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

Abstract

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 SiO 2 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 SiO 2 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}@SiO 2 material. Moreover, we show that grafting on SiO 2 lowers the E 1/2 of tyrosine radicals by ∼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.

Spin‐Injection in Graphene: An EPR and Raman Study

“…On the other hand, when tyrosine was intercalated in laponite clay, [30] the g‐value (g=2.0041) and 1 H‐hyperfine splitting were closed to free‐tyrosine radical in solution. Furthermore, we have recently demonstrated that incorporation of the tyrosine‐radical in an oligopeptide grafted on SiO 2 nanoparticles [31] retains the free‐tyrosine radical spin distribution. Taken in account this information, it is concluded that: [i] when tyrosine radicals are grafted on carbon matrices for example, carbon‐nanotubes, [33] graphene or GO, the spin of the radical tends to delocalize over the carbon matrix.…”

“…The 1 H‐hyprefine couplings are smaller than that of free‐tyrosine radical in solution, which agrees with less‐spin on the phenoxy‐ring. [ii] when the tyrosine radicals are not‐grafted i. e., simply intercalated in a solid‐matrix for example, such as a clay, [30] or incorporated in oligopeptides, [31] then the radical resembles free‐tyrosine radical in solution. Association of the tyrosine‐radical with the carbon matrix seems to be related with preference to diffuse the radical over the carbon‐matrix, as it has been observed originally in the case of carbon‐nanotubes [33] .…”

“…[21,29] The shift of the g value from 2.0027 (GO) to 2.0038, after the functionalization with tyrosyl groups at GO-f-Tyr, indicates a spin delocalization on the phenolic oxygen of the tyrosine. [30,31,32] Quantitation of the spins, showed that the untreated GO contained 0.64 μmoles of spin per g, while the GO-f-Tyr contained 2.7 μmoles of spin per g.…”

Tuning the 1O2 Oxidation of a Phenol at the Air/Solid Interface of a Nanoparticle: Hydrophobic Surface Increases Oxophilicity

“…We justify the choice of material, using silica nanoparticles in an effort to control the 1 O 2 reaction. Somewhat similarly, control of radical stabilization and photochemical reactions have been obtained on silica nanoparticles. − We propose that our 1 O 2 air–solid method could have general applicability in a variety of research areas, such as interfacial 1 O 2 photoimaging , and environmental chemistry. , Therefore, we provide a detailed description of SIM, which enables one to gauge Pr/ 1 O 2 adduct binding. This includes how to conduct the airborne and surface-associated 1 O 2 lifetime experiments, while differentiating how 1 O 2 plays important roles in oxidizing particulates − with intermediacy on surfaces , and in air. , …”

Nanoantioxidant Materials: Nanoengineering Inspired by Nature

“…According to Table 1 , among the most common oxygen-centered free radicals, namely radical species where the unpaired electron is located in the oxygen atom, are the hydroxyl radicals ( • OH) [ 64 ], the superoxide anion radicals ( • O 2 − ) [ 64 ], the hydroperoxyl (HO 2 • ) radical [ 64 ], the alkoxyl (RO • )[ 64 , 67 ], and peroxyl radical (ROO • ) [ 64 ], lipid alkoxyl (LO • )[ 64 , 67 ] and lipid peroxyl (LOO • ) radicals [ 64 ], semiquinone (SQ •− ) [ 68 ] radicals, and carbonate (CO 3 •− ) radicals [ 69 , 70 ]. Similarly to alkoxyl radicals, phenoxyl radicals (e.g., tyrosyl radical, Tyr • ) are common, especially in biological systems [ 71 , 72 ]. Moreover, sulfate radicals (SO 4 ●− ) [ 73 ] are generated via the activation of persulfates, such as peroxydisulfate (PDS, S 2 O 8 2− ) and permonosulfate (PMS, HSO 5 − ), characterized by the presence of an O–O bond (similar to hydrogen peroxide) [ 74 ].…”