Simulation analysis of the temperature dependence of lignin structure and dynamics

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja206839u· OSTI ID:1031537

Petridis, Loukas ^[1]; Schulz, Roland ^[1]; Smith, Jeremy C ^[1]

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1. ORNL

Lignins are hydrophobic, branched polymers that regulate water conduction and provide protection against chemical and biological degradation in plant cell walls. Lignins also form a residual barrier to effective hydrolysis of plant biomass pretreated at elevated temperatures in cellulosic ethanol production. Here, the temperature-dependent structure and dynamics of individual softwood lignin polymers in aqueous solution are examined using extensive (17ms) molecular dynamics simulations. With decreasing temperature the lignins are found to transition from mobile, extended to glassy, compact states. The polymers are comprised of blobs, inside which the radius of gyration of a polymer segment is a power-law function of the number of monomers comprising it. In the low temperature states the blobs are inter-permeable, the polymer does not conform to Zimm/Stockmayer theory, and branching does not lead to reduction of the polymer size, the radius of gyration being instead determined by shape anisotropy. At high temperatures the blobs become spatially separated leading to a fractal crumpled globule form. The low-temperature collapse is thermodynamically driven by the increase of the translational entropy and density fluctuations of water molecules removed from the hydration shell , thus distinguishing lignin collapse from enthalpically driven coil-globule polymer transitions and providing a thermodynamic role of hydration water density fluctuations in driving hydrophobic polymer collapse. Although hydrophobic, lignin is wetted, leading to locallyenhanced chain dynamics of solvent-exposed monomers. The detailed characterization obtained here provides insight at atomic detail into processes relevant to biomass pretreatment for cellulosic ethanol production and general polymer coil-globule transition phenomena.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Oak Ridge National Laboratory (ORNL); Center for Computational Sciences
• Sponsoring Organization: DOE Office of Science; SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1031537
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 50 Vol. 133; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
ANISOTROPY
AQUEOUS SOLUTIONS
BIOMASS
CELLULOSIC ETHANOL
ENTROPY
FLUCTUATIONS
FRACTALS
HYDRATION
HYDROLYSIS
LIGNIN
MONOMERS
PLANT CELLS
POLYMERS
PRODUCTION
TEMPERATURE DEPENDENCE
THERMODYNAMICS
WATER