Department of Chemistry
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The Redinbo Group

The Redinbo Group

The Redinbo Laboratory uses the tools of structural, molecular and chemical biology to examine a range of dynamic cellular processes central to human health. Current projects include the discovery of new antimicrobials targeted to drug-resistant bacteria, the design of novel proteins engineered to detect and eliminate toxic chemicals, and the development of small-molecule to cell-based methods to improve anticancer chemotherapeutics. In addition, we continue to focus on determining the crystal structures of macromolecular complexes, including those involving human nuclear receptors central to transcriptional regulation, bacterial proteins involved in DNA manipulation and human cell contact, and enzymes central to key cellular processes.

 

The Hicks Group

The Hicks Group

Research in the Hicks Group focuses on development and implementation of mass spectrometric approaches for protein characterization including post-translational modifications, as well as the identification of bioactive peptides/proteins from plants.

 

Valerie Ashby to Duke

Valerie Ashby

We are extending our heartfelt congratulations to Professor and Chair Valerie Ashby, who has been appointed the new Dean of Arts and Sciences at Duke University. As she has unfailingly done here at Carolina, she will most assuredly bring her outstanding leadership and charisma to that school. We are of course disappointed to see her go but are grateful for all that she has done for us here at the Department of Chemistry, and we wish her well in her new endeavor.

 

Hopping Diffusion of Nanoparticles

In a collaborative work, published in Macromolecules, researchers in the Rubinstein Group propose a hopping mechanism for diffusion of large nonsticky nanoparticles subjected to topological constraints in both unentangled and entangled polymer solids, networks and gels, and entangled polymer liquids, melts and solutions. Probe particles with size larger than the mesh size ax of unentangled polymer networks or tube diameter ae of entangled polymer liquids are trapped by the network or entanglement cells. At long time scales, however, these particles can diffuse by overcoming free energy barrier between neighboring confinement cells.

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The terminal particle diffusion coefficient dominated by this hopping diffusion is appreciable for particles with size moderately larger than the network mesh size ax or tube diameter ae. Much larger particles in polymer solids will be permanently trapped by local network cells, whereas they can still move in polymer liquids by waiting for entanglement cells to rearrange on the relaxation time scales of these liquids. Hopping diffusion in entangled polymer liquids and networks has a weaker dependence on particle size than that in unentangled networks as entanglements can slide along chains under polymer deformation. The proposed novel hopping model enables understanding the motion of large nanoparticles in polymeric nanocomposites and the transport of nano drug carriers in complex biological gels such as mucus.

 

Nanowire Solar Cells

Semiconductor nanowires, NWs, often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indices of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small volumes of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely determine the economic viability of NW-based solar cells. Published in Nano Letters, researchers in the Cahoon Group, demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielectric shells

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Scattering and absorption measurements on Si NWs coated with shells of SiNx or SiOx exhibit a broadband enhancement of light absorption by ≈50–200% and light scattering by ≈200–1000%. The increased light–matter interaction leads to a ≈80% increase in short-circuit current density in Si photovoltaic devices under 1 sun illumination. Optical simulations reproduce the experimental results and indicate the dielectric–shell effect to be a general phenomenon for groups IV, II–VI, and III–V semiconductor NWs in both lateral and vertical orientations, providing a simple route to approximately double the efficiency of NW-based solar cells.

 

Aerosol Analysis

Low-temperature plasma ionization, a technique that causes minimal fragmentation during ionization, has been investigated by the Glish Group as an ionization technique for mass spectrometric detection of the compounds in ambient organic aerosols in real time.

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The experiments presented in a paper published in Analytical Chemistry demonstrate that ions are generated from compounds in the aerosol particles. The utility of this technique for detection of both positive and negative ions from the pyrolysate of multiple natural polymers is presented. Ultimately, low-temperature plasma ionization is shown to be a promising ionization technique for detection of compounds in organic aerosols by mass spectrometry.

 

Layer-by-Layer Chromophore–Catalyst

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.

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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.

 

In-Cell Ribosome Structure Resolved

It has been known for decades that the ribosome, the cellular complex that synthesizes proteins, interconverts between "active" and "inactive" conformations. However, the physiological relevance of this widely observed switch remained unclear and unknown.

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Jennifer McGinnis, in the Weeks Lab, led a study, published in PNAS, in which newly developed in-cell SHAPE technologies were used to probe the structure of the ribosome in healthy living cells. In cells, one class of ribosome subunits exists predominantly in the classic "inactive" conformation and disrupting the ability to interconvert between active and inactive conformations compromises protein synthesis. In-cell RNA structure probing thus resolved this 40 year old challenge to reveal that the inactive state regulates ribosome function as a conformational switch.

 

 

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."