Bioorganometallic Redox Chemistry

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Redox reactions are essential to most living systems on Earth by serving as the energy supply for cells. However, malfunctions in the cellular redox machinery can cause a buildup of reactive oxygen species (ROS) and other oxidants. Oxidative stress occurs when this buildup exceeds the local supply of reductants, which can lead to oxidative damage of critical biomolecules, such as proteins and DNA. Oxidative stress, in turn, can trigger an acute immune response that leads to even more severe cell and tissue damage. The Tennyson Lab is developing organometallic complexes that catalytically reduce ROS and other biologically-relevant oxidants and, in doing so, thereby alleviate or inhibit oxidative stress. Our long-term goal in this research area is to develop catalytic redox therapeutics that are effective in artificial implant failure, diabetic cardiomyopathy, stroke, and transplant rejection, without requiring the use of any immunosuppressive drugs.

Selected Publications

Hydrogen peroxide as a hydride donor and biologically-relevant reductant. Yamin Htet, Zhuomin Lu, Sunia A. Trauger, and Andrew G. Tennyson. Chem. Sci., 2019, 10 (7), 2025–2033.

NAD+ as a Hydride Donor and Reductant. Yamin Htet and Andrew G. Tennyson. J. Am. Chem. Soc., 2016, 138 (49), 15833–15836.

Catalytic Radical Reduction in Aqueous Solution by a Ruthenium Hydride Intermediate. Yamin Htet and Andrew G. Tennyson. Angew. Chem., Int. Ed., 2016, 55 (30), 8556–8560.

Catalytic radical reduction in aqueous solution via oxidation of biologically-relevant alcohols. Yamin Htet and Andrew G. Tennyson. Chem. Sci., 2016, 7 (7), 4052–4058.

Generation, Translocation, and Action of Nitric Oxide in Living Systems. Andrew G. Tennyson and Stephen J. Lippard. Chemistry & Biology, 2011, 18 (10), 1211–1220.

Catalysis & Coordination Chemistry

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Catalysts enable kinetic control of chemical reactions by altering the activation energies of one or more reaction steps. Of particular importance are catalysts that can be controllably activated and/or deactivated via exogenous stimuli, such as light or electric potential. With this ability, it becomes possible to toggle catalyst activity (between “on” and “off”) and reactivity (between A→B vs. A→C) to achieve multiple chemical transformations in a single pot without requiring workup and purification between each individual step. The Tennyson Lab is developing small molecule activation and polymerization catalysts whose functions can be modulated via light, redox reactions, or phase changes. Our long-term goal in this research area is to develop methods for covalently tethering redox- and light-responsive catalysts to solid-phase supports for continuous “flow-through” processes that affect multiple transformations in tandem.

Selected Publications

Redox-Active Ligands: An Advanced Tool to Modulate Polyethylene Microstructure. W. Curtis Anderson Jr., Jennifer L. Rhinehart, Andrew G. Tennyson, and Brian K. Long. J. Am. Chem. Soc., 2016, 138 (3), 774–777.

Net charge effects in N-heterocyclic carbene–ruthenium complexes with similar oxidation states and coordination geometries. Anshuman Mangalum, Yamin Htet, Dallas A. Roe, Colin D. McMillen, and Andrew G. Tennyson. Inorg. Chim. Acta, 2015, 435, 320–326.

Synthesis, coordination chemistry and reactivity of transition metal complexes supported by a chelating benzimidazolylidene carboxylate ligand. Anshuman Mangalum, Colin D. McMillen, and Andrew G. Tennyson. Inorg. Chim. Acta, 2015, 426, 29–38.

Self-Protecting & Self-Healing Biomaterials

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Living systems are surprisingly harsh environments for synthetic materials, producing extreme chemical and mechanical stresses that can damage even the most robust substances, including stainless steel and fluoropolymer plastics. Even under rigorously sterile conditions, artificial materials provoke an acute immune response almost immediately upon implantation, whereupon immune cells adhere to and begin degrading the material via the release of reactive oxygen species (ROS) and other oxidants. If the surface of the artificial material is contaminated with bacteria or biofilms, the acute immune response is even more severe. The Tennyson Lab is developing biocompatible materials that (i) actively degrade ROS and other biologically-relevant oxidants before they can cause damage and (ii) actively prevent bacterial adhesion and biofilm formation. In addition, our lab is working on creating self-healing biomaterials in which any damage can be non-surgically repaired with simple heat or laser light. Our long-term goal in this research area is to develop inherently antibacterial/antifouling biomaterials that actively prevent foreign body reactions and any other adverse immune responses.

Selected Publications

Combining Agriculture and Energy Industry Waste Products to Yield Recyclable, Thermally-Healable Copolymers of Elemental Sulfur and Oleic Acid. Ashlyn D. Smith, Timmy Thiounn, Elliott W. Lyles, Emily K. Kibler, Rhett C. Smith, and Andrew G. Tennyson. J. Polym. Sci. A, 2019, Early View.

Thermally-Healable Network Solids of Sulfur-Crosslinked Poly(4-allyloxystyrene). Timmy Thiounn, Monte S. Bedford, Moira K. Lauer, Rhett C. Smith, and Andrew G. Tennyson. RSC Adv., 2018, 8 (68), 39074–39082.

Durable, Thermally-Recyclable Materials from Industrial Wastes

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Human agriculture generates gigaton quantities of high-carbon wastes that accumulate either because no economically-viable use has been devised or because they have formed from spoilage of more valuable products. Similarly, even though petroleum-derived S8 serves as the feedstock for all industrial sulfuric acid production globally, nearly 10 million tons of S8 go unused each year and accumulate in solid waste storage sites. The Tennyson Lab, in collaboration with the Rhett Smith Lab at Clemson University, is developing strategies for cross-linking high-carbon agricultural wastes with polymeric sulfur to produce high-sulfur thermosets and thermoplastics. Our long-term goal in this research area is to develop self-healing composites for medical and defense applications, as well as 100% thermally-recyclable construction materials for sustainable building practices.

Selected Publications

Valorisation of Waste to Yield Recyclable Composites of Elemental Sulfur and Lignin. Menisha S. Karunarathna, Moira K. Lauer, Timmy Thiounn, Rhett C. Smith,* and Andrew G. Tennyson. J. Mater. Chem. A, 2019, 7 (26), 15683–15690.