter unit linkages are β-O-4′) and significant amounts of condensed structures such as phenylcoumarans (β-5′, 14 %), resinols (β-β′, 7 %), spirodienones (β-1′, 5 %), and dibenzodioxocins (5-5′, 4 %). Furthermore, the analyses indicated that the lignin is partially acylated at the γ-OH (12 % acylation) by acetate groups and that acetylation occurs preferentially on syringyl-units. As in other plants, acetylation occurs at the monomer stage, and sinapyl acetate behaves as a real lignin monomer participating in lignification in cardoon stalks. The detailed structural characterization of cardoon lignin reported here will foster the industrial use of this biomass for the production of biofuels and other bio-based chemicals under the lignocellulosic biorefinery.

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“…The chemical shift assignments are based on the literature (Mörck and Kringstad 1985;Pu and Ragauskas 2005) and summarized in Table 5, along with the integrated peak areas of the lignin moieties. The integral of aromatic region (102-160 ppm) was calibrated to six, which represents six aromatic carbons (Landucci et al 1998;Ralph and Landucci 2010;Min et al 2013;Wells et al 2013). Quantitative evaluation of functional groups (OH phen and OMe) and carbohydrates was thus integrated related to this value (Robert 1992;Faix et al 1994;Ralph and Landucci 2010;Choi and Faix 2011;Min et al 2013).…”

Section: Quantitative Nmr Spectroscopymentioning

confidence: 99%

The molecular properties and carbohydrate content of lignins precipitated from black liquor

Zhu

Westman²,

Theliander³

2014

Holzforschung

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Precipitation and utilization of lignin from black liquor (BL) offers many promising advantages to modern kraft pulp mills. A novel process, known as "LignoBoost", has recently been introduced as a process for separating lignin from BL; it results in lignins with a low ash and high dry solid content. There is a lack of knowledge regarding the influences of process parameters on the behavior of lignin in the precipitation step. In this study, the yield of precipitated lignin and its average molecular weight (MWt) and carbohydrate content were the focus. Nuclear magnetic resonance (NMR) analysis showed that the lignin yield increased at lower pH and temperatures or when the ion strength of BL was elevated. High yield lignins contained more low MWt components and such lignins have more phenolic OH and methoxy groups. Xylan content of the lignins decreased with decreasing pH and increasing temperature, but glucomannan content was virtually unaffected by the conditions of precipitation.

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NMR of Lignins

Cited by 299 publications

References 277 publications

Tricin, a Flavonoid Monomer in Monocot Lignification

Tricin, a Flavonoid Monomer in Monocot Lignification

Isolation and Structural Characterization of Lignin from Cardoon (Cynara cardunculus L.) Stalks

The molecular properties and carbohydrate content of lignins precipitated from black liquor

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