Inorganic and ChemBio Seminar - Shiliang Tian

The Inorganic and ChemBio Seminar Series present: Shiliang Tian

Purdue University

Host: Yi Lu

Title: Visualizing Reactive Intermediates: Radical and High-Valent Chemistry Across Biological and Synthetic Catalysis

Location: WEL 2.122

Refreshments served at 3:15pm

Controlling highly reactive radical and high-valent metal intermediates is a central challenge in both biological catalysis and synthetic organometallic chemistry. My group integrates electron paramagnetic resonance (EPR) spectroscopy with cryogenic electron microscopy (cryo-EM) and computational approaches to directly observe and mechanistically characterize these fleeting species. In the first part of this talk, I will describe how substrate-triggered conformational dynamics activate and control radical chemistry in adenosylcobalamin-dependent mutases. Cryo-EM structures combined with EPR detection of paramagnetic intermediates, reveal that large-scale domain motions gate Co(III)–C bond homolysis and spatially confine the resulting 5′-deoxyadenosyl radical, providing a framework for how enzymes accelerate radical initiation while suppressing off-pathway damage. In the second part, I will show how EPR spectroscopy identifies and assigns transient high-valent copper and nickel intermediates in catalytic C–C bond formation. Capturing Cu(II), Cu(III), Ni(III), and formal Ni(IV) species under catalytic conditions provides direct evidence for radical-mediated oxidative addition pathways and unconventional high-valent redox cycles. Together, these studies demonstrate how combining structural, spectroscopic, and computational methods enables direct visualization of reactive intermediates and reveals unifying principles for controlling high-energy chemistry across biological and synthetic systems.