A basic -- and slightly acidic -- solution for hydrogen storage

 Sometimes, solutions for hard problems can turn out to be pretty basic. That's especially true for a team of researchers at the Office of Science's Brookhaven National Laboratory (Brookhaven Lab), where the solution for a hard problem they were working on turned out to be pretty basic…and also a bit acidic.

The hard problem they were working on was how to store hydrogen fuel. Hydrogen gas (H2) is a clean and powerful fuel, but it's also extremely light, which makes it difficult and costly to store. It's typically held in high pressure tanks, although researchers at another Office of Science lab recently found a possible way to keep it in naturally-formed frozen cages.

In a paper published March 18th in Nature Chemistry, researchers at Brookhaven Lab led by chemist Etsuko Fujita announced that they had found a safe and reversible way to store hydrogen under mild (and therefore hopefully much more economical) conditions, using a newly developed catalyst.

Their work began by seeing acids and bases in an unconventional way -- as potential carriers of hydrogen fuel. Students often learn about acids and bases as part of their science fair projects. The 'volcanic' reaction of vinegar (a mild acid) and baking soda (a mild base) has given many students an early interest in the sciences. That was true for Jonathan Hull, a lead researcher on the paper, who was intrigued by seeing a similar reaction blow the corks off wine bottles.

However, many acids and bases are actually watery solutions filled with hydrogen. In an acidic solution, the hydrogen atoms wander free. They're usually missing their electron too, which gives them a positive charge (atoms and molecules with either a positive or a negative charge are called ions). In a basic solution, the hydrogen atoms are usually connected with something else, a negative ion of some sort. And yes, when an acid and a base react with each other, they typically create something neutral, like water.

The catalyst created by researchers at Brookhaven Lab connects hydrogen gas and carbon dioxide, "storing" the hydrogen linked to (adduct to) carbon dioxide in a mildly basic solution. The reaction can be reversed -- and the hydrogen fuel released -- by adding a bit of acid. The entire process can be run, and easily reversed, in a watery solution under mild temperatures and pressures with no toxic byproducts, and at a faster rate than any previous catalyst.

As a consequence, Brookhaven Lab's new catalyst might be used in future hydrogen fuel vehicles, though additional testing will be needed to see if it can be economically scaled up to industrial production. It may show up in other high powered systems too -- time and technology will tell.

This new catalyst shows the best of the Office of Science and its labs at work: Researchers taking on truly challenging problems, and finding basic (and sometimes slightly acidic) solutions.

Story Source:

The above story is reprinted from materials provided by DOE/US Department of Energy. The original article was written by Charles Rousseaux.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Jonathan F. Hull, Yuichiro Himeda, Wan-Hui Wang, Brian Hashiguchi, Roy Periana, David J. Szalda, James T. Muckerman, Etsuko Fujita. Reversible hydrogen storage using CO2 and a proton-switchable iridium catalyst in aqueous media under mild temperatures and pressures. Nature Chemistry, 2012; DOI: 10.1038/nchem.1295

Protein adaptation shows that life on early earth lived in a hot, acidic environment

A new study reveals that a group of ancient enzymes adapted to substantial changes in ocean temperature and acidity during the last four billion years, providing evidence that life on Early Earth evolved from a much hotter, more acidic environment to the cooler, less acidic global environment that exists today.

The study found that a group of ancient enzymes known as thioredoxin were chemically stable at temperatures up to 32 degrees Celsius (58 degrees Fahrenheit) higher than their modern counterparts. The enzymes, which were several billion years old, also showed increased activity at lower pH levels -- which correspond to greater acidity.

"This study shows that a group of ubiquitous proteins operated in a hot, acidic environment during early life, which supports the view that the environment progressively cooled and became more alkaline between four billion and 500 million years ago," said Eric Gaucher, an associate professor in the School of Biology at the Georgia Institute of Technology.

The study, which was published April 3 in the advance online edition of the journal Nature Structural & Molecular Biology, was conducted by an international team of researchers from Georgia Tech, Columbia University and the Universidad de Granada in Spain.

Major funding for this study was provided by two grants from the National Aeronautics and Space Administration to Georgia Tech, a grant from the National Institutes of Health to Columbia University, and a grant from the Spanish Ministry of Science and Innovation to the Universidad de Granada.

Using a technique called ancestral sequence reconstruction, Gaucher and Georgia Tech biology graduate student Zi-Ming Zhao reconstructed seven ancient thioredoxin enzymes from the three domains of life -- archaea, bacteria and eukaryote -- that date back between one and four billion years old.

To resurrect these enzymes, which are found in nearly all known modern organisms and are essential for life in mammals, the researchers first constructed a family tree of the more than 200 thioredoxin sequences available from the three domains of life. Then they reconstructed the sequences of the ancestral thioredoxin enzymes using statistical methods based on maximum likelihood. Finally, they synthesized the genes that encoded these sequences, expressed the ancient proteins in the cells of modern Escherichia coli bacteria and then purified the proteins.

"By resurrecting proteins, we are able to gather valuable information about the adaptation of extinct forms of life to climatic, ecological and physiological alterations that cannot be uncovered through fossil record examinations," said Gaucher.

The reconstructed enzymes from the Precambrian period -- which ended about 542 million years ago -- were used to examine how environmental conditions, including pH and temperature, affected the evolution of the enzymes and their chemical mechanisms.

"Given the ancient origin of the reconstructed thioredoxin enzymes, with some of them predating the buildup of atmospheric oxygen, we thought their catalytic chemistry would be simple, but we found that thioredoxin enzymes use a complex mixture of chemical mechanisms that increases their efficiency over the simpler compounds that were available in early geochemistry," said Julio Fernández, a professor in the Department of Biological Sciences professor at Columbia University.

Fernández led a team that included Columbia University postdoctoral researchers Raul Perez-Jimenez, Jorge Alegre-Cebollada and Sergi Garcia-Manyes, and graduate student Pallav Kosuri in using an assay based on single molecule force spectroscopy to measure the activity level of the thioredoxin enzymes under different pH levels.

For their experiments, the researchers used an atomic force microscope to pick up and stretch an engineered protein in a solution containing thioredoxin. They first applied a constant force to the protein, causing it to rapidly unfold and expose its disulfide bonds to the thioredoxin enzymes. The rate at which a thioredoxin enzyme snipped the disulfide bonds determined the enzyme's level of efficiency.

The study results showed that the three oldest thioredoxin enzymes -- those thought to have inhabited Earth 4.2 to 3.5 billion years ago -- were able to operate in lower pH environments than the modern thioredoxin enzymes.

"Our analysis indicates that ancient thioredoxin enzymes were well adapted to function under acidic conditions and that they maintained their high level of activity as they evolved in more alkaline environments," said Fernández.

To measure the temperature range in which the enzymes operated, professor Jose Sanchez-Ruiz and graduate student Alvaro Inglés-Prieto from the Departamento de Química-Física at the Universidad de Granada in Spain used a technique called differential scanning calorimetry. This method measures the stability of enzymes by heating the enzymes at a constant rate and measuring the heat change associated with their unfolding.

The researchers found that the ancient proteins were stable at temperatures up to 32 degrees Celsius higher than the modern thioredoxins. The experiments showed that the enzymes exhibited higher temperature stability the older they were. The results provide evidence that ancestral thioredoxins adapted to the cooling trend of ancient oceans, as inferred from geological records.

"Our results confirm that life has the remarkable ability to adapt to a wide range of historical environmental conditions; and by extension, life will undoubtedly adapt to future environmental changes, albeit at some cost to many species," said Gaucher.

This study also showed that the experimental resurrection of ancient proteins together with the sensitivity of single-molecule techniques can be a powerful tool for understanding the origin and evolution of life on Earth.

The researchers are currently using this strategy to assess other enzymes to get a clearer picture of what life was like on Early Earth. They are also applying these tools to the field of biotechnology, where enzymes play important roles in many industrial processes.

"The functions and characteristics we observed in the ancestral enzymes show that our techniques can be implemented to generate improved enzymes for a wide range of applications," added Perez-Jimenez.

Provided by Georgia Institute of Technology (news : web)