Activation of Cellulose via Cooperative Hydroxyl-Catalyzed Transglycosylation of Glycosidic Bonds

Vineet J Maliekkal, Saurabh Maduskar, Derek Saxon, Mohammadreza Nasiri, Theresa M Reineke, Matthew Neurock, Paul J Dauenhauer

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The thermal activation of cellulose by initial glycosidic bond cleavage determines the overall rate of conversion to organic products for energy applications. Here, the kinetics of ether scission by transglycosylation of β-1,4-glycosidic bonds was measured using the "pulse-heated analysis of solid reactions" (PHASR) method from 400 to 500 °C. Levoglucosan (LGA) formation from cellulose was temporally resolved over the full extent of conversion, which was interpreted via a coupled reactant-product evolution model to determine an apparent barrier of LGA formation of 27.9 kcal mol -1 . In parallel, LGA formation from the glucose monomer of cellobiosan was measured at temperatures between 380 and 430 °C by isotopically labeling the 13 C 1 carbon; an apparent activation energy of LGA formation was measured as 26.9 ± 1.9 kcal mol -1 . The unusually low activation barrier for LGA formation at lower temperature is in agreement with previous PHASR studies for cellulose breakdown and is indicative of catalytic rather than thermal C-O bond activation. A catalytic mechanism was proposed wherein vicinal hydroxyl groups from neighboring cellulose sheets promote transglycosidic C-O bond activation. First-principle density functional theory (DFT) calculations showed that these vicinal hydroxyl groups cooperatively act to create an environment that (a) stabilizes charged transition states and (b) aids in proton transfer, thus leading to reduced activation barriers for transglycosylation. Models incorporating intrasheet H bonding of cellulose were also used to establish their influence on kinetics. The calculated apparent barrier (29.5 kcal mol -1 ) agreed well with the experimental apparent activation energy (26.9 ± 1.9 kcal mol -1 ) and establishes the dominant mode for cellulose activation and subsequent levoglucosan formation at lower temperatures (<467 °C) as site-specific, vicinal hydroxyl-catalyzed transglycosylation.

Original languageEnglish (US)
Pages (from-to)1943-1955
Number of pages13
JournalACS Catalysis
Volume9
Issue number3
DOIs
StatePublished - Mar 1 2019

Fingerprint

Cellulose
Hydroxyl Radical
Chemical activation
Activation energy
Kinetics
Proton transfer
Ether
Temperature
Labeling
Density functional theory
Glucose
1,6-anhydro-beta-glucopyranose
Ethers
Carbon
Monomers
Hot Temperature

Keywords

  • cellobiosan
  • cellobiose
  • cellulose
  • hydroxyl catalyzed
  • levoglucosan
  • transglycosylation

Cite this

Activation of Cellulose via Cooperative Hydroxyl-Catalyzed Transglycosylation of Glycosidic Bonds. / Maliekkal, Vineet J; Maduskar, Saurabh; Saxon, Derek; Nasiri, Mohammadreza; Reineke, Theresa M; Neurock, Matthew; Dauenhauer, Paul J.

In: ACS Catalysis, Vol. 9, No. 3, 01.03.2019, p. 1943-1955.

Research output: Contribution to journalArticle

Maliekkal, Vineet J ; Maduskar, Saurabh ; Saxon, Derek ; Nasiri, Mohammadreza ; Reineke, Theresa M ; Neurock, Matthew ; Dauenhauer, Paul J. / Activation of Cellulose via Cooperative Hydroxyl-Catalyzed Transglycosylation of Glycosidic Bonds. In: ACS Catalysis. 2019 ; Vol. 9, No. 3. pp. 1943-1955.
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AU - Maliekkal, Vineet J

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AU - Saxon, Derek

AU - Nasiri, Mohammadreza

AU - Reineke, Theresa M

AU - Neurock, Matthew

AU - Dauenhauer, Paul J

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AB - The thermal activation of cellulose by initial glycosidic bond cleavage determines the overall rate of conversion to organic products for energy applications. Here, the kinetics of ether scission by transglycosylation of β-1,4-glycosidic bonds was measured using the "pulse-heated analysis of solid reactions" (PHASR) method from 400 to 500 °C. Levoglucosan (LGA) formation from cellulose was temporally resolved over the full extent of conversion, which was interpreted via a coupled reactant-product evolution model to determine an apparent barrier of LGA formation of 27.9 kcal mol -1 . In parallel, LGA formation from the glucose monomer of cellobiosan was measured at temperatures between 380 and 430 °C by isotopically labeling the 13 C 1 carbon; an apparent activation energy of LGA formation was measured as 26.9 ± 1.9 kcal mol -1 . The unusually low activation barrier for LGA formation at lower temperature is in agreement with previous PHASR studies for cellulose breakdown and is indicative of catalytic rather than thermal C-O bond activation. A catalytic mechanism was proposed wherein vicinal hydroxyl groups from neighboring cellulose sheets promote transglycosidic C-O bond activation. First-principle density functional theory (DFT) calculations showed that these vicinal hydroxyl groups cooperatively act to create an environment that (a) stabilizes charged transition states and (b) aids in proton transfer, thus leading to reduced activation barriers for transglycosylation. Models incorporating intrasheet H bonding of cellulose were also used to establish their influence on kinetics. The calculated apparent barrier (29.5 kcal mol -1 ) agreed well with the experimental apparent activation energy (26.9 ± 1.9 kcal mol -1 ) and establishes the dominant mode for cellulose activation and subsequent levoglucosan formation at lower temperatures (<467 °C) as site-specific, vicinal hydroxyl-catalyzed transglycosylation.

KW - cellobiosan

KW - cellobiose

KW - cellulose

KW - hydroxyl catalyzed

KW - levoglucosan

KW - transglycosylation

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