Queen’s University chemistry professor Cathleen Crudden admits that neither she nor her Department of Chemistry colleague Hugh Horton had any commercial applications in mind when they began their work into the reaction of carbon-based ligands called carbenes with metal surfaces. Regardless, they found a brand new way of establishing such monolayers, which has opened up the prospect of just such applications for their technology.“We were really naive when we went into this,” Crudden says. “We didn’t go at this as a problem to be solved. It was a really basic chemistry idea that we extrapolated from the molecular literature into the materials literature.”
Crudden credits that idea to a lecture by Université Laval surface chemist Peter McBreen, who was an invited speaker at Queen’s campus several years ago. McBreen was one of the first to generate reactive carbene species on metal surfaces, and Crudden and Horton wanted to see if they could generate surfac e chemistry Haruko Hirukawa stable ones. What they did not realize was how well these would surpass sulphur-based molecules, which have been used for decades in a variety of applications, including in many medical diagnostic instruments.
Organics that can bond effectively with metallic surfaces could shield those surfaces from corrosion and other reactions. Photo credit: Haruko Hirukawa
The ligands in this bond break down under relatively modest changes in environment, which limits the possibilities of marrying thin films of organic receptors with metal components that could be integrated into electronic systems. “These systems need to be carefully handled and there is a limited range of applications because the film can be destroyed by exposure to air, harsh chemicals, or even not-so-harsh chemicals,” says Crudden.
With a more secure bond, however, a much wider range of potential applications should be possible. “Metals have unique properties — they’re conducting, they have a variety of electronic states,” she says. “You can do certain types of sensing with them, such as surface plasmon resonance or electrochemical measurements. Organic compounds are typically insulating, but they provide the unique opportunity to interface metals with the world we live in, the bio world, since it is organic — composed of amino acids, peptides, proteins, antibodies, and viruses.”
Crudden wondered why no one had investigated the possibility of using other ligands to create the interface, so she and Horton set about investigating the alternatives. They eventually turned to carbenes to create a gold-carbon bond, which succeeded beyond all expectations. “They survived everything: boiling acid, boiling base, boiling organic solvent, boiling water, long term water, even hydrogen peroxide,” she recalls. “We had great fun with it.”
The results, published in Nature Chemistry, have attracted the attention of commercial manufacturers who are already dusting off ideas for metallic-organic interfaces. The list includes friction-reducing monolayers that would serve as lubricants, reducing wear on components and energy use, as well as airtight skins that could protect metals from corrosion. “It would be like putting a nanometre-thick coating of olive oil on your surface, only it won’t come off,” Crudden says.