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

August 24, 2020 by Kayla Benson

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)O_x (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 (PdO_x 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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Free Virtual Physical Symposium

August 11, 2020 by Kayla Benson

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

August 4, 2020 by Kayla Benson

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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