This is progress on the cellulose
front and quite important. As described,
cellulose is tightly bound together and this hugely slows biological attack on
the cellulose. It is shown that
pretreatment protocols can loosen this up and more importantly points in the
proper direction for further work.
A five times improvement is
touted here but that is likely still a pretty lousy yield in terms of
industrial efficiency. It is still
serious progress.
Without question, conveniently converting
plant waste which is mostly cellulose and lignums into a fuel stock is an
attractive trick for agriculture. In
fact we presently have two potential options for plant waste besides the
wasteful application of burning. This
option is the best long term application because it will provide useful fuels
to the farm itself and allow a high level of self sufficiency. The second option is to convert plant waste into
biochar which even if it takes twenty years will go to a limit point in which
the soil is sufficiently improved as to become unnecessary.
In the meantime we are
approaching a world of cheap electrical energy and all this will become
unnecessary unfortunately.
JULY 20, 2011
Los Alamos has found a potential key for unlocking the energy
potential from non-edible biomass materials such as corn leaves and stalks, or
switch grass. A potential pretreatment method that can make plant
cellulose five times more digestible by enzymes that convert it into ethanol, a
useful biofuel.
Conversion of lignocellulose to biofuels is partly inefficient due to
the deleterious impact of cellulose crystallinity on enzymatic
saccharification. We demonstrate how the synergistic activity of cellulases was
enhanced by altering the hydrogen bond network within crystalline cellulose
fibrils. We provide a molecular-scale explanation of these phenomena through
molecular dynamics (MD) simulations and enzymatic assays. Ammonia
transformed the naturally occurring crystalline allomorph Iβ to IIII, which led
to a decrease in the number of cellulose intrasheet hydrogen bonds and an
increase in the number of intersheet hydrogen bonds. This rearrangement of the
hydrogen bond network within cellulose IIII, which increased the number of
solvent-exposed glucan chain hydrogen bonds with water by 50%, was accompanied
by enhanced saccharification rates by up to 5-fold (closest to amorphous
cellulose) and 60–70% lower maximum surface-bound cellulase capacity. The
enhancement in apparent cellulase activity was attributed to the
“amorphous-like” nature of the cellulose IIII fibril surface that facilitated
easier glucan chain extraction. Unrestricted substrate accessibility to
active-site clefts of certain endocellulase families further accelerated
deconstruction of cellulose IIII. Structural and dynamical features of
cellulose IIII, revealed by MD simulations, gave additional insights into the
role of cellulose crystal structure on fibril surface hydration that influences
interfacial enzyme binding. Subtle alterations within the cellulose hydrogen
bond network provide an attractive way to enhance its deconstruction and offer
unique insight into the nature of cellulose recalcitrance. This approach can
lead to unconventional pathways for development of novel pretreatments and engineered
cellulases for cost-effective biofuels production
.
Researchers find potential key for unlocking biomass energy
LANL molecular model helps expose cellulose weakness
LOS ALAMOS, New Mexico, July 20, 2011—Researchers at the U.S.
Department of Energy’s Los Alamos National Laboratory and Great Lakes Bioenergy
Research Center have found a potential key for unlocking the energy potential
from non-edible biomass materials such as corn leaves and stalks, or switch
grass.
In a paper appearing in today’s Journal of the American Chemical
Society, Los Alamos researchers S. Gnanakaran, Giovanni Bellesia, and Paul
Langan join Shishir Chundawat and Bruce Dale of Michigan State University, and
collaborators from the Great Lakes Bioenergy Research Center in describing a
potential pretreatment method that can make plant cellulose five times more
digestible by enzymes that convert it into ethanol, a useful biofuel.
Biomass is a desirable renewable energy source because fermentable
sugars within the cellulose network of plant cells can be extracted with
enzymes and then converted into ethanol—if only it were so simple. One of the
key difficulties in creating biofuels from plant matter is that the cellulose
tends to orient itself into a sheet-like network of highly ordered, densely
packed molecules. These sheets stack upon themselves and bond together very
tightly due to interactions between hydrogen atoms—somewhat like sheets of
chicken wire stacked together and secured by loops of bailing wire. This
stacking and bonding arrangement prevents enzymes from directly attacking most
of the individual cellulose molecules and isolating the sugar chains within
them.
Currently, ethanol can only be extracted in usable quantities if the
biomass is pretreated with costly, potentially toxic chemicals in an
energy-intensive process. Now, however, the research team has discovered a way
to develop potentially cost-effective pretreatment methods that could make
biomass an economically viable contender in the biofuels arena.
Using recent experimental data provided by their journal collaborators,
Gnanakaran and his Los Alamos colleagues used
state-of-the-art computational methods and molecular modeling to examine how
cellulose changes structurally into an intermediate form that can be
enzymatically attacked when pretreated with ammonia.
“Our modeling showed, and the experimental evidence confirmed, that the
pretreatment reduced the strength of hydrogen bonds in the cellulosic network,”
said Gnanakaran. It was as if the bailing wire in the bound chicken-wire
analogy had been removed and replaced more loosely with thread. This, in turn,
significantly reduced the tightness of the cellulose network and left it more
vulnerable to conversion into sugar by fungi-derived cellulolytic enzymes.
The end result is a potentially less costly and less energy intensive
pretreatment regimen that makes the cellulose five times easier to attack.
“This work helps address some of the potential cost barriers related to
using biomass for biofuels,” Gnanakaran said.
In addition to LANL, the GLBRC, and Michigan
State University ,
the paper included collaborators from American
University and the U.S. Department of Agriculture’s Forest Products
Laboratory in Madison , Wisconsin
The LANL work is funded in part by the Laboratory-Directed Research and
Development Program. Computing resources used in the research are housed at Los Alamos and provided under LANL institutional
computing.
Los Alamos National Laboratory, a multidisciplinary research
institution engaged in strategic science on behalf of national security, is
operated by Los Alamos National Security, LLC, a team composed of Bechtel
National, the University of California, The Babcock & Wilcox Company, and
URS for the Department of Energy’s National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and
reliability of the U.S. nuclear stockpile, developing technologies to reduce
threats from weapons of mass destruction, and solving problems related to
energy, environment, infrastructure, health, and global security concerns.
The Great Lakes Bioenergy Research Center (GLBRC) is one of three
Department of Energy Bioenergy Research Centers funded to make transformational
breakthroughs that will form the foundation of new cellulosic biofuels
technology. The GLBRC is led by the University of Wisconsin-Madison, with Michigan State University
LANL news media contact: James E. Rickman, (505) 665-9203, jamesr@lanl.gov
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