The Lockett Group uses a multidisciplinary approach, combining aspects of analytical chemistry, materials science, biochemistry, molecular biology, and biomedical engineering to develop new analytical tools and in vitro assays to predict and quantify molecular interactions occurring in a cell or within a community of cells.
We are particularly interested in developing new technologies to: i) fabricate arrays of biomolecules in which we could screen drug metabolism in a high-throughput manner; ii) study the response of enzymes and cells to environmental stresses in tissue-like constructs that mimic in vivo conditions. We focus keenly on analytical tools that are amenable to high-throughput screening, are easily assembled or setup, and provide quantitative data.
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.
One of thousands applicants, Adrienne Snyder, a graduate student in the Brustad Group, was selected as one of six national winner of a Thermo Scientific Pierce Scholarship. She was selected based on her essay about Engineered Transaminases. Congratulations, Adrienne!
The phenomenon of ion pairing in aqueous solutions is of widespread importance in chemistry and physics, and charge transfer between the ions is fundamental to understanding the behavior of aqueous ionic solutions. At the same time, it is of significant challenge to describe the charge transfer behavior using popular density functional theory, DFT, calculations in practice because of approximated exchange-correlation effects of electrons.
In work published as a Frontiers Article and also as the cover article in Chemical Physics Letter, the group of Professor Yosuke Kanai shows how advanced quantum Monte Carlo, QMC, calculation is used to accurately quantify the charge transfer behavior in the NaCl dimer. Accurate electron density is obtained from the so-called reptation Monte Carlo approach, and influence of fermion nodes of the many-body wavefunction on the charge transfer behavior was discussed in detail. It is anticipated that the QMC approach will be of great importance for investigating a wide range of the charge transfer phenomena for which present-day DFT calculations are not reliable.
Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structure/property relationships has been very challenging.
Through an international collaboration, members of the You Group discovered that a single parameter, hole mobility, determines the fill factor of bulk heterojunction photovoltaic devices in a series of copolymers with varying amount of fluorine substitution. The continuous increase of hole mobility upon further fluorination is related to a preferential face-on orientation and improved pi-pi stacking of the polymer backbones. The results shows the potential of properly-designed polymers to enable high fill factors in thick devices, as required by mass production technologies. These significant results appeared in JACS, and were also featured in JACS Spotlights.
Over the past decade, thermoplastics have been used as alternative substrates to glass and Si for microfluidic devices because of the diverse and robust fabrication protocols available for thermoplastics that can generate high production rates of the desired structures at low cost and with high replication fidelity, the extensive array of physiochemical properties they possess, and the simple surface activation strategies that can be employed to tune their surface chemistry appropriate for the intended application. While the advantages of polymer microfluidics are currently being realized, the evolution of thermoplastic-based nanofluidic devices is fraught with challenges. One challenge is assembly of the device, which consists of sealing a cover plate to the patterned fluidic substrate.
Typically, channel collapse or substrate dissolution occurs during assembly, making the device inoperable resulting in low process yield rates. Now, in an article published in Lab on a Chip as a "Hot Article," researchers in the Soper Group report a low temperature hybrid assembly approach for the generation of functional thermoplastic nanofluidic devices with high process yield rates, >90%, and with a short total assembly time of only sixteen minutes. The functionality of the assembled devices was demonstrated by studying the stretching and translocation dynamics of dsDNA in the enclosed thermoplastic nanofluidic channels.
As described in Chemical Science, members of the Dempsey Group, in collaboration with the Meyer Group, used a layer-by-layer procedure to prepare chromophore–catalyst assemblies consisting of phosphonate-derivatized porphyrin chromophores and a phosphonate-derivatized ruthenium water oxidation catalyst on the surfaces of tin oxide and titanium dioxide mesoporous, nanoparticle films. In the procedure, initial surface binding of the phosphonate-derivatized porphyrin is followed in sequence by reaction with a zirconium salt and then with the phosphonate-derivatized water oxidation catalyst.
Fluorescence from both the free base and zinc porphyrin derivatives on tin oxide is quenched; substantial emission quenching of the zinc porphyrin occurs on titanium dioxide. Transient absorption difference spectra provide direct evidence for appearance of the porphyrin radical cation on tin oxide via excited-state electron injection. For the chromophore–catalyst assembly on tin oxide, transient absorption difference spectra demonstrate rapid intra-assembly electron transfer oxidation of the catalyst following excitation and injection by the porphyrin chromophore.
Chemists have long sought new ways to create energy-rich fuels - ideally via reactions powered by a renewable resource such as the sun. But scientists still have a lot to learn about solar-powered reactions, and a new study by Thomas Eisenhart and Jillian Dempsey sheds light on how they occur. The proton-coupled electron transfer reaction, PCET, is a key light-driven step in the conversion of small molecules into energy-rich fuels. Although prior research has provided a basic understanding of PCET reactions between molecules in their ground states, much less is known about the reactions between electronically excited molecules.
In the article, which made the cover of JACS, and was also featured in JACS Spotlights, the team reports results from a mechanistic study of excited-state PCET reactions between two small molecules, acridine orange and tri-tert-butylphenol. The step-by-step process by which the reaction occurs has not been determined previously, but since each of the reaction components has a unique spectroscopic signature, the researchers can monitor each step with transient absorption spectroscopy. The results help explain the intimate coupling of light absorption with both proton and electron transfer, which the authors say will help pave the way for new avenues in solar fuel production.
Christine Herman, Ph.D., JACS
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."