Alkyl Aryl Ether

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Narayanaswamy Jayaraman - One of the best experts on this subject based on the ideXlab platform.

  • Multicolor Reversible Thermochromic Properties of Gallic Acid-Cored Polydiacetylenes Appended with Poly(Alkyl Aryl Ether) Dendrons
    Macromolecular Chemistry and Physics, 2016
    Co-Authors: Yashapal Singh, Narayanaswamy Jayaraman
    Abstract:

    This study describes synthesis of zero and first generation poly(Alkyl Aryl Ether) dendrons onto a gallic acid core, tEthered with three diacetylene moieties and their photopolymerization. Resulting polydiacetylenes are studied by (i) UV-vis, IR, Raman spectroscopies, and chromoisomerism by naked eye visualization; (ii) their stabilities by differential scanning calorimetry, thermogravimetric method, and (iii) structure, morphology, and emission behavior by scanning electron, transmission electron, atomic force microscopies, powder X-ray diffraction method, and fluorescence spectroscopy. The dendron-appended polydiacetylenes show robust nanoribbon morphologies and exhibit multicolor, reversible chromoisomerism at temperatures up to 300 degrees C. Reversibility of amide bond IR frequencies, as a function of temperature, shows the polymer stabilities, in addition to the results of thermal and powder X-ray diffraction studies. Temperature annealed polymers having red color phase exhibit emission maxima at 572 and 633 nm, that shift to higher wavelength upon heating and revert to the initial emission wavelengths on cooling.

  • Dynamic internal cavities of dendrimers as constrained media. A study of photochemical isomerizations of stilbene and azobenzene using poly(Alkyl Aryl Ether) dendrimers.
    The Journal of organic chemistry, 2012
    Co-Authors: Baskar Natarajan, Shipra Gupta, Nithyanandhan Jayaraj, Vaidhyanathan Ramamurthy, Narayanaswamy Jayaraman
    Abstract:

    Dendritic microenvironments defined by dynamic internal cavities of a dendrimer were probed through geometric isomerization of stilbene and azobenzene. A third-generation poly(Alkyl Aryl Ether) dendrimer with hydrophilic exterior and hydrophobic interior was used as a reaction cavity in aqueous medium. The dynamic inner cavity sizes were varied by utilizing Alkyl linkers that connect the branch junctures from ethyl to n-pentyl moiety (C2G3–C5G3). Dendrimers constituted with n-pentyl linker were found to afford higher solubilitiesof stilbene and azobenzene. Direct irradiation of trans-stilbene showed that C5G3 and C4G3 dendrimers afforded considerable phenanthrene formation, in addition to cis-stilbene, whereas C3G3 and C2G3 gave only cis-stilbene. An electron-transfer sensitized trans–cis isomerization, using cresyl violet perchlorate as the sensitizer, also led to similar results. Thermal isomerization of cis-azobenzene to trans-azobenzene within dendritic microenvironments revealed that the activation e...

  • Interfacial Regions Governing Internal Cavities of Dendrimers. Studies of Poly(Alkyl Aryl Ether) Dendrimers Constituted with Linkers of Varying Alkyl Chain Length
    The Journal of organic chemistry, 2011
    Co-Authors: Baskar Natarajan, Shipra Gupta, Vaidhyanathan Ramamurthy, Narayanaswamy Jayaraman
    Abstract:

    This report deals with a study of the properties of internal cavities of dendritic macromolecules that are capable of encapsulating and mediating photoreactions of guest molecules. The internal cavity structures of dendrimers are determined by the interfacial regions between the aqueous exterior and hydrocarbon like interior constituted by the linkers that connect symmetrically sited branch points constituting the dendrimer and head groups that cap the dendrimers. Phloroglucinol-based poly(Alkyl Aryl Ether) dendrimers constituted with a homologous series of Alkyl linkers were undertaken for the current study. Twelve dendrimers within first, second, and third generations, having ethyl, n-propyl, n-butyl, and n-pentyl groups as the linkers and hydroxyl groups at peripheries in each generation, were synthesized. Encapsulation of pyrene and coumarins by aqueous basic solutions of dendrimers were monitored by UV-vis and fluorescence spectroscopies, which showed that a lower generation dendrimer with an optimal Alkyl linker presented better encapsulation abilities than a higher generation dendrimer. Norrish type I photoreaction of dibenzyl ketone was carried out within the above series of dendrimers to probe their abilities to hold guests and reactive intermediate radical pairs within themselves. The extent of cage effect from the series of third generation dendrimers was observed to be higher with dendrimers having an n-pentyl group as the linker.

  • Synthesis and studies of Rh(I) catalysts within and across poly(Alkyl Aryl Ether) dendrimers
    Journal of Organometallic Chemistry, 2011
    Co-Authors: Baskar Natarajan, Narayanaswamy Jayaraman
    Abstract:

    In order to study the efficiencies of catalytic moieties within and across dendrimer generations, partially and fully functionalized dendrimers were synthesized. Poly(Alkyl Aryl Ether) dendrimers from zero to three generations, presenting 3 to 24 peripheral functionalities, were utilized to prepare as many as 12 catalysts. The dendrimer peripheries were partially and fully functionalized with triphenylphosphine in the first instance. A rhodium(I) metal complexation was performed subsequently to afford multivalent dendritic catalysts, both within and across generations. Upon synthesis, the dendritic catalysts were tested in the hydrogenation of styrene, in a substrate-to-catalyst ratio of 1:0.001. Turn-over-numbers were evaluated for each catalyst, from which significant increases in the catalytic activities were identified for multivalent catalysts than monovalent catalysts, both within and across generations.

  • efficient halogen lithium exchange reactions to functionalize poly Alkyl Aryl Ether dendrimers
    Tetrahedron, 2006
    Co-Authors: Jayaraj Nithyanandhan, Narayanaswamy Jayaraman
    Abstract:

    Abstract Poly(Alkyl Aryl Ether) dendrimers were functionalized with bromophenyl groups at their peripheries, so as to have 3, 6, 12, and 24 groups in the zero, first, second, and third generation dendrimers, respectively. The new bromophenyl functionalized dendrimers were assessed for their reactivities in C–heteroatom and C–C bond forming reactions. For this purpose, the bromophenyl functionalized dendrimers were converted quantitatively to their polylithiated derivatives, using n -BuLi in benzene. The polylithiated dendrimers were reacted either with D 2 O or with CO 2 , so as to afford the corresponding deuterated and carboxylic acid functionalized dendrimers, respectively. The carboxylic acid functionalized dendrimers were modified further to the methyl esters during their characterization.

Gregg T. Beckham - One of the best experts on this subject based on the ideXlab platform.

  • Mechanistic Study of a Ru-Xantphos Catalyst for Tandem Alcohol Dehydrogenation and Reductive Aryl-Ether Cleavage
    2016
    Co-Authors: Stephen C. Chmely, Seonah Kim, Peter N. Ciesielski, Robert S. Paton, Gonzalo Jiménez-osés, Gregg T. Beckham
    Abstract:

    We employ density functional theory (DFT) calculations and kinetics measurements to understand the mechanism of a xantphos-containing molecular ruthenium catalyst acting on an Alkyl Aryl Ether linkage similar to that found in lignin to produce acetophenone and phenol. The most favorable reaction pathway suggested from DFT is compared to kinetics measurements, and good agreement is found between the predicted and the measured activation barriers. The DFT calculations reveal several interesting features, including an unusual 5-membered transition state structure for oxidative insertion in contrast to the typically proposed 3-membered transition state, a preference for an O-bound over a C-bound Ru–enolate, and a significant kinetic preference for the order of product release from the catalyst. The experimental measurements confirm that the reaction proceeds via a free ketone intermediate, but also suggest that the conversion of the intermediate ketone to acetophenone and phenol does not necessarily require ketone dissociation from the catalyst. Overall, this work elucidates the kinetically and thermodynamically preferred reaction pathways for tandem alcohol dehydrogenation and reductive Ether bond cleavage by the ruthenium-xantphos catalyst

  • Mechanistic Study of a Ru-Xantphos Catalyst for Tandem Alcohol Dehydrogenation and Reductive Aryl-Ether Cleavage
    ACS Catalysis, 2013
    Co-Authors: Stephen C. Chmely, Seonah Kim, Peter N. Ciesielski, Gonzalo Jiménez-osés, Robert S. Paton, Gregg T. Beckham
    Abstract:

    We employ density functional theory (DFT) calculations and kinetics measurements to understand the mechanism of a xantphos-containing molecular ruthenium catalyst acting on an Alkyl Aryl Ether linkage similar to that found in lignin to produce acetophenone and phenol. The most favorable reaction pathway suggested from DFT is compared to kinetics measurements, and good agreement is found between the predicted and the measured activation barriers. The DFT calculations reveal several interesting features, including an unusual 5-membered transition state structure for oxidative insertion in contrast to the typically proposed 3-membered transition state, a preference for an O-bound over a C-bound Ru–enolate, and a significant kinetic preference for the order of product release from the catalyst. The experimental measurements confirm that the reaction proceeds via a free ketone intermediate, but also suggest that the conversion of the intermediate ketone to acetophenone and phenol does not necessarily require k...

Jorge Rencoret - One of the best experts on this subject based on the ideXlab platform.

  • CHANGES IN THE COMPOSITION AND STRUCTURE OF LIGNIN DURING THE GROWTH OF A EUCALYPTUS GLOBULUS CLONE
    2016
    Co-Authors: José C. Del Río, Jorge Rencoret, Ana Gutierrez, Lidia Nieto, J. Jiménez-barbero, Angel T Martinez
    Abstract:

    The content, composition and structure of lignin in a Eucalyptus globulus clone were studied at different growth stages (1 month, 18 months, and 9 years). The lignin content in the eucalypt woods increase during growth and the changes in its composition and structure were studied “in situ ” by Py-GC/MS and 2D-NMR of the whole wood. In addition, milled-wood lignins were isolated and analyzed by Py-GC/MS, 2D-NMR and thioacidolysis followed by Raney Nickel desulfurization. The data obtained indicated that H and G lignin units are deposited first at the earlier stages, whereas the woods are enriched in S lignin during late lignification. The main linkages present were β-O-4 ' Alkyl-Aryl Ether and resinol β-β', whereas other substructures (such as β-5 ' phenylcoumaran and β-1 ' spirodienones) were present in lower abundances during all stages of lignification. The differences in monomer deposition affect the distribution of the different linkages during lignification. I

  • Lignin–carbohydrate complexes from sisal (Agave sisalana) and abaca (Musa textilis): chemical composition and structural modifications during the isolation process
    Planta, 2016
    Co-Authors: Pepijn Prinsen, Ana Gutierrez, Edith M Cadena, Angel T Martinez, Jorge Rencoret
    Abstract:

    Main conclusion Two types of lignins occurred in different lignin–carbohydrate fractions, a lignin enriched in syringyl units, less condensed, preferentially associated with xylans, and a lignin with more guaiacyl units, more condensed, associated with glucans. Lignin–carbohydrate complexes (LCC) were isolated from the fibers of sisal ( Agave sisalana ) and abaca ( Musa textilis ) according to a plant biomass fractionation procedure recently developed and which was termed as “universally” applicable to any type of lignocellulosic material. Two LCC fractions, namely glucan–lignin (GL) and xylan–lignin (XL), were isolated and differed in the content and composition of carbohydrates and lignin. In both cases, GL fractions were enriched in glucans and comparatively depleted in lignin, whereas XL fractions were depleted in glucans, but enriched in xylans and lignin. Analysis by two-dimensional Nuclear Magnetic Resonance (2D-NMR) and Derivatization Followed by Reductive Cleavage (DFRC) indicated that the XL fractions were enriched in syringyl (S)-lignin units and β- O -4′ Alkyl-Aryl Ether linkages, whereas GL fractions have more guaiacyl (G)-lignin units and less β- O -4′ Alkyl-Aryl Ether linkages per lignin unit. The data suggest that the structural characteristics of the lignin polymers are not homogeneously distributed within the same plant and that two different lignin polymers with different composition and structure might be present. The analyses also suggested that acetates from hemicelluloses and the acyl groups (acetates and p -coumarates) attached to the γ-OH of the lignin side chains were extensively hydrolyzed and removed during the LCC fractionation process. Therefore, caution must be paid when using this fractionation approach for the structural characterization of plants with acylated hemicelluloses and lignins. Finally, several chemical linkages (phenylglycosides and benzyl Ethers) could be observed to occur between lignin and xylans in these plants.

  • Ferulates and lignin structural composition in cork
    Holzforschung, 2016
    Co-Authors: António Velez Marques, Jorge Rencoret, Ana Gutierrez, Helena Pereira
    Abstract:

    The structure of lignin and suberin, and ferulic acid (FA) content in cork from Quercus suber L. were studied. Extractive-free cork (Cork), suberin, desuberized cork (Corkₛₐₚ), and milled-cork lignins (MCL) from Cork and Corkₛₐₚ were 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 smaller amounts of resinols (ca. 2%) and dibenzodioxocins (1%). HSQC also revealed that cork lignin is heavily acylated (ca. 50%) exclusively at the side-chain γ-position. Ferulates possibly have an important function in the chemical assembly of cork cell walls with a cross-linking role between suberin, lignin and carbohydrates.

  • lignin carbohydrate complexes from sisal agave sisalana and abaca musa textilis chemical composition and structural modifications during the isolation process
    Planta, 2016
    Co-Authors: Pepijn Prinsen, Ana Gutierrez, Edith M Cadena, Angel T Martinez, Jorge Rencoret
    Abstract:

    Main conclusion Two types of lignins occurred in different lignin–carbohydrate fractions, a lignin enriched in syringyl units, less condensed, preferentially associated with xylans, and a lignin with more guaiacyl units, more condensed, associated with glucans. Lignin–carbohydrate complexes (LCC) were isolated from the fibers of sisal (Agave sisalana) and abaca (Musa textilis) according to a plant biomass fractionation procedure recently developed and which was termed as “universally” applicable to any type of lignocellulosic material. Two LCC fractions, namely glucan–lignin (GL) and xylan–lignin (XL), were isolated and differed in the content and composition of carbohydrates and lignin. In both cases, GL fractions were enriched in glucans and comparatively depleted in lignin, whereas XL fractions were depleted in glucans, but enriched in xylans and lignin. Analysis by two-dimensional Nuclear Magnetic Resonance (2D-NMR) and Derivatization Followed by Reductive Cleavage (DFRC) indicated that the XL fractions were enriched in syringyl (S)-lignin units and β-O-4′ Alkyl-Aryl Ether linkages, whereas GL fractions have more guaiacyl (G)-lignin units and less β-O-4′ Alkyl-Aryl Ether linkages per lignin unit. The data suggest that the structural characteristics of the lignin polymers are not homogeneously distributed within the same plant and that two different lignin polymers with different composition and structure might be present. The analyses also suggested that acetates from hemicelluloses and the acyl groups (acetates and p-coumarates) attached to the γ-OH of the lignin side chains were extensively hydrolyzed and removed during the LCC fractionation process. Therefore, caution must be paid when using this fractionation approach for the structural characterization of plants with acylated hemicelluloses and lignins. Finally, several chemical linkages (phenylglycosides and benzyl Ethers) could be observed to occur between lignin and xylans in these plants.

  • isolation and structural characterization of lignin from cardoon cynara cardunculus l stalks
    Bioenergy Research, 2015
    Co-Authors: Ana Lourenco, Jorge Rencoret, Ana Gutierrez, C Chemetova, Jorge Gominho, Helena Pereira
    Abstract:

    The lignin from Cynara cardunculus stalks was isolated by the classical Bjorkman 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.

Ana Gutierrez - One of the best experts on this subject based on the ideXlab platform.

  • CHANGES IN THE COMPOSITION AND STRUCTURE OF LIGNIN DURING THE GROWTH OF A EUCALYPTUS GLOBULUS CLONE
    2016
    Co-Authors: José C. Del Río, Jorge Rencoret, Ana Gutierrez, Lidia Nieto, J. Jiménez-barbero, Angel T Martinez
    Abstract:

    The content, composition and structure of lignin in a Eucalyptus globulus clone were studied at different growth stages (1 month, 18 months, and 9 years). The lignin content in the eucalypt woods increase during growth and the changes in its composition and structure were studied “in situ ” by Py-GC/MS and 2D-NMR of the whole wood. In addition, milled-wood lignins were isolated and analyzed by Py-GC/MS, 2D-NMR and thioacidolysis followed by Raney Nickel desulfurization. The data obtained indicated that H and G lignin units are deposited first at the earlier stages, whereas the woods are enriched in S lignin during late lignification. The main linkages present were β-O-4 ' Alkyl-Aryl Ether and resinol β-β', whereas other substructures (such as β-5 ' phenylcoumaran and β-1 ' spirodienones) were present in lower abundances during all stages of lignification. The differences in monomer deposition affect the distribution of the different linkages during lignification. I

  • Lignin–carbohydrate complexes from sisal (Agave sisalana) and abaca (Musa textilis): chemical composition and structural modifications during the isolation process
    Planta, 2016
    Co-Authors: Pepijn Prinsen, Ana Gutierrez, Edith M Cadena, Angel T Martinez, Jorge Rencoret
    Abstract:

    Main conclusion Two types of lignins occurred in different lignin–carbohydrate fractions, a lignin enriched in syringyl units, less condensed, preferentially associated with xylans, and a lignin with more guaiacyl units, more condensed, associated with glucans. Lignin–carbohydrate complexes (LCC) were isolated from the fibers of sisal ( Agave sisalana ) and abaca ( Musa textilis ) according to a plant biomass fractionation procedure recently developed and which was termed as “universally” applicable to any type of lignocellulosic material. Two LCC fractions, namely glucan–lignin (GL) and xylan–lignin (XL), were isolated and differed in the content and composition of carbohydrates and lignin. In both cases, GL fractions were enriched in glucans and comparatively depleted in lignin, whereas XL fractions were depleted in glucans, but enriched in xylans and lignin. Analysis by two-dimensional Nuclear Magnetic Resonance (2D-NMR) and Derivatization Followed by Reductive Cleavage (DFRC) indicated that the XL fractions were enriched in syringyl (S)-lignin units and β- O -4′ Alkyl-Aryl Ether linkages, whereas GL fractions have more guaiacyl (G)-lignin units and less β- O -4′ Alkyl-Aryl Ether linkages per lignin unit. The data suggest that the structural characteristics of the lignin polymers are not homogeneously distributed within the same plant and that two different lignin polymers with different composition and structure might be present. The analyses also suggested that acetates from hemicelluloses and the acyl groups (acetates and p -coumarates) attached to the γ-OH of the lignin side chains were extensively hydrolyzed and removed during the LCC fractionation process. Therefore, caution must be paid when using this fractionation approach for the structural characterization of plants with acylated hemicelluloses and lignins. Finally, several chemical linkages (phenylglycosides and benzyl Ethers) could be observed to occur between lignin and xylans in these plants.

  • Ferulates and lignin structural composition in cork
    Holzforschung, 2016
    Co-Authors: António Velez Marques, Jorge Rencoret, Ana Gutierrez, Helena Pereira
    Abstract:

    The structure of lignin and suberin, and ferulic acid (FA) content in cork from Quercus suber L. were studied. Extractive-free cork (Cork), suberin, desuberized cork (Corkₛₐₚ), and milled-cork lignins (MCL) from Cork and Corkₛₐₚ were 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 smaller amounts of resinols (ca. 2%) and dibenzodioxocins (1%). HSQC also revealed that cork lignin is heavily acylated (ca. 50%) exclusively at the side-chain γ-position. Ferulates possibly have an important function in the chemical assembly of cork cell walls with a cross-linking role between suberin, lignin and carbohydrates.

  • lignin carbohydrate complexes from sisal agave sisalana and abaca musa textilis chemical composition and structural modifications during the isolation process
    Planta, 2016
    Co-Authors: Pepijn Prinsen, Ana Gutierrez, Edith M Cadena, Angel T Martinez, Jorge Rencoret
    Abstract:

    Main conclusion Two types of lignins occurred in different lignin–carbohydrate fractions, a lignin enriched in syringyl units, less condensed, preferentially associated with xylans, and a lignin with more guaiacyl units, more condensed, associated with glucans. Lignin–carbohydrate complexes (LCC) were isolated from the fibers of sisal (Agave sisalana) and abaca (Musa textilis) according to a plant biomass fractionation procedure recently developed and which was termed as “universally” applicable to any type of lignocellulosic material. Two LCC fractions, namely glucan–lignin (GL) and xylan–lignin (XL), were isolated and differed in the content and composition of carbohydrates and lignin. In both cases, GL fractions were enriched in glucans and comparatively depleted in lignin, whereas XL fractions were depleted in glucans, but enriched in xylans and lignin. Analysis by two-dimensional Nuclear Magnetic Resonance (2D-NMR) and Derivatization Followed by Reductive Cleavage (DFRC) indicated that the XL fractions were enriched in syringyl (S)-lignin units and β-O-4′ Alkyl-Aryl Ether linkages, whereas GL fractions have more guaiacyl (G)-lignin units and less β-O-4′ Alkyl-Aryl Ether linkages per lignin unit. The data suggest that the structural characteristics of the lignin polymers are not homogeneously distributed within the same plant and that two different lignin polymers with different composition and structure might be present. The analyses also suggested that acetates from hemicelluloses and the acyl groups (acetates and p-coumarates) attached to the γ-OH of the lignin side chains were extensively hydrolyzed and removed during the LCC fractionation process. Therefore, caution must be paid when using this fractionation approach for the structural characterization of plants with acylated hemicelluloses and lignins. Finally, several chemical linkages (phenylglycosides and benzyl Ethers) could be observed to occur between lignin and xylans in these plants.

  • isolation and structural characterization of lignin from cardoon cynara cardunculus l stalks
    Bioenergy Research, 2015
    Co-Authors: Ana Lourenco, Jorge Rencoret, Ana Gutierrez, C Chemetova, Jorge Gominho, Helena Pereira
    Abstract:

    The lignin from Cynara cardunculus stalks was isolated by the classical Bjorkman 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.

Rencoret Jorge - One of the best experts on this subject based on the ideXlab platform.

  • Lignin from Tree Barks: Chemical Structure and Valorization
    'Wiley', 2020
    Co-Authors: Duarte Neiva, Rencoret Jorge, Gutiérrez Suárez Ana, Gominho J., Pereira Helena, Marques Gisela, Río Andrade, José Carlos Del
    Abstract:

    12 páginas.- 5 figuras.- 4 tablas.- 47 referencias.Lignins from different tree barks, including Norway spruce (Picea abies), eucalyptus (Eucalyptus globulus), mimosa (Acacia dealbata) and blackwood acacia (A. melanoxylon), are thoroughly characterized. The lignin from E. globulus bark is found to be enriched in syringyl (S) units, with lower amounts of guaiacyl (G) and p-hydroxyphenyl (H) units (H/G/S ratio of 1:26:73), which produces a lignin that is highly enriched in beta-Ether linkages (83 %), whereas those from the two Acacia barks have similar compositions (H/G/S ratio of approximate to 5:50:45), with a predominance of beta-Ethers (73-75 %) and lower amounts of condensed carbon-carbon linkages; the lignin from A. dealbata bark also includes some resorcinol-related compounds, that appear to be incorporated or intimately associated to the polymer. The lignin from P. abies bark is enriched in G units, with lower amounts of H units (H/G ratio of 14:86); this lignin is thus depleted in beta-O-4 ' Alkyl-Aryl Ether linkages (44 %) and enriched in condensed linkages. Interestingly, this lignin contains large amounts of hydroxystilbene glucosides that seem to be integrally incorporated into the lignin structure. This study indicates that lignins from tree barks can be seen as an interesting source of valuable phenolic compounds. Moreover, this study is useful for tailoring conversion technologies for bark deconstruction and valorization.This study was funded by the Spanish project AGL2017-83036-R (co-financed by Agencia Estatal de Investigacion, AEI, and Fondo Europeo de Desarrollo Regional, FEDER). Fundacao para a Ciencia e a Tecnologia (FCT) funded both CEF (Centro de Estudos Florestais) through UID/AGR/00239/2013, and Duarte Neiva PhD scholarship (PD/BD/52697/2014) under the SUSFOR doctoral program.Peer reviewe

  • Lignin from tree barks: chemical structure and valorization
    'Wiley', 2020
    Co-Authors: Neiva, Duarte M., Rencoret Jorge, Pereira Helena, Marques Gisela, Gutiérrez Ana, Gominho Jorge, Rio, José C. Del
    Abstract:

    Lignins from different tree barks, including Norway spruce (Picea abies), eucalyptus (Eucalyptus globulus), mimosa (Acacia dealbata) and blackwood acacia (A. melanoxylon), are thoroughly characterized. The lignin from E. globulus bark is found to be enriched in syringyl (S) units, with lower amounts of guaiacyl (G) and p-hydroxyphenyl (H) units (H/G/S ratio of 1:26:73), which produces a lignin that is highly enriched in bEther linkages (83%), whereas those from the two Acacia barks have similar compositions (H/G/S ratio of &5:50:45), with a predominance of b-Ethers (73–75%) and lower amounts of condensed carbon–carbon linkages; the lignin from A. dealbata bark also includes some resorcinol-related compounds, that appear to be incorporated or intimately associated to the polymer. The lignin from P. abies bark is enriched in G units, with lower amounts of H units (H/G ratio of 14:86); this lignin is thus depleted in b-O-4’ AlkylAryl Ether linkages (44%) and enriched in condensed linkages. Interestingly, this lignin contains large amounts of hydroxystilbene glucosides that seem to be integrally incorporated into the lignin structure. This study indicates that lignins from tree barks can be seen as an interesting source of valuable phenolic compounds. Moreover, this study is useful for tailoring conversion technologies for bark deconstruction and valorizationinfo:eu-repo/semantics/publishedVersio

  • Structural characteristics of the lignin in olive tree (Olea europaea) pruning residues
    Universidad de Córdoba, 2019
    Co-Authors: Rencoret Jorge, Gutiérrez Suárez Ana, Castro Eulogio, Río Andrade, José Carlos Del
    Abstract:

    Póster presentado en el 2nd International Workshop on Biorefinery of Lignocellulosic Materials 4-7 June 2019, Córdoba, SpainOlive 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 the lignocellulosic biorefineries. However, the presence of lignin in this residue hinders the transformation processes as it limits the access to cell wall polysaccharides. Moreover, 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 thoroughly characterized by 2D-NMR and thioacidolysis. The results demonstrated that the lignin was 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 were β–O–4ʹ 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 5–5ʹ, 4–O–5ʹ, β–5ʹ, β–1ʹ and β–βʹ. It is therefore possible to conclude that the high lignin content (25%), togEther with the low S/G ratio and the abundance of condensed (carbon–carbon linked) structures, confers a low reactivity of OTP during delignification pretreatments, especially those pretreatments intended to depolymerize the lignin polymer by cleaving the β–O–4′ Alkyl-Aryl Ether bonds, such as steam explosion or alkaline pulping. AcknowledgementsThis study has been funded by the Spanish projects CTQ2014-60764-JIN and AGL2017-83036-R (financed by Agencia Estatal de Investigación, AEI, and Fondo Europeo de Desarrollo Regional, FEDER).N

  • Lignin structure from Cynara cardunculus in comparison with other herbaceous species
    'Japanese Society of Applied Entomology & Zoology', 2018
    Co-Authors: Lourenço Ana, Rencoret Jorge, Gutiérrez Suárez Ana, Chemetova C., Gominho J., Pereira Helena, Río Andrade, José Carlos Del
    Abstract:

    Cardoon lignin was isolated by the Björkman method and its composition and structure were studied by Py-GC/MS, 2D-NMR and DFRC. Cardoon lignin has more guaiacyl (G) than syringyl (S) units (S/G 0.7), and no p-hydroxyphenyl (H) units. The linkages are predominantly of ß¿O¿4¿ Alkyl-Aryl Ether type (70% of all inter-unit linkages), but some condensed linkages such as ß-5¿ phenylcoumarans (14%), ß-ß¿ resinols (7%), ß-1¿ spirodienones (5%) and 5-5¿ dibenzodioxocins (4%) are also present. Lignin is partially acylated at the ¿-OH (12% acylation) by acetate groups, preferentially on syringyl-units. Cardoon lignin is structurally similar to wheat straw lignin, but different from sisal, jute and Mmiscanthus lignins regarding acylation type and degree.Thanks to Alejandro Rico, Manuel Angulo and Duarte Neiva for experimental assistance. Finance support was given by the Portuguese Science Foundation (FCT) through funding of the Forest Research Center (UID/AGR/00239/2013 project) and the Spanish projects AGL2014-53730-R and CTQ2014-60764-JIN (co-financed by FEDER funds). The first author was funded by FCT through her post-doctoral grant (SFRH/BPD/95385/2013).Peer Reviewe

  • Structural characteristics of the lignins from sugarcane bagasse and straw
    International Union of Forest Research Organizations, 2018
    Co-Authors: Río Andrade, José Carlos Del, Gutiérrez Suárez Ana, Ralph John, Colodette, Jorge Luiz, Lino, Alessandro Guarino, Rencoret Jorge
    Abstract:

    4 páginas.-- 1 figuras.-- 5 referencias.-- Comunicación oral presentada en el 14th European Workshop on Lignocellulosics and Pulp June 28-30, 2016 - Autrans, France.Sugarcane (Saccharum spp.) is a perennial monocotyledonous plant from the Gramineae family that is the main feedstock for the production of sugar and also ethanol. Two major residues are produced by the sugarcane industry, the fibrous fraction following juice extraction (named bagasse), and the harvest residue (straw). Sugarcane bagasse and straw are lignocellulosic resides basically composed of cellulose, hemicelluloses, and lignin, and are attractive feedstocks for the production of second-generation ethanol and other bio-based products, in the context of the so-called lignocellulosic biorefinery. Converting bagasse and straw to ethanol requires an enzymatic saccharification of the polysaccharides to reducing sugars and their subsequent fermentation to ethanol. However, the presence of recalcitrant lignin reduces the accessibility of the enzymes to the cellulose, and decreases the efficiency of the hydrolysis. Costly and harsh pretreatment processes are therefore needed to circumvent cell-wall recalcitrance by removing, or cleaving and redistributing, the lignin polymer. The efficiency of the pretreatment process is highly dependent on both the lignin content and structure, and therefore the knowledge of the structure of the lignin is important to develop appropriate pretreatment methods for delignification, as well as for potentially higher-value utilization of the lignin. In this paper, we report a detailed characterization of the lignins in sugarcane bagasse and straw by using different analytical techniques (Py-GC/MS, 2D-NMR, DFRC). The analyses indicate that the lignin from sugarcane bagasse is S-rich (H:G:S molar ratio of 2:38:60) whereas the lignin from sugarcane straw is G-rich (4:68:28). The compositional differences are also reflected in differences in the relative abundances of the various interunit linkages. Thus, the lignin from bagasse is mostly made up by ß¿O¿4¿ Alkyl-Aryl Ether units (83% of all linkages), followed by minor amounts of phenylcoumarans (6%) and other condensed units. The lignin from straw, on the other hand, has lower amounts of Alkyl-Aryl Ether units (75% of all linkages) and has higher amounts of condensed structures such as phenylcoumarans (15%) and dibenzodioxocins (3%). The differences observed in the lignins of the two sugarcane residues suggest that the bagasse material will pretreat more easily (because of its higher S-content and lower condensation degree) than the straw (with a higher content of condensed structures). In addition, the two residues contain significant levels of p-coumarate, ferulate, and tricin that might also be valuable to extract as commodity chemicals.This study has been funded by the projects AGL2014-53730-R and CTQ2014-60764-JIN (cofinanced by FEDER funds), and CSIC project 2014-40E-097. J. Ralph was funded through the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science DE-FC02-07ER64494). AGL thanks CAPES, and CFL and JLC thank CNPq for financial support.Peer Reviewe