Olive tree pruning (OTP) is an abundant and inexpensive agricultural lignocellulosic residue that... more Olive tree pruning (OTP) is an abundant and inexpensive agricultural lignocellulosic residue that is an interesting feedstock for producing bioethanol and other bio-products in the context of lignocellulosic biorefineries. However, the presence of lignin in OTP hinders the transformation processes as it limits the access to cell wall polysaccharides. On the other hand, the aromatic/phenolic structure of the lignin polymer makes it an interesting raw material for producing chemicals, fuels and other commodities that are nowadays produced from fossil fuels. Thus, the knowledge of the OTP lignin structure is crucial to develop tailor-made pretreatments for their removal as well as for additional valorization of the lignin polymer. In this work, the OTP lignin was isolated as milled wood lignin (MWL), a lignin preparation that is considered representative of the native lignin, and characterized by twodimensional nuclear magnetic resonance (2D-NMR) and thioacidolysis. The results demonstrated that the lignin is mainly composed of guaiacyl (G) and syringyl (S) lignin units in similar abundances (S/G ratio of ~1), with minor amounts of p-hydroxyphenyl (H) units. The most abundant lignin inter-unit linkages are β-O-4′ alkyl-aryl ethers (75% of all linkages), followed by the condensed phenylcoumarans (12%) and resinols (8%), and with lower amounts of dibenzodioxocins (2%) and spirodienones (3%). The analysis of the thioacidolysis dimers gave additional information regarding the distribution of the lignin units involved in condensed interunit linkages, including 5-5′, 4-O-5′, β-5′, β-1′ and β-β′. The high lignin content (25%), together with the relatively low S/G ratio and the abundance of condensed (carbon-carbon linked) structures, points to a low reactivity of OTP lignin during delignification pretreatments.
Journal of Agricultural and Food Chemistry, Oct 3, 2003
We regret that due to an unfortunate error during the writing of the paper, the chain lengths of ... more We regret that due to an unfortunate error during the writing of the paper, the chain lengths of the waxes identified were incorrectly assigned in the text. The error arises from Figure , which shows the mass spectra of, supposedly, waxes C 50 , C 52 , and C 54 , but that in fact corresponds to waxes C 44 , C 46 , and C 48 , as can be clearly deduced from the molecular ions at
Journal of Analytical and Applied Pyrolysis, Feb 1, 1994
Pyrograms of Ihree fulvic acids (FAs) or ditferenl origins and Ihe corresponding pyrosrams obtain... more Pyrograms of Ihree fulvic acids (FAs) or ditferenl origins and Ihe corresponding pyrosrams obtaincd by reactive pyrolysis wilh Iclramclhylammonium hydroxide (TMAH) are compared. Thi! proc.cdure inlroduces bolh slriking qualilalive and quanlilalive changes in lhe pyrolylic pallems of Ihe FAs. which are discussed in lerms of Ihe usefulness of Ihis approach lo slructural sludies. Sorne non•pyrolysis compounds (probably relained in Ihe macromolecular fulvic malrix) seem lo be released when Ihe FAs are pyrolysed in lhe presrnce of TMAH. A se{ of benzenecarboxylic acid slandards was also pyrolysed bolh in lhe abscnce and in Ihe prcscncc: oC TMAH. The resulls oblained suggcsl a lhennally assisled chemolysis ralher Ihan i" s;/u melhylalioD of lhe pyrolysis produclS. Fulvic &cids; humic substances; pyrolysiS; tetramelhylammonium hydroxide. Humic substances (HS) are widely distributed in almost all terrestrial and aquatic environments. Owing to their colloidal properties and high runctionality they play important roles in reactions and processes relaled lO the conservation and production of soil ecosystems. which have been recently reviewed [1,. The complex. variable composition of lhe fulvic acids (FAs) (lhe alkali and acid-soluble collodial humic fraction) has been investigated by many different methods with divergent results. Overall the struclural ínformation gained by analytical pyrolysis (Py) of FA is unexpectedly much lower than that given by the other humic fractíoDS (humic acids and humíos). Thus, FA givcs low yields of Py compounds. with major components bcíng characteristic of $Oíl polysao:harides, and a small numbcr of aromatic compounds, whereas Py of humíc acids gives much richer pyrograms. This
The structure of lignin and suberin, and ferulic acid (FA) content in cork fromQuercus suberL. we... more The structure of lignin and suberin, and ferulic acid (FA) content in cork fromQuercus suberL. were studied. Extractive-free cork (Cork), suberin, desuberized cork (Corksap), and milled-cork lignins (MCL) from Cork and Corksapwere isolated. Suberin composition was determined by GC-MS/FID, whereas the polymers structure in Cork, Corksap, and MCL was studied by Py-TMAH and 2D-HSQC-NMR. Suberin contained 94.4% of aliphatics and 3.2% of phenolics, with 90% of ω-hydroxyacids and α,ω-diacids. FA represented 2.7% of the suberin monomers, overwhelmingly esterified to the cork matrix. Py-TMAH revealed significant FA amounts in all samples, with about 3% and 6% in cork and cork lignins, respectively. Py-TMAH and 2D-HSQC-NMR demonstrated that cork lignin is a G-lignin (>96% G units), with a structure dominated by β–O–4′ alkyl-aryl ether linkages (80% and 77% of all linkages in MCL and MCLsap, respectively), followed by phenylcoumarans (18% and 20% in MCL and MCLsap, respectively), and small...
A variety of lac resin samples obtained from artists' suppliers, industrial manufacturers, and mu... more A variety of lac resin samples obtained from artists' suppliers, industrial manufacturers, and museum collections were analysed using gas chromatography mass spectrometry (GCMS) and reactive pyrolysis GCMS with quaternary ammonium reagents. These techniques allowed a detailed chemical characterisation of microgram-sized samples, based on the detection and identification of derivatives of the hydroxy aliphatic and cyclic (sesquiterpene) acids that compose the resin. Differences in composition could be related to the nature of the resin, e.g. wax-containing (unrefined), bleached, or aged samples. Furthermore, differences in the relative abundances of aliphatic hydroxyacids appear to be associated with the biological source of the resin. The diagnostic value of newly characterised lac components, including 8hydroxyacids, is discussed here for the first time. Identification of derivatised components was aided by AMDIS deconvolution software, and discrimination of samples was enhanced by statistical evaluation of data using principal component analysis. The robustness of the analyses, together with the minimal sample size required, make these very powerful approaches for the characterisation of lac resin in museum objects. The value of such analyses for enhancing the understanding of museum collections is illustrated by two case studies of objects in the collection of the Philadelphia Museum of Art: a restorer's varnish on a painting by Luca Signorelli, and a pictorial inlay in an early nineteenth-century High Chest by George Dyer.
Diferuloylputrescine has been found in a variety of plant species, and recent work has provided e... more Diferuloylputrescine has been found in a variety of plant species, and recent work has provided evidence of its covalent bonding into lignin. Results from nuclear magnetic resonance spectroscopy revealed the presence of bonding patterns consistent with homo-coupling of diferuloylputrescine and the possibility of cross-coupling with lignin. In the present work, density functional theory calculations have been applied to assess the energetics associated with radical coupling, rearomatization, and dehydrogenation for possible homo-coupled dimers of diferuloylputrescine and cross-coupled dimers of diferuloylputrescine and coniferyl alcohol. The values obtained for these reaction energetics are consistent with those reported for monolignols and other novel lignin monomers. As such, this study shows that there would be no thermodynamic impediment to the incorporation of diferuloylputrescine into the lignin polymer and its addition to the growing list of non-canonical lignin monomers.
Lignin is derived from the oxidative radical coupling of three main p-hydroxycinnamyl alcohols, t... more Lignin is derived from the oxidative radical coupling of three main p-hydroxycinnamyl alcohols, the monolignols p-coumaryl, coniferyl, and sinapyl alcohols. Recently, we discovered in grass lignins the first phenolic monomer from outside the canonical lignin biosynthetic pathway, the flavone tricin. In this work, we report the discovery of another polyphenolic compound from yet another biosynthetic pathway, the hydroxystilbene piceatannol, which also acts as a true lignin monomer in palm fruit endocarps. Piceatannol was released from these lignins upon derivatization followed by reductive cleavage (DFRC), a degradative method that cleaves β-ether bonds, indicating that at least a fraction of it is incorporated into the lignin through labile ether bonds. 2D-NMR revealed the occurrence of other structures involving piceatannol in the lignin polymer, and demonstrated that piceatannol acts as an authentic lignin monomer participating in coupling and cross-coupling reactions during lignification of palm fruit endocarps.
Journal of Agricultural and Food Chemistry, Dec 22, 2017
The lignins from different anatomical parts of macauba (Acrocomia aculeata) palm fruit, namely st... more The lignins from different anatomical parts of macauba (Acrocomia aculeata) palm fruit, namely stalks, epicarp, and endocarp, were studied. The lignin from stalks was enriched in S-lignin units (S/G 1.2) and β-ether linkages (84% of the total) and was partially acylated at the γ-OH of the lignin side-chains (26% lignin acylation), predominantly with phydroxybenzoates and acetates. The epicarp lignin was highly enriched in G-lignin units (S/G 0.2) and consequently depleted in β-ethers (65%) and enriched in condensed structures such as phenylcoumarans (24%) and dibenzodioxocins (3%). The endocarp lignin was strikingly different from the rest and presented large amounts of piceatannol units incorporated into the polymer. This resulted in a lignin polymer depleted in β-ethers but enriched in condensed structures and linked piceatannol moieties. The incorporation of piceatannol into the lignin polymer seems to have a role in seed protection.
The lignin from Cynara cardunculus stalks was isolated by the classical Björkman method and chara... more 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.
We provide first evidence that a heme-thiolate peroxidase is able to catalyze the hydroxylation o... more We provide first evidence that a heme-thiolate peroxidase is able to catalyze the hydroxylation of n-alkanes at the terminal position, a challenging reaction in organic chemistry, using H2O2 as the only cosubstrate. In addition to the primary product, 1-dodecanol, the conversion of dodecane yields dodecanoic, 12hydroxydodecanoic and 1,12-dodecanedioic acids, identified by GC-MS. Dodecanal could be detected only in trace amounts, and 1,12dodecanediol was not observed, suggesting that dodecanoic acid is the branch point between mono-and di-terminal hydroxylation. Simultaneously, oxygenation was observed at other hydrocarbon chain positions (preferentially C2 and C11). Similar results were obtained in tetradecane reactions. Taken together the pattern of products formed with data on incorporation of 18 O from the H2 18 O2 cosubstrate, we demonstrate that the enzyme acts as a peroxygenase being able to catalyze a cascade of mono-and diterminal oxidations from long-chain n-alkanes to carboxylic acids.
Papyrus (Cyperus papyrus L.) is a sedge plant with a high rate of biomass productivity that repre... more Papyrus (Cyperus papyrus L.) is a sedge plant with a high rate of biomass productivity that represents an interesting raw material to produce chemicals, materials and fuels, which are currently still obtained from fossil resources, in the context of a lignocellulosic biorefinery. In this work, the content and chemical composition of the lipids present in papyrus stems were thoroughly studied. For this, the papyrus stems were separated into the rind and the pith. The lipid content accounted for 4.1% in the rind and 4.9% in the pith (based on dry matter). The main compounds identified in both parts of the papyrus stem were hydrocarbons, n-fatty acids, 2-hydroxyfatty acids, alcohols, alkylamides, mono-and diglycerides, steroids (sterols, ketones, hydrocarbons, esters and glycosides), tocopherols, tocopherol esters, phytol, phytol esters, alkyl ferulates, w-carboxyalkyl ferulates (and their monoglycerides), and acylglycerol glycosides. The rind presented a predominance of n-fatty acids (6790 mg/kg; that represented 28.6% of all identified compounds), steroid compounds (6255 mg/kg; 26.3%), phytol and phytol esters (4985 mg/kg; 21.0%), and isoprenoid hydrocarbons, namely phytadiene and squalene (2660 mg/kg; 11.2%), while the most abundant lipids in the pith were steroids (8600 mg/kg; 44.4% of all identified compounds) and fatty acids (6245 mg/kg; 32.2%). Due to the great diversity and significant abundance of the compounds identified in papyrus, it can be considered as a potential raw material for biorefineries to obtain valuable phytochemicals of interest to various industrial sectors.
El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido ... more El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido facilitado todavía por el investigador a cargo del archivo del mismo.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
ACS Sustainable Chemistry & Engineering, Jun 19, 2020
Eucalyptus globulus (E. globulus) wood samples were treated in media containing acidified water a... more Eucalyptus globulus (E. globulus) wood samples were treated in media containing acidified water and methyl isobutyl ketone (MIBK) in order to achieve the one-pot conversion of the hemicellulosic an...
Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recentl... more Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recently established as an authentic monomer in grass lignification that likely functions as a nucleation site. It is linked onto lignin as an aryl alkyl ether by radical coupling with monolignols or their acylated analogs. However, the level of tricin that incorporates into lignin remains unclear. Herein, three lignin characterization methods: acidolysis; thioacidolysis; and derivatization followed by reductive cleavage; were applied to quantitatively assess the amount of lignin-integrated tricin. Their efficiencies at cleaving the tricin-(4 0-O-b)-ether bonds and the degradation of tricin under the corresponding reaction conditions were evaluated. A hexadeuterated tricin analog was synthesized as an internal standard for accurate quantitation purposes. Thioacidolysis proved to be the most efficient method, liberating more than 91% of the tricin with little degradation. A survey of different seed-plant species for the occurrence and content of tricin showed that it is widely distributed in the lignin from species in the family Poaceae (order Poales). Tricin occurs at low levels in some commelinid monocotyledon families outside the Poaceae, such as the Arecaceae (the palms, order Arecales) and Bromeliaceae (Poales), and the non-commelinid monocotyledon family Orchidaceae (Orchidales). One eudicotyledon was found to have tricin (Medicago sativa, Fabaceae). The content of lignin-integrated tricin is much higher than the extractable tricin level in all cases. Lignins, including waste lignin streams from biomass processing, could therefore provide a large and alternative source of this valuable flavone, reducing the costs, and encouraging studies into its application beyond its current roles.
Recent experimental work has revealed that the hydroxystilbene piceatannol can function as a mono... more Recent experimental work has revealed that the hydroxystilbene piceatannol can function as a monomeric unit in the lignification of palm fruit endocarp tissues. Results indicated that piceatannol homo-couples and crosscouples with monolignols through radical reactions and is integrally incorporated into the lignin polymer. The current work reports on the thermodynamics of the proposed reactions using density functional theory calculations. The results indicated that, in general, the energetics of both homo-coupling and cross-coupling are not dissimilar from those of the monolignol coupling, demonstrating the compatibility of piceatannol with the lignification process. Moreover, the DFT methods appear to predict the correct courses of post-coupling rearomatization reactions.
Olive tree pruning (OTP) is an abundant and inexpensive agricultural lignocellulosic residue that... more Olive tree pruning (OTP) is an abundant and inexpensive agricultural lignocellulosic residue that is an interesting feedstock for producing bioethanol and other bio-products in the context of lignocellulosic biorefineries. However, the presence of lignin in OTP hinders the transformation processes as it limits the access to cell wall polysaccharides. On the other hand, the aromatic/phenolic structure of the lignin polymer makes it an interesting raw material for producing chemicals, fuels and other commodities that are nowadays produced from fossil fuels. Thus, the knowledge of the OTP lignin structure is crucial to develop tailor-made pretreatments for their removal as well as for additional valorization of the lignin polymer. In this work, the OTP lignin was isolated as milled wood lignin (MWL), a lignin preparation that is considered representative of the native lignin, and characterized by twodimensional nuclear magnetic resonance (2D-NMR) and thioacidolysis. The results demonstrated that the lignin is mainly composed of guaiacyl (G) and syringyl (S) lignin units in similar abundances (S/G ratio of ~1), with minor amounts of p-hydroxyphenyl (H) units. The most abundant lignin inter-unit linkages are β-O-4′ alkyl-aryl ethers (75% of all linkages), followed by the condensed phenylcoumarans (12%) and resinols (8%), and with lower amounts of dibenzodioxocins (2%) and spirodienones (3%). The analysis of the thioacidolysis dimers gave additional information regarding the distribution of the lignin units involved in condensed interunit linkages, including 5-5′, 4-O-5′, β-5′, β-1′ and β-β′. The high lignin content (25%), together with the relatively low S/G ratio and the abundance of condensed (carbon-carbon linked) structures, points to a low reactivity of OTP lignin during delignification pretreatments.
Journal of Agricultural and Food Chemistry, Oct 3, 2003
We regret that due to an unfortunate error during the writing of the paper, the chain lengths of ... more We regret that due to an unfortunate error during the writing of the paper, the chain lengths of the waxes identified were incorrectly assigned in the text. The error arises from Figure , which shows the mass spectra of, supposedly, waxes C 50 , C 52 , and C 54 , but that in fact corresponds to waxes C 44 , C 46 , and C 48 , as can be clearly deduced from the molecular ions at
Journal of Analytical and Applied Pyrolysis, Feb 1, 1994
Pyrograms of Ihree fulvic acids (FAs) or ditferenl origins and Ihe corresponding pyrosrams obtain... more Pyrograms of Ihree fulvic acids (FAs) or ditferenl origins and Ihe corresponding pyrosrams obtaincd by reactive pyrolysis wilh Iclramclhylammonium hydroxide (TMAH) are compared. Thi! proc.cdure inlroduces bolh slriking qualilalive and quanlilalive changes in lhe pyrolylic pallems of Ihe FAs. which are discussed in lerms of Ihe usefulness of Ihis approach lo slructural sludies. Sorne non•pyrolysis compounds (probably relained in Ihe macromolecular fulvic malrix) seem lo be released when Ihe FAs are pyrolysed in lhe presrnce of TMAH. A se{ of benzenecarboxylic acid slandards was also pyrolysed bolh in lhe abscnce and in Ihe prcscncc: oC TMAH. The resulls oblained suggcsl a lhennally assisled chemolysis ralher Ihan i" s;/u melhylalioD of lhe pyrolysis produclS. Fulvic &cids; humic substances; pyrolysiS; tetramelhylammonium hydroxide. Humic substances (HS) are widely distributed in almost all terrestrial and aquatic environments. Owing to their colloidal properties and high runctionality they play important roles in reactions and processes relaled lO the conservation and production of soil ecosystems. which have been recently reviewed [1,. The complex. variable composition of lhe fulvic acids (FAs) (lhe alkali and acid-soluble collodial humic fraction) has been investigated by many different methods with divergent results. Overall the struclural ínformation gained by analytical pyrolysis (Py) of FA is unexpectedly much lower than that given by the other humic fractíoDS (humic acids and humíos). Thus, FA givcs low yields of Py compounds. with major components bcíng characteristic of $Oíl polysao:harides, and a small numbcr of aromatic compounds, whereas Py of humíc acids gives much richer pyrograms. This
The structure of lignin and suberin, and ferulic acid (FA) content in cork fromQuercus suberL. we... more The structure of lignin and suberin, and ferulic acid (FA) content in cork fromQuercus suberL. were studied. Extractive-free cork (Cork), suberin, desuberized cork (Corksap), and milled-cork lignins (MCL) from Cork and Corksapwere isolated. Suberin composition was determined by GC-MS/FID, whereas the polymers structure in Cork, Corksap, and MCL was studied by Py-TMAH and 2D-HSQC-NMR. Suberin contained 94.4% of aliphatics and 3.2% of phenolics, with 90% of ω-hydroxyacids and α,ω-diacids. FA represented 2.7% of the suberin monomers, overwhelmingly esterified to the cork matrix. Py-TMAH revealed significant FA amounts in all samples, with about 3% and 6% in cork and cork lignins, respectively. Py-TMAH and 2D-HSQC-NMR demonstrated that cork lignin is a G-lignin (>96% G units), with a structure dominated by β–O–4′ alkyl-aryl ether linkages (80% and 77% of all linkages in MCL and MCLsap, respectively), followed by phenylcoumarans (18% and 20% in MCL and MCLsap, respectively), and small...
A variety of lac resin samples obtained from artists' suppliers, industrial manufacturers, and mu... more A variety of lac resin samples obtained from artists' suppliers, industrial manufacturers, and museum collections were analysed using gas chromatography mass spectrometry (GCMS) and reactive pyrolysis GCMS with quaternary ammonium reagents. These techniques allowed a detailed chemical characterisation of microgram-sized samples, based on the detection and identification of derivatives of the hydroxy aliphatic and cyclic (sesquiterpene) acids that compose the resin. Differences in composition could be related to the nature of the resin, e.g. wax-containing (unrefined), bleached, or aged samples. Furthermore, differences in the relative abundances of aliphatic hydroxyacids appear to be associated with the biological source of the resin. The diagnostic value of newly characterised lac components, including 8hydroxyacids, is discussed here for the first time. Identification of derivatised components was aided by AMDIS deconvolution software, and discrimination of samples was enhanced by statistical evaluation of data using principal component analysis. The robustness of the analyses, together with the minimal sample size required, make these very powerful approaches for the characterisation of lac resin in museum objects. The value of such analyses for enhancing the understanding of museum collections is illustrated by two case studies of objects in the collection of the Philadelphia Museum of Art: a restorer's varnish on a painting by Luca Signorelli, and a pictorial inlay in an early nineteenth-century High Chest by George Dyer.
Diferuloylputrescine has been found in a variety of plant species, and recent work has provided e... more Diferuloylputrescine has been found in a variety of plant species, and recent work has provided evidence of its covalent bonding into lignin. Results from nuclear magnetic resonance spectroscopy revealed the presence of bonding patterns consistent with homo-coupling of diferuloylputrescine and the possibility of cross-coupling with lignin. In the present work, density functional theory calculations have been applied to assess the energetics associated with radical coupling, rearomatization, and dehydrogenation for possible homo-coupled dimers of diferuloylputrescine and cross-coupled dimers of diferuloylputrescine and coniferyl alcohol. The values obtained for these reaction energetics are consistent with those reported for monolignols and other novel lignin monomers. As such, this study shows that there would be no thermodynamic impediment to the incorporation of diferuloylputrescine into the lignin polymer and its addition to the growing list of non-canonical lignin monomers.
Lignin is derived from the oxidative radical coupling of three main p-hydroxycinnamyl alcohols, t... more Lignin is derived from the oxidative radical coupling of three main p-hydroxycinnamyl alcohols, the monolignols p-coumaryl, coniferyl, and sinapyl alcohols. Recently, we discovered in grass lignins the first phenolic monomer from outside the canonical lignin biosynthetic pathway, the flavone tricin. In this work, we report the discovery of another polyphenolic compound from yet another biosynthetic pathway, the hydroxystilbene piceatannol, which also acts as a true lignin monomer in palm fruit endocarps. Piceatannol was released from these lignins upon derivatization followed by reductive cleavage (DFRC), a degradative method that cleaves β-ether bonds, indicating that at least a fraction of it is incorporated into the lignin through labile ether bonds. 2D-NMR revealed the occurrence of other structures involving piceatannol in the lignin polymer, and demonstrated that piceatannol acts as an authentic lignin monomer participating in coupling and cross-coupling reactions during lignification of palm fruit endocarps.
Journal of Agricultural and Food Chemistry, Dec 22, 2017
The lignins from different anatomical parts of macauba (Acrocomia aculeata) palm fruit, namely st... more The lignins from different anatomical parts of macauba (Acrocomia aculeata) palm fruit, namely stalks, epicarp, and endocarp, were studied. The lignin from stalks was enriched in S-lignin units (S/G 1.2) and β-ether linkages (84% of the total) and was partially acylated at the γ-OH of the lignin side-chains (26% lignin acylation), predominantly with phydroxybenzoates and acetates. The epicarp lignin was highly enriched in G-lignin units (S/G 0.2) and consequently depleted in β-ethers (65%) and enriched in condensed structures such as phenylcoumarans (24%) and dibenzodioxocins (3%). The endocarp lignin was strikingly different from the rest and presented large amounts of piceatannol units incorporated into the polymer. This resulted in a lignin polymer depleted in β-ethers but enriched in condensed structures and linked piceatannol moieties. The incorporation of piceatannol into the lignin polymer seems to have a role in seed protection.
The lignin from Cynara cardunculus stalks was isolated by the classical Björkman method and chara... more 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.
We provide first evidence that a heme-thiolate peroxidase is able to catalyze the hydroxylation o... more We provide first evidence that a heme-thiolate peroxidase is able to catalyze the hydroxylation of n-alkanes at the terminal position, a challenging reaction in organic chemistry, using H2O2 as the only cosubstrate. In addition to the primary product, 1-dodecanol, the conversion of dodecane yields dodecanoic, 12hydroxydodecanoic and 1,12-dodecanedioic acids, identified by GC-MS. Dodecanal could be detected only in trace amounts, and 1,12dodecanediol was not observed, suggesting that dodecanoic acid is the branch point between mono-and di-terminal hydroxylation. Simultaneously, oxygenation was observed at other hydrocarbon chain positions (preferentially C2 and C11). Similar results were obtained in tetradecane reactions. Taken together the pattern of products formed with data on incorporation of 18 O from the H2 18 O2 cosubstrate, we demonstrate that the enzyme acts as a peroxygenase being able to catalyze a cascade of mono-and diterminal oxidations from long-chain n-alkanes to carboxylic acids.
Papyrus (Cyperus papyrus L.) is a sedge plant with a high rate of biomass productivity that repre... more Papyrus (Cyperus papyrus L.) is a sedge plant with a high rate of biomass productivity that represents an interesting raw material to produce chemicals, materials and fuels, which are currently still obtained from fossil resources, in the context of a lignocellulosic biorefinery. In this work, the content and chemical composition of the lipids present in papyrus stems were thoroughly studied. For this, the papyrus stems were separated into the rind and the pith. The lipid content accounted for 4.1% in the rind and 4.9% in the pith (based on dry matter). The main compounds identified in both parts of the papyrus stem were hydrocarbons, n-fatty acids, 2-hydroxyfatty acids, alcohols, alkylamides, mono-and diglycerides, steroids (sterols, ketones, hydrocarbons, esters and glycosides), tocopherols, tocopherol esters, phytol, phytol esters, alkyl ferulates, w-carboxyalkyl ferulates (and their monoglycerides), and acylglycerol glycosides. The rind presented a predominance of n-fatty acids (6790 mg/kg; that represented 28.6% of all identified compounds), steroid compounds (6255 mg/kg; 26.3%), phytol and phytol esters (4985 mg/kg; 21.0%), and isoprenoid hydrocarbons, namely phytadiene and squalene (2660 mg/kg; 11.2%), while the most abundant lipids in the pith were steroids (8600 mg/kg; 44.4% of all identified compounds) and fatty acids (6245 mg/kg; 32.2%). Due to the great diversity and significant abundance of the compounds identified in papyrus, it can be considered as a potential raw material for biorefineries to obtain valuable phytochemicals of interest to various industrial sectors.
El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido ... more El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido facilitado todavía por el investigador a cargo del archivo del mismo.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
ACS Sustainable Chemistry & Engineering, Jun 19, 2020
Eucalyptus globulus (E. globulus) wood samples were treated in media containing acidified water a... more Eucalyptus globulus (E. globulus) wood samples were treated in media containing acidified water and methyl isobutyl ketone (MIBK) in order to achieve the one-pot conversion of the hemicellulosic an...
Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recentl... more Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recently established as an authentic monomer in grass lignification that likely functions as a nucleation site. It is linked onto lignin as an aryl alkyl ether by radical coupling with monolignols or their acylated analogs. However, the level of tricin that incorporates into lignin remains unclear. Herein, three lignin characterization methods: acidolysis; thioacidolysis; and derivatization followed by reductive cleavage; were applied to quantitatively assess the amount of lignin-integrated tricin. Their efficiencies at cleaving the tricin-(4 0-O-b)-ether bonds and the degradation of tricin under the corresponding reaction conditions were evaluated. A hexadeuterated tricin analog was synthesized as an internal standard for accurate quantitation purposes. Thioacidolysis proved to be the most efficient method, liberating more than 91% of the tricin with little degradation. A survey of different seed-plant species for the occurrence and content of tricin showed that it is widely distributed in the lignin from species in the family Poaceae (order Poales). Tricin occurs at low levels in some commelinid monocotyledon families outside the Poaceae, such as the Arecaceae (the palms, order Arecales) and Bromeliaceae (Poales), and the non-commelinid monocotyledon family Orchidaceae (Orchidales). One eudicotyledon was found to have tricin (Medicago sativa, Fabaceae). The content of lignin-integrated tricin is much higher than the extractable tricin level in all cases. Lignins, including waste lignin streams from biomass processing, could therefore provide a large and alternative source of this valuable flavone, reducing the costs, and encouraging studies into its application beyond its current roles.
Recent experimental work has revealed that the hydroxystilbene piceatannol can function as a mono... more Recent experimental work has revealed that the hydroxystilbene piceatannol can function as a monomeric unit in the lignification of palm fruit endocarp tissues. Results indicated that piceatannol homo-couples and crosscouples with monolignols through radical reactions and is integrally incorporated into the lignin polymer. The current work reports on the thermodynamics of the proposed reactions using density functional theory calculations. The results indicated that, in general, the energetics of both homo-coupling and cross-coupling are not dissimilar from those of the monolignol coupling, demonstrating the compatibility of piceatannol with the lignification process. Moreover, the DFT methods appear to predict the correct courses of post-coupling rearomatization reactions.
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Papers by Jose C del Rio