New Hope For Biomass Fuels: Breaking The Ties That Bind

Los Alamos National Laboratory researchers have discovered a potential chink in the armor of fibers that make the cell walls of certain inedible plant materials so tough. The insight ultimately could lead to a cost-effective and energy-efficient strategy for turning biomass into alternative fuels.

In separate papers published in Biophysical Journal and recently in an issue of Biomacromolecules, Los Alamos researchers identify potential weaknesses among sheets of cellulose molecules comprising lignocellulosic biomass, the inedible fibrous material derived from plant cell walls. The material is a potentially abundant source of sugar that can be used to brew batches of methanol or butanol, which show potential as biofuels.

Cellulose is biosynthesized in plant cells when molecules of glucose—a simple sugar—join into long chains through a process called polymerization. The plant then assembles these chains of cellulose into sheets. The sheets are held together by hydrogen bonds—an electrostatic attraction of a positive portion of a molecule to a negative portion of the same or neighboring molecule. Finally, the sheets stack atop one another, sticking to themselves by other types of attractions that are weaker than hydrogen bonds. The plant then spins these sheets into high-tensile-strength fibers of material.

Not only are the fibers incredibly strong, but they are incredibly resistant to the action of enzymes called cellulases that can crack the fibers back into their simple-sugar components. The ability to economically and easily break cellulose into sugars is desirable because the sugars can be used to create fuel alternatives. However, due to the tenacity of cellulose fibers, the United States currently lacks an energy-efficient and cost-effective method for turning inedible biomass such as switch grass or corn husks into a sweet source of biofuels.

Working with researchers from the U.S. Department of Agriculture and the Centre de Recherches sur les Macromolécules Végétales in France, Los Alamos researcher Paul Langan used neutrons to probe the crystalline structure of highly crystalline cellulose, much like an X-ray is used to probe the hidden structures of the body. Langan and his colleagues found that although cellulose generally has a well-ordered network of hydrogen bonds holding it together, the material also displays significant amounts of disorder, creating a different type of hydrogen bond network at certain surfaces. These differences make the molecule potentially vulnerable to an attack by cellulase enzymes.

Moreover, in this month’s Biophysical Journal, Los Alamos researchers Tongye Shen and Gnana Gnanakaran describe a new lattice-based model of crystalline cellulose. The model predicts how hydrogen bonds in cellulose can shift to remain stable under a wide range of temperatures. This plasticity allows the material to swap different types of hydrogen bonds but also constrains the molecules so that they must form bonds in the weaker configuration described by Langan and his colleagues. Most important, Shen and Gnanakaran’s model identifies hydrogen bonds that can be manipulated via temperature differences to potentially make the material more susceptible to attack by enzymes that can crack the fibers into sugars for biofuel production.

“We have been able to identify a chink in the armor of a very tough and worthy adversary—the cellulose fiber,” said Gnanakaran, who leads the theoretical portion of a large, multidisciplinary biofuels project at Los Alamos.

“These results are some of the first to come from this team, and eventually could point us toward an economical and viable process for making biofuels from cellulosic biomass,” adds Langan, director of the biofuels project.

Funding for the project comes from Laboratory-Directed Research and Development (LDRD), which is the premier source of internally directed research-and-development funding at Los Alamos National Laboratory. The LDRD program invests in high-risk, potentially high-payoff projects at the discretion of the Laboratory Director. Strategic investments of the LDRD program help position Los Alamos to anticipate and prepare for emerging national security challenges.

Age of Energy

We are living in the Age of Energy. The fossil fuel based economy of the present must give way to the renewable energy based economy of the future. Getting there is the grandest challenge humanity faces. Chemistry can help meet this challenge by discovering new materials that efficiently harvest solar radiation, store energy for later use, and reconvert the stored energy when needed.

The Clean Energy project uses computational chemistry and the willingness of people to help look for the best molecules possible for: organic photovoltaics to provide inexpensive solar cells, polymers for the membranes used in fuel cells for electricity generation, and how best to assemble the molecules to make those devices. By helping us search combinatorially among thousands of potential systems, you can contribute to this effort.

Flight Of The Bumble Bee Is Based More On Brute Force Than Aerodynamic Efficiency

Brute force rather than aerodynamic efficiency is the key to bumblebee flight, Oxford University scientists have discovered.

See also:

Plants & Animals

Earth & Climate

Reference

In recent years scientists have modelled how insect wings interact with the air around them to generate lift by using computational models that are relatively simple, often simplifying the motion or shape of the wings.

"We decided to go back to the insect itself and use smoke, a wind tunnel and high-speed cameras to observe in detail how real bumblebee wings work in free flight," said Dr Richard Bomphrey of the Department of Zoology, co-author of a report of the research published this month in Experiments in Fluids. ‘We found that bumblebee flight is surprisingly inefficient – aerodynamically-speaking it’s as if the insect is ‘split in half’ as not only do its left and right wings flap independently but the airflow around them never joins up to help it slip through the air more easily.’

Such an extreme aerodynamic separation between left and right sets the bumblebee [Bombus terrestris] apart from most other flying animals.

"Our observations show that, instead of the aerodynamic finesse found in most other insects, bumblebees have a adopted a brute force approach powered by a huge thorax and fuelled by energy-rich nectar," said Dr Bomphrey. "This approach may be due to its particularly wide body shape, or it could have evolved to make bumblebees more manoeuvrable in the air at the cost of a less efficient flying style."

Professor Adrian Thomas of Oxford’s Department of Zoology, co-author of the report, said: "a bumblebee is a tanker-truck, its job is to transport nectar and pollen back to the hive. Efficiency is unlikely to be important for that way of life."

Observing insects in free – as opposed to tethered – flight is a considerable challenge. The Oxford team trained bumblebees to commute from their hive to harvest pollen from cut flowers at one end of a wind tunnel. They then used the wind tunnel to blow streams of smoke passed the flying bees, to reveal vortices in the air, and recorded the results with high-speed cameras taking up to 2000 images per second. From these images the team were able to visualise the airflow over flapping bumblebee wings.

The old myth that "bumblebees shouldn’t be able to fly" was based on calculations using the aerodynamic theory of 1918-19, just 15 years after the Wright brothers made the first powered flight. These early theories suggested that bumblebee wings were too small to create sufficient lift but since then scientists have made huge advances in understanding aerodynamics and how different kinds of airflow can generate lift.

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How does electricity affect the environment?

Of the total energy consumed in America, about 39% is used to generate electricity. Therefore, electricity consumption is an important portion of a consumer's environmental footprint.

All forms of electricity generation have some level of environmental impact. As the chart below shows, most of the electricity in the United States is generated from fossil fuels, such as coal, natural gas, and oil.

Electricity Generation Technologies

Various Energy Resources

Using energy more efficiently through more efficient end-uses or through more efficient generation, such as combined heat and power, reduces the amount of fuel required to produce a unit of energy output and reduces the corresponding emissions of pollutants and greenhouse gases. Electricity from renewable resources such as solar, geothermal, and wind technologies generally does not contribute to climate change or local air pollution since no fuels are combusted in these processes.

Opportunities also exist to reduce your environmental impact in the transportation sector. For more information, visit www.epa.gov/otaq.