On the Molecular Origins of Biomass Recalcitrance: The Interaction Network and Solvation Structures of Cellulose Microfibrils

Abstract

Biomass recalcitrance is a fundamental bottleneck to producing fuels from renewable sources. To understand its molecular origin, we characterize the interaction network and solvation structures of cellulose microfibrils via all-atom molecular dynamics simulations. The network is divided into three components: intrachain, interchain, and intersheet interactions. Analysis of their spatial dependence and interaction energetics indicate that intersheet interactions are the most robust and strongest component and do not display a noticeable dependence on solvent exposure. Conversely, the strength of surface-exposed intrachain and interchain hydrogen bonds is significantly reduced. Comparing the interaction networks of I(β) and I(α) cellulose also shows that the number of intersheet interactions is a clear descriptor that distinguishes the two allomorphs and is consistent with the observation that I(β) is the more stable form. These results highlight the dominant role of the often-overlooked intersheet interactions in giving rise to biomass recalcitrance. We also analyze the solvation structures around the surfaces of microfibrils and show that the structural and chemical features at cellulose surfaces constrict water molecules into specific density profiles and pair correlation functions. Calculations of water density and compressibility in the hydration shell show noticeable but not drastic differences. Therefore, specific solvation structures are more prominent signatures of different surfaces.

Unique Aspects of the Structure and Dynamics of Elementary Iβ Cellulose Microfibrils Revealed by Computational Simulations

“…One alternative is to use computational approaches, with numerous studies published in which molecular dynamics (MD) simulations have been performed on cellulose microfibrils, generally with a 36-chain model (Mazeau, 2005;Matthews et al, 2006Matthews et al, , 2011aMatthews et al, , 2011bMatthews et al, , 2012Bergenstråhle et al, 2007;Gross and Chu, 2010;Zhang et al, 2011;Chen et al, 2014). These simulations have investigated the structure and dynamics of the microfibrils, temperature dependence, H-bonding patterns, and effect of solvent water, and compared different carbohydrate force fields.…”

Direct Dissolution of Cellulose: Background, Means and Applications

“…It is obvious that hydrogen bonding is not the only relevant factor in the quest for a suitable solvent, yet the amphiphilic nature of cellulose is still widely overlooked. The last few years, a few eye-opening papers have taken this matter up to discussion [32][33][34][35][36][37]. A relatively new approach when trying to understand molecular interactions is computer simulations and modeling.…”

“…A relatively new approach when trying to understand molecular interactions is computer simulations and modeling. Some very recently published papers describe this method, showing molecular origins of the recalcitrance of biomass in the terms of decrystallization and dissolution, and showing quantitatively the need for taking cellulose amphiphilicity into account [36][37][38]. For comparison it may be useful to study cyclodextrins.…”

Probing cellulose amphiphilicity

“…Therefore, in order to efficiently dissolve cellulose, a good solvent needs also to overcome these inter-sheet hydrophobic interactions (Cho et al 2011;Medronho et al 2012;Bergenstråhle et al 2008;Gross, Chu 2010;Lindman et al 2010). This paper is divided into two parts; in the first section we discuss recent evidences in literature supporting cellulose amphiphilicity and the concomitant role of hydrophobic interactions while in the second part we discuss some examples from our own recent research supporting the role of hydrophobic interactions in dissolution and regeneration of cellulose.…”