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Nanotechnology & Environmental Heterogeneous Catalysis
Type: Inorganic & Materials Chemistry
Professor: Bert Chandler, Ph.D.
You probably know that a catalyst speeds up a reaction but is not consumed like a reactant is. Heterogeneous catalysts are solid materials that perform chemical reactions – essentially, the molecules stick to the catalyst surface from the liquid or gas phase. The surface then allows them to react via pathways (i.e. mechanisms) that aren’t available in solution (or in the gas phase). Heterogeneous catalysts are by far the most important industrial catalysts (petroleum refining, emissions control, fine chemicals production). They are also key components to many developing technologies, such as solar energy conversion and fuel cells. This makes catalysis one of the most important technologies in industrial chemistry, and means that future catalytic chemistries will be important parts of solutions to our most urgent societal and environmental needs for decades to come.
The Chandler group studies the art and science of supported nanoparticle catalysts, which are one of the most common classes of heterogeneous catalysts. These materials typically consist of a high surface area oxide (the support) that has metal nanoparticles (NPs) spread across the surface. The NPs are typically 1- 10 nm in diameter, or roughly 100 to 100,000 atoms. We are currently focused on Au catalysts, especially understanding reaction mechanisms over Au particles and learning to tune the unique chemistry of Au by incorporating other metals.
Some of the art comes in learning to prepare metal NPs in solution. We try to control how metal atoms assemble in solution so that we can control the structure and properties of the catalyst. In the picture above, we would like to control the number and types of atoms (pink vs. gray balls) on the surface of the metal particle. These particles can then be deposited onto a metal oxide support and the stabilizing molecules (which are added to control the synthesis) can be removed.
For the science, we are interested in studying what factors influence the reactivity of metal nanoparticles, how we can control them, and how we can use that knowledge to develop new reactions. We spend a lot of time trying to understand reaction mechanisms on catalysts and developing tools for using kinetics (especially biochemical kinetic tools) to probe catalyst properties. Mechanistic studies require kinetics studies , so there are always projects for students who are interested in learning about how molecules react and how we figure that out. We investigate many different types of reactions, including hydrogenations and oxidations, and are especially interested in the role that water can play as a co-catalyst. It turns out that, just like in organic chemistry, in heterogeneous catalysis, proton transfers can play important roles in reaction mechanisms – we are currently working to better understand th
Biochemistry & Bioinorganic Chemistry
Type: Organic Chemistry
Professor: Christina Cooley, Ph.D.
Research in the Cooley lab spans the interface of chemistry and biology. I believe strongly in the power of synthetic organic chemistry to access new approaches to solve problems. Students in my lab will have the opportunity to design and synthesize new molecules and assess their ability to detect and treat human disease under the following two major project areas.
The first project describes a new strategy to amplify molecular signals as a way to detect biomolecular interactions and potentially, disease. We have developed fluorogenic monomers that are not fluorescent in monomer form, but glow when incorporated into a polymer by atom transfer radical polymerization (ATRP, see figure). The fluorescence is quantifiable by fluorescence readers or visible to the naked eye. We are designing new monomers to improve their water solubility, optimizing our fluorogenic polymerization for detection applications, and working on the direct detection of proteins and biomolecuar interactions. Students in this sub-group synthesize molecules, run polymerization reactions, and analyze the polymers formed by NMR and other polymer and fluorescence analysis techniques.
The second project is generally in the field of drug delivery and prodrug synthesis and evaluation. A prodrug is a “caged” version of a drug that is inactive until release to the free drug is achieved under specific biological conditions. We are developing prodrugs for AA 147, a molecule that activates a stress-responsive signaling pathway that could be particularly helpful for treatment after reperfusion injury, where blood flow is lost and then restored, such as occurs during heart attacks and strokes. We are synthesizing prodrug versions of AA 147 that are selectively uncaged by the presence of reactive oxygen species (ROS), which occur at high levels during reperfusion events. We are also exploring other types of releasable AA 147 prodrugs to improve pharmacodynamics properties for in vivo animal studies. Students on this project design and synthesize prodrug conjugates, examine their stability and release kinetics to free drug in the presence of ROS such as hydrogen peroxide, and work with collaborators to evaluate their biological potential for disease treatment.
Biochemistry & Bioinorganic Chemistry
Type: Organic Chemistry
Professor: Joseph B. Lambert, Ph.D.
Amber is the fossilized end product of resinous materials exuded by plants millions of years ago (Figure 1). It is found on every continent except Antarctica. There are at least five chemically distinct types of amber, depending on the botanical material from which the original exudate came from. Nuclear magnetic resonance (NMR) spectroscopy can distinguish these different botanical sources and provide a means of determining authenticity of amber and learning about its geographical sources.
More generally, exudates are complex mixtures of organic compounds produced by plants, usually as the result of injury or disease. Secreted as liquids, exudates may harden to solids in hours to months (Figure 2) on the surface of the plant. These materials have found numerous practical applications throughout human history, and they provide a molecular window to the classification of plants (taxonomy). We have found that exudates are remarkably robust and consistent in their molecular constitution within a single plant and from plant to plant within a given species. There are several, distinct chemical constitutions of exudates. Resins, which can form amber through fossilization, are composed of terpenoid compounds. Gums are made of polysaccharides. Gum resins like frankincense and myrrh contain both materials. Kinos contain phenols. Although these four chemical groups are the largest, there are several other smaller but distinct chemical groups.
We are carrying out a worldwide survey of plant exudates from all plant families, and of amber, necessitating field acquisition of materials and analysis by NMR in the lab. We also are examining the effect of heat on the molecular structure of amber and its slightly younger colleague, copal. Heat has been used to alter the properties of amber prior to carving. Spectroscopic examination of artificially heated samples may clarify how structure change with heating.
Bioinorganic Chemistry; Computational Chemistry; X-ray Spectroscopy
Type: Inorganic Chemistry
Professor: Jason Scherer, Ph.D.
Research in the Shearer Group is broadly centered on understanding how the electronic structure of biologically and industrially relevant transition metal species contribute to their reactivity and physical properties. Central to our work is the synergistic use of synthetic, spectroscopic and computational chemistry. Although we perform some work with naturally occurring biological systems or industrial catalysts, we primarily study synthetic mimics of these systems to probe a specific aspect of their chemistry. Briefly outlined below are two projects currently being undertaken by the Shearer Group.
Probing Nickel Containing Superoxide Dismutase. Nickel containing superoxide dismutase (NiSOD) catalyzes the conversion of highly toxic superoxide (O2 – ) into dioxygen and hydrogen peroxide by making use of a NiII/NiIII redox couple. In the reduced NiII oxidation state the nickel-site is contained in a distorted square planar NiN2S2 coordination environment with ligands derived from Cys2, Cys6, the Nterminal amine nitrogen and an amidate nitrogen from Cys2. An unusual feature of the NiSOD active site that we have been probing is the fact that one of the coordinated Cys sulfur ligands is protonated, forming a Ni-S(H+)-Cys moiety. A number of roles for this moiety can be envisioned; our hypothesis is that protonation of the Cys sulfur ligand poises the nickel site for reactivity. We postulate that protonation raises the energy of orbitals that are predominantly nickel in character allowing for electron transfer from NiII to O2 – , thus generating O2 2– (peroxide) and NiIII. To test this hypothesis, we are preparing a number of metallopeptide based mimics of NiSOD along with small transition metal complexes that can support reversible Ni-S(H+)-Cys formation. By spectroscopically examining the influence of sulfur protonation in such mimics, we seek to understand the role(s) of the NiS(H+)-Cys moiety in NiSOD reactivity, and Ni-S-R containing compounds in general.
Metalloprotein Redesign. The repurposing of proteins and enzymes by organisms is a key evolutionary mechanism; through random changes to existing biological scaffolds an organism can generate new proteins with new functions. Biological chemists apply this strategy to the redesign of proteins with new and novel functions wherein a large library of random mutants is generated, screened, and refined over multiple generations. One can also apply a rational redesign strategy, wherein knowledge concerning protein folding and structure is applied towards creating specific protein scaffolds with desirable functions. We are currently redesigning small metalloproteins that are synthetically accessible. Use of synthetic methods allows us to screen proteins in a reasonably rapid manner. Also, we can incorporate unnatural amino-acids into the protein scaffold, which can impart unique attributes to the resulting system. For example, initial calculations suggest we can alter a zinc finger protein, which contains a structural zinc center, into a bluecopper like protein, which transfers electrons. To ligate Cu within this scaffold unnatural and d-amino acids need to be incorporated into the protein sequence. Substitution of Cu with Ni is predicted to generate a metalloenzyme that can perform organometallic transformations under biologically relevant conditions.
Bio-Organic and Supramolecular Chemistry
The chemistry of pharmaceuticals and medical diagnostics requires the ability to find a specific protein in a complex mixture, such as blood, and stick to it. Pharmaceuticals block the normal function of that protein. Medical diagnostics measure the quantity of that protein. The Urbach group develops new approaches to the “recognition” of specific proteins that are predictable from their sequences of amino acids, which are often known, and we develop applications of this science. Students are involved in experimental design and implementation, problem solving, data analysis, presentation, and publication.
Students in the Urbach research group learn a range of techniques, which can include organic synthesis to make peptides and other small molecules, polymer/material synthesis, protein semisynthesis, protein expression and purification, NMR spectroscopy, mass spectrometry, X-ray crystallography, microcalorimetry, stopped-flow spectroscopy, gel electrophoresis, UV-visible, fluorescence, and circular dichroism spectroscopy. This combination of methods and approaches offers students a breadth of technique and depth of study that is an excellent foundation for further study in organic chemistry, biophysical chemistry, medicinal chemistry, biochemistry, bioengineering, and biotechnology.
Current projects are focused in several areas: 1) Continuing to improve our ability to recognize proteins and proteins on the basis of their amino acid sequences. Our discoveries have established new rules for predictive protein recognition (Figure below), and we are currently working to expand the range of proteins that are accessible by our compounds, to target proteins in complex mixtures, and to increase the strength and selectivity of interaction. 2) Developing synthetic receptors with novel properties. 3) Developing technology for quality control of protein drug formulations. 4) Developing new approaches to protein drug formulation enabling long time-scale controlled release. Some of these applications are certainly biomedical, but please keep in mind that the work itself is almost entirely physical and organic chemistry. Dr. Urbach is always interested in discussing new ideas with students.