Control of Tyrosyl Radical Stabilization by {SiO2@Oligopeptide} Hybrid Biomimetic Materials

Tyrosine radicals are notoriously short-lived/unstable in solution, while they present an impressive degree of stability and versatility in bioenzymes. Herein, we have developed a library of hybrid biomimetic materials (HBMs), which consists of tyrosine-containing oligopeptides covalently grafted on SiO2 nanoparticles, and studied the formation, lifetime, and redox properties of tyrosyl radicals. Using electron paramagnetic resonance spectroscopy, we have studied the radical-spin distribution as a probe of the local microenvironment of the tyrosyl radicals in the HBMs. We find that the lifetime of the tyrosyl radical can be enhanced by up to 6 times, by adjusting three factors, namely, a proximal histidine, the length of the oligopeptide, and the interface with the SiO2 nanomatrix. This is shown to be correlated to a significant lowering of E-1/2 from +736 mV, in free tyrosine, to +548 mV in the {12-peptide}@SiO2 material. Moreover, we show that grafting on SiO2 lowers the E-1/2 of tyrosine radicals by similar to 50 mV in all oligopeptides. Analysis of the spin-distribution by EPR reveals that the positioning of a histidine at a H-bonding distance from the tyrosine further favors tyrosine radical stabilization.

Automated summary

This study investigates the formation, lifetime, and redox properties of tyrosyl radicals in hybrid biomimetic materials (HBMs) that consist of tyrosine-containing oligopeptides grafted on SiO2 nanoparticles. The results show that the lifetime of the tyrosyl radical can be enhanced by adjusting factors such as a proximal histidine, the length of the oligopeptide, and the interface with the SiO2 nanomatrix. The E-1/2 of tyrosine radicals is lowered when grafted on SiO2, and the positioning of a histidine at a H-bonding distance from the tyrosine further favors tyrosine radical stabilization.