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Matthews J.F.,National Renewable Energy Laboratory | Bergenstrahle M.,Cornell University | Bergenstrahle M.,KTH Royal Institute of Technology | Beckham G.T.,National Renewable Energy Laboratory | And 6 more authors.
Journal of Physical Chemistry B

We use molecular simulation to elucidate the structural behavior of small hydrated cellulose Iβ microfibrils heated to 227 °C (500 K) with two carbohydrate force fields. In contrast to the characteristic two-dimensional hydrogen-bonded layer sheets present in the cellulose Iβ crystal structure, we show that at high temperature a three-dimensional hydrogen bond network forms, made possible by hydroxymethyl groups changing conformation from trans-gauche (TG) to gauche-gauche (GG) in every second layer corresponding to "center" chains in cellulose Iβ and from TG to gauche-trans (GT) in the "origin" layer. The presence of a regular three-dimensional hydrogen bond network between neighboring sheets eliminates the possibility of twist, whereas two-dimensional hydrogen bonding allows for microfibril twist to occur. Structural features of this high-temperature phase as determined by molecular simulation may explain several experimental observations for which no detailed structural basis has been offered. This includes an explanation for the observed temperature and crystal size dependence for the extent of hydrogen/deuterium exchange, and diffraction patterns of cellulose at high temperature. © 2011 American Chemical Society. Source

Beckham G.T.,National Renewable Energy Laboratory | Beckham G.T.,Colorado School of Mines | Beckham G.T.,Renewable and Sustainable Energy Institute | Crowley M.F.,National Renewable Energy Laboratory
Journal of Physical Chemistry B

Chitin is the primary structural material of insect and crustacean exoskeletons and fungal and algal cell walls, and as such it is the one of the most abundant biological materials on Earth. Chitin forms linear polymers of β1,4-linked-N-acetyl-d-glucosamine (GlcNAc), and in Nature, enzyme cocktails deconstruct chitin to GlcNAc. The mechanism of chitin deconstruction, like that of cellulose deconstruction, has been under investigation due to its importance in the global carbon cycle and in production of renewable and sustainable products from biological matter. To further understand the nanoscale properties of chitin, here we simulate crystals of α-chitin, which is the most prevalent form in Nature. We find excellent agreement with the recently reported crystal structure and we report the salient features of the simulations related to crystalline stability. We also compute the thermodynamic work required to peel individual chains from α-chitin surfaces, which a chitinase enzyme must conduct to deconstruct chitin. Compared with previous simulations of native plant cellulose Iβ, α-chitin exhibits higher decrystallization work for chains in the middle of surfaces and similar work for chains on the edges of crystals. Unlike cellulose, the free energy profile is dominated by a single bifurcated hydrogen bond between chains formed by the GlcNAc side chains and the O6 atoms on the primary alcohol group. This study highlights the molecular features of chitin that make it such a tough, recalcitrant material, and provides a key thermodynamic parameter in our quantitative understanding of how enzymes contribute to the turnover of carbohydrates in the biosphere. © 2011 American Chemical Society. Source

Tawney L.,Markets and Enterprise Program | Miller M.,Renewable and Sustainable Energy Institute | Bazilian M.,International Institute For Applied Systems Analysis
Climate Policy

The development and transfer of clean energy technologies to achieve universal energy access is challenging due to the inherent complexities of the energy sector, and the energy governance and financial systems in developing economies. Innovation is an essential part of successfully addressing these difficulties. Duplicating the energy infrastructure models of developed countries will not be sufficient to meet the needs of poor consumers. To the extent that innovation can accelerate energy access, it is important to understand the specific types of innovations that are necessary and how they might be facilitated. The general features of existing international clean energy innovation systems, which are predominantly driven by the markets and emissions reduction mechanisms of developed and rapidly growing emerging economies, are reviewed and the alignment of these systems to the innovation processes required to extend energy access globally is evaluated. Drawing on the innovation policy literature, the attributes of effective international and domestic energy innovation systems that are pro-poor and the associated policy approaches are identified. © 2013 Taylor & Francis. Source

Chundawat S.P.S.,Great Lakes Bioenergy Research Center | Chundawat S.P.S.,Michigan State University | Beckham G.T.,National Renewable Energy Laboratory | Beckham G.T.,Colorado School of Mines | And 5 more authors.
Annual Review of Chemical and Biomolecular Engineering

Plants represent a vast, renewable resource and are well suited to provide sustainably for humankind's transportation fuel needs. To produce infrastructure-compatible fuels from biomass, two challenges remain: overcoming plant cell wall recalcitrance to extract sugar and phenolic intermediates, and reduction of oxygenated intermediates to fuel molecules. To compete with fossil-based fuels, two primary routes to deconstruct cell walls are under development, namely biochemical and thermochemical conversion. Here, we focus on overcoming recalcitrance with biochemical conversion, which uses low-severity thermochemical pretreatment followed by enzymatic hydrolysis to produce soluble sugars. Many challenges remain, including understanding how pretreatments affect the physicochemical nature of heterogeneous cell walls; determination of how enzymes deconstruct the cell wall effectively with the aim of designing superior catalysts; and resolution of issues associated with the co-optimization of pretreatment, enzymatic hydrolysis, and fermentation. Here, we highlight some of the scientific challenges and open questions with a particular focus on problems across multiple length scales. © Copyright 2011 by Annual Reviews. All rights reserved. Source

Beckham G.T.,National Renewable Energy Laboratory | Beckham G.T.,Colorado School of Mines | Beckham G.T.,Renewable and Sustainable Energy Institute | Bomble Y.J.,National Renewable Energy Laboratory | And 6 more authors.
Current Opinion in Biotechnology

Understanding the molecular-level mechanisms that enzymes employ to deconstruct plant cell walls is a fundamental scientific challenge with significant ramifications for renewable fuel production from biomass. In nature, bacteria and fungi use enzyme cocktails that include processive and non-processive cellulases and hemicellulases to convert cellulose and hemicellulose to soluble sugars. Catalyzed by an accelerated biofuels R&D portfolio, there is now a wealth of new structural and experimental insights related to cellulases and the structure of plant cell walls. From this background, computational approaches commonly used in other fields are now poised to offer insights complementary to experiments designed to probe mechanisms of plant cell wall deconstruction. Here we outline the current status of computational approaches for a collection of critical problems in cellulose deconstruction. We discuss path sampling methods to measure rates of elementary steps of enzyme action, coarse-grained modeling for understanding macromolecular, cellulosomal complexes, methods to screen for enzyme improvements, and studies of cellulose at the molecular level. Overall, simulation is a complementary tool to understand carbohydrate-active enzymes and plant cell walls, which will enable industrial processes for the production of advanced, renewable fuels. © 2010 Elsevier Ltd. Source

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