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Abstract
Enzymes provide optimal three-dimensional structures for substrate binding and the subsequent accelerated reaction. Such folding-dependent catalytic behaviors, however, are seldom mechanistically explored with reduced structural complexity. Here, we demonstrate that the α-helix, a much simpler structural motif of enzyme, can facilitate its own growth through the self-catalyzed polymerization of N-carboxyanhydride (NCA) in dichloromethane. The reversible binding between the N terminus of α-helical polypeptides and NCAs promotes rate acceleration of the subsequent ring-opening reaction. A two-stage, Michaelis–Menten-type kinetic model is proposed by considering the binding and reaction between the propagating helical chains and the monomers, and is successfully utilized to predict the molecular weights and molecular-weight distributions of the resulting polymers. This work elucidates the mechanism of helix-induced, enzyme-mimetic catalysis, emphasizes the importance of solvent choice in the discovery of new reaction type, and provides a route for rapid production of well-defined synthetic polypeptides by taking advantage of self-accelerated ring-opening polymerizations.
Highlights
Enzymes provide optimal three-dimensional structures for substrate binding and the subsequent accelerated reaction
An interesting question is whether a basic segment or a simpler molecular structure of enzyme, with reduced chemical and topological complexity, would elicit a Michaelis–Menten type of catalysis, capable of spatial- and site-specific substrate binding and accelerated reaction
The majority of the backbone N‒H and C=O groups within an α-helical polypeptide are intramolecularly connected via H-bonds, the four C=O groups at the C terminus and the four N‒H groups at the N terminus remain unbound owing to the lack of H-bonding partners
Summary
Enzymes provide optimal three-dimensional structures for substrate binding and the subsequent accelerated reaction. In solvents with low polarity, such as dichloromethane (DCM) or chloroform, NCA may bind to the terminus of an α-helical polypeptide with unsaturated groups, including the N terminus that functions as a nucleophile that opens the NCA ring and promotes the chain propagation (Fig. 1c).
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