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Fundamental Aspects of Lignin Carbohydrate Complexes (LCC): Mechanisms, Recalcitrance and Material concepts
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. (Wallenberg Wood Science Center)ORCID iD: 0000-0003-4266-0720
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Covalent bonds between lignin and carbohydrates, forming a matrix referred to as lignin carbohydrate complexes (LCC), remain one of the most controversial topics in wood chemistry. A key issue is whether they are formed during chemical and mechanical pretreatments of the compact wood structure or actually present in wood prior to isolation. A fundamental understanding of their origin and reactivity is vital to unravel their role in wood formation and recalcitrance. Recalcitrance, specifically, has affected the successful development of effective and clean fractionation of wood polymers.

To address the above-mentioned concerns, we have developed a novel mild universal and quantitative fractionation protocol of LCC that, when combined with robust spectroscopic analytical tools, including a variety of NMR techniques, GC MS and SEC, reveals deeper insights into the molecular structure of LCC.

This method was applied to both hardwood and softwood LCCs and revealed interesting findings on molecular-level regulatory mechanism for lignin carbohydrate (LC) bond formation such as the role of acetylation in hemicelluloses. Moreover, the role of LC bonds on recalcitrance during subcritical water extraction was unveiled.

Bio-mimicking in vitro lignin polymerization was adopted to investigate whether LC bonds are native or formed during isolation from wood. For the first time, direct evidence lending support that they are formed in wood cells was demonstrated, thus corroborating the mechanisms suggested in the literature.  

Furthermore, based on the overall LCC study, we suggest a sequence for how LC bonds may form in vitro.

Finally, of special interest to material science, the unveiled LC bond formation mechanism inspired a green, biomimetic, one-pot synthesis of functionalized lignin starting from monomeric components. Excellent selectivity of functionalization is reported and production of lignin-based recyclable materials, based on the premise of this functionalization philosophy, is discussed.

Abstract [sv]

Existensen av kovalenta bindningar mellan lignin och kolhydrater, som bildar en matris som kallas ligninkolhydratkomplex (LCC), förblir ett av de mest kontroversiella ämnena inom träkemi. En viktig fråga är om de bildas under isolering eller faktiskt finns närvarande i trä före isolering (där isolering innefattar kemiska och mekaniska förbehandlingar av den kompakta trästrukturen). Djupare insikter om deras ursprung och reaktivitet är avgörande för att utröna deras roll i träbildning och deras bidrag till extraktionssvårighet. Lignins bidrag till extraktionssvårighet är av särskilt intresse, då den länge hämmat den framgångsrika utvecklingen av effektiv och ren fraktionering av träpolymerer.För att ta itu med ovan nämnda problem har vi utvecklat ett nytt, milt, universellt och kvantitativt fraktioneringsprotokoll av LCC som i kombination med robusta spektroskopiska analysverktyg (vilka innefattar ett flertal NMR-tekniker samt GC MS och SEC) ger djupare insikt om LCCs molekylära struktur. Detta protokoll applicerades på både barr- och lövved och ledde till intressanta upptäckter beträffande de molekylära regler-mekanismerna för bildandet av lignin-kolhydrat-bindningar (LC). Dessa upptäckter berörde även vikten av hemicellulosors acetylering. Vidare presenterades hur LC-bindningar bidrar till extractionssvårighet under subkritisk vattenutvinning.Biomimetisk in vitro-ligninpolymerisation användes för att vidare undersöka huruvida LC-bindningar finns närvarande innan isolering av trä eller bildas under denna. I denna avhandling har för första gången direkta bevis till stöd för att de bildas nativt i träceller presenterats. Detta korroborerar tidigare mekanismer som föreslagits i litteraturen. Vidare erhölls djupare insikter på molekylär nivå för att föreslår en sekvens för hur LC-bindningar bildas in vitro.Slutligen, av särskilt intresse för materialvetenskap, inspirerade den framtagna LC-bindningsmedelsmekanismen en grön, biomimetisk enstegssyntes av funktionaliserat lignin utgående från monomera komponenter. Utmärkt funktionaliseringsselektivitet uppvisades och en produktion av ligninbaserade återvinningsbara material baserade på denna funktionaliseringsfilosofi diskuteras.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. , p. 95
Series
TRITA-CBH-FOU ; 2018:18
Keywords [en]
Lignin Carbohydrates Complexes; Phenyl Glycosides; Benzyl Ethers; Benzyl and γ-esters; Universal Mild Quantitative fractionation; LCC mechanism formation, Extracellular lignin; Dehydogenation polymer; Autohydrolysis; Recalcitrance; Acetylation role; HSQC, HMBC, HSQC-TOCSY, 13C, 31P NMR, Thioacidolysis-GC; SEC; Green, Biomimetic, One-pot-lignin functionalization; Lignin platform material.
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-227865ISBN: 978-91-7729-771-0 (print)OAI: oai:DiVA.org:kth-227865DiVA, id: diva2:1205464
Public defence
2018-06-11, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180514

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2019-05-15Bibliographically approved
List of papers
1. Structural features of mildly fractionated lignin carbohydrate complexes (LCC) from spruce
Open this publication in new window or tab >>Structural features of mildly fractionated lignin carbohydrate complexes (LCC) from spruce
2016 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 48, p. 42120-42131Article in journal (Refereed) Published
Abstract [en]

A protocol for the quantitative fractionation of lignin carbohydrate complexes (LCC) from wood under mild conditions has been developed. All operations occur at near-neutral pH conditions and low temperatures, in order to preserve the native structure. The protocol also achieved the fractionation of hemicelluloses of relatively high purity enabling for the first time estimates of hemicelluloses fractions not chemically bound to lignin in wood. 2D HSQC NMR was applied to decipher the structure of LCCs and was complemented by thioacidolysis-GC MS techniques. The carbohydrates linked to lignin in LCC are hemicelluloses, mainly arabinoglucuronoxylan (AGX) and galactoglucomannan (GGM). Benzylether (BE) and phenyl glycosidic (PG) linkages were detected. Significant structural differences in the lignin part of LCCs are also reported. The novelty of this work is that we report the first quantitative pH neutral protocol for LCC fractionation and detailed chemical analyses unveil important structural differences of relevance to fundamental knowledge in lignin polymerization and wood-based biorefineries.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2016
Keywords
lignin carbohydrate complexes (LCC), spruce, 2D HSQC, mild protocol
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-187681 (URN)10.1039/c6ra02399a (DOI)000375445500055 ()2-s2.0-84966331045 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20160530

Available from: 2016-05-26 Created: 2016-05-26 Last updated: 2018-05-14Bibliographically approved
2. Structural Basis for the Formation and Regulation of Lignin–Xylan Bonds in Birch
Open this publication in new window or tab >>Structural Basis for the Formation and Regulation of Lignin–Xylan Bonds in Birch
2016 (English)In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 4, no 10, p. 5319-5326Article in journal (Refereed) Published
Abstract [en]

The covalent connectivity between lignin and polysaccharides forming the so-called lignin–carbohydrate complexes (LCCs) is important to obtain fundamental knowledge on wood formation and may shed light on molecular aspects of wood processing. Although widely studied, unequivocal proofs of their existence in native-state biomass are still lacking, mainly because of harsh preanalytical fractionation conditions that could cause artifacts. In the present study, we applied a mild protocol for quantitative fractionation of LCCs and performed detailed structural studies using 2D HSQC NMR spectroscopy, 31P NMR spectroscopy, and thioacidolysis in combination with GC–MS and GC with flame ionization detection. The detailed structural analysis of LCCs, including both lignin and the carbohydrate skeleton, unveiled insights into the role of molecular structure of xylan on the type of lignin–carbohydrate (LC) bonds formed. More specifically, it is shown that xylan LCCs differ in the degree of substitution of hydroxyl functionality on the xylan skeleton by the presence of acetyl- or 4-O-methylglucuronic acid. The highly substituted xylan had a lower prevalence of phenyl glycosidic and benzyl ether LC bond types than the lowly substituted xylan. In addition, structural differences in the lignin part of the LCCs were observed. On the basis of the results, it is suggested that acetylation on xylan regulates the type and frequency of LC bonds.

Keywords
2D HSQC NMR; Acetylation; Benzyl ethers; Lignin carbohydrate complexes (LCCs); Mild quantitative fractionation; Phenyl glycosides; Xylan; γ-esters
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-190068 (URN)10.1021/acssuschemeng.6b00911 (DOI)000384791500023 ()2-s2.0-84990193059 (Scopus ID)
Conference
ACS 251th San Diego
Funder
Knut and Alice Wallenberg Foundation, 8107
Note

QC 20160808

Available from: 2016-08-03 Created: 2016-08-03 Last updated: 2018-05-14Bibliographically approved
3. Nativity of Lignin Carbohydrate Bonds substantiated by novel biomimetic synthesis
Open this publication in new window or tab >>Nativity of Lignin Carbohydrate Bonds substantiated by novel biomimetic synthesis
(English)Manuscript (preprint) (Other academic)
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-227868 (URN)
Note

QC 20180514

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2018-05-14Bibliographically approved
4. Structural Insights on Recalcitrance during Hydrothermal Hemicellulose Extraction from Wood
Open this publication in new window or tab >>Structural Insights on Recalcitrance during Hydrothermal Hemicellulose Extraction from Wood
2017 (English)In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 5, no 6, p. 5156-5165Article in journal (Refereed) Published
Abstract [en]

Hydrothermal extraction of hemicelluloses from lignocellulosic biomass for conversion to renewable materials or fuels has captured attention. The extraction is however partial and some lignin is codissolved. Herein, we investigated the role of molecular structure in the recalcitrance. Wood meal of Spruce and Birch were subjected to pressurized hydrothermal extraction at 160 °C for 2 h, which extracted 68–75% of the hemicelluloses. 2D heteronuclear single quantum coherence (HSQC) NMR, HSQC-TOCSY, and 13C NMR were applied for structural studies of both extracts and residues. Subsequent to the known partial hydrolysis of native carbon-2 and carbon-3 acetates in hemicellulose, some acetylation of primary alcohols on hemicelluloses and lignin was observed. Lignin carbohydrate complexes (LCC) were detected in both the extracts and residues. In Spruce extracts, only the phenyl glycoside-type of LCC was detected. Birch extracts contained both the phenyl glycoside and benzyl ether-types. In the hydrothermal wood residues of both species, benzyl ether- and gamma (γ)-ester-LCC were present. Structural changes in lignin included decrease in aryl ether (βO4) content and increases in resinol- (ββ) and phenyl coumaran (β5) contents. On the basis of the overall analysis, the mechanisms and contribution of molecular structure to recalcitrance is discussed.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
Keywords
13C NMR, 2D HSQC, Autohydrolysis, HSQC-TOCSY, LCC repolymerization, Lignin carbohydrate complexes (LCC), Recalcitrance, trans-Acetylation
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-208164 (URN)10.1021/acssuschemeng.7b00511 (DOI)000402950000076 ()2-s2.0-85020212464 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, 8107
Note

QC 20170613

Available from: 2017-06-01 Created: 2017-06-01 Last updated: 2018-05-14Bibliographically approved
5. Differences in extractability under subcritical water reveal interconnected hemicellulose and lignin recalcitrance in birch hardwoods
Open this publication in new window or tab >>Differences in extractability under subcritical water reveal interconnected hemicellulose and lignin recalcitrance in birch hardwoods
2018 (English)In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270Article in journal (Refereed) Published
Abstract [en]

Hardwoods constitute an essential renewable resource for the production of platform chemicals and bio-based materials. A method for the sequential extraction of hemicelluloses and lignin from hardwoods is proposed using subcritical water in buffered conditions without prior delignification. This allows the cascade isolation of mannan, xylan and lignin-carbohydrate complexes based on their extractability and recalcitrance in birch lignocellulose. The time evolution of the extraction was monitored in terms of composition, oligomeric mass profiling and sequencing of the hemicelluloses, and molecular structure of the lignin and lignin-carbohydrate complexes (LCCs) by heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR). The minor mannan and pectin populations are easily extractable at short times (<5 min), whereas the major glucuronoxylan (GX) becomes enriched at moderate extraction times. Longer extraction times results in major hydrolysis exhibiting GX fractions with tighter glucuronation spacing and lignin enrichment. The pattern of acetylation and glucuronation in GX is correlated with extractability and with connectivity with lignin through LCCs. This interconnected molecular heterogeneity of hemicelluloses and lignin has important implications for their supramolecular assembly and therefore determines the recalcitrance of hardwood lignocellulosic biomass.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-226948 (URN)10.1039/C8GC00385H (DOI)000434313100016 ()2-s2.0-85048032938 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20180509

Available from: 2018-04-29 Created: 2018-04-29 Last updated: 2018-06-27Bibliographically approved
6. A One-Pot Biomimetic Synthesis of Selectively Functionalized Lignins from Monomers: A Green Functionalization Platform
Open this publication in new window or tab >>A One-Pot Biomimetic Synthesis of Selectively Functionalized Lignins from Monomers: A Green Functionalization Platform
2018 (English)In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 21, no 11, p. 5579-5585Article in journal (Refereed) Published
Abstract [en]

Lignin is the most abundant renewable source of phenolic compound with great application potential in renewable materials, biofuels and platform chemicals. Current technology for producing cellulose-rich fibers co-produces heterogeneous lignin, which includes an untapped source of monomeric phenolics. One such monomer also happen to be the main monomer in soft wood lignin biosynthesis, namely coniferyl alcohol. Herein, we investigate the potential of coniferyl alcohol as a platform monomer for the biomimetic production of tailored functionalized oligolignols with desirable properties for material synthesis. Accordingly, a bifunctional molecule with at least one carboxyl-ended functionality is included with coniferyl alcohol in biomimetic lignin synthesis to, in one-pot, produce a functionalized lignin. The functionalization mechanism is a nucleophilic addition reaction to quinone methide intermediate of lignin polymerization. The solvent systems applied were pure water or 50% aqueous acetone. Several bi-functional molecules differing in the second functionality were successfully inserted in the lignin demonstrating the platform component of this work. Detailed characterizations were performed by a combination of NMR techniques which include 1H NMR, COSY-90, 31P NMR, 13C NMR, 13C APT, HSQC, HMBC and HSQC TOCSY. Excellent selectivity towards benzylic carbon and high functionalization degree were noted. The structure of lignin was tailored through solvent system choice, with the 50% aqeuous acetone producing a skeletal structure favorable for high functionalization degrees. Finally, material concepts are demonstrated using classical Thiol-ene- and Diels Alder- chemistries to show potential for thermoset- and thermoplastic- concepts, respectively. The functionalization concept presents unprecedentent opportunities for green production of lignin-based recyclable biomaterials.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-227163 (URN)10.1039/C8GC01145A (DOI)000434313100026 ()2-s2.0-85048051690 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20180509

Available from: 2018-05-03 Created: 2018-05-03 Last updated: 2019-11-07Bibliographically approved

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