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

    • 4 Citations

    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.

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

    Profile

    Lignin
    lignin
    oxidation
    Cells
    Cell Wall
    Delignification
    Catalytic oxidation
    Catalyst activity
    Monomers
    Oxidation
    structural change
    Alkalies
    Enzymatic hydrolysis
    Molecular weight distribution
    Aldehydes
    Hydrogen peroxide
    Alcohols
    Nuclear magnetic resonance
    Nanoparticles
    Transmission electron microscopy

    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

    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, Vol. 8, No. 1, 123, 20.08.2015.

    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.",
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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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    N2 - 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.

    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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    KW - Catalytic oxidation

    KW - Electron microscopy

    KW - Lignin

    KW - NMR spectroscopy

    KW - Plant cell walls

    KW - Pretreatment

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