Ions Stick the Landing
Discovery helps charged particles stay put on a surface
Results: For both gymnasts and peptides, a perfect landing after tumbling through the air can be a challenge. Peptides now have some help, thanks to scientists at the Pacific Northwest National Laboratory. At PNNL, scientists have discovered a new way to make peptides, small protein molecules, stick when they softly land on a surface.
Why does it matter? This is fundamental research on using mass spectrometry as a separation technique for preparing novel materials and exploring reactivity at interfaces. Softly landing molecules on a specially tailored self-assembled monolayer surface provides a convenient and flexible platform for tailoring properties and opens the door for preparing extremely pure, uniform layers of specific molecules on surfaces. Creating films of molecules strongly bound to surfaces could lead to better sensors, more efficient industrial processes and new materials.
Method: For this new method, researchers began by selecting the peptide containing the Arg-Gly-Asp (RGD) sequence. This motif is used in tests to recognize cancer cells and is known to stimulate cells ability to adhere to surfaces.
Next, the researchers introduced the peptides into the Soft Landing Apparatus, built by PNNL post-doc Omar Hadjar at the Environmental Molecular Sciences Laboratory, a national scientific user facility located at PNNL in Richland, Washington. Inside this device, a quadrupole mass spectrometer filters out the desired species from a sample that contains many other molecules. "Mass spectrometry allows us to deliver very pure material to the surface. More traditional purification methods can be tedious, and aren't always possible," said PNNL principal investigator Julia Laskin.
Once separated, the apparatus gently pushes the beam of peptides toward the surface. "We want a soft landing," said Laskin. "Not a crash landing."
The Soft Landing Apparatus allows researchers to manipulate the ion beam and pattern the molecules on the surface. At the time of the collision with the surface, the peptides react with the chemical groups on the surface and form strong electron-sharing bonds, called covalent bonds.
The next challenge was to characterize the surface to understand what happened to the molecules after the collision. "This is a big challenge to currently available techniques because of the very small amount of material present on the surface,"" said Peng Wang, a post-doc researcher working at PNNL.
The scientists succeeded in covering 60% of the desired surface with the peptides strongly bound to the substrate, which is comparable to traditional methods based on solution-phase chemistry with similar reaction times. "We achieved this percentage coverage because of local heating that occurs during the landing," said Laskin. "This promoted the otherwise slow chemical reactions at interfaces."
Next steps: The team is looking to use this method to induce reactions that cannot be carried out in solution. The team is interested in creating surfaces studded with peptides and other molecules that cannot be prepared using the traditional methods.
Acknowledgments: The research team on this project was Peng Wang, Omar Hadjar, and Julia Laskin of PNNL. In EMSL, staff members Paul Gassman and Zihua Zhu also contributed.
The research was funded by a grant from the Chemical Sciences Division, Office of Basic Energy Sciences of the U.S. Department of Energy and by the Pacific Northwest National Laboratory Directed Research and Development Program.
This work was performed on research equipment in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility located at PNNL in Richland, Washington.
Citation: Wang, P, Hadjar, O, and Laskin, J. 2007. "Covalent Immobilization of Peptides on Self-Assembled Monolayer Surfaces Using Soft-Landing of Mass-Selected Ions." Journal of the American Chemical Society 129 (28), 8682-8683, 2007.