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BiographyMichael Baldwin is an inorganic chemist with research interests in catalysis, spectroscopy, bioinorganic chemistry, and oxygen activation. He received a BS degree in chemistry from Seattle University in 1986, and a PhD in chemistry from Stanford University in 1992 for work with Edward Solomon on spectroscopic studies of copper-peroxide complexes modeling the oxygen transport protein oxyhemocyanin and the enzyme oxytyrosinase. As a NIH postdoctoral fellow with Professor Vincent Pecoraro at the University of Michigan, he worked on models of the photosynthetic oxygen evolving complex. In 1997, he joined the faculty at the University of Cincinnati.
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ResearchResearch in the Baldwin group is aimed at developing useful new applications that are inspired by bioinorganic chemistry. However, since strictly biomimetic chemistry is seldom able to improve on millions of years of evolution, we incorporate components that are not found in the biological system. Thus, by broadening the scope of metals or functional groups used beyond those found in the biological systems, we can hope to optimize the chemistry of interest in an application-specific manner that is different than what has evolved in nature. Two examples of our bio-inspired projects are described briefly below.
Agents for tight binding and light-triggered release of iron
One of our projects is inspired by the recently discovered marine siderophores, which are biomolecules synthesized by marine bacteria to sequester the sparse iron in seawater that is critical to the growth and survival of the bacteria. Once the iron is tightly bound as Fe(III) and delivered into the bacteria, these siderophores undergo a photochemical reaction to release the iron. Upon photolysis, an alpha-hydroxy acid functional group that coordinates to the iron is cleaved, generally by decarboxylation, and the iron is reduced to Fe(II) and released to the proteins in the bacterium. Synthetic agents inspired by these photoactive siderophores will be useful in a number of applications, including pharmaceutical, site-specific delivery of a flux of metal ions to activate metal-dependent chemotherapy agents, oxidation-state specific iron sensors, light activated coatings and others. We are developing "minimalist" versions of these siderophores and exploring the effect of changing the auxiliary chelating groups to modulate the relative binding constants for Fe(III) vs. Fe(II), the optimum wavelengths for photolysis, and other properties upon which successful applications of these iron storage/transport and light-triggered release agents depend.
Ni(II)-organic redox hybrids as catalysts for aerobic substrate oxidations
Use of oxygen as the terminal oxidant in substrate oxidation reactions is critical in biology, and environmentally preferable to use of metal-based stoichiometric oxidants in commercial oxidation chemistry. While these oxidations are often thermodynamically favorable, they are generally kinetically challenged. Thus, in both biological and anthropogenic applications, transition metal catalysts are needed to facilitate the reactions. Catalysis of aerobic substrate oxidations is a classic example of "green chemistry". While nature generally uses iron or copper metalloenzymes for this chemistry, successful commercializations of biomimetic catalysts have been few and far between. We have taken a different approach?using Ni(II), a metal oxidation state that generally does not react with oxygen. By combining Ni(II) with poly(oximate) chelate ligands, like TRISOX in the figure below, we find that we get a catalyst in which both the ligand and the metal participate intimately in the redox chemistry. This catalyst facilitates the aerobic oxidation of primary alcohols (including the relatively inert methanol) as well as amines to the aldehyde or imine, respectively. We are using a combination of several spectroscopic and spectroelectrochemical techniques to explore an observable Ni-iminoxyl radical intermediate and synthetic ligand modifications to optimize the reactivity.
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