Computer simulation studies of microcrystalline cellulose Iβ

James F. Matthews, Cathy E. Skopec, Philip E. Mason, Pierfrancesco Zuccato, Robert W. Torget, Junji Sugiyama, Michael E. Himmel, John W. Brady

Research output: Contribution to journalArticlepeer-review

355 Scopus Citations

Abstract

Molecular mechanics (MM) simulations have been used to model two small crystals of cellulose Iβ surrounded by water. These small crystals contained six different extended surfaces: (1 1 0), (11̄0), two types of (1 0 0), and two types of (0 1 0). Significant changes took place in the crystal structures. In both crystals there was an expansion of the unit cell, and a change in the γ angle to almost orthogonal. Both microcrystals developed a right-hand twist of about 1.5° per cellobiose unit, similar to the twisting of β-sheets in proteins. In addition, in every other layer, made up of the unit cell center chains, a tilt of the sugar rings of 14.8° developed relative to the crystal plane as a result of a transition of the primary alcohol groups in these layers away from the starting TG conformation to GG. In this conformation, these groups made interlayer hydrogen bonds to the origin chains above and below. No change in the primary alcohol conformations or hydrogen-bonding patterns in the origin chain layers was observed. Strong localization of the adjacent water was found for molecules in the first hydration layer of the surfaces, due to both hydrogen bonding to the hydroxyl groups of the sugar molecules and also due to hydrophobic hydration of the extensive regions of nonpolar surface resulting from the axial aliphatic hydrogen atoms of the 'tops' of the glucose monomers. Significant structuring of the water was found to extend far out into the solution. It is hypothesized that the structured layers of water might present a barrier to the approach of cellulase enzymes toward the cellulose surfaces in enzyme-catalyzed hydrolysis, and might inhibit the escape of soluble products, contributing to the slow rates of hydrolysis observed experimentally. Since the water structuring is different for the different surfaces, this might result in slower hydrolysis rates for some surfaces compared to others.

Original languageAmerican English
Pages (from-to)138-152
Number of pages15
JournalCarbohydrate Research
Volume341
Issue number1
DOIs
StatePublished - 2006

NREL Publication Number

  • NREL/JA-510-39648

Keywords

  • Cellulose fiber twist
  • Cellulose Iβ
  • Molecular dynamics
  • Molecular mechanics
  • Water structuring

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