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(Îµ-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.
Biological assays have dramatically improved in recent years due to the increasing use of living cells as "test tubes" for research studies. These cell-based assays have demanded that new technologies be developed for the life sciences in order to fully exploit the potential of designer drugs, stem cell engineering, and genetic medicine. The Allbritton Group is at the forefront of this technology development for biomedical and pharmaceutical research.
Traditional biochemical assays have limitations when used for assays in cells obtained from patients; therefore, the Allbritton Group has worked to develop new technologies that address critical needs for biochemical studies within live cells. The laboratory has pioneered advanced tools for analytical chemistry that now make it feasible to perform enzyme assays in individual cells taken directly from patients. In collaboration with colleagues David Lawrence and Marcey Waters in the Department of Chemistry and colleagues in the School of Medicine, the group is developing new chemical compounds that will act to report the abnormal behavior of specific enzymes in blood or biopsy specimens. This cell-by-cell measurement of enzyme activity in patients will have widespread value for individualizing or customizing patient therapy and will provide critical information for physicians using the new generation of molecularly targeted drugs used in the treatment of patients with cancer, autoimmune syndromes, neurodegenerative disorders, and a variety of other diseases.
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.
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.
Biological systems have the ability to program reversible shape changes in response to cues from their environment. While a variety of adaptive and stimuli-responsive materials like hydrogels, liquid crystalline elastomers, and shape memory materials have been developed, mimicking programmable behavior in a reversible way remains elusive.
Work published in Macromolecules by the Sheiko and Ashby groups, in collaboration with the University of Connecticut, Brookhaven and Oak Ridge National Labs, has shown that semi-crystalline elastomers may undergo reversible switching between well-defined shapes without applying any external forces. This behavior stems from the correlated interplay between a crystalline scaffold and a network of chemical crosslinks, each capable of encoding a distinct shape. The universal mechanism of reversible shapeshifting affords interesting opportunities for minimally invasive surgery, shape programmable biomedical implants, surgical sealants, and hands-free packaging.
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.
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.
Chemistry Professor and Chair, Valerie Ashby, was, along with Chancellor Folt and Graduate School Dean Steve Matson, one of the speakers as the Graduate School recently launched a program focused on academic success, professional development and degree completion for graduate students from diverse and underrepresented groups.
All three speakers highlighted the University's commitment to sustaining a diverse graduate student body and fostering a climate of inclusion and acceptance. Ashby, a faculty advisor for the program, said the Office of the Executive Vice Chancellor and Provost has made a significant financial commitment to the program. The new program's co-directors are Kacey Hammel and Kathy Wood. They will collaborate with faculty, staff, students and administrators to create targeted academic and professional development initiatives contributing to the successful degree completion of each graduate student.
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
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.
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.
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."