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May 2013

Catalyst Design Inspired by Nature

Researchers draw inspiration from nature to “beat the leaf”

Tyler Josephson & Ralph L. House

Scheme I: Schematic representation of the glucose to fructose isomerization reaction.

Effective catalysts are critical for developing efficient and clean chemical processes in industry. Numerous experimental and computational techniques are used to design better catalysts, but in many cases, we were beaten long ago by nature, which has been refining catalysts for life-sustaining reactions for billions of years. Many of the reactions that occur in a leaf are more efficient than those in our best chemical plants! Rather than starting from scratch, researchers at Department of Energy-sponsored Energy Frontier Research Centers have been looking to biological systems for inspiration as they press the boundaries of the state-of-the-art technology.

Using Nature’s Legacy for Solar Hydrogen: For billions of years, plants have converted the energy in sunlight into chemical energy via photosynthesis. Mimicking photosynthesis in an artificial process is the mission of the Center for Bio-Inspired Solar Fuel Production (BISFuel). A team of researchers led by Giovanna Ghirlanda at Arizona State University developed a new protein-based catalyst for producing hydrogen fuel from water and sunlight. This new catalyst is an artificial enzyme designed using insight from natural enzymes found in hydrogen-producing bacteria. Many of these bacteria have enzymes with a complex that contains two iron atoms as the active site for the reaction. The researchers synthesized an artificial amino acid (amino acids are the building blocks of proteins) that coordinates a similar active site. Then, they incorporated this amino acid into a test protein and demonstrated its performance as a catalyst for hydrogen production. The technique they used would allow them to incorporate this active site into any peptide sequence, opening the door to huge opportunities for designing proteins that optimize this reaction, and incorporating this reaction in a more complex reaction network.

Mimicking Nature’s Enzymes to Rearrange Sugar Molecules: Artificial photosynthesis is far from the only example where scientists are drawing inspiration from nature. For example, scientists can harness plant’s “biomass” by transforming it into useful products, such as chemicals, polymers and fuels. An important step for this to occur is the isomerization of sugars, particularly the isomerization of glucose to fructose, because fructose is closer in structure to many desirable renewable products. Isomers are molecules that share the same atoms but are structurally different (see Scheme I showing the isomerization of glucose to fructose). This reaction is traditionally carried out using an enzyme such as D-xylose isomerase XI that has metal atoms embedded in the protein structure. Although enzymes such as these are routinely used in industrial processes, they are limited to specific reaction conditions, are costly and have limited lifetimes.

Ideally, a similar catalytic architecture would emulate the mechanistic properties of these enzymes, but operate under more favorable conditions, such as low pH and high temperature with a high ionic strength, conditions where many enzymes break down. In the Proceedings of the National Academy of Sciences, a group from the Catalysis Center for Energy Innovation in collaboration with the Institute for Atom-Efficient Chemical Transformations described a system that fit this description perfectly. The group, led by Mark Davis, found that silica zeolites containing small amounts of titanium ions or tin ions (Ti4+ or Sn4+) mimicked the reaction pathway that the enzyme xylose isomerase XI uses, and could convert up to 45 weight percent aqueous solutions of glucose into fructose. This discovery is opening doors to new industrial processes that can utilize biomass as a feedstock for renewable chemicals and fuels.

Acknowledgments

The work by BISFuel is supported by the Center for Bio-Inspired Solar Fuel Production, an Energy Frontier Research Center funded by the Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences.

The work at Caltech and the University of Delaware was financially supported as part of the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the DOE, Office of Science, Office of Basic Energy Sciences. M Moliner acknowledges the Fundación Ramón Areces Postdoctoral Research Fellowship Program and the “Subprograma Ramon y Cajal” for financial support. R Bermejo-Deval acknowledges the Obra Social “la Caixa” for a graduate fellowship. A Palsdottir acknowledges the Caltech Summer Undergraduate Research Fellowship program (SURF) for financial support. The computational studies for this work were supported by DOE, and this material is based upon work supported as part of the Institute for Atom-efficient Chemical Transformations, an Energy Frontier Research Center funded by the DOE, Office of Science, Office of Basic Energy Sciences. The authors gratefully acknowledge grants of computer time from the Argonne National Laboratory Computing Resource Center and the Center for Nanoscale Materials. This research used resources of the National Energy Research Scientific Computing Center.

More Information

Roy A, C Madden, and G Ghirlanda. 2012. “Photo-induced Hydrogen Production in a Helical Peptide Incorporating a [FeFe] Hydrogenase Active Site Mimic.” Chemical Communications 48(79):9816-9818. DOI: 10.1039/c2cc34470j

Bermejo-Deval R, RS Assary, E Nikolla, M Moliner, Y Román-Leshkov, SJ Hwang, A Palsdottir, D Silverman, RF Lobo, LA Curtiss, and ME David. 2012. “Metalloenzyme-like Catalyzed Isomerizations of Sugars by Lewis Acid Zeolites.” Proceedings of the National Academy of Sciences 109(25):9727-9732. DOI: 10.1073/pnas.1206708109

About the author(s):

  • Tyler Josephson is a Ph.D. candidate at the University of Delaware and is a student in the Catalysis Center for Energy Innovation. He is advised by Dion Vlachos. He is using computational tools to fundamentally understand solvent effects in reactions used to produce fuels and chemicals from biomass. Tyler holds a B.S. in Chemical Engineering from the University of Minnesota.

  • Ralph L. House. A member of the Center for Solar Fuels (UNC-EFRC) Ralph is a Research Associate specializing in the use of multiple spectroscopic techniques to analyze the steps leading to the generation of solar fuels. Ralph is also helping lead the construction of an electrochemical bioreactor and is the UNC-EFRC Liaison for External Outreach and Collaboration.

Natural Structures Inspire Catalyst Designs

Small proteins and metal ions are key to new structures, insights

Many of the reactions that occur in a leaf are more efficient than those in our best chemical plants. Rather than start from scratch, scientists are looking to biological systems for inspiration as they press the boundaries of catalytic technologies.

In plants, bacteria and other living things, complex molecules known as enzymes increase the speed of life-sustaining reactions, such as photosynthesis. Synthetic catalysts are rarely as efficient, but adding natural features could improve their performance. Scientists at the Center for Bio-Inspired Solar Fuel Production combined an iron-based active site with an unusual amino acid inside a corkscrew-shaped protein, mimicking the behavior of enzymes involved in photosynthesis. When supplied with electrons from a sunlight-absorbing donor, the catalyst converts hydrogen ions into hydrogen fuel. The team’s technique could be used to create similar catalytic structures. At the Catalysis Center for Energy Innovation and the Institute for Atom-Efficient Chemical Transformations, scientists built a more durable catalyst, inspired by enzymes in plants, to rearrange sugar molecules for sustainable energy. The catalyst is a pure silica zeolite with a few titanium or tin ions added. The catalyst is effective and works at higher temperatures and acidic conditions than the enzyme catalyst. These studies answer fundamental questions needed to create catalysts for a sustainable energy future.

More Information

Roy A, C Madden, and G Ghirlanda. 2012. “Photo-induced Hydrogen Production in a Helical Peptide Incorporating a [FeFe] Hydrogenase Active Site Mimic.” Chemical Communications 48(79):9816-9818. DOI: 10.1039/c2cc34470j

Bermejo-Deval R, RS Assary, E Nikolla, M Moliner, Y Román-Leshkov, SJ Hwang, A Palsdottir, D Silverman, RF Lobo, LA Curtiss, and ME David. 2012. “Metalloenzyme-like Catalyzed Isomerizations of Sugars by Lewis Acid Zeolites.” Proceedings of the National Academy of Sciences 109(25):9727-9732. DOI: 10.1073/pnas.1206708109

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.