The composition and structure of lignin in different tissues-phellem (cork), phloem and xylem (wood)-of
was studied. Whole cell walls and their respective isolated milled lignins were analyzed by ...pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) and derivatization followed by reductive cleavage (DFRC). Different tissues presented varied
-hydroxyphenyl:guaiacyl:syringyl (H:G:S) lignin compositions. Whereas lignin from cork has a G-rich lignin (H:G:S molar ratio 2:85:13), lignin from phloem presents more S-units (H:G:S molar ratio of 1:58:41) and lignin from xylem is slightly enriched in S-lignin (H:G:S molar ratio 1:45:55). These differences were reflected in the relative abundances of the different interunit linkages. Alkyl-aryl ethers (β-
-4') were predominant, increasing from 68% in cork, to 71% in phloem and 77% in xylem, as consequence of the enrichment in S-lignin units. Cork lignin was enriched in condensed structures such as phenylcoumarans (β-5', 20%), dibenzodioxocins (5-5', 5%), as corresponds to a lignin enriched in G-units. In comparison, lignin from phloem and xylem presented lower levels of condensed linkages. The lignin from cork was highly acetylated at the γ-OH of the side-chain (48% lignin acetylation), predominantly over G-units; while the lignins from phloem and xylem were barely acetylated and this occurred mainly over S-units. These results are a first time overview of the lignin structure in xylem, phloem (generated by cambium), and in cork (generated by phellogen), in agreement with literature that reports that lignin biosynthesis is flexible and cell specific.
Lignin changes during plant growth were investigated in a selected Eucalyptus globulus clone. The lignin composition and structure were studied in situ by a new procedure enabling the acquisition of ...two-dimensional nuclear magnetic resonance (2D-NMR) spectra on wood gels formed in the NMR tube as well as by analytical pyrolysis-gas chromatography-mass spectrometry. In addition, milled-wood lignins were isolated and analyzed by 2D-NMR, pyrolysis-gas chromatography-mass spectrometry, and thioacidolysis. The data indicated that p-hydroxyphenyl and guaiacyl units are deposited at the earlier stages, whereas the woods are enriched in syringyl (S) lignin during late lignification. Wood 2D-NMR showed that β-O-4' and resinol linkages were predominant in the eucalypt lignin, whereas other substructures were present in much lower amounts. Interestingly, open β-1' structures could be detected in the isolated lignins. Phenylcoumarans and cinnamyl end groups were depleted with age, spirodienone abundance increased, and the main substructures (β-O-4' and resinols) were scarcely modified. Thioacidolysis revealed a higher predominance of S units in the ether-linked lignin than in the total lignin and, in agreement with NMR, also indicated that resinols are the most important nonether linkages. Dimer analysis showed that most of the resinol-type structures comprised two S units (syringaresinol), the crossed guaiacyl-S resinol appearing as a minor substructure and pinoresinol being totally absent. Changes in hemicelluloses were also shown by the 2D-NMR spectra of the wood gels without polysaccharide isolation. These include decreases of methyl galacturonosyl, arabinosyl, and galactosyl (anomeric) signals, assigned to pectin and related neutral polysaccharides, and increases of xylosyl (which are approximately 50% acetylated) and 4-O-methylglucuronosyl signals.
Recent studies demonstrate that several polyphenolic compounds produced from beyond the canonical monolignol biosynthetic pathways can behave as lignin monomers, participating in radical coupling ...reactions and being incorporated into lignin polymers. Here, we show various classes of flavonoids, the chalconoid naringenin chalcone, the flavanones naringenin and dihydrotricin, and the flavone tricin, incorporated into the lignin polymer of papyrus (Cyperus papyrus L.) rind. These flavonoids were released from the rind lignin by Derivatization Followed by Reductive Cleavage (DFRC), a chemical degradative method that cleaves the β-ether linkages, indicating that at least a fraction of each was integrated into the lignin as β-ether-linked structures. Due to the particular structure of tricin and dihydrotricin, whose C-3' and C-5' positions at their B-rings are occupied by methoxy groups, these compounds can only be incorporated into the lignin through 4'-O-β bonds. However, naringenin chalcone and naringenin have no substituents at these positions and can therefore form additional carbon-carbon linkages, including 3'- or 5'-β linkages that form phenylcoumaran structures not susceptible to cleavage by DFRC. Furthermore, Nuclear Magnetic Resonance analysis indicated that naringenin chalcone can also form additional linkages through its conjugated double bond. The discovery expands the range of flavonoids incorporated into natural lignins, further broadens the traditional definition of lignin, and enhances the premise that any phenolic compound present at the cell wall during lignification could be oxidized and potentially integrated into the lignin structure, depending only on its chemical compatibility. This study indicates that papyrus lignin has a unique structure, as it is the only lignin known to date that integrates such a diversity of phenolic compounds from different classes of flavonoids. This discovery will open up new ways to engineer and design lignins with specific properties and for enhanced value.
Two major residues are produced by the sugarcane industry, the fibrous fraction following juice extraction (bagasse), and the harvest residue (straw). The structures of the lignins from these ...residues were studied by pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS), nuclear magnetic resonance (NMR), and derivatization followed by reductive cleavage (DFRC). Whereas the lignin from bagasse has a syringyl-rich p-hydroxyphenyl:guaiacyl:syringyl (H:G:S) molar composition of 2:38:60, the lignin from straw is guaiacyl-rich (H:G:S of 4:68:28). The compositional differences were also reflected in the relative abundances of the different interunit linkages. Bagasse lignin was primarily β–O–4′ alkyl-aryl ether substructures (representing 83% of NMR-measurable linkages), followed by minor amounts of β–5′ (phenylcoumarans, 6%) and other condensed substructures. The lignin from straw has lower levels of β-ethers (75%) but higher relative levels of phenylcoumarans (β–5′, 15%) and dibenzodioxocins (5–5/4–O–β, 3%), consistent with a lignin enriched in G-units. Both lignins are extensively acylated at the γ-hydroxyl of the lignin side-chain (42% and 36% acylation in bagasse and straw), predominantly with p-coumarates (preferentially on S-units) but also with acetates (preferentially on G-units) to a minor extent. Tetrahydrofuran structures diagnostically arising from β–β-coupling (dehydrodimerization) of sinapyl p-coumarate or its cross-coupling with sinapyl alcohol were found in both lignins, indicating that sinapyl p-coumarate acts as a monomer participating in lignification. The flavone tricin was also found in the lignins from sugarcane, as also occurs in other grasses.
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•The lignins from sugarcane bagasse and straw are very different to each other.•Bagasse lignin is S-rich (H:G:S 2:38:60) and straw lignin is G-rich (H:G:S 4:68:28).•Bagasse lignin has mainly β–O–4′ -ethers with minor levels of phenylcoumarans.•Straw lignin has higher levels of phenylcoumarans and dibenzodioxocins.•Both lignins are extensively acylated at the side-chain γ-OH with p-coumarates.
2D NMR suggests that some angiosperms use monolignol acylation (at the γ–position) as a mechanism to control the molecular structure of lignin. Spectra revealed correlations between the ratio of ...acylated (
A′)-to-non-acylated (
A) units and both (i) the abundance of syringyl units, and (ii) the absence of β–β′ linkages in lignin.
Lignins from three nonwoody angiosperms were analyzed by 2D NMR revealing important differences in their molecular structures. The
Musa
textilis milled-wood-lignin (MWL), with a syringyl-to-guaiacyl (S/G) ratio of 9, was strongly acylated (near 85% of side-chains) at the γ-carbon by both acetates and
p-coumarates, as estimated from
1H–
13C correlations in C
γ-esterified and C
γ–OH units. The
p-coumarate H
3,5–C
3,5 correlation signal was completely displaced by acetylation, and disappeared after alkali treatment, indicating that
p-coumaric acid was esterified maintaining its free phenolic group. By contrast, the
Cannabis
sativa MWL (S/G ∼0.8) was free of acylating groups, and the
Agave
sisalana MWL (S/G ∼4) showed high acylation degree (near 80%) but exclusively with acetates. Extensive C
γ-acylation results in the absence (in
M.
textilis lignin) or low abundance (4% in
A.
sisalana lignin) of β–β′ resinol linkages, which require free C
γ-OH to form the double tetrahydrofuran ring. However, minor signals revealed unusual acylated β–β′ structures confirming that acylation is produced at the monolignol level, in agreement with chromatographic identification of γ-acetylated sinapyl alcohol among the plant extractives. In contrast, resinol substructures involved 22% side-chains in the
C.
sativa MWL. The ratio between β–β′ and β
-O-4′ side-chains in these and other MWL varied from 0.32 in
C.
sativa MWL to 0.02 in
M.
textilis MWL, and was inversely correlated with the degree of acylation. The opposite was observed for the S/G ratio that was directly correlated with the acylation degree. Monolignol acylation is discussed as a mechanism potentially involved in the control of lignin structure.
Rice (
L.) is a major cereal crop used for human nutrition worldwide. Harvesting and processing of rice generates huge amounts of lignocellulosic by-products such as rice husks and straw, which ...present important lignin contents that can be used to produce chemicals and materials. In this work, the structural characteristics of the lignins from rice husks and straw have been studied in detail. For this, whole cell walls of rice husks and straw and their isolated lignin preparations were thoroughly analyzed by an array of analytical techniques, including pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS), nuclear magnetic resonance (NMR), and derivatization followed by reductive cleavage (DFRC). The analyses revealed that both lignins, particularly the lignin from rice husks, were highly enriched in guaiacyl (G) units, and depleted in
-hydroxyphenyl (H) and syringyl (S) units, with H:G:S compositions of 7:81:12 (for rice husks) and 5:71:24 (for rice straw). These compositions were reflected in the relative abundances of the different interunit linkages. Hence, the lignin from rice husks were depleted in β-
-4' alkyl-aryl ether units (representing 65% of all inter-unit linkages), but presented important amounts of β-5' (phenylcoumarans, 23%) and other condensed units. On the other hand, the lignin from rice straw presented higher levels of β-
-4' alkyl-aryl ethers (78%) but lower levels of phenylcoumarans (β-5', 12%) and other condensed linkages, consistent with a lignin with a slightly higher S/G ratio. In addition, both lignins were partially acylated at the γ-OH of the side-chain (ca. 10-12% acylation degree) with
-coumarates, which overwhelmingly occurred over S-units. Finally, important amounts of the flavone tricin were also found incorporated into these lignins, being particularly abundant in the lignin of rice straw.
A method consisting of the alkaline hydrolysis of tomato pomace by-products has been optimized to obtain a mixture of unsaturated and polyhydroxylated fatty acids as well as a non-hydrolysable ...secondary residue. Reaction rates and the activation energy of the hydrolysis were calculated to reduce costs associated with chemicals and energy consumption. Lipid and non-hydrolysable fractions were chemically (infrared (IR) spectroscopy, gas chromatography/mass spectrometry (GC-MS)) and thermally (differential scanning calorimetry (DSC), thermogravimetric analysis (TGA)) characterized. In addition, the fatty acid mixture was used to produce cutin-based polyesters. Freestanding films were prepared by non-catalyzed melt-polycondensation and characterized by Attenuated Total Reflected-Fourier Transform Infrared (ATR-FTIR) spectroscopy, solid-state nuclear magnetic resonance (NMR), DSC, TGA, Water Contact Angles (WCA), and tensile tests. These bio-based polymers were hydrophobic, insoluble, infusible, and thermally stable, their physical properties being tunable by controlling the presence of unsaturated fatty acids and oxygen in the reaction. The participation of an oxidative crosslinking side reaction is proposed to be responsible for such modifications.
Pitch control is an important aspect in pulp and paper manufacture, and the first example where microbial biotechnology provided successful solutions in this industrial sector. Triglycerides cause ...deposits in softwood mechanical pulping, and both microbial and enzymatic products have been commercialized to be applied on wood and pulp, respectively. The former are based on colorless strains of sapstain fungi. The latter are improved lipases, including thermostable variants from directed evolution. These enzymes are among the additives of choice in pulping of high-resin-content softwoods. However, lipases are not useful when pitch originates from other lipids, such as steroids and terpenes, and the sapstain inocula are also only partially effective. In the search for stronger biocatalysts to degrade recalcitrant lipids, the potential of white-rot fungi and their enzymes has been demonstrated. When inocula of these fungi are used, wood treatment must be controlled to avoid cellulose degradation. However, the efficiency and selectivity of the laccase-mediator system permits its integration as an additional bleaching stage. A double benefit can be obtained from these treatments since pitch is controlled at the same time that residual lignin is removed facilitating the implementation of totally chlorine free pulp bleaching.
Rice (
L.) straw is a highly abundant, widely available, and low cost agricultural waste that can be used as a source to extract valuable phytochemicals of industrial interest. Hence, in the present ...work, the chemical composition of the lipophilic compounds present in rice straw was thoroughly characterized by gas chromatography and mass spectrometry using medium-length high-temperature capillary columns, which allowed the identification of a wide range of lipophilic compounds, from low molecular weight fatty acids to high molecular weight sterols esters, sterol glucosides, or triglycerides in the same chromatogram. The most abundant lipophilic compounds in rice straw were fatty acids, which accounted for up to 6,400 mg/kg (41.0% of all identified compounds), followed by free sterols (1,600 mg/kg; 10.2%), sterol glucosides (1,380 mg/kg; 8.8%), fatty alcohols (1,150 mg/kg; 7.4%), and triglycerides (1,140 mg/kg; 7.3%), along with lower amounts of high molecular weight wax esters (900 mg/kg; 5.8%), steroid ketones (900 mg/kg; 5.8%), monoglycerides (600 mg/kg; 3.8%), alkanes (400 mg/kg; 2.6%), diglycerides (380 mg/kg; 2.4%), sterol esters (380 mg/kg; 2.4%), tocopherols (340 mg/kg; 2.2%), and steroid hydrocarbons (60 mg/kg; 0.4%). This information is of great use for the valorization of rice straw to obtain valuable lipophilic compounds of interest for the nutraceutical, pharmaceutical, cosmetic, and chemical industries. Moreover, this knowledge is also useful for other industrial uses of rice straw, as in pulp and papermaking, since some lipophilic compounds are at the origin of the so-called pitch deposits during pulping.
Occurrence of Naturally Acetylated Lignin Units Del Río, José C; Marques, Gisela; Rencoret, Jorge ...
Journal of agricultural and food chemistry,
07/2007, Letnik:
55, Številka:
14
Journal Article
Recenzirano
Odprti dostop
This work examines the occurrence of native acetylated lignin in a large set of vascular plants, including both angiosperms and gymnosperms, by a modification of the so-called Derivatization Followed ...by Reductive Cleavage (DFRC) method. Acetylated lignin units were found in the milled wood lignins of all angiosperms selected for this study, including mono- and eudicotyledons, but were absent in the gymnosperms analyzed. In some plants (e.g., abaca, sisal, kenaf, or hornbeam), lignin acetylation occurred at a very high extent, exceeding 45% of the uncondensed (alkyl-aryl ether linked) syringyl lignin units. Acetylation was observed exclusively at the γ-carbon of the lignin side chain and predominantly on syringyl units, although a predominance of acetylated guaiacyl over syringyl units was observed in some plants. In all cases, acetylation appears to occur at the monomer stage, and sinapyl and coniferyl acetates seem to behave as real lignin monomers participating in lignification. Keywords: Lignin; angiosperms; gymnosperms; eudicotyledons; monocotyledons; coniferyl acetate; sinapyl acetate; abaca; sisal; kenaf; hornbeam; Derivatization Followed by Reductive Cleavage (DFRC)
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