The Miller Group designs multifunctional catalysts for the sustainable synthesis of fuels and chemicals. One class of catalyst features a strongly donating pincer core in which one donor is also part of a crown ether macrocycle. The macrocycle acts as a cation receptor site, capable of switching on catalyst activity and tuning catalyst selectivity in a variety of organic transformations.
Another class of catalyst are designed to absorb visible light in order to enhance reactivity. Visible light-promoted hydride transfer reactions relevant to solar energy storage in chemical fuels, including photoelectrochemical hydrogen evolution, have been realized using this strategy.
Mechanistic understanding drives research in the group forward, facilitating progress on challenging reactions and helping define new ligand-assisted mechanistic pathways for such transformations.
Research in the Nicewicz Group focuses on developing new catalysts and methods for organic synthesis. In particular, our group seeks to harness the power of photoinduced electron transfer processes to drive the development of new asymmetric bond forming reactions. Additionally, we seek to apply these new reactions to the synthesis of biologically-active, complex natural products.
Typically, diesel fuel is made from crude oil, but scientists can make high-grade diesel from coal, natural gas, plants or even agricultural waste, using a process called Fischer-Tropsch, or FT. Just about any carbon source is an option. FT Diesel is the ideal liquid transportation fuel for automobiles, trucks and jets. It's much cleaner burning than conventional diesel, and much more energy efficient than gasoline. But, FT Diesel is expensive to make and generates lots of waste.
With support from the National Science Foundation, NSF, and its Center for Enabling New Technologies Through Catalysis, CENTC, chemists from around the United States, including professor Maurice Brookhart from Carolina, are working together to improve the cost and energy efficiency of alternative fuels. CENTC scientists have invented and patented, and are bringing toward commercialization, catalysts that will convert light hydrocarbons into FT Diesel, improving the process, whether it's diesel made from traditional sources, such as oil, or alternative sources, such as biomass.
NSF: Miles O'Brien, Science Nation Correspondent; Ann Kellan, Science Nation Producer
The Energy Frontier Research Center for Solar Fuels (EFRC) at the University of North Carolina at Chapel Hill, led by led by Thomas J. Meyer, Arey Professor of Chemistry, received $10.8 million from the U.S. Department of Energy, Office of Basic Energy Sciences, to advance emerging solar energy technologies and to turn these technologies into devices that can efficiently produce fuels.
“We are delighted with the news of continued support by the Department of Energy for our leading edge research on a new approach to solar energy conversion and storage,” said Meyer. “Continued funding will allow us to move ahead in this important area with the twin goals of mastering the basic science behind the dye sensitized photoelectrosynthesis cell and applying it to water splitting into hydrogen fuel and oxygen and in reducing carbon dioxide to useful carbon fuels.”
Scientists in the Cahoon and Papanikolas groups, as published in the Journal of Physical Chemistry C, have studied ultrafast carrier dynamics in silicon nanowires with average diameters of 40, 50, 60, and 100 nm using transient absorption spectroscopy. After 388 nm photoexcitation near the direct band gap of silicon, broadband spectra from 400 to 800 nm were collected between 200 fs and 1.3 ns. The transient spectra exhibited both absorptive and bleach features that evolved on multiple time scales, reflecting contributions from carrier thermalization and recombination as well as transient shifts of the ground-state absorption spectrum. The initially formed “hot” carriers relaxed to the band edge within the first 300 fs, followed by recombination over several hundreds of picoseconds.
The charge carrier lifetime progressively decreased with decreasing diameter, a result consistent with a surface-mediated recombination process. Recombination dynamics were quantitatively modeled using the diameter distribution measured from each sample, and this analysis yielded a consistent surface recombination velocity of 2 × 104 cm/s across all samples. The results indicate that transient absorption spectroscopy, which interrogates thousands of individual nanostructures simultaneously, can be an accurate probe of material parameters in inhomogeneous semiconductor samples when geometrical differences within the ensemble are properly analyzed.
Primary patient samples are the gold standard for molecular investigations of tumor biology yet are difficult to acquire, heterogeneous in nature and variable in size. Patient-derived xenografts, PDXs, comprised of primary tumor tissue cultured in host organisms such as nude mice permit the propagation of human tumor samples in an in vivo environment and closely mimic the phenotype and gene expression profile of the primary tumor. Although PDX models reduce the cost and complexity of acquiring sample tissue and permit repeated sampling of the primary tumor, these samples are typically contaminated by immune, blood, and vascular tissues from the host organism while also being limited in size.
For very small tissue samples, on the order of 103 cells, purification by fluorescence-activated cell sorting, FACS, is not feasible while magnetic activated cell sorting, MACS, of small samples results in very low purity, low yield, and poor viability. Researchers in the Allbritton Group have now developed a platform for imaging cytometry integrated with micropallet array technology to perform automated cell sorting on very small samples obtained from PDX models of pancreatic and colorectal cancer using antibody staining of EpCAM, CD326, as a selection criteria. Published in Cytometry Part A, the data collected demonstrate the ability to automate and efficiently separate samples with very low number of cells.
Macromolecular crowding effects arise from steric repulsions and weak, nonspecific, chemical interactions. Steric repulsions stabilize globular proteins, but the effect of chemical interactions depends on their nature. Repulsive interactions such as those between similarly charged species should reinforce the effect of steric repulsions, increasing the equilibrium thermodynamic stability of a test protein. Attractive chemical interactions, on the other hand, counteract the effect of hard-core repulsions, decreasing stability.
Mohona Sarkar and Joe Lu, researchers in the Pielak Group, tested these ideas, published in Biochemistry, by using the anionic proteins from Escherichia coli as crowding agents and assessing the stability of the anionic test protein chymotrypsin inhibitor 2 at pH 7.0. The anionic protein crowders destabilize the test protein despite the similarity of their net charges. Thus, weak, nonspecific, attractive interactions between proteins can overcome the charge–charge repulsion and counterbalance the stabilizing effect of steric repulsion.
The synthesis of prodrugs is a common approach to overcome drug delivery issues, including poor aqueous solubility or permeability, and to provide site-specific release. Nanotechnology can be a powerful tool to improve drug delivery, but does so by altering the biodistribution of the encapsulated small molecule. In a report published in NanoLetters, researchers in the DeSimone Group, in collaboration with a number of Centers, Institutes, and Departments here at UNC, combined the merits of both approaches to improve the pharmacokinetics and toxicity of the chemotherapeutic docetaxel by passively targeting an encapsulated docetaxel prodrug to solid tumors, where it could selectively release and convert to active docetaxel.
The Group used PRINT technology, Particle Replication in Nonwetting Templates, to prepare nanoparticles to passively target solid tumors in an A549 subcutaneous xenograft model. An acid labile prodrug was delivered to minimize systemic free docetaxel concentrations and improve tolerability without compromising efficacy.
At the Department of Chemistry, we feel strongly that diversity is crucial to our pursuit of academic excellence, and we are deeply committed to creating a diverse and inclusive community. We support UNC's policy, which states that "the University of North Carolina at Chapel Hill is committed to equality of opportunity and pledges that it will not practice or permit discrimination in employment on the basis of race, color, gender, national origin, age, religion, creed, disability, veteran's status, sexual orientation, gender identity or gender expression."