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Calhoun Lab Featured Cover in J. Phys. Chem. C

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The Calhoun Lab was published in the Journal of Physical Chemistry C for their research “Leaving the Limits of Linearity for Light Microscopy” and it is a perspective on the recent advances in the field of nonlinear microscopy. This article is also the featured cover for the November 12, 2020 issue.

Graduate student authors include Marea Blake and Brandon Colon.  Blake is currently pursuing her Ph.D. in Chemistry at the University of Tennessee, Knoxville. Her current research focuses on probing small molecule-membrane interactions in living cells using nonlinear techniques such as second harmonic generation and two-photon fluorescence.

Colon received his B.S. degree (2016) in Chemistry from the University of West Florida in Pensacola, FL. He is a doctoral student at the University of Tennessee under the tutelage of Prof. Tessa Calhoun. He has been investigating the use of total internal reflection illumination geometries to apply nonlinear microscopy techniques to microfluidic samples.

In this paper, the group highlights recent developments within the past couple of years pertaining to how nonlinear microscopy methods such as transient absorption, 2D nonlinear microscopy, second order processes, and quantum microscopy are being implemented to probe different timescales, access information on interfaces and illuminate samples with novel excitation schemes. 

“Our group actually uses a few of these methods (such as TAM, SHG and TIR geometry excitation) in our lab so it was really exciting getting to portray that in this perspective and explore the directions they can grow,” Blake said.

Best Group’s Recent Work

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Recent work in the Best Group has culminated in the development of stimuli-responsive liposomes for drug delivery designed to release therapeutic cargo when they come into contact with diseased cells, specifically based on overexpressed enzymes and reactive oxygen species. “These smart liposomes show strong prospects for advancing drug delivery by targeting therapeutics directly to the site of the disease,” Jinchao Lou, graduate student in the Best Group, said.

Liposomes are effective nanocarriers for drug delivery due to their ability to encapsulate and deliver a wide variety of therapeutic cargo to cells. Nevertheless, liposome delivery would be improved by enhancing the ability to control the release of contents within diseased cells. Toward this end, stimuli-responsive liposomes, in which the drug carrier decomposes when it comes in contact with conditions associated with disease, are of great interest for enhancing drug potency while minimizing side effects.

While various stimuli have been explored for triggering liposome release, both enzymes and reactive oxygen species (ROS) provide excellent targets due to their key roles in biology and overabundance in diseased cells. In two separate papers, the Best Group presented a general approach to enzyme‐responsive liposomes exploiting targets that are commonly aberrant in disease, including esterases, phosphatases, and β‐galactosidases (Chem. Eur. J. 2020, 26, 8597-8607), as well as an ROS-responsive liposomal delivery platform (Bioconjugate Chem. 2020, 31, 2220-2230).

In both of the cases, responsive lipids designed to target each stimulus were designed and synthesized bearing a responsive headgroup attached via a self‐immolating linker to a non‐bilayer lipid scaffold. In this way, stimulus addition triggers chemical lipid decomposition in a manner that disrupts membrane integrity and releases contents. Release properties were fully characterized by fluorescence-based dye leakage assays, dynamic light scattering and electron microscopy, among other techniques.

Due to their recent works in this field, the Best group was also invited to write a review describing advances in the design of stimuli-responsive liposome strategies for drug delivery with an eye towards emerging trends in the field (Chem. Phys. Lipids. In Press. DOI 10.1016/j.chemphyslip.2020.104966). Smart liposomes show strong prospects for advancing drug delivery by targeting drugs directly to the site of the disease.

ORI Names Campagna Interim Director of Strategic Programs

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President Randy Boyd shared some developments at the Oak Ridge Institute at UT (ORI at UT). A national search for the first executive director and vice provost of the Oak Ridge Institute at UT is underway.

Shawn Campagna
Shawn Campagna

ORNL Director Thomas Zacharia and Randy Boyd, in consultation with UT Knoxville Chancellor Donde Plowman and UT Health Science Center Chancellor Steve Schwab, have named Michelle Buchanan, ORNL deputy for science and technology, and Stacey Patterson, UT System vice president for research, as interim co-directors of ORI at UT until a director is named. Suresh Babu, a UT-ORNL Governor’s Chair for Advanced Manufacturing and Bredesen Center Director, will serve as ORI at UT’s interim education director. Shawn Campagna, UT Knoxville associate department head of chemistry and Director of Science Alliance, will serve as the interim director of strategic programs. Jean Mercer, UT Knoxville assistant vice chancellor for research and director of the office of sponsored programs, will serve as interim director of operations.

Collier at Kennesaw State University

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Graham Collier, originally from Fayetteville, North Carolina, received his BS in chemistry in 2011 from the University of North Carolina Wilmington. Upon graduation, Collier enrolled in the graduate program at the University of North Carolina at Charlotte and studied porphyrin chromophores under the direction of Michael Walter. After graduating in 2013, Collier enrolled in the chemistry doctoral program at UT with a concentration in polymer chemistry.
 
Collier’s dissertation entailed studying structure-property relationships of purine-based polymers and chromophores under the guidance of Mike Kilbey. Collier received his PhD in 2017 and began his position as postdoctoral research associate at Georgia Tech studying conjugated polymers for electrochromic under the mentorship of John Reynolds. Collier joined the faculty of Kennesaw State University as a tenure-track assistant professor of Chemistry in the Department of Chemistry and Biochemistry in fall of 2020.
 
Research in the Collier Group resides at the interface of organic, polymer, and materials chemistry. “We are interested in utilizing precise monomer synthesis to incorporate functional building blocks into polymeric materials with targeted macromolecular properties,” said Collier. “Specific interests include synthesis and characterization of conjugated polymer and molecule systems to understand how structure influences optical and electrochemical properties.”
 
Research in the Collier Research Group at KSU will involve the synthesis and characterization of organic molecules and polymers that find applicability in thin film electronics. The group will work to develop new polymers and molecules by manipulating their fundamental chemical structure to obtain targeted properties.
 
 
 
 

 

Brantley & Long’s Collaborative Research

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The Brantley Lab and the Long Group published collaborative research “Vinyl-addition polymerizations of cycloallenes: synthetic access to congeners of cyclic-olefin polymers” in Polymer Chemistry. Co-first authors include Nick Galan with the Brantley Lab and Justin Burroughs with the Long Group. 

Their research demonstrates that vinyl-addition polymerization of cycloallenes is a potentially valuable strategy for preparing tunable analogues of cycloolefin polymers. Cycloallenes can be polymerized in a well-controlled manner at room temperature using a simple Ni catalyst. 

“This route does not require high strain monomers to achieve cyclic motif incorporation, and copolymerization with acyclic monomers is possible, but not required to achieve good conversion,” Galan said. “Taken together, these results suggest that vinyl-addition polymerizations of cyclic allenes could provide a reliable synthetic route toward heretofore inaccessible materials.”

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Musfeldt Group’s Recent Achievements

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The Musfeldt Group’s research area focuses on experimental materials chemistry and physics. They employ a variety of spectroscopic methods to reveal and control the properties of quantum materials. External stimuli are used to tune these properties in order to explore new physical phenomena and uncover properties of technological relevance.

The Musfeldt Group provides a very unique opportunity for students with the DMREF team (Designing Materials to Revolutionize and Engineer our Future). This year, the team received “The Creativity Extension which is the highest honor in DMR,” Musfeldt said. “The team received an extra $450,000 for it this year.”

The group has also been busy publishing papers such as “Piezochromism in the magnetic chalcogenide MnPS3” in npj Quantum Materials. Nathan Harms, graduate student in the Musfeldt Group, is the lead author. This research explores combining high-pressure optical spectroscopies and first-principles calculations to reveal piezochromism in MnPS3. Photographs are of piezochromic MnPS3 inside the diamond anvil cell at several characteristic pressures and also after release at room temperature. These images show a gasket hole diameter of 325 μm. The diamond culets are 500 μm.

Musfeldt was also published a cover article in Physics Today titled “Nanotubes from layered transition metal dichalcogenides.”

 

Dai Group Published in Nature Communications for Entropy-stabilized Single-atom Pd Catalysts Research

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The Dai Lab’s research “Entropy-stabilized single-atom Pd catalysts via high-entropy fluorite oxide supports” was published in Nature Communications. First Author Haidi Xu conducted research in the Dai Lab as a visiting scholar from Sichuan University, China. 

This work explores single-atom catalysts (SACs) as they have demonstrated superior catalytic performance in the catalysis community. Fabricating intrinsically stable SACs on traditional supports remains a formidable challenge, especially under high-temperature conditions.

The Dai Lab propose a new strategy to construct a sintering-resistant Pd single-atom on a novel equimolar high-entropy fluorite oxides (CeZrHfTiLa)Ox (HEFO) as the support by simply mechanical milling with calcination at 900 °C.

Characterization results reveal that single Pd atoms are incorporated into HEFO (Pd1@HEFO) sublattice by forming stable Pd–O–M bonds (M=Ce/Zr/La) compared to Pd-O-Pd (PdOx clusters) bonds of Pd@CeO2 synthesized by the same method with the traditional support, thus exhibiting not only higher low-temperature CO oxidation activity but also outstanding resistance to thermal and hydrothermal degradation. T

“This work exemplifies the superiority of high-entropy materials for the preparation of SACs,” Xu said.

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Jenkins Group Published in ACS Nano

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Kristina VailonisResearch from the Jenkins Group was recently published in ACS Nano for their work “In Situ Monitoring of the Seeding and Growth of Silver MetalOrganic Nanotubes by Liquid-Cell Transmission Electron Microscopy“. Kristina Vailonis was one of the primary authors of this piece. Vailonis recently graduated with her PhD from the University of Tennessee’s Department of Chemistry.

Metal–organic nanotubes (MONTs)  are highly ordered one-dimensional crystalline porous frameworks. Despite being nanomaterials, virtually all studies of MONTs rely on characterization of the bulk crystalline material (micron-sized) by single-crystal X-ray diffraction.

This research analyzes their formations under a variety of reaction conditions in solution, and employ liquid-cell transmission electron microscopy (LCTEM), which allows the early stages of MONT assembly to be monitored in real time.

Changing the metal-to-ligand ratio alters the local concentrations of reactant monomers, resulting in multiple nucleation and growth pathways and diverse morphologies at the nanoscale.

“As we develop MONTs, it is critical to characterize them on the nanoscale before they have grown into bulk 3D materials that are microns in size,” said Jenkins “By collaborating with experts on liquid cell-TEM, we can observe the chemical reactions and watch these 1D materials grow in real time.”

Free Virtual Physical Symposium

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Despite its introduction almost three decades ago, the ability to couple the measurement of nonlinear phenomena with the spatial resolution of a microscope objective has continued to rapidly evolve through both the application of more sophisticated techniques and the study of more complex systems. Progress in the field of nonlinear microscopy has afforded deep penetration in biological tissues, additional modalities for chemical contrast, and dynamics on ultrafast timescales. Challenges remain, however, in extracting new information from increasingly congested samples with minimal perturbation. Innovations in instrumentation, the development of new image analysis methodologies, and novel applications of existing techniques promise new insight into intrinsically heterogeneous samples. 

Tessa Calhoun, Associate Professor with the Department of Chemistry, has been co-organizing a symposium for the virtual ACS conference August 17-20, 2020. There will be live Zoom presentations that are free for anyone to participate in. Registration information can be found here. 

This symposium will gather scientists from the fields of chemistry, physics, engineering and biology into a collaborative environment where ideas of technology innovations and sample applications can be shared and discussed. Progress, existing challenges, impact will be emphasized.

While this symposium originated as part of the ACS Fall 2020 Virtual Conference, participation in these Zoom sessions is not limited to those registered for the conference. 

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Scientists Catch a Glimpse of Elusive Cell Membrane Nanodomains

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A collaborative team including University of Tennessee researchers has captured the first direct images of tiny cell membrane domains known as lipid rafts. The images were published in a research article in this week’s edition of Proceedings of the National Academy of Sciences of the USA.

First hypothesized over thirty years ago, rafts are specialized microenvironments found within cell membranes, the sheets of lipid and protein that both surround a cell and delineate its internal compartments. They are thought to play a crucial role in the way cells transport materials and communicate with each other. Some viruses, including influenza and HIV, have even co-opted rafts in their life cycle.

At nearly a thousand times smaller than the width of a human hair, rafts are impossible to detect with conventional microscopy. “Although their existence is well supported by biochemical evidence, the lack of direct visual observations of rafts has led to some healthy skepticism” said Fred Heberle, an assistant professor in the Chemistry Department at UT and lead author of the study.

The researchers used a powerful technique called cryogenic electron microscopy (cryoEM) to take the first pictures of the tiny structures. “An ordinary light microscope can’t resolve objects smaller than a few tenths of a micrometer, but cryoEM can visualize structures as small as a tenth of a nanometer” said Heberle. “It’s revolutionizing the field of structural biology, but to date has mostly been used to look at protein structure. We decided to zoom in on membranes and see if we could visualize rafts.”

The study grew out of a collaboration between Heberle and two research groups at the University of Texas Health Science Center at Houston led by cell biologist Ilya Levental and neurobiologist M. Neal Waxham. “We have a common interest in membrane structure but different ways of approaching it,” said Heberle. “My lab studies synthetic membranes, while Ilya and Neal specialize in more complicated biological membranes. We also have combined expertise in small-angle scattering, molecular simulations, and electron microscopy. Ultimately, we needed all of those tools to convince ourselves that we were really seeing rafts.”

The researchers first imaged model biomimetic membranes to show that cryoEM can resolve sub-nanometer differences in their thickness, a feature known to distinguish rafts from the surrounding membrane. They then used simulations to predict how rafts would appear in a cryoEM image and to fine-tune their analysis, before finally capturing images of raft domains in both biomimetic and biological membrane preparations. A team at the University of Washington led by Sarah Keller and graduate student Caitlin Cornell independently made a similar discovery using a variation of cryoEM called cryo-electron tomography, and the two articles were published together.

While the new images should settle some long-standing questions, many aspects of raft formation and structure remain poorly understood. At a basic level, rafts are a consequence of the immiscibility of different lipids found in cell membranes, much like a mixture of olive oil and vinegar will separate in a bottle of salad dressing. “Cell membranes are fluid mixtures of lipids and proteins, and some of the different types of lipids don’t mix well and can separate to form a raft,” Heberle said.

One problem that has confounded researchers is why rafts remain small rather than coalescing into larger structures, but Heberle says that the ability to finally visualize the domains may eventually provide answers. “A better understanding of rafts will not only give insights into the normal functioning of our own cells, but may also lead to improved therapies for viral infections.”

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