News
Congratulations to Emma!
Emma's paper on the 2+2 ORR mechanism of a bioinspired non-heme Fe-based complex is out now in J. Am. Chem. Soc., congratulations! Through mechanistic and catalytic experiments, Emma has identified reaction rate-laws, binding constants, and reaction barriers for almost the entirety of the proposed catalytic cycle.
https://pubs.acs.org/doi/10.1021/jacs.1c04572
Congratulations Asa, Emma, Peter, and Julia!
The final chapter of Asa's thesis is now in print in JACS, thanks to great supporting efforts from current graduate student Emma and former undergraduates Peter and Julia. This work builds on a previous publication (Chem. Commun. 2021, 57, 516–519) and deals with secondary-sphere effects in dioxygen reduction catalyzed by molecular cobalt complexes. The project was brought over the finish line thanks to our excellent collaborators from Prof. Hannah S. Shafaat's lab at the Ohio State University. Congratulations all!
Nichols, A.W.; Cook, E.N.; Gan, Y.J.; Miedaner, P.R.; Cook, E.N.; Dickie, D.A.; Shafaat, H.S.; Machan, C.W.# “Pendent Relay Enhances H2O2 Selectivity During Dioxygen Reduction Mediated by bpy-based Co-N2O2 Complexes” J. Am. Chem. Soc. ASAP DOI: 10.1021/jacs.1c03381.
Congratulations Shelby, Emma, and Amelia!
Shelby (Dr. Hooe), Emma, and Amelia have published in Chemical Science, congratulations!
The paper deals with the non-covalent assembly of p-benzoquinone anions for co-electrocatalytic dioxygen reduciton to water and details can be found here: https://doi.org/10.1039/D1SC01271A
Research Highlight: Efficient Nanocrystal Surface Cleaning by N-Heterocyclic Carbenes
Research Highlight: Efficient Nanocrystal Surface Cleaning by N-Heterocyclic Carbenes
By Emma Cook, UVA ChemSciComm
Perrin Godbold, Grayson Johnson, Akachukwu D. Obi, Rebecca Brown, Sooyeon Hwang, Robert J. Gilliard Jr., and Sen Zhang J. Am. Chem. Soc. 2021, 143, 2644-2648
Nanocrystals (NC) are nanometer-scale particles made of metal atoms that play key roles in catalysis, medicine, and technology applications because of their unique structural and chemical properties, which can differ significantly from the bulk material. The surfaces of NCs are stabilized by surfactants, which are typically long carbon-hydrogen atom chains attached to a polar group that binds to the NC surface. These surfactants play critical roles in NC synthesis and are used to control NC shape, size, and growth rate. Despite their key role in synthesis, surfactant bulkiness can inhibit catalysis by NC because they block potential surface-active sites. Consequently, there have been many surfactant removal methods developed in order to make these surface-active sites accessible, but these methods are often insufficient for strongly bound surfactants, such as phosphines.
In collaboration, Drs. Sen Zhang and Robert Gilliard and coworkers have developed a surfactant removal method that utilizes N-heterocyclic carbenes (NHC). In this two-step process, trioctylphosphine (TOP) surfactants on platinum, palladium, and gold NC surfaces were first exchanged with NHC ligands. Then, surface bound NHCs were reacted with concentrated acid and were subsequently removed from the NC surface to expose the NC active sites. These surfactant-free NCs demonstrated improved catalysis toward reactions that are important to the development of alternative energy applications. This new strategy of surfactant removal to expose NC surface active sites will improve the ability for NCs to be used in not only catalysis but other relevant applications, such as alternative energy and biomedical sensing technologies.
Highlight on Gilliard Group's Bismuth Cations
Understanding the Fundamentals of Stabilizing Mononuclear Bismuth Cations
By Anna Davis, UVA ChemSciComm
Article: Jacob E. Walley, Levi S. Warring, Guocang Wang, Diane A. Dickie, Sudip Pan, Gernot Frenking, and Robert J. Gilliard, Jr. Angew. Chem. Int. Ed. 2021, 60, 6682–6690
Catalytic reactions, where small amounts of additives greatly accelerate chemical transformations on a larger scale, are ubiquitous in research and industry. Many common catalysts include transition metals, elements with properties that result in unique catalytic activity. Unfortunately, many transition metals are expensive, toxic, and difficult to dispose, increasing the importance of developing catalysts with other types of elements. Main group metals are one possible alternative, since these could potentially offer similar types of catalytic activity without the associated high costs and safety hazards of transition metals.
The use of bismuth (Bi) in catalysis is relatively underdeveloped because although their corresponding complexes are reactive, they commonly exhibit poor selectivity in a reaction mixture as well as instability in air. If an appropriate fundamental understanding of Bi coordination chemistry can be developed, there is great potential in the field of main group catalysis. The Gilliard group at the University of Virginia has recently isolated a series of novel bismuth-centered complexes to address this knowledge gap.
Known bismuth complexes have previously relied on stabilization by nitrogen and chlorine atoms bearing a negative charge, which Gilliard and co-workers were able to exchange for negatively charged carbon atoms. Carbon atoms are generally unstable when bearing a negative charge, but bonding with a bismuth cation (positively charged atom or molecule) benefits both the ligand and the metal center, which represents a significant advancement in the field. This key accomplishment was achieved by carefully designing and changing the groups of atoms which support the negatively charged carbon atoms bound to bismuth, striking a delicate balance between stabilizing the carbon and facilitating bonding. These new structures suggest that additional classes of reactive bismuth complexes are possible which do not rely on nitrogen- and chlorine-stabilized structures.
In addition to creating this new class of molecules, the Gilliard group has developed Bi complexes with overall positive charges ranging from 1+ to 3+. As the complexes become more positively charged, they become more reactive with small molecules such as carbon monoxide, carbon dioxide, and hydrogen gas, which have potential relevance to future catalytic applications. Studies on the ability of these complexes to help harness clean energy are currently underway by the authors.
Write-up on the Pompano Lab by UVA ChemSciComm
Studying Immunity Through Lymph Nodes
Amelia Reid, UVA ChemSciComm
Article Link: Acute Lymph Node Slices Are a Functional Model System to Study Immunity Ex Vivo
A key aspect to understanding immune responses from vaccines, infectious diseases, cancer, or autoimmunity is to study responses in the lymph node. Lymph node structures are complex with at least three distinct regions that communicate with each other in order to produce an immune response. This communication can occur through direct physical contact between cells or indirectly through chemical signals, indicating a relationship between the structure of the lymph node to the immune response that it produces. Typically, studies are limited to the imaging of live tissues (in vivo) or the culturing of lymphoid cells (in vitro). In vitro cell cultures allow for the lymphatic cells to be studied during an immune response, but the importance of the structure of the organ is lost. In vivo imaging studies allow for the structural properties of the lymph node to be retained, but it is difficult to visualize and analyze all the processes occurring in a live organ.
In order to address the disadvantages of traditional methods, Dr. Rebecca Pompano and co-workers at the University of Virginia have recently developed a new method for imaging live organ structures outside the body (ex vivo) to study lymphatic immune responses. Ex vivo imaging allows for structural features of the organ to be retained while enabling more direct measurements of the chemical signaling response. In a typical experiment, live ex vivo lymph node slices are exposed to small molecules which simulate an immunoresponse (e.g. vaccine or infectious disease) and monitored. This method was inspired by previously developed methods to study the tissues of other organs such as the brain, heart, and lungs.
The results of this study showed that the new ex vivo method could reproduce results from in vivo and in vitro methods in a simultaneous measurement, demonstrating the analytical power of this technique. Importantly, the live organ slices remain viable ex vivo over the course of 24 hours, which will enable the interrogation of immune response over longer time periods than previously possible in future studies. Although this new method comes with many benefits, they are quick to point out some of challenges that remain, such as variation in the slices, the isolation of live tissue from the complete immune system, and lack of control over drug entry points. Considering all of the advantages and disadvantages of this method, Dr. Pompano and co-workers are “optimistic that live lymph node slices will provide a novel platform that will add to the immunologist’s tool box as a supplement to traditional experimental models.”
Machan Group Awarded NSF Grant
Today, a Notice of Award was recieved for our proposal to the NSF Division of Chemistry Catalysis Program: 2102156 - CAS: Developing Homogeneous Mn Catalyst Systems for the Oxygen Reduction Reaction. We are thrilled for this support to continue our efforts in advancing homogeneous electrocatalysis of the ORR!
Non-Technical Summary:
With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Charles W. Machan of the University of Virginia is studying the catalytic reduction of dioxygen by molecular manganese compounds. The reduction of dioxygen is important for producing energy from chemical bonds: the oxidation of energy-rich molecules in fuel cells is generally paired with the reduction of dioxygen, generating water as a benign co-product. The current best catalysts for this reaction are based on platinum metal, which is too precious and expensive for large-scale viability. In the search for earth-abundant alternatives, molecular catalysts containing iron and cobalt have been studied extensively, however, manganese versions of these systems are more poorly understood. Manganese metal centers have strong interactions with dioxygen and with proper understanding could demonstrate catalytic activity which rivals or exceeds that of iron and cobalt. These studies will achieve this by developing design principles for dioxygen reduction by manganese complexes, enabling optimized systems with improved performance. Integrated into these efforts is a research-focused educational outreach program, which will develop a scientific communication training program and a research-based lab experience. The integrated research and educational components will address fundamental challenges for the field and priorities of the current NSF Strategic Plan, with the goal of maximizing the health, environmental and economic benefits of renewable energy technologies.
Write-up on the Gunnoe Lab by UVAChemSciComm
Stilbenes: Important Molecules in Need of a Synthesis Makeover
Josh Prindle, UVA ChemSciComm
Article Link: Synthesis of Stilbenes by Rhodium-Catalyzed Aerobic Alkenylation of Arenes via C–H Activation
While stilbenes are found in nature as secondary plant metabolites, man-made stilbene derivatives find utility as precursors for the development of cancer-fighting drugs. The light-emitting properties of other stilbene derivatives make them excellent components in dyes, liquid crystal displays, and light-emitting diodes (LEDs). Current industrial methods for their synthesis require multiple steps and generate significant waste. There is therefore a need for new synthetic routes to these important commodity chemicals to satisfy demand and diminish the environmental footprint.
Dr. Brent Gunnoe and co-workers at the University of Virginia have recently developed a one-pot approach to synthesizing stilbene derivatives from abundant aryl and vinyl arene co-substrates. In the presence of a rhodium-based catalyst, which can selectively activate carbon-hydrogen bonds in the aryl co-substrate, stilbene products are selectively generated using an air-recycled Cu oxidant. The use of the rhodium catalyst is key to the improved reaction conditions, as it removes the need to prefunctionalize substrates common to other approaches, decreasing the amount of waste and improving the atom economy of the reaction.
By avoiding the laborious and wasteful task of separating and purifying precursor molecules and performing the entire synthesis in just one reactor, this approach simplifies the process of synthesizing stilbene derivatives. Dr. Gunnoe believes this new one-pot reaction offers the possibility for more efficient large-scale production of commercially relevant stilbenes. “We believe that the newly reported catalytic route developed by our group provides a substantial improvement in efficiency and can serve to significantly reduce chemical waste and energy consumption compared to existing synthetic methods. Thus, we anticipate that the catalytic process will be used for the preparation of existing and new compounds and materials that contain the stilbene unit.”
Julia Dressel Awarded NSF GRF!
Congratulations to undergraduate Julia Dressel, who has been awarded an NSF GRF to support her future graduate studies!
Write-up on the Gahlmann Lab by UVAChemSciComm
Gahlmann Lab Reports Advances in Bacterial Cell Imaging
Rob Dyer, UVA ChemSciComm
Bacteria and other germs remain a constant threat to our health and well-being, even as the science about infectious diseases continues to improve. Andreas Gahlmann and co-workers in the Department of Chemistry at the University of Virginia are taking strides to better understand how bacteria behave inside the human body by developing advanced imaging methods to observe critical host-pathogen interfaces in real-time. Tracking individual bacterial cells in complex environments has been a particular challenge, because bacteria are extremely small and high-resolution microscopy is generally not compatible with live cells.
In a recent publication, the Gahlmann lab shared a new approach called Bacterial Cell Morphometry 3D (BCM3D). BCM3D first utilizes a state-of-the-art fluorescence microscopy technique which is compatible with live cells, called light sheet microscopy. In a typical experiment, a linearly polarized light beam is stretched into a 2-D sheet using lenses and passed through a sample, while fluorescence images are taken from above. The microscopy data from this technique is then combined with deep learning convolutional neural networks (CNN), a computational method for data analysis which mimics how the brain learns and processes information. This integrated experimental-computational workflow enables researchers to visualize how multicellular bacterial communities operate in different environments.
The convolutional neural networks of BCM3D were shown to be able to classify individual bacterial cells according to their shapes. Prof. Gahlmann thinks that this technological breakthrough will open a window into the microscale interactions between bacterial populations in real time. “When living on and inside the human body, bacteria have to overcome a range of environmental challenges, such as attacks by the host’s immune cells or lengthy antibiotic drug treatments. In order to combat bacterial infections more efficiently, we need to better understand how different bacteria respond and adapt to these stressful situations.”
Nature Communications 11, Article number: 6151 (2020)
Left. Maximum intensity projection of a 3D M. xanthus fluorescence image. Cells were labeled with membrane-intercalating dye, FM4-64. Similar images were obtained at N = 120 different time points. Right. Maximum intensity projection of a CNN-based 3D segmentation result after LCuts post-processing. Cells that can be matched with the GT are displayed in the same colors as GT or otherwise colored in white. Reproduced with permission, according to a Creative Commons CC BY license.
Juanjo's Cr DFT Paper Published in Inorganic Chemistry
Former postdoc Juanjo's "DFT Study on the Electrocatalytic Reduction of CO2 to CO by a Molecular Chromium Complex" is out now in Inorganic Chemistry. Lots of new insight on the behavior and selectivity of our unique Cr catalyst system! Congratulations!
Publication with Giri Group is out!
The latest part of our ongoing collaboration with Prof. Guarav Giri in Chemical Engineering is finalized in Chemistry of Materials!
Congratulations to all involved, lead author Prince Verma made it all come together nicely!
Asa's paper is out in Chem. Commun.!
Asa's paper is now available in Just Accepted form in Chem. Commun.! Former MA student Joe, former undergrad researcher Brittany, and current undergraduate researcher Peter all contributed to this! Thanks as always to Dr. Dickie for solving our crystal. Congratulations!
JULIA DRESSEL WINS ACS AWARD
Congratulations to Julia Dressel, who has won the 2020 ACS Division of Inorganic Chemistry Award for Undergraduate Research! This award is given to three student/mentor teams annually, representing the categories of Primarily Undergraduate Institutions, Research Universities, and Corporate/National/Federal Laboratories. Together with her mentor, Asst. Prof. Charles Machan, Julia was recognized for her contributions to the development of molecular Cr-based electrocatalysts for the reduction of carbon dioxide. Julia will receive an honorarium and commemorative plaque in recognition of these achievements, present at a special symposium at the Fall 2021 National ACS Meeting in Atlanta, and be a guest of honor at a dinner held by the ACS INOR Executive Committee.
Julia’s published work: ACS Catalysis 2020, 10, 1146–1151.
Information on the award may be found here.
Announcement on UVA Chemistry Website: https://chemistry.as.virginia.edu/julia-dressel-wins-acs-award
New research with the Tolman Group is published!
Our collaborative effort with Bill Tolman and co-workers at Washington University in St. Louis is out in Chem. Commun.! Congratulations to Dr. Moreno-Diaz, Asa, and Shelby, as well as our distinguished collaborators!
Dr. Popowski was the driving force behind this great mechanistic study!
Asa's work on pendent relays is out in Inorg. Chem.!
In contrast to other systems, proton donors are directed to binding pockets adjacent to the active site, with the net result being an enhancement of activity and selectivity.
Joe and Shelby contributed to the effort, thanks again to Dr. Dickie as well!
Charles' Perspective on Dioxygen Reduction Published in ACS Catalysis
Learn about recent developments by our lab and others, as well as some strategies for improving molecular systems in the future!
Electrochemical CO2 Reduction in a Continuous Non-Aqueous Flow Cell
Part of our research collaboration with ExxonMobil is now published in Inorg. Chem.!
Led by Dr. Jiang, we examined how a well-known molecular electrocatalyst for CO2 reduction could be used in a continuous flow cell.
Thanks also to Asa and collaborator Dr. John Walzer!
Shelby and Julia make a place at the table for Cr!
Shelby and undergraduate Julia have disclosed the first report of a Cr-based molecular electrocatalyst for the reduction of carbon dioxide! Check out the details in ACS Catalysis.
Thanks to Dr. Dickie! Congratulations to all!
Shelby Receives ACS Women Chemists Travel Award
Congratulations to Shelby Hooe, who received the ACS Women Chemists Travel Award sponsored by Eli Lilly and Co. to support her attendance of the 260th ACS National Meeting in Philaelphia, PA!
Welcome Isobel!
Isobel Thomas, a visiting Master's student from the University of Bath, has joined the group for the year. Welcome Isobel!
Machan Group at 2019 GRC on Organometallics
Charles attended and gave a talk at the 2019 GRC on Organometallic Chemistry at Salve Regina University, RI on "First-Row Transition Metal Complexes for the Electrocatalytic Reduction of CO2 and O2".
Thanks to Al Barney (Strem Chemical) and Mitch Smith (Michigan State University) for organizing a wonderful conference!
Charles Attends the 23rd ACS Green Chemistry & Engineering Conference
Charles attends the 23rd Annual ACS GCANDE Conference in Reston, VA to give a talk on 'Developing Molecular Electrocatalysts and Scalable Systems for Renewable Fuels'.
The talk was for a session on CATALYSIS FOR CO2 CONVERSION organized by Gonghu Li, University of New Hampshire, and Jonathan Rochford, University of Massachusetts Boston.
Thanks Gonghu and Jonathan!
Charles Attends CVIS 2019
Charles attended the 2019 Cyclic Voltammetry International School at the Université Paris Diderot (soon to be the Université de Paris) from April 8-12. It was a wonderful week of lectures and practicals! Good luck to all the participants in the future!
