Catalyzing PET‐RAFT Polymerizations Using Inherently Photoactive Zinc Myoglobin

Abstract

Protein photocatalysts provide a modular platform to access new reaction pathways and affect product outcomes, but their use in polymer synthesis is limited because co‐catalysts and/or co‐reductants are required to complete catalytic cycles. Herein, we report using zinc myoglobin (ZnMb), an inherently photoactive protein, to mediate photoinduced electron/energy transfer (PET) reversible addition‐fragmentation chain transfer (RAFT) polymerizations. Using ZnMb as the sole reagent for catalysis, photomediated polymerizations of N,N‐dimethylacrylamide in PBS were achieved with predictable molecular weights, dispersity values approaching 1.1, and high chain‐end fidelity. We found that initial apparent rate constants of polymerization increased from 4.6×10–5 s−1 for zinc mesoporpyhrin IX (ZnMIX) to 6.5×10–5 s−1 when ZnMIX was incorporated into myoglobin to yield ZnMb, indicating that the protein binding site enhanced catalytic activity. Chain extension reactions comparing ZnMb‐mediated RAFT polymerizations to thermally‐initiated RAFT polymerizations showed minimal differences in block copolymer molecular weights and dispersities. This work enables studies to elucidate how protein modifications (e.g., secondary structure folding, site‐directed mutagenesis, directed evolution) can be used to modulate polymerization outcomes (e.g., selective monomer additions towards sequence control, tacticity control, molar mass distributions).