Peptides as Catalysts to Dissolve Rare Earth Metals

by Carol Stanier published: 2010-11-29

Danish scientists use bacteria to find the best catalyst.

The majority of chemical reactions that take place in biology are catalyzed to ensure that they are energy-efficient and selective. The catalysts of these reactions are most often proteins, of which there can be many different possible combinations. While catalysts can be made by synthetic chemists, this involves a lot of work and often the resulting catalysts are not as good as those found in nature. So, scientists are looking at ways of allowing nature to help with chemical and engineering problems. Areas of interest include directing shape and size of crystals and surface functionalization; both processes at which nature excels.

In a recent paper Stanley Brown and Signe Mathiasen from University of Copenhagen, Denmark, developed a method based on genetic selection that enabled them to search many possible catalysts using bacteria. They chose a simple dissociation reaction to study; release of the rare earth cation, Ho3+, from solid Ho2O3 or HoPO4. They added the holmium compounds to a library of bacteria with different peptides on their surfaces. Because holmium oxide is paramagnetic it was easy to recover bacteria that stuck to it well via the surface peptides. They then used a biotechnological technique to grow more of the desired peptides from bacteriophages and selected from the resulting peptides for the best catalyst.

Because the bacteria need phosphate to grow, peptides that released phosphate and holmium cations from the solids resulted in more prolific bacteria. This meant that the best peptide catalysts were near bacteria that grew well.

The best catalyst released thousands of holmium cations in less than one hour. The researchers believe that the peptides act by mimicking the Ho3+ cation and sticking to the surface of the oxide or phosphate while individual Ho3+ ions are released.

The researchers also successfully tested their method to look for
proteins that dissociate aggregates of carbon nanotubes without sonication
and suggest that this method may also be more generally applicable. They believe that their new methodology could be useful for patterned etching of surfaces for nanocomponents. They speculate that it should be possible to produce a solvating peptide lithography mask that would self-assemble and position features with resolution of a few nanometers; more accurate than the complex and painstaking manual positioning that would be needed to achieve this by current means. It is possible that bacteria may be used to produce future computer components.

S. Brown and S. Mathiasen, Adv. Mater. ; DOI: 10.1002/adma.201002130