On this page:
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 the role of protons in heterogeneous catalysis and are using our findings to think about new reactions.
Chemical Synthesis, Bioinorganic Chemistry and Polymer Chemistry
Professor: Christina Cooley, Ph.D.
Research in the Cooley lab applies the power of synthetic organic chemistry to solve problems in biology and human health. 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.
Our primary research area is in the development of new methods 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 synthesized by various methods, for example by atom transfer radical polymerization (ATRP). Polymer fluorescence is quantifiable by fluorescence readers or visible to the naked eye, and tracks with the concentration of polymerization initiator, which serves a model analyte.
This fluorogenic polymerization subgroup has many current research directions ranging from fundamental organic synthesis and polymerization studies to detection applications. Current projects are aimed toward the synthesis of new monomers to improve physical properties such as water solubility, development and evaluation of alternative light-initiated fluorogenic polymerization platforms, optimization of the fluorogenic polymerization approaches for analyte detection, and application to the direct detection of proteins and biomolecular interactions. Students working in this area will apply a range of organic, polymer and biochemical techniques, from the chemical synthesis of small molecules and free-radical polymerization techniques initiated by various methods from metal catalysts to irradiation with visible light, to analysis and characterization of the polymers formed by gel permeation chromatography, nuclear magnetic resonance spectroscopy, and fluorescence analysis methods.
The Cooley lab has a second subgroup in the general field of therapeutic drug delivery, utilizing the sensing of reactive oxygen species (ROS) for prodrug activation and therapeutic release in diseased tissues. 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 have synthesized and evaluated prodrugs of AA 147, which activates a stress-responsive signaling pathway as a therapeutic target for treatment following reperfusion events such as heart attacks and strokes. These prodrugs of AA 147 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, and the synthesis of fluorogenic ROS sensors for collaborative chemical applications. Students in this area will gain experience with small-molecule synthesis and characterization, and analyze their therapeutic release profile under biological conditions.
Professor: Joseph B. Lambert, Ph.D.
Amber is the fossilized end product of resinous materials exuded by plants millions of years ago. 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 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.
Photochemistry in Complex Aqueous Environments
Type: Inorganic Chemistry
Professor: Jason Scherer, Ph.D.
The Sun is the largest source of energy to the planet, and it controls, directly or indirectly, the vast majority of physical, chemical, and biological processes that take place on Earth. Photochemical processing of material drives the engine of atmospheric and environmental chemistry in planetary environments, largely through the formation and subsequent reactions of radical species. The reactivity of these radicals is controlled and mediated by the surrounding environmental conditions under which they were generated. Photochemically-generated organic radicals are particularly interesting because they offer an abiotic pathway to make larger, more complex organic molecules, which has applications to atmospheric chemistry, prebiotic chemistry, and astrobiology. This research is grounded in fundamental physical chemistry but is inherently interdisciplinary, drawing on organic chemistry, environmental chemistry, biophysics, and planetary science.
The Rapf lab examines the direct aqueous photochemistry of organic molecules under conditions relevant to planetary environments, including the modern and ancient Earth as well as other potentially habitable worlds. We conduct detailed photochemical experiments that allow us to examine, mechanistically, changes in reactivity that occur as a function of reaction conditions, including photon flux, atmospheric composition, and solution conditions (e.g. pH and salinity). Using model chemical systems, we can systematically increase the complexity of model systems to investigate the origins of emergent behavior.
In tandem with photochemical studies, we also explore how intermolecular interactions mediate chemistry, both through orientation and concentration at interfaces and through the formation of supramolecular assemblies. This is motivated by the repeated observations that in many cases the chemistry of single species in a bulk environment cannot be used to predict the reactivity of those species either in confined environments or in concert with other molecules. Of particular interest are recent literature reports that molecules at aqueous interfaces can undergo photochemistry that is not seen in the bulk. We explore how photochemistry is mediated by surface films composed of insoluble surfactants, such as long-tailed fatty acids like stearic and palmitic acid, using photochemical-initiator species, such as pyruvic acid.
Students will conduct photochemical experiments, which are analyzed using a combination of mass spectrometry, optical spectroscopy, and surface tension measurements. Students will also have opportunities for instrument development, as we build surface sensitive spectroscopic techniques to probe interfacial photochemistry directly.
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.
1. 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 N-terminal 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 O22– (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 Ni-S(H+)-Cys moiety in NiSOD reactivity, and Ni-S-R containing compounds in general.
2. Understanding Transition Metal Ligand Bonds Through the Lens of Valence Bond Theory. In modern chemical physics quantum mechanical descriptions of chemical bonding are described through three main models: molecular orbital, density functional, and valence bond (VB) theory. All of these approaches have distinct benefits and disadvantages. VB theory has the advantage of placing bonding in terms that chemists understand (covalent vs ionic bonding), and thus yields intuitive descriptions of bonding. However, it has only been in the past decade that VB theory methods have advanced to the point where larger systems of chemical interest can be tackled at a sufficiently high level of theory to yield accurate solutions. We have taken advantage of these recent advances in VB theory to explore the bonding, energetics, and reactivity of transition metal complexes involved in organometallic transformations. For example, we have recently investigated reductive elimination from [CuR4]– complexes (R = alkyl) and discovered a number of “hidden” features concerning the chemistry of such species. For example, one surprising aspect of such reactions is that they are not reductive eliminations in any physically meaningful sense of the word; instead they can be viewed as admixtures of radical C-C couplings and simple Lewis acid/base reactions.
Supramolecular Chemistry; Biosensing; Diagnostics; Drug Formulation
The chemistry of pharmaceuticals and medical diagnostics is designed to recognize a specific protein in a complex mixture, such as blood, and to stick to that protein. Pharmaceuticals block the normal function of that protein. Medical diagnostics measure the quantity of that protein. The Urbach lab develops new chemistry for the recognition of specific proteins, and we use this chemistry to solve important biomedical problems. 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, bioconjugates, hydrogels, and modified proteins; NMR spectroscopy; mass spectrometry; microcalorimetry; fluorescence spectroscopy; circular dichroism spectroscopy; and X-ray crystallography. 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 include: 1) Developing new chemistry to recognize proteins and proteins on the basis of their amino acid sequences. Our discoveries have established new rules for predictive protein recognition, and we are currently working to expand the range of proteins that are accessible by our compounds, and to increase the strength and selectivity of interaction. 2) Synthesizing new protein receptors with new properties. 3) Developing technology for the quality control of protein drug formulations. 4) Developing a new strategy for protein drug formulation that enables controlled time release. Dr. Urbach is always interested in discussing new ideas with students. These projects are funded by grants from the National Institutes of Health and the Welch Foundation.