Chemical and structural changes associated with Cu-catalyzed alkaline-oxidative delignification of hybrid poplar

Zhenglun Li, Namita Bansal, Ali Azarpira, Aditya Bhalla, Charles H. Chen, John Ralph, Eric L. Hegg, David B. Hodge

Research output: Contribution to journalArticle

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Abstract

Background: Alkaline hydrogen peroxide pretreatment catalyzed by Cu(II) 2,2′-bipyridine complexes has previously been determined to substantially improve the enzymatic hydrolysis of woody plants including hybrid poplar as a consequence of moderate delignification. In the present work, cell wall morphological and lignin structural changes were characterized for this pretreatment approach to gain insights into pretreatment outcomes and, specifically, to identify the extent and nature of lignin modification. Results: Through TEM imaging, this catalytic oxidation process was shown to disrupt cell wall layers in hybrid poplar. Cu-containing nanoparticles, primarily in the Cu(I) oxidation state, co-localized with the disrupted regions, providing indirect evidence of catalytic activity whereby soluble Cu(II) complexes are reduced and precipitated during pretreatment. The concentration of alkali-soluble polymeric and oligomeric lignin was substantially higher for the Cu-catalyzed oxidative pretreatment. This alkali-soluble lignin content increased with time during the catalytic oxidation process, although the molecular weight distributions were unaltered. Yields of aromatic monomers (including phenolic acids and aldehydes) were found to be less than 0.2 % (wt/wt) on lignin. Oxidation of the benzylic alcohol in the lignin side-chain was evident in NMR spectra of the solubilized lignin, whereas minimal changes were observed for the pretreatment-insoluble lignin. Conclusions: These results provide indirect evidence for catalytic activity within the cell wall. The low yields of lignin-derived aromatic monomers, together with the detailed characterization of the pretreatment-soluble and pretreatment-insoluble lignins, indicate that the majority of both lignin pools remained relatively unmodified. As such, the lignins resulting from this process retain features closely resembling native lignins and may, therefore, be amenable to subsequent valorization.

LanguageEnglish (US)
Article number123
JournalBiotechnology for Biofuels
Volume8
Issue number1
DOIs
StatePublished - Aug 20 2015

Profile

Delignification
Lignin
structural change
lignin
Cell Wall
oxidation
Catalytic oxidation
Cells
Alkalies
chemical
Catalyst activity
Monomers
Oxidation
2,2'-Dipyridyl
Enzymatic hydrolysis
Molecular weight distribution
woody plant
aldehyde
Aldehydes
Hydrogen peroxide

Keywords

  • Alkaline hydrogen peroxide (AHP) pretreatment
  • Catalytic oxidation
  • Electron microscopy
  • Lignin
  • NMR spectroscopy
  • Plant cell walls
  • Pretreatment

ASJC Scopus subject areas

  • Energy(all)
  • Management, Monitoring, Policy and Law
  • Biotechnology
  • Applied Microbiology and Biotechnology
  • Renewable Energy, Sustainability and the Environment

Cite this

Li, Z., Bansal, N., Azarpira, A., Bhalla, A., Chen, C. H., Ralph, J., ... Hodge, D. B. (2015). Chemical and structural changes associated with Cu-catalyzed alkaline-oxidative delignification of hybrid poplar. Biotechnology for Biofuels, 8(1), [123]. DOI: 10.1186/s13068-015-0300-5

Chemical and structural changes associated with Cu-catalyzed alkaline-oxidative delignification of hybrid poplar. / Li, Zhenglun; Bansal, Namita; Azarpira, Ali; Bhalla, Aditya; Chen, Charles H.; Ralph, John; Hegg, Eric L.; Hodge, David B.

In: Biotechnology for Biofuels, Vol. 8, No. 1, 123, 20.08.2015.

Research output: Contribution to journalArticle

Li Z, Bansal N, Azarpira A, Bhalla A, Chen CH, Ralph J et al. Chemical and structural changes associated with Cu-catalyzed alkaline-oxidative delignification of hybrid poplar. Biotechnology for Biofuels. 2015 Aug 20;8(1). 123. Available from, DOI: 10.1186/s13068-015-0300-5
Li, Zhenglun ; Bansal, Namita ; Azarpira, Ali ; Bhalla, Aditya ; Chen, Charles H. ; Ralph, John ; Hegg, Eric L. ; Hodge, David B./ Chemical and structural changes associated with Cu-catalyzed alkaline-oxidative delignification of hybrid poplar. In: Biotechnology for Biofuels. 2015 ; Vol. 8, No. 1.
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abstract = "Background: Alkaline hydrogen peroxide pretreatment catalyzed by Cu(II) 2,2′-bipyridine complexes has previously been determined to substantially improve the enzymatic hydrolysis of woody plants including hybrid poplar as a consequence of moderate delignification. In the present work, cell wall morphological and lignin structural changes were characterized for this pretreatment approach to gain insights into pretreatment outcomes and, specifically, to identify the extent and nature of lignin modification. Results: Through TEM imaging, this catalytic oxidation process was shown to disrupt cell wall layers in hybrid poplar. Cu-containing nanoparticles, primarily in the Cu(I) oxidation state, co-localized with the disrupted regions, providing indirect evidence of catalytic activity whereby soluble Cu(II) complexes are reduced and precipitated during pretreatment. The concentration of alkali-soluble polymeric and oligomeric lignin was substantially higher for the Cu-catalyzed oxidative pretreatment. This alkali-soluble lignin content increased with time during the catalytic oxidation process, although the molecular weight distributions were unaltered. Yields of aromatic monomers (including phenolic acids and aldehydes) were found to be less than 0.2 {\%} (wt/wt) on lignin. Oxidation of the benzylic alcohol in the lignin side-chain was evident in NMR spectra of the solubilized lignin, whereas minimal changes were observed for the pretreatment-insoluble lignin. Conclusions: These results provide indirect evidence for catalytic activity within the cell wall. The low yields of lignin-derived aromatic monomers, together with the detailed characterization of the pretreatment-soluble and pretreatment-insoluble lignins, indicate that the majority of both lignin pools remained relatively unmodified. As such, the lignins resulting from this process retain features closely resembling native lignins and may, therefore, be amenable to subsequent valorization.",
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AU - Li,Zhenglun

AU - Bansal,Namita

AU - Azarpira,Ali

AU - Bhalla,Aditya

AU - Chen,Charles H.

AU - Ralph,John

AU - Hegg,Eric L.

AU - Hodge,David B.

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AB - Background: Alkaline hydrogen peroxide pretreatment catalyzed by Cu(II) 2,2′-bipyridine complexes has previously been determined to substantially improve the enzymatic hydrolysis of woody plants including hybrid poplar as a consequence of moderate delignification. In the present work, cell wall morphological and lignin structural changes were characterized for this pretreatment approach to gain insights into pretreatment outcomes and, specifically, to identify the extent and nature of lignin modification. Results: Through TEM imaging, this catalytic oxidation process was shown to disrupt cell wall layers in hybrid poplar. Cu-containing nanoparticles, primarily in the Cu(I) oxidation state, co-localized with the disrupted regions, providing indirect evidence of catalytic activity whereby soluble Cu(II) complexes are reduced and precipitated during pretreatment. The concentration of alkali-soluble polymeric and oligomeric lignin was substantially higher for the Cu-catalyzed oxidative pretreatment. This alkali-soluble lignin content increased with time during the catalytic oxidation process, although the molecular weight distributions were unaltered. Yields of aromatic monomers (including phenolic acids and aldehydes) were found to be less than 0.2 % (wt/wt) on lignin. Oxidation of the benzylic alcohol in the lignin side-chain was evident in NMR spectra of the solubilized lignin, whereas minimal changes were observed for the pretreatment-insoluble lignin. Conclusions: These results provide indirect evidence for catalytic activity within the cell wall. The low yields of lignin-derived aromatic monomers, together with the detailed characterization of the pretreatment-soluble and pretreatment-insoluble lignins, indicate that the majority of both lignin pools remained relatively unmodified. As such, the lignins resulting from this process retain features closely resembling native lignins and may, therefore, be amenable to subsequent valorization.

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