Department of Chemistry
Custom Search

 

The Weeks Group

Weeks Group

The Weeks laboratory is inventing high-throughput technologies for analyzing the structure of RNA. In one recent result, the lab has reported the architecture and secondary structure of an entire HIV genome. Ongoing work focuses on creating new RNA chemistries, on drug discovery, and on analyzing RNA structure-function relationships inside viruses and cells.

 

The Ashby Group

The Ashby Group

Our focus in the Ashby Group is the synthesis of functional shape memory materials for biomedical applications. We have recently reported the topological control of mesenchymal stem cells by responsive poly(ε-caprolactone) surfaces in which we engineered a biocompatible shape memory surface to mechanically alter stem cell topology.

Group members are also developing scaffolds for nitric oxide release in collaboration with the Schoenfisch Group, and are working towards the synthesis of new iodinated polyesters for use in X-ray computed tomography.

 

Phototherapeutics

Light-activatable drugs offer the promise of controlled release with exquisite temporal and spatial resolution. However, light-sensitive prodrugs are typically converted to their active forms using short-wavelength irradiation, which displays poor tissue penetrance. Researchers in the David Lawrence Group report in Angewandte Chemie, International Edition, on erythrocyte-mediated assembly of long-wavelength-sensitive phototherapeutics.

Research Image

The activating wavelength of the constructs is readily preassigned by using fluorophores with the desired excitation wavelength λex. Drug release from the erythrocyte carrier was confirmed by standard analytical tools and by the expected biological consequences of the liberated drugs in cell culture: methotrexate, binding to intracellular dihydrofolate reductase; colchicine, inhibition of microtubule polymerization; dexamethasone, induced nuclear migration of the glucocorticoid receptor.

 

New Avenues in Solar Fuel Production

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.

Research Image

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

 

Lubrication by Polyelectrolyte Brushes

Published in Macromolecules, Professor Michael Rubinstein, in collaboration with Ekaterina Zhulina with the Institute of Macromolecular Compounds, Russian Academy of Sciences in Saint Petersburg, describe the development of a scaling model relating the friction forces between two polyelectrolyte brushes sliding over each other to the separation between grafted surfaces, number of monomers and charges per chain, grafting density of chains, and solvent quality. They demonstrate that the lateral force between brushes increases upon compression, but to a lesser extent than the normal force.

Research Image

The shear stress at larger separations is due to solvent slip layer friction. The thickness of this slip layer sharply decreases at distances on the order of undeformed brush thickness. The corresponding effective viscosity of the layer sharply increases from the solvent viscosity to a much higher value, but this increase is smaller than the jump of the normal force resulting in the drop of the friction coefficient. At stronger compression the group members predict the second sharp increase of the shear stress corresponding to interpenetration of the chains from the opposite brushes. In this regime the velocity-dependent friction coefficient between two partially interpenetrating polyelectrolyte brushes does not depend on the distance between substrates because both normal and shear forces are reciprocally proportional to the plate separation. Although lateral forces between polyelectrolyte brushes are larger than between bare surfaces, the enhancement of normal forces between opposing polyelectrolyte brushes with respect to normal forces between bare charged surfaces is much stronger resulting in lower friction coefficient. The model quantitatively demonstrates how polyelectrolyte brushes provide more effective lubrication than bare charged surfaces or neutral brushes.

 

Quantum Dynamics on Supercomputers

In the perspective paper published in Computing in Science and Engineering’s special topic issue on Advances in Leadership Computing, researchers in the Kanai Group and his collaborators at University of Illinois at Urbana Champaign and Lawrence Livermore National Laboratory describe the state-of-the-art computational method for simulating quantum dynamics of electrons in complex materials using supercomputers.

Research Image

They discuss a new first-principles computational method for simulating quantum dynamics of electrons in complex materials by propagating time-dependent wavefunctions. The method is designed to take advantage of a large number of processing cores in today’s supercomputers by utilizing multiple levels of different parallelization schemes. They demonstrate a strong scaling of the computational method over 1 million processing cores on an IBM supercomputer. As an example of how new material properties can be investigated using this state-of-the-art method, non-equilibrium energy transfer rate from a fast proton to the electronic excitation in bulk gold was calculated and compared to available experimental data. Importantly, the computer simulation provides detail information on how the electronic excitation is induced by the fast proton. This new first-principles quantum dynamics method enables theoretical investigations into various non-equilibrium phenomena of electrons in large complex systems.

 

RNA Structure in 3D

RNA molecules function as the central conduit of information transfer in biology. To do this, they encode information both in their sequences and in their higher-order structures. Understanding the higher-order structure of RNA remains challenging and slow. In work reported in PNAS and highlighted in Science, Phil Homan in the Weeks Lab led a collaboration that devised a simple, experimentally concise, and accurate approach for examining higher-order RNA structure.

Research Image

The researchers used massively parallel sequencing to invent an easily implemented single-molecule experiment for detecting through-space interactions and multiple conformations in RNA. This strategy, called RING-MaP, can be used to analyze higher-order RNA structure, detect biologically important hidden states, and refine accurate three-dimensional structure models.

 

Jefferson Award to Templeton

Francis Preston Venable Professor of Chemistry, Joseph Templeton, is the recipient of this year's Thomas Jefferson award, which was presented to him by Chancellor Folt at a recent Faculty Council meeting. "I would just like to add from my own chance to work so closely with Professor Templeton the last year how deserving and wonderful this award is," said Chancellor Folt.

Professor Joseph Templeton

The Thomas Jefferson Award was established in 1961 by the Robert Earll McConnell Foundation. It is presented annually to "that member of the academic community who through personal influence and performance of duty in teaching, writing, and scholarship has best exemplified the ideals and objectives of Thomas Jefferson." This award is, according to Department Chair, Professor Valerie Ashby, "a well-deserved honor for Professor Templeton that recognizes the many forms of his contributions to the university throughout his career."

 

 

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."