Molecular Origins of Simultaneous Chemo-, Enantio-, and Substrate Selectivity in Photoenzymatic Radical Reactions

Selective radical chemistry poses fundamental challenges for modern catalysis. Non-natural photoenzymes have recently emerged as appealing systems to address these challenges by offering unmatched control over chemo-, enantio-, and substrate selectivity, yet their underlying mechanisms remain unclear. Here, we reveal the complete molecular basis of triple selectivity control in photoenzyme GkOYE-G7 through computational simulations based on multiscale multireference-quantum-mechanics/molecular-mechanics modeling and bias-exchange metadynamics. Our findings demonstrate that control emerges from reaction-level mechanisms rather than binding preferences. We discover that productive photochemistry requires a previously unkown pre-activation step involving bond elongation. Stereochemical outcomes result from reaction barrier differences, while chemoselectivity exploits early-appearing crossing points between ground and excited electronic states that commit reactions before competing pathways activate. Substrate scope follows predictable electronic-steric rules, establishing fundamental principles for engineering next-generation photoenzymes with predictable selectivity profiles.