Quantifying the Sequence-Dependent Kinetic Protection of Reduced Heme in Peptide Amphiphile Nanofibers

Replicating the protective dielectric environment of natural cytochromes within synthetic assemblies is essential for the development of air-stable bioelectronics. We report a redox-triggered "supramolecular gate" in self-assembled peptide amphiphile (PA) nanofibers that provide significant kinetic protection to ferrous heme B under aerobic conditions. By systematically varying side-chain steric bulk and hydrophobicity in a series of c16HHX4K3 PAs, we identified a phenylalanine variant (c16HHFL3K3) that extends the ferrous lifetime to over five seconds. Using a comprehensive multicomponent kinetic model, we resolve an initial protection phase in the c16HHFL3K3 variant that is absent in smaller side-chain controls like alanine. Potentiometric titrations revealed massive redox hysteresis (ΔEm up to 305 mV), representing the mechanistic barrier required for the transition to a "locked" state. Circular dichroism spectra support this transition as a cooperative increase in superhelical twisting upon reduction. These findings establish sequence-specific design rules for stimulus-responsive "insulation" in peptide-based materials, enabling the protection of reactive redox centers in atmospheric environments.