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Structural Basis for the Formation and Regulation of Lignin–Xylan Bonds in Birch
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. (Wallenberg Wood Science Center)ORCID iD: 0000-0003-4266-0720
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. (Wallenberg Wood Science Center)ORCID iD: 0000-0002-8614-6291
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.

Place, publisher, year, edition, pages
2016. Vol. 4, no 10, p. 5319-5326
Keyword [en]
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: urn:nbn:se:kth:diva-190068DOI: 10.1021/acssuschemeng.6b00911ISI: 000384791500023Scopus ID: 2-s2.0-84990193059OAI: oai:DiVA.org:kth-190068DiVA, id: diva2:950903
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
In thesis
1. Fundamental Aspects of Lignin Carbohydrate Complexes (LCC): Mechanisms, Recalcitrance and Material concepts
Open this publication in new window or tab >>Fundamental Aspects of Lignin Carbohydrate Complexes (LCC): Mechanisms, Recalcitrance and Material concepts
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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 95
Series
TRITA-CBH-FOU ; 2018:18
Keyword
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:nbn:se:kth:diva-227865 (URN)978-91-7729-771-0 (ISBN)
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: 2018-05-14Bibliographically approved

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