The research results are being presented by Carnegie Mellon graduate student Anindya Ghosh on Wed., Sept. 10, in New York City at the 226th annual meeting of the American Chemical Society (paper 179, "A stable µ-oxo Fe(IV) dimer: Reaction of Fe(III)-TAML® activators with oxygen," Industrial and Engineering Chemistry Division).
These latest findings have the potential to extend tremendously the use of Fe-TAML activators to remediate environmental problems and to modify industrial processes to make them more efficient and productive.
"This chemistry is, to our knowledge, unprecedented in the scientific literature," said Terry Collins, the Thomas Lord Professor of Chemistry at Carnegie Mellon and the chief scientist on Fe-TAML investigations. "Oxygen is a natural, safe, cheap and abundant resource, so the fact that this oxidant works so well in our experiments with Fe-TAMLs is quite exciting."
Specifically, the new Fe-TAML activator works with oxygen to oxidize organic and inorganic chemicals.
Oxygen is essential for carrying out several different life processes including ones in which specific enzymes modify biologically relevant chemicals via a reaction called oxidative catalysis. Fe-TAML activators (TAML stands for tetra-amido macrocyclic ligand) are made from elements found in nature. Synthetic compounds, Fe-TAML activators function like enzymes when combined with oxygen.
To date, research with Fe-TAML activators and another oxidant, hydrogen peroxide, has yielded promising results for decontaminating a variety of dangerous environmental pollutants. Using oxygen rather than hydrogen peroxide could expand the known uses of Fe-TAMLs, according to Collins. Moreover, oxygen could eventually replace hydrogen peroxide, a compound that is more expensive and less abundant than oxygen, said Collins.
While nature is quite successful at using oxygen to catalyze many critical chemical processes associated with life, chemists have found it difficult to replicate these feats, said Collins. Existing synthetic catalysts that are designed to interact with oxygen fail to combine effectively with this molecule, and they cannot function well under mild conditions (room temperature and a neutral pH).
By inducing a reaction between oxygen and a Fe-TAML activator whose iron atom was in the specific chemical state of Fe (III), the state of iron found naturally in rust, the Collins team synthesized a Fe(IV),Fe(IV)-µ-oxo dimer with TAML ligands. This type of reaction is unprecedented--scientists have never before been able to induce a reaction of synthetic Fe(III) compounds with oxygen. Another characteristic that makes this enzyme-like active species unique is that it is generated under ambient conditions such as room temperature and pressure.
In introductory catalysis studies, the Carnegie Mellon chemists have found that in the presence of oxygen, this new Fe(IV),Fe(IV)-µ-oxo dimer catalyzes several elementary oxidation reactions.
For example, benzylic alcohols, which are alcohols commonly used in industrial processes, are oxidized to their corresponding aldehydes, which are themselves highly reactive and useful chemical compounds. The new Fe-TAML activator is efficient; thus far tens of equivalents of the benzylic alcohols have been converted using one equivalent of the Fe(IV),Fe(IV)-µ-oxo dimer.
Fe-TAML activators originated at Carnegie Mellon's Institute for Green Oxidation Chemistry under the leadership of Collins, who is a strong proponent of green chemistry to create environmentally friendly, sustainable technologies. Fe-TAML activators show enormous potential to provide clean, safe alternatives to existing industrial practices. They also provide ways to remediate other pressing problems that currently lack solutions.
As part of this September's American Chemical Society meeting symposium, "Green Chemistry: Multidisciplinary Science and Engineering Applied to Global Environmental Issues," the Collins group will present results of Fe-TAML activators' effectiveness in killing a simulant of a deadly biological warfare agent, cleaning wastewater from textile manufacturing, reducing fuel pollutants, treating pulp and paper processing byproducts and detoxifying pesticides.